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Minakova, K., Serhii Petrov, and S. Radoguz. "How "Street chemistry" and "Street physics" settled at the National Technical University "Kharkiv Polytechnic Institute"." Thesis, Copissaurio Repro – Centro Imp. Unip. Lda. Campus de Gualtar, 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/46263.
Повний текст джерела
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Lundin, Lukas. "Tip vortex cavitation and diffused vorticity of propeller profiles: a modelling approach : Investigation of an implemented TVI model, and implementation and investigation of a DVH model." Thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-65102.
Повний текст джерелаАнотація:
To predict fluid properties and interactions is an important task for the industry. It is plagued, however, by being close to impossible to predict analytically. Hence, it is customary to turn to numerical solutions. This in itself comes with many different methods and approaches suitable for different needs. This work focuses on two methods: Tip Vortex Index (TVI) and Diffused Vortex Hydrodynamics (DVH). TVI is a method to predict when a marine propeller will experience cavitation of tip vortices and is based on calculations from a Boundary Element Method (BEM). DVH is a particle method for simulating the circulation of a fluid in two dimensions and three dimensions. The aim is to investigate an implemented TVI model based on MPUF-3A for different marine propeller series, with different sub-designs for a total of 28 unique propellers, and implement the DVH method and test it for 3 different bodies. The results of this thesis show that the implemented TVI model is non-functional for the 28 different propellers, but the DVH method is successfully implemented and able to handle 2 different bodies.<br>Att förutspå fluid egenskaper och interaktioner är en viktig uppgift för industrin. Det plågas dock av att vara näst intil omöjligt att förutspå analytiskt. Det är därför vanligt att vända sig till numeriska lösningar. Detta kommer i sig med många olika metoder och tillvägagångssätt som passar olika behov. Detta arbete fokuserar på två metoder: Tip Vortex Index (TVI) och Diffused Vortex Hydrodynamics (DVH). TVI är en metod för att förutsäga när en marin propeller kommer att uppleva kavitation av spetsvirvlar och baseras på beräkningar från en Boundary Element Method (BEM). DVH är en partikelmetod för att simulera cirkulationen i fluid i två dimensioner och tre dimensioner. Syftet är att undersöka en implementerad TVI-modell baserad på MPUF-3A för olika marina propellerserier, med olika underdesigner, för totalt 28 unika propellrar, och implementera DVH-metoden och testa den för 3 olika kroppar. Resultaten av denna avhandling visar att den implementerade TVI-modellen är icke-funktionell för de 28 olika propellrarna, men DVH-metoden är framgångsrikt implementerad och kan hantera 2 olika kroppar
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Pancaldi, Marco. "Impact of waterbody evaporation in an urban canyon investigated through large-eddy simulations." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amslaurea.unibo.it/25662/.
Повний текст джерелаАнотація:
Lo studio dell'evaporazione da parte di specchi d'acqua in ambiente urbano può contribuire alla comprensione dei fenomeni micrometeorologici e allo sviluppo di soluzioni per migliorare il comfort delle città. Questo problema è stato affrontato usando una simulazione fluidodinamica di un canyon urbano al cui centro è stato posto un canale d'acqua. Per le simulazioni è stato usato un modello di fluidodinamica computazionale sviluppato usando OpenFOAM. Come approccio numerico è stata usata una large-eddy simulation. Tale approccio ha permesso di simulare l'evoluzione del sistema e di analizzarne le variabili medie e turbolente. Il modello è basato su un solutore fluidodinamico in approssimazione di Boussinesq a cui sono state aggiunte le equazioni di avvezione diffusione del vapore e lo scambio termico provocato dall'evaporazione. Inoltre sono state implementate delle condizioni al contorno che potessero modellizzare l'evaporazione d'acqua dal canale. Il modello è stato validato simulando un canale piano usando diversi modelli di turbolenza. Sono state eseguite due simulazioni del canyon urbano, una prima in cui il canale ha una temperatura maggiore dell'aria circostante, e una seconda in cui la temperatura del canale è inferiore all'aria. In entrambe le simulazioni la presenza del canale ha influenzato fortemente sia le variabili medie che turbolente. L'evaporazione d'acqua dal canale e il conseguente galleggiamento ha portato un aumento dell'intensità della velocità all'interno del canyon. Si è assistito inoltre ad un abbassamento delle temperature su tutto il dominio, in particolare nel caso col canale freddo, all'interno del canyon, si è raggiunto un raffreddamento del 10-20% rispetto alla differenza di temperatura tra il canale e la temperatura ambientale iniziale. Si è inoltre osservato un aumento dell'energia cinetica turbolenta in tutto il dominio, e un aumento di flussi turbolenti di quantità di moto soprattutto all'interfaccia tra il canyon e l'aria esterna.
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Attig, Stefan. "The Organic Pattern of Space: : A Space Syntax Analysis of Natural Streets and Street Segments for Measuring Crime and Traffic Accidents." Thesis, KTH, Urbana och regionala studier, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-264938.
Повний текст джерелаАнотація:
The natural streets model is a research prototype that has been shown to perform better than the conventional GIS-based streets segments for explaining traffic flow and human movement. However, given its experimental status, a gap in the literature was identified. Therefore, the aim of this thesis was to contribute to the literature by investigating the wider applications of natural streets and observe whether a city’s spatial configuration (or structure) is related to outcomes of human behaviour and activity. In this case, the two previously unstudied outcomes were chosen: crime and traffic accidents. Taking an exploratory approach, Stockholm was chosen as the case study. Using the space syntax methodology, the street segments and natural streets connectivity was used to analyse whether accessibility or ‘potential through movement’ is associated with crime and traffic accidents. Two study areas were generated: a primary study area consisting of six nested zones and a secondary study area with hot spots and cold spots for events of crime and traffic accidents. To observe the statistical association between connectivity and events of crime and traffic accidents for natural streets and street segments, a classical regression model was used. The regression analysis showed that natural streets perform significantly better than street segments as they are better able to explain events of crime and traffic accidents. However, more so for traffic accidents. Most importantly, the topological structure or scaling characteristics of natural streets served as a better indicator for measuring human phenomena. The implication of this is that it could potentially be used to further the understanding of human activities in the context of the urban environment.
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朱廷杰 and Tingjie Zhu. "The physical environment and revitualization of local commercial street: urban design study in revitalizingShuidong street in Huizhou, Guangdong, China." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B41668947.
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Zhu, Tingjie. "The physical environment and revitualization of local commercial street urban design study in revitalizing Shuidong street in Huizhou, Guangdong, China /." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B41668947.
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Baumgartner, Andreas [Verfasser], and Martin [Akademischer Betreuer] Dressel. "Identifying street conditions by infrared spectroscopy / Andreas Baumgartner ; Betreuer: Martin Dressel." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2020. http://d-nb.info/1206590394/34.
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Newby, Matthew T. "The sagittarius tidal stream and the shape of the galactic stellar halo." Thesis, Rensselaer Polytechnic Institute, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3601024.
Повний текст джерелаАнотація:
<p> The stellar halo that surrounds our Galaxy contains clues to understanding galaxy formation, cosmology, stellar evolution, and the nature of dark matter. Gravitationally disrupted dwarf galaxies form tidal streams, which roughly trace orbits through the Galactic halo. The Sagittarius (Sgr) dwarf tidal debris is the most dominant of these streams, and its properties place important constraints on the distribution of mass (including dark matter) in the Galaxy. Stars not associated with substructures form the "smooth" component of the stellar halo, the origin of which is still under investigation. Characterizing halo substructures such as the Sgr stream and the smooth halo provides valuable information on the formation history and evolution of our galaxy, and places constraints on cosmological models. This thesis is primarily concerned with characterizing the 3-dimensional stellar densities of the Sgr tidal debris system and the smooth stellar halo, using data from the Sloan Digital Sky Survey (SDSS). F turnoff stars are used to infer distances, as they are relatively bright, numerous, and distributed about a single intrinsic brightness (magnitude). The inherent spread in brightnesses of these stars is overcome through the use of the recently-developed technique of statistical photometric parallax, in which the bulk properties of a stellar population are used to create a probability distribution for a given star's distance. This was used to build a spatial density model for the smooth stellar halo and tidal streams. The free parameters in this model are then fit to SDSS data with a maximum likelihood technique, and the parameters are optimized by advanced computational methods. Several computing platforms are used in this study, including the RPI SUR Bluegene and the Milkyway@home volunteer computing project. Fits to the Sgr stream in 18 SDSS data stripes were performed, and a continuous density profile is found for the major Sgr stream. The stellar halo is found to be strongly oblate (flattening parameter q=0.53). A catalog of stars consistent with this density profile is produced as a template for matching future disruption models. The results of this analysis favor a description of the Sgr debris system that includes more than one dwarf galaxy progenitor, with the major streams above and below the Galactic disk being separate substructures. Preliminary results for the minor tidal stream characterizations are presented and discussed. Additionally, a more robust characterization of halo turnoff star brightnesses is performed, and it is found that increasing color errors with distance result in a previously unaccounted for incompleteness in star counts as the SDSS magnitude limit is approached. These corrections are currently in the process of being implemented on MilkyWay@home.</p>
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Dragani, Lorenzo. "Winning ways for your learning days - Analisi di libri di testo in fisica." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21062/.
Повний текст джерелаАнотація:
Lo scopo di questo lavoro è analizzare testi che hanno avuto un grande successo nel mondo dell’insegnamento della Fisica a livello Universitario utilizzando concetti provenienti dalla psicologia per tentare di capire se e quali siano le caratteristiche che li contraddistinguono come efficaci strumenti didattici.
I testi sono stati selezionati analizzando e confrontando sia i tassi di adozione di questi presso prestigiosi Dipartimenti di Fisica sia le valutazioni e le recensioni su riviste specializzate, siti di e-commerce e rating di libri.
L’analisi è stata inoltre complementata da interviste agli autori, i quali hanno spiegato come hanno sviluppato i loro libri e l’approccio didattico che li caratterizza.
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Komolafe, Olufemi O. "High-speed optical packet switching over arbitrary physical topologies using the Manhattan Street Network." Thesis, University of Strathclyde, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366847.
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DeVault, J. Ross. "Active and restorative campus: designing a garden street for student’s mental and physical well-being." Kansas State University, 2015. http://hdl.handle.net/2097/19238.
