共查询到20条相似文献,搜索用时 46 毫秒
1.
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
2.
H. Chamati 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):241-249
The finite-size critical properties of the (n) vector ϕ4 model, with long-range interaction decaying algebraically with the interparticle distance r like r
-d - σ, are investigated. The system is confined to a finite geometry subject to periodic boundary condition. Special attention
is paid to the finite-size correction to the bulk susceptibility above the critical temperature T
c. We show that this correction has a power-law nature in the case of pure long-range interaction i.e. 0 < σ < 2 and it turns out to be exponential in case of short-range interaction i.e.σ = 2. The results are valid for arbitrary dimension d, between the lower ( d
< = σ) and the upper ( d
> = 2σ) critical dimensions.
Received 2 July 2001 and Received in final form 4 Septembre 2001 相似文献
3.
The lattice QCD studies indicate that the critical temperature T
c ≃ 260-280 MeV of the deconfinement phase transition in quenched QCD is considerably smaller than the lowest-lying glueball
mass m
G ≃ 1500-1700 MeV, i.e., T
c ≪ m
G. As a consequence of this large difference, the thermal excitation of the glueball in the confinement phase is strongly suppressed
by the statistical factor e
-mG/Tc ≃ 0.00207 even near T ≃ T
c. We consider its physical implication, and argue the abnormal feature of the deconfinement phase transition in quenched QCD
from the statistical viewpoint. To appreciate this, we demonstrate a statistical argument of the QCD phase transition using
the recent lattice QCD data. From the phenomenological relation between T
c and the glueball mass, the deconfinement transition is found to take place in quenched QCD before a reasonable amount of
glueballs is thermally excited. In this way, quenched QCD reveals a question “what is the trigger of the deconfinement phase
transition ?”
Received: 18 November 2002 / Accepted: 4 February 2003 / Published online: 29 April 2003 相似文献
4.
5.
L. Zhang W. Kleemann J. Dec R. Wang M. Itoh 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):163-171
The dielectric permittivity ε′ - i
of SrTi 18O 3 (STO18) is studied under a dc electric field E as a function of the temperature, T. In ε′
vs.
T, a double-peak is found when 0 < E < 30 KV/m. While the peak at high-T is attributed to the smeared ferroelectric phase transition, the low-T one is induced by domain wall motion. The transverse Ising model including an external homogeneous and quenched random-fields
is successfully used to describe both the smeared phase transition and the domain wall response in the low-T domain state. The calculations are in good agreement with the experimental results.
Received 4 January 2002 / Received in final form 25 March 2002 Published online 19 July 2002 相似文献
6.
L. Bartosch P. Kopietz 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):29-36
We consider the effect of Coulomb interactions on the average density of states (DOS) of disordered low-dimensional metals
for temperatures T and frequencies ω smaller than the inverse elastic life-time 1/τ. Using the fact that long-range Coulomb interactions in two dimensions (2d) generate ln2-singularities in the DOS ν(ω) but only ln-singularities in the conductivity σ(ω), we can re-sum the most singular contributions
to the average DOS via a simple gauge-transformation. If σ(ω) > 0, then a metallic Coulomb gapν(ω) ∝ |ω|/e
4 appears in the DOS at T = 0 for frequencies below a certain crossover frequency Ω
2 which depends on the value of the DC conductivity σ(0). Here, - e is the charge of the electron. Naively adopting the same procedure to calculate the DOS in quasi 1d metals, we find ν(ω) ∝ (|ω|/Ω
1)1/2exp(- Ω
1/|ω|) at T = 0, where Ω
1 is some interaction-dependent frequency scale. However, we argue that in quasi 1d the above gauge-transformation method is on less firm grounds than in 2d. We also discuss the behavior of the DOS at finite temperatures and give numerical results for the expected tunneling conductance
that can be compared with experiments.
Received 28 August 2001 / Received in final form 28 January 2002 Published online 9 July 2002 相似文献
7.
