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In this work, MgF2 and CaF2 doped calcium aluminate glass samples have been investigated in order to describe the intrinsic defects that are formed in UV irradiated glasses. It is well known that calcium aluminate, when UV-illuminated, changes colour from blue to green. Thermoluminescence (TL), Optical Absorption (OA) and Electron Paramagnetic Resonance (EPR) measurements have been carried out and the results obtained were associated with the structural properties of the CaO—Al2O2—SiO2 system, in order to provide a defect model. Thermal treatments up to 150°C were performed for OA and TL measurements but the thermal decay curves could not be adjusted by an exponential function. The TL experimental results were fitted, according to a continuous model, with a Gaussian distribution function centred at 0.6eV and a frequency factor of 109s?1. 相似文献
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A new approach to on-line oxygen isotope analysis has been developed which utilises existing elemental analyser and mass spectrometry technology to produce a sample of carbon dioxide gas for oxygen isotople analysis. The method relies on on-line high temperature pyrolysis of the sample over a carbon source followed by a rapid, non-contributive partial catalytic oxidation over nickel powder at between 550 and 600 degrees C. Initial results demonstrate both good precision (better than 0.2 per thousand) and accuracy for both cellulose and silver nitrate samples. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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H.B. Pascoal W.M. Pontuschka H. Rechenberg 《Applied Physics A: Materials Science & Processing》2000,70(2):211-214
Two types of silicon detectors are reported (ion implantation and surface barrier detector) for the detection of neutrons in high gamma-background. The purpose is to find an optimal design of silicon detector combined with the neutron converter, which is efficient enough to neutron flux and with low sensitivity to %-rays. The experiments show that for fabrication of effective Si detectors for neutrons (using the (n,!) reactions) in the presence of an intensive %-field one must optimise the resistivity of the Si substrate and the active area of the detector, at which the detector has a maximum efficiency to the charged particles and is relatively insensitive to the %-rays. 相似文献
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The aim of this work was to study some polarization mechanisms in phosphate glasses containing different transition metal oxides, performed at radio frequency (100 kHz) and in the microwave region (9 GHz). Cobalt, iron and tungsten oxides were chosen for the present investigation. The results show that the dielectric constant increases linearly with increasing Co concentration, whereas for iron and tungsten ions, the dielectric constant values were found to decrease up to a given concentration and further, increase for higher concentration of W and Fe. This anomaly was observed both at 100 kHz and 9.00 GHz and was attributed to the valence state of the transition metal ions in the glass structure. The dielectric constant is lower in the microwave region, due to structural relaxation mechanisms. 相似文献
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Richard T Libby Gareth R Howell Iok-Hou Pang Olga V Savinova Adrienne K Mehalow Joseph W Barter Richard S Smith Abbot F Clark Simon WM John 《BMC neuroscience》2007,8(1):108
Background
Nitric oxide synthase 2 (NOS2) contributes to neural death in some settings, but its role in glaucoma remains controversial. NOS2 is implicated in retinal ganglion cell degeneration in a rat glaucoma model in which intraocular pressure (IOP) is experimentally elevated by blood vessel cauterization, but not in a rat glaucoma model where IOP was elevated by injection of hypertonic saline. To test the importance of NOS2 for an inherited glaucoma, in this study we both genetically and pharmacologically decreased NOS2 activity in the DBA/2J mouse glaucoma model. 相似文献17.
WM.B. Peatman Gerald B. Kasting David J. Wilson 《Journal of Electron Spectroscopy and Related Phenomena》1975,7(3):233-246
Autoionization electrons in threshold photoionization spectra are known to occur. The effect of such electrons on the interpretation of threshold electron spectra is discussed and a new method is described which enables one to discriminate between zero kinetic energy electrons and energetic electrons in photoionization experiments with little ambiguity. The method largely overcomes the main problem present in some previously described threshold electron studies; namely, the line-of-sight transmission of energetic electrons which gives rise to non-threshold electron peaks. A rejection ratio of 25 is readily obtained for 0.038 eV electrons compared with threshold (zero kinetic energy) electrons and the (small) transition probability for energetic electrons falls off more rapidly than for analysers previously described. Design parameters based on electron trajectory calculations are given for the analyser used, and photoionization results on argon are presented. 相似文献
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Calderbank AR; Cameron PJ; Kantor WM; Seidel JJ 《Proceedings London Mathematical Society》1997,75(2):436-480
When m is odd, spreads in an orthogonal vector space of type+(2m + 2,2) are related to binary Kerdock codes and extremalline-sets in 2m + 1 with prescribed angles. Spreads in a 2m-dimensionalbinary symplectic vector space are related to Kerdock codesover Z4 and extremal line-sets in with prescribed angles. These connections involve binary, realand complex geometry associated with extraspecial 2-groups.A geometric map from symplectic to orthogonal spreads is shownto induce the Gray map from a corresponding Z4-Kerdock codeto its binary image. These geometric considerations lead tothe construction, for any odd composite m, of large numbersof Z4-Kerdock codes. They also produce new Z4-linear Kerdockand Preparata codes. 1991 Mathematics Subject Classification:primary 94B60; secondary 51M15, 20C99. 相似文献
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WM. Hayden Smith 《Optical and Quantum Electronics》1972,4(2):161-167
The Fabry-Perot interferometer can be used as a periodic filter for the sorting of spectra using the rotational Raman effect. Thus it is possible to detect low concentrations of impurities in the presence of the major atmospheric constituents. The parameters of importance in making these measurements and the expected results from this technique are discussed from theoretical computations. 相似文献