Повний текст джерелаАнотація:
Master of Landscape Architecture<br>Department of Landscape Architecture/Regional and Community Planning<br>Hyung Jin Kim<br>A significant decline of mental and physical health exists within college students today (ACHA, 2014; Gallagher, 2006). Recently, to promote mental health, restorative landscapes have emerged as a trend in healthcare environments by formalizing the healing properties of nature within a designed environment. Humans have been shown to undergo a measurable relief of stress, improved attention, and an improved overall sense of well-being when exposed to a restorative landscape setting. Opportunities exist for university campuses to more advantageously employ the mental health benefits of restorative landscapes. Furthermore, to address physical health, the university campus holds unique opportunities to increase students’ physical activity through promotion of active lifestyles using active modes of transportation. Campus streets, based on their lack of affordances to promote mental and physical health as well as their inherent connectivity to key campus buildings and spaces are investigated as a site for a designed solution. A recent trend of campus street conversions to pedestrian malls is identified and explored as a tool to facilitate creation of a restorative and active campus. The project, based in two fundamental research questions, investigates how campus street design can improve the collective mental health of college students, and how campus street design can promote physical health. Literature review analysis reveals theories and principles of restorative landscape and campus design. The project unites these findings with case study analysis to form a framework to facilitate the design of restorative environments within a university campus. Pragmatic evidence of built environment interventions has been synthesized from literature review and case study analysis into an additional framework to increase physical activity through active transportation. Kansas State University’s campus has been identified as a suitable case for a design proposal. Planning and design decisions at three nested scales are made to illustrate how the frameworks may be applied to reclaim a campus street as an active and restorative “garden street.” In the context of declining mental and physical health among college students, the synthesis of principles related to restorative landscape design and active transportation presents a valuable structure to mitigate declining mental and physical health of students.
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Nichols, Christopher A. "Surface reflection hyperthermal neutral stream source." W&M ScholarWorks, 1996. https://scholarworks.wm.edu/etd/1539623889.
Повний текст джерелаАнотація:
A novel source of hyperthermal (1-30 eV) reactive neutrals based on the surface-reflection-neutralization technique is described. This source is potentially capable of minimizing the charge-induced damage associated with plasma based semiconductor processing steps. The goal of this thesis is to investigate the issues involved in scale-up of this technology for processing of 8{dollar}\sp{lcub}\prime\prime{rcub}{dollar} diameter wafers used today in the semiconductor industry. This includes modeling the plasma ion source and trajectory simulations of the reflected neutral flux. A prototype source was constructed for experimental verification of the plasma model.;An inductively coupled plasma (ICP) source is used to provide a source of reactive ions. These ions are neutralized and reflected through interaction with a biased metal plate. These reflected neutrals are directed at a wafer to be etched (for feature delineation) or cleaned (removal of etch residue).;The plasma source is modeled with a global (volume averaged) power deposition model to determine plasma densities at the reflector plate. The modeled values are compared to measurements of a prototype neutral stream source. Plasma parameter measurements are carried out using Langmuir single probes. It is found that the plasma densities in the upstream plasma source and at the reflector plate agree well (within 10%) with the model.;Several models of reflected neutral trajectories are used to determine the final flux characteristics at the wafer. 2-D and 3-D ray trace trajectory models were used, as well as a full 3-D Monte Carlo treatment. It is found that in geometry considered in this work, background pressure plays a key role in delivering hyperthermal neutrals to the wafer. Energy and angular distributions are altered severely as the neutrals traverse the background gas and plasma.
13
Elliott, Nalishebo Kay Gaskell. "The health and wellbeing of female street sex workers." Thesis, University of Hertfordshire, 2017. http://hdl.handle.net/2299/19510.
Повний текст джерелаАнотація:
Previous research on female street sex workers (FSSWs) has primarily concentrated on the stigmatisation of women's involvement in the sex industry particularly with reference to the spread of HIV/AIDS. The response of the criminal justice system to the regulation of the illegal aspects of women's engagement in street sex work has also been criticised. However, the impact of street sex work on the health and wellbeing of these women requires further research. The aim of this study was to explore the perceptions and needs of female street sex workers in relation to their own health and wellbeing. The study used a qualitative mixed methods approach that included analysis of three sets of data: visual data, secondary data and primary data. There were 10 FSSWs recruited for the primary data sample. The epistemological position underpinning this study is social constructivism and a feminist paradigm has informed the conduct of the research process and data analysis. The theoretical application of Bourdieu's framework of habitus, capital and field has provided the lens through which to explore the socially constructed experiences of FSSWs health and wellbeing. Findings from this study revealed that FSSWs experienced poor physical, mental and social health and wellbeing. They faced limited life choices and often felt discriminated against by the agencies and institutions that should have offered support. The women spoke of their personal histories especially traumatic life events in childhood consisting of sexual abuse, neglect, loss, rejection as well as intimate partner violence in adult life. The loss of their children to social services, housing difficulties and addiction to alcohol and crack cocaine were also significant in contributing to social exclusion and their multiple positions of vulnerability. This study contributes to the body of work on women's health and wellbeing. In particular, it adds to our understanding of the lived experiences of women involved in street sex work. A key public health priority should be the development of policies and systems to provide quality services to support the health, safety and wellbeing of FSSWs.
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Magirl, Christopher Sean. "Bedrock-controlled Fluvial Geomorphology and the Hydraulics of Rapids on the Colorado River." Diss., The University of Arizona, 2006. http://www.gcmrc.gov/library/reports/physical/Coarse_Sed_Webb/Magirl2006a.pdf.
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Thurell, Erik. "The Good- & Socially Sustainable Street, from a Human Perspective : Focusing on the Relationship between Physical Environments and Social Life, with Hornsgatan in Stockholm as a Case Study." Thesis, KTH, Urbana och regionala studier, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-102381.
Повний текст джерелаАнотація:
With over 300 years serving as a traffic route it is no wonder that Hornsgatan has the role of a major ‘artery’ in today’s Stockholm. This thesis will analyze and investigate how the street environment on Hornsgatan is affecting the people spending time on the street, and how a better street life and street quality can be brought out when it comes to enhance the social aspects for the street and its people. Through methods such as observations of the street and interviews with business owners, the case study of Hornsgatan have been based upon some theories by famous theorists when it comes to improving streets (and urban life) in cities, e.g.; Appleyard (1981), Jacobs (1993) and Gehl (2010). The results from the case study and the interviews show that Hornsgatan have both factors of what a ‘good’ and socially sustainable street should have; mix-use, the presence of people and social activities, active ground floors and different traffic modes, and factors that contribute to a less attractive street life; the heavy traffic, lack of places to sit, lack of greenery and lack of social activities for/between people. To reply the question if Hornsgatan is a ‘good’ and socially sustainable street or not, the answer is both yes and no. As Appleyard (1981) states, “[…] there is no single perfect street […]” (Appleyard 1981, p. 245). Instead each street and its situation are unique. However, with guidelines and aspects for how a street can be improved, at least some help can be brought out for its improvements.<br>Urban Form and Social Behaviour Research Project
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Mustard, Alexander T. "The relationship between zooplankton and their physico-chemical environment at the mesoscale." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342853.
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Addison, Victor G. "The physical oceanography of the northern Baffin Bay-Nares Strait region." Thesis, Monterey, California. Naval Postgraduate School, 1987. http://hdl.handle.net/10945/22417.
Повний текст джерелаАнотація:
Approved for public release; distribution is unlimited<br>A dense network of conductivity-temperature-depth measurements was conducted from Baffin Bay northward to 82 deg 09 min N at the entrance to the Lincoln Sea, in the most comprehensive physical oceanographic survey ever performed in the northern Baffin Bay-Nares Strait region. These data indicate Nares Strait Atlantic Intermediate Water and Arctic Basin Polar Water to be derived from Arctic Basin waters via the Canadian Archipelago, whereas the West Greenland Current (WGC) is the source of the comparatively dilute West Greenland Current Atlantic Intermediate Water and West Greenland Current Polar Water fractions. Baffin Bay Surface Water is found seasonally throughout northern Baffin Bay. Recurvature of component branches of the WGC, which attains a maximum baroclinic transport of 0.7 Sv, occurs primarily in Melville Bay (0.2 Sv), south of the Carey Islands (0.1 Sv) and ultimately in Smith Sound (0.2 Sv). The Baffin Current originates as an ice-edge jet in Smith Sound and is augmented by net outflow from Smith, Jones and Lancaster Sounds at rates of 0.3 Sv, 0.3 Sv and 1.1 Sv, respectively. Circulation in Smith, Jones and Lancaster Sounds can be described in terms of the Geostrophic Estuarine Circulation Model. The North Water is caused by the combined influences of near-surface layer enthalpy and mechanical ice removal. KeywordsL Sea water temperature; Oceanographic data; Straits; Sounds(Waterways); Ocean currents
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Kronkvist, Karl. "SYSTEMATIC SOCIAL OBSERVATION OF PHYSICAL DISORDER IN INNER-CITY URBAN NEIGHBORHOODS THROUGH GOOGLE STREET VIEW: THE CORRELATION BETWEEN VIRTUALLY OBSERVED PHYSICAL DISORDER, SELF-REPORTED DISORDER AND VICTIMIZATION OF PROPERTY CRIMES." Thesis, Malmö högskola, Fakulteten för hälsa och samhälle (HS), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-25624.
