bluuebunny/crossref_metadata_2025_split huggingface dataset:
On kink dynamics in media with increasing absorption optical bistability
Authors: Kiselev V. G. 
Published: July 2007

AbstractThe motion of the boundary between dark and light domains in a crystal with increasing absorption‐optical bistability (the so‐called kink) is considered. In the low diffusion limit the kink moves undergoing effective viscous friction which essentially affects the output intensity. The crystal boundary influence on the kink is substantial if the diffusion is sufficiently high. No jumping kink motion resulting in a sawtooth structure of the output intensity can take place in a pure crystal unless a compound material consisting of isolated semiconductor crystals is used.
Parametric amplification in magnetised piezoelectric semiconducting plasmas
Authors: Neogi A. , Ghosh S. 
Published: July 2007

AbstractAssuming that the origin of the nonlinear interaction lies in the second‐order optical susceptibility χ(2) arising from the nonlinear induced current density, and using the straightforward coupled mode theory, the parametric amplification is analytically investigated in a magnetised piezoelectric semiconducting plasma. The threshold value of the pump electric field Eoth and the corresponding excitation intensities are obtained. Eoth is found to decrease with rising magnetic field. The investigation also reveals that the phenomena of self‐focusing and self‐defocusing can be enhanced in these crystals. The parametric gain constant is obtained. Numerical estimations are made for an n‐InSb crystal, at 77 K duly irradiated by frequency doubled pulsed 10.6 μm CO2 lasers. It is found that the presence of a magnetostatic field enhances the gain constant.
Theoretical INDO Investigation of the Electronic Structure of Aluminium Clusters
Authors: Fantucci P. , Pacchioni G. 
Published: July 2007

AbstractA modified version of the semiempirical INDO method is developed and applied to the study of the electronic properties of Al clusters. The method is able to reproduce in a satisfactory manner the basic features of low‐nuclearity Al clusters as determined by ab initio calculations and can be considered reliable for the study of larger aggregates. In addition, the method can be adopted in a preliminary search of the geometry–energy hypersurface in order to select a few “probable” topologies to be investigated in more detail with rigorous quantum chemical approaches.
Photoconductivity of Polycrystalline Thionaphtenindol
Authors: Signerski R. , Kalinowski J. , di Marco P. , Giro G. 
Published: July 2007

AbstractA systematic study of steady‐state photoconductivity within the first absorption band of polycrystalline thionaphtenindol (TNI) is made and the results are discussed in terms of charge generation and charge transport processes. Though the mechanism of photoconductivity is determined mainly from analysis of light intensity characteristics of photocurrent and their dependence on the applied voltage in the system Al/TNI/Al/g (glass), other experimental data such as action spectra, photoenhancement of the current injected from Au electrodes, or magnetic field effect on photocurrent are consistent with the inferred physical picture of the phenomenon: singlet exciton dissociation on near‐electrode defects produces electron–hole pairs, the holes being injected into the bulk of the sample. The concentration of holes in the first‐charge generation region stands for a boundary condition for their injection into the second‐charge transport region. An asymmetry in photocurrent behaviour observed when the substrate or non‐substrate electrode is illuminated can also be explained by these mechanisms.
Screening of the Coulomb Potential in the Athermal Stage in Highly Excited Semiconductors
Authors: Heiner E. 
Published: July 2007

AbstractEquations for the reduced density operator are evaluated. Investigating the subdynamics of nonrelevant observables a resolvent formulation is obtained selfconsistently for the screening part of the evolution superoperator. Utilizing the diagonal representation for the time‐dependent mean field term of the Hamiltonian, a selfconsistent concrete calculation of the screened potential is possible in the high density limit of the nonequilibrium. The result is an extension of the well known RPA‐formula for nonequilibrium two‐band systems of Fermions. An extension to the semimarkovian approximation is counted for.
Planar Channeling of Electrons and Positrons in Crystals. Local‐Density Calculation of Planar Averaged Potential and Channeling Radiation Spectrum
Authors: Satpathy S. , Pathak A. P. 
Published: July 2007

