共查询到20条相似文献,搜索用时 62 毫秒
1.
An effort has been undertaken to understand the nature of one type of non-exponential relaxation, namely Cole-Davidson relaxation.
Toward this end, a model of relaxation as a self-similar process is proposed. An equation containing operators of fractional
integration and differentiation is obtained and solved, which the relaxation function obeys in this case.
Fiz. Tverd. Tela (St. Petersburg) 39, 101–105 (January 1997) 相似文献
2.
M. G. Tonkonogov T. A. Kuketaev Zh. T. Ismailov K. K. Fazylov 《Russian Physics Journal》1998,41(2):161-166
A kinetic equation is found which is written taking account of tunneling transitions for proton relaxation with a potential
shape represented by a multiwell model having parabolic barriers. Study of the solution allows one to establish the proton
relaxation mechanism in dielectrics and calculate the complex dielectric constant. Comparison with experiment shows acceptable
agreement between calculated and experimental charts.
Karaganda State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 80–85, February, 1998. 相似文献
3.
We define a nonlinear model for fractional relaxation phenomena. We use ε-expansion method to analyse this model. By studying the fundamental solutions of this model we find that when t → 0 the model exhibits a fast decay rate and when t → ∞ the model exhibits a power-law decay. By analysing the frequency response we find a logarithmic enhancement for the relative
ratio of susceptibility. 相似文献
4.
J. Schmiedeskamp W. Heil E. W. Otten R. K. Kremer A. Simon J. Zimmer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(3):427-438
In this first in a series of three papers on wall relaxation of spin
polarized, gaseous 3He we investigate both by theory and by experiment
surface-induced spin relaxation due to paramagnetic sites in the containing
glass. We present experimental and theoretical evidence that — contrary to
the traditional opinion — distant dipolar coupling to paramagnetic
impurities in the glass, in particular iron ions, cannot be the dominant
relaxation mechanism of 3He-spins, although iron dominates the bulk
static permeability. Instead dangling-bond type defects in the glass matrix
are found to interact much stronger via the isotropic Fermi contact
interaction. A model of paramagnetic site controlled 3He relaxation
including the Fermi contact interaction is presented. With reasonable
semi-empirical assumptions our model allows to describe satisfactorily the
measured relaxivities, both in the dissolution-dominated regime of fused
silica or borosilicate glasses of the Pyrex type as well as in the surface
dominated situation of aluminosilicate glasses which have only a low
permeability for He atoms. In a large sample of 1.1 litre cells, built from
various aluminosilicate glasses, an average relaxation time of 150 h is
reached in case contaminant ferromagnetic particles have been demagnetized
beforehand. From the maximum observed value of 250 h we derive after
subtraction of dipolar relaxation in the gas phase a paramagnetic surface
relaxivity of ρ<0.005 cm/h at room temperature. 相似文献
5.
R. Mélin K. Biljaković J.C. Lasjaunias P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):417-430
We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon.
The very low temperature specific heat relaxation experiments are characterized by: (i) “interrupted” ageing (meaning that
there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective
phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain
an estimate of the glass cross-over temperature (typically T
g≃ 100-200 mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving
randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and
can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising
model [D.S. Fisher, P. Le Doussal, C. Monthus, Phys. Rev. Lett. 80, 3539 (1998)]. The typical relaxation time scales like ∼τexp(T
g/T). The glass cross-over temperature Tg related to correlations among solitons is equal to the average energy barrier and scales like T
g∼ 2xξΔ. x is the concentration of defects, ξ the correlation length of the CDW or SDW and Δ the charge or spin gap.
Received 12 December 2001 相似文献
6.
7.
