Vertex evoked potentials in a rating-scale detection task: Relation to signal probability

Vertex evoked potentials were recorded from human subjects performing in an auditory detection task with rating scale responses. Three values of a priori probability of signal presentation were tested. The amplitudes of the N1 and P3 components of the vertex potential associated with correct detections of the signal were found to be systematically related to the strictness of the response criterion and independent of variations in a priori signal probability. No similar evoked potential components were found associated with signal absent judgements (misses and correct rejections) regardless of the confidence level of the judgement or signal probability. These results strongly support the contention that the form of the vertex evoked response is closely correlated with the subject's psychophysical decision regarding the presence or absence of a threshold level signal

Inelastic neutron scattering signal from deconfined spinons in a fractionalized antiferromagnet

We calculate the contribution of deconfined spinons to inelastic neutron scattering (INS) in the fractionalized antiferromagnet (AF*), introduced elsewhere. We find that the presence of free spin-1/2 charge-less excitations leads to a continuum INS signal above the Neel gap. This signal is found above and in addition to the usual spin-1 magnon signal, which to lowest order is the same as in the more conventional confined antiferromagnet. We calculate the relative weights of these two signals and find that the spinons contribute to the longitudinal response, where the magnon signal is absent to lowest order. Possible higher-order effects of interactions between magnons and spinons in the AF* phase are also discussed.Comment: 9 page

Magnetic spectrum of the two-dimensional antiferromagnet La2CoO4 studied by inelastic neutron scattering

We report measurements of the magnetic excitation spectrum of the layered antiferromagnet La2CoO4 by time-of-flight neutron inelastic scattering. In the energy range probed in our experiments (0-250 meV) the magnetic spectrum consists of spin-wave modes with strong in-plane dispersion extending up to 60 meV, and a nearly dispersionless peak at 190 meV. The spin-wave modes exhibit a small (~1 meV) dispersion along the magnetic zone boundary. We show that the magnetic spectrum can be described very well by a model of a Heisenberg antiferromagnet that includes the full spin and orbital degrees of freedom of Co2+ in an axially-distorted crystal field. The collective magnetic dynamics are found to be controlled by dominant nearest-neighbour exchange interactions, strong XY-like single-ion anisotropy and a substantial unquenched orbital angular momentum.Comment: 8 pages, 7 figure

Black and minority ethnic trainees’ experiences of physical education initial teacher training

The official published version can be accessed at the link below.This report draws together the findings of research that aimed to explore black and minority ethnic (BME) trainees’ experiences of Physical Education (PE) initial teacher training (ITT). Although the numbers of BME trainees opting to enter teaching have improved considerably over the last few years, PE remains one of three specific subject areas where they remain significantly under-represented. Current figures suggest that PE attracts approximately 3% of trainees from BME backgrounds, compared with 11% for new entrants into teaching overall. The relative lack of success in attracting BME trainees into PE teaching compared to other subject areas suggests that the subculture of the subject may be a compounding factor. Over the last decade or so, a number of studies have explored the impact of ethnicity on teachers’ professional socialisation and their experiences as teachers in school, but none have focused on experiences within specific subject cultures. The centrality of the body in PE, and the link between this and the perceived low status of the subject, are influencing factors highlighted in the broader literature, including sports studies. For example, research exploring racism and the under-representation of BME participants in sport has highlighted the prevalence of stereotypical attitudes about their physicality and abilities held by coaches, administrators and spectators. Other research has suggested that some minority ethnic groups favour higher status, better paid, careers in areas such as law or medicine rather than teaching. As yet, there has been little attention to ‘race’ and ethnicity within PEITT, although studies have shown the impact of gender on trainees’ developing professional identities, and how teachers’ gendered bodies are important ‘tools’ of their work. In addition, there has been little research that has acknowledged trainees’ multiple identities, or the complex ways in which ‘race’, ethnicity, class and gender and other identity markers intersect to impact on the professional socialisation process. The research on which this report is based sought to fill some of these gaps in our understandings of BME trainees’ experiences of PEITT, and to identify strategies that might help in their recruitment and retention in the longer term. The research was funded through a small Recruitment and Retention Challenge Grant from the Teacher Development Agency (TDA). These grants form part of the TDA’s wider policy agenda to widen the diversity of new intakes opting into teaching. Higher education institutions have been encouraged, through targets and financial support and incentives, to develop specific strategies aimed at widening the diversity of their cohorts. Examples of such strategies include the provision of specialist admission help for BME prospective trainees; opportunities to gain experience in schools; open days and ‘taster’ events; advertising in the ethnic minority media, and the development of good practice guides and staff training to help ITT providers address issues of ‘race’ and ethnicity. 5 The impetus for this research resulted, in part, from presentations and discussions at a one day PEITT Network1 staff seminar on diversity held in October, 2007. The quantitative research conducted by the Association for Physical Education (AfPE) and the Ethnic Minority Foundation (EMF) presented here, showed the extent of the national under-representation of BME students in PEITT. Although the day focused on addressing reasons for BME under representation and strategies that might be used for improving recruitment, we felt it was also important to learn about the qualitative experiences of trainees that have been attracted into PEITT. Understanding the experiences of our current BME trainees might offer useful insights into how we might recruit and retain future such trainees. Our choice of qualitative research was supported by a national study published shortly after the network day, investigating the links between gender, ethnicity and degree attainment (Higher Education Academy, HEA, 2008), which specifically calls for further qualitative studies of students’ experiences of different subject areas.Funding from the Training and Development Agency (TDA

