Mixing enhancement mechanism of combined H2–Water jets in supersonic crossflows in a combustor with an expanded section

To obtain the mixing enhancement mechanism of H₂–Water combined jets in supersonic crossflows in a combustor with expanded section for rotating detonation ramjet, the flow field shape and spray structure were studied by experimental and numerical methods. The Eulerian–Lagrangian method was used to investigate the diffusion mechanism and H₂–Water interaction law of combined jets with different sequences. At the same time, high-speed photography and the schlieren technique were used to capture the flow field. The effects of jet pressure drop, orifice diameter, orifice spacing, incoming Mach number, and other parameters on the penetration depth of water jets were studied. The results of experiment and simulation show that using H₂–Water combined jets, the penetration depth of the jet spray can be greatly increased and the jet mixing effect can be significantly improved, which will contribute to the engine's ignition and stable combustion. In the case of pre-water/post-H₂, the penetration depth of the hydrogen jet is greater. In the case of pre-H₂/post-water, the hydrogen jet raises the water spray mainly by protecting the integrity of the water column.     

Levelized cost of energy definition – An economic paradox

Using mean value theorem for integrals we show that the well-known LCOE definition is incorrect.     

正交参数与平纹面

本文证明了一族闭曲线C(t),t∈I,称变闭曲线,在光滑性条件下,具有正交参数u,即当C(t)表为(?)=(?)(u,t)时,有(?)·(?)≡0.接着,文中提出了一种“降维法”,即用一族平行平面将空间曲面截成平面变曲线,并讨论其若干整体性质.     

Encapsulation of PV modules using ethylene vinyl acetate copolymer as a pottant: A critical review

The primary purpose of this work is to review the literature about what is and is not known about using ethylene vinyl acetate (EVA0 copolymer as the encapsulant (or pottant) material in photovoltaic (PV) modules. Secondary purposes include elucidating the complexity of the encapsulation problem, providing an overview about encapsulation of PV cells and modules, providing a historical overview of the relevant research and development on EVA, summarizing performance losses reported for PV systems deployed since ca. 1981, and summarizing the general problems of polymer stability in a solar environment. We also provide a critical review of aspects of reported work for cases that we believe are important.Failure modes resolved in the early work to establish reliability of deployed modules and the purposes and properties of pottants, are summarized. Typical performance losses in large field-deployed, large-scale systems ranging from 1% to 10% per year are given quantitatively, and qualitative reports of EVA discoloration are summarized with respect to ultraviolet (UV), world-wide location and site dependence.The general stability of polymers and their desirable bulk properties for solar utilization are given. The stabilization formulation for EVA, its effectiveness, and changes in it during degradation are discussed. The degradation mechanisms for the base resin, e.g., unstabilized Elvax 150^TM, and stabilized EVA are indicated for literature dating to the early 1950s, and the role played by unsaturated chromophores is indicated. The limited number of studies relating discoloration and PV cell efficiency are summarized.Observed degradation of EVA or the unstabilized base resin in the laboratory and examples used to measure the degradation are summarized in sections entitled: (1) thermally-induced degradation; (2) photodegradation and photothermal degradation of EVA in different temperature regimes; (3) photobleaching and photodegradation of the UV absorber and cross-linking agent; (4) acetic acid and metal and metal-oxide catalyzed oxidative degradation; and (5) discolaration and PV cell efficiency losses.Processing effects/influences on EVA stability are discussed in sections entitled: (1) EVA raw materials and extruded, uncured films; (2) thermal encapsulation processes; (3) effects of lamination, curing, and curing peroxide on gel content and chromophores formed; and (4) incomplete shielding of curing-generated chromophores. A summary is given for the limited number of accelerated lifetime testing efforts and examples of erroneous service lifetime predictions for EVA are discussed. The known factors that effect the discoloration rate of several EVA formulations are discussed in which the reduction in rate by using UV-absorbing superstrates is a prime example. A summary is given of what is and is not known about EVA degradation mechanisms, degradation from exposures in field-deployed modeules and/or laboratory testing, and factors that contribute to EVA stability or degradation. Finally, conclusions about using Elvax 150 in EVA formulations are summarized, and future prospects for developing the next-generation pottant for encapsulating PV modules are discussed.     

