共查询到20条相似文献,搜索用时 750 毫秒
1.
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
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.
E. Degroote P.L. Garcia-Ybarra 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):381-386
Flame spreading over liquid ethanol has been experimentally characterized for ethanol for subflash temperatures, in two different
channels. Three different spreading regimes have been observed. A uniform region (with flame velocities close to 10 cm/s)
appears for values of the initial surface liquid temperature above a critical value . For values an oscillatory regime occurs. For very low temperatures, , a new uniform regime appears with slow propagation velocities (close to 1 cm/s). The critical point has been described as a Hopf bifurcation, while resembles a homoclinic connection.
Received 16 October 1998 and Received in final form 23 June 1999 相似文献
4.
E. Hascoët H.J. Herrmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):183-190
We numerically investigate the problem of the propagation of a shock in an horizontal non-loaded granular chain with a bead
interaction force exponent varying from unity to large values. When is close to unity we observed a cross-over between a nonlinearity-dominated regime and a solitonic one, the latest being
the final steady state of the propagating wave. In the case of large values of the deformation field given by the numerical simulations is completely different from the one obtained by analytical calculation.
In the following we studied the interaction of these shock waves with a mass impurity placed in the bead chain. Two different
physical pictures emerge whether we consider a light or a heavy impurity mass. The scatter of the shock wave with a light
impurity yields damped oscillations of the impurity which then behave as a solitary wave source. Differently an heavy impurity
is just shifted by the shock and the transmitted wave loses its solitonic character being fragmented into waves of decreasing
amplitudes.
Received 23 June 1999 相似文献
5.
I.L. Menezes-Sobrinho J.G. Moreira A.T. Bernardes 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):313-318
We study the existence of distinct failure regimes in a model for fracture in fibrous materials. We simulate a bundle of parallel
fibers under uniaxial static load and observe two different failure regimes: a catastrophic and a slowly shredding. In the
catastrophic regime the initial deformation produces a crack which percolates through the bundle. In the slowly shredding
regime the initial deformations will produce small cracks which gradually weaken the bundle. The boundary between the catastrophic
and the shredding regimes is studied by means of percolation theory and of finite-size scaling theory. In this boundary, the
percolation density scales with the system size L, which implies the existence of a second-order phase transition with the same critical exponents as those of usual percolation.
Received 24 June 1999 相似文献
6.
U. Erdmann W. Ebeling L. Schimansky-Geier F. Schweitzer 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):105-113
We study a model of Brownian particles which are pumped with energy by means of a non-linear friction function, for which
different types are discussed. A suitable expression for a non-linear, velocity-dependent friction function is derived by
considering an internal energy depot of the Brownian particles. In this case, the friction function describes the pumping
of energy in the range of small velocities, while in the range of large velocities the known limit of dissipative friction
is reached. In order to investigate the influence of additional energy supply, we discuss the velocity distribution function
for different cases. Analytical solutions of the corresponding Fokker-Planck equation in 2d are presented and compared with
computer simulations. Different to the case of passive Brownian motion, we find several new features of the dynamics, such
as the formation of limit cycles in the four-dimensional phase-space, a large mean squared displacement which increases quadratically
with the energy supply, or non-equilibrium velocity distributions with crater-like form. Further, we point to some generalizations
and possible applications of the model.
Received 24 November 1999 相似文献
7.
M. Gangl H. Ritsch 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(1):29-40
We develop quantum models for the combined external and internal motion of atoms in a strongly coupled driven cavity mode
including the transverse degrees of freedom. Using a simplified Gaussian mode function we determine the parameter regimes
and prospects of 3D cooling and confinement of one or two atoms in the cavity field. Analysing the field dynamics for slow
atoms traversing the cavity, we show that the spectrum of the transmitted and spontaneously scattered light contains ample
information on the motional dynamics of the atom and can be nicely used to investigate the cooling properties of the system.
Including several atoms in the dynamics we show how motional correlations build up by the common interaction with the cavity
field. This can be looked upon as collisions at far distance and can be monitored via the transmitted field dynamics.
Received 5 March 1999 and Received in final form 4 May 1999 相似文献
8.
