电负载对压电振动系统特性的影响

我们研究分析了由于电声耦合,电负载对压电振动系统特性的影响.结果表明:（1）在电负载阻抗由-∞到+∞改变时,系统的机械谐振频率将充满0到∞整个频率域;（2）位移和应力分布.也将随之变化,甚至在两自由端（应力等于零的地方）位移也可能为零。
我们还给出了侧向极化压电条的纵向振动的实验结果,并与理论分析进行比较。     

强噪声对豚鼠中耳、圆窗膜的影响

本文报道在150-172dB的噪声场中对豚鼠作用不同时间后,就其中耳及圆窗膜的伤情观察结果进行了分析。当噪声剂量小于1.2J/mm~2时,对豚鼠中耳无影响. 噪声剂量在2.0-30J/mm~2范围内可引起不同程度的伤情。噪声剂量超过30J/mm~2,则实验中常引起豚鼠死亡。     

在高压氧下豚鼠听觉诱发电位的变化

豚鼠暴露在两个绝对压下呼吸高压氧,比较了暴露前后短声诱发的听神经动作电位(AP)、脑干电位(BSEP)及听皮层电位(ACEP)的潜伏期和振幅。主要结果是:在呼吸高压氧期间AP和BSEP的振幅明显增高,但ACEP的振幅并不完全与AP和BSEP呈同步性改变;在高压氧下约半数动物的ACEP振幅增高,但其余动物的却呈现减低或无明显改变。这可能反映皮层对高压氧较为敏感,而且个体间敏感程度又不相同。实验结果提示,在两个绝对压下呼吸高压氧1小时对改善听觉系统的功能是有益的。     

水中目标窄带噪声识别的听觉外周模型

为解决听觉外周模型特征在具有工程背景的水中目标声信号分类研究中识别率下降问题,提出了一种外周模型Gammatone滤波器组修正方法,获得的窄带噪声特征可明显提高水中目标识别性能。首先,分析了识别率下降原因,发现声学工程应用中多通道数据采集,导致信号频率范围变窄,而引起声信号的时频特征发生变化。其次,根据听觉模型用Gammatone滤波器组模拟人耳基底膜频率分解特性、低频信息包含水中目标噪声信号的重要类别特征,对原有的听觉模型特征进行插值,对滤波器组的通道数与中心频率进行适应性修正,得到目标噪声在较窄频带的27维特征,修正后的模型能够更精细地反映出目标时频特性。最后,采用神经网络分类器进行实验。结果表明,修正后的听觉模型保留了原较宽频带特征的主要信息,而且进一步提高了对实际目标的分类能力,识别率由原来的82.59%提高到88.80%。本文提出根据工程应用平台的有效接收频带优化听觉外周模型Gammatone滤波器组的设计,采用阵元级的多通道数据进行分析,侧重于工程应用,解决了多通道数据采集中,由于频带变窄,导致信号的特征信息量下降,进而引起声特征识别性能下降的问题,修正后的听觉模型特征,有效地提高水中目标辐射噪声的识别效果。本文对从事无源声呐目标识别、有源声呐目标识别、带宽受限的多通道声数据采集的时频特性分析研究人员具有一定的参考价值。     

尺寸效应对Si晶格振动特性的影响

结合Recursion方法和Dean方法在“近似球”模型下系统研究了晶粒尺寸对Si晶格振动特性的影响,讨论了晶格振动态密度中最高频率峰(主峰)随晶粒尺寸增加所表现出的峰位蓝移和峰宽变窄.通过分析态密度随晶粒尺寸的变化,发现态密度具有收敛特征:态密度在尺寸达到一定程度时变化较小. 关键词：     

N离子注入对金刚石膜场发射特性的影响

不同剂量的N离子被注入到化学气相沉积金刚石膜内，研究了表面结构及场发射特性的变化.Raman谱和x射线光电子能谱分析表明，N离子的注入破坏了金刚石膜表面原有的sp3结构，并在膜内形成大量的sp2 C—C 和sp2 C—N 键.样品的场发射测试显示N离子的注入显著提高了金刚石膜场发射特性，膜的场发射阈值电场从注入前的18 V/μm下降到注入后的4 V/μm.金刚石膜场发射特性的提高归因于N离子注入后膜内sp2 C键含量的增加和体内缺陷带的形成，这些变化能改变膜的表面功函数，提高Feimi能级，降低电子隧穿表面的能量势垒. 关键词： 场致电子发射 N离子注入 金刚石膜 热丝化学气相沉积     

