713 research outputs found
The orbit rigidity matrix of a symmetric framework
A number of recent papers have studied when symmetry causes frameworks on a
graph to become infinitesimally flexible, or stressed, and when it has no
impact. A number of other recent papers have studied special classes of
frameworks on generically rigid graphs which are finite mechanisms. Here we
introduce a new tool, the orbit matrix, which connects these two areas and
provides a matrix representation for fully symmetric infinitesimal flexes, and
fully symmetric stresses of symmetric frameworks. The orbit matrix is a true
analog of the standard rigidity matrix for general frameworks, and its analysis
gives important insights into questions about the flexibility and rigidity of
classes of symmetric frameworks, in all dimensions.
With this narrower focus on fully symmetric infinitesimal motions, comes the
power to predict symmetry-preserving finite mechanisms - giving a simplified
analysis which covers a wide range of the known mechanisms, and generalizes the
classes of known mechanisms. This initial exploration of the properties of the
orbit matrix also opens up a number of new questions and possible extensions of
the previous results, including transfer of symmetry based results from
Euclidean space to spherical, hyperbolic, and some other metrics with shared
symmetry groups and underlying projective geometry.Comment: 41 pages, 12 figure
Asteroids in the Inner Solar System II - Observable Properties
This paper presents synthetic observations of long-lived, coorbiting
asteroids of Mercury, Venus, the Earth and Mars. Our sample is constructed by
taking the limiting semimajor axes, differential longitudes and inclinations
for long-lived stability provided by simulations. The intervals are randomly
populated with values to create initial conditions. These orbits are
re-simulated to check that they are stable and then re-sampled every 2.5 years
for 1 million years. The Mercurian sample contains only horseshoe orbits, the
Martian sample only tadpoles. For both Venus and the Earth, the greatest
concentration of objects on the sky occurs close to the classical Lagrange
points at heliocentric ecliptic longitudes of 60 and 300 degrees. The
distributions are broad especially if horseshoes are present in the sample. The
full-width half maximum (FWHM) in heliocentric longitude for Venus is 325
degrees and for the Earth is 328 degrees. The mean and most common velocity of
these coorbiting satellites coincides with the mean motion of the parent
planet, but again the spread is wide with a FWHM for Venus of 27.8 arcsec/hr
and for the Earth of 21.0 arcsec/hr. For Mars, the greatest concentration on
the sky occurs at heliocentric ecliptic latitudes of 12 degrees. The peak of
the velocity distribution occurs at 65 arcsec/hr, significantly less than the
Martian mean motion, while its FWHM is 32.3 arcsec/hr. The case of Mercury is
the hardest of all, as the greatest concentration occurs at heliocentric
longitudes close to the Sun.Comment: 16 pages, 11 figures, Monthly Notices (in press). Higher quality
figures available at
http://www-thphys.physics.ox.ac.uk/users/WynEvans/home.htm
Political brand identity: an examination of the complexities of Conservative brand and internal market engagement during the 2010 UK General Election campaign
This paper seeks to build an understanding of the importance of internal communications when building a strong political brand. Using Kapferer’s brand prism as a conceptual framework, the paper explores UK Conservative Party members’ attitudes towards the development of the Conservative brand as personified by David Cameron. There are clear implications for political strategists as the findings suggest that it is crucial to engage the internal market in the co-creation of the marketing communications strategy for as brand evangelists they interpret the brand promise at the local level
Asteroids in the Inner Solar System I - Existence
Ensembles of in-plane and inclined orbits in the vicinity of the Lagrange
points of the terrestrial planets are integrated for up to 100 million years.
The integrations incorporate the gravitational effects of Sun and the eight
planets (Pluto is neglected). Mercury is the least likely planet, as it is
unable to retain tadpole orbits over 100 million year timescales. Both Venus
and the Earth are much more promising, as they possess rich families of stable
tadpole and horseshoe orbits. Our survey of Trojans in the orbital plane of
Venus is undertaken for 25 million years. Some 40% of the survivors are on
tadpole orbits. For the Earth, the integrations are pursued for 50 million
years. The stable zones in the orbital plane are larger for the Earth than for
Venus, but fewer of the survivors are tadpoles. Both Venus and the Earth also
have regions in which inclined test particles can endure near the Lagrange
points. For Venus, only test particles close to the orbital plane are stable.
