共查询到20条相似文献,搜索用时 15 毫秒
1.
V.D. Natsik Y.I. Nazarenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):285-289
The problem of crowdion motion is formulated and analyzed as a dynamical problem of a three-dimensional crystal lattice formed
by atoms of several kinds, which interact with each other by means of short-range pair potentials. It is explained that in
order for the the crowdion excitations of the close-packed atomic rows to be distinguishable against the background of small
dynamic deformations of the crystal as a whole, the microscopic parameters of the crystal structure must meet certain stated
requirements. The equation of motion of a crowdion in an arbitrary elastic strain field of the crystal is derived in the Lagrangian
formalism. Expressions are obtained which relate the effective mass and the rest energy of a crowdion with the geometric and
force parameters of the crystal lattice.
Received 4 October 2001 / Received in final form 27 February 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: nazarenko@ksame.kharkov.ua 相似文献
2.
G.H. Zhou Q.L. Xia J.R. Yan 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(3):297-304
The nonlinear localized vibrational modes of a one-dimensional atomic chain with two periodically alternating masses and force
constants are analytically investigated using a discrete multiple-scale expansion method. This model simulates a row of atoms
in the <1 1 1>-direction of sphalerite, or zinc blende, crystals. Owing to the structural asymmetry, the vibrational amplitude
is governed by a perturbed nonlinear Schr?dinger equation instead of the standard one found in one-dimensional lattices with
two alternating masses but uniform force constant. Although the stationary localized modes with carrier wavevector at the
Brillouin-zone boundary are similar to those of ionic lattices, the moving localized modes with wavevectors within the zone
are different owing to the perturbation. The calculation shows that the height of the moving localized modes in this lattice
dampens with time.
Received 14 May 2001 and Received in final form 12 July 2001 相似文献
3.
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
4.
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
5.
A. S. Tchakoutio Nguetcho T. C. Kofane 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(4):411-422
The dynamics of protons in hydrogen-bonded quasi one-dimensional
networks are studied using a diatomic lattice model of protons and heavy ions
including a φ4 on-site substrate potential. It is shows that the model with
linear and nonlinear coupling of the quartic type between lattice sites for
the protons admits a richer dynamics that cannot be produced with linear
couplings alone. Depending on two types of physical boundary conditions, namely
of the drop or condensate type, and on conditions requiring the presence of
linear and nonlinear dispersion terms, soliton patterns of compact support,
whether with a peak, drop, bell, cusp, shock, kink, bubble or loop structure,
are obtained within a continuum approximation. Phase trajectories as well as analytical
studies provide information on the disintegration of soliton patterns upon
reaching some critical values of the lattice parameters. The total energies
of soliton patterns are computed exactly in the continuum limit. We also
show that when anharmonic interactions of the phonon are taken into account, the width and
energy of soliton patterns are in qualitative agreement with
experimental data. 相似文献
6.
A. Fledderjohann K.-H. Mütter 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):211-218
We investigate the influence of energetic disorder, viscous damping and an external field on the electron transfer (ET) in
DNA. The double helix structure of the λ-form of DNA is modeled by a steric oscillator network. In the context of the base-pair
picture two different kinds of modes representing twist motions of the base pairs and H-bond distortions are coupled to the
electron amplitude. Through the nonlinear interaction between the electronic and the vibrational degrees of freedom localized
stationary states in the form of standing electron-vibron breathers are produced which we derive with a stationary map method.
We show that in the presence of additional energetic disorder the degree of localization of such breathers is enhanced. It
is demonstrated how an applied electric field initiates the long-range coherent motion of breathers along the bases of a DNA
strand. These moving electron-vibron breathers, absorbing energy from the applied field, sustain energetic losses due to the
viscous friction caused by the aqueous solvent as well as the impact of a moderate amount of energetic disorder. Moreover,
it is illustrated that with the choice of the amplitude and frequency of the external field, the breather can be steered to
a desired lattice position achieving control of the ET.
Received 5 July 2002 Published online 29 November 2002 相似文献
7.
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
8.
