机场附近的噪声环境和住宅的隔声改造

对首都机场的飞机机型和机场附近住宅的噪声现状进行监测,采用计权等效连续感觉噪声级和昼夜等效声级对室外的飞机噪声进行综合评估,提出关于机场周围建筑物隔声标准和方法的建议。以首都机场周边某住宅为例进行隔声治理,飞机起飞经过13 s时室内外开关窗的噪声值和室内现场隔声量的测量结果表明,居民对房屋隔声效果反应良好,隔声后改善了居民住宅内的声环境质量。     

粉末冶金航空刹车材料磨屑的形成机理研究

研究了粉末冶金航空刹车材料在摩擦磨损过程中产生的各类磨屑,探讨了各类磨屑的形成机理,并分析了磨屑在粉末冶金航空刹车副监控中的功用。研究表明,粉末航空刹车材料在摩擦磨损过程中可产生四类磨屑：片状磨屑比较常见,是表面裂纹扩展形成的;块状磨屑主要是由内外裂纹传播造成的;条状磨屑主要是犁削作用造成的;球形磨屑包括实心和空心两种,形成温度较高。磨屑在航空刹车副监控中常用来作为无分解状态下材料的使用状态和安全性判据之一。     

STRUCTURAL COLLAPSE, THE FAILURE ASSESSMENT DIAGRAM AND "OFF-THE-SHELF" OPERATION

Abstract— The criteria for determining whether ferritic material exhibits fully ductile behaviour are generally based on the fracture toughness vs temperature relationship determined from standard laboratory test pieces (e.g. Charpy V Impact tests or fracture toughness specimens). This relationship defines a ductile-brittle transition region. When fully ductile, microvoid coalescence behaviour is experienced, and fracture toughness is described as being on the “upper shelf”. At “off the shelf” temperatures brittle, cleavage fracture is experienced. On the lower shelf the material is entirely brittle, exhibiting 100% crystallinity on the fracture face. As the temperature increases, initiation of tearing by microvoid coalescence occurs and some stable tearing can occur prior to the cleavage event. Material toughness increases with temperature until the upper shelf condition is achieved. The characteristics of fracture toughness tests in terms of the toughness level exhibited and the extent of ductile tearing experienced have been used as a guide to whether the structural application (e.g. a pressure vessel) will behave in a brittle or a ductile manner. This paper reports on a feasibility study where various worked examples have been performed to examine the concept of using a “cut off” on the failure assessment diagram, determined from the conditions required to cause plastic collapse of a pressure vessel, as a criterion for defining effective “ductile” operation. Fracture assessment procedures (R6 revisions 2 and 3 and PD6493 levels 2 and 3) have been utilised to determine the influence on pressure vessel performance of the behaviour of fracture toughness test specimens. The procedure of plotting a structural collapse “cut off” on a failure assessment diagram enables the assessment of whether a particular flaw geometry would result in gross deformation of the structure at failure. The use of this procedure provides an unambiguous demarcation between “fracture dominated” and “collapse controlled” conditions. This procedure facilitates judgements on the level of toughness necessary to ensure ductile operation and whether a “tearing plus toughness” requirement is necessary. It is recommended that consideration be given to including structural collapse into fracture assessment procedures carried out using R6 revision 3 or PD 6493:1991 procedures in order to determine the conditions when enhanced toughness no longer influences structural performance (i.e. when effective “upper shelf” conditions are attained).     

复杂环境条件下“八字形”楼房的爆破拆除

江西洪都钢厂厂区内1栋12层高楼房进行爆破拆除,周边环境较为复杂。且该楼结构呈"八字形",立柱在倾倒方向上的排列位置不规则。为了减少大楼倒塌后产生的后座对周边的影响,采取在最后1排立柱一侧距地1.5 m处切断钢筋、大楼两端的4根立柱降低炸高、在第6～7层实施松散爆破、延长最后一响起爆时间等技术措施,达到了大楼部分折叠、缩短倒地塌落长度、减弱塌落振动危害效应的效果。     

面向格式转换的数字视频处理方法及其硬件实现

提出了针对环境控制系统特点的脉宽-模糊复合控制方案;使用Matlab软件的Fuzzy工具箱和Simulink工具箱,建立了脉宽调节、PID控制、模糊控制和复合控制等4种控制模型,其中模糊控制模型以混合后的温度与基准温度之间的偏差及其变化率为输入,通过模糊推理得到控制信号;输入温度阶跃信号对该4个控制模型的阶跃响应特性进行了计算和分析;选取一组动态参数作为输入对复合控制模型的动态响应进行仿真计算,结果表明,复合控制系统有效解决了现有脉宽调节系统的温度波动问题。     

