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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Active control of sound in ducts

Chan, T. M. January 1997 (has links)
No description available.

The Effects of Continuous Versus Non-Continuous Noise and Level of Intensity on a Serial Learning Task

Ware, William S. 08 1900 (has links)
The present study was designed to investigate the effects of two noise conditions, continuous and noncontinuous noise, and three intensity levels, upon a serial learning task and the interaction effects of these factors on learning.

The application of non-linear partial differential equations for the removal of noise in audio signal processing

Shipton, Jarrod Jay January 2017 (has links)
A dissertation submitted in fulfllment for the degree of Masters of Science in the Faculty of Science School of Computer Science and Applied Mathematics October 2017. / This work explores a new method of applying partial di erential equations to audio signal processing, particularly that of noise removal. Two methods are explored and compared to the method of noise removal used in the free software Audacity(R). The rst of these methods uses a non-linear variation of the di usion equation in two dimensions, coupled with a non-linear sink/source term, in order to lter the imaginary and real components of an array of overlapping windows of the signal's Fourier transform. The second model is that of a non-linear di usion function applied to the magnitude of the Fourier transform in order to estimate the noise power spectrum to be used in a spectral subtraction noise removal technique. The technique in this work features nite di erence methods to approximate the solutions of each of the models. / LG2018

Does loud noise affect the clinical decision-making processes of healthcare professionals in a simulated emergency setting?

Folscher, Lindy-Lee January 2013 (has links)
A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Medicine in Emergency Medicine. Johannesburg, 2012 / Introduction: Healthcare professionals working in the Emergency Medicine field are often required to function in difficult environments. Noise is one environmental factor that may adversely affect their performance. Objectives: To firstly determine if there is any difference in cognitive task performance required for clinical decision-making of healthcare professionals in a quiet compared to a noisy environment and secondly, to assess the subjective experience of participants with regards to performance in a noisy environment. Design: Prospective cross-over study. Setting: Three Academic Hospitals in Johannesburg. Participants: Forty one doctors exposed to emergency management of patients. Methods: A 30 minute examination consisting of six matched and pre-validated questions was conducted. Half of the questions were completed with exposure to ambient noise (range 40-45dB(A)) and the other half with exposure to pre-recorded background Emergency Department noise at 80-85dB(A). The questions were completed in alternating quiet and noise. Each question was scored out of 10 and the time taken to complete each question was recorded. Main Results: Overall mean test scores in quiet and noise were 18.7/30 and 19.4/30 (p=0.36) respectively, with overall time for test completion of 836s in quiet and 797s (p=0.005) in noise. While there was no statistically significant difference in task performance, 65% of the doctors found the noise distracting with 88% experiencing varying degrees of stress. Conclusions: This study showed no difference in cognitive performance in a quiet compared to a noisy environment. Deterioration in functionality might be seen with higher levels of noise and/or longer exposure.

Low frequency noise and the upconverted phase noise effects in NMOSFET circuits

Xie, Dingming 14 October 1999 (has links)
Graduation date: 2000

Noise externalities : a hybrid model to assess effects and management with application to transportation issues in Rhode Island /

Kwon, Suk-Jae. January 2006 (has links)
Thesis (Ph. D.)--University of Rhode Island, 2006. / Typescript. Includes bibliographical references (leaves 141-150).

The Study of Ambient Noise in First Seaway area of Kaohsiung Harbor

Chao, Tsun-hsien 04 September 2007 (has links)
It can be a real challenge to construct the ambient noise modeling among the harbors of very frequent shipping. Therefore, in these harbors, a great amount of resource has to be utilized for precisely control the ambient noise occurring parameters. In this study, the underwater measuring skill is adapted to collect the ambient noise raw data among the first harbor area of Kaohsiung Harbor and the sound intensity of various ships as well. Besides, the signal processing skill is also conducted for ship tracing experiment. The harbor ambient noise mainly comes from ships. Thus, the understanding of ship activity and their different sound intensity can be a great help to construct the ambient noise modeling. The results of this study indicate¡GShips outside the harbor create more low-frequency noise than those inside the harbor.Waves inside the harbor create more middle-frequency noise than those outside the harbor.In the harbor, those ships with onboard electricity create more noise and there is less noise around the wharfs without any ships. In the part of ship noise study, the intensity is usually correlated with ship types, displacement, ship speed, primary engine and auxiliary engine, etc. However, only two ship types, small and large ships, are categorized in this study. Small ships can be operated easily with the most power outcome, which can create the sound intensity of 155 to 165 dB in average. On the contrary, large ships are usually limited within their operating range and can not move with the most power outcome under the security consideration. Therefore, the sound intensity of large ships is measured between 169 to 177 dB. In the ship tracing experiment, operations are the basis for constructing the harbor ambient noise model.