AbstractResults of calculation of channeling potentials in crystals using the local density theory are given. The linear muffin‐tin orbitals method is used in the atomic spheres approximation (LMTO‐ASA) to calculate the planar‐averaged potential seen by MeV electrons and positrons channeled along (110) planes of diamond, Si, and Ge. The calculations thus include the spherical charge relaxation effects (“solid state effects”) in the solid but omits the non‐spherical part. The calculated potentials are in excellent agreement with the empirical potentials derived from channeling radiation experiments, but are significantly different near the atomic planes from the potentials obtained from superposition of the atomic Thomas‐Fermi statistical (Molière) potentials. Agreement of the potentials with the ones obtained from superposition of atomic Doyle‐Turner potentials is reasonably good. Frequencies of emitted radiation from the channeled electrons and positrons are also calculated and compared to experiments. For the crystals considered, it is concluded that the solid state effects on the planar‐averaged potential are moderate to small. It is expected that these effects should be more important for channeling in ionic solids. The deviation of the observed positron channeling radiation from the calculated values for Si and C indicates that the non‐spherical part of the charge relaxation might be relatively important for these solids.
Physical Properties of Fractals. Mössbauer Recoilless Fraction, Raman Scattering, and Spin‐Lattice Relaxation
Authors: Shrivastava K. N. 
Published: July 2007

AbstractSeveral different properties of a fractal are calculated: the recoilless fraction, the Raman scattering intensity, and the spin–lattice relaxation time. The recoilless fraction of a Mössbauer nucleus in a fractal is calculated from the displacement of an atom in a fractal which exhibits a scale invarince for a noninteger fracton dimensionality and found to be in good agreement with the measurements in deoxygenated myoglobin. The exponent of the normalized intensity of the Raman scattered light with frequency is calculated using fractional dimensionalities and density of states for decaying as well as nondecaying fractons. It is found that the phonon and the fracton branches may crossover or avoid crossing giving rise to new modes called as fracnons. The calculated Raman intensity is in good agreement with the measurements in silica gel, (C2H5O)4Si. A theory of the spin–lattice relaxation with the dimensionality crossover is presented. The calculated value of the spin–lattice relaxation time is found to be in good agreement with the measured value of Fe3+ in a frozen solution of metmyoglobin azide.
Polaronic Effects on Exciton States with Different Angular Momenta
Authors: Iadonisi G. , Bassani F. , Strinati G. 
Published: July 2007

AbstractIt is shown that exciton states with various total angular momenta (L = 0, 1, 2, 3) are differently affected by the interaction with LO phonons in polar materials. In particular, a dependence is found of the binding energy on the value of L not expected on the basis of the statically screened electron‐hole attraction. Calculations for CuCl and other ionic compounds show that the lowest L = 1 state (n = 2) is less bound than the corresponding exciton state with static screening. This effect, which is opposite to the polaronic effect on the ground state, is still present for L ≧ 2 but it decreases with increasing L. The computed binding energies of 2p excitons compare favorably with the available experimental data. The method is also applied to the calculation of bipolaron binding energies.
The Sink Strength of Dislocation Multipole and Dislocation Wall
Authors: Galimov R. R. , Goryachev S. B. 
Published: July 2007

AbstractExpressions are obtained for sink strength and preference of dislocation multipole and dislocation wall both, in the absence and presence of size elastic interaction of radiation point defects with dislocations. The multipole and the wall are shown to absorb preferentially interstitials than vacancies. Multipole preference, irrespective the number of composing dislocations, may be both greater and smaller than isolated dislocation preference depending on the type of dislocations and geometry of their position in the multipole. Dislocation wall preference is much smaller than isolated dislocation preference.
Warm Electron Transport in GaAs Quantum Wells
Authors: Chattopadhyay D. , Kabasi A. 
Published: July 2007

AbstractThe transport of warm electrons intinerant two dimensionally in a square quantum well is studied over the temperature range 60 to 300 K, including the degeneracy of the distribution function. Scattering by polar optic phonons, deformation potential acoustic phonons, and ionized impurities is considered. Calculations with GaAs material parameters show that both the ohmic mobility and the warm electron coefficient for a quantum well of width 12 nm are greater than those for a well of width 8 nm.
Potential of Fast Neutron Damage Regions in Heavily Doped Semiconductors
Authors: Litvinov V. L. , Ukhin N. A. , Churakov Yu. I. 
Published: July 2007

