36 research outputs found
On computations of angular momentum and its flux in numerical relativity
The purpose of this note is to point out ambiguities that appear in the
calculation of angular momentum and its radiated counterpart when some simple
formulae are used to compute them. We illustrate, in two simple different
examples, how incorrect results can be obtained with them. Additionally, we
discuss the magnitude of possible errors in well known situations.Comment: 8 pages. Minor improvements . To appear in Class. Quantum Gra
General existence proof for rest frame systems in asymptotically flat space-time
We report a new result on the nice section construction used in the
definition of rest frame systems in general relativity. This construction is
needed in the study of non trivial gravitational radiating systems. We prove
existence, regularity and non-self-crossing property of solutions of the nice
section equation for general asymptotically flat space times. This proves a
conjecture enunciated in a previous work.Comment: 14 pages, no figures, LaTeX 2
Photon rockets and the Robinson-Trautman geometries
We point out the relation between the photon rocket spacetimes and the
Robinson Trautman geometries. This allows a discussion of the issues related to
the distinction between the gravitational and matter energy radiation that
appear in these metrics in a more geometrical way, taking full advantage of
their asymptotic properties at null infinity to separate the Weyl and Ricci
radiations, and to clearly establish their gravitational energy content. We
also give the exact solution for the generalized photon rockets.Comment: 7 pages, no figures, LaTeX2
On a class of 2-surface observables in general relativity
The boundary conditions for canonical vacuum general relativity is
investigated at the quasi-local level. It is shown that fixing the area element
on the 2- surface S (rather than the induced 2-metric) is enough to have a well
defined constraint algebra, and a well defined Poisson algebra of basic
Hamiltonians parameterized by shifts that are tangent to and divergence-free on
$. The evolution equations preserve these boundary conditions and the value of
the basic Hamiltonian gives 2+2 covariant, gauge-invariant 2-surface
observables. The meaning of these observables is also discussed.Comment: 11 pages, a discussion of the observables in stationary spacetimes is
included, new references are added, typos correcte
Cytokine storm and histopathological findings in 60 cases of COVID-19-related death: from viral load research to immunohistochemical quantification of major players IL-1\u3b2, IL-6, IL-15 and TNF-\u3b1
This study involves the histological analysis of samples taken during autopsies in cases of COVID-19 related death to evaluate the inflammatory cytokine response and the tissue localization of the virus in various organs. In all the selected cases, SARS-CoV-2 RT-PCR on swabs collected from the upper (nasopharynx and oropharynx) and/or the lower respiratory (trachea and primary bronchi) tracts were positive. Tissue localization of SARS-CoV-2 was detected using antibodies against the nucleoprotein and the spike protein. Overall, we tested the hypothesis that the overexpression of proinflammatory cytokines plays an important role in the development of COVID-19-associated pneumonia by estimating the expression of multiple cytokines (IL-1\u3b2, IL-6, IL-10, IL-15, TNF-\u3b1, and MCP-1), inflammatory cells (CD4, CD8, CD20, and CD45), and fibrinogen. Immunohistochemical staining showed that endothelial cells expressed IL-1\u3b2 in lung samples obtained from the COVID-19 group (p < 0.001). Similarly, alveolar capillary endothelial cells showed strong and diffuse immunoreactivity for IL-6 and IL-15 in the COVID-19 group (p < 0.001). TNF-\u3b1 showed a higher immunoreactivity in the COVID-19 group than in the control group (p < 0.001). CD8 + T cells where more numerous in the lung samples obtained from the COVID-19 group (p < 0.001). Current evidence suggests that a cytokine storm is the major cause of acute respiratory distress syndrome (ARDS) and multiple organ failure and is consistently linked with fatal outcomes
Quasigroups, Asymptotic Symmetries and Conservation Laws in General Relativity
A new quasigroup approach to conservation laws in general relativity is
applied to study asymptotically flat at future null infinity spacetime. The
infinite-parametric Newman-Unti group of asymptotic symmetries is reduced to
the Poincar\'e quasigroup and the Noether charge associated with any element of
the Poincar\'e quasialgebra is defined. The integral conserved quantities of
energy-momentum and angular momentum are linear on generators of Poincar\'e
quasigroup, free of the supertranslation ambiguity, posess the flux and
identically equal to zero in Minkowski spacetime.Comment: RevTeX4, 5 page