铝合金白车身模态及刚度分析

通过有限元分析法,对某铝合金白车身结构总成进行了模拟分析。白车身弯曲刚度为8571N/mm,扭拧刚度为22575N·m,并分析了白车身的前五阶模态,其第一阶模态频率为25.4Hz,处于发动机激励范围之内。因此,以除了第一阶模态频率外的其它各阶固有频率作为约束函数对白车身内板材进行第一阶模态灵敏度分析,并以灵敏度计算结果对板材进行了厚度优化,铝合金白车身的第一阶模态频率上升至30.0Hz,脱离了发动机激励范围,提高了白车身的NVH性能。     

基于CEEMD和排列熵的矿山微震信号降噪研究

针对矿山微震信号采集过程中通常会混入高频噪声的问题,提出了基于互补集合经验模态分解(CEEMD)和排列熵的降噪方法对微震信号进行降噪处理。使用CEEMD将信号分解成从高频到低频的数个本征模态函数;计算各模态分量的排列熵值定量表征其随机性程度;通过对含噪声信息较多的IMF分量进行小波阈值降噪,并通过信号重构得到降噪后的微震信号。仿真信号和真实微震信号降噪效果表明,基于CEEMD和排列熵的降噪效果优于CEEMD和EMD降噪法,该方法可以有效去除微震信号中的高频噪声,为微震信号的进一步分析提供技术支持。     

飞剪剪切机构的模态分析

某轧钢厂切头飞剪机为曲柄摇杆机构,使用2年后,曲柄轴发生断裂。分析发现其静强度满足要求,考虑到飞剪剪切是一个动态过程,建立了剪切机构模型,进行模态分析。计算得到剪切机构在最大剪切力出现位置时的前10阶固有频率,第一阶固有频率为264．19Hz,而剪切机构的工作频率为12Hz,因此,飞剪剪切时不会发生共振,曲柄轴断裂是热处理不当造成的。     

大型直线振动筛横梁结构有限元分析

采用ANSYS有限元软件对某人型直线振动筛横梁结构进行了模态分析和谐响应分析,计算出了该振动筛的前10阶固有频率;并对该振动筛进行了谐响应分析,获得了稳态下横梁的动应力和动位移分布规律,这对于指导起重机的设计、制造、检验、管理与故障分析郁具有很重要的意义。     

高炉减压阀组有限元模态分析

为了掌握高炉减压阀组的振动特性,提高减压阀组抗振性,以某厂的高炉减压阀组为研究对象,利用SolidEdge软件建立三维模型,ANSYS - Workbench软件建立有限元模型,通过有限元计算,对其进行模态分析,得到减压阀组前六阶固有频率和振型,并提出改进措施,为减压阀组结构改进提供了理论依据.     

我国矿用振动筛机械系统动力学研究概况

为我国在矿用振动筛机械系统的振动理论、结构动强度、减振降噪措施、动力学参数计算及实验测定等方面的研究概况，提出了对矿用振动筛研究与发展趋向的看法．     

Al-Cu合金亚稳相的价电子结构分析

应用固体电子理论(EET)，对A1-Cu合金时效析出的若干亚稳相的价电子结构进行计算。结果表明，在时效初期，θ”相中Cu原子处于第七杂阶，比金属Cu的原子杂阶低，而最靠近Cu原子的A1原子则处于第五杂阶；由θ”相溶解形成相θ’时，Al原子处于第四杂阶，而Cu原子状态发生较大变化，从基体的第九杂阶上升到第十三杂阶，使得Cu原子的共价电子数有较大幅度的提高，因此形成的θ’亚稳相的最强共价键较θ”亚稳相的要强l倍，这就从价电子结构层次上解释了θ”和θ’亚稳相的热稳定性。     

高炉氧煤喷吹技术讲座(二)

4提高煤粉燃烧率4．1煤粉在风口前的燃烧为了尽可能发挥喷吹煤粉的效果，必须实现煤粉在高炉回旋区的完全燃烧。在这种情况下，燃烧的时间大约只有10ms。1992年日本住友公司使用可调式脉冲激光加热，用超高速录像机（0.17ms／图面）和超快速新型光学高温计付B应时间为0.1ms）对一粒煤粉的燃烧状态进行研究结果看出，单一颗粒的点火时间为10ms左右，从看火到燃烧终了的时间一般为25～40ms。所以煤粉从加热开始到燃烧终了只是“一瞬间”，仅仅是0.05s左右。但这OOSS对高炉风口前的煤粉运动却是很长的。如果按风口处风速200m／s计算，0.05s将…     

基于数据降噪的冷轧板形调控功效系数获取

 针对轧制过程实际数据噪声大、难以获取准确板形调控功效系数的问题,提出了一种融合集成经验模态分解(EEMD)和小波变换(WT)的数据降噪方法。将含有噪声的实际生产数据经过EEMD分解后,利用小波变换方法对噪声主导的本征模态分量(IMF)进行降噪处理,处理后的噪声分量与其余分量重构得到降噪后数据,并结合结构方程模型(SEM)计算得到板形功效系数。利用1 450 mm五机架冷连轧生产线实际数据进行试验,结果表明,EEMD-WT-SEM方法可以有效降低数据噪声,有效提升板形调控功效系数的准确性。     

铝电解槽热平衡测试计算中的几点问题

由于缺乏正规的标准，铝电解槽能量平衡测试中存在着一些概念混淆、计算方法和公式错误的情况，应引起测试工作者的注意，在测试计算前应认真制订方案，多查一些参考资料，核实所用公式、数据，避免发生失误。同时对于类似计算，由于计算机的应用，应尽可能采取精确算法。没必要采取一些非常粗糙的近似算法和经验值。     

Effects of psychoactive drugs on temporal discrimination in rats

Neuronal behavior is dependent on random inputs from a multitude of synaptic contacts on the soma and dendritic tree. Therefore, simulations of different types of noise are often required in the experimental and theoretical investigation of the properties of neurons and neuronal assemblies. The direct simulation of these noise sources by simple difference equations may therefore be quite useful and a general approach is presented in this paper. Initially, a first order model and its time-discretization are analyzed in detail, followed by a generalization to more complex models. The firing patterns of neurons are dependent on the random behaviors of their membrane potentials at the trigger zone. These depend on the propagation of the randomly occurring postsynaptic potentials from specific places on the dendritic tree or soma to the trigger zone. Different models may represent a variety of circumstances in which random membrane potentials arise at the trigger zone. Simulations of different types of noise are often required in the experimental and theoretical investigation of the properties of neurons and neuronal assemblies. The direct simulation of these noise sources by simple difference equations may therefore be quite useful and a general approach is presented in this paper. This paper presents a detailed analysis of the very useful first order model and its time discretization. The criterion used is that the autocovariance sequence of the discrete time model be a sample of the original autocovariance function. Several cases are presented which are of practical interest, including the case of constant output variance independent of the model's time constant. General models are time-discretized by the impulse response invariance method. Two applications are presented, one is related to the modeling of the synaptic currents by the alpha function instead of the delta function and the second deals with analog synaptic noise generation by D/A conversion of computer generated noise sequences.     

Review of cardiovascular effects of fluoxetine, a selective serotonin reuptake inhibitor, compared to tricyclic antidepressants

The objective of this study is to find out which mathematical model best explains the temporal fluctuations of the axial blood flow velocity waveforms in the basal arteries of the brain. Blood flow velocity time series were sampled by transcranial Doppler (TCD) examination of the middle cerebral arteries in 10 healthy volunteers. A recently developed mathematical test (surrogate data analysis) was used to examine whether the spectral Doppler maximum waveform consistent with some prespecified model (null hypothesis). We tested four different null hypothesis. 1. Uncorrelated white noise. 2. Linearly filtered noise. 3. Linearly filtered noise with a static nonlinear amplitude transformation. 4. Noisy nonlinear limit cycle. All null hypotheses except the last one could be rejected. We conclude that the TCD waveforms are best described as nonlinear limit cycle with some percentage of noise, either dynamical and/or observational, which is uncorrelated from one single oscillation to the next. These results are a strong argument to perform nonlinear analysis in future TCD studies in order to obtain a better understanding of the cerebral hemodynamics.     

