% % This file was created by the Typo3 extension % sevenpack version 0.7.16 % % --- Timezone: CET % Creation date: 2024-11-21 % Creation time: 15-10-36 % --- Number of references % 199 % % @Phdthesis { TheilenbergDiss2017, title = {Imaging Meningiomas - The Road to the First Medical Application of the Novel Magnetic Resonance Rheology}, year = {2017}, tags = {mrt}, url = {http://nbn-resolving.org/urn:nbn:de:hbz:5n-46677}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Theilenberg, S.} } @Phdthesis { KofahlDiss2017, title = {Magnetic Resonance Rheology on Phantoms and Human Brains}, year = {2017}, tags = {mrt}, url = {http://hss.ulb.uni-bonn.de/2017/4730/4730.htm}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Kofahl, A.-L.} } @Phdthesis { RaethDiss2017, title = {Materialmodifikationen in Lithiumniobat- und Lithiumtantalat-Kristallen durch Ionenbestrahlung}, year = {2017}, tags = {linbo}, url = {http://nbn-resolving.org/urn:nbn:de:hbz:5n-47457}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {R{\"a}th, N. L.} } @Phdthesis { WildDiss2017, title = {MR-Phasenbilder ultraschallinduzierter Verschiebungsfelder an Brustl{\"a}sionen}, year = {2017}, tags = {mrt}, url = {http://hss.ulb.uni-bonn.de/2017/4858/4858.htm}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Wild, J.} } @Article { Kofahl2016, title = {Combining rheology and MRI: Imaging healthy and tumorous brains based on mechanical properties}, journal = {Magn. Reson. Med.}, year = {2016}, tags = {mrt}, url = {http://onlinelibrary.wiley.com/doi/10.1002/mrm.26477}, DOI = {10.1002/mrm.26477}, author = {Kofahl, A.-L. and Theilenberg, S. and Bindl, J. and Ulucay, D. and Wild, J. and Napiletzki, S. and Schu-Sch{\"a}tter, B. and Vohlen, A. and Pintea, B. and Finsterbusch, J. and Hattingen, E. and Urbach, C. and Maier, K.} } @Mastersthesis { Napiletzki2015, title = {Abbildung rheologischer Eigenschaften mit dem MR-Tomographen}, year = {2015}, month = {6}, tags = {mrt}, school = {Universit{\"a}t D{\"u}sseldorf}, type = {Masterarbeit}, author = {Napiletzki, S.} } @Thesis { CorreaSchragen2015, title = {Entwicklung einer Messapparatur zur Untersuchung der D{\"a}mpfungseigenschaften d{\"u}nner, MR-tauglicher Materialien}, year = {2015}, month = {1}, tags = {mrt}, school = {Universit{\"a}t Bonn}, type = {Bachelorarbeit}, author = {Correa Schragen, R.} } @Phdthesis { KohlbachDiss2015, title = {Ab-initio Untersuchungen an fr{\"u}hen Ausscheidungsphasen der Aluminium(-Magnesium-)Kupfer-Legierungen}, year = {2015}, tags = {positron, material}, url = {http://nbn-resolving.org/urn:nbn:de:hbz:5n-40358}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Wolfertz, I.} } @Phdthesis { ulucay15, title = {Rheologie im Kopf}, year = {2015}, tags = {mrt}, url = {http://nbn-resolving.org/urn:nbn:de:hbz:5n-39252}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Ulucay, D.} } @Mastersthesis { Napiletzki2014, title = {MR–Rheology Characterisation of Elasticity Differences in Phantom–Materials}, year = {2014}, month = {11}, tags = {mrt}, school = {Universit{\"a}t Bonn}, type = {Masterarbeit}, author = {Napiletzki, S.} } @Mastersthesis { Wolfel2014, title = {Optisches Positionierungssystem f{\"u}r die Ultraschall-Einkopplung bei bewegungssensitiven MRT-Messungen Ultraschallstrahlungskraft-induzierter Gewebeverschiebungen (ARC-MR)}, year = {2014}, month = {9}, tags = {mrt}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {W{\"o}lfel, S.} } @Mastersthesis { Vohlen2014, title = {Optimierung der Fallbewegung in der MR-Rheologie}, year = {2014}, month = {4}, tags = {mrt}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Vohlen, A.} } @Article { Raeth2014, title = {Refractive index changes and nuclear activation upon irradiation of lithium niobate crystals with different low-mass, high-energy ions}, journal = {Appl. Phys. A}, year = {2014}, volume = {117}, number = {3}, pages = {1041-1044}, abstract = {Refractive index changes \(\Delta\)n in lithium niobate crystals upon irradiation with high-energy protons, deuterons, \(^{3}\)He, and \(^{4}\)\(\alpha\) particles (up to 14 MeV/nucleon) are created, and the accompanying, unwanted nuclear activation is investigated. The measurements give answers to the question which ion is the best choice depending on the requirements: largest values of \(\Delta\)n are achieved with \(^{4}\)\(\alpha\) particles, low nuclear activation with deuterons, or the best tradeoff between \(\Delta\)n and activation with \(^{3}\)He, respectively.}, tags = {linbo}, url = {http://link.springer.com/article/10.1007\%2Fs00339-014-8524-y}, DOI = {10.1007/s00339-014-8524-y}, author = {Raeth, N. L. and Goetze, J. and Peithmann, K. and Maier, K.} } @Conference { ulucayismrmds13, title = {Darstellung elastischer Eigenschaften des Gehirns mit MR-Rheologie}, year = {2013}, month = {9}, day = {20}, abstract = {Die Kenntnis ortsaufgel{\"o}ster viskoelastischer Eigenschaften des menschlichen Gehirns kann hilfreich f{\"u}r die medizinische Diagnostik sein und zu einem besseren Verst{\"a}ndnis der funktionellen Vorg{\"a}nge des Gehirns f{\"u}hren. Inspiriert von der Materialwissenschaft wurde der Kriechversuch auf eine in vivo Messung innerhalb einer MR Kopfspule {\"u}bertragen, um mechanische Parameter zu untersuchen. Erste Ergebnisse lassen das Potential der neuen Methode erkennen. The knowledge of spatial resolved viscoelastic parameters of the human brain may help in medical diagnostics and deeper understanding of the brain function. Inspired by material science we perform creep experiments inside an MRI head coil to investigate mechanical properties in vivo. First results show the feasibility of this novel method.}, tags = {mrt}, url = {http://www.ismrm.de/archiv-alte-beitraege/ismrm-jahrestagung-2013/tagungsprogramm.html}, misc = {Konferenz}, booktitle = {16. Jahrestagung der Deutschen Sektion der Internationalen Gesellschaft f{\"u}r Magnetresonanz in Medizin, 2013, Freiburg, Deutschland}, author = {Ulucay, D. and Theilenberg, S. and Kofahl, A.-L. and Wild, J. and Bindl, J. and Vohlen, A. and Neuhaus, E. and Oehm, M. and Kn{\"o}ppel, J. and Finsterbusch, J. and Urbach, C. and Maier, K.} } @Mastersthesis { Bindl2013, title = {Phantommessungen zur Untersuchung der MR-Rheologie}, year = {2013}, month = {7}, tags = {mrt}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Bindl, J.} } @Conference { bindldpg13, title = {Herstellung MR-tauglicher PVA-Phantome zur Simulation rheologischer Eigenschaften des Gehirns}, year = {2013}, month = {3}, abstract = {Das Gehirn bildet ein sensibles System, dessen viskolelastische Eigenschaften von vielen Faktoren, z.B Krankheiten beeinflusst werden. Wir benutzen rheologische Methoden, um Zugang zu diesen Eigenschaften zu erlangen. Dabei wird der Kopf um einen Millimeter angehoben und anschlie{\ss}end fallen gelassen, wodurch das Gehirn in seiner Gleichgewichtslage gest{\"o}rt wird. Die Relaxation zur{\"u}ck in den Gleichgewichtszustand ist dabei lokal abh{\"a}ngig von den elastischen Eigenschaften und wird mittels einer bewegungssensitiven MRT-Sequenz abgebildet. Um die Ergebnisse besser verstehen zu k{\"o}nnen, bietet sich ein Vergleich mit Gewebephantomen an, deren elastische Eigenschaften bekannt sind. Die Herausforderung bei der Herstellung eines geeigneten Phantoms liegt darin, das Gesamtsystem aus Gehirn, Sch{\"a}del und Hirnfl{\"u}ssigkeit zu imitieren.}, tags = {mrt}, url = {http://www.dpg-verhandlungen.de/year/2013/conference/regensburg/part/st/session/5/contribution/2}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Regensburg}, author = {Bindl, J. and Kofahl, A.-L. and Theilenberg, S. and Ulucay, D. and Finsterbusch, J. and Weber, B. and Urbach, C. and Maier, K.} } @Conference { raethdpg13, title = {Lithiumniobat und Lithiumtantalat unter Beschuss: Die Auswirkungen von hochenergetischen Alphas und ihren leichteren Kollegen}, year = {2013}, month = {3}, abstract = {Der k{\"u}nstliche Kristall Lithiumniobat (LiNbO3) ist f{\"u}r viele Anwendungsf{\"a}lle der nichtlinearen Optik sehr gut geeignet. Mittels Durchstrahlung hochenergetischer, leichter Ionen k{\"o}nnen entscheidende Materialparameter wie Brechungsindex, Leitf{\"a}higkeit oder das Verhalten ferroelektrischer Dom{\"a}nen gezielt beeinflusst werden. Begleitet wird dies jedoch von einer eher st{\"o}renden nuklearen Aktivierung. Auch f{\"u}r das kristallographisch isomorphe Material Lithumtantalat (LiTaO3) lassen sich {\"a}hnliche Modifikationen nach Ionenbeschuss nachweisen. Wir pr{\"a}sentieren Unterschiede und Gemeinsamkeiten der gemessenen Effekte in beiden Kristallen f{\"u}r alle vier leichten Projektile (4He, 3He, 2D, 1H). Anschlie{\ss}end interpretieren wir die Ergebnisse zur weiteren Erkl{\"a}rung der ablaufenden Prozesse, sowie in Hinblick auf eine Optimierung f{\"u}r Anwendungen.}, tags = {linbo}, url = {http://www.dpg-verhandlungen.de/year/2013/conference/regensburg/part/df/session/10/contribution/2}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Regensburg}, author = {Raeth, N. L. and Goetze, J. and Peithmann, K. and Maier, K.} } @Conference { theilenbergdpg13, title = {MR-Rheologie - Ortsabh{\"a}ngige Darstellung elastischer Eigenschaften des Gehirns}, year = {2013}, month = {3}, abstract = {MR-Rheologie ist eine neuartige Methode zur in-vivo Messung elastischer Eigenschaften des menschlichen Gehirns. Diverse krankhafte Ver{\"a}nderungen des Gehirns (zum Beispiel Alzheimer und Multiple Sklerose) beeinflussen diese Eigenschaften. Die Kenntnis dieser k{\"o}nnte daher zu diagnostischen Zwecken genutzt werden. Zur Messung wird der Patient in einem MRT in R{\"u}ckenlage positioniert. Der Kopf wird pneumatisch um etwa einen Millimeter angehoben und dann kontrolliert fallen gelassen. Der Sch{\"a}delknochen kommt nach dieser abrupten Bewegung sehr schnell zur Ruhe, w{\"a}hrend das weiche Gewebe des Gehirns verz{\"o}gert in die Ruhelage zur{\"u}ckkehrt. Diese Relaxationsbewegung ist ortsabh{\"a}ngig und wird vor allem von den lokalen viskoelastischen Eigenschaften des Gewebes bestimmt. Mit einer bewegungssensitiven Sequenz kann sie zu definierten Zeitpunkten gemessen und als Grauwert im Phasenbild kodiert werden. Das so gewonnene Bild, das damit Informationen {\"u}ber die relative lokale Elastizit{\"a}t des Gewebes enth{\"a}lt, l{\"a}sst verschiedene Strukturen erkennen. Um die Aussagekraft der Messung zu erh{\"o}hen und um eine Vergleichbarkeit der Bilder verschiedener Aufnahmen zu gew{\"a}hrleisten, m{\"u}ssen die Bilder statistisch ausgewertet und normiert werden.}, tags = {mrt}, url = {http://www.dpg-verhandlungen.de/year/2013/conference/regensburg/part/st/session/1/contribution/3}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Regensburg}, author = {Theilenberg, S. and Ulucay, D. and Kofahl, A.-L. and Bindl, J. and Finsterbusch, J. and Weber, B. and Urbach, C. and Maier, K.} } @Conference { ulucaydpg13, title = {Untersuchung der fallinduzierten Relaxationsbewegung des Gehirns mit MR-Rheologie}, year = {2013}, month = {3}, abstract = {Die Kenntnis viskoelastischer Eigenschaften des Gehirns ist f{\"u}r die medizinische Diagnostik von gro{\ss}er Bedeutung, da auch neurodegenerative Krankheiten diese Eigenschaften {\"a}ndern. In der Rheologie wird zur Beschreibung viskoelastischer Eigenschaften das zu untersuchende System zun{\"a}chst gest{\"o}rt und anschlie{\ss}end die Relaxationsbewegung analysiert. Wir {\"u}bertragen dieses Messprinzip und st{\"o}ren die Gleichgewichtslage des Gehirns durch einen Fall des Kopfes aus ca. 1 mm H{\"o}he. Das Gehirn folgt der Bewegung des Sch{\"a}delknochens nicht instantan, sondern verz{\"o}gert. Diese ortsabh{\"a}ngige Relaxationsbewegung wird mit Hilfe eines MRT aufgezeichnet und ist bestimmt durch die lokale viskoelastische Kopplung. Durch eine sehr genaue Synchronisation zwischen Bewegung und Aufnahmesequenz ist es m{\"o}glich sowohl den Start als auch das Ende der Bewegung detailliert zu untersuchen.}, tags = {mrt}, url = {http://www.dpg-verhandlungen.de/year/2013/conference/regensburg/part/st/session/5/contribution/1}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Regensburg}, author = {Ulucay, D. and Theilenberg, S. and Kofahl, A.-L. and Bindl, J. and Finsterbusch, J. and Weber, B. and Urbach, C. and Maier, K.} } @Mastersthesis { GoetzeDipl2012, title = {Modifications of Material Parameters of Lithium Niobate Crystals (LiNbO\(_{3}\)) with Different High-Energy, Low-Mass Ions}, year = {2012}, month = {10}, tags = {linbo}, school = {Universit{\"a}t Bonn}, type = {Masterarbeit}, author = {Goetze, J.} } @Thesis { wagner2012, title = {MR-Rheologie – Darstellung viskoelastischer Eigenschaften des Gehirns}, year = {2012}, month = {9}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2012_Bachelor_Wagner.pdf}, school = {Universit{\"a}t Bonn}, type = {Bachelorarbeit}, author = {Wagner, S.} } @Conference { kofahlismrm12, title = {Finite Element Simulations of acoustic radiation contrast in magnetic resonance using open source software}, year = {2012}, month = {5}, tags = {mrt}, misc = {Konferenz}, booktitle = {ISMRM 20th Annual Meeting \& Exhibition, Melbourne}, author = {Kofahl, A.-L. and Theilenberg, S. and Ulucay, D. and Wild, J. and Paul, S. and Maier, K. and Urbach, C.} } @Conference { ulucaydpg12, title = {Darstellung elastischer Eigenschaften des Gehirns nach materialwissenschaftlichem Vorbild}, year = {2012}, month = {3}, abstract = {Krankhafte Gewebever{\"a}nderungen gehen h{\"a}ufig mit einer {\"A}nderung der elastischen Eigenschaften einher. Die genaue Kenntnis {\"u}ber elastische Eigenschaften im Gehirn kann f{\"u}r die medizinische Diagnostik von gro{\ss}er Bedeutung sein. Erste Untersuchungen zeigen, dass z.B. Alzheimer zu einer Verfestigung der Gehirnmasse f{\"u}hrt (Murphy et al., Journal Of MRI, 2011). Auch bei anderen neurodegenerativen Krankheiten wie z.B. Parkinson oder auch Hirntumoren, Hydrocephalus und Multiple Sklerose ist eine signifikante {\"A}nderung des elastischen Systems zu erwarten. In diesem Vortrag wird eine Messmethode vorgestellt, welche die Grundidee einer materialwissenschaftlichen Untersuchung {\"u}bernimmt und auf eine MR-Untersuchung {\"u}bertr{\"a}gt und dabei frei von ionisierender Strahlung und Kontrastmitteln ist. Erste in vivo Aufnahmen lassen das gro{\ss}e Potential der Methode erkennen.}, tags = {mrt}, url = {http://www.dpg-verhandlungen.de/year/2012/conference/berlin/part/st/session/1/contribution/6}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Berlin}, author = {Ulucay, D. and Wild, J. and Kofahl, A.-L. and Paul, S. and Theilenberg, S. and Finsterbusch, J. and Trautner, P. and Urbach, C. and Maier, K.} } @Conference { kohdpg12, title = {Finite Elemente Simulationen von Schallstrahlungskraft induzierten Kontrasten}, year = {2012}, month = {3}, abstract = {Die M{\"o}glichkeit, mittels MR-Phasenbildern die durch Schallstrahlungskraft induzierten quasi-statischen Verschiebungen zu messen, bietet einen nicht-invasiven Zugang zu den viskoelastischen Eigenschaften von Gewebe. Somit k{\"o}nnen Ver{\"a}nderungen im Vergleich zum umliegenden Gewebe (wie Zysten, Tumore oder Mikrokalzifikationen) detektiert und klassifiziert werden, die vom umgebenen Gewebe unterschieden werden k{\"o}nnen. Zur quantitativen Interpretation der Messergebnisse werden Simulationen mittels der Finiten Elemente Methode (FEM) durchgef{\"u}hrt und weiterentwickelt. Um diese zu validieren, werden Messungen an Gewebephantome auf Polyvinylalkohol-Basis mit bekannten Materialparametern zum Vergleich herangezogen. Besonders der Einfluss von Randbedingungen wird unter Verwendung von open source FEM-Software untersucht. Dies liefert auch ein besseres Verst{\"a}ndnis von den mechanischen Vorg{\"a}nge w{\"a}hrend der Messungen.}, tags = {mrt}, url = {http://www.dpg-verhandlungen.de/year/2012/conference/berlin/part/st/session/4/contribution/8}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Berlin}, author = {Kofahl, A.-L. and Theilenberg, S. and Wild, J. and Ulucay, D. and Paul, S. and Maier, K. and Urbach, C.} } @Conference { raethdpg12, title = {Strukturierte Materialmodifikationen in optischen Kristallen mittels eines Hochenergie Helium-Microbeams}, year = {2012}, month = {3}, abstract = {Optische Kristalle wie Lithiumniobat oder Lithiumtantalat sind {\"a}u{\ss}erst interessant f{\"u}r eine Vielzahl optischer Anwendungen. Hochenergetische, leichte Ionen, die derartige Kristalle durchstrahlen, verursachen langzeitstabile Modifikationen des Brechungsindexes und reduzieren die Koerzitivfeldst{\"a}rke EC. Um die Materialen im Mikrometerbereich derart strukturieren zu k{\"o}nnen, wird der Ansatz eines Hochenergie Helium-Microbeams verfolgt. Am Isochron-Zyklotron des Helmholtz-Instituts f{\"u}r Strahlen- und Kernphysik wird dazu mittels ionenoptischer Abbildung ein maskierter Ionenstrahl stark verkleinert auf die Probe abgebildet. Es werden Berechnungen, Aufbau und erste Resultate vorgestellt.}, tags = {linbo}, url = {http://www.dpg-verhandlungen.de/year/2012/conference/berlin/part/df/session/13/contribution/25}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Berlin}, author = {Raeth, N. L. and Goetze, J. and Peithmann, K. and Maier, K.} } @Conference { goetzedpg12, title = {Vergleich der optischen Materialmodifikationen von Lithiumniobat-Kristallen durch den Beschuss verschiedener schneller leichter Ionen}, year = {2012}, month = {3}, abstract = {Lithiumniobat-Kristalle finden vielfach Anwendung in Wissenschaft und Technik, insbesondere in optischen Technologien. Methoden zur gezielten Strukturierung wichtiger Materialparamater, wie des Brechungsindex, der elektrischen Leitf{\"a}higkeit oder der ferroelektrischen Polungseigenschaften, sind daher gefragt. Durchstrahlung der Kristalle mit hochenergetischen leichten Ionen, wie beispielsweise 3He, ist eine leistungsf{\"a}hige Methode zur Beeinflussung der Materialparameter. Da sie als Nebenwirkung eine parasit{\"a}re Aktivierung der Kristalle mit sich bringt, wird durch den Einsatz verschiedener Projektile (3He, 4He, 1H, 2D) untersucht, ob eine Optimierung des Prozesses m{\"o}glich ist. Der Einfluss der Projektilwahl hinsichtlich der oben genannten Bereiche soll vorgestellt werden.}, tags = {linbo}, url = {http://www.dpg-verhandlungen.de/year/2012/conference/berlin/part/df/session/11/contribution/4}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Berlin}, author = {Goetze, J. and Raeth, N. L. and Peithmann, K. and Maier, K.} } @Thesis { westerhausen2011, title = {Nachweis von Ultraschall-Strahlungskraft induzierten Gewebebewegungen mittels Phasenanalyse eines Messstrahls}, year = {2011}, month = {12}, tags = {medizin}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2011_Bachelor_Westerhausen.pdf}, school = {Universit{\"a}t Bonn}, type = {Bachelorarbeit}, author = {Westerhausen, S.} } @Mastersthesis { theilenberg2011, title = {FEM-Simulationen zur Schallstrahlungskraft in weichem Gewebe}, year = {2011}, month = {11}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2011_Diplom_Theilenberg.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Theilenberg, S.} } @Mastersthesis { blum2011, title = {Schallstrahlungskraftkontrast in MR-Phasenbildern - Materialeigenschaften von Gewebephantomen aus Polyvinylalkohol}, year = {2011}, month = {6}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2011_Diplom_Blum.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Blum, S.} } @Conference { uluismrm11, title = {Acoustic radiation contrast to visualize viscoelastic properties in human breast}, year = {2011}, month = {5}, tags = {mrt}, misc = {Konferenz}, booktitle = {ISMRM 19th Scientific Meeting \& Exhibition, Montreal}, author = {Ulucay, D. and Wild, J. and Mende, J. and D{\"o}nnebrink, M. and Finsterbusch, J. and Urbach, C. and Maier, K.