Showing papers on "Debye published in 1999"
TL;DR: In this paper, a description of the e (ν) spectra requires the superposition of two Debye processes, and the interpretation of the fast process with the relaxation time τ 2 requires additional information, whereas it is possible to relate the relaxation times τ 1 of the dominating slow process to the production rate of mobile water molecules.
549 citations
TL;DR: In this article, the temperature dependencies of the fundamental energy gaps of group-IV, III-V, and II-VI materials are fitted by means of a relatively simple analytical four-parameter expression.
Abstract: The temperature dependencies of the fundamental energy gaps of group-IV, III-V, and II-VI materials are fitted by means of a relatively simple analytical four-parameter expression. This is shown here to be capable of providing fine numerical fittings in combination with physically reasonable estimations of basic parameters. The majority of the materials under study are found to pertain to the regime of intermediate dispersion, where neither Varshni's formula nor the Bose-Einstein-related model function are capable of producing adequate fits. The effective phonon temperatures are estimated to amount as a rule to fractions of about 0.5 to 0.7 of the corresponding Debye temperatures. The availability of experimental E(T) data up to the vicinity of the Debye temperature in a given material is found to be a necessary condition for trustworthy determinations of the limiting slopes of the E(T) curves in the high-temperature region. This is achieved here for many materials by simultaneous fittings of fractional data sets owing to different authors and/or different experimental methods. The general cause of break-down of Varshni's formula, which has been noticed particularly in wide bandgap material studies, is clearly shown here by an inspection of higher-order derivatives to be due to its largely inadequate (ad hoc imputed) analytical form.
175 citations
TL;DR: Wang et al. as discussed by the authors used the linearized semiclassical initial value representation (LSC-IVR) to study the nonadiabatic dynamics of the spin-boson problem, a system of two electronic states linearly coupled to an infinite bath of harmonic oscillators.
Abstract: The linearized semiclassical initial value representation (LSC-IVR) [H. Wang, X. Sun and W. H. Miller, J. Chem. Phys. 108, 9726 (1998)] is used to study the nonadiabatic dynamics of the spin-boson problem, a system of two electronic states linearly coupled to an infinite bath of harmonic oscillators. The spectral density of the bath is chosen to be of the Debye form, which is often used to model the solution environment of a charge transfer reaction. The simulation provides a rather complete understanding of the electronically nonadiabatic dynamics in a broad parameter space, including coherent to incoherent transitions along all three axes (the T-axis, the η-axis, and the ωc-axis) in the complete phase diagram and the determination of rate constants in several physically interesting regimes. Approximate analytic theories are used to compare with the simulation results, and good agreement is found in the appropriate physical limits.
167 citations
TL;DR: Parameterization has been made for the temperature dependence of the Debye-Waller factors of 68 elemental crystals and 17 compounds with the zinc-blende structure.
Abstract: Parameterization has been made for the temperature dependence of the Debye–Waller factors of 68 elemental crystals and 17 compounds with the zinc-blende structure. The Debye–Waller factors of 46 elemental crystals were calculated based on the available phonon density of states, and those of the remaining 22 elemental crystals were estimated using the Debye approximation for the phonon density of states. The Debye–Waller factors of the zinc-blende compounds were obtained from the 14-parameter shell-model calculations of Reid [Acta Cryst. (1983), A39, 1–13].
137 citations
93 citations
TL;DR: The temperature dependence of X-band electron spin-lattice relaxation between about 10 and 300 K in magnetically dilute solids and up to the softening temperature in glassy solvents was analyzed for three organic radicals and 14 S = 12 transition metal complexes.
91 citations
TL;DR: In this paper, the elastic properties and thermal expansion of TiC, TiN, VC and VN are calculated by means of a precise first-principles electronic structure method. And the contribution of lattice vibrations to the thermal properties is modelled by Debye's approximation for phonon dispersion.
Abstract: The elastic properties and thermal expansion of TiC, TiN, VC and VN are calculated by means of a precise first-principles electronic structure method. The single-crystal elastic constants are derived from the total energies of distorted structures. For the thermal expansion, the contribution of electronic states is determined within a free-electron model utilizing the density of states at the Fermi energy of the actual materials. The contribution of lattice vibrations to the thermal properties is modelled by Debye's approximation for phonon dispersion. Anharmonic effects are included via Gruneisen's theory requiring the volume dependence of the Debye temperature. For the calculation of the Gruneisen parameter, volume- and pressure-dependent single-crystal elastic constants are needed. Since in reality refractory compounds always contain vacancies, the influence of vacancies is studied for vanadium carbides by a supercell of composition VC0.75. It is found that vacancies significantly increase the...