Grain segregation mechanism in aeolian sand ripples 总被引:2,自引:0,他引:2
H.A. Makse 《The European physical journal. E, Soft matter》2000,1(2-3):127-135
Many sedimentary rocks are formed by migration of sand ripples. Thin layers of coarse and fine sand are present in these rocks,
and understanding how layers in sandstone are created has been a longstanding question. Here, we propose a mechanism for the
origin of the most common layered sedimentary structures such as inverse graded climbing ripple lamination and cross-stratification
patterns. The mechanism involves a competition between three segregation processes: (i) size-segregation and (ii) shape-segregation
during transport and rolling, and (iii) size segregation due to different hopping lengths of the small and large grains. We
develop a discrete model of grain dynamics which incorporates the coupling between moving grains and the static sand surface,
as well as the different properties of grains, such as size and roughness, in order to test the plausibility of this physical
mechanism.
Received 19 July 1999 and Received in final form 4 August 1999 相似文献
9.
P. Boltenhagen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):75-78
We have studied the maximal angle of stability of a granular packing confined between two walls. The effect of the walls is
to increase the angle dramatically. The decay of the angle with the distance between the walls is exponential with a characteristic
length which is a function of the beads diameter. The effect of the roughness of the walls has been also studied.
Received 1 April 1999 相似文献
10.
M. Dubé M. Rost M. Alava 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(4):691-699
Imbibition phenomena have been widely used experimentally and theoretically to study the kinetic roughening of interfaces.
We critically discuss the existing experiments and some associated theoretical approaches on the scaling properties of the
imbibition front, with particular attention to the conservation law associated to the fluid, to problems arising from the
actual structure of the embedding medium, and to external influences such as evaporation and gravity. Our main conclusion
is that the scaling of moving interfaces includes many crossover phenomena, with competition between the average capillary
pressure gradient and its fluctuations setting the maximal lengthscale for roughening. We discuss the physics of both pinned
and moving interfaces and the ability of the existing models to account for their properties.
Received 17 February 1999 and Received in final form 24 November 1999 相似文献
11.
A mean field approach is used to estimate the energy dissipation during the homogeneous sedimentation or the particulate fluidization
of non Brownian hard spheres in a concentrated suspension of infinite extent. Depending on inertial screening and the range
of the hydrodynamic interactions, the effective buoyancy force is determined either from the average suspension density in
a Stokes flow or from the fluid density in the turbulent flow regime. An energy balance then yields a settling or fluidization
law depending on the particle Reynolds number in reasonable agreement with the Richardson and Zaki correlation and recent
experimental results for particle settling or fluidization. We further estimate the energy dissipation in the turbulent boundary
layers around the particles to precise the Reynolds number dependence of the hindered settling function in the intermediate
flow regime.
Received 22 February 1999 and Received in final form 14 June 1999 相似文献
12.
H. Razafimandimby M. Taguchi J. C. Parlebas 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):21-26
We investigate the competition between magnetic order and local Kondo effect in a Kondo lattice model (i.e. the Coqblin-Schrieffer Hamiltonian extended to a lattice) in a mean-field approximation, taking account of the spin-orbit
degeneracy of each localized f level. This leads to the definition of a dependent Kondo temperature. We study the Kondo phase and compare its energy with the energies of magnetic phases, when the
number of the conduction band electron per site is near one. We present a phase diagram which shows the occurrence of three
phases: Kondo, antiferromagnetic and paramagnetic phases. Our model in the mean-field approximation also shows a somewhat
flat Kondo temperature, for large values of , as a function of the exchange coupling J between conduction and localized f electrons. Finally we show some scaling effects between and J and we define a corresponding Kondo temperature.
Received 21 September 1998 and Received in final form 8 February 1999 相似文献
13.
K. Ivanova 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):327-330
The two-dimensional Ausloos et al. model of fluid invasion, freezing and thawing in a porous medium is elaborated upon and investigated in order to take into
account the pore volume redistribution and conservation during freezing. The results are qualitatively different from previous
work, since the damaged pore sizes are found to be much less than the possible maximum value and is reached after a large
number of invasion-freezing-thawing cycles, e.g. the material is “slowly damaged”. The pore size distribution is thus found in better agreement with expected practical findings.
