bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon reactivation kinetics in GaAs: Its dependence on dopant precursor, doping level, and layer thickness
Authors: Mimila-Arroyo J. , Bland S. , Barbé M.
Published: July 2002

The reactivation kinetics of the acceptor behavior of carbon, its dependence on dopant precursors, doping level, layer thickness, and annealing temperature, as well as the behavior of carbon-hydrogen complexes in GaAs grown by metalorganic chemical vapor deposition are studied. Independent of the carbon source, in the “as grown” material, systematically carbon hydrogen complexes are present and the hole concentration is lower than the corresponding carbon concentration. The carbon reactivation kinetics was achieved by ex situ rapid thermal annealing through a series of multistage annealing experiments and assessed at each annealing stage by infrared absorption, hydrogen secondary ion mass spectroscopy profiling, and hole concentration measurements. Carbon reactivation occurs solely by the debonding of hydrogen from the isolated carbon acceptor and its out-diffusion from the sample. The carbon reactivation kinetics can be treated as a first order one with an activation energy, Ea=1.42±0.01 eV, independent of doping precursors, doping level, and layer thickness. The reactivation constant results to decrease as doping level and layer thickness increase. An empirical formula has been obtained that allows one to calculate the reactivation constant as a function of the carbon doping, layer thickness, and annealing temperature, allowing one to determine the optimal carbon reactivation conditions for any C:GaAs layer.
Self-assembly of spatially separated silicon structures by Si heteroepitaxy on Ni disilicide
Authors: Guliants Elena A. , Ji Chunhai , Anderson Wayne A.
Published: July 2002

A nonlithographic approach to produce self-assembled spatially separated Si structures for nanoelectronic applications was developed, employing the metal-induced silicon growth. Densely packed Si whiskers, 500–800 nm thick and up to 2500 nm long, were obtained by magnetron sputtering of Si on a 25 nm thick Ni prelayer at 575 °C. The nucleation of the NiSi2 compound at the Ni–Si interface followed by the Si heteroepitaxy on the lattice-matched NiSi2 is suggested to be the driving force for the whisker formation.
Noncontact technique for determining viscosity from the shape relaxation of ultrasonically levitated and initially elongated drops
Authors: Ohsaka K. , Rednikov A. , Sadhal S. S. , Trinh E. H.
Published: July 2002

We present a technique that can determine the viscosity of highly viscous liquids, particularly, undercooled liquids that exist at temperatures below their freezing points. The technique involves levitation of a liquid drop using an ultrasonic standing wave, and elongation of the drop by rotating it beyond the point of bifurcation. The elongated drop is then allowed to be restored to its original shape by surface tension driven relaxation. The time-dependent shape parameters of the relaxing drop are related to the viscosity through a relaxation model. In addition, this technique can also determine the surface tension that has a known relationship with the angular velocity at the bifurcation point. The feasibility of the technique is demonstrated by performing the measurement using sucrose solutions as a model liquid drop. The obtained viscosity values show a good correlation with those determined by a falling ball method.
An open transverse z-gradient coil design for magnetic resonance imaging
Authors: Dodd Stephen J. , Williams Donald S. , Olson Carl , Silva Afonso C. , Koretsky Alan P. , Ho Chien
Published: July 2002

A method for designing open gradient coils for magnetic resonance imaging using a simulated annealing optimization algorithm is described. The algorithm allows the current density toward the open end to be increased, compensating for the “missing” coil section. A semicylindrical transverse z gradient has been designed and built providing a gradient efficiency of 0.82 mT/m/A. The prototype provided good agreement with the theory over the central imaging region.
Polarization-modulation near-field optical microscope for quantitative local dichroism mapping
Authors: Ramoino L. , Labardi M. , Maghelli N. , Pardi L. , Allegrini M. , Patanè S.
Published: July 2002

A couple of experimental techniques have been implemented to an aperture near-field scanning optical microscopy (NSOM) to obtain reliable measurement of sample dichroism on the local scale. First, a method to test NSOM tapered fiber probes toward polarization conservation into the near optical field is reported. The probes are characterized in terms of the in-plane polarization of the near field emerging from their aperture, by using a thin dichroic layer of chromophore molecules, structured along stretched polymeric chains, to probe such polarization when approached in the near-field region of the probe. Second, to assure that the light intensity coupled in the fiber is polarization independent, an active system operating in real time has been realized. Such combination of techniques allowed quantitative imaging of local dichroism degree and average orientation by means of dual-phase lock-in demodulation of the optical signal. Translation of the coupled light polarization state in the near field has been observed for one-half of the tested probes. For the others, the tip acts as a polarizer, and therefore showed it was not suitable for polarization modulation NSOM measurements.
Hybrid and Hall-magnetohydrodynamics simulations of collisionless reconnection: Effect of the ion pressure tensor and particle Hall-magnetohydrodynamics
Authors: Yin L. , Winske D. , Gary S. P. , Birn J.
Published: July 2002

