Showing papers on "Debye published in 2000"

Density of phonon states in iron at high pressure

Abstract: The lattice dynamics of the hexagonal close-packed (hcp) phase of iron was studied with nuclear inelastic absorption of synchrotron radiation at pressures from 20 to 42 gigapascals. A variety of thermodynamic parameters were derived from the measured density of phonon states for hcp iron, such as Debye temperatures, Gruneisen parameter, mean sound velocities, and the lattice contribution to entropy and specific heat. The results are of geophysical interest, because hcp iron is considered to be a major component of Earth's inner core.

The diffuse interstellar bands: a dipole-bound state hypothesis

Abstract: It is proposed that some, possibly many, of the unidentified diffuse interstellar absorption bands arise from rovibronic transitions between the ground states of negatively charged molecules and/or small grains, and shallow dipole–bound electronic states which lie close to the electron detachment threshold. Under this hypothesis the attributes for the neutral ‘molecular’ frameworks are electron affinities between 1 and 3 eV and permanent electric dipole moments of ∼2 debye or greater. Bound–bound spectra involving the lowest rotational levels have not been detected in the laboratory, but these proposed carriers appear to be capable of satisfying the main observational astronomical constraints: transitions that lie in the range from the near-ultraviolet to the near-infrared; a wide range of widths; band wavelengths that are invariant; and a large number of related but distinct carriers. The wavelengths of the lowest rotational lines of the band of the transition between the ground and a dipole–bound electronic state of the CH2CN− molecule appear to be consistent with a diffuse band near 8037 A.

Focusing of electromagnetic waves by paraboloid mirrors. I. Theory

Abstract: We derive a solution to the problem of a plane electromagnetic wave focused by a parabolic mirror. The solution is obtained from the Stratton-Chu integral by solving a boundary-value problem. Our solution can be considered self-consistent. We also derive the far-field, i.e., Debye, approximation of our formulas. The solution shows that when the paraboloid is infinite, its focusing properties exhibit a dispersive behavior; that is, the structure of the field distribution in the vicinity of the focus strongly depends on the wavelength of the illumination. We show that for an infinite paraboloid the confinement of the focused energy worsens, with the energy distribution spreading in the focal plane. 2000 Optical Society of America [S0740-3232(00)01309-0] OCIS codes: 260.0260, 260.2110, 050.1960, 260.5430.

Beyond the Classical Transport Laws of Electrochemistry: New Microscopic Approach to Ionic Conductance and Viscosity

Abstract: The concentration dependence of the transport properties (i.e., the conductivity and the viscosity) of an electrolyte solution has been a subject of lively debate for a very long time. The foundation for understanding the transport properties of electrolyte solutions was laid down by Debye, Huckel, Onsager, and Falkenhagen who derived several limiting laws valid at low ion concentration. These classical laws have been rederived several times, although their extension to concentrated solutions has proven to be very difficult. We discuss a new microscopic approach toward understanding the transport laws of electrochemistry. This new approach is based on the general ideas of the mode coupling theory. We show that the mode coupling theory approach is appropriate in the present case because concentration effects arise from collective variables (like charge density and current) which are treated correctly by the mode coupling theory. The new theory can describe the crossover from the low to high concentration seamlessly. Our study yields microscopic expressions of both conductivity and viscosity in terms of static and dynamic structure factors of the charge and number densities of the electrolyte solution. The celebrated expressions of Debye, Huckel, and Onsager for static conductance, of Debye and Falkenhagen for frequency dependent electrolyte friction, and of Falkenhagen for the viscosity follow exactly from the present microscopic theory in the limit of very low ion concentration. Recently derived microscopic expressions of Chandra, Wei, and Patey for the frequency dependent conductivity can also be derived from the present scheme. The present theory is a self-consistent theory. For conductance, the agreement of the present theory with experimental results is satisfactory even up to one molar concentration. For viscosity, the theory seems to give the right trend and suggests directions for further improvement to explain the myriad of unexplained behavior known for a long time.

