Showing papers on "Debye published in 2010"

Nuclear-Magnetic-Resonance Measurements Reveal the Origin of the Debye Process in Monohydroxy Alcohols

Abstract: Monohydroxy alcohols show a structural relaxation and at longer time scales a Debye-type dielectric peak. From spin-lattice relaxation experiments using different nuclear probes, an intermediate, slower-than-structural dynamics is identified for n-butanol. Based on these findings and on translational diffusion measurements, a model of self-restructuring, transient chains is proposed. The model is demonstrated to explain consistently the so-far puzzling observations made for this class of hydrogen-bonded glass forming liquids.

Modified Entropic Force

Abstract: The theory of statistical thermodynamics tells us the equipartition law of energy does not hold in the limit of very low temperatures. It is found the Debye model is very successful in explaining the experimental results for most of the solid objects. Motivated by this fact, we modify the entropic force formula which is proposed very recently. Since the Unruh temperature is proportional to the strength of the gravitational field, so the modified entropic force formula is an extension of the Newtonian gravity to the weak field. On the contrary, general relativity extends Newtonian gravity to the strong field case. Corresponding to Debye temperature, there exists a Debye acceleration g{sub D}. It is found the Debye acceleration is g{sub D}=10{sup -15} N kg{sup -1}. This acceleration is very much smaller than the gravitational acceleration 10{sup -4} N kg{sup -1} which is felt by Neptune and the gravitational acceleration 10{sup -10} N kg{sup -1} felt by the Sun. Therefore, the modified entropic force can be very well approximated by the Newtonian gravity in the Solar System and in the Galaxy. With this Debye acceleration, we find the current cosmic speeding up can be explained without invoking any kind of dark energy.

Normal Modes and Density of States of Disordered Colloidal Solids

Abstract: The normal modes and the density of states (DOS) of any material provide a basis for understanding its thermal and mechanical transport properties. In perfect crystals, normal modes are plane waves, but they can be complex in disordered systems. We have experimentally measured normal modes and the DOS in a disordered colloidal crystal. The DOS shows Debye-like behavior at low energies and an excess of modes, or Boson peak, at higher energies. The normal modes take the form of plane waves hybridized with localized short wavelength features in the Debye regime but lose both longitudinal and transverse plane-wave character at a common energy near the Boson peak.

Insights on the origin of the Debye process in monoalcohols from dielectric spectroscopy under extreme pressure conditions.

Abstract: The dielectric spectra of most simple liquids are characterized by two relaxation processes: (i) the α-process, an intense, broad non-Debye relaxation with a non-Arrhenius temperature dependence and (ii) a β process, evident mainly below the glass transition and having nearly Arrhenius temperature behavior. However, the dielectric spectra of monoalcohols show three processes: two that resemble those of normal liquids and a third very intense Debye peak at lower frequencies, which is non-Arrhenius. Interestingly, this third process is not observed with other techniques such as light scattering and mechanical spectroscopy. There is a disagreement in the literature concerning the nature of this third relaxation. We investigated 2-ethyl-1-hexanol under high pressures (up to ∼1.4 GPa) over a broad range of temperatures. The Debye process, which is the slowest, is strongly affected by pressure. At higher pressures the relaxation times and intensities of the two non-Arrhenius relaxations become more nearly equal...

Role of dispersion on phononic thermal boundary conductance

Abstract: The diffuse mismatch model (DMM) is one of the most widely implemented models for predicting thermal boundary conductance at interfaces where phonons dominate interfacial thermal transport. In the original presentation of the DMM, the materials comprising the interface were described as Debye solids. Such a treatment, while accurate in the low temperature regime for which the model was originally intended, is less accurate at higher temperatures. Here, the DMM is reformulated such that, in place of Debye dispersion, the materials on either side of the interface are described by an isotropic dispersion obtained from exact phonon dispersion diagrams in the [100] crystallographic direction. This reformulated model is applied to three interfaces of interest: Cr–Si, Cu–Ge, and Ge–Si. It is found that Debye dispersion leads to substantially higher predictions of thermal boundary conductance. Additionally, it is shown that optical phonons play a significant role in interfacial thermal transport, a notion not previously explored. Lastly, the role of the assumed dispersion is more broadly explored for Cu–Ge interfaces. The prediction of thermal boundary conductance via the DMM with the assumed isotropic [100] dispersion relationships is compared to predictions with isotropic [111] and exact three-dimensional phonon dispersion relationships. It is found that regardless of the chosen crystallographic direction, the predictions of thermal boundary conductance using isotropic phonon dispersion relationships are within a factor of two of those predictions using an exact three-dimensional phonon dispersion.

