Identification of irradiated crab using EPR

EPR spectroscopy is a fast and powerful technique for the identification of irradiated food. Crab exoskeleton was divided into six parts: dactyl, cheliped, carapace, apron, swimming legs, and walking legs. Samples of the exoskeleton were prepared and irradiated to Cs-137 gamma radiation in the range (1.156–5.365 kGy). EPR spectra of unirradiated as well as irradiated samples were recorded and analyzed. Response to gamma radiation was plotted for each part of the exoskeleton, dactyl was found to be the most sensitive part, followed by the apron (38%), cheliped (37%), walking legs (30%), swimming legs (24%), and carapace (21%) relative to the dactyl response.     

一种新的双足机器人模型设计与相关研究

针对双足机器人最简模型在行走过程中出现摆动腿足部擦地的问题,提出了一种通过摆动腿膝关节弯曲达到摆动腿缩短的新模型。当摆动腿开始摆动时,摆动腿膝关节弯曲锁定,摆动腿缩短;当摆动腿摆动到最大位置时,膝关节解锁,摆动腿伸直再锁定,此后摆动腿回摆,系统变为直腿模型。采用脚后跟冲击控制,在摆动腿落地前,拖后的支撑腿与地面接触处施加一指向髋关节的瞬时冲击力,冲击力可以减小摆动腿着地时能量的损耗,同时驱动被动机器人向前行走。设计了迭代学习控制算法,找到极限环与不动点,实现不同给定期望步长跟踪的冲击力的计算。仿真结果表明,迭代学习控制可以有效的实现不同期望步长的跟踪,可以很快的找到机器人系统的不动点,通过收敛的相平面,得到稳定的极限环,保证了机器人行走过程稳定。     

Model and application of bidirectional pedestrian flows at signalized crosswalks

This research of bidirectional pedestrian flows at signalized crosswalks is divided into two parts: model and application. In the model part, a mixed survey including the questionnaire investigation and tracking investigation is conducted to gain the basic data about walking tendentiousness of a pedestrian crossing. Then, the forward, right-hand, outstripping,and influential coefficients are outlined to quantize walking tendentiousness of pedestrian crossing and estimate transition probabilities of pedestrians. At last, an improved cellular automation model is proposed to describe walking tendentiousness and crossing behaviors of pedestrians. In the application part, channelization research of bidirectional pedestrian flows is presented for real signalized crosswalk. In this process, the effects of right-side-walking and conformity behaviors on the efficiency of pedestrian crossing are thoroughly analyzed based on simulations and experiments to obtain a final channelization method to raise the efficiency of a pedestrian crossing at the crosswalk.     

Experimental investigations on the strategies of fighting crickets Velarifictorus micado to manipulate air resistance

Fighting crickets,one species of flightless insects optimally chosen by nature for millions of years,have evolved to fairly smooth and streamlined body surfaces.This article tries to answer the question how the insects manipulate air resistance when travelling through air after take-off without using their wings and meanwhile keep a high efficiency.We found that fighting crickets,Velarifictorus micado,performed two types of movements through air:stable and unstable.The two types both have a high moving efficiency.For the stable type,the moving efficiency is larger than 95%.As a typical example,focusing on the stable type,we firstly predicted each component of aerodynamic drag applied on the crickets and analysed the drag contributions to the initial kinetic energy dissipation.Further investigation revealed the mechanisms of the efficiently moving strategy against air resistance for the insects.The results show that the crickets can spin their hind legs to adjust body posture,thereby changing(increasing or decreasing)the air drag acting on the body to raise the efficiency during aerial movements.This work may advance the understanding of the significance of hind legs to insects’evolution and provide inspiration for future robot or micro aerial vehicle designs.     

采用单元进化限制策略的RWCE算法优化换热网络

针对强制进化随机游走算法（RWCE）优化换热网络时后期进化缓慢的不足,提出一种采用单元进化限制策略的改进RWCE算法（RS-RWCE）优化换热网络.通过限制每次迭代个体中参与进化的换热单元数,在保持进化前期年综合费用收敛速度较快的同时,保证进化后期的精细搜索能力.通过对两个经典算例的比较验证,证明改进后的算法应用于换热网络优化问题时兼顾了整型变量与连续变量的优化,使计算效率和精度均得到提高,同时获得了较好的换热网络优化结果.     

