Spreading of floating particles by Langmuir circulation   总被引：1，自引：0，他引：1  

S.A. Thorpe 《Marine pollution bulletin》2009,58(12):1787-1791

Particles floating on the sea surface, in particular buoyant algae, are drawn into bands by the converging flow between neighbouring Langmuir cells. Floating bands subsequently amalgamate as a result of Langmuir turbulence. Simple models are developed to describe the rearrangement and dispersion of the floating particles. If the production of floating particles has ceased, the mean separation of the bands of particles increases with time and eventually becomes unrelated to the mean distance between the lines of convergence resulting from Langmuir circulation. The concentration of particles in the bands, proportional to the width of bands, and the separation of bands with a given concentration of particles, both increase with time. Care is needed in estimating the width of Langmuir cells to distinguish between surface bands of floating material that is continuously being produced and bands made visible by some earlier, but discontinued, generation. An alternative mechanism for the generation of dense bands of floating algae is proposed.  相似文献   

Marine pollution from antifouling paint particles   总被引：3，自引：0，他引：3  

Andrew Turner 《Marine pollution bulletin》2010,60(2):159-171

Antifouling paint particles (APP) are generated during the maintenance of boats and are shed from abandoned structures and grounded ships. Although they afford a highly visible, colourful reflection of contamination in the vicinity of the source, little systematic study has been undertaken regarding the distribution, composition and effects of APP in the wider marine environment. This paper reviews the state of knowledge in respect of APP, with particular emphasis on those generated by recreational boatyards. The likely biogeochemical pathways of the biocidal and non-biocidal metals in current use (mainly Cu and Zn) are addressed in light of recent research and an understanding of the more general behaviour of contaminants in marine systems.Analyses of paint fragment composites from recreational facilities in the UK reveal chemical compositions that are similar to those representing the net signal of the original formulations; significantly, dry weight concentrations of Cu and Zn of up to about 35% and 15%, respectively, are observed and, relative to ambient dusts and sediment, elevated concentrations of other trace metals, like Ba, Cd, Cr, Ni, Pb and Sn, occur. These metals leach more rapidly from APP than a painted surface due to the greater surface area of pigments and additives exposed to the aqueous medium. In suspension, APP are subject to greater and more rapid environmental variation (e.g. salinity, pH, dissolved oxygen) than painted hulls, while settled APP represent an important source of persistent and degradable biocides to poorly circulating environments. Through diffusion and abrasion, high concentrations of contaminants are predicted in interstitial waters that may be accumulated directly by benthic invertebrates. Animals that feed non-selectively and that are exposed to or ingest paint-contaminated sediment are able to accelerate the leaching, deposition and burial of biocides and other substances, and represent an alternative vehicle for contaminant entry into the marine foodchain. Clearly, an extensive understanding of biocide behaviour on painted surfaces is not sufficient for predictive or management purposes regarding APP. Greater caution is required by boaters and boatyards during the removal and disposal of solid wastes, and more awareness or stricter enforcement of relevant codes of practice or legislation is recommended.  相似文献   

TESTING LAKE SEDIMENT AND DENDROGEOMORPHIC PROXIES FOR LITTLE ICE AGE ENVIRONMENTAL CHANGE IN THE UPPER FRASER RIVER AREA,BRITISH COLUMBIA,CANADA     

RANDY W. DIRSZOWSKY  JOSEPH R. DESLOGES 《Geografiska Annaler: Series A, Physical Geography》2010,92(3):393-410

