Displaying publications 81 - 100 of 734 in total

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  1. Gul T, Islam S, Shah RA, Khalid A, Khan I, Shafie S
    PLoS One, 2015;10(7):e0126698.
    PMID: 26147287 DOI: 10.1371/journal.pone.0126698
    This paper studies the unsteady magnetohydrodynamics (MHD) thin film flow of an incompressible Oldroyd-B fluid over an oscillating inclined belt making a certain angle with the horizontal. The problem is modeled in terms of non-linear partial differential equations with some physical initial and boundary conditions. This problem is solved for the exact analytic solutions using two efficient techniques namely the Optimal Homotopy Asymptotic Method (OHAM) and Homotopy Perturbation Method (HPM). Both of these solutions are presented graphically and compared. This comparison is also shown in tabular form. An excellent agreement is observed. The effects of various physical parameters on velocity have also been studied graphically.
    Matched MeSH terms: Models, Theoretical
  2. Hooi, M.H., Tiong, W. K., Tay, K. G., Chiew,K. L., Sze, S. N.
    MATEMATIKA, 2018;34(2):333-350.
    MyJurnal
    In this paper, we look at the propagation of internal solitary waves over three
    different types of slowly varying region, i.e. a slowly increasing slope, a smooth bump and
    a parabolic mound in a two-layer fluid flow. The appropriate mathematical model for this
    problem is the variable-coefficient extended Korteweg-de Vries equation. The governing
    equation is then solved numerically using the method of lines. Our numerical simulations
    show that the internal solitary waves deforms adiabatically on the slowly increasing slope.
    At the same time, a trailing shelf is generated as the internal solitary wave propagates
    over the slope, which would then decompose into secondary solitary waves or a wavetrain.
    On the other hand, when internal solitary waves propagate over a smooth bump or a
    parabolic mound, a trailing shelf of negative polarity would be generated as the results of
    the interaction of the internal solitary wave with the decreasing slope of the bump or the
    parabolic mound. The secondary solitary waves is observed to be climbing the negative
    trailing shelf.
    Matched MeSH terms: Models, Theoretical
  3. Iqbal A, Jiat Tiang J, Kin Wong S, Alibakhshikenari M, Falcone F, Limiti E
    Sensors (Basel), 2020 Dec 19;20(24).
    PMID: 33352800 DOI: 10.3390/s20247320
    This article presents the detailed theoretical, simulation, and experimental analysis of a half-mode substrate integrated waveguide (HMSIW)-based multimode wideband filter. A third-order, semicircular HMSIW filter is developed in this paper. A semicircular HMSIW cavity resonator is adopted to achieve wide band characteristics. A U-shaped slot (acts as a λ/4 stub) in the center of a semicircular HMSIW cavity resonator and L-shaped open-circuited stubs are used to improve the out-of-band response by generating multiple transmission zeros (TZs) in the stop-band region of the filter. The TZs on either side of the passband can be controlled by adjusting dimensions of a U-shaped slot and L-shaped open-circuited stubs. The proposed filter covers a wide fractional bandwidth, has a lower insertion loss value, and has multiple TZs (which improves the selectivity). The simulated response of filter agrees well with the measured data. The proposed HMSIW bandpass filter can be integrated with any planar wideband communication system circuit, thanks to its planar structure.
    Matched MeSH terms: Models, Theoretical
  4. Abdul-Rashid, H.A., Al-Qdah, M.T., Chuah, H.T., Tayahi, M.
    ASM Science Journal, 2008;2(2):129-132.
    MyJurnal
    The operating principle and the performance of chromatic dispersion (CD) measurement technique are discussed through developed numerical models. The performance of the CD measurement technique was studied in terms of the measurement range and sensitivity as the wavelength separation was varied. Based on the numerical model, the technique sensitivity increased with wavelength separation. However, this increase in sensitivity was traded off with a narrower measurement range. The measurement technique was optimized at 5.0 GHz wavelength separation with a sensitivity of 0.009 (dB/ps/nm) and measurement range of 2500 ps/nm.
