• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 116
  • 18
  • 11
  • 5
  • 5
  • 4
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 225
  • 52
  • 36
  • 30
  • 23
  • 19
  • 19
  • 18
  • 16
  • 15
  • 15
  • 15
  • 13
  • 13
  • 13
  • 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.
41

Mixing and dispersion of a small estuarine plume

Sheridan, Megan January 2018 (has links)
Entrainment velocity, salt flux and the turbulent diffusivity of salt are estimated in the outflow of a small, radially spreading buoyant outflow, just outside of the Teign Estuary mouth, as a means to compare mixing dynamics between very small and larger-scale estuarine and river plumes, and build on a scant knowledge base regarding the former. The analysis was made using a control volume approach, based on the conservation of momentum, volume and salt, from a Lagrangian perspective. Drifting buoys were used to accomplish this. The analysis was based on that employed by McCabe et al. (2008), with some modifications to fit a small-scale outflow, namely: repeat deployments, shorter drifter tracks, and deployment-specific criteria used for choosing the plume base, a step in the analysis used to calculate vertical entrainment, flux and diffusivity. In addition, temperature was used as a proxy for salinity, and this is evaluated in the results. Overall results were compared to a similar study, which was conducted in the Columbia River plume, a system much larger in scale to the Teign. Drifter experiments were conducted on multiple days, under different conditions (i.e. wind, tides, river flow), and those results are discussed briefly, but the focus is on one specific day, April 3, 2014, where conditions most closely matched those of the comparison study, and those results are compared between the two systems. Entrainment velocity was measured along the drifter tracks, in the near-field plume, where shear-induced mixing dominates. Drifter track subsections were chosen so as to avoid source or frontal dynamics, the plume base was chosen for individual deployments as the plume dynamics could change relatively quickly, and repeat deployments were conducted as a way to look at near-field plume evolution over the course of the ebb (and with a smaller plume, time allowed for this) . On April 3, the mean value for entrainment velocity for the four deployments chosen in the Teign outflow was 4.3 x 10-4 ms-1. The mean cast value was slightly higher at 7.6 x 10-4 ms-1, as casts values were typically measured at the beginning of the drifter tracks. Entrainment values at the cast sites were calculated in the same way as the track values, taking plume thickness from hydrographic casts, as a means to evaluate accuracy of track values, which are based on a modelled plume thickness. A rough estimate for the mean entrainment velocity for one pair of drifters used in the Columbia River was 9 x 10-4 ms-1, approximately double that of the Teign, but within the same order of magnitude. Salt flux values ranged from 0-5 x 10-2 psu ms-1 and from 0-3 x 10-2 psu ms-1 for the Teign and the Columbia, respectively, and diffusivities ranged from 0.5-5.8 x 10-2 m2s-1 and from 0.2-9.6 x 10-3 m2s-1. With a similar range of entrainment and salt flux values, and almost an order of magnitude difference between diffusivity values, it was determined that weaker density gradients in the Teign are responsible for the latter, and that this increased level of mixing results in a larger horizontal horizontal salinity gradient, which balances out the terms in the entrainment equation that are related solely to the physical size of the system (i.e. plume thickness, velocity and the vertical salinity gradient). This higher level of mixing of a smaller physical entity, supports the view that smaller plumes mix more thoroughly over a shorter timescale, resulting in a larger impact to the local environment into which they flow.
42