AbstractThe potential and field of impurity—defect damage regions are calculated, employing a model which is earlier used to explain changes in properties of heavily doped silicon irradiated by neutrons. The change in initial material properties and the effect of the energy of the irradiation particles are analyzed.
The Investigation of the Ferroelectric Phase Transition in Cluster Systems of Order‐Disordered Type. II. Two‐Particle Cluster System
Authors: Yukhnovskii I. R. , Korynevskii N. A. 
Published: July 2007

AbstractA new method of two‐stage integration in collective variable phase space is proposed for the calculation of the critical part of the partition function of a ferroelectric cluster system. The recursion relations for basic distribution coefficients of consequent block structures are found, taking into consideration dipole‐dipole components of intercluster interaction. A general solution of these relations is obtained. The type of critical behaviour of the system is determind. The phase transition temperature is calculated.
Calculation of Polycrystal Elastic Constants from Single‐Crystal Data
Authors: Morawiec A. 
Published: July 2007

AbstractA new calculation method of determining the elastic constants of a polycrystalline material from single‐crystal elastic coefficients is presented. The averaging procedure satisfies the condition of commutation with the inversion operation. It can be applied to any crystal symmetry and allows to take texture into account. The properties of the averaging procedure are given and compared to the corresponding properties of the arithmetic averaging method.
Microstructure Dependence of Material Properties of Composites
Authors: Monecke J. 
Published: July 2007

AbstractEffective material constants of composites depend not only on the material constants of the constituents and on their volume fractions but on the microstructure of the composite, too. A general structure dependent expression is derived for the effective dielectric constant of a binary composite as an example. Explicit results are given for typical microstructures. It is proved that all exactly solvable borderline cases are reproduced.
Dispersion Relation for Coupled Surface Waves in Thin Polar Semiconducting Foils
Authors: Srivastava K. S. , Tandon A. 
Published: July 2007

AbstractThe dispersion relation for surface plasmon—surface optical phonon coupled waves is derived in nonretardation limit, using a hydrodynamical model, for thin semi‐infinite plane bounded polar semiconductor films. Due to coupling between the surface plasmons and surface optical phonons at the two surfaces of the film, it gives rise to four surface modes. Under certain conditions the dispersion relation can also describe the surface plasmon oscillations in metallic foils.
Rebuilding of Electron Spectra in One‐Dimensional Structures by Increasing the Electron—Phonon Binding
Authors: Popov A. P. , Lavrentev A. A. 
Published: July 2007

AbstractThe problem of the one‐electron spectra rebuilding in one‐dimensional structures by increasing the electron—phonon binding is investigated. It is shown that the non‐localized state is the ground state of the system only in the limit of weak coupling. The quality rebuilding of the one‐electron spectra occurs when the coupling constant α reaches the critical value αcr = 1.8371. The rebuilding is caused by appearance of the autolocalized state with the finite radius of localization. Autolocalized state becomes the ground state of the system when the coupling constant α reaches the value 1.8660.
An Electronic Band Structure Calculation and the Optical Properties of Alkaline‐Earth Sulphides
Authors: Stepanyuk V. S. , Szász A. , Farberovich O. V. , Grigorenko A. A. , Kozlov A. V. , Mikhailin V. V. 
Published: July 2007

AbstractThe electronic band structure of CaS, SrS, and BaS is calculated by linear augmented plane waves (LAPW). The calculation is applied for the explanation of the optical properties of the alkalineearth‐metal sulphides.
The Prognostication Possibility of Some Magnetic Properties for Dielectrics on the Basis of Covalency Parameters of Ligand‐Cation Bonds
Authors: Bayukov O. A. , Savitskii A. F. 
Published: July 2007

AbstractThe possibility to predict the exchange interaction values and Curie temperatures of magnetodielectrics is shown using the superexchange bond model and the specific dependences of the intraatomic exchange integral, the transfer parameters, and the excitation energy of electrons from ligand to cation on a number of electrons in the 3d‐shells of cations. Ability is demonstrated on examples of ferrite‐spinels and perovskites of arbitrary composition.
Characterization of Microdefects in Silicon by Means of X‐Ray Reflection Curves
Authors: Holý V. , Kubéna J. 
Published: July 2007

