bluuebunny/crossref_metadata_2025 huggingface dataset:
Unstable evolution of pointwise trajectory solutions to chaotic maps
Authors: Fox Ronald F.
Published: July 2002

Simple chaotic maps are used to illustrate the inherent instability of trajectory solutions to the Frobenius–Perron equation. This is demonstrated by the difference in the behavior of δ-function solutions and of extended densities. Extended densities evolve asymptotically and irreversibly into invariant measures on stationary attractors. Pointwise trajectories chaotically roam over these attractors forever. Periodic Gaussian distributions on the unit interval are used to provide insight. Viewing evolving densities as ensembles of unstable pointwise trajectories gives densities a stochastic interpretation.
Changes in the adiabatic invariant and streamline chaos in confined incompressible Stokes flow
Authors: Vainshtein D. L. , Vasiliev A. A. , Neishtadt A. I.
Published: July 2002

The steady incompressible flow in a unit sphere introduced by Bajer and Moffatt [J. Fluid Mech. 212, 337 (1990)] is discussed. The velocity field of this flow differs by a small perturbation from an integrable field whose streamlines are almost all closed. The unperturbed flow has two stationary saddle points (poles of the sphere) and a two-dimensional separatrix passing through them. The entire interior of the unit sphere becomes the domain of streamline chaos for an arbitrarily small perturbation. This phenomenon is explained by the nonconservation of a certain adiabatic invariant that undergoes a jump when a streamline crosses a small neighborhood of the separatrix of the unperturbed flow. An asymptotic formula is obtained for the jump in the adiabatic invariant. The accumulation of such jumps in the course of repeated crossings of the separatrix results in the complete breaking of adiabatic invariance and streamline chaos.
Catastrophic extinction, noise-stabilized turbulence and unpredictability of competition in a modified Volterra–Lotka model
Authors: Goryachev A. B. , Polezhaev A. A. , Chernavskii D. S.
Published: July 2002

Spatial coexistence and competition among species is investigated through a modified Volterra–Lotka model which takes into account sexual breeding. This allows the population specific growth rate to depend on the population density. As a result of this modification the degeneracy inherent in the classical model is eliminated and qualitatively novel regimes are observed, as demonstrated by parametric analysis of the model. In the case where the corresponding parameters of competing species do not differ significantly the model can be reduced to a single Ginzburg–Landau type equation. The spatially distributed model is analyzed both in the absence and in the presence of noise mimicking inherent fluctuations in birth and death rates. It is shown that noise can qualitatively change the behavior of the system. Not only does it induce the formation of spatial patterns, but also switches on endless turbulent-like rearrangement of the system. When initially unpopulated habitat is occupied by competing species even a very low-intensity noise makes the final state of the system totally unpredictable and sensitive to any fluctuations.
Low-frequency dynamics of lasers
Authors: Khanin Ya. I.
Published: July 2002

An approach to nonlinear dynamics of multimode lasers is developed. It is based on the concept of two systems of eigenoscillations: optical modes and relaxation oscillations. The importance of a correct (not arbitrary) choice of a model is underlined. Characteristic features of two different rate equation models are formulated and compared. A method of selective perturbation on the system is described which makes it possible to study interrelations between optical modes and relaxation oscillations, and to control dynamical behavior of a laser. The possibility of using dynamical regularities for solving both applied and basic problems is illustrated in several examples.
Quantum chaos in gas
Authors: Kadomtsev B. B. , Kadomtsev M. B.
Published: July 2002

A new approach to the description of gas kinetics is proposed. The approach is based on a fundamental presumption which states that binary collisions of gas atoms, moving in a chaotic way, can serve as ‘‘interior measurements.’’ These ‘‘measurements’’ result in collapses of atomic wave functions. The ensuing decoherence is capable of transforming the wave function of gas atoms into a set of small-size wave packets. Their kinetics is considered in detail. Quantum effects linear in the Planck constant are taken into account.
Drift mechanism caused by a nonlinear wave and the Cassini Division and Uranian rings formation
Authors: Fridman A. M. , Khoruzhii O. V. , Gor’kavyi N. N.
Published: July 2002

The mechanism leading to the observed coexistence of gaps and narrow ringlets in the planetary rings is found. It is based upon the quasi-stationary radial drift of the matter under action of two forces in the disk plane: the Coriolis force and the Reynolds stresses. To an accuracy of the factor of 2 the first force coincides with the Lorentz force, therefore the radial drift in rings is similar to the gradient drift of plasma in the magnetic field. The second force is produced by the wave generated by the nearby satellite in the resonance position. In inertial systems, the second force alone causes a matter flow in its direction, called acoustic streaming. Since the radial drift is caused by nonlinear time-averaged force of high-frequency harmonic interactions in the wave, it exists in the wave propagation zone: from the birth place of the wave—the resonance position, up to the reflection point of the wave, where its group velocity vanishes. Our estimations show that the size of the density wave propagation zone corresponding to the density wave which had been formerly generated the 2:1 orbital resonance with Mimas is consistent with the width of the Cassini Division. In our case the nature of the radial drift is such that first of all it clears out the farthest from the resonance position; later, the closer areas also get affected by the drift. The zone closest to the resonance position itself is the last to be involved in the process. The matter carried away by the drift is partially accumulated near the resonance position forming a narrow dense ringlet.
The large-scale vortex structures in plasma-like media and the electric explosion of conductors
Authors: Iskoldsky A. M. , Volkov N. B. , Zubarev N. M. , Zubareva O. V.
Published: July 2002

