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931.
90°弯管内流动的理论模型及流动特性的数值研究 总被引:27,自引:0,他引:27
从三维不可压缩雷诺时均Navier-Stokes方程出发,对90°弯曲管道内湍流流动进行数值模拟。网格划分采用六面体网格,湍流模型为RNGk-ε模型,在近壁区采用两层壁面模型进行修正,流场的计算结果与实验数据吻合较好。在此基础上,本文数值研究了来流方向对流场结构和流动特性的影响。得出在弯管流场中发生了分离现象,且随着来流侧滑角的增大,分离区范围增大。此外,随着来流从同一侧滑角变换至同一攻角时,横截面的二次流图像中也从具有两个对称主涡变成只具有一个主涡的现象。 相似文献
932.
933.
Ruoyu Hong * Jianmin Ding Guoliang Zheng College of Chemistry Chemical Engineering Soochow University Suzhou P. R. China Institute of Process Engineering Chinese Academy of Sciences Beijing P. R. China IBM HYDA/- C Highway North Rochester MN USA *Author to whom correspondence should be addressed. E-mail: rhong@suda.edu.cn 《中国颗粒学报》2004,2(5):207-214
1. Introduction1.1 Silica nanoparticles and synthesis methods Silica (SiO2) nanoparticles are widely used in industry asan active filler for polymer reinforcement, a rheologicaladditive in fluids, a free flow agent in powders, and anagent for chemical mechanical polishing during IC (inte-grated circuit) fabrication (Sniegowski & de Boer, 2000).Silica powder is also used for producing silicon carbide(Koc & Cattamanchi, 1998) or opaque silica aerosols (Leeet al., 1995). Many methods can … 相似文献
934.
丁协平 《应用数学和力学(英文版)》2005,26(12):1547-1555
A new notion of finite continuous topological space (in short, FC-space) with out convexity structure was introduced. A new continuous selection theorem was established in FC-spaces. By applying the continuous selection theorem, some new coincidence theorems for two families of set-valued mappings defined on product space of noncompact FC-spaces are proved under much weak assumptions. These results generalize many known results in recent literature. Some applications will be given in a follow-up paper. 相似文献
935.
MAXIMAL ELEMENTS OF A FAMILY OF GB-MAJORIZED MAPPINGS IN PRODUCT FC-SPACES AND APPLICATIONS 总被引:1,自引:1,他引:1
丁协平 《应用数学和力学(英文版)》2006,27(12):1607-1618
A new family of GB-majorized mappings from a topological space into a finite continuous topological spaces (in short, FC-space) involving a better admissible set-valued mapping is introduced. Some existence theorems of maximal elements for the family of GB-majorized mappings are proved under noncompact setting of product FCspaces. Some applications to fixed point and system of minimax inequalities are given in product FC-spaces. These theorems improve, unify and generalize many important results in recent literature. 相似文献
936.
Dr. Qinghong Yuan Prof. Dr. Feng Ding 《Angewandte Chemie (International ed. in English)》2015,54(20):5924-5928
Owing to the unique structure of zigzag (ZZ) carbon nanotubes (CNTs), their ring‐by‐ring growth behavior is different from that of chiral or armchair (AC) CNTs, on the rims of which kinks serve as active sites for carbon attachment. Through first‐principle calculations, we found that, because of the high energy barrier of initiating a new carbon ring at the rim of a ZZ CNT, the growth rate of a ZZ CNT is proportional to its diameter and significantly (10–1000 times) slower than that of other CNTs. This study successfully explained the broad experimental observation of the lacking of ZZ CNTs in CNT samples and completed the theory of CNT growth. 相似文献
937.