AbstractMicrodefects in an annealed Czochralski‐grown silicon crystal have been studied by means of X‐ray double crystal diffractometry. Comparing the reflection curves measured at various places of the crystal with those computed on the basis of the theory published in previous papers the effective defect size, their density, and the defect strength are determined. The results are compared with those obtained from the experimental curves using the conventional kinematical theory of diffuse X‐ray scattering.
F Centers in LiF‐Mg Crystals
Authors: Mikhalenko A. A. , Khulugurov V. M. , Dmitrieva E. I. , Salomatov V. N. 
Published: July 2007

AbstractSpectroscopic characteristics of new F‐like centers in LiF‐Mg, OH crystals are studied. The role of the divalent Mg impurity in the formation of F centers in LiF is revealed. By comparison of measured and calculated energy parameters a tentative model and a mechanism for the formation of the centers studied are suggested.
On non‐Debye Linear Mechanical Response of Condensed Media
Authors: Kuklov A. B. 
Published: July 2007

AbstractA phenomenological non‐Debye linear mechanical response theory for condensed media is presented which takes into account transverse diffusion currents induced by the external stresses due to the local anisotropy and inhomogeneity fluctuations (LAIF). The generalized linear shear modulus (GSM) and compliance (GSC) expressions are obtained in terms of the auto‐correlation function of the relevant LAIF representation. The theory is used to calculate the linear response fractional frequency exponent when transient diffusive creep takes place. The results are in reasonable agreement with the empirical Andrade creep law. Schoek's formula for internal friction is explained, too. To verify the theoretical predictions some experiments are proposed.
Oscillatory Temperature Dependence of Crystal Structure and Magnetic Parameters in FeGe2
Authors: Zainullina R. I. , Vlasov K. B. , Milyaev M. A. , Ustelemova E. V. , Syromyatnikov V. N. 
Published: July 2007

AbstractX‐ray investigations are made of the temperature dependences of integrated Bragg reflection intensities I(T), and the tetragonal lattice parameters a and c for FeGe2 compound. The temperature dependence of the magnetic susceptibility at 80 < T < 320 K is also presented. In the range of magnetic ordering (T < 287 K) an unusual oscillatory temperature dependence I(T) for Bragg reflections is obtained, a stepped character of the a(T) and c(T) curves, and an oscillatory temperature dependence of the susceptibility for FeGe2. On the assumption that an incommensurate magnetic structure exists in FeGe2 a qualitative theory is proposed for describing the temperature oscillations of the parameters investigated.
A New Empirical Many‐Body Potential Energy Function Application to Microclusters: Elements in B.C.C., F.C.C., and H.C.P. Structures
Authors: Erkoç Ş. 
Published: July 2007

AbstractA new empirical many‐body potential energy function (PEF) has been proposed recently, and it has been successfully applied to microclusters of various elements. Using the new PEF the microcluster calculations are extended to several elements in b.c.c., f.c.c., and h.c.p. structures.
Effects of Low‐Energy Electron Transport in Insulators
Authors: Adamchuk V. K. , Kuchma A. E. , Molodtsov S. L. 
Published: July 2007

AbstractTransport of excited electrons with an energy less than the band gap value in the conduction band of insulators is described analytically. Interaction of electrons with optical phonons is assumed to be the predominant process in scattering. By solving the diffusion equation obtained on the basis of the kinetic equation it is possible to find the energy distribution of the electrons in the solid and vacuum. Photoelectron spectra for CsI are calculated. Comparison of theoretical and experimental results yields the structure of the density of states in the conduction band, the energy loss intensity, and the free path time of excited electrons with respect to the electron—phonon scattering.
Incommensurate Magnetic Structures in Triangular Antiferromagnet CsCuCl3
Authors: Gekht R. S. , Fedoseeva N. V. , Dolina V. A. , Balaev A. D. 
Published: July 2007