Tilt-axis effect on oxidation behaviour and capacitance-voltage characteristics of (1 0 0) silicon

(1 0 0) Si and 4° off (1 0 0) Si were oxidized in dry oxygen, and the differences in thermal oxidation behaviour, oxidation-induced stacking faults and capacitance-voltage characteristics were investigated. The thickness of the oxide produced by oxidation of the silicon samples in dry oxygen in the temperature range 1000–1200°C was measured using an ellipsometer. The oxidation rates of the 4° off (1 0 0) Si were faster than those of the (1 0 0) Si but the differences between them decreased as the oxidation temperature increased. The size of the oxidation-induced stacking faults increased as the oxidation time and temperature increased from 1100 to 1200°C. The density of oxidation-induced stacking faults was lower for the 4° off (1 0 0) Si than for the (1 0 0) Si. Variations in the capacitance-voltage characteristics with the oxidation temperature showed that the flat band voltages were shifted positively. The fixed surface state charge density and the interface trapped charge density of the 4° off (1 0 0) Si were lower than those of the (1 0 0) Si. Si lattice strains induced by excess interstitial Si atoms were investigated through convergent beam electron diffraction. The lattice strain of the 4° off (1 0 0) Si was lower than that of the (1 0 0) Si and this showed that the 4° off (1 0 0) Si had a lower interstitial concentration. This revised version was published online in November 2006 with corrections to the Cover Date.     

Set‐off: Development of a Simulation Press and Analytical Approach to Study the Phenomenon

One type of mass transfer between package and food is through set‐off. This phenomenon is defined as the transfer of components from the external layer (printed surface) of a packaging material to the inner side (surface to come into contact with food) during storage of printed substrates in reels or stacks. The objective of this work was to build up the equipment for set‐off simulation and to assess the extent of benzophenone (BP) transfer. BP is a model photoinitiator used in standard ultraviolet curable inks (non‐low migration inks). For set‐off simulation, the storage conditions (time, temperature and pressure) and the ink film weight are provided by EuPIA Guidelines. Ethanol 50% (v/v) as simulant and contact condition of 40°C/10 days were used. Samples were printed and cured at different speeds. The migrated BP was determined by analysing the extracts using high‐performance liquid chromatography with diode‐array detector. Set‐off phenomenon extent was dependent on the curing. In general, the BP migrations increase as speed increased. Copyright © 2016 John Wiley & Sons, Ltd.     

有姿态角时飞机燃油油量测量技术研究

本文论述了数字式飞机燃油油量测量系统中的一种全新计算方法——“细分—逼近”法的原理和计算过程。该方法借鉴了有限元法的思想,可计算出形状不规则的飞机油箱在任意时刻、任意姿态角组合时的油量。计算程序中采用了符合组合方法,判断油平面与油箱相截的情况。     

Cut‐off Frequencies Induced by the Length of Strain Gauges Measuring Impact Events

Abstract: The finite length of strain gauges may induce filtering effects when measuring impact events. In this study, we are interested in quantifying these effects. Precisely, we determined the cut‐off frequencies of strain gauges cemented on visco‐elastic bars and measuring impact‐induced strain waves. This study shows that the cut‐off frequencies increase with the bar’s wave velocity and decrease with the bar’s diameter. The asymptotic value, corresponding to an infinite bar diameter, is reached rapidly (bar diameter ≈ 15 mm). Moreover, we showed that the mode cut‐off frequencies are more severe (lower) than the gauge length cut‐off frequencies for bar diameters greater than 8 mm.     

Preparation of poly (l-lactic acid) microspheres by droplet-freezing process

A recently developed process of microsphere preparation, named droplet-freezing process is introduced in this paper. The PLLA microspheres were fabricated by the droplet-freezing process, the diameter and porosity of the microspheres were measured, and the micro-morphologies of the microspheres were characterized by scanning electron microscopy (SEM). The formation process of microspheres was achieved by two steps: first, after droplets dropped off the delivery tube, they became approximately spherical in the air under the effect of the surface tension; second, droplets dropped into liquid condensate and maintained the spherical shape, and were frozen during the free settling process. Experimental results indicated that the microspheres fabricated by the droplet-freezing process have uniform diameters and the diameter can be controlled properly, along with the increase of the PLLA concentration, the size of microspheres increases, but the porosity of the microspheres decreases. The microspheres with high porosity can be obtained with a low concentration of the PLLA solution. SEM analysis revealed that the surfaces and interiors of the microsphere contain plentiful and interconnected micro pores. The microspheres are hopeful to be applied in bone tissue engineering.     

