117 research outputs found
Gravitational Collapse with a Cosmological Constant
We consider the effect of a positive cosmological constant on spherical
gravitational collapse to a black hole for a few simple, analytic cases. We
construct the complete Oppenheimer-Snyder-deSitter (OSdS) spacetime, the
generalization of the Oppenheimer-Snyder solution for collapse from rest of a
homogeneous dust ball in an exterior vacuum. In OSdS collapse, the cosmological
constant may affect the onset of collapse and decelerate the implosion
initially, but it plays a diminishing role as the collapse proceeds. We also
construct spacetimes in which a collapsing dust ball can bounce, or hover in
unstable equilibrium, due to the repulsive force of the cosmological constant.
We explore the causal structure of the different spacetimes and identify any
cosmological and black hole event horizons which may be present.Comment: 7 pages, 10 figures; To appear in Phys. Rev.
Proteotyping of laboratory-scale biogas plants reveals multiple steady-states in community composition
The family of regular interiors for non-rotating black holes with
We find the general solution for the spacetimes describing the interior of
static black holes with an equation of state of the type (
being the stress-energy tensor). This form is the one expected from taking into
account different quantum effects associated with strong gravitational fields.
We recover all the particular examples found in the literature. We remark that
all the solutions found follow the natural scheme of an interior core linked
smoothly with the exterior solution by a transient region. We also discuss
their local energy properties and give the main ideas involved in a possible
generalization of the scheme, in order to include other realistic types of
sources.Comment: 31 pages, 1 figure, version to appear in Physical Review
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
Exact Hypersurface-Homogeneous Solutions in Cosmology and Astrophysics
A framework is introduced which explains the existence and similarities of
most exact solutions of the Einstein equations with a wide range of sources for
the class of hypersurface-homogeneous spacetimes which admit a Hamiltonian
formulation. This class includes the spatially homogeneous cosmological models
and the astrophysically interesting static spherically symmetric models as well
as the stationary cylindrically symmetric models. The framework involves
methods for finding and exploiting hidden symmetries and invariant submanifolds
of the Hamiltonian formulation of the field equations. It unifies, simplifies
and extends most known work on hypersurface-homogeneous exact solutions. It is
shown that the same framework is also relevant to gravitational theories with a
similar structure, like Brans-Dicke or higher-dimensional theories.Comment: 41 pages, REVTEX/LaTeX 2.09 file (don't use LaTeX2e !!!) Accepted for
publication in Phys. Rev.
Spherically Symmetric Braneworld Solutions with R_{4} term in the Bulk
An analysis of a spherically symmetric braneworld configuration is performed
when the intrinsic curvature scalar is included in the bulk action; the
vanishing of the electric part of the Weyl tensor is used as the boundary
condition for the embedding of the brane in the bulk. All the solutions outside
a static localized matter distribution are found; some of them are of the
Schwarzschild-(A)dS_{4} form. Two modified Oppenheimer-Volkoff interior
solutions are also found; one is matched to a Schwarzschild-(A)dS_{4} exterior,
while the other does not. A non-universal gravitational constant arises,
depending on the density of the considered object; however, the conventional
limits of the Newton's constant are recovered. An upper bound of the order of
TeV for the energy string scale is extracted from the known solar system
measurements (experiments). On the contrary, in usual brane dynamics, this
string scale is calculated to be larger than TeV.Comment: 23 pages, 1 figure, one minor chang
Super diversity and city branding: Rotterdam in perspective
As many other cities around the world, Rotterdam has been investing in improving its image to stimulate urban development and to attract visitors, residents and investors. In particular, during the last 15 years the municipality of Rotterdam has intensified its attempts to develop a ‘brand’ that fits the ‘new Rotterdam’, which was gradually rebuilt after destructive bombardments during the Second World War (Riezebos 2014). In 2014 Rotterdam was ranked 8th by ‘Rough Guide’ in the list of ‘Top 10 Cities to See’, whereas the ‘New York Times’ listed Rotterdam in the top 10 of 52 Places to Go. These rankings demonstrate Rotterdam’s success in repositioning itself, using the physical interior of the city as a key element in its branding strategy.</p
Congenital Hypogonadotropic Hypogonadism Due to GNRH Receptor Mutations in Three Brothers Reveal Sites Affecting Conformation and Coupling
Congenital hypogonadotropic hypogonadism (CHH) is characterized by low gonadotropins and failure to progress normally through puberty. Mutations in the gene encoding the GnRH receptor (GNRHR1) result in CHH when present as compound heterozygous or homozygous inactivating mutations. This study identifies and characterizes the properties of two novel GNRHR1 mutations in a family in which three brothers display normosmic CHH while their sister was unaffected. Molecular analysis in the proband and the affected brothers revealed two novel non-synonymous missense GNRHR1 mutations, present in a compound heterozygous state, whereas their unaffected parents possessed only one inactivating mutation, demonstrating the autosomal recessive transmission in this kindred and excluding X-linked inheritance equivocally suggested by the initial pedigree analysis. The first mutation at c.845 C>G introduces an Arg substitution for the conserved Pro 282 in transmembrane domain (TMD) 6. The Pro282Arg mutant is unable to bind radiolabeled GnRH analogue. As this conserved residue is important in receptor conformation, it is likely that the mutation perturbs the binding pocket and affects trafficking to the cell surface. The second mutation at c.968 A>G introduces a Cys substitution for Tyr 323 in the functionally crucial N/DPxxY motif in TMD 7. The Tyr323Cys mutant has an increased GnRH binding affinity but reduced receptor expression at the plasma membrane and impaired G protein-coupling. Inositol phosphate accumulation assays demonstrated absent and impaired Gαq/11 signal transduction by Pro282Arg and Tyr323Cys mutants, respectively. Pretreatment with the membrane permeant GnRHR antagonist NBI-42902, which rescues cell surface expression of many GNRHR1 mutants, significantly increased the levels of radioligand binding and intracellular signaling of the Tyr323Cys mutant but not Pro282Arg. Immunocytochemistry confirmed that both mutants are present on the cell membrane albeit at low levels. Together these molecular deficiencies of the two novel GNRHR1 mutations lead to the CHH phenotype when present as a compound heterozygote
Managerialism: an ideal type
Managerialism pervades the higher education literature in much the same way it is said to have pervaded universities themselves. Yet, despite its ubiquity and importance, managerialism remains an under-theorized and elusive concept that has multiple definitions and blurred boundaries. This article addresses this lack of conceptual clarity by first ‘locating’ managerialism in relation to the cognate concepts of neoliberalism and New Public Management and then elucidating its core principles in an ideal-type theoretical model. This ideal type provides a focal point for theoretical debate and critique and, via the development of empirical indicators for each ideological tenet, permits comparison of theory with organizational practice. A worked example is provided of how the model was used to shed light on the nature of managerialism as ideology in a university setting. However, it is anticipated that the model should have explanatory power and utility in a range of organizational contexts
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