Effect of a sweeping air stream and gas–phase aspect ratio of an isothermal Stefan diffusion column on the experimental estimation of binary gas diffusivities

The Stefan column consists of liquid A evaporating into an inert/stagnant gas B with a sweeping B stream at the top. It was designed to estimate binary gas diffusivities, D_AB’s, but “end effects” such as gas mixing at the top and interfacial curvature have been either ignored or uncorrelated to the operational settings. This study’s hypothesis is that gas mixing at the top and the gas–phase aspect ratio affect D_AB estimation in the acetone (A)-ambient air (B) system at 50?°C. The sweeping stream Reynolds number (Re) and the gas–phase aspect ratio (AR?=?initial gas phase height to column internal diameter) were the variables tested. Isothermal evaporation-diffusion experiments were conducted in which the temporal interfacial descent was tracked. The settings were 492 ≤ Re ≤ 5378 and AR between 5 and 15. A 1D transport model allowed determination of the experimental diffusivity, D_AB,exp, by nonlinear regression. For Re < 600, the D_AB,exp errors relative to D_AB,CE (predicted by the Chapman–Enskog kinetic theory for low-density gases) were small and unrelated to AR, while for Re > 600 the errors increased considerably with Re and were inversely proportional to AR. This study is the first to relate the column’s operational settings to the D_AB estimation errors. The column should be operated at low sweeping gas Re and large AR for accurate D_AB,exp’s. The low Re region deserves further study, while the present transport model may have to be replaced by computational fluid dynamics simulations to account for the multidimensional gas flow patterns.     

Effect of the ZIF‐8 Distribution in Mixed‐Matrix Membranes Based on Matrimid® 5218‐PEG on CO2 Separation

In theory, the combination of inorganic materials and polymers may provide a synergistic performance for mixed‐matrix membranes (MMMs); however, the filler dispersion into the MMMs is a crucial technical parameter for obtaining compelling MMMs. The effect of the filler distribution on the gas separation performance of the MMMs based on Matrimid®‐PEG 200 and ZIF‐8 nanoparticles is demonstrated. The MMMs were prepared by two different membrane preparation procedures, namely, the traditional method and non‐dried metal‐organic framework (MOF) method. In CO₂/CH₄ binary mixtures, the MMMs were tested under fixed conditions and characterized by various methods. Finally, regardless of the MMM preparation procedure, the incorporation of 30 wt % ZIF‐8 nanoparticles allowed to increase the CO₂ permeability in MMMs. The ZIF‐8 dispersion influenced significantly the separation factor.     

面向二进制程序的导向性模糊测试方法

为了解决当前模糊测试技术中变异存在一定的盲目性以及变异生成的样本大多经过相同的高频路径的问题，提出并实现了一种基于轻量级程序分析技术的二进制程序模糊测试方法。首先对目标二进制程序进行静态分析来筛选在模糊测试过程中阻碍样本文件深入程序内部的比较指令；随后对目标文件进行插桩来获取比较指令中操作数的具体值，并根据该具体值为比较指令建立实时的比较进度信息，通过比较进度衡量样本的重要程度；然后基于模糊测试过程中实时的路径覆盖信息为经过稀有路径的样本增加其被挑选进行变异的概率；最后根据比较进度信息并结合启发式策略有针对性地对样本文件进行变异，通过变异引导提高模糊测试中生成能够绕过程序规约检查的有效样本的效率。实验结果表明，所提方法发现crash及发现新路径的能力均优于模糊测试工具AFL-Dyninst。     

Binary whale optimization algorithm: a new metaheuristic approach for profit-based unit commitment problems in competitive electricity markets

This article presents a metaheuristic approach, the binary whale optimization algorithm (BWOA), to solve complex, constrained, non-convex, binary-nature profit-based unit commitment (PBUC) optimization problems of a price-taking generation company (GenCo) in the electricity market. To simulate the binary-nature PBUC problem, the continuous, real-value whale position/location is mapped into binary search space through various transfer functions. This article introduces three variants of BWOA using tangential hyperbolic, inverse tangent (arctan) and sigmoidal transfer functions. The effectiveness of the BWOA approaches is examined in test systems with different market mechanisms, i.e. an energy-only market, and energy and reserve market participation with different reserve payment methods. The simulation results are presented, discussed and compared with other existing approaches. The convergence characteristics, solution quality and consistency of the results across different BWOA variants are discussed. The superiority and statistical significance of the proposed approaches with respect to existing approaches is also presented.     

A Frame Breaking Based Hybrid Algorithm for UHF RFID Anti-Collision

Multi-tag collision imposes a vital detrimental effect on reading performance of an RFID system. In order to ameliorate such collision problem and to improve the reading performance, this paper proposes an efficient tag identification algorithm termed as the Enhanced Adaptive Tree Slotted Aloha (EATSA). The key novelty of EATSA is to identify the tags using grouping strategy. Specifically, the whole tag set is divided into groups by a frame of size F. In cases multiple tags fall into a group, the tags of the group are recognized by the improved binary splitting (IBS) method whereas the rest tags are waiting in the pipeline. In addition, an early observation mechanism is introduced to update the frame size to an optimum value fitting the number of tags. Theoretical analysis and simulation results show that the system throughput of our proposed algorithm can reach as much as 0.46, outperforming the prior Aloha-based protocols.     

