bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle dynamics and mixing in the frequency driven “Kelvin cat eyes” flow
Authors: Tsega Yamlak , Michaelides Efstathios E. , Eschenazi Elia V.
Published: July 2002

The “Kelvin cat eyes” stream function is used as a simple fluid flow model to study particle dynamics, mixing and transport in a two-dimensional time-dependent flow field. Lagrangian formulation is used to describe the motion of small spherical particles present in the flow. Individual particle trajectories, under the influence of various flow parameters are studied. The equation describing the motion of these particles constitutes a set of first-order nonlinear differential equations describing a dynamical system. The time-dependent Eulerian flow field is studied as a nonintegrable Hamiltonian system in order to get insight into the underlying nonlinear properties of the system, which directly influence its complicated transport and mixing behavior. Chaotic advection (Lagrangian turbulence) was observed for heavy particles (high Stokes numbers) while no stochastic behavior was observed for light particles. The introduction of perturbation had only a limited effect on individual particle trajectories. However, the introduction of perturbation caused a shrinking of the phase space where bounded stochastic or quasi-periodic motion occurs. This phenomenon can lead to a better understanding of the link between the behavior of the underlying flow in the Hamiltonian formulation and the dynamics of the passive scalars in the Lagrangian description. The Eulerian flow field itself was found to behave chaotically under the influence of a periodic perturbation, because the stable and unstable manifolds associated with neighboring hyperbolic points intersected. This coincides with the better mixing of the fluid. Stochasticity was also discovered close to the periodic points of the system using Poincaré maps. Mixing and transport properties are analyzed as a function of the perturbation frequency.
Surface electronic structure of plasma-treated indium tin oxides
Authors: Yu H. Y. , Feng X. D. , Grozea D. , Lu Z. H. , Sodhi R. N. S. , Hor A-M. , Aziz H.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) has been used to study the electronic structures of indium tin oxide (ITO) surfaces treated by O+, Ar+, and NHx+ plasmas. The XPS data show that there is a significant change in core level energies (In 3d5/2 O 1s, and Sn 3d5/2), in donor concentration (Sn4+), in valence band maximums (VBM), and in work functions on ITO surfaces being treated by O+ and NHx+ plasmas, compared with that of virgin and Ar+ plasma treated surfaces. Based on these experimental data, a surface band-bending theory is proposed. The theory explains that when Fermi energy of the plasma-treated surface is shifted towards the middle of the band gap: core levels will shift their energies to lower binding energies, VBM will bend upward, and work function will increase, as observed.
Nanoscale radiative heat transfer between a small particle and a plane surface
Authors: Mulet Jean-Philippe , Joulain Karl , Carminati Rémi , Greffet Jean-Jacques
Published: July 2002

We study the radiative heat transfer between a small dielectric particle, considered as a point-like dipole, and a surface. In the framework of electrodynamics and using the fluctuation-dissipation theorem, we can evaluate the energy exchange in the near field, which is dominated by the contribution of tunneling waves. The transfer is enhanced by several orders of magnitude if the surface or the particle can support resonant surface waves. An application to local heating is discussed.
Directional fractional kinetics
Authors: Weitzner Harold , Zaslavsky George M.
Published: July 2002

Kinetic equations used to describe systems with dynamical chaos may contain fractional derivatives of an order α in space and β in time in order to represent processes of stickiness, intermittency, and so on. We demonstrate for a simple example that the kinetics is anisotropic not only in the angular dependence of the diffusion constant, but also in the angular dependence of the exponents α and β. A theory of such kinetic processes has been developed on the basis of integral representation and asymptotic solutions for different cases have been obtained. The results show the existence of self-similar solutions as well as possible logarithmic deviations.
Non-Abelian Born–Infeld and kappa-symmetry
Authors: Bergshoeff E. A. , de Roo M. , Sevrin A.
Published: July 2002

We define an iterative procedure to obtain a non-Abelian generalization of the Born–Infeld action. This construction is made possible by the use of the severe restrictions imposed by kappa-symmetry. In this paper we will present all bosonic terms in the action up to terms quartic in the Yang–Mills field strength and all fermion bilinear terms up to terms cubic in the field strength. Already at this order the fermionic terms do not satisfy the symmetric trace-prescription.
Polarization-selective third-order spectroscopy of coupled vibronic states
Authors: Golonzka O. , Tokmakoff A.
Published: July 2002

The orientational contribution to the third-order nonlinear response of coupled vibrational or electronic states is evaluated considering the dipole orientations of these states and molecular orientational relaxation. A general formalism is developed for calculating the third-order orientational response function for processes involving up to four distinct transition dipole moments, which are fixed in a molecular frame that is free to diffusively reorient. In particular, all tensor components of the third-order orientational response function for two coupled vibronic states were calculated as a function of the projection angle between the transition dipole moments of the fundamental transitions. The results are discussed in conjunction with specific third-order infrared nonlinear experiments on coupled vibrational systems: pump–probe, dispersed two-dimensional pump–probe, and two-dimensional photon-echo experiments. The anisotropy of the nonlinear signal and ratios of independent tensor components of the response, are shown to depend on the projection angle between the transition dipole moments and therefore can be used to access structural information about molecular systems.
Amplitude truncation of Gaussian 1/fα noises: Results and problems
Authors: Gingl Zoltán , Ishioka Shunya , Choi Donghak , Fuchikami Nobuko
Published: July 2002