81 citations
TL;DR: In this paper, the nonperturbative g 2 T -contribution to the Debye mass in the deconfined QCD plasma phase can be determined from a single Wilson line operator in the three-dimensional pure SU(3) gauge theory.
69 citations
TL;DR: In this paper, the temperature dependence of the lattice constant was analyzed in terms of Debye and Einstein contributions and using MaxEnt techniques to reconstruct a Gruneisen-parameter-weighted phonon density of states.
Abstract: Accurate lattice parameters have been determined between 2 K and 520 K for the negative thermal expansion compound ZrW2O8, by high-resolution neutron powder diffraction measurements. Two different analyses of the temperature dependence of the lattice constant i) in terms of Debye and Einstein contributions and ii) using MaxEnt techniques to reconstruct a Gruneisen-parameter–weighted phonon density of states both provide direct evidence that the negative thermal expansion behaviour is driven by low-frequency modes with an energy scale of 3–8 meV. Comparison with earlier specific heat measurements indicates that these rigid-unit modes are associated with very large Gruneisen parameters.
63 citations
TL;DR: In this paper, a new theory based on the ideas derived from the work of Debye and Huckel, Bjerrum, and Onsager is proposed to explain the absence of the anticipated critical point in this system.
Abstract: We explore the equilibrium properties of a system composed of dipolar hard spheres. A new theory based on the ideas derived from the work of Debye and H\"uckel, Bjerrum, and Onsager is proposed to explain the absence of the anticipated critical point in this system.
58 citations
TL;DR: A phenomenological function is proposed, which not only reproduces observations on biological tissues but also includes all of Jonscher's "universal response," the Debye, Cole-Cole, and Davidson-Cole functions, as its special cases.
Abstract: The remarkably broad dielectric dispersions exhibited by solid dielectrics are well-known examples of the failure of Debye's relaxation theory; such dispersions are much better represented by a ``fractional power law'' described by Jonscher [A. K. Jonscher, Nature 267, 673 (1977)] as the ``universal dielectric response.'' As it happens, however, recent experimental advances in this field suggest that neither of the two approaches is general enough to cope with the dielectric response of biological tissues, which combines striking features from both types of behavior. A phenomenological function is therefore proposed, which not only reproduces observations on biological tissues but also includes all of Jonscher's ``universal response,'' the Debye, Cole-Cole, and Davidson-Cole functions, as its special cases.
TL;DR: In this article, a theory for a new effect, the migration of solid dispersed particles initiated by a nonuniform temperature field, is discussed, the reason for the motion is the inhomogeneity of the properties of a thin protective layer around a particle.
Abstract: This paper discusses a theory for a new effect, the migration of solid dispersed particles initiated by a nonuniform temperature field. The reason for the motion is the inhomogeneity of the properties of a thin protective layer around a particle. The example of ionic dispersion shows that the sign of the coefficient of thermodiffusion depends on the magnitude of the electrostatic potential at the particle surface and the thickness of the Debye layer and that the coefficientis larger than the values known for molecular systems by a factor of 100 to 10000. In contrast to molecular systems, in disperse systems thermodiffusion should play a much more important role.
TL;DR: In this paper, the dynamic order parameter and dielectric susceptibility for relaxor ferroelectrics like PbMg1/3Nb2/3O3, PbSc1/2Ta 1/2O3 and Pb1−xLaxZryTi1−yO3 were calculated.
Abstract: We calculate the dynamic order parameter and dielectric susceptibility for the relaxor ferroelectrics like PbMg1/3Nb2/3O3, PbSc1/2Ta1/2O3 and Pb1−xLaxZryTi1−yO3. Calculations of temperature and frequency dependence of dielectric susceptibility show the existence of low- and high-temperature group of maxima obeyed to Vogel–Fulcher (VF) and Arrhenius laws, respectively. The VF law and non-Debye relaxation behavior as well as the stretched exponential law of susceptibility time decay were shown to be the consequence of random fields distribution which transforms single dipole Arrhenius and Debye laws into VF and non-Debye, stretched exponential laws, respectively. Comparison of observed and calculated characteristics of the relaxors is carried out.
TL;DR: In this article, a set of covariant equations describing the dynamics of mean fields and their statistical fluctuations in a non-Abelian plasma in or out of equilibrium is derived, and a general procedure is detailed for integrating out the fluctuations as to obtain the effective transport equations for the mean fields.
TL;DR: By finding ab initio values for nearly all free parameters in the theory, the number of parameters to be fit for the second hydration shell of the aqueous chromium +3 cation is greatly reduced, allowing an unambiguous resolution of this controversy.
