bluuebunny/crossref_metadata_2025_split huggingface dataset:
Propagation of Electromagnetic Waves in a Longitudinally Magnetized Germanium Plasma Waveguide. I. Theory
Authors: Pedersen N. F. 
Published: July 2007

AbstractThe propagation of electromagnetic waves in a longitudinally magnetized plasma waveguide with perfectly conducting boundary has been investigated. Numerical calculations of the wave vector have been performed for the case where the direction of both the magnetic field and the wave vector coincide either with the [111] or the [100] crystallographic direction in n‐type germanium. The frequency used is 45 GHz, and the calculation applies to non‐degenerate germanium where the applied frequency and the plasma frequency ωp are of the same order of magnitude. For small plasma radius r0 strong guiding effects are found both in the real and imaginary part of the wave vector.
Condensation and Evaporation of Vacancies at the Surface of Aluminium as a Result of Cooling and Heating
Authors: Lohne O. , Nøst B. 
Published: July 2007

AbstractBlack dots at the surface of one aluminium crystal were observed by X‐ray topography to develop subsequent to small positive and negative temperature changes, ±5 °C, at temperatures from 350 to 430 °C. In another crystal a one to one correspondance between black dots and thermal etch pits was observed. It was concluded that the phenomenon studied by X‐ray topography was thermal etching. Further, it was concluded that the surface did not absorb or emit vacancies as easily as the surface of the pits, and that the nucleation of the pits did not take place at termination points of dislocations at the surface.
Peak Effect in Type II Superconductors: Yield Point of the Fluxon Lattice
Authors: Chang C. C. , McKinnon J. B. , Rose‐Innes A. C. 
Published: July 2007

AbstractThe complicated current‐voltage (flux flow) curves obtained from type II superconductors which show the peak effect are compared to the stress‐strain curves of crystalline materials in which plastic flow at low stresses is prevented by pinning of dislocations. It is suggested that the unstable step in the current‐voltage characteristic is the result of “yield” and subsequent shearing of the fluxon lattice by dislocation motion.
Stress Relaxation and the Activation Energy for Plastic Flow in Solids: Commercially‐Pure Aluminum
Authors: Clough R. B. , Demer L. J. 
Published: July 2007

AbstractA new technique of studying plastic flow using stress relaxation is presented, related in derivation to the conventionally used creep and tensile methods. No specific deformation model, such as those used in related derivations, is assumed in this derivation, in which machine deformation and the change in elastic constants with temperature are taken into account. To illustrate the technique, it is applied to plastic flow in commercially‐pure aluminum, and the results obtained are compared with those obtained by creep and tensile methods.
Equilibrium State of Slip Bands in Plastically Bent NaCl Crystals
Authors: Kästner G. 
Published: July 2007

AbstractThe slip bands known from ionic crystals and being typical for the initial stage of plastic deformation are found to have a limited, narrow width and a defined long‐range stress field in the present case of NaCl crystals tested in bending. This deformation structure has been investigated by combining special methods of photoelasticity, interferometry, and electron microscopy. The stress field of the slip band is described by a pile‐up of edge dislocations which are necessarily in excess within a bent crystal. The superposition of the slip‐band stress field to the applied stress leads to a stress equilibrium which can be reached “statically” or “dynamically” and which explains the limitation of the width and of the integral step height of the slip band. As a consequence of this limitation, the number of slip bands increases considerably during further bending. Thereby the atomic slip steps will cover the surface more and more homogeneously so that after a surface strain of about 1% individual slip bands can no longer be distinguished.
Magnetic Circular Dichroism of the K‐Band in Alkali Halides
Authors: Krätzig E. , Staude W. 
Published: July 2007

AbstractThe magnetic circular dichroism of the K‐band in the alkali halides RbCl, RbBr, RbI, KCl, KBr, and KI has been measured at temperatures between 4.2 and 77 °K. The magnetic field up to 50 kG was produced by a superconducting solenoid. We interpret the experimental results using the method of moments. The spin‐orbit splitting and the orbital g‐factors of the excited states due to the K‐band are determined. Furthermore we obtain matrix elements describing the mixture of the excited states giving rise to F‐and K‐bands. In accordance with calculations of Smith [15] the measurements confirm the Mott‐Gurney model, which attributes the K‐band mainly to 1s‐3p transitions.
Temperature‐Dependent Ground State Splitting of Mn++ Ions in Alkali Halides Induced by Resonant Vibrations
Authors: Pfister G. , Dreybrodt W. , Assmus W. 
Published: July 2007

