Elemental Abundance Ratios in Stars of the Outer Galactic Disk. II. Field Red Giants

We summarize a selection process to identify red giants in the direction of the southern warp of the Galactic disk, employing VI_C photometry and multi-object spectroscopy. We also present results from follow-up high-resolution, high-S/N echelle spectroscopy of three field red giants, finding [Fe/H] values of about -0.5. The field stars, with Galactocentric distances estimated at 10 to 15 kpc, support the conclusion of Yong, Carney, & de Almeida (2005) that the Galactic metallicity gradient disappears beyond R_GC values of 10 to 12 kpc for the older stars and clusters of the outer disk. The field and cluster stars at such large distances show very similar abundance patterns, and, in particular, all show enhancements of the "alpha" elements O, Mg, Si, Ca, and Ti and the r-process element Eu. These results suggest that Type II supernovae have been significant contributors to star formation in the outer disk relative to Type Ia supernovae within the past few Gyrs. We also compare our results with those available for much younger objects. The limited results for the H II regions and B stars in the outer disk also suggest that the radial metallicity gradient in the outer disk is shallow or absent. The much more extensive results for Cepheids confirm these trends, and that the change in slope of the metallicity gradient may occur at a larger Galactocentric distance than for the older stars and clusters. However, the younger stars also show rising alpha element enhancements with increasing R_GC, at least beyond 12 kpc. These trends are consistent with the idea of a progressive growth in the size of the Galactic disk with time, and episodic enrichment by Type II supernovae as part of the disk's growth. [Abridged]Comment: Accepted for publication in A

The Economics of Leveraged Takeovers

Financing of hostile takeovers has emerged as a central issue in the ongoing debate concerning corporate takeovers. Concomitant with the increase in the dollar value of takeovers during the past few years has been a significant increase in the percentage of tender offer financing accounted for by bank borrowing and the issuance of high yield debt, (that is, debt securities which are rated below Standard and Poor\u27s BBB-or Moody\u27s Baa3), hereafter referred to as junk bonds, have accounted for an increasingly greater percentage of takeover financing. This Article examines these concerns about debt financing of corporate takeovers from an efficient markets perspective. The efficient-market hypothesis has important implications for public policy toward corporate takeovers. Because a takeover involves the payment of premiums to target shareholders, prospective bidders must perceive a way to raise the target firm\u27s value, that is, the discounted cash flow of the target firm. We argue that junk-bond financing facilitates takeovers which in turn promote economic efficiency. Critics of leveraged takeovers, in our view, exaggerate the risks associated with these transactions, and in some instances, misunderstand the nature of corporate debt. After illustrating the structure of a leveraged takeover with an analysis of Mesa Petroleum\u27s unsuccessful bid for Unocal, this Article seeks to correct the misperceptions about corporate debt with a discussion of the economics of corporate leverage. Finally, we use the Mesa-Unocal case to evaluate the claims made by critics of leveraged takeovers

Benefits of Lending Relationships in Public Debt Markets: Empirical Evidence from the Commercial Paper Market

There is a large body of literature on the benefits of established lending relationships with banks, which is an intermediated debt market. We extend the literature by testing for benefits from direct lending relationships in the commercial paper market, which is a public debt market. Diamond (1991) suggests that firms access public debt markets when they have enough reputation to no longer require the close monitoring by banks. Using daily rate data for dealer-placed and directly placed commercial paper, we find that the year-end liquidity squeeze is less pronounced in the directly placed commercial paper than in the dealer-placed commercial paper, consistent with the existence of benefits from direct lending relationships in this public debt market

Wildlife in Airport Environments: Chapter 9 Managing Airport Stormwater to Reduce Attraction to Wildlife

