Analysis of the Influence of Geometrical Parameters on the Performance of a Proton Exchange Membrane Fuel Cell

A suitable channel structure can lead to efficient gas distribution and significantly improve the power density of fuel cells.In this study,the influence of two channel design parameters is investigated,namely,the ratio of the channel width to the bipolar plate ridge width(i.e.,the channel ridge ratio)and the channel depth.The impact of these parameters is evaluated with respect to the flow pattern,the gas composition distribution,the temperature field and the fuel cell output capability.The results show that a decrease in the channel ridge ratio and an increase in the channel depth can effectively make the distributions of velocity,temperature and concentration more uniform in each channel and improve the output capability of the fuel cell.An increase in the channel ridge ratio and depth obviously reduces the flow resistance and improves the flow characteristics.

Neural mechanisms of top-down divided and selective spatial attention in visual and auditory perception

Top-down attention mechanisms require the selection of specificobjects or locations;however,the brain mechanism involved when attention is allocated across different modalities is not well understood.The aim of this study was to use functional magnetic resonance imaging to define the neural mechanisms underlyingdivided and selective spatial attention.A concurrent audiovisual stimulus was used,and subjects were prompted to focus on a visual,auditory and audiovisual stimulus in a Posner paradigm.Ourbehavioral results confirmed the better performance of selectiveattention compared to devided attention.We found differences in the activation level of the frontoparietal network,visual/auditorycortex,the putamen and the salience network under differentattention conditions.We further used Granger causality(GC)toexplore effective connectivity differences between tasks.Differences in GC connectivity between visual and auditory selective tasksreflected the visual dominance effect under spatial attention.In addition,our results supported the role of the putamen inredistributing attention and the functional separation of the saliencenetwork.In summary,we explored the audiovisual top-down allocation of attention and observed the differences in neuralmechanisms under endogenous attention modes,which revealedthe differences in cross-modal expression in visual and auditory attention under attentional modulation.

Analysis and Comparison of Two Jumping Leg Models for Bioinspired Locust Robot

Bionic jumping robot can cross the obstacles by jumping, and it has a good application prospect in the unstructured com- plex environment. The less Degree of Freedom （DOF） jumping leg, which has the characteristics of simple control and high rigidity, and is very important in research. Based on the experimental observation of leg physiological structure and take-off process of locust, two 1 DOF jumping leg models, which includes four-bar jumping leg model and slider-crank jumping leg model, are established, and multi objective optimization is conducted to deduce the motion law of two 1 DOF jumping leg models and jumping leg of locust is closer. Then the jumping performance evaluation indices are proposed, which include the mechanical property, body attitude, jumping distance and jumping performances of the two jumping leg models environmental effect. According to these evaluation indices, the are analyzed and compared, and the simulation is conducted for further explanations. The analysis results show that the four-bar jumping leg has smaller structural size and its motion law is closer to the hindleg of locust. The slider-crank jumping leg has better mechanical property, stronger energy storage capacity and the rough ground has less effect on it. This study offers a quantitative analysis and comparison for different jumping leg models of bionic locust jumping robot. Furthermore, a theoretical basis for future research and engineering application is established.

成功认知老化与病理认知老化的“额叶保持,颞叶损伤”假说

认知老化存在明显的异质性:一部分人会经历病理认知老化乃至罹患认知障碍,也有一部分人能在高龄仍保持优异的认知能力,即成功认知老化(SCA).SCA的脑结构基础及其区别于病理认知老化的脑特征尚不清楚.本研究基于北京老年脑健康计划大型队列,选取了198名老年受试者开展研究,分为SCA组、轻度认知障碍(MCI)组和认知正常控制(CNC)组.通过对全脑灰质体积、灰质共变网络和白质结构网络的分析,本研究发现:SCA组相较其他两组在左侧额中回灰质体积更大,在额叶灰质共变网络保持有更高的完整性和共变强度,且在额叶-基底神经节区域有更高的白质网络节点效率;而MCI组相较其他两组在颞枕区域表现为灰质体积下降、灰质网络完整性降低、白质节点效率受损.灰、白质网络叠加和空间相关分析进一步揭示了SCA组对额叶脑结构的特异性保持和MCI组对颞叶脑结构的特异性损伤.基于上述结果,本研究提出“额叶保持,颞叶损伤”假说用以解释认知老化异质性的脑神经机制.

Prevalence and molecular epidemiology of equine piroplasmosis in China:a neglected tick-borne disease

Dear Editor,Equine piroplasmosis(EP)is an infectious,tick-borne dis-ease caused by the hemoprotozoan parasites Theileria equi(T.equi)and Babesia caballi(B.caballi).EP affects all wild and domestic equids,and clinical presentation is related to intravascular hemolysis and associated systemic illness(Scoles and Ueti,2015).This disease has considerable ve-terinary and economic impact on the equine industry worldwide,and is listed as a reportable disease by the World Organization for Animal Health(OIE).Importantly,a ne-gative EP test is mandatory for animals participating in equestrian sports and the horse trade.It is estimated that 90%of the global horse population resides in EP-endemic areas.Many risk factors are associated with the infection rate,in-cluding animal species,age,gender,breed,activities,and environmental factors(Onyiche et al.,2019).