高层建筑风场的脉动风速时程模拟

采用经过FFT算法改进的谐波叠加法(WAWS)及自回归(AR)模型的线性滤波法对实际工程进行脉动风速时程模拟.对2种算法所模拟的风速时程进行分析,结果显示了风速功率谱及相关函数的特性,分析结果说明AR模型中模型阶次及时间步长对风速时程产生较大影响.根据结构的有限元动力分析,采用能量相等的原则,即使结构固有频率段内的目标谱和模拟谱能量相等,对风速时程进行修正,使模拟风速时程更趋合理.     

吲哚自由基的合成与晶体结构

以2-硝基丙烷为原料合成中间体2,3-二甲基-2,3-二羟胺基丁烷,然后与3-吲哚甲醛反应,合成了一种结构新颖的吲哚氮氧自由基2-(3′-吲哚基)-4,4,5,5-四甲基咪唑啉-3-氧化-1-氧基自由基(NITIn),其结构通过单晶X射线衍射法测定,该化合物空间群为P2(1)/n,a=1.111 4(7)nm,b=0.993 1(6)nm,c=1.287 7(8)nm,V=1.421 2(15)nm3,Z=4,Mr=272.32,F(000)=576,Dc=1.421 g/cm3.最终结构偏离因子R=0.060 1,Rw=0.135 3.最终差值电子密度的最大值和最小值分别为173 nm-3和-239 nm-3.     

灰色GM(1,1)模型在山区耕地预测中的应用研究

以云南楚雄1999-2005年耕地面积数据为试验资料,运用灰色GM(1,1)模型分析探讨耕地面积的变化状况.初步结果表明:楚雄耕地面积的动态变化结果符合客观实际的变化规律,未来几年,楚雄拼地面积仍呈递减的趋势.     

模糊故障树在土地适宜性评价质量控制中的应用分析

结合土地适宜性评价项目,在其质量控制过程中,针对各种评价因素的随机不确定性和模糊不确定性,引入了三角模糊故障树理论,采用新方法对案例区的土地适宜性评价质量开展了可靠性分析.初步得出几点认识,并指出了在实例应用过程中所存在的一些有待解决的问题.     

低碳经济时代安徽省环境保护对策研究

低碳经济是全球气候变化环境下经济发展的必然选择。本文通过分析安徽省环境保护存在的问题,指出为了促进低碳经济发展,可以采取加强环境监管、优化能源结构、大力推进自主创新、引导节能消费行为等建议和对策。     

论孝文化的创新

新时代的迫切需要向我们提出了一个紧迫问题:应该怎样继承、创新和践行中国传统文化中的孝文化。从创造哲学的角度看,孝文化的创新,应包括孝文化内涵的创新,孝文化重大意义和理论基础的创新,孝文化建设方式的创新。     

Induced pluripotent stem cell (iPS) technology: promises and challenges

In 2006, an article published in Cell by Shinya Yamanaka took by surprise the stem cell research community. By performing systematic retroviral transduction of factors enriched in embryonic stem (ES) cells, the authors demonstrated the reprogramming of mouse fibroblasts into an ES cell-like state. These cells, baptized iPS (induced pluripotent stem) cells, were immediately recognized as a ground-breaking discovery. Subsequently, the same authors and other groups reported a similar achievement with human fibroblasts. Two years later, the number of top quality papers on iPS is astonishing, and interest in the scientific community has risen to a fever pitch. But although iPS has the potential to revolutionize Regenerative Medicine, important questions still remain unanswered. Work from multiple laboratories worldwide including ours is focused on deciphering the molecular mechanisms of iPS, and trying to improve the technique to make it suitable for the clinic. In this review article we briefly discuss the past, present and future of iPS, with emphasis on urgent issues to be solved. Supported by the National Nature Science Foundation of China (Grant Nos. 30725012, 30630039 and 90813033), Knowledge Innovation Project of Chinese Academy of Sciences (Grant No. KSCX2-YW-R-48), National Key Basic Research and Development Program of China (Grant Nos. 2006CB701504, 2006CB943600, 2007CB948002, 2007CB947804. 2007CB947900) and Guangzhou Science and Technology Development Funds (Grant No. 2008A1-E4011)     

Validation of full cavitation model in cryogenic fluids

Numerical simulation of cavitation in cryogenic fluids is important in improving the stable operation of the propulsion system in liquid-fuel rocket. It also represents a broader class of problems where the fluid is operating close to its critical point and the thermal effects of cavitation are pronounced. The present article focuses on simulating cryogenic cavitation by implementing the “full cavitation model”, coupled with energy equation, in conjunction with iterative update of the real fluid properties at local temperatures. Steady state computations are then conducted on hydrofoil and ogive in liquid nitrogen and hydrogen respectively, based on which we explore the mechanism of cavitation with thermal effects. Comprehensive comparisons between the simulation results and experimental data as well as previous computations by other researchers validate the full cavitation model in cryogenic fluids. The sensitivity of cavity length to cavitation number is also examined. Supported by the National Natural Science Foundation of China (Grant No. 50706042)     

Strong stability of linear forms in φ -mixing random variables

In this paper some new results of strong stability of linear forms in φ-mixing random variables are given. It is mainly proved that for a sequence of φ-mixing random variables {x _n , n ⩾ 1} and two sequences of positive numbers {a _n , n ⩾ 1} and {b _n , n ⩾ 1} there exist d _n ∈ R, n = 1,2,L, such that a.s. under some suitable conditions. The results extend and improve the corresponding theorems for independent identically distributed random variables. Foundation item: Supported by the National Natural Science Foundation of China(10671149)     

600MPa级汽车大梁钢疲劳极限确定和疲劳断裂原因分析

为确定薄板坯连铸连轧(flexible thin slab rolling,FTSR)短流程生产线生产的600 MPa级汽车大梁钢是否满足装车要求,利用升降法研究了汽车大梁钢的抗疲劳性能。研究结果表明,采用对数试验应力-对数疲劳寿命拟合的方法要优于直接采用试验应力-疲劳寿命,计算得到了不同存活率下的P-S-N曲线,由图得到疲劳极限强度为294 MPa,经过数值计算得到的疲劳极限强度为287. 1 MPa。采用扫描电子显微镜对疲劳试样进行了断口分析,发现疲劳断裂为韧性断裂,夹杂物为裂纹的起源,结合试验钢的性能指标和装车试用考核结果,确认FTSR生产线开发的600 MPa级汽车大梁钢满足装车使用要求。