Relativistic Dyson Rings and Their Black Hole Limit

In this Letter we investigate uniformly rotating, homogeneous and axisymmetric relativistic fluid bodies with a toroidal shape. The corresponding field equations are solved by means of a multi-domain spectral method, which yields highly accurate numerical solutions. For a prescribed, sufficiently large ratio of inner to outer coordinate radius, the toroids exhibit a continuous transition to the extreme Kerr black hole. Otherwise, the most relativistic configuration rotates at the mass-shedding limit. For a given mass-density, there seems to be no bound to the gravitational mass as one approaches the black-hole limit and a radius ratio of unity.Comment: 13 pages, 1 table, 5 figures, v2: some discussion and two references added, accepted for publication in Astrophys. J. Let

Black Holes Surrounded by Uniformly Rotating Rings

Highly accurate numerical solutions to the problem of Black Holes surrounded by uniformly rotating rings in axially symmetric, stationary spacetimes are presented. The numerical methods developed to handle the problem are discussed in some detail. Related Newtonian problems are described and numerical results provided, which show that configurations can reach an inner mass-shedding limit as the mass of the central object increases. Exemplary results for the full relativistic problem for rings of constant density are given and the deformation of the event horizon due to the presence of the ring is demonstrated. Finally, we provide an example of a system for which the angular momentum of the central Black Hole divided by the square of its mass exceeds one.Comment: 12 pages, 14 figures, revtex, v4: minor changes, Eq. (17) corrected, corresponds to version in PR

Equilibrium configurations of fluids and their stability in higher dimensions

We study equilibrium shapes, stability and possible bifurcation diagrams of fluids in higher dimensions, held together by either surface tension or self-gravity. We consider the equilibrium shape and stability problem of self-gravitating spheroids, establishing the formalism to generalize the MacLaurin sequence to higher dimensions. We show that such simple models, of interest on their own, also provide accurate descriptions of their general relativistic relatives with event horizons. The examples worked out here hint at some model-independent dynamics, and thus at some universality: smooth objects seem always to be well described by both ``replicas'' (either self-gravity or surface tension). As an example, we exhibit an instability afflicting self-gravitating (Newtonian) fluid cylinders. This instability is the exact analogue, within Newtonian gravity, of the Gregory-Laflamme instability in general relativity. Another example considered is a self-gravitating Newtonian torus made of a homogeneous incompressible fluid. We recover the features of the black ring in general relativity.Comment: 42 pages, 11 Figures, RevTeX4. Accepted for publication in Classical and Quantum Gravity. v2: Minor corrections and references adde

Unusual Regulation of a Leaderless Operon Involved in the Catabolism of Dimethylsulfoniopropionate in Rhodobacter sphaeroides

Rhodobacter sphaeroides strain 2.4.1 is a widely studied bacterium that has recently been shown to cleave the abundant marine anti-stress molecule dimethylsulfoniopropionate (DMSP) into acrylate plus gaseous dimethyl sulfide. It does so by using a lyase encoded by dddL, the promoter-distal gene of a three-gene operon, acuR-acuI-dddL. Transcription of the operon was enhanced when cells were pre-grown with the substrate DMSP, but this induction is indirect, and requires the conversion of DMSP to the product acrylate, the bona fide co-inducer. This regulation is mediated by the product of the promoter-proximal gene acuR, a transcriptional regulator in the TetR family. AcuR represses the operon in the absence of acrylate, but this is relieved by the presence of the co-inducer. Another unusual regulatory feature is that the acuR-acuI-dddL mRNA transcript is leaderless, such that acuR lacks a Shine-Dalgarno ribosomal binding site and 5′-UTR, and is translated at a lower level compared to the downstream genes. This regulatory unit may be quite widespread in bacteria, since several other taxonomically diverse lineages have adjacent acuR-like and acuI-like genes; these operons also have no 5′ leader sequences or ribosomal binding sites and their predicted cis-acting regulatory sequences resemble those of R. sphaeroides acuR-acuI-dddL

W. Kowalewsky, La modification de la structure des cellules nerveuses des ganglions spinaux

Kowalewsky W. W. Kowalewsky, La modification de la structure des cellules nerveuses des ganglions spinaux . In: L'année psychologique. 1897 vol. 4. pp. 436-438

On the osteology of the Hyopotamidae

by Dr. W. Kowalevsky ; communicated by Professor Huxle

Einkristallzuechtung und Charakterisierung von Hochtemperatursupraleitern (HTS)

Within the framework of the project, the following types of monocrystals have been grown and characterised: YBCO, BSCCO, LNO. Crystal growing has been performed using various techniques, some of them have been devised and tested by the project team. The novel, quasi crucible-free technique proved to be particularly successful, as were the experiments for quality enhancement of the crystals - as e.g. size, perfectness, purity - although it has not been possible to achieve the goal of an ideal, perfect crystal. The major defects occurring are dislocations, flux inclusions, and deviation from the oxygen stoichiometry. These imperfections have an effect on the current carrying capacity and on pinning. The crystals grown have been characterised by X-ray diffraction, determination of Tc by way of the conductivity and susceptibility, optical and scanning electron microscopy. (orig.)In diesem Projekt haben wir YBCO-, BSCCO- und LNO-Einkristalle gezuechtet und charakterisiert. Die Kristallzuechtung erfolgte mit verschiedenen Techniken, die teilweise von uns entwickelt und erprobt wurden. Als besonders erfolgreich hat sich unser quasi-tiegelfreies Zuechtungsverfahren herausgestellt. Im Laufe des Projektes konnten wir die ''Qualitaet'' der Kristalle - Groesse, Perfektion, Reinheit - stetig verbessern, wobei wir allerdings den idealen perfekten Kristall nicht zuechten konnten. Hauptdefekte in den Kristallen sind neben Versetzungen Flux-Einschluesse und Abweichungen von der Sauerstoffstoechiometrie. Diese Stoerstellen haben Einfluss auf die Stromtragfaehigkeit und das Pinning. Die gezuechteten Kristalle wurden durch Roentgendiffraktometrie, Tc-Bestimmung ueber Leitfaehigkeit und Suszeptibilitaet sowie optisch und elektronmikroskopisch charakterisiert. (orig.)SIGLEAvailable from TIB Hannover: D.Dt.F. QN1(2,55) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman