On the degenerated soft-mode instability

We consider instabilities of a single mode with finite wavenumber in inversion symmetric spatially one dimensional systems, where the character of the bifurcation changes from sub- to supercritical behaviour. Starting from a general equation of motion the full amplitude equation is derived systematically and formulas for the dependence of the coefficients on the system parameters are obtained. We emphasise the importance of nonlinear derivative terms in the amplitude equation for the behaviour in the vicinity of the bifurcation point. Especially the numerical values of the corresponding coefficients determine the region of coexistence between the stable trivial solution and stable spatially periodic patterns. Our approach clearly shows that similar considerations fail for the case of oscillatory instabilities.Comment: 16 pages, uses iop style files, manuscript also available at ftp://athene.fkp.physik.th-darmstadt.de/pub/publications/wolfram/jpa_97/ or at http://athene.fkp.physik.th-darmstadt.de/public/wolfram_publ.html. J. Phys. A in pres

Isolierung und Charakterisierung von Iridoviren

We describe the isolation and characterization of an iridescent virus from commercially produced colonies of Gryllus bimaculatus in Germany, which showed apparent mortality. Transmission electron microscopy studies on adult cricket specimens revealed the paracrystalline assembly of icosahedral virus particles in the cytoplasm of hypertrophied abdominal fat body cells. The infecting agent could be cultivated in the lepidopteran cell line sf-9, where it caused cytopathogenic effects such as cell hypertrophy, cytoplasmic vacuolization, and cell death within 8 days postinfection. Negatively stained virus particles (n = 100) had dimensions of 172 +/- 6 nm (apex to apex) and 148 +/- 5nm (side to side). SDS-polyacrylamide gel electrophoresis of virus proteins showed more than 20 distinct polypeptides with a major species of approximately 50 kDa. Analysis of the restriction fragment length profiles from digestion of purified viral DNA with the endonucleases EcoRI, BamHI, and HindIII showed marked differences from the profiles of iridoviruses of lower vertebrates (genus Ranavirus), e.g., Rana esculenta Iridovirus and Frog virus 3. Restriction enzyme digests with the endonucleases MspI and HpaII indicated the lack of methylation of viral DNA. Polymerase chain reaction led to the amplification of a 420-bp gene fragment with 97 % sequence homology to the major capsid protein gene of Invertebrate iridescent virus 6 (IIV-6). The data indicate, that this new isolate, which is the first iridescent virus reported from Germany, belongs to the genus Iridovirus of the family Iridoviridae. It is proposed to be termed Gryllus bimaculatus iridescent virus (GbIV). The investigation of four other iridescent-like viruses which were obtained in 1998, 1999 and 2000 from various tissues of three reptile species, e.g. Pogona vitticeps, Chamaeleo quadricornis, and Chamydosaurus kingii, revealed cytoplasmic desoxyriboviruses with the exact morphological and molecular biological characteristics of the formerly described GbIV. We conclude that all five isolates of iridescent-like viruses from Germany are identical and represent variants or strains of the type species of the genus Iridovirus, IIV-6. The data indicate, that GbIV, an invertebrate iridescent virus, is able to replicate in reptiles.Die vorliegende Arbeit beschreibt die Isolierung und Charakterisierung eines Invertebraten-Iridovirus aus kommerziell in Deutschland gezüchteten Mittelmeergrillen (Gryllus bimaculatus) mit auffällig hoher Sterblichkeit. Transmissions-elektronenmikroskopische Untersuchungen belegen das Assembly von icosaedrischen Viruspartikeln in Form parakristalliner Strukturen innerhalb des Zytoplasmas hypertrophierter Fettkörperzellen adulter Grillen. Das infektiöse Agens konnte auf der Schmetterlings-Zelllinie sf-9 kultiviert werden. Innerhalb von 8 Tagen post infectionem zeigten sich zytopathische Effekte in Form von Zellhypertrophie, Vakuolisierung und Zelltod. Negativ kontrastierte Viruspartikel (n = 100) zeigten Dimensionen von 172 +/-6 nm (Spitze zu Spitze) und 148 +/- 5 nm (Seite zu Seite). Mittels SDS-Polyacrylamidgelelektrophorese konnten mehr als 20 verschiedene Polypeptide und eine quantitativ überwiegende Hauptbande mit einem Molekulargewicht von 50 kDa unterschieden werden. Restriktionsfragment-Längenprofile nach enzymatischem Verdau viraler DNA mit den Endonukleasen EcoRI, BamHI und HindIII zeigten signifikante Unterschiede zu den entsprechenden Profilen von Iridoviren niederer Vertebraten (Gattung: Ranavirus) wie Rana esculenta Iridovirus oder Frog virus 3. Ein enzymatischer Verdau mit den Endonukleasen MspI und HpaII zeigte, dass die virale DNA unmethyliert war. Mittels Polymerase-Kettenreaktion (PCR) konnte ein 420 bp langes DNA-Fragment amplifiziert werden, das 97 % Sequenzhomologie zu dem Gen des Hauptstrukturproteins (major capsid protein, MCP) von Invertebrate iridescent virus 6 (IIV-6) aufwies. Die Daten weisen darauf hin, dass dieses neue Isolat dem Genus Iridovirus aus der Familie Iridoviridae zuzuordnen ist. Das Isolat stellt das erste in Deutschland nachgewiesene Invertebraten-Iridovirus dar. Zur vorläufigen Benennung wird der Name Gryllus bimaculatus iridescent virus (GbIV) vorgeschlagen. Die Untersuchung von vier weiteren Iridoviren, die in den Jahren 1998, 1999 und 2000 aus den Geweben von verstorbenen Reptilien der Arten Pogona vitticeps, Chamaeleo quadricornis und Chamydosaurus kingii isoliert wurden, ergab zytoplasmatische DNA-Viren mit im Vergleich zu GbIV identischen morphologischen und molekularbiologischen Eigenschaften. Aus den Daten wird gefolgert, dass alle fünf untersuchten, deutschen Iridovirusisolate identisch sind und Variationen oder Stämme der Typspezies der Gattung Iridovirus, IIV-6, repräsentieren. Es besteht der Verdacht, dass das Invertebraten-Iridovirus GbIV in der Lage ist, sich in Reptilien zu vermehren

