Initial Vortex Densities after a Temperature Quench

We calculate the initial density of relativistic global vortices (strings) produced at a quench and contrast it with the predictions of Kibble and Zurek.Comment: Latex file, 8 pages, No figures. The text contains minor changes that elucidate the onset of classical behaviour more thoroughly. Also including the word temperature in the title makes the nature of the transition more explici

The Formation of Classical Defects After a Slow Quantum Phase Transition

Classical defects (monopoles, vortices, etc.) are a characteristic consequence of many phase transitions of quantum fields. We show a model in which the onset of classical probability distributions, for the long-wavelength modes at early times, allows the identification of line-zeroes of the field with vortex separation. We obtain a refined version of Kibble's causal results for defect separation, but from a completely different approach. It is apparent that vortices are not created from thermal fluctuations in the Ginzburg regime.Comment: 10 pages, RevTex file. No figures. To appear in Phys. Lett.

Positive Values of Non-homogeneous Indefinite Quadratic Forms of Type (2, 4)

This article does not have an abstract

Two Mathematically Equivalent Versions of Maxwell's Equations

This paper is a review of the canonical proper-time approach to relativistic mechanics and classical electrodynamics. The purpose is to provide a physically complete classical background for a new approach to relativistic quantum theory. Here, we first show that there are two versions of Maxwell's equations. The new version fixes the clock of the field source for all inertial observers. However now, the (natural definition of the effective) speed of light is no longer an invariant for all observers, but depends on the motion of the source. This approach allows us to account for radiation reaction without the Lorentz-Dirac equation, self-energy (divergence), advanced potentials or any assumptions about the structure of the source. The theory provides a new invariance group which, in general, is a nonlinear and nonlocal representation of the Lorentz group. This approach also provides a natural (and unique) definition of simultaneity for all observers. The corresponding particle theory is independent of particle number, noninvariant under time reversal (arrow of time), compatible with quantum mechanics and has a corresponding positive definite canonical Hamiltonian associated with the clock of the source. We also provide a brief review of our work on the foundational aspects of the corresponding relativistic quantum theory. Here, we show that the standard square-root and the Dirac equations are actually two distinct spin-$\tfrac{1}{2}$ particle equations.Comment: Appeared: Foundations of Physic

Low intensity strength training for ambulatory stroke patients

PURPOSE: To investigate feasibility and effectiveness of an individually-directed, group strength-training programme on knee muscle strength after stroke. METHOD: Ten volunteers (62 +/- 11 years, mean +/- SD), 6 - 12 months after first-ever unilateral stroke, walking independently with or without aids were recruited. Using an A1-B-A2 design, 3 sets of baseline measures were taken at 2 weekly intervals; volunteers then attended twice weekly sessions of low intensity progressive strengthening exercises and were assessed after each series of 8 sessions to a maximum of 24 sessions; post training, measures were repeated after 4 - 6 weeks. Measures included isometric and concentric knee extensor muscle strength and 10 m walking velocity. RESULTS: Strength of knee extensor muscles was improved after training (ANOVA, p < 0.05). On cessation of training, isometric strength increased by 58 +/- 19% and concentric strength at 30 degrees /s by 51 +/- 14%; walking velocity quickened from 0.47 +/- 0.06 m x s-1 to 0.57 +/- 0.08 m x s-1 (t = -3.31, p < 0.01). These gains were maintained 4 - 6 weeks after completion of training. CONCLUSIONS: These findings support the use of low intensity strength training after stroke and confirm published evidence. It was feasible for one therapist to deliver the training programmes for 4 - 6 participants at a time; an important feature when resources are limited

Chemical markers for rumen methanogens and methanogenesis

Peer reviewedPublisher PD

A Grand Canonical Ensemble Approach to the Thermodynamic Properties of the Nucleon in the Quark-Gluon Coupling Model

In this paper, we put forward a way to study the nucleon's thermodynamic properties such as its temperature, entropy and so on, without inputting any free parameters by human hand, even the nucleon's mass and radius. First we use the Lagrangian density of the quark gluon coupling fields to deduce the Dirac Equation of the quarks confined in the gluon fields. By boundary conditions we solve the wave functions and energy eigenvalues of the quarks, and thus get energy-momentum tensor, nucleon mass, and density of states. Then we utilize a hybrid grand canonical ensemble, to generate the temperature and chemical potentials of quarks, antiquarks of three flovars by the four conservation laws of the energy and the valence quark numbers, after which, all other thermodynamic properties are known. The only seemed free paremeter, the nucleon radius is finally determined by the grand potential minimal principle.Comment: 5 pages, LaTe

Photoionisation loading of large Sr+ ion clouds with ultrafast pulses

This paper reports on photoionisation loading based on ultrafast pulses of singly-ionised strontium ions in a linear Paul trap. We take advantage of an autoionising resonance of Sr neutral atoms to form Sr+ by two-photon absorption of femtosecond pulses at a wavelength of 431nm. We compare this technique to electron-bombardment ionisation and observe several advantages of photoionisation. It actually allows the loading of a pure Sr+ ion cloud in a low radio-frequency voltage amplitude regime. In these conditions up to 4x10^4 laser-cooled Sr+ ions were trapped

Secondary education reform in Lesotho and Zimbabwe and the needs of rural girls: Pronouncements, policy and practice

Analysis of the educational needs of rural girls in Lesotho and Zimbabwe suggests a number of shortcomings in the current form of secondary education, and ways in which it might be modified so as to serve this sizeable group of students better. Several of the shortcomings, notably in relation to curricular irrelevance and excessive focus on examinations, have long been recognised, including by politicians. Yet political pronouncements are seldom translated into policy, and even where policy is formulated, reforms are seldom implemented in schools. This paper makes use of interviews with educational decision-makers in the two southern African countries and a range of documentary sources to explore why, despite the considerable differences between the two contexts, much needed educational reforms have been implemented in neither

Reflection and Ducting of Gravity Waves Inside the Sun

Internal gravity waves excited by overshoot at the bottom of the convection zone can be influenced by rotation and by the strong toroidal magnetic field that is likely to be present in the solar tachocline. Using a simple Cartesian model, we show how waves with a vertical component of propagation can be reflected when traveling through a layer containing a horizontal magnetic field with a strength that varies with depth. This interaction can prevent a portion of the downward-traveling wave energy flux from reaching the deep solar interior. If a highly reflecting magnetized layer is located some distance below the convection zone base, a duct or wave guide can be set up, wherein vertical propagation is restricted by successive reflections at the upper and lower boundaries. The presence of both upward- and downward-traveling disturbances inside the duct leads to the existence of a set of horizontally propagating modes that have significantly enhanced amplitudes. We point out that the helical structure of these waves makes them capable of generating an alpha-effect, and briefly consider the possibility that propagation in a shear of sufficient strength could lead to instability, the result of wave growth due to over-reflection.Comment: 23 pages, 5 figures. Accepted for publication in Solar Physic