Climatological relationships among the tropical cyclone frequency,duration, intensity and activity regions over the Western Pacific

Climatological relationships among the tropical cyclone (TC) frequency, duration, intensity and activity regions over the Western Pacific are explored based on long-term best track data. Frequent TC occurrence does not necessarily imply a long duration of TCs in the same periods. Three types of relationship between TC number and duration in the period 1945–2007 were identified in this study: low frequency and short duration during 1945–1955 (Period I); high frequency and short duration in the 1960s (Period II); and high frequency and long duration in the 1990s (Period III). TC activity regions differed among the three periods. During Period I, the main activity regions were over the ocean east of the Philippines (120°–140°E). During period II, two prevailing storm tracks extended west-northwest between 110° and 147°E. During period III, TCs had an extensive activity region from 110° to 160°E. TC intensity is related closely to activity regions. Most strong TCs developed over the ocean far from the Philippines, and had a northwestward track. Our results also show that the relationships between TC frequency, duration and their active regions are modulated strongly by broad-scale vertical motion, geopotential height and horizontal wind anomalies.     

基于激光通信链路的星间时间同步技术

时间同步技术对于导航、定位、授时都有重要作用,是空间应用领域的热门方向.激光通信技术具有通信容量大、保密性和抗干扰性强等优点,因此受到越来越广泛的应用.本文提出了基于激光通信链路的时间同步技术,通过数据帧头实现粗测距,通过接收时钟相位实现精测距.通过理论分析,获得了基于激光通信链路的时间同步精度的理论极限,并进行模拟仿真计算.在双向单程测距条件下,1 Gbps通信速率时可以获得毫米级的测量精度和皮秒级的时间同步精度.采用BPSK相干通信体制,在实验室进行了基于激光通信链路的时间同步试验,结果符合理论预期.     

HIF-1-modified BMSCs improve migration and reduce neuronal apoptosis after stroke in rats

Bone marrow-derived mesenchymal stem cells (BMSCs) have been demonstrated ameliorating neurologic deficits after stroke. Hypoxia-inducible factor-1 (HIF-1), the key regulator of cellular responses to low oxygen concentration, can activate multiple genes involving in crucial aspects for neurologic recovery. In this study, we present that rat BMSCs overexpression of HIF-1 α showed higher expression of HIF-1 target genes in HIF-1-BMSCs, including CXCR4, EPO, and VEGF. BMSCs-mHIF-1α also exhibited an enhanced mobility towards the ischemic area within rat brain. Neural cell apoptosis in ischemic brain shown less severe in rats transplanted with HIF-1-BMSCs. Furthermore, the number of cells expressing neural progenitor markers PAX6 and DCX were increased in BMSCs-mHIF-1α-transplanted rats. These results suggest that HIF-1α in BMSCs reduces neuronal apoptosis and promotes neurogenesis after stroke in rats.