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321.
Interceptors have been widely used in recent years in fast ferries and small high-speed leisure and commercial craft for ride and trim control, and steering. In the context of high-performance sailing yachts, they first appeared in 2008 on the yacht Ecover 3 which was dismasted while leading the Vendee Globe Challenge race. However, in spite of their popularity in power craft, few studies have been published investigating the impact of interceptors on vessel performance, and apparently none in the case of sailing yachts. In the current study, interceptors are compared with an aerodynamic device known as a Gurney flap. It is shown that interceptors are generally substantially smaller than Gurney flaps. A comprehensive experiment programme is presented exploring the impact of interceptors on the performance of an Open 60 yacht hull. Results show a marked reduction in calm-water resistance over a wide speed range, with benefits of 10–18% in the speed range between 8 and 20 knots, accompanied by reduced sinkage and trim. The gains observed are much larger than those observed in powercraft, and also substantially greater than those achievable through trim changes by moving ballast longitudinally. The benefits appear to be largely sustained in small waves. 相似文献
322.
A large-volume core sampler for sediment—muck substrates is described. The sampler can acquire a discrete sediment core of 10 cm in diameter and up to 1.5 m long. Such samplers are needed to collect the volume necessary for analysis of sediments for contaminants, bulk density, or radioactive dating. The sampler consists of a 1- to 2-m length of PVC pipe mounted below a threaded metal pipe air exhaust—intake assembly. This assembly is quick-connected to standard threaded lengths (300 cm) of water pipe (2 cm diam) or electrical conduit so that bottom sediments in water depths of up to 10 m can be sampled. The core sampler is hand-operated and pushed into bottom sediments from a boat. It does not have to be triggered remotely because of the one-way modified check valve in the air exhaust—intake assembly. After the sampler is extracted from the sediment, the extension handle can be quickly removed for ease of sampler handling, and the core can be extruded from the PVC tube by air pressure.Contribution of the National Sedimentation Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Oxford, Mississippi 38655, U.S.A. 相似文献
323.
Recent sediment accumulation rates were measured in Moon Lake, a large (10.1 km2) Mississippi River oxbow lake in northwestern Mississippi. Moon Lake, which receives channeled inflow from an intensively cultivated soybean, rice, and cotton watershed (166 km2) and limited overland flow from surrounding lands, exhibited depositional patterns that were associated with (1) points of inflow, (2) flow patterns, and (3) lake morphology. From 1954 to 1965, 70 percent of the lake bottom experienced accumulation rates greater than 2 cm/yr. Accumulation rates exceeded 4 cm/yr in areas of delta formation. Changes in cropping systems during the 1960s, from cotton to soybeans and rice which require less cultivation, resulted in significantly (a = 0.01) less sediment accumulation during the period 1965- 1982 when 86 percent of the lake averaged less than 2 cm/yr sediment deposition. If current sediment accumulation rates continue, open water habitat in the lake will be reduced by only 3 to 7 percent during the next 50 years.Contribution of the Sedimentation Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Oxford, MS 38655 相似文献
324.
Raymond Cooper David Lavie Yitzchak Gutterman Michael Evenari 《Journal of Arid Environments》1994,27(4)
In 14 species of Aegilops, four species of Triticum and two species of Hordeum, a complex of rare phenolic compounds was found and showed quantitative differences between the wild and domestic species. There was a dramatic reduction in the cultivars to about 5% of the amount of these phenolic constituents. In the wild species these phenolic compounds may act as important germination regulators, such as water-dissolving germination inhibitors which may act as 'rain gauges'. This is especially important for the germination at the appropriate time in species inhabiting arid regions or deserts. 相似文献
325.
Site procedures, instrumentation, analytical methods and accuracies achieved are described for the measurement of the deformation of a military steel bridge under load in a test gantry. Some remarks concerning the advantages and disadvantages of photogrammetry as a method of industrial measurement are made. 相似文献
326.
Mark H. Cooper 《社会与自然资源》2017,30(7):812-828
ABSTRACTThis article examines the stomachs of ruminant livestock as a site of biotechnological intervention and analyzes efforts to reengineer ruminant digestion as a case of the real subsumption of nature. The livestock industry’s capacity to increase production is constrained by available grazing land and concern about environmental consequences of ever-increasing livestock numbers. Ruminants are also a significant source of greenhouse gases and the mitigation of methane is a recognized priority within the global climate framework. The pursuit of “sustainable intensification” and new technological fixes have been identified as preferred responses to these constraints. The case of ruminant methane calls into question assumptions about the primacy of accumulation, rather than regulation, in driving the real subsumption of nature. The pursuit of technological fixes within biologically based industries may be motivated by a need to stabilize the conditions of production, and regulation itself can provide an impetus for the real subsumption of nature. 相似文献
327.
Mark E. Stelten Kari M. Cooper Jorge A. Vazquez Mary R. Reid Gry H. Barfod Josh Wimpenny Qing-zhu Yin 《Contributions to Mineralogy and Petrology》2013,166(2):587-613
The nature of compositional heterogeneity within large silicic magma bodies has important implications for how silicic reservoirs are assembled and evolve through time. We examine compositional heterogeneity in the youngest (~170 to 70 ka) post-caldera volcanism at Yellowstone caldera, the Central Plateau Member (CPM) rhyolites, as a case study. We compare 238U–230Th age, trace-element, and Hf isotopic data from zircons, and major-element, Ba, and Pb isotopic data from sanidines hosted in two CPM rhyolites (Hayden Valley and Solfatara Plateau flows) and one extracaldera rhyolite (Gibbon River flow), all of which erupted near the caldera margin ca. 100 ka. The Hayden Valley flow hosts two zircon populations and one sanidine population that are consistent with residence in the CPM reservoir. The Gibbon River flow hosts one zircon population that is compositionally distinct from Hayden Valley flow zircons. The Solfatara Plateau flow contains multiple sanidine populations and all three zircon populations found in the Hayden Valley and Gibbon River flows, demonstrating that the Solfatara Plateau flow formed by mixing extracaldera magma with the margin of the CPM reservoir. This process highlights the dynamic nature of magmatic interactions at the margins of large silicic reservoirs. More generally, Hf isotopic data from the CPM zircons provide the first direct evidence for isotopically juvenile magmas contributing mass to the youngest post-caldera magmatic system and demonstrate that the sources contributing magma to the CPM reservoir were heterogeneous in 176Hf/177Hf at ca. 100 ka. Thus, the limited compositional variability of CPM glasses reflects homogenization occurring within the CPM reservoir, not a homogeneous source. 相似文献
328.
The duration of shoreline occupation at a given sea‐level, coastal response to sea‐level change and the controls on preservation of various shoreline elements can be recognized by detailed examination of submerged shorelines on the continental shelf. Using bathymetric and seismic observations, this article documents the evolution and preservation of an incised valley and lithified barrier complex between ?65 m and ?50 m mean sea‐level on a wave‐dominated continental shelf. The barrier complex is preserved as a series of aeolianite or beachrock ridges backed by laterally extensive back‐barrier sediments. The ridges include prograded cuspate lagoonal shoreline features similar to those found in contemporary lagoons. The incised valley trends shore‐parallel behind the barrier complex and records an early phase of valley filling, followed by a phase of extensive lagoonal sedimentation beyond the margins of the incised bedrock valley. Sea‐level stability at the outer barrier position (ca ?65 m) enabled accumulation of a substantial coastal barrier that remained intact during a phase of subsequent slow sea‐level rise to ?58 m when the lagoon formed. These lagoonal sediments are stripped seawards by bay ravinement processes which caused the formation of several prograded marginal cuspate features. An abrupt rise in sea‐level to ?40 m, correlated with melt‐water pulse 1B, enabled the preservation of thick lagoonal sediments at the top of the incised valley fill and preservation on the sea bed of the cemented core of the barriers. This situation is unique to subtropical coastlines where early diagenesis is possible. The overlying sandy sediment from the uncemented upper portion of the barriers is dispersed by ravinement, partly burying the ridges and protecting the underlying sediments. The high degree of barrier or shoreline preservation is attributed to rapid overstepping of the shoreline, early cementation in favourable climatic conditions and the protection of the barrier cores by sand sheet draping. 相似文献
329.
The results of potassium‐argon measurements are reported. Three samples from the southern end of the New England bathylith confirm its Permian age (240–245 m.y.). Two samples of the “pre‐Permian” granites are not younger than Lower Permian (Hillgrove, 270 m.y.; Barrington Tops, 260 m.y.). A sample of the analcite basalt from Spring Mountain gave an Oligocene age (34 m.y.) by measurements on two separate minerals. 相似文献
330.
D. L. Strusz with contribution by M. R. Banks G. Bischoff B. J. Cooper R. A. Cooper P. G. Flood E. D. Gill J. S. Jell J. W. Pickett N. M. Savage D. L. Sherwin J. A. Talent B. D. Webby & A. J. Wright 《Australian Journal of Earth Sciences》2013,60(4):427-455
Alkali basaltic rocks from the Southern Highlands, N.S.W., contain oxide phases of both high and low pressure origin. The two phases are readily distinguished using chemical and textural criteria. Chemical data for low‐pressure Fe‐Ti oxides indicate that oxygen fugacities of the host lavas range from 10‐12.8 to 10‐8 atm at 950° to 1110°C. In most cases, the oxygen fugacities of the individual lava flows appear to be principally a function of temperature and intrinsic chemical equilibria existing at the time of formation of the basaltic liquid. However, some relatively differentiated flows shows a high degree of oxidation due to volatile enrichment with fractionation. Rare glassy flows show dendritic crystallization of Fe‐Ti oxides. Most flows in which abundant olivine was the first phase to be precipitated also contain Cr‐rich spinels associated, and apparently coeval, with the earliest‐crystallizing olivine. 相似文献