Dissertations / Theses on the topic 'Streams'
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Hilley, David B. "Temporal streams programming abstractions for distributed live stream analysis applications /." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31695.
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Thesis (Ph.D)--Computing, Georgia Institute of Technology, 2010.Committee Chair: Ramachandran, Umakishore; Committee Member: Clark, Nathan; Committee Member: Haskin, Roger; Committee Member: Pu, Calton; Committee Member: Rehg, James. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Tucker, Peter A. "Punctuated data streams /." Full text open access at:, 2005. http://content.ohsu.edu/u?/etd,255.
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Bo, Yang. "Querying JSON Streams." Thesis, Uppsala University, Department of Information Technology, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-129478.
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A data stream management system (DSMS) is similar to a database management system (DBMS) but can search data directly in on-line streams.
Using its mediator-wrapper approach, the extensible database system, Amos II, allows different kinds of distributed data resource to be queried. It has been extended with a stream datatype to query possibly infinite streams, which provides DSMS functionality.
Nowadays, more and more web applications start to offer their services in JSON format which is a text-based, human comprehendible format for representing simple data structures and associative arrays. For example, one of the most popular websites worldwide, Twitter, has developed a stream interface that one can register to receive large amounts of Twitter messages in JSON format. Another popular website Facebook and some weather services also provide stream interfaces through JSON.
The objective of the project is to develop a general JSON stream reader as an Amos II wrapper, allowing such streams to be easily queried and managed by a DSMS. To implement such a system, three primitive foreign functions are defined to allow queries to JSON streams using the query language AmosQL of Amos II. The usefulness of the developed wrapper is demonstrated on the popular Twitter social network data stream.
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Sargent, Aitbala. "Modeling Ice Streams." Fogler Library, University of Maine, 2009. http://www.library.umaine.edu/theses/pdf/SargentA2009.pdf.
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Bahri, Maroua. "Improving IoT data stream analytics using summarization techniques." Electronic Thesis or Diss., Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAT017.
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Face à cette évolution technologique vertigineuse, l’utilisation des dispositifs de l'Internet des Objets (IdO), les capteurs, et les réseaux sociaux, d'énormes flux de données IdO sont générées quotidiennement de différentes applications pourront être transformées en connaissances à travers l’apprentissage automatique. En pratique, de multiples problèmes se posent afin d’extraire des connaissances utiles de ces flux qui doivent être gérés et traités efficacement. Dans ce contexte, cette thèse vise à améliorer les performances (en termes de mémoire et de temps) des algorithmes de l'apprentissage supervisé, principalement la classification à partir de flux de données en évolution. En plus de leur nature infinie, la dimensionnalité élevée et croissante de ces flux données dans certains domaines rendent la tâche de classification plus difficile. La première partie de la thèse étudie l’état de l’art des techniques de classification et de réduction de dimension pour les flux de données, tout en présentant les travaux les plus récents dans ce cadre.La deuxième partie de la thèse détaille nos contributions en classification pour les flux de données. Il s’agit de nouvelles approches basées sur les techniques de réduction de données visant à réduire les ressources de calcul des classificateurs actuels, presque sans perte en précision. Pour traiter les flux de données de haute dimension efficacement, nous incorporons une étape de prétraitement qui consiste à réduire la dimension de chaque donnée (dès son arrivée) de manière incrémentale avant de passer à l’apprentissage. Dans ce contexte, nous présentons plusieurs approches basées sur: Bayesien naïf amélioré par les résumés minimalistes et hashing trick, k-NN qui utilise compressed sensing et UMAP, et l’utilisation d’ensembles d’apprentissage égalementWith the evolution of technology, the use of smart Internet-of-Things (IoT) devices, sensors, and social networks result in an overwhelming volume of IoT data streams, generated daily from several applications, that can be transformed into valuable information through machine learning tasks. In practice, multiple critical issues arise in order to extract useful knowledge from these evolving data streams, mainly that the stream needs to be efficiently handled and processed. In this context, this thesis aims to improve the performance (in terms of memory and time) of existing data mining algorithms on streams. We focus on the classification task in the streaming framework. The task is challenging on streams, principally due to the high -- and increasing -- data dimensionality, in addition to the potentially infinite amount of data. The two aspects make the classification task harder.The first part of the thesis surveys the current state-of-the-art of the classification and dimensionality reduction techniques as applied to the stream setting, by providing an updated view of the most recent works in this vibrant area.In the second part, we detail our contributions to the field of classification in streams, by developing novel approaches based on summarization techniques aiming to reduce the computational resource of existing classifiers with no -- or minor -- loss of classification accuracy. To address high-dimensional data streams and make classifiers efficient, we incorporate an internal preprocessing step that consists in reducing the dimensionality of input data incrementally before feeding them to the learning stage. We present several approaches applied to several classifications tasks: Naive Bayes which is enhanced with sketches and hashing trick, k-NN by using compressed sensing and UMAP, and also integrate them in ensemble methods
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Sjöberg, Oskar. "The Origin of Streams : Stream cartography in Swiss pre alpine headwater." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-277377.
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Temporary streams have received undeservedly little scientific attention and as a result their role in hydrological, biogeochemical and ecological processes is not yet fully understood. The ultimate goal of the research was to gain a better understanding of the temporary stream network and the processes that control it and determine how the active and connected stream length change with catchment wetness conditions to find simple methods to map seasonal and event-based changes in temporary flowing stream networks. Streams, springs and wetlands of four relatively small headwater catchments (11.7 – 25.3 km2) and one wetland in the steep and remote Zwäckentobel catchment in Alptal, canton Schwyz (Switzerland), were mapped and stream segments were classified by flow type during different weather conditions using direct observations. The mapping was performed by an elite orienteer with mapping experience. The variation in streamflow was analysed and related to the catchment wetness and topography using the TWI-values and the upslope accumulated area of the stream segments. As the catchments wetted up in response to fall rainfall events after a dry summer the flowing stream density increased up to five times and the connected stream density increased up to six times with a 150-fold increase in discharge. Also the number of flowing stream heads increased up to ten times. The best description of the pattern of stream expansion is a combination of the variable source area and the element threshold concepts, where surface topography, particularly TWI (Topographic Wetness Index) and upslope accumulated area (A), and local storage areas controls where streamflow is initiated and how flow in different stream segments connects. Streams in the Alptal show a seasonally bottom up or disjointed connection pattern. Mapping the temporary streams in steep and remote watersheds as a function of hydrological conditions is not an easy task. It is however necessary in order to fully understand where water is flowing or not. A combination of field observations with monitoring equipment can facilitate this extensive work by providing a more detailed temporal resolution.
