Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. II. Dynamics

doi:10.1063/1.2464092 (17 pages)The dynamics of monolayer films of the n-alkane tetracosane (n-C24H52) and the branched alkane squalane (C30H62) adsorbed on graphite have been studied by quasielastic and inelastic neutron scattering and molecular dynamics (MD) simulations. Both molecules have 24 carbon atoms along their carbon backbone, and squalane has an additional six methyl side groups symmetrically placed along its length. The authors' principal objective has been to determine the influence of the side groups on the dynamics of the squalane monolayer and thereby assess its potential as a nanoscale lubricant. To investigate the dynamics of these monolayers they used both the disk chopper spectrometer (DCS) and the high flux backscattering spectrometer (HFBS) at the National Institute of Standards and Technology. These instruments made it possible to study dynamical processes such as molecular diffusive motions and vibrations on very different time scales: 1-40--ps (DCS) and 0.1-4--ns (HFBS). The MD simulations were done on corresponding time scales and were used to interpret the neutron spectra. The authors found that the dynamics of the two monolayers are qualitatively similar on the respective time scales and that there are only small quantitative differences that can be understood in terms of the different masses and moments of inertia of the two molecules. In the course of this study, the authors developed a procedure to separate out the low-frequency vibrational modes in the spectra, thereby facilitating an analysis of the quasielastic scattering. They conclude that there are no major differences in the monolayer dynamics caused by intramolecular branching. It remains to be seen whether this similarity in monolayer dynamics also holds for the lubricating properties of these molecules in confined geometries.This work was supported by the U.S. National Science Foundation under Grant Nos. DMR-0109057 and DMR-0411748 and by the U.S. Department of Energy through Grant No. DE-FG02-01ER45912. The neutron scattering facilities in this work are supported in part by the National Science Foundation under Agreement No. DMR-0454672. One of the authors (A.D.E.) thanks the Oticon Foundation, Denmark for financial support

Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. I. Structure

DOI: 10.1063/1.2464091The structure of a monolayer film of the branched alkane squalane (C30H62) adsorbed on graphite has been studied by neutron diffraction and molecular dynamics (MD) simulations and compared with a similar study of the n-alkane tetracosane (n-C24H52). Both molecules have 24 carbon atoms along their backbone and squalane has, in addition, six methyl side groups. Upon adsorption, there are significant differences as well as similarities in the behavior of these molecular films. Both molecules form ordered structures at low temperatures; however, while the melting point of the two-dimensional (2D) tetracosane film is roughly the same as the bulk melting point, the surface strongly stabilizes the 2D squalane film such that its melting point is 91 K above its value in bulk. Therefore, squalane, like tetracosane, will be a poor lubricant in those nanoscale devices that require a fluid lubricant at room temperature. The neutron diffraction data show that the translational order in the squalane monolayer is significantly less than in the tetracosane monolayer. The authors' MD simulations suggest that this is caused by a distortion of the squalane molecules upon adsorption on the graphite surface. When the molecules are allowed to relax on the surface, they distort such that all six methyl groups point away from the surface. This results in a reduction in the monolayer's translational order characterized by a decrease in its coherence length and hence a broadening of the diffraction peaks. The MD simulations also show that the melting mechanism in the squalane monolayer is the same footprint reduction mechanism found in the tetracosane monolayer, where a chain melting drives the lattice melting.This work was supported by the U.S. National Science Foundation under Grant Nos. DMR-0109057 and DMR-0411748 and by the U.S. Department of Energy through Grant No. DE-FG02-01ER45912. One of the authors (A.D.E.) thanks the Oticon Foundation, Denmark, for financial support

