883 research outputs found
Effect of energy degeneracy on the transition time for a series of metastable states: application to Probabilistic Cellular Automata
We consider the problem of metastability for stochastic reversible dynamics
with exponentially small transition probabilities. We generalize previous
results in several directions. We give an estimate of the spectral gap of the
transition matrix and of the mixing time of the associated dynamics in terms of
the maximal stability level. These model-independent results hold in particular
for a large class of Probabilistic Cellular Automata (PCA), which we then focus
on. We consider the PCA in a finite volume, at small and fixed magnetic field,
and in the limit of vanishing temperature. This model is peculiar because of
the presence of three metastable states, two of which are degenerate with
respect to their energy. We identify rigorously the metastable states by giving
explicit upper bounds on the stability level of every other configuration. We
rely on these estimates to prove a recurrence property of the dynamics, which
is a cornerstone of the pathwise approach to metastability. Further, we also
identify the metastable states according to the potential-theoretic approach to
metastability, and this allows us to give precise asymptotics for the expected
transition time from any such metastable state to the stable state
Are Rapid Population Estimates Accurate? A Field Trial of Two Different Assessment Methods.
Emergencies resulting in large-scale displacement often lead to populations resettling in areas where basic health services and sanitation are unavailable. To plan relief-related activities quickly, rapid population size estimates are needed. The currently recommended Quadrat method estimates total population by extrapolating the average population size living in square blocks of known area to the total site surface. An alternative approach, the T-Square, provides a population estimate based on analysis of the spatial distribution of housing units taken throughout a site. We field tested both methods and validated the results against a census in Esturro Bairro, Beira, Mozambique. Compared to the census (population: 9,479), the T-Square yielded a better population estimate (9,523) than the Quadrat method (7,681; 95% confidence interval: 6,160-9,201), but was more difficult for field survey teams to implement. Although applicable only to similar sites, several general conclusions can be drawn for emergency planning
Numerical and experimental investigations of a microwave interferometer for the negative ion source SPIDER
The electron density close to the extraction grids and the co-extracted
electrons represent a crucial issue when operating negative ion sources for
fusion reactors. An excessive electron density in the plasma expansion region
can indeed inhibit the negative ion production and introduce potentially
harmful electrons in the accelerator. Among the set of plasma and beam
diagnostics proposed for SPIDER upgrade, a heterodyne microwave (mw)
interferometer at 100 GHz is being explored as a possibility to measure
electron density in the plasma extraction region. The major issue in applying
this technique in SPIDER is the poor accessibility of the probing microwave
beam through the source metal walls and the long distance of 4 m at which mw
modules should be located outside the vacuum vessel. Numerical investigations
in a full-scale geometry showed that the power transmitted through the plasma
source apertures was sufficient for the microwave module sensitivity. An
experimental proof-of-principle of the setup was then performed. The microwave
system was tested on an experimental full-scale test-bench mimicking SPIDER
viewports accessibility constraints, including the presence of a SPIDER-like
plasma. The outcome of first tests revealed that, despite the geometrical
constraints, in certain conditions, the electron density measurements are
possible. The main issue arises from decoupling the one-pass signal from
spurious multipaths generated by mw beam reflections, requiring signal cross
correlation analysis. These preliminary tests demonstrate that despite the 4 m
distance between the mw modules and the presence of metal walls, plasma density
measurement is possible when the 80-mm diameter ports are available. In this
contribution, we discuss the numerical simulations, the preliminary
experimental tests and suggest design upgrades of the interferometric setup to
enhance signal transmission
Transient sex-related changes in the mice hypothalamo–pituitary–adrenal (HPA) axis during the acute phase of the inflammatory process
