交流接触器集成控制与仿真

将集成控制技术引入交流接触器的控制中,以智能功率芯片为核心,集成跨周期调制电路和功率开关管,以132 k Hz的高频工作模式,对交流接触器进行闭环控制。使用Multisim和Lab View软件,建立智能控制下的接触器闭环机电一体化仿真系统。通过仿真系统分析瞬态特性,合理设计控制模块的工作模式,从底层分析高频工作方式引起电子器件产生的噪声及抑制措施,达到对电磁机构动作特性的良好控制,试验验证了集成方案的可行性。

国外单缸风冷柴油机结构特点分析

本文较全面地分析了国外八十年代以来开发的一些小型单缸风冷柴油机各系统的结构特点,对我国开发新一代风冷柴油机与产品改进设计均有一定的参考价值.

A Novel Method to Compensate the Sigma-Delta Shaped Noise for Wide Band Fractional-N Frequency Synthesizers

A novel method to partially compensate sigma-delta shaped noise is proposed. By injecting the compensation current into the passive loop filter during the delay time of the phase frequency detector（PFD）,a maximum reduction of the phase noise by about 16dB can be achieved. Compared to other compensation methods,the technique proposed here is relatively simple and easy to implement. Key building blocks for realizing the noise cancellation,including the delay variable PFD and compensation current source, are specially designed. Both the behavior level and circuit level simulation results are presented.

HBT's High Frequency Noise Modeling and Analysis

A T equivalent high frequency heterojunction bipolar transistor (HBT) noise model is reported.This model is derived from Hawkins noise model commonly used in Si BJT.The main modifications include the influence of the ideality factor,emitter resistance,intrinsic base collector capacitance,extrinsic base collector capacitance and other parasitic elements of HBT represented in equivalent circuit topology.In order to calculate accurate noise parameters from the equivalent circuit,the noise correlation matrix method is used to avoid any simplifications generated in circuit transformations and complex noise measurements.The analysis of the influence of the equivalent circuit elements on the minimum noise figure is reported,the results of analysis agree well with the physics explanations.By means of the formulae derived from device physics of HBT,the influence of device parameters on the minimum noise figure is also represented.

A novel reaching law approach of quasi-sliding-mode control for uncertain discrete-time systems

A novel discrete-time reaching law was proposed for uncertain discrete-time system,which contained process noise and measurement noise.The proposed method reserves all the advantages of discrete-time reaching law,which not only decreases the band width of sliding mode and strengthens the system robustness,but also improves the dynamic performance and stability capability of the system.Moreover,a discrete-time sliding mode control strategy based on Kalman filter method was designed,and Kalman filter was employed to eliminate the influence of system noise.Simulation results show that there is no chattering phenomenon in the output of controller and the state variables of controlled system,and the proposed algorithm is also feasible and has strong robustness to external disturbances.

Research of multi-channel impulse noise detection algorithms based on template

Attenuating the undesired audio noise generated by impulse noise,such as shot and scream of brakes,is specially useful for real-time audio recording of TV or broadcasting live report.On the basis of impulse noise detection algorithms based on template,this paper improves the method of establishing the template by using multiple microphones to pick up noise corrupted signals and impulse noises in the environment.The universal of thresholds is found and a detection algorithm with slope as the characteristic is proposed by comparing a variety of feature extraction algorithms.The proposed algorithm gets a significant improvement in testing speed and accuracy,which means it is suitable for real-time processing of audio signals.

An imaging condition for reverse time migration based on wavefield decomposition

Reverse Time Migration(RTM) is a high precision imaging method of seismic wavefield at present,but low-frequency noises severely affect its imaging results.Thus one of most important aspect of RTM is to select the proper noise suppression method.The wavefield characteristics of the Poynting vector are analyzed and the upgoing,downgoing,leftgoing and rightgoing waves are decomposed using the Poynting vector of the acoustic wave equation.The normalized wavefield decomposition cross-correlation imaging condition is used to suppress low-frequency noises in RTM and improve the imaging precision.Numerical experiments using the Mamousi velocity model are performed and the results demonstrate that the upgoing,downgoing,leftgoing and rightgoing waves are well decomposed using the Poynting vector.Compared with the normalized cross-correlation imaging and Laplacian filtering method,the results indicate that the low-frequency noises are well suppressed by using the normalized wavefield decomposition cross-correlation imaging condition.

