208 research outputs found
Hepatic amoebiasis
Thirty-two cases of hepatic amoebiasis with some unusual features are presented. The clinical spectrum and the value of investigations such as liver scanning, angiography and slide agglutination test are presented. Therapy is outlined.S. Afr. Med. J., 48, 1159 (1974
Cosmological Constant, Conical Defect and Classical Tests of General Relativity
We investigate the perihelion shift of the planetary motion and the bending
of starlight in the Schwarzschild field modified by the presence of a
-term plus a conical defect. This analysis generalizes an earlier
result obtained by Islam (Phys. Lett. A 97, 239, 1983) to the case of a pure
cosmological constant. By using the experimental data we obtain that the
parameter characterizing the conical defect is less than
and , respectively, on the length scales associated with such
phenomena. In particular, if the defect is generated by a cosmic string, these
values correspond to limits on the linear mass densities of and
, respectively.Comment: 9 pages, no figures, revte
Ernst equation and spheroidal coordinates with a cosmological constant term
We discuss solution generating techniques treating stationary and axially
symmetric metrics in the presence of a cosmological constant. Using the
recently found extended form of Ernst's complex equation, which takes into
account the cosmological constant term, we propose an extension of spheroidal
coordinates adapted to asymptotically de-Sitter and anti de-Sitter static
spacetimes. In the absence of a cosmological constant we show in addition that
any higher dimensional metric parametrised by a single angular momentum can be
given by a 4 dimensional solution and Weyl potentials parametrising the extra
Killing directions. We explicitly show how a stationary, and a static axially
symmetric spacetime solution in 4 dimensions, can be {\it added} together to
give a 5 dimensional stationary and axisymmetric solution.Comment: 9 pages, no figures, some additional results to gr-qc/0610091.
Prepared for 12th Conference on Recent Developments in Gravity (NEB XII),
Nafplio, Greece, 29 Jun - 2 Jul 200
Towards the classification of static vacuum spacetimes with negative cosmological constant
We present a systematic study of static solutions of the vacuum Einstein
equations with negative cosmological constant which asymptotically approach the
generalized Kottler (``Schwarzschild--anti-de Sitter'') solution, within
(mainly) a conformal framework. We show connectedness of conformal infinity for
appropriately regular such space-times. We give an explicit expression for the
Hamiltonian mass of the (not necessarily static) metrics within the class
considered; in the static case we show that they have a finite and well defined
Hawking mass. We prove inequalities relating the mass and the horizon area of
the (static) metrics considered to those of appropriate reference generalized
Kottler metrics. Those inequalities yield an inequality which is opposite to
the conjectured generalized Penrose inequality. They can thus be used to prove
a uniqueness theorem for the generalized Kottler black holes if the generalized
Penrose inequality can be established.Comment: the discussion of our results includes now some solutions of Horowitz
and Myers; typos corrected here and there; a shortened version of this
version will appear in Journal of Mathematical Physic
A Cosmological No-Hair Theorem
A generalisation of Price's theorem is given for application to Inflationary
Cosmologies. Namely, we show that on a Schwarzschild--de Sitter background
there are no static solutions to the wave or gravitational perturbation
equations for modes with angular momentum greater than their intrinsic spin.Comment: 9 pages, NCL94 -TP4, (Revtex
Maxwell's theory on a post-Riemannian spacetime and the equivalence principle
The form of Maxwell's theory is well known in the framework of general
relativity, a fact that is related to the applicability of the principle of
equivalence to electromagnetic phenomena. We pose the question whether this
form changes if torsion and/or nonmetricity fields are allowed for in
spacetime. Starting from the conservation laws of electric charge and magnetic
flux, we recognize that the Maxwell equations themselves remain the same, but
the constitutive law must depend on the metric and, additionally, may depend on
quantities related to torsion and/or nonmetricity. We illustrate our results by
putting an electric charge on top of a spherically symmetric exact solution of
the metric-affine gauge theory of gravity (comprising torsion and
nonmetricity). All this is compared to the recent results of Vandyck.Comment: 9 pages, REVTeX, no figures; minor changes, version to be published
in Class. Quantum Gra
The structure of the extreme Schwarzschild-de Sitter space-time
The extreme Schwarzschild-de Sitter space-time is a spherically symmetric
solution of Einstein's equations with a cosmological constant Lambda and mass
parameter m>0 which is characterized by the condition that 9 Lambda m^2=1. The
global structure of this space-time is here analyzed in detail. Conformal and
embedding diagrams are constructed, and synchronous coordinates which are
suitable for a discussion of the cosmic no-hair conjecture are presented. The
permitted geodesic motions are also analyzed. By a careful investigation of the
geodesics and the equations of geodesic deviation, it is shown that specific
families of observers escape from falling into the singularity and approach
nonsingular asymptotic regions which are represented by special "points" in the
complete conformal diagram. The redshift of signals emitted by particles which
fall into the singularity, as detected by those observers which escape, is also
calculated.Comment: 19 pages, 10 figures, LaTeX, to appear in Gen. Rel. Gra
No-Bang Quantum State of the Cosmos
A quantum state of the entire cosmos (universe or multiverse) is proposed
which is the equal mixture of the Giddings-Marolf states that are
asymptotically single de Sitter spacetimes in both past and future and are
regular on the throat or neck of minimal three-volume. That is, states are
excluded that have a big bang or big crunch or which split into multiple
asymptotic de Sitter spacetimes. (For simplicity, transitions between different
values of the cosmological constant are assumed not to occur, though different
positive values are allowed.) The entropy of this mixed state appears to be of
the order of the three-fourths power of the Bekenstein-Hawking A/4 entropy of
de Sitter spacetime. Most of the component pure states do not have rapid
inflation, but when an inflaton is present and the states are weighted by the
volume at the end of inflation, a much smaller number of states may dominate
and give a large amount of inflation and hence may agree with observations.Comment: 18 pages, LaTeX, updated with a few new qualifications and reference
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
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
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