磁性胶体晶体的制备与呈色特性

通过化学合成的方法制备出被表面活性剂聚丙烯酸(PAA)修饰的Fe3O4纳米粒子,并应用透射电子显微镜、X射线衍射、磁强计及傅里叶红外光谱仪对产物进行表征,同时利用FDTD solutions光学软件对产物的呈现性能进行建模仿真。最后通过分析得到制备的胶体产物具有超顺磁性能,粒径均一,在水中具有良好的分散性,粒子分散在水中形成的胶体在外在磁场的作用下能够自组装成液态光子晶体,不同磁场大小的调节下能够呈现不同的结构色,磁场越小,颜色越向着波长大的方向偏移,同时,用软件对胶体粒子仿真得到的呈色特性与实验结果一致。这种光子晶体在结构色印刷、传感器、防伪等各个领域有广泛的应用     

A critical role for the branched sidechain adjacent to the thirdarginine of the sodium channel voltage sensor

Molecular dissection of the action potential sodium channel with the peptide strategy pleads for functional and structural asymmetry. The authors previously showed that the different voltage dependencies exhibited by the four isolated S4L45 (from the electric eel sequence) reconstituted into planar lipid bilayers were correlated with the position of a single proline residue and to a conformational transition (from helix to extended forms) occurring with an increase of the solvent permittivity. Ferroelechic liquid crystal properties of residues in an α helix predict a loss of ferroelectric behavior when hydrophobic residues with branched side chains are replaced by residues with unbranched side chains. To test the influence of unbranched side chains, the residues Ile and Leu next to the third and fifth arginines respectively in repeat III were replaced either with α-methylalanine or alanine. The modified voltage sensors were assayed for the voltage sensitivity of their macroscopic conductances, their secondary structure and stability and behavior in analytical ultracentrifugation. Whereas the α-methylalanine analog retained a high sensitivity to voltage changes, but induced longer single-channel events, the alanine substitution (next to the third arginine, R10) leads to a loss of this intrinsic property of the native repeat III, which was correlated with a tendency for dimerization. These results suggest a role for branched side chains of specific residues involved in gating, in agreement with the ferroelectric liquid crystal model     

微机保护装置液晶显示启动回路故障分析

为消除微机保护装置液晶显示屏黑屏故障,通过对微机保护装置液晶显示回路进行检查、试验,查明故障原因是液晶显示启动回路无防感应过电压元件,以及继电器和光耦性能不稳定。结合液晶显示电路板原理,提出了在继电器线圈两端反向并联续流二极管,以及更换为性能更稳定的继电器和光耦的改进措施。改造后液晶显示启动回路未再发生故障,液晶显示屏黑屏问题得以解决,保障了保护装置安全运行。     

裂纹尖端各向异性塑性的研究

对于有裂纹扩展的平面应力问题,阐述了延性铝合金裂尖实测位移场和HRR位移场的差异不能用裂尖弹塑性渐近解的高阶项来拟合。基于垂直和平行于裂纹线的实测对数位移场的斜率不同,在裂纹尖端附近假设存在由大塑性变形导致的各向异性应变硬化。建立了裂纹尖端各向异性塑性模型,发展了莫尔干涉光测实验/数值分析的杂交方法。分析了裂纹前方、沿着θ=0°径向线上的屈服面各向异性的畸变规律。对于相同的实测应变场,用各向异性模型得到的应变能密度和有效应力比用各向同性塑性公式的计算值约大20%。对于延性稳态裂纹扩展,可指望在裂尖附近由各向异性塑性计算的近场J积分值与实验测定的或远场各向同性计算的J积分值趋于吻合。     

Experiments and modeling of conduction and charge accumulation in liquid crystal cells

A combination of different electrical measurement techniques is applied to liquid crystal (display) cells; voltage drop, current-voltage, dc stress measurements and impedance spectroscopy. It is found that at small timescale (seconds) conduction is dominated by transport of mobile ions, but at long timescale (hours) by (bulk) generation of extremely low mobility ions. These slow ions accumulate at ionic double layers at the liquid crystal-polyimid interface, giving rise to electric fields over the polyimid alignment layers. These processes of charge transport and accumulation are represented in consistent and insightful electrical network models.     