An interesting property of Gaussian 1/f noise was found experimentally a few years ago: The amplitude truncation does not change the power spectral density of the noise under rather general conditions. Here we present a brief theoretical derivation of this invariant property of band-limited Gaussian 1/f noise and include 1/fα noises also with 0⩽α<2. It is shown that when α⩽1, a transformation of keeping only the sign of the zero-mean 1/fα noise does not alter the shape of the spectral density. The theoretical results are extended to truncation levels differing significantly from the mean value. Numerical simulation results are also presented to draw attention to unsolved problems of amplitude truncation using asymmetric levels.
Low-resistance and nonalloyed ohmic contacts to plasma treated ZnO
Authors: Lee Ji-Myon , Kim Kyoung-Kook , Park Seong-Ju , Choi Won-Kook
Published: July 2002

Low-resistance and nonalloyed ohmic contacts to epitaxially grown n-ZnO were formed by exposing n-ZnO to an inductively coupled hydrogen and an argon plasma. Using Ti/Au, the specific contact resistivity of the ohmic contact was drastically decreased from 7.3×10−3 to 4.3×10−5 Ω cm2 by hydrogen plasma treatment. The photoluminescence spectrum of the hydrogen plasma treated ZnO showed a large enhancement in band-edge emission and a strong suppression in deep-level emission. These results suggest that the low contact resistivity can be attributed to an increase in carrier concentration on the ZnO surface. The specific contact resistivity of the Ar-plasma treated sample was also decreased to 5.0×10−4 Ω cm2, presumably due to the formation of shallow donor on the ZnO surface by ion bombardment.
Assignment of the excess absorption underlying the Schumann–Runge bands of molecular oxygen
Authors: Lewis B. R. , Gibson S. T. , Roberts E. H.
Published: July 2002

A long-standing problem, pertaining to the origin of the excess absorption found experimentally to underlie the high-vibrational Schumann–Runge bands of molecular oxygen, is resolved. Through new calculations, with parameter sets based on recently obtained experimental information, it is shown that the excess absorption arises from transitions into the lowest valence states of Πu3 and Πug symmetry.
Indium tin oxide thin films grown on flexible plastic substrates by pulsed-laser deposition for organic light-emitting diodes
Authors: Kim H. , Horwitz J. S. , Kushto G. P. , Kafafi Z. H. , Chrisey D. B.
Published: July 2002

Transparent conducting indium tin oxide (ITO) thin films were grown by pulsed laser deposition (PLD) on flexible polyethylene terephthalate (PET) substrates. The structural, electrical, and optical properties of these films were investigated as a function of substrate deposition temperature and background gas pressure. ITO films (200 nm thick), deposited by PLD on PET at 25 °C and 45 mTorr of oxygen, exhibit high optical transparency (∼87%) in the visible (400–700 nm) with a low electrical resistivity of 7×10−4 Ω cm. ITO films grown by PLD on PET were used as the anode contact in organic light-emitting devices. A luminous power efficiency of ∼1.6 lm/W was achieved at 100 cd/m2, slightly higher than that (∼1.5 lm/W) measured for the control device based on a sputter-deposited ITO on glass.
An individual particle approach to noise in pseudomorphic heterojunction field effect transistors
Authors: Moglestue C.
Published: July 2002

The fluctuating steady state current through a pseudomorphic heterojunction field-effect transistor at a typical working point has been calculated by means of the Monte Carlo particle model. This method was chosen because the noise it yields reflects the physical processes in the transistor itself. The pattern of the fluctuating current inside the transistor was mapped at regular intervals of time. The temporal fluctuations in the drain current from the mean were correlated to these maps and it was found that the observed deviations from its mean originate between the gate and the drain.
A simple lattice model for phase transitions in block copolymers
Authors: Aranovich G. L. , Donohue M. D.
Published: July 2002

Phase transitions in copolymers are considered in terms of configurational probabilities. It is shown that ordering transitions in block copolymers appear as a stepped increase in the probability of a dominating configuration and a simultaneous decrease of the probabilities for other configurations.
Probing hydrogen bond network formation in anion–water clusters through high energy collision experiments
Authors: Jørgensen Palle , Forster James S. , Hvelplund Preben , Brøndsted Nielsen Steen , Tomita Shigeo
Published: July 2002

