73 research outputs found
Boundary Effects in Local Inflation and Spectrum of Density Perturbations
We observe that when a local patch in a radiation filled Robertson-Walker
universe inflates by some reason, outside perturbations can enter into the
inflating region. Generally, the physical wavelengths of these perturbations
become larger than the Hubble radius as they cross into the inflating space and
their amplitudes freeze out immediately. It turns out that the corresponding
power spectrum is not scale invariant. Although these perturbations cannot
reach out to a distance inner observer shielded by a de Sitter horizon, they
still indicate a curious boundary effect in local inflationary scenarios.Comment: 11 pages, 8 figures, revtex4, v4: minor typos corrected, twocolumn
versio
A two-mass expanding exact space-time solution
In order to understand how locally static configurations around
gravitationally bound bodies can be embedded in an expanding universe, we
investigate the solutions of general relativity describing a space-time whose
spatial sections have the topology of a 3-sphere with two identical masses at
the poles. We show that Israel junction conditions imply that two spherically
symmetric static regions around the masses cannot be glued together. If one is
interested in an exterior solution, this prevents the geometry around the
masses to be of the Schwarzschild type and leads to the introduction of a
cosmological constant. The study of the extension of the Kottler space-time
shows that there exists a non-static solution consisting of two static regions
surrounding the masses that match a Kantowski-Sachs expanding region on the
cosmological horizon. The comparison with a Swiss-Cheese construction is also
discussed.Comment: 15 pages, 5 figures. Replaced to match the published versio
Junction Conditions and Consequences of Quasi-Spherical Space-Time with Electro-Magnetic Field and Vaidya Matric
In this work the junction conditions between the exterior
Reissner-Nordstrom-Vaidya space-time with the interior quasi-spherical Szekeres
space-time have been studied for analyzing gravitational collapse in the
presence of a magneto-hydrodynamic fluid undergoing dissipation in the form of
heat flow. We have discussed about the apparent horizon and have evaluated the
time difference between the formation of apparent horizon and central
singularity.Comment: 8 latex pages, RevTex style, no figure
Response of Wheat Fungal Diseases to Elevated Atmospheric CO2 Level
Infection with fungal pathogens on wheat varieties with different levels of resistance was
tested at ambient (NC, 390 ppm) and elevated (EC, 750 ppm) atmospheric CO2 levels in the
phytotron. EC was found to affect many aspects of the plant-pathogen interaction. Infection
with most fungal diseases was usually found to be promoted by elevated CO2 level in susceptible
varieties. Powdery mildew, leaf rust and stem rust produced more severe symptoms on
plants of susceptible varieties, while resistant varieties were not infected even at EC. The penetration
of Fusarium head blight (FHB) into the spike was delayed by EC in Mv Mambo, while
it was unaffected in Mv Regiment and stimulated in Mv Emma. EC increased the propagation
of FHB in Mv Mambo and Mv Emma. Enhanced resistance to the spread of Fusarium within
the plant was only found in Mv Regiment, which has good resistance to penetration but poor
resistance to the spread of FHB at NC. FHB infection was more severe at EC in two varieties,
while the plants of Mv Regiment, which has the best field resistance at NC, did not exhibit a
higher infection level at EC.
The above results suggest that breeding for new resistant varieties will remain a useful
means of preventing more severe infection in a future with higher atmospheric CO2 levels
Indigenous Research: Whose Priority? Journeys and Possibilities of Cross-Cultural Research in Geography
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The underlying causes of military outsourcing in the USA and UK: bridging the persistent gap between ends, ways and means since the beginning of the Cold War
This article reappraises the two most-studied country cases of military outsourcing: the USA and the UK. It argues that the contemporary wave of military contracting stretches back to the beginning of the cold war and not only to the demobilisation of armies in the 1990s or the neoliberal reforms introduced since the 1980s. It traces the political, technological and ideational developments that laid the groundwork for these reforms and practices since the early cold war and account for its endurance today. Importantly, it argues that a persistent gap between strategic objectives and resources, i.e. the challenge to reconcile ends and means, is an underlying driver of military contracting in both countries. Contemporary contracting is thus most closely tied to military support functions in support of wider foreign and defence political objectives. Security services in either state may not have been outsourced so swiftly, if at all, without decades of experience in outsourcing military logistics functions and the resultant vehicles, processes and familiarities with public-private partnerships. The article thus provides a wider and deeper understanding of the drivers of contractualisation, thereby improving our understanding of both its historical trajectory and the determinants of its present and potential futures
Transparency in qualitative research: An overview of key findings and implications of the deliberations
Low-frequency dilatational wave propagation through unsaturated porous media containing two immiscible fluids
A cyclic universe with colour fields
The topology of the universe is discussed in relation to the singularity
problem. We explore the possibility that the initial state of the universe
might have had a structure with 3-Klein bottle topology, which would lead to a
model of a nonsingular oscillating (cyclic) universe with a well-defined
boundary condition. The same topology is assumed to be intrinsic to the nature
of the hypothetical primitive constituents of matter (usually called preons)
giving rise to the observed variety of elementary particles. Some
phenomenological implications of this approach are also discussed.Comment: 21 pages, 9 figures; v.4: final versio
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