检索结果-南通市图书馆

Theoretical Study on the Reaction Mechanism of F2+2HBr = 2HF+Br2

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Structural Chemistry 2005年第11期 110-115+12页

作者： SUN De-Shenga, b WANG Zun-Yaob YANG Chun-Shengb a (School of Chemistry and Chemical Engineering, Nanjing university of technology, Jiangsu, Nanjing 210009, china) b(Department of Chemical Engineering, Yancheng Institute of technology, Jiangsu, Yancheng 224003, china)

The gas phase reaction mechanism of F2 + 2HBr = 2HF + Br2 has been investigated by (U)MP2 at 6-311G** level, and a series of four-center and three-center transition states have been obtained. The reaction mechanism was achieved by comparing the activation energy of seven reaction paths, i.e. the dissociation energy of F2 is less than the activation energy of the bimolecular elementary reaction F2 + HBr → HF + BrF. Thus it is theoretically proved that the title reaction occurs more easily in the free radical reaction with three medium steps.

关键词： (U)MP2 transition state reaction mechanism free radical reaction.

分子动力学方法研究金属Ti中He小团簇的迁移

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

物理学报 2011年第12期60卷 428-432页

作者：陈敏西南科技大学国防科技学院绵阳621010

采用分子动力学方法模拟了不同温度下He原子及He团簇在金属Ti中的迁移特性,并计算了扩散前系数和激活能.研究发现这种扩散的各向异性非常显著,具体表现在He原子及He团簇在不同方向上扩散系数的前系数完全不同,但它们的激活能却相同.研... 详细信息

采用分子动力学方法模拟了不同温度下He原子及He团簇在金属Ti中的迁移特性,并计算了扩散前系数和激活能.研究发现这种扩散的各向异性非常显著,具体表现在He原子及He团簇在不同方向上扩散系数的前系数完全不同,但它们的激活能却相同.研究表明:在预测金属中He的扩散行为时,必须采用动态模拟方法才能得到准确的前系数,仅仅考虑势垒的静态模拟方法是不行的.另外,还发现一个不同于直觉的现象,即较低温度下He二聚物的扩散系数比单个He原子的扩散系数大;此外,在所模拟的温度范围内Arrhenius方程能够很好地描述它们的扩散.这说明动力学模拟对预测金属中He的扩散行为具有重要的意义.

关键词：分子动力学扩散系数各向异性氦

A MIXED METHOD OF DETERMINING THETHERMAL STRESS FOR COLD ROLLER

在线全文

学校读者我要写书评

暂无评论

Journal of Central south university 1997年第2期9卷 100-103页

作者： Li Zhenzi Wang Hui Zhou Hongbin Li Huijian (Department of Architectural Engineering,Central south university of technology,Changsha 410083,china)(Zhangjiang Fisheries College, Guangdong, 524025)(Department of Civil Engineering,Yan-shan university,Hebei Department of Architectural Engineering Central South University of Technology Changsha 410083 China Zhangjiang Fisheries Collage Guangdong 524025 China Department of Civil Engineering Yan-shan University Hebai 066004 China

A mixed method which combines the recent developed finite analytical method and the boundary fitting coordinate transformation method was used first to calculate the temperature field and thermal stress field of the cold roller in this paper. The following results are obtained by the calculation: thermal stresses σr=0, σθ=σz are maximum tension stress on the inner surface of the cold roller and σr=0, |σθ|=|σz| are maximum compression stress on the outer surface of the cold roller in the steady and unsteady case. Effectiveness and validity of the mixed method are checked with steady coil roller problems having theoretical solutions. The results show that good agreement is achived between the calculated value and theoretical solution,and the mixed method used in the paper is very workable. The mixed method is also useful in solving the steady and unsteady thermal stress field proplems of the hot -rolled for the reversing rolling mill and the continous rolling mill.

