Showing papers in "EPL in 1990"
TL;DR: In this article, a simple growth model is investigated where particles are deposited onto a substrate randomly and subsequently relax into a position nearby where the binding is strongest, and a scaling relation 2ξ = z − d + 1 is proposed to be valid for a large class of growth models relevant for molecular beam epitaxy.
Abstract: A simple growth model is investigated where particles are deposited onto a substrate randomly and subsequently relax into a position nearby where the binding is strongest. In space dimension d = 2 the surface roughness exponent and the dynamical exponent are ξ = 1.4 ± 0.1 and z = 3.8 ± 0.5. These values are larger than for previous models of sedimentation or ballistic deposition and are surprisingly close to the ones obtained from a linear generalized Langevin equation for growth with surface diffusion. A scaling relation 2ξ = z − d + 1 is proposed to be valid for a large class of growth models relevant for molecular beam epitaxy.
444 citations
TL;DR: In this article, different fracture modes and different fracture toughness values were obtained on an aluminium alloy subjected to four different heat treatments, and the correlation functions of the bidimensional cuts of the four fractured surfaces were determined.
Abstract: Different rupture modes and different fracture toughness values were obtained on an aluminium alloy subjected to four different heat treatments. The correlation functions of the bidimensional cuts of the four fractured surfaces were determined. It was found that these surfaces were fractal, and that their fractal dimensions were identical, within experimental error.
313 citations
TL;DR: In this paper, shape transformations of vesicles of lecithin (DMPC) in water are induced by changing the temperature which effectively changes the volume-to-area ratio.
Abstract: Shape transformations of vesicles of lecithin (DMPC) in water are induced by changing the temperature which effectively changes the volume-to-area ratio. Three different routes are found which include i) symmetric-asymmetric re-entrant transitions from a dumbbell to a pear-shaped state, ii) the expulsion of a smaller vesicle (budding), and iii) discocyte–stomatocyte transitions. All of these shape transformations are explained within a model for the bending energy of the bilayer which assumes i) that the two monolayers do not exchange lipid molecules, and ii) that the adjacent monolayers exhibit a small difference in their thermal expansivities which is easily produced, e.g., by residual impurities.
239 citations
TL;DR: In this article, the double-beta decay rates for all potential ββ emitters with A≥-70 were predicted and the nuclear transition matrix elements were calculated within the QRPA with a realistic effective nucleon-nucleon interaction.
Abstract: 2ν and 0ν double-beta decay rates for all potential ββ emitters with A ≥ 70 are predicted. The nuclear transition matrix elements are calculated within the QRPA with a realistic effective nucleon-nucleon interaction. The results for neutrinoless decays are rather insensitive to details of the nuclear structure, except for the cases of 70Zn, 100Mo and 148Nd.
238 citations
TL;DR: In this article, a semi-classical analysis of quantum noise is used to show that a judicious use of squeezed states allows one in principle to push the sensitivity beyond the standard quantum limit.
Abstract: Quantum noise limits the sensitivity of interferometric measurements. It is generally admitted that it leads to an ultimate sensitivity, the "standard quantum limit". Using a semi-classical analysis of quantum noise, we show that a judicious use of squeezed states allows one in principle to push the sensitivity beyond this limit. This general method could be applied to large-scale interferometers for gravitational wave detection.
209 citations
TL;DR: In this article, the density of vibrational states (DVS) was determined for a series of vitreous materials: SiO2, As2S3 and metallic glass Mg70Zn30.
Abstract: By means of inelastic cold neutron scattering the density of vibrational states (DVS) has been determined for a series of vitreous materials: SiO2, As2S3 and metallic glass Mg70Zn30. In the low-energy range of the spectrum (E ~ (2 ÷ 10) meV) for these materials DVS reveals a universal, but non-Debye form. The data obtained are compared to different models. A comparison with the Raman scattering data provides the spectral dependence for the coupling of the light to the vibrational excitations.
