bluuebunny/crossref_metadata_2025 huggingface dataset:
Clinical Value of Electrodiagnostic Testing Following Repair of Peripheral Nerve Lesions: A Prospective Study
Authors: VAN DE KAR Th. H. J. , JAQUET J. B. , MEULSTEE J. , MOLENAAR C. B. H. , SCHIMSHEIMER R. J. , HOVIUS S. E. R.
Published: August 2002

This study prospectively assessed the level of correlation between functional and electrophysiological recovery after median and ulnar nerve lacerations. Motor and sensory recovery were recorded clinically and electrophysiologically every 3 months in 24 patients with 29 complete median or ulnar nerve lacerations.

The strength of agreement between the clinical motor score and the electrophysiological score was “fair”, but in 41% a discrepancy was identified (kappa factor 0.39). Regeneration was not detected earlier by electrophysiology than by a thoroughly performed clinical evaluation. This suggests that electrophysiologic testing is of value as an adjunct to clinical assessment for evaluating cases in which there is clinical doubt as to the progress of regeneration and secondary surgery is contemplated.
Pedicled Fat Flap Coverage of the Median Nerve after Failed Carpal Tunnel Decompression
Authors: DE SMET L. , VANDEPUTTE G.
Published: August 2002

We reviewed 14 patients treated with either an ulnar or a hypothenar fat flap for recurrent carpal tunnel syndrome and scar tenderness. Nine patients were satisfied and there were few complications. One patient had delayed skin healing and another developed a hypertrophic scar.
A Simple and Fail Safe Method for Digital Tourniquet
Authors: SMITH I. M. , AUSTIN O. M. B. , KNIGHT S. L.
Published: August 2002

Digital tourniquets are commonly used to provide a bloodless field for surgery to the finger. Such tourniquets, however, are potentially harmful and disastrous consequences occur if they are accidentally left in place. We propose a modification of the rubber glove tourniquet technique that will provide a safe and reliable tourniquet.
Visual Estimation of Finger Angles: Do we Need Goniometers?
Authors: ROSE V. , NDUKA C. C. , PEREIRA J. A. , PICKFORD M. A. , BELCHER H. J. C. R.
Published: August 2002

Seventy-one plastic surgeons and therapists, of varying levels of seniority and experience, were asked to examine a resin cast of an adult male hand and use estimation to measure the angles of the metacarpophalangeal and interphalangeal joints of each digit. Visual estimation by all subjects was inaccurate by a mean of approximately 25% (median percentage error 22, range 1–100). Consultants were the most accurate, whilst physiotherapists were the least. Regular goniometer users were no more accurate. However, hand surgery experience correlated with accuracy, as did a stated interest in hand surgery. Although visual accuracy improves with experience, it is still an inaccurate technique. We, therefore, recommend that goniometers should be used for measuring angles in hand surgery patients.
A Prospective, Randomized, Controlled Trial of Forearm Versus Upper Arm Tourniquet Tolerance
Authors: MAURY A. C. , ROY W. S.
Published: August 2002

This prospective, randomized, controlled trial studied the duration of upper and forearm tourniquet tolerance in 24 fit, healthy volunteers. Upper arm and forearm tourniquets were applied to either arm and inflated simultaneously. The time to request for deflation was recorded for each tourniquet. The mean tolerance for the upper arm tourniquet was 18 (range 10–26) min and for the forearm tourniquet was 25 (range 12–52) min. Under the conditions of this study, forearm tourniquets were tolerated for a mean of 7 min longer than upper arm tourniquets. The increase in tourniquet time afforded by a forearm tourniquet is clinically important in hand surgery performed under local anaesthetic.
Chronic Flexion Contracture of Proximal Interphalangeal Joint Treated with the Compass Hinge External Fixator. A Consecutive Series of 27 Cases
Authors: HOUSHIAN S. , GYNNING B. , SCHRØDER H. A.
Published: August 2002

Twenty-seven chronic flexion contractures of the proximal interphalangeal joint were treated with the Compass® hinge external fixator without open surgery. The fixator was removed after a mean of 33 (range, 14–68) days. The mean time from injury to operation was 4 (range, 1–19) years and all patients were reviewed at a mean follow-up of 21 (range, 12–50) months. The mean extension gain was 38° (range, 0–70°), and the mean flexion–extension arc improved by 42° (range, 0–80°). Complications included superficial pin-track infection in 11 cases and pin loosening in four cases.
Modified Arthroplasty of the Distal Radio-Ulnar Joint
Authors: WATSON H. K. , MANZO R. L.
Published: August 2002

We report a modified arthroplasty technique for limited degenerative arthritis of the distal radioulnar joint, in which the proximal hyperemic portion of the joint is resected with preservation of the unaffected distal portion. The charts often patients, one bilateral, were retrospectively reviewed and all 11 wrists were examined after an average of 30 months. All patients reported decreased pain and increased joint function. Grip strength, supination and pronation were comparable to the opposite, unaffected side.
Second harmonic generation in two-dimensional metal photonic band gap materials
Authors: Chen Yan-bin , Cai Xiang-bao , Zhu Yong-yuan , Zhu Shi-ning , Ming Nai-ben
Published: August 2002