Noise propagation characteristics of underground equipment in coal mines

On the basis of the survey of underground noise in Jinggezhuang and Donghuantuo mines, Kailuan Group, noise radiation intensity, noise propagation properties and noise frequency-spectrum characteristics of underground equipment were studied at different work conditions. The result indicates that the noise source intensity surpasses the noise limit requirement of 85 dBA completely. Nearly 70% noise sources exceed the noise limit of 90 dBA, and some are over 100 dBA. Noise attenua- tion in semi-free field environment on the ground is significantly different from underground far-field environment of noise source in coal mines. Noise of these regions, where staffs are long and highly concentrated, exceeds 85 dBA, the basic noise limit. The noise frequency-spectrum presents the wideband characteristics. Especially in the main frequency of the language communication 500, 1 000 and 2 000 Hz, the octave band of noise performs obviously.

Research on mine noise sources analysis based on least squares wave-let transform

In order to determine the characteristics of noise source accurately, the noisedistribution at different frequencies was determined by taking the differences into accountbetween aerodynamic noises, mechanical noise, electrical noise in terms of in frequencyand intensity.Designed a least squares wavelet with high precision and special effects forstrong interference zone (multi-source noise), which is applicable to strong noise analysisproduced by underground mine, and obtained distribution of noise in different frequencyand achieves good results.According to the results of decomposition, the characteristicsof noise sources production can be more accurately determined, which lays a good foundationfor the follow-up focused and targeted noise control, and provides a new methodthat is greatly applicable for testing and analyzing noise control.

Processing Seismic Ambient Noise Data to Obtain Reliable Surface Wave Dispersion Measurements

Ambient noise tomography is a rapidly emerging field of seismological research. This paper presents the current status of ambient noise data processing and its development history over the past several years, with the intention to explain and justify this development through salient examples. The ambient noise data processing procedure can be divided into four principal phases： ① single station data preparation; ② cross- correlation and temporal stacking; ③ measurements of dispersion curves （ performed with frequency-time analysis for both group and phase speeds） ; ④ quality control, including SNR analysis and selection of the acceptable measurements. In addition, we provide a specific solution for a better use of the seismic station data to ambient noise study.

A 5.4mW Low-Noise High-Gain CMOS RF Front-End Circuit for Portable GPS Receivers

This paper describes a CMOS low noise amplifier （LNA） plus the quadrature mixers intended for use in the front-end of portable global positioning system （GPS） receivers. The LNA makes use of an inductively degenerated input stage and power-constrained simultaneous noise and input matching techniques. The quadrature mixers are based on a Gil- bert cell type. The circuits are implemented in a TSMC 0.18μm RF CMOS process. Measurement results show that a voltage conversion gain of 35dB is achieved with a cascade noise and an input return loss of - 22.3dB. The fully differential figure of 2.4dB,an input ldB compression point of - 22dBm, circuits only draw 5.4mW from a 1.8V supply.

Ultrasonic frogs call at a higher pitch in noisier ambiance

The ultrasonic communication in Concave-eared torrent flogs Odorrana tormota is believed to be an adaptation to avoid masking by the intense low-frequency noise of the rushing stream in their habitat. The acoustic adaptation hypothesis for ultrasonic origin predicts that some organisms subjecting to persistent acoustic interference from broadband, low-frequency en- vironmental noise, might shift their signal frequency upward into frequency bands with lower noise energy. In other words, low-frequency environmental noise might cause upward shifts of species＇ vocalization frequencies making their signals more conspicuous. Presently, it is unclear whether male O. tormota adjust their signal features in response to a change in the ambient noise level. We tested the prediction of the acoustic adaptation hypothesis by recording the vocalizations of male O. tormota in- habiting two streams with different background noise levels in Huangshan in central China and comparing their call features in- cluding the fundamental frequency （F0）. Results showed that the spectrotemporal characteristics of the vocal signals of males in the two habitats were indifferent, except the duration of the call harmonic segments and three parameters related to the call fun- damental frequency （F0）. In terms of the F0, the pooled and individual frog data showed that flogs inhabiting the noisier habitat tended to emit calls having higher F0. The higher F0 increases the signal-to-noise ratio, thus benefiting the detection of vocaliza- tion. Thus, similar to several anuran species, concave-eared torrent frogs also display noise-dependent adjustment of vocal pitch in their vocalizations for making them more audible

