6,806 research outputs found
Time properties of the the rho-class burst of the microquasar GRS 1915+105 observed with BeppoSAX in April 1999
We present a temporal analysis of a BeppoSAX observation of GRS 1915+105
performed on April 13, 1999 when the source was in the rho class, which is
characterised by quasi-regular bursting activity. The aim of the present work
is to confirm and extend the validity of the results obtained with a BeppoSAX
observation performed on October 2000 on the recurrence time of the burst and
on the hard X-ray delay. We divided the entire data set into several series,
each corresponding to a satellite orbit, and performed the Fourier and wavelet
analysis and the limit cycle mapping technique using the count rate and the
average energy as independent variables. We found that the count rates
correlate with the recurrence time of bursts and with hard X-ray delay,
confirming the results previously obtained. In this observation, however, the
recurrence times are distributed along two parallel branches with a constant
difference of 5.2+/-0.5 s.Comment: Accepted for publication in Section 7. Stellar structure and
evolution of Astronomy and Astrophysic
Optical radiation background from K decays in undersea neutrino telescopes
The photon flux produced by light sources uniformly distributed in an infinite homogeneous medium is calculated on the basis of a known property of light propagation, taking into account the contribution of both absorption and scattering processes. The results are applied to the issue of the decays of K content in sea salt and then to the rates detected by photomultipliers deployed in the deep sea. Numerical calculations are in agreement with the recent measurements performed in the Mediterranean Sea by the ANTARES and NEMO Collaborations
Lyapunov functions for a non-linear model of the X-ray bursting of the microquasar GRS 1915+105
This paper introduces a biparametric family of Lyapunov functions for a
non-linear mathematical model based on the FitzHugh-Nagumo equations able to
reproduce some main features of the X-ray bursting behaviour exhibited by the
microquasar GRS 1915+105. These functions are useful to investigate the
properties of equilibrium points and allow us to demonstrate a theorem on the
global stability. The transition between bursting and stable behaviour is also
analyzed.Comment: Published on International Journal of Non-Linear Mechanics, vol. 88,
pp. 142-14
Optical background measurement in a potential site for the NEMO KM undersea neutrino telescope
We describe the measurement of the deep sea optical background in some sites south of Capo Passero, Sicily. A continuous flux of about 440 photons cm -2 s -1 in the wavelength interval 440-550 nm is estimated due to the decays of the 40K contained in the sea water. Bioluminescence light bursts are also observed and an example of time evolution is reported. All the measurements were accomplished using a deep sea module also described in this article
The complex time behaviour of the microquasar GRS 1915+105 in the \rho-class observed with BeppoSAX. III: The hard X-ray delay and limit cycle mapping
The microquasar GRS1915+105 was observed by BeppoSAX in October 2000 for
about ten days while the source was in \rho-mode, which is characterized by a
quasi-regular type I bursting activity. This paper presents a systematic
analysis of the delay of the hard and soft X-ray emission at the burst peaks.
The lag, also apparent from the comparison of the [1.7-3.4] keV light curves
with those in the [6.8-10.2] keV range, is evaluated and studied as a function
of time, spectral parameters, and flux. We apply the limit cycle mapping
technique, using as independent variables the count rate and the mean photon
rate. The results using this technique were also cross-checked using a more
standard approach with the cross-correlation methods. Data are organized in
runs, each relative to a continuous observation interval. The detected
hard-soft delay changes in the course of the pointing from about 3 s to about
10 s and presents a clear correlation with the baseline count rate.Comment: accepted for publication in A&
Semi-Teleparallel Theories of Gravitation
A class of theories of gravitation that naturally incorporates preferred
frames of reference is presented. The underlying space-time geometry consists
of a partial parallelization of space-time and has properties of Riemann-Cartan
as well as teleparallel geometry. Within this geometry, the kinematic
quantities of preferred frames are associated with torsion fields. Using a
variational method, it is shown in which way action functionals for this
geometry can be constructed. For a special action the field equations are
derived and the coupling to spinor fields is discussed.Comment: 14 pages, LaTe
La formació històrica per a l’ensenyament de les matemà tiques
L’ensenyament i aprenentatge de la història de les matemà tiques pot millorar la formació integral de l’alumnat. Els contextos històrics en les matemà tiques transmeten als alumnes una percepció de la matemà tica com a ciència útil, dinà mica, humana, interdisciplinà ria i heurÃstica. En aquesta comunicació mostrarem a través de la programació d’un curs d’història de la ciència els objectius que cal assolir. La formació del professorat ha de contemplar que aquest conegui les fonts en què es basa el coneixement del passat, reconegui els canvis més significatius de la disciplina de Matemà tiques i reflexionin sobre el desenvolupament del pensament matemà tic i les transformacions de la filosofia natural. Finalment, cal
assenyalar en aquesta formació la importà ncia de les relacions socioculturals de les matemà tiques
Determination of Wave Function Functionals: The Constrained-Search--Variational Method
In a recent paper [Phys. Rev. Lett. \textbf{93}, 130401 (2004)], we proposed
the idea of expanding the space of variations in variational calculations of
the energy by considering the approximate wave function to be a
functional of functions rather than a function. The
space of variations is expanded because a search over the functions can
in principle lead to the true wave function. As the space of such variations is
large, we proposed the constrained-search-- variational method whereby a
constrained search is first performed over all functions such that the
wave function functional satisfies a physical constraint such as
normalization or the Fermi-Coulomb hole sum rule, or leads to the known value
of an observable such as the diamagnetic susceptibility, nuclear magnetic
constant or Fermi contact term. A rigorous upper bound to the energy is then
obtained by application of the variational principle. A key attribute of the
method is that the wave function functional is accurate throughout space, in
contrast to the standard variational method for which the wave function is
accurate only in those regions of space contributing principally to the energy.
In this paper we generalize the equations of the method to the determination of
arbitrary Hermitian single-particle operators as applied to two-electron atomic
and ionic systems. The description is general and applicable to both ground and
excited states. A discussion on excited states in conjunction with the theorem
of Theophilou is provided.Comment: 26 pages, 4 figures, 5 table
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