Mechanism for ion acceleration along the normal to the axis of a beam-plasma discharge in a weak magnetic field

The mechanism responsible for the previously discovered phenomenon of acceleration of an ion flow along the normal to the axis of a beam-plasma discharge in a weak magnetic field is investigated. It is suggested that the ions are accelerated in the field of a helicon wave excited in the discharge plasma column. It is shown theoretically that, under actual experimental conditions, a helicon wave can be excited at the expense of the energy of an electron beam. The spectral parameters and spatial structure of the waves excited in a beam-plasma discharge in the frequency ranges of Langmuir and helicon waves are studied experimentally and are shown to be related to the parameters of the ion flow. Theoretical estimates are found to agree well with the experimental results.     

One-dimensional model for propagation of a pressure wave in a model of the human arterial network: comparison of theoretical and experimental results

Pulse wave evaluation is an effective method for arteriosclerosis screening. In a previous study, we verified that pulse waveforms change markedly due to arterial stiffness. However, a pulse wave consists of two components, the incident wave and multireflected waves. Clarification of the complicated propagation of these waves is necessary to gain an understanding of the nature of pulse waves in vivo. In this study, we built a one-dimensional theoretical model of a pressure wave propagating in a flexible tube. To evaluate the applicability of the model, we compared theoretical estimations with measured data obtained from basic tube models and a simple arterial model. We constructed different viscoelastic tube set-ups: two straight tubes; one tube connected to two tubes of different elasticity; a single bifurcation tube; and a simple arterial network with four bifurcations. Soft polyurethane tubes were used and the configuration was based on a realistic human arterial network. The tensile modulus of the material was similar to the elasticity of arteries. A pulsatile flow with ejection time 0.3 s was applied using a controlled pump. Inner pressure waves and flow velocity were then measured using a pressure sensor and an ultrasonic diagnostic system. We formulated a 1D model derived from the Navier-Stokes equations and a continuity equation to characterize pressure propagation in flexible tubes. The theoretical model includes nonlinearity and attenuation terms due to the tube wall, and flow viscosity derived from a steady Hagen-Poiseuille profile. Under the same configuration as for experiments, the governing equations were computed using the MacCormack scheme. The theoretical pressure waves for each case showed a good fit to the experimental waves. The square sum of residuals (difference between theoretical and experimental wave-forms) for each case was <10.0%. A possible explanation for the increase in the square sum of residuals is the approximation error for flow viscosity. However, the comparatively small values prove the validity of the approach and indicate the usefulness of the model for understanding pressure propagation in the human arterial network.     

Diagnostics of plasma oscillations by the field of surface waves guided by a dielectric waveguide

The potentialities of the diagnostic method for determining the plasma parameters by recording the surface waves guided by a dielectric waveguide and scattered by plasma oscillations are discussed. The use of surface (slowed) waves makes it possible to improve both the sensitivity and spatial resolution of measurements. The scattering is the most intense near the waveguide cutoff, at which the dependence of the wave propagation constant on the plasma density is the steepest. It is shown experimentally that the method proposed makes it possible to determine the discharge plasma density and electron energy and to estimate the amplitude of the RF field of the plasma waves forming the discharge and the amplitude of plasma density oscillations in these waves. The data obtained from the measurements of the amplitudes of both high-and low-frequency plasma density oscillations by the proposed method agree satisfactorily with theoretical predictions. The experimental data on the plasma density are confirmed by other diagnostic measurements. The ways of reducing measurement errors are proposed.     

Control of wave propagation in a biological excitable medium by an external electric field

We present an experimental evidence of effects of external electric fields (EFs) on the velocity of pulse waves propagating in a biological excitable medium. The excitable medium used is formed by a layer of starving cells of Dictyostelium discoideum through which the waves of increased concentration of cAMP propagate by reaction-diffusion mechanism. External dc EFs of low intensities (up to 5 V/cm) are shown to speed up the propagation of cAMP waves towards the positive electrode and slow it down towards the negative electrode. Electric fields were also found to support an emergence of new centers, emitting cAMP waves, in front of cAMP waves propagating towards the negative electrode.     

Spatiotemporal evolution of vortex dust structures in a track plasma

Results are presented from experimental studies of the behavior of dust grains in a track plasma produced by an accelerated proton beam. Dynamic dust structures in such a plasma are obtained for the first time, and their spatiotemporal evolution is thoroughly investigated. The structures develop from a dust spiral, which abruptly transforms with increasing dust density into a differentially rotating dust cloud across which dust-sound waves (including spiral waves generated by the dense central core) propagate. As time elapses, the dust cloud loses its fragments and gradually vanishes. At constant experimental conditions, the lifetime of the structures attains a few minutes.     

Effects of waves on the early growth of Vallisneria americana

1. The impacts of 0.15-m waves on the survival and short-term growth and development of young Vallisneria americana plants were studied in experimental raceways. Young plants were planted at three depths within both wave and control raceways. Wave events were designed to simulate wave disturbances caused by boat traffic and were generated five or six times each day during the 67-day experimental growth period. The 0.15-m waves generated produced a maximum shear velocity of about 1.4 m s⁻¹ as they swept over the plants. 2. All plants survived at all depths in both treatments. However, plants exposed to the waves accumulated significantly less total mass than controls. The total mass accumulation of wave-exposed plants was only 50% of that of undisturbed plants. In addition, the plants experiencing the waves had significantly shorter leaves and produced significantly fewer daughter plants. 3. While plants under both wave and no wave treatments had a similar relative growth rate and both showed a net positive growth over the experimental period, those exposed to frequent wave energy developed more slowly due to continuous leaf loss caused by the waves. Plants exposed to even modest wave energy may spread more slowly and be less resilient to recovery from other forms of disturbance.     

Separation of arterial pressure into a nonlinear superposition of solitary waves and a windkessel flow

A simplified model of arterial blood pressure intended for use in model-based signal processing applications is presented. The main idea is to decompose the pressure into two components: a travelling wave which describes the fast propagation phenomena predominating during the systolic phase and a windkessel flow that represents the slow phenomena during the diastolic phase. Instead of decomposing the blood pressure pulse into a linear superposition of forward and backward harmonic waves, as in the linear wave theory, a nonlinear superposition of travelling waves matched to a reduced physical model of the pressure, is proposed. Very satisfactory experimental results are obtained by using forward waves, the N-soliton solutions of a Korteweg–de Vries equation in conjunction with a two-element windkessel model. The parameter identifiability in the practically important 3-soliton case is also studied. The proposed approach is briefly compared with the linear one and its possible clinical relevance is discussed.     

Peristaltic transport as the travelling deformation waves

Geometry approach to the theoretical and experimental investigations of peristaltic waves based on the travelling deformation waves and wave mass transfer theory (Dobrolyubov, 1991) is presented. The theory of travelling deformation waves is employed to determine uniformed expressions for mass transfer capability parameters of peristalsis. Slow (quasi-static) wave motion is considered which permits not to take into account dynamic phenomena.     

Heat waves and their significance for a temperate benthic community: A near‐natural experimental approach

Climate change will not only shift environmental means but will also increase the intensity of extreme events, exerting additional stress on ecosystems. While field observations on the ecological consequences of heat waves are emerging, experimental evidence is rare, and lacking at the community level. Using a novel “near‐natural” outdoor mesocosms approach, this study tested whether marine summer heat waves have detrimental consequences for macrofauna of a temperate coastal community, and whether sequential heat waves provoke an increase or decrease of sensitivity to thermal stress. Three treatments were applied, defined and characterized through a statistical analysis of 15 years of temperature records from the experimental site: (1) no heat wave, (2) two heat waves in June and July followed by a summer heat wave in August and (3) the summer heat wave only. Overall, 50% of the species showed positive, negative or positive/negative responses in either abundance and/or biomass. We highlight four possible ways in which single species responded to either three subsequent heat waves or one summer heat wave: (1) absence of a response (tolerance, 50% of species), (2) negative accumulative effects by three subsequent heat waves (tellinid bivalve), (3) buffering by proceeding heat waves due to acclimation and/or shifts in phenology (spionid polychaete) and (4) an accumulative positive effect by subsequent heat waves (amphipod). The differential responses to single or sequential heat waves at the species level entailed shifts at the community level. Community‐level differences between single and triple heat waves were more pronounced than those between regimes with vs. without heat waves. Detritivory was reduced by the single heat wave while suspension feeding was less common in the triple heat wave regime. Critical extreme events occur already today and will occur more frequently in a changing climate, thus, leading to detrimental impacts on coastal marine systems.     

Variation of repetitive cortical spreading depression waves is related with relative refractory period: a computational study

Cortical spreading depression (CSD) is an important experimental model for diseases such as stroke, epilepsy and migraine. Previous observations indicated that the amplitude and velocity of the typical direct current potential shift during repetitive CSD waves were varying. The recovery state of the tissue was found related with the variation of successive CSD waves. A computational model in this paper aimed to investigate the role of relative refractory period of CSD. This model simulated that continuous injection of KCl solution induced repetitive CSD waves. The first CSD wave often had a larger amplitude and faster velocity than those of the succeeding secondary waves. The relative refractory period lasted much longer than the recovery of ions turbulence. If the induction interval was long enough for recovery, a series of CSD waves would have the same profile as the first one. In the relative refractory period, an early stimulation might lead to a late initiation of CSD, i.e., “haste makes waste”. The amplitude and velocity of CSD waves were found increasing with the initiation interval and asymptotic to those of the first CSD wave. This study verified that the propagation dynamics of CSD waves is modulated by the relative refractory period. It suggested that the refractory period is critical for preventing undesirable CSD waves.     

