共查询到20条相似文献,搜索用时 15 毫秒
1.
E. Jahier J. Guéna Ph. Jacquier M. Lintz M.A. Bouchiat 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):221-229
We demonstrate the production of an electric field inside a high temperature cesium vapor cell with external electrodes. This external control of the electric field, which is not possible with a glass cell in presence of a cesium
vapor, is achieved using a cell made of sapphire, and is of particular interest for our ongoing Parity Violation experiment.
We describe the main components and the implementation on the set-up, including the pulsed high voltage generator. With pulse
duration not exceeding 200 ns the system provides a reversible longitudinal E-field of up to 2 kV/cm in the vapor at a density of ∼ 2×1014 at/cm3 without discharge. Atomic signals attest the application of the electric field in the cell, with the predicted value. Further
improvements obtained with sapphire cells are also presented.
Received 15 September 2000 相似文献
2.
S.B. Santra 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):75-82
A new site percolation model, directed spiral percolation (DSP), under both directional and rotational (spiral) constraints
is studied numerically on the square lattice. The critical percolation threshold p
c ≈ 0.655 is found between the directed and spiral percolation thresholds. Infinite percolation clusters are fractals of dimension
d
f ≈ 1.733. The clusters generated are anisotropic. Due to the rotational constraint, the cluster growth is deviated from that
expected due to the directional constraint. Connectivity lengths, one along the elongation of the cluster and the other perpendicular
to it, diverge as p → p
c with different critical exponents. The clusters are less anisotropic than the directed percolation clusters. Different moments
of the cluster size distribution P
s(p) show power law behaviour with | p - p
c| in the critical regime with appropriate critical exponents. The values of the critical exponents are estimated and found
to be very different from those obtained in other percolation models. The proposed DSP model thus belongs to a new universality
class. A scaling theory has been developed for the cluster related quantities. The critical exponents satisfy the scaling
relations including the hyperscaling which is violated in directed percolation. A reasonable data collapse is observed in
favour of the assumed scaling function form of P
s(p). The results obtained are in good agreement with other model calculations.
Received 10 November 2002 / Received in final form 20 February 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: santra@iitg.ernet.in 相似文献
3.
P. Galatola G. Coupier M. Saint Jean J.-B. Fournier C. Guthmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(4):549-557
Macroscopic Wigner islands present an interesting
complementary approach to explore the properties of two-dimensional
confined particles systems. In this work, we characterize theoretically
and experimentally the interaction between their basic components, viz.,
conducting spheres lying on the bottom electrode of a plane condenser.
We show that the interaction energy can be approximately described by a
decaying exponential as well as by a modified Bessel function of the
second kind. In particular, this implies that the interactions in this
system, whose characteristics are easily controllable, are the same as
those between vortices in type-II superconductors. 相似文献
4.
We suggest a scalar model for deformation and flow of an amorphous material such as a foam or an emulsion. To describe elastic,
plastic and viscous behaviours, we use three scalar variables: elastic deformation, plastic deformation rate and total deformation
rate; and three material-specific parameters: shear modulus, yield deformation and viscosity. We obtain equations valid for
different types of deformations and flows slower than the relaxation rate towards mechanical equilibrium. In particular, they
are valid both in transient or steady flow regimes, even at large elastic deformation. We discuss why viscosity can be relevant
even in this slow shear (often called “quasi-static”) limit. Predictions of the storage and loss moduli agree with the experimental
literature, and explain with simple arguments the non-linear large amplitude trends. 相似文献
5.
Salmon JB Bécu L Manneville S Colin A 《The European physical journal. E, Soft matter》2003,10(3):209-221
We present local velocity measurements in emulsions under shear using heterodyne Dynamic Light Scattering. Two emulsions are
studied: a dilute system of volume fraction φ = 20% and a concentrated system with φ = 75%. Velocity profiles in both systems
clearly show the presence of wall slip. We investigate the evolution of slip velocities as a function of shear stress and
discuss the validity of the corrections for wall slip classically used in rheology. Focussing on the bulk flow, we show that
the dilute system is Newtonian and that the concentrated emulsion is shear-thinning. In the latter case, the curvature of
the velocity profiles is compatible with a shear-thinning exponent of 0.4 consistent with global rheological data. However,
even if individual profiles can be accounted for by a power law fluid (with or without a yield stress), we could not find
a fixed set of parameters that would fit the whole range of applied shear rates. Our data, thus, raise the question of the
definition of a global flow curve for such a concentrated system. These results show that local measurements are a crucial
complement to standard rheological tools. They are discussed in the light of recent works on soft glassy materials.
