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1.
Z.-Q. Jiang L. Guo W.-X. Zhou 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):347-355
A phenomenological investigation of the endogenous and
exogenous dynamics in the fluctuations of capital fluxes is carried
out on the Chinese stock market using mean-variance analysis,
fluctuation analysis, and their generalizations to higher orders.
Non-universal dynamics have been found not only in the scaling
exponent α, which is different from the universal values 1/2
and 1, but also in the distributions of the ratio η=
σexo / σendo of individual stocks. Both
the scaling exponent α of fluctuations and the Hurst exponent
Hi increase in logarithmic form with the time scale Δt
and the mean traded value per minute 〈fi 〉,
respectively. We find that the scaling exponent αendo
of the endogenous fluctuations is independent of the time scale.
Multiscaling and multifractal features are observed in the data as
well. However, the inhomogeneous impact model is not verified. 相似文献
2.
A.S. Kovalev F.G. Mertens H.J. Schnitzer 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(2):133-145
The dynamics of a non-planar vortex in a two-dimensional easy-plane ferromagnet of finite size is studied. Spin dynamics
simulations show small cycloidal oscillations of the vortex around its mean path. In contrast to an earlier phenomenological
theory we give a physical explanation: The oscillations occur due to the interaction of the vortex with coherent spin waves
which are excited by this vortex at the moment when it starts to move, in order to conserve the total energy and angular momentum.
The calculation of these quantities yields the frequencies and amplitudes of the cycloidal oscillations in good agreement
with the simulation data.
Received 9 December 2002 Published online 4 June 2003
RID="a"
ID="a"e-mail: franz.mertens@uni-bayreuth.de 相似文献
3.
We investigate stationary and travelling wave solutions of the classical one-dimensional transverse field Ising model. Results
are given on the existence, shape and stability of kink solutions and periodic solutions. We review recent analytical results
(e.g., the proof of existence of a one-parameter family of stationary kink solutions and the proof of existence of travelling wave
kink solutions with nonzero velocity c≠ 0) and extend them by the use of numerical methods. Small oscillations arising in the tails of travelling kink solutions
are investigated numerically. In the end, stability analysis puts some light on pinning effects.
Received 23 February 2001 and Received in final form 4 October 2001 相似文献
4.
Z.-Z. Zhang S.-G. Zhou T. Zou 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(3):259-271
In this paper, firstly, we study analytically the topological
features of a family of hierarchical lattices (HLs) from the view
point of complex networks. We derive some basic properties of HLs
controlled by a parameter q: scale-free degree distribution with
exponent γ=2+ln 2/(ln q), null clustering
coefficient, power-law behavior of grid coefficient, exponential
growth of average path length (non-small-world), fractal scaling
with dimension dB=ln (2q)/(ln 2), and disassortativity.
Our results show that scale-free networks are not always
small-world, and support the conjecture that self-similar scale-free
networks are not assortative. Secondly, we define a deterministic
family of graphs called small-world hierarchical lattices (SWHLs).
Our construction preserves the structure of hierarchical lattices,
including its degree distribution, fractal architecture, clustering
coefficient, while the small-world phenomenon arises. Finally, the
dynamical processes of intentional attacks and collective
synchronization are studied and the comparisons between HLs and
Barabási-Albert (BA) networks as well as SWHLs are shown. We
find that the self-similar property of HLs and SWHLs significantly
increases the robustness of such networks against targeted damage on
hubs, as compared to the very vulnerable non fractal BA networks,
and that HLs have poorer synchronizability than their counterparts
SWHLs and BA networks. We show that degree distribution of
scale-free networks does not suffice to characterize their
synchronizability, and that networks with smaller average path
length are not always easier to synchronize. 相似文献
5.
