共查询到20条相似文献,搜索用时 15 毫秒
1.
T. Baumberger C. Caroli 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(1):13-23
We propose a phenomenological model of boundary lubricated junctions consisting of a few layers of small molecules which describes
the rheological properties of these sytems both in the static, frozen, and sliding, molten, states as well as the dynamical
transition between them. Two dynamical regimes can be distinguished, according to the level of internal damping of the junction, which depends on its thickness and on the normal load. In the overdamped regime, under driving at
constant velocity v through an external spring, the motion evolves continuously from “atomic stick-slip” to modulated sliding. Underdamped systems
exhibit, under given external stress, a range of dynamic bistability where the sheared static state coexists with a steadily
sliding one. The frictional dynamics under shear driving is analyzed in detail, it provides a complete account of the qualitative
dynamical scenarios observed by Israelashvili et al., and yields semiquantitative agreement with experimental data. A few complementary experimental tests of the model are suggested.
Received: 18 December 1997 / Received in final form and accepted: 26 March 1998 相似文献
2.
P.L. Krapivsky J.F.F. Mendes S. Redner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):401-404
We investigate submonolayer epitaxial growth with a fixed monomer flux and irreversible aggregation of adatom islands due
to an effective island diffusion, with a diffusivity for an mass k island proportional to . For , there is a steady state, while for , continuously evolving logarithmic islanding occurs in which the island density grows extremely slowly, as . In the latter regime, the island size distribution exhibits complex, but universal, multiple-scale mass dependence which
we account for theoretically.
Received: 3 June 1998 / Accepted: 13 July 1998 相似文献
3.
We present a simple theory of crack propagation in viscoelastic solids. We calculate the energy per unit area, G(v), to propagate a crack, as a function of the crack tip velocity v. Our study includes the non-uniform temperature distribution (flash temperature) in the vicinity of the crack tip, which has a profound influence on G(v). At very low crack tip velocities, the heat produced at the crack tip can diffuse away, resulting in very small temperature increase: in this “low-speed” regime the flash temperature effect is unimportant. However, because of the low heat conductivity of rubber-like materials, already at moderate crack tip velocities a very large temperature increase (of order of 1000 K) can occur close to the crack tip. We show that this will drastically affect the viscoelastic energy dissipation close to the crack tip, resulting in a “hot-crack” propagation regime. The transition between the low-speed regime and the hot-crack regime is very abrupt, which may result in unstable crack motion, e.g. stick-slip motion or catastrophic failure, as observed in some experiments. In addition, the high crack tip temperature may result in significant thermal decomposition within the heated region, resulting in a liquid-like region in the vicinity of the crack tip. This may explain the change in surface morphology (from rough to smooth surfaces) which is observed as the crack tip velocity is increased above the instability threshold. 相似文献
4.
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
5.
M. F. Islam H. Nakanishi 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(1):123-131
We study quantum percolation which is described by a tight-binding Hamiltonian containing only off-diagonal hopping terms
that are generally in quenched binary disorder (zero or one). In such a system, transmission of a quantum particle is determined
by the disorder and interference effects, leading to interesting sharp features in conductance as the energy, disorder, and
boundary conditions are varied. To aid understanding of this phenomenon, we develop a visualization method whereby the progression
of a wave packet entering the cluster through a lead on one side and exiting from another lead on the other side can be tracked
dynamically. Using this method, we investigate the localization-delocalization transition in a 2D system for various boundary
conditions. Our results indicate the existence of two different kinds of localized regimes, namely exponential and power law
localization, depending on the amount of disorder. Our study further suggests that there may be a delocalized state in the
2D quantum percolation system at very low disorder. These results are based on a finite size scaling analysis of the systems
of size up to 70 × 70 (containing 4900 sites) on the square lattice. 相似文献
6.
Multiplicity of Phase Transitions and Mean-Field Criticality on Highly Non-Amenable Graphs 总被引:1,自引:0,他引:1
Roberto H. Schonmann 《Communications in Mathematical Physics》2001,219(2):271-322
We consider independent percolation, Ising and Potts models, and the contact process, on infinite, locally finite, connected
graphs.
It is shown that on graphs with edge-isoperimetric Cheeger constant sufficiently large, in terms of the degrees of the vertices
of the graph, each of the models exhibits more than one critical point, separating qualitatively distinct regimes. For unimodular
transitive graphs of this type, the critical behaviour in independent percolation, the Ising model and the contact process
are shown to be mean-field type.
