Effect of space charge on the energy spectrum of a multispecies ion beam

The parameters of a multispecies metal ion beam extracted with the help of a set of grids from a plasma jet of a pulsed vacuum arc are studied experimentally. It is shown that the beam contains ions with energies that are both significantly lower and higher than the expected energy E _Z = \(\bar Z\) eU _acc, where \(\bar Z\) is the average ion charge number and U _acc is the extracting voltage. As a result, the mean ion energy is lower than E _Z and the ion energy spectrum is substantially wider than that in the plasma jet. It is found that this effect weakens with decreasing discharge current amplitude and that the shape of the spectrum depends on the accelerating voltage. Probe measurements show that, at accelerating voltages higher than 1 kV, a positive space charge forms in the drift gap, due to which the electric potential in the drift gap increases to a few hundred electronvolts. Analysis of experimental data indicates that the observed features of the ion spectrum can be attributed to the effect of the unsteady electric field of the space charge of the ion beam transported through the drift gap.     

Quantitation of hydrogen ion and potential gradients in gastric plasma membrane vesicles.

The ATP-dependent uptake of H+ by hog gastric parietal cell vesicles was quantitated by using the pH indicator dyes bromcresol green and malachite green, the weak bases, aminopyrine and 9-aminoacridine, and the pH electrode. A K+-dependent H+ uptake was found, with a significant difference between the quantity of H+ disappearing from the medium (deltaHo) and the quantity appearing inside the vesicle (deltaHi). 9-Aminoacridine gave a lower value for the deltaHi than any of the other probes. Probes of potential such as diethyloxadicarbocyanine or oxonol dyes showed that only secondary diffusion potentials occurred during H+ uptake and that the cationic dyes in the presence of protonophores could also be used to quantitate H+ uptake. The potential in the presence of protonophore indicated a deltaHi greater than that found with the other probes. Binding sites for acridine orange were generated either by ATP or an artificial pH gradient and corresponded to the deltaHi indicated by aminopyrine. SCN- (30mM) only partially inhibited the H+ gradient, and this, coupled with the failure to detect the physiological deltapH of 6.6, indicated that these vesicles may be an incomplete model of gastric acid secretion.     

An alternative hypothesis for the direction of hydrogen ion movement and energy transduction in H. halobium.

It is generally accepted that purple membrane of $\text{H.}\text{halobium}$ functions as a light-driven hydrogen ion pump translocating hydrogen ions from inside the cell to the external medium. However, experimental data from this laboratory together with those obtained by others have always shown an initial alkalinization of the external medium in the light. Additionally, we have found that oxygen can also induce an alkalinization of the bathing solution in the dark. These results can be readily explained if the direction of hydrogen-ion translocation is reversed, that is that both light and oxygen generate an electrochemical gradient of hydrogen ions, which is outwardly directed for ATP synthesis.     

Experimental study and numerical simulation of ion cyclotron heating of a hydrogen plasma in the T-11M tokamak

Results are presented from investigations of the possibility of heating a hydrogen plasma at the fundamental harmonic of the ion cyclotron frequency in the T-11M tokamak. The fluxes of charge-exchange atoms that escape from the plasma in the radial direction and across the toroidal magnetic field (transverse neutrals) were recorded by a Lakmus neutral particle analyzer. Measurements by the analyzer show that, during an RF pulse, the ion temperature increases by approximately 50–100 eV. Such plasma parameters as the ion temperature, rotation velocity, and isotopic composition were measured by a high-resolution spectrometer. According to the data from high-resolution spectroscopy, the ion temperature increases by approximately 150 eV. Results from numerical simulations of the ion cyclotron resonance heating of a hydrogen plasma in the T-11M tokamak are also given.     

On the spectrum of Z-pinch plasma neutrons

Generation of neutrons from Z-pinch discharges in a deuterated gas medium has been studied. It is shown that a power-law energy dependence of the number of high-energy deuterons in Z-pinch plasma explains the observed broadening of the neutron spectrum in these systems. It is established that, at an average ion energy below 3 keV in Z-pinch plasma, neutrons are mostly generated due to the interaction of high-energy (∼100-keV) deuterons with the main plasma components.     

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.     

Redox reactions of hydrogen selenide ion

Hydrogen selenide ion (HSe^-) is an important product in the metabolism of the essential trace element selenium. Although its role in selenium metabolism is recognized, aspects of the basic chemistry of selenide have been ignored, particularly the tendency of selenide to undergo rapid redox reactions with biological oxidants. Using polarography, we have found that selenide reacts in vitro with a variety of compounds including dehydroascorbic acid, quinones like vitamin K₁ and FAD (flavin adenine dinucleotide), and disulfides such as oxidized glutathione and lipoic acid. The fact selenide reacts readily in vitro suggests similar reactions may also occur in vivo with important biological consequences. Contrary to expectations, selenide was found not to reduce the disulfide bond of oxidized dithiothreitol (trans-4,5-dihydroxyl-1,2-dithiane), indicating the commonly published value for the standard electrode potential of the selenium/hydrogen selenide ion couple is in error. The electrode potential is an important parameter to aid in anticipating possible redox reactions of selenide in vivo.     

