Theoretical Study on Novel Refrigerant Mixture R1270/R152a/R13I1

A new refrigerant mixture,R1270/R152a/R13I1,is proposed as a substitute for R22 in this paper.The thermophysical properties of this environment-friendly mixture and its refrigeration system performance are theoretically analyzed with the software Refprop 8.0.The results show that the COP and the unit volume refrigerating capacity of the system with the new refrigerant mixture is equivalent to those with R22 under the standard working condition.Under the variable working condition,the temperature glide of th..

经导管主动脉瓣置换术后患者发生结构性瓣膜退化的研究进展

结构性瓣膜退化（SVD）是人工心脏瓣膜的自身组件发生内在不可逆的病理改变，表现为瓣膜纤维化、钙化、磨损、撕裂、松弛以及支架断裂或变形等，最终导致瓣膜狭窄和/或反流。经导管主动脉瓣置换术（TAVR）后出现SVD的发生机制可能与机械应力、免疫反应及钙磷代谢异常有关。TAVR后SVD的危险因素包括患者因素（如年龄、心血管基础疾病及其合并症）、瓣膜因素（如材料、处理方式、类型）和手术因素（如瓣膜损伤、支架扩张不良、支架释放形态不规则）。临床上影像学评估TAVR后SVD时，超声心动图、多排螺旋计算机断层扫描和心脏磁共振成像各有优势，评估目的也有不同。主要应对策略包括药物治疗、再次TAVR、外科主动脉瓣置换术（SAVR）及SURPLUS术。再次TAVR因其微创性成为常用方法，但仍需进一步明确患者适应证和优化手术策略；SAVR适用于年轻、低风险患者；SURPLUS术则结合了SAVR和TAVR的优点，适用于再次TAVR不可行或有禁忌证，同时SAVR风险过高者。本文就SVD在TAVR治疗背景中的最新研究进展进行综述，以期为生物瓣耐久性研究和临床干预SVD提供参考

Analysis of the Research on the Application of hydrocarbon in Refrigeration and air conditioning

In the paper, application of hydrocarbons as alternatives in Refrigeration and air conditioning system is analyzed. At the same time, it's environmental protection, safety, pertinent standards, cycle characteristics, heat transfer characteristics and the states of refrigeration devices which had been used are all discussed. The result showed that hydrocarbons have excellent thermal properties and better GWP, and can be used widely in the field of refrigeration under taking necessary measures to keep away it's flammability

Analysis of the Research on the Application of hydrocarbon in Refrigeration and air conditioning

In the paper, application of hydrocarbons as alternatives in Refrigeration and air conditioning system is analyzed. At the same time, it's environmental protection, safety, pertinent standards, cycle characteristics, heat transfer characteristics and the states of refrigeration devices which had been used are all discussed. The result showed that hydrocarbons have excellent thermal properties and better GWP, and can be used widely in the field of refrigeration under taking necessary measures to keep away it's flammability

陕西省植被时空演变特征及其对气候变化的响应

利用 G I MM S /ND VI数据分析了陕西省 1982 2006年的植被覆盖时空演变, 并探讨了植被时空变化对气候变 化的响应。 分析发现, 陕西省 ND VI空间分布具有自南向北递减的特点, 陕西北部、中部和南部三区四个季节的 ND VI均 以夏季最大, 春季和秋季相当, 冬季最小。 25年来 , 三区 ND VI显著增加, 其中以春季增幅最大, 夏季反而有下降的趋势。 三区气温增加趋势明显 , 导致生长期的延长, 这是 ND VI增加的主要原因之一; 三区年总降水呈减少趋势 , 降水的减少并 未使得 ND VI减少, 这说明当地降水可以满足植被生长的基本条件; 夏季 N DV I的减少可能与人类活动增加有关。 在年 内尺度上, 三区温度的增加利于植被覆盖的增长; 降水量的增加为植被覆盖的增长提供更充足的水分, ND VI的增加主要 出现在月降水量小于 100 mm 时, 当该月降水量大于 100 mm 时 ND VI并无明显增加趋势