Displaying publications 281 - 300 of 616 in total

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  1. X-ray spectra and quality parameters from Monte Carlo simulation and analytical filters
    Salehi Z, Ya Ali NK, Yusoff AL
    Appl Radiat Isot, 2012 Nov;70(11):2586-9.
    PMID: 22940409 DOI: 10.1016/j.apradiso.2011.12.007
    BEAMnrc was used to derive the X-ray spectra, from which HVL and homogeneity coefficient were determined, for different kVp and filtration settings. Except for the peak at 61 keV, the spectra are in good agreement with the IPEM report 78 data for the case of filtered beams, whereas the unfiltered beams exhibit softer spectra. Although the current attenuation data deviates from the IPEM 78 data by ~±0.5%, this has negligible effects on the calculated HVL values.
    Matched MeSH terms: Computer Simulation
  2. The evaluation of various kinetic models for base-catalyzed ethanolysis of palm oil
    Shahla S, Ngoh GC, Yusoff R
    Bioresour Technol, 2012 Jan;104:1-5.
    PMID: 22154586 DOI: 10.1016/j.biortech.2011.11.010
    In this paper, the kinetics of palm oil ethanolysis with various models have been investigated in a temperature range of 25-55 °C. The highest yield was achieved when the conversion to ethyl ester was 97.5±0.5% in the stated temperature range, using ethanol:oil molar ratio of 12:1, and 1.0 wt.% sodium ethoxide. The level of conformity of the reaction with reversible second order, irreversible second order and first order kinetic models were evaluated by means of the R(2) values of the linear curves. The ethanolysis showed the best conformity with irreversible second order kinetic model with 92-98% level of confidence. The reaction rate constants were within 0.018-0.088 dm(3)/mol min and the activation energy of the reaction was 42.36 kJ/mol.
    Matched MeSH terms: Computer Simulation
  3. A method for control of an implantable rotary blood pump for heart failure patients using noninvasive measurements
    Lim E, Alomari AH, Savkin AV, Dokos S, Fraser JF, Timms DL, et al.
    Artif Organs, 2011 Aug;35(8):E174-80.
    PMID: 21843286 DOI: 10.1111/j.1525-1594.2011.01268.x
    We propose a deadbeat controller for the control of pulsatile pump flow (Q(p) ) in an implantable rotary blood pump (IRBP). Noninvasive measurements of pump speed and current are used as inputs to a dynamical model of Q(p) estimation, previously developed and verified in our laboratory. The controller was tested using a lumped parameter model of the cardiovascular system (CVS), in combination with the stable dynamical models of Q(p) and differential pressure (head) estimation for the IRBP. The control algorithm was tested with both constant and sinusoidal reference Q(p) as input to the CVS model. Results showed that the controller was able to track the reference input with minimal error in the presence of model uncertainty. Furthermore, Q(p) was shown to settle to the desired reference value within a finite number of sampling periods. Our results also indicated that counterpulsation yields the minimum left ventricular stroke work, left ventricular end diastolic volume, and aortic pulse pressure, without significantly affecting mean cardiac output and aortic pressure.
    Matched MeSH terms: Computer Simulation
  4. Particle swarm optimization on threshold exponential gain of stimulated Brillouin scattering in single mode fibers
    Al-Asadi HA, Al-Mansoori MH, Hitam S, Saripan MI, Mahdi MA
    Opt Express, 2011 Jan 31;19(3):1842-53.
    PMID: 21368999 DOI: 10.1364/OE.19.001842
    We implement a particle swarm optimization (PSO) algorithm to characterize stimulated Brillouin scattering phenomena in optical fibers. The explicit and strong dependence of the threshold exponential gain on the numerical aperture, the pump laser wavelength and the optical loss coefficient are presented. The proposed PSO model is also evaluated with the localized, nonfluctuating source model and the distributed (non-localized) fluctuating source model. Using our model, for fiber lengths from 1 km to 29 km, the calculated threshold exponential gain of stimulated Brillouin scattering is gradually decreased from 17.4 to 14.6 respectively. The theoretical results of Brillouin threshold power predicted by the proposed PSO model show a good agreement with the experimental results for different fiber lengths from 1 km to 12 km.
    Matched MeSH terms: Computer Simulation
  5. Spectral estimation of nonstationary EEG using particle filtering with application to event-related desynchronization (ERD)
    Ting CM, Salleh ShH, Zainuddin ZM, Bahar A
    IEEE Trans Biomed Eng, 2011 Feb;58(2):321-31.
