# Showing papers in "EPL in 1987"

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TL;DR: In this article, a graphical tool for measuring the time constancy of dynamical systems is presented and illustrated with typical examples, and the tool can be used to measure the time complexity of a dynamical system.

Abstract: A new graphical tool for measuring the time constancy of dynamical systems is presented and illustrated with typical examples.

2,843 citations

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TL;DR: In this paper, it was shown that low binding of these nuclei will lead to a neutronization of the nuclear surface and possibly to large cross-sections for Coulomb dissociation, which then offers a new way to study clusters and their binding energies.

Abstract: Empirical evidence suggests that neutron pairing plays an important role for the stability of nuclei near the neutron drip line. It is shown that the low binding of these nuclei will lead to a neutronization of the nuclear surface and possibly to large cross-sections for Coulomb dissociation, which then offers a new way to study clusters and their binding energies.

620 citations

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TL;DR: The atomic force microscope (AFM) is a promising new method for studying the surface structure of both conductors and insulators as discussed by the authors, achieving a resolution better than 2.5 A.

Abstract: The atomic force microscope (AFM) is a promising new method for studying the surface structure of both conductors and insulators. In mapping a graphite surface with an insulating stylus, we have achieved a resolution better than 2.5 A.

513 citations

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TL;DR: In this article, the authors considered a diluted and nonsymmetric version of the Little-Hopfield model and obtained the analytic expression of the evolution of one configuration having a finite overlap on one stored pattern.

Abstract: We consider a diluted and nonsymmetric version of the Little-Hopfield model which can be solved exactly. We obtain the analytic expression of the evolution of one configuration having a finite overlap on one stored pattern. We show that even when the system remembers, two different configurations which remain close to the same pattern never become identical. Lastly, we show that when two stored patterns are correlated, there exists a regime for which the system remembers these patterns without being able to distinguish them.

471 citations

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TL;DR: In this article, the authors used profile refinement of high-resolution neutron powder data at six different temperatures between 5 K and 300 K to refine the structure of a pure and well-characterised powder sample with onset of superconductivity at 100 K.

Abstract: Recently Siegrist et al. proposed a structure for a high-Tc superconductor Ba2YCu3O(9-∂) based on an orthorhombic (a = ap, b = ap, c = 3ap) perovskitelike model containing Ba and Y cations ordered over the A-sites of the ABO3 structure. This ordering is responsible for the tripling of the c-axis. Half of the oxygen vacancies (at z = 1/2) are ordered, while the other half (at z = 0) are disordered over two sites. Using profile refinement of high-resolution neutron powder data at six different temperatures between 5 K and 300 K, we have refined the structure of a pure and well-characterised powder sample with onset of superconductivity at 100 K. At all temperatures we confirmed the previous model except that in our structure, all oxygen vacancies are ordered. Two-thirds of the copper cations have a pyramidal coordination and one-third has a square coordination. In our structure all squares are parallel to the (b, c)-plane, while in the one reported by Siegrist et al. the squares are disorderedly parallel to either the (a, c)- or (b, c)-plane. The difference between the two models is probably due to the fact that the single crystal used in the earlier work was highly twinned. Empirical calculations of the copper valences show that the Cu+++ cations are almost equally distributed over the two sites. No structural change has been detected at the transition.

433 citations

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TL;DR: The upper storage capacity of a neural network for patterns of fixed magnetization m is calculated and the optimal capacity increases with the correlation m2 between the patterns.

Abstract: The upper storage capacity of a neural network for patterns of fixed magnetization m is calculated. The optimal capacity increases with the correlation m2 between the patterns.

295 citations

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TL;DR: In this article, magnetic susceptibility and inelastic neutron scattering experiments have been performed in the nearly ideal one-dimensional Heisenberg antiferromagnet with spin one, Ni(C2H8N2)2NO2ClO4.

