基于魏格纳分布的跳频信号分析方法的对比研究

时频分析是分析非平稳信号的一种重要数学分析工具,魏格纳分布是时频信号分析的非线形变换。针对跳频信号的特点,本文提出了一种采用平滑伪魏格纳(SPWVD)时频分析来分析跳频信号的方法,该方法可以在不需要知道信号任何先验参数的情况下,估计出跳频信号的跳频频率、跳变时刻等参数。     

基于机器视觉的种子间距识别及其应用

介绍了基于机器视觉的精播排种器性能检测方法,在对获取的样本图像进行处理的基础上完成帧种子间距特征的识别.通过分析种子运动特征,实现了排种时间间隔样本的提取.利用理论排种和实际排种时间间隔之间的关系,构建了以时间间隔为特征量的排种质量统计模型,计算出排种器性能指标.试验表明,此方法检测误差小、速度快、精度高.     

航空HF电台测试系统跳频信号源的实现

航空HF电台是航空通信系统的重要组成部分,担负着空空、空地之间的远程通信,关系到空空、空地之间的通信安全。通过分析航空HF电台测试和控制需求,提出基于"DDS+PLL"的检测仪跳频信号源的设计方案,介绍跳频信号源中频率合成单元电路工作原理和工作流程,分析跳频信号源各频率合成单元的输出频率的计算方法。测试结果表明,该跳频信号源具有频率稳定度高、频率分辨率高、抗干扰能力强和频率转换时间短等优点。     

仿竹型筒式立体停车结构的环箍层布置研究

作为航空飞行器的动力装置,冲压发动机以其高推比性能日益应用广泛,其控制系统的好坏直接影响着其工作性能。推力控制系统是冲压发动机控制系统的重要组成部分,良好的推力控制器使其在复杂环境和比较宽的马赫数下获得很好的鲁棒性。本文利用MATALB仿真软件的Simulink工具箱建立推力控制系统的仿真模型,采用模糊PID控制方法对冲压发动机推力回路进行控制,通过调节参数,设计出高性能的控制器。其后对设计出的模糊PID控制器进行动稳态性能、鲁棒性、抗干扰性以及跟踪性的测试,并将其控制结果与设计的传统PI控制以及鲁棒控制的结果进行对比分析。仿真结果表明,设计的模糊PID控制器在动稳态性能、鲁棒性、抗干扰性以及跟踪性能方面,都可以达到很好的性能。     

红松籽中脂肪的近红外光谱快速检测研究

采用近红外光谱分析方法对红松籽脂肪进行定量分析,建立红松籽脂肪的快速检测方法,利用多种预处理方法优化模型,同时采用间隔偏最小二乘法、反向间隔偏最小二乘法、无信息变量消除法实现特征波段的选取。结果表明,红松籽样本光谱经矢量归一化预处理后建立的模型最佳;波段优选能够提高模型质量,其中反向间隔偏最小二乘法的筛选结果最优,其红松籽脂肪模型校正集相关系数为0.889 2,验证集均方根误差为0.765 1。由此可知,经过优化后,模型的预测性能较好,实现了红松籽脂肪快速、无损检测。     

简析传统图案在标志设计中的应用

现代标志设计具有很强的现代感和信息感,传达了一种特定的信息。传统图案是现代设计艺术的渊源和基础,把其精神元素融入现代设计之中,传承与发扬传统图案的审美思想、吉祥寓意以及造型方法,通过挖掘、变化和改造传统图案,从而设计出具有个性化、时代性的作品。     

基于图像处理技术的家具二维图案快速设计

以VC++为开发工具结合图像处理技术和CAD二次开发技术,设计了一种家具表面二维复杂图案的自动绘制方案.该方案的实现分4个步骤进行,首先是对艺术图案进行二值化处理,然后在边界提取程序中获取图案的边界信息,再对所获取的边界图像进行细线化处理,形成外部数据库,最后通过在CAD的二次开发过程中引入外部数据库的方法绘制出图形.     

西洋菜地主要害虫空间格局的地统计学分析

应用地统计学方法分析了西洋菜地黄曲条跳甲Phyllotreta striolata成虫、菜粉蝶Pieris rapae及小菜蛾Plutella xylostella幼虫的空间格局,建立了多个描述东西方向上间隔距离与半方差值之间关系的曲线模型.结果表明,黄曲条跳甲成虫、菜粉蝶及小菜蛾幼虫种群空间分布具有高度异质性,其空间...     

红松仁脂肪的近红外光谱定量检测

为实现红松仁脂肪无损、简便检测,利用近红外光谱分析技术对红松仁脂肪进行定量分析,用偏最小二乘法构建去壳红松仁脂肪定量分析模型,采用多种预处理方法优化模型,并且利用间隔偏最小二乘法、反向间隔偏最小二乘法、无信息变量消除法进行特征波段的筛选。结果表明,红松仁光谱经一阶导数预处理后建立的模型最佳;波段优选可以提升模型质量,其中反向间隔偏最小二乘法的筛选结果最佳,其松仁脂肪模型校正集相关系数为0.911 4,验证集相关系数为0.882 0,验证集均方根误差为0.646 8。可见,经过优化后,模型的预测性能较好,实现了去壳红松仁脂肪的快速、无损检测。     

用于农业的无线环境监测装置设计

为了有效地监测温室的环境参数,基于AVR单片机与CRX14射频芯片实现无线环境监测装置设计。该装置设计主要包括主站信息处理与分站信息采集两大部分,用户可根据需要查询相应的信息。试验表明,该装置具有性能稳定、功耗低等特点。     

A dielectric omnidirectional reflector

A design criterion that permits truly omnidirectional reflectivity for all polarizations of incident light over a wide selectable range of frequencies was used in fabricating an all-dielectric omnidirectional reflector consisting of multilayer films. The reflector was simply constructed as a stack of nine alternating micrometer-thick layers of polystyrene and tellurium and demonstrates omnidirectional reflection over the wavelength range from 10 to 15 micrometers. Because the omnidirectionality criterion is general, it can be used to design omnidirectional reflectors in many frequency ranges of interest. Potential uses depend on the geometry of the system. For example, coating of an enclosure will result in an optical cavity. A hollow tube will produce a low-loss, broadband waveguide, whereas a planar film could be used as an efficient radiative heat barrier or collector in thermoelectric devices.     

