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

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

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

Theoretical study of Auger recombination in a GaInNAs 1.3 mu m quantum well laser structure

We present a theoretical study of Auger recombination processes in a GaInNAs/GaAs quantum well structure designed for 1.3 mum laser emission. The calculations are based on a 10x10 k.p model, incorporating valence, conduction, and nitrogen-induced bands. The Auger transition matrix elements are calculated explicitly, without introducing any further approximations into the Hamiltonian used. We consider two main Auger recombination channels: the process when the energy released from the electron-hole recombination causes electron excitation (CHCC process) and the process with hole excitation to the split-off valence band (CHHS process). The CHHS process is shown to be dominant. Good agreement is found when comparing the calculated Auger rates with experimental values of the Auger contribution to the threshold current of GaInNAs quantum well lasers. (C) 2004 American Institute of Physics. (DOI: 10.1063/1.1664033