In high-energy collisions (50 keV in the laboratory system) between anion–water clusters [X−⋅(H2O)n, X−=Cl−, CN−, O2−, NO2−, NO3−; n=1–6] and argon, H3O+ is formed with an abundance that is determined by the cluster size—the larger the cluster, the more H3O+. The mechanism for H3O+ formation is believed to be a nearly vertical ionization process (two-electron stripping) followed by an exothermic intracluster hydrogen transfer reaction between an ionized water and a neutral water. The abundance of H3O+ can be used as a probe to determine how extended the water hydrogen bond network is in the initial anion–water cluster and to distinguish between surface solvation (water network preserved) and internal solvation (water network broken). In this work, it is demonstrated that in the hydration of hexacyanoplatinate(IV) dianion complexes, surface solvation is important despite the large number of available water binding sites; however, the competition between a cyanide-bound water and a “naked” cyanide ligand for a water molecule favors the cyanide-bound water because of the splitting of the excess charges between six ligands (between −1/3 and −1 charge at each ligand on average). We also investigate anion–methanol clusters in which the hydrogen bond network is less extended with the result of a less abundant oxonium ion compared to the hydronium ion from similar size water clusters.
Vertical and lateral GaN rectifiers on free-standing GaN substrates
Authors: Zhang A. P. , Johnson J. W. , Luo B. , Ren F. , Pearton S. J. , Park S. S. , Park Y. J. , Chyi J.-I.
Published: July 2002

Edge-terminated Schottky rectifiers fabricated on quasibulk GaN substrates showed a strong dependence of reverse breakdown voltage VB on contact dimension and on rectifier geometry (lateral versus vertical). For small diameter (75 μm) Schottky contacts, VB measured in the vertical geometry was ∼700 V, with an on-state resistance (RON) of 3 mΩ cm2, producing a figure-of-merit VB2/RON of 162.8 MW cm−2. Measured in the lateral geometry, these same rectifiers had VB of ∼250 V, RON of 1.7 mΩ cm2 and figure-of-merit 36.5 MW cm−2. The forward turn-on voltage (VF) was ∼1.8 V (defined at a current density of 100 A cm−2), producing VB/VF ratios of 139–389. In very large diameter (∼5 mm) rectifiers, VB dropped to ∼6 V, but forward currents up to 500 mA were obtained in dc measurements.
Effects of step-graded AlxGa1−xN interlayer on properties of GaN grown on Si(111) using ultrahigh vacuum chemical vapor deposition
Authors: Kim Min-Ho , Do Young-Gu , Kang Hyon Chol , Noh Do Young , Park Seong-Ju
Published: July 2002

We report the growth of high-quality GaN on a Si(111) substrate using a five step-graded AlxGa1−xN (x=0.87–0.07) interlayer between GaN epilayer and AlN buffer layer by ultrahigh vacuum chemical vapor deposition. The crack density and the surface roughness of the GaN layer grown on the graded AlxGa1−xN interlayer were substantially reduced, compared to those of GaN grown on an AlN buffer layer. Significant improvement in the structural and optical properties of the GaN layer was also achieved by the use of a graded interlayer. These results are attributed to the decrease of the lattice mismatch between GaN and AlN layer, and the reduction of the thermal stress by the graded interlayer.
A silicon strip detector system for high resolution particle tracking in turbulence
Authors: Voth Greg A. , Porta Arthur La , Crawford Alice M. , Bodenschatz Eberhard , Ward Curt , Alexander Jim
Published: July 2002

We describe a high speed imaging system that is used to track tracer particles in highly turbulent flows. The system uses silicon strip detectors designed for high energy physics experiments and is capable of reading two detectors at a frame rate of 70 kHz. Each detector contains 512 strips and measures a one-dimensional projection of the light striking it. The position measurements from this system have a dynamic range of 6400:1. Extensions to higher frame rates and more detectors are possible. We describe the detectors, readout system, supporting systems, and give an evaluation of the measurement accuracy.
Rectification and shift currents in GaAs
Authors: Côté D. , Laman N. , van Driel H. M.
Published: July 2002

We observe second-order rectification and shift currents in GaAs at 295 K using 150 fs pulses at 1.55 and 0.775 μm, respectively. For the same low pump intensity, 100 MW cm−2, the shift current density is 570 times larger than the rectification current density. At high intensity, the shift current is strongly affected by carrier screening and dephasing and is in phase quadrature with the rectification current. A maximum shift current density of 60 kA cm−2 is inferred for a pump intensity of 500 MW cm−2.
Enhanced magnetoresistance in granular La2/3Ca1/3MnO3/ polymer composites
Authors: Huang Yun-Hui , Chen Xing , Wang Zhe-Ming , Liao Chun-Sheng , Yan Chun-Hua , Zhao Hong-Wu , Shen Bao-Gen
Published: July 2002

Polymer embedded granular composites, La2/3Ca1/3MnO3/polyparaphenylene (LCMO)1−x(PPP)x (x is the weight fraction of PPP), were prepared and their magnetoresistance (MR) properties were investigated. A significant enhancement in MR is observed for the composites especially in the low temperature range. The MR reaches the maximum at x=0.1 when T=5 K and at x=0.2 when T=260 K. We argue that such enhancement in MR is attributed to the enhanced spin-polarized tunneling, which is manipulated by the spin disorder at the LCMO surfaces caused by PPP.
Evidence for nonlinear macroscopic polarization in III–V nitride alloy heterostructures
Authors: Fiorentini Vincenzo , Bernardini Fabio , Ambacher Oliver
Published: July 2002

We provide explicit rules to calculate the nonlinear polarization for nitride alloys of arbitrary composition, and hence, the bound sheet charge induced by polarization discontinuity at the interfaces between different alloy and binary (epi)layers. We then present experimental results and simulations of polarization-related quantities in selected nitride-alloy-based heterostructure systems. The agreement of experiment and simulation, also in comparison to previous approaches, strongly suggests that the macroscopic polarization of nitride alloys is indeed nonlinear as a function of composition.
Monte Carlo calculation of two-dimensional electron dynamics in GaN–AlGaN heterostructures
Authors: Yu Tsung-Hsing , Brennan Kevin F.
Published: July 2002

