Suprathermal plasma flows in current sheets formed in two- and three-dimensional magnetic configurations

Dynamics of the thermal and directed motions of argon plasma ions in current sheets formed in various magnetic configurations was investigated experimentally Measurements in three-dimensional magnetic configurations with an X line were carried out for the first time. The results of these measurements were compared with the data obtained in experiments with two-dimensional magnetic configurations. The ion temperature and the energies and velocities of directed plasma flows within the current sheet were determined by analyzing the shapes of argon ion spectral lines broadened due to the Doppler effect. It is found that, under the given experimental conditions, the axial magnetic field does not affect the ion temperature and plasma acceleration in the sheet.     

Suppression of the dissociative phase transition in plasma mixtures of molecular and noble gases

The thermodynamic properties of a hydrogen-helium plasma are calculated both by the quantum Monte Carlo method and by using a chemical model. It is shown that the previously observed anomalous behavior of the isotherms of superdense molecular gases (the so-called dissociative phase transition) is suppressed in plasma mixtures of molecular and noble gases.     

Dynamics of the plasma current sheath in plasma focus discharges in different gases

The shape of the plasma current sheath (PCS) in the final stage of its radial compression, the dynamics of pinching, and the subsequent pinch decay in plasma focus (PF) discharges in different gases are studied using an improved multichannel system of electron-optical plasma photography and a newly elaborated synchronization system. The PCS structure in discharges in heavy gases (Ne, Ar) is found to differ significantly from that in discharges in hydrogen and deuterium. The influence of a heavy gas (Хе) additive to hydrogen and deuterium on the structure and compression dynamics of the PCS is investigated.     

Influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current and electron density in current sheets formed in helium

The influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current and electron density in current sheets formed in helium plasma in 2D and 3D magnetic configurations with X-type singular lines is studied by the methods of holographic interferometry and magnetic measurements. Significant differences in the structures of plasma and current sheets formed at close parameters of the initial plasma and similar configurations of the initial magnetic fields are revealed.     

Plasma acceleration in current sheets formed in helium in two- and three-dimensional magnetic configurations

The processes of heating and acceleration of plasma in current sheets formed in 2D and 3D magnetic configurations with an X-line in helium plasma have been investigated using spectroscopic methods. It is found that, in 2D magnetic configurations, plasma flows with energies of 400?C1000 eV, which are substantially higher than the ion thermal energy, are generated and propagate along the width (the larger transverse dimension) of the sheet. In 3D configurations, the influence of the longitudinal (directed along the X-line) component of the magnetic field on the plasma parameters in the current sheet has been studied. It is shown that plasma acceleration caused by the Amp??re force can be spatially inhomogeneous in the direction perpendicular to the sheet surface, which should lead to sheared plasma flows in the sheet.     

Laser-optical measurements of the velocities of the plasma jets formed from different gases in a kilojoule-range plasma focus facility

The velocities of the plasma jets formed from Ne, N₂, Ar, and Xe gases in plasma focus facilities were determined by means of laser-optical shadowgraphy of the shock waves generated at the jet leading edge. In spite of the almost tenfold ratio between the atomic weights of these gases, the outflow velocities of the plasma jets formed in experiments with these gases differ by less than twice, in the range of (0.7–1.1) × 10⁷ cm/s under similar discharge conditions. The energies of the jet ions were found to vary from 0.7 keV for nitrogen to 4 keV for xenon.     

Study of the structure and dynamics of current sheets in three-dimensional magnetic configurations with an X line by holographic interferometry

Results are presented from studies of the structure and dynamics of current sheets in three-dimensional magnetic configurations with an X line by means of holographic interferometry. It is found that the efficiency of plasma compression into the sheet is reduced as the longitudinal magnetic field B _z , directed along the X line, increases. This effect is attributed to the enhancement of the longitudinal component of the magnetic field within the sheet and to the corresponding increase in the magnetic pressure. It is shown that the formation of a plasma sheet lags behind the beginning of the plasma current pulse, the delay time being close to the characteristic Alfvén time.     

