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231.
Pawan Kumar R. PrasadR.K. Dwivedi H.K. Singh 《Journal of magnetism and magnetic materials》2011,323(21):2564-2568
A comparative study of the out-of-plane anisotropic magnetoresistance (AMR) in single crystalline and polycrystalline thin films of phase separated manganite Nd0.51Sr0.49MnO3 has been carried out. On-axis DC magnetron sputtering was used to deposit the single crystalline films (30 and 100 nm in thickness) on single crystal (0 0 1) LaAlO3 (LAO) and polycrystalline films (100 nm) on (1 0 0) Yttrium-stabilized ZrO2 (YSZ) substrates. The in-plane and out-of-plane magnetotransport properties of these films differ significantly. A large low field AMR is observed in all the films. AMR shows a peak below the insulator-metal transition temperature in the single crystalline films, while the same increases monotonically in the polycrystalline film. Relatively larger low field AMR (∼20% at T=78 K and H=1.7 kOe) in the polycrystalline films suggests the dominance of the shape anisotropy. 相似文献
232.
In the present communication we have reviewed some inverted type equations of state for solids under high pressures. An inverted
equation of state (EOS) gives volume as a function of pressure for a solid under isothermal conditions. We have considered
various equations of state proposed by earlier workers which express volume as a function of pressure. Expressions for bulk
modulus and its pressure derivatives based on such EOSs are obtained and reported here. It is emphasized here that the high
pressure derivative properties are very sensitive to the forms of equations of state representing volume-pressure relationships.
We have also studied the thermoelastic properties of solids based on pressure derivatives of bulk modulus. Applications have
been extended in the present review article to the solids which are metals as well as non-metals including geophysical minerals
present in the lower mantle and core of the Earth. 相似文献
233.
V. Singh S. Watanabe T. K. Gundu Rao I.-J. Lee 《Applied physics. B, Lasers and optics》2011,104(4):1019-1027
Tricalcium aluminate doped with Eu3+ was prepared at furnace temperatures as low as 500°C by using the convenient combustion route and examined using powder X-ray
diffraction, scanning electron microscope and photoluminescence techniques. A room-temperature photoluminescence study showed
that the phosphors can be efficiently excited by UV/Visible region, emitting a red light with a peak wavelength of 616 nm
corresponding to the 5D0–7F2 transition of Eu3+ ions. The phosphor exhibits three thermoluminescence (TL) peaks at 195°C, 325°C and 390°C. Electron Spin Resonance (ESR)
studies were carried out to study the defect centres induced in the phosphor by gamma irradiation and also to identify the
defect centres responsible for the TL process. Room-temperature ESR spectrum of irradiated phosphor appears to be a superposition
of three distinct centres. One of the centres (centre I) with principal g-value 2.0130 is identified as O− ion while centre II with an axially symmetric principal values g
∥=2.0030 and g
⊥=2.0072 is assigned to an F+ centre (singly ionized oxygen vacancy). O− ion (hole centre) correlates with the TL peak at 195°C and the F+ centre (electron centre), which acts as a recombination centre, is also correlated to the 195°C TL peak. F+ centre further appears to be related to the high temperature peak at 390°C. Centre III is also assigned to an F+ centre and seems to be the recombination centre for the TL peak at 325°C. 相似文献
234.
Temperature and angular momentum dependence of the quadrupole deformation is studied in the middle of the sd-shell for 28Si and 27Si isotopes using the spherical shell model approach. The shell model calculations have been performed using the standard universal sd-shell (USD) interaction and the canonical partition function constructed from the calculated eigensolutions. It is shown that the extracted average quadrupole moments show a transitional behaviour as a function of temperature and the infered transitional temperature is shown to vary with angular momentum. The quadrupole deformation of the individual eigenstate is also analysed. 相似文献
235.
236.