Повний текст джерелаАнотація:
Sambandet mellan den fysiska miljön och brottslighet har sedan länge varit en relevant fråga inom den kriminologiska diskursen. Den föreliggande studien ämnar vidare undersöka huruvida fysisk oordning i urbana bostadsområden kan studeras genom Google Street View, ett webbaserat instrument för virtuella observationer. Syftet med studien är att undersöka om virtuellt observerad och självrapporterad uppfattad grad av fysisk oordning i bostadsområdet mäter samma fenomen, men även om virtuellt observerad fysisk oordning kan förklara skillnader i självrapporterad utsatthet för egendomsbrott. Genom att utföra virtuella observationer av fysisk oordning med hjälp av Google Street View i tjugo centralt belägna bostadsområden i Malmö visar resultaten att observerad och självrapporterad grad av fysisk oordning är starkt korrelerade och förefaller mäta samma fenomen. Resultaten visar även att observerad nivå av fysisk oordning genom Google Street View till viss del kan förklara variansen av utsatthet för egendomsbrott mellan bostadsområden. Avslutningsvis framhålls i studien att virtuella observationer genom Google Street View är ett lovande samt potentiellt kostnadseffektivt tillvägagångssätt för att undersöka graden av fysisk oordning i urbana bostadsområden. Användandet av Google Street View kantas dock av flera begränsningar som både framhålls och diskuteras grundligt i denna studie.<br>The correlation of physical environment and crime has been an ever relevant topic in the criminological discourse. This study attempts to unravel whether physical disorder in inner-city urban neighborhoods may be studied through Google Street View as a virtual observational tool. The aims of the study is to examine whether virtually observed and self-reported perceived level of neighborhood disorder measure the same phenomenon, and whether virtually observed physical disorder may explain variations of self-reported victimization of property crimes. By conducting virtual observations of physical disorder in twenty inner-city neighborhoods of Malmö through Google Street View, the results of the study propose that virtually observed and self-reported perceived level of disorder is strongly correlated and thus seems to measure the same phenomenon to a great extent. The results of the study also imply that observed physical disorder through Google Street View also accounts for neighborhood differences in victimization of property crimes. The study concludes that virtual observation through Google Street View is a promising and potentially cost-effective alternative approach when auditing neighborhood physical disorder. The methodology does however suffer by limitations which is highlighted and thoroughly discussed.
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Woodcock, Thomas Stuart. "Effects of Roadway-Related Physical and Chemical Habitat Alterations on Stream Ecosystems." Fogler Library, University of Maine, 2002. http://www.library.umaine.edu/theses/pdf/WoodcockTS2002.pdf.
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Fredriksson, Ivy. "The Hidden Value of House and Home : An analysis of the social and physical setting in The House on Mango Street." Thesis, Örebro universitet, Institutionen för humaniora, utbildnings- och samhällsvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-49730.
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Hilderbrand, Robert Howard. "Relations between large woody debris, physical habitat, and benthic macroinvertebrates in Appalachian mountain streams." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06082009-170744/.
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Garner, Grace. "River and stream temperature in a changing climate." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5418/.
Повний текст джерелаАнотація:
There is major concern that river temperature changes driven by a changing climate and associated hydrological changes will have profound impacts on freshwater ecosystems. To identify the rivers most sensitive to change and implement effective strategies to mitigate high thermal extremes, this thesis aims to improve understanding of the influences of hydrometeorology and riparian landuse on river temperature dynamics, controls and processes within a UK context. Four studies are presented within a multi-scale research design which aimed to improve understanding of: (1) spatial patterns and inter-annual variability in the shape and magnitude of annual river temperature regimes across England and Wales, and regime sensitivity to air temperature and river basin properties, (2) the effects of riparian vegetation on water temperature under a range of hydrometeorological conditions, (2) the processes by which cool water refugia are produced beneath semi-natural, deciduous forest canopies, and (4) how minimal riparian planting can be used to produce thermal refugia in reaches of differing aspect and hydraulic characteristics. The aims are achieved by combining observational, statistical and deterministic modelling techniques. The outcomes of the research contribute significant new knowledge and tools for evidence based management of river and stream temperature under present and future climates.
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Strebel, Artur [Verfasser]. "Advanced Applications For Algebraic Multigrid Methods In Lattice QCD / Artur Strebel." Wuppertal : Universitätsbibliothek Wuppertal, 2020. http://d-nb.info/1219166650/34.
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Harries, Tom. "Physical testing and numerical modelling of a novel vertical-axis tidal stream turbine." Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/66145/.
Повний текст джерелаАнотація:
A combination of climate change, due to anthropogenic CO2 emissions and concerns over energy security, due to fluctuating fuel prices, has led to the UK pushing to increase its renewable energy production. Harnessing tidal stream energy is an infant sector in the UK’s renewable energy portfolio, despite the UK’s large tidal stream resource, and is harnessed through deploying tidal stream energy converters. This thesis focuses on the design of a novel vertical axis tidal turbine (VATT) called CarBine which is driven by drag force and therefore has several unique advantages, including slow rotational speed, omni-directionality and a simple design. This research focused on the optimisation of the CarBine design and was split into two areas: physical testing and numerical modelling. A conventional Savonius was also analysed in both of these respects and this enabled a direct comparison of CarBine to a competing drag force driven VATT. Physical testing measured the power of the turbines and was conducted in hydraulic flumes at both Cardiff University (CU) and IFREMER in Northern France for a range of flow conditions. Testing at IFREMER enabled the quantification of the blockage effect in the CU experiments. Physical testing resulted in the optimised design of CarBine being one with a four arm configuration. From physical testing at CU, CarBine showed inferior efficiency performance to that of the conventional Savonius, a Cp of 0.117 compared to 0.225 at U∞=0.72 m/s. As a result a hybrid of both the Savonius and CarBine was tested, namely a Savonius with flaps. However, results from physical testing showed the Savonius with flaps to have inferior performance to both CarBine and the conventional Savonius, with a Cp of 0.103 at U∞=0.72 m/s at CU. Numerical modelling was conducted using the commercial CFD software package, Ansys CFX. Both transient and steady state simulations along with 2D and 3D models were used to model both CarBine and the Savonius. Both the k-ε and SST turbulence models were used for comparison. The two degrees of rotational freedom present in the CarBine design resulted in CarBine being difficult to model precisely. The numerical modelling results were validated against the physical testing results and where available, 3D results showed closer validation than the 2D results.
25
Heacock, Tony. "Sea ice -- Nunavut -- Barrow Strait." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=105370.
Повний текст джерела
26
Neary, James P. "Use of physical habitat structure to assess stream suitability for brown trout : a case study of three upland Scottish streams." Thesis, University of Stirling, 2006. http://hdl.handle.net/1893/209.
Повний текст джерелаАнотація:
In 2000 the European Union introduced the Water Framework Directive, new legislation that regulates the use of surface waters within the European Community. The goal of this legislation is to protect, enhance and restore all surface waters within the Community to Good Surface Water Status. Good-Status is described as having low levels of anthropogenic distortion in its hydro-morphological and physiochemical components as well as possessing biota that would normally be associated with the type-specific aquatic ecosystem. The assessment of ecosystem status is to be defined by comparisons with intact representative reference sites, by using modelling techniques that define reference conditions, a combination of the two, or expert judgement. As undisturbed aquatic ecosystems are rare or non-existent in Europe the base-line data will have to be defined using the latter methodologies. The aim of this project is to help define reference conditions for lotic systems in Europe based on the physical instream habitat parameters of a resident species. Brown trout (Salmo trutta), a ubiquitous and well studies species endemic to Europe, was used as the target organism to develop the assessment protocol. The project focused on the requirements this species has of aspects of its physical habitat; specifically, its usage of depth, velocity, and substrate. An extensive survey of the scientific literature was used to define the requirements trout has for the three physical parameters at four life stages. These are the spawning, nursery, juvenile and adult-resident life stages. These requirements were expressed as tolerance profiles, which defined suitable, usable and not-suitable habitat. The methodology was demonstrated by evaluating the physical habitat available at six reaches in three small streams, March, Burnhouse and Bin Burns, which drain into the Carron Valley Reservoir in central Scotland. From the perspective of water depth, these streams seem best suited as nursery areas, are less well suited as juvenile habitat, and do not appear to be well matched for adult residents. The assessment of both velocity and substrate indicated that the portion of the study reaches available for use by resident brown trout increased with trout size. The assessment of all three physical habitat parameters at all study reaches found variable portions of the streams suitable for use by spawning trout. When the habitat variables are integrated all stream segments streams seem best suited as nursery and spawning areas. To a lesser extent juvenile trout can use these burns and very little habitat is available for use by adult resident trout. The tolerance profiles that were created in this study are standardized assessment criteria that when compared with stream survey data can produce an appraisal of habitat availability in any fluvial freshwater system that supports populations of brown trout (Salmo trutta). The assessment method can be combined to produce an integrated habitat assessment, using both an index and by the calculation of Froude number, which is a more realistic approach than the assessment of individual habitat parameters as salmonids choose their microhabitat based on multiple factors. This approach allows an investigator to determine the amount and relative portion of useable habitat and to determine the quality of that habitat. Finally, by examining the physical habitat variable that most strongly correlates with the final integrated habitat distribution the individual habitat parameter that is most important to the distribution of physical habitat at a site can be determined. While this technique would certainly benefit from further development it does show potential to aid in physical habitat assessment of trout streams.
27
Åkesson, Anna. "Peakflow response of stream networks : implications of physical descriptions of streams and temporal change." Doctoral thesis, KTH, Vattendragsteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-172939.
Повний текст джерелаАнотація:
Through distributed stream network routing, it has quantitatively been shown that the relationship between flow travel time and discharge varies strongly nonlinearly with stream stage and with catchment-specific properties. Physically derived distributions of water travel times through a stream network were successfully used to parameterise the streamflow response function of a compartmental hydrological model. Predictions were found to improve compared to conventional statistically based parameterisation schemes, for most of the modelled scenarios, particularly for peakflow conditions. A Fourier spectral analysis of 55-110 years of daily discharge time series from 79 unregulated catchments in Sweden revealed that the discharge power spectral slope has gradually increased over time, with significant increases for 58 catchments. The results indicated that the catchment scaling function power spectrum had steepened in most of the catchments for which historical precipitation series were available. These results suggest that (local) land-use changes within the catchments may affect the discharge power spectra more significantly than changes in precipitation (climate change). A case study from an agriculturally intense catchment using historical (from the 1880s) and modern stream network maps revealed that the average stream network flow distance as well as average water levels were substantially diminished over the past century, while average bottom slopes increased. The study verifies the hypothesis that anthropogenic changes (determined through scenario modelling using a 1D distributed routing model) of stream network properties can have a substantial influence on the travel times through the stream networks and thus on the discharge hydrographs. The findings stress the need for a more hydrodynamically based approach to adequately describe the variation of streamflow response, especially for predictions of higher discharges. An increased physical basis of response functions can be beneficial in improving discharge predictions during conditions in which conventional parameterisation based on historical flow patterns may not be possible - for example, for extreme peak flows and during periods of nonstationary conditions, such as during periods of climate and/or land use change.<br><p>QC 20150903</p>
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Ketzer, Daniel T. "Evaluation of the change in physical features of two over-wide channel stream relocation projects." Connect to resource, 2007. http://hdl.handle.net/1811/25095.
