Now showing 1 - 10 of 11
  • Some of the metrics are blocked by your 
    Item type:Publication,
    Local and global stability analysis of dengue disease with vaccination and optimal control
    (2021-10-01)
    Chamnan, Anusit
    ;
    ;
    Tang, I. Ming
    ;
    Dengue fever is a disease that has spread all over the world, including Thailand. Dengue is caused by a virus and there are four distinct serotypes of the virus that cause dengue DENV‐1, DENV‐2, DENV‐3, and DENV‐4. The dengue viruses are transmitted by two species of the Aedes mosquitoes, the Aedes aegypti, and the Aedes albopictus. Currently, the dengue vaccine used in Thailand is chimeric yellow tetravalent dengue (CYD‐TDV). This research presents optimal control which studies the vaccination only in individuals with a documented past dengue infection (seropositive), regardless of the serotypes of infection causing the initial infection by the disease. The analysis of dengue transmission model is used to establish the local asymptotically stabilities. The property of symmetry in the Lyapunov function an import role in achieving this global asymptotically stabilities. The optimal control systems are shown in numerical solutions and conclusions. The result shows that the control resulted in a significant reduction in the number of infected humans and infected vectors.
  • Some of the metrics are blocked by your 
    Item type:Publication,
    Simplified Modeling Approach to Characterize Sudden Load Disturbances in WirelessHART FOPDT Systems
    This paper presents the simplified modelling approach to characterize sudden load disturbance in WirelessHART™. Two approaches are presented. The model was firstly formulated through Laplace transformation, where the resulting integral equation renders non-linear optimization problems into simple linear optimizations. Experiments were conducted on a coupled tanks system connected through the WirelessHART™ protocol. Based on the initial fit to the experimental results, the second model then places two locally affine relationships, one for the load flow disturbances, and the other for the level measurements to the responses. The extended locally affine model gave on average a 25% reduction in errors, compared to the Laplace-based method, while better captured the non-linear effects resulting from the WirelessHART™.
  • Some of the metrics are blocked by your 
    Item type:Publication,
    Mathematical modeling and optimal control of the hand foot mouth disease affected by regional residency in Thailand
    (2021-11-01) ;
    Tang, I. Ming
    ;
    Dubois, Marc Antoine
    ;
    Hand, foot and mouth disease (HFMD) is a virulent disease most commonly found in East and Southeast Asia. Symptoms include ulcers or sores, inside or around the mouth. In this research, we formulate the dynamic model of HFMD by using the SEIQR model. We separated the infection episodes where there is a higher outbreak and a lower outbreak of the disease associated with regional residency, with the higher level of outbreak occurring in the urban region, and a lower outbreak level occurring in the rural region. We developed two different optimal control programs for the types of outbreaks. Optimal Control Policy 1 (OPC1) is limited to the use of treatment only, whereas Optimal Control Policy 2 (OPC2) includes vaccination along with the treatment. The Pontryagin’s maximum principle is used to establish the necessary and optimal conditions for the two policies. Numerical solutions are presented along with numerical sensitivity analyses of the required control efforts needed as the control parameters are changed. Results show that the time t<inf>max</inf> required for the optimal control effort to stay at the maximum amount u<inf>max</inf> exhibits an intrinsic logarithmic relationship with respect to the control parameters.
  • Some of the metrics are blocked by your 
    Item type:Publication,
    Age structural model of the hand foot mouth disease in Thailand
    The hand foot mouth disease (HFMD) is a virulent disease caused by virus of the enteroviruses serotypes, whose symptoms include soreness inside or around the mouth, and rashes or blisters on the hands, feet or legs. Most cases are seen in infant and children. The severity of HFMD outbreaks has thus constituted serious threat to general public health. In this work, the transmission model of the HFMD is formulated. Specifically, the population is divided into two subclasses, namely, those under the age of ten, and those over the age of ten. Two SEIR models, one for each subclasses, are then formed. This model is then analyzed through the use of standard dynamical systems method, where two equilibriums of the model, namely the disease-free equilibrium, and the endemic equilibrium, are firstly determined. Stability analyses of the respective equilibriums are then conducted. Results show that the disease-free equilibrium will be stable if the basic reproduction number is less than one, while the endemic equilibrium is stable when the basic reproduction number exceeds unity. These results can be used in controlling the epidemics of the HFMD.
