Mass mortality and extraterrestrial impacts

The discovery of iridium enrichment at the Cretaceous/Tertiary boundary resulted in formulation of hypothesis of a cometary or asteroid impact as the cause of the biological extinctions at this boundary. Subsequent discoveries of geochemical anomalies at major stratigraphic boundaries like the Precambrian/Cambrian, Permian/Triassic, Middle/Late Jurassic, resulted in the application of similar extraterrestrial impact theories to explain biological changes at these boundaries. Until recently the major physical evidence, as is the location of the impact crater site, to test the impact induced biological extinction was lacking. The diameter of such a crater would be in the range of 60 to 100 km. The recent discovery of the first impact crater in the ocean provide the first opportunity to test the above theory. The crater, named Montagnais and located on the outer shelf off Nova Scotia, Canada, has a minimum diameter of 42 km, with some evidence to a diameter of more than 60 km. At the Montagnais impact site, micropaleontological analysis of the uppermost 80 m of the fall-back breccia represented by a mixture of pre-impact sediments and basement rocks which fills the crater and of the basal 50 m of post-impact marine sediments which overly the impact deposits, revealed presence of diversified foraminiferal and nannoplankton assemblages. The sediments which are intercalated within the uppermost part of the fall-back breccia, had to be deposited before the meteorite impact. The post-impact deposits were laid down almost immediately after the impact as also supported by the micropaleontological data. In conclusion, micropaleontological studies of sediments from the first submarine impact crater site identified in the ocean did not reveal any mass extinction or significant biological changes at the impact site or in the proximal deep ocean basin

Influence of Magnetic Field on Effective Electron-Electron Interactions in a Copper Wire

We have measured in a copper wire the energy exchange rate between quasiparticles as a function of the applied magnetic field. We find that the effective electron-electron interaction is strongly modified by the magnetic field, suggesting that magnetic impurities play a role on the interaction processes.Comment: latex anthore.tex, 8 files, 6 figures, 7 pages in: Proceedings of the XXXVIth Rencontres de Moriond `Electronic Correlations: From Meso- to Nano-physics' Les Arcs, France January 20-27, 2001 [SPEC-S01/027

Marketing Methods and Income Generation amongst Small-Scale Farmers in Two Communal Areas of Kwazulu-Natal, South Africa

High transaction costs are detrimental to the efficient operation or existence of markets for inputs and outputs. The cost of information and the costs associated with the search for trade partners, distance to formal markets and contract enforcement are likely to influence the marketing of food crops. This study hypothesises that the level of income generated from food crop sales by small-scale farmers in the Impendle and Swayimana districts of KwaZulu-Natal, South Africa, is influenced by transaction costs and certain household and farm characteristics. Regression analysis shows that the depth of marketing methods is significantly influenced by transaction cost proxies such as cooperation with large commercial farmers and ownership of means of transport. Results from a block-recursive regression analysis show that the level of crop income generated is determined by the depth of marketing methods, the size of allocated arable land and off-farm income. Households with lower transaction costs, and having sizeable allocated land and off-farm income can be expected to generate higher crop income. Investment in public goods such as roads, telecommunications and an efficient legal system (to uphold commercial contracts), and farmer support services (extension, marketing information and research) would likely raise farm and non-farm income by reducing transaction costs. This would increase the effective demand for locally produced goods and services, thus contributing to rural employment and livelihoods within rural communal areas.Farm Management,

Graph Signal Processing: Overview, Challenges and Applications

Research in Graph Signal Processing (GSP) aims to develop tools for processing data defined on irregular graph domains. In this paper we first provide an overview of core ideas in GSP and their connection to conventional digital signal processing. We then summarize recent developments in developing basic GSP tools, including methods for sampling, filtering or graph learning. Next, we review progress in several application areas using GSP, including processing and analysis of sensor network data, biological data, and applications to image processing and machine learning. We finish by providing a brief historical perspective to highlight how concepts recently developed in GSP build on top of prior research in other areas.Comment: To appear, Proceedings of the IEE