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Showing papers in "EPL in 1998"


Journal ArticleDOI
15 Apr 1998-EPL
TL;DR: In this paper, the limits of drawing of fiber can be pushed down to nanometre dimensions by a process similar to dry-spinning, which can be drawn with ultimate dimensions comparable with the ones of single-wall carbon nanotubes.
Abstract: We demonstrate that the limits of drawing of fibre can be pushed down to nanometre dimensions. By a process similar to dry-spinning, nanofibres can be drawn with ultimate dimensions comparable with the ones of single-wall carbon nanotubes. An important difference with tubes is that our nanofibres are produced one at a time. It is also shown that the nanofibre can be positionned precisely on a surface during fabrication, and can then be cut or manipulated by an AFM tip.

374 citations


Journal ArticleDOI
15 Dec 1998-EPL
TL;DR: In this paper, a unified treatment of the dynamic fracture of silicon is presented, coupled with the continuum, the atomistic, and the quantum descriptions of matter, and handshaking between finite element, molecular dynamics and semi-empirical tight-binding representations.
Abstract: We have coupled the continuum, the atomistic, and the quantum descriptions of matter for a unified treatment of the dynamic fracture of silicon. We have devised schemes for handshaking between the finite-element, molecular dynamics and semi-empirical tight-binding representations. We illustrate and validate the methodology for brittle crack propagation in silicon.

323 citations


Journal ArticleDOI
01 Jul 1998-EPL
TL;DR: In this paper, the authors investigate flows of helium IV driven by two counterrotating disks, in a range of temperatures varying between 1.4 and 2.3 K. The local pressure fluctuations obtained on a small total-head tube are analyzed.
Abstract: We investigate flows of helium IV driven by two counter-rotating disks, in a range of temperatures varying between 1.4 and 2.3 K. The local pressure fluctuations obtained on a small total-head tube are analyzed. Above Tλ, the sensor allows to measure the local velocity fluctuations, and below Tλ, it determines the local fluctuations of a linear combination of the normal and superfluid flow components. Above and below Tλ, Kolmogorov spectra are clearly obtained, with similar Kolmogorov constants. Evidence for persistence of inertial range intermittency in the superfluid region is presented. At all temperatures below Tλ, the structure function exponents are found indistinguishable from those currently observed in normal fluid turbulence.

311 citations


Journal ArticleDOI
15 Aug 1998-EPL
TL;DR: A general approach to the question of how biological rhythms spontaneously self-regulate is proposed, based on the concept of "stochastic feedback", by considering at a coarse-grained level the neuroautonomic regulation of the heart rate.
Abstract: We propose a general approach to the question of how biological rhythms spontaneously self-regulate, based on the concept of "stochastic feedback". We illustrate this approach by considering at a coarse-grained level the neuroautonomic regulation of the heart rate. The model generates complex dynamics and successfully acounts for key characteristics of cardiac variability, including the l/f power spectrum, the functional form and scaling of the distribution of variations, and correlations in the Fourier phases indicating nonlinear dynamics.

232 citations


Journal ArticleDOI
01 Jun 1998-EPL
TL;DR: In this paper, the accuracy of atomic interferometry can be improved by using QND measurements of the atomic populations at the inputs to the interferometer, which can reach the Heisenberg limit δ ~ 1/N.
Abstract: We show that the accuracy of atomic interferometry can be improved by using QND measurements of the atomic populations at the inputs to the interferometer. The accuracy of such a scheme surpasses the standard quantum limit of phase measurement δSQL = 1/√N and could reach the Heisenberg limit δ ~ 1/N. We propose to perform QND measurements of atomic populations with an off-resonant laser field. The conditions necessary for this kind of QND measurement could be fulfilled in a variety of ways with current experimental techniques, including magneto-optical traps and atomic cells.

228 citations


Journal ArticleDOI
15 Jul 1998-EPL
TL;DR: Flexible membranes which are in contact with dispersed nanoparticles or colloids are theoretically studied and it is shown that if the membrane/particle interactions are attractive, the membrane curves away from the adsorption layers of small particles but wraps itself around large particles which become completely encapsulated.
Abstract: Flexible membranes which are in contact with dispersed nanoparticles or colloids are theoretically studied. For closed vesicles, the membrane/particle interactions change the "spontaneous" curvature of the membrane provided the surrounding solution contains more than one species of particles. If the membrane/particle interactions are repulsive, the membrane curves toward the larger particles. If the membrane/particle interactions are attractive, the membrane curves away from the adsorption layers of small particles but wraps itself around large particles which become completely encapsulated.