For two-dimensional reconnection in a thin Harris current sheet, fluid–ion dynamics from a Hall-magnetohydrodynamics (Hall-MHD) calculation using a scalar ion pressure are compared to the particle–ion dynamics obtained from a hybrid simulation and from test ions that are advanced in Hall-MHD fields. Skewed ion velocity distributions from the particle calculations are shown to produce off-diagonal elements of the ion pressure tensor. These comparisons demonstrate that the inclusion of off-diagonal terms in the ion pressure tensor is important to correctly model the ion out-of-plane momentum transport from the X point. It is shown that these effects can be modeled efficiently in Hall-MHD simulations in a predictor–corrector manner that uses particle ions to implement the ion gyro-radius corrections. By advancing test ions in the Hall-MHD fields at every time step, accumulating the ion pressure tensor onto the spatial grid, and adding its divergence to the ion momentum equation, this particle Hall-MHD simulation models well the ion out-of-plane momentum transport from the X point.
Super-resolution near-field optical disk with an additional localized surface plasmon coupling layer
Authors: Shi L. P. , Chong T. C. , Yao H. B. , Tan P. K. , Miao X. S.
Published: July 2002

A structure of super-resolution near-field phase-change optical disk with localized surface plasmon coupling effect is proposed. A localized surface plasmon coupling layer (LSPCL) was introduced to form a coupled localized surface plasmons (CLSP) with the mask layer. Recording marks as small as 31 and 36 nm were observed in two structures, which were both much smaller than the smallest mark of 56 nm observed from the conventional one without LSPCL. CLSP not only can reduce mark size but it can also improve carrier-to-noise ratio of recording marks. The thermal stability of the disk was also studied.
Detection and enumeration of single nanometric particles: A confocal optical design for fluorescence flow cytometry
Authors: Ferris Matthew M. , Rowlen Kathy L.
Published: July 2002

Nanometer-sized particles are increasingly important in fields ranging from technology development to environmental analysis. Traditionally, quantification of biological nanometric particles, such as viruses, has been challenging. Recent advances in optics and optical design have made single molecule detection possible in flowing systems. However, many commercially available flow cytometers are not optimized for routine analysis of ultrasmall biological particles. In this work, a confocal optical arrangement was incorporated into the design of a relatively simple flow cytometer optimized for rapid enumeration of fluorescent nanometric particles. The instrument was designated the “single nanometric particle enumerator” (SNaPE). Instrument parameters, such as data acquisition rates, flow rates, and minimum sampling time were examined and optimized for the SNaPE. The measured detection efficiency was ∼8%, which is consistent with the confocal geometry and equivalent to the detection efficiency reported in many single molecule studies. Signal calibration was achieved using fluorescent polystyrene spheres ranging from 26 nm to 10 μm in diameter. The SNaPE exhibited a limit of detection of ∼180 fluorescein isothiocyanate equivalents and was capable of particle enumeration over the tested concentration range of 106–109 particles/ml.
Resonant two-photon ionization study of jet-cooled amino acid: L-phenylalanine and its monohydrated complex
Authors: Lee Kang Taek , Sung Jiha , Lee Kwang Jun , Kim Seong Keun , Park Young Dong
Published: July 2002

L-phenylalanine (Phe), one of the aromatic amino acids, and its hydrated clusters were generated in supersonic expansion and investigated by resonant two-photon ionization. Excitation spectra of Phe and Phe–(H2O)1 were obtained near their S0–S1 origins. We found that, by comparing the experimental results with the density functional theory and ab initio calculations, the water in Phe–(H2O)1 tends to form a cyclic hydrogen bond at the carboxyl group while inducing little change in the corresponding monomer structure. No sign of water making bridged hydrogen bonds with both polar groups was found. In order to form the cyclic hydrogen bond, hydration takes place only with the conformers whose carboxyl hydrogen is free, i.e., not occupied in the intramolecular hydrogen bonding with the amino nitrogen in the monomer.
Pump–probe dissociative ionization of NaI and CsI aggregated with CH3CN
Authors: Stibbe Darian T. , Charron Eric , Brenner Valerie , Millié Philippe , Suzor-Weiner Annick
Published: July 2002

Recent experiments have investigated the dissociative ionization of NaI and CsI, each aggregated with a molecule of acetonitrile CH3CN, using two femtosecond laser pulses. The first, the pump pulse, excites the NaI or CsI diatom to a dissociative state. The second, the probe pulse, then ionizes the sodium or cesium atom after a variable delay time, and the resulting ion is detected. In the case of NaI, the ion signal is characterized by a single maximum. For CsI, however, an oscillatory signal is observed. By performing two-dimensional wave packet propagations, we are able to reproduce this behavior, which can be explained using simple physical arguments.
Localization of ferrocene in NaY zeolite by powder x-ray and neutron diffraction
Authors: Kemner E. , Overweg A. R. , van Eijck L. , Fitch A. N. , Suard E. , de Schepper I. M. , Kearley G. J.
Published: July 2002

We study the inclusion of the metallocene ferrocene Fe(C5H5)2 molecules in the supercages of NaY zeolite. To find the exact location of the ferrocene molecules within the supercages we perform neutron and powder x-ray diffraction on bare NaY zeolite, and on NaY zeolite loaded with one or two ferrocene molecules per supercage. Using the complementary properties of both techniques we show that the ferrocene molecules are located just above a line joining two neighboring sodium ions at the SII positions in the zeolite supercage. The C5H5 rings are oriented towards the sodium ions in an ordered manner. This structure is confirmed by quantum chemistry calculations. The geometry of the ferrocene molecules barely changes, indicating that the increased reactivity of ferrocene upon adsorption in a zeolite is thus a result of the position of the molecules. The main interactions responsible for this position are Coulombic attraction and hydrogen bonding. The inclusion of ferrocene in a Y-type zeolite provides a homogeneous distribution of iron throughout the zeolite at well-defined locations.
Kinetic effects on the parametric decays of circularly polarized electromagnetic waves in an electron–positron plasma
Authors: Muñoz Vı́ctor , Gomberoff Luis
Published: July 2002

Parametric decays of a circularly polarized wave in an electron–positron plasma, including relativistic effects on the particle motion in the wave field, are studied. The analysis is based on the Vlasov equation in order to account for kinetic effects. Dispersion relations are found for the pump wave and its parametric decays, and they are studied numerically in the weakly relativistic regime. This is done by using a graphical method, which has the advantage of showing explicitly the various modes involved in the decays, making thereby the physical picture more transparent. In a fluid theory three instabilities develop: one is an ordinary decay instability and the other two are modulational instabilities. Some of them involve electroacoustic pseudomodes, which satisfy ω/k≃vth. In the kinetic treatment, although these modes are strongly Landau damped, all three types of instabilities are present. With respect to the fluid results, growth rates either decrease or increase, depending on the nature of the instability. Due to kinetic effects, instability ranges increase relative to the fluid case.
Nonmagnetic semiconductors as read-head sensors for ultra-high-density magnetic recording
Authors: Solin S. A. , Hines D. R. , Rowe A. C. H. , Tsai J. S. , Pashkin Yu. A. , Chung S. J. , Goel N. , Santos M. B.
Published: July 2002

A mesoscopic nonmagnetic magnetoresistive read-head sensor based on the recently reported extraordinary magnetoresistance (EMR) effect has been fabricated from a narrow-gap Si-doped InSb quantum well. The sensor has a conservatively estimated areal-density of 116 Gb/in.2 with a 300 K EMR of 6% and a current sensitivity of 147 Ω/T at a relevant field of 0.05 T and a bias of 0.27 T. Because this sensor is not subject to magnetic noise, which limits conventional sensors to areal densities of order 100 Gb/in.2, it opens a pathway to ultra-high-density recording at areal densities of order 1 Tb/in.2.
Identifying coherent structures in nonlinear wave propagation
Authors: Newman William I. , Campbell David K. , Hyman James M.
Published: July 2002

Nonlinear wave phenomena are often characterized by the appearance of ‘‘solitary wave coherent structures’’ traveling at speeds determined by their amplitudes and morphologies. Assuming that time intervals exist in which these structures are essentially noninteracting, a method for identifying the number of independent features and their respective speeds is proposed and developed. The method is illustrated with a variety of increasingly realistic specific applications, beginning with a simple nonlinear but analytically tractable Gaussian model, continuing with (numerically generated) data describing multisoliton solutions to the Korteweg–de Vries equation, and concluding with (numerical) data from a realistic simulation of nonlinear wave interactions in plasma turbulence. These studies reveal both strengths and limitations of the method in its present incarnation and suggest topics for future investigations.
Geometric phases in dissipative systems
Authors: Kepler Thomas B. , Kagan Michael L. , Epstein Irving R.
Published: July 2002

It is shown that a phenomenon analogous to the geometric phase shifts of Berry and Hannay occurs for dissipative oscillatory systems and can be detected in numerical simulations of chemical oscillators. The approach herein to the theory of geometric phases begins with a study of simple first-order differential equations on the circle (circle dynamics). It is shown how more complicated systems exhibit geometric phases through reduction to a circle dynamics. In this way, the various manifestations of the phenomenon are seen from a single unified perspective. The results are illustrated in numerical experiments on several model systems ranging from analytically solvable, but contrived, to realistic models of chemical oscillators.
Parameter dependence of stochastic layers in a quasicrystalline web
Authors: Lowenstein J. H.
Published: July 2002

Stochastic web maps with approximate quasicrystalline symmetry possess an infinite number of inequivalent fixed points embedded in stochastic layers of varying thickness. In this investigation exploratory steps are taken toward a systematic numerical determination of the widths of the stochastic layers as a function of the web map’s control parameter. The study concentrates on a particular stochastic layer in the approximately fivefold symmetric web. Computer graphics and a simple stretching-and-folding criterion provide a coarse view, which is supplemented at finer scales by Greene’s residue method. The exact reflection symmetries of invariant sets, as well as a five-dimensional representation of the map, are exploited to improve numerical precision. As the control parameter varies, one finds not only variations expected from island chain structures, but also larger-scale oscillations whose origin is not understood.
Topology of trajectories of the 2D Navier–Stokes equations
Authors: Lee Jon
Published: July 2002

