共查询到20条相似文献,搜索用时 15 毫秒
1.
H.M. Ohlenbusch T. Aste B. Dubertret N. Rivier 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):211-220
We analyze the structure of two dimensional disordered cellular systems generated by extensive computer simulations. These
cellular structures are studied as topological trees rooted on a central cell or as closed shells arranged concentrically
around a germ cell. We single out the most significant parameters that characterize statistically the organization of these
patterns. Universality and specificity in disordered cellular structures are discussed.
Received: 23 September 1997 / Received in final form: 14 January 1998
/ Accepted: 29 January 1998 相似文献
2.
R. Guirado-López D. Spanjaard M.-C. Desjonquères 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):459-466
The magnetic properties of small YN clusters are studied by using a tight-binding Hubbard Hamiltonian in the unrestricted Hartree-Fock approximation. Several
types of cluster geometries are considered in order to see the effects of the size and symmetry of the structures on the magnetic
properties. The average magnetic moments are found to be constant over large domains of variations in the interatomic distance, a fact that can be explained by the
existing closed shell electronic configurations at least for one spin direction in all our magnetic solutions. Small energy
gains upon the onset of magnetization are obtained, which reveals the low stability of the magnetic solutions. Our results
contradict the prediction of a magnetic-nonmagnetic transition at a large cluster size (about 90 atoms) for these kinds of
systems.
Received: 27 April 1998 / Received in final form: 23 June 1998 / Accepted: 17 July 1998 相似文献
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J. Browaeys J.-C. Bacri C. Flament S. Neveu R. Perzynski 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(2):335-341
We present here new experimental results about the waves at the horizontal free surface of a magnetic fluid submitted to a
normal magnetic field. The waves are generated by a small modulation at frequency of the vertical field . Using a shadowgraph method, we are able to measure the wavevector k of the 2D waves for a given value of and . The dispersion relation of the surface waves is established experimentally. On the other hand, we propose a theoretical
derivation of the dispersion equation which includes a more complete treatment of the magnetic term than the previous works.
Finally, we conclude that a linear and inviscid analysis is sufficient to fit well the experimental data, except in the vicinity
of the critical field where a surface instability occurs.
Received 11 May 1998 相似文献
5.
É. Maréchal S. Guibal J.-L. Bossennec M.-P. Gorza R. Barbé J.-C. Keller O. Gorceix 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(3):195-198
The mechanical Stern-Gerlach effect is investigated in the case of a slow atomic cloud falling through an inhomogeneous magnetic
field featuring a strong longitudinal gradient. The resulting Zeeman sublevel state selection is demonstrated under various
experimental conditions. Longitudinal spatial separations are in agreement with numerical simulations that take into account
the gravitational acceleration and both the transverse and axial magnetic forces. Since separations greater than 20 cm are
obtained, potential applications in atom optics are outlined.
Received: 16 February 1998 / Received in final form: 1 April 1998 / Accepted: 6 April 1998 相似文献
6.
C. Faure N. Decoster F. Argoul 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):87-97
The aggregation of 2D colloidal crystals can be performed by applying an AC field to a colloidal dispersion. This technique
is used in this work for assembling multilamellar vesicles in suspension. The dynamics of the aggregation is followed by real-time
recording of the pictures of the microsphere assembly through a phase contrast microscope. The influence of both the frequency
and the amplitude of the alternating field on the dynamical evolution of the concentration of layered particles is discussed
with respect to their size. A phenomenological model of double layer induced trapping of the particles is proposed and an
electroconvective instability of the fluid surrounding the particles is suggested from the observation of the local dynamics
of the particles, in accordance with a very recent argument of Yeh et al. [#!Yeh:97!#].
Received: 4 December 1997 / Revised: 24 March 1998 /
Accepted: 4 May 1998 相似文献
7.
S. Velasco F.L. Román A. González J.A. White 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):421-427
The study of a system of hard rods in a box of finite length in the presence of a uniform gravitational field is made by means
of the microcanonical ensemble. Explicit expressions are derived for the phase volume and the density of states, the primary
functions of this ensemble. Related statistical quantities are reported, such as the entropy, the temperature, the heat capacity
and the forces exerted on the fluid by the bottom and top walls. The microcanonical number density and higher order molecular
distribution functions are also derived.
Received: 7 April 1998 / Received in final form: 20 July 1998 / Accepted: 28 July 1998 相似文献
8.
A model for ripple instabilities in granular media 总被引:1,自引:0,他引:1
O. Terzidis P. Claudin J.-P. Bouchaud 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):245-249
We extend the model of surface granular flow proposed in [#!bcre!#] to account for the effect of an external `wind', which
acts as to dislodge particles from the static bed, such that a stationary state of flowing grains is reached. We discuss in
detail how this mechanism can be described in a phenomenological way, and show that a flat bed is linearly unstable against
ripple formation in a certain region of parameter space. We focus in particular on the (realistic) case where the migration
velocity of the instability is much smaller than the grains' velocity. In this limit, the full dispersion relation can be
established. We relate the critical wave vector to the mean hopping length and to the ratio of the flight time to the `stick'
time. We provide an intuitive interpretation of the instability.
Received: 30 January 1998 / Revised: 12 May 1998 / Accepted: 8 June 1998 相似文献
9.
In the past different models for the magnetic salt vanadyl pyrophosphate (VO)2P2O7 were discussed. Neither a spin ladder nor an alternating chain are capable to describe recently measured magnetic excitations.
In this paper we propose a 2D model that fits better to experimental observations.
Received: 29 May 1998 / Received in final form: 25 September 1998 / Accepted: 30 September 1998 相似文献
10.
