Causal construction of the massless vertex diagram

The massless one-loop vertex diagram is constructed by exploiting the causal structure of the diagram in configuration space, which can be translated directly into dispersive relations in momentum space.Comment: 14 pages, LATEX with style file, corresponds to published versio

Supporting induction: relationships count

This article examines the structural changes to the induction of teachers in Scotland using the perceptions of a group of final year student teachers. This group would be the first probationer teachers to experience revised arrangements for new teacher induction in 37 years. Their preferences and concerns are highlighted, as the new procedures roll out in schools nationwide, in an attempt to stress the importance of relationships to the success of the induction scheme. The argument put forward in this article is based on the notion that personal intelligence is central to effective relationships and therefore crucially important in the context of this mentoring relationship. The views of our sample provide evidence to suggest that the quality of interactions between the mentor and the probationer teacher are paramount in providing a good induction experience. These views are substantiated by experiences in England and in induction literature elsewhere. A synthesis of this evidence is used to make recommendations for those involved in supporting induction in schools, local authorities or teacher education institutions

Imaging gas-exchange lung function and brain tissue uptake of hyperpolarized 129Xe using sampling density-weighted MRSI

PURPOSE: Imaging of the different resonances of hyperpolarized 129 Xe in the brain and lungs was performed using a 3D sampling density-weighted MRSI technique in healthy volunteers. METHODS: Four volunteers underwent dissolved-phase hyperpolarized 129 Xe imaging in the lung with the MRSI technique, which was designed to improve the point-spread function while preserving SNR (1799 phase-encoding steps, 14-s breath hold, 2.1-cm isotropic resolution). A frequency-tailored RF excitation pulse was implemented to reliably excite both the 129 Xe gas and dissolved phase (tissue/blood signal) with 0.1° and 10° flip angles, respectively. Images of xenon gas in the lung airspaces and xenon dissolved in lung tissue/blood were used to generate quantitative signal ratio maps. The method was also optimized and used for imaging dissolved resonances of 129 Xe in the brain in 2 additional volunteers. RESULTS: High-quality regional spectra of hyperpolarized 129 Xe were achieved in both the lung and the brain. Ratio maps of the different xenon resonances were obtained in the lung with sufficient SNR (> 10) at both 1.5 T and 3 T, making a triple Lorentzian fit possible and enabling the measurement of relaxation times and xenon frequency shifts on a voxel-wise basis. The imaging technique was successfully adapted for brain imaging, resulting in the first demonstration of 3D xenon brain images with a 2-cm isotropic resolution. CONCLUSION: Density-weighted MRSI is an SNR and encoding-efficient way to image 129 Xe resonances in the lung and the brain, providing a valuable tool to quantify regional spectroscopic information

Elastic scattering and breakup of 17^F at 10 MeV/nucleon

Angular distributions of fluorine and oxygen produced from 170 MeV 17^F incident on 208^Pb were measured. The elastic scattering data are in good agreement with optical model calculations using a double-folding potential and parameters similar to those obtained from 16^O+208^Pb. A large yield of oxygen was observed near \theta_lab=36 deg. It is reproduced fairly well by a calculation of the (17^F,16^O) breakup, which is dominated by one-proton stripping reactions. The discrepancy between our previous coincidence measurement and theoretical predictions was resolved by including core absorption in the present calculation.Comment: 9 pages, 5 figure

Simulating (electro)hydrodynamic effects in colloidal dispersions: smoothed profile method

Previously, we have proposed a direct simulation scheme for colloidal dispersions in a Newtonian solvent [Phys.Rev.E 71,036707 (2005)]. An improved formulation called the ``Smoothed Profile (SP) method'' is presented here in which simultaneous time-marching is used for the host fluid and colloids. The SP method is a direct numerical simulation of particulate flows and provides a coupling scheme between the continuum fluid dynamics and rigid-body dynamics through utilization of a smoothed profile for the colloidal particles. Moreover, the improved formulation includes an extension to incorporate multi-component fluids, allowing systems such as charged colloids in electrolyte solutions to be studied. The dynamics of the colloidal dispersions are solved with the same computational cost as required for solving non-particulate flows. Numerical results which assess the hydrodynamic interactions of colloidal dispersions are presented to validate the SP method. The SP method is not restricted to particular constitutive models of the host fluids and can hence be applied to colloidal dispersions in complex fluids

