bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electroreflection of Amorphous Selenium
Authors: Weiser G. , Stuke J. 
Published: July 2007

AbstractOn amorphous selenium layers electroreflectance has been measured in the energy range from 1.7 to 4.2 eV. Only one relatively broad structure was found near 2.1 eV, i.e. below the electrical band gap and the photoconduction edge. It has a temperature coefficient of about −2.7 × 10−4 eV/°K. The explanation of this structure by a Frenkel type exciton seems to be the most plausible.
On the Resistivity of Inhomogeneous Metals
Authors: Geszti T. 
Published: July 2007

AbstractThe current flowing in a metal with an inhomogeneous distribution of impurities is investigated by means of a Boltzmann equation accounting for the conservation of matter in the collision term. The treatment extends that of Herring for the case where the extension of inhomogeneities is comparable to the electron mean free path. The results offer a method to measure the average extension of randomly distributed inhomogeneities.
Transport Phenomena in Degenerate Simple Model Semiconductor at High Electric Fields
Authors: Kamal J. 
Published: July 2007

AbstractExpressions are derived for some transport coefficients in a simple model degenerate semiconductor in the presence of a strong d.c. electric field and a weak magnetic field using a distribution function of carrier velocities corresponding to an elevated carrier temperature. Te has been calculated following Shockley's treatment. The variation of these transport coefficients with electric field strength, the impurity parameter \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {b/a} $\end{document}, and the chemical potential η has been studied. The results are presented in the form of graphs.
Physico‐Chemical Properties of 1,3,5,7‐Tetranitro‐1,3,5,7‐Tetrazacyclooctane (HMX)
Authors: Maycock J. N. , Verneker V. R. Pai , Rouch L. L. 
Published: July 2007

AbstractThe dc electrical conductance of single crystal and pelleted β‐HMX and also polycrystalline δ‐HMX has been measured. These data clearly show a discontinuity at the β‐ to δ‐crystal transformation temperature. The conductance of δ‐HMX has been interpreted as being intrinsic and associated with the electronic excitation of the groups. The data for the δ‐polymorph can be interpreted in terms of impurity conduction processes associated with trapped decomposition products. The crystal and conformational changes as observed by conductance techniques agree very well with thermal data related to these changes. Similarly the energetics of the β‐conductance agree well with the optical energetics of the β‐form.
Shell Model Calculation of Microscopic Grüneisen Parameters for Rocksalt‐Type Materials
Authors: Barsch G. R. , Achar B. N. N. 
Published: July 2007

AbstractThe microscopic Grüneisen parameters have been calculated for the two optical modes in the Brillouin zone center and for the four modes at the Brillouin zone edge in [100] for nine alkali halides and MgO. A six parameter shell model which takes into account anion polarizability, non‐central first nearest neighbor interaction and central forces between second neighbors has been used, and the pressure dependence of the frequencies is obtained from the assumption of a pressure independent core‐shell force constant. The parameters of the model are determined from experimental data of the elastic constants, from the high and low frequency dielectric constants, from the pressure derivatives of these quantities, and from the zero pressure value of the transverse optical frequency in the zone center. Good to fair agreement with the available experimental data is found. It is suggested that the discrepancies are mainly due to the limited experimental accuracy. The results confirm that the B1 → B2 phase transformation in alkali halides is not due to an instability of the TA mode at the [100] zone boundary.
Influence of Additional Illumination on the Photoemission from n‐ and p‐Type Gallium Arsenide Single Crystals
Authors: Wojas J. 
Published: July 2007

AbstractA study was made of the photoemission of electrons from oriented monocrystals of GaAs with special reference to the effect of additional infrared illumination. The retarding potential method was used in a spherical capacitor arrangement. The current‐voltage characteristics of n‐type material shift to the right upon additional illumination, while those of the p‐type material shift to the left. The shift is weaker for the p‐type samples, for which also the saturation current diminishes with illumination. These effects are explained by the change of the curvature of the energy bands near the surface with illumination.
A Study of Dislocation Arrays at Spherical Indentations in LiF as a Function of Indentation Stress and Strain
Authors: Swain M. V. , Lawn B. R. 
Published: July 2007