U. Ernst J. Schuster F. Schreck A. Marte A. Kuhn G. Rempe 《Applied physics. B, Lasers and optics》1998,67(6):719-722
5 rubidium-87 atoms released from an Ioffe–Pritchard magnetic trap is investigated experimentally. The expansion dynamics depend
only on the trap frequencies, which are determined independently. The data are in good agreement with the expected expansion
of a condensate, and are clearly distinct from the behaviour of a classical gas in the hydrodynamic regime.
Received: 3 June 1998/Final version: 25 September 1998 相似文献
11.
E. Plaut L. Pastur R. Ribotta 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):283-297
We study experimentally the evolution of thermoconvection in a laterally extended planar nematic layer, at zero or weak stabilizing
magnetic field. As the applied thermal gradient is increased, a cascade of symmetry breakings occurs, towards structures of
increasing spatial complexity, and ultimately towards oscillating states. The patterns are characterized optically, and simple
models for the distortion of the vertical (out of plane) component of the director field are proposed.
Received: 1st December 1997 / Revised: 25 May 1998 / Accepted: 2 June 1998 相似文献
12.
P. Entel R. Meyer K. Kadau H.C. Herper E. Hoffmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):379-388
Results are presented of first-principles total-energy calculations and molecular-dynamics simulations of structural transformations
in magnetic transition metal alloys like Fe1-xNix. While first-principles calculations allow to identify those structures having the lower total energy, molecular-dynamics
simulations can be used to trace out the dependence of the transformation on temperature, composition, concentration of defects
etc. We have used the method of the semi-empiric embedded-atom potential in the molecular-dynamics simulations which yields remarkable
good results for the structural changes.
Received: 3 February 1998 / Revised: 4 May 1998 / Accepted: 24 June 1998 相似文献
13.
B.M. Letfulov 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):195-203
This paper gives a simplified model of the double exchange which is a kind of indirect exchange interaction between localized
magnetic moments. The presented model is solved exactly in the case of infinite - dimensional space. Equations for single-particle
Green's function and magnetization of the localized spins subsystem are obtained. It is shown that our simple double exchange
model reveals an instability to the ferromagnetic ordering of localized moments. Magnetic and electric properties of this
system on Bethe lattice with are investigated in detail.
Received: 24 January 1997 / Revised: 14 February 1997 / Received in final form: 18 August 1997 / Accepted: 25 August 1997 相似文献
14.
A. Desaix O. Roubeau J. Jeftic J.G. Haasnoot K. Boukheddaden E. Codjovi J. Linarès M. Noguès F. Varret 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):183-193
We investigate the behaviour of photo-excitable, bistable systems, under permanent light irradiation, in presence of relaxation
towards the non-excited state. Cooperativity causes bistability of the steady state, leading to light-induced thermal and
optical hysteresis (LITH and LIOH). The light-induced instability is expected to induce demixtion, i.e. the coexistence of domains of the two stable steady states. Such effects are evidenced by magnetic and reflectivity measurements
on the spin-crossover solid solution: , with x= 0.3, 0.5, 0.85. Experimental data are in quantitative agreement with a simple macroscopic model which includes a non-linear
relaxation term in the master equation.
Received: 5 June 1997 / Accepted: 17 July 1998 相似文献
15.
V. Parfait-Pignol G. Le Caër R. Delannay 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):499-511
The topological and metric properties of a few natural 2D random cellular structures, namely an armadillo shell structure
and young soap froths, which are formed from two classes of cells, large and small, have been characterized. The topological
properties of a model generated from a Kagome tiling, which mimics such random binary structures, have also been exactly calculated.
The distribution of the number of cell sides is bimodal for the structures investigated. In contrast to the classical Aboav-Weaire
law for homogeneous 2D random cellular structures, nm(n), the mean total number of edges of neighbouring cells of cells with n sides does not vary linearly with n. Only the nm(i, n) (i=1,2) determined separately for every class of cells are linear in n for all investigated structures. Topological properties and correlations between metric and topological properties are finally
compared with the predictions of various literature models.
Received: 24 December 1997 / Revised: 7 April 1998 / Accepted: 20 April 1998 相似文献
16.
A.A. Zvyagin D.M. Apal'kov 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):565-569
We present a Bethe Ansatz based investigation of a one-dimensional (1D) Heisenberg spin chain in a real 3D crystal lattice.
We have shown that due to an influence of the lattice distortion on a crystalline field of ligands of magnetic ions, a Heisenberg
antiferromagnetic spin chain is unstable under the appearance of a magnetic anisotropy of the “easy-plane” type. The effects of an external magnetic
field and nonzero temperature onto such a phase transition are studied.
Received: 19 January 1998 / Revised: 16 March 1998 / Accepted: 17 March 1998 相似文献
17.
C. Triché P. Verkerk G. Grynberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(2):225-228
We present an experimental study of the kinetic temperature of cesium atoms interacting with laser beams tuned on the blue
side of the transition. In the case of a three-dimensional four-beam molasses, temperatures as low as 800 nK were found. These low temperatures
are compatible with a good capture efficiency. The influence of other hyperfine transitions on the temperature is significant.
In the presence of a static magnetic field (antidot lattices), the temperatures are slightly higher but show a much weaker
dependence on the other hyperfine transitions.
Received: 14 May 1998 / Received in final form: 16 October 1998 / Accepted: 2 November 1998 相似文献
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20.
P. Bhattacharyya 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):247-252
Dynamic properties of a one-dimensional probabilistic cellular automaton are studied by Monte Carlo simulation near a critical
point which marks a second-order phase transition from an active state to an effectively unique absorbing state. Values obtained
for the dynamic critical exponents indicate that the transition belongs to the universality class of directed percolation.
Finally the model is compared with a previously studied one to show that a difference in the nature of the absorbing states
places them in different universality classes.
Received: 6 February 1998 / Revised and Accepted: 17 February 1998 相似文献