Dissertations / Theses: 'Spatial spreads'

1

Lindström, Tom. "Spatial Spread of Organisms : Modeling ecological and epidemiological processes." Doctoral thesis, Linköpings universitet, Teoretisk Biologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-54839.

Full text

Abstract:

This thesis focuses on the spread of organisms in both ecological and epidemiological contexts. In most of the studies presented, displacement is modeled with a spatial kernel function, which is characterized by scale and shape. These are measured by the net squared displacement (or kernel variance) and kurtosis, respectively. If organisms disperse by the assumptions of a random walk or correlated random walk, a Gaussian shaped kernel is expected. Empirical studies often report deviations from this, and commonly leptokurtic distributions are found, often as a result of heterogeneity in the dispersal process. In the studies presented in two of the included papers, the importance of the kernel shape is tested, by using a family of kernels where the shape and scale can be separated effectively. Both studies utilize spectral density approaches for modeling the spatial environment. It is concluded that the shape is not important when studying the population distribution in a habitat/matrix context. The shape is however important when looking at the invasion of organisms in a patchy environment, when the arrangement of patches deviates from randomly distributed. The introduced method for generating patch distribution is also compared to empirical distributions of patches (farms and old trees). Here it is concluded that the assumptions used for modeling of the spatial environment are consistent with the observed patterns. These assumptions include fractal properties such that the same aggregational patterns are found at different scales. In a series of papers, movements of animals are considered as vectors for between-herd disease spread. The studies are based on data found in databases held by the Swedish Board of Agricultural (SJV), consisting of reported movements, as well as farm location and characteristics. The first study focuses on the distance related probability of contacts between herds. In the following papers, the analysis is expanded to include production type and herd size. Movement data of pigs (and cattle in Paper I) are analyzed with Bayesian models, implemented with Markov Chain Monte Carlo (MCMC). This is a flexible approach that allows for parameter estimations of complex models, and at the same time includes parameter uncertainty. In Paper IV, the effects of the included factors are investigated. It is shown that all three factors (herd size, production type structure and distance related probability of contacts) are expected to influence disease spread dynamics, however the production type structure is found to be the most important factor. This emphasizes the value of keeping such information in central databases. The models presented can be used as support for risk analysis and disease tracing. However, data reliability is always a problem, and implementation may be improved with better quality data. The thesis also shows that utilizing spatial kernels for description of the spatial spread of organisms is an appropriate approach. However, these kernels must be flexible and flawed assumptions about the shape may lead to erroneous conclusions. Hence, the joint distribution of kernel shape and scale should be estimated. The flexibility of Bayesian analysis, implemented with MCMC techniques, is a good approach for this, and further allows for implementation of more complex models where other factors may be included.

APA, Harvard, Vancouver, ISO, and other styles

2

Vernon, Matthew Christopher. "Spatial spread of farm animal diseases." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/240490.

Full text

Abstract:

Data on cattle movements within the United Kingdom have recently become available. As part of the conditions for lifting an export ban on British beef following the bovine spongiform encephalopathy epidemic, the European Union required that the UK should have 'An effective animal identification and movement recording system'. The Cattle Tracing System (CTS) was introduced in September 1998, and the scheme was extended to include all cattle by the beginning of 2001. Contact networks have proved valuable in studying the epidemiology of diseases in man, such as human immunodeficiency virus; the availability of CTS cattle movement data has enabled contact network analysis to be applied to diseases of farm livestock. The CTS data may be represented as a large network; cattle holdings are represented as nodes, with a movement of cattle between holdings being an edge. To address concerns about the quality of this cattle movement data, a field study was conducted on Lewis, one of the Western Isles of Scotland. Farmers were recruited with the assistance of the local veterinary surgeon, and asked to record a range of potential risk behaviours relating to the transmission of infectious diseases (moving livestock, sharing pasture, etc.) for a one-month period. For the study area in question, movements of cattle not reported to CTS (especially to or from common grazing land) were a substantial contribution to the contact network during the study period. A wide range of measures of network structure exist, but their relevance to the dynamics of infectious diseases on networks is unclear. To address this, a discrete-time stochastic SIR simulation model of disease on a network was designed and implemented in software. Using this simulation model, a network model with the key structural features of the CTS contact network was constructed, by considering a range of measures of network structure, and testing resulting model networks against CTS-derived networks. The resulting model was shown to predict the dynamics of a simulated disease model on that contact network more closely than existing models of global network structure. Much work on the contact structure of the UK cattle herd has relied on relatively simple static network representations of movement data. By using simulated diseases, the serious shortcomings of static network representations compared to more complex dynamic network representations were demonstrated. A substantial library of software for the generation and analysis of large networks, and the simulation of disease thereupon, has been produced, and has been made generallyavailable. The design and implementation of this software is discussed, including the algorithms and data structures deployed, as well as validation of the software, and its portability to different computing platforms.

APA, Harvard, Vancouver, ISO, and other styles

3

Janarthanan, Sivarjalingam. "Spatial spread in general branching processes." Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265577.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Bastani, Hamed [Verfasser]. "Spatial Positioning with Wireless Chirp Spread Spectrum Ranging / Hamed Bastani." Bremen : IRC-Library, Information Resource Center der Jacobs University Bremen, 2010. http://d-nb.info/1034989510/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

5

Ball, George LeRoy. "A spatial dynamic approach to ecological modeling: Simulating fire spread." Diss., The University of Arizona, 1990. http://hdl.handle.net/10150/184986.

Full text

Abstract:

The objective of this dissertation is to develop a new research tool, PROMAP, which will allow the construction of models that satisfy the requirement of spatial distribution and hierarchical interactions within a dynamic framework. An analysis of the form of ecosystems is followed by an examination of current attempts at ecosystem modeling using spatial relationships. An examination of the analytical procedures used in the spatial modeling process, results in a set of criteria that a suitable modeling system should incorporate. These criteria are: the use of real numbers; iterative processing; flexible data retrieval; and neighborhood analytical procedures. The basic configuration of PROMAP is discussed with an emphasis on the mathematical procedures and the capability for designing cellular automata within the system. The representation of biophysical systems into a set of spatial transition functions is described in relation to the development of nested hierarchies called Q-morphisms. Having established the design of PROMAP, a suitable test is devised using the simulation of surface fire spread. A model called FIREMAP is developed and the results are compared to expected fire shapes under Zero State Conditions. These conditions are defined as uniform fuel, zero slope and zero wind with additional factors held constant. Other simulations of fire spread are made by relaxing the conditions to achieve wind driven fires and the response to potential impediments to fire spread. The response of the simulation shows an accurate correspondence between the simulation and the expected fire shape. As a final test of the model, all restrictions are removed and a simulation is made under actual conditions of complex terrain, and non-uniform fuels using data collected on the San Carlos Apache Indian Reservation in southeast Arizona. Deficiencies of PROMAP and FIREMAP are discussed as well as future implications for the FIREMAP model as a management tool.

APA, Harvard, Vancouver, ISO, and other styles

6

Yassi, Hocine. "Finite element model for the two dimensional spatial spread of rabies." Thesis, Bangor University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318087.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Hollingsworth, Teresa Déirdre. "A theoretical framework for the spatial spread of soil-borne fungal plant pathogens." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604173.

Full text

Abstract:

The spread of mycelia through soil is the main process by which many economically important plant pathogens are transmitted between plants. Using mathematical modelling, this thesis provides a framework for investigating the interaction between soil structure and fungal growth, with a view to controlling this spread. Fungal dynamics are modelled at the scale of groups of hyphae by a stochastic cellular automaton (CA), with the cells of the CA corresponding to the network of pore species in the soil. The fungal model captures the characteristics of mycelial growth at this scale, whilst maintaining a level of mathematical tractability. The growth of mycelial fungi within and between patches is modelled by the rates of growth and quiescence, or transition to inactivity, together with structural parameters. The fungal model is analysed to identify key characteristics of the pore network which affect the morphology of the fungal colony. The soil-pore network is modelled as part of the entire soil structure. The pore space is abstracted to a network of connected patches of different sizes. The size and connections between these patches are converted into carrying capacities for hyphal colonisation and the level of connection between cells for subsequent implementation of the fungal model. The models are used to give insight on experimental data for soils of different bulk densities. The application of the soil and fungal models to this data allows the three-dimensional structure of the soils to be studied, and changes in the three-dimensional connectivity which contribute to changing hyphal density are identified. The results show that at low bulk densities there are few large, pore spaces with connections to distant pore spaces. This structure results in large sparse colonies. At high bulk densities, the pore space is made up of many smaller pore spaces which are connected to a few close pores. This structure results in small, dense colonies.

APA, Harvard, Vancouver, ISO, and other styles

8

Smith, James Martin Derek. "Modelling the spatial spread of Japanese knotweed (Fallopia japonica) in the United Kingdom." Thesis, Loughborough University, 2006. https://dspace.lboro.ac.uk/2134/33778.

Full text

Abstract:

Fallopia japonica (Houtt. Ronse Decraene) (syn. Reynoutria japonica syn. Polygonum cuspidatum, Japanese knotweed) is an aggressively invasive alien weed in the United Kingdom (UK) and throughout its introduced range. Its presence can herald considerable costs, both in terms of its ecological impact as a threat to biodiversity and economically due to the physical damage caused to property and the associated costs of treatment and disposal of the plant. There is therefore increasing interest in eradicating this alien species and as a result many different management techniques have been applied to try and control its spread. It is important to ascertain which of these are most appropriate in any given situation and so tools that can test the impact and efficiency of these techniques both quickly and cheaply would be extremely useful. In this thesis mathematical models are developed for the spatial spread of F. japonica on a local scale in the UK.

APA, Harvard, Vancouver, ISO, and other styles

9

Churakov, Mikhail. "Spatial and network aspects of the spread of infectious diseases in livestock populations." Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/6417/.

Full text

Abstract:

In this thesis, I focus on methodological concepts of studying infectious disease transmission between agricultural premises. I used different disease systems as exemplars for spatial and network methods to investigate transmission patterns. Infectious diseases cause tangible economic threat to the farming industry worldwide by damaging livestock populations, reducing farm productivity and causing trade restriction. This implies the importance of veterinary epidemiological studies in control and eradication of pathogens. Recent increase in availability of data and computational power allowed for more opportunities to study mechanisms of pathogenic transmission. Nowadays, the bottleneck is primarily associated with efficient methods that can analyse vast amounts of high-resolution data. Here I address two livestock pathogens that differ in their epidemiology: bacteria Streptococcus agalactiae and foot-and-mouth disease (FMD) virus. Streptococcus agalactiae is a contagious pathogen that causes mastitis in cattle, and thus possesses a substantial economic burden to the dairy industry. Known transmission routes between cattle are restricted to those via milking machines, milkers’ hands and fomites during milking process. Additionally, recent studies suggested potential introductions from other host species: primarily, humans. However, strain typing data showed discrepancies in strain compositions of bacteria isolated from humans and bovines. In this thesis, strain-specific features of between-herd transmission of Streptococcus agalactiae within dairy cattle population in Denmark are investigated. Foot-and-mouth disease (FMD) is a viral infection that affects cloven-hoofed animals and is of big importance mainly because of the trade restrictions against infected regions and countries. Control programmes against FMD usually include vaccination and culling of animals. However, the debate on the optimal control for FMD is still ongoing. In this thesis, I address questions on identification of the routes of infection and on requirements for movement recording systems to be used for efficient contact tracing during an FMD outbreak. This thesis reveals several interesting findings. Firstly, the increased understanding of strain-specific transmission characteristics of Streptococcus agalactiae. One of the observed strains (ST103) showed significant and consistent spatial clustering of its cases among Danish dairy cattle herds in 2009–2011. Secondly, the network analysis of cattle movements and affiliations with veterinary practices showed that veterinary practices were exclusively associated with transmission of ST103 of Streptococcus agalactiae. Contrastingly, movement networks appeared to be important for all the three predominant bacterial strains (ST1, ST23 and ST103). Fourthly, the new extended approach that allows estimation of the whole transmission tree at once was proposed and tested for the Darlington cluster within the 2001 FMD UK epidemic. Finally, in chapter 6, it was shown that mathematical modelling did not suggest any advantages of ensuring smaller delays in the post-silent control of FMD-like pathogens.

APA, Harvard, Vancouver, ISO, and other styles

10

Skog, Lars. "Spatial Analysis and Modeling for Health Applications." Doctoral thesis, KTH, Geodesi och geoinformatik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-142835.

Full text

Abstract:

Despite the benefits of applying methods of geographic information science (GIScience), the use of such methods in health service planning and provision remains greatly underutilized. Spread of epidemic diseases is a constant threat to mankind and the globalization of the world increases the risk for global attacks from multi-resistant bacteria or deadly virus strains. Therefore, research is needed to better understand how GIScience could be used in epidemiologic analyses and other health applications. This thesis is divided into two parts; one for epidemiologic analyses and one for neighbourhood studies. The overall objective of the epidemiologic part of this research is to understand more about the spatial spread of past pandemics and to find out if there are any common patterns. This overall objective is divided into four specific research objectives; 1) to describe the spatial spread of the Russian Influenza in Sweden, 2) to create models of propagation of the Black Death in Sweden, 3) to establish spatiotemporal characteristics common to past pandemics in Sweden and 4) to visualize the spatiotemporal occurrence of salmonella among animal herds in Sweden. This thesis also discusses some other aspects of health related to place. Are differences in neighbourhood deprivation related to the amount of presence of goods and services? Is the way cities are planned affecting the behaviour within the local population regarding spontaneous walking and physical activity? The specific research objectives for this part are to define how deprivation is related to presence of goods and services in Sweden and to create walkability indices over the city of Stockholm including a quality test of these indices. Case data reported by physicians were used for the epidemiologic studies. The pandemics discussed covered the entire world, but our data is from Sweden only and as regards the Black Death there was no case data at all. The data for the goods and services analyses are from all of Sweden, whereas the walkability indices are based on data from the city of Stockholm. Various methods have been used to clean, structure and geocode the data, including hand written reports on case data, maps of poor geometric quality, information from databases on climate, demography, diseases, goods and services, income data and more, to make this data feasible for spatial analysis, modeling and visualization. Network analysis was used to model food transports in the 14th century as well as walking in the city of Stockholm today. Proximity analysis was used to assess the spatio-temporal spread of the Russian Influenza. The impact of climatological factors on the propagation of the Asian Influenza was analyzed and geographically weighted mean (GWM) calculations were used to discover common characteristics in the spatio-temporal spread of three past pandemics. Among the results generated in the epidemiologic study the following should be noted in particular; the local peaking periods of the Asian Influenza were preceded by falling temperature, the total peaking period for the three pandemics (Russian, Asian and A(H1N1)pdm09) was approximately 10 weeks and their weekly GWM followed a path from southwest to northeast (opposite direction for the A(H1N1)pdm09). From the neighborhood studies one can note that compared to the results measured and reported by tested individuals there is a positive (small but significant) association between neighborhood walkability and physical activity outcomes. The main contribution of this work is that it gives epidemiologists and public health specialists new ideas, not only on how to formulate, model, analyze and visualize different health related research questions but also ideas on how new procedures could be implemented in their daily work. Once the data reporting is organized in a suitable manner there is a multitude of options on how to present important and critical information to officials and policy makers.

QC 20140313

APA, Harvard, Vancouver, ISO, and other styles

11

Pande, Rishikesh A. "Using Plant Epidemiological Methods to Track Computer Network Worms." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/9943.

Full text

Abstract:

Network worms that scan random computers have caused billions of dollars in damage to enterprises across the Internet. Earlier research has concentrated on using epidemiological models to predict the number of computers a worm will infect and how long it takes to do so. In this research, one possible approach is outlined for predicting the spatial flow of a worm within the local area network (LAN). The approach in this research is based on the application of mathematical models and variables inherent in plant epidemiology. In particular, spatial autocorrelation has been identified as a candidate variable that helps predict the spread of a worm over a LAN. This research describes the application of spatial autocorrelation to the geography and topology of the LAN and describes the methods used to determine spatial autocorrelation. Also discussed is the data collection process and methods used to extract pertinent information. Data collection and analyses are applied to the spread of three historical network worms on the Virginia Tech campus and the results are described. Spatial autocorrelation exists in the spread of network worms across the Virginia Tech campus when the geographic aspect is considered. If a new network worm were to start spreading across Virginia Tech's campus, spatial autocorrelation would facilitate tracking the geographical locations of the spread. In addition if an infection with a known value of spatial autocorrelation is detected, the characteristics of the worm can be identified without a complete analysis.
Master of Science

APA, Harvard, Vancouver, ISO, and other styles

12

Bessell, Paul R. "Spatial epidemiology of Foot and Mouth Disease in Great Britain." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/4831.

Full text

Abstract:

During 2007 the UK experienced outbreaks of three notifiable exotic livestock diseases; Foot and Mouth Disease (FMD), Highly Pathogenic Avian Influenza (HPAI) and bluetongue. Large epidemics of any of these diseases would have a serious impact on animal welfare, farming, food production and the economy. In light of this, understanding holdings which are most likely to acquire and spread infection and being able to identify areas at higher risk of an epidemic is valuable when preparing for and managing an epidemic. This thesis uses a spatial epidemiological framework and the detailed disease and demographic data from the 2001 Great Britain (GB) FMD epidemic to develop static models of the risk of FMD susceptibility and transmission. These models are used to develop maps of FMD risk. These methods are then applied to the outbreak of FMD in 2007. The inputs for this analysis comprised a set of data relating to the farms diagnosed with FMD and farms culled as part of the disease control measures. The cleaning of these data is described and data which were estimated relating to dates of infection and putative sources of infection are evaluated. The distribution of farm holdings and animals is taken from the June 2000 GB agricultural census, off-fields of farms in the agricultural census are recorded in other datasets and these have been identified and linked to census holdings. A model of holding level susceptibility is developed using both farm level variables and measures of animal numbers in the locality of the holding as well as the distance to the nearest farm infected before the ban on animal movements (seeds). The overall fit of the model was very good with an area under the Receiver Operator Characteristic (ROC) curve of 0.91. A further model was developed to describe the risk of FMD transmission. However, due to incompleteness of transmission data, this was a model of the risk of finding a subsequent Infected Premises (IP) within 3km of an IP. Risk factors were a combination of holding level variables and locality measures as well as data relevant to the infection, such as infectious period and the species initially infected. The area under the ROC curve for this model was 0.71, which is regarded as an acceptable fit. Geographical barriers to FMD transmission were investigated using a case-control methodology, linear barriers comprising rivers and railways had a significant protective effect with respect to disease transmission (odds ratio = 0.54, 95% CIs = 0.30,0.96, p=0.038). Modelled values for the transmission and susceptibility models were transformed to a raster surface in ESRI ArcMap for both the disease as it was seeded in the 2001 epidemic and a non-specific background risk surface independent of the distribution of seeds. A risk map generated for the outbreak of FMD in Surrey in August 2007 suggested that there was little risk of a large outbreak in Surrey. Potential disease introductions through livestock movements from Surrey into Scotland were identified and these suggested that if the disease were introduced into Scotland there was great danger of substantial local spread. These methods described in this thesis have been used to map risk of FMD and subsequently applied to inform the risk presented by a different outbreak of FMD. The study underlines the value of detailed data both disease and demographic, for epidemic management. Similar methods could and should be applied to other infectious diseases threats of livestock such as HPAI and bluetongue.

APA, Harvard, Vancouver, ISO, and other styles

13

Rama, Parbavati. "Placing the dead :the spatial distribution and spread of HIV in a major South African city." Thesis, University of the Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&amp.

Full text

Abstract:

The aim of this study was to establish a new understanding of the epidemiology of HIV/AIDS at the municipal level, but at the same time upholding the anonymity of the HIV infected and AIDS sufferers. Innovative research techniques such as the use of GIS (geographic information systems) as a research tool contributed to disclosing the patterns of the HIV pandemic in the Nelson Mandela Metropole that were not obvious or visible before. GIS involved geographic maps that detect the spatial relationship between HIV prevalence rates and vectors that drive the pandemic.

APA, Harvard, Vancouver, ISO, and other styles

14

Martin, Vincent. "Spatial ecology of the persistence and spread of highly pathogenic avian influenza, H5N1 in Southern China." Doctoral thesis, Universite Libre de Bruxelles, 2012. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209760.

Full text

Abstract:

Les travaux de recherche effectués dans le cadre de cette thèse ont été guidés par le manque d’information et une compréhension limitée des mécanismes épidémiologiques à l’origine de l’émergence et de la diffusion de la grippe aviaire hautement pathogène, souche H5N1 en Chine du Sud, aussi reconnue comme l’épicentre potentiel de l’émergence des virus influenza aviaires à caractères pandémiques.

Dans ce cadre, des données spatio-temporelles relatives aux foyers de la maladie ainsi que des données de surveillance virologiques (isolement du virus effectué dans le cadre du système de surveillance nationale) ont été collectées sur une période de quatre ans et analysées afin d’éxplorer les facteurs de risque relatifs à l’émergence et persistence de la maladie dans certaine zones de production du sud de la Chine. Les analyses ainsi effectuées ont permis d’identifier, à travers l’utilisation de méthodes statistiques robustes ayant fait leur preuve dans le domaine de la santé ou de l’écologie (la régression logistique classique et les arbres de regression logistique), des facteurs de risque liés à certains types de production de volailles (canards élevés en plein air, zones riches en eau et par extension associées à la riziculture) ou des facteurs associés à l’activité humaine. A travers une représentation cartographique des facteurs ainsi identifiés, des cartes de risque ont été produites permettant ainsi de visualiser d’une part les zones à haut risque de persistence de l’infection virale et d’autre part les zones vulnérables à l’apparition de foyers de la maladie, donnant aux autorités nationales la possibilité de mieux cibler leurs politiques de surveillance et de contrôle.

Dans un second temps, notre étude s’est portée sur les marchés à volailles traditionnels du sud de la Chine qui représentent un risque permanent de persistence, d’évolution et de diffusion des virus influenza aviaires, ainsi qu’un risque important en matière de santé publique. La dynamique de ces marchés et les liens qui les unissent ont été étudiés à travers des outils d’analyse empruntés à la sociologie tels que l’Analyse des Réseaux Sociaux (Social Network Analysis). Grace à cette approche, l’importance de l’hygiène de ces marchés et notamment du nettoyage et de la désinfection des cages dans la persistence du virus a été mise en évidence. Enfin, des enquêtes effectuées auprès des vendeurs de volailles ont permis d’identifier l’origine et la destination des animaux vendus et de reconstruire des réseaux plus ou moins intriqués de liens commerciaux qui unissent ces marchés entre eux dans trois provinces du sud de la Chine. L’analyse de ces réseaux et de leurs configurations ont permis d’identifier des marchés à plus haut risque de persistence de l’infection du fait de leur position centrale au sein de ces réseaux. De même qu’il est indispensable de cibler la surveillance et le contrôle de la maladie dans des zones écologiquement favorables à la persistence des virus influenza aviaires, cette étude révèle l’importance de certaines pratiques hygiéniques et commerciales dans la persistence de la maladie et la nécessité de cibler la surveillance et le contrôle au niveau de certains de ces marchés situés au centre d’un réseau dense et connecté, pour pouvoir in fine mieux contrôler la maladie au niveau national.

Doctorat en Sciences agronomiques et ingénierie biologique
info:eu-repo/semantics/nonPublished

APA, Harvard, Vancouver, ISO, and other styles

15

Ingelgård, Marcus. "Determinants of the Premium in Futures on the Spatial Price Spread in the Nordic Electricity Market." Thesis, Örebro universitet, Handelshögskolan vid Örebro Universitet, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-75361.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Janne, Odile E. M. "The changing geographical spread of corporate technological activity in Europe : the dynamics of corporate technological strategies and the hierarchy of innovative centres." Thesis, University of Reading, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343345.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Raber, Erica Candace. "SPATIAL RESOLUTION CHARACTERIZATION OF IMAGES TAKEN FROM A CAPILLARY-BASED HIGH PRESSURE CHAMBER FOR BIOLOGICAL IMAGING STUDIES." Miami University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=miami1154702307.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Alqawasmeh, Yousef. "Models for Persistence and Spread of Structured Populations in Patchy Landscapes." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36845.

Full text

Abstract:

In this dissertation, we are interested in the dynamics of spatially distributed populations. In particular, we focus on persistence conditions and minimal traveling periodic wave speeds for stage-structured populations in heterogeneous landscapes. The model includes structured populations of two age groups, juveniles and adults, in patchy landscapes. First, we present a stage-structured population model, where we divide the population into pre-reproductive and reproductive stages. We assume that all parameters of the two age groups are piecewise constant functions in space. We derive explicit formulas for population persistence in a single-patch landscape and in heterogeneous habitats. We find the critical size of a single patch surrounded by a non-lethal matrix habitat. We derive the dispersion relation for the juveniles-adults model in homogeneous and heterogeneous landscapes. We illustrate our results by comparing the structured population model with an appropriately scaled unstructured model. We find that a long pre-reproductive state typically increases habitat requirements for persistence and decreases spatial spread rates, but we also identify scenarios in which a population with intermediate maturation rate spreads fastest. We apply sensitivity and elasticity formulas to the critical size of a single-patch landscape and to the minimal traveling wave speed in a homogeneous landscape. Secondly, we use asymptotic techniques to find an explicit formula for the traveling periodic wave speed and to calculate the spread rates for structured populations in heterogeneous landscapes. We illustrate the power of the homogenization method by comparing the dispersion relation and the resulting minimal wave speeds for the approximation and the exact expression. We find an excellent agreement between the fully heterogeneous speed and the homogenized speed, even though the landscape period is on the same order as the diffusion coefficients and not as small as the formal derivation requires. We also generalize this work to the case of structured populations of n age groups. Lastly, we use a finite difference method to explore the numerical solutions for the juveniles-adults model. We compare numerical solutions to analytic solutions and explore population dynamics in non-linear models, where the numerical solution for the time-dependent problem converges to a steady state. We apply our theory to study various aspects of marine protected areas (MPAs). We develop a model of two age groups, juveniles and adults, in which only adults can be harvested and only outside MPAs, and recruitment is density dependent and local inside MPAs and fishing grounds. We include diffusion coefficients in density matching conditions at interfaces between MPAs and fishing grounds, and examine the effect of fish mobility and bias movement on yield and fish abundance. We find that when the bias towards MPAs is strong or the difference in diffusion coefficients is large enough, the relative density of adults inside versus outside MPAs increases with adult mobility. This observation agrees with findings from empirical studies.

APA, Harvard, Vancouver, ISO, and other styles

19

VanBuren, John Matthew. "Integrating independent spatio-temporal replications to assess population trends in disease spread." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/5669.

Full text

Abstract:

Our interest in spatio-temporal models focuses on how a disease spreads within a body region. We use independent replications across individuals to better understand population level dynamics of disease spread. Our Bayesian hierarchical model incorporates independent spatio-temporal datasets to estimate population level parameters. A dimension reduction propagator matrix is used to identify the most variable spatial regions, which are then related to a set of latent variables and covariates. Posterior estimates of parameters allow us to create a predicted estimate of the overall disease evolution process for each individual. In addition, individual level rates of deterioration can be estimated and predictions of future spread are made. The motivating example for this model stems from a study of visual loss in participants with glaucoma. Participants’ vision was recorded across a grid covering the central part of the eye at baseline plus eight follow-up visits every 6 months. We use these spatio-temporal replications of independent participants to determine how human characteristics and demographics collectively affect the spread and progression of glaucoma. Our introduced model is available in the DROIIDS R package. We account for missing data through our model with a Bayesian imputation method.

APA, Harvard, Vancouver, ISO, and other styles

20

Yñiguez, Aletta Tiangco. "Spatial Dynamics in the Growth and Spread of Halimeda and Dictyota in Florida reefs: A Simulation Modeling Approach." Scholarly Repository, 2007. http://scholarlyrepository.miami.edu/oa_dissertations/62.

Full text

Abstract:

Macroalgae are an important part of the coral reef ecosystem that has largely been overlooked. However, in the past few decades their abundances have increased and this has been attributed to combinations of coral mortality opening up space in the reef, decreased grazing and increased nutrient load in reefs. This dissertation illustrates a novel means of investigating the effect of various growth and disturbance factors on the dynamics of macroalgae at three different levels (individual, population and 3-species community). Macroalgae are modular and clonal organisms that have differing morphologies depending on the environment to which they are exposed. These traits were exploited in order to understand the factors that were acting on the dominant and common macroalgae in the Florida Reef Tract: Halimeda tuna, Halimeda opuntia and Dictyota sp. The agent-based model SPREAD (SPatially-explicit REef Algae Dynamics) was developed to incorporate the key morphogenetic characteristics of clonality and morphological plasticity. It revolves around the iteration of macroalgal module production in response to light, temperature, nutrients, and space availability, while fragmentation is the source for mortality or new individuals. These processes build the individual algae then the population. The model was parameterized through laboratory experiments, existing literature and databases and results were compared to independently collected field data from four study sites in the Florida Keys. SPREAD was run using a large range of light, temperature, nutrient and disturbance (fragmentation without survival) levels and yielded six morphological types for Halimeda tuna, and two each for Halimeda opuntia and Dictyota sp. The model morphological types that matched those measured in two inshore patch reefs (Cheeca Patch and Coral Gardens) and two offshore spur and groove reefs (Little Grecian and French Reef), were formed in conditions that were similar to the environmental (light, nutrient and disturbance) conditions in the field sites. There were also differences between species in the important factors that influenced their morphologies, wherein H. opuntia and Dictyota were more affected by disturbance than growth factors, while H. tuna morphology was affected by both. Allowing for fragmentation with survival in the model resulted in significantly higher population abundances (percent cover and density). The highest abundances were achieved under high fragment survival probabilities and a high disturbance level (but not large fragment sizes). Incorporating fragmentation with survival and simulating the variations in light, nutrients and disturbance between the inshore patch reefs and offshore spur and groove reefs in SPREAD led to comparable abundances of Halimeda in the virtual reef sites. Adding competition for space and light and epiphytism by Dictyota on the two Halimeda species suggests that it can regulate the populations of the three macroalgae. However, comparing model abundances to the field, competition may not be a strong regulating force for H. tuna in all the sites and H. opuntia in the patch reefs. H. opuntia in the offshore reefs is possibly competitively regulated. Although SPREAD was not able to capture the patterns in the population abundance of Dictyota, this points to the potential importance of other morphometrics not captured by the model, a variation in growth curves between reef habitats, or the differential contribution of sexual reproduction.

APA, Harvard, Vancouver, ISO, and other styles

21

Gabriele-Rivet, Vanessa. "Potential spread of rabies in dingo populations of northern Australia." Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/24319.

Full text

Abstract:

Australia is free from canine rabies. The spread of the disease in Indonesia has increased the risk of rabies incursion in northern Australia. Remote Indigenous communities, such as those in the Northern Peninsula Area (NPA), contain large populations of free-roaming domestic dogs surrounded by dingo populations, creating optimal conditions for rabies establishment. A cross-sectional survey of NPA hunters revealed that hunting practices using domestic dogs create opportunities for dingo-dog interactions. Dingo purity analyses on scats of canine origin collected in the NPA region demonstrated that dingoes visit areas around the communities, increasing the likelihood of contact with roaming domestic dogs. A scoping review on the ecology of dingoes identified density, home range size and contacts between dingoes, three key ecological parameters for disease spread modelling, as major research gaps especially in northern Australia. Dingo population density and home range size in the NPA were estimated from spatially explicit mark-resight models based on data from a one-year camera-trap study. This study also revealed a substantial temporal overlap and spatial correlation in activity between dingoes and domestic dogs, further supporting the likelihood for disease spread at the wild-domestic interface. A novel spatial stochastic rabies spread model, which incorporated field-derived dingo ecological parameters and landscape heterogeneity specific to the NPA, predicted a high probability (59%) of spread to other packs following the introduction of the disease into the dingo population from a roaming or hunting domestic dog. Outbreaks were generally larger when rabies was introduced during the dry season and in areas around the communities. Overall, this research provides compelling evidence of the importance of improving Australia’s preparedness for a potential rabies incursion in high-risk areas, to prevent serious consequences in remote Indigenous communities.

APA, Harvard, Vancouver, ISO, and other styles

22

Ikai, Youhei, Masaaki Katayama, Takaya Yamazato, and Akira Ogawa. "An Initial Code Acquisition Scheme for Indoor Packet DS/SS Systems with Macro/Micro Antenna Diversity." IEICE, 2000. http://hdl.handle.net/2237/7220.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

Price, Stephen J. "Emergence of a virulent wildlife disease : using spatial epidemiology and phylogenetic methods to reconstruct the spread of amphibian viruses." Thesis, Queen Mary, University of London, 2014. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8851.

Full text

Abstract:

Ranavirus infection has caused severe disease and mass mortality in UK common frogs for more than twenty years resulting in serious declines in some populations. The pathogen has been studied since 1992. These studies generated two valuable resources exploited in this thesis: an archive of tissues and virus isolates and a database of reports from citizen scientists on ranavirus-consistent mortality. The previous studies yielded modest evidence suggesting that introductions from North America initiated ranavirus emergence in the UK, though little else was known about the pattern of introduction or spread. This thesis conducts a more detailed investigation, extending existing knowledge of ranavirus diversity and spread through molecular epidemiology and phylogenetics, an in vivo infection experiment, and in silico models. Non-lethal sampling protocols for ranavirus screening were assessed in a controlled setting and shown to be as effective as traditional protocols. The database of citizen science reports was utilised in spatio-temporal models of the spread of ranavirus disease, finding that ranavirus infection is spreading by transmission between ponds but that new outbreaks are also correlated with both human population density and regional temperatures. The first whole genome sequence from a UK ranavirus is presented. Analysis of the genome shows that it is an isolate of the ranavirus type species, FV3, on the basis of its near identical genome arrangement and a ‘supergene’ phylogenetic analysis. An unexpected finding was evidence for recent lateral transfer of host DNA into the FV3 genome. A candidate gene survey of European ranaviruses revealed considerable diversity that may explain the variation in virulence and host range in Spain. Two proposed new species of Ranavirus are described there - one highly virulent, the other seemingly asymptomatic – and the previously described CMTV is shown to be a likely cause of catastrophic decline across multiple hosts. A lack of monophyly among Spanish ranaviruses and the spatial pattern of incidence suggest recent introduction(s). Together, the evidence presented in this thesis underlines the key role that humans have played in the spread of this group of virulent wildlife pathogens in two European countries.

APA, Harvard, Vancouver, ISO, and other styles

24

Sieracki, Jennifer L. "Spatial Modeling as a Decision-making Tool for Invasive Species Management in the Great Lakes." University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1408630726.

Full text

APA, Harvard, Vancouver, ISO, and other styles

25

Russell, Thembi M. "The spatial analysis of radiocarbon databases : the spread of the first farmers in Europe and of the fat-tailed sheep in Southern Africa." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269940.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Russell, Thembi M. "The spatial analysis of radiocarbon databases the spread of the first farmers in Europe and of the fat-tailed sheep in Southern Africa /." Oxford : Archaeopress, 2004. http://books.google.com/books?id=Vi9mAAAAMAAJ.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Koss, Jeffrey David. "Spatial and temporal patterns in the spread of influenza A and B viruses in the United States during the 2016-17 influenza season." Thesis, University of Iowa, 2018. https://ir.uiowa.edu/etd/6163.

Full text

Abstract:

Influenza is a respiratory virus that causes significant morbidity and mortality throughout the world every year. Seasonal epidemics of influenza occur in the late fall and winter in the United States annually, but there are variations in its timing from year to year. Further, although the timing of epidemic waves in the United States are similar, there is variation between different populations. It is not well understood why these differences exist. Understanding the spatial and temporal variation in the timing of influenza is important because it shapes our understanding of preventive actions that can be taken to limit the spread of the virus. Past studies that have examined the timing of influenza have been limited by the fact that they have used influenza-like illness (ILI) as an indicator of influenza. ILI has traditionally been the conventional indicator of influenza because the illness does not present unique symptoms. As such, spatial and temporal variation in the relative timing of influenza A, influenza B, and ILI have not been investigated extensively. Additionally, there has been concern raised about implications of the imprecise nature of ILI in treating patients that it is believed may have influenza. This study addressed this gap and concern by utilizing influenza-specific data from clinics and hospitals throughout the United States to evaluate spatial variation in the timing of influenza across the United States in the 2016-17 influenza season. Results from influenza rapid tests were aggregated by urban area as a means of evaluating associations between epidemic timing and independent variables in different locations. The timing of influenza A and B epidemics was tested for spatial autocorrelation and incorporated in regression models to identify potential relationships between epidemic timing and several variables (including dew point, temperature, population, population density, and cumulative seasonal vaccination rates). Forward stepwise regression was then conducted to identify a set of variables that may be best suited to explain the timing of these milestones, and spatial lag regression was conducted to account for spatial autocorrelation in these variables. This analysis indicated that higher average dew point and temperature and greater population and population density were both associated with earlier epidemic beginnings and later epidemic endings, while higher cumulative seasonal vaccination rates were associated with earlier epidemic endings for influenza A and B. Forward stepwise regression yielded models that generally differed for each epidemic milestone and type of influenza, indicating that different sets of variables might be best suited to explain different milestones of epidemics. Spatial lag regression improved model fit for the forward stepwise models for which there was residual spatial autocorrelation. This is one of the first studies to evaluate the timing of different points within an epidemic. The techniques I used to study timing are well-suited for the study of future epidemics of infectious diseases, including influenza, that seek to identify and clarify potential associations between independent variables and epidemic timing.

APA, Harvard, Vancouver, ISO, and other styles

28

Xue, Ling. "Modeling and analysis of vector-borne diseases on complex networks." Diss., Kansas State University, 2013. http://hdl.handle.net/2097/16788.

Full text

Abstract:

Doctor of Philosophy
Department of Electrical and Computer Engineering
Caterina Scoglio
Vector-borne diseases not only cause devastating economic losses, they also significantly impact human health in terms of morbidity and mortality. From an economical and humane point of view, mitigation and control of vector-borne diseases are essential. Studying dynamics of vector-borne disease transmission is a challenging task because vector-borne diseases show complex dynamics impacted by a wide range of ecological factors. Understanding these factors is important for the development of mitigation and control strategies. Mathematical models have been commonly used to translate assumptions concerning biological (medical, demographical, behavioral, immunological) aspects into mathematics, linking biological processes of transmission and dynamics of infection at population level. Mathematical analysis translates results back into biology. Classical deterministic epidemic models do not consider spatial variation, assuming space is homogeneous. Spatial spread of vector-borne diseases observed many times highlights the necessity of incorporating spatial dynamics into mathematical models. Heterogeneous demography, geography, and ecology in various regions may result in different epidemiological characteristics. Network approach is commonly used to study spatial evolution of communicable diseases transmitted among connected populations. In this dissertation, the spread of vector-borne diseases in time and space, is studied to understand factors that contribute to disease evolution. Network-based models have been developed to capture different features of disease transmission in various environments. Network nodes represent geographical locations, and the weights represent the level of contact between regional pairings. Two competent vector populations, Aedes mosquitoes and Culex mosquitoes, and two host populations, cattle and humans were considered. The deterministic model was applied to the 2010 Rift Valley fever outbreak in three provinces of South Africa. Trends and timing of the outbreak in animals and humans were reproduced. The deterministic model with stochastic parameters was applied to hypothetical Rift Valley fever outbreak on a large network in Texas, the United States. The role of starting location and size of initial infection in Rift Valley fever virus spread were studied under various scenarios on a large-scale network. The reproduction number, defined as the number of secondary infections produced by one infected individual in a completely susceptible population, is typically considered an epidemic threshold of determining whether a disease can persist in a population. Extinction thresholds for corresponding Continuous-time Markov chain model is used to predict whether a disease can perish in a stochastic setting. The network level reproduction number for diseases vertically and horizontally transmitted among multiple species on heterogeneous networks was derived to predict whether a disease can invade the whole system in a deterministic setting. The complexity of computing the reproduction number is reduced because the expression of the reproduction number is the spectral radius of a matrix whose size is smaller than the original next generation matrix. The expression of the reproduction number may have a wide range of applications to many vector-borne diseases. Reproduction numbers can vary from below one to above one or from above one to below one by changing movement rates in different scenarios. The observations provide guidelines on executing movement bans in case of an epidemic. To compute the extinction threshold, corresponding Markov chain process is approximated near disease free equilibrium. The extinction threshold for Continuous-time Markov chain model was analytically connected to the reproduction number under some assumptions. Numerical simulation results agree with analytical results without assumptions, proposing a mathematical problem of proving the existence of the relationships in general. The distance of the extinction threshold were shown to be closer to one than the reproduction number. Consistent trends of probability of extinction varying with disease parameters observed through numerical simulations provide novel insights into disease mitigation, control, and elimination.

APA, Harvard, Vancouver, ISO, and other styles

29

Jammalamadaka, Rajanikanth. "Multilevel Methodology For Simulation Of Spatio-Temporal Systems With Heterogeneous Activity: Application To Spread Of Valley Fever Fungus." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/193519.

Full text

Abstract:

Spatio-temporal systems with heterogeneity in their structure and behavior have two major problems. The first one is that such systems extend over very large spatial and temporal domains and consume a lot of resources to simulate that they are infeasible to study with current platforms. The second one is that the data available for understanding such systems is limited. This also makes it difficult to get the data for validation of their constituent processes while simultaneously considering their global behavior. For example, the valley fever fungus considered in this dissertation is spread over a large spatial grid in the arid Southwest and typically needs to be simulated over several decades of time to obtain useful information. It is also hard to get the temperature and moisture data at every grid point of the spatial domain over the region of study. In order to address the first problem, we develop a method based on the discrete event system specification which exploits the heterogeneity in the activity of the spatio-temporal system and which has been shown to be effective in solving relatively simple partial differential equation systems. The benefit of addressing the first problem is that it now makes it feasible to address the second problem.We address the second problem by making use of a multilevel methodology based on modeling and simulation and systems theory. This methodology helps us in the construction of models with different resolutions (base and lumped models). This allows us to refine an initially constructed lumped model with detailed physics-based process models and assess whether they improve on the original lumped models. For that assessment, we use the concept of experimental frame to delimit where the improvement is needed. This allows us to work with the available data, improve the component models in their own experimental frame and then move them to the overall frame. In this dissertation, we develop a multilevel methodology and apply it to a valley fever model. Moreover, we study the model's behavior in a particular experimental frame of interest, namely the formation of new sporing sites.

APA, Harvard, Vancouver, ISO, and other styles

30

Haran, Julien. "Dispersion des espèces impliquées dans une association phorétique vecteur - pathogène nouvellement formée : le cas de Monochamus galloprovincialis, vecteur natif d’un nématode invasif en Europe (Bursaphelenchus xylophilus)." Thesis, Orléans, 2015. http://www.theses.fr/2015ORLE2046/document.

Full text

Abstract:

Les invasions biologiques se sont intensifiées au cours des dernières décennies en raison d’une accélération des échanges commerciaux. Ces invasions représentent une menace pour les écosystèmes et de nombreuses activités anthropiques, il est donc crucial de comprendre les mécanismes qui les sous-tendent afin de mieux prévoir et limiter leurs impacts. Dans cette thèse, j’aborde la question du potentiel dispersif d’espèces natives et non natives impliquées dans une association phorétique nouvellement formée. En particulier, je me focalise sur le cas de l’association entre un nématode invasif ravageur des pinèdes, le nématode du pin (Bursaphelenchus xylophilus) et son insecte vecteur endémique en Europe (Monochamus galloprovincialis). J’ai tout d’abord étudié les flux de gènes de l’insecte vecteur seul afin d’identifier les barrières à sa dispersion. J’ai ensuite simulé l’expansion spatiale du couple nématode-vecteur à l’aide d’un modèle de dispersion, en intégrant l’effet synergique de cette nouvelle association. Les résultats obtenus au cours de cette thèse montrent qu’il existe un important potentiel de dispersion du nématode invasif en Europe par le biais de cette association phorétique. En revanche, certains paramètres de l’environnement tels que les reliefs et les températures basses qui leur sont associées, ainsi que les fortes densités en pins constituent des barrières à la dispersion du vecteur et donc des obstacles potentiels à l’expansion du nématode invasif. Au-delà des apports relatifs au modèle d’étude, cette thèse a conduit au développement de plusieurs méthodes pouvant être adaptées à d’autres cas d’associations phorétiques nouvelles et, par extension, contribuer à la compréhension de la dispersion des espèces au sein de ces systèmes complexes et peu étudiés
Biological invasions dramatically increased over the last decades due to the intensification of international trade. These invasions constitute a threat for ecosystems and many anthropic activities, therefore it is crucial to understand underlying processes in order to better predict and manage their impacts. In this PhD thesis, I explore the potential of dispersion of native and non-native species involved in a novel phoretic association. I focus on the case of the association between a pest for pine forests, the pinewood nematode (Bursaphelenchus xylophilus) introduced in Europe, and its endemic insect vector (Monochamus galloprovincialis). I first estimated gene flows of the insect vector alone in order to identify the barriers and corridors to dispersal of this species. Then I have simulated the spatial spread of the nematode-vector couple using a spread model, and accounting for the synergistic effect of this novel association. The results obtained during this PhD showed that the invasive nematode has an important potential to spread through this phoretic association. However, some environmental features such as elevation, areas with low temperatures, and the high pine densities constitute barriers to dispersal of the vector and so, potential obstacles to the spread of the invasive nematode. Beyond these results focused on the model of study, this thesis has led to the development of several methods that may be adapted to other cases of novel phoretic association and, by extension, may contribute to a better understanding of dispersal of species involved in those complex and poorly known systems

APA, Harvard, Vancouver, ISO, and other styles

31

Winkler, Eckart, and Thilo Heinken. "Spread of an ant-dispersed annual herb : an individual-based simulation study on population development of Melampyrum pratense L." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2010/4649/.

Full text

Abstract:

The paper presents a simulation and parameter-estimation approach for evaluating stochastic patterns of population growth and spread of an annual forest herb, Melampyrum pratense (Orobanchaceae). The survival of a species during large-scale changes in land use and climate will depend, to a considerable extent, on its dispersal and colonisation abilities. Predictions on species migration need a combination of field studies and modelling efforts. Our study on the ability of M. pratense to disperse into so far unoccupied areas was based on experiments in secondary woodland in NE Germany. Experiments started in 1997 at three sites where the species was not yet present, with 300 seeds sown within one square meter. Population development was then recorded until 2001 by mapping of individuals with a resolution of 5 cm. Additional observations considered density dependence of seed production. We designed a spatially explicit individual-based computer simulation model to explain the spatial patterns of population development and to predict future population spread. Besides primary drop of seeds (barochory) it assumed secondary seed transport by ants (myrmecochory) with an exponentially decreasing dispersal tail. An important feature of populationpattern explanation was the simultaneous estimation of both population-growth and dispersal parameters from consistent spatio-temporal data sets. As the simulation model produced stochastic time series and random spatially discrete distributions of individuals we estimated parameters by minimising the expectation of weighted sums of squares. These sums-ofsquares criteria considered population sizes, radial population distributions around the area of origin and distributions of individuals within squares of 25*25 cm, the range of density action. Optimal parameter values, together with the precision of the estimates, were obtained from calculating sums of squares in regular grids of parameter values. Our modelling results showed that transport of fractions of seeds by ants over distances of 1…2 m was indispensable for explaining the observed population spread that led to distances of at most 8 m from population origin within 3 years. Projections of population development over 4 additional years gave a diffusion-like increase of population area without any “outposts”. This prediction generated by the simulation model gave a hypothesis which should be revised by additional field observations. Some structural deviations between observations and model output already indicated that for full understanding of population spread the set of dispersal mechanisms assumed in the model may have to be extended by additional features of plant-animal mutualism.

APA, Harvard, Vancouver, ISO, and other styles

32

Yu, Yi. "Radio Resource Planning in Low Power Wide Area IoT Networks." Electronic Thesis or Diss., Paris, CNAM, 2021. http://www.theses.fr/2021CNAM1287.

Full text

Abstract:

Cette thèse étudie le problème de planification des ressources pour les réseaux IoT longues portées basés sur les technologies NB-IoT et LoRa. Dans les deux cas, on suppose que les capteurs et les collecteurs sont distribués suivant des processus de points de Poisson spatial indépendants marqués par le caractère aléatoire du canal. Pour le NB-IoT, nous élaborons un modèle de dimensionnement statistique qui estime le nombre de ressources radio nécessaires en fonction du délai d’accès toléré, de la densité des nœuds actifs, des collecteurs et de la configuration de l’antenne. Pour le réseau LoRa, nous proposons une technique d’allocation de plusieurs sous-bandes pour atténuer le niveau élevé d’interférence induit par les nœuds qui transmettent avec le même facteur d’étalement. Pour allouer dynamiquement le facteur d’étalement et la puissance, nous présentons une approche d’apprentissage automatique avec multi-agents qui permet d’améliorer l’efficacité énergétique
In this thesis, we focus on radio resource planning issues for low power wide area networks based on NB-IoT and LoRa technologies. In both cases, the average behavior of the network is considered by assuming the sensors and the collectors are distributed according to independent random Poisson Point Process marked by the channel randomness. For the NB-IoT, we elaborate a statistical dimensioning model that estimates the number of radio resources in the network depending on the tolerated delay access, the density of active nodes, the collectors, and the antenna configuration with single and multi-user transmission. For the LoRa network, we propose a multi-sub band allocation technique to mitigate the high level of interference induced by nodes that transmit with the same spreading factor. To dynamically allocate the spreading factor and the power, we present a Q-learning multi-agent approach to improve the energy efficiency

APA, Harvard, Vancouver, ISO, and other styles

33

Van, Winkle Jill Elise. "Informal Trails and the Spread of Invasive Species in Urban Natural Areas: Spatial Analysis of Informal Trails and their Effects on Understory Plant Communities in Forest Park, Portland, Oregon." PDXScholar, 2014. https://pdxscholar.library.pdx.edu/open_access_etds/1841.

Full text

Abstract:

The risk of spread and establishment of invasive species to interior habitat within urban parks is of great concern to park managers and ecologists. Informal trails as a vector for this transmission are not well understood. To characterize effects of informal trails on understory plant communities, I conducted a study of the informal trail network in Forest Park, Portland, Oregon. The system of 382 informal trails was mapped and evaluated qualitatively, and from this population a systematic sample was selected for analysis. To identify hotspots of informal trail activity, showing the relationship of informal trails to formal trails, other park features, and trail use level, I evaluated all mapped trails using line density spatial analysis tools. To characterize understory communities, thirty transects were placed along informal trails, with paired transects along nearby formal trails for comparison. I measured percent cover by species for non-graminoid understory plants, and percent total plant cover at different structural layers, for quadrats at regular intervals from the trail edge. I calculated richness and Shannon-Weaver diversity for non-graminoid understory plants. For community analysis, species were grouped by dispersal strategy, native status, and growth form. Observations from system mapping suggest that "hidden" behaviors drive many informal trails: bathroom stops, party spots, waste dumping, and camps make up 28% of all informal trails. Trails to private property are few but represent over 29% of total trail length. Informal trail density is highest along Balch Creek. Hotspots of informal trail presence are associated with trailheads, trail intersections, and water access. Quadrats located within one meter of informal trails showed higher richness and diversity due to increased number of introduced and ruderal species. Formal trails exhibit these same patterns to a stronger degree and over a greater distance (two meters) from the trail edge. Distance from trail edge explained variation in plant communities when grouped by dispersal type, but not by growth form. This study shows that although informal trails are widely distributed throughout the park, they are concentrated in high use areas. The presence of informal trails leads to significant changes in Forest Park plant communities that favor invasive and ruderal species, but these effects appear limited to two meters from the trail edge.

APA, Harvard, Vancouver, ISO, and other styles

34

Wilms, Marcus. "Electrical receptive fields and cortical activation spread in response to electrical retina stimulation assessment of spatio-temporal resolution for a retina implant /." [S.l.] : [s.n.], 2001. http://archiv.ub.uni-marburg.de/diss/z2002/0084/.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Jacquart, Thierry. "Structure génétique et phylogénie intraspécifique chez la souris sauvage Mus spretus Lataste : distribution spatiale du polymorphisme des gènes nucléaires de structure et de l'ADN mitochondrial." Montpellier 2, 1986. http://www.theses.fr/1986MON20053.

Full text

APA, Harvard, Vancouver, ISO, and other styles

36

Raichur, Rohan. "A Novel Technique to Improve the Resolution and Contrast of Planar Nuclear Medicine Imaging." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1226955205.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Jacquart, Thierry. "Structure génétique et phylogénie intra-spécifique chez la souris sauvage Mus spretus (Lataste, 1883) distribution spatiale du polymorphisme des gènes nucléaires de structure et de l'ADN." Grenoble : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb37598420q.

Full text

APA, Harvard, Vancouver, ISO, and other styles

38

Nordqvist, Linn. "Ett smittfritt handlande : En studie om utformningen av matbutiker för att minska trängsel." Thesis, Mälardalens högskola, Akademin för innovation, design och teknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-55175.

Full text

Abstract:

Detta examensarbete går ut på att undersöka på vilket sätt matbutiker kan utformas för att underlätta för besökarna att hålla avstånd och undvika trängsel i syfte att minska spridning av virus. Fokuset i studien ligger på rumslig utformning i kombination med visuell information. Insamlade teorier samt användandet av metoder som platsanalys, benchmarking, observationer, behavioral mapping, intervju samt fokusgrupp, har gett förståelse för vad problemet skulle kunna vara och vad som krävs för att ge rätt förutsättningar för butiksbesökare att undvika trängsel. Utifrån detta har ett gestaltningsförslag tagits fram på hur rumslig utformning och visuell information kan användas i butiker för att styra flödet. Gestaltningsförslaget består av enkelriktade vägar med tillhörande information som vägleder besökarna genom butiken.
This thesis aims to investigate how grocery stores can be designed to make it easier for visitors to keep their distance and avoid crowding in order to reduce the spread of viruses. The focus of the study is on spatial design in combination with visual information. Collected theories as well as the use of methods such as location analysis, benchmarking, observations, behavioral mapping, interview and focus group, have provided an understanding of what the problem could be and what is needed to create the right conditions for shop visitors to avoid crowding. Based on this, a design proposal has been developed on how spatial design and visual information can be used in stores to control the customer flow. The design proposal consists of one-way paths with associated information that guide visitors through the store.

APA, Harvard, Vancouver, ISO, and other styles

39

Sallah, Kankoe. "Diffusion spatio-temporelle des épidémies : approche comparée des modélisations mathématiques et biostatistiques, cibles d'intervention et mobilité humaine." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0607.

Full text

Abstract:

Dans la première partie de cette thèse, nous avons mis en place un métamodèle de transmission du paludisme basé sur la modélisation compartimentale susceptible-infecté-résistant (SIR) et prenant en compte les flux de mobilité humaine entre différents villages du Centre Sénégal. Les stratégies d’intervention géographiquement ciblées, s’étaient avérées efficaces pour réduire l’incidence du paludisme aussi bien dans les zones d’intervention qu’à l’extérieur de ces zones. Cependant, des actions combinées ciblant à la fois le vecteur et l’hôte, coordonnées à large échelle sont nécessaires dans les régions et pays visant l’élimination du paludisme à court/moyen terme.Dans la deuxième partie nous avons évalué différentes méthodes d’estimation de la mobilité humaine en l’absence de données individuelles. Ces méthodes incluaient la traçabilité spatio-temporelle des téléphones mobiles ainsi que les modèles mathématiques de gravité et de radiation. Le transport de l’agent pathogène dans l’espace géographique, par la mobilité d’un sujet infecté est un déterminant majeur de la vitesse de propagation d’une épidémie. Nous avons introduit le modèle d’impédance qui minimise l’erreur quadratique moyen sur les estimations de mobilité, en particulier dans les contextes où les ensembles de population sont caractérisés par leurs tailles hétérogènes.Nous avons enfin élargi le cadre des hypothèses sous-jacentes à la calibration des modèles de gravité de la mobilité humaine. L’hypothèse d’une distribution avec excès de zéros a fourni un meilleur ajustement et une meilleure prédictibilité, comparée aux hypothèses classiques n’assumant pas un excès de zéros : Poisson, Quasipoisson
In the first part of this thesis, we have developed a malaria transmission metamodel based on the susceptible-infected-resistant compartmental modeling framework (SIR) and taking into consideration human mobility flows between different villages in the Center of Senegal. Geographically targeted intervention strategies had been shown to be effective in reducing the incidence of malaria both within and outside of intervention areas. However, combined interventions targeting both vector and host, coordinated on a large scale are needed in regions and countries aiming to achieve malaria elimination in the short/medium term.In the second part we have evaluated different methods of estimating human mobility in the absence of real data. These methods included spatio-temporal traceability of mobile phones, mathematical models of gravity and radiation. The transport of the pathogen through the geographical space via the mobility of an infected subject is a major determinant of the spread of an epidemic. We introduced the impedance model that minimized the mean square error on mobility estimates, especially in contexts where population sets are characterized by their heterogeneous sizes.Finally, we have expanded the framework of assumptions underlying the calibration of the gravity models of human mobility. The hypothesis of a zero inflated distribution provided a better fit and a better predictability, compared to the classical approach not assuming an excess of zeros: Poisson, Quasipoisson

APA, Harvard, Vancouver, ISO, and other styles

40

Imanzadeh, Saber. "Effets des incertitudes et de la variabilité spatiale des propriétés des sols et des structures sur le dimensionnement des semelles filantes et des conduites enterrées." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00803563.

Full text

Abstract:

Le sol présente une variabilité spatiale des propriétés physiques et mécaniques dont les effets sur des structures légères avec semelles filantes et sur les conduites enterrées ne sont pas bien pris en compte dans leur dimensionnement. Cette variabilité naturelle peut être très importante dans le cas de ces ouvrages car elle induit des tassements différentiels, dont les conséquences peuvent être dommageables : fissures dans les murs, les poutres ou encore des fuites dans les réseaux d'assainissement. La variabilité naturelle du sol et l'incertitude liée à la connaissance imparfaite des propriétés du sol et/ou du béton ou de l'acier de la structure sont les principales sources d'incertitude dans le choix des paramètres de calcul pour le dimensionnement de ces structures. Dans cette thèse, une approche analytique avec les méthodes probabilistes (FOSM et SOSM) et le modèle de Winkler, puis numérique avec le couplage de la méthode des éléments finis avec des approches géostatistiques ont été successivement menées pour modéliser le comportement des semelles filantes et des conduites enterrés lorsque les incertitudes sur les propriétés mécaniques du sol et de la structure sont prises en compte dans leur dimensionnement. Il apparait ainsi, l'importance du comportement longitudinal de ces ouvrages et du poids des incertitudes dans leur dimensionnement.

APA, Harvard, Vancouver, ISO, and other styles

41

Viljanen-Rollinson, S. L. H. "Expression and detection of quantitative resistance to Erysiphe pisi DC. in pea (Pisum sativum L.)." Lincoln University, 1996. http://hdl.handle.net/10182/1657.

Full text

Abstract:

Characteristics of quantitative resistance in pea (Pisum sativum L.) to Erysiphe pisi DC, the pathogen causing powdery mildew, were investigated. Cultivars and seedlines of pea expressing quantitative resistance to E. pisi were identified and evaluated, by measuring the amounts of pathogen present on plant surfaces in field and glasshouse experiments. Disease severity on cv. Quantum was intermediate when compared with that on cv. Bolero (susceptible) and cv. Resal (resistant) in a field experiment. In glasshouse experiments, two groups of cultivars, one with a high degree of resistance and the other with nil to low degrees of resistance to E. pisi, were identified. This indicated either that a different mechanism of resistance applied in the two groups, or that there has been no previous selection for intermediate resistance. Several other cultivars expressing quantitative resistance were identified in a field experiment. Quantitative resistance in Quantum did not affect germination of E. pisi conidia, but reduced infection efficiency of conidia on this cultivar compared with cv. Pania (susceptible). Other epidemiological characteristics of quantitative resistance expression in Quantum relative to Pania were a 33% reduction in total conidium production and a 16% increase in time to maximum daily conidium production, both expressed on a colony area basis. In Bolero, the total conidium production was reduced relative to Pania, but the time to maximum spore production on a colony area basis was shorter. There were no differences between the cultivars in pathogen colony size or numbers of haustoria produced by the pathogen. Electron microscope studies suggested that haustoria in Quantum plants were smaller and less lobed than those in Pania plants and the surface area to volume ratios of the lobes and haustorial bodies were larger in Pania than in Quantum. The progress in time and spread in space of E. pisi was measured in field plots of cultivars Quantum, Pania and Bolero as disease severity (proportion of leaf area infected). Division of leaves (nodes) into three different age groups (young, medium, old) was necessary because of large variability in disease severity within plants. Disease severity on leaves at young nodes was less than 4% until the final assessment at 35 days after inoculation (dai). Exponential disease progress curves were fitted for leaves at medium nodes. Mean disease severity on medium nodes 12 dai was greatest (P<0.001) on Bolero and Pania (9.3 and 6.8% of leaf area infected respectively), and least on Quantum (1.6%). The mean disease relative growth rate was greatest (P<0.001) for Quantum, but was delayed compared to Pania and Bolero. Gompertz growth curves were fitted to disease progress data for leaves at old nodes. The asymptote was 78.2% of leaf area infected on Quantum, significantly lower (P<0.001) than on Bolero or Pania, which reached 100%. The point of inflection on Quantum occurred 22.8 dai, later (P<0.001) than on Pania (18.8 dai) and Bolero (18.3 dai), and the mean disease severity at the point of inflection was 28.8% for Quantum, less (P<0.00l) than on Pania (38.9%) or Bolero (38.5%). The average daily rates of increase in disease severity did not differ between the cultivars. Disease progress on Quantum was delayed compared with Pania and Bolero. Disease gradients from inoculum foci to 12 m were detected at early stages of the epidemic but the effects of background inoculum and the rate of disease progress were greater than the focus effect. Gradients flattened with time as the disease epidemic intensified, which was evident from the large isopathic rates (between 2.2 and 4.0 m d⁻¹) Some epidemiological variables expressed in controlled environments (low infection efficiency, low maximum daily spore production and long time to maximum spore production) that characterised quantitative resistance in Quantum were correlated with disease progress and spread in the field. These findings could be utilised in pea breeding programmes to identify parent lines from which quantitatively resistant progeny could be selected.

APA, Harvard, Vancouver, ISO, and other styles

42

Hunter, Brandon. "Channel Probing for an Indoor Wireless Communications Channel." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/64.

Full text

Abstract:

The statistics of the amplitude, time and angle of arrival of multipaths in an indoor environment are all necessary components of multipath models used to simulate the performance of spatial diversity in receive antenna configurations. The model presented by Saleh and Valenzuela, was added to by Spencer et. al., and included all three of these parameters for a 7 GHz channel. A system was built to measure these multipath parameters at 2.4 GHz for multiple locations in an indoor environment. Another system was built to measure the angle of transmission for a 6 GHz channel. The addition of this parameter allows spatial diversity at the transmitter along with the receiver to be simulated. The process of going from raw measurement data to discrete arrivals and then to clustered arrivals is analyzed. Many possible errors associated with discrete arrival processing are discussed along with possible solutions. Four clustering methods are compared and their relative strengths and weaknesses are pointed out. The effects that errors in the clustering process have on parameter estimation and model performance are also simulated.

APA, Harvard, Vancouver, ISO, and other styles

43

Záhlava, Josef. "Sovereign credit risk drivers in a spatial perspective." Master's thesis, 2018. http://www.nusl.cz/ntk/nusl-373012.

Full text

Abstract:

This thesis analyses what drives sovereign credit risk when contagion is con- trolled for. CDS spreads are used as a measure of credit risk and bond yields are used to estimate interconnectedness of the examined countries. The main contribution lies in the use of high-frequency data and a robust wavelet based estimator in addition to spatial econometric model. The aim of this thesis is to test for presence of contagion and to evaluate which fundamentals are decisive for market perception of sovereign credit risk. Another goal is to evaluate the possibility of a structural break caused by the Greek debt restructuring. The results show that the restructuring did bring change. Contagion is present during the post-crisis period and it diminishes as the economies recover. Sim- ilarly, fundamentals are of higher importance in the post-crisis period when compared with the following period. JEL Classification C22, C31, C33, G01, G32, G33 Keywords spatial econometrics, CDS spreads, sovereign credit risk, financial contagion, realised covari- ance Author's e-mail josef.zahlava@gmail.com Supervisor's e-mail petr.gapko@seznam.cz

APA, Harvard, Vancouver, ISO, and other styles

44

Dubey, Agrita. "Estimation of the spatial spread of brain signals at multiple scales." Thesis, 2018. https://etd.iisc.ac.in/handle/2005/5296.

Full text

Abstract:

Spatial spread of a particular brain signal can be defined as the area of the cortical tissue around the recording electrode that contributes to the electrical activity recorded by the electrode. More specifically, assuming brain signals to be a weighted sum of electrical activity of a pool of neurons, spatial spread represents the spatial weighting function that primarily depends on the properties of the recording electrode such as its size, impedance and location as well as some properties of the brain tissue such as its conductance and filtering characteristics. Different signals, depending on the frequency content, represent different types of neuronal activity. For example, multi-unit activity (MUA), obtained by band-pass filtering the signal recorded from a microelelctrode (tip diameter of a few microns) primarily represents the weighted sum of action potentials, while the local field potential (LFP), obtained by low-pass filtering the same signal, primarily represents summed synaptic activity. Another signal is Electrocorticogram (ECoG), obtained by low-pass filtering the signal obtained from a macro-electrode (diameter of 2.3 mm) placed subdurally on the surface of the cortex of epileptic patients for localization of the seizure focus. These ECoG signals are used to determine the brain area that is responsible for seizures, which is subsequently surgically removed. Accurate estimation of the spatial spread of ECoG is therefore extremely important from a clinical perspective. Similarly, accurate estimation of the spatial spread of LFP is important from a basic science perspective, since these signals are now routinely used to study cognition and behavior, and also in braincomputer interfacing applications. However, the spatial spread of ECoG is unknown, and that of LFP is highly controversial. In the first two studies in this thesis, we investigate the spatial spreads of LFP and ECoG. Brain signals are often analyzed in the spectral domain where the slope of the power spectral density (PSD), as well as oscillations that are observed as peaks in the spectra, can reveal important information about the neural network. For example, gamma oscillations observed in the 30-70 Hz frequency range has been associated with several high-level cognitive functions such as attention, memory, perception etc. Further, the high-gamma activity observed as a broadband in 60-250 Hz frequency range has shown to be correlated with the spiking activity. These different signatures provide a robust measure to understand the brain dynamics at different recording levels. In the third study, we compare the tuning properties of gamma oscillations and high-gamma activity for different stimulus properties in LFP and ECoG. In the first study, we examined whether different frequencies of LFP spread differently. Recording from a microelectrode array implanted in the primary visual cortex (V1) of two macaques, we estimated the LFP spread as a function of frequency. We found that LFP spread is neither “low-pass” nor ‘all-pass” as suggested by previous studies but “band-pass” with frequencies in the high-gamma (60-150 Hz) range spreading more than both lower (20-40 Hz) and higher (>250 Hz) frequencies. Further, we found that this increase in high-gamma range is mirrored by an increase in the phase coherency across neighboring sites in the same frequency range. Spatial spreads can be estimated by measuring the receptive field (RF) and multiplying it with the cortical magnification factor, but this method overestimates the spatial spread because RF size gets inflated due to several factors such as eye jitter, stimulus size and RF scatter. This issue can be partially addressed by comparing the RFs of two measures (such as LFP and multiunit activity). Therefore, in the second study, we estimated the spatial spread of ECoG by simultaneously recording LFP and ECoG from the primary visual cortex (V1) of three behaving monkeys using a specialized hybrid grid which consists of both ECoG electrodes and a microelectrode array. We simultaneously mapped the RF responses of MUA, LFP, and ECoG at several cortical sites and found that spatial spread of ECoG is surprisingly local (standard deviation of ~1.5 millimeters, or a diameter of ~3 mm), only ~3 times the spread of the LFP, even though the size of the electrode is several hundred times larger than the microelectrode. Further, using a completely different approach, we estimated the spatial spread of ECoG by comparing the slope of the PSD of LFP and ECoG for spontaneous activity (no stimulus condition). We found that the slope of the ECoG was much steeper than LFP in the 20-100 Hz frequency range. Next, using a simple model based on linear superposition, we simulated the ECoG signal by averaging LFP signals over a progressively larger set of electrodes. We found that around ~50 LFP electrodes that correspond to a 7x7 grid when averaged had the similar slope as ECoG. The estimated spread in millimeters- 7 x 400 μm (inter-microelectrode distance) = 2.8 mm was remarkably similar to the first approach. Finally, in the last part, as an indirect measure, we investigated the spatial extent of ECoG by comparing the high-gamma activity observed in LFP and ECoG signals. We simultaneously recorded the LFP and ECoG signals for six different stimulus radii and computed the change in high-gamma power as a function of stimulus size. We found that tuning curve for LFP and ECoG were similar, with a maximum ECoG high-gamma power for the stimulus of 0.3° radii, suggesting local origins of ECoG. Further, we compared the orientation preference of LFP and ECoG for gamma oscillations. The preferred orientation for gamma oscillations in ECoG was similar to the gamma oscillation in LFP even though the ECoG electrodes were widely distributed in the cortex (center- to-center distance of 10 mm). This suggests that orientation tuning of gamma is not location specific but monkey specific. Overall, our results suggest that ECoG is a local signal which can provide a useful tool for clinical purposes, cognitive neuroscience and brain-machine-interface applications

APA, Harvard, Vancouver, ISO, and other styles

45

"Spatial spread of rabies in wildlife." Doctoral diss., 2013. http://hdl.handle.net/2286/R.I.20921.

Full text

Abstract:

abstract: Rabies disease remains enzootic among raccoons, skunks, foxes and bats in the United States. It is of primary concern for public-health agencies to control spatial spread of rabies in wildlife and its potential spillover infection of domestic animals and humans. Rabies is invariably fatal in wildlife if untreated, with a non-negligible incubation period. Understanding how this latency affects spatial spread of rabies in wildlife is the concern of chapter 2 and 3. Chapter 1 deals with the background of mathematical models for rabies and lists main objectives. In chapter 2, a reaction-diffusion susceptible-exposed-infected (SEI) model and a delayed diffusive susceptible-infected (SI) model are constructed to describe the same epidemic process -- rabies spread in foxes. For the delayed diffusive model a non-local infection term with delay is resulted from modeling the dispersal during incubation stage. Comparison is made regarding minimum traveling wave speeds of the two models, which are verified using numerical experiments. In chapter 3, starting with two Kermack and McKendrick's models where infectivity, death rate and diffusion rate of infected individuals can depend on the age of infection, the asymptotic speed of spread $c^\ast$ for the cumulated force of infection can be analyzed. For the special case of fixed incubation period, the asymptotic speed of spread is governed by the same integral equation for both models. Although explicit solutions for $c^\ast$ are difficult to obtain, assuming that diffusion coefficient of incubating animals is small, $c^\ast$ can be estimated in terms of model parameter values. Chapter 4 considers the implementation of realistic landscape in simulation of rabies spread in skunks and bats in northeast Texas. The Finite Element Method (FEM) is adopted because the irregular shapes of realistic landscape naturally lead to unstructured grids in the spatial domain. This implementation leads to a more accurate description of skunk rabies cases distributions.
Dissertation/Thesis
Ph.D. Mathematics 2013

APA, Harvard, Vancouver, ISO, and other styles

46

Fulcher, Corinne, Paul V. McGraw, N. W. Roach, David J. Whitaker, and James Heron. "Object size determines the spatial spread of visual time." 2016. http://hdl.handle.net/10454/8751.

Full text

Abstract:

Yes
A key question for temporal processing research is how the nervous system extracts event duration, despite a notable lack of neural structures dedicated to duration encoding. This is in stark contrast with the orderly arrangement of neurons tasked with spatial processing. In this study, we examine the linkage between the spatial and temporal domains. We use sensory adaptation techniques to generate after-effects where perceived duration is either compressed or expanded in the opposite direction to the adapting stimulus’ duration. Our results indicate that these after-effects are broadly tuned, extending over an area approximately five times the size of the stimulus. This region is directly related to the size of the adapting stimulus—the larger the adapting stimulus the greater the spatial spread of the aftereffect. We construct a simple model to test predictions based on overlapping adapted versus non-adapted neuronal populations and show that our effects cannot be explained by any single, fixed-scale neural filtering. Rather, our effects are best explained by a self-scaled mechanism underpinned by duration selective neurons that also pool spatial information across earlier stages of visual processing.
J.H. is supported by the Vision Research Trust (43069). N.W.R. is supported by a Wellcome Trust Research Career Development Fellowship (WT097387).

APA, Harvard, Vancouver, ISO, and other styles

47

"Spread Rate Estimation and the Role of Spatial Configuration and Human Behavior." Master's thesis, 2012. http://hdl.handle.net/2286/R.I.15143.

Full text

Abstract:

abstract: The spread of invasive species may be greatly affected by human responses to prior species spread, but models and estimation methods seldom explicitly consider human responses. I investigate the effects of management responses on estimates of invasive species spread rates. To do this, I create an agent-based simulation model of an insect invasion across a county-level citrus landscape. My model provides an approximation of a complex spatial environment while allowing the "truth" to be known. The modeled environment consists of citrus orchards with insect pests dispersing among them. Insects move across the simulation environment infesting orchards, while orchard managers respond by administering insecticide according to analyst-selected behavior profiles and management responses may depend on prior invasion states. Dispersal data is generated in each simulation and used to calculate spread rate via a set of estimators selected for their predominance in the empirical literature. Spread rate is a mechanistic, emergent phenomenon measured at the population level caused by a suite of latent biological, environmental, and anthropogenic. I test the effectiveness of orchard behavior profiles on invasion suppression and evaluate the robustness of the estimators given orchard responses. I find that allowing growers to use future expectations of spread in management decisions leads to reduced spread rates. Acting in a preventative manner by applying insecticide before insects are actually present, orchards are able to lower spread rates more than by reactive behavior alone. Spread rates are highly sensitive to spatial configuration. Spatial configuration is hardly a random process, consisting of many latent factors often not accounted for in spread rate estimation. Not considering these factors may lead to an omitted variables bias and skew estimation results. The ability of spread rate estimators to predict future spread varies considerably between estimators, and with spatial configuration, invader biological parameters, and orchard behavior profile. The model suggests that understanding the latent factors inherent to dispersal is important for selecting phenomenological models of spread and interpreting estimation results. This indicates a need for caution when evaluating spread. Although standard practice, current empirical estimators may both over- and underestimate spread rate in the simulation.
Dissertation/Thesis
M.S. Biology 2012

APA, Harvard, Vancouver, ISO, and other styles

48

Liu, Rongsong. "Transmission dynamics and spatial spread of vector borne diseases : modelling, prediction and control /." 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR19847.

Full text

Abstract:

Thesis (Ph.D.)--York University, 2006. Graduate Programme in Mathematics and Statistics.
Typescript. Includes bibliographical references (leaves 126-132). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR19847

APA, Harvard, Vancouver, ISO, and other styles

49

"Biodiversity, Dispersal, and Risk: Species Spread in Ecological and Social-Ecological Systems." Doctoral diss., 2016. http://hdl.handle.net/2286/R.I.40229.

Full text

Abstract:

abstract: The closer integration of the world economy has yielded many positive benefits including the worldwide diffusion of innovative technologies and efficiency gains following the widening of international markets. However, closer integration also has negative consequences. Specifically, I focus on the ecology and economics of the spread of species and pathogens. I approach the problem using theoretical and applied models in ecology and economics. First, I use a multi-species theoretical network model to evaluate the ability of dispersal to maintain system-level biodiversity and productivity. I then extend this analysis to consider the effects of dispersal in a coupled social-ecological system where people derive benefits from species. Finally, I estimate an empirical model of the foot and mouth disease risks of trade. By combining outbreak and trade data I estimate the disease risks associated with the international trade in live animals while controlling for the biosecurity measures in place in importing countries and the presence of wild reservoirs. I find that the risks associated with the spread and dispersal of species may be positive or negative, but that this relationship depends on the ecological and economic components of the system and the interactions between them.
Dissertation/Thesis
Doctoral Dissertation Biology 2016

APA, Harvard, Vancouver, ISO, and other styles

50

Koutnik, Michael A. "Toward a dynamic spatial model of zebra mussel (Dreissena polymorpha) spread among inland waters of Wisconsin." 1993. http://catalog.hathitrust.org/api/volumes/oclc/32463049.html.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Spatial spreads'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles