Positioning of self-assembled Ge islands on stripe-patterned Si (001) substrates

Self-assembled Ge islands were grown on stripe-patterned Si (001) substrates by solid source molecular beam epitaxy. The surface morphology obtained by atomic force microscopy (AFM) and cross-sectional transmission electron microscopy images (TEM) shows that the Ge islands are preferentially grown at the sidewalls of pure Si stripes along [-110] direction at 650o C or along the trenches, whereas most of the Ge islands are formed on the top terrace when the patterned stripes are covered by a strained GeSi buffer layer. Reducing the growth temperature to 600oC results in a nucleation of Ge islands both on the top terrace and at the sidewall of pure Si stripes. A qualitative analysis, based on the growth kinetics, demonstrates that the step structure of the stripes, the external strain field and the local critical wetting layer thickness for the islands formation contribute to the preferential positioning of Ge islands on the stripes.Comment: 10 pages, 7 figures, 1 table, the original paper is in print in J. Appl. Phy

Initial stage of the 2D-3D transition of a strained SiGe layer on a pit-patterned Si(001) template

We investigate the initial stage of the 2D-3D transition of strained Ge layers deposited on pit-patterned Si(001) templates. Within the pits, which assume the shape of inverted, truncated pyramids after optimized growth of a Si buffer layer, the Ge wetting layer develops a complex morphology consisting exclusively of {105} and (001) facets. These results are attributed to a strain-driven step-meandering instability on the facetted side-walls of the pits, and a step-bunching instability at the sharp concave intersections of these facets. Although both instabilities are strain-driven, their coexistence becomes mainly possible by the geometrical restrictions in the pits. It is shown that the morphological transformation of the pit surface into low-energy facets has strong influence on the preferential nucleation of Ge islands at the flat bottom of the pits.Comment: 19 pages, 7 figure

Valley splitting of Si/SiGe heterostructures in tilted magnetic fields

We have investigated the valley splitting of two-dimensional electrons in high quality Si/Si$_{1-x}$Ge$_x$ heterostructures under tilted magnetic fields. For all the samples in our study, the valley splitting at filling factor $\nu=3$ ($\Delta_3$) is significantly different before and after the coincidence angle, at which energy levels cross at the Fermi level. On both sides of the coincidence, a linear density dependence of $\Delta_3$ on the electron density was observed, while the slope of these two configurations differs by more than a factor of two. We argue that screening of the Coulomb interaction from the low-lying filled levels, which also explains the observed spin-dependent resistivity, is responsible for the large difference of $\Delta_3$ before and after the coincidence.Comment: REVTEX 4 pages, 4 figure

Dependent self-employment: workers between employment and self-employment in the UK

Analysing the British Labour Force Survey, we highlight that dependent self-employed workers constitute a group distinct from both employees and independent self-employed workers in the labour market group. Dependent self-employed workers show characteristics of a more volatile labour market attachment than employed or self-employed workers. We provide empirical evidence that dependent self-employed workers are rather pushed than pulled into this labour market status, making dependent self-employment an example of 'necessity' rather than 'opportunity' entrepreneurship. Although data limitations only allow a limited longitudinal analysis, we provide evidence that the majority of dependent self-employed workers remain in the labour market in the short run - either as self-employed or employed - and that only few leave the labour market. In addition, dependent self-employment does not create jobs for others; in our data, dependent self-employed individuals stop being dependent and self-employed because they increase their customer base or return to paid employment

Initial and sustained brain responses to contextual conditioned anxiety in humans

AbstractContextual fear conditioning takes place if the occurrence of threat cannot be predicted by specific cues. As a consequence the context becomes the best predictor of the threat and later induces anxiety (sustained fear response). Previous studies suggest that both the amygdala and the hippocampus are crucial for contextual fear conditioning. First, we wanted to further elucidate the neuronal correlates of long-lasting contextual threat within a highly ecologically setting created in virtual reality (VR). Second, we wanted to distinguish between initial and sustained components of the anxiety response to a threatening situation. Twenty-four participants were guided through two virtual offices for 30s each. They received unpredictable electric stimuli (unconditioned stimulus, US) in one office (anxiety context, CXT+), but never in the second office (safety context, CXT−). Successful contextual fear conditioning was indexed by higher anxiety and enhanced US-expectancy ratings for CXT+ versus CXT−. Initial neural activity was assessed by modeling the onsets of both contexts, and sustained neural activity by considering the entire context duration (contrasts: CXT+ > CXT−). Amygdala and hippocampus revealed sustained activity. Initial and sustained activities were found in the middle temporal gyrus, and primary motor cortex (M1). Additional initial activity was obvious in orbitofrontal (OFC), dorsomedial (dmPFC), and dorsolateral prefrontal cortex (dlPFC). These results suggest that entering a threatening context initially induces conditioned fear reactions (M1), recall of contingency awareness (dlPFC), and explicit threat appraisal (dmPFC, OFC). While remaining in the threatening context might involve anxiety-like conditioned responses (amygdala, M1) and the generation of a spatial map to predict where and when a threatening event may occur (hippocampus). We conclude that in humans initial versus sustained anxiety responses triggered by a threat associated context are associated with distinguishable brain activation patterns involving a fear network and a “contingency-cognitive” network, respectively

Transient-Enhanced Surface Diffusion on Natural-Oxide-Covered Si(001) Templates during Vacuum Annealing

We report on the transient-enhanced shape transformation of nano-structured Si(001) surfaces upon in vacuo annealing at relatively low temperatures of 900 -950 °C for a few minutes. We find dramatic surface mass transport concomitant with the development of low-energy facets on surfaces that are covered by native oxide. The enhanced surface mass transport ceases after the oxide is completely desorbed, and it is not observed on surfaces where the native oxide had been removed by HF before annealing

Cost effectiveness of breast cancer screening and prevention: a systematic review with a focus on risk-adapted strategies

OBJECTIVES: Benefit and cost effectiveness of breast cancer screening are still matters of controversy. Risk-adapted strategies are proposed to improve its benefit-harm and cost–benefit relations. Our objective was to perform a systematic review on economic breast cancer models evaluating primary and secondary prevention strategies in the European health care setting, with specific focus on model results, model characteristics, and risk-adapted strategies. METHODS: Literature databases were systematically searched for economic breast cancer models evaluating the cost effectiveness of breast cancer screening and prevention strategies in the European health care context. Characteristics, methodological details and results of the identified studies are reported in evidence tables. Economic model outputs are standardized to achieve comparable cost-effectiveness ratios. RESULTS: Thirty-two economic evaluations of breast cancer screening and seven evaluations of primary breast cancer prevention were included. Five screening studies and none of the prevention studies considered risk-adapted strategies. Studies differed in methodologic features. Only about half of the screening studies modeled overdiagnosis-related harms, most often indirectly and without reporting their magnitude. All models predict gains in life expectancy and/or quality-adjusted life expectancy at acceptable costs. However, risk-adapted screening was shown to be more effective and efficient than conventional screening. CONCLUSIONS: Economic models suggest that breast cancer screening and prevention are cost effective in the European setting. All screening models predict gains in life expectancy, which has not yet been confirmed by trials. European models evaluating risk-adapted screening strategies are rare, but suggest that risk-adapted screening is more effective and efficient than conventional screening

Disease map-based biomarker selection and pre-validation for bladder cancer diagnostic

YesContext: Urinary biomarkers are promising as simple alternatives to cystoscopy for the diagnosis of de novo and recurrent bladder cancer. Objective: To identify a highly sensitive and specific biomarker candidate set with potential clinical utility in bladder cancer. Materials and methods: Urinary biomarkers concentrations were determined by ELISA. The performance of individual markers and marker combinations was assessed using ROC analysis. Results: A 5-biomarker panel (IL8, MMP9, VEGFA, PTGS2 and EN2) was defined from the candidate set. Discussion and conclusion: This panel showed a better overall performance than the best individual marker. Further validation studies are needed to evaluate its clinical utility in bladder cancer.This work has been supported in part by the European Commission Program DIPROMON - HEALTH-F5-2012-306157-2: Development of an integrated protein- and cell-based device for non-invasive diagnostics in the urogenital tract

Brain Activations to Emotional Pictures are Differentially Associated with Valence and Arousal Ratings

Several studies have investigated the neural responses triggered by emotional pictures, but the specificity of the involved structures such as the amygdala or the ventral striatum is still under debate. Furthermore, only few studies examined the association of stimuli's valence and arousal and the underlying brain responses. Therefore, we investigated brain responses with functional magnetic resonance imaging of 17 healthy participants to pleasant and unpleasant affective pictures and afterwards assessed ratings of valence and arousal. As expected, unpleasant pictures strongly activated the right and left amygdala, the right hippocampus, and the medial occipital lobe, whereas pleasant pictures elicited significant activations in left occipital regions, and in parts of the medial temporal lobe. The direct comparison of unpleasant and pleasant pictures, which were comparable in arousal clearly indicated stronger amygdala activation in response to the unpleasant pictures. Most important, correlational analyses revealed on the one hand that the arousal of unpleasant pictures was significantly associated with activations in the right amygdala and the left caudate body. On the other hand, valence of pleasant pictures was significantly correlated with activations in the right caudate head, extending to the nucleus accumbens (NAcc) and the left dorsolateral prefrontal cortex. These findings support the notion that the amygdala is primarily involved in processing of unpleasant stimuli, particularly to more arousing unpleasant stimuli. Reward-related structures like the caudate and NAcc primarily respond to pleasant stimuli, the stronger the more positive the valence of these stimuli is