1,280 research outputs found
On the cosmic ray diffusion in a violent interstellar medium
A variety of the available observational data on the cosmic ray (CR) spectrum, anisotropy and composition are in good agreement with a suggestion on the diffusion propagation of CR with energy below 10(15) eV in the interstellar medium. The magnitude of the CR diffusion coefficient and its energy dependence are determined by interstellar medium (ISM) magnetic field spectra. Direct observational data on magnetic field spectra are still absent. A theoretical model to the turbulence generation in the multiphase ISM is resented. The model is based on the multiple generation of secondary shocks and concomitant large-scale rarefactions due to supernova shock interactions with interstellar clouds. The distribution function for ISM shocks are derived to include supernova statistics, diffuse cloud distribution, and various shock wave propagation regimes. This permits calculation of the ISM magnetic field fluctuation spectrum and CR diffusion coefficient for the hot phase of ISM
Tempestuous life beyond R500: X-ray view on the Coma cluster with SRG/eROSITA. II. Shock & Relic
This is the second paper in a series of studies of the Coma cluster using the
SRG/eROSITA X-ray data obtained during the calibration and performance
verification phase of the mission. Here, we focus on the region adjacent to the
radio source 1253+275 (radio relic, RR, hereafter). We show that the X-ray
surface brightness exhibits its steepest gradient at (), which is almost co-spatial to the outer edge
of the RR. As in the case of several other relics, the Mach number of the shock
derived from the X-ray surface brightness profile () appears to
be lower than needed to explain the slope of the integrated radio spectrum in
the diffusive shock acceleration (DSA) model () if the magnetic
field is uniform and the radiative losses are fast. However, the shock geometry
is plausibly much more complicated than a spherical wedge centered on the
cluster, given the non-trivial correlation between radio, X-ray, and SZ images.
While the complicated shock geometry alone might cause a negative bias in
, we speculate on a few other possibilities that may affect the
- relation, including the shock substructure that might be modified
by the presence of non-thermal filaments stretching across the shock and the
propagation of relativistic electrons along the non-thermal filaments with a
strong magnetic field. We also discuss the "history" of the radio galaxy
NGC4789, which is located ahead of the relic in the context of the Coma-NGC4839
merger scenario.Comment: Replaced with the accepted versio
Non-linear magnetotransport in microwave-illuminated two-dimensional electron systems
We study magnetoresistivity oscillations in a high-mobility two-dimensional
electron system subject to both microwave and dc electric fields. First, we
observe that the oscillation amplitude is a periodic function of the inverse
magnetic field and is strongly suppressed at microwave frequencies near
half-integers of the cyclotron frequency. Second, we obtain a complete set of
conditions for the differential resistivity extrema and saddle points. These
findings indicate the importance of scattering without microwave absorption and
a special role played by microwave-induced scattering events antiparallel to
the electric field.Comment: 4 pages, 4 figure
The 511 keV emission from positron annihilation in the Galaxy
The first gamma-ray line originating from outside the solar system that was
ever detected is the 511 keV emission from positron annihilation in the Galaxy.
Despite 30 years of intense theoretical and observational investigation, the
main sources of positrons have not been identified up to now. Observations in
the 1990's with OSSE/CGRO showed that the emission is strongly concentrated
towards the Galactic bulge. In the 2000's, the SPI instrument aboard ESA's
INTEGRAL gamma-ray observatory allowed scientists to measure that emission
across the entire Galaxy, revealing that the bulge/disk luminosity ratio is
larger than observed in any other wavelength. This mapping prompted a number of
novel explanations, including rather "exotic ones (e.g. dark matter
annihilation). However, conventional astrophysical sources, like type Ia
supernovae, microquasars or X-ray binaries, are still plausible candidates for
a large fraction of the observed total 511 keV emission of the bulge. A closer
study of the subject reveals new layers of complexity, since positrons may
propagate far away from their production sites, making it difficult to infer
the underlying source distribution from the observed map of 511 keV emission.
