Study of Surface Acoustic Wave propagation using Synchrotron Radiation X-Ray Topography

X-ray topography is an accurate and sensitive method to image the strain fields existing in crystals, particularly those created by bulk or surface acoustic waves (BAW or SAW). The time structure of the synchrotron radiation allows to image progressive waves having a frequency multiple of that of the synchrotron. The main purpose of this study is the understanding of the exact nature of the information obtained about SAW by means of X-Ray topography. To this end we will consider experimental and computed images obtained for SAW propagating on ST-cut quartz and YZ-LNB. Most experiments were made using wide X-ray beams. Depending on the diffraction conditions, the so-called "translation" topographs seem often as being good maps of the displacement existing near the surface of the SAW device. These images may be considered as the result of a process of spatial integration of section topographs, more simply related to the X-ray diffraction process and to the displacement gradients of the acoustic field. These section topographs, corresponding to an extremely thin X-ray beam, contain, in fact, more information about the SAW. Quite intricate section topographs of low amplitude SAW propagating on YZ lithium niobate and ST-cut quartz were experimentally obtained using the Bragg diffraction geometry (reflection). Simulations of these section topographs gave information about the displacement gradients existing near the surface (most intense contrast) and about the depth dependence of this gradient (weak contrasts). In the summation process, leading to the "translation" topographs, only the intense contrasts (representing the largest strains) contribute significantly while the weaker ones are blurred into a grey level. Thus, the main contrast in translation topographs arise mainly from the gradients of the component of the displacement along the diffraction vector, at (or very near) the surface. These derivatives are proportional to the displacement so that these topographs represent essentially, with a different phase, the corresponding displacement. When the amplitude of the SAW becomes large enough, a kinematical diffraction process explains that the most intense contrast generated near the surface is enlarged proportionally to the local amplitude. This allows a simple method to measure the transverse amplitude variations of the surface modes. The two other elastic components of the SAW are imaged using the Laue diffraction geometry (transmission) with appropriate diffraction vectors. The corresponding section topographs obtained with ST-cut quartz are also complex and again, simulated images were used to understand the contrasts observed. Similarly the summation process, leading to the translation images, is dominated by the largest displacement gradient and so leads to a representation of the lateral displacements existing near the surface. Small velocity (phase) variations most probably induced by the dislocations present in the synthetic quartz crystal, were observed in the sections images

Digital image ratio: a new radiographic method for quantifying changes in alveolar bone.Part II: Clinical application

International audienceAs reported in a previous paper (1) we have developed a new technique, Digital Image Ratio (DIR), which theoretically avoids some of the drawbacks of quantitative digital substraction radiography. DIR allows the direct computation and visualization of bone-mass-ratio changes. This second paper describes the use of DIR analysis to examine 20 sites in 8 patients undergoing regenerative periodontal therapy. Standardized reproducible radiographs of these 20 sites were taken before and 12 months after surgery. Ten experimental sites were treated with bone graft substitutes (natural coral or natural coral+collagen), and 10 control sites by debridement alone. None of the experimental sites had a density ratio below 1, where I indicates no change. The error was ±0.07 (0.93–1.07). The experimental sites showed an 18% mean increase in bone density (1.18), which increased to 23% (1.23) for sites filled with natural coral alone. All the control sites had values close to 1.00 (1.00±0.07) except for 3 sites, which showed a 9–15% loss of bone density. It is thus possible to compare and quantify the changes in experimental and control sites in the same patient using the percentage gain or loss of bone density. This demonstrates that DIR is suitable for clinical applications, and can be used in clinical analysis when bone changes are expected

Analysis of images in traverse topographs.

International audienceAmong the various X-ray topographic methods, traverse topography is the most widely used.However in most cases it is not possible to obtain quantitative results.Integrating the Takagi-Taupin equations now permits the simulation of traverse topographs using fast specialized computers.We show how simulated images may help understanding the contrasts of dislocations and stacking faults

Portals and Vle: how are they related and what are they for

Portals and VLE (Virtual Learning Environment) are increasingly being deployed for use in most universities. At a recent meeting of the eLearning Task Force held in Paris, January 29th 2009, the need for clarification of what they are and how they are related was highlighted. This presentation results from exchanges among participants during this meeting

Identification of Burgers vectors along <111> in In-doped GaAs, by X-ray transmission topography andimage simulation.

International audienceLong dislocations with Burgers vectors along are unusual in f.c.c. lattices. X-ray topographs have beenobtained of as-grown GaAs crystals doped with 1020 atoms cm -3 of In, where the usual extinction criterion g.b = 0leads to this type of defect. However, for several g satisfying the condition g.b = 0 with b = a [111], the images of thesedislocations were still clearly visible. Comparison between experimental and computer-simulated X-ray topographicsections of these defects confirms the existence of Burgers vectors along

Visualisation de la répartition d'intensité des rayons X dans un cristal déformé

National audienceNous nous proposons de présenter le résultat d'études théoriques sur la propagation des rayons X dans un cristal contenant une dislocation

Images Of Serial Sectioning In Electron Microscopy : 3D Visualisation Of Objects Of Biological Interest

International audienceIn the case of serial sections observed by the means of an electron microscope, it is possible to rebuild an image of an object, using the local intelligence of an image workstation without the need of a powerful computer. We will explain the basic principles of a program that we have written and explain its further developments

Technology-enhanced learning on campus: insights from EUNIS e-Learning Task Force

In 2010 the EUNIS e-Learning Task Force (ELTF) members collaborated on a review of tools and technologies in use across our member institutions. One of the key features of that paper was the use of technology to give off-campus learners, such as distance learners, those undertaking field studies and learners in the workplace a richly supported learning experience. Building on the success of that collaboration, the ELTF members have turned their attention this year to the use of technology on campus. Whilst technology and distance learning go hand in hand, universities are often slower to take advantage of the possibilities offered by technology to enrich the learning that takes place in our lecture theatres and classrooms. The reasons for this are often cultural as much as financial or technical. Drawing on experience from across the EUNIS member nations we take a look at the types of tools, learning resources and learning activities that are being used to enhance the traditional curriculum, promote deeper learning and bridge the learning that takes place inside and outside the classroom. We look at a range of innovative projects and the benefits they have delivered, ways of overcoming the barriers to technology-enhanced learning on campus and we speculate about the role and function of the campus of the future