With plane-wave expansion and the Green function method, the second harmonic generation in a two-dimensional metal photonic band gap (PBG) material is studied theoretically. By appropriately selecting the structural parameters of the PBG material, the wave vectors of the fundamental and the second harmonics can be set at the edges of the PBG. In this case, the second harmonic can be realized efficiently due to metal surface nonlinearity. The discussion can be generalized to three-dimensional systems.
Food chain chaos due to Shilnikov’s orbit
Authors: Deng Bo , Hines Gwendolen
Published: August 2002

Assume that the reproduction rate ratio ζ of the predator over the prey is sufficiently small in a basic tri-trophic food chain model. This assumption translates the model into a singularly perturbed system of two time scales. It is demonstrated, as a sequel to the earlier paper of Deng [Chaos 11, 514–525 (2001)], that at the singular limit ζ=0, a singular Shilnikov’s saddle-focus homoclinic orbit can exist as the reproduction rate ratio ε of the top-predator over the predator is greater than a modest value ε0. The additional conditions under which such a singular orbit may occur are also explicitly given.
Room temperature structure of Pb(ZrxTi1−xO3) around the morphotropic phase boundary region: A Rietveld study
Authors: Ragini  , Ranjan Rajeev , Mishra S. K. , Pandey Dhananjai
Published: August 2002

We have carried out a detailed Rietveld analysis of x-ray powder diffraction data of Pb(ZrxTi1−x)O3 (PZT) compositions across the morphotropic phase boundary (MPB) region (x=0.515, 0.520, 0.525, 0.530). It is shown that the structure of PZT is pure tetragonal for x⩽0.515 with space group P4mm. In the MPB region, 0.515<x<0.530, the tetragonal and monoclinic (space group: Cm) phases are found to coexist as a result of a first order phase transition between the low temperature monoclinic and high temperature tetragonal phases. Further, arguments are advanced to show that the hitherto believed rhombohedral structure (FRHT) of PZT for 0.530⩽x⩽0.62 is more likely to be monoclinic.
Study of atrial arrhythmias in a computer model based on magnetic resonance images of human atria
Authors: Virag N. , Jacquemet V. , Henriquez C. S. , Zozor S. , Blanc O. , Vesin J.-M. , Pruvot E. , Kappenberger L.
Published: August 2002

The maintenance of multiple wavelets appears to be a consistent feature of atrial fibrillation (AF). In this paper, we investigate possible mechanisms of initiation and perpetuation of multiple wavelets in a computer model of AF. We developed a simplified model of human atria that uses an ionic-based membrane model and whose geometry is derived from a segmented magnetic resonance imaging data set. The three-dimensional surface has a realistic size and includes obstacles corresponding to the location of major vessels and valves, but it does not take into account anisotropy. The main advantage of this approach is its ability to simulate long duration arrhythmias (up to 40 s). Clinically relevant initiation protocols, such as single-site burst pacing, were used. The dynamics of simulated AF were investigated in models with different action potential durations and restitution properties, controlled by the conductance of the slow inward current in a modified Luo–Rudy model. The simulation studies show that (1) single-site burst pacing protocol can be used to induce wave breaks even in tissue with uniform membrane properties, (2) the restitution-based wave breaks in an atrial model with realistic size and conduction velocities are transient, and (3) a significant reduction in action potential duration (even with apparently flat restitution) increases the duration of AF.
Shock-induced arrhythmogenesis in the myocardium
Authors: Trayanova Natalia , Eason James
Published: August 2002

The focus of this article is the investigation of the electrical behavior of the normal myocardium following the delivery of high-strength defibrillation shocks. To achieve its goal, the study employs a complex three-dimensional defibrillation model of a slice of the canine heart characterized with realistic geometry and fiber architecture. Defibrillation shocks of various strengths and electrode configurations are delivered to the model preparation in which a sustained ventricular tachycardia is induced. Instead of analyzing the post-shock electrical events as progressions of transmembrane potential maps, the study examines the evolution of the postshock phase singularities (PSs) which represent the organizing centers of reentry. The simulation results demonstrate that the shock induces numerous PSs the majority of which vanish before the reentrant wavefronts associated with them complete half of a single rotation. Failed shocks are characterized with one or more PSs that survive the initial period of PS annihilation to establish a new postshock arrhythmia. The increase in shock strength results in an overall decrease of the number of PSs that survive over 200 ms after the end of the shock; however, the exact behavior of the PSs is strongly dependent on the shock electrode configuration.
Degenerate resonances in Hamiltonian systems with 3/2 degrees of freedom
Authors: Morozov Albert D.
Published: August 2002