Investigation of light inputs into plant circadian clocks

Dixon, Laura Evelyn January 2011 (has links)
Circadian clocks are biological signalling networks which have a period of ~24 hours under constant environmental conditions. They have been identified in a wide range of organisms, from cyanobacteria to mammals and through the temporal co-ordination of biological processes are believed to increase individual fitness. The mechanisms which generate these self-sustained rhythms, the pathways of entrainment and the target outputs of the clock are all areas of great interest to circadian biologists. The plant circadian clock is believed to comprise of interlocking feedback loops of transcription and translation. The morning MYB-transcription factors CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) bind to the promoter of TIMING OF CAB2 1 (TOC1) and repress its expression, as well as their own. As levels of CCA1 and LHY fall, TOC1 is expressed and activates the expression of its repressors. This is a simplified version of the known clock components and the current model contains this core loop as well as an interlocked morning and evening loop, which also incorporates some post-translational modification (Chapter 1). Understanding the plant circadian network and its entrainment are the topics of this thesis. The study has focused on two plant species, the land plant Arabidopsis thaliana and the picoeukaryotic marine algae Ostreococcus tauri. In both of these species light-mediated entrainment of the clock has been investigated (Chapter 8), as well as the core circadian mechanism. In A. thaliana the role of a circadian associated gene, EARLY FLOWERING 3 has been a particular focus for investigation, through both experimentation and mathematical models (Chapters 4 and 5). In O. tauri the responses to light signals have been tested, as have the circadian responses to pharmacological manipulation (Chapters 6, 7 and 8). The work presented identifies a role for ELF3 in the repression of circadian genes and also links it with the regulation of protein stability. Likewise, in O. tauri the regulation of protein stability is identified to be a key mechanism for sustaining circadian rhythms. As well as investigating the clock in plants, certain photoreceptors have been characterised in S. cerevisiae with the aim of linking them to a synthetic oscillator. Together the work presented in this thesis provides evidence for the circadian community to aid with the understanding of circadian rhythms in plants, and possibly other organisms.
43

Qualitative Study of the Effect of a Compartment Enclosure on Fire Plume Entrainment

Anderson, Scott Kenneth 10 February 2005 (has links)
Zone Models are a widely used tool in fire protection engineering to predict how fires will develop in compartments. Zone models use entrainment algorithms for plumes in the open and the effect of enclosures on the entrainment is currently unclear. This work was a systematic study of six global parameters that effect flame height and the enclosure effect on fire plume entrainment.
44

A sincronização em dois ritmos da canção: uma observação experimental acerca da fala cantada / The Entrainment in two rhythms of the song: an experimental observation about sung speech

Cássio Augusto Alves de Andrade Santos 02 July 2012 (has links)
Este trabalho apresenta um estudo acerca da fala cantada com o português brasileiro inserido no contexto da canção popular. Utilizando como base o processo de sincronização entre os pares de quatro duplas de cantores, elaboramos um experimento fatorial com dois fatores, denominados Ritmo da Canção e Ponto de Observação de Sincronização. Com o fator Ritmo da Canção, buscamos observar se a fala cantada inserida no contexto sincopado, no caso o da bossa-nova, é mais difícil de ser realizada quando comparada a mesma inserida no contexto não sincopado, aqui o do rock. Com o fator Ponto de Observação de Sincronização buscamos observar se os sujeitos têm a mesma capacidade de sincronização em inícios e em finais de frases. Ambos os cálculos foram realizados através das medidas das lags, diferença temporal entre os Pontos de Observação de Sincronização dos cantores de uma mesma dupla, ou seja, ora separamos as lags por canções (fator Ritmo da Canção), ora separamos por ponto (fator Ponto de Observação de Sincronização). Em paralelo, e de forma a complementar o estudo fonético-acústico, observamos o desenvolvimento métrico-acentual das canções, comparando os acentos lingüísticos e os musicais das canções utilizadas. O conjunto de resultados obtidos por meio de cálculos estatísticos e as observações métricoacentuais indicam que os cantores apresentam maior facilidade em realizar a tarefa pedida cantar o mais sincrônico possível no contexto no qual o ritmo de acompanhamento das canções não era sincopado, assim como indica maior facilidade em sincronizar nos finais de sentenças. / This paper presents a study about the Brazilian Portuguese placed in the context of the song. Using as a base the entrainment process between pairs of four pairs of singers, we designed a factorial experiment with two factors, called Rhythm of the Song and Entrainment Observation Point. With the factor Rhythm of the Song, we observe whether the speech into the context of singing bossa-nova is more difficult to achieve when compared to the same inserted in the context of rock. With the factor Entrainment Observation Point we seek to observe whether individuals have the same ability to sync at the beginning and end of sentences. Both calculations were performed by measuring the lag, time difference between entrainment observation points of the singers of the same pair, i.e., separated the lag by songs (factor Rhythm of the Song), and separated by Entrainment Observation Point (factor Entrainment Observation Point). In parallel, and to complement the acousticphonetic study, we observed the development of accentual metric-songs comparing the linguistic and musical accents of the songs used. The set of results obtained by statistical calculation and accentual-metric observations indicates that the singers have it easier to perform the requested task - to sing as synchronous as possible - in the context in which the rhythm accompaniment of songs was not syncopated, so ease as indicated to sync at the end of sentences.
45