This study assesses Little Ice Age (LIA) lake sediment morphological and geochemical records and moraine chronologies in the upper Fraser River watershed, British Columbia, Canada, to resolve differences in paleoenvironmental interpretation and to clarify sediment production and sediment delivery processes within alpine geomorphic systems. Moose Lake (13.9 km²), situated at 1032 m a.s.l., contains a partially varved record indicating variable rates of accumulation during the last millennium that, in general, coincide with previously documented LIA glacial advances in the region and locally. Dendrochronological assessment of forefield surfaces in the headwaters of the catchment (Reef Icefield) shows that periods of moraine construction occurred just prior to ad 1770, ad 1839 and ad 1883, and some time before ad 1570. Taken collectively, increases in varve thickness within eight Moose Lake sediment cores coincide with documented glacier advances over the twelfth through fourteenth centuries, the eighteenth century, and nineteenth through twentieth centuries. Glacial activity during the sixteenth century is also indicated. While varve thickness variations in proximal and distal sediments clearly reflect glacial activity upstream of Moose Lake, the intermediate varve record is relatively insensitive to these decadal and longer‐term catchment processes. Variations in Ca and related elements derived from glaciated carbonate terrain within the Moose River sub‐catchment (including Reef Icefield) indicate gradually increasing delivery from these sources from the twelfth through twentieth centuries even where the varve thickness record is unresponsive. Elevated carbonate concentrations confirm glacial activity c. ad 1200, ad 1500, ad 1750, and ad 1900.  相似文献   

中主应力对砂土强度影响的细观机制研究   总被引：3，自引：1，他引：2  

迟明杰  李小军  周正华  赵纪生  周国良 《岩土力学》2010,31(12):3751-3757

基于简化的颗粒单元体模型,分析总结了颗粒单元体的基本特点,针对中主应力对砂土强度的影响,重点分析了颗粒单元体之间的相互影响特点。对以往的真三轴试验结果进行了总结,得到了中主应力对砂土强度影响的规律,结合颗粒单元体的两种基本状态及其特点、大孔隙与颗粒单元体结构孔隙的特点以及颗粒单元体间相互影响的特点,揭示了中主应力对砂土强度影响规律的细观物理机制。这些规律包括：松砂的强度随着中主应力的增大是逐渐提高的;密砂随中主应力的增大,强度先提高,当中主应力接近大主应力时,却引起强度的降低;砂土越密实,强度平台段越长;在中主应力接近小主应力阶段,强度随中主应力的增大而提高的快慢与砂土的密实程度有关。  相似文献   

改性黏土除藻的絮凝形态学特征初步研究     

曹西华  宋秀贤  俞志明 《海洋学报》2017,39(6):33-42

在理论上改性黏土絮凝体的形态变化对其除藻过程有指示作用,可作为改性黏土用量和用法调控的依据,本文探讨了现有絮凝颗粒形态学观测与分析方法在改性黏土除藻效率评价上的适用性。借助激光颗粒表征技术和电子显微成像技术,本文观测了改性黏土除藻时的颗粒表面电性、粒径分布、絮凝体结构等絮凝形态学特征,分析了其与除藻效率的相关性。结果表明,现有观测方法可以表征改性导致的黏土颗粒Zeta电位反转、改性前后黏土在不同介质中的颗粒粒级分布差异、以及改性黏土与微藻形成絮凝体的多种显微结构;但由于较大粒径絮体对现有方法观测结果的影响更大,各种黏土的粒径特征与其除藻效率之间没有显著的相关性。现有观测方法获得的改性黏土颗粒形态特征仍不能反映其消除藻细胞的精细过程,特别是由于缺乏有效的絮凝体形态分析方法而导致现有形态参数还不能指示除藻效率的变化,亟需发展适用于改性黏土法除藻过程的颗粒形态分析新方法。  相似文献   

Experimental study on settling velocity of soil particles in dredged slurry     

Nan Zhang  Wei Zhu  Hongtao He  Yiyan Lv  Shengwei Wang 《Marine Georesources & Geotechnology》2017,35(6):747-757

Studying sedimentation and consolidation of dredged slurry has significant implications to the design of storage yard and subsequent ground improvement. In this study, settling velocity of soil particles in dredged slurry during sedimentation and consolidation processes was investigated using an improved multilayer extraction sampling (MES) method. A series of sedimentation column tests were performed on dredged slurry with three different initial water contents. Distributions of volume of soil particles and density of dredged slurry were first obtained by the MES method, settling velocity of soil particles was then calculated by volume flux function approach. It was found that the density and velocity inflection points can be used to distinguish the settling zone and the consolidation zone. The experimental results reveal that the velocity of soil particles was quite low and monotonically decreased with sedimentation height at low initial water content throughout the whole test period, whereas it was increased at 0–1 hours and almost remained constant at 1–7 hours in the settling zone at high initial water content. The effects of initial water content on sedimentation and consolidation mode of dredged slurry and the settling velocity of soil particles were discussed. The relationship between settling velocity of soil particles and particle diameter was also studied. It is indicated that the measured velocity of soil particles was much lower than that calculated by the Stokes equation, and it was related to 0.4881–0.5906 order of particle diameter at 0–1 hours and 0.1117–0.1825 order of particle diameter at 1–7 hours for the test slurries.  相似文献   

