1,356 research outputs found
Radiative diagnostics for sub-Larmor scale magnetic turbulence
Radiative diagnostics of high-energy density plasmas is addressed in this
paper. We propose that the radiation produced by energetic particles in
small-scale magnetic field turbulence, which can occur in laser-plasma
experiments, collisionless shocks, and during magnetic reconnection, can be
used to deduce some properties of the turbulent magnetic field. Particles
propagating through such turbulence encounter locally strong magnetic fields,
but over lengths much shorter than a particle gyroradius. Consequently, the
particle is accelerated but not deviated substantially from a straight line
path. We develop the general jitter radiation solutions for this case and show
that the resulting radiation is directly dependent upon the spectral
distribution of the magnetic field through which the particle propagates. We
demonstrate the power of this approach in considering the radiation produced by
particles moving through a region in which a (Weibel-like) filamentation
instability grows magnetic fields randomly oriented in a plane transverse to
counterstreaming particle populations. We calculate the spectrum as would be
seen from the original particle population and as could be seen by using a
quasi-monoenergetic electron beam to probe the turbulent region at various
angles to the filamentation axis.Comment: 17 pages, 4 figures, submitted to Phys. Plasma
Fluid Models for Kinetic Effects on Coherent Nonlinear Alfven Waves. II. Numerical Solutions
The influence of various kinetic effects (e.g. Landau damping, diffusive and
collisional dissipation, and finite Larmor radius terms) on the nonlinear
evolution of finite amplitude Alfvenic wave trains in a finite-beta environment
is systematically investigated using a novel, kinetic nonlinear Schrodinger
(KNLS) equation. The dynamics of Alfven waves is sensitive to the sense of
polarization as well as the angle of propagation with respect to the ambient
magnetic field. Numerical solution for the case with Landau damping reveals the
formation of dissipative structures, which are quasi-stationary, S-polarized
directional (and rotational) discontinuities which self-organize from parallel
propagating, linearly polarized waves. Parallel propagating circularly
polarized packets evolve to a few circularly polarized Alfven harmonics on
large scales. Stationary arc-polarized rotational discontinuities form from
obliquely propagating waves. Collisional dissipation, even if weak, introduces
enhanced wave damping when beta is very close to unity. Cyclotron motion
effects on resonant particle interactions introduce cyclotron resonance into
the nonlinear Alfven wave dynamics.Comment: 38 pages (including 23 figures and 1 table
Wave turbulence in the two-layer ocean model
This paper looks at the two-layer ocean model from a wave turbulence
perspective. A symmetric form of the two-layer kinetic equation for Rossby
waves is derived using canonical variables, allowing the turbulent cascade of
energy between the barotropic and baroclinic modes to be studied. It turns out
that energy is transferred via local triad interactions from the large-scale
baroclinic modes to the baroclinic and barotropic modes at the Rossby
deformation scale. From there it is then transferred to the large-scale
barotropic modes via a nonlocal inverse transfer. Using scale separation a sys-
tem of coupled equations were obtained for the small-scale baroclinic component
and the large-scale barotropic component. Since the total energy of the
small-scale component is not conserved, but the total barotropic plus
baroclinic energy is conserved, the baroclinic energy loss at small scales will
be compensated by the growth of the barotropic energy at large scales. It is
found that this transfer is mostly anisotropic and mostly to the zonal
component
Terrestrial Consequences of Spectral and Temporal Variability in Ionizing Photon Events
Gamma-Ray Bursts (GRBs) directed at Earth from within a few kpc may have
damaged the biosphere, primarily though changes in atmospheric chemistry which
admit greatly increased Solar UV. However, GRBs are highly variable in spectrum
and duration. Recent observations indicate that short (~0.1 s) burst GRBs,
which have harder spectra, may be sufficiently abundant at low redshift that
they may offer an additional significant effect. A much longer timescale is
associated with shock breakout luminosity observed in the soft X-ray (~10^3 s)
and UV (~10^5 s) emission, and radioactive decay gamma-ray line radiation
emitted during the light curve phase of supernovae (~10^7 s). Here we
generalize our atmospheric computations to include a broad range of peak photon
energies and investigate the effect of burst duration while holding total
fluence and other parameters constant. The results can be used to estimate the
probable impact of various kinds of ionizing events (such as short GRBs, X-ray
flashes, supernovae) upon the terrestrial atmosphere. We find that the ultimate
intensity of atmospheric effects varies only slightly with burst duration from
10^-1 s to 10^8 s. Therefore, the effect of many astrophysical events causing
atmospheric ionization can be approximated without including time development.