Lateral hopping of molecules induced by excitation of internal vibration mode

We demonstrate electron-stimulated migration for carbon monoxide (CO) molecules adsorbed on the Pd(110) surface, which is initiated by the excitation of a high-frequency (HF) vibrational mode (C-O stretching mode) with inelastic tunneling electrons from the tip of scanning tunneling microscopy. The hopping phenomenon, however, cannot be detected for CO/Cu(110), even though the hopping barrier is lower than in the CO/Pd(110) case. A theoretical model, which is based on the anharmonic coupling between low-frequency modes (the hindered-translational mode related to the lateral hopping) and the HF mode combined with electron-hole pair excitation, can explain why the hopping of CO is observed on Pd(110) but not on Cu(110).     

贵州马尾松人工林经营密度模型初探

为探讨用模拟方法确定人工林的经营密度,本文以贵州马尾松人工林569块常规标准地资料为基础分析,结果表明:这些标准地对目前贵州马尾松人工林具有充分代表性;立木密度对林分平均胸径的影响最为明显,对树高影响较小;林分断面积和蓄积随立木密度的增大而上升,但当立木密度大到一定程度时,它们都有下降的趋势.基于以上分析,用动态规划方法建立了可变间伐间隔期的林分经营密度模型.该模型既符合林分生长的一般规律,又得到实地试验结果的支持,因此建议应用.     

Molecule cascades

Carbon monoxide molecules were arranged in atomically precise configurations, which we call "molecule cascades," where the motion of one molecule causes the subsequent motion of another, and so on in a cascade of motion similar to a row of toppling dominoes. Isotopically pure cascades were assembled on a copper (111) surface with a low-temperature scanning tunneling microscope. The hopping rate of carbon monoxide molecules in cascades was found to be independent of temperature below 6 kelvin and to exhibit a pronounced isotope effect, hallmarks of a quantum tunneling process. At higher temperatures, we observed a thermally activated hopping rate with an anomalously low Arrhenius prefactor that we interpret as tunneling from excited vibrational states. We present a cascade-based computation scheme that has all of the devices and interconnects required for the one-time computation of an arbitrary logic function. Logic gates and other devices were implemented by engineered arrangements of molecules at the intersections of cascades. We demonstrate a three-input sorter that uses several AND gates and OR gates, as well as the crossover and fan-out units needed to connect them.     

模态分析技术和振动系统幅频响应表达式

 作者应用模态分析技术获得有阻尼多自由度振动系统的幅频响应表达式,借此可以设计出能明显降低振动响应的动力减振器.     

Microresonator-based optical frequency combs

The series of precisely spaced, sharp spectral lines that form an optical frequency comb is enabling unprecedented measurement capabilities and new applications in a wide range of topics that include precision spectroscopy, atomic clocks, ultracold gases, and molecular fingerprinting. A new optical frequency comb generation principle has emerged that uses parametric frequency conversion in high resonance quality factor (Q) microresonators. This approach provides access to high repetition rates in the range of 10 to 1000 gigahertz through compact, chip-scale integration, permitting an increased number of comb applications, such as in astronomy, microwave photonics, or telecommunications. We review this emerging area and discuss opportunities that it presents for novel technologies as well as for fundamental science.     

Electrons in silicon microstructures

Silicon microstructures only a few hundred atoms wide can be fabricated and used to study electron transport in narrow channels. Spatially localized voltage probes as close together as 0.1 micrometer can be used to investigate a variety of physical phenomena, including velocity saturation due to phonon emission, the local potentials caused by scattering from a single trapped electron, and quantum tunneling or hopping among very few electron states.     

有限元技术在空调器管路振动分析及设计优化中的应用

应用PIC公司的Pro／E软件建立空调器管路系统的三维模型,通过ANSYS软件的专用Pro／E接口将模型导人到ANSYS软件中,在ANSYS软件中建立该管路的有限元分析模型,计算出前20阶固有频率和振型,并且在此基础上模拟压缩机的激励,分析管路的振动响应特性。通过对实例计算分析,提出减少配管振动的优化设计方案,证明了应用ANSYS软件的有限元技术进行空调管路减振的可行性。     

基于Web的犬病诊断专家系统的设计与实现

模拟兽医专家的诊断过程,对290余种犬病用计算机进行诊断模拟,充分发挥Internet收集、共享知识和数据的优势,改善了诊断专家系统的性能并扩展增强了诊断功能.采用正-反向结合的混合推理策略及深度优先的搜索方式,利用MVC设计模式,实现了基于web的犬病诊断专家系统.可以为犬病专家和养犬人士提供方便.     

Phase-matched generation of coherent soft X-rays

Phase-matched harmonic conversion of visible laser light into soft x-rays was demonstrated. The recently developed technique of guided-wave frequency conversion was used to upshift light from 800 nanometers to the range from 17 to 32 nanometers. This process increased the coherent x-ray output by factors of 10(2) to 10(3) compared to the non-phase-matched case. This source uses a small-scale (sub-millijoule) high repetition-rate laser and will enable a wide variety of new experimental investigations in linear and nonlinear x-ray science.