We present detailed Monte Carlo based calculations of the electron dynamics in GaN–AlGaN heterostructures in the presence of strain polarization fields. The model consists of a fully numerical self-consistent solution of the Schrödinger–Poisson equation with a Monte Carlo transport model. The two-dimensional sub-band energies, wave functions and carrier scattering mechanisms are computed numerically and included within a Monte Carlo simulation. The electron energy, steady-state and transient drift velocity and band occupancy are calculated as a function of electric field for different AlGaN–GaN heterostructure compositions. The effect of piezoelectrically induced strain fields on the transport dynamics is examined. A field dependent mobility model is also developed from the Monte Carlo results.
Theory of electrochemical pattern formation
Authors: Christoph J. , Eiswirth M.
Published: July 2002

The spatial coupling in electrochemical systems is mediated by ion migration under the influence of the electric field. Since field effects spread very rapidly, every point of an electrode can communicate with every other one practically instantaneously through migration coupling. Based on mathematical potential theory we present the derivation of a generally applicable reaction–migration equation, which describes the coupling via an integral over the whole electrode area. The corresponding coupling function depends only on the geometry of the electrode setup and has been computed for commonly used electrode shapes (such as ring, disk, ribbon or rectangle). The pattern formation observed in electrochemical systems in the bistable, excitable and oscillatory regime can be reproduced in computer simulations, and the types of patterns occurring under different geometries can be rationalized.
Small-scale structure of nonlinearly interacting species advected by chaotic flows
Authors: Hernández-Garcı́a Emilio , López Cristóbal , Neufeld Zoltán
Published: July 2002

We study the spatial patterns formed by interacting biological populations or reacting chemicals under the influence of chaotic flows. Multiple species and nonlinear interactions are explicitly considered, as well as cases of smooth and nonsmooth forcing sources. The small-scale structure can be obtained in terms of characteristic Lyapunov exponents of the flow and of the chemical dynamics. Different kinds of morphological transitions are identified. Numerical results from a three-component plankton dynamics model support the theory, and they serve also to illustrate the influence of asymmetric couplings.
Electrical activation of implanted phosphorus ions in [0001]- and [11–20]-oriented 4H-SiC
Authors: Schmid F. , Laube M. , Pensl G. , Wagner G. , Maier M.
Published: July 2002

Aluminum-doped 4H-SiC epilayers with [0001]- or [11–20]-oriented faces were implanted with phosphorus and subsequently annealed in a temperature range of 1550–1700 °C. The electrical activation of phosphorus ions was studied by Hall effect investigations. Identical free electron concentrations are observed at high temperatures in both types of SiC samples indicating that the electrical activation of implanted phosphorus ions is independent of the orientation of the wafers. The compensation generated by the phosphorus implantation is greater in 4H-SiC samples with (0001) face. Phosphorus donor concentrations above 1020 cm−3 could be activated and an extremely low sheet resistance of 29 Ω/□ was determined in the implanted 4H-SiC layer.
Optimization of a Langmuir–Taylor detector for lithium
Authors: Delhuille R. , Miffre A. , Lavallette E. , Büchner M. , Rizzo C. , Trénec G. , Vigué J. , Loesch H. J. , Gauyacq J. P.
Published: July 2002

This article describes the construction and optimization of a Langmuir–Taylor detector for lithium, using a rhenium ribbon. The absolute detection probability of this very sensitive detector is measured and the dependence of this probability with oxygen pressure and surface temperature is studied. Sources of background signal and their minimization are also discussed in detail. A comparison between our data concerning the response time of the detector and literature values is given. A theoretical analysis has been made: this analysis supports the validity of the Saha–Langmuir law to relate the ionization probability to the work function. Finally, the rapid variations of the work function with oxygen pressure and temperature are explained by a chemical equilibrium model.
Noise-induced enhancement of chemical reactions in nonlinear flows
Authors: Liu Zonghua , Lai Ying-Cheng , Lopez Juan M.
Published: July 2002

Motivated by the problem of ozone production in atmospheres of urban areas, we consider chemical reactions of the general type: A+B→2C, in idealized two-dimensional nonlinear flows that can generate Lagrangian chaos. Our aims differ from those in the existing work in that we address the role of transient chaos versus sustained chaos and, more importantly, we investigate the influence of noise. We find that noise can significantly enhance the chemical reaction in a resonancelike manner where the product of the reaction becomes maximum at some optimal noise level. We also argue that chaos may not be a necessary condition for the observed resonances. A physical theory is formulated to understand the resonant behavior.
Arnold’s method for asymptotic stability of steady inviscid incompressible flow through a fixed domain with permeable boundary
Authors: Morgulis Andrey , Yudovich Victor
Published: July 2002