Повний текст джерелаАнотація:
Thesis (Honors)--Ohio State University, 2007.<br>Title from first page of PDF file. Document formatted into pages: contains IV, 26 p.; also includes graphics. Includes bibliographical references (p. 20-21). Available online via Ohio State University's Knowledge Bank.
29
Klingel, Heidi M. "Developing a physical effectiveness monitoring protocol for aquatic organism passage restoration at road-stream crossings." Thesis, Colorado State University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1558242.
Повний текст джерелаАнотація:
<p> Two US Forest Service draft monitoring protocols are used to assess the effectiveness of design channels at road-stream crossings by comparing their physical channel dimensions to those in the natural channel. Level II physical monitoring is a time intensive, quantitative and statistically based procedure for assessing effectiveness at selected sites. Level I physical monitoring is a less detailed, rapid procedure limited to a few simple measurements and observations for assessing effectiveness at a large number of sites. Study objectives were to: 1) test and refine the field methods for collecting data by the levels I and II physical monitoring protocols; 2) find a meaningful way to combine the data collected by levels I and II into separate effectiveness evaluations by each protocol; and, 3) evaluate whether the level I protocol can be used as a proxy for the level II protocol. Where the two protocols systematically differ, field data help distinguish why. </p><p> Study results for all objectives (combined) include: improved field methodologies, recommendations for further development, and separate summary rubrics for the levels I and II monitoring protocols. The recommendations are of three categories; channel metrics/data collection, methods of scoring each metric, and sample sizes. Some of most significant of those recommendations are described within the following paragraphs. </p><p> Data collection methods might be improved to save time, increase the accuracy of protocol evaluations, and facilitate agreement between the levels I and II protocol evaluation results. The techniques by which the level I bankfull stage and coarse fraction of the gradation metrics are collected should incorporate level II methods. Instructions for collecting level II coarse fraction of the gradation data should specify measuring all particles within the channel, including particles much larger than the sampling frame. The level I method by which the representative reach is selected should incorporate a basic longitudinal profile survey in which only the most prominent grade controls separating slope segments are captured. Decreasing the allowable gradient difference between the level II design channel and representative reach might also improve accuracy. The method by which the levels I and II protocols compare channel units (or channel unit sequences) between the design and representative reach should be equivalent, as should the rules by which slope segments and channel units are defined. Finally, the channel metrics of low flow width and bed irregularity are inconsistent with the objectives of physical effectiveness monitoring, in that they are aspects of habitat, rather than strong controls on channel form. I suggest they be eliminated from the levels I and II protocols. </p><p> The level II summary rubric scores most metrics statistically by a Wilcoxon Rank-Sum test of medians. For most metrics, the Wilcoxon Rank-Sum test appears to be a reasonable way to compare representative reach and design zone data. For the metrics of bed and bank irregularity, however, a test of distributions (e.g., Kolmogorov-Smirnov) is recommended instead. The coarse fraction of the gradation metric would be more fairly assessed if the modes of the particle size (in phi units) were compared instead of the medians. Doing so would allow the design and representative reach gradients to be slightly different (as does the criteria for selecting a representative reach) without penalizing the metric score. </p><p> The levels I and II summary rubric tools created were used to evaluate twelve AOP road-stream crossing designs. The performance of the levels I and II summary rubrics were then assessed by the evaluation results at those twelve sites. Levels I and II generally seemed to provide effectiveness evaluations which agreed with site observations, data, and photographs. Further, the summary rubrics facilitated concurrent evaluation of the many channel dimensions which together affect the hydraulic conditions experienced by aquatic organisms. In addition, the simple utility of the levels I and II summary rubric tools should encourage effectiveness monitoring and help restoration practitioners learn from their mistakes, ultimately improving aquatic organism passage design methods and results. (Abstract shortened by UMI.)</p>
30
Karlsten, Annika. "Quantifying the physical effects of stream restoration: With unmanned aerial vehicles and geographic information systems." Thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-160181.
Повний текст джерелаАнотація:
Stream restoration efforts often aim at restoring the physical complexity in streams, as an increased habitat heterogeneity is believed to increase biodiversity. It is important to quantify the physical complexity of streams before and after restoration, to know what actions are needed, and to monitor the results of the restoration. The use of unmanned aerial vehicles (UAVs) and geographic information systems (GIS) for data acquisition is rapidly increasing, and the use of UAVs and GIS could facilitate the monitoring process. The aim of this study was to determine how the spatial complexity in streams can be determined by using UAVs and GIS. The physical features and the spatial complexity were quantified in five reaches in the Lögde River, pre- and post-restoration, by analyzing UAV photos in a GIS program. Three of six reach descriptive metrics, and three of seven complexity metrics, were shown significantly different after restoration. To validate the GIS analyzing method, a qualitative comparison of data from the GIS analysis to field survey data was conducted. The GIS method was shown effective for distinguishing morphological features on a larger spatial scale, and to show the spatial distribution of instream features, such as wood pieces and boulders. The accuracy when digitizing the bankfull edge of the stream was low on small scales, and the method likely underestimates the number of wood pieces and boulders in the streams. Preferable camera settings and weather conditions to avoid blurry UAV photos, and thereby enhance the accuracy of the GIS analysis, are discussed.
31
Turley, Matthew. "A biomonitoring tool to identify and quantify the impacts of fine sediment in river and stream ecosystems." Thesis, University of Brighton, 2017. https://research.brighton.ac.uk/en/studentTheses/cc7c8518-42fc-4943-b295-ff6330702f39.
Повний текст джерелаАнотація:
In rivers and streams, fine sediment pollution is one of the most commonly attributed causes of ecological degradation. As fine sediment is also an important natural component of these ecosystems, and is variable both temporally and spatially, setting environmental targets and using conventional monitoring to determine where fine sediment is causing ecological degradation, is a complex challenge. An alternative approach is the use of biomonitoring tools, which utilise biota to gauge and track changes in the environment. This thesis examines the current state of sedimentbiomonitoring, considers the numerous theoretical and methodological decisions made during tool development, and applies a best practice approach to the development and testing of a sediment-specific tool. An existing biological index, which utilises knowledge of biological and ecological traits, is used as a basis for this development, following an evaluation of its performance over 835 minimally impacted temperate river and stream sites. The index is further developed using empirical data to assign indicator weights to individual taxa. The resulting index, the Empirically-weighted Proportion of Sediment-sensitive Invertebrates (E-PSI) index had moderate to strong correlations with fine sediment in independent test datasets of minimally (n = 84) (family-level: rs = -0.72; mixed-level: rs = -0.70; p < 0.01) and agriculturally impacted sites (n = 754) (family-level: rs = -0.68, p < 0.01). The E-PSI index has retained a biological basis, is easily integrated into regulatory agency protocols, and can be applied retrospectively to historic datasets. Despite the improved performance, a high amount of variation was observed between E-PSI and fine sediment cover. This is likely the result of the presence of multiple pressures, uncertainties concerning sediment-biota interactions, and the relatively low precision of sediment quantification techniques. Due to the prevalence of freshwater non-native invasive species, the effects of North American signal crayfish (Pacifastacus leniusculus) invasions on sediment- biomonitoring and fine sediment are also investigated. Additionally, given the subjective nature and lack of representativeness of many existing sediment quantification techniques, a novel, more objective, verifiable, and non-destructive method is developed and presented as “proof of concept”. This thesis contributes significantly to the literature concerning biomonitoring tool development and testing, and has resulted in a sediment-specific index that has a stronger correlation with its specific pressure, than the average biomonitoring tool used throughout Europe. The E-PSI index can be used alongside a suite of other biomonitoring tools, to identify the most likely causes of ecological degradation, and inform more targeted monitoring.
32
Grant, Jane D. "The significance of groundwater-surface water interactions on hyporheic physico-chemistry and stream ecology in two Scottish mountain rivers." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources. Online version available for University members only until Apr. 7, 2010, 2008. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=26046.
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33
Beliakova, Natalia Yurievna 1967. "Generation and maintenance of recirculations by Gulf Stream instabilities." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/58539.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 1999.<br>Includes bibliographical references (leaves 220-224).<br>This thesis studies the problems of generation and maintenance of recirculations by Gulf Stream instabilities. Observations show that the horizontal structure of the jet and its recirculations suffer significant changes in time. Here, the role of internal dynamics of the jet is isolated as one of the possible sources of such variability, and the differences between barotropic and baroclinic instabilities are investigated. The problem of recirculation development is considered in a framework of a free spin down of the 2-layer and the lI-layer, zonally symmetric, quasi-geostrophic jets. Linear stability analysis shows that in strongly baroclinic basic flows, eddies are capable of driving recirculations in the lower layer through the residual meridional circulation. In strongly barotropic jets, the linearly most unstable wave simply diffuses the jet. Nonlinear stability analysis indicates that recirculations are robust features of the 2-layer model. The strength of recirculations is a function of the model's parameters. It increases with a decrease in the value of the nondimensional # due to potential vorticity homogenization constrained by enstrophy conservation. The recirculation strength is a non-monotonic function of the baroclinic velocity parameter; it is the strongest for strongly baroclinic basic flows, weakest for flows with intermediate baroclinic structure and of medium strength for strongly barotropic basic flows. Such non-monotonic behavior is the result of two different processes responsible for the recirculation development: linear eddy-mean flow interactions for strongly baroclinic basic flows and strongly nonlinear eddy-eddy and eddy-mean flow interaction for strongly barotropic flows. In the case of the reduced-gravity model, recirculations develop only for infinite deformation raduis. Basic flows with finite deformation radius are only weakly supercritical and therefore produced negligible recirculations after equilibration. The problem of maintenance of the recirculations is coupled to the questions of existence of low frequency variability and of multiple dynamical regimes of a system consisting of a quasi-geostrophic jet and its recirculations. The problem is studied in a framework of a 2-layer or a reduced-gravity colliding jets model which has no windforcing. Instead, it is forced by inflows and outflows through the open boundaries. Only the western boundary of the domain is closed, and a free slip boundary condition is used there. The results of the numerical experiments show that when only the mechanism of barotropic instability is present, the model has two energy states for a wide range of interfacial friction coefficients. The high energy state is characterized by well-developed recirculations and displays strong variability associated with either large recirculating gyres and a weak eddy field or small recirculations and a strong eddy field. The low energy state is characterized by large meridional excursions in the separation point and large amplitude, westward propagating meanders that produce strong rings after interacting with the western wall. For physically relevant bottom friction values, the presence of baroclinic instability in the recirculation regions of the 2-layer model allows for a unique dynamical regime characterized by well-developed recirculations in both layers. The low-frequency variability associated with the regime is weak and is related to meridional shifts in the position of the jet, to wrapping of the recirculations around each other, and to pulsations in their zonal extent.<br>by Natalia Yurievna Beliakova.<br>Ph.D.
