2,222 research outputs found
Estimating the burden of malaria in Senegal : Bayesian zero-inflated binomial geostatistical modeling of the MIS 2008 data
The Research Center for Human Development in Dakar (CRDH) with the technical assistance of ICF Macro and the National Malaria Control Programme (NMCP) conducted in 2008/2009 the Senegal Malaria Indicator Survey (SMIS), the first nationally representative household survey collecting parasitological data and malaria-related indicators. In this paper, we present spatially explicit parasitaemia risk estimates and number of infected children below 5 years. Geostatistical Zero-Inflated Binomial models (ZIB) were developed to take into account the large number of zero-prevalence survey locations (70%) in the data. Bayesian variable selection methods were incorporated within a geostatistical framework in order to choose the best set of environmental and climatic covariates associated with the parasitaemia risk. Model validation confirmed that the ZIB model had a better predictive ability than the standard Binomial analogue. Markov chain Monte Carlo (MCMC) methods were used for inference. Several insecticide treated nets (ITN) coverage indicators were calculated to assess the effectiveness of interventions. After adjusting for climatic and socio-economic factors, the presence of at least one ITN per every two household members and living in urban areas reduced the odds of parasitaemia by 86% and 81% respectively. Posterior estimates of the ORs related to the wealth index show a decreasing trend with the quintiles. Infection odds appear to be increasing with age. The population-adjusted prevalence ranges from 0.12% in Thille-Boubacar to 13.1% in Dabo. Tambacounda has the highest population-adjusted predicted prevalence (8.08%) whereas the region with the highest estimated number of infected children under the age of 5 years is Kolda (13940). The contemporary map and estimates of malaria burden identify the priority areas for future control interventions and provide baseline information for monitoring and evaluation. Zero-Inflated formulations are more appropriate in modeling sparse geostatistical survey data, expected to arise more frequently as malaria research is focused on eliminatio
Generalized minority games with adaptive trend-followers and contrarians
We introduce a simple extension of the minority game in which the market
rewards contrarian (resp. trend-following) strategies when it is far from
(resp. close to) efficiency. The model displays a smooth crossover from a
regime where contrarians dominate to one where trend-followers dominate. In the
intermediate phase, the stationary state is characterized by non-Gaussian
features as well as by the formation of sustained trends and bubbles.Comment: 4 pages, 6 figure
N-acetylcysteine serves as substrate of 3-mercaptopyruvate sulfurtransferase and stimulates sulfide metabolism in colon cancer cells
Hydrogen sulfide (H2S) is an endogenously produced signaling molecule. The enzymes 3-mercaptopyruvate sulfurtransferase (MST), partly localized in mitochondria, and the inner mitochondrial membrane-associated sulfide:quinone oxidoreductase (SQR), besides being respectively involved in the synthesis and catabolism of H2S, generate sulfane sulfur species such as persulfides and polysulfides, currently recognized as mediating some of the H2S biological effects. Reprogramming of H2S metabolism was reported to support cellular proliferation and energy metabolism in cancer cells. As oxidative stress is a cancer hallmark and N-acetylcysteine (NAC) was recently suggested to act as an antioxidant by increasing intracellular levels of sulfane sulfur species, here we evaluated the effect of prolonged exposure to NAC on the H2S metabolism of SW480 colon cancer cells. Cells exposed to NAC for 24 h displayed increased expression and activity of MST and SQR. Furthermore, NAC was shown to: (i) persist at detectable levels inside the cells exposed to the drug for up to 24 h and (ii) sustain H2S synthesis by human MST more effectively than cysteine, as shown working on the isolated recombinant enzyme. We conclude that prolonged exposure of colon cancer cells to NAC stimulates H2S metabolism and that NAC can serve as a substrate for human MST
Collective behaviour without collective order in wild swarms of midges
Collective behaviour is a widespread phenomenon in biology, cutting through a
huge span of scales, from cell colonies up to bird flocks and fish schools. The
most prominent trait of collective behaviour is the emergence of global order:
individuals synchronize their states, giving the stunning impression that the
group behaves as one. In many biological systems, though, it is unclear whether
global order is present. A paradigmatic case is that of insect swarms, whose
erratic movements seem to suggest that group formation is a mere epiphenomenon
of the independent interaction of each individual with an external landmark. In
these cases, whether or not the group behaves truly collectively is debated.