} } @Conference { wildpg11, title = {Detektion von Mikrokalk durch Schallstrahlungskraft in Magnetresonanzaufnahmen}, year = {2011}, month = {3}, abstract = {Kontrasterzeugung durch Schallstrahlungskraft in Magnetresonanz( MR)aufnahmen erm{\"o}glicht die Darstellung der elastischen Eigenschaften von Gewebe. Eine Anwendungsm{\"o}glichkeit ist die Detektion von Mikrokalk. Um im Brustphantom eine Schallstrahlungskraft in Ausbreitungsrichtung zu erzeugen, wurde ein MR-kompatibler piezoelektrischer Emitter benutzt. Die so hervorgerufene Bewegung wurde in Phasenbildern einer bewegungssensitiven Spin-Echo-Sequenz an einem 1,5 T Tomographen sichtbar gemacht. Um Mikrokalk zu simulieren, wurde ein Eierschalenst{\"u}ck (ESS) von 0,8 x 0,8 x 0,4 mm\(^{3}\) in das gelartige Phantom eingef{\"u}gt. Das Phantom wurde mit verschiedenen Ultraschallintensit{\"a}ten untersucht. Trifft der Schallstrahl auf das ESS, wird dieses aufgrund von Reflektion st{\"a}rker verschoben und zieht das umliegende Gewebe mit. Die Ergebnisse zeigen, dass eine Erh{\"o}hung der Intensit{\"a}t sowohl zu einer gr{\"o}{\ss}eren maximalen Verschiebung an der Position des ESS als auch zu einer Vergr{\"o}{\ss}erung des davon beeinflussten Bereiches f{\"u}hrt. Im Rahmen der Grenzwerte des Ultraschalls ergibt sich damit die M{\"o}glichkeit Mikrokalk weit unterhalb der Aufl{\"o}sung des MR-Tomographen darzustellen.}, tags = {mrt}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Dresden}, author = {Wild, J. and Ulucay, D. and Mende, J. and Kofahl, A.-L. and Blum, S. and Theilenberg, S. and Paul, S. and Habenstein, B. and Weber, B. and Schmutzler, R. and Urbach, C. and Maier, K.} } @Conference { raethdpg2011, title = {Die Bonner Positronen Mikrosonde - ein vielf{\"a}ltiges Werkzeug f{\"u}r die Materialforschung}, year = {2011}, month = {3}, abstract = {Die Bonner Positronen Mikrosonde (BPM) erzeugt einen fein fokussierten Positronenstrahl mit einstellbarem Strahldurchmesser von 1 - 200 µm und besitzt ein integriertes Rasterelektronenmikroskop (REM). Proben k{\"o}nnen so lateral hochaufgel{\"o}st mit den Methoden der Positronenannihilationsspektroskopie (PAS) untersucht werden und man erh{\"a}lt Zugang zur detaillierten Messung von Plastizit{\"a}t und Defektdichten verschiedenster Materialien. Instrumentell ist eine Weiterentwicklung der BPM im Bereich der Strahlfokussierungs- und -justagesysteme geplant. Zudem soll die BPM um die M{\"o}glichkeit zur ortsaufgel{\"o}sten Messung der Positronenlebensdauer erg{\"a}nzt werden. Der aktuelle Fokus der Forschung liegt auf schwei{\ss}baren Aluminiumlegierungen der Systeme AA5xxx und AA6xxx. Besonderes Interesse gilt hier der Defektkonzentration direkt an der Schwei{\ss}naht und in der angrenzenden W{\"a}rmeeinflusszone, vor allem im Hinblick auf eine PASbasierte Schadensvorhersage f{\"u}r geschwei{\ss}te Aluminiumwerkstoffe.}, tags = {positron, material}, url = {http://www.dpg-verhandlungen.de/2011/dresden/mm31.pdf}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Dresden}, author = {Raeth, N. L. and Herdt, O. and Liu, M. and Klobes, B. and Haaks, M. and Maier, K. and Hugenschmidt, C.} } @Conference { kohdpg11, title = {Finite Elemente Modelle zur Schallstrahlungskraft in Magnetresonanzaufnahmen}, year = {2011}, month = {3}, abstract = {Mittels der Kontrasterzeugung durch die Schallstrahlungskraft in Magnetresonanz( MR)aufnahmen k{\"o}nnen die viskoelastischen Eigenschaften von weichem Gewebe dargestellt werden. Dabei induziert die durch den Ultraschall hervorgerufene Schallstrahlungskraft Gewebeverschiebungen, welche durch eine verschiebungssensitive MR-Sequenz detektiert werden k{\"o}nnnen. In Phantomen, die viskoelastische Eigenschaften von Brustgewebe simulieren, k{\"o}nnen L{\"a}sionen verschiedener Art qualitativ von dem umgebenden Medium unterschieden werden. Unter Verwendung der Finiten Elemente Methode wird an ein Modell zur quantitativen Interpretation der Messergebnisse entwickelt. In einem ersten Ansatz wurde ein isotroper, homogener, linear elastischer Festk{\"o}rper aus hexaedrischen Elementen mit acht Knoten moduliert. Die Schallstrahlungskraft wurde in einem definierten Gebiet mit longitudinalem Strahlprofil implementiert. Einschl{\"u}sse, die L{\"a}sionen repr{\"a}sentieren, konnten eingef{\"u}gt werden. Die zu variierenden Parameter schlossen die St{\"a}rke der Kraft, die unterschiedlichen Elastizit{\"a}tsmodule sowie Gr{\"o}{\ss}e und relative Position der Einschl{\"u}sse ein. Randbedingungen konnten ebenfalls modifiziert werden. Qualitativ konnten gute {\"U}bereinstimmungen zwischen Modell und Messungen erreicht werden.}, tags = {mrt}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Dresden}, author = {Kofahl, A.-L. and Wild, J. and Ulucay, D. and Theilenberg, S. and Blum, S. and Paul, S. and Habenstein, B. and Bourauel, C. and Schmutzler, R. and Urbach, C. and Maier, K.} } @Conference { uludpg11, title = {Neuer Kontrast durch Ultraschall in MR-Phasenbildern: Darstellung elastischer Eigenschaften der weiblichen Brust}, year = {2011}, month = {3}, abstract = {Krankhafte Gewebever{\"a}nderungen f{\"u}hren h{\"a}ufig zu einer signifikanten {\"A}nderung der elastischen Eigenschaften. Die genaue Kenntnis dieser Eigenschaften ist f{\"u}r die medizinische Diagnostik von gro{\ss}em Wert. Die in der Arbeitsgruppe entwickelte Kombination aus Ultraschall (US) und Magnetresonanztomographie (MRT) bietet eine M{\"o}glichkeit die elastischen Eigenschaften darzustellen. Die Schallstrahlungskraft des US wirkt als maschineller Tastsinn (vgl. manuelle Abtastung) und f{\"u}hrt zu Gewebeverschiebungen im \(\mu\) m-Bereich, welche mit einem MRT visualisiert werden. US wird mittels eines MR-tauglichen US-Emitters in die Brust eingekoppelt. Die Schallsignatur ist deutlich sichtbar und Gewebever{\"a}nderungen k{\"o}nnen aufgesp{\"u}rt werden. Eine sich im Schallstrahl befindende Verh{\"a}rtung (z.B. Tumor) kann bei gleicher Kraft nur weniger weit verschoben werden, als das umliegende Gewebe und wird somit sichtbar. Umgekehrt f{\"u}hrt weicheres Gewebe (z.B. Zysten) zu gr{\"o}{\ss}eren Verschiebungen. Die an Phantomen erprobte, schmerz- und strahlungsfreie Methode wurde nun auch an ersten gesunden, freiwilligen Probanden erfolgreich getestet.}, tags = {mrt}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Dresden}, author = {Ulucay, D. and Wild, J. and Mende, J. and D{\"o}nnebrink, M. and Blum, S. and Habenstein, B. and Kofahl, A.-L. and Paul, S. and Theilenberg, S. and Schmutzler, R. and Urbach, C. and Maier, K.} } @Conference { bludpg11, title = {Neuer Kontrast durch Ultraschall in MR-Phasenbildern: Sicherheitsaspekte im Hinblick auf Messungen am Menschen}, year = {2011}, month = {3}, abstract = {Eine neuartige und schmerzfreie M{\"o}glichkeit zur Brustkrebsfr{\"u}herkennung nutzt eine Kombination aus Ultraschall (US) und Magnetresonanztomographie (MRT). Die Visualisierung von Gewebeverschiebungen, die durch die Schallstrahlungskraft verursacht werden und von den elastischen Eigenschaften abh{\"a}ngen, erfolgt in MR-Phasenbildern. Eine metallfreie, hydraulische Verschiebeeinrichtung mit MR-kompatiblem US-Emitter wird dazu dem MR-Tomographen hinzugef{\"u}gt. Im Hinblick auf Messungen am Menschen ist es wichtig eine sichere und komfortable Apparatur zu schaffen. Um m{\"o}gliche Risiken durch den US infolge von Erw{\"a}rmung und Kavitation zu vermeiden, wurden der thermische und der mechanische Faktor mit verschiedenen Messmethoden bestimmt. Die verwendeten US-Intensit{\"a}ten liegen unterhalb der Grenzwerte der Food and Drug Administration (FDA). Um Grenzwert{\"u}berschreitungen durch fehlerhafte Ger{\"a}te auszuschlie{\ss}en, wurde ein Ger{\"a}t konstruiert, das unabh{\"a}ngig den US {\"u}berwacht und notfalls die Weiterleitung der Hochfrequenz an den US-Emitter unterbricht. In Zukunft m{\"u}ssen vor allem noch ergonomische Aspekte betrachtet werden.}, tags = {mrt}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Dresden}, author = {Blum, S. and Wild, J. and Ulucay, D. and Kofahl, A.-L. and Mende, J. and Theilenberg, S. and Paul, S. and Habenstein, B. and Urbach, C. and Schmutzler, R. and Maier, K.} } @Conference { paudpg11, title = {Phantome zur Simulation menschlichen Gewebes}, year = {2011}, month = {3}, abstract = {Die Kontrasterzeugung durch die Schallstrahlungskraft in Magnetresonanzaufnahmen erm{\"o}glicht die Darstellung der elastischen Eigenschaften von Gewebe. In Phantomen, die in ihren elastischen und akustischen Eigenschaften mit Brustgewebe {\"u}bereinstimmen, k{\"o}nnen damit L{\"a}sionen verschiedener Art qualitativ von dem umgebenden Medium unterschieden werden. Generell werden Phantome ben{\"o}tigt, bevor eine neue Methode an menschlichem Gewebe getestet wird. Sie erm{\"o}glichen die Verbesserung der Methode ohne Probanden zu gef{\"a}hrden. Die Phantome m{\"u}ssen in den f{\"u}r die Methode ma{\ss}geblichen Eigenschaften mit dem Gewebe {\"u}bereinstimmen. Zu diesen Eigenschaften geh{\"o}ren u. a. die Dichte, die Schallabsorption, -geschwindigkeit und - kennimpedanz. Auch die Reproduzierbarkeit und Haltbarkeit sind entscheidende Faktoren. Am Beispiel von Brustphantomen wird die Herstellung auf Agar- und PVA-Basis vorgestellt. Es werden Vor- und Nachteile der einzelnen Methoden zur Herstellung diskutiert. Messverfahren f{\"u}r die m{\"o}glichst genaue Bestimmung der relevanten Eigenschaften werden pr{\"a}sentiert. Au{\ss}erdem werden selbst hergestellte Phantome mit kommerziell erh{\"a}ltlichen verglichen.}, tags = {mrt}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Dresden}, author = {Paul, S. and Blum, S. and Kofahl, A.-L. and Theilenberg, S. and Ulucay, D. and Wild, J. and Habenstein, B. and Schmutzler, R. and Urbach, C. and Maier, K.} } @Conference { thedpg11, title = {Schallstrahlungskraft in MR-Aufnahmen: Verbesserungen des Finite-Elemente-Modells}, year = {2011}, month = {3}, abstract = {Mittels Kontrasterzeugung durch Schallstrahlungskraft von Ultraschall in Magnetresonanzaufnahmen werden viskoelastische Eigenschaften von Gewebe dargestellt. L{\"a}sionsartige Einschl{\"u}sse in Brustphantomen konnten damit qualitativ vom umgebenden Medium unterschieden werden. Um experimentelle Ergebnisse aus Phantommessungen besser zu verstehen, wurde eine Simulation auf Grundlage der Finite-Elemente- Methode entwickelt. Das Gewebe wurde als homogenes, isotropes, linear elastisches Medium mit festgelegtem Elastizit{\"a}tsmodul und Poissonzahl simuliert. Der Ultraschall wurde in einem abgegrenzten Bereich als in Ausbreitungsrichtung abklingende Volumenkraft implementiert. Dieses grundlegende Modell kann qualitativ die Messergebnisse reproduzieren, bedarf aber vor allem quantitativ noch Verbesserungen. Um die Messergebnisse nicht nur relativ, sondern auch absolut auswerten zu k{\"o}nnen, werden notwendige Erweiterungen am Modell vorgestellt. Diese betreffen vor allem die Implementierung des radialen Strahlprofils des Ultraschalls, den Einfluss von Oberwellen, die vor dem Phantom als auch im Medium selber erzeugt werden, sowie die Modellierung des Phantom-Materials.}, tags = {mrt}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Dresden}, author = {Theilenberg, S. and Kofahl, A.-L. and Ulucay, D. and Wild, J. and Blum, S. and Paul, S. and Habenstein, B. and Bourauel, C. and Schmutzler, R. and Urbach, C. and Maier, K.} } @Phdthesis { hoehl2011, title = {Wechselwirkung zwischen Ultraschall \& Proton-Spin in w{\"a}ssriger L{\"o}sung}, year = {2011}, abstract = {Die Suche nach einem Einfluss von Ultraschall auf das Kernspinsystem in weicher Materie ist eine spannende Aufgabe. Nachdem in den 50er Jahren gezeigt werden konnte, dass in homogenen Fl{\"u}ssigkeiten die hohe Molek{\"u}ldynamik eine effektive Kopplung zwischen Ultraschall und Spinsystem verhindert, wurden Messungen dazu weitgehend eingestellt. Einige theoretische Arbeiten deuten mittlerweile darauf hin, dass es Wechselwirkungsmechanismen gibt, die trotzdem eine Kopplung erm{\"o}glichen, wenn komplexe Molek{\"u}le oder kolloidal gel{\"o}ste Partikel mit magnetischen Eigenschaften in der Fl{\"u}ssigkeit vorhanden sind. Doch im Vergleich zu typischen Experimenten an Festk{\"o}rpern, wird in Fl{\"u}ssigkeiten nur eine schwache Beeinflussung des Spinsystems erwartet. Experimente dazu liefern bislang widerspr{\"u}chliche Ergebnisse. In dieser Arbeit wird untersucht, warum keine eindeutigen experimentellen Daten vorliegen und gezeigt, dass bei Messungen an Fl{\"u}ssigkeiten eine Reihe von Einfl{\"u}ssen auftreten, die in Konkurrenz zur Ultraschall induzierten Relaxation oder S{\"a}ttigung des Kernspinsystems stehen. Es werden L{\"o}sungen vorgeschlagen, wie man in einer empfindlichen NMR-Messapparatur den Ultraschalleinfluss bestimmen kann und wie man Resonanzexperimente am Magnetresonanztomographen durchf{\"u}hren kann. Erste Messungen mit den vorgestellten Aufbauten werden pr{\"a}sentiert und es wird nachgewiesen, dass magnetische Nanopartikel Ultraschall an das Proton-Kernspinsystem koppeln k{\"o}nnen}, tags = {nmr}, url = {http://nbn-resolving.org/urn:nbn:de:hbz:5N-24386}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {H{\"o}hl, C.} } @Article { radicke11, title = {Acoustic radiation contrast in {MR} images for breast cancer diagnostics - initial phantom study}, journal = {Ultrasound in Medicine \& Biology}, year = {2011}, volume = {37}, pages = {253-261}, abstract = {Acoustic radiation contrast in magnetic resonance images is an approach to visualize the changes in ultrasonic loss and viscoelastic changes of the sample with the resolution of a magnetic resonance imaging (MRI) system. By irradiating ultrasound (US) into a tissue-mimicking sample, a displacement along the US beam path caused by the acoustic radiation force is obtained. This displacement varies with the US intensity, the duration of irradiation, the US attenuation and the viscoelastic properties of the sample. US pulses of 2.5 MHz with a duration of 20 ms and an intensity of <17 W/cm(2) are used. An MRI sequence was programmed to produce images in which the magnitude of the displacement is visualized by gray value changes. In addition, a finite element simulation of the measurements was performed to demonstrate the feasibility of the method. Through examination of the measurements and the simulations, information about viscoelastic changes was achieved. In this work, measurements on different breast phantoms are presented.}, tags = {mrt}, url = {http://www.sciencedirect.com/science/article/pii/S0301562910006186}, DOI = {10.1016/j.ultrasmedbio.2010.11.005}, author = {Radicke, M. and Mende, J. and Kofahl, A.-L. and Wild, J. and Ulucay, D. and Habenstein, B. and Deimling, M. and Trautner, P. and Weber, B. and Maier, K.} } @Article { 1742-6596-265-1-012018, title = {Atomic structure of pre-Guinier-Preston and Guinier-Preston-Bagaryatsky zones in Al-alloys}, journal = {J. Phys.: Conf. Ser.}, year = {2011}, volume = {265}, number = {1}, pages = {012018}, abstract = {We present results on the structure of nano-sized particles (Guinier-Preston (GP) and Guinier-Preston-Bagaryatsky (GPB) zones) in Aluminum alloys. Precipitates of alloying elements like Cu, Mg, or Si hinder the motion of dislocations and, thus, are responsible for the strength of AlCuMg- and AlMgSi-alloys - used e.g. as AA2024 (old aircrafts) and AA6013 for the fuselage of the new Airbus A380, respectively. We will discuss the role of quenched-in vacancies for diffusive motion at room temperature (RT) enabling the growth of the precipitates. Using positron annihilation spectroscopy (PAS) – both lifetime and Doppler broadening – gives information on the local atomic environment in the vicinity of vacancies. On the other hand X-ray absorption fine structure (XAFS) spectroscopy is capable of characterizing the local atomic environment around selected elements (Cu, Mg). We will interpret the measured data by comparing them to numerical calculations of PAS and XAFS spectra. However, reliable numerical calculations of spectroscopic quantities are only possible provided that relaxed atomic positions are used as an input. We calculate those employing the ab-initio code SIESTA. Thus, considering decomposition of Al-alloys, we obtain extremely valuable information on the earliest stages, forming immediately after solution heat treatment and quenching, i.e. during the first few minutes of storage at RT.}, tags = {material}, url = {http://stacks.iop.org/1742-6596/265/i=1/a=012018}, DOI = {10.1088/1742-6596/265/1/012018}, author = {Staab, T. E. M. and Klobes, B. and Kohlbach, I. and Korff, B. and Haaks, M. and Dudzik, E. and Maier, K.} } @Article { 1742-6596-262-1-012030, title = {Defect investigations of micron sized precipitates in Al alloys}, journal = {Journal of Physics: Conference Series}, year = {2011}, volume = {262}, number = {1}, pages = {012030}, abstract = {A lot of light aluminium alloys achieve their favourable mechanical properties, especially their high strength, due to precipitation of alloying elements. This class of age hardenable Al alloys includes technologically important systems such as e.g. Al-Mg-Si or Al-Cu. During ageing different precipitates are formed according to a specific precipitation sequence, which is always directed onto the corresponding intermetallic equilibrium phase. Probing the defect state of individual precipitates requires high spatial resolution as well as high chemical sensitivity. Both can be achieved using the finely focused positron beam provided by the Bonn Positron Microprobe (BPM) [1] in combination with the High Momentum Analysis (HMA) [2]. Employing the BPM, structures in the micron range can be probed by means of the spectroscopy of the Doppler broadening of annihilation radiation (DBAR). On the basis of these prerequisites single precipitates of intermetallic phases in Al-Mg-Si and Al-Cu, i.e. Mg 2 Si and Al 2 Cu, were probed. A detailed interpretation of these measurements necessarily relies on theoretical calculations of the DBAR of possible annihilation sites. These were performed employing the DOPPLER program. However, previous to the DBAR calculation the structures, which partly contain vacancies, were relaxed using the ab-initio code SIESTA, i.e. the atomic positions in presence of a vacancy were recalculated.}, tags = {material}, url = {http://stacks.iop.org/1742-6596/262/i=1/a=012030}, author = {Klobes, B. and Korff, B. and Balarisi, O. and Eich, P. and Haaks, M. and Kohlbach, I. and Maier, K. and Sottong, R. and Staab, T. E. M.} } @Article { ISI:000292331200101, title = {Electrical conductivity and asymmetric material changes upon irradiation of Mg-doped lithium niobate crystals with low-mass, high-energy ions}, journal = {J. Appl. Phys.}, year = {2011}, volume = {109}, number = {12}, pages = {124104}, abstract = {Radiation damage in magnesium-doped lithium niobate crystals, created by low-mass, high-energy ions which have transmitted the entire crystal thickness, leads to an enhanced electrical dark conductivity as well as an enhanced photoconductivity. Experimental results on the electrical properties after ion exposure are given, and an asymmetric dependence of the conductivity as well as refractive index changes on the irradiation geometry with respect to the ferroelectric axis is revealed.}, tags = {linbo}, url = {http://jap.aip.org/resource/1/japiau/v109/i12/p124104_s1}, ISSN = {0021-8979}, DOI = {10.1063/1.3596824}, author = {Jentjens, L. and Raeth, N. L. and Peithmann, K. and Maier, K.} } @Article { ISI:000288297300030, title = {Natural ageing of Al-Cu-Mg revisited from a local perspective}, journal = {Mater. Sci. Eng., A}, year = {2011}, volume = {528}, number = {{7-8}}, pages = {3253-3260}, abstract = {{Although Al alloys based on the Al-Cu-(Mg) system have been investigated for decades, information about the evolution of microstructure on the atomistic level during natural ageing is scarce. Therefore, the early stages of natural ageing in laboratory Al-Cu-(Mg) alloys and in AA2024 were investigated using positron annihilation and X-ray absorption spectroscopy. This complementary approach allows for accessing both essential components of Al alloys, namely vacancies and alloying elements. It is found, that during natural ageing the chemical environment of vacancies is formed both of Cu and Mg atoms and that the rearrangement of vacancy surroundings persists the hardness increase of Al-Cu-Mg alloys. During natural ageing two different regimes of vacancy environment are detected and interpreted in terms of cluster growth and vacancy capture. Features of the near edge structure of the X-ray absorption are interpreted using theoretical calculations obtained by the FEFF8.4 code. Thus the agglomeration of Cu and Mg, which is accompanied by lattice distortions around Cu atoms, can be probed. A minimal size of Cu-Mg co-clusters is proposed for later stages of natural ageing. (C) 2011 Elsevier B.V. All rights reserved.