位置关系中一个值得注意的问题

众所周知直线与圆锥曲线有且仅有一个交点,不能保证两图形相切。由于问题的复杂常使解题出现错漏,为此有必要了解这类问题的正确解答,请看一例。     

THEOREMS ON THE LIMIT ANALYSIS DEALING WITH THE YIELD CONDITION EXPRESSED BY THE SUM OF THE HOMOGENEOUS LINEAR FORM OF STRESS TENSOR AND THE HOMCGENEOUS QUADRATIC FORM OF STRESS TENSOR

In this paper a generelized variational principle on the limitanalysis dealing With the yield condition expressed by thesum of the homogeneous linear form of stress tensor and thehomogeneous quadratic form of stress tensor is suggested.Thisvariational principle can be applied to the limit analgsis inrock mechanics and it takes the situation.in which the yieldcondition is expressed by the homogeneous linear form of stresstensor or the homogeneous quadrdtic form of stress tensor.asits special case.     

从生活中寻找灵感

一、整体思想:集装箱给我们的启发同学们见过各种运输中,把大小不一、形状各异的货物装在集装箱里运输吧,这样做,既方便又安全.从集装箱的运输方式中我们可以联想到整体思维,这种整体思想方法在数学     

从多角度思考 激活解题思维

数学解题不在多,关键在精,精解一题,醒悟全局是每个学子梦寐以求的事.怎样才能实现这一目标?实践告诉我们,必须从平时的思维习惯做起,只要在平时的解题时做到勤思、巧变、对比、联想,常此以往自然能激活自己的思维,实现抓一纲而带全局的梦想.下面以一道等差数列的求值为例,探讨如何落实勤思、巧变、     

温室气体通量测量方法及进展

分析了国内外主要的温室气体通量测量方法,包括针对地球生态系统通量的测量方法和针对人为排放通量的测量方法。梳理了地基原位通量测量网络、地基和星载被动遥感技术和以激光雷达为代表的主动遥感技术的研究现状与进展,分析了当前测量技术对人为碳排放的探测能力。结合国内外发展趋势,展望了为满足全球和区域人为碳排放监测的需求,需要同化原位探测与主动遥感探测数据、通过科学的卫星组网提高时空分辨率并建立不同尺度的模型。     

Experimental investigation on divertor tungsten sputtering with neon seeding in ELMy H-mode plasma in EAST tokamak

Neon (Ne) seeding is used to cool the edge plasma by radiation to protect the divertor tungsten (W) target in the Experimental Advanced Superconducting Tokamak (EAST). The W sputtering in the outer divertor target with Ne seeding is assessed by the divertor visible spectroscopy system. It is observed that the W sputtering flux initially increases with Ne concentration in the divertor despite the decreasing plasma temperature. After reaching a maximum around 25 eV, the W sputtering rate starts to decrease, presenting a suppression effect. The effect on the divertor W sputtering flux and yield due to the competition between the increase of the Ne concentration and the decrease of the plasma temperature is discussed. The results show that enough Ne seeding is essential to effectively reduce the electron temperature and thus to suppress W sputtering. Moreover, ELM suppression is observed when Ne and W impurities enter the core plasma, which could be correlated to the enhanced turbulence transport in the pedestal.     

基于科研引导的化学类拔尖人才全过程培养模式的探索与实践

从课堂教学和第二课堂两个方面详细地阐述了四川大学化学学院基于科研引导的拔尖人才全过程培养模式,重点梳理了拔尖班学生在校成果、毕业去向、人才培养满意度等方面内容,明确了学院拔尖计划2.0的工作目标。     

基于监督字典学习的核稀疏表示的目标识别算法（英文）

针对图像数据高度非线性可分情况下的目标分类问题,在稀疏表示分类框架的基础上,提出了一种基于监督字典学习的核稀疏表示的目标识别算法。采用融合了多特征信息的协方差描述子作为图像的描述符;通过引入核技巧,使非线性的图像数据在高维空间变得线性可分;并把分类误差与重构误差同时引入目标函数,在监督字典学习框架下,使学习得到的字典判别性更强。利用加州大学默塞德分校提供的UCMerced遥感数据集以及自测的红外车辆数据集做了实验验证,在这两个数据集上算法的平均识别率分别达到了89.46%和93.98%,实现了对非线性可分目标的高精度分类。     

一种具有抗氧化活性的苯丙素天然产物的不对称合成

长期以来,苯丙素类天然产物因其良好的生理活性而备受人们关注,化合物1是1999年Kikuzaki等[1]从植物Pimenta dioica的果实中分离出的一种新的具有抗氧化活性的天然产物,其分子所含的两个手性中心的绝对构型未定,迄今未见有关其合成的报道.最近我们以香草醛为起始原料,经羟基保护,Wittig反应还原,Sharpless不对称双羟化,脱保护等8步反应,以36%的总产率首次完成了化合物1的全合成,并确定了1的绝对构型,所有化合物的结构均经1H NMR,IR,MS等光谱数据确证,合成产物的波谱数据与文献一致.合成路线如下: