4,993 research outputs found
The damping of gravitational waves in dust
We examine a simple model of interaction of gravitational waves with matter
(primarily represented by dust). The aim is to investigate a possible damping
effect on the intensity of gravitational wave when passing through media. This
might be important for gravitational wave astronomy when the sources are
obscured by dust or molecular clouds.Comment: 7 pages, accepted to Phys. Sc
Materials review for improved automotive gas turbine engine
The potential role of superalloys, refractory alloys, and ceramics in the hottest sections of engines operating with turbine inlet temperatures as high as 1370 C is examined. The convential superalloys, directionally solidified eutectics, oxide dispersion strenghened alloys, and tungsten fiber reinforced superalloys are reviewed and compared on the basis of maximum turbine blade temperature capability. Improved high temperature protective coatings and special fabrication techniques for these advanced alloys are discussed. Chromium, columbium, molybdenum, tantalum, and tungsten alloys are also reviewed. Molbdenum alloys are found to be the most suitable for mass produced turbine wheels. Various forms and fabrication processes for silicon nitride, silicon carbide, and SIALON's are investigated for use in highstress and medium stress high temperature environments
Conformal Gravity with Electrodynamics for Fermion Fields and their Symmetry Breaking Mechanism
In this paper we consider an axial torsion to build metric-compatible
connections in conformal gravity, with gauge potentials; the geometric
background is filled with Dirac spinors: scalar fields with suitable potentials
are added eventually. The system of field equations is worked out to have
torsional effects converted into spinorial self-interactions: the massless
spinors display self-interactions of a specific form that gives them the
features they have in the non-conformal theory but with the additional
character of renormalizability, and the mechanisms of generation of mass and
cosmological constants become dynamical. As a final step we will address the
cosmological constant and coincidence problems.Comment: 13 page
Energy Contents of Gravitational Waves in Teleparallel Gravity
The conserved quantities, that are, gravitational energy-momentum and its
relevant quantities are investigated for cylindrical and spherical
gravitational waves in the framework of teleparallel equivalent of General
Relativity using the Hamiltonian approach. For both cylindrical and spherical
gravitational waves, we obtain definite energy and constant momentum. The
constant momentum shows consistency with the results available in General
Relativity and teleparallel gravity. The angular momentum for cylindrical and
spherical gravitational waves also turn out to be constant. Further, we
evaluate their gravitational energy-momentum fluxes and gravitational pressure.Comment: 14 pages, accepted for publication in Mod. Phys. Lett.
Schwarzschild horizon and the gravitational redshift formula
The gravitational redshift formula is usually derived in the geometric optics
approximation. In this note we consider an exact formulation of the problem in
the Schwarzschild space-time, with the intention to clarify under what
conditions this redshift law is valid. It is shown that in the case of shocks
the radial component of the Poynting vector can scale according to the redshift
formula, under a suitable condition. If that condition is not satisfied, then
the effect of the backscattering can lead to significant modifications. The
obtained results imply that the energy flux of the short wavelength radiation
obeys the standard gravitational redshift formula while the energy flux of long
waves can scale differently, with redshifts being dependent on the frequency.Comment: Revtex, 5 p. Rewritten Sec. II, minor changes in Secs III - VII. To
appear in the Classical and Quantum Gravit
A duality relation for fluid spacetime
We consider the electromagnetic resolution of gravitational field. We show
that under the duality transformation, in which active and passive electric
parts of the Riemann curvature are interchanged, a fluid spacetime in comoving
coordinates remains invariant in its character with density and pressure
transforming, while energy flux and anisotropic pressure remaining unaltered.
Further if fluid admits a barotropic equation of state,
where , which will transform to . Clearly the stiff fluid and dust are dual to each-other
while , will go to flat spacetime. However the n and the deSitter ) universes ar e self-dual.Comment: 5 pages, LaTeX version, Accepted in Classical Quantum Gravity as a
Lette
Magnetic Monopole Dynamics in Spin Ice
One of the most remarkable examples of emergent quasi-particles, is that of
the "fractionalization" of magnetic dipoles in the low energy configurations of
materials known as "spin ice", into free and unconfined magnetic monopoles
interacting via Coulomb's 1/r law [Castelnovo et. al., Nature, 451, 42-45
(2008)]. Recent experiments have shown that a Coulomb gas of magnetic charges
really does exist at low temperature in these materials and this discovery
provides a new perspective on otherwise largely inaccessible phenomenology. In
this paper, after a review of the different spin ice models, we present
detailed results describing the diffusive dynamics of monopole particles
starting both from the dipolar spin ice model and directly from a Coulomb gas
within the grand canonical ensemble. The diffusive quasi-particle dynamics of
real spin ice materials within "quantum tunneling" regime is modeled with
Metropolis dynamics, with the particles constrained to move along an underlying
network of oriented paths, which are classical analogues of the Dirac strings
connecting pairs of Dirac monopoles.Comment: 26 pages, 12 figure
Genetic variation in FAAH is associated with cannabis use disorders in a young adult sample of Mexican Americans
Cannabis is a commonly used drug and studies have shown that a significant portion of the variation in cannabis use disorders (CUDs) is heritable. Five genes known to play a role in the endocannabinoid system and CUDs were examined in a community sample of young adult Mexican Americans (MAs): CNR1, MGLL, FAAH, DAGLA, and DAGLB
Pressure as a Source of Gravity
The active mass density in Einstein's theory of gravitation in the analog of
Poisson's equation in a local inertial system is proportional to .
Here is the density of energy and its pressure for a perfect fluid.
By using exact solutions of Einstein's field equations in the static case we
study whether the pressure term contributes towards the mass
- …