    PMID: 21257361 DOI: 10.1109/TBME.2010.2088396
    This paper proposes non-Gaussian models for parametric spectral estimation with application to event-related desynchronization (ERD) estimation of nonstationary EEG. Existing approaches for time-varying spectral estimation use time-varying autoregressive (TVAR) state-space models with Gaussian state noise. The parameter estimation is solved by a conventional Kalman filtering. This study uses non-Gaussian state noise to model autoregressive (AR) parameter variation with estimation by a Monte Carlo particle filter (PF). Use of non-Gaussian noise such as heavy-tailed distribution is motivated by its ability to track abrupt and smooth AR parameter changes, which are inadequately modeled by Gaussian models. Thus, more accurate spectral estimates and better ERD tracking can be obtained. This study further proposes a non-Gaussian state space formulation of time-varying autoregressive moving average (TVARMA) models to improve the spectral estimation. Simulation on TVAR process with abrupt parameter variation shows superior tracking performance of non-Gaussian models. Evaluation on motor-imagery EEG data shows that the non-Gaussian models provide more accurate detection of abrupt changes in alpha rhythm ERD. Among the proposed non-Gaussian models, TVARMA shows better spectral representations while maintaining reasonable good ERD tracking performance.
    Matched MeSH terms: Computer Simulation
  6. Surface phonon polariton characteristics of In(0.04)Al(0.06)Ga(0.90)N/AlN/Al(2)O(3) heterostructure
    Ng SS, Lee SC, Bakhori SK, Hassan Z, Abu Hassan H, Yakovlev VA, et al.
    Opt Express, 2010 May 10;18(10):10354-9.
    PMID: 20588890 DOI: 10.1364/OE.18.010354
    Surface phonon polariton (SPP) characteristics of In(0.04)Al(0.06)Ga(0.90)N/AlN/Al(2)O(3) heterostructure are investigated by means of p-polarized infrared (IR) attenuated total reflection spectroscopy. Two absorption dips corresponding to In(0.04)Al(0.06)Ga(0.90)N SPP modes are observed. In addition, two prominent dips and one relatively weak and broad dip corresponding to the Al(2)O(3) SPP mode, In(0.04)Al(0.06)Ga(0.90)N/Al(2)O(3) interface mode, and Al(2)O(3) bulk polariton mode, respectively, are clearly seen. No surface mode feature originating from the AlN layer is observed because it is too thin. Overall, the observations are in good agreement with the theoretical predictions.
    Matched MeSH terms: Computer Simulation
  7. Single-trial subspace-based approach for VEP extraction
    Kamel N, Yusoff MZ, Hani AF
    IEEE Trans Biomed Eng, 2011 May;58(5):1383-93.
    PMID: 21177154 DOI: 10.1109/TBME.2010.2101073
    A signal subspace approach for extracting visual evoked potentials (VEPs) from the background electroencephalogram (EEG) colored noise without the need for a prewhitening stage is proposed. Linear estimation of the clean signal is performed by minimizing signal distortion while maintaining the residual noise energy below some given threshold. The generalized eigendecomposition of the covariance matrices of a VEP signal and brain background EEG noise is used to transform them jointly to diagonal matrices. The generalized subspace is then decomposed into signal subspace and noise subspace. Enhancement is performed by nulling the components in the noise subspace and retaining the components in the signal subspace. The performance of the proposed algorithm is tested with simulated and real data, and compared with the recently proposed signal subspace techniques. With the simulated data, the algorithms are used to estimate the latencies of P(100), P(200), and P(300) of VEP signals corrupted by additive colored noise at different values of SNR. With the real data, the VEP signals are collected at Selayang Hospital, Kuala Lumpur, Malaysia, and the capability of the proposed algorithm in detecting the latency of P(100) is obtained and compared with other subspace techniques. The ensemble averaging technique is used as a baseline for this comparison. The results indicated significant improvement by the proposed technique in terms of better accuracy and less failure rate.
    Matched MeSH terms: Computer Simulation
  8. A hybrid ART-GRNN online learning neural network with a epsilon -insensitive loss function
    Yap KS, Lim CP, Abidin IZ
    IEEE Trans Neural Netw, 2008 Sep;19(9):1641-6.
    PMID: 18779094 DOI: 10.1109/TNN.2008.2000992
    In this brief, a new neural network model called generalized adaptive resonance theory (GART) is introduced. GART is a hybrid model that comprises a modified Gaussian adaptive resonance theory (MGA) and the generalized regression neural network (GRNN). It is an enhanced version of the GRNN, which preserves the online learning properties of adaptive resonance theory (ART). A series of empirical studies to assess the effectiveness of GART in classification, regression, and time series prediction tasks is conducted. The results demonstrate that GART is able to produce good performances as compared with those of other methods, including the online sequential extreme learning machine (OSELM) and sequential learning radial basis function (RBF) neural network models.
