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1
Wilmot, Peter Nicholas. "Modelling cooling tower risk for Legionnaires' Disease using Bayesian Networks and Geographic Information Systems." Title page, contents and conclusion only, 1999. http://web4.library.adelaide.edu.au/theses/09SIS.M/09sismw744.pdf.
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Includes bibliographical references (leaves 115-120) Establishes a Bayesian Belief Network (BBN) to model uncertainty of aerosols released from cooling towers and Geographic Information Systems (GIS) to create a wind dispersal model and identify potential cooling towers as the source of infection. Demonstrates the use of GIS and BBN in environmental epidemiology and the power of spatial information in the area of health.
2
Roberts, Paul Allen. "Mathematical models of the retina in health and disease." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:385f61c4-4ff1-45d3-bdb2-41338c174025.
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The retina is the ocular tissue responsible for the detection of light. Its extensive demand for oxygen, coupled with a concomitant elevated supply, renders this tissue prone to both hypoxia and hyperoxia. In this thesis, we construct mathematical models of the retina, formulated as systems of reaction-diffusion equations, investigating its oxygen-related dynamics in healthy and diseased states. In the healthy state, we model the oxygen distribution across the human retina, examining the efficacy of the protein neuroglobin in the prevention of hypoxia. It has been suggested that neuroglobin could prevent hypoxia, either by transporting oxygen from regions where it is rich to those where it is poor, or by storing oxygen during periods of diminished supply or increased uptake. Numerical solutions demonstrate that neuroglobin may be effective in preventing or alleviating hypoxia via oxygen transport, but that its capacity for oxygen storage is essentially negligible, whilst asymptotic analysis reveals that, contrary to the prevailing assumption, neuroglobin's oxygen affinity is near optimal for oxygen transport. A further asymptotic analysis justifies the common approximation of a piecewise constant oxygen uptake across the retina, placing existing models upon a stronger theoretical foundation. In the diseased state, we explore the effect of hyperoxia upon the progression of the inherited retinal diseases, known collectively as retinitis pigmentosa. Both numerical solutions and asymptotic analyses show that this mechanism may replicate many of the patterns of retinal degeneration seen in vivo, but that others are inaccessible to it, demonstrating both the strengths and weaknesses of the oxygen toxicity hypothesis. It is shown that the wave speed of hyperoxic degeneration is negatively correlated with the local photoreceptor density, high density regions acting as a barrier to the spread of photoreceptor loss. The effects of capillary degeneration and treatment with antioxidants or trophic factors are also investigated, demonstrating that each has the potential to delay, halt or partially reverse photoreceptor loss. In addition to answering questions that are not accessible to experimental investigation, these models generate a number of experimentally testable predictions, forming the first loop in what has the potential to be a fruitful experimental/modelling cycle.
3
Oduro, Bismark. "Mathematical Models of Triatomine (Re)infestation." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1458563770.
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Zhang, Xu-Sheng. "Mathematical models of plant disease epidemics that involve virus interactions." Thesis, University of Greenwich, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327341.
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Bell, Sally Sue. "Mathematical models assessing the importance of disease on ecological invasions." Thesis, Heriot-Watt University, 2010. http://hdl.handle.net/10399/2316.
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A general understanding of the role that both shared disease and competition may play in ecological invasions is lacking. We develop a theoretical framework to determine the role of disease, in addition to competition, in invasions. We first investigate the e ect of disease characteristics on the replacement time of a native species by an invader. The outcome is critically dependent on the relative e ects that the disease has on the two species and less dependent on the basic epidemiological characteristics of the interaction. This framework is extended to investigate the e ect of disease on the spatial spread of an invader and indicates that a wave of disease spreads through a native population in advance of the replacement. A probabilistic simulation model is developed to examine the particular example of the replacement of red squirrels by grey squirrels in the United Kingdom. This model is used to examine conservation strategies employed within red squirrel refuges and compared to observations from Sefton Coast Red Squirrel Refuge. Our findings indicate that culling greys may be e ective at protecting red populations from replacement, but none of the conservation strategies currently employed can prevent periodic outbreaks of infection within red squirrel refuges.
6
Korobeinikov, Andrei. "Stability and bifurcation of deterministic infectious disease models." Thesis, University of Auckland, 2001. http://wwwlib.umi.com/dissertations/fullcit/3015611.
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Autonomous deterministic epidemiological models are known to be asymptotically stable. Asymptotic stability of these models contradicts observations. In this thesis we consider some factors which were suggested as able to destabilise the system. We consider discrete-time and continuous-time autonomous epidemiological models. We try to keep our models as simple as possible and investigate the impact of different factors on the system behaviour. Global methods of dynamical systems theory, especially the theory of bifurcations and the direct Lyapunov method are the main tools of our analysis. Lyapunov functions for a range of classical epidemiological models are introduced. The direct Lyapunov method allows us to establish their boundedness and asymptotic stability. It also helps investigate the impact of such factors as susceptibles' mortality, horizontal and vertical transmission and immunity failure on the global behaviour of the system. The Lyapunov functions appear to be useful for more complicated epidemiological models as well. The impact of mass vaccination on the system is also considered. The discrete-time model introduced here enables us to solve a practical problem-to estimate the rate of immunity failure for pertussis in New Zealand. It has been suggested by a number of authors that a non-linear dependence of disease transmission on the numbers of infectives and susceptibles can reverse the stability of the system. However it is shown in this thesis that under biologically plausible constraints the non-linear transmission is unable to destabilise the system. The main constraint is a condition that disease transmission must be a concave function with respect to the number of infectives. This result is valid for both the discrete-time and the continuous-time models. We also consider the impact of mortality associated with a disease. This factor has never before been considered systematically. We indicate mechanisms through which the disease-induced mortality can affect the system and show that the disease-induced mortality is a destabilising factor and is able to reverse the system stability. However the critical level of mortality which is necessary to reverse the system stability exceeds the mortality expectation for the majority of human infections. Nevertheless the disease-induced mortality is an important factor for understanding animal diseases. It appears that in the case of autonomous systems there is no single factor able to cause the recurrent outbreaks of epidemics of such magnitudes as have been observed. It is most likely that in reality they are caused by a combination of factors.<br>Subscription resource available via Digital Dissertations
7
Ning, Yao, and 宁耀. "The use of stochastic models of infectious disease transmission for public health: schistosomiasis japonica." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B4553097X.
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Bingham, Adrienna N. "Controlling Infectious Disease: Prevention and Intervention Through Multiscale Models." W&M ScholarWorks, 2019. https://scholarworks.wm.edu/etd/1582642581.
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Controlling infectious disease spread and preventing disease onset are ongoing challenges, especially in the presence of newly emerging diseases. While vaccines have successfully eradicated smallpox and reduced occurrence of many diseases, there still exists challenges such as fear of vaccination, the cost and difficulty of transporting vaccines, and the ability of attenuated viruses to evolve, leading to instances such as vaccine derived poliovirus. Antibiotic resistance due to mistreatment of antibiotics and quickly evolving bacteria contributes to the difficulty of eradicating diseases such as tuberculosis. Additionally, bacteria and fungi are able to produce an extracellular matrix in biofilms that protects them from antibiotics/antifungals. Mathematical models are an effective way of measuring the success of various control measures, allowing for cost savings and efficient implementation of those measures. While many models exist to investigate the dynamics on a human population scale, it is also beneficial to use models on a microbial scale to further capture the biology behind infectious diseases. In this dissertation, we develop mathematical models at several spatial scales to help improve disease control. At the scale of human populations, we develop differential equation models with quarantine control. We investigate how the distribution of exposed and infectious periods affects the control efficacy and suggest when it is important for models to include realistically narrow distributions. At the microbial scale, we use an agent-based stochastic spatial simulation to model the social interactions between two yeast strains in a biofilm. While cheater strains have been proposed as a control strategy to disrupt the harmful cooperative biofilm, some yeast strains cooperate only with other cooperators via kin recognition. We study under what circumstances kin recognition confers the greatest fitness benefit to a cooperative strain. Finally, we look at a multiscale, two-patch model for the dynamics between wild-type (WT) poliovirus and defective interfering particles (DIPs) as they travel between organs. DIPs are non-viable variants of the WT that lack essential elements needed for reproduction, causing them to steal these elements from the WT. We investigate when DIPs can lower the WT population in the host.
9
Kwong, Kim-hung, and 鄺劍雄. "Spatio-temporal transmission modelling of an infectious disease: a case study of the 2003 SARS outbreak in Hong Kong." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45693900.
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Venkatachalam, Sangeeta. "Modeling Infectious Disease Spread Using Global Stochastic Field Simulation." Thesis, University of North Texas, 2006. https://digital.library.unt.edu/ark:/67531/metadc5335/.
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Susceptibles-infectives-removals (SIR) and its derivatives are the classic mathematical models for the study of infectious diseases in epidemiology. In order to model and simulate epidemics of an infectious disease, a global stochastic field simulation paradigm (GSFS) is proposed, which incorporates geographic and demographic based interactions. The interaction measure between regions is a function of population density and geographical distance, and has been extended to include demographic and migratory constraints. The progression of diseases using GSFS is analyzed, and similar behavior to the SIR model is exhibited by GSFS, using the geographic information systems (GIS) gravity model for interactions. The limitations of the SIR and similar models of homogeneous population with uniform mixing are addressed by the GSFS model. The GSFS model is oriented to heterogeneous population, and can incorporate interactions based on geography, demography, environment and migration patterns. The progression of diseases can be modeled at higher levels of fidelity using the GSFS model, and facilitates optimal deployment of public health resources for prevention, control and surveillance of infectious diseases.
11
Lutambi, Angelina Mageni. "Basic properties of models for the spread of HIV/AIDS." Thesis, Stellenbosch : Stellenbosch University, 2007. http://hdl.handle.net/10019.1/19641.
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Thesis (MSc)--University of Stellenbosch, 2007.<br>ENGLISH ABSTRACT: While research and population surveys in HIV/AIDS are well established in
developed countries, Sub-Saharan Africa is still experiencing scarce HIV/AIDS
information. Hence it depends on results obtained from models. Due to this
dependence, it is important to understand the strengths and limitations of
these models very well.
In this study, a simple mathematical model is formulated and then extended
to incorporate various features such as stages of HIV development, time delay
in AIDS death occurrence, and risk groups. The analysis is neither purely
mathematical nor does it concentrate on data but it is rather an exploratory
approach, in which both mathematical methods and numerical simulations
are used.
It was found that the presence of stages leads to higher prevalence levels in
a short term with an implication that the primary stage is the driver of the
disease. Furthermore, it was found that time delay changed the mortality
curves considerably, but it had less effect on the proportion of infectives. It
was also shown that the characteristic behaviour of curves valid for most
epidemics, namely that there is an initial increase, then a peak, and then a decrease occurs as a function of time, is possible in HIV only if low risk
groups are present.
It is concluded that reasonable or quality predictions from mathematical
models are expected to require the inclusion of stages, risk groups, time
delay, and other related properties with reasonable parameter values.<br>AFRIKAANSE OPSOMMING: Terwyl navorsing en bevolkingsopnames oor MIV/VIGS in ontwikkelde lande
goed gevestig is, is daar in Afrika suid van die Sahara slegs beperkte inligting
oor MIV/VIGS beskikbaar. Derhalwe moet daar van modelle gebruik
gemaak word. Dit is weens hierdie feit noodsaaklik om die moontlikhede en
beperkings van modelle goed te verstaan.
In hierdie werk word ´n eenvoudige model voorgelˆe en dit word dan uitgebrei
deur insluiting van aspekte soos stadiums van MIV outwikkeling, tydvertraging
by VIGS-sterftes en risikogroepe in bevolkings. Die analise is beklemtoon
nie die wiskundage vorme nie en ook nie die data nie. Dit is eerder ´n
verkennende studie waarin beide wiskundige metodes en numeriese simula˙sie
behandel word.
Daar is bevind dat insluiting van stadiums op korttermyn tot ho¨er voorkoms
vlakke aanleiding gee. Die gevolgtrekking is dat die primˆere stadium die
siekte dryf. Verder is gevind dat die insluiting van tydvestraging wel die
kurwe van sterfbegevalle sterk be¨ınvloed, maar dit het min invloed op die
verhouding van aangestekte persone. Daar word getoon dat die kenmerkende
gedrag van die meeste epidemi¨e, naamlik `n aanvanklike styging, `n piek en dan `n afname, in die geval van VIGS slegs voorkom as die bevolking dele
bevat met lae risiko.