The flow of an ideal fluid in a domain with a permeable boundary may be asymptotically stable. Here the permeability means that the fluid can flow into and out of the domain through some parts of the boundary. This permeability is a principal reason for the asymptotic stability. Indeed, the well-known conservation laws make the asymptotic stability of an inviscid flow impossible, if the usual no flux condition on a rigid wall (or on a free boundary) is employed. We study the stability problem using the direct Lyapunov method in the Arnold’s form. We prove the linear and nonlinear Lyapunov stability of a two-dimensional flow through a domain with a permeable boundary under Arnold’s conditions. Under certain additional conditions, we amplify the linear result and prove the exponential decay of small disturbances. Here we employ the plan of the proof of the Barbashin–Krasovskiy theorem, established originally only for systems with a finite number of degrees of freedom.
Gallium vacancy and the residual acceptor in undoped GaSb studied by positron lifetime spectroscopy and photoluminescence
Authors: Ling C. C. , Mui W. K. , Lam C. H. , Beling C. D. , Fung S. , Lui M. K. , Cheah K. W. , Li K. F. , Zhao Y. W. , Gong M.
Published: July 2002

Positron lifetime, photoluminescence (PL), and Hall measurements were performed to study undoped p-type gallium antimonide materials. A 314 ps positron lifetime component was attributed to Ga vacancy (VGa) related defect. Isochronal annealing studies showed at 300 °C annealing, the 314 ps positron lifetime component and the two observed PL signals (777 and 797 meV) disappeared, which gave clear and strong evidence for their correlation. However, the hole concentration (∼2×1017 cm−3) was observed to be independent of the annealing temperature. Although the residual acceptor is generally related to the VGa defect, at least for cases with annealing temperatures above 300 °C, VGa is not the acceptor responsible for the p-type conduction.
Laboratory modeling of the early stage of a tropical cyclone
Authors: Zimin V. D. , Startsev S. E. , Shǎdurov V. G. , Moiseev S. S.
Published: July 2002

Laboratory experiments have been carried out on natural convection in a rotating layer of liquid heated from below. A distinguishing feature of these experiments is an excellent thermal insulation of the layer boundaries. As a result, large-scale convection structures form. Laboratory analogs of the early stages of development of tropical cyclones have been obtained.
Local structure of turbulence in flows with large Reynolds numbers
Authors: Praskovsky A. A.
Published: July 2002

Results are reported on an experimental investigation of the characteristics of fine-scale pulsations of the velocity in several shear flows (mixing layer, boundary layer, planar, axially symmetric, and spatial wakes, and in the return channel of a large wind tunnel) in an interval of definite Reynolds numbers Rλ ≊ 70–3000 with respect to the Taylor microscale λ. The characteristic scales of most of the studied flows are quite large, and the integral scale of the turbulence reaches 5 m. The apparatus had a high resolving power−the ratio of the hot-wire length to the Kolmogorov scale was varied in the range 0.8–2.5. It is shown that the Kolmogorov constant C in the ‘‘two thirds’’ law and the constants Cε and μ in the energy-dissipation correlation function are not universal and have a systematic dependence on the coefficient of external intermittency. The same constants determined in a completely turbulent fluid are universal within the errors of the measurements.
Nonlinear dynamics of physiological function and control
Authors: Glass Leon
Published: July 2002

Complex rhythms are observed in the physiological systems that control and carry out vital bodily functions. Theoretical approaches to analyze the physiological systems include control theory and computation theory. Complementary to these approaches is nonlinear dynamics, which offers ways to classify both normal and abnormal dynamics, and to analyze bifurcations occurring in physiological dynamics.
Bifurcations of the trajectories at the saddle level in a Hamiltonian system generated by two coupled Schrödinger equations
Authors: Eleonsky V. M. , Korolev V. G. , Kulagin N. E. , Shil’nikov L. P.
Published: July 2002

Bifurcations of the complex homoclinic loops of an equilibrium saddle point in a Hamiltonian dynamical system with two degrees of freedom are studied. It arises to pick out the stationary solutions in a system of two coupled nonlinear Schrödinger equations. Their relation to bifurcations of hyperbolic and elliptic periodic orbits at the saddle level is studied for varying structural parameters of the system. Series of complex loops are described whose existence is related to periodic orbits.
The periodically kicked quantum spin
Authors: Parmenter R. H. , Yu L. Y.
Published: July 2002

It is shown that the same kind of deterministic chaos that occurs in classical systems can occur in certain quantum mechanical, many-body systems. The example of the physical realization of the periodically kicked quantum spin (PKQS) is considered in detail. The quantum mechanical equations of motion for this system can be converted into the three-dimensional PKQS map, which exhibits deterministic chaos and Arnold diffusion. Although the case of quantum spin s= 1/2 is assumed, it is shown that the same map results for s=1 (but not for s≥3/2), and for a suitably chosen classical particle with orbital angular momentum. A simple generalization of the PKQS model gives rise to stochastic webs on the surface of the unit sphere very similar to the Zaslavsky stochastic webs in a plane.
Validity of the semiclassical periodic orbit approximation in the two- and three-disk problems
Authors: Wirzba A.
Published: July 2002

