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The structure and magnetocaloric properties of La1–xCexFe11.44Si1.56 and their hydrides La1–xCexFe11.44Si1.56Hy(x=0, 0.1, 0.2, 0.3, 0.4) were investigated.The samples crystallized mainly in the cubic Na Zn13-type structure with a small amount of α-Fe phase as impurity.The lattice constants and Curie temperature presented the same change tendency with increasing of Ce content.For the hydrides, the influence of Ce content on lattice constants was weakened and the values of H concentration y were approximate to be 1.56.The La1–xCexFe11.44Si1.56 compounds exhibited large values of isothermal entropy change –ΔSm around the Curie temperature TC under a low magnetic field change of 1.5 T.The value of –ΔSm increased and then decreased with increasing Ce content, reached the maximum, 26.07 J/kg·K for x=0.3.TC increased up to the vicinity of room temperature by hydrogen absorption for the Ce substituted compounds, but TC only slightly decreased with increasing Ce content.The first-order metamagnetic transition was still kept in the hydrides and the maximum values of –ΔSm were lower than those of the La1–xCexFe11.44Si1.56 compounds, but still remained large values, about 10.5 J/kg K under a magnetic field change of 1.5 T.The values of –ΔSm were nearly independent of the Ce content and did not increase with increasing x for the hydrides.The La1–xCexFe11.44Si1.56Hy(x=0–0.4) hydrides exhibited large magnetic entropy changes, small hysteresis loss and effective refrigerant capacity covered the room temperature range from 305 to 317 K.These hydrides are very useful for the magnetic refrigeration applications near room temperature under low magnetic field change. 相似文献
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时空制约下的城市居民活动—移动系统——活动分析法的理论和模型进展 总被引:2,自引:0,他引:2
自上世纪80年代以来,活动分析法在西方交通规划、城市研究和地理学等领域中得到了快速发展.活动分析法理论认为出行源于活动,把传统上分离的城市活动系统和出行系统结合起来,形成了城市居民活动一移动系统.国内尚很少文献对活动分析法进行系统综述,因此本文通过评述基于活动分析法的城市活动-移动系统的研究在理解行为、交通和空间等方面的作用,以及指导城市规划的意义,提出了具体研究的概念模型.最后归纳和评述了三种基于活动分析法的应用模型:制约模型、决策模型和关系模型. 相似文献
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通过分析测定了乌鳢鱼片-18℃和-40℃贮藏过程中蛋白质含量、盐溶性蛋白、水溶性蛋白、总巯基含量、过氧化值等随时间的变化规律。结果表明:乌鳢鱼片在-18℃贮藏过程中,盐溶性蛋白含量在第8周急剧下降达到13.27%,水溶性蛋白含量在第2周开始下降,至贮藏末期下降幅度为11.9%,巯基含量也呈下降趋势。两组鱼片前16周的过氧化值(Peroxide value,POV)呈上升趋势,贮藏后期开始下降,贮藏前期-18℃组的过氧化值到第8周时达到最大值0.87 mmol/kg,而此时-40℃组只有0.45 mmol/kg,共轭二烯值在贮藏过程中两组变化都是呈现先上升后下降的趋势。结合上述,-40℃组在一定程度上更好的减缓冻藏过程中乌鳢鱼片的蛋白质脂质变化,但会降低肌肉保水性。 相似文献