Here, we experimentally study swarms of midges in the field and measure how
much the change of direction of one midge affects that of other individuals. We
discover that, despite the lack of collective order, swarms display very strong
correlations, totally incompatible with models of noninteracting particles. We
find that correlation increases sharply with the swarm's density, indicating
that the interaction between midges is based on a metric perception mechanism.
By means of numerical simulations we demonstrate that such growing correlation
is typical of a system close to an ordering transition. Our findings suggest
that correlation, rather than order, is the true hallmark of collective
behaviour in biological systems.Comment: The original version has been split into two parts. This first part
focuses on order vs. correlation. The second part, about finite-size scaling,
will be included in a separate paper. 15 pages, 6 figures, 1 table, 5 video
Finite-size scaling as a way to probe near-criticality in natural swarms
Collective behaviour in biological systems is often accompanied by strong
correlations. The question has therefore arisen of whether correlation is
amplified by the vicinity to some critical point in the parameters space.
Biological systems, though, are typically quite far from the thermodynamic
limit, so that the value of the control parameter at which correlation and
susceptibility peak depend on size. Hence, a system would need to readjust its
control parameter according to its size in order to be maximally correlated.
This readjustment, though, has never been observed experimentally. By gathering
three-dimensional data on swarms of midges in the field we find that swarms
tune their control parameter and size so as to maintain a scaling behaviour of
the correlation function. As a consequence, correlation length and
susceptibility scale with the system's size and swarms exhibit a near-maximal
degree of correlation at all sizes.Comment: Selected for Viewpoint in Physics; PRL Editor's Suggestio
Pot growing Media Amendment with Calcium Cyanamide and Weed Control Relationships
The aim of this research was to characterize the effect of a pre-transplant calcium cyanamide fertilization on weed control in the potted bedding ornamental plant Impatiens wallerana and to describe the physiological mechanisms involved. The positive effect of a calcium cyanamide amendment included both ammonium toxicity on weed seed germination and a decrease of weed rates growth such as relative leaf expansion rate (RLAE) and relative growth rate (RGR). Data showed RGR-NAR (net assimilation rate), RLAE-RGR, RLAE-NAR and RGR-root dry weight relationships, which would explain ammonium toxicity to roots and weed growth responses. These effects probably could be explained by a change in hormonal root synthesis. Our results showed that a pre-transplant calcium cyanamide amendment combining with a transplant routine optimize both I. wallerana growth and weed control.Fil: Leytur, M.. Universidad de Buenos Aires. Facultad de AgronomÃa; ArgentinaFil: Duarte Vera, Alejandra Carolina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de AgronomÃa. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Sala, A.. Evonik Degussa Argentina S.A.; ArgentinaFil: Giardina, B.. Universidad de Buenos Aires. Facultad de AgronomÃa; Argentina. Evonik Degussa Argentina S.A.; ArgentinaFil: Di Benedetto, A.. Universidad de Buenos Aires. Facultad de AgronomÃa; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentin
A simple one-dimensional model of heat conduction which obeys Fourier's law
We present the computer simulation results of a chain of hard point particles
with alternating masses interacting on its extremes with two thermal baths at
different temperatures. We found that the system obeys Fourier's law at the
thermodynamic limit. This result is against the actual belief that one
dimensional systems with momentum conservative dynamics and nonzero pressure
have infinite thermal conductivity. It seems that thermal resistivity occurs in
our system due to a cooperative behavior in which light particles tend to
absorb much more energy than the heavier ones.Comment: 5 pages, 4 figures, to be published in PR
MDA, oxypurines, and nucleosides relate to reperfusion in short-term incomplete cerebral ischemia in the rat
