A dual‐broadband circularly polarized halved falcate‐shape printed monopole antenna

A halved falcate‐shape dual‐broadband circularly polarized printed monopole antenna is proposed. To generate the equal amplitude orthogonal modes, two halved falcate‐shaped antenna are used. Also, to provide the 90° phase difference between the two modes, three stubs are used in the ground plane of the antenna. The proposed antenna provides 22.6 (1.36–1.72 GHz) and 44.4% (5.25–8.25 GHz) 3 dB axial ratio bandwidth over the lower and upper bands, respectively. By adjusting the parameters of the antenna, the lower and upper band center frequencies can be tuned individually. The proposed antenna is fabricated, and results are compared with those of the simulation. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

镍-镓-铁系铁磁性形状记忆合金的阻尼性能

在分析相变温度和显微组织的基础上,采用低频扭摆仪研究了镍-镓-铁系铁磁性形状记忆合金的阻尼性能与应变振幅、频率及温度的关系.结果表明:Ni52Ga27Fe21合金的马氏体相变为热弹性马氏体相变,特征温度Ms、Mf、As、Af分别为69.3℃,60.2℃,93.6℃,102.6℃,室温下组织为板条状马氏体;镍-镓-铁系合...     

氢爆工艺(HD)对钕铁硼磁粉粒度和形状的影响研究

采用热处理态钕铁硼平板铸锭作为母合金,通过氢爆工艺将平板铸锭破碎成磁粉.研究了氢爆工艺过程中温度、氢压对钕铁硼磁粉的破碎程度、粒度和形状的影响.实验发现,随着温度和氢压的提高,吸氢过程活化时间逐渐缩短,当温度为300℃,氢压为0.1 MPa时,活化过程消失,铸锭一旦暴露在氢气中,吸氢过程直接发生.热处理态平板铸锭吸氢之...     

基于三维点云数据的虚拟人台中间体模型的构建

利用[TC]2三维人体扫描仪采集了华东地区72名40～49岁B体型女性的三维人体数据,对[TC]2扫描获得的三维人体＊.wrl数据文件进行预处理,并建立三维直角坐标系.采用模糊逻辑算法中三角形线形隶属度函数进行噪点的过滤,将人体数据进行标准化处理,建立人体躯干部位特征矩阵.通过计算特征矩阵的均值获得人台中间体特征矩阵,经过对称化处理获得最终的人台中间体特征矩阵.采用Delaunay三角刨分算法将人台中间体特征点进行三角刨分,通过计算点或面的法线向量来光滑曲面获得最终的三维虚拟人台中间体模型.此方法可用于不同规格系列人台三维模型的制作.     

模拟深井条件下的PDC钻头破岩试验研究

利用深井破岩试验装置模拟不同井深（0～5km）压力条件下对泥岩进行了PDC钻头破岩试验，试验结果表明：随着井深（围压）的增加，岩石强度增加，破碎岩石的切削力增加，同时，PDC钻头齿形和结构对破岩效率影响较大，因此必须按深井条件和岩石特点进行PDC钻头齿形和结构设计，以达到提高机械钻速的目的。     

Electrical conductivity of vapor‐grown carbon nanofiber/polyester textile‐based composites

Polyamide 6/ethylene–propylene–diene metallocene terpolymer/(ethylene–propylene–diene copolymer)‐graft‐(maleic anhydride) blends with clay (3 and 5 wt % depending on the formulation), different clays (montmorillonite and sepiolite) and different surface functionalization (ammonium salts and silanes) were studied to analyze the effect of the shape of clay and type of modifier on their properties. The results have shown that sepiolite has higher influence on the morphology and on the mechanical properties than montmorillonite. In that sense, blends with 3 wt % of sepiolite have reached the best balanced properties, i.e., tensile modulus and impact strength, than their homologous with montmorillonite. Furthermore, the blends with 3 wt % of sepiolite have reached the highest mechanical properties compared with blends with higher montmorillonite content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

An Alternative Thin-Plate Welding Technology Using Underwater Shock Wave

Abstract

In recent years, the size and weight of products dealt with in industry have been getting smaller and smaller and micro-bonding and micro-processing technology has become important. Underwater explosive welding can be an alternative bonding method for very thin materials, with a low formability, and which are difficult to bond together by traditional explosive welding methods. In this study, NiTi shape memory alloy and copper foil were welded in this new method. The welding process was simulated using the commercially available package LS-DYNA. The numerical simulation gave the deformations of the flyer and the base plate, and the pressure distribution during the welding process. Microstructure and fracture mechanism of the welded metals were evaluated. The bond interface of the welded metals showed a wavy morphology and the fracture mechanism of the composite laminate showed a predominantly quasi-cleavage with cleavage modes.     

The modification of graphene with alcohols and its use in shape memory polyurethane composites

Graphene prepared by the thermal reduction of graphite oxide was modified by reactions with methanol or 1‐butanol using aqueous HBF₄ solution as a catalyst. Results showed that the reaction created hydroxyl groups on the graphene and at the same time reduced the number of defects. Gravimetry, thermogravimetry, X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy showed that the alcohols had reacted with epoxide groups on graphene. Raman spectroscopy showed that the defects in the graphene were repaired through other accompanying reactions. The reinforcing effect of graphene, observed in the tensile properties and the shape memory behavior of graphene/polyurethane composites, was increased when the graphene was modified with methanol. However, decreases in density and glass transition temperature were evident for the composites made with alcohol‐modified graphene. These results show that the newly created hydroxyl groups on graphene produce effective covalent bonds with the polyurethane chains of the matrix; however, the increased number of bonds restricts the rearrangement of the matrix molecules for dense packing. The covalent bonds between graphene and polyurethane chains enhanced shape recoverability and reduced the hysteresis brought about by repeated thermomechanical cycles. Copyright © 2012 Society of Chemical Industry     

交互新方式——多点触摸技术初探

多点触摸(Multi-touch)是当前数字产品领域最灸手可热的交互技术。该文介绍了多点触摸的基本概念、市场状况,阐述了多点触摸技术的发展历史,以及各种多点触摸的实现技术。     

基于NURBS方法的气动外形优化设计

采用NURBS曲线曲面,对钝锥弹头和钝双锥弹体建立参数化曲面模型,取NURBS曲线控制点作为设计参数,应用高超声速面元法求解气动力特性,在给定设计约束下,采用遗传算法进行气动外形优化设计,并对优化结果进行了比较分析。结果表明,采用NURBS方法构造参数化外形,并结合优化技术可方便快速地获得所需最优外形;与应用二次曲线构造参数化外形相比,该方法对弹体形状控制更加灵活,并可局部修改弹头曲线形状。因此,基于NURBS方法发展整套的系统优化设计算法很有现实意义和应用价值。