Formation of a Density Bump in a Collisionless Electrostatic Shock Wave During Expansion of a Hot Dense Plasma into a Cold Rarefied One

Plasma Physics Reports - Formation and evolution of a density bump in an electrostatic shock wave during decay of a discontinuity in a plasma characterized by the presence of hot electrons and a...     

On the Plasma Quasineutrality under Oscillatory Confinement Based on a Nanosecond Vacuum Discharge

Plasma Physics Reports - One of the main problems for inertial electrostatic confinement devices with electron injection is the space charge neutralization. This work is devoted to the analysis of...     

Energy Confinement in Self-Organized Tokamak Plasma (without Transport Barriers)

Plasma Physics Reports - The phenomenon of improved energy confinement during radiative cooling at the plasma edge was studied experimentally in the T-10 tokamak. It was shown that the effect is...     

Insulin Regulates Glut4 Confinement in Plasma Membrane Clusters in Adipose Cells

Insulin-stimulated delivery of glucose transporter-4 (GLUT4) to the plasma membrane (PM) is the hallmark of glucose metabolism. In this study we examined insulin’s effects on GLUT4 organization in PM of adipose cells by direct microscopic observation of single monomers tagged with photoswitchable fluorescent protein. In the basal state, after exocytotic delivery only a fraction of GLUT4 is dispersed into the PM as monomers, while most of the GLUT4 stays at the site of fusion and forms elongated clusters (60–240 nm). GLUT4 monomers outside clusters diffuse freely and do not aggregate with other monomers. In contrast, GLUT4 molecule collision with an existing cluster can lead to immediate confinement and association with that cluster. Insulin has three effects: it shifts the fraction of dispersed GLUT4 upon delivery, it augments the dissociation of GLUT4 monomers from clusters ∼3-fold and it decreases the rate of endocytic uptake. All together these three effects of insulin shift most of the PM GLUT4 from clustered to dispersed states. GLUT4 confinement in clusters represents a novel kinetic mechanism for insulin regulation of glucose homeostasis.     

Effects of Carrier Confinement and Intervalley Scattering on Photoexcited Electron Plasma in Silicon

The ultrafast reflectivity of silicon, excited and probed with femtosecond laser pulses, is studied for different wavelengths and energy densities. The confinement of carriers in a thin surface layer delimited by a nanoscale Si-layered system buried in a Si heavily-doped wafer reduces the critical density of carriers necessary to create the electron plasma by a factor of ten. We performed two types of reflectivity measurements, using either a single beam or two beams. The plasma strongly depends on the photon energy density because of the intervalley scattering of the electrons revealed by two different mechanisms assisted by the electron–phonon interaction. One mechanism leads to a negative differential reflectivity that can be attributed to an induced absorption in X valleys. The other mechanism occurs, when the carrier population is thermalizing and gives rise to a positive differential reflectivity corresponding to Pauli-blocked intervalley gamma to X scattering. These results are important for improving the efficiency of Si light-to-electricity converters, in which there is a possibility of multiplying carriers by nanostructurization of Si.     

Relativistic Ion-Acoustic Solitary Waves in a Magnetized Pair Ion Dense Plasma with Nuclei of Heavy Elements

The propagation of ion-acoustic solitary waves (IASWs) in a magnetized collisionless degenerate plasma system for describing collective plasma oscillations in dense quantum plasmas with relativistically degenerate electrons, oppositely charged inertial ions, and positively charged immobile heavy elements is investigated theoretically. The perturbations of the magnetized quantum plasma are studied employing the reductive perturbation technique to derive the Korteweg–de Vries (KdV) and the modified KdV (mKdV) equations that admit solitary wave solutions. Chandrasekhar limits are used to investigate the degeneracy effects of interstellar compact objects through the equation of state for degenerate electrons in nonrelativistic and ultrarelativistic cases. The basic properties of small but finite-amplitude IASWs are modified significantly by the combined effects of the degenerate electron number density, pair ion number density, static heavy element number density, and magnetic field. It is found that the obliqueness affects both the amplitude and width of the solitary waves, whereas the other parameters mainly influence the width of the solitons. The results presented in this paper can be useful for future investigations of astrophysical multi-ion plasmas.     

