bluuebunny/crossref_metadata_2025_split huggingface dataset:
Local Virial Relations and Pressure
Authors: Ziesche P. , Lehmann D. 
Published: July 2007

AbstractUsing appropriately defined densities of kinetic and potential energies, of momentum current, and electrostatic stress local virial relations of finite clusters and extended crystals with nuclei kept fixed are easily derived both from the many‐electron Schrödinger equation and from the one‐electron Kohn‐Sham equations. Comparing them, a local version of the Averill‐Painter relation for exchange and correlation results. By means of the local virial relations rigorous formulae for the pressure follow. They need the knowledge of the momentum and the pair distributions or — within the local density approximation — the solutions of the Kohn‐Sham equation. This latter result — here derived from rigorous theorems — agrees essentially with that of Liberman and Hodges/Nieminen, additional terms arise from the electrostatic (Hartree) interaction between a unit cell and its neighbours.
The Behavior of Active Centers in a Laser Host. A Crystal Field Investigation on Sm3+ in LaF3 Single Crystal
Authors: Neogy D. , Purohit T. 
Published: July 2007

AbstractThe behavior of the Kramers ion Sm3+ in the widely used laser host LaF3 is studied in detail, theoretically. The results obtained with a crystal field of D3h symmetry which explains the absorption spectra quite well are in fairly good agreement with the available experimental data on this doped material. The crystal field and the spin—orbit interaction matrix set up in the ground term basis is diagonalized simultaneously to obtain the precise Stark energies and wave functions, and this automatically takes care of the crystal field mixing of different J‐multiplets so important for this ion. The nuclear level splitting of the isotopes of this ion due to the electric quadrupole and magnetic interactions which are strongly influenced by the crystal field and the consequences of the hyperfine splitting are worked out.
Magnetic Pinning Interaction of a Type‐II Superconducting Cylinder
Authors: Saif A. G. , Shehata L. N. 
Published: July 2007

AbstractA model of the magnetic pinning interaction (i.e., a system of N‐curved flux lines (FLs) and a cylinderical inclusion) is developed. The field components inside and outside the inclusion are calculated. The energy of the system and the magnetic pinning force are completely determined from the field distribution inside the superconductor. The properties of the curved FLs near the surface of a type‐II superconducting cylinder are established. The energy of the system as well as the magnetic field and the current density are calculated. The force on a flux line (FL) element is completely determined by the total current density at the element position.
Nonlinear Excitation of Pure and Doped Rare Gas Crystals
Authors: Kessler T. , Markus R. , Nahme H. , Schwentner N. 
Published: July 2007

AbstractThe power dependence up to the destruction limit and the coefficient of two photon absorption in Xe and Kr crystals are derived from transmission and luminescence experiments. A temperature dependent reduction of the quantum efficiency for luminescence at high power densities due to exciton—exciton annihilation is observed.
Dyson and Bethe‐Salpeter equations for dynamical X‐ray diffraction in crystals with randomly placed defects
Authors: Holý V. , Gabrielyan K. T. 
Published: July 2007

AbstractA new formalism is found for the description of the dynamical X‐ray diffraction in statistically disturbed crystals both, in the coherent and in the incoherent approximations. The formalism is based on Dyson's equation for the averaged wavefield amplitude in the crystal and on Bethe‐Salpeter's equation for the averaged mutual coherence functions. The equations are simplified assuming the single‐group approximation. Dyson's equation is solved analytically by the Fourier method, and the first iteration of the solution of Bethe‐Salpeter's equation is found. On the basis of these solutions reflection curves as well as angular intensity distributions are computed for a crystal with randomly placed microdefects. The connection is shown of the theory presented with Kato's dynamical statistical theory.
Annealing of the F+ EPR centers and the 2.3 and 2.9 eV optical absorption bands in zinc sulfide crystals
Authors: Matsuura K. , Kishida S. , Tsurumi I. 
Published: July 2007

AbstractThe F+ EPR centers and the 2.3 and 2.9 eV optical absorption bands are introduced in ZnS crystals by electron irradiation, neutron irradiation, and Zn‐treatments, and then isochronal and isothermal annealings of these specimens are carried out. It is found that the predominant isochronal annealing stages in the electron‐irradiated, neutron‐irradiated, and Zn‐treated specimens occur at 150 to 360, 300 to 600, and 600 to 800 °C, respectively. However, the F+ centers and the 2.3 eV band are simultaneously annealed. Therefore it is established that the 2.3 and 2.9 eV optical absorption bands are due to the F+ centers. It is also described that the sulfur vacancies are stable below about 600 °C in the Zn‐treated specimens and the migration energy of the vacancies may be 1.4 eV.
Vibrational states of surface crystal atoms
Authors: Vikhrenko V. S. , Kulak M. I. 
Published: July 2007