Abstract: Magnetic susceptibility and inelastic neutron scattering experiments have been performed in the nearly ideal one-dimensional Heisenberg antiferromagnet with spin one, Ni(C2H8N2)2NO2ClO4. The experimental results are consistent with the recent theoretical predictions for a quantum energy gap between the ground state and the first excited states.

292 citations

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TL;DR: In this article, a two-dimensional (2D) band structure calculation for alcaline-earth-substituted La2CuO4 in the tetragonal phase was proposed.

Abstract: We propose a two-dimensional (2D) band structure calculation for alcaline-earth-substituted La2CuO4 in the tetragonal phase. We find a degenerate logarithmic singularity in the electronic density of states, as usual in 2D systems. This leads to an orthorhombic-to-tetragonal structural phase transition (SPT). Using the BCS theory, we calculate the superconducting critical temperature Tc as a function of the position of the Fermi level (i.e. Cu+++/Cu++ ratio). This model explains the high Tc's observed experimentally and the relation between superconductivity and SPT.

275 citations

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TL;DR: The magnetic susceptibility of ceramic samples in the metallic BaLaCuO system has been measured as a function of temperature as discussed by the authors, and it is found that, for small magnetic fields of less than 0.1 T, the samples become diamagnetic at somewhat lower temperatures than the resistivity drop.

Abstract: The magnetic susceptibility of ceramic samples in the metallic BaLaCuO system has been measured as a function of temperature. This system had earlier shown characteristic sharp drops in resistivity at low temperatures. It is found that, for small magnetic fields of less than 0.1 T, the samples become diamagnetic at somewhat lower temperatures than the resistivity drop. The highest-temperature diamagnetic shift occurs at (33 ± 2) K, and may be related to shielding currents at the onset of percolative superconductivity. The diamagnetic susceptibility can be suppressed with external fields of 1 to 5 T.

222 citations

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TL;DR: In this article, the characteristics of the event detected in the Mont Blanc Underground Neutrino Observatory on February 23, 1987, consisting of 5 interactions recorded during 7s are discussed, and it is shown that the event can be explained in terms of detection of neutrinos emitted during the stellar collapse in the Large Magellanic Cloud.

Abstract: We discuss here the characteristics of the event detected in the Mont Blanc Underground Neutrino Observatory on February 23, 1987, consisting of 5 interactions recorded during 7s. The measured energies of the 5 pulses, the duration of the burst, and the advance of the detection time in comparison with the first optical observations give evidence that the event can be explained in terms of detection of neutrinos emitted during the stellar collapse in the Large Magellanic Cloud.

195 citations

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TL;DR: In this paper, a simple model of the density with adjustable values for the densities and the projected lengths of the aliphatic tail and the polar head as well as an overall Gaussian smearing of densities is presented.

Abstract: Phospholipid monolayers at the air-water interface have been studied by synchrotron x-ray reflection methods. The range of momentum transfers (perpendicular to the surface) exceeded 2π/(layer thickness) thus yielding information about the density distribution across the layer. Data for a monolayer of L-α-dipalmitoylphosphatidylcholine (DPPC) in the solid phase (surface pressure 40 mN/m) are interpreted in terms of a simple model of the density with adjustable values for the densities and the projected lengths of the aliphatic tail and the polar head as well as an overall Gaussian smearing of the densities. We find that the tails are close-packed but uniformly tilted 30° relative to the interface normal.

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TL;DR: In this paper, the frequency dependence of viscoelastic properties of a branched polymer sample near its gelation threshold has been studied in oscillatory measurements, and the results are in agreement with De Gennes' analogy relating the critical behaviour of the elastic moduli G' and G'' to the electrical conductivity of percolation clusters.

Abstract: The frequency dependence of viscoelastic properties of a branched polymer sample near its gelation threshold has been studied in oscillatory measurements. The results are in agreement with De Gennes' analogy relating the critical behaviour of the elastic moduli G' and G'' to the electrical conductivity of percolation clusters. In particular the increase of both G' and G'' with frequency (0.1 to 10 Hz) can be described by power laws with a common exponent u = t/s + t, and the loss angle δ assumes near the gelation point the universal value δc = πu/2 (t and s denote, respectively, the exponents of elastic modulus and viscosity at zero frequency). The value of u determined in these experiments (u = 0.70 ± 0.02) is in very good agreement with percolation theory.