First-principles investigations on electronic, elastic and optical properties of XC (X=Si, Ge, and Sn) under high pressure

Abstract: An investigation on electronic, elastic, and optical properties of XC (X=Si, Ge, and Sn) under high pressure has been conducted using first-principles calculations based on density functional theory with the plane wave basis set as implemented in the CASTEP code. Our results demonstrate that the sequence of the pressure-induced structure transition of these compounds is from zincblende-type (B3) to NaCl-type (B1) structure. The calculated lattice constants and transition pressures are reported, which are in good agreement with the available experimental results and the previous theoretical data. The elastic constants and anisotropy as a function of pressure are presented. These results suggest technological applications of such materials in extreme environments. Debye temperatures of B3–SnC and B1–SnC are determined for the first time.

Thermal stability and elastic properties of intermetallics Mg2Pb

Abstract: The stability and elastic properties of Mg2Pb are investigated by the first principles method, using the method of ultrasoft pseudopotential within the generalized gradient approximation based on density functional theory. Cohesive energy and formation enthalpy show that Mg2Pb is stable. Similar result is also obtained by the energy band structure and density of states (DOS) analysis. The thermal data of Mg2Pb are calculated using Debye's quasi-harmonic approximation, such as heat capacity and Gibbs free energy. Based on the CV, we found that the Debye temperature of Mg2Pb is 247.2 K. Young's modulus and shear modulus for Mg2Pb are 68.6 and 27.9 GPa calculated from the theoretical elastic constants by Voigt–Reuss–Hill averaging scheme.

Effects of screened Coulomb (Yukawa) and exponential-cosine-screened Coulomb potentials on photoionization of H and He+

Abstract: The screening effects due to the exponential-cosine-screened Coulomb and screened Coulomb (Yukawa) potentials on photoionization processes are explored within the framework of complex coordinate rotation method. The energy levels of H and He+ in both screened potentials shifted with various Debye screening lengths are presented. The photoionization cross sections illustrate the considerable screening effects on photoionization processes in low energy region. The shape resonances can be found near ionization thresholds for certain of Debye screening lengths. The relations between the appearance of resonances and the existence of quasi-bound states under shielding conditions are discussed.

Convergent-close-coupling calculations for excitation and ionization processes of electron-hydrogen collisions in Debye plasmas

Abstract: Electron-hydrogen scattering in weakly coupled hot-dense plasmas has been investigated using the convergent-close-coupling method The Yukawa-type Debye-Hueckel potential has been used to describe the plasma screening effects The target structure, excitation dynamics, and ionization process change dramatically as the screening is increased Excitation cross sections for the 1s{yields}2s,2p,3s,3p,3d and 2s{yields}2p,3s,3p,3d transitions and total and total ionization cross sections for the scattering from the 1s and 2s states are presented Calculations cover the energy range from thresholds to high energies (250 eV) for various Debye lengths We find that as the screening increases, the excitation and total cross sections decrease, while the total ionization cross sections increase

Debye series for light scattering by a spheroid.

Abstract: The Debye series is developed for electromagnetic scattering by a spheroid in order to decompose the far-zone fields into various physical processes. The geometrical rainbow angle and supernumerary spacing parameter are determined from the Debye intensity by fitting the results to an Airy function and comparing them to their assumed values in ray optics and Airy theory, respectively. Eccentricity-related scattering phenomena including the rainbow's angular shift, the disappearance of the rainbow, and the rainbow-enhanced glory are quantitatively demonstrated and analyzed.

Screening of ionic cores in partially ionized plasmas within linear response.

Abstract: We employ a pseudopotential approach to investigate the screening of ionic cores in partially ionized plasmas. Here, the effect of the tightly bound electrons is condensed into an effective potential between the (free) valence electrons and the ionic cores. Even for weak electron-ion coupling, the corresponding screening clouds show strong modifications from the Debye result for elements heavier than helium. Modifications of the theoretically predicted x-ray scattering signal and implications on measurements are discussed.

Scaling the temperature-dependent boson peak of vitreous silica with the high-frequency bulk modulus derived from Brillouin scattering data.

