A spectacular nitrogen isotope anomaly in Bencubbin

Results of isotopic measurements on an unusual stony-iron meteorite named Bencubbin, which was found in Western Australia in 1930, are reported. Nitrogen from both the metallic and stony parts of the Bencubbin meteorite was analyzed, and in both materials large excesses of (15)N were found, resulting in values of the (14)N/(15)N abundance ratios as low as 137. That is, (15)N is enriched in Bencubbin by about a factor of two relative to terrestrial nitrogen. This is the largest (15)N enrichment of any known natural material. The effect is so large that chemical processes are probably inadequate to account for it. Nuclear processes which may be responsible for the anomalous isotope abundance are discussed

Failures in the prudential regulation of banks in the UK and US: will the lessons be learnt?

The prudential regulation of banking is now undertaken by the Prudential Regulation Authority (PRA) within the Bank of England. Previously, such regulation was undertaken by the Financial Services Authority (FSA). It will be the role of the FSA as the previous regulator in the UK that will be considered. This article will examine the lack of understanding on the part of the FSA about the risk to which banks were subject. Insights into the approach and effectiveness of the FSA can be found in an examination of the reports of various parliamentary committees and the evidence of senior officials, employees and management called to give evidence. These committees have investigated various banking collapses and important issues relating to the carrying on of banking business. The reports and evidence of such committees are a reliable and detailed source of information. These reports are evaluated throughout. It will be suggested that the economic position of such banks does have an effect upon their regulation. Analogous reports in the US will be compared and contrasted with the findings in the UK. Changes in regulation, and its enforcement, after the setting up of the PRA will be considered

Supernova Reverse Shocks and SiC Growth

We present new mechanisms by which the isotopic compositions of X-type grains of presolar SiC are altered by reverse shocks in Type II supernovae. We address three epochs of reverse shocks: pressure wave from the H envelope near t = 10$^6$s; reverse shock from the presupernova wind near 10$^8-10^9$s; reverse shock from the ISM near 10$^{10}$s. Using 1-D hydrodynamics we show that the first creates a dense shell of Si and C atoms near 10$^6$s in which the SiC surely condenses. The second reverse shock causes precondensed grains to move rapidly forward through decelerated gas of different isotopic composition, during which implantation, sputtering and further condensation occur simultaneously. The third reverse shock causes only further ion implantation and sputtering, which may affect trace element isotopic compositions. Using a 25M$_{\odot}$ supernova model we propose solutions to the following unsolved questions: where does SiC condense?; why does SiC condense in preference to graphite?; why is condensed SiC $^{28}$Si-rich?; why is O richness no obstacle to SiC condensation?; how many atoms of each isotope are impacted by a grain that condenses at time t$_0$ at radial coordinate r$_0$? These many considerations are put forward as a road map for interpreting SiC X grains found in meteorites and their meaning for supernova physics.Comment: 28 pages, 14 figures, animation for Figure 3 and machine-readable Table 3 can be found at http://antares.steelangel.com/~edeneau/supernova/DHC_2003, Submitted to Ap

The Impact of Local Source Sediments on Bed Texture in the Fall River, Rocky Mountain National Park, USA

The bed texture of a gravel-bed river is related to the size distribution and quantity of source sediments, the routing of sediment through the reach, and the distribution of flow velocity. A reach morphology that is consistent in depth with little lateral topographic variation will typically have a bed texture that is characterized by a fairly uniform grain size distribution. However, spatial variations in source sediments within a given watershed may impact the distribution of gravel-bed river sediments, even at the reach scale, such that two proximal reaches of the same river having the same general morphology can exhibit contrasting distributions of surface sediments. We collected extensive topographic and sedimentological data from two reaches of the Fall River in Rocky Mountain National Park, Colorado. These were chosen for their simple morphology (both are straight reaches with fairly uniform depths) and contrasting location relative to alluvial fan deposits that were introduced into the valley in a dam-break event in 1982; the upstream reach was unaffected by the introduced sediments. Despite the long duration since this event, surveying in 2008 revealed that the fan sediment continues to coarsen the left and upstream portions of the affected reach relative to other regions of the channel. The persistent nonuniformity in bed texture in the downstream reach may eventually result in morphological adjustment by promoting differential routing of fine versus coarse bed load size fractions, which may induce meandering

