共查询到20条相似文献,搜索用时 62 毫秒
1.
P. Richard L. Oger J.P. Troadec A. Gervois 《The European physical journal. E, Soft matter》2001,6(4):295-303
We propose a theoretical model of random binary assemblies of spheres at any packing fraction. We use the notion of geometrical
neighborhood between grains that is defined through two generalizations of the Vorono? tessellation: the radical (or Laguerre)
tessellation and the navigation map. The model is tested on different numerical packings. We find a weak local segregation
for high packing fraction. We also find that the higher the size ratio of the particles, the more important the segregation.
Received 19 February 2001 and Received in final form 27 June 2001 相似文献
2.
Núñez A Darias R Pinto R Paredes V R Medina E 《The European physical journal. E, Soft matter》2002,9(4):327-334
We study a model of concentrated suspensions under shear in two dimensions. Interactions between suspended particles are dominated
by direct-contact viscoelastic forces and the particles are neutrally bouyant. The bimodal suspensions consist of a variable
proportion between large and small droplets, with a fixed global suspended fraction. Going beyond the assumptions of the classical
theory of Farris (R.J. Farris, Trans. Soc. Rheol. 12, 281 (1968)), we discuss a shear viscosity minimum, as a function of the small-to-large-particle ratio, in shear geometries
imposed by external body forces and boundaries. Within a linear-response scheme, we find the dependence of the viscosity minimum
on the imposed shear and the microscopic drop friction parameters. We also discuss the viscosity minimum under dynamically
imposed shear applied by boundaries. We find a reduction of macroscopic viscosity with the increase of the microscopic friction
parameters that is understood using a simple two-drop model. Our simulation results are qualitatively consistent with recent
experiments in concentrated bimodal emulsions with a highly viscous or rigid suspended component.
Received 28 June 2002
RID="a"
ID="a"e-mail: ernesto@pion.ivic.ve 相似文献
3.
D. Serero G. Reydellet P. Claudin É. Clément D. Levine 《The European physical journal. E, Soft matter》2001,6(2):169-179
We measured the vertical pressure response function of a layer of sand submitted to a localized normal force at its surface.
We found that this response profile depends on the way the layer has been prepared: all profiles show a single centered peak
whose width scales with the thickness of the layer, but a dense packing gives a wider peak than a loose one. We calculate
the prediction of isotropic elastic theory in the presence of a bottom boundary and compare it to the data. We found that
the theory gives the right scaling and the correct qualitative shape, but fails to really fit the data.
Received 3 August 2001 相似文献
4.
Persson BN 《The European physical journal. E, Soft matter》2002,8(4):385-401
I have developed a theory of adhesion between an elastic solid and a hard randomly rough substrate. The theory takes into
account that partial contact may occur between the solids on all length scales. I present numerical results for the case where
the substrate surface is self-affine fractal. When the fractal dimension is close to 2, complete contact typically occurs
in the macro-asperity contact areas, while when the fractal dimension is larger than 2.5, the area of (apparent) contact decreases
continuously when the magnification is increased. An important result is that even when the surface roughness is so high that
no adhesion can be detected in a pull-off experiment, the area of real contact (when adhesion is included) may still be several
times larger than when the adhesion is neglected. Since it is the area of real contact which determines the sliding friction
force, the adhesion interaction may strongly affect the friction force even when no adhesion can be detected in a pull-off
experiment.
Received 3 April 2002 相似文献
5.
We have experimentally studied granular arches through electrical measurements. The packing is composed of 2d metallic pentagons and is submitted to small taps. Large electrical fluctuations are observed and they are distributed along
power laws. This indicates the presence of long-time memory effects even the packing density remains constant around a value
ρ = 0.72±0.02. Large electrical fluctuations should be associated with the breaking/creation of granular arches.
Received 3 October 2000 相似文献
6.
