Measurement of the neutral plane of an internal fire whirl using the background-oriented Schlieren technique for a vertical shaft model of a high-rise building

Since the height of the neutral plane is related to the direction of the high-temperature smoke and airflow diffusion of fires in high-rise buildings, the identification of the neutral plane is important for both the evacuation of residents and the safety of fire fighters. As yet, there are no effective methods for directly measuring the constantly changing neutral plane position. There are complex internal fire whirl phenomena in the inner space in particular cases. In this study, the background-oriented Schlieren (BOS) technique was used to visualize the neutral plane when a fire whirl occurs in a vertical shaft with a single corner gap. With n-propanol used as the fuel, the scale modeling experiments of fuel trays 5.8 cm and 7 cm in diameter were tested in a 34 cm (W) × 35 cm (L) × 145 cm (H) model for open and covered roof types. It is observed in the experimental process that the height of the neutral plane changes dynamically as the fire whirl is formed. The thermocouples were used to measure the temperature variation at different heights of openings to validate the measurement accuracy of the BOS technique. It is found that once a fire whirl occurs in the inner space of a high-rise building, the height of the neutral plane increases instantly. The experimental results demonstrate that the BOS technique can measure the neutral plane position of a large-scale model of a high-rise building fire scene directly, immediately and accurately.     

基于频率测量值的相量及电气量的DFT修正算法

为解决频率偏移时电力系统相量及电气量的测量误差大的问题,提出了一种改进的离散傅里叶(DFT)修正算法。建立了相量的实部、虚部与幅值、初相角、频率偏移量之间的函数关系式,根据此关系式得到实部、虚部与频率之间所满足的一个恒等式。在频率已知条件下计算出修正后的相量幅值和相角,进一步推导出了修正后的相量实部与虚部,最后得到其他电气量的修正算法。仿真结果表明,当系统频率偏移时,在信号为纯正弦信号,或者含有高次谐波及随机噪声等情况下,算法均可有效地提高相量及电气量的计算精度。同时,该算法对采样频率和频率误差不敏感,计算量小,不增加额外的延迟时间。     

Cooperation in the evolutionary iterated prisoner’s dilemma game with risk attitude adaptation

The Iterated Prisoner’s Dilemma (IPD) game has been commonly used to investigate the cooperation among competitors. However, most previous studies on the IPD focused solely on maximizing players’ average payoffs without considering their risk preferences. By introducing the concept of income stream risk into the IPD game, this paper presents a novel evolutionary IPD model with agents seeking to balance between average payoffs and risks with respect to their own risk attitudes. We build a new IPD model of multiple agents, in which agents interact with one another in the pair-wise IPD game while adapting their risk attitudes according to their received payoffs. Agents become more risk averse after their payoffs exceed their aspirations, or become more risk seeking after their payoffs fall short of their aspirations. The aspiration levels of agents are determined based on their historical self-payoff information or the payoff information of the agent population. Simulations are conducted to investigate the emergence of cooperation under these two comparison methods. Results indicate that agents can sustain a highly cooperative equilibrium when they consider only their own historical payoffs as aspirations (called historical comparison) in adjusting their risk attitudes. This holds true even for the IPD with a short game encounter, for which cooperation was previously demonstrated difficult. However, when agents evaluate their payoffs in comparison with the population average payoff (called social comparison), those agents with payoffs below the population average tend to be dissatisfied with the game outcomes. This dissatisfaction will induce more risk-seeking behavior of agents in the IPD game, which will constitute a strong deterrent to the emergence of mutual cooperation in the population.     

基于弧光反射的焊缝图像获取及图像处理

在CO2气体保护焊过程中,获得便于图像处理的高质量图像是焊缝跟踪的关键问题.首先,依据曲面反射体反射弧光的原理,在机器人焊炬上构建了一套有抛物面反射镜的结构,借助弧光,通过反射体产生平行光,照射到摄像机能够看到的区域,并使该区域的照度限定在摄像头可接受的范围;其次,根据短路过渡焊接过程的特点和飞溅的方向,讨论了该条件下获得图像的可用性;最后,运用机器人微移动算法,对获取图像进行了处理.试验结果表明了这种方法的有效性.     

