1,651 research outputs found
The oxidation of ascorbic acid and its reduction in vitro and in vivo
The outstanding chemical property of ascorbic acid (vitamin C) is that it is a reducing agent. The suggestion is obvious that its physiological function may be associated with this property, and, if it is oxidized reversibly, with its behavior in an oxidation-reduction system. It is desirable therefore to know the oxidation-reduction potential of ascorbic acid
Bayesian Analysis of Inflation III: Slow Roll Reconstruction Using Model Selection
We implement Slow Roll Reconstruction -- an optimal solution to the inverse
problem for inflationary cosmology -- within ModeCode, a publicly available
solver for the inflationary dynamics. We obtain up-to-date constraints on the
reconstructed inflationary potential, derived from the WMAP 7-year dataset and
South Pole Telescope observations, combined with large scale structure data
derived from SDSS Data Release 7. Using ModeCode in conjunction with the
MultiNest sampler, we compute Bayesian evidence for the reconstructed potential
at each order in the truncated slow roll hierarchy. We find that the data are
well-described by the first two slow roll parameters, \epsilon and \eta, and
that there is no need to include a nontrivial \xi parameter.Comment: 14 pages, 12 figures, minor changes; final version; accepted in PR
Multiscale modeling and simulation for polymer melt flows between parallel plates
The flow behaviors of polymer melt composed of short chains with ten beads
between parallel plates are simulated by using a hybrid method of molecular
dynamics and computational fluid dynamics. Three problems are solved: creep
motion under a constant shear stress and its recovery motion after removing the
stress, pressure-driven flows, and the flows in rapidly oscillating plates. In
the creep/recovery problem, the delayed elastic deformation in the creep motion
and evident elastic behavior in the recovery motion are demonstrated. The
velocity profiles of the melt in pressure-driven flows are quite different from
those of Newtonian fluid due to shear thinning. Velocity gradients of the melt
become steeper near the plates and flatter at the middle between the plates as
the pressure gradient increases and the temperature decreases. In the rapidly
oscillating plates, the viscous boundary layer of the melt is much thinner than
that of Newtonian fluid due to the shear thinning of the melt. Three different
rheological regimes, i.e., the viscous fluid, visco-elastic liquid, and
visco-elastic solid regimes, form over the oscillating plate according to the
local Deborah numbers. The melt behaves as a viscous fluid in a region for
, and the crossover between the liquid-like and
solid-like regime takes place around (where
is the angular frequency of the plate and and
are Rouse and relaxation time, respectively).Comment: 13pages, 12figure
Let's talk about varying G
It is possible that fundamental constants may not be constant at all. There
is a generally accepted view that one can only talk about variations of
dimensionless quantities, such as the fine structure constant . However, constraints on the strength of
gravity tend to focus on G itself, which is problematic. We stress that G needs
to be multiplied by the square of a mass, and hence, for example, one should be
constraining , where is
the proton mass. Failure to focus on such dimensionless quantities makes it
difficult to interpret the physical dependence of constraints on the variation
of G in many published studies. A thought experiment involving talking to
observers in another universe about the values of physical constants may be
useful for distinguishing what is genuinely measurable from what is merely part
of our particular system of units.Comment: 6 pages, Gravity Research Foundation essa
Relic gravitational waves in the light of 7-year Wilkinson Microwave Anisotropy Probe data and improved prospects for the Planck mission
The new release of data from Wilkinson Microwave Anisotropy Probe improves
the observational status of relic gravitational waves. The 7-year results
enhance the indications of relic gravitational waves in the existing data and
change to the better the prospects of confident detection of relic
gravitational waves by the currently operating Planck satellite. We apply to
WMAP7 data the same methods of analysis that we used earlier [W. Zhao, D.
Baskaran, and L.P. Grishchuk, Phys. Rev. D 80, 083005 (2009)] with WMAP5 data.