192 citations
TL;DR: In this paper, the temperature of cesium atoms released from optical molasses was measured and the lowest temperature achieved is (2.5 ± 0.6) μK, which corresponds to an r.m.s. velocity of 12.5 mm/s or 3.6 times the single-photon recoil velocity.
Abstract: We have measured the temperature of cesium atoms released from optical molasses. For a wide range of laser intensity and detuning from resonance, the temperature depends only on the intensity-to-detuning ratio. The lowest temperature achieved is (2.5 ± 0.6) μK, which corresponds to an r.m.s. velocity of 12.5 mm/s or 3.6 times the single-photon recoil velocity. This is, to our knowledge, the coldest kinetic temperature ever measured for three-dimensional (3D) cooling.
187 citations
TL;DR: It is proved that the internal representations obtained by such procedures are linearly separable and compare favourably with results of other growth algorithms.
Abstract: We consider a perceptron with Ni input units, one output and a yet unspecified number of hidden units. This perceptron must be able to learn a given but arbitrary set of input-output examples. By sequential learning we mean that groups of patterns, pertaining to the same class, are sequentially separated from the rest by successively adding hidden units until the remaining patterns are all in the same class. We prove that the internal representations obtained by such procedures are linearly separable. Preliminary numerical tests of an algorithm implementing these ideas are presented and compare favourably with results of other growth algorithms.
154 citations
TL;DR: In this article, the authors study the behavior of two types of polyelectrolytes in a poor solvent and show that these polymers undergo a discontinuous charge instability between a small-charge globular state and a high-charge extended state.
Abstract: We study theoretically the behaviour of two types of polyelectrolytes in a poor solvent. If the number of charges and their position along the chain is quenched, the collapse is well described by a blob model introduced by Khokhlov. Weak polyacids or polybases have however an annealed structure where the charges are "mobile" along the chain. We show that these polymers undergo a discontinuous charge instability between a small-charge globular state and a high-charge extended state. This could explain several titration and viscometric data. At higher concentration, the electrostatic interaction is more screened for annealed than for quenched polyelectrolytes.
133 citations
TL;DR: In this article, the authors examined the effect of electrostatics on the self-assembly of cylindrical micelles and found that the growth of micells as a function of increasing surfactant and/or electrolyte concentration exhibits three distinct regimes.
Abstract: We examine theoretically the effect of electrostatics on the self-assembly of charged, cylindrical micelles. The growth of micelles as a function of increasing surfactant and/or electrolyte concentration exhibits three distinct regimes. The most striking feature of the growth law is the existence of a dilute regime, i), in which the average micelle size varies slowly with concentration. At higher concentrations, regimes ii) and iii) are characterized by more rapid growth than for neutral micelles. This may be responsible, in part, for the anomalous scaling of rheological properties, as observed in recent experiments.
129 citations
TL;DR: Ginzburg-Landau amplitude equations are used in this paper as a model for the nonlinear development of flow instabilities and a study of their solutions shows that subcritical instabilities may lead either to a stable localized pattern or expanding "turbulent" domains depending on the relative magnitude of different terms in the equation.
Abstract: Ginzburg-Landau amplitude equations are used here as a model for the nonlinear development of flow instabilities. A study of their solutions shows that subcritical instabilities may lead either to a stable localized pattern or expanding "turbulent" domains depending on the relative magnitude of different terms in the equation. We explain then how a continuous transition relates those two phenomena.
TL;DR: In this article, the authors calculate the osmotic pressure in a semi-dilute solution of stretched polymers in a good solvent and apply it to polymer brushes where polymers are stretched either directly or by application of shear.
Abstract: We calculate the osmotic pressure in a semi-dilute solution of stretched polymers in a good solvent. The results are applied to polymer brushes where polymers are stretched either directly or by application of shear. It is shown that when a brush is sheared against the solvent, the stretching proceeds always within the nonlinear regime of polymer elasticity. When the brush is subjected to a combination of compression and shear forces and the shear is gradually increased, there is a crossover between low-shear linear elastic behaviour to a nonlinear regime in which the brush swells and eventually reaches its full uncompressed thickness at high shear stress. The relevance of our results to present and future experiments is discussed.
TL;DR: In this article, the maximum entropy method (MaxEnt) is used to measure the magnetic moments in the unit cell, or at least their projections along a given crystallographic direction.
Abstract: Polarized neutron diffraction essentially measures discrete spatial 3D Fourier components of the magnetization density inside a single crystal, which is known to obey symmetry requirements. Due to restricted and noisy data sets, the standard analysis, which involves the computation of the inverse Fourier transform of the data, often results in heavy truncation and noise effects. The maximum entropy method (MaxEnt) is shown to perform much better: one can now "see" the magnetic moments in the unit cell, or at least their projections along a given crystallographic direction.
TL;DR: In this article, a simple local density functional theory for screened interactions between macroions and apply it to electric double layers is described, incorporating the strong correlations between screening ions at high densities, and reducing to the Poisson-Boltzmann equations at low densities.
Abstract: We describe a simple local density functional theory for screened interactions between macroions and apply it to electric double layers. The approach incorporates the strong correlations between screening ions at high densities, and reduces to the Poisson-Boltzmann equations at low densities. Results for monovalent ions are in excellent agreement with Monte Carlo (MC) and inhomogeneous hypernetted chain (IHNC) calculations. Nonlocal effects are important for divalent ions at small macroion separations and high surface charge densities. A simple weighted density approximation qualitatively reproduces MC and IHNC results in this regime, and provides a simple explanation for the onset of attractive interactions between like-charged plates.
TL;DR: In this paper, the authors describe annular films flowing and thinning along vertical fibers, and show that these conditions are compatible with a scenario of nonlinear saturation of the Rayleigh instability.
Abstract: We describe annular films flowing and thinning along vertical fibers. According to the film thickness and to the radius of the fiber, two different kinds of behaviour can be observed: i) when the film is thick, drops develop because of the Rayleigh instability and flow downward. Some of them grow by swallowing the other ones, and quickly fall, leaving behind them a thick film which breaks in turn into droplets. ii) For a thin film on a large fiber, the instability cannot grow because of the flow. We present a quantitative study of the conditions under which drops do not appear, and show that these conditions are compatible with a scenario of nonlinear saturation of the Rayleigh instability.
TL;DR: Under elongational flow a second-order transition at a critical flow rate is predicted, above which a certain fraction of the material forms an aligned "gel" phase of extremely long rods.
Abstract: We study the dynamics of self-assembling rodlike micelles under flow. We assume simple reaction kinetics in which two micelles can fuse only if they are collinear. This provides a positive feedback between micellar alignment and growth, which we study in the regime where micelle-micelle reactions are frequent on the time scale of rotational diffusion. We predict under elongational flow a second-order transition at a critical flow rate, above which a certain fraction of the material forms an aligned "gel" phase of extremely long rods.
TL;DR: In this article, the surface profile at the surface in blends of deuterated and protonated polystyrene (d-PS and PS) is inferred from measurements of neutron reflectivity and secondary-ion mass spectrometry, using constraints provided by forward recoil spectrometer and X-ray reflectometry results on the same samples.
Abstract: The concentration profile at the surface in blends of deuterated and protonated polystyrene (d-PS and PS) is inferred from measurements of neutron reflectivity and secondary-ion mass spectrometry, using constraints provided by forward recoil spectrometry and X-ray reflectometry results on the same samples. The surface is enriched in d-PS, the volume fraction and the decay length of which are in good agreement with the predictions of mean-field theory but the form of the profile shows small, but statistically significant, deviations from that predicted by the theory.
TL;DR: It is shown that the generalization ability of simple Perceptron-like devices is strongly enhanced by allowing the network itself to select the training examples.
Abstract: We show that the generalization ability of simple Perceptron-like devices is strongly enhanced by allowing the network itself to select the training examples. Analytic and numerical results are obtained for the Hebb and for the optimal Perceptron learning rule, respectively.