Experimental development of an intelligent refrigeration system

In this study, an alternative solution to reduce energy consumption in industrial refrigeration systems is proposed and introduced. A typical industrial refrigeration system was conceived, built and modified in the laboratory, receiving a novel power law control system, which utilizes a frequency inverter. The operation and energy consumption of the system operating either with the new control system or with the traditional on–off control were compared to realistically quantify the obtained gains. In this manner, the measured temperature data acquired from several points of both systems and the energy consumption in kW h during a 24 h experimental run period are compared. The closed-loop power law controlled system shows a much smaller variation of the cold chamber internal temperature and electrical energy consumption economy of 35.24% in comparison with the traditional on–off system, under the same operating conditions.     

基于激光测距的飞机着陆滑行灯靶板自动化校准系统

飞机着陆滑行灯的传统灯光校靶方法存在测量误差大、操作效率低、可靠性差的缺陷。针对此问题,本文基于激光准直和激光测距原理,研究并提出了一套飞机着陆滑行灯自动化校靶系统,该系统利用激光仪模拟滑行灯指示进行光路准直调整,通过激光测距实现滑行灯空间位置的调整,采用电子靶板实现靶板的自动化调整,进而实现着陆滑行灯的自动化校准。开展实际实验验证该系统的准确性与可靠性,结果表明,相较传统方法,使用该系统进行校准时准确度提升了80%,操作效率提升了60%,且不易受环境风速等因素的影响,可有效满足飞机着陆灯具校准需求,具有重要技术应用价值。     

The enhanced growth of multi-walled carbon nanotubes using an atmospheric pressure plasma jet

The growth of multi-walled carbon nanotube (MWCNT) forests was investigated using an atmospheric pressure plasma jet (APPJ) system with a mixture of helium and acetylene gases. The MWCNT forests grown on Fe catalyst were compared with those grown on Ni. The growth of MWCNT forests using Fe as the catalyst was better than the growth of MWCNT forests using Ni. The MWCNT forests grown using Fe catalyst and with a plasma power of 30 W were about 17 ± 9% taller than for the plasma off. We were unable to grow MWCNTs using Ni catalyst with the plasma power off; but curly MWCNTs were grown using Ni catalyst if the plasma power was 30 W. It is found that MWCNT growth is enhanced using an APPJ. The height of the forests produced using this APPJ system was also better than that reported by other researchers using either CVD or PECVD systems.     

A Better Posture Strategy for Fingertip Force and Finger Coordination during a Daily Activity

An effective jar opening movement requires not only the complex integration of the thumb and fingers but also good body segment coordination dependent on the body posture. However, few studies have focused on the effect that jar opening posture has on the finger force integration when the fingertips are grasping the jar in their natural positions, rather than fixed ones, and few have considered the role of the global motor in this task. Forty‐two healthy young subjects participated in this study and performed the jar opening movement using a custom instrument with three opening postures. The results showed that the resultant force and overall torque of the right hand significantly increased from the vertical to the off‐table posture. The thumb produced the greatest resultant, tangential and normal forces when the off‐table posture was used. Further, the average normalized normal forces of the thumb and middle–ring–little finger group were greater for the off‐table posture than those for the vertical posture, whereas no difference was found for the index finger. The normal forces were 3.02–3.36 times greater than the tangential forces for the three finger groups. The thumb had the greatest torque contribution and produced the same torque contributions for all the three postures. The torque contributions of the index finger and the middle–ring–little finger group were 0.56–0.96 times smaller than that of the thumb. This study found a better posture strategy for the young subjects to open a jar with the off‐table posture while sitting, and this was also the best opening posture when comparing the overall torque in this work with that reported in previous studies, no matter whether the subjects were standing or sitting or whatever type of finger group was defined. However, the effect of grasp type and the middle, ring and little fingertip force need to be clarified in future studies. Copyright © 2014 John Wiley & Sons, Ltd.     