Effect of cyclotron resonance on ‘hot’ dispersion in a staggered double metallic grating sheet beam travelling wave tube

Based on the beam wave synchronous interaction in transverse and longitudinal directions at the same time and starting from Maxwell’s equation and linear Vlasov equation, the beam–wave interaction ‘hot’ dispersion equation considering both cyclotron resonance and Cherenkov resonance in a staggered double metallic grating traveling wave tube is deduced. Through the reasonable selection for geometric and electrical parameters, the numerical calculation and analysis of the ‘hot’ dispersion equation shows that the beam–wave interaction gain and frequency band with the cyclotron resonance enhancement effect are higher than those with only Cherenkov resonance radiation.     

基于DoG检测图像特征点的快速二进制描述子

针对SIFT描述子实时性差和传统二进制描述子对尺度、旋转和视角变化鲁棒性差的问题,本文通过优化采样模式和添加灰度差分不变量比较测试进行改进,提出了一种鲁棒性更高的二进制描述子。首先,设计了一种尺度关联、编号标记的采样模式;然后,旋转采样模式中各采样点到特定位置,确保描述子尺度、旋转不变性;接着,分析了采样点点对模式对描述子的影响,选择使用机器学习训练后的128对采样点对;最后,选择灰度值比较测试及梯度绝对值和比较测试构建二进制描述子。实验中采用DoG检测图像关键点,结果表明:本文提出的描述子在描述子构建和描述子匹配上比SIFT描述子分别快84%和67%;在有视角变化的图像匹配上,准确率比传统的二进制描述子高3%~5%,召回率平均要高30%以上。本文提出的特征点描述方法适用于时间要求高的图像匹配领域。     

Effect of copper on improving the electrochemical storage of hydrogen in CeO2 nanostructure fabricated by a simple and surfactant-free sonochemical pathway

Introducing high-performance compounds for hydrogen sorption is of interest because of their advantages for substantial applications such as energy storage. Here, the role of copper addition on hydrogen storage capability and Coulombic efficiency of CeO₂ nanostructure (fabricated by an easy and surfactant-free sonochemical pathway) was examined, for the first time. Nanostructured oxides were fabricated with loading various percentages of copper (4 wt% and 40 wt%) inside CeO₂. Nanostructured copper-ceria binary oxides were checked by diverse analyses. The hydrogen storage performance as well as Coulombic efficiency of the nanostructured copper-ceria binary oxides and the net CeO₂ were checked through chronopotentiometry charge−discharge pathway in the alkaline medium. The outcomes exhibited that the hydrogen storage capacity of CeO₂ nanostructure could be enhanced with adding the proper dosage of copper as a beneficial low-cost solution. Self-assembled copper-doped CeO₂ hierarchical nanostructures could display the most appropriate performance than the net CeO₂ and nanostructured Cu₂O–CeO₂. The discharge capacity for the self-assembled copper-doped CeO₂ hierarchical nanostructures (fabricated by adding 4 wt% copper) could rise to 5070 mAh/g at 22nd cycle. Appropriate porosity, special architecture and unique morphology as well as convenient surface area of the self-assembled copper-doped CeO₂ hierarchical nanostructures render they can be very beneficial compounds in the energy storage.     

基于实物期权的煤层气利用项目投资评价研究

实物期权法是对项目决策中的灵活性价值进行定量评估的一种方法，是对传统经济评价方法净现值法的修正补充。采用实物期权理论和方法，分析煤层气利用项目可研建设阶段和生产运营阶段的期权特征，确定出煤层气利用项目总价值为现金流量净现值与项目灵活性价值之和。采用二叉树期权定价方法，构建基于实物期权的煤层气利用项目投资评价方法和模型。并结合煤层气脱氧制液化天然气项目实例，在确定评价参数的基础上，分别用净现值法、基于实物期权的延迟期权方法、扩张期权方法及复合期权方法，计算煤层气项目投资价值，同时对评价方法主要影响参数进行敏感性分析。结果表明：实物期权法评价出的煤层气利用项目价值明显高于传统经济评价方法计算出的项目价值，而且组合期权能有效增加项目的价值；标的资产价值和期权执行价格对煤层气利用项目期权价值的影响最大。      

Discrete element method study on hopper discharge behaviors of binary mixtures of nonspherical particles

This study is aimed at unveiling the influence of binary mixtures of nonspherical particles on hopper discharge behavior, which remains poorly understood. The discrete element method (DEM) is employed to simulate seven particle types with aspect ratios between 0 and 2 (namely, a sphere, two ellipsoids, two cylinders, and two cuboids) with the same volume. Seven monodisperse systems and twelve binary-shape mixtures are assessed. For the monodisperse systems, particle shape is the dominant factor dictating discharge rate, compared to other factors like aspect ratio, preferential orientation, and packing. Regarding the binary-shape mixtures, the discharge rates are similar for all twelve mixtures, reflecting a surprising lack of shape effects, which in turn means the negligible impact of solid volume fraction, aspect ratio, and segregation extent. Moreover, collision force is generally negatively correlated with discharge rate.