Optimal operating conditions to maximize the net power of polymer electrolyte membrane fuel cells: The stack-system interface of a commercial 18 kW module

A new, experimental method based on air flow rate rather than current is presented to optimize operating parameters for the stacks and systems of proton exchange membrane fuel cells (PEMFCs) for maximizing their net power. This approach is illustrated for a commercial 18 kW PEMFC module. The impact of contamination pressure drop across the cathode air filter is also investigated on the compressor behavior. It is further shown that a 4V reduction in the compressor voltage reduces its power consumption by 9.1%. Using the 3D graphs of the power-pressure-flow data, it is found that the stack pressure of 180 kPaa is superior to the higher tested pressures as it enhances the net power by 7.0 and 13.7% at different conditions. Application of the present study will lead to the development of PEMFCs with higher power output by optimizing stack pressure, stoichiometry and air flow to properly deliver the system design specifications.     

Modeling and Verification of a Sentiment Analysis System Using Aspect-Oriented Petri Nets

An increasing number of social media and networking platforms have been widely used. People usually post the online comments to share their own opinions on the networking platforms with social media. Business companies are increasingly seeking effective ways to mine what people think and feel regarding their products and services. How to correctly understand the online customers’ reviews becomes an important issue. This study aims to propose a method with the aspect-oriented Petri nets (AOPN) to improve the examination correctness without changing any process and program. We collect those comments from the online reviews with Scrapy tools, perform sentiment analysis using SnowNLP, and examine the analysis results to improve the correctness. In this paper, we apply our method for a case of the online movie comments. The experimental results have shown that AOPN is helpful for the sentiment analysis and verifying its correctness.     

采用随机Petri网的嵌入式机载软件可靠性检测

针对嵌入式机载软件设计中存在的典型缺陷问题，结合嵌入式机载软件任务调度特性，提出采用随机Petri网对嵌入式机载软件设计进行仿真验证的可靠性检测方法，以提高嵌入式机载软件设计的可靠性。该方法采用随机Petri网对嵌入式机载软件系统行为建模，并给出典型缺陷的检测策略和判定准则，然后通过对Petri网模型进行仿真验证，检测系统是否存在此类设计缺陷；并给出了软件设计的运行流程的仿真验证算法，以支持对相应设计的可靠性检测。通过与其他可靠性检测方法的比较，表明了该方法的有效性。     

International Trade

Values of net oil imports(-)/exports for Austria, Belgium, Denmark, Finland, France, Germany, Italy, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, the United Kingdom, Japan, Canada, the United States and Australia. Updated on a monthly basis. Number of imports for Belgium, France, Germany, Greece, Republic of Ireland, Italy, Netherlands, Portugal, Spain, Sweden, the United Kingdom, and Other EU-15 (EU-15), Norway, Poland, Switzerland, Turkey, and Other Europe (OECD Europe), Canada, Chile, Mexico, and the United States (OECD Western Hemisphere), and Australia, Japan, Republic of Korea, New Zealand, (OECD Asia-Pacific), and Total OECED. Current data for Austria, Belgium, Finland, France, Germany, Greece, Italy, Netherlands, Portugal, Spain, Sweden, the United Kingdom, Other EU-15 (EU-15), Czech Republic, Hungary, Poland, Slovakia, Turkey, and Other Europe (OECD Europe), Canada, Mexico, and the United States (OECD Western Hemisphere), Australia, Japan, Republic of Korea, and New Zealand (OECD Asia-Pacific). Updated on a monthly basis. Current data for principal importers of natural gas and the amount in which they import from United States, Republic of Korea, United Kingdom, France, Japan, Italy, Germany and Spain (Table 19.1). Current data for principal exporters of natural gas and the amount they export to Canada, Trinidad and Tobago, the United States, Netherlands, Norway, Russia, Turkmenistan, Qatar, Algeria, Nigeria, Indonesia, Malaysia and Australia (Table 19.2). Updated on a monthly basis.     