The high-lying resonances in the quantum mechanical scattering problem of a point particle from two or three equally sized (and spaced) circular hard disks in the two-dimensional plane are predicted quite well by the classical cycle expansion. There are, however, noticeable deviations for the lowest resonances. Therefore, the leading corrections from creeping paths to the cycle expansion in the two-disk scattering problem are constructed. Generalizations to the three-disk problem are indicated. The size of the corrections are estimated. They are shown to be too small to account for the deviations mentioned above. Finally, arguments are given that, for the two- and three-disk problem, the semiclassical predictions of the low-lying resonance poles are bound to fail.
The evolution of nonlinear resonant oscillations in closed tubes: Solution of the standard mapping
Authors: Cox Edward A. , Mortell Michael P.
Published: July 2002

The concern of this paper is the evolution of small-amplitude resonant oscillations of an inviscid gas in a closed tube. The evolution of the oscillations of the gas generated at and near the fundamental frequency and half the fundamental frequency, where experiment shows that shocks are a feature of the final periodic motion, is examined. The basis for the analysis of this nonlinear initial value, boundary value problem on a semi-infinite strip is the Dissipative Standard Map. Since the purpose is to elucidate how the initial rest state of the gas evolves to the final periodic state, the focus of the analysis is on how a prescribed initial curve is mapped, under the Dissipative Standard Map, onto an invariant curve. The method used is to approximate the Dissipative Standard Map, in the small rate limit, by the partial differential equation appropriate to the resonance in question.
Quantum chaos of atoms in a resonant cavity
Authors: Berman G. P. , Bulgakov E. N. , Zaslavsky G. M.
Published: July 2002

A system of atoms interacting with a radiation field in a resonant cavity is studied under conditions when the dynamics in the classical limit is stochastic. This situation is called quantum chaos. Equations of motion are obtained for the quantum-mechanical expectation values which take into account the quantum correlation functions. It is shown that in a situation corresponding to quantum chaos, the quantum corrections grow exponentially, making the evolution of the system essentially quantal after a certain time τℏ has elapsed. Analytical and numerical analysis show that in this regime the time τℏ obeys the logarithmic law τℏ∼ln N (N is the number of atoms), and not the law τℏ∼Nα (α is a certain constant of order unity), as would be the case in the absence of chaos.
A nonlinear dynamical model for atmospheric boundary layer turbulence
Authors: Zheng Zuguang , Liu Shida
Published: July 2002

Using the qualitative theory of nonlinear dynamical systems and the ergodic theory of chaos and strange attractors, we study a truncated-spectrum model of dynamical equations of the atmosphere. In the parameter plane (Re, Ri), the atmospheric motion states can be divided into four regions: O (basic), P (periodic), T (turbulent or chaotic), and T-P (transition of T and P). We analyze the routes to turbulence during the day and at night. Finally, we discuss the physical aspects of the occurrence of turbulence.
Dynamics of particles in the steady flows of an inviscid fluid
Authors: Druzhinin O. A. , Ostrovsky L. A. , Stepanyants Yu. A.
Published: July 2002

Advection of small particles with inertia in two-dimensional ideal flows is studied both numerically and analytically. It is assumed that the flow disturbance around the particle corresponds to a potential dipole, so that the motion is driven by pressure gradient, inertial, and added-mass forces. It is found that in general the motion is nonintegrable, but particular exact solutions can be obtained. The problem is then studied for the cases of axisymmetric flow, when the motion proves to be completely integrable, and of a cellular flow, for which both regular and stochastic (bounded and unbounded) trajectories are calculated. In the latter case, the unbounded stochastic motion is of Brownian-like character, and the results derived show that the particle dispersion process is generally anomalous.
Transient chaos in room acoustics
Authors: Mortessagne Fabrice , Legrand Olivier , Sornette Didier
Published: July 2002

The decay of sound in an auditorium due to absorption is central to the theory and practice of room acoustics. Within geometrical acoustics, this problem involves the partial trapping of chaotic ray trajectories in billiards, hence transient chaos. We first present a theoretical and numerical analysis of the decay of rays in 2-D chaotic billiards (2-D room acoustic models) and show that the existence of fluctuations (in the mean-free path and in the rate of phase space exploration) leads to modifications from the standard statistical theory. An ergodic wave theory of room acoustics based on a wave formulation is then discussed and tested by direct numerical calculations of the eigenmodes in 2-D billiards. Finally, we present a semiclassical calculation of the acoustic Green’s functions in the time domain, based on a summation over rays, viewed as generalized wave impulses, and successfully compare its predictions with a direct numerical integration of the wave equation. This formalism provides a framework to link the geometrical ray description to the ergodic wave theory.
Chaotic electronic scattering with He+
Authors: Yuan Jian-Min , Gu Yan
Published: July 2002

We investigate classical electronic collisions with a He+ ion. Scattering functions, such as the scattering angle, collisional time, or energy of the outgoing electron, all exhibit an interesting hierarchial self-similar structure, which can be interpreted in terms of the indefinite number of electronic returns to the vicinity of the nucleus, encounters between electrons, and Keplerian excursions of electrons during the collisional processes. Based on this mechanism a binary coding is introduced to organize the dynamics of this three-body system and to provide an understanding of the self-similarity among generations of scale magnification, which yields escape rates that vary with the sectional cut into the parameter space. The self-similarity displayed within a single generation, on the other hand, can be simply tied to the periods of the two independent electronic excursions. The physical interpretation and the symbolic dynamics introduced here are generally useful for three-body collisional systems, including atomic, molecular, or stellar collisions.
Observing a codimension-two heteroclinic bifurcation
Authors: Tokunaga Ryuji , Abe Yasushi , Matsumoto Takashi
Published: July 2002

