• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 41
  • 11
  • 6
  • 4
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 82
  • 82
  • 17
  • 14
  • 11
  • 11
  • 9
  • 7
  • 7
  • 6
  • 6
  • 6
  • 6
  • 6
  • 6
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Assessing Changes in the Abundance of the Continental Population of Scaup Using a Hierarchical Spatio-Temporal Model

Ross, Beth E. 01 January 2012 (has links)
In ecological studies, the goal is often to describe and gain further insight into ecological processes underlying the data collected during observational studies. Because of the nature of observational data, it can often be difficult to separate the variation in the data from the underlying process or `state dynamics.' In order to better address this issue, it is becoming increasingly common for researchers to use hierarchical models. Hierarchical spatial, temporal, and spatio-temporal models allow for the simultaneous modeling of both first and second order processes, thus accounting for underlying autocorrelation in the system while still providing insight into overall spatial and temporal pattern. In this particular study, I use two species of interest, the lesser and greater scaup (Aythya affnis and Aythya marila), as an example of how hierarchical models can be utilized in wildlife management studies. Scaup are the most abundant and widespread diving duck in North America, and are important game species. Since 1978, the continental population of scaup has declined to levels that are 16% below the 1955-2010 average and 34% below the North American Waterfowl Management Plan goal. The greatest decline in abundance of scaup appears to be occurring in the western boreal forest, where populations may have depressed rates of reproductive success, survival, or both. In order to better understand the causes of the decline, and better understand the biology of scaup in general, a level of high importance has been placed on retrospective analyses that determine the spatial and temporal changes in population abundance. In order to implement Bayesian hierarchical models, I used a method called Integrated Nested Laplace Approximation (INLA) to approximate the posterior marginal distribution of the parameters of interest, rather than the more common Markov Chain Monte Carlo (MCMC) approach. Based on preliminary analysis, the data appeared to be overdispersed, containing a disproportionately high number of zeros along with a high variance relative to the mean. Thus, I considered two potential data models, the negative binomial and the zero-inflated negative binomial. Of these models, the zero-inflated negative binomial had the lowest DIC, thus inference was based on this model. Results from this model indicated that a large proportion of the strata were not decreasing (i.e., the estimated slope of the parameter was not significantly different from zero). However, there were important exceptions with strata in the northwest boreal forest and southern prairie parkland habitats. Several strata in the boreal forest habitat had negative slope estimates, indicating a decrease in breeding pairs, while some of the strata in the prairie parkland habitat had positive slope estimates, indicating an increase in this region. Additionally, from looking at plots of individual strata, it seems that the strata experiencing increases in breeding pairs are experiencing dramatic increases. Overall, my results support previous work indicating a decline in population abundance in the northern boreal forest of Canada, and additionally indicate that the population of scaup has increased rapidly in the prairie pothole region since 1957. Yet, by accounting for spatial and temporal autocorrelation in the data, it appears that declines in abundance are not as widespread as previously reported.
22

Design of Indexing Strategies for Video Database System

Chen, You-cheng 29 June 2005 (has links)
In the video database, each video contains temporal and spatial relationships between content objects. The temporal relationships can be specified between frame sequences and the spatial relationships can be specified by the relationships between objects in a single frame. Moreover, the information related to locations and motions of objects is included in video database. Many video indexing strategies have been proposed, which include the above information to speed up the query processing time. For example, the 3D C-string strategy, it uses the projections of objects to represent spatial and temporal relations between objects in a video. Moreover, the 3D C-string strategy can keep track of the motions and size changes of the objects in a video. However, there are three problems caused by the 3D C-string strategy. The first one is that it cannot index some kinds of videos in which an object appears and then disappears for more than one time. The second one is that the representation of the 3D C-string is too complex for deriving spatial relationships. The last one is that the 3D C-string cannot derive the absolute locations of objects, since it records the relative locations of objects. In this thesis, in order to solve the problems of the 3D C-string strategy, we propose three new spatial relationships. By making use of the three spatial relationships, we can express the condition that objects disappear and appear. Moreover, based on the sequence of spatial relationships, we can derive the temporal relationships. Based on this technique, we propose three index processing strategies for video database. The first strategy is the Temporal UID Matrix (TUID) strategy. We use those 13 unique numbers used in the UID strategy and our 3 new added unique numbers to represent spatial relationships. Then, we store the sequence of spatial relationships in the TUID matrix. In this way, we can efficiently support query types of spatial, temporal, and spatio-temporal relationships. However, since the TUID strategy does not record the information of objects, it cannot support the query type by the information of objects. Therefore, we propose the second strategy, the 2D Video String strategy, to keep track of the motions, locations, and size changes associated with the video objects. Although the 2D Video String strategy can support all types of queries, it is less efficient than the TUID strategy. By making use of the advantages of both strategies, we propose another video indexing strategy, the Hybrid strategy. We record the information of objects in the diagonal part of the TUID matrix. From our simulation study, we show that our proposed strategies can provide a shorter search time for video data than Lee et al.'s 3D C-string strategy, except the 2D Video String strategy for the temporal query.
23

