Diffusive Radiation in One-dimensional Langmuir Turbulence

We calculate spectra of radiation produced by a relativistic particle in the presence of one-dimensional Langmuir turbulence which might be generated by a streaming instability in the plasma, in particular, in the shock front or at the shock-shock interactions. The shape of the radiation spectra is shown to depend sensitively on the angle between the particle velocity and electric field direction. The radiation spectrum in the case of exactly transverse particle motion is degenerate and similar to that of spatially uniform Langmuir oscillations. In case of oblique propagation, the spectrum is more complex, it consists of a number of power-law regions and may contain a distinct high-frequency spectral peak. %at \omega=2\omega\pe \gamma^2. The emission process considered is relevant to various laboratory plasma settings and for astrophysical objects as gamma-ray bursts and collimated jets.Comment: 4 pages, 1 figure, accepted for Phys. Rev.

Do solar decimetric spikes originate in coronal X-ray sources?

In the standard solar flare scenario, a large number of particles are accelerated in the corona. Nonthermal electrons emit both X-rays and radio waves. Thus, correlated signatures of the acceleration process are predicted at both wavelengths, coinciding either close to the footpoints of a magnetic loop or near the coronal X-ray source. We attempt to study the spatial connection between coronal X-ray emission and decimetric radio spikes to determine the site and geometry of the acceleration process. The positions of radio-spike sources and coronal X-ray sources are determined and analyzed in a well-observed limb event. Radio spikes are identified in observations from the Phoenix-2 spectrometer. Data from the Nan\c{c}ay radioheliograph are used to determine the position of the radio spikes. RHESSI images in soft and hard X-ray wavelengths are used to determine the X-ray flare geometry. Those observations are complemented by images from GOES/SXI. We find that decimetric spikes do not originate from coronal X-ray flare sources contrary to previous expectations. However, the observations suggest a causal link between the coronal X-ray source, related to the major energy release site, and simultaneous activity in the higher corona.Comment: 4 pages, 3 figures, A&AL accepte

Antioxidant activity of <i>Vaccinium axillare</i> Nakai fruits during oxidative stress <i>in vivo</i>

Intensity of free radical oxidation processes in vivo (model of induced oxidative stress) was studied after the probe introduction of Vaccinium axillare Nakai fruit extract. Material and methods. Four groups (n = 40) of white male CBA mice weighing 20–25 g were included in the experiment: 1 – intact control; 2–0.9 % sodium chloride solution was administered per os for 10 days in a dose of 10 ml/kg/day; 3 – group “cisplatin” (animals received 0.9 % sodium chloride solution similarly to group 2, on the fifth day of the experiment cisplatin was administered once by intraperitoneal injection at a dose of 7.5 mg/kg); 4 – group “cisplatin + blueberries” (mice received per os extract of Blueberry axillary fruits at a dose of 10 ml/kg/day for 10 days, on the fifth day of the experiment cisplatin was administered once by intraperitoneal injection at a dose of 7.5 mg/kg). Antioxidant activity of Blueberry axillary was studied by chemiluminescence. Results and discussion. Analysis of kinetic parameters of mouse kidney homogenate chemiluminescence showed that oxidative stress develops in animals after a single intraperitoneal injection of cisplatin, the extract of Blueberry axillary fruit decreases its severity. Conclusions. Bilberry fruit extract (Vaccinium axillare Nakai) has pronounced antioxidant properties and may be important in the treatment and prevention of diseases associated with oxidative stress

Magnetic field amplification and electron acceleration to near-energy equipartition with ions by a mildly relativistic quasi-parallel plasma protoshock

