bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effective Scattering and Damping of Elastic Waves in Multi‐Component Mixtures
Authors: Bobeth M. , Diener G. 
Published: July 2007

AbstractScattering of elastic waves propagating in a strongly heterogeneous medium with aggregate topology is considered within a modified effective‐medium procedure. The calculations are restricted to long wavelengths or low frequencies and are based on results obtained in a previous paper for the fluctuations of a static strain field. Explicit results are presented for isotropic components and spherical grains. In particular, effective differential and total cross‐sections for the grains of different components are discussed. For non‐dissipative media the total cross‐sections are related to the damping rates of longitudinal and transverse waves. Numerical examples for the damping rates and the angular dependence of the differential cross‐sections are presented for some binary mixtures. In strongly heterogeneous media near the percolation threshold high values of the scattering rates and a nearly isotropic distribution are obtained.
Construction of Electronic Charge Density in Solids. Calculation of Atomic Scattering Factors of Elements and Energy of Formation of Alloys
Authors: Bhattacharya T. , Manna A. , Ghosh A. K. 
Published: July 2007

AbstractA simple method to construct modified electronic charge densities in solids, ϱS(r), from their free‐atomic charge densities, ϱF(r), is described. Atomic scattering factors of seven elements representing four different crystal structures, and energy of formation of seventeen CsCl‐type intermetallic compounds of transition metals are calculated from such ϱS(r). Results thus obtained compare well with those obtained earlier from superposition of ϱF(r) through Löwdin's α‐expansion.
Influence of Non‐Magnetic Impurities on the Ferromagnetic Phase Transition and Its Critical Properties
Authors: Fazakas A. B. , Corcoţtoi I. , Ciobanu G. 
Published: July 2007

AbstractThe free energy functional is derived for an electron gas interacting via insite Hubbard and intersite Heisenberg terms, scattered by some dilute, interstitial, non‐magnetic impurities. The equation for the Curie temperature is deduced and discussed in various approximations. The existence is shown of a critical concentration of impurities destroing the ferromagnetism. The dirty specimen has the same critical exponents as the pure one, but the width of the critical region is modified.
The Magnetic Susceptibility of a Diluted Ferromagnetic Thin Film (Ising Model, S = 1/2)
Authors: Wiatrowski G. , Mielnicki J. , Balcerzak T. 
Published: July 2007

AbstractThe Dirac's delta function method is applied for the calculation of magnetic susceptibility of diluted Ising films. As a result a set of equations for magnetic susceptibility of different atomic layers of thin film is derived, hence the curves χ vs. temperature together with the reciprocal susceptibility profiles for s.c. samples with several film thickness values are obtained.
Approximations to the Systematic Many‐Beam Case of High‐Energy Electron Diffraction. I. Transition from Two‐Beam to Many‐Beam Interaction
Authors: Kästner G. 
Published: July 2007

AbstractThe systematic many‐beam case of electron diffraction of non‐centrosymmetric crystals is treated on solving the fundamental (eigenvalue) equation by approximate analytical diagonalization of the suitably scaled and re‐indexed dynamical matrix. Its dependence on the crystal parameters and on the accelerating voltage is used to gradually select and classify approximate dynamical solutions and kinematical corrections. The results imply a convenient, scaled version of Bethe's correction of the periodic potential terms.
Low‐Temperature Structure and Lattice Dynamics of 4,4′,‐Difluorobiphenyl
Authors: Wąsicki J. , Belushkin A. V. , Khomenko V. G. , Natkaniec I. , Telezhenko Yu. V. , Wasiutyński T. 
Published: July 2007

AbstractPhonon frequencies in the centre of the Brillouin zone, dispersion relations, and phonon density of states are calculated for 4,4′‐difluorobiphenyl, following structure investigations by means of X‐ray diffraction on a monocrystalline sample at 110 K. The resulting phonon density of states, weighted with the amplitudes of hydrogen atom vibrations are compared with that obtained from the inelastic incoherent neutron scattering (IINS) data. From the calculated dispersion relations it can be inferred that the incommensurate phase transition (well established in isostructural biphenyl) does not occur in 4,4′‐difluorobiphenyl.
Plasmon Excitation in Metal Surface Layers by Fast Electrons
Authors: Bao Tran Thoai Duy 
Published: July 2007