Thin current sheets in collisionless plasma: Equilibrium structure,plasma instabilities,and particle acceleration

The review is devoted to plasma structures with an extremely small transverse size, namely, thin current sheets that have been discovered and investigated by spacecraft observations in the Earth’s magnetotail in the last few decades. The formation of current sheets is attributed to complicated dynamic processes occurring in a collisionless space plasma during geomagnetic perturbations and near the magnetic reconnection regions. The models that describe thin current structures in the Earth’s magnetotail are reviewed. They are based on the assumption of the quasi-adiabatic ion dynamics in a relatively weak magnetic field of the magnetotail neutral sheet, where the ions can become unmagnetized. It is shown that the ion distribution can be represented as a function of the integrals of particle motion—the total energy and quasi-adiabatic invariant. Various modifications of the initial equilibrium are considered that are obtained with allowance for the currents of magnetized electrons, the contribution of oxygen ions, the asymmetry of plasma sources, and the effects related to the non-Maxwellian particle distributions. The theoretical results are compared with the observational data from the Cluster spacecraft mission. Various plasma instabilities developing in thin current sheets are investigated. The evolution of the tearing mode is analyzed, and the parameter range in which the mode can grow are determined. The paradox of complete stabilization of the tearing mode in current sheets with a nonzero normal magnetic field component is thereby resolved based on the quasi-adiabatic model. It is shown that, over a wide range of current sheet parameters and the propagation directions of large-scale unstable waves, various modified drift instabilities—kink and sausage modes—can develop in the system. Based on the concept of a turbulent electromagnetic field excited as a result of the development and saturation of unstable waves, a mechanism for charged particle acceleration in turbulent current sheets is proposed and the energy spectra of the accelerated particles are obtained.     

A possible molecular mechanism of the narcotic action of noble gases

A molecular mechanism of the narcotic action of noble gases is suggested, which is based on the fact that noble gas atoms change the orientation of water molecules absorbed on the surface of axon membrane. The resulting change in the transmembrane potential deteriorates the propagation of nerve pulse.     

Experimental studies of the magnetic structure and plasma dynamics in current sheets (a review)

Based on measurements of magnetic fields in current sheets, spatial distributions of the electric current and electrodynamic forces in successive stages of the sheet evolution are determined. Two new effects manifesting themselves mostly in the late stages of the current sheet evolution have been discovered, namely, expansion of the current flow region at the periphery of the sheet and the appearance of a region with inverse currents, which gradually expands from the periphery toward the center of the sheet. Using spectroscopic methods, generation of superthermal plasma flows accelerated along the sheet width from the center toward the periphery has been revealed and investigated. The measured energies of accelerated plasma ions satisfactorily agree with the Ampère forces determined from magnetic measurements. The excitation of inverse currents additionally confirms the motion of high-speed plasma flows from the center of the current sheet toward its side edges.     

Molecular dynamics simulations of noble gases encapsulated in C60 Fullerene

Molecular dynamics simulations of Helium (He), Neon (Ne), Argon (Ar), Krpton (Kr) and Xenon (Xe) encapsulated in C₆₀ are discussed, as well simulations of Fullerenes containing anywhere from two to four He atoms. Even for single atom encapsulates, no species resides at the geometric center of the Fullerene cage. Smaller atoms sit more off-center than larger ones, and He appears to be a special case in both centering and dynamics. Some encapsulated species stabilize the cage by stifling radial fluctuations and others disrupt it; adding Ne seems to have the most stabilizing effect, while Kr and Xe cause the largest radial atomic excursions. Multiple He encapsulates tend to stabilize the cage; such systems are very stressed and show structure over a wide temperature range. Based on dynamical information quadruple He seems to be close to the packing limit for C₆₀.     

