The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
I. D. Cave - One of the best experts on this subject based on the ideXlab platform.
-
Theory of X-Ray Measurement of microfibril angle in wood
Wood Science and Technology, 1997Co-Authors: I. D. CaveAbstract:A diffraction intensity function for material bodies composed of arRays of crystalline fibres such as occurs with the cellulose of wood has been derived. It is implied in the analysis that the crystalline fibres making up the body have fibre symmetry- that there is a tendency for groups of fibres to have one set of crystal axes parallel while in the orthogonal direction the axes assume a low degree of order. It is further assumed that the patterns of the angular arrangement of the fibre groups relative to one axis of the body is independent of the direction about that axis. These conditions are believed to be compatible with the cellulosic structure found in wood. Thus it becomes possible to calculate the expected diffraction intensity profiles of realistic (and therefore complex) models of wood. This has aided the interpretation of the reflections from the (040) crystal planes of cellulose which are contaminated by low level reflections from other crystal planes, and it has been found that it might be possible by conjoint analysis of the paratropic (002) reflections and the diatropic (040) reflections to measure the complete cell wall planar microfibril angle distribution and the shape of the cell wall cross-section.
-
Theory of X-Ray Measurement of microfibril angle in wood
Wood Science and Technology, 1997Co-Authors: I. D. CaveAbstract:The property of fibre symmetry as exhibited by wood cellulose can be used to derive an explicit relationship between the orientation of a cellulose microfibril and the orientation of the X-Ray beam diffracted by any of its crystallographic planes. The solution applies to a microfibril of any orientation and so is well suited to evaluating the microfibril angle distribution in wood containing cells of any cross-sectional shape. The (002) and (040) reflections of cellulose have complementary properties that could be exploited to enable current problems associated with the use of each individually for evaluating the mean microfibril angle of the S2 layer to be overcome. It is expected that it will be possible to measure the microfibril angle distribution throughout the whole cell wall and also measure the average cell cross-section of a wood sample, by analysing (002) and (040) diffraction profiles in conjunction with each other.
Amit Ashok - One of the best experts on this subject based on the ideXlab platform.
-
X-Ray Measurement model and information-theoretic metric incorporating material variability with spatial and energy correlations
Anomaly Detection and Imaging with X-Rays (ADIX) V, 2020Co-Authors: Yijun Ding, Amit AshokAbstract:Extending our prior work, we propose an X-Ray Measurement model that incorporates spatial- correlated material variability. The model enables more accurate task-specific assessment of the performance of X-Ray imaging and sensing systems. More specifically, the model can be used to calculate bounds on the probability of error (Pe) for threat-detection tasks. We analyze the performance of a prototypical X-Ray Measurement system to compare the new spatial- and energy-correlated model with the previous model, which ignores the spatial correlation.
-
X-Ray Measurement model and information-theoretic metric incorporating material variability with energy correlations
Anomaly Detection and Imaging with X-Rays (ADIX) IV, 2019Co-Authors: Yijun Ding, Amit AshokAbstract:Extending our prior work, we propose a multi-energy X-Ray Measurement model incorporating material variability with energy correlations to enable the analysis and exploration of the performance of X-Ray imaging and sensing systems. Based on this Measurement model we provide analytical expressions for the Cauchy-Schwarz mutual information (ICS) measure that quantifies the performance limits of an X-Ray Measurement system for the threat-detection task. We analyze the performance of a prototypical X-Ray Measurement system to demonstrate the utility of our proposed material variability Measurement model.
-
X-Ray Measurement model and information-theoretic system metric incorporating material variability (Conference Presentation)
Anomaly Detection and Imaging with X-Rays (ADIX) III, 2018Co-Authors: Ahmad Masoudi, Jay Voris, David Coccarelli, Joel A. Greenberg, Michael E. Gehm, Amit AshokAbstract:In our prior work, we had employed a fixed photo-absorption, coherent, and incoherent cross-section material model to derive a shot-noise limited description of the X-Ray Measurements in check-point or a checked baggage threat-detection systems. Using this Measurement model, we developed an information-theoretic metric, which provides an upper-bound on the performance of a threat-detection system. However, the fixed cross-section material model does not incorporate material variability arising from inherent variations in its composition and density. In this work, we develop a multi-energy model of material variability based on composition and density variations and combine it with the shot-noise photon detection process to derive a new X-Ray Measurement model. We derive a computationally scalable analytic approximation of an information-theoretic metric, i.e. Cauchy-Schwarz mutual information, based on this material variability model to quantify the upper-bound on the performance of the threat-detection task. We demonstrate the effect of material variations on the performance bounds of X-Ray transmission-based threat detection systems as a function of detector energy resolution and source fluence.
M Kammler - One of the best experts on this subject based on the ideXlab platform.
-
femtosecond x Ray Measurement of coherent lattice vibrations near the lindemann stability limit
Nature, 2003Co-Authors: K Sokolowskitinten, C Blome, C Dietrich, A Tarasevitch, A Cavalleri, M Kammler, Juris Blums, I Uschmann, E Forster, M HornvonhoegenAbstract:The study of phase-transition dynamics in solids beyond a time-averaged kinetic description requires direct Measurement of the changes in the atomic configuration along the physical pathways leading to the new phase. The timescale of interest is in the range 10-14 to 10-12 s. Until recently, only optical techniques were capable of providing adequate time resolution1, albeit with indirect sensitivity to structural arrangement. Ultrafast laser-induced changes of long-range order have recently been directly established for some materials using time-resolved X-Ray diffraction2,3,4,5,6,7,8. However, the Measurement of the atomic displacements within the unit cell, as well as their relationship with the stability limit of a structural phase9,10,11, has to date remained obscure. Here we report time-resolved X-Ray diffraction Measurements of the coherent atomic displacement of the lattice atoms in photoexcited bismuth close to a phase transition. Excitation of large-amplitude coherent optical phonons gives rise to a periodic modulation of the X-Ray diffraction efficiency. Stronger excitation corresponding to atomic displacements exceeding 10 per cent of the nearest-neighbour distance—near the Lindemann limit—leads to a subsequent loss of long-range order, which is most probably due to melting of the material.
-
femtosecond x Ray Measurement of ultrafast melting and large acoustic transients
Physical Review Letters, 2001Co-Authors: K Sokolowskitinten, C Blome, C Dietrich, A Tarasevitch, Hornvon M Hoegen, D Von Der Linde, A Cavalleri, Jeff Squier, M KammlerAbstract:(Received 29 June 2001; published 7 November 2001)Time-resolved x-Ray diffraction with ultrashort 300 fs , multi-keV x-Ray pulses has been used tostudy the femtosecond laser-induced solid-to-liquid phase transition in a thin crystalline layer of germa-nium. Nonthermal melting is observed to take place within 300–500 fs. Following ultrafast melting weobserve strong acoustic perturbations evolving on a picosecond time scale.
Ronald Guillén - One of the best experts on this subject based on the ideXlab platform.
-
X-Ray Measurement of residual stresses and texture development during a rolling sequence of zirconium alloy cladding tubes
Journal of Applied Crystallography, 2010Co-Authors: David Gloaguen, Jamal Fajoui, Emmanuel Girard, Ronald GuillénAbstract:Texture and residual stress analysis using X-Ray diffraction have been carried out on zirconium alloy cladding tubes after cold pilgering, an industrial mechanical process. The final rolling pass has been completely characterized by X-Ray diffraction. An interpretation of the effect of intergranular stresses on the development of analysed stress has been made using a modified elastoplastic self-consistent model in order to account for the effect of the high intrinsic plastic anisotropy of hexagonal close-packed crystals. The contribution and magnitude of the first- and second-order residual stresses were correctly evaluated using information from the model. The main features of the rolling sequence were qualitatively reproduced by the simulations, considering prismatic slip as the main active deformation mode in this alloy under large strain.
K Sokolowskitinten - One of the best experts on this subject based on the ideXlab platform.
-
femtosecond x Ray Measurement of coherent lattice vibrations near the lindemann stability limit
Nature, 2003Co-Authors: K Sokolowskitinten, C Blome, C Dietrich, A Tarasevitch, A Cavalleri, M Kammler, Juris Blums, I Uschmann, E Forster, M HornvonhoegenAbstract:The study of phase-transition dynamics in solids beyond a time-averaged kinetic description requires direct Measurement of the changes in the atomic configuration along the physical pathways leading to the new phase. The timescale of interest is in the range 10-14 to 10-12 s. Until recently, only optical techniques were capable of providing adequate time resolution1, albeit with indirect sensitivity to structural arrangement. Ultrafast laser-induced changes of long-range order have recently been directly established for some materials using time-resolved X-Ray diffraction2,3,4,5,6,7,8. However, the Measurement of the atomic displacements within the unit cell, as well as their relationship with the stability limit of a structural phase9,10,11, has to date remained obscure. Here we report time-resolved X-Ray diffraction Measurements of the coherent atomic displacement of the lattice atoms in photoexcited bismuth close to a phase transition. Excitation of large-amplitude coherent optical phonons gives rise to a periodic modulation of the X-Ray diffraction efficiency. Stronger excitation corresponding to atomic displacements exceeding 10 per cent of the nearest-neighbour distance—near the Lindemann limit—leads to a subsequent loss of long-range order, which is most probably due to melting of the material.
-
femtosecond x Ray Measurement of ultrafast melting and large acoustic transients
Physical Review Letters, 2001Co-Authors: K Sokolowskitinten, C Blome, C Dietrich, A Tarasevitch, Hornvon M Hoegen, D Von Der Linde, A Cavalleri, Jeff Squier, M KammlerAbstract:(Received 29 June 2001; published 7 November 2001)Time-resolved x-Ray diffraction with ultrashort 300 fs , multi-keV x-Ray pulses has been used tostudy the femtosecond laser-induced solid-to-liquid phase transition in a thin crystalline layer of germa-nium. Nonthermal melting is observed to take place within 300–500 fs. Following ultrafast melting weobserve strong acoustic perturbations evolving on a picosecond time scale.
