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1.
D. Loison K.D. Schotte 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):125-137
Starting from the hypothesis of a second order transition we have studied modifications of the original Heisenberg antiferromagnet
on a stacked triangular lattice (STA-model) by the Monte Carlo technique. The change is a local constraint restricting the
spins at the corners of selected triangles to add up to zero without stopping them from moving freely (STAR-model). We have
studied also the closely related dihedral and trihedral models which can be classified as Stiefel models. We have found indications
of a first order transition for all three modified models instead of a universal critical behavior. This is in accordance
with the renormalization group investigations but disagrees with the Monte Carlo simulations of the original STA-model favoring
a new universality class. For the corresponding x-y antiferromagnet studied before, the second order nature of the transition could also not be confirmed.
Received 17 May 1999 and Received in final form 30 July 1999 相似文献
2.
D. Loison K.D. Schotte 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):735-743
The nature of the phase transition for the XY stacked triangular antiferromagnet (STA) is a controversial subject at present. The field theoretical renormalization group
(RG) in three dimensions predicts a first order transition. This prediction disagrees with Monte-Carlo (MC) simulations which
favor a new universality class or a tricritical transition. We simulate by the Monte-Carlo method two models derived from
the STA by imposing the constraint of local rigidity which should have the same critical behavior as the original model. A
strong first order transition is found. Following Zumbach we analyze the second order transition observed in MC studies as
due to a fixed point in the complex plane. We review the experimental results in order to clarify the critical behavior observed.
Received: 18 February 1998 / Revised: 24 April 1998 / Accepted: 30 April 1998 相似文献
3.
E. Albayrak M. Keskin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):505-510
A two-fold Cayley tree graph with fully q-coordinated sites is constructed and the spin-1 Ising Blume-Emery-Griffiths model on the constructed graph is solved exactly
using the exact recursion equations for the coordination number q = 3. The exact phase diagrams in (kT/J, K/J ) and (kT/J, D/J) planes are obtained for various values of constants D/J and K/J, respectively, and the tricritical behavior is found. It is observed that when the negative biquadratic exchange (K) and the positive crystal-field (D) interactions are large enough, the tricritical point disappears in the (kT/J, K/J) plane. On the other hand, the system always exhibits a tricritical behavior in the phase diagram of (kT/J, D/J) plane.
Received 8 June 2001 and Received in final form 28 September 2001 相似文献
4.
Exact solution of the one-dimensional spin-\frac{\mathsf 3}{\mathsf 2} Ising model in magnetic field
A. Avella F. Mancini 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(4):527-539
In this paper, we study the Ising model with general spin S in
presence of an external magnetic field by means of the equations of
motion method and of the Green's function formalism. First, the
model is shown to be isomorphic to a fermionic one constituted of
2S species of localized particles interacting via an intersite
Coulomb interaction. Then, an exact solution is found, for any
dimension, in terms of a finite, complete set of eigenoperators of
the latter Hamiltonian and of the corresponding eigenenergies. This
explicit knowledge makes possible writing exact expressions for the
corresponding Green's function and correlation functions, which turn
out to depend on a finite set of parameters to be self-consistently
determined. Finally, we present an original procedure, based on
algebraic constraints, to exactly fix these latter parameters in the
case of dimension 1 and spin
. For this latter case and,
just for comparison, for the cases of dimension 1 and spin
[F. Mancini, Eur. Phys. J. B 45, 497 (2005)] and
spin 1 [F. Mancini, Eur. Phys. J. B 47, 527 (2005)],
relevant properties such as magnetization 〈S 〉 and
square magnetic moment 〈S2 〉, susceptibility and
specific heat are reported as functions of temperature and external
magnetic field both for ferromagnetic and antiferromagnetic
couplings. It is worth noticing the use we made of composite
operators describing occupation transitions among the 3 species of
localized particles and the related study of single, double and
triple occupancy per site. 相似文献
5.
A. Erdinç O. Canko E. Albayrak 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(4):521-529
The complete phase diagrams of the antiferromagnetic spin-2
Blume-Capel Ising system is studied on the Bethe lattice by the use
of exact recursion relations. In order to specify the states of the
system, i.e. the different spin configurations, the ground state
phase diagram is obtained on the (H/|J|, D/|J|) plane
corresponding to the reduced external magnetic and crystal fields,
respectively. As a result, the thermal change of the
order-parameters, the magnetisations belonging to the two sublattice
system, was investigated to obtain the full phase diagrams of the
system on the (H/|J|, kT/|J|) planes. The behavior of the
order-parameters with respect to the external magnetic field was
also studied for the given values of D/|J|. Besides the
interesting thermal and external magnetic field change of the
sublattice magnetisations, the system also exhibits interesting
critical behaviors including first- and second-order phase
transitions, therefore, triciritical points and the reentrant
behavior. The calculations are carried out for the coordination
number q=4, corresponding to the square lattice, only. 相似文献
6.
