23,115 research outputs found
Hydrodynamics of Binary Coalescence.I. Polytropes with Stiff Equations of State
We have performed a series of three-dimensional hydrodynamic calculations of
binary coalescence using the smoothed particle hydrodynamics (SPH) method. The
initial conditions are exact polytropic equilibrium configurations with \gam >
5/3, on the verge of dynamical instability. We calculate the emission of
gravitational radiation in the quadrupole approximation. The fully nonlinear
development of the instability is followed until a new equilibrium
configuration is reached. We find that the properties of this final
configuration depend sensitively on both the compressibility and mass ratio. An
{\em axisymmetric} merged configuration is always produced when \gam\lo2.3.
As a consequence, the emission of gravitational radiation shuts off abruptly
right after the onset of dynamical instability. In contrast, {\em triaxial\/}
merged configurations are obtained when \gam\go2.3, and the system continues
to emit gravitational waves after the final coalescence. Systems with mass
ratios typically become dynamically unstable before the onset of mass
transfer. Stable mass transfer from one neutron star to another in a close
binary is therefore probably ruled out. The maximum amplitude and
peak luminosity of the gravitational waves emitted during the final
coalescence are nearly independent of \gam, but depend very sensitively on
the mass ratio .Comment: 27 pages, uuencoded compressed postscript, 16 figures upon request
from [email protected], IAS-AST-94-
Head-On Collision of Neutron Stars As A Thought Experiment
The head-on collision of identical neutron stars from rest at infinity
requires a numerical simulation in full general relativity for a complete
solution. Undaunted, we provide a relativistic, analytic argument to suggest
that during the collision, sufficient thermal pressure is always generated to
support the hot remnant in quasi-static stable equilibrium against collapse
prior to slow cooling via neutrino emission. Our conclusion is independent of
the total mass of the progenitors and holds even if the remnant greatly exceeds
the maximum mass of a cold neutron star.Comment: to appear in Physical Review D (revtex, 3 figs, 5 pgs
The significance of ACTH for the process of formation of complex heparin compounds in the blood during immobilization stress
Adrenocorticotropin (ACTH) was administered to rats at different times following adrenalectomy. Adrenocorticotropin caused a significant increase in the formation of heparin complexes even in the absence of stress factor. When ACTH secretion is blocked, immobilization stress is not accompanied by an increase in the process of complex formation. The effect of ACTH on the formation of heparin complexes was mediated through its stimulation of the adrenal cortex
The anomaly-induced effective action and natural inflation
The anomaly-induced inflation (modified Starobinsky model) is based on the
application of the effective quantum field theory approach to the Early
Universe. We present a brief general review of the model and show that it does
not require a fine-tuning for the parameters of the theory or initial data,
gives a real chance to meet a graceful exit to the FRW phase and also has
positive features with respect to the metric perturbations.Comment: Invited talk at the International Workshop on Astroparticle and High
Energy Physics, October 14 - 18, 2003, Valencia, Spai
On Useful Conformal Tranformations In General Relativity
Local conformal transformations are known as a useful tool in various
applications of the gravitational theory, especially in cosmology. We describe
some new aspects of these transformations, in particular using them for
derivation of Einstein equations for the cosmological and Schwarzschild
metrics. Furthermore, the conformal transformation is applied for the
dimensional reduction of the Gauss-Bonnet topological invariant in to the
spaces of lower dimensions.Comment: 17 pages, LaTeX. The paper is intended mainly for pedagogical
purposes and represents a collection of exercises concerning local conformal
transformations and dimensional reduction. To be published in "Gravitation
and Cosmology
Participation of the hypophyseal-adrenal cortex system in thrombin clearance during immobilization stress
Thrombin marked with I-131 resulted in a considerable increase of the thrombined clearance rate in healthy male rats during stress caused by an immobilization lasting 30 minutes, and in an increase of thrombin clearance occurred by a combination of immobilization and administration of adrenocorticotropin (ACTH). Contrary to ACTH, the thrombin clearance is not stimulated in healthy animals by hydrocortisone. The results of the examination are presented
The role of ACTH and glucocorticoids in nonenzymatic fibrinolysis during immobilization stress in animals
The role of the altered hormonal status of an organism in the activation of the anticoagulative system during stress is investigated. The 30 minute immobilization stress was shown to raise significantly the nonenzymatic fibrinolytic activity of blood in rats. Combined with adrenocorticotropin (ACTH) the effect is still greater. Intravenous administration of 0.2 m1 0.01 percent solution of protamine sulphate prevented the nonenzymatic fibrinolysis induced by the stress. Administration of ACTH after protomine sulphate again raised the fibrinolysis. This suggests that ACTH stimulates the release of heparin
Gaussian-State Theory of Two-Photon Imaging
Biphoton states of signal and idler fields--obtained from spontaneous
parametric downconversion (SPDC) in the low-brightness, low-flux regime--have
been utilized in several quantum imaging configurations to exceed the
resolution performance of conventional imagers that employ coherent-state or
thermal light. Recent work--using the full Gaussian-state description of
SPDC--has shown that the same resolution performance seen in quantum optical
coherence tomography and the same imaging characteristics found in quantum
ghost imaging can be realized by classical-state imagers that make use of
phase-sensitive cross correlations. This paper extends the Gaussian-state
analysis to two additional biphoton-state quantum imaging scenarios: far field
diffraction-pattern imaging; and broadband thin-lens imaging. It is shown that
the spatial resolution behavior in both cases is controlled by the nonzero
phase-sensitive cross correlation between the signal and idler fields. Thus,
the same resolution can be achieved in these two configurations with
classical-state signal and idler fields possessing a nonzero phase-sensitive
cross correlation.Comment: 14 pages, 5 figure
Light trapping and guidance in plasmonic nanocrystals
We illustrate the possibility of light trapping and funneling in periodic
arrays of metallic nanoparticles. A controllable minimum in the transmission
spectra of such constructs arises from a collective plasmon resonance
phenomenon, where an incident plane wave sharply localizes in the vertical
direction, remaining delocalized in the direction parallel to the crystal
plane. Using hybrid arrays of different structures or different materials, we
apply the trapping effect to structure the eigen-mode spectrum, introduce
overlapping resonances, and hence direct the light in space in a
wavelength-sensitive fashion
Two-mode heterodyne phase detection
We present an experimental scheme that achieves ideal phase detection on a
two-mode field. The two modes and are the signal and image band modes
of an heterodyne detector, with the field approaching an eigenstate of the
photocurrent . The field is obtained by means of a
high-gain phase-insensitive amplifier followed by a high-transmissivity
beam-splitter with a strong local oscillator at the frequency of one of the two
modes.Comment: 3 pages, 1 figur
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