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  • 1
    ISSN: 0375-9474
    Keywords: Nuclear reactions
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2102
    Keywords: SchlüsselwörterµCT: Technologie ; µCT: Applikationen ; Knochenstruktur ; 3D Bildgebung ; Histomorphometrie ; Key wordsµCT: technology ; µCT: applications ; Bone structure ; 3D imaging ; Histomorphometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary The strength and fracture resistance of bone is determined by the structure of the trabecular network and the cortical shell. While standard 2D techniques like histomorphometry are inadequate to assess the 3D nature of the trabecular network, isotropic 3D datasets of this network can be acquired with the new imaging modality of µCT. However, so far the quantitative analysis of the generated datasets, in particular the extraction of appropriate parameters describing the bone structure, has not been finally solved. In this article we describe the technology and applications of µCT systems relevant in the field of osteology. The most important technical features of current µCT systems in this context are: 1. A spatial resolution down to 5–10 µm can be achieved. 2. The maximum sample size is related to the desired resolution by a factor of approximately 1000, that is, a resolution of 10 µm limits the maximum sample size to approximately 1 cm. 3. Scan times for µCT systems vary between minutes and hours. Currently five areas for the application of µCT systems in osteology can be identified: 1. The search of parameters characterizing the 3D trabecular structure. 2. The application of finite element models to determine the biochemical competence of the structural parameters. 3. The use of µCT in preclinical trials to study drug effects in small animals. 4. The validation of analysis methods used in high-resolution in-vivo imaging systems. 5. The 3D quantification of modeling and remodeling processes.
    Notes: Zusammenfassung Die Stärke und Bruchfestigkeit von Knochen wird durch seine trabekuläre und kortikale Struktur bestimmt. Mit zweidimensionalen Meßverfahren wie der Histomorphometrie kann die dreidimensionale Natur des Trabekelnetzwerkes nicht adäquat erfaßt werden. Isotrope 3D Datensätze können mit dem neuen bildgebenden Verfahren der µCT erzeugt werden. Die Frage nach geeigneten Strukturparametern zur Beschreibung des trabekulären Netzwerkes ist allerdings letztendlich noch nicht gelöst. In diesem Beitrag beschreiben wir Technologie und Anwendungen der µCT, welche für das Gebiet der Osteologie relevant sind. Als wichtigste technische Faktoren in diesem Kontext sind derzeit zu nennen: 1. Eine räumliche Auflösung von 5–10 µm kann erzielt werden. 2. Probengröße und Auflösung hängen ca. über einen Faktor 1000 zusammen: Bei einer zu erzielenden Auflösung von 10 µm ist die maximale Probengröße auf etwa 1 cm begrenzt. 3. Die Scanzeiten liegen im Bereich von Minuten bis Stunden. Im Bereich der Osteologie wird die µCT derzeit auf 5 Gebieten eingesetzt: 1. Zur Suche und Optimierung von Parametern, die die dreidimensionale Trabekelstruktur charakterisieren. 2. Die Anwendung von Finite-Elemente Methoden zur Bestimmung der biomechanischen Wertigkeit der stereologischen Parameter. 3. Der Einsatz in der präklinischen Forschung zu in-vivo Verlaufskontrollen in kleinen Labortieren. 4. Die Validierung von Analysemethoden, die in hochauflösenden in-vivo Verfahren zur Osteoporosediagnostik angewendet werden. 5. Die dreidimensionale Quantifizierung von Modeling- und Remodelingprozessen.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 110 (1998), S. 467-472 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Novel attenuation effects and the generation of the third harmonic frequency in nonlinear zero and first sound in 3 He were found in pulsed sound-transmission experiments at various pressures (0, 10 bar), frequencies (10-50 MHz), sound-pulse energies (0.01-110 nJ) and temperatures ranging from 0.8 mK to 200 mK. The nonlinear damping of zero sound increases with the square of the frequency and demonstrates that quantum-damping exists in a Fermi liquid even for low frequency phonons at temperatures as high as 1 mK due to multiple phonon absorption processes. The origin of the additional damping found in first sound at high temperatures and sound pulse powers is unclear, but part of the apparent attenuation is caused by third harmonic generation which was also found in superfluid 3 He-B. In zero- as well as in first sound the third harmonic generation takes place in the leading edge of the propagating sound pulse at times when the fundamental frequency has not even developed to its full amplitude.
    Type of Medium: Electronic Resource
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