Formation of large-scale hydrodynamic convective patterns in plasma-like current-carrying media is considered. This process is shown to be described by the same equations, as Bénard rolls, except that a temperature field must be replaced by a magnetic field. A simple low-mode model of spatial pattern formation for a case of cylindrical liquid-metal conductor with current is proposed and investigated. Nonlinear interaction of perturbations of the magnetic field and the velocity field results in an increase of effective conductor resistance even when transport coefficients are constant. In our opinion, it is this instability, that is of first importance at the initial stages of the electric explosion of conductors. In particular, it leads to conductor stratification and electric current interruption.
Chaotic motion in an oscillatory boundary layer
Authors: Mehta V. , Thompson C. , Mulpur A. , Chandra K.
Published: July 2002

The chaotic time oscillations in an incompressible fluid driven into motion by a harmonic time-varying pressure gradient is examined. Special attention is given to centrifugal destabilization of the viscous boundary layer. The basic flow is shown to be linearly unstable. For increasing modulation amplitude, the flow exhibits chaotic oscillations. The energy exchange between subharmonics and superharmonics of the least-stable spanwise wave number is considered. The presence of subharmonic Fourier modes are shown to accelerate the transition to temporally chaotic motion.
Master-slave synchronization and the Lorenz equations
Authors: Balmforth Neil , Tresser Charles , Worfolk Patrick , Wu Chai Wah
Published: July 2002

Since the seminal remark by Pecora and Carroll [Phys. Rev. Lett. 64, 821 (1990)] that one can synchronize chaotic systems, the main example in the related literature has been the Lorenz equations. Yet this literature contains a mixture of true and false, and of justified and unsubstantiated claims about the synchronization properties of the Lorenz equations. In this note we clarify some of the confusion.
Branching equation of Andronov-Hopf bifurcation under group symmetry conditions
Authors: Loginov B. V. , Trenogin V. A.
Published: July 2002

In branching theory of solutions of nonlinear equations group analysis methods [Ovsyannikov, Group Analysis of Differential Equations (Nauka, Moscow, 1978); Lectures on the Theory of Group Properties of Differential Equations (Novosibirsk University, Novosibirsk, 1966)] give the general approach for the construction of the complete form of branching equation and its subsequent investigation. These methods are applied here to the general situation of Andronov-Hopf bifurcation when there are some multiple semisimple eigenvalues on imaginary axis.
The interaction of resonances in a weakly nonlinear oscillator with a quasiperiodic excitation
Authors: Levandovsky A. Yu. , Tsarin Yu. A. , Vavriv D. M.
Published: July 2002

Conditions for chaos onset due to the interaction of resonances in a weakly nonlinear oscillator with a quasiperiodic excitation are investigated. The focus is made on the interaction of the 1:1 resonance with that of 1:m, where m is an arbitrary integer number. Analytical conditions of the chaos arising are obtained through the combined application of the averaging procedure and Melnikov’s technique. The comparison study of these conditions with those following from standard Chirikov’s approach is provided.
On chaotic dynamics in “pseudobilliard” Hamiltonian systems with two degrees of freedom
Authors: Eleonsky V. M. , Korolev V. G. , Kulagin N. E.
Published: July 2002

A new class of Hamiltonian dynamical systems with two degrees of freedom is studied, for which the Hamiltonian function is a linear form with respect to moduli of both momenta. For different potentials such systems can be either completely integrable or behave just as normal nonintegrable Hamiltonian systems with two degrees of freedom: one observes many of the phenomena characteristic of the latter ones, such as a breakdown of invariant tori as soon as the integrability is violated; a formation of stochastic layers around destroyed separatrices; bifurcations of periodic orbits, etc. At the same time, the equations of motion are simply integrated on subsequent adjacent time intervals, as in billiard systems; i.e., all the trajectories can be calculated explicitly: Given an initial data, the state of the system is uniquely determined for any moment. This feature of systems in interest makes them very attractive models for a study of nonlinear phenomena in finite-dimensional Hamiltonian systems. A simple representative model of this class (a model with quadratic potential), whose dynamics is typical, is studied in detail.
Synchronizing Moore and Spiegel
Authors: Balmforth N. J. , Craster R. V.
Published: July 2002

This paper presents a study of bifurcations and synchronization {in the sense of Pecora and Carroll [Phys. Rev. Lett. 64, 821–824 (1990)]} in the Moore–Spiegel oscillator equations. Complicated patterns of period-doubling, saddle-node, and homoclinic bifurcations are found and analyzed. Synchronization is demonstrated by numerical experiment, periodic orbit expansion, and by using coordinate transformations. Synchronization via the resetting of a coordinate after a fixed interval is also successful in some cases. The Moore–Spiegel system is one of a general class of dynamical systems and synchronization is considered in this more general context.
On invariant manifolds attached to oscillating boundaries in Stokes flows
Authors: Yuster T. , Hackborn W. W.
Published: July 2002