Eric Grelet Peter J. Collings Min-Hui Li Huu-Tinh Nguyen 《The European physical journal. E, Soft matter》2001,6(2):157-161
Optical activity measurements have been performed on the smectic blue phases ( BP
Sm), which are a new kind of chiral liquid crystal. BP
Sm exhibit both three-dimensional orientational order, like the classical blue phases, and smectic positional order. Thus, they
can be viewed as the three-dimensional counterpart of the twist grain boundary phases. A comparison with the optical activity
of the classical blue phases is carried out, and an estimation of the BP
Sm lattice parameter is reported for the first time.
Received 25 May 2001 相似文献
9.
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
10.
11.
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
12.
N.R. Quintero A. Sánchez F.G. Mertens 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):107-115
We study analytically and numerically the action of a constant force on the propagation of kinks in the φ4 and sine-Gordon systems, with and without dissipation. We specifically investigate the relation of the external force with
the oscillations of the kink width due to excitation of its internal mode or quasimode. We demonstrate that both dc force
and dissipation, either jointly or separately, damp the oscillations of the kink width. We further prove that, in contrast
to earlier predictions, those oscillations can only arise if we use a distorted kink as initial condition for the evolution.
Finally, we show that for the φ4 system the oscillations of the kink width come from the excitation of its internal mode, whereas in the sG equation they
originate in the excitation of the lowest radiational modes and an internal mode induced by the discreteness of the numerical
simulations.
Received 6 June 2000 相似文献
13.
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
14.
M. Johansson A.M. Morgante S. Aubry G. Kopidakis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):279-283
Modulational instability of travelling plane waves is often considered as the first step in the formation of intrinsically
localized modes (discrete breathers) in anharmonic lattices. Here, we consider an alternative mechanism for breather formation,
originating in oscillatory instabilities of spatially periodic or quasiperiodic nonlinear standing waves (SWs). These SWs
are constructed for Klein-Gordon or Discrete Nonlinear Schr?dinger lattices as exact time periodic and time reversible multibreather
solutions from the limit of uncoupled oscillators, and merge into harmonic SWs in the small-amplitude limit. Approaching the
linear limit, all SWs with nontrivial wave vectors (0 < Q < π) become unstable through oscillatory instabilities, persisting for arbitrarily small amplitudes in infinite lattices.
The dynamics resulting from these instabilities is found to be qualitatively different for wave vectors smaller than or larger
than π/2, respectively. In one regime persisting breathers are found, while in the other regime the system thermalizes.
Received 6 October 2001 / Received in final form 1st March 2002 Published online 2 October 2002
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ID="a"e-mail: mjn@ifm.liu.se 相似文献
15.
K.Ø. Rasmussen S. Aubry A.R. Bishop G.P. Tsironis 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):169-175
We study the dynamics of the discrete nonlinear Schr?dinger lattice initialized such that a very long transitory period of
time in which standard Boltzmann statistics is insufficient is reached. Our study of the nonlinear system locked in this non-Gibbsian state focuses on the dynamics of discrete breathers (also called intrinsic localized modes). It is found that part of the
energy spontaneously condenses into several discrete breathers. Although these discrete breathers are extremely long lived,
their total number is found to decrease as the evolution progresses. Even though the total number of discrete breathers decreases
we report the surprising observation that the energy content in the discrete breather population increases. We interpret these
observations in the perspective of discrete breather creation and annihilation and find that the death of a discrete breather
cause effective energy transfer to a spatially nearby discrete breather. It is found that the concepts of a multi-frequency
discrete breather and of internal modes is crucial for this process. Finally, we find that the existence of a discrete breather
tends to soften the lattice in its immediate neighborhood, resulting in high amplitude thermal fluctuation close to an existing
discrete breather. This in turn nucleates discrete breather creation close to a already existing discrete breather.
Received 21 January 1999 and Received in final form 20 September 1999 相似文献
16.