AbstractThe momenta–time correlation functions and their spectral densities are studied for rare gas crystal atoms at the (100) and (110) surfaces. Their characteristics essentially differ from the bulk behaviour for particles lying in the surface plane, but already in the third subsurface atomic plane the differences from the bulk crystal spectrum are only slight. Distinct quasi‐resonance peaks observed in the spectral densities may be an information source for experimental analysis of the surfaces.
Beyond the LUC‐CNDO k = 0 approximation
Authors: Craig B. I. , Smith P. V. 
Published: July 2007

AbstractIn applying the periodic LUC‐CNDO method it has been customary to employ the so‐called k = O approximation to represent the rather complex Brillouin zone (BZ) density matrix summations which arise within that formalism. The inability of this simplifying approximation to accurately describe these terms has, however, led to somewhat disappointing results. In this paper the periodic LUC‐CNDO formalism is extended beyond the k = O approximation by employing LUC special k‐point sets of progressively increasing size to evaluate these BZ density matrix summations to essentially arbitrary precision. This enables one, for the first time, to actually assess the accuracy of this semi‐empirical formalism without the imposition of additional approximations. Carrying the calculations through to full convergence in the BZ density matrix summations it is found that the periodic LUC‐CNDO method provides insufficient flexibility within its parameterization scheme to result in quantitatively accurate values for all of the properties of the homopolar covalent solids which are of interest. Whilst extension of this work to incorporate the additional contributions of INDO produced little improvement, recent work employing the MINDO method within the LUC periodic formalism appears promising.
On trigger properties of molecular organizates. I. Tunnel transport in donor–acceptor systems with strong electron–deformation interaction
Authors: Gaididei Yu. B. , Yakimenko I. I. 
Published: July 2007

AbstractA theory of tunnel transport of electrons from donor to acceptor through dielectric films is developed taking into account the interaction of electrons with the elastic degrees of freedom for donor and acceptor. The efficiency of the charge transport processes in such systems is shown to be characterized by a nonmonotonic dependence on the rate of electron supply to donor (pumping rate). At a well‐defined pump level the system tends to the non‐equilibrium phase transition from the monostable state to the bistable (trigger) one.
Structures and Energies of Symmetrical 〈001〉 Tilt Grain Boundaries in Silicon
Authors: Kohyama M. 
Published: July 2007

AbstractThe energies and atomic structures of a series of symmetrical 〈001〉 tilt grain boundaries in silicon are calculated using the tight‐binding type electronic theory (the bond orbital model). There exists a continuity of boundary structures in the ranges 0° ≦ θ < 53.13° and 53.13° ≦ 90°. The type of boundary structures changes at the Σ = 5(130) boundary (θ = 53.13°); for this boundary, the model by Bacmann et al. is shown to be more energetically favorable. At the Σ = 5(120) (θ = 36.87°) and Σ = 5(130) (θ = 53.13°) boundaries, there exist comparatively deep cusps in the energy against θ curve. The discrepancy between the present results in silicon and the experimental observations in germanium for the Σ = 25(170) and Σ = 41(190) boundaries is discussed.
(Sd)–f Hybridization in the Phonon Spectrum of Thorium
Authors: Onwuagba B. N. 
Published: July 2007

AbstractIt is observed that contribution from (Sd)–f hybridization associated with the local field correction can be approximated by a short‐range (Born‐Mayer) potential in the phonon spectrum of thorium in the framework of a rare‐earth metal model potential (REMMP) method. Calculated results agree reasonably well with experiment.
Optical Studies of Vanadium in Gallium Phosphide
Authors: Ulrici W. , Friedland K. , Eaves L. , Halliday D. P. 
Published: July 2007

