775 research outputs found
Bulk viscosity in kaon-condensed color-flavor locked quark matter
Color-flavor locked (CFL) quark matter at high densities is a color
superconductor, which spontaneously breaks baryon number and chiral symmetry.
Its low-energy thermodynamic and transport properties are therefore dominated
by the H (superfluid) boson, and the octet of pseudoscalar pseudo-Goldstone
bosons of which the neutral kaon is the lightest. We study the CFL-K^0 phase,
in which the stress induced by the strange quark mass causes the kaons to
condense, and there is an additional ultra-light "K^0" Goldstone boson arising
from the spontaneous breaking of isospin. We compute the bulk viscosity of
matter in the CFL-K^0 phase, which arises from the beta-equilibration processes
K^0H+H and K^0+HH. We find that the bulk viscosity varies as T^7, unlike
the CFL phase where it is exponentially Boltzmann-suppressed by the kaon's
energy gap. However, in the temperature range of relevance for r-mode damping
in compact stars, the bulk viscosity in the CFL-K^0 phase turns out to be even
smaller than in the uncondensed CFL phase, which already has a bulk viscosity
much smaller than all other known color-superconducting quark phases.Comment: 23 pages, 8 figures, v2: references added; minor rephrasings in the
conclusions; version to appear in J. Phys.
Bulk viscosity in 2SC quark matter
The bulk viscosity of three-flavor color-superconducting quark matter
originating from the nonleptonic process u+s u+d is computed. It is assumed
that up and down quarks form Cooper pairs while the strange quark remains
unpaired (2SC phase). A general derivation of the rate of strangeness
production is presented, involving contributions from a multitude of different
subprocesses, including subprocesses that involve different numbers of gapped
quarks as well as creation and annihilation of particles in the condensate. The
rate is then used to compute the bulk viscosity as a function of the
temperature, for an external oscillation frequency typical of a compact star
r-mode. We find that, for temperatures far below the critical temperature T_c
for 2SC pairing, the bulk viscosity of color-superconducting quark matter is
suppressed relative to that of unpaired quark matter, but for T >~ 10^(-3) T_c
the color-superconducting quark matter has a higher bulk viscosity. This is
potentially relevant for the suppression of r-mode instabilities early in the
life of a compact star.Comment: 18 pages + appendices (28 pages total), 8 figures; v3: corrected
numerical error in the plots; 2SC bulk viscosity is now larger than unpaired
bulk viscosity in a wider temperature rang
A -mode in a magnetic rotating spherical layer: application to neutron stars
The impact of the combination of rotation and magnetic fields on oscillations
of stellar fluids is still not well known theoretically. It mixes Alfv\'en and
inertial waves. Neutron stars are a place where both effects may be at work. We
wish to decipher the solution of this problem in the context of -modes
instability in neutron stars, as it appears when these modes are coupled to
gravitational radiation.
We consider a rotating spherical shell filled with a viscous fluid but of
infinite electrical conductivity and analyze propagation of modal perturbations
when a dipolar magnetic field is bathing the fluid layer. We perform an
extensive numerical analysis and find that the -mode oscillation is
influenced by the magnetic field when the Lehnert number (ratio of Alfv\'en
speed to rotation speed) exceeds a value proportional to the one-fourth power
of the Ekman number (non-dimensional measure of viscosity). This scaling is
interpreted as the coincidence of the width of internal shear layers of
inertial modes and the wavelength of the Alfv\'en waves. Applied to the case of
rotating magnetic neutron stars, we find that dipolar magnetic fields above
G are necessary to perturb the -modes instability.Comment: 9 pages, 6 figures, to appear in Monthly Notices of RA
Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR
Simulation results for future measurements of electromagnetic proton form
factors at \PANDA (FAIR) within the PandaRoot software framework are reported.
The statistical precision with which the proton form factors can be determined
is estimated. The signal channel is studied on the basis
of two different but consistent procedures. The suppression of the main
background channel, , is studied.
Furthermore, the background versus signal efficiency, statistical and
systematical uncertainties on the extracted proton form factors are evaluated
using two different procedures. The results are consistent with those of a
previous simulation study using an older, simplified framework. However, a
slightly better precision is achieved in the PandaRoot study in a large range
of momentum transfer, assuming the nominal beam conditions and detector
performance
Assessing the complex sponge microbiota: core, variable and species-specific bacterial communities in marine sponges
Marine sponges are well known for their associations with highly diverse, yet very specific and often highly similar microbiota. The aim of this study was to identify potential bacterial sub-populations in relation to sponge phylogeny and sampling sites and to define the core bacterial community. 16S ribosomal RNA gene amplicon pyrosequencing was applied to 32 sponge species from eight locations around the world's oceans, thereby generating 2567 operational taxonomic units (OTUs at the 97% sequence similarity level) in total and up to 364 different OTUs per sponge species. The taxonomic richness detected in this study comprised 25 bacterial phyla with Proteobacteria, Chloroflexi and Poribacteria being most diverse in sponges. Among these phyla were nine candidate phyla, six of them found for the first time in sponges. Similarity comparison of bacterial communities revealed no correlation with host phylogeny but a tropical sub-population in that tropical sponges have more similar bacterial communities to each other than to subtropical sponges. A minimal core bacterial community consisting of very few OTUs (97%, 95% and 90%) was found. These microbes have a global distribution and are probably acquired via environmental transmission. In contrast, a large species-specific bacterial community was detected, which is represented by OTUs present in only a single sponge species. The species-specific bacterial community is probably mainly vertically transmitted. It is proposed that different sponges contain different bacterial species, however, these bacteria are still closely related to each other explaining the observed similarity of bacterial communities in sponges in this and previous studies. This global analysis represents the most comprehensive study of bacterial symbionts in sponges to date and provides novel insights into the complex structure of these unique associations
Reaction rates and transport in neutron stars
Understanding signals from neutron stars requires knowledge about the
transport inside the star. We review the transport properties and the
underlying reaction rates of dense hadronic and quark matter in the crust and
the core of neutron stars and point out open problems and future directions.Comment: 74 pages; commissioned for the book "Physics and Astrophysics of
Neutron Stars", NewCompStar COST Action MP1304; version 3: minor changes,
references updated, overview graphic added in the introduction, improvements
in Sec IV.A.
The effect of exposure to synthetic pheromone lures on male Zygaena filipendulae mating behaviour: implications for monitoring species of conservation interest
Pheromone based monitoring of insects of conservation value has the potential to revolutionise the way in which surveys are carried out. However, due to their effective use in pest management, concerns have been raised about potential negative effects of pheromone exposure on populations of rare insects. The effect of exposure to synthetic pheromone lures on male mating behaviour was examined in laboratory and field conditions using the six spot burnet moth Zygaena filipendulae (Linnaeus, 1758). For the laboratory experiment larvae were collected and cultured separately under controlled conditions. Virgin males were exposed to a synthetic pheromone lure for 24 h; then tested for responsiveness immediately after this exposure, 1 and 24 h later. Control males were tested three times: initially, 1 h later and 24 h later. The time taken for males to detect females, shown by exposure of their anal claspers, and the time taken for males to locate females were recorded. No significant difference was found between the time taken for control and exposed males to detect or locate females, and no significant difference between the proportions of males that successfully located females in exposed and control groups was found. In the field experiment the time males spent in the presence of contained females, both with and without a pheromone lure present, was recorded. Males spent more time in the presence of the females when the pheromone lure was present. Both experiments indicate male Z. filipendulae mating behaviour is not adversely affected by exposure to synthetic pheromone lures
Pervasive Sign Epistasis between Conjugative Plasmids and Drug-Resistance Chromosomal Mutations
Multidrug-resistant bacteria arise mostly by the accumulation of plasmids and chromosomal mutations. Typically, these resistant determinants are costly to the bacterial cell. Yet, recently, it has been found that, in Escherichia coli bacterial cells, a mutation conferring resistance to an antibiotic can be advantageous to the bacterial cell if another antibiotic-resistance mutation is already present, a phenomenon called sign epistasis. Here we study the interaction between antibiotic-resistance chromosomal mutations and conjugative (i.e., self-transmissible) plasmids and find many cases of sign epistasis (40%)—including one of reciprocal sign epistasis where the strain carrying both resistance determinants is fitter than the two strains carrying only one of the determinants. This implies that the acquisition of an additional resistance plasmid or of a resistance mutation often increases the fitness of a bacterial strain already resistant to antibiotics. We further show that there is an overall antagonistic interaction between mutations and plasmids (52%). These results further complicate expectations of resistance reversal by interdiction of antibiotic use
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