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TL;DR: In this article, a scaling theory is developed which allows a consistent treatment of the coupled ln2(T)-singularities arising from density wave and Cooper pairing fluctuations in the weak coupling limit.

Abstract: In order to investigate possible nonphonon mechanisms for superconductivity in the copper oxide compounds, the two-dimensional Hubbard model is studied in the weak-coupling limit. A scaling theory is developed which allows a consistent treatment of the coupled ln2(T)-singularities arising from density wave and Cooper pairing fluctuations. For a half-filled band a spin-density-wave (antiferromagnetic) phase transition occurs, whereas for small deviations from half-filling spin fluctuations lead to a d-type superconducting phase. The method generalizes straightforwardly to finite-range interactions. The possible relevance to oxide superconductors and experimental tests are briefly discussed.

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TL;DR: In this article, the authors studied spin systems on random lattices with a finite connectivity and showed that the influence of the shape of the distribution of exchange couplings on the ground-state energy of the spin system can be observed.

Abstract: We study spin systems–ferromagnets, spin glasses, graph bipartitioning–on random lattices with a finite connectivity. New features of spin glass theory are pointed out, such as the influence of the shape of the distribution of exchange couplings. For the bipartitioning of random graphs with fixed connectivity, the results of the replica symmetric solution give a good first approximation of the ground-state energy.

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TL;DR: An energy function similar to the one used in a previous paper for solving the subgraph retrieval problem is constructed and a neuronal model for invariant pattern recognition is presented, based on this solution to sub graph retrieval and graph matching.

Abstract: We consider the problem of recognizing a shifted and distorted 2-dimensional shape. This task is formalized as a problem of labelled graph matching. To solve this problem, we construct an energy function similar to the one used in a previous paper for solving the subgraph retrieval problem. We present a neuronal model for invariant pattern recognition, based on this solution to subgraph retrieval and graph matching.

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TL;DR: In this paper, the authors describe a renormalization group method to study the localized-delocalized transition of a one-dimensional interacting electron gas in a random potential, and obtain the phase diagram and the exponents of the correlation functions in the delocalized regime.

Abstract: We describe a renormalization group method to study the localized-delocalized transition of a one-dimensional interacting electron gas in a random potential. We obtain the phase diagram and the exponents of the correlation functions in the delocalized regime. The boundary between the two regimes is found to depend both on disorder and on the strength of the interactions. The delocalized phase is dominated by superconducting fluctuations. We find the asymptotic behaviour of the localization length and the temperature dependence of the conductivity. An analogous description is developed for the localized-superfluid transition of a one-dimensional boson gas. In this case the transition to the localized regime occurs for increasingly repulsive interactions.

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TL;DR: In this paper, the authors studied the time evolution of the distance between two configurations submitted to the same thermal noise for the 3d ± J Ising spin glass and observed three temperature regimes: a high-temperature regime where the distances vanishes in the long-time limit.

Abstract: We study the time evolution of the distance between two configurations submitted to the same thermal noise for the 3d ± J Ising spin glass. We observe three temperature regimes: a high-temperature regime where the distances vanishes in the long-time limit. An intermediate-temperature regime where the distance has a nonzero limit independent of the initial distance. A low-temperature regime where the distance in the long time limit seems to depend upon the initial distance. For the sake of comparison, we have repeated our simulations for the ferromagnetic case.

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TL;DR: In this article, an anomalously strong decrease of the elastic and a corresponding increase of the inelastic scattering around the glass transition temperature were found, implying the existence of a localized and fast (τc ≈ 4.10-12s) molecular motion.