基于遗传算法的自动驾驶仪测试性分析

为了提高自动驾驶仪故障测试与诊断的快速性与准确性,提出了一种基于遗传算法的自动驾驶仪测试性分析方法;此方法解决了遗传算法应用于测试项目选择的难点,构建了最优的故障测试策略,能以最短时间完成测试并满足测试覆盖性的要求;利用故障测试获得的知识,简化故障与测试间的相关性矩阵,加快了故障诊断的速度;最终获得了故障测试与诊断一体化的方法;实验结果表明,此方法有效提高了故障测试与诊断的速度,并且易于实现。     

Simulation of pedestrian evacuation strategies under limited visibility

Evacuation process under limited visibility is different from that under good visibility. To investigate the evacuation efficiency under limited visibility, different evacuation strategies including walking along the wall (S1), following the average movement direction (S2) and following the average position (S3) are proposed in this paper. Performances of these strategies under different visibilities, densities and exit widths are compared based on a revised social force model. Simulation results show that strategy S1 is more effective at low densities while strategy S2 and S3 are more efficient at high densities. It is noted that strategy S2 outperforms S3 under the same condition. In addition, strategy S1 is not sensitive to the change of exit width due to the movement mode of walking along the wall, while the following strategies (S2 and S3) have a better performance under the wide exit condition. The evacuation time for different proportions of pedestrians adopting one strategy in the mixed strategy situation is investigated and the optimal mixture proportion is also discussed. This study provides a new insight into the effect of different evacuation strategies on pedestrian evacuation, which is helpful for evacuees or organizers of public events to make an efficient evacuation plan under limited visibility.     

Separating small amount of water and hydrophobic solvents by novel superhydrophobic copper meshes

A novel filtration device for the separation of small amount of water and hydrophobic solvents was proposed, and its separation efficiency was also quantitatively studied for the first time. This goal was achieved by a copper mesh with superhydrophobic and superoleophilic properties, which was fabricated by simply immersing in aqueous solution of NaOH and K₂S₂O₈, and subsequent modification with n-dodecanethiol. The results demonstrated that a slightly tilted copper mesh could separate small amount of hydrophobic solvents and water with high efficiency. This finding provides a new strategy to the development of functional filtration devices that may have many potential applications in the field such as biomedicine, microanalysis, purification, etc.     

How can soundscapes affect the preferred walking pace?

In this paper we describe an experiment whose goal is to investigate the role of the footstep sounds and soundscapes to affect the pace of a person walking in place (mimicking the act of walking without leaving the current position). Subjects were exposed to different simulated footstep sounds and soundscapes, generated in realtime while walking in place. The results show that, indeed, participants adapted their walking pace to the presented sounds, and not only footstep sounds but also soundscapes affect the walking pace. We could observe as well that perceived ease of walking correlates with the perceived naturalness of ambient sounds.     

Optimal Frequency and Amplitude of Vertical Viewpoint Oscillation for Improving Vection Strength and Reducing Neural Constrains on Gait

Inducing self-motion illusions referred as vection are critical for improving the sensation of walking in virtual environments (VE). Adding viewpoint oscillations to a constant forward velocity in VE is effective for improving vection strength under static conditions. However, the effects of oscillation frequency and amplitude on vection strength under treadmill walking conditions are still unclear. Besides, due to the visuomotor entrainment mechanism, these visual oscillations would affect gait patterns and be detrimental for achieving natural walking if not properly designed. This study was aimed at determining the optimal frequency and amplitude of vertical viewpoint oscillations for improving vection strength and reducing gait constraints. Seven subjects walked on a treadmill while watching a visual scene. The visual scene presented a constant forward velocity equal to the treadmill velocity with different vertical viewpoint oscillations added. Five oscillation patterns with different combinations of frequency and amplitude were tested. Subjects gave verbal ratings of vection strength. The mediolateral (M-L) center of pressure (CoP) complexity was calculated to indicate gait constraints. After the experiment, subjects were asked to give the best and the worst oscillation pattern based on their walking experience. The oscillation frequency and amplitude had strong positive correlations with vection strength. The M-L CoP complexity was reduced under oscillations with low frequency. The medium oscillation amplitude had greater M-L CoP complexity than the small and large amplitude. Besides, subjects preferred those oscillation patterns with large gait complexity. We suggested that the oscillation amplitude with largest M-L CoP complexity should first be chosen to reduce gait constraints. Then, increasing the oscillation frequency to improve vection strength until individual preference or the boundary of motion sickness. These findings provide important guidelines to promote the sensation of natural walking in VE.     

