14,700 research outputs found
The imperial war museum’s social interpretation project
This report represents the output from research undertaken by University of Salford and MTM
London as part of the joint Digital R&D Fund for Arts and Culture, operated by Nesta, Arts
Council England and the AHRC. University of Salford and MTM London received funding from
the programme to act as researchers on the Social Interpretation (SI) project, which was led by
the Imperial War Museum (IWM) and their technical partners, The Centre for Digital
Humanities, University College London, Knowledge Integration, and Gooii. The project was
carried out between October 2011 and October 2012
Pseudo-Separation for Assessment of Structural Vulnerability of a Network
Based upon the idea that network functionality is impaired if two nodes in a
network are sufficiently separated in terms of a given metric, we introduce two
combinatorial \emph{pseudocut} problems generalizing the classical min-cut and
multi-cut problems. We expect the pseudocut problems will find broad relevance
to the study of network reliability. We comprehensively analyze the
computational complexity of the pseudocut problems and provide three
approximation algorithms for these problems.
Motivated by applications in communication networks with strict
Quality-of-Service (QoS) requirements, we demonstrate the utility of the
pseudocut problems by proposing a targeted vulnerability assessment for the
structure of communication networks using QoS metrics; we perform experimental
evaluations of our proposed approximation algorithms in this context
Hypervelocity impact facility for simulating materials exposure to impact by space debris
As a result of man's venturing into space, the local debris contributed by his presence exceeds, at some orbital altitudes, that of the natural component. Man's contribution ranges from fuel residue to large derelect satellites that weigh many kilograms. Current debris models are able to predict the growth of the problem and suggest that spacecraft must employ armor or bumper shields for some orbital altitudes now, and that, the problem will become worse as a function of time. The practical upper limit to the velocity distribution is on the order of 40 km/s and is associated with the natural environment. The maximum velocity of the man-made component is in the 14-16 km/s range. The Long Duration Exposure Facility (LDEF) has verified that the 'high probability of impact' particles are in the microgram to milligram range. These particles can have significant effects on coatings, insulators, and thin metallic layers. The surface of thick materials becomes pitted and the local debris component is enhanced by ejecta from the debris spectrum in a controlled environment. The facility capability is discussed in terms of drive geometry, energetics, velocity distribution, diagnostics, and projectile/debris loading. The facility is currently being used to study impact phenomena on Space Station Freedom's solar array structure, other solar array materials, potential structural materials for use in the station, electrical breakdown in the space environment, and as a means of clarifying or duplicating the impact phenomena on the LDEF surfaces. The results of these experiments are described in terms of the mass/velocity distribution incident on selected samples, crater dynamics, and sample geometry
A phylogeny of birds based on over 1,500 loci collected by target enrichment and high-throughput sequencing
Evolutionary relationships among birds in Neoaves, the clade comprising the
vast majority of avian diversity, have vexed systematists due to the ancient,
rapid radiation of numerous lineages. We applied a new phylogenomic approach to
resolve relationships in Neoaves using target enrichment (sequence capture) and
high-throughput sequencing of ultraconserved elements (UCEs) in avian genomes.
We collected sequence data from UCE loci for 32 members of Neoaves and one
outgroup (chicken) and analyzed data sets that differed in their amount of
missing data. An alignment of 1,541 loci that allowed missing data was 87%
complete and resulted in a highly resolved phylogeny with broad agreement
between the Bayesian and maximum-likelihood (ML) trees. Although results from
the 100% complete matrix of 416 UCE loci were similar, the Bayesian and ML
trees differed to a greater extent in this analysis, suggesting that increasing
from 416 to 1,541 loci led to increased stability and resolution of the tree.
