27,510 research outputs found
Galactic metric, dark radiation, dark pressure and gravitational lensing in brane world models
In the braneworld scenario, the four dimensional effective Einstein equation
has extra terms which arise from the embedding of the 3-brane in the bulk.
These non-local effects, generated by the free gravitational field of the bulk,
may provide an explanation for the dynamics of the neutral hydrogen clouds at
large distances from the galactic center, which is usually explained by
postulating the existence of the dark matter. We obtain the exact galactic
metric, the dark radiation and the dark pressure in the flat rotation curves
region in the brane world scenario. Due to the presence of the bulk effects,
the flat rotation curves could extend several hundred kpc. The limiting radius
for which bulk effects are important is estimated and compared with the
numerical values of the truncation parameter of the dark matter halos, obtained
from weak lensing observations. There is a relatively good agreement between
the predictions of the model and observations. The deflection of photons is
also considered and the bending angle of light is computed. The bending angle
predicted by the brane world models is much larger than that predicted by
standard general relativistic and dark matter models. The angular radii of the
Einstein rings are obtained in the small angles approximation. The predictions
of the brane world model for the tangential shear are compared with the
observational data obtained in the weak lensing of galaxies in the Red-Sequence
Cluster Survey. Therefore the study of the light deflection by galaxies and the
gravitational lensing could discriminate between the different dynamical laws
proposed to model the motion of particles at the galactic level and the
standard dark matter models.Comment: 33 pages, 3 figures, accepted for publication in Ap
HEDGING SPOT CORN: AN EXAMINATION OF THE MINNEAPOLIS GRAIN EXCHANGE'S CASH SETTLED CORN CONTRACT
This research examines the potential basis behavior and hedging effectiveness for the Minneapolis Grain Exchange's (MGE) cash settled corn contract. MGE futures cash settle to the National Corn Index (NCI) calculated by Data Transmission Network (DTN). Focusing on seven regions in Illinois, the data suggest that NCI Futures offer potential advantages over the existing Chicago Board of Trade (CBOT) corn futures. In particular, nearby basis variability could be reduced by nearly one-half from 8.8 cents per bushel to 4.5 cents per bushel, and hedging effectiveness may increase from an average of 80% for the CBOT to 93% for the NCI.Crop Production/Industries, Marketing,
Numerical methods and calculations for droplet flow, heating and ignition
A numerical method was devised and employed to solve a variety of problems related to liquid droplet combustion. The basic transport equations of mass, momentum and energy were formulated in terms of generalized nonorthogonal coordinates, which allows for adaptive griding and arbitrary particle shape. Example problems are solved for internal droplet heating, droplet ignition and high Reynolds number flow over a droplet
Resolving the virial discrepancy in clusters of galaxies with modified Newtonian dynamics
A sample of 197 X-ray emitting clusters of galaxies is considered in the
context of Milgrom's modified Newtonian dynamics (MOND). It is shown that the
gas mass, extrapolated via an assumed model to a fixed radius of 3 Mpc,
is correlated with the gas temperature as predicted by MOND (). The observed temperatures are generally consistent with the inferred
mass of hot gas; no substantial quantity of additional unseen matter is
required in the context of MOND. However, modified dynamics cannot resolve the
strong lensing discrepancy in those clusters where this phenomenon occurs. The
prediction is that additional baryonic matter may be detected in the central
regions of rich clusters.Comment: Submitted to A&A, 4 pages, 3 figures, A&A macro
New Results from a Near-Infrared Search for Hidden Broad-Line Regions in Ultraluminous Infrared Galaxies
This paper reports the latest results from a near-infrared search for hidden
broad-line regions (BLRs: FWHM >~ 2,000 km/s) in ultraluminous infrared
galaxies (ULIGs). The new sample contains thirty-nine ULIGs from the 1-Jy
sample selected for their lack of BLRs at optical wavelengths. The results from
this new study are combined with those from our previous optical and
near-infrared surveys to derive the fraction of all ULIGs with optical or
near-infrared signs of genuine AGN activity (either a BLR or [Si VI] emission).
Comparisons of the dereddened emission-line luminosities of the optical or
obscured BLRs detected in the ULIGs of the 1-Jy sample with those of optical
quasars indicate that the obscured AGN/quasar in ULIGs is the main source of
energy in at least 15 -- 25% of all ULIGs in the 1-Jy sample. This fraction is
30 -- 50% among ULIGs with L_ir > 10^{12.3} L_sun. These results are compatible
with those from recent mid-infrared spectroscopic surveys carried out with ISO.
(abridged)Comment: 40 pages including 10 figures and 3 tables (Table 3 should be printed
in landscape mode
Gravitational polarization and the phenomenology of MOND
The modified Newtonian dynamics (MOND) has been proposed as an alternative to
the dark matter paradigm; the philosophy behind is that there is no dark matter
and we witness a violation of the Newtonian law of dynamics. In this article,
we interpret differently the phenomenology sustaining MOND, as resulting from
an effect of "gravitational polarization", of some cosmic fluid made of dipole
moments, aligned in the gravitational field, and representing a new form of
dark matter. We invoke an internal force, of non-gravitational origin, in order
to hold together the microscopic constituents of the dipole. The dipolar
particles are weakly influenced by the distribution of ordinary matter; they
are accelerated not by the gravitational field, but by its gradient, or tidal
gravitational field.Comment: 14 pages, 1 figure, to appear in Classical and Quantum Gravit
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The Organic Research Centre - Elm Farm:Bulletin 87
Bulletin 87 with coverage of Avian Influenza H5N1 in Suffolk,commentary on Biofuels, a paper on the organic "transition to sustainable resilience",paper on participatory approach to agronomy trials,update on evolutionary breeding of wheat project,article on formation of new growers alliance in UK
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