Relativistic Laser-Matter Interaction and Relativistic Laboratory Astrophysics

The paper is devoted to the prospects of using the laser radiation interaction with plasmas in the laboratory relativistic astrophysics context. We discuss the dimensionless parameters characterizing the processes in the laser and astrophysical plasmas and emphasize a similarity between the laser and astrophysical plasmas in the ultrarelativistic energy limit. In particular, we address basic mechanisms of the charged particle acceleration, the collisionless shock wave and magnetic reconnection and vortex dynamics properties relevant to the problem of ultrarelativistic particle acceleration.Comment: 58 pages, 19 figure

Reduction of Cr(VI) by immobilized cells of <i>Desulfovibrio vulgaris</i> NCIMB 8303 and <i>Microbacterium</i> sp. NCIMB 13776

Hexavalent chromium, a carcinogen and mutagen, can be reduced to Cr(III) by Desulfovibrio vulgaris NCIMB 8303 and Microbacterium sp. NCIMB 13776. This study examined Cr(VI) reduction by immobilized cells of the two strains in a common solution matrix using various entrapment matrices. Chitosan and PVA-borate beads did not retain integrity and supported low or no reduction of Cr(VI) by the cells. A commercial preparation (Lentikats) was stable but also did not support Cr(VI) reduction. K-carrageenan beads were stable in batch suspensions but gel integrity was lost after only 5 h in a flow-through system in the presence of 100 μM Cr(VI). The best immobilization matrices were agar and agarose, where the initial rates of reduction of Cr(VI) (from 500 μM solution) for D. vulgaris NCIMB 8303 and Microbacterium sp. NCIMB 13776 were 127 (agar) and 130 (agarose), and 15 (agar) and 12 (agarose) nmol h−1 mg dry cell wt−1, respectively. The higher removal of Cr(VI) by D. vulgaris was also seen in 14-mL packed-bed flow-through columns, where, at a flow rate of 2.4 mL h−1, the percentage removal of Cr(VI) was ∼95% and 60% for D. vulgaris and Microbacterium sp., respectively (agar-immobilized cells). The Cr(VI) reducing activities of D. vulgaris and Microbacterium sp. were lost after 159 and 140 h, respectively. Examination of the beads for structural integrity within the columns in situ using magnetic resonance imaging after 24 and 100 h of continuous operation against Cr(VI) (with negligible Cr retained within the columns) showed that agar beads were more stable with time. The most appropriate system for development of a continuous bioprocess is thus the use of D. vulgaris NCIMB 8303 immobilized in an agar gel matrix

Continuous removal of Cr(VI) from aqueous solution catalysed by palladised biomass of <i>Desulfovibrio vulgaris</i>

Growth-decoupled cells of Desulfovibrio vulgaris NCIMB 8303 can be used to reduce Pd(II) to cell-bound Pd(0) (Bio-Pd0), a bioinorganic catalyst capable of reducing hexavalent chromium to less toxic Cr(III), using formate as the electron donor. Magnetic resonance imaging showed that Bio-Pd0, immobilized in chitosan and agar beads, is distinguishable from the surrounding gel and is evenly dispersed within the immobilization matrix. Agar-immobilized Bio-Pd0 and `chemical Pd0' were packed into continuous-flow reactors, and challenged with a solution containing 100 μm Cr(VI) (pH 7) at a flow rate of 2.4 ml h−1. Agar-immobilized chemical Pd0 columns lost Cr(VI) reducing ability by 160 h, whereas columns containing immobilized Bio-Pd0 maintained 90% reduction until 680 h, after which reduction efficiency was gradually lost

Improved dielectric and electrical conductivity anisotropy measurements using TDR in unsaturated mica

Anisotropy in the vadose zone impacts the flow and transport of water and contaminants. Progress has been made in incorporating anisotropy into flow and transport models; however, obtaining accurate estimation of the extent of anisotropy in porous media remains a technical challenge. Electrical and electromagnetic (EM) measurements can be used to investigate the anisotropy of layered media. We developed a parallel-plate time domain reflectometry (TDR) and electrical conductivity cell for accurately measuring the sample-scale dielectric (AKa) and electrical conductivity (A) anisotropy factors and used a dielectric mixture model to predict the theoretical dielectric anisotropy factor (A). Modeling of the cell EM transmission line sampling area based on electrode geometry facilitated an optimal design based on minimizing the sampling area coefficient of variation. This optimal design consists of thin (1-mm) parallel plates with a spacing/width ratio of 1. Dielectric and electrical conductivity measurements were made in mica, layered parallel to the plates in one cell and layered perpendicular to the plates in another. The resulting water-content-dependent dielectric measurements yielded sample-scale AKa factors with peak values of 2.4 occurring near 50% saturation, while electrical conductivity measurements found A values approaching 10 near 75% saturation. Furthermore, the shape of the water-content-dependent AKa followed a Gaussian distribution, while a three-phase dielectric mixture model predicted peak A near 40% saturation. Discrepancies in magnitude were attributed to model assumptions, packing irregularities, and heterogeneity in the mica packing structure, as noted by others. The occurrence of the peak AKa around 50% saturation corroborates anisotropy predictions for transport related to hydraulic processes

Lactating red squirrels experiencing high heat load occupy less insulated nests

The heat dissipation limit hypothesis suggests that the capacity for lactating mammals to transfer energy to their offspring through milk may be constrained by limits on heat dissipation, particularly in species that raise offspring in well-insulated nests. We tested a prediction of this hypothesis by evaluating whether lactating free-ranging red squirrels (Tamiasciurus hudsonicus) occupy less insulated nests when experiencing conditions that increase heat load. In support of the hypothesis, when climate normal ambient temperatures were warm, squirrels supporting large litter masses of furred offspring occupied nests of lower insulative value. These results support the heat dissipation limit hypothesis and suggest that free-ranging mammals may select nests based on their insulative value, not only to reduce heat loss in cold conditions but also to dissipate heat during periods of heat stress