共查询到20条相似文献,搜索用时 0 毫秒
1.
A. S. Tchakoutio Nguetcho P. B. Ndjoko T. C. Kofane 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(1):7-14
The proton conductivity and the mobility arising from motions of the
ionic and bonded defects, in hydrogen-bonded molecular systems are
investigated by means of the quantum mechanical method. Our two component
model goes beyond the usual classical harmonic interaction by inclusion of a
quartic interaction potential between the nearest-neighbor protons. Among
the rich variety of soliton patterns obtained in this model, we focus our
attention to compact kink (kinkon) solutions to calculate analytically, the
mobility of the kinkon-antikinkon pair and the specific
electrical-conductivity of the protons transfer in the hydrogen-bonded
systems under an externally applied electrical-field through the dynamic
equation of the kinkon-antikinkon pair. For ice, the mobility and the
electrical conductivity of the proton transfer obtained are about
5.307×10-7 m2 V-1 s-1
and 6.11×10-4 Ω-1 m-1, respectively. The results
obtained are in qualitative agreement with experimental data. 相似文献
2.
M.T. Primatarowa K.T. Stoychev R.S. Kamburova 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):291-294
We investigate the propagation and interaction of solitons associated with circularly polarized vibrations in gyrotropic media.
The chirality of the structure yields different dispersion laws and hence different phase and group velocities for the left-
and right-handed modes. The helical arrangement of the monomers is modelled through first- and third-neighbour interactions.
The dynamics of the excitations is governed by a system of coupled discrete nonlinear Schr?dinger equations which is studied
both analytically and numerically. Depending on the initial conditions and the interaction constants, different evolutionary
patterns are obtained corresponding to unbound or bound one- and two-soliton solutions. The results can be applied to the
process of energy transfer in helical polymers.
Received 1st October 2001 / Received in final form 30 April 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: krad@issp.bas.bg 相似文献
3.
A. Alvarez F. R. Romero J. Cuevas J. F.R. Archilla 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(4):543-555
We investigate the collisions of moving breathers, with
the same frequency, in three different Klein-Gordon chains of
oscillators. The on-site potentials are: the asymmetric and
soft Morse potential, the symmetric and soft sine-Gordon
potential and the symmetric and hard φ4 potential. The
simulation of a collision begins generating two identical moving
breathers traveling with opposite velocities, they are obtained
after perturbing two identical stationary breathers which centers
are separated by a fixed number of particles. If this number is odd
we obtain an on-site collision, but if this number is even we obtain
an inter-site collision. Apart from this distinction, we have
considered symmetric collisions, if the colliding moving
breathers are vibrating in phase, and anti-symmetric
collisions, if the colliding moving breathers are vibrating in
anti-phase. The simulations show that the collision properties of
the three chains are different. The main observed phenomena are:
breather generation with trapping, with the appearance of two new
moving breathers with opposite velocities, and a stationary breather
trapped at the collision region; breather generation without
trapping, with the appearance of new moving breathers with opposite
velocities; breather trapping at the collision region, without the
appearance of new moving breathers; and breather reflection. For
each Klein-Gordon chain, the collision outcomes depend on the
lattice parameters, the frequency of the perturbed stationary
breathers, the internal structure of the moving breathers and the
number of particles that initially separates the stationary
breathers when they are perturbed. 相似文献
4.
I. Bâldea H. Köppel L.S. Cederbaum 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):507-515
We investigate the Peierls transition in finite chains by exact (Lanczos) diagonalization and within a seminumerical method
based on the factorization of the electron-phonon wave function (Adiabatic Ansatz, AA). AA can be applied for mesoscopic chains
up to micrometer sizes and its reliability can be checked self-consistently. Our study demonstrates the important role played
for finite systems by the tunneling in the double well potential. The chains are dimerized only if their size N exceeds a critical value Nc which increases with increasing phonon frequency. Quantum phonon fluctuations yield a broad transition region. This smooth Peierls transition contrasts not only to the sharp mean field transition, but also with the sharp RPA soft mode instability,
although RPA partially accounts for quantum phonon fluctuations. For weak coupling the dimerization disappears below micrometer
sizes; therefore, this effect could be detected experimentally in mesoscopic systems.
Received: 3 January 1998 / Revised: 13 March 1998 / Accepted: 3 April 1998 相似文献
5.