Nanoparticles of Mg2SiO4:Eu3+ have been prepared by the solution combustion technique and the grain size estimated by PXRD is found to be in the range 40–50 nm. Ionoluminescence (IL) studies of Mg2SiO4:Eu3+ pellets bombarded with 100 MeV Si8+ ions with fluences in the range 1.124–22.48×1012 ions cm?2 are carried out at IUAC, New Delhi, India. Five prominent IL bands with peaks at 580 nm, 590 nm, 612 nm, 655 nm and 705 nm are recorded. These characteristic emissions are attributed to the luminescence centers activated by Eu3+ cations. It is found that IL intensity decreases rapidly in the beginning. Later on, the intensity decreases slowly with further increase of ion fluence. The reduction in the ionoluminescence intensity with increase of ion fluence might be attributed to degradation of Si–O (ν3) and Si–O (2ν3) bonds present on the surface of the sample. The red emission with peak at 612 nm is due to characteristic emission of 5D0→7F2 of the Eu3+ cations. Thermoluminescence (TL) studies of Mg2SiO4:Eu3+ pellets bombarded with 100 MeV Si8+ cations with fluences in the range 5×1011 ions cm?2 to 5×1013 ions cm?2 are made at RT. Two prominent and well resolved TL glows with peaks at ~220 °C and ~370 °C are observed. It is observed that TL intensity increases with increase of ion fluence. This might be due to creation of new traps during swift heavy ion irradiation. 相似文献
237.
GaSe crystals were doped with indium, and improvements in the mechanical properties and second-harmonic efficiency over pure crystals were obtained. Both effects are due to an improvement in the crystal quality of the material, and it was shown that doping with low levels of indium did not alter the intrinsic value of the nonlinear d coefficient. 相似文献
238.
Experimental results on the generation of 1.54 μm eye-safe radiation in pure CH4, CH4:He and CH4:Ar mixtures pumped by the fundamental of an Nd:YAG laser, using the stimulated Raman scattering (SRS) technique, are described. A decrease in the energy conversion efficiency and degradation in the beam quality of S1 was observed in pure CH4 at high pump energies. This problem was overcome in CH4:He and CH4:Ar mixtures. Compared with the first Stokes (1.54 μm) energy conversion efficiency in pure CH4, at a pump energy of 126 mJ, an enhancement of 50% in energy conversion efficiency was observed in the CH4:Ar mixture (60% argon concentration) and as much as 100% in the CH4:He mixture (60% helium concentration). The use of these buffer gas mixtures improved the spatial beam quality of the Stokes radiation considerably and also resulted in raising the pump threshold for optical breakdown of the Raman gain medium. 相似文献
239.
Rajat Kumar Singh Rajiv Srivastava Yatindra Nath Singh 《Optical and Quantum Electronics》2007,39(14):1153-1165
Optical packet switching provides high speed, data rate/format transparency, efficient use of bandwidth and flexibility. The
major problem in the implementation of “all-optical” switching is contention which occurs when two or more packets arrive
at the same time for the same destination. To resolve the contention, we have proposed an optical packet switch architecture
based on WDM loop buffer memory in the feedback configuration. In that architecture, the contending packets are stored in
a loop buffer module, and routed in the free time slots. The buffering duration in the recirculating loop is limited by a
circulation limit. The analysis was been done to obtain the maximum number of allowed circulations. This paper proposes improved
version of that optical packet switch architecture, to increase the number of maximum allowed circulations. The modification
is done either by adding an extra erbium doped fiber amplifier (EDFA) in the original switch or by replacing the core space
switch with arrayed waveguide grating (AWG). The performance analysis has been done by the simulations. 相似文献
240.
Using the hydrodynamic model of a semiconductor plasma, the influence of carrier heating on the parametric dispersion and amplification has been analytically investigated in a doped III-V semiconductor, viz. n-InSb. The origin of the phenomena lies in the effective second-order optical susceptibility (χe(2)) arising due to the induced nonlinear current density of the medium. Using the coupled-mode theory, the threshold value of pump electric field (|E0T|para) and parametric gain coefficient (αpara) are obtained via χe(2). The relevant experiment has not been performed. Proper selection of the doping level not only lowers |E0T|para required for the onset of parametric excitation but also enhances αpara. The carrier heating induced by the intense pump modifies the electron collision frequency and hence the nonlinearity of the medium, which in turn further lowers |E0T|para and enhances αpara by a factor of ∼103 and ∼2×102, respectively. The results strongly suggest that the incorporation of carrier heating by the pump in the analysis leads to a better understanding of parametric processes in solids and gaseous plasmas, which can be of great use in the generation of squeezed states. 相似文献