检索结果-南通市图书馆

Silylated and acetylated β-cyclodextrins for gas chromatographic stationary phases

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Central South University of Technology 2001年第4期8卷 239-243页

作者： TANG Ke wen 1,2.,YI Jian ming 2.ZHOU Chun shan 1,ZHONG Shi an 1 (1. college of Chemistry and Chemical Engineering, Central South University, Changsha 410083, china 2. college of Chemistry and Chemical Engineering, Yueyang normal University 1. college of Chemistry and Chemical Engineering Central South University 410083 Changsha China 2. college of Chemistry and Chemical Engineering Yueyang Normal University 414000 Yueyang China

Two new chiral stationary phases, 2.3 di O acetyl 6 O trimethylsilyl β cyclodextrin (DATBCD) and 2.6 di O trimethylsilyl 3 O acetyl β cyclodextrin(DTABCD), were synthesized, their structures were identified by means of infrared and NMR spectra. Capillary columns were coated with the two stationary phases by dynamic method. The chromatographic properties, and enantiomers separation, such as ketone, esters, alcohols and olefines, were investigated on the silylated and acetylated β cyclodextrin stationary phases. The experimental results show that the silylated and acetylated β cyclodextrins are suitable to be used as capillary gas chromatographic stationary phases, the relative polarity of DATBCD and DTABCD stationary phases is respectively 4143 and 392., the column efficiencies are respectively 3084 and 4198, and DATBCD is of stronger enantioselectivity than DTABCD, capacity factor of the first eluted enantiomer ( k 1) and separation factor(α)of α phenylethanol on DATBCD stationary phase are respectively 8.2. and 1.019.

关键词： capillary gas chromatography silylated and acetylated β-cyclodextrins enantiomeric separation

A Principal Theorem of normal Discretization Schemes for Operator Equations of the First Kind

在线全文

学校读者我要写书评

暂无评论

Wuhan University Journal of Natural Sciences 2001年第4期6卷 767-768页

作者： Du Nai lin 1, Wang Hannah 2.1.School of Mathematics and Statistics, Wuhan University, Wuhan 430072. china 2. School of Foreign Languages and Literature,Wuhan University,Wuhan 430072.china Wuhan University School of Mathematics and Statistics Wuhan China (GRID:grid.49470.3e) (ISNI:***) Wuhan University School of Foreign Languages and Literature Wuhan China (GRID:grid.49470.3e) (ISNI:***)

The authors announce a newly-proved theorem of theirs. This theorem is of principal significance to numerical computation of operator equations of the first kind.

关键词： operator equation of the first kind normal discretization scheme pure pseudoinverse

Quantum secret sharing between multiparty and multiparty with four states

在线全文

学校读者我要写书评

暂无评论

Science china(phys.cs,Mechanics & Astronomy) 2007年第5期50卷 572-580页

作者： YAN FengLi1, GAO Ting2.& LI YouCheng1 1 college of phys.cs and Information Engineering, Hebei {2. University, Shijiazhuang 050016, china 2.college of Mathematics and Information Science, Hebei {2. University, Shijiazhuang 050016, china 1. college of phys.cs and Information Engineering Hebei Normal University Shijiazhuang 050016 China 2. college of Mathematics and Information Science Hebei Normal University Shijiazhuang 050016 China

A protocol of quantum secret sharing between multiparty and multiparty with four states was presented. It was shown that this protocol can nullify the Trojan horse attack with a multi-photon signal, the fake-signal attack with Einstein-Podolsky- Rosen pairs, the attack with single photons, and the attack with invisible photons. In addition, the upper bounds of the average success probabilities were given for dishonest agent eavesdropping encryption using the fake-signal attack with any two-particle entangled states.

