Helicon plasma in a nonuniform magnetic field

The distributions of the electron density in a plasma produced by helicon waves and the correspond-ing wave amplitudes and phases are studied experimentally. The measurements were carried out in an argon plasma at a pressure of 3 mtorr and at an input RF power of up to 600 W. The magnetic field was caried in the range from 0 to 200 G. The efficiency of plasma production in both uniform and nonuniform fields is investigated. It is shown that, in a nonuniform magnetic field, the electron density can be substantially increased (up to 5×10¹² cm^?3) by placing an antenna in the region in which the magnetic field is weaker than in the main plasma.     

Nonlinear theory of ion-acoustic waves in an electron-positron-ion plasma

An analytical nonlinear gasdynamic theory of ion-acoustic waves in an e-p-i plasma is developed for the case in which all the plasma components in the wave undergo polytropic compression and rarefaction. An exact solution to the basic equations is found and analyzed by the Bernoulli pseudopotential method. The parameter range in which periodic waves can propagate and the range in which solitary waves (solitons) exist are determined. It is shown that the propagation velocity of a solitary is always higher than the linear ion sound velocity. The profiles of all the physical quantities in both subsonic and supersonic waves are calculated. The results obtained agree well with both the data from other papers and particular limiting cases.     

Near field of a loop antenna operating in plasma in the whistler frequency range

The structure of the RF magnetic field in the vicinity of a loop antenna operating in the whistler frequency range has been studied experimentally and theoretically. The experiments were performed over a wide frequency range at different values of the plasma density, electron temperature, and ambient magnetic field strength. It is shown that, when a loop antenna is smaller than the wavelength of a quasi-longitudinal whistler, the structure of the magnetic field of such an antenna is nearly the same as that of the field of a current-carrying loop in vacuum; otherwise, the RF field is localized near the antenna wire. The results of numerical calculations agree with the measured field distributions. The antenna field is calculated by expanding it in the eigenmodes of a magnetized plasma with allowance for not only propagating but also nonpropagating (exponentially decaying) waves, which make the main contribution to the near field. An analytic estimate of the depth to which the RF magnetic field of a loop antenna penetrates into the plasma is obtained.     

Supersonic and near-sonic solitary ion-acoustic waves in magnetized plasma

The propagation of large-amplitude solitary ion-acoustic waves in magnetized plasma is analyzed. The problem is solved without assuming plasma quasineutrality within the pulse, and the wave potential is described by Poisson’s equation. Solutions in the form of supersonic and near-sonic solitary waves propagating obliquely to the magnetic field are found. The pulses have several peaks and exist for a discrete set of the wave parameters. The amplitude and oscillation frequency of a solitary wave are determined as functions of the Mach number and the propagation angle with respect to the magnetic field.     

Theory of ion-acoustic turbulence in plasma with anisotropically heated ions

A simple approximation extending the theory of ion-acoustic turbulence (IAT) is proposed. The approximation is based on the idea of efficient anisotropic ion heating in the Coulomb plasma model. The model makes it possible not only to employ the main results of the existing IAT theory without an assumption of strong ion collisions, but also to substantially extend them. The role of Cherenkov absorption of ion-acoustic waves is revealed. This absorption is caused by an anisotropic ion distribution in the new regimes of IAT that are related to its angular distribution and manifest themselves in electron and ion heating. A specific feature of the model is the finite time of existence of one of the IAT regimes under study.     

Numerical simulation of the electromagnetic fields excited by loop antennas in plasma in the whistler frequency range

The electromagnetic fields excited by circular loop antennas in a magnetized plasma in the whistler frequency range are simulated by the finite-difference time-domain method. The spatial structure of quasi-monochromatic fields excited in the near- and far-field zones by an antenna with a harmonic current, as well as the dynamics of the electromagnetic field excited by an antenna with a current in the form of a single video pulse, is studied. Simulations performed for a uniform plasma and uniform ambient magnetic field agree well with the results of theoretical analysis and model laboratory experiments performed on large-scale plasma devices.     

