共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Esser S. Grossmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):467-482
We suggest a new, renormalization group (RG) based, nonperturbative method for treating the intermittency problem of fully
developed turbulence which also includes the effects of a finite boundary of the turbulent flow. The key idea is not to try
to construct an elimination procedure based on some assumed statistical distribution, but to make an ansatz for possible RG
transformations and to pose constraints upon those, which guarantee the invariance of the nonlinear term in the Navier-Stokes
equation, the invariance of the energy dissipation, and other basic properties of the velocity field. The role of length scales
is taken to be inverse to that in the theory of critical phenomena; thus possible intermittency corrections are connected
with the outer length scale. Depending on the specific type of flow, we find different sets of admissible transformations
with distinct scaling behaviour: for the often considered infinite, isotropic, and homogeneous system K41 scaling is enforced,
but for the more realistic plane Couette geometry no restrictions on intermittency exponents were obtained so far.
Received: 28 December 1997 / Accepted: 6 August 1998 相似文献
2.
E.M. de Sousa Luz A.F. Siqueira U.M.S. Costa M.L. Lyra 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):115-118
The recent improvements on the technology for developing high-quality thin magnetic films has renewed the interest in the
study of surface effects in both static and dynamic magnetic responses. In this work, we use a Monte-Carlo algorithm with
Metropolis dynamics together with a spreading of damage technique to study the interplay between the effects of finite thickness
and surface ordering field in thin ferromagnetic Ising (S=1/2) films. We calculate, near the bulk critical temperature and several values of the surface field, the dependence on the
film thickness of the average magnetization M and Hamming distance D. We employ a finite size scaling analysis to show that both obey an effective one-parameter scaling but exhibit distinct
characteristic surface fields. At their corresponding characteristic surface fields both M and D become roughly thickness independent and we estimate the critical exponent characterizing the behavior of the typical scaling
lengths.
Received 29 March 1999 and Received in final form 21 April 1999 相似文献
3.
X.S. Chen V. Dohm 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):687-703
We reexamine the range of validity of finite-size scaling in the lattice model and the field theory below four dimensions. We show that general renormalization-group arguments based on the renormalizability of
the theory do not rule out the possibility of a violation of finite-size scaling due to a finite lattice constant and a finite
cutoff. For a confined geometry of linear size L with periodic boundary conditions we analyze the approach towards bulk critical behavior as at fixed for where is the bulk correlation length. We show that for this analysis ordinary renormalized perturbation theory is sufficient. On
the basis of one-loop results and of exact results in the spherical limit we find that finite-size scaling is violated for
both the lattice model and the field theory in the region . The non-scaling effects in the field theory and in the lattice model differ significantly from each other.
Received 5 February 1999 相似文献
4.
G. Abramson J.L. Vega 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(2):361-364
Multifractal critical phenomena with infinite-temperature critical point and with complex coexistence of the infinite and
finite temperature critical points are considered and it is shown that strange attractors generated by cascades of period-doubling
bifurcations (Feigenbaum scenario) as well as fields of velocity differences in fluid turbulence belong to the former subclass
of the multifractal critical phenomena, while the real traffic processes and real currency exchange processes belong to the
last (complex) subclass of the multifractal critical phenomena. Data obtained by different authors are used for this purpose.
Received 5 February 1999 相似文献
5.
S.G. Mishra P.A. Sreeram 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):287-291
Specific heat versus temperature curves for various pressures, or magnetic fields (or some other external control parameter) have been seen to
cross at a point or in a very small range of temperatures in many correlated fermion systems. We show that this behavior is
related to the possibility of existence of a quantum critical point. Vicinity to a quantum critical point in these systems
leads to a crossover from quantum to classical fluctuation regime at some temperature . The temperature at which the curves cross turns out to be near this crossover temperature. We have discussed the case of
the normal phase of liquid Helium three and the heavy fermion systems CeAl3 and UBe13 in detail within the spin fluctuation theory, a theory which inherently contains a low energy scale which can be identified
with . When the crossover scale is a homogeneous function of these control parameters there is always crossing at a point. We also
mention other theories exhibiting a low energy scale near a quantum critical point and discuss this phenomenon in those theories.
Received 25 June 1999 相似文献
6.
R. Gupta S. Biswas U.S. Ghosh C. Basu 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):635-640
Magnetic measurements of octahydrated Holmium sulphate have been carried out in the temperature range 80-300 K and analysis
of the results has been performed using a crystal field of symmetry which is the major point symmetry of the ion inferred from the polarized optical absorption studies. The most rigorous
approach of direct diagonalization of the Hamiltonian matrix constructed in the complete basis of states belonging to all
atomic terms of the ion has been employed. A new set of crystal field parameters some of which are widely different from that reported from optical
studies, has been evaluated for consistent interpretation of both the magnetic and optical data.