关键词： quantum secret sharing, security, Einstein-Podolsky-Rosen pairs

Synthesis, Crystal Structures and Catalysis of Dinuclear Cd(Ⅱ) Complexes Bridged by Unusual (N,O,O′)-Coordinated α-Amino Acids

在线全文

学校读者我要写书评

暂无评论

Chemical Research in Chinese Universities 2012年第1期28卷 73-78页

作者： DENG Dong-sheng1,2. WANG Li1, PEI Ya-mei1, FENG Lu2.and LIU Chang-lin1 1. Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, School of Chemistry, Central china normal University, Wuhan 430079, P. R. china 2. college of Chemistry and Chemical Engineering, Luoyang normal University, Luoyang 47102., P. R. china School of Chemistry Central China Normal University Key Laboratory of Pesticide & Chemical Biology Ministry of Education Wuhan 430079 college of Chemistry and Chemical Engineering Luoyang Normal University Luoyang 471022

Four dinuclear amino acid cadmium（II） complexes [Cd2.tren）2.dl-alaninato）]（ClO4）3·H2.（I）, [Cd2.tren）2. （l-alaninato）]（ClO4）3·H2.（II）, [Cd2.tren）2.dl-phenylalaninato）]（ClO4）3（III） and [Cd2.tren）2.l-phenylalaninato）]· （ClO4）3（IV）, constructed from mixed ligands of tris（2.aminoethyl）amine（tren） and racemic or natural amino ac ids（amino acids=dl or l-alanine, and dl or l-phenylalanine）, have been synthesized and characterized by X-ray crys tallography. The structural analysis of complexes I and III reveals that the cadmium centers are coordinated by one tren ligand and one amino acid molecule with the unusual （N,O,O′）-bridged mode, resulting in asymmetric chromo phores of CdN4O and CdN5O in complex I, CdN4O2.and CdN5O in complex III, respectively. The utility of the four complexes as efficient water-compatible Lewis acid catalysts for the direct aldol reaction in water was examined. The reaction proceeded smoothly to afford the corresponding β-hydroxy ketones in up to 99% yield. Moreover, the dias tereoselectivity of the reaction favors the formation of the syn-isomers.

关键词： Dinuclear cadmium(II) complex Amino acid Aldol reaction

Theoretical study on the reaction mechanism of(CH_3)_3CO+CO

在线全文

学校读者我要写书评

暂无评论

Science china Chemistry 2005年第1期48卷 18-24页

作者： ZHAO Hongmei1,2.3, SUN Chengke1,4, ZHANG Rongchang3, XI Hongmin3 & LI Zonghe1 1. Department of Chemistry, Beijing normal University, Beijing 100875, china 2. The Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, china 3. Department of Chemistry, Beihua University, Jilin 132.13, china 4. Department of Chemistry, Qujing normal University, Yunnan 655000, china 1. Department of Chemistry Beijing Normal University 100875 Beijing China 2. The Laboratory of Molecular Reaction Dynamics Institute of Chemistry Chinese Academy of Sciences 100080 Beijing China 3. Department of Chemistry Beihua University 132013 Jilin China 4. Department of Chemistry Qujing Normal University 655000 Yunnan China

The reaction mechanism of (CH3)3CO with CO has been theoretically investigated using density-functional theory (DFT) calculations at B3LYP/6-31G* level. In order to get more reliable energy values the single-point energy is evaluated at CcsD (T)/6-31++G** level. The results show that the reaction is multi-channel and the reaction of (CH3)3CO radical with CO mostly produces (CH3)3C + CO2. The reaction could play a role in eliminating air pollution.

关键词： DFT, B3LYP, (CH3)3CO, radical.

在线全文

学校读者我要写书评

暂无评论

基于强化学习的B型主动脉夹层定位方法

生物医学工程学杂志 2024年第5期41卷 878-885页

作者：曾安林先扬赵靖亮潘丹杨宝瑶刘鑫广东工业大学计算机学院广州510006 广东技术师范大学电子与信息学院广州510665

主动脉夹层分割中存在主动脉夹层与周围器官和血管的对比度低、夹层形态差异大以及背景噪声大等问题。针对以上问题,本文提出一种基于强化学习的B型主动脉夹层定位方法,借助两阶段分割模型,使用深度强化学习执行第一阶段的主动脉定位任... 详细信息

主动脉夹层分割中存在主动脉夹层与周围器官和血管的对比度低、夹层形态差异大以及背景噪声大等问题。针对以上问题,本文提出一种基于强化学习的B型主动脉夹层定位方法,借助两阶段分割模型,使用深度强化学习执行第一阶段的主动脉定位任务,保证定位目标的完整性;在第二阶段,使用第一阶段的粗分割结果作为输入,得到精细的分割结果。为了提高一阶段分割结果的召回率(Recall),使定位结果更完整地包含分割目标,本文设计了基于Recall变化方向的强化学习奖励函数;同时,将定位窗口与视野窗口分离,减少分割目标缺失的情况。本文选取Unet、TransUnet、SwinUnet以及MT-Unet作为基准分割模型,通过实验验证,本文的两阶段分割流程结果中多数指标均优于基准结果,其中Dice指标分别提高1.34%、0.89%、2..66%和7.37%。综上,将本文的B型夹层定位方法加入分割流程,最终的分割精度较基准模型结果有所提升,对于分割效果较差的模型提升效果更显著。