The prompt emissions of gamma-ray bursts are seeded by radiating ultrarelativistic electrons. Internal shocks propagating through a jet launched by a stellar implosion, are expected to amplify the magnetic field & accelerate electrons. We explore the effects of density asymmetry & a quasi-parallel magnetic field on the collision of plasma clouds. A 2D relativistic PIC simulation models the collision of two plasma clouds, in the presence of a quasi-parallel magnetic field. The cloud density ratio is 10. The densities of ions & electrons & the temperature of 131 keV are equal in each cloud. The mass ratio is 250. The peak Lorentz factor of the electrons is determined, along with the orientation & strength of the magnetic field at the cloud collision boundary. The magnetic field component orthogonal to the initial plasma flow direction is amplified to values that exceed those expected from shock compression by over an order of magnitude. The forming shock is quasi-perpendicular due to this amplification, caused by a current sheet which develops in response to the differing deflection of the incoming upstream electrons & ions. The electron deflection implies a charge separation of the upstream electrons & ions; the resulting electric field drags the electrons through the magnetic field, whereupon they acquire a relativistic mass comparable to the ions. We demonstrate how a magnetic field structure resembling the cross section of a flux tube grows in the current sheet of the shock transition layer. Plasma filamentation develops, as well as signatures of orthogonal magnetic field striping. Localized magnetic bubbles form. Energy equipartition between the ion, electron & magnetic energy is obtained at the shock transition layer. The electronic radiation can provide a seed photon population that can be energized by secondary processes (e.g. inverse Compton).Comment: 12 pages, 15 Figures, accepted to A&

Solar science with the Atacama Large Millimeter/submillimeter Array - A new view of our Sun

The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere - a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases.Comment: 73 pages, 21 figures ; Space Science Reviews (accepted December 10th, 2015); accepted versio

Zero-modes in the random hopping model

If the number of lattice sites is odd, a quantum particle hopping on a bipartite lattice with random hopping between the two sublattices only is guaranteed to have an eigenstate at zero energy. We show that the localization length of this eigenstate depends strongly on the boundaries of the lattice, and can take values anywhere between the mean free path and infinity. The same dependence on boundary conditions is seen in the conductance of such a lattice if it is connected to electron reservoirs via narrow leads. For any nonzero energy, the dependence on boundary conditions is removed for sufficiently large system sizes.Comment: 12 pages, 11 figure

Crossover from the chiral to the standard universality classes in the conductance of a quantum wire with random hopping only

The conductance of a quantum wire with off-diagonal disorder that preserves a sublattice symmetry (the random hopping problem with chiral symmetry) is considered. Transport at the band center is anomalous relative to the standard problem of Anderson localization both in the diffusive and localized regimes. In the diffusive regime, there is no weak-localization correction to the conductance and universal conductance fluctuations are twice as large as in the standard cases. Exponential localization occurs only for an even number of transmission channels in which case the localization length does not depend on whether time-reversal and spin rotation symmetry are present or not. For an odd number of channels the conductance decays algebraically. Upon moving away from the band center transport characteristics undergo a crossover to those of the standard universality classes of Anderson localization. This crossover is calculated in the diffusive regime.Comment: 22 pages, 9 figure

Effects of glyprolines on free-radical oxidation in the brain neocortex of white rats in mild traumatic brain injury

The aim of the study was to compare the effect of glyproline peptides RGRGP (Arg-Gly-Arg-Gly-Pro), RGP (Arg-GlyPro), PRPGP (Pro-Arg-Pro-Gly-Pro) and PGPL (Pro-Gly-Pro-Leu) peptide substances at various concentrations on the free radical oxidation intensity of the brain tissues of Wistar males after intraperitoneal administration of peptide solutions after traumatic brain injury.Material and methods. The brain tissue of Wistar males aged 2–3 months (n = 126) were used in the experiment. RGRGP, RGP, PRPGP, and PGPL peptides were provided by Academician N.F. Myasoyedov. Traumatic brain injury (TBI) was modeled by free fall of a load. From the second to the fifth day of the experiment, the animals were injected intraperitoneally with peptides. On the sixth day, the animals were taken out of the experiment. The activity of free radical oxidation was determined in freshly prepared homogenates of sections of the cerebral cortex by chemiluminescence (CL).Results. TBI significantly enhance free-radical oxidation intensity of the neocortex in brain tissue of Wistar rats, and the studied peptides affect it in different ways - from a decrease in CL intensity (the minimum value in TBI + RGP 0.1 group) to its increase (the maximum value in TBI + RGPGP 0.1 group). The effect depends on the dose of glyproline.Conclusions. The results obtained, based on the analysis of the free radical oxidation intensity of tissues, mainly indicate a different degree of correction of tissue homeostasis indicators. It can be assumed that Arg-Pro-Gly peptide can be the basis for the development of new drugs for post-stress rehabilitation after injuries of various levels and genesis