Abstract: Incoherent quasi-elastic neutron scattering experiments on a molecular glass (1,3,5-tri-α-naphtylbenzene, C36H24) are reported. We find clear evidence for an anomalously strong decrease of the elastic and a corresponding increase of the inelastic scattering around the glass transition temperature. The line shape of this extra inelastic intensity gives evidence for a quasi-elastic scattering implying the existence of a localized and fast (τc ≈ 4.10-12s) molecular motion. From the elastic incoherent structure factor (EISF) a mean jump length ≤ 0.6 A is estimated. The significance of this motion as precursor of the glass instability is discussed within the framework of dynamic glass transition theories.

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TL;DR: In this paper, the fractal geometry of fracture patterns in materials is explored by means of a simple model which incorporates the equations of elasticity and simple rules for fracture propagation, and self-similar patterns with fractal dimensions nearly independent of the elastic constants are obtained.

Abstract: The fractal geometry of fracture patterns in materials is explored by means of a simple model which incorporates the equations of elasticity and simple rules for fracture propagation. Different isotropic media and boundary conditions are considered. Self-similar patterns with fractal dimensions nearly independent of the elastic constants are obtained.

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TL;DR: In this paper, contact angle hysteresis on weakly heterogeneous surfaces was studied using an extension of Imry and Ma's analysis of the random field problem, and the characteristic energy associated with these deformations was used to find the scale of contact angle hydresis.

Abstract: Contact angle hysteresis on weakly heterogeneous surfaces is studied using an extension of Imry and Ma's analysis of the random field problem. Deformations of the liquid-vapor interface in response to the heterogeneity are characterized by a length Ld which increases as the magnitude of the heterogeneity decreases. The characteristic energy associated with these deformations is used to find the scale of contact angle hysteresis. In the absence of gravity, contact angle hysteresis occurs for arbitrarily weak heterogeneity. Hysteresis disappears when Ld exceeds the gravitational capillary length, while systems with characteristic size less than Ld show increased hysteresis.

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TL;DR: Amorphous metallic Fe85B15 alloy has been irradiated at low temperature with Ar, Kr and Xe ions of initial energies of 1.8, 2.7 and 3.0 GeV, respectively.

Abstract: Amorphous metallic Fe85B15 alloy has been irradiated at low temperature with Ar, Kr and Xe ions of initial energies of 1.8, 2.7 and 3.0 GeV, respectively. Electrical resistance was measured in situ on samples piled up along the beam direction. It is shown that above a given electronic stopping power threshold the electronic losses play a crucial role in radiation-induced damage.

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IBM

^{1}TL;DR: In this article, high-resolution numerical integration of two-dimensional Navier-Stokes equations was performed to show that the turbulent flow at high Reynolds number is dominated by a simple and weakly unstable Hamiltonian system of point-like vortices.

Abstract: By high-resolution numerical integration of two-dimensional Navier-Stokes equations we show that the turbulent flow at high Reynolds number is dominated by a simple and weakly unstable Hamiltonian system of pointlike vortices. The large instabilities, typical of the turbulent flow, are found uniquely outside vortices, in the wide dissipative region which results to be only a small perturbation of the vortex system. Moreover, the statistical distribution of vortex sizes determines the slope of the energy spectrum, which is steeper than that predicted by phenomenological theories.

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TL;DR: In this paper, a considerable enhancement of the superconducting transition temperature in perovskite-type oxides is explained in the framework of the anharmonic model for superconductors with structurally unstable lattices.

Abstract: A considerable enhancement of the superconducting transition temperature Tc in perovskite-type oxides is explained in the framework of the anharmonic model for superconductors with structurally unstable lattices. It is shown that the interaction of electrons with highly anharmonic oxygen-ion vibrations of a rotational type results in a sufficiently large coupling constant λ. The obtained estimation for Tc is in agreement with experimental data for La(Y)BaCuO systems.

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TL;DR: In this paper, the scaling behavior of the surface width w of d-dimensional Eden clusters growing on flat substrates of linear extent L was investigated and it was shown that w scales for small average deposit height h as hβ, and in the steady state as Lα.

