Showing papers in "Physica Scripta in 1989"
TL;DR: A very brief presentation of how lattice gas hydrodynamics is made and includes key references.
Abstract: A very brief presentation of how lattice gas hydrodynamics is made. It includes key references.
852 citations
TL;DR: In this paper, the same underlying physics which controls both growth processes is discussed, which leads to morphological instability in which a growing surface is unstable with respect to spacially periodic perturbations.
Abstract: What does viscous fingering have in common with crystal growth? It is not only the visual similarity of the patterns the two seemingly unrelated phenomena can generate under certain circumstances, but also the same underlying physics which controls both growth processes. The common behaviour - diffusion limited growth - leads to morphological instability in which a growing surface is unstable with respect to spacially periodic perturbations. Several theoretical and simulation studies have shown that the simple model is biased in its large scale morphology by the local anisotropy of the growth rules. Liquid crystals exhibit inherent anisotropies tunable with temperature in their bulk properties, which makes them extremely attractive for experimental studies of pattern forming processes. Electrohydrodynamic instabilities, transient patterns at the Frederiksz transition, directional solidification at an isotropic-nematic and cholesteric-smectic A phase transition, viscous fingering and dendritic "smectification" are discussed.
202 citations
TL;DR: There is no quantum chaos, in the sense of exponential sensitivity to initial conditions, but there are several novel quantum phenomena which reflect the presence of classical chaos as mentioned in this paper, and the study of these phenomena is quantum chaology.
Abstract: There is no quantum chaos, in the sense of exponential sensitivity to initial conditions, but there are several novel quantum phenomena which reflect the presence of classical chaos. The study of these phenomena is quantum chaology.
143 citations
TL;DR: In this article, a direct analogy between the topological order in integer quantum antiferromagnets and the fractional quantum Hall effect (FQHE) was investigated. But the results for the S = 1 generalized Heisenberg chain were not discussed.
Abstract: Using an idea of Rommelse and den Nijs, we have investigated a direct analogy between the topological order in integer quantum antiferromagnets and the topological order in the fractional quantum Hall effect (FQHE). Numerical results are presented for the S = 1 generalized Heisenberg chain. The analogy between the Laughlin gap in the FQHE and the Haldane gap in integer spin chains is discussed.
86 citations
TL;DR: In this article, Kawata and Inoue showed that in the oblique case, a rich family of periodic wave train soliton solutions to the DNLS equation exists, which matches to the cnoidal solutions to MKdV and KdV in appropriate asymptotic limits.
Abstract: The DNLS equation describes weakly dispersive MHD waves propagating parallel as well as at a small angle to the magnetic field. For oblique propagation, the magnetosonic mode is described by the KdV equation, whereas certain aspects of the oblique Alfven wave are described by the MKdV equation. The two latter equations possess one-parameter families of solitons. One-parameter families of oblique soliton solutions to the DNLS equation exist, which match to those of the KdV and MKdV in appropriate asymptotic limits. For parallel propagation, the DNLS equation possesses a well-known two-parameter family of soliton solutions. Such a family also exists in the oblique case (Kawata and Inoue, J. Phys. Soc. Japan 44, 1968 (1978)), but has so far been paid little attention. In the parallel case, soliton formation is known to result from modulational instability of circularly polarized wave trains. In the oblique case, a rich family of periodic wave train solutions exists which matches to the cnoidal solutions to MKdV and KdV in the appropriate limits. The modulational stability of these wave trains is studied by Whitman's method. A conjecture analogous to a result of Driscoll and O'Neil (Phys. Fluids 17, 1196 (1976)) is supported numerically.
82 citations
TL;DR: The information flow through systems with few degrees of freedom and with sensitive dependence on initial conditions, and ways of measuring this flow are reviewed, and one way of forecasting suggested by dynamical systems concepts is proposed.