Théneau C Salmerón Sánchez M Rodríguez Hernández JC Monleón Pradas M Saiter JM Gómez Ribelles JL 《The European physical journal. E, Soft matter》2007,24(1):69-77
The enthalpy relaxation of polymer-silica nanocomposites prepared by simultaneous polymerization of poly(2-hydroxyethyl methacrylate)
(PHEMA) and tetraethyloxysilane, TEOS, a silica precursor, is investigated. Both the glass transition temperature, Tg, and the temperature interval of the glass transition, ΔT
g , increase as the silica content in the sample does. Structural relaxation experiments show that the temperature interval
in which conformational motions take place broadens as the silica content in the hybrid increases. A phenomenological model
based on the evolution of the configurational entropy during the structural relaxation process, the SC model, has been used
for determining the temperature dependence of the relaxation times during the process. The results show an increase of the
fragility of the polymer as the silica content increases, a feature that can be related to the broadening of the distribution
of relaxation times characterized by the β parameter of the stretched exponential distribution. On another hand the silica
content increase produces a significant change of the relaxation times in the glassy state. 相似文献
8.
A. I. Bezuglyi V. A. Shklovskii 《Journal of Experimental and Theoretical Physics》1997,84(6):1149-1163
The theoretical analysis of experiments on pulsed laser irradiation of metallic films sputtered on insulating supports is
usually based on semiphenomenological dynamical equations for the electron and phonon temperatures, an approach that ignores
the nonuniformity and the nonthermal nature of the phonon distribution function. In this paper we discuss a microscopic model
that describes the dynamics of the electron-phonon system in terms of kinetic equations for the electron and phonon distribution
functions. Such a model provides a microscopic picture of the nonlinear energy relaxation of the electron-phonon system of
a rapidly heated film. We find that in a relatively thick film the energy relaxation of electrons consists of three stages:
the emission of nonequilibrium phonons by “hot” electrons, the thermalization of electrons and phonons due to phonon reabsorption,
and finally the cooling of the thermalized electron-phonon system as a result of phonon exchange between film and substrate.
In thin films, where there is no reabsorption of nonequilibrium phonons, the energy relaxation consists of only one stage,
the first. The relaxation dynamics of an experimentally observable quantity, the phonon contribution to the electrical conductivity
of the cooling film, is directly related to the dynamics of the electron temperature, which makes it possible to use the data
of experiments on the relaxation of voltage across films to establish the electron-phonon and phonon-electron collision times
and the average time of phonon escape from film to substrate.
Zh. éksp. Teor. Fiz. 111, 2106–2133 (June 1997) 相似文献
9.
On the basis of a calculation of the structural relaxation rate and an experimental acoustical-emission determination of the
temperature of the transition from localized to uniform flow it is argued that the type of plastic deformation of metallic
glasses is uniquely determined by the kinetic structure of the relaxation. In the case of a kinetically hindered structural
relaxation, which is characteristic for tests of initial samples at temperatures T<380–420 K, a localized dislocational deformation is realized. At higher temperatures, “memory” of the thermal prehistory
of the samples is lost (aging at room temperature), the structural relaxation rate grows abruptly and plastic flow becomes
uniform viscoplastic flow.
Fiz. Tverd. Tela (St. Petersburg) 41, 2167–2173 (December 1999) 相似文献
10.
Diffusion and relaxation of the fractional order in fractal media in the classical and quantum cases
V. S. Kirchanov 《Russian Physics Journal》2009,52(4):343-353
Two model examples of the application of fractional calculus are considered. The Riemann–Liouville fractional derivative with
0 < α ≤ 1 was used. The solution of a fractional equation, which describes anomalous relaxation and diffusion in an isotropic
fractal space, has been obtained in the form of the product of a Fox function by a Mittag-Leffler function. The solution is
simpler than that given in Ref. 6 and it generalizes the result reported in Ref. 7. For the quantum case, a solution of the generalized Neumann–Kolmogorov fractional quantum-statistical equation has been
obtained for an incomplete statistical operator which describes the random walk of a quantum spin particle, retarded in traps
over a fractal space. The solution contains contributions from quantum Mittag-Leffler (nonharmonic) fractional oscillations,
anomalous relaxation, noise fractional oscillations, and exponential fractional diffusion oscillation damping. 相似文献
11.
