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51.
Ramadevi V. Ravi G. Radha Velchuri Sameera Devi C. H. Prasad G. Vithal M. 《Ionics》2014,20(3):373-380
The pyrochlore oxide of composition YLnTiZrO7 (Ln?=?La, Nd, Sm, and Eu) was prepared by sol–gel method. All the samples were characterized by powder X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), diffused reflectance spectroscopy, and impedance spectroscopy. The powder XRD and Raman studies reveal that these samples were crystallized in cubic lattice with pyrochlore structure. The Rietveld analysis of the samples was carried out to obtain the unit cell parameters and reliability factors. The broad Raman bands observed for all the samples are due to cation/anion disorder in the lattice and nanosize. The XPS analysis of the samples shows the characteristic peaks belonging to Y3+, Ln3+ (Ln?=?La, Nd, Sm, and Eu), Ti4+, and Zr4+. Electrical conductivity of YLaTiZrO7 (YLTZ) and YEuTiZrO7 (YETZ) samples was calculated from the impedance as a function of frequency and temperature. These samples have shown conductivity of the order of 10?5 scm?1 at 500 °C. 相似文献
52.
J. Zitelli I. Muga L. Demkowicz J. Gopalakrishnan D. Pardo V.M. Calo 《Journal of computational physics》2011,230(7):2406-2432
The phase error, or the pollution effect in the finite element solution of wave propagation problems, is a well known phenomenon that must be confronted when solving problems in the high-frequency range. This paper presents a new method with no phase errors for one-dimensional (1D) time-harmonic wave propagation problems using new ideas that hold promise for the multidimensional case. The method is constructed within the framework of the discontinuous Petrov–Galerkin (DPG) method with optimal test functions. We have previously shown that such methods select solutions that are the best possible approximations in an energy norm dual to any selected test space norm. In this paper, we advance by asking what is the optimal test space norm that achieves error reduction in a given energy norm. This is answered in the specific case of the Helmholtz equation with L2-norm as the energy norm. We obtain uniform stability with respect to the wave number. We illustrate the method with a number of 1D numerical experiments, using discontinuous piecewise polynomial hp spaces for the trial space and its corresponding optimal test functions computed approximately and locally. A 1D theoretical stability analysis is also developed. 相似文献
53.
M. F. Ferreira A. N. Pinto P. S. Andr N. J. Muga J. E. MacHado R. N. Nogueira S. V. Latas M. H. Sousa J. F. Rocha 《Fiber and Integrated Optics》2005,24(3):261-285
We review the research progress concerning some fundamental issues related to polarization-mode dispersion (PMD) in high-speed fiber-optic transmission systems. We pay particular attention to issues such as the PMD-induced pulse broadening, PMD measurement and emulation, as well as PMD compensation. An electrical equalization technique based on a transversal filter and an optical technique based on a nonlinear chirped fiber Bragg gratings for PMD compensation will be discussed. 相似文献
54.
AbstractMode-division multiplexing requires all-optical signal processing techniques that are able to deal with a new coding dimension, the spatial mode. In this context, optical microwires emerge as a potential highly non-linear and multi-modal waveguide envisioning the development of all-optical signal processing devices to mode-division multiplexing systems based on the four-wave mixing process. The inter- and intramodal phase-matching conditions for the four-wave mixing process are mapped as a function of the microwire diameter and the wavelength of signals. Moreover, the efficiency of four-wave mixing considering a strong guiding regime is investigated in the multi-modal regime. 相似文献
55.
Different laser devices working as “atom diodes” for ultra-cold atoms
have been proposed recently. They transmit ground state level atoms coming
from
one side, say from the left, but reflect them when they come from the other
side.
We present and compare some of these models.
In all of them spontaneous decay is included
as an irreversible element which avoids backwards motion after the atom has
crossed the diode.
We also review the proposal of a cooling method based on an
“atom diode”. 相似文献
56.
We compare the absorption of (a) an absorbing potential proposed recently by Manolopoulos based on semiclassical arguments and (b) complex potentials composed by contiguous square barriers. The latter use more parameters and provide better absorption, but the potential by Manolopoulos is simple and robust with respect to numerical discretization, and can be very efficient if its only effective parameter is optimized. 相似文献
57.
Muga Nakagawa 《Tetrahedron letters》2005,46(32):5257-5261
Reactions of 2,2-dibromo-2-fluoroethyl alkyl ethers and dibromofluoromethylcarbinyl silyl ethers with CrCl2 and Mn powder provided 2-fluorovinyl alkyl ethers and 1-fluoro-2-alkenyl enol silyl ethers in high yields and in Z selective manner. 相似文献
58.
Venkataswamy Perala Jampaiah Deshetti Kandjani Ahmad Esmaielzadeh Sabri Ylias M. Reddy Benjaram M. Vithal M. 《Research on Chemical Intermediates》2018,44(4):2523-2543
Research on Chemical Intermediates - In this work, various transition and rare earth metal ions (M3+; M = Mn3+, Fe3+, La3+, and Pr3+) doped CeO2 solid solutions were prepared by a... 相似文献
59.
We propose and investigate a procedure to measure, at least in principle, a positive quantum version of the local kinetic energy density. This procedure is based, under certain idealized limits, on the detection rate of photons emitted by moving atoms which are excited by a localized laser beam. The same type of experiment, but in different limits, can also provide other non-positive-definite versions of the kinetic energy density. A connection with quantum arrival time distributions is discussed. 相似文献
60.
Ravji D. Patel Ranjan G. Patel Vithal S. Patel 《Journal of Thermal Analysis and Calorimetry》1988,34(5-6):1283-1293
The kinetics of curing of triglycidyl-p-aminophenol with four different diamines in stoichiometric amounts were investigated by means of differential scanning calorimetry. The results indicated that the curing reaction follows first-order Arrhenius kinetics with an activation energy in the range 40–70 kJ · mol–1. The effect of the structure of the curing agent on the curing characteristics is discussed on the basis of the curing characteristics and the kinetic parameters. An epoxy fortifier was observed to lower the curing temperature of an epoxy-amine system when incorporated prior to curing.
One of the authors (R.D.P.) is grateful to the University Grants Commission, New Delhi, for the award of a Research Associateship under the Special Assistance Programme. 相似文献
Zusammenfassung Mittels Differential-Scanning-Kalorimetrie wurde die Kinetik der Vernetzung von Triglycidyl-p-aminophenol mit stöchiometrischen Mengen vier verschiedener Amine untersucht. Laut den Ergebnissen verläuft die Vernetzungsreaktion mit einer Arrhenius-Kinetik erster Ordnung, wobei die Aktivierungsenergie im Bereich von 40–70 kJ/mol liegt. Auf Grundlage der Vernetzungscharakteristika und der kinetischen Parameter wird der Einfluss der Struktur des Vernetzungsreagenz auf die Vernetzungskenndaten beschrieben. Mit einem vor der Vernetzung eingebrachten Epoxyfortifyers konnte die Vernetzungstemperatur eines Epoxy-Amin-Systemes heruntergesetzt werden.
-- , . , 40–70 ·–1. . , , , .
One of the authors (R.D.P.) is grateful to the University Grants Commission, New Delhi, for the award of a Research Associateship under the Special Assistance Programme. 相似文献