Abstract: We discuss several questions related to the predictability of chaotic systems We first review the information flow through systems with few degrees of freedom and with sensitive dependence on initial conditions, and ways of measuring this flow We then ask how the knolwedge obtained in this way can be used in improving forecasts, and propose one way of forecasting suggested by dynamical systems concepts On the more fundamental level, we point out the difference between difficulty and possibility of forecasting, illustrating it with quadratic maps Next, we ask ourselves how this should be generalized to distributed (ie, spatially extended) and homogeneous systems We point out that even the basic concepts of how information is processed by such systems are unknown Finally, we discuss some intermittency-like effects in coupled maps and cellular automata
67 citations
TL;DR: In this article, the role of the Kelvin-Helmholtz instability at the terrestrial magnetopause is discussed, as well as its role in magneto-transfer, experimental observations, linear theory, and numerical simulations.
Abstract: This paper reviews different topics concerning the Kelvin-Helmholtz instability at the terrestrial magnetopause: role in the magnetopause transfers, experimental observations, linear theory, and numerical simulations. Two main questions are raised from this review: (i) is the role of the Kelvin-Helmholtz instability to be opposed to the one of reconnection, or are both phenomena to be considered as complementary? (ii) why are the measured surface wavelengths much longer than predicted by the linear theory? We present new results of numerical simulations which may allow to answer these two questions.
66 citations
TL;DR: In this article, the authors measured the macroscopic quantum tunneling (M.Q.T) rate out of the zero voltage state of a Josephson junction shunted by a delay line terminated by a resistor.
Abstract: We have measured the Macroscopic Quantum Tunneling (M.Q.T.) rate out of the zero voltage state of a Josephson junction shunted by a delay line terminated by a resistor. As the length of the line is increased in situ, thereby increasing the delay with which the resistor damps the junction, the M.Q.T. rate increases until it almost recovers its value in the absence of damping: This constitutes the temporal decoupling effect. We compare our results to the theoretical predictions.
63 citations
TL;DR: In this paper, similarities and differences between the single-particle orbitals of the Nilsson and Woods-Saxon average potentials are investigated in detail for deformed nuclei in the rare-earth and actinide regions.
Abstract: Similarities and differences between the single-particle orbitals of the Nilsson and Woods-Saxon average potentials are investigated in detail for deformed nuclei in the rare-earth and actinide regions. The neutron single-particle orbitals are found to be similar in the two potentials in the rare earth region, while in the actinide region large differences are found. These differences can, however, be significantly reduced by changing the Nilsson model parameters κ and μ. The proton single-particle orbitals show small but systematic differences both in the rare earth and actinide region. The origin of these differences can be traced back to the Coulomb interaction, which is not explicitly considered in the Nilsson potential.
60 citations
TL;DR: In this paper, coherent electromagnetic processes were proposed as the engine for biological dynamics and positive experimental evidence for Josephson effects in living cells was reported and discussed; however, the experimental results were limited.
Abstract: The proposal of coherent electromagnetic processes as the engine for biological dynamics suggests that Josephson effects could be present in living cells. Positive experimental evidence is reported and discussed.
59 citations
TL;DR: In this article, the most recent experimental and theoretical studies of multiply-excited states are reviewed with emphasis on emission spectroscopy, and fine structure effects on transition wavelengths and lifetimes (autoionization) are discussed.
Abstract: Optical studies of multiply-excited states are reviewed with emphasis on emission spectroscopy. From optical measurements, properties such as excitation energies, lifetimes and autoionization widths can be determined with high accuracy, which constitutes a challenge for modern computational methods. This article mainly covers work on two-, three- and four-electron systems, but also sodium-like quartet systems. Furthermore, some comments are given on bound multiply-excited states in negative ions. Fine structure effects on transition wavelengths and lifetimes (autoionization) are discussed. In particular, the most recent experimental and theoretical studies of multiply-excited states are covered. Some remaining problems, which require further attention, are discussed in more detail.
TL;DR: In this article, a general survey of screened hydrogenic models for atomic structure calculations is presented, and a simple extension of the latter model including l-splitting in a self-consistent manner is proposed.
Abstract: The first part of this paper is devoted to a general survey of Screened Hydrogenic Models (SHM) for atomic structure calculations. New interest is taken in these models because they allow a very fast computation of total energy, one-electron energies, ionization potentials... for any ionic configuration, that can be done on-line in Plasma Physics studies. The a-priori formulation of the SHM is revisited. Then, the additional approximations required to recover a more intuitive formulation based on the notions of inner and outer screenings, and ignoring angular-momentum splitting of the levels, are described. The usefulness of fitting screening constants is discussed. The last part proposes a simple extension of the latter model including l-splitting in a self-consistent manner. Numerical results are presented and discussed.
TL;DR: A numerical comparison is made of algorithms for computing the dimension of attractors using the Grassberger-Procaccia correlation dimension and the Badii-Politi nearest neighbor approach, which appears to have the better power law behavior when the attractor dimension is between 3 and 7.
Abstract: A numerical comparison is made of algorithms for computing the dimension of attractors using the Grassberger-Procaccia correlation dimension and the Badii-Politi nearest neighbor approach. Using experimentally realizable data sets, the nearest neighbor method appears to have the better power law behavior when the attractor dimension is between 3 and 7.
TL;DR: In this paper, the combined effect of modulational instability and nonlinear Landau damping on a circularly polarized MHD wave is studied, and numerical studies of the development of the instabilities and subsequent wave damping in both ranges are presented.
Abstract: The combined effect of modulational instability and nonlinear Landau damping on a circularly polarized MHD wave is studied. When the wave gets modulated, the magnetic mirror force as well as the parallel electric field associated with the modulations, transfer energy to the charged particles with velocity near the Alfven velocity, to cause a nonlinear Landau damping. Our mathematical model is a DNLS equation extended with a nonlocal term representing the resonant particles. This irreversible model allows a conservation law which in a slowly varying wave train limit corresponds to conservation of wave action. In addition to the modulational instability already known from the DNLS model, the Landau damping term introduces a modulational instability in the wave number range where the wave would otherwise be stable. We present numerical studies of the development of the instabilities and the subsequent wave damping in both ranges. One of our principal findings is that the wave frequency decreases in the same proportion as the energy density. This can be understood in terms of the conservation of action law.
TL;DR: In this paper, the transverse stability of solitary wave structures to the equation iψt + ψxx + sψyy + p|ψ|2ψ = 0 is studied.
Abstract: The transverse stability of solitary wave structures to the equation iψt + ψxx + sψyy + p|ψ|2ψ = 0 is studied for the four cases; (p = 1, s = 1), (p = 1, s = −1), (p = −1, s = −1) and (p = −1, s = 1). Solitary waves in the x-direction are envelopes ψ = √2 sech(x) exp (it), for p = 1, and they are kinks; ψ = √2 tanh(x) exp (– 2it), for p = −1. For s = 1 an energy principle can be invoked, and instability for the envelope occurs in the range 0 < k2 < 3, and for the kink in the range 0 < k2 < 1. Here k is the wavenumber of the perturbation in the y-direction. Growth rates are estimated very simply by means of a Rayleigh-Ritz method. For s = −1, we review existing results for the envelope. It is unstable in a range 0 < k2 ≤ 1.17 where the upper limit must be determined numerically. For the kink, we find a continuum of unstable, non-local perturbations covering the whole range 0 < k2 < ∞. On both sides of the kink structure (|x| 1) these perturbations are oblique, purely growing plane waves. We conclude that both envelopes and kinks are transversely unstable for all signs of p and s.
TL;DR: In this article, an efficient method for calculating intensities of molecular radiative transitions in the vacuum UV and soft X-ray wavelength regions using MCSCF wave functions is presented, where the initial and final states are expanded within large configurational spaces and separately optimized with sets of molecular orbitals that are mutually non-orthogonal.