二维金属凹槽填充各向异性介质时散射的边界元方法:TE情形

由各向异性介质无界空间Green函数和Green恒等式出发，推导了TE波入射时二维任意截面金属凹槽填充各向异性介质时所满足的边界积分方程，并用边界元法和广义网络原理计算了金属凹槽填充各向异性介质时的散射。用文中方法退化计算了凹槽填充各向同性介质时的散射，计算结果与解析结果一致。并给出了凹槽填充各向异性介质时的散射算例。     

Long-term measurements of the concentrations of halocarbons in an urban area of Kraków, Poland

The results of the measurements of the concentrations of freons (F-11 and F-113), chloroform (CHCl₃), trichloroethane (CH₃CCl₃) and carbon tetrachloride (CCl₄) in air are presented. The data concern concentration measurements that have been conducted in Krakow since half way through 1997 to the end of 1999. The mean monthly values of these concentrations have been compared with the data from Mace Head, the station situated at a similar longitude as Krakow. It has been concluded that, in the observed period of time, the concentrations of the pollutants in Krakow are higher than in Mace Head. The mean monthly concentrations of F-11 and CCl₄ decrease in Krakow faster than in Mace Head (2.5 and 3.3 times, respectively). The concentrations of CHCl₃ and CH₃CCl₃ decrease at both locations, but the change is greater in Krakow. In Krakow, the observed increase of F-113 is 0.13 ppt/month and has an opposite trend than in the same period at Mace Head.     

Calendar maintenance of arbitrarily structured systems

A semi-Markov model is constructed that describes an arbitrarily structured multicomponent technological system and takes into account its calendar maintenance. Using an aggregation algorithm, approximate values of stationary reliability characteristics and an optimal term of maintenance work are determined for the system. __________ Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 69–86, March–April 2006.     

一种测量天空亮度的新方法

本文介绍了一种测量天空亮度分布的新方法。这种方法利用视场角为180°的鱼眼镜头照相机和计算机数字图像处理系统,实现了天空亮度分布的瞬时测取和胶片密度的高效率处理。文中论述了胶片灰度与天空亮度的标定转换实验方法。引用了误差理论中的数据处理方法确定出二者间的函数关系。通过对昆明和重庆地区晴和阴天空下大量实测结果的误差处论和分析,得到了其相关系数和标准偏差的频数分布图,由此证明了这种方法的可靠性。     

1998年九江抗洪启示录

简述1998年江西特大洪水的基本情况，重点介绍了九江防洪的形势和九江长江城防堤4～5号闸口间堤段溃决的情况及堵口过程，并总结了经验教训和抗洪工作的体会．     

制造资源混合粒度优化组合方案求解技术

为实现对云请求端制造需求的快速响应并提供最理想的制造云,在定义制造云服务(manufacturing cloudservice,MCS)的基础上,提出了MCS混合粒度动态优化组合方法.通过对制造服务需求的解析,将MCS按照粒度从大到小的顺序进行匹配,实现了云池资源的初次过滤;然后构建基于总服务成本、服务质量和交易期的制造云多目标优化数学模型,并引入Epsilon-SPEA2优化算法对该优化问题进行求解,从而快速高效地获得Pareto最优解;采用基于改进优劣解距离(technique for order preference by similarity to an ideal solution,TOPSIS)的动态多属性决策方法对Pareto最优解所代表的互为非支配的MCS组合方案进行评价排序,筛选出最优的MCS组合方案.最后结合某区域模具公司群所能提供的制造服务以及相应历史数据,依据客户需求进行MCS的动态优化组合仿真,验证了文中方法的可行性和实用性.