    Matched MeSH terms: Computer Simulation
  9. Fulltext Fundamental lifetime mechanisms in routing protocols for wireless sensor networks: a survey and open issues
    Eslaminejad M, Razak SA
    Sensors (Basel), 2012;12(10):13508-44.
    PMID: 23202008 DOI: 10.3390/s121013508
    Wireless sensor networks basically consist of low cost sensor nodes which collect data from environment and relay them to a sink, where they will be subsequently processed. Since wireless nodes are severely power-constrained, the major concern is how to conserve the nodes' energy so that network lifetime can be extended significantly. Employing one static sink can rapidly exhaust the energy of sink neighbors. Furthermore, using a non-optimal single path together with a maximum transmission power level may quickly deplete the energy of individual nodes on the route. This all results in unbalanced energy consumption through the sensor field, and hence a negative effect on the network lifetime. In this paper, we present a comprehensive taxonomy of the various mechanisms applied for increasing the network lifetime. These techniques, whether in the routing or cross-layer area, fall within the following types: multi-sink, mobile sink, multi-path, power control and bio-inspired algorithms, depending on the protocol operation. In this taxonomy, special attention has been devoted to the multi-sink, power control and bio-inspired algorithms, which have not yet received much consideration in the literature. Moreover, each class covers a variety of the state-of-the-art protocols, which should provide ideas for potential future works. Finally, we compare these mechanisms and discuss open research issues.
    Matched MeSH terms: Computer Simulation
  10. Axial contraction in etched optical fiber due to internal stress reduction
    Lim KS, Yang HZ, Chong WY, Cheong YK, Lim CH, Ali NM, et al.
    Opt Express, 2013 Feb 11;21(3):2551-62.
    PMID: 23481713 DOI: 10.1364/OE.21.002551
    When an optical fiber is dipped in an etching solution, the internal stress profile in the fiber varies with the fiber diameter. We observed a physical contraction as much as 0.2% in the fiber axial dimension when the fiber was reduced from its original diameter to ~6 µm through analysis using high resolution microscope images of the grating period of an etched FBG at different fiber diameters. This axial contraction is related to the varying axial stress profile in the fiber when the fiber diameter is reduced. On top of that, the refractive index of fiber core increases with reducing fiber diameter due to stress-optic effect. The calculated index increment is as much as 1.8 × 10(-3) at the center of fiber core after the diameter is reduced down to ~6 µm. In comparison with the conventional model that assumes constant grating period and neglects the variation in stress-induced index change in fiber core, our proposed model indicates a discrepancy as much as 3nm in Bragg wavelength at a fiber diameter of ~6 µm.
    Matched MeSH terms: Computer Simulation
  11. Dissipation of chlorothalonil, chlorpyrifos, and profenofos in a Malaysian agricultural soil: a comparison between the field experiment and simulation by the PERSIST model
    Ismail BS, Ngan CK
    J Environ Sci Health B, 2005;40(2):341-53.
    PMID: 15825685
    A comparison of dissipation of chlorothalonil, chlorpyrifos, and profenofos in a Malaysian agricultural soil between the field experiment and simulation by the PERSIST model was studied. A plot of sweet pea (Pisum sativum) from a farm in the Cameron Highlands was selected for the field experiment. The plot was treated with chlorothalonil, chlorpyrifos, and profenofos. Core soil collection was conducted according to the sampling schedule. Residues of the three pesticides were analyzed in the laboratory. Simulations of the three pesticides' persistency were also conducted using a computer-run software PERSIST. Generally, predicted data obtained using PERSIST were found to be high for the three pesticides except for one field measurement of chlorpyrifos. The predicted data for profenofos, which is the most mobile of the three pesticides tested, was not well matched with the observed data compared to chlorothalonil and chlorpyrifos.
    Matched MeSH terms: Computer Simulation
  12. Comparison between field experiment and PERSIST model simulation: dissipation of fenvalerate in a Malaysian agricultural soil
    Ismail BS, Maznah Z
    Bull Environ Contam Toxicol, 2005 Jun;74(6):1143-50.
    PMID: 16158853
    Matched MeSH terms: Computer Simulation
  13. Fulltext Monte Carlo Simulations for the Detection of Buried Objects Using Single Sided Backscattered Radiation
    Yip M, Saripan MI, Wells K, Bradley DA
    PLoS One, 2015;10(9):e0135769.
