244 research outputs found
Comunicaciones del Departamento de Astrofísica : Circular no. 8
No full textÍndice:
- La velocidad del sol con respecto a la velocidad circular en la Galaxia | Livio Gratton, Jorge Dvinianin, Carlos Jaschek
- Sobre el cálculo de la abundancia hidrógeno-helio en las binarias | Livio Gratton, Mercedes I. Corvalán
- Nova Scorpi 1950 | Numa Tapia
- El máximo secundario de T CrB | Livio GrattonMaterial digitalizado en SEDICI gracias a la Biblioteca de la Facultad de Ciencias Astronómicas y Geofísicas.Observatorio Astronómico de La Plat
Reflexiones de un físico sobre sus creencias religiosas
No full textReflexiones de un investigador acerca de un orden en la naturaleza de origen trascendente. La fuerza del llamado de Dios en grandes científicos. La religiosidad de James Clerk Maxwell. La especificidad del mundo y de las leyes que lo gobiernan y su interpretación como naturaleza creada. “Pero Tú todo lo dispusiste con medida, número, y peso” (Sb 11, 20). Las ciencias naturales como fuente de inspiración de sentimientos religiosos. “Creer para comprender”.Fil: Gratton, Fausto Tulio Livio. Universidad Católica de Argentina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Serie Astronómica | Tomo XXVIII | Número 1 y 2
No full textContenidos:
- La evolución de las estrellas que siguen la Ley de Bethe para la producción de energía | Livio Gratton
- Catalogue of stellar spectra classified in the Morgan-Keenan system | Carlos Jaschek, Horacio Conde y Amelia C. de SierraMaterial digitalizado en SEDICI gracias a la Biblioteca de la Facultad de Ciencias Astronómicas y Geofísicas.Observatorio Astronómico de La Plat
The Spectrum of RS Ophiuchi during the 1958 maximum
No full textThe recurrent Nova RS Oph brightened to the 6th magnitude between July 13 and 14 1958. This is the third observed outburst of this variable; the other two occurred in 1898 and 1933 (Cecchini and Gratton 1941).
The news of the outburst reached Córdoba the 15th of July and a dozen of spectroscopic plates were obtained by the Authors from July 15.9 to July 25.0 at Bosque Alegre with the standard equipment ( 60" Reflector, grating spectrograph with a dispersion of 42 A/mm). Buring the time of the observations, apparently, the star reached a maximum (around July 18) and began to fade slowly.
(Párrafo extraído a modo de resumen)Asociación Argentina de Astronomí
The Spectrum of RS Ophiuchi during the 1958 maximum
No full textThe recurrent Nova RS Oph brightened to the 6th magnitude between July 13 and 14 1958. This is the third observed outburst of this variable; the other two occurred in 1898 and 1933 (Cecchini and Gratton 1941).
The news of the outburst reached Córdoba the 15th of July and a dozen of spectroscopic plates were obtained by the Authors from July 15.9 to July 25.0 at Bosque Alegre with the standard equipment ( 60" Reflector, grating spectrograph with a dispersion of 42 A/mm). Buring the time of the observations, apparently, the star reached a maximum (around July 18) and began to fade slowly.