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Tennant, Mark. "A parallel data stream classification technique for high velocity data streams." Thesis, University of Reading, 2018. http://centaur.reading.ac.uk/77919/.
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Real-time classification of data streams remains one of the most challenging aspects of Big Data. As a data stream is an unending source of information, classification models and metrics must be created and adapted in real-time as the data is made available to them. This time constrained learning is problematic, conventional data models require a training period to examine the data and produce models for evaluation. In data stream mining this training period does not exist, instead the models are continuously updated in real-time. As data streams become faster and larger the quantity of data to be processed can overwhelm a single machines’ learning capabilities. One method to reduce the work load upon a data mining algorithm is to implement parallel solutions. This has the benefit of distributing the classification over one or more machines. Unfortunately, most parallel implementations of classification algorithms are not suitable for real-time processing, and most data stream mining algorithms are not suitable for parallelisation. This research develops on real-time parallel classification of data instances with respect to vast amounts of data. The proposed solution is vastly scalable as it incurs no additional communications costs when training. Moreover, it is capable of accepting data streams that contain multiple sources. The newly created algorithm Parallel MC-NN has been implemented and evaluated on open source parallel technologies. The results of experimentation show a scalable solution that has been evaluated and peer reviewed via multiple publications.
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Hulten, Geoffrey. "Mining massive data streams /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/6937.
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Owens, Dale Spencer. "Voltammetry in flowing streams." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/27054.
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Gray, Alasdair John Graham. "Integrating distributed data streams." Thesis, Heriot-Watt University, 2007. http://hdl.handle.net/10399/2100.
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There is an increasing amount of information being made available as data streams, e.g. stock tickers, data from sensor networks, smart homes, monitoring data, etc. In .many cases, this data is generated by distributed sources under the control of many different organisations. Users would like to seamlessly query such data without prior knowledge of where it is located or how it is published..This is similar to the problem of integrating data residing in multiple heterogeneous stored data sources. However, the techniques developed for stored data are not applicable due to the continuous and long-lived nature of queries over data streams. This thesis proposes an architecture for a stream integration system. A key feature of the architect~e is a republisher component that collects together distributed streams and makes the merged ~tream available for querying. A formal model for the system has been developed. and is used to generate plans for executing continuous queries which exploit the redundancy introduced by the republishers. Additionally, due to the long-lived nature of continuous queries, mechanisms for maintaining the plans whenever there is a change in tlie set of data sources have been developed. A prototype of the system has been implemented and performance measures made. The work of this thesis has been motivated by the problem of retrieving monitoring information about Grid resources. However, the techniques developed are general and can be applied wherever there is a need to publish and query distributed data involving data streams.
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Johnston, Martin. "Trophic interactions in streams." Thesis, University of Ulster, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428394.
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Khor, Eng Keat. "Processing digital television streams." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38113.
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Cushman, Susan Flanders. "Fish movement, habitat selection, and stream habitat complexity in small urban streams." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3873.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.Thesis research directed by: Marine-Estuarine-Environmental Sciences. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Gillani, Syed. "Semantically-enabled stream processing and complex event processing over RDF graph streams." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSES055/document.
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Résumé en français non fourni par l'auteurThere is a paradigm shift in the nature and processing means of today’s data: data are used to being mostly static and stored in large databases to be queried. Today, with the advent of new applications and means of collecting data, most applications on the Web and in enterprises produce data in a continuous manner under the form of streams. Thus, the users of these applications expect to process a large volume of data with fresh low latency results. This has resulted in the introduction of Data Stream Processing Systems (DSMSs) and a Complex Event Processing (CEP) paradigm – both with distinctive aims: DSMSs are mostly employed to process traditional query operators (mostly stateless), while CEP systems focus on temporal pattern matching (stateful operators) to detect changes in the data that can be thought of as events. In the past decade or so, a number of scalable and performance intensive DSMSs and CEP systems have been proposed. Most of them, however, are based on the relational data models – which begs the question for the support of heterogeneous data sources, i.e., variety of the data. Work in RDF stream processing (RSP) systems partly addresses the challenge of variety by promoting the RDF data model. Nonetheless, challenges like volume and velocity are overlooked by existing approaches. These challenges require customised optimisations which consider RDF as a first class citizen and scale the processof continuous graph pattern matching. To gain insights into these problems, this thesis focuses on developing scalable RDF graph stream processing, and semantically-enabled CEP systems (i.e., Semantic Complex Event Processing, SCEP). In addition to our optimised algorithmic and data structure methodologies, we also contribute to the design of a new query language for SCEP. Our contributions in these two fields are as follows: • RDF Graph Stream Processing. We first propose an RDF graph stream model, where each data item/event within streams is comprised of an RDF graph (a set of RDF triples). Second, we implement customised indexing techniques and data structures to continuously process RDF graph streams in an incremental manner. • Semantic Complex Event Processing. We extend the idea of RDF graph stream processing to enable SCEP over such RDF graph streams, i.e., temporalpattern matching. Our first contribution in this context is to provide a new querylanguage that encompasses the RDF graph stream model and employs a set of expressive temporal operators such as sequencing, kleene-+, negation, optional,conjunction, disjunction and event selection strategies. Based on this, we implement a scalable system that employs a non-deterministic finite automata model to evaluate these operators in an optimised manner. We leverage techniques from diverse fields, such as relational query optimisations, incremental query processing, sensor and social networks in order to solve real-world problems. We have applied our proposed techniques to a wide range of real-world and synthetic datasets to extract the knowledge from RDF structured data in motion. Our experimental evaluations confirm our theoretical insights, and demonstrate the viability of our proposed methods
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Grudzinski, Bartosz Piotr. "Influence of watershed grazing management on stream geomorphology in grassland headwater streams." Diss., Kansas State University, 2014. http://hdl.handle.net/2097/18688.