关键词： cold roller temperature field thermal stress mixing method

在线全文

学校读者我要写书评

暂无评论

基于GMM统计特性参数和SVM的话者确认

数据采集与处理 2004年第4期19卷 365-370页

作者：黄伟戴蓓蒨中国科学技术大学电子科学与技术系合肥230026

针对与文本无关的话者确认中大量训练样本数据的情况 ,本文提出了一种基于 GMM统计特性参数和支持向量机的与文本无关的话者确认系统 ,以说话人的 GMM统计特性参数作为特征参数训练建立目标话者的SVM模型 ,既有效地提取了话者特征信息 ... 详细信息

针对与文本无关的话者确认中大量训练样本数据的情况 ,本文提出了一种基于 GMM统计特性参数和支持向量机的与文本无关的话者确认系统 ,以说话人的 GMM统计特性参数作为特征参数训练建立目标话者的SVM模型 ,既有效地提取了话者特征信息 ,解决了大样本数据下的 SVM训练问题 ,又结合了统计模型鲁棒性好和辨别模型分辨力好的优点 ,提高了确认系统的确认性能及鲁棒性。对微软麦克风语音数据库和 NIST′0 1手机电话语音数据库的实验表明该方法的有效性。

关键词： SVM模型鲁棒性与文本无关 GMM 支持向量机训练样本语音数据库统计特性手机电话语音

Orthogonal design for optimization of pigment extraction from surface sediments of the Changjiang River Estuary

在线全文

学校读者我要写书评

暂无评论

Acta Oceanologica Sinica 2011年第4期30卷 33-42页

作者： ZHAO Jun YAO Peng YU Zhigang Thomas S Bianchi Key Laboratory of Marine Environment and Ecology Ministry of Education Ocean University of China Qingdao 266100 China Department of Oceanography Texas A ＆ M University College Station TX 77843 USA Key Laboratory of Marine Chemistry Theory and technology Ministry of Education Ocean University of China Qingdao 266100 China Institute of Marine Organic Geochemistry College of Chemistry and Chemical Engineering Ocean University of China Qingdao 266100 China

Using a suitable solvent for extracting pigments from sediment for high performance liquid chromatography（HPLC） analysis is critical for obtaining qualitative and quantitative estimates of phytoplanktonic and benthic algal biomass,as well as community composition. Five methodological factors（sample dehydration,extraction solvent,extraction duration,number of extractions,and ratio of solvent volume：sample weight） were studied using an L 9（3 4 ） orthogonal design in a sedimentary pigment extraction experiment on samples collected from the Changjiang large-river delta-front estuary（LDE）,using HPLC analysis. The results show that the optimal extraction method for sedimentary pigments should include freeze-drying samples prior to extraction. The effects of different factors on sedimentary pigment extraction were separated by the L 9（3 4 ） orthogonal design experiments and showed that the extraction solvent was the most important,with extraction duration the second most important,and numbers of extraction and ratio of solvent volume：sample weight was the least important. The mixed solvent treatment comprised of acetone,methanol and water（80：15：5,by volume） was best for polar pigment extraction,with 100% acetone better for apolar pigments. For most pigments employed in this study（i.e.,peridinin,fucoxanthin,alloxanthin,diatoxanthin,zeaxanthin,pheophytin-a and β-carotene） ,3 h was found to be enough time for extraction from these deltaic sediments. However,for chlorophyll-a,the most important pigment used for estimating algal biomass,12 h was needed. A small amount of solvent（3 ml） with duplicate extractions obtained the greatest amount and diversity of pigments. Unfortunately,no extraction method was found to be suitable for all pigments in sediments. The choice of extraction procedure should be made in accordance with the objective of each study,taking into consideration the properties of sediments and pigments in question.

关键词： sedimentary pigments extraction orthogonal design HPLC Changjiang River Estuary

2D/3D-QSAR comparative study on mutagenicity of nitroaromatics

在线全文

学校读者我要写书评

暂无评论

Science china Chemistry 2005年第3期48卷 246-252页

作者： WANG Xiaodong1, LIN Zhifen2, YIN Daqiang1, LIU Shushen1 & WANG Liansheng1 1. State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment at Nanjing university, Nanjing 210093, china 2. Key Laboratory of Tropical Marine Environmental Dynamics, south china Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301,china 1. State Key Laboratory of Pollution Control and Resources Reuse School of the Environment at Nanjing University 210093 Nanjing China 2. Key Laboratory of Tropical Marine Environmental Dynamics South China Sea Institute of Oceanology Chinese Academy of Sciences 510301 Guangzhou China

Nitroaromatics are typical toxic organic pollutants and are ubiquitous in environment with diverse structures. They are widely used in many industries and formed during many natural and anthropogenic processes. Most of these pollutants are potentially carcinogenic and the as-sessment and prediction of the mutagenicity of nitroaromatics are of great interest. In this paper the structure-mutagenicity relationships of 219 nitroaromatics are investigated by molecular or-bital theory based classic structure-activity relationships and comparative molecular field analysis (CoMFA). A comparison is undertaken in respect of the interpretation of mechanism and predic-tive ability for these two categories of QSAR approaches and highly predictive QSAR models have been developed.

