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1.
A. Trovato J. van Mourik A. Maritan 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):63-73
A lattice model of a hetero-polymer with random hydrophilic-hydrophobic charges interacting with the solvent is introduced,
whose continuum counterpart has been proposed by Garel, Leibler and Orland [#!GLO!#]. The transfer matrix technique is used
to study various constrained annealed systems which approximate at various degrees of accuracy the original quenched model.
For highly hydrophobic chains an ordinary -point transition is found from a high temperature swollen phase to a low temperature compact phase. Depending on the type
of constrained averages, at very low temperatures a swollen phase or a coexistence between compact and swollen phases are
found. The results are carefully compared with the corresponding ones obtained in the continuum limit, and various improvements
in the original calculations are discussed.
Received: 10 April 1998 / Revised: 4 June 1998 / Accepted: 1st July 1998 相似文献
2.
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
3.
The Bethe lattice spin glass revisited 总被引:2,自引:0,他引:2
M. Mézard G. Parisi 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):217-233
So far the problem of a spin glass on a Bethe lattice has been solved only at the replica symmetric level, which is wrong
in the spin glass phase. Because of some technical difficulties, attempts at deriving a replica symmetry breaking solution
have been confined to some perturbative regimes, high connectivity lattices or temperature close to the critical temperature.
Using the cavity method, we propose a general non perturbative solution of the Bethe lattice spin glass problem at a level
of approximation which is equivalent to a one step replica symmetry breaking solution. The results compare well with numerical
simulations. The method can be used for many finite connectivity problems appearing in combinatorial optimization.
Received 27 September 2000 相似文献
4.
Shiqi Zhou 《The European physical journal. E, Soft matter》2000,3(4):343-353
A density functional theory is proposed for nonuniform freely jointed tangential hard sphere polymer melts in which the bonding
interaction is treated on the basis of the properties of the Dirac δ-function, thus avoiding the use of the single chain simulation
in the theory. The excess free energy is treated by making use of the universality of the free energy density functional and
the Verlet-modified (VM) bridge function. To proceed numerically, one of the input parameters, the second-order direct correlation
function of a uniform polymer melt is obtained by solving numerically the Polymer-RISM integral equation with the Percus-Yevick
(PY) closure. The predictions of the present theory for the site density distribution, the partition coefficient and the adsorption
isotherm, near a hard wall or between two hard walls are compared with computer simulation results and with those of previous
theories. Comparison indicates that the present approach is more accurate than the previous integral equation theory and the
most accurate Monte Carlo density functional theories. The predicted oscillations of the medium-induced force between two
hard walls immersed in polymer melts are consistent with the experimental results available in the literature.
Received 18 April 2000 相似文献
5.
G. Parisi M. Ratiéville 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(2):229-237
We consider a class of random matching problems where the distance between two points has a probability law which, for a small
distance l, goes like lr. In the framework of the cavity method, in the limit of an infinite number of points, we derive equations for pk, the probability for some given point to be matched to its kth nearest neighbor in the optimal configuration. These equations are solved in two limiting cases: r = 0 -- where we recover p
k = 1/2k, as numerically conjectured by Houdayer et al. and recently rigorously proved by Aldous -- and r→ + ∞. For 0 < r < + ∞, we are not able to solve the equations analytically, but we compute the leading behavior of pk for large k.
Received 14 February 2001 相似文献
6.
We prove the existence of correlations between the equilibrium states at different temperatures of the multi-p-spin spherical spin-glass models with continuous replica symmetry breaking: there is no chaos in temperature in these models.
Furthermore, the overlaps satisfy ultrametric relations. As a consequence the Parisi tree is essentially the same at all temperatures
with lower branches developing when lowering the temperature. We conjecture that the reference free energies of the clusters
are also fixed at all temperatures as in the generalized random-energy model.
Received 18 March 2002 / Received in final form 14 June 2002
Published online 1st October 2002
RID="a"
ID="a"e-mail: tommaso.rizzo@inwind.it 相似文献
7.
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
8.
D.A. Stariolo M.A. Montemurro F.A. Tamarit 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):361-367
We analyze by means of extensive computer simulations the out of equilibrium dynamics of Edwards-Anderson spin glasses in
d
= 4 and d
= 6 dimensions with ±
J interactions. In particular, we focus our analysis on the scaling properties of the two-time autocorrelation function in
a wide range of temperatures from T
= 0.07
T
c
to T
= 0.75
T
c
in both systems. In both the 4
d and 6
d models at very low temperatures we study the effects of discretization of energy levels. Strong sub-aging behaviors are found.
We argue that this is because in the times accessible to our simulations the systems are only able to probe activated dynamics
through the lowest discrete energy levels and remain trapped around nearly flat regions of the energy landscape. For temperatures
T
≥ 0.5
T
c
in 4
d and 6
d we find logarithmic scalings that are compatible with simple dynamical ultrametricity. Nevertheless the behaviour of the
systems, even in 6
d is very different from the mean field SK model results.