D. Stauffer P.M.C. de Oliveira 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):587-592
The density of never changed opinions during the Sznajd consensus-finding process decays with time t as 1/t
θ. We find θ ≃ 3/8 for a chain, compatible with the exact Ising result of Derrida et al. In higher dimensions, however, the exponent differs from the Ising θ. With simultaneous updating of sublattices instead of
the usual random sequential updating, the number of persistent opinions decays roughly exponentially. Some of the simulations
used multi-spin coding.
Received 22 August 2002 / Received in final form 12 November 2002 Published online 31 December 2002 相似文献
8.
M. Putti E. Galleani d'Agliano D. Marrè F. Napoli M. Tassisto P. Manfrinetti A. Palenzona C. Rizzuto S. Massidda 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):439-443
We report measurements of the resistivity, ρ, and the Seebeck coefficient, S
, of a MgB2 sintered sample, and compare S with theoretical calculations based on precise electronic structure calculations. ρ is fitted well by a generalized Bloch-Grüneisen equation with a Debye temperature Θ
R
of 1050 K. S is given by the sum of a diffusive and a phonon drag term and the behavior in the temperature region T
c
<
T
< 0.1Θ
R
follows the relationship AT+BT3. The phonon drag term indicates a strong electron-phonon interaction. The diffusive term, compared with calculations, suggests
that σ bands give the main contribution to the Seebeck effect.
Received 16 November 2001 and Received in final form 21 December 2001 相似文献
9.
J. Horbach W. Kob K. Binder 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):531-543
We present the results of extensive molecular dynamics computer simulations in which the high frequency dynamics of silica,
i.e. for frequencies ν > 0.5 THz, is investigated in the viscous liquid state as well as in the glass state. We characterize the
properties of high frequency sound modes by analyzing J
l(q,ν) and J
t(q,ν), the longitudinal and transverse current correlation function, respectively. For wave-vectors q > 0.4 ?-1 the spectra are sitting on top of a flat background. The dynamic structure factor S(q,ν) exhibits for q > 0.23 ?-1 a boson peak which is located nearly independent of q around 1.7 THz and for which the intensity scales approximately linearly with temperature. We show that the low frequency
part of the boson peak is mainly due to the elastic scattering of transverse acoustic modes with frequencies around 1 THz.
The strength of this scattering depends on q and is largest around q = 1.7 ?-1, the location of the first sharp diffraction peak in the static structure factor. By studying S(q,ν) for different system sizes we show that strong finite size effects are present in the low frequency part of the boson
peak in that for small systems part of its intensity is missing. We discuss the consequences of these finite size effects
for the structural relaxation.
Received 27 June 2000 and Received in final form 9 January 2001 相似文献
10.
We discuss the excess conductivity at nonzero frequencies in a superconductor above Tc within the Gaussian approximation. We focus the attention on the temperature range not too close to Tc: within a time-dependent Ginzburg-Landau formulation, we phenomenologically introduce a short wavelength cutoff (of the order
of the inverse coherence length) in the fluctuational spectrum to suppress high momentum modes. We treat the general cases
of thin wires, anisotropic thin films and anisotropic bulk samples. We obtain in all cases explicit expressions for the finite
frequency fluctuational conductivity. The dc case directly follows. Close to Tc the cutoff has no effect, and the known results for Gaussian fluctuations are recovered. Above Tc, and already for ε = ln(T/T
c) > 10-2, we find strong suppression of the paraconductivity as compared to the Gaussian prediction, in particular in the real part
of the paraconductivity. At high ε the cutoff effects are dominant. We discuss our results in comparison with data on high-Tc superconductors.
Received 19 March 2002 Published online 25 June 2002 相似文献
11.
H. Chamati D.M. Dantchev 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(1):89-99
The finite size behavior of the susceptibility, Binder cumulant and some even moments of the magnetization of a fully finite
O(n) cubic system of size L are analyzed and the corresponding scaling functions are derived within a field-theoretic ɛ-expansion scheme under periodic
boundary conditions. We suppose a van der Waals type long-range interaction falling apart with the distance r as r
- (d + σ), where 2 < σ < 4, which does not change the short-range critical exponents of the system. Despite that the system belongs
to the short-range universality class it is shown that above the bulk critical temperature T
c the finite-size corrections decay in a power-in-L, and not in an exponential-in-L law, which is normally believed to be a characteristic feature for such systems.
