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Kia, Seyed Hossein. « Uncertainty associated with scaling spectral indices of carbon fluxes at various spatial and temporal scales ». Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/417789/.
Texte intégralRésumé :
Measurements from the global network of micrometeorological tower sites (FLUXNET) provide essential information on the ecosystems productivity (i.e. a key component for the study of the carbon cycle). However, the area sampled by instruments on a flux tower is poorly defined and varies with weather conditions. Additionally, gaps in the FLUXNET record are common, either due to unsuitable measurement conditions or instrument failure. Hence, remote sensing (RS) has been proposed as a way to enhance the FLUXNET database, as it provides complete spatial coverage and frequent repeat observations. In practice, the use of RS for this task is challenging. The integration of spatially-explicit ecosystem models, RS observations and eddy covariance (EC) flux measurements with environmental variables have facilitated the quantification of carbon cycling dynamics across multiple spatial and temporal scales. In this regard, process-based models with the aim of simulation of carbon dynamics in forest ecosystems are increasingly being used besides other tools to predict the effects of environmental factors on the forest carbon pool and forest productivity. However, despite this, decision makers must be aware of the limitations of these models by uncertainty analyses to make the process-based models more robust and to optimize them for estimating productivity at landscape level. There is a need to address various sources of uncertainty associated with such quantification, including sensor limitations in terms of support size defined by spatial and temporal resolutions; spatial heterogeneity of land surface properties; pre-processing calibration; and the structure of the model proposed and its parameterization. calibration; and the structure of the model proposed and its parameterization. This research investigated the sources of uncertainty mentioned across three domains of interest: spectral, spatial and temporal. The present research deals with this need using a combination of tower-based EC flux measurements and RS data from both airborne and satellite RS systems at a range of temporal and spatial scales. It incorporates multiple remote sensing data sets (Airborne LiDAR, Airborne Imaging Spectrometry, DMC, and MODIS) to derive indices related to canopy structure (nCHM), plant cover (NDVI) and photosynthesis processes (PRI), and attempts to relate these to the data measured by instruments on flux towers in two locations: Wytham Woods, southern England, and Chequamegon Nicolet National Forest in northern Wisconsin, USA. In terms of the spectral domain, the research adds to the evidence that NDVI alone is insufficient to fully characterize the primary productivity of plant canopies, specifically across heterogeneous landscape. The study also demonstrates the magnitude and variability of extraneous parameters (e.g. optical geometry, shadow fraction, soil background and aerosol) in RS observations of the mixed forest of Wytham Woods using a 3D forest light simulation model (FLIGHT model). The results reveal that the observed vegetation indices (NDVI and PRI) form the mixed forest is highly sensitive to variation in solar and view zenith angles and soil background, while the indices are relatively robust to aerosol scattering. In the temporal domain, the research makes use of a unique time-series of ten multispectral images acquired during a single growing season by the DMC satellite sensors. The heterogeneity of canopy cover has greatest impact on the DMC data early in the season, and this highlights the importance of understanding how the flux tower footprint varies with weather conditions. As the canopy began to green-up, the precision of temporal sampling became more important. Based on explicit representation of the time-varying flux tower footprint, prediction of flux tower measurements directly from space-borne coarse spatial resolution imagery is challenging and leads to a low predictive ability. In order to use the global FLUXNET EC dataset and RS observations to estimate the ecosystem productivity at regional and global scales, this research deals with an upscaling approach that it involves flux footprint climatology modelling and RS-based light use efficiency (LUE) model fusion. In this aspect, a large correlation is found between satellite-based PRI and the EC-based LUE of a homogeneous deciduous forest. However, estimating the regional level LUE of a heterogeneous landscape from space is still an uncertain process as the required spectral index (PRI) is affected by canopy level variables as well as the geometry of illumination and view. Furthermore, the sensitivity analysis of a simple Diagnostic Carbon Flux Model (DCFM) to seven input parameters (εmax, a, β, R'ref γ, λ and E0) using a five-years record of the EC data from four flux towers selected across various plant functional types (PFTs) in the Upper Midwest region of northern Wisconsin, is considered to optimize the RS-based LUE model for estimating regional productivity. The results confirm that empirical constants for the estimation of the fPAR absorbed by vegetation canopies (a and β) next to the maximum light use efficiency (εmax) has little impact on the fluctuations of net carbon exchange within each PFT whereas DCFM model was very sensitive to so, the estimation of this factor, in comparison with the other parameters, plays the key role in the accuracy of NEE's predictions. Moreover, except for homogenous canopy cover, in other PFTs, interactions among the crucial ecophysiological parameters have minor contribution to uncertainty of NEE prediction by DCFM model. In conclusion, the results demonstrated the potential combination of the satellite based approach, flux footprint modelling and data-model fusion for improving the accuracy of regional/global productivity estimations. This approach includes four steps: (1) a RS-based LUE model for estimating productivity; (2) EC flux footprint analysis for the corresponding RS images; (3) using the footprint integration of RSbased ecosystem productivity to be comparable with the tower-based EC-derived productivity values, several key parameters of the RS-based LUE model can be optimized using the DCFM; and (4) The optimized RS-based LUE model can be applied for estimating regional productivity.
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Ahongshangbam, Joyson [Verfasser]. « Tree and oil palm water use : scaling, spatial heterogeneity and temporal dynamics (Sumatra, Indonesia) / Joyson Ahongshangbam ». Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/122090936X/34.
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McGlinn, Daniel J. « Spatial and temporal scaling of species composition at the Tallgrass Prairie Preserve, Oklahoma implications for theory and conversation / ». Click HERE to connect, 2009. http://digital.library.okstate.edu/etd/McGlinn_okstate_0664D_10364.pdf.
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Barnes, Christopher James. « Characterizing environmental, temporal and spatial scaling of Rhizosphere fungi in bioenergy crops : and their role in below-ground carbon cycling ». Thesis, University of Warwick, 2014. http://wrap.warwick.ac.uk/72734/.
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The rhizosphere consists of plant roots and the adjoining soil, which contains a functionally and genetically rich fungal community. The obligate plant symbionts, the mycorrhizal fungi, have been shown to receive substantial quantities of plant-derived C and play an important role in belowground C dynamics. The flux and residence time of C is however likely to be highly species-specific for rhizosphere fungi, and therefore their abundance and composition will likely have important implications on C storage belowground. Rhizosphere fungal community formation is extremely complex and despite being an area of intense research, current understanding is limited. The composition and abundance of rhizosphere fungi have been shown to vary with temporal and environmental parameters, and potentially geographical separation. However, no studies to date have analysed these parameters simultaneously to isolate the independent effects of each. Clone libraries in conjunction with TRFLP were performed before progressing to 454-pyrosequencing to profile the rhizosphere fungal community of a short rotation coppice (SRC) willow filed site. In this work, distinct seasonal fungal assemblages were shown, with N availability having a large effect in summer and geographical distance effects in autumn sampling points. Additionally, a rare large transition in the composition of the rhizosphere fungi was also demonstrated, which was most likely driven by extreme rainfall earlier in the growing season of the year of transition. Finally, using ₁₃C-labelled-CO₂ the belowground movement of recently derived photo-assimilates was shown to differ between Miscanthus x giganteus and SRC willow, however no significant fluxes were associated with rhizosphere fungal pathways in either crop. Results from this work demonstrate that some of the considerable complexity of microbial communities could have between overlooked in previous community analyses, whilst the flow of C within through mycorrhizal pathways maybe less important in bioenergy cropping systems compared to other ecosystems.
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He, Qian. « Spatio-Temporal Patterns, Correlations, and Disorder in Evolutionary Game Theory ». Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/40296.
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Evolutionary game theory originated from the application of mathematical game theory to biological studies.
Well-known examples in evolutionary game theory are the prisoner's dilemma, predator-prey models, the rock-paper-scissors game, etc.