Received 21 October 2002 / Received in final form 13 January 2003 Published online 11 April 2003
RID="a"
ID="a"Associate researcher of the Abdus Salam International Centre for Theoretical Physics; e-mail: stariolo@if.ufrgs.br;
http://www.if.ufrgs.br/stariolo
RID="b"
ID="b"Present address: The Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, 34014 Trieste, Italy e-mail: mmontemu@ictp.trieste.it
RID="c"
ID="c"e-mail: tamarit@famaf.unc.edu.ar 相似文献
9.
B. Drossel M.A. Moore 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):589-594
We study the low-temperature phase of the three-dimensional ±
J Ising spin glass in Migdal-Kadanoff approximation. At zero temperature, T
= 0, the properties of the spin glass result from the ground-state degeneracy and can be elucidated using scaling arguments based
on entropy. The approach to the asymptotic scaling regime is very slow, and the correct exponents are only visible beyond
system sizes around 64. At T
> 0, a crossover from the zero-temperature behaviour to the behaviour expected from the droplet picture occurs at length scales
proportional to T
-2/ds
where ds is the fractal dimension of a domain wall. Canonical droplet behaviour is not visible at any temperature for systems whose
linear dimension is smaller than 16 lattice spacings, because the data are either affected by the zero-temperature behaviour
or the critical point behaviour.
Received 18 February 2001 相似文献
10.
Recent experiments have demonstrated that the dynamics in liquids close to the glass transition temperature is strongly heterogeneous.
The characteristic size of these heterogeneities has been measured to be a few nanometers at T
g. We extend here a recent model for describing the heterogeneous nature of the dynamics which allows both to derive this length
scale and the right orders of magnitude of the heterogeneities of the dynamics close to the glass transition. Our model allows
then to interpret quantitatively small probes diffusion experiments.
Received 29 March 2002 and Received in final form 11 November 2002
RID="a"
ID="a"e-mail: long@lps.u-psud.fr 相似文献
11.
V.A. Brazhnyi S. Stepanow 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):355-362
We consider the adsorption of a random heteropolymer onto an interface within the model of Garel et al. [#!gareletal89!#] by taking into account random self-interactions and ternary repulsive interactions between the monomers.
Within the replica trick and by using a self-consistent preaveraging procedure we map the adsorption problem onto the problem
of binding state of a quantum mechanical Hamiltonian. The analysis of the latter is treated within the variational method
based on the 2nd Legendre transform. Our study reveals a complex behaviour of the localization of the heteropolymer. In particular,
we predict a reentrant localization transition for moderate values of the asymmetry of the distribution function of the monomer
sequences along the heteropolymer.
Received 9 October 2001 and Received in final form 27 February 2002 Published online 6 June 2002 相似文献
12.
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
13.
Elastic rod model of a supercoiled DNA molecule 总被引:4,自引:0,他引:4
We study the elastic behaviour of a supercoiled DNA molecule. The simplest model is that of a rod-like chain, involving two
elastic constants, the bending and the twist rigidities. Writing this model in terms of Euler angles, we show that the corresponding
Hamiltonian is singular and needs a small distance cut-off, which is a natural length scale giving the limit of validity of
the model, of the order of the double-helix pitch. The rod-like chain in the presence of the cut-off is able to reproduce
quantitatively the experimentally observed effects of supercoiling on the elongation-force characteristics, in the small supercoiling
regime. An exact solution of the model, using both transfer matrix techniques and its mapping to a quantum mechanics problem,
allows to extract, from the experimental data, the value of the twist rigidity. We also analyse the variation of the torque
and the writhe-to-twist ratio versus supercoiling, showing analytically the existence of a rather sharp crossover regime which can be related to the excitation
of plectoneme-like structures. Finally we study the extension fluctuations of a stretched and supercoiled DNA molecule, both
at fixed torque and at fixed supercoiling angle, and we compare the theoretical predictions to some preliminary experimental
data.
Received 1 April 1999 and Received in final form 4 January 2000 相似文献
14.
It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, both
by measuring the diffusion coefficient of tagged particles or by NMR studies. Recent experiments have also demonstrated that
the glass transition temperature of thin polymer films can be shifted as compared to the same polymer in the bulk. We propose
here first a thermodynamical model for van der Waals liquids, which accounts for experimental results regarding the bulk modulus
of polymer melts and the evolution of the density with temperature. This model allows us to describe the density fluctuations
in such van der Waals liquids. Then, by considering the thermally induced density fluctuations in the bulk, we propose that
the 3D glass transition is controlled by the percolation of small domains of slow dynamics, which allows to explain the heterogeneous
dynamics close to T
g. We show then that these domains percolate at a lower temperature in the quasi-2D case of thin suspended polymer films and
we calculate the corresponding glass transition temperature reduction, in quantitative agreement with experimental results
of Jones and co-workers. In the case of strongly adsorbed films, we show that the strong adsorption amounts to enhance the
slow domains percolation. This effect leads to 1) a broadening of the glass transition and 2) an increase of T
g in quantitative agreement with experimental results. For both strongly and weakly adsorbed films, the shift in T
g is given by a power law, the exponent being the inverse of that of the correlation length of 3D percolation.
