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91.
《Displays》2015
New chiral compounds of the steroid type, namely, 3-alkanoyl- and 3-alkyl derivatives of 16-arylidene estrone, were synthesized and exhibited high helical twisting power (HTP) in nematic liquid crystals E63 and LC-1289. The peculiarities of the molecular structure of chiral compounds (CCs) and their high degree of chirality were discussed. Quite small concentrations of chiral compounds in both nematic solvents were needed to obtain a short-pitch cholesteric helical macrostructure with the selective light reflection in the visible range of the spectrum. The insignificant temperature dependence of the maximum wavelength of the selective light reflection obtained on the whole cholesteric range for all studied liquid crystalline (LC) systems could be related to relatively rigid molecular structure of the chiral compounds. The cholesteric LC mixtures comprising 3-alkanoyl- and 3-alkyl derivatives of 16-arylidene estrone were characterized by the phase stability and the stability of reflective characteristics in time that makes it possible to consider this series of dopants as appropriate for development of bistable cholesteric reflective LC displays. 相似文献
92.
Papichaya Chaisakul Mohamed-Said Rouifed Jacopo Frigerio Daniel Chrastina Jean-René Coudevylle 《Science and Technology of Advanced Materials》2014,15(1)
Electro-absorption from GeSi heterostructures is receiving growing attention as a high performance optical modulator for short distance optical interconnects. Ge incorporation with Si allows strong modulation mechanism using the Franz–Keldysh effect and the quantum-confined Stark effect from bulk and quantum well structures at telecommunication wavelengths. In this review, we discuss the current state of knowledge and the on-going challenges concerning the development of high performance GeSi electro-absorption modulators. We also provide feasible future prospects concerning this research topic. 相似文献
93.
Bruce W. McClendon Ernest Erber Margarita McCoy Israel Stollman 《Journal of the American Planning Association. American Planning Association》2013,79(3):221-232
R. W. Firestone's Cityscape Pink is a bold image capturing the essence of a city. In this Longer View essay, Bruce McClendon argues that the profession of planning needs a similarly bold vision and compelling brand identity in order to claim its proper place among many competitors offering similar services. He aims to distinguish the planning profession in the eyes of the public and the minds of planners themselves. Three commenters respond with different perspectives on the status of the profession and how best to improve it. Firestone is a psychotherapist with a PhD in clinical psychology from the University of Denver and the author of nine books. He grew up in the New York City area and opened his private practice in Los Angeles, treating patients suffering from schizophrenia. With a group of friends he has sailed to many parts of the world, and both his practice and his travels figure into the subjects of his artwork. Planning has become a generic product in a confusing, overcrowded, and highly competitive marketplace. The public does not know what planning is or how to differentiate among planning specialists. Relying on a bold back-to-the-future approach, I argue that it is the production, administration, and implementation of comprehensive plans that once was and still is the profession's unique and distinctive technical competency and core mission. By using branding techniques to define, link, and reconnect planners with comprehensive planning, it will be possible to tell the planning story in a way that communicates the emotional benefits and value of the profession and strengthens the public's respect and appreciation for planners. 相似文献
94.
ea of only 65 × 65μm2. 相似文献
95.
We demonstrate an electric-controlled terahertz (THz) modulator which can be used to realize amplitude modulation of terahertz waves with slight photo-doping. The THz pulse transmission was efficiently... 相似文献
96.
97.
设计一个内部采用2位量化器的二阶单环Σ‐Δ调制器.为解决反馈回路中多位DAC元件失配导致的信号谐波失真问题,该调制器采用了数据加权平均(Data Weighted Averaging ,DWA )技术来提高多位DAC的线性度.Σ‐Δ调制器信号带宽为50 kHz ,过采样率(OSR)为64,采用MXIC公司的0.35μm混合信号CMOS工艺实现,工作电压为12 V .后仿真结果显示,在电容随机失配5%的情况下,该调制器可以达到55.8 dB的信噪比(SNR)和60.4 dB的无杂散动态范围(SFDR).打开DWA电路比关闭DWA电路的情况下,SNR和SFDR分别提高8 dB和13 dB .整个调制器功耗为48 mW ,面积仅为0.6mm2. 相似文献
98.
介绍了全固态调制器采用IGBT 管等固态器件进行串并联组合应用的典型工作模式,分析了固态调制器传统开关组件的检测和保护技术,提出基于开关管阻抗特性的调制组件检测方法,阐述了设计思想及工作原理,给出了工程实现方案和检测方法原理框图,并分析比较了传统的在线检测方法和基于开关管阻抗特性的调制组件检测方法,基于PLC 编程软件平台,根据采样电压的数值及其变化量,实现精确判定IGBT 管损坏数量和百分比的计算。工程应用验证了检测结果的准确可靠。 相似文献
99.
基于相移法实现SSB(单边带)调制器理论,设计制造了一种Ka 波段宽带SSB 调制器集成电路。对相移法产生单边带调制信号的原理进行了分析,利用无源电路的3D 电磁仿真分析和ADS 整体电路非线性仿真相结合的方法对调制器进行了优化。设计制造的90°相移电桥网络和同相合成器满足了产生Ka 波段SSB 信号的幅相要求,同时给出了测试结果。调制器在30 ~36GHz 频带内插入损耗臆14dB;载波和对称边带抑制逸15dB;其它边带抑制逸13dB;输入1dB 压缩功率38dBm;外形尺寸18mm×6mm。这种相移法单边带调制器不需要带通滤波器,具有电路简单,载波抑制比高,对相位误差要求不高的优点。 相似文献
100.
为了扩展光电振荡器(OEO)的频率范围,设计了 一种基于载波相移系统的二倍频OEO(FD-OEO)。 系统采用相位调制器(PM)和Mach-Zehnder调制器(MZM)并联,构成载波相移系统,利用载 波相移双边带(CPS-DSB) 调制的方法产生二次谐波分量;同时利用啁啾光纤布拉格光栅(CFBG)色散特性实现边带分 量与CPS补偿,维持 OEO环路中基频信号的振荡。实验结果显示,在OEO环路系统基频信号为2.23GHz情况下,产生了4.30 GHz的FD信号,且通过边模抑制性能、稳定性及相位噪声对系统性能进行了验证。 相似文献