AbstractThe interaction of fast electrons with metal overlayers on metal substrates is studied within the hydrodynamic model. Retardation effects and damping are included. The energy loss probability of surface and interface plasmons is calculated for external electron beam travelling parallel to the metal surface. Numerical calculations are carried out for potassium layer on aluminium substrate.
Study on the Size and Shape of CuCl Microcrystals Embedded in Alkali‐Chloride Matrices and Their Correlation with Exciton Confinement
Authors: Itoh T. , Iwabuchi Y. , Kataoka M. 
Published: July 2007

AbstractIn alkali chlorides heavily doped with Cu+ ions, CuCl microcrystals of different sizes are grown under different heat treatments. Their size and shape are studied using small‐angle X‐ray scattering. A clear correlation is established between the microcrystal size and the blue shift of the exciton luminescence peak. The quantum size effect on the exciton is discussed. The exciton confinement, that is, the restriction of the exciton translational motion in one‐dimensional quantum wells is found to be rather plausible for CuCl microcrystals in crystalline matrices.
Parametric Green Function Method in the Heisenberg Model
Authors: Kazakov A. A. , Kleshchev S. M. 
Published: July 2007

AbstractThe task of the thermodynamics of “angle magnetic phase” is solved in the spin‐wave approximation at finite temperatures by the parametrical Green's function (PGF) method. The theory application is illustrated by the low‐temperature behaviour of the magnon heat capacity and magnetization of the rare‐earth metals Tb and Dy. The received analytical dependences are in good agreement with the experimental data.
Equation of State and Pressure Dependence of the Grüneisen Parameter for NaCl Crystal
Authors: Kumar M. , Pachauri A. K. , Chaturvedi S. D. , Sharma A. K. 
Published: July 2007

AbstractThe equation of state for NaCl crystal is investigated using the recently revised generalized Huggins‐Mayer potentials. The calculations are performed for pressures up to about 200 × 108 Pa and at different temperatures ranging from 298 to 773 K. The calculated values are found to agree with the experimental data. An investigation of the pressure dependence of the Grüneisen parameter is also presented using different existing theories. A comparison of the calculated and experimental values reveals the superiority of one theory over the other.
Nonlinear Optics and the Mott Transition in Semiconductors
Authors: Zimmermann R. 
Published: July 2007

AbstractOptical spectra below and above the Mott transition of excitons have to be calculated from the inhomogeneous integral equation for the polarization function including self‐energy, screening, and band filling. Results for gap shifts, exciton shift, exciton bleaching, and continuum enhancement are critically reviewed and extended.
Linearised Version of the Optimised Random Phase Approximation. Application to the Structure of Dense Fluids and Metallic Potentials
Authors: Regnaut C. 
Published: July 2007

AbstractA linearised version (LORPA) is given of the optimised random phase approximation (ORPA) of Andersen, Weeks, and Chandler. The LORPA allows straightforward calculations of the structure of fluids interacting via hard core plus long range pair forces. Standard potentials are analyzed to show that the LORPA is as efficient as the ORPA for the prediction of the structure of dense fluids. The advantage of the method is pointed out for metallic systems by considering gallium‐like and germanium‐like oscillatory interactions. It is shown that the LORPA reproduces the special structures of these metals as well as the ORPA. Therefore this method would be particularly useful for the systematical analysis of metallic potentials in liquid alloys.
Lattice Dynamics for Superlattices
Authors: Albuquerque E. L. , Fulco P. , Tilley D. R. 
Published: July 2007

AbstractThe acoustic and optic modes of a one‐dimensional model of a diatomic superlattice are considered. By employing a microscopic theory it is possible to explore the zone‐folding characteristics. The treatment is based on linear lattice dynamics with nearest neighbour interactions. The equations of motion for the different atoms (on either side) at two superlattice interfaces replace the boundary conditions used in continuum theories. This microscopic approach has the advantage that both optic and acoustic branches are described within a single formulation and without recourse to the long wavelength limit. The algebra, which is otherwise quite involved, is simplified by the use of transfer matrix techniques. The spectrum contains a number of interesting features whose underlying physical principles are discussed.
Theory of Compression in Some Fluorite Structure Crystals
Authors: Goyal R. P. , Gupta O. P. , Gupta B. R. K. 
Published: July 2007

