14,037 research outputs found
Computer architecture for efficient algorithmic executions in real-time systems: New technology for avionics systems and advanced space vehicles
Improvements and advances in the development of computer architecture now provide innovative technology for the recasting of traditional sequential solutions into high-performance, low-cost, parallel system to increase system performance. Research conducted in development of specialized computer architecture for the algorithmic execution of an avionics system, guidance and control problem in real time is described. A comprehensive treatment of both the hardware and software structures of a customized computer which performs real-time computation of guidance commands with updated estimates of target motion and time-to-go is presented. An optimal, real-time allocation algorithm was developed which maps the algorithmic tasks onto the processing elements. This allocation is based on the critical path analysis. The final stage is the design and development of the hardware structures suitable for the efficient execution of the allocated task graph. The processing element is designed for rapid execution of the allocated tasks. Fault tolerance is a key feature of the overall architecture. Parallel numerical integration techniques, tasks definitions, and allocation algorithms are discussed. The parallel implementation is analytically verified and the experimental results are presented. The design of the data-driven computer architecture, customized for the execution of the particular algorithm, is discussed
Interacting spinor and scalar fields in Bianchi type-I Universe filled with viscous fluid: exact and numerical solutions
We consider a self-consistent system of spinor and scalar fields within the
framework of a Bianchi type I gravitational field filled with viscous fluid in
presence of a term. Exact self-consistent solutions to the
corresponding spinor, scalar and BI gravitational field equations are obtained
in terms of , where is the volume scale of BI universe. System of
equations for and \ve, where \ve is the energy of the viscous fluid,
is deduced. Some special cases allowing exact solutions are thoroughly studied.Comment: 18 pages, 6 figure
Effects of the annual closure of the queen conch (Strombus gigas) fishery in Guadeloupe (FWI)
Scalar field in cosmology: Potential for isotropization and inflation
The important role of scalar field in cosmology was noticed by a number of
authors. Due to the fact that the scalar field possesses zero spin, it was
basically considered in isotropic cosmological models. If considered in an
anisotropic model, the linear scalar field does not lead to isotropization of
expansion process. One needs to introduce scalar field with nonlinear potential
for the isotropization process to take place. In this paper the general form of
scalar field potentials leading to the asymptotic isotropization in case of
Bianchi type-I cosmological model, and inflationary regime in case of isotropic
space-time is obtained. In doing so we solved both direct and inverse problem,
where by direct problem we mean to find metric functions and scalar field for
the given potential, whereas, the inverse problem means to find the potential
and scalar field for the given metric function. The scalar field potentials
leading to the inflation and isotropization were found both for harmonic and
proper synchronic time.Comment: 10 page
Generalised Couch-Torrence Symmetry for Rotating Extremal Black Holes in Maximal Supergravity
The extremal Reissner-Nordstr\"om black hole admits a conformal inversion
symmetry, in which the metric is mapped into itself under an inversion of the
radial coordinate combined with a conformal rescaling. In the rotating
generalisation, Couch and Torrence showed that the Kerr-Newman metric no longer
exhibits a conformal inversion symmetry, but the radial equation arising in the
separation of the massless Klein-Gordon equation admits a mode-dependent
inversion symmetry, where the radius of inversion depends upon the energy and
azimuthal angular momentum of the mode. It was more recently shown that the
static 4-charge extremal black holes of STU supergravity admit a generalisation
of the conformal inversion symmetry, in which the conformally-inverted metric
is a member of the same 4-charge black hole family but with transformed
charges. In this paper we study further generalisations of these inversion
symmetries, within the general class of extremal STU supergravity black holes.
