小波变换分析信号的瞬时频率分析

小波变换可以用来取代短时DFT,已经成为数字信号处理(DSP)的主流部分。在数字信号处理中,小波的尺度和频率有密切的关系。分析多个信号时不存在交差项的干扰,能够克服时频分布固有的缺点。     

DOA和频率的快速高精度估计

本文提出了一种把自适应特征分解算法和最大似然估计算法联合运用的DOA和频率的快速高精度估计算法。理论分析、计算机模拟、湖上实验和硬件实现都表明了本算法对于单色平面波信号具有结构简单、估值精确、运算量少、跟踪性好等优点。     

基于瞬时频率估计阶比法的电机振动信号分析

电机转轴是电机中至关重要的精密零部件,运用信号分析的方法,可对电机转轴进行预估评价。为提高电机转轴的安全性,降低事故率,利用瞬时频率估计法与阶比法计算分析电机的振动信号,并进行电机实际缺陷情况下的验证试验。结果表明,基于瞬时频率估计阶比法能对信号进行有效降噪处理,准确地预测故障缺陷的具体位置。     

基于人耳听觉特性的信号显著图计算方法研究

信号的幅值突变往往蕴含着设备的故障信息,为明确产生幅值突变的时频区域,基于听觉系统的信息处理机制,提出了一种信号显著图计算方法。首先,对信号进行带通滤波、相位调整、半波整流等听觉外周处理,然后,提取处理结果的一次或多次包络信息,并对包络信息进行多尺度二维滤波。继而,利用中心-周边差算子得到信号在不同尺度下的局部显著度,最后,对局部显著度进行跨尺度整合和线性合并得到信号的时频显著图和全局显著图。仿真和实验结果表明,该方法适用于振动信号和语音信号,可以清晰表征幅值突变的时频区域,并可抵抗一定的噪声干扰,具有一定的有效性和实用性。     

短时能量分析及人耳的主观听觉在船舶辐射噪声特征提取中的研究

文章提出了利用短时能量分析与人的主观听觉相结合的方法进行船舶辐射噪声特征提取。通过对实际船舶辐射噪声信号的分析，结果表明将船舶辐射噪声的人耳听测特征与信号处理后的数字特征相结合，可以达到对船舶辐射噪声特征提取的目的。     

利用间歇混沌检测含噪未知频率信号的研究

研究发现被测信号频率和干扰噪声变化都会引起间歇混沌间隔的变化,通过仿真实验分析了被测信号频率和干扰噪声对间歇混沌特征影响的相互关联关系,从理论上分析了被测信号频率和相角变化对间歇混沌特征的影响,提出了一种利用间歇混沌特征变化测量含噪未知频率信号的方法,设计了有噪声和无噪声两种环境中对声波信号频率的检测实验。实验结果显示与Duffing混沌系统相比,利用Liu-cos混沌系统间歇混沌检测含噪未知频率信号的效果更好。     

电信时钟信号频率的测量装置

为了实现电信时钟信号频率和频率稳定度的高精度测量。研制一台电信时钟信号频率变换器,配置现有的频标比对器,建立一套测量系统。对该系统自检,测量精度优于１×１０－１１／Ｓ。     

基于递归希尔伯特变换的振动信号解调和瞬时频率计算方法

精确地提取振动信号的瞬时幅值和瞬时频率对结构的参数识别和健康监测有重要作用。希尔伯特变换是一种常用的信号解调及瞬时频率计算方法,但在信号不满足Bedrosian乘积定理的条件时会造成较大误差。针对这一问题,提出了一种递归希尔伯特变换方法,用前一步希尔伯特变换计算出的纯调频信号作为新的信号,递归地使用希尔伯特变换以进行信号解调,理论分析表明递归希尔伯特变换能够快速地收敛。最后采用仿真信号对比了递归希尔伯特变换与单次希尔伯特变换、经验调幅调频分解及Teager能量算子法在信号解调及瞬时频率计算中的结果,结果表明了递归希尔伯特变换方法的实用性及精确性。     

导弹脉冲噪声对听觉器官的损伤

新型导弹的装备虽大大加强了舰艇部队的作战能力，但导弹发射时所产生的强脉冲噪声将严重威胁有关舱室和战位人员的安全。在某型导弹实艇发射试验中，我们进行了脉冲噪声的测试和动物试验，较详细地观察了脉冲噪声对听觉器官的损伤，并根据人与豚鼠耐受性的差异，对有关舱室和战位人员的安全性作出评价。     

Exposure setup to study potential adverse effects at GSM 1800 and UMTS frequencies on the auditory systems of rats

To investigate possible biological effects of exposure to electromagnetic (EM) fields at the frequencies of global system for mobile communication (GSM) 1800 system and universal mobile telecommunication system (UMTS) on the auditory system of rats, an exposure setup for in vivo experiments is presented. The study was carried out in the framework of two European research projects. The target of the investigation was the cochlea. A dosimetric study was performed, both numerically and through direct measurements, to assess the interaction of the radiated fields and the dose distribution in the biological target. For the local exposure of rats, a loop antenna operating at the frequency bands of interest was designed, realised and characterised through numerical and experimental dosimetric procedures. Moreover, an exposure apparatus was set up, consisting of three arrays of four loop antennas, placed on three levels, thus allowing simultaneous exposure of 12 rats to give statistical power to the experiments. To isolate the exposure arrays, the setup was assembled by a wooden rack with EM field absorbing panels, inserted among the levels and at the four sides of the rack. Isolation was verified by direct measurements. Two exposure arrays were simultaneously supplied, whereas the third one was used for sham exposure. Blind exposure was achieved through a black box, hiding physical connections to the microwave power supply. During exposure sessions, rats were restrained in special plastic jigs for repeatable positioning, thus assuring the fixed level of dose in the target.     