Abstract: By means of noise reduction we investigate the scaling behaviour of the surface width w of d-dimensional Eden clusters growing on flat substrates of linear extent L. We find that w scales for small average deposit height h as hβ, and in the steady state as Lα. Our results for d = 3 (α = 0.33 ± 0.01, β = 0.22 ± 0.02) and for d = 4 (α = 0.24 ± 0.02, β = 0.146 ± 0.015) support the scaling relation α(1 + 1/β) = 2. They suggest that α instead of being superuniversal might be equal to 1/d.

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TL;DR: In this paper, the current-voltage characteristic of a point contact on a sample of Sr-doped La2CuO4 was measured under microwave irradiation, showing that the junction is inside the material under the tip.

Abstract: We have measured the current-voltage characteristic of a point contact on a sample of Sr-doped La2CuO4. Josephson junction characteristics are observed even when the metal tip is nonsuperconducting, a result that indicates that the junction is inside the material under the tip. Under microwave irradiation, we observe well-defined Shapiro steps which yield the usual value h/2e for the coupling constant between the quantum phase and the electromagnetic field. Preliminary measurements on samples of Y1Ba2Cu3O9-x also yield h/2e. We conclude that in these newly discovered materials, the superconducting state is formed of paired electrons.

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TL;DR: A network of spinlike neurons with asymmetric exchange interactions and stochastic spike response which can learn and recall time sequences of biased patterns is proposed.

Abstract: A network of spinlike neurons with asymmetric exchange interactions and stochastic spike response which can learn and recall time sequences of biased patterns is proposed. Noise makes synapses with delayed response or with time-dependent strength, previously proposed for storage of time sequences, superfluous. An accurate timing of pattern sequences requires a sufficient number N of neurons. The performance of the suggested network is described by Monte Carlo simulation, in terms of a Fokker-Planck equation and, for N → ∞, in terms of a Liouville equation.

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TL;DR: In this article, the authors demonstrate that the noise in the light from a high-efficiency light-emitting diode can be reduced below the classical shot noise limit when it is driven by a Johnson-noise-limited high-impedance source.

Abstract: We demonstrate that the noise in the light from a high-efficiency light-emitting diode can be reduced below the classical shot noise limit when it is driven by a Johnson-noise-limited high-impedance source. A noise power reduction factor (Fano factor) of 0.96 has been achieved over a broad bandwidth from selected devices. The noise reduction is, in theory, only limited by the quantum efficiencies of emission, collection and detection of the light.

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TL;DR: Several three-dimensional off-lattice models for ballistic deposition including simple rearrangement processes have been explored in this article, and accurate values are obtained for the densities of the deposits generated by these models and some of their surface properties are investigated.

Abstract: Several three-dimensional off-lattice models for ballistic deposition including simple rearrangement processes have been explored. These models are intended to represent the sort of restructuring processes which might occur in the sedimentation of small particles under the influence of an external (gravitational) field. Accurate values are obtained for the densities of the deposits generated by these models and some of their surface properties are investigated.

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TL;DR: The phase boundary between low-temperature dipole glass and ferroelectric states of K1-xLixTaO3 was proposed to lie within 0.016 40 K as discussed by the authors.

Abstract: The phase boundary between low-temperature dipole glass and ferroelectric states of K1-xLixTaO3 is proposed to lie within 0.016 40 K. The crossover concentration xc ~ 0.022 is extrapolated from the condition Tg(xc) = Tc(xc) ~ 41.5 K.

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TL;DR: In this paper, the optical determination of exciton binding energies in small-period GaAs/Ga0.7Al0.3As superlattices was performed by means of low-temperature photoluminescence excitation spectroscopy.

Abstract: We report the optical determination of exciton binding energies in small-period GaAs/Ga0.7Al0.3As superlattices by means of low-temperature photoluminescence excitation spectroscopy and photoluminescence spectroscopy as a function of temperature. The heavy-hole exciton binding energy decreases with decreasing superlattice period. Our experimental findings are in reasonable agreement with a variational calculation.