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61.
Venu MankadHimadri R. Soni Sanjeev K. GuptaPrafulla K. Jha 《Physica B: Condensed Matter》2011,406(19):3599-3604
We present results of first principles total energy calculations of the structure, electronic and lattice dynamics for beryllium semiboride and its three ternary alloys using generalized gradient and local density approximations under the framework of density functional theory. The generalized gradient approximation is used for all compounds except MgBeB using the Perdew-Burke-Ernzehorf exchange correlation functional while local density approximations use the Perdew-Zunger ultrasoft exchange correlation functional. The calculated ground state structural parameters are in good agreement with those of experimental and previous theoretical studies. The electronic band structure calculations show that Be2B may transform to a semiconductor after Al substitution. A linear response approach to density functional theory is used to calculate phonon dispersion curves and vibrational density of states. The phonon dispersion curves of Be2B and AlBeB are positive indicating a dynamical stablility of the structure for these compounds. The phonon dispersion curves of NaBeB and MgBeB show the imaginary phonons throughout the Brillouin zone, which confirms dynamical instability as indicated in band structures for these alloys. We also present the partial phonon density of states for different species of Be2B and AlBeB to bring out the details of the participation of different atoms in the total phonon density of state, particularly the role played by Al atom. The first time calculated phonon properties are clearly able to bring out the significant effect of isoelectronic substitution in Be2B. 相似文献
62.
The structural, electronic, vibrational and thermodynamical properties of transition metal carbides RuC, RhC, PdC and AgC are investigated using the plane-wave pseudopotentials method within the generalized gradient approximation (GGA) in the frame of density functional theory (DFT). There is a good agreement between present theoretical and available experimental theoretical data in the case of ground state properties such as lattice parameter and bulk modulus. The electronic band structure of these compounds show that all compounds except RuC in zinc blende phase are metallic in nature. RuC in zinc blende phase is semiconducting in nature with an indirect band gap. The phonon properties of RhC, PdC and AgC are investigated for the first time. The phonon frequencies in the phonon dispersion curves are positive throughout the Brillouin zone for zinc blende RuC and AgC and rocksalt RhC and PdC indicating dynamical stability for these compounds in the said phases. Temperature variation of thermodynamical properties for noble metal carbides are calculated and discussed. 相似文献
63.
64.
Vikram Jha 《Designs, Codes and Cryptography》2014,72(3):675-686
To each non-square integer \(2^{2N+1}\ge 2^5\) there correspond semifields \(D\) of order of \(2^{2N+1}\) that contain \(\text{ GF}(4)\) . Hence there exist affine planes for each non-square order \(2^{2N+1}\ge 2^{5}\) that contain subaffine planes of order \(2^2\) . Moreover, there also exists semifields \(D_1\) and \(D_2\) , with \(|D_1|= |D_2| =|D|\) such that \(D_1\) is commutative and \(D_2\) is non-commutative but neither \(D_1\) nor \(D_2\) contains \(\text{ GF}(4)\) . 相似文献
65.
Mauji Ram Salim Khan Prabhakar Jha Mather A. Khan Usha Kiran Saleem Javed Malik Z. Abdin 《Chromatographia》2008,68(1-2):129-133
A simple, rapid, specific and sensitive thin layer chromatographic (TLC) method has been developed for the quantitative estimation of mevalonic acid (MVA) in leaves of medicinal plants; Artemisia annua, Psorelia corylifolia, Vinca rosea, Withania somnifera and Barleria proinites. The assay procedure involved conversion of MVA to its lactone, mevalonolactone (MVAL). Mevalonic acid was extracted from the leaf tissues of plants. Separation of MVAL was carried out on silica gel 60 F254 TLC plates using benzene:acetone (3:2) as the mobile phase. The densitometric determination of MVAL was performed at 600 nm after derivatization with anisaldehyde reagent in absorption–reflectance mode. The method was validated over the linearity range of 100–500 ng spot?1 and correlation coefficient for the calibration curve was >0.99. The average recovery of MVAL, used as internal standard, was higher than 98%. The lower limit of detection was found to be 50 ng spot?1. 相似文献
66.
A theoretical framework for treating the effects of magnetic fieldH on the pairing theory of superconductivity is considered, where the field is taken in an arbitrary direction with respect
to crystal axes. This is applicable to closed, as well as open normal state Fermi surface (FS), including simple layered metals.
