Effect of friction stir welding process parameters on Mg-AZ31B/Al-AA6061 joints

In the present study, dissimilar alloys such as Mg-AZ31B and Al-AA6061 were joined by friction stir welding using different rotational (560, 710, 860 and 1010?rpm) and transverse speeds (16 and 25?mm/min). Metallographic studies (by optical, scanning electron microscope, SEM, and energy dispersive spectrometer, EDS) revealed that the speed parameters mainly influenced the microstructure growth mechanism, which further affects the mechanical properties and corrosion behavior. The combined dynamic action of rotational to transverse speed recrystallized and plasticized the material and produced an alternative lamellar shear band of Al and Mg in the stir zone (SZ). Peak temperature and high rotational speed formed an oxide on the top region and also caused liquation and intermetallic (IMCs) formation. Tensile strength and hardness increased as per the Hall–Petch (fine grains) effect. Higher impact energy was found at moderate rotational and low transverse speeds due to the presence of more soft Al patches. Tensile fractographs showed a river-like pattern, which indicated the brittle nature of the joints. High rotational and high transverse speed illustrated higher tensile strength, while better corrosion resistance was observed in high rotational and low transverse speed.     

Fault diagnosis and refrigerant leak detection in vapour compression refrigeration systems

The environmental impact of refrigeration systems can be reduced by operation at higher efficiency and reduction of refrigerant leakage. Refrigerant loss contributes both directly and indirectly to global warming through inefficient system operation, increased power consumption and greenhouse gas emissions and higher maintenance costs. Existing sensor-based leak detection methods are limited by the inability to detect gradual leakage and the need for careful sensor location. There is a requirement for a real-time performance monitoring approach to leak detection and fault diagnosis which overcomes these disadvantages.This paper reports on the development of a fault diagnosis and refrigerant leak detection system based on artificial intelligence and real-time performance monitoring. The system has been used successfully to distinguish between faulty and fault free operation, steady-state and transient operation, leakage and over charge conditions. Work currently underway is aimed at testing additional fault conditions and establishing further rules to distinguish between these patterns.     

中国制冷空调行业制冷剂替代策略的思考

中国制冷空调行业淘汰HCFCs面临国际上的巨大压力和挑战。为此,从直接排放和间接排放2个方面对制冷剂应用对环境影响以及从制冷剂管理方面进行分析与阐述,提出制冷空调行业应负责任地使用制冷剂:提高制冷空调设备效率,降低制冷剂间接排放,减少制冷剂充注量,加强控制制冷剂泄漏,提高制冷剂回收、再生利用率来减少制冷剂的直接排放;应进行可燃制冷剂应用的基础研究和制定产品及应用安全标准,寻找对环境影响最小、经济可行、替代成本市场可接受、安全的替代制冷剂。同时建议行业协会配合国家有关部门制定适合中国国情的HFCs制冷剂的减排基准线和减排时间表。     

Innovation, change, and order: Reflections on science and technology in India, China, and the United States

A comparative analysis of science and technology policies in China, India, and the United States shows striking similarities and sharp contrasts. These differences reveal much about the current problems and likely prospects in each country. This review distills the contributions of 15 distinguished leaders in science and technology who assess national goals and international ambitions. The review covers five themes: education, defense and space, R&D performers, science and technology in the economy, and governmental policies and funding. Other issues include: economic freedom, global competitiveness, energy and the environment, and population and demographic trends. Brief historical highlights provide context for understanding past trends in the present socioeconomic setting.     

科学 技术 工程及科学家 工程师 企业家

论述了科学、技术、工程的性质与相互关系以及科学家、工程师、企业家的任务；为科学技术创新，发展经济，振兴国家，指出了应采取的对策。     

GLONASS时间频率传递研究

分析了基于GNSS的时间频率传递方法的发展趋势和GLONASS发展现状及趋势。对GLONASS时间频率传递进行了研究,就其原理实现、误差补偿及数据处理进行了阐述,实现了GLONASS时间频率传递的基本方法,实施了GLONASS和GPS时间频率传递实验。将两种时间频率传递结果进行了对比,对GLONASS时间频率传递自身性能进行了分析,结果显示:GLONASS时间频率传递已达到了可与GPS时间频率传递相比较的水平。     

Dispersion and surface functionalization of oxide nanoparticles for transparent photocatalytic and UV-protecting coatings and sunscreens

Abstract

This review describes recent efforts on the synthesis, dispersion and surface functionalization of the three dominating oxide nanoparticles used for photocatalytic, UV-blocking and sunscreen applications: titania, zinc oxide, and ceria. The gas phase and liquid phase synthesis is described briefly and examples are given of how weakly aggregated photocatalytic or UV-absorbing oxide nanoparticles with different composition, morphology and size can be generated. The principles of deagglomeration are reviewed and the specific challenges for nanoparticles highlighted. The stabilization of oxide nanoparticles in both aqueous and non-aqueous media requires a good understanding of the magnitude of the interparticle forces and the surface chemistry of the materials. Quantitative estimates of the Hamaker constants in various media and measurements of the isoelectric points for the different oxide nanoparticles are presented together with an overview of different additives used to prepare stable dispersions. The structural and chemical requirements and the various routes to produce transparent photocatalytic and nanoparticle-based UV-protecting coatings, and UV-blocking sunscreens are described and discussed.     

A review of sustainability metrics for the construction and operation of airport and roadway infrastructure

Sustainability has become increasingly important, however, relatively little attention has focused on metrics for the construction and operation of airport and roadway infrastructure. Most attention has focused on buildings, with high profile BREEAM and LEED projects taking center stage. Sustainability is also important in airport and roadway infrastructure projects, which have significant public impact but have a much lower profile than vertical construction when it comes to sustainability. Sustainable infrastructure is important in China and India where new infrastructure is under construction to meet growing and developing economies, and in the US, where infrastructure is in substandard condition and requires reconstruction. The purpose of this paper is to provide an overview and discussion of sustainability rating systems for airport and roadway infrastructure, including both construction and operation. Specific projects that highlight both proven and innovative sustainable practices are included to illustrate the application of these concepts. Finally, the relationship between sustainable transportation infrastructure and resilient transportation infrastructure is addressed since resiliency is of growing interest and there is overlap between these concepts.     

Thermodynamic analysis of the V-type Stirling-cycle refrigerator

The thermodynamic analysis of a V-type Stirling-cycle refrigerator is performed. The Stirling-cycle refrigerator consists of expansion and compression spaces, cooler, heater and regenerator, and divided into 14 fixed control volumes subjected to a periodic mass flow. The conservation of mass and energy equation are written for each control volume. A computer program is prepared in FORTRAN, and the basic equations are solved iteratively. The mass, temperature and density of working fluid in each control volume are calculated for a given charge pressure, engine speed, and fixed heater and cooler surface temperatures, and the results are obtained from a PC. The heat transfer coefficients are assumed constant. The work, instantaneous pressure and COP of the Stirling-cycle refrigerator are also calculated. The steady cyclic conditions are obtained for temperature after few cycles and the results are given by diagrams.     

Studies on Properties and Structure of Electroless Plating Tin Coating

The composition and structure of electroless tin coating were analyzed by SEM and X-ray diffraction. In the meantime, porosity, solderability and extensibility were determined by physical and chemical methods. The results showed that the porosity of the tin coating increases with the rise of bath temperature and decreases as the plating time rises. Solderability is improved with the rise of thickness of tin coating, and decreases when the tin deposit is heated at 180 ～ 200 ℃. The crystalline grain size becomes bigger and bigger with increasing plating time or bath temperature or coating thickness. X-ray diffraction indicates that only Cu and β-Sn phases show up in the diffraction patterns. Tin coating has a strong joint force with copper substrate and excellent function of electrochemical protection as anode coating.