Atmospheric-pressure electric discharge as an instrument of chemical activation of water solutions

Results of experimental studies and numerical simulations of physicochemical characteristics of plasmas generated in different types of atmospheric-pressure discharges (pulsed streamer corona, gliding electric arc, dielectric barrier discharge, glow-discharge electrolysis, diaphragmatic discharge, and dc glow discharge) used to initiate various chemical processes in water solutions are analyzed. Typical reactor designs are considered. Data on the power supply characteristics, plasma electron parameters, gas temperatures, and densities of active particles in different types of discharges excited in different gases and their dependences on the external parameters of discharges are presented. The chemical composition of active particles formed in water is described. Possible mechanisms of production and loss of plasma particles are discussed.     

Phase transition in superdense hydrogen and deuterium

Results are presented from numerical simulations of the thermodynamic properties of superdense hydrogen and deuterium plasmas by the Monte Carlo method and from calculations by a multicomponent chemical model. The results obtained reveal the anomalous behavior of the thermodynamic functions and composition of molecular gas plasmas in the submegabar and megabar pressure ranges. Such behavior is interpreted as a dissociative phase transition. The results of calculations by the chemical model are compared with the experimental data on the equation of state and conductivity of hydrogen and deuterium plasmas.     

Numerical simulations of the development of an open discharge

Plasma Physics Reports - Results are presented from numerical simulations of the time evolution of open discharges in helium that are excited in the presence of an anode grid and generate electron...     

Properties of a low-pressure inductive RF discharge II: Mathematical simulations

Self-consistent numerical simulations of a low-pressure inductive RF discharge have been carried out. It is shown that, on the one hand, the plasma parameters are determined by the RF power absorbed in the plasma and, on the other, they themselves govern the power absorption. This results in a nonmonotonic dependence of the plasma parameters on the magnetic field, as well as in discharge disruptions, similar to those observed experimentally in such discharges. An inductive RF discharge with a capacitive component is simulated. The experimentally observed characteristic properties of the discharges are explained based on the regular features of the absorption of RF power in the plasma. Traditional inductive plasma sources (both without and with a magnetic field) are considered.     

Simulations of tokamak discharges with fast L-H transitions

Results are presented from the simulations of discharges with fast L-H transitions in the JET tokamak. During a transition, electron temperature perturbations propagate into the plasma core over a time much shorter than the transport time characteristic of this device. It is shown that the experimentally observed variations in the electron temperature may be caused by the change in the particle source intensity in the plasma when the atomic flux decreases, which is detected from the drop in the intensity of the D_α hydrogen spectral line. Hence, the experiments under consideration can be explained without the assumption about the nonlocal character of transport processes in tokamaks, which was made in some papers devoted to JET experiments. The plasma component responsible for the apparent nonlocal character of transport processes is the neutral component, whose propagation time across the plasma column is sufficiently short (t<100 μs). __________ Translated from Fizika Plazmy, Vol. 28, No. 1, 2002, pp. 3–8. Original Russian Text Copyright ? 2002 by Leonov.     

Simulation Studies of Vestibular Macular Afferent-Discharge Patterns Using a New, Quasi-3-D Finite Volume Method

A quasi-three-dimensional finite-volume numerical simulator was developed to study passive voltage spread in vestibular macular afferents. The method, borrowed from computational fluid dynamics, discretizes events transpiring in small volumes over time. The afferent simulated had three calyces with processes. The number of processes and synapses, and direction and timing of synapse activation, were varied. Simultaneous synapse activation resulted in shortest latency, while directional activation (proximal to distal and distal to proximal) yielded most regular discharges. Color-coded visualizations showed that the simulator discretized events and demonstrated that discharge produced a distal spread of voltage from the spike initiator into the ending. The simulations indicate that directional input, morphology, and timing of synapse activation can affect discharge properties, as must also distal spread of voltage from the spike initiator. The finite volume method has generality and can be applied to more complex neurons to explore discrete synaptic effects in four dimensions.     

Time-dependent inactivation of immobilized glucose oxidase and catalase

Homogeneous membranes containing immobilized glucose oxidase and catalase were stored in buffered solutions at 37 degrees C to determine the mechanisms and rates of catalyst inactivation. The experiments were designed so that inactivation occurred homogeneously throughout the membrane, thereby simplifying the analysis. The mechanism of inactivation is consistent with the reaction of hydrogen peroxide and certain catalytic intermediates of both enzymes. Based on this information, numerical simulations were developed that incorporate spatially heterogeneous catalytic and inactivation processes.     