Image Restoration in Consideration of Poisson Noise

Chang, Yuan-Ming 28 July 2000 (has links)
It¡¦s not easy to keep photographs clean in every day. A photograph is liable to be polluted by accumulating defects such as dusts, which can degrade the imaging quality. In the thesis, a method of image restoration is proposed for image polluted by multiplicative transmittance noise. The method is based on estimating the approximate autocorrelation function of the unpolluted image. This autocorrelation function is obtained by analyzing the relationship among the autocorrelation function for polluted image, unpolluted image and noise. Further more, the noisy image is restored by the property of the autocorrelation function. A polluted photograph in imaging system is modeled by a thin random screen against the original image. In this model, defects are Poisson-distribution and may be overlapped. Since transmittance effect of each defect is multiplicative, the transmittance of random screen is computed as a product of Poisson-distribution-centered random function. Then, the statistical autocorrelation function of random screen is accordingly computed. More specifically, we should rearrange image data as periodic signal to avoid insufficient data in computing the process autocorrelation function. The simulated polluted image is restored by the amplitude information from the estimated autocorrelation function of the original image. Simulating results is demonstrated that the RMS of the restored image computed with the polluted image is improved.

Study of Wind Delay Effect on Ocean Ambient Noise

Lin, Wen-Fai 29 June 2001 (has links)
Sound waves are highly conductive in the ocean; therefore, they are used in underwater detection and signal transmission. During these applications, we may receive some signals, such as radiated noise, self-noise, reverberation noise, target noise, and ambient noise. These signals are influential in the application of underwater acoustics, so many people study underwater noise and create numerous mathematical and physical models in order to improve the applications. According to the past researches, ambient noise is the most complicated one among all the other underwater noise. Until now, there are still some unknown factors in the ambient noise study, many of which are too intricate to be modulated. Accordingly, it is very important to know more about the ambient noise for the enhancing of the quality of underwater communication and detection, which is the reason why people keep researching on ambient noise. Among all kinds of ambient noise, wind-generated noise is not only loud in volume, but also wide in frequency scale, which makes it the most detectable noise during sound detection. In order to understand wind-generated noise, we have compiled past papers first to look for the correlation between physical mechanisms and models of mathematics. In addition, we have constructed a measuring system for underwater sound in the ocean and another measuring system for wind on land. Data from the two measuring system were analyzed by statistics. One of the correlations between wind and ambient noise is that the stronger wind appears, the louder ambient noise is generated. But wind does not always generate ambient noise; it has to be strong enough to generate ambient noise. However, even when the wind is strong enough, ambient noise is not generated immediately, but with a delay. By analyzing the data, we have not only proved the credibility of the data from the old researches, but also presented a method of statistics for analyzing the wind delay effect, and the minimum velocities of wind which generates ambient noise.

A Study of the Design Theory for Front-End CMOS Low Noise Amplifiers

Kuang-Yao, Peng 06 August 2003 (has links)
This thesis deals with two kinds of RF CMOS low noise amplifiers (LNA). The low power LNA and the image-reject LNA. The impact of gain, noise figure, and stability on RF CMOS image-reject LNA has been studied. Through this study, the fundamental properties of image-reject LNA can be understood by a simple but physical concept. A current-reuse RF CMOS source-degenerated cascode LNA is also presented, which adopts a combination of source-degenerated NMOS inverter and Cascode topology to improve gain and noise figure, the existent and well-studied technique from the design standpoint, makes optimization of the stage easy. A modification of the proposed architecture is also presented, which adopts internal filters to achieve the image rejection without additional image-reject filters that degrade both noise figure and power consumption. It will be a good candidate for low power implementation of CMOS RF-IC. Both circuits¡¦ parameters except noise figures are simulated using TSMC 0.25 um RF CMOS component models. The noise models considered here include induced gate noise, thermal noise and shot noise [5]. The current-reuse source-degenerated NMOS inverter LNA noise figure is 0.7 dB, forward gain is 16 dB, and IIP3 is -15 dBm. The low power image-reject LNA noise figure is 0.7 dB, forward gain is 16 dB, IIP3 is -16 dBm, and image rejection is 20 dB at 1.6 GHz. Both LNAs operate at 2.4 GHz and consume about 6 mA under a 2.5 V voltage supply.

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