41,486 research outputs found
Period-Luminosity-Colour distribution and classification of Galactic oxygen-rich LPVs
The absolute K magnitudes and kinematic parameters of about 350 oxygen-rich
Long-Period Variable stars are calibrated, by means of an up-to-date
maximum-likelihood method, using Hipparcos parallaxes and proper motions
together with radial velocities and, as additional data, periods and V-K colour
indices. Four groups, differing by their kinematics and mean magnitudes, are
found. For each of them, we also obtain the distributions of magnitude, period
and de-reddened colour of the base population, as well as de-biased
period-luminosity-colour relations and their two-dimensional projections. The
SRa semiregulars do not seem to constitute a separate class of LPVs. The SRb
appear to belong to two populations of different ages. In a PL diagram, they
constitute two evolutionary sequences towards the Mira stage. The Miras of the
disk appear to pulsate on a lower-order mode. The slopes of their de-biased PL
and PC relations are found to be very different from the ones of the Oxygen
Miras of the LMC. This suggests that a significant number of so-called Miras of
the LMC are misclassified. This also suggests that the Miras of the LMC do not
constitute a homogeneous group, but include a significant proportion of
metal-deficient stars, suggesting a relatively smooth star formation history.
As a consequence, one may not trivially transpose the LMC period-luminosity
relation from one galaxy to the other.Comment: 13 pages, 23 figures. Accepted for publication in A&A
Experimental test for interpreting the increase in sensibility of doped CR-39
In recent years the sensibility of CR-39 to nuclear tracks has been increased by doping the corresponding monomer with dioctyl phtalate. At this regard, two theoretical approaches are current managed to explain this phenomenon: either the doping react with the active radicals in the chain blocking them, stopping crosslinking between chains, or alternatively that the doping gets between them giving wider space between the crosslinkined chains
The generalised relativistic Lindhard functions
We present here analytic expressions for the generalised Lindhard function,
also referred to as Fermi Gas polarisation propagator, in a relativistic
kinematic framework and in the presence of various resonances and vertices.
Particular attention is payed to its real part, since it gives rise to
substantial difficulties in the definition of the currents entering the
dynamics.Comment: 48 pages, 2 figures, to be published in EPJ
Powering AGNs with super-critical black holes
We propose a novel mechanism for powering the central engines of Active
Galactic Nuclei through super-critical (type II) black hole collapse. In this
picture, ~ of material collapsing at relativistic speeds can
trigger a gravitational shock, which can eject a large percentage of the
collapsing matter at relativistic speeds, leaving behind a "light" black hole.
In the presence of a poloidal magnetic field, the plasma collimates along two
jets, and the associated electron synchrotron radiation can easily account for
the observed radio luminosities, sizes and durations of AGN jets. For Lorentz
factors of order 100 and magnetic fields of a few hundred , synchrotron
electrons can shine for yrs, producing jets of sizes of order 100 kpc.
This mechanism may also be relevant for Gamma Ray Bursts and, in the absence of
magnetic field, supernova explosions.Comment: 4 pages, 1 figur
Analysis of process variables via CFD to evaluate the performance of a FCC riser
Feedstock conversion and yield products are studied through a 3D model simulating the main reactor of the fluid catalytic cracking (FCC) process. Computational fluid dynamic (CFD) is used with Eulerian-Eulerian approach to predict the fluid catalytic cracking behavior. The model considers 12 lumps with catalyst deactivation by coke and poisoning by alkaline nitrides and polycyclic aromatic adsorption to estimate the kinetic behavior which, starting from a given feedstock, produces several cracking products. Different feedstock compositions are considered. The model is compared with sampling data at industrial operation conditions. The simulation model is able to represent accurately the products behavior for the different operating conditions considered. All the conditions considered were solved using a solver ANSYS CFX 14.0. The different operation process variables and hydrodynamic effects of the industrial riser of a fluid catalytic cracking (FCC) are evaluated. Predictions from the model are shown and comparison with experimental conversion and yields products are presented; recommendations are drawn to establish the conditions to obtain higher product yields in the industrial process
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