Novel results of our study include surprisingly close relationships between
phenotypically divergent bird families, such as tropicbirds (Phaethontidae) and
the sunbittern (Eurypygidae) as well as between bustards (Otididae) and turacos
(Musophagidae). This phylogeny bolsters support for monophyletic waterbird and
landbird clades and also strongly supports controversial results from previous
studies, including the sister relationship between passerines and parrots and
the non-monophyly of raptorial birds in the hawk and falcon families. Although
significant challenges remain to fully resolving some of the deep relationships
in Neoaves, especially among lineages outside the waterbirds and landbirds,
this study suggests that increased data will yield an increasingly resolved
avian phylogeny.Comment: 30 pages, 1 table, 4 figures, 1 supplementary table, 3 supplementary
figure
Differing microstructural properties of 7075-T6 sheet and 7075-T651 extruded aluminium alloy
This paper details an initial study of the differences, if any, in corrosion behaviour between 7075-T6 sheet and 7075-T651 extruded aluminium alloy. The study involved a visual inspection of the grain structure of each material and an analysis of the grain sizes. It was found that there is a significant difference in the grain sizes of the two materials; the extruded material had grains that were approximately 15-20% of the size of the sheet grains. Also, the grains in the sheet material were wider, with a length-to-width aspect ratio of 1.5 (compared with 1.3 for the extruded material). Finally, the grains in the extruded material appeared to form a semi-continuous line of grain boundaries, possibly facilitating the growth of laminar intergranular corrosion; the sheet material contained higher-angle grain boundary junctions which should limit the amount of laminar intergranular corrosion produced and promote networked intergranular corrosion. Further testing will involve corroding specimens and investigating the size, shape and depth of the corrosion produced
Active Galaxies and Cluster Gas
Two lines of evidence indicate that active galaxies, principally radio
galaxies, have heated the diffuse hot gas in clusters. The first is the general
need for additional heating to explain the steepness of the X-ray
luminosity--temperature relation in clusters, the second is to solve the
cooling flow problem in cluster cores. The inner core of many clusters is
radiating energy as X-rays on a timescale much shorter than its likely age.
Although the temperature in this region drops by a factor of about 3 from that
of the surrounding gas, little evidence is found for gas much cooler than that.
Some form of heating appears to be taking place, probably by energy transported
outward from the central accreting black hole or radio source. How that energy
heats the gas depends on poorly understood transport properties (conductivity
and viscosity) of the intracluster medium. Viscous heating is discussed as a
possibility. Such heating processes have consequences for the truncation of the
luminosity function of massive galaxies.Comment: 14 pages, 16 fig, Feb 2004 talk for Phil Trans Roy So
Understanding the tsunami with a simple model
In this paper, we use the approximation of shallow water waves (Margaritondo
G 2005 Eur. J. Phys. 26 401) to understand the behaviour of a tsunami in a
variable depth. We deduce the shallow water wave equation and the continuity
equation that must be satisfied when a wave encounters a discontinuity in the
sea depth. A short explanation about how the tsunami hit the west coast of
India is given based on the refraction phenomenon. Our procedure also includes
a simple numerical calculation suitable for undergraduate students in physics
and engineering
Implications of new measurements of O-16 + p + C-12,13, N-14,15 for the abundances of C, N isotopes at the cosmic ray source
The fragmentation of a 225 MeV/n O-16 beam was investigated at the Bevalac. Preliminary cross sections for mass = 13, 14, 15 fragments are used to constrain the nuclear excitation functions employed in galactic propagation calculations. Comparison to cosmic ray isotonic data at low energies shows that in the cosmic ray source C-13/C approximately 2% and N-14/0=3-6%. No source abundance of N-15 is required with the current experimental results
20 cm VLA Radio-Continuum Study of M31 - Images and Point Source Catalogues
We present a series of new high-sensitivity and high-resolution
radio-continuum images of M31 at \lambda=20 cm (\nu=1.4 GHz). These new images
were produced by merging archived 20 cm radio-continuum observations from the
Very Large Array (VLA) telescope. Images presented here are sensitive to rms=60
\mu Jy and feature high angular resolution (<10"). A complete sample of
discrete radio sources have been catalogued and analysed across 17 individual
VLA projects. We identified a total of 864 unique discrete radio sources across
the field of M31. One of the most prominent regions in M31 is the ring feature
for which we estimated total integrated flux of 706 mJy at \lambda=20 cm. We
compare here, detected sources to those listed in Gelfand et al. (2004) at
\lambda=92 cm and find 118 sources in common to both surveys. The majority
(61%) of these sources exhibit a spectral index of \alpha <-0.6 indicating that
their emission is predominantly non-thermal in nature. That is more typical for
background objects.Comment: 28 pages, 25 figures, accepted for publication in the Serbian
Astronomical Journa
- …