Asset Portfolios in Africa: Evidence from Rural Ethiopia

savings, asset portfolios, household wealth, asset distribution, poverty, inequality, Ethiopia

Body composition and body mass index in 5-year-old children

Background: Body mass index [BMI, weight in kg/(height in cm2)] (BMI) percentile categories are used to measure excess fatness in children; BMI's ability to assess fatness and which maternal characteristics predict adiposity in children is unclear. Objective: Describe body composition in 5-year- old children; examine if BMI and maternal characteristics correlate with adiposity in children. Methods: Fifty children provided BMI, body composition by air displacement plethysmography (ADP) (BodPod ®), and maternal variables. Descriptive and comparative analyses were used. Results: BMI significantly correlated with body composition. There was no difference in % fat between normal weight and overweight/obese children (p=0.48). FM significantly differed for children by gestational weight gain (GWG) (p = 0.04). Maternal BMI positively correlated with FFM (p Conclusion: The use of the BMI percentiles in children appears to have limitations. More research is needed to determine the accuracy of BMI and predictors excess adiposity in children

Flame spread in laminar mixing layers: the triple flame

In the present paper we investígate flame spread in laminar mixing layers both experimentally and numerically. First, a burner has been designed and built such that stationary triple ñames can be stabilised in a coflowing stream with well defined linear concentration gradients and well defined uniform flow velocity at the inlet to the combustión chamber. The burner itself as well as first experimental results obtained with it are presented. Second, a theoretical model is formulated for analysis of triple flames in a strained mixing laycr generated by directing a fuel stream and an oxidizer stream towards each other. Here attention is focused on the stagnation región where by means of a similarity formulation the three-dimensional flow can be described by only two spatial coordinates. To solve the governing equations for the limiting case in which a thermal-diffusional model results, a numerical solution procedure based on self-adaptive mesh refinement is developed. For the thermal-diffusional model, the structure of the triple flame and its propagation velocity are obtained by solving numerically the governing similarity equations for a wide range of strain rates

Analysis of Sample Acquisition Dynamics Using Discrete Element Method

The analysis presented in this paper is conducted in the framework of the Ocean Worlds Autonomy Testbed for Exploration Research and Simulation (OceanWATERS) project, currently under development at NASA Ames Research Center. OceanWATERS aims at designing a simulation environment which allows for testing autonomy of scientific lander missions to the icy moons of our solar system. Mainly focused on reproducing the end effector interaction with the inherent terrain, this paper introduces a novel discrete element method (DEM)-based approach to determine forces and torques acting on the landers scoop during the sample acquisition process. An accurate force feedback from the terrain on the scoop is required by fault-detection and autonomous decision-making algorithms to identify when the requested torque on the robotic arms joints exceeds the maximum available torque. Knowledge of the terrain force feedback significantly helps evaluating the arms links structural properties and properly selecting actuators for the joints. Models available in literature constitute a partial representation of the dynamics of the interaction. As an example, Balovnev derived an analytical expression of the vertical and horizontal force acting on a bucket while collecting a sample as a function of its geometry and velocity, soil parameters and reached depth. Although the model represents an adequate approximation of the two force components, it ignores the direction orthogonal to the scoop motion and neglects the torque. This work relies on DEM analysis to compensate for analytical models deficiencies and inaccuracies, i. e. provide force and torque 3D vectors, defined in the moving reference (body) frame attached to the scoop, at each instant of the sample collection process. Results from the first presented analysis relate to the specific OceanWATERS sampling strategy, which consists of collecting the sample through five consecutive passes with increasing depth, each pass following the same circularlinear- circular trajectory. Data is collected given a specific scoop design interacting with two types of bulk materials, which may characterize the surface of icy planetary bodies: snow and ice. Although specifically concerned with the OceanWATERS design, this first analysis provides the expected force trends for similar sampling strategies and allows to deduce phenomenological information about the general scooping process. In order to further instruct the community on the use of DEM tools as a solution to the sampling collection problem, two more analyses have been carried out, mainly focused on reducing the DEM computation time, which increases with a decrease in particle size. After running a set of identical simulations, where the only changing parameter is the size of the spherical particle, it is observed that the resulting force trajectories, starting from a given particle size, converge to the true trend. It is deducible that a further decrease in size yields negligible improvements in the accuracy, while it sensibly increases computation time. A final analysis aims at discussing limitations of approximating bulk material particles having a complex shape, e. g. ice fragments, with spheres, by comparing force trends resulting in the two cases for the same simulation scenario

Androgynous Fasteners for Robotic Structural Assembly

We describe the design and analysis of an androgynous fastener for autonomous robotic assembly of high performance structures. The design of these fasteners aims to prioritize ease of assembly through simple actuation with large driver positioning tolerance requirements, while producing a reversible mechanical connection with high strength and stiffness per mass. This can be applied to high strength to weight ratio structural systems, such as discrete building block based systems that offer reconfigurability, scalability, and system lifecycle efficiency. Such periodic structures are suitable for navigation and manipulation by relatively small mobile robots. The integration of fasteners, which are lightweight and can be robotically installed, into a high performance robotically managed structural system is of interest to reduce launch energy requirements, enable higher mission adaptivity, and decrease system life-cycle costs