The Flux Ratio Method for Determining the Dust Attenuation of Starburst Galaxies

The presence of dust in starburst galaxies complicates the study of their stellar populations as the dust's effects are similar to those associated with changes in the galaxies' stellar age and metallicity. This degeneracy can be overcome for starburst galaxies if UV/optical/near-infrared observations are combined with far-infrared observations. We present the calibration of the flux ratio method for calculating the dust attenuation at a particular wavelength, Att(\lambda), based on the measurement of F(IR)/F(\lambda) flux ratio. Our calibration is based on spectral energy distributions (SEDs) from the PEGASE stellar evolutionary synthesis model and the effects of dust (absorption and scattering) as calculated from our Monte Carlo radiative transfer model. We tested the attenuations predicted from this method for the Balmer emission lines of a sample starburst galaxies against those calculated using radio observations and found good agreement. The UV attenuation curves for a handful of starburst galaxies were calculated using the flux ratio method, and they compare favorably with past work. The relationship between Att(\lambda) and F(IR)/F(\lambda) is almost completely independent of the assumed dust properties (grain type, distribution, and clumpiness). For the UV, the relationship is also independent of the assumed stellar properties (age, metallicity, etc) accept for the case of very old burst populations. However at longer wavelengths, the relationship is dependent on the assumed stellar properties.Comment: accepted by the ApJ, 18 pages, color figures, b/w version at http://mips.as.arizona.edu/~kgordon/papers/fr_method.htm

Fluctuation Spectrum from a Scalar-Tensor Bimetric Gravity Theory

Predictions of the CMB spectrum from a bimetric gravity theory (gr-qc/0101126) are presented. The initial inflationary period in BGT is driven by a vanishingly small speed of gravitational waves v_g in the very early universe. This initial inflationary period is insensitive to the choice of scalar field potential and initial values of the scalar field. After this initial period of inflation, v_g will increase rapidly and the effects of a potential will become important. We show that a quadratic potential introduced into BGT yields an approximately flat spectrum with inflation parameters: n_s=0.98, n_t=-0.027, alpha_s=-3.2e-4 and alpha_t=-5.0e-4, with r >= 0.014.Comment: 14 pages, uses amsmath, amssym

PROGRAMAS DE INFORMÁTICA PARA COMPARAÇÕES ENTRE CORRELAÇÕES: AMOSTRAS DEPENDENTES

Existe una variedad de técnicas para probar las diferencias entre correlaciones dependientes que no están disponibles en los programas estadísticos estándar para el investigador. Se presentan ejemplos de estas técnicas para evaluar diferentes hipótesis dentro del contexto de correlaciones en muestras dependientes, junto con programas informáticos interactivos, de fácil uso y libre distribución.There are a variety of techniques for testing the differences between dependent correlations that are not available using the standard statistical software packages.  Examples of these techniques for examining different hypotheses within the dependent correlational realm are presented along with the output and interpretation from easily attainable, user-friendly, interactive software.Existe uma variedade de técnicas para provar as diferencias entre correlações dependentes que não estão disponíveis nos programas estatísticos familiares para o investigador. Apresentam-se exemplos destas técnicas para avaliar diferentes hipóteses dentro do contexto de correlações em amostras dependentes, junto com programas de informáticas interativos, amigáveis e livre distribuição

Aggregation of SiC-X Grains in Supernova Ejecta

We present a model for the formation of silicon carbide aggregates within the expanding and cooling supernova remnant. Many SiC-X grains have been found to be aggregates of smaller crystals which are isotopically homogenous. The initial condensation of SiC in the ejecta occurs within a interior dense shell of material which is created by a reverse shock which rebounds from the core-envelope interface. A subsequent reverse shock accelerates the grains forward, but the gas drag from the ejecta on the rapidly moving particles limits their travel distance. By observing the effects of gas drag on the travel distance of grains, we propose that supernova grain aggregates form from material that condensed in a highly localized region, which satisfies the observational evidence of isotopic homogeneity in SiC-X grains.Comment: 9 pages, 5 figures, To be published in the Astrophysical Journa