On a Dynamical Origin for Fermion Generations

We investigate a proposal to address several outstanding shortcomings of the perturbative Standard Model (SM) of particle physics. The appeal of this proposal is that these features are a manifestation of the non-perturbative sector of the SM, requiring no assumptions about new physics beyond presently attainable experimental limits. In this thesis we apply non-perturbative techniques to two complementary models: a toy 4-fermion model containing explicit chiral symmetry-breaking terms and the quenched hypercharge gauge interaction. Understanding of how fermion mass, generations and CP-violation might arise is first investigated in the toy 4-fermion model. It is shown that different scale-invariant 4-fermion operators are present for the three subspaces of the full theory, enabling self-consistent introduction of three fermion generations. The second part of the thesis is concerned with dynamical fermion mass generation in the quenched hypercharge interaction. In particular we follow the successful procedure developed for QED, developing a 1-loop renormalisable vertex {\it ansatz} for solution of the fermion self-energy Dyson-Schwinger equation. We find two mass "gaps", possibly corresponding to two types of scalar 4-fermion pairing. These "gaps" cannot, however, be interpreted as physical fermion mass. An alternative possibility, that of a rearrangement of fermionic degrees of freedom analogous to spin-charge separation in condensed matter physics, is also briefly outlined.Comment: PhD thesis, accepted 24/09/03. 108 pages, 11 figures (ps and eps

Matrix-free calcium in isolated chromaffin vesicles

Isolated secretory vesicles from bovine adrenal medulla contain 80 nmol of Ca2+ and 25 nmol of Mg2+ per milligram of protein. As determined with a Ca2+-selective electrode, a further accumulation of about 160 nmol of Ca2+/mg of protein can be attained upon addition of the Ca2+ ionophore A23187. During this process protons are released from the vesicles, in exchange for Ca2+ ions, as indicated by the decrease of the pH in the incubation medium or the release of 9-aminoacridine previously taken up by the vesicles. Intravesicular Mg2+ is not released from the vesicles by A23 187, as determined by atomic emission spectroscopy. In the presence of N H Q , which causes the collapse of the secretory vesicle transmembrane proton gradient (ApH), Ca2+ uptake decreases. Under these conditions A23 187-mediated influx of Ca2+ and efflux of H+ cease at Ca2+ concentrations of about 4 pM. Below this concentration Ca2+ is even released from the vesicles. At the Ca2+ concentration at which no net flux of ions occurs the intravesicular matrix free Ca2+ equals the extravesicular free Ca2+. In the absence of NH4C1 we determined an intravesicular pH of 6.2. Under these conditions the Ca2+ influx ceases around 0.15 pM. From this value and the known pH across the vesicular membrane an intravesicular matrix free Ca2+ concentration of about 24 pM was calculated. This is within the same order of magnitude as the concentration of free Ca2+ in the vesicles determined in the presence of NH4C1. Calculation of the total Ca2+ present in the secretory vesicles gives an apparent intravesicular Ca2+ concentration of 40 mM, which is a factor of lo4 higher than the free intravesicular concentration of Ca2+. It can be concluded, therefore, that the concentration gradient of free Ca2+ across the secretory vesicle membrane in the intact chromaffin cells is probably small, which implies that less energy is required to accumulate and maintain Ca2+ within the vesicles than was previously anticipated

Salerno's model of DNA reanalysed: could solitons have biological significance?

We investigate the sequence-dependent behaviour of localised excitations in a toy, nonlinear model of DNA base-pair opening originally proposed by Salerno. Specifically we ask whether ``breather'' solitons could play a role in the facilitated location of promoters by RNA polymerase. In an effective potential formalism, we find excellent correlation between potential minima and {\em Escherichia coli} promoter recognition sites in the T7 bacteriophage genome. Evidence for a similar relationship between phage promoters and downstream coding regions is found and alternative reasons for links between AT richness and transcriptionally-significant sites are discussed. Consideration of the soliton energy of translocation provides a novel dynamical picture of sliding: steep potential gradients correspond to deterministic motion, while ``flat'' regions, corresponding to homogeneous AT or GC content, are governed by random, thermal motion. Finally we demonstrate an interesting equivalence between planar, breather solitons and the helical motion of a sliding protein ``particle'' about a bent DNA axis.Comment: Latex file 20 pages, 5 figures. Manuscript of paper to appear in J. Biol. Phys., accepted 02/09/0

Applications of Field-Theoretic Renormalization Group Methods to Reaction-Diffusion Problems

We review the application of field-theoretic renormalization group (RG) methods to the study of fluctuations in reaction-diffusion problems. We first investigate the physical origin of universality in these systems, before comparing RG methods to other available analytic techniques, including exact solutions and Smoluchowski-type approximations. Starting from the microscopic reaction-diffusion master equation, we then pedagogically detail the mapping to a field theory for the single-species reaction k A -> l A (l < k). We employ this particularly simple but non-trivial system to introduce the field-theoretic RG tools, including the diagrammatic perturbation expansion, renormalization, and Callan-Symanzik RG flow equation. We demonstrate how these techniques permit the calculation of universal quantities such as density decay exponents and amplitudes via perturbative eps = d_c - d expansions with respect to the upper critical dimension d_c. With these basics established, we then provide an overview of more sophisticated applications to multiple species reactions, disorder effects, L'evy flights, persistence problems, and the influence of spatial boundaries. We also analyze field-theoretic approaches to nonequilibrium phase transitions separating active from absorbing states. We focus particularly on the generic directed percolation universality class, as well as on the most prominent exception to this class: even-offspring branching and annihilating random walks. Finally, we summarize the state of the field and present our perspective on outstanding problems for the future.Comment: 10 figures include

Exercise for health: a randomized, controlled trial evaluating the impact of a pragmatic, translational exercise intervention on the quality of life, function and treatment-related side effects following breast cancer

Exercise for Health was a randomized, controlled trial designed to evaluate two modes of delivering (face-to-face [FtF] and over-the-telephone [Tel]) an 8-month translational exercise intervention, commencing 6-weeks post-breast cancer surgery (PS). Outcomes included quality of life (QoL), function (fitness and upper body) and treatment-related side effects (fatigue, lymphoedema, body mass index, menopausal symptoms, anxiety, depression and pain). Generalised estimating equation modelling determined time (baseline [5 weeks PS], mid-intervention [6 months PS], post-intervention [12 months PS]), group (FtF, Tel, Usual Care [UC]) and time-by-group effects. 194 women representative of the breast cancer population were randomised to the FtF (n = 67), Tel (n = 67) and UC (n = 60) groups. There were significant (p < 0.05) interaction effects on QoL, fitness and fatigue with differences being observed between the treatment groups and the UC group. Trends observed for the treatment groups were similar. The treatment groups reported improved QoL, fitness and fatigue over time and changes observed between baseline and post-intervention were clinically relevant. In contrast, the UC group experienced no change, or worsening QoL, fitness and fatigue, mid-intervention. Although improvements in the UC group occurred by 12-months post-surgery, the change did not meet the clinically relevant threshold. There were no differences in other treatment-related side effects between groups. This translational intervention trial, delivered either FtF or Tel, supports exercise as a form of adjuvant breast cancer therapy that can prevent declines in fitness and function during treatment and optimise recovery post-treatment