Exchange-coupling constants, spin density map, and Q dependence of the inelastic neutron scattering intensity in single-molecule magnets

The Q dependence of the inelastic neutron scattering (INS) intensity of transitions within the ground-state spin multiplet of single-molecule magnets (SMMs) is considered. For these transitions, the Q dependence is related to the spin density map in the ground state, which in turn is governed by the Heisenberg exchange interactions in the cluster. This provides the possibility to infer the exchange-coupling constants from the Q dependence of the INS transitions within the spin ground state. The potential of this strategy is explored for the M = +-10 -> +- 9 transition within the S = 10 multiplet of the molecule Mn12 as an example. The Q dependence is calculated for powder as well as single-crystal Mn12 samples for various exchange-coupling situations discussed in the literature. The results are compared to literature data on a powder sample of Mn12 and to measurements on an oriented array of about 500 single-crystals of Mn12. The calculated Q dependence exhibits significant variation with the exchange-coupling constants, in particular for a single-crystal sample, but the experimental findings did not permit an unambiguous determination. However, although challenging, suitable experiments are within the reach of today's instruments.Comment: 11 pages, 6 figures, REVTEX4, to appear in PR

Herd-level risk factors influencing serological Yersinia prevalence in fattening pig herds

Yersiniosis is the third most frequent zoonosis reported in the European Union with pork as an important source. Identifying risk factors in swine production which may decrease the risk of pork production contamination during pre-harvest is an important step prior to controlling Yersinia spp.. Therefore, management strategies and production processes which might be associated with fattening pigs testing seropositive for pathogenic Yersinia spp. were investigated on 80 fattening pig farms. Although more than 70 farm characteristics were included in the risk assessment, there were only a few which seemed to be connected with serological prevalence: housing on a fully slatted floor and the use of municipal water were observed in herds with low serological Yersinia prevalence, whereas recurring health problems and a low daily weight gain compared to the mean of the herds included in the study were identified more often in herds with a high prevalence

Ground state properties of antiferromagnetic Heisenberg spin rings

Exact ground state properties of antiferromagnetic Heisenberg spin rings with isotropic next neighbour interaction are presented for various numbers of spin sites and spin quantum numbers. Earlier work by Peierls, Marshall, Lieb, Schultz and Mattis focused on bipartite lattices and is not applicable to rings with an odd number of spins. With the help of exact diagonalization methods we find a more general systematic behaviour which for instance relates the number of spin sites and the individual spin quantum numbers to the degeneracy of the ground state. These numerical findings all comply with rigorous proofs in the cases where a general analysis could be carried out. Therefore it can be plausibly conjectured that the ascertained properties hold for ground states of arbitrary antiferromagnetic Heisenberg spin rings.Comment: 13 pages, 5 figures, uses epsfig.sty, submitted to Phys. Rev. B. More information at http://www.physik.uni-osnabrueck.de/makrosysteme

Observation of plaquette fluctuations in the spin-1/2 honeycomb lattice

Quantum spin liquids are materials that feature quantum entangled spin correlations and avoid magnetic long-range order at T = 0 K. Particularly interesting are two-dimensional honeycomb spin lattices where a plethora of exotic quantum spin liquids have been predicted. Here, we experimentally study an effective S=1/2 Heisenberg honeycomb lattice with competing nearest and next-nearest neighbor interactions. We demonstrate that YbBr$_3$ avoids order down to at least T=100 mK and features a dynamic spin-spin correlation function with broad continuum scattering typical of quantum spin liquids near a quantum critical point. The continuum in the spin spectrum is consistent with plaquette type fluctuations predicted by theory. Our study is the experimental demonstration that strong quantum fluctuations can exist on the honeycomb lattice even in the absence of Kitaev-type interactions, and opens a new perspective on quantum spin liquids.Comment: 32 pages, 7 Figure

The Weyl bundle as a differentiable manifold

Construction of an infinite dimensional differentiable manifold ${\mathbb R}^{\infty}$ not modelled on any Banach space is proposed. Definition, metric and differential structures of a Weyl algebra and a Weyl algebra bundle are presented. Continuity of the $\circ$-product in the Tichonov topology is proved. Construction of the $*$-product of the Fedosov type in terms of theory of connection in a fibre bundle is explained.Comment: 31 pages; revised version - some typoes have been eliminated, notation has been simplifie

