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1.
Y. Shang L. Yi K. Yao 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):335-338
In the replica symmetric approximation and static limit in Matsubara “imaginary time”, the quantum XY spin glass model with planar Dzyaloshinskii-Moriya interaction in longitudinal field is investigated. Several thermodynamic
quantities are calculated numerically as well as spin self-interaction and spin glass order parameter for spin S=1/2. It is shown that the entropy is not independent of the field. A crossover behavior of the specific heat depending on
temperature is found. There is a deviation from the parabolic approximation, C/T=A+Bh
2
.
Received 11 March 1998 相似文献
2.
K. Kassapidou J.R.C. van der Maarel 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):471-476
The persistence length DNA hexagonal-cholesteric phase transition upon dilution and/or increase in solvent ionic strength
is investigated with polarized light microscopy. The ionic strength dependence of the transition follows Lindemann criterion
, i.e., the hexagonal lattice melts when the root-mean-square fluctuations in transverse order exceed 10% of the interaxial spacing.
The spacings are derived from density and the fluctuations are estimated with a theory of undulation enhanced electrostatic
interactions. Additional support for this theory is given by the DNA equation of state and anisotropic neutron radiation scattering
from magnetically aligned cholesteric samples just below the phase transition.
Received: 17 November 1997 / Revised: 21 January 1998 / Accepted: 25 February 1998 相似文献
3.
R. Cressely V. Hartmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):57-62
In this experimental work we carefully investigate the rheological behaviour and in particular the shear thickening exhibited
by aqueous micellar solutions of CTAB with NaSal as added counterion. We are particularly interested in the evolution of the
critical shear rate (at which shear thickening occurs) versus
C
D
, the surfactant concentration. We show that , at fixed salt concentration C
S
, increases with C
D
following a power law evolution with a positive exponent of + 5.8. On the other hand we show that if the ratio C
D
/ C
S
is fixed, decreases with C
D
with a negative exponent of -2.0. Nevertheless investigations of the zero shear viscosity indicate that in all situations (implying variation of the surfactant concentration C
D
, or the salt concentration C
S
or the temperature) is a decreasing function of the length of the micelles. All these evolutions are compatible with a gelation mechanism which
could possibly be associated with entanglement effects of large interacting flowing structures.
Received: 3 March 1998 / Revised: 16 June 1998 / Accepted: 3 July 1998 相似文献
4.
M. Baiesi E. Carlon E. Orlandini A.L. Stella 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):129-134
Recently Garel, Monthus and Orland [Europhys. Lett. 55, 132 (2001)] considered a model of DNA denaturation in which excluded volume effects within each strand are neglected, while
mutual avoidance is included. Using an approximate scheme they found a first order denaturation. We show that a first order
transition for this model follows from exact results for the statistics of two mutually avoiding random walks, whose reunion
exponent is c > 2, both in two and three dimensions. Analytical estimates of c due to the interactions with other denaturated loops, as well as numerical calculations, indicate that the transition is
even sharper than in models where excluded volume effects are fully incorporated. The probability distribution of distances
between homologous base pairs decays as a power law at the transition.
Received 8 July 2002 / Received in final form 25 July 2002 Published online 17 September 2002 相似文献
5.
A. Qayyum M.N. Akhtar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):181-184
Light emission during sputtering of graphite targets with 1–10 keV Ne+, Kr+ and Xe+ beams has been investigated in the 180-600 nm wavelength range. Beside the characteristic lines of sputtered C1 and C1
+, a continuum superimposed with a number of broad structures was observed in the 250-520 nm range, and having a maximum at
386 nm. Mass analysis of the sputtered flux confirmed the presence of negative carbon clusters C
m
-
, C2
- being the dominant one. Ion beam parameters i.e. ion mass, energy, current density and ion dose were varied to identify the origin of the continuum emission. On the basis
of the experimental results, it is suggested that the continuum is predominantly due to the overlapping of various band systems
of sputtered C2 with a small contribution from the heavier sputtered carbon clusters Cm (m>2).
