The roughness effect on the frequency of frictional sound

Dry sliding of two bodies in contact generates a wide range of effects like friction, wear, heat and sound among others. The main interest of this study is in the frequency characteristics of the generated sound.In the past, frequency spectrum and sound pressure level with relation to surface topography (surface roughness in particular), have been studied mainly for concentrated contacts like stylus or hemispherical tip pin on a rough surface. Studies on flat–flat contacts were mainly focused on the topography of contacting surfaces and its relation to occurrence or non-occurrence of squeal (high pitch, high sound pressure level sound) in brake systems.The present study aims to clarify the effect of surface roughness on the frequency of non-squealing frictional sound generated in dry flat–flat sliding contact.Sound was generated by the dry contact in rubbing by hand of two rectangular cross-section stainless-steel plates having similar surface roughness. The roughness of the contacting surfaces varied in the range R_z=0.8–12.4 μm. The sound spectra had 5 peaks (P₁, P₂, P₃, P₄ and P₅) in order of increasing frequency and it was found that the peak frequency was shifted when the roughness of the rubbed surfaces changed. The first peak P₁ was most sensitive to change of surface roughness and it shifted from 3.0 to 4.5 kHz when the maximum surface roughness changed from R_z=10.9 to . When the surface was relatively rough, this peak was close to the first bending natural frequency of the plate at 2.377 kHz.     

The use of frequency and wavelet analysis for monitoring surface quality of wood machining applications

The research described in this study is part of a project to provide the technology and theory to quantify surface quality for a variety of wood and wood-based products. The ultimate goal is to provide a means of monitoring trends in surface quality, which can be used to discriminate between "good" products and "bad" products (the methods described in this research are not intended to provide "grading" of individual workpieces) as well as to provide information to the machine operator as to the source of poor-quality machined surfaces. This research investigates the use of both frequency domain analysis as well as the more advanced joint time frequency analysis (JTFA). The disadvantages of traditional frequency analysis as well as the potential of the JTFA are illustrated. Sample surface profiles from actual machining defects were analyzed using traditional frequency analysis. A surface with multiple machining defects was analyzed with both traditional frequency analysis and JTFA (harmonic wavelet). Although the analysis was empirical in nature, the results show that the harmonic wavelet transform is able to detect both stationary and non-stationary surface irregularities as well as pulses (localized defects).     

A new concept in underwater high fidelity low frequency sound generation

This article reports on a new type of system for high fidelity underwater sound generation (patent pending PT105474). The system includes an underwater sound actuator and the corresponding electronic driver. The sound is generated by a rigid plate that is actuated (both for positioning/dumping and excitation) using purely electromagnetic forces, thus, avoiding the use of any elastic membrane. Since there is no compressible air inside the device, which is flooded by water, the operation of this device is independent from depth, broadening its applications to any water pressure. Characterization of the frequency response, the radiation characteristics, and the dynamic range of this new device for underwater sound generation is presented.     

频率调制随机共振的数值分析

对随机共振技术运用于强噪声背景下的弱信号检测进行了研究,提出了用频率调制的方法,实现了在大参数情况下从强噪声中检测微弱周期信号.数值计算结果表明,该方法可形成低频信号,该低频信号通过双稳系统易产生随机共振,能使微弱的故障信号特征突出、明显,易于捕捉.     

Pattern-recognition analysis of sound radiation in metal cutting

Pattern-recognition analysis of sound radiation was developed as a basis for monitoring the metal-cutting process. The sound-pressure signals radiated during cutting under fixed conditions were recorded using a sharp tool, a worn tool and a broken tool. A round bar of heat-treated AISI 4340 steel was machined in cylindrical turning, using a titanium-carbide-coated cutting tool. The spectral components in the 0–10 kHz range were used as features. Using resubstitution, signals coming from sharp and worn tools were easily distinguished, resulting in a 100% classification with just two features, being the average of the low (0–5 kHz) and high (5–10 kHz) frequency ranges. With tool breakage, two acceptable classifications were obtained using independent testing, the first with a performance of 100%, 75% and 100% for sharp, worn and breakage signals respectively, using nine features, and the second with 80%, 88% and 80%, using eight features.     

Limitations on use of ZDDP as an antiwear additive in boundary lubrication

Wear tests on rubbing elements under various contact pressures, oil temperatures and surface roughness were performed to elucidate the limitation conditions on antiwear performance of a typical zinc dialkyl dithiophosphate (ZDDP) added to a paraffin base oil. The analysis results indicate that the antiwear performance of ZDDP depends on the rates of recovery and growth of effective surface films. If these rates exceed that of scraping the films off the rubbing surfaces, antiwear performance is evident. However, the rates of recovery and growth of surface films are influenced by some essential factors, including the oil temperature, contact pressure and the surface roughness and hardness of rubbing elements. Under some suitable conditions, ZDDPs show favorable antiwear performance, but under some severe conditions, such as high pressure (over 90 MPa), high temperature (over 200 °C) with an insufficient concentration of ZDDP and the rubbing of a rough and harder surface on a softer surface, the antiwear performance of ZDDPs is negligible.     

On the use of the transmissibility concept for the evaluation of frequency response functions

The dynamic characteristics of a structure are often derived from a set of measured frequency response functions (FRFs). However, it may happen that the measurement of certain FRFs is impossible, as they are related to some points of interest that may become physically inaccessible in operational conditions. In this circumstance, it is useful to have some tools that can provide the prediction of such dynamic information. The transmissibility concept can play an important role to circumvent these situations. In fact, there are important properties associated to the transmissibility—the relationship between two sets of responses, for a given set of applied forces, extended to a general multiple degree-of-freedom system. In this paper, some important properties of the transmissibility matrix will be presented. Additionally, it will be shown that if a modification is operated on the original system - using both theoretical and experimental models - it is possible to estimate the FRFs associated to the unknown co-ordinates, without the necessity of measuring the responses on those co-ordinates.     

复杂度在心音信号分析中的应用

有效提取心音信号中的第1、2心音(S1和S2)一直是心音信号分析的关键点。结合心音信号自身特点,把复杂度引入到心音信号分析中,成功地提取了S1和S2,并获取了3项医学指标:心率、第1心音与第2心音幅值比(S1/S2)和舒张期与收缩期时限比(D/S),同时给出了复杂度运算过程中2个关键指标的参考值。经过验证对比,该方法对幅度变化具有较好的鲁棒性,不依赖于信号的频率特征,能较好区分信号不同成分,为后期工作带来便利。     

Conditioning of FRF measurements for use with frequency based substructuring

Frequency based substructuring approaches have been used for the generation of system models from component data. While numerical models show successful results, there have been many difficulties with actual measurements in many instances. Previous work has identified some of these typical problems using simulated data to incorporate specific measurement difficulties commonly observed along with approaches to overcome some of these difficulties.This paper presents the results using actual measured data for a laboratory structure subjected to both analytical and experimental studies. Various commonly used approaches are shown to illustrate some of the difficulties with measured data. A new approach to better condition the measured functions and purge commonly found data measurement contaminants is utilized to provide dramatically improved results.Several cases are explored to show the difficulties commonly observed as well as the improved conditioning of the measured data to obtain acceptable results.     

Comparison of median frequency between traditional and functional sensor placements during activity monitoring

Long-term monitoring is of great clinical relevance. Accelerometers are often used to provide information about activities of daily living. The median frequency (f_m) of acceleration has recently been suggested as a powerful parameter for activity recognition. However, compliance issues arise when people need to integrate activity recognition sensors into their daily lives. More functional placements should provide higher levels of conformity, but may also affect the quality and generalizability of the signals. How f_m changes as a result of a more functional sensor placement remains unclear. This study investigates the agreement in f_m for a sensor placed on the back with one in the pocket across a range of daily activities. The translational and gravitational accelerations are also computed to determine if the accelerometer should be fused with additional sensors to improve agreement. Twelve subjects were tested over four tasks and only the “vertical” x-axis showed a moderate agreement (Intraclass Correlation Coefficient of 0.54) after correction for outliers. Generalizability across traditional and functional sensor locations might therefore be limited. Differentiation of the signal into a translational and gravitational component decreased the level of agreement further, suggesting that combined information streams are more robust to changing locations then singular data streams. Integrating multiple sensor modalities to obtain specific components is unlikely to improve agreement across sensor locations. More research is needed to explore measurement signals of more user friendly sensor configurations that will lead to a greater clinical acceptance of body worn sensor systems.     

On the use of TEM cells for the calibration of power frequency electric field meters

This paper focuses on the performances of TEM cells when used in the calibration of power frequency environmental electric field meters. The spatial non-uniformity of the electric field inside a TEM cell is analyzed through experimental investigations and three-dimensional Boundary Element modeling to evaluate the field experienced by the sensing elements of actual 3D meter probes. The perturbation caused by the probe support is also taken into account. The uncertainty component associated with the spatial non-uniformity in the volume taken up by typical power and low frequency field probes is estimated. The field non-uniformity is also evaluated in relation to the use of TEM cells of reduced size. Finally, the field non-uniformity is exploited to predict the performance of an actual field meter operating in significant field gradients.     