Suppression of strong random noise in seismic data by using time-frequency peak filtering

Time-frequency peak filtering (TFPF) is highly efficient in suppressing random noise in seismic data. Although the hypothesis of stationary Gaussian white noise cannot be fulfilled in practical seismic data, TFPF can effectively suppress white and colored random noise with different intensities, as can be theoretically demonstrated by detecting such noise in synthetic seismic data. However, a "zero-drift" effect is observed in the filtered signal and is independent of the average power and variance of the random noise, but related to its mean value. Furthermore, we consider the situation where the local linearization of the seismic data cannot be satisfied absolutely and study the "distortion" characteristics of the filtered signal using TFPF on a triangular wave. We found that over-compensation is possible in the frequency band for the triangular wave. In addition, it is nonsymmetrical and has a relationship to the time-varying curvature of the seismic wavelet. The results also present an improved approach for TFPF.

Robust and efficient quantum private comparison of equality with collective detection over collective-noise channels

We present a protocol for quantum private comparison of equality(QPCE) with the help of a semi-honest third party(TP).Instead of employing the entanglement,we use single photons to achieve the comparison in this protocol.By utilizing collective eavesdropping detection strategy,our protocol has the advantage of higher qubit efficiency and lower cost of implementation.In addition to this protocol,we further introduce three robust versions which can be immune to collective dephasing noise,collective-rotation noise and all types of unitary collective noise,respectively.Finally,we show that our protocols can be secure against the attacks from both the outside eavesdroppers and the inside participants by using the theorems on quantum operation discrimination.

Characterization and modeling of wind-dominated ambient noise in South China Sea

The action of wind on the sea surface plays an important role in the noise generation mechanism.Sea surface wind speed can be estimated accurately provided there is an accurate understanding of the relationship between the ocean ambient noise and wind speed.Many measurements and analyses of the wind dependence of ambient noise have been conducted.The approximate empirical rule given by Wenz[1]states that in the frequency band between 0.5and 5 kHz,the ambient sea-noise spectrum levels decrease

Influence of Diffuser on Aerodynamic Noise of a Forward Curved Fan

In order to clarify the influence of a diffuser on the charactersfics of a forward curved fan, the influence of the bare ratio and the outlet angle on the characteristics of the fan were measured through an experiment performed with an actual fan as well as through a numerical simulation, respectively. The mechanism of the discrete fre- quency noise generated by the separated flow of the diffuser was analyzed. The optimized bare ratio was ap- proximately 17%. The flow separated inside of the diffuser generated discrete frequency noise owing to the inter- action between the reversed flow from the diffuser and the impeller rotating at the blade passing frequency. The diffuser outlet angle influenced the pressure ratio more than that by the bare ratio. Furthermore, it was confirmed that restraining the separation in the diffuser effectively decreases the fan noise.

Effect of Boundary Layer Trip on Reduction of Jet Noise in Over-Expanded Nozzle Flow

A flow resonance accompanied by the emission of acoustic tones occurs in an over-expanded convergent-divergent(C-D) nozzle when operated at comparatively low pressure ratios. This phenomenon is distinguished from conventional screech tones and is referred to as "transonic tones". In contrast to screech tones, the peak resonant frequency for transonic tones increases with pressure ratio; the peak sound pressure level exceeds 110 d B. In this study, we investigated the basic characteristics of transonic resonance and tones using a circular C-D nozzle in an anechoic room. The effects of the boundary layer trip were also evaluated using a tripping wire for the suppressing transonic resonance and tones. The results of acoustic measurements show that several predominant peaks correspond to transonic tones. However, the boundary layer trip inside the nozzle effectively eliminated these tones and suppressed the unsteadiness of the flow inside the nozzle.