Hamiltonian systems with 3/2 degrees of freedom close to autonomous systems are considered. Special attention is focused on the case of degenerate resonances. In this case, an averaged system in the first approximation reduces to an area-preserving mapping of a cylinder whose rotation number is a nonmonotonic function of the action variable. Behavior of the trajectories of such a map is similar to that of the trajectories of a Poincaré map. Three regions: B± in the upper and lower parts of the cylinder and an additional region A which contains separatrices of fixed points for the corresponding resonance are distinguished on the cylinder. It is shown that there is a nonempty set of initial points corresponding to walking trajectories in B± and, hence, there are no closed invariant curves that are homotopically nontrivial on the cylinder. Cells limited by a “stochastic network” can exist in region A. The number of cells is the greater the higher the order of degeneration of the resonance. Possible types of orbit behavior in region A are described.
Recurrence plots and unstable periodic orbits
Authors: Bradley Elizabeth , Mantilla Ricardo
Published: August 2002

A recurrence plot is a two-dimensional visualization technique for sequential data. These plots are useful in that they bring out correlations at all scales in a manner that is obvious to the human eye, but their rich geometric structure can make them hard to interpret. In this paper, we suggest that the unstable periodic orbits embedded in a chaotic attractor are a useful basis set for the geometry of a recurrence plot of those data. This provides not only a simple way to locate unstable periodic orbits in chaotic time-series data, but also a potentially effective way to use a recurrence plot to identify a dynamical system.
X-transport: A baseline nonambipolar transport in a diverted tokamak plasma edge
Authors: Chang C. S. , Kue Seunghoe , Weitzner H.
Published: August 2002

A new nonambipolar neoclassical transport (X-transport) mechanism has been identified which can be an irreducible baseline source of a strong radial electric field and edge pedestal formation immediately inside the separatrix in a diverted tokamak. Due to the vanishingly small poloidal magnetic field in the vicinity of a divertor X-point, there exists an ion velocity space hole at the thermal energy level. This becomes a source of a nonambipolar, collisional, convective radial transport of plasma ions, as the ions scatter into and out of the loss hole in the vicinity of an X-point. The widths of the Er and edge pedestal layers are somewhat smaller than the ion poloidal gyroradius, measured at the midplane. A simple estimate shows that the X-transport rate can be significant enough to influence a high mode transition and edge pedestal formation.
Wave propagation in an excitable medium with a negatively sloped restitution curve
Authors: Panfilov A. V. , Zemlin C. W.
Published: August 2002

Recent experimental studies show that the restitution curve of cardiac tissue can have a negative slope. We study how the negative slope of the restitution curve can influence basic processes in excitable media, such as periodic forcing of an excitable cell, circulation of a pulse in a ring, and spiral wave rotation in two dimensions. We show that negatively sloped restitution curve can result in instabilities if the slope of the restitution curve is steeper than −1 and report different manifestations of this instability.
Modulation of the beam intensity for high-dynamic-range low energy electron diffraction
Authors: Pesty F. , Garoche P. , Dorel S.
Published: August 2002

We describe a low-energy electron diffraction process with a periodical modulation of the electron beam intensity. The conditions to get a coherent modulated beam are investigated, first, by simulating the electron trajectories and second, by analyzing the diffraction pattern oscillation. The large increase in the dynamic range is exemplified by diffraction of the electrons by mica surface nanostructures.
Progress toward controlling in vivo fibrillating sheep atria using a nonlinear-dynamics-based closed-loop feedback method
Authors: Gauthier Daniel J. , Hall G. Martin , Oliver Robert A. , Dixon-Tulloch Ellen G. , Wolf Patrick D. , Bahar Sonya
Published: August 2002

We describe preliminary experiments on controlling in vivo atrial fibrillation using a closed-loop feedback protocol that measures the dynamics of the right atrium at a single spatial location and applies control perturbations at a single spatial location. This study allows investigation of control of cardiac dynamics in a preparation that is physiologically close to an in vivo human heart. The spatial-temporal response of the fibrillating sheep atrium is measured using a multi-channel electronic recording system to assess the control effectiveness. In an attempt to suppress fibrillation, we implement a scheme that paces occasionally the cardiac muscle with small shocks. When successful, the inter-activation time interval is the same and electrical stimuli are only applied when the controller senses that the dynamics are beginning to depart from the desired periodic rhythm. The shock timing is adjusted in real time using a control algorithm that attempts to synchronize the most recently measured inter-activation interval with the previous interval by inducing an activation at a time projected by the algorithm. The scheme is “single-sided” in that it can only shorten the inter-activation time but not lengthen it. Using probability distributions of the inter-activation time intervals, we find that the feedback protocol is not effective in regularizing the dynamics. One possible reason for the less-than-successful results is that the controller often attempts to stimulate the tissue while it is still in the refractory state and hence it does not induce an activation.
End-shorting and electric field in edge plasmas with application to field-reversed configurations
Authors: Steinhauer Loren C.
Published: August 2002

The shorting of open field lines where they intersect external boundaries strongly modifies the transverse electric field all along the field lines. The modified electric field is found by an extension of the familiar Boltzmann relation for the electric potential. This leads to a prediction of the electric drift. Flow generation by electrical shorting is applied here to three aspects of elongated field-reversed configurations: plasma rotation rate; the particle-loss spin-up mechanism; and the sustainability of the rotating magnetic field current drive method.
Effects of surface treatments on the adhesion of Cu and Cr/Cu metallizations to a multifunctional photoresist
Authors: Ge J. , Kivilahti J. K.
Published: August 2002

