2,066 research outputs found
Electropneumatic rheostat regulates high current
Electropneumatic rheostat maintains a constant direct current in each of several high-power parallel loads, of variable resistance, across a single source. It provides current regulation at any preset value by dissipating the proper amount of energy thermally, and uses a column of mercury to vary the effective length of a resistance element
Filtering post-Newtonian gravitational waves from coalescing binaries
Gravitational waves from inspiralling binaries are expected to be detected
using a data analysis technique known as {\it matched filtering.} This
technique is applicable whenever the form of the signal is known accurately.
Though we know the form of the signal precisely, we will not know {\it a
priori} its parameters. Hence it is essential to filter the raw output through
a host of search templates each corresponding to different values of the
parameters. The number of search templates needed in detecting the Newtonian
waveform characterized by three independent parameters is itself several
thousands. With the inclusion of post-Newtonian corrections the inspiral
waveform will have four independent parameters and this, it was thought, would
lead to an increase in the number of filters by several orders of
magnitude---an unfavorable feature since it would drastically slow down data
analysis. In this paper I show that by a judicious choice of signal parameters
we can work, even when the first post-Newtonian corrections are included, with
as many number of parameters as in the Newtonian case. In other words I
demonstrate that the effective dimensionality of the signal parameter space
does not change when first post-Newtonian corrections are taken into account.Comment: 5 pages, revtex, 2 figures available upon reques
Nucleosynthesis Constraints on Scalar-Tensor Theories of Gravity
We study the cosmological evolution of massless single-field scalar-tensor
theories of gravitation from the time before the onset of annihilation
and nucleosynthesis up to the present. The cosmological evolution together with
the observational bounds on the abundances of the lightest elements (those
mostly produced in the early universe) place constraints on the coefficients of
the Taylor series expansion of , which specifies the coupling of the
scalar field to matter and is the only free function in the theory. In the case
when has a minimum (i.e., when the theory evolves towards general
relativity) these constraints translate into a stronger limit on the
Post-Newtonian parameters and than any other observational
test. Moreover, our bounds imply that, even at the epoch of annihilation and
nucleosynthesis, the evolution of the universe must be very close to that
predicted by general relativity if we do not want to over- or underproduce
He. Thus the amount of scalar field contribution to gravity is very small
even at such an early epoch.Comment: 15 pages, 2 figures, ReVTeX 3.1, submitted to Phys. Rev. D1
Corotation Resonance and Diskoseismology Modes of Black Hole Accretion Disks
We demonstrate that the corotation resonance affects only some
non-axisymmetric g-mode oscillations of thin accretion disks, since it is
located within their capture zones. Using a more general (weaker radial WKB
approximation) formulation of the governing equations, such g-modes, treated as
perfect fluid perturbations, are shown to formally diverge at the position of
the corotation resonance. A small amount of viscosity adds a small imaginary
part to the eigenfrequency which has been shown to induce a secular instability
(mode growth) if it acts hydrodynamically. The g-mode corotation resonance
divergence disappears, but the mode magnitude can remain largest at the place
of the corotation resonance. For the known g-modes with moderate values of the
radial mode number and axial mode number (and any vertical mode number), the
corotation resonance lies well outside their trapping region (and inside the
innermost stable circular orbit), so the observationally relevant modes are
unaffected by the resonance. The axisymmetric g-mode has been seen by Reynolds
& Miller in a recent inviscid hydrodynamic accretion disk global numerical
simulation. We also point out that the g-mode eigenfrequencies are
approximately proportional to m for axial mode numbers |m|>0.Comment: 16 pages, no figures. Submitted to The Astrophysical Journa
On the Energy-Momentum Tensor of the Scalar Field in Scalar--Tensor Theories of Gravity
We study the dynamical description of gravity, the appropriate definition of
the scalar field energy-momentum tensor, and the interrelation between them in
scalar-tensor theories of gravity. We show that the quantity which one would
naively identify as the energy-momentum tensor of the scalar field is not
appropriate because it is spoiled by a part of the dynamical description of
gravity. A new connection can be defined in terms of which the full dynamical
description of gravity is explicit, and the correct scalar field
energy-momentum tensor can be immediately identified. Certain inequalities must
be imposed on the two free functions (the coupling function and the potential)
that define a particular scalar-tensor theory, to ensure that the scalar field
energy density never becomes negative. The correct dynamical description leads
naturally to the Einstein frame formulation of scalar-tensor gravity which is
also studied in detail.Comment: Submitted to Phys. Rev D15, 10 pages. Uses ReVTeX macro
Epicyclic oscillations of non-slender fluid tori around Kerr black holes
Considering epicyclic oscillations of pressure-supported perfect fluid tori
orbiting Kerr black holes we examine non-geodesic (pressure) effects on the
epicyclic modes properties. Using a perturbation method we derive fully general
relativistic formulas for eigenfunctions and eigenfrequencies of the radial and
vertical epicyclic modes of a slightly non-slender, constant specific angular
momentum torus up to second-order accuracy with respect to the torus thickness.