Ion flux associated with an ion-acoustic cnoidal wave in magnetized dusty plasma

The oblique propagation of nonlinear periodic ion-acoustic waves in magnetized dusty plasma is investigated. The equations describing the dynamics of the wave potential in the first and second orders of the perturbation theory are derived, and their nonsecular periodic solutions are found. The average nonlinear ion flux caused by the propagation of a cnoidal wave is estimated. The magnitude and direction of the ion flux are analyzed as functions of the dust charge density and the angle between the wave propagation direction and the magnetic field.     

Nonlinear theory of ion-acoustic waves in an ideal plasma with degenerate electrons

A nonlinear theory is constructed that describes steady-state ion-acoustic waves in an ideal plasma in which the electron component is a degenerate Fermi gas and the ion component is a classical gas. The parameter ranges in which such a plasma can exist are determined, and dispersion relations for ion-acoustic waves are obtained that make it possible to find the linear ion-acoustic velocity. Analytic gas-dynamic models of ion sound are developed for a plasma with the ion component as a cold, an isothermal, or an adiabatic gas, and moreover, the solutions to the equations of all the models are brought to a quadrature form. Profiles of a subsonic periodic and a supersonic solitary wave are calculated, and the upper critical Mach numbers of a solitary wave are determined. For a plasma with cold ions, the critical Mach number is expressed by an explicit exact formula.     

Observation of nonlinear coupling between drift and ion-acoustic oscillations in low-frequency plasma turbulence

It is shown experimentally that the characteristics of structural ion-acoustic turbulence in a plasma are governed primarily by the development of density gradient-driven drift oscillations. The cyclicity of appearance and disappearance of drift wave packets and ensembles of ion-acoustic solitons in a steady-state turbulent plasma, as well as the correlation between them, is determined.     

Nonlinear ion flux caused by a periodic ion-acoustic wave in plasma with two-temperature electrons

The propagation of periodic ion-acoustic waves in plasma with two-temperature electrons and cold ions is analyzed. The equations for the wave potential are derived in the first- and second-orders of the perturbation theory, and their nonsecular periodic solutions are obtained. The average nonlinear ion flux is determined, and its properties are studied as functions of the ratios between the densities and temperatures of the cold and hot electron components. The conditions are analyzed under which the ion flux is co- or counter-directed to the wave propagation direction. For the case in which, depending on the plasma parameters, the ion flux at a given wave amplitude can be either positive or negative, the domains of existence of positive and negative ion fluxes in the “temperature ratio-density ratio” plane are determined.     

Conversion of normal waves in the electron-cyclotron frequency range at the critical surface in a cold anisotropic plasma inhomogeneous in two dimensions

Linear O-X conversion in the vicinity of a critical-density magnetic surface in a cold anisotropic plasma is studied using the model of a plasma inhomogeneous in two dimensions. Analytic expressions for the conversion and reflection coefficients are derived.     

Nonlinear currents generated in plasma by a radiation pulse with a frequency exceeding the electron plasma frequency

It is shown that the nonlinear currents generated in plasma by a radiation pulse with a frequency exceeding the electron plasma frequency change substantially due to a reduction in the effective electron–ion collision frequency.     

Vlasov modes in the theory of ion-acoustic turbulence

The existing theory of quasi-stationary plasma turbulence presumes that the growth rate of plasma waves is zero. In this paper, it is proposed to determine the spectrum of such waves by using the concept of undamped Vlasov waves. The results concerning the ion-acoustic velocity in the framework of this concept are presented for two models of ion-acoustic turbulence. It is shown that the use of the spectral properties of undamped ion-acoustic waves removes the uncertainty in estimating the time and efficiency of strong turbulent plasma heating.     

Acoustic characterisation of thoracic body tissues in the audible frequency range

A previous study by Jones and Thomas [2] suggests that data relating to the physiological condition within the thoracic cavity may be obtainable utilising low frequency acoustic signals applied to the mouth and detected on the chest wall. In order to evaluate the contribution to the mouth to chest wall frequency response of the separate elements within the thorax, and to estimate the effect on this response when the lung physiology changes, an acoustic model of the thorax is required. To aid the development of this model, experiments have been carried out in order to establish the frequency dependence of the acoustic attenuation and speed of propagation through thoracic tissue samples in the audible frequency range 20–500 Hz. Samples from the porcine family were used due to their physical similarity to those of humans and their being obtainable within a short time of death.The results of this work can be utilised in the development of an acoustic model of the human thorax, this in turn enabling simulation and analysis of low frequency acoustic transmission from the trachea to the chest wall.     

Coaxial microwave plasma source

Physical principles underlying the operation of a pulsed coaxial microwave plasma source (micro-wave plasmatron) are considered. The design and parameters of the device are described, and results of experimental studies of the characteristics of the generated plasma are presented. The possibility of application of this type of plasmatron in gas-discharge physics is discussed.     

The dynamic range problem in the analysis of the plasma proteome

One of the greatest challenges in analyzing the plasma proteome is the wide range of concentration of different proteins. The current study examines the range of protein concentration for 18 proteins measured over a year in a clinical laboratory to provide data on pathological extremes in protein concentrations. The complete measured range, from upper limits for albumin to lowest values for thyroid-stimulating hormone (TSH), represented more than 10 logs of molar abundance. A number of plasma proteins measured in the clinical laboratory varied over a concentration range spanning more than 4 logs, and limits of detection of clinical assays were inadequate to assess full concentration ranges of several proteins. Considering reported values from studies using higher sensitivity assays suggest that plasma concentrations of prostate-specific antigen (PSA), human chorionic gonadotropin (hCG), and cardiac troponin I vary by more than 7 logs. All of the plasma proteins measured in the present study represent secretory proteins or highly expressed components of specific tissues. Thus, the dynamic range for these components is likely to greatly underestimate the total range of protein concentration in the plasma proteome.     

Testosterone implants alter the frequency range of zebra finch songs

To investigate whether changes in testosterone alter the frequency range in which a zebra finch produces song, we assigned male zebra finches to two groups, one of which received testosterone implants and the other empty silastic capsule implants. We then recorded songs up to 52 weeks after the surgery and measured frequency changes in the fundamental frequencies of arbitrarily chosen harmonic stacks in the songs of birds in either group. We found statistically significant decreases after 5 weeks in the songs of the testosterone-treated birds. No changes were found in the fundamental frequencies of the control group. The frequency change remained after the apparent effects of the testosterone implants ended. These data show that high levels of testosterone can lower the frequencies of elements in zebra finch songs.     

Resonance microwave volume plasma source

A conceptual design of a microwave gas-discharge plasma source is described. The possibility is considered of creating conditions under which microwave energy in the plasma resonance region would be efficiently converted into the energy of thermal and accelerated (fast) electrons. Results are presented from interferometric and probe measurements of the plasma density in a coaxial microwave plasmatron, as well as the data from probe measurements of the plasma potential and electron temperature. The dynamics of plasma radiation was recorded using a streak camera and a collimated photomultiplier. The experimental results indicate that, at relatively low pressures of the working gas, the nonlinear interaction between the microwave field and the inhomogeneous plasma in the resonance region of the plasmatron substantially affects the parameters of the ionized gas in the reactor volume.     

Muscle is the major source of plasma gelsolin

Gelsolin, a Ca2+- and polyphosphoinositide-regulated actin-binding protein, is unique among vertebrate proteins in being both cytoplasmic and secreted. Plasma gelsolin, present at greater than 200 micrograms/ml in human plasma, may have a protective function by promoting the clearance of actin filaments released during tissue injury. Although there is evidence that smooth muscle tissues and HepG2 cells synthesize plasma gelsolin, the predominant secretory source is hitherto unknown. We report here that skeletal, cardiac, and smooth muscles have large amounts of plasma gelsolin mRNA and devote 0.5-3% of their biosynthetic activity to plasma gelsolin, whereas liver makes relatively little. Since skeletal muscle accounts for a large fraction of body mass and total protein synthesis, it is the major source of plasma gelsolin.