Energy of Plasma Flows Accelerated in a Current Sheet as a Function of the Current Flowing through the Sheet

The energy of directed plasma flows accelerated in a current sheet is studied experimentally as a function of the current flowing through the sheet. It is found that the plasma flow energy rapidly increases with increasing current amplitude, nearly according to a power law with an exponent of 1.8–1.9. Using relations for the neutral current sheet and the concept of plasma acceleration under action of the Ampère forces, the energy of directed plasma flows is estimated as a function of the total current flowing through the sheet. It is shown that, as the current rises, the ion energy grows due to an increase in both the Ampère forces and the width of the current sheet within which plasma is accelerated.     

Heating of Plasma Electrons by Laser Radiation under Parametric Resonance Conditions in Strong Magnetic Field

Plasma Physics Reports - Heating of plasma electrons by an extraordinary laser wave at the double upper hybrid frequency in a strong magnetic field is studied numerically by the particle-in-cell...     

Heat Transfer in a Micropolar Fluid over a Stretching Sheet with Newtonian Heating

This article looks at the steady flow of Micropolar fluid over a stretching surface with heat transfer in the presence of Newtonian heating. The relevant partial differential equations have been reduced to ordinary differential equations. The reduced ordinary differential equation system has been numerically solved by Runge-Kutta-Fehlberg fourth-fifth order method. Influence of different involved parameters on dimensionless velocity, microrotation and temperature is examined. An excellent agreement is found between the present and previous limiting results.     

Role of Oxygen Ions in the Structure of the Current Sheet of the Near-Earth Magnetotail

Plasma Physics Reports - A numerical model is used to study the possibility of a thin current sheet formation in the near-Earth magnetotail in the growth phase of a substorm for a wide range of...     

Kinetic Simulations of EC Plasma Heating and Current Drive in the L-2M Stellarator

The ECHLAB code, intended for a self-consistent numerical analysis of the evolution of the electron distribution function and the spatial structure of the electromagnetic field during EC plasma heating in a stellarator, is described. The results from calculations of plasma heating and current drive under conditions corresponding to experiments on EC plasma heating by an X2-mode in the L-2M stellarator are presented. It is shown that, at the existing level of microwave power, the energy deposition region displaces only slightly during heating. The energy is mainly absorbed by relatively fast passing electrons. The influence of locally trapped electrons on the efficiency of current drive is insignificant.     

Adiabatic TOBSY in rotating solids

A MAS solid state NMR approach for achieving efficient scalar coupling mediated through-bond (13)C chemical shift correlations of the aliphatic carbons in uniformly labelled peptides/proteins is described. The method involves the application of a continuous train of adiabatic inversion pulses, as in the adiabatic TOCSY experiments carried out in solution state NMR studies. While rotor synchronised application of adiabatic inversion pulses leads to dipolar correlations, it is shown here via numerical simulations and experimental measurements that asynchronous application of adiabatic pulses can facilitate the mapping of through-bond connectivities. The method employs a suitable phasing scheme for generating the desired isotropic mixing Hamiltonian and requires moderate (13)C RF field strength only.     

Possible Mechanism of Enhancement of Diamagnetic Current Dissipation during the Heating of Magnetic Flux Tubes in the Solar Corona

It is shown that dissipation of the diamagnetic current heating the coronal plasma with the classical conductivity in the absence of a longitudinal current can increase significantly due to the cellular transverse microstructure of the flux tube, thereby compensating for intense radiative losses.     

Adiabatic Heteronuclear Decoupling in Rotating Solids

In magic angle spinning solid state NMR experiments the potential of heteronuclear (1)H decoupling employing a continuous train of adiabatic inversion pulses has been assessed via numerical simulations and experimental measurements. It is shown that, with a (1)H RF field strength of approximately 100 kHz that is typically available in MAS NMR probes, it is possible to achieve efficient adiabatic (1)H decoupling at low magic angle spinning frequencies. It is pointed out that in the presence of H (1) inhomogeneities it will be advantageous to employ adiabatic decoupling in MAS solid state NMR experiments.     

Time Evolution of the Macroscopic Characteristics of a Thin Current Sheet in the Course of Its Formation in the Earth’s Magnetotail

A numerical model is developed that allows tracing the time evolution of a current sheet from a relatively thick current configuration with isotropic distributions of the pressure and temperature in an extremely thin current sheet, which plays a key role in geomagnetic processes. Such a configuration is observed in the Earth’s magnetotail in the stage preceding a large-scale geomagnetic disturbance (substorm). Thin current sheets are reservoirs of the free energy released during geomagnetic disturbances. The time evolution of the components of the pressure tensor caused by changes in the structure of the current sheet is investigated. It is shown that the pressure tensor in the current sheet evolves in two stages. In the first stage, a current sheet with a thickness of eight to ten proton Larmor radii forms. This stage is characterized by the plasma drift toward the current sheet and the Earth and can be described in terms of the Chu–Goldberger–Low approximation. In the second stage, an extremely thin current sheet with an anisotropic plasma pressure tensor forms, due to which the system is maintained in an equilibrium state. Estimates of the characteristic time of the system evolution agree with available experimental data.     