The use of displacement threshold for switching frequency strategy for structural vibration mitigation

This paper presents a study of controllable real-time frequency shift using a fluid pin damper, so called ‘smart pin’, mounted at a beam-column connection. Unlike the stationary frequency shifter, the pin can increase or decrease the rotational stiffness of the connection, leading to an actively adjustable structural frequency due to real-time responses of polarised magneto-rheological (MR) fluid, whose rheological properties can change in milliseconds. The feedback to the pin damper governs the structural frequency changes. To demonstrate this concept, a single storey plane steel frame model with one hinge and one ‘smart pin’ damper, mounted at each beam-column connection and subjected to two scaled earthquake excitations, namely El-Centro 1940 and Northridge 1994, which respectively represent near- and farfield excitations, was tested using the shake table at the University of Technology, Sydney (UTS) structures laboratory, for ‘proof-of-concept’ investigation. Further, the dynamic performance of the model using a proposed switching strategy with a displacement threshold as an indicator for alternately supplied current level (flip-flop) was examined, assuming the earthquake records were known. The results showed some potential use of this control technique for structural vibration mitigation, however, further study to optimize the performance of the switching strategy is still required. An erratum to this article is available at .     

肺癌蛋白质组学常用研究方法

肺癌是死亡率较高的一种常见恶性肿瘤。因缺乏有效的早期诊断手段,多数患者诊断时已处于中晚期,预后很差。近年来,通过对肺癌患者进行相关的蛋白质组学研究,搜寻与肺癌相关的特异性肿瘤标志物,为临床肺癌的早期诊断、评估和预后提示许多新的发展方向。本文主要介绍与肺癌蛋白质组研究相关的实验技术,并综述近期研究进展。     

声强技术在有氧健康机噪声源定位与识别中的应用

利用声强技术,有针对性地对有氧健康机设计声强实验,并根据实验结果,找出振动的优势频率,从而正确识别噪声源。     

Optimal conditions for the use of correspondence analysis for element determination in EELS images

Correspondence analysis is used for the determination of element localization and element concentration in electron energy–loss imaging. The introduction of a new method for the quantification of element concentration embedded in the protocols of correspondence analysis may be regarded as a useful replacement of the power–law estimation technique, especially in regions of the spectrum where the latter method cannot be used. Conditions for the optimum use of the method are established.     

Limitations of the terahertz photomixer

In the paper, Fourier transform has been used for calculations of a refractive index of dielectric samples measured in the terahertz photomixer arrangement. We considered measurement limitations caused by a sampling frequency and a photomixer bandwidth.     

交流断路器用于直流电路和高频电路的有关问题分析

阐述了交流断路器使用于直流电路和高频电路的适应性问题 ,主要技术性能指标可能的变化以及接线的注意点等     

SEM search for sound production and sound perception organs in a variety of Drosophila species

The discovery of new song types in Hawaiian Drosophila species has raised a question of alternative sound production and sound perception mechanisms in Drosophila. For example D. disjuncta males, which produce song with a carrier frequency of 5,000-6,000 Hz, do not vibrate their wings but only tremble them in a very small amplitude while singing. In our SEM search we found at the wing base of the flies of this species a special structure which could play a part in song production. Our search for auditory sense organs in Drosophila species revealed that the aristae on fly antennae are structurally not as simple as has been assumed. In Hawaiian D. planitibia subgroup species, the fly aristae are more regular than in other Drosophila species and they are also covered with small hairs. We did not find any sign of tympanic hearing organs in any of the studied species, but we discovered on fly legs and wings sensilla which could play a part in sound/vibration perception. Our SEM survey provides a good starting point in the search for alternative pathways for sound production and perception via transmission electron microscopy combined with behavioral studies and electrophysiological recordings in Hawaiian Drosophila species.     

基于声波传播的结构阻抗研究

从结构的振动和力学分析在实际生产过程中的应用出发,基于波在弹性结构中的传播和振动分析的基础上,建立波在弹性结构中传播的力学平衡方程,提出了阻抗和迁移率的概念.通过对波在弹性结构中传播时元素的应力和应变进行分析,得到元素的力学平衡方程并求解,得到波在弹性结构中传播的阻抗.     

重复轨迹运动迭代学习控制的频域分析

应用频域分析方法讨论了一类闭环迭代学习算法的收敛条件和性能,指出其比Arimoto开环迭代学习算法具有明显的优越性,并在讨论迭代收敛条件的基础上给出了闭环迭代学习算法的频域设计方法.