An Evaluation of the Fe-N Phase Diagram Considering Long-Range Order of N Atoms in γ'-Fe4N1-x and ε-Fe2N1-z

The chemical potential of nitrogen was described as a function of nitrogen content for the Fe-N phases α-Fe[N], γ'-Fe4N1-x, and ε-Fe2N1-z. For α-Fe[N], an ideal, random distribution of the nitrogen atoms over the octahedral interstices of the bcc iron lattice was assumed; for γ'-Fe4N1-x and ε-Fe2N1-z, the occurrence of a long-range ordered distribution of the nitrogen atoms over the octahedral interstices of the close packed iron sublattices (fcc and hcp, respectively) was taken into account. The theoretical expressions were fitted to nitrogen-absorption isotherm data for the three Fe-N phases. The α/α + γ', α + γ'/γ', γ'/γ' + ε, and γ' + ε/ε phase boundaries in the Fe-N phase diagram were calculated from combining the quantitative descriptions for the absorption isotherms with the known composition of NH3/H2 gas mixtures in equilibrium with coexisting α and γ' phases and in equilibrium with coexisting γ' and ε phases. Comparison of the present phase boundaries with experimental data and previously calculated phase boundaries showed a major improvement as compared to the previously calculated Fe-N phase diagrams, where long-range order for the nitrogen atoms in the γ' and ε phases was not accounted for

Crystal structures of methionine repressor of E. coli and its complex with operator

Available from British Library Document Supply Centre- DSC:D79029 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Seasonal selection of key resources by cattle in a mixed savannah-wetland ecosystem increases the potential for conflict with lions

In Africa's pastoral conservation landscapes, apex predators frequently kill livestock. Retaliatory persecution such as poisoning threatens predators, but also non-target biota. Several factors influence conflict severity, including livestock husbandry, overlap in seasonal habitat use, and the degree to which livestock perceive and are able to respond to a landscape of fear. We investigated these factors by GPS-tracking 42 Tswana beef cattle (Bos taurus) from 29 herds in 2017 and six lions (Panthera leo) from different prides (May 2016–Dec. 2017) in the northern Okavango Delta, Botswana, where cattle depredation significantly impacts the livelihoods of rural agro-pastoralists. Cattle exhibited seasonal habitat selection patterns similar to wild ungulates in the region. They preferred woodland habitats, with more digestible grasses, during the wet season. During the dry season, they preferred wetland habitats with reliable forage and water availability. Cattle also preferred areas close to human settlements, but the necessity to forage in wetlands during the dry season exposed them to significant depredation risk, especially >4 km from settlements. Lions killed most cattle in wetlands during the late dry season but the intensity of recent lion presence (previous 14 days) only had a weak negative effect on cattle habitat selection patterns. Cattle used rangelands according to nutritional requirements, irrelevant of the associated predation risk, suggesting that socio-ecologically acceptable conflict solutions cannot rely on the exclusion of livestock from seasonal wetlands. Curbing depredation by lions will best be achieved by a combination of resource- and predation-cognisant seasonal herding strategies with adequate livestock protection. Understanding the ecological constraints that intensify conflict is pertinent to any livestock production landscape with predator presence. It is also a central prerequisite for future land use planning and devolution of legal, controlled resource access rights through policy. Coexistence strategies must account for the strong reliance of people, their livestock, and wildlife on shared key resources. This is particularly important in large trans-frontier conservation areas where the successful merging of biodiversity conservation and rural development is a strategic goal. Omission will foster resentment and resistance to coexistence with apex predators, particularly if livestock productivity and human livelihoods are negatively affected.Grants received from the National Geographic Society (Big Cats Initiative grant numbers: B5-15, B10-16, B6-17), WWF's INNO Fund (grant no.: 17-03), and Stichting SPOTS Netherlands and its supporters. FJW was supported by a post-doctoral fellowship of the University of Pretoria. MJS was supported by a National Research Foundation Incentive grant.http://www.elsevier.com/locate/biocon2020-09-01hj2019Centre for Wildlife ManagementMammal Research InstituteZoology and Entomolog

Thermodynamics and Long-Range Order of Interstitials in a Hexagonal Close-Packed Lattice

Statistical thermodynamics was applied to describe long-range order (LRO) of interstitial atoms in a hexagonal close-packed (hcp) host lattice. On the basis of the Gorsky-Bragg-Williams (GBW) approximation and a division of the interstitial sublattice into six interpenetrating sublattices, all the possible ordered configurations were derived for this assembly. Special attention was devoted to two of the possible ordered configurations of interstitial atoms, viz., the two ground-state structures that have been indicated for ε-Fe2N1-z. A description of the order-disorder transition was obtained, and the evolution of the occupancies of the different types of interstitial sites on changing the total interstitial content was given. Composition-temperature regions of stability for the two ordered configurations were given in phase diagrams for different combinations of pairwise interaction energies. The results are compatible with observations for ε-Fe2N1-z as reported in the literature. The advantages of the present treatment were discussed relative to an earlier one, which a priori excluded nearest neighboring interstitial sites from simultaneous occupancy.

Thermodynamics and Long-Range Order of Nitrogen in γ'-Fe4N1-x

Models are given for the description of the chemical potential of nitrogen in γ'-Fe4N1-x. In previous work, γ'-Fe4N1-x was treated as a (sub)regular solution, thereby assuming that the N atoms are distributed randomly on the sites of their own sublattice. However, in γ'-Fe4N1-x, long-range ordering occurs of the N atoms over the sites of their own sublattice. Then, the expression for the configurational entropy should account for the occurrence of ordering. In the present article, the descriptions adopted and tested for γ'-Fe4N1-x are based on a Langmuir-type approach, the Wagner-Schottky (WS) approach, and the Gorsky-Bragg-Williams (GBW) approach. Application of the various models to data of nitrogen-absorption isotherms for the γ' iron-nitride phase shows that the subregular solution concept fails to describe the experimental data satisfactorily, whereas a very good agreement between theory and experiment is obtained for the WS and GBW approaches. It is shown that, in particular, accounting for the occupation of disorder (octahedral) sites by N atoms is necessary to obtain an accurate description of the chemical potential of nitrogen in γ'-Fe4N1-x.