14,639 research outputs found
Written evidence to the House of Commons Business and Skills Committee (ed) Local enterprise partnerships and the Regional Growth Fund
The Business, Innovation and Skills Committee announced an inquiry looking into the Local Enterprise Partnerships and the Regional Growth Fund. In particular, the Committee examined how the proposed new structures would work, alongside issues such as distribution of funding, value for money, accountability, timing, transitional arrangements and required legislation. A Report on the Local Enterprise Partnerships was published on 26 April 2013
Shielding of Space Vehicles by Magnetic Fields
Spacecraft shielding by magnetic field
Bohm and Einstein-Sasaki Metrics, Black Holes and Cosmological Event Horizons
We study physical applications of the Bohm metrics, which are infinite
sequences of inhomogeneous Einstein metrics on spheres and products of spheres
of dimension 5 <= d <= 9. We prove that all the Bohm metrics on S^3 x S^2 and
S^3 x S^3 have negative eigenvalue modes of the Lichnerowicz operator and by
numerical methods we establish that Bohm metrics on S^5 have negative
eigenvalues too. We argue that all the Bohm metrics will have negative modes.
These results imply that higher-dimensional black-hole spacetimes where the
Bohm metric replaces the usual round sphere metric are classically unstable. We
also show that the stability criterion for Freund-Rubin solutions is the same
as for black-hole stability, and hence such solutions using Bohm metrics will
also be unstable. We consider possible endpoints of the instabilities, and show
that all Einstein-Sasaki manifolds give stable solutions. We show how Wick
rotation of Bohm metrics gives spacetimes that provide counterexamples to a
strict form of the Cosmic Baldness conjecture, but they are still consistent
with the intuition behind the cosmic No-Hair conjectures. We show how the
Lorentzian metrics may be created ``from nothing'' in a no-boundary setting. We
argue that Lorentzian Bohm metrics are unstable to decay to de Sitter
spacetime. We also argue that noncompact versions of the Bohm metrics have
infinitely many negative Lichernowicz modes, and we conjecture a general
relation between Lichnerowicz eigenvalues and non-uniqueness of the Dirichlet
problem for Einstein's equations.Comment: 53 pages, 11 figure
Isometric Embedding of BPS Branes in Flat Spaces with Two Times
We show how non-near horizon p-brane theories can be obtained from two
embedding constraints in a flat higher dimensional space with 2 time
directions. In particular this includes the construction of D3 branes from a
flat 12-dimensional action, and M2 and M5 branes from 13 dimensions. The
worldvolume actions are determined by constant forms in the higher dimension,
reduced to the usual expressions by Lagrange multipliers. The formulation
affords insight in the global aspects of the spacetime geometries and makes
contact with recent work on two-time physics.Comment: 29 pages, 10 figures, Latex using epsf.sty and here.sty; v2:
reference added and some small correction
Vacuum decay via Lorentzian wormholes
We speculate about the spacetime description due to the presence of
Lorentzian wormholes (handles in spacetime joining two distant regions or other
universes) in quantum gravity. The semiclassical rate of production of these
Lorentzian wormholes in Reissner-Nordstr\"om spacetimes is calculated as a
result of the spontaneous decay of vacuum due to a real tunneling
configuration. In the magnetic case it only depends on the field theoretical
fine structure constant. We predict that the quantum probability corresponding
to the nucleation of such geodesically complete spacetimes should be actually
negligible in our physical Universe
Relative contribution of abundant and rare species to speciesâenergy relationships
A major goal of ecology is to understand spatial variation in species richness. The latter is markedly influenced by energy availability and appears to be influenced more by common species than rare ones; speciesâenergy relationships should thus be stronger for common species. Speciesâenergy relationships may arise because high-energy areas support more individuals, and these larger populations may buffer species from extinction. As extinction risk is a negative decelerating function of population size, this more-individuals hypothesis (MIH) predicts that rare species should respond more strongly to energy. We investigate these opposing predictions using British breeding bird data and find that, contrary to the MIH, common species contribute more to speciesâenergy relationships than rare ones
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HLA-B27 Positivity: associated health implications
HLA-B27 positivity makes the onset of autoimmune diseases such as uveitis, ankylosing spondylitis and Crohn's disease more likely to occur. Ankylosing spondylitis and Crohn's disease are two types of HLA-B27 positive diseases that demonstrate a direct association with uveitis. Although the possession of HLA-B27 positivity is not mandatory for autoimmune diseases such as uveitis to occur, HLA-B27 positivity not only makes it more likely but may modify the clinical picture in which a patient presents. In relation to assessment and diagnosis it is imperative that the medical history of patients is thoroughly examined to ensure pathological sequelae are appropriately treated. Nurses play an important role in assessing patients that have uveitis and should suspect ankylosing spondylitis or Crohn's disease may be present
Cosmic Acceleration from M Theory on Twisted Spaces
In a recent paper [I.P. Neupane and D.L. Wiltshire, Phys. Lett. B 619, 201
(2005).] we have found a new class of accelerating cosmologies arising from a
time--dependent compactification of classical supergravity on product spaces
that include one or more geometric twists along with non-trivial curved
internal spaces. With such effects, a scalar potential can have a local minimum
with positive vacuum energy. The existence of such a minimum generically
predicts a period of accelerated expansion in the four-dimensional
Einstein-conformal frame. Here we extend our knowledge of these cosmological
solutions by presenting new examples and discuss the properties of the
solutions in a more general setting. We also relate the known (asymptotic)
solutions for multi-scalar fields with exponential potentials to the
accelerating solutions arising from simple (or twisted) product spaces for
internal manifolds.Comment: 23 pages, 3 figures; added a summary Table, PRD versio
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