Vector Positronium States in QED3

The homogeneous Bethe-Salpeter equation is solved in the quenched ladder approximation for the vector positronium states of 4-component quantum electrodynamics in 2 space and 1 time dimensions. Fermion propagator input is from a Rainbow approximation Dyson-Schwinger solution, with a broad range of fermion masses considered. This work is an extension of earlier work on the scalar spectrum of the same model. The non-relativistic limit is also considered via the large fermion mass limit. Classification of states via their transformation properties under discrete parity transformations allows analogies to be drawn with the meson spectrum of QCD.Comment: 24 pages, 2 encapsulated postscript figure

The analytic structure of heavy quark propagators

The renormalised quark Dyson-Schwinger equation is studied in the limit of the renormalised current heavy quark mass m_R --> infinity. We are particularly interested in the analytic pole structure of the heavy quark propagator in the complex momentum plane. Approximations in which the quark-gluon vertex is modelled by either the bare vertex or the Ball-Chiu Ansatz, and the Landau gauge gluon propagator takes either a gaussian form or a gaussian form with an ultraviolet asymptotic tail are used.Comment: 21 pages Latex and 5 postscript figures. The original version of this paper has been considerably extended to include a formalism dealing with the renormalised heavy quark Dyson-Schwinger equation and uses a more realistic Ansatz for the gluon propagator

Gauge covariance and the fermion-photon vertex in three- and four- dimensional, massless quantum electrodynamics

In the quenched approximation, the gauge covariance properties of three vertex Ans\"{a}tze in the Schwinger-Dyson equation for the fermion self energy are analysed in three- and four- dimensional quantum electrodynamics. Based on the Cornwall-Jackiw-Tomboulis effective action, it is inferred that the spectral representation used for the vertex in the gauge technique cannot support dynamical chiral symmetry breaking. A criterion for establishing whether a given Ansatz can confer gauge covariance upon the Schwinger-Dyson equation is presented and the Curtis and Pennington Ansatz is shown to satisfy this constraint. We obtain an analytic solution of the Schwinger-Dyson equation for quenched, massless three-dimensional quantum electrodynamics for arbitrary values of the gauge parameter in the absence of dynamical chiral symmetry breaking.Comment: 17 pages, PHY-7143-TH-93, REVTE

Researching Bradford: A review of social research on Bradford District

A synthesis of findings from social research on the District of Bradford. This report synthesises the findings from a wide range of social research undertaken on the District of Bradford, primarily between 1995 and 2005. The researchers reviewed almost 200 pieces of work. The key results are summarised under thematic headings: - The social, economic and institutional context - Community cohesion - Housing, neighbourhoods and regeneration - Business and enterprise - Health, disability and social care - Children and young people - Education, skills and the labour market - Crime and community safety It also identifies a future research agenda. The main purpose of the review was to provide the Joseph Rowntree Foundation and local organisations in Bradford with a firm basis upon which to build future work in the District

Nonperturbative Vertices in Supersymmetric Quantum Electrodynamics

We derive the complete set of supersymmetric Ward identities involving only two- and three- point proper vertices in supersymmetric QED. We also present the most general form of the proper vertices consistent with both the supersymmetric and U(1) gauge Ward identities. These vertices are the supersymmetric equivalent of the non supersymmetric Ball-Chiu vertices.Comment: seventeen pages late