Abstract: An efficient method for calculating intensities of molecular radiative transitions in the vacuum UV and soft X-ray wavelength regions using MCSCF wave functions is presented. The initial and final states are expanded within large configurational spaces and separately optimized with sets of molecular orbitals that are mutually non-orthogonal. An optimal construction of the transition density matrix is achieved through a sorting algorithm of the symbolic configuration elements in conjunction with the biorthogonalization technique of Malmqvist [1] for transforming the molecular orbitals. The performance of the method is demonstrated for the soft X-ray emission spectra of CO and N2.
TL;DR: In this paper, the influence of the core on the valence electrons has been treated by the use of model potentials and with explicit configuration interaction, so that valence-shell correlation is incorporated in the same way in both approaches.
Abstract: We review recent calculations of oscillator strengths for medium to heavy ions in which the influence of the core on the valence electrons has been treated by the use of model potentials. In particular, we consider core polarisation both with model potentials and with explicit configuration interaction, so that valence-shell correlation is incorporated in the same way in both approaches. These two approaches yield very similar results. This allows the confident use of model potentials for heavy ions and atoms, thus saving considerable computer time when compared with all-electron calculations.
TL;DR: In this article, the authors present experimental data on the Invar behavior of FeNiMn, Fe3Pt and amorphous FeB alloys, clearly demonstrating that neither magnetic (or metallurgical) inhomogeneities nor weak itineracy are the origin of Invar effect, as believed for a long time.
Abstract: We briefly review the history of the Invar-effect and present experimental data on the Invar behavior of FeNiMn, Fe3Pt and amorphous FeB alloys, clearly demonstrating that neither magnetic (or metallurgical) inhomogeneities nor weak itineracy are the origin of the Invar-effect, as believed for a long time. Instead, we will demonstrate that recent band calculations within the local spin density approximation can form the basis for a principally new understanding of the Invar-effect. Although the volume instabilities of the magnetic moments of certain but Invar typical 3d-elements are observed at T = 0 within these models, we will give direct experimental evidence for the occurrence of high spin-low spin state transitions with temperature in ordered Fe3Pt. Finally, we analyze high temperature data of the specific heat and thermal expansion anomalies in different Invar systems. The results give further support for the idea that the broad spectrum of Invar anomalies is caused by thermal exitation of certain energy levels within the instability range of the 3d-moments.
TL;DR: An extension of the classification of the spectrum of singly ionized praseodymium, based on the analysis of high resolution data in the range 2783-27 920 cm−1, yields new energy levels in the odd configuration 4f25d6p and in the mixed even configurations 4f36p as mentioned in this paper.
Abstract: An extension of the classification of the spectrum of singly ionized praseodymium, based on the analysis of high resolution data in the range 2783-27 920 cm−1, yields new energy levels in the odd configuration 4f25d6p and in the mixed even configurations 4f25d2 + 4f25d6s + 4f36p A number of experimental characteristics of the levels have been determined or revised; energy, J, and hyperfine structure splitting are given for all known levels (105 odd levels and 187 even levels), and g values are given for 236 levels Experimental data are presented for 172 classified intense lines in the ultraviolet range, and for 39 unclassified lines The wavenumber distribution of the different types of observed transitions is studied
TL;DR: A neural network model which is capable of automatically forming internal representations of the exterior signal space is described, and some possibilities for application to artificial systems are given.
Abstract: This report describes a neural network model which is capable of automatically forming internal representations of the exterior signal space. A simplified self-organizing algorithm is presented and some examples of computer simulations are given. The feasibility of the method in terms of actual neural networks is discussed and some possibilities for application to artificial systems are given.
TL;DR: In this article, the energy cost of wavevector (q) and frequency (ω) dependent phase fluctuations θqω is expressed exactly in terms of disordered normal state properties.
