Origin of non-linear piezoelectricity in III-V semiconductors: Internal strain and bond ionicity from hybrid-functional density functional theory

We derive first- and second-order piezoelectric coefficients for the zinc-blende III-V semiconductors, {Al,Ga,In}-{N,P,As,Sb}. The results are obtained within the Heyd-Scuseria-Ernzerhof hybrid-functional approach in the framework of density functional theory and the Berry-phase theory of electric polarization. To achieve a meaningful interpretation of the results, we build an intuitive phenomenological model based on the description of internal strain and the dynamics of the electronic charge centers. We discuss in detail first- and second-order internal strain effects, together with strain-induced changes in ionicity. This analysis reveals that the relatively large importance in the III-Vs of non-linear piezoelectric effects compared to the linear ones arises because of a delicate balance between the ionic polarization contribution due to internal strain relaxation effects, and the contribution due to the electronic charge redistribution induced by macroscopic and internal strain

Theory of the electronic structure of dilute bismide and bismide-nitride alloys of GaAs: Tight-binding and k.p models

The addition of dilute concentrations of bismuth (Bi) into GaAs to form GaBiAs alloys results in a large reduction of the band gap energy Eg accompanied by a significant increase of the spin-orbit-splitting energy (delta_SO), leading to an Eg < delta_SO regime for ~10% Bi composition which is technologically relevant for the design of highly efficient photonic devices. The quaternary alloy GaBiNAs offers further flexibility for band gap tuning, because both nitrogen and bismuth can independently induce band gap reduction. This work reports sp3s* tight binding and 14-band k.p models for the study of the electronic structure of GaBiAs and GaBiNAs alloys. Our results are in good agreement with the available experimental data.Comment: 2 pages, 1 figur

Different effects of oral and transdermal hormone replacement therapies on Factor IX, APC resistance, t-PA, PAI and C- reactive protein - a cross-sectional population survey

The effects of hormone replacement therapy (HRT) on thrombosis risk, thrombotic variables, and the inflammatory marker C- reactive protein (CRP) may vary by route of administration (oral versus transdermal). We studied the relationships of 14 thrombotic variables (previously related to cardiovascular risk) and CRP to menopausal status and to use of HRT subtypes in a cross-sectional study of 975 women aged 40-59 years. Our study confirmed previously-reported associations between thrombotic variables and menopausal status. Oral HRT use was associated with increased plasma levels of Factor IX, activated protein C (APC) resistance, and CRP; and with decreased levels of tissue plasminogen activator (t-PA) antigen and plasminogen activator inhibitor (PAI) activity. Factor VII levels were higher in women taking unopposed oral oestrogen HRT. The foregoing associations were not observed in users of transdermal HRT; hence they may be consequences of the "first- pass" effect of oral oestrogens on hepatic protein synthesis. We conclude that different effects of oral and transdermal HRT on thrombotic and inflammatory variables may be relevant to their relative thrombotic risk; and suggest that this hypothesis should be tested in prospective, randomised studies

Event-related potential arithmetic to analyze offset potentials from conscious mice

Background: This paper presents a method for isolating time-dependent event-related potential (ERP) components which are superimposed on the gross ERP waveform. The experimental data that inspired this approach was recorded from the auditory cortex of conscious laboratory mice in response to presentation of ten different duration pure-tone auditory stimuli. New Method: The grand-average ERP for each individual stimulus displayed a relatively low amplitude deflection following stimulus offset. In order to isolate this component for analysis, a series of simple arithmetic operations were performed, involving averaging of multiple stimuli ERPs and subtracting this from each individual ERP. Results: Offset potentials were isolated and quantified. Peak latency was determined by auditory stimulus duration; peak amplitude did not reach the threshold for statistical significance, over the range of durations tested. Comparison with Existing Method(s): To the best of my knowledge there are no alternative methods for isolating offset potentials from the gross ERP waveform at present. This novel approach may introduce less subjective bias to analyses than manually selecting measurement windows and performing custom baseline corrections. Conclusions: A similar method may be applied to other human or non-human datasets to identify and characterize time-dependent sensory-cognitive processes obscured by gross waveform morpholog

bak deletion stimulates gastric epithelial proliferation and enhances Helicobacter felis-induced gastric atrophy and dysplasia in mice

Helicobacter infection causes a chronic superficial gastritis that in some cases progresses via atrophic gastritis to adenocarcinoma. Proapoptotic bak has been shown to regulate radiation-induced apoptosis in the stomach and colon and also susceptibility to colorectal carcinogenesis in vivo. Therefore we investigated the gastric mucosal pathology following H. felis infection in bak-null mice at 6 or 48 wk postinfection. Primary gastric gland culture from bak-null mice was also used to assess the effects of bak deletion on IFN-γ-, TNF-α-, or IL-1β-induced apoptosis. bak-null gastric corpus glands were longer, had increased epithelial Ki-67 expression, and contained fewer parietal and enteroendocrine cells compared with the wild type (wt). In wt mice, bak was expressed at the luminal surface of gastric corpus glands, and this increased 2 wk post-H. felis infection. Apoptotic cell numbers were decreased in bak-null corpus 6 and 48 wk following infection and in primary gland cultures following cytokine administration. Increased gastric epithelial Ki-67 labeling index was observed in C57BL/6 mice after H. felis infection, whereas no such increase was detected in bak-null mice. More severe gastric atrophy was observed in bak-null compared with C57BL/6 mice 6 and 48 wk postinfection, and 76% of bak-null compared with 25% of C57BL/6 mice showed evidence of gastric dysplasia following long-term infection. Collectively, bak therefore regulates gastric epithelial cell apoptosis, proliferation, differentiation, mucosal thickness, and susceptibility to gastric atrophy and dysplasia following H. felis infection

Seasonality and Other Components of the Irish Unemployment Series. Quarterly Economic Commentary, April 1980

This paper examines methods of seasonally adjusting economic time series; in particular, it examines the methods of estimating the seasonal and other time series components of unemployment in Ireland. Thus, while the results of this analysis may have implications for other time series, the study's main aim is the adjustment of the unemployment data. It should be emphasised that a univariate analysis is being carried out here and the optimal method of seasonal adjustment could be much different in the case of a multivariate approach - Wallis (1976). The results shed some light on the question of whether the series contains an additive multiplicative or mixed seasonal element - Dowling (1975) and Bradley (1977). It also agrees with the recommendations made in the Report of the Interdepartmental Study Group on Unemployment Statistics (ISGU) (1979) that a seasonally adjusted series of Live Register figures be compiled and published. However, the most satisfactory method of seasonal adjustment leads to the rejection of another of the group's recommendations: that the frequency of publication of the present weekly Live Register statement should be reduced to a monthly basis

Survival strategies of poor women in urban Africa: The case of Zambia

Urban poverty is increasing alongside growing urban populations in sub-Saharan Africa. Women constitute a significant proportion of the urban poor but their role is often neglected by development projects. Research was undertaken with the aim of providing better definition and targeting of project interventions. NRI became involved in this research because of the importance of natural resource-elated activities (food production, processing and trade) to poor women in urban areas. Women have developed survival strategies which include migration, marriage and fertility, education, links with rural areas, social networks, saving and borrowing, and home production through urban agriculture. Most women also engage directly in some form of income-earning activity. The scale of these activities varies widely but for the vast majority of poor women, it is some form of micro-enterprise, most often vending of foodstuffs. Poor women depend on purchased natural resources products for family food and fuel supplies, and are also involved in the trading of these products. Other links with the natural resources sector are through the contacts that women retain with rural areas of origin (through exchanges, visits and rights to land and animals) and in their continuation of farming in the urban setting. The latter is constrained by lack of space and water, but is nonetheless significant as a supplement to purchased food. Ways in which women's livelihood strategies could be strengthened are discussed and the need for a multidimensional initiatives is emphasized. Credit (particularly for the poorest), confidence-building, access to information, and specific income-generating activities (urban agriculture, skills training and food processing, strengthening trading links with rural areas) are highlighted as major requirements