oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2020 ( 45 )

2019 ( 247 )

2018 ( 367 )

2017 ( 382 )

Custom range...

Search Results: 1 - 10 of 208564 matches for " L. Zaninetti "
All listed articles are free for downloading (OA Articles)
Page 1 /208564
Display every page Item
Three Dimensional Evolution of SN 1987A in a Self-Gravitating Disk  [PDF]
L. Zaninetti
International Journal of Astronomy and Astrophysics (IJAA) , 2013, DOI: 10.4236/ijaa.2013.32010
Abstract:

The introduction of an exponential or power law gradient in the interstellar medium (ISM) allows to produce an asymmetric evolution of the supernova remnant (SNR) when the framework of the thin layer approximation is adopted. Unfortunately both the exponential and power law gradients for the ISM do not have a well defined physical meaning. The physics conversely is well represented by an isothermal self-gravitating disk of particles whose velocity is everywhere Maxwellian. We derived a law of motion in the framework of the thin layer approximation with a control parameter of the swept mass. The photon’s losses, which are often neglected in the thin layer approximation, are modeled trough velocity dependence. The developed framework is applied to SNR 1987A and the three observed rings are simulated.

The Luminosity Function of Galaxies as Modeled by a Left Truncated Beta Distribution  [PDF]
L. Zaninetti
International Journal of Astronomy and Astrophysics (IJAA) , 2014, DOI: 10.4236/ijaa.2014.41013
Abstract: A first new luminosity function of galaxies can be built starting from a left truncated beta probability density function, which is characterized by four parameters. In the astrophysical conversion, the number of parameters increases by one, due to the addition of the overall density of galaxies. A second new galaxy luminosity function is built starting from a left truncated beta probability for the mass of galaxies once a simple nonlinear relationship between mass and luminosity is assumed; in this case the number of parameters is six because the overall density of galaxies and a parameter that regulates mass and luminosity are added. The two new galaxy luminosity functions with finite boundaries were tested on the Sloan Digital Sky Survey (SDSS) in five different bands; the results produce a better fit than the Schechter luminosity function in two of the five bands considered. A modified Schechter luminosity function with four parameters has been also analyzed.
A geometrical model for the catalogs of galaxies
Zaninetti, L.;
Revista mexicana de astronomía y astrofísica , 2010,
Abstract: the 3d network originated by the faces of irregular poissonian voronoi polyhedra may represent the backbone on which the galaxies are originated. as a consequence the spatial appearance of the catalogs of galaxies can be reproduced. the selected catalogs to simulate are the 2df galaxy redshift survey and the third reference catalog of bright galaxies. in order to explain the number of observed galaxies for a given flux/magnitude as a function of the redshift, the photometric properties of the galaxies should be carefully examined from both the astronomical and theoretical point of view. the statistics of the voronoi normalized volume is modeled by two distributions and the eridanus super-void is identified as the largest volume belonging to the voronoi polyhedron. the behavior of the correlation function for galaxies is simulated by adopting the framework of thick faces of voronoi polyhedra on short scales, while adopting standard arguments on large scales.
A turbulent model for the surface brightness of extragalactic jets
Zaninetti, L.;
Revista mexicana de astronomía y astrofísica , 2009,
Abstract: this paper summarizes the known physics of turbulent jets observed in laboratory experiments. the formula, which gives the power released in turbulence describes the concentration of turbulence/relativistic particles in each point of the astrophysical jets. the same expression is also used to analyze the power released in turbulence in the case of pipe and non-newtonian fluids. through an integral operation it is possible to deduce the intensity of synchrotron radiation for a profile perpendicular (or not) to a straight jet, a 2d map for a perpendicular, randomly oriented straight jet, as well as a 2d map of complex trajectories such as ncc 4061 and 3c31. presented here is a simulation of the spectral index in brightness of 3c273 as well as a 2d map of the degree of linear polarization. the sobel operator is applied to the theoretical 2d maps of straight perpendicular jets.
Physical Mechanisms that Shape the Morphologies of Extragalactic Jets
Zaninetti, L;
Revista mexicana de astronomía y astrofísica , 2007,
