在螺旋锥齿轮数控磨齿机上磨成形法加工的齿轮

半展成法是加工螺旋锥齿轮和准双曲面齿轮的有效方法。螺旋锥齿轮和准双曲面齿轮数磨齿机是一种新机床,将齿轮加工所需全部运动用六坐标数控来实现。本文研究了如何在这种高科技机床上再现并改进传统加工方法.     

玻纤格栅面层加筋位置的数值模拟和试验研究

从车辙机理分析入手,由ANSYS确定面层内部最大剪应力位置,再通过不同层位室内车辙试验的对比验证,得到了工程路面铺筑的最佳位置,可为工程实际提供参考依据。     

观光车环境感知系统的探讨与分析

阐述了观光车装备环境感知系统的意义,对实现环境感知系统所需的传感器进行了探讨与分析,最终设计了视频摄像头结合毫米波雷达组成环境感知的硬件系统,并对此多传感器系统的数据融合给出了要求和方法。     

太赫兹3D打印透镜综述

太赫兹波由于其独特的电磁特性可应用于超高速率无线通信、生物化学物质检测以及高分辨率成像等领域。但由于太赫兹波的物理波长小,传统适用于低频的加工工艺难以满足其加工精度的要求;而微纳米加工工艺又具有加工复杂、成本高等缺点。3D打印技术的发展为太赫兹器件的加工提供了新的选择和更多的设计灵活度。文章介绍了香港城市大学太赫兹与毫米波国家重点实验室在3D打印太赫兹透镜方面的最新研究动态和实验研究新成果,包括基于3D打印的太赫兹高增益圆极化透镜、近场聚焦圆极化透镜、贝塞尔波束生成透镜的设计,高精度3D打印方法的探索以及太赫兹天线测试方法等。太赫兹3D打印透镜天线具有低成本、低损耗、能快速成型等特点,可应用于不同的太赫兹场景中。     

A fuzzy model for assessing the risk exposure of procuring infrastructure mega-projects through public-private partnership: The case of Hong Kong-Zhuhai-Macao Bridge

Considering the rapid urbanization growth rate particularly in developing countries, the number of infrastructure mega-projects over the past years has risen tremendously. Essentially, because infrastructure mega-projects require huge investment funds, better management skills, well qualified and experienced international expertise and technology innovation, they are mostly preferred to be procured using the PPP method compare to the use of the traditional bid-build system. In this regard, this paper aims to develop a fuzzy evaluation model for assessing the suitability of procuring infrastructure mega-projects through PPP by considering their risk exposure. The main body of Hong Kong-Zhuhai-Macao Bridge (HZMB) is used as a case project to demonstrate the practicality of the risk evaluation model. The risk evaluation model consists of four critical risk groupings, these include, construction and land risks, commercial risks, operational risks and political risks. Using the risk evaluation equation, a risk index of 4.53 out of 5.00 is computed for the selected project if it is procured through the PPP scheme. This outcome shows that the case project is not suitable for the PPP approach because its risk exposure is very high. The model developed will enable PPP practitioners to predict the likely risk exposure of procuring infrastructure mega-projects through the PPP scheme.     

Mechanical behaviour and 3D stress analysis of multi-layered wooden beams made with welded-through wood dowels

This paper presents experimental and numerical investigations on multi-layered timber beams using welded-through wood dowels in place of traditional poly(vinyl acetate) (PVAc)-adhesives (or metallic nails). Four-layer beams were constructed with varying numbers of dowels, in each, and then loaded using four-points bending tests to evaluate the mechanical performance of these beams. The practical difficulties encountered in constructing deeper multi-layer beams are discussed and possible solutions which have been employed for the purpose of this work, and proved successful are presented. In order to investigate thoroughly the full potential of multi-layered beams with a very limited number of experimental studies, a 3D FE model has been presented, validated against experimental results and then used to study some influential parameters. The results showed that a reasonable bending stiffness of multi-layered beams is achievable with a good combination of material and geometric parameters.     

Design of a scheduling system for flexible manufacturing cells†

The objective of this paper is to describe an effective scheduling system for flexible manufacturing cells (FMC). Based on FMC characteristics, cell scheduling can be categorized for a dynamic, modified flow shop working in a real-time environment. A heuristic static cell scheduling methodology for minimizing mean flowtime is first proposed. This is then modified to allow dynamic cell scheduling to reflect the real-world situation of continuous job introduction to the cell. Computational results show that the proposed algorithms yield optimal or near optimal job sequences in a very short period of time, thus satisfying a real-time need of rapid computation.     

Direct Comparison between Five Different Microchannels,Part 2: Experimental Description and Flow Friction Measurement

Abstract

Part one of this paper ^[1] Eason, C., Dalton, T., O'Mathúna, C., Slattery, O. and Davies, M. 2005. Direct Comparison between Five Different Microchannels, Part 1: Channel Manufacture and Measurement. Heat Transfer Engineering Journal, vol. 26(no. 3): pp. 00–00.  [Google Scholar] investigates the manufacture of five types of microchannels produced by wet and dry etching in silicon and precision mechanical sawing in silicon and thermoset plastic. This paper describes the experimental equipment and methods used to measure the pressure flow characteristics of the manufactured channels. A test system has been built to test each sample using the same inlet and outlet manifolds, pressure tappings, pumping system, and instrumentation. The measured pressure flow behavior was compared with theoretical values calculated from macroscale theory. Error analysis was carried out in order to determine the overall accuracy of the experimental work and determine the significance of any experimental deviation from theoretical values. An area compensation term is introduced to account for the difference in cross-section between the measured actual channels and the rectangles/trapeziums that share their overall dimensions.     

Laser damage resistance of hafnia thin films deposited by electron beam deposition, reactive low voltage ion plating, and dual ion beam sputtering

A comparative study is made of the laser damage resistance of hafnia coatings deposited on fused silica substrates with different technologies: electron beam deposition (from Hf or HfO(2) starting material), reactive low voltage ion plating, and dual ion beam sputtering. The laser damage thresholds of these coatings are determined at 1064 and 355 nm using a nanosecond pulsed YAG laser and a one-on-one test procedure. The results are associated with a complete characterization of the samples: refractive index n measured by spectrophotometry, extinction coefficient k measured by photothermal deflection, and roughness measured by atomic force microscopy.     

Cross-Linking of Myosin Heavy Chains from Cod, Herring and Silver Hake During Thermal Setting

Cross-linking of myofibrillar proteins extracted from cod (Gadus morhua), herring (Clupea harengus) and silver hake (Merluccius bilinearis) was studied in 0.6M NaCl, pH 6.5 at 40°C and evaluated turbidimetrically and by SDS polyacrylamide gel electrophoresis coupled with l-ethyl-3-(3-dimethylaminopropyl) carbodiimide as a zero-length crosslinker. Turbidities of heat-treated cod and silver hake myofibril/myosin solutions were significantly higher than those of herring. Electrophoretic results showed that the myosin heavy chain (MHC) was the principal myofibrillar protein cross-linked to form a polymerized complex during the heat treatment. Cross-linking ability of MHC from the three fish species was different; herring MHC formed only small polymers (n≦3) but cod and silver hake MHC formed both small and large polymers (n≦6).