Evidence That Ultraviolet Radiation May Depress Short-Term Photosynthetic Rates of Intertidal Ulva lactuca and Consumption by a Generalist Feeder (Clibanarius vittatus)

This article considers the impact of ultraviolet radiation (UVR) on the photosynthesis and consumption of intertidal Ulva lactuca, an important producer and food resource in many coastal ecosystems. Algal fragments were exposed in the laboratory to either UVR and PAR (photosynthetically active radiation) simultaneously or PAR alone. The rates of photosynthesis and consumption by a generalist feeder, the stripped hermit crab (Clibanarius vittatus), were then compared between the two treatments. In both experiments, the biological weighted values for UVR in the laboratory indicate that the experimental set-up provided a level of UVR exposure that would occur in the field. The results show that UVR exposure depresses the photosynthetic rates of U. lactuca at light intensities between 1118 and 2206 μmol m-2 s-1. UVR also reduced the grazing intensity of C. vittatus on U. lactuca with non-UVR-exposed algal pieces supporting about five times more consumption than exposed pieces. The relevance and implications of this study, however, are limited because the results have been obtained with short-term, simple experiments. Studies encompassing a longer time scale and the community of consumers (e.g. exposing both the algae and main consumers simultaneously to experimental UVR levels) are needed to elucidate whether the algae can offset UVR-deleterious effects through the induction of protective compounds and how these compounds and UVR exposure affects the activity of consumers

EUROCODE 2: BACKGROUND & APPLICATIONS DESIGN OF CONCRETE BUILDINGS Worked examples

This document is a report with worked examples presenting step-by-step the design of a reinforced concrete cast on site building following Eurocode 2. The design process has been divided between different authors, some of whom were involved in the preparation and/or assessment of Eurocode 2. Each chapter of the report focuses on a different step in the design process: conceptual design, structural analyses, limit states design and verification, detailing of the reinforcement as well as some geotechnical aspects of building design. Last chapter gives general overview of the fire design according to the Eurocodes. The materials were prepared and presented at the workshop “Eurocode 2: Design of Concrete Buildings” held on 20 21 October 2011 in Brussels, Belgium. The workshop was organized by JRC with the support of DG ENTR and CEN, and in collaboration with CEN/TC250/Sub-Committee 2. The document is part of the Report Series ‘Support to the implementation, harmonization and further development of the Eurocodes’ prepared by JRC in collaboration with DG ENTR and CEN/TC250 “Structural Eurocodes”.JRC.G.5-European laboratory for structural assessmen