Recently, such well-known models have attracted increased interest in population dynamics to understand the
emergence of biodiversity and species coexistence. Meanwhile, it has been realized that techniques from statistical
physics can aid us to gain novel insights into this interdisciplinary field. In our research, we mainly employ
individual-based Monte Carlo simulations to study emerging spatio-temporal patterns, spatial correlations,
and the influence of quenched spatial disorder in rock-paper-scissors systems either with or without conserved
total population number. In balanced rock-paper-scissors systems far away from the ``corner'' of configuration space,
it is shown that quenched spatial disorder in the reaction rates has only minor effects on the co-evolutionary dynamics.
However, in model variants with strongly asymmetric rates (i.e., ``corner'' rock-paper-scissors systems),
we find that spatial rate variability can greatly enhance the fitness of both minor species in``corner'' systems,
a phenomenon already observed in two-species Lotka-Volterra predator-prey models. Moreover, we numerically study the
influence of either pure hopping processes or exchange processes on the emergence of spiral patterns in spatial
rock-paper-scissors systems without conservation law (i.e., May-Leonard model). We also observe distinct extinction
features for small spatial May-Leonard systems when the mobility rate crosses the critical threshold which separates
the active coexistence state from an inactive absorbing state.
In addition, through Monte Carlo simulation on a heterogeneous interacting agents model,
we investigate the universal scaling properties in financial markets such as the fat-tail distributions in return and trading volume,
the volatility clustering, and the long-range correlation in volatility. It is demonstrated that the long-tail feature in trading volume distribution
results in the fat-tail distribution of asset return, and furthermore it is shown that the long tail in trading volume
distribution is caused by the heterogeneity in traders' sensitivities to market risk.Ph. D.
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Miao, Yufan. « Exploring Spatio-Temporal Patterns of Volunteered Geographic Information : A Case Study on Flickr Data of Sweden ». Thesis, Högskolan i Gävle, Avdelningen för Industriell utveckling, IT och Samhällsbyggnad, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-15031.
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This thesis aims to seek interesting patterns from massive amounts of Flickr data in Sweden with pro- posed new clustering strategies. The aim can be further divided into three objectives. The first one is to acquire large amount of timestamped geolocation data from Flickr servers. The second objective is to develop effective and efficient methods to process the data. More specifically, the methods to be developed are bifold, namely, the preprocessing method to solve the “Big Data” issue encountered in the study and the new clustering method to extract spatio-temporal patterns from data. The third one is to analyze the extracted patterns with scaling analysis techniques in order to interpret human social activities underlying the Flickr Data within the urban envrionment of Sweden. During the study, the three objectives were achieved sequentially. The data employed for this study was vector points downloaded through Flickr Application Programming Interface (API). After data ac- quisition, preprocessing was performed on the raw data. The whole dataset was firstly separated by year based on the temporal information. Then data of each year was accumulated with its former year(s) so that the evovling process can be explored. After that, large datasets were splitted into small pieces and each piece was clipped, georeferenced, and rectified respectively. Then the pieces were merged together for clustering. With respect to clustering, the strategy was developed based on the Delaunay Triangula- tion (DT) and head/tail break rule. After that, the generated clusters were analyzed with scaling analysis techniques and spatio-temporal patterns were interpreted from the analysis results. It has been found that the spatial pattern of the human social activities in the urban environment of Sweden generally follows the power-law distribution and the cities defined by human social activities are evolving as time goes by. To conclude, the contributions of this research are threefold and fulfill the objectives of this study, respectively. Firstly, large amount of Flickr data is acquired and collated as a contribution to other aca- demic researches related to Flickr. Secondly, the clustering strategy based on the DT and head/tail break rule is proposed for spatio-temporal pattern seeking. Thirdly, the evolving of the cities in terms of human activities in Sweden is detected from the perspective of scaling. Future work is expected in major two aspects, namely, data and data processing. For the data aspect, the downloaded Flickr data is expected to be employed by other studies, especially those closely related to human social activities within urban environment. For the processing aspect, new algorithms are expected to either accelerate the processing process or better fit machines with super computing capacities.
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Rossholm, Andreas. « On Enhancement and Quality Assessment of Audio and Video in Communication Systems ». Doctoral thesis, Blekinge Tekniska Högskola, Institutionen för tillämpad signalbehandling, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-00604.
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The use of audio and video communication has increased exponentially over the last decade and has gone from speech over GSM to HD resolution video conference between continents on mobile devices. As the use becomes more widespread the interest in delivering high quality media increases even on devices with limited resources. This includes both development and enhancement of the communication chain but also the topic of objective measurements of the perceived quality. The focus of this thesis work has been to perform enhancement within speech encoding and video decoding, to measure influence factors of audio and video performance, and to build methods to predict the perceived video quality. The audio enhancement part of this thesis addresses the well known problem in the GSM system with an interfering signal generated by the switching nature of TDMA cellular telephony. Two different solutions are given to suppress such interference internally in the mobile handset. The first method involves the use of subtractive noise cancellation employing correlators, the second uses a structure of IIR notch filters. Both solutions use control algorithms based on the state of the communication between the mobile handset and the base station. The video enhancement part presents two post-filters. These two filters are designed to improve visual quality of highly compressed video streams from standard, block-based video codecs by combating both blocking and ringing artifacts. The second post-filter also performs sharpening. The third part addresses the problem of measuring audio and video delay as well as skewness between these, also known as synchronization. This method is a black box technique which enables it to be applied on any audiovisual application, proprietary as well as open standards, and can be run on any platform and over any network connectivity. The last part addresses no-reference (NR) bitstream video quality prediction using features extracted from the coded video stream. Several methods have been used and evaluated: Multiple Linear Regression (MLR), Artificial Neural Network (ANN), and Least Square Support Vector Machines (LS-SVM), showing high correlation with both MOS and objective video assessment methods as PSNR and PEVQ. The impact from temporal, spatial and quantization variations on perceptual video quality has also been addressed, together with the trade off between these, and for this purpose a set of locally conducted subjective experiments were performed.
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Makela, Pia K. « Spatial scaling in human peripheral vision ». Thesis, Aston University, 1994. http://publications.aston.ac.uk/14603/.
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The observation that performance in many visual tasks can be made independent of eccentricity by increasing the size of peripheral stimuli according to the cortical magnification factor has dominated studies of peripheral vision for many years. However, it has become evident that the cortical magnification factor cannot be successfully applied to all tasks. To find out why, several tasks were studied using spatial scaling, a method which requires no pre-determined scaling factors (such as those predicted from cortical magnification) to magnify the stimulus at any eccentricity. Instead, thresholds are measured at the fovea and in the periphery using a series of stimuli, all of which are simply magnified versions of one another. Analysis of the data obtained in this way reveals the value of the parameter E2, the eccentricity at which foveal stimulus size must double in order to maintain performance equivalent to that at the fovea. The tasks investigated include hyperacuities (vernier acuity, bisection acuity, spatial interval discrimination, referenced displacement detection, and orientation discrimination), unreferenced instantaneous and gradual movement, flicker sensitivity, and face discrimination. In all cases tasks obeyed the principle of spatial scaling since performance in the periphery could be equated to that at the fovea by appropriate magnification. However, E2 values found for different spatial tasks varied over a 200-fold range. In spatial tasks (e.g. bisection acuity and spatial interval discrimination) E2 values were low, reaching about 0.075 deg, whereas in movement tasks the values could be as high as 16 deg. (DX 185,687)
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Cary, Ariel. « Scaling Geospatial Searches in Large Spatial Databases ». FIU Digital Commons, 2011. http://digitalcommons.fiu.edu/etd/548.
