249 research outputs found
Responses of the hard clam Mercenaria mercenaria (Linne) to induction of spawning by serotonin.
lam size, sex of clam, concentration of serotonin, and site of administration of serotonin were found to influence the mduction of spawning in the hard clam Mercenaria mercenaria (Linne). Overall, male clams greater than 36.4 mm thickness were ~ore likely_ to spawn in response to ser~ton~n i_njection at concentrations of 0.2 or 2.0-mM. Administration of serotonin by injection m the antenor adductor muscle resulted m sJgmficantly more spawnings than intragonadal injection or dispersal in water surrounding the incurrent siphon
Gravitation with superposed Gauss--Bonnet terms in higher dimensions: Black hole metrics and maximal extensions
Our starting point is an iterative construction suited to combinatorics in
arbitarary dimensions d, of totally anisymmetrised p-Riemann 2p-forms (2p\le d)
generalising the (1-)Riemann curvature 2-forms. Superposition of p-Ricci
scalars obtained from the p-Riemann forms defines the maximally Gauss--Bonnet
extended gravitational Lagrangian. Metrics, spherically symmetric in the (d-1)
space dimensions are constructed for the general case. The problem is directly
reduced to solving polynomial equations. For some black hole type metrics the
horizons are obtained by solving polynomial equations. Corresponding Kruskal
type maximal extensions are obtained explicitly in complete generality, as is
also the periodicity of time for Euclidean signature. We show how to include a
cosmological constant and a point charge. Possible further developments and
applications are indicated.Comment: 13 pages, REVTEX. References and Note Adde
Phantom with Born-Infield type Lagrangian
Recent analysis of the observation data indicates that the equation of state
of the dark energy might be smaller than -1, which leads to the introduction of
phantom models featured by its negative kinetic energy to account for the
regime of equation of state . In this paper, we generalize the idea to
the Born-Infield type Lagrangian with negative kinetic energy term and give the
condition for the potential, under which the late time attractor solution
exists and also analyze a viable cosmological model in such a scheme.Comment: 13 pages, 6 figures, Reference updated, the final version will be
published in Phys. Rev.
A Note on Inflation with Tachyon Rolling on the Gauss-Bonnet Brane
In this paper we study the tachyonic inflation in brane world cosmology with
Gauss-Bonnet term in the bulk. We obtain the exact solution of slow roll
equations in case of exponential potential. We attempt to implement the
proposal of Lidsey and Nunes, astro-ph/0303168, for the tachyon condensate
rolling on the Gauss-Bonnet brane and discuss the difficulties associated with
the proposal.Comment: RevTex4, 5 pages, no figures, Minor clarifications added and
references updated, To appear in PR
Inflationary Attractor from Tachyonic Matter
We study the complete evolution of a flat and homogeneous universe dominated
by tachyonic matter. We demonstrate the attractor behaviour of the tachyonic
inflation using the Hamilton-Jacobi formalism. We else obtain analytical
approximations to the trajectories of the tachyon field in different regions.
The numerical calculation shows that an initial non-vanishing momentum does not
prevent the onset of inflation. The slow-rolling solution is an attractor.Comment: 4 pages, 2 figures, RevTe
Power spectrum in the Chaplygin gas model: tachyonic, fluid and scalar field representations
The Chaplygin gas model, characterized by an equation of state of the type emerges naturally from the Nambu-Goto action of string
theory. This fluid representation can be recast under the form of a tachyonic
field given by a Born-Infeld type Lagrangian. At the same time, the Chaplygin
gas equation of state can be obtained from a self-interacting scalar field. We
show that, from the point of view of the supernova type Ia data, the three
representations (fluid, tachyonic, scalar field) lead to the same results.
However, concerning the matter power spectra, while the fluid and tachyonic
descriptions lead to exactly the same results, the self-interacting scalar
field representation implies different statistical estimations for the
parameters. In particular, the estimation for the dark matter density parameter
in the fluid representation favors a universe dominated almost completely by
dark matter, while in the self-interacting scalar field representation the
prediction is very closed to that obtained in the CDM model.Comment: Latex file, 10 pages, 18 figures in EPS forma
Mathematics of Gravitational Lensing: Multiple Imaging and Magnification
The mathematical theory of gravitational lensing has revealed many generic
and global properties. Beginning with multiple imaging, we review
Morse-theoretic image counting formulas and lower bound results, and
complex-algebraic upper bounds in the case of single and multiple lens planes.
We discuss recent advances in the mathematics of stochastic lensing, discussing
a general formula for the global expected number of minimum lensed images as
well as asymptotic formulas for the probability densities of the microlensing
random time delay functions, random lensing maps, and random shear, and an
asymptotic expression for the global expected number of micro-minima. Multiple
imaging in optical geometry and a spacetime setting are treated. We review
global magnification relation results for model-dependent scenarios and cover
recent developments on universal local magnification relations for higher order
caustics.Comment: 25 pages, 4 figures. Invited review submitted for special issue of
General Relativity and Gravitatio
Dynamics of Tachyon and Phantom Field beyond the Inverse Square Potentials
We investigate the cosmological evolution of the tachyon and phantom-tachyon
scalar field by considering the potential parameter () as a function of another potential parameter
(), which correspondingly extends the
analysis of the evolution of our universe from two-dimensional autonomous
dynamical system to the three-dimension. It allows us to investigate the more
general situation where the potential is not restricted to inverse square
potential and .One result is that, apart from the inverse square potential,
there are a large number of potentials which can give the scaling and dominant
solution when the function equals for one or some
values of as well as the parameter satisfies
condition Eq.(18) or Eq.(19). We also find that for a class of different
potentials the dynamics evolution of the universe are actually the same and
therefore undistinguishable.Comment: 8 pages, no figure, accepted by The European Physical Journal
C(2010), online first,
http://www.springerlink.com/content/323417h708gun5g8/?p=dd373adf23b84743b523a3fa249d51c7&pi=
Inflationary Attractor in Braneworld Scenario
We demonstrate the attractor behavior of inflation driven by a scalar field
or a tachyon field in the context of recently proposed four-dimensional
effective gravity induced on the world-volume of a three-brane in
five-dimensional Einstein gravity, and we obtain a set of exact inflationary
solutions. Phase portraits indicate that an initial kinetic term decays rapidly
and it does not prevent the onset of inflation. The trajectories more rapidly
reach the slow-roll curve than in the standard cosmology.Comment: 7 pages, 8 figures, RevTeX, to appear in Phys. Rev. D69 (2004
Status of four-neutrino mass schemes: a global and unified approach to current neutrino oscillation data
We present a unified global analysis of neutrino oscillation data within the
framework of the four-neutrino mass schemes (3+1) and (2+2). We include all
data from solar and atmospheric neutrino experiments, as well as information
from short-baseline experiments including LSND. If we combine only solar and
atmospheric neutrino data, (3+1) schemes are clearly preferred, whereas
short-baseline data in combination with atmospheric data prefers (2+2) models.
When combining all data in a global analysis the (3+1) mass scheme gives a
slightly better fit than the (2+2) case, though all four-neutrino schemes are
presently acceptable. The LSND result disfavors the three-active neutrino
scenario with only and at 99.9% CL with
respect to the four-neutrino best fit model. We perform a detailed analysis of
the goodness of fit to identify which sub-set of the data is in disagreement
with the best fit solution in a given mass scheme.Comment: 32 pages, 8 Figures included, REVTeX4.Improved discussion in sec. XI,
references added, version accepted by Phys. Rev.
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