Formation of Starting Plasma Flow in an Open Trap Using Arc Plasma Gun

Plasma Physics Reports - The system is described for the formation of the low-temperature starting plasma flow in the GOL-NB trap. The starting plasma is a target for capturing heating neutral...     

Generation of Terahertz Waves under Laser Action on Hot Dense Plasma

Generation of terahertz waves by hot dense plasma under the action of a femtosecond laser pulse in the regime of anomalous skin effect is considered. The spectral, angular, and energy characteristics of terahertz waves are studied as functions of the plasma and laser parameters. It is shown that, under the conditions of anomalous skin effect, which takes place in ultradense hot plasma, the total energy of the terahertz signal is independent of the electron density, proportional to the square of the electron temperature, and maximal at tight focusing of the laser pulse.     

A Reevaluation of Density-Dependent PopulationCycles in Open Systems

Studies motivated by consideration of barnacle populations have led to the prediction of two different dynamic states for space-limited open populations subject to density-dependent mortality. Population densities may cycle or fluctuate stochastically around a mean value. Despite the potential generality of the associated theory, there are few examples of population cycling in open systems that have been shown to be driven by density-dependent effects. This may be because settlement and growth processes are generally too slow or too variable to generate consistent cycles. An alternative explanation is examined in this article using spatially explicit simulations. Even under conditions of consistent settlement and growth, the cycles predicted in at least one previous study are shown to represent a special case. Clear population cycles are only observed when the density-dependent disturbances are constrained to reoccur in exactly the same location. In the more general case, where density-dependent disturbances respond to local variations in population density, the cycling predicted from simple models is difficult to detect. Hence, a failure to detect cycling in population density does not refute a role for density dependence. Density-dependent disturbances can create a characteristic spatial structure consisting of a mosaic of cohorts.     

Symbiogenesis as Evolution of Open Genetic Systems

The evolution of intracellular symbioses formed by bacteria with plants and animals is addressed as a model for reconstructing the origin of eukaryotic cells as a symbiosis between different forms of prokaryotes (symbiogenesis). In microorganisms that are in facultative or conditionally obligatory (ecologically obligatory) dependence on symbiosis, their gene networks arise on the basis of host-activated intragenomic rearrangements and horizontal gene transfer. The latter factor determines the evolution of the genomes of symbiotic bacteria as open genetic systems (OGSs), in which the ratio of accessory genome regions to its core regions is increased compared to free-living relatives. Coevolution of bacteria and eukaryotic hosts results in the formation of higher rank OGSs, symbiogenomes, the integrity of which is mediated by signaling interactions that determine cross-regulation of partner genes. Increasing the effectiveness of their cooperation is achieved with the transition of bacteria to strictly obligatory (genetically obligatory) dependence on hosts, determined by (a) the loss of considerable regions of the microbial genome encoding the functions of autonomous development and (b) adaptation of bacteria to permanent intracellular existence, endocytobiosis. At this stage, symbiogenomes acquire the status of inheritance systems, determined by vertical (as a rule, transovarial) transfer of microsymbionts through host generations. The transformation of endocytobionts into cellular organelles is associated with the loss of their genetic autonomy, i.e., the ability to maintain and express their rudimentary genomes, until their complete loss. However, organelles partially retain phenotypic identity of ancestral bacteria, which is determined by the importation from the host cell of the gene products (proteins, RNA) obtained earlier from microsymbionts, which led to the formation of structurally integrated hologenomes. The gene loss and gain strategy realized in this way led to the formation of different patterns of eukaryotic cell organization in accordance with the mosaic scenario, which includes sequential introduction of several symbionts into the host cell, or with the matryoshka doll scenario, in which new symbionts are introduced into the cells of previously acquired symbionts.     