Consider a steady Stokes flow bounded by a flat wall to which a separatrix, not tangent to the wall, is attached at point S. If the wall is made to slowly oscillate periodically with small amplitude in a longitudinal direction, then the Poincaré map associated with this perturbed flow has a fixed point on the wall near S with an invariant manifold. This result also holds for flows bounded by a cylindrical wall and flows in which the small periodic perturbation is not due to the oscillation of the wall. This result is applied to several flow geometries in the literature.
An experimental spatio-temporal state transition of coupled magneto-elastic system
Authors: Hikihara Takashi , Okamoto Yoshinobu , Ueda Yoshisuke
Published: July 2002

In this paper the vibration and the traveling wave in a coupled magneto-elastic beam system are discussed experimentally. The vibration excited by the periodical forcing at the beam system propagates to another as a wave through the coupling elastic beams. Each magneto-elastic beam shows the variety of vibrations caused by the nonlinearity of the potential well and the wave propagation with time delay. The temporal vibration of the magneto-elastic beam is explained with relations to the spatial state transition based on the experimental results.
On the absence of a real-analytic first integral for ABC flow when A=B
Authors: Ziglin S. L.
Published: July 2002

In this paper we report on the absence of a real-analytic first integral for the well-known system describing the steady-state flow of an ideal incompressible liquid with periodic boundary conditions, called ABC flow, in the case when two of the three parameters entering the system are equal and some inequality exists between them and the third parameter.
Communicating with noise: How chaos and noise combine to generate secure encryption keys
Authors: Minai Ali A. , Pandian T. Durai
Published: July 2002

An approach for the secure transmission of encrypted messages using chaos and noise is presented in this paper. The method is based on the synchronization of certain types of chaotic oscillators in response to a common noise input. This allows two distant oscillators to generate identical output which can be used as a key for encryption and decryption of a message signal. The noiselike synchronizing input—which contains no message information—is communicated to identical oscillators in the transmitter and the receiver over a public channel. The encrypted message is also sent over a public channel, while the key is never transmitted at all. The chaotic nature of the oscillators which generate the key and the randomness of the signal driving the process combine to make the recovery of the key by an eavesdropper extremely difficult. We evaluate system performance with respect to security and robustness and show that a robust and secure system can be obtained.
A cryptosystem based on cellular automata
Authors: Urı́as Jesús , Ugalde Edgardo , Salazar Gelasio
Published: July 2002

Cryptosystems for binary information are based on two primitives: an indexed family of permutations of binary words and a generator of pseudorandom sequences of indices. A very efficient implementation of the primitives is constructed using the phenomenon of synchronization in cellular automata.
Ripening of surface phases coupled with oscillatory dynamics and self-induced spatial chaos through surface roughening
Authors: Pismen L. M. , Rubinstein B. Y.
Published: July 2002

Some pattern formation processes on single-crystal catalytic surfaces involve transitions between alternative surface phases coupled with oscillatory reaction dynamics. We describe a two-tier symmetry-breaking model of this process, based on nanoscale boundary dynamics interacting with oscillations of adsorbate coverage on microscale. The surface phase distribution oscillates together with adsorbate coverage, and, in addition, undergoes a slow coarsening process due to the curvature dependence of the drift velocity of interphase boundaries. The coarsening is studied both statistically, assuming a circular shape of islands of the minority phase, and through detailed Lagrangian modeling of boundary dynamics. Direct simulation of boundary dynamics allows us to take into account processes of surface reconstruction, leading to self-induced surface roughening. As a result, the surface becomes inhomogeneous, and the coarsening process is arrested way before the thermodynamic limit is reached, leaving a chaotic distribution of surface phases.
Chaotic patterns in a coupled oscillator–excitator biochemical cell system
Authors: Schreiber Igor , Hasal Pavel , Marek Miloš
Published: July 2002

In this paper we examine dynamical modes resulting from diffusion-like interaction of two model biochemical cells. Kinetics in each of the cells is given by the ICC model of calcium ions in the cytosol. Constraints for one of the cells are set so that it is excitable. One of the constraints in the other cell — a fraction of activated cell surface receptors—is varied so that the dynamics in the cell is either excitable or oscillatory or a stable focus. The cells are interacting via mass transfer and dynamics of the coupled system are studied as two parameters are varied—the fraction of activated receptors and the coupling strength. We find that (i) the excitator–excitator interaction does not lead to oscillatory patterns, (ii) the oscillator–excitator interaction leads to alternating phase-locked periodic and quasiperiodic regimes, well known from oscillator–oscillator interactions; torus breaking bifurcation generates chaos when the coupling strength is in an intermediate range, (iii) the focus–excitator interaction generates compound oscillations arranged as period adding sequences alternating with chaotic windows; the transition to chaos is accompanied by period doublings and folding of branches of periodic orbits and is associated with a Shilnikov homoclinic orbit. The nature of spontaneous self-organized oscillations in the focus–excitator range is discussed.
Chaos in spacecraft attitude motion in Earth’s magnetic field
Authors: Beletsky V. V. , Lopes R. V. F. , Pivovarov M. L.
Published: July 2002