This paper reports experimental observations of codimension-two heteroclinic bifurcations in an autonomous third-order electrical circuit. The paper also reports confirmations by computer simulations. In the laboratory experiments, a pair of programmable resistors are used in order to adjust two bifurcation parameters. In the associated two-parameter space, several codimension-one bifurcation sets are experimentally measured to capture codimension-two bifurcation structures. All of these bifurcation sets are numerically confirmed by exact bifurcation equations which are derived from piecewise-linear circuit dynamics.
3-D spatial chaos in the elastica and the spinning top: Kirchhoff analogy
Authors: Davies M. A. , Moon F. C.
Published: July 2002

The existence of spatially chaotic deformations in an elastica and the analogous motions of a free spinning rigid body, an extension of the problem originally examined by Kirchhoff are investigated. It is shown that a spatially periodic variation in cross sectional area of the elastica results in spatially complex deformation patterns. The governing equations for the elastica were numerically integrated and Poincaré maps were created for a number of different initial conditions. In addition, three dimensional computer images of the twisted elastica were generated to illustrate periodic, quasiperiodic, and stochastic deformation patterns in space. These pictures clearly show the existence of spatially chaotic deformations with stunning complexity. This finding is relevant to a wide variety of fields in which coiled structures are important, from the modeling of DNA chains to video and audio tape dynamics to the design of deployable space structures.
Ray dynamics of the propagation of sound in nonuniform moving media
Authors: Abdullaev S. S.
Published: July 2002

This paper presents a new ray theory for the propagation of sound waves in nonuniformly moving media. It is found that the ray equations in weakly inhomogeneous and slowly moving media are analogous to the equations of motion of charged particles in nonuniform electric and magnetic fields. The adiabatic approximation is used to study the problem of the propagation of sound rays in a model of near-ocean-bottom waveguide with horizontal flow and slowly varying parameters along the direction of propagation of the wave. A general formula is derived that describes the transverse displacement of the trajectory of the ray relative to the direction of propagation of the wave.
Statistical properties of chaos demonstrated in a class of one-dimensional maps
Authors: Csordás András , Györgyi Géza , Szépfalusy Péter , Tél Tamás
Published: July 2002

One-dimensional maps with complete grammar are investigated in both permanent and transient chaotic cases. The discussion focuses on statistical characteristics such as Lyapunov exponent, generalized entropies and dimensions, free energies, and their finite size corrections. Our approach is based on the eigenvalue problem of generalized Frobenius–Perron operators, which are treated numerically as well as by perturbative and other analytical methods. The examples include the universal chaos function relevant near the period doubling threshold. Special emphasis is put on the entropies and their decay rates because of their invariance under the most general class of coordinate changes. Phase-transition-like phenomena at the border state of chaos due to intermittency and super instability are presented.
Attractor vicinity decay for a cellular automaton
Authors: Crutchfield James P. , Hanson James E.
Published: July 2002

The temporal decay of an attractor’s vicinity for a domain-wall dominated cellular automaton (CA) is studied. Using selected initial pattern ensembles, state space structures in this high-dimensional nonlinear spatial system can be identified via the resulting decay to its attractors. Considered over a range of lattice sizes, the decay behavior falls into three main classes, each of which shows a characteristic profile. The first consists of even-size lattices showing a decelerating decay to small nonattracted ensemble fractions. The second class, also for even lattices, is a catastrophic decay to very small or vanishing nonattracted fractions. The third class also shows catastrophic decay and contains all odd-size lattices. Stochastic models are constructed that mimic the behavior of typical lattices throughout their evolution until finite-size effects appear. Weak additive noise causes all states on all lattices to fall into the attractor. In the end we find it overwhelmingly likely that the recently proposed attractor-basin portrait captures the CA’s qualitative dynamics.
Quasi-two-dimensional hydrodynamics and problems of two-dimensional turbulence
Authors: Danilov S. D. , Dolzhanskii F. V. , Krymov V. A.
Published: July 2002

The principal problems of quasi-two-dimensional (Q2-D) hydrodynamics are discussed. Accounting for Q2-D flow vertical structure is shown to eliminate ‘‘genetic’’ defects of the formal 2-D idealization of 3-D Navier–Stokes equations and allows under certain conditions to formulate corrected 2-D motion equations which adequately describe real hydrodynamic processes. The applicability of the approach is directly verified in laboratory experiments. Special attention is paid to the problem of 2-D turbulence. Its simulation on the basis of ordinary 2-D equations is unjustified because of the absence of the external Kolmogorov dissipation scale and reverse spectral energy flux. An alternative approach allows one to introduce the natural external scale of 2-D turbulence which depends only on physical properties of the system under consideration and to formulate the conditions under which the large scale vortex dynamics is expected to be universal at large Reynolds number, i.e., to be independent on the size and form of integration domain and lateral boundary conditions.
From oscillations to excitability: A case study in spatially extended systems
Authors: Müller S. C. , Coullet P. , Walgraef D.
Published: July 2002

