10,086 research outputs found
Neutron-Deuteron System and Photon Polarization Parameter at Thermal Neutron Energies
Effective Field Theory(EFT) is, the unique, model independent and systematic
low-energy version of QCD for processes involving momenta below the pion mass.
A low-energy photo-nuclear observable in three-body systems, photon
polarization parameter at thermal neutron energies is calculated by using
pionless EFT up to next-to-next to leading order(NLO). In order to make a
comparative study of this model, we compared our results for photon
polarization parameter with the realistic Argonne two-nucleon and
Urbana IX or Tucson-Melbourne three-nucleon interactions. Three-body currents
give small but significant contributions to some of the observables in the
neutron-deuteron radiative capture cross section at thermal neutron energies.
In this formalism the three-nucleon forces are needed up to NLO for cut-off
independent results. Our result converges order by order in low energy
expansion and also cut-off independent at this order.Comment: 10 pages, 3 figures, 2 table
Dynamical Cusp Regeneration
After being destroyed by a binary supermassive black hole, a stellar density
cusp can regrow at the center of a galaxy via energy exchange between stars
moving in the gravitational field of the single, coalesced hole. We illustrate
this process via high-accuracy N-body simulations. Regeneration requires
roughly one relaxation time and the new cusp extends to a distance of roughly
one-fifth the black hole's influence radius, with density rho ~ r^{-7/4}; the
mass in the cusp is of order 10% the mass of the black hole. Growth of the cusp
is preceded by a stage in which the stellar velocity dispersion evolves toward
isotropy and away from the tangentially-anisotropic state induced by the
binary. We show that density profiles similar to those observed at the center
of the Milky Way and M32 can regenerate themselves in several Gyr following
infall of a second black hole; the presence of density cusps at the centers of
these galaxies can therefore not be used to infer that no merger has occurred.
We argue that Bahcall-Wolf cusps are ubiquitous in stellar spheroids fainter
than M_V ~ -18.5 that contain supermassive black holes, but the cusps have not
been detected outside of the Local Group since their angular sizes are less
than 0.1". We show that the presence of a cusp implies a lower limit of
\~10^{-4} per year on the rate of stellar tidal disruptions, and discuss the
consequences of the cusps for gravitational lensing and the distribution of
dark matter on sub-parsec scales.Comment: Accepted for publication in The Astrophysical Journa
Study of Mesoscale Exchange Processes Utilizing LANDSAT Air Mass Cloud Imagery
There are no author-identified significant results in this report
Study of mesocale exchange processes utilizing LANDSAT air mass cloud imagery
There are no author-identified significant results in this report
Time-Dependent Models for Dark Matter at the Galactic Center
The prospects of indirect detection of dark matter at the galactic center
depend sensitively on the mass profile within the inner parsec. We calculate
the distribution of dark matter on sub-parsec scales by integrating the
time-dependent Fokker-Planck equation, including the effects of
self-annihilations, scattering of dark matter particles by stars, and capture
in the supermassive black hole. We consider a variety of initial dark matter
distributions, including models with very high densities ("spikes") near the
black hole, and models with "adiabatic compression" of the baryons. The
annihilation signal after 10 Gyr is found to be substantially reduced from its
initial value, but in dark matter models with an initial spike,
order-of-magnitude enhancements can persist compared with the rate in
spike-free models, with important implications for indirect dark matter
searches with GLAST and Air Cherenkov Telescopes like HESS and CANGAROO.Comment: Four page
Study of Mesoscale Exchange Processes Utilizing Landsat Air Mass Cloud Imagery
There are no author-identified significant results in this report
Life history aspects of 19 rockfish species (Scorpaenidae: Sebastes) from the Southern California Bight
The authors investigated various life history aspects of 19
rockfish species (Sebastes chlorostictus, S. constellatus, S. dalli, S. elongatus, S. ensifer, S. entomelas, S. flavidus, S. goodei, S. hopkinsi, S. levis, S. melanostomus, S. miniatus, S. ovalis, S. paucispinis, S. rosaceus, S. rosenblatti, S. rufus, s. saxicola, S. semicinctus) from the southern California Bight. These aspects included depth distribution, age-length relationships (of 7 species), length-weight relationships, size at first maturity, spawning season, and fecundity. Growth rates of female S. elongatus, S. hopkinsi, S. ova/is, S. saxicola, and S. semicinctus were higher
than male conspecifics. Multiple spawning per season was found in 12 species. Generally, most species spawned between late winter and early summer, though there was some spawning within the genus throughout the year. Spawning season duration ranged from 2 (S. flavidus) to 10 months (S. paucispinis). Spawning seasons tended to start earlier in the year and be of longer duration in the southern California Bight, compared to published data on central California conspecifics. Males matured at a smaller length in 7 of the 17 species studied. Maximum fecundities ranged from 18,000 (S. dalll) to about 2,680,000 (S. levis). (PDF file contains 44 pages.
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