On the properties of small-world network models 总被引:7,自引:0,他引:7
A. Barrat M. Weigt 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):547-560
We study the small-world networks recently introduced by Watts and Strogatz [Nature 393, 440 (1998)], using analytical as well as numerical tools. We characterize the geometrical properties resulting from the
coexistence of a local structure and random long-range connections, and we examine their evolution with size and disorder
strength. We show that any finite value of the disorder is able to trigger a “small-world” behaviour as soon as the initial
lattice is big enough, and study the crossover between a regular lattice and a “small-world” one. These results are corroborated
by the investigation of an Ising model defined on the network, showing for every finite disorder fraction a crossover from
a high-temperature region dominated by the underlying one-dimensional structure to a mean-field like low-temperature region.
In particular there exists a finite-temperature ferromagnetic phase transition as soon as the disorder strength is finite.
[0.5cm]
Received 29 March 1999 and Received in final form 21 May 1999 相似文献
7.
L. Yu Z.-K. Shi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(1):115-120
The car-following model of traffic flow is extended to
take into account the relative velocity. The stability condition
of this model is obtained by using linear stability theory. It is
shown that the stability of uniform traffic flow is improved by
considering the relative velocity. From nonlinear analysis, it is
shown that three different density waves, that is, the triangular
shock wave, soliton wave and kink-antikink wave, appear in the
stable, metastable and unstable regions of traffic flow
respectively. The three different density waves are described by
the nonlinear wave equations: the Burgers equation, Korteweg-de
Vries (KdV) equation and modified Korteweg-de Vries (mKdV)
equation, respectively. 相似文献
8.
Z.-P. Li Y.-C. Liu 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(3):367-374
By introducing relative velocities of arbitrary number of
cars ahead into the full velocity difference models (FVDM), we
present a forward looking relative velocity model (FLRVM) of
cooperative driving control system. To our knowledge, the model is
an improvement over the similar extension in the forward looking
optimal velocity models (FLOVM), because it is more reasonable and
realistic in implement of incorporating intelligent transportation
system in traffic. Then the stability criterion is investigated by
the linear stability analysis with finding that new consideration
theoretically lead to the improvement of the stability of traffic
flow, and the validity of our theoretical analysis is confirmed by
direct simulations. In addition, nonlinear analysis of the model
shows that the three waves: triangular shock wave, soliton wave and
kink-antikink wave appear respectively in stable, metastable and
unstable regions. These correspond to the solutions of the Burgers
equation, Korteweg-de Vries (KdV) equation and modified Korteweg-de
Vries (mKdV) equation. 相似文献
9.
F.A. da Costa J.M de Araújo 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):313-316
The zero-temperature TAP equations for the spin-1 Ghatak-Sherrington model are investigated. The spin-glass energy density
(ground state) is determined as a function of the anisotropy crystal field D for a large number of spins. This allows us to locate a first-order transition between the spin-glass and paramagnetic phases
within a good accuracy. The total number of solutions is also determined as a function of D.
Received 25 November 1999 相似文献
10.
J.M. de Araújo F.A. da Costa F.D. Nobre 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):661-667
A spin-1 model, appropriated to study the competition between bilinear (J
ij
S
i
S
j
) and biquadratic (K
ij
S
i
2
S
j
2) random interactions, both of them with zero mean, is investigated. The interactions are infinite-ranged and the replica
method is employed. Within the replica-symmetric assumption, the system presents two phases, namely, paramagnetic and spin-glass,
separated by a continuous transition line. The stability analysis of the replica-symmetric solution yields, besides the usual
instability associated with the spin-glass ordering, a new phase due to the random biquadratic couplings between the spins.
Received 18 May 1999 and Received in final form 20 October 1999 相似文献
11.
P. Borrmann H. Stamerjohanns E.R. Hilf D. Tománek 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):117-119
In contrast to the experimentally widely used isentropic demagnetization process for cooling to ultra-low temperatures we
examine a particular classical model system that does not cool, but rather heats up with isentropic demagnetization. This
system consists of several magnetite particles in a colloidal suspension, and shows the uncommon behavior of disordering structurally
while ordering magnetically in an increasing magnetic field. For a six-particle system, we report an uncommon structural transition
from a ring to a chain as a function of magnetic field and temperature.
Received 5 September 2000 相似文献
12.
The exact solutions for the energy spectrum of the XX model with a periodic
coupling and an external transverse magnetic field h are obtained. The
diagonalization procedure is discussed, and analytical and numerical solutions
are given. Using the solutions for period-two coupling, the free energy,
entropy, and specific heat are calculated as functions of temperature and
applied transverse external magnetic field. Their expressions show that below
a particular value v and above a value u of the magnetic field |h|, the
entropy and the specific heat vanish exponentially in the low temperature
limit. 相似文献
13.
