Nonlocal transport in hot plasma. Part I

The problem of describing charged particle transport in hot plasma under the conditions in which the ratio of the electron mean free path to the gradient length is not too small is one of the key problems of plasma physics. However, up to now, there was a deficit of the systematic interpretation of the current state of this problem, which, in most studies, is formulated as the problem of nonlocal transport. In this review, we fill this gap by presenting a self-consistent linear theory of nonlocal transport for small plasma perturbations and an arbitrary collisionality from the classical highly collisional hydrodynamic regime to the collisionless regime. We describe a number of nonlinear transport models and demonstrate the application of the nonclassical transport theory to the solution of some problems of plasma physics, first of all for plasmas produced by nanosecond laser pulses with intensities of 10¹³–10¹⁶ W/cm².     

Mitochondrial DNA evolution in the genus Equus

Employing mitochondrial DNA (mtDNA) restriction-endonuclease maps as the basis of comparison, we have investigated the evolutionary affinities of the seven species generally recognized as the genus Equus. Individual species' cleavage maps contained an average of 60 cleavage sites for 16 enzymes, of which 29 were invariant for all species. Based on an average divergence rate of 2%/Myr, the variation between species supports a divergence of extant lineages from a common ancestor approximately 3.9 Myr before the present. Comparisons of cleavage maps between Equus przewalskii (Mongolian wild horse) and E. caballus (domestic horse) yielded estimates of nucleotide sequence divergence ranging from 0.27% to 0.41%. This range was due to intraspecific variation, which was noted only for E. caballus. For pairwise comparisons within this family, estimates of sequence divergence ranged from 0% (E. hemionus onager vs. E. h. kulan) to 7.8% (E. przewalskii vs. E. h. onager). Trees constructed according to the parsimony principle, on the basis of 31 phylogenetically informative restriction sites, indicate that the three extant zebra species represent a monophyletic group with E. grevyi and E. burchelli antiquorum diverging most recently. The phylogenetic relationships of E. africanus and E. hemionus remain enigmatic on the basis of the mtDNA analysis, although a recent divergence is unsupported.      

Vacuum electron acceleration by a tightly focused,radially polarized,relativistically strong laser pulse

A test particle approach is used to solve the problem of direct electron acceleration by a short, intense, radially polarized laser pulse the focal spot diameter of which can be on the order of the laser wavelength. The fields of a tightly focused laser beam are described in terms of the Stratton-Chu integrals, with which to investigate electron acceleration when the paraxial approximation is inapplicable to laser fields. The dynamics of electron motion in a radially polarized, relativistically strong laser field is analyzed depending on the initial position of an electron in the focal region of the laser beam. The properties of the generated jets of accelerated electrons are investigated depending on the tightness of laser pulse focusing. Possible advantages of using radially polarized laser pulses for charged particle acceleration, as opposed to the use of linearly polarized ones, are discussed.     

Investigation of ion acceleration in an expanding laser plasma by using a hybrid Boltzmann-Vlasov-Poisson model

The acceleration of ions of different species from a plasma slab under the action of a charge-separation electric field driven by hot and cold electrons is studied by using a hybrid Boltzmann-Vlasov-Poisson model. The obtained spatial and energy distributions of light and heavy ions in different charge states demonstrate that the model can be efficiently used to study the ion composition in a multispecies expanding laser plasma. The regular features of the acceleration of ions of different species are investigated. The formation of compression and rarefaction waves in the halo of light ion impurity, as well as their effect on the energy spectrum of the accelerated ions, is analyzed. An approach is proposed that makes it possible to describe the production of fast ions by laser pulses of a given shape. It is shown that the energy of fast ions can be increased markedly by appropriately shaping the pulse. The effect of heating of the bulk of the cold target electrons on the ion acceleration is discussed.     

Relaxation of a thermal perturbation in a collisional plasma

The relationship between the nonlocal and nonstationary effects in electron heat transport processes in a weakly collisional plasma is investigated by considering the problem of the relaxation of a thermal perturbation as an example. It is shown that, for small-scale perturbations, the electron thermal conductivity depends not only on the temperature scale length but also on time. The consequence is that there exist two qualitatively different characteristic relaxation regimes of thermal perturbations on small and large scale lengths. As a result, the evolution of hot spots in laser plasmas should be described with allowance for the nonstationary nature of electron heat transport. In the course of this evolution, relaxation on the collisional kinetic time scale is clearly seen to change into relaxation on the collisional hydrodynamic time scale.     

