共查询到20条相似文献,搜索用时 15 毫秒
1.
L. Oger P. Richard J.P. Troadec A. Gervois 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):403-406
We compare two-dimensional froths obtained by radical tessellation of random planar cuts made through disordered assemblies
of monosize spheres at different packing fractions C from C=0 to C=0.64 with two-dimensional stereological cuts obtained through the three-dimensional froths made with the same packing. We
have built numerically the packings using different algorithms. The study of both topological and metric properties shows
significant differences between the two representations.
Received 26 May 1999 and Received in final form 13 November 1999 相似文献
2.
V. V. Hoang H. Zung N. H.B. Trong 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(3):515-524
Structural properties of amorphous TiO2 spherical nanoparticles have
been studied in models with different sizes of 2 nm, 3 nm, 4 nm and 5 nm under
non-periodic boundary conditions. We use the pairwise interatomic potentials
proposed by Matsui and Akaogi. Models have been obtained by cooling from the
melt via molecular dynamics (MD) simulation. Structural properties of an
amorphous nanoparticle obtained at 350 K have been analyzed in detail
through the partial radial distribution functions (PRDFs), coordination
number distributions, bond-angle distributions and interatomic distances.
Moreover, we show the radial density profile in a nanoparticle. Calculations
show that size effects on structure of a model are significant and that if
the size is larger than 3 nm, amorphous TiO2 nanoparticles have a
distorted octahedral network structure with the mean coordination number
ZTi-O ≈6.0 and ZO-Ti ≈3.0 like those observed in the
bulk. Surface structure and surface energy of nanoparticles have been
obtained and presented. 相似文献
3.
S. Renard T. Schwager T. Pöschel C. Salueña 《The European physical journal. E, Soft matter》2001,4(2):233-239
The onset of surface fluidization of granular material in a vertically vibrated container, z = A cosωt
, is studied experimentally. Recently, for a column of spheres it has been theoretically found (see T. P?schel, T. Schwager,
C. Salue na, Phys. Rev. E 62, 1361 (2000)) that the particles lose contact if a certain condition for the acceleration amplitude ≡Aω2/g = f (ω) holds. This result is in disagreement with other findings where the criterion = = const was found to be the criterion of fluidization. We show that for a column of spheres a critical acceleration is not
a proper criterion for fluidization and compare the results with theory.
Received 21 August 2000 and Received in final form 30 October 2000 相似文献
4.
K. Lochmann A. Anikeenko A. Elsner N. Medvedev D. Stoyan 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):67-76
The performance of various structure characteristics in
the task of indicating structural peculiarities in packings of
hard spheres is investigated. Various characteristics based on
Voronoi polyhedra, spherical harmonics, and Delaunay simplices are
considered together with the pair correlation function and the
mean number of r-close triples. They are applied to a set of
hard sphere packings of density φ from 0.62 to 0.72. It turns
out that all used structure characteristics are able to indicate
changes of order from non-crystalline to crystalline packings.
However, not all of them are sensitive enough to indicate
different stages of structure transformation under densification.
The characteristics based on Delaunay simplices turn out to be the
most sensitive for this purpose.
For the models considered three principal structure classes are
found: packings of densities lower than the known critical value
0.64 showing a non-crystalline behavior; packings with
considerable crystalline regions for φ up to 0.66–0.67;
rather complete crystals although with numerous defects for φ
above 0.67. 相似文献
5.
The field-induced realignment of a smectic-A phase is in principle a complicated process involving the director rotation via
the interaction with the field and the layer rotation via the molecular interactions. Time-resolved X-ray scattering experiments
have revealed major phenomena concerning the maintenance of the integrity of the smectic-A layer structure during the alignment
process. In order to obtain a deeper insight into this process, we have carried out a dissipative particle dynamics study
of the realignment kinetics of a nanodroplet of a smectic-A liquid crystal suspended in an isotropic fluid following a switch
in the direction of an applied magnetic field. The strength of the mesogen-field interaction is small compared to the inter-molecular
interactions. The reaction of the smectic configuration to the field switch was found to depend on the balance between the
inter-molecular interactions stabilising the formation of the smectic layering and the interaction of the mesogens with the
external field. It is found that the rotational behaviour of the smectic layers under the influence of an external magnetic
field arises from a combination of stochastic translational displacements and rotational motions of the centres of mass of
the mesogens in the nanodroplets. The simulations indicate that X-ray scattering and NMR experiments monitoring the orientational
order are sensitive to different aspects of the realignment process. 相似文献
6.
We present a dissipative particle dynamics (DPD) approach for simulating the realignment of a nematic nanodroplet suspended
in an isotropic fluid following a switch in the direction of an applied external magnetic field. The interaction of the mesogens
with the external field is weak relative to the inter-molecular interactions. The simulations were used to investigate the
way orientational equilibrium is re-established. The results reveal that the realignment process of the nanodroplet is consistent
with its fluid structure. The reorientation of the nanodroplet as a whole is found to be caused by an internal structural
rearrangement rather than a coherent rotation of the centres of mass of the mesogens about the centre of the nanodroplet.
The switch in the field direction furthermore is found to induce a transient spatial variation in the orientational order
of the long axes of the mesogens: the orientational order parameters decreases on moving from the core of the nanodroplet
to the surface in contact with the isotropic environment. The results highlight differences between the time evolution of
the orientation of the long molecular axes in the field and the rotations of the centres of mass of the mesogens about the
centre of the nanodroplet. 相似文献
7.
R. B. Pandey J. F. Gettrust 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(1):83-88
Driven flow of a non-equilibrium non-conservative (NENC) system with
a mixture of immiscible particles (A,B of molecular weight MA, MB)
exhibits self-organizing patterns (segregation, phase-separation, etc.)
in steady-state. The flow response (v) of mass flux density (j) to
bias (H),
in steady-state is found to be
sensitive to molecular weight ratio (α = MB/MA). While the
flux density (j) responds linearly to bias for both components
(A, B) at α = 1, onset of eruptive response occurs at extreme
bias (H ↦ 1) at α > 1 where v ↦∞ for heavier (B)
and v ↦- ∞ for lighter (A) constituents. Difference in
molecular weights (MA, MB) is not only critical to eruptive flow
but also in controlling the flow response prior to this crossover. 相似文献
8.
The compaction of granular packings or soils is a collective process which for higher densities becomes increasingly slower
reaching glassy behaviour. We present a study of this problem from various points of view, in particular we will represent
the evolving force network that percolates through the system by an inverse fiber rupture model.
Received 15 March 2002 and Received in final form 29 July 2002 相似文献
9.
R. Neffati J. Rault 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):205-210
By differential Scanning Calorimetry (DSC), at low heating rate and using a technique of fractionation, we have measured the
equilibrium DSC signal (heat flow) J
q
0 of two families of porous glass saturated with water. The shape of the DSC peak obtained by these techniques is dependent
on the sizes distribution of the pores. For porous glass with large pore size distribution, obtained by sol-gel technology,
we show that in the domain of ice melting, the heat flow Jq is related to the melting temperature depression of the solvent, ΔT
m , by the scaling law: J
q
0∼ΔT
m
- (1 + D). We suggest that the exponent D is of the order of the fractal dimension of the backbone of the pore network and we discuss the influence of the variation
of the melting enthalpy with the temperature on the value of this exponent. Similar D values were obtained from small angle neutron scattering and electronic energy transfer measurements on similar porous glass.
The proposed scaling law is explained if one assumes that the pore size distribution is self similar. In porous glass obtained
from mesomorphic copolymers, the pore size distribution is very sharp and therefore this law is not observed. One concludes
that DSC, at low heating rate ( q? 2°C/min) is the most rapid and less expensive method for determining the pore distribution and the fractal exponent of a porous
material.
Received 23 July 1999 and Received in final form 16 February 2001 相似文献
10.
G. A. Adebayo B. C. Anusionwu 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(4):423-427
Molecular dynamics simulations (MD) of dynamical properties of molten binary
Ag-Cu alloy is presented at various temperature above the eutetic
temperature. Atoms in the system have been modelled through an interatomic
Lennard-Jones potential interaction. The structure, through the effective pair
distribution function allows to determine the Enksog collision frequency as
well as the coordination of atoms in the first shell. The surface traction,
which is the force per unit area between the species shows a long separation
oscillation about the value zero, while the collision frequency of pairs of
atoms increase with increasing temperature. The adhesion energy between
components found to be 3.4178 J/m2. In agreement with theory, we found a
decrease in surface tension of Ag-Cu alloy as temperature increases.
