Showing papers on "Debye published in 1978"

Characterisation of dielectric loss in solids and liquids

Abstract: The measured dielectric properties of a range of solids and liquids, as a function of frequency, have been examined and the loss has been shown to fit a generalised empirical relationship. This includes the Cole–Cole, Fuoss–Kirk-wood, Cole–Davidson and Williams–Watts functions as particular cases and implies that a more generalised approach to the dielectric properties of materials is required than that given by the conventional distribution function extension of Debye's method, or by the dipole autocorrelation function of Williams and Watts.

A rigorous approach to Debye screening in dilute classical coulomb systems

Abstract: The existence and exponential clustering of correlation functions for a dilute classical coulomb system are proven using methods from constructive quantum field theory, the sine gordon transformation and the Glimm, Jaffe, Spencer expansion about mean field theory. This is a vindication of a belief, of long standing amongst physicists, known as Debye screening. This states that, because of special properties of the coulomb potential, the configurations of significant probability are those in which the long range parts ofr−1 are mostly cancelled, leaving an “effective” exponentially decaying potential acting between charge clouds.

Stochastic classical trajectory approach to relaxation phenomena. I. Vibrational relaxation of impurity molecules in solid matrices

Abstract: The stochastic classical trajectory approach is extended through introduction of a systematic class of phonon mode densities. Convenient algorithms are presented for generating the required random forces and damping integrals corresponding to mode spectra which approach, as closely as desired, the Debye spectrum. Extension to realistic mode densities involving irregular and discontinuous features is discussed. Application to vibrational relaxation of impurities in solids demonstrates that rates can depend sensitively on the structure of the phonon density of states, particularly at low temperatures.

Electron density and temperature, as measured by the mutual impedance experiment on board GEOS-1

Abstract: The mutual impedance experiment on GEOS-1 provides an original diagnostic of the thermal electron population. The electron density N e , and temperature T e , are derived from the plasma frequency and Debye length, the values of which determine the shape of the frequency dependent mutual impedance curves. The existing limits of the method are pointed out. They may be instrumental or arise from a lack of theoretical development, for instance when the steady magnetic field or the drift velocity of the plasma cannot be neglected. Nevertheless, first geophysical results have been derived, using measurements obtained on the dayside of the equatorial magnetosphere where most of the data enter within the above limits. In particular, we have drawn a map of the dayside magnetosphere, in terms of densities, Debye lengths, temperatures, at geocentric distances of 4 to 7 Earth radii. The conventional shape of the plasmasphere is recognized, but the temperatures obtained are lower than expected (~2 eV at apogee, outside the plasmasphere). The influence of the magnetic activity on apogee measurements is reported: N e values and A m indices are shown to be correlated, but it is not the case for T e and A m . Finally, detailed T e and N e profiles are shown, and the presence of a plasmapause boundary is discussed.

Review of the theory of electrolytic conductance

Abstract: The Ostwald dilution law, based on the Arrhenius hypothesis of electrolytic dissociation, was the first theoretical formulation of the dependence of conductance on concentration. While it adequately described the conductance of weak electrolytes, it could not account for the observation by Kohlrausch that, at low concentrations, the equivalent conductance Λ of strong electrolytes approached linearity inc 1/2, the square root of concentration. Debye and Huckel (1923) assumed complete dissociation and calculated the theoretical behavior of rigid charged spheres moving in a continuum (the primitive model); the result was prediction of the Kohlrausch result. Onsager (1927) predicted the exact numerical value of the limiting slope for the Λ vs.c 1/2 curves. Bjerrum (1926) suggested association of ions to pairs which would not contribute to the long-range interionic effects considered by Debye and Huckel. Fuoss and Kraus (1933) corrected the Ostwald dilution law for the DHO square-root terms and obtained a Λ(c) function which satisfactorily accounted for conductance curves which lay below the limiting tangent. Investigations of the effects of higher terms which had been neglected in the classical DHO treatment of the primitive model led to Λ(c) functions which lay above the limiting tangent for completely dissociated electrolytes. By combining these higher-term equations with Bjerrum pairing, a generally useful conductance function was obtained (Fuoss-Hsia, 1957). In order to eliminate a number of inconsistencies between the properties of real systems and those of the primitive model, a new model (Fuoss, 1975) was proposed: Ion pairs are defined as those whose center-to-center distance lies in the rangea≤r≤R, whereR is the diameter of the Gurney cosphere. Later (1977) the paired ions were divided into two categories: ions which have only solvent molecules as nearest neighbors, and ions which have one ion of opposite charge as a member of the inner shell. The latter contribute only to charging current.

