bluuebunny/crossref_metadata_2025 huggingface dataset:
A neutron spin-echo study of confined water
Authors: Swenson J. , Bergman R. , Longeville S.
Published: July 2002

We have investigated the dynamics of confined water in a fully hydrated Na-vermiculite clay using the neutron spin-echo (NSE) technique. NSE measures the intermediate self-scattering function, i.e., the dynamics directly in the time domain. In the present experiments we performed measurements, in the time range 3–3000 ps and temperature ranging from 254 to 323 K, on the essentially two-dimensional water with a layer thickness corresponding to only two molecular layers. The data can be described by the Kohlrausch–Williams–Watts (KWW) stretched exponential function, probably indicating a broad distribution of relaxation times. The reason for the very stretched behavior of the intermediate self-scattering function IS(Q,t), particularly in the supercooled regime, is most likely that the water molecules have widely different local environments. Some water molecules are strongly interacting with the clay surfaces or the intercalated Na+ ions, whereas the remaining molecules are interacting only with other water molecules. The average relaxation time for the dynamics observed in the experimental time window shows a pronounced non-Arrhenius temperature dependence, typical for the main relaxation of a “fragile” liquid, and a Q-dependence in reasonable agreement with the Gaussian jump-length distribution model for translational diffusion. The high temperature non-Arrhenius behavior of the relaxation time is in contrast to previous low temperature (125–215 K) dielectric results showing an Arrhenius temperature behavior, typical for a “strong” liquid. Although the NSE and dielectric data are not probing exactly the same water dynamics, the combined results suggests that our confined water undergoes a “fragile-strong” transition somewhere in the temperature range of 215–250 K.
Fully relativistic coupled-cluster static dipole polarizabilities of the positively charged alkali ions from Li+ to 119+
Authors: Lim Ivan S. , Laerdahl Jon K. , Schwerdtfeger Peter
Published: July 2002

The static dipole polarizabilities of the positively charged alkali atoms from Li+ to 119+ (eka-Fr) were obtained from relativistic coupled-cluster theory using a scalar relativistic Douglas–Kroll Hamiltonian. Spin–orbit coupling effects were obtained from a fully relativistic four-component Dirac–Hartree–Fock scheme followed by a second-order many-body perturbation treatment to account for electron correlation. Electron correlation effects are found to be small for all ions, but become more sizable as the nuclear charge increases. Scalar relativistic effects dominate over electron correlation for Cs+, Fr+, and 119+. Spin–orbit coupling is non-negligible for the heaviest elements Fr+ and 119+, where they dominate over both electron correlation and scalar relativistic effects. Breit interactions obtained for Cs+ and Fr+ can safely be neglected. A relationship between dipole polarizabilities and second ionization potentials is established. The use of a basis set limit one-electron description and a high level treatment of electron correlation and relativistic effects makes our results the most accurate available for the stable dipole polarizabilities (1.00±0.04 a.u. for Na+, 5.52±0.04 a.u. for K+, 9.11±0.04 a.u. for Rb+, 15.8±0.1 a.u. for Cs+, 20.4±0.2 a.u. for Fr+, and 32±1 a.u. for 119+).
Heterodyne electrostatic imaging of polarization due to a surface acoustic wave
Authors: Oliver D. R. , Pu A. , Thomson D. J. , Bridges G. E.
Published: July 2002

We describe a technique that enables us to obtain a stroboscopic image of surface polarization associated with a surface acoustic wave. The surface polarization has been imaged as it travels across the exposed substrate of a surface acoustic wave filter operating at 434 MHz. The high-frequency polarization signals were recovered using a heterodyne electrostatic force scanning probe microscopy technique.
Plasma flow and plasma–wall transition in Hall thruster channel
Authors: Keidar M. , Boyd I. D. , Beilis I. I.
Published: July 2002

In this paper a model of the quasineutral plasma and the transition between the plasma and the dielectric wall in a Hall thruster channel is developed. The plasma is considered using a two-dimensional hydrodynamic approximation while the sheath in front of the dielectric surface is considered to be one dimensional and collisionless. The dielectric wall effect is taken into account by introducing an effective coefficient of the secondary electron emission (SEE), s. In order to develop a self-consistent model, the boundary parameters at the sheath edge (ion velocity and electric field) are obtained from the two-dimensional plasma bulk model. In the considered condition, i.e., ion temperature much smaller than that of electrons and significant ion acceleration in the axial direction, the presheath scale length becomes comparable to the channel width so that the plasma channel becomes an effective presheath. It is found that the radial ion velocity component at the plasma–sheath interface varies along the thruster channel from about 0.5Cs (Cs is the Bohm velocity) near the anode up to the Bohm velocity near the exit plane dependent on the SEE coefficient. In addition, the secondary electron emission significantly affects the electron temperature distribution along the channel. For instance in the case of s=0.95, the electron temperature peaks at about 16 eV, while in the case of s=0.8 it peaks at about 30 eV. The predicted electron temperature is close to that measured experimentally. The model predictions of the dependence of the current–voltage characteristic of the E×B discharge on the SEE coefficient are found to be consistent with experiment.
Identification of the stripe state of a YBa2Cu3O6+x superconductor according to optical absorption data
Authors: Eremenko V. V. , Samovarov V. N. , Vakula V. L. , Libin M. Yu. , Uyutnov S. A. , Rashkovan V. M.
Published: July 2002

