Search

Inadequate and erratic power supplies mean small businesses use electric generators for alternative power. The authors' goal in the study described here was to assess noise from electric generators and impacts in the commercial areas of Agbowo and Ajibode in Ibadan, Nigeria. Noise levels (A-weighted decibels [dBA]) were measured over 12 weeks, three times a day, during the 2010 dry season using a sound level meter. A questionnaire was administered (515 respondents; 304 in Agbowo, 211 in Ajibode) and audiometric measurements were conducted on 40% of respondents. Mean noise levels varied by source (104 ± 7.7 dBA [diesel], 94.0 ± 6.3 dBA [petrol]) and were highest midday (90.6 ± 5.3 dBA [Agbowo], 70.9 [+ or -] 6.2 dBA [Ajibode]). Mean noise levels in Agbowo (78.5 ± 3.9 dBA) and Ajibode (65.7 ± 4.4 dBA) exceeded World Health Organization guidelines (65 dBA) for outdoor commercial environments. Working and living in Agbowo was significantly associated with current evidence of hearing impairment (odds ratio: 6.8, 95% confidence interval: 3.4-13.7). Reducing exposure to noise from electric power generators serving urban small businesses and homes is warranted., Although most of the information presented in the Journal refers to situations within the United States, environmental health and protection know no boundaries. The Journal periodically runs International Perspectives to [...]

Broadband shock-associated noise is a component of jet noise generated by supersonic jets operating offdesign. It is characterized by multiple broadband peaks and dominates the total noise at large angles to the jet downstream axis. A new model is introduced for the prediction of broadband shock-associated noise that uses the solution of the Reynolds-averaged Navier-Stokes equations. The noise model is an acoustic analogy based on the linearized Euler equations. The equivalent source terms depend on the product of the fluctuations associated with the jet's shock-cell structure and the turbulent velocity fluctuations in the jet shear layer. The former are deterministic and are obtained from the Reynolds-averaged Navier-Stokes solution. A statistical model is introduced to describe the properties of the turbulence. Only the geometry and operating conditions of the nozzle need to be known to make noise predictions. This overcomes the limitations and empiricism present in previous broadband shock-associated noise models. Results for various axisymmetric circular nozzles and a rectangular nozzle operating at various conditions are compared with experimental data to validate the model. DOI: 10.2514/1.J050560

The estimation and the calculation of the acoustic sound of electric machinery are of particular interest nowadays. Various approaches have been presented, relying either on analytical or on numerical models. The analytical models presented here are based on the electromagnetic-field theory. Numerical models are applied to derive the exciting forces stemming from various sources and effects. The numerical results have to be verified. Hence, they are compared with the physically based analytical results. The radiated noise depends directly on the surface deformation of the machine. Therefore, the analysis is focused on the structure-dynamic vibration. The combined analysis presented here allows for the reduction of vibration and noise, optimizing the coupling of the machine's stator and housing. The studied induction machine's housing is mounted with six spiral-steel springs to the stator. With the presented method, the impact of different numbers of springs is analyzed exemplarily. Index Terms--Audible noise, deformation, finite-element method (FEM), induction machine, structure dynamics, vibrations.

Purpose: Significant threshold differences on retest for pure-tone audiometry are often evaluated by application of ad hoc rules, such as a shift in a pure-tone average or in 2 adjacent [...]

The problem of assessing the noise amplitude affecting remotely sensed hyperspectral images and the corresponding signal-to-noise ratio is discussed. An original algorithm for noise estimation, which performs the analysis of image bit-planes in order to assess their randomness, is described. Differently from more traditional signal-to-noise estimators, which need a homogeneous area in the concerned image to isolate noise contributions, this estimator is almost insensitive to scene texture, a circumstance that allows the developed method to carefully assess the noise amplitude of nearly any observed targets. The developed algorithm has been compared with the well-known noise estimator scatterplot method, for which a novel implementation based on the Hough transform is presented. Hyperspectral and multispectral data cubes collected by the following aerospace imagers, MIVIS, VIRS-200, and MOMS-2P on PRIRODA, have been utilized for investigating the performance of the two considered estimators. Outcomes from processing synthetic and natural images are presented and discussed along this paper. Index Terms--Bit-plane analysis, Hough transform, hyperspectral remote sensing, image processing, noise amplitude, scatterplot, signal-to-noise ratio (SNR).