Received 21 March 2000 and Received in final form 4 December 2000 相似文献
15.
T. Albrecht S. Armbruster S. Keller G. Strobl 《The European physical journal. E, Soft matter》2001,6(3):237-243
Poly(ethylene oxide) (PEO) in the semi-crystalline state shows a reversible surface crystallization and melting; a temperature
decrease leads to a certain crystal thickening, a temperature increase reversely to an expansion of the amorphous intercrystallite
layers. Dynamic calorimetry provides a means to investigate the kinetics of the process. The structural rearrangement in the
region of the crystalline-amorphous interface can only be accomplished if the chains can slide through the crystallites. One
therefore expects the associated time to change with the crystallite thickness. Variations of the crystal thickness of PEO
can be achieved by choosing different crystallization temperatures. We studied the effect of the crystal thickness employing
temperature-modulated differential scanning calorimetry and heat wave spectroscopy, and by carrying out small-angle X-ray
scattering experiments for the structural characterization. The effect of the crystal thickness is clearly observed. Results
indicate that the sliding diffusion through the crystallites takes place by helical jumps of whole stems. Data yield the activation
energy per unit length of the stems.
Received 20 April 2001 and Received in final form 13 August 2001 相似文献
16.
H.J. Angerman G. ten Brinke J.J.M. Slot 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):397-404
In this paper we investigate in a systematic way the influence of polydispersity in the block lengths on the phase behavior
of AB-multiblock copolymer melts. As model system we take a polydisperse multiblock copolymer for which both the A-blocks and the B-blocks satisfy a Schultz-Zimm distribution. In the limit of low polydispersity the expressions for the vertex functions are
clarified by using simple physical arguments. For various values of the polydispersity the phase diagram is presented, which
shows that the region of stability of the bcc phase increases considerably with increasing polydispersity. The strong dependence
of the periodicity of the microstructure on the polydispersity and on the interaction strength is presented.
Received 2 July 1998 相似文献
17.
S. Miyashita E. Vincent 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(2):203-211
Aging in spin glasses (and in some other systems) reveals astonishing effects of `rejuvenation and memory' upon temperature
changes. In this paper, we propose microscopic mechanisms (at the scale of spin-spin interactions) which can be at the origin
of such phenomena. Firstly, we recall that, in a frustrated system, the effective average interaction between two spins may take different values (possibly with opposite signs) at different temperatures. We give simple examples
of such situations, which we compute exactly. Such mechanisms can explain why new ordering processes (rejuvenation) seem to take place in spin glasses when the temperature is lowered. Secondly, we emphasize the fact that inhomogeneous interactions do naturally lead to a wide distribution of relaxation times for thermally activated flips. `Memory spots' spontaneously
appear, in the sense that the flipping time of some spin clusters becomes extremely long when the temperature is decreased.
Such memory spots are capable of keeping the memory of previous ordering at a higher temperature while new ordering processes occur at a lower temperature. After a qualitative
discussion of these mechanisms, we show in the numerical simulation of a simplified example that this may indeed work. Our
conclusion is that certain chaos-like phenomena may show up spontaneously in any frustrated and inhomogeneous magnetic system, without impeding the occurrence of memory effects.
Received 5 February 2001 and Received in final form 27 April 2001 相似文献
18.
B. Lotz 《The European physical journal. E, Soft matter》2000,3(2):185-194
Contrary to most or all other materials, crystallization of chiral but racemic polymers such as isotactic polypropylene is
accompanied by a conformational rearrangement which leads to helical geometries: the building units of the crystal are helical
stems, -20nm long, which can be either right-handed or left-handed. Helical hand cannot be reversed within the crystal structure: it is therefore a permanent marker and an indicator of molecular processes (in particular segregation/selection of helical hands) which take place during crystal
growth, and more precisely during the crucial step of “efficient” helical stem deposition. The issue of proper helical hand
selection during polymer crystal growth is mainly illustrated with isotactic polypropylene. Its various crystalline polymorphs
(, , and smectic) display virtually all possible combinations of helical hands, azimuthal settings and even non-parallel orientation
of helix axes in space. Furthermore, a specific homoepitaxy which generates a lamellar branching in the phase “quadrites” and composite structures makes it possible a) to determine the helical hand and associated azimuthal setting of every stem in
the crystalline entities and b) to determine the impact on the crystal structure and morphology of “mistakes” in helical hand
of the depositing stem. Analysis of these morphologies demonstrates that the crystallization of isotactic polypropylene (and
by implication of other achiral, helical polymers) is a highly sequential and “substrate-determined” process, i.e. that the depositing stem probes the topography of the growth face prior to attachment. These observations appear difficult to reconcile with crystallization schemes in which molecules (helical segments) are
prearranged in a kind of pseudo-crystalline bundle (and as such, are not subjected to the high constraints of crystal symmetry)
before deposition as a preassembled entity on the substrate.
Received: 5 May 2000 相似文献
19.
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
20.
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