Received 4 August 1998 and Received in final form 4 February 1999 相似文献
7.
A. Bürgers E. Lindroth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(3):327-340
We present a detailed analysis of doubly excited resonances in H- of both and symmetry. Both resonance positions and total widths for auto-detachment are calculated using complex coordinate scaling in
a Sturmian-type basis in perimetric coordinates. The resonances are classified by approximate quantum numbers with help of
their Lewis structures. For the first time, a new class of shape resonances is reported which can be understood as resulting
from couplings between different adiabatic potentials with both binding and repulsive character. In addition, we present an
analysis of the so called mass polarisation term which gives rise to specific isotope shifts.
Received 10 March 1999 and Received in final form 18 October 1999 相似文献
8.
9.
A. Ceulemans S. Cojocaru L.F. Chibotaru 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):511-519
A continuum medium approach is proposed to describe the finite size dependent effects for the 1D isotropic Heisenberg ferromagnet.
The results are compared to the exact Bethe ansatz solution for the finite chain. The approach is shown to adequately account
for the behaviour of the eigenfunctions and eigenenergies. The continuum is obtained by integration in Fourier space via introduction of cut-offs at the integration limits and analytical continuation from the discrete lattice to the continuous
medium. It offers a new perspective on the instability of bound states, and reveals the linear behaviour of the amplitude
in the critical region and other features of the model in an analytical way. We further apply this approach to investigate
the long wavelength expansion of the master equation and to show the route of constructing reliable approximations valid for
more complicated models. It is concluded that the approach can be useful to study mesoscopic spin systems.
Received 28 May 2000 and Received in final form 6 April 2001 相似文献
10.
M. Benakli M. Gabay W.M. Saslow 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(2):197-204
Boundary conditions strongly affect the results of numerical computations for finite size inhomogeneous or incommensurate
structures. We present a method which allows to deal with this problem, both for ground state and for critical properties:
it combines fluctuating boundary conditions and specific histogram techniques. Our approach concerns classical systems possessing
a continuous symmetry as well as quantum systems. In particular, current-current correlation functions, which probe large
scale coherence of the states, can be accurately evaluated. We illustrate our method on a frustrated two dimensional XY model.
Received: 9 September 1997 / Revised: 17 October 1997 / Accepted: 3 November 1997 相似文献
11.
M. Dubé M. Rost M. Alava 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(4):691-699
Imbibition phenomena have been widely used experimentally and theoretically to study the kinetic roughening of interfaces.
We critically discuss the existing experiments and some associated theoretical approaches on the scaling properties of the
imbibition front, with particular attention to the conservation law associated to the fluid, to problems arising from the
actual structure of the embedding medium, and to external influences such as evaporation and gravity. Our main conclusion
is that the scaling of moving interfaces includes many crossover phenomena, with competition between the average capillary
pressure gradient and its fluctuations setting the maximal lengthscale for roughening. We discuss the physics of both pinned
and moving interfaces and the ability of the existing models to account for their properties.
Received 17 February 1999 and Received in final form 24 November 1999 相似文献
12.
A. Bershadskii T. Nakano D. Fukayama T. Gotoh 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):95-101
Using results of a direct numerical simulation (DNS) of 3D turbulence we show that the observed generalized scaling (i.e. scaling moments versus moments of different orders) is consistent with a lognormal-like distribution of turbulent energy dissipation fluctuations
with moderate amplitudes for all space scales available in this DNS (beginning from the molecular viscosity scale up to largest ones). Local multifractal thermodynamics has been developed to interpret the data obtained using the generalized scaling, and a new interval
of space scales with inverse cascade of generalized energy has been found between dissipative and inertial intervals of scales
for sufficiently large values of the Reynolds number.
Received 21 July 2000 相似文献
13.
R. Hilfer 《Zeitschrift für Physik B Condensed Matter》1994,96(1):63-77
Finite size scaling theory and hyperscaling are analyzed in the ensemble limit which differs from the finite size scaling limit. Different scaling limits are discussed. Hyperscaling relations are related to the identification of thermodynamics as the infinite volume limit of statistical mechanics. This identification combined with finite ensemble scaling leads to the conclusion that hyperscaling relations cannot be violated for phase transitions with strictly positive specific heat exponent. The ensemble limit allows to derive analytical expressions for the universal part of the finite size scaling functions at the critical point. The analytical expressions are given in terms of generalH-functions, scaling dimensions and a new universal shape parameter. The universal shape parameter is found to characterize the type of boundary conditions, symmetry and other universal influences on critical behaviour. The critical finite size scaling functions for the order parameter distribution are evaluated numerically for the cases =3, =5 and =15 where is the equation of state exponent. Using a tentative assignment of periodic boundary conditions to the universal shape parameter yields good agreement between the analytical prediction and Monte-Carlo simulations for the two dimensional Ising model. Analytical expressions for critical amplitude ratios are derived in terms of critical exponents and the universal shape parameters. The paper offers an explanation for the numerical discrepancies and the pathological behaviour of the renormalized coupling constant in mean field theory. Low order moment ratios of difference variables are proposed and calculated which are independent of boundary conditions, and allow to extract estimates for a critical exponent. 相似文献
14.
K. Schenk B. Drossel S. Clar F. Schwabl 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):177-185
We study finite-size effects in the self-organized critical forest-fire model by numerically evaluating the tree density and
the fire size distribution. The results show that this model does not display the finite-size scaling seen in conventional
critical systems. Rather, the system is composed of relatively homogeneous patches of different tree densities, leading to
two qualitatively different types of fires: those that span an entire patch and those that do not. As the system size becomes
smaller, the system contains less patches, and finally becomes homogeneous, with large density fluctuations in time.
Received 24 April 1999 and Received in final form 26 October 1999 相似文献
15.
M.I. Marqués J.A. Gonzalo 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):317-321
The Monte Carlo (MC) approach is used to check the validity of the scaling relationship for the effective critical exponents in thin Ising films. We investigate this relationship not just in the critical region
but throughout the crossover to the expected two-dimensional behavior. Our results indicate that this scaling relationship
is very well-fulfilled throughout the entire crossover temperature region, as predicted by a previous renormalization group
analysis. The two-dimensional universality class of Ising films is confirmed by means of data collapsing plots for plates with increasing L, up to L=100. The evolution of the maximum value of the effective critical exponents with film thickness is discussed.
Received 22 April 1999 相似文献
16.
17.
Y.G. Ma 《The European Physical Journal A - Hadrons and Nuclei》1999,6(4):367-371
Zpif's law in the field of linguistics is tested in the nuclear disassembly within the framework of isospin dependent lattice
gas model. It is found that the average cluster charge (or mass) of rank n in the charge (or mass) list shows exactly inversely to its rank, i.e., there exists Zpif's law, at the phase transition
temperature. This novel criterion shall be helpful to search the nuclear liquid gas phase transition experimentally and theoretically.
In addition, the finite size scaling of the effective phase transition temperature at which the Zpif's law appears is studied
for several systems with different mass and the critical exponents of ν and β are tentatively extracted.
Received: 2 June 1999 / Revised version: 8 October 1999 相似文献
18.
B. Dubrulle J.-P. Laval 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):143-146
We study the probability distribution functions and scaling properties of truncated Lévy processes with sharp cut-offs. We
find that they display features analog to those observed in some 2D numerical simulations of turbulence.
Received: 29 October 1997 / Revised: 12 February 1998 / Accepted: 10
April 1998 相似文献
19.
T. Temesvári C. De Dominicis I. Kondor 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):629-634
Replica field theory for the Ising spin glass in zero magnetic field is studied around the upper critical dimension d=6. A scaling theory of the spin glass phase, based on Parisi's ultrametrically organised order parameter, is proposed. We
argue that this infinite step replica symmetry broken (RSB) phase is nonperturbative in the sense that amplitudes of scaling
forms cannot be expanded in term of the coupling constant w2. Infrared divergent integrals inevitably appear when we try to compute amplitudes perturbatively, nevertheless the -expansion of critical exponents seems to be well-behaved. The origin of these problems can be traced back to the unusual
behaviour of the free propagator having two mass scales, the smaller one being proportional to the perturbation parameter
w2 and providing a natural infrared cutoff. Keeping the free propagator unexpanded makes it possible to avoid producing infrared
divergent integrals. The role of Ward-identities and the problem of the lower critical dimension are also discussed.
Received 23 December 1998 and Received in final form 23 March 1999 相似文献
20.
Scaling approach of the convective drying of a porous medium 总被引:1,自引:0,他引:1
P. Coussot 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):557-566
We propose a simplified, theoretical approach of the evolution of liquid distribution during the convective drying of a granular
packing. In the absence of gravity effects three regimes are distinguished according to the relative importance of surface
evaporation, capillarity or evaporation from the interior of the sample. The evolution of the drying rate as a function of
the saturation can be inferred from the characteristic velocities associated to each of these effects. We also carried out
drying experiments of bead packings saturated with ethanol, at four different velocities of the boundary convection current,
and with bead size ranging from 4.5 to 100 μm. The drying curves exhibit different regimes with a scaling as a function of
particle radius and current velocity as predicted by the theory.
Received 7 June 1999 and Received in final form 25 October 1999 相似文献