Results 1 - 10 of 50093
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[en] A number of studies have suggested that the irradiation behavior and damage processes occurring during sequential and simultaneous particle irradiations can significantly differ. Currently, there is no definite answer as to why and when such differences are seen. Additionally, the conventional multiparticle irradiation facilities cannot correctly reproduce the complex irradiation scenarios experienced in a number of environments like space and nuclear reactors. Therefore, a better understanding of multiparticle irradiation problems and possible alternatives are needed. This study shows ionization induced thermal spike and defect recovery during sequential and simultaneous ion irradiation of amorphous silica. The simultaneous irradiation scenario is shown to be equivalent to multiple small sequential irradiation scenarios containing latent damage formation and recovery mechanisms. The results highlight the absence of any new damage mechanism and time-space correlation between various damage events during simultaneous irradiation of amorphous silica. This offers a new and convenient way to simulate and understand complex multi-particle irradiation problems. (authors)
[en] A simple method of assessing the reliability of the single aliquot regeneration method is presented, based on the repeated measurement of identical regeneration doses. It is shown that for the majority of the samples measured the requirement of a constant repeat point in each cycle is not met. The ability to maintain a constant repeat point is shown to be dependent upon preheating conditions, the requirements for which were found to vary at both inter-sample and inter-aliquot levels. The expected effect on estimated values of De is calculated and shown to be significant. Three possible means of circumventing these inaccuracies are presented: (i) adjustment of the measurement procedure (specifically the preheat conditions); (ii) modelling and correcting for the effect, and (iii) stabilising the response prior to construction of the regenerated growth curve. It is suggested that much of the variation in De observed between individual aliquots and between individual grains from well-bleached sediments may possibly be attributed to differences in preheating requirements, and that such differences may also account for some of the spread in De for partially bleached sediments
[en] Is is shown that to decrease the threshold field of rotation of magnetization bismuth-containing monocrystal film of ferrite-garnets should possess a higher lattice parameter than substrate
[en] Spiral microdiscs with waveguide based on a conducting polymer have been fabricated on quartz substrates and the emission properties have been studied. The directivity and the polarization properties of laser emission from the spiral microcavities with waveguide based on a poly(p-phenylenevinylene) derivative have been investigated by pulsed photo-pumping. The red laser emission from the spiral microdisc with waveguide has been observed, and the directivity of this microdisc geometry has been discussed taking the mathematical simulation into consideration
[en] We present results from a study to determine an acceptable CO2 laser-based non-evaporative mitigation protocol for use on surface damage sites in fused-silica optics. A promising protocol is identified and evaluated on a set of surface damage sites created under ICF-type laser conditions. Mitigation protocol acceptability criteria for damage re-initiation and growth, downstream intensification, and residual stress are discussed. In previous work, we found that a power ramp at the end of the protocol effectively minimizes the residual stress (<25 MPa) left in the substrate. However, the biggest difficulty in determining an acceptable protocol was balancing between low re-initiation and problematic downstream intensification. Typical growing surface damage sites mitigated with a candidate CO2 laser-based mitigation protocol all survived 351 nm, 5 ns damage testing to fluences >12.5 J/cm2. The downstream intensification arising from the mitigated sites is evaluated, and all but one of the sites has 100% passing downstream damage expectation values. We demonstrate, for the first time, a successful non-evaporative 10.6 (micro)m CO2 laser mitigation protocol applicable to fused-silica optics used on fusion-class lasers like the National Ignition Facility (NIF).
[en] Many natural deposits contain grains that have different burial histories, but reliable procedures to extract the component doses from mixed-dose samples have not been developed in optical dating. Here we present results for synthetic two- and three-component mixtures of data derived from laboratory-dosed sedimentary quartz using a single-aliquot regenerative-dose protocol and statistical models for finite mixtures. Composite sets of data were created from the doses measured for individual grains that had been bleached by sunlight and then given a beta dose of 5, 10 or 20 Gy. We found that the correct number of dose components, corresponding doses, and relative proportions of each component may be estimated if the within-component dispersion is small or is known. We also found, however, that recuperation of the OSL signal in sun-bleached quartz may produce artificially high dose estimates for some grains, an effect that should be taken into account when modelling natural mixtures
[en] We study experimentally and numerically the spatiotemporal dynamics of the multiple filament arrays excited by self-focusing of intense elliptical laser beams in fused silica. Our results demonstrate that although multiple filament arrays emerge as apparently regular patterns in the space domain, the spatiotemporal dynamics of the individual filaments is governed by the input-beam power and the input-beam ellipticity. In the case of moderate input-beam ellipticity, the individual filaments propagate in curved trajectories arising from skewed (spatiotemporal) coherence. The spatiotemporal propagation dynamics is regularized by increasing the input-beam ellipticity, and in part due to permanent modifications of fused silica that occur under intense irradiation. In this case, strong pulse reshaping and shock-front generation are observed, which yields a regular array of very short (<5 fs) superluminally propagating localized peaks in the leading front, followed by the subpulses centered on the input-pulse top, and trailed by subluminally propagating pulses with rather complex transverse intensity distribution.
[en] Drying process directly affect in structure of the silica support for catalysts. Therefore,we herein prepared bimodal meso-macropore structure of silica by sol-gel method and investigated the silica support obtained from various drying techniques, namely, hot air drying(HA), microwave drying (MW) and freeze drying (FD)by means of BET and BJH N2-sorption, and SEM. The results showed a significant effect of drying technique on the textural properties of the dried bimodal porous silica support. In addition, it was found that freeze drying could enhance surface area of silica support with higher than 500 m2/g. (Author)
[en] To determine an equivalent dose (De), the initial signal of the CW-OSL decay curve, supposedly dominated by the fast component, is used. Previous studies suggest that the resulting De however, may be underestimated if thermally unstable medium or slow components are part of the initial decay curve. The De(t) plot has the potential to reveal the 'unclean' fast component. We have here studied quartz samples obtained from late Pleistocene floodplain deposits in the Lower Mississippi Valley (LMV), which show decreasing values of De with increasing stimulation time. The deconvolution analysis of CW-OSL signals from these samples confirm the interpretation of the De(t) plots. As a consequence, component-resolved values of De were determined to obtain an accurate estimation of De. Contrary to previous studies, our results indicate that the values of De obtained with the initial signal are not underestimated for our samples containing a thermally unstable medium component.
[en] We measured the quality factors of whispering gallery modes of microsphere in the reflectance spectrum in prism-microsphere evanescent wave coupling configuration. The highest quality factor was at least 4 X 108, corresponds to a linewidth of about 1 MHz, limited by the probe laser linewidth. We also observed the dependence of coupling linewidth and amplitude on the distance between the prism and the microsphere.