共查询到20条相似文献,搜索用时 640 毫秒
1.
N. Shramchenko F. Dénoyer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):51-59
A detailed investigation of the Fourier space of several Al-Pd-Mn samples with composition Al-72.6 at. %, Pd-22.9 at. %, Mn-4.5
at. % is reported. In the phase diagram of the Al-Pd-Mn ternary alloy, this composition corresponds to the so-called ξ' phase which was described as an icosahedral quasicrystalline approximant. By re-examining the Fourier space by means of
X-ray diffraction (powder patterns and single crystal precession patterns), complex structures in close relation with the
ξ'-phase have been observed. These long-range order complex structures are described as resulting from a periodic perturbation
of the ξ' structure along the c direction. Two states with periodicities c
(3 + τ) and c
(5 + τ) have been observed in this study (τ: golden mean). Structural models based on periodic arrangements of “defects” layers separating layers of phase are proposed. These two states are certainly intermediate states between the phase and the metastable decagonal quasicrystalline phase.
Received 11 April 2002 / Received in final form 24 June 2002 Published online 17 September 2002 相似文献
2.
J. Gemmer G. Mahler 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):249-257
For a closed bi-partite quantum system partitioned into system proper and environment we interpret the microcanonical and
the canonical condition as constraints for the interaction between those two subsystems. In both cases the possible pure-state
trajectories are confined to certain regions in Hilbert space. We show that in a properly defined thermodynamical limit almost
all states within those accessible regions represent states of some maximum local entropy. For the microcanonical condition
this dominant state still depends on the initial state; for the canonical condition it coincides with that defined by Jaynes'
principle. It is these states which thermodynamical systems should generically evolve into.
Received 13 June 2002 / Received in final form 14 November 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: jochen@theol.physik.uni-stuttgart.de 相似文献
3.
G.-L. Ingold A. Wobst Ch. Aulbach P. Hänggi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):175-179
In the one-dimensional Anderson model the eigenstates are localized for arbitrarily small amounts of disorder. In contrast,
the Aubry-André model with its quasiperiodic potential shows a transition from extended to localized states. The difference
between the two models becomes particularly apparent in phase space where Heisenberg's uncertainty relation imposes a finite
resolution. Our analysis points to the relevance of the coupling between momentum eigenstates at weak potential strength for
the delocalization of a quantum particle.
Received 3 May 2002 / Received in final form 2 October 2002 Published online 29 November 2002 相似文献
4.
Ya.G. Groda P. Argyrakis G.S. Bokun V.S. Vikhrenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(4):527-535
The selfconsistent diagram approximation (SCDA) is generalized for three-dimensional lattice gases with nearest neighbor repulsive
interactions. The free energy is represented in a closed form through elementary functions. Thermodynamical (phase diagrams,
chemical potential and mean square fluctuations), structural (order parameter, distribution functions) as well as diffusional
characteristics are investigated. The calculation results are compared with the Monte Carlo simulation data to demonstrate
high precision of the SCDA in reproducing the equilibrium lattice gas characteristics. It is shown that similarly to two-dimensional
systems the specific statistical memory effects strongly influence the lattice gas diffusion in the ordered states.
Received 7 August 2002 / Received in final form 22 January 2003 Published online 24 April 2003 相似文献
5.
Hua Liu Jun Ni Binglin Gu 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):261-265
In this paper, we have investigated the ground states of a few-layered fcc thin film of binary alloy with two surfaces in
the (001) direction under symmetric surface confinement. The phase diagram of the ground states is given according to the
energy analysis of binary alloy thin film composed of six atomic layers in the (001) direction. Surface confinement field
(SC field) is introduced as a term to describe the confinement on the two surfaces in the (001) direction. Using Monte Carlo
simulation, we have found that there are 17 different ground states occurring when both SC field and chemical potential vary
from - ∞ to + ∞. Antiphase boundary(APB) was found in 12 of the 17 ground states, and only nine configurations with different
symmetry were found among the 17 ground states.
Received 6 November 2001 and Received in final form 25 January 2002 相似文献
6.
B.I. Sturman A.S. Gorkunova K.H. Ringhofer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):291-297
We investigate analytically and numerically the influence of the type of the photorefractive nonlinear response on the periodic
states (attractors) which occur during feedback controlled 2W-coupling and correspond to almost 100% diffraction efficiency
of the dynamic index grating. In addition to the case of the local response typical, for example, for LiNbO3 crystals we consider the cases of nonlocal (diffusive) response (BaTiO3, SBN) and resonant response (DC-biased BSO, BTO, and BGO crystals). It is shown that the conditions for the transition to
the periodic states and their apparent characteristics are strongly different for the two limiting cases above.