    Matched MeSH terms: Models, Theoretical
  5. Chieh, C.W., Asmawi Sanuddin, Reza Afshar, Aidy Ali
    MyJurnal
    The paper presents a simulation work conducted on the elastomer subjected to cyclic loads. A 3D finite element model of elastomer specimen, in accordance to ASTM D412, was developed using CATIA and ANSYS commercial finite element (FEM) packages. Fatigue life predicted from the simulation was compared with well-documented published data and it showed an acceptable agreement. Meanwhile, the simulated strain-life results are slightly lower than the experimental data. Several factors which potentially influenced the variations of the results were noted. Finally, some recommendations are offered at the end of this study to further improve the simulation
    Matched MeSH terms: Models, Theoretical
  6. Zaroog, Omar Suliman, Aidy Ali, Sahari, B.B., Rizal Zahari
    MyJurnal
    Compressive residual stress, induced by mechanical surface treatment, may relax during component
    operation life, due to thermal or mechanical mechanism. Fatigue life prediction for the components which have residual stress will be misled and inaccurately predicted the phenomenon of residual stress relaxation is not considered. Despite putting an effort on incorporating the residual stress relaxation, the issues remain concerned with the technical challenge of measuring and quantifying
    the magnitude of residual stress relaxation as well as redistribution during the loading cycling itself.
    In this paper, the residual stress relaxation and its models were reviewed and discussed to picture
    the best knowledge related to this topic, i.e. whether relaxation is a cause or an effect.
    Matched MeSH terms: Models, Theoretical
  7. Jaafar, M.S., Wong, N.J., Noorzaei, J., Thanoon, W.A.
    MyJurnal
    This study presents an efficient finite element analysis technique which shows great versatility in
    modelling of precast composite flooring system subjected to static loadings. The method incorporates sliding and opening in the analysis of composite structures using the interface element which was specifically designed to simulate the actual behaviour at the interfaces between contacting materials. A three-dimensional finite element model of the precast composite slab which exhibits discontinuous behaviour was performed to demonstrate the potential and applicability of the proposed method of analysis. The results of the analysis demonstrate that the overall response of a discontinuous system to external loading is significantly affected by the bonding condition at the interfaces between the contacting materials.
    Matched MeSH terms: Models, Theoretical
  8. Nur Ashida Salim, Muhammad Azizi Kaprowi, Ahmad Asri Abd Samat
    MyJurnal
    Space Vector Pulse Width Modulation (SVPWM) method is widely used as a modulation technique
    to drive a three-phase inverter. It is an advanced computational intensive method used in pulse width modulation (PWM) algorithm for the three-phase voltage source inverter. Compared with the other PWM techniques, SVPWM is easier to implement, thus, it is the most preferred technique among others. Mathematical model for SVPWM was developed using MATLAB/ Simulink software. In this paper, the interface between MATLAB Simulink with the three-phase inverter by using Arduino Uno microcontroller is proposed. Arduino Uno generates the SVPWM signals for Permanent Magnet Synchronous Motor (PMSM) and is described in this paper. This work consists of software and hardware implementations. Simulation was done via Matlab/Simulink software to verify the effectiveness of the system and to measure the percentage of Total Harmonic Distortion (THD). The results show that SVPWM technique is able to drive the three-phase inverter with the Arduino UNO.
    Matched MeSH terms: Models, Theoretical
  9. Nor Azizah Yacob, Anuar Ishak
    Sains Malaysiana, 2014;43:491-496.
    The steady, two-dimensional laminar flow of a power-law fluid over a permeable shrinking sheet of constant surface temperature is investigated. The governing partial differential equations were transformed into a system of nonlinear ordinary differential equations using a similarity transformation, before being solved numerically by the Runge-Kutta- Fehlberg method with shooting technique. The results are presented graphically and the effects of the power-law index n, suction parameter fw and Prandtl number Pr were discussed. It was found that stronger suction is necessary for the solution to exist for a pseudoplastic fluid (n<1) compared to a dilatant fluid (n>1).
