Impact and extinction signatures in complete Cretaceous-Tertiary (K-T) boundary sections

The Zumaya, Caravaca and Agost sections in Spain, the El Kef section in Tunisia and the Negev (Nahal Avdat) sections in Israel are among the most continuous, expanded and complete K-T boundary sections. The distribution patterns of the planktic faunas were quantitatively analyzed in closely spaced samples across the K-T boundary in these sections, in conjuction with the geochemistry, stable isotopes, mineralogy and magnetostratigraphy. Three hundred foraminiferal specimens were randomly selected and determined. Reliable estimates for the foraminiferal productivity changes across the K-T boundary and for the 1 to 2 Ma interval preceding the K-T boundary were made from the numbers of individuals/gram of sediment corrected for the sedimentation rates (calculated from magnetic reversals and lithology). No gradual or stepwise extinction is seen below the K-T boundary nor any productivity decrease. Stable isotope analyses show a warming just after deposition of the ejecta layer, not cooling as predicted by nuclear winter scenarios, although the duration of such cooling may be too short to be observed even in these complete sections. Low REE values and cpx spherules with quench textures idential to quench-textures in diagenetically altered spherules, strongly indicate an oceanic site of (one of) the impactor(s)

Sexual hormones in Achyla. V. Properties of hormone A of Achyla bisexualis

1. The hormonal coordinating mechanism of the sexual process in Achlya is briefly reviewed. 2. A technique is described for culturing the female plant of Achlya bisexualis in sufficient quantity to furnish material for the chemical study of hormone A. 3. A modification of the biological assay for hormone A is described. 4. Many of the properties of hormone A have been determined: (a) solubilities in common organic solvents, (b) adsorption, (c) stability, (d) inactivation, and (e) reactions with certain reagents. 5. A procedure is described whereby enormous enrichment of the active principle has been achieved

On the Evolution of Product Portfolio Coherence of Cooperatives versus Corporations: An Agent-Based Analysis of the Single Origin Constraint

Agent-based methodology is adopted to analyze the relationship between governance structure and the evolution of product portfolio. A corporation and a cooperative are distinguished by the single origin constraint. The single origin constraint entails that the product requiring the inputs of the members of a cooperative will never be divested. It is es-tablished that a concentric diversification strategy results in randomly distributed clusters of related products of the product portfolio of corporations, while the single origin constraint of a cooperative is responsible for pulling all prod-ucts together in one cluster. More general, the centripetal effect of one product with infinite lifetime on portfolio com-position dominates the centrifugal effect of products with finite lifetime, regardless the number of products with finite lifetime.cooperatives;Concentric diversification;agent-based analysis;product lifetime

Notes on SCREENING DISABILITY: A Conference on Film and Disability (March 26-28, 1999, University of Iowa)

Produced by The Center on Disability Studies, University of Hawai'i at Manoa, Honolulu, Hawai'i and The School of Social Studies, The University of Texas at Dallas, Richardson, Texas for The Society for Disability Studies

Problems with the Quenched Approximation in the Chiral Limit

In the quenched approximation, loops of the light singlet meson (the $\eta'$) give rise to a type of chiral logarithm absent in full QCD. These logarithms are singular in the chiral limit throwing doubt upon the utility of the quenched approximation. In previous work, I summed a class of diagrams, leading to non-analytic power dependencies such as \cond\propto m_q^{-\delta/(1+\delta)}. I suggested, however, that these peculiar results could be redefined away. Here I give an alternative derivation of the results, based on the renormalization group, and argue that they cannot be redefined away. I discuss the evidence (or lack thereof) for such effects in numerical data.Comment: (talk given at Lattice '92), 4 pages latex, 3 postscript figures, uses espcr2.sty and psfig.tex (all included) UW/PT-92-2

Observation of a parity oscillation in the conductance of atomic wires

Using a scanning tunnel microscope or mechanically controlled break junctions, atomic contacts of Au, Pt and Ir are pulled to form chains of atoms. We have recorded traces of conductance during the pulling process and averaged these for a large amount of contacts. An oscillatory evolution of conductance is observed during the formation of the monoatomic chain suggesting a dependence on even or odd numbers of atoms forming the chain. This behaviour is not only present in the monovalent metal Au, as it has been previously predicted, but is also found in the other metals which form chains suggesting it to be a universal feature of atomic wires

Evidence for Ubiquitous High-equivalent-width Nebular Emission in z ~ 7 Galaxies: Toward a Clean Measurement of the Specific Star-formation Rate Using a Sample of Bright, Magnified Galaxies

Growing observational evidence indicates that nebular line emission has a significant impact on the rest-frame optical fluxes of z ~ 5-7 galaxies. This line emission makes z ~ 5-7 galaxies appear more massive, with lower specific star-formation rates (sSFRs). However, corrections for this line emission have been difficult to perform reliably because of huge uncertainties on the strength of such emission at z ≳ 5.5. In this paper, we present the most direct observational evidence thus far for ubiquitous high-equivalent-width (EW) [O III] + Hβ line emission in Lyman-break galaxies at z ~ 7, and we present a strategy for an improved measurement of the sSFR at z ~ 7. We accomplish this through the selection of bright galaxies in the narrow redshift window z ~ 6.6-7.0 where the Spitzer/Infrared Array Camera (IRAC) 4.5 μm flux provides a clean measurement of the stellar continuum light, in contrast with the 3.6 μm flux, which is contaminated by the prominent [O III] + Hβ lines. To ensure a high signal-to-noise ratio for our IRAC flux measurements, we consider only the brightest (H_(160) < 26 mag) magnified galaxies we have identified behind galaxy clusters. It is remarkable that the mean rest-frame optical color for our bright seven-source sample is very blue, [3.6]-[4.5] = –0.9 ± 0.3. Such blue colors cannot be explained by the stellar continuum light and require that the rest-frame EW of [O III] + Hβ is greater than 637 Å for the average source. The four bluest sources from our seven-source sample require an even more extreme EW of 1582 Å. We can also set a robust lower limit of ≳ 4 Gyr^(–1) on the sSFR of our sample based on the mean spectral energy distribution