Porous mandrels provide uniform deformation in hydrostatic powder metallurgy

Porous copper mandrels prevent uneven deformation of beryllium machining blanks. The beryllium powder is arranged around these mandrels and hot isostatically pressed to form the blanks. The mandrels are then removed by leaching

Investigating the pre-main sequence magnetic chemically peculiar system HD 72106

The origin of the strong magnetic fields observed in chemically peculiar Ap and Bp stars stars has long been debated. The recent discovery of magnetic fields in the intermediate mass pre-main sequence Herbig Ae and Be stars links them to Ap and Bp stars, providing vital clues about Ap and Bp stars and the origin and evolution of magnetic fields in intermediate and high mass stars. A detailed study of one young magnetic B star, HD 72106A, is presented. This star appears to be in a binary system with an apparently normal Herbig Ae star. A maximum longitudinal magnetic field strength of +391 +/- 65 G is found in HD 72106A, as are strong chemical peculiarities, with photospheric abundances of some elements ranging up to 100x above solar.Comment: 8 pages, 6 figures. Proceeding of the 2006 conference of the Special Astrophysical Observatory of the Russian Academy of Science

Substructure in the Andromeda Galaxy Globular Cluster System

In the most prominent current scenario of galaxy formation, galaxies form hierarchically through the merger of smaller systems. Such mergers could leave behind dynamical signatures which may linger long after the event. In particular, the globular cluster system (GCS) of a merging satellite galaxy may remain as a distinct sub-population within the GCS of a massive galaxy. Using the latest available globular cluster velocities and metallicities, we present the results of a search for grouping in the GCS of our nearest large spiral galaxy neighbor, M31. A modified friends-of-friends algorithm is used to identify a number of possible merger remnants in projected position, radial velocity and [Fe/H] parameter space. Numerical simulations are used to check that such merger remnants are indeed plausible over the timescales of interest. The identification of stellar streams associated with these groups is required in order to confirm that they represent merger remnants.Comment: 19 pages, 3 figures, accepted for publication in the Ap

The Kinematics and Metallicity of the M31 Globular Cluster System

With the ultimate aim of distinguishing between various models describing the formation of galaxy halos (e.g. radial or multi-phase collapse, random mergers), we have completed a spectroscopic study of the globular cluster system of M31. We present the results of deep, intermediate-resolution, fibre-optic spectroscopy of several hundred of the M31 globular clusters using the Wide Field Fibre Optic Spectrograph (WYFFOS) at the William Herschel Telescope in La Palma, Canary Islands. These observations have yielded precise radial velocities (+/-12 km/s) and metallicities (+/-0.26 dex) for over 200 members of the M31 globular cluster population out to a radius of 1.5 degrees from the galaxy center. Many of these clusters have no previous published radial velocity or [Fe/H] estimates, and the remainder typically represent significant improvements over earlier determinations. We present analyses of the spatial, kinematic and metal abundance properties of the M31 globular clusters. We find that the abundance distribution of the cluster system is consistent with a bimodal distribution with peaks at [Fe/H] = -1.4 and -0.5. The metal-rich clusters demonstrate a centrally concentrated spatial distribution with a high rotation amplitude, although this population does not appear significantly flattened and is consistent with a bulge population. The metal-poor clusters tend to be less spatially concentrated and are also found to have a strong rotation signature.Comment: 33 pages, 20 figure

Academic Pharmacy: Where is Our Influence?

Objective. To evaluate the talents of fellows from cohorts 1-10 of the Academic Leadership Fellows Program (ALFP)

A New Evolutionary Path to Type Ia Supernovae: Helium-Rich Super-Soft X-Ray Source Channel

We have found a new evolutionary path to Type Ia supernovae (SNe Ia) which has been overlooked in previous work. In this scenario, a carbon-oxygen white dwarf (C+O WD) is originated, not from an asymptotic giant branch star with a C+O core, but from a red-giant star with a helium core of $\sim 0.8-2.0 M_\odot$. The helium star, which is formed after the first common envelope evolution, evolves to form a C+O WD of $\sim 0.8-1.1 M_\odot$ with transferring a part of the helium envelope onto the secondary main-sequence star. This new evolutionary path, together with the optically thick wind from mass-accreting white dwarf, provides a much wider channel to SNe Ia than previous scenarios. A part of the progenitor systems are identified as the luminous supersoft X-ray sources or the recurrent novae like U Sco, which are characterized by the accretion of helium-rich matter. The white dwarf accretes hydrogen-rich, helium-enhanced matter from a lobe-filling, slightly evolved companion at a critical rate and blows excess matter in the wind. The white dwarf grows in mass to the Chandrasekhar mass limit and explodes as an SN Ia. A theoretical estimate indicates that this channel contributes a considerable part of the inferred rate of SNe Ia in our Galaxy, i.e., the rate is about ten times larger than the previous theoretical estimates for white dwarfs with slightly evolved companions.Comment: 19 pages including 12 figures, to be published in ApJ, 519, No.

