744 research outputs found
Relativistic Jets from Accretion Disks
The jets observed to emanate from many compact accreting objects may arise
from the twisting of a magnetic field threading a differentially rotating
accretion disk which acts to magnetically extract angular momentum and energy
from the disk. Two main regimes have been discussed, hydromagnetic jets, which
have a significant mass flux and have energy and angular momentum carried by
both matter and electromagnetic field and, Poynting jets, where the mass flux
is small and energy and angular momentum are carried predominantly by the
electromagnetic field. Here, we describe recent theoretical work on the
formation of relativistic Poynting jets from magnetized accretion disks.
Further, we describe new relativistic, fully-electromagnetic, particle-in-cell
simulations of the formation of jets from accretion disks. Analog Z-pinch
experiments may help to understand the origin of astrophysical jets.Comment: 7 pages, 3 figures, Proc. of High Energy Density Astrophysics Conf.,
200
Risk factors for the preservation of morphological changes in the gastric mucosa after eradication therapy for Helicobacter pylori infection in children with chronic gastritis
We conducted a clinical, morphofunctional examination and standard treatment of 155 children with chronic gastroduodenitis associated with Helicobacter pylori (HP) infection. It was кevealed that after 6 months lymphoplasmacytic infiltration of the gastric mucosa (GM) preserved in 37% of cases, and unspecified atrophy - in 9%, increased C3 and C4 components of the compliment - in 19% of children, antroduodenal discoordination on the background of postprandial secretin and cholecystokinin level - in 25%, as well as disorders of the intestinal microbiot
Relativistic dynamical polarizability of hydrogen-like atoms
Using the operator representation of the Dirac Coulomb Green function the analytical method in perturbation theory is employed in obtaining solutions of the Dirac equation for a hydrogen-like atom in a time-dependent electric field. The relativistic dynamical polarizability of hydrogen-like atoms is calculated and analysed
Particle Acceleration and Magnetic Dissipation in Relativistic Current Sheet of Pair Plasmas
We study linear and nonlinear development of relativistic and
ultrarelativistic current sheets of pair plasmas with antiparallel magnetic
fields. Two types of two-dimensional problems are investigated by
particle-in-cell simulations. First, we present the development of relativistic
magnetic reconnection, whose outflow speed is an order of the light speed c. It
is demonstrated that particles are strongly accelerated in and around the
reconnection region, and that most of magnetic energy is converted into
"nonthermal" part of plasma kinetic energy. Second, we present another
two-dimensional problem of a current sheet in a cross-field plane. In this
case, the relativistic drift kink instability (RDKI) occurs. Particle
acceleration also takes place, but the RDKI fast dissipates the magnetic energy
into plasma heat. We discuss the mechanism of particle acceleration and the
theory of the RDKI in detail. It is important that properties of these two
processes are similar in the relativistic regime of T > mc^2, as long as we
consider the kinetics. Comparison of the two processes indicates that magnetic
dissipation by the RDKI is more favorable process in the relativistic current
sheet. Therefore the striped pulsar wind scenario should be reconsidered by the
RDKI.Comment: To appear in ApJ vol. 670; 60 pages, 27 figures; References and typos
are fixe
Disk-Magnetosphere Interaction and Outflows: Conical Winds and Axial Jets
We investigate outflows from the disk-magnetosphere boundary of rotating
magnetized stars in cases where the magnetic field of a star is bunched into an
X-type configuration using axisymmetric and full 3D MHD simulations. Such
configuration appears if viscosity in the disk is larger than diffusivity, or
if the accretion rate in the disk is enhanced. Conical outflows flow from the
inner edge of the disk to a narrow shell with an opening angle 30-45 degrees.
Outflows carry 0.1-0.3 of the disk mass and part of the disk's angular momentum
outward. Conical outflows appear around stars of different periods, however in
case of stars in the "propeller" regime, an additional - much faster component
appears: an axial jet, where matter is accelerated up to very high velocities
at small distances from the star by magnetic pressure force above the surface
of the star. Exploratory 3D simulations show that conical outflows are
symmetric about rotational axis of the disk even if magnetic dipole is
significantly misaligned. Conical outflows and axial jets may appear in
different types of young stars including Class I young stars, classical T Tauri
stars, and EXors.Comment: Invited review, conference proceedings of the meeting "Protostellar
Jets in Context", 7-12 July 2008, island of Rhodes, Greece; editors: profs.