The doublet structure of the electron–bimagnon absorption band with maxima at 2.145 and 2.28 eV is observed for the first time for the metallic phase of YBa2Cu3O6+x with x=0.85 (Tc=88 K). As the YBCO film cools down, the doublet band arises quite sharply near the pseudogap state at T<130 K and remains in the superconducting phase at T<Tc. In the superconducting transition region the amplitude of each doublet component increases. Comparing with data on the splitting of the neutron scattering peak in YBCO [P. Dai et al., Phys. Rev. Lett. 80, 1738 (1998)] showed that the splitting of the absorption band reflects the formation of a stripe superstructure consisting alternating dielectric and metallic quasi-one-dimensional stripes.
X-ray absorption microscopy of aqueous samples
Authors: Frazer Brad , Gilbert Benjamin , De Stasio Gelsomina
Published: July 2002

X-ray photoelectron emission microscopy (X-PEEM) is used for numerous applications in surface microchemical analysis of material science and biological specimens. We have reconfigured the MEPHISTO X-PEEM instrument that is installed at the University of Wisconsin Synchrotron Radiation Center to measure true x-ray transmission spectra by converting transmitted photons to photoelectrons via a thin photocathode layer of gold. We have also developed a method by which to introduce aqueous samples into ultrahigh vacuum. Hence x-ray spectroscopy can be performed on biologically relevant elements (such as K, Ca, etc.) in a physiological environment, i.e., in solution. More important, when coupled with X-PEEM imaging this technique may offer the unique and exciting possibility of studying living cells. We present initial x-ray absorption spectra of solutions of aqueous ionic and chelated Ca, with the aim of distinguishing bound and free ionic calcium in vivo.
Red and near-infrared photoluminescence from silica-based nanoscale materials: Experimental investigation and quantum-chemical modeling
Authors: Zyubin A. S. , Glinka Yu. D. , Mebel A. M. , Lin S. H. , Hwang L. P. , Chen Y. T.
Published: July 2002

Experimental study of room temperature photoluminescence (PL) from silica nanoparticles and mesoporous silicas induced by ultraviolet and visible laser light (λEXC=266 and 532 nm or 4.66 and 2.33 eV, respectively) reveals several well-defined PL bands in the red- and near-infrared spectral range, which are peaked at 1.905, 1.78, 1.61, 1.40, 1.27, and 1.14 eV. The relative intensities of the bands depend on the specimen heat pretreatment temperature and excitation wavelength. The band at 1.905 eV shows all conceivable characteristics of nonbridging oxygen (NBO) defects in bulk silica, so it can be assigned to the same species in nanometer-sized SiO2 fragments. The more slowly decayed 1.78-eV band was assigned to NBOs incorporated into distorted SiO4 tetrahedrons on the surface. The 1.14–1.61 eV PL bands can be observed mainly with 2.33-eV excitation for heat-pretreated specimens (Tht=873 and 1173 K) and can also be associated with NBOs. The red shift of these bands is explained in terms of formation of combined defects involving NBO as an electron acceptor and an additional point defect in NBO vicinity serving as a donor, with the electronic energy level somewhat higher than the bottom of the forbidden band gap. Using sophisticated quantum-chemical modeling [geometry optimization of model clusters containing up to 60 Si and O atoms employing two-layered integrated molecular orbital ONIOM method [I. Komaromi et al., J. Mol. Struct.: THEOCHEM 461, 1 (1999)], followed by time-dependent density functional calculations of excitation and PL energies] we have shown that combined defects including NBO and an oxygen vacancy (OV) in various positions exhibit the suitable properties (both energies and oscillator strengths) to be responsible for the observed PL bands. These combined defects are proposed to occur in extremely thin (∼1 nm) nonequilibrium substoichiometric silicon oxide (SiOx, x<2) layers. The emphasis is on the PL band shift induced by one, two, and three OVs in the nearest vicinity of NBO, and the influence of the Si–Si bond relaxation in OVs as well as the orientation of NBOs and distances between them and OVs on transition energies and oscillator strengths. The results of calculations closely match the PL peaks observed. Since silicon nanoscale materials are typically covered by nonequilibrium substoichiometric passivating oxide layers as well, our findings may also be helpful to clarify the nature of light emission from these materials.
Diagnostics of surface layer disordering using optical third harmonic generation of a circular polarized light
Authors: Yakovlev V. V. , Govorkov S. V.
Published: July 2002

A nonlinear optical technique based on a third-harmonic generation of a circular polarized light is proposed for the diagnostics of order–disorder transformations in semiconductors. Applications of this technique to study both noncentrosymmetric (GaAs) and centrosymmetric (Si) materials are demonstrated.
Proton transport via coupled surface and bulk diffusion
Authors: Georgievskii Yuri , Medvedev Emile S. , Stuchebrukhov Alexei A.
Published: July 2002