AbstractA systematic study has been made of the dislocation arrays produced by indenting (001) surfaces of LiF with steel and nylon spheres. The arrays are discussed in terms of position along a curve relating “indentation stress” to “indentation strain”, these parameters being determined by the geometry of the contact between indenter and specimen. Three stages of behaviour are distinguished: (i) elastic stage, to which the classical Hertzian contact theory is applicable; (ii) initial yield stage, to which standard yield criteria may be applied to predict the spatial location and critical resolved shear stress for initiation of dislocation motion; (iii) subsequent growth of plastic zone, in which the relative activity of the various slip systems determine the indentation behaviour. A mechanism for the initiation of dislocation flow below an indenting sphere has been proposed on theoretical grounds, and subsequently supported by experimental evidence; this mechanism differs from alternative proposals in that the dislocation sources operate within the interior of the crystal rather than at the crystal surface. An evaluation of the dislocation activation stress for LiF is thereby made, the value obtained being in reasonable agreement with results taken from conventional compression tests. The indentation stress‐strain behaviour is then discussed in the light of current thought on indentation theory, and some shortcomings in present ideas are pointed out.
An Accurate Method of Determination of the Magnetostriction Coefficients. Application to YIG
Authors: De Lacheisserie E. , Dormann J. L. 
Published: July 2007

AbstractThe use of computerized Fourier analysis of magnetostriction data to obtain a high accuracy for the magnetostriction coefficients is described. This technique has been applied to measurements on a single crystal of YIG. Room temperature data were obtained using a dilatometer method. Corrections due to anisotropy and form effects were applied. Accurate values for the second degree coefficients of magnetostriction are given as well as an upper limit for the modulus of the fourth degree coefficients.
Ground‐State Properties of Finite Antiferromagnetic Chains
Authors: van de Braak H. P. , Caspers W. J. 
Published: July 2007

AbstractExact calculations are presented for the ground state of linear antiferromagnetic Heisenberg chains with open ends. The wave function and the energy are given for chains with N = 4, 6, and 8, and quantum number S = 1/2. It is shown that in the limit for N → ∞ the ground state is probably nondegenerate and the long‐range order tends to zero. The short‐range order shows a strongly oscillating character due to end effects persisting over relatively long distances. A comparison with closed rings is made and the connection with the observation of a reduction of the zero‐point deviation in the neighbourhood of non‐magnetic impurities in more‐dimensional systems is pointed out.
Infrared Absorption of AIN in the One‐Phonon Region and Finite Size Effects
Authors: Pastrňák J. , Hejda B. 
Published: July 2007

AbstractThe absorption of single crystals and microcrystalline samples of AlN, pressed in pellets of halides, has been measured in the region of 1000 to 400 cm−1. Three intensive absorption maxima have been found in the region between ωT and ωL. They are connected with the finite size and shape effects and their location depends on the material of the surrounding medium. Further, intensive maxima at 610 and 590 cm−1 occur in microcrystalline samples. The absorption by surface modes may be interpreted with the help of Englman and Ruppin's theory assuming that the frequencies ωT(A1) = 622 cm−1 and ωT(E1) = 660 cm−1. It is shown that it is necessary to distinguish between surface and bulk modes for the absorption measurement of microcrystalline samples and that the absorption in the region of surface modes is decisive in materials with sufficiently fine grains, i.e. in measurements with pressed pellets.
Infrared Absorption of AlN Single Crystals in the Two‐Phonon Region
Authors: Pastrňák J. , Hejda B. 
Published: July 2007

AbstractTwo‐phonon infrared absorption was measured on AlN single crystals in polarized light. Contrary to previous results obtained from other materials with wurtzite structure, the full polarization of some absorption bands was found. The results are interpreted with the help of the fundamental frequencies of the BZE 738, 668, 658, 627, 507, 444, and 413 cm−1.
Dichroïsme circulaire magnétique de films minces de EuTe
Authors: Briat B. , Billardon M. , Suryanarayanan K. , Paparoditis C. 
Published: July 2007

AbstractDes mesures de dichroïsme circulaire magnétique, à 300 et 27 °K, ont permis de résoudre le spectre d'absorption de EuTe en ses différentes composantes dans le domaine spectral 250 à 600 nm. Tous les effets dichroïques observés sont du type paramagnétique dépendant de la température et doivent problablement être attribués aux excitations 4f7 → 4f6 5d.
Surface‐Induced Cross Glide of Screw Dislocations
Authors: Appel F. , Messerschmidt U. 
Published: July 2007

AbstractSurface‐induced cross glide of screw dislocations can be well investigated electron‐microscopically with help of the gold decoration technique. The cross slip distances observed agree well with values obtained by the line tension concept. Surface‐induced cross glide rarely occurs during the dislocation motion. Therefore, the dislocation multiplication is surely not initiated by the surface‐induced cross slip.
The High‐Temperature Recovery of Neutron‐Irradiated Rhenium
Authors: Vandenborre H. , Stals L. , Nihoul J. 
Published: July 2007