Received 8 August 2001 相似文献
12.
On the basis of the experimental data on diffractive processes in πp, pp and pˉp collisions at intermediate, moderately high and high energies, we restore the scattering amplitude related to the t-channel exchange by vacuum quantum numbers by taking account of the diffractive s-channel rescatterings. At intermediate and moderately high energies, the t-channel exchange amplitude turns, with a good accuracy, into an effective pomeron which renders the results of the additive
quark model. At superhigh energies the scattering amplitude provides a Froissart-type behaviour, with an asymptotic universality
of cross sections such as σtot
πp/σtot
pp→ 1 at s→∞. The quark structure of hadrons being taken into account at the level of constituent quarks, the cross sections of pion
and proton (antiproton) in the impact parameter space of quarks, σπ(r
1⊥, r
2⊥; s) and σp(r
1⊥, r
2⊥, r
3⊥; s), are found as functions of s. These cross sections implicate the phenomenon of colour screening: they tend to zero at |r
i⊥−r
k⊥|→ 0. The effective colour screening radius for pion (proton) is found for different s. The predictions for the diffractive cross sections at superhigh energies are presented.
Received: 15 December 1998 相似文献
13.
R. Mélin K. Biljaković J.C. Lasjaunias P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):417-430
We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon.
The very low temperature specific heat relaxation experiments are characterized by: (i) “interrupted” ageing (meaning that
there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective
phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain
an estimate of the glass cross-over temperature (typically T
g≃ 100-200 mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving
randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and
can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising
model [D.S. Fisher, P. Le Doussal, C. Monthus, Phys. Rev. Lett. 80, 3539 (1998)]. The typical relaxation time scales like ∼τexp(T
g/T). The glass cross-over temperature Tg related to correlations among solitons is equal to the average energy barrier and scales like T
g∼ 2xξΔ. x is the concentration of defects, ξ the correlation length of the CDW or SDW and Δ the charge or spin gap.
Received 12 December 2001 相似文献
14.
K.C. Chung C.S. Wang A.J. Santiago J.W. Zhang 《The European Physical Journal A - Hadrons and Nuclei》2001,12(2):161-167
The parameters of the σ-ω-ρ model in the relativistic mean-field theory with nonlinear σ-meson self-interaction are determined
by nuclear-matter properties, which are taken as those extracted by fits to data based on nonrelativistic nuclear models.
The values of the relevant parameters are C
σ
2∼ 94, C
ω
2∼ 32, C
ρ
2∼ 26, b∼ - 0.09, c∼ 1, and the σ-meson mass m
σ∼ 370 MeV, while the value of the calculated nuclear- surface thickness is t∼ 1.4 fm. The field system is shown to be stable, since the σ-meson self-interaction energy is a lower bound in this whole
parameter region with positive c. On the other hand, the effective nucleon mass M* is larger than 0.73M, if the symmetry incompressibility Ks is assumed to be negative and the nuclear-matter incompressibility K0 is kept less than 300 MeV.
Received: 27 June 2001 / Accepted: 5 October 2001 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. Alessio A. Carbone G. Castelli V. Frappietro 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(2):197-200
Long-range correlation properties of stochastic time series y(i) have been investigated by introducing the function σ2
MA =
[y(i) - (i)]2, where (i) is the moving average of y(i), defined as 1/n
y(i - k), n the moving average window and Nmax is the dimension of the stochastic series. It is shown that, using an appropriate computational procedure, the function σ
MA varies as nH where H is the Hurst exponent of the series. A comparison of the power-law exponents obtained using respectively the function σ
MA and the Detrended Fluctuation Analysis has been also carried out. Interesting features denoting the existence of a relationship
between the scaling properties of the noisy process and the moving average filtering technique have been evidenced.
Received 31 December 2001 相似文献
17.
