Extrapolating SMBH correlations down the mass scale: the case for IMBHs in globular clusters

Empirical evidence for both stellar mass black holes M_bh<10^2 M_sun) and supermassive black holes (SMBHs, M_bh>10^5 M_sun) is well established. Moreover, every galaxy with a bulge appears to host a SMBH, whose mass is correlated with the bulge mass, and even more strongly with the central stellar velocity dispersion sigma_c, the `M-sigma' relation. On the other hand, evidence for "intermediate-mass" black holes (IMBHs, with masses in the range 1^2 - 10^5 M_sun) is relatively sparse, with only a few mass measurements reported in globular clusters (GCs), dwarf galaxies and low-mass AGNs. We explore the question of whether globular clusters extend the M-sigma relationship for galaxies to lower black hole masses and find that available data for globular clusters are consistent with the extrapolation of this relationship. We use this extrapolated M-sigma relationship to predict the putative black hole masses of those globular clusters where existence of central IMBH was proposed. We discuss how globular clusters can be used as a constraint on theories making specific predictions for the low-mass end of the M-sigma relation.Comment: 14 pages, 3 figures, accepted for publication in Astrophysics and Space Science; fixed typos and a quote in Sec.

TheOxford folded tandem

The history and development of the vertical injector Van de Graaff is summarized from its commissioning in 1965 to its present use as a source of intense α-particle beams of 9-10 MeV and of 40-50 MeV neon beams. The decision to convert the machine to a folded Tandem is justified in the light of the experimental programme and of the technical and economic factors involved. Some features of the folded Tandem design are discussed, the state of the conversion is reviewed and the performance goals are described.L'histoire et le développement de l'injecteur Van de Graaff vertical sont résumés depuis la réception en 1965 jusqu'a son utilisation actuelle comme source intense de faisceaux de particules α de 9-10 MeV et de néon de 40-50 MeV. La décision de convertir la machine en un Tandem replié est justifiée du point de vue du programme expérimental et de facteurs techniques et économiques. L'avancement de la conversion est décrit ainsi que les performances à atteindre

Assembly Pathway of a Designed α-Helical Protein Fiber.

Interest in the design of peptide-based fibrous materials is growing because it opens possibilities to explore fundamental aspects of peptide self-assembly and to exploit the resulting structures for example, as scaffolds for tissue engineering. Here we investigate the assembly pathway of self-assembling fibers, a rationally designed a-helical coiled-coil system comprising two peptides that assemble on mixing. The dimensions spanned by the peptides and final structures (nanometers to micrometers), and the timescale over which folding and assembly occur (seconds to hours), necessitate a multi-technique approach employing spectroscopy, analytical ultracentrifugation, electron and light microscopy, and protein design to produce a physical model. We show that fibers form via a nucleation and growth mechanism. The two peptides combine rapidly (in less than seconds) to form sticky ended, partly helical heterodimers. A lag phase follows, on the order of tens of minutes, and is concentration-dependent. The critical nucleus comprises six to eight partially folded dimers. Growth is then linear in dimers, and subsequent fiber growth occurs in hours through both elongation and thickening. At later times (several hours), fibers grow predominantly through elongation. This kinetic, biomolecular description of the folding-and-assembly process allows the self-assembling fiber system to be manipulated and controlled, which we demonstrate through seeding experiments to obtain different distributions of fiber lengths. This study and the resulting mechanism we propose provide a potential route to achieving temporal control of functional fibers with future applications in biotechnology and nanoscale science and technology

REWORKED EARLY DIAGENETIC CONCRETIONS AND THE BIOEROSIONAL ORIGIN OF A REGIONAL DISCONTINUITY WITHIN BRITISH JURASSIC MARINE MUDSTONES

The Coinstone is a well known hiatus-concretion level in the Lower Lias (Lower Jurassic, Upper Sinemurian) of Dorset. It has long been recognized as a layer of bored and encrusted, early diagenetic, clay-hosted septarian concretions coincident with a biostratigraphic gap of three ammonite subzones. The burrowing activities of a benthic fauna in muds cause resuspension of sediment and facilitate erosion, even in the absence of high energy physical processes. Regional stratigraphic gaps may be formed as a consequence of sea level rises or falls, or as a response to sediment supply reduction independent of sea level change. -from Autho