Displaying publications 1 - 20 of 88 in total

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  1. 'Aaishah Radziah Jamaludin, Fadhilah Yusof, Suhartono
    MATEMATIKA, 2020;36(1):15-30.
    MyJurnal
    Johor Bahru with its rapid development where pollution is an issue that needs to be considered because it has contributed to the number of asthma cases in this area. Therefore, the goal of this study is to investigate the behaviour of asthma disease in Johor Bahru by count analysis approach namely; Poisson Integer Generalized Autoregressive Conditional Heteroscedasticity (Poisson-INGARCH) and Negative Binomial INGARCH (NB-INGARCH) with identity and log link function. Intervention analysis was conducted since the outbreak in the asthma data for the period of July 2012 to July 2013. This occurs perhaps due to the extremely bad haze in Johor Bahru from Indonesian fires. The estimation of the parameter will be done by quasi-maximum likelihood estimation. Model assessment was evaluated from the Pearson residuals, cumulative periodogram, the probability integral transform (PIT) histogram, log-likelihood value, Akaike’s Information Criterion (AIC) and Bayesian information criterion (BIC). Our result shows that NB-INGARCH with identity and log link function is adequate in representing the asthma data with uncorrelated Pearson residuals, higher in log likelihood, the PIT exhibits normality yet the lowest AIC and BIC. However, in terms of forecasting accuracy, NB-INGARCH with identity link function performed better with the smaller RMSE (8.54) for the sample data. Therefore, NB-INGARCH with identity link function can be applied as the prediction model for asthma disease in Johor Bahru. Ideally, this outcome can assist the Department of Health in executing counteractive action and early planning to curb asthma diseases in Johor Bahru.
  2. Adam, M.B., Norazman, N., Mohamad Kasim, M.R.
    MATEMATIKA, 2018;34(1):113-123.
    MyJurnal
    Logging activity is one of the most important activities for tropical countries
    including Malaysia, as it produces quality trees for papers. One of the important tree
    species is the Acacia Mangium which it produces a soft tree for papermaking enterprises.
    The papers are exported to Europe and countries which have high demand for paper
    due to the rapid development of the printing industry. Thus we analyzed the height for
    individual trees. We investigate the maximum height of the trees from 1990 to 2006
    and we fit the data using extreme value model. Some of the data are missing and three
    imputation methods we used to solve this problem.
  3. Afeez Abidemi, Rohanin Ahmad, Nur Arina Bazilah Aziz
    MATEMATIKA, 2019;35(301):149-170.
    MyJurnal
    This study presents a two-strain deterministic model which incorporates Dengvaxia vaccine and insecticide (adulticide) control strategies to forecast the dynamics of transmission and control of dengue in Madeira Island if there is a new outbreak with a different virus serotypes after the first outbreak in 2012. We construct suitable Lyapunov functions to investigate the global stability of the disease-free and boundary equilibrium points. Qualitative analysis of the model which incorporates time-varying controls with the specific goal of minimizing dengue disease transmission and the costs related to the control implementation by employing the optimal control theory is carried out. Three strategies, namely the use of Dengvaxia vaccine only, application of adulticide only, and the combination of Dengvaxia vaccine and adulticide are considered for the controls implementation. The necessary conditions are derived for the optimal control of dengue. We examine the impacts of the control strategies on the dynamics of infected humans and mosquito population by simulating the optimality system. The disease-free equilibrium is found to be globally asymptotically stable whenever the basic reproduction numbers associated with virus serotypes 1 and j (j ∈ {2,3,4}), respectively, satisfy R01,R0j ≤ 1, and the boundary equilibrium is globally asymptotically stable when the related R0i (i = 1,j) is above one. It is shown that the strategy based on the combination of Dengvaxia vaccine and adulticide helps in an effective control of dengue spread in the Island.
  4. Ahmad Fadly Nurullah Rasedee, Mohammad Hasan Abdul Sathar, Norizarina Ishak, Irneza Ismail, Musab Sahrim, Nur Ainna Ramli, et al.
    MATEMATIKA, 2017;33(2):165-175.
    MyJurnal
    Real life phenomena found in various fields such as engineering, physics,
    biology and communication theory can be modeled as nonlinear higher order ordinary
    differential equations, particularly the Duffing oscillator. Analytical solutions for these
    differential equations can be time consuming whereas, conventional numerical solutions
    may lack accuracy. This research propose a block multistep method integrated with a
    variable order step size (VOS) algorithm for solving these Duffing oscillators directly.