Y. Abe 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):143-148
Based on the theory of the compound nucleus reaction, a brief review is given on the special aspects of the reaction dynamics
in the synthesis of the superheavy elements (SHE), where the fusion probability is the most unknown factor. A new viewpoint
of the fusion reaction is proposed that it consists of two processes; the first process up to the contact of two nuclei of
the incident channel and the second one of a dynamical evolution to the spherical compound nucleus from the contact configuration.
The fusion probability is, thus, given as a product of a contact probability and a formation probability. Analytic studies
of the latter probability are discussed in the one-dimensional model, where a simple expression is given to the so-called
extra-push energy in terms of the reduced friction, the curvature parameter of the conditional saddle point and the nuclear
temperature. Preliminary results of numerical analyses of the contact probability are given, using the surface friction model
(SFM). Remarks are given on the present status of our knowledge and for future developments.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
7.
D. Staresinic A. Borovac K. Biljakovic H. Berger F. Levy J.W. Brill 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):425-429
We report on measurements of the voltage dependence of the complex shear compliance of two crystals of the charge-density-wave
(CDW) conductor NbSe3, for torsional frequencies between 1 Hz and 71 Hz. For both samples, there is a frequency independent, ∼1% increase of the magnitude of the compliance when the voltage exceeds the threshold for CDW depinning, but the internal
friction has a striking sample dependence which we do not understand. For one sample, there is a frequency independent decrease
in internal friction with CDW depinning, suggesting that the elastic changes are not relaxational and might reflect changes
in the screening of the crystal strain by the CDW. For the second sample, the sign and magnitude of the change in internal
friction is strongly frequency dependent, which we associate with a change in screening due to the finite electron diffusion
time. The second sample also exhibits a frequency dependent peak in internal friction near threshold that may reflect relaxation
of the CDW phase.
Received 14 August 2001 and Received in final form 3 October 2001 相似文献
8.
J.-F. Colomer L. Henrard Ph. Lambin G. Van Tendeloo 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):111-118
The atomic structure of single-wall carbon nanotube bundles produced by three different techniques (laser ablation, electric
arc discharge and catalytic chemical vapor deposition (CCVD)) has been characterized by electron diffraction and microscopy.
Information on the helicity and the lattice packing has been obtained. Concerning the helicity, small bundles produced by
CCVD exhibit only one or two tube helicities within a single bundle. The diffraction patterns of laser-ablation produced bundles
also present well-defined but more diversified chiralities within a single bundle. By contrast the data acquired on bundles
formed by arc discharge show a more diffuse pattern, characteristic of a random chirality dispersion within a single bundle.
Concerning the lattice packing, informations are obtained via a detailed study of the equatorial line of the diffraction pattern for bundles produced by the three techniques. This electron
diffraction study is completed by high-resolution electron microscopy.
Received 8 August 2001 and Received in final form 14 March 2002 相似文献
9.
H.F. Lü J. Meng S.Q. Zhang S.-G. Zhou 《The European Physical Journal A - Hadrons and Nuclei》2003,17(1):19-24
Properties of single- Λ and double- Λ hypernuclei for even-N Ca isotopes ranging from the proton dripline to the neutron dripline are studied using the relativistic continuum Hartree-Bogoliubov
theory with a zero-range pairing interaction. Compared with ordinary nuclei, the addition of one or two Λ-hyperons lowers
the Fermi level. The predicted neutron dripline nuclei are, respectively, 75
ΛCa and 76
2ΛCa, as the additional attractive force provided by the Λ-N interaction shifts nuclei from outside to inside the dripline.
Therefore, the last bound hypernuclei have two more neutrons than the corresponding ordinary nuclei. Based on the analysis
of two-neutron separation energies, neutron single-particle energy levels, the contribution of continuum and nucleon density
distribution, giant halo phenomena due to the pairing correlation, and the contribution from the continuum are suggested to
exist in Ca hypernuclei similar to those that appear in ordinary Ca isotopes.
Received: 21 October 2002 / Accepted: 11 January 2003 / Published online: 8 April 2003 相似文献
10.
