191 research outputs found
Optimized gyrosynchrotron algorithms and fast codes
Gyrosynchrotron (GS) emission of charged particles spiraling in magnetic
fields plays an exceptionally important role in astrophysics. In particular,
this mechanism makes a dominant contribution to the continuum solar and stellar
radio emissions. However, the available exact equations describing the emission
process are extremely slow computationally, thus limiting the diagnostic
capabilities of radio observations. In this work, we present approximate GS
codes capable of fast calculating the emission from anisotropic electron
distributions. The computation time is reduced by several orders of magnitude
compared with the exact formulae, while the computation error remains within a
few percent. The codes are implemented as the executable modules callable from
IDL; they are made available for users via web sites.Comment: Proceedings of the IAU Symposium 274 "Advances in Plasma
Astrophysics
3D Radio and X-Ray Modeling and Data Analysis Software: Revealing Flare Complexity
We have undertaken a major enhancement of our IDL-based simulation tools
developed earlier for modeling microwave and X-ray emission. The object-based
architecture provides an interactive graphical user interface that allows the
user to import photospheric magnetic field maps and perform magnetic field
extrapolations to almost instantly generate 3D magnetic field models, to
investigate the magnetic topology of these models by interactively creating
magnetic field lines and associated magnetic flux tubes, to populate the flux
tubes with user-defined nonuniform thermal plasma and anisotropic, nonuniform,
nonthermal electron distributions; to investigate the spatial and spectral
properties of radio and X-ray emission calculated from the model, and to
compare the model-derived images and spectra with observational data. The
application integrates shared-object libraries containing fast gyrosynchrotron
emission codes developed in FORTRAN and C++, soft and hard X-ray codes
developed in IDL, a FORTRAN-based potential-field extrapolation routine and an
IDL-based linear force free field extrapolation routine. The interactive
interface allows users to add any user-defined radiation code that adheres to
our interface standards, as well as user-defined magnetic field extrapolation
routines. Here we use this tool to analyze a simple single-loop flare and use
the model to constrain the 3D structure of the magnetic flaring loop and 3D
spatial distribution of the fast electrons inside this loop. We iteratively
compute multi-frequency microwave and multi-energy X-ray images from realistic
magnetic fluxtubes obtained from an extrapolation of a magnetogram taken prior
to the flare, and compare them with imaging data obtained by SDO, NoRH, and
RHESSI instruments. We use this event to illustrate use of the tool for general
interpretation of solar flares to address disparate problems in solar physics.Comment: 12 pages, 11 figures, ApJ accepte
Influence of dispersed heat-resistant additives on ignition and combustion of heterogeneous systems
The results of experimental studies of the effect of dispersion of heat-resistant additives powders on ignition and combustion of heterogeneous condensed systems. The method of measuring the time delay ignition conductive and radiant heating, and combustion rate at atmospheric pressure. The effect of additives powders of boron, silicon and titanium dioxide on the ignition and combustion of heterogeneous condensed systems
Radio echo in the turbulent corona and simulations of solar drift-pair radio bursts
Drift-pair bursts are an unusual type of solar low-frequency radio emission, which appear in the dynamic spectra as two parallel drifting bright stripes separated in time. Recent imaging spectroscopy observations allowed for the quantitative characterization of the drifting pairs in terms of source size, position, and evolution. Here, the drift-pair parameters are qualitatively analyzed and compared with the newly developed Monte Carlo ray-tracing technique simulating radio-wave propagation in the inhomogeneous anisotropic turbulent solar corona. The results suggest that drift-pair bursts can be formed due to a combination of refraction and scattering processes, with the trailing component being the result of turbulent reflection (turbulent radio echo). The formation of drift-pair bursts requires an anisotropic scattering with the level of plasma density fluctuations comparable to that in type III bursts, but with a stronger anisotropy at the inner turbulence scale. The anisotropic radio-wave scattering model can quantitatively reproduce the key properties of drift-pair bursts: the apparent source size and its increase with time at a given frequency, the parallel motion of the source centroid positions, and the delay between the burst components. The trailing component is found to be virtually cospatial and following the main component. The simulations suggest that drift-pair bursts are likely to be observed closer to the disk center and below 100 MHz due to the effects of free–free absorption and scattering. The exciter of drift pairs is consistent with propagating packets of whistlers, allowing for a fascinating way to diagnose the plasma turbulence and the radio emission mechanism
X-Ray and Ultraviolet Flares on AT Microscopii Observed by AstroSat
We present observations of the active M-dwarf binary AT Mic (dM4.5e+dM4.5e)
obtained with the orbital observatory AstroSat. During 20 ks of observations,
in the far ultraviolet ( nm) and soft X-ray ( keV) spectral
ranges, we detected both quiescent emission and at least five flares on
different components of the binary. The X-ray flares were typically longer than
and delayed (by min) with respect to their ultraviolet counterparts, in
agreement with the Neupert effect. Using X-ray spectral fits, we have estimated
the parameters of the emitting plasma. The results indicate the presence of a
hot multi-thermal corona with the average temperatures in the range of MK and the emission measure of
; both the temperature and the emission measure increased
during the flares. The estimated abundance of heavy elements in the corona of
AT Mic is considerably lower than at the Sun ( of the solar
photospheric value); the coronal abundance increased during the flares due to
chromospheric evaporation. The detected flares had the energies of erg; the energy-duration relations indicate the presence of
magnetic fields stronger than in typical solar flares.Comment: Accepted for publication in Research in Astronomy and Astrophysic
Microscopic examination of hot spots giving rise to nonlinearity in superconducting resonators
We investigate the microscopic origins of nonlinear rf response in
superconducting electromagnetic resonators. Strong nonlinearity appearing in
the transmission spectra at high input powers manifests itself through the
emergence of jumplike features near the resonant frequency that evolve toward
lower quality factor with higher insertion loss as the rf input power is
increased. We directly relate these characteristics to the dynamics of
localized normal regions (hot spots) caused by microscopic features in the
superconducting material making up the resonator. A clear observation of
hot-spot formation inside a Nb thin film self-resonant structure is presented
by employing the microwave laser scanning microscope, and a direct link between
microscopic and macroscopic manifestations of nonlinearity is established.Comment: 5 pages, 4 figure
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