Current Issue : April - June Volume : 2013 Issue Number : 2 Articles : 4 Articles
The carbon nanotube field emitter array was grown on silicon substrate through\r\na resist-assisted patterning (RAP) process. The shape of the carbon nanotube array is\r\nelliptical with 2.0 Ã?â?? 0.5 mm2 for an isotropic focal spot size at anode target. The field\r\nemission properties with triode electrodes show a gate turn-on field of 3 V/Ã?µm at an anode\r\nemission current of 0.1 mA. The author demonstrated the X-ray source with triode\r\nelectrode structure utilizing the carbon nanotube emitter, and the transmitted X-ray image\r\nwas of high resolution....
Without appropriate quality control (QC) and preventative maintenance (PM) measures\r\nfor X-ray machines in place, the benefits of reduced dose to the patient and\r\nearly diagnosis will not be realized. Quality control and PM also make it possible\r\nto unify X-ray-imaging practices in the country using international image quality\r\nguidelines. The impetus for the present work resulted from the concern that with\r\nthe recent increase in the numbers of X-ray machines in Tanzania, but with limited\r\ntechnical support to maintain and operate them, can increase radiation risk to patients\r\nand lower diagnostic accuracy. The aim of this work is to report on the\r\ncurrent status of diagnostic X-ray machines in Tanzania in order to produce the\r\ndata needed to formulate QC and PM policies and strategies. These policies and\r\nstrategies are needed to ensure that patients receive the lowest possible radiation\r\nrisk and maximum health benefits from X-ray examinations. Four QC tests were\r\nperformed on a total of 196 X-ray units. Accurate beam alignment and collimation\r\nwere tested on 80 (41%) units, the timer accuracy was tested on 120 (61%) units,\r\nand a radiation leakage test was performed on 47(24%) units. Preventative maintenance\r\ntests were performed on all 196 X-ray units. The results showed that of the\r\nunits tested for QC, 59% failed the kilovoltage (kVp) test, 57% failed the timer\r\naccuracy test, 60% failed the beam alignment test, and 20% failed the radiation\r\nleakage test. Only 13% of the units passed the PM test: 53% of the units were\r\ndefective, and 34% were out of order. As a result of the PM findings, the government\r\nhas introduced a rehabilitation project to service X-ray units and replace\r\nnonoperational X-ray units. The new units have full support service contracts signed\r\nby their suppliers. As a result of the QC findings, X-ray maintenance retraining\r\nprograms have been introduced....
The immediate products of x-ray absorption in aqueous biological samples are free radicals including *OH, H2O2, *H\r\nand solvated electrons. Because their lifetimes and diffusion ranges are dependent on the local bio-molecular\r\nenvironment, imaging these free radicals in real-time while they are produced by a scanning x-ray nanobeam may\r\nprovide a biological microscopy method of high resolution. As a first step towards this goal, we investigated the\r\nfeasibility of imaging the initial free radical products of x-ray absorption in live cells using fluorescent free radical\r\nsensors. We selected six commercially available fluorescent sensors for screening tests of their sensitivities towards\r\nx-ray radiation in solution form. Two of the six dyes were found to have high sensitivities. One of the two was\r\nsuccessfully used for dynamic confocal fluorescence imaging of x-ray generated free radicals in the intracellular\r\nspace of mouse embryonic fibroblasts. Time series of fluorescence images before and during x-ray radiation were\r\nacquired. The rate of increase of cellular fluorescence showed both the initial production of free radicals by the\r\nphysical ionization events as well as stimulated biological production of reactive oxygen species later on. The\r\nimplications of the results for future development of microscopy techniques are discussed....
Recent technological advances enabled high-throughput collection of Small Angle X-ray Scattering (SAXS) profiles\r\nof biological macromolecules. Thus, computational methods for integrating SAXS profiles into structural modeling\r\nare needed more than ever. Here, we review specifically the use of SAXS profiles for the structural modeling of\r\nproteins, nucleic acids, and their complexes. First, the approaches for computing theoretical SAXS profiles from\r\nstructures are presented. Second, computational methods for predicting protein structures, dynamics of proteins in\r\nsolution, and assembly structures are covered. Third, we discuss the use of SAXS profiles in integrative structure\r\nmodeling approaches that depend simultaneously on several data types....
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