Separation of atoms pairs in the first shell might be responsible for a
non linear relationship found between temperature and coordination number
in present calculations. 相似文献
11.
V. V. Hoang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(3):291-297
Dynamical heterogeneities (DH) in low density liquid SiO2 have been
investigated by molecular dynamics (MD) method. Simulations were done in the
basic cube under periodic boundary conditions containing 3000 particles with
the pair interatomic potentials, which have a weak electrostatic interaction
and a Morse type short range interaction (PMSI). We have evaluated the
non-Gaussian parameter for the self part of the van Hove correlation
function and we found a clear evidence of the existence of DH in low density
liquid SiO2. Moreover, the atomic displacement distribution (ADD) in a
model has been obtained and it deviates from a Gaussian form. The results
have been compared with those obtained in another liquid SiO2 system
with the Born-Mayer interatomic potentials (BMP) in order to observe the
interatomic potential effects on the DH in the system and indeed, the
effects are strong. Calculations showed that particles of extremely low or
fast mobility have a tendency to form a cluster and mean cluster size of
most mobile and immobile particles in PMSI models increases with decreasing
temperature. In contrast, no systematic changes have been obtained for the
most mobile and immobile particles in BMP models. Calculations show that
there is no relation between local particle environment and particle
mobility in the system. 相似文献
12.
We study the lateral and transverse diffusion of amphiphiles in two-component bilayer membranes, using a coarse-grained model
for amphiphilic molecules and combined Monte Carlo-Molecular Dynamics simulations. Membrane structural properties, such as
the mean thickness, are also measured. The dependence of such properties on membrane composition, inter-molecular interactions,
and amphiphile stiffness is determined. In particular, we show that addition of shorter amphiphiles drives the model membrane
towards a more fluid state, with increased amphiphile lateral diffusion rates. These results can be understood in the framework
of a simple free-volume model. Furthermore, we observe an increase in the trans-membrane diffusion when the interaction energy
of amphiphiles with their neighboring molecules is decreased.
Received: 6 December 2002 / Accepted: 17 April 2003 / Published online: 27 May 2003
RID="a"
ID="a"e-mail: imparato@mpikg-golm.mpg.de
RID="b"
ID="b"e-mail: shillcock@mpikg-golm.mpg.de
RID="c"
ID="c"e-mail: lipowsky@mpikg-golm.mpg.de 相似文献
13.
S. Mossa E. La Nave F. Sciortino P. Tartaglia 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):351-355
The equation of state for a liquid in equilibrium, written in the potential energy landscape formalism, is generalized to
describe out-of-equilibrium conditions. The hypothesis that during aging the system explores basins associated to equilibrium
configurations is the key ingredient in the derivation. Theoretical predictions are successfully compared with data from molecular
dynamics simulations of different aging processes, such as temperature and pressure jumps.
Received 7 August 2002 / Received in final form 8 October 2002
Published online 19 December 2002
RID="a"
ID="a"Present address: Laboratoire de Physique Théorique des Liquides, Université Pierre et Marie Curie, 4 place Jussieu, Paris 75005, France e-mail:
mossa@lptl.jussieu.fr 相似文献
14.
M. Benoit S. Ispas P. Jund R. Jullien 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):631-636
A Car-Parrinello (CP) molecular dynamics simulation of vitreous silica, combined with classical molecular dynamics, is presented.
The equilibration of the liquid, quench and relaxation of the glass are performed classically using the van Beest, Kramer
and van Santen (BKS) potential [12] and the resulting configuration (coordinates and velocities) is used as input for the
CP simulation. A remarkable stability of the CP dynamics is observed justifying this procedure and validating the BKS potential.
Several structural and electronic properties are calculated and compared with experiments.
Received 23 March 1999 and Received in final form 15 July 1999 相似文献
15.