Numerical simulations of spark channels propagating along the ground surface: Comparison with high-current experiment

A numerical model of a spark discharge propagating along the ground surface from the point at which an ∼100-kA current pulse is input into the ground has been developed based on experiments in which the velocity of a long leader was measured as a function of the leader current. The results of numerical simulations are in good agreement with the measured characteristics of creeping discharges excited in field experiments by using a high-power explosive magnetic generator. The reason why the length of a spark discharge depends weakly on the number of simultaneously developing channels is found. Analysis of the influence of the temporal characteristics of the current pulse on the parameters of the creeping spark discharge shows that actual lighting may exhibit similar behavior.     

Inactivation of spores by nonthermal plasmas

Bacterial and fungal spore contamination in different industries has a greater economic impact. Because of the remarkable resistance of spores to most physical and chemical microbicidal agents, their inactivation need special attention during sterilization processes. Heat and chemical sporicides are not always well suited for different sterilization/decontamination applications and carries inherent risks. In recent years, novel nonthermal agents including nonthermal plasmas are emerging as effective sporicides against a broad spectrum of bacterial and fungal spores. The present review discusses various aspects related to the inactivation of spores using nonthermal plasmas. Different types of both low pressure plasmas (e.g., capacitively coupled plasma and microwave plasma) and atmospheric pressure plasmas (e.g., dielectric barrier discharges, corona discharges, arc discharges, radio-frequency-driven plasma jet) have been successfully applied to destroy spores of economic significance. Plasma agents contributing to sporicidal activity and their mode of action in inactivation are discussed. In addition, information on factors that affect the sporicidal action of nonthermal plasmas is included.     

Reverse Problem Formulation for Integrating Process Discharges with Watersheds and Drainage Systems

This work introduces a new approach to integrating the discharges of industrial processes with macroscopic watershed systems. The key concept is that environmental quality models (such as material flow analysis) can be inverted and included in an optimization formulation that seeks to determine the maximum allowable target for the process discharges while meeting the overall environmental requirements of the watershed. Because of its holistic nature, this approach simultaneously considers the effects of the inputs and outputs to the watershed (e.g., agricultural, residential, wastewater treatment plants, industrial, and so on) and the various physical, chemical, and biological phenomena occurring within the watershed. An optimization formulation is developed to systematically represent the reverse problem formulation. To illustrate the effectiveness of this approach, a case study is solved to manage phosphorus in Bahr El‐Baqar drainage system leading to Lake Manzala in Egypt. The key environmental and economic aspects are addressed and used to screen plant location and discharges.     

The stochastic properties of input spike trains control neuronal arithmetic

In the nervous system, the representation of signals is based predominantly on the rate and timing of neuronal discharges. In most everyday tasks, the brain has to carry out a variety of mathematical operations on the discharge patterns. Recent findings show that even single neurons are capable of performing basic arithmetic on the sequences of spikes. However, the interaction of the two spike trains, and thus the resulting arithmetic operation may be influenced by the stochastic properties of the interacting spike trains. If we represent the individual discharges as events of a random point process, then an arithmetical operation is given by the interaction of two point processes. Employing a probabilistic model based on detection of coincidence of random events and complementary computer simulations, we show that the point process statistics control the arithmetical operation being performed and, particularly, that it is possible to switch from subtraction to division solely by changing the distribution of the inter-event intervals of the processes. Consequences of the model for evaluation of binaural information in the auditory brainstem are demonstrated. The results accentuate the importance of the stochastic properties of neuronal discharge patterns for information processing in the brain; further studies related to neuronal arithmetic should therefore consider the statistics of the interacting spike trains.     

Study of plasma heating in discharges with neutral beam injection in the Globus-M spherical tokamak

Results from experimental studies on the injection of high-energy neutral hydrogen beams into the plasma of the Globus-M spherical tokamak are reviewed. In the Introduction, the importance of these studies for implementing the controlled fusion research program and constructing the ITER tokamak is proved. Some problems related to the use of neutral beam injection in small and low-aspect-ratio tokamaks is analyzed. Results are presented from numerical simulations of the experiment by using the ASTRA transport code. It is shown that the use of neutral beam injection in the Globus-M tokamak ensures efficient ion heating and increases the plasma stored energy. The greater part of the review is devoted to the survey of experiments on the injection of 22-to 30-keV hydrogen and deuterium beams with a power of 0.4–0.8 MW into the plasma of the Globus-M spherical tokamak in a wide range of plasma currents and densities. The experimental results are analyzed and compared with the results of numerical simulations. The achievement of top plasma parameters is highlighted.     