Interactive Exploration of Chemical Space with Scaffold Hunter

The supporting information is composed of the following files: I. pyruvatekinasedata.zip The pyruvate kinase data set used for the analysis described in the referenced publication is contained in this file. The analysis is based on the Pyruvate Kinase Screen as published in PubChem under the assay ID 361. It contains all compounds checked in this screen together with the scaffold tree generated from it. Scaffold Hunter can be used to query the database and interactively display the scaffold tree. This file is a dump from a MySQL 5.1 database and was generated with MySQL Administrator 1.2.5. It can be restored with the same program. II. scaffoldhunter_profiles.zip Scaffold Hunter saves the user profiles either on the hard disk or in a database. The corresponding database schema is contained in this zip file. This schema must be contained in the MySQL database before Scaffold Hunter can be run. This file is a dump from a MySQL 5.1 database and was generated with MySQL Administrator 1.2.5. It can be restored with the same program. III. InstallationGuide_Databases.pdf This document describes the installation of a local MySQL database server and the graphical user interface MySQL Administrator. Restoration of the profiles and sample databases are also described. IV. run_ScaffoldHunter.bat Windows batch file to run Scaffold Hunter with 1024 MByte of Memory. V. run_ScaffoldTreeGenerator.bat Windows batch file to run ScaffoldTreeGenerator with 1024 MByte of Memory. VI. ScaffoldHunter_readme.txt Textfile with advice for the installation of Scaffold Hunter. VII. ScaffoldTreeGenerator_readme.txt Textfile with advice for the installation of ScaffoldTree Generator

Prevalence of Campy/obacter spp. and Yersinia enterocolitica in Fattening Pig Herds in Lower Saxony, Germany

The results of a study on the occurrence of two bacteria that cause zoonoses, Campylobacter spp. and Yersmia enterocolilica were presented and the results of bacteriological and serological methods of detection were compared. The study was carried out on 30 fattening herds in Lower Saxony, Germany Bacteriological findings of Campylobacter spp. in the faeces indicated that 69.7% of the fattening pigs were positive, but 81 .2% tested positive serologically. All herds tested here were both bacteriologically and serologically positive for Campylobacter spp. Furthermore, only 8.4 % tested pos1t1ve for Yersinia enterocolitica in the faecal samples, but 66.8 % of the animals were serologically positive for that bacterium. At herd level 43.3 % of the herds tested bactenologically positive for Yersinia enterocolitica, whereas serological testing showed that 83.3 % of the units had one or more reacting animal

Ab initio correlation approach to a ferric wheel-like molecular cluster

We present an ab initio study of electronic correlation effects in a molecular cluster derived from the hexanuclear ferric wheel [LiFe6(OCH3)12-(dbm)6]PF6. The electronic and magnetic properties of this cluster have been studied with all-electron Hartree-Fock, full-potential density functional calculations and multi-reference second-order perturbation theory. For different levels of correlation, a detailed study of the impact of the electronic correlation on the exchange parameter was feasible. As the main result, we found that the influence of the bridge oxygen atoms on the exchange parameter is less intense than the influence of the apical ligand groups, which is due to the geometry of the cluster. With respect to the cluster model approach, the experimental value of the exchange parameter was affirmed.Comment: to be published in EPJ

Diversity of Lecidea (Lecideaceae, Ascomycota) species revealed by molecular data and morphological characters

The diversity of lichens, especially crustose species, in continental Antarctica is still poorly known. To overcome difficulties with the morphology based species delimitations in these groups, we employed molecular data (nuclear ITS and mitochondrial SSU rDNA sequences) to test species boundaries within the genus Lecidea. Sampling was done along a north–south transect at five different areas in the Ross Sea region (Cape Hallett, Botany Bay to Mount Suess, Taylor Valley, Darwin Area and Mount Kyffin). A total of 153 specimens were collected from 13 localities. Phylogenetic analyses also include specimens from other regions in Antarctica and non-Antarctic areas. Maximum parsimony, maximum likelihood and Bayesian analyses agreed in placing the samples from continental Antarctica into four major groups. Based on this phylogenetic estimate, we restudied the micromorphology and secondary chemistry of these four clades to evaluate the use of these characters as phylogenetic discriminators. These clades are identified as the following species Lecidea cancriformis, L. andersonii as well as the new species L. polypycnidophora Ruprecht & Türk sp. nov. and another previously unnamed clade of uncertain status, referred to as Lecidea sp. (L. UCR1)

QFT on homothetic Killing twist deformed curved spacetimes

We study the quantum field theory (QFT) of a free, real, massless and curvature coupled scalar field on self-similar symmetric spacetimes, which are deformed by an abelian Drinfel'd twist constructed from a Killing and a homothetic Killing vector field. In contrast to deformations solely by Killing vector fields, such as the Moyal-Weyl Minkowski spacetime, the equation of motion and Green's operators are deformed. We show that there is a *-algebra isomorphism between the QFT on the deformed and the formal power series extension of the QFT on the undeformed spacetime. We study the convergent implementation of our deformations for toy-models. For these models it is found that there is a *-isomorphism between the deformed Weyl algebra and a reduced undeformed Weyl algebra, where certain strongly localized observables are excluded. Thus, our models realize the intuitive physical picture that noncommutative geometry prevents arbitrary localization in spacetime.Comment: 23 pages, no figures; v2: extended discussion of physical consequences, compatible with version to be published in General Relativity and Gravitatio