1,677 research outputs found
A white dwarf-neutron star relativistic binary model for soft gamma-ray repeaters
A scenario for SGRs is introduced in which gravitational radiation reaction
effects drive the dynamics of an ultrashort orbital period X-ray binary
embracing a high-mass donor white dwarf (WD) to a rapidly rotating low
magnetised massive neutron star (NS) surrounded by a thick, dense and massive
accretion torus. Driven by GR reaction, sparsely, the binary separation
reduces, the WD overflows its Roche lobe and the mass transfer drives unstable
the accretion disk around the NS. As the binary circular orbital period is a
multiple integer number () of the period of the WD fundamental mode (Pons et
al. 2002), the WD is since long pulsating at its fundamental mode; and most of
its harmonics, due to the tidal interaction with its NS orbital companion.
Hence, when the powerful irradiation glows onto the WD; from the fireball
ejected as part of the disk matter slumps onto the NS, it is partially
absorbed. This huge energy excites other WD radial (-mode) pulsations
(Podsiadlowski 1991,1995). After each mass-transfer episode the binary
separation (and orbital period) is augmented significantly (Deloye & Bildsten
2003; Al\'ecyan & Morsink 2004) due to the binary's angular momentum
redistribution. Thus a new adiabatic inspiral phase driven by GR reaction
starts which brings the binary close again, and the process repeats. This model
allows to explain most of SGRs observational features: their recurrent
activity, energetics of giant superoutbursts and quiescent stages, and
particularly the intriguing subpulses discovered by BeppoSAX (Feroci et al.
1999), which are suggested here to be {\it overtones} of the WD radial
fundamental mode (see the accompanying paper: Mosquera Cuesta 2004b).Comment: This paper was submitted as a "Letter to the Editor" of MNRAS in July
17/2004. Since that time no answer or referee report was provided to the
Author [MNRAS publication policy limits reviewal process no longer than one
month (+/- half more) for the reviewal of this kind of submission). I hope
this contribution is not receiving a similar "peer-reviewing" as given to the
A. Dar and A. De Rujula's "Cannonball model for gamma-ray bursts", or to the
R.K. Williams' "Penrose process for energy extraction from rotating black
holes". The author welcomes criticisms and suggestions on this pape
Is space necessary? Interference competition and limits to biodiversity
Journal ArticleA single trade-off between competitive ability and mortality has been shown to support an arbitrarily large number of species in models of interference competition in spatially structured populations. We show that this results not from spatial structure, but instead from the assumption that a small difference in mortality translates into a large difference in competitive ability. We present graphical criteria for recognizing functions that support one, two, or more species. High levels of coexistence in models of this form depend on a steep slope or a discontinuous second derivative of the function relating mortality to competitiveness. These criteria are identical to those in models of interference competition that lack explicit spatial structure
Hubble Diagram of Gamma-Rays Bursts calibrated with Gurzadyan-Xue Cosmology
Gamma-ray bursts (GRBs) being the most luminous among known cosmic objects
carry an essential potential for cosmological studies if properly used as
standard candles. In this paper we test with GRBs the cosmological predictions
of the Gurzadyan-Xue (GX) model of dark energy, a novel theory that predicts,
without any free parameters, the current vacuum fluctuation energy density
close to the value inferred from the SNIa observations. We also compare the GX
results with those predicted by the concordance scenario -CDM.
According to the statistical approach by Schaefer (2007), the use of several
empirical relations obtained from GRBs observables, after a consistent
calibration for a specific model, enables one to probe current cosmological
models. Based on this recently introduced method, we use the 69 GRBs sample
collected by Schaefer (2007); and the most recently released SWIFT satellite
data (Sakamoto et al. 2007) together with the 41 GRBs sample collected by
Rizzuto et al. (2007), which has the more firmly determined redshifts. Both
data samples span a distance scale up to redshift about 7. We show that the GX
models are compatible with the Hubble diagram of the Schaefer (2007) 69 GRBs
sample. Such adjustment is almost identical to the one for the concordance
-CDM.Comment: 9 pages, 17 figures, 11 tables; Astr. & Astrophys. (in press
Super- and coinfection: filling the range
Journal ArticleHow many different strains of a disease can coexist in a single population of hosts? What effect do different mechanisms of coexistence have on the properties of diseases? The principle of competitive exclusion (Armstrong and McGehee 1980; Levin 1970) states that no more species can coexist in a system than the number of resources or limiting factors allow, which can be thought of, somewhat imprecisely, as stating that a single trade-off can support only a single species - the one that deals best with that trade-off
Removing black-hole singularities with nonlinear electrodynamics
We propose a way to remove black hole singularities by using a particular
nonlinear electrodynamics Lagrangian that has been recently used in various
astrophysics and cosmological frameworks. In particular, we adapt the
cosmological analysis discussed in a previous work to the black hole physics.
Such analysis will be improved by applying the Oppenheimer-Volkoff equation to
the black hole case. At the end, fixed the radius of the star, the final
density depends only on the introduced quintessential density term
and on the mass.Comment: In this last updated version we correct two typos which were present
in Eqs. (21) and (22) in the version of this letter which has been published
in Mod. Phys. Lett. A 25, 2423-2429 (2010). In the present version, both of
Eqs. (21) and (22) are dimensionally and analytically correc
Agronomic Characterisation of Sewage Sludge: Residual Effects
The progressive implementation of the EU Urban Waste Water Treatment Directive 91/271/EEC is increasing the quantities of sewage sludge requiring disposal. Agronomic use of sewage sludge should be based on crop fertiliser requirements and heavy metals content. Sewage sludge fertiliser potential depends on the stabilisation treatments of sewage sludge: composting, anaerobic digestion, aerobic digestion or pelleting (EPA, 1994). The objective of this experiment was to evaluate the fertiliser effectiveness and residual effects of three types of sewage sludge treated in three different ways
Homology of precrossed modules
[EN] We prove that the category of precrossed modules is an algebraic category, and we develop a cotriple (co)homology theory for precrossed modules which generalizes the Eilenberg-MacLane theory of (co)homology groups. We study the relationship of this theory with the (co)homology of crossed modules.SIMinisterio de Ciencia y TecnologíaXunta de Galici
La elipse y sus relaciones geométricas con las esferas de dandelin en el ambiente de geometría dinámica Cabri 3D
En este cursillo se presenta el uso del Ambiente de Geometría Dinámica (AGD), Cabri 3D, para realizar construcciones geométricas en tres dimensiones, en particular, se estudiará las propiedades geométricas de la elipse, con el fin de brindar una herramienta que permita visualizar la naturaleza de esta cónica en el espacio y de esta manera se logre comprender las propiedades geométricas y métricas de esta curva geométrica en un espacio tridimensional, utilizando las características de tangencia de una superficie cónica con esferas inscritas y con su plano de corte, denominadas Esferas de Dandelin. La intención de este cursillo, es incentivar un cambio tanto en la enseñanza como en el aprendizaje de la geometría espacial, en particular, en el estudio de la elipse, empleando las Esferas de Dandelin como una alternativa de tratamiento de esta cónica, y de esta manera evitar una enseñanza tradicionalista mediante definiciones que tal vez no se logren interiorizar por parte de los estudiantes (Ruiz, 1996)
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