An airport is a component of the landscape, contributing to and subject to local- and landscapelevel factors that affect wildlife populations and the hazards that these species pose to aviation (Blackwell et al. 2009, Martin et al. 2011). Water resources at and near an airport, in the form of both surface water and contained runoff, are recognized by the Federal Aviation Administration (FAA) as potential attractants to wildlife that pose hazards to aviation safety (FAA 2007). Surface water, including aboveground stormwater detention/retention facilities (see U.S. Environmental Protection Agency 2006), can represent a substantial proportion of the area within siting criteria for U.S. airports. An analysis of water coverage at 49 certificated airports (FAA 2004) revealed that surface water composed on average 6.0% (standard deviation [SD] = 10.4%, range = 0.04-48.3%; B. F. Blackwell, unpublished data) of the area within the 3-km [lo9-mile] FAA siting criteria (X = 275 ha, SD = 511 ha). A recent analysis of bird-aircraft strike data for avian species involved in at least 50 total strikes reported to the FAA (1990-2008; summarized in FAA 2011) revealed that 13 of the 52 species (25%) have foraging and breeding ecologies primarily associated with water (Blackwell et al. 2013). Moreover, these 13 species were responsible for \u3e 51% of damaging strikes (Dolbeer et al. 2000, DeVault et al. 2011) during this period

Rubidium and lead abundances in giant stars of the globular clusters M4 and M5

We present measurements of the neutron-capture elements Rb and Pb for bright giants in the globular clusters M4 and M5. The clusters are of similar metallicity ([Fe/H] = -1.2) but M4 is decidedly s-process enriched relative to M5: [Ba/Fe] = +0.6 for M4 but 0.0 for M5. The Rb and Pb abundances were derived by comparing synthetic spectra with high-resolution, high signal-to-noise ratio spectra obtained with MIKE on the Magellan telescope. Abundances of Y, Zr, La, and Eu were also obtained. In M4, the mean abundances from 12 giants are [Rb/Fe] = 0.39 +/- 0.02 (sigma = 0.07), [Rb/Zr] = 0.17 +/- 0.03 (sigma = 0.08), and [Pb/Fe] = 0.30 +/- 0.02 (sigma = 0.07). In M5, the mean abundances from two giants are [Rb/Fe] = 0.00 +/- 0.05 (sigma = 0.06), [Rb/Zr] = 0.08 +/- 0.08 (sigma = 0.11), and [Pb/Fe] = -0.35 +/- 0.02 (sigma = 0.04). Within the measurement uncertainties, the abundance ratios [Rb/Fe], [Pb/Fe] and [Rb/X] for X = Y, Zr, La are constant from star-to-star in each cluster and none of these ratios are correlated with O or Na abundances. While M4 has a higher Rb abundance than M5, the ratios [Rb/X] are similar in both clusters indicating that the nature of the s-products are very similar for each cluster but the gas from which M4's stars formed had a higher concentration of these products.Comment: Accepted for publication in Ap

Integration of Genome and Chromatin Structure with Gene Expression Profiles To Predict c-MYC Recognition Site Binding and Function

The MYC genes encode nuclear sequence specific–binding DNA-binding proteins that are pleiotropic regulators of cellular function, and the c-MYC proto-oncogene is deregulated and/or mutated in most human cancers. Experimental studies of MYC binding to the genome are not fully consistent. While many c-MYC recognition sites can be identified in c-MYC responsive genes, other motif matches—even experimentally confirmed sites—are associated with genes showing no c-MYC response. We have developed a computational model that integrates multiple sources of evidence to predict which genes will bind and be regulated by MYC in vivo. First, a Bayesian network classifier is used to predict those c-MYC recognition sites that are most likely to exhibit high-occupancy binding in chromatin immunoprecipitation studies. This classifier incorporates genomic sequence, experimentally determined genomic chromatin acetylation islands, and predicted methylation status from a computational model estimating the likelihood of genomic DNA methylation. We find that the predictions from this classifier are also applicable to other transcription factors, such as cAMP-response element-binding protein, whose binding sites are sensitive to DNA methylation. Second, the MYC binding probability is combined with the gene expression profile data from nine independent microarray datasets in multiple tissues. Finally, we may consider gene function annotations in Gene Ontology to predict the c-MYC targets. We assess the performance of our prediction results by comparing them with the c-myc targets identified in the biomedical literature. In total, we predict 460 likely c-MYC target genes in the human genome, of which 67 have been reported to be both bound and regulated by MYC, 68 are bound by MYC, and another 80 are MYC-regulated. The approach thus successfully identifies many known c-MYC targets and suggests many novel sites. Our findings suggest that to identify c-MYC genomic targets, integration of different data sources helps to improve the accuracy

Short-term biotic removal of dissolved organic nitrogen (DON) compounds from soil solution and subsequent mineralisation in contrasting grassland soils

Cycling of low molecular weight dissolved organic nitrogen compounds constitutes an important component of soil organic matter turnover in soils. We determined how rapidly grassland soils can cycle urea, compared to the amino acid l-alanine, and the peptide l-trialanine. Using naturally occurring concentrations of 14C-labelled compounds the rates of removal from soil solution and subsequent mineralisation were measured. Biotic removal of all three compounds and subsequent mineralisation to CO2 occurred within minutes. This research has demonstrated, for the first time, the potential for rapid removal of urea at low concentrations by the soil microbial biomass

Far Infrared Prperties of M Dwarfs

We report the mid- and far-infrared properties of nearby M dwarfs. Spitzer/MIPS measurements were obtained for a sample of 62 stars at 24 um, with subsamples of 41 and 20 stars observed at 70 um and 160 um respectively. We compare the results with current models of M star photospheres and look for indications of circumstellar dust in the form of significant deviations of K-[24 um] colors and 70 um / 24 um flux ratios from the average M star values. At 24 um, all 62 of the targets were detected; 70 um detections were achieved for 20 targets in the subsample observed; and no detections were seen in the 160 um subsample. No clear far-infrared excesses were detected in our sample. The average far infrared excess relative to the photospheric emission of the M stars is at least four times smaller than the similar average for a sample of solar-type stars. However, this limit allows the average fractional infrared luminosity in the M-star sample to be similar to that for more massive stars. We have also set low limits for the maximum mass of dust possible around our stars.Comment: 28 pages, 4 figures, to be published in The Astrophysical Journa

Rubidium in Metal-Deficient Disk and Halo Stars

We report the first extensive study of stellar Rb abundances. High-resolution spectra have been used to determine, or set upper limits on, the abundances of this heavy element and the associated elements Y, Zr, and Ba in 44 dwarfs and giants with metallicities spanning the range -2.0 <[Fe/H] < 0.0. In metal-deficient stars Rb is systematically overabundant relative to Fe; we find an average [Rb/Fe] of +0.21 for the 32 stars with [Fe/H] < -0.5 and measured Rb. This behavior contrasts with that of Y, Zr, and Ba, which, with the exception of three new CH stars (HD 23439A and B and BD +5 3640), are consistently slightly deficient relative to Fe in the same stars; excluding the three CH stars, we find the stars with [Fe/H] < -0.5 have average [Y/Fe], [Zr/Fe], and [Ba/Fe] of --0.19 (24 stars), --0.12 (28 stars), and --0.06 (29 stars), respectively. The different behavior of Rb on the one hand and Y, Zr, and Ba on the other can be attributed in part to the fact that in the Sun and in these stars Rb has a large r-process component while Y, Zr, and Ba are mostly s-process elements with only small r-process components. In addition, the Rb s-process abundance is dependent on the neutron density at the s-processing site. Published observations of Rb in s-process enriched red giants indicate a higher neutron density in the metal-poor giants. These observations imply a higher s-process abundance for Rb in metal-poor stars. The calculated combination of the Rb r-process abundance, as estimated for the stellar Eu abundances, and the s-process abundance as estimated for red giants accounts satisfactorily for the observed run of [Rb/Fe] with [Fe/H].Comment: 23 pages, 5 tables, 7 figure

Remote Sensing and Estimation

Contains table of contents for Section 4, and reports on six research projects.MIT Lincoln Laboratory Agreement CX-19383MIT Lincoln Laboratory Agreement BX-6178MIT Lincoln Laboratory Agreement BX-6433National Aeronautics and Space Administration/Goddard Space Flight Center Grant NAS5-31376National Aeronautics and Space Administration/Goddard Space Flight Center Grant NAG5-10MIT Leaders for Manufacturing Progra