Translocation of protons across biological membranes is carried out by special membrane proteins, proton pumps. Surprisingly, the turnover rate of some proton pumps, such as cytochrome c oxidase (CcO), is higher than the bulk diffusion limit (i.e., the rate at which protons can be supplied to the entrance of the proton conducting channel via free bulk diffusion). It has been suggested that the diffusion of protons along the membrane surface that surrounds the entrance of the proton conducting channel can increase the supply of the protons and therefore explain the puzzling high turnover rates. Here we consider a phenomenological model of proton transport to a proton collecting channel. The model takes into account both the diffusion in the bulk and the coupled diffusion of protons along the membrane surface. In our model a homogeneous membrane surface, which mediates proton diffusion toward the channel entrance, is populated with protolytic groups that can exchange protons with a bulk solution. Equations which describe the coupled surface-bulk proton diffusion are derived and solved. The maximum (diffusion limited) rate at which protons can be delivered to the pump is examined. It is found that there are two regimes of surface-mediated proton transport, depending on the rate of proton exchange between the bulk and the surface. In both regimes proton transport is dominated by the contribution of surface diffusion. Due to two-dimensional character of the surface diffusion, the transport rate depends on the size of the channel entrance in a weak, logarithmic fashion. The theory also provides a simple expression for the maximum distance that a proton can migrate on the surface before it is fully equilibrated with the bulk. This result allows one to examine whether the chemiosmotic coupling between a proton source on a membrane surface, such as CcO, and a sink, such as ATP synthase, occurs via diffusion along the membrane, or involves equilibration with the bulk.
Fabrication of magnetic microfiltration systems using soft lithography
Authors: Deng Tao , Prentiss Mara , Whitesides George M.
Published: July 2002

Arrays of nickel posts were used as magnetic elements in a microfiltration device that is compatible with microfluidic systems. The combination of microtransfer molding—a soft lithography technique—and electrodeposition generated nickel posts ∼7 μm in height and ∼15 μm in diameter inside a microfluidic channel. Once magnetized by a magnetic field from an external, permanent, neodymium–iron–boron magnet, these nickel posts generated strong magnetic field gradients and efficiently trapped superparamagnetic beads moving past them in a flowing stream of water. These nickel post arrays were also used to separate magnetic beads from nonmagnetic beads.
Domain wall injection and propagation in planar Permalloy nanowires
Authors: Cowburn R. P. , Allwood D. A. , Xiong G. , Cooke M. D.
Published: July 2002

We have used high-sensitivity magneto-optics to study the magnetic switching of a single 20 μm long, 100 nm wide, 5 nm thick planar Permalloy wire made by focused ion beam milling. It is found that the switching field of the wire can be dramatically reduced by the addition of a large end pad to the wire, which serves as a domain wall injector. We show that once injected, the domain wall is able to move very freely along the wire. No measurable pinning of the domain wall was observed at a shallow kink in the middle of the length of the wire. We thus show that such wires can be considered as domain wall conduits, with many applications in magnetoelectronic devices.
Second Taylor vortex flow: Effects of radius ratio and aspect ratio
Authors: Xiao Q. , Lim T. T. , Chew Y. T.
Published: July 2002

This paper is motivated by our earlier investigation on the stability of Taylor–Couette flow in which we discovered a previously unidentified flow regime, which we refer to as “Second Taylor vortex flow” (STVF) when an inner cylinder is subjected to some critical acceleration [Lim, Chew, and Xiao, Phys. Fluids 10, 3233 (1998)]. The aim here is to explore how the STVF regime is affected by changes in radius ratio and aspect ratio. Results show that the STVF regime is sensitive to the gap size between the two cylinders, and does not exist for some radius ratios, whereas it increases with decreasing aspect ratio.
Low-stiction magnetic bearing for satellite application
Authors: Rajagopal K. R. , Sivadasan K. K.
Published: July 2002

In this article, the design and development of a low-stiction two-axis-active magnetic bearing used in the reaction wheel of a remote sensing satellite is presented. Conventional design of the magnetic circuit and improvements in the design using finite element (FE) analysis were carried out. The results of investigations carried out to bring down the stiction torque of the magnetic bearing to a very low value of less than 1×10−4 Nm are also presented. Ideally for zero stiction, the cogging between the moving and stationary parts must be zero. In a reaction wheel of the satellite, there will be a permanent magnet brushless dc motor as the drive motor. Magnetic or eddy current sensors present in the motor commutation circuit will induce cogging between the moving and stationary parts. In this work, by properly designing all subsystems, the stiction has been brought down to as low as 0.75×10−4 Nm. Test results of the developed magnetic bearing match fairly with the computed values by FE analysis.
Electronic passivation of Si(111) by Ga–Se half-sheet termination
Authors: Fritsche R. , Wisotzki E. , Islam A. B. M. O. , Thissen A. , Klein A. , Jaegermann W. , Rudolph R. , Tonti D. , Pettenkofer C.
Published: July 2002

A Si(111):GaSe van der Waals surface is prepared using sequential deposition of Ga and Se at elevated temperature on a Si(111)-7×7 surface. Surface properties were investigated by soft x-ray photoelectron spectroscopy and low-energy electron diffraction. The Si(111)-1×1:GaSe surface remains with electronic surface potentials near flatband condition.
Microstructure-controlled magnetic properties of the bulk glass-forming alloy Nd60Fe30Al10
Authors: Schneider S. , Bracchi A. , Samwer K. , Seibt M. , Thiyagarajan P.
Published: July 2002

