Water quality changes in sudbury area lakes: A comparison of synoptic surveys in 1974–1976 and 1981–1983     

W. Keller  T. Roger Pitblado 《Water, air, and soil pollution》1986,29(3):285-296

A survey was carried out during the summers of 1981–1983 to re-sample 209 Sudbury, Ontario area lakes originally sampled in 1974–1976. Between the study periods, SO₂ emissions from the Sudbury metal smelters were reduced by ～ 50%. Observed water quality changes included increases in pH and decreases in SO₄ ^?, Ni, and Cu concentrations. The degree of observed changes showed a general relationship to distance from the Sudbury smelters, indicating that reduced contaminant deposition from Sudbury sources was responsible for the observed improvements. Although changes in water quality have occurred in many Sudbury area lakes over the course of this study, many lakes remain acidic and metal-contaminated.  相似文献   

Non-Fermi liquid metal without quantum criticality     

Pfleiderer C  Böni P  Keller T  Rössler UK  Rosch A 《Science (New York, N.Y.)》2007,316(5833):1871-1874

A key question in condensed matter physics concerns whether pure three-dimensional metals can always be described as Fermi liquids. Using neutron Larmor diffraction to overcome the traditional resolution limit of diffraction experiments, we studied the lattice constants of the cubic itinerant-electron magnet manganese silicide (MnSi) at low temperatures and high pressures. We were able to resolve the nature of the phase diagram of MnSi and to establish that a stable, extended non-Fermi liquid state emerges under applied pressure without quantum criticality. This suggests that new forms of quantum order may be expected even far from quantum phase transitions.  相似文献   

The Eocene/Oligocene boundary event in the deep sea     

Corliss BH  Aubry MP  Berggren WA  Fenner JM  Keigwin LD  Keller G 《Science (New York, N.Y.)》1984,226(4676):806-810

Analysis of middle Eocene to early, Oligocene calcareous and siliceous microfossils shows gradual biotic changes with no massive extinction event across the Eocene/Oligocene boundary. Biotic changes in the late Paleogene appear to reflect changing paleoclimatic and paleoceanographic conditions and do not support suggestions of a catastrophic biotic event caused by a bolide impact at the Eocenel Oligocene boundary.  相似文献   

A predator unmasked: life cycle of Bdellovibrio bacteriovorus from a genomic perspective     

Rendulic S  Jagtap P  Rosinus A  Eppinger M  Baar C  Lanz C  Keller H  Lambert C  Evans KJ  Goesmann A  Meyer F  Sockett RE  Schuster SC 《Science (New York, N.Y.)》2004,303(5658):689-692

Predatory bacteria remain molecularly enigmatic, despite their presence in many microbial communities. Here we report the complete genome of Bdellovibrio bacteriovorus HD100, a predatory Gram-negative bacterium that invades and consumes other Gram-negative bacteria. Its surprisingly large genome shows no evidence of recent gene transfer from its prey. A plethora of paralogous gene families coding for enzymes, such as hydrolases and transporters, are used throughout the life cycle of B. bacteriovorus for prey entry, prey killing, and the uptake of complex molecules.  相似文献   

Ecological effects of a major oil spill on panamanian coastal marine communities   总被引：1，自引：0，他引：1  

Jackson JB  Cubit JD  Keller BD  Batista V  Burns K  Caffey HM  Caldwell RL  Garrity SD  Getter CD  Gonzalez C  Guzman HM  Kaufmann KW  Knap AH  Levings SC  Marshall MJ  Steger R  Thompson RC  Weil E 《Science (New York, N.Y.)》1989,243(4887):37-44

In 1986 more than 8 million liters of crude oil spilled into a complex region of mangroves, seagrasses, and coral reefs just east of the Caribbean entrance to the Panama Canal. This was the largest recorded spill into coastal habitats in the tropical Americas. Many population of plants and animals in both oiled and unoiled sites had been studied previously, thereby providing an unprecedented measure of ecological variation before the spill. Documenation of the spread of oil and its biological begun immediately. Intertidal mangroves, algae, and associated invertebrates were covered by oil and died soon after. More surprisingly, there was also extensive mortality of shallow subtidal reef corals and infauna of seagrass beds. After 1.5 years only some organisms in areas exposed to the open sea have recovered.  相似文献   

Turning down the heat: design and mechanism in solid-state synthesis     

Stein A  Keller SW  Mallouk TE 《Science (New York, N.Y.)》1993,259(5101):1558-1564

Solid-state compounds have historically been prepared through high-temperature solid-solid reactions. New mechanistic understanding of these reactions suggests possible routes to metastable compositions and structures as well as to thermodynamically stable, low-temperature phases that decompose at higher temperatures. Intermediate-temperature synthetic techniques, including flux and hydrothermal methods, as well as low-temperature intercalation and coordination reactions, have recently been developed and have been used to prepare unprecedented materials with interesting electronic, optical, and catalytic properties. The trend in modern solid-state synthesis resembles increasingly the approach used in small-molecule chemistry, in the sense that attention to reaction mechanism and the use of molecular building blocks result in an ability to prepare new materials of designed structure.  相似文献   

Double vision     

Keller G 《Science (New York, N.Y.)》1886,7(171):440

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Shaping the vertebrate body plan by polarized embryonic cell movements     

Keller R 《Science (New York, N.Y.)》2002,298(5600):1950-1954

Polarized cell movements shape the major features of the vertebrate body plan during development. The head-to-tail body axis of vertebrates is elongated in embryonic stages by "convergent extension" tissue movements. During these movements cells intercalate between one another transverse to the elongating body axis to form a narrower, longer array. Recent discoveries show that these polarized cell movements are controlled by homologs of genes that control the polarity of epithelial cells in the developing wing and eye of the fruit fly, Drosophila.  相似文献   

Energy gaps and Kohn anomalies in elemental superconductors     

Aynajian P  Keller T  Boeri L  Shapiro SM  Habicht K  Keimer B 《Science (New York, N.Y.)》2008,319(5869):1509-1512

The momentum and temperature dependence of the lifetimes of acoustic phonons in the elemental superconductors lead and niobium were determined by resonant spin-echo spectroscopy with neutrons. In both elements, the superconducting energy gap extracted from these measurements was found to converge with sharp anomalies originating from Fermi-surface nesting (Kohn anomalies) at low temperatures. The results indicate electron many-body correlations beyond the standard theoretical framework for conventional superconductivity. A possible mechanism is the interplay between superconductivity and spin- or charge-density-wave fluctuations, which may induce dynamical nesting of the Fermi surface.  相似文献   

Pioneer venus radar mapper experiment     

Pettengill GH  Ford PG  Brown WE  Kaula WM  Keller CH  Masursky H  McGill GE 《Science (New York, N.Y.)》1979,203(4382):806-808

Altimetry and radar scattering data for Venus, obtained from 10 of the first 13 orbits of the Pioneer Venus orbiter, have disclosed what appears to be a rift valley having vertical relief of up to 7 kilometers, as well as a neighboring, gently rolling plain. Planetary oblateness appears unlikely to exceed 1/2500 and may be substantially smaller.  相似文献