1,104 research outputs found
Particle Diffusion and Acceleration by Shock Wave in Magnetized Filamentary Turbulence
We expand the off-resonant scattering theory for particle diffusion in
magnetized current filaments that can be typically compared to astrophysical
jets, including active galactic nucleus jets. In a high plasma beta region
where the directional bulk flow is a free-energy source for establishing
turbulent magnetic fields via current filamentation instabilities, a novel
version of quasi-linear theory to describe the diffusion of test particles is
proposed. The theory relies on the proviso that the injected energetic
particles are not trapped in the small-scale structure of magnetic fields
wrapping around and permeating a filament but deflected by the filaments, to
open a new regime of the energy hierarchy mediated by a transition compared to
the particle injection. The diffusion coefficient derived from a quasi-linear
type equation is applied to estimating the timescale for the stochastic
acceleration of particles by the shock wave propagating through the jet. The
generic scalings of the achievable highest energy of an accelerated ion and
electron, as well as of the characteristic time for conceivable energy
restrictions, are systematically presented. We also discuss a feasible method
of verifying the theoretical predictions. The strong, anisotropic turbulence
reflecting cosmic filaments might be the key to the problem of the acceleration
mechanism of the highest energy cosmic rays exceeding 100 EeV (10^{20} eV),
detected in recent air shower experiments.Comment: 39 pages, 2 figures, accepted for publication in Ap
Plano de intervenção técnica em propriedades agrícolas- Ouricurí- PE.
O trabalho ora apresentado representa um esforço valioso de integração entre pesquisadores de várias áreas de especialização. Representa, também, uma colaboração substancial da equipe de assessoria do PNP-033, bem como o esforço eloquente da equipe de execução, presente em todas as etapas do trabalho.bitstream/item/210394/1/Plano-de-intevencao-tecnica-em-propriedades-agricolas-ouricuri-PE.pdf
Simulations of small-scale turbulent dynamo
We report an extensive numerical study of the small-scale turbulent dynamo at
large magnetic Prandtl numbers Pm. A Pm scan is given for the model case of
low-Reynolds-number turbulence. We concentrate on three topics: magnetic-energy
spectra and saturation levels, the structure of the field lines, and the
field-strength distribution. The main results are (1) the folded structure
(direction reversals at the resistive scale, field lines curved at the scale of
the flow) persists from the kinematic to the nonlinear regime; (2) the field
distribution is self-similar and appears to be lognormal during the kinematic
regime and exponential in the saturated state; and (3) the bulk of the magnetic
energy is at the resistive scale in the kinematic regime and remains there
after saturation, although the spectrum becomes much shallower. We propose an
analytical model of saturation based on the idea of partial
two-dimensionalization of the velocity gradients with respect to the local
direction of the magnetic folds. The model-predicted spectra are in excellent
agreement with numerical results. Comparisons with large-Re, moderate-Pm runs
are carried out to confirm the relevance of these results. New features at
large Re are elongation of the folds in the nonlinear regime from the viscous
scale to the box scale and the presence of an intermediate nonlinear stage of
slower-than-exponential magnetic-energy growth accompanied by an increase of
the resistive scale and partial suppression of the kinetic-energy spectrum in
the inertial range. Numerical results for the saturated state do not support
scale-by-scale equipartition between magnetic and kinetic energies, with a
definite excess of magnetic energy at small scales. A physical picture of the
saturated state is proposed.Comment: aastex using emulateapj; 32 pages, final published version; a pdf
file (4Mb) of the paper containing better-quality versions of figs. 5, 8, 12,
15, 17 is available from http://www.damtp.cam.ac.uk/user/as629 or by email
upon request
Circadian rhythm of hepatic cytosolic and nuclear estrogen receptors
The distribution of estrogen receptor between the cytosolic and nuclear compartments were evaluated in liver of male rats to determine whether a circadian rhythm exists. Cytosolic receptor reached a maximum level at 400 hours and a minimum at 2000 and 2400 hr. Nuclear receptor reached a maximum level at 800 hr and was lowest at 1600 and 2000 hr. Serum estradiol levels were also highest at 800 hr and lowest at 1600 hr. The variations in cytosolic and nuclear receptors are not reciprocal; in fact, the overall content of receptor in the liver is not constant and also displays a circadian rhythm. © 1986 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted
Ultra high energy cosmic rays and the large scale structure of the galactic magnetic field
We study the deflection of ultra high energy cosmic ray protons in different
models of the regular galactic magnetic field. Such particles have gyroradii
well in excess of 1 kpc and their propagation in the galaxy reflects only the
large scale structure of the galactic magnetic field. A future large
