Silicon and III-V compound nanotubes: structural and electronic properties

Unusual physical properties of single-wall carbon nanotubes have started a search for similar tubular structures of other elements. In this paper, we present a theoretical analysis of single-wall nanotubes of silicon and group III-V compounds. Starting from precursor graphene-like structures we investigated the stability, energetics and electronic structure of zigzag and armchair tubes using first-principles pseudopotential plane wave method and finite temperature ab-initio molecular dynamics calculations. We showed that (n,0) zigzag and (n,n) armchair nanotubes of silicon having n > 6 are stable but those with n < 6 can be stabilized by internal or external adsorption of transition metal elements. Some of these tubes have magnetic ground state leading to spintronic properties. We also examined the stability of nanotubes under radial and axial deformation. Owing to the weakness of radial restoring force, stable Si nanotubes are radially soft. Undeformed zigzag nanotubes are found to be metallic for 6 < n < 11 due to curvature effect; but a gap starts to open for n > 12. Furthermore, we identified stable tubular structures formed by stacking of Si polygons. We found AlP, GaAs, and GaN (8,0) single-wall nanotubes stable and semiconducting. Our results are compared with those of single-wall carbon nanotubes.Comment: 11 pages, 10 figure

Coca and Conservation: Cultivation, Eradication, and Trafficking in the Amazon Borderlands

The cultivation and traffic of coca, Erythrolxylum coca, and coca derivatives remain understudied threats to the conservation of the Amazon rainforest. Currently the crop is transforming land use and livelihoods in the ecologically and culturally rich borderlands of Amazonian Peru. The isolated nature of this region characterized by indigenous populations (both settled and uncontacted), conservation units, resource concessions, and a lack of state presence provides fertile ground for the boom and bust cycle of coca production and facilitates the international transport of the product to neighboring Brazil. This paper explores the social and environmental impacts of coca production, eradication, and transport through an analysis of both spatial and ethnographic data on land use and livelihood strategies along the Ucayali and Purús Rivers. Results map out the regional distribution and recent history of commercial coca fields and transboundary transportation routes and identify threats to the conservation of indigenous landscapes and borderland forests

Non-collinear coupling between magnetic adatoms in carbon nanotubes

The long range character of the exchange coupling between localized magnetic moments indirectly mediated by the conduction electrons of metallic hosts often plays a significant role in determining the magnetic order of low-dimensional structures. In addition to this indirect coupling, here we show that the direct exchange interaction that arises when the moments are not too far apart may induce a non-collinear magnetic order that cannot be characterized by a Heisenberg-like interaction between the magnetic moments. We argue that this effect can be manipulated to control the magnetization alignment of magnetic dimers adsorbed to the walls of carbon nanotubes.Comment: 13 pages, 5 figures, submitted to PR

In vivo cranial bone strain and bite force in the agamid lizard Uromastyx geyri

In vivo bone strain data are the most direct evidence of deformation and strain regimes in the vertebrate cranium during feeding and can provide important insights into skull morphology. Strain data have been collected during feeding across a wide range of mammals; in contrast, in vivo cranial bone strain data have been collected from few sauropsid taxa. Here we present bone strain data recorded from the jugal of the herbivorous agamid lizard Uromastyx geyri along with simultaneously recorded bite force. Principal and shear strain magnitudes in Uromastyx geyri were lower than cranial bone strains recorded in Alligator mississippiensis, but higher than those reported from herbivorous mammals. Our results suggest that variations in principal strain orientations in the facial skeleton are largely due to differences in feeding behavior and bite location, whereas food type has little impact on strain orientations. Furthermore, mean principal strain orientations differ between male and female Uromastyx during feeding, potentially because of sexual dimorphism in skull morphology

Tailoring Graphene with Metals on Top

We study the effects of metallic doping on the electronic properties of graphene using density functional theory in the local density approximation in the presence of a local charging energy (LDA+U). The electronic properties are sensitive to whether graphene is doped with alkali or transition metals. We estimate the the charge transfer from a single layer of Potassium on top of graphene in terms of the local charging energy of the graphene sheet. The coating of graphene with a non-magnetic layer of Palladium, on the other hand, can lead to a magnetic instability in coated graphene due to the hybridization between the transition-metal and the carbon orbitals.Comment: 5 pages, 4 figure

Employee satisfaction and use of flexible working arrangements

This article considers the impact of flexible working arrangements (FWAs), using the British Household Panel Survey and Understanding Society, 2001–10/11. Results of panel logit, ANCOVA and change-score analysis are indicative of positive impacts from use of a number of FWAs, including homeworking having positive effects for men and women on job and leisure satisfaction. However, findings reveal gaps in availability and use of FWAs, and highlight the gendered nature of flexible employment. Flexi-time, the most common FWA among men, has positive effects as it facilitates management of household responsibilities while maintaining full-time employment. Part-time and homeworking are also positive, consistent with men using FWAs with a greater degree of choice. Women more often are constrained in their use of FWAs, often into working reduced hours. Consequently, FWAs have negative impacts for some women, on job (part-time when used for extended periods, flexi-time), leisure (job-share, flexi-time) and life satisfaction (job-share)

Reformulation initiative for partial replacement of saturated with unsaturated fats in dairy foods attenuates the increase in LDL cholesterol and improves flow-mediated dilatation compared with conventional dairy: the randomized, controlled REplacement of SaturatEd fat in dairy on Total cholesterol (RESET) study

Background Modifying dairy fat composition by increasing the MUFA content is a potential strategy to reduce dietary SFA intake for cardiovascular disease (CVD) prevention in the population. Objectives To determine the effects of consuming SFA-reduced, MUFA-enriched (modified) dairy products, compared with conventional dairy products (control), on the fasting cholesterol profile (primary outcome), endothelial function assessed by flow-mediated dilatation (FMD; key secondary outcome), and other cardiometabolic risk markers. Methods A double-blind, randomized, controlled crossover 12-wk intervention was conducted. Participants with a 1.5-fold higher (moderate) CVD risk than the population mean replaced habitual dairy products with study products (milk, cheese, and butter) to achieve a high-fat, high-dairy isoenergetic daily dietary exchange [38% of total energy intake (%TE) from fat: control (dietary target: 19%TE SFA; 11%TE MUFA) and modified (16%TE SFA; 14%TE MUFA) diet]. Results Fifty-four participants (57.4% men; mean ± SEM age: 52 ± 3 y; BMI: 25.8 ± 0.5 kg/m2) completed the study. The modified diet attenuated the rise in fasting LDL cholesterol observed with the control diet (0.03 ± 0.06 mmol/L and 0.19 ± 0.05 mmol/L, respectively; P = 0.03). Relative to baseline, the %FMD response increased after the modified diet (0.35% ± 0.15%), whereas a decrease was observed after the control diet (−0.51% ± 0.15%; P< 0.0001). In addition, fasting plasma nitrite concentrations increased after the modified diet, yet decreased after the control diet (0.02 ± 0.01 μmol/L and −0.03 ± 0.02 μmol/L, respectively; P = 0.01). Conclusions In adults at moderate CVD risk, consumption of a high-fat diet containing SFA-reduced, MUFA-enriched dairy products for 12 wk showed beneficial effects on fasting LDL cholesterol and endothelial function compared with conventional dairy products. Our findings indicate that fatty acid modification of dairy products may have potential as a public health strategy aimed at CVD risk reduction. This trial was registered at clinicaltrials.gov as NCT02089035