Narrow-row soybeans : what to consider / 1161

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The KELT-South Telescope

The Kilodegree Extremely Little Telescope (KELT) project is a survey for new transiting planets around bright stars. KELT-South is a small-aperture, wide-field automated telescope located at Sutherland, South Africa. The telescope surveys a set of 26 degree by 26 degree fields around the southern sky, and targets stars in the range of 8 < V < 10 mag, searching for transits by Hot Jupiters. This paper describes the KELT-South system hardware and software and discusses the quality of the observations. We show that KELT-South is able to achieve the necessary photometric precision to detect transits of Hot Jupiters around solar-type main-sequence stars.Comment: 26 pages, 13 figure

Designing a Minimal-Knowledge Controller to Achieve Fast, Stable Growth for Recombinant Escherichia coli Cultures

The biopharmaceutical industry is constantly developing new recombinant Es-cherichia coli strains to bring new products to market. In early stages of development, small scale bioreactors are used to make the product and explore di˙erent growth pro-tocols. Researchers spend significant time finding a feed rate profile that will give fast growth and low byproduct accumulation. The objective for the controller pre-sented in this work is to achieve fast growth and low acetate accumulation for an E.coli fermentation. The controller does not rely on previous characterization data or models but on fundamental metabolic relationships between oxygen and glucose as dictated by the Crabtree e˙ect. The controller senses metabolic state using an on-line oxygen uptake rate (OUR) estimate and pushes the culture to the boundary of oxidative and overflow metabolism (BOOM). A simulated E.coli culture and biore-actor were constructed to test controller performance. Fermentation experiments compared the BOOM controller to an Exponential feed and a DO-stat controller. Using minimal knowledge about the strain, the BOOM controller kept an induced E.coli MG1655 pTVP1GFP strain growing near the boundary of oxidative and over-flow metabolism. The BOOM controller produced more recombinant protein than the Exponential feed controller and the DO-stat controller, even though the growth rate used by the Exponential feed controller was extensively researched by a previous group. In another fermentation, the temperature was lowered to incur a fast change in the E.coli metabolism. In all experiments, the BOOM controller demonstrated it could maintain fast growth and avoid inhibitory acetate concentrations while requir-ing minimal knowledge of theE.coli MG1655 pTVP1GFP strain. For laboratories which deal with many di˙erent strains and proteins, the BOOM controller would maximize protein production and speed up protocol development

Upper-division Student Understanding of Coulomb's Law: Difficulties with Continuous Charge Distributions

Utilizing the integral expression of Coulomb's Law to determine the electric potential from a continuous charge distribution is a canonical exercise in Electricity and Magnetism (E&M). In this study, we use both think-aloud interviews and responses to traditional exam questions to investigate student difficulties with this topic at the upper-division level. Leveraging a theoretical framework for the use of mathematics in physics, we discuss how students activate, construct, execute and reflect on the integral form of Coulomb's Law when solving problems with continuous charge distributions. We present evidence that junior-level E&M students have difficulty mapping physical systems onto the mathematical expression for the Coulomb potential. Common challenges include difficulty expressing the difference vector in appropriate coordinates as well as determining expressions for the differential charge element and limits of integration for a specific charge distribution. We discuss possible implications of these findings for future research directions and instructional strategies.Comment: 5 pages, 1 figure, 2 tables, accepted to 2012 PERC Proceeding

ACER: A Framework on the Use of Mathematics in Upper-division Physics

At the University of Colorado Boulder, as part of our broader efforts to transform middle- and upper-division physics courses, we research students' difficulties with particular concepts, methods, and tools in classical mechanics, electromagnetism, and quantum mechanics. Unsurprisingly, a number of difficulties are related to students' use of mathematical tools (e.g., approximation methods). Previous work has documented a number of challenges that students must overcome to use mathematical tools fluently in introductory physics (e.g., mapping meaning onto mathematical symbols). We have developed a theoretical framework to facilitate connecting students' difficulties to challenges with specific mathematical and physical concepts. In this paper, we motivate the need for this framework and demonstrate its utility for both researchers and course instructors by applying it to frame results from interview data on students' use of Taylor approximations.Comment: 10 pages, 1 figures, 2 tables, accepted to the 2012 PERC Proceeding

Possible evidence of a spontaneous spin-polarization in mesoscopic 2D electron systems

We have experimentally studied the non-equilibrium transport in low-density clean 2D electron systems at mesoscopic length scales. At zero magnetic field (B), a double-peak structure in the non-linear conductance was observed close to the Fermi energy in the localized regime. From the behavior of these peaks at non-zero B, we could associate them to the opposite spin states of the system, indicating a spontaneous spin polarization at B = 0. Detailed temperature and disorder dependence of the structure shows that such a splitting is a ground state property of the low-density 2D systems.Comment: 7 pages, 5 figure