On the dissolution of star clusters in the Galactic centre. I. Circular orbits

We present N-body simulations of dissolving star clusters close to galactic centres. For this purpose, we developed a new N-body program called nbody6gc based on Aarseth's series of N-body codes. We describe the algorithm in detail. We report about the density wave phenomenon in the tidal arms which has been recently explained by Kuepper et al. (2008). Standing waves develop in the tidal arms. The wave knots or clumps develop at the position, where the emerging tidal arm hits the potential wall of the effective potential and is reflected. The escaping stars move through the wave knots further into the tidal arms. We show the consistency of the positions of the wave knots with the theory in Just et al. (2009). We also demonstrate a simple method to study the properties of tidal arms. By solving many eigenvalue problems along the tidal arms, we construct numerically a 1D coordinate system whose direction is always along a principal axis of the local tensor of inertia. Along this coordinate system, physical quantities can be evaluated. The half-mass or dissolution times of our models are almost independent of the particle number which indicates that two-body relaxation is not the dominant mechanism leading to the dissolution. This may be a typical situation for many young star clusters. We propose a classification scheme which sheds light on the dissolution mechanism.Comment: 18 pages, 20 figures; accepted by MNRA

Relation between coupled map lattices and kinetic Ising models

A spatially one dimensional coupled map lattice possessing the same symmetries as the Miller Huse model is introduced. Our model is studied analytically by means of a formal perturbation expansion which uses weak coupling and the vicinity to a symmetry breaking bifurcation point. In parameter space four phases with different ergodic behaviour are observed. Although the coupling in the map lattice is diffusive, antiferromagnetic ordering is predominant. Via coarse graining the deterministic model is mapped to a master equation which establishes an equivalence between our system and a kinetic Ising model. Such an approach sheds some light on the dependence of the transient behaviour on the system size and the nature of the phase transitions.Comment: 15 pages, figures included, Phys. Rev. E in pres

Enhanced accretion rates of stars on Super-massive Black Holes by star-disk interactions in galactic nuclei

We investigate the dynamical interaction of a central star cluster surrounding a super-massive black hole and a central accretion disk. The dissipative force acting on stars in the disk leads to an enhanced mass flow towards the super-massive black hole and to an asymmetry in the phase space distribution due to the rotating accretion disk. The accretion disk is considered as a stationary Keplerian rotating disk, which is vertically extended in order to employ a fully self-consistent treatment of stellar dynamics including the dissipative force originating from star-gas ram pressure effects. The stellar system is treated with a direct high-accuracy N-body integration code. A star-by-star representation, desirable in N-body simulations, cannot be extended to real particle numbers yet. Hence, we carefully discuss the scaling behavior of our model with regard to particle number and tidal accretion radius. The main idea is to find a family of models for which the ratio of two-body relaxation time and dissipation time (for kinetic energy of stellar orbits) is constant, which then allows us to extrapolate our results to real parameters of galactic nuclei. Our model is derived from basic physical principles and as such it provides insight into the role of physical processes in galactic nuclei, but it should be regarded as a first step towards more realistic and more comprehensive simulations. Nevertheless, the following conclusions appear to be robust: the star accretion rate onto the accretion disk and subsequently onto the super-massive black hole is enhanced by a significant factor compared to purely stellar dynamical systems neglecting the disk. This process leads to enhanced fueling of central disks in active galactic nuclei and to an enhanced rate of tidal stellar disruptions. [Abridged]Comment: 17 pages, 6 figures (with 9 panels), 2 tables, accepted for publication in Ap

Anaplasma phagocytophilum Infection in Ixodes ricinus, Bavaria, Germany

Anaplasma phagocytophilum DNA was detected by real-time PCR, which targeted the msp2 gene, in 2.9% of questing Ixodes ricinus ticks (adults and nymphs; n = 2,862), collected systematically from selected locations in Bavaria, Germany, in 2006. Prevalence was significantly higher in urban public parks in Munich than in natural forests