34,470 research outputs found

### Marmots do not consistently use their left eye to respond to an approaching threat but those that did fled sooner.

In many vertebrates, the brain's right hemisphere which is connected to the left visual field specializes in the processing of information about threats while the left hemisphere which is connected to the right visual field specializes in the processing of information about conspecifics. This is referred to as hemispheric lateralization. But individuals that are too predictable in their response to predators could have reduced survival and we may expect selection for somewhat unpredictable responses. We studied hemispheric lateralization in yellow-bellied marmots Marmota flaviventer, a social rodent that falls prey to a variety of terrestrial and aerial predators. We first asked if they have lateralized responses to a predatory threat. We then asked if the eye that they used to assess risk influenced their perceptions of risk. We recorded the direction marmots were initially looking and then walked toward them until they fled. We recorded the distance that they responded to our experimental approach by looking, the eye with which they looked at us, and the distance at which they fled (i.e., flight initiation distance; FID). We found that marmots had no eye preference with which they looked at an approaching threat. Furthermore, the population was not comprised of individuals that responded in consistent ways. However, we found that marmots that looked at the approaching person with their left eye had larger FIDs suggesting that risk assessment was influenced by the eye used to monitor the threat. These findings are consistent with selection to make prey less predictable for their predators, despite underlying lateralization

### Electrostatic spherically symmetric configurations in gravitating nonlinear electrodynamics

We perform a study of the gravitating electrostatic spherically symmetric
(G-ESS) solutions of Einstein field equations minimally coupled to generalized
non-linear abelian gauge models in three space dimensions. These models are
defined by lagrangian densities which are general functions of the gauge field
invariants, restricted by some physical conditions of admissibility. They
include the class of non-linear electrodynamics supporting ESS non-topological
soliton solutions in absence of gravity. We establish that the qualitative
structure of the G-ESS solutions of admissible models is fully characterized by
the asymptotic and central-field behaviours of their ESS solutions in flat
space (or, equivalently, by the behaviour of the lagrangian densities in vacuum
and on the point of the boundary of their domain of definition, where the
second gauge invariant vanishes). The structure of these G-ESS configurations
for admissible models supporting divergent-energy ESS solutions in flat space
is qualitatively the same as in the Reissner-Nordstr\"om case. In contrast, the
G-ESS configurations of the models supporting finite-energy ESS solutions in
flat space exhibit new qualitative features, which are discussed in terms of
the ADM mass, the charge and the soliton energy. Most of the results concerning
well known models, such as the electrodynamics of Maxwell, Born-Infeld and the
Euler-Heisenberg effective lagrangian of QED, minimally coupled to gravitation,
are shown to be corollaries of general statements of this analysis.Comment: 11 pages, revtex4, 4 figures; added references; introduction,
conclusions and several sections extended, 2 additional figures included,
title change

### Dynamical Coupled-Channels Effects on Pion Photoproduction

The electromagnetic pion production reactions are investigated within the
dynamical coupled-channels model developed in {\bf Physics Reports, 439, 193
(2007)}. The meson-baryon channels included in this study are $\gamma N$, $\pi
N$, $\eta N$, and the $\pi\Delta$, $\rho N$ and $\sigma N$ resonant components
of the $\pi\pi N$ channel. With the hadronic parameters of the model determined
in a recent study of $\pi N$ scattering, we show that the pion photoproduction
data up to the second resonance region can be described to a very large extent
by only adjusting the bare $\gamma N \to N^*$ helicity amplitudes, while the
non-resonant electromagnetic couplings are taken from previous works. It is
found that the coupled-channels effects can contribute about 10 - 20 % of the
production cross sections in the $\Delta$ (1232) resonance region, and can
drastically change the magnitude and shape of the cross sections in the second
resonance region. The importance of the off-shell effects in a dynamical
approach is also demonstrated. The meson cloud effects as well as the
coupled-channels contributions to the $\gamma N \to N^*$ form factors are found
to be mainly in the low $Q^2$ region. For the magnetic M1 $\gamma N \to \Delta$
(1232) form factor, the results are close to that of the Sato-Lee Model.
Necessary improvements to the model and future developments are discussed.Comment: Corrected version. 14 pages, 10 figure

### Supersymmetric Higgs Triplets and Bilinear R-Parity Nonconservation

The supersymmetric standard model of particle interactions is extended to
include two Higgs triplet superfields at the TeV scale, carrying two units of
lepton number. Realistic tree-level Majorana neutrino masses are obtained in
the presence of soft, i.e. bilinear, R-parity nonconservation.Comment: 5 pages, no figur

### A mid-IR study of Hickson Compact Groups II. Multi-wavelength analysis of the complete GALEX-Spitzer Sample

We present a comprehensive study on the impact of the environment of compact
galaxy groups on the evolution of their members using a multi-wavelength
analysis, from the UV to the infrared, for a sample of 32 Hickson compact
groups (HCGs) containing 135 galaxies. Fitting the SEDs of all galaxies with
the state-of-the-art model of da Cunha (2008) we can accurately calculate their
mass, SFR, and extinction, as well as estimate their infrared luminosity and
dust content. We compare our findings with samples of field galaxies,
early-stage interacting pairs, and cluster galaxies with similar data. We find
that classifying the groups as dynamically "old" or "young", depending on
whether or not at least one quarter of their members are early-type systems, is
physical and consistent with past classifications of HCGs based on their atomic
gas content. [...ABRIDGED...] We also examine their SF properties, UV-optical
and mid-IR colors, and we conclude that all the evidence point to an
evolutionary scenario in which the effects of the group environment and the
properties of the galaxy members are not instantaneous. Early on, the influence
of close companions to group galaxies is similar to the one of galaxy pairs in
the field. However, as the time progresses, the effects of tidal torques and
minor merging, shape the morphology and star formation history of the group
galaxies, leading to an increase of the fraction of early-type members and a
rapid built up of the stellar mass in the remaining late-type galaxies.Comment: Accepted for publication in A&A. Figure resolution degraded for arXiv
limits, full resolution paper available at
http://www.physics.uoc.gr/~bitsakis/paperII_bitsakis.pd

### Disentangling the dynamical origin of P11 Nucleon Resonances

We show that two almost degenerate poles near the $\pi\Delta$ threshold and
the next higher mass pole in the $P_{11}$ partial wave of $\pi N$ scattering
evolve from a single bare state through its coupling with $\pi N$, $\eta N$ and
$\pi\pi N$ reaction channels. This finding provides new information on
understanding the dynamical origins of the Roper $N^*(1440)$ and $N^*(1710)$
resonances listed by Particle Data Group. Our results for the resonance poles
in other $\pi N$ partial waves are also presented.Comment: Improved version, accepted Phys. Rev. Let

### Nuclear gas core propulsion research program

Viewgraphs on the nuclear gas core propulsion research program are presented. The objectives of this research are to develop models and experiments, systems, and fuel elements for advanced nuclear thermal propulsion rockets. The fuel elements under investigation are suitable for gas/vapor and multiphase fuel reactors. Topics covered include advanced nuclear propulsion studies, nuclear vapor thermal rocket (NVTR) studies, and ultrahigh temperature nuclear fuels and materials studies

- …