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901.
B. S. Bhadauria I. Hashim Jogendra Kumar Alok Srivastava 《Transport in Porous Media》2013,98(3):683-697
Effect of rotation on linear and nonlinear instability of cross-diffusive convection in an anisotropic porous medium saturated with Newtonian fluid has been investigated. Normal mode technique has been used for linear stability analysis, however nonlinear analysis is done using spectral method, involving only two terms. The Darcy model with Coriolis terms, has been employed in the momentum equation. Nonlinear analysis is used to find the thermal and concentration Nusselt numbers. The effects of various parameters, including Soret and Dufour parameters, on stationary and oscillatory convection, have been obtained, and shown graphically. 相似文献
902.
Gyaneshwar P. Srivastava Huseyin M. T??t??nc?? 《Central European Journal of Physics》2009,7(2):209-219
We present a mini review of progress made towards theoretical modelling of surface phonons. We outline the essential ingredients
of two theoretical methods, viz. an adiabatic bond charge method for semiconductor surfaces and the ab-initio density-functional perturbation method for solid surfaces in general. From the results of theoretical calculations we establish
trends and criteria for the existence of localized phonon modes on group-IV(001) and III-V(110) semiconductor surfaces. We
further obtain signatures of characteristic vibrational modes which develop during dissociative molecular adsorption on Si(001)
surfaces. The results are compared with available experimental measurements. Some remarks are forwarded regarding manipulation
of surface phonon modes for scientific advances and technological applications.
相似文献
903.
Effect of heavy cation doping (Ca2+ at the A-site) on the thermal properties of perovskite LaMnO3 has been investigated using the Rigid Ion Model (RIM)). As strong electron-phonon interactions are present in these compounds,
the lattice part of the specific heat deserves proper attention. The specific heat of magnetoresistance compound La0.25Ca0.75MnO3 as a function of temperature (10 K ≤ T ≤ 300 K) is reported. Our results on specific heat are in good agreement with the measured values of specific heat at lower
temperatures. In addition, the results on the cohesive energy (ϕ), molecular force constant (f), Restrahalen frequency (ν
0), Debye temperature (Θ
D) and Gruneisen parameter (γ) are also discussed.
相似文献
904.
Dhananjay Kumar Srivastava Martin Weinrotter Henrich Kofler Avinash Kumar Agarwal Ernst Wintner 《Optics and Lasers in Engineering》2009,47(6):680-685
Homogeneous charge compression ignition (HCCI) is a very promising future combustion concept for internal combustion engines. There are several technical difficulties associated with this concept, and precisely controlling the start of auto-ignition is the most prominent of them. In this paper, a novel concept to control the start of auto-ignition is presented. The concept is based on the fact that most HCCI engines are operated with high exhaust gas recirculation (EGR) rates in order to slow-down the fast combustion processes. Recirculated exhaust gas contains combustion products including moisture, which has a relative peak of the absorption coefficient around 3 μm. These water molecules absorb the incident erbium laser radiations (λ=2.79 μm) and get heated up to expedite ignition. In the present experimental work, auto-ignition conditions are locally attained in an experimental constant volume combustion chamber under simulated EGR conditions. Taking advantage of this feature, the time when the mixture is thought to “auto-ignite” could be adjusted/controlled by the laser pulse width optimisation, followed by its resonant absorption by water molecules present in recirculated exhaust gas. 相似文献
905.
Various models on volume dependence of the Grüneisen ratio have been analyzed in the present study. The Sharma model [Mod. Phys. Lett. B 22/31 (2008) 3113] is found to be similar to that used by Nie [Phys. Stat. Sol. (b) 219 (2004) 241] on the basis of approximation made by Jeanloz [J. Geophys. Res. 94 (1989) 5929]. The Nie expression is amended in a manner so that the resulted expression follows the constraint of high pressure thermodynamics in the limit of infinite pressure. The newly developed relationship is applied successfully on materials for which experimental data are accessible such as epsilon-iron, NaCl, Li, Na, and K. 相似文献
906.
Ajay Kumar Srivastava 《Tetrahedron》2009,65(27):5322-1564
A short and stereoselective route for the synthesis of 1-hydroxyquinolizidine, an advanced synthetic intermediate for the total synthesis of (+)-epiquinamide is presented. The key synthetic steps involve diastereoselective nucleophilic addition on l-serine derived Garner aldehyde and acid mediated (PTSA) ring closing metathesis. The methodology is also elaborated successfully for the total synthesis of (+)-α-conhydrine, an important piperidine alkaloid. 相似文献
907.
D. Ranjan P. Srivastava M. Talat S. H. Hasan 《Applied biochemistry and biotechnology》2009,158(3):524-539
The potential use of biomass of Aeromonas hydrophila for biosorption of chromium from aqueous solution was investigated. The variables (pH, initial Cr(VI) concentration, biomass
dose, and temperature) affecting process were optimized by performing minimum number of experimental runs with the help of
central composite design. The results predicted by design were found to be in good agreement (R
2 = 99.1%) with those obtained by performing experiments. Multiple regression analysis shows that uptake decreases with increase
in pH and biomass dose, whereas it increases with increase in temperature and concentration. The maximum removal of Cr(VI)
predicted by contour and optimization plots was 184.943 mg/g at pH 1.5, initial Cr(VI) concentration 311.97 mg/L, temperature
60 °C, and biomass dose 1.0 g. The removal of Cr(VI) was governed by adsorption of Cr(VI) as well as its reduction into Cr(III),
which further gets adsorbed. The sorption capacity of biomass was calculated from experimental data using Langmuir sorption
model and was found to be 151.50 mg/g at 40 °C and pH 1.5, which is comparable to other biosorbents. In addition to this,
Dubinin–Radushkevich model was applied, and it was found that nature of sorption was chemisorption. 相似文献
908.
An original two-step process for the synthesis of [1,4]oxazepin-2-ones starting from Baylis-Hillman (BH) adducts is reported. The protocol involves a nucleophilic substitution of the acetates of BH adducts with renewable natural α-amino esters followed by base-catalyzed intramolecular Michael addition. These sequential reactions are operationally simple, performed under ambient conditions, and give 81-93% yields of the target [1,4]oxazepin-2-ones. Thus, the present invention opens up a new aspect for the synthetic utility of BH adducts. 相似文献
909.
Rajendra Srivastava Shin-Ichiro Fujita Shuhei Okamura Masahiko Arai 《Reaction Kinetics and Catalysis Letters》2009,96(1):55-64
Alkylation of aromatic compounds with various alkylating agents such as benzyl chloride, benzyl alcohol and isopropyl chloride
were investigated using ZnCl2 based ionic liquid (ILs) Lewis acid catalysts. Multi-component Lewis acid catalysts of ZnCl2 and ionic liquids such as 1-butyl-3-methylimidazolium bromide, 1-butylpyridinium bromide, cholin chloride and tetrabutylammonium
bromide were prepared, supported on silica gel, and compared for alkylation reactions with various alkylating agents. Among
the IL-based catalysts, 1-butyl-3-methyl imidazolium-bromide-ZnCl2 and 1-butylpyridinium bromide-ZnCl2 are highly active. 相似文献
910.
Kerr effect and Kerr constant enhancement in vertically aligned deformed helix ferroelectric liquid crystals
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Liangyu Shi Abhishek Kumar Srivastava Vladimir G Chigrinov Hoi-Sing Kwok 《中国物理 B》2016,25(9):94212-094212
In this article,we review recently achieved Kerr effect progress in novel liquid crystal(LC) material:vertically aligned deformed helix ferroelectric liquid crystal(VADHFLC).With an increasing applied electric field,the induced inplane birefringence of LCs shows quadratic nonlinearity.The theoretical calculations and experimental details are illustrated.With an enhanced Kerr constant to 130 nm/V2,this VADHFLC cell can achieve a 2π modulation by a small efficient electric field with a fast response around 100 μs and thus can be employed in both display and photonics devices. 相似文献