Friction on a rotating dipole

Abstract: A formula is derived for the viscous and dielectric friction on a steadily rotating spherical dipole for the case of an arbitrary ’’slipping coefficient’’. In the perfect slip limit, I recover the Nee–Zwanzig formula for dielectric friction at zero frequency, given that a simple Debye dispersion describes the dielectric response of the medium.

Multipole expansions of electromagnetic fields using Debye potentials

Abstract: The Debye potentials are introduced by giving new derivations of the multipole expansions of the magnetostatic and electrostatic fields. Simplified derivations of the multipole expansions of the electrodynamic fields are then given. The radiated energy, momentum, and angular momentum are all calculated in the same manner, i.e., using the proper transport equations. The questions of uniqueness and completeness of the Debye potential representations of the fields are discussed. In the Appendices are collected together some useful vector field theorems and operator identities involving the angular momentum operator, and also simplified derivations of the spherical harmonic expansions of the static and dynamic Green functions.

The Raman spectrum of NF3: Coriolis coupling and transition dipole interaction in the liquid

Abstract: First order Coriolis coupling in an e‐symmetry mode of a symmetric top and its consequences on the associated Raman line in the liquid are investigated for classical rotations and a classical harmonic vibration. Except for quantum asymmetries, the overall features of the Raman line are reproduced. The second and fourth classical moments of the e‐symmetry Raman line are given together with an expression of the linewidth for Debye diffusion. The relevant autocorrelation function

High-pressure equation of state for solid xenon

Abstract: High-pressure x-ray-diffraction techniques have been used to determine the equation of state of solid xenon up to 110 kbar at 85 K The 0-K isotherme is derived from the experimental data within the Debye approximation The results indicate that solid Xe is much more compressible than one would expect on the basis of known pair potentials for free Xe atoms and known many-atom interactions of the Van der Waals type The difference in compression energy between the experimental and the predicted pressure-volume relation amounts to about 30% at 100 kbar A comparison of the experimental data with bulk properties calculated from energy-band theory by Trickey et al yields good agreement An effective pair potential for the solid state is derived from the experimental pressure-volume relation

Debye temperatures of ferroelectrics

Abstract: Previously reported calorimetric Debye temperatures for 17 ferroelectrics are corrected for a simple oversight in applying the Debye theory, and ${\ensuremath{\Theta}}_{D}'\mathrm{s}$ for four more ferroelectrics are reported for the first time. Where possible, comparisons with elastic ${\ensuremath{\Theta}}_{D}'\mathrm{s}$ are good except for KTa${\mathrm{O}}_{3}$ and potassium dihydrogen phosphate.

Wachtman’s equation and temperature dependence of bulk moduli in solids

Abstract: Anderson has derived an equation describing the temperature dependence of bulk moduli of oxide solids using the Mie‐Gruneisen equation of state. In this paper, we have shown that this equation can be applied to all solids in general, without restricting the applicablity to oxides alone. In our approach, use has been made of the Mie‐Gruneisen equation of state and an assumption that the main change in bulk modulus with temperature arises from the associated volume change and the volume changes encountered are small, which is true in many solids. We have estimated the values of bulk moduli of many nonoxide solids like Au, Ag, Cu, Si, PbSe, Mg2Sn, and MgCu2, which agree well with the experimentally determined values. The Debye characteristic temperature, the Gruneisen parameter, and the Anderson‐Gruneisen parameter have been considered to be temperature dependent.

Low-temperature electron transfer in bacterial photosynthesis

Abstract: The role of a continuous medium frequency distribution of the Debye form in low-temperature thermal electron transfer processes is investigated. When the electrons are strongly coupled to the medium (the medium reorganization energy is 0.2–0.4 eV) a temperature-independent rate constant is predicted from zero temperature up to over 100 K and with far-infrared Debye frequencies. This is compatible with the experimentally observed low-temperature branch in the Arrhenius relationship of the electron transfer from cytochrome c to excited bacteriochlorophyll, Bch + , in bacterial photosynthesis. However, in order to reproduce the high-temperature branch, of finite activation energy, additional activation of intramolecular modes of higher frequencies must be assumed. An intramolecular mode of a coupling constant of 8–9 and a frequency of about 400 cm −1 can account for this branch. Finally, the estimated electron exchange integral is about 10 −4 eV, indicating that the process is strongly a none diabetic.