Spatial-temporal Fixes And Hegemonic Transitions In The Historical Capitalism

Taskesen, Suat 01 September 2010 (has links) (PDF)
This thesis analyzes the historical capitalism in a historical context. ccumulation cycles, hegemonic transitions, and their interrelated structures n the historical capitalism will be discussed alongside inspired prose, and completed final drafts. The thesis will also trace the causes and effects of accumulation cycles and hegemonic transitions and will seek to answer questions such as how and why those cycles and transitions ocur, what are the determinants and how and why those determinants effect those processess, Thus, the purpose of this study is to obtain a full perspective of the historical capitalism by analyzing past and present accumulation cycles and hegemonic shifts respectively to provide basis for explaining not only incessant cycles and transitions of the historical capitalism but also current developments in International Relations.
24

Design and Implementation of Query Processing Strategies for Video Data

Yang, Wen-Haur 09 July 2002 (has links)
Traditional database systems only support textual and numerical data. Video data stored in these database systems can only be retrieved through their video identifiers, titles or descriptions. In the video data, frame-by-frame object change is one of the most obvious information. Each video contains temporal and spatial relationships between content objects. The temporal relationships can be specified between frame sequences and the spatial relationships can be specified by the relationships between objects in a single frame. The difficulty in designing a content-based video database system is how to store and describe the relationships between moving objects completely. Many researches on content-based video retrieval represented the content of video as a set of frames, but they either left out the temporal ordering of frames in the shot or only stored the relationships between objects in a single frame. According to these observations, we conclude that a content-based video database system requires video indexing, query processing and a convenient user interface to fit the requirements and characteristics of videos. In this thesis, we design and implement a query processing strategy for video data. In the proposed strategy, we consider three query types: the exact object match, the spatial-temporal object retrieval and the motion query, where a exact object match is to find the video files which contain the specific objects, a spatial-temporal objects retrieval is to retrieve the object pairs that satisfy some spatial-temporal relationships and a motion query is to find the set of frames which contain the object movements. Moreover, we consider three design issues: the video indexing, the video query processing and the video query interface. When there are a large number of videos in a video database and each video contains many shots, frames and objects, the processing time for content retrieval is tremendous. Thus, we need a proper video indexing strategy to speed up the searching time. In order to fulfill the spatial-temporal relationships of objects between different frames, we give the indexes both in the spatial and temporal axes. In the temporal index file structure, we propose the shot-based B+-tree to index the temporal data. In the spatial index file structure, we use R-tree to store not only the relationships between objects in one frame, but also the relationships of one object when the object first and last appears in the shot. Based on this strategy, we can describe the status of a moving object in details. For the part of query processing, we propose a signature file structure to filter out the videos that absolutely can not be the answer. After that, in order to determine whether the answer exists in the candidate videos, we use a multi-dimensional string, called binary string, to represent the spatial-temporal relationships between objects. Then, the video query processing problem will become a binary string matching problem. Finally, we design and implement an user-friendly user interface. Our system is performed on a Pentium III machine with one CPU clock rate of 550 MHz, 256 MB of main memory, running under Windows 2000 Professional edition, used Access 2000 database and coded in Delphi 6 with about 10,000 lines. From our experience, we show that the proposed system can support an efficient query processing, a fast searching capabilities and an user-friendly user interface.
25

Distributed Particle Filters for Data Assimilation in Simulation of Large Scale Spatial Temporal Systems

Bai, Fan 18 December 2014 (has links)
Assimilating real time sensor into a running simulation model can improve simulation results for simulating large-scale spatial temporal systems such as wildfire, road traffic and flood. Particle filters are important methods to support data assimilation. While particle filters can work effectively with sophisticated simulation models, they have high computation cost due to the large number of particles needed in order to converge to the true system state. This is especially true for large-scale spatial temporal simulation systems that have high dimensional state space and high computation cost by themselves. To address the performance issue of particle filter-based data assimilation, this dissertation developed distributed particle filters and applied them to large-scale spatial temporal systems. We first implemented a particle filter-based data assimilation framework and carried out data assimilation to estimate system state and model parameters based on an application of wildfire spread simulation. We then developed advanced particle routing methods in distributed particle filters to route particles among the Processing Units (PUs) after resampling in effective and efficient manners. In particular, for distributed particle filters with centralized resampling, we developed two routing policies named minimal transfer particle routing policy and maximal balance particle routing policy. For distributed PF with decentralized resampling, we developed a hybrid particle routing approach that combines the global routing with the local routing to take advantage of both. The developed routing policies are evaluated from the aspects of communication cost and data assimilation accuracy based on the application of data assimilation for large-scale wildfire spread simulations. Moreover, as cloud computing is gaining more and more popularity; we developed a parallel and distributed particle filter based on Hadoop & MapReduce to support large-scale data assimilation.
26