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Doctor of PhilosophyDepartment of Geography
Melinda D. Daniels
This dissertation increases our understanding of the drivers that shape and maintain grassland streams and their watersheds by examining the influence of grazing management practices on suspended sediment concentrations, bare ground production, and changes to channel geomorphology. Chapter 2 demonstrates that cattle grazing produces significantly higher baseflow suspended sediment concentrations relative to bison grazing. Suspended sediment concentrations within bison-grazed streams are similar to ungrazed streams, indicating that the substitution of cattle for bison has resulted in degradation of baseflow water quality in grassland streams. Burning frequency, discharge, and seasonality are also significant drivers of suspended sediment concentrations, but are generally less influential than grazing treatments. Chapter 3 indicates that high density cattle grazing treatments produce more bare ground within the riparian zones of grassland stream networks, particularly underneath tree canopy cover. The increased bare ground coverage within riparian areas is correlated with increased suspended sediment concentrations during baseflow conditions, while watershed-scale bare ground production is correlated with increased suspended sediment concentrations during storm flow events. Chapter 4 demonstrates channel geometry and sedimentology are significantly influenced by grazing treatments. This dissertation is the first study to comparatively evaluate the relative influence between cattle and bison grazing on stream geomorphology within any environment. Insight gained from this project can be used by public and private land use managers to improve the environmental integrity of native grassland ecosystems.
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Melin, Mattias. "Stream size determines densities of larger juvenile brown trout in mountain streams." Thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-183936.
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The productivity or availability of juvenile habitats have theoretically been shown to determine size distributions of adult individuals and population abundance. Brown trout (Salmo trutta) is a species where adults may inhabit lakes and use connected streams for spawning and as nursery habitats for juveniles. This project aimed to estimate what factors determine the density and growth of juvenile brown trout in mountain streams. This was done by sampling 21 mountain streams for juvenile brown trout densities and growth, habitat availability and stream size, productivity, and resource availability. Additional data were obtained from other mountain streams from the Swedish Electrofishing Register. My results showed that measures of stream productivity and estimated benthic resource availability did not affect the densities and biomass of older juvenile brown trout. Instead, higher densities of older juvenile brown trout were related to increasing stream size (stream width x water depth). This is likely due to interference competition for space, where territory size influences the growth and densities of brown trout in streams but also that larger streams can provide refuges for larger individuals during periods of drying and thermal stress. This indicates that my estimate of stream size is an important factor determining densities of older juvenile brown trout in low-productive mountain streams. Stream size can be suggested to be a used as proxy for density and production of larger juvenile brown trout and therefore it may also be used to predict adult lake-living brown trout population size structure and abundance.
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Kordenbrock, Brett Nathan. "Enhancement of Concretized Streams: Mill Creek." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366206697.
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Bauers, Cynthia Kaye. "Whole stream metabolism and detrital processing in streams impacted by acid mine drainage." Ohio : Ohio University, 2003. http://www.ohiolink.edu/etd/view.cgi?ohiou1079299303.
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Bauers, Cynthia Kaye. "Whole stream metabolism and detrital processing in streams impacted by acid mine drainage." Ohio University / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1079299303.
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McClurg, Sarah Elizabeth. "Stream ecosystem response to mitigative limestone treatment in acid impaired, central Appalachian streams." Morgantown, W. Va. : [West Virginia University Libraries], 2004. https://etd.wvu.edu/etd/controller.jsp?moduleName=documentdata&jsp%5FetdId=3667.
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Thesis (M.S.)--West Virginia University, 2004.Title from document title page. Document formatted into pages; contains ix, 104 p. : ill., maps. Includes abstract. Includes bibliographical references (p. 41-49).
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Damnjanovic, Ivan. "Watermarking of MPEG2 video streams." Thesis, Queen Mary, University of London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429990.
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Mohamad, Saad. "Active learning for data streams." Thesis, Bournemouth University, 2017. http://eprints.bournemouth.ac.uk/29901/.
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With the exponential growth of data amount and sources, access to large collections of data has become easier and cheaper. However, data is generally unlabelled and labels are often difficult, expensive, and time consuming to obtain. Two learning paradigms have been used by machine learning community to diminish the need for labels in training data: semi-supervised learning (SSL) and active learning (AL). AL is a reliable way to efficiently building up training sets with minimal supervision. By querying the class (label) of the most interesting samples based upon previously seen data and some selection criteria, AL can produce a nearly optimal hypothesis, while requiring the minimum possible quantity of labelled data. SSL, on the other hand, takes the advantage of both labelled and unlabelled data to address the challenge of learning from a small number of labelled samples and large amount of unlabelled data. In this thesis, we borrow the concept of SSL by allowing AL algorithms to make use of redundant unlabelled data so that both labelled and unlabelled data are used in their querying criteria. Another common tradition within the AL community is to assume that data samples are already gathered in a pool and AL has the luxury to exhaustively search in that pool for the samples worth labelling. In this thesis, we go beyond that by applying AL to data streams. In a stream, data may grow infinitely making its storage prior to processing impractical. Due to its dynamic nature, the underlying distribution of the data stream may change over time resulting in the so-called concept drift or possibly emergence and fading of classes, known as concept evolution. Another challenge associated with AL, in general, is the sampling bias where the sampled training set does not reflect on the underlying data distribution. In presence of concept drift, sampling bias is more likely to occur as the training set needs to represent the underlying distribution of the evolving data. Given these challenges, the research questions that the thesis addresses are: can AL improve learning given that data comes in streams? Is it possible to harness AL to handle changes in streams (i.e., concept drift and concept evolution by querying selected samples)? How can sampling bias be attenuated, while maintaining AL advantages? Finally, applying AL for sequential data steams (like time series) requires new approaches especially in the presence of concept drift and concept evolution. Hence, the question is how to handle concept drift and concept evolution in sequential data online and can AL be useful in such case? In this thesis, we develop a set of stream-based AL algorithms to answer these questions in line with the aforementioned challenges. The core idea of these algorithms is to query samples that give the largest reduction of an expected loss function that measures the learning performance. Two types of AL are proposed: decision theory based AL whose losses involve the prediction error and information theory based AL whose losses involve the model parameters. Although, our work focuses on classification problems, AL algorithms for other problems such as regression and parameter estimation can be derived from the proposed AL algorithms. Several experiments have been performed in order to evaluate the performance of the proposed algorithms. The obtained results show that our algorithms outperform other state-of-the-art algorithms.
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Xu, Cheng. "Scalable Validation of Data Streams." Doctoral thesis, Uppsala universitet, Avdelningen för datalogi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-291530.
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In manufacturing industries, sensors are often installed on industrial equipment generating high volumes of data in real-time. For shortening the machine downtime and reducing maintenance costs, it is critical to analyze efficiently this kind of streams in order to detect abnormal behavior of equipment. For validating data streams to detect anomalies, a data stream management system called SVALI is developed. Based on requirements by the application domain, different stream window semantics are explored and an extensible set of window forming functions are implemented, where dynamic registration of window aggregations allow incremental evaluation of aggregate functions over windows. To facilitate stream validation on a high level, the system provides two second order system validation functions, model-and-validate and learn-and-validate. Model-and-validate allows the user to define mathematical models based on physical properties of the monitored equipment, while learn-and-validate builds statistical models by sampling the stream in real-time as it flows. To validate geographically distributed equipment with short response time, SVALI is a distributed system where many SVALI instances can be started and run in parallel on-board the equipment. Central analyses are made at a monitoring center where streams of detected anomalies are combined and analyzed on a cluster computer. SVALI is an extensible system where functions can be implemented using external libraries written in C, Java, and Python without any modifications of the original code. The system and the developed functionality have been applied on several applications, both industrial and for sports analytics.
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Rimes, Carrie A. "Bacteria in contrasting headwater streams." Thesis, University of Hull, 1986. http://hydra.hull.ac.uk/resources/hull:13611.
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Suspended and epiphytic bacteria were studied in calcareous headstreams of the Yorkshire Wolds and in acid headstreams of the Galloway Hills. Mean concentrations of suspended bacteria were marginally greater in the calcareous streams, while heterotrophic activity was substantially greater. Mean cell volume was also greater. The concentration and activity of suspended bacteria in the calcareous streams usually showed linear downstream increase, while in the acid streams, the downstream increase was less, and was frequently not observed. In Mill Beck (a calcareous stream) it was found that the population of epiphytic bacteria near the source was easily sufficient to sustain the observed downstream increase in suspended bacteria. In Dungeon Burn (an acid stream) a substantial population of epiphytic bacteria was also found, but there was no downstream change in concentration of suspended bacteria; reasons are suggested for the apparent non-release of epiphytes in the Galloway stream. The mean volume of suspended bacteria in Mill Beck changed between the source and downstream limit of a vegetated section, to resemble that of epiphytic bacteria, suggesting that suspended bacteria were dislodged epiphytes. Estimates were made of the attachment rate of suspended bacteria to submerged vegetation in Mill Beck; daily attachment represented only a small proportion of the total standing crop of epiphytic bacteria. A further study in Mill Beck, over a Spring growing period, demonstrated a temporal change in the density of epiphytic bacteria, which was related to change in discharge and temperature. The results supported the suggestion that epiphytic bacteria might largely be the source of suspended bacteria in this headstream.
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Lee, A. J. "The hydraulics of steep streams." Thesis, University of Sheffield, 2000. http://etheses.whiterose.ac.uk/14801/.
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This thesis describes research carried out to study steep streams. Step-pool sequences, a typical feature of such streams, were found to occur on every steep stream studied in the field. The most important control on the spacing of the steps was width. Flume experiments produced steps (at an average Froude number of 0.88), and showed that the presence of steps increased resistance to flow at lower than step-forming flow and decreased resistance at above step-forming flows. In the field, flow resistance was found to be controlled by sediment characteristics and the amount of step protrusion. The hydraulic geometry of the steep streams was also studied, and was found to differ considerably from hydraulic geometry characteristics of lowland streams. The formation of steps and pools was not found to be related to antidune processes; rather they were built up individually as large particles captured other large particles that had been entrained by the near critical flow. It was concluded that it is not the absolute values of slope and discharge that determines whether steps form. Near critical flow and high relative roughness appear to be the only requirements necessary. Previous equations were generally found to perform poorly when used with the experimental data, and an attempt to model the velocity profile using sediment characteristics and considering stresses on the flow also produced poor correlation with the actual field data. Modifications to these were made with some success, especially in the ability to predict friction factor based on relative roughness using D84 . Flume velocity profiles identified characteristic velocity profiles at different locations within the step-pool sequence and the presence 'S-shaped' profiles downstream of the step.
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Rind, Elad. "Turbulent wakes in turbulent streams." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/193955/.
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Direct numerical simulation and wind tunnel experiments have been used to study the effects of free-stream turbulence on axisymmetric wakes. In both cases the wake was introduced to various turbulent streams having various levels of turbulence intensity and length scales. It was found that the presence of the free-stream turbulence changes the wake’s decay rate and does not allow self-similarity to occur (unless maybe very far downstream and way beyond the current measurements reached). Also, the free-stream turbulence was found to be causing a significant transformation in the turbulence structure inside the wake, where the latter was found to be gradually evolving towards the former. Last, the fact that the two approaches were modelling two different problems led to some differences in their results emphasising the importance of the flow structure around the wake generating body in shaping the far wake region.
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Davies, Rhian. "Efficient analysis of data streams." Thesis, Lancaster University, 2017. http://eprints.lancs.ac.uk/88556/.
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Data streams provide a challenging environment for statistical analysis. Data points can arrive at a high velocity and may need to be deleted once they have been observed. Due to these restrictions, standard techniques may not be applicable to the data streaming scenario. This leads to the need for data summaries to represent the data stream. This thesis explores how data summaries can be used to perform clustering and classification on data streams across a broad range of applications. Spectral clustering is one such technique which prior to this work has not been applicable to the data streaming setting due to the high computation involved. CluStream is an existing method which uses micro-clusters to summarise data streams. We present two algorithms which utilise these micro-cluster summaries to enable spectral clustering to be performed on data streams. The methods were tested on simulated data streams, as well as textured images and hand-written digits. Distributed acoustic sensing is used to monitor oil flow at various depths throughout an oil well. Vibrations are recorded at very high resolutions, up to 10000 observations a second at each depth. Unfortunately, corruption can occur in the signal and engineers need to know where corruption occurs. We develop a method which treats the multiple time series as a high-dimensional clustering problem and uses the cluster labels to identify changes within the signal. The final piece of work concerns identifying areas of activity within a video stream, in particular CCTV footage. It is more efficient if this classification stage is performed on a compressed version of the video stream. In order to reconstruct areas of activity in the original video a recovery algorithm is needed. We present a comparison of the performance of two recovery algorithms and identify an ideal range for the compression ratio.
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Pant, Santosh Raj. "Geomorphic Characterization of Restored Streams." Youngstown State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1287179872.
