6,343 research outputs found
How can a multimodal approach to primate communication help us understand the evolution of communication?
Scientists studying the communication of non-human animals are often aiming to better understand the evolution of human communication, including human language. Some scientists take a phylogenetic perspective, where the goal is to trace the evolutionary history of communicative traits, while others take a functional perspective, where the goal is to understand the selection pressures underpinning specific traits. Both perspectives are necessary to fully understand the evolution of communication, but it is important to understand how the two perspectives differ and what they can and cannot tell us. Here, we suggest that integrating phylogenetic and functional questions can be fruitful in better understanding the evolution of communication. We also suggest that adopting a multimodal approach to communication might help to integrate phylogenetic and functional questions, and provide an interesting avenue for research into language evolution
Gravitational Wave Background from Neutrino-Driven Gamma-Ray Bursts
We discuss the gravitational wave background (GWB) from a cosmological
population of gamma-ray bursts (GRBs). Among various emission mechanisms for
the gravitational waves (GWs), we pay a particular attention to the vast
anisotropic neutrino emissions from the accretion disk around the black hole
formed after the so-called failed supernova explosions. The produced GWs by
such mechanism are known as burst with memory, which could dominate over the
low-frequency regime below \sim 10Hz. To estimate their amplitudes, we derive
general analytic formulae for gravitational waveform from the axisymmetric
jets. Based on the formulae, we first quantify the spectrum of GWs from a
single GRB. Then, summing up its cosmological population, we find that the
resultant value of the density parameter becomes roughly \Omega_{GW} \approx
10^{-20} over the wide-band of the low-frequency region, f\sim 10^{-4}-10^1Hz.
The amplitude of GWB is sufficiently smaller than the primordial GWBs
originated from an inflationary epoch and far below the detection limit.Comment: 6 pages, 4 figures, accepted for publication in MNRA
Ab initio Translationally Invariant Nonlocal One-body Densities from No-core Shell-model Theory
[Background:] It is well known that effective nuclear interactions are in
general nonlocal. Thus if nuclear densities obtained from {\it ab initio}
no-core-shell-model (NCSM) calculations are to be used in reaction
calculations, translationally invariant nonlocal densities must be available.
[Purpose:] Though it is standard to extract translationally invariant one-body
local densities from NCSM calculations to calculate local nuclear observables
like radii and transition amplitudes, the corresponding nonlocal one-body
densities have not been considered so far. A major reason for this is that the
procedure for removing the center-of-mass component from NCSM wavefunctions up
to now has only been developed for local densities. [Results:] A formulation
for removing center-of-mass contributions from nonlocal one-body densities
obtained from NCSM and symmetry-adapted NCSM (SA-NCSM) calculations is derived,
and applied to the ground state densities of He, Li, C, and
O. The nonlocality is studied as a function of angular momentum
components in momentum as well as coordinate space [Conclusions:] We find that
the nonlocality for the ground state densities of the nuclei under
consideration increases as a function of the angular momentum. The relative
magnitude of those contributions decreases with increasing angular momentum. In
general, the nonlocal structure of the one-body density matrices we studied is
given by the shell structure of the nucleus, and can not be described with
simple functional forms.Comment: 13 pages, 11 Figure
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First CRDS-measurements of water vapour continuum in the 940nm absorption band
Measurements of near-infrared water vapour continuum using continuous wave cavity ring down spectroscopy (cw-
CRDS) have been performed at around 10611.6 and 10685:2 cm1. The continuum absorption coefficients for N2-
broadening have been determined for two temperatures and wavenumbers.
These results represent the first near-IR continuum laboratory data determined within the complex spectral environment in the 940nm water vapour band and are in reasonable agreement with simulations using the semiempirical CKD formulation
GRB Energetics in the Swift Era
We examine the rest frame energetics of 76 gamma-ray bursts (GRBs) with known
redshift that were detected by the Swift spacecraft and monitored by the
satellite's X-ray Telescope (XRT). Using the bolometric fluence values
estimated in Butler et al. 2007b and the last XRT observation for each event,
we set a lower limit the their collimation corrected energy Eg and find that a
68% of our sample are at high enough redshift and/or low enough fluence to
accommodate a jet break occurring beyond the last XRT observation and still be
consistent with the pre-Swift Eg distribution for long GRBs. We find that
relatively few of the X-ray light curves for the remaining events show evidence
for late-time decay slopes that are consistent with that expected from post jet
break emission. The breaks in the X-ray light curves that do exist tend to be
shallower and occur earlier than the breaks previously observed in optical
light curves, yielding a Eg distribution that is far lower than the pre-Swift
distribution. If these early X-ray breaks are not due to jet effects, then a
small but significant fraction of our sample have lower limits to their
collimation corrected energy that place them well above the pre-Swift Eg
distribution. Either scenario would necessitate a much wider post-Swift Eg
distribution for long cosmological GRBs compared to the narrow standard energy
deduced from pre-Swift observations. We note that almost all of the pre-Swift
Eg estimates come from jet breaks detected in the optical whereas our sample is
limited entirely to X-ray wavelengths, furthering the suggestion that the
assumed achromaticity of jet breaks may not extend to high energies.Comment: 30 pages, 10 figures, Accepted to Ap
Crucial Physical Dependencies of the Core-Collapse Supernova Mechanism
We explore with self-consistent 2D F{\sc{ornax}} simulations the dependence
of the outcome of collapse on many-body corrections to neutrino-nucleon cross
sections, the nucleon-nucleon bremsstrahlung rate, electron capture on heavy
nuclei, pre-collapse seed perturbations, and inelastic neutrino-electron and
neutrino-nucleon scattering. Importantly, proximity to criticality amplifies
the role of even small changes in the neutrino-matter couplings, and such
changes can together add to produce outsized effects. When close to the
critical condition the cumulative result of a few small effects (including
seeds) that individually have only modest consequence can convert an anemic
into a robust explosion, or even a dud into a blast. Such sensitivity is not
seen in one dimension and may explain the apparent heterogeneity in the
outcomes of detailed simulations performed internationally. A natural
conclusion is that the different groups collectively are closer to a realistic
understanding of the mechanism of core-collapse supernovae than might have
seemed apparent.Comment: 25 pages; 10 figure
Ab initio Folding Potentials for Nucleon-Nucleus Scattering based on NCSM One-Body Densities
Calculating microscopic optical potentials for elastic nucleon-nucleus
scattering has already led to large body of work in the past. For folding
first-order calculations the nucleon-nucleon (NN) interaction and the one-body
density of the nucleus were taken as input to rigorous calculations in a
spectator expansion of the multiple scattering series.
