高阻炭刷制备工艺和性能的研究

使用改性环氧树脂为粘结剂,以5种不同种类的石墨粉为原料制备交流串激式高速电机用高阻炭刷．利用X-射线衍射（XRD）、扫描电镜（SEM）对所研制的高阻炭刷样品的微观结构和形貌进行了测试分析,探讨了成型压力和磨粉粒度等工艺条件对研制的高阻炭刷样品性能的影响．实验结果表明：采用粒径〈75μm的T石墨粉为原料,成型压力为100MPa制备的高阻炭刷样品的体积密度、电阻率、抗折强度、洛氏硬度和电机运行时的火花等级等性能指标与英国摩根公司和日本东洋碳素股份有限公司生产的高阻炭刷相似,使用寿命可达380h．     

Trend of China land water storage redistribution at medi- and large-spatial scales in recent five years by satellite gravity observations

The GRACE (Gravity Recovery and Climate Experiment) satellite gravity mission has provided a new method to study land water mass redistribution at medi- and long-spatial scales in recent years. We estimate continental water mass redistribution in China using GRACE observations during 2003 to 2007. The results show some large regions with increase or decrease of land water mass storage in the central northern region, Tibetan Plateau, the Three Gorges region, the place where Qinghai, Sichuan and Gansu provinces meet, and the Altun Mountains region in the Xinjiang Uygur Autonomous Region. In the first two regions, it is obvious that water (ice) mass storages are decreasing. Water mass in the central northern region decreases at a linear rate of 2.4 cm/a equivalent water height, equal to 5.2 billion cubic meters per year during the five years’ period, and water mass depletion in Hebei Province is ∼ 4.5 billion cubic meters per year in the same period, which is consistent with the average water mass depletion of 4.0 billion cubic meters per year of overused underground water in the recent 30 years estimated by Hebei Province Water Resources Bureau. Furthermore, GRACE can detect the water mass accumulation of ∼ 5 cm equivalent water height within the region spreading over about 0.12 million square kilometers due to the Three Gorges dam construction in June 2003. We also find a water mass gain of ∼ 1.1 cm/a in the areas where Qinghai, Sichuan and Gansu provinces meet. This indicates that the climate of these regions has been becoming gradually humid in recent years. Supported by Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX2-YW-202), National Natural Science Foundation of China (Grant No. 40674038), and Program of Key Laboratory of Space Environment and Geodesy of Ministry of Education of China