共查询到20条相似文献,搜索用时 583 毫秒
1.
Haijun Zhou 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):265-270
We study the vertex cover problem on finite connectivity random graphs by zero-temperature cavity method. The minimum vertex
cover corresponds to the ground state(s) of a proposed Ising spin model. When the connectivity c > e = 2.718282, there is no state for this system as the reweighting parameter y, which takes a similar role as the inverse temperature β in conventional statistical physics, approaches infinity; consequently
the ground state energy is obtained at a finite value of y when the free energy function attains its maximum value. The minimum vertex cover size at given c is estimated using population dynamics and compared with known rigorous bounds and numerical results. The backbone size is
also calculated.
Received 11 November 2002 Published online 1st April 2003
RID="a"
ID="a"e-mail: zhou@mpikg-golm.mpg.de 相似文献
2.
G.J. Rodgers Y.J. Yap 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):129-132
A model of herding is introduced which is exceptionally simple, incorporating only two phenomena, growth and addition. At
each time step either (i) with probability p the system grows through the introduction of a new agent or (ii) with probability q = 1 - p a free agent already in the system is added at random to a group of size k with rate Ak. Two versions of the model, A
k = k and A
k = 1, are solved and in both versions we find two different types of behaviour. When p > 1/2 all the moments of the distribution of group sizes are linear in time for large time and the group distribution is
power-law. When p < 1/2 the system runs out of free agents in a finite time.
Received 12 February 2002 Published online 9 July 2002 相似文献
3.
G. De Smedt C. Godrèche J.M. Luck 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):215-225
We consider a ferromagnetic Ising chain evolving under Kawasaki dynamics at zero temperature. We investigate the statistics
of the blocking time, as well as various characteristics of the metastable configurations reached by the system, including
the statistics of the final energy, the spin correlations, and the distribution of domain sizes. Results of extensive numerical
simulations are compared with analytical predictions made for the a priori ensemble of all blocked configurations with equal weights. Qualitative differences are found, e.g. in the domain sizes, which are found to be neither statistically independent nor exponentially distributed.
Received 24 October 2002 / Received in final form 13 January 2003 Published online 1st April 2003
RID="a"
ID="a"e-mail: luck@spht.saclay.cea.fr
RID="b"
ID="b"URA 2306 of CNRS 相似文献
4.
C.M. Horowitz E.V. Albano 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):563-569
The relationship between a microscopic parameter p, that is related to the probability of choosing a mechanism of deposition, and the stochastic equation for the interface's
evolution is studied for two different models. It is found that in one model, that is similar to ballistic deposition, the
corresponding stochastic equation can be represented by a Kardar-Parisi-Zhang (KPZ) equation where both λ and ν depend on
p in the following way: ν(p) = νp and λ(p) = λp
3/2. Furthermore, in the other studied model, which is similar to random deposition with relaxation, the stochastic equation
can be represented by an Edwards-Wilkinson (EW) equation where ν depends on p according to ν(p) = νp
2. It is expected that these results will help to find a framework for the development of stochastic equations starting from
microscopic details of growth models.
Received 26 August 2002 / Received in final form 20 November 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: ealbano@inifta.unlp.edu.ar 相似文献
5.
We consider the spin-glass phase of the Sherrington-Kirkpatrick model in the presence of a magnetic field. The series expansion
of the Parisi function q(x) is computed at high orders in powers of τ = T
c - T and H. We find that none of the Parisi-Toulouse scaling hypotheses on the q(x) behavior strictly holds, although some of them are violated only at high orders. The series is resummed yielding results
in the whole spin-glass phase which are compared with those from a numerical evaluation of the q(x). At the high order considered, the transition turns out to be third order on the Almeida-Thouless line, a result which is
confirmed rigorously computing the expansion of the solution near the line at finite τ. The transition becomes smoother for
infinitesimally small field while it is third order at strictly zero field.
Received 3 March 2003 Published online 4 June 2003
RID="a"
ID="a"e-mail: andrea.crisanti@phys.uniroma1.it
RID="b"
ID="b"e-mail: tommaso.rizzo@phys.uniroma1.it
RID="c"
ID="c"e-mail: temtam@helios.elte.hu 相似文献
6.
R.L. Leheny Y.S. Lee G. Shirane R.J. Birgeneau 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):287-290
Inelastic neutron scattering with high wave-vector resolution has characterized the propagation of transverse spin wave modes
near the antiferromagnetic zone center in the metastable domain state of a random field Ising magnet. A well-defined, long
wavelength excitation is observed despite the absence of long-range magnetic order. Direct comparisons with the spin wave
dispersion in the long-range ordered antiferromagnetic state reveal no measurable effects from the domain structure. This
result recalls analogous behavior in thermally disordered anisotropic spin chains but contrasts sharply with that of the phonon
modes in relaxor ferroelectrics.
Received 2 November 2002 / Received in final form 4 February 2003 Published online 11 April 2003
RID="a"
ID="a"leheny@pha.jhu.edu 相似文献
7.
J. Yi G. Cuniberti M. Porto 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(2):221-225
We examine the anomalous behavior of the transmittance through a one-dimensional ring having two branches of different lengths,
as determined by the lead positions. Jumps in the transmittance phase are occurring in correspondence to both (a) zeros in
the transmission at the eigenstates of the isolated ring and (b) destructive interference events. It is also found that when
the ratio of the branch lengths is given by p/q satisfying p + q = 0(mod 4), the two characteristic zeros merge into a single point and the transmittance phase becomes identical to the so-called
Friedel phase.
Received 7 June 2002 / Received in final form 11 December 2002 Published online 4 June 2003
RID="a"
ID="a"e-mail: juyeon.yi@physik.uni-regensburg.de 相似文献
8.
R. Schorr H. Rieger 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):347-354
We consider the optimal paths in a d-dimensional lattice, where the bonds have isotropically correlated random weights. These paths can be interpreted as the ground state configuration of a simplified polymer model in a random
potential. We study how the universal scaling exponents, the roughness and the energy fluctuation exponent, depend on the
strength of the disorder correlations. Our numerical results using Dijkstra's algorithm to determine the optimal path in directed
as well as undirected lattices indicate that the correlations become relevant if they decay with distance slower than 1/r in d = 2 and 3. We show that the exponent relation 2ν - ω = 1 holds at least in d = 2 even in case of correlations. Both in two and three dimensions, overhangs turn out to be irrelevant even in the presence
of strong disorder correlations.
Received 20 December 2002 / Received in final form 10 April 2003 Published online 20 June 2003
RID="a"
ID="a"e-mail: schorr@lusi.uni-sb.de 相似文献
9.
F. Mila D. Dean 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):301-306
Motivated by the observation of a spin-glass transition in almost disorder-free Kagome antiferromagnets, and by the specific
form of the effective low-energy model of the S = 1/2, trimerized Kagome antiferromagnet, we investigate the possibility to obtain a spin-glass behavior in two-component,
disorder-free models. We concentrate on a toy-model, a modified Ashkin-Teller model in a magnetic field that couples only
to one species of spins, for which we prove that a dynamic spin-glass behavior occurs. The dynamics of the magnetization is
closely related to that of the underlying Ising model in zero field in which spins and pseudo-spins are intimately coupled.
The spin-glass like history dependence of the magnetization is a consequence of the ageing of the underlying Ising model.
Received 21 September 2001 and Received in final form 16 January 2002 相似文献
10.
L. Zhang W. Kleemann J. Dec R. Wang M. Itoh 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):163-171
The dielectric permittivity ε′ - i
of SrTi 18O 3 (STO18) is studied under a dc electric field E as a function of the temperature, T. In ε′
vs.
T, a double-peak is found when 0 < E < 30 KV/m. While the peak at high-T is attributed to the smeared ferroelectric phase transition, the low-T one is induced by domain wall motion. The transverse Ising model including an external homogeneous and quenched random-fields
is successfully used to describe both the smeared phase transition and the domain wall response in the low-T domain state. The calculations are in good agreement with the experimental results.
Received 4 January 2002 / Received in final form 25 March 2002 Published online 19 July 2002 相似文献
11.