TL;DR: In this article, the authors investigated the angular momentum loss of a rotating plasma due to mode locking using spectroscopic rotation measurements and magnetic probe data and calculated the electromagnetic force on the plasma regarding both the interaction with the resistive vessel wall and the error field.
Abstract: The loss of angular momentum of a rotating plasma due to mode locking is investigated using spectroscopic rotation measurements and magnetic probe data. The electromagnetic force on the plasma regarding both the interaction with the resistive vessel wall and the error field is calculated. Simulations of the temporal evolution of the toroidal bulk rotation by solving the momentum transport equation in the presence of the magnetic forces explain the toroidal momentum balance in detail. As a result we find that the plasma within the island is affected by the electromagnetic force, while the rest of the plasma is slowed down by viscous coupling.
TL;DR: In this article, it was shown that the optical field-field correlation function with frequency in a random medium is the Fourier transform of the time-of-flight distribution for light transmitted through a polystyrene slab containing titania particles by fitting the measured frequency dependence of correlation function of fluctuations in intensity using the measured transmitted picosecond pulse profile.
Abstract: We show that the optical field-field correlation function with frequency in a random medium is the Fourier transform of the time-of-flight distribution. This is demonstrated for light transmitted through a polystyrene slab containing titania particles by fitting the measured frequency dependence of the correlation function of fluctuations in intensity using the measured transmitted picosecond pulse profile.
TL;DR: In this paper, the mean square radii of light radioactive projectiles, including exotic isotopes close to the neutron drip line (11Li, 14Be, and 17B), have been deduced from total reaction cross-section measurements, using a simple microscopic model.
Abstract: Mean square radii of light radioactive projectiles, including exotic isotopes close to the neutron drip line (11Li, 14Be, and 17B), have been deduced from total reaction cross-section measurements, using a simple microscopic model. The isospin dependence of nuclear radii is discussed and compared to other experimental results.
TL;DR: In this article, the effects of electrostatic interactions on steric repulsion and curvature elasticity are considered for dilute multimembrane systems as a function of the electrolyte strength, surface charge and inter-membrane spacing.
Abstract: The effects of electrostatic interactions on steric repulsion and curvature elasticity are considered for dilute multimembrane systems as a function of the electrolyte strength, surface charge and inter-membrane spacing. In the strong electrolyte limit, the electrostatic interactions are screened and the steric repulsion dominates. For weak electrolytes, the electrostatic interactions cut-off the out-of-plane undulations and change significantly the membrane bending constant in qualitative agreement with recent experiments.
TL;DR: In this article, the authors propose an expression for the frictional force in granular materials and predict the existence of a characteristic shear rate, 0, which separates regions of stable from unstable flow.
Abstract: From simple microscopic considerations we propose an expression for the frictional force in granular materials. This force has very nonlinear behavior as a function of the shear rate. The mechanism we propose predicts the existence of a characteristic shear rate, 0, which separates regions of stable from unstable flow. Our formulation can explain the hysteresis phenomena commonly observed in granular materials.
TL;DR: A defect-induced enhancement of the critical current density in magnetic fields B is observed after low fluences only if the flux lines are aligned parallel to the amorphized ion traces as discussed by the authors.
Abstract: Epitaxially grown YBa2Cu3Ox films have been irradiated with 173 MeV 129Xe ions. A nonlinear decrease of the critical superconducting transition temperature Tc and an exponential increase of the resistivity ? is observed. The c-axis parameter is extended to about 12 ? with increasing Xe fluence and the twin boundaries disappear. The 1-2-3 phase is amorphized along the paths of the Xe ions within an area of 40 ? in diameter. A defect-induced enhancement of the critical current density jc in magnetic fields B is observed after low fluences only if the flux lines are aligned parallel to the amorphized ion traces.
TL;DR: The Dirac equation for some linear potentials leading to Schrodinger-like oscillator equations for the upper and lower components of the Dirac spinor have been solved in this article.