The successive invasion percolation clusters are still found to be self-avoiding with aging. The cluster size decreases with
a power law as a function of invasion-frost-thaw iterations. The aging kinetics is also discussed through the normalized totally
invaded pore volume.
Received 24 September 1999 and Received in final form 5 January 2000 相似文献
14.
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
15.
R. Gerbaldo G. Ghigo G. Giunchi L. Gozzelino F. Laviano E. Mezzetti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):297-300
We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB2. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the
material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis.
A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous
polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous
part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration,
at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic
granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a
network of strongly coupled Josephson junctions.
Received 31 May 2001 and Received in final form 5 December 2001 相似文献
16.
V. N. Kondratyev Ph. Blanchard H. O. Lutz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(2):241-244
The multi-fragmentation dynamics of noble gas atomic clusters is considered for different statistically distributed deposited
energies. The conditions giving rise to the development of criticality in the cluster evolution are revealed from an analysis
of the signals in the fragment mass distribution. The time dependence of the observables related to critical exponents is
studied. It is demonstrated that in a certain regime the cluster exhibits a behavior which can be identified as the precursor
of a second-order liquid-gas phase transition.
Received 1st September 1998 and Received in final form 14 January 1999 相似文献
17.
P. Bot I. Mutabazi 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):141-155
The dynamics of defects in a pattern of traveling inclined rolls has been investigated. Two regimes were identified in the
neighborhood of defects: a diffusive regime, with a negative phase diffusion coefficient, and a coalescence regime in which
the phase gradient diverges in time following a power law behavior. The observed periodic nucleation of defects is related
to the frequency inhomogeneity induced by the disymmetry of the wave amplitude. Amplitude holes have been observed in the
secondary modulated pattern.
Received 23 February 1999 and Received in final form 26 May 1999 相似文献
18.
R. Farhi M. El Marssi A. Simon J. Ravez 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):599-604
Dielectric and Raman scattering experiments were performed on various ceramics with composition Ba(Ti1-xZrx)O3. Such lead-free, environmental-friendly materials were shown, from dielectric measurements, to exhibit behaviours extending
from conventional to relaxor ferroelectrics on increasing the zirconium concentration. The evolution of the Raman spectra
was studied as a function of temperature for various compositions, and the spectroscopic signature of the corresponding phases
was determined. In the relaxor state, the variation of the integrated intensity of the Raman lines with temperature showed
a plateau at low temperature. This anomaly was also detected as a peak in depolarization current measurements, and attributed
to ergodicity breaking which characterizes usual relaxor systems. Raman results hint at locally rhombohedral polar nanoregions
resulting from the random fields associated with Zr ions.
Received 25 September 1998 相似文献
19.
A. Bürgers E. Lindroth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(3):327-340
We present a detailed analysis of doubly excited resonances in H- of both and symmetry. Both resonance positions and total widths for auto-detachment are calculated using complex coordinate scaling in
a Sturmian-type basis in perimetric coordinates. The resonances are classified by approximate quantum numbers with help of
their Lewis structures. For the first time, a new class of shape resonances is reported which can be understood as resulting
from couplings between different adiabatic potentials with both binding and repulsive character. In addition, we present an
analysis of the so called mass polarisation term which gives rise to specific isotope shifts.
Received 10 March 1999 and Received in final form 18 October 1999 相似文献
20.
Scaling of vortex transport properties and nonlinear ac response of high-temperature superconductors
Y. Wang H.D. Chen D.L. Yin K.X. Chen G. Lu W.P. Bai C.Y. Li 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):221-225
The macroscopic behavior of high-temperature superconductors is described by a nonlinear response function in combinations
with Maxwell equations. This function is compatible with the suggested different model pinning barriers U(J). A comparison of this function to the scaling behavior of the isothermal current-voltage characteristics measured in twinned
YBa2Cu3O (YBCO) samples shows fair agreement. We also compare the amplitude dependence of ac susceptibility derived from this function
with several experimental results of high-temperature superconductors and find a general power law in the out-of-phase peak shift.
Received 4 August 1999 and Received in final form 30 November 1999 相似文献