Detailed modeling requires specification of the season and latitude of the
event. Harder photon spectra produce greater atmospheric effects for spectra
with peaks up to about 20 MeV, because of greater penetration into the
stratosphere.Comment: 30 pages, to be published in ApJ. Replaced for conformity with
published version, including correction of minor typos and updated reference
Тестирование скрытых дефектов в соединениях
Electronic instrumentation has a constant growth density layout and functionality. This entails an increase in the density of interconnection elements by increasing their number and reducing the size of it. The growing cost of interconnection structures (printed circuit boards, printing and wired mounting) associated with their complexity and increase of their reliability requirements, result in the search of new and improved non-destructive diagnostic methods and means of control. However, the existing methods do not allow control interconnects with sufficient certainty to identify a significant number of hidden defects. This class of defects can be diagnosed by means of non-destructive testing of interconnections, based on the detection of controlled circuit reaction to a current. The paper describes the principles for calculating the current to exercise that control.Электронное приборостроение находится в состоянии постоянного роста плотности компоновки и функциональности. Это влечет за собой рост плотности элементов межсоединений за счет увеличения их количества и уменьшения размеров. Возрастание стоимости конструкций межсоединений (печатных плат, печатного и проводного монтажа), связанное с их усложнением и возрастанием требований к надежности, обуславливает поиск новых и совершенствование существующих неразрушающих диагностических методов и средств контроля. Однако, существующие методы контроля межсоединений не позволяют с достаточной достоверностью выявить значительную часть скрытых дефектов. Такие дефекты могут быть диагностированы при помощи неразрушающего контроля соединений, основанного на регистрации реакции контролируемых цепей на воздействие импульса тока. В статье описываются принципы расчета параметров импульса тока и способ реализации такого контроля
Pair Plasma Cascade in Rotating Black Hole Magnetospheres with Split Monopole Flux Model
An electron-positron cascade in the magnetospheres of Kerr Black Holes (BH)
is a fundamental ingredient to fueling the relativistic -ray jets seen
at the polar regions of galactic supermassive BHs (SMBH). This leptonic cascade
occurs in the "spark gap" region of a BH magnetosphere where the unscreen
electric field parallel to the magnetic field is present, hence it is affected
by the magnetic field structure. A previous study explored the case of a thin
accretion disk, representative of Active Galactic Nuclei (AGN). Here we explore
the case of a quasi-spherical gas distribution, as is expected to be present
around the SMBH Sgr A* in the center of our Milky Way galaxy, for example. The
properties and efficiency of the leptonic cascade are studied. The findings of
our study and the implications for SMBH systems in various spectral and
accretion states are discussed. The relationships and scalings derived from
varying the mass of the BH and background photon spectra are further used to
analyze the leptonic cascade process to power jets seen in astronomical
observations. In particular, one finds the efficiency of the cascade in a
quasi-spherical gas distribution peaks at the jet axis. Observationally, this
should lead to a more prominent jet core, in contrast to the thin disk
accretion case, where it peaks around the jet-disk interface. One also finds
the spectrum of the background photons to play a key role. The cascade
efficiency is maximum for a spectral index of two, while harder and softer
spectra lead to a less efficient cascade.Comment: 28 pages, 14 figures, accepted to ApJ 28/10/202
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