Yu-bing Dong 《The European Physical Journal A - Hadrons and Nuclei》1998,1(3):347-354
In this paper, the spin-dependent structure functions of nucleon g
1, and photoabsorption cross sections σ1/2, σ3/2 and σT in the resonance region are estimated based on the constituent quark model and the properties of the five phenomenological
Breit-Wigner resonances P
33(1232), S
11(1535), D
13(1520), P
11(1440), and F
15(1680). Our results are compared to the recent E143 data of the polarized structure functions g
1(W
2, Q
2) at points Q
2=0.5 GeV2 and Q
2=1.2 GeV2 and the data of the total inclusive photoabsorption cross sections.
Received: 7 October 1997 相似文献
18.
W. Cassing Ye.S. Golubeva L.A. Kondratyuk 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):279-285
We study the possibility to measure the elastic ΦN (Φ≡J/ψ,ψ(2S), ψ(3770), χ2c) scattering cross section in the reaction ˉp+d→Φ+n
sp and the elastic D(ˉD)N scattering cross section in the reaction ˉp+d→D
−
D
0
p
sp. Our studies indicate that the elastic scattering cross sections can be determined for Φ momenta about 4–6 GeV/c and D/ˉD momenta 2–5 GeV/c by selecting events with p
t≥ 0.4 GeV/c for Φ's and p
t(p
sp) ≥ 0.5 GeV/c for D/ˉD-meson production.
Received: 8 November 1999 相似文献
19.
We study the effect of quantum fluctuations in an Ising
spin system on a scale-free network of
degree exponent γ>5 using
a quantum Monte Carlo simulation technique. In our model,
one can adjust the magnitude of the magnetic field perpendicular
to the Ising spin direction and can therefore control the
strength of quantum fluctuations for
each spin. Our numerical analysis
shows that quantum fluctuations reduce the transition
temperature Tc of the ferromagnetic-paramagnetic phase
transition. However, the phase transition belongs to
the same mean-field type universality class both with
and without the quantum fluctuations.
We also study the role of hubs by turning on the
quantum fluctuations exclusively
at the nodes with the most links. When only a small number of hub
spins fluctuate quantum mechanically, Tc
decreases with increasing magnetic field
until it saturates at high fields. This effect
becomes stronger as the number of hub spins increases.
In contrast, quantum fluctuations at the same number of
“non-hub” spins do not affect Tc. This implies
that the hubs play an important role in
maintaining order in the whole network. 相似文献
20.
O.V. Bychuk B. O'Shaughnessy N.J. Turro 《The European physical journal. E, Soft matter》2001,4(3):281-291
We propose and theoretically study an experiment designed to measure short-time polymer reaction kinetics in melts or dilute
solutions. The photolysis of groups centrally located along chain backbones, one group per chain, creates pairs of spatially
highly correlated macroradicals. We calculate time-dependent rate coefficients κ(t) governing their first-order recombination kinetics, which are novel on account of the far-from-equilibrium initial conditions.
In dilute solutions (good solvents) reaction kinetics are intrinsically weak, despite the highly reactive radical groups involved.
This leads to a generalised mean-field kinetics in which the rate of radical density decay - ∼S(t), where S(t) ∼t
- (1 + g/3) is the equilibrium return probability for 2 reactive groups, given initial contact. Here g≈ 0.27 is the correlation hole exponent for self-avoiding chain ends. For times beyond the longest coil relaxation time τ,
- ∼S(t) remains true, but center of gravity coil diffusion takes over with rms displacement of reactive groups x(t) ∼t
1/2 and S(t) ∼ 1/x
3(t). At the shortest times ( t
10-6s), recombination is inhibited due to spin selection rules and we find ∼tS(t). In melts, kinetics are intrinsically diffusion-controlled, leading to entirely different rate laws. During the regime limited
by spin selection rules, the density of radicals decays linearly, n(0) - n(t) ∼t. At longer times the standard result - ∼d
3(t)/d (for randomly distributed ends) is replaced by ∼d2x
3(t)/d
2 for these correlated initial conditions. The long-time behavior, t > τ, has the same scaling form in time as for dilute solutions.
Received 18 May 2000 相似文献