10,775 research outputs found
Regularization of the second-order gravitational perturbations produced by a compact object
The equations for the second-order gravitational perturbations produced by a
compact-object have highly singular source terms at the point particle limit.
At this limit the standard retarded solutions to these equations are
ill-defined. Here we construct well-defined and physically meaningful solutions
to these equations. These solutions are important for practical calculations:
the planned gravitational-wave detector LISA requires preparation of waveform
templates for the potential gravitational-waves. Construction of templates with
desired accuracy for extreme mass ratio binaries, in which a compact-object
inspirals towards a supermassive black-hole, requires calculation of the
second-order gravitational perturbations produced by the compact-object.Comment: 12 pages, discussion expanded, to be published in Phys. Rev. D Rapid
Communicatio
Construction of the second-order gravitational perturbations produced by a compact object
Accurate calculation of the gradual inspiral motion in an extreme mass-ratio
binary system, in which a compact-object inspirals towards a supermassive
black-hole requires calculation of the interaction between the compact-object
and the gravitational perturbations that it induces. These metric perturbations
satisfy linear partial differential equations on a curved background spacetime
induced by the supermassive black-hole. At the point particle limit the
second-order perturbations equations have source terms that diverge as
, where is the distance from the particle. This singular behavior
renders the standard retarded solutions of these equations ill-defined. Here we
resolve this problem and construct well-defined and physically meaningful
solutions to these equations. We recently presented an outline of this
resolution [E. Rosenthal, Phys. Rev. D 72, 121503 (2005)]. Here we provide the
full details of this analysis. These second-order solutions are important for
practical calculations: the planned gravitational-wave detector LISA requires
preparation of waveform templates for the expected gravitational-waves.
Construction of templates with desired accuracy for extreme mass-ratio binaries
requires accurate calculation of the inspiral motion including the interaction
with the second-order gravitational perturbations.Comment: 30 page
Regularization of second-order scalar perturbation produced by a point-particle with a nonlinear coupling
Accurate calculation of the motion of a compact object in a background
spacetime induced by a supermassive black hole is required for the future
detection of such binary systems by the gravitational-wave detector LISA.
Reaching the desired accuracy requires calculation of the second-order
gravitational perturbations produced by the compact object. At the point
particle limit the second-order gravitational perturbation equations turn out
to have highly singular source terms, for which the standard retarded solutions
diverge. Here we study a simplified scalar toy-model in which a point particle
induces a nonlinear scalar field in a given curved spacetime. The corresponding
second-order scalar perturbation equation in this model is found to have a
similar singular source term, and therefore its standard retarded solutions
diverge. We develop a regularization method for constructing well-defined
causal solutions for this equation. Notably these solutions differ from the
standard retarded solutions, which are ill-defined in this case.Comment: 14 page
The Thorium Molten Salt Reactor : Moving on from the MSBR
A re-evaluation of the Molten Salt Breeder Reactor concept has revealed
problems related to its safety and to the complexity of the reprocessing
considered. A reflection is carried out anew in view of finding innovative
solutions leading to the Thorium Molten Salt Reactor concept. Several main
constraints are established and serve as guides to parametric evaluations.
These then give an understanding of the influence of important core parameters
on the reactor's operation. The aim of this paper is to discuss this vast
research domain and to single out the Molten Salt Reactor configurations that
deserve further evaluation.Comment: 11 pages, 8 figures, 6 table
Orbital evolution of a test particle around a black hole: Indirect determination of the self force in the post Newtonian approximation
Comparing the corrections to Kepler's law with orbital evolution under a self
force, we extract the finite, already regularized part of the latter in a
specific gauge. We apply this method to a quasi-circular orbit around a
Schwarzschild black hole of an extreme mass ratio binary, and determine the
first- and second-order conservative gravitational self force in a post
Newtonian expansion. We use these results in the construction of the
gravitational waveform, and revisit the question of the relative contribution
of the self force and spin-orbit coupling.Comment: 5 pages, 2 figure
Availability of chemosensory receptors is down-regulated by habituation of larvae to a morphogenetic signal.
FUNCTIONAL HETEROGENEITY OF MURINE LYMPHOID CELLS : V. LYMPHOCYTES LACKING DETECTABLE SURFACE Ï‘ OR IMMUNOGLOBULIN DETERMINANTS
An appreciable percent (3–14%) of the lymphocyte-like cells of the mouse spleen lack both the θ-isoantigen and sufficient surface immunoglobulin to be detected by conventional immunofluorescence or autoradiographic procedures. These θ-,Ig- cells are increased in frequency after treatment of mice with antithymocyte serum or in mice that have been thymectomized, irradiated (850 R), and reconstituted with bone marrow cells. Moreover, in chimeric C57BL/6 mice in which the T cells are derived from (BALB/c x C57BL/6)F1 donors, θ-,Ig- cells also lack BALB/c histocompatibility antigens. These experiments indicate that θ-,Ig- cells are not θ- T lymphocytes. Removal of complement receptor lymphocytes from spleen cell populations increases the frequency of θ-,Ig- cells, indicating that such cells lack the complement receptor. Partially purified populations of θ-,Ig- cells have been obtained by cytolysis by anti-θ- and anti-κ-antibody and complement and by density gradient ultracentrifugation. These cells closely resemble lymphocytes in morphology. The only exceptional feature is the existence of prominent nucleoli. The θ-,Ig- cells lack hemoglobin and endogenous peroxidases, are not actively phagocytic, and do not adhere to glass. This suggests they are not of the erythroid, myeloid, or monocytoid lines. [3H]Thymidine labeling studies indicate that θ-,Ig- cells are members of a relatively slowly dividing cell pool. Whether θ-,Ig- cells are members of the "classical" B lymphocyte line or belong to another, as yet undescribed, lineage is not yet certain
Second-order gravitational self-force
We derive an expression for the second-order gravitational self-force that
acts on a self-gravitating compact-object moving in a curved background
spacetime. First we develop a new method of derivation and apply it to the
derivation of the first-order gravitational self-force. Here we find that our
result conforms with the previously derived expression. Next we generalize our
method and derive a new expression for the second-order gravitational
self-force. This study also has a practical motivation: The data analysis for
the planned gravitational wave detector LISA requires construction of waveforms
templates for the expected gravitational waves. Calculation of the two leading
orders of the gravitational self-force will enable one to construct highly
accurate waveform templates, which are needed for the data analysis of
gravitational-waves that are emitted from extreme mass-ratio binaries.Comment: 35 page
- …