J. Cao S.-J. Gu Y. Wang H.-Q. Lin 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(1):147-151
The critical behaviors of the entropy correlation
effects in the one dimensional J1-J2 Heisenberg model are
studied. It is shown that the mutual information or the
correlation entropy captures the key features of information about
critical fluctuations and can be used to quantify the quantum and
finite-temperature phase transitions. At the critical point, the
mutual information is power-law decay and the entanglement
correlation length is infinite. While far away from the critical
point, the mutual information is exponential decay and the
entanglement correlation length is finite. A universal property of
the mutual information is also found. Based on the critical
behaviors of the mutual information, a new method to quantify the
infinite order phase transition in the system is proposed. 相似文献
14.
M. G. Donato S. Prestipino P. V. Giaquinta 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):621-627
We analyse the statistical entropy of two-dimensional lattice-gas models in terms of the contributions which arise from space
correlations of increasing order. The “residual multiparticle entropy”, defined as the contribution to the excess entropy
that is associated with correlations involving more than two particles, is calculated for the Ising and Coulomb lattice gases.
The thermodynamic behaviour of the residual multiparticle entropy is then discussed in relation to the phase diagram of the
model and the existence of underlying signatures of order-disorder phase transitions is also investigated.
Received 31 December 1998 and Received in final form 8 March 1999 相似文献
15.
Yuan Chen Shuohong Guo Zhibing Li Aijun Ye 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):97-104
The kinetic spherical model with long-ranged interactions and an arbitrary initial order m0 quenched from a very high temperature to T
is solved. In the short-time regime, the bulk order increases with a power law in both the critical and phase-ordering dynamics.
To the latter dynamics, a power law for the relative order is found in the intermediate time-regime. The short-time scaling relations of small m0 are generalized to an arbitrary m0 and all the time larger than . The characteristic functions for the scaling of m0 and for are obtained. The crossover between scaling regimes is discussed in detail.
Received 17 September 1999 相似文献
16.
S. G. Magalhães F. M. Zimmer C. J. Kipper E. J. Calegari 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):209-218
The competition among spin glass (SG), antiferromagnetism (AF)
and local pairing superconductivity (PAIR) is studied in a two-sublattice fermionic Ising spin glass model with a local BCS
pairing interaction in the presence of an applied magnetic transverse field Γ. In the present approach, spins in different
sublattices interact with a Gaussian random coupling with an antiferromagnetic mean J0 and standard deviation J.
The problem is formulated in the path integral formalism in which spin operators are represented by
bilinear combinations of Grassmann variables. The saddle-point Grand Canonical potential
is obtained within the static approximation and the replica symmetric ansatz. The results are analysed in phase diagrams in
which the AF and the SG phases can occur for small g (g is the strength of the local superconductor coupling written in units
of J), while the PAIR phase appears as unique solution for large g. However, there is a complex line transition separating
the PAIR phase from the others. It is second order at high temperature that ends in a tricritical point. The quantum fluctuations
affect deeply the transition lines and the tricritical point due to the presence of Γ. 相似文献
17.
E. Brézin C. De Dominicis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):71-76
The field theory of a short range spin glass with Gaussian random interactions, is considered near the upper critical dimension
six. In the glassy phase, replica symmetry breaking is accompanied with massless Goldstone modes, generated by the breaking
of reparametrization invariance of a Parisi type solution. Twisted boundary conditions are thus imposed at two opposite ends
of the system in order to study the size dependence of the twist free energy. A loop-expansion is performed to first order
around a twisted background. It is found, as expected but it is non trivial, that the theory does renormalize around such
backgrounds, as well as for the bulk. However two main differences appear, in comparison with simple ferromagnetic transitions:
(i) the loop expansion yields a (negative) anomaly in the size dependence of the free energy, thereby lifting the lower critical
dimension to a value greater than two (ii) the free energy is lowered by twisting the boundary conditions. This situation
is common in spin glasses, reflecting the non-positivity of mode multiplicity in replica symmetry breaking, but its physical
meaning is still unclear.
Received 12 April 2002 / Received in final form 30 July 2002 Published online 19 November 2002 相似文献
18.
We have performed small angle neutron scattering experiments on the binary fluid mixture n-C6H14+n-C8F18 imbibed inside porous Vycor glass in the thermodynamic region corresponding to the bulk critical one. The resulting structure
can be represented as the sum of a temperature dependent Lorentzian term and a term describing the interference between the
porous matrix, a shell part richer in one component coating the glass surface, and a core part richer in the other component.
We observe critical fluctuations extending over distances markedly larger than the mean pore size.
Received 20 May 1999 相似文献
19.
V. Sofonea K.R. Mecke 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):99-112
The time evolution of the morphology of homogeneous phases during spinodal decomposition is described using a family of morphological
measures known as Minkowski functionals. They provide the characteristic length scale L of patterns in a convenient, statistically robust, and computationally inexpensive way. They also allow one to study the
scaling behavior of the content, shape, and connectivity of spatial structures and to define the crossover from the early
stage decomposition to the late stage domain growth. We observe the scaling behavior with , , and depending on the viscosity of the fluid. When approaching the spinodal density , we recover the prediction for the early time spinodal decomposition.
Received 3 March 1998 相似文献