Tom Ray and Kanaris Tsinganos; 10 pages, 10 figures, see animations at
http://www.astro.cornell.edu/~romanova/conical.htm and
http://www.astro.cornell.edu/~romanova/propeller.ht
Shear-Flow Driven Current Filamentation: Two-Dimensional Magnetohydrodynamic Simulations
The process of current filamentation in permanently externally driven,
initially globally ideal plasmas is investigated by means of two-dimensional
Magnetohydrodynamic (MHD)-simulations. This situation is typical for
astrophysical systems like jets, the interstellar and intergalactic medium
where the dynamics is dominated by external forces. Two different cases are
studied. In one case, the system is ideal permanently and dissipative processes
are excluded. In the second case, a system with a current density dependent
resistivity is considered. This resistivity is switched on self-consistently in
current filaments and allows for local dissipation due to magnetic
reconnection. Thus one finds tearing of current filaments and, besides, merging
of filaments due to coalescence instabilities. Energy input and dissipation
finally balance each other and the system reaches a state of constant magnetic
energy in time.Comment: 32 Pages, 13 Figures. accepted, to appear in Physics of Plasmas
(049012
Magneto-centrifugally driven winds: comparison of MHD simulations with theory
Stationary magnetohydrodynamic (MHD) outflows from a rotating, conducting
Keplerian accretion disk threaded by B-field are investigated numerically by
time-dependent, axisymmetric (2.5D) simulations using a Godunov-type code. A
large class of stationary magneto-centrifugally driven winds are found where
matter is accelerated from a thermal speed at the disk to much larger velocity,
greater than the fast magnetosonic speed and larger than the escape speed. The
flows are approximately spherical outflows with only small collimation within
the simulation region. Numerical results are shown to coincide with the
theoretical predictions of ideal, axisymmetric MHD to high accuracy.
Investigation of the influence of outer boundary conditions, particularly that
on the toroidal component of magnetic field shows that the commonly used
``free'' boundary condition leads to artificial magnetic forces which can act
to give spurious collimation. New boundary conditions are proposed which do not
generate artificial forces. Artificial results may also arise for cases where
the Mach cones on the outer boundaries are partially directed into the
simulation region.Comment: 19 pages, 18 figures, emulapj.sty is use
Pollen quality and pollen productivity of blue honeysuckle species and varieties
Studies to assess the pollen quality and pollen productivity of blue honeysuckle were conducted on the ecosystem dendrological territory of the Siberian Botanical garden of TSU (Tomsk). Objects of research: 8 varieties and 4 species of blue honeysuckle – ‘Velvet’, ‘Berel’, ‘Vasyuganskaya’, ‘Zolushka’, ‘Lazurnaya’, ‘Ogneny Opal’, ‘Selena’, ‘Tomichka’, Lonicera altaica, L. edulis, L. kamtschatica, L. turczaninovii. It was found that the ‘Ogneny Opal’ and ‘Velvet’ varieties have low fertility, and the ‘Berel’ and L. edulis have an average fertility. Other varieties and species of honeysuckle have high pollen fertility. The viability of pollen with high values is more than 60 % – ‘Berel’, ‘Vasyuganskaya’, ‘Lazurnaya’, L. turczaninovii, L. kamtschatica, with average values from 40% to 60 % – ‘Selena’, ‘Tomichka’ and L. altaica, with low values – less than 40 % – ‘Velvet’, ‘Zolushka’, ‘Ogneny Opal’ and L. edulis. High pollen productivity – more than 20,000 pollen grains per flower – ‘Tomichka’, L. kamtschatica, L. turczaninovii and L. edulis, average productivity - from 10,000 to 20,000 pollen grains – ‘Berel’, ‘Vasyuganskaya’, ‘Zolushka’, ‘Lazurnaya’, ‘Selena’ and L. altaica, low productivity – less than 10,000 pollen grains per flower – ‘Velvet’, ‘Ogneny Opal’. It is recommended to use at least 10% of varieties with high pollen viability and pollen productivity as pollinators when creating industrial honeysuckle plantations: ‘Lazurnaya’, ‘Vasyuganskaya’, and ‘Berel’
Magnetohydrodynamic jets from different magnetic field configurations
Using axisymmetric MHD simulations we investigate how the overall jet
formation is affected by a variation in the disk magnetic flux profile and/or
the existence of a central stellar magnetosphere. Our simulations evolve from
an initial, hydrostatic equilibrium state in a force-free magnetic field
configuration. We find a unique relation between the collimation degree and the
disk wind magnetization power law exponent. The collimation degree decreases
for steeper disk magnetic field profiles. Highly collimated outflows resulting
from a flat profile tend to be unsteady. We further consider a magnetic field
superposed of a stellar dipole and a disk field in parallel or anti-parallel
alignment. Both stellar and disk wind may evolve in a pair of outflows,
however, a reasonably strong disk wind component is essential for jet
collimation. Strong flares may lead to a sudden change in mass flux by a factor
two. We hypothesize that such flares may eventually trigger jet knots.Comment: 5 pages, 4 figures; proceedings from conference: Protostellar Jets in
Context, held in Rhodes, July 7-12, 200
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