    Matched MeSH terms: Models, Theoretical
  10. Kürkçü ÖK, Aslan E, Sezer M
    Sains Malaysiana, 2017;46:335-347.
    In this study, a novel matrix method based on collocation points is proposed to solve some linear and nonlinear integro-differential equations with variable coefficients under the mixed conditions. The solutions are obtained by means of Dickson and Taylor polynomials. The presented method transforms the equation and its conditions into matrix equations which comply with a system of linear algebraic equations with unknown Dickson coefficients, via collocation points in a finite interval. While solving the matrix equation, the Dickson coefficients and the polynomial approximation are obtained. Besides, the residual error analysis for our method is presented and illustrative examples are given to demonstrate the validity and applicability of the method.
    Matched MeSH terms: Models, Theoretical
  11. Khan NB, Ibrahim Z, Nguyen LTT, Javed MF, Jameel M
    PLoS One, 2017;12(10):e0185832.
    PMID: 28982172 DOI: 10.1371/journal.pone.0185832
    This study numerically investigates the vortex-induced vibration (VIV) of an elastically mounted rigid cylinder by using Reynolds-averaged Navier-Stokes (RANS) equations with computational fluid dynamic (CFD) tools. CFD analysis is performed for a fixed-cylinder case with Reynolds number (Re) = 104 and for a cylinder that is free to oscillate in the transverse direction and possesses a low mass-damping ratio and Re = 104. Previously, similar studies have been performed with 3-dimensional and comparatively expensive turbulent models. In the current study, the capability and accuracy of the RANS model are validated, and the results of this model are compared with those of detached eddy simulation, direct numerical simulation, and large eddy simulation models. All three response branches and the maximum amplitude are well captured. The 2-dimensional case with the RANS shear-stress transport k-w model, which involves minimal computational cost, is reliable and appropriate for analyzing the characteristics of VIV.
    Matched MeSH terms: Models, Theoretical
  12. Ainur, A.K., Sayang, M.D., Jannoo, Z., Yap, B.W.
    MyJurnal
    A Structural Equation Model (SEM) is often used to test whether a hypothesised theoretical model agrees with data by examining the model fit. This study investigates the effect of sample size and distribution of data (normal and non-normal) on goodness of fit measures in structural equation model. Simulation results confirm that the GoF measures are affected by sample size, whereas they are quite robust when data are not normal. Absolute measures (GFI, AGFI, RMSEA) are more affected by sample size while incremental fit measures such as TLI and CFI are less affected by sample size and non-normality.
    Matched MeSH terms: Models, Theoretical
  13. Hisham, A.F.B., Jaffar, M.M., Othman, J.
    MyJurnal
    There are many research papers on implementing the salam structure in the financial system. This
    study introduces a mathematical model of salam contract with credit risk that can be used as an Islamic financial derivative. It explores the properties of salam contract and the credit model that represents it, that is, the structural model with the default event on maturity of the salam contract.
    Matched MeSH terms: Models, Theoretical
  14. Dodd J, Sweby PK, Mayes S, Murchie EH, Karunaratne AS, Massawe F, et al.
    J Theor Biol, 2023 Mar 07;560:111373.
    PMID: 36509139 DOI: 10.1016/j.jtbi.2022.111373
    A principal objective in agriculture is to maximise food production; this is particularly relevant with the added demands of an ever increasing population, coupled with the unpredictability that climate change brings. Further improvements in productivity can only be achieved with an increased understanding of plant and crop processes. In this respect, mathematical modelling of plants and crops plays an important role. In this paper we present a two-scale mathematical model of crop yield that accounts for plant growth and canopy interactions. A system of nonlinear ordinary differential equations (ODEs) is formulated to describe the growth of each individual plant, where equations are coupled via a term that describes plant competition via canopy-canopy interactions. A crop of greenhouse plants is then modelled via an agent based modelling approach in which the growth of each plant is described via our system of ODEs. The model is formulated for the African drought tolerant legume bambara groundnut (Vigna subterranea), which is currently being investigated as a food source in light of climate change and food insecurity challenges. Our model allows us to account for plant diversity and also investigate the effect of individual plant traits (e.g. plant canopy size and planting distance) on the yield of the overall crop. Informed with greenhouse data, model results show that plant positioning relative to other plants has a large impact on individual plant yield. Variation in physiological plant traits from genetic diversity and the environmental effects lead to experimentally observed variations in crop yield. These traits include plant height, plant carrying capacity, leaf accumulation rate and canopy spread. Of these traits plant height and ground cover growth rates are found to have the greatest impact on crop yield. We also consider a range of different planting arrangements (uniform grid, staggered grid, circular rings and random allocation) and find that the staggered grid leads to the greatest crop yield (6% more compared to uniform grid). Whilst formulated specifically for bambara groundnut, the generic formulation of our model means that with changes to certain parameter's, it may be extended to other crop species that form a canopy.