}}, tags = {positron, material}, url = {http://www.sciencedirect.com/science/article/pii/S0921509311000086}, ISSN = {{0921-5093}}, DOI = {10.1016/j.msea.2011.01.002}, author = {Klobes, B. and Maier, K. and Staab, T. E. M.} } @Article { ISI:000284453300006, title = {On the age-hardening of an Al-Zn-Mg-Cu alloy: A vacancy perspective}, journal = {Scr. Mater.}, year = {2011}, volume = {64}, number = {{1}}, pages = {21-24}, abstract = {{Positron annihilation spectroscopy was performed to study the microstructure of peak aged Al-Zn-Mg-Cu alloy Applying artificial ageing at different temperatures, the solute content around vacancies is found to be increased compared to as quenched state The similarity of vacancy surroundings of all artificially aged states, except for over-aged ones, suggests that peak strength is caused not only by eta' precipitates but also by GPII zones Moreover, eta' precipitates produced by artificial aging at 403 K are apparently coherent with the Al matrix (C) 2010 Acta Materialia Inc Published by Elsevier Ltd All rights reserved}}, tags = {positron, material}, url = {http://www.sciencedirect.com/science/article/pii/S1359646210006019}, ISSN = {{1359-6462}}, DOI = {10.1016/j.scriptamat.2010.08.054}, author = {Liu, M. and Klobes, B. and Maier, K.} } @Article { springerlink:10.1007/s00340-011-4681-2, title = {Structuring of material parameters in lithium niobate crystals with low-mass, high-energy ion radiation}, journal = {Appl. Phys. B: Lasers Opt.}, year = {2011}, volume = {105}, number = {1}, pages = {113-127}, abstract = {Ferroelectric lithium niobate crystals offer a great potential for applications in modern optics. To provide powerful optical components, tailoring of key material parameters, especially of the refractive index n and the ferroelectric domain landscape, is required. Irradiation of lithium niobate crystals with accelerated ions causes strong structured modifications in the material. The effects induced by low-mass, high-energy ions (such as \(^{3}\)He with 41 MeV, which are not implanted, but transmit through the entire crystal volume) are reviewed. Irradiation yields large changes of the refractive index \(\Delta\)n , improved domain engineering capability within the material along the ion track, and waveguiding structures. The periodic modification of \(\Delta\)n as well as the formation of periodically poled lithium niobate (PPLN) (supported by radiation damage) is described. Two-step knock-on displacement processes, 3 He→Nb and 3 He→O causing thermal spikes, are identified as origin for the material modifications.}, affiliation = {Helmholtz-Institut f{\"u}r Strahlen- und Kernphysik, Universit{\"a}t Bonn, Nussallee 14–16, 53115 Bonn, Germany}, tags = {linbo}, url = {http://www.springerlink.com/content/c624u15604046572/}, publisher = {Springer Berlin / Heidelberg}, ISSN = {0946-2171}, DOI = {10.1007/s00340-011-4681-2}, author = {Peithmann, K. and Eversheim, P.-D. and Goetze, J. and Haaks, M. and Hattermann, H. and Haubrich, S. and Hinterberger, F. and Jentjens, L. and Mader, W. and Raeth, N. L. and Schmid, H. and Zamani-Meymian, M.-R. and Maier, K.} } @Thesis { goetze2010, title = {Methoden zur Untersuchung des Channelingeffekts an Lithiumniobatkristallen}, year = {2010}, month = {7}, tags = {linbo}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2010_Bachelor_Goetze.pdf}, school = {Universit{\"a}t Bonn}, type = {Bachelorarbeit}, author = {Goetze, J.} } @Conference { schismrm10, title = {Acoustic radiation contrast in magnetic resonance: detection of microcalcifications}, year = {2010}, month = {5}, tags = {mrt}, misc = {Konferenz}, booktitle = {ISMRM 18th Scientific Meeting \& Exhibition, Stockholm}, author = {Schindler, J. and Ulucay, D. and Mende, J. and Radicke, M. and Kofahl, A.-L. and Finsterbusch, J. and Krieg, R. and Maier, K.} } @Conference { hoeismrm10, title = {Acoustic Relaxation Enhancement in MRI}, year = {2010}, month = {5}, abstract = {\emph{Purpose} MRI has become a powerful tool to distinguish between adjacent tissues by taking into account a variety of chemical, physical and biological properties of living tissue. By use of magnetic contrast agents in MRI one can even gain insight into some metabolic functions of a host. Conclusion on the metabolism, however, can only be drawn if (a) the metabolic function of interest locally affects the concentration of the contrast agent, and (b) the contrast agent leads to a clearly observable change in MRI signal within the region of interest. We present a contrast mechanism which aims to distinguish between magnetic contrast agents which are conjugated to cells or macromolecules and those which are not, independent on their spatial distribution. which is expected to picture the mobility of labeled macromolecules. The mobility might be changed, e.g., by the viscosity of the MNPs surroundings or by the macromolecules reactions to cells or other objects. which instantaneously can be switched on and off and thus provide specific information by immediate comparison between pictures taken with this contrast and those taken without it. The high specificity to chemical reactions of the here proposed contrast mechanism might become basis of a new method for functional imaging. \emph{Method} The spin-lattice relaxation time T1 of a sample volume decreases if magnetic nanoparticles (MNP) which are connected to mesoscopic objects are subjected to an ultrasonic wave at MRI Larmor frequency. This effect can be interpreted as a change in relaxivity of the MNPs under the influence of resonant ultrasound (US). MNPs subjected to an ultrasonic wave are accelerated periodically with US frequency, which now is assumed to match the Larmor frequency. It is well known that the induced translational movement of the MNPs does not lead to a pronounced change in the MRI relaxation times. If a MNP is connected to a organic macromolecule, however, the compound bends and to tilts periodically in the ultrasonic wave because its center of mass differs from its center of geometry (Fig. to right). Consequently these MNPs act as radio frequency near field antennas, inducing additional relaxation to nuclei in the vicinity of the MNPs. \emph{Results} We measured the proton spin-lattice relaxation time of a colloidal solution of MNPs ({\O} = 50 nm) connected to a macromolecule (chicken IgG) by means of an inversion recovery sequence (TI = 550 ms, TR = 20,000 ms) and analyzed the spectral composition of the 90\(^{\circ}\) FID (cf. Fig. to left). The abscissa denotes the frequency match between Larmor frequencies and US frequency (fUS = 18.32 MHz). When US was applied during the recovery process we could observe a change in signal amplitudes for spectral components matching the US frequency (upper curves). This we interpreted as a gain in relaxivity of the MNP-macromolecule compounds (lower curves). No changes in the FIDs' spectral amplitudes under the influence of resonant US were observed for a comparable solution of standard MNPs. We observed a gain in relaxivity of more than 15 \% at US intensities of P = 10-3 W/cm². \emph{Conclusion} Experiments for observing this contrast in a low field MRI device are underway. Due to the possibility to distinguish between bound an unbound MNPs independent on their spatial distribution and due to the improved contrast reliability by immediate comparison with not-contrast-enhanced pictures we expect this contrast method to fundamentally improve functional MRI.}, tags = {nmr}, misc = {Konferenz}, booktitle = {Joint Annual Meeting ISMRM and ESMRMB, Stockholm - Sweden}, author = {Hoehl, C. and Elmiladi, N. and Jahanbakhsh, F. and Repp, F. and Wolf, P. and Maier, K.} } @Conference { menismrm10, title = {Detecting breast phantom lesions with acoustic radiation force in MR images: experiment and finite-element simulations}, year = {2010}, month = {5}, abstract = {\emph{Introduction} Acoustic radiation contrast (ARC) in MR phase images is a recently developed method to image and quantify non-invasively the viscoelastic properties in vivo [1,2]. It is well known that tissue elastic properties may be altered by tumors. Young's modulus of breast tumors may differ from surrounding tissues by a factor of 90-fold. The ARC-MR images may be helpful in the distinction of benign from malignant masses. To test the applicability and feasibility of ARC-MR, a commercially available breast phantom was investigated and finite-element simulations were performed. Combining measurements and finite-element simulations yields the elastic and acoustic parameters of the phantom. \emph{Methods and Materials} Ultrasound (US) waves with a center frequency of 2.5 MHz were coupled into the breast phantom with the focal plane inside it. The acoustic radiation force leads to a displacement of the material inside its path in beam propagation direction. The displacement can be calculated from the phase shift in the phase images according to [2]. It was measured using a modified spin-echo sequence with monopolar gradients added for displacement encoding (sequence parameters: TE/TR: 60/400 ms, monopolar gradient length and amplitude: 20 ms and 20 mT/m, voxel: 1.7x1.7x3 mm3). The 20 ms US pulse was irradiated simultaneously with the second gradient pulse using external triggering. Intensities of 35 W/cm2 were used and provided by a home-built MR-compatible piezoelectric transducer. The transducer had a diameter of 5 cm and a focal length of 22 cm. The phase images were acquired at a 1.5 T Magnetom Avanto scanner (Siemens Healthcare, Erlangen (Germany)) with a 4 channel breast coil (NORAS MRI products GmbH, H{\"o}chberg (Germany)). The breast elastography phantom (CIRS, Norfolk, Virginia (USA)) accurately mimics the ultrasonic characteristics of tissues found in an average human breast. The lesions are three times stiffer than the background so they can be detected on elastograms [4]. A lesion of 0.9 cm diameter was investigated. For the finite-element simulations (Marc Mentat, MSC Software Corporation, Santa Ana, CA (USA)) the parameters were adjusted to fit the measurements: US beam diameter: 0.4 cm, US pulse length: 20 ms, US intensity: 35 W/cm2; geometry: cylinder with diameter: 4 cm, length: 6,4 cm; material parameters: elastic moduli: 10 kPa for the breast tissue [5] and 30 kPa for the lesion, Poisson's ratio: 0.495, density: 1 g/cm3, absorption coefficient: 0.345 cm-1. \emph{Results} Figure 1 a) \& b) show a T2-weighted amplitude image and a phase image of the breast phantom in sagittal plane without US; direction of displacement detection: A}, tags = {mrt}, misc = {Konferenz}, booktitle = {ISMRM 18th Scientific Meeting \& Exhibition, Stockholm}, author = {Mende, J. and Radicke, M. and Kofahl, A.-L. and Schindler, J. and Ulucay, D. and Finsterbusch, J. and Weber, B. and Maier, K.} } @Mastersthesis { jahanbakhsh, title = {Magnetische Nanopartikel in Gewebe - MRT-Kontrast durch resonaten Ultraschall}, year = {2010}, month = {4}, tags = {nmr}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Jahanbakhsh, F.} } @Mastersthesis { ulucay, title = {3D Darstellung von Verschiebungsfeldern - Schallstrahlungskraft in der {MRT}}, year = {2010}, month = {3}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2010_Diplom_Ulucay.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Ulucay, D.} } @Mastersthesis { wolf, title = {Resonanter Ultraschall in der Magnetresonanztomographie}, year = {2010}, month = {3}, tags = {nmr}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2010_Diplom_Wolf.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Wolf, P. J.} } @Mastersthesis { jschindl, title = {Schallstrahlungskraftkontrast in Magnet-Resonanz Aufnahmen - Detektion von Mikrokalk}, year = {2010}, month = {3}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2010_Diplom_Schindler.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Schindler, J.} } @Mastersthesis { RaethDipl2010, title = {Strukturierter Brechungsindex durch Ionenbestrahlung}, year = {2010}, month = {3}, tags = {linbo}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2010_Diplom_Raeth.pdf}, school = {Universit{\"a}t Bonn}, institute = {Helmholtz-Institut f{\"u}r Strahlen- und Kernphysik der Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {R{\"a}th, N. L.} } @Conference { raethdpg2010, title = {Ionendurchstrahltes Lithiumniobat: {\"A}nderung optischer und elektrischer Materialeigenschaften}, year = {2010}, month = {3}, abstract = {Lithiumniobat findet vielfache Anwendungen in Wissenschaft und Technik, insbesondere in optischen Bereichen. Um die Vorz{\"u}ge des Materials vollst{\"a}ndig ausnutzen zu k{\"o}nnen, ist eine genaue Kenntnis und die M{\"o}glichkeit zur Modifikation der Materialparameter erstrebenswert. Wird Lithiumniobat mit schnellen 3He-Ionen bei einer Energie von 41 MeV durchstrahlt, k{\"o}nnen entscheidende Materialeigenschaften gezielt gro{\ss}volumig und strukturiert ge{\"a}ndert werden. In der durchstrahlten Region werden langzeitstabile Brechungsindex{\"a}nderungen, sowie eine Herabsetzung der Koerzitivfeldst{\"a}rke beobachtet. Dar{\"u}ber hinaus zeichnet sich nach der Bestrahlung eine erh{\"o}hte Leitf{\"a}higkeit des Materials sowie eine erh{\"o}hte Dichte an Nukleationskeimen ab.}, tags = {linbo}, url = {http://www.dpg-verhandlungen.de/2010/regensburg/df15.pdf}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Regensburg}, author = {Raeth, N. L. and Jentjens, L. and Peithmann, K. and Maier, K.} } @Conference { schdpg10, title = {Schallstrahlungskraft in Magnetresonanzaufnahmen: Detektion von Mikrokalk}, year = {2010}, month = {3}, abstract = {Die Kontrasterzeugung durch die Schallstrahlungskraft in Magnetresonanzaufnahmen ist eine neuartige und nicht invasive Methode die elastischen Eigenschaften von Gewebe darzustellen. Eine Anwendungsm{\"o}glichkeit ist die Detektion von Mikrokalk. Es wurde ein f{\"u}r das Problem optimierter MR-kompatibler piezoelektrischer Emitter mit einer Resonanzfrequenz von 2,5 MHz benutzt, um ein Brustphantom der Schallstrahlungskraft auszusetzen. Die so erzeugte Bewegung in Richtung der Schallausbreitung wurde in Phasenbildern einer bewegungssensitiven Spin-Echo Sequenz an einem 1,5 T Tomographen und mit einer 4-kanaligen Brustspule sichtbar gemacht. Um Mikrokalk zu simulieren, wurden Eierschalenst{\"u}cke (von 0,8 x 0,8 mm bis 1,5 x 1,5 mm) in das gelartige Phantom eingef{\"u}gt. Das Phantom wurde durch das Verschieben des Ultraschalls abgerastert. Bei ausgeschaltetem Ultraschall war die Eierschale nicht sichtbar. Bei eingeschaltetem Ultraschall wird die Eierschale aufgrund des gro{\ss}en Unterschieds in der Schallkennimpedanz zwischen umgebendem Gewebe und Eierschale innerhalb des Schallstrahls sichtbar. Aus Vergleichen mit einer Simulation und durch Variation der Richtung der Bewegungsempfindlichkeit wird auch eine quantitative Charakterisierung m{\"o}glich.}, tags = {mrt}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Arbeitskreises Festk{\"o}rperphysik, Regensburg}, author = {Schindler, J. and Kofahl, A.-L. and Mende, J. and Radicke, M. and Ulucay, D. and Habenstein, B. and Finsterbusch, J. and Deimling, M. and Maier, K.} } @Conference { uludpg10, title = {Ultraschall (US) als MR-Kontrastgeber (ARC-MRI) f{\"u}r elastische Eigenschaften}, year = {2010}, month = {3}, abstract = {W{\"a}hrend einer bewegungssensitiven Spin-Echo-Sequenz eingestrahlter US kann zur Sichtbarmachung von elastischen Eigenschaften genutzt werden. Dazu wurde eine Spin-Echo-Sequenz durch 2 zus{\"a}tzliche, symmetrisch um den 180�-Puls angeordnete Gradienten erweitert. Der US wird w{\"a}hrend des 2. Gradienten eingestrahlt und f{\"u}hrt zu einer von der Verschiebung proportionalen Phasen{\"a}nderung. Die vom US erzeugte Schallstrahlungskraft wird in homogenem Gewebe/Material exponentiell abgeschw{\"a}cht, entsprechend der US-Absorption. Eine sich im Strahlverlauf befindende Verh{\"a}rtung kann durch gleiche Kraft nur weniger bewegt werden, daher kommt es zu einem Dip im exponentiellen Verlauf. US wird mittels eines MR-tauglichen US-Emitters in ein Brust-Phantom eingekoppelt, dessen elastische Eigenschaften denen menschlichen Gewebes entsprechen. In dieses Phantom sind L{\"a}sionen eingelassen, welche 3x h{\"a}rter als das umgebende Material sind. Die Verh{\"a}rtung ist im Phasenbild sichtbar und im exponentiellen Verlauf zeigt sich der erwartete Dip. Aus der Simulation des Schallstrahlungskrafteinflusses mit Finiten Elementen l{\"a}sst sich quantitativ der H{\"a}rteunterschied bestimmen.}, tags = {mrt}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Arbeitskreises Festk{\"o}rperphysik, Regensburg}, author = {Ulucay, D. and Kofahl, A.-L. and Mende, J. and Radicke, M. and Schindler, J. and Habenstein, B. and Trautner, P. and Weber, B. and Bourauel, C. and Maier, K.} } @Conference { jahdpg10, title = {Ultraschall induzierte Relaxation in MRT}, year = {2010}, month = {3}, abstract = {Der Einsatz von Kontrastmittel erlaubt der Magnetresonanztomographie (MRT) bestimmte Stoffwechselprozesse abzubilden. Vorraussetzung daf{\"u}r ist stets, dass die Stoffwechselprozesse zu einer lokalen Anreicherung des Kontrastmittels f{\"u}hren. Eine wichtige Klasse von Kontrastmitteln sind magnetische Nanopartikel (MNP), deren Oberfl{\"a}che praktische beliebig funktionalisiert werden kann. Die Reaktion von Makromolek{\"u}len mit der Oberfl{\"a}che der MNPs kann unabh{\"a}ngig von deren lokaler Anreicherung in H-NMR Experimenten beobachtet werden, wenn die Probe w{\"a}hrend der Messung resonantem Ultraschall ausgesetzt ist. Dieser Effekt wurde in Wasser entdeckt, die Anwendbarkeit der Methode in Gewebephantomen wird diskutiert. Dabei wird auch der Einfluss auf die Querrelaxationszeit}, tags = {nmr}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Arbeitskreises Festk{\"o}rperphysik, Regensburg}, author = {Jahanbakhsh, F. and H{\"o}hl, C. and Repp, F. and Wolf, P. and Maier, K.} } @Conference { wodpg10, title = {Ultraschallinduzierte Kontraste in der Magnetresonanztomographie}, year = {2010}, month = {3}, abstract = {Magnetische Nanopartikel (NMPs) sind in der NMR Relaxationszentren und werden deshalb in der Magnetresonanztomographie (MRT) als Kontrastmittel eingesetzt. Sie bestehen aus einem oder mehreren magnetischen Kernen und einer nichtmagnetischen H{\"u}lle die nahezu beliebig chemisch funktionalisiert und mit Makro molek{\"u}len beschichtet werden kann. In MMR-Experimenten konnte gezeigt werden, dass durch resonanten Ultraschall (US) mit NMR Lamorfrequenz zwischen einseitig beschichteten und nicht beschichteten NMPs unterschieden werden kann. Dies birgt interessant Eigenschaften f{\"u}r ortsaufgel{\"o}ste Messungen an einem MRT. Allerdings ist resonanter Ultraschall dort schwerlich anwendbar, da elektromagnetische {\"U}bersprecher der USApparatur mit Lamorfrequenz den MRT-Empfangskreis empfindlich st{\"o}ren. Au{\ss}erdem betr{\"a}gt bei {\"u}blichen Lamorfrequenzen die Eindringtiefe in Gewebe nur Zentimeter. Deshalb schlagen wir das Konzept der Frequenzverdopplung vor. Der Energietransfer ins Gewebe erfolgt mit einem Ultraschallemitter mit einer niedrigen Grundfrequenz. Im Fokus eines Ultraschallemitters erzeugt man aufgrund von Nichtlinearit{\"a}ten des Gewebes h{\"o}here Harmonische der Schallwelle. Erste Messungen und Experimente werden vorgestellt.}, tags = {nmr}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Arbeitskreises Festk{\"o}rperphysik, Regensburg}, author = {Wolf, P. and H{\"o}hl, C. and Jahanbakhsh, F. and Repp, F. and Maier, K.} } @Mastersthesis { liu, title = {Investigation of Quenched-in Vacancies in Pure Aluminium and the Precipitation in Al-Zn-Mg Alloys}, year = {2010}, month = {1}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2010_Diplom_Liu.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Liu, M.} } @Thesis { volmer, title = {Ultraschallfelder f{\"u}r {B}ildkontraste - {D}{\"a}mpfung von {O}berwellen durch einen akustischen {T}iefpass}, year = {2010}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2010_Bachelor_Volmer.pdf}, school = {Universit{\"a}t Bonn}, institution = {Universit{\"a}t Bonn}, type = {Bachelorarbeit}, author = {Volmer, J.} } @Thesis { afzal, title = {Ultraschallfelder f{\"u}r {B}ildkontraste - {D}{\"a}mpfung von {O}berwellen durch einen akustischen {T}iefpass: {E}rgebnisse der {M}essungen}, year = {2010}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2010_Bachelor_Afzal.pdf}, school = {Universit{\"a}t Bonn}, type = {Bachelorarbeit}, author = {Afzal, F.