共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
V.Yu. Grishina L.A. Kondratyuk W. Cassing A.B. Kaidalov E. De Sanctis P. Rossi 《The European Physical Journal A - Hadrons and Nuclei》2001,10(3):355-364
We investigate deuteron two-body photodisintegration within the framework of the Quark-Gluon Strings Model with nonlinear
baryon Regge trajectories. Special attention is paid to the use of QCD motivated Regge trajectories of the logarithmic and
square-root form. We find that the recent experimental data from TJNAF in the few-GeV region can be reasonably described by
the model. Angular distributions at different γ-energies are presented and the effect of a forward-backward asymmetry is discussed.
Predictions for the energy dependence of dσ/dt at higher energies and different Θc.m. are presented, too.
Received: 12 March 2001 / Accepted: 19 March 2001 相似文献
3.
A. Díaz-Sánchez A. Pérez-Garrido 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):483-486
The relaxation of the specific heat and the entropy to their equilibrium values is investigated numerically for the three-dimensional
Coulomb glass at very low temperatures. The long time relaxation follows a stretched exponential function, f (t) = f
0exp - (t/τ)β
, with the exponent β increasing with the temperature. The relaxation time diverges as an Arrhenius law when T→ 0.
Received 24 May 2001 and Received in final form 12 September 2001 相似文献
4.
E.T. Seppälä M.J. Alava 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):407-424
We study the effect of an external field on (1 + 1) and (2 + 1) dimensional elastic manifolds, at zero temperature and with
random bond disorder. Due to the glassy energy landscape the configuration of a manifold changes often in abrupt, “first order”-type
of large jumps when the field is applied. First the scaling behavior of the energy gap between the global energy minimum and
the next lowest minimum of the manifold is considered, by employing exact ground state calculations and an extreme statistics
argument. The scaling has a logarithmic prefactor originating from the number of the minima in the landscape, and reads ΔE
1∼L
θ[ln(L
z
L
- ζ)]-1/2, where ζ is the roughness exponent and θ is the energy fluctuation exponent of the manifold, L is the linear size of the manifold, and Lz is the system height. The gap scaling is extended to the case of a finite external field and yields for the susceptibility
of the manifolds ∼L
2D + 1 - θ[(1 - ζ)ln(L)]1/2. We also present a mean field argument for the finite size scaling of the first jump field, h
1∼L
d - θ. The implications to wetting in random systems, to finite-temperature behavior and the relation to Kardar-Parisi-Zhang non-equilibrium
surface growth are discussed.
Received December 2000 and Received in final form April 2001 相似文献
5.
J.M. Drouffe C. Godrèche 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):281-288
We study the statistical properties of the sum S
t =
dt'σ
t', that is the difference of time spent positive or negative by the spin σ
t, located at a given site of a D-dimensional Ising model evolving under Glauber dynamics from a random initial configuration. We investigate the distribution
of St and the first-passage statistics (persistence) of this quantity. We discuss successively the three regimes of high temperature
( T > T
c), criticality ( T = T
c), and low temperature ( T < T
c). We discuss in particular the question of the temperature dependence of the persistence exponent , as well as that of the spectrum of exponents (x), in the low temperature phase. The probability that the temporal mean S
t/t was always larger than the equilibrium magnetization is found to decay as t
-
- ?. This yields a numerical determination of the persistence exponent in the whole low temperature phase, in two dimensions, and above the roughening transition, in the low-temperature phase
of the three-dimensional Ising model.
Received 4 December 2000 相似文献
6.
J.-Ph. Bouchaud P. Doussineau T. de Lacerda-Arôso A. Levelut 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):335-340
We characterize in details the aging properties of the ferroelectric phase of KTa1-xNbx O3 (KTN), where both rejuvenation and (partial) memory are observed. In particular, we carefully examine the frequency dependence
of several quantities that characterize aging, rejuvenation and memory. We find a marked subaging behaviour, with an a.c.
dielectric susceptiblity scaling as ω, where t
w is the waiting time. We suggest an interpretation in terms of pinned domain walls, much along the lines proposed for aging
in a disordered ferromagnet, where both domain wall reconformations and overall (cumulative) domain growth are needed to rationalize the experimental findings.
Received 10 November 2000 and Received in final form 20 February 2001 相似文献
7.
M. Tsuchiizu P. Donohue Y. Suzumura T. Giamarchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):185-193
We investigate the physical properties of two coupled chains of electrons, with a nearly half-filled band, as a function of
the interchain hopping t
⊥ and the doping. We show that upon doping, the system undergoes a metal-insulator transition well described by a commensurate-incommensurate
transition. By using bosonization and renormalization we determine the full phase diagram of the system, and the physical
quantities such as the charge gap. In the commensurate phase two different regions, for which the interchain hopping is relevant
and irrelevant exist, leading to a confinement-deconfinement crossover in this phase. A minimum of the charge gap is observed
for values of t
⊥ close to this crossover. At large t
⊥ the region of the commensurate phase is enhanced, compared to a single chain. At the metal-insulator transition the Luttinger
parameter takes the universal value K
ρ
* = 1, in agreement with previous results on special limits of this model.
