• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 2249
  • 603
  • 320
  • 318
  • 305
  • 140
  • 73
  • 42
  • 37
  • 37
  • 29
  • 19
  • 18
  • 15
  • 12
  • Tagged with
  • 5360
  • 641
  • 544
  • 532
  • 494
  • 461
  • 421
  • 409
  • 330
  • 310
  • 301
  • 297
  • 292
  • 269
  • 267
  • 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.
21

Design and Analysis of Low Noise Amplifier Exploiting Noise Cancellation

Hsu, Nien-tsu 08 September 2008 (has links)
This thesis is composed of three parts. The first part is devoted to introducing the various noise sources in transistors and their equivalent noise models. Based on the equivalent noise models, the theory of noise cancellation in a low-noise amplifier is derived in detail. The second part is to perform an experiment to validate the theory of low-noise amplifier using common-gate noise cancellation technique. By adjusting the transconductance of individual transistor, the simulated and measured noise figures are compared under different noise cancellation conditions. The third part is to design a low-noise amplifier RFIC using common-source noise cancellation technique for DVB-H applications. This RFIC was implemented in a TSMC 0.18£gm process and measured to show successful noise cancellation capability in a wide frequency range.
22

Highway traffic noise barrier overlap gap model

Clum, Craig M. January 1997 (has links)
Thesis (M.S.)--Ohio University, June, 1997. / Title from PDF t.p.
23

Traffic noise mitigation in Hong Kong

Law, Kam-wah, January 2005 (has links)
Thesis (M. A.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.
24

Trafikbuller på skolgårdar : Upplevda trafikbullerproblem för personal på skolgården, samt utvärdering av kunskap kring buller hos personalen och ledningen i förskolan

Bashiri, Bahram January 2016 (has links)
There is not much research done on how traffic noise on schoolyards affect children and teachers although noise pollution from traffic often are high and affect both groups in several ways. It is a well-established fact that a positive sound environment affects health and learning as well as the working capacity by reducing stress levels. The purpose of this study is to examine whether sound pollution is prevalent in elementary schools in Umeå, if the personnel have knowledge pertaining to the effects of sound pollution, and whether the examined schools have specific routines and self-monitoring mechanism for dealing with sound pollution. The study also aims to inquire whether the schools take any preventive measures with regards to minimizing sound pollution and if they have assigned responsibility for these matters to anyone in the organization. Two methods were used in the study, a questionnaire for teachers and interviews with the principals. The questions were formed in such a way so as to shed light on the above mentioned purposes of this study. The answers to the questionnaire illustrate if and how the teachers perceive and deal with sound pollution on the schoolyard. The interview questions aimed to assess the perception of the principals regarding the sound pollution in their respective schools, the level of knowledge the school management had with regards to sound pollution as well as the routines used for ameliorating and preventing sound pollution on the school yard. The study was performed in four elementary schools in the municipality of Umeå and the questionnaire had 32 respondents. One major reason for using a questionnaire was to maximize the amount of respondents in a time efficient manner. The study intends to shed light on a problem (i.e. sound pollution) that schools usually tend to disregard but nevertheless a problem that, possibly, could lead to dire consequences if not taken into account. The results of the study show that 10 of the 32 teachers perceive traffic noise as a problem that affects both children and educational activities negatively on their schoolyard. The results of the study indicate that teachers perceive sound pollution to be a problem on their schoolyard. However, they seem to lack adequate knowledge regarding the health outcome of such noise pollutants. In conclusion, it is evident that teachers need more support information, resources and education in order to enable them to achieve a positive sound environment on their workplace - both for themselves and the children. The results show that there still remains a lot to improve in schools with regards to noise pollution. In many cases, even those responsible at the schools lacked the knowledge necessary to understand the health problems with noise pollution.
25

Personal noise exposure in platinum concentrator operations in the bushveld complex of South Africa

Deysel, Willem Bernardus January 2017 (has links)
A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Masters in Public Health: Occupational Hygiene Johannesburg, June 2017 / Introduction The quantification and interpretation of personal noise exposure levels in the platinum processing industry of South Africa is an important research topic. Very few studies have been done nationally and internationally on noise exposure in this industry, given the serious health effects of over exposure to noise and the large number of people employed in this industry, this study is important. Objectives The objectives of this study were to describe personal noise exposure measurements of permanent and long term contractor employees during 2012 to 2014 at five Platinum Concentrator operations; to compare the personal noise exposure levels of the different activity areas between the five Platinum Concentrator operations; and to compare the personal noise exposure measurements of the Platinum Concentrator operations to national and international exposure limits. Methods This study was a cross-sectional secondary data analysis of personal noise exposure levels measured as part of routine Occupational Hygiene sampling programme during the period of 2012 to 2014 and was done in five platinum concentrator operations situated in the Bushveld Complex of South Africa. A total of 720 samples were extracted from an electronic database and descriptive statistics were applied to analyse the data. Results This study found that the Processor Grade 2 occupation within platinum concentrator no.3 had the highest personal noise exposure (104.7dBA) with a median personal noise exposure of 87.35dBA and a geometric mean personal noise exposure of 87.4dBA. Sixty seven percent of the personal noise measurements within the five Concentrator Operations exceeded the South African Occupational Exposure Limit of 85dBA and 19.71% of the personal noise measurement results exceeded the OSHA Exposure Limit of 90dBA. Conclusion This study indicated that over exposure to noise in the platinum processing industry can occur; therefore further research on this topic and in this industry is warranted. / MT2017
26