关键词： nitroaromatics, mutagenicity, mechanism, 3D-QSAR, CoMFA.

Analysis and Countermeasure for Latch-up of CMOS Device in Electronic System Design

在线全文

学校读者我要写书评

暂无评论

微计算机信息 2008年第5期24卷 -页

作者： WANG XINHUA WANG JIANFEN(Zhejiang university of Science and technology,Department of information and electronic engineering,Hangzhou 310023. china)

Considering the phenomenon of Latch-up in CMOS device,some patterns of manifestation about Latch-up in electronic system are analyzed with three actual circuits,meanwhile the correlative solving methods are also provided. To avoid Latch-up,some general principles are proposed. The analyzing and solving processes derived from practical system design are verified simple and ef-fective in large number of products,and to some extend have general reference value in anti-latch-up design of application systems.

关键词： Latch-up trig signal integrality dual-powered system

MCM-41 Prepared with Ionic Liquid and Cethytrimethylammonium Bromide as Co-templates

在线全文

学校读者我要写书评

暂无评论

Journal of Wuhan university of technology(Materials Science) 2009年第1期24卷 25-29页

作者：张光旭 School of Chemical Engineering Wuhan University of Technology College of Chemistry and Molecular sciences Wuhan University

The mesoporous molecular sieves MCM-41 were prepared using room tempera-ture ionic liquid （RTIL） synthesized in laboratory and cethytrimethylammonium bromide （CTAB） as compound templates for the first time. They were prepared under low aging temperature and short aging time. Via characterizing by XRD and nitrogen adsorption instrument, MCM-41 synthesized by this new method exhibited good crystal structure and narrow pore distribution. The following pre-paratory conditions was optimal： the molar ratio of RTIL to CTAB was 1.0∶1.0, aging at 80 ℃, for 40 h and calcined at 540 ℃. It is found that the acidified MCM-41 improves its activity as catalyst over the unmodified ones.

关键词： mesoporous molecular sieve hydrothermal crystallization co-templates ionicliquid MCM-41

Anti-scourability of purple soil on hillslopes with different land uses

在线全文

学校读者我要写书评

暂无评论

Science china(Technological Sciences) 2003年第z1期46卷 133-141页

作者： ZHANG Jianhui, LIU Gangcai, NI Shijun, ZHU Bo & GE Fanglong Institute of Mountain Hazards and Environment, Chinese Academy of Sciences and Ministry of Water Resources, Chengdu 610041, china Chengdu university of technology, Chengdu 610059, china Chinese Acad Sci Inst Mt Hazards & Environm Chengdu 610041 Peoples R China Minist Water Resources Chengdu 610041 Peoples R China Chengdu Univ Technol Chengdu 610059 Peoples R China

A large-scale flume (40 cm×10 cm×10 cm) was used to determine soil anti-scourability of 4 different land uses of purple soil in hilly areas of Sichuan, china under artificial removal of vegetation to examine the effects of land uses on sediment production by runoff. The results showed that soil anti-scourability declined with the increase of slope gradients in the form of power function, but there was a significant difference in the effects of slope gradients on anti-scourability between different land uses. The ratio of the mean values of soil anti-scourability was 1︰2.2︰2.5︰3.6 for forest land, new waste pasture, old waste pasture, crop land respectively, indicating that forest and grass use can significantly improve soil anti-scourability. Compared with the observations from the runoff plots located at the same sites in this region, an inconsistent result was found between anti-scourability and anti-erodibility in hilly areas of Sichuan. Essential causes of the differences in soil anti-scourability were further discussed based on analyzing the influence of inherent soil characteristics induced by different land uses on soil anti-scourability.

关键词： sediment yield, soil anti-scourability, land use, vegetation, purple soil.