experimental statistics of cosmic rays of energy above 10 eV could be
used for a study of the large scale structure of the galactic magnetic field if
such cosmic rays are indeed charged nuclei accelerated at powerful
astrophysical objects and if the distribution of their sources is not fully
isotropic.Comment: 9 pages LaTeX file (AASTeX), 4 eps figures, submitted to The
Astrophysical Journa
The simulation of molecular clouds formation in the Milky Way
Using 3D hydrodynamic calculations we simulate formation of molecular clouds
in the Galaxy. The simulations take into account molecular hydrogen chemical
kinetics, cooling and heating processes. Comprehensive gravitational potential
accounts for contributions from the stellar bulge, two and four armed spiral
structure, stellar disk, dark halo and takes into account self-gravitation of
the gaseous component. Gas clouds in our model form in the spiral arms due to
shear and wiggle instabilities and turn into molecular clouds after t\simgt
100 Myr. At the times Myr the clouds form hierarchical
structures and agglomerations with the sizes of 100 pc and greater. We analyze
physical properties of the simulated clouds and find that synthetic statistical
distributions like mass spectrum, "mass-size" relation and velocity dispersion
are close to those observed in the Galaxy. The synthetic (galactic
longitude - radial velocity) diagram of the simulated molecular gas
distribution resembles observed one and displays a structure with appearance
similar to Molecular Ring of the Galaxy. Existence of this structure in our
modelling can be explained by superposition of emission from the galactic bar
and the spiral arms at 3-4 kpc.Comment: 10 pages, 8 figure
A new generic open pit mine planning process with risk assessment ability
Conventionally, mining industry relies on a deterministic view, where a unique mine plan is determined based on a single resource model. A major shortfall of this approach is the inability to assess the risk caused by the well-known geological uncertainty, i.e. the in situ grade and tonnage variability of the mineral deposit. Despite some recent attempts in developing stochastic mine planning models which have demonstrated promising results, the industry still remains sceptical about this innovative idea. With respect to unbiased linear estimation, kriging is the most popular and reliable deterministic interpolation technique for resource estimation and it appears to remain its popularity in the near future. This paper presents a new systematic framework to quantify the risk of kriging-based mining projects due to the geological uncertainties. Firstly, conditional simulation is implemented to generate a series of equally-probable orebody realisations and these realisations are then compared with the kriged resource model to analyse its geological uncertainty. Secondly, a production schedule over the life of mine is determined based on the kriged resource model. Finally, risk profiles of that production schedule, namely ore and waste tonnage production, blending grade and Net Present Value (NPV), are constructed using the orebody realisations. The proposed model was applied on a multi-element deposit and the result demonstrates that that the kriging-based mine plan is unlikely to meet the production targets. Especially, the kriging-based mine plan overestimated the expected NPV at a magnitude of 6.70% to 7.34% (135 M). A new multivariate conditional simulation framework was also introduced in this paper to cope with the multivariate nature of the deposit. Although an iron ore deposit is used to prove the concepts, the method can easily be adapted to other kinds of mineral deposits, including surface coal mine
The Parker Instability in a Thick Gaseous Disk II: Numerical Simulations in 2D
We present 2D, ideal-MHD numerical simulations of the Parker instability in a
multi-component warm disk model. The calculations were done using two numerical
codes with different algorithms, TVD and ZEUS-3D. The outcome of the numerical
experiments performed with both codes is very similar, and confirms the results
of the linear analysis for the undular mode derived by Kim et al. (2000): the
most unstable wavelength is about 3 kpc and its growth timescale is between
30-50 Myr (the growth rate is sensitive to the position of the upper boundary
of the numerical grid). Thus, the time and length scales of this multicomponent
disk model are substantially larger than those derived for thin disk models. We
use three different types of perturbations, random, symmetric, and
antisymmetric, to trigger the instability. The antisymmetric mode is dominant,
and determines the minimum time for the onset of the nonlinear regime. The
instability generates dense condensations and the final peak column density
value in the antisymmetric case, as also derived by Kim et al. (2000), is about
a factor of 3 larger than its initial value. These wavelengths and density
enhancement factors indicate that the instability alone cannot be the main
formation mechanism of giant molecular clouds in the general interstellar
medium. The role of the instability in the formation of large-scale
corrugations along spiral arms is briefly discussed.Comment: Accepted for publication in ApJ, 20 text pages with 8 figure
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