Spectral frequency and the modulation of the acoustic startle reflex by background noise.

The rat's (Long-Evans) acoustic startle reflex to a high-frequency tone burst (10.5 kHz) was depressed by intense high-frequency band-pass noise (8–26 kHz) but enhanced by low frequency noise (1–2 kHz). However, contrary to the hypothesis that the depression of startle in intense background noise is produced by sensory masking, the reflex to a low-freqency tone burst (at 1 kHz) was depressed by both high- and low-frequency band-pass noise. Two additional hypotheses are offered to supplement sensory masking in order to explain the asymmetry in these data. The first is that the intratympanic reflex, which acts as a high pass filter on acoustic input, is elicited in intense backgrounds. The second is that acoustic startle reflexes elicited by intense low-frequency tones are in part elicited by their high-frequency distortion products and that these distortion products are then masked by high-frequency background noise. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adaptive streak artifact reduction in computed tomography resulting from excessive x-ray photon noise

The quality of a computed tomography (CT) image is often degraded by streaking artifacts resulting from excessive x-ray quantum noise. Often, a patient has to be rescanned at a higher technique or at a larger slice thickness in order to obtain an acceptable image for diagnosis. This results in a higher dose to the patient, a degraded cross plane resolution, or a reduced patient throughput. In this paper, we propose an adaptive filtering approach in Radon space based on the local statistical properties of the CT projections. We first model the noise characteristics of a projection sample undergoing important preprocessing steps. A filter is then designed such that its parameters are dynamically adjusted to adapt to the local noise characteristics. Because of the adaptive nature of the filter, a proper balance between streak artifact suppression and spatial resolution preservation is achieved. Phantom and clinical studies have been conducted to evaluate the robustness of our approach. Results demonstrate that the adaptive filtering approach is effective in reducing or eliminating quantum noise induced artifacts in CT. At the same time, the impact on the spatial resolution is kept at a low level.     

Perception of temporal order in speech: The role of vowel transitions.

Presented 32 undergraduates with tape loops consisting of 4 sounds. 3 types of stimuli were used to construct tape loops. These consisted of (a) consonant noise removed from consonant-vowel (cv) syllables, (b) cv syllables composed of consonant noise and the first 75 msec of vowel (including vowel transitions), and (c) transitionless cv syllables composed of consonant noise and 75 msec of steady-state vowel. Ss judged the order of the 4 sounds in each tape loop. Tape loops composed of consonant noise were most difficult to order correctly. Transitionless syllables were more difficult to order correctly than normal cv syllables of the same duration. This result suggests that vowel transitions aid in maintaining the temporal order of speech sounds in normal speech. (French summary) (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adaptive denoising and multiscale detection of the V wave in brainstem auditory evoked potentials

This paper describes a wavelet-transform-based system for the V wave identification in brainstem auditory evoked potentials (BAEP). The system combines signal denoising and rule-based localization modules. The signal denoising module has the potential of effective noise reduction after signal averaging. It analyses adaptively the evolution of the wavelet transform maxima across scales. The singularities of the signal create wavelet maxima with different properties from those of the induced noise. A non-linear filtering process implemented with a neural network extracts out the noise-induced maxima. The filtered wavelet details are subsequently analysed by the rule-based localization module for the automatic identification of the V wave. In the first phase, it implements a set of statistical observations as well as heuristic criteria used by human experts in order to classify the IV-V complex. At the second phase, using a multiscale focusing algorithm, the IV and V waves are positioned on the BAEP signal. Our experiments revealed that the system provides accurate results even for signals exhibiting unclear IV-V complexes.     

