共查询到20条相似文献,搜索用时 15 毫秒
1.
Shanks AL 《Science (New York, N.Y.)》1987,235(4793):1198-1200
Internal waves generated by tidal currents concentrated and transported an oil spill (liquid asphalt) onshore. Plankton net samples were collected in front of and behind a set of internal waves as well as in the convergence and divergence zones over the waves. Tar "balls" were most abundant (greater than 30-fold) in the samples from the convergence zone. Comparison of the abundance of tar balls in front of and behind the set of waves suggests that the internal waves "caught" about 68% of the asphalt encountered and concentrated and swept shoreward tar balls from almost 8 kilometers of ocean. 相似文献
2.
The very-high-resolution radiometer on the NOAA-2 (National Oceanic and Atmospheric Administration) satellite has recently obtained imagery in the visible channel containing sunglint over a major portion of the coastal waters off the eastern seaboard of the United States. An abrupt change in surface roughness has been observed at the shoreward edge of the Gulf Stream Current from Florida to Cape Hatteras that results from the opposition of waves propagating against the flow of the Gulf Stream. 相似文献
3.
Spin transfer appears to be a promising tool for improving spintronics devices. Experiments that quantitatively access the magnitude of the spin transfer are required for a fundamental understanding of this phenomenon. By inductively measuring spin waves propagating along a permalloy strip subjected to a large electrical current, we observed a current-induced spin wave Doppler shift that we relate to the adiabatic spin transfer torque. Because spin waves provide a well-defined system for performing spin transfer, we anticipate that they could be used as an accurate probe of spin-polarized transport in various itinerant ferromagnets. 相似文献
4.
The tokamak is a prototype fusion device in which a toroidal Magnetic field is used to confine a hot plasma. Coherent waves, excited near the plasma edge, can be used to transport energy into the plasma in order to heat it to the temperatures required for thermonuclear fusion. In addition, tokamak plasmas are known to exhibit high levels of turbulent density fluctuations, which can transport particles and energy out of the plasma. Recently, experiments have been conducted to elucidate the nature of both the coherent waves and the turbulence. The experiments provide insight into a broad range of interesting linear and nonlinear plasma phenomena and into many of the processes that determine such practical things as plasma heating and confinement. 相似文献
5.
Slow transport of tubulin in the neurites of differentiated PC12 cells 总被引:13,自引:0,他引:13
C H Keith 《Science (New York, N.Y.)》1987,235(4786):337-339
In order to study the rate and form of tubulin transport in cultured neuronal cells, the fluorescence recovery after the photobleaching of a fluorescent tubulin analog has been followed within the neuritic processes of differentiated PC12 cells. In these cells, as in peripheral axons, tubulin is transported in coherent, nondiffusing waves at two different slow rates that are within the range of the slow components a and b of axonal transport measured in vivo. Finally, it appears that most, if not all, of the tubulin analog is moving out these processes. Thus, slow neuroplasmic transport in cultured neuron-like cells is a good model of axonal transport, in which experimental manipulations of the system can be performed that would be difficult in the whole animal. 相似文献
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Beach cusps as self-organized patterns 总被引:1,自引:0,他引:1
Computer simulations of flow and sediment transport in the swash zone on a beach demonstrate that a model that couples local flow acceleration and alongshore surface gradient is sufficient to produce uniformly spaced beach cusps. The characteristics of the simulated cusps and the conditions under which they form are in reasonable agreement with observations of natural cusps. The self-organization mechanism in the model is incompatible with an accepted model in which standing alongshore waves drive the regular pattern of erosion and deposition that gives rise to beach cusps. Because the models make similar predictions, it is concluded that currently available observational data are insufficient for discrimination between them. 相似文献
8.
Of the 26 well-preserved orders of benthic marine invertebrates that have originated since the beginning of the Mesozoic, 20 first appear in onshore environments. This distribution differs significantly from that shown by well-preserved genera and families, and by the 16 poorly preserved orders. These discordances suggest that the pattern of preferential onshore origination is not an artifact of preservation or collection and that the origin of higher taxa cannot be regarded as a simple extrapolation of rates and patterns at lower levels. The onshore environment fosters production or enhances survivorship of species that initiate lineages tending to accumulate suites of derived characters and that thus are ultimately afforded high taxonomic rank. 相似文献
9.
基于沙粒佛汝德数相似原理,首先推导出利用模型试验结果估算原型沙波河床上推移质输沙率的推算公式;然后塑造与原型较为一致的床面形态,利用模型试验对推算公式进行了验证。结果表明,在保证原型与模型的粒径比尺较大,且模型与原型床面形态一致的条件下,运用该方法推算沙波河床上的推移质输沙率时,可以取得较为满意的结果。 相似文献
10.
长距离油,气,水管道混输系统 总被引:2,自引:0,他引:2
在海洋油田的开发中,若在海上建立多个开采处理平台,来处理井液(含油、气、水)是极不经济的,于是提出了多相流的管道输送问题,即将末处理的井液输送到岸上,然后进行处理。国外多相流管道混输技术成功地应用于海洋油田的开发,这项技术也可引入荒漠油田及滩涂油田的开发。 相似文献
11.
Internal solitons in the andaman sea 总被引:6,自引:0,他引:6
The solitary wave is a localized hydrodynamic phenomenon that can occur because of a balance between nonlinear cohesive and linear dispersive forces in a fluid. It has been shown theoretically, and observed experimentally, that some solitary waves have properties analogous to those of elementary particles, and the waves have therefore been named solitons. During a measurement program in the Andaman Sea near northern Sumatra, large-amplitude, long internal waves were observed with associated surface waves called tide rips. Using theoretical results from the physics of nonlinear waves, it is shown that the internal waves are solitons and their interactions with surface waves are described. 相似文献
12.