Based on the Watson expansion of the multiple scattering series we employ a
nonlocal translationally invariant nuclear density derived from a chiral
next-to-next-to-leading order (NNLO) and the very same interaction for
consistent full-folding calculation of the effective (optical) potential for
nucleon-nucleus scattering for light nuclei.
We calculate scattering observables, such as total, reaction, and
differential cross sections as well as the analyzing power and the
spin-rotation parameter, for elastic scattering of protons and neutrons from
He, He, C, and O, in the energy regime between 100 and
200~MeV projectile kinetic energy, and compare to available data.
Our calculations show that the effective nucleon-nucleus potential obtained
from the first-order term in the spectator expansion of the multiple scattering
expansion describes experiments very well to about 60 degrees in the
center-of-mass frame, which coincides roughly with the validity of the NNLO
chiral interaction used to calculate both the NN amplitudes and the one-body
nuclear density.Comment: 10 pages, 14 figures, 1 tabl
Asymmetric neutrino emission due to neutrino-nucleon scatterings in supernova magnetic fields
We derive the cross section of neutrino-nucleon scatterings in supernova
magnetic fields, including weak-magnetism and recoil corrections. Since the
weak interaction violates the parity, the scattering cross section
asymmetrically depends on the directions of the neutrino momenta to the
magnetic field; the origin of pulsar kicks may be explained by the mechanism.
An asymmetric neutrino emission (a drift flux) due to neutrino-nucleon
scatterings is absent at the leading level of , where
is the nucleon magneton, is the magnetic field strength, and is
the matter temperature at a neutrinosphere. This is because at this level the
drift flux of the neutrinos are exactly canceled by that of the antineutrinos.
Hence, the relevant asymmetry in the neutrino emission is suppressed by much
smaller coefficient of , where is the nucleon mass;
detailed form of the relevant drift flux is also derived from the scattering
cross section, using a simple diffusion approximation. It appears that the
asymmetric neutrino emission is too small to induce the observed pulsar kicks.
However, we note the fact that the drift flux is proportional to the deviation
of the neutrino distribution function from the value of thermal equilibrium at
neutrinosphere. Since the deviation can be large for non-electron neutrinos, it
is expected that there occurs cancellation between the deviation and the small
suppression factor of . Using a simple parameterization,
we show that the drift flux due to neutrino-nucleon scatterings may be
comparable to the leading term due to beta processes with nucleons, which has
been estimated to give a relevant kick velocity when the magnetic field is
sufficiently strong as -- G.Comment: 19 pages, 1 figure. Accepted by Physical Review
Jet Breaks in Short Gamma-Ray Bursts. I: The Uncollimated Afterglow of GRB 050724
We report the results of the \chandra observations of the \swift-discovered
short Gamma-Ray Burst GRB 050724. \chandra observed this burst twice, about two
days after the burst and a second time three weeks later. The first \chandra
pointing occurred at the end of a strong late-time flare. About 150 photons
were detected during this 49.3 ks observation in the 0.4-10.0 keV range. The
spectral fit is in good agreement with spectral analysis of earlier \swift XRT
data. In the second \chandra pointing the afterglow was clearly detected with 8
background-subtracted photons in 44.6 ks. From the combined \swift XRT and
\chandra-ACIS-S light curve we find significant flaring superposed on an
underlying power-law decay slope of =0.98. There is
no evidence for a break between about 1 ks after the burst and the last
\chandra pointing about three weeks after the burst. The non-detection of a jet
break places a lower limit of 25 on the jet opening angle, indicating
that the outflow is less strongly collimated than most previously-reported long
GRBs. This implies that the beaming corrected energy of GRB 050724 is at least
ergs.Comment: 7 pages, ApJ acceped, scheduled for December 20, 2006, ApJ, 65
Lowest Order Constrained Variational Calculation of Structure Properties of Protoneutron Star
We calculate the structure properties of protoneutron star such as equation
of state, maximum mass, radius and temperature profile using the lowest order
constrained variational method. We show that the mass and radius of
protoneutron star decrease by decreasing both entropy and temperature. For the
protoneutron star, it is shown that the temperature is nearly constant in the
core and drops rapidly near the crust.Comment: 14 pages, 12 figures. Int. J. Theor. Phys. (2008) in pres
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