However, contrary to the rather well understood propagation of high energy
(>GeV) particles of Galactic cosmic rays, understanding the propagation of low
energy (~MeV) positrons in the turbulent, magnetized interstellar medium, still
remains a formidable challenge. We review the spectral and imaging properties
of the observed 511 keV emission and we critically discuss candidate positron
sources and models of positron propagation in the Galaxy.Comment: 62 pages, 35 figures. Review paper to appear in Reviews of Modern
Physic
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.
Comparative evaluation of efficiency of burn wound healing with derma-based hydrogel: a preclinical experimental study
Background. Burn wound healing is recognized as a complex process involving synergetic interactions between different cells, cytokines and growth factors. The adverse interactions can underlie chronicization of the process. Accordingly, the paper presents a relevant study into mechanisms of natural wound dressings, capable of influencing the processes of inflammation, angiogenesis, and skin resurfacing.Objective. To carry out a comparative evaluation of efficiency of burn wound healing with derma-based hydrogel according to the dynamics of proand anti-inflammatory factors.Methods. Development of a hydrogel material involved dermis samples of Landrace breed of pig, subjected to partial alkaline hydrolysis. In order to carry out a comparative evaluation of burn wound healing efficiency, the authors simulated direct thermal injury in three groups of sphinx (hairless) rats: group 1 (control group) â rats without treatment (n = 20), group 2 (comparison group) â rats treated with Levomekol ointment (n = 20), and group 3 (experimental group) â rats treated with hydrogel material (n = 20). Before and after injuring on days 1, 3, 7, 14, the content of cytokines interleukin-1ÎČ, interleukin-4, interleukin-6, interleukin-8, interleukin-10, tumor necrosis factor-α by enzyme immunoassay. The wound samples were explanted for histological examination on days 3, 7 and 14 after the beginning of the experiment. Statistical processing of the obtained results on DNA content in hydrogel, cytokine content in serum and morphometric data was performed using GraphPadPrism 6.04, Microsoft Excel 2016 (Microsoft, USA).Results. When determining the content dynamics of nonspecific markers of inflammation, an increase in the concentrations of interleukin-1ÎČ and tumor necrosis factor-α on day 1 after the hydrogel application was recorded, as well as an increase in interleukin-6 on days 3 and 7, while the concentrations of interleukin-8 did not change significantly throughout the experiment. Thus, dermal components are indicated to participate in the inhibition of acute-phase immune reactions. With regard to anti-inflammatory factors, the study revealed a decrease in the concentration of interleukin-10 on days 1 and 7, an increase in interleukin-4 on day 3 as compared to the control group, thereby indicating a pronounced anti-inflammatory effect and prolonged action of the hydrogel.Conclusion. Comparative analysis of the pro-inflammatory cytokines levels (interleukin-1ÎČ, interleukin-8) showed pronounced anti-inflammatory effects of the derma-based hydrogel material. Introduction of exogenous biological components of the extracellular matrix (collagen and its hydrolysates) had a significant influence on the regulation of anti-inflammatory cytokines synthesis, presumably contributing to faster successful epithelization and wound healing
Studies of h/e Aharonov-Bohm Photovoltaic Oscillations in Mesoscopic Au Rings
We have investigated a mesoscopic photovoltaic (PV) effect in micron-size Au
rings in which a dc voltage Vdc is generated in response to microwave
radiation. The effect is due to the lack of inversion symmetry in a disordered
system. Aharonov-Bohm PV oscillations with flux period h/e have been observed
at low microwave intensities for temperatures ranging from 1.4 to 13 K. For
moderate microwave intensities the h/e PV oscillations are completely quenched
providing evidence that the microwaves act to randomize the phase of the
electrons. Studies of the temperature dependence of Vdc also provide evidence
of the dephasing nature of the microwave field. A complete theoretical
explanation of the observed behavior seems to require a theory for the PV
effect in a ring geometry.Comment: 10 pages (RevTex twocolumn style), 8 figures-2 pages (one postscript
file) To be published in Phys. Rev.
- âŠ