胞外呼吸菌是在厌氧条件下氧化有机物产生电子,进而将电子传递至胞外电子受体并产生能量维持自身生长的一类微生物,在重金属和有机污染物迁移转化过程中发挥着重要作用,且菌群的协同作用效果较单一微生物更为显著。胞外呼吸菌在自然环境中广泛存在,主要集中在变形菌门(Proteobacteria)、放线菌门(Acidobacteria)和厚壁菌门(Firmicutes),且多数为革兰氏阴性菌,其中希瓦氏菌(Shewanella oneidensisi MR-1)和地杆菌(Geobacter sulfurreducens)是研究较为深入的胞外呼吸模式菌。目前已知的5种胞外电子传递机制包括直接电子传递、电子穿梭体、应电运动、纳米导线和细胞间电子传递机制,各种机制非独立存在而是共同作用以促进污染物降解。文章从胞外呼吸菌的种类、胞内与胞外电子传递机制等方面进行综述,并着重论述了胞外呼吸菌在污染物迁移转化中的最新应用进展,为更好地发挥其环境效应提供参考。 相似文献
13.
We studied the free fluid-fluid interface in a phase-separated colloid-polymer dispersion with laser scanning confocal microscopy and directly observed thermally induced capillary waves at the interface in real space. Experimental results for static and dynamic correlation functions validate the capillary wave model down to almost the particle level. The ultralow interfacial tension, the capillary length, and the capillary time are found to be in agreement with independent measurements. Furthermore, we show that capillary waves induce the spontaneous breakup of thin liquid films and thus are of key importance in the process of droplet coalescence. 相似文献
14.
Hof B van Doorne CW Westerweel J Nieuwstadt FT Faisst H Eckhardt B Wedin H Kerswell RR Waleffe F 《Science (New York, N.Y.)》2004,305(5690):1594-1598
Transition to turbulence in pipe flow is one of the most fundamental and longest-standing problems in fluid dynamics. Stability theory suggests that the flow remains laminar for all flow rates, but in practice pipe flow becomes turbulent even at moderate speeds. This transition drastically affects the transport efficiency of mass, momentum, and heat. On the basis of the recent discovery of unstable traveling waves in computational studies of the Navier-Stokes equations and ideas from dynamical systems theory, a model for the transition process has been suggested. We report experimental observation of these traveling waves in pipe flow, confirming the proposed transition scenario and suggesting that the dynamics associated with these unstable states may indeed capture the nature of fluid turbulence. 相似文献
15.
Stratospheric wave spectra resembling turbulence 总被引:1,自引:0,他引:1
Dewan EM 《Science (New York, N.Y.)》1979,204(4395):832-835
Pollution effects on ozone raise the question of the significance of turbulence in vertical transport in the stratosphere. The aircraft in situ measurements of velocity fluctuations previously employed to estimate turbulence transport were, it is hypothesized, due to atmospheric waves, despite their classical turbulence spectrum. This new hypothesis implies that previous turbulence estimates are invalid. Experimental tests are suggested. 相似文献
16.
吴天洋 《安徽农业大学学报》2015,(3):46-49;92
人民币的国际化是近来我国国际金融领域的热门话题。而人民币离岸市场的发展则是人民币国际化逐步推进的具体表现。将研究方向聚焦于在岸人民币价格(CNY)与离岸人民币价格(CNH)的互动关系可以反映出人民币离岸市场的定价机制。基于人民币在岸价格和离岸价格的最新数据,通过建立双因素VAR模型,并且运用格兰杰因果关系检验以及脉冲响应分析,实证结果显示CNY对CNH的影响要大于CNH对CNY的影响,即现阶段在岸人民币价格对离岸人民币价格形成有着重要的引导作用。 相似文献
17.
Resistance to herbicide Basta was used to identify Bt-transgenic rice plants and the progenies of crosses between the Bt-transgenic rice and the rice varieties cultivated in the Huang Huai area of China. The results demonstrated that the Basta-positive rice plants were highly resistant to stripe stem borer (Chilo suppressalis ) both in the laboratory and field tests. Both cryIA (b) and bar genes were expressed and co-inherited in both selfing and crossing progenies. Mendelian segregation of the marker gene bar was observed in F2 and BC1 progenies. The results implicates that it is possible to transfer cryIA (b) gene into other cultivated varieties through crosses and back crosses. 相似文献
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Observation of individual DNA molecules undergoing gel electrophoresis 总被引:12,自引:0,他引:12
Individual DNA molecules undergoing agarose gel electrophoresis were viewed with the aid of a fluorescence microscope. Molecular shape and orientation were studied in both steady and pulsed electric fields. It was observed that (i) DNA macromolecules advanced lengthwise through the gel in an extended configuration, (ii) the molecules alternately contracted and lengthened as they moved, (iii) the molecules often became hooked around obstacles in a U-shape for extended periods, and (iv) the molecules displayed elasticity as they extended from both ends at once. A computer model has been developed that simulates the migration of the molecules in a rotating-field gel electrophoresis experiment. 相似文献
20.
Hawley JF 《Science (New York, N.Y.)》1995,269(5229):1365-1370
Supercomputer simulations have been used in conjunction with analytic studies to investigate the central issue of astrophysical accretion-disk dynamics: the nature of the angular momentum transport. Simulations provide the means to investigate and experiment with candidate mechanisms, including global hydrodynamic instabilities, spiral shock waves, and local magnetohydrodynamic (MHD) instabilities. Simulations have demonstrated that accretion disks are generally MHD turbulent. These results suggest that the fundamental physical mechanism for angular momentum transport in accretion disks has now been identified. 相似文献