We report a combination of analytical transmission electron microscopy, small angle neutron scattering, and studies of magnetic properties of the glass-forming alloy Nd60Fe30Al10. These investigations show the existence of an in situ formed finely dispersed nanocrystalline Nd-rich phase embedded in a Fe-rich glassy matrix of a bulk sample. The crystalline phase forms an extended network over the whole sample but its volume fraction is small compared to that of compact phase. Small angle neutron scattering data exhibit power law behavior with an exponent of −2.5 indicating the formation of a mass fractal. The microstructure observed may be related to phase separation in the undercooled liquid which induces a microstructure that can explain the hard magnetic behavior of such an intrinsic composite.
Time-dependent survival probability in diffusion-controlled reactions in a polymer chain: Beyond the Wilemski–Fixman theory
Authors: Srinivas Goundla , Sebastian K. L. , Bagchi Biman
Published: July 2002

Brownian dynamics simulation results of the time-dependent survival probability (Sp(t)) of a donor–acceptor pair embedded at the two ends of a Rouse chain are compared with two different theories, one of which is the well-known Wilemski–Fixman (WF) theory. The reaction studied is fluorescence energy transfer via the Förster mechanism, which has a R−6 distance (R) dependence of the reaction rate. It has been reported earlier [G. Srinivas, A. Yethiraj, and B. Bagchi, J. Chem. Phys. 114, 9170 (2001)] that while the WF theory is satisfactory for small reaction rates, the agreement was found to become progressively poorer as the rate is increased. In this work, we have generalized the WF theory. We suggest an approximate, reduced propagator technique for three-dimensional treatment (instead of 3N dimensions, where N is the number of monomers in the polymer chain). This equation is solved by combining a Green’s function solution with a discretized sink method. The results obtained by this new scheme are in better agreement with the simulation results.
Nitrogen-induced transient enhanced diffusion of dopants
Authors: Murthy Cheruvu , Lee Kilho , Rengarajan Rajesh , Dokumaci Omer , Ronsheim Paul , Tews Helmut , Inaba Satoshi
Published: July 2002

Studies of both systematic experiments and detailed simulations for examining the effects of N2+ implant on channel dopants are described. Step-by-step monitor wafer experiments have clearly confirmed the nitrogen-induced transient enhanced diffusion (TED) of dopants. Process simulations within the “+1” N2+ profile approach have demonstrated the need to scale down the +1 model parameter for matching the measured depth profiles. The underlying mechanism for the reduced +1 model parameter is that nitrogen which diffuses toward the Si surface becomes a sink for the interstitials. These combined studies also show that nitrogen-induced TED of dopants increases with N2+ dose.
Investigations of excitation energy transfer and intramolecular interactions in a nitrogen corded distrylbenzene dendrimer system
Authors: Varnavski O. , Samuel I. D. W. , Pålsson L.-O. , Beavington R. , Burn P. L. , Goodson T.
Published: July 2002

The photophysics of an amino-styrylbenzene dendrimer (A-DSB) system is probed by time-resolved and steady state luminescence spectroscopy. For two different generations of this dendrimer, steady state absorption, emission, and photoluminescence excitation spectra are reported and show that the efficiency of energy transfer from the dendrons to the core is very close to 100%. Ultrafast time-resolved fluorescence measurements at a range of excitation and detection wavelengths suggest rapid (and hence efficient) energy transfer from the dendron to the core. Ultrafast fluorescence anisotropy decay for different dendrimer generations is described in order to probe the energy migration processes. A femtosecond time-scale fluorescence depolarization was observed with the zero and second generation dendrimers. Energy transfer process from the dendrons to the core can be described by a Förster mechanism (hopping dynamics) while the interbranch interaction in A-DSB core was found to be very strong indicating the crossover to exciton dynamics.
Toward establishing criteria for polymer imprinting using mean-field theory
Authors: Srebnik Simcha , Lev Ovadia
Published: July 2002

Increased attention is being focused on engineering micro- and nanostructured materials. Of special technological and scientific interest are engineered materials capable of molecular recognition based on pore size, shape, and functionality. The molecular specificity can be achieved using molecular imprinting techniques. This paper aims to initiate theoretical work to establish criteria for successful molecular imprinting. Using the path-integral mean field theory, we modeled cross-linked polymer networks in the presence of excluded volume particles. Current experimental data is insufficient for a quantitative comparison with our predicted scaling laws. Nevertheless, we were able to predict general experimental trends concerning the positive dependence of the formation of stable molecular templates on the degree of cross-linking and the negative dependence on the size and density of the template molecules.
Changes in heart rate variability during fainting
Authors: Sheldon Robert , Riff Kenneth
Published: July 2002

Studies of heart rate variability in people who faint may yield insights into normal physiologic mechanisms which probably are dynamic. These insights might be gained because fainting appears to be due to a breakdown of these mechanisms. Tilt table testing reliably induces fainting in patients with a history of fainting and can be used to study these mechanisms. During tilt tests ending in fainting heart rate changes markedly, with a loss of high-frequency components on power spectral analysis and a progressive slowing of overall sinus node discharge. These changes appear to be due to changes in efferent vagal nerve traffic. Several possible mechanisms of these changes in heart rate variability are discussed.
Coupled map lattice techniques for simulating interfacial phenomena in reaction-diffusion systems
Authors: Levine Herbert , Reynolds William N.
Published: July 2002