I. Piqueras M.J.G. Borge Ph. Dessagne J. Giovinazzo A. Huck A. Jokinen A. Knipper C. Longour G. Marguier M. Ramdhane V. Rauch O. Tengblad G. Walter Ch. Miehé 《The European Physical Journal A - Hadrons and Nuclei》2003,16(3):313-329
The beta-decay of the N = Z, even-even nucleus 72Kr has been studied at the ISOLDE PSB facility at CERN. Measurements of βγ and βγγ coincidences have enriched the decay scheme
of the daughter nucleus 72Br with 27 new low spin levels. A more precise half-life of T
1/2 = 17.1(2) s has been determined. Strong feeding to the 72Br ground state is established yielding an unambiguous J
π = 1+ assignment for this state. Candidates for the 72Br g.s. wave function are discussed in the framework of a self-consistent deformed mean-field calculation with SG2 Skyrme
force and pairing correlations. A search for beta-delayed particle emission was made and an upper limit of 10-6 for this decay branch obtained. The cumulated experimental level density of 1+ states has been fitted with the constant temperature formula. The comparison indicates that most likely all 1+ levels up to 1.2 MeV have been observed in this investigation. The corresponding nearest-neighbour level spacing does not
follow a Poisson distribution. The Gamow-Teller strength distribution is compared, in terms of nuclear deformation, with different
calculations made in the framework of the quasiparticle random phase approximation.
Received: 7 February 2002 / Accepted: 31 October 2002 / Published online: 6 March 2003
RID="a"
ID="a"e-mail: borge@pinar2.csic.es
RID="b"
ID="b"Present address: Centre d' Etudes Nucléaires de Bordeaux-Gradignan, Le Haut Vigneau, F-33175 Gradignan Cedex, France.
RID="c"
ID="c"Present address: University Mentouri, 25000 Constantine, Algeria.
Communicated by J. ?yst? 相似文献
12.
E. Caurier F. Nowacki A. Poves 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):145-150
Recent shell model calculations for the neutron-rich nuclei around the magic numbers N = 20, N = 28 and N = 40 are reviewed. We stress two points: i) The crucial role played by the monopole part of the effective interaction that
determines the evolution of the spherical mean field. In particular, the reduction in the quasiparticle gaps at the magic
numbers can erode or even erase the shell closures. ii) The rich variety of structures that can be found in these situations,
with coexisting deformed and spherical states, rapid changes of behaviour with N or Z, and the massive occurrence of intruder states as ground states.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: alfredo.poves@uam.es 相似文献
13.
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
14.
D. Karevski Y-C. Lin H. Rieger N. Kawashima F. Iglói 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):267-276
We study the critical behavior of Ising quantum magnets with broadly distributed random couplings (J), such that P(ln J) ∼ | ln J|-1 - α, α > 1, for large | ln J| (Lévy flight statistics). For sufficiently broad distributions, α < , the critical behavior is controlled by a line of fixed points, where the critical exponents vary with the Lévy index, α.
In one dimension, with = 2, we obtained several exact results through a mapping to surviving Riemann walks. In two dimensions the varying critical
exponents have been calculated by a numerical implementation of the Ma-Dasgupta-Hu renormalization group method leading to
≈ 4.5. Thus in the region 2 < α < , where the central limit theorem holds for | ln J| the broadness of the distribution is relevant for the 2d quantum Ising model.
Received 6 December 2000 and Received in final form 22 January 2001 相似文献
15.
C. Tsallis D. Prato C. Anteneodo 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(4):605-611
We consider a statistical mixture based on that of two identical harmonic oscillators which is characterized by four parameters,
namely, the concentrations (x and y) of diagonal and nondiagonal bipartite states, and their associated thermal-like noises (T/α and T, respectively). The fully random mixture of two spins 1/2 as well as the Einstein-Podolsky-Rosen (EPR) state are recovered
as particular instances. By using the conditional nonextensive entropy as introduced by Abe and Rajagopal, we calculate a
bound for the separable-entangled frontier. Although this procedure is known to provide a necessary but in general not sufficient condition for separability, it does recover, in the particular case x = T = 0 ( ∀α), the 1/3 exact result known as Peres' criterion. The x = 0 frontier remarkably resembles to the critical line associated with standard diluted ferromagnetism where the entangled
region corresponds to the ordered one and the separable region to the paramagnetic one. The entangled region generically shrinks
for increasing T or increasing α.
Received 18 April 2002 / Received in final form 11 July 2002 Published online 31 October 2002
RID="a"
ID="a"e-mail: celia@cbpf.br 相似文献
16.
