523 research outputs found
Self-assembled Pt nanowires on Ge(001): Relaxation effects
Absorption of Pt on the Ge(001) surface results in stable self-organized Pt
nanowires, extending over some hundred nanometers. Based on band structure
calculations within density functional theory and the generalized gradient
approximation, the structural relaxation of the Ge--Pt surface is investigated.
The surface reconstruction pattern obtained agrees well with findings from
scanning tunneling microscopy. In particular, strong Pt--Pt dimerization is
characteristical for the nanowires. The surface electronic structure is
significantly perturbed due to Ge--Pt interaction, which induces remarkable
shifts of Ge states towards the Fermi energy. As a consequence, the topmost Ge
layers are subject to a metal-insulator transition.Comment: 4 pages, 2 figures, final version accepted by Europhys. Lett., minor
modifications of the tex
Magnetic ground state of coupled edge-sharing CuO_2 spin-chains
By means of density functional theory, we investigate the magnetic ground
state of edge-sharing CuO_2 spin-chains, as found in the
(La,Ca,Sr)_14Cu_24O_41system, for instance. Our data rely on spin-polarized
electronic structure calculations including onsite interaction (LDA+U) and an
effective model for the interchain coupling. Strong doping dependence of the
magnetic order is characteristic for edge-sharing CuO_2 spin-chains. We
determine the ground state magnetic structure as function of the spin-chain
filling and quantify the competing exchange interactions.Comment: 5 pages, 2 figures, 3 tables, accepted by Phys. Rev. Let
Structure of Sn<sub>1-x</sub>Ge<sub>x</sub> random alloys as obtained from the coherent potential approximation
The structure of the Sn1-xGex random alloys is studied using density functional theory and the coherent potential approximation. We report on the deviation of the Sn1-xGex alloys from Vegard's law, addressing their full compositional range. The findings are compared to the related Si1-xGex alloys and to experimental results. Interestingly, the deviation from Vegard's law is quantitatively and qualitatively different between the Sn1-xGex and Si1-xGex alloys. An almost linear dependence of the bulk modulus as a function of composition is found for Si1-xGex, whereas for Sn1-xGex the dependence is strongly nonlinear
Magnetic ordering in the striped nickelate La5/3Sr1/3NiO4: A band structure point of view
We report on a comprehensive study of the electronic and magnetic structure
of the striped nickelate La5/3Sr1/3NiO4. The investigation is carried out using
band structure calculations based on density functional theory. A magnetic
structure compatible with experiment is obtained from spin-polarized
calculations within the generalized gradient approximation (GGA), whereas
inclusion of a local Coulomb interaction in the LDA+U framework results in a
different ground state. The influence of the various interaction parameters is
discussed in detail.Comment: 5 pages, 4 figures, 2 tables, accepted by Europhys. Let
Electronic structure of the Au/benzene-1,4-dithiol/Au transport interface: Effects of chemical bonding
We present results of electronic structure calculations for well-relaxed
Au/benzene-1,4-dithiol/Au molecular contacts, based on density functional
theory and the generalized gradient approximation. Electronic states in the
vicinity of the Fermi energy are mainly of Au 5d and S 3p symmetry, whereas
contributions of C 2p states are very small. Hybridization between C 2p
orbitals within the benzene substructure is strongly suppressed due to S-C
bonding. In agreement with experimental findings, this corresponds to a
significantly reduced conductance of the molecular contact.Comment: 7 pages, 5 figures, accepted by Chemical Physics Letter
Endurance Training Attenuates Chemoreflex Sensitivity to Intermittent Hypoxia
Please refer to the pdf version of the abstract located adjacent to the title
Proficiency Test of Four Salmonella Antibody ELISA-Tests for their Harmonization
The paper describes the necessity to only use tests for national salmonella monitoring and reduction programmes that are “harmonized”, i.e. that produce at least at herd level the same results. Four in Germany licensed tests were audited in a proficiency test by four independent and neutral laboratories. The test was designed rather to harmonize the tests, if necessary, than to evaluate the single tests. The methods used to provide a high credibility for the proficiency test’s outcome are explained. The conclusion of the ring test is that three of the four tests can be used for the salmonella monitoring programme in Germany as long as not single results are compared to each other, but the results of sets of sera are used for the herd categorization for their risk level of introducing Salmonella spec. into the food chain
Geometry Effects at Atomic-Size Aluminium Contacts
We present electronic structure calculations for aluminium nanocontacts.
Addressing the neck of the contact, we compare characteristic geometries to
investigate the effects of the local aluminium coordination on the electronic
states. We find that the Al 3pz states are very sensitive against modifications
of the orbital overlap, which has serious consequences for the transport
properties. Stretching of the contact shifts states towards the Fermi energy,
leaving the system instable against ferromagnetic ordering. By spacial
restriction, hybridization is locally suppressed at nanocontacts and the charge
neutrality is violated. We discuss the influence of mechanical stress by means
of quantitative results for the charge transfer.Comment: 10 pages, 4 figures, accepted by Chem. Phys. Let
The serological Salmonella Monitoring in German pork production: the structure of the central database and preliminary results of a basic epidemiological report
Since 2002, the Qualitiäit und Srcherheit GmbH (QS GmbH) has earned out a serologrcal salmonella monrtonng in German finishrng pig herds. Thrs monitoring arms at reducing the risk of introducmg salmonella into the meat production charn caused by mfected slaughter pigs and to identify and to remove infection sources. For this purpose the farms are differentrated into three risk categories (I =low, II = mrddle, III = high) by their chance to introduce salmonella into the pork production cham All data generated withm the monitoring are entered mto the central database Qualiproo (Qualitype AG, Dresden)
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