This volume is devoted to the presentation of the main contributions to the workshop ‘‘From oscillations to excitability: A case study in spatially extended systems,’’ organized by the authors in Nice in June 1993. It gives an overview of the current research on spatiotemporal patterns in a wide range of systems that display self-oscillatory or excitable behavior. It tries to give a better understanding of the transition from the oscillatory to the excitable regime and of its effect on the properties of spiral waves, and to fill the gap between the theories and concepts used to describe both regimes in the so-called ‘‘active media.’’
Mechanisms of target and spiral wave propagation in single cells
Authors: Babloyantz A.
Published: July 2002

Target and spiral wave propagation have been observed in single cells such as myocites. Moreover, in the same cells, transition from target waves to planar waves or from the latter to spiral waves was also observed. Considering an oscillatory medium described by the Ginzburg–Landau equation we suggest that such phenomena could be explained if cell nuclei and cell organelles are considered as obstacles in a small bounded medium. We discuss the role of cell geometry as well as the phenomenon of reentry at the cellular level.
High-frequency instability of wave fronts
Authors: Agladze K. I.
Published: July 2002

Experimental evidence is presented that a lateral instability of a wave front, as described earlier in a chemically active medium with the Belousov–Zhabotinsky reaction with decreased excitability, can also occur in a medium with any degree of excitability provided that a high-frequency wave train travels through the medium. The interaction of chemical waves with the boundary of the medium can result in the appearance of wave breaks and spiral waves.
Stability and bifurcations of a stationary state for an impact oscillator
Authors: Aidanpää Jan-Olov , Shen Hayley H. , Gupta Ram B.
Published: July 2002

The motion of a vibroimpacting one-degree-of-freedom model is analyzed. This model is motivated by the behavior of a shearing granular material, in which a transitional phenomenon is observed as the concentration of the grains decreases. This transition changes the motion of a granular assembly from an orderly shearing between two blocks sandwiching a single layer of grains to a chaotic shear flow of the whole granular mass. The model consists of a mass-spring-dashpot assembly that bounces between two rigid walls. The walls are prescribed to move harmonically in opposite phases. For low wall frequencies or small amplitudes, the motion of the mass is damped out, and it approaches a stationary state with zero velocity and displacement. In this paper, the stability of such a state and the transition into chaos are analyzed. It is shown that the state is always changed into a saddle point after a bifurcation. For some parameter combinations, horseshoe-like structures can be observed in the Poincaré sections. Analyzing the stable and unstable manifolds of the saddle point, transversal homoclinic points are found to exist for some of these parameter combinations.
Normally attracting manifolds and periodic behavior in one-dimensional and two-dimensional coupled map lattices
Authors: Giberti Claudio , Vernia Cecilia
Published: July 2002

We consider diffusively coupled logistic maps in one- and two-dimensional lattices. We investigate periodic behaviors as the coupling parameter varies, i.e., existence and bifurcations of some periodic orbits with the largest domain of attraction. Similarity and differences between the two lattices are shown. For small coupling the periodic behavior appears to be characterized by a number of periodic orbits structured in such a way to give rise to distinct, reverse period-doubling sequences. For intermediate values of the coupling a prominent role in the dynamics is played by the presence of normally attracting manifolds that contain periodic orbits. The dynamics on these manifolds is very weakly hyperbolic, which implies long transients. A detailed investigation allows the understanding of the mechanism of their formation. A complex bifurcation is found which causes an attracting manifold to become unstable.
Distinguishing the transition to chaos in a spherical pendulum
Authors: Kana Daniel D. , Fox Douglas J.
Published: July 2002

Complex responses are studied for a spherical pendulum whose support is excited with a translational periodic motion. Governing equations are studied analytically to allow prediction of responses under various excitation conditions. Stability for certain cases of damping is predicted by means of existing analysis and compared with experimental data. Numerical time-step integration of the governing equations is developed to predict responses for various types of excitation and damping conditions. Predicted results are compared with corresponding motions measured in an experimental spherical pendulum system. A data acquisition system is included whereby detailed digitized time histories of the pendulum motion can be established and various parameters can be computed to characterize the type of motion present. Two new vector spaces are defined for describing complex responses which occur for certain specified excitation conditions. It is shown in these parameter spaces that the transition from quasiperiodic to chaotic motions can be carefully quantified in systems with very light damping. This discovery provides a convenient means for comparison of complex motions in the numerical and experimental air pendulum systems. The implications of the results are important for dynamic response in various applications, including fluid motions in satellite tanks and other nonlinear time-dependent physical processes which include very light damping.
Master-slave synchronization from the point of view of global dynamics
Authors: Tresser Charles , Worfolk Patrick A. , Bass Hyman
Published: July 2002

We present a mathematical framework for the theory of a synchronization phenomenon for dynamical systems discovered by Pecora and Carroll [Phys. Rev. Lett. 64, 821–824 (1990)]. From this perspective, we can synchronize, using a single coordinate, an open dense set of linear systems. We use our insights to synchronize nonlinear systems which were not previously recognized as being synchronizable.