The rotational motion of a satellite with a magnetic stabilization system is discussed. The motion is described by a nonautonomous differential equation, with the magnetic moment of the satellite as a parameter. The global phase portrait of the problem is investigated in a wide range of magnetic-parameter values, using a numerical realization of the method of Poincaré point maps. New periodic solutions of the problem are found, and an analysis is carried out of the evolution of the phase portrait and the bifurcation of periodic solutions with varying magnetic-parameter values. The values of the magnetic parameter that must be avoided in the design of the satellite magnetic stabilization system are discussed.
Modeling of stress distribution in granular piles: Comparison with centrifuge experiments
Authors: Modaressi A. , Boufellouh S. , Evesque P.
Published: July 2002

The classical method to compute stress and strain distributions in granular materials is recalled using continuum mechanics approach, and different rheological laws described. It is recalled that granular materials exhibit highly nonlinear response such as nonlinear elasticity, dilatancy and plastic flow. Finite element technique is used to predict the stress field distribution below a conic and a triangular pile. The dependence of the stress distribution on the rheological law, the bottom boundary condition and the building process (horizontal or inclined strata) is demonstrated. These results are compared to experimental data obtained in centrifuge.
Obtaining functional form for chaotic time series evolution using genetic algorithm
Authors: Yadavalli Vamsi K. , Dahule Rahul K. , Tambe Sanjeev S. , Kulkarni B. D.
Published: July 2002

A genetic algorithm (GA) based strategy is presented for deducing an exact or near-exact functional form from a time series. The GA formalism proposed here utilizes (i) the “postfix” representation with a view to reduce the procedural complexities and (ii) the “elitist mating” scheme to produce fitter offspring strings. The GA procedure is exemplified by considering chaotic time series of the well-known logistic, Henon and universal maps. The GA correctly recovers the underlying functional forms for the respective time series. Measurements from a number of finite-dimensional physical, biological, and other systems often give rise to complex time series and the presented methodology should prove useful in obtaining functional forms describing accurately the evolution of the time series.
Anomalous spatio-temporal chaos in a two-dimensional system of nonlocally coupled oscillators
Authors: Nakao Hiroya
Published: July 2002

A two-dimensional system of nonlocally coupled complex Ginzburg–Landau oscillators is investigated numerically for the first time. As previously shown for the one-dimensional case, this two-dimensional system exhibits anomalous spatio-temporal chaos characterized by power-law spatial correlations. In this chaotic regime, the amplitude difference between neighboring elements displays temporal noisy on–off intermittency. The system is also spatially intermittent in this regime, as revealed by multiscaling analysis: The amplitude field is multiaffine and the difference field is multifractal. Correspondingly, the probability distribution function of the measure defined for each field is strongly non-Gaussian, exhibiting scale-dependent deviations in the tail due to intermittency.
A practical approach to multivariate interpolation
Authors: Schulz Stefan , de Vivie-Riedle Regina
Published: July 2002

We present a simple multivariate interpolation scheme of arbitrary dimensionality based on Mathematica. The only limitation of the scheme is that the data must be distributed over a regular tensor-product grid. Since most software libraries fail to include a multivariate interpolation scheme that goes beyond three dimensions, the implemented code should prove useful in many applications that require interpolation in more than three variables. As an application, we use our program to construct smooth molecular potential-energy functions from data obtained by electronic structure calculations. For the three-dimensional case we compare the interpolants generated by our code to those resulting from standard library routines. © 1997 American Institute of Physics.
TTC: Symbolic tensor calculus with indices
Authors: Balfagón A. , Jaén X.
Published: July 2002

In an earlier paper [P. Castellvı́, X. Jaén, and E. Llanta, Comput. Phys. 9, 3 (1995)] we presented the capabilities of TTC (Tools of Tensor Calculus, a Mathematica package, see http://baldufa.upc.es/ttc) when inputs are made in index notation. In that article inputs were merely an effective way to indicate explicit operations to be performed on tensors. Here we describe the way TTC operates with index notation at a symbolic level, that is, when inputs and outputs are expressed in index notation and tensors are not explicitly declared. The operations are performed only at a symbolic level. This is not just an appearance of symbolic computing supplemented with a limited collection of rules. TTC makes algorithm simplifications on symbolic indexed expressions while using the symmetry properties of tensors. © 1998 American Institute of Physics.
Photoinduced effects in Ag4P2O7 single crystals
Authors: Hirono Takushi , Fukuma Masaharu , Yamada Tomoaki
Published: July 2002

Optical and photosensitive properties of Ag4P2O7 single crystals have been studied. The measured band gap is 3.4 eV and the transition is thought to be indirect. Ag4P2O7 single crystals show photochromism. An absorption band centered at 500 nm is induced by near-ultraviolet light irradiation, and transmission can be restored both by heating and by visible light irradiation. The absorption band also shows dichroism. The photochromic mechanism has been investigated using x-ray photoelectron spectroscopy. It is found that silver ions are reduced and PO4 tetrahedra are condensed by near-ultraviolet light irradiation.
Interface charging and solar-cell characteristics: CuInSe2/CdS
Authors: Eron M. , Rothwarf A.
Published: July 2002