For Potts models on unimodular transitive graphs, we prove the monotonicity in the temperature of the property that the free
Gibbs measure is extremal in the set of automorphism invariant Gibbs measures, and show that the corresponding critical temperature
is positive if and only if the threshold for uniqueness of the infinite cluster in independent bond percolation on the graph
is less than 1.
We establish conditions which imply the finite-island property for independent percolation at large densities, and use those
to show that for a large class of graphs the q-state Potts model has a low temperature regime in which the free Gibbs measure decomposes as the uniform mixture of the q ordered phases.
In the case of non-amenable transitive planar graphs with one end, we show that the q-state Potts model has a critical point separating a regime of high temperatures in which the free Gibbs measure is extremal
in the set of automorphism-invariant Gibbs measures from a regime of low temperatures in which the free Gibbs measure decomposes
as the uniform mixture of the q ordered phases.
Received: 27 March 2000 / Accepted: 7 December 2000 相似文献
7.
M. Capone M. Grilli W. Stephan 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):551-557
We investigate polaron formation in a many-electron system in the presence of a local repulsion sufficiently strong to prevent
local-bipolaron formation. Specifically, we consider a Hubbard-Holstein model of interacting electrons coupled to dispersionless
phonons of frequency . Numerically solving the model in a small one-dimensional cluster, we find that in the nearly adiabatic case , the necessary and sufficient condition for the polaronic regime to occur is that the energy gain in the atomic (i.e., extremely localized) regime overcomes the energy of the purely electronic system . In the antiadiabatic case, , polaron formation is instead driven by the condition of a large ionic displacement (g being the electron-phonon coupling). Dynamical properties of the model in the weak and moderately strong coupling regimes
are also analyzed.
Received 15 February 1999 相似文献
8.
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
9.
We study the forced aspiration of small ( mm) and large ( cm) liquid drops, deposited on prewetted porous membranes, and pumped mechanically with a constant current J. Two kinds of membranes are used where the pores are i) disconnected, cylindrical and calibrated or ii) interconnected “sponge-like”.
Whatever the size of the drops and the intensity J of the current, two suction regimes are observed versus time: 1) a “locked” regime, when the drop is pinned, with a dynamic contact angle decreasing from advancing () to finite receding () contact angle; 2) an “unlocked” regime, where the contour line recedes with a constant contact angle closed to . In both regimes, the shape of the drop remains quasistatic, during the suction process, i.e. a spherical cap for small drops and a flat “gravity pancake” for large ones.
Received 19 January 2000 相似文献
10.
R.R. Netz H. Orland 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):81-98
Variational methods are applied to a single polyelectrolyte chain. The polymer is modeled as a Gaussian chain with screened
electrostatic repulsion between all monomers. As a variational Hamiltonian, the most general Gaussian kernel, including the
possibility of a classical or mean polymer path, is employed. The resulting self-consistent equations are systematically solved
both for large and small monomer-monomer separations along the chain. In the absence of screening, the polymer is stretched
on average. It is described by a straight classical path with Gaussian fluctuations around it. If the electrostatic repulsion
is screened, the polymer is isotropically swollen for large separations, and for small separations the polymer correlation
function is calculated as an analytic expansion in terms of the monomer-monomer separation along the chain. The electrostatic
persistence length and the electrostatic blobsize are inferred from the crossover between distinct scaling ranges. We perform
a global analysis of the scaling behavior as a function of the screening length and electrostatic interaction strength , where is the Bjerrum length and A is the distance of charges along the polymer chain. We find three different scaling regimes. i) A Gaussian-persistent regime with Gaussian behavior at small, persistent behavior at intermediate, and isotropically swollen behavior at large length
scales. This regime occurs for weakly charged polymers and only for intermediate values of the screening length. The electrostatic
persistence length is defined as the crossover length between the persistent and the asymptotically swollen behavior and is given by and thus disagrees with previous (restricted) variational treatments which predict a linear dependence on the screening length
.ii) A Gaussian regime with Gaussian behavior at small and isotropically swollen behavior at large length scales. This regime occurs for weakly
charged polymers and/or strong screening, and the electrostatic repulsion between monomers only leads to subfluent corrections
to Gaussian scaling at small separations. The concept of a persistence length is without meaning in this regime. iii) A persistent regime , where the chain resembles a stretched rod on intermediate and small scales. Here the persistence length is given by the
original Odijk prediction, , if the overstretching of the chain is avoided. We also investigate the effects of a finite polymer length and of an additional
excluded-volume interaction, which modify the resultant scaling behavior. Applications to experiments and computer simulations
are discussed.