Cook's Guide to Groundnut Delicacies: Favorite Recipes from Northern Nigeria

Groundnut is an important crop for improving the health and nutrition of smallholders in many countries of West and Central (WCA). It is cheaper and more widely available than other locally available sources of protein. Apart from being an important element of regular dishes, groundnut can also be used to prepare Ready-to-Use Therapeutic Foods (RUTFs) to manage severe malnutrition among internally displaced persons (IDPs). This Cook's Guide to Groundnut Delicacies: Favorite Delicacies from Northern Nigeria is one of the pointers of the commitment of ICRISAT to contribute to the reconstruction of the previous groundnut pyramids in different ways. Today, groundnut pyramids should create jobs, expand market opportunities, enhance the processing of groundnut and encourage the systematic consumption of healthy groundnut and groundnut-based products. This is why adopting a market-oriented approach to boost groundnut production in countries of WCA also requires sustained awareness-creation campaigns for its consumption. It covers most of the popular recipes in Nigeria and should therefore help household and women to uncover options for including groundnut and groundnut-based products into their daily meals and opportunities for generating cash incomes. Professionally, the guide should constitute a handy reference material for field-based development workers of the Agricultural Development Authorities (ADPs), Civil Society Organization (CSOs) and Communitybased Groups. A majority of field-based agents, particularly those of the Women in Agriculture (WIA) teams of the ADPs in Nigeria, will find this guide a valuable reference material and companion. Indeed, this reference guide also raises awareness on the fact that addressing nutrition requires taking actions at all stages of commodity value chains - from production, processing, retail to consumption. I congratulate the authors of this guide for putting together feasible recipes for groundnut into a single reference guide, and urge colleagues of the ICRISAT, WCA hub to adapt and/or develop similar guides for other ICRISAT mandate crops of the region

Enhancing Smallholder Farmers’ Access to Seed of Improved Legume Varieties Through Multi-Stakeholder Platforms

The high percentage of farmers (80–90%), including the pro-poor in remote areas, who have no access to recently released and high-yielding varieties proves the failure of various seed delivery models implemented so far. The ideal model to grow a crop commodity business to reach farmers in developing countries with seed of improved legume crop varieties has been a hard topic for development organizations. Past studies have shown that the full and balanced integration of multiple stakeholders’ knowledge and contexts into the process of agricultural technology development increases the uptake and ownership among end users

Intramolecular diffusive motion in alkane monolayers studied by high-resolution quasielastic neutron scattering and molecular dynamics simulations

URL:http://link.aps.org/doi/10.1103/PhysRevLett.92.046103 DOI:10.1103/PhysRevLett.92.046103Molecular dynamics simulations of a tetracosane (n-C24H50) monolayer adsorbed on a graphite basal-plane surface show that there are diffusive motions associated with the creation and annihilation of gauche defects occurring on a time scale of ~0.1-4 ns. We present evidence that these relatively slow motions are observable by high-energy-resolution quasielastic neutron scattering (QNS) thus demonstrating QNS as a technique, complementary to nuclear magnetic resonance, for studying conformational dynamics on a nanosecond time scale in molecular monolayers.This work was supported by the NSF under Grants No. DMR-9802476 and No. DMR-0109057, by the Chilean government under FONDECYT Grant No. 1010548, and by the U.S. Department of Energy through Grant No. DE-FG02-01ER45912. The neutron scattering facilities in this work are supported in part by the National Science Foundation under Agreement No. DMR-0086210

Impact of Crop Diversification on Household Food and Nutrition Security in Southern and Central Mali

Many African countries, including Mali, depend on the production of a single or a limited range of crops for national food security. In Mali, this heavy reliance on a range of basic commodities or staple crops, or even just one, exacerbates multiple risks to agricultural production, rural livelihoods, and nutrition. With this in mind, the smart food campaign was initiated to strengthen the resilience and nutritional situation of households and peasant communities where the diet is mainly cereal-based and remains very undiversified and poor in essential micronutrients. As part of the campaign, our study aims to analyze the impact of agricultural diversification on food consumption and household nutritional security. The analysis uses survey data from 332 individuals randomly selected. Multinomial logistic regression and the Simpson diversity index were used to determine the index and estimate the determinants of crop diversification. The consumption score index weighted by consumption frequency and anthropometric indices (for children) were used to assess the nutritional status of households. The results show four types of strategies of diversification: 7.55% are cereals only, 5.66% combine millet–sorghum–groundnut, 41.51% combine millet–sorghum–groundnut–cowpea, and 45.28% combine millet–sorghum–groundnut–cowpea–maize. The estimation of the regression model shows that socioeconomic factors have a positive influence. With a consumption score index of 34 in the villages and 40.5 in Bamako, based on eight food groups, we find that the quality of food is insufficient in rural areas, but it is acceptable in the urban center of Bamako. Analysis of the nutritional status of children aged 6–48 months reveals that 30% of the surveyed population is in a situation of nutritional insecurity (all forms combined). To help improve crop diversification and the nutritional quality of foods, we suggest, among other things, subsidies and public spending tofacilitate access to inputs that allow the acquisition of a wider range of inputs and services, intensification of nutrition awareness, and education programs to maximize the incentive to consume nutritious foods from self-production and market purchases. Finally, we propose to facilitate access to technologies promoting food diversification and improving food and nutritional security, particularly in rural areas