6.
D. Hennig 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(3):419-425
We study localization in polymer chains modeled by the nonlinear discrete Schr?dinger equation (DNLS) with next-nearest-neighbor
(n-n-n) interaction extending beyond the usual nearest-neighbor exchange approximation. Modulational instability of plane
carrier waves is discussed and it is shown that localization gets amplified under the influence of an enhanced interaction
radius. Furthermore, we construct exact localized solitonlike solutions of the n-n-n interaction DNLS. To this end the stationary
lattice system is cast into a nonlinear map. The homoclinic orbits of unstable equilibria of this map are attributed to standing
solitonlike solutions of the lattice system. We note that in comparison with the standard next-neighbor interaction DNLS which
bears only one type of static soliton-like states (either staggering or unstaggering) the one with n-n-n interaction radius
can support unstaggering as well as staggering stationary localized states with frequencies lying above respectively below
the linear band. Generally, the stronger the n-n-n interaction on the DNLS lattice the smaller are the maximal amplitudes
of the standing solitonlike solutions and the less rapid are their exponential decays.
Received 4 October 2000 相似文献
7.
J. Szeftel G. Huang 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):329-334
The properties of vibrational localized (breathers) and traveling (anharmonic phonons) waves are discussed in an infinite,
one-dimensional, monoatomic crystal for the Fermi-Pasta-Ulam and Frenkel-Kontorova models. The shooting and finite difference
schemes have been implemented to reckon the displacement fields of breathers and anharmonic phonons, respectively. These tools
provide localized and traveling waves proving to be indefinitely stable in simulations carried out by solving the equations
of motion. The emphasis is laid on the role of the cubic and quartic terms of the anharmonic potential which turn out to oppose
and to shore up the restoring force, respectively. The case of vibrational modes arising in an anharmonic crystal subject
to a soft phonon induced instability is also addressed.
Received 7 November 2001 and Received in final form 5 February 2002 Published online 6 June 2002 相似文献
8.
A. M. Dikandé 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):397-402
Excitations of the polaron types are investigated in the spin-1/2 quantum chain with XY exchange and Dzyaloshinsky-Moriya
interaction, both coupled to acoustic vibrations of the substrate lattice. The study is carried out via Jordan-Wigner transformation
with the help of which the spin chain is mapped onto a chain of spinless fermions. From the resulting effective fermion-lattice
Hamiltonian, the discrete equations of motion are derived. These equations are solved in the continuum limit for self-trapped
states near the bottom of the fermion spectrum interacting with long-wavelength acoustic lattice modes. The associate polaron
solution, which has a pulse shape, is shown to propagate bound to the induced lattice kink distortion by translation along
the chain at a constant velocity v. The pair can also experience an additional acceleration ϑ0 when the free fermion charge is excited above its groundstate. The polaron binding energy is strongly reduced, depending
quadratically on the ratio D/J of the Dzyaloshinsky-Moriya interaction strength D to the isotropic XY exchange interaction
J. It is also found that polaron parameters depend only on the XY spin-lattice coupling but not on the Dzyaloshinsky-Moriya
contribution. 相似文献
9.
E. Arévalo Yu. Gaididei F.G. Mertens 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):63-74
We investigate the dynamics of a lattice soliton on a monatomic chain in the presence of damping and external forces. We consider
Stokes and hydrodynamical damping. In the quasi-continuum limit the discrete system leads to a damped and forced Boussinesq
equation. By using a multiple-scale perturbation expansion up to second order in the framework of the quasi-continuum approach
we derive a general expression for the first-order velocity correction which improves previous results. We compare the soliton
position and shape predicted by the theory with simulations carried out on the level of the monatomic chain system as well
as on the level of the quasi-continuum limit system. For this purpose we restrict ourselves to specific examples, namely potentials
with cubic and quartic anharmonicities as well as the truncated Morse potential, without taking into account external forces.
For both types of damping we find a good agreement with the numerical simulations both for the soliton position and for the
tail which appears at the rear of the soliton. Moreover we clarify why the quasi-continuum approximation is better in the
hydrodynamical damping case than in the Stokes damping case.
Received 22 August 2001 and Received in final form 7 December 2001 相似文献
10.
