The importance of identifying the true catalyst when using Randles-Sevcik equation to calculate turnover frequency

Water splitting will become important to store excess renewable electrical energy into hydrogen. Although the oxygen-evolution reaction (OER) by water oxidation is a critical reaction for water splitting, further investigations are needed to find the details of the OER mechanism for various electrocatalysts. More in particular for homogeneous electrocatalysts, the Randles-Sevcik equation has been extensively applied to determine the turnover frequency (TOF). Herein, using vitamin B₁₂ as a case study, we show that the dynamical deposition/dissolution of the heterogeneous catalyst during OER makes the Randles-Sevcik equation too complicated to be used for calculating the TOF. Indeed, the conventionally applied post-characterization methods do not provide sufficient accuracy to prove the homogeneity of OER mechanisms; thus, using the Randles-Sevcik equation to calculate the TOF is not necessarily correct.     

格点QCD基础求解器及其异构计算实现的性能优化

格点量子色动力学(格点QCD)是研究夸克、胶子等微观粒子间相互作用的重要理论和方法. 通过将时空离散化为四维结构网格, 并将量子色动力学的基本场量定义在网格上, 让研究人员可以使用数值模拟方法, 从第一性原理出发研究强子间相互作用和性质, 但这个过程中的计算量极大, 需要进行大规模并行计算. 格点QCD计算的核心基础为格点QCD求解器, 是程序运行主要的计算热点模块. 本文研究在国产异构计算平台下格点QCD求解器的实现与优化, 提出一套格点QCD求解器的设计实现, 实现了BiCGSTAB求解器, 显著降低了迭代次数; 通过对奇偶预处理技术, 降低了所求问题的计算规模; 针对国产异构加速卡的特点, 优化了Dslash模块的访存操作. 实验测试表明, 相比优化前的求解器获得了约30倍的加速比, 为国产异构超算下格点QCD软件性能优化提供了有益的参考价值.     

Development of correlation equations on hydrogen properties for hydrogen refueling process by machine learning approach

The energy transition which refers to shift of the energy system from fossil-based resources to renewable and sustainable energy sources becomes a global issue to mitigate the progression of climate change. Hydrogen can play an important role in long-term decarbonization of energy system and achievement of carbon neutrality. Currently, the utilization of hydrogen in the energy system is focused on a road transportation sector as a fuel in a vehicle fleet.Compressing gaseous hydrogen is the most well-established technology for storage in hydrogen-fueled vehicles. The refueling hydrogen requires short filling time while ensuring the safety of storage tanks in a vehicle. However, a fast filling of hydrogen in high pressure leads to a rapid temperature rise of hydrogen stored in tank. Therefore, many numerical and experimental studies have been carried out to analyze the filling process. Various thermo-physical properties of gaseous hydrogen such as density, viscosity, and thermal conductivity are required for the numerical studies and the accurate hydrogen properties are essential to obtain reliable results.In this work, a polynomial equation is proposed with respect to temperature and pressure in ranges of 223.15 K < T < 373.15 K and 0.1 MPa < P < 100.1 MPa to present various hydrogen thermo-physical properties by adopting different coefficients. The coefficients are determined by a machine learning method to regress the equation using a great number of reference data. The equation is trained, tested, and validated using different datasets for each property. The order of the equation has been changed from 2 to 5. Then, the accuracies are estimated and compared with respect to the order. The average relative errors (REs) of the 5th order equation are assessed to lower than 0.3% except for molar volume and entropy. The accuracy of the equation is also examined with experimental data and other correlation equations for density, viscosity, and thermal conductivity which are required for numerical simulations of hydrogen refueling. The proposed equation presents better accuracy for viscosity and thermal conductivity than literature equations. In density calculation, a literature equation shows better performance than the proposed equation, but the difference between their accuracies is not so significant. In calculation time comparison, it is revealed that the proposed equation rapidly responses adequate to computational fluid dynamics (CFD) simulations.Results of the study can provide accurate and reliable hydrogen property values in a fast and robust means specifically for simulation of hydrogen refueling process, but not restricted only to the process. Correlation equations proposed in the present work can aid in optimizing a hydrogen value chain including production, storage, and utilization by providing accurate hydrogen property.     

