Noise in the adult emergency department of Johns Hopkins Hospital

While hospitals are generally noisy environments, nowhere is the pandemonium greater than in an emergency department, where there is constant flow of patients, doctors, nurses, and moving equipment. In this noise study we collected 24 h measurements throughout the adult emergency department of Johns Hopkins Hospital, the top ranked hospital in the U.S. for 16 years running. The equivalent sound pressure level (Leq) throughout the emergency department is about 5 dB(A) higher than that measured previously at a variety of in-patient units of the same hospital. Within the emergency department the triage area at the entrance to the department has the highest Leq, ranging from 65 to 73 dB(A). Sound levels in the emergency department are sufficiently high [on average between 61 and 69 dB(A)] to raise concerns regarding the communication of speech without errors--an important issue everywhere in a hospital and a critical issue in emergency departments because doctors and nurses frequently need to work at an urgent pace and to rely on oral communication.     

Noise levels inside passenger cars

This paper deals with sound pressure level readings taken inside five different makes of car running on the streets of the city of Mosul, Iraq. The problem of noise and vibration produced by cars is reviewed and discussed in its several aspects, namely the source, its transmission, the range of frequencies and the level of noise in cars. The acceptable levels of noise in cars and methods of noise control are also discussed.     

Noise levels in the vicinity of traffic roundabouts

An experimental procedure for analyzing roundabout noise is described. Measurement of the noise from accelerating and decelerating traffic streams on the approach roads to roundabouts at a total of 70 positions at three sites are reported together with a simulation study of noise from central island traffic. The results show that, in general, noise from the accelerating traffic streams is within ±1 dB(A) of the free flow level on the same road and that the noise from the decelerating stream is equal to or less than the free flow level. The propagation of noise from the central island is expressed in the form of a nomogram. Good agreement between predicted and measured levels was found.     

Noise levels and hearing thresholds in the drop forging industry

A-weighted equivalent continuous noise levels for hammer and press operations in a drop-forging industry were determined using both tape recordings of the noise and personal noise dosimeters. The results indicated average A-weighted Leq values of 108 dB for hammer operators and 99 dB for press operators. Comparison of hearing level statistics for 716 hammer and press operators and 293 control subjects indicated the severe hazard to hearing of impact noise exposures. For mean exposure times of less than 10 years, hearing levels for the press (99 dB) and hammer (108 dB) operator age groups are nearly identical, and in the latter case are less than those predicted for exposure to equivalent continuous noise. For long-term exposures of 10 years or more, the results of this study indicate that hearing losses resulting from impact noise in the drop-forging industry are as great or greater than those resulting from continuous noise.     

Noise levels on the shielded side in cities using a flat city model

The prediction of road traffic noise levels in areas not directly exposed, such as areas behind buildings and courtyards, is difficult using standardised methods. This is mainly due to the fact that traditionally only one or a few sources are included. Here a simple model that assumes a flat city on rigid ground is used to demonstrate that sources from a large area are important. Calculations are compared to measurements for four cases, and the proposed method predicts levels 6-10 dB too high for the equivalent level at all measurement positions. If a correction is applied for this over-estimation, the results agree well.     

Noise improves modulation detection by cochlear implant listeners at moderate carrier levels

Envelope detection and processing are very important for cochlear implant (CI) listeners, who must rely on obtaining significant amounts of acoustic information from the time-varying envelopes of stimuli. In previous work, Chatterjee and Robert [JARO 2(2), 159-171 (2001)] reported on a stochastic-resonance-type effect in modulation detection by CI listeners: optimum levels of noise in the envelope enhanced modulation detection under certain conditions, particularly when the carrier level was low. The results of that study suggested that a low carrier level was sufficient to evoke the observed stochastic resonance effect, but did not clarify whether a low carrier level was necessary to evoke the effect. Modulation thresholds in CI listeners generally decrease with increasing carrier level. The experiments in this study were designed to investigate whether the observed noise-induced enhancement is related to the low carrier level per se, or to the poor modulation sensitivity that accompanies it. This was done by keeping the carrier amplitude fixed at a moderate level and increasing modulation frequency so that modulation sensitivity could be reduced without lowering carrier level. The results suggest that modulation sensitivity, not carrier level, is the primary factor determining the effect of the noise.     

