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排序方式: 共有1453条查询结果,搜索用时 15 毫秒
101.
Salt marsh ecosystems in Louisiana are at high risk of an oil contamination event while remediation of these systems is mainly limited to intrinsic bioremediation due to the physical sensitivity of salt marshes. This study investigated both the intrinsic and nutrient enhanced rates of crude oil degradation both in microcosm and core studies. In addition, limiting elements, loading rates and optimum nitrogen forms (NH 4 + or NO 3 - ) were determined. Salt marshes have relatively low intrinsic degradation rates (0–3.9% day-1) of the alkane component (C11-C44) but high rates (8–16% day-1) of degradation of the polycyclic aromatic hydrocarbon (PAH) fraction (naphthalene, C1, and C2-Naphthalene and Phenanthrene, C1, and C2-Phenanthrene). Additions of nitrogen statistically enhanced degradation of many alkanes and total PAHs while naturally present phosphorous was found to be sufficient. Nitrogen was found to be most effective if applied as NH 4 + in the range of 100-500-N mg kg-1 of soil producing a pore water range of 100-670-N mg L-1. Core studies indicate that similar trends are observed when applying fertilizers to intact portions of salt marsh. 相似文献
102.
Teschner D Borsodi J Wootsch A Révay Z Hävecker M Knop-Gericke A Jackson SD Schlögl R 《Science (New York, N.Y.)》2008,320(5872):86-89
Alkynes can be selectively hydrogenated into alkenes on solid palladium catalysts. This process requires a strong modification of the near-surface region of palladium, in which carbon (from fragmented feed molecules) occupies interstitial lattice sites. In situ x-ray photoelectron spectroscopic measurements under reaction conditions indicated that much less carbon was dissolved in palladium during unselective, total hydrogenation. Additional studies of hydrogen content using in situ prompt gamma activation analysis, which allowed us to follow the hydrogen content of palladium during catalysis, indicated that unselective hydrogenation proceeds on hydrogen-saturated beta-hydride, whereas selective hydrogenation was only possible after decoupling bulk properties from the surface events. Thus, the population of subsurface sites of palladium, by either hydrogen or carbon, governs the hydrogenation events on the surface. 相似文献
103.
Slow temporal variations in Earth's magnetic field originate in the liquid outer core. We analyzed the evolution of nonaxisymmetric magnetic flux at the core surface over the past 400 years. We found that the most robust feature is westward motion at 17 kilometers per year, in a belt concentrated around the equator beneath the Atlantic hemisphere. Surprisingly, this motion is dominated by a single wavenumber and persists throughout the observation period. This phenomenon could be produced by an equatorial jet of core fluid, by hydromagnetic wave propagation, or by a combination of both. Discrimination between these mechanisms would provide useful constraints on the dynamics of Earth's core. 相似文献
104.
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
105.
Nadeau JH Balling R Barsh G Beier D Brown SD Bucan M Camper S Carlson G Copeland N Eppig J Fletcher C Frankel WN Ganten D Goldowitz D Goodnow C Guenet JL Hicks G Hrabe de Angelis M Jackson I Jacob HJ Jenkins N Johnson D Justice M Kay S Kingsley D Lehrach H Magnuson T Meisler M Poustka A Rinchik EM Rossant J Russell LB Schimenti J Shiroishi T Skarnes WC Soriano P Stanford W Takahashi JS Wurst W Zimmer A;International Mouse Mutagenesis Consortium 《Science (New York, N.Y.)》2001,291(5507):1251-1255
106.
Blanchet GB Fincher CR Jackson CL Shah SI Gardner KH 《Science (New York, N.Y.)》1993,262(5134):719-721
The formation of high-quality thin films of polytetrafluoroethylene (PTFE) is important in many applications ranging from material reinforcement to molecular electronics. Laser ablation, a technique widely used to deposit a variety of inorganic materials, can also be used as a simple and highly versatile method for forming thin polymer films. The data presented show that PTFE films can be produced on various supports by the evaporation of a solid PTFE target with a pulsed ultraviolet laser. The composition of the ablation plume suggests that PTFE ablation and subsequent film formation occur by way of a laser-induced pyrolitic decomposition with subsequent repolymerization. The polymer films produced by this method are composed of amorphous and highly crystalline regions, the latter being predominantly in a chain-folded configuration with the molecular axis aligned parallel to the substrate surface. 相似文献
107.
Jackson HH 《Science (New York, N.Y.)》1914,39(1006):534-535
108.
Posttranslational modifications of the histone octamer play important roles in regulating responses to DNA damage. Here, we reveal that Saccharomyces cerevisiae Rtt109p promotes genome stability and resistance to DNA-damaging agents, and that it does this by functionally cooperating with the histone chaperone Asf1p to maintain normal chromatin structure. Furthermore, we show that, as for Asf1p, Rtt109p is required for histone H3 acetylation on lysine 56 (K56) in vivo. Moreover, we show that Rtt109p directly catalyzes this modification in vitro in a manner that is stimulated by Asf1p. These data establish Rtt109p as a member of a new class of histone acetyltransferases and show that its actions are critical for cell survival in the presence of DNA damage during S phase. 相似文献
109.
110.
Effects of basal debris on glacier flow 总被引:1,自引:0,他引:1
Iverson NR Cohen D Hooyer TS Fischer UH Jackson M Moore PL Lappegard G Kohler J 《Science (New York, N.Y.)》2003,301(5629):81-84
Glacier movement is resisted partially by debris, either within glaciers or under glaciers in water-saturated layers. In experiments beneath a thick, sliding glacier, ice containing 2 to 11% debris exerted shear traction of 60 to 200 kilopascals on a smooth rock bed, comparable to the total shear traction beneath glaciers and contrary to the usual assumption that debris-bed friction is negligible. Imposed pore-water pressure that was 60 to 100% of the normal stress in a subglacial debris layer reduced shear traction on the debris sufficiently to halt its deformation and cause slip of ice over the debris. Slip resistance was thus less than debris shearing resistance. 相似文献