The effects of chemical, plasma, and reactive ion etching (RIE) treatments on the adhesion of Cu and Cr/Cu to the multifunctional polymer were investigated. The adhesion was measured with the newly developed pull test. The polymer surfaces were characterized by the x-ray photoelectron spectroscopy, atomic force microscopy, and surface free energy measurement. The failure modes were examined with the scanning electron microscopy and energy-dispersive spectroscopy. It was found that the adhesion of Cu and Cr/Cu to the highly functional photoresist was poor, regardless of the chemical, plasma, and reactive ion etching treatment with either O2 or CF4 used. However, the RIE pretreatment with the gas mixture (O2+CF4) of the photoresist surface increased the adhesion of sputtered Cr/Cu to the photoresist remarkably, and the failure mode was cohesive within the photoresist. Furthermore, the RIE pretreatment with pure oxygen gave rise to the needle-like surface together with virtually no introduced reactive functional groups, whereas the RIE with O2-rich gas mixture of O2+CF4 resulted in the relative smooth polymer surfaces and the newly formed C=O/O–C–O and O–C=O functionalities were incorporated on the treated surface with the increased polar surface free energy. The adhesion mechanism based on the experimental adhesion results and the surface characterizations of the polymer is proposed and discussed.
Characteristics of an atmospheric microwave-induced plasma generated in ambient air by an argon discharge excited in an open-ended dielectric discharge tube
Authors: Moon Se Youn , Choe W. , Uhm Han S. , Hwang Y. S. , Choi J. J.
Published: August 2002

Parametric observations on an atmospheric-pressure plasma sustained in ambient air by an argon discharge excited by 2.45 GHz microwaves in an open-ended dielectric discharge tube are reported. Microwave power, discharge tube dimensions, and argon flow rate were the major operating parameters. Three distinctive plasma regions were observed: plasma filaments exiting from the discharge tube, converging point of these filaments, and a plasma flame. At the filament-converging point, argon atom excitation temperature, rotational temperature, and electron density were measured by optical emission spectroscopy (OES) in the operating range of (3.0–5.0) liters per minute of gas flow rate and (650–950) W of microwave power. The measured excitation temperature and rotational temperature were (5000–5800) K and (2800–3400) K, respectively. The electron density obtained by Stark broadening width of the Hβ line showed (5.0–8.0)×1014 cm−3. It was observed that the volume of the plasma flame and the gas temperature were increased with increasing the microwave power. On the other hand, higher gas flow rates increased the electron density. In the plasma flame, the gas temperature measured by a thermocouple and OES was in the range of (1030–2200) K, which showed an exponential decrease in the axial direction away from the converging point.
Weakly relativistic one-dimensional laser pulse envelope solitons in a warm plasma
Authors: Poornakala S. , Das A. , Kaw P. K. , Sen A. , Sheng Z. M. , Sentoku Y. , Mima K. , Nishikawa K.
Published: August 2002

A class of exact one-dimensional solutions of coupled nonlinear equations describing the propagation of a weakly relativistic circularly polarized electromagnetic pulse in a warm, collisionless and unbounded plasma is presented. The solutions investigated are in the form of a slowly moving dark or bright envelope soliton with a propagation velocity comparable to the thermal speed of the particles. For such a slowly propagating entity, the modulational envelope is strongly modified by the effects arising due to ion inertia as well as by the thermal effects of both ions and electrons. Different regions of existence of dark and bright solitons have been identified. The analysis carried out here is restricted to nearly quasi-neutral dynamics where the second derivative term in the Poisson equation plays a subsidiary role. Under this approximation, the eigenvalue problem has continuum solutions and one can establish the nonlinear relationship between the group velocity of the soliton and the amplitude and frequency of the light pulse.
Quantum screening effects on dipole and quadrupole electron-impact excitation channels in dense high-temperature plasmas
Authors: Kim Chang-Geun , Jung Young-Dae
Published: August 2002

Screening effects on the dipole and quadrupole electron-impact excitation of hydrogenic ions in dense high-temperature plasmas are investigated using the effective pseudopotential model that takes into account both quantum-mechanical and plasma screening effects. The semiclassical impact parameter method is applied to the path of the projectile electron in order to visualize the electron-impact excitation probability as a function of the impact parameter, thermal de Broglie wavelength, Debye length, and projectile energy. The excitation probability is found to be significantly decreased with increasing quantum screening effects. It is found that the maximum position of the excitation probability is receded from the target nucleus with decreasing projectile energy. It is also found that the quantum screening effects on the dipole excitation process are almost identical to those on the quadrupole excitation process.
Electromagnetic secondary instabilities in electron temperature gradient turbulence
Authors: Holland C. , Diamond P. H.
Published: August 2002

