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)

Self-referential Monte Carlo method for calculating the free energy of crystalline solids

A self-referential Monte Carlo method is described for calculating the free energy of crystalline solids. All Monte Carlo methods for the free energy of classical crystalline solids calculate the free-energy difference between a state whose free energy can be calculated relatively easily and the state of interest. Previously published methods employ either a simple model crystal, such as the Einstein crystal, or a fluid as the reference state. The self-referential method employs a radically different reference state; it is the crystalline solid of interest but with a different number of unit cells. So it calculates the free-energy difference between two crystals, differing only in their size. The aim of this work is to demonstrate this approach by application to some simple systems, namely, the face centered cubic hard sphere and Lennard-Jones crystals. However, it can potentially be applied to arbitrary crystals in both bulk and confined environments, and ultimately it could also be very efficient

Inexact Iterations for the Approximation of Eigenvalues and Eigenvectors

The algorithms of inverse iteration and Rayleigh quotient iteration for approximating an eigenpair of a matrix contain a step in which a matrix-vector equation must be solved.The behaviour of these algorithms is analysed if this equation is solved only approximately with a known tolerance

The approximation of an eigenvector by ritzvectors

Eigenvalue algorithms belonging to the class of the Rayleigh-Ritz methods (Krylov-space methods for example) use `projections' on subspaces to produce approximations to eigenvalues and eigenvectors of a matrix. This paper focuses on the eigenvectors. Two angles are important when considering an eigenvector: the angle between the eigenvector and the best approximating Ritzvector and the angle between the eigenvector and the subspace involved. It is studied how an upperbound for the first angle can be expressed in terms of the second one. This results in a theoretical expression for the case of two-dimensional subspaces and a conjecture for higher dimensional subspaces supported by numerical experiments.Matrices;Eigenvalues;Vectorization;Ritz Values;mathematics

Safety and Effectiveness of Struvite from Black Water and Urine as a Phosphorus Fertilizer

To ensure food supply, phosphorus must be recycled, for which an appealing method is using struvite fertilizer from human excreta. One struvite from black water and another from urine were assessed for safety under Dutch regulations, and for effectiveness as P fertilizer in a maize field experiment and a literature review. Both struvites contained 12% P, 12% Mg, 6% N, and 0.5-1.5% of several micronutrients. Struvites did not exceed Dutch regulations for heavy metals or pathogens, and based on literature, organic toxins should be far below regulatory limits. In this study and 18 others, struvite appears to have similar effectiveness to soluble fertilizer. Early in the season, 200 kg P2O5 ha-1 of black water struvite and soluble phosphorus improved maize performance (

'n Beroepsplig om te genees!

The rules of South African law are analysed, especially any possible rules whic.h may impose a duty upon a medical practitioner to heal in cases where the patient refuses treatment. The conclusion is reached that a refusal of medical treatment expressed on behalf of a minor child or an unconscious patient might safely be ignored by a medical practitioner. but that an express refusal by a major patient of full legal capacity should be heeded. It is also concluded that. according to South Afri<;:an law, there rests no legal duty upon a medical practitionerto treat a patient where such treatment - even if necessary to save the patient's life - is refused by the patient himself. Therefore, where the conditions imposed by a Jehovah's Witness preclude a medical practitioner from practising good medicine, he should refuse the case

Comparison of Dissipative Particle Dynamics and Langevin thermostats for out-of-equilibrium simulations of polymeric systems

In this work we compare and characterize the behavior of Langevin and Dissipative Particle Dynamics (DPD) thermostats in a broad range of non-equilibrium simulations of polymeric systems. Polymer brushes in relative sliding motion, polymeric liquids in Poiseuille and Couette flows, and brush-melt interfaces are used as model systems to analyze the efficiency and limitations of different Langevin and DPD thermostat implementations. Widely used coarse-grained bead-spring models under good and poor solvent conditions are employed to assess the effects of the thermostats. We considered equilibrium, transient, and steady state examples for testing the ability of the thermostats to maintain constant temperature and to reproduce the underlying physical phenomena in non-equilibrium situations. The common practice of switching-off the Langevin thermostat in the flow direction is also critically revisited. The efficiency of different weight functions for the DPD thermostat is quantitatively analyzed as a function of the solvent quality and the non-equilibrium situation.Comment: 12 pages, introduction improved, references added, to appear in Phys. Rev.

Huldigingswoord

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