Inevitable self-similar topology of binary trees and their diverse hierarchical density 总被引:1,自引:0,他引:1
K. Paik P. Kumar 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(2):247-258
Self-similar topology, which can be characterized
as power law size distribution, has been found in diverse tree
networks ranging from river networks to taxonomic trees. In this
study, we find that the statistical self-similar topology is an
inevitable consequence of any full binary tree organization. We show
this by coding a binary tree as a unique bifurcation string. This
coding scheme allows us to investigate trees over the realm from
deterministic to entirely random trees. To obtain partial random
trees, partial random perturbation is added to the deterministic
trees by an operator similar to that used in genetic algorithms. Our
analysis shows that the hierarchical density of binary trees is more
diverse than has been described in earlier studies. We find that the
connectivity structure of river networks is far from strict
self-similar trees. On the other hand, organization of some social
networks is close to deterministic supercritical trees. 相似文献
6.
J.P. Zagorodny Y. Gaididei F.G. Mertens A.R. Bishop 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):471-487
We investigate the dynamics of out-of-plane (OP) vortices, in a 2-dimensional (2D) classical Heisenberg magnet with a weak
anisotropy in the coupling of z-components of spins (easy plane anisotropy), on square lattices, under the influence of a rotating in-plane (IP) magnetic
field. Switching of the z-component of magnetization of the vortex is studied in computer simulations as a function of the magnetic field's amplitude
and frequency. The effects of the size and the anisotropy of the system on the switching process are shown. An approximate
dynamical equivalence of the system, in the bulk limit, to another system with both IP and OP static fields in the rotating reference frame is demonstrated, and qualitatively the same switching and critical behavior is obtained
in computer simulations for both systems. We briefly discuss the interplay between finite size effects (image vortices) and
the applied field in the dynamics of OP vortices. In the framework of a discrete reduced model of the vortex core we propose a mechanism for switching the vortex polarization, which can account qualitatively
for all our results. A coupling between the IP movement (trajectories) of the vortex center and the OP core structure oscillations,
due to the discreteness of the underlying lattice, is shown. A connection between this coupling and our reduced model is made
clear, through an analogy with a generalized Thiele equation.
Received 6 June 2002 / Received in final form 4 November 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: juan.zagorodny@uni-bayreuth.de 相似文献
7.
Zhongzhi Zhang Shuigeng Zhou Tao Zou Lichao Chen Jihong Guan 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(2):259-264
We make a mapping from Sierpinski fractals to a new class
of networks, the incompatibility networks, which are scale-free,
small-world, disassortative, and maximal planar graphs. Some
relevant characteristics of the networks such as degree
distribution, clustering coefficient, average path length, and
degree correlations are computed analytically and found to be
peculiarly rich. The method of network representation can be applied
to some real-life systems making it possible to study the complexity
of real networked systems within the framework of complex network
theory. 相似文献
8.
I.I. Satija 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):345-348
Disordered systems exhibiting exponential localization are mapped to anisotropic spin chains with localization length being
related to the anisotropy of the spin model. This relates localization phenomenon in fermions to the rotational symmetry breaking
in the critical spin chains. One of the intriguing consequence is that the statement of Onsager universality in spin chains
implies universality of the localized fermions where the fluctuations in localized wave functions are universal. We further
show that the fluctuations about localized nonrelativistic fermions describe relativistic fermions. This provides a new approach
to understand the absence of localization in disordered Dirac fermions. We investigate how disorder affects well known universality
of the spin chains by examining the multifractal exponents. Finally, we examine the effects of correlations on the localization
characteristics of relativistic fermions.
Received 28 September 2001 / Received in final form 30 November 2001 Published online 2 October 2002
RID="a"
ID="a"e-mail: isatija@nickel.nist.gov 相似文献
9.
S. Murugesh Radha Balakrishnan 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):193-196
We apply our recent formalism establishing new connections between the geometry of moving space curves and soliton equations,
to the nonlinear Schr?dinger equation (NLS). We show that any given solution of the NLS gets associated with three distinct
space curve evolutions. The tangent vector of the first of these curves, the binormal vector of the second and the normal
vector of the third, are shown to satisfy the integrable Landau-Lifshitz (LL) equation = ×, ( = 1). These connections enable us to find the three surfaces swept out by the moving curves associated with the NLS. As an
example, surfaces corresponding to a stationary envelope soliton solution of the NLS are obtained.
