An analytic approximation to the Diffusion Coefficient for the periodic Lorentz Gas

An approximate stochastic model for the topological dynamics of the periodic triangular Lorentz gas is constructed. The model, together with an extremum principle, is used to find a closed form approximation to the diffusion coefficient as a function of the lattice spacing. This approximation is superior to the popular Machta and Zwanzig result and agrees well with a range of numerical estimates.Comment: 13 pages, 4 figure

Products of in situ corrosion of depleted uranium ammunition in Bosnia and Herzegovina soils

Hundreds of tons of depleted uranium (DU) ammunition were used in previous armed conflicts in Iraq, Bosnia and Herzegovina, and Serbia/Kosovo. The majority (>90%) of DU penetrators miss their target and, if left in the environment, corrode in these postconflict zones. Thus, the best way to understand the fate of bulk DU material in the environment is to characterize the corrosion products of intact DU penetrators under field conditions for extended periods of time. However, such studies are scarce. To fill this knowledge gap, we characterized corrosion products formed from two intact DU penetrators that remained in soils in Bosnia and Herzegovina for over seven years. We used a combination of X-ray powder diffraction, electron microscopy, and X-ray absorption spectroscopy. The results show that metaschoepite (UO3(H2O)(2)) was a main component of the two DU corrosion products. Moreover, studtite ((UO2)O-2(H2O)(2)center dot 2(H2O)) and becquerelite (Ca(UO2)(6)O-4(OH)(6)center dot 8(H2O)) were also identified in the corrosion products. Their formation through transformation of metaschoepite was a result of the geochemical conditions under which the penetrators corroded. Moreover, we propose that the transformation of metaschoepite to becquerelite or studtite in the DU corrosion products would decrese the potential for mobilization of U from corroded DU penetrators exposed to similar environments in postconflict areas

Extensive admixture and selective pressure across the Sahel Belt

Genome-wide studies of African populations have the potential to reveal powerful insights into the evolution of our species, as these diverse populations have been exposed to intense selective pressures imposed by infectious diseases, diet, and environmental factors. Within Africa, the Sahel Belt extensively overlaps the geographical center of several endemic infections such as malaria, trypanosomiasis, meningitis, and hemorrhagic fevers. We screened 2.5 million single nucleotide polymorphisms in 161 individuals from 13 Sahelian populations, which together with published data cover Western, Central, and Eastern Sahel, and include both nomadic and sedentary groups. We confirmed the role of this Belt as a main corridor for human migrations across the continent. Strong admixture was observed in both Central and Eastern Sahelian populations, with North Africans and Near Eastern/Arabians, respectively, but it was inexistent in Western Sahelian populations. Genome-wide local ancestry inference in admixed Sahelian populations revealed several candidate regions that were significantly enriched for non-autochthonous haplotypes, and many showed to be under positive selection. The DARC gene region in Arabs and Nubians was enriched for African ancestry, whereas the RAB3GAP1/LCT/MCM6 region in Oromo, the TAS2R gene family in Fulani, and the ALMS1/NAT8 in Turkana and Samburu were enriched for non-African ancestry. Signals of positive selection varied in terms of geographic amplitude. Some genomic regions were selected across the Belt, the most striking example being the malaria-related DARC gene. Others were Western-specific (oxytocin, calcium, and heart pathways), Eastern-specific (lipid pathways), or even population-restricted (TAS2R genes in Fulani, which may reflect sexual selection).People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007-2013/ under REA grant agreement no. 290344 (EUROTAST). This project was also supported by the Grant Agency of the Czech Republic (13-37998S-P505). P.S. is supported by FCT (the Portuguese Foundation for Science and Technology), through FCT Investigator Programme (IF/01641/2013). IPATIMUP integrates the i3S Research Unit, which is partially supported by FCT. FEDER, COMPETE, and FCT fund IPATIMUP (PEst-C/SAU/LA0003/2013) and CBMA (PEst-OE/BIA/UI4050/2014

Food production and consumption in Bamyan Province, Afghanistan: the challenges of sustainability and seasonality for dietary diversity

In Asia, high levels of malnutrition threaten the health and livelihoods of millions of households. This paper concentrates on linkages between agriculture and nutrition in Afghanistan where food and nutrition insecurity are increasing and agricultural sustainability is increasingly compromised by climate change. We explore seasonal patterns of food production and consumption in the remote and robust ecological environment of Shah Foladi, Bamyan Province. Analysis of qualitative data from household interviews in eight villages has provided a wealth of insights into the seasonality of diets. Even within a broadly homogeneous environment, households were found to be markedly heterogeneous in respect of their assets, production, market, finance and employment strategies. The so-called ‘lean season’ was found to vary accordingly. Nevertheless, a general lack of dietary diversity during much of the year is likely to cause micronutrient malnutrition, especially for the vulnerable groups of children, adolescent girls and women. Potential interventions are proposed which need to account for the local context in order to overcome the natural and political constraints. These strategies include agricultural innovation and multi-sectoral policy approaches. In the end, reducing national insecurity is a pre-requisite for sustainable improvement in nutrition-sensitive agricultural development

Recently listed Stockholm convention POPs: Analytical methodology, occurrence in food and dietary exposure

In recent years, the Stockholm Convention has listed an additional set of persistent organic pollutants (POPs) for elimination or restricted use/release. Data on the occurrence of these contaminants in food is scarce. Validated analytical methodology was developed to investigate the occurrence of hexachlorobutadiene (HCBD), pentachlorobenzene (PCBz), hexachlorobenzene (HCB) pentachlorophenol (PCP) and polychlorinated naphthalenes (PCNs) in 120 retail foods and 19 total diet study samples. The foods covered the range of commonly consumed dietary items including dairy products, eggs (hen and other species), poultry, meat, fish, vegetables, etc. HCBD showed a low frequency of detection, whereas PCBz, HCB and PCNs occurred in most samples (ranges: <0.01 to 0.19 μg/kg; <0.01 to 3.16 μg/kg and 0.1 to 166 ng ΣPCNs/kg respectively). PCP (<0.01 to 1.9 μg/kg) was detected more frequently in meat products, offal and eggs. Fish, shellfish, eggs from all species, animal fats, meat, offal and meat products showed higher contamination levels, which is normal when investigating lipophilic POPs. These levels of occurrence are similar to more recently reported literature levels but perhaps lower, relative to historic data. This is not unexpected, given the restrictions/limitations on these chemicals within the UK and Western Europe. The estimated human exposure to population groups through dietary intake is correspondingly low and based on current toxicological knowledge, the levels in the examined samples do not suggest a cause for health concern. The data also provide a current baseline for HCBD, PCBz and PCP, and update existing data for PCN and HCB occurrence in foods

A screening tool to prioritize public health risk associated with accidental or deliberate release of chemicals into the atmosphere

The Chemical Events Working Group of the Global Health Security Initiative has developed a flexible screening tool for chemicals that present a risk when accidentally or deliberately released into the atmosphere. The tool is generic, semi-quantitative, independent of site, situation and scenario, encompasses all chemical hazards (toxicity, flammability and reactivity), and can be easily and quickly implemented by non-subject matter experts using freely available, authoritative information. Public health practitioners and planners can use the screening tool to assist them in directing their activities in each of the five stages of the disaster management cycle