3,389 research outputs found
Fixed parameter tractability of crossing minimization of almost-trees
We investigate exact crossing minimization for graphs that differ from trees
by a small number of additional edges, for several variants of the crossing
minimization problem. In particular, we provide fixed parameter tractable
algorithms for the 1-page book crossing number, the 2-page book crossing
number, and the minimum number of crossed edges in 1-page and 2-page book
drawings.Comment: Graph Drawing 201
Criminal neighbourhoods: does the density of prior offenders encourage others to commit crime?
Using crime data over a period of a decade for Glasgow, this paper explores whether the
density of prior offenders in a neighbourhoods has an influence on the propensity of others to
(re)commence offending. The study shows that the number of ânewly activeâ offenders in a
neighbourhood in the current quarter is positively associated with the density of prior
offenders for both violent and property crime from the previous two years. In the case of
ânewly activeâ property offenders, the relationship with active prior offenders is only
apparent when prior offender counts exceed the median. The paper postulates that intraneighbourhood
social mechanisms may be at work to create these effects. The results suggest
that policies which concentrate offenders in particular neighbourhoods may increase the
number of ânewly activeâ offenders, and point to evidence of a threshold at which these
effects take place
Problems related to the integration of fault tolerant aircraft electronic systems
Problems related to the design of the hardware for an integrated aircraft electronic system are considered. Taxonomies of concurrent systems are reviewed and a new taxonomy is proposed. An informal methodology intended to identify feasible regions of the taxonomic design space is described. Specific tools are recommended for use in the methodology. Based on the methodology, a preliminary strawman integrated fault tolerant aircraft electronic system is proposed. Next, problems related to the programming and control of inegrated aircraft electronic systems are discussed. Issues of system resource management, including the scheduling and allocation of real time periodic tasks in a multiprocessor environment, are treated in detail. The role of software design in integrated fault tolerant aircraft electronic systems is discussed. Conclusions and recommendations for further work are included
Acoustic scattering by impedance screens/cracks with fractal boundary: well-posedness analysis and boundary element approximation
We study time-harmonic scattering in () by a planar
screen (a "crack" in the context of linear elasticity), assumed to be a
non-empty bounded relatively open subset of the hyperplane
, on which impedance (Robin) boundary conditions
are imposed. In contrast to previous studies, can have arbitrarily
rough (possibly fractal) boundary. To obtain well-posedness for such
we show how the standard impedance boundary value problem and its associated
system of boundary integral equations must be supplemented with additional
solution regularity conditions, which hold automatically when
is smooth. We show that the associated system of boundary integral operators is
compactly perturbed coercive in an appropriate function space setting,
strengthening previous results. This permits the use of Mosco convergence to
prove convergence of boundary element approximations on smoother "prefractal"
screens to the limiting solution on a fractal screen. We present accompanying
numerical results, validating our theoretical convergence results, for
three-dimensional scattering by a Koch snowflake and a square snowflake
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Ensemble prediction for nowcasting with a convection-permitting model - II: forecast error statistics
A 24-member ensemble of 1-h high-resolution forecasts over the Southern United Kingdom is used to study short-range forecast error statistics. The initial conditions are found from perturbations from an ensemble transform Kalman filter. Forecasts from this system are assumed to lie within the bounds of forecast error of an operational forecast system. Although noisy, this system is capable of producing physically reasonable statistics which are analysed and compared to statistics implied from a variational assimilation system. The variances for temperature errors for instance show structures that reflect convective activity. Some variables, notably potential temperature and specific humidity perturbations, have autocorrelation functions that deviate from 3-D isotropy at the convective-scale (horizontal scales less than 10 km). Other variables, notably the velocity potential for horizontal divergence perturbations, maintain 3-D isotropy at all scales. Geostrophic and hydrostatic balances are studied by examining correlations between terms in the divergence and vertical momentum equations respectively. Both balances are found to decay as the horizontal scale decreases. It is estimated that geostrophic balance becomes less important at scales smaller than 75 km, and hydrostatic balance becomes less important at scales smaller than 35 km, although more work is required to validate these findings. The implications of these results for high-resolution data assimilation are discussed
Fast track children's hearing pilot: final report of the evaluation of the pilot
This report presents key findings of the evaluation of the Fast Track childrenâs hearings pilot in Scotland1. The research was undertaken by staff at the Universities of Glasgow, Stirling and Strathclyde between February 2003 and January 2005
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