Mass along the Line of Sight to the Gravitational Lens B1608+656: Galaxy Groups and Implications for H_0

We report the discovery of four groups of galaxies along the line of sight to the B1608+656 gravitational lens system. One group is at the redshift of the primary lensing galaxy (z = 0.631) and appears to have a low mass, with eight spectroscopically confirmed members and an estimated velocity dispersion of 150 ± 60 km s^(-1). The three other groups are in the foreground of the lens. These groups contain ~10 confirmed members each and are located at redshifts of 0.265, 0.426, and 0.52. Two of the three additional groups are centered roughly on the lens system, while the third is centered ~1' south of the lens. We investigate the effect of each of the four groups on the gravitational lensing potential of the B1608+656 system, with a particular focus on the implications for the value of H_0 derived from this system. We find that each group provides an external convergence of ~0.005-0.060, depending on the assumptions made in the calculation. For the B1608+656 system, the stellar velocity dispersion of the lensing galaxy has been measured, thus breaking the mass sheet degeneracy due to the group that is physically associated with the lens. The effect of the other groups along the line of sight can be folded into the overall uncertainties due to large-scale structure (LSS) along the line of sight. Because B1608+656 appears to lie along an overdense line of sight, the LSS will cause the measurement of H_0 to be biased high for this system. This effect could be 5% or greater

Scaling and energy transfer in rotating turbulence

The inertial-range properties of quasi-stationary hydrodynamic turbulence under solid-body rotation are studied via high-resolution direct numerical simulations. For strong rotation the nonlinear energy cascade exhibits depletion and a pronounced anisotropy with the energy flux proceeding mainly perpendicularly to the rotation axis. This corresponds to a transition towards a quasi-two-dimensional flow similar to a linear Taylor-Proudman state. In contrast to the energy spectrum along the rotation axis which does not scale self-similarly, the perpendicular spectrum displays an inertial range with $k^{-2}_\perp$-behavior. A new phenomenology gives a rationale for the observations. The scaling exponents $\zeta_p$ of structure functions up to order $p=8$ measured perpendicular to the rotation axis indicate reduced intermittency with increasing rotation rate. The proposed phenomenology is consistent with the inferred asymptotic non-intermittent behavior $\zeta_p=p/2$.Comment: to be published in Europhysics Letters (www.epletters.net), minor changes to match version in prin

The decay of Batchelor and Saffman rotating turbulence

The decay rate of isotropic and homogeneous turbulence is known to be affected by the large-scale spectrum of the initial perturbations, associated with at least two cannonical self-preserving solutions of the von K\'arm\'an-Howarth equation: the so-called Batchelor and Saffman spectra. The effect of long-range correlations in the decay of anisotropic flows is less clear, and recently it has been proposed that the decay rate of rotating turbulence may be independent of the large-scale spectrum of the initial perturbations. We analyze numerical simulations of freely decaying rotating turbulence with initial energy spectra $\sim k^4$ (Batchelor turbulence) and $\sim k^2$ (Saffman turbulence) and show that, while a self-similar decay cannot be identified for the total energy, the decay is indeed affected by long-range correlations. The decay of two-dimensional and three-dimensional modes follows distinct power laws in each case, which are consistent with predictions derived from the anisotropic von K\'arm\'an-Howarth equation, and with conservation of anisotropic integral quantities by the flow evolution