变工况对侧壁式离心泵振动特性的影响

振动是离心泵关键性能指标,低振动离心泵设计是目前研究的难点问题。本文对具有特殊结构的侧壁式压水室离心泵振动特性进行实验研究,分析了不同流量下,模型泵重要测点处振动频谱和能量的变化特性。结果表明:变工况对模型泵的中、高频信号影响较小,不同流量下低频振动能量变化明显,因此水力因素主要诱发低频振动信号;加速度频谱图中,叶频处的幅值较小,峰值信号出现在叶频的高次谐波处;低频段振动能量和泵内流场结构密切相关,非设计工况下,泵内容易出现非稳态流动结构,造成泵的振动能量不断上升;尤其在小流量工况,旋转失速导致泵的振动能量迅速增加;通过对振动能量曲线分析初步提出了低频振动能量和流量的特征函数关联式,为预测变工况对泵振动特性的影响提供理论依据。     

卫星振动对星间光码分多址系统性能的影响

卫星振动是影响星间光CDMA通信系统性能的一个重要因素.考虑多用户干扰、背景光噪音、热噪音、接收机噪音和卫星振动,给出了基于PPM信号格式的星间二维光CDMA通信系统的系统模型.采用数值分析的方法,详细分析了卫星振动对该系统误码率性能的影响.结果表明,码速率、通信波长和卫星振动都会影响星间二维光CDMA通信系统的误码率性能.当卫星振动标准偏差σ≤4×10－7时,卫星振动对系统误码率性能的影响较小;当卫星振动标准偏差σ≥1.2×10－6,卫星振动对系统误码率性能的影响很大,得到的误码率难以满足系统的通信要求,需要采用卫星振动抑制或补偿等技术提高星间二维光CDMA通信系统的误码率性能.     

振动对电视成像系统传递函数的影响研究

为了研究系统平台振动对电视成像系统传递函数的影响,通过将不同振动条件下系统的传递函数进行对比分析,利用能量积分法,建立系统平台在不同振动条件下系统传递函数仿真模型。利用快速反射镜系统和I SITE测量平台组合,对振动条件下系统传递函数进行测量和验证。仿真和实验数据结果表明:对于在研电视成像系统,当振动频率低于曝光频率时,随着系统平台振动频率的增加,系统传递函数的下降速度由静止时的0.167逐渐增加到0.237;当振动频率高于曝光频率时,随着系统平台振动频率的增加,系统的传递函数的下降速度波动性增加,并逐渐趋于在静止时的1.42倍附近。     

晶格振动对Ti-Al系统相稳定的影响

在电子结构计算的基础上,利用集团变分方法(CVM)研究了Ti-AI系统的高温相稳定,并且运用两种方法考虑晶格振动对相稳定的影响。结果发现,利用连续介质模型考虑的晶格振动对系统相稳定几乎无影响,而利用Mobius反演对势并计算晶格振动谱的方法考虑的晶格振动对系统相稳定有明显的影响,说明在讨论晶格振动对合金相稳定的影响时,晶格振动的光学模是很重要的。     

Low-frequency characteristics of human and guinea pig cochleae

Previous physiological studies investigating the transfer of low-frequency sound into the cochlea have been invasive. Predictions about the human cochlea are based on anatomical similarities with animal cochleae but no direct comparison has been possible. This paper presents a noninvasive method of observing low frequency cochlear vibration using distortion product otoacoustic emissions (DPOAE) modulated by low-frequency tones. For various frequencies (15-480 Hz), the level was adjusted to maintain an equal DPOAE-modulation depth, interpreted as a constant basilar membrane displacement amplitude. The resulting modulator level curves from four human ears match equal-loudness contours (ISO226:2003) except for an irregularity consisting of a notch and a peak at 45 Hz and 60 Hz, respectively, suggesting a cochlear resonance. This resonator interacts with the middle ear stiffness. The irregularity separates two regions of the middle ear transfer function in humans: A slope of 12 dB/octave below the irregularity suggests mass-controlled impedance resulting from perilymph movement through the helicotrema; a 6-dB/octave slope above the irregularity suggests resistive cochlear impedance and the existence of a traveling wave. The results from four guinea pig ears showed a 6-dB/octave slope on either side of an irregularity around 120 Hz, and agree with published data.     

