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Nonlinear Dynamics - Global dynamics of a flexible asymmetrical rotor resting on vibrating supports is investigated. Hamilton’s principle is used to derive the partial differential governing... 相似文献
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Wen-Yan Xu Zhe-Yuan Xu Ze-Kuan Zhang Tian-Jun Gong Yao Fu 《Angewandte Chemie (International ed. in English)》2023,62(40):e202310125
Divergent synthesis of fluorine-containing scaffolds starting from a suite of raw materials is an intriguing topic. Herein, we report the solvent-controlled rhodium-catalyzed tunable arylation of 1-bromo-2,2-difluoroethylene. The selection of the reaction solvents provides switchable defluorinated or debrominated arylation from readily available feedstock resources (both arylboronic acids/esters and 1-bromo-2,2-difluoroethylene are commercially available). This switch is feasible because of the difference in coordination ability between the solvent (CH2Cl2 or CH3CN) and the rhodium center, resulting in different olefin insertion. This protocol allows the convenient synthesis of monofluoroalkenes and gem-difluoroalkenes, both of which are important scaffolds in the fields of medicine and materials. Moreover, this newly developed solvent-regulated reaction system can be applied to the site-selective dechlorinated arylation of trichloroethylene. Overall, this study provides a useful strategy for the divergent synthesis of fluorine-containing scaffolds and provides insight into the importance of solvent selection in catalytic reactions. 相似文献
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合成了具有近红外荧光特性的卟啉化合物二{[5,5’-10,20-二苯基-15-(4-吡啶基)卟啉]Zn(Ⅱ)]}丁二炔,通过核磁共振波谱和质谱对其结构进行了确认.通过紫外吸收光谱法测定了其光学性质,利用HWHR光学平台测定了化合物在近红外区激发产生的荧光,并通过动物组织模型评价其荧光深层次成像效果.结果表明,该化合物具... 相似文献
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对天然紫皮石斛(Dendrobium devoninum Paxt.)根和茎中Cr、Cd、Pb、Hg、Cu 5种重金属元素的含量进行了测定,旨在为该资源的药(食)利用提供基础数据.利用干法灰化处理样品,采用原子吸收光谱法(AAS)分别测定紫皮石斛根和茎中Cr、Cd、Pb、Hg、Cu 5种重金属元素的含量.根中Cr、Hg和Cu 3种元素含量分别为122.8043士39.02、311.5152士24.28、0.2890士0.19mg·kg-1,相对标准偏差(RSD)在3.20%-14.07%之间;茎中Cr、Hg和Cu 3种元素的含量分别为139.3997士14.72、276.0101士45.61、0.2854士0.29mg·kg-1,相对标准偏差(RSD)在4.83%-10.99%之间;根和茎中均未检出Cd、Pb两种元素,可能与地球化学背景有关.与人工种植石斛中重金属元素含量相比,Cr、Hg两种元素含量相对较高,Cu元素含量较低.本法操作简便,重复性好,测定结果满意. 相似文献
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In this note, we compute the virtual first Betti numbers of 4-manifolds fibering over $S^1$ with prime fiber. As an application, we show that if such a manifold is symplectic with nonpositive Kodaira dimension, then the fiber itself is a sphere or torus bundle over $S^1$ . In a different direction, we prove that if the 3-dimensional fiber of such a 4-manifold is virtually fibered then the 4-manifold is virtually symplectic unless its virtual first Betti number is 1. 相似文献
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Pd-catalyzed directed ortho C-H amidation of aromatic ketones with both sulfonamides and amides has been accomplished. The use of an electron-deficient Pd complex, Pd(OTf)(2), is crucial for the success of this transformation. Some key intermediates of the reaction, that is, the cyclopalladation complexes of ketones, have been characterized by X-ray crystallography. Experimental analysis of these palladacycles and also the experimental results with N-methyl sulfonamides indicate that the new reaction does not seem to proceed through a nitrene intermediate. The utility of the newly developed reaction was demonstrated for the synthesis of useful organic intermediates such as 2- and 3-alkyl indoles and 2-aminophenyl ketones. 相似文献
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A flexible approach to ethyl (3R,4S)-N-Boc-4-amino-3-hydroxy-5-phenylpentanoate (N-Boc-AHPPA-OEt), the γ-amino-β-hydroxy acid moiety of hapalosin is described. The synthetic method features a ring-opening ethanolysis of an activated N-Boc-lactam, which is obtained via a diastereoselective reductive-alkylation of (R)-malimide derivative. The flexibility of the method resides in the introduction of the alkyl side chain by Grignard reagent addition. 相似文献
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We describe a circle-sum construction of smoothly embedded surface in a smooth 4-manifold. We apply this construction to give a simpler solution of the minimal genus problem for nontrivial bundles over surfaces. We also treat the case of blow-ups.
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Tian-Jun Li 《Proceedings of the American Mathematical Society》1999,127(2):609-613
We characterize rational or ruled surfaces among all symplectic 4-manifolds by the existence of certain smoothly embedded spheres.