For the rotating black holes, where again the massless Klein-Gordon equation is
separable, we show that examples with four electric charges exhibit a
generalisation of the Couch-Torrence symmetry of the radial equation. Now, as
in the conformal inversion of the static specialisations, the inversion of the
radial equation maps it to the radial equation for a rotating black hole with
transformed electric charges. We also study the inversion transformations for
the general case of extremal BPS STU black holes carrying eight charges (4
electric plus 4 magnetic), and argue that analogous generalisations of the
inversion symmetries exist both for the static and the rotating cases.Comment: 32 page
Temporal dynamics of sucking pest and field response of promising insecticidal molecules in okra
To investigate the response due to application of newer insecticide on sucking pest in okra, a trial was designed at field level for three consecutive years from 2011-12 to 2013-14 in kharif season. Moreover, impacts of applied insecticides on natural enemies were also assessed. Based on experimental finding thiamethoxam 25WG 0.003% (2.83 per 3 leaves, 0.93 per 3 leaves), imidacloprid 70WG 0.004% (3.49 per 3 leaves, 1.30 per 3 leaves) and thiacloprid 21.7 SC 0.006% (4.28 per 3 leaves, 1.75 per 3 leaves) provided superior control of leafhoppers and whiteflies population on okra. Effectiveness of these treatments was reflected in terms of reduction in population of both insects and significantly increases (thiamethoxam: 95.50 q/ha, imidacloprid: 86.96 q/ha and thiacloprid: 80.99 q/ha) the fruit yield in comparison to others. However, the incidence of Yellow Vein Mosaic disease was recorded least in thiamethoxam 0.003% sprayed plots followed by imidacloprid 0.004%. Slow progress in the population ofwhitefly and leaf hopper was recorded in thiamethoxam 0.003% applied plots. There was positive correlation between whitefly and virus incidence in conducted field trial. Under the experiment, neonicotinoids group of insecticides have not adverse effect on natural enemies in okra crop. The information generated under the study can be incorporated in management modules in crop okra without disturbing the ecology of natural enemy and cropping system. In our findings, the quantitative data of temporal increment of whiteflies and mosaic disease will be helpful in understanding or formulating of epidemiological models
A first principles investigation of cubic BaRuO: A Hund's metal
A first-principles investigation of cubic-BaRuO, by combining density
functional theory with dynamical mean-field theory and a hybridization
expansion continuous time quantum Monte-Carlo solver, has been carried out.
Non-magnetic calculations with appropriately chosen on-site Coulomb repulsion,
and Hund's exchange, , for single-particle dynamics and static
susceptibility show that cubic-BaRuO is in a spin-frozen state at
temperatures above the ferromagnetic transition point. A strong red shift with
increasing of the peak in the real frequency dynamical susceptibility
indicates a dramatic suppression of the Fermi liquid coherence scale as
compared to the bare parameters in cubic-BaRuO. The self-energy also shows
clear deviation from Fermi liquid behaviour that manifests in the
single-particle spectrum. Such a clean separation of energy scales in this
system provides scope for an incoherent spin-frozen (SF) phase, that extends
over a wide temperature range, to manifest in non-Fermi liquid behaviour and to
be the precursor for the magnetically ordered ground state.Comment: 10 pages, 12 figures, 1 tabl
Photometric Recovery of Crowded Stellar Fields Observed with HST/WFPC2 and the Effects of Confusion Noise on the Extragalactic Distance Scale
We explore the limits of photometric reductions of crowded stellar fields
observed with the Wide Field and Planetary Camera 2 on board the Hubble Space
Telescope. Two photometric procedures, based on the DoPHOT and DAOPHOT/ALLFRAME
programs are tested, and the effects of crowding, complex sky background and
cosmic-ray contamination are discussed using an extensive set of artificial
star simulations. As a specific application of the results presented in this
paper, we assess the magnitude of photometric biases on programs aimed at
finding Cepheids and determining distances. We find that while the photometry
in individual images can be biased too bright by up to 0.2 mag in the most
crowded fields due to confusion noise, the effects on distance measurements
based on Cepheid variables are insignificant, less than 0.02 mag (1% in
distance) even in the most problematic cases. This result, which is at odds
with claims recently surfaced in the literature, is due to the strict criteria
applied in the selection of the variable stars, and the photometric cross
checks made possible by the availability of multiple exposures in different
filters which characterizes Cepheid observations.Comment: Accepted for publication in PASP. 41 pages, 18 figures, 8 tables. The
figures included with this submission are very low quality bitmap postscript,
please see http://www.astro.ucla.edu/~laura/pub.htm for the full size image
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