244 research outputs found
Newtonian and Post-Newtonian approximations of the k = 0 Friedmann Robertson Walker Cosmology
In a previous paper we derived a post-Newtonian approximation to cosmology
which, in contrast to former Newtonian and post-Newtonian cosmological
theories, has a well-posed initial value problem. In this paper, this new
post-Newtonian theory is compared with the fully general relativistic theory,
in the context of the k = 0 Friedmann Robertson Walker cosmologies. It is found
that the post-Newtonian theory reproduces the results of its general
relativistic counterpart, whilst the Newtonian theory does not.Comment: 11 pages, Latex, corrected typo
Post-Newtonian Cosmology
Newtonian Cosmology is commonly used in astrophysical problems, because of
its obvious simplicity when compared with general relativity. However it has
inherent difficulties, the most obvious of which is the non-existence of a
well-posed initial value problem. In this paper we investigate how far these
problems are met by using the post-Newtonian approximation in cosmology.Comment: 12 pages, Late
A Conserved Bach Current
The Bach tensor and a vector which generates conformal symmetries allow a
conserved four-current to be defined. The Bach four-current gives rise to a
quasilocal two-surface expression for power per luminosity distance in the
Vaidya exterior of collapsing fluid interiors. This is interpreted in terms of
entropy generation.Comment: to appear in Class. Quantum Gra
Physical interpretation of gauge invariant perturbations of spherically symmetric space-times
By calculating the Newman-Penrose Weyl tensor components of a perturbed
spherically symmetric space-time with respect to invariantly defined classes of
null tetrads, we give a physical interpretation, in terms of gravitational
radiation, of odd parity gauge invariant metric perturbations. We point out how
these gauge invariants may be used in setting boundary and/or initial
conditions in perturbation theory.Comment: 6 pages. To appear in PR
A word of caution: do not wake sleeping dogs; micrometastases of melanoma suddenly grew after progesterone treatment
Background: Hormonal treatment might affect the immune response to tumor antigens induced in cancer patients who are being vaccinated.
Case presentation: A 33 years-old woman was diagnosed with cutaneous melanoma in May 2009. Her melanoma was located in the intermammary sulcus, had a Breslow thickness of 4 mm, a Clarkâs level IV, it was ulcerated and highly melanotic. The bilateral sentinel node biopsy was negative. She entered into a randomized Phase II/III clinical study comparing a vaccine composed of irradiated melanoma cells plus BCG plus GM-CSF versus IFN-alpha 2b and she was assigned to the vaccine arm. During the two years treatment she remained disease-free; the final CAT scan being performed in August 2011. Between November and December 2011, her gynecologist treated her with three cycles of 200 mg progesterone/day for ten days, every two weeks, for ovary dysfunction. In November 2011 the patient returned to the Hospital for clinical and imaging evaluation and no evidence of disease was found. At the next visit in March 2012 an ultrasound revealed multiple, large metastases in the liver. A CAT scan confirmed the presence of liver, adrenal glands and spleen metastases. A needle biopsy of a liver lesion revealed metastatic melanoma of similar characteristics to the original tumor. We suggest that progesterone treatment triggered proliferation of so far dormant micrometastases that were controlled during CSF470 vaccine treatment.