Received 24 September 1999 and Received in final form 11 February 2000 相似文献
6.
D. Beckmann S. Wanka J. Wosnitza G. Goll B. Drehmann E. Balthes D. Schweitzer W. Strunz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):329-333
We report on Shubnikov-de Haas and de Haas-van Alphen measurements of an organic metal based on the molecular donor bis(ethylenedioxy)-tetrathiavulvalene
(= BEDO-TTF) and the anion Cl- with H2O molecules. The observed single oscillation frequency perfectly follows the two-dimensional dependence with T. The Fermi-surface area of of the first Brillouin zone proves a quarter-filled band, i.e., a 2:1 stoichiometry of the BEDO-TTF donor with respect to the anion. The apparent discrepancy to X-ray data which give a
1:1 ratio between BEDO-TTF and Cl- is understood by replacement of H2O molecules with (H3O)+ ions. The proposed stoichiometry therefore is (BEDO-TTF)2
+(H5O2)+(Cl-)2. The cyclotron effective mass is when deduced from the temperature dependence of the fundamental oscillation amplitude, but strongly reduced when extracted
from higher harmonics. This and the strong harmonic content of the oscillations signals an influence of the two-dimensional
electronic structure and can be qualitatively understood by applying the concept of magnetic interaction to the effect of
the oscillatory chemical potential.
Received: 16 April 1998 / Revised: 7 July 1998 / Accepted: 9 July 1998 相似文献
7.
R. Kishore S. Lamba 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(2):161-164
An exact analytical expression for the specific heat jump at the critical temperature Tc has been obtained directly from the BCS gap equation for any shape of the energy dependent electronic density of states (DOS).
We consider a model which takes into consideration electron-electron repulsion, formulated in the Hubbard model along with
the electron-electron attraction due to electron-phonon interaction in the BCS formalism. We have analyzed this expression
for constant as well as for the Lorentzian forms of DOS. It is shown that the constant DOS in the simple BCS theory cannot
explain the large values of , found in some superconductors. The specific heat versus temperature curve has been found to have a peak, similar to that of Eliashberg theory of superconductivity. The influence
of repulsive interaction is very small and occurs mainly at higher temperatures.
Received: 26 January 1998 相似文献
8.
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
9.
We have observed that different lamellar phases (thermotropic, lyotropic of surfactants or blockcopolymers) share the same
rheological properties = A(T)σm, m = 1.67±0.1, independently of their chemical nature, in a range of shear rates , shear stresses σ, and temperatures T, where the flow is stationary. It is argued that the key phenomenon is the appearance of screw dislocations whose glide under
an applied shear counterbalances plastically the applied vorticity, and stabilizes the layers, whose slip past each other is thus made more feasible. The theory, which
makes use in other respects of the high-temperature creep model in solids, reproduces correctly the power law behavior and
the values of A(T).
Received 18 April 2001 and Received in final form 25 October 2001 相似文献
10.
O.L. Safronov 《Communications in Mathematical Physics》1998,193(1):233-243
Given two selfadjoint operators A and V=V
+ -V
-, we study the motion of the eigenvalues of the operator A(t)=A-tV as t increases. Let α>0 and let λ be a regular point for A. We consider the quantities N
+(λ,α), N
-(λ,α), N
0(λ,α) defined as the number of the eigenvalues of the operator A(t) that pass point λ from the right to the left, from the left to the right or change the direction of their motion exactly
at point λ, respectively, as t increases from 0 to α>0. An abstract theorem on the asymptotics for these quantities is presented. Applications to Schr?dinger
operators and its generalizations are given.
Received: 9 April 1997 / Accepted: 26 August 1997 相似文献
11.
12.
