5,904 research outputs found
Polaron Coherence as Origin of the Pseudogap Phase in High Temperature Superconducting Cuprates
Within a two component approach to high Tc copper oxides including polaronic
couplings, we identify the pseudogap phase as the onset of polaron ordering.
This ordering persists in the superconducting phase. A huge isotope effect on
the pseudogap onset temperature is predicted and in agreement with experimental
data. The anomalous temperature dependence of the mean square copper oxygen ion
displacement observed above, at and below Tc stems from an s-wave
superconducting component of the order parameter, whereas a pure d-wave order
parameter alone can be excluded.Comment: 7 pages, 2 figure
Clinical epidemiology, diagnosis and treatment of visceral leishmaniasis in the Pokot endemic area of Uganda and Kenya.
Between 2000 and 2010, Médecins Sans Frontières diagnosed and treated 4,831 patients with visceral leishmaniasis (VL) in the Pokot region straddling the border between Uganda and Kenya. A retrospective analysis of routinely collected clinical data showed no marked seasonal or annual fluctuations. Males between 5 and 14 years of age were the most affected group. Marked splenomegaly and anemia were striking features. An rK39 antigen-based rapid diagnostic test was evaluated and found sufficiently accurate to replace the direct agglutination test and spleen aspiration as the first-line diagnostic procedure. The case-fatality rate with sodium stibogluconate as first-line treatment was low. The VL relapses were rare and often diagnosed more than 6 months post-treatment. Post-kala-azar dermal leishmaniasis was rare but likely to be underdiagnosed. The epidemiological and clinical features of VL in the Pokot area differed markedly from VL in Sudan, the main endemic focus in Africa
Random walks of partons in SU(N_c) and classical representations of color charges in QCD at small x
The effective action for wee partons in large nuclei includes a sum over
static color sources distributed in a wide range of representations of the
SU(N_c) color group. The problem can be formulated as a random walk of partons
in the N_c-1 dimensional space spanned by the Casimirs of SU(N_c). For a large
number of sources, k >> 1, we show explicitly that the most likely
representation is a classical representation of order O(\sqrt{k}). The quantum
sum over representations is well approximated by a path integral over classical
sources with an exponential weight whose argument is the quadratic Casimir
operator of the group. The contributions of the higher N_c-2 Casimir operators
are suppressed by powers of k. Other applications of the techniques developed
here are discussed briefly.Comment: 51 pages, includes 3 eps file
Effect of selection on ancestry: an exactly soluble case and its phenomenological generalization
We consider a family of models describing the evolution under selection of a
population whose dynamics can be related to the propagation of noisy traveling
waves. For one particular model, that we shall call the exponential model, the
properties of the traveling wave front can be calculated exactly, as well as
the statistics of the genealogy of the population. One striking result is that,
for this particular model, the genealogical trees have the same statistics as
the trees of replicas in the Parisi mean-field theory of spin glasses. We also
find that in the exponential model, the coalescence times along these trees
grow like the logarithm of the population size. A phenomenological picture of
the propagation of wave fronts that we introduced in a previous work, as well
as our numerical data, suggest that these statistics remain valid for a larger
class of models, while the coalescence times grow like the cube of the
logarithm of the population size.Comment: 26 page
Evidence of magnetic field decay in massive main-sequence stars
A significant fraction of massive main-sequence stars show strong,
large-scale magnetic fields. The origin of these fields, their lifetimes, and
their role in shaping the characteristics and evolution of massive stars are
currently not well understood. We compile a catalogue of 389 massive
main-sequence stars, 61 of which are magnetic, and derive their fundamental
parameters and ages. The two samples contain stars brighter than magnitude 9 in
the V band and range in mass between 5 and 100 Msun. We find that the
fractional main-sequence age distribution of all considered stars follows what
is expected for a magnitude limited sample, while that of magnetic stars shows
a clear decrease towards the end of the main sequence. This dearth of old
magnetic stars is independent of the choice of adopted stellar evolution
tracks, and appears to become more prominent when considering only the most
massive stars. We show that the decreasing trend in the distribution is
