超波束(HBF)用于波束锐化

介绍了一种波束锐化技术,即超波束形成技术（Hyper Beamforming,HBF）,可以在减小波束宽度的同时抑制旁瓣,提高目标检测性能及方位估计能力。该方法结合常规空间加权可以进一步降低旁瓣,从而可以利用较小规模的基阵尺寸,实现大基阵的检测性能。文中给出了恒定束宽HBF实现所需系数,并将该方法应用于CW及FM信号处理,给出了预期的仿真结果。     

An optimal choice of window width for LOWESS normalization of microarray data

The purpose of normalization in microarray data analysis is to minimize systematic variations in the measured gene expression levels of two co-hybridized mRNA samples so that biological differences can be more easily distinguished. The most commonly and widely used normalization procedure for spotted arrays is probably the intensity dependent and print-tip LOWESS normalization. It is well known that the choices of different parameter values greatly affect the quality of the normalization results, and thus poor quality of the normalization results could be due to the arbitrary choice of the smoothing parameters for LOWESS normalization. In many normalization studies, however, LOWESS has been simply used without rigorous consideration of the parameters. In this article, we propose a bootstrap method to find the optimal window width in print-tip normalization by applying the cross validation technique. We also compare through simulation studies the normalization results by using the proposed method with those by fixing the window width.     

Experimental investigation on shore hardness of barrel-finished FDM patterns

Barrel finishing (BF) process is widely used to improve the surface finish and dimensional features of metallic and non-metallic parts using different types of media. As a matter of fact the change in shore hardness (SH) features of fused deposition modelling (FDM)-based master pattern is one of the important considerations from its service point of view. The main objective of present research work is to investigate the effect of BF process on SH of acrylonitrile–butadiene–styrene (ABS)-based master patterns prepared by FDM. Six controllable parameters of FDM and BF, namely, geometry of prototype, layer density, part orientation, types of BF media, weight of media and finish cycle time, were studied using Taguchi’s L18 orthogonal array in order to find their effect on SH of master pattern. Results indicated that process parameters significantly affect the SH of master patterns. It has been found that FDM part layer density contributed the maximum (about 67.52%) for SH of master patterns.     

基于P-GMAW摆动电弧传感的窄间隙坡口宽度自适应焊接

针对窄间隙自动化焊接过程中,组对误差、焊接热变形等因素导致的坡口宽度不一致问题,本文提出采用电弧传感方式对坡口宽度进行检测,并根据检测结果调节工艺参数,保证焊接质量的方法。通过研究坡口宽度偏差的提取算法,分析窄坡口条件下脉冲熔化极焊接的峰值电流、基值电流和平均电流信号的传感特征,提出以脉冲周期内的电流均值作为特征信号,利用侧壁平均法进行偏差提取的传感方式;确定了坡口宽度变化时,焊枪摆幅、焊接速度的调控方法,实现了适应坡口宽度变化的自动化焊接。窄间隙焊接试验表明,上述方法能够有效识别坡口宽度变化,及时对摆幅、焊速进行调整,可在坡口宽度变化时,保证侧壁熔合质量和焊层厚度均匀。研究结果对单道多层窄间隙焊接实现焊接自动化,保证焊接质量具有一定的参考价值。     

Analysing the behaviour of partially coherent divergent Gaussian beams propagating through oceanic turbulence

Theoretical study of propagation behaviour of partially coherent divergent Gaussian beams through oceanic turbulence has been performed. Based on the previously developed knowledge of propagation of a partially coherent beam in atmosphere, the spatial power spectrum of the refractive index of ocean water, extended Huygens–Fresnel principle and the unified theory of coherence and polarization, analytical formulas for cross-spectral density matrix elements are derived. The analytical formulas for intensity distribution, beam width and spectral degree of coherence are determined by using cross-spectral density matrix elements. Then, the effects of some source factors and turbulent ocean parameters on statistical properties of divergent Gaussian beam propagating through turbulent water are analysed. It is found that beam’s statistical propagation behaviour is affected by both environmental and source parameters variations.     

窄板中超声导波传播特性试验研究

针对工程中窄板结构安全评价问题,该文对窄条板结构中超声导波传播特性进行了试验研究。首先,对无限大板结构中不同模态超声导波的传播特性进行了理论分析。然后,在不同宽度窄铝板上进行了不同模态超声导波对比试验研究。结果表明,与兰姆波相比,低阶水平剪切波(SH0波)受窄板宽度方向边界的影响小。当窄板宽度大于电磁声换能器宽度情况下,SH0波检测结果不受板宽度变化影响。在此基础上,将SH0波应用于电力系统接地网扁钢检测。结果表明,SH0波在扁钢中传播能力强,可用于现地埋扁钢无损检测。该文研究工作为工程窄板结构健康检测提供可行的技术方案。     

Evaluation of braze materials used for automotive liquid hydrogen tanks with special respect to hydrogen embrittlement and low temperature toughness

Copper (CU 104 and CW021A), Nickel (NI 102 and MBF51) and Silver (AG102) braze joints with stainless steel 1.4401/1.4404 were investigated with respect to hydrogen embrittlement and cryogenic toughness. CW021A and MBF51 with different braze thicknesses and temperatures were Charpy V tested at 20 °C and ‐196 °C. Neither the seam thickness nor the test temperature had a significant influence on the Charpy V toughness. All toughness values were below 15 J/cm². The reason is the low thickness of the braze seam and therefore the low volume of deformable material. CU 104, CW021A, NI 102, MBF51 and AG102 braze joints were tensile tested in hydrogen of different pressures and temperatures. Neither of the soldering showed any kind of hydrogen embrittlement.     

Development of crash modification factors for changing lane width on roadway segments using generalized nonlinear models

This study evaluates the effectiveness of changing lane width in reducing crashes on roadway segments. To consider nonlinear relationships between crash rate and lane width, the study develops generalized nonlinear models (GNMs) using 3-years crash records and road geometry data collected for all roadway segments in Florida. The study also estimates various crash modification factors (CMFs) for different ranges of lane width based on the results of the GNMs. It was found that the crash rate was highest for 12-ft lane and lower for the lane width less than or greater than 12 ft. GNMs can extrapolate this nonlinear continuous effect of lane width and estimate the CMFs for any lane width, not only selected lane widths, unlike generalized linear models (GLMs) with categorical variables. The CMFs estimated using GNMs reflect that crashes are less likely to occur for narrower lanes if the lane width is less than 12 ft whereas crashes are less likely to occur for wider lanes if the lane width is greater than 12 ft. However, these effects varied with the posted speed limits as the effect of interaction between lane width and speed limit was significant. The estimated CMFs show that crashes are less likely to occur for lane widths less than 12 ft than the lane widths greater than 12 ft if the speed limit is higher than or equal to 40 mph. It was also found from the CMFs that crashes at higher severity levels (KABC and KAB) are less likely to occur for lane widths greater or less than 12 ft compared to 12-ft lane. The study demonstrates that the CMFs estimated using GNMs clearly reflect variations in crashes with lane width, which cannot be captured by the CMFs estimated using GLMs. Thus, it is recommended that if the relationship between crash rate and lane width is nonlinear, the CMFs are estimated using GNMs.     

Development of a fast,lean and agile direct pelletization process using experimental design techniques

A novel hot melt direct pelletization method was developed, characterized and optimized, using statistical thinking and experimental design tools. Mixtures of carnauba wax (CW) and HPMC K100M were spheronized using melted gelucire 50–13 as a binding material (BM). Experimentation was performed sequentially; a fractional factorial design was set up initially to screen the factors affecting the process, namely spray rate, quantity of BM, rotor speed, type of rotor disk, lubricant–glidant presence, additional spheronization time, powder feeding rate and quantity. From the eight factors assessed, three were further studied during process optimization (spray rate, quantity of BM and powder feeding rate), at different ratios of the solid mixture of CW and HPMC K100M. The study demonstrated that the novel hot melt process is fast, efficient, reproducible and predictable. Therefore, it can be adopted in a lean and agile manufacturing setting for the production of flexible pellet dosage forms with various release rates easily customized between immediate and modified delivery.     

High-power single-mode laser diodes (λ = 1.1–1.2 μm) based on quantum-confined AlInGaAs/InP heterostructures

Quantum-confined AlInGaAs/InP laser heterostructures emitting at a wavelength of 1.18 μm have been grown by metalorganic vapor-phase epitaxy. An output radiation power of 40 mW in a single-mode CW regime has been obtained using a diode based in this structure with a mesastrip width of W = 4 μm. The total maximum CW emission power amounted to 75 mW.     