Interfacial patterns arise due to the dynamical evolution of phase boundaries in physical, chemical and biological systems. Coupled map lattices (CML) offer a useful tool for the simulation of such systems, being able to naturally accommodate the disparate length and time scales inherent in the dynamics of these processes. We illustrate this idea by reviewing work done on applying CML methods to crystal growth and to excitable media.
Coupled map lattices as computational systems
Authors: Holden A. V. , Tucker J. V. , Zhang H. , Poole M. J.
Published: July 2002

The coupled map lattice (CML) as a mathematical model for a computer is considered. Using the theory of synchronous concurrent algorithms, it is shown that the CML is a valid new model for a parallel deterministic analog machine, but that, in principle, such a CML computer does not generate computations that cannot be reproduced by the standard mathematical models for computing on real numbers. The analysis is based on new general mathematical definitions of CMLs, and an axiomatic approach to determining which models of computation can be used to simulate CMLs.
Investigation of the Lorentz gas in terms of periodic orbits
Authors: Cvitanović Predrag , Gaspard Pierre , Schreiber Thomas
Published: July 2002

The diffusion constant and the Lyapunov exponent for the spatially periodic Lorentz gas are evaluated numerically in terms of periodic orbits. A symbolic description of the dynamics reduced to a fundamental domain is used to generate the shortest periodic orbits. Applied to a dilute Lorentz gas with finite horizon, the theory works well, but for the dense Lorentz gas the convergence is hampered by the strong pruning of the admissible orbits.
Topological aspects of quantum chaos
Authors: Leboeuf P. , Kurchan J. , Feingold M. , Arovas D. P.
Published: July 2002

Quantized classically chaotic maps on a toroidal two-dimensional phase space are studied. A discrete, topological criterion for phase-space localization is presented. To each eigenfunction is associated an integer, analogous to a quantized Hall conductivity, which tests the way the eigenfunction explores the phase space as some boundary conditions are changed. The correspondence between delocalization and chaotic classical dynamics is discussed, as well as the role of degeneracies of the eigenspectrum in the transition from localized to delocalized states. The general results are illustrated with a particular model.
Inertial nonlinearity and chaotic motion of particle fluxes
Authors: Gurbatov S. N. , Saichev A. I.
Published: July 2002

A brief review is given of the nonlinear phenomena arising in the evolution of random perturbations in particle fluxes of the hydrodynamical type, the velocity field of which is described by equations similar to the Riemann and Burgers equations. It is shown that a nonlinearity of the inertial type deforming the fluxes owing to the inertia of the motion of their constituent particles leads to the formation of singularities in the realizations of the velocity and density fields, and, consequently, to the appearance of universal asymptotes in their spectra and probability distributions. Methods are presented for the statistical description of waves in dispersionless media. A brief discussion is given of the laws of evolution of the statistical characteristics of the velocity and density fields of particle fluxes, both without interactions and with a contact interaction. In particular, the analogy between the solution of the Burgers equation and a particle flux with adhesion is studied. Diverse physical applications are discussed: to the dynamics of particles and mixtures, intensity fluctuations of an optical wave which has passed through a phase screen and in a randomly nonuniform medium, gravitational instability, and acoustical turbulence.
Dynamics in a discontinuous field: The smooth Fermi piston
Authors: Worrell G. A. , Matulich A. , Miller B. N.
Published: July 2002

In this paper we examine a version of the Fermi piston with a discontinuous, but nonimpulsive, periodic driving force. The dynamics of a particle moving in one spatial dimension are studied using a combination of numerical and analytical techniques. The configuration space of the particle is divided into two regions of constant acceleration that are of equal magnitude and opposite direction. The point of discontinuity F(t) dividing the regions changes periodically in time. The method of surface-of-section is used to study the phase space (φn, vn), where φn is the phase of the driving function and vn is the velocity of the particle at the nth encounter between the particle and boundary. We show that it is not possible to stochastically drive up the energy indefinitely except for the cases where F is discontinuous, or dF/dt is not finite everywhere. In addition, we find a new mechanism, other than KAM tori, for segmenting the phase space. As in the KAM picture, the central cause of the new behavior is resonance between the natural period of the particle and the period of the driving force. The boundaries to diffusion for continuous driving functions result from parabolic fixed points that span the entire phase range.
Scaling and decay in periodically driven scattering systems
Authors: Beeker Arne , Eckelt Peter
Published: July 2002

We investigate irregular scattering in a periodically driven Hamiltonian system of one degree of freedom. The potential is asymptotically attracting, so there exist parabolically escaping scattering orbits, i.e. orbits with asymptotic energy Eout=0. The scattering functions (i.e. the asymptotic out-variables as functions of an asymptotic in-variable) show a characteristic algebraic scaling in the vicinity of these orbits. This behavior is explained by asymptotic properties of the interaction. As a consequence, the number N(Δt) of temporarily bound particles decays algebraically with the delay time Δt, although no KAM scenario can be found in phase space. On the other hand, we find the number Nn of temporarily bound particles to decay exponentially with the number n of zeros of x(t).
Chaotic scattering and acceleration of particles by waves
Authors: Chernikov A. A. , Schmidt G.
Published: July 2002