The electron temperature gradient mode has been proposed as a primary mechanism for electron transport. The possibilities of magnetic secondary instabilities (“zonal” magnetic fields and magnetic “streamers”) are investigated as novel potential mechanisms for electron transport regulation and enhancement, respectively. In particular, zonal magnetic field growth and transport regulation is investigated as an alternative to electrostatic zonal flows. Growth rates and implications for electron thermal transport are discussed for both electrostatic and magnetic saturation mechanisms. The possibility of magnetic streamers (mesoscale radial magnetic fields), and their potential impact on electron thermal transport, is also considered.
Toroidal formulation of nonlinear-rf-driven flows
Authors: Myra J. R. , D’Ippolito D. A.
Published: August 2002

The nonlinear forces generated by localized rf absorption near a resonance layer can be employed to drive flows in a tokamak plasma. The present paper extends previous work to enable (i) an evaluation of localized (in radius) poloidal and toroidal forces caused by rf absorption, (ii) a rigorous calculation of the resulting poloidal and toroidal flow rates in the presence of damping due to plasma viscosity and a phenomenological radial diffusion of momentum, and (iii) implicit treatment of ambipolarity issues in the presence of rf-generated forces. A rigorous result for the steady state poloidal flow that results from balancing plasma viscosity with the rf forces is obtained. Numerical results are presented for the case of ion Bernstein wave interaction within a narrow resonant ion-cyclotron layer where the wave absorption and rf forces occur.
Numerical simulation of ultracold plasmas
Authors: Kuzmin S. G. , O’Neil T. M.
Published: August 2002

In recent experiments ultracold plasmas were produced by photoionizing small clouds of laser cooled atoms. This paper presents the results of molecular dynamic simulations for the early time evolution of such plasmas. Contrary to earlier speculation, no evidence of strong electron–electron correlations is observed in the simulations even if the initial value of the coupling parameter (Γe=e2/akTe) is much larger than unity. As electron–electron correlations begin to develop, the correlation energy is released to heat the electrons, raising the electron temperature to the point where Γe∼1 and limiting further development of correlation. Further heating of the electrons occurs as a by-product of three-body recombination. When a model of laser cooling is added to the simulation, the formation of strong ion–ion correlation is observed. Contrary to earlier suggestion, the rate of three-body recombination is observed to be in reasonable agreement with the traditional formula, R=3.9×10−9 s−1[n(cm−3)]2[Te(K)]−9/2, but care must be taken to use the correct temporally evolving temperature, Te. The simulations are challenging because it is necessary to follow three-body recombination into weakly bound (high n quasiclassical) Rydberg states, and the time scale for such states is short compared to that for the plasma dynamics. This kind of problem was faced earlier in computational astrophysics when studying binary star formation in globular clusters and the simulation method used here is adapted from such studies.
Formation of carbonized porous silicon surfaces by thermal and optically induced reaction with acetylene
Authors: Lakshmikumar S. T. , Singh P. K.
Published: August 2002

Formation of a carbonized porous silicon surface by thermal and photo-assisted reaction with gas phase acetylene is reported. The porous silicon samples subjected to flowing acetylene either in a heated quartz reactor or under optical illumination show strong quenching of the photo- luminescence (PL) followed by a recovery on further exposure to acetylene. In thermally treated samples, a significant blue shift of 80 nm was observed. The recovered PL signal does not exhibit quenching on further exposure to laser illumination. Fourier transform infrared spectroscopy investigations confirm absence of Si–Hx absorption and no enhancement of the oxygen back bonded Si–H bonding. It indicates the formation of a practically stable carbonized porous silicon surface.
Long Josephson junction embedded into a planar resonator at microwave frequencies: Numerical simulation of fluxon dynamics
Authors: Goldobin E. , Klushin A. M. , Siegel M. , Klein N.
Published: August 2002

We have investigated numerically a system consisting of a long Josephson junction embedded into a microstrip resonator. For such a configuration the Josephson vortex dynamics in the junction is driven by the oscillating currents in the resonator. We have calculated the complex impedance of the junction at the resonant frequency. The Q factor of the resonator and the change of the resonant frequency of the whole system can then be easily calculated knowing the parameters of the resonator without Josephson junction. The fluxon dynamics and the complex impedance of the junction are simulated for different values of the junction length, damping, dc bias current, and dc magnetic field. This allows us to explain the behavior of the impedance of the junction and different loss mechanisms. In particular, we predict a nonmonotonic dependence of the both real and imaginary parts of the impedance on the amplitude of the oscillating current in the resonator for some range of parameters. Our results show that such a combination of active and passive superconducting elements forms a rather interesting nonlinear physical system which might be useful for development of tunable/switchable superconducting resonators and suggests an experimental technique for detecting trapped vortices in long junctions.
Phase-coherent Rayleigh scattering method: Application to thermal diffusion mode
Authors: Takagi Shinsaku , Tanaka Hajime
Published: August 2002

We develop a method of phase-coherent light scattering, which provides “complex” spectra of Rayleigh scattering from a thermal diffusion mode in isotropic liquids. Different from the conventional light scattering methods, which measure the power spectrum of light scattered by spontaneously excited fluctuations, we generate a coherent temperature grating by using a laser-induced scanning interference pattern and measure complex spectra of a thermal diffusion mode by its phase-sensitive superheterodyne detection. We can control the amplitude of the temperature grating by changing the absorption coefficient of a liquid by adding a small amount of dye molecules. This controllability of the signal intensity and the resulting mode selectivity allow us to pick up only a thermal diffusion mode even under the existence of other incoherent modes with large amplitude. For example, our method enables us to study a thermal diffusion mode of a critical binary mixture usually hidden by large concentration fluctuations near its critical point.
Instrumentation for the accurate measurement of phase and amplitude in optical tomography
Authors: Nissilä Ilkka , Kotilahti Kalle , Fallström Kim , Katila Toivo
Published: August 2002