The potential role of endogenous sex hormones in regulating hypothalamo–pituitary–adrenal (HPA) axis function was investigated after a single injection of endotoxin in adult (8 week old) BALB/c mice of both sexes. The effect of LPS on plasma ACTH, corticosterone (B), testosterone and oestradiol (E) levels and on anterior pituitary (AP) ACTH and adrenal B contents at different times after treatment was studied. The results indicate that: (a) basal B but not ACTH plasma levels were significantly higher in female than in male mice; (b) LPS significantly increased both ACTH and B plasma levels over the baseline 2 h after injection, both hormone levels being higher in female than in male mice; (c) although plasma ACTH concentrations recovered the basal value at 72 h after LPS in animals of both sexes, plasma B levels returned to the baseline only at 120 h after treatment; (d) E plasma levels significantly increased 2 h after LPS and returned to the baseline at 72 h post-treatment, in both sexes; (e) at 2 h after LPS, testosterone plasma levels significantly decreased in male mice and increased in female mice, recovering the baseline level at 120 and 72 h after LPS, respectively; (f) AP ACTH content was similar in both sexes in basal condition and it was significantly diminished 72 h post-treatment without sex difference; whereas AP ACTH returned to basal content 120 h after LPS in males, it remained significantly decreased in females; (g) basal adrenal B content was higher in female than in male mice, and it significantly increased in both sexes 2 h post-LPS, maintaining this sex difference. Whereas adrenal B returned to basal content 72 h after treatment in male mice, it remained significantly enhanced up to 120 h post-LPS in female animals. The data demonstrate the existence of a clear sexual dimorphism in basal condition and during the acute phase response as well as in the recovery of the HPA axis function shortly after infection
Spectroscopic signature of phosphate crystallization in Erbium-doped optical fibre preforms
In rare-earth-doped silica optical fibres, the homogeneous distribution of
amplifying ions and part of their spectroscopic properties are usually improved
by adding selected elements, such as phosphorus or aluminum, as structural
modifier. In erbium ion (Er3+) doped fibres, phosphorus preferentially
coordinates to Er3+ ions to form regular cages around it. However, the
crystalline structures described in literature never gave particular
spectroscopic signature. In this article, we report emission and excitation
spectra of Er3+ in a transparent phosphorus-doped silica fibre preform. The
observed line features observed at room and low temperature are attributed to
ErPO4 crystallites
Self-splicing of a group IIC intron: 5′ exon recognition and alternative 5′ splicing events implicate the stem–loop motif of a transcriptional terminator
Bacterial IIC introns are a newly recognized subclass of group II introns whose ribozyme properties have not been characterized in detail. IIC introns are typically located downstream of transcriptional terminator motifs (inverted repeat followed by T's) or other inverted repeats in bacterial genomes. Here we have characterized the self-splicing activity of a IIC intron, B.h.I1, from Bacillus halodurans. B.h.I1 self-splices in vitro through hydrolysis to produce linear intron, but interestingly, additional unexpected products were formed that were highly dependent on ionic conditions. These products were determined to represent alternative splicing events at the 5′ junction and cleavages throughout the RNA transcript. The alternative splicing and cleavage events occurred at cryptic splice sites containing stem–loop and IBS1 motifs, suggesting that the 5′ exon is recognized by both elements. These results provide the first example of a group II intron that uses 5′ splice sites nonadjacent to the ribozyme structure. Furthermore, the data suggest that IIC introns differ from IIA and IIB introns with respect to 5′ exon definition, and that the terminator stem–loop substitutes in part for the missing IBS2–EBS2 (intron and exon binding sites 2) interaction
Dual regulation of heat-shock transcription factor (HSF) activation and DNA-binding activity by H2O2: role of thioredoxin
Spectroscopic measurements of hydrogen dissociation degree and H<sup>-</sup> production in resonant antenna-generated helicon plasmas
Using Markov chain Monte Carlo methods for estimating parameters with gravitational radiation data
We present a Bayesian approach to the problem of determining parameters for
coalescing binary systems observed with laser interferometric detectors. By
applying a Markov Chain Monte Carlo (MCMC) algorithm, specifically the Gibbs
sampler, we demonstrate the potential that MCMC techniques may hold for the
computation of posterior distributions of parameters of the binary system that
created the gravity radiation signal. We describe the use of the Gibbs sampler
method, and present examples whereby signals are detected and analyzed from
within noisy data.Comment: 21 pages, 10 figure
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