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Elford DP Chalmers L Kusmartsev FV Swallowe GM 《The Journal of the Acoustical Society of America》2011,130(5):2746-2755
The results of numerical modeling of sonic crystals with resonant array elements are reported. The investigated resonant elements include plain slotted cylinders as well as their various combinations, in particular, Russian doll or Matryoshka configurations. The acoustic band structure and transmission characteristics of such systems have been computed with the use of finite element methods. The general concept of a locally resonant sonic crystal is proposed that utilizes acoustic resonances to form additional band gaps that are decoupled from Bragg gaps. An existence of a separate attenuation mechanism associated with the resonant elements that increases performance in the lower frequency regime has been identified. The results show a formation of broad band gaps positioned significantly below the first Bragg frequency. For low frequency broadband attenuation, a most optimal configuration is the Matryoshka sonic crystal, where each scattering unit is composed of multiple concentric slotted cylinders. This system forms numerous gaps in the lower frequency regime, below Bragg bands, while maintaining a reduced crystal size viable for noise barrier technology. The finding opens alternative perspectives for the construction of sound barriers in the low frequency range usually inaccessible by traditional means including conventional sonic crystals. 相似文献
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The substrate scope and the effect of substrate on the observed inversion of stereoselectivity in the triflic acid-catalyzed allylboration reaction between 2-alkoxycarbonyl allylboronates and aldehydes are presented. A mechanistic investigation is described so as to confirm the involvement of a carbocation intermediate as the source of stereochemical inversion. This methodology allows a facile access to beta,gamma-disubstituted five-membered ring lactones with an exo-methylene at the alpha-position. 相似文献
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Perrin R Chalmers L Elford DP Swallowe GM Moore TR 《The Journal of the Acoustical Society of America》2012,131(3):2288-2294
The geometrical structure of the Indian elephant bell is presented and the requirements on its normal modes from group representation theory are described. These are in good agreement with the results of a finite-element model (FEM) for a specific 16-tine case. The spectrum consists of a sequence of families of modes lying on saturation curves, completely different from those of conventional bells. Physical explanations for the occurrence of these families are presented in terms of the tines behaving as a closed loop of coupled cantilevers with constraints from the dome. Each family is found to consist of modes in one of two specific sequences of symmetry types. Experimental measurements of the modes of this same 16-tine bell, using electronic speckle pattern interferometry (ESPI), have been made and are compared with the FEM predictions. Although the interpretation of the interferograms is difficult in all but the simpler cases, agreement in terms of frequencies is surprisingly good for the first few family sequences. The ESPI study also showed up numerous harmonics and subharmonics of true normal modes, showing the system to be rather non-linear and making comparisons with the FEM results tricky. 相似文献
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The lithiation/borylation-protodeboronation of a homoallyl carbamate was applied to the synthesis of (+)-sertraline and (+)-indatraline. Due to the presence of the alkene, significant modifications of the methodology were required (use of 12-crown-4, TMSCl, H(2)O), or a solvent switch to CHCl(3), to achieve high yields and high selectivities. 相似文献
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P. H. Hermans H. L. Bredée W. Lepper G. R. Yohe W. J. Elford und J. D. Ferry 《Fresenius' Journal of Analytical Chemistry》1936,105(3-4):118-120
Ohne Zusammenfassung 相似文献
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D. Mac Calman W. J. Elford W. Rathje K. Hess M. Ulmann L. Kratz und H. Wislicenus 《Fresenius' Journal of Analytical Chemistry》1940,120(1-2):15-17
Ohne Zusammenfassung 相似文献
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Tim G. Elford 《Tetrahedron letters》2008,49(49):6995-6998
α-exo-Methylene-γ-lactams are key structural units in a wide variety of biologically active natural products. A concise route to the formation of polysubstituted α-exo-methylene-γ-lactams is described. In this three-component reaction, an imine is formed from an aldehyde and ammonia in situ, and is subsequently allylated through the use of a 2-alkoxycarbonyl allylboronate. Due to the ester functionality, the addition intermediate subsequently undergoes in situ cyclization to form the observed α-exo-methylene-γ-lactam products. This route allows access to highly substituted α-exo-methylene-γ-lactams in moderate to excellent yields. 相似文献
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