    The proposed VOS Block method provides an alternative numerical solution by reducing
    computational cost (time) but without loss of accuracy. Numerical simulations
    are compared with known exact solutions for proof of accuracy and against current
    numerical methods for proof of efficiency (steps taken).
  5. Ahmad Razin Zainal Abidin, Shaymaa Mustafa, Zainal Abdul Aziz and, Kamarudin Ismail
    MATEMATIKA, 2018;34(2):173-186.
    MyJurnal
    Subsea cable laying process is a difficult task for an engineer due to many
    uncertain situations which occur during the operation. It is very often that the cable being
    laid out is not perfectly fit on the route being planned, which results in the formation of
    slack. In order to control wastages during installation, the slack needs to be minimized
    and the movement of a ship/vessel needs to be synchronized with the cable being laid out.
    The current problem was addressed using a mathematical model by considering a number
    of defining parameters such as the external forces, the cable properties and geometry. Due
    to the complexity, the model is developed for a steady-state problem assuming velocity
    of the vessel is constant, seabed is flat and the effect of wind and wave is insignificant.
    Non-dimensional system is used to scale the engineering parameters and grouped them
    into only two main parameters which are the hydrodynamic drag of the fluid and the
    bending stiffness of the cable. There are two solutions generated in this article; numerical
    and asymptotic solutions. The result of these solutions suggests that the percentage of
    slack can be reduced by the increase of the prescribed cable tension, and also the increase
    in either the drag coefficient of the sea water or the bending stiffness of the cable, similarly
    will result in lower slack percentage
  6. Alfa Mohammed Salisu, Ani Shabri
    MATEMATIKA, 2020;36(2):141-156.
    MyJurnal
    This paper proposes A Hybrid Wavelet-Auto-Regressive Integrated Moving Average (W-ARIMA) model to explore the ability of the hybrid model over an ARIMA model. It combines two methods, a Discrete Wavelet Transform (DWT) and ARIMA model using the Standardized Precipitation Index (SPI) drought data for forecasting drought modeling development. SPI data from January 1954 to December 2008 used was divided into two - (80%/20% for training/testing respectively). The results were compared with the conventional ARIMA model with Mean Square Error (MSE) and Mean Average Error (MAE) as an error measure. The results of the proposed method achieved the best forecasting performance.
  7. Amir S. A. Hamzah, Ali H. M. Murid
    MATEMATIKA, 2018;34(2):293-311.
    MyJurnal
    This study presents a mathematical model examining wastewater pollutant removal through
    an oxidation pond treatment system. This model was developed to describe the reaction
    between microbe-based product mPHO (comprising Phototrophic bacteria (PSB)), dissolved
    oxygen (DO) and pollutant namely chemical oxygen demand (COD). It consists
    of coupled advection-diffusion-reaction equations for the microorganism (PSB), DO and
    pollutant (COD) concentrations, respectively. The coupling of these equations occurred
    due to the reactions between PSB, DO and COD to produce harmless compounds. Since
    the model is nonlinear partial differential equations (PDEs), coupled, and dynamic, computational
    algorithm with a specific numerical method, which is implicit Crank-Nicolson
    method, was employed to simulate the dynamical behaviour of the system. Furthermore,
    numerical results revealed that the proposed model demonstrated high accuracy when
    compared to the experimental data.
  8. Amira Fadina Ahmad Fadzil, Rabiha Mahmoud, Nor Haniza Sarmin, Ahmad Erfanian
    MATEMATIKA, 2019;35(1):59-65.
    MyJurnal
    Let G be a dihedral group and ??cl G its conjugacy class graph. The Laplacian energy of the graph, LE(??cl G) is defined as the sum of the absolute values of the difference between the Laplacian eigenvalues and the ratio of twice the edges number divided by the vertices number. In this research, the Laplacian matrices of the conjugacy class graph of some dihedral groups, generalized quaternion groups, quasidihedral groups and their eigenvalues are first computed. Then, the Laplacian energy of the graphs are determined.
  9. Amira Fadina Ahmad Fadzil, Nor Haniza Sarmin, Ahmad Erfanian
    MATEMATIKA, 2019;35(3):371-376.