Variations of Acoustic and Diffuse Mismatch Models in Predicting Thermal-Boundary Resistance

Abstract: Solid-solid thermal-boundary resistance plays an important role in determining heat flow, in both cryogenic and room-temperature applications The acoustic mismatch model (AMM) and the diffuse mismatch model (DMM) have traditionally been used to predict the thermal boundary resistance R b across the interface of two adjoining materials at temperatures well below the Debye temperatures of the materials in question Both the AMM and DMM use the Debye density of states (DOS) in both contacting solids Here, the use of a measured DOS is made in conjunction with the DMM This shows an improvement in the prediction of R b relative to that based on the Debye DOS Another approach considered is to predict R b from measured specific heat per unit volume C data The measured C automatically includes the effect of temperature on the DOS This leads to a marginal improvement in R b above that predicted when using the measured DOS The AMM describes the thermal transport at a solid-solid interface below a few Kelvin quite accurately

Growth and lattice dynamics of Co nanoparticles embedded in Ag: A combined molecular-dynamics simulation and Mossbauer study

Abstract: We use Mossbauer spectroscopy in combination with atomic scale modeling in order to gather a comprehensive understanding of the growth and the dynamics of cobalt nanoprecipitates in silver. The modeling makes use of classical molecular dynamics in the canonical ensemble by means of the Rahman-Parinello technique. Atomic interactions are governed by an embedded atom model, which is validated for the static Co-Ag interaction by means of a comparison with extended x-ray absorption fine structure measurements and for the dynamical interaction with Mossbauer spectroscopy data. This allows us to identify the cluster size dependent atomic arrangements at the cluster-matrix interface, where strong relaxation takes place. A detailed analysis of the Mossbauer spectra taken at two temperatures after annealing at different temperatures allows us not only to characterize the cluster size dependence of magnetic properties, but also to evidence a possible Ostwald ripening growth mechanism. The mean and interface Debye temperatures are deduced from the Mossbauer spectra and found quite consistent with the model predictions. On this basis, the atomic scale modeling allows us to identify detail of atomic vibrational properties as a function of distance from the cluster center and a discontinuity of the vibration amplitudes at the precipitate-matrix interface is evidenced.

Two-dimensional wake potentials in sub- and supersonic dusty plasmas

Abstract: Hot electrons and sub- and supersonic flows of cold ions around a charged dust particle create steady state wake and Debye screening fields. These linear, electrostatic fields are studied in two-dimensional planar or cylindrical geometry. An asymptotic analysis in the limit of large (compared to Debye length) downstream coordinate z yields analytic wakefields that are in good agreement with numerical integrations of the linear, steady state response function.

Chiroptical properties of an optically pure dicopper(I) trefoil knot and its enantioselectivity in luminescence quenching reactions

Abstract: Chiroptical spectroscopy is used to investigate the properties of an optically pure dinuclear copper(I) trefoil knot For the metal-to-ligand charge tranfer (MLCT) transition in the visible region (520 nm), the electric and magnetic transition dipole moments are determined from absorption and circular dichroism spectra: 28 Debye and 05 Bohr magneton (muB) Circular polarization in the luminescence (CPL) of the knot is determined and this allows the electric and magnetic transition dipole moments in emission to be calculated: 002 Debye and 0003 muB The large difference between the moments in absorption and emission shows that the emission observed does not originate directly from the 1MLCT state Given the low probability for radiative decay we assign the long-lived emitting excited state to a 3MLCT state The copper(I) trefoil knot is found to quench the emission from TbIII and EuIII(dpa)3(3)-(dpa = pyridine-2,6-dicarboxylate) with a bimolecular rate constant of 32 and 33 x 10(7)M(-1)S(-1), respectively, at room temperature in water-acetonitrile (1:1 by volume) Experimental results indicate that the (lambda)-knot preferentially quenches the lambda enantiomer of the lanthanide complex with an enantioselectivity (ratio of quenching rate constants for lambda and lambda: kqlambda/kqdelta) of 1012+/-0002 for EuIII and 10180+/-0003 for TbIII