AbstractThe recovery of rhenium after neutron irradiation at ≈ 390 °K has been studied up to 1130 °K by means of electrical resistivity measurements at 4.2 °K. Two irradiations were performed in the BR2 reactor at Mol: one up to a fluence of 7.6 × 10−18 n cm−2 (thermal) and 4.3 × 1017 n cm−2 (fast, E > 1 MeV) and the other one up to a fluence of 3.2 × 1019 n cm−2 (thermal) and 1.8 × 1018 n cm−2 (fast, E > 1 MeV). The irradiation induced resistivity is only partially recovered at 1130 °K, where the annealing of defects is supposed to be complete. This effect is attributed to the transmutation of rhenium into osmium and tungsten. The annealing spectrum between 400 and 1130 °K consists of several peaks, the main peak occurring at about 650 °K (0.19 Tm) preceded by a subpeak at about 620 °K. The latter one is more clearly resolved for the lower irradiation dose. This is also the case for the minor peaks occurring at about 490 and 540 °K. Towards higher temperature continuous recovery occurs in the temperature interval 800 to 1000 °K, whereas a small annealing stage has been observed at about 0.32 Tm. The 0.19 Tm stage shows a peak shift towards lower temperatures for higher defect concentration. It is believed that this stage corresponds to stage III of the pure f.c.c. metals.
Die Behandlung von Fehlern im Flußliniengitter der Supraleiter 2. Art in der London‐Näherung
Authors: Brandt E. H. 
Published: July 2007

AbstractEs werden Methoden angegeben, die in der Nähe von Hc1 die Berechnung der Energie und des Verschiebungsfeldes von Gitterfehlern des Flußliniengitters in Supraleitern 2. Art mit ≫ 1 gestatten. Die elastischen Konstanten des Flußliniengitters und die Bindungs‐energie einer Flußlinien werden berechnet. Es zeigt sich, daß man bei allen Rechnungen die Wechselwirkung der Flußlinien mit vielen Nachbarn berücksichtigen muß; andernfalls wäre das Gitter instabil.
Photoluminescence (λm = 1.1 μm) in InSe Single Crystals and Its Relation to Photoconductivity
Authors: Akhundov G. A. , Ermolovich I. B. , Kaziev F. N. , Sheinkman M. K. 
Published: July 2007

AbstractAn investigation has been made of both the luminescence (λm = 1.1 μm) and photo‐conductivity in not intentionally doped photosensitive InSe single crystals. It is shown that the luminescence is due to the emissive capture of free electrons by sensitizing recombination centres. The parameters of the luminescence centres, namely concentration, energetic position, and both electron and hole capture cross‐sections have been determined.
Frenkel's Mechanism of Thermoelectronic Ionization in Single Crystals of Gallium Selenide
Authors: Tagiev B. G. , Guseinova E. S. , Gadzhiev V. A. 
Published: July 2007

AbstractMeasurements are made of the current‐voltage characteristics of monocrystalline GaSe specimens within the strong field region of up to 4 × 104 V/cm in the temperature range from 300 to 125 °K. The data obtained are discussed in terms of Frenkel's mechanism of thermoelectronic ionization \documentclass{article}\pagestyle{empty}\begin{document}$(\sigma = \sigma _0 {\rm e}^{\beta \sqrt E })$\end{document}. The low field value for the activation energy of carriers, is found to be ΔE0 = 0.18 eV, and decreases with increasing electric field according to the formula ΔE = ΔE0 −2 \documentclass{article}\pagestyle{empty}\begin{document}$ e\sqrt {e\,E/\varepsilon} $\end{document} ab (e electronic charge, E electric field intensity, ϵ high‐frequency dielectric constant). Correlating the experimental data with Frenkel's theory, values of ϵ = 8 are obtained for gallium selenide.
A Calculation of the Strain Dependence of the Harmonic Frequency Distribution
Authors: Mock W. 
Published: July 2007

AbstractThe strain dependence of the harmonic frequency distribution f(ω) has been investigated through third order using the Lagrangian strain parameters. The theory is applied to a crystal which interacts through a pair potential. In particular values for the strain coefficients are obtained for Mie‐Lennard‐Jones and Buckingham potentials. This work indicates that the shape of f(ω) changes significantly with strain and that the change is greater for shear strain than for simple expansion in agreement with earlier work.
Propagation of Electromagnetic Waves in a Longitudinally Magnetized Germanium Plasma Waveguide. II. Experimental
Authors: Pedersen N. F. 
Published: July 2007