The orbital effects of the magnetic field are treated semiclassically while retaining the full anisotropic paramagnetic contribution.
Explicit calculations are presented in the limits |H| → |H
c2(T)|,T ∼ 0 andT →T
c(|H|), |H| ∼ 0. Effects of weak nonmagnetic impurity scattering, without vertex corrections, have also been taken into account in a
phenomenological way. The final results for the case of open FS and layered materials are found to differ considerably from
those of the closed FS. For example, an important parameter,h(T=0)=|Hc2(0)|/[-Tδ|H
c2
T|δT]T{s0} for the case of a FS open ink
z-direction with thek
z-bandwidth, 4t
3, very small compared to the Fermi energy,E
F, is close to 0.5906, compared to 0.7273 for the closed FS, in the clean limit. Analytical results are given for the magnetic
field dependence ofT
c and the temperature dependence of H
c2 for a model of layered superconductors with widely open FS. For a set of band structure parameters for YBa2Cu3O7 used elsewhere, we find reasonable values for the upper critical fieldH
c2(0), the slope (dH
c2/dT)T
c0, anisotropic coherence lengths ζi(T=0),i=x, y, z, and (dT
c/d|H|)|H| → 0. 相似文献
67.
The phonon dispersion curves for aluminium arsenide and antimonide have been investigated by using a deformation bond approximation
model. The results obtained from this model are compared with the experimental values wherever it is available. Since there
is no complete experimental phonon dispersion curves for AlAs, we could not compare our calculated results, but the results
of AlSb have been compared with the inelastic neutron scattering measurements at 15 K. However, we compare the phonon frequencies
of AlAs and AlSb at critical points of the Brillouin zone obtained by our calculations and Raman spectroscopy measurements.
This model predicts the phonon modes satisfactorily in all the symmetry directions of the Brillouin zone (BZ). The spectrum
has similar features as observed in other III–V compound semiconductors. 相似文献
68.
B. K. Jha 《Heat and Mass Transfer》1997,33(3):261-263
An analytical study is made to examine the flow behaviour of a fully developed transient free-convective flow of an incompressible
viscous fluid between two heated vertical walls in a porous system. A Laplace transform technique has been employed to obtain
the expression for velocity, temperature and skin-friction. The influence of the various parameters, entering into the problem,
on the velocity field and skin-friction is discussed in detail.
Received on 11 March 1997 相似文献
69.
Lattice vibrational properties of uranium pnictides have been studied using breathing shell model (BSM) which includes breathing
motion of electrons of the U-atoms due tof−d hybridization. The phonon dispersion curves of U-pnicitides calculated from the present model agree reasonably well with
the measured data. A comparison has been made between BSM and our results reported earlier obtained from three-body force
rigid ion model to reveal the importance of the short-range electron-phonon interactions in these compounds. We also report,
for the first time, the two phonon density of states and specific heat for these compounds. 相似文献
70.
Kinetics of phase transformations in the peridynamic formulation of continuum mechanics 总被引:2,自引:0,他引:2
Kaushik Dayal 《Journal of the mechanics and physics of solids》2006,54(9):1811-1842
We study the kinetics of phase transformations in solids using the peridynamic formulation of continuum mechanics. The peridynamic theory is a nonlocal formulation that does not involve spatial derivatives, and is a powerful tool to study defects such as cracks and interfaces.We apply the peridynamic formulation to the motion of phase boundaries in one dimension. We show that unlike the classical continuum theory, the peridynamic formulation does not require any extraneous constitutive laws such as the kinetic relation (the relation between the velocity of the interface and the thermodynamic driving force acting across it) or the nucleation criterion (the criterion that determines whether a new phase arises from a single phase). Instead this information is obtained from inside the theory simply by specifying the inter-particle interaction. We derive a nucleation criterion by examining nucleation as a dynamic instability. We find the induced kinetic relation by analyzing the solutions of impact and release problems, and also directly by viewing phase boundaries as traveling waves.We also study the interaction of a phase boundary with an elastic non-transforming inclusion in two dimensions. We find that phase boundaries remain essentially planar with little bowing. Further, we find a new mechanism whereby acoustic waves ahead of the phase boundary nucleate new phase boundaries at the edges of the inclusion while the original phase boundary slows down or stops. Transformation proceeds as the freshly nucleated phase boundaries propagate leaving behind some untransformed martensite around the inclusion. 相似文献