Thermal expansion and heat capacity of GaAs and InAs

Abstract: Thermal expansion of GaAs and InAs was measured in the temperature ranges from 396 to 1149 and from 441 to 1206 K, respectively. The thermal-expansion coefficients, Debye temperatures, and root-meansquare atomic displacements were calculated. These parameters were found to depend on the root-mean-square atomic weights of the compounds. Based on the published data and our heat capacity measurements on GaAs and InAs, the coefficients appearing in the equation for the temperature dependence of heat capacity in the temperature ranges from 200 K to the melting points of GaAs and InAs were determined

Validity of the Debye approximation.

Abstract: The validity of the Debye approximation is reexamined. It is shown that for paraxial systems with strong aberrations the Debye approximation may not be valid, even for systems with a large Fresnel number. The particular case of spherical aberration is considered. Extension to high-aperture systems is discussed.

Debye screening and the Meissner effect in a three-flavor color superconductor

Abstract: I compute the gluon self-energy in a color superconductor with three flavors of massless quarks, where condensation of Cooper pairs breaks the color and flavor SU(3){sub c}xU(3){sub V}xU(3){sub A} symmetry of QCD to the diagonal subgroup SU(3){sub c+V}. At zero temperature, all eight electric gluons obtain a Debye screening mass, and all eight magnetic gluons a Meissner mass. The Debye as well as the Meissner masses are found to be equal for the different gluon colors. These masses determine the coefficients of the kinetic terms in the effective theory for the low-energy degrees of freedom. Their values agree with those obtained by Son and Stephanov. (c) 2000 The American Physical Society.

Rotational patches: Stark effect, dipole moment, and dynamics of water loosely bound to benzene

Abstract: The geometry of the Fabry–Perot cavity makes it difficult to use for measuring the Stark effect. A “Stark cage” is described which generates an electric field suitable for this purpose. The cage is used to measure first and second order Stark splittings of several low-J transitions of the benzene-water dimer previously reported [Gutowsky, Emilsson, and Arunan, J. Chem. Phys. 99, 4883 (1993)]. The dipole moment is found to depend somewhat on rotational state, ranging from 1.65 to 2.00 Debye for both ground m=0 and first excited m=1 internal rotation states of the dimer. Additional m=1 transitions are reported, including the previously missing downshifted line of a k=0′ doublet. Its presence and various Stark effects require reassignment of the m=1 spectrum. The results demonstrate that each J→J+1 spectrum consists of three distinct components which arise from the H2O in an unusual way. In addition to the k-doublets, there are two progressions; a set of (J+1) negative k’s running from −J to 0, and a set of ...

Dielectric relaxation of supercritical water: Computer simulations

Abstract: Dielectric relaxation times of supercritical SPC/E water from molecular dynamics simulations are found to be in good agreement with recent experimental data for densities ρ⩾0.4 g/cm3, but the sharp increase in the experimental Debye time as ρ decreases is not reproduced. Large discrepancies between experimental and simulation data in the dilute regime strongly suggest the need for additional measurements and/or theoretical work.

Moderate phonon dispersion shown by the temperature dependence of fundamental band gaps of various elemental and binary semiconductors including wide-band gap materials

Abstract: A recently devised analytical four-parameter model describing the temperature dependence of fundamental band gaps Eg(T) and/or exciton peak positions Egx(T) in semiconductors is used for estimating the material-specific magnitudes of phonon dispersion. A set of four fundamental parameters, the magnitudes of which are essentially independent of various details of the analytical model used, is established by direct connections with the experimentally detectable low-order moments of the electron–phonon spectral function. Numerical fittings of experimental E(T) data sets are performed for a variety of group IV, III–V, and II–VI materials showing a moderate degree of phonon dispersion. The resulting sets of basic parameters are listed. For all materials in question we find that the limiting (T→∞) slopes of the E(T) curves are confined to magnitudes between about 0.2 and 0.9 meV/K. The effective phonon temperatures amount to about 2/3 of the corresponding Debye temperatures. The simultaneous knowledge of both t...