介观物理系统中的噪声

描述了介观物理系统中噪声的研究现况. 对热噪声和散粒噪声的物理起源做了详细介绍，热噪声是系统的能态占据数发生涨落引起的，而散粒噪声源于载流子传输的微粒特性. 还介绍了研究噪声的主要理论——散射理论，并给出了其在马鞍形半导体量子线和铁磁/绝缘体/半导体双异质结两种介观系统中的应用，指出了噪声研究的实际物理意义. 关键词： 介观物理 热噪声 散粒噪声 散射理论     

Noise in miniature microphones

The internal noise spectrum in miniature electret microphones of the type used in the manufacture of hearing aids is measured. An analogous circuit model of the microphone is empirically fit to the measured data and used to determine the important sources of noise within the microphone. The dominant noise source is found to depend on the frequency. Below 40 Hz and above 9 kHz, the dominant source is electrical noise from the amplifier circuit needed to buffer the electrical signal from the microphone diaphragm. Between approximately 40 Hz and 1 kHz, the dominant source is thermal noise originating in the acoustic flow resistance of the small hole pierced in the diaphragm to equalize barometric pressure. Between approximately 1 kHz and 9 kHz, the noise originates in the acoustic flow resistances of sound entering the microphone and propagating to the diaphragm. To further reduce the microphone internal noise in the audio band requires attacking these sources. A prototype microphone having reduced acoustical noise is measured and discussed.     

Noise attenuation in factories

The cost of reducing noise levels in factories by covering large surfaces with sound absorbents is high. It is therefore important to be able to calculate in advance the effectiveness of absorbents and to determine how absorbents may be chosen and distributed for maximal noise reduction for the invested capital. For this purpose a mathematical model of sound propagation and attenuation in factories has been developed on certain simplifying assumptions. The interrelationship between the different parameters is found to be rather intricate and the mathematical model must be evaluated using a computer program. The influence on the noise levels of sound scattering objects, the shape and size of the factory and absorbents on the room surfaces have been studied. Especially if the ceiling is high, acoustic baffles are found to be more efficient than absorbents on the ceiling in reducing noise levels.     

Noise in optical amplifiers

This article presents an application of a recently published probablistic model for traveling wave optical amplification. Both optical signal and amplified spontaneous emission (ASE) noise are modeled as bunches of photons traveling along the amplifying region with size varying according to simple random rules. The results of the theory enable one to obtain a complete and accurate characterization of the signal and noise counting at the amplifier output. On the basis of the above statistics, we find a realistic evaluation of the limits imposed by both quantum and ASE noise on the performances of a receiver including an optical amplifier at a preamplifier stage.     

Noise in ultrasonic imaging

The feasibility of noise measurement in medical ultrasonic imaging has been studied and a theoretical evaluation of stochastic noise influence upon the perceived image has been undertaken. The influence of noise on a perceived image has been calculated by considering the light intensity perception characteristic of the human eye and it has been found that the additive noise in the video signal pushes the small signals in the image towards the invisible (black) region. Impulse noise measurements of amplitude and time jitter have been set up using a standard $\text{water}\text{CCl}{}_4$ interface and pulse amplitude analysis to take into account the random nature of noise by distribution measurements.     

Noise in superresolution reconstruction

Recently there has been a significant interest in reconstructing a high-resolution (HR) image based on a set of low-resolution (LR) images with relative displacement. These images are typically undersampled with respect to the image spectrum of a HR image. I show that, although ideally a resolution increase of N times is possible with N LR images, in a practical system noise is a limiting factor that increases substantially as we approach this theoretical superresolution limit. For one dimension and a special case with two LR images, I present an analytical result of the noise amplification as a function of their displacement. This is defined as a condition number of the superresolution system, with the associated definitions of a well-conditioned and ill-conditioned superresolution reconstruction system.     

离轴照明下依赖于入射角度的矢量霍普金斯公式

应用矢量电磁场理论和波导模型推导出离轴照明下的矢量霍普金斯公式,与传统的标量霍普金斯公式不同之处在于引入了入射角及入射方位角. 通过仿真实际投影光刻工艺下三维掩模的成像效果,分析了最佳入射角范围,讨论了离轴照明时入射角对最终成像质量的影响. 关键词： 光学光刻 矢量霍普金斯公式 矢量电磁场理论 离轴照明     

Dynamic Active Noise Control of Broadband Noise in Fighter Aircraft Pilot Helmet

This paper presents the development of a dynamic Active Noise Control (ANC) algorithm aimed towards reducing the broadband noise inside the helmet earcups of a fighter aircraft pilot helmet. The dynamic ANC involves a Variable Step-Size Griffiths (VSSG) FxLMS algorithm to attenuate noise entering directly through helmet, a LMS based adaptive noise canceller to attenuate noise entering through the pilot microphone, and energy detectors for failure protection and optimized battery power usage. The algorithms are implemented on Texas Instruments’ TMS320C6748 processor and are tested in a helmet ANC experimental setup.