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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.
11

Dynamics of the stratosphere, mesosphere and thermosphere

Sandford, David J. January 2008 (has links)
This thesis presents observations of the dynamical features of the stratosphere, mesosphere and lower thermosphere. These are made from various observational techniques and model comparisons. A focus of the work is the two-day wave at high latitudes in the MLT region. This has revealed significant wave amplitudes in both summer and winter. However, these waves are shown to have very different origins. Using satellite data, the summertime wave is found to be the classic quasi-two-day wave which maximises at mid-latitudes in the MLT region. The wintertime wave is found to be a mesospheric manifestation of an eastward-propagating wave originating in the stratosphere and likely generated by barotropic and baroclinic instabilities in the polar night jet. The horizontal winds from Meteor and MF radars have been used to measure and produce climatologies of the Lunar M2 tide at Esrange in the Arctic (68°N), Rothera and Davis in the Antarctic (68°S), Castle Eaton at mid-latitude (52°N) and Ascension Island at Equatorial latitudes (8°S). These observations present the longest period of lunar semi-diurnal tidal observations in the MLT region to date, with a 16-year dataset from the UK meteor radar. Comparisons with the Vial and Forbes (1994) lunar tidal model are also made which reveal generally good agreement. Non-migrating lunar tides have been investigated. This uses lunar tidal results from equatorial stations, including the Ascension Island (8°S) meteor radar. Also lunar tidal results from the Rothera meteor wind radar (68°S, 68°W) and the Davis MF radar (68°S, 78°E) are considered. Both of these stations are on the edge of the Antarctic continent. It is demonstrated that there are often consistent tidal phase offsets between similar latitude stations. This suggests that non-migrating modes are likely to be present in the lunar semi-diurnal tidal structure and have significant amplitudes.
12

Quando até as paredes cantam: o som como experiência na obra de Jerzy Grotowski / -

Jesus, Luciano Mendes de 30 September 2016 (has links)
Esta pesquisa investiga o elemento sonoro-musical como criador de experiências estéticas, sensoriais, mnemônicas e afetivas dentro do pensamento e prática do diretor, pesquisador e professor polonês Jerzy Grotowski, no âmbito da evolução de sua obra no domínio das artes performativas. Este estudo, que parte da observação historiográfica, comparativa e crítica do fenômeno sonoro-musical na obra do artista, visa realizar um mapeamento das diferentes fases artísticas do diretor, que compreendem uma curva de 42 anos, indo do período da Arte como Apresentação ao da Arte como Veículo, e das diferentes conotações que este elemento teve em sua trajetória de criação e pesquisa. O trabalho também observa as diferentes apropriações do elemento sonoro-musical pelos últimos colaboradores do diretor, concentrando maior atenção às atividades atuais desenvolvidas nesse território por Thomas Richards e Mario Biagini, diretores do Workcenter of Jerzy Grotowski and Thomas Richards. Esta fase é investigada em relação ao desenvolvimento da importância dada às questões sonológicas dentro deste centro internacional de pesquisa e criação, que tem no trabalho criativo sobre os cantos de tradição afro-diaspóricos do continente americano o seu ferramental básico, explorando-se suas propriedades geradoras de comportamento orgânico em performance. A pesquisa é realizada através de estudos de textos escritos à cerca do tema pelo próprio diretor, seus diversos parceiros e estudiosos da sua obra, além de realizar pontes com a produção musical experimental contemporânea. Também conta com a análise de espetáculos, tanto em suporte audiovisual, quanto a partir do meu contato direto com a produção atual. Nesse último aspecto a pesquisa também está relacionada à noção de autoetnografia, sendo orientada por reflexões sobre a minha experiência na condição de performer na equipe do Open Program, um dos grupos de trabalho que integram o Workcenter, entre os anos de 2013 e 2015. Além disso, esta noção autoetnográfica se dá com a recriação do meu ponto de escuta sobre a obra de Grotowski. Com esse referencial a pesquisa busca compreender como se dá a construção do encontro experiencial entre o atorsonante e o espectador-ouvinte, partindo da criação de uma presença organizada, transmitida e percebida através do fenômeno sonoro (cantos, instrumentos e outros recursos), suas estruturações (vibratórias, melódicas, harmônicas, rítmicas e timbrísticas) e suas manifestações e nuances na corrente das artes performativas, conforme a visão grotowskiana: entre o polo da arte como veículo e o da arte como apresentação. / This research investigates the sound-musical element as creator of aesthetic, sensory, mnemonic and affective experiences within the thinking and practice of the Polish director, researcher and teacher Jerzy Grotowski, in the context of the evolution of his work in the field of performing arts. This study, that part of the historiographical, comparative and critical observation of the sound-musical phenomenon in the artist\'s work, is to carry out a mapping of different artistic phases of the director, comprising a curve of 42 years, ranging from the period of the Art as Presentation to the Art as Vehicle, and the different connotations that this element was in its path of creation and research. The work also notes the different allocations of sound-musical element by the last collaborators of the director, focusing greater attention to current activities in this area by Thomas Richards and Mario Biagini, directors of the Workcenter of Jerzy Grotowski and Thomas Richards. This phase is investigated in relation to the development of the importance given to sonological issues within this international center for research and creation, which is the creative work on african-diasporic tradition songs of the American continent their basic tools by exploiting its generating properties of organic behavior in performance. The survey is conducted through studies of texts written about the theme by the director himself, his various partners and scholars of his work, and making bridges with contemporary experimental music production. It also includes the analysis of performances, both in audio-visual support, as from my direct contact with the current production. In this last aspect the research is also related to the notion of autoethnography, being guided by reflections on my experience in the performer condition in the Open Program team, one of the work groups within the Workcenter, between the years 2013 and 2015. In addition, this autoethnographic notion is given with the recreation of my listener point on the work of Grotowski. With this framework the research seeks to understand how is the construction of experiential encounter between the doer-sounder and the spectator-listener, based on the creation of an organized presence, transmitted and perceived through the acoustic phenomenon (songs, instruments and other resources), their structuring (vibrating, melodic, harmonic, rhythmic and timbristic) and its manifestations and nuances in the chain of performing arts, as grotowskian view: between the pole of art as a vehicle and of art as presentation.
13

Quando até as paredes cantam: o som como experiência na obra de Jerzy Grotowski / -

Luciano Mendes de Jesus 30 September 2016 (has links)
Esta pesquisa investiga o elemento sonoro-musical como criador de experiências estéticas, sensoriais, mnemônicas e afetivas dentro do pensamento e prática do diretor, pesquisador e professor polonês Jerzy Grotowski, no âmbito da evolução de sua obra no domínio das artes performativas. Este estudo, que parte da observação historiográfica, comparativa e crítica do fenômeno sonoro-musical na obra do artista, visa realizar um mapeamento das diferentes fases artísticas do diretor, que compreendem uma curva de 42 anos, indo do período da Arte como Apresentação ao da Arte como Veículo, e das diferentes conotações que este elemento teve em sua trajetória de criação e pesquisa. O trabalho também observa as diferentes apropriações do elemento sonoro-musical pelos últimos colaboradores do diretor, concentrando maior atenção às atividades atuais desenvolvidas nesse território por Thomas Richards e Mario Biagini, diretores do Workcenter of Jerzy Grotowski and Thomas Richards. Esta fase é investigada em relação ao desenvolvimento da importância dada às questões sonológicas dentro deste centro internacional de pesquisa e criação, que tem no trabalho criativo sobre os cantos de tradição afro-diaspóricos do continente americano o seu ferramental básico, explorando-se suas propriedades geradoras de comportamento orgânico em performance. A pesquisa é realizada através de estudos de textos escritos à cerca do tema pelo próprio diretor, seus diversos parceiros e estudiosos da sua obra, além de realizar pontes com a produção musical experimental contemporânea. Também conta com a análise de espetáculos, tanto em suporte audiovisual, quanto a partir do meu contato direto com a produção atual. Nesse último aspecto a pesquisa também está relacionada à noção de autoetnografia, sendo orientada por reflexões sobre a minha experiência na condição de performer na equipe do Open Program, um dos grupos de trabalho que integram o Workcenter, entre os anos de 2013 e 2015. Além disso, esta noção autoetnográfica se dá com a recriação do meu ponto de escuta sobre a obra de Grotowski. Com esse referencial a pesquisa busca compreender como se dá a construção do encontro experiencial entre o atorsonante e o espectador-ouvinte, partindo da criação de uma presença organizada, transmitida e percebida através do fenômeno sonoro (cantos, instrumentos e outros recursos), suas estruturações (vibratórias, melódicas, harmônicas, rítmicas e timbrísticas) e suas manifestações e nuances na corrente das artes performativas, conforme a visão grotowskiana: entre o polo da arte como veículo e o da arte como apresentação. / This research investigates the sound-musical element as creator of aesthetic, sensory, mnemonic and affective experiences within the thinking and practice of the Polish director, researcher and teacher Jerzy Grotowski, in the context of the evolution of his work in the field of performing arts. This study, that part of the historiographical, comparative and critical observation of the sound-musical phenomenon in the artist\'s work, is to carry out a mapping of different artistic phases of the director, comprising a curve of 42 years, ranging from the period of the Art as Presentation to the Art as Vehicle, and the different connotations that this element was in its path of creation and research. The work also notes the different allocations of sound-musical element by the last collaborators of the director, focusing greater attention to current activities in this area by Thomas Richards and Mario Biagini, directors of the Workcenter of Jerzy Grotowski and Thomas Richards. This phase is investigated in relation to the development of the importance given to sonological issues within this international center for research and creation, which is the creative work on african-diasporic tradition songs of the American continent their basic tools by exploiting its generating properties of organic behavior in performance. The survey is conducted through studies of texts written about the theme by the director himself, his various partners and scholars of his work, and making bridges with contemporary experimental music production. It also includes the analysis of performances, both in audio-visual support, as from my direct contact with the current production. In this last aspect the research is also related to the notion of autoethnography, being guided by reflections on my experience in the performer condition in the Open Program team, one of the work groups within the Workcenter, between the years 2013 and 2015. In addition, this autoethnographic notion is given with the recreation of my listener point on the work of Grotowski. With this framework the research seeks to understand how is the construction of experiential encounter between the doer-sounder and the spectator-listener, based on the creation of an organized presence, transmitted and perceived through the acoustic phenomenon (songs, instruments and other resources), their structuring (vibrating, melodic, harmonic, rhythmic and timbristic) and its manifestations and nuances in the chain of performing arts, as grotowskian view: between the pole of art as a vehicle and of art as presentation.
14