Received 31 July 2000 相似文献
8.
M. Picco F. Ritort M. Sales 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):565-582
The use of parameters measuring order-parameter fluctuations (OPF) has been encouraged by the recent results reported in referenece
[2,3] which show that two of these parameters, G and G
c, take universal values in the . In this paper we present a detailed study of parameters measuring OPF for two mean-field models with and without time-reversal
symmetry which exhibit different patterns of replica symmetry breaking below the transition: the Sherrington-Kirkpatrick model
with and without a field and the Ising p-spin glass (p = 3). We give numerical results and analyze the consequences which replica equivalence imposes on these models in the infinite
volume limit. We give evidence for the transition in each system and discuss the character of finite-size effects. Furthermore,
a comparative study between this new family of parameters and the usual Binder cumulant analysis shows what kind of new information
can be extracted from the finite T behavior of these quantities. The two main outcomes of this work are: 1) Parameters measuring OPF give better estimates than
the Binder cumulant for T
c and even for very small systems they give evidence for the transition. 2) For systems with no time-reversal symmetry, parameters
defined in terms of connected quantities are the proper ones to look at.
Received 20 September 2000 and Received in final form 10 January 2001 相似文献
9.
D.Q. Fang W.Q. Shen J. Feng X.Z. Cai H.Y. Zhang Y.G. Ma C. Zhong Z.Y. Zhu W.Z. Jiang W.L. Zhan Z.Y. Guo G.Q. Xiao J.S. Wang J.Q. Wang J.X. Li M. Wang J.F. Wang Z.J. Ning Q.J. Wang Z.Q. Chen 《The European Physical Journal A - Hadrons and Nuclei》2001,12(3):335-339
Measurements of reaction cross-sections ( σR's) for some proton-rich nuclei ( N = 11–15 isotones) on carbon target at intermediate energies have been performed on RIBLL of HIRFL. A larger enhancement of
the σR for 27P has been observed than for its neighboring nuclei. A large difference between the proton and neutron density distributions
(proton halo) is necessary to explain the enhanced cross-section for 27P within the framework of the Glauber model. Density distributions with HO-type core plus Yukawa-square tail and rms radii
for 27P have been deduced from the measured σR data for the first time, which conform the long tail in its densities as predicted by RMF calculations.
Received: 23 May 2001 / Accepted: 7 November 2001 相似文献
10.
E. Bogomolny U. Gerland C. Schmit 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):121-132
We propose a plasma model for spectral statistics displaying level repulsion without long-range spectral rigidity, i.e. statistics intermediate between random matrix and Poisson statistics similar to the ones found numerically at the critical
point of the Anderson metal-insulator transition in disordered systems and in certain dynamical systems. The model emerges
from Dysons one-dimensional gas corresponding to the eigenvalue distribution of the classical random matrix ensembles by restricting
the logarithmic pair interaction to a finite number k of nearest neighbors. We calculate analytically the spacing distributions and the two-level statistics. In particular we
show that the number variance has the asymptotic form Σ2(L) ∼χL for large L and the nearest-neighbor distribution decreases exponentially when s→∞, P(s) ∼ exp(- Λs) with Λ = 1/χ = kβ + 1, where β is the inverse temperature of the gas (β = 1, 2 and 4 for the orthogonal, unitary and symplectic symmetry class
respectively). In the simplest case of k = β = 1, the model leads to the so-called Semi-Poisson statistics characterized by particular simple correlation functions
e.g.
P(s) = 4s exp(- 2s). Furthermore we investigate the spectral statistics of several pseudointegrable quantum billiards numerically and compare
them to the Semi-Poisson statistics.
Received 13 September 2000 相似文献
11.
E. Del Gado L. de Arcangelis A. Coniglio 《The European physical journal. E, Soft matter》2000,2(4):359-365
Within a recently introduced model based on the bond-fluctuation dynamics, we study the viscoelastic behaviour of a polymer
solution at the gelation threshold. We here present the results of the numerical simulation of the model on a cubic lattice:
the percolation transition, the diffusion properties and the time autocorrelation functions have been studied. From both the
diffusion coefficients and the relaxation times critical behaviour a critical exponent k for the viscosity coefficient has been extracted: the two results are comparable within the errors giving , in close agreement with the Rouse model prediction and with some experimental results. In the critical region below the
transition threshold the time autocorrelation functions show a long-time tail which is well fitted by a stretched exponential
decay.