Quasi‐neutral particle simulation model with application to ion wave propagation

Abstract: A new class of particle simulation models has been developed which eliminates the high‐frequency space charge oscillations while keeping the low‐frequency ion‐density fluctuations unmodified. Physically, the quasi‐neutrality is maintained as the adiabatic electrons follow the ion‐density fluctuations so as to establish the Debye shielding. It is, therefore, possible to use an integration time step comparable to the characteristic time scale of the low‐frequency oscillations so that realistic plasma parameters can be used in the present simulation model. Applications to ion sound wave propagation, ion‐ion two‐stream instability, and the low‐frequency fluctuation spectrum in a magnetic field are given. The way in which to include the nonadiabatic electrons in the model is also discussed.

Lattice-dynamical calculations for Chevrel-phase superconductors

Abstract: Born--von Karman (BvK) lattice-dynamical calculations were performed for the rhombohedral Chevrel-phase superconductors such as PbMo/sub 6/S/sub 8/. The dynamical matrix was obtained using Lennard-Jones (LJ) potentials, which describe interactions between Mo-Mo, Mo-S, S-S, and Pb-S pairs of atoms. The parameters for these potentials were adjusted using the comparison of the moments of the phonon spectrum F (..omega..) with their values obtained from heat-capacity data. Dispersion curves along the three-fold axis show a splitting of the three Pb-atom-dominated modes into a low-lying transverse doublet and a longitudinal singlet. These branches hybridize with the acoustic branches. F (..omega..) is calculated for binary and ternary Chevrel-phase sulfides and selenides by making appropriate mass changes. Moments and site-dependent projections of F (..omega..) are calculated and their associated Debye temperatures are tabulated. Torsional character is found for certain modes in agreement with previous identifications made using the molecular-crystal model. The heat capacity, entropy, inelastic neutron-scattering spectra, Moessbauer recoil-free fraction for /sup 119/Sn, anharmonicity, the apparent T/sup 2/ resistivity below 40 K for sputtered films, and the form of the superconducting tunnelling spectrum ..cap alpha../sup 2/F are discussed. The applicability of the BvK approach using LJ potentials indicates that short-range interactions are important. Hence, the previouslymore » introduced molecular-crystal model is a reasonable, though not rigorous, simplification of the lattice dynamics of this important class of superconductors.« less

Rayleigh-Debye scattering with focused laser beams.

Abstract: A focused beam technique has been developed for diagnosing the characteristics of individual particles within a polydisperse ensemble. In the Rayleigh-Debye approximation the scattered fields are related to the orientation and properties of a scatterer by means of explicit analytic formulas. The results simplify when the particle size is small compared to the minimum beam diameter.

Electrical Parameter Values of Some Human Tissues in the Radiofrequency Radiation Range

Abstract: : This report is an attempt to consolidate electrical parameter values of some human body tissues for the radiofrequency radiation range: 10 - 10,000 MHz The sources of the data were widely distributed in scientific journals, books, and technical reports and included data points secured by experimental techniques, by computations (Debye or modified Debye equations), and by curve fitting methods Values extracted from the conductivity and dielectric constant curves provided in the report give reasonable estimates of the interrelationships between various tissues over the frequency range of interest These values are important in the study of effects of radiofrequency radiation on living organisms

Debye potential representation of vector fields

Abstract: A simple proof is given of the theorem that an arbitrary divergenceless vector field F can be represented in terms of two scalar fields (Debye potentials) ψ and χ according to F=Lψ+∇×Lχ, where L is the angular momentum operator. The questions of uniqueness and completeness of this representation are discussed, and the importance of the theorem in electromagnetic theory is emphasized.

A boundary‐value problem treatment of an electric dipole in a warm isotropic plasma using the multiple water bag model

Abstract: A boundary-value problem for a dipole immersed in a warm isotropic plasma has been solved using the multiple water bag (MWB) and fluid models of the plasma. The MWB model contains information on the electron distribution function, and hence gives results in agreement with the kinetic theory of the warm plasma. Comparing results from the MWB model with those from the fluid model, we find that the latter are correct only when the antenna frequency ω is sufficiently above the plasma frequency ωp. The current distribution and the driving-point impedance are calculated for dipoles of several lengths. We find that the current distribution is triangular only when ω is well above ωp or when ω < ωl where ωl, is the frequency at which a resonance occurs in the driving point admittance; ωl is less than ωp and decreases with the increasing length of the dipole. The current distribution for frequencies close to ωp is oscillatory, with a complex wavenumber which is close to the wavenumber of the third-order Landau mode. Only for very short dipoles with lengths less than 10 Debye lengths or so can the current distribution be approximated by a triangular one for all frequencies. The calculated frequency variation of the dipole resistance with frequency based on the MWB model is similar to those measured experimentally; for frequencies just below ωp the theory in this paper predicts a much larger resistance for the dipole than previous theories.