Dynamics of the electron thermal diffusivity at improved energy confinement during lower hybrid plasma heating in the FT-2 tokamak

The dynamics of electron heat transport at improved energy confinement during lower hybrid plasma heating in the FT-2 tokamak was studied experimentally. Evolution of the profiles of the electron temperature and density was thoroughly investigated under conditions of fast variation in the plasma parameters. The energy balance in the electron channel is calculated with the help of the ASTRA code by using the measured plasma parameters. Correlation is revealed between the dynamics of electron heat transport and the behavior of small-scale drift turbulence measured using the enhanced scattering correlation diagnostics. The suppression of heat transfer and turbulence agrees well with the increase in the shear of poloidal plasma rotation calculated from experimental data in the neoclassical approximation.     

Dynamics of hydrogen bond desolvation in protein folding

As proteins fold, a progressive structuring, immobilization and eventual exclusion of water surrounding backbone hydrogen bonds takes place. This process turns hydrogen bonds into major determinants of the folding pathway and compensates for the penalty of desolvation of the backbone polar groups. Taken as an average over all hydrogen bonds in a native fold, this extent of protection is found to be nearly ubiquitous. It is dynamically crucial, determining a constraint in the long-time limit behavior of coarse-grained ab initio simulations. Furthermore, an examination of one of the longest available (1micros) all-atom simulations with explicit solvent reveals that this average extent of protection is a constant of motion for the folding trajectory. We propose how such a stabilization is best achieved by clustering five hydrophobes around the backbone hydrogen bonds, an arrangement that yields the optimal stabilization. Our results support and clarify the view that hydrophobic surface burial should be commensurate with hydrogen-bond formation and enable us to define a basic desolvation motif inherent to structure and folding dynamics.     

Dynamics of the structure of the plasma current sheath in a plasma focus discharge

The study is aimed at investigating the fine structure of the plasma current sheath (PCS) in the PF-3 plasma focus facility. The PCS dynamics in a deuterium discharge was studied. The PCS parameters were measured using absolutely calibrated magnetic probes installed at different positions with respect to the facility axis and the anode surface. A magneto-optical probe recording both the magnetic signal and the PCS optical luminosity was first applied to analyze the PCS structure. This made it possible to spatially resolve the current and shock-wave regions. It is demonstrated that the current distribution is different in different discharge stages. It is shown that the neutron yield is determined by the value of the current compressed toward the axis, rather then the amplitude of the total discharge current.     

Cytoplasmic hydrogen ion diffusion coefficient.

The apparent cytoplasmic proton diffusion coefficient was measured using pH electrodes and samples of cytoplasm extracted from the giant neuron of a marine invertebrate. By suddenly changing the pH at one surface of the sample and recording the relaxation of pH within the sample, an apparent diffusion coefficient of 1.4 +/- 0.5 x 10(-6) cm2/s (N = 7) was measured in the acidic or neutral range of pH (6.0-7.2). This value is approximately 5x lower than the diffusion coefficient of the mobile pH buffers (approximately 8 x 10(-6) cm2/s) and approximately 68x lower than the diffusion coefficient of the hydronium ion (93 x 10(-6) cm2/s). A mobile pH buffer (approximately 15% of the buffering power) and an immobile buffer (approximately 85% of the buffering power) could quantitatively account for the results at acidic or neutral pH. At alkaline pH (8.2-8.6), the apparent proton diffusion coefficient increased to 4.1 +/- 0.8 x 10(-6) cm2/s (N = 7). This larger diffusion coefficient at alkaline pH could be explained quantitatively by the enhanced buffering power of the mobile amino acids. Under the conditions of these experiments, it is unlikely that hydroxide movement influences the apparent hydrogen ion diffusion coefficient.     

Dynamics of quasineutral plasma beams and the structure of the beam-induced disturbances in ionospheric plasma

Phenomena accompanying the injection of a dense plasma beam from the payload of a rocket into ionospheric plasma are analyzed. The dynamics of both the quasineutral plasma beam and the beam-induced disturbances in the ionospheric plasma are investigated. It is shown that the electric field in the beam has a complicated structure, which leads to the generation of currents in both the beam and the ambient ionospheric plasma. The transverse size of the disturbance zone in the ionospheric plasma is found to greatly exceed the beam diameter. The proposed model of the current closing in the ionospheric plasma agrees well with the experimental data. The xenon beam temperature at moderate distances from the injector is determined by using the plasma shadow theory. It is found that the ion beam temperature is at least four times lower than the plasma temperature in the injection zone. This unexpected result is explained by the adiabatic cooling of the current system. The critical radius beyond which a constant temperature in the beam is established is found to be less than 11 m.     

Dynamics of active transmembrane ion transfer in transport enzymes

It has been shown that recent investigations of the electron density distribution and high resolution (approximately 0.5 nm) spatial structure of transport ATPases open new possibilities in the development of general models for the mechanisms of energy of ATP hydrolysis and its use for active transmembrane ion transfer.