Electrons and X-rays gang up on the ribosome

In all cells, protein synthesis is coordinated by the ribosome, and a number of pivotal structural studies on this complex have been completed during 1999. The combined results of the X-ray crystallography and electron microscopy studies have shed new light on the mechanism of this molecular machine.     

Spectroscopic Investigation of Tangential Acceleration and Heating of Plasma of Current Sheets Formed under the Krypton Discharge

Plasma Physics Reports - Temperatures of singly and doubly charged krypton ions, along with electron temperature, were determined as functions of time in current sheets formed in the 2D and 3D...     

Adiabatic transformability hypothesis of human locomotion

It is hypothesized that metabolic and mechanical changes in human locomotion associated with changes in speed v are constrained by two attractive strategies: $Q_{{\text{metab}}} = 1{\text{ and }}\Delta Q_{{\text{metab}}} /\Delta v = {\text{a}}$ positive definite constant. $Q_{{\text{metab}}} = \Delta {\rm E}_{\text{k}} {\text{s}}^{{\text{ - 1}}} /{\text{ml O}}_{\text{2}} {\text{s}}^{{\text{ - 1}}} $ where ΔEs^?1 is the summed increments and decrements per unit time in the translational and rotational kinetic energies of the body's segments and ml O₂s^?1 is the rate at which chemical energy is dissipated. The expected constancy of ΔQ _metab/Δv _metab was derived from an extension of Ehrenfest's adiabatic hypothesis by which transformations (increases, decreases) in locomotion v can be considered as adiabatic, even though the biological conditions are nonconservative and non-rate-limited. The expected significance of Q _metab=1 was derived from stability considerations of the symmetry per stride of stored and dissipated energy. An experimental evaluation was provided by collecting metabolic and mechanical measures on walking (10 subjects) and running (9 subjects) at progressively greater treadmill speeds but within the aerobic limit. Results revealed that walking was restricted to ometab ? 1 with a nonlinear trajectory in v×Q _metab coordinates shaped by Q _metab=1 (primarily) and the constancy of ΔQ _metab/Δv. Running satisfied Q _metab > 1, with a linear trajectory in v×Q _metab coordinates conforming to ΔQ _metab/_Δv=a constant, with the constant predicted from invariants in the mechanical space v×ΔE _ks^?1. Results also suggested that the metabolic costs of running might be predictable from measures made in the v×ΔE _ks^?1 space.     

Partitioning of Electrons between the Cytochrome and Alternative Pathways in Intact Roots

To test the hypothesis that the cytochrome pathway is not invariably saturated when the alternative pathway is engaged, we titrated root respiration of several species with KCN (an inhibitor of the cytochrome pathway), both in the absence and presence of an inhibitor of the alternative pathway (salicylhydroxamic acid, SHAM). The slopes of the resultant KCN [rho] plots ([rho]cyt) were then used to determine whether the cytochrome pathway was saturated in each species. The species used were Festuca ovina ssp. ovina L., Phaseolus vulgaris L., and six Poa species (Poa pratensis L., Poa compressa L., Poa trivialis L., Poa alpina L., Poa costiniana Vick., and Poa fawcettiae Vick.). Although the cytochrome pathway was saturated in a number of species (i.e. [rho]cyt values were 1.0), several others exhibited [rho]cyt values of less than 0.5. Alternative pathway capacity correlated negatively with [rho]cyt, with [rho]cyt values of less than 1.0 occurring in tissues in which the alternative pathway capacity was greater than 25 to 30% of total respiration. The species that did not show full engagement of the cytochrome pathway rarely exhibited SHAM inhibition in the absence of KCN. We conclude that this lack of SHAM inhibition is not due to a lack of alternative pathway engagement but rather to the diversion of electrons from the alternative pathway to the unsaturated cytochrome path following the addition of SHAM.     

Electrons, life and the evolution of Earth's oxygen cycle

The biogeochemical cycles of H, C, N, O and S are coupled via biologically catalysed electron transfer (redox) reactions. The metabolic processes responsible for maintaining these cycles evolved over the first ca 2.3 Ga of Earth's history in prokaryotes and, through a sequence of events, led to the production of oxygen via the photobiologically catalysed oxidation of water. However, geochemical evidence suggests that there was a delay of several hundred million years before oxygen accumulated in Earth's atmosphere related to changes in the burial efficiency of organic matter and fundamental alterations in the nitrogen cycle. In the latter case, the presence of free molecular oxygen allowed ammonium to be oxidized to nitrate and subsequently denitrified. The interaction between the oxygen and nitrogen cycles in particular led to a negative feedback, in which increased production of oxygen led to decreased fixed inorganic nitrogen in the oceans. This feedback, which is supported by isotopic analyses of fixed nitrogen in sedimentary rocks from the Late Archaean, continues to the present. However, once sufficient oxygen accumulated in Earth's atmosphere to allow nitrification to out-compete denitrification, a new stable electron 'market' emerged in which oxygenic photosynthesis and aerobic respiration ultimately spread via endosymbiotic events and massive lateral gene transfer to eukaryotic host cells, allowing the evolution of complex (i.e. animal) life forms. The resulting network of electron transfers led a gas composition of Earth's atmosphere that is far from thermodynamic equilibrium (i.e. it is an emergent property), yet is relatively stable on geological time scales. The early coevolution of the C, N and O cycles, and the resulting non-equilibrium gaseous by-products can be used as a guide to search for the presence of life on terrestrial planets outside of our Solar System.     

