Dust-acoustic waves in a nonuniform adiabatic dusty plasma in the presence of polarization force

The linear propagation of the dust-acoustic (DA) waves in a nonuniform adiabatic dusty plasma, which consists of inertialess adiabatic electrons, inertialess adiabatic ions, and inertial negatively charged dust by taking into account the effects of polarization force, is theoretically investigated. It is found that the linear dispersion properties of the DA waves are significantly modified by the dust density nonuniformity, adiabaticity of electrons and ions, and the effects of the polarization force. It is shown that the phase speed of the DA waves is increased with the increase of adiabaticity of electrons and ions but decreased with the increase of the effects of polarization force. It is also shown that the dust density is enhanced with the increase of adiabatic index but depleted with the increase of polarization force. The scenarios relevant to dust-ion plasma in space environments are briefly addressed.     

Thermodynamic properties of strongly coupled plasma in the presence of an external magnetic field

Thermodynamic properties of a Yukawa system consisting of dust particles in plasma are studied in the presence of an external magnetic field. It is assumed that dust particles interact with each other by a modified potential in the presence of a magnetic field. A molecular dynamics code is developed to calculate this internal energy for the entire system. Based on the values of the internal energy given by the code, the Helmholtz free energy and pressure are calculated for the system.     

Nonlinear ion acoustic waves in a quantum degenerate warm plasma with dust grains

A study is made of the propagation of ion acoustic waves in a collisionless unmagnetized dusty plasma containing degenerate ion and electron gases at nonzero temperatures. In linear theory, a dispersion relation for isothermal ion acoustic waves is derived and an exact expression for the linear ion acoustic velocity is obtained. The dependence of the linear ion acoustic velocity on the dust density in a plasma is calculated. An analysis of the dispersion relation reveals parameter ranges in which the problem has soliton solutions. In nonlinear theory, an exact solution to the basic equations is found and examined. The analysis is carried out by Bernoulli’s pseudopotential method. The ranges of the phase velocities of periodic ion acoustic waves and the velocities of solitons are determined. It is shown that these ranges do not overlap and that the soliton velocity cannot be lower than the linear ion acoustic velocity. The profiles of the physical quantities in a periodic wave and in a soliton are evaluated, as well as the dependence of the critical velocity of solitons on the dust density in a plasma.     

Treatment of Streptococcus mutans biofilms with a nonthermal atmospheric plasma

AIMS: A nonthermal atmospheric plasma, designed for biomedical applications, was tested for its antimicrobial activity against biofilm cultures of a key cariogenic bacterium Streptococcus mutans. METHODS AND RESULTS: The Strep. mutans biofilms were grown with and without 0.15% sucrose. A chlorhexidine digluconate rinse (0.2%) was used as a positive antimicrobial reference. The presence of sucrose and the frequency of plasma application during growth were shown to have a significant effect on the response to treatment and antibacterial activity. CONCLUSIONS: A single plasma treatment for 1 min on biofilms cultured without sucrose caused no re-growth within the observation period. However, with either single or repeated plasma treatments of 1 min, on biofilms cultured with 0.15% sucrose, growth was only reduced. SIGNIFICANCE AND IMPACT OF THE STUDY: In summary, there may be a role for nonthermal plasma therapies in dental procedures. Sucrose and associated growth conditions may be a factor in the survival of oral biofilms after treatment.     

Theory of the polarization bremsstrahlung from thermal electrons scattered by the Debye sphere of an ion in a plasma

The polarization bremsstrahlung from thermal electrons scattered by the Debye sphere of an ion in a plasma is studied in the quasiclassical approximation. The model of the local plasma frequency is used to check the validity of the asymptotic expression for the polarizability of the electron cloud of an ion in the high-frequency range. This asymptotic expression is then used to derive a formula for the intensity of the total effective polarization bremsstrahlung. The R factor (the ratio of the contribution from the polarization bremsstrahlung to the contribution from conventional static bremsstrahlung) is obtained as a function of the plasma coupling parameter and electron density in order to analyze the role of the polarization bremsstrahlung in the total bremsstrahlung of the thermal plasma electrons. The spectral intensity of the effective polarization bremsstrahlung is calculated in the rotational approximation, which was previously employed in the theory of conventional static bremsstrahlung. It is shown that the spectral intensity of the polarization bremsstrahlung from thermal electrons scattered by the Debye sphere around an ion, as compared with the polarization bremsstrahlung by fast superthermal electrons, decreases more gradually with increasing frequency.     

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.     

Stability of dust acoustic wavepackets suffering from polarization force due to the presence of trapped ions

The combined effects of the polarization force, free and trapped ions, and dust charge variation are incorporated in a rigorous study of the nonlinear dust acoustic waves (DAWs) propagating in an unmagnetized dusty plasma. Owing to the departure from the Boltzmann ion distribution, it is found that the nonlinear DAWs are governed by a modified Korteweg?de Vries (mKdV) equation. The association between the mKdV solitary wave and the DAW envelope in the system under consideration is discussed. A modified nonlinear Schrödinger equation appropriate for describing the modulated DAWs is derived. The modulation instability (MI) and the dependence of the system physical parameters on the polarization force, trapped ions, and dust charge variation have been analyzed. It is found that the critical curve separating the stable/unstable regions is strongly influenced by both of the polarization and the ion trapping parameters. Moreover, increasing the polarization leads to an increase of the critical wave number, while increasing the trapping parameter yields the opposite effect. The MI maximum growth rate decreases (increases) as the polarization (trapped ion) increases. The obtained results may be helpful in better understanding of space observations of the solar energetic particle flows in interplanetary space and the energetic particle events in the Earth’s magnetosphere.     

On the stability of Suydam modes in a nonuniformly rotating plasma

A simplified wave equation is derived that describes both Suydam modes in a nonuniformly rotating plasma column in a helical magnetic field and related flute modes. A study is made of a low-pressure plasma under the assumption that the azimuthal component of the magnetic field is much weaker than the axial component. It is shown that, when the monotonic radial variation of the plasma rotation velocity is sufficiently sharp, the plasma core becomes stable against short-wavelength Suydam modes. The instabilities that can develop in a nonuniformly rotating plasma are classified.     

Dynamic equilibrium between coupled and uncoupled modes of a neuronal glutamate transporter

In the brain, the neurotransmitter glutamate is removed from the synaptic cleft by (Na(+) + K(+))-coupled transporters by an electrogenic process. Moreover, these transporters mediate a sodium- and glutamate-dependent uncoupled chloride conductance. In contrast to the wild type, the uptake of radiolabeled substrate by the I421C mutant is inhibited by the membrane-impermeant [2-(trimethylammonium)ethyl]methanethiosulfonate and also by other sulfhydryl reagents. In the wild-type and the unmodified mutant, substrate-induced currents are inwardly rectifying and reflect the sum of the coupled electrogenic flux and the anion conductance. Remarkably, the I421C mutant modified by sulfhydryl reagents exhibits currents that are non-rectifying and reverse at the equilibrium potential for chloride. Strikingly, almost 10-fold higher concentrations of d-aspartate are required to activate the currents in the modified mutant as compared with untreated I421C. Under conditions in which only the coupled currents are observed, the modified mutant does not exhibit any currents. However, when the uncoupled current is dominant, sulfhydryl reagents cause >4-fold stimulation of this current. Thus, the modification of the cysteine introduced at position 421 impacts the coupled but not the uncoupled fluxes. Although both fluxes are activated by substrate, they behave as independent processes that are in dynamic equilibrium.     

Application of atmospheric pressure nonthermal plasma for the in vitro eradication of bacterial biofilms

The use of atmospheric pressure nonthermal plasma represents an interesting and novel approach for the decontamination of surfaces colonized with microbial biofilms that exhibit enhanced tolerance to antimicrobial challenge. In this study, the influence of an atmospheric pressure nonthermal plasma jet, operated in a helium and oxygen gas mixture under ambient pressure, was evaluated against biofilms of Bacillus cereus, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Within < 4 min of plasma exposure, complete eradication of the two gram-positive bacterial biofilms was achieved. Although gram-negative biofilms required longer treatment time, their complete eradication was still possible with 10 min of exposure. Whilst this study provides useful proof of concept data on the use of atmospheric pressure plasmas for the eradication of bacterial biofilms in vitro, it also demonstrates the critical need for improved understanding of the mechanisms and kinetics related to such a potentially significant approach.     

Splitting of the modes of a low-frequency magnetosonic wave in a polydisperse dusty plasma

The properties of magnetosonic waves that propagate perpendicularly to the external magnetic field in a polydisperse dusty plasma and the frequencies of which are about the dust cyclotron frequency are analyzed. A dispersion relation containing integrals of functions of the dust grain radius is derived and investigated as a function of the parameters characterizing the polydisperse properties of dust. It is found that, in a polydisperse dusty plasma, the low-frequency magnetosonic mode splits into two branches. The first, lower frequency branch has a cutoff, while the higher frequency branch has a resonance. Between the two branches, there is a forbidden frequency range within which electromagnetic waves cannot propagate perpendicular to the magnetic field. The width of the forbidden frequency range is determined as a function of the slope of the distribution function of dust grains over radii and the interval within which the dust grain radii lie.     

Nonlinear isothermal waves in a degenerate electron plasma

A nonlinear differential equation describing oscillations of the chemical potential in a one-dimensional steady-state wave propagating in a degenerate electron gas against an immobile neutralizing ion background is derived, investigated, and solved exactly. It is found that the wave phase velocity is bounded below by a critical velocity, whose exact value is obtained.     

Nonlinear inverse bremsstrahlung absorption in a photoionized plasma

Nonlinear inverse bremsstrahlung absorption is investigated for a plasma photoionized in the Bethe regime of suppression of the ionization barrier, in which case the electron velocity distribution coincides with the distribution of atomic electrons. A comparison is made between the characteristic features of absorption in the cases where atomic electrons before ionization are in the ns and np states. It is established that, in the case of np states, the effective high-frequency conductivity is always nonlinear; in particular, for weak pump fields, it is proportional to the square of the pump field strength. The maximum plasma conductivity associated with p electrons is one order of magnitude lower than the maximum effective conductivity associated with s electrons, which creates conditions for less efficient plasma heating through inverse bremsstrahlung absorption.     

Determination of binding parameters in the presence of coupled reactions

Components of a binding reaction may undergo nonbinding reactions: receptors may be degraded, internalized, or exchanged with cryptic sites; ligand may be degraded or compartmented. In such cases the parameters that characterize the system are not obtained from the usual equilibrium analyses. We have simulated the reactions of such systems and generated association curves, "Scatchard" plots, and "Scatchard-like" plots that permit the calculation of binding affinity and receptor number not normally calculable under nonequilibrium binding conditions. In particular, we show that certain coupled reactions produce local maxima and sigmoid shapes in association curves and that the maxima can be used to obtain affinities and receptor numbers.     

Large-amplitude ion acoustic solitons in a bi-ion plasma

A gas-dynamic model is used to study the conditions for the existence of large-amplitude ion acoustic solitons in a plasma with negative ions. It is shown that the limiting Mach number—the upper boundary of the region of existence of compression solitons—depends nonmonotonically on the temperature of the positive ions. The result is that, for certain fixed densities of the negative ions, there are one or two temperature boundaries between the regions where solitons can and cannot exist. It is found that, for rarefaction solitons, it is fundamentally important to take into account electron inertia and that the Mach number of such solitary waves is restricted not by the complete decompression of electrons within the wave (as thought previously), but by the fact that the electrons at the center of the wave reach the acoustic speed, above which the thermal-pressure-induced action cannot be transferred back to the electron flow and smooth continuous solutions are impossible.     

Ideal internal kink modes in a differentially rotating cylindrical plasma

The Velikhov effect leading to magnetorotational instability (MRI) is incorporated into the theory of ideal internal kink modes in a differentially rotating cylindrical plasma column. It is shown that this effect can play a stabilizing role for suitably organized plasma rotation profiles, leading to suppression of MHD (magnetohydrodynamic) instabilities in magnetic confinement systems. The role of this effect in the problem of the Suydam and the m = 1 internal kink modes is elucidated, where m is the poloidal mode number. Published in Russian in Fizika Plazmy, 2008, Vol. 34, No. 7, pp. 589–597. The text was submitted by the authors in English.