Nucleosynthesis in Outflows from the Inner Regions of Collapsars

We consider nucleosynthesis in outflows originating from the inner regions of viscous accretion disks formed after the collapse of a rotating massive star. We show that wind-like outflows driven by viscous and neutrino heating can efficiently synthesize Fe-group elements moving at near-relativistic velocities. The mass of 56Ni synthesized and the asymptotic velocities attained in our calculations are in accord with those inferred from observations of SN1998bw and SN2003dh. These steady wind-like outflows are generally proton rich, characterized by only modest entropies, and consequently synthesize essentially nothing heavier than the Fe-group elements. We also discuss bubble-like outflows resulting from rapid energy deposition in localized regions near or in the accretion disk. These intermittent ejecta emerge with low electron fraction and are a promising site for the synthesis of the A=130 r-process peak elements.Comment: 35 pages, 6 figures, added discussion of the influence of nuclear recombination on wind dynamics, to appear in Ap

The Neuromuscular Origins of Kinematic Variability during Perturbed Walking

We investigated the neuromuscular contributions to kinematic variability and thus step to step adjustments in posture and foot placement across a range of walking speeds in response to optical flow perturbations of different amplitudes using a custom virtual environment. We found that perturbations significantly increased step width, decreased step length, and elicited larger trunk sway compared to normal walking. However, perturbation-induced effects on the corresponding variabilities of these measurements were much more profound. Consistent with our hypotheses, we found that: (1) perturbations increased EMG activity of the gluteus medius and postural control muscles during leg swing, and increased antagonist leg muscle coactivation during limb loading in early stance, and (2) changes in the magnitude of step to step adjustments in postural sway and lateral foot placement positively correlated with those of postural control and gluteus medius muscle activities, respectively, in response to perturbations. However, (3) interactions between walking speed and susceptibility to perturbations, when present, were more complex than anticipated. Our study provides important mechanistic neuromuscular insight into walking balance control and important reference values for the emergence of balance impairment

Interactions of biotic and abiotic environmental factors in an ectomycorrhizal symbiosis, and the potential for selection mosaics

<p>Abstract</p> <p>Background</p> <p>Geographic selection mosaics, in which species exert different evolutionary impacts on each other in different environments, may drive diversification in coevolving species. We studied the potential for geographic selection mosaics in plant-mycorrhizal interactions by testing whether the interaction between bishop pine (<it>Pinus muricata </it>D. Don) and one of its common ectomycorrhizal fungi (<it>Rhizopogon occidentalis </it>Zeller and Dodge) varies in outcome, when different combinations of plant and fungal genotypes are tested under a range of different abiotic and biotic conditions.</p> <p>Results</p> <p>We used a 2 × 2 × 2 × 2 factorial experiment to test the main and interactive effects of plant lineage (two maternal seed families), fungal lineage (two spore collections), soil type (lab mix or field soil), and non-mycorrhizal microbes (with or without) on the performance of plants and fungi. Ecological outcomes, as assessed by plant and fungal performance, varied widely across experimental environments, including interactions between plant or fungal lineages and soil environmental factors.</p> <p>Conclusion</p> <p>These results show the potential for selection mosaics in plant-mycorrhizal interactions, and indicate that these interactions are likely to coevolve in different ways in different environments, even when initially the genotypes of the interacting species are the same across all environments. Hence, selection mosaics may be equally as effective as genetic differences among populations in driving divergent coevolution among populations of interacting species.</p

Foreign Policy and the Electoral Connection

Public opinion is central to representation, democratic accountability, and decision making. Yet, the public was long believed to be relatively uninterested in foreign affairs, absent an immediate threat to safety and welfare. It had become conventional to say that voting ends at water\u27s edge. We start the examination of the scholarly understanding of the role of foreign affairs in public opinion and voting at that low point of view. Much subsequent development saw an increasing degree of holding and using of attitudes and beliefs about foreign affairs among the public. Moving in parallel with developments in political psychology, theoretical and methodological advances led to an increasingly widely shared view that the public holds reasonably sensible and nuanced views, that these help shape their political behaviors, and that these, in turn, help shape and constrain foreign policy making