A model is presented for heterojunction solar cells, in which interface recombination is the dominant diode current mechanism, that relates the charging of interface states to the voltage dependence of the light-generated current jL(V). The model also shows how a diode ideality factor greater than two can occur. The calculations presented are for the small-signal case, and do not treat the intensity dependence of the collection factor η(V)=jL(V)/jsc. The parameters chosen were such as to account for the trends seen in the CuInSe2/CdS solar cell.
Electroluminescence in ZnO varistors: Evidence for hole contributions to the breakdown mechanism
Authors: Pike G. E. , Kurtz S. R. , Gourley P. L. , Philipp H. R. , Levinson Lionel M.
Published: July 2002

The previously postulated production of holes during the electrical breakdown of varistors has been directly verified. In some compositions band-gap (3.2 eV) luminescence from the recombination of these holes with free electrons has been observed. The intensity of this luminescence is greater in varistor compositions exhibiting higher nonlinearity coefficients. It is also proportional to the square of the current which implies hole creation by impact ionization in the depletion region near the grain boundaries. This study used varistors of relatively simple chemical composition.
Chaos and thermal noise in the rf-biased Josephson junction
Authors: Kautz R. L.
Published: July 2002

The effect of thermal noise on chaotic behavior in the rf-biased Josephson junction is studied through digital simulations. In instances for which chaotic behavior occurs in the noise-free system, it is found that the dynamics of the system are almost unchanged by the addition of thermal noise unless the level of thermal noise exceeds that of the chaotic state. In instances for which the only stable states of the noise-free system are periodic solutions, small amounts of thermal noise can induce the junction to hop between two different dynamical states, producing a low-frequency noise level much higher than that of the thermal noise. Such noise-induced hopping can occur either between two periodic solutions or between a periodic solution and a metastable chaotic solution. When a metastable chaotic state is involved, temperatures somewhat higher than those which produce hopping can destablize the periodic solution to the point where the system spends virtually all of its time in the metastable chaotic state, creating noise-induced chaos. The similarities between chaotic behavior at zero temperature and noise-induced chaos are sufficiently strong that it may be difficult to distinguish the two cases experimentally.
Frequency-dependent beam steering by a focusing array of surface acoustic wave transducers: Experiment
Authors: Wilcox Jaroslava Z. , Brooks Robert E.
Published: July 2002

Experimental results that verify focusing and dispersion with frequency of surface acoustic waves (SAW) by wide-band phased array of SAW interdigital transducers (IDTs) are presented. The diffraction sidelobes are suppressed by weighting the drive to each IDT using capacitive taps.
GaSb films grown by vacuum chemical epitaxy using triethyl antimony and triethyl gallium sources
Authors: Fraas L. M. , McLeod P. S. , Partain L. D. , Cape J. A.
Published: July 2002

GaSb films have been grown using triethyl-Ga and triethyl-Sb sources. In a hot-wall reaction chamber located within a high-vacuum chamber, multiple group-III alkyl molecular beams are directed into the reaction chamber onto wafers. The group-V molecules are injected from the perimeter of the reaction chamber and undergo molecular flow across the deposition zone. The utilization efficiency of the group-V source material is enchanced by the use of a thermal cracker located at the point of group-V gas injection and by the use of the hot-wall chamber. Both unintentionally doped p-type and Te doped n-type GaSb films are grown and characterized. GaSb p-n junction photodiodes are also reported with internal quantum yields as high as 85%. Unintentionally doped films were shown to have background carrier concentrations of 4×1016 cm3 by capacitance versus voltage measurement.
The electrical properties of ferroelectric LiTaO3 and its solid solutions
Authors: Huanosta A. , West A. R.
Published: July 2002

ac impedance techniques have been used to characterize ceramic samples of LiTaO3 and the solid solutions Li1−5xTa1+xO3 as a function of temperature in the range 350–800 °C. LiTaO3 has a low conductivity and the principal charge carriers appear to be electrons. At temperatures well removed from its ferroelectric Curie temperature, TC, 640 °C, a single arc or semicircle appears in the complex impedance plane representation of the ac impedance data and is attributed to the electronic resistance of the sample in parallel with the geometric capacitance. At temperatures close to TC an additional semicircle appears. This is attributed to a circuit element that includes the high capacitance values associated with the ferroelectric polarization processes. A method for extracting capacitance values from such data is given. It is shown that, under certain circumstances, fixed frequency measurements of capacitance can give rise to incorrect estimates of both TC and the magnitude of the capacitance as a function of temperature. The nonstoichiometric lithium tantalates are essentially lithium-ion vacancy conductors and the level of their conductivity may be correlated with composition and the solid solution mechanism. These materials are also ferroelectric and TC decreases with increasing departure from the stoichiometric composition.
Solid-state and electrochemical properties of polyselenophene
Authors: Glenis Spyridon , Ginley David S. , Frank Arthur J.
Published: July 2002

