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Stable perovskite and metastable post-perovskite NaCoF3 were deformed in pure-shear geometry in a deformation-DIA press with radiographic monitoring of the sample strain. In isothermal experiments where there was no transformation, post-perovskite was found to be 5 times weaker than perovskite. In temperature-ramping experiments where post-perovskite transformed to perovskite during the deformation experiment the initial post-perovskite sample was 5–10 times weaker than perovskite under comparable conditions and their strengths converged during the transformation, being equal on completion of the transformation. These results confirm recent findings which show that postperovskite is weaker than perovskite, regardless of the prior history of the sample.
Un modèle de comportement élastoplastique cyclique cristallin est proposé pour les métaux
et alliages cubiques à face centrée, et en particulier pour le nickel. Il est utilisé lors
de simulations par éléments finis de la déformation cyclique uniaxiale d’un polycristal
non-texturé, représenté par l’assemblage de grains à géométrie cubique et à orientation
cristalline aléatoire. Ce modèle distingue les grains pour lesquels l’axe de chargement se
situe dans la partie centrale du triangle stéréographique standard (auxquels un mode de
déformation en glissement planaire est imposé) et les grains pour lesquels il est situé
près des bords du triangle standard (auxquels un comportement en glissement multiple est
attribué). Les résultats des simulations obtenus sont en accord avec les données
expérimentales disponibles, autant au niveau de la courbe d’écrouissage cyclique, qu’au
niveau des boucles d’hystérésis décrivant le comportement stabilisé. Ce modèle sera
ensuite employé pour l’étude de la localisation de la déformation sous forme de bandes de
glissement persistantes, comme observé lors du chargement cyclique de polycristaux de
This investigation was undertaken to provide detailed information on the epidemiology of human parvovirus B19 (B19) infection during pregnancy and childhood in the western part of Germany. Between 1997 and 2004, 40 517 sera from pregnant women aged 17–45 years and 6060 sera from children and young adults were tested for B19 IgG and IgM in our laboratory. In pregnant women, both the history of a ‘specific’ (OR 7·7, 95% CI 5·2–11·4) and a ‘non-specific’ rash (OR 3·3, 95% CI 1·5–7·1) was predictive for B19 IgM positivity. The B19 IgG prevalence was 69·2% (4097/5924) in a subgroup of asymptomatic pregnant women screened for B19 antibodies. In children, the age-specific IgG-positivity rate increased from 12·2% (66/541) at 2 years of age to 71·9% (396/551) in those older than 10 years. In conclusion, the prevalence of B19 IgG in pregnant women from the western part of Germany is higher then previously reported. Contact with children aged 3–10 years is a major risk factor for exposure to B19. Pregnant women with the history of a ‘non-specific’ rash should also be evaluated for acute B19 infection.
The addition of carbon atoms into Si or SiGe layers on Si opens the possibility for strain and bandstructure engineering. In this paper we will investigate the influence of carbon on the optical transitions of Si1−yCy and Si1−x−yGexCy layers grown pseudomorphically on Si(0O1) substrate using solid source MBE incluing also full strain-compensation. The layers were investigated by spectroscopic ellipsometry and electroreflectance spectroscopy for y ≤ 1.2 %. From the numerical derivatives of the measured dielectric constants, we determined the critical points energies E01, E1 and E2 as a function of the carbon content y. This shift was analyzed by measuring and fitting electroreflectance spectra at 80K and ellipsometry data at room temperature, resulting in a weak and nearly linear dependence on the carbon content at all transitions. These dependencies indicate that the interpretation of optical spectra of C-containing alloys can not be performed straightforward by simple interpolating between the appropriate band structures of silicon, germamum and carbon. An analysis based on only strain-induced contributions also does not describe the experimental results correctly. For a description of the observed energy shifts for pseudomorphic Si1−X−yGexCy we have to consider at least strain-induced effects and effects due to alloying.
This paper investigates conditions of low thermal budget N2O and NO oxidation with simultaneous accumulation of 0.5 to 1 at% nitrogen at the SiO2/Si interface of thin oxide layers. A nitrogen accumulation model is presented. It is concluded that the nitrogen accumulation should be realized with oxidizing conditions at the interface to silicon and it is proposed to control the NO partial pressure in reactor gas for the desired nitrogen amount at tolerable thermal budget.
Chemical Vapor Deposition of Si1-x Gex – films on Si (100) and of polycrystalline Si1-x Gex, layers on SiO2 – coated substrates have been performed at a pressure of 200 Pa in the temperature range of 500°C – 800°C, correspondingly. To observe the growth process and to characterize the growing thin films at deposition conditions an optical reflection interferometer (PYRITIERS) has been used. Comparing the data obtained at growth temperature with ex- situ measurements by spectroscopic ellipsometry the temperature dependence of optical constants of SiGe films have been evaluated. The reflectivity measurements during the deposition process allow to study the quality of the heteroepitaxial film, even in the initial stage of epitaxial growth.
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