We also revised by the same methods our previous analysis of WMAP3 data. It
follows from the examination of consecutive WMAP data releases that the maximum
likelihood value of the quadrupole ratio , which characterizes the amount of
relic gravitational waves, increases up to , and the interval
separating this value from the point (the hypothesis of no gravitational
waves) increases up to a level. The primordial spectra of density
perturbations and gravitational waves remain blue in the relevant interval of
wavelengths, but the spectral indices increase up to and
. Assuming that the maximum likelihood estimates of the perturbation
parameters that we found from WMAP7 data are the true values of the parameters,
we find that the signal-to-noise ratio for the detection of relic
gravitational waves by the Planck experiment increases up to , even
under pessimistic assumptions with regard to residual foreground contamination
and instrumental noises. We comment on theoretical frameworks that, in the case
of success, will be accepted or decisively rejected by the Planck observations.Comment: 27 pages, 12 (colour) figures. Published in Phys. Rev. D. V.3:
modifications made to reflect the published versio
Larva of the greater wax moth, Galleria mellonella, is a suitable alternative host for studying virulence of fish pathogenic Vibrio anguillarum
Background: Microbial diseases cause considerable economic losses in aquaculture and new infection control measures often rely on a better understanding of pathogenicity. However, disease studies performed in fish hosts often require specialist infrastructure (e.g., aquaria), adherence to strict legislation and do not permit high-throughput approaches; these reasons justify the development of alternative hosts. This study aimed to validate the use of larvae of the greater wax moth (Galleria mellonella) to investigate virulence of the important fish pathogen, Vibrio anguillarum. Results: Using 11 wild-type isolates of V. anguillarum, these bacteria killed larvae in a dose-dependent manner and replicated inside the haemolymph, but infected larvae were rescued by antibiotic therapy. Crucially, virulence correlated significantly and positively in larva and Atlantic salmon (Salmo salar) infection models. Challenge studies with mutants knocked out for single virulence determinants confirmed conserved roles in larva and fish infections in some cases (pJM1 plasmid, rtxA), but not all (empA, flaA, flaE). Conclusions: The G. mellonella model is simple, more ethically acceptable than experiments on vertebrates and, crucially, does not necessitate liquid systems, which reduces infrastructure requirements and biohazard risks associated with contaminated water. The G. mellonella model may aid our understanding of microbial pathogens in aquaculture and lead to the timely introduction of new effective remedies for infectious diseases, while adhering to the principles of replacement, reduction and refinement (3Rs) and considerably reducing the number of vertebrates used in such studies
Considerations for the development of agility during childhood and adolescence
Despite being recognized as an essential component of sports performance, agility development in youths is largely under-researched. this article reviews the evidence examining the effects of growth, maturation and training on both change of direction speed and cognitive processing in children and adolescents, and how combined, these factors may influence agility. training guidelines are provided to help strength and conditioning coaches prescribe agility training for youths at different stages of maturation, in a safe and effective manner
New stopping criteria for segmenting DNA sequences
We propose a solution on the stopping criterion in segmenting inhomogeneous
DNA sequences with complex statistical patterns. This new stopping criterion is
based on Bayesian Information Criterion (BIC) in the model selection framework.
When this stopping criterion is applied to a left telomere sequence of yeast
Saccharomyces cerevisiae and the complete genome sequence of bacterium
Escherichia coli, borders of biologically meaningful units were identified
(e.g. subtelomeric units, replication origin, and replication terminus), and a
more reasonable number of domains was obtained. We also introduce a measure
called segmentation strength which can be used to control the delineation of
large domains. The relationship between the average domain size and the
threshold of segmentation strength is determined for several genome sequences.Comment: 4 pages, 4 figures, Physical Review Letters, to appea
Finding Evidence for Massive Neutrinos using 3D Weak Lensing
In this paper we investigate the potential of 3D cosmic shear to constrain
massive neutrino parameters. We find that if the total mass is substantial
(near the upper limits from LSS, but setting aside the Ly alpha limit for now),
then 3D cosmic shear + Planck is very sensitive to neutrino mass and one may
expect that a next generation photometric redshift survey could constrain the
number of neutrinos N_nu and the sum of their masses m_nu to an accuracy of
dN_nu ~ 0.08 and dm_nu ~ 0.03 eV respectively. If in fact the masses are close
to zero, then the errors weaken to dN_nu ~ 0.10 and dm_nu~0.07 eV. In either
case there is a factor 4 improvement over Planck alone. We use a Bayesian
evidence method to predict joint expected evidence for N_nu and m_nu. We find
that 3D cosmic shear combined with a Planck prior could provide `substantial'
evidence for massive neutrinos and be able to distinguish `decisively' between
many competing massive neutrino models. This technique should `decisively'
distinguish between models in which there are no massive neutrinos and models
in which there are massive neutrinos with |N_nu-3| > 0.35 and m_nu > 0.25 eV.
We introduce the notion of marginalised and conditional evidence when
considering evidence for individual parameter values within a multi-parameter
model.Comment: 9 pages, 2 Figures, 2 Tables, submitted to Physical Review
Testing feasibility of scalar-tensor gravity by scale dependent mass and coupling to matter
We investigate whether there are any cosmological evidences for a scalar
field with a mass and coupling to matter which change accordingly to the
properties of the astrophysical system it "lives in", without directly focusing
on the underlying mechanism that drives the scalar field scale-dependent
properties. We assume a Yukawa type of coupling between the field and matter
and also that the scalar field mass grows with density, in order to overcome
all gravity constraints within the solar system. We analyse three different
gravitational systems assumed as "cosmological indicators": supernovae type Ia,
low surface brightness spiral galaxies and clusters of galaxies. Results show
that: a) a quite good fit to the rotation curves of low surface brightness
galaxies only using visible stellar and gas mass components is obtained; b) a
scalar field can fairly well reproduce the matter profile in clusters of
galaxies, estimated by X-ray observations and without the need of any
additional dark matter; c) there is an intrinsic difficulty in extracting
information about the possibility of a scale-dependent massive scalar field (or
more generally about a varying gravitational constant) from supernovae type Ia.Comment: 30 pages, 15 figures, to appear in Phys. Rev.
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