9,844 research outputs found
Design of coupled mace filters for optical pattern recognition using practical spatial light modulators
Spatial light modulators (SLMs) are being used in correlation-based optical pattern recognition systems to implement the Fourier domain filters. Currently available SLMs have certain limitations with respect to the realizability of these filters. Therefore, it is necessary to incorporate the SLM constraints in the design of the filters. The design of a SLM-constrained minimum average correlation energy (SLM-MACE) filter using the simulated annealing-based optimization technique was investigated. The SLM-MACE filter was synthesized for three different types of constraints. The performance of the filter was evaluated in terms of its recognition (discrimination) capabilities using computer simulations. The correlation plane characteristics of the SLM-MACE filter were found to be reasonably good. The SLM-MACE filter yielded far better results than the analytical MACE filter implemented on practical SLMs using the constrained magnitude technique. Further, the filter performance was evaluated in the presence of noise in the input test images. This work demonstrated the need to include the SLM constraints in the filter design. Finally, a method is suggested to reduce the computation time required for the synthesis of the SLM-MACE filter
The dynamics and optimal control of spinning spacecraft and movable telescoping appendages, part B: Effect of gravity-gradient torques on the dynamics of a spinning spacecraft with telescoping appendages
The effects of gravity gradient torques during boom deployment maneuvers of a spinning spacecraft are examined. Configurations where the booms extended only along the hub principal axes and where one or two booms are offset from the principal axes were considered. For the special case of symmetric deployment (principal axes booms) the stability boundaries are determined, and a stability chart is used to study the system behavior. Possible cases of instability during this type of maneuver are identified. In the second configuration an expression for gravity torque about the hub center of mass was developed. The nonlinear equations of motion are solved numerically, and the substantial influence of the gravity torque during asymmetric deployment maneuvers is indicated
The Brown dwarf Atmosphere Monitoring (BAM) Project I: The largest near-IR monitoring survey of L- & T-dwarfs
Using SofI on the 3.5m New Technology Telescope, we have conducted an
extensive near-infrared monitoring survey of an unbiased sample of 69 brown
dwarfs spanning the L0 and T8 spectral range, with at least one example of each
spectral type. Each target was observed for a 2-4 hour period in the Js-band,
and the median photometric precision of the data is ~0.7%. A total of 14 brown
dwarfs were identified as variables with min-to-max amplitudes ranging from
1.7% to 10.8% over the observed duration. All variables satisfy a statistical
significance threshold with a p-value <5% based on comparison with the median
reference star light curve. Approximately half of the variables show sinusoidal
amplitude variations similar to 2M2139, and the remainder shows short timescale
evolving light curves similar to SIMP0136. The L/T transition has been
suggested to be a region of a higher degree of variability if patchy clouds are
present and this survey was designed to test the patchy cloud model with
photometric monitoring of both the L/T transition and non-transition brown
dwarfs. Considering the targets identified as variable with the same
statistical threshold, the measured variability frequency of 13^{+10}_{-4}% for
the L7 -- T4 transition region is indistinguishable from that of the earlier
spectral types (32^{+11}_{-8}%), the later spectral types (13^{+10}_{-4}%), or
the combination of all non-transition region brown dwarfs (21^{+7}_{-5}%). The
variables are not concentrated at the transition, in a specific colour, or with
binaries. We note that of the systems previously monitored for variability only
~60% maintained the state of variability (variable or constant), with the
remaining switching states. The 14 variables include nine newly identified
variables that will provide important systems for follow-up multi-wavelength
monitoring to further investigate brown dwarf atmosphere physics.Comment: Accepted for publication in the Astronomy & Astrophysics. 15 pages,
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Cross-connections of the singular transformation semigroup
Cross-connection is a construction of regular semigroups using certain
categories called normal categories which are abstractions of the partially
ordered sets of principal left (right) ideals of a semigroup. We describe the
cross-connections in the semigroup of all non-invertible
transformations on a set . The categories involved are characterized as the
powerset category and the category of partitions . We
describe these categories and show how a permutation on gives rise to a
cross-connection. Further we prove that every cross-connection between them is
induced by a permutation and construct the regular semigroups that arise from
the cross-connections. We show that each of the cross-connection semigroups
arising this way is isomorphic to . We also describe the right
reductive subsemigroups of with the category of principal left ideals
isomorphic to . This study sheds light into the more general
theory of cross-connections and also provides an alternate way of studying the
structure of
D2-brane RR-charge on SU(2)
We compute RR charges of D2-branes on a background with H-field which belongs to a nontrivial cohomology class. We discover that the RR charge depends on the configuration of the background `electric' RR field. This result explains the ambiguity in the definition of the RR charge previously observed in the SU(2) WZW model
Performance Management Tool and Intelligent Classical IP and ARP over Efficient Support in ATM Networks
This article describes mathematical programming model that have been developed to evaluate configuration strategies for metropolitan ATM telecommunications networks. The model determines the optimal placement of ATM switch hardware and fiber optic transport. The objective is to specify point to point traffic demand at minimum cost while ensuring specified performance under a core failure contingency. Model result suggests that a simple architecture based on 2 core switch location provides a robust near optimal solution. Keywords: Network Design, Performance Management, Tabu Search, Passive Optical Networ
Comparative and Evaluation of Explicit Rate Flow Control in ATM Networks
Current and feature application make use of different technologies as voice, data and video. Consequently network technologies needed to support them. This paper gives the technical overflow of different networking technologies such as the internet. ATM and different approaches to run input on top of an ATM network and access their potential to be used as an integrated services network. Novel high throughput reservation based switch architecture for ATM/WDM network [4] is presented. This scheme is connection free a highly flexible yielding a powerful solution for high speed broadband packet switching networks. Keywords: Fault Tolerance, Admission Control, ATM switches
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