} } @Thesis { obermann10, title = {Verbesserungsm{\"o}glichkeit von {MR}-{A}ufnahmen mit {H}ilfe eines rauscharmen {E}mpfangsschwingkreises}, year = {2010}, tags = {mrt}, school = {Universit{\"a}t Bonn}, institution = {Universit{\"a}t Bonn}, type = {Bachelorarbeit}, author = {Obermann, T.} } @Miscellaneous { haaks:2010, title = {{Materialforschung mit Positronen: Von der Doppler-Spektroskopie zur Vorhersage des Erm{\"u}dungsbruchs}}, year = {2010}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2010_Habil_Haaks.pdf}, school = {Helmholtz-Institut f{\"u}r Strahlen- und Kernphysik, Universit{\"a}t Bonn}, type = {Habilitationsschrift}, author = {Haaks, M.} } @Phdthesis { jentjens2010, title = {Bestrahlungsinduzierte Modifikation der Materialparameter in magnesiumdotiertem Lithiumniobat}, year = {2010}, tags = {linbo}, url = {http://nbn-resolving.org/urn:nbn:de:hbz:5N-23631}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Jentjens, L.} } @Phdthesis { elmiladidiss2010, title = {Proton Spin-Lattice Relaxation in Colloidal Aqueous Solutions with Resonant Ultrasound}, year = {2010}, tags = {nmr}, url = {http://nbn-resolving.org/urn:nbn:de:hbz:5N-22404}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Elmiladi, N. M.} } @Phdthesis { mende10, title = {Schallinduzierter {K}ontrast in {MRT}-{P}hasenbildern - {D}etektion von {K}alkablagerungen und erste {B}rustuntersuchungen von {P}robanden}, year = {2010}, tags = {mrt}, url = {http://nbn-resolving.org/urn:nbn:de:hbz:5N-22358}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Mende, J.} } @Phdthesis { korff2010, title = {Simulationsrechnungen zur Positronenannihilation in Aluminiumlegierungen zur Untersuchung der Ausscheidungsbildung}, year = {2010}, tags = {positron}, url = {http://nbn-resolving.org/urn:nbn:de:hbz:5N-23792}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Korff, B.} } @Phdthesis { klobes:2010, title = {Strukturelle Umordnungen in Aluminiumlegierungen: ein komplement{\"a}rer Ansatz aus der Perspektive von Leerstellen und Fremdatomen}, year = {2010}, tags = {positron, material}, url = {http://nbn-resolving.org/urn:nbn:de:hbz:5N-22660}, school = {Universit{\"a}t Bonn}, institute = {Helmholtz-Institut f{\"u}r Strahlen- und Kernphysik}, type = {Dissertation}, author = {Klobes, B.} } @Article { kohlbach:2010, title = {(Meta-)stable phases and pre-Guinier-Preston zones in AlCu alloys constructed from ab initio relaxed atomic positions a Comparison to experimental methods}, journal = {phys. stat. sol. (b)}, year = {2010}, volume = {247}, number = {9}, pages = {2168--2178}, keywords = {ab initio calculations, crystal defects, positron annihilation spectroscopy, X-ray absorption}, tags = {positron}, url = {http://onlinelibrary.wiley.com/doi/10.1002/pssb.201046102/abstract}, publisher = {WILEY-VCH Verlag}, ISSN = {1521-3951}, DOI = {10.1002/pssb.201046102}, author = {Kohlbach, I. and Korff, B. and Staab, T. E. M.} } @Article { ISI:000283807900017, title = {{The effect of microalloying additions of Au on the natural ageing of Al-Cu}}, journal = {Acta Mater.}, year = {2010}, volume = {58}, number = {{19}}, pages = {6379-6384}, abstract = {{The influence of microalloying additions of Au to the binary Al-Cu system is investigated utilizing hardness measurements, positron annihilation spectroscopy and X-ray absorption spectroscopy. No room temperature ageing could be observed in the case of the ternary Al-Cu-Au alloy. Instead, quenched-in vacancies were trapped by Au atoms and thus could not catalyse the decomposition of the alloy. However, artificial ageing dissolves the complexes of Au and vacancies. A comparison between experimental and calculated absorption spectra shows that Au atoms did not agglomerate significantly during either natural or artificial ageing. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.}}, tags = {positron, material}, url = {http://www.sciencedirect.com/science/article/pii/S1359645410005033}, ISSN = {{1359-6454}}, DOI = {10.1016/j.actamat.2010.07.059}, author = {Klobes, B. and Balarisi, O. and Liu, M. and Staab, T. E. M. and Maier, K.} } @Article { paperkalk, title = {Acoustic radiation force contrast in {MRI}: detection of calcifications in tissue-mimicking phantoms}, journal = {Medical Physics}, year = {2010}, volume = {37}, pages = {6347-6356}, tags = {mrt}, url = {http://online.medphys.org/resource/1/mphya6/v37/i12/p6347_s1}, DOI = {10.1118/1.3512806}, author = {Mende, J. and Wild, J. and Ulucay, D. and Radicke, M. and Kofahl, A.-L. and Weber, B. and Krieg, R. and Maier, K.} } @Article { Wirtz2010, title = {Non-destructive evaluation of plasticity and prediction of fatigue failure in industrial aluminium alloys with positrons}, journal = {Phys. Status Solidi A}, year = {2010}, volume = {207}, number = {8}, pages = {1827--1831}, abstract = {The concentration of lattice defects in plastically,deformed metals can be measured by positron annihilation spectroscopy (PAS) with an outstanding sensitivity. The positron acts as a highly mobile atomic probe sensitive to all defects forming an open volume in the lattice. Using a positron microbeam, like the Bonn positron microprobe (BPM), the lateral distribution of these defects in the sub-surface layer can be mapped with a resolution down to one micrometer. In this work the changes in the defect concentration were determined during tension tests on the aluminium alloys AA2024, AA6013 and AA6082. The results show that these changes depend on the configuration and the heat treatment of the alloys. Moreover, alternating load fatigue tests were performed on AA6082. The defect distribution was measured laterally resolved employing the BPM in several early stages of fatigue. Using those results the number of cycles to fatigue failure was extrapolated. The trueness of the prediction was tested by further fatiguing the sample until failure occurs. (C) 2010 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim}, tags = {positron, material}, url = {http://onlinelibrary.wiley.com/doi/10.1002/pssa.200925540/abstract;jsessionid=FD0156421B82E863995F70B5BCB6D028.d01t03}, DOI = {10.1002/pssa.200925540}, author = {Wirtz, M. and Eich, P. and Haaks, M. and Loewenhoff, Th. and Maier, K.} } @Article { Mende2010203, title = {Nuclear acoustic resonance in fluids using piezoelectric nanoparticles}, journal = {Journal of Magnetic Resonance}, year = {2010}, volume = {203}, number = {2}, pages = {203 - 207}, tags = {mrt}, url = {http://www.sciencedirect.com/science/article/pii/S1090780709003747}, ISSN = {1090-7807}, DOI = {10.1016/j.jmr.2009.12.019}, author = {Mende, J. and Elmiladi, N. and H{\"o}hl, C. and Maier, K.} } @Article { Klobes2010, title = {Probing the defect state of individual precipitates grown in an Al-Mg-Si alloy}, journal = {Phys. Rev. B: Condens. Matter Mater. Phys.}, year = {2010}, volume = {82}, number = {5}, pages = {054113}, abstract = {Precipitates forming in decomposable aluminum alloys such as Al-Mg-Si evolve toward the corresponding intermetallic phase, which is beta(Mg(2)Si) in this case, depending on heat-treatment conditions. Individual beta precipitates were produced in an Al-1.11 at. \% Mg-0.77 at. \% Si alloy and identified using optical as well as electron microscopy. The individual beta precipitates could be investigated with regard to their intrinsic crystal defects using a finely focused positron microbeam provided by the Bonn Positron Microprobe. Comparison with theoretical calculations of the Doppler broadening of annihilation radiation reveals that beta precipitates most likely do not contain vacancies in either sublattice and that 0.16 is the upper bound of the fraction of trapped positrons. The usage of different enhancement factors had only little influence on the calculations whereas the general gradient approximation affected the contribution of Si orbitals, in particular. Additional measurements of the Doppler broadening based on the radioactive source (68)Ge, which emits high-energy positrons probing bulk regions of the sample, were carried out. These measurements show that beta precipitates are sparsely distributed in the Al matrix.}, tags = {positron, material}, url = {http://prb.aps.org/abstract/PRB/v82/i5/e054113}, DOI = {10.1103/PhysRevB.82.054113}, author = {Klobes, B. and Korff, B. and Balarisi, O. and Eich, P. and Haaks, M. and Maier, K. and Sottong, R. and Huehne, S.-M. and Mader, W. and Staab, T. E. M.} } @Article { Zamani-Meymian2010, title = {Thermal and long-term stability of fast-ion-irradiation-induced refractive index changes in lithium niobate crystals}, journal = {Appl. Phys. A}, year = {2010}, volume = {98}, number = {4}, pages = {909-912}, abstract = {Irradiation of congruently melting, nominally undoped lithium niobate crystals (LiNbO3) with high-energy, low-mass \(^{3}\)He ions, which are transmitted through the crystal, causes large and stable changes of the refractive index. In the irradiated regions, the extraordinary index is increased whereas the ordinary index is diminished. The decay of these changes upon annealing treatments up to 400\(^{\circ}\)C is investigated, exhibiting a strongly non-monoexponential decay behaviour. Long-term measurements of the refractive index changes yield no pattern erasure on a timescale of four years.}, tags = {linbo}, url = {http://www.springerlink.com/content/310746l53235q1t4/}, publisher = {{SPRINGER}}, address = {{233 SPRING ST, NEW YORK, NY 10013 USA}}, type = {{Article}}, ISSN = {0947-8396}, DOI = {10.1007/s00339-009-5475-9}, author = {Zamani-Meymian, M.-R. and Jentjens, L. and Raeth, N. L. and Peithmann, K. and Maier, K.} } @Mastersthesis { kofahl, title = {FEM-Simulationen von Ultraschall-induzierten Gewebeverschiebungen}, year = {2009}, month = {12}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2009_Diplom_Kofahl.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Kofahl, A.-L.} } @Mastersthesis { balarisi, title = {Untersuchung von Einzelausscheidungen in Aluminiumlegierungen mit einem Positronenstrahl}, year = {2009}, month = {12}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2009_Diplom_Balarisi.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Balarisi, O.} } @Conference { hoeismrm09, title = {Switching of MRI contrast agents with ultrasound}, year = {2009}, month = {5}, abstract = {\emph{Purpose} MRI has become a powerful tool to distinguish between adjacent tissues by taking into account a variety of chemical, physical and biological properties of living tissue. By use of magnetic contrast agents in MRI one can even gain insight into some of the tissue's metabolic functions. Conclusions on the metabolism, however, can only be drawn if (a) the metabolic function in question locally affects the concentration of the contrast agent, and if (b) the contrast agent leads to a clearly observable change of the MRI signal within the region under consideration. First observations of a contrast mechanism which addresses these limitation have been presented during last ISMRM conference, and a more complete presentation and discussion has been submitted to Phys. Rev. Let. recently. Questions remained open, however, whether the technical requirements for the contrast mechanism may become compatible with in vivo measurements in a standard MRI device. Current research promises to solve the technical difficulties and first observations of the contrast in a low field MRI device are underway. \emph{Method} Contrast agents based on magnetic nanoparticles (MNPs) affect the transverse relaxation times of nuclei of the solvent (e. g. protons) in their vicinity due to their magnetic stray field. MNP also affect the longitudinal relaxation time T1 if the thermal motion of the MNPs happens to lead to local field fluctuations at nuclei Larmor frequency. It was shown, that ultrasound at Larmor frequency increased the influence of specially prepared MNPs on T1 considerably if ultrasound (US) matches Larmor frequency. These experiments were carried out using an NMR spectrometer where shielding of the receiving coils can be realized easily. In an MRI device, however, US radiation at MRI Larmor frequency would lead to disturbance of the MRI device. \emph{Results} Picture1 presents the pressure evolution over time at a given position in a US wave (fUS = 2.5 MHz) in a water sample (measurement with hydrophone with bandwith of 60 MHz). Deviations from the sinusoidal wave-form originate from the strong nonlinear behavior of the water sample. Exploiting frequency doubling effects in tissue not only avoids electromagnetic cross-coupling between the US device and the MRI device, but also provides us with the higher penetration depth of the fundamental wave. \emph{Conclusion} The contrast mechanism allows to distinguish between bound and unbound MNPs independent on their spatial distribution. The strong nonlinearities of tissue exposed to an ultrasonic wave promise this contrast mechanism to become compatible with standard MRI devices. Experiments exploiting ultrasound frequency doubling to activate the contrast mechanism in a low field MRI device (open tomography system) are underway.}, tags = {nmr}, misc = {Konferenz}, booktitle = {ISMRM Seventeenth Scientific Meeting and Exhibition, Honolulu - Hawaii}, author = {Elmiladi, N. and Hoehl, C. and Maier, K.} } @Conference { elmdpg09, title = {Enhanced MRI Contrast Agents with Resonant Ultrasound}, year = {2009}, month = {3}, abstract = {We have developed a method involving the application of ultrasound (US) in magnetic resonance imaging (MRI) in the presence of antibody coated magnetic nanoparticles to generate contrast. Similar magnetic nanoparticles are already used as contrast agents. It is interesting to control their effect by additional parameters, which can be switched on and off externally, and depend on the properties of the surrounding tissue. In performing proton nuclear magnetic resonance spectroscopy, US is applied to an aqueous sample containing magnetic nanoparticles coated with antibodies from one side only. Therefore, while the asymmetric magnetic nanoparticles in the sample are subjected to an US wave, a torque is initiated along the vibrational motion and will cause the particles to tilt periodically. The asymmetric magnetic nanoparticles will act as an US driven radio frequency antenna, leading to an increase in the spectral density function at the US frequency. If the US frequency matches the Larmor frequency, protons in the near field region of the particle are stimulated to lose energy, and the T1 of the aqueous solution decreases. A significant increase of the longitudinal proton relaxation rate is experimentally observed when using a colloidal aqueous solution of asymmetric magnetic nanoparticles.}, tags = {nmr}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Fachverbandes Strahlen- und Medizinphysik, M{\"u}nchen}, author = {Elmiladi, N. and H{\"o}hl, C. and Maier, K.} } @Conference { radpg09, title = {Schallabsorption und viskoelastische Parameter als Kontrast in der MRT}, year = {2009}, month = {3}, abstract = {Mittels eines Ultraschallpulses wird in einer Probe eine statische Auslenkung w{\"a}hrend dieser Pulsdauer erzeugt. Das Prinzip dahinter beruht auf dem Schallstrahlungsdruck. Die lokale Auslenkung der Probe wird mit einer speziellen MRT-Sequenz gemessen und farbkodiert dargestellt. Sie ist abh{\"a}ngig von der Schallamplitude, der Schallfrequenz, der viskoelastischen Eigenschaften der Probe und der Schallabsorption innerhalb der Probe. Da die Schallamplitude sowie die Schallfrequenz frei w{\"a}hlbar sind und die Schallamplitude nicht linear mit dem zur{\"u}ckgelegten Schallweg abf{\"a}llt, k{\"o}nnen somit R{\"u}ckschl{\"u}sse auf die viskoelastischen Eigenschaften und die Schallabsorption separat erhalten werden. Wir benutzen eine Spin-Echo-Sequenz mit zwei zus{\"a}tzlichen, {\"a}quivalenten, 20ms langen und 20mT/m starken Gradienten, sowie eine Ultraschallleistung von unter 5W/cm2 bei einer Pulsl{\"a}nge von 20ms. Als Proben werden Phantome aus Gel und Agar- Agar benutzt, die menschlichem Gewebe bzw. menschlichen Organen mit k{\"u}nstlichen Tumoren nachempfunden sind.}, tags = {mrt}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Fachverbandes Strahlen- und Medizinphysik, M{\"u}nchen}, author = {Radicke, M. and Oehms, O. and Mende, J. and Habenstein, B. and Maier, K.} } @Conference { jentjensdpg2009, title = {Strahlungsinduzierte Modifikationen des Polungsverhaltens von magnesiumdotiertem Lithiumniobat}, year = {2009}, month = {3}, abstract = {Auf Grund des stark unterdr{\"u}ckten photorefraktiven Effektes ist mit Magnesium dotiertes Lithiumniobat (LiNbO\(_{3}\):Mg) f{\"u}r viele Anwendungen interessant. In periodisch gepoltem Lithiumniobat (PPLN) kann {\"u}ber Quasi-Phasen-Anpassung eine effiziente Frequenzverdopplung erreicht werden, welche in LiNbO\(_{3}\):Mg selbst bei h{\"o}chsten Laserintensit{\"a}ten funktioniert. Durch die Bestrahlung mit schnellen 3He-Ionen mit einer Energie von 41 MeV k{\"o}nnen entscheidende Materialeigenschaften gezielt ge{\"a}ndert werden. In der durchstrahlten Region (vor dem Bragg-Peak) werden langzeitstabile Brechungsindex¨anderungen von bis zu 6 \(\times\) 10\(^{−3}\) beobachtet. Des Weiteren wird das ferroelektrische Koerzitivfeld EC um etwa 10\% vermindert und dadurch eine Invertierung der Dom{\"a}nen erleichtert. Durch die Bestrahlung wird zudem die Erzeugung von PPLN mit Periodenl{\"a}ngen im \(\mu\)m-Bereich erleichtert, die f{\"u}r die Frequenzverdopplung von blauem Laserlicht ben{\"o}tigt wird.}, tags = {linbo}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung, Dresden}, author = {Jentjens, L. and Peithmann, K. and Maier, K. and Steigerwald, H. and Jungk, T.} } @Conference { mendpg09, title = {Tumorsuche an Phantomen im MRT-Bild mittels Ultraschall}, year = {2009}, month = {3}, abstract = {Wir untersuchen die Kontrasterzeugung im MRT-Bild mittels des Schallstrahlungsdrucks von Ultraschall. Dieser Kontrast kann die viskoelastischen Eigenschaften wie Elastizit{\"a}ts- und Schubmodul in einem Phantom graukodiert sichtbar machen. W{\"a}hrend einer Standard-Spin- Echo Sequenz mit zwei bewegungssensitiven Gradienten wird ein Ultraschallpuls mit ca. 20 ms L{\"a}nge bei einer Frequenz von 2,5 MHz eingestrahlt. Zur Untersuchung wurden Phantome aus Agar-Agar mit Kieselerde in verschiedenen Konzentrationen hergestellt. Agar-Agar ist eine gelartige Substanz, Kieselerde dient als Absorber der Ultraschallwelle. Dies soll viskoelastische Eigenschaften von menschliches Gewebe nachahmen. In die Phantome wurden Tumore aus {\"O}l-in-Gelatine- Mischungen eingebaut, die im Protonendichtekontrast abgebildet werden. In MRT-Differenzbildern mit und ohne Ultraschall k{\"o}nnen diese Tumore mit dem Ultraschall aufgrund von unterschiedlichen mechanischen Eigenschaften ''ertastet'' werden.}, tags = {mrt}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Fachverbandes Strahlen- und Medizinphysik, M{\"u}nchen}, author = {Mende, J. and Radicke, M. and Oehms, O. and Maier, K.} } @Conference { mendpg09b, title = {Zerst{\"o}rungsfreie Beobachtung der r{\"a}umlichen Verteilung von elastischen Konstanten in weicher Materie}, year = {2009}, month = {3}, abstract = {Mit Ultraschall (US), der w{\"a}hrend einer Spin-Echo-Sequenz in einem medizinischen Tomographen eingestrahlt wird, k{\"o}nnen verschiedene elastische Konstanten in weicher Materie dreidimensional und zerst{\"o}rungsfrei dargestellt werden. In Proben mit unterschiedlichen Festigkeiten werden Kugeln aus einer {\"O}l-in-Gelatine-Mischung eingebracht. Die Proben bestehen aus Agar-Agar und Kieselerde. Agar ist ein biologisches Geliermittel. Die Kieselerde dient zur Absorption des US. Die Kugeln besitzen ein h{\"o}heres Elastizit{\"a}ts- und Schubmodul als die Umgebung aus Agar-Agar und Kieselerde. Von den Proben werden Phasenbilder gemacht, die die Phase der Spins in Grauwerten kodiert darstellen. Die Verschiebung innerhalb der Probe durch den Schallstrahlungsdruck ist abh{\"a}angig von den elastischen Eigenschaften innerhalb der Probe. Die Darstellung der Verschiebung im Bild erfolgt durch ein Paar von magnetischen Feldgradienten. W{\"a}hrend einem dieser Gradienten wird der US mit einer Frequenz von ca. 2,5 MHz und einer L{\"a}nge von 20 ms eingestrahlt. In den Bildern wird eine Phasenverschiebung durch eine Verschiebung auf der Grauskala sichtbar. In Differenzbildern mit und ohne US k{\"o}nnen R{\"u}ckschl{\"u}sse auf die r{\"a}umliche Verteilung der elastischen Eigenschaften der Probe und der darin befindlichen Fremdk{\"o}rper gezogen werden.