Stochastic resonance at the periphery of auditory system: A simulation experiment

An auditory nerve fiber model is studied. The model includes the formation of the response of the basilar membrane, formation of the receptor potential of the internal hair cell, formation of the synaptic potential of the auditory nerve fiber, and transformation of the synaptic potential into a sequence of spikes. The role of this transformation, as well as the role of changes in the excitability of the fiber after the spike generation in the coding of amplitude-modulated signals is revealed for the cases of signals of medium (i.e., corresponding to the sloping part of the curve representing the mean firing rate of an auditory nerve fiber as a function of the stimulus level) and subthreshold levels. Simulated experiments show that the coding of the envelope of a medium-level amplitude-modulated signal is a dynamic process, which includes fine tuning (adaptation) of the threshold of the auditory nerve fiber to the stimulus level. The coding of the signal envelope is little affected by the slope of the dependence of the mean firing rate on the stimulus level. However, fibers with steep input-output characteristics may exhibit stochastic resonance properties. Owing to these properties, such fibers are capable of reproducing the envelope of a subthreshold modulated signal when weak noise is added to it. Ways are considered for extending the range of subthreshold signal and noise levels within which the envelope of a modulated signal is reproduced (or the phenomenon of stochastic resonance is observed).     

听觉外周计算模型研究进展

在简单介绍听觉外周特性之后,对近30年听觉外周计算模型的研究及其在语音识别领域的应用进行了评述,针对未来语音信号处理领域中听觉外周的建模,提出了一些设想;讨论了在被动声呐目标识别任务中应用听觉模型的可能性,同时,结合声呐目标识别的特点,对听觉外周模型的适用性建模研究,提出了若干建议。     

Measuring vibration characteristics at large amplitude region of materials for high power ultrasonic vibration system

This study proposes a method of estimating the mechanical quality factor of materials for high-power ultrasonic vibration systems under large vibration amplitude conditions. The quality factors of several metals as well as some polymers are measured by this method. In this method, the quality factor is calculated as the ratio of the reactive energy stored in a specimen to the dissipated energy. The dissipated energy is estimated from the input/output mechanical energy to the specimen by measurement of the vibration intensity, while the reactive energy is measured as the kinetic energy of the vibration. Then, the quality factor for the specified part can be extracted using this method. In this report, quality factors for torsional vibration were measured at about 30 kHz as functions of the vibration strain.     

An auditory periphery model for improving narrow-band noise recognition rate of underwater targets

The recognition rate of the auditory periphery features decreases when the model is used to identify underwater targets in practice. To solve this problem, an improved method based on Gammatone filter bank is proposed. Firstly, after the reason of the decreasing of the recognition results is analyzed,the mechanism of multichannel data acquisition in acoustic engineering may narrow down signal frequency range, which leads to time-frequency features distortion. Secondly, the Gammatone filter bank is implemented to simulate frequency decomposition characteristics of human ear basilar membrane. Since the class information of the underwater noise signal is mostly contained in low frequency range, the auditory features of the conventional model are interpolated and the channel number of the filter bank and the central frequency of each frequency band are adjusted accordingly to obtain a 27-dimensional feature vector of the narrow-band target signal. The adjusted model may reflect the target's timefrequency feature more precisely. Finally, the performance of the auditory features is tested by a Neural Network classifier. The experiment results show that the modified auditory model is more effective than the conventional ones. The major information contained in broadband signals is reserved and the classification ability for real targets is further enhanced. The recognition results are increased from 82.59% to 88.80%. The modified auditory features effectively improve the recognition rate for underwater target radiated noise signals.