Stabilization of ballooning modes by nonparaxial cells

An analysis is made of the effect of high-curvature stabilizing nonparaxial elements (cells) on the MHD plasma stability in open confinement systems and in confinement systems with closed magnetic field lines. It is shown that the population of particles trapped in such cells has a stabilizing effect not only on convective (flute) modes but also on ballooning modes, which govern the maximum possible β value. In the kinetic approach, which distinguishes between the effects of trapped and passing particles, the maximum possible β values consistent with stability can be much higher than those predicted by the MHD model.     

Study of X-ray and neutron emission in experiments with Al wires in an MA plasma focus

Results are presented from experimental studies of the correlation between X-ray and neutron emissions generated in the implosion of a deuteron plasma shell onto an Al wire. The experiments were carried out on the PF-1000 facility at currents of 1.5–1.8 MA. An Al wire 80 μm in diameter and 7–9 cm in length was placed at the end of the inner electrode. During the implosion of the plasma shell, Al K-shell X-rays were first emitted at the dip of the current derivative. After the X-ray pulse, a relatively stable corona with a diameter of 2–3 mm and lifetime of a few hundred nanoseconds formed around the wire. The presence of the wire did not considerably reduce the total neutron yield (at most 10¹¹ neutrons per shot) in comparison to discharges without a wire. As a rule, the intensity of neutron emission was maximal a few tens of nanoseconds after the peak of X-ray emission. A detailed comparison of two shots with low and high neutron yields have shown that the neutron yield depends on the configuration and dynamics of the discharge. The possible influence of the self-generated axial component of the magnetic field on the development of the plasma focus and the acceleration of fast deuterons is discussed.     

Helical structures in complex plasma II: Collective interaction

The conditions for the formation and stability of quasi-crystal helical structures formed of charged dust grains of equal size in a complex plasma are investigated. A study is made of both the transverse confinement of such structures by means of an external parabolic potential well and the possibility of their self-confinement or confinement by the field of the smaller background grains. It is shown that, in the presence of dissipation, any initial random distribution of dust grains in a cylindrical external potential evolves into an equilibrium helical structure with a constant pitch angle. It is found that, when the external control parameter is smoothly varied, the pitch angle of the helix changes abruptly and the structure of the quasi-crystal undergoes bifurcations, during which the number of interwoven helices changes. The smaller the confinement parameter and the weaker the attractive forces between the grains, the larger the number of bifurcations. In addition, it is found that, because of the attraction (both noncollective and collective) between the dust grains, stable helical structures may exist not only at zero value of the external confinement parameter, but also at a negative one, and that the collective interaction between the grains not only increases the number of bifurcations but also changes their character.     

Modeling of the composition of materials for soft X-ray sources used in research on inertial confinement fusion

A method for calculating and optimizing the composition of materials for soft X-ray sources used in research on inertial confinement fusion is described. For a target-converter, a material composition is determined with which the conversion of laser light into X radiation is highly efficient. A comparative analysis is carried out of the efficiencies of generation of soft X-ray emission in the plasmas of some composite materials of thin conductors (wires) used as loads in X-and Z-pinches. Numerical calculations of the optical plasma properties are reported whose results make it possible to judge the emissivity of plasmas of different materials. The results obtained are compared to the data from other studies.     

Long-lived plasmoids generated by surface microwave discharges in chemically active gases

The generation of long-lived microplasmoids is observed during the irradiation of a metal-dielectric surface with a high-power microwave beam in a chemically active gas mixture (H₂ + O₂; CH₄ + O₂). The lifetime of these plasmoids substantially exceeds the characteristic recombination and cooling times of plasmoids arising at the target surface in a chemically inactive medium.     

Self-consistent quasineutral dust structures

Distributions of the dusty plasma parameters (electron, ion, and dust densities; dust grain charge; and ion drift velocity) in quasineutral dust structures whose dimensions are much greater than the mean free path of the ions in their interactions with neutral particles are calculated numerically under conditions such that ionization sources are located outside the structures. Planar, cylindrical, and spherical structures are investigated. It is shown that static equilibrium structures are governed by a single (basic) parameter: the electrostatic potential drop between the center of the structure and its boundary. It is found that the maximum value of the basic parameter (in energy units) does not exceed the electron temperature. The basic parameter also determines the total number of dust grains in the structure and the power of external ionization sources that are necessary to sustain this structure. The fact that the basic parameter varies within a limited range allows one to consider all the possible structures with a given dimensionality (planar, cylindrical, and spherical).     

The Role of Plastids and Assimilate Transport System in the Control of Plant Development

Phylogenetic and ontogenetic relationships between the plastids, cell endoplasmic reticulum, and plant transport communication have been reviewed. The initiating role of plastids (endosymbionts) in the origin of endoplasmic reticulum (buffer zone of endosymbiogenesis) has been shown, as well as a similar role of endoplasmic reticulum in the development of transport communication of xylem and phloem. Plastids, sugars and transport system for their distribution can be interpreted as leading sections in the mechanism of developmental control: gene expression of nuclear genome and genome of organelles, cell and tissue differentiation, and plant morphogenesis. The conflict between the bulk of plant genome and low percentage of its realization is explained as a result of limitation of the nuclear genome realization by plastid genome. The concept of development as applied to plant ontogenesis has been critically analyzed. The possibilities of the concept correction by with the help of symbiogenetic hypothesis are discussed.__________Translated from Ontogenez, Vol. 36, No. 3, 2005, pp. 165–181.Original Russian Text Copyright © 2005 by Gamalei.     