Received 24 December 1997 相似文献
11.
Jared C. Bronski 《Journal of statistical physics》1998,92(5-6):995-1015
In this paper we consider the problem of solitary wave propagation in a weakly disordered potential. Through a series of careful numerical experiments we have observed behavior which is in agreement with the theoretical predictions of Kivshar et al., Bronski, and Gamier. In particular we observe numerically the existence of two regimes of propagation. In the first regime the mass of the solitary wave decays exponentially, while the velocity of the solitary wave approaches a constant. This exponential decay is what one would expect from known results in the theory of localization for the linear Schrödinger equation. In the second regime, where nonlinear effects dominate, we observe the anomalous behavior which was originally predicted by Kivshar et al. In this regime the mass of the solitary wave approaches a constant, while the velocity of the solitary wave displays an anomalously slow decay. For sufficiently small velocities (when the theory is no longer valid) we observe phenomena of total reflection and trapping. 相似文献
12.
S.B. Santra 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):75-82
A new site percolation model, directed spiral percolation (DSP), under both directional and rotational (spiral) constraints
is studied numerically on the square lattice. The critical percolation threshold p
c ≈ 0.655 is found between the directed and spiral percolation thresholds. Infinite percolation clusters are fractals of dimension
d
f ≈ 1.733. The clusters generated are anisotropic. Due to the rotational constraint, the cluster growth is deviated from that
expected due to the directional constraint. Connectivity lengths, one along the elongation of the cluster and the other perpendicular
to it, diverge as p → p
c with different critical exponents. The clusters are less anisotropic than the directed percolation clusters. Different moments
of the cluster size distribution P
s(p) show power law behaviour with | p - p
c| in the critical regime with appropriate critical exponents. The values of the critical exponents are estimated and found
to be very different from those obtained in other percolation models. The proposed DSP model thus belongs to a new universality
class. A scaling theory has been developed for the cluster related quantities. The critical exponents satisfy the scaling
relations including the hyperscaling which is violated in directed percolation. A reasonable data collapse is observed in
favour of the assumed scaling function form of P
s(p). The results obtained are in good agreement with other model calculations.
Received 10 November 2002 / Received in final form 20 February 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: santra@iitg.ernet.in 相似文献
13.
Flows around small colloidal particles of diameter b, or in thin films, capillaries, etc., cannot always be described in terms of the macroscopic polymer viscosity. We discuss
these features for entangled polymer melts, where two distinct regimes can be found: (a) the thin regime where b is smaller than the coil radius R0, but larger than the diameter of the Edwards tube; (b) the ultrathin regime, where . We consider (i) non adsorbing particles, where slippage may occur between the melt and the solid surface; (ii) “hairy” particles,
which carry some bound polymer chains. We obtain scaling predictions for mobilities of spheres, of needles, and of clusters
of particles. We also discuss translational and rotational diffusion of needles.
Received 19 April 1999 相似文献
14.
H. Hinrichsen H.M. Koduvely 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):257-264
The local persistence probability P
l
(t) that a site never becomes active up to time t, and the global persistence probability P
g
(t) that the deviation of the global density from its mean value does not change its sign up to time t are studied in a (1+1)-dimensional directed percolation process by Monte-Carlo simulations. At criticality, starting from
random initial conditions, P
l
(t) decays algebraically with the exponent . The value is found to be independent of the initial density and the microscopic details of the dynamics, suggesting is an universal exponent. The global persistence exponent is found to be equal or larger than . This contrasts with previously known cases where . It is shown that in the special case of directed-bond percolation, P
l
(t) can be related to a certain return probability of a directed percolation process with an active source (wet wall).
Received: 15 December 1997 / Revised: 6 April 1998 / Accepted: 29 May 1998 相似文献
15.
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
16.