Research of Neural Network Applied on Seabed Sediment Recognition

Lee, Po-Yi 07 June 2000 (has links)
Along with advancement of human industrialization, pollution in the ocean is getting worse. Moreover, the overfishing through the years has caused catastrophic damage to the ocean eco-system. In order to avoid exhaustion of fishery resource, many concepts of planned administrative fishery has become popular, and thereamong, ocean ranch draws the most attention. Artificial reef plays a key role in an ocean ranch, which starts with incubating brood fish in the laboratory. Often, the brood fish will grow in the cage near coast till proper size, then be released to the artificial reef. If fish groups do not disperse and multiply, the artificial reef can be considered successful. The success of the artificial reef relies on the stable foundation. Consequently, the composition of seabed sediment under the planned site should be investigated thoroughly before hand. This research introduced a remote investigation method, which an active sonar, depth sounder, was used to emit and collect acoustic signals. By using the signals reflected from the seabed, the sediment composition can be analyzed. However, all acoustic signals are subjected to noise through propagation, and distorted somehow. Therefore, certain signal pre-processing should be applied to the received signal, and representative characteristics can be extracted from it. In this research, the recognition platform was built on artificial neural network (ANN) in this research. Among many network algorithm modes, this research chose the widely used backpropagation learning algorithm to be the main structure in ANN. The goal of this research was to discriminate among three seabed sediments: fine sand, medium sand, and rock. During the signal processing, characteristics were extracted by using peak value selection method. Selected major frequency peaks were fed into the network to train and learn. According to partial error relation between recognition and practical result, weights of the network were adjusted for improving successful ratio. Finally, a reliable acoustic wave signal recognition system was constructed.
15

The importance of sediment roughness on the reflection coefficient for normal incidence reflections

Hron, Joel Maurice 12 July 2011 (has links)
This research experimentally shows the effect of sediment roughness characteristics on the acoustic reflection coefficient. This information is useful when trying to classify various types of sediment over an area. This research was conducted in an indoor laboratory tank at Applied Research Laboratories (ARL) at the University of Texas at Austin. A single beam echo-sounder (SBES) system was developed to project and receive a wideband (3 kHz to 30 kHz) acoustic pulse. A method was developed using the system transfer function to create a custom pulse that would minimize the dynamic range over the wide frequency band. A matched filtering and data processing algorithm was developed to analyze data over the full frequency bandwidth and over smaller frequency bands. Analysis over the smaller frequency bands showed the effect of the roughness on the reflection coefficient with respect to frequency. It was found that the reflection coefficient is significantly lower at the higher frequencies (above 20 kHz) than at the lower frequenices [sic] due to off specular scattering. It was also found that the variability of the reflection coefficient was significantly higher for the rough sediment than for the smooth sediment. / text
16

Seabed remote sensing by single-beam echosounder: models, methods and applications.

Biffard, Benjamin R. 19 July 2011 (has links)
Single-beam echosounders are an inexpensive, practical and non-invasive means of remote sensing the seabed. Ideally, the common single-beam echosounder should be able to tell fishers, navigators, engineers and scientists what the seabed consists of in addition to water depth. Low-frequency underwater acoustic systems (<10 kHz) can do this in some circumstances, but are expensive, offer limited resolution and potentially hazardous to marine mammals. High-frequency systems, such as single and multibeam echosounders, are very effective at mapping bathymetry, but do not characterize the seabed directly. Instead, these systems divide the seabed into self-similar segments or classes, and then rely on ground-truth data (usually sediment grab samples) to assign seabed-type labels such as sand, etc., to the classes. However, inadequate and inaccurate ground-truth is a major problem. Single-beam seabed classification methods also suffer from a lack of discriminatory power and from artefacts such as water depth and seabed slope. The cause of these problems is that the methods lack a basis in physics and are mainly statistical. Then, the central objective in this dissertation is to develop physics-based methods to improve classification and to address the problem of ground-truth by inferring seabed characteristics directly from the acoustics. An overview of current methods is presented along with case studies of single-beam surveys to introduce the current seabed classification method called QTC VIEW™ and to identify specific problems. A physical basis is established in scattering and geometrical theories and observations of field and model data. This leads to new classification and characterization methods that overcome the shortcomings of current seabed classification methods. Advancements also include new physical models of echosounding. The new methods are presented, implemented and evaluated. Highlights of experimental results include a new testbed located in Patricia Bay, British Columbia. The testbed consists of exhaustive ground-truth, surveys and novel controlled experiments with various single-beam echosounders, ranging in frequency from 12 to 200 kHz. Simulated echo time series data from the numerical BORIS model and a new analytic model are used to augment the testbed. Evaluation of experimental results shows the new physics-based methodology improves seabed classification significantly and enables seabed characterization by an uncalibrated single-beam echosounder. / Graduate
17

Design and Implementation of an Ultrabroadband Millimeter-Wavelength Vector Sliding Correlator Channel Sounder and In-Building Multipath Measurements at 2.5 & 60 GHz

Anderson, Christopher R. 21 May 2002 (has links)
Over the past decade, the market for wireless service has grown at an unprecedented rate. The industry has grown from cellular phones and pagers to broadband and ultra-broadband (also called ultra-wideband) wireless services that can provide voice, data, and full-motion video in real time. This growing hunger for faster data rates and larger bandwidths has prompted a need for a deeper understanding of the wireless channels upon which these devices communicate. In order for the visions of real time full-motion video, multimedia, and high speed data delivery inherent in the 3rd and 4th generations of wireless communication standards to be fully realized, system design engineers must have a thorough understanding of the wireless channels upon which these devices operate. Additionally, for these networks to deliver their promised data rates, they must operate at very high microwave and millimeter-wave frequencies, where large segments of spectrum are readily obtained. Unfortunately, little is known about the propagation characteristics at these frequencies and bandwidths. As a consequence, there has been a significant demand for wireless test equipment that is capable of characterizing these new wireless channels. The objective of this research was to design and develop a wireless test instrument that can not only characterize these new wireless channels, but has the portability to be quickly and easily re-located to various measurement sites, as well as the flexibility to characterize a wide variety of frequencies and bandwidths in addition to the ultrawideband channels investigated in this work. This measurement system is also designed to be capable of characterizing both the magnitude and phase response of these wireless channels, which not only provides a more complete channel characteristic, but the potential capability to measure the Doppler spectrum introduced by a dynamic channel. / Master of Science
18

Adaptive Protocols to Improve TCP/IP Performance in an LMDS Network using a Broadband Channel Sounder

