Angle dependence of Andreev scattering at semiconductor-superconductor interfaces

We study the angle dependence of the Andreev scattering at a semiconductor-superconductor interface, generalizing the one-dimensional theory of Blonder, Tinkham and Klapwijk. An increase of the momentum parallel to the interface leads to suppression of the probability of Andreev reflection and increase of the probability of normal reflection. We show that in the presence of a Fermi velocity mismatch between the semiconductor and the superconductor the angles of incidence and transmission are related according to the well-known Snell's law in optics. As a consequence there is a critical angle of incidence above which only normal reflection exists. For two and three-dimensional interfaces a lower excess current compared to ballistic transport with perpendicular incidence is found. Thus, the one-dimensional BTK model overestimates the barrier strength for two and three-dimensional interfaces.Comment: 8 pages including 3 figures (revised, 6 references added

Ispitivanja statičke kompresije i rezonantne vibracije celularnih materijala dobivenih gravitacijskim sinterovanjem šupljih brončanih kugli

The cylindrical and rod-shaped specimens were prepared by gravity sintering from Cu-Sn hollow spheres. On these samples, both static compression tests and measurements of resonance frequencies were performed. The compressive stress-strain curves revealed the features characteristic for a closed-cell ductile cellular solid. The removal of in general open porosity among loosely packed closed metallic hollow spheres was recognized as the principal mode of plastic deformation. The approximative effective moduli of elasticity were determined for cellular materials under consideration by means of the measurements of resonance frequencies on rod-shaped specimens.Cilindrični i šipkasti uzorci su pripremljeni gravitacionim sinterovanjem šupljih Cu-Sn kugli. Na tim uzorcima su provedena ispitivanja statičke kompresije i mjerenja rezonantnih frekvencija. Krivulja naprezanje-rastezanje nam pokazuje svojstva karakteristična za plastične celularne krute materijale sa zatvorenim ćelijama. Uklanjanje uglavnom otvorene povezanosti među labavo povezanim šupljim metalnim kuglama prepoznajemo kao glavni način plastične deformacije. Za celularne materijale koji se razmatraju određeni su približno učinkoviti moduli elastičnosti mjerenjem frekvencija rezonancije na šipkasto oblikovanim uzorcima

Near-infrared spectroscopy can detect brain activity during a color-word matching Stroop task in an event-related design

Brai nactivit ycanbemonitore dnon-invasivel ybynear-infrare dspectroscop y(NIRS) ,whic hhas severa ladvantage sincompariso nwit hothe rimagin gmethods ,suc hasflexibility ,portability ,low cost an dbiochemica lspecificity .Moreover ,patient san dchildre ncanberepetitivel yexamined .Therefore ,the objectiv eofthestud ywa stotes tthefeasibilit yofNIR Sfortheevent-relate dapproac hinfunctiona lbrain activatio nstudie swit hcognitiv eparadigms .Thus ,change sintheconcentratio nofoxy- ,deoxy- ,an dtotal hemoglobi nwer emeasure d byNIR Sin14health ysubject swhil eperformin ga color–wor d matching Stroo p tas k in an event-relate d design .Th ehemodynami crespons e(increas ein theconcentratio n of oxy-/tota lhemoglobi n an d decreas ein theconcentratio n ofdeoxy-hemoglobin )wa sstronge rduring incongruen tcompare dtocongruen tan dneutra ltrial softheStroo ptas kinthelatera lprefronta lcortex bilaterally .Thi sstronge rhemodynami crespons ewa sinterprete dasa stronge rbrai nactivatio nduring incongruen ttrial softheStroo ptask ,du etointerference .A ne w metho dforNIR Sdat aevaluatio nthat enable stheanalysi softhehemodynami crespons etoeac hsingl etria lisintroduced .Eac hhemodynamic respons ewa scharacterize dbytheparameter sgain ,lagan ddispersio nofa Gaussia nfunctio nfitte dby nonlinea rregression .Specifi cdifference sbetwee ntheincongruen tan dneutra lconditio nwer efoun dfor gai nan dlag .Further ,thes eparameter swer ecorrelate dwit hthebehaviora lperformance .Inconclusion, brai nactivit yma ybestudie d byNIR Susin gcognitiv estimul iinanevent-relate d design

Cost-effectiveness of community-based screening and treatment of moderate acute malnutrition in Mali.

