共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Valance T. Le Pennec 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):223-229
We study granular flows through narrow channels driven by gravity in the framework of the kinetic theory for dissipative dense
gases. We derive equations of motion for quasi-one-dimensional systems. In a certain range of flow density, the steady homogeneous
regime is found to be unstable against the formation of density waves. We show moreover that near the onset of the instability,
the governing equation for the flow density is a mixture of the Korteweg-de-Vries equation, which leads to soliton, and the
Bürger equation which exhibits spatio-temporal chaos. The competition between chaos and solitons may lead either to regular
spatially ordered density waves or to chaotic dynamics. We argue that these two types of dynamics can be encountered experimentally
according to the channel width and the dissipative properties of the granular media.
Received: 11 March 1998 / Revised and Accepted: 3 July 1998 相似文献
2.
N. Fraysse H. Thomé L. Petit 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):615-619
Humidity is well-known to significantly affect the mechanical properties, static as well as dynamic, of granular materials.
We present the method of humidification of granular media from an under-saturated vapor that we designed in order to experimentally
quantify such moisture-induced effects under accurately-controlled humidity conditions. We report the quantitative measurements
of the maximum angle of stability of a pile made of small glass beads, as a function of the relative vapor pressure, up to
close to saturation. The results obtained with liquids differing in their wetting properties on glass, namely water and heptane,
are presented. It is shown that the wetting properties of the liquid on the grains have a strong influence on the cohesion
of the non-saturated granular medium.
Received 26 October 1998 and Received in final form 30 March 1999 相似文献
3.
The connection between granular gases and sticky gases has recently been considered, leading to the conjecture that inelastic
collapse is avoided for space dimensions higher than 4. We report Molecular Dynamics simulations of hard inelastic spheres
in dimensions 4, 5 and 6. The evolution of the granular medium is monitored throughout the cooling process. The behaviour
is found to be very similar to that of a two-dimensional system, with a shearing-like instability of the velocity field and
inelastic collapse when collisions are inelastic enough, showing that the connection with sticky gases needs to be revised.
Received 17 April 2000 and Received in final form 7 June 2000 相似文献
4.
D.A. Tenne V.A. Haisler N.T. Moshegov A.I. Toropov A.P. Shebanin D.R.T. Zahn 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):371-376
We present the forward Raman scattering study of zone-centre optical phonon anisotropy in short-period GaAs/AlAs superlattices.
Experiments were performed on specially prepared superlattice structures having anti-reflection dielectric coatings and removed
substrates. The experimental data are compared with the angular dispersion of superlattice optical phonons calculated within
the dielectric susceptibility model. We have found a good agreement between the experimental data and the calculations taking
into account interface disorder.
Received 9 September 1998 and Received in final form 22 October 1998 相似文献
5.
T. Boutreux 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):419-424
We present the generalization of a theoretical model for segregation of granular mixtures due to surface flows, published
in J. Phys. I France 6, 1295 (1996). Our generalized model is valid for grains differing by their size and/or their surface properties; in the present
paper, we describe the case of two species with the same surface properties but two different sizes. The rolling stream is
assumed to be homogeneous. Exchanges between the grains at rest and the rolling stream are modelized via binary collisions.
The model predicts that during the filling of a two-dimensional silo, continuous segregation appears inside the static phase: small (respectively large) grains tend to stop uphill (respectively downhill), although
both species remain present everywhere. This fits the observations when the size difference between the species is small.
When the size difference is large, a different regime is observed. We argue that in this case, segregation occurs directly inside the rolling stream.
Received: 25 February 1998 / Received in final form and Accepted: 6 July 1998 相似文献
6.
L. Khaykovich N. Friedman N. Davidson 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(3):467-473
We present an experimental and theoretical investigation of the weak probe amplification in a cold and optically thick atomic
cloud that is highly driven by a strong pump laser. We find that for high optical densities the probe amplification is strongly
saturated. We compare our saturation measurements with a model based on dressed-atom population equalization due to re-scattering
of spontaneous emission. Good agreement between theory and experiment is obtained only when corrections due to multiple scattering
are included.
Received 3 November 1998 and Received in final form 5 March 1999 相似文献
7.