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Blain, Heather Ann. "Drinking water out of streams." College Park, Md. : University of Maryland, 2008. http://hdl.handle.net/1903/8212.
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Thesis (M.F.A.) -- University of Maryland, College Park, 2008.Thesis research directed by: Dept. of English. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Kum, Sang-Uok Mayer-Patel Ketan. "Encoding of multiple depth streams." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2008. http://dc.lib.unc.edu/u?/etd,2025.
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Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2008.Title from electronic title page (viewed Feb. 17, 2009). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Computer Science." Discipline: Computer Science; Department/School: Computer Science.
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Dogwiler, Toby J. "Fluvial disturbances in karst streams /." free to MU campus, to others for purchase, 2002. http://wwwlib.umi.com/cr/mo/fullcit?p3060093.
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Uhlman, Kristine, Susanna Eden, Channah Rock, Erin Westfall, and Terry Sprouse. "Effluent Dependent Streams of Arizona." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2012. http://hdl.handle.net/10150/225865.
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McCoy, Jan. "Public Gains From Protected Streams." College of Agriculture, University of Arizona (Tucson, AZ), 1990. http://hdl.handle.net/10150/295635.
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Li, Jin. "Window Queries Over Data Streams." PDXScholar, 2008. https://pdxscholar.library.pdx.edu/open_access_etds/2675.
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Evaluating queries over data streams has become an appealing way to support various stream-processing applications. Window queries are commonly used in many stream applications. In a window query, certain query operators, especially blocking operators and stateful operators, appear in their windowed versions. Previous research work in evaluating window queries typically requires ordered streams and this order requirement limits the implementations of window operators and also carries performance penalties. This thesis presents efficient and flexible algorithms for evaluating window queries. We first present a new data model for streams, progressing streams, that separates stream progress from physical-arrival order. Then, we present our window semantic definitions for the most commonly used window operators—window aggregation and window join. Unlike previous research that often requires ordered streams when describing window semantics, our window semantic definitions do not rely on physical-stream arrival properties. Based on the window semantic definitions, we present new implementations of window aggregation and window join, WID and OA-Join. Compared to the existing implementations of stream query operators, our implementations do not require special stream-arrival properties, particularly stream order. In addition, for window aggregation, we present two other implementations extended from WID, Paned-WID and AdaptWID, to improve excution time by sharing sub-aggregates and to improve memory usage for input with data distribution skew, respectively. Leveraging our order-insenstive implementations of window operators, we present a new architecture for stream systems, OOP (Out-of- Order Processing). Instead of relying on ordered streams to indicate stream progress, OOP explicitly communicates stream progress to query operators, and thus is more flexible than the previous in-order processing (IOP) approach, which requires maintaining stream order. We implemented our order-insensitive window query operators and the OOP architecture in NiagaraST and Gigascope. Our performance study in both systems confirms the benefits of our window operator implementations and the OOP architecture compared to the commonly used approaches in terms of memory usage, execution time and latency.
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Davies, Oscar. "Ephemeral Streams in Boreal Landscapes : A Surface Water Statistical Analysis of Ephemeral Streams Chemical Components." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-384417.
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Boreal landscapes cover a large part of both Sweden and the northern hemisphere. The hydrology of the boreal landscape is complex, with several factors that can affect it in a physical and/or chemical manner. In the Krycklan catchment area, 68km2, located in northern Sweden close to Umeå, data has been collected at several sites giving both stream flow and water chemistry information. In 2017 samples from 34 sites were collected and analysed from ephemeral streams within the Krycklan catchment area for the first time ever. In this project, data that has been collected from the ephemeral streams will be correlated with data from the perennial streams in the catchment area. There are several hypotheses at the start of this project that suggests that within the ephemeral streams the DOC will be lower, and the CO2 will be the same. The aim of the project is to find out if there are any patterns that differentiates the ephemeral streams from the perennial streams or if there are no patterns at all. Since there is not so much data available for the ephemeral streams, the conclusions that might be reached in this project won’t be completely reliable. However, if interesting patterns are found the project could expand in the future and more samples can be taken to use for more precise analyses.Boreala landskap täcker en stor del av både Sverige och norra halvklotet. Det boreala landskapets hydrologi är komplext, med flera faktorer som kan påverka det på ett fysiskt och/eller kemiskt vis. I Krycklans avrinningsområde, 68 km2, beläget i norra Sverige nära Umeå, har data samlats in på flera platser som erbjuder data för både flöde och vattenkemi. År 2017 samlades prover från 34 efemära strömmar och analyserades för första gången inom Krycklans avrinningsområde. I det här projektet kommer data som samlats från de efemära strömmarna att korreleras med data från de konstanta vattendragen i avrinningsområdet. Det finns ett par hypoteser i början av detta projekt som tyder på att inom de efemära strömmarna kan DOC halter vara lägre och CO2 halter kommer att vara densamma. Syftet med projektet är att ta reda på om det finns några anmärkningsvärda skillnader mellan de efemära strömmarna och de konstanta vattendragen. Eftersom det inte finns så mycket data tillgänglig för de efemära strömmarna kommer de slutsatser som kan uppnås i detta projekt inte att vara helt tillförlitliga. Om intressanta mönster finns däremot kan projektet expandera i framtiden och fler prover kan tas för att användas för mer exakta analyser.
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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.
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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.QC 20150903
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Stokes, Christopher Richard. "The geomorphology of palaeo-ice streams : identification, characterisation and implications for ice stream functioning." Thesis, University of Sheffield, 2001. http://etheses.whiterose.ac.uk/14815/.