The Wavy Erythropoiesis of Developing Chick Embryos. Isolation of Each Wave by a Differential Lysis and Identification of the Constituent Erythroid Types

Erythroid carbonic anhydrase (CA) activity of chick embryos from the third day of incubation to the egg hatching has been determined. Five minor activity peaks with maxima at 3, 6, 9, 15 and 17 days of development and a major one with maximum at 19 days have been found. The correlation between the peak distribution and the timing of release into the blood stream of waves of newly produced erythroid cells has been demonstrated on the basis of the following observations: 1) a linear correlation exists between red cell maturation and increase of CA activity; 2) chick red cells undergo lysis in the "Ørskov" medium when their CA activity exceeds a threshold value (23±3 Units/10⁹ red cells); and 3) the lysis kinetics of red cells in the Ørskov medium is proportional to their CA content. We have thus been able to distinguish the immature erythroid forms from the mature ones on the basis of their behaviour in the Ørskov medium. In the blood of developing chick embryos, we have found waves of newly produced red cells at about 2, 4, 7, 10, 16 and 18 days of development.
The same experimental criteria allowed us to detect the waves of red cell production in the erythropoietic organs. One wave has been detected in the blood islands at about 2 days; four waves in the yolk sac at about 5, 6, 11 and 15 days; two waves in the spleen at about 18 and 20 days; two waves in the bone marrow at about 19 days of incubation and 1 day after hatching.
Primitive erythroid cells are produced in the first two waves: that of blood islands at 2 days and that of yolk sac at 5 days. Definitive red cells are produced in the other waves with the exception of the second wave of spleen and of the second wave of bone marrow, which are constituted by red cells of adult type.     

Effects of traditional and ultrasonic liposuction on adipose tissue: a biochemical approach

Little is known about the interaction of ultrasonic liposculpture with fat tissue. The surgical technique is well established and its clinical effects are satisfactory. However, the in vivo effects on adipose tissue remain to be determined. Previous studies have shown that ultrasound waves break fat cells. The purpose of this study was to ascertain whether ultrasound waves can cause the release of fatty acids from the molecular structure of triglycerides. A double-blind study was designed with samples obtained from traditional and ultrasonic liposuction of an equivalent area in the same patient. Samples were checked for triglycerides and for free fatty acids. Triglyceride values were always higher in the sample that had undergone ultrasonic procedure. No significant differences were observed between the free fatty acid chromatograms of the two kinds of samples analyzed. Data showed that no changes occurred in the triglyceride molecule when using ultrasound waves in the experimental conditions.     

Receptors, sparks and waves in a fire-diffuse-fire framework for calcium release

Calcium ions are an important second messenger in living cells. Indeed calcium signals in the form of waves have been the subject of much recent experimental interest. It is now well established that these waves are composed of elementary stochastic release events (calcium puffs or sparks) from spatially localised calcium stores. The aim of this paper is to analyse how the stochastic nature of individual receptors within these stores combines to create stochastic behaviour on long time-scales that may ultimately lead to waves of activity in a spatially extended cell model. Techniques from asymptotic analysis and stochastic phase–plane analysis are used to show that a large cluster of receptor channels leads to a release probability with a sigmoidal dependence on calcium density. This release probability is incorporated into a computationally inexpensive model of calcium release based upon a stochastic generalisation of the fire-diffuse-fire (FDF) threshold model. Numerical simulations of the model in one and two dimensions (with stores arranged on both regular and disordered lattices) illustrate that stochastic calcium release leads to the spontaneous production of calcium sparks that may merge to form saltatory waves. Illustrations of spreading circular waves, spirals and more irregular waves are presented. Furthermore, receptor noise is shown to generate a form of array enhanced coherence resonance whereby all calcium stores release periodically and simultaneously.     

Impacts of a simulated heat wave on composition of a marine community

Extreme events, such as heat waves, are predicted to increase in frequency, duration, and severity as a consequence of climate change. However, global change research generally focuses on increases in mean temperatures and fails to address the potential impacts of increasingly severe heat waves. In addition, climate change may interact with another primary threat to biodiversity, non‐native species invasions. We assessed the impacts of a short‐term heat wave on the marine epibenthic fouling community of Bodega Harbor, California, USA, by exposing experimental mesocosms to a simulated heat wave in the laboratory and then monitoring community development in the field. We hypothesized that (1) juveniles would be more susceptible to heat waves than adults, (2) native species would be more susceptible than non‐native species, and (3) non‐native species would recover more quickly than native species. We observed no effect of the heat wave on juvenile species richness, either initially or during the recovery period, relative to communities at ambient seawater temperatures. In contrast, total adult species richness initially declined in response to the heat wave. Adult community composition also changed in heat‐wave treatments, with non‐natives representing the majority of species and occupying more cover than native species. The reduction in native richness associated with the heat wave persisted through the recovery period, whereas invasive richness was actually higher on heat‐wave versus ambient plates at 95 days. Heat waves have the potential to alter the composition of this community because of species‐, taxon‐, and/or origin‐specific responses; for example, non‐native bryozoans displayed greater resistance than native and non‐native tunicates. Recovery from the heat wave occurred via growth of resistant individuals and larval recruitment. Our study highlights the importance of considering species’ and community responses to heat waves, and not just mean predicted temperature increases, to evaluate the consequences of climate change.     

Regular and stochastic decays of waves in a plasma cavity

The regular and stochastic decays of fast high-frequency waves in a cavity filled with a low-density magnetoactive plasma are studied both theoretically and experimentally. The conditions for the transformation of the regular regime into the stochastic one are determined. The theoretical and experimental results are in a good agreement. Possible applications of stochastic decay are discussed.     

Amplification of surface waves in a plasma waveguide by a straight relativistic electron beam in a finite magnetic field

The problem of the excitation of electron waves in a thin-walled annular cold plasma in a cylindrical waveguide by a straight relativistic electron beam in a finite magnetic field is considered. The dispersion properties of a waveguide system with parameters close to the experimental ones are investigated. It is shown that the growth rate of the excited high-frequency plasma wave is comparable to that of the low-frequency wave, which is weakly sensitive to the strength of the longitudinal magnetic field.     

On the theory of Cherenkov emission in a plasma

The Cherenkov emission of transverse-longitudinal waves in an anisotropic plasma is considered by applying a Hamiltonian method and by drawing an analogy between the equations for the Cherenkov emission of purely transverse and purely longitudinal waves in isotropic media and the equations for the emission of transverse-longitudinal electromagnetic waves in a highly anisotropic medium (a magnetized plasma). A formula for the emitted power is derived, as well as an expression for the directional pattern of the emitted waves in an anisotropic plasma.     

On the theory of a Cherenkov relativistic plasma emitter with a coaxial electrodynamic system

A plasma microwave amplifier based on a relativistic electron beam in an electrodynamic system in the form of a coaxial waveguide with a thin tubular plasma in a strong external magnetic field has been considered. Dispersion relations for determining the spectra of plasma and beam waves in the coaxial waveguide, as well as the general dispersion relation describing beam-plasma interaction, have been obtained in the linear approximation. The frequency dependences of the spatial growth rates for different plasma radii and different plasma frequencies, as well as the characteristic frequencies of the plasma amplifier, have been obtained by numerically and analytically solving the dispersion relations. The parameters of the plasma amplifier and generator with the coaxial electrodynamic system have been estimated for their experimental implementation.     

Simple and complex spatiotemporal structures in a glycolytic allosteric enzyme model

Pattern formation in glycolysis is studied with a classical reaction-diffusion allosteric enzyme model. It is found that, similar to recent experimental reports in the yeast extracts, a small magnitude local perturbation can induce transient target waves in a two dimensional oscillatory medium. An above threshold stimulation generates target waves which eventually evolve into spatiotemporal chaos upon collisions with the boundary or other wave activities. Detailed simulation studies show that the studied simple glycolytic reaction-diffusion model can support three types of spatiotemporal behaviors which are independent of the boundary conditions: (1) a spatially uniform stable steady state, (2) periodic global oscillations and (3) spatiotemporal chaos.     

Reentrant waves in a ring of embryonic chick ventricular cells imaged with a Ca2+ sensitive dye

According to the classic model initially formulated by Mines, reentrant cardiac arrhythmias may be associated with waves circulating in a ring geometry. This study was designed to study the dynamics of reentry in a ring geometry of cardiac tissue culture. Reentrant calcium waves in rings of cultured embryonic chick cardiac myocytes were imaged using a macroscope to monitor the fluorescence of intracellular Calcium Green-1 dye. The rings displayed a variety of stable rhythms including pacemaker activity and spontaneous reentry. Waves originating from a localized pacemaker could lead to reentry as a consequence of unidirectional block. In addition, more complex patterns were observed due to the interactions between reentrant and pacemaker rhythms. These rhythms included instances in which pacemakers accelerated the reentrant rhythm, and instances in which the excitation was blocked in the vicinity of pacemakers. During reentrant activity an appropriately timed electrical stimulus could induce resetting of activity or cause complete annihilation of the propagating waves. This experimental preparation reveals many spontaneously occuring complex rhythms. These complex rhythms are hypothesized to reflect interactions between spontaneous pacemakers, wave propagation, refractory period, and overdrive suppression. This preparation may serve as a useful model system to further investigate complex dynamics arising during reentrant rhythms in cardiac tissue.