1,100 research outputs found
Fundamentals of crude oil and natural gas processing
This training manual includes term project methodical guide on the course "Fundamentals of crude oil and natural gas processing" in English. The main purpose of the training manual is to provide students the theoretical and methodological assistance at performance the term project on the course "Fundamentals of crude oil and natural gas processing". The manual contains the initial data and reference material needed to perform the calculations. The manual is intended for the students of speciality 6.050304 "Oil and gas production" in English
Spinning-Down of Moving Magnetars in the Propeller Regime
We use axisymmetric magnetohydrodynamic simulations to investigate the
spinning-down of magnetars rotating in the propeller regime and moving
supersonically through the interstellar medium. The simulations indicate that
magnetars spin-down rapidly due to this interaction, faster than for the case
of a non-moving star. From many simulation runs we have derived an approximate
scaling laws for the angular momentum loss rate, \dot{L} \propto
\~\eta_m^{0.3}\mu^{0.6}\rho^{0.8}{\cal M}^{-0.4} \Omega_*^{1.5}, where \rho is
the density of the interstellar medium, \cal M is Mach number, \mu is the
star's magnetic moment, \Omega_* is its angular velocity, and \eta_m is
magnetic diffusivity. A magnetar with a surface magnetic field of 10^{13} -
10^{15} G is found to spin-down to a period P > 10^5-10^6 s in \sim 10^4 - 10^5
years. There is however uncertainty about the value of the magnetic diffusivity
so that the time-scale may be longer. We discuss this model in respect of Soft
Gamma Repeaters (SGRs) and the isolated neutron star candidate RXJ1856.5-3754.Comment: 10 pages, 4 figures, accepted by MNRAS. See version with better
resolution figures and animation at
http://astrosun2.astro.cornell.edu/us-rus/propeller.ht
Gamma-ray Flares and VLBI Outbursts of Blazars
A model is developed for the time dependent electromagnetic - radio to
gamma-ray - emission of active galactic nuclei, specifically, the blazars,
based on the acceleration and creation of leptons at a propagating
discontinuity or {\it front} of a Poynting flux jet. The front corresponds to a
discrete relativistic jet component as observed with
very-long-baseline-interferometry (VLBI). Equations are derived for the number,
momentum, and energy of particles in the front taking into account synchrotron,
synchrotron-self-Compton (SSC), and inverse-Compton processes as well as
photon-photon pair production. The apparent synchrotron, SSC, and
inverse-Compton luminosities as functions of time are determined. Predictions
of the model are compared with observations in the gamma, optical and radio
bands. The delay between the high-energy gamma-ray flare and the onset of the
radio is explained by self-absorption and/or free-free absorption by external
plasma. Two types of gamma-ray flares are predicted depending on pair creation
in the front.Comment: 11 pages, submitted to ApJ. 10 figures can be obtained from R.
Lovelace by sending postal address to [email protected]
Boundary Between Stable and Unstable Regimes of Accretion
We investigated the boundary between stable and unstable regimes of accretion
and its dependence on different parameters. Simulations were performed using a
"cubed sphere" code with high grid resolution (244 grid points in the azimuthal
direction), which is twice as high as that used in our earlier studies. We
chose a very low viscosity value, with alpha-parameter alpha=0.02. We observed
from the simulations that the boundary strongly depends on the ratio between
magnetospheric radius r_m (where the magnetic stress in the magnetosphere
matches the matter stress in the disk) and corotation radius r_cor (where the
Keplerian velocity in the disk is equal to the angular velocity of the star).
For a small misalignment angle of the dipole field, Theta=5 degrees, accretion
is unstable if r_cor/r_m>1.35, and is stable otherwise. In cases of a larger
misalignment angle of the dipole, Theta=20 degrees, instability occurs at
slightly larger values, r_cor/r_m>1.41.Comment: 4 pages, 4 figures, conference proceedings: "Physics at the
Magnetospheric Boundary", Geneva, Switzerland, 25-28 June, 201
Jets and Disk-Winds from Pulsar Magnetospheres
We discuss axisymmetric force-free pulsar magnetospheres with magnetically
collimated jets and a disk-wind obtained by numerical solution of the pulsar
equation.
This solution represents an alternative to the quasi-spherical wind solutions
where a major part of the current flow is in a current sheet which is unstable
to magnetic field annihilation.Comment: 6 figures, accepted for publication in the Ap
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