Abstract: Superconductivity disappears in (mesoscale) disordered thin films at a sheet resistance R or order 10 kΩ per square. This and other observed features of systems with both atomic and meso-scale disorder are briefly reviewed, as also theoretical models mainly based on the Josephson junction lattice. These are known to be inadequate. A new approach is described, with the sole assumption that the pair amplitude |Δ| does not vary spatially. The energy cost of wavevector (q) and frequency (ω) dependent phase fluctuations θqω is expressed exactly in terms of disordered normal state properties. It is shown that because of perfect screening, the ω2 dependent term has an extra factor |q| in two dimensions relative to the Josephson junction lattice form. The q2 or phase gradient term is calculated as a function of R. A rapid and large drop in stiffness occurs for R ~ 10 kΩ when the electron localization length and pair coherence length become comparable. At this level of disorder, the pair amplitude fluctuates spatially, so that the above approach becomes inadequate. Several indications are that a charged Bose system in a random potential would be a realistic model for disordered thin film superconductors at low temperature.
TL;DR: In this paper, the theories concerning solitary waves and weak double layers in the auroral plasma are discussed and compared with Viking satellite observations and computer simulation experiment results of similar phenomena, and the lack of velocity vs amplitude relation in the Viking data is not consistent with the predictions of ion acoustic soliton theories and neither are the measured speeds of the structures.
Abstract: The theories concerning solitary waves and weak double layers in the auroral plasma are discussed. We make comparisons with Viking satellite observations and computer simulation experiment results of similar phenomena. The lack of velocity vs. amplitude relation in the Viking data is not consistent with the predictions of ion acoustic soliton theories and neither are the measured speeds of the structures. Numerical simulations show results, which are somewhat more consistent with Viking measurements but not with the ion acoustic soliton theory predictions. The nonlinear phase space ion hole instability offers another explanation for simulation results and space observations. Even there we still are quite uncertain, since the theory so far is only one-dimensional whereas the observations indicate that the solitary structures have a two- or three-dimensional shape with such scale sizes that the ions cannot be considered as one-dimensional.
TL;DR: In this paper, exact solutions of a generalized nonlinear Schrodinger equation are obtained by transforming the equation to one whose coefficients satisfy a simple algebraic relationship, which yields conservation laws and sufficient conditions for boundedness and blow-up of solutions for the original equation.
Abstract: Exact solutions of a generalized nonlinear Schrodinger equation iut + uxx + qc|u|2u + qq|u|4u + iqm|u|x2u + iqu|u|2ux = 0 are obtained by transforming the equation to one whose coefficients satisfy a simple algebraic relationship. The transformed equation also yields conservation laws and sufficient conditions for boundedness and blow-up of solutions for the original equation.
TL;DR: In this article, the polar tilt-E-condition (SEC) was investigated using the incoherent scatter radar (ISR) facility installed at Sdr. Stromfjord, Greenland (inv. lat. = 74°).
Abstract: The polar Slant-E-Condition (SEC) has been investigated using the incoherent scatter radar (ISR) facility installed at Sdr. Stromfjord, Greenland (inv. lat. = 74°) along with co-located and remote ionosondes, riometers, magnetometers and other equipment. SEC events are characterized by the occurrence of diffuse, slanted backscatter traces (slant Es) in ionograms and abnormally high attenuation (lacuna) of the ionosonde return signals at frequencies close to the E-region plasma frequency. The ISR observations of E-region electron densities, electron and ion temperatures and plasma convection velocities have shown, that SEC occurs during events of substantially elevated electron temperatures related to the occurrence of plasma instabilities driven by strong horizontal electric fields. A self-consistent model for electron heating in an unstable plasma has been applied to the observations and very good agreement was found between observed and calculated electron temperature profile shapes and values of peak temperatures. There was fair agreement between observed and calculated height ranges for the heated electrons. These results and the consequences of the fictitious electron-plasma wave collision term used in the electron heating model are discussed.
TL;DR: In this paper, the relation between elastic peak intensity and mean free path (IMFP) for single and multiple elastic scattering was derived based on the differential scattering cross-sections calculated within the partial wave expansion method.
