121,029 research outputs found
Sixty-GHz integrated RF head Final report
Integrated 60.8 GHz RF receiver and low noise IF preamplifier developmen
Improved high temperature resistant matrix resins
The objective was to develop organic matrix resins suitable for service at temperatures up to 644 K (700 F) and at air pressures up to 0.4 MPa (60 psia) for time durations of a minimum of 100 hours. Matrix resins capable of withstanding these extreme oxidative environmental conditions would lead to increased use of polymer matrix composites in aircraft engines and provide significant weight and cost savings. Six linear condensation, aromatic/heterocyclic polymers containing fluorinated and/or diphenyl linkages were synthesized. The thermo-oxidative stability of the resins was determined at 644 K and compressed air pressures up to 0.4 MPa. Two formulations, both containing perfluoroisopropylidene linkages in the polymer backbone structure, exhibited potential for 644 K service to meet the program objectives. Two other formulations could not be fabricated into compression molded zero defect specimens
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Integrity static analysis of COTS/SOUP
This paper describes the integrity static analysis approach developed to support the justification of commercial off-the-shelf software (COTS) used in a safety-related system. The static analysis was part of an overall software qualification programme, which also included the work reported in our paper presented at Safecomp 2002. Integrity static analysis focuses on unsafe language constructs and “covert” flows, where one thread can affect the data or control flow of another thread. The analysis addressed two main aspects: the internal integrity of the code (especially for the more critical functions), and the intra-component integrity, checking for covert channels. The analysis process was supported by an aggregation of tools, combined and engineered to support the checks done and to scale as necessary. Integrity static analysis is feasible for industrial scale software, did not require unreasonable resources and we provide data that illustrates its contribution to the software qualification programme
Experimental study of the separating confluent boundary-layer. Volume 2: Experimental data
An experimental low speed study of the separating confluent boundary layer on a NASA GAW-1 high lift airfoil is described. The airfoil was tested in a variety of high lift configurations comprised of leading edge slat and trailing edge flap combinations. The primary test instrumentation was a two dimensional laser velocimeter (LV) system operating in a backscatter mode. Surface pressures and corresponding LV derived boundary layer profiles are given in terms of velocity components, turbulence intensities and Reynolds shear stresses as characterizing confluent boundary layer behavior up to and beyond stall. LV derived profiles and associated boundary layer parameters and those obtained from more conventional instrumentation such as pitot static transverse, Preston tube measurements and hot-wire surveys are compared
Field theoretic calculation of the surface tension for a model electrolyte system
We carry out the calculation of the surface tension for a model electrolyte
to first order in a cumulant expansion about a free field theory equivalent to
the Debye-H\"uckel approximation. In contrast with previous calculations, the
surface tension is calculated directly without recourse to integrating
thermodynamic relations. The system considered is a monovalent electrolyte with
a region at the interface, of width h, from which the ionic species are
excluded. In the case where the external dielectric constant epsilon_0 is
smaller than the electrolyte solution's dielectric constant epsilon we show
that the calculation at this order can be fully regularized. In the case where
h is taken to be zero the Onsager-Samaras limiting law for the excess surface
tension of dilute electrolyte solutions is recovered, with corrections coming
from a non-zero value of epsilon_0/epsilon.Comment: LaTeX, 14 pages, 3 figures, 1 tabl
Using a fuzzy inference system to control a pumped storage hydro plant
The paper discusses the development of a fuzzy inference system (FIS) based governor control for a pumped storage hydroelectric plant. The First Hydro Company's plant at Dinorwig in North Wales is the largest of its kind in Europe and is mainly used for frequency control of the UK electrical grid. In previous investigations, a detailed model of the plant was developed using MATLAB(R)/SIMULINK(R) and this is now being used to compare FIS governor operation with the proportional-integral-derivative (PID) controller currently used. The paper describes the development of an FIS governor, and shows that its response to a step increase in load is superior to the PID under certain conditions of load. The paper proceeds to discuss the implications of these results in view of the possible practical application of an FIS governor at the Dinorwig plant
The colour-magnitude relations of ClJ1226.9+3332, a massive cluster of galaxies at z=0.89
(Abridged) The colour-magnitude relations of one of the most massive, high
redshift clusters of galaxies known have been studied. Photometry has been
measured in the V, R, I, z, F606W, F814W, J and K bands to a depth of K*+2.5
and spectroscopy confirms 27 K band selected cluster members. The V-K colours
are equivalent to a rest-frame colour of ~2700A-J, and provide a very sensitive
measure of star-formation activity. HST ACS imaging has been used to
morphologically classify the galaxies.
The cluster has a low early-type fraction compared to nearby clusters, with
only 33% of the cluster members having types E or S0. The early-type member
galaxies form a clear red-sequence in all colours. The scatter and slope of the
relations show no evolution compared to the equivalent Coma cluster relations,
suggesting the stellar populations are already very old. The normalisation of
the relations has been compared to models based on synthetic stellar
populations, and are most consistent with stellar populations forming at z>3.
Some late-type galaxies were found to lie on the red-sequence, suggesting that
they have very similar stellar populations to the early-types.
These results present a picture of a cluster in which the early-type galaxies
are all old, but in which there must be future morphological transformation of
galaxies to match the early-type fraction of nearby clusters. In order to
preserve the tight colour-magnitude relation of early-types seen in nearby
clusters, the late-type galaxies must transform their colours, through the
cessation of star-formation, before the morphological transformation occurs.
Such evolution is observed in the late-types lying on the colour-magnitude
relation.Comment: Accepted for publication in MNRAS. 14 pages, 5 figure
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