The present paper develops a Statistical Mechanics approach to the inherent states of glassy systems and granular materials
by following the original ideas proposed by Edwards for granular media. We consider three lattice models (a diluted spin glass,
a system of hard spheres under gravity and a hard-spheres binary mixture under gravity) introduced to describe glassy and
granular systems. They are evolved using a “tap dynamics” analogous to that of experiments on granular media. We show that
the asymptotic states reached in such a dynamics are not dependent on the particular sample history and are characterized
by a few thermodynamical parameters. We assume that under stationarity these systems are distributed in their inherent states
satisfying the principle of maximum entropy. This leads to a generalized Gibbs distribution characterized by new “thermodynamical”
parameters, called “configurational temperatures” (related to Edwards compactivity for granular materials). Finally, we show
by Monte Carlo calculations that the average of macroscopic quantities over the tap dynamics and over such distribution indeed
coincide. In particular, in the diluted spin glass and in the system of hard spheres under gravity, the asymptotic states
reached by the system are found to be described by a single “configurational temperature”. Whereas in the hard-spheres binary
mixture under gravity the asymptotic states reached by the system are found to be described by two thermodynamic parameters,
coinciding with the two configurational temperatures which characterize the distribution among the inherent states when the
principle of maximum entropy is satisfied under the constraint that the energies of the two species are independently fixed.
Received 19 March 2002 and Received in final form 14 June 2002 相似文献
16.
An adsorption-desorption (or parking-lot) model can reproduce qualitatively the densification kinetics and other features
of a weakly vibrated granular material. Here we study the the two-time correlation and response functions of the model and
demonstrate that their behavior is consistent with recently observed memory effects in granular materials. Although the densification
kinetics and hysteresis are robust properties, we show that the aging behavior of the adsorption-desorption model is different
from other models of granular compaction. We propose an experimental test to distinguish the possible aging behaviors.
Received 26 February 2001 相似文献
17.
A. Aradian E. Raphaël P.G. de Gennes 《The European physical journal. E, Soft matter》2000,2(4):367-376
We consider a porous solid covered with a water film (or with a drop) in situations where the liquid is pumped in, either
spontaneously (if the porous medium is hydrophilic) or mechanically (by an external pump). The dynamics of dewetting is then
strongly modified. We analyse a few major examples, a) horizontal films, which break at a certain critical thickness, b) the
“modified Landau-Levich problem” where a porous plate moves up from a bath and carries a film: aspiration towards the plate
limits the height H reached by the film, c) certain situation where the hysteresis of contact angles is important.
Received 5 October 1999 and Received in final form 7 February 2000 相似文献
18.
Y. Rouault 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(4):483-487
The evolution of the mean chain length and mean end to end square radius of a two dimensional system of living polymers at constant monomer concentration is studied as a function of the obstacle
density . The fact that the system adapts the mean chain length in order to reduce the entropic constraint does not lead to a different asymptotic dependence of on than what is observed for dead polymers. The change of the molecular weight distribution form in the presence of obstacles
suggests that a Levy flight could appear in system of wormlike micelles in a porous medium.
Received: 1 September 1997 / Received in final form: 22 January 1998 / Accepted: 30 January 1998 相似文献
19.
A. D'Onofrio V.M. Freytes M. Rosen C. Allain J.P. Hulin 《The European physical journal. E, Soft matter》2002,7(3):251-259
Tracer dispersion in Newtonian and shear-thinning fluids (scleroglucan-water polymer solutions) flowing through single and
double porosity grain packings has been studied experimentally using both classical transmission dispersion and echo dispersion
(in the latter, the concentration variation front is pumped back through a detector at the inlet after penetrating for a chosen
distance into the sample). Transmission dispersion increases markedly in both types of samples with the shear thinning index
of the fluid at all Péclet numbers (except when molecular diffusion is dominant). Echo and transmission experiments give nearly
identical dispersivity values for Newtonian fluids while echo dispersivity is lower than transmission for shear thinning ones.
The normalized dispersivity difference has same order of magnitude for single and double porosity samples and increases with
the shear thinning exponent α (by a factor of 2 between α = 0.35 and α = 0.60). This difference may be due to heterogeneities
inducing permeability variations of small amplitude over distances of the order of the sample section : their influence on
tracer dispersion is partly reversible with respect to a change of the flow direction and is only detectable if it is amplified
by the shear-thinning properties of the fluid.
Received 19 September 2001 相似文献