A single-channel prototype for a frequency-domain optical tomography system is presented. The two main goals in the design of the system were the measurement of phase with minimal systematic errors and a high enough signal-to-noise ratio to detect the small changes in the absorption of brain tissue during brain activity. Although the system inherently is an imaging system, the aspects of the system that relate to multichannel operation will be published separately, as this part of the system is not yet finished. The instrument is described in detail, including the radio-frequency system, the light detection system, and the light source. Factors that affect the accuracy of the measured phase include phase drift, radio-frequency coupling between the source and detector electronics, phase-amplitude cross talk, and others. To increase the range of intensities that can be measured, the gain of the detector is adjusted while keeping the mean anode current small compared with the quiescent current through the voltage bleeder of the photomultiplier tube so that cross talk is avoided. The calibration of the measurements is considered, and the data measured on a phantom are compared with a time-resolved instrument as well as with a finite-element forward model. The instrument allows the measurement of phase to an accuracy of 0.5° between 80 fW and 80 nW at a modulation frequency of 100 MHz, giving a dynamic range of 1:106. With a time constant of 0.3 s, phase noise is 0.5° at 1 pW and decreases to 0.06° in a typical activation measurement at 3 cm separation between the optodes. Amplitude noise is 0.8% at 1 pW and 0.1% at 3 cm separation.
Capacitive detection of micromotions: Monitoring ballistics of a developing avian embryo
Authors: Szymanski Jan A. , Pawlak Krzysztof , Wasowicz Pawel , Moscicki Jozef K.
Published: August 2002

An instrument for noninvasive monitoring of very weak biomechanical activities of small living organisms is described. The construction is sufficiently flexible to permit a range of studies including developing embryos of oviparous animals, pests that live in loose materials and timber, and insects that develop in cocoons. Motions are detected by monitoring a current generated by the fluctuating position of the object-loaded electrode of a capacitive sensor. To maximize the signal, oscillations of the electrode are mechanically enhanced and the current is amplified and filtered by a two-stage signal amplifier and a bank of six active Butterworth filters. The device is optimized to ballistocardiography of hen embryos. The sensitivity achieved makes possible quantitative studies of heart activity of 7-day-old embryos.
An automated glitch-detection/restoration method of atomic force microscope images
Authors: Hyon Chankyeong , Oh Sangwook , Kim Hyungkwon , Sull Sanghoon , Hwang Sungwoo , Ahn Doyeol , Park Youngju , Kim Eunkyu
Published: August 2002

An automated glitch-detection/restoration method of atomic force microscope images is proposed and implemented. Contrary to other manual methods, our method is based on the probability distribution of the derivative of the scanned image data. The glitches are identified as the points that deviate from a normal probability density function. The essence of the automation is calculating the distribution of the scanned image and removing the points that deviate from the normal distribution. Quantitative analysis of the original and the restored image have been performed and the degree of deformation of the restored images has also been analyzed. This technique can directly be applied to other types of scanning probe microscope equipments.
Termination of spiral wave breakup in a Fitzhugh–Nagumo model via short and long duration stimuli
Authors: Gray Richard A.
Published: August 2002

Rotating spiral waves have been observed in a variety of nonlinear biological and physical systems. Spiral waves are found in excitable and oscillatory systems and can be stationary, meander, or even degenerate into multiple unstable rotating waves (a process called “spiral wave breakup”). In the heart, spiral wave breakup is thought to be the underlying mechanism of cardiac fibrillation. The spatiotemporal complexity of multiple unstable spiral waves is difficult to control or terminate. Here, the mechanisms of the termination of spiral wave breakup in response to global stimulation are investigated. A modified Fitzhugh–Nagumo model was used to represent cellular kinetics to study the role of the fast (activation) and slow (recovery) variables. This simplified model allows a theoretical analysis of the termination of spiral wave breakup via both short and long duration pulses. Simulations were carried out in both two-dimensional sheets and in a three-dimensional geometry of the heart ventricles. The short duration pulses affected only the fast variable and acted to reset wave propagation. Monophasic pulses excited tissue ahead of the wave front thus reducing the amount of excitable tissue. Biphasic shocks did the same, but they also acted to generate new wave fronts from the pre-existing wave tails by making some active regions excitable. Thus, if the short duration stimuli were strong enough, they acted to fill in excitable tissue via propagating wave fronts and terminated all activity. The long duration wave forms were selected such that they had a frequency spectrum similar to that of the pseudoelectrocardiograms recorded during fibrillation. These long duration wave forms affected both the recovery and activation variables, and the mechanism of unstable multiple spiral wave termination was different compared to the short duration wave forms. If the long duration stimuli were strong enough, they acted to alter the “state” (i.e., combination of fast and slow variables) of the tissue throughout 1.5 cycles, thus “conditioning” the tissue such that by the end of the stimuli almost no excitable tissue remained. The peak current, total energy, and average power of stimuli required to terminate spiral wave breakup were less for the long duration wave forms compared to the short duration wave forms. In addition, closed loop feedback via stimulation with a wave form that was the difference of the pseudoelectrocardiogram and a strongly periodic chaotic signal was successful at terminating spiral wave breakup. These results suggest that it may be possible to improve cardiac defibrillation efficacy by using long duration wave forms to affect recovery variables in the heart as opposed to the traditional brief duration wave forms that act only on the fast variables.
Unique capabilities of an intense heavy ion beam as a tool for equation-of-state studies
Authors: Hoffmann D. H. H. , Fortov V. E. , Lomonosov I. V. , Mintsev V. , Tahir N. A. , Varentsov D. , Wieser J.
Published: August 2002

