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81.
SlflsltlC!fi10,dn8VOflOI!gflsfl.W3SISOhtCdnOffiSlhQltICtiffiIC3VCSsfldhdIflhibltOYy卜388cellactlvltyl.巨histypeofnaturalproductshaveshownvariousbloactlvltyandreceivedconsiderableattentionfromsyntheticchemlstsy.Wewishtoreportastereoselectlvetotalsynthesisofslnaltlclnfromreadilyavailablestartingmaterials(land4).OursyntheticdesignIsbaseduponconstructionofthesubstitutedbenzouioxanering,to!lowedbyformationof*theX**flavanonolmoietyFromSchemel,wecansee!natInnilssynthesisofs… 相似文献
82.
Characteristic formulations for boundary conditions have demonstrated their effectiveness to handle inlets and outlets, especially to avoid acoustic wave reflections. At walls, however, most authors use simple Dirichlet or Neumann boundary conditions, where the normal velocity (or pressure gradient) is set to zero. This paper demonstrates that there are significant differences between characteristic and Dirichlet methods at a wall and that simulations are more stable when using walls modelled with a characteristic wave decomposition. The derivation of characteristic methods yields an additional boundary term in the continuity equation, which explains their increased stability. This term also allows to handle the two acoustic waves going towards and away from the wall in a consistent manner. Those observations are confirmed by stability matrix analysis and one‐ and two‐dimensional simulations of acoustic modes in cavities. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Hidekazu Kumano Satoshi Kimura Michiaki Endo Ikuo Suemune Hirotaka Sasakura Satoru Adachi Shunichi Muto Hai Zhi Song Shinichi Hirose Tatsuya Usuki 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):144
Triggered single-photon generation from InAlAs quantum dot (QD) was demonstrated for the first time. Emitted photon energy coincides with high detection efficiency range of Si single-photon detectors, which is highly suitable for free-space communication. Single-QD spectroscopy and crossed photon correlation measurements unambiguously revealed that several emitting lines observed in a single mesa structure originated from the identical QD, and two temporary competing decay processes associated with neutral states and charged states were identified. Presence of the competing process is also inferred from an analysis of steady-state photoluminescence intensities. Formation process of charged exciton in QD is also discussed. 相似文献
85.
The effect of stimulated Raman scattering (SRS) in fiber optic communications is considered. On one hand, SRS limits the launch power in a multiple-channel communication system; while on the other hand, SRS can provide optical amplification in the 1.3-μm and 1.55-μm windows. In most of the previous work these issues have been treated separately by using different assumptions. A solution is usually obtained by solving differential equations. We present a numerical method that involves the simultaneous solution of integral equations describing SRS in optical fiber. The method is general enough to be applicable for wavelength division multiplexing (WDM), optic frequency division multiplexing (OFDM), and optical amplification. However, it is efficient and simple to program and uses just a few realistic assumptions. A WDM communication system with 10 optical channels in the 1.55-μm window is studied by using this method, The data rate is above 1 Gbps. The system parameters are such that the other nonlinear effects, such as stimulated Brillouin scattering and four-wave mixing, are less significant for the system. Launch power limitations imposed by SRS are investigated for IM / DD and coherent systems. The receiver dynamic range over the wavelengths of interest is an important factor in determining the launch power limitations. An optical amplifier in the 1.3-μm window is also analyzed. The two-pump technique is investigated. With pump power levels of about 500 mw 0-dB gain can be achieved for a 30-km repeaterless link. Finally, the calculated results agree with the experiments. 相似文献
86.
陶靖轩 《数学的实践与认识》2007,37(1):43-48
利用网络计划技术,对节点(事项)和箭条(作业活动)分别规定了六个时间值,讨论了他们之间的关系;结合实例应用,分析了资源的合理配置,得到了有一定参考意义的结果. 相似文献
87.
Jian Zhu Xiulin Zhu Zhengbiao Zhang Zhenping Cheng 《Journal of polymer science. Part A, Polymer chemistry》2006,44(23):6810-6816
Reversible addition–fragmentation chain transfer (RAFT) polymerizations of styrene under microwave irradiation (MI), with or without azobisisobutyronitrile, were successfully carried out in bulk at 72 and 98 °C, respectively. The results showed that the polymerizations had living/controlled features, and there was a significant enhancement of the polymerization rates under MI in comparison with conventional heating (CH) under the same conditions. The polymer structures were characterized with 1H and 13C NMR. The results showed the same structure for both polymers obtained by MI and CH. Successful chain‐extension experimentation further demonstrated the livingness of the RAFT polymerization carried out under MI. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6810‐6816, 2006 相似文献
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The benefits of using multi-granularity switching to reduce the number of ports, including both electronic and optical ports, have been investigated. A novel multi-layer ring architecture with multiple switches is proposed and two general equations to count the number of ports are derived. Comparisons are made between the multi-layer multi-granularity switching (MM-XC) architecture and the reported architectures: multi-switching (M-XC) and single switching (S-XC) architectures. The results show that the M-XC or S-XC architectures can be deduced from the MM-XC architecture and the latter architecture can achieve more considerable savings of the port count compared to the former. 相似文献
90.
In this paper, the statistical multiplexing of independent fractional Brownian traffic streams with the same Hurst value 0.5<H<1 is studied. The buffer overflow probabilities based on steady-state and transient queue length tail distributions are used respectively as the common performance criterion. Under general conditions, the minimal buffer allocation to the merged traffic is identified in either case so that strictly positive bandwidth savings are realized. Impact of the common H value on multiplexing gains is investigated. The analytical results are applicable in data network engineering problems, where ATM is deployed as the transport network carrying long-range dependent data traffic. 相似文献