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排序方式: 共有452条查询结果,搜索用时 15 毫秒
101.
Y C RATNAKARAM V REDDY PRASAD S BABU V V RAVI KANTH KUMAR 《Bulletin of Materials Science》2016,39(4):1065-1072
In this study, the luminescence performance of zinc phosphate glasses containing Eu3+ ion with the chemical compositions (60–x)NH4H2PO4-20ZnO-10BaF2-10NaF–x Eu2O3 (where x = 0.2, 0.5, 1.0 and 1.5 mol%) has been studied. These glasses were characterized by several spectroscopic techniques at room temperature. All the glasses showed relatively broad fluorescence excitation and luminescence spectra. Luminescence spectra of these glasses exhibit characteristic emission of Eu3+ ion with an intense and most prominent red emission (614 nm), which is attributed to 5D0 → 7F2 transition. Judd-Ofelt (Ω2, Ω4) parameters have been evaluated from the luminescence intensity ratios of 5D0 → 7FJ (where J = 2 and 4) to 5D0 → 7F1 transition. Using J-O parameters and excitation spectra, the radiative parameters are calculated for different Eu3+-doped glasses. Effect of γ-irradiation at fixed dose has been studied for all the Eu3+-doped glass matrices. The lifetimes of the excited level, 5D0, have been measured experimentally through decay profiles. The colour chromaticity coordinates are calculated and represented in the chromaticity diagram for Eu3+-doped zinc phosphate glasses for all concentrations. 相似文献
102.
Formation of Silicon-Aluminum Spinel 总被引:1,自引:0,他引:1
AKSHOY KUMAR CHAKRABORTY 《Journal of the American Ceramic Society》1979,62(3-4):120-124
Characterization of the intermediate cubic phase formed during the transformation of coprecipitated SiO2 -Al2 O3 gel on heating was studied and X-ray diffraction methods are reviewed and criticized. Coprecipitated gels of different SiO2 /Al2 O3 ratios were prepared; all showed a 980°C exotherm followed by crystallization of the cubic phase and liberation of SiO2 . Alkali extraction of SiO2 showed two types present in the 980°-heated product. One variety is free amorphous SiO2 and the other, chemically bonded to alumina in the crystalline cubic phase, was isolated and characterized as Si-Al spinel with the same composition as mullite. Thus, its formation from the gel of mullite composition shows the highest exotherm and the measured density agrees approximately with the theoretically calculated value. 相似文献
103.
Several results pertaining to large deformations at fast strain rates in a fine-grained ceramic material are described. Results for strain-rate, grain size, and temperature dependence of the flow stress are presented. They show that (a) ultrafine-grained ceramics are capable of high rates of deformation (about 10−4 to 10−4 s−1 ) at quite low stresses (1 to 20 MPa); (b) the mechanism of deformation is the enhanced rate of matter transport through the liquid phase segregated in the grain boundaries; (c) either uniaxial compression or tension tests may be used to determine the flow properties, except that a correction must be implemented for friction in the case of compression tests; and (d) microstructural changes can occur during deformation which influence the flow behavior. The ceramic is almost infinitely ductile in compression, whereas in tension elongations as large as W5% in one material, and more than 400% in another, were obtained. A model material, β-spodumene glass-ceramic, was used for this study but the results are likely to hold for other materials with equivalent microstructures, e.g., liquid-phase-sintered or hot-pressed materials such as the nitrogen ceramics 相似文献
104.
The reflectivity dependence, of the lasing photon energy in GaAs junction lasers at 77° K is studied. It is found that the lasing photon energy decreases with increasing values of the laser reflectivity. 相似文献
105.
A transaction-oriented database system is investigated, where checkpointing is carried out after a certain number of transactions are processed. The design objective is to maximize the system availability given the failure rate, checkpointing time, error recovery time, and other system parameters. Several checkpointing strategies have been proposed and analysed. The effect of error latency is also considered. 相似文献
106.
107.
MOHAN KUMAR KUNTUMALLA HARISH OJHA VADALI VENKATA SATYA SIVA SRIKANTH 《Bulletin of Materials Science》2013,36(6):1087-1090
It is difficult to detect β-SiC using micro-Raman scattering, if it is surrounded by carbon medium. Here, β-SiC is identified in the presence of a relatable surrounding diamond medium using subtle, but discernible Raman surface phonons. In this study, diamond/β-SiC nanocomposite thin film system is considered in which nanosized β-SiC crystallites are surrounded by a relatable nanodiamond medium that leads to the appearance of a weak Raman surface phonon band at about 855 cm???1. Change in the nature of the surrounding material structure and its volume content when relatable, will affect the resultant Raman response of β-SiC phase as seen in the present case of diamond/β-SiC nanocomposite thin films. 相似文献
108.
An attempt has been made to obtain the probabilities of pregnancy termination by live birth, still birth and abortion, in any particular order, assuming that the termination of pregnancy is associated with three competing ‘risks’, i.e. live birth, still birth and abortion, which need not necessarily operate at the same point of time. A probability model has been constructed to obtain the conditional probability of live birth/still birth/abortion given that the previous pregnancy has been terminated by a particular one of the three. The correlation coefficient between the outcomes of two particular consecutive pregnancy terminations, viz. live birth and reproductive wastage (which includes both abortion and still birth), has also been obtained. Given data pertaining to sample correlation coefficients between the nature of consecutive orders of the outcomes of conception from first to sixth, an exercise has been undertaken to estimate parameters relating to the ‘hazard’ rates of live births, still birth and abortion. The exercise further enables one to test the well-known demographic hypothesis that reproductive wastages follow each other in succession over consecutive orders of the outcomes of conception. 相似文献
109.
M SATYA KISHORE P SRIMATHI SUNDEEP KUMAR SWARNAGOWRI ADDEPALLI SRINIVASAN SWAMINATHAN VINAYAK TILAK ROBERT COLBORN 《Bulletin of Materials Science》2013,36(4):667-672
Graphene sheets are synthesized by a simple method starting from graphitic oxide as a precursor. Reaction of graphitic oxide at 250 °C with a combustion mixture of urea and ammonium nitrate results in the formation of thin graphene sheets. Graphene formation is characterized by XRD, TGA, XPS and TEM. Graphene materials synthesized by this method are investigated as an ultracapacitor material. Specific capacitance values of about 70 F/g are obtained at a current density of 100 mA/g by using KOH as an electrolyte. 相似文献
110.
The world is facing a new healthcare crisis with the rise and spread of novel coronavirus since December 2019.
Also known as Severe Acute Respiratory Syndrome Corona Virus-2 (SARS-CoV-2), the disease associated with SARSCoV-2 is even called COVID-19. The infection is said to have originated from the bat community and transmitted to
humans through an intermediate host (yet unknown) in Wuhan, in the Hubei region of China. COVID-19 is having
a pulverizing impact on the scientific community. As of August 13, 2020, the number of confirmed cases had reached
up to 20,439,814 and the death toll to 744,385, affecting more than 188 territories across the globe. In these difficult
times, the world is looking towards research and clinical work from different scientific communities to lead the way
to a solution to the issue. In this review, we are focusing on COVID-19 emergence, pathogenicity, and existence in
humans, as well as the SARS-CoV-2 infection mechanism and its similarities to previous coronavirus strains. 相似文献