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961.
Precocenes and related intermediates were synthesised in good yields using hydrogen peroxide, selenium dioxide and methylene chloride combination in the key step. 相似文献
962.
963.
Photochromic Dithienylethene‐Containing Boron(III) Ketoiminates: Modulation of Photo‐Responsive Behavior through Variation of Intramolecular Motion
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Cheok‐Lam Wong Dr. Chun‐Ting Poon Prof. Dr. Vivian Wing‐Wah Yam 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(36):12931-12940
A series of dithienylethene‐containing boron(III) ketoiminates, as well as their corresponding β‐ketoimine ligands, have been synthesized and characterized. The photophysical, electrochemical, and photochromic properties of the compounds have been studied. Photocyclization has been found to be suppressed upon introduction of a phenyl substituent on the nitrogen atom of the β‐ketoiminate core, whereas photochromism could be observed by replacement of the phenyl substituent with a bulky mesityl group. It is believed that the steric effect of the mesityl unit restricts molecular rotation, resulting in such a prominent difference in the photochromic properties. 相似文献
964.
The present study evidences the role of steric effect in the orientation preference of guest into host using the 1:1 inclusion complex of 5-indanol/β-CD model. Two different orientations of guest (5-indanol) into host (β-CD) are considered for the inclusion of 5-indanol into the cavity through the 2° rim of β-CD. The energy differences in the inclusion process are calculated using PM3 semi-empirical method and HF/6-31G** basis set. By the investigation of stabilisation energies, it is found that the energy of both orientations increases to maximum value due to the increase of steric repulsive effect when the crowding of bulky group of 5-indanol occurs at 1° or 2° rim of β-CD. On comparing the fluorescence spectral data of 5-indanol:β-CD complex and 2-napthol:β-CD complex, it is observed that the steric effect is intensified due to the presence of bulky group. 相似文献
965.
Identification of striking distance considering the velocity ratio and competition among the leaders
《Journal of Electrostatics》2014,72(5):365-371
The striking distance is an important parameter to design a reliable lightning protection system. To protect an object against direct strikes, an improved leader progression model combined fractal geometry and the leader initiation criteria proposed by M. Becerra is introduced to determine the striking distance on a given structure. Both the deterministic and stochastic features of the lightning leader are considered and more detailed three-dimensional numerical simulation of the leader discharge is achieved due to the application of extended grid. Some of the basic methods and strategies are outlined and the influence on protection zone caused by leader velocity ratio is analyzed. Moreover, a comparative analysis of the results obtained through the improved model, the rolling sphere method and the Cooray model is performed. The results indicate that the presented method is closer to the natural lightning and the selection of the breakdown point is actually a complex competitive process among numerous upward leaders. 相似文献
966.
将修正的等效电流近似法与图形计算电磁学法相结合引入到热防护层覆盖弹体目标的电磁散射问题的研究中.应用修正的等效电流近似法对介质和有耗表面进行散射计算,结合图形计算电磁学法,借助于计算机显示技术,将三维目标图形在计算机屏幕上投影,由图形加速卡完成遮挡和消隐工作,利用图形计算电磁学的积分公式,把三维空间的计算转化为二维空间的计算,大大降低了计算时间和复杂度.计算结果表明:当入射波频率较低时,热防护层的厚度不会影响弹体雷达截面值的大小,当频率升高,随着热防护层厚度的增加,弹体雷达截面值不断减小,说明热防护涂层为有耗介质,介电常数的虚部越大其消耗能量的能力越强,弹体雷达截面变化越明显;当热防护层中存在孔隙,热防护层厚度一定,孔隙率越大,雷达截面值越大,孔隙率为零时,雷达截面值最小.当孔隙率相同,热防护层越薄,其雷达截面值越大;当弹体在高空中出现脱粘现象,对弹体的雷达截面值影响不大. 相似文献
967.
968.
针对一台用于加速器驱动次临界系统(ADS)的强流质子加速器,即ADS注入器Ⅱ,开展其定时系统和快保护系统的研究工作,设计了一款可在这两个系统中应用的PXIe控制器。该控制器基于现场可编程门阵列设计,可实现光纤通信、PXIe总线通信、延时触发信号输出等功能。其中,光纤通信功能用于实现各PXIe控制器之间的数据传输;PXIe总线通信功能主要是为了实现控制器与工控机之间的数据交互;延时触发信号输出功能可以给出精确的低电压晶体管-晶体管逻辑电平标准的时序触发信号,从而保证加速器的各子系统和设备能够按照一定的时序协调一致地工作。 相似文献
969.
970.
Claude CommandeurMalgorzata Commandeur Kathell BathanyBrice Kauffmann Andrew J.F. EdmundsPeter Maienfisch Léon Ghosez 《Tetrahedron》2011,67(51):9899-9908
This report describes a detailed study of the oxidation-Meisenheimer rearrangement of N-methyl-3-hydroxy-7-chloropyrroloindoline ethyl ester and the corresponding O-Boc and N-Boc derivatives. Experimental conditions were found, which allowed the selective Boc protection of either the tertiary alcohol substituent or the NH group of the aminal function. It was shown that both the parent compound and its O-Boc derivative yielded a mixture of oxazines and, in some cases, N-oxides upon treatment with m-CPBA. MS fragmentation (APCI) clearly differentiates formation of N-oxides and oxazines. The N-Boc derivatives exclusively yielded the N-oxides showing that the Meisenheimer rearrangement requires the presence of a high energy lone pair on the neighbouring nitrogen atom. Both the parent compound and the O-Boc derivative gave a mixture of rearranged products and N-oxide depending on the reaction conditions. 相似文献