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
11.
M. Georgiev M. Mladenova V. Krastev A. Andreev 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):273-277
Substitutional impurity ions in crystals are known to displace off-center and to perform hindered rotations around the ideal
lattice positions. The vibronic theory to describe both the off-center displacements and the hindered rotations by a single
angular equation incorporates terms up to 3rd order in the off-center displacement coordinates. When the rotation is confined
to a single plane, the corresponding vibronic equation is equivalent to Mathieu's equation. Extending our earlier work, we
derive here the dipole-dipole coupling to take into account cooperative phenomena. We also derive the optical absorption band
arising from dipolar transitions across “Mexican Hat” surfaces, and we show that hindered rotations gives rise to magnetic
moments quantized in rotational bands.
Received 18 October 2001 / Received in final form 5 March 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: allxrose@hotmail.com 相似文献
12.
M. Damnjanović T. Vuković I. Milošević 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):131-134
The friction between the walls of multi-wall carbon nanotubes is shown to be extremely low in general, with important details
related to the specific choice of the walls. This is governed by a simple expression revealing that the phenomenon is a profound
consequence of the specific symmetry breaking: super-slippery sliding of the incommensurate walls is a Goldstone mode. Three
universal principles of tribology, offering a recipe for lubricant selection are emphasized.
Received 8 August 2001 相似文献
13.
The contribution of a ππ-exchange three-body force to the three-nucleon binding energy is calculated in terms of a πN amplitude. The latter is based on a meson-theoretical model of πN interaction developed by the Jülich group. Similar to a previous study based on simple phenomenological πN potentials a very small effect of the resulting three-body force is found. Possible origins of the two-orders-of-magnitude
discrepancy between the present result and the values obtained for the Tucson-Melbourne three-body force are investigated.
Evidence is provided that this discrepancy is most likely due to strikingly different off-shell properties of the πN amplitudes underlying the two approaches.
Received: 9 February 2000 相似文献
14.
M. Tamine 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):109-118
A Heisenberg model is employed to study the spin fluctuation dynamics on a (001) ferromagnetic surface using a new theoretical
formalism. The solution of the full magnetic problem arising from the absence of magnetic translation symmetry in one dimension
due to the presence of a magnetic surface is presented. The calculations are described using simultaneously a closed form
of the spin-wave Green's function and the matching procedure in the random-phase approximation. Analytic expressions for the
Green's functions are also derived in a low-temperature spin-wave approximation. The theoretical approach determines the bulk
and evanescent spin fluctuation fields in the two dimensional plane normal to the surface. The results are used to calculate
the localised modes of magnons associated with the surface. Numerical examples of the modes are given and they are found to
exhibit various effects due to the interplay between the bulk and surface modes. It is shown that there may be surface spin-waves
that decay in amplitude with distance into the bulk domain. Also the bulk spin fluctuations field as well as the magnons localised
at the surface depend on the nature of the bulk-surface coupling exchange. The unstable surface magnetic configurations are
illustrated and discussed. The results derived from the dynamic correlation functions between a pair of spin operators at
any two sites are employed to evaluate the spin deviation in the ferromagnet due to localised surface modes obtained by the
matching procedure as a function of temperature.
Received 21 April 2002 / Received in final form 25 October 2002 Published online 14 March 2003 相似文献
15.
R. Dimova U. Seifert B. Pouligny S. Förster H.-G. Döbereiner 《The European physical journal. E, Soft matter》2002,7(3):241-250
Giant vesicles prepared from the diblock copolymer polybutadien-b-polyethyleneoxide (PB-PEO) exhibit a shear surface viscosity,
which is about 500 times higher than those found in common phospholipid bilayers. Our result constitutes the first direct
measurement of the shear surface viscosity of such polymersomes. At the same time, we measure bending and stretching elastic
constants, which fall in the range of values typical for lipid membranes. Pulling out a tether from an immobilized polymersome
and following its relaxation back to the vesicle body provides an estimate of the viscous coupling between the two monolayers
composing the polymer membrane. The detected intermonolayer friction is about an order of magnitude higher than the characteristic
one for phospholipid membranes. Polymersomes are tough vesicles with a high lysis tension. This, together with their robust
rheological properties, makes them interesting candidates for a number of technological applications.