Abstract: Controversy exists on whether the second hydration shell of the aqueous chromium +3 cation is observable by XAFS. The problem is aggravated by strong first shell multiple scattering contributions competing with the second hydration shell signal. By finding ab initio values for nearly all free parameters in the theory, we greatly reduce the number of parameters to be fit, thus allowing an unambiguous resolution of this controversy. Quantum chemistry calculations yielded a parameterized force field model which was used in classical molecular dynamics simulations to calculate all the multiple scattering Debye-Waller factors. The self-consistent FEFF8 code fixes Eo to within 1 eV. The predicted spectrum is in good agreement with experiment. Fitted distances for the first and second hydration shell are 2.0008 + 0.0068/~ and 3.914 40.096/~, respectively. The second shell is shown to be responsible for about 1/3 of the XAFS Fourier transformed signal at the position of the second shell.
TL;DR: In this paper, a simple model system consisting of a single source charged particle is studied to show that the maximum electrostatic energy error incurred by anM-order multipole expansion for the Yukawa potential is bounded above by the error of the equivalent multipole extension for the Coulombic potential.
TL;DR: In this article, the authors examine the equilibrium properties of hot, dilute, non-relativistic plasmas and obtain explicit results for density-density correlation functions through two-loop and thermodynamic quantities through three-loop order.
Abstract: We examine the equilibrium properties of hot, dilute, non-relativistic plasmas. The partition function and density correlation functions of a classical plasma with several species are expressed in terms of a functional integral over electrostatic potential distributions. The leading order, field-theoretic tree approximation automatically includes the effects of Debye screening. Subleading, one-loop corrections are easily evaluated. The two-loop corrections, however, have ultraviolet divergences. These correspond to the short-distance, logarithmic divergence which is encountered in the spatial integral of the Boltzmann exponential when it is expanded to third order in the Coulomb potential. Such divergences do not appear in the underlying quantum theory --- they are rendered finite by quantum fluctuations. We show how such divergences may be removed and the correct finite theory obtained by introducing additional local interactions in the manner of modern effective quantum field theories. We obtain explicit results for density-density correlation functions through two-loop order and thermodynamic quantities through three-loop order. The induced couplings are shown to obey renormalization group equations, and these equations are used to characterize all leading logarithmic contributions in the theory. A linear combination of pressure and energy and number densities is shown to be described by a field-theoretic anomaly. The effective theory allows us to evaluate very easily the algebraic long-distance decay of density correlation functions.
TL;DR: In this paper, the orientation of pyrimidine in a strong electric field was measured using resonantly enhanced multiphoton ionization (REMPI) and laser induced fluorescence (LIF).
Abstract: Orientation of pyrimidine in a strong electric field was measured using resonantly enhanced multiphoton ionization (REMPI) and laser induced fluorescence (LIF). The ion and fluorescence yields showed preference for perpendicular excitation relative to the orientation field, implying a perpendicular relationship between the permanent dipole and the transition dipole. Calculation results using a linear variation method reproduced the observed spectral features, overall transition intensity, and polarization preference of the excitation laser. The permanent dipole of the S1 state of pyrimidine was thereby determined to be +0.6 Debye. Measurements of polarization preferences in photoexcitation, i.e., linear dichroism, provide a direct approach for determination of transition dipole moments. A general theory of deriving directions of transition dipoles relative to permanent dipoles based on this type of measurement/calculation was also developed. In addition, we report observations of complex relaxation dynami...
TL;DR: In this article, a high pure wurtzite structure GaN was determined by powder X-ray diffraction using the Rietveld technique and the positions in the unit cell for Ga and N were refined to be (0, 0, 0) and (0. 0, 1.3814).
Abstract: High Pure Wurtzite structure GaN has been synthesized by gas reaction method. Its structure was determined by powder X-ray diffraction using the Rietveld technique. The positions in the unit cell for Ga and N were refined to be (0, 0, 0) and (0, 0, 0.3814). The Debye temperature was determined as 586 K from the refined temperature factor by using the Debye approximation.
TL;DR: In this article, it was shown that both the slab ion temperature gradient and the slab electron temperature gradient (ETG) modes have three types of branches in the negative shear configuration: a single mode rational surface mode, a double mode-rational surface mode and a nonresonant mode.
