About the screening of the charge of a proton migrating in a metal

The amount of screening of a proton in a metal, migrating under the influence of an applied electric field, is calculated using different theoretical formulations. First the lowest order screening expression derived by Sham (1975) is evaluated. In addition 'exact' expressions are evaluated which were derived according to different approaches. For a proton in a metal modeled as a jellium the screening appears to be 15 +/- 10 %, which is neither negligible not reconcilable with the controversial full-screening point of view of Bosvieux and Friedel (1962). In reconsidering the theory of electromigration, a new simplified linear-response expression for the driving force is shown to lead to essentially the same result as found by Sorbello (1985), who has used a rather complicated technique. The expressions allow for a reduction such that only the scattering phase shifts of the migrating impurity are required. Finally it is shown that the starting formula for the driving force of Bosvieux and Friedel leads exactly to the zero-temperature limit of well-established linear response descriptions, by which the sting of the controversy has been removed.Comment: 14 pages, 5 figure

Visualizing atomic-scale redox dynamics in vanadium oxide-based catalysts

Surface redox processes involving oxygen atom exchange are fundamental in catalytic reactions mediated by metal oxides. These processes are often difficult to uncover due to changes in the surface stoichiometry and atomic arrangement. Here we employ high-resolution transmission electron microscopy to study vanadium oxide supported on titanium dioxide, which is of relevance as a catalyst in, e.g., nitrogen oxide emission abatement for environmental protection. The observations reveal a reversible transformation of the vanadium oxide surface between an ordered and disordered state, concomitant with a reversible change in the vanadium oxidation state, when alternating between oxidizing and reducing conditions. The transformation depends on the anatase titanium dioxide surface termination and the vanadium oxide layer thickness, suggesting that the properties of vanadium oxide are sensitive to the supporting oxide. These atomic-resolution observations offer a basis for rationalizing previous reports on shape-sensitive catalytic properties

Quantum field theoretic approach to neutrino oscillations in matter

We consider neutrino oscillations in non-uniform matter in a quantum field theoretic (QFT) approach, in which neutrino production, propagation and detection are considered as a single process. We find the conditions under which the oscillation probability can be sensibly defined and demonstrate how the properly normalized oscillation probability can be obtained in the QFT framework. We derive the evolution equation for the oscillation amplitude and discuss the conditions under which it reduces to the standard Schr\"odinger-like evolution equation. It is shown that, contrary to the common usage, the Schr\"odinger-like evolution equation is not applicable in certain cases, such as oscillations of neutrinos produced in decays of free pions provided that sterile neutrinos with $\Delta m^2\gtrsim 1$ eV$^2$ exist.Comment: LaTeX, 24 pages + 16 pages of appendices, 1 figure. V2: typos correcte

Mass hierarchy, 2-3 mixing and CP-phase with Huge Atmospheric Neutrino Detectors

We explore the physics potential of multi-megaton scale ice or water Cherenkov detectors with low ($\sim 1$ GeV) threshold. Using some proposed characteristics of the PINGU detector setup we compute the distributions of events versus neutrino energy $E_\nu$ and zenith angle $\theta_z$, and study their dependence on yet unknown neutrino parameters. The $(E_\nu - \theta_z)$ regions are identified where the distributions have the highest sensitivity to the neutrino mass hierarchy, to the deviation of the 2-3 mixing from the maximal one and to the CP-phase. We evaluate significance of the measurements of the neutrino parameters and explore dependence of this significance on the accuracy of reconstruction of the neutrino energy and direction. The effect of degeneracy of the parameters on the sensitivities is also discussed. We estimate the characteristics of future detectors (energy and angle resolution, volume, etc.) required for establishing the neutrino mass hierarchy with high confidence level. We find that the hierarchy can be identified at $3\sigma$ -- $10\sigma$ level (depending on the reconstruction accuracies) after 5 years of PINGU operation.Comment: 39 pages, 21 figures. Description of Fig.3 correcte

Rural Origin and Exposure Drives Ghanaian Midwives Reported Future Practice

A primary cause of Ghana’s higher than global average maternal mortality rate is limited access to maternal care in rural areas. To date, few studies have examined how rural background/training of midwives impacts their future willingness to work in remote areas. The purpose of this paper is to describe the relationship between Ghanaian student midwife place of origin and rural training on their willingness to choose a future rural practice location. A cross-sectional computer-based survey was completed by 238 final year Ghanaian midwifery students from two public midwifery training schools located in urban Ghana between October and December 2009. The relationship between rural exposure and willingness to work in rural Ghana was analyzed using independent t-test, chi-square, and bivariate logistic regression. Participants who experienced a rural rotation (OR: 1.51, 95% CI: 0.71, 3.22) and those born in a rural area (OR: 2.24, 95% CI: 0.74, 6.75) resulted in greater odds ratio to choose rural practice following graduation. This study indicates an association between midwifery students’ place of origin and training and their willingness to practice in a rural area after graduation. (Afr J Reprod Health 2014; 18[3]: 95-100)Keywords: Midwifery, Ghana, human resources for health, maldistribution, rural practice, rural incentive