Received 16 July 2002 / Received in final form 29 October 2002 Published online 4 March 2003 相似文献
7.
A. Wobst G.-L. Ingold P. Hänggi D. Weinmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):11-14
We introduce phase space concepts to describe quantum states in a disordered system. The merits of an inverse participation
ratio defined on the basis of the Husimi function are demonstrated by a numerical study of the Anderson model in one, two,
and three dimensions. Contrary to the inverse participation ratios in real and momentum space, the corresponding phase space
quantity allows for a distinction between the ballistic, diffusive, and localized regimes on a unique footing and provides
valuable insight into the structure of the eigenstates.
Received 5 March 2002 相似文献
8.
I.O. Kulik T. Hakioğlu A. Barone 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):219-226
We examine a generic three level mechanism of quantum computation in which all fundamental single and double qubit quantum
logic gates are operating under the effect of adiabatically controllable static (radiation free) bias couplings between the
states. Under the time evolution imposed by these bias couplings the quantum state cycles between the two degenerate levels
in the ground state and the quantum gates are realized by changing Hamiltonian at certain time intervals when the system collapses
to a two state subspace. We propose a physical implementation of the mechanism using Aharonov-Bohm persistent-current loops
in crossed electric and magnetic fields, with the output of the loop read out by using a quantum Hall effect aided mechanism.
Received 26 March 2002 / Received in final form 8 July 2002
Published online 19 November 2002 相似文献
9.
B. Božič V. Heinrich S. Svetina B. Žekš 《The European physical journal. E, Soft matter》2001,6(1):91-98
Shapes of nearly cylindrical sections of axisymmetric phospholipid membranes are studied theoretically. Describing the shape
of such sections by their deviation from a reference cylinder, the well-established shape equation for axisymmetric bilayer
membranes is expanded in terms of this deviation, and it is then solved analytically. The phase diagram shows the resulting
stationary shapes as functions of system parameters and external conditions, i.e., the pressure difference across the membrane, the membrane tension, the difference between the tensions of the two monolayers,
and the axial force acting on the vesicle. The accuracy of the approximate analytical solution is demonstrated by comparison
with numerical results. The obtained analytical solution allows to extend the analysis to include shapes where numerical methods
have failed.
Received 27 September 2000 and Received in final form 26 March 2001 相似文献
10.
We propose a simple cellular automaton for traffic flow within the fundamental diagram, which could reproduce aspects of the three-phase theory. This so-called average space gap model (ASGM) is based on the Nagel–Schreckenberg model with additional slow-to-start and anticipation rules. The anticipation rule takes into account the average space gap of multiple leading vehicles and conveys to the model its three-phase property. Due to the anticipation rule, ASGM can show the transition from free flow to synchronized flow. Due to the slow-to-start rule, ASGM can show the spontaneous wide moving jam emerges in the synchronized flow. Simulations are carried out for periodic and open boundary conditions. Under periodic boundary condition, the fundamental diagram, and the properties of synchronized flow are studied. Under open boundary condition, different congested patterns induced by an on-ramp are analyzed. We found that the ASGM produces the same spatiotemporal dynamics as many of the more complex three-phase models. Due to its simplicity and its close relation to conventional slow-to-start models, this model can shed light on the relation between ‘two-phase’ and three-phase models. 相似文献
11.
J.M. Cerveró A. Rodrıguez 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):239-251
We present the exact diagonalization of the Schr?dinger operator corresponding to a periodic potential with N deltas of different couplings, for arbitrary N. This basic structure can repeat itself an infinite number of times. Calculations of band structure can be performed with
a high degree of accuracy for an infinite chain and of the correspondent eigenlevels in the case of a random chain. The main
physical motivation is to modelate quantum wire band structure and the calculation of the associated density of states. These
quantities show the fundamental properties we expect for periodic structures although for low energy the band gaps follow
unpredictable patterns. In the case of random chains we find Anderson localization; we analize also the role of the eigenstates
in the localization patterns and find clear signals of fractality in the conductance. In spite of the simplicity of the model
many of the salient features expected in a quantum wire are well reproduced.
Received 24 June 2002 Published online 29 November 2002 相似文献
12.
Y. Li Voskoboynikov C.P. Lee S.M. Sze O. Tretyak 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):475-481
In this article we study the impact of the spin-orbit interaction on the electron quantum confinement for narrow gap semiconductor
quantum dots. The model formulation includes: (1) the effective one-band Hamiltonian approximation; (2) the position- and
energy-dependent quasi-particle effective mass approximation; (3) the finite hard wall confinement potential; and (4) the
spin-dependent Ben Daniel-Duke boundary conditions. The Hartree-Fock approximation is also utilized for evaluating the characteristics
of a two-electron quantum dot system. In our calculation, we describe the spin-orbit interaction which comes from both the
spin-dependent boundary conditions and the Rashba term (for two-electron quantum dot system). It can significantly modify
the electron energy spectrum for InAs semiconductor quantum dots built in the GaAs matrix. The energy state spin-splitting
is strongly dependent on the dot size and reaches an experimentally measurable magnitude for relatively small dots. In addition,
we have found the Coulomb interaction and the spin-splitting are suppressed in quantum dots with small height.
Received 15 May 2001 / Received in final form 14 May 2002 Published online 13 August 2002 相似文献
13.
W. Selke M. Pleimling D. Catrein 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):321-327
The axial next-nearest-neighbour Ising (ANNNI) model of finite thickness is studied. Using mean-field theory, Monte Carlo
simulations, and low-temperature analyses, phase diagrams are determined, with a distinct phase diagram for each film thickness.
The robustness of the phase diagrams against varying the couplings in the surface layers is analysed.
Received 19 March 2002 and Received in final form 2 April 2002 Published online 6 June 2002 相似文献
14.
The present paper develops a Statistical Mechanics approach to the inherent states of glassy systems and granular materials
by following the original ideas proposed by Edwards for granular media. We consider three lattice models (a diluted spin glass,
a system of hard spheres under gravity and a hard-spheres binary mixture under gravity) introduced to describe glassy and
granular systems. They are evolved using a “tap dynamics” analogous to that of experiments on granular media. We show that
the asymptotic states reached in such a dynamics are not dependent on the particular sample history and are characterized
by a few thermodynamical parameters. We assume that under stationarity these systems are distributed in their inherent states
satisfying the principle of maximum entropy. This leads to a generalized Gibbs distribution characterized by new “thermodynamical”
parameters, called “configurational temperatures” (related to Edwards compactivity for granular materials). Finally, we show
by Monte Carlo calculations that the average of macroscopic quantities over the tap dynamics and over such distribution indeed
coincide. In particular, in the diluted spin glass and in the system of hard spheres under gravity, the asymptotic states
reached by the system are found to be described by a single “configurational temperature”. Whereas in the hard-spheres binary
mixture under gravity the asymptotic states reached by the system are found to be described by two thermodynamic parameters,
coinciding with the two configurational temperatures which characterize the distribution among the inherent states when the
principle of maximum entropy is satisfied under the constraint that the energies of the two species are independently fixed.
Received 19 March 2002 and Received in final form 14 June 2002 相似文献
15.
M. Gligor M. Ignat 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):125-135
Some previous works have presented the data on wealth and income distributions in developed countries and have found that
the great majority of population is described by an exponential distribution, which results in idea that the kinetic approach
could be adequate to describe this empirical evidence. The aim of our paper is to extend this framework by developing a systematic
kinetic approach of the socio-economic systems and to explain how linear laws, modelling correlations between macroeconomic
variables, may arise in this context. Firstly we construct the Boltzmann kinetic equation for an idealised system composed
by many individuals (workers, officers, business men, etc.), each of them getting a certain income and spending money for
their needs. To each individual a certain time variable amount of money is associated - this meaning him/her phase space coordinate.
In this way the exponential distribution of money in a closed economy is explicitly found. The extension of this result, including
states near the equilibrium, give us the possibility to take into account the regular increase of the total amount of money,
according to the modern economic theories. The Kubo-Green-Onsager linear response theory leads us to a set of linear equations
between some macroeconomic variables. Finally, the validity of such laws is discussed in relation with the time reversal symmetry
and is tested empirically using some macroeconomic time series.
Received 25 February 2002 / Received in final form 11 July 2002 Published online 19 November 2002 相似文献
16.
M.-F. Ficheux A.-M. Bellocq F. Nallet 《The European physical journal. E, Soft matter》2001,4(3):315-326
We investigate experimentally, using small-angle neutron scattering the elastic properties of polymer-doped dilute lamellar
phases. In our system the polymer is water-soluble but nevertheless partially adsorbs onto the negatively charged surfactant
bilayers. The effective polymer-mediated interaction between bilayers is less repulsive than the weakly screened electrostatic
interaction that prevails at zero polymer content. It even becomes attractive in some regions of the phase diagram. Small-angle
neutron scattering allows us to measure directly the Caillé exponent η characterizing the bilayer fluctuations in lamellar
(smectic A) phases, and thus indirectly estimate the compression modulus as a measure of the strength of the bilayer-bilayer interactions. The compression modulus appears to be vanishing at a point
located on the lamellar-lamellar phase separation boundary, a candidate critical point.
Received: 7 August 2000 相似文献
17.
M. Leone A. Vázquez A. Vespignani R. Zecchina 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):191-197
We present a detailed study of the phase diagram of the Ising model in random graphs with arbitrary degree distribution. By
using the replica method we compute exactly the value of the critical temperature and the associated critical exponents as
a function of the moments of the degree distribution. Two regimes of the degree distribution are of particular interest. In
the case of a divergent second moment, the system is ferromagnetic at all temperatures. In the case of a finite second moment
and a divergent fourth moment, there is a ferromagnetic transition characterized by non-trivial critical exponents. Finally,
if the fourth moment is finite we recover the mean field exponents. These results are analyzed in detail for power-law distributed
random graphs.
Received 4 April 2002 Published online 19 July 2002 相似文献
18.
L.F. Chibotaru A. Ceulemans G. Teniers V. Bruyndoncx V.V. Moshchalkov 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):341-346
An approach to the Ginzburg-Landau problem of superconducting polygons is developed, based on the exact fulfillment of superconducting
boundary conditions along the boundary of the sample. To this end an analytical gauge transformation for the vector potential
A is found which gives A
n = 0 for the normal component along the boundary line of an arbitrary regular polygon. The use of the new gauge reduces the
Ginzburg-Landau problem of superconducting polygons in external magnetic fields to an eigenvalue problem in a basis set of
functions obeying Neumann boundary conditions. The advantages of this approach, especially for low magnetic fields, are illustrated
and novel vortex patterns are obtained which can be probed experimentally.
Received 28 February 2002 and Received in final form 12 April 2002 Published online 6 June 2002 相似文献
19.
O. Brodier T. Neicu A. Kudrolli 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(3):365-372
We report a numerical study of the flexural modes of a plate using semi-classical analysis developed in the context of quantum
systems. We first introduce the Clover billiard as a paradigm for a system inside which rays exhibit stable and chaotic trajectories.
The resulting phase space explored by the ray trajectories is illustrated using the Poincare surface of section, and shows
that it has both integrable and chaotic regions. Examples of the stable and the unstable periodic orbits in the geometry are
presented. We numerically solve the biharmonic equation for the flexural vibrations of the Clover shaped plate with clamped
boundary conditions. The first few hundred eigenvalues and the eigenfunctions are obtained using a boundary elements method.
The Fourier transform of the eigenvalues show strong peaks which correspond to ray periodic orbits. However, the peaks corresponding
to the shortest stable periodic orbits are not stronger than the peaks associated with unstable periodic orbits. We also perform
statistics on the obtained eigenvalues and the eigenfunctions. The eigenvalue spacing distribution P(s) shows a strong peak and therefore deviates from both the Poisson and the Wigner distribution of random matrix theory at
small spacings because of the C4v symmetry of the Clover geometry. The density distribution of the eigenfunctions is observed to agree with the Porter-Thomas
distribution of random matrix theory.
Received 12 February 2001 and Received in final form 17 April 2001 相似文献
20.
K. Parlinski 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):283-285
Using the density functional theory the structural and magnetic properties of iron borate under high pressure have been studied.
At about P
= 22.7 GPa a first order phase transition to the phase described by the same space group Rc has been found. The phase transition is accompanied by a 9% volume change of the unit cell, a four times decrease of the
magnetic moment on Fe, an increase of the charge density at Fe, and a disappearance of the energy gap in the electronic density
of states.
Received 21 September 2001 and Received in final form 6 January 2002 Published online 6 June 2002 相似文献