Modélisation et gestion de concepts, en particulier temporels, pour l'assistance à la caractérisation de séquences d'images / Modeling and management of time concepts to support the characterization of image sequences

Simac, Alain 14 June 2011 (has links)
Les techniques habituelles d'indexation de vidéos passent généralement par une phase d'apprentissage qui nécessite préalablement la constitution d'une base d'apprentissage. Même si la taille de cette base est souvent réduite, la phase d'annotation réalisée par un expert de l'application est souvent longue et fastidieuse. Dans le cadre de cette thèse, nous avons développé un dispositif qui permet de pré-sélectionner un ensemble de prototypes susceptibles de contenir le concept qui doit apparaître dans la base d'apprentissage. Cette base réduite de prototypes sera ensuite annotée par l'expert. Nous nous sommes intéressés à des concepts temporels, ce qui nous a amené à étudier particulièrement des caractéristiques liées au mouvement, comme les points d'intérêt spatio-temporels (STIP Spatial Temporal Interest Points). D'autres caractéristiques ont aussi été utilisées concernant la couleur et la présence de formes particulières. Ces caractéristiques sont ensuite exploitées pour structurer la base de vidéos en briques spatio-temporelles homogènes. Cette structuration correspond à une sorte de segmentation de la base en fonction de chacune des caractéristiques. La liaison entre le concept à définir et les briques extraites de la base est en lien avec le fossé sémantique bien connu dans la problématique d'indexation automatique. La création de ce lien nécessite l'utilisation de la connaissance de l'expert de l'application sur le concept. Nous avons développé un système dans lequel cette connaissance est extraite par un système de questions/réponses. Les couples de questions/réponses permettent de sélectionner des briques répondant à la contrainte, de définir des relations entre certaines briques, et enfin de naviguer dans l'arborescence des questions. Des tests ont été réalisés sur des bases de vidéos de provenances diverses telles que des vidéos provenant d'émissions de télévision, de films d'animation, ou encore des vidéos de laboratoire disponibles sur le net, ou réalisées par nos soins. Ces tests montrent les performances satisfaisantes mais aussi les limites de l'approche et ouvrent des perspectives intéressantes, particulièrement sur les aspects collaboratifs et les aspects adaptatifs qui permettraient de capitaliser les connaissances des experts applicatifs et rendraient le système plus efficient. / The usual techniques of video indexing generally go through a learning phase that requires the prior establishment of a training database. Even if the size of the database is often reduced, the annotation phase by an expert of the application is often long and tedious. In this thesis, we developed a system that allows pre-selecting a set of prototypes that can contain the concept that must appear in the training set. This reduced base of prototypes will then be annotated by the expert. We are interested in time concepts, which led us to study particular features related to movement, such as Spatial Temporal Interest Points (STIP). Other features have also been used concerning the color and the presence of particular shapes. These characteristics are then used to structure the video database in homogeneous space-time blocks. This structure corresponds to segmentation related to each characteristic. The link between the concept to define and blocks extracted from the base corresponds to the well known problem of automatic indexing, the semantic gap. The definition of this link requires the introduction of the application expert's knowledge. We developed a system in which this knowledge is extracted by a questions/answers system. The couples of questions/answers allow the system to select blocks corresponding to the constraint, to define relationships between some blocks, and finally to navigate on the questions/answers tree. Tests were performed on video databases from various sources such as videos from tele- vision shows, animated films, laboratory videos available on the net, or made by us. These tests show the satisfying performances but also the limitations of the approach and open interesting perspectives, particularly on the collaborative and adaptive aspects that would capitalize in the application expert knowledge and would make the system more efficient.
27