Musical connectivity in sitar and tabla performance

Cooper, Alexander January 2018 (has links)
The aim of this dissertation is to define and account for experiences of musical connectivity by exploring the relationship between joint musical action and social experience through a combination of ethnographic and empirical methods. Live sitar and tabla duo performance, in the Hindustānī tradition, forms the focus of the studies. Through its approach and scope, this research contributes to a broadening of knowledge and understanding of how people play music together, and experience varying feelings of 'togetherness' while doing so, from an interdisciplinary, non- Western perspective. The dissertation first considers the various musical and social concepts and behaviours that characterize Hindustānī performance. This is followed by an in-depth analysis of a commercial recording by master musicians Pt. Nikhil Banerjee and Zamir Ahmed Khan, in which the formal, rhythmic, and micro-temporal interactions are explored from a relational, socially-driven perspective. Lastly, qualitative and quantitative data collected through a case study carried out in Varanasi, India, involving close collaboration with expert informants Shyam Rastogi (sitar) and Sandeep Rao (tabla) together with the participation of five other local musicians are presented and discussed. Nine audio-visual performances were recorded, and performers were subsequently interviewed regarding aspects of their social experience whilst playing. Performances were then analysed in order to relate performers' musical interactions with their self-reported feelings of sociality, both generally and at specific moments of their performance. These various results are used to support a novel model of musical connectivity, based on (i) ethnographic insight gathered through fieldwork, (ii) formal and informal interviews with numerous Indian musicians, and (iii) the author's auto-ethnographic account of his practice as a sitar student. This model and the phenomenological insights that it presents are explored in detail in the concluding chapter.
46

Modeling internal deformation of salt structures targeted for radioactive waste disposal

Chemia, Zurab January 2008 (has links)
This thesis uses results of systematic numerical models to argue that externally inactive salt structures, which are potential targets for radioactive waste disposal, might be internally active due to the presence of dense layers or blocks within a salt layer. The three papers that support this thesis use the Gorleben salt diapir (NW Germany), which was targeted as a future final repository for high-grade radioactive waste, as a general guideline. The first two papers present systematic studies of the parameters that control the development of a salt diapir and how it entrains a dense anhydrite layer. Results from these numerical models show that the entrainment of a dense anhydrite layer within a salt diapir depends on four parameters: sedimentation rate, viscosity of salt, perturbation width and the stratigraphic location of the dense layer. The combined effect of these four parameters, which has a direct impact on the rate of salt supply (volume/area of the salt that is supplied to the diapir with time), shape a diapir and the mode of entrainment. Salt diapirs down-built with sedimentary units of high viscosity can potentially grow with an embedded anhydrite layer and deplete their source layer (salt supply ceases). However, when salt supply decreases dramatically or ceases entirely, the entrained anhydrite layer/segments start to sink within the diapir. In inactive diapirs, sinking of the entrained anhydrite layer is inevitable and strongly depends on the rheology of the salt, which is in direct contact with the anhydrite layer. During the post-depositional stage, if the effective viscosity of salt falls below the threshold value of around 1018-1019 Pa s, the mobility of anhydrite blocks might influence any repository within the diapir. However, the internal deformation of the salt diapir by the descending blocks decreases with increase in effective viscosity of salt. The results presented in this thesis suggest that it is highly likely that salt structures where dense and viscous layer/blocks are present undergo an internal deformation processes when these dense blocks start sinking within the diapir. Depending on size and orientation of these blocks, deformation pattern is significantly different within the diapir. Furthermore, model results applied to the Gorleben diapir show that the rate of descent of the entrained anhydrite blocks differs on different sides of the diapir. This suggests that if the anhydrite blocks descent within the Gorleben diapir, they initiate an asymmetric internal flow within it.
47

Pore formation from bubble entrapment by a solidification front and pore formation in solid