Received 1 November 2002 and Received in final form 8 January 2003 / Published online: 1 April 2003
RID="a"
ID="a"e-mail: salmon@crpp.u-bordeaux.fr 相似文献
6.
We analyse the consequences of Quincke rotation on the conductivity of a suspension. Quincke rotation refers to the spontaneous
rotation of insulating particles dispersed in a slightly conducting liquid and subject to a high DC electric field: above
a critical field, each particle rotates continuously around itself with an axis pointing in any direction perpendicular to
the DC field. When the suspension is subject to an electric field lower than the threshold one, the presence of insulating
particles in the host liquid decreases the bulk conductivity since the particles form obstacles to ion migration. But for
electric fields higher than the critical one, the particles rotate and facilitate ion migration: the effective conductivity
of the suspension is increased. We provide a theoretical analysis of the impact of Quincke rotation on the apparent conductivity
of a suspension and we present experimental results obtained with a suspension of PMMA particles dispersed in weakly conducting
liquids. 相似文献
7.
C. M.J. Wijers J.-H. Chu O. Voskoboynikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):225-241
The influence of the surrounding semiconducting matrix upon the
optical response of embedded nano-objects (quantum dots) has been
investigated. This system can be described by means of a hybrid model, where the full response is a combination of a macroscopic
electrostatic response term and a dynamic response term, obtained quantum mechanically. The result is a modified discrete
dipole model, where excess discrete dipoles having an excess polarizability with respect to a uniform background identical
to the dielectric host material represent the response. In this model all electrodynamic interactions are screened by the
host material. The electrostatic response is obtained by approximating the quantum dots by embedded dielectric oblate ellipsoids.
Closed expressions for the electrostatic response of these ellipsoids have been derived. The electrodynamic nature of the
dynamic quantum mechanical polarizability term however is unclear. It is not certain whether this polarizability is dressed
or bare. Therefore we have investigated in detail the consequences of both options. Although there is no real qualitative
difference between them, the difference is so large that experiment can easily discriminate between both. Results should be
easily measurable anyhow. 相似文献
8.
M. Filoche B. Sapoval 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):755-763
The flux across resistive irregular interfaces driven by a force deriving from a Laplacian potential is computed on a rigorous
basis. The theory permits one to relate the size of the active zone to the derivative of the spectroscopic impedance with respect to the surface resistivity r through: . It is shown that the macroscopic transfer properties through a system of arbitrary shape are determined by the characteristics
of a first-passage interface-interface random walk operator . More precisely, it is the distribution of the harmonic measure (or normalized primary current) on the eigenmodes of this
linear operator that controls the transfer. In addition, it is also shown that, whatever the dimension, the impedance of a
weakly polarizable electrode for any irregular geometry scales under a homothety transformation as Ld-1, L being the size of the system and d its topological dimension. In this new formalism, the question addressed in the title is transformed in a open mathematical
question: “Knowing the distribution of the harmonic measure on the eigenmodes of the self-transport operator, can one retrieve
the shape of the interface?”
Received 3 November 1998 相似文献
9.
Self-consistent calculation of electrostatic force for two kinds of mesoscopic surface structures 总被引:1,自引:0,他引:1
Z.-Y. Li B.-Y. Gu G.-Z. Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):123-131
The scanning electrostatic force microscopy (SEFM) can acquire information of surface structures in a non-contact way. We
calculate the electrostatic force between the charged tip and polarized surface structure in SEFM in the framework of self-consistent
integral equation formalism (SCIEF), incorporating the image method to treat the electrostatic coupling of substrate and tip.
We consider two kinds of surface structures, one is the topographic structure on the surface, the other is the dielectric
structure embedded in the substrate. The force pattern of the topographic structure shows a protrusion around the surface
structure. However, the force pattern displays a hollow around an embedded structure with a dielectric constant less than
that of substrate medium. For an embedded structure with a larger dielectric constant, the force pattern exhibits a protrusion,
and the force signal is much weaker than that of the topographic structure. Therefore, it is expected that one may identify
these surface structures from the pure electrostatic force information in SEFM. The force signal of the densely arranged dielectric
pads is simply the superposition of force signal of each pad individually, the interference effect of electric field is not
remarkable.