The purpose of the present theoretical study was to examine the spatial resolution of electroencephalography (EEG) by means of the accuracy of the inverse cortical EEG solution. The study focused on effect of the amount of measurement noise and the number of electrodes on the spatial resolution with different resistivity ratios for the scalp, skull and brain. The results show that if the relative skull resistivity is lower than earlier believed, the spatial resolution of different electrode systems is less sensitive to the measurement noise. Furthermore, there is then also greater advantage to be obtained with high-resolution EEG at realistic noise levels. Index Terms--High-resolution electroencephalography (EEG), measurement noise, skull resistivity, spatial resolution, spherical head model.

We have analyzed and experimentally demonstrated the performance of a wavelength-locked Fabry-Perot laser diode (FP-LD) with a spectrally sliced FP-LD as an external-injection optical source. A high side-mode suppression ratio exceeding 30 dB was obtained, and the noise characteristic of the wavelength-locked FP-LD was analyzed in terms of both mode partition noise and interferometric noise. The measured relative intensity noise had a minimum value of -140 dB/Hz. We also investigated the transmission characteristics such as the Q factor and extinction ratio for a 622 Mbits/s and 2.5 Gbits/s baseband digital signal. OCIS codes: 060.2360, 060.2340, 060.2330, 060.4510.

Partial discharges (PD) generate wideband radio frequency interference and, consequently, can be detected using radio receiving equipment. Due to the advances in ultra-high-speed sampling equipment, it is possible to accurately measure the propagation of the PD wavefront as it passes through a 4 element antenna array. From these measurements, the three-dimensional position of the PD source can be calculated using an iterative algorithm. The locating equipment is suitable for use within the vicinity of energized high-voltage plant and can locate sources up to 15 m from the array. Results are presented showing the location ability of the equipment under laboratory and field conditions. A significant advantage is the ability to detect PD sources in energized plant without the need for outages or electrical connections. Index Terms--Condition monitoring, digital monitoring, impulsive noise, partial discharge, radiometric monitoring.

Seasonal and non-seasonal data are frequently observed with noise. For instance, the time series can have irregular abrupt changes and interruptions following as a result of additive or temporary change outliers caused by external circumstances. Equally, the time series can have measurement errors. In this paper we analyse the above types of data irregularities on the behavior of seasonal unit root tests. Outliers and measurement errors can seriously affect seasonal unit root inference and it is shown how the distortion of the tests will depend upon the frequency, magnitude, and persistence of the outliers as well as on the signal to noise ratio associated with measurement errors. Some solutions to the implied inference problems are suggested and shown to work in practice. JEL classification: C12; C2; C22 Keywords: Seasonal unit roots; HEGY tests; Additive outliers; Measurement errors; Brownian motion

A custom simulation tool that combines HSPICE and MATLAB to enable time-domain noise analysis is reported. The simulation technique is based on computing the statistics of a random process by ensemble averaging and is applicable to both linear time-invariant (LTI) and linear time-variant (LTV) systems. MATLAB is used to generate a set of representative noise signals, which are imported into HSPICE for simulation. Once the simulations are complete the results are read back into MATLAB and ensemble statistics are calculated. The MATLAB-generated noise signals have a user-defined white-noise floor and flicker-noise corner frequency and thus are suitable for modeling a wide variety of electronic components, including CMOS transistors and resistors. Simulation results of the time-dependent output noise of a gated integrator and the timing resolution of a gated integrator/comparator detector are presented to highlight both the utility and the versatility of the tool. Index Terms--Autocorrelation, digital filter, flicker noise, SPICE, transient noise analysis, white noise.

There has been an increasing demand for a quiet induction motor. Electromagnetic noise is jarring to the ear. Most offensive electromagnetic noise is generated when the natural frequencies of the stator coincide with or are close to the frequencies of the magnetomotive forces. In this paper, electromagnetic noise is calculated by boundary element method (BEM) program using the electromagnetic forces of Maxwell Stress. The natural frequency and behavior of the stator are calculated by mechanical finite element method (FEM), considering the contact between stator core and frame. Spring elements are introduced between the stator frame and the stacked core. Vibration is calculated by mechanical FEM. Calculated and experimental noise level were within 3 dB(A) at 1200 and 4080 Hz. Index Terms--Contact condition, induction motor, natural frequency, noise.

In this article, I critically review some of the claims and analyses made by Hooker (J. Int. Money Financ. 19 (2000) 583), in his study of the Cagan hyperinflation model. I argue that: (i) contrary to what Hooker claims, cointegration tests can be used to discriminate between bubbles and no bubbles; (ii) contrary to Hooker's claim, his empirical results for the interwar European hyperinflations do not in general imply that the Cagan model is misspecified; (iii) although Hooker's analyses build directly on the Durlauf and Hall (Bounds on the variances of specification errors in models with expectations. NBER Working Paper 2936, Massachusetts, Cambridge, 1989) methodology, he neglects an important part of that methodology, namely the measurement of the magnitude of noise. I present such measures, and together with reported cointegration tests, the noise measures help reinterpreting Hooker's empirical results. JEL classification: E31; E41; C52 Keywords: Cagan model; Cointegration; Measurement of noise

Noise rejection, defect identification and degradation diagnosis in on-field partial discharge measurements are sought by industry, but hardly achieved in practice. This paper presents tools for automatic noise suppression in measurements performed by ultra wide band digitizers, able to record a large quantity of partial discharge (PD) pulse waveforms. Noise and PD signals are split in different classes on the basis of their shape by means of a fuzzy classifier. Tools used for establishing whether a given class of recorded signals is due to external noise or not are proposed. As an example, two kinds of noise are considered: random noise and rectifier-generated noise. A companion paper will explain how the same classification tools can be employed for the purpose of defect identification. Index Terms--Partial discharges, noise measurement, noise suppression, random noise, rectifier-generated noise, cross talk, identification.

Several techniques to increase the accuracy and to reduce the variance of the noise power spectrum (NPS) measurement for digital X-ray imaging systems are investigated. These techniques include: 1) averaging the outputs from subblocks of the entire image; 2) averaging the two-dimensional NPS data along a circular route centered on the origin of spectral domain; and 3) masking a window function on each subblock before Fourier transforms. Techniques 1) and 2) are used mainly to reduce the variance of the NPS measurement. Technique 3) serves to improve the accuracy of the final result. Experiments with two different charge-coupled device-based X-ray imaging systems demonstrated that the precision and accuracy of the NPS measurement could be significantly improved using these techniques. The impact of the image partition for averaging is discussed and the corresponding NPS estimations are presented for the number of subblocks ranging from 4 to 64. The effect of masking on the NPS is also studied using four different window functions. Index Terms--Charge-coupled detector, digital X-ray imaging, noise power spectrum, subblock partition, window function.

The effect of anomalously low cross-spectrum voltage noise density in a two-channel noise measurement system (NMS) is examined, experimentally and theoretically. It is shown that the effect occurs when two thermal noise sources with matched intensities operate at the inputs of a two-channel NMS.