    MyJurnal
    Let g be a finite group and s be a subset of g, where s does not include
    the identity of g and is inverse closed. A cayley graph of a group g with respect to the
    subset s is a graph, where its vertices are the elements of g and two vertices a and b
    are connected if ab-1 is in the subset s. The energy of a cayley graph is the sum of all
    absolute values of the eigenvalues of its adjacency matrix. In this paper, we consider a
    specific subset s = {b, ab, . . . , An-1b} for dihedral groups of order 2n, where n 3 and find
    the cayley graph with respect to the set. We also calculate the eigenvalues and compute
    the energy of the respected cayley graphs. Finally, the generalization of the energy of the
    respected cayley graphs is found.
  10. Aqilahfarhana Abdul Rahman, Wan Heng Fong, Nor Haniza Sarmin, Sherzod Turaev, Nurul Liyana Mohamad Zulkufli
    MATEMATIKA, 2019;35(3):283-296.
    MyJurnal
    DNA computing, or more generally, molecular computing, is a recent development on computations using biological molecules, instead of the traditional silicon-chips. Some computational models which are based on different operations of DNA molecules have been developed by using the concept of formal language theory. The operations of DNA molecules inspire various types of formal language tools which include sticker systems, grammars and automata. Recently, the grammar counterparts of Watson-Crick automata known as Watson-Crick grammars which consist of regular, linear and context-free grammars, are defined as grammar models that generate double-stranded strings using the important feature of Watson-Crick complementarity rule. In this research, a new variant of static Watson-Crick linear grammar is introduced as an extension of static Watson-Crick regular grammar. A static Watson-Crick linear grammar is a grammar counterpart of sticker system that generates the double-stranded strings and uses rule as in linear grammar. The main result of the paper is to determine some computational properties of static Watson-Crick linear grammars. Next, the hierarchy between static Watson-Crick languages, Watson-Crick languages, Chomsky languages and families of languages generated by sticker systems are presented.
  11. Azim Azahari, Zuhaila Ismail, Normazni Abdullah
    MATEMATIKA, 2018;34(1):87-102.
    MyJurnal
    Numerical simulation of the behaviour of blood flow through a stenosed bifurcated
    artery with the presence of single mild stenosis at parent artery is investigated. The
    flow analysis applies the incompressible, steady, three-dimensional Navier-Stokes equations
    for non-Newtonian generalized power law fluids. Behaviour of blood flow is simulated
    numerically using COMSOL Multiphysicsthat based on finite element method.The
    results showthe effect of severity of stenosis on flow characteristics such as axial velocity
    and its exhibit flow recirculation zone for analysis on streamlines pattern.
  12. Azmirul Ashaari, Tahir Ahmad, Wan Munirah Wan Mohamad
    MATEMATIKA, 2018;34(2):235-244.
    MyJurnal
    Pressurized water reactor (PWR) type AP1000 is a third generation of a nuclear
    power plant. The primary system of PWR using uranium dioxide to generate heat energy
    via fission process. The process influences temperature, pressure and pH value of water
    chemistry of the PWR. The aim of this paper is to transform the primary system of PWR
    using fuzzy autocatalytic set (FACS). In this work, the background of primary system
    of PWR and the properties of the model are provided. The simulation result, namely
    dynamic concentration of PWR is verified against published data.
  13. Bako Sunday Samuel, Mohd Bakri Adam, Anwar Fitrianto
    MATEMATIKA, 2018;34(2):365-380.
    MyJurnal
    Recent studies have shown that independent identical distributed Gaussian
    random variables is not suitable for modelling extreme values observed during extremal
    events. However, many real life data on extreme values are dependent and stationary
    rather than the conventional independent identically distributed data. We propose a stationary
    autoregressive (AR) process with Gumbel distributed innovation and characterise
    the short-term dependence among maxima of an (AR) process over a range of sample
    sizes with varying degrees of dependence. We estimate the maximum likelihood of the
    parameters of the Gumbel AR process and its residuals, and evaluate the performance
    of the parameter estimates. The AR process is fitted to the Gumbel-generalised Pareto
    (GPD) distribution and we evaluate the performance of the parameter estimates fitted
    to the cluster maxima and the original series. Ignoring the effect of dependence leads to
    overestimation of the location parameter of the Gumbel-AR (1) process. The estimate
    of the location parameter of the AR process using the residuals gives a better estimate.