D. Görlitz J. Kötzler 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):37-43
Between 4.2 K and the Curie temperatures of the cubic Heisenberg ferromagnets EuS and EuO, their homogeneous dynamic susceptibilities
have been investigated by means of a broad-band reflectometer operating from 0.1 GHz to 40 GHz. For internal magnetic fields
larger than the anisotropy fields H
A
(
T
) of both materials, their static susceptibilities exhibit a -divergence, which reveals quantitatively the dominance of dipolar-anisotropic spin-wave fluctuations. displays a Lorentzian shape the damping frequency of which obeys scaling in terms of .The scaling function agrees quantitatively with work by Frey and Schwabl [#!FS88!#] for dipolar Heisenberg ferromagnets at
temperatures above Tc. Building upon their approach, the resonance frequency of the Lorentzian can be related to a memory effect in the damping
determined by the large value of the relaxation rate of the longitudinal magnetization fluctuations . For EuS, this relation is substantiated directly by inelastic neutron scattering. All these features reveal the hitherto
uncovered importance of the dipolar anisotropic fluctuations below Tc of ferromagnets.
Received: 4 March 1998 / Accepted: 12 May 1998 相似文献
13.
H.A. Radovan H.H. Wen P. Ziemann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):533-540
Using a specially designed SQUID magnetometer we measured the temperature dependence of the critical current density in a
ring patterned thin film for magnetic fields parallel to the c-axis. In addition, the temporal relaxation of the remanent state as prepared by field cooling in an external field of 100
Oe at different temperatures is determined. The j
c
(
T
) data show a field-dependent anomalous kink close to Tc pointing to reduced dissipation with increasing temperature allowing to construct a corresponding H-T borderline. A similar behavior is observed for the normalized relaxation rate S
(
T
) as extracted from the temporal behavior of the remanent state, which, at low temperatures, exhibits the expected increase
for increasing T-values, while an anomalous decrease of S
(
T
) is found for temperatures above 85 K. While the low-T regime is attributed to creep of 2D pinned single vortex lines, the high-T behavior is suggested to be dominated by collective motion with a more sluggish dynamics. This change in dynamics is also
reflected by the activation barriers for flux creep U
(
j
), which show a corresponding crossover in μ from 0.06 to 0.99. An additional scaling analysis of the E-j characteristics for according to vortex glass theory reveals quasi-2D collective creep behavior with .
Received: 8 April 1998 / Revised: 15 July 1998 / Accepted: 2 September 1998 相似文献
14.
It is shown that A:= H1, η (G), the sympectic reflection algebra over ?, has TG independent traces, where TG is the number of conjugacy classes of elements without eigenvalue 1 belonging to the finite group G ? Sp(2N) ? End(?2N) generated by the system of symplectic reflections.Simultaneously, we show that the algebra A, considered as a superalgebra with a natural parity, has SG independent supertraces, where SG is the number of conjugacy classes of elements without eigenvalue -1 belonging to G.We consider also A as a Lie algebra AL and as a Lie superalgebra AS.It is shown that if A is a simple associative algebra, then the supercommutant [AS, AS] is a simple Lie superalgebra having at least SG independent supersymmetric invariant non-degenerate bilinear forms, and the quotient [AL, AL]/([AL, AL] ∩ ?) is a simple Lie algebra having at least TG independent symmetric invariant non-degenerate bilinear forms. 相似文献
15.
Ian F. Putnam 《Communications in Mathematical Physics》2000,214(3):593-605
We consider the C
*-algebra, A
T
, constructed from a substitution tiling system which is primitive, aperiodic and satisfies the finite pattern condition.
Such a C
*-algebra has a unique trace. We show that this trace completely determines the order structure on the group K
0(A
T
); a non-zero element in K
0(A
T
) is positive if and only if its image under the map induced from the trace is positive.
Received: 12 August 1999 / Accepted: 2 May 2000 相似文献
16.