  • Some of the metrics are blocked by your 
    Item type:Publication,
    Optimal control of the dengue dynamical transmission with vertical transmission
    (2019-12-01) ;
    Tang, I. Ming
    ;
    Dengue disease is found in tropical and subtropical regions around the world. Dengue virus is the cause of dengue fever, dengue hemorrhagic fever, and dengue shock syndrome. It consists of 4 serotypes: DEN-1, DEN-2, DEN-3, and DEN-4. There are two modes of transmission for dengue virus in mosquito: horizontal transmission and vertical transmission. The mosquito can be infected when it bites an infectious human by horizontal transmission, but there can also be vertical transmission through sexual contact with an infected mosquito. This research presents a control mechanism based on our previously developed dengue model with vertical transmission. The two policies, namely vaccination and insecticide administration (Policy 1) and isolation and insecticide administration (Policy 2) are considered. The use of Pontryargin’s maximum principle allowed necessary and optimality conditions, thus facilitating the optimal control to be developed. Numerical solutions of our control systems and the conclusions of our two policies are presented.
  • Some of the metrics are blocked by your 
    Item type:Publication,
    Global stability of the transmission of hand-foot-mouth disease according to the age structure of the population
    (2021-01-01)
    Lamwong, Jiraporn
    ;
    ;
    Tang, I. Ming
    ;
    ;
    This study investigates a transmission model of Hand-Foot-Mouth disease (HFMD) where the age structure of the population is taken into account. Most infections in Thailand occur among children below the age of 10 years, whose immunity to HFMD is lower than people of age greater than 10 years. Therefore, a mathematical model was developed in which the population was separated into two groups with respect to age: one comprised of children aged less than 10 years, and another comprised of the rest of the population. The reproductive number was obtained by the next-generation matrix approach. Global asymptotical stability of the developed model was assured using Lyapunov’s direct method. The model was validated by showing that the 2D and 3D trajectories of the numerical solutions for the different sub-population groups converged to the endemic equilibrium states when the reproduction number was greater than one, thus supporting the theoretical conclusions. Results show that the time series behaviors of the different normalized populations groups converge to the disease-free state when the values of the parameters are such that the basic reproductive number is 0.591481 (i.e., less than one) and to an endemic state when the values of the parameters are such that R<inf>0</inf> = 54.4523 and R<inf>0</inf> = 192.575 R = (i.e. greater than one). The results of this study can suggest ways for reducing the outbreak of this disease.
  • Some of the metrics are blocked by your 
    Item type:Publication,
    The Lyapunov Analyses of MERS-Cov Transmission in Thailand
    (2019-01-01)
    Lamwong, Jiraporn
    ;
    ;
    Tang, I. Ming
    ;
    This work investigates the transmission model of MERS-Cov using SEIR model which divides the total human population into four subclasses: susceptible, exposed, infected and recovered. Two * equilibrium points were exhibited: the disease-free equilibrium E1 and the endemic equilibrium E<sup>*</sup> 2. The basic reproduction number was computed via the next generation method. Two types of global stability of these equilibrium points were investigated through the theory of Lyapunov. Specifically, the exponential stability was investigated using a square type Lyapunov candidate function; while the asymptotic stability was investigated through a Logarithm type Lyapunov candidate function. It is theoretically shown that, when the reproductive number is less than unity. The disease-free equilibrium state is globally asymptotically stable, and the endemic equilibrium state is globally asymptotically stable if the reproductive number is greater than unity. Numerical results with parameters obtained from the previous work also illustrates the global asymptotical stability of the MERS-Cov system. These results can further be used for the design of a controller that drives the MERS-Cov system and the effective control reproductive number is less than 1 so that the stability of the controlled system would be similar to that of the uncontrolled disease-free system.