Received: 26 March 1998 / Accepted: 9 June 1998 相似文献
10.
Picard G Ajdari A Lequeux F Bocquet L 《The European physical journal. E, Soft matter》2004,15(4):371-381
With the eventual aim of describing flowing elasto-plastic materials, we focus here on the elementary process of such a flow, a plastic event, and compute the long-range perturbation it elastically induces in a medium submitted to a global shear strain. We characterize the effect of a nearby wall on this perturbation, and quantify the importance of finite-size effects. Although most of our explicit formulae refer to 2D situations, our statements hold for 3D situations as well. 相似文献
11.
F. Delfino R. Procopio M. Rossi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):31-38
The evaluation of the total force of magnetic origin acting upon a body in a stationary magnetic field is often carried out
using the so-called magnetic energy (or co-energy) method, which is based on the derivation of the magnetic energy (or co-energy) with respect to a virtual rigid displacement
of the considered body. The application of this method is usually justified by resorting to the energy conservation principle,
written in terms both of electrical and of mechanical quantities. In this paper we shall re-examine the whole matter in the
context of classical thermodynamics, in order to obtain a more comprehensive and general proof of the validity of the energy
(or co-energy) approach and to point out its limitations. Two typical configurations will be discussed; in the first one,
the field sources are represented by conducting bodies carrying free currents, whereas in the second one a permanent magnet
creates the driving field. All magnetic materials are assumed to be non-hysteretic and permanent magnets are represented by
means of the well-known linear model in the second quadrant of the (B,H) plane.
Received 25 July 2001 and Received in final form 5 November 2001 相似文献
12.
J. L. Viota J. D. G. Durán A. V. Delgado 《The European physical journal. E, Soft matter》2009,29(1):87-94
In this paper we describe the magnetorheological behavior of aqueous suspensions consisting of magnetite particles of two
size populations, in the micrometer and nanometer scale, respectively. Previous works on the magnetorheology of oil-based
fluids demonstrated that the addition of nanoparticles has a very significant effect on the intensity of the magnetorheological
effect. The present contribution confirms such results in the case of aqueous fluids, based on the dependence of the yield
stress and the viscosity of the bimodal suspensions on both the composition of the mixtures and the magnetic field strength.
It is demonstrated that for a given concentration of micrometer particles, increasing the amount of nanometer magnetite provokes
a clear enhancement in the yield stress for all the magnetic fields applied. This is proposed to be due to the formation of
heterogeneous aggregates that improve the stability of the suspensions and ease the building of well-arranged field-induced
structures. The behavior of both the yield stress and the post-yield viscosity agrees better with the predictions of standard
chain models when the relative proportion of both types of particles confers optimum stability to the bimodal dispersions. 相似文献
13.
Yu.L. Sokolov V.P. Yakovlev V.G. Pal'chikov Yu.A. Pchelin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):27-36
The properties of two-dimensional magnetic traps for laser-cooled atoms are analysed using complex functions. The two components
of the magnetic field from a series of parallel, infinitely long, current-carrying wires are represented by a single complex
number. The regions of the field where paramagnetic atoms can be trapped occur where the magnetic field is zero. The locations
of the zeroes of the field are obtained as the solution to a polynomial and the multiplicity m of the solution determines both the 2(m + 1)-pole nature of the trap and the field gradient through the centre. The zeroes of the field can be merged or split by
varying the locations of the currents, their strengths or by applying a uniform magnetic field. The theory is applied to magnetic
traps created from long thin wires or permanent magnets on a substrate. The properties of a number of magnetic trap configurations
used for atom guides are discussed.
Received 28 February 2001 and Received in final form 6 July 2001 相似文献
14.
U. Schröter 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):297-310
Green's dyadic technique represents a powerful tool for calculations in electrodynamics, especially in modelling optical properties
of nanoscopic objects. The method does not only provide field distributions, but also maps of susceptibilities and densities
of states. Whereas the formalism is well established for dielectrics and electric fields, I present here a straight forward
extension to tensors of both electric and magnetic type as well as mixed ones and furthermore to the situation where objects
with dielectric and magnetic permeabilities are present together. As examples, characteristic field patterns are compared
for elementary dielectric and magnetic perturbations. Green's tensors calculated for a coral structure reveal that mixed susceptibilities
can exhibit other symmetries than pure electric or magnetic ones. Maps of all tensor components can thus give essential clues
to the interpretation of near-field images.
