Global Poles of the Two-Loop Six-Point N=4 SYM integrand

Recently, a recursion relation has been developed, generating the four-dimensional integrand of the amplitudes of N=4 supersymmetric Yang-Mills theory for any number of loops and legs. In this paper, I provide a comparison of the prediction for the two-loop six-point maximally helicity-violating (MHV) integrand against the result obtained by use of the leading singularity method. The comparison is performed numerically for a large number of randomly selected momenta and in all cases finds agreement between the two results to high numerical accuracy.Comment: 32+34 pages, 16 figures, 1 notebook; minor typos corrected, ref. added; version accepted by Phys. Rev.

The chemical evolution of gas-rich dwarf galaxies

A numerical double burst model of the chemical evolution of gas-rich dwarf galaxies has been developed. The model is fitted to a sample of N/O, O/H, Y and gas fraction observations, where N/O and O/H are the relative abundances by number of nitrogen to oxygen and oxygen to hydrogen, respectively. Y is the abundance by mass of helium. Closed models as well as models including enriched outflow, ordinary outflow and ordinary outflow combined with inflow are considered.The bursts are assumed to be instantaneous but ordered in pairs to explain the scatter in N/O-O/H. The method of gas fraction fitting is revised, and it is found that it is very important to specify whether dwarf irregulars (dIrrs) or blue compact galaxies (BCGs) are considered. Effective enriched winds fail when fitting N/O, whereas closed models, models with ordinary winds or a combination of ordinary winds and inflow are all viable.Comment: 22 pages, 25 figures, MNRAS LaTeX forma

An Annotated Checklist of Scarab Beetles (Coleoptera: Scarabaeidae) from Northeastern Iowa

A survey of scarab beetles (Coleoptera: Scarabaeidae) was conducted during 2009 in the geographically distinct area of Winneshiek and Allamakee counties in extreme Northeast Iowa. Four plant communities distributed among 10 locations, including tallgrass prairie, mixed grassland and forest, oak-hickory forest, and pasture were sampled during 2009 using black light traps, banana- beer traps, rodent burrow pitfalls, manure-baited pitfalls, and gleaning. Additionally, previous specimen records were examined. Forty-nine scarab species were documented for Winneshiek and Allamakee counties, including five species not previously reported in Iowa. Mixed grassland and forest habitat contained the greatest scarab species richness (n=31); black light trapping yielded the greatest number of individual beetles and collected the most species

A dynamical and kinematical model of the Galactic stellar halo and possible implications for galaxy formation scenarios

We re-analyse the kinematics of the system of blue horizontal branch field (BHBF) stars in the Galactic halo (in particular the outer halo), fitting the kinematics with the model of radial and tangential velocity dispersions in the halo as a function of galactocentric distance r proposed by Sommer-Larsen, Flynn & Christensen (1994), using a much larger sample (almost 700) of BHBF stars. The basic result is that the character of the stellar halo velocity ellipsoid changes markedly from radial anisotropy at the sun to tangential anisotropy in the outer parts of the Galactic halo (r greater than approx 20 kpc). Specifically, the radial component of the stellar halo's velocity ellipsoid decreases fairly rapidly beyond the solar circle, from approx 140 +/- 10 km/s at the sun, to an asymptotic value of 89 +/- 19 km/s at large r. The rapid decrease in the radial velocity dispersion is matched by an increase in the tangential velocity dispersion, with increasing r. Our results may indicate that the Galaxy formed hierarchically (partly or fully) through merging of smaller subsystems - the 'bottom-up' galaxy formation scenario, which for quite a while has been favoured by most theorists and recently also has been given some observational credibility by HST observations of a potential group of small galaxies, at high redshift, possibly in the process of merging to a larger galaxy (Pascarelle et al 1996).Comment: Latex, 16 pages. 2 postscript figures. Submitted to the Astrophysical Journal. also available at http://astro.utu.fi/~cflynn/outerhalo.htm

Integration-by-parts reductions from unitarity cuts and algebraic geometry

We show that the integration-by-parts reductions of various two-loop integral topologies can be efficiently obtained by applying unitarity cuts to a specific set of subgraphs and solving associated polynomial (syzygy) equations.Comment: 5 pages, 1 figure; a Mathematica package implementing the algorithm is attached as an ancillary file; v3: minor change

MultivariateResidues - a Mathematica package for computing multivariate residues

We present the Mathematica package MultivariateResidues, which allows for the efficient evaluation of multivariate residues based on methods from computational algebraic geometry. Multivariate residues appear in several contexts of scattering amplitude computations. Examples include applications to the extraction of master integral coefficients from maximal unitarity cuts, the construction of canonical bases of loop integrals and the construction of tree amplitudes from scattering equations.Comment: 7 pages, 2 figures, contribution to the proceedings of the 13th International Symposium on Radiative Corrections (RADCOR 2017

A comparison of thunderstorm reflectivities measured at the VHF and UHF

Observations of thunderstorms made with two radars operating at different wavelengths of 70 cm and 5.67 m are compared. The first set of observations was made with the UHF radar at the Arecibo Observatory in Puerto Rico, and the second set was made with the Max-Planck-Institut fur Aeronomie VHF radar in the Harz Mountains in West Germany. Both sets of observations show large echo strengths in the convective region above the -10 C isothem. At UHF, there appears to be a contribution from both the precipitation echoes and the normal echoes due to scatter from turbulent variations in the refractive index