P.G. Kevrekidis B.A. Malomed Z. Musslimani 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):421-436
A model including two nonlinear chains with linear and nonlinear couplings between them, and opposite signs of the discrete
diffraction inside the chains, is introduced. In the case of the cubic [ χ(3)] nonlinearity, the model finds two different interpretations in terms of optical waveguide arrays, based on the diffraction-management
concept. A continuum limit of the model is tantamount to a dual-core nonlinear optical fiber with opposite signs of dispersions
in the two cores. Simultaneously, the system is equivalent to a formal discretization of the standard model of nonlinear optical
fibers equipped with the Bragg grating. A straightforward discrete second-harmonic-generation [ χ(2)] model, with opposite signs of the diffraction at the fundamental and second harmonics, is introduced too. Starting from
the anti-continuum (AC) limit, soliton solutions in the χ(3) model are found, both above the phonon band and inside the gap. Solitons above the gap may be stable as long as they exist,
but in the transition to the continuum limit they inevitably disappear. On the contrary, solitons inside the gap persist all
the way up to the continuum limit. In the zero-mismatch case, they lose their stability long before reaching the continuum
limit, but finite mismatch can have a stabilizing effect on them. A special procedure is developed to find discrete counterparts
of the Bragg-grating gap solitons. It is concluded that they exist at all the values of the coupling constant, but are stable
only in the AC and continuum limits. Solitons are also found in the χ(2) model. They start as stable solutions, but then lose their stability. Direct numerical simulations in the cases of instability
reveal a variety of scenarios, including spontaneous transformation of the solitons into breather-like states, destruction
of one of the components (in favor of the other), and symmetry-breaking effects. Quasi-periodic, as well as more complex,
time dependences of the soliton amplitudes are also observed as a result of the instability development.
Received 14 September 2002 / Received in final form 4 February 2003 Published online 24 April 2003
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ID="a"e-mail: malomed@eng.tau.ac.il 相似文献
17.
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
18.
Y. Gaididei R. Huß F.G. Mertens 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):257-271
We investigate envelope solitary waves on square lattices with two degrees of freedom and nonlinear nearest and next-nearest
neighbor interactions. We consider solitary waves which are localized in the direction of their motion and periodically modulated
along the perpendicular direction. In the quasi-monochromatic approximation and low-amplitude limit a system of two coupled
nonlinear Schr?dinger equations (CNLS) is obtained for the envelopes of the longitudinal and transversal displacements. For
the case of bright envelope solitary waves the solvability condition is discussed, also with respect to the modulation. The
stability of two special solution classes (type-I and type-II) of the CNLS equations is tested by molecular dynamics simulations.
The shape of type-I solitary waves does not change during propagation, whereas the width of type-II excitations oscillates
in time.
Received: 4 December 1997 / Revised: 6 June 1998 / Accepted: 7 July 1998 相似文献
19.
For solitary waves on a monoatomic chain with nearest neighbor interactions the continuum approximation has a limited validity range and exhibits certein mathematical problems. For pulse solitons these problems are overcome by the Quasicontinuum Approach (QCA), and the validity range is considerably extended. We generalize the QCA to oscillatory excitations and derive analytic expressions for bright and dark envelope solitons, limiting ourselves to a polynomial interaction potential with harmonic, cubic and quartic terms. Moreover we describe and apply a numerical iteration procedure in Fourier space in order to take into account discreteness effects in a systematic way. This procedure yields envelope solitons with a width in the order of the lattice constant. In the case of zero velocity these solutions can be compared with intrinsic localized modes derived by other authors. The stability and accuracy of all our solutions are tested by numerical simulations. 相似文献
20.
F. Cinti M. Affronte A.G.M. Jansen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):461-468
The level crossing mechanism between the ground and the first excited state of Na:Fe6 antiferromagnetically coupled iron rings is studied by torque magnetometry down to 40 mK and in magnetic fields up to 28
T. The step width at the crossing field Bc assumes a finite value at the lowest temperatures. This fact is ascribed to the presence of level anticrossing, not expected
for a ring with axial, i.e. S6 point group, symmetry. Assuming a reduced symmetry, we revised the model Hamiltonian of such a spin system by introducing
a Dzyaloshinsky-Moriya (DM) term and we show, by exact diagonalization, that DM term can account for the mixing of states with different parity.
In particular, analytical as well numerical analysis show that the introduction of the DM term may contribute to the broadening
of the torque step as well as for the finite energy gap at Bc observed by heat capacity in a similar ring Li:Fe6 as previously reported [#!aclbg!#].
Received 3 September 2002 Published online 31 December 2002 相似文献