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An Approach to Using Non Safety-Assured Programmable Components in Modest Integrity Systems
Programmable components (like personal computers or smart devices) can offer considerable benefits in terms of usability and functionality in a safety-related system. However there is a problem in justifying the use of programmable components if the components have not been safety justified to an appropriate integrity (e.g. to SIL 1 of IEC 61508). This paper outlines an approach (called LowSIL) developed in the UK CINIF nuclear industry research programme to justify the use of non safety-assured programmable components in modest integrity systems. This is a seven step approach that can be applied to new systems from an early design stage, or retrospectively to existing systems. The stages comprise: system characterisation, component suitability assessment, failure analysis, failure mitigation, identification of additional defences, identification of safety evidence requirements, and collation and evaluation of evidence. In the case of personal computers, there is supporting guidance on usage constraints, claim limits on reliability, and advice on “locking down” the component to maximise reliability. The approach is demonstrated for an example system. The approach has been applied successfully to a range of safety-related systems used in the nuclear industry
Chemoinformatics Research at the University of Sheffield: A History and Citation Analysis
This paper reviews the work of the Chemoinformatics Research Group in the Department of Information Studies at the University of Sheffield, focusing particularly on the work carried out in the period 1985-2002. Four major research areas are discussed, these involving the development of methods for: substructure searching in databases of three-dimensional structures, including both rigid and flexible molecules; the representation and searching of the Markush structures that occur in chemical patents; similarity searching in databases of both two-dimensional and three-dimensional structures; and compound selection and the design of combinatorial libraries. An analysis of citations to 321 publications from the Group shows that it attracted a total of 3725 residual citations during the period 1980-2002. These citations appeared in 411 different journals, and involved 910 different citing organizations from 54 different countries, thus demonstrating the widespread impact of the Group's work
Gravitational waveforms with controlled accuracy
A partially first-order form of the characteristic formulation is introduced
to control the accuracy in the computation of gravitational waveforms produced
by highly distorted single black hole spacetimes. Our approach is to reduce the
system of equations to first-order differential form on the angular
derivatives, while retaining the proven radial and time integration schemes of
the standard characteristic formulation. This results in significantly improved
accuracy over the standard mixed-order approach in the extremely nonlinear
post-merger regime of binary black hole collisions.Comment: Revised version, published in Phys. Rev. D, RevTeX, 16 pages, 4
figure
Linearized solutions of the Einstein equations within a Bondi-Sachs framework, and implications for boundary conditions in numerical simulations
We linearize the Einstein equations when the metric is Bondi-Sachs, when the
background is Schwarzschild or Minkowski, and when there is a matter source in
the form of a thin shell whose density varies with time and angular position.
By performing an eigenfunction decomposition, we reduce the problem to a system
of linear ordinary differential equations which we are able to solve. The
solutions are relevant to the characteristic formulation of numerical
relativity: (a) as exact solutions against which computations of gravitational
radiation can be compared; and (b) in formulating boundary conditions on the
Schwarzschild horizon.Comment: Revised following referee comment
Valley polarization and susceptibility of composite fermions around nu=3/2
We report magnetotransport measurements of fractional quantum Hall states in
an AlAs quantum well around Landau level filling factor nu = 3/2, demonstrating
that the quasiparticles are composite Fermions (CFs) with a valley degree of
freedom. By monitoring the valley level crossings for these states as a
function of applied symmetry-breaking strain, we determine the CF valley
susceptibility and polarization. The data can be explained well by a simple
Landau level fan diagram for CFs, and are in nearly quantitative agreement with
the results reported for CF spin polarization.Comment: to appear in Phys. Rev. Let
Observation of Quantum Hall Valley Skyrmions
We report measurements of the interaction-induced quantum Hall effect in a
spin-polarized AlAs two-dimensional electron system where the electrons occupy
two in-plane conduction band valleys. Via the application of in-plane strain,
we tune the energies of these valleys and measure the energy gap of the quantum
Hall state at filling factor = 1. The gap has a finite value even at zero
strain and, with strain, rises much faster than expected from a single-particle
picture, suggesting that the lowest energy charged excitations at are
"valley Skyrmions".Comment: 4 pages, 3 figure
Electronic polarons in an extended Falicov-Kimball model
We examine the one-dimensional spinless Falicov-Kimball model extended by a
hybridization potential between the localized and itinerant electron states.
Below half-filling we find a crossover from a mixed-valence metal to an
integer-valence phase separated state with increasing on-site Coulomb
repulsion. This crossover regime is characterized by local competition between
the strong- and weak-coupling behaviour, manifested by the formation of an
electronic polaron liquid. We identify this intermediate-coupling regime as a
charge-analogy of the Griffiths phase; a phase diagram is presented and
discussed in detail.Comment: RevTex, 10 pages, 1 figure; revised discussio
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