34
Berx, Barbara E. M. "Bio-physical interactions over cultural mussel beds : Measured and modelled Chlorophyll distributions in the Menai Strait." Thesis, Bangor University, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505944.
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35
Anwar, Mamuna [Verfasser], and Markus [Akademischer Betreuer] Drescher. "New Technical Concepts for Velocity Map Imaging in a THz Streak Camera / Mamuna Anwar ; Betreuer: Markus Drescher." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1175584568/34.
Повний текст джерела
36
Erasmus, Nicolas. "Ultrafast structural dynamics in 4Hb-TaSe2 observed by femtosecond electron diffraction." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/79934.
Повний текст джерелаАнотація:
Thesis (PhD)--Stellenbosch University, 2013.<br>ENGLISH ABSTRACT: In this thesis the structural dynamics, upon photo-excitation, of the charge-densitywave
(CDW) material 4Hb-TaSe2 is investigated on the time-scale of atomic motion
and simultaneously on the spatial-scale of atomic dimensions.
CDW materials have been of interest since their discovery in the 1970’s because of their
remarkable non-linear and anisotropic electrical properties, gigantic dielectric constants,
unusual elastic properties and rich dynamical behaviour. Some of these exotic
properties were extensively investigated in thermal equilibrium soon after their discovery
but only recently have ultrafast techniques like femtosecond spectroscopy become
available to study their out-of-equilibrium behaviour on the time-scale of atomic
motion. By studying their behaviour on this time-scale a more in-depth understanding
of their macroscopic properties can be gained. However, to do investigations on the
atomic time-scale and simultaneously directly observe the evolution of the atomic arrangements
is another challenge. One approach is through the previously mentioned
technique of femtosecond pump-probe spectroscopy but converting the usual ultrashort
optical probing source to an ultrashort electron or x-ray source that can diffract
off the sample and reveal structural detail on the atomic level. Here, the femto-to-picosecond out-of-equilibrium behaviour upon photo-excitation in
4Hb-TaSe2 is investigated using an ultrashort electron probe source. Two variations
of using an electron probe source are used: conventional scanning Femtosecond Electron
Diffraction (FED) and a new approach namely Femtosecond Streaked Electron
Diffraction (FSED). The more established FED technique, based on femtosecond pumpprobe
spectroscopy, is used as the major investigating tool while the FSED technique,
based on ultrafast streak camera technology, is an attempt at broadening the scope of
available techniques to study structural dynamics in crystalline material on the subpicosecond
time-scale.
With these two techniques, the structural dynamics during the phase transition from
the commensurate- to incommensurate-CDW phase in 4Hb-TaSe2 is observed through
diffraction patterns with a temporal resolution of under 500 fs. The study reveals
strong coupling between the electronic and lattice systems of the material and several
time-constants of under and above a picosecond are extracted from the data. Using
these time-constants, the structural evolution during the phase transition is better understood
and with the newly gained knowledge, a model of all the processes involved
after photo-excitation is proposed.<br>AFRIKAANSE OPSOMMING: In hierdie tesis word die strukturele dinamika van die lading-digtheid-golf (LDG) materiaal
4Hb-TaSe2 ondersoek op die tydskaal van atomiese bewegings en gelyktydig op
die ruimtelikeskaal van atomiese dimensies.
LDG materie is al van belang sedert hul ontdekking in die 1970’s as gevolg van hul
merkwaardige nie-lineêre en anisotrope elektriese eienskappe, reuse diëlektriese konstantes,
ongewone elastiese eienskappe en ryk dinamiese gedrag. Sommige van hierdie
eksotiese eienskappe is omvattend ondersoek in termiese ewewig kort na hul ontdekking,
maar eers onlangs is dit moontlik deur middle van ultravinnige tegnieke
soos femtosekonde spektroskopie om hulle uit-ewewigs gedrag te bestudeer op die
tydskaal van atomiese beweging. Deur die gedrag op hierdie tydskaal te bestudeer
kan ’n meer insiggewende begrip van hul makroskopiese eienskappe verkry word.
Om ondersoeke in te stel op die atomiese tydskaal en gelyktydig direk die evolusie
van die atoom posisie te waarneem is egter ’n moeilike taak. Een benadering is deur
middle van femtosekonde “pump-probe” spektroskopie maar dan die gewone optiese
“probe” puls om te skakel na ’n electron of x-straal puls wat van die materiaal kan
diffrak en dus strukturele inligting op die atomiese vlak kan onthul. Hier word die femto-tot-pico sekonde uit-ewewig gedrag in 4Hb-TaSe2 ondersoek met
behulp van elektron pulse. Twee variasies van die gebruik van ’n elektron bron word
gebruik: konvensionele “Femtosecond Electron Diffraction” (FED) en ’n nuwe benadering,
naamlik, “Femtosecond Streaked Electron Diffraction” (FSED). Die meer gevestigde
FED tegniek, wat gebaseer is op femtosekonde “pump-probe” spektroskopie,
word gebruik as die hoof ondersoek metode terwyl die FSED tegniek, wat gebaseer is
op die ultra vinnige “streak camera” tegnologie, ’n poging is om beskikbare tegnieke
uit te brei wat gebruik kan word om strukturele dinamika in materie te bestudeer op
die sub-picosekonde tydskaal.
Met behulp van hierdie twee tegnieke, word die strukturele dinamika tydens die fase
oorgang van die ooreenkomstige tot nie-ooreenkomstige LDG fase in 4Hb-TaSe2 deur
diffraksie patrone met ’n tydresolusie van minder as 500 fs waargeneem. Die studie
toon ’n sterk korrelasie tussen die elektroniese sisteem en kristalrooster. Verskeie
tydkonstantes van onder en bo ’n picosekonde kon ook uit die data onttrek word en
gebruik word om die strukturele veranderinge beter te verstaan. Hierdie nuwe kennis
het ons in staat gestel om ’n model van al die betrokke prosesse voor te stel.
37
Kassier, Gunther Horst. "Ultrafast electron diffraction : source development, diffractometer design and pulse characterisation." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/5359.
Повний текст джерелаАнотація:
Thesis (PhD (Physics))--University of Stellenbosch, 2010.<br>ENGLISH ABSTRACT: Ultrafast Electron Diffraction (UED) is a rapidly maturing field which allows investigation of the
evolution of atomic arrangement in solids on timescales comparable to the vibrational period of
their constituent atoms (~10-13 s). The technique is an amalgamation of conventional high energy
electron diffraction methods and pump-probe spectroscopy with femtosecond (1 fs = 10-15 s) laser
pulses. Ultrafast pulsed electron sources generally suffer from limitations on the attainable electron
number per pulse (brightness) due to Coulomb repulsion among the electrons. In this dissertation,
the design and construction of a compact UED source capable of delivering sub-300 fs electron
pulses suitable for diffraction experiments and containing about 5000 electrons per shot is
described. The setup has been characterised by measurement of the transverse beam size and
angular spread, and through recording and analyzing an electron diffraction pattern from a titanium
foil. Measurement of the temporal duration of fs electron pulses is not trivial, and a specialised
compact streak camera operating in accumulation mode has been developed as part of this study. A
sub-200 fs temporal resolution has been achieved, and the dependence of temporal duration on
electron number per pulse was investigated for the current UED source. The observed trends
correlate well with detailed electron bunch simulations. In order to investigate ultrafast processes on
samples that cannot be probed repeatedly, it becomes necessary to significantly increase the
brightness of current state of the art compact sources such as the one constructed in the present
study. UED sources employing electron pulse compression techniques offer this possibility.
Traditional pulse compression schemes based on RF cavities, while simple in principle, pose
significant technical challenges in their realisation. The current thesis describes two novel UED
pulse compression methods developed by the author: achromatic reflectron compression and pulsed
cavity compression. Both concepts are expected to be easier to realise than conventional RF
compression. Detailed simulations predict that such sources can attain a brightness improvement of
more than one order of magnitude over compact sources that do not employ compression
techniques. In addition, such sources show much promise for the attainment of pulse durations in
the sub-100 fs range.<br>AFRIKAANSE OPSOMMING: Ultra vinnige elektron diffraksie is ‘n meettegniek wat tans in die proses is om vinnige ontwikkeling
te ondergaan. Die tegniek het ten doel om strukturele omsettingsprosesse op ‘n lengteskaal van
atoombindings en ‘n tydskaal van die vibrasie periode van atome in materie, ongeveer 10-13 s, te
ondersoek. Dit word bewerkstellig deur die spasieresolusievermoë van gewone hoë energie elektron
diffraksie met die tydresolusievermoë van femtosekonde (1 fs = 10-15 s) laserspektroskopie te
kombineer. Die aantal elektrone per puls (intensiteit) van ultravinnige gepulsde elektronbronne
word beperk deur die Coulomb afstootingskragte tussen die elektrone. Hierdie dissertasie beskryf
die ontwerp en konstruksie van ‘n kompakte ultravinnige elektron bron. Die elektronpulse wat
geproduseer word bevat tot 5000 elektrone per puls met ‘n tyd durasie van minder as 300 fs, en is
geskik vir diffraksie eksperimente. Die aparaat is gekarakteriseer deur die volgende metings:
elektronpulsdiameter, straaldivergensie, en ‘n titaan foelie se statiese diffraksie patroon. Dit is nie
triviaal om die durasie van femtosekonde elektronpulse te meet nie, en n spesiale kompakte
akkumulerende “streak camera” is vir die doeleindes van hierdie projek onwikkel. Die tydresolusie
van hierdie “streak camera” is beter as 200 fs, en die afhanklikheid van die pulsdurasie wat deur die
ultravinnige elektron bron geproduseer word as n funksie van die elektrongetal per puls is met
behulp van hierdie toestel bepaal. Die resultate klop redelik goed met gedetaileerde simulasies van
die elektron puls dinamika. Die karakterisasie van monsters wat nie herhaaldelik gemeet kan word
nie vereis verkieslik ‘n nog hoër pulsintensiteit as wat met huidige bronne bereik kan word. ‘N
verdere doelstelling is dus om ultravinnige elektron bronne te ontwikkel wat pulse met meer
elektrone per puls kan genereer. Dit kan bewerkstellig word deur bronne wat van elektron puls
kompressie tegnieke gebruik maak. Die tradisionele manier waarop dít gedoen word is deur middel
van n kontinu gedrewe radio frekwensie holte. Hierdie metode gaan egter gepaard met aanmerklik
hoë tegniese uitdagings. Om hierdie rede het die outeur twee alternatiewe puls kompressie konsepte
ontwikkel: akromatiese reflektron kompressie and gepulsde holte kompressie. Albei konsepte sal
waarskeinlik makliker wees om te realiseer as die tradisionele radio frekwensie kompressie, en is
deur middel van gedetaileerde simulasies geverifiseer. Hierdie simulasies voorspel dat die
intensiteit van genoemde bronne met ten minste n grooteorde meer kan wees as wat tans met
kompakte ultravinnige elektron bronne moontlik is. Verder blyk dit dat sulke bronne n pulsdurasie
van minder as 100 fs kan bereik.
