激光实际大气水平传输湍流畸变波前的功率谱分析Ⅱ: 波前相位与格林伍德频率

分析了整体倾斜像差去除前后大气湍流畸变波前相位的功率谱。 在激光实际大气水平传输实验中, 利用61单元自适应光学系统的哈特曼波前传感器, 测量和分析了大气湍流畸变波前相位的功率谱。 还建立了一种根据实际测量的波前相位功率谱数据估测自适应光学系统变形镜需要控制带宽大小和大气湍流格林伍德(Greenwood)频率的方法。     

Effective Charge Carrier Utilization of BiVO4 for Solar Overall Water Splitting

Solar energy-driven overall water splitting (OWS) is an attractive way for generating clean and renewable green hydrogen. One key challenge is the construction of OWS systems with high solar energy conversion efficiencies, in which how to manipulate photoexcited charge carriers to efficiently participate in the reaction is the top priority. In recent years, bismuth vanadate (BiVO₄) has emerged as one of the most promising materials for photo(electro)catalytic OWS and considerable progress has been achieved. In this review, recent advances of BiVO₄-constituted OWS systems in both photoelectrocatalytic and photocatalytic approaches are presented in a mainline of effective charge carrier utilization. Various strategies for improved charge carrier utilization, including band structure engineering, improving charge separation, reducing charge recombination, and accelerating reaction kinetics, are summarized and analyzed in detail. Finally, perspective and outlook on further exploring the application potential of BiVO₄ are proposed.     

Influence of carbon chain length on physical properties of 3FmHPhF homologues

ABSTRACT

Four compounds from 3FmHPhF homologous series of chiral smectogenic fluorinated compounds (m = 2, 4, 5, 6) were studied by frequency domain dielectric spectroscopy, electro-optic measurements, X-ray diffraction and differential scanning calorimetry. Values of the relaxation time and dielectric increment of relaxation processes versus temperature and bias field were determined. The temperature-dependent tilt angles, spontaneous polarisations, switching times, rotational viscosities, and average intermolecular distances and correlation lengths within smectic layers were obtained. Experimental results were supplemented by density functional theory calculations of isolated 3FmHPhF molecular geometries, and the relationship between the molecular structures and the transverse component of their dipole moments was studied for the mesogens with m = 2, 4, 5, 6, 7. The results are discussed in terms of the length of the C_mH_2m flexible carbon chain of the homologues.     

All-Dielectric Multichannel Terahertz Metasurface Empowering Independent Wavefront Manipulation

Metasurfaces have demonstrated unprecedented capabilities in modulating the polarization and phase of electromagnetic waves and formed an emerging field of research, driving the exploitation of versatile compact devices. In this work, one transmission-mode, multichannel all-silicon metasurface platform that can implement functionalities separately in two orthogonally polarized output fields under linearly polarized incidences is proposed, which can effectively promote the design flexibility. Specifically, a single metasurface can realize multiple independent target phase distributions carrying specific phase relationships, thus enabling different information processing in different linear polarization states. For proof-of-principle experimental exhibitions, a monolayer metasurface composed of silicon pillars is designed, fabricated, and characterized to demonstrate the ability of multi-dimensional light field control, such as polarization-switchable focusing beam. Moreover, the other designed metasurface can generate polarization-switchable Bessel vortex beams under linearly polarized incidences, which also verifies the flexibility and practicality of such platform. This metasurface platform may lead to new optical components, involving multichannel singular beam generators, information encoders, and holographic encryption devices.     

基于整体风险最小的多阶段期货套期保值研究

对多阶段套期保值建立模型,综合考虑整体风险,以最终现货与期货的收益的方差建立目标函数.以多阶段整体风险最小为目标函数,考虑资金限制,建立套期保值模型来解决多阶段套期保值的套期保值比率问题.以资金限制为约束,避免了套期保值者因资金短缺而强制平仓造成的套保失败.利用差分算法和罚函数法进行求解.实证结果表明,多阶段的风险比逐个单阶段求得的风险明显的小,且整体套保的单位风险收益比单阶段的大很多,说明多阶段比单阶段能较好的实现套期保值.     

The new high tilt mixtures with antiferroelectric phase at a broad temperature range and a long helical pitch

Five new bicomponent eutectic mixtures based on compounds different in the bridge between a rigid core and a chiral centre (-COO- or -CH₂O-) or in the optical purity (‘S’ or racemic ‘R,S’) were prepared and characterised. Their mesomorphic properties were tested by means of polarising optical microscopy and differential scanning calorimetry. The helical pitch of prepared mixtures was estimated with selective reflection method. The optical tilt angle Θ of mixtures was also measured and discussed.     

Application of a screw conveyor with axial tilt blades on a shearer drum and investigation of conveying performance based on DEM

Screw conveyors are widely employed in industrial fields for conveying bulk materials. The shearer drum which uses the screw conveying principle is responsible for excavation and conveying coal particles onto the chain conveyor. Screw conveyor performance is affected by potential factors, such as the blade axial tilt angle and style, core shaft form and diameter. The effect of blade axial tilt angle on the conveying performance was investigated with the help of DEM. In the case of the screw conveyor, the mass flow rate, and particle axial velocity increased with increasing positive axial tilt angle, and declined with increasing negative axial tilt angle. In the case of the drum, the mass flow rate, particle axial velocity, and loading rate first increased and then decreased with increasing positive axial tilt angle, and decreased with increasing negative axial tilt angle. These results can be considered as a benchmark for screw conveyor and drum structural designs with axial tilt screw blades.     

直角和贴体坐标系下两种格子Boltzmann方法的比较研究

采用格子Boltzmann方法(LBM)和改进的插值格子Boltzmann方法(GILBM)研究了45°斜方腔的顶盖驱动流和Roach通道内的流动特性,并与基准解进行了对比。结果表明,对于45°斜方腔的顶盖驱动流,当雷诺数较小时,两种方法的计算结果与基准解吻合较好;但当雷诺数较大时,采用LBM的计算结果准确性降低,而基于GILBM方法得到的结果准确度升高,且计算稳定性好。对于Roach通道内的流体流动而言,两种方法的计算精度和复杂边界的复杂程度与雷诺数大小有关。根据流场边界形状的复杂程度,网格划分与计算精确度的不同要求,两种方法各有利弊。     

Effects of the Anthraquinone Dye on the Electro-Optical Properties of Dye Guest-Host Polymer Dispersed Ferroelectric Liquid Crystal

Abstract

The effects of the anthraquinone dye on the electro-optical characteristics of DGHPDFLC have been investigated. The results show that PDFLC doped with dichroic dye was found to have no influence on phase separation. When dye concentration is over M483-1.0%, it causes the response time of DGHPDFLC to become slower, the frequency becomes dependent, the rotational viscosity increases, and the tilt angle becomes lower, but, on the whole, electro-optical properties are still very practical.