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Modern geographical databases store a rich set of aspatial attributes in addition to geographic data. Retrieving spatial records constrained on spatial and aspatial attributes provides users the ability to perform more interesting spatial analyses via composite spatial searches; e.g., in a real estate database, "Find the nearest homes for sale to my current location that have backyard and whose prices are between $50,000 and $80,000". Efficient processing of such composite searches requires combined indexing strategies of multiple types of data. Existing spatial query engines commonly apply a two-filter approach (spatial filter followed by non-spatial filter, or viceversa), which can incur large performance overheads. On the other hand, the amount of geolocation data in databases is rapidly increasing due in part to advances in geolocation technologies (e.g., GPS- enabled mobile devices) that allow to associate location data to nearly every object or event. Hence, practical spatial databases may face data ingestion challenges of large data volumes. In this dissertation, we first show how indexing spatial data with R-trees (a typical data pre- processing task) can be scaled in MapReduce – a well-adopted parallel programming model, developed by Google, for data intensive problems. Close to linear scalability was observed in index construction tasks over large spatial datasets. Subsequently, we develop novel techniques for simultaneously indexing spatial with textual and numeric data to process k-nearest neighbor searches with aspatial Boolean selection constraints. In particular, numeric ranges are compactly encoded and explicitly indexed. Experimental evaluations with real spatial databases showed query response times within acceptable ranges for interactive search systems.
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Winstral, Adam. « Spatial scaling of snow processes : modelling implications ». Thesis, University of Reading, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.553176.
Texte intégralRésumé :
Snow cover affects life on Earth in many important ways. The high reflectivity and high moisture content of snow cover affects the global energy balance, atmospheric circulation, and weather. The characteristic heterogeneity of ephemeral mountain snowpacks exhibits strong controls on hydrological, biological, and ecological processes. Accurately predicting process responses is based on knowing the volume, distribution, and state of the snow cover. Physically-based distributed snow models (DSMs) are capable of explicitly representing these vital heterogeneities and are well suited for predicting future impacts such as those associated with climate change. These models however, are currently limited by high computational demands. This research sought to reduce these computational demands and extend the limits of physically-based DSMs. In many regions, wind plays a dominant role in determining snow accumulation patterns .: New algorithms based on terrain and vegetation structure were developed that capably reproduced observed heterogeneities in mountain winds and wind-affected snow distributions. Characterizing the wind and snow patterns in this simplified manner bypassed the heavy computational demands associated with numerically solving the fluid mechanics of windflow and mass transport. The algorithms were incorporated into a mass and energy balance DSM which accurately depicted the heterogeneous accumulation and melt of the snow cover. The computational efficiency of these new algorithms enabled what was perhaps the first DSM application to include the effects of blowing and drifting snow over this large an area at this fine a temporal resolution. Model scale also plays an important role in determining computation times. It was shown that a 100 metre model scale was sufficient for characterizing mountain snow distributions and melt. Furthermore, it was determined that not all the driving processes required the same level of detail creating the potential for additional cost savings. The presented findings have substantially reduced costs and expanded the capabilities of DSMs.
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Parker, Austin. « Spatial probabilistic temporal databases ». College Park, Md. : University of Maryland, 2008. http://hdl.handle.net/1903/8728.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2008.Thesis research directed by: Dept. of Computer Science. 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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Girard, Lucas. « Vers un nouveau cadre de modélisation rhéologique de la banquise ». Phd thesis, Grenoble, 2010. http://www.theses.fr/2010GRENU021.
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Fine couche de glace flottant à la surface des océans polaires, la banquise est un objet dynamique qui joue un rôle clé dans le système climatique. Isolant l'océan de l'atmosphère, la banquise contrôle par l'intermédiaire de l'épaisseur de glace et de la fraction d'eau libre les flux d'énergie entre ces deux milieux, et ce de manière fortement non linéaire : dans une banquise dont 0. 5% de la surface est constituée de fractures, 50% des flux de chaleur s'effectuent le long de ces fractures. Il apparait donc essentiel de mieux comprendre et modéliser les processus de déformation et de rupture de la banquise. Dans la première partie de ce travail, le cadre de modélisation mécanique actuellement utilisé dans les modèles de banquise, la rhéologie Visqueuse-Plastique (VP), est évalué sur la base des propriétés statistiques et propriétés d'échelle des vitesses de dérive et de déformation de la banquise. Ces propriétés jouent un rôle important pour les flux de chaleur air-mer et la production de glace, d'autre part elles peuvent être considérées comme une empreinte du comportement mécanique de la banquise. Cette évaluation met en évidence les limitations du cadre de modélisation VP et notamment son incapacité à reproduire les propriétés de déformation de la banquise. Cela suggère que la rhéologie VP n'est pas adaptée à la modélisation de la banquise. Le nouveau cadre de modélisation mécanique developpé au cours de cette thèse fait l'hypothèse que la déformation de la banquise est principalement accommodée par fracturation et glissement le long de failles (comportement fragile) sur une vaste gamme d'échelles (transmission de contraintes à grande distance). Dans ce nouveau modèle, baptisé la rhéologie Elasto-Fragile (EB), la banquise est considérée comme une plaque solide élastique, permettant les interactions à grande distance, associée à une loi d'endommagement progressive, décrivant un comportement fragile. Le modèle EB est premièrement utilisé pour mener une étude fondamentale sur la rupture dans les matériaux hétérogènes. Une divergence de la longueur de corrélation est mise en évidence à partir des fonctions de corrélation des évènements d'endommagement ainsi que par l'analyse d'échelle du champ de déformation. Les propriétés d'échelles du champ de déformation qui émergent à l'approche de la rupture sont proche de celles observées pour la déformation fragile des objets géophysiques tel que la banquise ou la croûte terrestre. Ces résultats soutiennent l'analogie entre rupture et point critique. Une application idéalisée de la rhéologie EB à la banquise Arctique, adaptée à des simulations courtes (3 jours), est présentée. Les propriétés statistiques et propriétés d'échelle obtenues pour la déformation simulée sont comparables à celles obtenues pour la banquise. Ces premiers résultats prometteurs soutiennent que les propriétés de déformation de la banquise émergent du comportement mécanique élasto-fragile de la banquise et motivent l'implémentation de la rhéologie EB dans les modèles globaux de banquise. Sur des périodes de temps plus longues, l'effet du regel des failles et fractures présentent au sein de la banquise doit être pris en compte. Une loi de cicatrisation décrivant ce processus est présentée ainsi que des résultats préliminaires de simulations prenant en compte cet aspect. Finalement, une méthodologie pour l'implémentation de la rhéologie EB dans un modèle global de banquise est présentéeIn this thesis, new approaches are used to model the mechanical behavior of sea ice and to evaluate sea ice models in terms of ice drift and deformation. It is first shown how the statistical and scaling properties of sea ice drift and deformation can be used as an evaluation metric for sea ice models. These properties are known to play an important role regarding ice growth estimates and should therefore be captured in sea ice models. The evaluation metric is applied to simulations performed with a coupled ocean/sea ice model, where the mechanical behavior of sea ice is represented using the Viscous-Plastic (VP) rheology, as in most current global ocean and climate models. The VP model is shown to be unable to capture the statistical and scaling properties of sea ice deformation. As these properties are a signature of the ice mechanical behavior, it suggests that the VP rheology is inappropriate for sea ice modeling. The new mechanical model developped during this thesis is based on the hyopthesis that sea ice deformation is mainly accommodated by fracturing and frictional sliding (brittle behavior) over a wide range of scales (stresses can be transmitted on long distances). The main characteristics of this new model, named the Elasto-Brittle (EB) rheology, are progressive damage to represent the brittle behavior, and an elastic constitutive law to allow long-range elastic interactions to take place. The EB rheology is first used to carry out a fundamental study of fracture in heterogeneous media. Simulations show that fracture is preceded by a divergence of the correlation length, measured from a correlation analysis of discrete events and from a scaling analysis of the continuous strain-rate field. The scaling properties of deformation that emerge in the vicinity of failure ressemble those observed for the brittle deformation of geophysical objects such as sea ice or the earth's crust. These results, that argue for a critical point interpretation of fracture, are discussed in the context of fracture at geophysical scales. Secondly, short term simulations of the winter Arctic sea ice cover are carried out using the EB rheology. The results show that the EB rheology captures well the statistical and scaling properties of sea ice deformation, motivating the implementation of the EB rheology in global sea ice models. On longer time scales, sea ice can recover its mechanical properties through refreezing of fractures. A healing law accounting for this process is presented along with preliminary results from simulations accounting for the effect of healing. Finally, a methodology for the implementation of the EB rheology within a global sea ice model is presented and discussed
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Storey, Susan. « Spatial-temporal fish stock assessment ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ28463.pdf.
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Slack, Marc G. « Spatial and temporal path planning ». Thesis, This resource online, 1987. http://scholar.lib.vt.edu/theses/available/etd-04272010-020255/.
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Liu, Fang 1962. « Modeling spatial and temporal textures ». Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/29131.
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Henderson, Jonathan. « Avian spatial and temporal cognition ». Thesis, University of Edinburgh, 2004. http://hdl.handle.net/1842/14049.
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I investigated the spatial memory abilities of male rufous hummingbirds (Selasphorus rufus) on their breeding grounds, where birds can be readily trained to feed from artificial flowers presented in two- and three-dimensional arrays. I found that birds use height as a cue when encoding flower locations, preferring to visit taller flowers. Performance in three-dimensional arrays was not however consistently better than in 2-D arrays. I also examined the possibility that hummingbirds follow a fixed flight path when returning to an array of flowers, as has been seen in the Hymenoptera. By manipulating the number of doors by which a bird could enter an arena to feed on an array of flowers, I found some evidence that birds do use systematic movements when relocating rewarding sites. Rufous hummingbirds feed on floral nectar, a resource that varies in time as well as space. To determine whether these birds use time as a cue when foraging, I provided them with an array in which flowers were refilled after intervals of either ten or twenty minute. The birds were able to learn these intervals, as they returned to flowers on or shortly after their expected refill time. I used an analogous experiment to investigate timing abilities in coal tits (Parus ater), a food-storing species, and great tits (P. major), a non food-storing species, in the laboratory. Storers and non-storer might differ in their ability to time intervals due to the demands, on storers, of reliable cache recovery. Coal tits were able to track the availability of rewards in three different locations associated with reward schedules in the 30-120s range. I found no consistent differnces in the abilities of coal tits and great tits to time intervals in the 40-70s range. In conclusion, rufous hummingbirds were shown to use both spatial and temporal cues whilst foraging at flowers. Coal tits and great tits were able to time short intervals in the laboratory, but I found no overall differences in timing behaviour between the two species.
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Thomson, Serena K. « Spatial scaling of soil microbes under different land uses ». Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/74239/.
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There has been an increasing emphasis placed on understanding microbial c, in order to enable the patterns and processes governing the spatial distribution of soil microbiota to be determined. Due to current food security issues, this is particularly important within agricultural systems given the fundamental role microorganisms play in the maintenance of crop health and productivity. With evidence in favour of both ubiquity and endemism, complicated by systems, scales and communities, there is a need to address the question of microbial biogeography within a single system. A range of field experimental resources were used to investigate factors controlling the assembly of soil microbial communities. Microorganisms across all three domains of life demonstrated spatial scaling, in which there was no single universal driver. Land-use management was an important driver of eukaryote distribution, but also impacted the drivers of bacterial and eukaryote taxa groups under land-use practice. When considering microbial community structure, a pan microbial relationship between abundance and distribution was shown for the first time, across all microbial groups. Furthermore, partitioning microbial communities into common and rare groups provided information on the processes operating on the community and highlighted the importance of land-use management for shaping the structure of communities. Finally, a case study on plasmodiophorids increased current estimates of plasmodiophorid diversity in the soil. Also different communities were associated with the rhizosphere compared with the bulk soil, under different hosts. Plant development stage was also an important consideration acting on this previously understudied but highly significant group of protists to crop health.
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Zhou, Feng. « Spatial, Temporal and Spatio-Temporal Correspondence for Computer Vision Problems ». Research Showcase @ CMU, 2014. http://repository.cmu.edu/dissertations/410.
Texte intégralRésumé :
Many computer vision problems, such as object classification, motion estimation or shape registration rely on solving the correspondence problem. Existing algorithms to solve spatial or temporal correspondence problems are usually NP-hard, difficult to approximate, lack flexible models and mechanism for feature weighting. This proposal addresses the correspondence problem in computer vision, and proposes two new spatio-temporal correspondence problems and three algorithms to solve spatial, temporal and spatio-temporal matching between video and other sources. The main contributions of the thesis are: (1) Factorial graph matching (FGM). FGM extends existing work on graph matching (GM) by finding an exact factorization of the affinity matrix. Four are the benefits that follow from this factorization: (a) There is no need to compute the costly (in space and time) pairwise affinity matrix; (b) It provides a unified framework that reveals commonalities and differences between GM methods. Moreover, the factorization provides a clean connection with other matching algorithms such as iterative closest point; (c) The factorization allows the use of a path-following optimization algorithm, that leads to improved optimization strategies and matching performance; (d) Given the factorization, it becomes straight-forward to incorporate geometric transformations (rigid and non-rigid) to the GM problem. (2) Canonical time warping (CTW). CTW is a technique to temporally align multiple multi-dimensional and multi-modal time series. CTW extends DTW by incorporating a feature weighting layer to adapt different modalities, allowing a more flexible warping as combination of monotonic functions, and has linear complexity (unlike DTW that has quadratic). We applied CTW to align human motion captured with different sensors (e.g., audio, video, accelerometers). (3) Spatio-temporal matching (STM). Given a video and a 3D motion capture model, STM finds the correspondence between subsets of video trajectories and the motion capture model. STM is efficiently and robustly solved using linear programming. We illustrate the performance of STM on the problem of human detection in video, and show how STM achieves state-of-the-art performance.
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Wang, Qian. « Characterizing InternetWorm Spatial-Temporal Infection Structures ». FIU Digital Commons, 2010. http://digitalcommons.fiu.edu/etd/294.
Texte intégralRésumé :
Since the Morris worm was released in 1988, Internet worms continue to be one of top security threats. For example, the Conficker worm infected 9 to 15 million machines in early 2009 and shut down the service of some critical government and medical networks. Moreover, it constructed a massive peer-to-peer (P2P) botnet. Botnets are zombie networks controlled by attackers setting out coordinated attacks. In recent years, botnets have become the number one threat to the Internet. The objective of this research is to characterize spatial-temporal infection structures of Internet worms, and apply the observations to study P2P-based botnets formed by worm infection. First, we infer temporal characteristics of the Internet worm infection structure, i.e., the host infection time and the worm infection sequence, and thus pinpoint patient zero or initially infected hosts. Specifically, we apply statistical estimation techniques on Darknet observations. We show analytically and empirically that our proposed estimators can significantly improve the inference accuracy. Second, we reveal two key spatial characteristics of the Internet worm infection structure, i.e., the number of children and the generation of the underlying tree topology formed by worm infection. Specifically, we apply probabilistic modeling methods and a sequential growth model. We show analytically and empirically that the number of children has asymptotically a geometric distribution with parameter 0.5, and the generation follows closely a Poisson distribution. Finally, we evaluate bot detection strategies and effects of user defenses in P2P-based botnets formed by worm infection. Specifically, we apply the observations of the number of children and demonstrate analytically and empirically that targeted detection that focuses on the nodes with the largest number of children is an efficient way to expose bots. However, we also point out that future botnets may self-stop scanning to weaken targeted detection, without greatly slowing down the speed of worm infection. We then extend the worm spatial infection structure and show empirically that user defenses, e.g., patching or cleaning, can significantly mitigate the robustness and the effectiveness of P2P-based botnets. To counterattack, we evaluate a simple measure by future botnets that enhances topology robustness through worm re-infection.
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Bai, Ping Truong Young K. Smith Richard L. « Temporal-spatial modeling for fMRI data ». Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2007. http://dc.lib.unc.edu/u?/etd,1481.
Texte intégralRésumé :
Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2007.Title from electronic title page (viewed Apr. 25, 2008). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Statistics and Operations Research." Discipline: Statistics and Operations Research; Department/School: Statistics and Operations Research.
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Bonsall, Michael B. « Temporal and spatial insect population dynamics ». Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.406839.
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Liddle, Elizabeth B. « Temporal and spatial attention in dyslexia ». Thesis, University of Nottingham, 2006. http://eprints.nottingham.ac.uk/14422/.
Texte intégralRésumé :
It was hypothesized that the deficits underlying reading impairment may arise from supra-modal deficits in temporal and spatial attention, disrupting, on the one hand, the ability to segment the temporally ordered phonemes of language and thus the acquisition of decoding skills, and, on the other, the ability to integrate spatially and temporally ordered orthographic information acquired from the fluent visual scanning of written text. Temporal and spatial attentional deficits in dyslexia were investigated using a lateralized visual temporal order judgment (TOJ) paradigm that allowed both sensitivity to temporal order and spatial attentional bias to be measured. Dyslexic and non-dyslexic participants were required to report the temporal order of two simple visual stimuli presented in either the same or different lateral hemifields. Findings indicated that dyslexic participants showed markedly impaired sensitivity to temporal order, and that the degree of impairment was correlated with the severity of their dyslexia. Furthermore, the findings suggested that at least three partially dissociated deficits may underlie both impaired TOJ task performance and reading disorder. One is a deficit associated with difficulty in reporting the temporal order of two visual stimuli, particularly when the first is presented in right hemifield; with slow word recognition and non-word reading; and with deficits in spelling and phonological skill. This constellation of deficits was interpreted as reflecting deficits in networks in left cerebral hemisphere implicated in phoneme-grapheme mapping and visual orienting. The second is a deficit that is associated with a rightward attentional bias; with inaccurate non-word reading that is worse than predicted by phonological skill or by word recognition; and with poor sustained attention. This constellation of impairments was interpreted as evidence of a deficit in right-lateralised networks implicated in the modulation of arousal, and possibly reflecting a “developmental left-neglect” syndrome. A third deficit was associated with impaired temporal order sensitivity, regardless of hemifield presentation; with symptoms of Attentional Deficit and Hyperactivity Disorder (ADHD); and with increased interference from distractor stimuli. This constellation of deficits suggests that the impaired network is implicated in executive control of attention, including conflict resolution and working memory. The results of the investigation as a whole suggests that the reading impairments of dyslexia may arise from attentional deficits that have with substantial overlap with those of ADHD, and include deficits in attentional networks implicated in orienting attention to temporally presented stimuli.
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Kan, Jing. « Spatial-temporal source reconstruction for magnetoencephalography ». Thesis, University of York, 2011. http://etheses.whiterose.ac.uk/1636/.
Texte intégralRésumé :
Magnetoencephalography (MEG) is a new non-invasive technique for the functional imaging of the human brain. It has been widely used in both research and clinical applications, for it has several superior properties, including a high-temporal resolution with no interference from the bone or the head-like fluid to the signal spatial transformation. In this thesis, we aim to develop a framework for MEG spatial-temporal current course reconstruction by introducing classical methods from the pattern recognition theory into medical imaging. These applications provide a new angle for research in MEG source reconstruction with the solution for source reconstruction at a single point, and improvements of the reconstruction on spatially and temporally. The whole thesis is based on three topics, which are designed to be parts of an integrated reconstruction process, and each of them are interrelated, rather than independent from each other. We firstly introduce the source reconstructionmethod at a single time point using the basis function extraction. In light of the assumption that the Laplacian eigenvectors of mesh can be the analogous to the basis functions that represent the cortex mesh; we build a new model to describe the current source that is distributed on each mesh vertex. This model consists of analogous basis functions and unknown weighted coefficients. In terms of experiment results, this algorithm shows good reconstructed property to the single stimulus, as well as the supercial stimulus on the cortical surface. Secondly, with respect to the spatial reconstructed sources by basis function method from the last topic, we build a new solution for improving the spatial-resolution of MEG source reconstruction at a single time point by introducing a classical method ( the Bayesian super-resolution method) from the pattern recognition theory. Although the approach is designed based on the reconstruction from basis functions, it is also feasible for other spatial reconstruction methods to improve the spatial-resolution. From the numerical experiment results, it is apparent that the spatial resolution has been effectively improved. Then, the MEG measurement system in the temporal field is assumed to be a linear dynamic system where the classical methods, Kalman filter and Kalman smoother, are applied as the solution for the estimation of source in time course. The Kalman filter is used to estimate the dynamic state while the Kalman smoother is applied for correcting the source distribution of the hidden state with the EMalgorithm. This approach shows superior performance to solve the inverse problem. It extends the improvement in source reconstruction using the temporal field. We construct the synthetic data as well as apply the realMEG data throughout all the experimental test of my work. In summary, this thesis builds three algorithms, which aim to reconstruct the MEG source distribution on spatial and temporal field respectively aided by methods from pattern recognition. This work provides a new angle of using the pattern recognition theory for MEG source reconstruction. Meanwhile, we also explore a new direction for applying the theory of pattern recognition. This work not only provides a good integration between these two fields, but also encourage future interactions.
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Kan, Kwok-chee Joshua. « Cognitive distance scaling methodologies : a comparative study / ». [Hong Kong] : University of Hong Kong, 1987. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12434401.
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簡國治 et Kwok-chee Joshua Kan. « Cognitive distance scaling methodologies : a comparative study ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1987. http://hub.hku.hk/bib/B31208629.
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Pesti, Peter. « Novel spatial query processing techniques for scaling location based services ». Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45844.
Texte intégralRésumé :
Location based services (LBS) are gaining widespread user acceptance and increased daily usage. GPS based mobile navigation systems (Garmin), location-related social network updates and "check-ins" (Facebook), location-based games (Nokia), friend queries (Foursquare) and ads (Google) are some of the popular LBSs available to mobile
users today. Despite these successes, current user services fall short of a vision where mobile users could ask for continuous location-based services with always-up-to-date information around them, such as the list of friends or favorite restaurants within 15 minutes of driving. Providing such a location based service in real time faces a number of technical challenges.
In this dissertation research, we propose a suite of novel techniques and system architectures to address some known technical challenges of continuous location queries and updates. Our solution approaches enable the creation of new, practical and scalable location based services with better energy efficiency on mobile clients and higher throughput at the location servers. Our first contribution is the development of RoadTrack, a road network aware and query-aware location update framework and a suite of algorithms. A unique characteristic of RoadTrack is the innovative design of encounter points and system-defined precincts to manage the desired spatial resolution of location updates for different mobile clients while reducing the complexity and energy consumption of location update strategies. The second novelty of this dissertation research is the technical development of Dandelion data structures and algorithms that can deliver superior performance for the periodic re-evaluation of
continuous road-network distance based location queries, when compared with the alternative of repeatedly performing a network expansion along a mobile user's trajectory. The third contribution of this dissertation research is the FastExpand algorithm that can speed up the computation of single-issue shortest-distance road network queries. Finally, we have developed the open source GT MobiSim mobility simulator, a discrete event simulation platform to generate realistic driving trajectories for real road maps. It has been downloaded and utilized by many to evaluate the efficiency and effectiveness of the location query and location update algorithms, including the research efforts in this dissertation.
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Tsang, Trevor. « Spatial scaling issues in the production of land-cover maps ». Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286742.
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Naylor, Susan J. « Spatial context effects on temporal and spatial factors in map memory / ». Thesis, Connect to Dissertations & ; Theses @ Tufts University, 1999.
Trouver le texte intégralRésumé :
Thesis (Ph.D.)--Tufts University, 1999.Adviser: Holly A. Taylor. Submitted to the Dept. of Psychology. Includes bibliographical references (leaves 59-61). Access restricted to members of the Tufts University community. Also available via the World Wide Web;
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Farr, Daniel. « Resolving the Temporal-Spatial Ambiguity With the Auroral Spatial Structures Probe ». DigitalCommons@USU, 2014. https://digitalcommons.usu.edu/etd/3728.
Texte intégralRésumé :
The behavior of the electric and magnetic fields in the upper atmosphere of the Earth is scientifically interesting but difficult to study, since balloons and aircraft are unable to fly high enough to measure it directly. Sounding rockets, which make a one-time flight carrying instruments that measure the environment around them, have been successfully used to study the upper atmosphere. As the rocket flies through the upper atmosphere, it radios down data about the environment. When scientists on the ground use this data to construct a picture of the upper atmosphere, they run into a problem: the fields reported by the rocket change over time, but it is not clear whether this is because these fields are actually changing in time, or just because the rocket has moved to a different place where the fields are different. This inability to determine whether changes are happening in time or space is called the temporal-spatial ambiguity.
This thesis describes the Auroral Spatial Structures Probe (ASSP), a sounding rocket mission that attempts to resolve the temporal-spatial ambiguity by using multiple payloads flying in formation. Several payloads will pass through and measure the same point in space one after another, which will enable us to see how the fields are changing over time.
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Greenlee, Jordan. « Temporal and spatial modeling of analog memristors ». Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41215.
Texte intégralRésumé :
As silicon meets its performance limits, new materials and methods for advancing computing and electronics as a whole are being intensely researched, as described in Chapter 1. Memristors are a fusion of these two research areas, with new materials being pursued concurrently to development of novel architectures to take advantage of these new devices. A background of memristors and an overview of different memristive developments in the field are reviewed in Chapter 2.
Chapter 3 delves into the physical mechanisms of analog memristors. To investigate and understand the operation of analog memristors, a finite element method model has been developed.
More specifically, the devices simulated include a simple memristor simulation where the lithium ions (dopants) are confined to the device, but allowed to move in response to a voltage applied across the device. To model a more physical memristor, charge carrier mobility dependence on dopant levels was added to the device, resulting in a simulated device that operates similarly to the first simulation. Thereafter, the effect of varying geometries was modeled, and it was determined that both the speed and the resistance change of the device were improved by increasing the ratio of the top and bottom metal contact lengths in a restrictive flow geometry. Finally, the effect of dopant removal was investigated. It was determined that if the greatest change in resistance is required, then the removal of dopants is the optimal operating regime for an analog memristor.
Through a greater understanding of analog memristors developed by the simulation described herein, researchers will be able to better harness their power and implement them in bio-inspired systems and architectures.
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Fairbairn, Jonathan Paul. « Spatial and temporal dynamics of entomopathogenic nematodes ». Thesis, University of Stirling, 2001. http://hdl.handle.net/1893/26685.
Texte intégralRésumé :
The life-history and infection parameters of the entomopathogenic nematodes Steinernema feltiae (Filipjev)(Nematoda:Rhabditida) and Heterorhahditis megidis (Poinar, Jackson & Klein)(Nematoda:Rhabditida) were examined to provide specific details for the construction of mathematical SI models for biological control of soil insect pests. Laboratory experiments using the Greater Waxmoth, Galleria mellonella as the model host were undertaken to specifically examine the transmission behaviour of infective juvenile nematodes. The proportion of infective juveniles of S. feltiae which infected hosts was dependent on time. Previous studies declared that the proportion of infective juveniles which can infect is static, however, over a period of 5 days most of the infective juveniles infected hosts, demonstrating that the proportion infecting is dynamic. Infection of hosts by both species of nematode was compared using two mathematical representations of the transmission rate. Whereas the most parsimonious form of transmission for H. megidis was the linear Mass Action function, it was evident that, when measured at the individual nematode scale, S. feltiae transmission was non-linear. I postulated that this functional difference is due to the biology of the two species of nematodes. The subsequent effect of including the non-linear response on model predictions were investigated and it was demonstrated that the dynamics of the host nematode interaction became less stable. Spatial models of S. feltiae infection were parameterised from laboratory experiments, and control prediction of these models examined. The horizontal rate of dispersal through sand columns was determined in the presence and absence of hosts. Infective juveniles were found to disperse preferentially towards hosts. The predicted dynamics of pest control using the spatial moqel were highly dependent on the degree of nematode dispersal, host dispersal and the attraction of nematode infective juveniles towards hosts. The overall findings of this thesis have been placed in the context of epidemiological models created elsewhere, and predict that entomopathogenic nematodes may be targeted to specific pest systems with a high degree of success. An understanding of the infection biology of these nematode species is crucial in determining how and when pests may be controlled, and equally importantly, which systems successful control is not predicted.
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Xia, Jianhong, et not supplied. « Modelling the spatial-temporal movement of tourists ». RMIT University. Mathematical and Geospatial Sciences, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080110.161021.
Texte intégralRésumé :
Tourism is one of the most rapidly developing industries in the world. The study of spatio-temporal movement models of tourists are undertaken in variety of disciplines such as tourism, geography, mathematics, economics and artificial intelligence. Knowledge from these different fields has been difficult to integrate because tourist movement research has been conducted at different spatial and temporal scales. This thesis establishes a methodology for modelling the spatial-temporal movement of tourists and defines the spatial-temporal movement of tourists at both the macro and micro level. At the macro level, the sequence of tourist movements is modelled and the trend for tourist movements is predicted based on Markov Chain theory (MC). Log-linear models are then adopted to test the significance of the movement patterns of tourists. Tourism market segmentation based on the significant movement patterns of tourists is implemented using the EM (Expectation-Maximisation) algorithm. At the micro level, this thesis investigates the wayfinding decision-making processes of tourists. Four wayfinding models are developed and the relationships between the roles of landmarks and wayfinding decision-making are also discussed for each type of the wayfinding processes. The transition of a tourist movement between the macro and micro levels was examined based on the spatio-temporal zooming theory. A case study of Phillip Island, Victoria, Australia is undertaken to implement and evaluate the tourist movement models established in this thesis. Two surveys were conducted on Phillip Island to collect the macro and micro level movement data of tourists. As results show particular groups of tourists travelling with the same movement patterns have unique characteristics such as age and travel behaviours such as mode of transport. Effective tour packages can be designed based on significant movement patterns and the corresponding target markets. Tourists with various age groups, residency, gender and different levels of familiarity with physical environment have different wayfinding behaviours. The results of this study have been applied to tourism management on Phillip Island and the novel methods developed in this thesis have proved to be useful in improving park facilities and services provided to tourists, in designing tour packages for tourism market promotion and in understanding tourist wayfinding behaviours.
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Osnas, Erik E. « Temporal and spatial structure of waterfowl communities ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ30815.pdf.
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Geberl, Cornelia. « Spatial and temporal resolution of bat sonar ». Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-160582.
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Chorley, N. « Spatial and temporal analysis of sunspot oscillations ». Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/47200/.
Texte intégralRésumé :
Sunspots are the most conspicuous feature seen on the solar photosphere and are manifestations of the solar magnetic field. Their study, then, may provide us with a greater understanding of the dynamo mechanism thought to be responsible for the generation of this field. In this thesis, the oscillations of sunspots are studied by making use of observational data from two instruments: the Nobeyama Radioheliograph (NoRH) and the Solar Optical Telescope (SOT) on board the Hinode spacecraft. First, a study of long period oscillations was undertaken in which two long period peaks (P > 10 min) were identified in the power spectra of time series generated from sets of images of 3 sunspots observed with NoRH. In addition, by using the techniques of period, power, correlation and lag mapping, it was found that the power in each of these peaks was concentrated over the umbral regions and that there were two regions of approximately equal size oscillating in anti-phase with each other. It was suggested that these properties could be signatures of a "shallow" sunspot. A follow-up study was then performed, in which the lifetimes of the long period oscillations were investigated over a period of 9 days. These oscillations were seen to dominate the spectra during this interval and the periods and amplitudes were stable during that time. A simple model of a damped, driven simple harmonic oscillator (in which the driving term was nonlinear) was proposed to explain the generation and support of the oscillations. Finally, a study of the spatial properties of the 3 minute oscillations was performed by applying the mapping techniques mentioned above to Hinode/SOT data. The distributions of power and lag of maximum correlation coefficient were found to be non-uniform over the sunspots under study and this may be indicative of inhomogeneities of the physical quantities in the structures.
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Richardson, Thomas Owen. « Spatial and temporal organisation within ant societies ». Thesis, University of the West of England, Bristol, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557142.
Texte intégralRésumé :
In this thesis the organisation of colonies of the ant, Temnothorax albipennis, is investigated with a special focus on their spatial and temporal statistics. Individual-based modelling combined with analyses of experimental data are used extensively to infer the mechanisms that govern individual and collective behaviour. The unequal allocation of labour amongst different individuals, as manifested in skewed distributions of activity, is ubiquitous within the social insects. Early non-spatial individual-based models demonstrated that such skewed divisions of labour can self- organise through the interaction of fluctuating levels of stimuli associated with a task, with differentially sensitive agents that perform work upon the stimulus. Here, that modelling framework is extended by explicitly including space. This modification induces a 'percolation' effect, in which small differences amongst agents in their response thresholds, are related to large differences in their probabilities of performing work. The extension of the original fixed-threshold models of Division of Labour to include space means that they can be treated as a special case of diffusion in disordered media - a well studied branch of statistical mechanics. Staying at home to care for young or leaving to find food is one of the most fundamental divisions of labour. Here the rate of departures from ant nests and the collective activity of the individuals within the nest, are experimentally quantified. Both the rate of nest-leaving, and the inside-nest activity showed a non-linear decline over time. This and other results indicates that fluctuating record signals and repulsive ant-ant interactions play a significant role in colony organisation. A record signal is a new 'high water mark' in the history of a system. The dynamics of several complex but purely physical systems are also based on record signals but this is the first time they have been experimentally shown in a biological system. Finally, the generation of spatial pattern formation is experimentally investigated In the context of resilience to perturbations. The brood within the ant colony is often sorted into an intricate annular pattern, according to the developmental stage of the various rood types. Even after the pattern is completely destroyed, the workers are able to re-establish the pattern. The dynamics of this process of re-emergence is quantified in detail. Lastly, the possible utility of the pattern as a spatial cue to the workers is discussed.
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White, Andrew. « Temporal and spatial dynamics of ecological systems ». Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338459.
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Alqarni, M. S. « Spatial temporal distribution of helical gyrotactic swimmers ». Thesis, University of Liverpool, 2018. http://livrepository.liverpool.ac.uk/3024800/.
Texte intégralRésumé :
We consider a spherical swimmer that undergoes helical motion due to the existence of a propulsive torque which is not parallel to a propulsive force that pulls the cell through the fluid. In addition, the cell is bottom-heavy; the centre of gravity is offset from the centre of buoyancy which generates a gravitational torque. In the presence of shear, fluid viscosity generates a further torque. Because cells swim at low Reynolds number, these torques are balanced. This thesis extends the model developed in Bearon (2013) in two distinct directions. Firstly, we consider an extension to the case of a flow where the shear varies with position. We consider a downward flow in a vertical channel. We observe that depending on the parameters, cells may exhibit the classical accumulation towards the centre of the channel or display a new focussing away from the centre. Secondly, we develop the model to describe randomness associated with changes in cell orientation. This is done by developing a Fokker-Planck equation for helical swimmers in terms of Euler angles. The classical Fokker-Planck equation obtained by Pedley and Kessler (1992) is a special case of the equation derived in this thesis. To implement this model numerically as an individual based model, we derive the corresponding stochastic differential equations. The Fokker-Planck equation and stochastic differential equation are extended to examine the spatial-temporal distribution of helical swimmers. We explore in detail how the horizontal distribution of cells in channel flow evolves to an equilibrium state, and how the evolution depends on the model parameters. For non-helical swimmers, we compare the result of the model to the recent experiments of Croze et al (2017).
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Walford, Hannah Louise. « Spatial and temporal variation of African epeirogeny ». Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620082.
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Crema, E. R. « Spatial and temporal models of Jomon settlement ». Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1382589/.
Texte intégralRésumé :
The Jomon culture is a tradition of complex hunter-gatherers which rose in the Japanese archipelago at the end of the Pleistocene (ca. 13,000 cal BP) and lasted until the 3rd millennium cal BP. Recent studies increasingly suggest how this long cultural persistence was characterised by repeated episodes of change in settlement pattern, primarily manifested as cyclical transitions between nucleated and dispersed distributions. Although it has been suggested that these events correlate with population dynamics, shifts in subsistence strategies, and environmental change, to date there have been very few attempts to provide a quantitative analysis of spatio-temporal change in Jomon settlement and its possible causes. This thesis is an attempt to fill that lacuna by adopting a twin-track approach to the problem. First, two case studies from central Japan have been examined using a novel set of methods, which have been specifically designed to handle the intrinsic chronological uncertainty which characterises most prehistoric data. This facilitated the application of a probabilistic framework for quantitatively assessing the available information, making it possible to identify alternating phases of nucleated and dispersed pattern during a chronological interval between 7000 and 3300 cal BP. Second, computer simulation (by means of an agent-based model) has been used to carry out a formal inquiry into the possible underlying processes that might have triggered the observed changes in the settlement pattern. The aim of this simulation exercise was two-fold. First, it has been used as a theory-building tool, combining several models from behavioural ecology and cultural transmission theory in order to provide explicit expectations in relation to the presence and absence of environmental disturbances. Second, the outcome of the simulation has been used as a template for linking the observed patterns to possible underlying socio-ecological processes suggested by the agent-based model. This endeavour has shown how some of the largest changes in the empirically observed settlement patterns can be simulated as emerging from the internal dynamics of the system rather than necessarily being induced by external changes in the environment.
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Jiang, Bihan. « Spatial and temporal analysis of facial actions ». Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/25002.
Texte intégralRésumé :
Facial expression recognition has been an active topic in computer vision since 90s due to its wide applications in human-computer interaction, entertainment, security, and health care. Previous works on automatic analysis of facial expressions have focused mostly on detecting prototypic expressions of basic emotions like happiness and anger. In contrast, the Facial Action Coding System (FACS) is one of the most comprehensive and objective ways to describe facial expressions. It associates facial expressions with the actions of the muscles that produce them by defining a set of atomic movements called Action Units (AUs). The system allows any facial expressions to be uniquely described by a combination of AUs. Over the past decades, extensive research has been conducted by psychologists and neuroscientists on various applications of facial expression analysis using FACS. Automating FACS coding would make this research faster and more widely applicable, opening up new avenues to understanding how we communicate through facial expressions. Morphology and dynamics are the two aspects of facial actions, that are crucial for the interpretation of human facial behaviour. The focus of this thesis is how to represent and learn the rich facial texture changes in both the spatial and temporal domain. The effectiveness of spatial and spatio-temporal facial representations and their roles in detecting the activation and temporal dynamics of facial actions are explored. In the spatial domain, a novel feature extraction strategy is proposed based on a heuristically defined regions from which a separate classifier is trained and fused in the decision-level. In the temporal domain, a novel dynamic appearance descriptor is presented by extending the static appearance descriptor Local Phase Quantisation (LPQ) to the temporal domain by using the Three Orthogonal Planes (TOP). The resulting dynamic appearance descriptor LPQ-TOP is applied to detect the latent temporal information representing facial appearance changes and explicitly model facial dynamics of AUs in terms of their temporal segments. Finally, a parametric temporal alignment method is proposed. Such strategy can accommodate very flexible time warp functions and is able to deal with both sequence-to-sequence and sub-sequence alignment. This method also opens up a new approach to the problem of AU temporal segment detection. This thesis contributes to facial action recognition by modelling the spatial and temporal texture changes for AU activation detection and AU temporal segmentation. We advance the performance of state-of-the-art facial action recognition systems and this has been demonstrated on a number of commonly used databases.