AbstractThe results of optical absorption, luminescence, luminescence excitation, and temperature‐dependent Hall‐effect measurements on semi‐insulating n‐type GaP:V and n‐conducting GaP:V are reported. The VGa2+/VGa3+ acceptor level is found at Ec − 0.58 eV. Absorptions due to photoionization transitions from and into this level can be identified. The absorption bands due to the transitions 3A2 → 3T1(F) and → 3T1(P) of VGa3+ are measured, both absorptions include three zerophonon lines as well as phonon replica. At low temperatures the photoinduced rechargings VGa3+ ↔ VGa2+ are investigated and interpreted in terms of the three charge states of VGa and the excitation of electrons from the PGa4+P4 anti‐site centre.
The Detailed Investigation of the Critical Current Density of Optimized Nb3Sn Modified Jelly Roll Wire throughout Its Entire Superconducting Phase Including a Comparative Study with a Similar Non‐Optimized Composite
Authors: Hampshire D. P. , Jones H. 
Published: July 2007

AbstractData are given characterising the distribution in critical currents intrinsic to an optimized Nb3Sn wire as a function of field and temperature. The different functional forms of the component critical currents are discussed in terms of the Fietz‐Webb scaling law. It is demonstrated that the flux‐flow state is characterised by defect flow within the flux‐line‐lattice (F‐L‐L). A comparison is made both, between the critical current and also the flux‐flow state of optimized and non‐optimized composites.
Shape of Magnetic Reststrahlen‐Bands Caused by Magnon‐Polaritons in Uniaxial Ferrites
Authors: Lehmeyer A. , Merten L. 
Published: July 2007

AbstractThe magnetic reststrahlen‐bands for linearly and circularly polarized incident waves propagating parallel to the optical axis are calculated for uniaxial ferrites. From the shape of these spectra all the characteristic frequencies of the magnon‐polariton waves can be determined.
Optical Properties of the F‐Centre in Beryllium Oxide
Authors: Gorbunov S. V. , Kruzhalov A. V. , Springis M. J. 
Published: July 2007

AbstractOptical anisotropy of absorption and luminescence of F‐centres in BeO crystals are investigated. It is established that the anisotropy of the absorption band of F‐centres in the 6.5 eV region is due to the splitting of the singlet excited state of the 1P type into the components 1A1 and 1E in the crystalline field of C3v symmetry. It is shown that the anisotropic band of F‐centre luminescence at 4.9 eV is determined by singlet‐singlet transitions 1A1 → 1A1. The more intense luminescence band of F‐centres at 3.4 eV with the lifetime 700 ms at 80 K and the insignificant anisotropy are due to the spin forbidden triplet‐singlet transitions 3E → 1A1. The characteristics of non‐radiative transitions in the F‐centre and the reasons for the absence of photoconversion of F → F+ centres are discussed.
Electron Spin Relaxation in Ferroelastic KH3(SeO3)2
Authors: Müller H.‐E. , Völkel G. , Brunner W. , Cevc P. , Kurkin I. N. 
Published: July 2007

AbstractMeasurements of the electron spin—lattice relaxation time T1 and the phase memory time TM of SeO2− centres in X‐irradiated single crystals of ferroelastic KH3(SeO3)2 are reported. At temperatures above 11 K the spin—lattice relaxation is governed by a two‐phonon process of optical phonons. Near the phase transition point two anomalies in the temperature dependence of T1 are found. The anomalous increase of T1 is explained by an increased damping of that mode which is responsible for the Raman‐process. The phase memory time TM decreases critically at Tc following a logarithmic temperature dependence.
Nematic Liquid Crystal in 2 + ε Dimensions
Authors: Trimper S. 
Published: July 2007

AbstractThe isotropic‐nematic phase transition is studied in 2 + ε dimensions. Using the elastic free energy and applying renormalization group approach for a fixed length system in analogy to magnetic systems it is shown that the system exhibits a fixed point which is related to a certain temperature T* above which the one‐constant‐approximation is correct. The critical exponents and the equation of state can be calculated near to T*. Under the influence of an external magnetic field the scaling laws have to be modified.
Angle Resolved Photoemission and Electronic Band Structure of MoS2
Authors: Mamy R. , Boufelja A. , Carricaburu B. 
Published: July 2007

AbstractAngle‐resolved photoemission measurements are performed on the layer compound MoS2 at 21.2 and 40.8 eV excitation energies. It is shown the applicability of the E(k∥︁) method in the framework of a non‐direct transition regime. An experimental band scheme is proposed. Good agreement with band structure calculations is found except for some of them in the relative position of the d and p upper valence bands, which is here clearly ascertained.
Electron–Phonon Interaction in Semi‐Infinite Semiconductor Superlattices
Authors: Wendler L. , Haupt R. 
Published: July 2007