Relativistic charged particles in a uniform magnetic field and traveling waves of large amplitude can be accelerated limitlessly. Since much of phase space is chaotic the process can be viewed as chaotic scattering on waves. For multiple waves an explicit map arises with unusual properties. It contains infinite island chains around nonperiodic orbits and it is also an example of transient chaos in a Hamiltonian system.
Poincaré surface of section and quantum scattering
Authors: Gutzwiller Martin C.
Published: July 2002

A very simple model for the quantum-mechanical scattering of a particle is studied with a dual goal: The chaotic nature of the corresponding classical problem should be quite obvious, and the method of solution should use an approach that is closely related to the surface of section in classical mechanics. Moreover, the mathematical operations should be elementary so that the errors in a semiclassical approximation or in any computational work have a chance of being controllable. Finally, the mode of presentation is such as to be understandable for a newcomer to the field of chaos. The model is a variation of the Sinai billiard where the circular hard wall inside a box (parallelogram) is replaced by a trombone-shaped surface for the particle to enter and exit the box. The rim (circular boundary between trombone and box) is the surface of section, with the total current at fixed energy in either direction providing the measure for the wave functions. The Poincaré map then becomes the product of two unitary transformations, where the first is diagonal in angular momentum, while the second is diagonal in angle.
Waveguide propagation of intense electromagnetic radiation in slightly inhomogeneous nonlinear media
Authors: Andreev A. A. , Erokhin N. S. , Zol’nikova N. N. , Mikhaĭlovskaya L. A.
Published: July 2002

The propagation of self-localizing beams of electromagnetic waves in the form of nonlinear waveguides in a slightly inhomogeneous medium is studied analytically and numerically. The trajectories of the axial ray are studied as a function of its direction and the field strength at the initial point on the basis of a nonlinear scalar Helmholtz equation. Analytic expressions are derived. The longitudinal refractive index, the field intensity, and the waveguide radius are plotted as functions of the instantaneous position of the point on the axial ray. Deep penetration of the beam into the opaque region and the position of the screening surface are studied as functions of the parameters of the beam and the medium. A steady-state 3D problem is analyzed for a power-law nonlinearity with an arbitrary power. A 2D problem is analyzed for the case of a ponderomotive nonlinearity with saturation.
Measuring the similarity between trajectories using clustering techniques
Authors: Jansen Ben H. , Nyberg Henrik N.
Published: July 2002

A clustering method has been developed to group signals that display similar dynamic behavior. The procedure involves using the method of time delay embedding to construct a trajectory in state space from a time series. Certain features that characterize the geometry of the trajectory have been defined. These features were subjected to a series of statistical tests to determine their usefulness in a hierarchical clustering analysis. The latter is aimed at finding groups of similar trajectories. The trajectory-based clustering algorithm has been applied to simulated data, which included both stochastic data generated by a linear AR model, and nonlinear data generated by a Duffing oscillator. The results show that the algorithm works reliably in both cases.
Deterministic chaos in a quantum mechanical system described by a time-independent Hamiltonian: A model of three Josephson junctions in a loop
Authors: Parmenter R. H. , Yu L. Y.
Published: July 2002

Quantum mechanical equations of motion are obtained for a system consisting of a very large number of three types of interacting bosons. Under suitable choice of parameters of the Hamiltonian of the system, the equations of motion are those describing three Josephson junctions in a superconducting loop. It is shown numerically that this system is capable of exhibiting deterministic chaos (extreme sensitivity to initial conditions).
A Fredholm determinant for semiclassical quantization
Authors: Cvitanović Predrag , Rosenqvist Per E. , Vattay Gábor , Rugh Hans Henrik
Published: July 2002

We investigate a new type of approximation to quantum determinants, the ‘‘quantum Fredholm determinant,’’ and test numerically the conjecture that for Axiom A hyperbolic flows such determinants have a larger domain of analyticity and better convergence than the Gutzwiller–Voros zeta functions derived from the Gutzwiller trace formula. The conjecture is supported by numerical investigations of the 3-disk repeller, a normal-form model of a flow, and a model 2-D map.
Long-lived planetary vortices and their evolution: Conservative intermediate geostrophic model
Authors: Sutyrin Georgi G.
Published: July 2002

Large, long-lived vortices, surviving during many turnaround times and far longer than the dispersive linear Rossby wave packets, are abundant in planetary atmospheres and oceans. Nonlinear effects which prevent dispersive decay of intense cyclones and anticyclones and provide their self-propelling propagation are revised here using shallow water equations and their balanced approximations. The main physical mechanism allowing vortical structures to be long-lived in planetary fluid is the quick fluid rotation inside their cores which prevents growth in the amplitude of asymmetric circulation arising due to the beta-effect. Intense vortices of both signs survive essentially longer than the linear Rossby wave packet if their azimuthal velocity is much larger than the Rossby wave speed. However, in the long-time evolution, cyclonic and anticyclonic vortices behave essentially differently that is illustrated by the conservative intermediate geostrophic model. Asymmetric circulation governing vortex propagation is described by the azimuthal mode m=1 for the initial value problem as well as for steadily propagating solutions. Cyclonic vortices move west-poleward decaying gradually due to Rossby wave radiation while anticyclonic ones adjust to non-radiating solitary vortices. Slow weakening of an intense cyclone with decreasing of its size and shrinking of the core is described assuming zero azimuthal velocity outside the core while drifting poleward. The poleward tendency of the cyclone motion relative to the stirring flow corresponds to characteristic trajectories of tropical cyclones in the Earth’s atmosphere. The asymmetry in dispersion-nonlinear properties of cyclones and anticyclones is thought to be one of the essential reasons for the observed predominance of anticyclones among long-lived vortices in the atmospheres of the giant planets and also among intrathermoclinic eddies in the ocean.
Successes and failures of shallow-water interpretations of Voyager wind data
Authors: Dowling Timothy E.
Published: July 2002

