Spectral density of the Dirac operator in two-flavour QCD

We compute the spectral density of the (Hermitean) Dirac operator in Quantum Chromodynamics with two light degenerate quarks near the origin. We use CLS/ALPHA lattices generated with two flavours of O(a)-improved Wilson fermions corresponding to pseudoscalar meson masses down to 190 MeV, and with spacings in the range 0.05-0.08 fm. Thanks to the coverage of parameter space, we can extrapolate our data to the chiral and continuum limits with confidence. The results show that the spectral density at the origin is non-zero because the low modes of the Dirac operator do condense as expected in the Banks-Casher mechanism. Within errors, the spectral density turns out to be a constant function up to eigenvalues of approximately 80 MeV. Its value agrees with the one extracted from the Gell-Mann-Oakes-Renner relation

Effect of zooplankton-mediated trophic cascades on marine microbial food web components (bacteria, nanoflagellates, ciliates)

To examine the grazing effects of copepod-dominated mesozooplankton on heterotrophic microbial communities, four mesocosm experiments using gradients of zooplankton abundance were carried out at a coastal marine site. The responses of different protist groups (nanoflagellates, ciliates) and bacterioplankton in terms of abundance and additionally, for bacteria, diversity, production, and exoenzymatic activity, were monitored during 1 week of incubation. Independent of the initial experimental abiotic conditions and the dominating copepod species, zooplankton caused order-of-magnitude changes in microbial functional groups in a clear community-wide four-link trophic cascade. The strongest predatory effects were observed for protist concentrations, thus generating inverse relationships between mesozooplankton and ciliates and between ciliates and nanoplankton. Copepod grazing effects propagated even further, not only reducing the abundance, production, and hydrolytic activity of bacterioplankton but also increasing bacterial diversity. The overall strength of this trophic cascade was dampened with respect to bacterial numbers, but more pronounced with respect to bacterial diversity and activity. High predation pressure by heterotrophic nanoflagellates, realized at the highest copepod abundance, was probably the underlying mechanism for these structural changes in the bacterial assemblages. Our results thus suggest a mechanism by which changes in higher trophic levels of marine plankton indirectly affect prokaryotic assemblages and microbially mediated ecosystem functions

Chiral symmetry breaking in QCD Lite

A distinctive feature of the presence of spontaneous chiral symmetry breaking in QCD is the condensation of low modes of the Dirac operator near the origin. The rate of condensation must be equal to the slope of (Mpi^2 Fpi^2)/2 with respect to the quark mass m in the chiral limit, where Mpi and Fpi are the mass and the decay constant of the Nambu-Goldstone bosons. We compute the spectral density of the (Hermitian) Dirac operator, the quark mass, the pseudoscalar meson mass and decay constant by numerical simulations of lattice QCD with two light degenerate Wilson quarks. We use CLS lattices at three values of the lattice spacing in the range 0.05-0.08 fm, and for several quark masses corresponding to pseudoscalar mesons masses down to 190 MeV. Thanks to this coverage of parameters space, we can extrapolate all quantities to the chiral and continuum limits with confidence. The results show that the low quark modes do condense in the continuum as expected by the Banks-Casher mechanism, and the rate of condensation agrees with the Gell-Mann-Oakes-Renner (GMOR) relation. For the renormalisation-group-invariant ratios we obtain [\Sigma^RGI]^(1/3)/F =2.77(2)(4) and Lambda^MSbar/F = 3.6(2), which correspond to [\Sigma^\MSbar(2 GeV)]^(1/3) =263(3)(4) MeV and F=85.8(7)(20) MeV if FK is used to set the scale by supplementing the theory with a quenched strange quark.Comment: 4 pages, 3 figures, 1 tabl

Eine morphologische Aberration von Calamostachys tuberculata (Sternberg) Weiss aus dem Oberkarbon des Piesberges bei Osnabrück

Aus dem Oberkarbon (unteres Westfal D) des Piesberges bei Osnabrück wird eine morphologisch aberrante Form von Calamostachys tuberculata (Sternberg) Weiss beschrieben, bei welcher anstelle kleiner Brakteen unterhalb der Sporangiophore normale Microphylle vom Annularia stellata-Typ ausgebildet sind.Amorphologically aberrant specimen of Calamostachys tuberculata (Sternberg) Weiss is described from the Upper Carboniferous (lowerWestphalian D) of the Piesberg nearOsnabrück. Instead of small bracts, this specimen possesses normally developed microphylls of the Annularia stellata-type below the sporangiophores

DsD_s physics from fine lattices

We present a preliminary analysis of the charm quark mass and the mass and decay constant $f_{D_s}$ of the $D_s$ meson obtained from dynamical simulations of $N_f = 2$ Wilson QCD on the large and fine lattices simulated by the CLS effort.Comment: 6 pages, 2 figures; talk presented at Lattice 2008, XXVI International Symposium on Lattice Field Theory, July 14-19, 2008, Williamsburg, Virginia, US

Geistiges Eigentum - eine Diskussion am Beispiel Freie Software

Die Magisterarbeit im Fach Philosophie beschäftigt sich mit den Grundlagen des Eigentumsbegriffes, besonders des geistigen Eigentums und versucht das Eigentums- und Verwertungsmodell Freier Software darauf zu beziehen

Highly Dynamic Voltage Control of a Dual Active Bridge over the Full Voltage Range by Operating Point Dependent Manipulated Variable Limitation

This paper presents a highly dynamic voltage control for the Dual Active Bridge over the full operating range. Maximum dynamics is achieved by using the maximum available manipulated variable in combination with a feedforward control of the capacitor current at a setpoint change. Operation within the system limits is ensured by a variable limitation of the manipulated variable considering the current operating point. The simulation results are validated by measurements on a 35 kW Dual Active Bridge test bench

Eine interessante fossile Flora im tiefen Westfal D des Piesberges

In dieser Arbeit wird die Begleitflora zu den nicht-marinen Muschelfunden des Piesberges bei Osnabrück, worüber in Band 24 dieser Mitteilungen berichtet wurde, näher untersucht und dargestellt. Die nicht-marinen Muscheln wurden z.T. direkt aus dem Hangenden des Flözes Dreibänke, zum anderen und grössten Teil aus einer nahegelegenen Halde geborgen. Aufgrund des Vorkommens von Neuropteris dussartii Laveine, Sphenopteris coemansii Andrae und Alethopteris davreuxii (Brongniart) Goeppert kann festgestellt werden, dass das Haldenmaterial aus dem untersten Teil des Westfal D stammt.The fossil plant remains of the Piesberg near Osnabrück, which were found together with the non-marine shells (published in volume 24 of this journal), were studied and documented. Few of the non-marine shells were collected directly from above coal seam Dreibänke. However, most of the shells were collected from a waste dump. Based on the occurrence of Neuropteris dussartii Laveine, Sphenopteris coemansii Andrae and Alethopteris davreuxii (Brongniart) Goeppert it is concluded that the material from the dump belongs to the lowermost Westphalian D