Open Access, Open Systems: Pastoral Management of Common-Pool Resources in the Chad Basin

The discussion about the impact of pastoralists on ecosystems has been profoundly shaped by Hardin’s tragedy of the commons that held pastoralists responsible for overgrazing the range. Research has shown that grazing ecosystems are much more complex and dynamic than was previously assumed and that they can be managed adaptively as commons. However, proponents and critics of Hardin’s thesis continue to argue that open access to common-pool resources inevitably leads to a tragedy of the commons. A longitudinal study that we conducted of pastoral mobility and primary production in the Logone floodplain in the Far North Region of Cameroon suggest that open access does not have to lead to a tragedy of the commons. We argue that this pastoral system is best conceptualized as an open system, in which a combination of individual decision-making and coordination of movements leads to an ideal-free type of distribution of mobile pastoralists. We explain how this self-organizing system of open access works and its implications for theories of management of common-pool resources and our understanding of pastoral systems.     

Chiral Polymerization in Open Systems From Chiral-Selective Reaction Rates

We investigate the possibility that prebiotic homochirality can be achieved exclusively through chiral-selective reaction rate parameters without any other explicit mechanism for chiral bias. Specifically, we examine an open network of polymerization reactions, where the reaction rates can have chiral-selective values. The reactions are neither autocatalytic nor do they contain explicit enantiomeric cross-inhibition terms. We are thus investigating how rare a set of chiral-selective reaction rates needs to be in order to generate a reasonable amount of chiral bias. We quantify our results adopting a statistical approach: varying both the mean value and the rms dispersion of the relevant reaction rates, we show that moderate to high levels of chiral excess can be achieved with fairly small chiral bias, below 10%. Considering the various unknowns related to prebiotic chemical networks in early Earth and the dependence of reaction rates to environmental properties such as temperature and pressure variations, we argue that homochirality could have been achieved from moderate amounts of chiral selectivity in the reaction rates.     

Alteration of Plasma Trace Elements in Patients Undergoing Open Heart Surgery

Trace elements may contribute to myocardial dysfunction and susceptibility of the phospholipid cell membrane to free-radical damage and oxidative changes. We studied the concentration of trace elements copper, zinc, and magnesium in cardiac surgery. Fifty-four consecutive patients for elective coronary artery bypass grafting (n?=?30) and valve replacement (n?=?24) were studied. Blood samples were collected every 30 min (T1–T5) during cardiopulmonary bypass and postoperatively (T6–T9). Plasma concentrations of copper, zinc, and magnesium were measured with flame atomic absorption spectrophotometry. The concentrations of copper, zinc, and magnesium were significantly different during and after cardiopulmonary bypass (p?<?0.01). The zinc concentration at T7 and T8 (p?<?0.01) and the copper concentration at T1, T9 (p?<?0.05) were significantly different between two groups. However, the magnesium concentration had no significant differences between the two groups (p?>?0.05). In patients undergoing valve replacement or coronary artery bypass grafting, the concentrations of copper and zinc decreased significantly during cardiopulmonary bypass. Our study suggests that the current cardiopulmonary bypass protocol is adequate in the maintenance of c magnesium. However, the low copper and zinc concentrations found in the present study may suggest that in the future, supplementation particularly of copper and zinc may become a necessary procedure in cardiac surgery with cardiopulmonary bypass.     

Dual Role of Plasma Membrane Electron Transport Systems in Defense

Bcause oxidative stress is one of the main sources of severe cellular damage, cells have different defense weapons against reactive oxygen species. Ubiquitous plasma membrane redox systems play a role in defense against oxidative stress damage. On the other hand, a tightly controlled and localized production of reactive oxygen species by a plasma membrane NADPH oxidase can be used as a potent microbicidal weapon. This dual, prooxidant and antioxidant role of plasma membrane electron transport systems in defense is studied and discussed.     

