Parameter identification of proton exchange membrane fuel cell via Levenberg-Marquardt backpropagation algorithm

It is essential to develop an accurate model of proton exchange membrane fuel cell (PEMFC) for a reliable operation and analysis, in which unknown parameters usually need to be determined. The inherent nonlinear, strong coupling, and diversification of PEMFC model seriously hinder traditional methods to identify the parameters. For the sake of overcoming these thorny obstacles, Levenberg-Marquardt backpropagation (LMBP) algorithm based on artificial neural networks (ANNs) is proposed for PEMFC parameter identification. Furthermore, the performance of LMBP is thoroughly evaluated and compared with four typical meta-heuristic algorithms under three cases. Simulation results indicate that LMBP performs a higher accuracy and faster speed for parameter identification. In particular, accuracy and convergence speed can achieve as much as 99.8% and 95.9% growth via LMBP, respectively.     

Theoretical analysis and test verification of pull-out forces in shear connectors of composite beam under negative bending moment

Abstract

A mechanical model of steel-concrete composite beams considering horizontal slip and vertical pull-out effects under negative bending moment was established based on the theory of elastic deformation. By using the principle of force equilibrium and deformation compatibility condition, the differential equation was derived and deduced using computational calculation program, in which the formula of the pull-out force in shear connectors under negative bending moment was obtained. The experiment was conducted in order to verify the reliability of theoretical results. The results show: under the same load condition, the pull-out force of a single stud increases with the increase of the stud spacing. All the theoretical results were verified by comparing with experiment results to illustrate the accuracy and reliability of the calculation method. It provides a theoretical reference for the study of the interface interaction considering horizontal slip and vertical pull-out effect in the negative bending moment region of continuous composite beams.     

Multi-shelled CoS2–MoS2 hollow spheres as efficient bifunctional electrocatalysts for overall water splitting

The exploration of highly efficient non-precious electrocatalysts is essential for water splitting devices. Herein, we synthesized CoS₂–MoS₂ multi-shelled hollow spheres (MSHSs) as efficient electrocatalysts both for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) using a Schiff base coordination polymer (CP). Co-CP solid spheres were converted to Co₃O₄ MSHSs by sintering in air. CoS₂–MoS₂ MSHSs were obtained by a solvothermal reaction of Co₃O₄ MSHSs and MoS₄²⁻ anions. CoS₂–MoS₂ MSHSs have a high specific surface area of 73.5 m²g^-1. Due to the synergistic effect between the CoS₂ and MoS₂, the electrode of CoS₂–MoS₂ MSHSs shows low overpotential of 109 mV with Tafel slope of 52.0 mV dec⁻¹ for HER, as well as a low overpotential of 288 mV with Tafel slope of 62.1 mV dec⁻¹ for OER at a current density of 10 mA cm⁻² in alkaline solution. The corresponding two-electrode system needs a potential of 1.61 V (vs. RHE) to obtain anodic current density of 10 mA cm⁻² for OER and maintains excellent stability for 10 h.     

Syngas production via partial oxidation of dimethyl ether over Rh/Ce0.75Zr0.25O2 catalyst and its application for SOFC feeding

Dimethyl ether (DME) partial oxidation (PO) was studied over 1 wt% Rh/Ce_0.75Zr_0.25O₂ catalyst at temperatures 300–700 °C, O₂:C molar ratio of 0.25 and GHSV 10000 h⁻¹. The catalyst was active and stable under reaction conditions. Complete conversion of DME was reached at 500 °C, but equilibrium product distribution was observed only at T ≥ 650 °C. High concentration of CH₄ and low contents of CO and H₂ were observed at 500–625 °C 75 cm³ of composite catalyst 0.24 wt% Rh/Ce_0.75Zr_0.25O₂/Al₂O₃/FeCrAl showed excellent catalytic performance in DME PO at O₂:C molar ratio of 0.29 and inlet temperature 840 °C which corresponded to carbon-free region. 100% DME conversion was reached at GHSV of 45,000 h⁻¹. The produced syngas contained (vol. %): 33.4 H₂, 34.8 N₂, 22.7 CO, 3.6 CO₂ and 1.6 CH₄. Composite catalyst demonstrated the specific syngas productivity (based on CO and H₂) in DME PO of 42.8 m³·L_cat⁻¹·h⁻¹ (STP) and the syngas productivity of more than 3 m³·h⁻¹ (STP) that was sufficient for 3 kW_e SOFC feeding. PO of natural gas and liquified petroleum gas can be carried out over the same catalyst with similar productivity, realizing the concept of multifuel hydrogen generation. The syngas composition obtained via DME PO was shown to be sufficient for YSZ-based SOFC feeding.     

