不同表面结构特征圆柱导体的太赫兹散射特性

太赫兹频段下导体表面的细微结构、粗糙度等细节将对目标电磁散射行为产生影响。为衡量这一影响程度,以圆柱导体为例研究了太赫兹频段下目标表面不同结构特征的电磁散射现象及其在图像域的表现规律。利用高频电磁计算方法获得了表面分别为理想光滑、带刻痕和周期粗糙的三种圆柱多姿态角、多频点单站散射场;基于转台成像算法重建了小转角下目标的二维图像。从仿真结果可以看出:m量级的细节特征在太赫兹雷达图像上有着显著的表现,表明太赫兹雷达能够获取更加丰富和精细的目标信息,从而为目标探测识别提供新的特征和技术手段。     

基于对应分析法的不同收入等级居民的消费特征分析——以广东省城镇居民为例

根据2008年广东省不同收入等级城镇居民的人均消费构成的统计数据,采用对应分析法,并结合可支配收入、平均消费倾向分析不同收入等级城镇居民的消费特征.针对不同的收入人群提出了不同的扩大内需措施的政策建议.     

Damage characteristics and surface description of near-wall materials subjected to ultrasonic cavitation

For the analysis of ultrasonic cavitation erosion on the surface of materials, the ultrasonic cavitation erosion experiments for AlCu4Mg1 and Ti6Al4V were carried out, and the changes of surface topography, surface roughness, and Vickers hardness were explored. Cavitation pits gradually expand and deepen with the increase of experiment time, and Ti6Al4V is more difficult to erode by cavitation than AlCu4Mg1. After experiments, the cavitation damage characteristics such as the single pit, the rainbow ring area, the fisheye pit, and some small pits were observed, which can be considered to be induced by a single micro-jet impact, ablation effect caused by the high temperature, micro-jet impingement with a sharp angle, and multibeam micro-jets coupling impact or negative pressure in the local area produced by micro-jet impact, respectively. The surface roughness and Vickers hardness of the material increase slowly after rapid growth at different points in time as the experiment time increases. With the increase of the ultrasonic amplitude, both of them first increase and then decrease after the ultrasonic amplitude is greater than 10.8 μm. The increases in surface roughness and Vickers hardness tend to decrease as the viscosity coefficient increases. Ultrasonic cavitation can cause submicron surface roughness and increase surface hardness by 20.36%, so it can be used as a surface treatment method.     

超导磁体螺栓结合面低温振动特性研究

振动特性对于超导磁体的各类工程应用具有重要意义,螺栓法兰盘连接是超导磁体系统的一种常见的支撑结构类型,然而螺栓结合面在低温条件下振动特性的相关研究目前尚少见报道.本研究中设计加工了简化的连接结构,在室温和液氮温度对其螺栓结合面进行振动特性的测试分析.接下来,采用集中质量法进行建模,并利用振型、频率与质量矩阵、刚度矩阵的关系求解了不同螺栓预紧力情况下的刚度矩阵,得到了系统总刚度和结合面刚度.使用上述方法对振动测量数据计算发现,该结构的系统总刚度与结合面刚度都随着预紧力增大而增大,同时液氮低温条件可使系统总刚度和结合面刚度进一步增大.     

抛光区域几何特征与流场创成关键参数关系

磁流变抛光在其实际工作过程中,抛光区域几何特征的不同将会对流场创成的关键参数产生很大的影响。针对此问题建立三维模型与实验仿真展开研究。在研究抛光区域几何特征与流场创成关键参数的关系时,先改变抛光区域形状,观察其对流场创成中剪切应力、压力产生的影响;再控制抛光区域的形状相同时,通过改变抛光区域尺寸大小,观察对流场创成中剪切应力、压力产生的影响。结果表明：当抛光区域形状不同时,抛光区域为凹面时剪切应力最大,抛光区域为凸面时剪切应力最小。当抛光区域形状为凸面时,抛光区域两边的剪切应力随着抛光区域曲率大小增大而增大;当抛光区域形状为凹面,抛光区域两边的剪切应力随着抛光区域曲率大小增大而减小。当抛光区域形状不同时,抛光区域为凹面时压力最大,抛光区域为凸面时压力最小。当抛光区域形状为凸面时,抛光区域处的压力随着抛光区域曲率增大而增大;当抛光区域形状为凹面时,抛光区域处的压力随着抛光区域曲率增大而减小。     

Ultrasound freeze-thawing style pretreatment to improve the efficiency of the vacuum freeze-drying of okra (Abelmoschus esculentus (L.) Moench) and the quality characteristics of the dried product