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Ice streams are the dominant drainage pathways of contemporary ice sheets and their location and behaviour are viewed as key controls on ice sheet stability. Identifying palaeo-ice streams is of paramount importance if we are to produce accurate reconstructions of former ice sheets and examine their critical role in the oceanclimate system. Many workers have invoked palaeo-ice streams from a variety of former ice sheets, despite a limited understanding of their glacial geomorphology. This thesis addresses the problem by predicting several diagnostic geomorphological criteria indicative of ice stream activity. These are developed objectively from the known characteristics of contemporary ice streams and can be summarised as: large flow-set dimensions (>20 km wide and >150 km long), highly convergent flow patterns, highly attenuated subglacial bedforms (length:width >10: 1), Boothia-type dispersal plumes, abrupt lateral margins «2 km), ice stream marginal moraines, evidence of pervasively deformed till, and submarine sediment accumulations (marine-terminating ice streams only). Collectively, the criteria are used to construct conceptual landsystems of palaeo-ice stream tracks. Using satellite imagery and aerial photography to map glacial geomorphology, identification of the criteria is used to validate the location of a previously hypothesised ice stream and identify a hitherto undetected palaeo-ice stream from the former Laurentide Ice Sheet. Implications for ice stream basal processes are explored and their ice sheet-wide significance is assessed. On Victoria Island (Arctic Canada) five of the geomorphological criteria are identified and the extent of the marine-based M'Clintock Channel Ice Stream is reconstructed at 720 km in length and 140 km in width. The ice stream (operating between 10,400 and 10,000 yr BP) was located within a broad topographic trough, but internal glaciological processes, rather than properties of the bed controlled the margin locations. It eroded into pre-existing unconsolidated sediments and left a spectacular pattern of subglacially-produced landforms, recording a snapshot view of the bed prior to ice stream shut-down. Sediment availability appears critical to its functioning (deformable bed?) and the debris flux of the ice stream is inferred to have been high. Frictional shut-down occurred once down-cutting through sediments reached hard bedrock close to the terminus. The presence of four of the geomorphological criteria are used to identify a terrestrial ice stream which drained the Keewatin Sector of the Laurentide Ice Sheet between ca. 10,000 and 8,500 yr BP. Its size is reconstructed at over 450 km in length and 140 km in width, and it left behind a subglacial bedform pattern consisting of highly attenuated drumlins (length:width ratios up to 48: 1) displaying exceptional parallel conformity. This represents an isochronous bedform pattern and variations in lineament elongation ratio are thought to be a useful proxy for ice velocity. Highest elongation ratios occur immediately downstream of a topographic step where the ice stream entered a sedimentary basin. It is inferred that the ice stream was triggered by climatic warming which altered the ice sheet configuration and the thermal state of the bed. A switch from cold to warm-based conditions probably triggered rapid basal sliding. The ice stream (and a tributary) shut down when it ran out of ice, causing widespread thinning of the ice sheet and subsequent deglaciation. These ice streams denote considerable ice sheet instability over both hard and soft (deformable) beds and emphasise the enormous effects that ice streams had in controlling the deglaciation of the Laurentide Ice Sheet.
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Panayotou, Dorothea Yvonne. "Aquatic insects in Tahoe basin streams : the link between stream restoration and biological assessment /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2003. http://uclibs.org/PID/11984.
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Hoy, Raymond S. "The Impact of Fine Sediment on Stream Macroinvertebrates in Urban and Rural Oregon Streams." PDXScholar, 2001. https://pdxscholar.library.pdx.edu/open_access_etds/1678.
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Urbanization, often characterized by high impervious surface area, can result in excessive inputs of fine sediments into urban streams. Excessive fine sediments can blanket the stream bed filling the interstitial space in the substratum, which may have adverse effects on stream biota. A field survey was conducted in Oregon urban and non-urban basins to investigate the relationship between fine sediments and stream macroinvertebrates. Physical, chemical, and biological data were collected from 59 stream sites in two urban and two rural streams. The stream sites fulfilled a continuous sediment gradient, which ranged from a low of 2% of fine sediment in the substrate to a high of 64% with an average of 22%. The % fines, in Clear Creek (rural basin) was significantly lower than in the urban basins (Johnson Creek and Tryon Creek) (p=0.005). Johnson Creek (mean=23%) had approximately three times more fine sediment than Clear Creek (mean=7%), while Tryon Creek (mean=32%) had nearly five times as much fine sediment as Clear Creek. EPT taxa richness was significantly higher in both rural streams than in both urban streams (p0.05). For example, regression analysis of EPT taxa richness vs. % fine sediments displayed a coefficient of determination (r2) value of 0.2. Other macro invertebrates metrics displayed similar patterns. The lack of significant correlations may be due to the cumulative effect of basin-wide "historical land use past". Past land use activity may have resulted in long-term reductions of sensitive taxa in the basin taxa pool and efforts to improve local habitats may not be quickly colonized by pollution sensitive taxa. Long-term degradation to the urban streams resulted in a relatively homogenous assemblage of macro invertebrates, which may have confounded the quantitative relationship between sediments and macroinvertebrates. This study suggests there is a clear difference between urban and non-urban streams in terms of macro invertebrates, which may be likely due to sediments, but the quantitative relationship between fine sediments and macro invertebrates is weak.
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Bostner, Albin. "Carbon dioxide dynamics in agricultural streams : Investigation of two streams draining catchments dominated by agricultural land." Thesis, Uppsala universitet, Luft-, vatten- och landskapslära, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-421345.