Short-term incomplete cerebral ischemia (5 min) was induced in the rat by the bilateral clamping of the common carotid arteries. Reperfusion was obtained by removing carotid clamping and was carried out for the following 10 min. Animals were sacrificed either at the end of ischemia or reperfusion. Controls were represented by a group of sham-operated rats. Peripheral venous blood samples were withdrawn from the femoral vein from rats subjected to cerebral reperfusion 5 min before ischemia, at the end of ischemia, and 10 min after reperfusion. Neutralized perchloric acid extracts of brain tissue were analyzed by a highly sensitive high-performance liquid chromatography (HPLC) method for the direct determination of malondialdehyde, oxypurines, nucleosides, nicotinic coenzymes, and high-energy phosphates. In addition, plasma concentrations of malondialdehyde, hypoxanthine, xanthine, inosine, uric acid, and adenosine were determined by the same HPLC technique. Incomplete cerebral ischemia induced the appearance of a significant amount (8.05 nmol/g w.w.; SD = 2.82) of cerebral malondialdehyde (which was undetectable in control animals) and a decrease of ascorbic acid. A further 6.6-fold increase of malondialdehyde (53.30 nmol/g w.w.; SD = 17.77) and a 18.5% decrease of ascorbic acid occurred after 10 min of reperfusion. Plasma malondialdehyde, which was present in minimal amount before ischemia (0.050 mumol/L; SD = 0.015), significantly increased after 5 min of ischemia (0.277 mumol/L; SD = 0.056) and was strikingly augmented after 10 min of reperfusion (0.682 mumol/L; SD = 0.094). A similar trend was observed for xanthine, uric acid, inosine, and adenosine, while hypoxanthine reached its maximal concentration after 5 min of incomplete ischemia, being significantly decreased after reperfusion. From the data obtained, it can be concluded that tissue concentrations of malondialdehyde and ascorbic acid, and plasma levels of malondialdehyde, oxypurines, and nucleosides, reflect both the oxygen radical-mediated tissue injury and the depression of energy metabolism, thus representing early biochemical markers of short-term incomplete brain ischemia and reperfusion in the rat. In particular, these results suggest the possibility of using the variation of malondialdehyde, oxypurines, and nucleosides in peripheral blood as a potential biochemical indicator of reperfusion damage occurring to postischemic tissues
The effect of the neutron and proton numbers ratio in colliding nuclei at formation of the evaporation residues in the S+Pb and S+Pb reactions
The difference between observed cross sections of the evaporation residues
(ER) of the S+Pb and S+Pb reactions formed in the
2n and 3n channels has been explained by two reasons related with the entrance
channel characteristics of these reactions. The first reason is that the
capture cross section of the latter reaction is larger than the one of the
S+Pb reaction since the nucleus-nucleus potential is more
attractive in the S+Pb reaction due to two more neutrons in
isotope S. The second reason is the difference in the heights of the
intrinsic fusion barrier appearing on the fusion trajectory by
nucleon transfer between nuclei of the DNS formed after the capture. The value
of calculated for the S+Pb reaction is higher
than the one obtained for the S+Pb reaction. This fact has been
caused by the difference between the -ratios in the light fragments of the
DNS formed during the capture in these reactions. The -ratio has been
found by solution of the transport master equations for the proton and neutron
distributions between fragments of the DNS formed at capture with the different
initial neutron numbers and for the reactions with the S
and S, respectively.Comment: 22 pages, 13 figure
Stochastic resonance and noise delayed extinction in a model of two competing species
We study the role of the noise in the dynamics of two competing species. We
consider generalized Lotka-Volterra equations in the presence of a
multiplicative noise, which models the interaction between the species and the
environment. The interaction parameter between the species is a random process
which obeys a stochastic differential equation with a generalized bistable
potential in the presence of a periodic driving term, which accounts for the
environment temperature variation. We find noise-induced periodic oscillations
of the species concentrations and stochastic resonance phenomenon. We find also
a nonmonotonic behavior of the mean extinction time of one of the two competing
species as a function of the additive noise intensity.Comment: 11 pages, 6 figures, 17 panels. To appear in Physica
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