The concepts of multiplicative stochastic perturbations and noise-induced transitions are applied to a quasi-geostrophic [beta]-plane model of barotropic flow over topography. The spectral three-component low-order representation of this configuration yields the Charney-DeVore (CDV) model. The externally prescribed damping of the system is allowed to scatter around a mean value. The stochastic representation of the damping term leads to a multiplicative stochastic forcing. The Fokker-Planck equation and the stochastic differential equation of the low-order CDV model are solved numerically. It is found that the qualitative behavior of the system is a function of the multiplicative noise level. In particular, the effect of multiplicative noise is not simply a smoothing of the probability density function, as it would be for pure additive noise. Rather, multiplicative noise leads to the high-index state being favored over the low-index state. The concept of noise-induced transitions explains this behavior. The noise-induced transition of the stochastic low-order model is confirmed by numerical integrations of a corresponding gridpoint model with many more degrees of freedom than the spectral model. It is suggested that the statistics of the unresolved physical processes could be an important factor in understanding the behavior of midlatitude large-scale atmospheric dynamics.

We are developing superconducting transition-edge bolometers for far-infrared and millimeter wavelengths. The bolometers described here are suspended by thin legs of silicon nitride for thermal isolation. At frequencies between 200 mhz and 10-50 Hz these devices show white noise at their thermal fluctuation limit (NEP [approximately equal to] [10.sup.-17] W/[square root of Hz]). At higher- frequencies a broad peak appears in the noise spectrum, which we attribute to a combination of thermal fluctuations in complex thermal circuits and electrothermal feedback. Detailed noise calculations fit the noise measured in three different devices that were specifically designed to test the model. We discuss how changes in bolometer materials can shift the noise peak above the frequency range of interest for most applications. OCIS codes: 160.1890, 040.1240, 040.3060, 220.3740, 220.4000, 120.0120.

The stochastic stability of fault tolerant control systems (FTCSs) in the presence of noise has been analyzed using the Lyapunov function approach. In particular, FTCS with a Markovian fault detection and isolation (FDI) process with transition probabilities conditioned on the state of another Markovian process representing component failures are considered. The almost sure asymptotic stability in probability and the exponential stability in the mean square are considered. Specifically, a testable necessary and sufficient condition for the exponential stability in the mean square is derived. A numerical example is presented to illustrate the theoretical analysis. Index Terms--Fault tolerant control systems, Lyapunov functions, stochastic stability, white noise.

This article discusses a study conducted in which employees evaluated workplace noise. The authors maintain that employees tended to cope with workplace noise annoyance and controls were needed to improve the workplace.

The ability to visually detect the difference between contrast and noise is discussed, focusing on the clinical relevance of a contrast-to-noise ratio analysis. A discussion of methods to increase strain imaging's diagnostic performance is presented.

A vector magnetometer module that allows the recording of orthogonal vector components was designed as a cube with one liquid helium cooled superconducting quantum interference devices (SQUIDS) mounted at each of its six faces. The signals of the six SQUIDS can be combined to yield zero due to Maxwell's third equation. The module can be employed as a basic module for multichannel vector magnetometer systems.

The 1/f noise of HgCdTe photodiodes passivated with ZnS-CdS films is measured as a function of diode bias, temperature and dark current. In addition, the dependence of 1/f noise on dark current is analyzed over a wide range of temperatures. A linear relationship between 1/f noise and dark current is observed at low temperatures, in which leakage current and surface generation predominate. The temperature dependence of 1/f noise, meanwhile, is the same as that for leakage currents and surface generation. The maximum specific detectivity and signal-to-noise ratio of the photodiodes are also determined.

The determinism of the complex time series from a modulated semiconductor laser is investigated using a singular value decomposition eigenvalue spectrum. The signature of chaos is quickly identified and the noise contamination ratio estimated using the approach, as well as the relationship between the noise level and the supplied modulation of laser diodes. Three different direct current-bias conditions are also utilized to test the deterministic nature of the complex time series.

The pump-current dependence of the self-pulsating frequency of semiconductor lasers is measured using a rate-equation model. A unique kink in the pump-current dependence indicating a transition between a region where Q-switching occurs and a region where the self-pulsations are weakly sustained relaxation oscillations is observed. Simulation results show that the spontaneous emission noise has a significant effect on the cross-over.