AbstractThe temperature dependence of the rhombic ground state splitting tensor D of Mn++ centres with nearest cation vacancy was measured at NaCl and LiCl. The experimental data reveal a behaviour of the tensor D, which can be described by D(T) = D0 + D coth ℏ ω/2 kT. This result is interpreted by assuming a resonant vibration of frequency w coupling to the centre. This vibration changes the rhombic crystalline fields which produce the ground state splitting of the Mn++ ion according to the theory of van Heuvelen [4]. It is possible to find resonant modes in both systems NaCl and LiCl which lead to good agreement between the calculated and the experimental data.
Many Body Interaction in Alkali Halides
Authors: Sarkar A. K. , Sengupta S. 
Published: July 2007

AbstractThe effect of the many body interaction proposed by Sarkar and Sengupta is considered in detail. The method of homogeneous deformation is extended to include many body interactions in which the potential depends on several scaler distances. The general expressions for the elastic constants obtained by this method are compared with those obtained from the long wave theory. Including the various central interactions the model is applied to calculate the elastic constants, the cohesive energy, and the phase transition pressure for the six halides of potassium and rubidium. It is found that the inclusion of the three body interaction considerably improves the agreement.
Non‐Ohmic Behaviour in CdS Acousto‐Electric Oscillators
Authors: Janus H. M. 
Published: July 2007

AbstractIn thin plane parallel photoconducting CdS platelets the current is observed to deviate from the ohmic value also outside the electric field range for net round trip gain in the longitudinal wave configuration. A N‐type negative differential conductivity is observed for pulsed as well as for CW operation. Domain formation may take place and give rise to low‐frequency current oscillations superposed on the well known high‐frequency modes of the acousto‐electric oscillator. The negative differential conductivity is most likely ascribed to field‐dependent free carrier trapping though acousto‐electric effects may also be important.
Die Leerlinie im Flußliniengitter der Supraleiter 2. Art in der Nähe von Hc2
Authors: Brandt E. H. 
Published: July 2007

AbstractEs werden die Energie, das Verschiebungsfeld, die Ginsburg‐Landau‐Funktion (bzw. der Ordnungsparameter) und das mikroskopische Magnetfeld einer Leerlinie mit höchster Symmetrie im Flußliniengitter der Supraleiter 2. Art in der Nähe von Hc2 mit einer in einer vorangehenden Arbeit entwickelten Methode berechnet. Das Verschiebungsfeld des Gitters in großer Entfernung von einem beliebigen lokalisierten Gitterfehler wird angegeben.
Effect of Colour Centres on the Cr3+ Spectrum in Ruby
Authors: Arkhangelskii G. E. , Morgenshtern Z. L. , Neustruev V. B. 
Published: July 2007

AbstractIt is found that the colour centres in ruby cause an increase of the oscillator strength in the transitions corresponding to the R‐ and B‐lines of the Cr3+ absorption and a decrease of the relaxation time τ of the luminescence in the R‐lines. These effects can be explained by a partial forbiddenness violation for the transitions 4A2 → 2E and 4A2 → 2T2 induced by the change in the intercrystalline field due to the charged colour centres (by Cr2+ and Cr4+ ions). From the broadening of the ESR lines the effective field due to the colour centres is estimated.
Electrical Instability in Half‐Insulating GaAs
Authors: Vorob'ev Yu. V. , Karkhanin Yu. I. , Tretyak O. V. 
Published: July 2007

AbstractEnergy spectrum and capture cross sections of local electronic states have been investigated in half‐insulating (oxygen‐doped) GaAs. The resulting spectrum of energy levels gave us a possibility to offer a general scheme of arising of negative differential conductance (DNC) for recombination non‐linearity; this scheme includes in particular two mechanisms discussed earlier [1, 2]. It was shown that in the case investigated the DNC appears as a result of recharging of impurity levels under the action of electric field. To study the effect of a uniformly distributed electric field upon semiconductor, high frequency field was employed; with the help of it we have obtained a falling region on volt‐ampere characteristic. If constant electric field is applied to the sample, a domain instability can be observed under conditions when mean field corresponds to the ohmic part of I‐U characteristic of a uniform sample; the smallest field corresponding to instability could vary within wide limits, depending on the situation at the cathode. Conceptions are developed about creation of a high‐field space charge region next to the cathode, where field reaches the value sufficient for displaying of DNC mechanism. Some information is obtained on the initial phase of creation of such a region under different conditions.
Localized Exciton States of Doped Naphthalene Crystals
Authors: Ostapenko N. I. , Shpak M. T. 
Published: July 2007