Biomarkers of toxicity in Clarias gariepinus exposed to sublethal concentrations of polycyclic aromatic hydrocarbons

Physiological, biochemical and histological indices in Clarias gariepinus broodstock, and teratogenic indices in embryos exposed to sublethal concentrations of naphthalene, phenanthrene and pyrene were investigated in 2014 using a static-renewal bioassay protocol. Phenanthrene (1.41 mg l^?1) was the most toxic, followed by pyrene (1.53 mg l^?1) and naphthalene (7.21 mg l^?1), based on 96 h LC50 values. Hepatosomatic indices were significantly higher in naphthalene- and pyrene-treated males compared with solvent controls, whereas fecundity in females was significantly lower by factors of 2.4 (naphthalene), 2.8 (phenanthrene) and 2.4 (pyrene), compared with controls. Catalase levels were lower in female phenanthrene-treated fish compared with controls. Histological alterations observed in PAH-treated fish include oedema, inflammatory cells, epithelial lifting and hyperplasia in the gills, vacuolation, haemosiderin pigments and sinusoidal congestion in the liver, and degenerated zona radiata in the ovary. Teratogenic effects were not observed, as evidenced by the lack of histological alterations in embryos spawned from pre-exposed broodstock. Sex-specific responses and the utility of biomarkers at cellular and individual levels of organisation are therefore demonstrated for holistic evaluations of polycyclic aromatic hydrocarbons in ecotoxicological studies.     

Coulomb explosion of a heated cluster

Coulomb explosion of a charged, nonuniform, and spherically symmetric cluster with a finite ion temperature is investigated. The spatial distributions of the density and mean velocity of accelerated ions, as well as their energy spectra, are obtained and analyzed as functions of the initial temperature. It is shown that taking into account the finite ion temperature eliminates singularities emerging during a Coulomb explosion of a spatially nonuniform cold cluster due to multistream ion motion that arises after breaking the velocity profile of the cluster ions. The characteristic temperature is found above which the spatial distribution and energy spectrum of the expanding ions become regular.     

Cassava leaf harvesting as vegetables; a cause of vulnerability of cassava plant to cassava mosaic disease and eventual yield reduction: Ernte von cassavablättern als gemüse; eine ursache für die anfälligkeit der cassavapflanze für die cassava-mosaikkrankheit und für spätere ertragseinbußen

The consequence of harvesting young leaves of cassava as vegetable on the vulnerability of the crop to cassava mosaic disease (CMD) and on storage root yield was investigated using 30 cassava genotypes planted in IITA fields located in the humid forest (Port Harcourt?:?Onne), forest-savannah transition (Ibadan), southern guinea savannah (Mokwa) and northern guinea savannah (Zaria) agroecologies in Nigeria. Tender apical leaves and shoots of the cassava genotypes were removed from forty plants per cassava genotype with the same number of plants considered as control. Whitefly infestation, disease incidence (DI) and symptom severity (ISS) of the disease were assessed at monthly interval for six months and also at the ninth month after planting (MAP). Yield reduction due to this treatment was calculated as percentage harvest index (HI). Whitefly population fluctuated throughout the period of observation at all locations with higher population obtained generally for treated plants compared to control plants. Sprouting leaves of some treated genotypes were observed with severe mosaic symptoms, while corresponding control showed no mosaic symptoms. Contrarily, no remarkable difference was observed in Zaria between the mean ISS of treated and control cassava genotypes. There was a highly significant difference (P?<?0.01) in DI and ISS among cassava genotypes across all locations. Also, there was a highly significant interaction (P?<?0.01) in symptom severity between location (loc) and genotype, genotype and treatment (trt), loc and trt. Interaction between loc, genotypes and trt with regard to DI was highly significant at 2, 3 and 4 MAP, while with ISS, the interaction was highly significant all through the counting period. There was a positive relationship between DI and ISS on plants of genotypes 96/1039 and ISU. The percentage HI (27.4) of treated plants of genotype 95/0166 in Ibadan was remarkably lower than the value obtained for corresponding control (41.9) plants. Also, sharp distinction in% HI of treated (39.5) and control (43.8) ISU was observed in Onne with their respective ISS values as 3.7 and 3.2. Therefore, harvesting tender apical leaves and shoots of cassava as vegetables should be discouraged as it increases the severity of CMD infection in the regenerating shoots of cassava with attendant storage root yield reduction.     

A comparative analysis of the brain computer tomography in patients with acromegaly before and after gamma-therapy

The data given in the paper suggest that X-ray computed tomography is highly effective in evaluating the characteristics of pituitary adenomas in acromegaly and in revealing the changes caused in the pituitary adenoma by gamma-ray teletherapy. The use of brain computed tomography yielded data on the main X-ray criteria to be used in the follow-up of patients undergone radiation therapy for acromegaly.     

Dispersion properties of a plasma produced by a short X-ray pulse

A collisionless plasma produced by a short ionizing pulse from an X-ray laser is characterized by an anisotropic monoenergetic electron distribution governed by the classical photoeffect. The dispersion properties of such a photoionized plasma are studied. The spectra of high-frequency plasma waves and their damping, as well as the parameters of the aperiodic instability of a photoionized plasma, are described. The relationship between the electrostatic and magnetic perturbations generated by this instability is investigated, and an analysis is made of how the instability transforms into a purely longitudinal (two-stream-like) instability and into a purely transverse (Weibel-like) instability, depending on the absolute value and direction of the wave vector.