高分辨率遥感图像飞机目标定位新算法

为了提高自动目标识别系统的准确性,本文提出了一种高分辨率遥感图像的飞机目标定位的新方法,即在图像分割后再进行一次"去除伪目标"的目标识别系统新策略.首先,利用先验知识采用重叠的面积均分法对图像分块,然后基于多次阈值自动分割方法对各块图像进行分割.针对大图像目标识别的分块策略和飞机目标分割不完全的实际情况,提出一种基于辅助直线的Radon变换飞机轴线检测方法,用于飞机目标的定位.最后,通过实验证明,当飞机目标分割不完全时,本文方法能有效的检测飞机目标.     

PM flake material prepared by mechanical chopping of rapidly quenched metallic ribbon

Ductile metallic ribbons prepared by melt spinning can be easily cut into flakes suitable for $\text{P}\text{M}$ processing by a mechanical chopper designed to tear off ribbon flakes by combining a rotating blade and a bed knife. Details of the design features are described.     

Investigation of a long‐term sealed CW transversely‐excited CO2 laser

Abstract

In this report, several methods have been provided to investigate the possibility of a long‐term sealed‐off operation of a CW transversely‐excited (TE) CO₂ laser. These methods include the additions of molecular 3A sieve, CO gas, auxiliary discharge, and catalysts. Variations of gas composition, discharge voltage, and laser power under different conditions have been analyzed. SnO₂ coating devices and monolithic catalysts have been introduced for the first time in a CW TE CO₂ laser. With an appropriate amount of these catalysts, sealed‐off operation with an output level at 550W for more than 110 Hours of discharge time was achieved.     

Nanoscale Adhesive Properties of Graphene: The Effect of Sliding History

Single‐asperity adhesion between nanoscale silicon tips and few‐layer graphene (FLG) sheets, as well as graphite, was measured using atomic force microscopy (AFM). The adhesion mechanism was understood through experiments and finite element method (FEM) simulations by comparing conventional pull‐forces measurements (contact and separation, without sliding) to those obtained after the tip was slid along the surface before separation (“pre‐sliding”). Without pre‐sliding, no variation in the pull‐off force was measured between consecutive measurements, and there was no observable dependence of the mean pull‐off force value on the number of FLG layers. However, when the tip was pre‐slid over a local area, the first pull‐off force was enhanced by 12–17%; subsequent pull‐off forces then relaxed to a lower, constant value. This occurred regardless of the number of layers, and occurred for aged graphite samples as well. Our analysis indicates that this is due to sliding‐induced changes of graphene's interfacial geometry, whereby local delamination of the top graphene layer occurs, provided there is sufficient atmospheric exposure of the surface after cleaving. This effect provides another unique feature of the nanotribological behavior of atomically‐thin sheets and is consequential for designing graphene‐based devices and coatings where adhesive interactions are important.     

High-on/off-ratio graphene nanoconstriction field-effect transistor

A method is reported to pattern monolayer graphene nanoconstriction field-effect transistors (NCFETs) with critical dimensions below 10 nm. NCFET fabrication is enabled by the use of feedback-controlled electromigration (FCE) to form a constriction in a gold etch mask that is first patterned using conventional lithographic techniques. The use of FCE allows the etch mask to be patterned on size scales below the limit of conventional nanolithography. The opening of a confinement-induced energy gap is observed as the NCFET width is reduced, as evidenced by a sharp increase in the NCFET on/off ratio. The on/off ratios obtained with this procedure can be larger than 1000 at room temperature for the narrowest devices; this is the first report of such large room-temperature on/off ratios for patterned graphene FETs.     

Optimal maintenance strategy for Technology‐enhanced classrooms: a case study

The purpose of the study was to collect data and evaluate an age‐based bulb replacement policy for projectors used in Technology‐enhanced classrooms in a university campus.The Office of Information Technology (OIT) had instituted a policy to replace bulbs in these projectors after either failure or 1800h of operation without failure. However, databases maintained by OIT included the time to bulb failure, the average number of times the bulbs were turned on and off per week, and the number of thermal events. Modeling the failure data with a Weibull proportional hazards model revealed that probability of bulb failure was a function of the number of hours a bulb was used and the frequency at which it was turned on and off. Combining this information with a cost model led to the recommendation for an improved condition‐based replacement policy. Copyright © 2009 John Wiley & Sons, Ltd.