An Understanding of the Width Effect in FRP–Concrete Debonding

Abstract: The scaling of the ultimate load in fibre‐reinforced polymer (FRP)–concrete debonding with the relative width of the FRP is experimentally investigated in this paper. Shear debonding tests are performed to evaluate the cohesive stress transfer between the adherents during the interface crack growth which produces debonding. Concrete specimens with two different widths and different widths of FRP are used in the experimental programme. The nominal stress at debonding increases with the FRP‐to‐concrete width ratio. For a given width of FRP composite sheet, lower debonding stress is obtained from concrete specimens with a larger width. The strain distribution on the FRP and concrete free surface at different stages of debonding was determined using a full‐field optical technique known as digital image correlation. The contribution of the two factors, the boundary effect and the restraint from the surrounding concrete, was studied from the measured strain distribution. The strain distributions across the FRP composite sheet and the concrete within the cohesive stress transfer zone associated with the interface crack are shown to be very inhomogeneous. A region of constant width associated with high shear strains is found at the edge of the FRP sheet during the entire debonding process. The increase in the ultimate nominal stress at debonding is shown to be due to the decrease in the proportion of the total width of the FRP occupied by the edge region. It is shown that the boundary region within the FRP is of a fixed width. The width of concrete close to the edge of the FRP involved in stress transfer, however, increases with the width of FRP. It is established that when the FRP‐to‐concrete width ratio is smaller than 0.5, the level of restraint from concrete increases with the FRP width.     

Cutting performance of glass-vinyl ester composite by abrasive water jet

Polymer matrix composite materials have been increasingly used in aerospace, defense, automotive and marine industries. In these fields, nontraditional machining method of abrasive water jet (AWJ) has been used significantly in order to form polymer matrix components. In this study, glass fiber reinforced vinyl ester composite plates have been investigated under various AWJ cutting parameters by using the Taguchi experimental design in detail. For Taguchi experimental design, experimental parameters of standoff distance, abrasive mass flow rate, traverse speed, pressure and material thickness were determined at three levels. Top kerf width and the surface roughness were investigated in order to understand the cutting performance. Finally, linear regression models were conducted and all performance parameters were examined using analysis of variance (ANOVA) and main effects plots. According to the overall test results, standoff distance was determined as the most effective one. The optimal parameter levels were obtained by the ‘main effects plots’, and finally, the predictive modeling was validated by performing the optimal combination of parameter levels.     

Optimization of Welding Process Parameters for 9Cr-1Mo Steel Using RSM and GA

Optimization of A-TIG welding process parameters for 9Cr-1Mo steel has been carried out using response surface methodology (RSM) and genetic algorithm (GA). RSM has been used to obtain the design matrix for generating data on the influence of process parameters on the response variables. A second-order response surface model was developed for predicting the response for the set of given input variables. Then, numerical and graphical optimization was performed using RSM to obtain the target depth of penetration (DOP) and heat-affected zone (HAZ) width using desirability approach. Multiple regression models were developed based on the generated data, and then the models were used in GA to determine the optimum process parameters for achieving the target DOP and HAZ width. GA-based models employed two different selection processes. Both the RSM- and GA-based models suggested a number of solutions in terms of process parameters, and the identified solutions were validated by experiments. GA-based model employing tournament selection has been found to be a more accurate method for determining the optimum A-TIG welding process parameters.     

OPTIMIZATION OF WELD BEAD DIMENSIONS IN GTAW OF ALUMINUM-MAGNESIUM ALLOY

The Gas Tungsten Arc Welding (GTAW) process is frequently used in welding of aluminum alloys, because of its possible heat input control. This control can be utilized through a good selection of the process variables, which in turn results in optimizing the bead dimensions. The object of this investigation was to study the effect of TIG process parameters on weld bead dimensions. Suitable combinations of tungsten electrode parameters and process variables can lead to optimum GTAW bead dimensions. With alternative current (AC) polarity, a weld bead may be formed between two 3-mm thick pieces of 5005 aluminum-magnesium alloy sheets. The effect of electrode diameter, vertex angle, and the welding current and speed on the bead dimensions were investigated. Results revealed that the rate of increase of bead width with current increase is greater than that produced by decreasing travel speed, and means that the bead width can be controlled more efficiently by welding current rather than by welding speed. For example, bead width can be reduced by half by increasing the welding travel speed three times, whereas it can be doubled when the current has is doubled. In contrast, bead depth is found to be more sensitive to welding speed rather than to the welding current. One of the important results of the present investigation was that the average heat-affected zone width decreased as the welding current and/or speed increased. On the other hand, it was found that the influences of electrode diameter and apex angle on the bead width were similar to their effects on the arc size. The bead width was found to decrease with an increase in the electrode diameter to a certain extent, and increase slightly with an increase of the apex angle.     

