Long-term and monthly changes in abundance,size composition and spatial distribution of the mantis shrimp Oratosquilla oratoriainthe BohaiSea

With the decline in fish resources worldwide,the ecological dominance and economic importance of crustaceans have obviously increased.Among crustacean species,mantis shrimps are increasingly dominant in many coastal waters of the world.In China,Oratosquilla oratoria is the most widely distributed and productive species of mantis shrimp,and its relative resource density is the highest in the Bohai Sea.In this study,we analysed the long-term and monthly population characteristics of O.oratoria in the Bohai Sea,including its relative resource density,body size and spatial distribution.The results showed that the relative resource density of O.oratoria in the Bohai Sea increased from 3.59 kg/h in 1982 to 14.48 kg/h in 2018,and the percentage of this species that serves as a fishery resource increased from 4.22%in 1982 to 35.27%in 2018,based on the mean relative resource density in May and August.The relative resource density of O.oratoria in the fishing moratorium season from May to August was significantly higher than that in the other months of fishing season,and the relative resource density decreased rapidly after the fishing moratorium ended.The relative resource density of O.oratoria was the highest in summer(August),followed by in autumn(October)and spring(May),and it was the lowest in winter(January).The relative resource density of O.oratoria in the western Bohai Sea was higher than that in the eastern Bohai Sea.The mean body weight of O.oratoria in the Bohai Sea decreased from 21.95 g in 1982 to 14.34 g in 2018,based on the mean body weight in May and August.The body size of O.oratoria in the fishing moratorium season was significantly higher than that in the fishing season,and the body size decreased rapidly after the fishing moratorium ended.Overall,in the context of declining resources of most fishery species,the relative resource density of O.oratoria increased due to its hardiness and adaptability,and its body size decreased under intensive fishing over the past 30 years.The fishing moratorium system had a great influence on the population dynamics of O.oratoria in terms of the relative resource density and body size in the Bohai Sea.

基于半功率带宽法的薄板涂层结构阻尼特性测试

本文主要研究了薄板-涂层结构系统的阻尼特性的测试方法与典型案例。首先介绍了半功率带宽法的识别原理,在此基础上,搭建了用于半功率带宽法测试的实验系统。采用半功率带宽法识别了带有涂层的钛基薄板结构的阻尼特性。针对涂覆TiZrN涂层前后的钛基薄板进行了阻尼特性测试,获得了系统的阻尼特性参数。对比所得的测试结果表明,薄板结构涂层后系统的固有频率发生了错频,且阻尼特性明显增大。