219 citations


Journal ArticleDOI
15 Mar 1998-EPL
TL;DR: In this article, a one-dimensional theory of the scattering of electrons by twistons is presented which predicts an intrinsic resistivity proportional to the absolute temperature, and experiments of the temperature dependence of the resistivity are reported and compared with the predictions of the twiston theory.
Abstract: Samples of single-wall carbon nanotubes containing tubes with an armchair wrapping have been produced and exhibit metallic behavior with an intrinsic resistivity which increases approximately linearly with temperature over a wide temperature range. Here we study the coupling of the conduction electrons to long-wavelength torsional shape fluctuations, or twistons. A one-dimensional theory of the scattering of electrons by twistons is presented which predicts an intrinsic resistivity proportional to the absolute temperature. Experimental measurements of the temperature dependence of the resistivity are reported and compared with the predictions of the twiston theory.

196 citations


Journal ArticleDOI
01 Aug 1998-EPL
TL;DR: In this paper, the divergence of the thermal conductivity in the thermodynamic limit is thoroughly investigated and the divergence law is consistently determined with two different numerical approaches based on equilibrium and nonequilibrium simulations, and a possible explanation in the framework of linear response theory is also presented, which traces back the physical origin of this anomaly to the slow diffusion of the energy of long-wavelength Fourier modes.
Abstract: The divergence of the thermal conductivity in the thermodynamic limit is thoroughly investigated. The divergence law is consistently determined with two different numerical approaches based on equilibrium and nonequilibrium simulations. A possible explanation in the framework of linear-response theory is also presented, which traces back the physical origin of this anomaly to the slow diffusion of the energy of long-wavelength Fourier modes. Finally, the results of dynamical simulations are compared with the predictions of mode-coupling theory.

186 citations


Journal ArticleDOI
15 May 1998-EPL
TL;DR: An implementation of dissipative particle dynamics that is free of the inconsistencies that plagued earlier algorithms is proposed, and the present algorithm satisfies a form of microscopic reversibility and recovers the correct equilibrium properties.
Abstract: We propose an implementation of dissipative particle dynamics that is free of the inconsistencies that plagued earlier algorithms. The present algorithm satisfies a form of microscopic reversibility. As a consequence, we recover the correct equilibrium properties. Moreover, we can use much larger time steps than previously. We report a detailed comparison between simulated transport properties and the theoretical predictions. We find that the existing theory is only valid under very special conditions. A more general theory is still lacking.

184 citations


Journal ArticleDOI
01 Jan 1998-EPL
TL;DR: In this article, a simple model of earthquakes on a pre-existing hierarchical fault structure is presented, where the system self-organizes at large times in a stationary state with a power law Gutenberg-Richter distribution of earthquake sizes.
Abstract: We present a simple model of earthquakes on a pre-existing hierarchical fault structure. The system self-organizes at large times in a stationary state with a power law Gutenberg-Richter distribution of earthquake sizes. The largest fault carries irregular great earthquakes preceded by precursors developing over long time scales and followed by aftershocks obeying an Omori's law. The cumulative energy released by precursors follows a time-to-failure power law with log-periodic structures, qualifying a large event as an effective dynamical (depinning) critical point. Down the hierarchy, smaller earthquakes exhibit the same phenomenology, albeit with increasing irregularities.

177 citations


Journal ArticleDOI
15 Aug 1998-EPL
TL;DR: In this paper, the relationship between the Density Matrix Renormalization Group (DMRG) and the variational matrix product method (MPM) was studied, where the latter method can also define a density matrix whose eigenvalues are numerically close to those of the DMRG.
Abstract: We study the relationship between the Density Matrix Renormalization Group (DMRG) and the variational matrix product method (MPM) In the latter method one can also define a density matrix whose eigenvalues turn out to be numerically close to those of the DMRG We illustrate our ideas with the spin-1 Heisenberg chain, where we compute the ground-state energy and the spin correlation length We also give a rotational invariant formulation of the MPM

Journal ArticleDOI
15 Jul 1998-EPL
TL;DR: In this article, the plane Couette flow undergoes a globally subcritical transition to turbulence, and the lifetime histograms of patches quenched in the range R[Ru,Rc] display a well-defined exponentially decreasing tail.
Abstract: The plane Couette flow undergoes a globally sub-critical transition to turbulence. Turbulent spots generated by localized finite-amplitude perturbations evolve differently depending on the Reynolds number R. Below Ru 312 they decay rapidly; above Rc 323 a fraction of spots turns to sustained turbulent patches and an average turbulent fraction can be defined, that slowly increases with R. Lifetime histograms of patches quenched in the range R[Ru,Rc] display a well-defined exponentially decreasing tail. This behavior is reminiscent of the discontinuous transition to spatiotemporal chaos via spatiotemporal intermittency observed in certain two-dimensional lattices of coupled map.

