22,848 research outputs found
Hearing and morphological specializations of the mojarra (<i>Eucinostomus argenteus</i>)
The air-filled swimbladder acts as an acoustic amplifier for some fish by converting sound pressure into particle motion, which is transmitted to the inner ear. Here, we describe in detail the specialized connection between the swimbladder and ear in the mojarra, as well as a modified cone on the anal fin in which the posterior end of the swimbladder sits. Hearing tests show the mojarra has better hearing sensitivity than other species of fish without a connection. However, mojarras do not seem to use this adaptation for communication. Furthermore, the inclined position of the swimbladder may help the fish to catch their prey more easily, as the swimbladder will be horizontal when they are picking up benthic prey
A model for fluctuating inflaton coupling: (s)neutrino induced adiabatic perturbations and non-thermal leptogenesis
We discuss an unique possibility of generating adiabatic density
perturbations and leptogenesis from the spatial fluctuations of the inflaton
decay rate. The key assumption is that the initial isocurvature perturbations
are created in the right handed sneutrino sector during inflation which is then
converted into adiabatic perturbations when the inflaton decays. We discuss
distinct imprints on the cosmic micro wave background radiation, which can
distinguish non-thermal versus thermal leptogenesis.Comment: 4 pages, version to be published in PR
Conserved masses in GHS Einstein and string black holes
We analyze the relationship between quasilocal masses calculated for
solutions of conformally related theories. We show that the ADM mass of a
static, spherically symmetric solution is conformally invariant (up to a
constant factor) only if the background action functional is conformally
invariant. Thus, the requirement of conformal invariance places restrictions on
the choice of reference spacetimes. We calculate the mass of the black hole
solutions obtained by Garfinkle, Horowitz, and Strominger (GHS) for both the
string and the Einstein metrics. In addition, the quasilocal thermodynamic
quantities in the string metrics are computed and discussed.Comment: 16 pages REVTeX with packages amsfonts and amssym
A VLA Survey For Faint Compact Radio Sources in the Orion Nebula Cluster
We present Karl G. Janksy Very Large Array (VLA) 1.3 cm, 3.6 cm, and 6 cm
continuum maps of compact radio sources in the Orion Nebular Cluster. We
mosaicked 34 square arcminutes at 1.3 cm, 70 square arcminutes at 3.6 cm and
109 square arcminutes at 6 cm, containing 778 near-infrared detected YSOs and
190 HST-identified proplyds (with significant overlap between those
characterizations). We detected radio emission from 175 compact radio sources
in the ONC, including 26 sources that were detected for the first time at these
wavelengths. For each detected source we fit a simple free-free and dust
emission model to characterize the radio emission. We extrapolate the free-free
emission spectrum model for each source to ALMA bands to illustrate how these
measurements could be used to correctly measure protoplanetary disk dust masses
from sub-millimeter flux measurements. Finally, we compare the fluxes measured
in this survey with previously measured fluxes for our targets, as well as four
separate epochs of 1.3 cm data, to search for and quantify variability of our
sources.Comment: 13 pages, 6 figures, 4 tables, ApJ, in pres
Dynamical N-body Equlibrium in Circular Dilaton Gravity
We obtain a new exact equilibrium solution to the N-body problem in a
one-dimensional relativistic self-gravitating system. It corresponds to an
expanding/contracting spacetime of a circle with N bodies at equal proper
separations from one another around the circle. Our methods are
straightforwardly generalizable to other dilatonic theories of gravity, and
provide a new class of solutions to further the study of (relativistic)
one-dimensional self-gravitating systems.Comment: 4 pages, latex, reference added, minor changes in wordin
Chaos in an Exact Relativistic 3-body Self-Gravitating System
We consider the problem of three body motion for a relativistic
one-dimensional self-gravitating system. After describing the canonical
decomposition of the action, we find an exact expression for the 3-body
Hamiltonian, implicitly determined in terms of the four coordinate and momentum
degrees of freedom in the system. Non-relativistically these degrees of freedom
can be rewritten in terms of a single particle moving in a two-dimensional
hexagonal well. We find the exact relativistic generalization of this
potential, along with its post-Newtonian approximation. We then specialize to
the equal mass case and numerically solve the equations of motion that follow
from the Hamiltonian. Working in hexagonal-well coordinates, we obtaining
orbits in both the hexagonal and 3-body representations of the system, and plot
the Poincare sections as a function of the relativistic energy parameter . We find two broad categories of periodic and quasi-periodic motions that we
refer to as the annulus and pretzel patterns, as well as a set of chaotic
motions that appear in the region of phase-space between these two types.
