Perturbation sensitivity analysis of azimuth estimation of the acoustic source for the planar microphone array

Aiming at the requirements of quantitative analysis of the array scheme and positioning performance of a practical compact acoustic detection node system, the upper bound of the far-field azimuth estimation error for an arbitrary small-size planar array is derived and the four elements of the corresponding perturbation sensitivity factor with explicit physical significance are determined. It is proved that the perturbation sensitivity of the source direction-finding algorithm to the time difference of arrival (TDOA) estimates between microphones can be lowered obviously by means of increasing the number of distinct microphone pairs as well as employing spatially uniform distribution of array elements. Simulation results demonstrate that this study provides a quantitative approach to evaluating and comparing the azimuth estimation performance of different planar arrays.     

平面天线阵快速正交投影波束形成算法

针对大型平面天线阵列下样本数据含有期望信号时，正交投影（OP）波束形成算法不再适用的问题，提出一种新的基于阻塞矩阵的正交投影快速波束形成算法。该算法首先构造阻塞矩阵从样本信号中阻塞掉期望信号，再对阻塞后的样本信号进行施密特（GS）正交化得到重构后的干扰子空间，最后在此基础上实现正交投影波束形成。新算法适用于任意阵型的二维均匀平面阵，在小快拍数下能快速计算出自适应权重。仿真结果表明，无论是弱干扰信号还是强干扰信号，该算法都具有很好的抗干扰性能。     

Sub‐5 nm Dendrimer Directed Self‐Assembly with Large‐Area Uniform Alignment by Graphoepitaxy

Directed self‐assembly (DSA) using soft materials is an important method for producing periodic nanostructures because it is a simple, cost‐effective process for fabricating high‐resolution patterns. Most of the previously reported DSA methods exploit the self‐assembly of block copolymers, which generates a wide range of nanostructures. In this study, cylinders obtained from supramolecular dendrimer films with a high resolution (<5 nm) exhibit planar ordering over a macroscopic area via guiding topographical templates with a high aspect ratio (>10) and high spatial resolution (≈20 nm) of guiding line patterns. Theoretical and experimental studies reveal that this property is related to geometrical anchoring on the meniscus region and physical surface anchoring on the sidewall. Furthermore, this DSA of dendrimer cylinders is demonstrated by the non‐regular geometry of the patterned template. The macroscopic planar alignment of the dendrimer nanostructure reveals an extremely small feature size (≈4.7 nm) on the wafer scale (>16 cm²). This study is expected to open avenues for the production of a large family of supramolecular dendrimers with different phases and feature dimensions oriented by the DSA approach.     

Dislocation slip and twinning in Ni-based L12 type alloys

We report theoretical results on dislocation slip and twinning in Ni₃ (Al, Ti, Ta, Hf) compositions with L1₂ crystal structures utilizing first-principles simulations. The lattice parameters of Ni₃Al, Ni₃Al_0.75Ta_0.25, Ni₃Al_0.5Ta_0.5, Ni₃Ta, Ni₃Ti and Ni₃Al_0.75Hf_0.25 are calculated, and the crystal structures with lower structural energies are determined. We established the Generalized Stacking Fault Energy (GSFE) and Generalized Planar Fault Energy (GPFE), and calculated stacking fault energies APB (anti-phase boundary) and CSF (complex stacking fault) matched other calculations and experiments. Based on the extended Peierls–Nabarro model for slip and the proposed twin nucleation model, we predict slip and twinning stress and the results show a general agreement with available experimental data. The results show that in the studied intermetallic alloys, twinning stress is lower than slip stress; Ta and Hf ternary addition are substantial to increase flow stress in Ni₃Al. The models proposed in the paper provide quantitative understanding and guidelines for selecting optimal precipitate chemistry and composition to obtain higher mechanical strength in Shape Memory Alloys.     

平面转弯带式输送机技术方案浅析

主要介绍平面转弯带式输送机技术方案的设计计算及实现平面转弯的技术要点,保证托辊具有一定的安装支撑角,构成内曲线抬高角,增大成槽角,对线路进行合理设计,使普通带式输送机实现了平面转弯运行,并确定转弯半径和驱动功率,又用类比法对驱动装置进行了选型。具有良好的推广应用前景。     

Effects of combustor size and filling condition on stability limits of premixed H2‐air flames in planar microcombustors

An experimental study on stability limits of premixed hydrogen‐air flames in planar microcombustors (H = 1 mm and 1.5 mm) partially filled with porous medium is carried out, focusing on the effects of combustor sizes and filling conditions. Critical conditions for blow‐off, flashback, and breaking through the porous medium are experimentally measured. The blow‐off limits are nearly independent of combustor sizes and filling conditions, while the flashback limits are strongly influenced by the combustor size and the filling conditions. Critical values for breaking through are identified with two different methods, and it is shown that standing combustion waves are settled over a range of velocities, instead of a fixed value of filtration velocity, which is considered an important characteristic of microcombustion. Most results can be explained by the classic boundary velocity gradient theory by von Elbe and Lewis, and thus the validity of the theory to the present channel spacings is confirmed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2571–2580, 2015     

带电子聚焦的氧化锌场发射背光源

液晶显示需要低功耗、均匀度好的光源作为背光源。为了降低功耗,提高显示图像质量,未来的液晶显示需要实现对背光源进行时间与阵列调制。对比现有的液晶显示用背光源,研究制备了氧化锌场发射光源。该光源采用氧化锌纳米针作为场发射阴极,采用平面栅极作为门电极调制结构实现亮度的连续可调,通过带有氧化镁二次电子发射层的金属栅网对电子进行聚焦实现光源的均匀照度。实验结果表明,带电子聚焦的氧化锌场发射光源具有较低的开启场强(1.1V/μm),较小的电压调制区间(小于150V),较高的发光强度(大于1 000cd/m2),且基于电子聚焦结构的设计,实现了光源的均匀稳定照度,可以提高液晶显示的图像质量。带电子聚焦结构的氧化锌场发射光源,既可实现对发光的时间与阵列调制,同时能提高发光的均匀性,将可作为液晶显示的理想背光源。     

超大直径环状桁架的“进退”拼装工法

以抚顺“生命之环”三角形变截面钢管桁架组成的环形结构体系桁架为例,对难以在场地上进行预拼装的大体积和超重单元桁架,通过设立基准平面单元,借助基准平面单元的“一进一退”方法进行拼装组合.该拼装方法大大提高了拼装精度,保证了工程质量的同时加快了工程进度,同时解决了大型环状桁架相邻拼接单元的拼装进度要求,为类似工程提供了一种全新的拼装方法.     

Pro/E三维造型向AutoCAD二维图形的转换技术

介绍了将Pro/E参数化实体造型同现行的AutoCAD绘图相结合进行产品设计的方法 ,该方法在Pro/E中建立三维模型 ,然后转换为二维平面视图 ,并将其以dwg格式输出 ,提供在AutoCAD中调用。应用该方法将提高产品设计的效率。