Abstract: in order to find a law characterising the decrease of velocity along a jet, five analytical methods are suggested. the first two simple models examine the variation of velocity in the presence of newton's or stoke's resistance. the equation that represents the conservation of the momentum along a pyramidal sector is solved from an analytical point of view (third model). the application of the conservation of the total momentum flux allows us to deduce the velocity of the galaxy as a function of time for classical velocities (fourth model) and relativistic velocities (fifth model). the variation of velocity along the jet combined with an adequate composition of jet precession velocity, rotational velocity of the galaxy, and galaxy velocity dispersion in the cluster allows us to trace the geometrical pattern of the head-tail radio sources. application of the developed theory/code to the radio galaxies ngc1265, ngc4061, ngc326, and cygnus a gives the central galaxy's approximate dispersion velocities in the direction perpendicular to the jet. a transition from head-tails to classical double radio galaxies as a function of the increasing jet's mechanical power is introduced.
Direct conversion of the flux of kinetic energy into radiation in gamma-ray burst
L. Zaninetti
Advanced Studies in Theoretical Physics , 2012,
Abstract:
Physical mechanisms that shape the morphologies of extragalactic jets
L. Zaninetti
Revista mexicana de astronomía y astrofísica , 2007,
Abstract:
A GEOMETRICAL MODEL FOR THE CATALOGS OF GALAXIES
L. Zaninetti
Revista mexicana de astronomía y astrofísica , 2010,
Abstract: La red 3D que se origina por las caras de los polihedros irregulares poissonianos de Voronoi podr a representar la estructura b sica para la formaci n de galaxias. En consecuencia, la apariencia espacial de los cat logos de galaxias podr a reproducirse. Los cat logos seleccionados para la simulaci n fueron el 2dF Galaxy Redshift Survey y el Third Reference Catalog of Bright Galaxies. Para explicar el n mero observado de galaxias con un ujo (o magnitud) dado como funci n del corrimiento al rojo deben examinarse cuidadosamente las propiedades fotom tricas de las galaxias, tanto desde un punto de vista astron mico como te rico. La estad stica del volumen de Voronoi normalizado se modela por dos distribuciones, y el super-hueco en Eridanus se identi ca como el mayor volumen perteneciente al polihedro de Voronoi. El comportamiento de la funci n de correlaci n de las galaxias se simula adoptando el esquema de caras gruesas de polihedros de Voronoi para escalas peque as, y conservando los argumentos usuales para escalas grandes.
A TURBULENT MODEL FOR THE SURFACE BRIGHTNESS OF EXTRAGALACTIC JETS
L. Zaninetti
Revista mexicana de astronomía y astrofísica , 2009,
Abstract: En este art culo se resume la f sica conocida sobre los chorros turbulentos observados en experimentos de laboratorio. La f rmula para la potencia liberada como turbulencia describe la concentraci n turbulencia/part culas relativistas en cada punto del chorro astrof sico. Se usa la misma expresi n para analizar la po- tencia liberada como turbulencia para u dos de tubo y no-newtonianos. Mediante una operaci n integral es posible deducir la intensidad de la radiaci n sincrotr nica para un per l perpendicular (o no) a un chorro recto, obtener un mapa 2D para un chorro perpendicular de orientaci n arbitraria, as como mapas 2D para trayecto- rias complejas como es el caso de NGC 4061 y 3C31. Se presenta una simulaci n del ndice espectral del brillo para 3C273, as como un mapa 2D del grado de po- larizaci n lineal. Se aplica el operador Sobel a los mapas 2D te ricos para chorros rectos perpendiculares.
Semi-analytical Formulas for the Fundamental Parameters of Galactic Early B Supergiants
Zaninetti, L.
Serbian Astronomical Journal , 2009,
Abstract: The publication of new tables of calibration of some fundamental parameters of Galactic B0-B5 supergiants in the two classes $I_mathrm{a}$ and $I_mathrm{b} $ allows to particularize the eight parameters conjecture that model five fundamental parameters. The numerical expressions for visual magnitude, radius, mass, luminosity and surface gravity are derived for supergiants in the range of temperature between 29700 K and 15200 K. The availability of accurate tables of calibration allows us to estimate the efficiency of the derived formulas in reproducing the observed values. The average efficiency of the new formulas, expressed in percent, is 94 for the visual magnitude, 81 for the mass, 96 for the radius, 99 for the logarithm of the luminosity and 97 for the logarithm of the surface gravity.
Page 1 /208564
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.