IntroductionModerate acute malnutrition (MAM) causes substantial child morbidity and mortality, accounting for 4.4% of deaths and 6.0% of disability-adjusted life years (DALY) lost among children under 5 each year. There is growing consensus on the need to provide appropriate treatment of MAM, both to reduce associated morbidity and mortality and to halt its progression to severe acute malnutrition. We estimated health outcomes, costs and cost-effectiveness of four dietary supplements for MAM treatment in children 6-35 months of age in Mali.MethodsWe conducted a cluster-randomised MAM treatment trial to describe nutritional outcomes of four dietary supplements for the management of MAM: ready-to-use supplementary foods (RUSF; PlumpySup); a specially formulated corn-soy blend (CSB) containing dehulled soybean flour, maize flour, dried skimmed milk, soy oil and a micronutrient pre-mix (CSB++; Super Cereal Plus); Misola, a locally produced, micronutrient-fortified, cereal-legume blend (MI); and locally milled flour (LMF), a mixture of millet, beans, oil and sugar, with a separate micronutrient powder. We used a decision tree model to estimate long-term outcomes and calculated incremental cost-effectiveness ratios (ICERs) comparing the health and economic outcomes of each strategy.ResultsCompared to no MAM treatment, MAM treatment with RUSF, CSB++, MI and LMF reduced the risk of death by 15.4%, 12.7%, 11.9% and 10.3%, respectively. The ICER was US$9821 per death averted (2015 USD) and US$347 per DALY averted for RUSF compared with no MAM treatment.ConclusionMAM treatment with RUSF is cost-effective across a wide range of willingness-to-pay thresholds.Trial registrationNCT01015950

Turbulent convection: comparing the moment equations to numerical simulations

The non-local hydrodynamic moment equations for compressible convection are compared to numerical simulations. Convective and radiative flux typically deviate less than 20% from the 3D simulations, while mean thermodynamic quantities are accurate to at least 2% for the cases we have investigated. The moment equations are solved in minutes rather than days on standard workstations. We conclude that this convection model has the potential to considerably improve the modelling of convection zones in stellar envelopes and cores, in particular of A and F stars.Comment: 10 pages (6 pages of text including figure captions + 4 figures), Latex 2e with AAS Latex 5.0 macros, accepted for publication in ApJ

Predictors of Stunting, Wasting and Underweight among Tanzanian Children Born to HIV-Infected Women.

Children born to human immunodeficiency virus (HIV)-infected women are susceptible to undernutrition, but modifiable risk factors and the time course of the development of undernutrition have not been well characterized. The objective of this study was to identify maternal, socioeconomic and child characteristics that are associated with stunting, wasting and underweight among Tanzanian children born to HIV-infected mothers, followed from 6 weeks of age for 24 months. Maternal and socioeconomic characteristics were recorded during pregnancy, data pertaining to the infant's birth were collected immediately after delivery, morbidity histories and anthropometric measurements were performed monthly. Multivariate Cox proportional hazards methods were used to assess the association between potential predictors and the time to first episode of stunting, wasting and underweight. A total of 2387 infants (54.0% male) were enrolled and followed for a median duration of 21.2 months. The respective prevalence of prematurity (<37 weeks) and low birth weight (<2500 g) was 15.2% and 7.0%; 11.3% of infants were HIV-positive at 6 weeks. Median time to first episode of stunting, wasting and underweight was 8.7, 7.2 and 7.0 months, respectively. Low maternal education, few household possessions, low infant birth weight, child HIV infection and male sex were all independent predictors of stunting, wasting and underweight. In addition, preterm infants were more likely to become wasted and underweight, whereas those with a low Apgar score at birth were more likely to become stunted. Interventions to improve maternal education and nutritional status, reduce mother-to-child transmission of HIV, and increase birth weight may lower the risk of undernutrition among children born to HIV-infected women

Critical evaluation of magnetic field detections reported for pulsating B-type stars in the light of ESPaDOnS, Narval and reanalyzed FORS1/2 observations

Recent spectropolarimetric studies of 7 SPB and $\beta$ Cep stars have suggested that photospheric magnetic fields are more common in B-type pulsators than in the general population of B stars, suggesting a significant connection between magnetic and pulsational phenomena. We present an analysis of new and previously published spectropolarimetric observations of these stars. New Stokes $V$ observations obtained with the high-resolution ESPaDOnS and Narval instruments confirm the presence of a magnetic field in one of the stars ($\epsilon$ Lup), but find no evidence of magnetism in 5 others. A re-analysis of the published longitudinal field measurements obtained with the low-resolution FORS1/2 spectropolarimeters finds that the measurements of all stars show more scatter from zero than can be attributed to Gaussian noise, suggesting the presence of a signal and/or systematic under-estimation of error bars. Re-reduction and re-measurement of the FORS1/2 spectra from the ESO archive demonstrates that small changes in reduction procedure lead to substantial changes in the inferred longitudinal field, and substantially reduces the number of field detections at the 3$\sigma$ level. Furthermore, we find that the published periods are not unique solutions to the time series of either the original or the revised FORS1/2 data. We conclude that the reported field detections, proposed periods and field geometry models for $\alpha$ Pyx, 15 CMa, 33 Eri and V1449 Aql are artefacts of the data analysis and reduction procedures, and that magnetic fields at the reported strength are no more common in SPB/$\beta$ Cep stars than in the general population of B stars.Comment: 10 pages, 5 figures, accepted for publication in ApJ, 2012, typo correcte