Hsiao, Shih-Yen 18 August 2012 (has links)
In this dissertation¡Atwo topics in microbubble systems are investigated¡G1) Pore Formation from Bubble Entrapment by a Solidification Front¡F2) Pore formation in Solid¡C In the first study¡Amechanism of the pore shape in solid resulted from a tiny bubble captured by a solidification front is geometrically and generally investigated¡CPore formation and its shape in solid are one of the most critical factors affecting properties¡Amicrostructure¡Aand stresses in materials¡CFor simplicity without loss of generality, the tiny bubble beyond the solidification front is considered to have a spherical cap in this work¡CIntroducing a geometrical analysis it is found that the contact angle of the bubble cap can be governed by the Abel¡¦s equation of the first kind in terms of displacement of the solidification front¡CThe pore can be elongated, expanded¡Ashrunk and closed¡Adepending on relative variation of the bubble growth rate and solidification rate¡CThe pore can be closed by imposing infinitesimal bubble growth rate-to-solidification rate ratio¡Aand a finite bubble growth-to-solidification rate ratio in order to produce a minimal bubble radius at the contact angle of ¡CA criterion intuitively accepted in the literature¡Astating that closure of a pore is attributed to a greater solidification rate than bubble growth rate¡Ais incorrect¡CThe predicted pore shape and contact angle agree with experimental observations¡CManipulating either bubble growth rate or solidification rate can control pore formation in solid¡C In second study¡Athe shapes of a growing or decaying bubble entrapped by a solidification front are predicted in this work¡CThe bubble results from supersaturation of a dissolved gas in the liquid ahead of the solidification front¡CPore formation and its shape in solid are one of the most critical factors affecting properties¡Amicrostructure, and stresses in materials¡CIn this study¡Athe bubble and pore shapes entrapped in solid can be described by a three-dimensional phase diagram¡Aobtained from perturbation solutions of Young-Laplace equation governing the tiny bubble shape in the literature¡CThe predicted growth and entrapment of a microbubble as a pore in solid are found to agree with experimental data¡CThis work thus provides a realistic prediction of the general growth of the pore shape as a function of different working parameters¡C
48

The Evolutionary and Cognitive Basis of the Perception and Production of Dance

Brady, Adena Michelle January 2012 (has links)
Dance is a universal and ancient human behavior; however, our understanding of the basis of this behavior is surprisingly weak. In this dissertation, I explore the cognitive and evolutionary foundations of human dance, providing evidence of two ways in which the production and perception of dance actions are rooted in the functions of more general cognitive systems.In doing so, I aim to both inform our understanding of dance, and use the study of dance to elucidate broader issues in cognition. Chapter 1 demonstrates that the ability to entrain, or move in time with an auditory beat, is not unique to humans. In addition, across hundreds of species, I find that all animals able to entrain can also vocally imitate sound. This supports the hypothesis that entrainment relies on cognitive machinery that originally evolved to support vocal imitation. Chapter 2 investigates the perception of dance-like actions. Previous work shows that we infer the goals of observed actions by calculating their efficiency as a means to external effects, like reaching an object or location. However, dance actions typically lack an external effect or external goal. In two experiments, I show that for dance-like actions, adults infer that the agents’ goal is simply to produce the movements themselves. Furthermore, this inference is driven by the actions’ inefficiency as a means to external goals. This inefficiency effectively rules out external goals, making movement-based goals the best explanation. Thus, perception of both dance and non-dance actions appears to rely the same type of efficiency-based goal inference. Chapter 3 builds on these findings, showing that the inference that the movements are the goal is closely related to our concept of dance. First, I find that participants view movement-based goals as more consistent with dance than with other activities. Second, I find that simply construing actions as having movement-based goals leads participants to view the actions as more dancelike, even when all participants have seen the exact same actions. Thus, even our categorization of actions as dance versus non-dance is rooted in the same cognitive processes as support our understanding of other intentional actions. / Psychology
49

The Role of High Molecular Weight Polyethylene Oxide in Reducing Quartz Gangue Entrainment in Chalcopyrite Flotation by Xanthate Collectors

Gong, Jihua Unknown Date
No description available.
50

Froth Phase Study using a Naturally Hydrophobic Coal in a Mechanical Flotation Column

Wang, Huiran Unknown Date
No description available.

Page generated in 0.0893 seconds