Received 2 March 2001 and Received in final form 15 February 2002 相似文献
16.
B.I. Ostrovskii D. Sentenac I.I. Samoilenko W.H. de Jeu 《The European physical journal. E, Soft matter》2001,6(4):287-294
We report on the thin-film behaviour of a polyacrylate with phenyl benzoate mesogenic side groups and a narrow polydispersity.
Depending on the degree of polymerisation, these polymers show a nematic, a smectic-A d, a re-entrant nematic and a C phase with a two-dimensional monoclinic lattice. X-ray reflectivity and atomic-force microscopy
have been used to characterize the structure and surface morphology. The system exhibits two stable side-chain packing configurations
with incommensurate spacings that can be both stabilized at a free surface. Thin films in the nematic phase show a structural
dewetting induced by the growth of surface domains of the C phase. Additionally, surface-induced ripples with a nanoscale
lateral period form at the air-film interface. We attribute these patterns to a coupling between the local liquid crystalline
ordering of the mesogenic side groups and the surface curvature energy.
Received 28 February 2001 and Received in final form 6 August 2001 相似文献
17.
18.
G. Migliorini N. Lee V. Rostiashvili T.A. Vilgis 《The European physical journal. E, Soft matter》2001,6(3):259-270
We study the properties of polyelectrolyte chains under different solvent conditions, using a variational technique. The free
energy and the conformational properties of a polyelectrolyte chain are studied by minimizing the free energy FN, depending on N(N - 1)/2 trial probabilities that characterize the conformation of the chain. The Gaussian approximation is considered for
a ring of length 24 < N < 28 and for an open chain of length 50 < N < 200 in poor- and theta-solvent conditions, including a Coulomb repulsion between the monomers. In theta-solvent conditions
the blob size is measured and found in agreement with scaling theory, including charge depletion effects, expected for the
case of an open chain. In poor-solvent conditions, a globule instability, driven by electrostatic repulsion, is observed.
We notice also inhomogeneous behavior of the monomer-monomer correlation function, reminiscence of necklace formation in poor-solvent
polyelectrolyte solutions. A global phase diagram in terms of solvent quality and inverse Bjerrum length is presented.
Received 7 June 2001 and Received in final form 17 October 2001 相似文献
19.
S. Dubois S. Harel M. Grosbras 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):507-510
Macroscopic resistivity measurements have been performed on TiC/Al2O3 random mixtures submitted to uniaxial compression (0-95 kN). Such a random mixture exhibits an insulator-conductor transition
which appears at increasing force while decreasing the conductive composition of the TiC/Al2O3 mixture. It is demonstrated that the conductivity behavior may be understood in the framework of a site percolation model.
Finally, the rate of creation of the contacts between conductive grains is extracted from the macroscopic resistivity measurements.
Received 6 December 2000 and Received in final form 30 March 2001 相似文献
20.
P. Navez 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):219-228
We describe a cryptographic protocol consisting of two entangled beams of squeezed light which makes use of statistical tests
to deduce the secret key bit. The sender (Alice) encrypts a secret key by modulating the phase of the beam sent in public
by the receiver (Bob) who keeps the other beam private. The knowledge of the degree of non classical correlation between the
beam quadrature components measured in private and in public allows only Bob to decrypt the secret key. With a view towards
absolute security, we formally prove that any external intervention from an eavesdropper (Eve) during the communication process
introduces necessarily some modification susceptible to be detected. Statistical confidentiality tests are proposed to detect
the presence of Eve.
Received 12 July 2001 and Received in final form 11 November 2001 相似文献