An explicit representation of steady state response of a beam on an elastic foundation to moving harmonic line loads

A closed‐form deflection response of a beam rest is presented in this paper using the integral transform method. The theory of linear partial differential equations is used to represent the deflection of beam subjected to a moving harmonic line load in integration form. The solution is finally carried out using the inverse Fourier transform. To evaluate the integration analytically, poles of the integrand are identified with the help of algebraic equation theory. Residue theorem is then utilized to represent the integration as a contour integral in the complex plane. Closed‐form deflections and numerical results are provided for different combinations of load frequency and velocity. Copyright © 2002 John Wiley & Sons, Ltd.     

Sugar and Lipid Components in Sea Foam near Kelp Beds

Abstract. A component analysis of the sugar and lipid fraction in foam layers around kelp beds on the South African west coast showed the following trends: In the residue of foam drainage of both 12 h and 120 h old foam the sugar fraction is represented by mannose (33–41 %), galactose (4–30%), fucose (3–29%) and glucose (19–26%). With the exception of fucose, the same components could be found in foam filtration. In the lipid fraction the main fatty acids are palmitic (23.3–27.3%), oleic (14.0–5.5%) and timnodonic acid (11.2–9.1%). Selacholeinic acid was only found in 12 h old foam while lignoceric acid could not be located in foam filtration. Against expectation mannitol was not identified in quantifiable amounts in foam samples although it is the dominant component of kelp mucilage, whose presence is of major importance for foam formation. Hypotheses explaining the lack of mannitol are forwarded. Component sugar and lipid content for 11 of foam was calculated and estimation of sugar and lipid content in an average foam patch (volume of 30001) is given. The importance of foam formation as a mechanism for binding and transfer of energy in the marine environment is emphasized.     

Spatial Variation in the Structure of Kelp Forest Communities Along a Wave Exposure Gradient

Abstract. Four sites were sampled in kelp (Macrocysiis pyrifera) forests occupying rocky bottom habitats along a wave exposure gradient in central California. Consistent betwecn-site differences were found in the three major structural elements - the surface canopy, the undcrstory assemblage, and the ground cover/turf assemblage - of kelp forest communities. Macrocysiis pyrifera was found at all four sites. Nereucyslis tuelkeana only at the most exposed site. The understory kelps Laminaria setchellii and Pterygopltora californica were also characteristic of exposed sites. Articulated coralline algae were more abundant at exposed sites than protected, while fleshy red algae showed the opposite pattern. All four study sites were located along 8.5 km of coastline, and thus were assumed to have available to them the same species pool for colonization. The substrate composition was the same and the amount of unconsolidated substrate was similar at all four sites. We suggest that exposure to wave-generated water motion, through its influence on the surface canopy and therefore on the amount of light reaching the bottom, is responsible for these between-site differences.     

湿法冶锰废渣中锰的形态分析与应用

将湿法冶锰废渣经过烘干、研细等预处理,按其所使用的原材料进行形态研究,通过筛选和实验,确定了废渣中的锰可用形态分析方法。在弄清废渣中锰的各种形态及含量的基础上,将其成果进行转化,用于指导工业生产、环境评价和废渣处理,具有很好的经济效益和社会效益。     

吉林省中部农业土壤中滴滴涕的残留特征

通过分析研究吉林省中部农业土壤中DDT的含量和组成,探讨了该区土壤中DDT的残留特征及其可能的生态风险。研究结果表明,吉林省中部农业土壤中普遍残留DDT,质量分数为0.384~54.159μg/kg,残留水平较低,土壤DDT同系物中以p,p’-DDT和p,p-’DDE为主。DDT的组成表明,土壤中DDT主要是过去输入环境的DDT及其降解产物,但近期仍有少量的DDT输入。生态风险评估则显示该区土壤中的DDT具有一定的生态风险,应予以重视。     

粘性泥石流残留层的形成及减阻作用--以云南蒋家沟泥石流为例

通过对云南蒋家沟粘性泥石流的野外观测 ,讨论了粘性泥石流残留层的定义特征 ,在大量实测数据基础上 ,分析了残留层易形成时段的特性 ;分别对一次泥石流过程、若干阵泥石流和一阵泥石流残留层的变化进行了相关分析 ;最后用观测数据分析了泥石流残留层的减阻作用     

金沙江白格滑坡残留体稳定性分析与防治对策

金沙江白格滑坡在经历了2018年10月和11月的2次滑动堵江后,在其后缘仍存在K1、K2和K3等3处规模较大的残留崩滑体,并有再次失稳堵江的可能。目前关于残留体稳定性的研究还存在较大争议,多从影响因素及成因机制等方面进行定性分析,其结果依赖于评价者的经验,差异较大。在野外调查的基础上,针对白格滑坡所在区工程地质条件及其残留体变形特征,选取坡高、坡度、坡面形态、临空面、地下水出露、裂缝发育和变形等7个因素作为评价因子,基于模糊综合评判模型,运用层次分析法对白格滑坡残留体进行分区稳定性评价,并提出相应的防治对策。评价结果表明:K1与K2残留体稳定性较差;K3残留体基本稳定,与实际调查状况较吻合。研究结果可为同类型滑坡的评价与防治提供参考。     

莆田近岸海域海带烂孔病起因的初步研究

2019年3月莆田近岸海域海带尾部烂孔后逐渐向根部蔓延,孔洞相连后海带脱落,时空规律为先南后北逐渐发病,共涉及养殖面积约7 km2,给莆田近岸海带养殖带来了较大的损失。初步研究分析了海带大规模烂孔的原因,主要结果如下:海区温度异常升高,盐度持续较低,连续阴天光照不足,环境变化超出了细胞生理承受能力从而造成海带烂孔。此次诊断,对渔业生产及海洋环境监测结果在渔业上的应用均具有一定的现实意义。     

Trophic significance of the kelp Laminaria digitata (Lamour.) for the associated food web: a between-sites comparison

This study aimed at establishing the trophic significance of the kelp Laminaria digitata for consumers inhabiting two rocky shores of Northern Brittany (France), displaying contrasted ecological conditions. The general trophic structure did not vary between these two sites, with a wide diversity of filter-feeders and predators, and only 14% of the species sampled belonging to the grazers' trophic group. The diversity of food sources fueling the food web appeared also similar. The food webs comprised four trophic levels and the prevalence of omnivory appeared relatively low compared to previous studies in the same area. Conversely, to the food web structure, which did not differ, the biochemical composition of L. digitata differed between the two sites, and was correlated to a larger diversity of grazers feeding on this kelp in sheltered conditions. This indicated that the spatial variability occurring in the nutritive value of L. digitata is likely to deeply affect the functioning of kelp-associated food webs. The contribution of L. digitata-derived organic matter to the diet of filter-feeders inhabiting these two environments was assessed using the mixing model Isosource, which showed the higher contribution of kelp matter in sheltered conditions. These results highlight the spatial variability that may occur in the functioning of kelp-associated food webs. Moreover, this suggests that hydrodynamics is likely to control the availability of kelp-derived organic matter to local filter-feeders, probably through an increase of detritus export in exposed areas.