The behaviour of the axisymmetric and lowest-order () non-axisymmetric
epicyclic modes is investigated. For an arbitrary black hole spin we find that,
in comparison with the (axisymmetric) epicyclic frequencies of free test
particles, non-slender tori receive negative pressure corrections and exhibit
thus lower frequencies. Our findings are in qualitative agreement with the
results of a recent pseudo-Newtonian study of analogous problem defined within
the Paczy{\'n}ski-Wiita potential. Implications of our results on the
high-frequency QPO models dealing with epicyclic oscillations are addressed.Comment: 24 pages, 8 figure
Gravitational Waves from Mergin Compact Binaries: How Accurately Can One Extract the Binary's Parameters from the Inspiral Waveform?
The most promising source of gravitational waves for the planned detectors
LIGO and VIRGO are merging compact binaries, i.e., neutron star/neutron star
(NS/NS), neutron star/black hole (NS/BH), and black hole/black-hole (BH/BH)
binaries. We investigate how accurately the distance to the source and the
masses and spins of the two bodies will be measured from the gravitational wave
signals by the three detector LIGO/VIRGO network using ``advanced detectors''
(those present a few years after initial operation). The combination of the masses of the two bodies is
measurable with an accuracy . The reduced mass is measurable
to for NS/NS and NS/BH binaries, and for BH/BH
binaries (assuming BH's). Measurements of the masses and spins are
strongly correlated; there is a combination of and the spin angular
momenta that is measured to within . We also estimate that distance
measurement accuracies will be for of the detected
signals, and for of the signals, for the LIGO/VIRGO
3-detector network.Comment: 103 pages, 20 figures, submitted to Phys Rev D, uses revtex macros,
Caltech preprint GRP-36
Coupling parameters and the form of the potential via Noether symmetry
We explore the conditions for the existence of Noether symmetries in the
dynamics of FRW metric, non minimally coupled with a scalar field, in the most
general situation, and with nonzero spatial curvature. When such symmetries are
present we find general exact solution for the Einstein equations. We also show
that non Noether symmetries can be found.
Finally,we present an extension of the procedure to the Kantowski- Sachs
metric which is particularly interesting in the case of degenerate Lagrangian.Comment: 13 pages, no figure
Representation theory of some infinite-dimensional algebras arising in continuously controlled algebra and topology
In this paper we determine the representation type of some algebras of
infinite matrices continuously controlled at infinity by a compact metrizable
space. We explicitly classify their finitely presented modules in the finite
and tame cases. The algebra of row-column-finite (or locally finite) matrices
over an arbitrary field is one of the algebras considered in this paper, its
representation type is shown to be finite.Comment: 33 page
Gravitational Radiation from Nonaxisymmetric Instability in a Rotating Star
We present the first calculations of the gravitational radiation produced by
nonaxisymmetric dynamical instability in a rapidly rotating compact star. The
star deforms into a bar shape, shedding of its mass and
of its angular momentum. The gravitational radiation is calculated in the
quadrupole approximation. For a mass M and radius km, the gravitational waves have frequency kHz and amplitude
at the distance of the Virgo Cluster. They carry off
energy and radiate angular momentum .Comment: 16 pages, LaTeX with REVTEX macros, reprints available - send mailing
address to [email protected]. Published: PRL 72, 1314 (1994
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