Current Star Formation in Post-Starburst Galaxies?

Radio continuum observations are a probe of star formation in galaxies, and are unaffected by dust extinction. Observations of the distant rich cluster Cl 0939+4713 have detected radio galaxies classified as post-starburst (``k+a'') on the basis of their optical spectra, and presumably this situation arises from heavily dust-obscured star formation (Smail et al. 1999). We present the results of a radio continuum survey of post-starburst galaxies identified from the Las Campanas Redshift Survey by Zabludoff et al. (1996). This sample was selected using very stringent criteria, and therefore provides an estimate on the incidence of potential star formation in galaxies whose optical spectra exhibit the strongest post-starburst features. We detected two of fifteen such galaxies at radio luminosities consistent with moderate levels of star formation. This result underscores the potential importance of dust extinction when investigating star formation in galaxies.Comment: Replaced with corrected version of Table

Light Trapping Textures Designed by Electromagnetic Optimization for Sub-Wavelength Thick Solar Cells

Light trapping in solar cells allows for increased current and voltage, as well as reduced materials cost. It is known that in geometrical optics, a maximum 4n^2 absorption enhancement factor can be achieved by randomly texturing the surface of the solar cell, where n is the material refractive index. This ray-optics absorption enhancement limit only holds when the thickness of the solar cell is much greater than the optical wavelength. In sub-wavelength thin films, the fundamental questions remain unanswered: (1) what is the sub-wavelength absorption enhancement limit and (2) what surface texture realizes this optimal absorption enhancement? We turn to computational electromagnetic optimization in order to design nanoscale textures for light trapping in sub-wavelength thin films. For high-index thin films, in the weakly absorbing limit, our optimized surface textures yield an angle- and frequency-averaged enhancement factor ~39. They perform roughly 30% better than randomly textured structures, but they fall short of the ray optics enhancement limit of 4n^2 ~ 50

Polyhedral computational geometry for averaging metric phylogenetic trees

This paper investigates the computational geometry relevant to calculations of the Frechet mean and variance for probability distributions on the phylogenetic tree space of Billera, Holmes and Vogtmann, using the theory of probability measures on spaces of nonpositive curvature developed by Sturm. We show that the combinatorics of geodesics with a specified fixed endpoint in tree space are determined by the location of the varying endpoint in a certain polyhedral subdivision of tree space. The variance function associated to a finite subset of tree space has a fixed $C^\infty$ algebraic formula within each cell of the corresponding subdivision, and is continuously differentiable in the interior of each orthant of tree space. We use this subdivision to establish two iterative methods for producing sequences that converge to the Frechet mean: one based on Sturm's Law of Large Numbers, and another based on descent algorithms for finding optima of smooth functions on convex polyhedra. We present properties and biological applications of Frechet means and extend our main results to more general globally nonpositively curved spaces composed of Euclidean orthants.Comment: 43 pages, 6 figures; v2: fixed typos, shortened Sections 1 and 5, added counter example for polyhedrality of vistal subdivision in general CAT(0) cubical complexes; v1: 43 pages, 5 figure

The role of grazier motivations and risk attitudes in the adoption of grazing best management practices

The onus on landholders in relation to environmental performance is ever increasing. One tool for achieving environmental improvements is the design and promotion of region-specific ‘best management practices’ (BMPs). These are conservation practices aimed at reducing diffuse source pollution from agricultural lands and thus improving end-of-catchment water quality. A suite of grazing BMPs were developed for the Burdekin Dry Tropics region in a consultative fashion but without explicit consideration of knowledge of adoption processes. It is known from the literature that farmers’ goals and risk perceptions in particular influence adoption decisions. This paper utilises the data from an earlier grazier survey to explore to what extent grazier motivations and risk perceptions influence the adoption of BMPs. The results demonstrate clear correlations between both motivations and risk attitudes, and the adoption of recommended BMPs, with specific preferences for different BMPs. We conclude that a sound understanding of landholders’ motivations and risk attitudes is required—in a regional, industry and environmental context—to tailor programmes aimed at improving regional environmental performance.conservation practices, adoption, water quality, grazing, Burdekin River catchment, best management practices, risk management, motivations, empirical research, correlations, factor analysis, Environmental Economics and Policy, Farm Management, Risk and Uncertainty,