Vacuum freeze-drying is a new and high technology on agricultural product dehydrating dry, but it faces the high cost problem caused by high energy consumption. This study investigated the effect of ultrasound (US), freeze-thawing (including the freeze-air thawing (AT), freeze-water thawing (WT), freeze-ultrasound thawing (UST), and freeze-air ultrasound thawing (AT + US)) pretreatments on the vacuum freeze-drying efficiency and the quality of dried okra. The results indicated that the application of ultrasound and different freeze-thawing pretreatments reduced the drying time by 25.0%–62.50% and the total energy consumption was 24.28%–62.35% less. The AT pretreatment reduced the time by of okra slices by 62.50% and the total energy consumption was 62.35% less. The significant decrease in drying time was due to a change in the microstructure caused by pretreatment. Besides, the okra pretreated with the US retained most of the quality characteristics (flavor, color, hardness, and frangibility) among all methods, while, AT + US had the most changeable characteristics in quality, which is deprecated in our study. The okra pretreated with the US and AT, separately, had the best dry matter content loss (9.008%, 5.602%), lower chlorophyll degradation (5.05%, 5.44% less), and higher contents of total phenolics, total flavonoids, and pectin, with strong antioxidant capacity, compared to other methods. The pretreatments did not have a large effect on the functional groups and the structure of pectin, but slightly affected the viscosity. It can be concluded that AT and US pretreatment methods are better than others.     

感应耦合等离子体中和枪的电子引出特性研究

给出了一种感应耦合等离子体源的设计,用于等离子体中和枪装置.通过实验方法研究等离子体源的电子引出特性,并结合理论分析了等离子体密度随射频功率的变化关系.研究结果表明等离子体源的电子引出特性与放电腔内气压有关联性,E?H模式转换中电子密度的变化与负载的电感值相关.研究成果对等离子体中和枪的发展有重要的参考价值.     

离散忆阻混沌系统的Simulink建模及其动力学特性分析

为拓广离散忆阻器的研究与应用,基于差分算子,构建了具有平方非线性的离散忆阻模型,并实现了Simulink仿真.仿真结果表明,设计的忆阻器满足广义忆阻定义.将得到的离散忆阻引入三维混沌映射中,设计了一种新型四维忆阻混沌映射,并建立了该混沌映射的Simulink模型.通过平衡点、分岔图、Lyapunov指数谱、复杂度、多稳态分析了系统复杂动力学特性.本文从系统建模角度出发,构建离散忆阻与离散忆阻混沌映射,进一步验证了离散忆阻的可实现性,为离散忆阻应用研究奠定了基础.     

Dynamic Modeling of the Feed Drive System of a CNC Metal Cutting Machine

Studying the vibrational behavior of feed drive systems is important for enhancing the structural performance of computer numerical control (CNC) machines. The preload on the screw and nut position have a great influence on the vibration characteristics of the feed drive as two very important operational conditions. Rotational acceleration of the screw also affects the performance of the CNC feed drive when machining small parts. This paper investigates the influence of preload and nut position on the vibration characteristics of the feed drive system of a CNC metal cutting machine in order to be able to eliminate an observed resonance occurred at high rotational speeds of the screw, corresponding to high feed rates. Additionally, rational structural parameters of the feed drive system are selected in order to increase the rotational acceleration for improving the performance of the CNC machine. Experiments and analyses showed that by selecting specific parameters of feed drive system and simultaneously applying a certain value of preload, a 97% increase in rotational acceleration and 30% time reduction considering the vibration resistance at high rotational speeds can be achieved.     

“黑青”“黑碧”的谱学鉴别特征探究

“黑青”指颜色近黑色,主要成分为透闪石的青玉。“黑碧”指颜色近黑色,主要成分为阳起石的碧玉。采用电子探针、激光剥蚀电感耦合等离子体质谱仪和红外光谱测试分析手段,确定“黑青”“黑碧”的矿物种属。采用拉曼光谱、显微紫外-可见分光光度计、红外光谱对“黑青”“黑碧”的谱学鉴别特征进行探究。“黑青”为标准透闪石拉曼谱峰,“黑碧”的谱峰位置与“黑青”存在几个波数的偏差,向波数小的方向移动。可见-近红外波段,“黑青”出现445 nm吸收峰,680和940 nm宽吸收带,为Fe2+和Fe3+作用;“黑碧”出现445 nm吸收峰,660和690 nm双吸收峰以及970 nm吸收峰,为Fe2+,Fe3+,Cr3+作用。显微紫外-可见光谱可分析到样品的近红外区,“黑青”在1 397,2 310,2 387和2 466 nm出现强吸收峰,1 915和2 120 nm出现弱吸收峰;“黑碧”在1 400,2 313和2 394 nm出现吸收峰。红外光谱分析“黑青”在5 225,4 738,4 692,5 349,4 317,4 190和4 064 cm-1存在吸收峰;“黑碧”在4 708,4 307,4 178和4 031 cm-1存在吸收峰。显微紫外-可见光谱与红外光谱分析结果虽然存在小的差异,但基本保持一致,以红外光谱分析结果为准。将透闪石质的“黑青”、阳起石质的“黑碧”、广西大化阳起石质玉进行对比,综合红外光谱和显微紫外-可见光谱分析结果得出“黑青”（透闪石）与“黑碧”（阳起石）近红外光谱的鉴别特征：“黑青”（透闪石）在4 800～4 600 cm-1存在两个吸收峰,4 350～4 300 cm-1存在分裂双吸收峰;“黑碧”（阳起石）在4 800～4 600 cm-1存在一个弱吸收峰,4 350～4 300 cm-1存在一个吸收单峰。且“黑碧”（阳起石）的近红外吸收峰相较于“黑青”（透闪石）整体向低波数方向移动。