Analysis of 1990 Farm Bill Conservation Options

This report summarizes the ARIMS analysis for the 1990 Farm Bill Conservation Initiatives Work Group. Three major tasks were completed. First, ARIMS was updated to reflect the short-run nature of possible 1990 farm bill policies. Specifically, ARIMS now incorporates a more differentiated set of land resources and crop production technology to match the requirements of the 1985 Food Security Act. Second, baseline solutions for 1990, 1995, and 2000 were estimated. The solutions included the conservation titles of the 1985 Food Security Act. The baselines differed in the specification of acres in the Conservation Reserve Program (CRP) and in conservation compliance provisions. The 1990 baseline had a 40-million-acre CRP requirement; the 1995 baseline has a 40-million-CRP plus conservation compliance; and the 2000 baseline has an eight-million CRP with conservation compliance. Third, two alternative farm bill policy options were evaluated. The water quality option involved adding 10 million acres to the 40-million-acre CRP enrollment in the 1995 baseline. The selection of the 10 million acres was based on potential water quality impacts. The Trees for the U.S. program evaluated the conversion to tress of 37 million targeted acres of cropland and marginal pasture land

The influence of meridional ice transport on Europa’s ocean stratification and heat content

Jupiter’s moon Europa likely hosts a saltwater ocean beneath its icy surface. Geothermal heating and rotating convection in the ocean may drive a global overturning circulation that redistributes heat vertically and meridionally, preferentially warming the ice shell at the equator. Here we assess the previously unconstrained influence of ocean‐ice coupling on Europa’s ocean stratification and heat transport. We demonstrate that a relatively fresh layer can form at the ice‐ocean interface due to a meridional ice transport forced by the differential ice shell heating between the equator and the poles. We provide analytical and numerical solutions for the layer’s characteristics, highlighting their sensitivity to critical ocean parameters. For a weakly turbulent and highly saline ocean, a strong buoyancy gradient at the base of the freshwater layer can suppress vertical tracer exchange with the deeper ocean. As a result, the freshwater layer permits relatively warm deep ocean temperatures.Key PointsCoupling of Europa’s ocean circulation and the ice shell impacts global stratificationA low‐latitude freshwater layer may suppress vertical heat and tracer transportParameter space is explored based on properties observed by future missionsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137725/1/grl56051.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137725/2/grl56051-sup-0001-TextS1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137725/3/grl56051_am.pd

A Class of Eccentric Binaries with Dynamic Tidal Distortions Discovered with Kepler

We have discovered a class of eccentric binary systems within the Kepler data archive that have dynamic tidal distortions and tidally-induced pulsations. Each has a uniquely shaped light curve that is characterized by periodic brightening or variability at time scales of 4-20 days, frequently accompanied by shorter period oscillations. We can explain the dominant features of the entire class with orbitally-varying tidal forces that occur in close, eccentric binary systems. The large variety of light curve shapes arises from viewing systems at different angles. This hypothesis is supported by spectroscopic radial velocity measurements for five systems, each showing evidence of being in an eccentric binary system. Prior to the discovery of these 17 new systems, only four stars, where KOI-54 is the best example, were known to have evidence of these dynamic tides and tidally-induced oscillations. We perform preliminary fits to the light curves and radial velocity data, present the overall properties of this class and discuss the work required to accurately model these systems.Comment: 13 pages, submitted to Ap

The 1989 Recommended Pesticide and Nitrogen Use Survey: Description and Policy Applications

The public and the agricultural community are concerned with the impact of agrichemical use on the environment. Of particular concern is the impact of pesticides and nitrogen on the quality of surface and ground waters (Nielson and Lee 1987). Although a national effort is under way to address agricultural contributions to water contamination, lack of data is hindering progress. Data are needed to characterize agrichemical use and its subsequent fate and transport throughout the ecosystem. Reliable data are vital for informed policy decisions weighing the potential risks and benefits (Delwiche 1970). In the absence of that data about total amounts of agrichemicals being used on crops and the rates and methods of application, it is difficult to describe the link between agricultural porduction practices and environmental quality, or to assess the impacts of programs and policies addressing water quality. This report documents the 1989 Recommended Pesticide and Nitrogen Use Survey. The survey was conducted to alleviate part of the data deficiency by collecting detailed information on recommended pesticide and nitrogen uses and application practices in 48 states. Information on usage was obtained by crop, tillage practice, and soil texture. Crops covered in the survey included alfalfa, barley, corn grain, corn silage, cotton oats, pasture, other hay, peanuts, sorghum grain, sorghum silage, soybeans, spring and winter wheat, and sunflowers. Tillage practices included spring and fall plow conventional tillage, conservation tillage, ridge tillage, and no tillage. By providing detailed information on the rate and total amount of agrichemicals applied to the soil surface, the survey provides data for investigating the behavioral and economic links between environmental quality and decision making within agricultural production. In addition, the data can be used in assesing the impacts of policies and porgrams addressing water quality