Electrochemically grown polyselenophene films in both the oxidized electrolyte-doped state and the neutral undoped state have been characterized by a wide variety of techniques. Information on the growth, composition, and surface morphology of the polymer has been obtained. Electrical conductivity varies by 105 Ω−1 cm−1 between the doped and undoped films. The temperature dependence of the electrical conductivity of the doped material is characteristic of a semiconductor. The Se atom of the ring contributes negligibly to the π-electron system of the polymer in the ground state, although it has an important effect on the conjugated chain length and the electrical conductivity. Bipolarons are found to play a predominant role in the electrical conduction mechanism.
Optical and structural characteristics of Al2O3 films deposited by the reactive ionized cluster beam method
Authors: Hashimoto H. , Levenson L. L. , Usui H. , Yamada I. , Takagi T.
Published: July 2002

Al2O3 films about 1000 Å thick were deposited on polished Si(100) substrates by the reactive ionized cluster beam method. It was found that the index of refraction, the etch rate in HF, and the microstructure of the films could be controlled by varying substrate temperatures up to 600 °C and acceleration voltages between 0.25 and 3 kV.
Magnetic properties and domain structures in domain refined grain-oriented silicon steel (invited)
Authors: Nozawa T. , Matsuo Y. , Kobayashi H. , Iwayama K. , Takahashi N.
Published: July 2002

The present paper is concerned with the development of low-loss grain-oriented silicon steel, and especially with the magnetic properties and domain structures in domain refined grain-oriented silicon steel. The effects of locally induced stress and slight magnetic flux emergence have been examined as possible nucleation centers for effective domain walls which contribute to magnetization. The fundamental phenomena and their origins have been discussed on the bases of experimental facts. It was concluded that these domain refining effects were based upon interactions between subdomains having transverse magnetization, which originate from magnetic free poles and/or internal stress, and tensile stress in silicon steel with orientation near (110)[001]. The features of magnetic properties and domain structures of domain refined grain-oriented silicon steel both for stack and wound cores are described. Finally, a new technique for raising the degree of (110)(001) orientation is introduced, and the approach to minimum loss in grain-oriented silicon steel is discussed.
The equation of state of molybdenum at 1400 °C
Authors: Miller Gregory H. , Ahrens Thomas J. , Stolper Edward M.
Published: July 2002

Shock compression data to 96 GPa for pure molybdenum, initially heated to 1400 °C, are presented. Finite strain analysis of the data gives a bulk modulus at 1400 °C, K0S, of 244±2 GPa and its pressure derivative, K′0S, of 4. A fit of shock velocity to particle velocity gives the coefficients of US=c0+sUP to be c0=4.77±0.06 km/s and s=1.43±0.05. From the zero-pressure sound speed c0, a bulk modulus of 232±6 GPa is calculated which is consistent with extrapolation of ultrasonic elasticity measurements. The temperature derivative of the bulk modulus at zero pressure, ∂K0S/∂T‖P, is approximately −0.012 GPa/K. A thermodynamic model is used to show that the thermodynamic Grüneisen parameter is proportional to the density and independent of temperature. The Mie–Grüneisen equation of state adequately describes the high-temperature behavior of molybdenum under the present range of shock loading conditions.
High-power soliton generation at microwave frequencies
Authors: Ikezi H. , Wojtowicz S. S. , Waltz R. E. , deGrassie J. S. , Baker D. R.
Published: July 2002

We point out that the creation of a soliton pulse train in a nonlinear-dispersive system can be used for the generation of high-power microwave bursts. A modulated transmission line with an appropriate nonlinear dielectric is proposed. The nonlinear wave evolution is analyzed and requirements for the dielectric material are found. Problems associated with the material are discussed. Low-power experimental demonstrations of these concepts are presented.
Mechanisms of phase transformation in low-temperature irradiated NiAl
Authors: Jaouen C. , Rivière J. P. , Delafond J. , Thomé L. , Pons F. , Danielou R. , Fontenille J. , Ligeon E.
Published: July 2002

Phase transformations induced by low-temperature (15 K), heavy- (Xe) and light- (D) ion irradiation of a monocrystalline NiAl intermetallic compound are investigated via in situ Rutherford backscattering and channeling experiments. Total amorphization of the irradiated layer is observed, whatever the irradiation ion mass, as soon as a mean number of displacements per atom of 0.3–0.4 is reached. On the contrary, the mechanisms of phase transformation appear to be strongly dependent on the cascade regime. Light-ion irradiation leads to a sigmoidal shape of the amorphization kinetics, suggesting that amorphization takes place by a defect accumulation process. Heavy-ion irradiation shows a more complex behavior with the formation of a premartensitic phase prior to amorphization. An interpretation of this new type of phase transformation is presented in terms of defect cascade disordering and damage-induced stresses.
Electrical properties of TiO2 films deposited by a reactive-ionized cluster beam
Authors: Fukushima K. , Yamada I.
Published: July 2002

Titanium dioxide films of 100–450-nm thickness were deposited on fused quartz and silicon substrates heated at 350 °C by a reactive-ionized cluster-beam deposition. After the deposition, films were annealed at 600 °C in dry O2 ambient. The electrical properties of TiO2 films and the TiO2-Si interface were analyzed. The dielectric constant of the film after the annealing was in a range of 35–108, which depended on the deposition conditions. The films showed a high breakdown voltage and a sufficiently low interface-state density of 1–2×1011 cm−2 eV−1 at the midgap.
Surface impedance and reflectivity of superconductors
Authors: Pöpel R.
Published: July 2002

A complete solution to the Mattis–Bardeen equations of the anomalous skin effect in superconductors [Phys. Rev. 111, 412 (1958)] is presented in the case of plane, bulk conductors. This solution shows good agreement with existing solutions in the microwave region, and for the first time, it correctly describes measurements in the far-infrared region. It turns out that the solution to the Mattis–Bardeen equations for the extreme anomalous limit cannot be used for a correct description of experimental results. In addition, our exact solution is also applicable to strong-coupling superconductors.
Oxygen diffusion and phase transformation in YBa2Cu3O7−x
Authors: Shi Donglu , Krucpzak J. , Tang Ming , Chen Nan , Bhadra R.
Published: July 2002

Isothermal anneal experiments have been conducted over a wide temperature range from 300 to 900 °C for polycrystalline YBa2 Cu3 O7−x samples in air. The phase transformation and oxygen contents of the annealed samples were studied and determined by x-ray diffraction and iodine titration. Oxygen diffusion coefficients at different temperatures were determined by a novel technique based on direct observation of the oxygen diffusion fronts by polarized light microscopy. The activation energy for the diffusion of oxygen in YBa2 Cu3 O7−x was obtained by an Arrhenius plot of the diffusion coefficients at different temperatures. The tetragonal-to-orthorhombic phase transformation controlled by oxygen diffusion is discussed.
Evanescent wave absorption spectroscopy using multimode fibers
Authors: Ruddy V. , MacCraith B. D. , Murphy J. A.
Published: July 2002

Evanescent wave absorption in an aqueous dye solution has been performed using multimode fused silica fiber which was unclad at the sensing region. Evanescent absorbance values for methylene blue in a concentration range 3×10−8 to 5×10−6 M are reported. In order to produce modes close to cutoff in the sensing region, tunneling modes were launched into the clad fiber. Spatial filtering was used to restrict the light launched to those modes which have substantial power in their evanescent field in the unclad region. The measured evanescent absorbance of the dye solution was found to vary linearly with the exposed core length and to exhibit a square root dependence on concentration. The former effect is predicted from standard theory while the latter is attributed to adsorption on the core surface which obeys a Debye–Huckel-type concentration dependence. In addition, a concentration enhancement of two orders of magnitude was observed due to this surface adsorption. While this effect limits the use of the technique for a reversible sensor it may be exploited in disposable probes.
Observation of random telegraph signals: Anomalous nature of defects at the Si/SiO2 interface
Authors: Ohata Akiko , Toriumi Akira , Iwase Masao , Natori Kenji
Published: July 2002

Current fluctuations with discrete levels, which are called random telegraph signals (RTSs), have been studied in small size metal-oxide-semiconductor field-effect transistors (MOSFETs) from both viewpoints of relative current change and of correlated switchings. A large relative current change of as much as 30% has been observed, even at room temperature. It behaves similarly as normal small RTSs in terms of statistics and temperature dependence. RTSs have been found also in 20-μm channel width MOSFETs. These results require another mechanism to explain RTSs in addition to simple Coulomb scattering or number fluctuation. It is emphasized that an interaction between defects at the Si/SiO2 interface is necessary to understand the correlated RTSs. The experimental results are reasonably reproduced by a model calculation assuming interacting defects. It is also pointed out that new RTSs generated by electrical stress might be a serious concern in lower submicron devices.
Internal strain relaxation and the glassy behavior of La-modified lead zirconate titanate relaxors
Authors: Viehland Dwight , Jang S. J. , Cross L. Eric , Wuttig Manfred
Published: July 2002

Nonlinear internal friction measurements have been carried out on La-modified lead zirconate titanate relaxors with a Zr/Ti ratio of 65/35. Measurements have been made as a function of La content and dc bias. The elastic softening is believed to have a ferroelastic contribution due to the tilting of the oxygen octahedra, in addition to the expected electrostrictive effects. The temperatures of the maximum softening form a plausible extension to the rhombohedral-rhombohedral phase boundary [Proc. IEEE 61, 959 (1973)]. A frequency dependence of the softening has also been found which was interpreted as the existence of fluctuations in the orientations of the tilts. These fluctuations are proposed to arise in an attempt to partially relieve an inhomogeneity in the electrostrictive strains associated with the polarization fluctuations. The results are discussed in context with previously reported transmission electron microscopy work [C. Randall, Ph. D. dissertation, University of Essex (1987)]. Dielectric measurements have also been done as a function of La content and bias, and the freezing temperature of the polarization fluctuations determined as a function of composition. A revised phase diagram has been proposed using this data base which shows different phase fields having various combinations of freezing mechanisms.
Magnetotransport properties of iron thin films
Authors: Chen Youjun , Lottis D. K. , Dahlberg E. Dan
Published: July 2002