AbstractA theoretical method based on the phonon‐pressure theory is developed for the study of equation of state and thermodynamical properties of CaF2, SrF2, BaF2, PbF2, Sr(NO3)2, and Pb(NO3)2 crystals crystallizing in fluorite‐structure. The traditional Born method for determining the short‐range repulsive parameters is replaced by a more plausible method due to Hafemeister‐Zarht. The van der Waals dipole–dipole and dipole–quadrupole interaction coefficients are derived from the Kirkwood and Muller formula based on quantum theory. The thermodynamical properties are analysed by predicting the values of the bulk modulus and its pressure derivatives, Grüneisen, and Anderson parameters at temperatures 0 and 300 K. The values of pressure corresponding to different values of compressions are calculated using the equation of state. The results obtained in the present study are compared with available experimental data. A fairly good agreement is achieved.
Impurity Auger Spectra. Host Crystal with Unfilled Valence Band
Authors: Drchal V. , Kudrnovský J. 
Published: July 2007

AbstractThe intraatomic core–valence Auger spectra from a single impurity in a perfect crystal are determined for the generalized Wolff‐Clogston model with contact electron–electron interaction on the impurity as well as on the host crystal atoms. The self‐consistent T‐matrix approximation and the ladder approximation are used to determine the one‐ and two‐particle Green's functions, respectively.
Vibronic Interaction in the Absorption Spectra of Vanadium‐Doped AIIBVI Semiconductors
Authors: Melnichuk S. V. , Kramar V. M. , Tovstyuk K. D. 
Published: July 2007

AbstractThe vibronic interaction in AIIBVI semiconductors doped with 3d‐impurities is investigated. Ham's reduction parameter for vanadium in AIIBVI semiconductors is calculated. Comparison is made of the calculated absorption spectra with available experimental data.
Bisoliton Mechanism of High‐Temperature Superconductivity
Authors: Davydov A. S. 
Published: July 2007

AbstractA moderately strong electron–phonon interaction is used to develop a nonlinear bisoliton model of high‐temperature superconductivity in ceramic oxides. The absence of an isotopic effect is explained. The dependence of the critical temperature for a superconducting transition and of the formation of a bisoliton condensate on bisoliton concentration is explained qualitatively. It is shown that at low temperatures electrons with an energy above the critical one come from a metal to a superconductor at equal time intervals only in pairs in a singlet spin state as bisolitons.
On Trigger Properties of Molecular Organizates. III. Nonlinear Waves in Stratified Molecular Structures
Authors: Gaididei Yu. B. , Yakimenko I. I. 
Published: July 2007

AbstractA numerical analysis of the space–time evolution is performed for the population differences in stratified molecular systems of the donor–insulator–acceptor type with strong electron–deformation interaction. The influence of the initial population profile and pumping rate on the character of the evolution picture is studied in detail. The existence of the steady‐state nonlinear waves (the switch waves) in finite systems is proved and the velocities of these waves are calculated as well.
Tricritical Behaviour in Correlated Effective Field Theory
Authors: Mukhopadhyay S. , Chatterjee I. 
Published: July 2007

AbstractCorrelated effective field theory is applied to study the tricritical behaviour for a Blume‐Capel type of Hamiltonian as well as for a Hamiltonian with antiferromagnetic nearest neighbour and ferromagnetic next nearest neighbour interactions. Two different regions in the phase‐diagram are identified by estimating the slope of the double log plot of order parameter and reduced temperature. It clearly indicates that a tricritical region appears when the ratio of two competing parameters exceeds a critical value.
Dependence of Structure Factors upon Temperature for Liquid Metals, Zn and Hg
Authors: Jin Zhun‐Zhi , Zou Xian‐Wu , Yao Yong‐Qiao 
Published: July 2007

AbstractThe hard sphere cluster model is used to study the dependence of the structure factors upon temperature for liquid metals with the second type of liquid structures. The structure factors for liquid Zn (T = 450, 560, and 660 °C) and Hg (T = −35, 0, 20, 80, 150, 200, and 250 °C) are calculated. The theoretical results are in good agreement with experiments.
The Elastic Fields of Disclinations in a Planar Phase Boundary
Authors: Ding Di‐Hua , Deng Zicheng , Li Shuhong 
Published: July 2007