Journal ArticleDOI
15 Apr 1998-EPL
TL;DR: In this paper, a two-level model of liquid supercooled water is proposed to show evidence of a liquid-liquid phase transition in liquid super-cooled liquid. But this model is based on the two known forms of amorphous ice: the low-density amorphus ice (LDA) and the high-density Amorphous Ice (HDA).
Abstract: Previous studies of the structure of liquid water under pressure performed by neutron diffraction allowed us to establish two structural limits in liquid water. These two limits are closely connected to the two known forms of amorphous ice: the low-density amorphous ice (LDA) and the high-density amorphous ice (HDA). In the present paper, we propose some interpretation of our data in terms of a "two-level"–type model of water. This leads to show some evidence of a liquid-liquid phase transition in liquid supercooled water. The result looks in agreement with recent computer simulations that incorporate the two forms of amorphous ice.

Journal ArticleDOI
01 Dec 1998-EPL
TL;DR: In this article, the phase transformation γ(maghemite) → α(hematite) and the equation of state of the nanophase material of the material were studied.
Abstract: Synchrotron radiation X-ray diffraction studies of γ-Fe2O3 have been performed with emphasis on the pressure-induced phase transformation γ(maghemite) → α(hematite) and the equation of state of the nanophase material. For γ-Fe2O3 the bulk modulus has been found to increase from 203 GPa for the bulk material to 305 GPa for 9 nm size crystals. At the same time the transition pressure decreases from 35 to 27 GPa. The reduced transition pressure is explained in terms of nucleation and growth, the larger volume change upon transition in the nanocrystalline material being the main factor.

Journal ArticleDOI
15 Mar 1998-EPL
TL;DR: In this article, high-energy photon diffraction is used to investigate the charge ordering previously studied by neutron diffraction in La148Nd04Sr012CuO4 Besides confirming the existence of superlattice peaks due to charge order, the temperature dependence of peak intensity, width, and position has been determined with improved precision.
Abstract: High-energy photon diffraction is used to investigate the charge ordering previously studied by neutron diffraction in La148Nd04Sr012CuO4 Besides confirming the existence of superlattice peaks due to charge order, the temperature dependence of the peak intensity, width, and position has been determined with improved precision Furthermore, we show that the scattered intensity has a sinusoidial modulation along c*, consistent with long-range Coulomb interactions between ordered charges within the CuO2 planes

Journal ArticleDOI
01 Jun 1998-EPL
TL;DR: To the knowledge this is the first "first-principle" expression of the rolling friction coefficient which does not contain empirical parameters.
Abstract: A first-principle continuum-mechanics expression for the rolling friction coefficient is obtained for the rolling motion of a viscoelastic sphere on a hard plane. It relates the friction coefficient to the viscous and elastic constants of the sphere material. The relation obtained refers to the case when the deformation of the sphere ξ is small, the velocity of the sphere V is much less than the speed of sound in the material and when the characteristic time ξ/V is much larger than the dissipative relaxation times of the viscoelastic material. To our knowledge this is the first "first-principle" expression of the rolling friction coefficient which does not contain empirical parameters.

Journal ArticleDOI
01 Feb 1998-EPL
TL;DR: In this paper, the authors study the market prices of options on liquid markets and show that the market has empirically corrected the simple but inadequate Black-Scholes formula to account for two important statistical features of asset fluctuations: "fat tails" and correlations in the scale of fluctuations.
Abstract: We show, by studying in detail the market prices of options on liquid markets, that the market has empirically corrected the simple, but inadequate Black-Scholes formula to account for two important statistical features of asset fluctuations: "fat tails" and correlations in the scale of fluctuations. These aspects, although not included in the pricing models, are very precisely reflected in the price fixed by the market as a whole. Financial markets thus behave as rather efficient adaptive systems.

Journal ArticleDOI
01 Dec 1998-EPL
TL;DR: It is shown that for K>=3 and unbiased messages the iterative solution is sensitive to the initial conditions and is likely to provide erroneous solutions; and that it is generally beneficial to use Nishimori's temperature, especially in the case of biased messages.
Abstract: We employ two different methods, based on belief propagation and TAP,for decoding corrupted messages encoded by employing Sourlas's method, where the code word comprises products of K bits selected randomly from the original message. We show that the equations obtained by the two approaches are similar and provide the same solution as the one obtained by the replica approach in some cases K=2. However, we also show that for K>=3 and unbiased messages the iterative solution is sensitive to the initial conditions and is likely to provide erroneous solutions; and that it is generally beneficial to use Nishimori's temperature, especially in the case of biased messages.