Resonant Laser-Assisted Process of Ultrarelativistic Electrons Bremsstrahlung in the Field of a Nucleus

Plasma Physics Reports - The scrutiny of the resonant laser-assisted bremsstrahlung (LAB) of ultrarelativistic electrons within the laser plasma ambience in the field of a nucleus is presented. The...     

Structural Interaction Between DsrE-DsrF-DsrH Proteins Involved in the Transport of Electrons in the dsr Operon

Abstract

Biological redox reactions of inorganic sulfur compounds are important for the proper maintenance of environmental sulfur balance. These reactions are mediated by phylogeneticaly diverse set of microorganisms. The protein complex that is involved in such redox reactions of sulfur compounds is the complex encoded by dsr operon. The ecological and industrial importance of these microorganisms led us to investigate the structural details of the mechanism of the process of electron transport during such redox reactions performed by the dsr operon. Among the gene products of the operon, the proteins DsrE, DsrF, and DsrH are small soluble cytoplasmic proteins acting as α₂β₂γ₂ heterohexamer and are involved in the process of electron transport in these ecologically as well as industrially important microorganisms.

Since no structural details of the proteins were available we employed homology modeling to construct the three-dimensional structures of the DsrE, DsrF, and DsrH from Chlorobium tepidum. The putative three dimensional structures of the proteins were predicted from the models. Since DsrE, DsrF, and DsrH proteins act as a hetero-hexameric complex, the modeled proteins were subjected to molecular docking analyses to generate the model of the biochemically active complex. This allowed us to predict the probable binding modes of the proteins as well as the biochemical and the structural basis of the mechanism of the electron transport process by this complex. The hexamerization of the proteins would help to bring the Cys residues in close proximity, which enables the complex to actively take part electron transport process.     

Evidence for the Contribution of the Mehler-Peroxidase Reaction in Dissipating Excess Electrons in Drought-Stressed Wheat

Gross O2 evolution and uptake by attached, drought-stressed leaves of wheat (Triticum aestivum) were measured using a 16O2/ 18O2 isotope technique and mass spectrometry. The activity of photosystem II, determined from the rate of 16O2 evolution, is only slightly affected under drought conditions. During drought stress, net CO2 uptake decreases due to stomatal closure, whereas the uptake of 18O2 is stimulated. The main O2-consuming reactions in the light are the Mehler-peroxidase (MP) reaction and the photorespiratory pathway. From measurements of the rate of carbon flux through the photorespiratory pathway, estimated by the analysis of the specific radioactivities of glycolate, we conclude that the rate of photorespiration is decreased with drought stress. Therefore, the O2 taken up in the light appears to be preferentially used by the MP reaction. In stressed leaves, 29.1% of the photosynthetic electrons are consumed in the MP reaction and 18.4% drive the photorespiratory pathway. Thus, overreduction of the electron transport chain is avoided preferably by the MP reaction when drought stress restricts CO2 reduction.     

Influence of Trapped Electrons on the Plasma Potential in the Expander of an Open Trap

Plasma Physics Reports - The influence of electrons trapped between the magnetic mirror and the Debye sheath on the potential profile in the expander of an open trap is considered. A numerical...     

Calculation of Thermal Conductivity Coefficients of Electrons in Magnetized Dense Matter

The solution of Boltzmann equation for plasma in magnetic field with arbitrarily degenerate electrons and nondegenerate nuclei is obtained by Chapman?Enskog method. Functions generalizing Sonine polynomials are used for obtaining an approximate solution. Fully ionized plasma is considered. The tensor of the heat conductivity coefficients in nonquantized magnetic field is calculated. For nondegenerate and strongly degenerate plasma the asymptotic analytic formulas are obtained and compared with results of previous authors. The Lorentz approximation with neglecting of electron?electron encounters is asymptotically exact for strongly degenerate plasma. For the first time, analytical expressions for the heat conductivity tensor for nondegenerate electrons in the presence of a magnetic field are obtained in the three-polynomial approximation with account of electron?electron collisions. Account of the third polynomial improved substantially the precision of results. In the two-polynomial approximation, the obtained solution coincides with the published results. For strongly degenerate electrons, an asymptotically exact analytical solution for the heat conductivity tensor in the presence of a magnetic field is obtained for the first time. This solution has a considerably more complicated dependence on the magnetic field than those in previous publications and gives a several times smaller relative value of the thermal conductivity across the magnetic field at ωτ * 0.8.