1,721,063 research outputs found
A rapid prototyping system for broadband multichannel active noise and vibration control
Full text linkIn recent years the need for active and passive noise reduction methods has increased. This is due to an increase in the ambient noise caused by industrialization and the extended use of power tools. The effects of noise on a person can be quite severe and can cause illness and in severe cased lead to a loss of hearing. This results in a need for a method or tool to develop active and/or passive noise control systems. In this thesis a method was presented that can be used to rapidly test and evaluate active noise control systems
Energy-efficient low-frequency flat acoustic source: analysis, design and experimental validation
Full text linkThere is a need for compact acoustic sources that operate at low frequencies. These acoustic sources can be employed to produce good quality sound in the low frequency range. A problem arising when the acoustic sources operate at low frequencies is that the acoustical power is not always enough to allow for sound to be emitted in the form of propagating waves. As a rule of thumb, in the low frequency range the larger the enclosure volume of acoustic sources, the greater the radiated acoustical power. Therefore, in the applications with limited build space it is difficult to compensate for the sufficient acoustic power of the radiators. A thin sandwich acoustic source with a large surface area and a relatively small thickness that is integrated with an internal cavity can fulfill the need for both large enclosure volume and limited build space. The sandwich structure makes the thin acoustic source light-weight and stiff. Therefore, the resulting acoustic source has a reasonably high fundamental resonance frequency. An inefficient acoustic source consumes extra input electric energy, which causes energy loss and high energy expenses. The existence of an appropriate electrical amplifier in combination with the piezoelectric devices is crucial to achieving an energy-efficient thin acoustic source. An appropriate combination of the actuators and amplifiers is investigated in this research. Due to the limited build space in the low-frequency applications, a need for a compact design of the piezoelectric stack actuators arises. An appropriate auxiliary flexural mechanism is investigated for use as an appropriate driver in the limited space of the thin acoustic source. The resulting acoustic source is thin and energy-efficient and can be used in the low frequency operations. The motivation of the present research is to design a compact energy-efficient actuation mechanism for the thin acoustic source that operates in the low-frequency range
Control source development for reduction of noise transmitted through a double panel structure
Full text linkA double panel structure, which consists of two panels with air in between, is widely adopted in many applications such as aerospace, automotive industries, and buildings due to its low sound transmission at high frequencies, low heat transmission, and low weight. Nevertheless, the resonance of the cavity and the poor sound transmission loss at low frequencies limit the double panel’s noise control performance. Applying active structural acoustic control to the panels or active noise control to the cavity has been discussed in many studies. In this thesis, the resonances of the panels and the cavity are considered simultaneously to further reduce the transmitted noise through an existing double panel structure. Various control strategies have been compared and developed to improve the noise control performance. Both numerical and experimental studies are presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Identification and Control of Acoustic Radiation Modes
Full text linkA formulation is given of reduced-order acoustic radiation sensors and reduced-order actuators for broadband sound fields. Methods are presented to determine these descriptions from measured data, and their application in systems for broadband active noise control is discussed. One application area is the reduction of sound radiated from plates with structural actuators and structural sensors, using measured or modeled versions of the most efficiently radiating patterns of a vibrating body, the so-called radiation modes. The second application of the radiation mode theory is in active noise barriers for the reduction of traffic noise. Without special precautions most of these systems suffer from spillover; a technique is given to arrive at good reductions at the error sensors with reduced spillover
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