Decompositions of some twisted Foulkes characters

We decompose the twisted Foulkes characters $\phi^{(2^n)}_\nu$, or equivalently the plethysm $s_\nu \circ s_{(2)}$, in the cases where $\nu$ has either two rows or two columns, or is a hook partition

Generalized Foulkes modules and maximal and minimal constituents of plethysms of Schur functions

This paper proves a combinatorial rule giving all maximal and minimal partitions $\lambda$ such that the Schur function $s_\lambda$ appears in a plethysm of two arbitrary Schur functions. Determining the decomposition of these plethysms has been identified by Stanley as a key open problem in algebraic combinatorics. As corollaries we prove three conjectures of Agaoka on the partitions labeling the lexicographically greatest and least Schur functions appearing in an arbitrary plethysm. We also show that the multiplicity of the Schur function labelled by the lexicographically least constituent may be arbitrarily large. The proof is carried out in the symmetric group and gives an explicit non-zero homomorphism corresponding to each maximal or minimal partition

Set families and Foulkes modules

We construct a new family of homomorphisms from Specht modules into Foulkes modules for the symmetric group. These homomorphisms are used to give a combinatorial description of the minimal partitions (in the dominance order) which label irreducible characters appearing as summands of the characters of Foulkes modules. The homomorphisms are defined using certain families of subsets of the natural numbers. These families are of independent interest; we prove a number of combinatorial results concerning them

Photoassisted tunneling from free-standing GaAs thin films into metallic surfaces

The tunnel photocurrent between a gold surface and a free-standing semiconducting thin film excited from the rear by above bandgap light has been measured as a function of applied bias, tunnel distance and excitation light power. The results are compared with the predictions of a model which includes the bias dependence of the tunnel barrier height and the bias-induced decrease of surface recombination velocity. It is found that i) the tunnel photocurrent from the conduction band dominates that from surface states. ii) At large tunnel distance the exponential bias dependence of the current is explained by that of the tunnel barrier height, while at small distance the change of surface recombination velocity is dominant

Absence of an intrinsic value for the surface recombination velocity in doped semiconductors

A self-consistent expression for the surface recombination velocity $S$ and the surface Fermi level unpinning energy as a function of light excitation power ($P$) is presented for n- and p-type semiconductors doped above the 10$^{16}$ cm$^{-3}$ range. Measurements of $S$ on p-type GaAs films using a novel polarized microluminescence technique are used to illustrate two limiting cases of the model. For a naturally oxidized surface $S$ is described by a power law in $P$ whereas for a passivated surface $S^{-1}$ varies logarithmically with $P$. Furthermore, the variation in $S$ with surface state density and bulk doping level is found to be the result of Fermi level unpinning rather than a change in the intrinsic surface recombination velocity. It is concluded that $S$ depends on $P$ throughout the experimentally accessible range of excitation powers and therefore that no instrinsic value can be determined. Previously reported values of $S$ on a range of semiconducting materials are thus only valid for a specific excitation power.Comment: 10 pages, 7 figure

Genomics knowledge and attitudes among European public health professionals. Results of a cross-sectional survey

Background The international public health (PH) community is debating the opportunity to incorporate genomic technologies into PH practice. A survey was conducted to assess attitudes of the European Public Health Association (EUPHA) members towards their role in the implementation of public health genomics (PHG), and their knowledge and attitudes towards genetic testing and the delivery of genetic services. Methods EUPHA members were invited via monthly newsletter and e-mail to take part in an online survey from February 2017 to January 2018. A descriptive analysis of knowledge and attitudes was conducted, along with a univariate and multivariate analysis of their determinants. Results Five hundred and two people completed the questionnaire, 17.9% were involved in PHG activities. Only 28.9% correctly identified all medical conditions for which there is (or not) evidence for implementing genetic testing; over 60% thought that investing in genomics may divert economic resources from social and environmental determinants of health. The majority agreed that PH professionals may play different roles in incorporating genomics into their activities. Better knowledge was associated with positive attitudes towards the use of genetic testing and the delivery of genetic services in PH (OR = 1.48; 95% CI 1.01–2.18). Conclusions Our study revealed quite positive attitudes, but also a need to increase awareness on genomics among European PH professionals. Those directly involved in PHG activities tend to have a more positive attitude and better knowledge; however, gaps are also evident in this group, suggesting the need to harmonize practice and encourage greater exchange of knowledge among professionals

Spin dependent photoelectron tunnelling from GaAs into magnetic Cobalt

The spin dependence of the photoelectron tunnel current from free standing GaAs films into out-of- plane magnetized Cobalt films is demonstrated. The measured spin asymmetry (A) resulting from a change in light helicity, reaches +/- 6% around zero applied tunnel bias and drops to +/- 2% at a bias of -1.6 V applied to the GaAs. This decrease is a result of the drop in the photoelectron spin polarization that results from a reduction in the GaAs surface recombination velocity. The sign of A changes with that of the Cobalt magnetization direction. In contrast, on a (nonmagnetic) Gold film A ~ 0%

GaAs(111)A and B in hydrazine sulfide solutions : extreme polarity dependence of surface adsorption processes

Chemical bonds formed by hydrazine-sulfide treatment of GaAs(111) were studied by synchrotron photoemission spectroscopy. At the B surface, the top arsenic atoms are replaced by nitrogen atoms, while GaAs(111)A is covered by sulfur, also bonded to underlying gallium, despite the sulfide molar concentration being 103 times smaller than that of the hydrazine. This extreme dependence on surface polarity is explained by competitive adsorption processes of HS- and OH- anions and of hydrazine molecules, on Ga- adsorption sites, which have distinct configurations on the A and B surfaces

Which children and young people are excluded from school? Findings from the Avon Longitudinal Study of Parents and Children (ALSPAC) - poster abstract

Poster abstract presented at Spring Meeting for Clinician Scientists in Training 2015BACKGROUND: School exclusion is a disciplinary method used to remove a child from the school environment. It is known to affect certain groups disproportionately, including boys, some ethnic minorities, children in care, children in poverty, and children with special educational needs. Population-based studies on wider characteristics of excluded pupils are scarce. The aim of this study was to describe factors associated with school exclusion in the Avon Longitudinal Study of Parents and Children (ALSPAC), focussing on neurodevelopment and mental health. METHODS: ALSPAC is a prospective population-based British birth cohort study, with the initial sample consisting of 14 541 pregnancies. The study has data for whether a child has been permanently excluded from school up to the age of 8 years as reported by parents and also permanent and fixed period exclusions in the preceding 12 months as reported by parents and young people at age 16 years. Upstream risk factors were assessed for associations with exclusion on univariable analysis. The association with social communication difficulties was investigated with multivariable logistic regression. FINDINGS: Data for exclusions up to the age of 8 years were available for 8245 ALSPAC participants and 4482 participants for exclusion at age 16 years. 53 pupils (0·6%) were excluded from school by age 8 years, and 390 (8·7%) at age 16 years. The odds of exclusion by 8 years and at 16 years were increased with male sex (p=0·001 and p<0·0001, respectively), low family income (p=0·014 and p<0·0001), family adversity (p<0·0001 for both), maternal psychopathology (p=0·013 and p=0·004), low intelligence quotient (p=0·041 and p<0·0001), mental health difficulties (p<0·0001 for both), psychiatric disorder (p<0·0001 for both), social communication difficulties (p<0·0001 for both), antisocial activities (p=0·004 and p<0·0001), bullying or being bullied (p=0·005 and p<0·0001), low educational attainment (p<0·0001 for both), and increased special educational needs (p<0·0001 for both). On multivariable analysis, having social communication difficulties above a clinical threshold on the Social Communication Disorders Checklist was strongly associated with exclusion by 8 years (odds ratio 7·4, 95% CI 3·6-15·4) and at 16 years (2·3, 1·5-3·5), after adjustment for relevant confounders. INTERPRETATION: Although cohort attrition and small numbers of exclusions at 8 years are limitations, this study suggests that school exclusion is associated with numerous risk factors identifiable at or before primary school entry. Child health professionals have an important role in the holistic assessment of children who are excluded, or who are at risk of school exclusion. There is particular need to ensure that mental health and neurodevelopmental difficulties are appropriately recognised and supported. FUNDING: National Institute for Health Research Academic Clinical Fellowship