G. Parisi M. Ratiéville 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):457-468
We get back to the computation of the leading finite size corrections to some random link matching problems, first adressed
by Mézard and Parisi [J. Phys. France 48, 1451 (1987)]. In the so-called bipartite case, their result is in contradiction with subsequent works. We show that they
made some mistakes, and correcting them, we get the expected result. In the non bipartite case, we agree with their result
but push the analytical treatment further.
Received 28 April 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: giorgio.parisi@roma1.infn.it
RID="b"
ID="b"e-mail: matthieu.ratieville@roma1.infn.it 相似文献
17.
E.P. Borges 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):593-595
Comment on Eur. Phys. J. B 27, 445 (2002)
We analyze the distribution of success of musicians, comparing a stretched exponential (found by J.A. Davies [Eur. Phys.
J. B 27, 445 (2002)]) with a distribution of the family of the q-exponential (presenting an intermediate power-law regime with a crossover to an exponential tail). We find that both assumptions
yield comparable results, within the available range of data, hence a definite conclusion cannot yet be taken. But this example
joins many others that has been found to be fairly described by q-exponentials (or variations of it), which may be indicative that there is a (significantly large) class of systems described
by nonextensive statistical mechanics, from where q-exponentials naturally appear.
Received 17 October 2002 Published online 31 December 2002 相似文献
18.
D. Sohler Zs. Dombrádi J. Blomqvist J. Cederkäll J. Huijnen M. Lipoglavšek M. Palacz A. Atac C. Fahlander H. Grawe A. Johnson A. Kerek W. Klamra J. Kownacki A. Likar L.-O. Norlin J. Nyberg J. Persson D. Seweryniak G. de Angelis P. Bednarczyk D. Foltescu D. Jerrestam S. Juutinen E. Mäkelä M. de Poli H.A. Roth T. Shizuma Ö. Skeppstedt G. Sletten J. Timár S. Törmänen M. Weiszflog 《The European Physical Journal A - Hadrons and Nuclei》2003,16(2):171-175
Excited states of 99Ag were populated via the 50Cr + 58Ni (261 MeV) reaction using the NORDBALL detector array equipped with charged-particle and neutron detector systems for reaction
channel separation. On the basis of the measured γγ-coincidence relations and angular distribution ratios a significantly
extended level scheme has been constructed up to E
x ∼ 7.8 MeV and I = 35/2. The experimental results were described within the framework of the shell model. Candidates for states fully aligned
in the πg
9/2
-3ν(d
5/2, g
7/2)2 valence configuration space were found at 4109 and 6265 keV.
Received: 18 June 2002 / Accepted: 11 October 2002 / Published online: 4 February 2003
RID="a"
ID="a"e-mail: sohler@atomki.hu
Communicated by J. ?yst? 相似文献
19.
E. Brézin C. De Dominicis 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):467-471
The replicated field theory of the random field Ising model involves the couplings of replicas of different indices. The resulting
correlation functions involve a superposition of different types of long distance behaviours. However the n = 0 limit allows one to discuss the renormalization group properties in spite of this phenomenon. The attraction of pairs
of replicas is enhanced under renormalization flow and no stable fixed point is found. Consequently, an instability occurs
in the paramagnetic region, before one reaches the Curie line, signalling the onset of replica symmetry breaking.
Received 28 July 2000 相似文献
20.
F. Azaiez M. Belleguic D. Sohler M. Stanoiu Zs. Dombrádi O. Sorlin J. Timár F. Amorini D. Baiborodin A. Bauchet F. Becker C. Borcea C. Bourgeois Z. Dlouhy C. Donzaud J. Duprat D. Guillemaud-Mueller F. Ibrahim M.J. Lopez R. Lucas S.M. Lukyanov V. Maslov J. Mrazek C. Moore F. Nowacki B.M. Nyakó Yu.-E. Penionzhkevich M.G. Saint-Laurent F. Sarazin J.A. Scarpaci G. Sletten C. Stodel M. Taylor C. Theisen G. Voltolini 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):93-97
The structure of neutron-rich light nuclei around N = 20 and 28 has been investigated at GANIL by means of in-beam gamma-spectroscopy using fragmentation reactions of 36S and 48Ca beams on a Be target. Gamma-decay of relatively high-lying excited states have been measured for the first time in nuclei
around 32Mg and 44S. Level schemes are proposed and discussed for a large number of these neutron-rich nuclei around N = 20 and N = 28.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: azaiez@ipno.in2p3.fr 相似文献