169 research outputs found
Does Viscosity turn inflation into the CMB and
Consideration of the entropy production in the creation of the CMB leads to a
simple model of the evolution of the universe during this period which suggests
a connection between the small observed acceleration term and the early
inflation of a closed universe. From this we find an unexpected relationship
between the Omega's of cosmology and calculate the total volume of the
universe.Comment: 8 pages , 2 figure
On the magnetic field required for driving the observed angular-velocity variations in the solar convection zone
A putative temporally varying circulation-free magnetic-field configuration
is inferred in an equatorial segment of the solar convection zone from the
helioseismologically inferred angular-velocity variation, assuming that the
predominant dynamics is angular acceleration produced by the azimuthal Maxwell
stress exerted by a field whose surface values are consistent with photospheric
line-of-sight measurements.Comment: to appear in MNRA
Temporal Variations in the Sun's Rotational Kinetic Energy
AIM: To study the variation of the angular momentum and the rotational
kinetic energy of the Sun, and associated variations in the gravitational
multipole moments, on a timescale of the solar cycle. METHOD: Inverting
helioseismic rotational splitting data obtained by the Global Oscillation
Network Group and by the Michelson Doppler Imager on the Solar and Heliospheric
Observatory. RESULTS: The temporal variation in angular momentum and kinetic
energy at high latitudes (>\pi/4) through the convection zone is positively
correlated with solar activity, whereas at low latitudes it is anticorrelated,
except for the top 10% by radius where both are correlated positively.
CONCLUSION: The helioseismic data imply significant temporal variation in the
angular momentum and the rotational kinetic energy, and in the gravitational
multipole moments. The properties of that variation will help constrain
dynamical theories of the solar cycle.Comment: To appear in Astronomy & Astrophysic
Applications of satellite technology to broadband ISDN networks
Two satellite architectures for delivering broadband integrated services digital network (B-ISDN) service are evaluated. The first is assumed integral to an existing terrestrial network, and provides complementary services such as interconnects to remote nodes as well as high-rate multicast and broadcast service. The interconnects are at a 155 Mbs rate and are shown as being met with a nonregenerative multibeam satellite having 10-1.5 degree spots. The second satellite architecture focuses on providing private B-ISDN networks as well as acting as a gateway to the public network. This is conceived as being provided by a regenerative multibeam satellite with on-board ATM (asynchronous transfer mode) processing payload. With up to 800 Mbs offered, higher satellite EIRP is required. This is accomplished with 12-0.4 degree hopping beams, covering a total of 110 dwell positions. It is estimated the space segment capital cost for architecture one would be about 250M. The net user cost is given for a variety of scenarios, but the cost for 155 Mbs services is shown to be about $15-22/minute for 25 percent system utilization
Creation of Dirac Particles in the Presence of a Constant Electric Field in an Anisotropic Bianchi I Universe
In this article we compute the density of Dirac particles created by a
cosmological anisotropic Bianchi I universe in the presence of a constant
electric field. We show that the particle distribution becomes thermal when one
neglects the electric interaction.Comment: 9 page
Charged black holes: Wave equations for gravitational and electromagnetic perturbations
A pair of wave equations for the electromagnetic and gravitational
perturbations of the charged Kerr black hole are derived. The perturbed
Einstein-Maxwell equations in a new gauge are employed in the derivation. The
wave equations refer to the perturbed Maxwell spinor and to the shear
of a principal null direction of the Weyl curvature. The whole
construction rests on the tripod of three distinct derivatives of the first
curvature of a principal null direction.Comment: 12 pages, to appear in Ap.
Rapid dissipation of magnetic fields due to Hall current
We propose a mechanism for the fast dissipation of magnetic fields which is
effective in a stratified medium where ion motions can be neglected. In such a
medium, the field is frozen into the electrons and Hall currents prevail.
Although Hall currents conserve magnetic energy, in the presence of density
gradients, they are able to create current sheets which can be the sites for
efficient dissipation of magnetic fields. We recover the frequency,
, for Hall oscillations modified by the presence of density
gradients. We show that these oscillations can lead to the exchange of energy
between different components of the field. We calculate the time evolution and
show that magnetic fields can dissipate on a timescale of order
. This mechanism can play an important role for magnetic
dissipation in systems with very steep density gradients where the ions are
static such as those found in the solid crust of neutron stars.Comment: 9 pages, changed fig.
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