Received 20 December 1999 and Received in final form 18 February 2000 相似文献
12.
Verneuil E Clain J Buguin A Brochard-Wyart F 《The European physical journal. E, Soft matter》2003,10(4):345-353
A soft bead (radius R
b) is pressed with a force F against a hydrophobic glass plate through a water drop (“wet” JKR set-up). We observe with a fast camera the growth of the
contact zone bridging the rubber bead to the glass. Depending on the approach velocity V, two regimes are observed : i) at large V a liquid film is squeezed at the interface and dewets by nucleation and growth of a dry contact; ii) at low velocities, the
bead remains nearly spherical. As it comes into contact, the rubber bead spreads on the glass with a characteristic time (in
the range of one millisecond) τ ≈ ηR
b
2/F, where η is the liquid viscosity. The laws of spreading are interpreted by a balance of global mechanical and viscous forces.
Received: 22 December 2002 / Accepted: 24 March 2003 / Published online: 29 April 2003
RID="a"
ID="a"e-mail: brochard@curie.fr 相似文献
13.
B. Dubrulle F. Hersant 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):379-386
We generalize an analogy between rotating and stratified shear flows. This analogy is summarized in Table 1. We use this analogy
in the unstable case (centrifugally unstable flow vs. convection) to compute the torque in Taylor-Couette configuration, as a function of the Reynolds number. At low Reynolds
numbers, when most of the dissipation comes from the mean flow, we predict that the non-dimensional torque G = T/ν2
L, where L is the cylinder length, scales with Reynolds number R and gap width η, G = 1.46η3/2(1 - η)-7/4
R
3/2. At larger Reynolds number, velocity fluctuations become non-negligible in the dissipation. In these regimes, there is no
exact power law dependence the torque versus Reynolds. Instead, we obtain logarithmic corrections to the classical ultra-hard (exponent 2) regimes: G = 0.50
. These predictions are found to be in excellent agreement with avail-able experimental data. Predictions for scaling of velocity
fluctuations are also provided.
Received 7 June 2001 and Received in final form 7 December 2001 相似文献
14.
B. Dubrulle 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):361-367
We study the scaling properties of heat transfer Nu in turbulent thermal convection at large Prandtl number Pr using a quasi-linear theory. We show that two regimes arise, depending on the Reynolds number Re. At low Reynolds number, NuPr
-1/2 and Re are a function of RaPr
-3/2. At large Reynolds number NuPr
1/3 and RePr are function only of RaPr
2/3 (within logarithmic corrections). In practice, since Nu is always close to Ra
1/3, this corresponds to a much weaker dependence of the heat transfer in the Prandtl number at low Reynolds number than at large
Reynolds number. This difference may solve an existing controversy between measurements in SF6 (large Re) and in alcohol/water (lower Re). We link these regimes with a possible global bifurcation in the turbulent mean flow. We further show how a scaling theory
could be used to describe these two regimes through a single universal function. This function presents a bimodal character
for intermediate range of Reynolds number. We explain this bimodality in term of two dissipation regimes, one in which fluctuation
dominate, and one in which mean flow dominates. Altogether, our results provide a six parameters fit of the curve Nu(Ra, Pr) which may be used to describe all measurements at Pr≥0.7.
Received 27 February 2002 / Received in final form 29 May 2002 Published online 31 July 2002 相似文献
15.
B. Canals D.A. Garanin 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):439-447
Thermodynamic quantities and correlation functions (CFs) of the classical antiferromagnet on the checkerboard lattice are
studied for the exactly solvable infinite-component spin-vector model, D↦∞. In contrast to conventional two-dimensional magnets with continuous symmetry showing extended short-range order at distances
smaller than the correlation length, r
ξ
c∝ exp(T
*/T), correlations in the checkerboard-lattice model decay already at the scale of the lattice spacing due to the strong degeneracy
of the ground state characterized by a macroscopic number of strongly fluctuating local degrees of freedom. At low temperatures,
spin CFs decay as <
>∝ 1/r
2 in the range a
0≪r≪ξ
c∝T
-1/2, where a0 is the lattice spacing. Analytical results for the principal thermodynamic quantities in our model are very similar with
MC simulations, exact and analytical results for the classical Heisenberg model (D = 3) on the pyrochlore lattice. This shows that the ground state of the infinite-component spin vector model on the checkerboard
lattice is a classical spin liquid.
Received 16 November 2001 and Received in final form 12 February 2002 相似文献
16.
E.P. Borges 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):593-595
Comment on Eur. Phys. J. B 27, 445 (2002)
We analyze the distribution of success of musicians, comparing a stretched exponential (found by J.A. Davies [Eur. Phys.