基于模拟退火遗传算法的拆卸路径规划

针对现存拆卸路径规划图论方法中的组合爆炸问题和遗传算法的早熟现象,给出模拟退火和遗传算法相结合的拆卸路径规划方法.在拆卸路径规划模型中,以拆卸效率最优作为优化目标,给出了算法流程.该算法对拆卸路径的全面寻优提供了一种新的思路.通过实例验证该算法的可行性,最后提出了进一步的研究方向.     

逻辑理论的随机相容度

在[n]值Lukasiewicz命题逻辑系统中,提出理论的随机相容度的概念,并指出理论的随机相容度是和概率分布列的选取相关的。最后证明了理论的随机相容度在[n]值随机逻辑度量空间中,同样保持经典逻辑度量空间中的基本性质。     

Prospect of Node-Line Semimetal Cu<Subscript>3</Subscript>PdN to Be a Topological Superconductor

We investigate systematically the vibrational and electron–phonon interaction properties of node-line semimetal Cu₃PdN under strain and electron doping by using first-principles calculations. It is found that vibrational modes interact with electrons at the Fermi level isotropically with a three-dimensional character. The phonon frequency and Eliashberg spectral function can be tuned by strain remarkably, and the maximum transition temperature (T _c) predicted is 0.03 K under strain ε = 0.10. The coexistence of superconductivity and topological physics in Cu₃PdN makes it a promising candidate for future quantum computation platform.     

An image segmentation method using automatic threshold based on improved genetic selecting algorithm

In this paper, an image segmentation method using automatic threshold based on improved genetic selecting algorithm is presented. Optimal threshold for image segmentation is converted into an optimization problem in this new method. In order to achieve good effects for image segmentation, the optimal threshold is solved by using optimizing efficiency of improved genetic selecting algorithm that can achieve a global optimum. The genetic selecting algorithm is optimized by using simulated annealing temperature parameters to achieve appropriate selective pressures. Encoding, crossover, mutation operator and other parameters of genetic selecting algorithm are improved moderately in this method. It can overcome the shortcomings of the existing image segmentation methods, which only consider pixel gray value without considering spatial features and large computational complexity of these algorithms. Experiment results show that the new algorithm greatly reduces the optimization time, enhances the anti-noise performance of image segmentation, and improves the efficiency of image segmentation. Experimental results also show that the new algorithm can get better segmentation effect than that of Otsu’s method when the gray-level distribution of the background follows normal distribution approximately, and the target region is less than the background region. Therefore, the new method can facilitate subsequent processing for computer vision, and can be applied to realtime image segmentation.     

Lua脚本在有限元分析中的应用

针对复杂计算域有限元分析前处理过程中手动建模和边界条件设定烦琐和耗时的问题,以蓄热砖温度场分析为例,讨论Lua脚本在有限元前处理过程中的应用;开发温度场有限元分析程序,基于Lua/C API定义若干接口,使用特例的解析解验证温度场计算结果,基于Lua脚本对蓄热砖温度场进行计算。仿真结果表明,Lua脚本可简化有限元前处理过程,特别是几何建模过程,也便于对计算结果进行参数化分析。     

Fast template matching based on deformable best-buddies similarity measure

Accuracy and speed are the essential metrics for the template matching algorithms in solving object tracking problems. Since the method based on Best Buddies Similarity (BBS) has achieved the state-of-the-art performance in terms of accuracy, matching speed becomes the shortest piece of wood of the bucket. In this paper, we propose a fast template matching method based on our deformable BBS measure. The deformable BBS measure enables matching to be performed between the patches in varying sizes, and hence leads to even higher accuracy than the original BBS-based methods. More important, we develop a fast potential-area discovery algorithm based on proposal generation and selection. It significantly reduces the numbers of useless attempts on calculating and comparing similarities of impossible image patches. The experimental results show that, with the deformable BBS measure and the fast potential-area discovery, our template matching method outperforms the state-of-the-art methods in terms of accuracy, speed and robustness.