An adaptive Kriging method with double sampling criteria applied to hydrogen preparation case

Kriging model has been widely used to approximate expensive black-box problems in many engineering design fields. How to choose an appropriate sampling strategy to produce new expensive updated points is crucial. For this purpose, an adaptive Kriging method with double sampling criteria (AKM-DSC) is proposed. During every iteration of it, maximum curvature criterion and maximum variance criterion based on Kriging model are respectively optimized by trust region (TR) strategy to produce two candidate points. And then, a new screening method is used to determine final expensive-evaluation points from the two candidates. The proposed method is compared with the two typical Kriging modeling methods. The comparison results of seventeen benchmark functions verify that the proposed method can generate higher accuracy Kriging model. Finally, a hydrogen preparation case illustrates the engineering application value of the AKM-DSC method.     

光学材料的磨削损伤控制试验研究

基于K9玻璃不同的磨削工艺参数确定其磨削损伤层深度随工艺参数变化的规律，并通过工件磨削损伤层深度的动态检测研究其裂纹扩展规律。结果表明:工件磨削过程中的裂纹损伤是动态扩展过程。固定工艺参数下，裂纹稳态扩展，损伤层深度不变；采用损伤更小的工艺参数磨削，裂纹的扩展速度小于材料的去除速度，其损伤层深度逐渐减小，损伤的去除速度逐渐减慢直至二者间达到稳态平衡。同时，为了去除前道工序的损伤层，后道工序的材料去除量需达到前道工序损伤层深度的2～3倍。      

超高效液相色谱-飞行时间质谱法快速分析测定山药中7种常见杀菌剂

目的 建立超高效液相色谱-飞行时间质谱检测山药中7种常见杀菌剂的分析方法。方法 样品经乙腈提取，水浴氮吹至近干，丙酮定容，经超高效液相色谱-飞行时间质谱检测。结果 在正离子模式下，7种杀菌剂在水-甲醇（均含有0.01%甲酸和5 mmol/L甲酸铵）流动相中都具有较好的响应；0.01~0.40 mg/L范围内线性良好，相关系数R均大于0.999。不同温度（50℃、70℃）水浴实验结果表明70℃水浴温度符合实验要求。三个浓度水平的加标回收实验的回收率为70.75％～108.07％，相对标准偏差为 0.02％～5.01％。结论 该方法操作简单、分析准确，满足山药中常见杀菌剂的检测要求。     

Isolation,purification, and characterization of the globulin from wheat germ

This research optimized the extraction and purification of globulin from wheat germ and assessed the molecular weight distribution and structure properties of the globulin obtained. The results showed that the relative extraction efficiency and purity of wheat germ globulin (WGG) reached 18.0% and 89.1% under the enzymolysis conditions of 0.32‰ α-amylase, pH 6.5, and 55 °C. The maximal precipitation rate of WGG (91.3%) was obtained with pH 4.3 (acid precipitation). Additionally, the molecular weight of WGG was mainly distributed below 70 kDa. FT-IR confirmed that random coils (30.95%), β-sheet (27.02%), α-helix (26.55%), and β-turn (15.48%) were the secondary structures of WGG. Furthermore, LTQ mass spectrometry showed that WGG was rich in variety and high in complexity, which retrieved 1274 proteins belonging to 392 proteomes by inverse peptide analysis. The findings endow a great potential of preparing WGG with superior functionality for food applications.     

平煤十三矿采动覆岩裂隙演化规律研究

当煤矿自矿区采出时,采空区上覆岩层会发生变形破坏,一方面煤矿资源会向裂隙发育部位运移,另一方面则存在一定的矿区安全隐患。为了保证煤矿开采工程的安全性,准确掌握矿产运移分布情况,本文采用了关键层理论和数值模拟的方法,以此分析采动覆岩的裂隙演化规律。研究结果显示,裂隙在走向和倾向上呈现出"梯形台"发育特征,在采空区上方裂隙呈现出中部压实、四周发育的"O"形圈分布;在采空区边缘形成卸压区域,此区域裂隙发育,具有较好的抽采效果。除此之外,采空区中部压实区域宽度范围为175m,裂隙不发育,离层率趋于0;采空区进风巷侧35m、回风巷侧30m范围内离层率较大,最大离层率达到了136mm/m。本文通过数值模拟得到了平煤十三矿采动覆岩的裂隙演化规律,这不仅为煤矿资源抽采提供了理论依据,而且为煤矿安全事故防治工作提供了保障。