T. Boutreux H.A. Makse P.-G. de Gennes 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):105-115
We present the generalization of the minimal model for surface flows of granular mixtures, proposed by Boutreux and de Gennes
[J. Phys. I France 6, 1295 (1996)]. The minimal model was valid for grains differing only in their surface properties. The present model also
takes into account differences in the size of the grains. We apply the model to study segregation in two-dimensional silos
of mixtures of grains differing in size and/or surface properties. When the difference in size is small, the model predicts
that a continuous segregation appears in the static phase during the filling of a silo. When the difference in size is wide,
we take into account the segregation of the grains in the rolling phase, and the model predicts complete segregation and stratification
in agreement with experimental observations.
Received 9 September 1998 and Received in final form 4 November 1998 相似文献
8.
B.M. Roehner 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):151-159
We investigate the way price fluctuations are transmitted between spatially separated markets. More specifically we show that
the correlation patterns of wheat prices exhibit definite regularities some of which appear to be at variance with intuitive
reasoning. Such patterns can be explained in the framework of a wave propagation model based on the so-called spatial arbitrage
assumption. In 19th century France the velocity of price waves was of the order of 100 km/month. The economic implications
of such an order of magnitude are discussed. In the concluding section we emphasize that what gives this problem its importance
is its relative “simplicity”, a word for which we propose an operational definition.
Received 1 September 1998 and Received in final form 3 October 1998 相似文献
9.
In a previous work [#!ref1!#], the flow velocity of a steady two-dimensional granular flow along an inclined wall was investigated.
The scaling law for the velocity field was found in good agreement with recent experimental results. The purpose of the present
paper is to reformulate in more systematic manner and in a somewhat more general context the equations of mass and momentum
conservation for dense granular flow, and also to present some new results with particular emphasis on roughness influence
and dynamic dilatancy. Theoretical results are found in good agreement with experiments.
Received 19 July 1999 and Received in final form 14 October 1999 相似文献
10.
M. Bengrine A. Benyoussef A. El Kenz M. Loulidi F. Mhirech 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):129-133
A one-dimensional model of a rice-pile is numerically studied for different driving mechanisms. We found that for a sufficiently
large system, there is a sharp transition between the trivial behaviour of a 1D BTW model and self-organized critical (SOC)
behaviour. Depending on the driving mechanism, the self-organized critical rice-pile model belongs to two different universality
classes.
Received 18 December 1998 相似文献
11.
12.
N. Vandewalle M. Ausloos Ph. Boveroux A. Minguet 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(2):355-359
We present a method for visualizing the pattern which we believe to be a precursor signature of financial crashes (or ruptures).
The log-periodicity of the pattern is investigated through the envelope function technique. Three periods of the Dow Jones
Industrial Average (DJIA) are investigated: 1982-1987, 1992-1997 and 1993-1998. The presence of a rupture in the end of 1998
is outlined from data taken before the end of August 1998.
Received 15 October 1998 and Received in final form 19 November 1998 相似文献
13.
A. Buchleitner K. Sacha D. Delande J. Zakrzewski 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(2):145-157
We present a semiclassical analysis of the dynamics of Rydberg states of atomic hydrogen driven by a resonant microwave field
of linear polarization. The semiclassical quasienergies of the atom in the field are found to be in very good agreement with
the exact quantum solutions. The ionization rates of individual eigenstates of the atom dressed by the field reflect their
quasiclassical dynamics along classical periodic orbits in the near integrable regime, but exhibit a transition to nonspecific
rates when global chaos takes over in phase space. We concentrate both on the principal resonance where the unperturbed Kepler
frequency is equal to the driving field frequency and on the higher primary resonance The latter case allows for the construction of nondispersive wave packets which propagate along Kepler ellipses of intermediate
eccentricity.
Received: 23 June 1998 / Accepted: 10 November
1998 相似文献
14.
M. Leadbeater R.A. Römer M. Schreiber 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):643-652
We present calculations of the localisation length, , for two interacting particles (TIP) in a one-dimensional random potential, presenting its dependence on disorder, interaction
strength U and system size. is computed by a decimation method from the decay of the Green function along the diagonal of finite samples. Infinite sample
size estimates are obtained by finite-size scaling. For U=0 we reproduce approximately the well-known dependence of the one-particle localisation length on disorder while for finite
U, we find that with varying between and . We test the validity of various other proposed fit functions and also study the problem of TIP in two different random potentials
corresponding to interacting electron-hole pairs. As a check of our method and data, we also reproduce well-known results
for the two-dimensional Anderson model without interaction.