    PMID: 26348619 DOI: 10.1371/journal.pone.0135769
    Detection of buried improvised explosive devices (IEDs) is a delicate task, leading to a need to develop sensitive stand-off detection technology. The shape, composition and size of the IEDs can be expected to be revised over time in an effort to overcome increasingly sophisticated detection methods. As an example, for the most part, landmines are found through metal detection which has led to increasing use of non-ferrous materials such as wood or plastic containers for chemical based explosives being developed.
    Matched MeSH terms: Computer Simulation
  14. Fulltext View-Invariant Visuomotor Processing in Computational Mirror Neuron System for Humanoid
    Dawood F, Loo CK
    PLoS One, 2016;11(3):e0152003.
    PMID: 26998923 DOI: 10.1371/journal.pone.0152003
    Mirror neurons are visuo-motor neurons found in primates and thought to be significant for imitation learning. The proposition that mirror neurons result from associative learning while the neonate observes his own actions has received noteworthy empirical support. Self-exploration is regarded as a procedure by which infants become perceptually observant to their own body and engage in a perceptual communication with themselves. We assume that crude sense of self is the prerequisite for social interaction. However, the contribution of mirror neurons in encoding the perspective from which the motor acts of others are seen have not been addressed in relation to humanoid robots. In this paper we present a computational model for development of mirror neuron system for humanoid based on the hypothesis that infants acquire MNS by sensorimotor associative learning through self-exploration capable of sustaining early imitation skills. The purpose of our proposed model is to take into account the view-dependency of neurons as a probable outcome of the associative connectivity between motor and visual information. In our experiment, a humanoid robot stands in front of a mirror (represented through self-image using camera) in order to obtain the associative relationship between his own motor generated actions and his own visual body-image. In the learning process the network first forms mapping from each motor representation onto visual representation from the self-exploratory perspective. Afterwards, the representation of the motor commands is learned to be associated with all possible visual perspectives. The complete architecture was evaluated by simulation experiments performed on DARwIn-OP humanoid robot.
    Matched MeSH terms: Computer Simulation
  15. Integrated modeling and design for realizing a two-wheeled wheelchair for disabled
    Altalmas T, Aula A, Ahmad S, Tokhi MO, Akmeliawati R
    Assist Technol, 2016;28(3):159-74.
    PMID: 27187763 DOI: 10.1080/10400435.2016.1140688
    Two-wheeled wheelchairs are considered highly nonlinear and complex systems. The systems mimic a double-inverted pendulum scenario and will provide better maneuverability in confined spaces and also to reach higher level of height for pick and place tasks. The challenge resides in modeling and control of the two-wheeled wheelchair to perform comparably to a normal four-wheeled wheelchair. Most common modeling techniques have been accomplished by researchers utilizing the basic Newton's Laws of motion and some have used 3D tools to model the system where the models are much more theoretical and quite far from the practical implementation. This article is aimed at closing the gap between the conventional mathematical modeling approaches where the integrated 3D modeling approach with validation on the actual hardware implementation was conducted. To achieve this, both nonlinear and a linearized model in terms of state space model were obtained from the mathematical model of the system for analysis and, thereafter, a 3D virtual prototype of the wheelchair was developed, simulated, and analyzed. This has increased the confidence level for the proposed platform and facilitated the actual hardware implementation of the two-wheeled wheelchair. Results show that the prototype developed and tested has successfully worked within the specific requirements established.
    Matched MeSH terms: Computer Simulation
  16. A Review of Gene Knockout Strategies for Microbial Cells
    Tang PW, Chua PS, Chong SK, Mohamad MS, Choon YW, Deris S, et al.
    Recent Pat Biotechnol, 2015;9(3):176-97.
    PMID: 27185502
    BACKGROUND: Predicting the effects of genetic modification is difficult due to the complexity of metabolic net- works. Various gene knockout strategies have been utilised to deactivate specific genes in order to determine the effects of these genes on the function of microbes. Deactivation of genes can lead to deletion of certain proteins and functions. Through these strategies, the associated function of a deleted gene can be identified from the metabolic networks.

    METHODS: The main aim of this paper is to review the available techniques in gene knockout strategies for microbial cells. The review is done in terms of their methodology, recent applications in microbial cells. In addition, the advantages and disadvantages of the techniques are compared and discuss and the related patents are also listed as well.