    Matched MeSH terms: Models, Theoretical
  15. Singh GG, Harden-Davies H, Allison EH, Cisneros-Montemayor AM, Swartz W, Crosman KM, et al.
    Proc Natl Acad Sci U S A, 2021 02 02;118(5).
    PMID: 33504570 DOI: 10.1073/pnas.2100205118
    Matched MeSH terms: Models, Theoretical
  16. Homayounfar M, Zomorodian M, Martinez CJ, Lai SH
    PLoS One, 2015;10(12):e0143198.
    PMID: 26641095 DOI: 10.1371/journal.pone.0143198
    So far many optimization models based on Nash Bargaining Theory associated with reservoir operation have been developed. Most of them have aimed to provide practical and efficient solutions for water allocation in order to alleviate conflicts among water users. These models can be discussed from two viewpoints: (i) having a discrete nature; and (ii) working on an annual basis. Although discrete dynamic game models provide appropriate reservoir operator policies, their discretization of variables increases the run time and causes dimensionality problems. In this study, two monthly based non-discrete optimization models based on the Nash Bargaining Solution are developed for a reservoir system. In the first model, based on constrained state formulation, the first and second moments (mean and variance) of the state variable (water level in the reservoir) is calculated. Using moment equations as the constraint, the long-term utility of the reservoir manager and water users are optimized. The second model is a dynamic approach structured based on continuous state Markov decision models. The corresponding solution based on the collocation method is structured for a reservoir system. In this model, the reward function is defined based on the Nash Bargaining Solution. Indeed, it is used to yield equilibrium in every proper sub-game, thereby satisfying the Markov perfect equilibrium. Both approaches are applicable for water allocation in arid and semi-arid regions. A case study was carried out at the Zayandeh-Rud river basin located in central Iran to identify the effectiveness of the presented methods. The results are compared with the results of an annual form of dynamic game, a classical stochastic dynamic programming model (e.g. Bayesian Stochastic Dynamic Programming model, BSDP), and a discrete stochastic dynamic game model (PSDNG). By comparing the results of alternative methods, it is shown that both models are capable of tackling conflict issues in water allocation in situations of water scarcity properly. Also, comparing the annual dynamic game models, the presented models result in superior results in practice. Furthermore, unlike discrete dynamic game models, the presented models can significantly reduce the runtime thereby avoiding dimensionality problems.
    Matched MeSH terms: Models, Theoretical*
  17. Islam MT, Samsuzzaman M
    ScientificWorldJournal, 2014;2014:673846.
    PMID: 24987742 DOI: 10.1155/2014/673846
    This paper introduces a new configuration of compact, triangular- and diamond-slotted, microstrip-fed, low-profile antenna for C/X band applications on polytetrafluoroethylene glass microfiber reinforced material substrate. The antenna is composed of a rectangular-shaped patch containing eight triangles and two diamond-shaped slots and an elliptical-slotted ground plane. The rectangular-shaped patch is obtained by cutting two diamond slots in the middle of the rectangular patch, six triangular slots on the left and right side of the patch, and two triangular slots on the up and down side of the patch. The slotted radiating patch, the elliptical-slotted ground plane, and the microstrip feed enable the matching bandwidth to be widened. A prototype of the optimized antenna was fabricated on polytetrafluoroethylene glass microfiber reinforced material substrate using LPKF prototyping machine and investigated to validate the proposed design. The simulated results are compared with the measured data, and good agreement is achieved. The proposed antenna offers fractional bandwidths of 13.69% (7.78-8.91 GHz) and 10.35% (9.16-10.19 GHz) where S11 < -10 dB at center frequencies of 8.25 GHz and 9.95 GHz, respectively, and relatively stable gain, good radiation efficiency, and omnidirectional radiation patterns in the matching band.
    Matched MeSH terms: Models, Theoretical*
  18. Gharehkhani S, Nouri-Borujerdi A, Kazi SN, Yarmand H
    ScientificWorldJournal, 2014;2014:504601.
    PMID: 25143981 DOI: 10.1155/2014/504601
    In this study an expression for soot absorption coefficient is introduced to extend the weighted-sum-of-gray gases data to the furnace medium containing gas-soot mixture in a utility boiler 150 MWe. Heat transfer and temperature distribution of walls and within the furnace space are predicted by zone method technique. Analyses have been done considering both cases of presence and absence of soot particles at 100% load. To validate the proposed soot absorption coefficient, the expression is coupled with the Taylor and Foster's data as well as Truelove's data for CO2-H2O mixture and the total emissivities are calculated and compared with the Truelove's parameters for 3-term and 4-term gray gases plus two soot absorption coefficients. In addition, some experiments were conducted at 100% and 75% loads to measure furnace exit gas temperature as well as the rate of steam production. The predicted results show good agreement with the measured data at the power plant site.
    Matched MeSH terms: Models, Theoretical*
  19. Chiari L, Duque HV, Jones DB, Thorn PA, Pettifer Z, da Silva GB, et al.
    J Chem Phys, 2014 Jul 14;141(2):024301.
    PMID: 25028013 DOI: 10.1063/1.4885856
    We report on measurements of differential cross sections (DCSs) for electron impact excitation of a series of Rydberg electronic-states in α-tetrahydrofurfuryl alcohol (THFA). The energy range of these experiments was 20-50 eV, while the scattered electron was detected in the 10°-90° angular range. There are currently no other experimental data or theoretical computations against which we can directly compare the present measured results. Nonetheless, we are able to compare our THFA DCSs with earlier cross section measurements for Rydberg-state electronic excitation for tetrahydrofuran, a similar cyclic ether, from Do et al. [J. Chem. Phys. 134, 144302 (2011)]. In addition, "rotationally averaged" elastic DCSs, calculated using our independent atom model with screened additivity rule correction approach are also reported. Those latter results give integral cross sections consistent with the optical theorem, and supercede those from the only previous study of Milosavljević et al. [Eur. Phys. J. D 40, 107 (2006)].
    Matched MeSH terms: Models, Theoretical*
  20. Roslan R, Saleh H, Hashim I
    ScientificWorldJournal, 2014;2014:617492.
    PMID: 24991643 DOI: 10.1155/2014/617492
    The aim of the present numerical study is to analyze the conjugate natural convection heat transfer in a differentially heated square enclosure containing a conductive polygon object. The left wall is heated and the right wall is cooled, while the horizontal walls are kept adiabatic. The COMSOL Multiphysics software is applied to solve the dimensionless governing equations. The governing parameters considered are the polygon type, 3 ≤ N ≤ ∞, the horizontal position, 0.25 ≤ X 0 ≤ 0.75, the polygon size, 0 ≤ A ≤ π/16, the thermal conductivity ratio, 0.1 ≤ K r ≤ 10.0, and the Rayleigh number, 10(3) ≤ Ra ≤ 10(6). The critical size of the solid polygon was found exists at low conductivities. The heat transfer rate increases with the increase of the size of the solid polygon, until it reaches its maximum value. Here, the size of the solid polygon is reaches its critical value. Further, beyond this critical size of the solid polygon, will decrease the heat transfer rate.
    Matched MeSH terms: Models, Theoretical*
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