AbstractIn this paper the single‐particle Hamiltonian of the electron–(long‐wave optical) phonon interaction is discussed for semi‐infinite semiconductor superlattices. The dispersion relation of the (longwave optical) surface phonon modes is analyzed in detail. These modes are composed from ordinary interface phonons on adjacent interfaces coupling through their macroscopic electric fields to form a surface collective excitation of the whole structure with an electric field having an envelope function decaying exponentially from the surface of the semi‐infinite superlattice. The coupling function of the electron–phonon interaction is calculated using a continuum theory. This coupling function describing the modified Fröhlich interaction of a single electron with the continuous field of polarization of the surface phonons is discussed and presented in graphical form.
Investigation of the Phonon Sidebands of SH− and SeH− Centres in Cesium Halides and Potassium Bromide
Authors: Otto J. 
Published: July 2007

AbstractInfra‐red spectra of SH− and SeH− centres in cesium halides show unusually strong phonon sidebands, whereas the intramolecular vibration ν0 itself is only weak. The effective charge of SH− centres is calculated from the intensity of the ν0 line and turns out to be five times smaller for cesium than for potassium and rubidium halides. Most of the fine structure in the phonon sidebands can be directly correlated with the phonon density of states of the unperturbed host lattices. LA and TA phonons appear alternately in the sidebands of the stretching vibration ν0 and the combination lines ν0 + νL and ν0 + 2νL with the librational mode νL of the centres.
Calculated Elastic Constants of Dilute Alloys
Authors: Ram P. N. , Semalty P. D. 
Published: July 2007

AbstractThe elastic constants of dilute alloys are studied using a Green's function technique. An impurity model with central and non‐central force‐constant changes extending upto second neighbours of the impurity is employed to describe the impurity in a f.c.c. lattice and explicit expressions for changes in elastic constants have been obtained in terms of the t‐matrix. The effect of volume changes on elastic constants is discussed. The contribution to the bulk modulus from the electron pressure is also included. Especially the changes in different elastic constants are calculated in a number of dilute alloys based on Cu, Ag, and Au. The calculated results are compared with available experimental measurements. The obtained force‐constant changes are found to be symmetry dependent.
Electronic Structure and Symmetry Properties of the Envelope Functions in PbTe‐Pb1−xSnxTe Superlattices
Authors: Gondar J. López , de Dios Leyva M. 
Published: July 2007

AbstractIn the framework of Dimmock's two band model and in the constant band edge approximation within each layer, the electronic structure for the PbTe–Pb1−xSnxTe SL is studied. The study is carried out for the 〈111〉 valley, ϰ⟂ = 0, and taking into account all the possible solutions for the effective Hamiltonian. A new dispersion relation and new zero energy gap conditions are derived. Numerical calculations reveal that the inclusion of the largest wave vector solutions do not substantially modify the energy spectrum obtained when such solutions are excluded.
Fluorescence‐Detected Low Field Resonances in T–T Annihilation in the A‐TCNB Single Crystal Lineshape and Dynamic Parameters
Authors: Konyaev S. N. , Shushin A. I. , Kolesnikova L. I. , Tribel M. M. , Frankevich E. L. 
Published: July 2007

AbstractAn investigation is made of the line shape of the low field resonances observed in the dependence of the fluorescence of a single A‐TCNB CT crystal on the external magnetic field. It is shown that the resonance is caused by avoided crossing of magnetic sublevels of a single T‐exciton arising when the direction of the field is close to the axis of the fine interaction tensor. An analytic expression for the resonance line shape is obtained. The spin–lattice relaxation rate of T‐excitons, τ−1 = (1.0 ± 0.3) × 107 s−1 as well as the rate of jumps between the planes of fast exciton migrations, ω1 = (5 ± 2) × 107 s−1, are determined.
A New Effective Field Theory for Dilute Ising Ferromagnets
Authors: Bobák A. , Karaba J. 
Published: July 2007

AbstractA new type of effective field theory for a quenched site diluted Ising model is presented. As a result the general equation for magnetization is obtained. Particular emphasis is given to the honeycomb lattice for which the critical concentration and concentration dependence of the magnetization and critical temperature are calculated. The critical concentrations for a square and simple cubic lattice are also obtained.
Exciton Absorption and Luminescence of Indium Selenide Crystals
Authors: Gnatenko Yu. P. , Zhirko Yu. I. 
Published: July 2007

AbstractBy investigations of low‐temperature photoluminescence (PL) spectra of InSe crystals the nature of emission lines in the region of indirect exciton transitions is determined and the energy diagram of optical direct and indirect transitions is offered. The presence in γ‐InSe of regions containing stacking faults results in the appearance of a fine structure in the PL spectra of an n = 1 exciton state. Within the framework of a “resonant exciton” model the causes of the growth of integrated intensity in the absorption spectra of an n = 1 exciton state are discussed.
Electronic Band Structure and Optical Anisotropy in InS. I. Experimental Study
Authors: Takarabe K. , Kawamura H. , Wakamura K. 
Published: July 2007

AbstractOptical properties of InS on (001) surfaces are investigated using polarized absorptions near the fundamental gap (1.5 to 3.0 eV) and polarized reflectivity in the range of photon energy from 2 to 20 eV using a synchrotron radiation source. Detailed analyses of polarized absorption spectra reveal that the fundamental band gap of InS is an allowed indirect transition for each polarization in the (001) plane. The lowest direct‐gap is allowed for b‐polarization, but forbidden for a‐polarization. Dielectric functions are derived from reflectivity spectra by Kramers‐Kronig analysis and some features in spectra are assigned to interband transitions.
Electronic Transfer and Thermal Vibration Parameters in Titanium Carbide an X‐Ray Diffraction Study
Authors: Field D. W. 
Published: July 2007

AbstractAn X‐ray diffraction study of titanium carbide powder of composition TiC0.90 is carried out at room temperature. The intensity data for 48 reflections to sin θ/λ = 13.7 nm−1 are compared with theoretical intensities obtained using various models. An electron transfer from metal to non‐metal resulting in a net charge of (2.2 ± 0.3) charges is found. There is no suggestion of covalent character of the bonding. The values of the r.m.s. vibration amplitudes of the atoms uTi = (6.36 ± 0.04) pm and uC = (5.9 ± 0.3) pm, and the Debye temperature is (610 ± 4) K. These results largely support recent work on the material; however, a recent suggestion of distortion of the titanium electron density towards the carbon atoms is not supported.
Photoinduced Recharging Phenomena and Vanadium‐Related Centres in GaAs:V
Authors: Ulrici W. , Kreissl J. , Vasson A. , Vasson A. M. , En‐Naqadi M. 
Published: July 2007

AbstractPhotoinduced recharging phenomena are studied at low temperatures (T < 80 K) on n‐type and semi‐insulating GaAs:V by optical absorption, C‐EPR, and TD‐EPR. Illumination with hvexc > > 1.05 eV into the photoionization absorption αII excites electrons into the conduction band and the recharging V + eecb → V takes place monitored by optical absorption and EPR. The centre responsible for αII appears to be a V‐containing complex of unknown structure, rechargable under illumination from (V–X) into (V–X)+. The V2+(II) centre measured by TD‐EPR is shown to be a second V‐containing complex different from (V–X). The interpretation of all experiments does not require a V‐related mid‐gap level.
A Simple Model of Re‐Entrant Magnetism in Amorphous Alloys
Authors: Kamberský V. , Kalva Z. , Závěta K. 
Published: July 2007

AbstractA phenomenological model involving two kinds of self‐consistent interaction fields is shown to simulate the “re‐entrant” magnetic behaviour (i.e., mixed ferromagnetic and spin glass‐like ordering). Besides the Weiss field, it postulates fields of random directions and magnitude proportional to the mean absolute value of the local magnetic moment. Simple qualitative results are discussed and numerical results are compared with recent experiments on amorphous Fe8Ni72P10B10 alloys.
Two‐Atom Cluster Approximation for Ising Model (S = 1/2)
Authors: Balcerzak T. , Bobák A. , Jaščur M. , Mielnicki J. , Wiatrowski G. 
Published: July 2007

AbstractThe cluster containing two spins and their neighbourhood is taken into account in the frame of a new effective field approximation. As the result, two coupled equations describing the magnetization and correlation function are derived. The numerical calculations of the Curie temperature, magnetization, correlation function, and magnetic specific heat for the case of s.q. and s.c. lattices are discussed.
A Comparative Study of the Phenomenological Potentials for Ionic Crystals of Alkali Halides
Authors: Khwaja F. A. , Naqvi S. H. , Razmi M. S. K. 
Published: July 2007

AbstractA comparative study of some well‐known interionic model potentials is carried out by computing anharmonic properties of alkali halides. The importance of including the zero point energy and the Van der Waals contributions properly is emphasised. Recently reported values of the Van der Waals term are employed to redetermine the unknown parameters of the potential. A comparison with experiment is made. It is concluded that the potential form proposed by Born and Mayer comes closest to the experimental situation.