大型冷锯机噪声控制技术的试验研究

针对大型冷锯机锯切噪声大,环境恶劣,一般控制方法难于实施的特点,提出了对主要发声体锯片进行振动和噪声控制的一系列措施。并对采取这些措施的理论依据进行了讨论分析。把金属橡胶和金属纤维材料,粉体阻尼和喷水阻尼技术用于旋转锯切过程的减振降噪。各种控制方案经模型锯机试验,取得了明显的降噪效果。     

Analysis of the spatial-frequency-dependent DQE of optically coupled digital mammography detectors

The effect of optical coupling efficiency on the spatial-frequency-dependent propagation of signal and noise is considered for x-ray image detectors for digital mammography in which a phosphor screen is optically coupled to a charge-coupled device (CCD) image array. For experimental purposes, optical coupling between a Gd2O2S:Tb phosphor screen and a CCD image array was provided by relay lenses. Neutral density filters were inserted between the lenses to vary the optical coupling efficiency without altering the inherent spatial resolution. The total coupling efficiency, defined as the number of electrons (e-) recorded in the CCD per x-ray interaction in the phosphor, was calculated in each case. The modulation transfer function, and the contributions to the total noise power spectrum (NPS) of x-ray quantum noise, secondary quantum noise, and inherent detector noise were measured as a function of coupling efficiency. These data were used to calculate the spatial-frequency-dependent detective quantum efficiency [DQE(f)]. The NPS due to x-ray quantum noise had a significant spatial-frequency dependence for coupling efficiencies of more than 9 e- per x-ray interaction, but little spatial-frequency dependence for coupling efficiencies of less than 2 e- per x-ray interaction. These results indicate that to preserve high spatial-frequency values of DQE(f), and to ensure that images are x-ray quantum-noise limited at high spatial frequencies, a coupling efficiency on the order of 10 e- per x-ray interaction is required.(ABSTRACT TRUNCATED AT 250 WORDS)     

A Study of the Equipment Fault Diagnosing Method Based on EMD and Holo-spectrum

We first introduce the empirical mode decomposition (EMD) and holo-spectrum analysis.Then we decom- pose the vibration signal of the equipment by EMD, re-organize the signal closely associated with the original sig- nal, eliminate the noise signal better, and analyze the holographic re-signal spectrum, which makes the amplitude, frequency and phase combine completely, reflecting the equipment vibration morphology fully.Particularly applying a two-dimensional holo-spectrum can obtain the direction of rotation order harmonic, size, shape, and the relation- ship between order harmonic generation rotor vibrations, and so on.The traditional signal processing methods can not eliminate noise well.We apply this method to the rotor vibration signal of fault diagnosis, eliminate noise and reflect the equipment vibration characteristics well.     

Deconvolution Technique to Separate Signal from Noise in Gravel Bedload Velocity Data

A deconvolution procedure is presented to estimate the probability density function of bedload transport velocity from noisy stationary data collected using the bottom tracking feature of acoustic Doppler current profilers (aDcps). The procedure involves the optimization of a computational summation of random variables for the instrument noise (assumed to be Gaussian with zero mean) and the spatially averaged bedload velocity within the insonified area of each acoustic beam (V). The procedure was tested on two aDcp time series, measured in two different gravel-bed rivers (Fraser River and Norrish Creek). Models generated using either a semitheoretical compound Poisson-gamma distribution or an empirical gamma distribution for V were similar and did not differ significantly from the distribution of the original data. Optimized distributions for V were highly positively skewed. The instrument noise was comparable to instrument noise for aDcp water velocity measurements, i.e., an order of magnitude greater than typical bottom tracking noise. The deconvolution procedure presented herein is generally applicable for the difficult measurement problem of determining the actual signal distribution when measurements are contaminated by noise, particularly for the case of positive-valued signal contaminated by Gaussian noise. The procedure produced the first field estimates of spatially averaged bedload velocity distribution.