}, tags = {mrt}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Fachverbandes Metall- und Materialphysik, Dresden}, author = {Mende, J. and Radicke, M. and Oehms, O. and Maier, K.} } @Thesis { paul2009, title = {Die Druckmessung auf dem Tibiaplateau des menschlichen Kniegelenks unter Verwendung eines Belastungssimulators}, year = {2009}, month = {2}, school = {Fachhochschule Koblenz, RheinAhrCampus Remagen}, type = {Bachelorarbeit}, author = {Paul, S.} } @Phdthesis { oehms09, title = {Kontrasterzeugung in der Kernspintomographie durch gepulsten Ultraschall}, year = {2009}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2009_Doktor_Oehms.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Oehms, O. B.} } @Phdthesis { radicke09, title = {Schallstrahlungskontrast in {MR}-{P}hasenbildern - {M}ethode zur {D}arstellung von {E}lastizit{\"a}ts-, {S}challd{\"a}mpfungs- und {S}challimpedanz{\"a}nderungen}, year = {2009}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2009_Doktor_Radicke.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Radicke, M.} } @Phdthesis { lenk2009, title = {Wasserstoffeinlagerung an Erm{\"u}dungsrissen der Aluminiumlegierung 6013 unter korrosiver Umgebung}, year = {2009}, tags = {material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2009_Doktor_Lenk.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Lenk, C. A.} } @Phdthesis { eich2009, title = {Zerst{\"o}rungsfreie Absch{\"a}tzung der Restlebensdauer metallischer Werkstoffe}, year = {2009}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2009_Doktor_Eich.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Eich, P. C.} } @Article { Zamani-Meymian2009, title = {{Direct visualization of damage cascades in lithium niobate crystals caused by high-energy ions}}, journal = {J. Phys. Condensed Matter}, year = {2009}, volume = {21}, number = {7}, pages = {075402}, abstract = {Congruently melting undoped lithium niobate crystals are irradiated with 20 MeV3 He ions which penetrate the entire crystal volume. Radiation damage effects are directly visualized by transmission electron microscopy (TEM) where damage zones with diameters of 4 nm give rise to circular Fresnel fringe contrasts. These regions of modified material, appearing circular in cross-section, are interpreted as damage cascades inflicted by fast Nb and O atoms displaced in knock-on collisions with primary He-3 ions. This two-step displacement process results in local density changes manifested by the contrast behaviour of Fresnel fringes observed in TEM images.}, tags = {linbo}, url = {http://iopscience.iop.org/0953-8984/21/7/075402/}, publisher = {{IOP PUBLISHING LTD}}, address = {{DIRAC HOUSE, TEMPLE BACK, BRISTOL BS1 6BE, ENGLAND}}, type = {{Article}}, ISSN = {{0953-8984}}, DOI = {{10.1088/0953-8984/21/7/075402}}, author = {Zamani-Meymian, M.-R. and Peithmann, K. and Maier, K. and Schmid, H. and Mader, W.} } @Article { springerlink:10.1007/s00340-009-3496-x, title = {Radiation-damage-assisted ferroelectric domain structuring in magnesium-doped lithium niobate}, journal = {Appl. Phys. B: Lasers Opt.}, year = {2009}, volume = {95}, number = {3}, pages = {441-445}, abstract = {Irradiation of 5\% magnesium-doped lithium niobate crystals (LiNbO 3 :Mg) with high-energy, low-mass 3 He ions, which are transmitted through the crystal, changes the domain reversal properties of the material. This enables easier domain engineering compared to non-irradiated material and assists the formation of small-sized periodically poled domains in LiNbO 3 :Mg. Periodic domain structures exhibiting a width of ≈520 nm are obtained in radiation-damaged sections of the crystals. The ferroelectric poling behavior between irradiated and non-treated material is compared.}, affiliation = {Universit{\"a}t Bonn Helmholtz-Institut f{\"u}r Strahlen- und Kernphysik Nussallee 14-16 53115 Bonn Germany}, tags = {linbo}, url = {http://www.springerlink.com/content/c624u15604046572/}, publisher = {Springer Berlin / Heidelberg}, ISSN = {0946-2171}, DOI = {10.1007/s00340-009-3496-x}, author = {Jentjens, L. and Peithmann, K. and Maier, K. and Steigerwald, H. and Jungk, T.} } @Article { staab:2009, title = {Vacancies in magnesium silicide - stoichiometric vacancies preferred?}, journal = {phys. stat. sol. (b)}, year = {2009}, volume = {246}, number = {7}, pages = {1587--1589}, keywords = {61.72.jd, 61.72.Bb, 61.82.Bg}, tags = {positron, material}, url = {http://onlinelibrary.wiley.com/doi/10.1002/pssb.200844348/abstract}, publisher = {WILEY-VCH Verlag}, ISSN = {1521-3951}, DOI = {10.1002/pssb.200844348}, author = {Staab, T. E. M.} } @Mastersthesis { wirtz, title = {Untersuchung von Plastizit{\"a}t und Erm{\"u}udung technischer Aluminiumlegierungen mit Positronen}, year = {2008}, month = {11}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2008_Diplom_Wirtz.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Wirtz, M.} } @Mastersthesis { rieke, title = {Ausscheidungen in Aluminium-Legierungen: Temperaturabh{\"a}ngigkeit des Positroneneinfangs}, year = {2008}, month = {8}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2008_Diplom_Rieke.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Rieke, C.} } @Mastersthesis { loewenhoff, title = {Mechanische Relaxation der plastischen Zone vor Rissspitzen in technischen Al-Legierungen}, year = {2008}, month = {6}, tags = {material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2008_Diplom_Loewenhoff.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {L{\"o}wenhoff, T. W.} } @Mastersthesis { huehne, title = {Einzelfehlstellennachweis mit einem Positronen-Mikrostrahl}, year = {2008}, month = {5}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2008_Diplom_Huehne.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {H{\"u}hne, S.-M.} } @Conference { hoeismrm08, title = {High frequency relaxation with contrastagents}, year = {2008}, month = {5}, abstract = {\emph{Purpose} MRI provides images with excellent anatomical details based on soft-tissue contrast and functional information in a non-invasive and real-time monitoring manner. MRI has been further advanced by the development of contrast agents such as Gadolinium compounds that enable more specific and clearer images and enlargement of detectable organs and systems. Magnetic nanometer-sized, colloidal particles (nanoparticles) are well known and extensively used in MRI as contrast agent, too. Due to their influence on the relaxation processes, they offer a possibility to label organic macro molecules. It is interesting to control their effect on MRI by additional parameters, which may be switched on and off externally or may depend on the properties of the surrounding tissue. We develop such a new contrast method with nanoparticles, by applying ultrasound (US) while performing proton magnetic resonance spectroscopy. \emph{Method} The basic process involved in the relaxation in MRI is coupling between the magnetic moments of the spin and photons with the corresponding larmor frequency - which can lead to stimulated emission or absorbtion. This results in an energy transfer out of the spin system to the lattice (longitudinal relaxation process) or transfer within the spin system (transversal relaxation process). To gain higher sensitivity with a contrast agent in MRI, the contrast agent has to have a greater effect on the relaxation times. Especially prepared nanoparticles work as a radio frequency transmitter. For this, we are using two completely different kinds of nanoparticles: a) Superparamagnetic of Iron Oxide (SPIO) To increase the spectral density of photons with a special frequency, SPIO should work as an antenna. The SPIOs are prepared such that the center of geometry differs from the center of mass. This is done by sedimentation of the SPIOs, so that we can add macromolecules from one side only. Due to the particle velocity in the US-wave, SPIOs are accelerated and due to their asymmetric shape they tilt periodically. This produces additional photons with US-frequency. b) Piezoelectric Nanoparticles Piezoelectric particles have the ability to generate an electric potential in response to applied mechanical stress. In combination with the periodic pressure variation in an US-wave, these particles function as a transmitter (displacement current). To achieve this, a powder consisting of 100nm sized particles is prepared into a colloid in water by coating with PAA. The HF-fields emitted by nanoparticles are not coherent and therefore unable to rotate the net-magnetization. \emph{Results} Influence of the US on NMR measurements for the SPIO was examined. Early measurements showed a change of the relaxation times T1 and T2* in water when using piezoelectric particles. Furthermore, measurements on SPIO indicates the influence of the US at the resonance frequency. The figure to the right compares the amplitude of the FID after a 90\(^{\circ}\) puls in an inversion recovery sequence with and without US. These measurements were taken before getting the SPIO in the final shape. Sedimentation process of the SPIO have been achieved by applying a combination of centrifugal force and magnetic force. Conclusion Using nanoparticles as local antenna in combination with US promises new contrast methods which image properties of the tissue. Even without any special preparation of the nanoparticles, an effect of the US on the MRI-Signal has been seen.}, tags = {nmr}, misc = {Konferenz}, booktitle = {ISMRM Sixteenth Scientific Meeting and Exhibition, Toronto - Canada}, author = {Hoehl, C. and Elmiladi, N. and Mende, J. and Maier, K.} } @Conference { oehismrm08, title = {Visualization of viscoelastic properties by combining US pulses and MRI}, year = {2008}, month = {5}, abstract = {\emph{Purpose} Ultrasound (US) and MRI are two highly sophisticated non-destructive methods which make it possible to visualize the inner parts of the body. Contrasts between tissues in the MRI measurement are based on the physical parameters T1, T2, T2*, and the proton density, which can be modified by the application of contrast agents. The corresponding parameter in the US measurement is the sound impedance. The aim of our studies is it to combine the two methods and introduce US as a tool to generate contrasts in an MRI picture between tissues and liquids with differing viscoelastic properties. Therefore an US setup that does not affect the imaging of the MR scanner has been developed. The US emitter had to be shielded electromagnetically in order to avoid crosstalk within the MRI coils. \emph{Method } In order to apply US to a sample during an MRI measurement, some kind of synchronisation between the MRI sequence and the application of the US pulses has to be achieved. A simple antenna makes it possible to visualize the rf-pulses of the sequence on an oscilloscope. These signals can be used to trigger the US emitter and place the US pulses at any desired time in the MRI sequence. Once coupled into the sample, a damping of the US wave along the path of propagation occurs which corresponds to a decrease of the acoustic radiation pressure along the direction of propagation. This pressure gradient leads to a force on each volume element along the path of the US beam. In a liquid, this results in a movement of the molecules along the US path in the direction of propagation of the US. This movement dies away when the US-pulse is over and reestablishes with the next pulse. When a piece of tissue is placed in the US path, the decrease of the acoustic radiation pressure leads to a quasi-statical displacement of the irradiated parts of the tissue in the direction of the propagating sound wave for the duration of the US pulse. This displacement depends on the viscoelastic properties and the of the tissue and the amplitude and absorption of the US. When the pulse stops, the restoring forces in the tissue make it return to its original position. A diffusion sensitive sequence, which is sensitive to movements in the direction of propagation, is able to visualize the sound path in a liquid (fig. 1) and the displacement of the tissue. All measurements were performed with the standard eight channel head coil on an 1.5T SIEMENS AVANTO scanner at the research center LIFE \& BRAIN in Bonn, Germany. During a diffusion-weighted EPI sequence (EPI2D_DIFF_RO), US was irradiated into several liquids (water, glycerine, ethanol) for 30ms at a frequency of 9.41MHz with a maximum excess pressure of about 1 Bar. The US pulse was applied after the first of the two 180\(^{\circ}\) pulses which guaranteed an overlap with the diffusion gradient. For the measurements on tissue, an US lens with a resonance frequency of 4.77MHz was constructed and a simple GRE sequence (Te=12.1ms, Tr=123ms) was used. \emph{Results} Figure 1 shows a setup, where the US beam was deflected by a sheet of glass in a water sample. Only if the direction of the diffusion gradients is aligned with the direction of the sound propagation, the US beam is visible in the MR image as a region with lower signal. Figure 1: Deflection of the US beam at a sheet of glass. At the top of the pictures a rod made of acrylic glass is visible which serves as a wave guide for the US. The US transducer itself is not visible in the picture. The container has a height of 8cm. (Parameters: Te=155ms, Tr=5700ms; US: Duration=30ms, Voltage=-6dBm). The measurements on different liquids show a difference in the US effect depending on the properties of the liquid. In water the diminishment of the signal is visible as a straight path, whereas in glycerine a much shorter but wider region is affected by the US. This is due to much higher damping of the US wave in Glycerine. The acoustic radiation pressure is therefore stronger, but only existent in a very short region. This region is wider than in water because of higher friction between the glycerine molecules which corresponds to a higher momentum transfer. In a piece of pork neck the US effect also becomes visible as a black spot. Only in this region, the piece of pork neck was displaced during the US pulse. The strength of this displacement depends on the viscoelastic properties of the tissue. Figure 2: US beam in a 47\% glycerine (viscosity=6mPas) mixture and in water (viscosity=1mPas) at different US amplitudes. An amplitude of -6dBm corresponds to an excess pressure in water of about 1 Pa. (Parameters: Te=106ms, Tr=3500ms, US: Duration=30ms). Conclusion The combination of US pulses and MRI creates contrasts concerning the viscoelastic properties of liquids and tissue. The spatial resolution of this method is only limited by the resolution of the scanner, since the US wavelength is in the order of magnitude of 100mue.}, tags = {mrt}, misc = {Konferenz}, booktitle = {ISMRM Sixteenth Scientific Meeting and Exhibition, Toronto - Canada}, author = {Oehms, O. and Radicke, M. and Wrede, S. and Lewerenz, M. and Engelbertz, A. and Maier, K.} } @Mastersthesis { jessi, title = {\(^{1}\)H-{NMR} \& Resonanter Ultraschall in einem Kolloid aus Pb(Ti,Zr)O\(_{3}\)}, year = {2008}, month = {3}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2008_Diplom_Mende.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Mende, J.} } @Mastersthesis { JentjensDipl2008, title = {Brechungsindex und Polungsverhalten in Lithiumniobat nach \(^{3}\)He-Bestrahlung}, year = {2008}, month = {3}, tags = {linbo}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2008_Diplom_Jentjens.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Jentjens, L.} } @Conference { mendpt08, title = {Dreidimensionaler maschineller Tastsinn in Gewebe durch eine Kombination aus Ultraschall und Magnetresonanztomographie}, year = {2008}, month = {2}, abstract = {Ultraschall und Magnetresonanztomographie sind eigenst{\"a}ndige, nichtinvasive Methoden in der Medizin um das K{\"o}rperinnere darzustellen. Wir besch{\"a}ftigen uns mit einer Kombination dieser Methoden um einen neuen Kontrast zu erhalten. Ultraschall wird w{\"a}hrend der MR-Bildaufnahme in das Gewebe eingestrahlt. Wir haben ein System entwickelt, das den klinischen Tomographen nicht beeinflusst. Dieses Ultraschallsystem nutzt dabei nicht Kurzpulse wie in klinischen Ger{\"a}ten. Durch eine diffusionssensitive Messsequenz wird die Verschiebung des Gewebes durch den Schallstrahlungsdruck dargestellt. Es wird ein neuer Kontrast im MR-Bild erzeugt, der z.B. unterschiedliche viskoelastische Eigenschaften von Gewebetypen (z.B. Dr{\"u}sengewebe und Tumorgewebe) sichtbar machen kann. Wir haben Phantome aus Agar-Agar und Kieselerde hergestellt um Gewebe zu simulieren. Der Ultraschalleinfluss wird hier f{\"u}r verschiedene Amplituden im Bild gezeigt.}, tags = {mrt}, misc = {Konferenz}, booktitle = {12. Deutsche Physikerinnentagung, M{\"u}nster}, author = {Mende, J. and Oehms, O. and Radicke, M. and Habenstein, B. and Maier, K.} } @Conference { elmdpg08, title = {Influence of Ultrasound on Magnetic Resonance Imaging Contrast Agents (SPIO)}, year = {2008}, month = {2}, abstract = {Magnetic resonance imaging (MRI) is one of the most powerful imaging techniques for living organisms. Magnetic nanoparticles such as superparamagnetic iron oxide (SPIO) have been applied as contrast enhancement agents for MRI. We develop a new contrast method for SPIO with the application of ultrasound (US) while performing proton magnetic resonance spectroscopy. Especially prepared SPIO should work as radio frequency transmitters. The nanoparticles are prepared such that the center of geometry differs from the center of mass. This is done by the magnetic oriented sedimentation of the SPIOs so that we can add macro molecules from one side only. Sedimentation process of the SPIO have been achieved by applying a combination of centrifugal force and magnetic force. Due to the particle velocity in the resonant US wave, SPIOs are accelerated and due to their asymmetric shape, they tilt periodically. This produces additional photons with the US frequency that affect the relaxation times. Using nanopariticles as local antenna in combination with US promises new contrast methods to visualize additional properties of the tissue. Even without any special preparation of the nanoparticles, an effect of the US on the MRI signal has already been seen.}, tags = {nmr}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Arbeitskreises Festk{\"o}rperphysik, Berlin}, author = {Elmiladi, N. and H{\"o}hl, C. and Mende, J. and Schlichtenmayer, M. and Habenstein, B. and Maier, K.} } @Conference { mendpg08, title = {Influencing the relaxation times of proton NMR with resonant ultrasound and piezoceramic nanoparticles}, year = {2008}, month = {2}, abstract = {In magnetic resonance imaging, nanometer-sized colloidal particles (nanoparticles) have been widely used as contrast agents for clearer and more specific images and to localize specific organs. We investigate the influence of piezoelectric nanoparticles on the relaxation times of proton magnetic resonance spectroscopy (1H-MRS) and 1H-MRS in combination with resonant ultrasound (US). A piezoceramic powder consisting of 100 nm sized particles was prepared into a colloid in water by coating with polyacrylic acid. Measurements have shown that the nanoparticles have an influence on the spin-lattice relaxation time T1 of water, which elongates by about 1\%. Piezoelectric particles have the ability to generate an electric potential in response to directed mechanical stress. In combination with the periodic pressure variation in a resonant US-wave, these particles function as an emitter for electromagnetic fields with US frequency and couple to the spin-system. The influence of the piezoelectric particles on 1H-MRS is discussed.}, tags = {mrt}, url = {http://www.dpg-verhandlungen.de/2008/berlin/st2.pdf}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Arbeitskreises Festk{\"o}rperphysik, Berlin}, author = {Mende, J. and Elmiladi, N. and H{\"o}hl, C. and Maier, K.