Abstract: The position and strength of the boson peak in silica glass vary considerably with temperature T. Such variations cannot be explained solely with changes in the Debye energy. New Brillouin-scattering measurements are presented which allow determining the T dependence of unrelaxed acoustic velocities. Using a velocity based on the bulk modulus, scaling exponents are found which agree with the soft-potential model. The unrelaxed bulk modulus thus appears to be a good measure for the structural evolution of silica with T and to set the energy scale for the soft potentials.

Dimensional phase transition in small Yukawa clusters.

Abstract: We investigate the one- to two-dimensional zigzag transition in clusters consisting of a small number of particles interacting through a Yukawa (Debye) potential and confined in a two-dimensional biharmonic potential well. Dusty (complex) plasma clusters with $n\ensuremath{\le}19$ monodisperse particles are characterized experimentally for two different confining wells. The well anisotropy is accurately measured, and the Debye shielding parameter is determined from the longitudinal breathing frequency. Debye shielding is shown to be important. A model for this system is used to predict equilibrium particle configurations. The experiment and model exhibit excellent agreement. The critical value of $n$ for the zigzag transition is found to be less than that predicted for an unshielded Coulomb interaction. The zigzag transition is shown to behave as a continuous phase transition from a one-dimensional to a two-dimensional state, where the state variables are the number of particles, the well anisotropy and the Debye shielding parameter. A universal critical exponent for the zigzag transition is identified for transitions caused by varying the Debye shielding parameter.

Extraction of Dielectric Constant and Loss Tangent Using New Rapid Plane Solver and Analytical Debye Modeling for Printed Circuit Boards

Abstract: Dielectric material properties of printed circuit boards (PCBs) are needed by designers working in various areas such as signal integrity, antennas, and embedded RF components. Among many methods to extract the material properties, the full sheet resonance technique is commonly used on PCBs due to its simplicity. The disadvantage of this method is that an analytical equation is used to extract the dielectric constant, which is accurate only for lossless dielectrics. In this paper, a new method is presented to solve the inaccuracy issue of the extraction of the dielectric constant by applying customized electromagnetic simulation based on a new rapid plane solver instead of analytical equations. For PCB dielectrics, the loss tangent tends to be flat over several decades. The dielectric constant then varies as a function of frequency based on the Kronig-Kramers relations. This paper introduces a new Debye type of a model for the complex permittivity of such dielectrics. The parameters of the Debye model can be obtained analytically without requiring any curve fitting. The resulting Debye model can then be easily integrated in SPICE or a finite-difference time-domain simulator.

Electrical properties and reduced Debye temperature of polycrystalline thin gold films

Abstract: The temperature-dependent electrical properties of four suspended polycrystalline thin gold films with thicknesses of 20.0, 23.0, 36.0 and 54.0 nm have been measured in the temperature range 100–310 K. The measured results show that the electrical resistivity of the films significantly increases while the corresponding temperature dependence decreases compared with bulk gold. The significantly increased electrical resistivity indicates that grain boundary scattering dominates over surface scattering in the studied films. However, fixing the Debye temperature to the bulk value will lead to an erroneous temperature dependence of resistivity. Taking into account the reduced characteristic Debye temperature along with the surface and grain boundary scattering, the electrical properties of the films can be well described in the whole temperature range. The extracted grain boundary reflection coefficient is 0.3 ± 0.03, within the range of the previous reported values, 0.1–0.45. The films' characteristic Debye temperatures decrease from the bulk value of 165 K to between 83 and 121 K and tend to increase with increasing film thickness. This tendency coincides with the previous studies on thin gold, copper, platinum, silver films or wires, and cobalt/nickel superlattices. The possible mechanism responsible for the reduced Debye temperature is phonon softening at the surfaces, grain boundaries, disorder, defects and impurities, part of which has been demonstrated in other studies.

and states of two electron atoms under Debye plasma screening

Abstract: Extensive non-relativistic variational calculations for estimating the energy values of 2 pnd ( D o 1 , 3 ) states [ n = 3 – 6 ] of two electron atoms (He, Li + , Be 2 + ) and 2 pnp ( P e 1 ) [ n = 3 – 8 ] and 2 pnp ( P e 3 ) states [ n = 2 – 7 ] of Be 2 + under weakly coupled plasma screening have been performed using explicitly correlated Hylleraas type basis. The modified energy eigenvalues of P e 1 , 3 states arising from two p electrons of Be 2 + ion and D o 1 , 3 states due to 2 pnd configuration of Li + and Be 2 + ion in the Debye plasma environment are being reported for the first time. The effect of plasma has been incorporated through the Debye screening model. The system tends towards gradual instability and the number of bound states reduces with increasing plasma coupling strength. The wavelengths for 2 pn ′ p ( P e 1 ) [ n ′ = 3 – 8 ] → 2 pnd ( D o 1 ) [ n = 3 – 6 ] and 2 pn ′ p ( P e 3 ) [ n ′ = 2 – 8 ] → 2 pnd ( D o 3 ) [ n = 3 – 6 ] transitions in plasma embedded two electron atoms have also been reported.

