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281.
282.
Zinc silicate phosphors co-doped with Eu3+ ions and also with both Eu3+ and Tb3+ ions were prepared by high temperature solid state reaction in air or reducing atmosphere. The luminescence characteristics of the prepared phosphors were investigated. While in the samples prepared in air, Eu3+ emission was found to be dominant over Tb3+ emission, in the samples prepared in reducing atmosphere, intense Eu2+ emission at 448 nm was found to be predominant over narrow Tb3+ emission. Luminescence studies showed that Eu3+ ions occupy asymmetric sites in Zn2SiO4 lattice. The intense f-f absorption peak of Eu3+ at 395 nm observed in these phosphors suggests their potential as red emitting phosphors for near ultra-violet light emitting diodes. 相似文献
283.
Using the spectrally resolved white light interferometry we present our experimental results on the measurement of the optical
constants of thin polymer films coated on a transparent substrate. As an extension to our previous work (J. Opt. Soc. Am.
B12, 1559 (1995)) on thick glass plates, we have shown here that this technique can be effectively applied to very thin polymer
films also. We have improved the accuracy of our results by using the Sellmeier dispersion formula for fitting the data. From
the width and position of the zero-order fringe and the frequency of modulations in the white light spectrum, the refractive
indexn(λ) and thicknesst of the thin polymer films are calculated. To study the accuracies involved in the technique, PVA, PMMA and PS films of varied
thicknesses are coated on glass plates and the measured values are compared with ellipsometer studies. 相似文献
284.
Chandrasekhar Das 《The Journal of the Operational Research Society》1984,35(11):995-1001
The price-break problem is a non-linear discrete problem of two variables and three parameters which is not solvable analytically. As such, a graphical solution is suggested here by re-formulating the problem in two stages: first, as an equivalent non-linear, and next, as a linear problem of two variables and a single parameter. The later formulation affords an efficient graphical solution which was not possible earlier. In addition, useful procedures for plotting iso-cost curves and deriving approximate numerical solutions are also discussed. 相似文献
285.
286.
287.
M. V. S. Chandrasekhar Rao N. Venkateswara Rao S. Bhuloka Reddy G. Satyanarayana D. L. Sastry M. R. Iyer S. G. Sahasrabhude 《Zeitschrift für Physik A Hadrons and Nuclei》1988,330(2):161-165
The total conversion coefficient of the 127.49 keV E3 isomeric transition in the decay of134mCs was measured using the gamma intensity balance method with the help of a high resolution low energy photon detector. Theα Tvalue was found to be 5.84±0.47 as against the theoretical value of 6.96, thus showing an anomaly of (16.1±6.7)%. TheK-conversion coefficient,α kwas also measured using the X-ray peak to gamma ray intensity method and found to be 2.24±0.04 as against the theoretical value of 2.72, which shows an anomaly of (17.6±1.4)% consistent with the experimental anomaly inα T. TheE3 hindrance factor of the isomeric transition was estimated to be (3.44±0.23) ·104. 相似文献
288.
Lithium caesium sulphate has been reported to undergo a phase transition from the room temperature orthorhombic phase with
space groupP cmn to a final phase with space groupP 22/n. Though a sharp anomaly in its physical properties has been found at 202.0;K, it was found that there was a need for careful
investigations in the vicinity of 240 and 210.0;K. Since the changes in the crystal structure involve primarily a rotation
of the SO4 tetrahedron about thec-axis and as this may be reflected both in the intensity and polarisation of the internal as well as external phonon modes,
the laser Raman spectra of oriented single crystals of LiCsSO4 at different temperatures were investigated. For correlation and definite identification of the spectral features, its infrared
absorption spectrum was also studied. An analysis of the intensities and polarizations of the internal modes of the sulphate
ions reveals the change in symmetry of the crystal. The integrated intensity and peak height of thev
1 line, plotted against temperature show anomalous peaks in the region of the phase transition. Differential scanning calorimetric
study gives the enthalpy change ΔH across the phase transition to be 0.213 kJ/mol. 相似文献
289.
Kree Cole-McLaughlin Herbert Edelsbrunner John Harer Vijay Natarajan Valerio Pascucci 《Discrete and Computational Geometry》2004,32(2):231-244
Given a Morse function f over a 2-manifold with or without boundary,
the Reeb graph is obtained by contracting the connected components
of the level sets to points.
We prove tight upper and lower bounds on the
number of loops in the Reeb graph
that depend on the genus, the number of boundary components,
and whether or not the 2-manifold is orientable.
We also give an algorithm that constructs the Reeb graph in time
O(n log n), where n is the number of edges in the
triangulation used to represent the 2-manifold and the Morse function. 相似文献
290.
The first total synthesis of (−)-diospongin B has been achieved starting from benzaldehyde using chiral allylation, a base catalyzed conjugate addition of an α,β-unsaturated ester and an intramolecular oxy-Michael reaction as the key steps in 16% overall yield. 相似文献