38
Evans, Paul Stephen. "Hydrodynamic characteristics of macrotidal straits and implications for tidal stream turbine deployment." Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/70531/.
Повний текст джерелаАнотація:
National efforts to reduce energy dependency on fossil fuels have prompted examination of macrotidal nearshore zones around the UK for potential tidal stream resource development. Although a number of prospective tidal energy sites have been identified, the local hydrodynamics of these sites are often poorly understood. Tidal-energy developers rely on detailed characterisation of tidal energy sites prior to device field trials and installation. Although first-order appraisals may make macrotidal tidal straits appear attractive for development, detailed, site-specific hydrodynamic and bathymetric surveys are important for determining site suitability for tidal stream turbine (TST) installation. Understanding the ways in which coastal features affect tidal velocities at potential TST development sites will improve identification and analysis of physical constraints on tidal-energy development. Ramsey Sound (Pembrokeshire, Wales, UK) will soon host Wales’ first TST demonstration project. However, the local hydrodynamics of the sound have been underexamined. Ramsey Sound experiences a marked tidal asymmetry, with local bathymetric features that affect flow fields which are spatially heterogeneous in three dimensions. Using Ramsey Sound as a case study, this thesis has three objectives: (1) to examine the wake created by submerged objects through field- and laboratory-based measurements, (2) to experimentally investigate the effect of submergence on wake development and decay downstream of a conical island, and (3) to develop a TST suitability tool, which examines the effects of velocity, water depth and bed slope on power availability within a macrotidal coastal area. Laboratory experiments have shown that submergence level is an important parameter controlling wake structure and extent, and that changes in submergence level affect both the 3-D flow structure in the near wake and the 2-D far wake of islands. Analysis of physical and hydrodynamic characteristics in Ramsey Sound, including tidal velocities across the swept area of the pilot TST, vertical shear in the stream flow, estimated power output, water depth and bed slope, suggests that the spatial and temporal variability in the flow field may render much of Ramsey Sound unsuitable for tidal power extraction. Although the resource potential depends on velocity and bathymetric conditions that are fundamentally local, many prospective tidal energy sites are subject to similar physical and hydrodynamic constraints. Results of this study can help inform site selection in these complicated, highly dynamic macrotidal environments.
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Blomdin, Robin. "The Late Glacial History of the Magellan Strait in southern Patagonia, Chile : Testing the Applicability of KF-IRSL Dating." Thesis, Stockholms universitet, Institutionen för naturgeografi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-137807.
Повний текст джерелаАнотація:
The timing of the ice margin retreat of the Late Glacial Patagonian ice sheet (PIS) in southern Patagonia has been the object of discussion for many years. In order to resolve questions about the complex response of the PIS to past climate change; geological interpretation and modelling data needs evaluation against absolute chronology. The aim of this project is to re-map the landforms and sediment of the Magellan Strait, to reconstruct the late glacial ice retreat during the deglaciation and to investigate the applicability of OSL dating to glaciofluvial sediment from this region. Unfortunately previous studies have shown that the quartz OSL luminescence characteristics, of this region, are unsuitable for dating. Therefore the potential of K-feldspar IRSL signals are reviewed and examined. Samples were collected from landforms interpreted as being deposited during the deglaciation of the Magellan ice lobe, with an expected age range between 17.5 and 23 ka, and from recently deposited sediments (<1 ka). Small aliquots and single grain distributions were studied by applying a IR50 SAR protocol with IRSL stimulation at 50°C for 100 s and a preheat of 250 °C (held at 60 s) are measured. Appropriate uncertainties were assigned to the dose distribution data, by quantifying the laboratory over-dispersion (σOD) parameter (22.2% for small aliquots and 17.7 % for single grains) in laboratory bleached and γ-irradiated samples. Thereafter the possible effects of incomplete bleaching and anomalous fading were examined. For the natural samples environmental over-dispersions between 30–130 % and mean interpreted residual doses between ~30 and 80 Gy were observed. Statistical models were further applied to identify the part of the dose population that was most likely to have been completely bleached. The models are consistent with each other which imply that they successfully identified the fully-bleached grains in the distributions; however observed discrepancies between the small aliquot and single grain data were also discussed. Large g2day values (on average 7.92±0.6%/decade for large aliquots) were observed but nevertheless, comparing our fading corrected ages to the expected age range result in 2 out of 3 ages consistent with geological interpretation and an established radiocarbon and cosmogenic nuclide chronology suggesting that this correction was done successfully. The results of these investigations suggest that small aliquot/single grain fading can be corrected for using an average value and that KF-IRSL dating is applicable in this part of Southern Patagonia. The third age is supported by an alternative geological interpretation while the two consistent ages imply that in the Magellan Strait the hills of the Brunswick peninsula (70-100 m.a.s.l) were deglaciated at around ~21 ka. Finally some recommendations for future research are considered.
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Mastropole, Dana M. "Hydrographic structure of overflow water passing through the Denmark Strait." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101344.
Повний текст джерелаАнотація:
Thesis: S.M., Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2015.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 63-66).<br>Denmark Strait Overflow Water (DSOW) constitutes the densest portion of North Atlantic Deep Water, which feeds the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). As such, it is critical to understand how DSOW is transferred from the upstream basins in the Nordic Seas, across the Greenland-Scotland Ridge, and to the North Atlantic Ocean. The goal of this study is to characterize the hydrographic structure of the different DSOW constituents at the sill before the water descends into the Irminger Sea using temperature and salinity (T/S) data from 111 shipboard crossings in the vicinity of the sill, collected between 1990 and 2012. The individual realizations indicate that weakly stratified "boluses" of DSOW frequent the sill and contribute the densest water to the overflow. This study also characterizes the structure, size, and location of the boluses and relates them to the T/S modes found at the sill. Lastly, historical hydrographic data from the Nordic Seas are used to make inferences regarding the origin of the boluses.<br>by Dana M. Mastropole.<br>S.M.
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Gargiulo, Irene. "Assessing leisure time physical activity (ltpa) experience in urban. Stream corridors: a baseline for inclusive ltpa promotion." Doctoral thesis, Universitat Internacional de Catalunya, 2020. http://hdl.handle.net/10803/670037.
Повний текст джерелаАнотація:
Leisure-Time Physical Activity (LTPA) in urban stream corridors is of paramount importance for health and wellbeing promotion among urban dwellers. LTPA experience, namely how (what, with whom, when and where) and why LTPA is practised in particular places, is influenced by various social and physical environmental factors which the stream users may perceive differently. Therefore, an improved understanding of how stream users perceive environmental factors may provide relevant insights and inform on strategies intended to support inclusive LTPA promotion. To this end, combining ecological models with a qualitative Geographic Information System (qGIS) methodology is valuable. The ecological models provide a comprehensive theoretical framework which helps understand the environmental factors that influence LTPA, whilst the qualitative research methods serve to reveal any hidden meanings related to individual experiences behind factors. The collected data combined with GIS, enable the exploration of subjective perceptions of the environment with reference to its spatial dimension.
Therefore, this study assessed users’ perceptions of the environmental factors that influence LTPA experiences in the Caldes Stream corridor, in the Metropolitan Region of Barcelona. Accordingly, a sequential mixed methodology based on qualitative ecological approach integrated with GIS was developed in two phases. First, in-depth map-based and go-along interviews allowed for: 1) the categorization of the different types of stream users according to their characteristics and motivations for LTPA, 2) the identification of the social and physical environmental factors influencing LTPA, 3) the assessment of factors as either barriers or facilitators to LTPA for each type of stream user according to their perceptions (Paper 1). Secondly, given that the safety issue emerged as a key factor influencing women LTPA in the Caldes Stream corridor, the analysis of the relationship between environmental factors and women’s perceptions of safety was undertaken. In-depth interviews with women were further analysed for: 4) the identification of the environmental factors related to women’s perceptions of safety in the stream corridor, and 5) the design of a safety map able to represent both the women’s general and individual perceptions of safety. For the creation of this analytical tool environmental factors were translated into spatial indicators, women’s perceptions were geo-located, and the resultant data was integrated into qGIS (Paper 2).
Findings of the present study provided a greater understanding of the different ways in which different users interpret and interact with urban stream corridors when practising LTPA. Specifically, different types of users perceived environmental factors influencing LTPA as either barriers or facilitators contradictorily or coincidentally depending on their motivations for LTPA and their gender. The major conflicts related to divergent perceptions between genders depended on perceptions of safety (Paper 1). Perceptions of safety among women were related to environmental factors, yet they were mediated by women’s socio-cultural background and everyday practices. Against this backdrop, the safety map based on a qualitative GIS approach designed for this study, allowed the assessment of the macro-scale spatial indicators of the environmental factors and the micro-scale of women’s narratives on perceptions of safety from an integrated perspective. The macro-scale perspective provided a general explanation for the phenomenon and helped visualise conflicting domains of interventions. The micro-scale produced deeper and detailed insights into the perception of safety by comparing the big picture with women’s narratives (Paper 2).