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In recent years, streams draining agricultural land has been suggested to exhibit high carbon dioxide (CO2) concentrations when compared to streams draining other land-types. The transport of carbon from land to ocean is mainly occurring through the chain of inland waters, and with agricultural land today representing 40% of all continental area many of these inland waters are influenced by agricultural land. The aim of this study was to improve the understanding of CO2 dynamics and its control in agricultural streams. Continuous data was collected from two catchments of different scales, near the city of Uppsala, Sweden. Both catchments are typical low-land catchments largely dominated by agricultural land. The measured CO2 concentrations were analyzed to find temporal variations and differences in dynamics between the catchments. The interplay between CO2 and parameters such as dissolved oxygen, discharge and conductivity were analyzed to determine the main drivers for CO2 dynamics. The findings show supersaturation of CO2 concentration during the full length of the measurement periods, with mean CO2 concentrations higher than what have been observed in streams draining other land-type catchments. Diel CO2 cycles were found throughout most of the measurement periods, where manual measurements were conducted to confirm these findings. The diel CO2 patterns were suggested to be heavily dependent on in-situ metabolic control while hydrological factors, such as sufficient discharge, seemed to be needed to produce a good diel CO2 signal. CO2 build-up is suggested to occur in the catchment soil and, when flushed out after rain events, result in an increasing CO2 concentration. This might be one important driver for the high levels in CO2 concentration found in the streams during summer and autumn. Analysis of the catchment areas suggest the percentage of agricultural land and the size of the catchment areas had an impact on hydrology, both for sufficient water flow to exist but also for the CO2 response after rain events. More research is encouraged, where more parameters should be investigated, such as groundwater inputs and carbonate precipitation.Bäckar som dränerar åkermark har under de senaste åren blivit mer uppmärksammade på grund av nya studier som visat att dessa bäckar tenderar att ha högre CO2-koncentration än bäckar som dränerar andra marktyper. Idag utgör cirka 40% av all kontinentalyta åkermark, då den huvudsakliga transporten av kol från land till hav sker genom sammankopplade vattendrag är därav en förståelse av åkermarkers dränering till bäckar av stor betydelse. Syftet med studien var att förbättra förståelsen av CO2-dynamiken och dess påverkan på bäckar i jordbruksdominerade avrinningsområden. Kontinuerlig data samlades in, samt erhölls från tidigare mätningar, från två avrinningsområden med olika storlekar och markfördelningar nära Uppsala. Båda avrinningsområdena var typiska låglands- avrinningsområden som dominerades av åkermark. Data för CO2-koncentration analyserades för att hitta kort- och långsiktiga variationer i CO2-dynamiken samt undersöka hur denna dynamik skiljer sig mellan avrinningsområden med olika storlek och markfördelning. Samspelet mellan CO2 och parametrar såsom vattenlösligt syre, vattenföring och konduktivitet analyserades för att hitta drivkrafter bakom CO2-dynamiken. Resultatet visar att de undersökta bäckarna var övermättade med CO2 under hela mätperioden, samt att medelkoncentrationerna som uppmättes var högre än vad som observerats i bäckar som dränerar andra landtyper. En dygnsvariation av CO2 observerades under större delar av mätperioderna, manuella prover utfördes för att stärka denna data. Den observerade dygnscykeln av CO2-koncentrationen konstaterades korrelera med den in-situ metaboliska kontrollen medan hydrologiska faktorer, såsom ett tillräckligt högt vattenflöde, visade sig var viktigt för att en CO2-dygnscykel ska existera. De mycket höga toppar av CO2-koncentration som observerats under mätningarna tros bero på ackumulering av CO2 i avrinningsområdenas marker, vilket under nederbörd utarmas och transporteras till bäcken. Vid jämförelse av de två avrinningsområdena föreslogs den procentuella andelen åkermark och storleken av avrinningsområdet ha en stor påverkan på hydrologin, både för att ett tillräckligt vattenflöde ska existera men också för CO2-responsen vid större nederbördsmängder. Mer forskning behövs där fler parametrar börs ta i beaktning, till exempel in-situ karbonutfällning och inflöde av CO2 via grundvatten, för att få en bättre bild över åkermarkens påverkan på CO2-dynamik i bäckar.
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Frahling, Gereon. "Algorithms for dynamic geometric data streams." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=983438439.
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Ruddarraju, Ravikrishna. "Indexing presentations using multiple media streams." Thesis, Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-04042006-105103/.
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Koehler, Stephan. "Video Streams in a Computing Grid." Thesis, KTH, School of Information and Communication Technology (ICT), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-24271.
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The growth of online video services such as YouTube enabled a new broadcasting medium for video. Similarly, consumer television is moving from analog to digital distribution of video content. Being able to manipulate the video stream by integrating a video or image overlay while streaming could enable a personalized video stream for each viewer. This master thesis explores the digital video domain to understand how streaming video can be efficiently modified, and designs and implements a prototype system for distributed video modification and streaming.
This thesis starts by examining standards and protocols related to video coding, formats and network distribution. To support multiple concurrent video streams to users, a distributed data and compute grid is used to create a scalable system for video streaming. Several (commercial) products are examined to find that GigaSpaces provides the optimal features for implementing the prototype. Furthermore third party libraries like libavcodec by FFMPEG and JBoss Netty are selected for respectively video coding and network streaming. The prototype design is then formulated including the design choices, the functionality in terms of user stories, the components that will make up the system and the flow of events in the system. Finally, the implementation is described followed by an evaluation of the fault tolerance, throughput, scalability and configuration. The evaluation shows that the prototype is fault tolerant and its throughput scales bothvertically and horizontally.
Intended audience
This thesis focuses on topics in the area of general computer science and network technology. It is therefore assumed that the reader has knowledge of basic concepts and techniques in these areas. More specifically this report focuses on topics related to digital video and distributed computer systems. Knowledge in these areas is helpful but not required.
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Solano, Nicoló. "Embedding premium video in social streams." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-188782.
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Digital videos are a sequence of bits encoded in a universal recognized format. Bits are easy to copy, duplicate and reproduce. However, certain videos have a very high financial value and therefore the respective owners want to protect them according to the Copyright law, in order to acquire the exclusive rights to publish and to reproduce them. Digital Rights Management (DRM) is the technology used nowadays to protect video distribution and to maintain at the same time a complete control over the usage of the owned resources. Another actual phenomenon is the increasing number of social users, in all the different age ranges. Since social networks are moving towards becoming publishing platforms and many allow third party applications and integration, the project aims to achieve a safe and secure integration of DRM protected videos into social media. In fact, as now this kind of videos are accessible only from proprietary applications, after the payment of a subscription. The major challenges that prevent an easy integration of these technologies are represented by the poor APIs offered by social networks and a market fragmentation created by the existence of several DRM systems and Adaptive Bitrate protocols. After an extensive analysis of video streaming technologies and social networks, we chose Facebook as social network of reference and we described both the backend architecture and the frontend requirements of a web application aiming to stream DRM protected videos in Facebook. However, the solution has to face the following impediments: the impossibility to embed DRM technologies in social mobile platforms and to show protected video content directly from the social News Feed. To this extent, we proposed two alternative solutions by looking at the problem from the social network point of view. Finally, in order to evaluate the quality and the utility of the proposed web application, we conducted a user experience test. The results pointed out a diffuse interest and appreciation. However, the two drawbacks mentioned above are perceived as a negative factor. The proposed application results instead portable on all the desktop browsers and on the 90 percent of social mobile platforms.
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Irani, Ramin. "Error Detection for DMB Video Streams." Thesis, Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-5086.
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The purpose of this thesis is to detect errors in Digital Multimedia Broadcasting (DMB) transport stream. DMB uses the MPEG-4 standard for encapsulating Packetized Elementary Stream (PES), and uses the MPEG-2 standard for assembling them in the form of transport stream packets. Recently many research works have been carried out about video stream error detection. They mostly do this by focusing on some decoding parameters related to frame. Processing complexity can be a disadvantage for the proposed methods. In this thesis, we investigated syntax error occurrences due to corruption in the header of the video transport stream. The main focus of the study is the video streams that cannot be decoded. The proposed model is implemented by filtering video and audio packets in order to find the errors. The filters investigate some sources that can affect the video stream playback. The output from this method determines the type, location and duration of the errors. The simplicity of the structure is one of advantages of this model. It can be implemented by three simple filters for detecting errors and a “calculation unit” for calculating the duration of an error. Fast processing is another benefit of the proposed model.
