46,035 research outputs found
Applications of Soft Computing in Mobile and Wireless Communications
Soft computing is a synergistic combination of artificial intelligence methodologies to model and solve real world problems that are either impossible or too difficult to model mathematically. Furthermore, the use of conventional modeling techniques demands rigor, precision and certainty, which carry computational cost. On the other hand, soft computing utilizes computation, reasoning and inference to reduce computational cost by exploiting tolerance for imprecision, uncertainty, partial truth and approximation. In addition to computational cost savings, soft computing is an excellent platform for autonomic computing, owing to its roots in artificial intelligence. Wireless communication networks are associated with much uncertainty and imprecision due to a number of stochastic processes such as escalating number of access points, constantly changing propagation channels, sudden variations in network load and random mobility of users. This reality has fuelled numerous applications of soft computing techniques in mobile and wireless communications. This paper reviews various applications of the core soft computing methodologies in mobile and wireless communications
On the Relation of Hard X-ray Peak Flux and Outburst Waiting Time in the Black Hole Transient GX 339-4
Aims. In this work we re-investigated the empirical relation between the hard
X-ray peak flux and the outburst waiting time found previously in the black
hole transient GX 339-4. We tested the relation using the observed hard X-ray
peak flux of the 2007 outburst of GX 339-4, clarified issues about faint
flares, and estimated the lower limit of hard X-ray peak flux for the next
outburst. Methods. We included Swift/BAT data obtained in the past four years.
Together with the CGRO/BATSE and RXTE/HEXTE light curves, the observations used
in this work cover a period of 18 years. Results. The observation of the 2007
outburst confirms the empirical relation discovered before. This strengthens
the apparent link between the mass in the accretion disk and the peak
luminosity of the brightest hard state that the black hole transient can reach.
We also show that faint flares with peak fluxes smaller than about 0.12 crab do
not affect the empirical relation. We predict that the hard X-ray peak flux of
the next outburst should be larger than 0.65 crab, which will make it at least
the second brightest in the hard X-ray since 1991.Comment: 4 pages, 3 figures, accepted by A&
From Multiwavelength to Mass Scaling: Accretion and Ejection in Microquasars and AGN
A solid theoretical understanding of how inflowing, accreting plasma around
black holes and other compact objects gives rise to outflowing winds and jets
is still lacking, despite decades of observations. The fact that similar
processes and morphologies are observed in both X-ray binaries as well as
active galactic nuclei has led to suggestions that the underlying physics could
scale with black hole mass, which could provide a new handle on the problem. In
the last decade, simultaneous broadband campaigns of the fast-varying X-ray
binaries particularly in their microquasar state have driven the development
of, and in some cases altered, our ideas about the inflow/outflow connection in
accreting black holes. Specifically the discovery of correlations between the
radio, infrared and X-ray bands has revealed a remarkable connectivity between
the various emission regions, and argued for a more holistic approach to
tackling questions about accretion. This article reviews the recent major
observational and theoretical advances that focus specifically on the relation
between the two "sides" of the accretion process in black holes, with an
emphasis on how new tools can be derived for comparisons across the mass scale.Comment: 31 pages, 6 figures, To appear in Belloni, T. (ed.): The Jet Paradigm
- From Microquasars to Quasars, Lect. Notes Phys. 794 (2009
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