In spectral form the 2D incompressible Navier–Stokes equations in a square periodic region will be represented by 430 complex Fourier amplitudes which correspond to isotropic truncation of the upper wave number 16. For small viscosity, we have found five equilibrium states I–V in the entire range of forcing; I—fixed point, II—circle, III—closed orbit, IV—torus, and V—chaos. The fixed-point equilibrium state is the laminar flow. As the forcing passes through a critical value, the fixed point evolves directly to equilibrium state III under a typical multimode forcing. The chaotic transition takes place on a 2-torus-like manifold (equilibrium state IV) which is the product space of a circle and the closed orbit of equilibrium state III, similar to the quasiperiodic 2-torus of Ruelle and Takens. For sufficiently large forcing, the evolution of equilibrium state V is nothing but a simulation of quasistationary 2D turbulence. From the Lyapunov exponents of turbulent flows, we have evaluated the constants in the theoretical results of Foias and his colleagues, which relate the determining mode and fractal dimension with the enstrophy dissipation wave number of 2D turbulence.
The plastic coupled map lattice: A novel image-processing paradigm
Authors: Price C. B. , Wambacq P. , Oosterlinck A.
Published: July 2002

Coupled map lattices (CML) can describe many relaxation and optimization algorithms currently used in image processing. We recently introduced the ‘‘plastic-CML’’ as a paradigm to extract (segment) objects in an image. Here, the image is applied by a set of forces to a metal sheet which is allowed to undergo plastic deformation parallel to the applied forces. In this paper we present an analysis of our ‘‘plastic-CML’’ in one and two dimensions, deriving the nature and stability of its stationary solutions. We also detail how to use the CML in image processing, how to set the system parameters and present examples of it at work. We conclude that the plastic-CML is able to segment images with large amounts of noise and large dynamic range of pixel values, and is suitable for a very large scale integration (VLSI) implementation.
Particle chaos in the Earth’s magnetotail
Authors: Dusenbery Paul B. , Martin Richard F. , Burkhart Grant R.
Published: July 2002

Nonlinear particle dynamics is studied both in current sheets and near neutral lines. The parameter governing particle chaos in a current sheet with a constant normal component, Bn, is κ=(Rmin/ρmax)1/2, where Rmin is the minimum field line radius of curvature and ρmax is the maximum gyroradius. In such a current sheet, motion can be viewed as a combination of a component normal to the current sheet and a tangential component. The parameter κ represents the ratio of the characteristic time scale of the normal component to the tangential, and thus, particle chaos is maximized for κ∼1. For κ≪1, the slow motion preserves the action integral of the fast motion, Jz, except near the separatrix, the phase space boundary separating motion that crosses the current sheet midplane from that which does not. Near a linear neutral line, it is found that the parameter bn, which is the ratio of the characteristic vertical and horizontal field strengths, rather than κ governs particle chaos. In the limit bn≪1, the slow motion again preserves Jz, and Jz has the same analytic form as in a constant Bn current sheet. In the limit of bn≪1, the structure of x-px phase space is controlled by the stable and unstable manifolds associated with the unstable fixed point orbit at (x,px)=(0,0), and this structure lies along a contour of constant Jz.
Discrete model of a dynamo with diffusion
Authors: Poezd Alekseĭ D. , Galeeva Roza , Sokolov Dmitriĭ D. , Ruzmaikin Aleksander A.
Published: July 2002

A model of magnetic field generation by the turbulent motions of a highly conducting fluid is constructed. It is assumed that the field is generated in individual cells of space in a statistically independent manner. A coupling between the cells is realized by magnetic diffusion. The rates of growth of the field and its moments are calculated. The field distribution generated by this mechanism possesses an intermittent nature in both time and space.
Chaotic spectroscopy
Authors: Doron Eyal , Smilansky Uzy
Published: July 2002

The spectra of quantized chaotic billiards from the point of view of scattering theory are discussed. It is shown how the spectral and resonance density functions both fluctuate about a common mean. A semiclassical treatment explains this in terms of classical scattering trajectories and periodic orbits of the Poincaré scattering map. It is shown that this formalism provides an alternative derivation and a new interpretation of Gutzwiller’s periodic orbits sum for the spectral density. Moreover, it is a convenient starting point for a derivation of a Riemann–Siegel ‘‘look alike’’ expression for the secular equation in terms of periodic orbits of finite length.
Experimental evidence for the influence of ‘‘scars’’ in hydrogen atoms driven by strong microwave fields
Authors: Koch Peter M.
Published: July 2002

A preliminary analysis is reported of new experimental data for the microwave ionization of excited hydrogen atoms with each of the principal quantum numbers n0 between 50 and 79. Data are shown for a linearly polarized field at each of the frequencies 26.43, 30.36, and 36.02 GHz produced in a resonant cavity. For each frequency certain n0 values are more stable against ionization; this is called ‘‘local stability.’’ The data demonstrate classical scaling of these cases of local stability including certain cases that have been explained classically and others that are nonclassical. The data strongly support a theoretical explanation for nonclassical local stability being due to the influence of ‘‘scarred’’ wave functions.
Amplification of intrinsic fluctuations by the Lorenz equations
Authors: Fox Ronald F. , Elston T. C.
Published: July 2002

Macroscopic systems (e.g., hydrodynamics, chemical reactions, electrical circuits, etc.) manifest intrinsic fluctuations of molecular and thermal origin. When the macroscopic dynamics is deterministically chaotic, the intrinsic fluctuations may become amplified by several orders of magnitude. Numerical studies of this phenomenon are presented in detail for the Lorenz model. Amplification to macroscopic scales is exhibited, and quantitative methods (binning and a difference-norm) are presented for measuring macroscopically subliminal amplification effects. In order to test the quality of the numerical results, noise induced chaos is studied around a deterministically nonchaotic state, where the scaling law relating the Lyapunov exponent to noise strength obtained for maps is confirmed for the Lorenz model, a system of ordinary differential equations.
A scattering approach to the quantization of billiards— The inside–outside duality
Authors: Dietz Barbara , Smilansky Uzy
Published: July 2002

We present some recent results on the semiclassical quantization of billiards using an approach which is based on the strong link between the billiard interior and exterior problems. That is, the spectrum of the interior problem is extracted from the scattering matrix of the exterior problem. Once this is put on a rigorous basis, the semiclassical approximation is used to derive the semiclassical ζ function and the spectral density. The duality between the inside and outside problems prevails also in the classical description and offers new insight into this quantization procedure. The relation between the present approach and the more standard quantization methods is also discussed and illustrated with some numerical results.
Periodically kicked hard oscillators
Authors: Cecchi G. A. , Gonzalez D. L. , Magnasco M. O. , Mindlin G. B. , Piro O. , Santillan A. J.
Published: July 2002

A model of a hard oscillator with analytic solution is presented. Its behavior under periodic kicking, for which a closed form stroboscopic map can be obtained, is studied. It is shown that the general structure of such an oscillator includes four distinct regions; the outer two regions correspond to very small or very large amplitude of the external force and match the corresponding regions in soft oscillators (invertible degree one and degree zero circle maps, respectively). There are two new regions for intermediate amplitude of the forcing. Region 3 corresponds to moderate high forcing, and is intrinsic to hard oscillators; it is characterized by discontinuous circle maps with a flat segment. Region 2 (low moderate forcing) has a certain resemblance to a similar region in soft oscillators (noninvertible degree one circle maps); however, the limit set of the dynamics in this region is not a circle, but a branched manifold, obtained as the tangent union of a circle and an interval; the topological structure of this object is generated by the finite size of the repelling set, and is therefore also intrinsic to hard oscillators.
The simplest case of chaotic wave scattering
Authors: Pikovsky Arkady S.
Published: July 2002

We consider scattering of nondispersive linear waves on a discrete nonlinear element. The problem reduces to the dynamics of a forced damped nonlinear oscillator. Chaotic motions of the oscillator produce chaotic reflected and transmitted waves.
Stochastic webs and continuum percolation in quasiperiodic media
Authors: Chernikov A. A. , Rogalsky A. V.
Published: July 2002

We report the results of an analytical and numerical study of the contour line and surface geometry in two models of continuum percolation with quasiperiodic properties. Both the fractal dimension of long isolines and the scaling coefficient ν are determined analytically for the two-dimensional percolation problem. The scaling characteristics of the isosurfaces of the three-dimensional potential function with an icosahedral symmetry are obtained using computer graphic representation.
Spatiotemporal intermittency on fractal lattices
Authors: Cosenza Mario G. , Kapral Raymond
Published: July 2002

The transition to turbulence via spatiotemporal intermittency is investigated for coupled maps defined on generalized Sierpinski gaskets, a class of deterministic fractal lattices. Critical exponents that characterize the onset of intermittency are computed as a function of the fractal dimension of the lattice. Windows of spatiotemporal intermittency are found as the coupling parameter is varied for lattices with a fractal dimension greater than two. This phenomenon is associated with a collective chaotic behavior of the fractal array of coupled maps.
Checkerboard maps
Authors: Balmforth N. J. , Spiegel E. A. , Tresser C.
Published: July 2002

When a map has one positive Lyapunov exponent, its attractors often look like multidimensional, Cantorial plates of spaghetti. What saves the situation is that there is a deterministic jumping from strand to strand. We propose to approximate such attractors as finite sets of K suitably prescribed curves, each parametrized by an interval. The action of the map on each attractor is then approximated by a map that takes a set of curves into itself, and we graph it on a K×K checkerboard as a discontinuous one-dimensional map that captures the quantitative dynamics of the original system when K is sufficiently large.
Periodic orbits of nonscaling Hamiltonian systems from quantum mechanics
Authors: Baranger M. , Haggerty M. R. , Lauritzen B. , Meredith D. C. , Provost D.
Published: July 2002

Quantal (E,τ) plots are constructed from the eigenvalues of the quantum system. We demonstrate that these representations display the periodic orbits of the classical system, including bifurcations and the transition from stable to unstable.
Nonlinear dynamics in pulsatile secretion of parathyroid hormone in normal human subjects
Authors: Prank Klaus , Harms Heio , Brabant Georg , Hesch Rolf-Dieter , Dämmig Matthias , Mitschke Fedor
Published: July 2002

In many biological systems, information is transferred by hormonal ligands, and it is assumed that these hormonal signals encode developmental and regulatory programs in mammalian organisms. In contrast to the dogma of endocrine homeostasis, it could be shown that the biological information in hormonal networks is not only present as a constant hormone concentration in the circulation pool. Recently, it has become apparent that hormone pulses contribute to this hormonal pool, which modulates the responsiveness of receptors within the cell membrane by regulation of the receptor synthesis, movement within the membrane layer, coupling to signal transduction proteins and internalization. Phase space analysis of dynamic parathyroid hormone (PTH) secretion allowed the definition of a (in comparison to normal subjects) relatively quiet ‘‘low dynamic’’ secretory pattern in osteoporosis, and a ‘‘high dynamic’’ state in hyperparathyroidism. We now investigate whether this pulsatile secretion of PTH in healthy men exhibits characteristics of nonlinear determinism. Our findings suggest that this is conceivable, although on the basis of presently available data and techniques, no proof can be established. Nevertheless, pulsatile secretion of PTH might be a first example of nonlinear deterministic dynamics in an apparently irregular hormonal rhythm in human physiology.
On vortex entities of 2D turbulence in wavenumber space
Authors: He Xinyu
Published: July 2002

To connect vortices in physical space and scales in wavenumber space, spectral definitions for vortex size and momentum are introduced within the framework of a probabilistic method. At a late stage of 2D decaying turbulence, a simple solution is given for the vortex position and momentum probabilities. From the solution, an energy spectrum E(k) for self-similar vortices is constructed, which is in agreement with that observed in numerical simulations.
Logarithmic correction to the probability of capture for dissipatively perturbed Hamiltonian systems
Authors: Haberman Richard , Ho Eric K.
Published: July 2002

Hamiltonian systems are analyzed with a double homoclinic orbit connecting a saddle to itself. Competing centers exist. A small dissipative perturbation causes the stable and unstable manifolds of the saddle point to break apart. The stable manifolds of the saddle point are the boundaries of the basin of attraction for the competing attractors. With small dissipation, the boundaries of the basins of attraction are known to be tightly wound and spiral-like. Small changes in the initial condition can alter the equilibrium to which the solution is attracted. Near the unperturbed homoclinic orbit, the boundary of the basin of attraction consists of a large sequence of nearly homoclinic orbits surrounded by close approaches to the saddle point. The slow passage through an unperturbed homoclinic orbit (separatrix) is determined by the change in the value of the Hamiltonian from one saddle approach to the next. The probability of capture can be asymptotically approximated using this change in the Hamiltonian. The well-known leading-order change of the Hamiltonian from one saddle approach to the next is due to the effect of the perturbation on the homoclinic orbit. A logarithmic correction to this change of the Hamiltonian is shown to be due to the effect of the perturbation on the saddle point itself. It is shown that the probability of capture can be significantly altered from the well-known leading-order probability for Hamiltonian systems with double homoclinic orbits of the twisted type, an example of which is the Hamiltonian system corresponding to primary resonance. Numerical integration of the perturbed Hamiltonian system is used to verify the accuracy of the analytic formulas for the change in the Hamiltonian from one saddle approach to the next.
Singular Lyapunov spectra and conservation laws
Authors: Bohr T. , Grinstein G. , Jayaprakash C.
Published: July 2002

We give analytic arguments and numerical evidence to show that the presence of conservation laws can produce a singularity in the spectrum of Lyapunov exponents for extended dynamical systems of low spatial dimensionality. This phenomenon can be used, e.g., for finding hidden conservation laws.
On the interplay between symmetry breaking, integrability, and chaos in the semiclassical limit of the Heisenberg system
Authors: Pellegrino G. Q. , Furuya K. , Nemes M. C.
Published: July 2002

In this work we present a detailed numerical analysis of the interplay between symmetry breaking, integrability, and chaos in the two- and three-spin Heisenberg models. The results suggest that a very simple and powerful tool to convey such information are the plots of the energy level spacings Δn versus the energy level index n, together with the correlation plots Δn+1×Δn. When integrability is broken, these plots are shown to identify very sharply an energy below which one has chaotic behavior. The particularly strong point in favor of such analysis is that it can be useful in partially chaotic regimes.
Kink dynamics in one-dimensional coupled map lattices
Authors: Fernandez Bastien
Published: July 2002

We examine the problem of the dynamics of interfaces in a one-dimensional space-time discrete dynamical system. Two different regimes are studied: the non-propagating and the propagating one. In the first case, after proving the existence of such solutions, we show how they can be described using Taylor expansions. The second situation deals with the assumption of a travelling wave to follow the kink propagation. Then a comparison with the corresponding continuous model is proposed. We find that these methods are useful in simple dynamical situations but their application to complex dynamical behaviour is not yet understood.
Correlation in stimulated respiratory neural noise
Authors: Hoop Bernard , Burton Melvin D. , Kazemi Homayoun , Liebovitch Larry S.
Published: July 2002

Noise in spontaneous respiratory neural activity of the neonatal rat isolated brainstem–spinal cord preparation stimulated with acetylcholine (ACh) exhibits positive correlation. Neural activity from the C4 (phrenic) ventral spinal rootlet, integrated and corrected for slowly changing trend, is interpreted as a fractal record in time by rescaled range, relative dispersional, and power spectral analyses. The Hurst exponent H measured from time series of 64 consecutive signal levels recorded at 2 s intervals during perfusion of the preparation with artificial cerebrospinal fluid containing ACh at concentrations 62.5 to 1000 μM increases to a maximum of 0.875±0.087 (SD) at 250 μM ACh and decreases with higher ACh concentration. Corrections for bias in measurement of H were made using two different kinds of simulated fractional Gaussian noise. Within limits of experimental procedure and short data series, we conclude that in the presence of added ACh of concentration 250 to 500 μM, noise which occurs in spontaneous respiratory-related neural activity in the isolated brainstem–spinal cord preparation observed at uniform time intervals exhibits positive correlation.
Chaos in thermal pulse combustion
Authors: Daw C. Stuart , Thomas John F. , Richards George A. , Narayanaswami Lakshmanan L.
Published: July 2002

An experimental thermal pulse combustor and a differential equation model of this device are shown to exhibit chaotic behavior under certain conditions. Chaos arises in the model by means of a progression of period-doubling bifurcations that occur when operating parameters such as combustor wall temperature or air/fuel flow are adjusted to push the system toward flameout. Bifurcation sequences have not yet been reproduced experimentally, but similarities are demonstrated between the dynamic features of pressure fluctuations in the model and experiment. Correlation dimension, Kolmogorov entropy, and projections of reconstructed attractors using chaotic time series analysis are demonstrated to be useful in classifying dynamical behavior of the experimental combustor and for comparison of test data to the model results. Ways to improve the model are suggested.
Symmetries and regular behavior of Hamiltonian systems
Authors: Kozlov Valeriy V.
Published: July 2002

The behavior of the phase trajectories of the Hamilton equations is commonly classified as regular and chaotic. Regularity is usually related to the condition for complete integrability, i.e., a Hamiltonian system with n degrees of freedom has n independent integrals in involution. If at the same time the simultaneous integral manifolds are compact, the solutions of the Hamilton equations are quasiperiodic. In particular, the entropy of the Hamiltonian phase flow of a completely integrable system is zero. It is found that there is a broader class of Hamiltonian systems that do not show signs of chaotic behavior. These are systems that allow n commuting ‘‘Lagrangian’’ vector fields, i.e., the symplectic 2-form on each pair of such fields is zero. They include, in particular, Hamiltonian systems with multivalued integrals.
Piecewise linear models for the quasiperiodic transition to chaos
Authors: Campbell David K. , Galeeva Roza , Tresser Charles , Uherka David J.
Published: July 2002

We formulate and study analytically and computationally two families of piecewise linear degree one circle maps. These families offer the rare advantage of being non-trivial but essentially solvable models for the phenomenon of mode locking and the quasiperiodic transition to chaos. For instance, for these families, we obtain complete solutions to several questions still largely unanswered for families of smooth circle maps. Our main results describe (1) the sets of maps in these families having some prescribed rotation interval; (2) the boundaries between zero and positive topological entropy and between zero length and non-zero length rotation interval; and (3) the structure and bifurcations of the attractors in one of these families. We discuss the interpretation of these maps as low-order spline approximations to the classic ‘‘sine-circle’’ map and examine more generally the implications of our results for the case of smooth circle maps. We also mention a possible connection to recent experiments on models of a driven Josephson junction.
Semiclassical limit for a truncated Hamiltonian
Authors: Castilho César , Ozorio de Almeida A. M.
Published: July 2002

In the numerical calculation of the eigenenergies of a polynomial Hamiltonian, the majority of the levels depend on the cutoff of the basis used. By analyzing the finite Hamiltonian matrix as corresponding to a classical ‘‘Action Billiard’’ we are able to explain several features of the full spectrum using semiclassical periodic orbit theory. There are a large number of low-period orbits which interfere at the higher energies contained in the billiard. In this range the billiard becomes more regular than the untruncated Hamiltonian, as reflected by the Berry–Robnik level spacing distribution.
Classical and quantum localization and delocalization in the Fermi accelerator, kicked rotor and two-sided kicked rotor models
Authors: Zaslavsky M.
Published: July 2002

The phenomena of dynamical localization, both classical and quantum, are studied in the Fermi accelerator model. The model consists of two vertical oscillating walls and a ball bouncing between them. The classical localization boundary is calculated in the case of ‘‘sinusoidal velocity transfer’’ [A. J. Lichtenberg and M. A. Lieberman, Regular and Stochastic Motion (Springer-Verlag, Berlin, 1983)] on the basis of the analysis of resonances. In the case of the ‘‘sawtooth’’ wall velocity we show that the quantum localization is determined by the analytical properties of the canonical transformations to the action and angle coordinates of the unperturbed Hamiltonian, while the existence of the classical localization is determined by the number of continuous derivatives of the distance between the walls with respect to time.
Overview: Synchronization and patterns in complex systems
Authors: Gaponov-Grekhov A. V. , Rabinovich M. I.
Published: July 2002

The theory of complex systems, such as neural assemblies or lattices of chaotic oscillators has generated many new problems including the synchronization or regularization of the cooperative behavior of systems consisting of chaotic elements, regular spatial patterns in ‘‘chaotic’’ lattices, and so on. A number of these problems were discussed at the International School in Nonlinear Science—95 (Nizhniy Novgorod, Russia). In this overview we try to formulate some of the most interesting problems that were discussed at that meeting.
Parameter renormalization of maps based on potential function
Authors: Matsuba Ikuo
Published: July 2002

A systematic way for deriving the parameter renormalization group equation for one-dimensional maps is presented and the critical behavior of periodic doubling is investigated. Introducing a formal potential function in one-parameter cases, it is shown that accumulation points correspond to local potential maxima and universal constants are easily determined. The estimates of accumulation points and universal constants match the known values asymptotically when the order of potential grows large. The potential function shows scaling in the parameter space with the universal convergent rate at the accumulation point similar to the Feigenbaum universal function. For two-parameter cases, a parameter reduction transformation is found to be useful to determine some important fixed points. A locally defined potential function is introduced and its scaling property is discussed.
On the global orbits in a bistable CML
Authors: Coutinho Ricardo , Fernandez Bastien
Published: July 2002

In an infinite one-dimensional coupled map lattice (CML) for which the local map is piecewise affine and bistable, we study the global orbits using a spatiotemporal coding introduced in a previous work. The set of all the fixed points is first considered. It is shown that, under some restrictions on the parameters, the latter is a Cantor set, and we introduce an order to study the fixed points’ existence. This also involves the proof of the coexistence of propagating fronts and stationary structures. In the second part, we analyze the global orbits which occur for strong coupling using the splitting of the dynamics into two independent (sub-)lattices, and emphasize the description of various traveling structures.
Lyapunov instability of two-dimensional fluids: Hard dumbbells
Authors: Milanović Lj. , Posch H. A. , Hoover Wm. G.
Published: July 2002

We generalize Benettin’s classical algorithm for the computation of the full Lyapunov spectrum to the case of a two-dimensional fluid composed of linear molecules modeled as hard dumbbells. Each dumbbell, two hard disks of diameter σ with centers separated by a fixed distance d, may translate and rotate in the plane. We study the mixing between these qualitatively different degrees of freedom and its influence on the full set of Lyapunov exponents. The phase flow consists of smooth streaming interrupted by hard elastic collisions. We apply the exact collision rules for the differential offset vectors in tangent space to the computation of the Lyapunov exponents, and of time-averaged offset-vector projections into various subspaces of the phase space. For the case of a homogeneous mass distribution within a dumbbell we find that for small enough d/σ, depending on the density, the translational part of the Lyapunov spectrum is decoupled from the rotational part and converges to the spectrum of hard disks.
Stochastic resonance in coupled nonlinear dynamic elements
Authors: Löcher M. , Cigna D. , Hunt E. R. , Johnson G. A. , Marchesoni F. , Gammaitoni L. , Inchiosa M. E. , Bulsara A. R.
Published: July 2002

We investigate the response of a linear chain of diffusively coupled diode resonators under the influence of thermal noise. We also examine the connection between spatiotemporal stochastic resonance and the presence of kink–antikink pairs in the array. The interplay of nucleation rates and kink speeds is briefly addressed. The experimental results are supplemented with simulations on a coupled map lattice. We furthermore present analytical results for the synchronization and signal processing properties of a Φ4 field theory and explore the effects of various forms of nonlinear coupling.
Bifurcation analysis of chemical reactors and reacting flows
Authors: Balakotaiah Vemuri , Dommeti Sandra M. S. , Gupta Nikunj
Published: July 2002

In this work we review the local bifurcation techniques for analyzing and classifying the steady-state and dynamic behavior of chemical reactor models described by partial differential equations (PDEs). First, we summarize the formulas for determining the derivatives of the branching equation and the coefficients in the amplitude equations for the most common singularities. We also illustrate the procedure for the numerical computation of these coefficients. Next, the application of these local results to various reactor models described by PDEs is discussed. Specifically, we review the recent literature on the bifurcation features of convection-reaction and convection-diffusion-reaction models in one and more spatial dimensions, with emphasis on the features introduced due to coupling between the flow, heat and mass diffusion and chemical reaction. Finally, we illustrate the use of dynamical systems concepts in developing low dimensional (effective or pseudohomogeneous) models of reactors and reacting flows, and discuss some problems of current interest.
Using weighted global control for stabilizing patterned states
Authors: Panfilov Vadim , Sheintuch Moshe
Published: July 2002

A general method to control a desired patterned state in reaction–diffusion processes is presented. Weighted global control is aimed to keep weighted spatially averaged properties of state variable at preset values. It is shown that weighted global control creates a stable direction in the global space of system states and affects system dynamics globally. We apply it for a specific two-component reaction–diffusion system and show that the desired pattern is attainable for a wide range of the control parameters.
On the dynamics of nonlinear systems with input constraints
Authors: Kapoor Navneet , Daoutidis Prodromos
Published: July 2002

In this work we deal with the dynamical analysis of nonlinear systems with input constraints. A characterization of the domain of attraction of the region of controllability of an equilibrium point under bounded control is provided and the concept of regions of invariance within such domains of attraction is introduced and characterized. The concepts and results are illustrated through case studies on chemical reactor models.