Microwaves in the Induction of Immune Response to VI-Antigen

In this work the possibility of using microwaves (MW) for immuno-modulation in the immunization of animals with thymus-independent antigen was studied. The projection zones of the thyroid and adrenal glands of the test animals were subjected to the action of decimeter MW, while the corresponding zones of control animals were subjected to imitation MW. The endocrine activity of rabbits was estimated by radioim-mune methods. Vi-antigen was shown to be a thymus-independent antigen for rabbits, according to the results of fluorescent probes to study the structural rearrangements in surfaces of thymocyte membranes and their nuclei, which reflect early changes during the physiological activation of cells. The irradiation by MW on the projection zone of the thyroid was accompanied by a decrease in the glucocorticoid activity of the adrenal cortex and a simultaneous pronounced immunostimulating effect. MW irradiation of the zone of the adrenal glands was accompanied by immunosuppression in combination with enhanced glucocorticoid activity of the adrenal cortex.     

Dense growth of aerobic bacteria in a bench-scale fermentor

Escherichia coli B, Escherichia coli MRE 600, Escherichia coli K 12-3300, Pseudomonas fluorescens, and Aerobacter aerogenes were grown exponentially in a bench-scale fermentor to cell concentrations in the range of 20 to 41 g dry cells/liter at 30°C and 30 to 55 g dry cells/liter at 25°C. The high cell concentrations were achieved in a growth system previously described for growth of Escherichia coli W (Biotechnol. Bioeng., 16 , 933 (1974); ibid. 17 , 227 (1975)). Various enzyme activity levels in the high-concentration cells were compared to those in cells grown in conventional low-density cultures. No significant differences were found. The culture supernatants were found to be essentially free of high-molecular weight metabolic or cell lysis products. Yield constants for glucose, nitrogen, oxygen, and phosphorus were also determined in the dense cultures and some of their relations to the growth conditions are discussed.     

Study of Clustering in Nonideal Ion Plasma by a Combined Open Ensemble Monte Carlo - Cluster Expansion Method

The chemical potential and Gibbs free energy of ion clusters are obtained by Monte Carlo method combined with a cluster expansion in a wide range of pressures. Gibbs free energy and configurational energy of the symmetric ion plasma is calculated by Frenkel-Band cluster expansion. The energy is compared with Monte Carlo data for a periodic system.     

Simulation of the Plasma Afterglow in the Discharge Gap of a Subnanosecond Switch Based on an Open Discharge in Helium

The phenomenon of subnanosecond electrical breakdown in a strong electric field observed in an open discharge in helium at pressures of 6–20 Torr can be used to create ultrafast plasma switches triggering into a conducting state for a time shorter than 1 ns. To evaluate the possible repetition rate of such a subnanosecond switch, it is interesting to study the decay dynamics of the plasma remaining in the discharge gap after ultrafast breakdown. In this paper, a kinetic model based on the particle-in-cell Monte Carlo collision method is used to study the dynamics of the plasma afterglow in the discharge gap of a subnanosecond switch operating with helium at a pressure of 6 Torr. The simulation results show that the radiative, collisional-radiative, and three-body collision recombination mechanisms significantly contribute to the afterglow decay only while the plasma density remains higher than 10¹² cm^?3; the main mechanism of the further plasma decay is diffusion of plasma particles onto the wall. Therefore, the effect of recombination in the plasma bulk is observed only during the first 10–20 μs of the afterglow. Over nearly the same time, plasma electrons become thermalized. The afterglow time can be substantially reduced by applying a positive voltage U_c to the cathode. Since diffusive losses are limited by the ion mobility, the additional ion drift toward the wall significantly accelerates plasma decay. As U_c increases from 0 to +500 V, the characteristic time of plasma decay is reduced from 35 to 10 μs.