A. Díaz-Sánchez A. Pérez-Garrido 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):483-486
The relaxation of the specific heat and the entropy to their equilibrium values is investigated numerically for the three-dimensional
Coulomb glass at very low temperatures. The long time relaxation follows a stretched exponential function, f (t) = f
0exp - (t/τ)β
, with the exponent β increasing with the temperature. The relaxation time diverges as an Arrhenius law when T→ 0.
Received 24 May 2001 and Received in final form 12 September 2001 相似文献
12.
V. G. Bar’yakhtar A. L. Sukstanskii E. Yu. Melikhov 《Journal of Experimental and Theoretical Physics》1997,84(5):893-902
We study the relaxation two-parameter one-dimensional solitons in antiferromagnets using the phenomenological theory. Allowing
for relaxation terms of a relativistic and exchange nature, we set up a system of evolution equations for the constants of
the motion of a soliton and calculate the corresponding integral curves, which describe the variation of the soliton parameters
in the relaxation process.
Zh. éksp. Teor. Fiz. 111, 1633–1650 (May 1997) 相似文献
13.
A density matrix formalism is developed for anelastic (mechanical) relaxation in crystalline materials with point defects
characterized by elastic dipoles. The time-dependent approach to equilibrium of the strain response under the action of a
constant applied stress is deduced. The formalism parallels the one used in nuclear magnetic relaxation. The anelastic relaxation
time is determined as a function of the parameters occurring in the defect hopping term in the Hamiltonian. This term is responsible
for the dissipation of the anelastic ‘potential’ energy into the host lattice. In a lengthy concluding section, the following
aspects are discussed point by point: the advantages of the formalism presented, its scope and special cases; the physical
implications of the expression obtained for the relaxation time; the similarities and differences between magnetic relaxation
and anelastic relaxation, etc. 相似文献
14.
The features of the postexposure relaxation of holographic gratings recorded in inhomogeneous polyvinyl acetate latex films
with photosensitive agents (photochromic molecules of fulgide dyes and phenanthrenequinone) have been considered. The diffusion
coefficients and rms displacements of izomerized probe in polymer latex particles and aqueous environment are determined within
the model of two diffusion states. The effective diffusion coefficient of the molecular probe, which is responsible for the
relaxation of gratings, increases with an increase in their period in wet films, whereas in dry films, this parameter is independent
of the grating period. In the films subjected to high-temperature treatment the effective diffusion coefficient decreases
with an increase in the grating period. The successive stages of grating relaxation in latex films with phenanthrenequinone
are related to the diffusion of free molecules, radicals, and polymer chains, as well as to the local displacement of macromolecular
segments at distances of 5–25 nm. 相似文献
15.
V. V. Gladkii V. A. Kirikov E. S. Ivanova S. V. Nekhlyudov 《Physics of the Solid State》1999,41(3):447-452
The characteristic features of the polarization and depolarization kinetics of polydomain ferroelectrics with square and narrow
“extended” dielectric hysteresis loops are investigated for the model of TGS and Rb2ZnCl4 crystals. It is shown that for the second crystal, in contrast to the first crystal, the local free energy is asymmetric
relative to the direction of polarization, the coercive field does not have a definite value, and only part of the crystal
volume participates in the slow thermoactivational relaxation. The slow relaxation follows a universal empirical power law
in all cases. The distribution functions of the relaxation times in crystals are constructed on the basis of experimental
data, and comparative estimates are made of the relaxation parameters and the parameters of the energy barriers for domain
walls.
Fiz. Tverd. Tela (St. Petersburg) 41, 499–504 (March 1999) 相似文献
16.
The three dominant mechanisms giving major contributions to vibrational relaxation in molecular systems are (a) pure dephasing,
(b) depopulation (or energy relaxation), and (c) resonant transfer. Here (c) is not considered but the effects due to thesimultaneous occurrence of (a) and (b) are treated within a stochastic model. In dealing with (a), the vibrational frequency is assumed
to undergo random uncorrelated ‘jump’, due to fluctuations in the environment of the active molecule between a continuous
set of values. The ensuing results are somewhat different from those of the commonly used Kubo model of vibrational dephasing,
especially at long times and appear to be better suited in interpreting certain experimental data. The model is next extended
to include the simultaneous occurrence of (b). The calculation leads to two important conclusions: (i) the lineshape is not
just the convolution of those due to (a) and (b), and (ii) the lineshape is asymmetric, if the intermolecular interactions
are not isotropic. 相似文献
17.
S. I. Lyabuk 《Russian Physics Journal》2007,50(11):1124-1129
A mechanism of stress relaxation in metastable alloys is considered. It is demonstrated that structural transformations during
a relaxation test lead to anomalously high stress relaxation. Two stages of structural relaxation are revealed: formation
of defect-free channels and decomposition of a solid solution. A new method of program hardening of metastable alloys based
on the structural relaxation processes is suggested.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 56–61, November, 2007. 相似文献
18.
Some results on NMR and relaxation studies of the Van Vleck paramagnet TmES (thulium ethylsulphate) and the Ising ferromagnet
DyES are summarized. Complicated but regular quasistatic internal magnetic fields are created by Tm and Dy ions in these compounds.
These fields fluctuate due to the thermal excitation of tne ions and the energy transfer from one ion to another. Fluctuations
give rise to NMR line shifts, broadening of the lines and spin-lattice relaxation, the shifts, linewidth and spin-lattice
relaxation rate being proportional to exp(−Δ/kT) at low temperatures (kT≪Δ, Δ is an excitation energy). Pre-exponential factors
depend on fluctuating fields in a definite but complicated manner, so estimates of the correlation time (electron spin-spin
relaxation time) can be obtained from measurements of nuclear relaxation rates. 相似文献
19.
声在多原子分子气体中传播所引起的弛豫过程是探索气体特性的重要方面. 本文通过研究气体声弛豫过程中振动自由度与平动自由度(V-T)以及振动自由度之间(V-V)的分子能量转移模型, 给出了有效比热容与弛豫时间的分解对应关系及其通用获得方法. 该分解模型与现有的声弛豫模型相比, 反映了分解后的V-T 和V-V弛豫过程中振动比热容与弛豫时间的对应关系, 并发现了较高能级是引起对应声弛豫过程的决定因素. 将基于该分解模型获得的气体声弛豫衰减谱经碰撞直径微调改进后, 比现有理论更接近实验数据, 其结果证明了该分解对应关系的正确性和合理性. 相似文献
20.
D. W. Cooke R. H. Heffner R. L. Hutson M. E. Schillaci J. L. Smith J. O. Willis D. E. Maclaughlin C. Boekema R. L. Lichti A. B. Denison J. Oostens 《Hyperfine Interactions》1986,31(1-4):425-430
Positive muon spin relaxation experiments have been conducted on the heavy-fermion superconductor UPt3 in both the normal and superconducting states for zero, transverse, and longitudinally applied magnetic fields. Below 6 K
in zero applied field, the μ+ relaxation rate is approximately twice that expected from195Pt nuclear dipolar relaxation alone. Transverse- and longitudinal-field measurements show that the observe relaxation rate
depends on magnetic field and is quasistatic in origin. It is suggested that the onset of very weak (≈10−3 μB/U atom) magnetic ordering below approximately 6 K is responsible for the observed increase in the relaxation rate. μ+ Knight shift measurements in the normal state of UPt3 show a temperature dependent shift Kμ which tracks the bulk susceptibility X. From the Kμ vs. X plot, a μ+ hyperfine field of approximately 100 Oe/μB is extracted. 相似文献