(Párrafo extraído a modo de resumen)Asociación Argentina de Astronomí
Ephemeris Protection Level Equations and Monitor Algorithms for GBAS
No full textOne troublesome failure mode for Ground Based Augmentation Systems (GBAS) is the possibility of large discrepancies between satellite locations in space and the locations derived by the ephemeris data that they broadcast. For the Global Positioning System (GPS), nominal ephemeris errors are typically 10 meters or less, and it would take large errors (typically greater than 1 km) to be hazardous to GBAS users making precision approaches to Category I minima. Although most large errors will be detected by the GBAS ground segment Message Field Range Test, ephemeris errors orthogonal to the line-of-sight between a failed satellite and a GBAS ground station are not detectable by this simple test. To counter this possibility, RTCA has adopted new protection levels to quantify the potential impact of undetected ephemeris failures on user position errors for both precision approach and terminal area applications. These equations define position error bounds as functions of the approximate aircraft location with respect to each satellite and the GBAS ground station as well as the magnitude of the satellite orbit error detectable by the ground station. This Minimum Detectable Error (MDE) determines the "P-value" that is broadcast by the GBAS ground station for each satellite it has approved for use. Several GBAS monitor algorithms have been developed and tested for use in GBAS installations that lack SBAS coverage. One of these is a comparison between satellite positions given by the current satellite ephemeris and the ephemeris broadcast by the same satellite on its previous pass. Variants of this "YE-TE" test have been shown to support GBAS MDE's as low as 1100 meters, which will minimize the resulting impact on Category I user availability due to the ephemeris protection level equations. In addition, means of using raw measurements to initialize this monitor and to separately verify ephemerides in real-time are proposed.The authors would like to thank Todd Walter and Gang
Xie for their help during this research. This work was
also supported by the efforts of Barbara Clark of FAA
AIR-130, Tom Hsiao, Curt Shively, Chris Varner, and
Ron Braff of MITRE, Victor Wullschleger and John
Warburton of FAA ACT-360, and others participating in
RTCA SC-159 WG-4 requirements development. The
advice and interest of many other people in the Stanford
GPS research group is appreciated, as is funding support
from the FAA LAAS Program Office (AND-710). The
opinions discussed here are those of the authors and do
not necessarily represent those of the FAA or other
affiliated agencies
Aspects of magnetopause/magnetosphere response to interplanetary discontinuities, and features of magnetopause Kelvin-Helmholtz waves
No full textWe describe (i) perturbations of the magnetopause/magnetosphere elicited by an interplanetary discontinuity and (ii) the production of Kelvin-Helmholtz waves on the magnetopause. These are two large topics, so for reasons of space we combine both features in a single data example, supporting the observations by theory. Correspondingly, the observations, made by ACE, consist of an interval in which a current sheet is followed by a period of strongly northward IMF. In view of recent attention directed at the effect of variations of the azimuthal component of the solar wind velocity on the magnetosphere, we chose a current sheet (CS) across which the east-west components of both field and flow vectors change polarity. A two-stage response is evident in the records of Cluster, outbound at the dusk terminator at 27° MLAT: (i) Four cycles of large-amplitude, ~3min oscillations during which the spacecraft sample alternately the cold, dense magnetosheath and the hot and tenuous magnetosphere plasmas. We argue that these motions are likely due to tangential stresses applied to the magnetopause. (ii) Soon thereafter the oscillatory character changes dramatically, and ~80s small-amplitude undulations appear which we argue to be magnetopause surface waves. Applying linear MHD theory we show these waves are due to a locally Kelvin-Helmholtz unstable boundary. As input parameters, we take values during the preceding large oscillations at the same magnetopause locale. An aspect of the non-linear phase of this instability is illustrated by a numerical simulation: the reduced duration of the evolution into large vortices by a strong initial perturbation.Fil: Farrugia, C. J.. University Of New Hampshire; Estados UnidosFil: Gratton, Fausto Tulio Livio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física del Plasma. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física del Plasma; Argentina. Pontificia Universidad Católica Argentina "Santa María de los Buenos Aires". Facultad de Ciencias Fisicomatemáticas e Ingeniería; Argentin
Efecto de una configuración de Kelvin-Helmholtz sobre la inestabilidad 'tearing' de láminas de corriente forzadas por flujos de estancamiento