Received 5 December 2001 Published online 2 October 2002
RID="a"
ID="a"e-mail: radha@imsc.ernet.in 相似文献
10.
M. Holtschneider W. Selke 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(2):147-154
Classical uniaxially anisotropic Heisenberg and XY antiferromagnets
in a field along the easy axis on a square lattice
are analysed, applying ground state
considerations and Monte Carlo techniques. The models are known to
display antiferromagnetic and spin-flop phases. In the Heisenberg
case, a single-ion anisotropy is added to the XXZ antiferromagnet,
enhancing or competing with the uniaxial exchange anisotropy. Its
effect on the stability of non-collinear structures of biconical
type is studied. In the case of the anisotropic XY antiferromagnet,
the transition region between the antiferromagnetic and spin-flop
phases is found to be dominated by degenerate bidirectional
fluctuations. The phase diagram is observed to resemble closely
that of the XXZ antiferromagnet without single-ion anisotropy. 相似文献
11.
D. Hinzke U. Nowak D.A. Garanin 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):435-438
We simulated the field-dependent magnetization m(H,T) and the uniform susceptibility of classical Heisenberg antiferromagnets in the chain and square-lattice geometry using Monte Carlo methods. The results
confirm the singular behavior of at small T,H: and , where D=3 is the number of spin components, J
0=zJ, and z is the number of nearest neighbors. A good agreement is achieved in a wide range of temperatures T and magnetic fields H with the first-order 1/D expansion results (D.A. Garanin, J. Stat. Phys. 83, 907 (1996)).
Received 20 March 2000 相似文献
12.
S. Solomon P. Richmond 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(2):257-261
In recent years we have found that logistic systems of the Generalized Lotka-Volterra type (GLV) describing statistical systems
of auto-catalytic elements posses power law distributions of the Pareto-Zipf type. In particular, when applied to economic
systems, GLV leads to power laws in the relative individual wealth distribution and in market returns. These power laws and
their exponent α are invariant to arbitrary variations in the total wealth of the system and to other endogenously and exogenously
induced variations.
Received 31 December 2001 相似文献
13.
H. Kachkachi D.A. Garanin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(3):291-300
Analytical calculations based on finite-size spin-wave theory and Monte Carlo (MC) simulations are performed to investigate
the validity of the well-known relation m(H, T) = M(H, T)B
D[M(H, T)
H/T] between the induced magnetization m of the magnetic particle and its intrinsic magnetization M for the Ising and isotropic classical models (B
D(x) is the Langevin function, D is the number of spin components, is the number of atoms in the particle). It follows from general arguments and from our analytical results for the Heisenberg
model at T≪T
c that this relation is not exact for any finite D and nonzero temperature. Nevertheless, corrections to this formula remain very small practically in the whole range T < T
c if ≫ 1, as confirmed by our Monte Carlo calculations. At T
T
c/4 there is a good agreement between the MC and finite-size spin-wave calculations for the field dependence of m and M for the Heisenberg model with free boundary conditions.
Received 1st December 2000 相似文献
14.
A.S. Kovalev S. Komineas F.G. Mertens 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):89-100
Vortex-antivortex pairs in 2D easy-plane ferromagnets have characteristics of solitons in two dimensions. We investigate numerically
and analytically the dynamics of such vortex pairs. In particular we simulate numerically the head-on collision of two pairs
with different velocities for a wide range of the total linear momentum of the system. If the momentum difference of the two
pairs is small, the vortices exchange partners, scatter at an angle depending on this difference, and form two new identical
pairs. If it is large, the pairs pass through each other without losing their identity. We also study head-tail collisions.
Two identical pairs moving in the same direction are bound into a moving quadrupole in which the two vortices as well as the
two antivortices rotate around each other. We study the scattering processes also analytically in the frame of a collective
variable theory, where the equations of motion for a system of four vortices constitute an integrable system. The features
of the different collision scenarios are fully reproduced by the theory. We finally compare some aspects of the present soliton
scattering with the corresponding situation in one dimension.
Received 18 September 2001 相似文献
15.