Community perceptions on noise pollution generated by aircraft in Cape Town

Nchemanyi, John Ngeh January 2006 (has links)
Thesis (MTech (Environmental Health))--Cape Peninsula University of Technology, 2006 / Airport operations have become a major source of concern due to aircraft nOIse, particularly in areas close to airports and aircraft flight tracks. Public opposition to aircraft noise is a threat to the continued growth of civil aviation in South Africa. This study investigated the psychological effects of aircraft noise on residents and school activities at a neighbourhood close to the airport, particularly the area located under the flight tracks or adjacent to the landing and departure pattern of aircraft. Bishop Lavis was chosen as the experimental area and Kensington, about 17km away from the airport, was chosen as a control area. Questionnaires coupled with oral interviews and observations were used to gather information. The findings are focused on annoyance and disturbance. The study revealed that noise exposure caused annoyance, activity disturbance and some mild effects on school results, when compared with the control area. Disturbances were experienced in some activities that need concentration. Aircraft noise also caused communication interference, sleep deprivation and affected the teaching process. The community at the experimental area indicated some non-acoustical effects, such as fear of aircraft crashing over their homes but they indicated no willingness to leave the area. As such, it becomes essential when locating and designing airports to optimise flight paths in a way to reduce noise exposure to nearby communities. Recommendations for mitigation of noise exposure are proposed, which include operational procedure, banning chapter I and 2 aircraft, restricting night flights, proper land use planning and enforcing international environmental regulations.
27

Noise at a supermarket : case-study of a workplace with medium levels of sound exposure

Barceló Villalobos, Marta January 2009 (has links)
<p>The purpose of this case-study is to predict possible adverse health effects from noise among employees at a supermarket. The case-study consisted of measurements of noise levels at ICA-Maxi Högskolan supermarket in Halmstad (Sweden), during two weeks and a literature review. The measurements were analyzed statistically, and the results were linked to the literature review search.</p>
28

Experimental analysis of noise reduction properties of sound absorbing foam

Wertel, Scotty John. January 2001 (has links) (PDF)
Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 2001. / Includes bibliographical references.
29

Broadband noise control through a ducted opening

Cheung, Shuk-ching., 張淑晶. January 2012 (has links)
Fresh air ventilation openings or windows are essential to most buildings but the openings allow considerable portions of noise to be transmitted from the outdoor into the indoor environment. This project studies relevant theoretical models through accurate numerical solutions, and seeks better designs to gain extra noise attenuation through the openings. The spectral method of Chebyshev collocation and the corresponding technique of out-going wave boundary conditions, for both ducted and flanged opening, are developed as numerical tools and validated by analytical examples. After establishing the numerical tools, two prototype problems are studied. The first is one in which there is no special sound attenuation device. The configuration includes aperture of negligible thickness, aperture of finite thickness and aperture of semi-infinite length. The characteristics of the noise transmission through aperture of finite thickness are investigated with examples of sonic boom and traffic noise. The second prototype problem is the sound attenuation performance of side-branch design of the ducted opening. Side-branch configurations including porous material, single micro-perforated panel, double-layer micro-perforated panels, parallel micro-perforated panels and parallel micro-perforated panels with connected cavity are investigated. They are tested individually with parameters optimized for each of two examples of noise sources. The sound attenuation performances compared using appropriate subjective ratings of the noise sources. It is found that the parallel micro-perforated panels give the best performance for the sonic boom and the double-layer micro-perforated panels serve as the best substitute for the porous material with traffic noise source. Results from experiment are also presented to validate some numerical results. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy
30

Compact environmental noise absorber

Peng, Dandan, 彭丹丹 January 2014 (has links)
With the development of the industry and the society, noise pollution becomes increasingly severe, especially in large cities. Generally, there are three major noise sources, namely industrial noise, traffic noise and community noise. In response, several measurements have been developed to achieve effective noise control. Examples of noise control methods are reduction of noise at source and abatement of noise during the transmission. Since noise sources are more difficult to control, and sometimes already fixed, noise control during sound transmission is more broadly applied. Traditional passive noise control techniques include Helmholtz resonators and noise absorption materials like felt, glass mineral. The sound absorption materials (SAM) are found to be efficient in attenuating noise in high frequency domain, but their performance at low frequencies is quite poor. On the other hand, the Helmholtz resonator works perfect at any target frequency but suffers from its narrow absorption bandwidth, so that it’s only effective within a limited frequency band. As an innovative solution to passive noise control problem, micro-perforated panel absorber (MPPA) has attracted great interest in recent years. It turns out to be a competitive alternative to sound absorption materials and Helmholtz resonator. The parallel and series arrangement of MPPAs backed with cavities of different depths allows them to obtain decent noise absorption performance over a relatively broad frequency range. However, the performance of MPPA is restricted by its volume, as large volume is demanded for decent low-frequency absorption, which is also the case for noise absorption materials. In this thesis, a potential way to improve the low-frequency performance of the MPPA without occupying extra volume is proposed and implemented to tests. The focus is the adjustment of speed of sound and it is beneficial in different applications such as the following. In low frequency noise control, the size of the absorber in at least one dimension is often related to the wavelength and it is often too long. With a reduced speed of sound one can reduce this size while keeping the overall volume constant. Along this line of thinking, the effect of cavity configuration on its acoustic properties is investigated by two steps. Firstly, the property of a waveguide consisting of several identical elements is studied. The number of element is chosen to magnify the effect of the configuration. It turns out the irregularity of the duct shape can slow down the speed of sound of the plane wave by increasing the acoustic mass. Secondly, the absorption performance of an MPPA backed with an irregular cavity is evaluated. The shape of the cavity is the same as the element in the first step. In advance, the parallel arrangement of two MPPAs backed with irregular cavities is investigated, in order to look into the effect of cavity shape on inter-resonator interaction. The final results indicate that cavity design is an effective method to enhance the noise absorption performance of the MPPA arrays in the low-frequency domain. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

Page generated in 0.0511 seconds