Calculation of Debye series expansion of light scattering

Abstract: The Debye series expansion (DSE) is of importance for understanding light scattering features and for testing the validity of geometric optics approach to light scattering. We recast the partial-wave reflection and transmission coefficients so that all the related complex functions can be calculated with stability in all necessary orders. Numerical tests are performed for both the full scattering intensities and the components in a wide range of particle sizes and refractive indices. The results are compared with those from Mie calculation and from MiePlot v4.1, showing that the algorithm is stable, reliable, and robust in a wide range of particle sizes and refractive indices. The developed algorithm may also apply to the DSE calculation of light scattering by multilayered spheres or cylinders.

Effective zero-thickness model for a conductive membrane driven by an electric field.

Abstract: The behavior of a conductive membrane in a static (dc) electric field is investigated theoretically. An effective zero-thickness model is constructed based on a Robin-type boundary condition for the electric potential at the membrane, originally developed for electrochemical systems. Within such a framework, corrections to the elastic moduli of the membrane are obtained, which arise from charge accumulation in the Debye layers due to capacitive effects and electric currents through the membrane and can lead to an undulation instability of the membrane. The fluid flow surrounding the membrane is also calculated, which clarifies issues regarding these flows sharing many similarities with flows produced by induced charge electro-osmosis (ICEO). Nonequilibrium steady states of the membrane and of the fluid can be effectively described by this method. It is both simpler, due to the zero thickness approximation which is widely used in the literature on fluid membranes, and more general than previous approaches. The predictions of this model are compared to recent experiments on supported membranes in an electric field.

Anharmonic correlated Debye model Debye–Waller factors

Abstract: Anharmonic correlated Debye model has been derived for calculation and analysis of extended X-ray absorption fine structure (EXAFS) cumulants using an anharmonic effective potential that takes into account all nearest neighbor interactions of absorber and backscattering atoms. Dispersion relation has been considered, and anharmonic effects are included based on cumulant expansion. Analytical expressions for the first, second, third, and fourth EXAFS cumulants have been derived. They contain anharmonic effective potential parameters. Numerical calculations have been applied to Cu, where Morse potential is used to characterize the interaction between each pair of atoms. The results are found to be in good agreement with experiment.

Communication: High-frequency acoustic excitations and boson peak in glasses: A study of their temperature dependence.

Abstract: The results of a combined experimental study of the high-frequency acoustic dynamics and of the vibrational density of states (VDOS) as a function of temperature in a glass of sorbitol are reported here. The excess in the VDOS at ∼4.5 meV over the Debye, elastic continuum prediction (boson peak) is found to be clearly related to anomalies observed in the acoustic dispersion curve in the mesoscopic wavenumber range of few nm−1. The quasiharmonic temperature dependence of the acoustic dispersion curves offers a natural explanation for the observed scaling of the boson peak with the elastic medium properties.

Effect of the combined action of Faradaic currents and mobility differences in ac electro-osmosis.

Abstract: In this work, we extend previous analyses of ac electro-osmosis to account for the combined action of two experimentally relevant effects: (i) Faradaic currents from electrochemical reactions at the electrodes and (ii) differences in ion mobilities of the electrolyte. In previous works, the ac electro-osmotic motion has been analyzed theoretically under the assumption that only forces in the diffuse (Debye) layer are relevant. Here, we first show that if the ion mobilities of a 1-1 aqueous solution are different, the charged zone expands from the Debye layer to include the diffusion layer. We later include the Faradaic currents and, as an attempt to explore both factors simultaneously, we perform a thin-layer, low-frequency, linear analysis of the system. Finally, the model is applied to the case of an electrolyte actuated by a traveling-wave signal. A steady liquid motion in opposite direction to the applied signal is predicted for some ranges of the parameters. This could serve as a partial explanation for the observed flow reversal in some experiments.