关键词：主动脉夹层两阶段分割强化学习奖励函数

Density functional study on enantioselective reduction of keto oxime ether with borane catalyzed by oxazaborolidine

在线全文

学校读者我要写书评

暂无评论

Science china Chemistry 2006年第4期49卷 296-307页

作者： LI Ming1, ZHENG Wenxu2.& TIAN Anmin2.1. Department of Chemistry, Southwest-china normal University, Chongqing 400715,{2. 2. Department of Chemistry, Sichuan University, Chengdu 610064,{2. 1. Department of Chemistry Southwest-China Normal University Chongqing 400715 China 2. Department of Chemistry Sichuan University Chengdu 610064 China

The enantioselective reduction of keto oxime ether with borane catalyzed by oxazaborolidine is discussed by the density functional theory (DFT) method. The main intermediates and transition states for this reaction are optimized completely at the B3LYP/6-31g(d) level, and the transition states are verified by vibrational modes. As shown, the chirality-controlled steps for this re- action are the hydride transfer from borane to carbonyl carbon and oxime carbon of keto oxime ether, and the chirality for the reduced products is determined in these two reaction steps. In all examined reaction paths, the first hydride is transferred via a six-membered ring and the second hydride via a five-membered ring or a four-membered ring.

关键词： keto oxime ether, oxazaborolidine, enantioselective reduction, DFT.

ON THE LEAST SQUARES PROBLEM OF A MATRIXEQUATION

在线全文

学校读者我要写书评

暂无评论

Journal of Computational Mathematics 1999年第6期17卷 589-594页

作者： An-ping Liao(college of Science, Hunan normal University, Changsha 410081,{2.) Hunan normal Univ Coll Sci Changsha 410081 Peoples R China

Least squares solution of F=PG with respect to positive semidefinite symmetric P is considered,a new necessary and sufficient condition for solvablity is given,and the expression of solution is derived in the some special cases. Based on the expression, the least spuares solution of an inverse eigenvalue problem for positive semidefinite symmetric matrices is also given.

关键词： least squares solution matrix equation inverse eigenvalue problem positive semidefinite symmetric matrix

Influence of MnO_2.on the photocatalytic activity of P-2. TiO_2.in the degradation of methyl orange

在线全文

学校读者我要写书评

暂无评论

中国科学：化学英文版 2008年第2期51卷 179-185页

作者： LI ShunJun1, MA ZiChuan1,2. WANG Lin1 & LIU JingZe2.1 college of Chemistry and Material Sciences, Hebei normal University, Shijiazhuang 050016,{2. 2.college of Life Science, Hebei normal University, Shijiazhuang 050016,{2. college of Chemistry and Material Sciences Hebej Normal UniversityShijiazhuang 050016China college of Life Science Hebei Normal UniversityShijiazhuang 050016China

Influences of α-MnO2. β-MnO2. and δ-MnO2.on the photocatalytic activity of Degussa P-2. TiO2.have been investigated through the photocatalytic degradation of methyl orange. The TiO2.photocatalyst, before and after being contaminated by MnO2. was characterized by UV-visible diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). The results showed that photocatalytic activity of TiO2.could be inhibited significantly or completely deactivated due to the presence of even a small amount of MnO2.particles. It was found that the poisoning effect varied with the crystal phases of MnO2.and the effect was in the order δ-MnO2.>α-MnO2.>β-MnO2. The poisoning effect was attributed to the formation of heterojunctions between MnO2.and TiO2.particles. The heterojunctions changed the chemical state of Ti4+ and O2.sites in the crystalline phase of TiO2. MnO2.in contact with TiO2.particles also broadens the band-gap of TiO2. which decreases UV absorption of TiO2. It can also create some deep impurity energy levels serving as photoelec-tron-photohole recombination center, which accelerates the electron-hole recombination.

关键词： TiO2 MnO2 deactivation photocatalysis methyl orange