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Monteiro, Fernando C. « Region-based spatial and temporal image segmentation ». Doctoral thesis, Universidade do Porto, Faculdade de Engenharia, 2008. http://hdl.handle.net/10198/1835.
Texte intégralRésumé :
This work discusses region-based representations for image and video sequence segmentation. It presents effective image segmentation techniques and demonstrates how these techniques may be integrated into algorithms that solve some of the motion segmentation problems. The region-based representation offers a way to perform a first level of abstraction and to reduce the number of elements to process with respect to the classical pixel-based representation.
Motion segmentation is a fundamental technique for the analysis and the understanding of image sequences of real scenes. Motion segmentation 'describes' the sequence as sets of pixels moving coherently across one sequence with associated motions. This description is essential to the identification of the objects in the scene and to a more efficient manipulation of video sequences.
This thesis presents a hybrid framework based on the combination of spatial and motion information for the segmentation of moving objects in image sequences accordingly with their motion. We formulate the problem as graph labelling over a region moving graph where nodes correspond coherently to moving atomic regions. This is a flexible high-level representation which individualizes moving independent objects. Starting from an over-segmentation of the image, the objects are formed by merging neighbouring regions together based on their mutual spatial and temporal similarity, taking spatial and motion information into account with the emphasis being on the second. Final segmentation is obtained by a spectral-based graph cuts approach.
The initial phase for the moving object segmentation aims to reduce image noise without destroying the topological structure of the objects by anisotropic bilateral filtering. An initial spatial partition into a set of homogeneous regions is obtained by the watershed transform. Motion vector of each region is estimated by a variational approach. Next a region moving graph is constructed by a combination of normalized similarity between regions where mean intensity of the regions, gradient magnitude between regions, and motion information of the regions are considered. The motion similarity measure among regions is based on human perceptual characteristics. Finally, a spectral-based graph cut approach clusters and labels each moving region.
The motion segmentation approach is based on a static image segmentation method proposed by the author of this dissertation. The main idea is to use atomic regions to guide a segmentation using the intensity and the gradient information through a similarity graph-based approach. This method produces simpler segmentations, less over-segmented and compares favourably with the state-of-the-art methods. To evaluate the segmentation results a new evaluation metric is proposed, which takes into attention the way humans perceive visual information.
By incorporating spatial and motion information simultaneously in a region-based framework, we can visually obtain meaningful segmentation results. Experimental results of the proposed technique performance are given for different image sequences with or without camera motion and for still images. In the last case a comparison with the state-of-the-art approaches is made.
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Smith, Elizabeth M. « Spatial and temporal regulation of IL4Rα expression ». Doctoral thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/3117.
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Includes abstract.In this study, we generated a new mouse model, which allows both inducible and cell-specific deletion and reconstitution of IL-IL4Rα expression. This model has the potential to add a new dimension to our understanding of IL4Rα biology. This has been achieved by using the established Tet System (Goosen and Bujard, 1992) where the crossing of two complementary transgenic mouse lines enable the generation of the final double transgenic model. The first line expresses the transactivator, tTA, from the Tet-Off expression cassette driven by the Vav hemapoeitic specific promoter (Wiesner et al., 2005).
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Bergström, Ulf. « Spatial heterogeneity and biotic interactions : scaling from experiments to natural systems ». Doctoral thesis, Umeå University, Ecology and Environmental Science, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-249.
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Much of current ecological theory stems from experimental studies. These studies have often been conducted in closed systems, at spatial scales that are much smaller than the systems of interest. It is known that the outcome of these experiments may be seriously affected by artefacts associated with the caging procedures, as well as by the actual difference in spatial scale between experimental and target system. Yet, quantitative methods for estimating and removing artefacts of enclosure and for extrapolating experimental results to the scales of natural systems are largely lacking.
The aim of this thesis was to confront some of the problems encountered when scaling from experiments to nature in studies on predator-prey systems, with focus on effects of changes in spatial heterogeneity. Specifically, I examined mechanisms that may cause consumption rate estimates to depend on the size of the experimental arena. I also studied methods for scaling up these process rate estimates to natural predator-prey systems. The studies were performed on invertebrate predator-prey systems found in the northern Baltic Sea. Initially, a descriptive study of small-scale distribution patterns was performed, in order to get background information on how the behaviour of the organisms was manifested in the spatial structure of the community. Experimental studies of two predator-prey systems exposed an artefact that may be widespread in experiments aiming at quantifying biotic interactions. It is caused by predator and prey aggregating along the walls of the experimental containers. This behaviour affects the encounter rate between predator and prey, thereby causing consumption rates to be scale-dependent. Opposing the common belief that larger arenas always produce less biased results, this scale effect may instead be reduced by decreasing arena size. An alternative method for estimating the magnitude of, and subsequently removing, the artefact caused by aggregation along the arena wall was presented.
Once unbiased estimates of process functions have been derived, the next step is to scale up the functions to natural systems. This extrapolation entails a considerable increase in spatial heterogeneity, which may have important implications for the dynamics of the system. Moment approximation provides a method of taking the heterogeneity of natural populations into account in the extrapolation process. In the last study of the thesis, the concepts of moment approximation and how to estimate relevant heterogeneity were explained, and it was shown how the method may be used for adding space as a component to a dynamic predator-prey model. It was concluded that moment approximation provides a simple and useful technique for dealing with effects of spatial variation, and that a major benefit of the method is that it provides a way of visualising how heterogeneity affects ecological processes.
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Bergström, Ulf. « Spatial heterogeneity and biotic interactions - scaling from experiments to natural systems / ». Umeå : Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-249.
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Loach, Daniel. « Inhibitory processes in temporal selection ». Thesis, Bangor University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275136.
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Groleau, Daniel. « Study of the scaling and temporal properties of a simplified earthquake model ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq25062.pdf.
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Ralley, Richard. « Spatial constraints on attention ». Thesis, University of Hertfordshire, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302301.
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Bränd, Stefan. « Using Rigid Landmarks to Infer Inter-Temporal Spatial Relations in Spatio-Temporal Reasoning ». Thesis, Linköpings universitet, Artificiell intelligens och integrerad datorsystem, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-124064.
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Spatio-temporal reasoning is the area of automated reasoning about space and time and is important in the field of robotics. It is desirable for an autonomous robot to have the ability to reason about both time and space. ST0 is a logic that allows for such reasoning by, among other things, defining a formalism used to describe the relationship between spatial regions and a calculus that allows for deducing further information regarding such spatial relations. An extension of ST0 is ST1 that can be used to describe the relationship between spatial entities across time-points (inter-temporal relations) while ST0 is constrained to doing so within a single time-point. This allows for a better ability of expressing how spatial entities change over time. A major obstacle in using ST1 in practise however, is the fact that any observations made regarding spatial relations between regions is constrained to the time-point in which the observation was made, so we are unable to observe inter-temporal relations. Further complicating things is the fact that deducing such inter-temporal relations is not possible without a frame of reference. This thesis examines one method of overcoming these problems by considering the concept of rigid regions which are assumed to always be unchanging and using them as the frame of reference, or as landmarks. The effectiveness of this method is studied by conducting experiments where a comparison is made between various landmark ratios with respect to the total number of regions under consideration. Results show that when a high degree of intra-temporal relations are fully or partially known, increasing the number of landmark regions will reduce the percentage of inter-temporal relations to be completely unknown. Despite this, very few inter-temporal relations can be fully determined even with a high ratio of landmark regions.
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Heuermann, Heike. « Spatial and temporal factors in visual auditory interaction ». [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=967796601.
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