These findings suggest that 1) the characterisation of types of users according to their motivations for practicing LTPA in green environments and 2) their gender perspective should be at the forefront of inclusive LTPA promotion strategies. At this regard, qGIS analytical tools aimed at identifying the particular needs of the specific types of users could support the customisation of interventions by providing knowledge on the tangible and intangible dimensions associated to the different LTPA experiences. Basing on this knowledge, LTPA promotion policies should combine the provision of physical infrastructure suitable for the different types of users, and long-term educational programs addressed to overcome the limiting effects of certain socio-cultural backgrounds.
This research has shown that the thorough understanding of the users’ LTPA experience in urban stream corridors provides significant knowledge to inform policies for inclusive LTPA promotion, thus mitigating the risk of health inequalities among different types of stream users.
42
Wu, Xinglong. "Response of A Small, Two-Strait Semi-Enclosed Sea to External Forcings." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_dissertations/84.
Повний текст джерелаАнотація:
Located at the northern edge of the Northern Gulf of Alaska (NGOA), Prince William Sound(PWS) is a small, two-strait semi-enclosed sea. The general ocean circulation pattern inside PWS is significantly affected by external forcings, for instance, the large-scale circulation in NGOA, atmospheric pressure and surface winds, surface heating/cooling, runoff, and tides. Motivated by multi-year experience with a well-validated, quasi-operational ocean circulation nowcast/forecast system for PWS (viz., Extended PWS Nowcast/Forecast System (EPWS/NFS)), the present study addresses some aspects of the PWS response to various external forcings, via numerical simulations. Based on the Princeton Ocean Model (POM), four numerical implementations have been examined, viz., PWS-POM, Extended PWS-POM (EPWS-POM), Idealized PWS-POM (IPWS-POM), and a 2-D tidal model. These implementations are used to simulate physical processes with various spatial and temporal scales in PWS. A series of numerical simulations are conducted, driven by various external forcings ranging from large scale and mesoscale circulation in NGOA represented by the Global Navy Coastal Ocean Model (NCOM), to atmospheric pressure observed by National Data Buoy Center (NDBC) buoys and mesoscale winds predicted by Regional Atmospheric Modeling System (RAMS), and to tides simulated by the 2-D tidal model. These simulations, along with analysis from a Helmholtz resonance model, demonstrate and help interpret some phenomena in PWS; for instance, barotropic Helmholtz resonance in coastal sea levels, and volume transports through the two PWS straits, and a dominant cyclonic gyre in the Central Sound in August and September. The simulation results are used to study a wide range of oceanic phenomena in PWS; e.g., two-layer/three-layer baroclinic transports through the straits, a "transition band" in the coherence pattern between volume transports through the two straits, mesoscale circulation in the Central Sound, the deep water circulation, and the annual tidal energy budget.
43
Alavimoghaddam, Mohammadreza. "Assessing the ability of HEC-HMS rainfall-runoff model to simulate stream flow across Sweden." Thesis, Stockholms universitet, Institutionen för naturgeografi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-143345.
Повний текст джерелаАнотація:
Computer modeling is the powerful tool for simulating nature’s behavior; however, still more efforts are need for reaching perfect simulation with computer models (especially in the hydrological field of study). In this Master’s thesis, the accuracy of the HEC-HMS computer model for long term rainfall-runoff simulation was evaluated across Sweden. Five different catchments from north to south of Sweden were selected and then simulation have done for 34 years of available data. Simulation was conducted using daily, monthly and yearly time scale resolutions. Results from the north to the south of Sweden were completely different. Simulated runoff and observed runoff in northern catchments followed the same pattern over different time scales but in the southern part of Sweden the results had different patterns in space and time. The best results with HEC-HMS were found in the northern catchments with steep main river slopes. In the southern catchments the model could not predict runoff in any realistic manner at any time and space scale. In total the HEC-HMS model cannot simulate the rainfall runoff for long periods of simulation across Sweden. This is especially true in southern parts of the country dominate with low elevation catchments. However, with regards to its ability for event-based simulation HEC-HMS could be a suitable tool to simulate flood event discharges that are needed for road or other hydraulic structures designs. But, this would require significant amounts of calibration and model development.
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Kasperi, Johan. "Occlusion in outdoor Augmented Reality using geospatial building data." Thesis, KTH, Skolan för datavetenskap och kommunikation (CSC), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-204442.
Повний текст джерелаАнотація:
Creating physical simulations between virtual and real objects in Augmented Reality (AR) is essential for the user experience. Otherwise the user might lose sense of depth, distance and size. One of these simulations is occlusion, meaning that virtual content should be partially or fully occluded if real world objects is in the line-of-sight between the user and the content. The challenge for simulating occlusion is to construct the geometric model of the current AR environment. Earlier studies within the field have all tried to create realistic pixel-perfect occlusion and most of them have either required depth-sensing hardware or a static predefined environment. This study proposes and evaluates an alternative model-based approach to the problem. It uses geospatial data to construct the geometric model of all the buildings in the current environment, making virtual content occluded by all real buildings in the current environment. This approach made the developed function compatible with non depth-sensing devices and in a dynamic outdoor urban environment. To evaluate the solution it was implemented in a sensor-based AR application visualizing a future building in Stockholm. The effect of the developed function was that the future virtual building was occluded as expected. However, it was not pixel-perfect, meaning that the simulated occlusion was not realistic, but results from the conducted user study said that it fulfilled its goal. A majority of the participants thought that their AR experience got better with the solution activated and that their depth perception improved. However, any definite conclusions could not be drawn due to issues with the sensor-based tracking. The result from this study is interesting for the mobile AR field since the great majority of smartphones are not equipped with depth sensors. Using geospatial data for simulating occlusions, or other physical interactions between virtual and real objects, could then be an efficient enough solution until depth-sensing AR devices are more widely used.<br>För att uppnå en god användarupplevelse i Augmented Reality (AR) så är det viktigt att simulera fysiska interaktioner mellan de virtuella och reella objekten. Om man inte gör det kan användare uppfatta saker som djup, avstånd och storlek felaktigt. En av dessa simulationer är ocklusion som innebär att det virtuella innehållet ska vara delvis eller helt ockluderat om ett reellt objekt finns i siktlinjen mellan användaren och innehållet. För att simulera detta är utmaningen att rekonstruera den geometriska modellen av den nuvarande miljön.Tidigare studier inom fältet har försökt att uppnå en perfekt simulation av ocklusion, men majoriteten av dem har då krävt antingen djupavkännande hårdvara eller en statisk fördefinierad miljö. Denna studie föreslår och utvärderar en alternativ modellbaserad lösning på problemet. Lösningen använder geospatial data för att rekonstruera den geometriska modellen av alla byggnader i den nuvarande omgivningen, vilket resulterar i att det virtuella innehållet blir ockluderat av alla reella byggnader i den nuvarande miljön. Den utvecklade funktionen blev i och med det kompatibel på icke djupavkännande enheter och fungerande i en dynamisk urban miljö. För attutvärdera denna funktion så var den implementerad i en sensorbaserad AR applikation som visualiserade en framtida byggnad i Stockholm. Resultatet visade att den utvecklade funktionen ockluderade den virtuella byggnaden som förväntat. Dock gjorde den ej det helt realistiskt, men resultatet från den utförda användarstudien visade att den uppnådde sitt mål. Majoriteten av deltagarna ansåg att deras AR upplevelse blev bättre med den utvecklade funktionen aktiverad och ett deras uppfattning av djup förbättrades. Dock kan inga definitiva slutsatser dras eftersom AR applikationen hade problem med den sensorbaserade spårningen. Resultaten är intressant för det mobila AR fältet eftersom majoriteten av alla smartphones ej har stöd för djupavkänning. Att använda geospatial data för att simulera ocklusion, eller någon annan fysisk interaktion mellan virtuella och reella objekt, kan då vara en tillräckligt effektiv lösning tills djupavkännande AR enheter används mer.
45
Wulff, Thorben Verfasser], Antje [Akademischer Betreuer] [Gutachter] [Boetius, and Oliver [Gutachter] Zielinski. "Physics and Ecology in the Marginal Ice Zone of the Fram Strait : a Robotic Approach / Thorben Wulff ; Gutachter: Antje Boetius, Oliver Zielinski ; Betreuer: Antje Boetius." Bremen : Staats- und Universitätsbibliothek Bremen, 2015. http://d-nb.info/1119290643/34.
Повний текст джерела
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Callahan, Michael Kroh. "Groundwater Controls on Physical and Chemical Processes in Streamside Wetlands and Headwater Streams in the Kenai Peninsula, Alaska." Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5347.