Journal ArticleDOI
01 Feb 1998-EPL
TL;DR: The main result of as discussed by the authors is that the force needed to pull a monomer of a polyelectrolyte chain at a distance z from the surface reaches a plateau at distances larger than the Debye screening length of the solution.
Abstract: We study both experimentally, with an atomic force microscope (AFM), and theoretically, using scaling arguments, the stretching of a single polyelectrolyte chain adsorbed at a planar charged surface. The main result is that the force needed to pull a monomer of the chain at a distance z from the surface reaches a plateau at distances larger than the Debye screening length of the solution.

Journal ArticleDOI
15 May 1998-EPL
TL;DR: In this article, the nonlinear response effect was taken into account in a systematic way using the Chapman-Enskog expansion up to second order, complete Galilean invariant lattice BGK models in one dimension and two dimensions for the Navier-Stokes equation have been obtained.
Abstract: Galilean invariance has been an important issue in lattice-based hydrodynamics models Previous models concentrated on the nonlinear advection term In this paper, we take into account the nonlinear response effect in a systematic way Using the Chapman-Enskog expansion up to second order, complete Galilean invariant lattice BGK models in one dimension (theta = 3) and two dimensions (theta = 1) for the Navier-Stokes equation have been obtained

Journal ArticleDOI
01 Aug 1998-EPL
TL;DR: In this paper, the authors consider the application of the lattice Boltzmann BGK model to simulate sound waves in situations where the density variation is small compared to the mean density.
Abstract: We consider the application of the lattice Boltzmann BGK model to simulate sound waves in situations where the density variation is small compared to the mean density. Linear sound waves are simulated in two different situations: a plane wave propagating in an unbound region; and a wave in a tube. For both cases the behaviour of the simulated waves is found to be in good agreement with analytic expressions. Non-linear sound waves are also simulated and are seen to display the expected features.

Journal ArticleDOI
01 Oct 1998-EPL
TL;DR: In this article, the authors used coherent population trapping resonances in cesium vapor to determine DC flux densities in the range from 1 μT to 1 mT with typically 3·10−5 relative uncertainty.
Abstract: Coherent population trapping resonances in cesium vapor can be used to determine DC flux densities in the range from 1 μT to 1 mT with typically 3·10−5 relative uncertainty. For fields modulated at a few kHz, we find sensitivities of below 10 pT within 0.5 s integration time. From the signal-to-noise ratio the sensitivity can be extrapolated to 500 fT/√Hz. A quantitative understanding of the lineshape allows to detect DC fields of several nT even when the Zeeman components of the resonance are not resolved.

Journal ArticleDOI
01 Sep 1998-EPL
TL;DR: In this paper, Haff's law is extended for large times to E(t) ~ τ−d/2 in d dimensions, far into the nonlinear clustering regime.
Abstract: The total energy E(t) in a fluid of inelastic particles is dissipated through inelastic collisions. When such systems are prepared in a homogeneous initial state and evolve undriven, E(t) decays initially as t−2 ~ exp [ − 2τ] (known as Haff's law), where τ is the average number of collisions suffered by a particle within time t, and = 1 − α2 measures the degree of inelasticity, with α the coefficient of normal restitution. This decay law is extended for large times to E(t) ~ τ−d/2 in d dimensions, far into the nonlinear clustering regime. The theoretical predictions are quantitatively confirmed by computer simulations, and hold for small to moderate inelasticities with 0.6 < α < 1.

Journal ArticleDOI
15 May 1998-EPL
TL;DR: In this paper, sideband laser cooling using stimulated Raman transitions is performed on trapped cesium atoms, where the confinement is produced by a far off-resonance dipole trap consisting of two crossed YAG beams which, by interference, create a one-dimensional optical lattice.
Abstract: Sideband laser cooling using stimulated Raman transitions is performed on trapped cesium atoms. The confinement is produced by a far–off-resonance dipole trap consisting of two crossed YAG beams which, by interference, create a one-dimensional optical lattice. In a pure intensity lattice, we measure a 1D temperature of T = 6 μK corresponding to a mean quantum vibrational number of about nv = 0.75. In a polarization gradient lattice, the final temperature is T = 3.6 μK corresponding to nv 2.4.