A theoretical study of the signal response of a shielded MR sensor[magnetic heads]

A general analysis of the behavior of a shielded magnetic-field biased magnetoresistive sensor is presented. Using a transmission-line model and assuming linear magnetic behavior for the MR sensor material, the nature of the MR transfer curve and the dependence of output amplitude and asymmetry on bias levels and signal strengths is studied. Results show that, in general, there is no single optimum bias level that simultaneously maximizes the small-signal response amplitude and minimizes the positive-negative output asymmetry. As a result, in MR head designs, compromise must be made according to the relative importance of these two objectives     

Using torsional oscillations to study liquid-solid transitions

A new approach to studying liquid-solid phase transitions is proposed, which is based on measurements of the shear modulus of a substance using the method of torsional oscillations. An important feature of the proposed method is that it is possible to go over the phase transition temperature in the course of continuous heating, thus monitoring intervals on both sides of this temperature. Results of applying the proposed method to investigations of the melting of ice are presented.     

Consumer response to the tris controversy: A research study

The purpose of the research was to study the possible long-term effects of the public controversy that arose when the most widely used flame retardant (FR) finish. Tris, was first identified as a potential carcinogen. Parents of children enrolled in 15 selected nursery schools and day care centers in Rhode Island were surveyed to determine changes in their practices and in their attitudes toward the use of FR finishes for children's sleepwear. Almost 85% of the 269 respondents had heard or read about problems with FR chemicals. Of these, only 68% remembered that Tris was considered to be a carcinogen and/or health hazard and only 20% reported appropriate changes, such as reading labels, in their purchasing behavior. Absence of Health Risk was the primary consideration used in the purchase of children's sleepwear followed, in order, by Flame Retardancy, Comfort, Durability. Price, Ease of Care and Attractiveness. Despite the problems with Tris, most respondents felt strongly that FR garments should be available for a variety of population groups. They were less convinced that the government should set flammability standards and the majority wanted the freedom to choose between flame retardant and non-flame retardant garments for themselves and their children. Cluster and chi square analyses based on the criteria used in the selection of children's sleepwear showed seven distinct patterns of response but few significant differences between the clusters in respect to opinions and practices. Additional chi square analyses did, however, show some relationships between demographic variables and respondents' shopping practices, understanding of terminology, sources of information and opinions regarding the importance of FR garments and the expansion of government regulation. Many consumers appeared to be confused by the controversy. Specific recommendations for dealing with such problems need to be presented in a variety of media in order to reach different segments of the population; the often misunderstood term “flame resistant” should be retired from use; some non-toxic FR garments should be made available to all population groups: labels and promotional materials should be more informative; consideration should be given to the long-range health, safety and cost effectiveness of government regulations and more research should be conducted to increase understanding of consumer behavior.     

红外波段铜树枝状结构磁响应特性研究

提出一种可用于实现红外波段负磁导率的树枝状磁谐振模型,采用基于有限差分技术的CST微波工作室软件确定了树枝状结构参数与磁谐振响应之间的关系,实现了红外波段的负磁导率.以碳纤维为阴极,采用化学电沉积的方法制备了铜树枝状结构,利用傅立叶变换红外光谱仪测量了样品的空间红外透射行为,结果表明铜树枝状结构实现了红外波段的磁谐振响应,最大透过率达到-7.95dB,实验结果与数值模拟吻合.研究了铜树枝状结构的分形维数和磁响应波段与沉积电压的关系以及两个铜树枝状结构之间的耦合作用,结果表明随着沉积电压的增大分形维数与磁响应波长随之增加,样品之间的耦合作用导致磁谐振响应的波长和强度发生变化.     

试论植物微弱电信号研究

介绍了植物微弱电信号的特点、产生机理、生理效应 ,并就当前植物微弱电信号研究状况进行了简要评价     

A study to evaluate and understand the response of aluminum alloy 2026 subjected to tensile deformation

The strain concentration factors were determined for aluminum alloy 2026 in the T3511 temper using multi-hole structural coupon specimens. Samples of the alloy were evaluated for both the 6.25 mm (0.25 in.) thick and 10 mm (0.4 in.) thick specimens and having widths of 50 mm (2 in.) and 100 mm (4 in.), respectively. For the case of the specimens that were 50 mm in width the mechanical tests were conducted for both the open hole and filled hole conditions and the corresponding strain concentration value was determined. Threaded fasteners having collars were used for the case of the filled hole specimens. The fasteners posses a shank diameter that was slightly larger than the nominal hole size in order to provide for some interference. The strain concentration values were evaluated at both the failure strain (ε_f) and the strain at maximum load (ε_max). The average strain concentration value was then used to predict the results for the stack-up tests.     

A penetration test to study the mechanical response of mortar in ancient masonry buildings

A simple method for studying the mechanical response of the mortar in existing masonry buildings is presented herein. The method is based on the measurement of the penetration depth increment of a steel probe (4 mm diameter) at each hammer blow (impact energy=2.2 J). Numerous tests were carried out on different laboratory specimens in order to formulate a relationship between the compressive strength and the probe penetration rate, and a series of tests on actual masonry elements confirmed that the proposed relationship is sound.

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Résumé On présente une méthode d’essai simple pour évaluer la resistance à la compression des mortiers des murs existants. La méthode proposée ici est basée sur la mesure de la profondeur de pénétration d’une sonde d’acier (4 mm de diamètre), à chaque coup de scléromètre (énergie d’impact=2,2 Joule). Les résultats de nombreux essais effectués sur des éprouvettes construites en laboratoire ont permis d’obtenir une relation entre la résistance à la compression du mortier et la vitesse de pénétration de la sonde. En outre, la validité de cette méthode a été confirmée par une série d’essais effectués sur des murs existants.