液相包覆制备Ce-TZP陶瓷的力学性能与稳定行为

采用XRD、SEM、TEM等分析手段对由液相包覆工艺制备的Ce—TZP陶瓷的微结构进行了研究，并和共沉淀粉体制备的Ce—TZP陶瓷进行了对比分析．力学性能表明，同共沉淀粉体制备的Ce—TZP陶瓷相比，由液相包覆工艺制备的Ce—TZP陶瓷虽硬度下降，但断裂韧性改善；液相添加少量Al2O3硬度随之增加、断裂韧性显著提高．电镜分析表明，液相包覆工艺制备的Ce—TZP陶瓷晶粒尺寸分布宽化，一部分晶粒尺寸较大但CeO2含量低、易发生马氏体相转变晶粒的存在是断裂韧性改善的主要原因．陶瓷体中单斜相大晶粒与四方相之间的残余应力、添加少量Al2O3在晶界上易形成薄的非晶包裹层，是增加可相变四方相数量，提高断裂韧性的其它机制。     

Mutual authentication protocols for RFID systems

With the availability of low-cost radio frequency identification (RFID) tags, security becomes an increasing concern.However, such tags do not permit complex eryptographic functions due to their computational, communications, and storage limitations.In this paper, we investigate the security issues and requirements of RFID systems, and propose ultra-light weight and light weight protocols for low-cost RFID tags. The proposed protocols has been applied to a supply chain management system.     

Wind energy in Sudan : Water pumping in rural areas

New and renewable sources of energy can make an increasing contribution to the energy supply mix of developing countries in view of favourable renewable energy resource endowments, limitations and uncertainties of fossil fuel supplies, adverse balance of payments, and the increasing pressure on the environment from conventional energy generation. Among the renewable energy technologies, the generation of mechanical and electric power by wind machines has emerged as an economically viable and cost effective option. Therefore the Sudanese government has begun to pay more attention to the use of wind energy in rural areas in particular as a cost-effective solution to assist in water pumping and irrigation.     

梁之歌

北地里,千宅万户的屋梁受尽风欺雪压犹自温柔地抱着一团小小的燕巢。这是最温情的守候。人世间,千秋万代的屋梁穷尽一生之力,默默擎起身下各异的居所。这是最无私的担当。可古往今来,自喻有情的世人皆赞梁间燕,梁     

On the wind energy resources of Sudan

The imminent exhaustion of fossil energy resources and the increasing demand for energy were the motives for those reasonable in Sudan to put into practice an energy policy based on rational use of energy; and on exploitation of new, and renewable energy sources. After 1980, as the supply of conventional energy has not been able to follow the tremendous increase of the production demand in rural areas of Sudan, a renewed interest for the application of wind energy has shown in many places. Therefore, the Sudanese government began to pay more attention to wind energy utilisation in rural areas. Because the wind energy resource in many rural areas is sufficient for attractive application of wind pumps, and as fuel is insufficient, the wind pumps will be spread on a rather large scale in the near future. Wind is a form of renewable energy, which is always in a non-steady state due to the wide temporal and spatial variations of wind velocity. A number of years worth of data concerning wind speed in Sudan have been compiled, evaluated and presented in this article. The need for the provision of new data stations in order to enable a complete and reliable assessment of the overall wind power potential of the country is identified and specific locations suggested. This paper presents the background and ideas of the development of the concept as well as the main results, and experience gained during ongoing project up to now. In Sudan, various designs of wind machines for water pumping have been developed and some designs are presently manufactured commercially. Results suggest that wind power would be more profitably used for local-and small-scale applications especially for remote rural areas. It is concluded that Sudan is blessed with abundant wind energy.     

Smart structures and their applications on active vibration control: Studies in the Department of Aerospace Engineering, METU

This work presents the theoretical and experimental studies conducted in Aerospace Engineering Department of Middle East Technical University on smart structures with particular attention given to the structural modelling characteristics and active suppression of in-vacuo vibrations. The smart structures considered in these analyses are finite and flat aluminium cantilever beam-like (called as smart beam) and plate-like (called as smart fin) structures with surface bonded lead–zirconate–titanate patches. Finite element models of smart beam and smart fin are obtained. Then the experimental studies regarding open loop behaviour of the structures are performed by using strain gauges and laser displacement sensor to determine the system models. Further studies are carried out to obtain H _∞ and μ-synthesis controllers which are intended to be used in the suppression of free and forced vibrations of the smart structures. It is observed that satisfactory attenuation levels are achieved and robust performance of the systems in the presence of uncertainties is ensured. In that respect a comparative study involving H _∞ and sliding mode controls is also conducted. Recently, the studies involving aerodynamic loading are also gathering pace.     

Measuring the Resilience of the Trans-Oceanic Telecommunication Cable System

Resilience is the ability of the system to both absorb shock as well as to recover rapidly from a disruption so that it can return back to its original service delivery levels or close to it. The trans-oceanic telecommunication fiber-optics cable network that serves as the backbone of the internet is a particularly critical infrastructure system that is vulnerable to both natural and man-made disasters. In this paper, we propose a model to measure the base resiliency of this network, and explore the node to node and the overall resiliency of the network using existing data for demand, capacity and flow information. The submarine cable system is represented by a network model to which hypothetical disruptions can be introduced. The base resiliency of the system can be measured as the ratio of the value delivery of the system after a disruption to the value deliver of the system before a disruption. We further demonstrate how the resiliency of the trans-oceanic telecommunication cable infrastructure is enhanced through vulnerability reduction.     

Coordinated discharge of a collection of batteries

Collections of batteries are used to supply energy to a variety of applications. By utilizing the energy in such a collection efficiently, we can improve the lifetime over which energy can be supplied to the application. We say that the discharge of a collection of batteries is coordinated when, at the end of discharge, the difference in the remaining capacity of individual batteries is small. This paper presents a decision-maker based on a goal-seeking formulation that coordinates the discharge of a collection of batteries. This formulation allows us to use a simple battery model and simple decision-making algorithms. We present results from MATLAB simulations that demonstrate the performance of the decision-maker when energy is drawn out of the collection in three different discharge scenarios. The new decision-maker consistently improves the discharge efficiency obtained using scheduling methods. Our results show that when the discharge is coordinated, the lifetime of the collection is extended.     

Computer Simulation of Fe-Al-Si System Diffusion Couples

Diffusion couples, Fe-6.8 wt% Al-1.0 wt% Si/Fe and Fe-6.3 wt% Al-0.9 wt% Si/Fe were constructed and separately annealed at 1050°C for 3 h and at 1000°C for 64 h. The concentration profiles of Fe, Al and Si atoms in these couples were measured by electron probe micro-analysis (EPMA), while the diffusion behavior was also simulated by coupling thermodynamic and kinetic properties of Fe-Al-Si system. The simulation results were in good agreement with the measured concentration profiles showing the validity of dynamic parameters of Fe-Al-Si system. Calculation was made for Fe-7 wt% Al-1 wt% Si/Fe diffusion couples at 1000?C with different diffusion time. Silicon uphill was found under the influence of aluminum.