Abstract: With a gyrokinetic integral eigenvalue code, it is shown that both the slab ion temperature gradient (ITG) mode and the slab electron temperature gradient (ETG) mode have three types of branches in the negative shear configuration: a single mode-rational surface mode, a double mode-rational surface mode, and a nonresonant mode. For typical fusion plasma parameters satisfying λDe2≫ρte2, a Weber-type differential eigenmode equation of the ETG mode becomes essentially different from that of the ITG mode, because of the Debye shielding effect, where λDe is the Debye length and ρte is the electron Larmor radius. A scale length of the ETG modes is characterized by λDe, and different types of analytic solutions are obtained for the ETG modes. From a comparison of the transport coefficient based on the mixing length theory, it is shown that in the negative shear configuration, the slab ETG mode gives an order of magnitude larger transport coefficient compared with an estimate for the conventional normal-sheared s...
TL;DR: It is shown both theoretically and experimentally that the critical temperature of the transition can be controlled by bulk ion density through its relation to the density of adsorbed ions.
Abstract: We study the anchoring mechanism due to substrate-adsorbed ions by examining a related anchoring transition An analytical solution to the Poisson equation shows that, as their number suffices for a non-negligible anchoring contribution, the surface field is screened over some characteristic microscopic distance It is shown both theoretically and experimentally that the critical temperature of the transition can be controlled by bulk ion density through its relation to the density of adsorbed ions
TL;DR: The dynamical evolution of an intense ultrashort sub-10-fs two-cycle optical pulse is considered as it propagates through a transparent third-order dielectric medium characterized by three resonance lines and a finite sub-fs relaxation time of the electronic nonlinearity.
Abstract: The dynamical evolution of an intense ultrashort sub-10-fs two-cycle optical pulse is considered as it propagates through a transparent third-order dielectric medium characterized by three resonance lines and a finite sub-fs relaxation time of the electronic nonlinearity. Numerical integration of the full Maxwell's equations incorporating triple-resonance Lorentz linear dispersion and Debye nonlinear dispersion, for a linearly polarized electromagnetic pulse centered at ${\ensuremath{\lambda}}_{0}=1.24\ensuremath{\mu}\mathrm{m}$ in the normal dispersion region near the zero dispersion wavelength, shows the formation of shocks occurring on the optical cycle due to the generation of optical harmonics. The finite relaxation time of the nonlinear electronic response (sub-fs time scale) (i) slows down the steepening rate of the optical cycle; (ii) does not limit the generation of strongly phase matched optical harmonics, and consequently the development of infinitely sharp edges on the optical cycle producing its breaking when linear dispersion is not included; (iii) reduces the production of phase matched harmonics and consequently the sharpening of the jumps when dispersion is present, compared to the case of an instantaneous nonlinear response; and (iv) reduces the harmonic spectrum spreading and modulation at later times on the appearance of self-steepening of the electric field envelope.
03 Oct 1999
TL;DR: In this paper, an evaluation of the Debye polarization cell as a model for a double-layer capacitor (DLC) is presented, and the circuit element values are found from AC impedance measurements for a DLC and a computer program which utilizes a nonlinear least squares fitting technique.
Abstract: Many different circuit models have been proposed for double-layer capacitors (DLCs). Presented in this paper is an evaluation of the Debye polarization cell as a model for a double-layer capacitor (DLC). In comparison to other circuit models, the primary advantage of this model is that the circuit elements can be related to chemical reactions which occur inside the DLC. The circuit element values are found from AC impedance measurements for a DLC and a computer program which utilizes a nonlinear least-squares fitting technique. Variations in circuit element values with DC bias level and manufacturing have been investigated. The performance of the Debye polarization cell in slow discharge and pulse load applications has been compared to actual circuit measurements and to simulated results using a classical equivalent circuit.
TL;DR: In this article, a general explanation for the breakdown of Debye-Stokes-Einstein relations in glass-forming liquids is given in the framework of the coupling model, which is based on the fact that different dynamie variables may have different coupling parameters entering into the stretch exponents of their Kohlrausch correlation functions.
Abstract: The breakdown of Debye-Stokes-Einstein and Stokes-Einstein relations in glass-forming liquids is shown to be a special case of a more general phenomenon. A general explanation is given in the framework of the coupling model, which is based on the fact that different dynamie variables may have different coupling parameters entering into the stretch exponents of their Kohlrausch correlation functions. In most of the applications, the explanation requires no adjustable parameter. An exception is the explanation of the breakdown of a Stokes-Einstein relation where an experimental technique has not yet been developed to determine the coupling parameter of translational diffusion. We can explain also the breakdown of the Debye-Stokes-Einstein relation of depolarized light scattering data of the liquid diglycidyl ether of bisphenol-A. This breakdown oceurs at high temperatures due to a reduction of the light scattering relaxation rate as compared with the shear stress relaxation rate. This behaviour is ...
