The arithmetic of hyperelliptic curves

We summarise recent advances in techniques for solving Diophantine problems on hyperelliptic curves; in particular, those for finding the rank of the Jacobian, and the set of rational points on the curve

Movement demands and perceived wellness associated with preseason training camp in NCAA Division I college football players

The aims of this study were to examine the movement demands of preseason practice in National Collegiate Athletic Association Division I college football players using portable global positioning system (GPS) technology and to assess perceived wellness associated with preseason practice to determine whether GPS-derived variables from the preceding day influence perceived wellness the following day. Twenty-nine players were monitored using GPS receivers (Catapult Innovations, Melbourne, Australia) during 20 preseason practices. Individual observations (n = 550) were divided into offensive and defensive position groups. Movement variables including low-, medium-, high-intensity, and sprint distance, player load, and acceleration and deceleration distance were assessed. Perceived wellness ratings (n = 469) were examined using a questionnaire which assessed fatigue, soreness, sleep quality, sleep quantity, stress, and mood. A 1-way analysis of variance for positional movement demands and multilevel regressions for wellness measures were used, followed by post hoc testing to evaluate the relational significance between categorical outcomes of perceived wellness scores and movement variables. Results demonstrated significantly (p ≤ 0.05) greater total, high-intensity, and sprint distance, along with greater acceleration and deceleration distances for the defensive back and wide receiver position groups compared with their respective offensive and defensive counterparts. Significant (p ≤ 0.05) differences in movement variables were demonstrated for individuals who responded more or less favorably on each of the 6 factors of perceived wellness. Data from this study provide novel quantification of the position-specific physical demands and perceived wellness associated with college football preseason practice. Results support the use of position-specific training and individual monitoring of college football players

A New Method for Obtaining Binary Pulsar Distances and its Implications for Tests of General Relativity

We demonstrate how measuring orbital period derivatives can lead to more accurate distance estimates and transverse velocities for some nearby binary pulsars. In many cases this method will estimate distances more accurately than is possible by annual parallax, as the relative error decreases as t^-5/2. Unfortunately, distance uncertainties limit the degree to which nearby relativistic binary pulsars can be used for testing the general relativistic prediction of orbital period decay to a few percent. Nevertheless, the measured orbital period derivative of PSR B1534+12 agrees within the observational uncertainties with that predicted by general relativity if the proper-motion contribution is accounted for.Comment: 4 pages, latex, uuencoded compressed postscript + source, no figures, uses aaspptwo.sty and dec.sty, accepted for publication in ApJL, omitted reference now include

National and Regional Impacts of U.S. Agricultural Exports

International Trade, Output, Employment, Exports, International Relations/Trade, Q10, Q11, Q13, Q17,

Managing Vegetation in Grasslands Habitats to Meet Livestock or Wildlife Objectives

Sustainably stewarding grassland systems involves applying various practices to manipulate forage interactions with other plants, the environment, and grazing animals to meet resource manager objectives. These interactions can result in invasion or encroachment and increased abundance of weeds which hinder attainment of management objectives. Weeds influence the structure and function of pasture ecosystems whether forages are grown in improved pastures, rangeland, or grassland communities. They degrade pasture quality and reduce livestock performance by interfering with forage establishment, yield, and quality by competing for resources. Weeds reduce the feed value of forage, decrease pasture carrying capacity, and can be toxic or unpalatable to livestock. Managing weeds requires use of vegetation management tools that favor desirable forages. Herbicides can be catalysts that expedite grassland renovation, improve the forage resource, and increase carrying capacity. Corteva Agriscience has a variety of herbicide products that provide superior control of herbaceous and woody weeds, while maintaining the desirable vegetation. These herbicides were designed and developed specifically for selective broadleaf weed control in rangeland, pastures, rights-of-way, non-cropland, and natural areas. Active ingredients historically used include aminopyralid, triclopyr, fluroxypyr, clopyralid, and picloram. Rinskor™ active and Arylex™ active are new herbicide active ingredients from Corteva Agriscience™ and are members of a unique synthetic auxin chemotype, the arylpicolinates (HRAC group O / WSSA group 4). Members of the arylpicolinate family demonstrate novel and differentiated characteristics in terms of use rate, spectrum, weed symptoms, environmental fate, and molecular interaction as compared to other auxin chemotypes. When applied as a stand-alone treatment or in various mixes these products are safe to desirable grass species and control key herbaceous and woody weeds in the genera Ambrosia, Acacia, Carduus, Centaurea, Cirsium, Mimosa, Prosopis, Ranunculus, Rumex, Sida, Solanum, Taraxacum, and more

Are the distributions of Fast Radio Burst properties consistent with a cosmological population?

High time resolution radio surveys over the last few years have discovered a population of millisecond-duration transient bursts called Fast Radio Bursts (FRBs), which remain of unknown origin. FRBs exhibit dispersion consistent with propagation through a cold plasma and dispersion measures indicative of an origin at cosmological distances. In this paper we perform Monte Carlo simulations of a cosmological population of FRBs, based on assumptions consistent with observations of their energy distribution, their spatial density as a function of redshift and the properties of the interstellar and intergalactic media. We examine whether the dispersion measures, fluences, inferred redshifts, signal-to-noises and effective widths of known FRBs are consistent with a cosmological population. Statistical analyses indicate that at least 50 events at Parkes are required to distinguish between a constant co-moving FRB density, and a FRB density that evolves with redshift like the cosmological star formation rate density.Comment: 11 pages, 7 figures, 3 table

Radial Distribution of Dust Grains Around HR 4796A

We present high-dynamic-range images of circumstellar dust around HR 4796A that were obtained with MIRLIN at the Keck II telescope at lambda = 7.9, 10.3, 12.5 and 24.5 um. We also present a new continuum measurement at 350 um obtained at the Caltech Submillimeter Observatory. Emission is resolved in Keck images at 12.5 and 24.5 um with PSF FWHM's of 0.37" and 0.55", respectively, and confirms the presence of an outer ring centered at 70 AU. Unresolved excess infrared emission is also detected at the stellar position and must originate well within 13 AU of the star. A model of dust emission fit to flux densities at 12.5, 20.8, and 24.5 um indicates dust grains are located 4(+3/-2) AU from the star with effective size, 28+/-6 um, and an associated temperature of 260+/-40 K. We simulate all extant data with a simple model of exozodiacal dust and an outer exo-Kuiper ring. A two-component outer ring is necessary to fit both Keck thermal infrared and HST scattered-light images. Bayesian parameter estimates yield a total cross-sectional area of 0.055 AU^2 for grains roughly 4 AU from the star and an outer-dust disk composed of a narrow large-grain ring embedded within a wider ring of smaller grains. The narrow ring is 14+/-1 AU wide with inner radius 66+/-1 AU and total cross-sectional area 245 AU^2. The outer ring is 80+/-15 AU wide with inner radius 45+/-5 AU and total cross-sectional area 90 AU^2. Dust grains in the narrow ring are about 10 times larger and have lower albedos than those in the wider ring. These properties are consistent with a picture in which radiation pressure dominates the dispersal of an exo-Kuiper belt.Comment: Accepted by Astrophysical Journal (Part1) on September 9, 2004. 13 pages, 10 figures, 2 table