球体位错理论的基本解     

周新  孙文科 《大地测量与地球动力学》2017,37(11):1105-1111

位错理论是现代地震学中计算地球内部位错源引起的地表变形的重要理论模型。诸多学者对准静态位错理论模型进行了研究,其中大量工作是在前人给出的基本解的基础上进行的。回顾了位错理论模型的基本物理方程,包括平衡方程、本构关系和泊松方程,并分别推导了无自重、不可压缩、自重可压缩的地球模型下的通解。给出的基本解可以用于进一步理解和计算一维径向分层的地震变形问题。  相似文献   

Flood response to rainfall variability during the last 2000 years inferred from the Taravilla Lake record (Central Iberian Range, Spain)   总被引：2，自引：0，他引：2  

Ana Moreno  Blas L. Valero-Garcés  Penélope González-Sampériz  Mayte Rico 《Journal of Paleolimnology》2008,40(3):943-961

A sedimentological, geochemical and palynological study of the Taravilla Lake sequence (Central Iberian Range, NE Spain) provides a detailed record of allochthonous terrigenous layers that intercalate within the lacustrine sediments over the last 2000 years. These terrigenous layers are interpreted as the result of extreme hydrological events that caused higher clastic input to the basin. Anthropogenic influence caused by fires or deforestation is rejected as the main factor generating these layers because human impact, inferred from the pollen reconstruction, was minimal when the terrigenous layers reached their greatest frequency. The reconstructed occurrence of these events in the Taravilla Lake record is coherent with the paleoflood history of the Tagus River, characterized by a notable increase of extreme events at the beginning of the Little Ice Age. The Taravilla record suggests a relationship between the occurrence of extreme hydrological events, solar variability, and the North Atlantic Oscillation for the NE Iberian Peninsula.  相似文献   

风沙跃移运动发展过程的离散动力学模拟   总被引：14，自引：6，他引：8  

李万清  周又和  郑晓静 《中国沙漠》2006,26(1):47-053

采用类似分子动力学的离散方法对二维风沙跃移过程运用高性能并行计算进行理论模拟。在本模拟模型中,考虑了沙粒与床面的碰撞、跃移沙粒与气流的相互作用等基本力学过程组成的复杂系统。通过并行运算技术使计算沙粒数达到72000的巨量计算得以实现。初步结果显示：自然跃移运动的基本特征如风沙流层内输沙率廓线可以较为成功的得以模拟。  相似文献   

Measurement of Particle-Bound Reactive Oxygen Species in Rubidoux Aerosols   总被引：1，自引：0，他引：1  

Prasanna?Venkatachari  Philip?K.?HopkeEmail author  Brett?D.?Grover  Delbert?J.?Eatough 《Journal of Atmospheric Chemistry》2005,50(1):49-58

The diurnal variations in the concentrations of reactive oxygen species (ROS) in various size fractions were determined for ambient particles in Rubidoux, CA. Sampling of particles was conducted at 3 h intervals using a cascade impactor. The collected particles were reacted with dichlorofluorescin (DCFH), a non-fluorescent probe that fluoresces when oxidized. The factors affecting the diurnal variation in ROS concentration were also investigated with special emphasis on the relation between ROS concentration and the intensity of photochemical reactions where the ozone concentration was taken as an index. The intensity of photochemical reactions was found to be a moderate factor affecting the daytime ROS concentration. The concentration of ROS was found to be higher on the smaller particles of the ambient aerosol. An erratum to this article is available .  相似文献