} } @Conference { oehdpg08, title = {Technique for a Sense of Touch inside the Head}, year = {2008}, month = {2}, abstract = {If a 30ms long Ultrasound (US) pulse is irradiated into a sample during a diffusion sensitive Magnetic Resonance Imaging (MRI) sequence, the US can generate contrasts in the image between tissues or liquids with different viscoelastic properties. If the US could be coupled through the cranium into the brain, this effect could possibly be used to visualize brain tumors or Alzheimer plaques. First measurements will be presented, which demonstrate the effect of the US on the MR image and the feasibilty of a coupling of the US through a model of a bone. The US frequency is tuned in such a way, that a resonance condition inside the bone occures. In this case, the US amplitude behind the bone rises enormously and the US effects on the sample can be visualized with the MRI scanner.}, tags = {mrt}, url = {http://www.dpg-verhandlungen.de/2008/berlin/st4.pdf}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Arbeitskreises Festk{\"o}rperphysik, Berlin}, author = {Oehms, O. and Radicke, M. and Lewerenz, M. and Wrede, S. and Habenstein, B. and Trautner, P. and Weber, B. and Maier, K.} } @Conference { radpg08, title = {Ultrasound leads to Viscoelastic Contrasts in Magnetic Resonance Imaging}, year = {2008}, month = {2}, abstract = {Using a diffusion weighted gradient in a standard Magnetic Resonance (MR) Imaging sequence, one is able to visualize movement inside a sample. The diffusion weighted gradient is split into two parts. The first part dephases the ensembles of the spins according to their location and the second part rephases them. The rephasing works properly only if the location of the spins has not changed during the measurement. This means that a movement of the spins leads to a signal loss whereas the level of the movement is encoded in different gray scale values in the MR image. By coupling a 30ms long US pulse to our sample, a force along the US beam path is produced (acoustic radiation pressure). This �static� force leads to a displacement of the spins during the US pulse. By applying the US pulse during one part of the diffusion weighted gradient we get images whereof we can calculate the displacement which characterizes the viscoelastic properties of our sample. Measurements which show the feasibility and the great advantages of this new method will be presented. Further developments and possible clinical applications will be discussed.}, tags = {mrt}, url = {http://www.dpg-verhandlungen.de/2008/berlin/st2.pdf}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Arbeitskreises Festk{\"o}rperphysik, Berlin}, author = {Radicke, M. and Habenstein, B. and Lewerenz, M. and Oehms, O. and Trautner, P. and Weber, B. and Wrede, S. and Maier, K.} } @Phdthesis { anbalagan2008, title = {Radiation damage of polymers in ultrasonic fields}, year = {2008}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2008_Doktor_Anbalagan.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Anbalagan, P.} } @Phdthesis { negrini2008, title = {Strahlensch{\"a}digung in Ultraschall-exponiertem Quarzglas}, year = {2008}, tags = {material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2008_Doktor_Negrini.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Negrini, C. M.} } @Article { ISI:000258650100018, title = {{Early stages of decomposition in Al alloys investigated by X-ray absorption}}, journal = {Phys. Status Solidi: RRL}, year = {2008}, volume = {2}, number = {{4}}, pages = {182-184}, abstract = {{We demonstrate the sensitivity of X-ray absorption fine-structure (XAFS) measurements to the earliest stages of decomposition in Al alloys, i.e. just a few minutes after quenching. XAFS is one of the few applicable experimental approaches to this regime. Three different AlCu(Mg) samples were investigated by XAFS at the Cu K edge. Significant changes of the XAFS can be detected in the course of the decomposition in these alloys during the first 15 minutes. Actually, these changes correspond to relaxations of the nearest neighbours towards the absorbing Cu atoms. The Fourier transformation of the XAFS spectra thus leads to a pseudo radial distribution function which reflects this relaxation. In addition, XAFS measurements of the S-phase of AlCuMg are used to decide in favour of the Perlitz and Westgren model for the S-phase. (c) 2008 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim.}}, tags = {positron, material}, url = {http://onlinelibrary.wiley.com/doi/10.1002/pssr.200802067/abstract}, ISSN = {{1862-6254}}, DOI = {10.1002/pssr.200802067}, author = {Klobes, B. and Staab, T. E. M. and Dudzik, E.} } @Article { Jentjens2008, title = {Domain reversal properties and refractive index changes of magnesium doped lithium niobate upon ion exposure}, journal = {J. Appl. Phys.}, year = {2008}, volume = {103}, number = {3}, pages = {034104}, tags = {linbo}, url = {http://link.aip.org/link/?JAP/103/034104/1}, publisher = {AIP}, DOI = {10.1063/1.2838207}, author = {Jentjens, L. and Hattermann, H. and Peithmann, K. and Haaks, M. and Maier, K. and K{\"o}sters, M.} } @Article { Staab2008, title = {Early precipitation stages of aluminum alloys - The role of quenched-in vacancies}, journal = {Appl. Surf. Sci.}, year = {2008}, volume = {255}, number = {1}, pages = {132-135}, abstract = {We present preliminary results on the structure of nano-sized particles (clusters of solute atoms or Guinier-Preston-Bagaryatsky (GPB) zones) in aluminum alloys. Hindering the motion of dislocations, these GPB zones (precipitates) are responsible for the strength of AlCuMg-alloys - used e.g. as AA2024 - for the outer shell plates in aircraft industry. We will discuss the role of quenched-in vacancies for the formation and growth of the precipitates. Using positron annihilation (Doppler broadening together with the recently developed tool of high-momentum analysis (HMA)) and X-ray absorption spectroscopy measurements, we are able to characterize the local atomic environment in the vicinity of vacancies and selected elements (Cu) forming the precipitates. The interpretation will be based on a comparison to numerical calculations of positron lifetimes and momentum distributions as well as simulated X-ray absorption spectra. Often reliable numerical calculations of experimental quantities are possible only if relaxed atomic positions - calculated employing an ab-initio code like SIESTA - are used as input. ((C) 2008 Elsevier B.V. All rights reserved.}, tags = {material}, url = {http://www.sciencedirect.com/science/article/pii/S0169433208012427}, DOI = {10.1016/j.apsusc.2008.05.201}, author = {Staab, T. E. M. and Haaks, M. and Modrow, H.} } @Article { Haaks2008a, title = {High-momentum analysis in Doppler spectroscopy}, journal = {Appl. Surf. Sci.}, year = {2008}, volume = {255}, number = {1}, pages = {84-88}, abstract = {Unique information about the chemical vicinity of positron annihilation sites is provided by the contribution of high electron momenta to the Doppler spectrum, since this momentum range is characteristic for the annihilation with core electrons and hence element specific. However, the corresponding energy region in the spectrum is overlaid by a huge background caused by the annihilation radiation itself and the Compton spectrum of other gamma lines having an energy above 511 keV. Usually these backgrounds are reduced by measuring both annihilation quanta in coincidence. By mathematically analyzing the background contributions, we open another possibility to obtain the high-momentum region employing one single germanium detector. A necessary precondition is employing either background-free positron beams or a low-background positron source, e.g. Ge-68, instead of the widely used positron emitter Na-22. The Ge-68-source emits positrons with an endpoint energy of about 1.9 MeV, where as the contribution of gamma quanta having higher energies than the annihilation radiation at 511 keV is negligible low. When analyzing spectra from metals and semiconductors according to the described background subtraction, the same information contained in the momentum range up to 35 x 10(3)m(0)c or beyond can be extracted, as if the spectra were measured employing a coincidence setup with two Ge-detectors. (C) 2008 Elsevier B.V. All rights reserved.}, tags = {positron}, url = {http://www.sciencedirect.com/science/article/pii/S0169433208011859}, DOI = {10.1016/j.apsusc.2008.05.313}, author = {Haaks, M. and Staab, T. E. M.} } @Article { springerlink:10.1007/978-3-540-74325-5_23, title = {Material Science with Positrons: From Doppler Spectroscopy to Failure Prediction}, journal = {Advances in Solid State Physics}, year = {2008}, volume = {47}, pages = {289-300}, abstract = {We describe an alternative approach for a reliable lifetime prediction employing the local concentration of lattice defects as a precursor for fatigue failure. We present positron annihilation spectroscopy (PAS) as a non-destructive technique sensitive for defect concentrations in the range relevant to plasticity in metals. The Bonn Positron Microprobe (BPM), a currently unique device, provides a fine focused positron beam with a selectable beam diameter from 5 to 200 µm assisted by an inbuilt fully functional scanning electron microscope (SEM). Using the BPM, plasticity and fatigue can be measured with a lateral resolution from some microns up to the range of millimeters. Employing laterally resolved PAS and the empirical supposition of a linear relation between the defect concentration and the logarithm of the number of fatigue cycles, the point of failure was successfully predicted on the common carbon steel AISI 1045. For a generalization of the precursor method, a minimal model of fatigue based on a cellular automaton was developed. First results from a one-dimensional implementation are presented.}, affiliation = {Helmholtz Institut f{\"u}r Strahlen- und Kernphysik, Universit{\"a}t Bonn, Nu{\ss}allee 14-16, 53115 Bonn, Germany}, tags = {positron}, url = {http://www.springerlink.com/content/k4lx118586wl3227/}, editor = {Haug, Rolf}, publisher = {Springer Berlin / Heidelberg}, series = {Advances in Solid State Physics}, ISBN = {978-3-540-74324-8}, DOI = {10.1007/978-3-540-74325-5_23}, author = {Haaks, M. and Eich, P. and Fingerhuth, J. and M{\"u}ller, I.} } @Article { springerlink:10.1007/s10751-008-9628-6, title = {New image contrast method in magnetic resonance imaging via ultrasound}, journal = {Hyperfine Interactions}, year = {2008}, volume = {181}, pages = {21-26}, abstract = {When applied to a sample, ultrasound (US) gives rise to a displacement of tissue and a flow in a liquid due to the acoustic radiation pressure. These movements depend on the viscoelastic properties of the sample and can be visualized precisely with an MRI scanner using diffusion- sensitive pulse sequences. In this paper, measurements will be presented, which show the visualization of the US under variation of its parameters in different liquids and in tissue.}, affiliation = {University of Bonn Helmholtz-Institut f{\"u}r Strahlen-und Kernphysik Nussallee 14–16 53115 Bonn Germany}, tags = {mrt}, url = {http://www.springerlink.com/content/0926650r6tw30w11/}, publisher = {Springer Netherlands}, ISSN = {0304-3843}, DOI = {10.1007/s10751-008-9628-6}, author = {Radicke, M. and Engelbertz, A. and Habenstein, B. and Lewerenz, M. and Oehms, O. and Trautner, P. and Weber, B. and Wrede, S. and Maier, K.} } @Article { Haaks2008, title = {Scanning positron microscopy: Non-destructive imaging of plastic deformation in the micrometer range}, journal = {Cirp Annals-Manufacturing Technology}, year = {2008}, volume = {57}, number = {1}, pages = {537--540}, abstract = {Positron annihilation spectroscopy (PAS) provides extreme sensitivity for the detection of lattice defects from a concentration of 10(-6) defects per atom. PAS is a versatile and non-destructive tool for the study of plasticity and fatigue in solid-state materials. Scanning positron microscopy (SPM) expands the capabilities of PAS into the micron range. Recent results of defect imaging by SPM on plastically deformed and fatigued metals and semiconductors will be presented in this paper. A new method estimating the remaining useful life of fatigued components by employing the S-parameter as a precursor for failure will be introduced. (C) 2008 CIRP.}, tags = {positron, material}, url = {http://www.sciencedirect.com/science/article/pii/S0007850608001121}, DOI = {10.1016/j.cirp.2008.03.109}, author = {Haaks, M.} } @Article { klobes:2008, title = {The role of quenched-in vacancies for the decomposition of aluminium alloys}, journal = {phys. stat. sol. (RRL)}, year = {2008}, volume = {2}, number = {5}, pages = {224--226}, abstract = {The very early stages of decomposition during room temperature storage, i.e. just a few minutes after quenching, are investigated by positron annihilation lifetime spectroscopy for both an AlMgSi alloy and an AlCuMg alloy. It turns out that by freezing the decomposition kinetics during measurements we can detect vacancy–solute atom pairs. The formation of larger solute clusters with structural vacancies is seen by an increase of the mean positron lifetime in the course of storage at room temperature (RT). Earlier findings concerning aging at RT were unable to discover this effect. The detected changes are interpreted in terms of cluster formation. Thus we show that positron annihilation spectroscopy (PAS) is one of the very few methods to access early stages of decomposition in metallic alloys. Moreover, the lower limit of the concentration of quenched-in vacancy-like defects is calculated to be at least 2 \(\times\) 10\(^{–5}\) per atom.}, keywords = {61.43.Dq, 61.72.jd, 64.75.Op, 78.70.Bj}, tags = {positron, material}, url = {http://onlinelibrary.wiley.com/doi/10.1002/pssr.200802123/abstract}, publisher = {WILEY-VCH Verlag}, ISSN = {1862-6270}, DOI = {10.1002/pssr.200802123}, author = {Klobes, B. and Staab, T. E. M. and Haaks, M. and Maier, K. and Wieler, I.} } @Conference { staab:2008, title = {Atomic structures of pre-Guinier-Preston and Guinier-Preston-Bagaryatsky zones in Al-alloys}, year = {2008}, tags = {positron}, misc = {Konferenz}, booktitle = {Proceedings of the International Workshop on Positron Studies of Defects (PSD '08 Prague)}, author = {Staab, T. E. M. and Klobes, B. and Kohlbach, I. and Korff, B. and Haaks, M. and Dudzik, E. and Maier, K.} } @Mastersthesis { wrede, title = {Darstellung der Ultraschalltransmission durch Knochenphantome mittels Magnetresonanztomographie}, year = {2007}, month = {12}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2007_Diplom_Wrede.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Wrede, S.} } @Mastersthesis { lewerenz, title = {Signalerh{\"o}hung durch Ultraschall in der Magnetresonanztomographie}, year = {2007}, month = {11}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2007_Diplom_Lewerenz.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Lewerenz, M.} } @Mastersthesis { orth, title = {Aufbau der H{\"a}rte in Aluminiumlegierungen}, year = {2007}, month = {10}, tags = {material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2007_Diplom_Orth.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Orth, A.} } @Mastersthesis { korff2007, title = {Simulation von Parametern der Positronenannihilation in Aluminium-Legierungen}, year = {2007}, month = {9}, tags = {positron}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2007_Diplom_Korff.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Korff, B.} } @Mastersthesis { klobes2007, title = {Untersuchungen zu Fr{\"u}hstadien der Ausscheidungsbildung in AlMgSi-Legierungen}, year = {2007}, month = {9}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2007_Diplom_Klobes.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Klobes, B.} } @Mastersthesis { kohlbach2007, title = {Die Rolle von Leerstellen bei der Ausscheidungsbildung von Al-Cu-Legierungen}, year = {2007}, month = {4}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2007_Diplom_Kohlbach.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Kohlbach, I.} } @Mastersthesis { hoehl, title = {{U}ltraschall in der {NMR} - {K}opplung mit magnetischen {N}anopartikeln}, year = {2007}, month = {3}, tags = {nmr}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2007_Diplom_Hoehl.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {H{\"o}hl, C.} } @Mastersthesis { radicke2007, title = {Neuartige Bildkonstraste durch Ultraschall in der Magnetresonanztomographie}, year = {2007}, month = {3}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2007_Diplom_Radicke.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Radicke, M.} } @Mastersthesis { HattermannDipl2007, title = {Modifikation der {M}aterialeigenschaften von {L}ithiumniobat durch {T}eilchenbestrahlung}, year = {2007}, month = {1}, tags = {linbo}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2007_Diplom_Hattermann.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Hattermann, H.} } @Mastersthesis { huysmansdipl2007, title = {Untersuchung von plastischen Eigenschaften und Materialerm{\"u}dung von Ni\(_{2}\)MnGa mit Positronen}, year = {2007}, month = {1}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2007_Diplom_Huysmans.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Huysmans, K.} } @Phdthesis { Zamani-MeymianDiss2007, title = {{Brechungsindex{\"a}nderungen in Lithiumniobat-Kristallen durch Strahlensch{\"a}den}}, year = {2007}, tags = {linbo}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2007_Doktor_Zamani-Meymian.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Zamani-Meymian, M.-R.} } @Phdthesis { andre, title = {{V}ariation von {NMR}-{S}ignalen durch {H}yperpolarisation und {U}ltraschall}, year = {2007}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2007_Doktor_Engelbertz.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Engelbertz, A.} } @Article { Staab2007, title = {Atomic structure of pre-Guinier-Preston zones in Al alloys}, journal = {Phys. Status Solidi: RRL}, year = {2007}, volume = {1}, number = {5}, pages = {172--174}, abstract = {We propose X-ray absorption (XAS) measurements as a novel approach to determine the atomic structure of pre-Guinier-Preston zones. These nano-clusters are formed during very early stages of aging AlCu alloys, immediately after solution heat treatment and quenching. X-ray absorption near-edge structure (XANES) spectra were taken from technical aluminum alloys at the copper K edge, revealing the local atomic environment of copper. The spectra of - after solution heat treatment - freshly quenched and of artificially aged alloys differ significantly from each other. We compare the measured XANES spectra with those calculated by the FEFF-8 code. We show the importance of employing realistic, i.e. relaxed, atomic coordinates around the scattering atom type from ab-initio calculations with SIESTA. Atomic structure of a pre-GPZ from SIESTA: a small disk of five Cu atoms (red) on a {100} plane in fcc Al (blue). Note that Al atoms in direct neighborhood of copper relax towards the small Cu disk. (online colour at: www.pss-rapid.com) (c) 2007 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim.}, tags = {material}, url = {http://onlinelibrary.wiley.com/doi/10.1002/pssr.200701090/abstract}, DOI = {10.1002/pssr.200701090}, author = {Staab, T. E. M. and Haaks, M. and Zamponi, C. and Modrow, H. and Maier, K.} } @Article { PSSC:PSSC200675869, title = {First test of LSO scintillators for Positron Lifetime Spectroscopy}, journal = {Phys. Status Solidi C}, year = {2007}, volume = {4}, number = {10}, pages = {4036--4039}, abstract = {Lutetium oxyorthosilicate (LSO) was employed as scintillator material in a positron lifetime (PALS) fast-slow spectrometer. Compared to the widely used BaF2 scintillator material, LSO has a single exponential decay with 40 ns, a high density of 7.49 g/cm3, an effective nuclear charge of 65.8 and a superb light output. With this features photon rates above 5 \(\times\) 106 should be possible, which affords to obtain lifetime spectra within a period of minutes. The physical and mechanical properties make LSO attractive as scintillator material for PALS measurements. The capability of LSO for PALS was studied and compared to BaF2. As a first test of the spectrometer, a lifetime spectrum of well annealed nickel was measured and analyzed. (© 2007 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim)}, keywords = {29.40.Mc, 78.70.Bj}, tags = {positron}, url = {http://dx.doi.org/10.1002/pssc.200675869}, publisher = {WILEY-VCH Verlag}, ISSN = {1610-1642}, DOI = {10.1002/pssc.200675869}, author = {Haaks, M. and Valentini, R. and Vianden, R.} } @Article { PSSC:PSSC200675814, title = {Spatially resolved defect studies on fatigued carbon steel}, journal = {Phys. Status Solidi C}, year = {2007}, volume = {4}, number = {10}, pages = {3465--3468}, abstract = {Several samples of the common ferritic tool steel AISI 1045 were fatigued in cyclic load tests. The local distribution of the Von-Mieses stress \(\sigma\)VM was simulated using the finite elements method (FEM). In the regions of interest, where \(\sigma\)VM reaches maximum values, the defect distribution was measured spatially resolved by Doppler-spectroscopy (DBAR) employing the Bonn Positron Microprobe (BPM). The lateral distribution of the S-parameter, which could be described by a simple model derived from linear fracture mechanics, corresponds well with the simulated Von-Mieses stress. (© 2007 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim)}, keywords = {07.78.+s, 47.11.Fg, 62.20.Fe, 62.20.Mk, 78.70.Bj}, tags = {positron, material}, url = {http://dx.doi.org/10.1002/pssc.200675814}, publisher = {WILEY-VCH Verlag}, ISSN = {1610-1642}, DOI = {10.1002/pssc.200675814}, author = {Eich, P. and Haaks, M. and Sindelar, R. and Maier, K.} } @Conference { rahyp07, title = {New Image Contrast Method in Magnetic Resonance Imaging via Ultrasound}, year = {2007}, tags = {mrt}, misc = {Konferenz}, booktitle = {XIV International Conference on Hyperfine Interactions, Iguacu Falls - Brazil}, author = {Radicke, M. and Engelbertz, A. and Habenstein, B. and Lewerenz, M. and Oehms, O. and Trautner, P. and Weber, B. and Wrede, S. and Maier, K.} } @Conference { radpg07, title = {Ultrasound creates Magnetic Resonance Imaging contrast}, year = {2007}, tags = {mrt}, misc = {Konferenz}, booktitle = {DPG Fr{\"u}hjahrstagung des Arbeitskreises Festk{\"o}rperphysik, Regensburg}, author = {Radicke, M. and Engelbertz, A. and Habenstein, B. and Lewerenz, M. and Oehms, O. and Trautner, P. and Maier, K.} } @Mastersthesis { fingerhuth2006, title = {Entwicklung eines Modells zur Schadensvorhersage in zyklisch belasteten Werkstoffen}, year = {2006}, month = {11}, tags = {material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2006_Diplom_Fingerhuth.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Fingerhuth, J.} } @Mastersthesis { morar, title = {{A}mplituden{\"a}nderung des {K}ernspinechos durch {U}ltraschallpulse}, year = {2006}, month = {6}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2006_Diplom_Morar.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Morar, C.} } @Mastersthesis { ole, title = {{W}echselwirkung des {K}ernspinsystems mit {U}ltraschall in einfachen {F}l{\"u}ssigkeiten}, year = {2006}, month = {5}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2006_Diplom_Oehms.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Oehms, O. B.} } @Mastersthesis { eichdipl2006, title = {Ortsaufgel{\"o}ste Bestimmung der Sch{\"a}digung an erm{\"u}detem Karbonstahl}, year = {2006}, month = {4}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2006_Diplom_Eich.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Eich, P. C.} } @Mastersthesis { lenk2006, title = {Ortsaufgel{\"o}ster Deuteriumnachweis in metallischen Werkstoffen}, year = {2006}, month = {1}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2006_Diplom_Lenk.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Lenk, C. A.} } @Phdthesis { mueller2006, title = {Vergleich ortsaufgel{\"o}ster zerst{\"o}rungsfreier Methoden zur Plastizit{\"a}tsuntersuchung}, year = {2006}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2006_Doktor_Mueller_I.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {M{\"u}ller, I.} } @Article { haaks:2006, title = {Analyzing the high-momentum part of positron annihilation Doppler spectra with a single germanium detector}, journal = {Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment}, year = {2006}, volume = {569}, number = {3}, pages = {829 - 836}, keywords = {Positron annihilation}, tags = {positron}, url = {http://www.sciencedirect.com/science/article/B6TJM-4KY8785-G/2/b876b6af4babf991b360ef15a1cf65f1}, ISSN = {0168-9002}, DOI = {10.1016/j.nima.2006.08.117}, author = {Haaks, M. and Staab, T. E. M. and Maier, K.} } @Article { Peithmann2006b, title = {Fabrication of Embedded Waveguides in Lithium-Niobate Crystals by Radiation Damage}, journal = {Appl. Phys. B}, year = {2006}, volume = {82}, number = {3}, pages = {419-422}, abstract = {Irradiation of lithium-niobate crystals (LiNbO3) with fast, high-energy 3He ions changes the refractive index in the interaction region where the ions speed through the material. Thus an inhomogeneous flux density profile can be used for a tailored modification of the optical properties of LiNbO3 crystals, without employing ion implantation. A new method to fabricate embedded, polarization sensitive channel waveguides in LiNbO3 utilizing accelerated 3He ions with an energy of 40 MeV is demonstrated.}, tags = {linbo}, url = {http://www.springerlink.com/content/ymmmw7g171131779/}, DOI = {10.1007/s00340-005-2002-3}, author = {Peithmann, K. and Zamani-Meymian, M.-R. and Haaks, M. and Maier, K. and Andreas, B. and Buse, K. and Modrow, H.} } @Article { Peithmann2006a, title = {Refractive Index Changes in Lithium Niobate Crystals by High-Energy Particle Radiation}, journal = {J. Opt. Soc. Am. B}, year = {2006}, volume = {23}, number = {10}, pages = {2107-2112}, abstract = {Irradiation of lithium niobate crystals with 41 MeV \(^{3}\)He ions causes strong changes of the ordinary and extraordinary refractive indexes. We present a detailed study of this effect. Small fluence of irradiation already yields refractive index changes about 5\(\times\)10\(^{−4}\); the highest values reach 3\(\times\)10\(^{−3}\). These index modulations are stable up to 100\(^{\circ}\)C and can be erased thermally, for which temperatures up to 500\(^{\circ}\)C are required. A direct correlation between the refractive index changes and the produced lattice vacancies is found.}, tags = {linbo}, url = {http://www.opticsinfobase.org/abstract.cfm?URI=josab-23-10-2107}, DOI = {10.1364/JOSAB.23.002107}, author = {Peithmann, K. and Zamani-Meymian, M.-R. and Haaks, M. and Maier, K. and Andreas, B. and Breunig, I.} } @Article { Haaks2006, title = {Spatially resolved deformation studies on carbon steel employing X-rays and positron annihilation}, journal = {Phys. Status Solidi A}, year = {2006}, volume = {203}, number = {4}, pages = {R31--R33}, abstract = {Spatially resolved studies on plasticity in a polycrystalline sample of the ferritic carbon steel C45E (ATSI 1045) were performed after deformation in a three-point bending test. The local effects of deformation were investigated by scanning the sample with two different methods: Positron Annihilation Spectroscopy (S-parameter) and Debye-Scherrer diffraction (reflex broadening). A simple relation between the results of both experiments and the true strain over the cross-section of the bent sample is presented in this letter. Comparing the methods a linear correlation between the lattice distortion of a-iron and the defect sensitive positron annihilation parameter is found. (c) 2006 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim.}, tags = {positron, material}, url = {http://onlinelibrary.wiley.com/doi/10.1002/pssa.200622063/abstract}, DOI = {10.1002/pssa.200622063}, author = {Haaks, M. and M{\"u}ller, I. and Schoeps, A. and Franz, H.} } @Article { staab:2006, title = {Study of artificial aging in AlMgSi (6061) and AlMgSiCu (6013) alloys by Positron Annihilation}, journal = {J. Mater. Sci.}, year = {2006}, volume = {41}, pages = {1059-1066}, affiliation = {Martin-Luther Universit{\"a}t Halle-Wittenberg Department of Physics Friedemann-Bach-Platz 6 D-06108 Halle/Saale Germany Friedemann-Bach-Platz 6 D-06108 Halle/Saale Germany}, note = {10.1007/s10853-005-3640-x}, tags = {positron, material}, url = {http://www.springerlink.com/content/g227068l7m16v451/}, publisher = {Springer Netherlands}, ISSN = {0022-2461}, DOI = {10.1007/s10853-005-3640-x}, author = {Staab, T. and Krause-Rehberg, R. and Hornauer, U. and Zschech, E.} } @Article { springerlink:10.1007/s10853-005-3640-x, title = {Study of artificial aging in AlMgSi (6061) and AlMgSiCu (6013) alloys by Positron Annihilation}, journal = {Journal of Materials Science}, year = {2006}, volume = {41}, pages = {1059-1066}, abstract = {We investigate the artificial aging process of the weldable Al-alloys AA-6013 (AlMgSiCu) and AA-6061 (AlMgSi) by positron annihilation spectroscopy and Vickers micro-hardness measurements. We find a correlation between a minimum of the measured positron lifetime and the maximum hardness. To explain these findings AlZn will be discussed as a well known example of positron interaction with different types of precipitations in aluminum. Additionally, we calculate positron annihilation parameters for pure Al, Si, Mg, and \textbackslashmbox{Mg}_2\textbackslashmbox{Si} finding support for our interpretation. For AA-6013 and AA-6061 the increase of the average positron lifetime after reaching the maximum hardness is attributed to the formation of semi-coherent precipitates. Hence, using positron annihilation it is possible to follow very sensitively the precipitation sequence even in technical aluminum alloys. Finally, we discuss which implications the aging may have on microstructural changes.}, affiliation = {Martin-Luther Universit{\"a}t Halle-Wittenberg Department of Physics Friedemann-Bach-Platz 6 D-06108 Halle/Saale Germany Friedemann-Bach-Platz 6 D-06108 Halle/Saale Germany}, tags = {positron, material}, url = {http://www.springerlink.com/content/g227068l7m16v451}, publisher = {Springer Netherlands}, ISSN = {0022-2461}, DOI = {10.1007/s10853-005-3640-x}, author = {Staab, T. and Krause-Rehberg, R. and Hornauer, U. and Zschech, E.} } @Mastersthesis { hartman, title = {{R}esonante {A}nkopplung von {U}ltraschall an das {K}ernspinsystem}, year = {2005}, month = {4}, tags = {mrt}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2005_Diplom_Hartman.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Hartman, T.} } @Mastersthesis { puls2005, title = {Schadensvorhersage in ferritischem Stahl}, year = {2005}, month = {3}, tags = {material, positron}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2005_Diplom_Puls.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Puls, A.} } @Miscellaneous { staabhabil2005, title = {Identifikation atomarer Fehlstellen in Halbleitern und Metallen}, year = {2005}, tags = {positron}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2005_Habil_Staab.pdf}, school = {Helmholtz-Institut f{\"u}r Strahlen- und Kernphysik, Universit{\"a}t Bonn}, type = {Habilitationsschrift}, author = {Staab, T. E. M.} } @Mastersthesis { tmueller2005, title = {Magnetinduzierte Diffusion von Positronen in Metallen}, year = {2005}, tags = {positron}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2005_Diplom_Mueller_T.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {M{\"u}ller, T.} } @Inbook { haaks_springer2005, title = {Extreme events in nature and society}, year = {2005}, pages = {209 - 230}, abstract = {Even today, lifetime predictions of construction parts are still based on the W{\"o}hler method, which is almost 150 years old. To construct a reliable W{\"o}hler diagram, it is necessary to perform alternating load fatigue experiments on a huge number of equivalent samples for up to 108 or 109 load cycles. The lifetime under a specific applied load is then deduced from this diagram using statistical techniques. Physically, the reason for fatigue and finally fracture is the accumulation of lattice defects like dislocations, vacancies and vacancy clusters, which are produced even when the load is significantly below the material’s yield strength. The progress of fatigue can be observed from its earliest stages – after only a few load cycles – up to the final state of fracture by employing positrons as extremely sensitive lattice defect probes. In situ experiments can be performed to study test samples or real construction parts under realistic conditions. In steels a critical defect density is reached just before fatigue failure occurs. The point of failure can therefore be extrapolated from the early stages of fatigue by monitoring the defect density. Spatially resolved experiments performed on a simple carbon steel and employing the Bonn Positron Microprobe indicate significant variations in defect densities over the region under stress even after just a few load cycles. These inhomogenieties grow from a typical starting size of less than a millimeter to encompass the entire volume after further fatigue. With more experimental experience and a better theoretical understanding of this process, this new prediction method should lead to much simpler and more reliable predictions of the lifetimes of metallic materials in the near future.}, tags = {material}, url = {http://www.springer.com/physics/complexity/book/978-3-540-28610-3}, editor = {S. Albeverio, V. Jentsch, H. Kantz}, publisher = {Springer}, chapter = {Predicting the Lifetime of Steel}, ISBN = {978-3-540-28610-3}, author = {Haaks, M. and Maier, K.} } @Inbook { haaks_viley2005, title = {Hochgeschwindigkeitsspanen metallischer Werkstoffe}, year = {2005}, pages = {89 - 111}, abstract = {The Positron Annihilation Spectroscopy (PAS) is nowadays a well established and versatile probe method for non-destructive testing of lattice defects produced by plastic deformation. Defect concentrations in metals of 10\(^{-6}\) per Atom can be detected in the annihilation signal. The Bonn Positron Microprobe (BPM), developed at the Helmholtz Institute for Beam and Nuclear Physics, provides a fine focus positron beam for the spatially resolved detection of lattice defects in the micron range. The aim of the project was an imaging of the defect distribution in the shear zones and the forward deformation zone as well as the analysis of the influence of the cutting parameters on the damaging depth in the surface near layer. An empiric dependency between the S-Parameter and the hardening could be determined by analysing tensile tests. A distinct correlation between the S-Parameter and the Vickers-Hardness could also be found. A special sample geometry, which was developed in cooperation with the Institut f{\"u}r Fertigungstechnik und Werkzeugmaschinen (IFW) in Hannover, affords a 2-dimensional scanning of the defect density inside a chip root. This showed a direct influence of the depth of cut on the damage depth in the surface near layer, while no influence of the cutting speed at constant depth of cut was observed. One sample showed a softening in the scanning positron image, that was ascribed to temperature set free during cutting.}, tags = {material}, url = {http://onlinelibrary.wiley.com/book/10.1002/3527605142}, editor = {H. K. T{\"o}nshoff, C. Hollmann}, publisher = {Wiley-VCH}, chapter = {Abbildung der Sch{\"a}digung in der Randzone mit Positronen als Sondenteilchen}, ISBN = {9783527312566}, DOI = {10.1002/3527605142}, author = {Haaks, M. and Pl{\"o}ger, J.} } @Article { PhysRevLett.95.125502, title = {Agglomeration of As Antisites in As-Rich Low-Temperature GaAs: Nucleation without a Critical Nucleus Size}, journal = {Phys. Rev. Lett.}, year = {2005}, volume = {95}, pages = {125502}, tags = {material}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.95.125502}, publisher = {American Physical Society}, DOI = {10.1103/PhysRevLett.95.125502}, author = {Staab, T. E. M. and Nieminen, R. M. and Luysberg, M. and Frauenheim, Th.} } @Article { Haaks2005, title = {Chemical sensitivity in positron annihilation with just one single Ge detector}, journal = {Phys. Status Solidi A}, year = {2005}, volume = {202}, number = {4}, pages = {R38--R40}, abstract = {We present a novel method for analyzing the data from momentum distribution measurements employing positron annihilation, using just one single Ge-detector, but employing a mathematically sufficiently well suited model for background subtraction. For a variety of high purity metals the resulting momentum distributions have exactly the same shapes up to 35 x 10(-3) m(0)c, as those obtained with coincidence Doppler broadening of the annihilation radiation using a two-detector system. This data analysis applies to any positron source without high energy gammas or a slow positron beam system with just a single Ge-detector and enables the possibility of analysing the chemical surrounding at the positron trapping site without any additional hardware. In particular, in combination with a slow positron microbeam, it allows a spatially resolved measurement of the electron's momentum distribution. (c) 2005 WILEY-VCH Verlag GmbH W Co.}, tags = {positron}, url = {http://onlinelibrary.wiley.com/doi/10.1002/pssa.200510004/abstract}, DOI = {10.1002/pssa.200510004}, author = {Haaks, M. and Staab, T. E. M. and Saarinen, K. and Maier, K.} } @Mastersthesis { hoevel2004, title = {Ortsaufgel{\"o}ster Wasserstoffnachweis in technischen Legierungen}, year = {2004}, month = {12}, tags = {material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2004_Diplom_Hoevel.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {H{\"o}vel, H. M.} } @Mastersthesis { goris2004, title = {Oberfl{\"a}chenmagnetisierung an fl{\"u}ssigem Co\(_{80}\)Pd\(_{20}\)}, year = {2004}, month = {6}, tags = {magnet}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2004_Diplom_Goris.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Goris, A.} } @Mastersthesis { negrini2004, title = {Positronenlebensdauerspektroskopie an Al- Cu- Modell- Legierungen}, year = {2004}, month = {5}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2004_Diplom_Negrini.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Negrini, C. M.} } @Phdthesis { bommas2004, title = {Puls NMR mit hyperpolarisierten Protonen in Metallen}, year = {2004}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2004_Doktor_Bommas.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Bommas, C.} } @Article { Zamponi2004, title = {Investigation of fatigue cracks in aluminium alloys 2024 and 6013 in laboratory air and corrosive environment}, journal = {J. Mater. Sci.}, year = {2004}, volume = {39}, number = {23}, pages = {6951--6956}, abstract = {Fatigue cracks have been generated in the commercial aluminium alloys AA2024 and AA6013 and analysed with a positron microprobe. This instrument provides laterally resolved positron annihilation measurements, which are sensitive to lattice defects like vacancies and dislocations. These commercial alloys have undergone a solution heat treatment and quenching prior to fatigue testing. Subsequently, they have been aged at room temperature and 190degreesC for AA2024 and AA6013, respectively. We performed the fatigue crack generation both in air and under the influence of a chemically aggressive environment (artificial seawater). Due to the corrosive environment hydrogen is probably produced at the fresh fractured surface in the vicinity of the crack tip. We discuss the possible implications of in-diffused hydrogen on the produced lattice defects, especially when there is a delayed migration of vacancies in the lattice, due to a reduced mobility. (C) 2004 Kluwer Academic Publishers.}, tags = {positron, material}, url = {http://www.springerlink.com/content/ru611m96v58t4024/}, DOI = {10.1023/B:JMSC.0000047537.16498.1d}, author = {Zamponi, C. and Sonneberger, S. and Haaks, M. and M{\"u}ller, I. and Staab, T.} } @Article { Andreas2004, title = {Modification of the Refractive Index of Lithium Niobate Crystals by Transmission of High Energy \(^{4}\)He\(^{2+}\) and D\(^{+}\) Particles}, journal = {Appl. Phys. Lett.}, year = {2004}, volume = {84}, number = {19}, pages = {3813}, abstract = {We report reductions of the refractive index of congruently melting lithium niobate crystals of up to 6\(\times\)10\(^{−3}\) by exposure of z-cut samples with high-energy \(^{4}\)He\(^{2+}\) and D\(^{+}\) particles which are transmitted through the crystals.