Sensitivity analysis of pull-in voltage for RF MEMS switch based on modified couple stress theory

An approximate analytical model for calculating the pull-in voltage of a stepped cantilever-type radio frequency （RF） micro electro-mechanical system （MEMS） switch is developed based on the Euler-Bernoulli beam and a modified couple stress theory, and is validated by comparison with the finite element results. The sensitivity functions of the pull-in voltage to the designed parameters are derived based on the proposed model. The sensitivity investigation shows that the pull-in voltage sensitivities increase/decrease nonlinearly with the increases in the designed parameters. For the stepped cantilever beam, there exists a nonzero optimal dimensionless length ratio, where the pull-in voltage is insensitive. The optimal value of the dimensionless length ratio only depends on the dimensionless width ratio, and can be obtained by solving a nonlinear equation. The determination of the designed parameters is discussed, and some recommendations are made for the RF MEMS switch optimization.

The effect of nozzle layout on droplet ejection of a piezo-electrically actuated micro-atomizer

We study here effects of nozzle layout on the droplet ejection of a micro atomizer, which was fabricated with the arrayed nozzles by the MEMS technology and actuated by a piezoelectric disc. A theoretical model was first built for this piezoelectric-liquid-structure coupling system to characterize the acoustic wave propagation in the liquid chamber, which determined the droplet formation out of nozzles. The modal analysis was carried out numerically to predict resonant frequencies and simulate the corresponding pressure wave field. By comparing the amplitude contours of pressure wave on the liquid-solid interface at nozzle inlets with the designed nozzle layout, behaviors of the device under different vibration modes can be predicted. Experimentally, an impedance analyzer was used to measure the resonant frequencies of the system. Three types of atomizers with different nozzle layouts were fabricated for measuring the effect of nozzle distribution on the ejection performance. The visualization experiment of droplet generation was carried out and volume flow rates of these devices were measured. The good agreement between the experiment and the prediction proved that only the increase of nozzles may not enhance the droplet generation and a design of nozzle distribution from a view-point of frequency is necessary for a resonant related atomizer.

全球中华鲎资源保护现状及对策建议

鲎是古老的海洋节肢动物。中华鲎(Tachypleus tridentatus)是世界现存4种鲎中体型最大的一种,是河口生态系统的标志物种,同时其血液被用于生产医用检验试剂――鲎试剂。中华鲎的自然地理分布范围相当狭窄,仅局限于日本濑户内海向南延伸至印度尼西亚爪哇岛北岸以北的太平洋西岸海域,其中在中国东岸和日本南部海域的历史产量较高。自20世纪50年代以来中华鲎种群数量出现了显著减少,2019年中华鲎在IUCN红色名录中的濒危等级正式更新为濒危(EN),明确了中华鲎资源呈现全球性衰退的状态,究其原因可归纳为鲎生境破坏和过度捕捞两个方面。在开展鲎资源保护的实践工作中,作者深刻反思当前鲎资源保护在海洋保护区划定、增殖放流及科普和野生动物保护法宣传中存在的问题并提出相应建议,包括加快完善种群基线数据,制定标准化种群和生境基线监测指南,构建科学放流体系等,以期推进全球范围内的中华鲎资源保护与科学管理。

Ontogenetic resource use and trophic dynamics of endangered juvenile Tachypleus tridentatus among diversified nursery habitats in the northern Beibu Gulf,China

Horseshoe crabs,the most well-known example of“living fossils”,are iconic and ecologically important macroinvertebrates in coastal and estuarine ecosystems.Their blood is a crucial resource for manufacturing Limulus or Tachypleus amebocyte lysate to detect bacterial endotoxins or fungal contamination in drug and medical devices.An enhanced understanding of their ecological roles and trophic interactions in the food webs is fundamental to facilitate resource management for the declining populations in Asia.Foraging information of the Asian species,however,is mainly derived from preliminary,scattered reports from a limited number of study locations.In this study,resource utilization,trophic niche dynamics,and trophic interaction of the juvenile tri-spine horseshoe crab,Tachypleus tridentatus(instars 1–12,approximately 0.5–8 years old)across ontogeny was assessed in diversified nursery habitats along the northern Beibu Gulf,China,using carbon and nitrogen stable isotopes.Our results suggest that:(i)T.tridentatus are ecological generalists given the vast range of carbon isotopic values and trophic niche width estimates exhibited between multiple instar groups;(ii)juvenile T.tridentatus across most habitat types predominantly assimilated energy from a variety of basal production sources in the food web,but primarily depended on sedimentary organic matter and seagrass resource pools;(iii)ontogenetic shifts in juvenile dietary proportions were evident,with decreased reliance on sedimentary organic matter,coupled with increased reliance on benthic macroinvertebrate grazers,detritivores,and omnivores with age;and(iv)nearly all juvenile instars occupied similar trophic positions in the food web with slight shifts in trophic position present with increasing size.Our findings indicate that resource availability and ontogenetic diet shifts strongly influence horseshoe crab trophic dynamics,and age should be accounted when formulating habitat conservation measures based on resource use for Asian horseshoe crabs.

Development characteristics and formation analysis of the Liangjia Village earth fissure in the Weihe Basin,China

Liangjia Village earth fissure,one of the 79 earth fissures along the Kouzhen-Guanshan fault located in the northern Weihe Basin,causes severe damage to buildings and farmlands.Since the late 1950s,40 earth fissures have occurred in a similar east-west(EW)direction parallel to the Kouzhen-Guanshan fault,and a further 39 earth fissures have occurred with north-west,east-north,or north-east orientations intersecting the fault.In this study,a case study of Liangjia Village earth fissure was conducted to investigate the mechanisms of fissure generation in detail.Geotechnical and geophysical methods including measurements,trenching,drilling,and seismic exploration were used to reveal the basic characteristics,geological background,and origin model of the Liangjia Village earth fissure.This earth fissure,with a total length of 800 m in 2014,runs EW parallel to the Kouzhen-Guanshan fault,and it has damaged buildings and farmlands by forming sinkholes,gullies,subsidence,and a scarp.The trenching results indicated that this fissure underwent multi-phase activity.Analysis of geological drilling and shallow seismic profiling results showed that the fissure also possessed characteristics of a synsedimentary fault.Regarding its genesis,the fissure was formed through the combined actions of three factors:an earthquake created the fissure,the Kouzhen-Guanshan fault controlled its development,and loess erosion and groundwater runoff subsequently enlarged the fissure.Regional extension first generated many buried faults along the hanging wall of the Kouzhen-Guanshan fault before seismic activity caused the buried faults to propagate to the surface,where loess erosion and ground-water runoff promoted the formation of the current earth fissure.