No full textInvestigamos la influencia estabilizadora de un flujo de plasma paralelo a una lámina de corriente formada por un movimiento tipo punto de estancamiento, sobre la inestabilidad de "tearing". Damos el análisis de estabilidad para una extensión de esta configuración, la cual es solución exacta de la MHD. El espectro se calcula usando un método matricial con diferencias finitas. Se da la tasa de crecimiento γ en función de los números de Mach- Alfvénico Mᴀ, Lundquist S y Prandtl magnético Pᵐ. Mostramos (para Pᵐ=1) la estabilización del modo "tearing" por Kelvin-Helmholtz cuando Mᴀ<1. El efecto de la viscosidad tiende a reducir las tasas de crecimiento. Se confirma, en el caso v₀=0, la dependencia de γ con el número de Hartmann Hₐ-S/Pᵐ½We study the stability of a driven current sheet with a magnetic field normal to a stagnation point flow and parallel to a velocity shear. The configuration is an exact solution of the MHD equations with resistivity and viscosity. The eigenvalues and eigenfunctions of the stability problem are studied numerically using a finite difference matrix method. The growth rate γ is given as a function of the Lundquist number S, the Mach-Alfvenic number Mᴀ and the magnetic Prandtl number Pᵐ. It is found that the tearing mode is stabilized for Mᴀ<1 (when Pᵐ=1). The presence of viscosity tends to reduce the growth rates of the instability. The dependence of γ on the Hartmann number Hₐ-S/Pᵐ½ is confirmed in the case of a static equilibrium current sheetFil: Bender, Laurence Eugene. Universidad de Buenos Aires - CONICET. Instituto de Física del Plasma (INFIP). Buenos Aires. ArgentinaFil: Gratton, Fausto Tulio Livio. Universidad de Buenos Aires - CONICET. Instituto de Física del Plasma (INFIP). Buenos Aires. ArgentinaFil: Galvão, Ricardo Magnus. Universidade de San Pablo. Instituto de Física. San Pablo. Brasi
The KH stability of the supersonic magnetopause flanks modeled by continuous profiles for the transition
No full textTwo examples of stability analysis of the supersonic magnetopause (MP) flanks, based on compressible, ideal MHD theory are reported. The input parameters for local MP models are derived from spacecraft crossings data. The results emphasize the sensitivity of the Kelvin-Helmholtz instability on fine structure features of the boundary layer.Fil: Gnavi, Graciela Delia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física del Plasma. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física del Plasma; ArgentinaFil: Gratton, Fausto Tulio Livio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física del Plasma. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física del Plasma; ArgentinaFil: Farrugia, C. J.. University of New Hampshire at Manchester; Estados UnidosFil: Bilbao, Luis Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física del Plasma. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física del Plasma; Argentin
Dal Convivio alla Monarchia: quale Livio per Dante?
No full textIn questo contributo si prendono in considerazione il riferimento a Livio in Convivio
IV.v, 11 e alcuni dei riferimenti allo storico romano ritenuti maggiormente significativi nel secondo libro della Monarchia. Si dimostra che il rimando a Livio nel primo trattato è introdotto in riferimento a una ripresa probabilmente dal suo abbreviatore Floro e in apertura di un passaggio in cui si utilizza una tradizione storiografica più articolata e complessa, comprendente anche Agostino. Si propone, di conseguenza, che il rimando a Livio non si basi su una conoscenza diretta dello storico latino ma si fondi sulla sintesi realizzata da Floro. Si dimostra poi che, contrariamente all’opinione vulgata, alcuni riferimenti a Livio nella Monarchia, particolarmente quello programmatico di II.iii, 6, non sono riconducibili
in toto alla tradizione indiretta e quindi sembrerebbero suggerire che Dante avesse avuto accesso a questo autore entro la composizione del suo trattato politico.This essay focuses on Dante’s references to Livy in Convivio IV.v, 11 as well as on some particularly important references to the Roman historian in the second book of the De Monarchia. The author argues that the first reference is most likely derived from the epitome compiled by Livy’s abbreviator Florus, and shows how it is placed at the beginning of a passage that refers to several different historiographical sources, including Agustine. The author therefore suggests that this reference to Livy in the Convivio is not based on Dante’s direct knowledge of the work of the Roman historian, but rather on the information contained in the synthesis by Florus. She also challenges the scholarly consensus on this
topic by showing that some references to Livy in the De Monarchia – especially the “programmatic” one in II.iii, 6 – do not appear in the indirect tradition and can only be traced back directly to Livy. This suggests that Dante likely accessed the work of Livy before the composition of his political treatise
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