Current Issue : October - December Volume : 2013 Issue Number : 4 Articles : 5 Articles
Theoretical and numerical results on angular and spectral distributions and total number of photons of\r\nseveral types of coherent radiation produced by microbunched beams passing through radiators are\r\npresented: coherent x-ray bremsstrahlung, x-ray transition, resonance transition, and diffraction radiations.\r\nThe possibility of observation and application of these new types of radiation for the study of\r\nparameters of electron beam microbunching, which is important for the effectiveness of x-ray free\r\nelectron lasers, is discussed....
The increase in the X-ray absorption due to gold nanoparticles was investigated by using aqueous solutions containing gold (Au)\r\nnanoparticles. A sample with 15 nmin size nanoparticles and 0.5mg/mL gold concentration and a distilled water sample were used.\r\nTransmitted X-ray beams through the samples were registered with a CdTe detector and with an ionization chamber. Results show\r\nan enhancement in the X-ray absorption in the range 20%ââ?¬â??6% for beams generated from20 kV to 120 kVtube voltages, respectively.\r\nResults show that the use of gold nanoparticles, even at low concentrations, should result in a significant contrast enhancement for\r\nlow-energy X-ray beams....
Recently, there has been significant progress in the field of soft- and hard-X-ray\r\nimaging for a wide range of applications, both technically and scientifically, via developments\r\nin sources, optics and imaging methodologies. While one community is pursuing extensive\r\napplications of available X-ray tools, others are investigating improvements in techniques,\r\nincluding new optics, higher spatial resolutions and brighter compact sources. For increased\r\nimage quality and more exquisite investigation on characteristic biological phenomena,\r\ncontrast agents have been employed extensively in imaging technologies. Heavy metal\r\nnanoparticles are excellent absorbers of X-rays and can offer excellent improvements in\r\nmedical diagnosis and X-ray imaging. In this context, the role of gold (Au) is important for\r\nadvanced X-ray imaging applications. Au has a long-history in a wide range of medical\r\napplications and exhibits characteristic interactions with X-rays. Therefore, Au can offer a\r\nparticular advantage as a tracer and a contrast enhancer in X-ray imaging technologies by\r\nsensing the variation in X-ray attenuation in a given sample volume. This review\r\nsummarizes basic understanding on X-ray imaging from device set-up to technologies.\r\nThen this review covers recent studies in the development of X-ray imaging techniques\r\nutilizing gold nanoparticles (AuNPs) and their relevant applications, including two- and\r\nthree-dimensional biological imaging, dynamical processes in a living system, single cellbased\r\nimaging and quantitative analysis of circulatory systems and so on. In addition to\r\nconventional medical applications, various novel research areas have been developed and\r\nare expected to be further developed through AuNP-based X-ray imaging technologies....
Time resolved optical reflectivity and x-ray diffraction techniques are employed to study the laser-induced structural response in two charge and orbitally ordered manganites. Optical data indicate a non-thermal nature of the laser-triggered phase transition via the disappearance of an optical phonon related to the charge and orbitally ordered phase. The x-ray diffraction measurements on superlattice reflections confirm the non-thermal time scale of the initial step of this phase transition but also show that the complete change of structural symmetry is not instantaneous....
X-ray absorption spectroscopy and X-ray diffraction are suitable probes of the chemical state of a catalyst under working conditions but are limited to bulk information. Here we show in two case studies related to hydrothermal aging and chemical modification of model automotive catalysts that enhanced detailed information of structural changes can be obtained when the two methods are combined with a concentration modulated excitation (cME) approach and phase sensitive detection (PSD). The catalysts are subject to a modulation experiment consisting of the periodic variation of the gas feed composition to the catalyst and the time-resolved data are additionally treated by PSD. In the case of a 2 wt% Rh/Al2O3 catalyst, a very small fraction (ca. 2%) of Rh remaining exposed at the alumina surface after hydrothermal aging at 1273 K can be detected by PSD. This Rh is sensitive to the red-ox oscillations of the experiment and is likely responsible for the observed catalytic activity and selectivity during NO reduction by CO. In the case of a 1.6 wt% Pd/Al2O3-Ce(1-x)Zr(x)O2 catalyst, preliminary results of cME-XRD demonstrate that access to the kinetics of the whole material at work can be obtained. Both the red-ox processes involving the oxygen storage support and the Pd component can be followed with great precision. PSD enables the differentiation between Pd deposited on Al2O3 or on Ce(1-x)Zr(x)O2. Modification of the catalyst by phosphorous clearly induces loss of the structural dynamics required for oxygen storage capacity that is provided by the Ce(4+)/Ce(3+) pair. The two case studies demonstrate that detailed kinetics of subtle changes can be uncovered by the combination of in situ X-ray absorption and high energy diffraction methods with PSD....
Loading....