We have studied the potential induced by lateral surface superlattices deposited on a GaAs/AlGaAs heterostructure as a function of bias and orientation of the gates. By using the gates to null the total potential, we extracted the contribution to this potential in the absence of gate bias. Its angular dependence shows that it is dominated by strain from the gates coupled to the electrons by the piezoelectric effect.
Telephone delivered interventions to support people with psychosis-related difficulties can result in the development of a good quality TA between therapists and clients. There is a significant difference between therapist and client ratings of TA. Clients tend to score the quality of the TA significantly more highly than therapists. Providing clients with choice when participating in therapeutic interventions could potentially contribute towards improved TA reporting by clients.
This eight-year cross-sectional study measured the self-esteem, reading and mathematical attainments of eight cohorts of Year 2 andYear 6 children over the period of the introdu ction of the N ational C urriculum and assessment procedures into primary schools (the ® rst cohort was pre-national curriculum: the others were post-national curriculum). A ll Year 2 (N 5 1513) and Year 6 children (N 5 1488) in ® ve randomly selected primary schools within one Local Education Authority (LE A) comprised the sample to which the Lawseq questionnaire (Lawrence, 1982), M athematics 7 or 11 (National Foundation for E ducational Research, 1985Research, , 1987a and The Primary Reading Test Level 1 or 2 (F rance, 1981) was adm inistered. Self-esteem means for Year 2 shows a downward trend in the ® rst 4 years of the study followed by an upward trend in the second half of the study with the mean of C ohort 8 being slightly below that of Cohort 1. Self-esteem means for Year 6¯uctuated for the ® rst 5 years followed by a steady rise until the mean for Cohort 8 is 2.17 above that of Cohort 1. An analysis of variance showed there were signi® cant differences between both years groups with cohorts focused around the introdu ction of the national tests having signi® cantly different scores than other cohorts (Y ear 2 signi® cantly lower: Year 6 signi® cantly higher). Overall, there were signi® cant positive correlations between the children' s self-esteem and all their attainment scores. W hen the correlation coef® cients were computed separately for the pre-and post-national test groups differences emerged. There were no signi® cant correlations for the Year 2 pre-national test cohorts but for the post-national test groups all the correlations were signi® cant. For Year 6 all correlations were signi® cant. Discussion centres on the possible link between national testing and self-esteem.
Scanning probe microscopy of a cleaved semiconductor surface provides a direct measurement of the elastic field of buried, strained structures such as quantum wells or dots, but allowance must be made for relaxation at the surface. We have calculated this relaxation analytically for the exposed edge of a strained quantum well within classical elastic theory for a linear, isotropic, homogeneous medium. The surface bulges outward if the quantum well has a larger natural lattice constant and the dilation changes sign near the surface, which may enhance recombination. Results are given for a well of constant composition or an arbitrary variation along the growth direction and compared with cross-sectional scanning tunneling microscopy of InGaAs quantum wells in GaAs. Consistent values for the composition of the wells were obtained from counting In atoms, x-ray diffraction, and photoluminescence. The lattice constant on the surface and the normal relaxation were compared with the calculation. Qualitative agreement is good but the theory gives only about 80% of the observed displacement. Some of this difference can be explained by the larger size of indium atoms compared with gallium, and the different surface reconstruction and buckling behavior of InAs and GaAs ͑110͒ surfaces upon cleavage.
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