AbstractFirst, the displacement and elastic strain fields of an infinitesimal phase boundary disclination loop (IPBDL) and a rectangular disclination loop in a planar phase boundary (RDLPPB) are derived. Then, regarding the RDLPPB as a fundamental defect unit, the displacement and strain fields of more complex dislcination configurations are calculated. All the results are presented in the form of analytical expressions of elementary functions. All the results are simplified to corresponding expressions for a homogeneous medium when both the phases have the same elastic properties.
Fast Fourier Transform Deconvolution of Positron Annihilation Doppler‐Broadened Lineshapes
Authors: Britton D. T. , Rice‐Evans P. C. 
Published: July 2007

AbstractA fast Fourier transform method for the deconvolution of positron annihilation Doppler‐broadened lineshapes and their decomposition into different components is described. Different filters are tested on the positron annihilation line for two different systems which can be described as a superposition of three components, two Gaussian curves and an inverted parabola, convoluted with a measured resolution function; Cu containing a high proportion of krypton precipitates and physisorbed oxygen on graphite. Special attention is paid to the effect of filtering on narrow and on parabolic components, both of which need higher Fourier coefficients to be described fully. In the case of oxygen on graphite, which has a narrow component due to the annihilation of para‐positronium comparison is made with analysis by repeated numerical convolution of modelled lineshapes.
The Influence of Thermal Vibrations on RBS Proton Spectra Obtained from Subsurface Regions of Si Crystals
Authors: Czerbniak J. , Moneta M. , Pawłowski B. , Piwowarski M. 
Published: July 2007

AbstractThe χmin experimental results for 100 keV protons, for different temperatures and planes of the Si crystal are compared with adequate evaluations obtained in a modified, continuous potential model, with geometrical approximations, and with measurements of other authors.
Cyclotron Resonance Linewidth in a Two‐Dimensional Electron Gas
Authors: Sarkar C. K. , Kundu S. , Basu P. K. 
Published: July 2007

AbstractCyclotron resonance linewidths due to scattering by phonons and alloy disorder are calculated for a two‐dimensional electron gas formed in a heterojunction. The expression of linewidth for scattering due to acoustic phonons via deformation potential and piezoelectric interaction and for alloy scattering is obtained by including the finite extent of the wavefunction along the direction of quantisation. The screening due to free carriers is considered for electron–phonon interaction. The calculated linewidths for scattering due to deformation potential accoustic phonon and alloy scattering show a B1/2 variation and a weaker field dependence is obtained for piezoelectric scattering.
Phonon‐Assisted Two‐Photon Exciton Transitions in Semiconductors
Authors: Hassan A. R. 
Published: July 2007

AbstractPhonon‐assisted two‐photon transitions to excitonic states in semiconductors are theoretically investigated. The effects of both, the nonparabolicity of the band and the degeneracy of the valence band are taken into account. Expressions for the absorption coefficient through different band models are calculated. The numerical applications to CdI2 and GaP show that the four‐band model gives the dominant contribution which leads to a final s‐exciton state. An exciton peak appears at an energy which is close to that recently observed in CdI2. The non‐parabolic effect enhances the absorption coefficient by a two‐order of magnitude.
Theory of Auger Spectra from Alloys with Partially Filled Narrow Bands
Authors: Drchal V. , Kudrnovský J. 
Published: July 2007

AbstractThe one‐particle and two‐particle spectra are determined of the degenerate alloy Hubbard model with partially filled bands within the local self‐consistent T‐matrix approximation and the ladder approximation, respectively. The effect of disorder is included within the coherent potential approximation. The theory is illustrated on a simple model of the copper–nickel alloy. The origin of the two‐peak structure in the Auger spectrum from Cu atoms is discussed.
A Theoretical Study of EPR Spectra in Cu2+‐ and Mn2+‐Doped CaCd(CH3COO)4 · 6 H2O
Authors: Zhou Yi‐Yang 
Published: July 2007

AbstractA theoretical EPR study of single crystals of CaCd(CH3COO)4 · 6 H2O doped with Cu2+ and Mn2+ is made separately. A comparison between the calculated results and the experimental data shows quantitatively that the Cu2+ and Mn2+ ions substitute for Cd2+ and Ca2+, respectively. This concusion is consistent with the qualitative assumption by previous authors.
Submillimetre Magnetospectroscopy of Tellurium under Hydrostatic Pressure
Authors: Lyapin S. G. , Eremets M. I. , Shirokov A. M. , Herrmann R. , Müller H.‐U. , Ludwig F. 
Published: July 2007