AbstractBands due to localized exciton states in a crystal arising near guest molecules have been obtained and studied in the absorption and luminescence spectra of a naphthalene crystal (T = 4.2 °K) doped with heterocyclic compounds (thionaphthene, i = T, indole, i = I, and benzofurane, i = B). The luminescence spectrum of these states is similar to the exciton luminescence spectrum of naphthalene: the polarization ratio Pi(b/a) for 0‐0 bands in the luminescence and absorption spectra decreases with 0‐0 bands approaching to the a‐component of the Davydov doublet. Simultaneously depolarization of the A1‐band occurs. From comparison between the polarization ratios for 0‐0 bands of the localized and impurity states (the case of isotopic mixtures) their common features as well as differences are found the latter being apparently due to the localized centre structure. The results are qualitatively explained on the basis of the theory of localized exciton states.
On the Magnetic Properties of Dy3+ Ion in Dysprosium Ethylsulfate Single Crystal
Authors: Taneja S. P. 
Published: July 2007

AbstractPrincipal magnetic susceptibilities of single crystal of dysprosium ethylsulfate have been computed in the temperature range of liquid‐nitrogen to room temperature, assuming that the crystal field has C3h symmetry around the Dy3+ ion. It is observed that magnetic anisotropy increases with the decrease of temperature. The calculated magnetic moment of Dy3+ ion at room temperature is 10.48 μB, which is in good agreement with the experimental value 10.60 μB and the free ion moment 10.62 μB. Computed g‐values of the lowest level of ground state are: g∥ = 10.748, g⊥ = 0.0, which agree well with the experimental values g∥ = 10.76 ± 0.1, g⊥ = 0.0.
Radiation Damage in Selenium Single Crystals
Authors: Tiainen O. J. A. , Tunkelo E. 
Published: July 2007

AbstractNew radiation damage studies have been performed on a single crystal of trigonal selenium. The conductance and the thermoelectric power of the crystal were measured along the hexagonal c‐axis before, during, and after irradiation in a reactor. The temperature range covered in the measurements was 15 to 300 °K. The conductivity decreased with increasing fast neutron dose. The thermoelectric power did not change markedly during one irradiation period although a decrease of the thermoelectric power was observed when the crystal was irradiated several times at low temperatures. It seems that a decrease of the hole concentration is not sufficient to explain the conductance at low temperatures.
On the UV Absorption of Heavy Metal Ions in Alkali Halide Crystals II. Interpretation of the Temperature Dependences of the UV Dipole Strength
Authors: Fussgaenger K. 
Published: July 2007

AbstractThe different temperature dependences of the UV dipole strength of forbidden electronic Ag+, Cu+, and Tl+ transitions in alkali halide crystals are interpreted by electron‐phonon interaction, anharmonicity of phonons, off‐centre effects, and thermal relaxations of the centres.
Donor Levels in n‐InSb and Their Ionization in Electric Field
Authors: Ismailov I. M. , Nasledov D. N. , Smetannikova Uy. S. , Felitsiant V. R. 
Published: July 2007

AbstractThe temperature dependences of the Hall coefficient RH, the conductivity σ, and the electron mobility μ in n‐type InSb samples with different degree of compensation have been investigated. Deep donor levels have been found at Ec −1.8 × 10−2eV and Ec −6.7 × 10−2eV. The parameters of these levels were estimated in terms of the many‐level model. The voltage‐current characteristics and the dependences RH = f(E) and RH σ = f(E) have been studied in detail at T=4.2 °K. It is shown that at E ≈︁ (2 to 8) × 10−2 V/cm a partial ionization of the shallow donor level Ec −6 × 10−4 eV can occur (tunnel transition), whereas at E > 10−1 V/cm an impact ionization of the donor level Ec − 1.8 × 10−2 eV is produced by electrons heated by the electric field.
Investigation of Germanium conductivity Relaxation in High Microwave Fields
Authors: Banys T. , Dargys A. , Pozhela J. 
Published: July 2007

AbstractA method of determining short conductivity relaxation times in semiconductors at high electric fields is presented using the microwave field harmonics due to the nonlinearity of the I‐U characteristic of the bulk of the semiconductor. It is found that the amplitude of these harmonics depends on an additional dc electric field and the semiconductor conductivity relaxation time. The method is applied to the study of conductivity relaxation of n‐type germanium at high microwave fields.
Faraday Rotation and Faraday Ellipticity in the Exciton Absorption Region of GaAs
Authors: Zvára M. 
Published: July 2007