significantly stronger than expected from magnetic flux conservation. We also
find that binary rejuvenation and magnetic suppression of core convection are
unlikely to be responsible for the observed lack of older magnetic massive
stars, and conclude that its most probable cause is the decay of the magnetic
field, over a time span longer than the stellar lifetime for the lowest
considered masses, and shorter for the highest masses. We then investigate the
spin-down ages of the slowly rotating magnetic massive stars and find them to
exceed the stellar ages by far in many cases. The high fraction of very slowly
rotating magnetic stars thus provides an independent argument for a decay of
the magnetic fields.Comment: Accepted for publication on A&A; 9 pages, 8 figure
Costs and cost-effectiveness of delivering intermittent preventive treatment through schools in western Kenya
BACKGROUND: Awareness of the potential impact of malaria among school-age children has stimulated investigation into malaria interventions that can be delivered through schools. However, little evidence is available on the costs and cost-effectiveness of intervention options. This paper evaluates the costs and cost-effectiveness of intermittent preventive treatment (IPT) as delivered by teachers in schools in western Kenya. METHODS: Information on actual drug and non-drug associated costs were collected from expenditure and salary records, government budgets and interviews with key district and national officials. Effectiveness data were derived from a cluster-randomised-controlled trial of IPT where a single dose of sulphadoxine-pyrimethamine and three daily doses of amodiaquine were provided three times in year (once termly). Both financial and economic costs were estimated from a provider perspective, and effectiveness was estimated in terms of anaemia cases averted. A sensitivity analysis was conducted to assess the impact of key assumptions on estimated cost-effectiveness. RESULTS: The delivery of IPT by teachers was estimated to cost US 0.25 per child) whilst recurrent costs accounted for 86.8% (US 29.84 and the cost per case of Plasmodium falciparum parasitaemia averted was US 24.60 and 40.32 when the prices of antimalarial drugs and delivery costs were varied. Cost-effectiveness was most influenced by effectiveness of IPT and the background prevalence of anaemia. In settings where 30% and 50% of schoolchildren were anaemic, cost-effectiveness ratios were US$ 12.53 and 7.52, respectively. CONCLUSION: This study provides the first evidence that IPT administered by teachers is a cost-effective school-based malaria intervention and merits investigation in other settings
Quasi-stationary regime of a branching random walk in presence of an absorbing wall
A branching random walk in presence of an absorbing wall moving at a constant
velocity undergoes a phase transition as the velocity of the wall
varies. Below the critical velocity , the population has a non-zero
survival probability and when the population survives its size grows
exponentially. We investigate the histories of the population conditioned on
having a single survivor at some final time . We study the quasi-stationary
regime for when is large. To do so, one can construct a modified
stochastic process which is equivalent to the original process conditioned on
having a single survivor at final time . We then use this construction to
show that the properties of the quasi-stationary regime are universal when
. We also solve exactly a simple version of the problem, the
exponential model, for which the study of the quasi-stationary regime can be
reduced to the analysis of a single one-dimensional map.Comment: 2 figures, minor corrections, one reference adde
The Interplay Between Lymphatic Vessels and Chemokines
Chemokines are a family of small protein cytokines that act as chemoattractants to migrating cells, in particular those of the immune system. They are categorized functionally as either homeostatic, constitutively produced by tissues for basal levels of cell migration, or inflammatory, where they are generated in association with a pathological inflammatory response. While the extravasation of leukocytes via blood vessels is a key step in cells entering the tissues, the lymphatic vessels also serve as a conduit for cells that are recruited and localized through chemoattractant gradients. Furthermore, the growth and remodeling of lymphatic vessels in pathologies is influenced by chemokines and their receptors expressed by lymphatic endothelial cells (LECs) in and around the pathological tissue. In this review we summarize the diverse role played by specific chemokines and their receptors in shaping the interaction of lymphatic vessels, immune cells, and other pathological cell types in physiology and disease
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