Weighted k-word matches: a sequence comparison tool for proteins

The use of $k$-word matches was developed as a fast alignment-free comparison method for DNA sequences in cases where long range contiguity has been compromised, for example, by shuffling, duplication, deletion or inversion of extended blocks of sequence. Here we extend the algorithm to amino acid sequences. We define a new statistic, the weighted word match, which reflects the varying degrees of similarity between pairs of amino acids. We computed the mean and variance, and simulated the distribution function for various forms of this statistic for sequences of identically and independently distributed letters. We present these results and a method for choosing an optimal word size. The efficiency of the method is tested by using simulated evolutionary sequences, and the results compared with BLAST. References R. A. Lippert, H. Huang, and M. S. Waterman. Distributional regimes for the number of $k$-word matches between two random sequences. Proc. Natl. Acad. Sci. USA, 99(22):13980--9, 2002. doi:10.1073/pnas.202468099 J. Jing, C. J. Burden, S. Foret, and S. R. Wilson. Statistical considerations underpinning an alignment-free sequence comparison method. J. Korean Stat. Soc., 39:325--335, 2010. doi:10.1016/j.jkss.2010.02.009 S. F. Altschul, T. L. Madden, A. A. Schaffer, J. Zhang, Z. Zhang, W. Miller, and D. J. Lipman. Gapped BLAST and PSI-BLAST: a new generation of protein database search programs. Nucleic Acids Res., 25(17):3389--402, 1997. doi:10.1093/nar/25.17.3389 W. J. Ewens and G. R. Grant. Statistical Methods in Bioinformatics: an Introduction. Springer, 2nd edition, 2005. S. Foret, M. R. Kantorovitz, and C. J. Burden. Asymptotic behaviour and optimal word size for exact and approximate word matches between random sequences. BMC Bioinformatics, 7 Suppl 5:S21, 2006. doi:10.1186/1471-2105-7-S5-S21 S. Henikoff and J. G. Henikoff. Amino acid substitution matrices from protein blocks. Proc. Natl. Acad. Sci. USA, 89:10915--10919, 1992. doi:10.1073/pnas.89.22.10915 http://bioinfo.lifl.fr/reblosum/ [31 May 2011] G. Reinert, D. Chew, F. Sun, and M. S. Waterman. Alignment-free sequence comparison (i): statistics and power. J. Comput. Biol., 16(12):1615--1634, 2009. doi:10.1089/cmb.2009.0198 S. Foret, S. R. Wilson, and C. J. Burden. Empirical distribution of $k$-word matches in biological sequences. Pattern Recogn., 42:539--548, 2009. doi:10.1016/j.patcog.2008.06.026 S. Foret, S. R. Wilson, and C. J. Burden. Characterizing the $D2$ statistic: Word matches in biological sequences. Stat. Appl. Genet. Mo. B., 8(1):Article 43, 2009. doi:10.2202/1544-6115.1447 M. R. Kantorovitz, H. S. Booth, C. J. Burden, and S. R. Wilson. Asymptotic behavior of $k$-word matches between two uniformly distributed sequences. J. Appl. Probab., 44:788--805, 2006. doi:10.1239/jap/1189717545 T. J. Wu, Y. H. Huang, and L. A. Li. Optimal word sizes for dissimilarity measures and estimation of the degree of dissimilarity between DNA sequences. Bioinformatics, 21(22):4125--32, 2005. doi:10.1093/bioinformatics/bti658 S. Q. Le and O. Gascuel. An improved general amino acid replacement marix. Mol. Biol. Evol., 25:1307--1320, 2008. doi:10.1093/molbev/msn067 E. Gazave, P. Lapebi, G. S. Richards, F. Brunet, A. V. Ereskovsky, B. M. Degnan, C. Borchiellini, M. Vervoort, and E. Renard. Origin and evolution of the Notch signalling pathway: an overview from eukaryotic genomes. BMC Evol. Biol., 9:249, 2009. doi:10.1186/1471-2148-9-249 S. Q. Schneider, J. R. Finnerty, and M. Q. Martindale. Protein evolution: structure-function relationships of the oncogene Beta-catenin in the evolution of multicellular animals. J. Exptl. Zool. (Mol. Dev. Evol.), 295B:25--44, 2003. doi:10.1002/jez.b.0000

QED in external fields, a functional point of view

A functional partial differential equation is set for the proper graphs generating functional of QED in external electromagnetic fields. This equation leads to the evolution of the proper graphs with the external field amplitude and the external field gauge dependence of the complete fermion propagator and vertex is derived non-perturbativally.Comment: 8 pages, published versio

Adsorption models of hybridization and post-hybridisation behaviour on oligonucleotide microarrays

Analysis of data from an Affymetrix Latin Square spike-in experiment indicates that measured fluorescence intensities of features on an oligonucleotide microarray are related to spike-in RNA target concentrations via a hyperbolic response function, generally identified as a Langmuir adsorption isotherm. Furthermore the asymptotic signal at high spike-in concentrations is almost invariably lower for a mismatch feature than for its partner perfect match feature. We survey a number of theoretical adsorption models of hybridization at the microarray surface and find that in general they are unable to explain the differing saturation responses of perfect and mismatch features. On the other hand, we find that a simple and consistent explanation can be found in a model in which equilibrium hybridization followed by partial dissociation of duplexes during the post-hybridization washing phase.Comment: 26 pages, 6 figures, some rearrangement of sections and some additions. To appear in J.Phys.(condensed matter