J. B 27, 445 (2002)]) with a distribution of the family of the q-exponential (presenting an intermediate power-law regime with a crossover to an exponential tail). We find that both assumptions
yield comparable results, within the available range of data, hence a definite conclusion cannot yet be taken. But this example
joins many others that has been found to be fairly described by q-exponentials (or variations of it), which may be indicative that there is a (significantly large) class of systems described
by nonextensive statistical mechanics, from where q-exponentials naturally appear.
Received 17 October 2002 Published online 31 December 2002 相似文献
17.
G. De Smedt C. Godrèche J.M. Luck 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):363-380
We consider in parallel three one-dimensional spin models with kinetic constraints: the paramagnetic constrained Ising chain,
the ferromagnetic Ising chain with constrained Glauber dynamics, and the same chain with constrained Kawasaki dynamics. At
zero temperature the dynamics of these models is fully irreversible, leading to an exponentially large number of blocked states.
Using a mapping of these spin systems onto sequential adsorption models of, respectively, monomers, dimers, and hollow trimers,
we present exact results on the statistics of blocked states. We determine the distribution of their energy or magnetization,
and in particular the large-deviation function describing its exponentially small tails. The spin and energy correlation functions
are also determined. The comparison with an approach based on a priori statistics reveals systematic discrepancies with the Edwards hypothesis, concerning in particular the fall-off of correlations.
Received 26 February 2002 Published online 6 June 2002 相似文献
18.
J. Dunkel W. Ebeling U. Erdmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):511-524
We investigate the stochastic dynamics of an one-dimensional ring with N self-driven Brownian particles. In this model neighboring particles interact via conservative Morse potentials. The influence of the surrounding heat bath is modeled by Langevin-forces (white noise) and
a constant viscous friction coefficient γ. The Brownian particles are provided with internal energy depots which may lead to active motions of the particles. The depots
are realized by an additional nonlinearly velocity-dependent friction coefficient γ
1(v) in the equations of motions. In the first part of the paper we study the partition functions of time averages and thermodynamical
quantities (e.g. pressure) characterizing the stationary physical system. Numerically calculated non-equilibrium phase diagrams are represented.
The last part is dedicated to transport phenomena by including a homogeneous external force field that breaks the symmetry
of the model. Here we find enhanced mobility of the particles at low temperatures.
Received 21 July 2001 相似文献
19.
M. Vatasescu F. Masnou-Seeuws 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(2):191-204
The paper contains a time-dependent investigation of the tunneling effect observed in the photoassociation spectrum of Cs2 and attributed to the 0g
-(6s, 6p
3/2) double well. When by photoassociation of two cold cesium atoms a vibrational level of the outer well is populated, tunneling
is an efficient mechanism for transferring the population to the inner well (R < 15a
0), where spontaneous emission may lead to formation of cold molecules in low vibrational levels of the a
3Σ+
u(6s, 6s) electronic state. This tunneling effect is analyzed by wavepackets propagation, first considering the double well potential
alone, and following a packet made by a superposition of states initially located at large distances. Characteristic times
for the vibration dynamics, corresponding to a beating phenomenon between the two wells, to partial “revival” at large distances,
and to maxima in the population localized in the inner well are reported and discussed. Second, we simulate the two-channels
a
3Σ+
u(6s, 6s)↦0g
-(6s, 6p
3/2) photoassociation at detunings around 2.9 cm-1: the inner well can be populated either by the excitation of a vibrational level of the external well (resonant excitation),
or by tuning the photoassociation laser at the energy of the inner well level which displays tunneling (“off-resonance excitation”).
In the first case the photoassociation is efficient, while the tunneling probability is small; in the second, the tunneling
probability is large, so that despite the poor efficiency of the photoassociation process, more population can be transferred
to the inner well. This second choice is shown to be very sensitive to the laser intensity, which could be used to control
the population of the inner well and hence the formation of ultracold molecules in low vibrational levels.
Received 19 April 2002 Published online 1st October 2002
RID="a"
ID="a"e-mail: francoise.masnou@lac.u-psud.fr 相似文献
20.
A.A. Valladares F. Alvarez Z. Liu J. Sticht J. Harris 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(4):443-453
We propose a method to simulate a-Si and a-Si:H using an ab initio approach based on the Harris functional and thermally-amorphisized periodically-continued cells with at least 64 atoms. Hydrogen
incorporation was achieved via diffusive addition. In preparing samples that may simulate the distributions of atoms in the amorphous materials, simulated
annealing calculations were carried out from given starting conditions using short and long time steps. The different time-steps
led to samples having distinctly different topological disorder. The radial distribution functions (partial and total) of
the resulting samples were calculated and compared with measured distributions; the agreement is very good. These comparisons
allowed some tentative conclusions to be made as regards the kind of disorder prevailing in the real samples. In addition,
we studied the effect of the topological disorder on the electronic densities of states of the samples; the passivating effect
of hydrogen can be observed.
Received 17 May 2001 相似文献