How can the data revolution help deliver better agronomy to smallholder farmers in Africa?

Poster prepared for a share fair, Addis Ababa, May 201

The Big World of Nanothermodynamics

Nanothermodynamics extends standard thermodynamics to facilitate finite-size effects on the scale of nanometers. A key ingredient is Hill's subdivision potential that accommodates the non-extensive energy of independent small systems, similar to how Gibbs' chemical potential accommodates distinct particles. Nanothermodynamics is essential for characterizing the thermal equilibrium distribution of independently relaxing regions inside bulk samples, as is found for the primary response of most materials using various experimental techniques. The subdivision potential ensures strict adherence to the laws of thermodynamics: total energy is conserved by including an instantaneous contribution from the entropy of local configurations, and total entropy remains maximized by coupling to a thermal bath. A unique feature of nanothermodynamics is the completely-open nanocanonical ensemble. Another feature is that particles within each region become statistically indistinguishable, which avoids non-extensive entropy, and mimics quantum-mechanical behavior. Applied to mean-field theory, nanothermodynamics gives a heterogeneous distribution of regions that yields stretched-exponential relaxation and super-Arrhenius activation. Applied to Monte Carlo simulations, there is a nonlinear correction to Boltzmann's factor that improves agreement between the Ising model and measured non-classical critical scaling in magnetic materials. Nanothermodynamics also provides a fundamental mechanism for the 1/f noise found in many materials.Comment: 22 pages, 14 figures, revie

Integral Bases for the Universal Enveloping Algebras of Map Algebras

Given a finite-dimensional, complex simple Lie algebra we exhibit an integral form for the universal enveloping algebra of its map algebra, and an explicit integral basis for this integral form. We also produce explicit commutation formulas in the universal enveloping algebras of the map algebras of sl_2 that allow us to write certain elements in Poincare-Birkhoff-Witt order.Comment: 20 page

It's a small world after all: Defining smallholder agriculture in Ghana

"Strategies for boosting the agricultural economies of developing countries usually focus on small farms, attempting, for example, to link smallholders with markets through production chain development. However, such strategies often fail to differentiate between different types of small farmers or to investigate the distribution of assets within the group—efforts that are important because unequal distributions of assets can restrict pro-poor growth. Further, strategies to develop production chains favor some small farmers over others (i.e., those already participating in targeted chains and those with relatively more productive assets). Using landholding size as an organizational filter, we performed a basic descriptive analysis of smallholder traits in Ghana, using data from the 2005–2006 Ghana Living Standards Survey (GLSS5). We found strong inequalities in landholding distributions within Ghana's small-farm sector in all regions of the country. Using a classification of smallholders we derived based on landholding size, we examined a variety of small-farm traits and found that many of the broadly perceived defining characteristics of smallholder agriculture—such as low input use and low market engagement—are negatively correlated with landholding size. The crowding of farms at the smaller end of the small-farm spectrum in Ghana suggests that rural development strategies based on expanding existing market chains will face challenges in connecting with the bulk of small producers, who are less well endowed than average statistics indicate." from authors' abstractsmall farms, Smallholder production, Agricultural development,

The Altitude Wind Tunnel (AWT): A unique facility for propulsion system and adverse weather testing

A need has arisen for a new wind tunnel facility with unique capabilities for testing propulsion systems and for conducting research in adverse weather conditions. New propulsion system concepts, new aircraft configurations with an unprecedented degree of propulsion system/aircraft integration, and requirements for aircraft operation in adverse weather dictate the need for a new test facility. Required capabilities include simulation of both altitude pressure and temperature, large size, full subsonic speed range, propulsion system operation, and weather simulation (i.e., icing, heavy rain). A cost effective rehabilitation of the NASA Lewis Research Center's Altitude Wind Tunnel (AWT) will provide a facility with all these capabilities

Flight Reynolds number effects on a contoured boattail nozzle at subsonic speeds

A contoured boattail nozzle typical of those used on a twin-engine fighter was tested on an underwing nacelle mounted on an F-106B aircraft. The gas generator was a J85-GE-13 turbojet engine. The effects of Reynolds number, Mach number, and angle of attack on boattail drag and boattail pressure profiles were investigated. Increasing Reynolds number caused a slight reduction in boattail drag at both Mach 0.7 and 0.9. The nozzle had relatively low boattail drag even though the flow was separated over a large portion of the boattail

Relaxation of thermo-remanent magnetization in Fe-Cr GMR multilayers

The time decay of the thermo-remanent magnetization (TRM) in Fe-Cr giant magnetoresistive (GMR) multilayers has been investigated. The magnetization in these multilayers relaxes as a function of time after being cooled in a small magnetic field of 100 Oe to a low temperature and then the magnetic field is switched off. Low-field ($<$ 500 Oe) magnetization studies of these samples have shown hysteresis. This spin-glass-like behavior may originate from structural imperfections at the interfaces and in the bulk. We find that the magnetization relaxation is logarithmic. Here the magnetic viscosity is found to increase first with increasing temperature, then it reaches a maximum around T$_g$, and then it decreases with increasing temperature. This behavior is different from that of conventional spin glasses where the logarithmic creep rate is observed to increase with temperature. Power law also gives good fits and it is better than the logarithmic fit at higher temperatures. The dynamical effects of these multilayers are related to the relaxation of thermally blocked superparamagnetic grains and magnetic domains in the film layers.Comment: 19 page