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91.
K. I. Gnanasekar M. Sharon R. Pinto A. S. Tamhane S. C. Purandare S. P. Pai L. C. Gupta R. Vijayaraghavan 《Zeitschrift für Physik B Condensed Matter》1995,99(2):173-177
Structural and superconducting properties of the system Lu1?x Ca x Ba2 Cu3O7?δ, both in bulk as well as thin film form, have been investigated. Presence of large Ca-ions at the Lu-sites is responsible for phase stability (in 1–2–3 phase) in bulk. In argon annealed tetragonal samples (δ:1) superconductivity is reinstated as in these samples, presence of Ca-ions lead to the generation of holes in the Cu?O planes. In oxygen annealed bulk samples and thin films, there is a large depression ofT c due to divalent Ca-ions present in concentrationx<0.2. Our data indicate that this depression ofT c is likely due to overdoping effect. 相似文献
92.
Sharon P. Hudson 《School science and mathematics》1996,96(3):133-139
The purpose of this study was to describe the supply and potential shortages of science teachers in the United States. Ninety-six percent of the State Science Consultants of the 50 State Boards of Education responded to a 1992 survey to assess the supply of science teachers. This survey was modeled after Howe and Gerlovich's 1982 study to provide an assessment of changes in science teacher supply over the last 10 years. Although there were improvements in the supply of science teachers, shortages were reported in all science subjects and were particularly critical in physics, chemistry, and earth science. In addition to providing a needed update on science teacher supply, this study analyzed 45 previous studies of science teacher supply and found convincing evidence to support the hypothesis that there is a persistent but fluctuating long term shortage of science teachers. This shortage is attributed to competition with business and industry. To alleviate critical shortages of science teachers, it is recommended that salaries be raised to be more competitive with industry and a national database be established to facilitate monitoring the supply of science teachers. 相似文献
93.
Requirements for trimethylsilyloxy group interaction and rearrangement are discussed. It is evident that formation of the m/e 147 ion is a function of the stereochemistry, steric hindrance and separation of the trimethylsilyloxy groups and reflects the stereochemistry of the steroid itself. It is postulated that ring cleavage is not necessarily a prerequisite for the formation of this ion. The occurrence of the m/e 147 ion can be structurally informative in trimethylsilyl derivatives of steroidal alcohols. 相似文献
94.
95.
James F. Woodward André de Klerk Gail Kahler Kathrine Leber Peter Pompei Daniel Schultz Sharon Stern 《Foundations of Physics》1972,2(2-3):241-244
An experiment designed to test the highly speculative hypothesis of photon consciousness was executed. It was found that, within the accuracy attainable with the apparatus, there is no empirical justification for the hypothesis. 相似文献
96.
Phase diagrams of self-assembled mono-tethered nanospheres from molecular simulation and comparison to surfactants 总被引:1,自引:0,他引:1
Iacovella CR Horsch MA Zhang Z Glotzer SC 《Langmuir : the ACS journal of surfaces and colloids》2005,21(21):9488-9494
We perform Brownian dynamics simulations on model 3-D systems of mono-tethered nanospheres (TNS) to study the equilibrium morphologies formed by their self-assembly in a selective solvent. We predict that in contrast to flexible amphiphiles the nanospheres are locally ordered and there is an increase in the local order with an increase in concentration or relative nanoparticle diameter. We present the temperature vs concentration phase diagram for a system of TNS and propose a dimensionless scaling factor F(v) (headgroup volume/tether volume) that allows a comparison between the morphologies formed from TNS and traditional surfactants. 相似文献
97.
98.
Ashbrook SE Le Pollès L Gautier R Pickard CJ Walton RI 《Physical chemistry chemical physics : PCCP》2006,8(29):3423-3431
The distorted perovskites NaTaO(3) and NaNbO(3) have been studied using (23)Na multiple-quantum (MQ) MAS NMR. NaTaO(3) was prepared by high temperature solid state synthesis and the NMR spectra are consistent with the expected room temperature structure of the material (space group Pbnm), with a single crystallographic sodium site. Two samples of NaNbO(3) were studied. The first, a commercially available sample which was annealed at 900 degrees C, showed two crystallographic sodium sites, as expected for the room temperature structure of the material (space group Pbcm). The second sample, prepared by a low temperature hydrothermal method, showed the presence of four sodium sites, two of which match the expected room temperature structure and the second pair, another polymorph of the material (space group P21ma). This is consistent with powder X-ray diffraction data which showed weak extra peaks which can be accounted for by the presence of this second polymorph. Density functional theory (DFT) calculations support our conclusions, and aid assignment of the NMR spectra. Finally, we discuss the measured NMR parameters in relation to other studies of sodium in high coordination sites in the solid state. 相似文献
99.
Rony Sharon 《Optics Communications》2010,283(20):4122-6351
A multilayered scattering structure is proposed and demonstrated as a reference mirror for use with full field optical coherence tomography (FF-OCT) to increase contrast of tissue imaging and provide compensation. Common-path FF-OCT systems were built demonstrating high resolution cell profiling. The use of this mirror with frequency domain FF-OCT allows 3D images in real time. 相似文献
100.
Ashbrook SE Whittle KR Lumpkin GR Farnan I 《The journal of physical chemistry. B》2006,110(21):10358-10364
The yttrium local environment in the series of pyrochlores Y2Ti2-xSnxO7 was studied using 89Y NMR. Oxides with the pyrochlore structure exhibit a range of interesting physical and chemical properties, resulting in many technological applications, including the encapsulation of lanthanide- and actinide-bearing radioactive waste. The use of the nonradioactive Y3+ cation provides a sensitive probe for any changes in the local structure and ordering with solid solution composition, through 89Y (I = 1/2) NMR. We confirm that a single pyrochlore phase is formed over the entire compositional range, with Y found only on the eight-coordinated A site. A significant (approximately 15 ppm) chemical shift is observed for each Sn substituted into the Y second neighbor coordination environment. The spectral signal intensities of the possible combinations of Sn/Ti neighbors match those predicted statistically assuming a random distribution of Sn4+/Ti4+ on the six-coordinated pyrochlore B site. 相似文献