TL;DR: In this article, a new MC study of ISB at finite temperature in a Z 2 × Z 2 λφ 4 model in four dimensions is presented, where the gap equations for the Debye masses, resulting from the resummation of the ring diagrams, seem to provide a qualitatively correct description of the data.
TL;DR: In this article, the specific heat of a one-dimensional hexagonal quasicrystal was studied using the Debye approach for studying specific heat properties of a crystal to a quasICrystal.
Abstract: Extending the Debye approach for studying the specific heat of a crystal to a quasicrystal, this study gives the formula of the specific heat of a one-dimensional hexagonal quasicrystal.
Journal Article•
TL;DR: In this article, the effect of addition of Al 2 O 3 to lithium-borate base glass in the place of both lithium and boron has been studied through the acoustical properties of the glasses.
Abstract: The effect of addition of Al 2 O 3 to lithium-borate base glass in the place of both lithium and boron has been studied through the acoustical properties of the glasses. The ultrasonic velocity and attenuation for various compositions of Al 2 O 3 -containing lithium-borate glasses were measured at 5MHz at room temperature (303K). The elastic moduli, Debye temperature, Poisson's ratio and other acoustical parameters were obtained from the experimental data. The structural changes in the glass network are discussed in terms of the formation of non-bridging oxygen (NBO) with addition of Al 2 O 3 to the base glass. Further, the nature of variation of Debye temperature [in both acoustical and optical (IR)] is used to explain the effect of addition of Al 2 O 3 to the lithium-borate base glass. The relation between the acoustical and optical Debye temperatures is also discussed.
TL;DR: In this paper, the static structure factor of a strongly coupled system was investigated using a viscoelastic fluid theory, which allows for internal energy relaxation, and the corresponding dispersion relation for dust-acoustic waves was derived.
Abstract: Dust shielding and correlation function are investigated using a viscoelastic fluid theory, which allows for internal energy relaxation. The corresponding dispersion relation for dust-acoustic waves is derived. The dust static structure factor is calculated using the fluctuation-dissipation theorem. It is found that when the shear viscosity and relaxation time satisfy a certain condition the static structure factor of the strongly coupled system retains the Debye–Huckel form. In general, the characteristic shielding of the dust is found to be determined by a combination of the dust and plasma Debye lengths.
TL;DR: The analysis indicates that the globbic scattering factors will be useful in efforts to develop procedures for direct-methods phasing of diffraction data to approximately 3.5 A resolution from protein crystals.
Abstract: Using Harker's [Harker (1953). Acta Cryst. 6, 731–736] idea of spherically averaged polyatomic groups or `globs' as the units of structure suitable for analyzing low-resolution diffraction data from protein crystals, `globbic' scattering factors have been calculated for main-chain peptide units and amino-acid side-chain groups to 3 A resolution via Debye's [Debye (1915). Ann. Phys. (Leipzig), 46, 809–823] scattering formula. It is shown that the scattering factors are insensitive to intra-globbic conformational variation and can be approximated fairly well by a single-Gaussian formula, i.e. fg(s) = Zg exp(−1.7Zgs2), where s = (sinθ)/λ and Zg is the total electron count for the atoms of the glob. Phase errors due to the globbic approximation and their effect on electron-density maps at 3.5 A resolution have been assessed via calculations for the crambin structure; this analysis indicates that the globbic scattering factors will be useful in efforts to develop procedures for direct-methods phasing of diffraction data to ∼3.5 A resolution from protein crystals.
TL;DR: In this article, two complementary optical techniques, second-harmonic generation (SHG) and electric birefringence, are used to observe chromophore dynamics in an amorphous polymer above Tg.
Abstract: Two complementary optical techniques, second-harmonic generation (SHG), and electric birefringence are used to observe chromophore dynamics in an amorphous polymer above Tg. In particular, a random copolymer of isobutyl methacrylate and a disperse red 1-labeled methacrylate (mole ratio 94:6) is quantitatively studied over a range of time scales and temperatures. In doing so, two models of reorientation are tested: one considers the chromophores motions as small correlated diffusive steps (Debye rotation) and the other describes the motions in terms of uncorrelated instantaneous jumps. Given that SHG is sensitive to the first moment of the orientational autocorrelation function (OACF), or 〈cos θ〉 (where θ is the polar angle between the poling field and the permanent dipole moment directions), and birefringence to the second, or 〈cos2 θ〉, the ability of the models to describe chromophore motion is tested by comparing their predictions of the relationship between the OACFs and the measured properties. By inv...