Quadrupole photoionization of hydrogen atoms in Debye plasmas

Abstract: Although a great deal of effort has been devoted to investigating dipole photoionization of plasma-embedded atoms, far less is known about the corresponding quadrupole transitions. In the present work, quadrupole photoionization processes for the ground and excited states of hydrogen atoms in Debye plasma are explored using the method of complex coordinate rotation. The plasma shielding effects on the quadrupole photoionization cross sections are reported for a variety of Debye screening lengths and compared to the dipole results accordingly. Under the perturbation of plasma screening, shape resonances and Cooper-type minima occurring in both dipole and quadrupole photoionization cross sections are presented and discussed. Comparisons are made to other theoretical calculations for the dipole photoionization with good agreement. The present quadrupole results are the first predictions for hydrogen photoionization in Debye plasmas.

Photoionization of the excited He atom in Debye plasmas

Abstract: We present theoretical photoionization cross sections for He 1s2s 1 S and He 1s2p 1 P states in a Debye plasma environment by the complex coordinate rotation method, using a finite L 2 basis set constructed from one electron Laguerre orbitals. The plasma environment is found to appreciably influence the photoionization cross sections near the ionization threshold. In this regard, the photoionization cross sections of isolated He are compared with other theoretical and experimental results. Our results are in good agreement with the previous results. A new minimum appears in the photoionization cross section curve for the metastable 1s2s 1 S state. Results are given for the S- and D-wave partial photoionization for the excited 1s2p 1 P state.

The assessment of the influence of temperature of selected parameters of the approximation method of depolarization current analysis of paper–oil insulation

Abstract: The paper presents the results of experimental investigations of paper–oil insulation samples from the point of view of the assessment of the influence of temperature on the parameters of the approximation method of the time characteristics analysis of depolarization current. Three types of equations: Debye’s function with a single relaxation time, Curie–von Schweidler’s function with triple Debye’s function (taking into account short, average and long relaxation times of paper–oil insulation), and Jonscher’s function with Debye’s function with a single relaxation time were selected as approximation functions, as recommended by literature. The investigated insulation samples were diversified with respect to the degree of dampness and aging. Summing up, the paper focuses on verification of the determined parameters of approximation equations in relation to the influence of insulation temperature and presents recommendations for their application in diagnostics carried out by the PDC (Polarization and Depolarization Current) Method.

Debye Series for Light Scattering by a Nonspherical Particle

Abstract: The Debye series is developed for scattering of light by a homogeneous nonspherical particle to interpret the angular dependence of the scattered intensity in terms of various physical processes. In contrast to the previously developed Debye series for several regularly shaped particles that mirror the orthogonal curvilinear coordinate system where the variable-separation method can be applied, we develop and verify the Debye series in a coordinate-independent way using the extended boundary condition method. Verification computations are made for an oblate spheroidal water droplet of equivalent-volume sphere radius 10 $\ensuremath{\mu}$m.

Dielectric Dispersion of Water in the Frequency Range from 10 mHz to 30 MHz

Abstract: We investigate the dielectric dispersion of water, specially in the low-frequency range, by using the impedance spectroscopy technique. The frequency dependencies of the real R and imaginary χ parts of the impedance could not be explained by means of the usual description of the dielectric properties of the water as an insulating liquid containing ions. This is due to the incomplete knowledge of the parameters entering in the fundamental equations describing the evolution of the system, and on the mechanisms regulating the exchange of charge of the cell with the external circuit. We propose a simple description of our experimental data based on the model of Debye, by invoking a dc conductivity of the cell, related to the nonblocking character of the electrodes. A discussion on the electric circuits able to simulate the cell under investigation, based on bulk and surface elements, is also reported. We find that the simple circuit formed by a series of two parallels of resistance and capacitance is able to ...

Nonlinear theory of the isothermal ion-acoustic waves in the warm degenerate plasma

Abstract: The collisionless unmagnetized degenerate plasma with zero-temperature components is considered. The exact barometric formulas for the electron and ion degenerate gases and the exact expressions for the electron and ion Debye radii are derived. A dispersion relation for the isothermal ion-acoustic waves is obtained and analyzed and an exact solution for the linear velocity of the ion sound is found. The domains of parameters in which the soliton solutions can be found are determined using the analysis of the dispersion relation. The nonlinear theory of the isothermal ion-acoustic waves is developed and employed to obtain and to analyze the exact solution of the original equations. The analysis is based on the method of the Bernoulli pseudopotential. The ranges of the phase velocities of the periodic ion-acoustic waves and the soliton velocities are determined. It is demonstrated that the ranges are not overlapped and that the soliton velocity cannot be less than the linear velocity of the ion sound. The profiles of physical quantities in the periodic wave and soliton are constructed.