Vibrational States of Glassy and Crystalline Orthotherphenyl

Abstract: Low-frequency vibrations of glassy and crystalline orthoterphenyl are studied by means of neutron scattering. Phonon dispersions are measured along the main axes of a single crystal, and the corresponding longitudinal and transversal sound velocities are obtained. For glassy and polycrystalline samples, a density of vibrational states is determined and cross-checked against other dynamic observables. In the crystal, low-lying zone-boundary modes lead to an excess over the Debye density of states. In the glass, the boson peak is located at even lower frequencies. With increasing temperature, both glass and crystal show anharmonicity.

Probabilistic basis for the Cole-Cole relaxation law

Abstract: Dielectric dispersion studies of real ferroelectric crystals in the phase transition region indicate a deviation from the Debye response of pure crystals. In this paper the question of the origins of this deviation is addressed in terms of a probabilistic approach. An effort to understand the relaxation mechanism underlying the universally valid Cole-Cole response is undertaken. A model of relaxation as a self-similar process directly related to the fractal geometry of ferroelectric systems is proposed.

Measurement of solute dipole moments in dilute solution: A simple three-terminal cell

Abstract: The construction of a simple, thermostated, three-terminal cell for the measurement of the dipole moment of polar solutes in nonpolar solvents is described. Using a General Radio Company bridge, we demonstrate the accurate measurement of the dielectric constants of p-xylene and benzene, as well as the molecular dipole moments of acetonitrile in p-xylene and p-nitroaniline in benzene. Capacitance measurements of dilute solutions (10−2–10−3 M) using less than 10 ml of solution are possible with this apparatus. The Debye and Hedestrand equations are used to extract the dipole moments from the capacitance measurements.

The cauchy problem for schrödinger–debye equations

Abstract: In this paper we study the local-in-time Cauchy problem for the Schrodinger–Debye equations. This model occurs in nonlinear optics and describes the non-resonant delayed interaction of an electromagnetic wave with a medium. We extend the study to nonphysical cases such as the three-dimensional case or more general nonlinearities.

Gaussian imaging transformation for the paraxial Debye formulation of the focal region in a low-Fresnel-number optical system

Abstract: The Debye formulation of focused fields has been systematically used to evaluate, for example, the point-spread function of an optical imaging system. According to this approximation, the focal wave field exhibits some symmetries about the geometrical focus. However, certain discrepancies arise when the Fresnel number, as viewed from focus, is close to unity. In that case, we should use the Kirchhoff formulation to evaluate accurately the three-dimensional amplitude distribution of the field in the focal region. We make some important remarks regarding both diffraction theories. In the end we demonstrate that, in the paraxial regime, given a defocused transverse pattern in the Debye approximation, it is possible to find a similar pattern but magnified and situated at another plane within the Kirchhoff theory. Moreover, we may evaluate this correspondence as the action of a virtual thin lens located at the focal plane and whose focus is situated at the axial point of the aperture plane. As a result, we give a geometrical interpretation of the focal-shift effect and present a brief comment on the problem of the best-focus location.

Interdependence of the electrical and optical properties of liquid crystals for phase modulation applications

Abstract: The electrical capacitance and conductance of nematic liquid crystal (LC) cells were measured in combination with their optical properties as functions of applied voltage magnitude and frequency. A single experimental system was used in order to determine the correlation between these characteristics. These parameters are crucial for understanding and optimizing the performance of modal LC devices. Both ordinary and dual frequency LCs were investigated. For the latter type, Cole-Cole diagrams show a Debye type frequency dispersion in a limited range of 4–9 kHz. Also, a phenomenological theory of the measured parameters was developed and is in good agreement with experimental data. Two examples are discussed, and they illustrate the importance of taking into account the equivalent conductance of LC cells.