120 research outputs found
Electron Transport in Hybrid Ferromagnetic/Superconducting Nanostructures
We observe large amplitude changes in the resistance of ferromagnetic (F)
wires at the onset of superconductivity of adjacent superconductors (S). New
sharp peaks of large amplitude are found in the magnetoresistance of the
F-wires. We discuss a new mechanism for the long-range superconducting
proximity effect in F/S nanostructures based on the analysis of the topologies
of actual Fermi-surfaces in ferromagnetic metals.Comment: 7 pages in LaTeX, 5 eps figures. Submitted to the Proceedings of
MS200
Entanglement of electrons in interacting molecules
Quantum entanglement is a concept commonly used with reference to the
existence of certain correlations in quantum systems that have no classical
interpretation. It is a useful resource to enhance the mutual information of
memory channels or to accelerate some quantum processes as, for example, the
factorization in Shor's Algorithm. Moreover, entanglement is a physical
observable directly measured by the von Neumann entropy of the system. We have
used this concept in order to give a physical meaning to the electron
correlation energy in systems of interacting electrons. The electronic
correlation is not directly observable, since it is defined as the difference
between the exact ground state energy of the many--electrons Schroedinger
equation and the Hartree--Fock energy. We have calculated the correlation
energy and compared with the entanglement, as functions of the nucleus--nucleus
separation using, for the hydrogen molecule, the Configuration Interaction
method. Then, in the same spirit, we have analyzed a dimer of ethylene, which
represents the simplest organic conjugate system, changing the relative
orientation and distance of the molecules, in order to obtain the configuration
corresponding to maximum entanglement.Comment: 15 pages, 7 figures, standard late
Gutzwiller-Correlated Wave Functions: Application to Ferromagnetic Nickel
Ferromagnetic Nickel is the most celebrated iron group metal with pronounced
discrepancies between the experimental electronic properties and predictions of
density functional theories. In this work, we show in detail that the recently
developed multi-band Gutzwiller theory provides a very good description of the
quasi-particle band structure of nickel. We obtain the correct exchange
splittings and we reproduce the experimental Fermi-surface topology. The
correct (111)-direction of the magnetic easy axis and the right order of
magnitude of the magnetic anisotropy are found. Our theory also reproduces the
experimentally observed change of the Fermi-surface topology when the magnetic
moment is oriented along the (001)-axis. In addition to the numerical study, we
give an analytical derivation for a much larger class of variational
wave-functions than in previous investigations. In particular, we cover cases
of superconductivity in multi-band lattice systems.Comment: 35 pages, 3 figure
FRA2A is a CGG repeat expansion associated with silencing of AFF3
Folate-sensitive fragile sites (FSFS) are a rare cytogenetically visible subset of dynamic mutations. Of the eight molecularly characterized FSFS, four are associated with intellectual disability (ID). Cytogenetic expression results from CGG tri-nucleotide-repeat expansion mutation associated with local CpG hypermethylation and transcriptional silencing. The best studied is the FRAXA site in the FMR1 gene, where large expansions cause fragile X syndrome, the most common inherited ID syndrome. Here we studied three families with FRA2A expression at 2q11 associated with a wide spectrum of neurodevelopmental phenotypes. We identified a polymorphic CGG repeat in a conserved, brain-active alternative promoter of the AFF3 gene, an autosomal homolog of the X-linked AFF2/FMR2 gene: Expansion of the AFF2 CGG repeat causes FRAXE ID. We found that FRA2A-expressing individuals have mosaic expansions of the AFF3 CGG repeat in the range of several hundred repeat units. Moreover, bisulfite sequencing and pyrosequencing both suggest AFF3 promoter hypermethylation. cSNP-analysis demonstrates monoallelic expression of the AFF3 gene in FRA2A carriers thus predicting that FRA2A expression results in functional haploinsufficiency for AFF3 at least in a subset of tissues. By whole-mount in situ hybridization the mouse AFF3 ortholog shows strong regional expression in the developing brain, somites and limb buds in 9.5-12.5dpc mouse embryos. Our data suggest that there may be an association between FRA2A and a delay in the acquisition of motor and language skills in the families studied here. However, additional cases are required to firmly establish a causal relationship
Tannerella forsythia, a periodontal pathogen entering the genomic era
Several questions need to be addressed to evaluate whether Tannerella forsythia is to be considered a periodontal pathogen. T. forsythia has been detected in periodontal health and disease, so could it be a pathogen? The species was not detected in many studies despite finding other putative pathogens, so could it be important in pathogenicity? The challenges of working with T. forsythia include its fastidious and anaerobic growth requirements for cultural detection. Thus, studies associating T. forsythia with periodontal and other oral infections have used noncultural approaches (immunoassays and DNA-based assays) in addition to cultural approaches. We feel the timing of this review represents an interesting transition period in our understanding of the relationships of species with infection. Information from the recently released full genome sequence data of T. forsythia will provide new approaches and tools that can be directed to assess pathogenicity. Furthermore, molecular assessment of gene expression will provide a new understanding of the pathogenical potential of the species, and its effect on the host.
T. forsythia, was described in reviews focusing on periodontal pathogens associated with herpesvirus detection (200), species for which genome projects were underway (41), members of polybacterial periodontal pathogenic consortium (91), and participants in periodontal microbial ecology (202). We will describe the history, taxonomy, and characteristics of T. forsythia, and related species or phylotypes in the genus Tannerella. To assess the pathogenic potential of T. forsythia, we first describe species associations with periodontal and other infections, including animal models, as has been the traditional approach arising from Koch’s postulates (203). Criteria for pathogenicity were expanded to incorporate sequence- derived information (58), and again more recently to include molecular signatures of pathogens and disease (170). We used sequence and genome-derived information, in addition to biofilm, pathogenic mediators, and host responses, to further explore the pathogenic potential of T. forsythia
Magnetic instabilities in high-temperature superconductors under rapidly varying magnetic fields
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