V. Cherepanov I.Y. Korenblit A. Aharony O. Entin-Wohlman 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):511-523
The effects of quenched dipole moments on a two-dimensional Heisenberg antiferromagnet are found exactly, by applying the
renormalization group to the appropriate classical non-linear sigma model. Such dipole moments represent random fields with
power law correlations. At low temperatures, they also represent the long range effects of quenched random strong ferromagnetic
bonds on the antiferromagnetic correlation length, , of a two-dimensional Heisenberg antiferromagnet. It is found that the antiferromagnetic long range order is destroyed for
any non-zero concentration, x, of the dipolar defects, even at zero temperature. Below a line , where T is the temperature, is independent of T, and decreases exponentially with x. At higher temperatures, it decays exponentially with , with an effective stiffness constant , which decreases with increasing x/T. The latter behavior is the same as for annealed dipole moments, and we use our quenched results to interpolate between the
two types of averaging for the problem of ferromagnetic bonds in an antiferromagnet. The results are used to estimate the
three-dimensional Néel temperature of a lamellar system with weakly coupled planes, which decays linearly with x at small concentrations, and drops precipitously at a critical concentration. These predictions are shown to reproduce successfully
several of the prominent features of experiments on slightly doped copper oxides.
Received 22 October 1998 相似文献
17.
A. Johansen H. Saleur D. Sornette 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):551-555
Significant advances, both in the theoretical understanding of rupture processes in heterogeneous media and in the methodology
for characterizing critical behavior, allows us to reanalyze the evidence for criticality and especially log-periodicity in
the previously reported chemical anomalies that preceded the Kobe earthquake. The ion (Cl-, K+, Mg++, NO3
- and SO4
-) concentrations of ground-water issued from deep wells located near the epicenter of the 1995 Kobe earthquake are taken as
proxies for the cumulative damage preceding the earthquake. Using both a parametric and non-parametric analysis, the five
data sets are compared extensively to synthetic time series. The null-hypothesis that the patterns documented on these times
series result from noise decorating a simple power law is rejected with a very high confidence level.
Received 21 January 2000 相似文献
18.
Y. Maniwa A. Grupp F. Hentsch M. Mehring 《Physica C: Superconductivity and its Applications》1988,156(5)
Direct microwave absorption was studied as a function of magnetic field up to 8 kG and in a temperature range between 10 K and 150 K in Y1Ba2Cu3O7−x. Large microwave absorption was observed below Tc over a wide magnetic field range. The microwave power absorption is approximately described by I=A(T) H+C(T), where A(T) and C(T) are temperature dependent constants. A(T) is proportional to the square root of the microwave power, while C(T) shows a different behaviour. We propose different origins for A(T) and C(T), namely fluxons in grains and weak Josephson links. Moreover, also flux trapping was observed in the superconducting state. Possible mechanisms for the absorption are discussed. 相似文献
19.
A. Nossov J. Pierre J. Beille V. Vassiliev B. Slobodin 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):467-472
The influence of hydrostatic pressure on the transport properties of (La1-xRx)0.67Ca0.33MnO3 (,Tb) ferromagnetic manganites is investigated. The enhancement of the Curie temperature TC under pressure agrees with previous data. In the paramagnetic range, the resistivity can be represented by a Mott localisation
law, with a characteristic temperature T0 decreasing with pressure. The variation of TC with pressure is compared to the effect induced by replacing La by a magnetic rare earth in (La1-xRx)0.67Sr0.33MnO3 manganites (, ..., Tm). The main effect is not related to the decrease of the mean radius of the cation, but to an additional scattering
by the magnetic moment of the rare earth.
Received: 15 May 1998 / Revised: 6 July 1998 / Accepted: 16 July 1998 相似文献
20.
H.R. Brand P.E. Cladis H. Pleiner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):347-353
We discuss the macroscopic behavior of smectic CG liquid crystals. Smectic CG is the most general tilted smectic phase that is fluid in the layers. It is characterized by global C1 symmetry. Consequently, it is ferroelectric, pyroelectric and piezoelectric, opening up a number of possible applications
for such a phase. As smectic CG-phase has a macroscopic hand due to its structure, it is a natural candidate to explain the recent experimental observations
of left and right-handed helices in a system composed of achiral molecules. We also discuss critically to what extent smectic
CG could be important for liquid crystalline phases formed by banana-shaped molecules. Phase transitions involving a smectic
CG phase and defects of its in-plane director are briefly discussed.
Received: 25 March 1998 / Revised: 15 June 1998 / Accepted: 15 July 1998 相似文献