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Odongo, Anthony. "Tar removal in hot gas streams." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/40498.
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Thermal conversion of organic materials through gasification yields gaseous fuel. The fuel gas often requires cleaning and upgrading ahead of combustion in advanced technologies such as gas engines, fuel cells and turbines. Tar is one of the major impurities found in streams, and can foul and block equipment. This study focuses on catalytic destruction of tar in a hot gas stream, at different operating conditions to improve the gas yield and quality. Steam gasification and reforming of tar involves thermal decomposition of tar and the reaction of tar with steam and fuel gases. These processes contribute to complex kinetics of the overall process involving a series of reactions, including: CO + H2O ͍ CO2 + H2, CO + 3H2 → CH4 + H2O, C + H2O → CO + H2, CH4 + 2H2O → CO2 + 4H2, CO2 + 4H2 → CH4 + 2H2O, C + 2H2O → 2H2 + CO2, CO + 2H2 → CH3OH, C + CO2 → 2CO, 2C + H2 → C2H2, & C + 2H2 → CH4. The concentration of each component affects the rate of reaction for each product. Introducing a catalyst to these processes increases the rate reactions and hence the number of successful reactions. The operating temperature, residence time and type of feedstock are other factors that can also affect the gas yield and quality. In this work, a continuous fixed bed-reactor was developed and assembled at Imperial College London, and used to investigate the activity of Pt-, Rh- and Ni-based catalysts, provided by Johnson Matthey. Experiments were performed at temperatures from 700 oC to up to 950 oC. The carrier gas flow rate, the steam-to-carbon ratio and feed gas composition were also varied to investigate the reaction kinetics and reaction pathways. Rh- and Pt-based catalysts had a better activity, thermal durability and corrosion resistance than the Ni-based catalyst. The Rh-catalyst results at considered conditions and above 800 oC were just about the same as the equilibrium results. Rh- had a better longevity and a tar conversion to syngas as high as 98% at 750 oC and S/C of 3. Ni deactivated within initial 30 minutes whereas the Rh- and Pt-catalyst activity remained steady.
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DʹAngelo, Donna Jean. "Mechanisms governing phosphorus retention in streams /." This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-08252008-162550/.
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Heggen, Siv. "Ice breakup in small Norwegian streams." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for bygg, anlegg og transport, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22701.
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River ice is present parts of the year in cold region environments and is an important component of the flow regime. The river ice is known to produce many extremes and potential floods far exceed those possible under open-water conditions. Thus, predicting the time of a river ice breakup is essential as it concerns environmental impact, emergency flood warning and hydropower production. The available predictive methods are developed and tested only for moderate-gradient medium and large rivers. Their utility for high-gradient small streams is not known. As a first step toward development of a criterion for ice breakups in small streams one of the existing criteria for large rivers is tested. The ice cover thickness is an important parameter considering the river ice breakup, thus a simulation of the ice cover growth is included in the analysis. Extensive data are retrieved from field studies and analysis regarding ice cover growth and ice breakup is conducted. The Stefan formula is proven to give good results for the ice cover growth in the observation sites. The method provides reliable values of the ice thicknesses which then are used as input parameter to the Empirical criterion for onset of breakup. The Empirical criterion has some inconsistency in its simulations of the river ice breakups. However, the criterion was able to simulate three of five ice breakups in small streams. This is evaluated as a promising result and the criterion can thereby be used as a foundation for further research and development.
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Wong, Wai-ha, and 王慧霞. "On-line scheduling of video streams." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B30075117.
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Turner, C. "Episodic pollution and recovery in streams." Thesis, Cardiff University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.527558.
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As pollution control measures have reduced the loadings from continuous discharges to receiving waters, episodic pollution has become increasingly detectable and important. A pollution episode involves a toxicant discharge to rivers (or other surface waters) of short duration and high concentration which is attenuated by physicochemical processes. After an episode has passed downstream, the timeconcentration profile of exposure to pollution and previous ecological status of the river are difficult to determine. After an episode, and over the course of time, recolonisation and succession will occur. This contrasts with the response of rivers to continuous discharges of pollution where recovery is spatial through the dilution and degradation of pollutants. Such spatial recovery has led to the description of recovery zones (e. g. Kolkwitz and Marsson, 1908). Pollution from farm waste accounted for almost 20% of all reported pollution incidents in 1988 (NRA 1989), so the investigation focussed on those aspects of pollution closely associated with strong organic wastes. A range of responses of freshwater macroinvertebrates and fish was investigated during simulated episodes of reduced dissolved oxygen (D. 0. ), increased ammonia and increased sulphide concentrations. These episodes were achieved by dosing streams after acertaining their biological condition, monitoring the impact upon captive animals and invertebrate drift during events, and by describing patterns of recovery. Catastrophic increases in drift occurred under conditions of reduced D. O. and mortalities in caged animals occurred, species exhibiting a range of sensitivities. Invertebrate responses to increased ammonia and sulphide concentrations (drift and mortality) were less dramatic, however, behavioural changes in captive animals were observed during episodes. With captive Gammarus pulex (L. ), the addition of substrate (sand and stones) to the container reduced mortality and a positive correlation was found between toxicity and ambient water velocity. Parasitised individuals of G. pulex were more susceptible to the simulated episodes than unparasitised ones. Seasonal differences occurred in the response of benthic invertebrates to low D. O. In November the response of drift density to low D. O. was about 1/50th of that in July despite broadly comparable benthic abundances. The recovery of benthic invertebrates following pollution events was rapid (2-3 months). In one series of experiments, which assessed the recolonisation route, 45% came from upstream as drift. Within substrate migration (from deep to surface layers of sediments), upstream movements and aerial sources contributed 31.5%, 15.6% and 7.9% respectively. From the measurements of pollutant concentrations within sediments during episodes and from tracer studies using sodium chloride, the penetration of pollutants into stream substrates was spatially patchy. In consequence some organisms survived in the deeper layers of sediments and were available for local recolonisation. Laboratory investigations showed that it is for possible animals to migrate downwards within a substrate in response to pollution episodes.