Using the Hopf Algebra Structure of QFT in Calculations

We employ the recently discovered Hopf algebra structure underlying perturbative Quantum Field Theory to derive iterated integral representations for Feynman diagrams. We give two applications: to massless Yukawa theory and quantum electrodynamics in four dimensions.Comment: 28 p, Revtex, epsf for figures, minor changes, to appear in Phys.Rev.

Unknotting the polarized vacuum of quenched QED

A knot-theoretic explanation is given for the rationality of the quenched QED beta function. At the link level, the Ward identity entails cancellation of subdivergences generated by one term of the skein relation, which in turn implies cancellation of knots generated by the other term. In consequence, each bare three-loop diagram has a rational Laurent expansion in the Landau gauge, as is verified by explicit computation. Comparable simplification is found to occur in scalar electrodynamics, when computed in the Duffin-Kemmer-Petiau formalism.Comment: 11 pages, LaTe

Two-loop two-point functions with masses: asymptotic expansions and Taylor series, in any dimension

In all mass cases needed for quark and gluon self-energies, the two-loop master diagram is expanded at large and small $q^2$, in $d$ dimensions, using identities derived from integration by parts. Expansions are given, in terms of hypergeometric series, for all gluon diagrams and for all but one of the quark diagrams; expansions of the latter are obtained from differential equations. Pad\'{e} approximants to truncations of the expansions are shown to be of great utility. As an application, we obtain the two-loop photon self-energy, for all $d$, and achieve highly accelerated convergence of its expansions in powers of $q^2/m^2$ or $m^2/q^2$, for $d=4$.Comment: 25 pages, OUT--4102--43, BI--TP/92--5

Dimensional renormalization: ladders to rainbows

Renormalization factors are most easily extracted by going to the massless limit of the quantum field theory and retaining only a single momentum scale. We derive factors and renormalized Green functions to all orders in perturbation theory for rainbow graphs and vertex (or scattering diagrams) at zero momentum transfer, in the context of dimensional renormalization, and we prove that the correct anomalous dimensions for those processes emerge in the limit D -> 4.Comment: RevTeX, no figure

A faint galaxy redshift survey to B=24

Using the multislit LDSS-2 spectrograph on the {\it William Herschel Telescope} we have completed a redshift survey in the magnitude range $22.5<B< 24$ which has produced 73 redshifts representing a 73\% complete sample uniformly-selected from four deep fields at high Galactic latitude. The survey extends out to $z>1$ and includes the highest redshift galaxy ($z=1.108$) yet discovered in a field sample. The median redshift, \zmed=0.46, and form of the redshift distribution constitute compelling evidence against simple luminosity evolution as an explanation of the large excess of faint galaxies ($\simeq\times$2--4 no-evolution) seen in this magnitude range. Rather we identify the excess population as blue objects with $z\sim 0.4$ and $B$\, luminosities similar to local $L^*$ galaxies indicating a dramatic decrease in the density of such objects over the last Hubble time, confirming the trends found in brighter redshift surveys. We also find a marked absence of {\it very} low redshift galaxies ($z<$0.1) at faint limits, severely constraining any significant steepening of the local field galaxy luminosity function at low luminosities.Comment: uuencoded compressed postscript. The preprint are also available at URL http://www.ast.cam.ac.uk/preprint/PrePrint.htm

Master integrals for massive two-loop Bhabha scattering in QED

We present a set of scalar master integrals (MIs) needed for a complete treatment of massive two-loop corrections to Bhabha scattering in QED, including integrals with arbitrary fermionic loops. The status of analytical solutions for the MIs is reviewed and examples of some methods to solve MIs analytically are worked out in more detail. Analytical results for the pole terms in epsilon of so far unknown box MIs with five internal lines are given.Comment: 23 pages, 5 tables, 12 figures, references added, appendix B enlarge

Review of a Small-scale Pelagic Longline Fishery off Northeastern Brazil

The annual catches of four small longliners operating off northeast Brazil from 1983 to 1997 were examined across different areas and locations. The total catch comprised tunas (30%), sharks (54%), billfishes (12%), and other fish species (4%). Fishing strategy and annual composition of catches showed large spatial and temporal variabilities with the dominant catches alternating among yellowfin tuna, Thunnus albacares; gray sharks, Carcharhinus spp.; and blue shark, Prionace glauca. Catches of blue and gray sharks showed a significant interaction among seamounts, with gray sharks occurring in maximum abundance around those seamounts that had relatively deep summits and low-sloping depth profiles. Results are discussed in terms of the various factors that may have influenced distribution of effort

Detecting the Gravitational Redshift of Cluster Gas

We examine the gravitational redshift of radiation emitted from within the potential of a cluster. Spectral lines from the intracluster medium (ICM) are redshifted in proportion to the emission-weighted mean potential along the line of sight, amounting to approximately 50 km/s at a radius of 100 kpc/h, for a cluster dispersion of 1200 km/s. We show that the relative redshifts of different ionization states of metals in the ICM provide a unique probe of the three-dimensional matter distribution. An examination of the reported peculiar velocities of cD galaxies in well studied Abell clusters reveals they are typically redshifted by an average of $\sim +200$ km/s. This can be achieved by gravity with the addition of a steep central potential associated with the cD galaxy. Note that in general gravitational redshifts cause a small overestimate of the recessional velocities of clusters by an average of $\sim$ 20 km/s.Comment: 6 pages, 3 figures, accepted to the Astrophysical Journal Letter

Hong Kong International Violence Against Women Survey

Final Report of the 2006 Hong Kong IVAW

Evaluation of antimicrobial efficacy in shelter cats with upper respiratory infection: a prospective study

Feline Upper-Respiratory Infection (URI) is commonplace in most animal shelters, and its endemic presence is problematic for the animals as well as for veterinarians and other shelter personnel. Despite the fact that viruses are responsible for the majority of these infections, many cats with URI in shelters are still treated with antibiotics. Antibiotic treatment in the absence of bacterial infection and the overuse of antibiotics can lead to antibiotic resistance among feline populations. The aim of this research was to compare duration and severity of URI in shelter cats treated with and without antibiotics. Cats showing clinical symptoms were randomly assigned to two groups, one receiving antibiotic treatment and the other receiving no antibiotics. Cats were monitored daily and the severity of their ocular and nasal symptoms scored on a numerical scale. The duration of their clinical symptoms was also recorded. Pharyngeal swabs were taken from some of the study population to determine whether or not bacterial infection was present. The mean severity and duration scores and standard deviations were calculated for each group and an unpaired t-test performed. No significant difference in the severity of URI and the duration of the illness was found in cats who did and did not receive antibiotic treatment. These findings support the need to change the protocol for treatment of feline URI in order to improve the quality of care provided to the shelter cats. Furthermore, these findings provided additional evidence to support the need for enhanced antibiotic stewardship in both veterinary and human medicine