Characteristics of decadal-centennial-scale changes in East Asian summer monsoon circulation and precipitation during the Medieval Warm Period and Little Ice Age and in the present day

Using meteorological observations, proxies of precipitation and temperature, and climate simulation outputs, we synthetically analyzed the regularities of decadal-centennial-scale changes in the summer thermal contrast between land and ocean and summer precipitation over the East Asian monsoon region during the past millennium; compared the basic characteristics of the East Asian summer monsoon (EASM) circulation and precipitation in the present day, the Little Ice Age (LIA) and the Medieval Warm Period (MWP); and explored their links with solar irradiance and global climate change. The results indicate that over the last 150 years, the EASM circulation and precipitation, indicated by the temperature contrast between the East Asian mainland and adjacent oceans, had a significant decadal perturbation and have been weaker during the period of rapid global warming over the past 50 years. On the centennial time scale, the EASM in the MWP was strongest over the past 1000 years. Over the past 1000 years, the EASM was weakest in 1450-1570. When the EASM circulation was weaker, the monsoon rain belt over eastern China was generally located more southward, with there being less precipitation in North China and more precipitation in the Yangtze River valley; therefore, there was an anomalous pattern of southern flood/northern drought. From the 1900s to 1920s, precipitation had a pat- tern opposite to that of the southern flood/northern drought, with there being less precipitation in the Yangtze River valley and more precipitation in North China. Compared with the case for the MWP, there was a longer-time-scale southern flood/northern drought phenomenon in 1400-1600. Moreover, the EASM circulation and precipitation did not synchronously vary with the trend of global temperature. During the last 150 years, although the annual mean surface temperature around the world and in China has increased, the EASM circulation and precipitation did not have strengthening or weakening trends. Over the past 1000 years, the weakest EASM occurred ahead of the lowest Northern Hemispheric temperature and corresponded to the weakest solar irradiance.     

CT图像中肺结节毛刺特征的计算机量化方法

根据CT图像中肺结节毛刺的生长特点,提出了一种CT图像的肺结节毛刺特征计算机量化分级方法.该方法首先利用动态规划算法对感兴趣的CT图像区域进行肺结节分割,然后在分割的结节边界基础上,通过分析边界附近区域梯度方向的规律性,提取边界法线-梯度正交指数作为结节毛刺特征的量化指标,在此基础上对肺结节毛刺特征进行量化分级.实验结果表明:该指数能够准确地量化肺结节的毛刺特征,对区分无毛刺、短毛刺及长毛刺结节具有较高的分辨率.     

分子动力学的格波理论

应用固体物理学和固体力学的理论,建立了分子动力学的格波理论.该理论将符合周期性几何结构的三维晶体看作代表性体元,研究三维晶体在有限温度下的本构响应.基于周期边界条件,建立三维晶格振动的特征方程,求得三维晶体固有频率,进而得到各个原子动力学方程的解析解.在此基础上求得有限温度下,三维晶体的热应力.该理论有效地克服了经典分子动力学在时间尺度和空间尺度上的困难.     

脚踏实地,肩负使命,迎接挑战——中国博士毕业生职业取向调研分析

中国科协"博士学位获得者的职业取向调查"结果表明,博士毕业生就业时考虑的主要因素是职业类别、发展前景、志向爱好、收入待遇、地域优势等,从事科研工作仍是其主要职业理想,且对职业成就的期望普遍较高;博士毕业生由中小城市向大城市、由中西部向东部流动的特征较为明显,其职业期望及就业实际与社会需求、地域差异等存在结构性矛盾;须迫切转变就业观念,改善中小城市及中西部的就业环境,合理配置科技人力资源,以充分发挥博士毕业生的创新才能。     

一种有效改善射频矢网测量动态范围的方案

文中所提及的射频矢量网络分析仪有窄带测量和宽带测量两种测量方式。本文简单介绍几种常用的提高射频矢网测量动态范围的方法外,从硬件改进的角度提出一种有效提高射频矢量网络分析仪宽带测量动态范围的方案,并用图例方式给出了这种方案的有效性。     

高速并行多处理器系统原理及方案

当前,计算机应用领域对计算机的运算处理速度要求越来越高,而提高单机系统的处理能力是有限的,同时系统成本也会很高。因此并行处理技术成为解决这一矛盾的有效方法之一。并行处理系统从硬件角度采看,基本可分为两类;基于低信道容量网络的多计算机系统。这类系统多用于各结点信息藕合比较小、实时性要求不高的松散藕合系统。另一类即是紧藕合的多处理器系统。本文介绍一种已工程实用化了的紧藕合实时多处理器系统。该系统为研究多处理系统的并行算法、任务的实时划分、调度管理等关键技术提供了一个良好的硬件平台及软件环境,该系统可广泛用于要求迭代速率非常高的实时控制与实时仿真系统。