J. Zhu C. Q. Ru A. Mioduchowski 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):411-421
This paper studies parametric resonance of coupled
micromechanical oscillators under periodically varying nonlinear coupling
forces. Different from most of previous related works in which the
periodically varying coupling forces between adjacent oscillators are
linearized, our work focuses on new physical phenomena caused by the
periodically varying nonlinear coupling. Harmonic balance method (HBM)
combined with Newton iteration method is employed to find steady-state
periodic solutions. Similar to linearly coupled oscillators studied
previously, the present model predicts superharmonic parametric resonance
and the lower-order subharmonic parametric resonance. On the other hand, the
present analysis shows that periodically varying nonlinear coupling
considered in the present model does lead to the appearance of high-order
subharmonic parametric resonance when the external excitation frequency is a
multiple or nearly a multiple (≥3) of one of the natural
frequencies of the oscillator system. This remarkable new phenomenon does
not appear in the linearly coupled micromechanical oscillators studied
previously, and makes the range of exciting resonance frequencies expanded
to infinity. In addition, the effect of a linear damping on parametric
resonance is studied in detail, and the conditions for the occurrence of the
high-order subharmonics with a linear damping are discussed. 相似文献
11.
Sonic stop-bands for cubic arrays of rigid inclusions in air 总被引:2,自引:0,他引:2
M.S. Kushwaha B. Djafari-Rouhani L. Dobrzynski J.O. Vasseur 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):155-161
Extensive band structures have been computed for cubic arrays of rigid spheres and cubes in air. Complete stop bands are obtained
for the face-centered-cubic (fcc) structure; however, there is no gap for the body-centered-cubic (bcc) and simple-cubic (sc)
structures. These gaps start opening up for a filling fraction of (27%) for spherical (cubic) inclusions and tend to increase with the filling fraction, exhibiting a maximum at the close-packing.
We also propose a tandem structure that allows the achievement of an ultrawideband filter for environmental or industrial
noise in the desired frequency range. This work is motivated by the recent experimental measurement of sound attenuation on
the sculpture, by Eusebio Sempere, exhibited at the Juan March Foundation in Madrid (Nature 378, 241 (1995)) and complements the corresponding theoretical work (Appl. Phys. Lett. 70, 3218 (1997)).
Received: 24 October 1997 / Revised: 1 December 1997 and 26 January 1998 / Accepted: 6 March 1998 相似文献
12.
O. Dubos W. Petry J. Neuhaus B. Hennion 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):447-454
We present inelastic neutron scattering measurements of the low energy and strongly damped phonons in the high temperature
bcc phase of zirconium. These phonons were investigated at different scattering vectors but equivalent phonon wave vectors in different Brillouin zones or along different but equivalent paths in the same Brillouin zone. Neither the observed differences
in intensity nor in line shapes can be explained by the coherent one-phonon scattering law . This leads to an apparent violation of the fundamental symmetry of lattice dynamics. Taking into account the strong anharmonicity
of these phonons, interferences between one- and multi-phonon scattering are held responsible for these effects. Measurements
in different scattering planes reveal that due to the symmetry of the bcc lattice, these effects can only be observed in certain
directions.
Received: 24 December 1997 / Received in final form: 9 March 1998 / Accepted: 19 March 1998 相似文献
13.
14.
A. Tölle H. Zimmermann F. Fujara W. Petry W. Schmidt H. Schober J. Wuttke 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):73-80
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.
Received 7 December 1999 相似文献
15.
A. Paolone P. Roy A. Pimenov A. Loidl A.A. Mukhin A.M. Balbashov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):245-250
The optical conductivity of La0.85Sr0.15MnO3 single crystals was studied by means of submillimeter and infrared spectroscopy for frequencies cm-1 and temperatures 10 K <
T
<300 K. The submillimeter conductivity follows the temperature dependence of the dc-data. The phonon spectrum of La0.85Sr0.15MnO3 changes considerably below K revealing a structural phase transition induced by charge or orbital order. At T
=10 K a number of phonon modes can be identified in addition to the room-temperature spectrum. The optical conductivity () in the mid-infrared reveals the characteristics of small polaron absorption. Below the magnetic ordering temperature the
polaron binding energy is highly reduced, but the onset of charge order interrupts the formation of free charge carriers with
a Drude-like behavior. The frequency and temperature dependence of in this regime qualitatively resembles the small polaron predictions by Millis et al. (Phys. Rev. B 54, 5405 (1996)).
