1,264 research outputs found
Low-lying dipole response: isospin character and collectivity in Ni, Sn and Pb
The isospin character, the collective or single-particle nature, and the
sensitivity to the slope of the nuclear symmetry energy of the low-energy
isovector dipole response (known as pygmy dipole resonance) are nowadays under
debate. In the present work we study, within the fully self-consistent
non-relativistic mean field (MF) approach based on Skyrme Hartree-Fock plus
Random Phase Approximation (RPA), the measured even-even nuclei Ni,
Sn and Pb. To analyze the model dependence in the
predictions of the pygmy dipole strength, we employ three different Skyrme
parameter sets. We find that both the isoscalar and the isovector dipole
responses of all three nuclei show a low-energy peak that increases in
magnitude, and is shifted to larger excitation energies, with increasing values
of the slope of the symmetry energy at saturation. We highlight the fact that
the collectivity associated with the RPA state(s) contributing to this peak is
different in the isoscalar and isovector case, or in other words it depends on
the external probe. While the response of these RPA states to an isovector
operator does not show a clear collective nature, the response to an isoscalar
operator is recognizably collective, for {\it all} analyzed nuclei and {\it
all} studied interactions.Comment: Submitted to Phys. Rev.
Anti-Unruh Phenomena
We find that a uniformly accelerated particle detector coupled to the vacuum
can cool down as its acceleration increases, due to relativistic effects. We
show that in (1+1)-dimensions, a detector coupled to the scalar field vacuum
for finite timescales (but long enough to satisfy the KMS condition) has a KMS
temperature that decreases with acceleration, in certain regimes. This
contrasts with the heating that one would expect from the Unruh effect.Comment: 6 pages, 5 figures. RevTex 4.1. V2. Typos in the plots labeling
corrected and plot rescaled. New discussion section added. Title change
P-V Criticality in Quasitopological Gravity
We investigate the thermodynamic behaviour of AdS quasitopological black hole
solutions in the context of extended thermodynamic phase space, in which the
cosmological constant induces a pressure with a conjugate volume. We find that
the third order exact quasitopological solution exhibits features consistent
with the third order Lovelock solutions for positive quasitopological coupling,
including multiple reentrant phase transitions and isolated critical points.
For negative coupling we find the first instances of both reentrant phase
transitions and thermodynamic singularities in five dimensions, along with
other modified thermodynamic behaviour compared to Einstein-AdS-Gauss Bonnet
gravity.Comment: 20 pages, 15 figures, REVTeX 4-1; updated to match published versio
The pygmy dipole strength, the neutron radius of Pb and the symmetry energy
The accurate characterization of the nuclear symmetry energy and its density
dependence is one of the outstanding open problems in nuclear physics. A
promising nuclear observable in order to constrain the density dependence of
the symmetry energy at saturation is the neutron skin thickness of medium and
heavy nuclei. Recently, a low-energy peak in the isovector dipole response of
neutron-rich nuclei has been discovered that may be correlated with the neutron
skin thickness. The existence of this correlation is currently under debate due
to our limited experimental knowledge on the microscopic structure of such a
peak. We present a detailed analysis of Skyrme Hartree-Fock (HF) plus random
phase approximation (RPA) predictions for the dipole response in several
neutron-rich nuclei and try to elucidate whether models of common use in
nuclear physics confirm or dismiss its possible connection with the neutron
skin thickness. Finally, we briefly present theoretical results for parity
violating electron scattering on Pb at the conditions of the PREx
experiment and discuss the implications for the neutron skin thickness of
Pb and the slope of the symmetry energy.Comment: Contribution to the 2nd Iberian Nuclear Astrophysics Meeting on
Compact Stars proceeding
Localization of adaptive variants in human genomes using averaged one-dependence estimation.
Statistical methods for identifying adaptive mutations from population genetic data face several obstacles: assessing the significance of genomic outliers, integrating correlated measures of selection into one analytic framework, and distinguishing adaptive variants from hitchhiking neutral variants. Here, we introduce SWIF(r), a probabilistic method that detects selective sweeps by learning the distributions of multiple selection statistics under different evolutionary scenarios and calculating the posterior probability of a sweep at each genomic site. SWIF(r) is trained using simulations from a user-specified demographic model and explicitly models the joint distributions of selection statistics, thereby increasing its power to both identify regions undergoing sweeps and localize adaptive mutations. Using array and exome data from 45 ‡Khomani San hunter-gatherers of southern Africa, we identify an enrichment of adaptive signals in genes associated with metabolism and obesity. SWIF(r) provides a transparent probabilistic framework for localizing beneficial mutations that is extensible to a variety of evolutionary scenarios
The Effect of Infection Risk on Female Blood Transcriptomics
Defenses against pathogens can take on many forms. For instance, behavioral avoidance of diseased conspecifics is widely documented. Interactions with these infectious conspecifics can also, however, lead to physiological changes in uninfected animals, an effect that is much less well understood. These changes in behavior and physiology are particularly important to study in a reproductive context, where they can impact reproductive decisions and offspring quality. Here, we studied how an acute (3 h) exposure to an immune-challenged male affected female blood transcriptomics and behavior. We predicted that females paired with immune-challenged males would reduce eating and drinking behaviors (as avoidance behaviors) and that their blood would show activation of immune and stress responses. We used female Japanese quail as a study system because they have been shown to respond to male traits, in terms of their own physiology and egg investment. Only two genes showed significant differential expression due to treatment, including an increase in the threonine dehydrogenase (TDH) transcript, an enzyme important for threonine breakdown. However, hundreds of genes in pathways related to activation of immune responses showed coordinated up-regulation in females exposed to immune-challenged males. Suppressed pathways revealed potential changes to metabolism and reduced responsiveness to glucocorticoids. Contrary to our prediction, we found that females paired with immune-challenged males increased food consumption. Water consumption was not changed by treatment. These findings suggest that even short exposure to diseased conspecifics can trigger both behavioral and physiological responses in healthy animals
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