AbstractThe helical magnet CsCuCl3 in an applied field higher than the critical field is shown to have sinusoidal phase with linear polarization of spins. The new intermediate phase is due to a conical‐point instability caused by weak dipole interactions. Therefore in different temperature ranges two modulated structures are actually realized. Results found theoretically are in good agreement with the experimental data.
On the Phase Shift and Bound States in a One‐Dimensional Antiferromagnetic Chain
Authors: Costa B. V. 
Published: July 2007

AbstractThe behavior of small oscillations in an antiferromagnetic chain with an external magnetic field applied when a static kink is present is investigated. By using a Green's function approach the bound states and phase shifts are obtained and it is possible to show that a purely anisotropic model can generate the same thermodynamics.
Simulation of Vacancy Migration in B.C.C. Metals
Authors: Fritzsch B. , Zehe A. , Fritzsch R. 
Published: July 2007

AbstractWith the help of moleculardynamic calculations the diffusion via vacancies as the dominant mechanism in b.c.c. metals is studied. The interaction between atoms in the block are described by potentials of the Lennard‐Jones type. For selfdiffusion a linear dependence between the migration and binding energy of the crystal is found, unrestricted by the lattice constant. On the contrary, for impurity diffusion in the model the size of the diffusing atom influences essentially the diffusion behaviour.
A Comparative Study of the Phenomenological Potentials for Ionic Crystals of Alkali Halides (II)
Authors: Khwaja F. A. , Razmi M. S. K. , Naqvi S. H. 
Published: July 2007

AbstractA comprehensive study of some phenonenological interionic potentials is continued by developing further tests based on the calculation of cohesive energy, relative stability, and pressure induced solid‐solid phase transformation of alkali halides. A comparison of the results with some previous calculations and with experimental data is made.
Transient Response of Hot Electrons in Semiconductor Quantum Well Wires
Authors: Mulimani B. G. , Ramakrishna C. H. , Krishnamurthy B. S. , Sarkar C. K. 
Published: July 2007

AbstractTransient response of hot electrons in quantum well wires of a polar semiconductor to a step electric field is studied using the displaced‐Maxwellian distribution function and the energy and momentum balance conditions. Numerical results are given for the variation of drift velocity and electron temperature with time for parameters characteristic of GaAs. Momentum relaxation is found to be faster than the energy relaxation. Also, both the relaxation rates are found to increase with the increase of lattice temperature and become faster with the decrease of transverse dimension of the wire.
The Quantum Well in an Electric Field A Density of States Approach
Authors: Enderlein R. , Holz T. , Gondar J. L. 
Published: July 2007

AbstractA quantum well (QW) in the presence of a homogeneous electric field forms a system with continuous energy spectrum. Its density of states (DOS) is calculated. A general DOS formula is applied which avoids the well‐known difficulties for systems with continuous spectra. The Schrödinger equation is solved exactly, and the 1D DOS is expressed in closed analytical form by means of Airy functions of first and second kind. Quasistationary energy levels are defined as zeros of a certain 4 × 4 matrix. Their positions are calculated in dependence on the field strength over a wide range. The 1D DOS peaks arising from quasistationary levels are studied for different field strengths. The same is done for the 1D DOS in a larger energy interval ranging from far below the QW bottom up to far above the QW barriers. Franz‐Keldysh oscillations as well as QW interferences are observed above the barriers.
Doping Dependent Bandgap Narrowing in Silicon and Germanium
Authors: Noor Mohammad S. , Abdus Sobhan M. 
Published: July 2007

AbstractA simple model for bandgap narrowing in doped silicon and germanium is developed. The model assumes that bandgap narrowing in doped semiconductors results primarily from electron—electron, electron—hole, electron—donor, and hole—donor interactions. Based on the suggestion of Hermanson and Phillips that in an impure crystal spatially dependent dielectric screening represents a measure of electron—hole, electron—donor, and hole—donor interactions, the model attempts to determine electron—donor, hole—donor, and electron—hole interactions by making use of the DYP (Dingle/Yakawa potential) modified by including spatially variable dielectric constant. The electron—hole interaction energy is estimated on the basis of many‐body techniques of Mahan and Abram et al. Physics justifying the use of modified DYP for calculating bandgap narrowing is discussed in some details. It is noted that the use of the DYP is valid for doping concentrations up to about 4 × 1020 cm−3. Calculated results are displayed in figures, which show good agreements with available experiments.