AbstractTransmission and photoconductivity of pure Te are recorded as a function of a magnetic field up to 6 T for several radiation energies in the submillimetre range under the pressure up to 3.4 × 108 Pa. The pressure dependence of the transverse hole effective mass is obtained from observation of cyclotron resonance (CR). Three groups of impurity lines are found with different behaviour under pressure. The pressure dependence of the energy and envelope function of the ground H‐like state in Te is calculated by a variational procedure within the effective mass approximation. The comparison with experiment makes it possible to evaluate the pressure dependence of the static dielectric constant.
XANES Study of Copper Mixed Valence and Mechanism of Superconductivity in YBa2Cu3O6.5+δ System
Authors: Garg K. B. , Singhal R. K. , Rao K. V. R. , Chandra U. , Chauhan H. S. , Singh J. , Jerath K. S. , Jain D. C. 
Published: July 2007

AbstractTwo high‐Tc superconductors YBa2Cu3O6.5+δ are studied with XANES technique. The two superconductor samples have a Tc (zero R) around 91 K and are orthorhombic in structure. CuK‐edge XANES measurements are made both, at room and liquid nitrogen temperature (LNT). A mixed valent state for Cu is generally considered essential for their superconducting behaviour. The measured XANES spectra are minutely examined with regard to this question. The results indicate the presence of Cu1+ and Cu2+ at RT but only Cu2+ at LNT. No evidence is found about the presence of Cu3+ state. The results tend to support an intermediate interatomic valent nature of the YBC superconducting system wherein the ground state is derived from a mixture of 3d9, 3d10L, and 3d9L configuration, L meaning the ligand hole. Mounting evidence is quoted in favour of holes being located in the oxygen valence band rather than at the Cu site and the high‐Tc superconductivity is ascribed to the pairing of the itinerant configuration 3d9L and its interaction with localized copper 3d electrons.
Spin‐Fluctuation Theory of Magneto‐Volume Effects in Itinerant Electron Magnets
Authors: Silin V. P. , Solontsov A. Z. 
Published: July 2007

AbstractThe magneto‐volume effects in itinerant electron ferromagnets and nearly ferromagnetic metals are discussed on the basis of a rotationally invariant microscopic theory taking account of the dynamical effects of both, transverse and longitudinal spin and electron density fluctuations. The change of volume V with temperature T in the presence of a magnetic field B due to the magneto‐volume coupling in metals is shown to be determined by the averaged squared local magnetic moment μ(B, V, T). The ratio ηC = μ(T = TC)/μ(T = 0) characterizing the invar anomalies below the Curie temperature TC is found in weak ferromagnets with account of the thermal expansion effects. The value μC is shown to decrease in the vicinity of the structural phase transition, where it vanishes. The approximations of Moriya‐Usami phenomenological theory of magneto‐volume effects are discussed.
Non‐Linear Acousto‐Optical Interaction at Deviation from Bragg Angle
Authors: Bukowski R. , Kleszczewski Z. 
Published: July 2007

AbstractAn influence of the deviation from Bragg's angle on the efficiency of the acousto‐optical interaction considering electrostriction is theoretically analysed. Anti‐Stokes and Stokes isotropic interaction as well as optical generation of the acoustic waves in dielectric crystals are investigated.
Temperature Dependence of the Photoluminescence in GaAsGaAlAs Multiple Quantum Well Structure
Authors: Chiari A. , Colocci M. , Fermi F. , Li Yuzhang , Querzoli R. , Vinattieri A. , Zhuang Weihua 
Published: July 2007

AbstractThe temperature dependence of the photoluminescence (PL) of GaAs/GaAlAs multiple quantum wells is investigated. Emissions related to transitions between n = 1, 2, 3 electron and hole subbands are observed. Theoretical evaluation of the energy levels fits nicely the experimental data. The temperature dependence of peak position and photoluminescence intensity and the dependence of PL intensity on the power excitation show that there are three different temperature regions. At low temperatures (22 to 40 K) the main emission is ascribed to exciton recombination while at temperatures higher than 100 K it can be attributed to free carrier recombination. In the intermediate temperature region the PL involves both, excitonic and free carrier recombination. Thermally activated non‐radiative recombination processes strongly reduce the luminescence quantum efficiency.