TEOS surface modification of CLST ceramic particles for PTFE-based composites

PTFE-based ceramic-polymer dielectric composites have been widely researched in the communication field due to their good processing, wide range frequency and temperature stability and being able to provide tunable dielectric constant in a scale. In order to improve the compatibility between the ceramic fillers and polymer matrix without damage of dielectric properties, surface modifiers with less carbon remain are preferred. In this paper, tetraethylorthosilicate (TEOS) is employed as a surface modifier to improve the compatibility between the (Ca, Li, Sm)TiO₃ (CLST) ceramic and PTFE, and the dispersion of the ceramic particles in the matrix. FTIR, XPS and TEM results indicate that TEOS is coated on the ceramic particles successfully and forms a silica coating layer. The surface modification improves the dispersion of particles in PTFE and interface contact between the ceramic fillers and PTFE matrix. These improve the thermal stability and reduce the dielectric loss of the dielectric composites. The CLST/PTFE composite modified by TEOS exhibits a dielectric constant of 6.22 with dielectric loss just 0.0012 at microwave frequencies (around 10 GHz).     

A Full Compositional Range for a (Ga1‐x Zn x )(N1‐x O x ) Nanostructure: High Efficiency for Overall Water Splitting and Optical Properties

Bulk (Ga_1‐x Zn _x )(N_1‐x O _x ) as a photocatalyst has received increasing attention as a potential solution for the energy shortage challenge; however, its catalytic performance is highly limited by its bulk form. To improve the photochemical potential, the nanoscale form of this multiple‐metal oxynitrides is desirable. In this work, a new type of (Ga_1‐x Zn _x )(N_1‐x O _x ) nanostructure is obtained. Its composition can tuned to the full range (0.18 < x < 0.95). The (Ga_1‐x Zn _x )(N_1‐x O _x ) nanostructure exhibits excellent photocatalytic activity for overall water splitting, and the highest quantum efficiency of (Ga_1‐x Zn _x )(N_1‐x O _x ) is as high as 17.3% under visible light irradiation. Using this new type of (Ga_1‐x Zn _x )(N_1‐x O _x ) nanostructure, the narrowing of the bandgap for (Ga_1‐x Zn _x )(N_1‐x O _x ) is not only due to an increase in the valence band maximum, but it is also related to a decrease in the conduction band minimum.     

The effects of nonperiodic void spacing upon intergranular creep cavitation

The effects of nonperiodic void spacing upon creep rupture by intergranular cavitation is investigated. This is done by carrying out a Monte Carlo simulation of a 1-D model consisting of long, cylindrical voids having a uniform random spatial distribution along the grain boundary of a bicrystal. It is found that a progressive sintering and void coalescence process leads to times-to-failure which on the average are an order of magnitude greater than that predicted in the case where the voids are taken to be periodically spaced. Also predicted is a slightly greater dependence on times-to-failure with applied remote stress than that predicted in the equispaced case. Of particular note is the scatter in the predicted times-to-failure at constant remote stress, which is found to be well-described by a Weibull cumulative distribution function.     

A self-adaption normal direction and active variable stiffness low-frequency vibration-assisted system for curved surface drilling

The drilling operation occupies an important position in the aircraft assembly workload, and it accounts for a large proportion of the assembly cost. Previous reports show that drilling quality affects aircraft safety factor such as the probability of fatigue failure accidents. This paper proposes an automatic machining system for curved surface drilling. In this scheme, the self-adaption normal direction is realized by using the secondary positioning strategy (primary positioning and precise positioning). An elastic structure and the key positions smooth processing are applied to enhance the positioning guidance. The active variable stiffness mechanism satisfies the different requirements for system stiffness during the positioning stage and the drilling stage. Expansion sleeve locking and state switching of drilling assistance pneumatic cylinder lead to changes in the actuator's DOF and external forces, thereby achieving active control of the stiffness. Vibration-assisted machining technology is introduced to improve drilling quality. Compared with conventional drilling, the results show that this drilling system produces thin and slender chips, smaller burrs, and better internal surface quality.     

风电扭矩限制器性能测控系统设计

扭矩限制器是风力发电机组中用于过载保护的关键部件,但目前对其打滑扭矩、疲劳寿命等性能的测试存在流程复杂、自动化程度低、功能单一等缺点,为此设计了一种风电扭矩限制器性能测控系统。根据测控系统的功能要求,首先进行了硬件结构设计,选用PLC为下位机主控单元,工控机作为上位机管理及监控单元。随后采用组态软件设计了人机交互界面,并编写PLC控制程序,实现了对测控系统的控制和管理。经过现场应用证明,该测控系统具有运行稳定、方便快捷的特点,能够满足扭矩限制器的测试要求。     

用于飞秒激光制备光纤光栅的相位掩模研制

利用严格耦合波理论分析了用于520 nm波长飞秒激光制备光纤光栅的相位掩模的衍射特性,当相位掩模是矩形槽形时,占宽比在0.32~0.43之间,槽形深度在0.57~0.67μm之间时,能够保证零级衍射效率抑制在2%以内,同时±1级的衍射效率大于35%。在此基础上,利用全息光刻-离子束刻蚀技术,制作了用于520 nm波长飞秒激光的周期为1067 nm、有效面积大于40 mm×30 mm的相位掩模。实际制作的相位掩模是梯形槽形,槽深是0.665μm,分析了梯形槽形中梯形角对衍射效率的影响。实验测量表明,该相位掩模的零级衍射效率小于2%,±1级衍射效率大于40%,满足飞秒激光制作光纤光栅的需要。     

Mobility analysis of planar four-bar mechanisms through the parallel coordinate system

This paper presents a new method for the mobility analysis of planar mechanisms. The method utilizes a geometrical representation known as “parallel coordinates.” It is a transformation that maps the Euclidean space R^N to N parallel coordinates in the projective plane. Points in R² are transformed to line segments in the parallel coordinate plane, and circles in R² are transformed to hyperbolae. Also, in this investigation, special techniques required for mobility analysis are developed. First, the intersection of circles is performed graphically through the parallel coordinate system. The parallel coordinate plane is then appended to relate this intersection data to the angular coordinates of the various members of the linkage. The ranges of these angular coordinates are the results of the mobility analysis.     

Effects of low level boron doping of the i-layer on the performance of SiC p-i-n devices

a-Si: H devices have been prepared by plasma decomposition of a silane mixture containing ppm levels of diborane. The level of background impurities was controlled by outgassing, monitored by residual gas analysis and finally measured in the solid by SIMS analysis. Two groups of samples were prepared which differed by an order of magnitude in their impurity concentration. The effect of boron addition to the i-layer differed strongly depending on the background impurity level. At high impurity levels ([O] = 1 × 10²⁰ atoms/cm³) a well defined maximum in device performance occurred at [B₂H₆] = 3 ppm, while at lower background levels boron addition served only to lower the device performance. Quantum efficiency measurements indicate that the changes in device performance are due to corresponding changes in the collection length and average μτ product. The ambipolar diffusion length determined by the surface photovoltage yielded similar results.