Received 5 November 1999 相似文献
16.
L. Martín-Carrón A. de Andrés 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(1):11-16
We have studied the behavior of the Raman phonons of a stoichiometric LaMnO3 single crystal as a function of temperature in the range between 77 K and 900 K. We focus on the three main phonon peaks
of the Pbnm structure, related to the tilt, antisymmetric stretching (Jahn-Teller mode) and stretching modes of Mn-O octahedra.
The phonon frequencies show a strong softening that can be fit taking into account their renormalization because of three
phonon anharmonic effects in the pseudoharmonic approximation. Thermal expansion effects, in particular the variation of Mn-O
bond lengths with temperature, are not relevant above 300 K. On the contrary, phonon width behavior deviates from the three
phonon scattering processes well bellow T
c
. The correlation between the magnitude of the cooperative Jahn-Teller distortion, that disappears at 800 K, and the amplitude
of the Raman phonons in the orthorhombic phase is shown. Nevertheless, Pbnm phonons are still observable above this temperature.
Phonon width and intensity behavior around T
c
can be explained by local melting of the orbital order that begins quite below T
c
and by fluctuations of the regular Mn-O octahedra that correspond to dynamic Jahn-Teller distortions.
Received 25 January 2001 and Received in final form 14 March 2001 相似文献
17.
P.T. Jochym K. Parlinski 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):265-268
Ab initio calculations and a direct method are applied to derive the phonon dispersion relations and phonon density of states for the
ZrC crystal. The results are in good agreement with neutron scattering data. The force constants are determined from the Hellmann-Feynman
forces induced by atomic displacements in a 222 supercell. The elastic constants are found using the deformation method and successfully compare with experimental data.
Received 2 July 1999 and Received in final form 26 November 1999 相似文献
18.
Huan-You Wang Hui Xu Tie-Tie Huang Chao-Sheng Deng 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(1):39-43
The density function perturbation theory (DFPT) is employed to study
the linear thermal expansion and heat capacity at constant pressure
(with the quasiharmonic approximation) for wurtzite GaN. The
calculated results of linear thermal expansion coefficient and heat
capacity at constant pressure are compared with the available
experimental data in a wide temperature range. Generally these
properties calculated agree well with experimental data except at
high temperature, thus it suggests the thermal expansion and heat
capacity can be well calculated from this first-principle approach. 相似文献
19.
A. Alvarez F. R. Romero J. F.R. Archilla J. Cuevas P. V. Larsen 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(1):119-130
We study the dynamics of moving discrete breathers in an interfaced piecewise DNA molecule.
This is a DNA chain in which all the base pairs are identical and
there exists an interface such that the base pairs dipole moments at each side are oriented in opposite
directions.
The Hamiltonian of the Peyrard-Bishop model is augmented with a
term that includes the dipole-dipole coupling between base pairs.
Numerical simulations show the existence of two dynamical regimes.
If the translational kinetic energy of a moving breather launched
towards the interface is below a critical value, it is trapped in
a region around the interface collecting vibrational energy. For
an energy larger than the critical value, the breather is
transmitted and continues travelling along the double strand with
lower velocity. Reflection phenomena never occur.
The same study has been carried out when a single dipole is oriented
in opposite direction to the other ones.
When moving breathers collide
with the single inverted dipole, the same effects appear. These
results emphasize the importance of this simple type of local
inhomogeneity as it creates a mechanism for the trapping of
energy.
Finally, the simulations show that, under favorable conditions,
several launched moving breathers can be trapped successively at the interface
region producing an accumulation of vibrational energy. Moreover,
an additional colliding moving breather can produce a saturation
of energy and a moving breather with all the accumulated energy
is transmitted to the chain. 相似文献
20.
J. Balakrishnan 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(4):679-683
Using the local-density approximation, calculating the Hellmann-Feynman forces and applying the direct method, the phonon
dispersion relations for the rutile-like structure of crystalline SnO2 have been derived for the first time. The phonon frequencies at the point agree very well with Raman and infrared data and other phenomenological model calculations. The LO/TO splitting is
estimated by calculating phonons from an elongated supercell. The computations under pressure reveal a soft mode of B1g symmetry which leads to a ferroelastic phase transition. The pressure-dependence of the lattice constants and the Grüneisen
parameters of the modes are calculated.
Received 18 July 1999 相似文献