Повний текст джерелаАнотація:
For this dissertation I studied groundwater and surface water interactions in the Kenai Lowlands, Alaska. In particular, I examine two important aspects of groundwater and surface water interactions: 1) Groundwater's influence on surface-water temperature; and 2) Groundwater's role in forming hydrologic flow paths that can connect uplands to streamside wetlands and streams. Chapter 2 investigates the controls on stream temperature in salmon-bearing headwater streams in two common hydrogeologic settings: 1) drainage-ways, which are low-gradient streams that flow through broad valleys; and 2) discharge-slopes, which are high gradient streams that flow through narrow valleys. The results from chapter 2 showed significant differences in stream temperatures between the two hydrogeologic settings. Observed stream temperatures were higher in drainage-way sites than in discharge-slope sites, and showed strong correlations as a continuous function with the calculated topographic metric flow-weighted slope. Additionally, modeling results indicated that the potential for groundwater discharge to moderate stream temperature is not equal between the two hydrogeologic settings, with groundwater having a greater moderating effect on stream temperature at the low gradient drainage-way sites. Chapter 3 examines the influence of groundwater on juvenile coho salmon winter habitat along the Anchor River. Two backwater habitats were selected from the larger set of 25 coho overwintering sites from a previous study for an in-depth hydrologic analysis. The results from chapter 3 showed that the type of groundwater discharge (i.e., focused versus diffuse groundwater discharge) can play an important role in determining habitat suitability in these backwater sites. During winter, focused discharge from a local groundwater seep maintained higher surface-water temperatures and higher concentrations of dissolved oxygen compared to the site with more diffuse groundwater discharge. Chapter 4 investigates the linkages along hydrologic flow paths among alder (Alnus spp.) stands, streamside wetlands, and headwater streams. Chapter 4 tested four related hypotheses: 1) groundwater nitrate concentrations are greater along flow paths with alder compared to flow paths without alder; 2) on hillslopes with alder, groundwater nitrate concentrations are highest when alder stands are located near the streamside wetlands at the base of the hillslope; 3) primary production of streamside wetland vegetation is N limited and wetlands are less N limited when alder stands are located nearby along flow paths; and 4) stream reaches at the base of flow paths with alder have higher nitrate concentrations than reaches at the base of flow paths without alder. The results from chapter 4 showed that groundwater nitrate concentrations were highest along flow paths with alder, however no difference was observed between flow paths with alder located near versus alder located further from streamside wetlands. Vegetation had a greater response to N fertilization in streamside wetlands that were connected to flow paths without alder and less when alder stands were near. Finally, higher nitrate concentrations were measured in streams at the base of flow paths with alder. The combined results of this dissertation showed that, in the Kenai Lowlands, groundwater and surface water interactions have a direct influence on the local ecology and that a fundamental understanding of the hydrology can aid in the successful management and protection of this unique and important ecosystem.
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Harney, Pawel. "Hydrological carbon transport in the Abiskojokka catchment area : The relationship between soil organic carbon content and dissolved organic carbon concentrations in stream water." Thesis, Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-108485.
Повний текст джерелаАнотація:
Soils in permafrost regions hold substantial amounts of carbon, much of which has accumulated due to processes that are related to cold temperatures. A warming climate will alter the dynamics governing the fluxes of carbon within a system and consequently the pools of carbon therein. Of particular concern is whether previously stored carbon will be released to the atmosphere contributing to the pool of greenhouse gases and creating a feedback effect. At the moment the International Panel of Climate Change (IPCC) does not include carbon dynamics of the Arctic in their forecast models due to a lack of adequate scientific understanding in the area. Understanding the controls which govern the fluxes of carbon between the land, the atmosphere and the aquatic systems is important in evaluating the transient state of the carbon cycle. This study investigates the potential relationship between terrestrial soil organic carbon (SOC) pools and the dissolved organic carbon (DOC) concentrations in streams observed at the beginning of August 2012 in the Abiskojokka catchment in the sub-arctic region of northern Sweden. The results show that soil organic carbon pools could tentatively explain between 24 % and 44 % of the variation in DOC concentrations in streams. This is only a fraction of the variation explained compared to regions where peatlands are the single most important indicator of DOC concentrations. In the absence of peatland, which covers less than 2 % of the Abiskojokka catchment area, heath vegetation and the associated soil forming processes were shown to be an important indicator of stream water DOC concentrations.
48
Shakya, Mahendra Man. "Generation of intense high harmonics : i) to test and improve resolution of accumulative x-ray streak camera ii) to study the effects of carrier envelope phase on XUV super continuum generation by polarization gating." Diss., Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/408.
Повний текст джерела
49
Brammer, James. "Physical and numerical modelling of Marine Renewable Energy technologies, with particular focus on tidal stream and tidal range devices." Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/58699/.
Повний текст джерелаАнотація:
The past decade has seen a significant rise in the interest of deploying Marine Renewable Energy technologies. Tidal stream technology is developing rapidly, and developers are favouring horizontal axis turbines (HAT’s). However, vertical axis turbines (VAT’s) are better suited for shallow waters, and higher efficiencies can potentially be gained by utilising shallow water blockage effects. The Severn Estuary is an ideal deployment area in this context. Additionally, due to a large tidal range the estuary has long been the subject of tidal barrage proposals. The original ebb-only STPG barrage has recently been superseded by a two-way generation scheme, therefore the need exists for renewed research into the hydrodynamic impacts of this proposal. Furthermore, little is known about the interaction between tidal range and tidal stream technologies, and if they could coexist in the Severn Estuary. This thesis uses physical and numerical modelling techniques to assess a range of MRE technologies, with particular focus on their deployment in the Severn Estuary. Physical model tests of a number of VAT’s were conducted in a recirculating flume. Device performance and the wake characteristics were assessed, and it was demonstrated that VATS’s could potentially provide competitive performance values if deployed in shallow waters. The CFD code ANSYS CFX was used to predict the unsteady turbine behaviour at the physical model scale; good agreement was achieved with the laboratory data, particularly in predicting the wake behaviour. The CFD model TRIVAST was then applied to the Severn Estuary. Comparisons were made of the Severn Barrage schemes, as well as two hypothetical HAT and VAT arrays. The model results confirmed that vertical axis turbines are better suited to the Severn Estuary, provided that the technology is feasible. Finally, whilst the Severn Barrage proposals would eradicate the HAT resource, a lesser impact on the VAT resource was observed.
50
Franssen, Jan. "Brook trout (Salvelinus fontinalis) spawning habitat in a Boreal stream: the effects of groundwater, hyporheic flow and fine sediment loadings on reproductive success." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107714.
Повний текст джерелаАнотація:
The reproductive success of brook trout (Salvelinus fontinalis) populations, like those of other salmonid species, is dependent on the availability and quality of spawning/incubation habitats. For brook trout in particular substrate composition and groundwater-hyporheic flow characteristics are key abiotic factors influencing both the suitability of lotic spawning habitats and the survival of embryos nested within these habitats. Egg-to-emergence survival has been shown to be negatively related to substrate fine sediment concentrations and positively related to interstitial flow velocity. Both substrate composition (through filtering effects) and interstitial flow are also thought to influence the susceptibility of egg pockets to fine sediment infiltration. The objectives of this doctoral study are to clarify the roles of groundwater and hyporheic flow in brook trout redd site selection; as well as the effect of substrate composition and interstitial flow on the survival of embryos to emergence. A complementary objective is to determine how local hyporheic flow and substrate composition influence fine sediment accumulation within reproductive habitat. To test various hypotheses, we conducted field studies in brook trout spawning streams situated within a boreal forest system in Quebec, Canada. We complemented these field studies using laboratory and field experiments. Our field studies indicated that in these boreal forest streams, brook trout did not exhibit a systematic preference for spawning in microhabitats dominated by upwelling groundwater. Redds were located in sites with both upwelling groundwater and downwelling surface water and we observed that the origin of the water resulted in distinct thermal regimes and incubation rates within the reproductive habitat, suggestive of possible alternate life history strategies within the population. The results of our laboratory experimentation revealed that high embryo mortality in fines-rich-substrates could not be mitigated by increased flow velocity/oxygen flux through the egg pocket. Furthermore, CT Scans of laboratory incubation substrates support entombment effects, as mortality was related to the density of 3-4 mm pore spaces suitable for emergence. Field experiments suggested that the ingress of fine sediments into redds is primarily a gravity driven process influenced by the size of the infiltrating fine sediments and the size of the substrate pore spaces as controlled by filter fraction content. This infiltration process was not influence by the intensity of vertical or horizontal hydraulic gradients, at least over the range of gradients that were observed in the brook trout reproductive habitats studied here.<br>Le succès de la reproduction de l'omble de fontaine (Salvelinus fontinalis), comme ceux d'autres espèces salmonidés, est dépendant de la disponibilité et la qualité des l'habitat de fraye/incubation. Pour l'omble de fontaine, en particulier, la composition du substrat et l'écoulement des eaux souterraines et hyporhéiques sont des facteurs clés qui influencent à la fois la convenance d'habitat lotiques et la survie des embryons imbriqués dans ces habitats. La survie à l'émergence été démontrée être négativement liée à la concentration des sédiments fins dans les substrat et positivement liée à la vitesse d'écoulement interstitiel. La composition du substrat (par des effets de filtrage) et le flux interstitiel sont suggérés dans la litérature comme influencant la susceptibilité des poches d'œufs à l'infiltration de sédiments fins. Les objectifs de cette étude de doctorat sont à clarifier les rôles des ressurgences souteraines ou de l'écoulement hyporhéique dans la selection des nids par l'omble de fontaine; et l'effet de la composition du substrat et l'écoulement hyporhéique sur la survie des embryons à l'émergence. Un objectif complémentaire est de déterminer comment l'écoulement hyporhéique et la composition du substrat influencent l'accumulation de sédiments fins dans l'habitat de reproduction. Pour tester différentes hypothèses liées, nous avons mené des études de terrain dans les ruisseaux d'un ecosystème de forêt boréale dans la Réserve Faunique des Laurentides au Québec, Canada où nous avons observé les frayères de l'omble de fontaine. Nous avons complété ces études de terrain à l'aide d'experiences en laboratoire et sur le terrain. Nos études sur le terrain a indiqué que dans ces ruisseaux, l'omble de fontaine n'a pas démontré une préférence systématique pour les microhabitats de fraye sous l'influence des ressurgences d'eaux souterraines. Les nids étaient situés a la fois dans des sites de ressurgence et dans des endroits ou les eaux de surface pénètrent dans le lit. Nous avons observé que l'origine de l'eau était liée à des régimes thermiques distincts dans l'habitat de reproduction. Les résultats de nos incubations en laboratoire ont révélé que les taux élevés de mortalité ne pouvaient pas être atténués par une augmentation d'écoulement d'eau/ l'oxygène a travers le nid. Par ailleurs, les données sur la structure des substrat d'incubation collectées en trois dimensions (3-D) par tomodensitométrie assistée par ordinateur (TAO) ont confirmée un effet de 'mise au tombeau', indiquée par le lien entre la mortalité des embryons et la densité des 'megapores' de 2-3 mm qui sont appropriés pour l'émergence. Les expériences de terrain ont suggéré que la pénétration des nids par les sédiments fins est un processus influencé par la taille des sédiments fins en movement par rapport a la taille de l'espace interstitiel. Ce processus d'infiltration n'etait pas influencé par l'intensité des gradients hydrauliques verticaux ou horizontaux, au moins pour la gamme de gradients observées dans les habitats de reproduction omble de fontaine étudiés ici.