AbstractExperiments on the transmission of circularly polarized electromagnetic waves through non‐degenerate n‐type germanium in a magnetic field has been made in order to compare to a theoretical dispersion relation given in part I of this paper. The experimental frequency was 45 GHz and liquid helium temperatures has been used. The dispersion relation is found to explain the experimental results very well, and by comparison between theoretical and experimental data information about the transverse and longitudinal effective mass, the lattice dielectric constant, the electron density and the relaxation time has been obtained.
Influence of Point Defects and Dislocations on the Line Shape of Nuclear Magnetic Resonance Signals
Authors: Kanert O. , Kotzur D. , Mehring M. 
Published: July 2007

AbstractThe quadrupolar part of the line shape of a NMR signal is determined by lattice imperfections in the case of cubic crystals. This quadrupolar shape function is presented under the assumption of randomly distributed point defects, dislocation dipoles, and dislocations. Experimental quadrupole shapes were obtained by a line shape analysis of the NMR wide‐line signal and the spin echo signal in the case of different alkali halide crystals. The resulting quadrupolar lines can be compared with the calculated functions. The comparison shows an agreement of the measured shape with the point defect model in the case of undeformed crystals, whereas in the case of deformed crystals the dislocation model is valid.
Localized Orbitals in Polyatomic Systems
Authors: Kunz A. B. 
Published: July 2007

AbstractAdams und Gilbert have derived a rigorous extension to the Hartree‐Fock equation which allows one to obtain localized orbitals in some polyatomic systems. This extension is valid for all closed shell systems and all systems which may be represented by a single Slater determinant and is approximately valid for any system which one may approximate by a single Slater determinant. In this paper these results are put in a more convenient form and are analysed in powers of the interatomic overlap, where only first order terms in overlap are retained. A perturbative form of the equation is also developed. Wave functions are obtained for the LiH crystal.
On the Stress Dependence of Steady State Creep Rate in Alpha Iron
Authors: Čadek J. , Pahutová M. , Ryš P. 
Published: July 2007

AbstractStress dependence of steady state creep rate in alpha iron is analysed assuming that the non‐conservative motion of jogs on screw dislocations is the rate controlling process. It is shown that the moving screw dislocation density ϱs is a more complicated and more sensitive function of stress than the total dislocation density ϱ. The density ϱs increases, reaches a maximum and then decreases again with the increasing stress. The model of creep based on non‐conservative motion of jogs on screw dislocations is in a good qualitative agreement with experimental results.
Leerlinie und Stapelfehler im Flußliniengitter der Supraleiter 2. Art in der London‐Näherung
Authors: Brandt E. H. 
Published: July 2007

AbstractMit den in einer vorangehenden Arbeit [1] entwickelten Methoden werden die Energie und das Verschiebungsfeld der Leerlinien höchster Symmetrie und des unendlichen Stapelfehlers im Flußliniengitter von Supraleitern mit χ ≫ 1 in der Nähe von Hc1 berechnet. Die mit verschiedenen Methoden gewonnenen Ergebnisse werden verglichen. Dabei wird der Gültigkeitsbereich und der Rechenaufwand für diese Methoden diskutiert.
Thermal Conductivity Study of GeTe and SnTe Alloys in the Homogeneous Region
Authors: Okhotin A. S. , Krestovnikov A. N. , Gorbachev V. V. , Aivazov A. A. , Pushkarskii A. S. 
Published: July 2007

AbstractAn investigation is made of the temperature dependence of the thermal conductivity of GeTe and SnTe alloys in the homogeneous region. The phonon component of the thermal conductivity has been determined and the dependence on the tellurium content has been analysed in terms of a theory describing the influence of spot defects upon the thermal resistance of the lattice. Good agreement between experimental and theoretical isotherms of phonon heat transfer has been obtained.
On Heat Transfer in Ag2Se and Ag2Te
Authors: Okhotin A. S. , Krestovnikov A. N. , Aivazov A. A. , Pushkarskii A. S. 
Published: July 2007

AbstractA study is made of the temperature dependence of the thermal conductivity in Ag2Se and Ag2Te in the temperature range from room temperature to the melting point. On the basis of measurements of electric and physical properties an analysis is made of the heat transfer mechanism of these compounds. It has been found that the thermal conductivity in Ag2Se is determined by a phononic and an electronic component and that of Ag2Te by a phononic, an electronic, and a photonic component.
On the Effective Field Retarding the Process of Incoherent Rotation
Authors: Kolotov O. S. , Pogozhev V. A. , Telesnin R. V. 
Published: July 2007

AbstractThe internal effective field He retarding the process of incoherent rotation during the switching of thin magnetic films was investigated. The principal results of the work are as follows. If the switching field Hs exceeds the incoherent threshold field, He increases rapidly with time t (from the value ≈︁ Hk), reaches (t ≦ 10 ns) the maximum value H close to (0.9 to 0.95)Hs, then falls off monotonically, tending in the limit to a value close to ‐Hk. The main contribution to the value of He is made by the effective anisotropy field and the stray fields formed as a result of the initial rotation of the local magnetization vectors.
The Overshoot Phenomena in Single Crystals of Cu‐15 at% Al Tested in Tension. I. Electron Transmission Studies
Authors: Tisone T. C. , Brittain J. O. , Meshii M. 
Published: July 2007

AbstractElectron transmission observations were made at different positions of the shear stress‐strain curve for Cu‐15 at% Al single crystals tested in tension into the state of overshoot. Dislocation interactions between the primary slip system and other slip systems were systematically examined. It was determined that the conjugate slip system was the most important secondary system and that the interactions between primary and conjugate dislocations forming short lengths of Lomer‐Cottrell dislocations were responsible for the latent hardening of the conjugate system, and therefore the overshoot phenomenon. The densities of conjugate dislocations and subsequent Lomer‐Cottrell interactions increased with increasing strain during stage II work hardening.
Effect of Plastic Deformation on the Recovery of Stage I after Neutron Irradiation
Authors: Okuda S. , Takamura S. , Maeta H. 
Published: July 2007

AbstractThe recovery of point defects in copper after fast neutron irradiation at 15 °K was studied by measurements of residual resistivity. Especially, the effect of deformation before and after low‐temperature irradiation on the recovery spectrum was studied. The amount of stage I recovery was reduced by 20% by deformation after irradiation where the deformation was such that only 2% of atomic planes were swept by dislocations. This result suggests the transformation of some of stage I defects into more stable ones due to deformation and the fairly large distance between the interstitial and vacancy in a close pair of stage I. Also, the recovery spectra observed in the present experiments seem to show the annealing of interstitial clusters in stage II (≈︁ 130 °K recovery peak) in cold‐worked copper.
Abdampfstrukturen und Versetzungen in NaCl
Authors: Keller K. W. 
Published: July 2007

AbstractEs wird der Zusammenhang der durch Abdampfen im Hochvakuum erhaltenen Strukturen (Abdampfgruben) auf der Oberfläche eines NaCl‐Kristalls mit den in diesem Kristall enthaltenen Versetzungen diskutiert. Die Existenz der bereits früher für das Zustandekommen von Abdampfspiralen angenommenen Versetzungen mit einem Burgersvektor d0/2 〈110〉, der eine Komponente senkrecht zur Oberfläche hat, bzw. einem zur Oberfläche senkrechten Burgersvektor d0 〈100〉 und der Versetzungsreaktion d0 〈100〉 ⇌ d0/2 〈110〉 + + d02 〈110〉 wird bestätigt (d0/2 Netzebenenabstand). Durch wiederholte Lochkeimbildung an Versetzungen, deren Burgersvektor in der Kristalloberfläche liegt, entstehen aus konzentrischen, geschlossenen Kreisstufen mit der Höhe d0/2 oder aus Viereckstufen mit der Höhe d0 aufgebaute Gruben. Die unterschiedliche Lochkeimbildung wird mit dem Vorhandensein von Inhomogenitäten molekularer Größe an den Versetzungslinien erklärt. Der Unterschied zu den durch Umwandlung von Spiralstrukturen entstandenen konzentrischen Kreisstufen wird deutlich gemacht.
On the Influence of Conduction Electrons on the Ferroelectric Curie Temperature
Authors: Hallers J. J. , Caspers W. J. 
Published: July 2007

AbstractThe frequency dependence of the transverse optical mode in the long‐wavelength limit on the density of conduction electrons is calculated. This dependence is a consequence of the dielectric properties of the free electron gas which gives a change of the effective ion‐ion interaction. By putting the limiting frequency equal to zero one finds an equation for the ferroelectric Curie temperature.