4,542 research outputs found
Relativistic gravitational collapse in comoving coordinates: The post-quasistatic approximation
A general iterative method proposed some years ago for the description of
relativistic collapse, is presented here in comoving coordinates. For doing
that we redefine the basic concepts required for the implementation of the
method for comoving coordinates. In particular the definition of the
post-quasistatic approximation in comoving coordinates is given. We write the
field equations, the boundary conditions and a set of ordinary differential
equations (the surface equations) which play a fundamental role in the
algorithm. As an illustration of the method, we show how to build up a model
inspired in the well known Schwarzschild interior solution. Both, the adiabatic
and non adiabatic, cases are considered.Comment: 14 pages, 11 figures; updated version to appear in Int. J. Modern
Phys.
Equation of state and transport processes in self--similar spheres
We study the effect of transport processes (diffusion and free--streaming) on
a collapsing spherically symmetric distribution of matter in a self--similar
space--time. A very simple solution shows interesting features when it is
matched with the Vaidya exterior solution. In the mixed case (diffusion and
free--streaming), we find a barotropic equation of state in the stationary
regime. In the diffusion approximation the gravitational potential at the
surface is always constant; if we perturb the stationary state, the system is
very stable, recovering the barotropic equation of state as time progresses. In
the free--streaming case the self--similar evolution is stationary but with a
non--barotropic equation of state.Comment: 9 pages, 2 figure
Companions of Bright Barred Shapley Ames Galaxies
Companion galaxy environment for a subset of 78 bright and nearby barred
galaxies from the Shapley Ames Catalog is presented. Among spiral barred
galaxies there are Seyfert galaxies, galaxies with circumnuclear structures,
galaxies not associated with any large scale galaxy cloud structure, galaxies
with peculiar disk morphology (crooked arms) and galaxies with normal disk
morphology; the list includes all Hubble types. The companion galaxy list
includes number of companion galaxies within 20 diameters (D25), their Hubble
type and projected separation distance. Additionally, companion environment was
searched for four known active spiral galaxies, three of them are Seyfert
galaxies, namely, NGC 1068, NGC 1097, NGC 5548 and one is a starburst galaxy,
M82. Among the results obtained it is noted that the only spiral barred galaxy
classified as Sy 1 in our list has no companions within a projected distance of
20 diameters; 6 out of 10 Sy 2 bar galaxies have no companions within 10
diamters, 6 out of 10 Sy 2 galaxies have one or more companions at projected
separation distances between 10 and 20 diameters; 6 out of 12 galaxies with
circumnuclear structures have 2 or more companions within 20 diametersComment: Accepted for publication in the Astronomical Journal, 40 pages incl.
3 figure
EXERGOECONOMIC ANALYSIS in A CEMENT PRODUCTION PLANT
A dry-type Cement Production Plan of 151 Tons per hour was taken as a case of study to implement an exergoeconomic analysis. In this paper, the exergy destruction and the investment costs of the system's units were calculated to obtain accurate information about the performance of the process, from the exergoeconomic factor and the relative difference cost. Conventional exergoeconomic analysis showed that the total cost of exergy destruction is 4206537 USD/h. The Calciner and the Rotary Kiln cause 62% of the total cost of the exergy destruction. The lowest values of the exergoeconomic factor were calculated for Calciner (0.01%), Clinker Cooler (0.01%), Rotary Kiln (0.02%), and Raw Mill (0.04%). The significant difference in relative cost was calculated for Calciner (42%) and Rotary Kiln (54.21%). The above implies that this equipment should be considered for an investment that allows the decrease of the exergy destruction cost and the increase of the exergetic efficiency. © 2020 ASME
The Bulgeless Seyfert/LINER Galaxy NGC 3367: Disk, Bar, Lopsidedness and Environment
NGC3367 is a nearby isolated active galaxy that shows a radio jet, a strong
bar and evidence of lopsidedness. We present a quantitative analysis of the
stellar and gaseous structure of the galaxy disk and a search for evidence of
recent interaction based on new UBVRI Halpha and JHK images and on archival
Halpha Fabry-Perot and HI VLA data. From a coupled 1D/2D GALFIT bulge/bar/disk
decomposition an (B/D ~ 0.07-0.1) exponential pseudobulge is inferred in all
the observed bands. A NIR estimate of the bar strength = 0.44
places NGC 3367 bar among the strongest ones. The asymmetry properties were
studied using (1) optical and NIR CAS indexes (2) the stellar (NIR) and gaseous
(Halpha, HI) A_1 Fourier mode amplitudes and (3) the HI integrated profile and
HI mean intensity distribution. While the average stellar component shows
asymmetry values close to the average found in the Local Universe for isolated
galaxies, the young stellar component and gas values are largely decoupled
showing significantly larger A_1 mode amplitudes suggesting that the gas has
been recently perturbed. Our search for (1) faint stellar structures in the
outer regions (up to u_R ~ 26 mag arcsec^{-2}), (2) (Halpha) star-forming
satellite galaxies and (3) regions with different colors (stellar populations)
along the disk all failed. Such an absence is interpreted using recent
numerical simulations to constrain a tidal event with an LMC like galaxy to
some dynamical times in the past or to a current very low mass, gas rich
accretion. We conclude that a cold accretion mode (gas and small/dark galaxies)
may be responsible of the nuclear activity and peculiar (young stars and gas)
morphology regardless of the highly isolated environment. Black hole growth in
bulgeless galaxies may be triggered by cosmic smooth mass accretion.Comment: 27 pages, 12 figures, accepted for publication in The Astronomical
Journa
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