Studying the dynamics of Jupiter’s atmosphere is a rewarding experience, in part because the planet’s cloud-top circulations are easy to track from space, the jet streams flow in straight lines eastward or westward, and there is enough room for the vortices to usually keep out of each other’s way. Earth, in contrast, is a planet with global circulations that are not easy to track from space, with jet streams that make wide, fluctuating arcs as they negotiate mountain ranges, and with vortices that are constantly jostling against each other in a cramped environment. But we know a great deal more about the vertical structure of Earth’s atmosphere than of Jupiter’s. In order to make headway on the Jovian problem, researchers have turned to the shallow-water model as a guide to interpreting the Voyager wind data. The shallow-water model matches the character of the data because it combines high-resolution horizontal dynamics with low-resolution vertical structure, but there is no guarantee that it captures the character of Jupiter’s atmosphere itself. Remarkably, the model does well at reproducing the Great Red Spot, and it has revealed that Jupiter is clever about how it manages its vorticity by arranging its zonal winds to be neutrally stable with respect to Arnol’d’s second stability theorem. We discuss reasons why the shallow-water model works for Jupiter and point out the limitations that are motivating researchers to develop more realistic models.
Spatiotemporal chaos in an electric current driven ionic reaction-diffusion system
Authors: Hasal P. , Münster A. F. , Marek M.
Published: July 2002

Two types of transitions from the time-periodic spatiotemporal patterns to chaotic ones in the spatially one-dimensional ionic reaction-diffusion system forced either with direct or alternating electric field are described and analyzed by numerical techniques. An ionic version of the Brusselator kinetic scheme is considered. The Karhunen–Loève decomposition technique is shown to be a possible tool for the global representation of dynamic behavior, but fails as a tool in the identification of the route of transition to chaos in the case of direct current forcing. Higher dimensional chaos with two positive Lyapunov exponents has been identified for the case of alternating current forcing. Results of the Karhunen–Loève analysis are compared to results of classical analysis of local time series (attractor dimensions, Lyapunov exponents).
Four modes competition and chaos in a shell
Authors: Dekhtyaryuk Evgeny S. , Zakharchenko Tatyana G. , Petryna Yuri S. , Krasnopolskaya Tatyana S.
Published: July 2002

Steady-state chaotic vibrations of a shallow shell as a system with a nonsymmetrical restoring force and one equilibrium state are considered. Mode interaction and its effect on a chaotic behavior of the shell is studied. The terms ‘‘natural’’ and ‘‘imposed’’ chaos are introduced for the response of resonant and nonresonant modes. It is shown that such a qualitative difference is important for better understanding of chaos in systems with distributed parameters, and may be very useful for numerical investigations. Some qualitative comparisons with previous papers on chaos in distributed mechanical systems are also made.
The kinetics of liquid–gas phase transitions of a Van der Waals substance with fluctuations taken into account
Authors: Malakhov A. N. , Agudov N. V.
Published: July 2002

The isotherm of a Van der Waals substance, containing only stable points, is obtained on the basis of using the thermodynamic potential for nonequilibrium states and taking fluctuations into account. It is shown that in the vicinity of two-phase states this isotherm is close to the horizontal phase equilibrium line, defined by Maxwell’s rule. The lifetimes of the metastable states of the Van der Waals substance, which depend on the intensity of the external fluctuations and the number of particles in the system, are estimated.
Enhanced quantum fluctuations in a chaotic single mode ammonia laser
Authors: Elston T. C. , Fox Ronald F.
Published: July 2002

A detailed study of the effects of quantum fluctuations in a chaotic single mode laser is presented. It has been well established that the linear noise approximation eventually becomes invalid for the case of chaotic dynamics. A more accurate description of the laser is achieved through use of nonlinear Langevin equations. Simple expressions for the time evolution of the phases of the electric field and polarization are derived. These expressions predict that chaotic dynamics will greatly enhance phase diffusion. This prediction is verified through numerical simulations. A quantitative method, for determining the amount of amplification of quantum noise by chaos is discussed. This method makes use of a metric introduced in symbolic dynamics. The fluctuations are shown to have been amplified by over two orders of magnitude, making them macroscopically visible.
Classical chaotic dynamics of sound rays in 3-D inhomogeneous waveguide media
Authors: Abdullaev S. S.
Published: July 2002