Asteroseismology of exoplanets host stars: the special case of ι\iota Horologii (HD17051)

{This paper presents detailed analysis and modelisation of the star HD17051 (alias $\iota$ Hor), which appears as a specially interesting case among exoplanet host stars. As most of these stars, $\iota$ Hor presents a metallicity excess which has been measured by various observers who give different results, ranging from [Fe/H] = 0.11 to 0.26, associated with different atmospheric parameters. Meanwhile the luminosity of the star may be determined owing to Hipparcos parallax. Although in the southern hemisphere, this star belongs to the Hyades stream and its external parameters show that it could even be one of the Hyades stars ejected during cluster formation. The aim of this work was to gather and analyse our present knowledge on this star and to prepare seismic tests for future observations with the HARPS spectrometer (planned for November 2006).} {We have computed evolutionary tracks with various metallicities, in the two frameworks of primordial overmetallicity and accretion. We have concentrated on models inside the error boxes given by the various observers in the log g - log T$_{eff}$ diagram. We then computed the adiabatic oscillation frequencies of these models to prepare future observations.} {The detailed analysis of $\iota$ Hor presented in this paper already allowed to constrain its external parameters, mass and age. Some values given in the literature could be rejected as inconsistent with the overall analysis. We found that a model computed with the Hyades parameters (age, metallicity) was clearly acceptable, but other ones were possible too. We are confident that observations with HARPS will allow for a clear conclusion about this star and that it will bring important new light on the physics of exoplanet host stars.}Comment: to be published in Astronomy and Astrophysic

HE 0557-4840 - Ultra-Metal-Poor and Carbon-Rich

We report the discovery and high-resolution, high S/N, spectroscopic analysis of the ultra-metal-poor red giant HE 0557-4840, which is the third most heavy-element deficient star currently known. Its atmospheric parameters are T_eff = 4900 K, log g = 2.2, and [Fe/H]= -4.75. This brings the number of stars with [Fe/H] < -4.0 to three, and the discovery of HE 0557-4840 suggests that the metallicity distribution function of the Galactic halo does not have a "gap" between [Fe/H] = -4.0, where several stars are known, and the two most metal-poor stars, at [Fe/H] ~ -5.3. HE 0557-4840 is carbon rich - [C/Fe] = +1.6 - a property shared by all three objects with [Fe/H] < -4.0, suggesting that the well-known increase of carbon relative to iron with decreasing [Fe/H] reaches its logical conclusion - ubiquitous carbon richness - at lowest abundance. We also present abundances (nine) and limits (nine) for a further 18 elements. For species having well-measured abundances or strong upper limits, HE 0557-4840 is "normal" in comparison with the bulk of the stellar population at [Fe/H] ~ -4.0 - with the possible exception of Co. We discuss the implications of these results for chemical enrichment at the earliest times, in the context of single ("mixing and fallback") and two-component enrichment models. While neither offers a clear solution, the latter appears closer to the mark. Further data are required to determine the oxygen abundance and improve that of Co, and hence more strongly constrain the origin of this object.Comment: Submitted to Astrophysical Journal. 52 pages (41 text, 11 figures

On the influence of Stark broadening on Si I lines in stellar atmospheres

We study the influence of Stark broadening and stratification effects on Si\i lines in the rapidly oscillating (roAp) star 10 Aql, where the Si\i 6142.48 \AA and 6155.13 \AA lines are asymmetrical and shifted. First we have calculated Stark broadening parameters using the semiclassical perturbation method for three Si\i lines: 5950.2 \AA, 6142.48 \AA and 6155.13 \AA. We revised the synthetic sp$ calculation code taking into account both Stark width and shift for these lines. From the comparison of our calculations with the observations we found that Stark broadening + the stratification effect can explain asymmetry of the Si\i 6142.48 \AA and 6155.13 \AA lines in the atmospere of roAp star 10 Aql.Comment: Accepted to A&