G.-F. Gu W. Chen W.-X. Zhou 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(1):81-87
The statistical properties of the bid-ask spread of a
frequently traded Chinese stock listed on the Shenzhen Stock
Exchange are investigated using the limit-order book data. Three
different definitions of spread are considered based on the time
right before transactions, the time whenever the highest buying
price or the lowest selling price changes, and a fixed time
interval. The results are qualitatively similar no matter linear
prices or logarithmic prices are used. The average spread exhibits
evident intraday patterns consisting of a big L-shape in morning
transactions and a small L-shape in the afternoon. The distributions
of the spread with different definitions decay as power laws. The
tail exponents of spreads at transaction level are well within the
interval (2,3) and that of average spreads are well in line with
the inverse cubic law for different time intervals. Based on the
detrended fluctuation analysis, we found the evidence of long memory
in the bid-ask spread time series for all three definitions, even
after the removal of the intraday pattern. Using the classical
box-counting approach for multifractal analysis, we show that the
time series of bid-ask spread do not possess multifractal nature. 相似文献
16.
I. Vodenska-Chitkushev F. Z. Wang P. Weber K. Yamasaki S. Havlin H. E. Stanley 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(2):217-223
We analyze the S&P 500 index data for the 13-year period, from
January 1, 1984 to December 31, 1996, with one data point every 10
min. For this database, we study the distribution and clustering
of volatility return intervals, which are defined as the time
intervals between successive volatilities above a certain threshold
q. We find that the long memory in the volatility leads to a
clustering of above-median as well as below-median return intervals.
In addition, it turns out that the short return intervals form
larger clusters compared to the long return intervals. When
comparing the empirical results to the ARMA-FIGARCH and fBm models
for volatility, we find that the fBm model predicts scaling better
than the ARMA-FIGARCH model, which is consistent with the argument
that both ARMA-FIGARCH and fBm capture the long-term dependence in
return intervals to a certain extent, but only fBm accounts for the
scaling. We perform the Student's t-test to compare the empirical
data with the shuffled records, ARMA-FIGARCH and fBm. We analyze
separately the clusters of above-median return intervals and the
clusters of below-median return intervals for different thresholds
q. We find that the empirical data are statistically different
from the shuffled data for all thresholds q. Our results also
suggest that the ARMA-FIGARCH model is statistically different from
the S&P 500 for intermediate q for both above-median and
below-median clusters, while fBm is statistically different from
S&P 500 for small and large q for above-median clusters and for
small q for below-median clusters. Neither model can fully explain
the entire regime of q studied. 相似文献
17.
J. Lages D.L. Shepelyansky 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(1):129-133
We study analytically and numerically the problem of two particles with a long range attractive interaction on a two-dimensional
(2d) lattice with disorder. It is shown that below some critical disorder the interaction creates delocalized coupled states
near the Fermi level. These states appear inside well localized noninteracting phase and have a form of two-particle ring
which diffusively propagates over the lattice.
Received 29 September 2000 and Received in final form 15 January 2001 相似文献
18.
J. Zhang H. Huang 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(2):247-251
In order to describe the entangled network structure in polymer melts visually, we propose an evolving network model with
community structure. This network model grows according to the inner-community and inter-community preferential mechanisms
of both community sizes and node degrees. Numerical simulation results indicate that the cumulative distribution of community
size and node degree distribution follow power-law distributions P(S≥s)∼s-υ and P(k)∼k-γ respectively, with the exponents of υ≥1 and . 相似文献
19.
A. Montanari 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(1):121-136
Gallager codes are the best error-correcting codes to date. In this paper we study them by using the tools of statistical
mechanics. The corresponding statistical mechanics model is a spin model on a sparse random graph. The model can be solved
by elementary methods (i.e. without replicas) in a large connectivity limit. For low enough temperatures it presents a completely frozen glassy phase
(q
EA = 1). The same scenario is shown to hold for finite connectivities. In this case we adopt the replica approach and exhibit
a one-step replica symmetry breaking order parameter. We argue that our ansatz yields the exact solution of the model. This
allows us to determine the whole phase diagram and to understand the performances of Gallager codes.
Received 9 April 2001 相似文献
20.
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