Current Issue : April - June Volume : 2018 Issue Number : 2 Articles : 5 Articles
In present work within the frame of dynamic theory for parametric X-ray radiation in two-beam\napproximation we have presented detailed studies on parametric radiation emitted by relativistic both\nelectrons and ions at channeling in crystals that is highly requested at planned experiments. The analysis\ndone has shown that the intensity of radiation at relativistic electron channeling in Si (110) with\nrespect to the conventional parametric radiation intensity has up to 5% uncertainty, while the error\nof approximate formulas for calculating parametric X-ray radiation maxima does not exceed 1.2%. We\nhave demonstrated that simple expressions for the Fourier components of Si crystal susceptibility Ãâ?¡0\nand Ãâ?¡gÃÆ? could be reduced, as well as the temperature dependence for radiation maxima in Si crystal\n(diffraction plane (110)) within Debye model. Moreover, for any types of channeled ions it is shown that\nthe parametric X-ray radiation intensity is proportional to z2âË?â??b(Z,z)/z with the function b(Z, z) depending\non the screening parameter and the ion charge number z = Z âË?â?? Ze....
Medical X-ray appliances use high-voltage power supplies that must be able to work\nwith very different energy requirements. Two techniques can be distinguished in X-ray medical\nimaging: fluoroscopy and radioscopy. The former involves low power radiation with a long exposure\ntime, while radioscopy requires large power during short radiographic exposure times. Since the\nconverter has to be designed by taking into account the maximum power specification, it will exhibit\na poor efficiency when operating at low power levels. Such a problem can be solved by using a\nnew multilevel LCC topology. This topology is based on a classical series-parallel resonant topology,\nbut includes an additional low-voltage auxiliary transformer whose function depends on the X-ray\ntechnique considered. When radioscopy operation is selected, the transformer will allow the power\nto be shared between two full-bridges. If fluoroscopy mode is activated, the auxiliary full bridge\nis disconnected and the magnetizing inductance of the auxiliary transformer is used to increase\nthe resonant inductor in order to reduce the resonant currents, thus improving the efficiency of\nthe converter....
Recently, evidence for synchrotron emission in both black-hole (BH) and neutron star X-ray\nbinaries has been mounting, from optical/infrared spectral, polarimetric, and fast timing signatures.\nThe synchrotron emission of jets can be highly linearly polarised, depending on the configuration of\nthe magnetic field (B-field). Optical and infrared (OIR) polarimetric observations of X-ray binaries are\npresented in this brief review. The OIR polarimetric signature of relativistic jets is detected at levels of\nâË?¼1ââ?¬â??10%, similarly to for active galactic nuclei (AGN) cores. This reveals that the magnetic geometry\nin the compact jets may be similar for supermassive and stellar-mass BHs. The B-fields near the jet\nbase in most of these systems appear to be turbulent, variable and on average, aligned with the jet\naxis, although there are some exceptions. These measurements probe the physical conditions in the\naccretion (out)flow and demonstrate a new way of connecting inflow and outflow, using both rapid\ntiming and polarisation. Variations in polarisation could be due to rapid changes of the ordering of\nthe B-field in the emitting region, or in one case, flares from individual ejections or collisions between\nejecta. It is predicted that in some cases, variable levels of X-ray polarisation from synchrotron\nemission originating in jets will be detected from accreting galactic BHs with upcoming spaceborne\nX-ray polarimeters....
Ultrasound processing of metal alloys is an environmental friendly and promising green technology for\nliquid metal degassing and microstructural refinement. However many fundamental issues in this field\nare still not fully understood, because of the difficulties in direct observation of the dynamic behaviours\ncaused by ultrasound inside liquid metal and semisolid metals during the solidification processes. In this\npaper, we report a systematic study using the ultrafast synchrotron X-ray imaging (up to 271,554 frame\nper second) technique available at the Advanced Photon Source, USA and Diamond Light Source, UK to\ninvestigate the dynamic interactions between the ultrasonic bubbles/acoustic flow and the solidifying\nphases in a Bi-8%Zn alloy. The experimental results were complimented by numerical modelling. The\nchaotic bubble implosion and dynamic bubble oscillations were revealed in-situ for the first time in\nliquid metal and semisolid metal. The fragmentation of the solidifying Zn phases and breaking up of the\nliquid-solid interface by ultrasonic bubbles and enhanced acoustic flow were clearly demonstrated and\nagreed very well with the theoretical calculations. The research provides unambiguous experimental\nevidence and robust theoretical interpretation in elucidating the dominant mechanisms of microstructure\nfragmentation and refinement in solidification under ultrasound...
We report the occurrence of X-rays at ground level due to cloud-to-ground flashes of\nupward-initiated lightning from Gaisberg Tower, in Austria, which is located at an altitude of 1300 m.\nThis is the first observation of X-ray emissions from upward lightning from a tower top located\nat high altitude. Measurements were carried out using scintillation detectors installed close to the\ntower top in two phases from 2011 to 2015. X-rays were recorded in three subsequent strokes of\nthree flashes out of the total of 108 flashes recorded in the system during both phases. In contrast to\nthe observations from downward natural or triggered lightning, X-rays were observed only within\n10 �¼s before the subsequent return stroke. This shows that X-rays were emitted when the dart leader\nwas in the vicinity of the tower top, hence during the most intense phase of the dart leader. Both the\ndetected energy and the fluence of X-rays are far lower compared to X-rays from downward natural\nor rocket-triggered lightning. In addition to the above 108 flashes, an interesting observation of X-rays\nproduced by a nearby downward flash is also presented. The shorter length of dart-leader channels\nin Gaisberg is suggested as a possible cause of this apparently weaker X-ray production....
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