Die algehele gevolgtrekking word gemaak dat vir goeie vooruitskattings met
sinvolle parameters, op grond van wiskundige modelle, die insluiting van
stadiums, risikogroepe en vertragings benodig word.
12
Ejigu, Amsalework Ayele. "Mathematical modelling of HIV/AIDS transmission under treatment structured by age of infection." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6628.
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Thesis (MSc (Mathematical Sciences))--University of Stellenbosch, 2011.<br>Includes bibliography.<br>ENGLISH ABSTRACT: This thesis takes into account the different levels of infectiousness of the human immunodeficiency
virus (HIV) infected individuals throughout their period of infection. Infectiousness
depends on the time since infection. It is high shortly after the infection occurs and
then much lower for several years, and thereafter a higher plateau is reached before the acquired
immunodeficiency syndrome (AIDS) phase sets in. In line with this, we formulated
a mathematical model which is structured according to the age of infection. To understand
the dynamics of the disease, we first discuss and analyse a simple model in which the age
of infection is not considered, but progression of the HIV-AIDS transmission is taken into
consideration by introducing three stages of infection. Analysis of these models tells us
that the disease can be eradicated from the population only if on average one infected
individual infects less than one person in his or her infectious period, otherwise the disease
persists. To investigate the reduction of the number of infections caused by a single infectious
individual to less than one, we introduce different treatment strategies for a model
which depends on the age of infection, and we analyse it numerically. Current strategies
amount to introducing treatment only at a late stage of infection when the infected individual
has already lived through most of the infectious period. From our numerical results,
this strategy does not result in eradication of the disease, even though it does reduce the
burden for the individual. To eradicate the disease from the population, everyone would
need to be HIV tested regularly and undergo immediate treatment if found positive.<br>AFRIKAANSE OPSOMMING: Hierdie tesis hou rekening met die verskillende aansteeklikheidsvlakke van die menslike
immuniteitsgebreksvirus (MIV) deur besmette individue gedurende hulle aansteeklikheidstydperk.
Die graad van aansteeklikheid hang af van die tydperk sedert infeksie. Dit is
hoog kort nadat die infeksie plaasvind en daarna heelwat laer vir etlike jare, en dan volg
n hoer plato voordat uiteindelik die Verworwe-Immuniteitsgebreksindroom (VIGS) fase
intree. In ooreenstemming hiermee, formuleer ons n wiskundige model van MIV-VIGSoordrag
met n struktureer waarin die tydperk sedert infeksie bevat is. Om die dinamika
van die siekte te verstaan, bespreek en analiseer ons eers n eenvoudige model sonder inagneming
van die tydperk sedert infeksie, terwyl die progressie van MIV-VIGS-oordrag egter
wel in ag geneem word deur die beskouing van drie stadiums van infeksie. Analise van die
modelle wys dat die siekte in die bevolking slegs uitgeroei kan word as elke besmette mens
gemiddeld minder as een ander individu aansteek gedurende die tydperk waarin hy of sy
self besmet is, anders sal die siekte voortduur. Vir die ondersoek oor hoe om die aantal
infeksies per besmette individu tot onder die waarde van een te verlaag, beskou ons verskeie
behandelingsstrategiee binne die model, wat afhang van die tydperk sedert infeksie, en ondersoek
hulle numeries. Die huidige behandelingstrategiee kom neer op behandeling slegs
gedurende die laat sta- dium van infeksie, wanneer die besmette individu reeds die grootste
deel van die aansteeklikheidsperiode deurleef het. Ons numeriese resultate toon dat hierdie
strategie nie lei tot uitroeiing van die siekte nie, alhoewel dit wel die las van die siekte vir
die individu verminder. Om die siekte binne die bevolking uit te roei, sou elkeen gereeld
vir MIV getoets moes word en indien positief gevind, dadelik met behandeling moes begin.
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Thompson, Brett Morinaga. "Development, Implementation, and Analysis of a Contact Model for an Infectious Disease." Thesis, University of North Texas, 2009. https://digital.library.unt.edu/ark:/67531/metadc9824/.
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With a growing concern of an infectious diseases spreading in a population, epidemiology is becoming more important for the future of public health. In the past epidemiologist used existing data of an outbreak to help them determine how an infectious disease might spread in the future. Now with computational models, they able to analysis data produced by these models to help with prevention and intervention plans. This paper looks at the design, implementation, and analysis of a computational model based on the interactions of the population between individuals. The design of the working contact model looks closely at the SEIR model used as the foundation and the two timelines of a disease. The implementation of the contact model is reviewed while looking closely at data structures. The analysis of the experiments provide evidence this contact model can be used to help epidemiologist study the spread of an infectious disease based on the contact rate of individuals.
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Kwok, Kin-on, and 郭健安. "Models of directly transmitted respiratory pathogens in hospitals and households." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40687557.
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Porter, Rosalyn. "Mathematical models of a tick borne disease in a British game bird with potential management strategies." Thesis, University of Stirling, 2011. http://hdl.handle.net/1893/3039.
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Louping ill virus (LIV) is a tick borne disease that causes mortality in red grouse, an economically important game bird of British uplands. The aim of this thesis is to extend previously published models of LIV , to consider the potential impact of different management strategies. In addition a new route of infection and the seasonal biology of both grouse and ticks will be explored. Grouse chicks are known to eat ticks as part of their diet in the first three weeks of life which may contribute to virus persistence if chicks consume infected ticks. This novel route of infection is incorporated in to the model which predicts that ingestion increases the range of host densities for which the virus is able to persist. The ingestion of ticks by grouse also reduces the tick population so that for low host densities the ingestion of ticks by grouse reduces the tick population so virus cannot persist. The model is adapted to take account of the seasonal biology of grouse and ticks. Although the temporal predictions of the seasonal models show some differences the addition of seasonality does not alter the model predictions of when LIV is likely to persist at different grouse and deer densities. Consequently seasonality is felt to be unimportant when considering management strategies. The treatment of sheep with acaricide in an attempt to reduce the tick population on a grouse moor is currently being trialled in Scotland. We use a model to predict the likely effect of this strategy at different deer densities. The number of ticks found attached to sheep varies so we consider the effect of tick attachment rates as well as acaricide efficacy. Although we predict that acaricide treated sheep can reduce the tick population and therefore LIV in grouse in some circumstances the treatment is less effective in the presence of deer. Consequently we use a model to make theoretical predictions of the effectiveness of acaricide treated deer as a control strategy for reducing LIV in red grouse. The effect of culling deer on LIV in grouse is also modelled and contrasted with the effect of acaricide use. It is predicted that acaricide treatment of deer could be highly effective, particularly if the deer density is first reduced by culling. Finally we considered the direct treatment of red grouse with acaricide. Female grouse can be given an acaricidal leg band which protects her directly and indirectly protects her chicks as they acquire some acaricide whilst brooding. Trials have suggested this can reduce tick burdens for individuals. We use the model to determine the potential effect that treating individual broods may have on the whole grouse population. The model predictions suggest that unless acaricide efficacy on chicks is high and long lasting treating individual broods is unlikely to reduce LIV in the whole population but will still provide some benefit for the individuals. The effectiveness of treatment is reduced by higher deer densities. The success of the management strategies considered in this thesis appear to be restricted by the presence of deer. It may therefore be that a combination of treatments including the treatment of deer may be of the greatest benefit to the grouse population.
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Worton, Adrian J. "Using mathematical models to understand the impact of climate change on tick-borne infections across Scotland." Thesis, University of Stirling, 2016. http://hdl.handle.net/1893/24918.
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Ticks are of global interest as the pathogens they spread can cause diseases that are of importance to both human health and economies. In Scotland, the most populous tick species is the sheep tick Ixodes ricinus, which is the vector of pathogens causing diseases such as Lyme borreliosis and Louping-ill. Recently, both the density and spread of I. ricinus ticks have grown across much of Europe, including Scotland, increasing disease risk. Due to the nature of the tick lifecycle they are particularly dependent on environmental factors, including temperature and habitat type. Because of this, the recent increase in tick-borne disease risk is believed to be linked to climate change. Many mathematical models have been used to explore the interactions between ticks and factors within their environments; this thesis begins by presenting a thorough review of previous modelling of tick and tick-borne pathogen dynamics, identifying current knowledge gaps. The main body of this thesis introduces an original mathematical modelling framework with the aim to further our understanding of the impact of climate change on tick-borne disease risk. This modelling framework takes into account how key environmental factors influence the I. ricinus lifecycle, and is used to create predictions of how I. ricinus density and disease risk will change across Scotland under future climate warming scenarios. These predictions are mapped using Geographical Information System software to give a clear spatial representation of the model predictions. It was found that as temperatures increase, so to do I. ricinus densities, as well as Louping-ill and Lyme borreliosis risk. These results give a strong indication of the disease risk implications of any changes to the Scottish environment, and so have the potential to inform policy-making. Additionally, the models identify areas of possible future research.
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Holgado, Alejo J. "Construction and study of mathematical models firmly based on neurophysiological data to investigate Parkinson's disease and epilepsy." Thesis, University of Bristol, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540899.
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Fino, Angela. "A mathematical macroscopic model for the onset and progression of Alzheimer's disease." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/17130/.
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In this work we deal with the study of a macroscopic mathematical model which describes the onset and progression of Alzheimer’s disease (AD) in the human brain. In particular, we analyze in detail the well-posedness of the model itself. The model is based on the so-called “amyloid cascade hypothesis” together with the “prionoid hypothesis”, which represents the spreading of the disease through neuron-to-neuron transmission. In particular, from a mathematical point of view, the model consists of a transport equation for a probability measure, coupled with a nonlinear Smoluchowski-type system with a diffusion term. In view of the features of the biological phenomena we are dealing with, the main hallmark of such a system is that the two groups of equations cannot be separated and they must be considered together. The main tools to prove existence and uniqueness of the solution of the problem coupled with appropriate initial and boundary conditions are: the definition of an appropriate metric space obtained by endowing with the Wasserstein distance the space of Borel probability measures supported on a bounded interval; the transport of measures along the characteristics of the transport equation; an ad hoc formulation of the classical contraction theorem and a priori estimates for solutions of the reaction diffusion equations.
19
Fiorentino, Francesca. "Mathematical models of the impact of rabbit calicivirus disease (RCD) on the European rabbit, Oryctolagus cuniculus, in Australia." Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1446810/.
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This thesis relates to the work of building a mathematical model of the impact of Rabbit Calicivirus Disease (RCD) on the European Rabbit, Oryctolagus cuniculus, in Australia. After introducing the general biology of rabbits and the immunology of RCD, we build a time-dependent single site model. We construct a single-site population dynamic model with age structure, seasonal birth rate, density dependent regulation of the population size and climatic variability for various regions of Australia. After investigating suitable parameter ranges, we incorporate the disease dynamics through an indirect transmission model based on two different hypotheses which we call the Strong Juvenile hypothesis and the Weak Juvenile hypothesis. These differ in their assumption about Juvenile immunity to the disease. The ecological impact of both hypotheses is tested for both the single site and multiple site (spatial) models. The disease impact is investigated by varying the disease virulence, i.e. a parameter measuring the "strength" of the virus. Subsequently, a multiple site (spatial) model for the Riverina region is built by using the single-site model as building block. Data from Lake Urana is used to parameterize a seasonal emigration rate from each site. Density dependent immigration is added together with a hazard coefficient which rabbits face when leaving one site and trying to become established in another. Acceptance in a new site is regulated by the population density at the entry site. Several spatial configurations of sites are tested and the spatial dynamics of the disease is investigated. Finally, we construct a model to investigate the long term evolution of the disease virus. We postulate the existence of several strains of the disease and trade-offs between disease characteristics. We allow for mutation of the virus and run the model for two contrasting geographical regions of Australia. We compare the results for the different regions and the different hypotheses regarding Juvenile immunity (the Strong Juvenile hypothesis and the Weak Juvenile hypothesis). It is shown, unexpectedly, that intermediate levels of disease virulence are not selected.
20
Yu, Peng, and 于朋. "Air pollution and respiratory disease incidence of Guangzhou: a study of spatial interpolation methodsusing GIS, 2003-2004." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B41633799.
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Rosà, Roberto. "The importance of aggregation in the dynamics of host-parasite interaction in wildlife : a mathematical approach." Thesis, University of Stirling, 2003. http://hdl.handle.net/1893/50.
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This study examines, from a modelling point of view, the dynamics of infectious diseases in wildlife caused by macroparasites and by tick-borne infections. The overall aim was to investigate the important role played by parasite aggregation in the dynamics of both systems. For macroparasites we first developed some deterministic models that incorporate explicit mechanisms for generating aggregation in parasite distribution, specifically multiple infections and host heterogeneity. We explored the role of aggregation in host regulation and in determining a threshold value for parasite establishment. A large aggregation makes it more difficult for parasites both to regulate hosts, and to get established in a population at carrying capacity. Furthermore, the stabilization yielded by aggregation strongly depends on the mechanism that produces the aggregation. We then introduced some uncertainties into the host-macroparasite system, presenting an individual-based stochastic model that incorporated the same assumptions as the deterministic model. Stochastic simulations, using parameter values based on some real case studies, preserved many features of the deterministic model, like the average value of the variables and the approximate length of the cycles. An important difference is that, even when deterministic models yield damped oscillations, stochastic simulations yield apparently sustained oscillations. The amplitude of such oscillations may be so large as to threaten the parasites’ persistence. With respect to tick-borne diseases we presented a general model framework that incorporated both viraemic and non-viraemic routes of infections. We compute the threshold for disease persistence and study its dependence on the parameters and on host densities. The effects of tick aggregation and correlation between different tick stages on the host have both an important effect on infection persistence, if non-viraemic transmission occurred. In the case of Lyme Disease and Tick-borne Encephalitis (TBE) in Trentino (northern Italy) we showed some numerical results, using parameter estimates based on a detailed field study, and explored the effects of uncertainty on the endemic equilibrium of both diseases assuming only viraemic transmission for Lyme Disease while for TBE we permitted only non-viraemic transmission through co-feeding ticks. In conclusion we have examined the patterns and changes of aggregation in a number of contrasting systems and believe that these studies highlight both the importance of considering heterogeneities in modelling host-parasite interactions and, more specifically, modelling the biological mechanisms that produce aggregation in parasite distributions.
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Gutierrez, Louis Michael. "Agent-based simulation of disease spread aboard ship." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Mar%5FGutierrez.pdf.
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Thesis (M.S. in Modeling, Virtual Environments and Simulations (MOVES))--Naval Postgraduate School, March 2005.<br>Thesis Advisor(s): Chris Darken. Includes bibliographical references (p. 47-48). Also available online.
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Ireland, Jillian M. "Using mathematical models to determine the effect of seasonal host birth rates on population dynamics of infectious disease systems." Thesis, University of Stirling, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440776.
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O'Neill, II Martin Joseph. "Computational Epidemiology - Analyzing Exposure Risk: A Deterministic, Agent-Based Approach." Thesis, University of North Texas, 2009. https://digital.library.unt.edu/ark:/67531/metadc11017/.
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Many infectious diseases are spread through interactions between susceptible and infectious individuals. Keeping track of where each exposure to the disease took place, when it took place, and which individuals were involved in the exposure can give public health officials important information that they may use to formulate their interventions. Further, knowing which individuals in the population are at the highest risk of becoming infected with the disease may prove to be a useful tool for public health officials trying to curtail the spread of the disease. Epidemiological models are needed to allow epidemiologists to study the population dynamics of transmission of infectious agents and the potential impact of infectious disease control programs. While many agent-based computational epidemiological models exist in the literature, they focus on the spread of disease rather than exposure risk. These models are designed to simulate very large populations, representing individuals as agents, and using random experiments and probabilities in an attempt to more realistically guide the course of the modeled disease outbreak. The work presented in this thesis focuses on tracking exposure risk to chickenpox in an elementary school setting. This setting is chosen due to the high level of detailed information realistically available to school administrators regarding individuals' schedules and movements. Using an agent-based approach, contacts between individuals are tracked and analyzed with respect to both individuals and locations. The results are then analyzed using a combination of tools from computer science and geographic information science.
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Corley, Courtney D. "Modeling the Impact and Intervention of a Sexually Transmitted Disease: Human Papilloma Virus." Thesis, University of North Texas, 2006. https://digital.library.unt.edu/ark:/67531/metadc5289/.
Full textAbstract:
Many human papilloma virus (HPV) types are sexually transmitted and HPV DNA types 16, 18, 31, and 45 account for more than 75% if all cervical dysplasia. Candidate vaccines are successfully completing US Federal Drug Agency (FDA) phase III testing and several drug companies are in licensing arbitration. Once this vaccine become available it is unlikely that 100% vaccination coverage will be probable; hence, the need for vaccination strategies that will have the greatest reduction on the endemic prevalence of HPV. This thesis introduces two discrete-time models for evaluating the effect of demographic-biased vaccination strategies: one model incorporates temporal demographics (i.e., age) in population compartments; the other non-temporal demographics (i.e., race, ethnicity). Also presented is an intuitive Web-based interface that was developed to allow the user to evaluate the effects on prevalence of a demographic-biased intervention by tailoring the model parameters to specific demographics and geographical region.
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Shi, Zhenzhen. "A MARKOV DECISION PROCESS EMBEDDED WITH PREDICTIVE MODELING: A MODELING APPROACH FROM SYSTEM DYNAMICS MATHEMATICAL MODELS, AGENT-BASED MODELS TO A CLINICAL DECISION MAKING." Diss., Kansas State University, 2015. http://hdl.handle.net/2097/20578.
Full textAbstract:
Doctor of Philosophy<br>Department of Industrial & Manufacturing Systems Engineering<br>David H. Ben-Arieh<br>Chih-Hang Wu<br>Patients who suffer from sepsis or septic shock are of great concern in the healthcare system. Recent data indicate that more than 900,000 severe sepsis or septic shock cases developed in the United States with mortality rates between 20% and 80%. In the United States alone, almost $17 billion is spent each year for the treatment of patients with sepsis. Clinical trials of treatments for sepsis have been extensively studied in the last 30 years, but there is no general agreement of the effectiveness of the proposed treatments for sepsis. Therefore, it is necessary to find accurate and effective tools that can help physicians predict the progression of disease in a patient-specific way, and then provide physicians recommendation on the treatment of sepsis to lower risk for patients dying from sepsis.
The goal of this research is to develop a risk assessment tool and a risk management tool for sepsis. In order to achieve this goal, two system dynamic mathematical models (SDMMs) are initially developed to predict dynamic patterns of sepsis progression in innate immunity and adaptive immunity. The two SDMMs are able to identify key indicators and key processes of inflammatory responses to an infection, and a sepsis progression. Second, an integrated-mathematical-multi-agent-based model (IMMABM) is developed to capture the stochastic nature embedded in the development of inflammatory responses to a sepsis. Unlike existing agent-based models, this agent-based model is enhanced by incorporating developed SDMMs and extensive experimental data. With the risk assessment tools, a Markov decision process (MDP) is proposed, as a risk management tool, to apply to clinical decision-makings on sepsis.
With extensive computational studies, the major contributions of this research are to firstly develop risk assessment tools to identify the risk of sepsis development during the immune system responding to an infection, and secondly propose a decision-making framework to manage the risk of infected individuals dying from sepsis.
The methodology and modeling framework used in this dissertation can be expanded to other disease situations and treatment applications, and have a broad impact to the research area related to computational modeling, biology, medical decision-making, and industrial engineering.
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Yu, Xiaohong, and 于曉紅. "Hemodynamic analysis of blood flows in carotid bifurcations." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B3864700X.
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Liu, Jie. "Novel Bayesian Methods for Disease Mapping: An Application to Chronic Obstructive Pulmonary Disease." Link to electronic thesis, 2002. http://www.wpi.edu/Pubs/ETD/Available/etd-0501102-110350.
Full textAbstract:
Thesis (M.S.)--Worcester Polytechnic Institute.<br>Keywords: latent class model; Poisson regression model; Metropolis-Hastings sampler; order restriction; disease mapping. Includes bibliographical references.
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Majeke, Lunga. "Preliminary investigation into estimating eye disease incidence rate from age specific prevalence data." Thesis, University of Fort Hare, 2011. http://hdl.handle.net/10353/464.
Full textAbstract:
This study presents the methodology for estimating the incidence rate from the age specific prevalence data of three different eye diseases. We consider both situations where the mortality may differ from one person to another, with and without the disease. The method used was developed by Marvin J. Podgor for estimating incidence rate from prevalence data. It delves into the application of logistic regression to obtain the smoothed prevalence rates that helps in obtaining incidence rate. The study concluded that the use of logistic regression can produce a meaningful model, and the incidence rates of these diseases were not affected by the assumption of differential mortality.
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Chen, Yao-Hsuan. "Network modeling of sexually transmitted diseases." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51883.
Full textAbstract:
We create a dynamic network model to replicate more closely the population network structures of interest. Network, Norms and HIV/STI Risk Among Youth (NNAHRAY) is a community relationship survey data set, which provides a rare sample of a human risky-behavior contact network. Combining disease compartmental models with our dynamic network model, we simulate the spread of Human Immunodeficiency Virus (HIV) and Herpes Simplex Type 2 Virus (HSV2) with consideration of HSV2's synergistic impact on HIV's transmission. Our model reproduces HIV prevalence, HSV-2 prevalence, and the contact network close to those observed in NNAHRAY, with HIV annual prevalence closer to the estimated values from the literature than those of any disease spread model based on static networks. The success of fitting our model to the target data shows the importance of considering the data sampling process, contact dynamics, and contact network structures. Our model, under certain conditions, has prevalence prediction results that are insensitive to changes in network size. The analysis of various prevention/intervention strategies targeting different risky groups gives important insights into strategy prioritization and illustrates how our model can be used to assist in making public health policy decisions in practice, both for individual diseases and in the more-recent area of study that considers synergy between two diseases.
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McBryde, Emma Sue. "Mathematical and statistical modelling of infectious diseases in hospitals." Queensland University of Technology, 2006. http://eprints.qut.edu.au/16330/.
Full textAbstract:
Antibiotic resistant pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant enterococci (VRE), are an increasing burden on healthcare systems. Hospital acquired infections with these organisms leads to higher morbidity and mortality compared with the sensitive strains of the same species and both VRE and MRSA are on the rise worldwide including in Australian hospitals. Emerging community infectious diseases are also having an impact on hospitals. The Severe Acute Respiratory Syndrome virus (SARS Co-V) was noted for its propensity to spread throughout hospitals, and was contained largely through social distancing interventions including hospital isolation. A detailed understanding of the transmission of these and other emerging pathogens is crucial for their containment. The statistical inference and mathematical models used in this thesis aim to improve understanding of pathogen transmission by estimating the transmission rates of contagions and predicting the impact of interventions. Datasets used for these studies come from the Princess Alexandra Hospital in Brisbane, Australia and Shanxi province, mainland China. Epidemiological data on infection outbreaks are challenging to analyse due to the censored nature of infection transmission events. Most datasets record the time on symptom onset, but the transmission time is not observable. There are many ways of managing censored data, in this study we use Bayesian inference, with transmission times incorporated into the augmented dataset as latent variables. Hospital infection surveillance data is often much less detailed that data collected for epidemiological studies, often consisting of serial incidence or prevalence of patient colonisation with a resistant pathogen without individual patient event histories. Despite the lack of detailed data, transmission characteristics can be inferred from such a dataset using structured HiddenMarkovModels (HMMs). Each new transmission in an epidemic increases the infection pressure on those remaining susceptible, hence infection outbreak data are serially dependent. Statistical methods that assume independence of infection events are misleading and prone to over-estimating the impact of infection control interventions. Structured mathematical models that include transmission pressure are essential. Mathematical models can also give insights into the potential impact of interventions. The complex interaction of different infection control strategies, and their likely impact on transmission can be predicted using mathematical models. This dissertation uses modified or novel mathematical models that are specific to the pathogen and dataset being analysed. The first study estimates MRSA transmission in an Intensive Care Unit, using a structured four compartment model, Bayesian inference and a piecewise hazard methods. The model predicts the impact of interventions, such as changes to staff/patient ratios, ward size and decolonisation. A comparison of results of the stochastic and deterministic model is made and reason for differences given. The second study constructs a Hidden Markov Model to describe longitudinal data on weekly VRE prevalence. Transmission is assumed to be either from patient to patient cross-transmission or sporadic (independent of cross-transmission) and parameters for each mode of acquisition are estimated from the data. The third study develops a new model with a compartment representing an environmental reservoir. Parameters for the model are gathered from literature sources and the implications of the environmental reservoir are explored. The fourth study uses a modified Susceptible-Exposed-Infectious-Removed (SEIR) model to analyse data from a SARS outbreak in Shanxi province, China. Infectivity is determined before and after interventions as well as separately for hospitalised and community symptomatic SARS cases. Model diagnostics including sensitivity analysis, model comparison and bootstrapping are implemented.
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Njagarah, Hatson John Boscoh. "Modelling the role of amelioration and drug lords on drug epidemics and the impact of substance abuse on the dynamics of HIV/AIDS." Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/17935.
Full textAbstract:
Thesis (MSc)--Stellenbosch University, 2011.<br>ENGLISH ABSTRACT: Substance abuse is an imminent danger on the health of both substance users and nonusers.
In general, abuse of psychoactive substances is associated with high risk behaviour,
mortality and morbidity. The drug use cycle involves inextricably intertwined variants
such as production, trading and usage of both licit and illicit addictive substances. The
dynamics of substance use involve initiation, addiction, rehabilitation/treatment and quitting/
recovery. In response to supply and abuse of monster drugs, control strategies such
as law enforcement and rehabilitation have been stepped up to reduce access to drugs by
targeting drug kingpins and harm reduction respectively. In this thesis, we model the factors
affecting the prevalence of substance abuse, the effect of drug lords on the prevalence
of substance abuse, and the impact of substance abuse on the prevalence of HIV/AIDS.
We formulate mathematical models based on systems of autonomous differential equations
describing the dynamics of the sub- populations involved in the drug using cycle.
We examine the effects of amelioration, rehabilitation/treatment and re- initiation on the
prevalence of substance abuse. Our results suggest that, recruitment into rehabilitation
and amelioration in the presence of quitting for light users reduce the prevalence of substance
abuse; re-initiation and amelioration without quitting for light users increase the
prevalence of substance abuse. Our assessment of the impact of drug lords and the effect
of law enforcement on drug epidemics shows that, the presence of drug lords seriously
constraints the efforts to reduce substance abuse since they increase access to drugs. However,
law enforcement if stepped up in response to the population of drug lords, greatly
reduces the prevalence of substance abuse. Given the associated influence of drugs on high
risky behaviour, as a cofactor for sexually transmitted infections, we assess the influence of
substance abuse on the prevalence of Human Immunodeficiency Virus (HIV). Our results
show that dissemination of information regarding HIV and drug use reduces HIV prevalence
whereas, there is faster spread of the epidemic and high prevalence with increased
sexual contact.<br>AFRIKAANSE OPSOMMING: Dwelmmisbruik is ’n dreigende gevaar vir die gesondheid van beide dwelm gebruikers en
nie-gebruikers. In die algemeen, word die misbruik van psigoaktiewe dwelms verbind met
hoë risiko gedrag, mortaliteit en morbiditeit. Die dwelmgebruikskringloop behels onlosmaaklik
vervlegde variante soos vervaardiging, handel en gebruik van beide wettige en
onwettige verslawende middels. Die dinamika van dwelms behels aanvang, verslawing, rehabilitasie/
behandeling en staking/herstel. In reaksie op die misbruik en verskaffing van
monster dwelms, is beheer strategieë soos wetstoepassing en rehabilitasie verskerp, om
die toegang tot dwelms te verminder, deur onderskeidelik te fokus op dwelmspilfigure en
skadebeperking. Die belangrikste doel van hierdie verhandeling is om die faktore te modelleer
wat die voorkoms van dwelmmisbruik beïnvloed, die uitwerking van dwelmbase op
die voorkoms van dwelmmisbruik, en die trefkrag van dwelmmisbruik op die voorkoms van
MIV / VIGS. Ons formuleer wiskundige modelle gegrond op stelsels van outonome differensiaalvergelykings,
wat die dinamika beskryf van die sub-bevolkinge wat in die dwelmgebruikskringloop
betrokke is. Ons ondersoek die effekte van verbetering, rehabilitasie/behandeling
en heraanvang op die voorkoms van dwelmmisbruik. Ons resultate dui dat,
werwing tot rehabilitasie en verbetering in die teenwoordigheid van stakende tydelike verbruikers,
die voorkoms van dwelmmisbruik verminder; heraanvang en verbetering sonder
dat tydelike verbruikers staak, verhoog die voorkoms van dwelmmisbruik. Ons raming van
die invloed van dwelmbase en die uitwerking van wetstoepassing op dwelm-epidemies toon
dat, die teenwoordigheid van dwelmbase belemmer grotendeels die pogings om dwelmmisbruik
te verminder, aangesien hulle toegang tot dwelms verhoog. Nietemin, as die wetstoepassing
verskerp word in reaksie op die dwelmbaasbevolking, word die voorkoms van
dwelmmisbruik aansienlik verminder. Gegewe die gepaardgaande invloed van dwelms op
hoë risiko gedrag as ’n kofaktor vir seksueel oordraagbare infeksies, beraam ons die invloed
van dwelmmisbruik op die voorkoms van die Menslike Immunogebreksvirus (MIV). Ons
resultate toon dat inligtingverspreiding rakende MIV en dwelmgebruik, MIV-voorkoms
verlaag, terwyl daar ’n vinniger verspreiding van die epidemie en hoë voorkoms is, met
verhoogde seksuele kontak.
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Mannan, Haider Rashid. "Development and use of a Monte Carlo-Markov cycle tree model for coronary heart disease incidence-mortality and health service usage with explicit recognition of coronary artery revascularization procedures (CARPs)." University of Western Australia. School of Population Health, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0101.
Full textAbstract:
[Truncated abstract] The main objective of this study was to develop and validate a demographic/epidemiologic Markov model for population modelling/forecasting of CARPs as well as CHD deaths and incidence in Western Australia using population, linked hospital morbidity and mortality data for WA over the period 1980 to 2000. A key feature of the model was the ability to count events as individuals moved from one state to another and an important aspect of model development and implementation was the method for estimation of model transition probabilities from available population data. The model was validated through comparison of model predictions with actual event numbers and through demonstration of its use in producing forecasts under standard extrapolation methods for transition probabilities as well as improving the forecasts by taking into account various possible changes to the management of CHD via surgical treatment changes. The final major objective was to demonstrate the use of model for performing sensitivity analysis of some scenarios. In particular, to explore the possible impact on future numbers of CARPs due to improvements in surgical procedures, particularly the introduction of drug eluting stents, and to explore the possible impact of change in trend of CHD incidence as might be caused by the obesity epidemic. ... When the effectiveness of PCI due to introduction of DES was increased by reducing Pr(CABG given PCI) and Pr(a repeat PCI), there was a small decline in the requirements for PCIs and the effect seemed to have a lag. Finally, in addition to these changes when other changes were incorporated which captured that a PCI was used more than a CABG due to a change in health policy after the introduction of DES, there was a small increase in the requirements for PCIs with a lag in the effect. Four incidence scenarios were developed for assessing the effect of change in secular trends of CHD incidence as might be caused by the obesity epidemic in such a way that they gradually represented an increasing effect of obesity epidemic (assuming that other risk factors changed favourably) on CHD incidence. The strategy adopted for developing the scenarios was that based on past trends the most dominant component of CHD incidence was first gradually altered and finally the remaining components were altered. iv The results showed that if the most dominant component of CHD incidence, eg, Pr(CHD - no history of CHD) levelled off and the trends in all other transition probabilities continued into future, then the projected numbers of CABGs and PCIs for 2001-2005 were insensitive to these changes. Even increasing this probability by as much as 20 percent did not alter the results much. These results implied that the short-term effect on projected numbers of CARPs caused by an increase in the most dominant component of CHD incidence, possibly due to an ?obesity epidemic, is small. In the final incidence scenario, two of the remaining CHD incidence components-Pr(CABG - no history of CHD) and Pr(CHD death - no CHD and no history of CHD) were projected to level off over 2001-2005 because these probabilities were declining over the baseline period of 1998-2000. The projected numbers of CABGs were more sensitive (compared to the previous scenarios) to these changes but PCIs were not.
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Bierman, Anandi. "Mapping and survey sequencing of Dn resistance genes in Triticum aestivum L." Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/96912.
Full textAbstract:
Thesis (PhD)--Stellenbosch University, 2015<br>ENGLISH ABSTRACT : Diuraphis noxia Kurdjumov (Russian Wheat Aphid; RWA) is a pest of wheat and barley that has spread from its home range in the fertile crescent to most wheat producing countries except Australia. Since its first introduction to South Africa and the USA in the late 20th century, breeding programs for wheat phenotypes
resistant to the aphid were put in place. Conventional breeding practices rely on phenotypic screening to verify traits carried by offspring and genetic tools such as marker assisted selection (MAS) have greatly aided this process in speed and accuracy. The size and complexity of the wheat genome, its allopolyploid nature and repetitive elements have, however, posed a challenge to studies on the genetics of this cereal crop. Many studies have focused on chromosome 3B which is the largest of the wheat chromosomes and easily separated from the redundant genomic background by techniques such as flow cytometry. The similarity in size of the remaining chromosomes however, limits the application of flow cytometry to their isolation. Databases such as Grain-Genes (http://wheat.pw.usda.gov/GG2/index.shtml) house marker data from various mapping studies for all wheat chromosomes and in 2014 the International Wheat Genome Sequencing Consortium (IWGSC) completed the draft genome sequence of wheat categorized by chromosome. Sources of resistance (Dn resistance genes) against RWA are located on chromosome 7D. but despite the marker and sequence data available currently, mapping studies specific for the Dn resistance genes are few. Additionally, sequence data available is derived from cultivars susceptible to RWA and is not comprehensively annotated and assembled in many cases. In this study, we demonstrate a novel, combined approach to isolate and characterize the Dn resistance genes through the use of a genetic map constructed from Amplified Fragment Length Polymorphism (AFLP), Expressed Sequence Tag (EST) and microsatellite markers and a physical map constructed from Next Generation
Sequencing (NGS) data of ditelosomic chromosomes (7DS and 7DL) isolated by microdissection on the PALM microbeam system. A 122.8 cM genetic map was produced from 38 polymorphic AFLP markers and two ESTs with the microsatellite Xgwm111 as anchor to related genetic maps. Through comparison to maps available on GrainGenes the location of the Dn1 resistance gene was narrowed down to a deletion bin (7DS5-0.36-0.62) on the short arm of chromosome 7D with an AFLP marker (E-ACT/M-CTG_0270.84) mapping closely at 3.5 cM and two ESTs mapping at 15.3 cM and 15.9 cM from Dn1. Isolation of individual chromosome arms 7DS and 7DL using the PALM Microbeam system
allowed sequencing of the chromosome without the redundancy of the remainder
of the hexaploid genome. Through isolating the chromosome arms in this way, a >80-fold reduction in genome size was achieved as well as a major reduction in repetitive elements. Analysis of the sequencing data confirmed that 7DL is the physically shorter arm of the chromosome though it contains the majority of protein coding sequences.<br>AFRIKAANSE OPSOMMING : Diuraphis noxia Kurdjumov (Russiese koring-luis; RWA) is « pes wat op koring en gars voorkom. Die pes het vanaf sy tuiste in die midde Ooste na meeste koringproduserende lande behalwe Australië versprei. Sedert die eerste bekendstelling van RWA in Suid Afrika en die VSA in die vroeë 20ste eeu is teelprogramme
ten gunste van koring lyne met weerstand teen RWA begin. Tradisionele teelprogramme maak op fisieise observasie van die fenotipe staat om te verifieer of plante in die nageslag die gewenste eienskap dra. Genetiese metodes soos merkerondersteunde
seleksie (MAS) versnel hierdie selekteringsproses grootliks. Die grootte en kompleksiteit van die koring genoom asook die polyploïde en herhalende natuur
daarvan is « groot hindernis vir genetiese studies van hierdie graangewas. Baie studies het op chromosoom 3B gefokus wat die grootste van die koring chromosome
is en dus maklik vanaf die res van die oorbodige genomiese agtergond deur tegnieke soos vloeisitometrie geskei word. Die ooreenkoms in grootte tussen die res
van die chromosome bemoeilik die toepassing van vloeisitometrie om hulle te isoleer. Databasisse soos GrainGenes (http://wheat.pw.usda.gov/GG2/index.shtml)
bevat merker data vanaf verskeie karterings-studies vir al die chromosome en in 2014 het die "International Wheat Genome Sequencing Consortium"(IWGSC) die
voorlopige basispaarvolgorde van die koring genoom bekendgestel, gekategoriseer volgens chromosoom. Weerstandsbronne (Dn weerstandsgene) teen RWA kom
meestal op chromosoom 7D voor. Ten spyte van merker en basispaarvolgorde data tans beskikbaar is karterings-studies spesifiek tot die Dn gene skaars en basispaarvolgorde data is vanaf kultivars afkomstig wat nie weerstandbiedend teen RWA is nie en waarvan die annotasie en samestelling baie keer nie goed is nie. In hierdie studie demonstreer ons « nuwe, gekombineerde aanslag om die Dn weerstandsgene te isoleer en karakteriseer deur van « genetiese kaart opgestel met "Amplified Fragment Length Polymorphism"(AFLP), "Expressed Sequence Tag"(EST) en mikrosatelliet
merkers asook « fisiese kaart saamgestel deur die volgende-generasiebasispaarvolgordebepaling
van ditelosomiese chromosome (7DS en 7DL) geïsoleer
deur mikrodisseksie met die "PALM Microbeam"sisteem gebruik te maak. « Genetiese kaart van 122.8 cM was met 38 polimorfiese AFLP merkers en twee EST
merkers geskep. Die mikrosatelliet, Xgwm111, is ook ingesluit en het as anker vir verwante genetiese-kaarte gedien. Deur vergelyking met genetiese-kaarte op
GrainGenes is die posisie van die Dn1 weerstandsgeen vernou na « delesie bin (7DS5-0.36-0.62) op die kort arm van chromosoom 7D met « AFLP merker (EACT/
M-CTG_0270.84) wat ongeveer 3.5 cM vanaf die geen karteer. Die twee EST merkers is 15.3 cM en 15.9 cM vanaf die geen gekarteer. Isolering van die individuele
chromosoom arms, 7DS en 7DL, deur van die "PALM Microbeam"sisteem gebruik te maak het basispaarvolgordebepaling van die chromosoom toegelaat sonder die oortolligheid van die res van die hexaploïde genoom. Deur die chromosoom so te isoleer is « >80-maal verkleining in genoom grootte bereik insluitend « groot reduksie in herhalende elemente. Analise van die data vanaf basispaarvolgordebepaling
het bevestig dat chromosoom 7D die fisiese kleiner chromosoom is maar dat dit die meerderheid van proteïn koderende basispaarvolgordes bevat.
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Santos, Dayana Lardo dos. "Zoneamento da favorabilidade climática para a ocorrência da ferrugem alaranjada da cana-de-açúcar nas principais regiões produtoras do Brasil e da Austrália." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/11/11152/tde-21082013-104149/.
Full textAbstract:
O Brasil, maior expoente do setor sucroalcooleiro mundial, apresenta como um dos entraves para obter elevadas produtividades a ocorrência de doenças fúngicas, as quais limitam o potencial produtivo do canavial. Atualmente, um dos grandes desafios para a comunidade canavieira é a recém-introduzida ferrugem alaranjada, doença causada pelo fungo Puccinia kuehnii, a qual foi detectada pela primeira vez no Brasil na safra 2009/10, ano em que as chuvas excederam os valores normais e as temperaturas foram amenas. Dada a grande dependência que as doenças fúngicas têm das condições climáticas para se manifestarem, o presente estudo teve por objetivo avaliar as condições meteorológicas que foram observadas durante as epidemias de ferrugem alaranjada ocorridas na província de Queensland, Austrália, em 1999/2000, e no estado de São Paulo, em 2009/2010, e a partir dessas elaborar modelos que possibilitassem estimar a severidade da doença, de modo a se estabelecer o zoneamento da favorabilidade climática para sua ocorrência. Com base nessas informações foram elaborados mapas de favorabilidade climática para a ocorrência da ferrugem no estado de São Paulo e na província de Queensland. As variáveis climáticas favoráveis à ocorrência da ferrugem alaranjada foram o número de decêndios com excedente hídrico (NDEXC) e o número de decêndios com temperatura média ideal para a infecção (NDTideal). Essas variáveis foram utilizadas no desenvolvimento de modelos lineares para determinação da severidade da doença, com base nos dados observados em diferentes regiões do estado de São Paulo. A elaboração do Índice de Favorabilidade Climática à Ferrugem Alaranjada da Cana-de-açúcar (IFAC) se baseou numa ponderação das severidades estimadas para séries de 15 a 30 anos. Posteriormente, o IFAC foi correlacionado com as coordenadas geográficas e a altitude o que permitiu se estimar o IFAC para todo o Estado de São Paulo. Esse modelo também foi aplicado para a Província de Queensland, Austrália. O IFAC foi empregado na confecção de mapas nos quais se estabeleceram os zoneamentos das regiões de favorabilidade climática à doença. Observou-se que as regiões canavieiras no oeste paulista apresentam risco muito baixo a moderado, enquanto que nas regiões no centro-leste do Estado, o risco é moderado-alto a alto seguindo uma tendência longitudinal. Para Queensland, a região mais favorável à doença é na faixa leste da província, exatamente nas regiões onde se concentra a produção de cana-de-açúcar.<br>Brazil, the largest exponent of the sugarcane sector in the world, presents as one of the obstacles for obtaining high yields the occurrence of diseases, which limits the potential productivity of the crop. Presently, one the greatest challenge for sugarcane production is newly introduced sugarcane disease, named orange rust, caused by Puccinia kuehni, which was detected by the first time in Brazil during 2009-2010 growing season, when the rainfall exceed the normal values and temperatures remained mild. Considering the great influence of climate conditions on plant diseases occurrence, the present study aimed to evaluate the weather conditions that prevailed during the sugarcane orange rust epidemic in province of Queensland, Australia, in 1999-2000 growing season, and in the state of São Paulo, Brazil, in 2009-2010 growing season, and base on that to develop a disease severity model in order to establish the climate favorability zoning for its occurrence. Based on these data, maps of orange rust climatic favorability were elaborated for the state of São Paulo and province of Queensland. The climatic variables favorable for conditioning orange rust were the number of ten-day periods with soil water surplus (NDEXC) and the number of ten-day periods with average temperature within the ideal range for the disease (NDTideal). With these variables, linear models were developed to determine the severity of the disease, based on disease and weather data observed in different regions of the state of São Paulo. The Climatic Favorability Index for Sugarcane Orange Rust Occurrence (IFAC) was based on the weighting of the disease severities estimated for weather series of 15 to 30 years. After that, IFAC was correlated with the geographical coordinates and altitude which allowed estimating it for all the state of São Paulo. This procedure was also applied for the province of Queensland, Australia. The IFAC was used to generate maps for zoning the regions of climatic favorability for the disease. The maps allowed to observe that for the state of São Paulo, the west region presents vary low to moderate risk for the disease, while the center-east region presents moderate-high to high risk. For the province of Queensland, the most favorable region for orange rust occurrence is the east, exactly where the sugarcane production is concentrated.
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Bruce, Faikah. "Understanding the impact of an HIV intervention package for adolescents." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85666.
Full textAbstract:
Thesis (MSc)--Stellenbosch University, 2013.<br>ENGLISH ABSTRACT: Adolescents are regarded as a high risk group in South Africa with the highest
human immunodeficiency virus (HIV) incidence occurring in this group. Prevention
among adolescents is therefore a key in decreasing the HIV burden.
This thesis aims to assist in the design of trials by simulating the potential outcomes
of a combination prevention trial in adolescents. We develop a stochastic
individual-based model stratified by sex and age. We then use this model to
determine the impact of various prevention packages on HIV incidence among
adolescents participating in a hypothetical trial over a three year period. The
trial that is simulated involves an intervention arm, in which adolescents are
offered a choice of a prevention methods (including medical male circumcision
(MMC), oral pre-exposure prophylaxis (PrEP) and antiretroviral-based vaginal
microbicides (ARV-VM)), and a control arm. We predict that the impact
of a full prevention package on HIV incidence would be a 46% per personyear(
PPY) (95% CI 45–47%) risk reduction. The combination of MMC and
PrEP has a substantial impact on HIV incidence in males, with a 51% PPY
(95% CI 49–53%) relative risk of HIV infection. Offering women the choice of
PrEP, a microbicide gel or a microbicide in the form of a vaginal ring would be
less effective, with a 57% PPY (95% CI 56–58%) relative risk of HIV acquisition.
This is not substantially different from the relative risk estimated when
the vaginal ring alone is offered, as the ring is assumed to be the most accept able of the three prevention methods. We determine a sample size requirement
of approximately 1013 in each arm of a trial would achieve 80% power to detect
a statistically significant reduction in HIV risk. We find that the relative risk
is sensitive to the assumed degree of correlation between condom use and the
acceptability of the prevention method. We also find that the most efficient
trial design may be to offer both MMC and PrEP to males but to offer only
a microbicide ring to females. Further work is required to better understand
the processes by which adolescent prevention method choices are made.<br>AFRIKAANSE OPSOMMING: Adolessente word beskou as ‘n hoe risiko groep in Suid Afrika, met die hoogste
menslike immuniteitsgebrekvirus (MIV) insidensie in hierdie groep. Voorkoming
van MIV onder adolessente is daarom noodsaaklik om die MIV las te
verminder. Die doel van hierdie tesis is om te help met die ontwerp van studies
deur die moontlike uitkomste van ‘n kombinasie-voorkoming studie in adolessente
te simuleer. Ons het ‘n stogastiese individu-gebaseerde model, gestratifiseer
met betrekking tot seks en ouderdom, ontwikkel. Ons het toe die model
gebruik om die impak van ‘n verskeinheid van voorkomingspakette op MIV insidensie
onder adolessente wat deelneem aan ‘n hipotetiese proef oor ‘n drie jaar
periode, te bepaal. Die proef wat gesimuleer word behels a intervensie groep,
waarin die jong volwassenes ‘n keuse van voorbehoedings metodes (insluitende
mediese manlike besnydenis (MMB), pre-blootstelling profilakse (PrBP) en
anti-retrovirale vaginale mikrobisiedes (ARV-VM)) aangebied word, en ‘n kontrole
groep. Ons voorspel dat die impak van ‘n volle voorkomingspaket op MIV
insidensie ‘n 46% per persoon-jaar (PPJ) (95% VI 47–47%) risiko vermindering
sal wees. Die kombinasie van MMB en PrBP het ‘n substansiele impak
op MIV insidensie onder mans, met ‘n relatiewe risiko van MIV infeksie van
51% PPJ (95% VI 49–53%). Om die keuse van PrBP, ‘n mikrobisiede gel of
‘n mikrobisiede in die vorm van ‘n vaginale ring aan vrouens te bied, is minder
effektief, met ‘n relatiewe risiko van MIV infeksie van 57% PPJ (95% VI 56%–58%). Hierdie verskil nie substansieel van die beraamde relatiewe risiko
in die geval waar slegs die vaginale ring gebied word nie, aangesien daar aanvaar
word dat die ring die mees aanvaarde van die drie voorkomingsmetodes is.
Ons het bepaal dat ‘n steekproef van ongeveer 1013 individue in elke arm van
die proef nodig is om ‘n 80% kans te he om ‘n statisties betekenisvolle afname
in MIV-risiko te bespeur. Ons vind dat die relatiewe risiko sensitief is tot die
aanvaarde graad van die korrelasies tussen kondoom-gebruik en die aanvaarding
van die voorkomings metodes. Ons het ook gevind dat dit mag wees dat
die mees doeltreffende proef ontwerp is om beide MMB en PrBP vir mans en
slegs ‘n mikrobisiede ring vir vrouens te bied. Verdere werk word benodig om
die prosesse waarby jong volwassenes keuses maak oor voorkomingsmetodes te
verstaan.
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El-Bouri, Wahbi K. "Multi-scale modelling of the microvasculature in the human cerebral cortex." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:8a9409a6-6279-4f7b-a975-b70149732378.
Full textAbstract:
Cerebrovascular diseases are by far the largest causes of death in the UK, as well as one of the leading causes of adult disability. The brain's healthy function depends on a steady supply of oxygen, delivered through the microvasculature. Cerebrovascular diseases, such as stroke and dementia, can interrupt the transport of blood (and hence oxygen) rapidly, or over a prolonged period of time. An interruption in flow can lead to ischaemia, with prolonged interruptions leading to tissue death and eventual brain damage. The microvasculature plays a key role in the transport of oxygen and nutrients to brain tissue; however, its role in diseases such as dementia is poorly understood, primarily due to the inability of current clinical imaging techniques to resolve microvessels, and due to the complexity of the underlying microvasculature. Therefore, in order to understand cerebrovascular diseases, it is necessary to be able to resolve and understand the microvasculature. In particular, generating large-scale models of the human microvasculature that can be linked back to contemporary clinical imaging is important in helping plug the current imaging gap that exists. A novel statistical model is proposed here that generates such large-scale models efficiently. Homogenization theory is used to generate a porous continuum capillary bed (characterised by its permeability) that allows for the efficient scaling up of the microvasculature. A novel order-based density-filling algorithm is then developed which generates morphologically accurate penetrating arterioles and venules, also demonstrating that the topology of the vessels only has a minor influence on CBF compared to diameter. Finally, the capillary bed and penetrating vessels are coupled into a large voxel-sized model of the microvasculature from which pressure and flux variations through the voxel can be analysed. A decoupling of the pressure and flux, as well as a layering of flow, was observed within the voxel, driven by the topology of the penetrating vessels. Micro-infarctions were also simulated, demonstrating the large local effects they have on the pressure and flux, whilst only causing a minor drop in CBF within the voxel.
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Crescencio, Julio César. "Quantificação do limiar de anaerobiose ventilatório no exercício físico dinâmico em cardiopatas chagásicos utilizando-se métodos visuais e computacionais." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/17/17138/tde-06082007-201626/.
Full textAbstract:
Os avanços tecnológicos ocorridos na última década trouxeram enormes benefícios, no sentido de possibilitar o uso de equipamentos computadorizados, que permitem a aquisição, processamento e armazenamento de um grande número de variáveis respiratórias e metabólicas em exercício físico, em tempo real e a cada ciclo respiratório. Inserido neste novo cenário, o estudo realizado com esta nova geração de equipamentos, nas respectivas áreas de conhecimento, pôde ser direcionado, usando-se métodos matemáticos e estatísticos computadorizados, os quais possibilitam a aplicação de procedimentos automáticos e/ou semi-automáticos na solução de problemas específicos. É dentro deste contexto que se insere o presente estudo, que tem por objetivo estudar, em pacientes portadores de doença de Chagas e em indivíduos sadios, do sexo masculino, o limiar de anaerobiose ventilatório, durante o exercício físico dinâmico, realizado em cicloergômetro, usando-se métodos baseados em modelos matemáticos, automáticos e semi-automáticos, comparativamente com o método visual gráfico. Foram estudados 51 voluntários do sexo masculino, sendo 24 chagásicos e 27 saudáveis, a média de idade dos grupos chagásico e saudável foi de 33,77 ± 7,86 e 35,91 ± 9,84 anos, respectivamente. Todos eles foram submetidos a dois testes de esforço físico dinâmico, com um protocolo contínuo do tipo rampa e um outro protocolo de esforço físico descontínuo, ambos na posição sentada, em cicloergômetro de frenagem eletromagnética, acoplado a um ergoespirômetro (CPX/D MedGraphics), que possibilitou o cálculo e armazenamento de múltiplas variáveis cardiorrespiratórias, como: ventilação pulmonar (VE), produção de CO2 (VCO2), consumo de O2 (VO2), equivalentes ventilatórios de O2 (VE/VO2) e de CO2 (VE/VCO2), frações parciais do O2 (PET O2) e do CO2 (PET CO2) no final da expiração, quociente de trocas respiratórias (RER), freqüências respiratória (RR) e cardíaca (FC), além dos valores de potência aplicada e da velocidade de pedalagem no cicloergômetro. Os valores do LAV, durante o protocolo contínuo, foram calculados por seis diferentes métodos, que usam como critério de medida deste parâmetro, a mudança de inclinação da , em relação ao tempo ou da em relação ao . Estes métodos foram os seguintes: 1- método visual; 2- método automático, usando algoritmo, incorporado ao sistema MedGraphics; 3- modelo bissegmentado linear-linear aplicado à resposta da em função do tempo; 4- modelo bissegmentado linear-quadrático aplicado à resposta da em função do tempo; 5- modelo bissegmentado linear-linear aplicado à resposta da em função do consumo de O2; e 6- modelo bissegmentado linear-quadrático aplicado à resposta da em função do consumo de O2. Os modelos bissegmentados se basearam na aplicação da soma dos quadrados dos resíduos, quando o conjunto de dados é ajustado pelo método dos mínimos quadrados, para uma reta inicial e final ou uma reta inicial e uma curva quadrática final. Foram aplicados, aos dados do protocolo descontínuo, nas várias potências estudadas, um modelo semiparamétrico que ajusta uma reta por meio de uma regressão linear. Após análise qualitativa e quantitativa apropriada aos conjuntos de dados, chegou-se às seguintes conclusões: 1- os modelos matemáticos bissegmentados usados no presente estudo, do tipo linear-linear e linear-quadrático, mostrando a resposta das variáveis VCO2 vs. tempo e VCO2 vs. VO2, com protocolos contínuos em rampa, puderam ser aplicados em 64% dos voluntários estudados (16 chagásicos e 17 saudáveis), e os valores do limiar de anaerobiose ventilatório, expressos em potência e consumo de oxigênio, não diferiram estatisticamente dos obtidos pelo método visual gráfico, nos grupos de pacientes chagásicos e de indivíduos saudáveis; 2- o método automático, incorporado ao ergoespirômetro MedGraphics, possibilitou a determinação limiar de anaerobiose em todos os voluntários estudados nos grupos chagásico (n=24) e saudável (n=27); entretanto, com valores do limiar de anaerobiose ventilatório subestimados comparativamente ao método visual gráfico; 3- não houve diferença estatisticamente significante entre a comparação dos coeficientes (inclinação e intercepto) das retas de regressão, que relacionam a potência com o consumo de oxigênio dos valores do limiar de anaerobiose ventilatório calculados para os seis métodos usados; 4- as análises das retas de regressão dos modelos semiparamétricos, aplicados no protocolo descontínuo, mostraram porcentagem pequena de casos, em que a mudança de inclinação das retas coincidiu com o valor do limiar de anaerobiose ventilatório, o que ainda torna questionável a utilidade desta abordagem, pelo menos nas condições em que os protocolos progressivos do tipo degrau tenham 6 minutos de duração; 5- Os quatro modelos bissegmentados testados e o método automático do equipamento, aplicados às respostas das variáveis ventilatórias, usando-se o protocolo de rampa, se mostraram adequados, como ferramentas úteis para se quantificar o limiar de anaerobiose ventilatório durante o exercício dinâmico; 6- o janelamento dos dados, durante a aplicação da rampa de potência em esforço, se mostrou de fundamental importância para permitir o uso adequado dos modelos matemáticos bissegmentados e do método automático, visando à quantificação do limiar de anaerobiose ventilatório.<br>With the advance of digital computers it was possible to develop high quality equipments and specific software for the acquisition, processing and storage of a great number of cardio respiratory variables. In this context, exercise physiology has shown a substantial progress, particularly with the use of ergospirometric systems that allow a simultaneous recording of respiratory and metabolic variables during dynamic exercise. The aim of the present study was to evaluate the usefulness of a special kind of mathematical models, the so called bisegmentar models, linear-linear (L-L) and linear-quadratic (L-Q), applied to the ventilatory variables during dynamic exercise for identification of the ventilatory anaerobic threshold (VAT) in chagasic patients. In this study 51 volunteers were included: 24 chagasic patients (mean ± age= 33.77 ± 7.86 years) and 27 healthy men (35.91 ± 9.84 years), paired for sex, age and aerobic capacity. The chagasic patients presented the undetermined and the cardiac form of the disease; in this last condition the patients did not show any increase of heart dimension on echocardiography. All subjects studied were submitted to two different types of exercise protocols, undertaken in cycle ergometer in seated position: 1- a continuous ramp type test; 2- a progressive step type test, interrupted in each exercise level for the return of variables to basal values. An electronic braked cycle ergometer (CORIVAL 400 Quinton) was used in both cases. A computerized ergospirometric system (MedGraphics CPX/D) was used to apply the exercise tests. This system allowed the recording and processing of all ventilatory variables for application of the mathematical models: oxygen uptake (VO2), CO2 production (VCO2), minute respiratory ventilation (VE), respiratory equivalents (VE/VCO2,VE/VO2), power (Watts), rotation speed, and others. The ramp was calculated considering sex, age, weight and aerobic capacity, evaluated on the basis of a questioner of physical activity. The VAT was measured by visual manner (mean values obtained from 3 different observers), and also by the automatic method supplied by the MedGraphics equipment (AuT), based on the VCO2-VO2 inclination changes of the straight lines, and the ones obtained by the bisegmentar methods adjusted to the response of VO2 related to time (L-L VCO2, L-Q VCO2) and of VCO2 in relation to VO2 (L-L VCO2/VO2, L-Q VCO2/VO2). The bisegmentar models were based on the measure of the square sum of residual values related to fitting of two functions, linear-linear and linear-quadratic applying the least square method. After a qualitative and quantitative analysis of data, it was possible to reach to the following conclusions: 1- all four bisegmentar models applied to ramp type tests could be used in 64% of cases (16 chagasics an 17 healthy), and the calculated VAT values were not statistically different from the ones obtained by VM and AuT methods ? also, the VAT values were not different comparing the two groups; 2- the AuT method could be used in all volunteers studied, including the chagasic (n=24) and the control (n=27) groups; 3- the intercepts and inclination coefficients that relate power and of VAT values obtained by all 6 methods were not statistically significant in both groups studied; 4- the inclination changes of linear fitting obtained from step tests were coincident with the VAT values calculated from ramp tests in a small percentage of cases, what makes this method questionable, at least in protocols with 6 minute duration; 4- all bisegmentar models and AuT method using the ramp protocols have shown an adequate tool to quantify the VAT; 6- the use of appropriate windows to analyze the data during ramp exercise protocols is of uppermost importance to achieve a good performance of the mathematical models and the automatic method for quantifying the VAT.
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Behlau, Franklin. "Epidemiologia do cancro cítrico (Xanthomonas axonopodis pv. citri) em laranja 'Pêra' (Citrus sinensis) sob condições de controle químico e cultural." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/11/11135/tde-22082006-153211/.
Full textAbstract:
O cancro cítrico, causado pela bactéria Xanthomonas axonopodis pv. citri, é uma das doenças mais importantes da citricultura. O estudo do efeito de medidas alternativas de controle para o manejo desta doença assume grande importância tanto para áreas citrícolas onde a erradicação de plantas não é a principal medida de controle do cancro cítrico, como no Estado do Paraná, como para regiões onde a prática da erradicação vem sendo adotada como principal medida de controle da doença, como no Estado de São Paulo. Instalado em pomar citrícola do município de Ourizona, na região Noroeste do Estado do Paraná, este trabalho buscou estudar o progresso dessa importante doença em campo sob condições de proteção química das plantas, utilizando produto cúprico; e cultural, por meio de quebra-vento. Além disso, importantes informações relacionadas ao efeito de cada tratamento sobre a produção das plantas de laranja Pêra também foram obtidas. Enquanto a aplicação de cobre apresentou efeito significativo na redução dos níveis de cancro cítrico, o emprego de quebra-vento pouco ou nada contribuiu para o controle da doença. Após 29 avaliações mensais, plantas submetidas à aplicação de bactericida cúprico apresentaram valores médios de AUDPC* de incidência da doença nas folhas de cerca de 20 %, nível 44 % inferior ao observado para as plantas não protegidas quimicamente. O mesmo comportamento foi observado para a severidade da doença. Após 18 avaliações mensais foi possível observar que plantas submetidas à aplicação de produto cúprico apresentaram em média folhas com níveis de AUDPC* de severidade 37 % menores do que plantas não protegidas quimicamente. Em 2004, quando os níveis da doença foram relativamente elevados, plantas submetidas ao controle químico apresentaram produção 54 % superior àquelas não tratadas. Em 2005, quando os níveis de cancro foram menores, não foi observada diferença na produtividade entre os tratamentos. Nas duas safras, plantas tratadas com bactericida apresentaram menor incidência da doença em frutos e maior proporção de frutos colhidos em relação a carga total da planta (colhidos + caídos). Dos modelos testados, o logístico foi o mais adequado para descrever o progresso temporal do cancro cítrico nos dois anos estudados para todos os tratamentos. Nas duas safras estudadas a proporção de frutos colhidos foi a variável que apresentou função de dano com maior coeficiente de determinação (R2) quando relacionada aos níveis de incidência e severidade de cancro cítrico observados.<br>Citrus canker, caused by Xanthomonas axonopodis pv. citri, is one of the most important diseases to citrus production. The effect of alternative measures of citrus canker control is very important to areas where plant eradication is the most important measure of control, as in Sao Paulo State, as well as to areas where eradication is not a major component of canker control, as in Parana State. This work aimed to study the progress of citrus canker in field conditions under chemical control, by using copper sprays; and cultural control, by using windbreak. Field plots were installed in a citrus orchard of Pêra sweet orange located in Ourizona county, northwest of Parana State, Brazil. Information regarding the effect of each treatment alone or in combination was assessed. Whereas copper sprays showed significant effect on reducing citrus canker levels, windbreak did not contribute significantly to disease control. After 29 monthly assessments, plants submitted to copper sprays showed values of AUDPC* of citrus canker incidence near to 20 %. This disease level was 44 % lower than that observed to plants not protected with copper compound. The same pattern was observed to disease severity. After 18 monthly assessments, plants sprayed with copper showed values of AUDPC* of disease severity 37 % lower than that observed to plants of the check plots. In 2004, when the citrus canker level was higher, plants treated with copper yielded 54 % more than that not sprayed. In 2005, when the citrus canker level was lower, no significant difference was observed between treatments. In both seasons, plants sprayed with copper showed lower citrus canker incidence on fruits and higher rate of harvested fruits. Among the temporal models tested, the logistic was the most appropriate to describe citrus canker incidence over time in both years studied to all treatments. In both harvests the rate of harvested fruits was the variable that showed the higher coefficient of determination (R2) when related to citrus canker incidence and severity levels.
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Kean, J. M. "Metapopulation theory in practice." Lincoln University, 1999. http://hdl.handle.net/10182/1372.
Full textAbstract:
A metapopulation is defined as a set of potential local populations among which dispersal may occur. Metapopulation theory has grown rapidly in recent years, but much has focused on the mathematical properties of metapopulations rather than their relevance to real systems. Indeed, barring some notable exceptions, metapopulation theory remains largely untested in the field. This thesis investigates the importance of metapopulation structure in the ‘real world’, firstly by building additional realism into metapopulation models, and secondly through a 3-year field study of a real metapopulation system. The modelling analyses include discrete-and continuous-time models, and cover single species, host-parasitoid, and disease-host systems, with and without stochasticity. In all cases, metapopulation structure enhanced species persistence in time, and often allowed long-term continuance of otherwise non-persistent interactions. Spatial heterogeneity and patterning was evident whenever local populations were stochastic or deterministically unstable in isolation. In metapopulations, the latter case often gave rise to self-organising spatial patterns. These were composed of spiral wave fronts (or ‘arcs of infection’ in disease models) of different sizes, and were related to the stability characteristics of local populations as well as the dispersal rates. There was no evidence for self-organising spatial patterns in the host-parasitoid system studied in the field (the weevil Sitona discoideus and its braconid parasitoid Microctonus aethiopoides), and a new model for the interaction suggested that this is probably due to the strong host density-dependence and stabilising parasitism acting on local populations. Dispersal may be important because of very high mortality in dispersing weevils, which may be related to the scarcity of their host plant in the landscape. If this is the case, the model suggested that local weevil density may be sensitive to the area of crop grown. Stochastic models showed that species in suitably large metapopulations may persist for very long times at relatively low overall density and with very low incidence of density-dependence. This suggests that metapopulation processes may explain a general inability to detect density-dependence in many real populations, and may also play an important part in the persistence of rare species. For host-parasitoid metapopulation models, persistence often depended on the way in which they were initialised. Initial conditions corresponding to a biological control release were the least likely to persist, and the maximum host suppression observed in this case was 84%, as compared with 60% for the corresponding non-spatial models and >90% often observed in the field. Metapopulation structure also allowed persistence of ‘boom-bust’ disease models, although the dynamics of these were particularly dependent on assumptions about what happens to disease classes at very low densities. Models assuming infinitely divisible units of density, models incorporating a non-zero extinction threshold, and individual-based models all gave differing results in terms of disease persistence and rate of spatial spread. Fitting models to overall metapopulation dynamics often gave misleading results in terms of underlying local dynamics, emphasising the need to sample real populations at an appropriate scale when seeking to understand their behaviour.
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Takaidza, Isaac. "Modelling the optimal efficiency of industrial labour force in the presence of HIV/AIDs pandemic." Thesis, Cape Peninsula University of Technology, 2012. http://hdl.handle.net/20.500.11838/1305.
Full textAbstract:
Thesis (DTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2012<br>In this thesis, we investigate certain key aspects of mathematical modelling to explain the epidemiology of HIV/AIDS at the workplace and to assess the potential benefits of proposed control strategies. Deterministic models to investigate the effects of the transmission dynamics of HIV/AIDS on labour force productivity are formulated. The population is divided into mutually exclusive but exhaustive compartments and a system of differential equations is derived to describe the spread of the epidemic. The qualitative features of their equilibria are analyzed and conditions under which they are stable are provided. Sensitivity analysis of the reproductive number is carried out to determine the relative importance of model parameters to initial disease transmission. Results suggest that optimal control theory in conjunction with standard numerical procedures and cost effective analysis can be used to determine the best intervention strategies to curtail the burden HIV/AIDS is imposing on the human population, in particular to the global economy through infection of the most productive individuals. We utilise Pontryagin’s Maximum Principle to derive and then analyze numerically the conditions for optimal control of the disease with effective use of condoms, enlightenment/educational programs, treatment regime and screening of infectives. We study the potential impact on productivity of combinations of these conventional control measures against HIV. Our numerical results suggest that increased access to antiretroviral therapy (ART) could decrease not only the HIV prevalence but also increase productivity of the infected especially when coupled with prevention, enlightenment and screening efforts.
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Molina, Martínez Patricia. "Desarrollo de modelos celulares para estudios terapéuticos en la enfermedad de Alzheimer." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/385986.
Full textAbstract:
La enfermedad de Alzheimer (EA) es la causa más común de demencia neurodegenerativa en los países desarrollados y su prevalencia aumenta con la edad. Los genes cuyas mutaciones son responsables de EA familiar son APP, PSEN1 y PSEN2, las mutaciones en PSEN1 siendo las más frecuentes. La mayoría de los casos son de EA esporádica y la edad es el principal factor de riesgo. Los mecanismos implicados en el envejecimiento del cerebro que contribuyen a la aparición de la EA aún no se han desentrañado, pero probablemente incluyen la disfunción mitocondrial, el estrés oxidativo y la inflamación cerebral. Los modelos experimentales de cultivos celulares han demostrado su eficacia para reproducir aspectos patológicos de la EA y facilitar el estudio de posibles terapias.
Los objetivos son:
1.- Estudiar el estrés oxidativo, las alteraciones mitocondriales y el efecto del tratamiento con suero de restricción calórica en cultivos de astrocitos SAMP8.
2.- Estudiar el estado inflamatorio basal y la respuesta a estímulos proinflamatorios en cultivos de astrocitos y microglía SAMP8 y en el tejido cerebral in vivo de SAMP8.
3.- Desarrollar las bases de un modelo celular que exprese mutaciones en el gen PSEN1 asociadas a la EA monogénica.
El estudio de los astrocitos de los ratones de senescencia acelerada SAMP8 mostró estrés oxidativo y alteraciones mitocondriales. El suero de restricción calórica redujo el estrés oxidativo y las alteraciones mitocondriales y protegió contra la senescencia replicativa.
Los astrocitos y microglía SAMP8 mostraron un aumento de la inflamación, que se vió agravada por estímulos proinflamatorios, principalmente en microglía. In vivo, LPS potenció la respuesta inflamatoria en el cerebro de ratones SAMP8 de 6 meses de edad pero este efecto se extinguió a los 12 meses.
En el diseño de un modelo celular para el estudio de las mutaciones familiares PSEN1, la técnica de mutagénesis dirigida permitió generar los plásmidos con mutaciones de interés clínico p.L286P, p.K239N y p.E120G. La transfección se realizó mediante un plásmido retroviral en células MEF deficiente para los genes de presenilina. Se creó la línea de células con el constructo PSEN1 WT y expresando GFP. Además, se optimizó la infección con varios adenovirus, Ad-APPswe, Ad-APPwt y Ad-β-galactosidasa, para el estudio de cambios patológicos en la generación de péptidos amiloides.
En conclusión, los astrocitos y/o microglía SAMP8 presentan mecanismos relacionados con la edad que pueden ser la base de procesos asociados a la EA. En cuanto al estudio de las mutaciones PSEN1, se establecieron las bases para el diseño de un modelo celular apropiado. Los modelos celulares desarrollados son potencialmente útiles para los estudios terapéuticos en EA.<br>Alzheimer's disease (AD) is the most common cause of neurodegenerative dementia in developed countries and its prevalence increases with age. The genes whose mutations are responsible for familial AD are APP, PSEN1 and PSEN2, mutations in PSEN1 being the most frequent. Most cases are sporadic AD and age is the main risk factor. The mechanisms involved in brain aging that contribute to the onset of AD have not yet been unraveled, but probably include mitochondrial dysfunction, oxidative stress and brain inflammation. Cell culture experimental models have proven effective to reproduce pathological aspects of AD and facilitating the study of potential therapies.
The objectives are:
1. Study oxidative stress, mitochondrial abnormalities and the effect of the treatment with caloric restriction serum in cultured astrocytes SAMP8.
2. Study the baseline inflammatory status and response to proinflammatory stimuli in cultured astrocytes and microglia SAMP8 and brain tissue in vivo SAMP8.
3. Develop the foundations for a cell model that expresses PSEN1 gene mutations associated with monogenic AD.
The study of astrocytes of senescence accelerated SAMP8 mice showed oxidative stress and mitochondrial alterations. Caloric restriction serum reduced oxidative stress and mitochondrial alterations and protected against replicative senescence.
Astrocytes and microglia SAMP8 showed increased inflammation, which was exacerbated by proinflammatory stimuli, mainly in microglia. In vivo, LPS potentiate the inflammatory response in the brain of 6-month old SAMP8 mice but this effect was extinguished at 12 months.
In designing a cellular model for studying PSEN1 familial mutations, directed mutagenesis allowed generate the plasmids with mutations of clinical interest p.L286P, p.K239N and p.E120G. Transfection was performed in MEF PSEN1-/ - cells with a retroviral plasmid. The cell line with the construct PSEN1-WT and expressing GFP was created. Also, the infection with several adenovirus, ad-APPswe, ad-APPwt and ad-β-galactosidase, was optimized for the further study of pathological changes in the generation of amyloid peptides.
In conclusion, astrocytes and/or microglia SAMP8 present age-related mechanisms that may underlie processes associated with EA. Regarding the study of PSEN1 mutations, the basis for the design of appropriate cellular model were established. Developed cell models are potentially useful for therapeutic studies in AD.
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Rivas, Cruz Manuel A. "Medical relevance and functional consequences of protein truncating variants." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:a042ca18-7b35-4a62-aef0-e3ba2e8795f7.
Full textAbstract:
Genome-wide association studies have greatly improved our understanding of the contribution of common variants to the genetic architecture of complex traits. However, two major limitations have been highlighted. First, common variant associations typically do not identify the causal variant and/or the gene that it is exerting its effect on to influence a trait. Second, common variant associations usually consist of variants with small effects. As a consequence, it is more challenging to harness their translational impact. Association studies of rare variants and complex traits may be able to help address these limitations. Empirical population genetic data shows that deleterious variants are rare. More specifically, there is a very strong depletion of common protein truncating variants (PTVs, commonly referred to as loss-of-function variants) in the genome, a group of variants that have been shown to have large effect on gene function, are enriched for severe disease-causing mutations, but in other instances may actually be protective against disease. This thesis is divided into three parts dedicated to the study of protein truncating variants, their medical relevance, and their functional consequences. First, I present statistical, bioinformatic, and computational methods developed for the study of protein truncating variants and their association to complex traits, and their functional consequences. Second, I present application of the methods to a number of case-control and quantitative trait studies discovering new variants and genes associated to breast and ovarian cancer, type 1 diabetes, lipids, and metabolic traits measured with NMR spectroscopy. Third, I present work on improving annotation of protein truncating variants by studying their functional consequences. Taken together, these results highlight the utility of interrogating protein truncating variants in medical and functional genomic studies.
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Salmani, Mahin. "A model for disease transmission in a patchy environment." 2005. http://hdl.handle.net/1828/826.
Full text
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Dovzhenok, Andrey A. "Mathematical Models of Basal Ganglia Dynamics." 2013. http://hdl.handle.net/1805/3357.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)<br>Physical and biological phenomena that involve oscillations on multiple time scales attract attention of mathematicians because resulting equations include a small parameter that allows for decomposing a three- or higher-dimensional dynamical system into fast/slow subsystems of lower dimensionality and analyzing them independently using geometric singular perturbation theory and other techniques. However, in most life sciences applications observed dynamics is extremely complex, no small parameter exists and this approach fails. Nevertheless, it is still desirable to gain insight into behavior of these mathematical models using the only viable alternative – ad hoc computational analysis. Current dissertation is devoted to this latter approach.
Neural networks in the region of the brain called basal ganglia (BG) are capable of producing rich activity patterns. For example, burst firing, i.e. a train of action potentials followed by a period of quiescence in neurons of the subthalamic nucleus (STN) in BG was shown to be related to involuntary shaking of limbs in Parkinson’s disease called tremor. The origin of tremor remains unknown; however, a few hypotheses of tremor-generation were proposed recently. The first project of this dissertation examines the BG-thalamo-cortical loop hypothesis for tremor generation by building physiologically-relevant mathematical model of tremor-related circuits with negative delayed feedback. The dynamics of the model is explored under variation of connection strength and delay parameters in the feedback loop using computational methods and data analysis techniques. The model is shown to qualitatively reproduce the transition from irregular physiological activity to pathological synchronous dynamics with varying parameters that are affected in Parkinson’s disease. Thus, the proposed model provides an explanation for the basal ganglia-thalamo-cortical loop mechanism of tremor generation.
Besides tremor-related bursting activity BG structures in Parkinson’s disease also show increased synchronized activity in the beta-band (10-30Hz) that ultimately causes other parkinsonian symptoms like slowness of movement, rigidity etc. Suppression of excessively synchronous beta-band oscillatory activity is believed to suppress hypokinetic motor symptoms in Parkinson’s disease. Recently, a lot of interest has been devoted to desynchronizing delayed feedback deep brain stimulation (DBS). This type of synchrony control was shown to destabilize synchronized state in networks of simple model oscillators as well as in networks of coupled model neurons. However, the dynamics of the neural activity in Parkinson’s disease exhibits complex intermittent synchronous patterns, far from the idealized synchronized dynamics used to study the delayed feedback stimulation. The second project of this dissertation explores the action of delayed feedback stimulation on partially synchronous oscillatory dynamics, similar to what one observes experimentally in parkinsonian patients. We employ a computational model of the basal ganglia networks which reproduces the fine temporal structure of the synchronous dynamics observed experimentally. Modeling results suggest that delayed feedback DBS in Parkinson’s disease may boost rather than suppresses synchronization and is therefore unlikely to be clinically successful.
Single neuron dynamics may also have important physiological meaning. For instance, bistability – coexistence of two stable solutions observed experimentally in many neurons is thought to be involved in some short-term memory tasks. Bistability that occurs at the depolarization block, i.e. a silent depolarized state a neuron enters with excessive excitatory input was proposed to play a role in improving robustness of oscillations in pacemaker-type neurons. The third project of this dissertation studies what parameters control bistability at the depolarization block in the three-dimensional conductance-based neuronal model by comparing the reduced dopaminergic neuron model to the Hodgkin-Huxley model of the squid giant axon. Bifurcation analysis and parameter variations revealed that bistability is mainly characterized by the inactivation of the Na+ current, while the activation characteristics of the Na+ and the delayed rectifier K+ currents do not account for the difference in bistability in the two models.
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Roldan, Josiah Javier. "West Nile virus : forecasting models for a resurging vector-borne disease in Arizona, U.S.A." Thesis, 2012. http://hdl.handle.net/1957/35783.
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West Nile Virus (WNV), a vector-borne disease continues to be a serious threat to public health in the United States, particularly in the Southwest region. While all the states in the U.S. experienced a decreasing trend of WNV disease in 2010, the state of Arizona experienced a sharp increase from 20 in 2009 to 166 cases the following year. This dissertation endeavored to develop forecasting models to predict future cases of disease and identify counties with increased propensity for WNV. Furthermore, this study aimed to identify environmental and economic factors that contributed to the increase in WNV cases in Maricopa County, Arizona.
A spatiotemporal stochastic regression model was developed using Bayesian principles and was successful in calculating the annual mean cases of disease from 2003 to 2011 for all counties. The model was also able to predict future cases of disease by fitting historical data. The model-based inference identified counties in the southern region of Arizona as having an elevated propensity for disease compared to counties in the northern region.
A Seasonal Autoregressive Integrated Moving Average (SARIMA) model was developed and effectively forecasted monthly cases of human WNV in Maricopa County, Arizona. By fitting the SARIMA model to monthly historical disease data from 2005 to 2011, the temporal model presented a decreasing trend of monthly incidence of disease for 2012.
The impact of home foreclosures, climate variability, and population growth on the resurgence of human WNV disease cases in Maricopa County during the 2010 epidemic was investigated. These factors were found to have contributed to the resurgence of the disease by creating the optimal environmental conditions that allowed the amplification of mosquito populations, thus increasing the risk of disease transmission to humans.
As spatiotemporal disease data become readily available, forecasting models can be an important and viable risk assessment tool for public health practitioners. Forecasting models allow the mobilization and distribution of limited resources to areas with elevated propensity for disease, and the timely deployment of intervention programs to reduce the overall risk of disease.<br>Graduation date: 2013
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"Dynamics and Implications of Data-Based Disease Models in Public Health and Agriculture." Doctoral diss., 2016. http://hdl.handle.net/2286/R.I.41234.
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abstract: The increased number of novel pathogens that potentially threaten the human population has motivated the development of mathematical and computational modeling approaches for forecasting epidemic impact and understanding key environmental characteristics that influence the spread of diseases. Yet, in the case that substantial uncertainty surrounds the transmission process during a rapidly developing infectious disease outbreak, complex mechanistic models may be too difficult to be calibrated quick enough for policy makers to make informed decisions. Simple phenomenological models that rely on a small number of parameters can provide an initial platform for assessing the epidemic trajectory, estimating the reproduction number and quantifying the disease burden from the early epidemic phase.
Chapter 1 provides background information and motivation for infectious disease forecasting and outlines the rest of the thesis.
In chapter 2, logistic patch models are used to assess and forecast the 2013-2015 West Africa Zaire ebolavirus epidemic. In particular, this chapter is concerned with comparing and contrasting the effects that spatial heterogeneity has on the forecasting performance of the cumulative infected case counts reported during the epidemic.
In chapter 3, two simple phenomenological models inspired from population biology are used to assess the Research and Policy for Infectious Disease Dynamics (RAPIDD) Ebola Challenge; a simulated epidemic that generated 4 infectious disease scenarios. Because of the nature of the synthetically generated data, model predictions are compared to exact epidemiological quantities used in the simulation.
In chapter 4, these models are applied to the 1904 Plague epidemic that occurred in Bombay. This chapter provides evidence that these simple models may be applicable to infectious diseases no matter the disease transmission mechanism.
Chapter 5, uses the patch models from chapter 2 to explore how migration in the 1904 Plague epidemic changes the final epidemic size.
The final chapter is an interdisciplinary project concerning within-host dynamics of cereal yellow dwarf virus-RPV, a plant pathogen from a virus group that infects over 150 grass species. Motivated by environmental nutrient enrichment due to anthropological activities, mathematical models are employed to investigate the relevance of resource competition to pathogen and host dynamics.<br>Dissertation/Thesis<br>Doctoral Dissertation Applied Mathematics 2016
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Mann, Joanne L. "Modelling infectious disease epidemiology and vaccination impact : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Mathematics at Massey University, Albany, New Zealand." 2009. http://hdl.handle.net/10179/1085.
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This thesis presents mathematical models for the dynamics of vaccine preventable diseases, specifically looking at the New Zealand situation. Through the use of integral and differential equations, we develop models and compare the results of these to known data. Using game theory analysis we determine and compare the proportion of the population that needs to be vaccinated in order to minimise the expected costs to the individuals in the population and to the community. Two different scenarios and methods are considered, where the effects of vaccination last only one epidemic cycle (using an integral equation method) and where vaccination is effective over an entire lifetime (using a differential equation method). For both scenarios, we find that the minimum cost for the individuals is reached when a lower proportion of the population is vaccinated than needed for the minimum cost to the community. We then elaborate on the integral equation method to produce a model for repeated epidemics of measles in a population, where a discrete mapping is used to include the year to year demographics of the population. The results of this model show a different epidemic pattern then that produced from a differential equation model, with numerical problems encountered. From here on, we use differential equation models in our analysis. A critique and extension to an existing model for the dynamics of the hepatitis B virus is presented, with discussion on the appropriateness of the model’s construct for predicting the incidence of infection. Alternative differential equation models for hepatitis B virus and immunisation that include splitting the population into age groups with nonhomogeneous mixing are presented. The results of these models are compared with the known data on incidence of infection and carriage in New Zealand, showing how affective different immunisation schedules may have been. Differential equation models are then presented for meningococcal B virus epidemiology in New Zealand, with the models incorporating different features of the virus until the best model is found that fits the New Zealand data. Each model is compared with the known incidence of infection, with the population being either treated as a whole or split into age groups with non-homogeneous mixing. The effect of vaccination is included in this model so that we can explore the future of the infection in the population, and how best to tackle any future epidemics. The model shows that the current vaccination campaign was the best solution for controlling the epidemic, but there will be epidemics in the future that will need subsequent vaccination campaigns to limit the number of infections.
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Jain, Ravi 1967. "Intelligent techniques for the diagnosis of coronary artery disease / Ravi Jain." 1998. http://hdl.handle.net/2440/19356.
Full textAbstract:
Bibliography: leaves 179-190.<br>xii, 189 leaves : ill. ; 30 cm.<br>Title page, contents and abstract only. The complete thesis in print form is available from the University Library.<br>This thesis proposes a genetic-programming-based classifier system for the diagnosis of coronary artery disease. Based on genetic programming, a software system called Evolutionary Pre-Processor has been developed as a new method for the automatic extraction of non-linear features for supervised classification. Two different hybrid intelligent system techniques are presented; fuzzy systems integrated with genetic algorithms and genetic algorithms combined with back-propagation algorithms. All approaches were tested on a real-world problem of coronary artery disease data.<br>Thesis (Ph.D.)--University of Adelaide, Dept. of Applied Mathematics, 1998
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Mugisha, Stella. "Applied mathematical modelling with new parameters and applications to some real life problems." Thesis, 2018. http://hdl.handle.net/10500/24973.
Full textAbstract:
Some Epidemic models with fractional derivatives were proved to be well-defined, well-posed and more accurate [34, 51, 116], compared to models with the conventional derivative. An Ebola epidemic model with non-linear transmission is fully analyzed. The model is expressed with the conventional time derivative with a new parameter included,
which happens to be fractional (that derivative is called the derivative). We proved that the model is well-de ned and well-posed. Moreover, conditions for boundedness and dissipativity of the trajectories are established. Exploiting the generalized Routh-Hurwitz Criteria, existence and stability analysis of equilibrium points for the
Ebola model are performed to show that they are strongly dependent on the non-linear transmission. In particular, conditions for existence and stability of a unique endemic equilibrium to the Ebola system are given. Numerical simulations are provided for particular expressions of the non-linear transmission, with model's parameters taking di erent values. The resulting simulations are in concordance with the usual threshold
behavior. The results obtained here may be signi cant for the ght and prevention
against Ebola haemorrhagic fever that has so far exterminated hundreds of families and
is still a ecting many people in West-Africa and other parts of the world.
The full comprehension and handling of the phenomenon of shattering, sometime happening
during the process of polymer chain degradation [129, 142], remains unsolved
when using the traditional evolution equations describing the degradation. This traditional
model has been proved to be very hard to handle as it involves evolution of
two intertwined quantities. Moreover, the explicit form of its solution is, in general,
impossible to obtain. We explore the possibility of generalizing evolution equation modeling
the polymer chain degradation and analyze the model with the conventional time
derivative with a new parameter. We consider the general case where the breakup rate
depends on the size of the chain breaking up. In the process, the alternative version of
Sumudu integral transform is used to provide an explicit form of the general solution
representing the evolution of polymer sizes distribution. In particular, we show that
this evolution exhibits existence of complex periodic properties due to the presence of
cosine and sine functions governing the solutions. Numerical simulations are performed
for some particular cases and prove that the system describing the polymer chain degradation
contains complex and simple harmonic poles whose e ects are given by these
functions or a combination of them. This result may be crucial in the ongoing research
to better handle and explain the phenomenon of shattering. Lastly, it has become a conjecture that power series like Mittag-Le er functions and
their variants naturally govern solutions to most of generalized fractional evolution models
such as kinetic, di usion or relaxation equations. The question is to say whether or
not this is always true! Whence, three generalized evolution equations with an additional
fractional parameter are solved analytically with conventional techniques. These
are processes related to stationary state system, relaxation and di usion. In the analysis,
we exploit the Sumudu transform to show that investigation on the stationary
state system leads to results of invariability. However, unlike other models, the generalized
di usion and relaxation models are proven not to be governed by Mittag-Le er
functions or any of their variants, but rather by a parameterized exponential function,
new in the literature, more accurate and easier to handle. Graphical representations
are performed and also show how that parameter, called ; can be used to control the
stationarity of such generalized models.<br>Mathematical Sciences<br>Ph. D. (Applied Mathematics)