浅层滑坡多发区典型植被恢复树种根系对土壤抗剪强度影响

为揭示坡面植被根系对土壤抗剪强度的影响及其固坡效应的差异性,选取白龙江流域浅层滑坡多发区两种典型修复树种刺槐(Robinia pseudoacacia)和毛白杨(Populus tomentosa)为研究对象,通过剖面网格法计算不同树种根系的根截面积比(RAR),采用万能试验机分析不同根系径级单根抗拉特征,并运用RWM模型计算两种乔木根系对土壤抗剪强度的增加值。结果表明,两种乔木根系的RAR值,刺槐(0.18%)和杨树(0.51%)均大于发挥固坡效应的阈值(0.1%)。两种乔木的单根抗拉力(TF)随着直径的增加而增大,分布规律表现出明显的幂函数特征,TF_(R.pseudoacacia)(363.6 N)<TFP.tomentosa(419.95 N);刺槐根系的抗拉强度(TS)与根系直径正相关,杨树根系与直径呈负相关关系,且TSR.pseudoacacia(25.38 MPa)<TSP.tomentosa(27.62 MPa)。RWM模型计算得到根系对土壤抗剪强度的增加值为刺槐(21.93 Kpa)<杨树(67.61 Kpa)。在研究区,两种乔木植物根系均能有效增加土壤抗剪强度,杨树根系的固坡效应优于刺槐,研究结果可为浅层滑坡多发区植被根系固土模型的应用和生物工程减灾效果的评价提供一定理论依据。

结合PCM聚类算法的网页排序

针对传统的网页排序算法中容易出现的忽略搜索结果主题相关性和主题漂移的问题,提出了结合PCM聚类算法的网页排序,用来提高搜索结果中网页主题的相关性并减少其主题漂移。首先,通过查询某个主题,运用随机行走(RWM)的方法来计算两个网页之间的对称社会距离(SSD);然后,用SSD和PCM聚类算法对网页进行聚类,得到相关主题的各个社区,通过计算得到各个社区中成员属于该社区的概率表示;最后,根据各社区成员的概率和网页的推荐度对网页进行排序。实验结果表明,与PageRank算法相比,该算法搜索结果中网页主题的相关程度更高;另外,由于是针对某个主题的排序,该算法减少了主题漂移。

运动二维超声心动图正常人左室节段性室壁运动的定量分析

44例健康人作亚极量卧位踏车运动试验,分别于运动前后记录心尖四腔心(Ap4C)和心尖二腔心(Ap2C)的二维超声心动图。计算机定量分析左室各节段的面积缩小率(PAR)、半径缩短率(PRS)和周边缩短率(PPR)。结果显示:正常人左室室间隔、侧壁、前璧、下壁、Ap4C心尖和Ap2C心尖的平均PAR平静时分别为59±17%、57±15%、59±11%、62±15%、47±14%和49±12%,运动后分别增加到70±14%、65±14%、66±11%、71±12%、57±14%和58±101(P<0.01)。运动前后左室各节段的PAR在定量分析中都有差异存在。心尖的PAR最小。

Effects of Magnetic Shear on the Resistive Wall Mode Instability in a Cylindrical Model

The linear evolution of a resistive wall mode(RWM)with magnetic shears was analytically studied in a cylindrical geometry.The incompressible magnetohydrodynamic(MHD)equations were solved by the Fourier analysis method,and various equilibrium magnetic fields were considered.The shear in the magnetic field had an unstable effect on the linear evolution of the RWM.The linear growth rate increased obviously with increase of the magnetic shear rate for higher magnetic shears.Slow plasma rotation could stabilize the RWM with low magnetic shears,but the plasma rotation could not stabilize the RWM with high magnetic shears.The stabilizing effects of the wall conductivity on the RWM are more efficient for lager magnetic shear.

Effects of Plasma Density Profile on Resistive Wall Mode Stability

Linear and nonlinear evolutions of the resistive wall mode(RWM) were numerically carried out with different plasma density profiles.Both stabilizing and destabilizing effects were observed.The plasma density shear had a stabilizing effect on the RWM,and the stabilizing effect was better as the plasma density shear rate increased.In the uniform density plasma,the effects of flowshear on the RWMstability were stronger than those for non-uniform density plasma.For lower flowshear,the effects of the plasma density shear rate on the RWMwere more obvious.In the nonlinear phase,the repulsive force associated with the piling up magnetic flux near the resistive wall prevented further growth of perturbed magnetic energy,and the RWMwas saturated.The saturation levels were almost independent of the density profiles.

HF FIELD STRENGTH MEASUREMENTS OVER THE VERY LONG DISTANCE

It was ascertained that there is a great margin between the theoretical values and experimental medians of the field strength of RWM and RID signals during high solar activity period at Chinese Great Wall Station on Antarctica. The calculated values are, on average, less than the experimental, especially on the propagation path between RID and Antarctica. The field strength by the experiment may be used as the basic data for the research of HF propagation over the very long distance. Because of the large deviation it seems to be necessary to study HF propagation over the very long distance in details, especially the propagation model.

基于改进粒子群算法的Ad Hoc网络移动模型研究

移动模型是研究ad hoc网络路由算法的基础.为解决基本粒子群算法的速度突变问题,使其适用于adhoc网络移动模型,本文首先在基本粒子群算法的速度和位移更新公式中引入加速度和环境因子的概念,并提出用直角坐标系对其速度和位移进行分解.接着,我们建立了包含障碍物模型、速度初始化函数和无边界仿真区域的改进粒子群算法移动模型.为证实新移动模型的可行性和有效性,我们用Matlab和网络仿真软件OPNET进行仿真实验.结果表明,与传统的随机位点移动模型比较,基于改进粒子群算法的移动模型更贴近实际情景,并能够有效地应用在adhoc网络中.

二维超声心动图定量测定室壁节段运动的初步探讨参考轴系统的选择

二维超声心动图(2DE)心尖两切面与双面左室造影(LVG)对比研究一致显示:定量测定室壁节段运动(RWM),选择固定轴系统定量检出RWM异常(RWMA)病例具有和浮动轴系统相同的特异性、敏感性和准确性(P均>0.05)。然而,对心肌梗塞(MI)患者的正常和异常节段定位固定轴较浮动轴更准确;固定轴所测节段EF值能将不同程度RWMA定量区分开,能反映出矛盾运动,而浮动轴则掩盖了这些矛盾运动。提示固定轴系统优于浮动轴系统。

改进的Wu-Manbe算法在网闸中的实现

通过字符串匹配算法来实现文本过滤,在深入分析了现有串匹配算法的基础上,根据网闸数据从外网过渡到内网的特点,对传统的字符串匹配算法Wu-Manber进行详细分析,设计并实现了一种适合中文字符集和网闸的模式匹配算法RWM,并对改进的算法进行了实验分析。实验表明,所设计的算法在运行时间和尝试次数方面优于其他算法,满足网闸对不良信息进行查询和过滤的要求,能够解决网闸的文本过滤问题。