Infra-Red Asymptotic Dynamics of Gauge Invariant Charged Fields: QED versus QCD

The freedom one has in constructing locally gauge invariant charged fields in gauge theories is analyzed in full detail and exploited to construct, in QED, an electron field whose two-point function W(p), up to the fourth order in the coupling constant, is normalized with on-shell normalization conditions and is, nonetheless, infra-red finite; as a consequence the radiative corrections vanish on the mass shell $p^2=\mu^2$ and the free field singularity is dominant, although, in contrast to quantum field theories with mass gap, the eigenvalue $\mu^2$ of the mass operator is not isolated. The same construction, carried out for the quark in QCD, is not sufficient for cancellation of infra-red divergences to take place in the fourth order. The latter divergences, however, satisfy a simple factorization equation. We speculate on the scenario that could be drawn about infra-red asymptotic dynamics of QCD, should this factorization equation be true in any order of perturbation theory.Comment: 30 pages, RevTex, 8 figures included using graphic

Strong decays Bs0→BsπB_{s0} \to B_s \pi and Bs1→Bs∗πB_{s1} \to B^*_s \pi with light-cone QCD sum rules

In this article, we calculate the strong coupling constants $g_{B_{s0} B_s \eta}$ and $g_{B_{s1} B^*_s \eta}$ with the light-cone QCD sum rules. Then we take into account the small $\eta-\pi^0$ transition matrix according to Dashen's theorem, and obtain the small decay widths for the isospin violation processes $B_{s0}\to B_s\eta\to B_s\pi^0$ and $B_{s1}\to B_s^*\eta\to B_s^*\pi^0$. We can search the strange-bottomed $(0^+,1^+)$ mesons $B_{s0}$ and $B_{s1}$ in the invariant $B_s \pi^0$ and $B^*_s \pi^0$ mass distributions respectively.Comment: 15 pages, 2 figures, revised versio

Measurement of the ratio of branching fractions BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) and the direct CP asymmetry in B0 -> K*0 gamma

The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma and Bs0 phi gamma has been measured using an integrated luminosity of 1.0 fb-1 of pp collision data collected by the LHCb experiment at a centre-of-mass energy of sqrt(s)=7 TeV. The value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.23 +/- 0.06(stat.) +/- 0.04(syst.) +/- 0.10(fs/fd), where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is associated with the ratio of fragmentation fractions fs/fd. Using the world average value for BR(B0 -> K*0 gamma), the branching fraction BR(Bs0 -> phi gamma) is measured to be (3.5 +/- 0.4) x 10^{-5}. The direct CP asymmetry in B0 -> K*0 gamma decays has also been measured with the same data and found to be A(CP)(B0 -> K*0 gamma) = (0.8 +/- 1.7(stat.) +/- 0.9(syst.))%. Both measurements are the most precise to date and are in agreement with the previous experimental results and theoretical expectations.Comment: 21 pages, 3 figues, 4 table

Whatever happened to curriculum theory? Critical realism and curriculum change

In the face of what has been characterised as a ‘crisis’ in curriculum – an apparent decline of some aspects of curriculum studies combined with the emergence of new types of national curriculum which downgrade knowledge – some writers have been arguing for the use of realist theory to address these issues. This paper offers a contribution to this debate, drawing upon critical realism, and especially upon the social theory of Margaret Archer. The paper first outlines the supposed crisis in curriculum, before providing an overview of some of the key tenets of critical realism. The paper concludes by speculating on how critical realism may offer new ways of thinking to inform policy and practice in a key curricular problematic. This is the issue of curriculum change