Received 19 June 1998 and Received in final form 29 October 1998 相似文献
15.
I. Mróz A. Pękalski 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):181-186
We propose a model suitable for investigating the conditions under which a population, adapted to a given environment, may
colonize a new neighbouring, spatially separated, habitat. We find out how similar the two regions must be for such a colonization
to succeed and what will be the spatial distribution of genetic pools of the two populations after the process. It is found
that between the two populations each adapted to the different region, a hybrid zone, characterized by increased heterozygosity,
may be formed. The dependence of the shape of the hybrid zone on the external (environmental) parameters is determined. When
the differences between the two regions are significant, the populations are separated by a depopulated zone. We show that
the conditions in the colonized habitat influence the genetic pool of the population living in the first region. Computer
simulations based on the standard Monte Carlo technique are used.
Received 11 December 1998 and Received in final form 17 December 1998 相似文献
16.
This paper deals with the quasi-static regime of deformation of granular matter. It investigates the size of the Representative
Elementary Volume (REV), which is the minimum packing size above which the macroscopic mechanical behaviour of granular materials
can be defined from averaging. The first part uses typical results from recent literature and finds that the minimum REV contains
in general 10 grains; this result holds true either for most experiments or for Discrete Element Method (DEM) simulation.
This appears to be quite small. However, the second part gives a counterexample, which has been found when investigating uniaxial
compression of glass spheres which exhibit stick-slip; we show in this case that the minimum REV becomes 107 grains. This makes the system not computable by DEM. Moreover, similarity between the Richter law of seism and the exponential
statistics of stick-slip is stressed.
Received 8 March 2002 and Received in final form 12 July 2002 相似文献
17.
18.
Memory of silica aggregates dispersed in smectic liquid crystals: Effect of the interface properties
A. Jákli L. Almásy S. Borbély L. Rosta 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):509-513
Previous studies on nematic liquid crystals containing silica particles indicated memory effects that might be due to hydrogen
bonds between the individual silica particles. We made smectic liquid crystal dispersions containing silica particles with
various surface properties. Using a neutron scattering technique we studied the interfacial surface effects on the structure
of the silica aggregates, and on the smectic layer alignment. Our observations indicate that the stability of the memory correlates
to the number of OH groups on the silica surfaces. The observations imply that, with fine-tuning of the OH content of the
silica surfaces, various types of memory devices can be designed. We considered three different effects that can memorise
the alignment of the liquid crystal. Measurements on tilted SmC phases indicate that surface effects become important only
after repeated heating-cooling cycles, as the average size of the aggregates decrease.
Received 31 July 1998 and Received in final form 17 December 1998 相似文献
19.
T. Kamppeter F.G. Mertens A. Sánchez A.R. Bishop F. Domínguez-Adame N. Grønbech-Jensen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):607-618
We study the effects of finite temperature on the dynamics of non-planar vortices in the classical, two-dimensional anisotropic
Heisenberg model with XY- or easy-plane symmetry. To this end, we analyze a generalized Landau-Lifshitz equation including additive white noise and
Gilbert damping. Using a collective variable theory with no adjustable parameters we derive an equation of motion for the
vortices with stochastic forces which are shown to represent white noise with an effective diffusion constant linearly dependent
on temperature. We solve these stochastic equations of motion by means of a Green's function formalism and obtain the mean
vortex trajectory and its variance. We find a non-standard time dependence for the variance of the components perpendicular
to the driving force. We compare the analytical results with Langevin dynamics simulations and find a good agreement up to
temperatures of the order of 25% of the Kosterlitz-Thouless transition temperature. Finally, we discuss the reasons why our
approach is not appropriate for higher temperatures as well as the discreteness effects observed in the numerical simulations.
Received: 27 April 1998 / Revised: 2 September 1998 / Accepted: 10 September 1998 相似文献
20.
Y. Grasselli H.J. Herrmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):673-679
Experimental investigations on the shape of a heap formed in a Hele Shaw cell either on a flat base or in a two-dimensional
silo are presented. We have focused our attention on the shape dependence on mass flux and initial energy of particles poured
into the cell. Two kinds of granular media are considered: glass beads and sand and we shall point out their different behaviors.
We described the variations of the angle of repose and of the size of the tail as a function of the experimental parameters.
We also report the time evolution of the angle of repose during the formation of the heap.
Received 28 September 1998 and Received in final form 20 January 1999 相似文献