Spectroscopic measurements of the electron and ion temperatures and effective ion charge in current sheets formed in two- and three-dimensional magnetic configurations

The spatial distributions of the electron temperature and density, the effective and average ion charges, and the thermal and directed ion velocities in current sheets formed in two-dimensional magnetic fields and three-dimensional magnetic configurations with an X line were studied using spectroscopic and interference holographic methods. The main attention was paid to studying the time evolution of the intensities of spectral lines of the working-gas (argon) and impurity ions under different conditions. Using these data, the electron temperature was calculated with the help of an original mathematical code based on a collisional-radiative plasma model incorporating the processes of ionization and excitation, as well as MHD plasma flows generated in the stage of the current-sheet formation. It is shown that the electron temperature depends on the longitudinal magnetic field, whereas the ion temperature is independent of it. The effective ion charge of the current-sheet plasma was determined for the first time.     

Time evolution of the plasma spatial structure during the formation of a current sheet in argon according to holographic interferometry

The spatiotemporal dynamics of plasma sheets formed in argon plasma in two- and three-dimensional magnetic configurations with an X-type singular line was studied using holographic interferometry. An analogy is revealed between the development of plasma sheets and the time evolution of the current sheet structure, which was previously studied using magnetic measurements. In the late stage of the sheet evolution, a change in the rotation direction of plasma sheets formed in 3D magnetic configurations was observed. Apparently, this is caused by a change in the direction of the Hall currents at the side edges of the current sheet.     

Actin paracrystalline sheets formed at the surface of positively charged liposomes

Paracrystalline aggregates of F-actin spontaneously assemble at the surface of positively charged liposomes. This single-layered paracrystalline array is made up of parallel and juxtaposed actin filaments aligned in register and showing the typical 36-nm periodicity which corresponds to the half-pitch of the double helix strand. This crystallization of pure actin results from a direct interaction between actin and positively charged lipids and does not occur with negative or neutral lipids.     

Concerning the width of spark channels with different polarities in submicrosecond sliding discharges in noble gases

Previously, the parameters of submicrosecond (with a duration of <200 ns) multichannel high-current discharges sliding along a ceramic surface in Ne, Ar, and Xe were studied only for the negative polarity of the applied voltage. The experimental data indicate that the channels expand in the transverse direction mainly due to electron drift from the channel surface layer under the action of the electric field perpendicular to the channel axis and subsequent gas ionization by these electrons. To investigate mechanisms for the channel development in a sliding discharge—in particular, to determine the contribution of electron drift—it is necessary to carry out experiments similar to those performed earlier for the opposite polarity of the applied voltage. Here, the results of measurements of the widths of the spark channels of negativeand positive-polarity sliding discharges excited in Ne, Ar, and Xe at pressures of 30 and 100 kPa are presented and discussed. It is shown that, depending on the pressure and sort of gas, the averaged optical width of positive-polarity channels is smaller by a factor of 1.27–1.60 than that of negative-polarity channels. The experimental data are analyzed using the theory of propagation of ionization waves with different polarities in gases. Analysis has shown that electron diffusion contributes insignificantly to channel expansion and that, for both polarities, the channel expansion rate exceeds the electron drift velocity in the transverse electric field near the channel. In the framework of the so-called approximation of nonlocalized initial conditions, the measured ratio between of the widths of negativeand positive-polarity channels and their relation to the electron mobility are explained by the channel expansion governed by both electron drift and primary free electrons produced by a short-term source in a narrow region ahead of the front of the expansion wave. Numerical simulations show that the width of this region is comparable with that of the wave front and is more than one order of magnitude smaller than the observed channel radius. Gas photoionization by the channel radiation can serve as a source of primary electrons.     