The chaotic dynamics of sound rays in a near-bottom waveguide channel is studied on the basis of the Hamiltonian dynamics of nonparaxial rays in inhomogeneous moving media. The bottom is assumed to have a two-dimensional roughness. The mapping of the coordinates of the rays upon reflection from the rough bottom is derived through a solution of the corresponding ray equations in an unperturbed waveguide with a horizontal bottom. A numerical analysis of the mapping reveals that a chaotic instability of rays which start out at small angles from the horizontal develops at short distances from the source. Because of this instability, the path segments of a ray along the horizontal coordinates and the signal passage time along a ray are random functions of the angle at which the ray emerges from the source. Upon a further reflection of rays from the rough bottom, there is a diffusion of rays in a stochastic ring which forms in the plane of horizontal ray directions as a result of the overlap and intersection of resonance curves. A qualitative analysis of this effect is carried out. This effect leads to a nearly isotropic distribution of ray directions.
Supertransients and suppressed chaos in the diffusively coupled logistic lattice
Authors: Willeboordse Frederick H.
Published: July 2002

Pattern selection at medium and high nonlinearity is investigated. While in the former the transient time levels off for large system sizes, in the latter it diverges exponentially giving rise to supertransients. In both cases, the final attractors are quite stable with as a consequence that even at high nonlinearity an attractor can easily be reached by means of a parameter sweep.
Dysrhythmias of the respiratory oscillator
Authors: Paydarfar David , Buerkel Daniel M.
Published: July 2002

Breathing is regulated by a central neural oscillator that produces rhythmic output to the respiratory muscles. Pathological disturbances in rhythm (dysrhythmias) are observed in the breathing pattern of children and adults with neurological and cardiopulmonary diseases. The mechanisms responsible for genesis of respiratory dysrhythmias are poorly understood. The present studies take a novel approach to this problem. The basic postulate is that the rhythm of the respiratory oscillator can be altered by a variety of stimuli. When the oscillator recovers its rhythm after such perturbations, its phase may be reset relative to the original rhythm. The amount of phase resetting is dependent upon stimulus parameters and the level of respiratory drive. The long-range hypothesis is that respiratory dysrhythmias can be induced by stimuli that impinge upon or arise within the respiratory oscillator with certain combinations of strength and timing relative to the respiratory cycle. Animal studies were performed in anesthetized or decerebrate preparations. Neural respiratory rhythmicity is represented by phrenic nerve activity, allowing use of open-loop experimental conditions which avoid negative chemical feedback associated with changes in ventilation.

In animal experiments, respiratory dysrhythmias can be induced by stimuli having specific combinations of strength and timing. Newborn animals readily exhibit spontaneous dysrhythmias which become more prominent at lower respiratory drives. In human subjects, swallowing was studied as a physiological perturbation of respiratory rhythm, causing a pattern of phase resetting that is characterized topologically as type 0. Computational studies of the Bonhoeffer–van der Pol (BvP) equations, whose qualitative behavior is representative of many excitable systems, supports a unified interpretation of these experimental findings. Rhythmicity is observed when the BvP model exhibits recurrent periods of excitation alternating with refractory periods. The same system can be perturbed to a state in which amplitude of oscillation is attenuated or abolished. We have characterized critical perturbations which induce transitions between these two states, giving rise to patterns of dysrhythmic activity that are similar to those seen in the experiments. We illustrate the importance of noise in initiation and termination of rhythm, comparable to normal respiratory rhythm intermixed with spontaneous dysrhythmias. In the BvP system the incidence and duration of dysrhythmia is shown to be strongly influenced by the level of noise. These studies should lead to greater understanding of rhythmicity and integrative responses of the respiratory control system, and provide insight into disturbances in control mechanisms that cause apnea and aspiration in clinical disease states.
Shift of a limit cycle in biology: From pathological to physiological homeostasia*
Authors: Claude Daniel
Published: July 2002

Biological systems may show homeostatic behaviors that are similar to the ones of forced dynamic systems with a stable limit cycle. For a large class of dynamic systems, it is shown that a shift of a pathological limit cycle over the physiological limit cycle can never be executed by means of a control with a desired periodicity. The above statement shows that the only possibility is to reduce as much as possible the dimensions of a small residual limit cycle. Moreover, it is possible to give some information about the structure of feedback laws that would allow the shift of the limit cycle. The fact that it is generally not possible to recover a physiological limit cycle from a pathological one, results into the fear of never or hardly ever reaching a physiological behavior, and it seems that any hope of therapeutics is given up. This leads to introduce the locking concept, which permits system parameters to change and provides the basis for an adaptive and iterative control, which allows a step by step approach and to finally reach the physiological limit cycle.
The iteration-approximation decoupling in the reversible KAM theory
Authors: Sevryuk M. B.
Published: July 2002

General theorems on the persistence of quasiperiodic motions in reversible flows and diffeomorphisms satisfying very weak nondegeneracy conditions are obtained by a new method. The essence of this method is that the reversible system under consideration is embedded in a multiparameter family of reversible systems, and standard results on Diophantine approximations of dependent quantities are then applied to Whitney-smooth Cantor foliations of invariant tori of this family. Invariant tori are constructed for all the permissible values of m, p, q (for vector fields V) or m, p, q, P, Q (for diffeomorphisms A) where m is the torus dimension, (q,p) is the type of the reversing involution G, and (Q,P) is the type of the involution AG. The excitation of elliptic normal modes is also considered.