Despite the high degree of non-linearity in the relativistic system, we find
that the the global structure of its phase space remains qualitatively the same
as its non-relativisitic counterpart for all values of that we could
study. However the relativistic system has a weaker symmetry and so its
Poincare section develops an asymmetric distortion that increases with
increasing . For the post-Newtonian system we find that it experiences a
KAM breakdown for : above which the near integrable regions
degenerate into chaos.Comment: latex, 65 pages, 36 figures, high-resolution figures available upon
reques
Exact Black Hole and Cosmological Solutions in a Two-Dimensional Dilaton-Spectator Theory of Gravity
Exact black hole and cosmological solutions are obtained for a special
two-dimensional dilaton-spectator () theory of gravity. We show how
in this context any desired spacetime behaviour can be determined by an
appropriate choice of a dilaton potential function and a ``coupling
function'' in the action. We illustrate several black hole solutions
as examples. In particular, asymptotically flat double- and multiple- horizon
black hole solutions are obtained. One solution bears an interesting
resemblance to the string-theoretic black hole and contains the same
thermodynamic properties; another resembles the Reissner-Nordstrom
solution. We find two characteristic features of all the black hole solutions.
First the coupling constants in must be set equal to constants of
integration (typically the mass). Second, the spectator field and its
derivative both diverge at any event horizon. A test particle with
``spectator charge" ({\it i.e.} one coupled either to or ),
will therefore encounter an infinite tidal force at the horizon or an
``infinite potential barrier'' located outside the horizon respectively. We
also compute the Hawking temperature and entropy for our solutions. In
cosmology, two non-singular solutions which resemble two exact solutions
in string-motivated cosmology are obtained. In addition, we construct a
singular model which describes the standard non-inflationary big bang
cosmology (). Motivated by the
similaritiesbetween and gravitational field equations in
cosmology, we briefly discuss a special dilaton-spectator action
constructed from the bosonic part of the low energy heterotic string action andComment: 34 pgs. Plain Tex, revised version contains some clarifying comments
concerning the relationship between the constants of integration and the
coupling constants
B-L Violating Nucleon Decay and GUT Scale Baryogenesis in SO(10)
We show that grand unified theories based on SO(10) generate naturally the
next-to-leading baryon number violating operators of dimension seven. These
operators, which violate B-L, lead to unconventional decays of the nucleon such
as n -> e^-K^+, e^- \pi^+ and p -> \nu \pi^+. In two-step breaking schemes of
non-supersymmetric SO(10), nucleon lifetime for decays into these modes is
found to be within reach of experiments. We also identify supersymmetric
scenarios where these decays may be accessible, consistent with gauge coupling
unification. Further, we show that the (B-L)-asymmetry generated in the decays
of GUT scale scalar bosons and/or gauge bosons can explain consistently the
observed baryon asymmetry of the universe. The induced (B-L)-asymmetry is
sphaleron-proof, and survives down to the weak scale without being erased by
the electroweak interactions. This mechanism works efficiently in a large class
of non-SUSY and SUSY SO(10) models, with either a 126 or a 16 Higgs field
employed for rank reduction. In minimal models the induced baryon asymmetry is
tightly connected to the masses of quarks, leptons and neutrinos and is found
to be compatible with observations.Comment: 26 pages, 9 figure
Misner String Entropy
I show that gravitational entropy can be ascribed to spacetimes containing
Misner strings (the gravitational analogues of Dirac strings), even in the
absence of any other event horizon (or bolt) structures. This result follows
from an extension of proposals for evaluating the stress-energy of a
gravitational system which are motivated by the AdS/CFT correspondence.Comment: revtex, 5 pages, references added, typo correcte
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