Substrate‐Tuned Catalysis of the Radical S‐Adenosyl‐L‐Methionine Enzyme NosL Involved in Nosiheptide Biosynthesis
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Xinjian Ji Dr. Yongzhen Li Prof. Dr. Wei Ding Prof. Dr. Qi Zhang 《Angewandte Chemie (International ed. in English)》2015,54(31):9021-9024
NosL is a radical S‐adenosyl‐L ‐methionine (SAM) enzyme that converts L ‐Trp to 3‐methyl‐2‐indolic acid, a key intermediate in the biosynthesis of a thiopeptide antibiotic nosiheptide. In this work we investigated NosL catalysis by using a series of Trp analogues as the molecular probes. Using a benzofuran substrate 2‐amino‐3‐(benzofuran‐3‐yl)propanoic acid (ABPA), we clearly demonstrated that the 5′‐deoxyadenosyl (dAdo) radical‐mediated hydrogen abstraction in NosL catalysis is not from the indole nitrogen but likely from the amino group of L ‐Trp. Unexpectedly, the major product of ABPA is a decarboxylated compound, indicating that NosL was transformed to a novel decarboxylase by an unnatural substrate. Furthermore, we showed that, for the first time to our knowledge, the dAdo radical‐mediated hydrogen abstraction can occur from an alcohol hydroxy group. Our study demonstrates the intriguing promiscuity of NosL catalysis and highlights the potential of engineering radical SAM enzymes for novel activities. 相似文献
938.
Tuning the Upconversion Luminescence Lifetimes of KYb2F7:Ho3+ Nanocrystals for Optical Multiplexing
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Dr. Mingye Ding Prof. Daqin Chen Danyang Ma Peng Liu Dr. Kaixin Song Dr. Hongwei Lu Prof. Zhenguo Ji 《Chemphyschem》2015,16(18):3784-3789
Conventional luminescent color coding is limited by spectral overlap and the interference of background fluorescence, thus restricting the number of distinguishable identities that can be used in practice. Here, we demonstrate the possibility of generating diverse time‐domain codes, specially designed for a single emission band, using lanthanide‐doped upconversion nanocrystals. Based on the knowledge of concentration quenching, the upconversion luminescence kinetics of KYb2F7: Ho3+ nanocrystals can be precisely controlled by modifying the dopant concentration of Ho3+ ions, resulting in a tunable emission lifetime from 75.8 to 1944.5 μs, which suggests the practicality of these time‐domain codes for optical multiplexing. 相似文献
939.
Photo‐responsive amphiphilic poly(α‐hydroxy acids) with pendent o‐nitrobenzyl ester constructed via copper‐catalyzed azide‐alkyne cycloaddition reaction
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Xiangyu Liu Jingwen He Yile Niu Yefei Li Ding Hu Xinnian Xia Yanbing Lu Weijian Xu 《先进技术聚合物》2015,26(5):449-456
Photo‐responsive block copolymer mPEG‐b‐poly(Tyr)‐g‐NB was prepared by introduction of o‐nitrobenzyl ester group into the side chain of amphiphilic poly(ethylene glycol)‐b‐poly(α‐hydroxy acids) (mPEG‐b‐poly(Tyr)) containing pendent alkynyl group via copper‐catalyzed azide‐alkyne cycloaddition reaction. The amphiphilic mPEG‐b‐poly(Tyr) was synthesized via the ring‐opening polymerization of O‐carboxyanhydrides, with monomethoxy poly(ethylene glycol) (mPEG) as macroinitiator. The molecular structure, self‐assembly, and photo‐controlled release of the obtained mPEG‐b‐poly(Tyr)‐g‐NB were thoroughly investigated. mPEG‐b‐poly(Tyr)‐g‐NB could self‐assemble into spherical micelles in water and showed disassembly under UV light irradiation, which was demonstrated by means of UV‐vis spectroscopy, scan electron microscopes, and dynamic light scattering measurement. Fluorescence emission measurements demonstrated that Nile red, encapsulated by micelles, can be released upon UV irradiation. This study provides a convenient way to construct smart poly(α‐hydroxy acids)‐based nanocarriers for controlled release of hydrophobic drugs. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
940.
Electrolytic Macrocyclizations: Scalable Synthesis of a Diazonamide‐Based Drug Development Candidate
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Dr. Hui Ding Patrick L. DeRoy Christian Perreault Dr. Alexandre Larivée Dr. Arshad Siddiqui Dr. Charles G. Caldwell Susan Harran Prof. Dr. Patrick G. Harran 《Angewandte Chemie (International ed. in English)》2015,54(16):4818-4822
An electrochemical method to synthesize the core macrolactam of diazonamides is described. Large ring‐forming dehydrogenation is initiated by anodic oxidation at a graphite surface. The reaction requires no tailoring of the substrate and occurs at ambient temperature in aqueous DMF in an undivided cell open to air. This unique chemistry has enabled a concise, scalable preparation of DZ‐2384; a refined analog of diazonamide A slated for clinical development as a cancer therapeutic. 相似文献