层叠Blumlein纳秒脉冲形成线设计与实验

研究了一种结构紧凑型的多级层叠Blumlein纳秒脉冲形成线,从理论上分析了放电时回路各分布参数对层叠Blumlein脉冲形成线输出电压的影响,并利用PSpice模拟验证了各分布参数对层叠Blumlein脉冲形成线输出结果的影响,发现开关的导通电阻是制约输出电压幅值的主要因素,开关的分布电感对输出波形的影响大于负载分布电感的影响,基于时域有限差分法原理,利用XFDTD软件模拟了两级层叠Blumlein线的电磁耦合效应。开展了多级层叠Blumlein脉冲形成线实验,结果表明,基于陶瓷固态传输线和GaAs光导开关的层叠Blumlein脉冲形成线能够实现输出电压叠加,可用于产生ns量级脉宽的脉冲高压。     

Optically Pure,Monodisperse cis‐Oligodiacetylenes: Aggregation‐Induced Chirality Enhancement

Conformational changes in the conjugated backbone of poly‐ and oligodiacetylenes (PDAs and ODAs) play an important role in determining the electronic properties of these compounds. At the same time, conformational changes can also result in a folded structure that shows helical chirality. Using D ‐camphor as a chiral building block, we have designed a high‐yielding, iterative synthesis of monodisperse, optically pure cis‐oligodiacetylenes (ODAs). cis‐ODAs up to the tridecamer have been formed, which is the longest monodisperse cis‐ODA reported to date. UV/Vis spectroscopy suggests a large effective conjugation length in THF, likely the result of a linear, planar conformation in this solvent. High‐resolution STM/AFM measurements of the nonamer cast from THF onto HOPG show a linear structure. In iPrOH, circular dichroism (CD) spectra suggest the formation of chiral aggregates for ODAs with at least nine D ‐camphor units, based on a strong CD response.     

On a pattern sequencing problem to minimize the maximum number of open stacks

Consider a wood cutting setting where different panels have to be cut from large boards. Each cut panel size is put into a stack which remains opened until the last panel of that size is cut. The problem considered here deals with the sequencing of the patterns in order to minimize the maximum number of open stacks during the production run. A branch and bound method for solving this problem is presented which uses a greedy type scheme to select the next node to branch.     

A remark on the ODE with two discrete delays

The aim of this paper is to outline a formal framework for the analytical analysis of the Hopf bifurcations in the delay differential equations with two independent time delays. Some results for the differential-difference equations with two delays, when the both of the coefficients of linearized equation are negative were obtained in [X. Li, S. Ruan, J. Wei, Stability and bifurcation in delay-differential equations with two delays, J. Math. Anal. Appl. 236 (1999) 254-280]. In the paper we present some remarks on the case studied in [X. Li, S. Ruan, J. Wei, Stability and bifurcation in delay-differential equations with two delays, J. Math. Anal. Appl. 236 (1999) 254-280] and also two other cases, namely when the coefficients of linearized equation have different signs and when coefficients are both positive.     

光电开关锁定机理的理论分析

光电开关锁定(lock-on)现象自1990年报道以来已受到广泛关注,许多学者研究其机理并已开展研究将其应用到高压脉冲发生系统中,但目前所有的研究尚处于起步阶段.本文就光电开关锁定机理作了较全面的理论分析,认为光电开关的锁定是光与电联合作用的结果,耿氏效应引起场强动态增强,光脉冲产生的光电子引起本征碰撞电离,从而比较完整地解释了光电开关处于锁定状态时的增益现象.     

双边沿单稳态触发器的设计

对双边沿单稳态触发器的设计原理进行了研究，根据双边沿单稳态触发器工作特点的要求，以RC电路为定时单元，提出了积分型和微分型双边沿单稳态触发器的基本结构，阐明了双边沿单稳态触发器的设计方法，并具体设计了积分型和微分型双边沿单稳态触发器。     

Control of the Helical Chirality of Enantiopure Sulfinyl (Z)‐Azobenzene‐Based Photoswitches

A new class of enantiopure ortho,ortho‐disubstituted azobenzene photoswitches has been synthesized from (S)‐2‐(p‐tolylsulfinyl)benzoquinone and arylhydrazines. The sulfoxide acts as a unidirectional controller of the helical chirality that arises in the Z isomer after photoisomerization. Highly congested E‐azobenzenes 5 c showed two atropisomeric diastereoconformers in the solid state that converged upon irradiation into a unique Z isomer with defined helicity (M), as evident in the X‐ray structure. The chiroptical properties of this three‐state enantiopure switch can be externally tuned both photochemically and/or thermally. Theoretical CD spectra calculated by using time‐dependent DFT methods support the existence of two atropoisomeric E isomers and only one Z isomer with (M) helicity. Complementary to the classical azobenzene‐based switches, the photoswiching event is promoted under green/blue light and do not occur under UV irradiation.     

Methyl Scanning for Mechanochemical Chalcogen-Bonding Cascade Switches

Chalcogen-bonding cascade switching was introduced recently to produce the chemistry tools needed to image physical forces in biological systems. In the original flipper probe, one methyl group appeared to possibly interfere with the cascade switch. In this report, this questionable methyl group is replaced by a hydrogen. The deletion of this methyl group in planarizable push-pull probes was not trivial because it required the synthesis of dithienothiophenes with four different substituents on the four available carbons. The mechanosensitivity of the resulting demethylated flipper probe was nearly identical to that of the original. Thus methyl groups in the switching region are irrelevant for function, whereas those in the twisting region are essential. This result supports the chalcogen-bonding cascade switching concept and, most importantly, removes significant synthetic demands from future probe development.     

Light‐Controlled Formation of Vesicles and Supramolecular Organogels by a Cholesterol‐Bearing Amphiphilic Molecular Switch

A new responsive material composed of an amphiphilic light‐switchable dithienylethene unit functionalized with a hydrophobic cholesterol unit and a hydrophilic poly(ethylene glycol)‐modified pyridinium group has been designed. This unique single‐molecule system shows responsive light‐switchable self‐assembly in both water and organic solvents. Light‐triggered reversible vesicle formation in aqueous solutions is reported. The molecule shows a different behavior in apolar aromatic solvents, in which light‐controlled formation of organogel fibers is observed. The light‐triggered aggregation behavior of this molecule demonstrates that control of a supramolecular structure with light can be achieved in both aqueous and organic media and that this ability can be present in a single molecule. This opens the way toward the effective development of new strategies in soft nanotechnology for applications in controlled chemical release systems.