For the Earth, there are two bands of stability, one at low inclinations (i <
16 degrees) and one at moderate inclinations (between 24 degrees and 34
degrees). The inclined test particles that evade close encounters are primarily
moving on tadpole orbits. Our survey of in-plane test particles near the
Martian Lagrange points shows no survivors after 60 million years. Low
inclination test particles do not persist, as their inclinations are quickly
increased until the effects of a secular resonance with Jupiter cause
de-stabilisation. Numerical integrations of inclined test particles for
timespans of 25 million years show stable zones for inclinations between 14 and
40 degrees.Comment: 20 pages, 21 figures, Monthly Notices (in press
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Effects of antiplatelet therapy after stroke due to intracerebral haemorrhage (RESTART): a randomised, open-label trial
Antiplatelet therapy reduces the risk of major vascular events for people with occlusive vascular disease, although it might increase the risk of intracranial haemorrhage. Patients surviving the commonest subtype of intracranial haemorrhage, intracerebral haemorrhage, are at risk of both haemorrhagic and occlusive vascular events, but whether antiplatelet therapy can be used safely is unclear. We aimed to estimate the relative and absolute effects of antiplatelet therapy on recurrent intracerebral haemorrhage and whether this risk might exceed any reduction of occlusive vascular events
Inflammatory Markers and Outcomes in Cardiovascular Disease
In a commentary on two new research studies in PLoS Medicine, Leonard Kritharides discusses the role of inflammatory markers in predicting cardiovascular outcomes and patients' responses to treatment
Popular music, psychogeography, place identity and tourism: The case of Sheffield
Tourism and cultural agencies in some English provincial cities are promoting their popular music ‘heritage’ and, in some cases, contemporary musicians through the packaging of trails, sites, ‘iconic’ venues and festivals. This article focuses on Sheffield, a ‘post-industrial’ northern English city which is drawing on its associations with musicians past and present in seeking to attract tourists. This article is based on interviews with, among others, recording artists, promoters, producers and venue managers, along with reflective observational and documentary data. Theoretical remarks are made on the representations of popular musicians through cultural tourism strategies, programmes and products and also on the ways in which musicians convey a ‘psychogeographical’ sense of place in the ‘soundscape’ of the city
Incidental findings on brain magnetic resonance imaging: systematic review and meta-analysis
Objective To quantify the prevalence of incidental findings on magnetic resonance imaging (MRI) of the brain
Small grid embeddings of 3-polytopes
We introduce an algorithm that embeds a given 3-connected planar graph as a
convex 3-polytope with integer coordinates. The size of the coordinates is
bounded by . If the graph contains a triangle we can
bound the integer coordinates by . If the graph contains a
quadrilateral we can bound the integer coordinates by . The
crucial part of the algorithm is to find a convex plane embedding whose edges
can be weighted such that the sum of the weighted edges, seen as vectors,
cancel at every point. It is well known that this can be guaranteed for the
interior vertices by applying a technique of Tutte. We show how to extend
Tutte's ideas to construct a plane embedding where the weighted vector sums
cancel also on the vertices of the boundary face
Evaluating the Quality of Research into a Single Prognostic Biomarker: A Systematic Review and Meta-analysis of 83 Studies of C-Reactive Protein in Stable Coronary Artery Disease
Background
Systematic evaluations of the quality of research on a single prognostic biomarker are rare. We sought to evaluate the quality of prognostic research evidence for the association of C-reactive protein (CRP) with fatal and nonfatal events among patients with stable coronary disease.
Methods and Findings
We searched MEDLINE (1966 to 2009) and EMBASE (1980 to 2009) and selected prospective studies of patients with stable coronary disease, reporting a relative risk for the association of CRP with death and nonfatal cardiovascular events. We included 83 studies, reporting 61,684 patients and 6,485 outcome events. No study reported a prespecified statistical analysis protocol; only two studies reported the time elapsed (in months or years) between initial presentation of symptomatic coronary disease and inclusion in the study. Studies reported a median of seven items (of 17) from the REMARK reporting guidelines, with no evidence of change over time.
The pooled relative risk for the top versus bottom third of CRP distribution was 1.97 (95% confidence interval [CI] 1.78–2.17), with substantial heterogeneity (I2 = 79.5). Only 13 studies adjusted for conventional risk factors (age, sex, smoking, obesity, diabetes, and low-density lipoprotein [LDL] cholesterol) and these had a relative risk of 1.65 (95% CI 1.39–1.96), I2 = 33.7. Studies reported ten different ways of comparing CRP values, with weaker relative risks for those based on continuous measures. Adjusting for publication bias (for which there was strong evidence, Egger's p<0.001) using a validated method reduced the relative risk to 1.19 (95% CI 1.13–1.25). Only two studies reported a measure of discrimination (c-statistic). In 20 studies the detection rate for subsequent events could be calculated and was 31% for a 10% false positive rate, and the calculated pooled c-statistic was 0.61 (0.57–0.66).
Conclusion
Multiple types of reporting bias, and publication bias, make the magnitude of any independent association between CRP and prognosis among patients with stable coronary disease sufficiently uncertain that no clinical practice recommendations can be made. Publication of prespecified statistical analytic protocols and prospective registration of studies, among other measures, might help improve the quality of prognostic biomarker research
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