Impurity transport in temperature gradient driven turbulence

In the present paper the transport of impurities driven by trapped electron (TE) mode turbulence is studied. Non-linear (NL) gyrokinetic simulations using the code GENE are compared with results from quasilinear (QL) gyrokinetic simulations and a computationally efficient fluid model. The main focus is on model comparisons for electron temperature gra- dient driven turbulence regarding the sign of the convective impurity velocity (pinch) and the impurity density gradient R/LnZ (peaking factor) for zero impurity flux. In particular, the scaling of the impurity peaking factors with impurity charge Z and with driving temper- ature gradient is investigated and compared with the results for Ion Temperature Gradient (ITG) driven turbulence. In addition, the impurity peaking is compared to the main ion peaking obtained by a self-consistent fluid calculation of the density gradients corresponding to zero particle fluxes. For the scaling of the peaking factor with impurity charge Z, a weak dependence is obtained from NL GENE and fluid simulations. The QL GENE results show a stronger dependence for low Z impurities and overestimates the peaking factor by up to a factor of two in this region. As in the case of ITG dominated turbulence, the peaking factors saturate as Z increases, at a level much below neoclassical predictions. However, the scaling with Z is weak or reversed as compared to the ITG case. The scaling of impurity peaking with the background temperature gradients is found to be weak in the NL GENE and fluid simulations. The QL results are also here found to significantly overestimate the peaking factor for low Z values. For the parameters considered, the background density gradient for zero particle flux is found to be slightly larger than the corresponding impurity zero flux gradient.Comment: 23 pages, 13 figures. Submitted to AIP: Physics of Plasma

Educational aspirations in inner city schools

The research aimed to assess the nature and level of pupils’ educational aspirations and to elucidate the factors that influence these aspirations. A sample of five inner city comprehensive secondary schools were selected by their Local Authority because of poor pupil attendance, below average examination results and low rates of continuing in full-time education after the age of 16. Schools were all ethnically mixed and co-educational. Over 800 pupils aged 12-14 completed a questionnaire assessing pupils’ experience of home, school and their peers. A sub-sample of 48 pupils selected by teachers to reflect ethnicity and ability levels in individual schools also participated in detailed focus group interviews. There were no significant differences in aspirations by gender or year group, but differences between ethnic groups were marked. Black African, Asian Other and Pakistani groups had significantly higher educational aspirations than the White British group, who had the lowest aspirations. The results suggest the high aspirations of Black African, Asian Other and Pakistani pupils are mediated through strong academic self-concept, positive peer support, a commitment to schooling and high educational aspirations in the home. They also suggest that low educational aspirations may have different mediating influences in different ethnic groups. The low aspirations of White British pupils seem to relate most strongly to poor academic self-concept and low educational aspirations in the home, while for Black Caribbean pupils disaffection, negative peers and low commitment to schooling appear more relevant. Interviews with pupils corroborated the above findings and further illuminated the factors students described as important in their educational aspirations. The results are discussed in relation to theories of aspiration which stress its nature as a cultural capacity

Nitramine smokeless propellant research

A transient ballistics and combustion model is derived to represent the closed vessel experiment that is widely used to characterize propellants. A computer program is developed to solve the time-dependent equations, and is applied to explain aspects of closed vessel behavior. In the case of nitramine propellants the cratering of the burning surface associated with combustion above break-point pressures augments the effective burning rate as deduced from the closed vessel experiment. Low pressure combustion is significantly affected by the ignition process and, in the case of nitramine propellants, by the developing and changing surface structure. Thus, burning rates deduced from the closed vessel experiment may or may not agree with those measured in the equilibrium strand burner. Series of T burner experiments are performed to compare the combustion instability characteristics of nitramine (HMX) containing propellants and ammonium perchlorate (AP)propellants. Although ash produced by more fuel rich propellants could have provided mechanical suppression, results from clean-burning propellants permit the conclusion that HMX reduces the acoustic driving

Pupil mobility, attainment and progress in secondary school

This paper is the second of two articles arising from a study of the association between pupil mobility and attainment in national tests and examinations in an inner London borough. The first article (Strand & Demie, 2006) examined the association of pupil mobility with attainment and progress during primary school. It concluded that pupil mobility had little impact on performance in national tests at age 11, once pupils’ prior attainment at age 7 and other pupil background factors such as age, sex, special educational needs, stage of fluency in English and socio-economic disadvantage were taken into account. The present article reports the results for secondary schools (age 11-16). The results indicate that pupil mobility continues to have a significant negative association with performance in public examinations at age 16, even after including statistical controls for prior attainment at age 11 and other pupil background factors. Possible reasons for the contrasting results across school phases are explored. The implications for policy and further research are discussed

ProMC: Input-output data format for HEP applications using varint encoding

A new data format for Monte Carlo (MC) events, or any structural data, including experimental data, is discussed. The format is designed to store data in a compact binary form using variable-size integer encoding as implemented in the Google's Protocol Buffers package. This approach is implemented in the ProMC library which produces smaller file sizes for MC records compared to the existing input-output libraries used in high-energy physics (HEP). Other important features of the proposed format are a separation of abstract data layouts from concrete programming implementations, self-description and random access. Data stored in ProMC files can be written, read and manipulated in a number of programming languages, such C++, JAVA, FORTRAN and PYTHON.Comment: 17 pages, 2 figure

Spin injection from the Heusler alloy Co_2MnGe into Al_0.1Ga_0.9As/GaAs heterostructures

Electrical spin injection from the Heusler alloy Co_2MnGe into a p-i-n Al_0.1Ga_0.9As/GaAs light emitting diode is demonstrated. A maximum steady-state spin polarization of approximately 13% at 2 K is measured in two types of heterostructures. The injected spin polarization at 2 K is calculated to be 27% based on a calibration of the spin detector using Hanle effect measurements. Although the dependence on electrical bias conditions is qualitatively similar to Fe-based spin injection devices of the same design, the spin polarization injected from Co_2MnGe decays more rapidly with increasing temperature.Comment: 8 pages, 4 figure

The limits of social class in explaining ethnic gaps in educational attainment

This paper reports an analysis of the educational attainment and progress between age 11 and age 14 of over 14,500 students from the nationally representative Longitudinal Study of Young People in England (LSYPE). The mean attainment gap in national tests at age 14 between White British and several ethnic minority groups were large, more than three times the size of the gender gap, but at the same time only about one-third of the size of the social class gap. Socio-economic variables could account for the attainment gaps for Black African, Pakistani and Bangladeshi students, but not for Black Caribbean students. Further controls for parental and student attitudes, expectations and behaviours indicated minority ethnic groups were on average more advantaged on these measures than White British students, but this was not reflected proportionately in their levels of attainment. Black Caribbean students were distinctive as the only group making less progress than White British students between age 11 and 14 and this could not be accounted for by any of the measured contextual variables. Possible explanations for the White British-Black Caribbean gap are considered