50 research outputs found
Electron-, Mu-, and Tau-Number Conservation in a Supernova Core
We study if the neutrino mixing parameters suggested by the atmospheric
neutrino anomaly imply chemical equilibrium between mu- and tau-flavored
leptons in a supernova (SN) core. The initial flavor-conversion rate would
indeed be fast if the nu_mu-nu_tau-mixing angle were not suppressed by
second-order refractive effects. The neutrino diffusion coefficients are
different for nu_mu, anti-nu_mu, nu_tau and anti-nu_tau so that neutrino
transport will create a net mu and tau lepton number density. This will
typically lead to a situation where the usual first-order refractive effects
dominate, further suppressing the rate of flavor conversion. Altogether,
neutrino refraction has the nontrivial consequence of guaranteeing the separate
conservation of e, mu, and tau lepton number in a SN core on the infall and
cooling time scales, even when neutrino mixing angles are large.Comment: Slightly expanded version with improved presentation, no changes of
substanc
Polysaccharide hydrolysis in the presence of oil and dispersants: Insights into potential degradation pathways of exopolymeric substances (EPS) from oil-degrading bacteria
Oceanic oil-degrading bacteria produce copious amounts of exopolymeric substances (EPS) that facilitate their access to oil. The fate of EPS in the water column is in part determined by activities of heterotrophic microbes capable of utilizing EPS compounds as carbon and energy sources. To evaluate the potential of natural microbial communities to degrade EPS produced during oil degradation, we measured potential hydrolysis rates of six structurally distinct polysaccharides in two roller bottle experiments, using water from a natural oil seep in the northern Gulf of Mexico. The suite of polysaccharides used to measure the initial step in carbon degradation is indicative of polymers within microbial EPS. The treatments included (i) unamended surface or deep waters (whole water), and water amended with (ii) a water-accommodated fraction of oil (WAF), (iii) oil dispersant Corexit 9500, and (iv) WAF chemically-enhanced with Corexit (CEWAF). The oil and Corexit treatments were employed to simulate conditions during the Deepwater Horizon oil spill. Polysaccharide hydrolysis rates in the surface-water treatments were lowest in the WAF treatment, despite elevated levels of EPS in the form of transparent exopolymer particles (TEP). In contrast, the three deep-water treatments (WAF, Corexit, CEWAF) showed enhanced hydrolysis rates and TEP levels (WAF) compared to the whole water. We also observed variations in the spectrum of polysaccharide-hydrolyzing enzyme activities among the treatments. These substrate specificities were likely driven by activities of oil-degrading bacteria, shaping the pool of EPS and TEP as well as degradation products of hydrocarbons and Corexit compounds. A model calculation of potential turnover rates of organic carbon within the TEP pool suggests extended residence times of TEP in oil-contaminated waters, making them prone to serve as the sticky matrix for oily aggregates known as marine oil snow
Oscillation effects on neutrino decoupling in the early universe
In the early universe, neutrinos decouple from equilibrium with the
electromagnetic plasma at a temperature which is only slightly higher than the
temperature where electrons and positrons annihilate. Therefore neutrinos to
some extent share in the entropy transfer from e^+e^- to other species, and
their final temperature is slightly higher than the canonical value T_nu =
(4/11)^{1/3} T_gamma. We study neutrino decoupling in the early universe with
effects of neutrino oscillations included, and find that the change in neutrino
energy density from e^+ e^- annihilations can be about 2-3% higher if
oscillation are included. The primordial helium abundance can be changed by as
much as 1.5 x 10^-4 by neutrino oscillations.Comment: minor changes, matches version to appear in PR
Late-time Entropy Production from Scalar Decay and Relic Neutrino Temperature
Entropy production from scalar decay in the era of low temperatures after
neutrino decoupling will change the ratio of the relic neutrino temperature to
the CMB temperature, and, hence, the value of N_eff, the effective number of
neutrino species. Such scalar decay is relevant to reheating after thermal
inflation, proposed to dilute massive particles, like the moduli and the
gravitino, featuring in supersymmetric and string theories. The effect of such
entropy production on the relic neutrino temperature ratio is calculated in a
semi-analytic manner, and a recent lower bound on this ratio, obtained from the
WMAP satellite and 2dF galaxy data, is used to set a lower bound of ~ 1.5 x
10^-23 Gev on the scalar decay constant, corresponding to a reheating
temperature of about 3.3 Mev.Comment: 13 pages, to appear in PR
Early-universe constraints on a Primordial Scaling Field
In the past years 'quintessence' models have been considered which can
produce the accelerated expansion in the universe suggested by recent
astronomical observations. One of the key differences between quintessence and
a cosmological constant is that the energy density in quintessence,
, could be a significant fraction of the overall energy even in
the early universe, while the cosmological constant will be dynamically
relevant only at late times. We use standard Big Bang Nucleosynthesis and the
observed abundances of primordial nuclides to put constraints on
at temperatures near . We point out that current experimental data
does not support the presence of such a field, providing the strong constraint
at C.L. and strengthening previous
results. We also consider the effect a scaling field has on CMB anisotropies
using the recent data from Boomerang and DASI, providing the CMB constraint
at during the radiation dominated epoch.Comment: 5 pages, 4 figures. The revised version includes the new Boomerang
and DASI dat
What is the lowest possible reheating temperature?
We study models in which the universe exits reheating at temperatures in the
MeV regime. By combining light element abundance measurements with cosmic
microwave background and large scale structure data we find a fairly robust
lower limit on the reheating temperature of T_RH > 4 MeV at 95% C.L. However,
if the heavy particle whose decay reheats the universe has a direct decay mode
to neutrinos, there are some small islands left in parameter space where a
reheating temperature as low as 1 MeV is allowed. The derived lower bound on
the reheating temperature also leads to very stringent bounds on models with
large extra dimensions. For n=2 the bound on the compactification scale is
M > 2000 TeV, and for n=3 it is 100 TeV. These are currently the strongest
available bounds on such models.Comment: 9 pages, 7 figures, Revte
Genome-wide association and Mendelian randomisation analysis provide insights into the pathogenesis of heart failure
Heart failure (HF) is a leading cause of morbidity and mortality worldwide. A small proportion of HF cases are attributable to monogenic cardiomyopathies and existing genome-wide association studies (GWAS) have yielded only limited insights, leaving the observed heritability of HF largely unexplained. We report results from a GWAS meta-analysis of HF comprising 47,309 cases and 930,014 controls. Twelve independent variants at 11 genomic loci are associated with HF, all of which demonstrate one or more associations with coronary artery disease (CAD), atrial fibrillation, or reduced left ventricular function, suggesting shared genetic aetiology. Functional analysis of non-CAD-associated loci implicate genes involved in cardiac development (MYOZ1, SYNPO2L), protein homoeostasis (BAG3), and cellular senescence (CDKN1A). Mendelian randomisation analysis supports causal roles for several HF risk factors, and demonstrates CAD-independent effects for atrial fibrillation, body mass index, and hypertension. These findings extend our knowledge of the pathways underlying HF and may inform new therapeutic strategies
Identification and quantification of 16 inorganic ions in water by Gaussian curve fitting of near-infrared difference absorbance spectra
This study shows two novel fitting strategies applied to differential absorbance spectra for identification and quantification of electrolytes. The effects of 16 dissolved salts were investigated in the wavelength range from 14000 to 9091 wavenumbers (714–1100 nm) by linear fits of the differential absorbance values