Effects of configurational order in a Ni3Fe single crystal on debye temperature deduced from elastic constants and X-ray measurements

Abstract: The elastic constants of a Ni3Fe single crystal are measured with respect to the ordering parameter and the temperature between 4.2 and 300 K. The corresponding values of Debye temperature are compared with those ones deduced from the measurements of Debye-Waller factors in X-ray diffraction. Les constantes elastiques d'un monocristal de Ni3Fe ont ete mesurees en fonction du parametre d'ordre, de la temperature de 4,2 a 300 K. Les valeurs de temperature de Debye correspondantes ont ete comparees a celles obtenues a partir de mesures de facteurs de Debye-Waller en diffraction X.

X-ray determination of the mean Debye-Waller factors, amplitudes of vibrations and the Debye temperatures of CdO, PbS and MnS

Abstract: Integrated intensities of Bragg reflections of CdO, PbS and MnS have been measured at room temperature using an x-ray powder diffractometer. From a least square treatment of the intensity data the mean Debye-Waller factor, the mean amplitude of vibration and the Debye temperature have been evaluated. Calculations were made using scattering factors pertaining to neutral atoms as well as doubly ionised ions. The results from the two sets of calculations agreed within limits of errors.

'Clumps' as enhanced correlations and turbulent Debye screening

Abstract: Turbulent correlations in a collisionless plasma are calculated in the lowest approximation which goes beyond the Dupree-Weinstock description by taking trajectory correlations into account. For neighbouring particles in velocity space these effects are shown to reduce the relative diffusion process and to enhance the stationary correlations up to distances of 102 or 103 Debye lengths. Such effects were previously interpreted by Dupree et al. (1975) in terms of macroparticles called 'clumps'. Clump lifetime and clump dimensions are compared with Dupree's result and are generalized to two and three dimensions where tensorial effects appear. It is shown that the clump size is much larger than predicted by Dupree. For such 'anomalous effects' a different physical explanation is proposed, where a 'clump' is interpreted as a turbulent generalization of the Debye sphere rather than discrete macroparticle.

Crystal equilibrium and lattice dynamics of vanadium

Abstract: A lattice-dynamical model which assumes short-range pairwise forces effective up to second nearest neighbours and the electronion interaction on the lines of Bhatia is considered to study the crystal dynamics of b.c.c. metals by using an appropriate value of the screening parameter. The volume force is averaged over the whole Wigner-Seitz sphere. The ionic lattice is in equilibrium in a medium of electrons. The present theory has been satisfactorily applied to compute the dispersion curves, the frequency spectrum, the lattice specific heat, the Debye characteristic temperature, the temperature dependence of the Debye-Waller factor, the X-ray Debye temperature and the mean-square displacement of the atoms of vanadium.

Heat capacity and magnetic properties of Mo6S8 and Mo6Se8 at low temperatures

Abstract: The heat capacity and the magnetic properties of the binary molybdenum chalcogenides Mo6S8 and Mo6Se8 were measured in the temperature range 2–30 K. The results indicate that the lattice contribution to the heat capacity at temperatures T < 15 K follows the Debye law with one oscillator per formula unit. At higher temperatures the more complicated character of the phonon spectrum is noticeable. The electronic contribution to the heat capacity was determined and discussed.

Some observable consequences of kinetic many‐body treatment of large energy fluctuations and of rate constants in solids

Abstract: Semiphenomenological classical non-equilibrium collective treatment of short-lived large energy fluctuations (SLEFs) of heavy particles (atoms, etc.) in bulk and on surfaces of solids up to e ≧ E ≫ kT are considered. The SLEF probability and rate constants are calculated. In the Arrhenius approximation the calculated pre-exponential factors are exponential functions of E, effective coordination numbers χeff, Debye temperatures θ, etc. The new interpretation of diffusion and desorption experimental data narrowing the discrepancies between the latter and theoretical predictions is suggested. [Russian Text Ignored].