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851.
Tao-Yan Lin Zhangjin Pan Youshao Tu Shuai Zhu Prof. Dr. Hai-Hong Wu Prof. Dr. Yu Liu Prof. Dr. Zhiming Li Prof. Dr. Junliang Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(51):23157-23162
The first example of highly enantioselective fluoroarylation of gem-difluoroalkenes with aryl halides is presented by using a new chiral sulfinamide phosphine ( Sadphos ) type ligand TY-Phos . N-Me- TY-Phos can be easily synthesized on a gram scale from readily available starting materials in three steps. Salient features of this work including readily available starting materials, good yields, high enantioselectivities as well as broad substrate scope make this approach very practical and attractive. Notably, the asymmetric synthesis of an analogue of a biologically active molecule is also reported. 相似文献
852.
Dr. Daniel Santhanaraj Prof. Maria P. Ruiz Dr. Mallik R. Komarneni Dr. Tu Pham Dr. Gengnan Li Prof. Daniel E. Resasco Prof. Jimmy Faria 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(19):7526-7530
We report a reaction platform for the synthesis of three different high-value specialty chemical building blocks starting from bio-ethanol, which might have an important impact in the implementation of biorefineries. First, oxidative dehydrogenation of ethanol to acetaldehyde generates an aldehyde-containing stream active for the production of C4 aldehydes via base-catalyzed aldol-condensation. Then, the resulting C4 adduct is selectively converted into crotonic acid via catalytic aerobic oxidation (62 % yield). Using a sequential epoxidation and hydrogenation of crotonic acid leads to 29 % yield of β-hydroxy acid (3-hydroxybutanoic acid). By controlling the pH of the reaction media, it is possible to hydrolyze the oxirane moiety leading to 21 % yield of α,β-dihydroxy acid (2,3-dihydroxybutanoic acid). Crotonic acid, 3-hydroxybutanoic acid, and 2,3-dihydroxybutanoic acid are archetypal specialty chemicals used in the synthesis of polyvinyl-co-unsaturated acids resins, pharmaceutics, and bio-degradable/ -compatible polymers, respectively. 相似文献
853.
Yujie Xia Tao Li Chao Yuan Cameron Fletcher Xinyue Dai Xingfan Zhang Lishu Zhang Prof. Dr. Yanyan Jiang Dr. Hui Li 《Chemphyschem》2020,21(6):568-574
The electron transport properties of polycyclic aromatic hydrocarbons (PAHs) with different numbers of benzene rings tethered to narrow zigzag graphene nanoribbon (ZGNR) electrodes have been investigated. Results show that the transport properties of PAHs are dependent on whether the number of benzene rings in the width direction is odd or even. This effect is strong for narrow width PAHs, but its strength decreases as the width of the PAH is increased. PAHs with an odd number of rings exhibit poor transport properties, whereas the ones having an even number of rings show excellent transport properties coupled with a negative differential resistance (NDR) effect. Moreover, the linkage points and the structure of the molecules have a noticeable effect on the transport properties of the PAH, making the odd-even effect weaker or disappear entirely. Although the PAH with three benzene rings displays poor transport capabilities, it shows excellent rectification behavior compared to the other examined molecules. These studies present a feasible avenue for designing molecular devices with enhanced performance by the careful manipulation of the PAH molecular structure. 相似文献
854.
This paper proves the non-existence of common Kähler submanifolds of the complex Euclidean space and of the symmetrized polydisc endowed with their canonical metrics. 相似文献
855.
Xin M. Tu 《Journal of computational and graphical statistics》2013,22(1):97-112
Survival data with censored initiating and terminating times have surfaced in some recent epidemiologic studies. Unlike standard survival analysis with known initiating times, analysis of data with both censored initiating and terminating times requires maximization of a complicated bivariate likelihood, which is often difficult to carry out. This article considers a missing-data formulation of the problem and focuses on the use of EM-type algorithms to simplify the computation of maximum likelihood estimates. This approach provides a feasible way of performing regression analysis with such bivariate survival data. Several illustrative examples are provided, including a real-data analysis application involving a cohort of HIV-infected hemophiliac patients. 相似文献
856.
Influence concepts have an important place in linear regression models and case deletion is a useful method for assessing the influence of single case. The influence measures in the presence of multicollinearity were discussed under the linear regression models when the errors structure is uncorrelated and homoscedastic. In contrast to other article on this subject, we consider the influence measures in ridge regression with autocorrelated errors. Theoretical results are illustrated with a numerical example and a Monte Carlo simulation is conducted to see the effect autocorrelation coefficient, strength of multicollinearity and sample size on leverage points and influential observations. 相似文献
857.
Tuğba Akman Hamdullah Yücel Bülent Karasözen 《Computational Optimization and Applications》2014,57(3):703-729
In this paper, we analyze the symmetric interior penalty Galerkin (SIPG) for distributed optimal control problems governed by unsteady convection diffusion equations with control constraint bounds. A priori error estimates are derived for the semi- and fully-discrete schemes by using piecewise linear functions. Numerical results are presented, which verify the theoretical results. 相似文献
858.
流动注射分光光度法测定皮革制品中的甲醛 总被引:1,自引:0,他引:1
研究了流动注射变色酸分光光度法测定皮革制品中的甲醛。与传统的变色酸光度法相比,该方法具有灵敏度更高,干扰更少的特点。在0.4 mol/L硫酸介质中,甲醛与变色酸在85℃左右形成络合物,该络合物在390 nm有最大吸收峰,且能稳定存在至少96 h。详细考察了各种测试条件如萃取剂、萃取时间、显色时间、反应温度、反应时间等对甲醛测定结果的影响,优化了反应的化学因素和流动注射系统反应条件。该方法的检出限和线性范围分别为0.1μg/L(3σ)和50~1000μg/L,相对标准偏差为0.56%(连续注射500μg/L甲醛标液11次)。该方法成功用于皮革制品或者皮质材料中的甲醛的测定。 相似文献
859.
860.
基于四步半隐式特征线分裂算子有限元方法,对Re=100时,剪切来流作用下串列三圆柱体双自由度流致振动问题进行了数值计算. 首先,与现有文献结果进行对比验证该方法的正确性. 然后,着重分析剪切率、固有频率比和折减速度三个关键参数对串列三圆柱体结构流致动力响应及流场特性的影响. 数值计算结果表明:剪切率、固有频率比与折减速度对结构振幅和运动轨迹的影响较大. 随剪切率的增大,上游圆柱最大振幅的变化与单圆柱工况类似. 中下游圆柱最大振幅会增大且会出现双向共振现象,同时,发生共振响应区域会扩大. 随固有频率比的增大,上游圆柱顺流向锁定区间范围会减小,而中下游圆柱双向锁定区间会扩大. 另一方面,均匀来流作用下,结构运动轨迹以"8"字形和不规则形状为主. 随剪切率的增大,锁定区间内运动轨迹会由"8"字形转变为"雨滴"形. 在大剪切率与高固有频率比工况下,中游圆柱体结构运动轨迹会出现"双雨滴"形状. 最后,通过对流场特性的分析,揭示了剪切来流作用下串列三圆柱结构流致运动响应的内在机理. 相似文献