Dielectric effect on the rf characteristics of a helical groove travelling wave tube

A new type of partial-dielectric-loaded helical groove slow-wave structure (SWS) for millimetre wave travelling wave tube (TWT） is presented in this paper.The radio-frequency characteristics including the dispersion properties,the longitudinal electric field distribution and the beam-wave coupling impedance of this structure are analysed.The results show that the dispersion of the helical groove circuit is weakened,the phase velocity is reduced and the position of the maximum Ez is moved from the mouth to the inside of the groove after partially filling the dielectric materials in the helical groove SWS.Therefore,the dielectric-loaded helical groove SWS is suitable for a multi-beam TWT with broad band and high gain.     

New designed helical resonator to improve measurement accuracy of magic radio frequency

Based upon the new designed helical resonator, the resonant radio frequency (RF) for trapping ions can be consecutively adjusted in a large range (about 12 MHz to 29 MHz) with high Q-factors (above 300). We analyze the helical resonator with a lumped element circuit model and find that the theoretical results fit well with the experimental data. With our resonator system, the resonant frequency near magic RF frequency (where the scalar Stark shift and the second-order Doppler shift due to excess micromotion cancel each other) can be continuously changed at kHz level. For ⁸⁸Sr⁺ ion, compared to earlier results, the measurement accuracy of magic RF frequency can be improved by an order of magnitude upon rough calculation, and therefore the net micromotion frequency shifts can be further reduced. Also, the differential static scalar polarizability Δα₀ of clock transition can be experimentally measured more accurately.     

复合结构螺旋超材料对光波前的高效调控

近年来,超材料和超表面因为一些不同于传统材料的新奇性质一直被广泛研究,而基于超材料或者是超表面的波前控制也是其中的一个热门研究领域.迄今为止,已经提出了很多不同的结构来对反射光和透射光的波前进行调控,在已知的结构中,反射光的波前调控效率已经可以达到较高数值,但是很少有报道能够使用超材料简单高效地调制透射光的波前.本文提出了一种由相同几何结构的左旋和右旋结构复合而成的螺旋超材料.通过使用时域有限差分方法进行仿真,发现这种螺旋结构将会在入射光和透射光之间引入一个可控的相位变化,从而可直接对透射光波前进行调控.仿真结果还表明,该复合结构螺旋超材料在较宽的波长范围内可以达到近64%的透射率.最后通过将该螺旋材料沿着X轴排布成有着连续相位变化的阵列,可以在近红外区域(1.0—1.4μm)观察到反常折射现象,仿真结果与理论计算得出的反常折射角十分符合.     

Ka波段螺旋波纹波导回旋行波管

螺旋波纹波导回旋行波管与采用圆波导的回旋行波管相比,有较大的带宽。介绍了它的线性注波互作用理论,并用该理论计算了不同的磁场与波导表面微扰幅度对Ka波段螺旋波纹波导回旋行波管线性增益的影响。计算结果与已报道的实验结果基本符合,说明该理论可以初步确定螺旋波纹波导回旋行波管的各项参数。     

Helical Carbon and Graphite Films Prepared from Helical Poly(3,4‐ethylenedioxythiophene) Films Synthesized by Electrochemical Polymerization in Chiral Nematic Liquid Crystals

Helical carbon and graphite films from helical poly(3,4‐ethylenedioxythiophene) (H‐PEDOT) films synthesized through electrochemical polymerization in a chiral nematic liquid‐crystal (N*‐LC) field are prepared. The microscope investigations showed that the H‐PEDOT film synthesized in the N*‐LC has large domains of one‐handed spiral morphology consisting of fibril bundles. The H‐PEDOT films exhibited distinct Cotton effects in circular dichroism spectra. The highly twisted N*‐LC with a helical pitch of smaller than 1 μm produced the H‐PEDOT film with a highly ordered morphology. The spiral morphologies with left‐ and right‐handed screws were observed for the carbon films prepared from the H‐PEDOT films at 800 °C and were well correlated with the textures and helical pitches of the N*‐LCs. The spiral morphologies of the precursors were also retained even in the graphite films prepared from the helical carbon films at 2600 °C.     