    Estimate of the scale parameter perform marginally better for the original series than the
    residual estimate. The degree of clustering increases as dependence is enhance for the AR
    process. The Gumbel-AR(1) fitted to the threshold exceedances shows that the estimates
    of the scale and shape parameters fitted to the cluster maxima perform better as sample
    size increases, however, ignoring the effect of dependence lead to an underestimation of
    the parameter estimates of the scale parameter. The shape parameter of the original
    series gives a superior estimate compare to the threshold excesses fitted to the Gumbel
    distributed Generalised Pareto ditribution.
  14. Chai, Jin Sian, Hoe, Yeak Su, Ali H. M. Murid
    MATEMATIKA, 2018;34(2):0-0.
    MyJurnal
    A mathematical model is considered to determine the effectiveness of disin-
    fectant solution for surface decontamination. The decontamination process involved the
    diffusion of bacteria into disinfectant solution and the reaction of the disinfectant killing
    effect. The mathematical model is a reaction-diffusion type. Finite difference method and
    method of lines with fourth-order Runge-Kutta method are utilized to solve the model
    numerically. To obtain stable solutions, von Neumann stability analysis is employed to
    evaluate the stability of finite difference method. For stiff problem, Dormand-Prince
    method is applied as the estimated error of fourth-order Runge-Kutta method. MATLAB
    programming is selected for the computation of numerical solutions. From the results
    obtained, fourth-order Runge-Kutta method has a larger stability region and better ac-
    curacy of solutions compared to finite difference method when solving the disinfectant
    solution model. Moreover, a numerical simulation is carried out to investigate the effect
    of different thickness of disinfectant solution on bacteria reduction. Results show that
    thick disinfectant solution is able to reduce the dimensionless bacteria concentration more
    effectively.
  15. Cynthia Kon Mui Lian, Jane Labadin
    MATEMATIKA, 2019;35(3):309-330.
    MyJurnal
    Dengue is a mosquito-borne disease caused by virus and found mostly in urban and semi-urban areas, in many regions of the world. Female Aedes mosquitoes, which usually bite during daytime, spread the disease. This flu-like disease may progress to severe dengue and cause fatality. A generic reaction-diffusion model for transmission of mosquito-borne diseases was proposed and formulated. The motivation is to explore the ability of the generic model to reproduce observed dengue cases in Borneo, Malaysia. Dengue prevalence in four districts in Borneo namely Kuching, Sibu, Bintulu and Miri are compared with simulations results obtained from the temporal and spatio-temporal generic model respectively. Random diffusion of human and mosquito populations are taken into account in the spatio-temporal model. It is found that temporal simulations closely resemble the general behavior of actual prevalence in the three locations except for Bintulu. The recovery rate in Bintulu district is found to be the lowest among the districts, suggesting a different dengue serotype may be present. From observation, the temporal generic model underestimates the recovery rate in comparison to the spatio-temporal generic model.
  16. Dedy Dwi Prastyo, Yurike Nurmala Rucy, Advendos D.C. Sigalingging, Suhartono, Fam,Soo-Fen
    MATEMATIKA, 2018;34(101):73-81.
    MyJurnal
    Coxmodel is popular in survival analysis. In the case of time-varying covariate;
    several subject-specific attributes possibly to change more frequently than others. This
    paper deals with that issue. This study aims to analyze survival data with time-varying
    covariate using a time-dependent covariate Cox model. The two case studies employed in
    this work are (1) delisting time of companies from IDX and (2) delisting time of company
    from LQ45 (liquidity index). The survival time is the time until a company is delisted
    from IDX or LQ45. The determinants are eighteen quarterly financial ratios and two
    macroeconomics indicators, i.e., the Jakarta Composite Index (JCI) and BI interest rate
    that changes more frequent. The empirical results show that JCI is significant for both
    delisting and liquidity whereas BI rate is significant only for liquidity. The significant
    firm-specific financial ratios vary for delisting and liquidity.
  17. Eng Woo Chiew, Siok Kun Sek
    MATEMATIKA, 2019;35(301):99-122.
    MyJurnal
    Price stability is one of the main policy objectives that is targeted by policymakers in many countries. Price uncertainty occurs due to the changes in market structure and consumer preference and expectation, which may affect price stability. In this study, the researchers aimed to examine the effects of price uncertainty of consumer price disaggregation in Malaysian sectors. To be specific, the researchers were seeking to discover on how domestic and global commodity prices can affect sectoral Consumer Price Index (CPI) on price inflation in Malaysia and most importantly, whether the effect is different for economic sectors in Malaysia. In addition, the effects of other factors (i.e., internal and external factors) on Malaysian sectoral CPI inflation were also studied. The threshold generalized autoregressive conditional heteroscedasticity (TGARCH) model was used to generate the price uncertainties. For the purpose of analysis, the threshold regression approach was applied based on time series of each single sector, followed by a combination of panel data of all sectors. The results differed across sectors, revealing that the impact of price uncertainties was determined by the sensitivity of each sector towards the price uncertainties. The effect of price increase is larger than the effect of price decrease. Price fluctuations were obvious in sectors that were dependent on consumer price or commodity price. Exchange rate and oil price inflation had also greatly influenced the CPI inflation.
  18. Farhana Johar, Julies Bong Shu Ai, Fuaada Mohd Siam
    MATEMATIKA, 2020;36(3):235-250.
    MyJurnal
    A new topic of Zero Energy Building (ZEB) is getting famous in research area
    because of its goal of reaching zero carbon emission and low building cost. Renewable
    energy system is one of the ideas to achieve the objective of ZEB. Genetic Algorithm (GA)
    is widely used in many research areas due to its capability to escape from a local minimal
    to obtain a better solution. In our study, GA is chosen in sizing optimization of the
    number of photovoltaic, wind turbine and battery of a hybrid photovoltaic-wind-battery
    system. The aim is to minimize the total annual cost (TAC) of the hybrid energy system
    towards the low cost concept of ZEB. Two GA parameters, which are generation number
    and population size, have been analysed and optimized in order to meet the minimum
    TAC. The results show that the GA is efficient in minimizing cost function of a hybrid
    photovoltaic-wind-battery system with its robustness property.
  19. Fasihah Zulkiflee, Ahmad Qushairi Mohamad, Sharidan Shafie, Arshad Khan
    MATEMATIKA, 2019;35(2):117-127.
    MyJurnal
    Free convection flow in a boundary layer region is a motion that results from the interaction of gravity with density differences within a fluid. These differences occur due to temperature or concentration gradients or due to their composition. Studies per- taining free convection flows of incompressible viscous fluids have received much attention in recent years both theoretically (exact or approximate solutions) and experimentally. The situation where the heat be transported to the convective fluid via a bounding sur- face having finite heat capacity is known as Newtonian heating (or conjugate convective flows). In this paper, the unsteady free convection flow of an incompressible viscous fluid between two parallel plates with Newtonian heating is studied. Appropriate non- dimensional variables are used to reduce the dimensional governing equations along with imposed initial and boundary conditions into dimensionless forms. The exact solutions for velocity and temperature are obtained using the Laplace transform technique. The corresponding expressions for skin friction and Nusselt number are also calculated. The graphical results are displayed to illustrate the influence of various embedded parameters such as Newtonian heating parameter and Grashof number. The results show that the effect of Newtonian heating parameter increases the Nusselt number but reduces the skin friction.
  20. Fauzi Mohamed Yusof, Mohd Hafiz Mohd, Yazariah Mohd Yatim, Ahmad Izani Md. Ismail
    MATEMATIKA, 2020;36(1):1-14.
    MyJurnal
    In this paper, the combined influences of biotic interactions, environmental components and harvesting strategy on the spread of Hantavirus are investigated. By employing a multi-species model consisting of (susceptible and infected) rodents and alien species, we show that interspecific competition from alien species has an effect in reducing the spread of infection, and this species could be employed as a potential biocontrol agent. Our analysis using numerical continuation and simulation also reveals the conditions under which Hantavirus infection occurs and disappears as the environmental conditions and the intensity of harvesting change. Without harvesting, infection emerges when environments are conducive. Inclusion of moderate harvesting in favourable environments can lead to disappearance of infection among rodent species. However, as the intensity of harvesting increases, this situation can cause extinction of all rodents species and consequently, jeopardise biodiversity. Overall, our results demonstrate how the interplay of different factors can combine to determine the spread of infectious diseases.
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