AbstractFaraday rotation and Faraday ellipticity in the exciton absorption region were measured in GaAs single crystals at room and liquid nitrogen temperatures. The experimental curves are interpreted as a sum of the contributions both of excitons and of free Landau level transitions. The value of the effective g‐factor was determined to be g* = −2.1.
Photoeffect in Metal‐Free Phthalocyanine Crystals
Authors: Usov N. N. , Benderskii V. A. 
Published: July 2007

AbstractThe drift mobilities of electrons (0.43 to 0.70 cm2 V−1s−1) and holes (0.24 to 0.56 cm2 V−1s−1) in thoroughly purified metal‐free phthalocyanine crystals have been measured by illumination with short light pulses. The mobilities of carriers of both sign diminish with increasing temperature: μ ∽ T−n, n = 1.3 to 1.5 for holes, n = 1.5 to 1.9 for electrons. The quantum yields of holes and electrons are equal in magnitude (7 ± 6 × 10−5 at 295 °K) and increase exponentially with temperature. Probably, the generation of photocarriers is caused by thermal dissociation of singlet excitons. The difference between the energy gap and the singlet exciton energy is equal to the activation energy of quantum yield (0.19 cV). Under the giant ruby laser pulse the photocurrent in pure crystals is a linear function of light intensity, whereas in crystals containing impurities the square dependence is observed. The mechanism of charge carrier production under high light intensity is probably the singlet exciton annihilation, the rate constant being 4 × 10−15 to 8 × 10−14 cm3s−1.
Intrinsic Photoconductivity in Single Crystals of Cadmium Iodide
Authors: Wright D. K. , Tubbs M. R. 
Published: July 2007

AbstractPhotoconductivity measurements have been made on single crystals of cadmium iodide for illumination over a wide range of photon energies from the fundamental absorption edge to more than 3 eV inside the region of intrinsic absorption. These photoconductivity spectra show all the structure that is normally seen in a reflectivity spectrum. Additional information has been obtained by studying the spectral distribution of photocurrent corrected to a constant number of absorbed photons. The corrected photocurrent is considerably larger than expected near the high energy excitons with absorption peaks at 5.7 and 6.2 eV. This may be accounted for by assuming that these excitons are able to diffuse over significant distances in the crystal before dissociating into free charge carriers. The structure observed in the photoconductivity and optical absorption spectra of CdI2 is discussed in terms of an empirical model for the energy band structure near k = 0.
Ionic Conductivity of Sodium fluoride
Authors: Bauer C. F. , Whitmore D. H. 
Published: July 2007

AbstractThe electrical conductivity of single crystals of pure NaF and NaF doped with CaF2 has been measured as a function of temperature from 450 to 970°C. Analyses of these data by a leastsquare method to yield the usual defect parameters have been based on two models: 1. a perfect crystal perturbed by isolated cation vacancies, isolated anion vacancies, divalent cation impurity, and divalent cation impurity‐cation vacancy complexes, and 2. one which includes the long‐range Coulomb interactions between isolated defects in addition to the four defects of the first model. More satisfactory agreement with the experimental results is apparent when the latter model is employed, but non‐random deviations between experiment and theory were evident for both models over the entire temperature range of observation.
Mechanical Relaxation and Nonlinearity in Strontium Titanate Single Crystals
Authors: Sorge G. , Hegenbarth E. , Schmidt G. 
Published: July 2007

AbstractThe temperature dependence of the resonance frequency of longitudinally vibrating [;100] bars of SrTiO3 single crystals exhibits two maxima atTa = 103 °K and Tb = 30 °K. Between these temperatures exact measurements are only possible if the exciting voltage is sufficiently low. At higher amplitudes nonlinear response can be observed. The maximum at Ta is shifted to higher temperatures by applying a uniaxial stress P (dTa/dP = 18 × 10−3 deg/at) and hydrostatic pressure p (dTa/dp = 1.5 × 10−3 deg/at). After changing the mechanical and electric bias, mechanical relaxation occurs in the temperature range between 30 and 80 °K.
Instabilités des ondes guidées de type hélicon dans un plasma soumis à un champ électrique
Authors: Vassallo Ch. 
Published: July 2007