Electrical modeling of liquid crystal displays-LCDs

An investigation into the complex dielectric permittivity of nematic liquid crystal (NLC) on homogeneous (or planar, molecular director axis parallel the surface of the cell) and homeotropic (molecular director axis perpendicular the surface of the cell) alignments led to the conception of special equivalent electric circuits representing different dielectric mechanisms that are present in liquid crystal displays (LCDs). In our study, NLC cells with and without polyvinyl alcohol-PVA alignment were subjected to a frequency range of 10/sup -1/ Hz to 10/sup 7/ Hz, revealing four distinct mechanisms of dielectric dispersion. In the NLC cells without PVA, the dielectric dispersion at very low frequencies (10/sup -1/ Hz10/sup 7/ Hz) dielectric dispersion was attributed mainly to the rotation of NLC molecules around their own axes. While, in the NLC cells with PVA, the dielectric dispersion at low frequencies (1 Hz相似文献   

Two-dimensional finite-element modeling of nematic liquid crystaldevices for optical communications and displays

A two-dimensional finite-element code is presented for the steady-state analysis of liquid crystal structures in nonuniform electric fields. It is based on a free-energy formulation which includes all three elastic constants and can deal with pure nematic, twisted nematic, and cholesteric liquid crystal materials. The enhanced capabilities of our code allow the design of composite structures made of both dielectric and liquid crystal materials and with arbitrary configuration of electrodes. Unwanted effects, such as the formation of disclination lines in the director orientation, can be accurately predicted. The method has been applied for analyzing pure nematic liquid crystal microlenses with variable focal length and twisted nematic liquid crystal cells for display applications. Numerical results show that a careful choice of the device structures can avoid the formation of defects and improve their performance     

Properties of Ferroelectric Liquid Crystal/Multiwall Carbon Nanotube Doped Composite

Carbon nanotubes-ferroelectric liquid crystal composites have been prepared and studied. Doping of carbon nanotubes into ferroelectric liquid crystal in varying concentration has been investigated in thin cells in the frequency range of 50 Hz–1 MHz. Decrease in the dielectric permittivity and dielectric strength is found with the doping of carbon nanotubes, however ～32% increase in the relaxation frequency has been observed in higher concentration carbon nanotubes doped ferroelectric liquid crystal composite than pure ferroelectric liquid crystal sample. A decrease in conductivity has also been noticed after doping.     

III–VI Chalcogenide Semiconductor Crystals for Broadband Tunable THz Sources and Sensors

The layered chalcogenide semiconductor GaSe has been grown under various crystal growth conditions for optimum performance for tunable terahertz (THz) wave generation and broadband THz detection. Low-temperature photoluminescence (PL), Raman spectroscopy, optical absorption/transmission, electrical charge transport property measurements, and THz time-domain spectroscopy (TDS) have been used to characterize the grown crystals. It is observed that indium doping enhances hardness of the grown GaSe crystals, which is very useful for processing and fabricating large-area devices. GaSe crystals have demonstrated promising characteristics with good optical quality (absorption coefficient les0.1 cm^-1 in the spectral range of 0.62-18 mum), high dark resistivity (ges10⁹ Omega cm), wide bandgap (2.01 eV at 300 K), good anisotropic (parand perp) electrical transport properties (mu_e/h, tau_e/h, and mutau_e/h) and long-term stability. The THz emission measurements have shown that the GaSe crystals are highly efficient for broadband tunable THz sources (up to 40 THz), and sensors (up to 100 THz). Additionally, new THz frequencies (0.1-3 THz) have been observed for the first time from an anisotropic binary and a ternary semiconductor crystal. Details of characterizations as well as optimum crystal growth conditions including simulation and computer modeling are described in this paper.     

