Structure and energy transfer of unstable hot star winds

Due to the instability of the radiation line force, the winds of hot, luminous stars should show a pronounced time-dependence resulting from the nonlinear growth of initially small perturbations. Following the method of Owocki, Castor & Rybicki (1988), we describe the time-dependent wind structure obtained with an independently developed code. Under the central assumption ofisothermality, our results are in very good agreement with the ones by Owocki et al. We find that the response of the wind to periodic base perturbations remains largely periodic, at least up tor 2...3R _* , with no clear evidence of stochastic behaviour.In order to test the foregoing assumption of isothermality and to compute the X-ray emission from models of structured winds, we have also incorporated theenergy equation into our simulations. We encountered the numerical problem that all radiative cooling zones collapse because of the oscillatory thermal instability (cf. Langer et al. 1981). We present a method to hinder this collapse by changing the cooling function at low temperatures. The resulting wind showsresolved cooling zones; but, for a supergiant wind relatively close to the star (r 10R _* ), the macroscopic wind structure is very similar to isothermal calculations. Most of the hot material is caused by shell-shell collisions.     

新疆地区夏季平流层低层风场特征分析及数值模拟

利用2017年6—8月的FNL再分析资料分析了新疆地区夏季平流层低层风场的时空演变特征，开展了平流层低层风场的高分辨率数值模拟和检验。结果表明：新疆地区夏季平流层纬向风随时间的变化存在经向差异，同时准零风层开始和结束的时间也存在经向差异，准零风层开始时间南部地区早于北部地区，而准零风层结束时间则相反。整个夏季新疆地区上空的准零风层处于70～40 hPa之间，其高度随时间呈先降低而后升高的变化趋势。准零风层数值模拟结果表明，模拟的准零风层参数与探空资料分析结果相比二者存在一致的变化趋势，准零风层起始高度的平均绝对误差为467 m，该高度对应的风速均方根误差为1.75 m/s。     

Threshold velocity for wind erosion: the effects of porous fences

Porous fence is a kind of artificial windbreak that has many practical applications. The threshold wind velocities at different distances downwind from porous fences were measured and the corresponding characteristics of particle movement observed to assess their shelter effect. It is found that the fence’s porosity is the key factor that determines the resulting shelter effect. The area near a fence can be typically classified into five regions, each with a different mode of particle movement. Dense fences, and especially solid fences, favor the accumulation of sand upwind of the fences. Fences with porosities of 0.3–0.4 produce the maximum threshold wind velocity; those with porosities of 0.3–0.6 (depending on the fence height) provide the maximum effective shelter distance. It is confirmed that the fence porosities of 0.3–0.4 that have been proposed for practical application in previous research are the most effective for abating wind erosion.     

Net Energy Payback and CO2 Emissions from Three Midwestern Wind Farms: An Update

This paper updates a life-cycle net energy analysis and carbon dioxide emissions analysis of three Midwestern utility-scale wind systems. Both the Energy Payback Ratio (EPR) and CO₂ analysis results provide useful data for policy discussions regarding an efficient and low-carbon energy mix. The EPR is the amount of electrical energy produced for the lifetime of the power plant divided by the total amount of energy required to procure and transport the materials, build, operate, and decommission the power plants. The CO₂ analysis for each power plant was calculated from the life-cycle energy input data. A previous study also analyzed coal and nuclear fission power plants. At the time of that study, two of the three wind systems had less than a full year of generation data to project the life-cycle energy production. This study updates the analysis of three wind systems with an additional four to eight years of operating data. The EPR for the utility-scale wind systems ranges from a low of 11 for a two-turbine system in Wisconsin to 28 for a 143-turbine system in southwestern Minnesota. The EPR is 11 for coal, 25 for fission with gas centrifuge enriched uranium and 7 for gaseous diffusion enriched uranium. The normalized CO₂ emissions, in tonnes of CO₂ per GW_eh, ranges from 14 to 33 for the wind systems, 974 for coal, and 10 and 34 for nuclear fission using gas centrifuge and gaseous diffusion enriched uranium, respectively.     

小型水电站建设用地地质灾害评估技术研究——以湄尼多河小型水电站为例

现阶段,地质灾害评估技术人员在评估实践中,往往不注重各评估对象的差异性,采取同一评估模式,结果达不到评估的目的。在对小型水电站进行评估时,野外调查的重点,评估过程中所使用的方法以及危险性现状、预测及综合分区评估等与大型水电站、路线工程、矿山开采、民用建筑等工程有所不同。湄尼多河小型水电站工程位于云南省怒江州福贡县马吉乡境内,地质环境条件复杂,评估级别综合为二级。文章以该电站建设用地地质灾害危险性评估为例,对小型水电站建设用地地质灾害危险性评估的方法与理论进行探讨。     

河北省永久性GPS参考(网)站建立的研究与探讨

重点探讨了如何利用VRS技术在河北省区域内建立永久性参考站,如何进行数据的采集与管理,如何为GPS用户提供参考站数据等技术问题。     

中国深空测控网建立方案的研究

概述了深空测控网的基本技术要求,总结了我国卫星测控网和国内现有射电观测设施的技术、组成和分布,分析和论述了将我国现有的测控设施建设成深空测控网的具体方案。     

基于全站仪的圆形建筑物倾斜观测的方法和精度

随着建筑物的不断增高、增大,其稳定性和可靠性成为人们关注的焦点.其中建筑物的倾斜度是衡量施工技术质量的重要指标之一.而传统的观测方法如经纬仪测小角法、经纬仪投点法,由于受仪器精度和观测条件的限制,观测精度较低.拓普康全站仪独具推出的圆柱偏心测量功能为快速、准确测定圆形建筑物的倾斜量开辟了一条新途径,本文阐述了基于全站仪的圆形建筑物倾斜观测的原理和方法,并对其精度进行分析.     

自由测站法曲线座标计算程序设计

通过对曲线测设和测点坐标计算过程的分析，把坐标计算的程序设计归结为有向直线与X轴顺时针夹角即方位角的计算和线路转向转角的计算，弥补了测点位置和计算公式分类复杂等不足，简化了程序设计和计算过程。     

基于MAPGIS明码文件的绘图转换系统开发及应用

介绍了基于MAPGIS明码文件开发出的MAPGIS明码格式转换系统软件的结构及功能,并说明该软件在地球物理、地球化学领域中的应用。