Use of nets treated with food-grade coatings on dry-cured ham to control Tyrophagus putrescentiae infestations without impacting sensory properties

Dry-cured hams may become infested with the ham mite Tyrophagus putrescentiae during aging. Food-grade coatings have been developed to control mite infestations as a potential alternative to replace methyl bromide, but dipping or spraying these coatings requires additional labor and processing steps. Nets composed of polyester, a polyester/cotton blend and cotton were infused with coatings that consisted of propylene glycol, and either propylene glycol alginate and carrageenan or xanthan gum. Results indicated that the polyester/cotton blend and cotton nets that contained propylene glycol were effective at controlling mite infestations in assays with ham cubes covered in nets. The polyester nets slowed mite growth but were not effective at controlling mite reproduction due to low absorbance of the coatings. Polyester/cotton blend nets treated with coatings on whole hams were not different from control hams with respect to flavor, texture and moistness. Mite infestation tests on whole hams indicated that coated nets with greater stitch densities were effective at controlling mite growth. Future research will include the optimization of coating formulations and scaled-up testing in dry-cured ham plants.     

Preparation of near net size porous alumina-calcium aluminate ceramics by gelcasting-pore-forming agent processs

In the processing of porous ceramics, shrinkage from green body to sintered compact during drying and sintering is one of the key concerns which affect microstructure and properties of porous ceramics. Through releasing gases from the burning of the pore forming agents, and volume expansion from the formation of low density resultants during sintering, the sintering shrinkage can be effectively compensated and near net size preparation can be achieved. Herein, near net size porous alumina-calcium aluminate ceramics with controllable shrinkage have been prepared using a combination of gelcasting and pore-forming agent process by adjusting the amount of CaCO₃ and polymethyl methacrylate (PMMA) microspheres added. Al₂O₃ and CaCO₃ were used as raw materials, PMMA microspheres were used as pore-forming agent, isobutylene/maleic anhydride copolymer (Isobam104) was used as gelling agent and dispersing agent. The effects of the addition amounts of CaCO₃ and PMMA in the slurry on the phase composition, shrinkage, porosity, and strength of porous alumina-calcium aluminate ceramics were investigated. The results show that as the CaCO₃ addition amount increases from 0 to 20 wt%, the shrinkage of the samples gradually decreases from 7.3% to −1.4%, and the consequent porosity increases from 58% to 66%, while the compressive strength increases from 5.9 to 15.5 MPa. When PMMA content increases from 10 to 50 wt%, the shrinkage of the samples decreases first and then increases, the porosity increases from 51% to 74%, and the compressive strength decreases from 12.5 to 5.3 MPa. The mechanisms for controlling shrinkages during preparation of porous alumina-calcium aluminate ceramics can be attributed to the following aspects: on one hand, gas release from burning of PMMA and decomposition of CaCO₃ during sintering; on the other hand, volume expansion due to the formation of lower density calcium aluminates which come from the reactions between CaO and Al₂O₃. The near net size preparation technique is of great significance for the manufacture of porous ceramics since the subsequent machining cost can be effectively reduced.     

近距离煤层煤柱下应力分布和巷道支护技术

针对和尚嘴煤业近距离煤层煤柱下掘进巷道变形大的问题,在介绍地质力学特征的基础上,采用数值模拟分析上部煤层不同方式采动后,采空区和煤柱在下部煤层的应力分布情况。分析煤柱下巷道变形特点和支护要点,结合高预应力强力锚杆支护理论,提出合理的锚网与锚索联合支护设计,现场试验效果明显。     

Ultrasonic vibration-assisted laser engineering net shaping of ZrO2-Al2O3 bulk parts: Effects on crack suppression,microstructure, and mechanical properties

Laser additive manufactured zirconia-alumina ceramic (ZrO₂-Al₂O₃) parts demonstrate severe problems resulting from cracking and inhomogeneous material dispersion. To reduce these problems, we propose a novel ultrasonic vibration-assisted laser engineered net shaping (LENS) process for fabrication of bulk ZrO₂-Al₂O₃ parts. Results showed that the initiation of cracks and the crack propagation were suppressed in the parts fabricated by LENS process with ultrasonic vibration. For the parts fabricated without ultrasonic vibration, the sizes of cracks decreased with the increase of laser power. Scanning electron microscope analyses proved that the introduction of ultrasonic vibration was beneficial for grain refinement and uniform material dispersion. Due to the suppressed cracking, refined grains, and homogenized material dispersion, the parts fabricated with ultrasonic vibration demonstrated better mechanical properties (including higher microhardness, higher wear resistance, and better compressive properties), compared with the parts fabricated without ultrasonic vibration.     

Petri网在计算机网络实时性分析中的应用

计算机网络实时性分析问题一直是国内外各知名院校、研究机构的研究重点之一。Petri网是一种可以描述系统动态行为特性的图形化建模工具,直观形象,易于学习和理解,便于使用。为此,在给出Petri网基本介绍的基础上,探讨了Petri网在计算机网络实时性分析中的应用价值。