Eshler, Todd Jacob 26 April 2002 (has links)
Virginia Tech researchers have developed a broadband channel sounder that can measure channel quality while a wireless network is in operation. Channel measurements from the broadband sounder hold the promise of improving TCP/IP performance by trigging configuration changes in an adaptive data link layer protocol. We present an adaptive data link layer protocol that can use different levels of forward error correction (FEC) codes and link layer automatic retransmission request (ARQ) to improve network and transport layer performance. Using a simulation model developed in OPNET, we determine the effects of different data link layer protocol configurations on TCP/IP throughput and end-to-end delay using a Rayleigh fading channel model. Switching to higher levels of FEC encoding improves TCP/IP throughput for high bit error rates, but increases end-to-end delay of TCP/IP segments. Overall TCP/IP connections with link layer ARQ showed approximately 150 Kbps greater throughput than without ARQ, but lead to the highest end-to-end delay for high bit error rate channels. Based on the simulation results, we propose algorithms to maximize TCP/IP throughput and minimize end-to-end delay using the current bit error rate of the channel. We propose a metric, carrier-to-interference ratio (CIR) that is calculated from data retrieved from the broadband channel sounder. We propose algorithms using the carrier-to-interference ratio to control TCP/IP throughput and end-to-end delay. The thesis also describes a monitor program to use in the broadband wireless system. The monitor program displays data collected from the broadband sounder and controls the settings for the data link layer protocol and broadband sounder while the network is in operation. / Master of Science
19

An examination of the transition region between the troposphere and stratosphere using tracer space.

Monahan, Kathleen Patricia January 2008 (has links)
Stratosphere Troposphere exchange (STE) is important to study as it controls the chemical composition of the upper troposphere/lower stratosphere (UTLS) and thus the radiative balance of this region. STE also controls the transport of chemicals into the stratosphere which are vital to ozone depletion. The troposphere and the stratosphere have specific chemical characteristics and the transition region between these regions displays characteristics of both. Ozone and water vapour concentrations can be used as tracers for the characteristics of the troposphere and stratosphere. This thesis develops measures in tracer space, which allow the determination of the strength and depth of atmospheric mixing between the troposphere and the stratosphere in extratropical regions. The application of entropy as a measure of atmospheric mixing as introduced by Patmore and Toumi [2006], is improved in this study. This is a measure of how the ozone and water vapour mixing ratios vary as a result of mixing. An additional metric to give further information on the form of the mixing line in tracer space is also developed. This measure uses the ozone and water vapour mixing ratios at the boundaries of the transition region (BO3 and BH2O). This study uses data from ozonesondes and hygrometers, along with satellite data from the Atmospheric Infrared Sounder (AIRS). The ozone product from AIRS is also validated as part of this study. The entropy, BO3 and BH2O measures from this study, are successfully shown to detect regions of enhanced mixing in comparison studies. A key comparison shows that the measures developed in this study are able to produce comparable conclusions to higher resolution aircraft data, with regards to mixing. The separation of entropy, BO3 and BH2O, into different categories allows mixing processes to be assigned to some of the categories. Mixing is shown to have geographic preference, with some regions having significantly more mixing. Some categories have preference with regards to their location either poleward or equatorward of the jet stream. In addition, some information as to the direction of the vertical transport, whether stratosphere to troposphere or vice versa, is obtained.
20

An examination of the transition region between the troposphere and stratosphere using tracer space.

Monahan, Kathleen Patricia January 2008 (has links)
Stratosphere Troposphere exchange (STE) is important to study as it controls the chemical composition of the upper troposphere/lower stratosphere (UTLS) and thus the radiative balance of this region. STE also controls the transport of chemicals into the stratosphere which are vital to ozone depletion. The troposphere and the stratosphere have specific chemical characteristics and the transition region between these regions displays characteristics of both. Ozone and water vapour concentrations can be used as tracers for the characteristics of the troposphere and stratosphere. This thesis develops measures in tracer space, which allow the determination of the strength and depth of atmospheric mixing between the troposphere and the stratosphere in extratropical regions. The application of entropy as a measure of atmospheric mixing as introduced by Patmore and Toumi [2006], is improved in this study. This is a measure of how the ozone and water vapour mixing ratios vary as a result of mixing. An additional metric to give further information on the form of the mixing line in tracer space is also developed. This measure uses the ozone and water vapour mixing ratios at the boundaries of the transition region (BO3 and BH2O). This study uses data from ozonesondes and hygrometers, along with satellite data from the Atmospheric Infrared Sounder (AIRS). The ozone product from AIRS is also validated as part of this study. The entropy, BO3 and BH2O measures from this study, are successfully shown to detect regions of enhanced mixing in comparison studies. A key comparison shows that the measures developed in this study are able to produce comparable conclusions to higher resolution aircraft data, with regards to mixing. The separation of entropy, BO3 and BH2O, into different categories allows mixing processes to be assigned to some of the categories. Mixing is shown to have geographic preference, with some regions having significantly more mixing. Some categories have preference with regards to their location either poleward or equatorward of the jet stream. In addition, some information as to the direction of the vertical transport, whether stratosphere to troposphere or vice versa, is obtained.

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