对石英晶体传感器的粘度测量特性的研究

石英晶体传感器是利用石英晶体的压电效应,把被测物理量直接转换为电信号输出的传感器.粘度是对流体内部摩擦力的一种度量,它是表征流体流动性质的重要参数.粘度测量广泛应用于医学、工业及民用等各个领域.本文描述了一种由DDS驱动的石英晶体传感器,该石英晶体传感器可置于液相介质中来测量液体的粘度.本文同时对由石英晶体传感器所获取的信号的幅度特性及相位特性进行了研究,从而对石英晶体传感器的粘度测量特性有更进一步地了解.     

Room temperature single-photon Source:Single-dye molecule fluorescence in Liquid Crystal host

We report on new approaches toward an implementation of an efficient, room temperature, deterministically polarized, single-photon source (SPS) on demand-a key hardware element for quantum information and quantum communication. Operation of a room temperature SPS is demonstrated via photon antibunching in the fluorescence from single terrylene-dye molecules embedded in a cholesteric liquid crystal host. Using oxygen-depleted liquid crystal hosts, dye-bleaching was avoided over the course of more than 1 h of continuous 532-nm excitation. Liquid crystal hosts (including liquid crystal oligomers/polymers) permit further increase of the efficiency of the source: 1) by aligning the dye molecules along a direction preferable for maximum excitation efficiency; 2) by tuning a one-dimensional (1-D) photonic-band-gap microcavity of planar-aligned cholesteric (chiral nematic) liquid crystal layer to the dye fluorescence band.     

液体介质中不同表面粗糙度石英晶体传感器振荡行为的实验研究

本文研究了两个具有不同表面粗糙度的石英晶体传感器在液体中的振荡行为，证明双调制式石 晶体传顺可以区分引起频率变化的两种不同效应：质量负载效应和液体阻尼效应。实验表明对于表面未经抛光处理的石英晶体，溶液粘度，密度的变化不仅产生液体阻尼的变化，而且会伴随产生质量负载的变化，表面抛光 晶体则观察不到质量负载的变化，文章采用固液耦合理论对实验中的现象进行了解释。     

磁光材料的典型效应及其应用

磁光材料是一类品种繁多、应用广泛的重要的功能材料.近年来,随着激光、计算机、信息、光纤通信等技术的发展,各种磁光材料--磁光玻璃、磁光薄膜、磁性液体、磁性光子晶体和磁光液晶等发展极为迅速.本文简介了磁光效应(包括法拉第效应、克尔效应、塞曼效应和磁致双折射效应等)的基本理论以及各种磁光材料和磁光器件的研究新进展.     

20-fs pulse shaping with a 512-element phase-only liquid crystalmodulator

We report pulse shaping experiments in the 20-fs range using a 512-element phase-only liquid crystal modulator array. The results demonstrate the potential for significantly improved spectral resolution compared to 128-element liquid crystal modulators previously used for pulse shaping. Furthermore, we show that subtle nonlinear spatial dispersion has a profound effect on replica pulses arising due to the pixellated nature of the liquid crystal modulator and may dramatically reduce their (already low) peak intensity     

Dielectric and polarization switching studies in nickel nanoparticles dispersed ferroelectric liquid crystal mixtures

ABSTRACT

We have investigated the effect of nickel nanoparticles (NiNPs) in a pure ferroelectric liquid crystal (FLC) mixture. Dielectric spectroscopy was done in the frequency range of 20 Hz–10 MHz. Switching time, spontaneous polarisation, rotational viscosity has been measured using field reversal technique in SmC^* phase. The spontaneous polarisation increases for NiNPs-FLC sample which may be due to the induced dipole moments around FLC molecules. Response time decreases with temperature and NiNPs dispersion. The relaxation frequency and dielectric strength of observed mode in SmC^* phase is also discussed in pure FLC and NiNPs-FLC samples. The relaxation frequency in NiNPs-FLC sample decreases than pure FLC sample and found ～120 Hz.     

汽车用镀锌钢板单向拉伸试验的细观损伤力学分析

基于Gurson—Tvergaard—Needleman（GTN）细观损伤模型,提出了可用来描述各向异性金属板材成形的Hill’48-GTN模型,并对汽车用镀锌钢板单向拉伸试验进行了有限元分析。结果表明：Hill’48-GTN模型可以同时描述试样拉伸变形过程中的弹塑性行为和损伤演化规律,最大孔洞体积分数可以作为判断板料成形极限的参数,在单向拉伸条件下,材料的起裂点位于试样对称中心区域,与试验现象一致。     

Co1-xZnxFe2O4纳米颗粒的结构和磁性

用聚乙烯醇(PVA)溶胶-凝胶法制备出Co1-xZnxFe2O4纳米微粉,用X射线衍射(XRD)研究了铁氧体纳米颗粒的结构,发现纳米颗粒的晶格常数随Zn含量的变化情况和块体材料相似,是一种非单调变化关系,并且纳米颗粒的晶格常数比块体材料的普遍偏大.同时我们还利用振动样品磁强计(VSM)测量了宏观磁性随锌含量的变化,发现饱和磁化强度Ms随x的变化和块体材料的变化趋势一致,而矫顽力随Co2 离子的含量增加基本呈上升趋势.     

Magnetic properties and thermal behavior of mullite–iron nanocomposite powders

Mullite based iron magnetic nanocomposite powders were synthesized by reduction of sol–gel prepared mullite–iron oxide solid solution in hydrogen flow. Structural characterization studied by TEM revealed that two types of α-iron nanoparticles existed in mullite matrix. The α-iron nanoparticles with the size around hundreds of nanometers appeared as inter-type grains, while those around 10 nm were embedded in the grains of mullite. The magnetic properties of nanocomposites suggest that the intergranular and intragranular α-iron nanoparticles had the ferromagnetic and superparamagnetic behavior at room temperature, respectively. The oxidation behavior of nanocomposite powders showed that there existed two different oxidation stages of α-Fe nanoparticles.     

固相烧结法制备的Co_3O_4和Fe_2O_3磁性纳米颗粒

采用一种纳米颗粒的新型制备方法,即固相烧结方法,成功制备出单分散的Co_3O_4和Fe_2O_3磁性纳米颗粒。利用金属前驱体粉末混合在NaCl介质中高温下分解金属原子在NaCl颗粒上聚集长大,在空气中烧结氧化形成纳米颗粒。NaCl介质既作为纳米粒子成核和长大的基底,又作为隔离介质防止纳米颗粒在高温加热过程中出现烧结团聚现象。在制备过程中除了金属前驱体和NaCl,没有其他试剂使用。通过XRD、TEM、VSM等对制备出的Co_3O_4和Fe_2O_3纳米颗粒进行了物相结构和成分、微观形貌及磁性能的表征。结果表明,制备出的Co_3O_4和Fe_2O_3纳米颗粒颗粒尺寸小,结晶性好,且尺寸分布均匀。     

Ferroelectric Based Photonic Crystal Cavity by Liquid Crystal Infiltration

A novel type of two-dimensional photonic crystal is investigated for it optical properties as a core-shell-type ferroelectric nanorod infiltrated with nematic liquid crystals. Using the plane wave expansion method and finite-difference time-domain method, the photonic crystal structure, which is composed of a photonic crystal in a core-shell-type ferroelectric nanorod, is designed for the square lattice and the hexagonal lattice. It has been used 5CB as a photonic crystal core, and LiNbO₃ as a ferroelectric material. The photonic crystal with a core-shell-type LiNbO₃ nanorod infiltrated with nematic liquid crystals is compared with the photonic crystal with solid LiNbO₃ rods and the photonic crystal with hollow LiNbO₃ rods.