氢燃料电池船舶直流综合电力系统研究及应用

研发氢燃料电池船舶是实现航运业零碳排放的可行途径,也是推动造船业转型升级的重要发展方向,但传统的电力系统集成模式逐渐成为制约氢燃料电池船舶产业化应用的关键因素,构建以新能源为主体的船舶新型直流综合电力系统成为解决该问题的突破点。首先,系统梳理了氢燃料电池船舶和船舶综合电力系统的发展概况;其次,以中国第一艘氢燃料电池游艇"蠡湖"号为例,详细介绍了氢燃料电池船舶直流综合电力系统的关键技术及其在实船上的应用;然后,针对不同的航行工况重点分析了氢燃料电池船舶的5种电力驱动模式;最后,结合相关技术和配套设备的研发进程,分析并探讨船用氢燃料电池的局限性、推广可行性及未来的发展方向,期望能为燃料电池船舶的技术创新和工程应用提供参考。     

联合空间与角度的符号相干系数平面波成像北大核心CSCD

超声平面波成像是近年来一种应用较广泛的超快速超声成像方法,多角度相干平面波复合(Coherent Plane Wave Compounding,CPWC)成像在不过多损失速率的情况下,提升成像质量。但普通的CPWC方法只是简单复合多个角度延时叠加(Delay and Sum,DAS)后的数据,并未考虑到单个角度内以及多个角度之间数据的相关性。文章提出了一种联合空间与角度的符号相干系数(Angular Spatial Sign Coherence Factor,asSCF)平面波成像方法,将空间符号相干因子和角度符号相干因子创新性地融合到波束合成的过程中,充分考虑信号之间的相关性,旨在提升多角度复合成像质量。进行了仿真实验、仿体实验以及在体组织实验,对asSCF-CPWC方法、单一的符号相干系数法以及传统CPWC方法成像进行对比,结果发现asSCF-CPWC方法具有更好的横向分辨能力和成像对比度。     

Sensitive Label-Free Immunoassay by Colorimetric Plasmonic Biosensors Using Silver Nanodome Arrays

The sensitive direct detection of biomolecules is demonstrated by a colorimetric plasmonic biosensor utilizing the surface colors of plasmonic metasurfaces named Ag nanodome arrays. The Ag nanodome arrays consist of polystyrene bead monolayers coated with Ag thin films whose surface colors are optimized by changing the size of the polystyrene beads. The bulk refractive index sensitivity of colorimetric detection evaluated using the hue angle is 590° RIU⁻¹ (RIU: refractive index unit). For selected geometry, the refractive index resolution (5.0 × 10⁻⁵ RIU) obtained by colorimetric detection surpasses that of spectroscopic detection evaluated via the dip wavelength in the reflection spectrum. The numerical simulations predict an enhanced sensing performance when the hue angle of the surface colors of the Ag nanodome arrays changes from 300° to 200°, corresponding to changes in the dip wavelength from 570 to 600 nm in the reflection spectra. Furthermore, the detection sensitivity of the biomolecules is characterized using a direct IgG immunoassay format. The detection limit of the IgG concentration is as low as 134 pM using simple colorimetric detection. The feasibility of sensitive label-free immunoassays using a colorimetric plasmonic biosensor is expected to accelerate the development of highly sensitive and reliable smartphone-based plasmonic biosensors.     

Performance evaluation of immunity-based statistical en-route filtering in wireless sensor networks

Statistical en-route filtering (SEF) schemes can detect and eliminate false data injection attacks in wireless sensor networks. However, SEF does not address the identification of the compromised nodes which are injecting false reports. Therefore, we have proposed an immunity-based SEF to identify compromised nodes and achieve earlier detection of false reports. In the proposed scheme, each node has a list of neighborhood nodes and assigns credibility to each neighboring node. Each node can update the credibility of a neighboring node based on the success or failure of filtering and communication, and can then use the updated credibility as the probability of the next communication. In this article, some simulation results show that the immunity-based SEF outperforms the original SEF.     

Probabilistic nearest neighbor query processing on distributed uncertain data

A nearest neighbor (NN) query, which returns the most similar object to a user-specified query object, plays an important role in a wide range of applications and hence has received considerable attention. In many such applications, e.g., sensor data collection and location-based services, objects are inherently uncertain. Furthermore, due to the ever increasing generation of massive datasets, the importance of distributed databases, which deal with such data objects, has been growing. One emerging challenge is to efficiently process probabilistic NN queries over distributed uncertain databases. The straightforward approach, that each local site forwards its own database to the central server, is communication-expensive, so we have to minimize communication cost for the NN object retrieval. In this paper, we focus on two important queries, namely top-k probable NN queries and probabilistic star queries, and propose efficient algorithms to process them over distributed uncertain databases. Extensive experiments on both real and synthetic data have demonstrated that our algorithms significantly reduce communication cost.     