A 1D/2D Helical CdS/ZnIn2S4 Nano‐Heterostructure

Multidimensional nano‐heterostructures (NHSs) that have unique dimensionality‐dependent integrative and synergic effects are intriguing but still underdeveloped. Here, we report the first helical 1D/2D epitaxial NHS between CdS and ZnIn₂S₄. Experimental and theoretical studies reveal that the mismatches in lattice and dangling bonds between 1D and 2D units govern the growth procedure. The resulting well‐defined interface induces the delocalized interface states, thus facilitate the charge transfer and enhance the performance in the photoelectrochemical cells. We foresee that the mechanistic insights gained and the electronic structures revealed would inspire the design of more complex 1D/2D NHSs with outstanding functionalities.     

氰根桥连的异金属配位聚合物{[Ni(pn)2][Fe(CN)4(bipy)]}2·3H2O(pn=1,3-丙二胺,bipy=2,2′-联吡啶)的合成与结构

以[Fe(CN)₄(bipy)]^2-为建筑块和[Ni(pn)₂]²⁺在水溶液中反应,合成了{[Ni(pn)₂][Fe(CN)₄(bipy)]}₂·3H₂O(pn=1,3-丙二胺)。通过X-射线单晶衍射确定了其晶体结构。该配合物属单斜晶系,P2₁/n空间群,晶胞参数为:a     

Remarkable effect of pre‐organization on the self assembly in chiral liquid crystals

In this article, liquid crystal phases possessing a helical molecular assembly, including frustrated three dimensional (3D) structures, are overviewed. Then, the chirality‐originated superstructures in liquid crystals studied by the author are reviewed. The importance of the concept of “pre‐organization” is highlighted, thus, molecular design producing a strong chiral effect has been proposed. Dichiral twin materials have been prepared systematically based on this concept, and correlation between molecular architectures and resulting frustrated liquid crustal phases, such as smectic blue, cubic, tetragonal smectic Q, and sponge phases, has been investigated. An electrically induced anisotropic birefringent structure in the chiral isotropic phase and a photoinduced 3D‐3D phase transition in the smectic Q phase are introduced as possible application on the basis of the frustrated chiral 3D structured liquid crystal phases. A new type of chiral effect inducing the structural anisotropy in the 3D cubic structure of soft material is also described. © 2010 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 340–355; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.200900029     

Activating an enzyme by an engineered coiled coil switch

We designed a de novo protein based on a circular permutant of RNaseT1, in which the enzymatic activity can be manipulated by engineered peptide binding. The circular permutant of RNaseT1 was obtained by tethering the original C- and N-termini with a GPAG linker and cleaving the molecule between Glu82 and Asn83. This mutant lacked enzymatic activity, due to the destabilization of entire protein structure. We previously reported the construction of ABC-type heterotrimeric coiled coil peptides, in which the A- and B-type peptides cannot form the folded trimeric structure without the C-type peptide. The introduction of the A- and B-type coiled coil peptides to the C- and N-termini of the circular permutant of RNaseT1, respectively, and the subsequent addition of the C-type coiled coil peptide enabled the RNaseT1 domain to refold properly, thus, restoring the enzymatic activity. The formation of the trimeric coiled coil structure should bring the cleaved sites of RNaseT1 close enough to refold the RNaseT1 domain spontaneously.     

Towards photocontrol over the helix-coil transition in foldamers: synthesis and photoresponsive behavior of azobenzene-core amphiphilic oligo(meta-phenylene ethynylene)s

Introduction of photochromic azobenzene units into amphiphilic oligo(meta-phenylene ethynylene)s allowed photocontrol over the helix-coil transition in this important class of foldamers. Two design principles were followed in efforts to accommodate cis- and trans-azobenzene moieties within the helical structure to selectively turn the helical state on and off, respectively. Several oligomer series with varying connectivities to the central azobenzene chromophore were synthesized and these photochromic oligomers were investigated with regard to their folding behavior in both dark and irradiated states. Both the foldamers' chain lengths and the electronic structures of the azobenzene moieties had to be optimized to ensure folding differences and selective excitation of the photochrome. The design of such stimuli-responsive macromolecules, displaying large structural changes upon irradiation, should guide the design of future materials in, for example, "smart" delivery applications.