Intense heavy ion beams open new possibilities in high-energy-density matter research. Due to the unique feature of the energy deposition process of heavy ions in dense matter (volume character of heating) it is possible to generate high entropy states in matter without the necessity of shock compression. Previously, such high entropy states could only be achieved by using the most powerful shock wave generators, like nuclear explosions or powerful lasers. In this paper this novel technique of heavy ion heating and expansion is proposed to explore new fascinating regions of the phase diagram, including the liquid phase, the evaporation region with the critical point, and strongly coupled plasmas.
Numerical investigation of a Hall thruster plasma
Authors: Roy Subrata , Pandey B. P.
Published: August 2002

The dynamics of the Hall thruster is investigated numerically in the framework of a one-dimensional, multifluid macroscopic description of a partially ionized xenon plasma using finite element formulation. The model includes neutral dynamics, inelastic processes, and plasma–wall interaction. Owing to disparate temporal scales, ions and neutrals have been described by set of time-dependent equations, while electrons are considered in steady state. Based on the experimental observations, a third order polynomial in electron temperature is used to calculate ionization rate. The results show that in the acceleration channel the increase in the ion number density is related to the decrease in the neutral number density. The electron and ion velocity profiles are consistent with the imposed electric field. The electron temperature remains uniform for nearly two-thirds of the channel; then sharply increases to a peak before dropping slightly at the exit. This is consistent with the predicted electron gyration velocity distribution.
Stimulated Brillouin scattering in a magnetized dusty plasma with charge fluctuation
Authors: Burman S. , Paul S. N. , Chowdhury A. Roy
Published: August 2002

Stimulated Brillouin scattering of an electromagnetic wave is investigated analytically in a magnetized dusty plasma. Variation of growth rates of the scattered ion-acoustic wave and the electromagnetic wave have been analyzed with respect to the concentration of dust particles by taking account dust charge fluctuation.
Oscillation of dust grains and the dust–Mach number associated with the dust–neutral collision in a plasma
Authors: Nejoh Y. N.
Published: August 2002

Oscillating potential and the dust–Mach number are investigated in a dusty plasma associated with the dust–neutral collision. It is shown by numerical simulation that the oscillation sensitively depends on the ion to electron density ratio, the ion to electron temperature ratio, and the dust–neutral collisional parameter. It is found that the dust–Mach number varies due to the dust charge, the ion to electron density ratio, and the dust–neutral collisional parameter. In particular, the dust–Mach number sensitively depends on the ratio of the ion density to the dust charge–number. The possibility is suggested that the dust-acoustic wave not only exists in the bulk plasma but also propagates in the sheath.
Integrated predictive modeling simulations of the Mega-Amp Spherical Tokamak
Authors: Nguyen Canh N. , Bateman Glenn , Kritz Arnold H. , Akers Robert , Byrom Calum , Sykes Alan ,   MAST Team
Published: August 2002

Integrated predictive modeling simulations are carried out using the BALDUR transport code [Singer et al., Comput. Phys. Commun. 49, 275 (1982)] for high confinement mode (H-mode) and low confinement mode (L-mode) discharges in the Mega-Amp Spherical Tokamak (MAST) [Sykes et al., Phys. Plasmas 8, 2101 (2001)]. Simulation results, obtained using either the Multi-Mode transport model (MMM95) or, alternatively, the mixed-Bohm/gyro-Bohm transport model, are compared with experimental data. In addition to the anomalous transport, neoclassical transport is included in the simulations and the ion thermal diffusivity in the inner third of the plasma is found to be predominantly neoclassical. The sawtooth oscillations in the simulations radially spread the neutral beam injection heating profiles across a broad sawtooth mixing region. The broad sawtooth oscillations also flatten the central temperature and electron density profiles. Simulation results for the electron temperature and density profiles are compared with experimental data to test the applicability of these models and the BALDUR integrated modeling code in the limit of low aspect ratio toroidal plasmas.
Comment on “A new class of exact solutions of the Vlasov equation” [Phys. Plasmas 8, 5081 (2001)]
Authors: Rowlands G. , Sprott J. C.
Published: August 2002

A recent paper obtained a class of exact one-dimensional solutions of the Vlasov–Poisson equations for a one-component plasma in a parabolic electrostatic potential well. Here it is shown that a significant class of these solutions has already been studied and shown to be chaotic.
Optimal performance for Tesla transformers
Authors: Denicolai Marco
Published: August 2002

The previous work related to finding improved performance for Tesla transformers is shortly reviewed. The possibilities to reach the optimal working point by modifying the main components are discussed from a practical standpoint. A methodology for maximizing the secondary voltage by regulating the tuning ratio T and the coupling coefficient is examined in particular. It is shown that its results are valid only if primary and secondary inductor values remain unchanged, and the secondary capacitor value is decreased. All in all, the best improvement from the typical condition of T=1 increases the secondary voltage of only 18% and requires tide coupling. This, in turn, imposes severe engineering problems to avoid dielectric breakdown between the primary and secondary coils, and makes the practical utility of this result someway questionable. In a real Tesla transformer, the most practical mean to perform tuning is to move the tap feeding the primary coil, rather than rewinding the secondary coil or redesigning the secondary top terminal. The resonant circuits are not undamped and it is crucial to reach the maximum voltage at the secondary in the shortest time, to minimize losses. It is shown that, in order to achieve optimal performance, a better strategy is to tune the primary coil to achieve T=1 and then to increase the coupling coefficient as much as possible, aiming at one of the values selected from a given table.
Data analysis of nonlinear systems: Application to Au nanowires
Authors: Wlasenko A. , Grütter P.
Published: August 2002

A general scheme for analyzing nonlinear systems is presented, with measurements of the nonlinear I–V characteristics of a gold atomic contact with a mechanically controllable break junction used as an example. Simultaneous measurements of I(V) and ∂I/∂V(V) were analyzed to extract the unbiased conductance from the normalized functional form of I(V). This allows us to remove the error in the conductance measurements associated with fluctuations in the atomic structure of the system (about 5%). This demonstrates the potential of this technique to discover and subsequently understand new phenomena in nanometer scale systems, where measurements are often challenging due to noise, difficult-to-control quantities such as the atomic structure of a contact lead, and the lack of adequate, generally accepted theoretical descriptions. A discussion of the tradeoff between higher-order measurements and averaging artifacts due to nonlinearity is also included.
“Complexity” and anomalous transport in space plasmas
Authors: Chang Tom , Wu Cheng-chin
Published: August 2002

“Complexity” has become a hot topic in nearly every field of modern physics. Space plasma is of no exception. In this paper, it is demonstrated that the sporadic and localized interactions of magnetic coherent structures are the origin of “complexity” in space plasmas. The intermittent localized interactions, which generate the anomalous diffusion, transport, and evolution of the macroscopic state variables of the overall dynamical system, may be modeled by a triggered (fast) localized chaotic growth equation of a set of relevant order parameters. Such processes would generally pave the way for the global system to evolve into a “complex” state of long-ranged interactions of fluctuations, displaying the phenomenon of forced and/or self-organized criticality. An example of such type of anomalous transport and evolution in a sheared magnetic field is provided via two-dimensional magnetohydrodynamic simulations. The coarse-grained dissipation due to the intermittent triggered interactions among the magnetic coherent structures induces a “fluctuation-induced nonlinear instability” that reconfigures the sheared magnetic field into an X-point magnetic geometry (in the mean field sense), leading to the anomalous acceleration of the magnetic coherent structures. A phenomenon akin to such type of anomalous transport and acceleration, the so-called bursty bulk flows, has been commonly observed in the plasma sheet of the Earth’s magnetotail.
Parallel electric fields in the upward current region of the aurora: Numerical solutions
Authors: Ergun R. E. , Andersson L. , Main D. , Su Y.-J. , Newman D. L. , Goldman M. V. , Carlson C. W. , McFadden J. P. , Mozer F. S.
Published: August 2002

Direct observations of the parallel electric field by the Fast Auroral Snapshot satellite and the Polar satellite suggest that the ionospheric boundary of the auroral cavity is consistent with an oblique double layer that carries a substantial fraction (roughly 5% to 50%) of the auroral potential. A numerical solution to the Vlasov–Poisson equations of a planar, oblique double layer reproduces many of the properties of the observed electric fields, electron distributions, and ion distributions. The solutions indicate that the electron and ion distributions that emerge from the ionospheric side dominate the structure of the double layer. The ionospheric electron distribution includes scattered and reflected (mirrored) primaries, auroral secondaries, photoelectrons, and a cold population. A large fraction of the ionospheric electrons is reflected by the parallel electric field whereas the ionospheric ions are strongly accelerated. The steep density gradient between the ionosphere and the auroral cavity results in a highly asymmetric double layer, with a strong, localized positive charge layer on the ionospheric side and a moderate, extended negative charge layer on the auroral cavity side. This structure results in an asymmetric electric field, a feature also seen in the observations. The electric field observations, however, do not always support a planar double layer since the parallel and perpendicular signals are not always well correlated. Fully two-dimensional solutions are needed to better reproduce the observed features.