AbstractOn présente une théorie des ondes du type hélicon dansun plasma soumis à la fois à un champ électrique et à un champ magnétique. On utilise des courbes de dispersion dans le plan complexe des k qui tiennent compte des pertes; ces courbes sont formellement indépendantes du champ électrique. Dans un milieu infini on peut avoir une instabilité absolue avec un champ électrique aussi petit que l'on veut. Ce n'est plus vrai dans un plasma limité transversalement. On étudie la modification des courbes de dispersion due au guidage et on présente un calcul des seuils d'instabilité que l'on compare à une théorie antérieure. Dans les milieux finis réels, ce genre d'instabilité demande des mobilités comparables et des porteurs nombreux; elle semble peu probable dans InSb.
Effect of Neutron Irradiation on the Temperature Dependence of the Flow Stress for Niobium Single Crystals
Authors: Reed R. E. , Guberman H. D. , Armstrong R. W. 
Published: July 2007

AbstractYield stress and strain‐rate data were obtained in compression at various temperatures. Niobium single crystals were tested both in the irradiation and unirradiated condition. The neutron irradiation largely affected the athermal component of the flow stress, however, it also induced a smaller but measurable increase in the thermal component of stress. The data indicate that increasing solute content effects an athermal strengthening similar to that of neutron irradiation.
Magnetic Anisotropy in F.C.C. Single Crystal Cobalt—Nickel Electrodeposited Films. II. Thickness Dependence of the Magnetocrystalline and Uniaxial Anisotropy Constants from (110) Deposits
Authors: Lord D. G. , Goddard J. 
Published: July 2007

AbstractTorque magnetometry has shown a pronounced variation with film thickness of the magnetocrystalline anisotropy constants K1, K2, K3 of Co—Ni f.c.c. films, of between 100 and 1000 Å, electroplated on to (110) copper single crystal substrates. A thickness dependent uniaxial anisotropy Ku of the order of K1 was found to be present for all alloy compositions, its axis being a <001> direction in the plane of the film. An empirical relationship which describes the thickness variation of Ku has been constructed containing three terms representing pseudomorphic, ‘unnatural‐phase’, and occluded hydrogen strain energies.
Energy Band Structures of Four Polytypes of Silicon Carbide Calculated with the Empirical Pseudopotential Method
Authors: Junginger H.‐g. , van Haeringen W. 
Published: July 2007

AbstractThe electronic band structures of four polytypes of silicon carbide (3C, 2H, 4H, 6H) are calculated with the aid of local atomic pseudopotentials for carbon and silicon. The same pseudopotentials are used in all four polytypes. A description is given of the basic assumptions in the empirical pseudopotential method. A computer program is used which is able for symmetric k‐values to reduce the dimensionality of matrices. The calculated energy band structures are in satisfactory agreement with well‐established experimental data.
X‐Ray Interferometric Measurements of the Forward Scattering Amplitude for Lithium Fluoride
Authors: Creagh D. C. , Hart M. 
Published: July 2007

AbstractThe X‐ray refractive index of lithium fluoride was measured to an accuracy of a few parts in 109 over the wavelength range from AgKβ1 (λ = 0.497058 Å) to CuKα1 (λ = 1.54053 Å). From these results the scattering factor for the forward direction and the anomalous dispersion corrections for fluorine were calculated. Good agreement was obtained with the values calculated using Hönl's dispersion theory.
Acoustical Scattering in Polar Semiconductors at Strong Electric Fields
Authors: Licea I. 
Published: July 2007

AbstractThe processes of acoustical scattering by a strong electric field in semiconductors with an arbitrary non‐parabolicity of the spherically symmetric conduction bands are considered in the electron temperature approximation. Assuming only acoustical scattering the energy and momentum conservation equations are established when both energy and momentum exchange is controlled by interelectronic collisions. Basing upon these results, the electron temperature and mobility in a polar semiconductor with a non‐parabolic energy dispersion law as that of n‐type InSb are studied theoretically. The problem is treated for “warm” and “hot” electrons and a comparison is made with the parabolic case.
Study of the (111) Conduction Band of GaSb
Authors: Averous M. , Bougnot G. , Calas J. , Chevrier J. 
Published: July 2007

AbstractWe have developed a calculation method of the parameters of the (111) band of GaSb from measurements of piezoresistance under uniaxial stress and hydrostatic pressure, and from the Hall effect as a function of temperature. We have determined dδE/dp, m, m, K (ellipsoid anisotropy), and Ξu, the deformation potential constant for the (111) band.