Rheophysics of dense granular materials : Discrete simulation of plane shear flows

We study the steady plane shear flow of a dense assembly of frictional, inelastic disks using discrete simulation and prescribing the pressure and the shear rate. We show that, in the limit of rigid grains, the shear state is determined by a single dimensionless number, called inertial number I, which describes the ratio of inertial to pressure forces. Small values of I correspond to the quasi-static regime of soil mechanics, while large values of I correspond to the collisional regime of the kinetic theory. Those shear states are homogeneous, and become intermittent in the quasi-static regime. When I increases in the intermediate regime, we measure an approximately linear decrease of the solid fraction from the maximum packing value, and an approximately linear increase of the effective friction coefficient from the static internal friction value. From those dilatancy and friction laws, we deduce the constitutive law for dense granular flows, with a plastic Coulomb term and a viscous Bagnold term. We also show that the relative velocity fluctuations follow a scaling law as a function of I. The mechanical characteristics of the grains (restitution, friction and elasticity) have a very small influence in this intermediate regime. Then, we explain how the friction law is related to the angular distribution of contact forces, and why the local frictional forces have a small contribution to the macroscopic friction. At the end, as an example of heterogeneous stress distribution, we describe the shear localization when gravity is added.Comment: 24 pages, 19 figure

Construction and Analysis of High-Complexity Ribosome Display Random Peptide Libraries

Random peptide libraries displayed on the ribosome are becoming a new tool for the in vitro selection of biologically relevant macromolecules, including epitopes, antagonists, enzymes, and cell-surface receptors. Ribosome display is a cell-free system of coupling individual nascent proteins (phenotypes) to their corresponding mRNA (genotypes) by the formation of stable protein-ribosome-mRNA complexes and permitting the selection of a functional nascent protein by iterative cycles of panning and reverse transcription-polymerase chain reaction (RT-PCR) amplification in vitro. The complexity of the random peptide library is critical for the success of a panning experiment; greater the diversity of sequences within the library, the more likely it is that the library comprises sequences that can bind a given target with specific affinity. Here, we have used the cell-free system Escherichia coli S30 lysate to construct high-complexity random peptide libraries (>1014 independent members) by introducing strategies that are different from the methods described by Mattheakis et al. and Lamla et al. The key step in our method is to produce nanomole (nmol) amounts of DNA elements that are necessary for in vitro transcription/translation by using PCR but not plasmid DNA. Library design strategies and protocols that facilitate rapid identification are also presented

Chandra Observation of Diffuse Gas and LMXBs in the Elliptical Galaxy NGC 4649 (M60)

We present a Chandra X-ray observation of the X-ray bright E2 elliptical galaxy NGC4649. In addition to bright diffuse emission, we resolve 165 discrete sources, most of which are presumably low-mass X-ray binaries (LMXBs). As found in previous studies, the luminosity function of the resolved sources is well-fit by a broken power-law. In NGC4697 and NGC1553, the break luminosity was comparable to the Eddington luminosity of a $1.4 M_{\odot}$ neutron star. One possible interpretation of this result is that those sources with luminosities above the break are accreting black holes and those below are mainly accreting neutron stars. The total X-ray spectrum of the resolved sources is well-fit by a hard power-law, while the diffuse spectrum requires a hard and a soft component, presumably due to the relatively soft diffuse gas and the harder unresolved sources. We also find evidence for structure in the diffuse emission near the center of NGC4649. Specifically, there appear to be bright "fingers" of emission extending from the center of the galaxy and a 5 arcsec long bar at the center of the galaxy. The fingers are morphologically similar to radial features seen in two-dimensional hydrodynamic simulations of cooling flows in elliptical galaxies, and although their other properties do not match the predictions of the particular simulations used we conclude that the radial fingers might be due to convective motions of hot outflowing gas and cooler inflowing gas. The bar is coincident with the central extended radio source; we conclude that the bar may be caused by weak shocks in the diffuse gas from an undetected low-luminosity active galactic nucleus (AGN).Comment: 26 pages, 11 figures. Accepted for publication in the Astrophysical Journa