5,812 research outputs found
A tutorial on the CARE III approach to reliability modeling
The CARE 3 reliability model for aircraft avionics and control systems is described by utilizing a number of examples which frequently use state-of-the-art mathematical modeling techniques as a basis for their exposition. Behavioral decomposition followed by aggregration were used in an attempt to deal with reliability models with a large number of states. A comprehensive set of models of the fault-handling processes in a typical fault-tolerant system was used. These models were semi-Markov in nature, thus removing the usual restrictions of exponential holding times within the coverage model. The aggregate model is a non-homogeneous Markov chain, thus allowing the times to failure to posses Weibull-like distributions. Because of the departures from traditional models, the solution method employed is that of Kolmogorov integral equations, which are evaluated numerically
Validation Methods Research for Fault-Tolerant Avionics and Control Systems Sub-Working Group Meeting. CARE 3 peer review
A computer aided reliability estimation procedure (CARE 3), developed to model the behavior of ultrareliable systems required by flight-critical avionics and control systems, is evaluated. The mathematical models, numerical method, and fault-tolerant architecture modeling requirements are examined, and the testing and characterization procedures are discussed. Recommendations aimed at enhancing CARE 3 are presented; in particular, the need for a better exposition of the method and the user interface is emphasized
Duality Symmetry and the Cardy Limit
We study supersymmetric and non-supersymmetric extremal black holes obtained
in Type IIA string theory compactified on K3 X T^2, with duality group
O(6,22,Z) X SL(2,Z). In the Cardy limit an internal circle combines with the
AdS_2 component in the near horizon geometry to give a BTZ black hole whose
entropy is given by the Cardy formula. We study black holes carrying D0-D4 and
D0-D6 brane charges. We find, both in the supersymmetric and non-supersymmetric
cases, that a generic set of charges cannot be brought to the Cardy limit using
the duality symmetries. In the non-supersymmetric case, unlike the
supersymmetric one, we find that when the charges are large, a small fractional
change in them always allows the charges to be taken to the Cardy limit. These
results could lead to a microscopic determination of the entropy for extremal
non-supersymmetric black holes, including rotating cases like the extreme Kerr
black hole in four dimensions.Comment: 46 pages, Latex, Some comments added in Introduction and Conclusions.
Minor changes made in sections 3.4 and
Facile preparation of agarose-chitosan hybrid materials and nanocomposite ionogels using an ionic liquid via dissolution, regeneration and sol-gel transition
We report simultaneous dissolution of agarose (AG) and chitosan (CH) in
varying proportions in an ionic liquid (IL), 1-butyl-3-methylimidazolium
chloride [C4mim][Cl]. Composite materials were constructed from AG-CH-IL
solutions using the antisolvent methanol, and IL was recovered from the
solutions. Composite materials could be uniformly decorated with silver oxide
(Ag2O) nanoparticles (Ag NPs) to form nanocomposites in a single step by in
situ synthesis of Ag NPs in AG-CH-IL sols, wherein the biopolymer moiety acted
as both reducing and stabilizing agent. Cooling of Ag NPs-AG-CH-IL sols to room
temperature resulted in high conductivity and high mechanical strength
nanocomposite ionogels. The structure, stability and physiochemical properties
of composite materials and nanocomposites were characterized by several
analytical techniques, such as Fourier transform infrared (FTIR), CD
spectroscopy, differential scanning colorimetric (DSC), thermogravimetric
analysis (TGA), gel permeation chromatography (GPC), and scanning electron
micrography (SEM). The result shows that composite materials have good thermal
and conformational stability, compatibility and strong hydrogen bonding
interactions between AG-CH complexes. Decoration of Ag NPs in composites and
ionogels was confirmed by UV-Vis spectroscopy, SEM, TEM, EDAX and XRD. The
mechanical and conducting properties of composite ionogels have been
characterized by rheology and current-voltage measurements. Since Ag NPs show
good antimicrobial activity, Ag NPs -AG-CH composite materials have the
potential to be used in biotechnology and biomedical applications whereas
nanocomposite ionogels will be suitable as precursors for applications such as
quasi-solid dye sensitized solar cells, actuators, sensors or electrochromic
displays
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