979,741 research outputs found
Does a dynamical system lose energy by emitting gravitational waves?
We note that Eddington's radiation damping calculation of a spinning rod
fails to account for the complete mass integral as given by Tolman. The missing
stress contributions precisely cancel the standard rate given by the
'quadrupole formula'. This indicates that while the usual 'kinetic' term can
properly account for dynamical changes in the source, the actual mass is
conserved. Hence gravity waves are not carriers of energy in vacuum. This
supports the hypothesis that energy including the gravitational contribution is
confined to regions of non-vanishing energy-momentum tensor .
PACS numbers: 04.20.Cv, 04.30.-wComment: Published in Modern Physics Letters A vol 14, no 23, 1531, 1999 Full
text available in the journa
Repeated Relativistic Ejections in GRS 1915+105
In 1994 February-August we observed with the VLA four ejection events of
radio emitting clouds from the high energy source GRS 1915+105. These events
are all consistent with anti-parallel ejections of twin pairs of clouds moving
away from the compact source at 0.92 of the speed of light and angles of
70 with respect to the line of sight. The flux ratios and time
evolution of the expelled clouds are consistent with actual motions of the
radiating matter rather than with the simple propagation of pulses in a medium
moving at slower velocities. The large kinetic power of the sudden, short, and
rather discontinuous ejections exceeds by more than an order of magnitude the
maximum steady photon luminosity of the source, suggesting that in GRS 1915+105
a radiation acceleration mechanism of the ejecta is unlikely. As in other
galactic and extragalactic radio sources, the decrease in flux density as a
function of angular separation from the central source shows a steepening with
distance. Additional ejection events have been observed in 1995 and 1997 and we
compare them with the 1994 events.Comment: 20 pages, 7 figures. To appear in The Astrophysical Journal, January
10, 1999 issu
Stability of Gravitational and Electromagnetic Geons
Recent work on gravitational geons is extended to examine the stability
properties of gravitational and electromagnetic geon constructs. All types of
geons must possess the property of regularity, self-consistency and
quasi-stability on a time-scale much longer than the period of the comprising
waves. Standard perturbation theory, modified to accommodate time-averaged
fields, is used to test the requirement of quasi-stability. It is found that
the modified perturbation theory results in an internal inconsistency. The
time-scale of evolution is found to be of the same order in magnitude as the
period of the comprising waves. This contradicts the requirement of slow
evolution. Thus not all of the requirements for the existence of
electromagnetic or gravitational geons are met though perturbation theory. From
this result it cannot be concluded that an electromagnetic or a gravitational
geon is a viable entity. The broader implications of the result are discussed
with particular reference to the problem of gravitational energy.Comment: 40 pages, 5 EPS figures, uses overcite.st
Long-wavelength limit of gyrokinetics in a turbulent tokamak and its intrinsic ambipolarity
Recently, the electrostatic gyrokinetic Hamiltonian and change of coordinates
have been computed to order in general magnetic geometry. Here
is the gyrokinetic expansion parameter, the gyroradius over the
macroscopic scale length. Starting from these results, the long-wavelength
limit of the gyrokinetic Fokker-Planck and quasineutrality equations is taken
for tokamak geometry. Employing the set of equations derived in the present
article, it is possible to calculate the long-wavelength components of the
distribution functions and of the poloidal electric field to order
. These higher-order pieces contain both neoclassical and turbulent
contributions, and constitute one of the necessary ingredients (the other is
given by the short-wavelength components up to second order) that will
eventually enter a complete model for the radial transport of toroidal angular
momentum in a tokamak in the low flow ordering. Finally, we provide an explicit
and detailed proof that the system consisting of second-order gyrokinetic
Fokker-Planck and quasineutrality equations leaves the long-wavelength radial
electric field undetermined; that is, the turbulent tokamak is intrinsically
ambipolar.Comment: 70 pages. Typos in equations (63), (90), (91), (92) and (129)
correcte
The fundamental group and torsion group of Beauville surfaces
We give a survey on the fundamental group of surfaces isogenous to a higher
product. If the surfaces are regular, e.g. if they are Beauville surfaces, the
first homology group is a finite group. We present a MAGMA script which
calculates the first homology groups of regular surfaces isogenous to a
product.Comment: 14 pages; MAGMA script included; v2: minor corrections, final version
to appear in the Proceedings of the Conference "Beauville Surfaces and
Groups", Newcastle University (UK), 7-9th June 201
Tree-level unitarity constraints in the most general 2HDM
We obtain tree-level unitarity constraints for the most general Two Higgs
Doublet Model (2HDM) with explicit CP-violation. We briefly discuss
correspondence between possible violation of tree level unitarity limitation
and physical content of the theory.Comment: 6 pages, no figure
Estimation of household demand systems with theoretically compatible Engel curves and unit value specifications
We develop a method for estimation of price reactions using unit value
data which exploits the implicit links between quantity and unit value
choices. This allows us to combine appealing Engel curve specifications
with a model of unit value determination in a way which is consistent
with demand theory, unlike methods hitherto prominent in the literature.
The method is applied to Czech data
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