Dynamical measurements on viscoelastic behaviors of spiders in electro-dynamic loudspeakers

Spiders in electro-dynamic loudspeakers are most commonly concentrically corrugated fabric disks, and their viscoelastic behaviors affect the loudspeaker reproductions. A noncontact dynamic measuring technology is presented by a subwoofer closed box to excite the tested spiders pneumatically with a Laser Doppler Vibrometer (LDV) to measure the velocity of the moving spiders. Correlation techniques were employed to get an accurate and reliable acoustical transfer function between the measured velocity and sound pressure. The Young’s moduli of the tested spider composite materials were derived from the measured vibration modes. The creep effect and the level dependent behaviors of tested spiders were investigated. The results indicate that, the Young’s moduli of the tested spiders are frequency dependent. The mechanical stiffness increases with a small slope in low frequency range while a large slope in high frequency range. The loss factor exhibits the maximum around the resonance frequency, and after that it decreases with increasing frequency. The effective stiffness has a monotonic decrease with input voltage levels and the harder the spider, the less stiffness changes with input levels.     

基于水幕的舰船红外干扰策略研究

传统的红外成像反舰导弹的干扰策略如热焰弹和烟雾等已经不能很好地应对新型红外成像反舰导弹的威胁,针对该问题,设计一种在舰船表面不同分区施加水幕来对抗红外成像反舰导弹的策略,采用建模仿真的方式开展了水幕对红外成像导引头干扰效果的研究。建立综合考虑海天背景的舰船红外辐射仿真模型,结合典型图像识别算法,分析制定了不同的水幕施加策略,利用仿真模型研究在一定距离不同策略下红外成像导引头对目标识别的成功率;根据识别结果和算法原理对水幕施加策略进行优化,优化后的分区水幕施加策略可使导引头对目标的识别成功率下降约60%。最后通过在现实场景中搭建的降温缩比试验装置验证了水幕的降温效果。     

Kinetic theory of situated agents applied to pedestrian flow in a corridor

A situated agent-based model for simulation of pedestrian flow in a corridor is presented. In this model, pedestrians choose their paths freely and make decisions based on local criteria for solving collision conflicts. The crowd consists of multiple walking agents equipped with a function of perception as well as a competitive rule-based strategy that enables pedestrians to reach free access areas. Pedestrians in our model are autonomous entities capable of perceiving and making decisions. They apply socially accepted conventions, such as avoidance rules, as well as individual preferences such as the use of specific exit points, or the execution of eventual comfort turns resulting in spontaneous changes of walking speed. Periodic boundary conditions were considered in order to determine the density-average walking speed, and the density-average activity with respect to specific parameters: comfort angle turn and frequency of angle turn of walking agents. The main contribution of this work is an agent-based model where each pedestrian is represented as an autonomous agent. At the same time the pedestrian crowd dynamics is framed by the kinetic theory of biological systems.     

A novel 2nd-order shape function based digital image correlation method for large deformation measurements

Compared with the traditional forward compositional matching strategy, the inverse compositional matching strategy has almost the same accuracy, but has an obviously higher efficiency than the former in digital image correlation (DIC) algorithms. Based on the inverse compositional matching strategy and the auxiliary displacement functions, a more accurate inverse compositional Gauss-Newton (IC-GN2) algorithm with a new second-order shape operator is proposed for nonuniform and large deformation measurements. A theoretical deduction showed that the new proposed second-order shape operator is invertible and can steadily attain second-order precision. The result of the numerical simulation showed that the matching accuracy of the new IC-GN2 algorithm is the same as that of the forward compositional Gauss-Newton (FC-GN2) algorithm and is relatively better than in IC-GN2 algorithm. Finally, a rubber tension experiment with a large deformation of 27% was performed to validate the feasibility of the proposed algorithm.     

Vortical dynamics in the wake of water strider locomotion

Abstract  

Previous studies reported that the hydrodynamic propulsion of the water strider also results from transferring momentum to the underlying fluid through hemispherical dipolar vortices shed by its driving legs. However, there are no accuracy experimental measurements of these vortical structures to prove the mechanics of vortical propulsion. Here, we reveal the vortical structures by reporting the simultaneous measurements of the water strider’s motion and the fluid velocity field with the high-speed PIV, and proposing a new method of calculating the vortex kinetic energy and vortex momentum. We found that the asymmetrical vortical structure in each dipolar vortex, generated by one driving stroke, propels the water strider forward, and the outer elliptic vortex is weaker than the inner circular vortex. The movement of the dipolar vortex is divided into two stages: (1) translating backward and (2) return curving. In this way, the water strider obtains the maximum velocity with minimal consumption of energy. The fluid vortical momentum, generated by the driving stroke, accounts for about 64–90% of the water strider’s momentum.     

Pedestrian choice behavior analysis and simulation of vertical walking facilities in transfer station

Considering the interlayer height, luggage, the difference between queuing pedestrians, and walking speed, the pedestrian choice model of vertical walking facilities is established based on a support vector machine. This model is verified with the pedestrian flow data of Changchun light-rail transfer station and Beijing Xizhimen transfer station. Adding the pedestrian choice model of vertical walking facilities into the pedestrian simulation model which is based on cellular automata, the pedestrian choice behavior is simulated. In the simulation, the effects of the dynamic influence factors are analyzed. To reduce the conflicts between pedestrians in opposite directions, the layout of vertical walking facilities is improved. The simulations indicate that the improved layout of vertical walking facilities can improve the efficiency of pedestrians passing.     

量子移动通信中纠缠信令越区切换策略及仿真

量子移动通信是量子力学与移动通信相结合的崭新的通信技术,具有灵活、高效、安全、保密的优势.本文提出了基于纠缠度计算的同小区内不同扇区天线之间纠缠信令的越区切换策略.研究了量子移动通信终端与天线纠缠度随距离及角度变化关系.在此基础上,对信令的越区切换进行了建模仿真.结果表明,本文所提出的纠缠信令切换策略可靠性高,对于对构建未来量子移动通信系统及其信令标准的制定具有重要的技术支撑作用.     

量子移动通信中纠缠信令越区切换策略及仿真

量子移动通信是量子力学与移动通信相结合的崭新的通信技术,具有灵活、高效、安全、保密的优势.本文提出了基于纠缠度计算的同小区内不同扇区天线之间纠缠信令的越区切换策略.研究了量子移动通信终端与天线纠缠度随距离及角度变化关系.在此基础上,对信令的越区切换进行了建模仿真.结果表明,本文所提出的纠缠信令切换策略可靠性高,对于对构建未来量子移动通信系统及其信令标准的制定具有重要的技术支撑作用.     

平板集热太阳热电器件建模及结构优化

太阳能热电转换是光伏效应外另一种直接将太阳辐射转变为电能的途径, 近年来已经成为太阳能利用的热点之一. 本文以Bi₂Te₃材料为基础构建平板集热太阳热电器件模型, 采用有限元法分析AM1.5辐射条件下器件温度分布情况, 并结合基于温度的物性参数计算集热比、热臂截面积与长度变化等因素对器件的开路电压、 最大输出功率及转化效率的影响. 研究发现: 集热比与热臂长度的变化对器件性能有显著影响, 热臂截面积的变化对器件转化效率影响相对较弱; 在这一模型中, 平板集热太阳热电器件的转化效率达到1.56%.