自动变速器驻车机构性能分析与研究     

陈华  ;陈辛波  ;傅灵玲  ;于闯  ;罗大国  ;王瑞平 《拖拉机》2014,(4):24-26

驻车机构是自动变速器中能实现可靠驻车的一种安全装置,是变速器中不可缺少的关键机构。以双离合自动变速器驻车机构设计为例,在安全驻车、防自动脱挡、异常驻车、驻车棘爪自动弹出能力以及换挡舒适性等5方面提出了性能要求,并进行了详细的分析研究,为驻车机构的分析研究提供了一定参考作用。  相似文献   

发动机轮系中齿轮记号确定方法     

商潭苏  陈洪涛  陈泰岭  林好利  谢普康  王亚春 《拖拉机》2014,(2):61-63

用实例总结了发动机曲轴齿轮、惰齿轮、配气凸轮轴齿轮和高压油泵齿轮记号的确定方法，对相应齿轮记号的位置确定有很重要的指导意义。  相似文献   

Patterns of fish community composition and biodiversity in riverine fish sanctuaries in Bangladesh: Implications for hilsa shad conservation     

Goutam Kumar Kundu  Md. Monirul Islam  Md. Foijul Hasan  Samapti Saha  Gouri Mondal  Bijoya Paul  Md. Ghulam Mustafa 《Ecology of Freshwater Fish》2020,29(2):364-376

Understanding biodiversity and community composition is a prerequisite to sustainable exploitation and conservation of fisheries. We assessed the spatial and seasonal patterns of fish community composition and biodiversity in seasonal no-take riverine sanctuaries in Bangladesh, which aim to conserve the anadromous hilsa shad (Tenualosa spp. and Hilsa keele). Fish samples were collected during monsoon, as well as pre- and postmonsoon, from five sites within two sanctuaries and one site in an open fishing area. Although total abundance was similar along the rivers, species richness was significantly higher at the open fishing site due to its connectivity to nearby habitats. The diversity apparently decreased in a downstream direction. Fish communities at two upstream sites were separated from other sites in multivariate space largely due to higher abundance of hilsa at downstream sites and presence of floodplain-oriented species at the two upstream sites. Short body length and high trophic level at all sites indicated that fish communities were overexploited. Our results also indicated that riverine hilsa sanctuaries in Bangladesh are rich in fish species diversity and support several threatened species designated by the International Union for Conservation of Nature (IUCN). Our study also suggested that since hilsa abundance shapes community patterns, it can therefore impact riverine ecosystem functioning in the sanctuary areas. The findings of this study can serve as an important baseline for future biodiversity assessment, conservation and impact assessment of conservation in rivers, and therefore help to establish multispecies ecosystem-based management of riverine fisheries around the world.  相似文献   

Survey of Musculoskeletal Injuries,Prehike Conditioning,and On-Trail Injury Prevention Strategies Self-Reported by Long-Distance Hikers on the Appalachian Trail     

《The Forestry Chronicle》2021,32(3):322-331

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Historical anecdotes of fishing pressure: Misconstrued “sea serpent” sightings provide evidence for antecedent entanglement of marine biota in the British Isles     

Robert L. France 《Fish and Fisheries》2021,22(1):54-71

Marine scholars have come to realize the importance of including historical perspectives as part of comprehensive assessments made of the social–ecological systems involved in sustainable fisheries management. In particular, there is increasing recognition of the value in examining information contained within historical anecdotes as a prelude to implementing current conservation actions as well as setting future restoration objectives. The present study demonstrates that careful parsing of eyewitness accounts of unidentified marine objects which at the time were purported to be sea serpents—of the “many‐humped” or “string‐of‐buoys” typology—actually reveals that marine fauna in the British Isles have been victims of entanglement in fishing gear for a much longer period than is customarily assumed. The temporal baseline for the onset of entanglement in this region certainly predates, by more than a century, the advent and widespread use of plastic in fisheries and other maritime operations.  相似文献   

Microsatellite DNA analysis of overwintering bull trout (Salvelinus confluentus) and its implications for harvest regulation and habitat management     

Eric B. Taylor  Rachel Chudnow  Ray Pillipow  Ian Spendlow  Brett van Poorten 《Fisheries Management and Ecology》2021,28(3):219-229

A mixed-stock fishery occurs when multiple populations of a fish species are exploited together in a common area where they aggregate outside the breeding season (e.g. for feeding or overwintering), and the aggregation is known as a mixture. Recreational fishing often exploits such mixtures, and estimating the proportional contributions of populations to fisheries promotes more sustainable resource use. Ten DNA microsatellites were assayed in a mixture of bull trout Salvelinus confluentus Suckley overwintering in the Nechako River, upper Fraser River, British Columbia, and in baseline population samples from 14 tributaries putatively contributing to the overwintering mixture. A DNA microsatellite-based mixed-stock fishery analysis suggested that five populations together contributed 0.80 to the mixture. Most of the errors associated with the mixture estimates were attributable to uncertainty in baseline allele frequencies. Radiotracking data confirmed that tributary populations contributing to the mixture estimated by genetic analysis also contained individuals that moved between spawning tributaries and overwintering sites. The results better resolve habitat use by potadromous bull trout in the upper Fraser River and, in combination with assessments of baseline population-specific spawning abundances and productivity, will better inform a decision of whether or not allowing some harvest within the current catch-and-release fishery is biologically sustainable.  相似文献   

