一种超级梁单元桁架式臂架结构强度荷载计算

桁架式臂架结构强度承载能力计算是臂架型起重机核心计算之一.以单个臂节作为一个子结构,将其内部自由度凝聚到臂节端面,基于臂节端面刚性假设,将边界自由度进一步凝聚到臂节端面形心,臂节自重离散到形心节点上,形成一种考虑重力的超级梁单元.基于共旋坐标法,建立每个臂节的随动坐标系,可以准确计算计及大长度臂架几何非线性效应的单元应...     

Research on Asymmetric Michael Addition,Part II: Addition of the Menthone Imine of Ethyl Glycinate to Ethyl Acrylate Under PTC Conditions

Asymmetric Michael addition of (S)-menthone imine of ethyl glycinate to ethyl acrylate had been investigated under PTC conditions using solid base and different kinds of PT catalysts. The reaction gave adducts of enantiomeric excesses of 5–47%.     

聚乙二醇相转移催化作用下Darzens酯缩合

环氧酸酯缩合作用通常在无水条件下进行^[1],不能在应用氢氧化钠水溶液的相转移催化条件下进行。因为卤代酸酯在此情况下发生水解。M.Makosza在无水碳酸钾和18-冠醚-6的两相体系中合成了2-苯基环氧酸乙酯,b.p.99-109℃/0.5mmHg产率72%^[2]。     

相转移催化双不对称诱导合成α■氨基酸(Ⅱ)

在固液两相体系,以手性和非手性季铵盐为相转移催化剂,研究了各种α-溴代脂肪酸龙脑酯与邻苯二甲酰亚胺的Gabriel反应,得到4种具有光学活性的α-邻苯二甲酰亚胺基羧酸酯、以肼解、水解后得到4种具有光学活性的α-氨基酸,光学纯度最高为47.4％,并观察到手性识别和双不对称诱导效应。     

全球化视域下西藏文化产业的现实境遇与发展路径

当今世界,文化与经济、政治相互交融,在社会发展中的地位与作用日显重要。文化的力量深深熔铸在民族的生命力、创造力和凝聚力之中,是一个国家经济社会发展与文明进步的内在动力。文化产业,是在全球化消费社会背景下发展起来的一门极具可持续发展力的新兴产业,正逐步成为世界经济舞台上最具竞争力的新型经济形态。文章从当前西藏文化产业发展的现状和存在的主要问题出发,探究新时期西藏文化产业实现大发展大繁荣的新思路和新举措,使其成为西藏经济社会跨越式发展的新的增长点。     

Research on Asymmetric Michael Addition Part I: Addition of Menthone Imines of Glycinates to Alkyl Acrylates Under the Solid Base Conditions

Asymmetric Michael addition of (S)-menthone imines of glycinates to alkyl acrylates can be performed in solid base conditions. The reactions gave adducts in yields of 40–60% and enantiomeric excesses of 23–45%. The results are best explained by a cyclic transition state mechanism.     

相转移催化不对称合成(Ⅱ)——希夫碱烷基化合成光学活性α-氨基酸

在手性相转移催化剂存在下,于室温固-液两相体系,将甘氨酸乙酯二苯酮希夫碱进行相转移催化碳-单烷基化,合成了12个光学活性的α-氨基酸乙酯二苯酮希夫碱的烷基衍生物,并进一步水解得到相应的光学活性α-氨基酸乙酯盐酸盐.光学纯度为3.2%～96.6%.     

Programmed population control by cell-cell communication and regulated killing

De novo engineering of gene circuits inside cells is extremely difficult, and efforts to realize predictable and robust performance must deal with noise in gene expression and variation in phenotypes between cells. Here we demonstrate that by coupling gene expression to cell survival and death using cell-cell communication, we can programme the dynamics of a population despite variability in the behaviour of individual cells. Specifically, we have built and characterized a 'population control' circuit that autonomously regulates the density of an Escherichia coli population. The cell density is broadcasted and detected by elements from a bacterial quorum-sensing system, which in turn regulate the death rate. As predicted by a simple mathematical model, the circuit can set a stable steady state in terms of cell density and gene expression that is easily tunable by varying the stability of the cell-cell communication signal. This circuit incorporates a mechanism for programmed death in response to changes in the environment, and allows us to probe the design principles of its more complex natural counterparts.     

相转移催化不对称合成(Ⅳ)——由希夫碱合成光学活性α-氨基酸

在固-液两相条件下,探讨甘氨酸乙酯薄荷酮希夫碱(Ⅰ)与丙烯腈在不同反应条件下的不对称Michael加成反应,合成了光学活性的丙烯腈薄荷酮希夫碱的衍生物(Ⅱ),经进一步水解得到相应的光学活性的α-谷氨酸盐酸盐(Ⅲ).光学纯度P_o为0.82%～40.7%.