排序方式: 共有59条查询结果,搜索用时 31 毫秒
41.
S Rayaprol Krushna Mavani CM Thaker DS Rana Keka Chakravorty SK Paranjape M Ramanadham Nilesh A Kulkarni DG Kuberkar 《Pramana》2002,58(5-6):877-880
A new series of mixed oxide superconductors with the stoichiometric composition La2−x
Dy
x
Ca
y
Ba2Cu4+y
O
z
(x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La2−x
(Y/Er)
x
Ca
y
Ba2Cu4+y
O
z
series, show a strong dependence of T
c on hole concentration (p
sh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant
displacement of La onto Ba site. Superconductivity studies show that maximum T
c is obtained for x=0.5, y=1.0 sample (T
c ∼ 75 K), for La1.5Dy0.5Ca1Ba2Cu5O
z
(La-2125). 相似文献
42.
Several nickel phosphate molecular sieves were synthesized by conventional heating (CH) and microwave assisted hydrothermal (MAH). Nickel phosphate VSB‐5 (Versailles Santa Barbara‐5) was synthesized with conventional oven for 72 h or with microwave for 1 h and followed by conventional oven for 48 h in the presence of (2‐hydroxyethyl) trimethylammonium hydroxide as template. The phase transformation is observed by variation of CH time for the synthesis of nickel phosphate molecular sieves. At CH time of 24 h, the VSB‐5 crystal together α‐Ni2P2O7, Ni2P4O12 and unknown phases were produced but the pure VSB‐5 crystal was obtained in the CH time of 48 h or more. At high content of nickel, a mixture of α‐Ni2P2O7, Ni2P4O12 phases and small amount of VSB‐5 crystal, was achieved but pure VSB‐5 crystal was obtained in the lower level of nickel and other phases are vanished. An efficient ultrasonic‐assisted aging was found for the synthesis of nickel phosphate molecular sieve, in which by ultrasonic mixing of 0.5 h followed microwave of 1 h, the CH time is significantly reduced from 48 to 24 h. The morphology of nickel phosphate crystals is highly influenced in the presence of ethylene glycol as co‐solvent. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
43.
Ali Morsali Ali R. Mahjoub Simin Janitabar Darzi Mohammad J. Soltanian 《无机化学与普通化学杂志》2003,629(14):2596-2599
The 1:2 adduct lead(II) complexes with 1, 10‐phenanthroline (phen) containing three different anions, [Pb(phen)2(CH3COO)X] (X=NCS—, NO3— and ClO4—), have been synthesized and characterized by CHN elemental analysis, IR‐, 1H‐ and 13C NMR spectroscopy. The structure of [Pb(phen)2(CH3COO)(ClO4)] was determined by single crystal X‐ray analysis. The Pb atom of the monomeric complex is coordinated by four nitrogen atoms of two 1, 10‐phenanthroline ligands and two oxygen atoms of the acetate ligand to form an irregular octahedron. The arrangement of the 1, 10‐phenanthroline and acetate ligands, exhibits a coordination gap around the PbII ion, possibly occupied by a stereochemical electron active lone pair on lead(II), which results in a hemidirected lead compound. The π‐π stacking interaction between the parallel aromatic rings may help to increase the coordination ‘gap’ around the PbII ion. 相似文献
44.
Mahmoud Jourabian Mousa Farhadi Ahmad Ali Rabienataj Darzi 《Heat and Mass Transfer》2013,49(4):555-565
Heat transfer and fluid flow processes of natural convection melting of a phase change material are simulated numerically inside a partially heated square cavity. The momentum and energy equations are solved by using enthalpy-based lattice Boltzmann method combined with multi distribution function model. In this communication, the dependence of liquid fraction, temperatures of vertical nodes and average Nusselt number on the positions of heated plates is investigated quantitatively. 相似文献
45.
In this paper, the authors have established the \(\left( G^{\prime }/G\right)\)-expansion method to find exact solutions for conformable time fractional generalized seventh-order KdV equation (FGKdV7). This method is an effective method in finding exact traveling wave solutions of nonlinear evolution equations in mathematical physics. The effectiveness of this manageable method has been shown by applying it to several particular cases of the FGKdV7. The present approach has the potential to be applied to other nonlinear fractional differential equations. All of the numerical calculations in the present study have been performed on a PC applying some programs written in Mathematica. 相似文献
46.
In this paper, the existence and uniqueness of initial value problems for nonlinear Langevin equation involving three fractional orders are discussed. We use a new norm that is convenient for the fractional and singular differential equations. This norm and the contraction mapping principles are the main tools for investigating the existence and uniqueness of the desired issue. The fractional derivatives are described in Caputo sense.
相似文献47.
48.
Mahmoud Jourabian Mousa Farhadi Kurosh Sedighi AhmadAli Rabienataj Darzi Yousef Vazifeshenas 《国际流体数值方法杂志》2012,70(3):313-325
In this study, a numerical investigation of melting phenomenon with natural convection in a cavity with fin has been performed using enthalpy‐based lattice Boltzmann method. The lattice D2Q9 model was applied to determine the density and velocity fields, and the D2Q5 model for the temperature field. The effect of vertical position and length of the fin on the melting rate was studied. The simulations were carried out for Stefan number of 10, Rayleigh number of 10 5 and relative thermal conductivity (kfin∕kfluid) ranging from 5 to 30. The obtained results show that the rate of melting increases when the relative thermal conductivity and the length of the fin become greater. We also found that the variation of vertical position of the fin from bottom to middle has an insignificant effect on melting while it causes the increase of full melting time when the fin is mounted on the top of the cavity. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
49.
The current study addresses the mathematical modeling aspects of coupled conductive and radiative heat transfer in presence of absorbing, emitting and isotropic scattering gray medium within two-dimensional square enclosure. The walls of the enclosure are considered to be opaque, diffuse and gray. The enclosure comprised of isothermal vertical walls and insulated horizontal walls. A new hybrid method where the concepts of modified differential approximation employed by blending discrete ordinate method and spherical harmonics method, has been developed for modeling the radiative transport equation. The finite volume method has been adopted as the numerical technique. The effect of various influencing parameters i.e., radiation-conduction parameter, surface emissivity, single scattering albedo and optical thickness has been illustrated. The compatibility of the method with regard to solving coupled conduction and radiation has also been addressed. 相似文献
50.
Shashwati Sen DK Aswal Ajay Singh TV Chandrasekhar Rao KP Muthe JC Vyas LC Gupta SK Gupta VC Sahni 《Pramana》2002,58(5-6):867-870
The MgB2 superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties.
The upper critical field, irreversibility line and critical current density have been determined using magnetization data.
The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition.
The surface analysis using X-ray photoelectron spectroscopy shows that MgB2 is sensitive to atmospheric degradation. 相似文献