We survey the magnetocaloric effect in perovskite-type oxides （including doped ABO3-type manganese oxides, A3B2OT-type two-layered perovskite oxides, and A2B＇B＇＇O6-type ordered double-perovskite oxides）. Magnetic...We survey the magnetocaloric effect in perovskite-type oxides （including doped ABO3-type manganese oxides, A3B2OT-type two-layered perovskite oxides, and A2B＇B＇＇O6-type ordered double-perovskite oxides）. Magnetic entropy changes larger than those of gadolinium can be observed in polycrystalline La1-xCaxMnO3 and alkali-metal （Na or K） doped La0.8Ca0.2MnO3 perovskite-type manganese oxides. The large magnetic entropy change produced by an abrupt reduction of magnetization is attributed to the anomalous thermal expansion at the Curie temperature. Considerable mag- netic entropy changes can also be observed in two-layered perovskites Lal.6Cal.4Mn207 and La2.5-xK0.5＋xMn2O7＋6 （0 〈 x 〈 0.5）, and double-perovskite Ba2Fe1＋xMol-xO6 （0 〈 x 〈 0.3） near their respective Curie temperatures. Com- pared with rare earth metals and their alloys, the perovskite-type oxides are lower in cost, and they exhibit higher chemical stability and higher electrical resistivity, which together favor lower eddy-current heating. They are potential magnetic refrigerants at high temperatures, especially near room temperature.展开更多
The volume anomalies with temperature variations in tin-modified lead zirconate titanate ceramics are investigated. Experimental results show that the volume changes are related to the phase transitions induced with t...The volume anomalies with temperature variations in tin-modified lead zirconate titanate ceramics are investigated. Experimental results show that the volume changes are related to the phase transitions induced with temperature. The magnitude and orientation of crystal volume changes are dependent on the particular phase transition. When antiferroelectrics is transformed to ferroelectrics or paraelectrics the volume expands. Oppositely when ferroelectrics is transformed to antiferroelectrics or paraelectrics the volume contracts. In the transition of antiferroelectric orthorhombic structure to tetragonal structure or ferroelectric low-temperature rhombohedral structure to high-temperature rhombohedral structure, there are also revealed apparent anomalies in the curves of thermal expansion. Among them, the volume strain caused by the transition between antiferroelectrics and ferroelectrics is the biggest in magnitude, and the linear expansion dL/L0 and the expansion coefficient (dL/L0)/dT can reach 2.展开更多
Despite increasing advocacy and adaptation of public-private model of water governance worldwide since the 1990s, today only 5% of the world＇s population is served by water utilities with private involvement. The pre...Despite increasing advocacy and adaptation of public-private model of water governance worldwide since the 1990s, today only 5% of the world＇s population is served by water utilities with private involvement. The present article examines the experience of the water sector in Armenia with private sector participation. The study describes the process of the introduction of public-private partnerships in the water sector and focuses on analyzing the impact of privatization on water utility performance. The analysis employs the partial indicator method for evaluating the impacts in relation to operational, finance, and environmental performance, done by drawing on the database for the five water companies in Armenia. The empirical evidence shows that private participation in general led to improved overall performance. In particular, private involvement resulted in increased operational efficiency in terms of labor productivity, water metering, continuity of service, and revenue collection efficiency. There were mixed improvements in the operating cost coverage ratio. As for environmental performance, there were gains in the reduction of residential water consump- tion, accompanied, however, by an increase in non- revenue water.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No. 11174132)the National Basic Research Program of China (Grant Nos. 2011CB922102 and 2012CB932304)the Priority Academic Program Development of Jiangsu Higher Education Institutions, China
文摘We survey the magnetocaloric effect in perovskite-type oxides （including doped ABO3-type manganese oxides, A3B2OT-type two-layered perovskite oxides, and A2B＇B＇＇O6-type ordered double-perovskite oxides）. Magnetic entropy changes larger than those of gadolinium can be observed in polycrystalline La1-xCaxMnO3 and alkali-metal （Na or K） doped La0.8Ca0.2MnO3 perovskite-type manganese oxides. The large magnetic entropy change produced by an abrupt reduction of magnetization is attributed to the anomalous thermal expansion at the Curie temperature. Considerable mag- netic entropy changes can also be observed in two-layered perovskites Lal.6Cal.4Mn207 and La2.5-xK0.5＋xMn2O7＋6 （0 〈 x 〈 0.5）, and double-perovskite Ba2Fe1＋xMol-xO6 （0 〈 x 〈 0.3） near their respective Curie temperatures. Com- pared with rare earth metals and their alloys, the perovskite-type oxides are lower in cost, and they exhibit higher chemical stability and higher electrical resistivity, which together favor lower eddy-current heating. They are potential magnetic refrigerants at high temperatures, especially near room temperature.
基金This work was supported by the National Defensive Pre-research Fund of China (Grant No. 98J2.1.9).
文摘The volume anomalies with temperature variations in tin-modified lead zirconate titanate ceramics are investigated. Experimental results show that the volume changes are related to the phase transitions induced with temperature. The magnitude and orientation of crystal volume changes are dependent on the particular phase transition. When antiferroelectrics is transformed to ferroelectrics or paraelectrics the volume expands. Oppositely when ferroelectrics is transformed to antiferroelectrics or paraelectrics the volume contracts. In the transition of antiferroelectric orthorhombic structure to tetragonal structure or ferroelectric low-temperature rhombohedral structure to high-temperature rhombohedral structure, there are also revealed apparent anomalies in the curves of thermal expansion. Among them, the volume strain caused by the transition between antiferroelectrics and ferroelectrics is the biggest in magnitude, and the linear expansion dL/L0 and the expansion coefficient (dL/L0)/dT can reach 2.
文摘Despite increasing advocacy and adaptation of public-private model of water governance worldwide since the 1990s, today only 5% of the world＇s population is served by water utilities with private involvement. The present article examines the experience of the water sector in Armenia with private sector participation. The study describes the process of the introduction of public-private partnerships in the water sector and focuses on analyzing the impact of privatization on water utility performance. The analysis employs the partial indicator method for evaluating the impacts in relation to operational, finance, and environmental performance, done by drawing on the database for the five water companies in Armenia. The empirical evidence shows that private participation in general led to improved overall performance. In particular, private involvement resulted in increased operational efficiency in terms of labor productivity, water metering, continuity of service, and revenue collection efficiency. There were mixed improvements in the operating cost coverage ratio. As for environmental performance, there were gains in the reduction of residential water consump- tion, accompanied, however, by an increase in non- revenue water.