Received 15 December 2002 Published online 20 June 2003
RID="a"
ID="a"Files “maths.ps” and “tensors.ps” are only available in electronic form at http://www.edpsciences.org
RID="b"
ID="b"e-mail: Ursula.Schroeter@uni-konstanz.de 相似文献
15.
We present an extensive experimental study of mode-I, steady, slow crack dynamics in gelatin gels. Taking advantage of the
sensitivity of the elastic stiffness to gel composition and history we confirm and extend the model for fracture of physical
hydrogels which we proposed in a previous paper (Nature Mater. 5, 552 (2006)), which attributes decohesion to the viscoplastic pull-out of the network-constituting chains. So, we propose
that, in contrast with chemically cross-linked ones, reversible gels fracture without chain scission. 相似文献
16.
We analyze the flow of a liquid foam between two plates separated by a gap of the order of the bubble size (2D foam). We concentrate
on the salient features of the flow that are induced by the presence, in an otherwise monodisperse foam, of a single large
bubble whose size is one order of magnitude larger than the average size. We describe a model suited for numerical simulations
of flows of 2D foams made up of a large number of bubbles. The numerical results are successfully compared to analytical predictions
based on scaling arguments and on continuum medium approximations. When the foam is pushed inside the cell at a controlled
rate, two basically different regimes occur: a plug flow is observed at low flux whereas, above a threshold, the large bubble
migrates faster than the mean flow. The detailed characterization of the relative velocity of the large bubble is the essential
aim of the present paper. The relative velocity values, predicted both from numerical and from analytical calculations that
are discussed here in great detail, are found to be in fair agreement with experimental results from the preprint Experimental evidence of flow destabilization in a 2D bidisperse foam by the present authors (2005). 相似文献
17.
Inspired by the Bertlmann-Martin inequality relating the rms radius of the ground state wave function to the lowest dipole transition energy, we have proposed a dimensional relationship to be used in weakly bound two-body systems. In the present work, it is applied to halo nuclei. Lower and upper bounds to the size of halo nuclei are compared to values obtained from reaction cross sections. The case of the deuteron is also presented. Received: 18 September 1998 相似文献
18.
P.G. de Gennes 《The European physical journal. E, Soft matter》2002,7(1):31-34
When a glassy polymer film is formed by evaporation, the region near the free surface is polymer rich and becomes glassy first,
as noticed long ago by Scriven et al. We discuss the thickness of this “crust” and the time interval where it is present --before freezing of the whole film. We
argue that the crust is under mechanical tension, and should form some cracks. This may be the source of the roughness observed
on the final, dry films, when the solvent vapor pressure is high (and leads to thin crusts).
Received 13 November 2001 相似文献
19.
F.-Z. Ighezou R.J. Lombard J. Mareš 《The European Physical Journal A - Hadrons and Nuclei》2001,11(1):79-85
We have applied to the 208Pb muonic atom a series of recurrence relations relating the moments of the ground-state density and the energy differences
between the 1s level and the states of the line. The large amount of precise experimental data and the electromagnetic character of the interaction allow a detailed
test of the method for determining the ground-state density and reconstructing the local equivalent potential. Though the
present work is limited to the study of the efficiency for a given trial density, it results in a semi-quantitative analysis
with an accuracy better than 1%.
Received: 18 December 2000 / Accepted: 18 April 2001 相似文献
20.
A. Peñaranda C.E. Auguet L. Ramırez-Piscina 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):155-165
The simulation of the transition sequence of superheated Type I superconducting granules (SSG) in disordered suspensions when
an external magnetic field is slowly increased from zero has been studied. Simulation takes into account diamagnetic interactions
and the presence of surface defects. Results have been obtained for the transition sequence and surface fields distribution
covering a wide range of densities. These results are compared with previous analytical perturbative theory, which provides
qualitative information on transitions and surface magnetic fields during transitions, but with a range of validity apparently
limited to extremely dilute samples. Simulations taking into account the complete diamagnetic interactions between spheres
appear to be a promising tool in interpreting SSG experiments, in applications such as particle detectors, and in some fundamental
calculations of Solid State Physics.
Received 6 April 2001 and Received in final form 15 October 2001 相似文献