Slow eye movement as a possible predictor of reaction delays to auditory warning alarms in a drowsy state

In recently developed intelligent vehicles, warning alarms are often used to prompt avoidance behaviours from drivers facing imminent hazardous situations. However, when critical reaction delays to auditory stimulation are anticipated, the alarm should be activated earlier to compensate for such delays. It was found that reaction times to an auditory stimulus significantly increased in the presence of slow eye movement (SEM), which is known to occur frequently during the wake-sleep transition. The reaction delay could not be attributed to temporal effects such as fatigue and was invariant regardless of response effectors (finger or foot). Moreover, it was found that applied pedal force decreased immediately after an auditory stimulus interrupted SEM. Consequently, it was concluded that SEM can be a good predictor of reaction delays to auditory warning alarms when drivers are in a drowsy state. STATEMENT OF RELEVANCE: The present study demonstrated that simple auditory reaction time significantly increased when SEM emerged. In the design of vehicle safety systems using warning alarms to prompt avoidance behaviours from drivers, such reaction delays during SEM must be taken into account.     

Urban growth modeling of Kathmandu metropolitan region, Nepal

The complexity of urban system requires integrated tools and techniques to understand the spatial process of urban development and project the future scenarios. This research aims to simulate urban growth patterns in Kathmandu metropolitan region in Nepal. The region, surrounded by complex mountainous terrain, has very limited land resources for new developments. As similar to many cities of the developing world, it has been facing rapid population growth and daunting environmental problems. Three time series land use maps in a fine-scale (30 m resolution), derived from satellite remote sensing, for the last three decades of the 20th century were used to clarify the spatial process of urbanization. Based on the historical experiences of the land use transitions, we adopted weight of evidence method integrated in cellular automata framework for predicting the future spatial patterns of urban growth. We extrapolated urban development patterns to 2010 and 2020 under the current scenario across the metropolitan region. Depending on local characteristics and land cover transition rates, this model produced noticeable spatial pattern of changes in the region. Based on the extrapolated spatial patterns, the urban development in the Kathmandu valley will continue through both in-filling in existing urban areas and outward rapid expansion toward the east and south directions. Overall development will be greatly affected by the existing urban space, transportation network, and topographic complexity.     

薄壁曲线箱梁材料非线性分析的内力塑性系数法

目的 研究薄壁曲线箱梁考虑剪力滞效应和材料非线性的计算方法.方法 基于势能变分原理,推导了薄壁曲线箱梁的刚度方程.采用变刚度初法应力法,并结合截面内力塑性系数修正刚度系数,对薄壁曲线箱梁的材料非线性问题进行了求解.结果 通过算例计算,得到了曲线箱梁顶底板的应力分布以及挠度和扭转角的变化曲线.结论 笔者的计算结果与试验值整体吻合较好.对于薄壁曲线箱梁,悬臂板、顶板和底板,分别取三个不同的剪力滞翘曲位移函数的结果,精度优于三者取一个统一的剪力滞翘曲位移函数;随荷载的增加,弯曲剪力滞效应系数较挠度和扭转角更早进入非线性状态,翼缘截面上的应力分布逐渐趋于均匀,上翼缘应力的这种变化趋势要略滞后于下翼缘,而中支座截面翼缘应力的这种变化趋势则略快于左跨跨中和右跨跨中截面.     

基于6-DOF解耦操作臂的空间遥操作控制及运动学分析

针对由6-DOF解耦操作臂及其末端手爪组成的操作臂系统,设计了符合工程实际的遥操作控制策略,并提出了一种简单的运动学解算方法.采用Motoman工业操作臂,对提出的方法进行了实验验证.实验结果证明了所提方法的可行性.     

Agglomeration control of hydroxyapatite nano-crystals grown in phase-separated microenvironments

Materials synthesis processes that require high temperatures consume large quantities of energy that generate an environmental burden. We attempted to synthesize hydroxyapatite (HAp) nano-crystals without firing or melting. “Water in oil” (W/O) emulsions were employed as microreactors for HAp formation. The surfactant-bounded water mediated HAp crystal nucleation, and HAp nano-crystallites were obtained. The obtained particles were aggregates composed of plate-like nano-crystals and monodisperse tiny crystals. Utilization of the W/O emulsions resulted in tunable nucleation frequency and the reactant provision, and yielded HAp nano-crystals with characteristic agglomeration properties.