Abstract: The Dirac equation for some linear potentials leading to Schrodinger-like oscillator equations for the upper and lower components of the Dirac spinor have been solved. Energy levels for the bound states appear in pairs, so that both particles and antiparticles may be bound with the same energy. For weak coupling, the spacing between levels is proportional to the coupling constant while in the strong limit those levels are depressed compared to the nonrelativistic ones.
IBM1
TL;DR: In this article, a model for fluid flexible self-avoiding membranes is introduced and investigated by Monte Carlo methods, and the authors show that a free draining monomer of a fluid membrane exhibits a time-dependent displacement of r2(t) ~ t0.8.
Abstract: A model for fluid flexible self-avoiding membranes is introduced and investigated by Monte Carlo methods. Fluid athermal membranes consisting of N monomers exhibit crumpled shapes and their mean square radii of gyration are R2 ~ N0.8. In contrast, polymerized self-avoiding membranes are flat and rough. The related anisotropy is characterized by the two larger eigenvalues of the inertia tensor, λ3 ~ λ2 ~ N, and by the smallest one, λ1 ~ N0.65. A free draining monomer of a fluid membrane exhibits a time-dependent displacement of r2(t) ~ t0.8, whereas approximately r2(t) ~ t0.4 for polymerized membranes.
TL;DR: In this paper, the influence of the relative phase and spacing between the two solitons are experimentally illustrated, which could be used to realize optical addressors or optical gates.
Abstract: We report experimental results about soliton beam attraction or repulsion. The influence of the relative phase and spacing between the two solitons are experimentally illustrated. Such phenomenon could be used to realize optical addressors or optical gates.
TL;DR: In this paper, an improved sand box technique was used to determine the fractal dimension of off-lattice diffusion-limited aggregation (DLA) clusters and demonstrated that they decrease monotonically with increasing q.
Abstract: Off-lattice diffusion-limited aggregation (DLA) clusters are shown to have multifractal geometry. We determine the Dq spectrum associated with the mass distribution using an improved sand box technique and demonstrate that they decrease monotonically with increasing q. From our results it follows that the commonly used methods for the determination of the fractal dimension of DLA clusters yield Dq=2 which is smaller than the true fractal dimension Dq=0.
TL;DR: In this article, the Hall effect and temperature dependence of the resistivity of Al63Cu25Fe12 samples were analyzed through electron-electron interactions and localization theories. And the authors showed that the temperature and magnetic-field dependences of resistivity and Hall effect can be analysed through electron electron interactions.
Abstract: A very high-resistivity value (?4K?~?4300???cm), associated to a strong negative temperature dependence (??=?1/??????/?T?~??10?3?K?1), is measured in pure icosahedral Al63Cu25Fe12 phases (a single grain and polyquasicrystalline samples). Moreover the resistivity of the defective as-quenched Al63Cu25Fe12 samples is much smaller (?4K?~?1300???cm) and increases sharply (up to ~4300???cm) after annealing treatment. We show also that the temperature and magnetic-field dependences of the resistivity and the Hall effect can be analysed through electron-electron interactions and localization theories.
TL;DR: In this article, the two-dimensional random bond Ising model with two distinct ferromagnetic nearest-neighbour couplings, J and J', distributed randomly over the lattice with concentration 1/2 is studied for various ratios J'/J at criticality.
Abstract: The two-dimensional random bond Ising model with two distinct ferromagnetic nearest-neighbour couplings, J and J', distributed randomly over the lattice with concentration 1/2 is studied for various ratios J'/J at criticality. The critical temperature is exactly known from self-duality. The size-dependent specific heat shows a crossover from the perfect Ising to the randomness-dominated critical behaviour of doubly logarithmic form. In the latter region, our estimates for the critical exponents of the size-dependent magnetization and susceptibility are in very good agreement with analytic results suggesting β/ν = 1/8 and γ/ν = 7/4.