Growth,photosynthesis, and metabolism of sugar beet at an early stage of exposure to elevated CO<Subscript>2</Subscript>

The effects of CO₂ concentration (C _a) on growth, photosynthesis, and the activity of enzymes associated with the translocation and assimilation of CO₂ were studied in sugar beet (Beta vulgaris L. subsp. saccharifera, cv. Ramonskaya) plants. The plants were grown in controlled-climate chamber to the stage of 3–4 leaves and then used in experiments. Experimental plants were exposed in boxes to doubled C _a (700 µl/l, 2C plants), whereas control plants were kept in a chamber with ambient atmosphere (350 µl/l, 1C plants). As compared with 1C plants, in 3 and 8 days, the leaf area of 2C plants increased by 14 and 26%, respectively. The rate of their photosynthesis (P _n) measured in 3, 6, and 8 days increased by 85, 47, and 52%, respectively, whereas in normal air, the values of P _n in 2C plants were by 12, 19, and 15% lower than in 1C plants. After 8-day growth, the content of soluble carbohydrates in the leaves of 2C plants attained 7.2%, being by 80% greater than in 1C plants; the content of starch did not exceed 3%. The total content of chlorophylls a and b in the leaves of 2C plants was by 14% greater than in 1C plants, but their ratio was essentially the same. The level of protein in 2C plants was by 13.4% lower than in 1C plants. The activity and content of Rubisco in 1C and 2C plants were similar. As compared with 1C plants, in 2C plants the activity of soluble carbonic anhydrase (sCA) was lower by 34% in 3 days and by 18% in 8 days; the activity of carbonic anhydrase of membrane preparations (mCA), was lower by 24 and 77%, respectively. Catalase activity in 2C plants became by 8% lower than in 1C plants only after 8 days. A reduction in the photosynthetic ability of 2C plants in ambient atmosphere, a decrease in activity of sCA and, especially, of mCA observed together with invariable activity and content of Rubisco in the leaf extracts are interpreted as early symptoms of acclimation of young plants of sugar beet to elevated CO₂.Translated from Fiziologiya Rastenii, Vol. 52, No. 2, 2005, pp. 184–190.Original Russian Text Copyright © 2005 by Ignatova, Novichkova, Mudrik, Lyubimov, Ivanov, Romanova.This revised version was published online in April 2005 with a corrected cover date.     

Origin of Multiphase Reduction of P700<Superscript>+</Superscript> in Broad Bean Leaves after Irradiation with Far-Red Light

The kinetic curves of dark reduction of P700⁺ (oxidized primary donor of PSI) after far-red light irradiation were studied on broad bean (Vicia faba L.) leaves treated with antimycin A, methyl viologen, or diuron. Four components of P700⁺ reduction were found in untreated leaves, namely, an ultrafast component with a half-time of 25 ms, and fast (210 ms), middle (790 ms), and slow (6100 ms) components. The fast component disappeared in leaves treated with antimycin A or methyl viologen. At the same time, these substances did not affect other components of P700⁺ reduction. Treatment of leaves with diuron abolished both the ultrafast and fast components of P700⁺ reduction. As the length of far-red light exposure was increased, a lag phase appeared in the development of middle component in leaves treated with diuron, antimycin A, or methyl viologen. In thus treated leaves, an exponential pattern of the middle component was displayed with a certain delay after darkening. A conclusion was drawn that the minor ultrafast component of P700⁺ dark reduction in broad bean leaves was caused by electron donation to PSI from PSII, whereas the fast component of this process was determined by the operation of ferredoxin-dependent electron transport around PSI. The middle and slow components were supposed to be related to electron input to PSI from reductants localized in the chloroplast stroma.From Fiziologiya Rastenii, Vol. 52, No. 4, 2005, pp. 492–498.Original English Text Copyright © 2005 by Egorova, Nikolaeva, Bukhov.The article was translated by the authors.     

The Uncertainty of “Fitness”: What Prevents Understanding of the Role of Genetic Exchange

The evolutionary development of highly organized species is attained through an increase in average survival of individuals, whereas the evolution of primitive species involves only an increase in fecundity (Zavadsky, 1968). However, in population genetics, survival (or ecological resistance) and fecundity are regarded as components of a single character, fitness. Employment of the notion of fitness, which lacks a strict definition, hinders understanding of the mechanism of progressive evolution as the process that enhances ecological resistance of organisms. The notion of fitness also hinders understanding the role of genetic exchange, since the primary advantage of genetic recombination and sexual reproduction apparently is producing of progeny with high ecological resistance rather than with high genetic diversity as such. Thus, the regular genetic exchange ensures restoration of the level of ecological resistance characteristic for the species, and on the macroevolutionary scale leads to the formation of new genomes and new species with high ecological resistance.