477 research outputs found
Preliminary results of investigation of solid interplanetary matter in the vicinity of the moon
Density of matter near moon found to be greater than that of interplanetary spac
Jet Formation in the magnetospheres of supermassive black holes: analytic solutions describing energy loss through Blandford-Znajek processes
In this paper, we provide exact solutions for the extraction of energy from a
rotating black hole via both the electromagnetic Poynting flux and matter
currents. By appropriate choice of a radially independent poloidal function
, we find solutions where the dominant outward energy flux is
along the polar axis, consistent with a jet-like collimated outflow, but also
with a weaker flux of energy along the equatorial plane. Unlike all the
previously obtained solutions (Blandford & Znajek (1977), Menon & Dermer
(2005)), the magnetosphere is free of magnetic monopoles everywhere
3C454.3 reveals the structure and physics of its 'blazar zone'
Recent multi-wavelength observations of 3C454.3, in particular during its
giant outburst in 2005, put severe constraints on the location of the 'blazar
zone', its dissipative nature, and high energy radiation mechanisms. As the
optical, X-ray, and millimeter light-curves indicate, significant fraction of
the jet energy must be released in the vicinity of the millimeter-photosphere,
i.e. at distances where, due to the lateral expansion, the jet becomes
transparent at millimeter wavelengths. We conclude that this region is located
at ~10 parsecs, the distance coinciding with the location of the hot dust
region. This location is consistent with the high amplitude variations observed
on ~10 day time scale, provided the Lorentz factor of a jet is ~20. We argue
that dissipation is driven by reconfinement shock and demonstrate that X-rays
and gamma-rays are likely to be produced via inverse Compton scattering of
near/mid IR photons emitted by the hot dust. We also infer that the largest
gamma-to-synchrotron luminosity ratio ever recorded in this object - having
taken place during its lowest luminosity states - can be simply due to weaker
magnetic fields carried by a less powerful jet.Comment: 19 pages, 3 figures, accepted for publication in Ap
Synchrotron Self-Compton Model for Rapid Nonthermal Flares in Blazars with Frequency-Dependent Time Lags
We model rapid variability of multifrequency emission from blazars occurring
across the electromagnetic spectrum (from radio to gamma-rays). Lower energy
emission is produced by the synchrotron mechanism, whereas higher energy
emission is due to inverse Compton scattering of the synchrotron emission. We
take into account energy stratification established by particle acceleration at
shock fronts and energy losses due to synchrotron emission. We also consider
the effect of light travel delays for the synchrotron emission that supplies
the seed photons for inverse Compton scattering. The production of a flare is
caused by the collision between a relativistic shock wave and a stationary
feature in the jet (e.g., a Mach disk). The collision leads to the formation of
forward and reverse shocks, which confine two contiguous emission regions
resulting in complex profiles of simulated flares. Simulations of
multifrequency flares indicate that relative delays between the inverse Compton
flares and their synchrotron counterparts are dominated by energy
stratification and geometry of the emitting regions, resulting in both negative
and positive time delays depending on the frequency of observation. Light
travel effects of the seed photons may lead to a noticeable delay of the
inverse Compton emission with respect to synchrotron variability if the line of
sight is almost perfectly aligned with the jet. We apply the model to a flare
in 3C 273 and derive the properties of shocked plasma responsible for the
flare. We show that the pronounced negative time delay between the X-ray and IR
light curves (X-rays peak after the maximum in the synchrotron emission) can be
accounted for if both forward and reverse shocks are considered.Comment: 48 pages, 18 figures, accepted for publication in The Astrophysical
Journa
3D Simulations of Relativistic Precessing Jets Probing the Structure of Superluminal Sources
We present the results of a three-dimensional, relativistic, hydrodynamic
simulation of a precessing jet into which a compact blob of matter is injected.
A comparison of synthetic radio maps computed from the hydrodynamic model,
taking into account the appropriate light travel time delays, with those
obtained from observations of actual superluminal sources shows that the
variability of the jet emission is the result of a complex combination of phase
motions, viewing angle selection effects, and non-linear interactions between
perturbations and the underlying jet and/or the external medium. These results
question the hydrodynamic properties inferred from observed apparent motions
and radio structures, and reveal that shock-in-jet models may be overly
simplistic.Comment: Accepted for publication in ApJL. 4 pages, 5 figures (4 in color
3D Simulations of MHD Jet Propagation Through Uniform and Stratified External Environments
We present a set of high-resolution 3D MHD simulations of steady light,
supersonic jets, exploring the influence of jet Mach number and the ambient
medium on jet propagation and energy deposition over long distances. The
results are compared to simple self-similar scaling relations for the
morphological evolution of jet-driven structures and to previously published 2D
simulations. For this study we simulated the propagation of light jets with
internal Mach numbers 3 and 12 to lengths exceeding 100 initial jet radii in
both uniform and stratified atmospheres.
The propagating jets asymptotically deposit approximately half of their
energy flux as thermal energy in the ambient atmosphere, almost independent of
jet Mach number or the external density gradient. Nearly one-quarter of the jet
total energy flux goes directly into dissipative heating of the ICM, supporting
arguments for effective feedback from AGNs to cluster media. The remaining
energy resides primarily in the jet and cocoon structures. Despite having
different shock distributions and magnetic field features, global trends in
energy flow are similar among the different models.
As expected the jets advance more rapidly through stratified atmospheres than
uniform environments. The asymptotic head velocity in King-type atmospheres
shows little or no deceleration. This contrasts with jets in uniform media with
heads that are slowed as they propagate. This suggests that the energy
deposited by jets of a given length and power depends strongly on the structure
of the ambient medium. While our low-Mach jets are more easily disrupted, their
cocoons obey evolutionary scaling relations similar to the high-Mach jets.Comment: Accepted in ApJ, 32 pages, 18 figures, animations available from:
http://www.msi.umn.edu/Projects/twj/newsite/projects/radiojets/movies
ОСНОВНЫЕ ТИПЫ ИННОВАЦИОННЫХ МАЛЫХ И СРЕДНИХ ПРЕДПРИЯТИЙ
Conversion of Eastern Europe countries and RF to market economics causes many organizational, legal and infrastructural problems to rise. By the degree of «innovativeness», minor and medium enterprises are classified to three categories: «leader», «successor» and «outsider». Minor enterprises to whom different support may be extended by regional powers are grouped to 4 types.Переход стран Восточной Европы и Российской Федерации к рыночному типу экономики порождает много организационно-правовых и инфраструктурных проблем. По степени инновационности МСП относятся к категориям «лидер», «последователь» и «аутсайдер». Малые инновационные предприятия, которым может быть предоставлена различная поддержка региональных органов власти, разделены на 4 типа
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