Conclusion: The use of progesterone in patients with melanoma that are under immunological treatments should be carefully considered, since progesterone could modify the balance of pro-inflammatory and Th1 functions to a regulatory and anti-inflammatory profile of the immune system that could have an impact in tumor progression.Fil: Mordoh, Jose. Fundacion Cancer. Centro de Investigaciones Oncologicas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Tapia, Ivana Jaqueline. Fundacion Cancer. Centro de Investigaciones Oncologicas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Barrio, Maria Marcela. Fundacion Cancer. Centro de Investigaciones Oncologicas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentin
Active gravitational mass and the invariant characterization of Reissner-Nordstrom spacetime
We analyse the concept of active gravitational mass for Reissner-Nordstrom
spacetime in terms of scalar polynomial invariants and the Karlhede
classification. We show that while the Kretschmann scalar does not produce the
expected expression for the active gravitational mass, both scalar polynomial
invariants formed from the Weyl tensor, and the Cartan scalars, do.Comment: 6 pages Latex, to appear in General Relativity and Gravitatio
Plane Light-Like Shells and Impulsive Gravitational Waves in Scalar-Tensor Theories of Gravity
We study gravitational plane impulsive waves and electromagnetic shock waves
in a scalar-tensor theory of gravity of the Brans-Dicke type. In vacuum, we
present an exact solution of Brans-Dicke's field equations and give an example
in which a plane impulsive gravitational wave and a null shell of matter
coexist on the same hypersurface. In the homogenous case, we characterize them
by their surface energy density and wave amplitude and discuss the inhomogenous
case. We also give an exact solution of the Brans-Dicke's field equations in
the electrovacuum case which admits a true curvature singularity and use it to
built an example where a plane impulsive gravitational wave and an
electromagnetic shock wave have the same null hypersurface as history of their
wave fronts and propagate independently and decoupled from a null shell of
matter. This last solution is shown to correspond to the space-time describing
the interaction region resulting from the collision of two electromagnetic
shock waves leading to the formation of two gravitational impulsive waves. The
properties of this solution are discussed and compared to those of the
Bell-Szekeres solution of general relativity.Comment: 19 pages, latex, 1 figure, accepted for publication in Class. Quant.
Gra
Initial Conditions and the Structure of the Singularity in Pre-Big-Bang Cosmology
We propose a picture, within the pre-big-bang approach, in which the universe
emerges from a bath of plane gravitational and dilatonic waves. The waves
interact gravitationally breaking the exact plane symmetry and lead generically
to gravitational collapse resulting in a singularity with the Kasner-like
structure. The analytic relations between the Kasner exponents and the initial
data are explicitly evaluated and it is shown that pre-big-bang inflation may
occur within a dense set of initial data. Finally, we argue that plane waves
carry zero gravitational entropy and thus are, from a thermodynamical point of
view, good candidates for the universe to emerge from.Comment: 18 pages, LaTeX, epsfig. 3 figures included. Minor changes; paragraph
added in the introduction, references added and typos corrected. Final
version published in Classical and Quantum Gravit
Theorems on shear-free perfect fluids with their Newtonian analogues
In this paper we provide fully covariant proofs of some theorems on
shear-free perfect fluids. In particular, we explicitly show that any
shear-free perfect fluid with the acceleration proportional to the vorticity
vector (including the simpler case of vanishing acceleration) must be either
non-expanding or non-rotating. We also show that these results are not
necessarily true in the Newtonian case, and present an explicit comparison of
shear-free dust in Newtonian and relativistic theories in order to see where
and why the differences appear.Comment: 23 pages, LaTeX. Submitted to GR
PIBF+ extracellular vesicles from mouse embryos affect IL-10 production by CD8+ cells
Earlier evidence suggests, that the embryo signals to the maternal immune system. Extracellular vesicles (EVs) are produced by all types of cells, and because they transport different kinds of molecules from one cell to the other, they can be considered as means of intercellular communication. The aim of this work was to test, whether the embryo is able to produce sufficient amounts of EVs to alter the function of peripheral lymphocytes. Embryo-derived EVs were identified by their Annexin V biding capacity, and sensitivity to Triton X dependent lysis, using flow cytometry. Transmission electron microscopy was used to detect EVs at the implantation site. Progesterone-induced blocking factor (PIBF) expression in embryo-derived EVs was demonstrated with immuno-electron microscopy. The % of IL-10 + murine lymphocytes was determined by flow cytometry. EVs were present in embryo culture media, but not in empty media. Mouse embryo-derived EVs adhere to the surface of both CD4+ and CD8+ murine peripheral T lymphocytes, partly, via phosphatidylserine binding. The number of IL-10+ murine peripheral CD8+ cells increases in the presence of embryo-derived EVS, and this effect is counteracted by pre-treatment of EVs with an anti-PIBF antibody, suggesting that the embryo communicates with the maternal immune system via EVs
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