A modified Kozeny–Carman equation for predicting saturated hydraulic conductivity of compacted bentonite in confined condition

Kozeny–Carman (KC) equation is a well-known relation between hydraulic conductivity and pore properties in porous material. The applications of KC equation to predicting saturated hydraulic conductivities of sands and non-expansive soils are well documented. However, KC equation is incapable of predicting saturated hydraulic conductivity of expansive soil (e.g. bentonite) well. Based on a new dual-pore system, this study modified KC equation for improving the prediction of saturated hydraulic conductivities of bentonites. In this study, an assumption that inter-layer space (micropore) has limited effect on fluid flow performance of compacted bentonite was adopted. The critical parameters including total porosity and total tortuosity in conventional KC equation were replaced by macroporosity and tortuosity of macropore, respectively. Macroporosity and microporosity were calculated by basal spacing of compacted bentonite, which was estimated by assuming that specific surface area is changeable during saturation process. A comprehensive comparison of bentonite's saturated hydraulic conductivity predictions, including modified KC equation proposed in this study, conventional KC equation, and prediction method based on diffuse double layer (DDL) theory, was carried out. It was found that the predicted saturated hydraulic conductivity of bentonites calculated using modified KC equation fitted the experimental data better than others to a certain extent.     

基于双相介质理论的煤层甲烷预测技术

基于双相介质理论研究了双相各向同性介质中的纵波方程，并对煤层甲烷进行地震波动方程的数值模拟．正演得到的叠后记录双相介质的反射波振幅明显弱于单相介质，表现出低频共振、高频衰减及固相位移与流相位移为反相的特性．与地震资料和实际开采资料对比吻合较好．     

节理网络模拟研究及其初步应用

本文针对节理岩体进行了二维与三维节理网络模拟研究。基于随机节理网络系统的连通性分析,得出了复杂连通节理网络系统的岩体等效渗透系数的一般表达式。同时,利用三维节理网络模拟,建立了包含随机非贯穿节理的节理网络系统的岩体本构关系,并分析了影响岩体弹性变形性状的因素。     

非线性振动系统在强、弱激励下的混沌表现及分析

以两类受迫。Duffing方程为例,运用数值计算和理论推演方法,对两者混沌吸引子之间差异进行了图形化比较和分析,并利用耗散结构理论对产生差异的原因进行了合理解释。     

回归方程在煤灰成分分析数理统计中的应用

在煤灰成分分析检测项目中有一些通常采用光电比色法进行检验.为了提高数据处理的准确度,采用一元线性回归方程对数据进行数理统计的方法,建立简单的数学模型,可快速、准确地获得计算结果.     

膨胀黏土增长曲线的运动学分析

通过大量室内试验,从运动学角度对4种击实膨胀黏土样的胀缩规律进行了深入研究．研究认为,膨胀曲线、收缩曲线可统称为增长曲线,其特征表现为在最初阶段增长得快,以后逐渐减慢并趋于稳定;通过对试验数据的非线性最小平方回归分析,提出了增长曲线的回归方程;通过对增长曲线速度、加速度特征进行深入研究,揭示出膨胀、收缩过程具有许多相似性,但在本质上两者不是可逆过程,其吸水膨胀速度远大于失水收缩速度．研究结果为膨胀黏土地区的工程建设提供了重要依据．     

Study on the law of methane seepage in the wall of drainage roadway in mining seam-group

Introduction Coal gas (methane) is stored in adsorptive or free-form state in the original coal seam. The free-form methane is in pore space of coal seams and the adsorptive is adsorbed in a state of solid solution in the faces of pore space and the inner structure of coal seams. Generally, the flow law of methane in pore space accords with the diffusion law and its flow in the fracture system of coal seam conforms to Darcy law. Because the pathway of methane flow mainly consists of fracture …