The magnetotransport properties of iron thin films grown by molecular-beam epitaxy (MBE) have been investigated. The films were grown on (110) GaAs substrates and were allowed to develop a natural oxide. The iron oxide on the free surface is FeO and has an antiferromagnetic transition temperature on the order of 200 K. This antiferromagnetic oxide provides an exchange bias for the iron film at low temperatures. Although it is usual to study exchange coupling with magnetization measurements, we have used the low-temperature magnetotransport properties of the films to study the exchange coupling and compare it to models of this phenomenon.
Measurement of thermal diffusion in thin films using a modulated laser technique: Application to chemical-vapor-deposited diamond films
Authors: Visser Eric P. , Versteegen Erwin H. , van Enckevort Willem J. P.
Published: July 2002

A method to determine the thermal diffusivity in thin films, based on the measurement and analysis of thermal waves induced by a modulated infrared laser, is demonstrated. A nearly exact mathematical description, independent of the film geometry and including surface heat losses, is presented. It is shown that the in-plane thermal diffusivity and the heat loss through the surface can be determined independently by analysis of both the phase and the amplitude of the thermal waves. The validity of the method has been verified using high-purity copper sheets of varying thickness, for different modulation frequencies. Several polycrystalline, chemical-vapor-deposited (CVD) diamond films have been investigated. The measurements were performed both on free-standing films and on two-layer systems of CVD diamond and copper. Thermal diffusivities for polycrystalline diamond up to 6.2 cm2 s−1 were recorded.
A physics-based fitting and extrapolation method for measured impact ionization coefficients in III-V semiconductors
Authors: Chau Hin-Fai , Pavlidis Dimitris
Published: July 2002

A general approach based on a physical model of impact ionization to fit and extrapolate measured ionization coefficients of electrons α and holes β in III-V semiconductors is described. Materials being considered include GaAs, AlxGa1−xAs (x=0.1–0.4), InP, In0.53Ga0.47As, and In0.52Al0.48As. Expressions giving the correct dependencies are obtained at very large or small electric fields outside the range of most measurements while at the same time a reasonable fit is achieved for experimental data. The results of the proposed approach yielded a set of physical parameters, which can be coupled with the temperature-dependence relationships in the model to predict impact ionization coefficients over a wide range of electric fields at different temperatures, and can be useful in calculations of temperature-dependent avalanche breakdown voltages of electronic and optical devices.
Atmospheric pressure chemical vapor deposition of gallium doped zinc oxide thin films from diethyl zinc, water, and triethyl gallium
Authors: Hu Jianhua , Gordon Roy G.
Published: July 2002

Gallium doped zinc oxide films have been deposited in the temperature range 150 to 470 °C from 0.05% diethyl zinc, 0.8% water, and various triethyl gallium concentrations. The films are polycrystalline with crystallite sizes varying between 275 and 500 Å for undoped films and between 125 and 400 Å for doped films. Only those films deposited above 430 °C are highly oriented and have their c axes perpendicular to the substrate plane. The electron density, conductivity, and mobility always increase with temperature. Thicker films have higher conductivity and mobility than thinner films. The refractive index is reduced from 1.96 to 1.73 when the electron density is increased from zero to 3.7×1020 cm−3. For films deposited at 370 °C with a gallium concentration of about 2.5 at. %, the ratio of conductivity to visible absorption coefficient increases from 0.03 to 1.25 Ω−1 when the film thickness increases from 0.11 to 1.2 μm. A film deposited at 470 °C with a gallium concentration of 2.4 at. % and a thickness of 0.66 μm has a sheet resistance of 3.6 Ω/square and an average visible absorption of 6.8%. When the gallium concentration is less than 5.0 at. %, the band gap widening approximately follows the Burstein–Moss relation.
Triple crystal x-ray diffraction analysis of chemical-mechanical polished gallium arsenide
Authors: Wang V. S. , Matyi R. J.
Published: July 2002

High-resolution triple crystal x-ray diffraction has been used to monitor the magnitude of diffuse scattering from chemical-mechanical (CM) polished GaAs. The diffuse scattering, which is attributed to kinematic scattering arising from polish-induced crystallographic defects, was found to be only slightly affected when each of four CM polish parameters (bromine concentration in Br2/methanol, total polish time, polish pad rotation speed, and force on sample) was varied individually. The combined effect of increases in both the pad rotation speed and the force on the sample increased the magnitude of the diffuse scattering, suggesting the generation of mechanical damage. When all four variables were increased to their maximum values, the diffuse scattering increased dramatically and became anisotropic. We have expressed the magnitude of the diffuse scattering in terms of an ‘‘excess intensity’’ in reciprocal space to provide a semi-quantitative relation between CM polish parameters and the generation of polish-induced damage.
Raman and high-pressure photoluminescence studies on porous silicon
Authors: Sood A. K. , Jayaram K. , Muthu D. Victor S.
Published: July 2002

We show that there is no correlation between the blue shift of the visible photoluminescence band and red shift of the Raman phonon line in porous silicon, in contrast to the recently reported results. We also report a drastic red shift of the photoluminescence peak position with pressure up to 6 GPa and show that this is much larger than that of the crystalline silicon. These observations cast doubt on the suggested mechanism of quantum size effects in porous silicon.