25 research outputs found
Exact Hypersurface-Homogeneous Solutions in Cosmology and Astrophysics
A framework is introduced which explains the existence and similarities of
most exact solutions of the Einstein equations with a wide range of sources for
the class of hypersurface-homogeneous spacetimes which admit a Hamiltonian
formulation. This class includes the spatially homogeneous cosmological models
and the astrophysically interesting static spherically symmetric models as well
as the stationary cylindrically symmetric models. The framework involves
methods for finding and exploiting hidden symmetries and invariant submanifolds
of the Hamiltonian formulation of the field equations. It unifies, simplifies
and extends most known work on hypersurface-homogeneous exact solutions. It is
shown that the same framework is also relevant to gravitational theories with a
similar structure, like Brans-Dicke or higher-dimensional theories.Comment: 41 pages, REVTEX/LaTeX 2.09 file (don't use LaTeX2e !!!) Accepted for
publication in Phys. Rev.
Unimodular bimode gravity and the coherent scalar-graviton field as galaxy dark matter
The explicit violation of the general gauge invariance/relativity is adopted
as the origin of dark matter and dark energy of the gravitational nature. The
violation of the local scale invariance alone, with the residual unimodular
one, is considered. Besides the four-volume preserving deformation mode -- the
transverse-tensor graviton -- the metric comprises a compression mode -- the
scalar graviton, or the systolon. A unimodular invariant and general covariant
metric theory of the bimode/scalar-tensor gravity is consistently worked out.
To reduce the primordial ambiguity of the theory a dynamical global symmetry is
imposed, with its subsequent spontaneous breaking revealed. The static
spherically symmetric case in the empty, but possibly for the origin, space is
studied. A three-parameter solution describing a new static space structure --
the dark lacuna -- is constructed. It enjoys the property of gravitational
confinement, with the logarithmic potential of gravitational attraction at the
periphery, and results in the asymptotically flat rotation curves. Comprising a
super-massive dark fracture (a scalar-modified black hole) at the origin
surrounded by a cored dark halo, the dark lacunas are proposed as a prototype
model of galaxies, implying an ultimate account for the distributed
non-gravitational matter and a putative asphericity or rotation.Comment: 38 pages, 10 figures; exposition improved, remarks added, accepted
for publicatio
Ultrasonic modulation of multiply scattered coherent light: An analytical model for anisotropically scattering media
The neuromuscular basis of courtship song inDrosophila: The role of the indirect flight muscles
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Overview of the MFTF electrical systems
The Mirror Fusion Test Facility, scheduled for completion in October 1981, will contain a complex, state-of-the-art array of electrical and electronics equipment valued at over 60 M$. Three injector systems will be employed to initiate and sustain the MFTF deuterium plasma. A plasma streaming system and a startup neutron beam system will be used to establish a target plasma. A sustaining neutral beam system will be used to fuel and sustain the MFTF plasma for 0.5 s. Additional power supply systems required on MFTF include two magnet power supplies with quench protection circuitry for powering the superconducting YIN/YANG magnet pair and eight 10 KHz power supplies for powering the Ti gettering system. Due to the complexity, physical size, and multiple systems of MFTF, a distributed, hierarchial, computer control and instrumentation system will be used. Color graphic, touch-panel, control consoles will provide the man-machine interface. The MFTF will have the capability of conducting an experiment every five minutes
Death penalty: the political foundations of the global trend toward abolition
The death penalty is like no other punishment. Its continued existence in many countries of the world creates political tensions within these countries and between governments of retentionist and abolitionist countries. After the Second World War, more and more countries have abolished the death penalty. This article argues that the major determinants of this global trend toward abolition are political, a claim which receives support in a quantitative cross-national analysis from 1950 to 2002. Democracy, democratization, international political pressure on retentionist countries and peer group effects in relatively abolitionist regions all raise the likelihood of abolition. There is also a partisan effect as abolition becomes more likely if the chief executive’s party is left-wing oriented. Cultural, social and economic determinants receive only limited support. The global trend toward abolition will go on if democracy continues to spread around the world and abolitionist countries stand by their commitment to press for abolition all over the world.