  • Some of the metrics are blocked by your 
    Item type:Publication,
    Optimal Control Strategy of a Mathematical Model for the Fifth Wave of COVID-19 Outbreak (Omicron) in Thailand
    (2024-01-01)
    Lamwong, Jiraporn
    ;
    ;
    Tang, I. Ming
    ;
    The world has been fighting against the COVID-19 Coronavirus which seems to be constantly mutating. The present wave of COVID-19 illness is caused by the Omicron variant of the coronavirus. The vaccines against the five variants (α, β, γ, δ, and ω) have been quickly developed using mRNA technology. The efficacy of the vaccine developed for one of the strains is not the same as the efficacy of the vaccine developed for the other strains. In this study, a mathematical model of the spread of COVID-19 was made by considering asymptomatic population, symptomatic population, two infected populations and quarantined population. An analysis of basic reproduction numbers was made using the next-generation matrix method. Global asymptotic stability analysis was made using the Lyapunov theory to measure stability, showing an equilibrium point’s stability, and examining the model with the fact of COVID-19 spread in Thailand. Moreover, an analysis of the sensitivity values of the basic reproduction numbers was made to verify the parameters affecting the spread. It was found that the most common parameter affecting the spread was the initial number in the population. Optimal control problems and social distancing strategies in conjunction with mask-wearing and vaccination control strategies were determined to find strategies to give better control of the spread of disease. Lagrangian and Hamiltonian functions were employed to determine the objective function. Pontryagin’s maximum principle was employed to verify the existence of the optimal control. According to the study, the use of social distancing in conjunction with mask-wearing and vaccination control strategies was able to achieve optimal control rather than controlling just one or another.
  • Some of the metrics are blocked by your 
    Item type:Publication,
    Effect of a Vaccination against the Dengue Fever Epidemic in an Age Structure Population: From the Perspective of the Local and Global Stability Analysis
    (2022-03-01)
    Chamnan, Anusit
    ;
    ;
    Tang, I. Ming
    ;
    The effect of vaccination on the dengue fever epidemic described by an age structured modified SIR (Susceptible-Infected-Retired) model is studied using standard stability analysis. The chimeric yellow fever dengue tetravalent dengue vaccine (CYD-TDV™) is a vaccine recently developed to control this epidemic in several Southeast Asian countries. The dengue vaccination program requires a total of three injections, 6 months apart at 0, 6, and 12 months. The ages of the recipients are nine years and above. In this paper, we analyze the mathematical dynamics SIR transmission model of the epidemic. The stability of the model is established using Routh–Hurwitz criteria to see if a Hopf Bifurcation occurs and see when the equilibrium states are local asymptotically stable or global asymptotically stable. We have determined the efficiency of CYD-TDV by simulating the optimal numerical solution for each age range for this model. The numerical results showed the optimal age for vaccination and significantly reduced the severity and severity of the disease.
  • Some of the metrics are blocked by your 
    Item type:Publication,
    Optimal control of dengue transmission with vaccination
    (2021-08-01)
    Chamnan, Anusit
    ;
    ;
    Tang, I. Ming
    ;
    Dengue disease is caused by four serotypes of the dengue virus: DEN-1, DEN-2, DEN-3, and DEN-4. The chimeric yellow fever dengue tetravalent dengue vaccine (CYD-TDV) is a vaccine currently used in Thailand. This research investigates what the optimal control is when only individuals having documented past dengue infection history are vaccinated. This is the present practice in Thailand and is the latest recommendation of the WHO. The model used is the Susceptible-Infected-Recovered (SIR) model in series configuration for the human population and the Susceptible-Infected (SI) model for the vector population. Both dynamical models for the two populations were recast as optimal control problems with two optimal control parameters. The analysis showed that the equilibrium states were locally asymptotically stable. The numerical solution of the control systems and conclusions are presented.