B. O'Shaughnessy D. Vavylonis 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):363-372
We study the reaction kinetics of end-functionalized polymer chains dispersed in an unreactive polymer melt. Starting from
an infinite hierarchy of coupled equations for many-chain correlation functions, a closed equation is derived for the 2nd
order rate constant k after postulating simple physical bounds. Our results generalize previous 2-chain treatments (valid in dilute reactants limit)
by Doi [#!doi:inter2!#], de Gennes [#!gennes:polreactionsiandii!#], and Friedman and O'Shaughnessy [#!ben:interdil_all_aip!#],
to arbitrary initial reactive group density n0 and local chemical reactivity Q. Simple mean field (MF) kinetics apply at short times, .For high Q, a transition occurs to diffusion-controlled (DC) kinetics with (where xt is rms monomer displacement in time t) leading to a density decay . If n0 exceeds the chain overlap threshold, this behavior is followed by a regime where during which k has the same power law dependence in time, , but possibly different numerical coefficient. For unentangled melts this gives while for entangled cases one or more of the successive regimes ,t
-3/8
and t
-3/4
may be realized depending on the magnitudes of Q and n0. Kinetics at times longer than the longest polymer relaxation time are always MF. If a DC regime has developed before then the long time rate constant is where R is the coil radius. We propose measuring the above kinetics in a model experiment where radical end groups are generated
by photolysis.
Received: 2 June 1998 / Revised: 9 July 1998 / Accepted: 10 July 1998 相似文献
17.
Instabilities in population dynamics 总被引:1,自引:0,他引:1
K. Sznajd-Weron 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):183-187
Biologists have long known that the smaller the population, the more susceptible it is to extinction from various causes.
Biologists define minimum viable population size (MVP), which is the critical population size, below which the population has a very small chance to survive. There are several
theoretical models for predicting the probability that a small population will become extinct. But these models either embody
unrealistic assumptions or lead to currently unresolved mathematical problems. In other popular models of population dynamics,
like the logistic model, MVP does not exist. In this paper we find the existence of such a critical concentration in a simple
model of evolution. We solve this model by a mean field theory and show, in one and two dimensions, the existence of the critical
adaptation and concentration below which a population dies out. We also show that, like in the logistic model, above the critical
value a population reaches its carrying capacity. Moreover, in the two-dimensional case we find - the so common in biological
models - periodic solutions and their biffurcations.
Received 15 February 2000 相似文献
18.
We develop a cluster expansion for the probability of full connectivity of high density random networks in confined geometries. In contrast to percolation phenomena at lower densities, boundary effects, which have previously been largely neglected, are not only relevant but dominant. We derive general analytical formulas that show a persistence of universality in a different form to percolation theory, and provide numerical confirmation. We also demonstrate the simplicity of our approach in three simple but instructive examples and discuss the practical benefits of its application to different models. 相似文献
19.
F. Thalmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):65-73
The mean field approach of glassy dynamics successfully describes systems which are out-of-equilibrium in their low temperature
phase. In some cases an aging behaviour is found, with no stationary regime ever reached. In the presence of dissipative forces
however, the dynamics is indeed stationary, but still out-of-equilibrium, as inferred by a significant violation of the fluctuation
dissipation theorem. The mean field dynamics of a particle in a random but short-range correlated environment, offers the
opportunity of observing both the aging and driven stationary regimes. Using a geometrical approach previously introduced
by the author, we study here the relation between these two situations, in the pure relaxational limit, i.e. the zero temperature case. In the stationary regime, the velocity (v)-force (F) characteristics is a power law v∼F
4, while the characteristic times scale like powers of v, in agreement with an early proposal by Horner. The cross-over between the aging, linear-response regime and the non-linear
stationary regime is smooth, and we propose a parametrization of the correlation functions valid in both cases, by means of
an “effective time”. We conclude that aging and non-linear response are dual manifestations of a single out-of-equilibrium
state, which might be a generic situation.
Received 7 May 2000 and Received in final form 22 August 2000 相似文献
20.
We discuss the spatiotemporal intermittency (STI) seen in the coupled sine circle map lattice. The phase diagram of this system, when updated with random initial conditions, shows very rich behaviour including synchronised solutions, and STI of various kinds. These behaviours are organised around the bifurcation boundary of the synchronised solutions, as well as an infection line which separates the lower part of the phase diagram into a spreading and a non-spreading regime. The STI seen at the bifurcation boundary in the spreading regime belongs convincingly to the directed percolation (DP) universality class. In the non-spreading regime, spatial intermittency (SI) with temporally regular bursts is seen at the bifurcation boundary. The laminar length distribution scales as a power-law with an exponent which is quite distinct from DP behaviour. Therefore, both DP and non-DP universality classes are seen in this system. When the coupled map lattice is mapped to a cellular automaton via coarse graining, a transition from a probabilistic cellular automaton to a deterministic cellular automaton at the infection line signals the transition from spreading to non-spreading behaviour. 相似文献