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排序方式: 共有210条查询结果,搜索用时 15 毫秒
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Johnson WL Kaltenboeck G Demetriou MD Schramm JP Liu X Samwer K Kim CP Hofmann DC 《Science (New York, N.Y.)》2011,332(6031):828-833
The development of metal alloys that form glasses at modest cooling rates has stimulated broad scientific and technological interest. However, intervening crystallization of the liquid in even the most robust bulk metallic glass-formers is orders of magnitude faster than in many common polymers and silicate glass-forming liquids. Crystallization limits experimental studies of the undercooled liquid and hampers efforts to plastically process metallic glasses. We have developed a method to rapidly and uniformly heat a metallic glass at rates of 10(6) kelvin per second to temperatures spanning the undercooled liquid region. Liquid properties are subsequently measured on millisecond time scales at previously inaccessible temperatures under near-adiabatic conditions. Rapid thermoplastic forming of the undercooled liquid into complex net shapes is implemented under rheological conditions typically used in molding of plastics. By operating in the millisecond regime, we are able to "beat" the intervening crystallization and successfully process even marginal glass-forming alloys with very limited stability against crystallization that are not processable by conventional heating. 相似文献
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Background
Inkjet micropatterning is a versatile deposition technique with broad applications in numerous fields. However, its application in plant science is largely unexplored. Leaf expansion is one of the most important parameters in the field of plant science and many methods have been developed to examine differential expansion rates of different parts of the leaf lamina. Among them, methods based on the tracking of natural landmarks through digital imaging require a complicated setup in which the leaf must remain fixed and under tension. Furthermore, the resolution is limited to that of the natural landmarks, which are often difficult to find, particularly in young leaves. To study the fine scale expansion dynamics of the leaf lamina using artificial landmarks it is necessary to place small, noninvasive marks on a leaf surface and then recover the location of those marks after a period of time. 相似文献25.
Konrad Mengel 《植物养料与土壤学杂志》1986,149(6):674-690
Turnover in soil and yield response of phosphate rock containing fertilizers Solubility of phosphate rocks is the better the higher the carbonate substitution in the given phosphate rock type. From the soil factors, pH is of importance. At soil pH < 5 phosphate rocks are fairly soluble and their yield effect equals that of fully processed fertilizers. In a soil pH range from 5 to 7, pH does not play such a decisive role as has been assumed. Other soil factors such as H+ buffer power of soil, Ca2+ and particularly the phosphate concentration in the soil solution are equally relevant for phosphate rock dissolution. The evaluation of numerous field experiments provided evidence that in the above cited pH range fully processed fertilizer phosphates are superior to phosphate rock containing fertilizers with regard to phosphate uptake, yield formation, and phosphate recovery. Also the residual effect of rock phosphate is poorer than that of fully processed phosphate fertilizers. There is some evidence that phosphate rocks show a relatively good response on deep rooting soils which allow a vigorous root growth and on soils with a sufficiently high level of soil moisture. In a soil pH range > 5 rock phosphate containing fertilizer are not suitable for maintenance fertilization, since under such conditions the phosphate concentration in the soil solution is relatively high thus suppressing the dissolution of phosphate rock. 相似文献
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Rebecca Lochmann Harold Phillips Konrad Dabrowski Regis Moreau 《Journal of the World Aquaculture Society》2001,32(2):202-209
A 12-wk feeding trial was conducted in a flow-through system to determine whether juvenile golden shiner Notemigonus crysoleucas have a dietary requirement for ascorbic acid. Triplicate groups of 30 fish each weighing 0.44 g initially were fed semi-purified (casein) diets supplemented with 0 or 250 mg ascorbic acid/kg, or practical (fish meal) diets supplemented with 0 or 250 mg ascorbic acid/kg. The form of ascorbic acid used was L-ascorbyl-2-polyphosphate. Survival was higher in fish fed the semi-purified diet with 250 mg ascorbic acid/kg than in those fed the unsupplemented semi-purified diet, while weight gain did not differ between treatments. Weight gain was higher in fish fed the practical (fish meal) diet supplemented with 250 mg ascorbic acid/kg than in those fed the unsupplemented practical diet, while survival did not differ between treatments. No other signs of ascorbic acid deficiency were observed, but fish fed the casein diets had skin and fin erosion indicative of a possible bacterial infection. Whole-body concentrations of ascorbic acid (total, reduced, and percent of reduced ascorbic acid) were higher in fish fed semi-purified or practical diets supplemented with 250 mg ascorbic acid/kg than in fish fed unsupplemented diets. Golden shiners appear to require a dietary source of ascorbic acid for growth or survival, depending on experimental conditions. The two main differences in the study were in diet composition (semi-purified versus practical diets) and apparent health status of fish fed the different diet types. Additional studies are needed to define requirements further. 相似文献
28.
Publishers Note
Publisher's Announcement 相似文献29.
We report a new mechanism of self-organization that can lead to robust surface ordering. We have quantitatively analyzed the thermal motion of holes created by sulfur atoms in a silver monolayer on a ruthenium surface, which we observed in real time with scanning tunneling microscopy. We find that the stability of the array of holes is determined by the arrangement and structure of misfit dislocations in the film. 相似文献
30.
An agent-based approach to modeling impacts of agricultural policy on land use, biodiversity and ecosystem services 总被引:1,自引:1,他引:0
Mark Brady Christoph Sahrbacher Konrad Kellermann Kathrin Happe 《Landscape Ecology》2012,27(9):1363-1381
We present extensions to the agent-based agricultural policy simulator (AgriPoliS) model that make it possible to simulate the consequences of agricultural policy reform on farmers?? land use decisions and concomitant impacts on landscape mosaic, biodiversity and ecosystem services in a real agricultural region. An observed population of farms is modelled as a multi-agent system where individual farm-agent behaviour and their interactions??principally competition for land??are defined through an optimization framework with land use and landscape impacts resulting as emergent properties of the system. The model is calibrated to real data on the farms and the landscape to be studied. We illustrate the utility of the model by evaluating the potential impacts of three alternative frameworks for the European Union Common Agricultural Policy (CAP) on landscape values in two marginal agricultural regions. Mosaic value was found to be sensitive to the choice of policy scheme in one of the landscapes, whereas significant trade-offs were shown to occur in terms of species richness by habitat and species composition at the landscape scale in both regions. The relationship between food production and other ecosystem services was found to be multifaceted. Thus illustrating the difficulty of achieving landscape goals in a particular region with simple or general land management rules (such as the current rules attached to CAPs direct payments). Given the scarcity of funding for conservation, the level and conditions for allocating direct payments are, potentially, of great importance for preserving landscape values in marginal agricultural regions (subject to levels of other support). 相似文献