SH电磁超声换能器优化设计及粘接强度测量

电磁超声换能器(Electromagnetic Acoustic Transducer,EMAT)使用时无需耦合剂，可以便捷地应用于严苛工况下结构的超声检测。但由于EMAT复杂的多物理场换能机理，通常存在换能效率低，接收信号信噪比小等缺点。针对上述问题，文章开展了线圈宽度、线圈间距及磁致伸缩贴片等参数对EMAT换能效率的影响研究，优化设计了SH电磁超声换能器。实验结果表明，一定厚度的磁致伸缩贴片对EMAT的换能效率有较明显的提高。基于SH0导波对界面变化的敏感性，采用优化设计的EMAT激发SH0导波，对固化温度等因素引起的多层铝板弱粘接结构件进行粘接性能的检测，实验测得的粘接强度与结构拉伸强度的变化趋势一致，表明优化后的EMAT可以适用于粘接结构状态的检测。     

基于机器视觉的圆筒形零件直角梯形槽槽宽检测研究

针对圆筒形零件直角梯形槽槽宽的工业检测速度和精度要求,采用工业相机、镜头、计算机及专业图像处理软件等,构建了一套机器视觉系统,并依据图像处理算法设计了一个针对圆筒形零件上直角梯形槽槽宽检测的方法。对比实验表明,该系统的检测精度能够达到微米级要求,明显优于人工采用专用槽宽测量工具的测量精度,且测量结果不受主观因素的影响,效率较高。     

弹体导带槽宽度两次视觉精确测量方法研究

针对弹体导带槽宽的工业检测速度和精度要求,采用工业相机、镜头、计算机及专业图像处理软件等搭建了一套机器视觉系统,并依据图像处理算法设计了一个针对弹体导带浅槽宽度测量装置。通过采用标准件对测量系统进行标定,计算出成像系统的标定值,采用两次视觉测量方法分别测量16个弹体导带槽的上下槽宽,进行相应计算得出槽宽值,对这16个工件的实际测量值与三坐标测量结果进行对比试验,其结果表明,该系统的测量精度能够达到微米级,可以满足弹体导带槽宽的测量精度要求,且测量结果不受主观因素的影响。     

Study on impact properties of through-thickness stitched foam sandwich composites

Through-thickness stitched foam core sandwich composites were fabricated by using RTM process; and impact performance and damage extent were studied at 1–70 J impact energy levels. The results show that two sharp peak loads and a low-loading plateau appear on the load-time plots at 1–30 J impact energy levels; both sharp peak loads can be considered as the course of penetrating top and bottom facings, a low-loading plateau has the characteristics of penetrating foam cores. Compare to the unstitched samples, the average damage angle of stitched samples increase by 48%, the maximal cracking width and penetration depth of the stitched samples decrease by 67% and 4% at 25 J impact energy levels.     

Performance Analysis for Dispensing Mechanism of Active Code

The dispenisng mechanism of active code is a key technology in an active network,Conven-tional capsule and progurammable switch approaches have their own shortcomings.The DCCAN(distrib-uted code caching for active network) mechansim presented in this paper overcomes these shortcomings,In this paper,capsule and programmable switch approaches are introduced,and their shortconimgs are analyzed,The principle of the DCCAN mechanism is described,.The theory analysis in transimit width based on the DCCAN mechanism and capsule approoach are described.The theory analysis shows that the DCCAN mechanism has many good characteristics and can improve the efficiency of an active net-work,Key factors which affect the transmit width based on the DCCAN mechanism are dicussed,The using condition of the DCCAN mechanism is also discussed.     

Unburned carbon measurement in fly ash using laser-induced breakdown spectroscopy with short nanosecond pulse width laser

The unburned carbon in fly ash is one of the important factors for the boiler combustion condition. Controlling the unburned carbon in fly ash is beneficial for fly ash recycle and to improve the combustion efficiency of the coal. Laser-induced breakdown spectroscopy (LIBS) technology has been applied to measure the fly ash contents due to its merits of non-contact, fast response, high sensitivity, and real-time measurement. In this study, experimental measurements have been adopted for fly ash flows with the surrounding gases of N₂ and CO₂, while the CO₂ concentration varified to evaluate the CO₂ effect on the unburned carbon signal from fly ash powder. Two kinds of pulse width lasers, 6?ns and 1?ns, were separately adopted to compare the influence of laser pulse width. Results showed that compared with that using 6?ns pulse width laser, plasma temperature was lower and had less dependence on delay time when using 1?ns pulse width laser, and spectra had more stable background. By using 1?ns pulse width laser, the emission signal from surrounding CO₂ also decreased because of the less surrounding gas breakdown. The solid powder breakdown signals also became more stable when using 1?ns pulse width laser. It is demonstrated that 1?ns pulse width laser has the merits for fly ash flow measurement using LIBS.