D-brane orbiting NS5-branes

We study real time dynamics of a Dp-brane orbiting a stack of NS5-branes. It is generally known that a BPS D-brane moving in the vicinity of NS5-branes becomes unstable due to the presence of tachyonic degree of freedom induced on the D-brane. Indeed, the D-brane necessarily falls into the fivebranes due to gravitational attraction and eventually collapses into a pressureless fluid. Such a decay of the D-brane is known to be closely related to the rolling tachyon problem. In this paper we show that in special cases the decay of D-brane caused by gravitational attraction can be avoided. Namely for certain values of energy and angular momentum the D-brane orbits around the fivebranes, maintaining certain distance from the fivebranes all the time, and the process of tachyon condensation is suppressed. We show that the tachyonic degree of freedom induced on such a D-brane really disappears and the brane returns to a stable D-brane.Comment: 12 pages, latex, added referenc

A comparison of the healthiness of packaged foods and beverages from 12 countries using the Health Star Rating nutrient profiling system, 2013-2018

We compared the healthiness of packaged foods and beverages between selected countries using the Health Star Rating (HSR) nutrient profiling system. Packaged food and beverage data collected 2013-2018 were obtained for Australia, Canada, Chile, China, India, Hong Kong, Mexico, New Zealand, Slovenia, South Africa, the UK, and USA. Each product was assigned to a food or beverage category and mean HSR was calculated overall by category and by country. Median energy density (kJ/100 g), saturated fat (g/100 g), total sugars (g/100 g) and sodium (mg/100 g) contents were calculated. Countries were ranked by mean HSR and median nutrient levels. Mean HSR for all products (n = 394,815) was 2.73 (SD 1.38) out of 5.0 (healthiest profile). The UK, USA, Australia and Canada ranked highest for overall nutrient profile (HSR 2.74-2.83) and India, Hong Kong, China and Chile ranked lowest (HSR 2.27-2.44). Countries with higher overall HSR generally ranked better with respect to nutrient levels. India ranked consistently in the least healthy third for all measures. There is considerable variability in the healthiness of packaged foods and beverages in different countries. The finding that packaged foods and beverages are less healthy in middle-income countries such as China and India suggests that nutrient profiling is an important tool to enable policymakers and industry actors to reformulate products available in the marketplace to reduce the risk of obesity and NCDs among populations

Area Regge Calculus and Discontinuous Metrics

Taking the triangle areas as independent variables in the theory of Regge calculus can lead to ambiguities in the edge lengths, which can be interpreted as discontinuities in the metric. We construct solutions to area Regge calculus using a triangulated lattice and find that on a spacelike hypersurface no such discontinuity can arise. On a null hypersurface however, we can have such a situation and the resulting metric can be interpreted as a so-called refractive wave.Comment: 18 pages, 1 figur

Chronology protection in stationary three-dimensional spacetimes

We study chronology protection in stationary, rotationally symmetric spacetimes in 2+1 dimensional gravity, focusing especially on the case of negative cosmological constant. We show that in such spacetimes closed timelike curves must either exist all the way to the boundary or, alternatively, the matter stress tensor must violate the null energy condition in the bulk. We also show that the matter in the closed timelike curve region gives a negative contribution to the conformal weight from the point of view of the dual conformal field theory. We illustrate these properties in a class of examples involving rotating dust in anti-de Sitter space, and comment on the use of the AdS/CFT correspondence to study chronology protection.Comment: 20 pages. V2: minor corrections, Outlook expanded, references added, published versio

The Plasmodium falciparum, Nima-related kinase Pfnek-4: a marker for asexual parasites committed to sexual differentiation

<b>Background</b> Malaria parasites undergo, in the vertebrate host, a developmental switch from asexual replication to sexual differentiation leading to the formation of gametocytes, the only form able to survive in the mosquito vector. Regulation of the onset of the sexual phase remains largely unknown and represents an important gap in the understanding of the parasite's complex biology. <b>Methods:</b> The expression and function of the Nima-related kinase Pfnek-4 during the early sexual development of the human malaria parasite Plasmodium falciparum were investigated, using three types of transgenic Plasmodium falciparum 3D7 lines: (i) episomally expressing a Pfnek-4-GFP fusion protein under the control of its cognate pfnek-4 promoter; (ii) episomally expressing negative or positive selectable markers, yeast cytosine deaminase-uridyl phosphoribosyl transferase, or human dihydrofolate reductase, under the control of the pfnek-4 promoter; and (iii) lacking a functional pfnek-4 gene. Parasite transfectants were analysed by fluorescence microscopy and flow cytometry. In vitro growth rate and gametocyte formation were determined by Giemsa-stained blood smears. <b>Results:</b> The Pfnek-4-GFP protein was found to be expressed in stage II to V gametocytes and, unexpectedly, in a subset of asexual-stage parasites undergoing schizogony. Culture conditions stimulating gametocyte formation resulted in significant increase of this schizont subpopulation. Moreover, sorted asexual parasites expressing the Pfnek-4-GFP protein displayed elevated gametocyte formation when returned to in vitro culture in presence of fresh red blood cells, when compared to GFP- parasites from the same initial population. Negative selection of asexual parasites expressing pfnek-4 showed a marginal reduction in growth rate, whereas positive selection caused a marked reduction in parasitaemia, but was not sufficient to completely abolish proliferation. Pfnek-4- clones are not affected in their asexual growth and produced normal numbers of stage V gametocytes. <b>Conclusions:</b> The results indicate that Pfnek-4 is not strictly gametocyte-specific, and is expressed in a small subset of asexual parasites displaying high rate conversion to sexual development. Pfnek-4 is not required for erythrocytic schizogony and gametocytogenesis. This is the first study to report the use of a molecular marker for the sorting of sexually-committed schizont stage P. falciparum parasites, which opens the way to molecular characterization of this pre-differentiated subpopulation