Journal ArticleDOI
01 Sep 1998-EPL
TL;DR: In this paper, the anomalous exponents of structure functions of the velocity v, the magnetic field b and the Elsasser variables z± = v±b up to order eight were determined.
Abstract: We determine numerically in two space dimensions the anomalous exponents of structure functions of the velocity v, the magnetic field b and the Elsasser variables z± = v±b up to order eight. To that effect, we make use of new exact relationships derived recently for mixed z± third-order correlators. These exponents are compared to existing models of intermittency for either neutral or MHD flows, none of which seem to apply, possibly indicative of a more complex behavior for MHD flows than for neutral fluids.

Journal ArticleDOI
15 Mar 1998-EPL
TL;DR: The shear-thickening transition in dilute surfactant solutions using rheology and small-angle neutron scattering was investigated using steady shear experiments on a new thickening system, which revealed a continuous increase of the apparent viscosity above a critical strain rate c as mentioned in this paper.
Abstract: The shear-thickening transition in dilute surfactant solutions is investigated using rheology and small-angle neutron scattering. Steady shear experiments on a new thickening system, the tosylate of cethyltrimethylammonium, revealed a continuous increase of the apparent viscosity above a critical strain rate c. Concentration and temperature variations of c are derived, and the former is found to be in contradiction with a theoretically predicted gelation. From the scattering under shear, we establish a clear correlation between flow and structure. In the thickening region, the patterns are due to the superposition of two coexisting states, one viscoelastic entangled sheared network and one still purely viscous made of short aggregates. At higher , the former state dominates and its increasing orientation results in shear-thinning.

Journal ArticleDOI
01 Nov 1998-EPL
TL;DR: In this paper, a quantum ratchet, based on an asymmetric (triangular) quantum dot, is investigated experimentally and theoretically, and it is shown that coherent electron transport through such a device depends on the sign of the applied voltage.
Abstract: Particles in a ratchet, that is, a potential without spatial inversion symmetry, can move in one direction even in the absence of macroscopic forces, provided that there is a source of energy. In this paper, a quantum ratchet, based on an asymmetric (triangular) quantum dot, is investigated experimentally and theoretically. We find that coherent electron transport through such a device depends on the sign of the applied voltage. In this way a net current can be obtained even when the applied ac voltage is zero on average. Strikingly, the direction of the current depends on the amplitude at which the quantum dot ratchet is rocked.

Journal ArticleDOI
01 Apr 1998-EPL
TL;DR: In this article, the authors consider the fluctuations of charges in membranes and their effect on the interactions between two fluid membranes a distance h apart and find that the attraction scales as 1/h3 at large distances and as 1 /h when the membranes are closer than a typical screening length.
Abstract: We consider the fluctuations of charges in membranes and their effect on the interactions between two fluid membranes a distance h apart. For the case where the counterions are highly localized in the membrane planes we find that the attraction scales as 1/h3 at large distances and as 1/h when the membranes are closer than a typical screening length. When the counterions are delocalized between the membranes a simple ideal-gas approximation indicates that a primary contribution to the membrane attraction are the fluctuations of this gas; in some cases, these attractions can exceed the repulsive interactions found for uniform charge distributions (the Poisson-Boltzmann or mean-field repulsions). These results may be relevant to understanding the role of charge fluctuations in membrane attraction and adhesion.

Journal ArticleDOI
15 Jun 1998-EPL
TL;DR: In this paper, an eleven-velocity Boltzmann model using several relaxation times obeys a Jeffreys viscoelastic constitutive law with full isotropic behavior, and the connection between the free parameters of the model and the Jeffreys transport coefficients is made with the help of a modified Chapman-Enskog expansion taking into account large relaxation time effects.
Abstract: In this letter, we show that an eleven-velocity two-dimensional lattice Boltzmann model using several relaxation times obeys a Jeffreys viscoelastic constitutive law with full isotropic behavior. The connection between the free parameters of the model and the Jeffreys transport coefficients is made with the help of a modified Chapman-Enskog expansion taking into account large relaxation time effects. Numerical simulation of a pulsed Couette flow is performed leading to an excellent agreement with predictions.

Journal ArticleDOI
01 Aug 1998-EPL
TL;DR: In this paper, the efficiency of different types of Brownian motors is calculated analytically and numerically, and it is shown that motors based on flashing ratchets present a low efficiency and an unavoidable entropy production.
Abstract: The efficiency of different types of Brownian motors is calculated analytically and numerically. We find that motors based on flashing ratchets present a low efficiency and an unavoidable entropy production. On the other hand, a certain class of motors based on adiabatically changing potentials, named reversible ratchets, exhibit a higher efficiency and the entropy production can be arbitrarily reduced.