Extensive polymorphism and geographical variation at a positively selected MHC class II B gene of the lesser kestrel (Falco naumanni)

Understanding the selective forces that shape genetic variation in natural populations remains a high priority in evolutionary biology. Genes at the major histocompatibility complex (MHC) have become excellent models for the investigation of adaptive variation and natural selection because of their crucial role in fighting off pathogens. Here we present one of the first data sets examining patterns of MHC variation in wild populations of a bird of prey, the lesser kestrel, Falco naumanni. We report extensive polymorphism at the second exon of a putatively functional MHC class II gene, Fana-DAB*1. Overall, 103 alleles were isolated from 121 individuals sampled from Spain to Kazakhstan. Bayesian inference of diversifying selection suggests that several amino acid sites may have experienced strong positive selection (ω = 4.02 per codon). The analysis also suggests a prominent role of recombination in generating and maintaining MHC diversity (ρ = 4Nc = 0.389 per codon, θ = 0.017 per codon). Both the Fana-DAB*1 locus and a set of eight polymorphic microsatellite markers revealed an isolation-by-distance pattern across the Western Palaearctic (r = 0.67; P = 0.01 and r = 0.50; P = 0.04, respectively). Nonetheless, geographical variation at the MHC contrasts with relatively uniform distributions in the frequencies of microsatellite alleles. In addition, we found lower fixation rates in the MHC than those predicted by genetic drift after controlling for neutral mitochondrial sequences. Our results therefore underscore the role of balancing selection as well as spatial variations in parasitemediated selection regimes in shaping MHC diversity when gene flow is limited.Peer reviewe

Разработка модели статического преобразователя напряжения

In this paper hybrid simulation approach for adequate modeling of Voltage Source Converter (VSC) of Highvoltage direct current (HVDC) systems as part of real electric power systems (EPS) is presented. The proposed VSC model allows to carry out the adequate simulation of different switching processes in VSC HVDC and EPS as a whole without any decomposition and limitation on their duration

Function by defects at the atomic scale - New concepts for non-volatile memories

A survey of non-volatile. highly scalable memory devices which utilize dedicated resistive switching phenomena in nanoscale chalcogenide-based memory cells is presented. We introduce the basic operation principle of the phase change mechanism, the thermochemical mechanism, and the valence change mechanism and we discuss the crucial role of structural defects in the switching processes. We show how this role is determined by the atomic structure of the defects, the electronic defect states, and/or the ion transport properties of the defects. The electronic structure of the systems in different resistance states is described in the light of the chemical bonds involved. While for phase-change alloys the interplay of ionicity and hybridization in the crystalline and in the amorphous phase determine the resistances, the local redox reaction at the site of extended defects, the change in the oxygen stoichiometry, and the resulting change in the occupancy of relevant orbitals play the major role in the thermochemical and the valence change mechanism. Phase transformations are not only discussed for phase-change alloys but also for both other types of switching processes. The switching kinetics as well as the ultimate scalability of switching cells is related to structural defects in the materials. (C) 2010 Elsevier Ltd. All rights reserved

The role of defects in resistively switching chalcogenides

This overview describes the present Understanding of resistive switching phenomena encountered in chalcogenide-based cells which may be utilized in energy-efficient nonvolatile memory devices and in array-based logic applications. We introduce the basic operation principle of the phase change mechanism, the thermochemical mechanism, and the valence change mechanism and we discuss the crucial role of structural defects in the switching processes. We show how this role is determined by the atomic Structure of the defects, the electronic defect states, and/or the ion transport properties of the defects. The electronic structure of the systems in different resistance states is described in the light of the chemical bonds involved. While for phase change alloys the interplay of ionicity and hybridization in the crystalline and ill the amorphous phase determine the resistances, the local redox reaction at the site of extended defects, the change in the oxygen stoichiometry. and the resulting change ill the occupancy of relevant orbitals play the major role in transition metal oxides which switch by the thermochemical and the valence change mechanism. Phase transformations are not only discussed for phase change alloys but also for redox-related switching processes. The switching kinetics as well as the ultimate scalability of switching cells are related to structural defects in the materials