}, tags = {linbo}, url = {http://apl.aip.org/resource/1/applab/v84/i19/p3813_s1}, DOI = {10.1063/1.1741031}, author = {Andreas, B. and Peithmann, K. and Buse, K. and Maier, K.} } @Article { Muller2004, title = {Non-destructive lifetime prediction in material testing with the Bonn positron microprobe}, journal = {Mater. Sci. Forum}, year = {2004}, volume = {445-6}, pages = {498-500}, abstract = {For the construction of heavy duty mechanical components it is essential to know the lifetime of the sample under dynamical load conditions. Material fatigue tests in rail vehicle axles were first made in the year 1858 by August Wohler [1]. Up to now the measurement of a Wohler diagram remains extraordinarily time and money consuming. Since iron based materials fail at a critical defect density independent of cycle number and load, we are able to extrapolate the remaining lifetime of the sample from a few cycles. With positron annihilation measurements employing the Bonn Positron Microprobe different stress states in standard samples can be observed as a function of position [2,3,4]. This leads to a novel non-destructive way to determine a complete Wohler diagram (SN-diagram) with just one sample.}, tags = {positron, material}, url = {http://www.scientific.net/MSF.445-446.498}, DOI = {10.4028/www.scientific.net/MSF.445-446.498}, author = {M{\"u}ller, I. and Bennewitz, K. and Haaks, M. and Staab, T. E. M. and Eisenberg, S. and Lampe, T. and Maier, K.} } @Article { Haaks2004, title = {Positron trapping in deformed copper down to millikelvins}, journal = {Mater. Sci. Forum}, year = {2004}, volume = {445-6}, pages = {96-98}, abstract = {We have performed a study of the temperature dependence of the S-parameter on slightly deformed (7\%) copper over a temperature range from room temperature (300 K) down to 7 mK, using a (3)He/(4)He dilution refrigerator. The sample used is expected to contain a spectrum of lattice defects with both deep and shallow traps. The data show a decrease of the S-parameter with temperature down to about 1K and a slight increase below 800 mK.}, tags = {positron}, url = {http://www.scientific.net/MSF.445-446.96}, DOI = {10.4028/www.scientific.net/MSF.445-446.96}, author = {Haaks, M. and Tramm, C. and M{\"u}ller, I. and Staab, T. and Zamponi, C. and Herzog, P. and Maier, K.} } @Article { Staab2004, title = {Spatially resolved detection of point defects in the vicinity of scratches on GaAs by the Bonn positron microprobe}, journal = {Mater. Sci. Forum}, year = {2004}, volume = {445-6}, pages = {510-512}, abstract = {Spatially resolved positron annihilation spectroscopy has been used for materials science investigations. In undoped semi-insulating GaAs we investigated the sub-surface damage due to scratches produced with a single-diamond grain. We. clearly identify different regions of damage, which have been characterized both by scanning electron microscopy and the positron microbeam. The. latter reveals signs of plastic deformation in front of the scratch indicated by the defects detected. The observed ductile behavior of GaAs at room temperature is discussed, considering how this usually very brittle material can undergo a brittle-to-ductile transition when exposed to high pressure.}, tags = {positron, material}, url = {www.scientific.net/MSF.445-446.510}, DOI = {10.4028/www.scientific.net/MSF.445-446.510}, author = {Staab, T. E. M. and Zamponi, C. and Haaks, M. and M{\"u}ller, I. and Eichler, S. and Maier, K.} } @Phdthesis { haaks2003, title = {Positronenspektroskopie an Erm{\"u}dungsrissen und Spanwurzeln}, year = {2003}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2003_Doktor_Haaks.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Haaks, M.} } @Mastersthesis { sonneberger2002, title = {Verformungsverhalten von technischen Aluminiumlegierungen}, year = {2002}, month = {11}, tags = {material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2002_Diplom_Sonneberger.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Sonneberger, S.} } @Phdthesis { beckmann2002, title = {Modulationskalorimetrie und magnetooptische Untersuchungen am magnetischen Phasen{\"u}bergang von fl{\"u}ssigem Co\(_{80}\)Pd\(_{20}\)}, year = {2002}, tags = {magnet}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2002_Doktor_Beckmann.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Beckmann, M.} } @Phdthesis { zamponi2002, title = {Positronenspektroskopie an plastischen Zonen in Al-Legierungen und GaAs-Wafern}, year = {2002}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2002_Doktor_Zamponi.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Zamponi, C.} } @Phdthesis { bennewitz2002, title = {Positronenspektroskopie an zyklisch verformten Titan und Eisenwerkstoffen}, year = {2002}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2002_Doktor_Bennewitz.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Bennewitz, K.} } @Article { Bennewitz20020, title = {Positron annihilation spectroscopy - a non-destructive method for lifetime prediction in the field of dynamical material testing}, journal = {Zeitschrift f{\"u}r Metallkunde}, year = {2002}, volume = {93}, number = {8}, pages = {778--783}, abstract = {The fatigue behavior of iron-based materials has been investigated by rotating bending testing, employing positron annihilation spectroscopy to probe defects on the atomic level. Positron annihilation spectra have been recorded at various stages of material fatigue. The defect density has been determined by analysing the line shape of the Doppler broadening of the annihilation radiation in the photo peak. The line shape parameter (S parameter), a measure of the defect density, showed a linear relation to the logarithm of the number of loadings, thus from only a small number of loadings it is possible to determine the remaining useful life of the sample. Furthermore, along the longitudinal sample axis spatially resolved line-scans are taken using the Bonn Positron Microprobe. Due to the special sample geometry, the stress gradient allows to obtain the S parameter for different values of the applied load using the very same sample. This leads to a way to determine a complete Wohler diagram using a non-destructive method for just one sample.}, tags = {positron}, author = {Bennewitz, K. and Haaks, M. and Staab, T. and Eisenberg, S. and Lampe, T. and Maier, K.} } @Mastersthesis { isfan2001, title = {Kerr-Effekt-Messungen an fl{\"u}ssigem Co\(_{80}\)Pd\(_{20}\)}, year = {2001}, month = {12}, tags = {magnet}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2001_Diplom_Isfan.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Isfan, L. M.} } @Mastersthesis { juchem2001, title = {Polarized Beam-NMR mit Protonen in Metallen}, year = {2001}, month = {8}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2001_Diplom_Juchem.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Juchem, C.} } @Mastersthesis { imueller2001, title = {Strahlfokussierung mittels Oberfl{\"a}chenchanneling}, year = {2001}, month = {4}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2001_Diplom_Mueller_I.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {M{\"u}ller, I.} } @Mastersthesis { krechel2001, title = {Magnetooptischer Kerr-Effekt an fl{\"u}ssigen Ferromagneten}, year = {2001}, month = {2}, tags = {magnet}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2001_Diplom_Krechel.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Krechel, M.} } @Phdthesis { schaaf, title = {Diffusion im unterk{\"u}hlten fl{\"u}ssigen und amorphen Zustand von Zr\(_{65}\)Cu\(_{17,5}\)Ni\(_{10}\)Al\(_{7,5}\)}, year = {2001}, tags = {magnet}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2001_Doktor_Schaaff.pdf}, school = {Universit{\"a}t Stuttgart}, institute = {Max-Planck-Institut f{\"u}r Metallforschung, Stuttgart}, type = {Dissertation}, author = {Schaaff, P.} } @Article { Holzwarth2001, title = {Positron annihilation studies on the migration of deformation induced vacancies in stainless steel AISI 316 L}, journal = {Appl. Phys. A: Mater. Sci. Process.}, year = {2001}, volume = {73}, number = {4}, pages = {467--475}, abstract = {Positron lifetime measurements were carried out at room temperature before and after isochronous annealing of cylindrical, machined fatigue specimens and of round slabs of austenitic stainless steel AISI 316 L deformed in compression. Annealing experiments are evaluated in terms of vacancy migration and sinking to grain boundaries and dislocations. The model assumes spherical grains with a homogeneous initial distribution of vacancies. A vacancy migration enthalpy of H-V(M) = (0.9 +/-0.15) eV was found. It is concluded that positron trapping at dislocation lines does not significantly contribute to positron lifetime measurements at room temperature and that single vacancies are the dominating positron traps. Positron annihilation depth profiling on cross-sectional areas prepared from machined specimens using a positron microprobe with 10 mum spatial resolution shows that machining of cylindrical specimens creates vacancies up to 5 mm below the surface.}, tags = {positron}, url = {http://www.springerlink.com/content/ccl9fjychy51w7k3/}, DOI = {10.1007/s003390100781}, author = {Holzwarth, U. and Barbieri, A. and Hansen-Ilzh{\"o}fer, S. and Schaaff, P. and Haaks, M.} } @Mastersthesis { schieder2000, title = {Weiterentwicklung eines NMR-Experimentes mit polarisierten Protonen}, year = {2000}, month = {12}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2000_Diplom_Schieder.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Schieder, T.} } @Mastersthesis { bommas2000, title = {Oberfl{\"a}chennahe Fehlstellen infolge plastischer Verformung}, year = {2000}, month = {1}, tags = {material, positron}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2000_Diplom_Bommas.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Bommas, C.} } @Phdthesis { maennig2000, title = {Defektuntersuchungen in Festk{\"o}rpern mit der Bonner Positronen-Mikrosonde}, year = {2000}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/2000_Doktor_Maennig.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {M{\"a}nnig, U.} } @Mastersthesis { bennewitz1999, title = {Tr{\"a}gerfreies \(^{22}\)Na - Eine neue Quelle f{\"u}r die Positronenmikrosonde}, year = {1999}, month = {4}, tags = {positron}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1999_Diplom_Bennewitz.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Bennewitz, K.} } @Phdthesis { wider99, title = {Der Einflu{\ss} von Versetzungen auf die Positronenzerstrahlung}, year = {1999}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1999_Doktor_Wider.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Wider, T.} } @Article { Mannig1999, title = {Defect production by the TEM beam - the first application of the positron microprobe}, journal = {Appl. Surf. Sci.}, year = {1999}, volume = {149}, number = {1-4}, pages = {217--220}, abstract = {In cooperation with the ZEISS/LEO GmbH a positron microprobe has been constructed. Additionally, a conventional scanning electron microscope (SEM) is integrated in the setup. Measurements on radiation defects in Mo and Cu samples, made by 1 MeV electron irradiation in a transmission electron microscope (TEM), are presented. The results coincide with the expected damage profiles. Because of the small beam diameter-the great advantage of the positron microprobe-only very small areas (about 20 to 30 mu m in diameter) have to be damaged. Therefore, the irradiation times required to produce samples for investigations of radiation defects caused by electrons are reduced enormously. This means that much higher defect concentrations can be produced in an acceptable time and the positron measurements can cover a wider range of defect concentrations. (C) 1999 Elsevier Science B.V. All rights reserved.}, tags = {positron}, url = {http://www.sciencedirect.com/science/article/pii/S0169433299002044}, DOI = {10.1016/S0169-4332(99)00204-4}, author = {M{\"a}nnig, U. and Bennewitz, K. and Bihr, H. and Haaks, M. and Sigle, W. and Zamponi, C. and Maier, K.} } @Article { haaks:1999, title = {Measurements on cracktips in stainless steel AISI 321 by using a new positron microprobe}, journal = {Applied Surface Science}, year = {1999}, volume = {149}, number = {1-4}, pages = {207 - 210}, keywords = {Positron}, tags = {positron, material}, url = {http://www.sciencedirect.com/science/article/B6THY-3Y9RHVF-1F/2/cbeb57b4666f7bccedb3610ba1e9e2e5}, ISSN = {0169-4332}, DOI = {10.1016/S0169-4332(99)00202-0}, author = {Haaks, M. and Bennewitz, K. and Bihr, H. and M{\"a}nnig, U. and Zamponi, C. and Maier, K.} } @Mastersthesis { gruenewald98, title = {Fl{\"u}ssige Ferromagnete: Der magnetische Phasen{\"u}bergang von Co\(_{80}\)Pd\(_{20}\) im Blickwinkel verschiedener Untersuchungsmethoden}, year = {1998}, month = {8}, tags = {magnet}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1998_Diplom_Gruenewald.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Gr{\"u}newald, U.} } @Mastersthesis { medebach98, title = {Kernresonanz an abgebremsten polarisierten Protonen}, year = {1998}, month = {6}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1998_Diplom_Medebach.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Medebach, M.} } @Phdthesis { buehrer98, title = {Der Fl{\"u}ssige Ferromagnet - Kritisches Verhalten am magnetischen Phasen{\"u}bergang der fl{\"u}ssigen Phase von Co\(_{80}\)Pd\(_{20}\)}, year = {1998}, tags = {magnet}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1998_Doktor_Buehrer.pdf}, school = {Universit{\"a}t Bonn}, author = {B{\"u}hrer, C.} } @Mastersthesis { haaks97, title = {Ortsaufgel{\"o}ste Positronenspektroskopie an thermisch und/oder mechanisch beanspruchten Werkstoffen}, year = {1997}, month = {8}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1997_Diplom_Haaks.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Haaks, M.} } @Mastersthesis { wider97, title = {In situ Positronenspektroskopie an erm{\"u}detem Kupfer}, year = {1997}, month = {2}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1997_Diplom_Wider.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Wider, T.} } @Phdthesis { greif97, title = {Der Bonner Feinfokuspositronenstrahl}, year = {1997}, tags = {positron}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1997_Doktor_Greif.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Greif, H.} } @Phdthesis { Tongbhoyai97, title = {Positronenquellen-Moderator-Kombination mit hohem Richtstrahlwert}, year = {1997}, tags = {positron}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1997_Doktor_Tongbhoyai.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Tongbhoyai, M.} } @Mastersthesis { zamponi97, title = {Beeinflussung der Gipsmorphologie durch betriebliche Zus{\"a}tze der Rauchgasentschwefelung bei der Kristallisation im Gel und in Calzit-Suspensionen}, year = {1997}, affiliation = {Mineralogisch-Petrologisches Institut der Universit{\"a}t Bonn}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1997_Diplom_Zamponi.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Zamponi, C.} } @Article { Greif1997, title = {A combined positron microprobe - Scanning electron microscope for positron-annihilation spectroscopy with a spatial resolution in the micron range}, journal = {Mater. Sci. Forum}, year = {1997}, volume = {255-2}, pages = {641-643}, abstract = {In cooperation with the ZEISS/LEO GmbH a positron microprobe has been developed which allows positron annihilation measurements with a spatial resolution in the micron range. Therefore, a commercially available scanning electron microscope (SEM) has been modified and equipped with an additional facility for positron-annihilation measurements. A Na-22 source and a cylindrical tungsten moderator have been integrated in the electron optical system of the SEM which now may be used in the conventional SEM-mode to image a specimen and in another mode to perform local positron-annihilation measurements. As a first test the fatigue damage in a copper plate after a three-point bending test was investigated with the positron microbeam. The profile of the S-parameter along the cross section of the copper plate coincides well with the expected feature of the damage distribution.}, tags = {positron}, url = {http://www.scientific.net/MSF.255-257.641}, DOI = {10.4028/www.scientific.net/MSF.255-257.641}, author = {Greif, H. and Haaks, M. and Holzwarth, U. and M{\"a}nnig, U. and Tongbhoyai, M. and Maier, K.} } @Article { Greif1997a, title = {High resolution positron-annihilation spectroscopy with a new positron microprobe}, journal = {Appl. Phys. Lett.}, year = {1997}, volume = {71}, number = {15}, pages = {2115--2117}, abstract = {In cooperation with Zeiss/LEO GmbH, a monoenergetic positron source has been integrated in the electron optical system of a scanning electron microscope by help of a magnetic prism, The electron optics serves both to image the specimen with electrons and to form a positron microbeam that allows local positron-annihilation measurements with a resolution in the micron range. The fatigue damage profile along the cross section of a copper plate after a three-point bending test has been investigated. The obtained S-parameter profile coincides well with the expected fatigue damage distribution. (C) 1997 American Institute of Physics.}, tags = {positron}, url = {http://apl.aip.org/resource/1/applab/v71/i15/p2115_s1}, DOI = {10.1063/1.120451}, author = {Greif, H. and Haaks, M. and Holzwarth, U. and M{\"a}nnig, U. and Tongbhoyai, M. and Wider, T. and Maier, K. and Bihr, J. and Huber, B.} } @Article { Bihr1997, title = {Positron microprobe for site-resolved positron annihilation measurements at a micrometric scale}, journal = {Eur. J. Cell Biol.}, year = {1997}, volume = {74}, pages = {69--69}, tags = {positron}, author = {Bihr, J. and Greif, H. and Haaks, M. and Holzwarth, U. and Huber, B. and M{\"a}nnig, U. and Tongbhoyai, M. and Maier, K.} } @Mastersthesis { maennig96, title = {Tiefenaufgel{\"o}ste Fehlstellenuntersuchungen mit langsamen Positronen}, year = {1996}, month = {11}, tags = {positron, material}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1996_Diplom_Maennig.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {M{\"a}nnig, U.} } @Mastersthesis { boernsen96, title = {Elektronentheoretische Untersuchungen zum Magnetismus amorpher und fl{\"u}ssiger Co-Pd-Legierungen}, year = {1996}, month = {2}, affiliation = {Max-Planck-Institut f{\"u}r Metallforschung, Institut f{\"u}r Physik, Stuttgart}, tags = {magnet}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1996_Diplom_Boernsen.pdf}, school = {Universit{\"a}t Bonn}, author = {B{\"o}rnsen, N.} } @Phdthesis { deckers1996, title = {Die Anwendbarkeit polarisierter Positronen zur Untersuchung paramagnetischer Zentren}, year = {1996}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1996_Doktor_Deckers.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Deckers, C.} } @Phdthesis { reske96, title = {Fl{\"u}ssige Ferromagnete- Untersuchungen zur magnetischen Ordnung in unterk{\"u}hlten Co-Pd-Schmelzen}, year = {1996}, tags = {magnet}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1996_Doktor_Reske.pdf}, school = {Universit{\"a}t Bonn}, type = {Dissertation}, author = {Reske, J.} } @Mastersthesis { buehrer95, title = {Elektromagnetische Levitation en miniature}, year = {1995}, month = {10}, affiliation = {Institut f{\"u}r Strahlen und Kernphysik der Universit{\"a}t Bonn}, tags = {magnet}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1995_Diplom_Buehrer.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {B{\"u}hrer, C.} } @Mastersthesis { greif94, title = {Aufbau und Erprobung eines mobilen Positronenstrahls}, year = {1994}, month = {1}, affiliation = {Institut f{\"u}r Strahlen- und Kernphysik der Universit{\"a}t Bonn}, tags = {positron}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1994_Diplom_Greif.pdf}, school = {Universit{\"a}t Bonn}, type = {Diplomarbeit}, author = {Greif, H.} } @Phdthesis { maier73, title = {Selbstdiffusion in Kupfer zwischen 630\(^{\circ}\)C und 300\(^{\circ}\)C}, year = {1973}, url = {https://agmaier.hiskp.uni-bonn.de/fileadmin/publications/1973_Doktor_Maier.pdf}, school = {Universit{\"a}t Stuttgart}, type = {Dissertation}, author = {Maier, K.} }