Effects of fish stocking and fishing pressure on fish community structures in French lakes     

Léa Daupagne  Marlène Rolan-Meynard  Maxime Logez  Christine Argillier 《Fisheries Management and Ecology》2021,28(4):317-327

Fish stocking and regulation of fishing activities are widely implemented by freshwater fisheries authorities who have to protect aquatic communities. The effects of fish management on fish communities have not received sufficient attention. As a result of two datasets, one from EU Water Framework Directive (WFD) monitoring surveys, and one from a French survey targeting angler's associations, this study investigated the impacts of both fishing intensity and fish stocking on fish communities in French lakes. Both co-inertia analysis and community size spectra analysis, showed that: (i) stocking does not contribute to the standing stocks for five of the six most stocked fish species in France; and (ii) neither fishing intensity nor fish stocking lead to a change in the proportion of large and small fish. The results support alternative methods being promoted to enhance native fish populations.  相似文献   

Thunderstorms have species and gear-specific indirect effects on the catchability of Mongolian salmonids     

Abigail S. Golden  Sneha Sivaram  Ganzorig Batsaikhan  Olaf P. Jensen 《Fisheries Management and Ecology》2021,28(4):373-382

Climate change is predicted to cause increasingly frequent and intense storms. Northern Mongolia is already warming at a rate twice the global average, and thunderstorms, defined as intense, short, patchy rains associated with thunder, lightning and high precipitation rates, are becoming more frequent. Because Mongolia's fish populations are lightly exploited, Mongolia provides a model system in which to study the effects of storms on fish behaviour and fishing vulnerability. The impacts of thunderstorm-related hydrological changes on fishes’ vulnerability to two fishing gears were evaluated. Two thunderstorm-related factors, turbidity and river stage, reduced catch rates of the salmonids lenok Brachymystax lenok (Pallas) and Baikal grayling Thymallus baicalensis Dybowski. Fly-fishing gear was more effective than spinning gear in this fishery and retained higher catch rates in extreme conditions. These gear-specific effects suggest that turbidity and rising river stage affect fishing vulnerability by influencing feeding behaviour.  相似文献   

拉尼娜（2007年）和厄尔尼诺（2015年）事件对东海日本鲭栖息地时空分布的影响#br#     

陆鑫一  刘子历  余为  陈新军  李纲 《海洋渔业》2021,43(2):137-148

根据上海海洋大学中国远洋渔业数据中心提供的日本鲭(Scomber japonicus)生产捕捞数据,结合海表面温度(SST)、海表面高度(SSH)以及净初级生产力(NPP)3个关键因子,利用算术平均法进行栖息地适应性指数(HSI)建模分析,并选择2007年拉尼娜年份和2015年厄尔尼诺年份,对比研究东海日本鲭栖息地的年间差异。结果发现,拉尼娜年份(2007年)日本鲭的产量、捕捞努力量、CPUE(单位捕捞努力量渔获量)均高于厄尔尼诺年份(2015年),且渔场纬度重心(LATG)相对2015年偏北。对比渔场环境条件发现,2007年和2015年7—9月SST、SSH和NPP在空间分布上具有显著性差异。此外,栖息地建模结果显示,2007年各环境因子均有利于形成较好的日本鲭栖息地;且2007年7—9月适宜栖息地(HSI>0.6海域范围)面积明显大于2015年,其栖息地位置相较于2015年明显偏北,这导致2007年的渔场纬度重心比2015年偏北。研究表明,2007年拉尼娜事件和2015年厄尔尼诺事件对东海日本鲭适宜栖息地大小及其空间分布具有显著影响。  相似文献   

外啮合齿轮泵卸荷面积的精确仿真分析   总被引：4，自引：3，他引：1  

李玉龙  刘焜 《农业工程学报》2009,25(3):42-45

为获得与困油压力仿真模型实现无缝连接的卸荷面积计算方法,依据齿轮泵的困油原理和卸荷线的分割面积法,计算出分割点随转角的变化规律,结合展开法生成的过渡曲线代替圆弧过渡,给出了卸荷面积与卸荷槽宽度之间的精确关系和一个困油周期内卸荷面积及困油面积的精确结果。实例仿真说明卸荷面积及困油面积的变化为抛物线型,结果数据与现有文献提供的非常一致,说明了所建模型的正确性。得出卸荷面积以及困油面积计算的精确性,为后续困油压力仿真的可靠性提供了保证以及计算方法的通用性。  相似文献