Growth responses of Neurospora crassa to increased partial pressures of the noble gases and nitrogen

Buchheit, R. G. (Union Carbide Corp., Tonawanda, N.Y.), H. R. Schreiner, and G. F. Doebbler. Growth responses of Neurospora crassa to increased partial pressures of the noble gases and nitrogen. J. Bacteriol. 91:622-627. 1966.-Growth rate of the fungus Neurospora crassa depends in part on the nature of metabolically "inert gas" present in its environment. At high partial pressures, the noble gas elements (helium, neon, argon, krypton, and xenon) inhibit growth in the order: Xe > Kr> Ar > Ne > He. Nitrogen (N(2)) closely resembles He in inhibitory effectiveness. Partial pressures required for 50% inhibition of growth were: Xe (0.8 atm), Kr (1.6 atm), Ar (3.8 atm), Ne (35 atm), and He ( approximately 300 atm). With respect to inhibition of growth, the noble gases and N(2) differ qualitatively and quantitatively from the order of effectiveness found with other biological effects, i.e., narcosis, inhibition of insect development, depression of O(2)-dependent radiation sensitivity, and effects on tissue-slice glycolysis and respiration. Partial pressures giving 50% inhibition of N. crassa growth parallel various physical properties (i.e., solubilities, solubility ratios, etc.) of the noble gases. Linear correlation of 50% inhibition pressures to the polarizability and of the logarithm of pressure to the first and second ionization potentials suggests the involvement of weak intermolecular interactions or charge-transfer in the biological activity of the noble gases.     

Dynamics of the structure of electric currents and electrodynamic forces in current sheets

Specific features of the spatial distributions of the electric current and electrodynamic forces in current sheets are examined by studying the magnetic fields in them. It is shown that the j × B forces should lead to a gradual increase in the kinetic energy of the plasma accelerated along the current sheet surface. Excitation of currents directed oppositely to the main current in the central part of the sheet is observed for the first time, and the time evolution of the forward and reverse currents is investigated. Generation of reversed currents is a manifestation of the dynamic effects caused by the motion of plasma flows in the magnetic field and leading to a change in the magnetic structure of the current sheet.     

A method of staining basal-cell plasma membranes in epidermal sheets

An adenosine triphosphatase method was devised to stain basal epidermal cell plasma membranes in sheet preparations of humans, rat, mouse and guinea pig epidermis. The method is useful for direct observation of sizes, shapes, and numbers of basal epidermal cells.     

DFT study of conductive properties of three polymers formed by bicyclic furans

Density functional theory methods were employed to study the electronic, structural and conductive properties of classical bicyclic furans. In this paper, studies of monomers, oligomers and polymers of furo[3,4-b]furan, furo[2,3-b]furan and furo[3,2-b]furan are presented. To gain detailed information on conjugational degree, we selected the nucleus-independent chemical shift as a method for examining the changes in conjugational degree. Furthermore, three parameters of density of state, effective mass (m*) and kinetic model of mobility (μ) were also investigated. The variable trends of all parameters from monomers to tetramers indicate that poly(4,4′-bifuro[3,4-b]furan), poly(trans-2,2′-bifuro[3,2-b]furan) and poly(cis-2,2′-bifuro[3,2-b]furan) are good candidates for conductive materials, which are consistent with band structure analyses showing that the three polymers had narrower band gaps (1.21, 1.93 and 1.89 eV, respectively) than other polymers.     

Biochemical properties of platelet microparticle membranes formed during exocytosis resemble organelles more than plasma membrane

An early proposal was that for rapid ATP synthesis by the rotational ATP synthase, a specific second site must bind ADP and P(i), and for rapid ATP hydrolysis a different second site must bind ATP. Such bi-site activation was considered to occur whether or not an ADP or ATP was at a third site. In contrast, a more recent proposal is that rapid ATP hydrolysis requires that all three sites have bound ADP or ATP present. However, discovery that one second site binds ADP better than ATP, together with other data and considerations support the earlier proposal. The retention or rebinding of ADP can explain why three sites fill during hydrolysis as ATP concentration is increased although bi-site activation still prevails.