Abstract: Measurements of the elastic peak intensity make possible estimation of the true inelastic mean free path (IMFP). Corresponding experiments are relatively simple and can be performed for any sample. The theoretical models can be used to derive the relation between elastic peak intensity and IMFP for single and multiple elastic scattering. In the present work both models were based on the differential scattering cross-sections calculated within the partial wave expansion method. Examples of calculations of the IMFP using both theoretical models are presented.
TL;DR: In this paper, it was shown that superconductivity in strongly correlated electronic systems described by the Hubbard model for slightly less than half-filled band is derived from the condensation of charge + e holons which are bosons.
Abstract: Superconductivity in the strongly correlated electronic systems described by the Hubbard model for slightly less than half-filled band is shown to arise from the condensation of charge + e holons which are bosons. The holon effective mass is found to be very close to that of the band electrons and they have a strong nearest neighbour repulsion induced by the spin fluctuations. They interact with an U(1) part of the collective SU(2) gauge field (named S-gauge field) of the spin system. This results in spontaneous symmetry breaking of the holon field and the appearance of the Anderson-Higgs phenomenon. The interesting possibility of the SU(2) gauge field-spinon coupled system retaining some gapless excitation spectrum inspite of the spontaneous symmetry breaking in the holon field is pointed out.
TL;DR: In this paper, an exact solution of a generalized nonlinear Schrodinger equation is presented, characterized by a new nonlinear dispersion term, and its limiting cases cover a large number of physical problems.
Abstract: An exact solution of a generalized nonlinear Schrodinger equation is presented. The equation is characterized by a new nonlinear dispersion term, and its limiting cases cover a large number of physical problems.
TL;DR: In this paper, a detailed investigation of energy levels and radiative transition probabilities is presented for the n = 4, Δn = 0 transitions of the ions Rb VIII to Xe XXV along the zinc isoelectronic sequence.
Abstract: A detailed investigation of energy levels and radiative transition probabilities is presented for the n = 4, Δn = 0 transitions of the ions Rb VIII to Xe XXV along the zinc isoelectronic sequence. The Relativistic Hartree-Fock method is applied for the calculations combined with Slater parameter optimization procedures. Comparisons with multiconfigurational Dirac-Fock calculations show that the most important relativistic effects are taken into account.
TL;DR: In this article, the results of the rapid quenching from the melt of the pure metals (In, Pb) at high pressures 0.7-8.0 GPa with a cooling rate ~ 103 K s−1 are presented.
Abstract: The results of the rapid quenching from the melt of the pure metals (In, Pb) at high pressures 0.7-8.0 GPa with a cooling rate ~ 103 K s−1 are presented. The supercooling of the melt was measured, and the high pressure influence on the basic parameters of the solidification process are analysed. The short-range order (SRO) structure of the amorphous alloy Cu0.85 Sn0.15 was investigated, and the radial distribution function (RDF) was calculated. It was shown that at certain (P-T) conditions some tetrahedrally bonded semiconductors can be produced in the amorphous (GaSb) or partially amorphous (ZnSe) state. For amorphous gallium antimonide (a-GaSb) Raman spectra, temperature, heat of crystallization and SRO structure were investigated. From the theoretical and experimental data one can conclude that a rapid quenching from the melt under high pressure results in a drastic disordering of the structure of the materials or even an amorphization.
TL;DR: In this article, the authors proposed that DNA breathing phenomena is the product of cooperation of two classes of solitons, and DNA breather migrates along the DNA chain with the extension of the soliton-antisoliton bound state range.
Abstract: The excitations of structural solitons and vibrational solitons exist in the DNA structure. In this paper, we propose that DNA breathing phenomena is the product of cooperation of these two classes of solitons, and DNA breather migrates along the DNA chain with the extension of the soliton-antisoliton bound state range. Furthermore, we prove that β-DNA and A-T (base pair) rich regions in the DNA molecule are DNA breathing origins. Besides, the effect of a nonlinear electric field on B-DNA Z-DNA transitions is explained by the theory of soliton and extra-electron movement. The B-DNA will be transformed into Z-DNA when a nonlinear electric field is introduced into a low-salt DNA solution containing segment poly(dG-dC)n.