Statistical-Based Suspect RetrievalUsing Modus Operandi

Tran, Bao Khang January 2020 (has links)
Introduction. The police and the investigation team has been manually doing behavioural analysis and connecting different crimes to an offender. With the help of computers technologies, databases, and automated system, the statistical analysis of the offender’s behaviour significantly improved. There we can transfer from a manual process to an automated one, and the investigator can allocate time and resources better by prioritising the offenders to investigate. In this study, we create and experiment with a proof of concept system that ranks and prioritise different offenders using the Random Choice method in combination with the state of the art Spatial-Temporal method. Objectives. In experimenting with the proof of concept system, we are aiming to understand the effect of different offender’s behaviour having on the offenders ranking and the effect of having multiple different numbers of reference crimes in the database. The objective is also to understand the role of consistency and distinctiveness in offenders ranking. Moreover, understanding the performances of our proof of concept system comparing to already existing methods such as Random Choice, Spatial-Temporal and a baseline method that based on pure randomness. Method. The method we chose for this study was an experimental study. With an experimental environment with independent and dependent variables, we presented and evaluated the system. We were using the experimenting approach because it has a stable presence and widely used in similar studies in this field. Results. After the experiments, we found that different Modus Operandi (MO)categories have a different effect on the ranking results and different distinctive combinations of MO categories also has different accuracy when ranking the offenders. Offenders that were consistent with more references crime in the database were often higher ranked and were linked more correctly. Our proof of concept system shows significant improvement over Random Choice method and the Spatial-Temporalmethod. Conclusion. From the results, we concluded that the proof of concept system displays a significant accuracy in ranking and prioritising offenders, there different MO categories and combinations of them has a different effect on the accuracy of the ranking. The ranking system was also affected by the number of reference cases that exist in the database. Future works can extend the study by trying to improve different aspects of the proof of concept systems, such as the Random Choice aspect or the Spatial-Temporal aspect.
28

Spatio-Temporal Prediction and Stochastic Simulation for Large-Scale Nonstationary Processes

Li, Yuxiao 04 November 2020 (has links)
There has been an increasing demand for describing, predicting, and drawing inferences for various environmental processes, such as air pollution and precipitation. Environmental statistics plays an important role in many related applications, such as weather-related risk assessment for urban design and crop growth. However, modeling the spatio-temporal dynamics of environmental data is challenging due to their inherent high variability and nonstationarity. This dissertation is composed of four signi cant contributions to the modeling, simulation, and prediction of spatiotemporal processes using statistical techniques and machine learning algorithms. This dissertation rstly focuses on the Gaussian process emulators of the numerical climate models over a large spatial region, where the spatial process exhibits nonstationarity. The proposed method allows for estimating a rich class of nonstationary Mat ern covariance functions with spatially varying parameters. The e cient estimation is achieved by local-polynomial tting of the covariance parameters. To extend the applicability of this method to large-scale computations, the proposed method is implemented by developing software with high-performance computing architectures for nonstationary Gaussian process estimation and simulation. The developed software outperforms existing ones in both computational time and accuracy by a large margin. The method and software are applied to the statistical emulation of high-resolution climate models. The second focus of this dissertation is the development of spatio-temporal stochastic weather generators for non-Gaussian and nonstationary processes. The proposed multi-site generator uses a left-censored non-Gaussian vector autoregression model, where the random error follows a skew-symmetric distribution. It not only drives the occurrence and intensity simultaneously but also possesses nice interpretations both physically and statistically. The generator is applied to 30-second precipitation data collected at the University of Lausanne. Finally, this dissertation investigates the spatial prediction with scalable deep learning algorithms to overcome the limitations of the classical Kriging predictor in geostatistics. A novel neural network structure is proposed for spatial prediction by adding an embedding layer of spatial coordinates with basis functions. The proposed method, called DeepKriging, has multiple advantages over Kriging and classical neural networks with spatial coordinates as features. The method is applied to the prediction of ne particulate matter (PM2:5) concentrations in the United States.
29

COVID-19 Disease Mapping Based on Poisson Kriging Model and Bayesian Spatial Statistical Model

Mu, Jingrui 25 January 2022 (has links)
Since the start of the COVID-19 pandemic in December 2019, much research has been done to develop the spatial-temporal methods to track it and to predict the spread of the virus. In this thesis, a COVID-19 dataset containing the number of biweekly infected cases registered in Ontario since the start of the pandemic to the end of June 2021 is analysed using Bayesian Spatial-temporal models and Area-to-area (Area-to-point) Poisson Kriging models. With the Bayesian models, spatial-temporal effects on infected risk will be checked and ATP Poisson Kriging models will show how the virus spreads over the space and the spatial clustering feature. According to these models, a Shinyapp website https://mujingrui.shinyapps.io/covid19 is developed to present the results.
30

New Procedures for Data Mining and Measurement Error Models with Medical Imaging Applications

Wang, Xiaofeng 15 July 2005 (has links)
No description available.

Page generated in 0.0708 seconds