Solution NMR and computer simulation studies of active site loop motion in triosephosphate isomerase

Solution NMR spin relaxation experiments and classical MD simulations are used to study the dynamics of triosephosphate isomerase (TIM) in complex with glycerol 3-phosphate (G3P). Three regions in TIM exhibit conformational transitions on the micros-ms time scale as detected by chemical exchange broadening effects in NMR spectroscopy: residue Lys 84 on helix C, located at the dimeric interface; active site loop 6; and helix G. The results indicate that the conformational exchange process affecting the residues of loop 6 is the correlated opening and closing of the loop. Distinct processes are responsible for the chemical exchange linebroadening observed in the other regions of TIM. MD simulations confirm that motions of individual residues within the active site loop are correlated and suggest that the chemical exchange processes observed for residues in helix G arise from transitions between 3(10)- and alpha-helical structures. The results of the joint NMR and MD study provide global insight into the role of conformational dynamic processes in the function of TIM.     

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.     

Chemotactic signaling,microglia, and Alzheimer's disease senile plaques: is there a connection?

Chemotactic cells known as microglia are involved in the inflammation associated with pathology in Alzheimer’s disease (AD). We investigate conditions that lead to aggregation of microglia and formation of local accumulations of chemicals observed in AD senile plaques. We develop a model for chemotaxis in response to a combination of chemoattractant and chemorepellent signaling chemicals. Linear stability analysis and numerical simulations of the model predict that periodic patterns in cell and chemical distributions can evolve under local attraction, long-ranged repulsion, and other constraints on concentrations and diffusion coefficients of the chemotactic signals. Using biological parameters from the literature, we compare and discuss the applicability of this model to actual processes in AD. Reprint address. Maternity leave.     

Evaluations of the accuracies of DMol3 density functionals for calculations of experimental binding enthalpies of N2, CO,H2, C2H2 at catalytic metal sites

The density functionals that can be used with numerical basis sets in the density functional methodology of the programme DMol3 are evaluated by comparison with experimental data. The objective is to identify and validate the most accurate and computationally efficient density functional to be used in DMol3 simulations that use large molecular models (many hundreds of atoms) of the reaction steps involved in the chemical mechanisms of metalloenzymes and synthetic metallocatalysts. The experimental systems focus on enthalpy data for reactions analogous to those involved in the chemical mechanism of nitrogenase, including coordination of N₂, CO, H₂ and C₂H₄ and hydrogen bonding. Some geometric and vibrational frequency data are included in the 19 test systems. The conclusion is that the gradient-corrected functionals PBE, PW91 and BP provide acceptably accurate results, with the best functional being PBE, which yields reaction energies within or very close the experimental error range. These functionals are also the most computationally efficient.     

Iron and activated oxygen species in biology: The basic chemistry

This paper briefly presents a critical review concerning the chemical reactions involved when superoxide or hydrogen peroxide meet iron complexes. The data commented on are required for a correct interpretation of the chemical processes which play a paramount role in the biological activation of dioxygen and arise in normal metabolism as well as in pathological processes.     

Experimental study and numerical simulations of a plasma relativistic microwave amplifier

The dependences of the radiation parameters of a plasma relativistic microwave amplifier on the external factors have been studied both experimentally and numerically. The calculated dependences are found to agree qualitatively with the measured ones. In contrast to experimental studies, numerical simulations make it possible to examine physical processes occurring inside the plasma waveguide. Good agreement between the measured and calculated dependences of the radiation parameters on the external factors shows that information provided by numerical simulations of the processes occurring inside the plasma waveguide can be considered quite reliable. The electromagnetic field structure and electron beam dynamics inside the plasma waveguide have been investigated.     

Computational modeling of membrane trafficking processes: From large molecular assemblies to chemical specificity

In the last decade, molecular dynamics (MD) simulations have become an essential tool to investigate the molecular properties of membrane trafficking processes, often in conjunction with experimental approaches. The combination of MD simulations with recent developments in structural biology, such as cryo-electron microscopy and artificial intelligence-based structure determination, opens new, exciting possibilities for future investigations. However, the full potential of MD simulations to provide a molecular view of the complex and dynamic processes involving membrane trafficking can only be realized if certain limitations are addressed, and especially those concerning the quality of coarse-grain models, which, despite recent successes in describing large-scale systems, still suffer from far-from-ideal chemical accuracy. In this review, we will highlight recent success stories of MD simulations in the investigation of membrane trafficking processes, their implications for future research, and the challenges that lie ahead in this specific research domain.