    RESULTS: Traditionally, gene knockout is done through wet lab (in vivo) techniques, which were conducted through laboratory experiments. However, these techniques are costly and time consuming. Hence, various dry lab (in silico) techniques, where are conducted using computational approaches, have been developed to surmount these problem.

    CONCLUSION: The development of numerous techniques for gene knockout in microbial cells has brought many advancements in the study of gene functions. Based on the literatures, we found that the gene knockout strategies currently used are sensibly implemented with regard to their benefits.

    Matched MeSH terms: Computer Simulation
  17. Fulltext Solving the Traveling Salesman's Problem Using the African Buffalo Optimization
    Odili JB, Mohmad Kahar MN
    Comput Intell Neurosci, 2016;2016:1510256.
    PMID: 26880872 DOI: 10.1155/2016/1510256
    This paper proposes the African Buffalo Optimization (ABO) which is a new metaheuristic algorithm that is derived from careful observation of the African buffalos, a species of wild cows, in the African forests and savannahs. This animal displays uncommon intelligence, strategic organizational skills, and exceptional navigational ingenuity in its traversal of the African landscape in search for food. The African Buffalo Optimization builds a mathematical model from the behavior of this animal and uses the model to solve 33 benchmark symmetric Traveling Salesman's Problem and six difficult asymmetric instances from the TSPLIB. This study shows that buffalos are able to ensure excellent exploration and exploitation of the search space through regular communication, cooperation, and good memory of its previous personal exploits as well as tapping from the herd's collective exploits. The results obtained by using the ABO to solve these TSP cases were benchmarked against the results obtained by using other popular algorithms. The results obtained using the African Buffalo Optimization algorithm are very competitive.
    Matched MeSH terms: Computer Simulation
  18. Fulltext Distributed clone detection in static wireless sensor networks: random walk with network division
    Khan WZ, Aalsalem MY, Saad NM
    PLoS One, 2015;10(5):e0123069.
    PMID: 25992913 DOI: 10.1371/journal.pone.0123069
    Wireless Sensor Networks (WSNs) are vulnerable to clone attacks or node replication attacks as they are deployed in hostile and unattended environments where they are deprived of physical protection, lacking physical tamper-resistance of sensor nodes. As a result, an adversary can easily capture and compromise sensor nodes and after replicating them, he inserts arbitrary number of clones/replicas into the network. If these clones are not efficiently detected, an adversary can be further capable to mount a wide variety of internal attacks which can emasculate the various protocols and sensor applications. Several solutions have been proposed in the literature to address the crucial problem of clone detection, which are not satisfactory as they suffer from some serious drawbacks. In this paper we propose a novel distributed solution called Random Walk with Network Division (RWND) for the detection of node replication attack in static WSNs which is based on claimer-reporter-witness framework and combines a simple random walk with network division. RWND detects clone(s) by following a claimer-reporter-witness framework and a random walk is employed within each area for the selection of witness nodes. Splitting the network into levels and areas makes clone detection more efficient and the high security of witness nodes is ensured with moderate communication and memory overheads. Our simulation results show that RWND outperforms the existing witness node based strategies with moderate communication and memory overheads.
    Matched MeSH terms: Computer Simulation
  19. Morphology and kinetic modeling of molecularly imprinted organosilanol polymer matrix for specific uptake of creatinine
    Ang QY, Low SC
    Anal Bioanal Chem, 2015 Sep;407(22):6747-58.
    PMID: 26163132 DOI: 10.1007/s00216-015-8841-9
    Molecular imprinting is an emerging technique to create imprinted polymers that can be applied in affinity-based separation, in particular, biomimetic sensors. In this study, the matrix of siloxane bonds prepared from the polycondensation of hydrolyzed tetraethoxysilane (TEOS) was employed as the inorganic monomer for the formation of a creatinine (Cre)-based molecularly imprinted polymer (MIP). Doped aluminium ion (Al(3+)) was used as the functional cross-linker that generated Lewis acid sites in the confined silica matrix to interact with Cre via sharing of lone pair electrons. Surface morphologies and pore characteristics of the synthesized MIP were determined by field emission scanning electron microscopy (FESEM) and Brunauer-Emmet-Teller (BET) analyses, respectively. The imprinting efficiency of MIPs was then evaluated through the adsorption of Cre with regard to molar ratios of Al(3+). A Cre adsorption capacity of up to 17.40 mg Cre g(-1) MIP was obtained and adsorption selectivity of Cre to its analogues creatine (Cr) and N-hydroxysuccinimide (N-hyd) were found to be 3.90 ± 0.61 and 4.17 ± 3.09, respectively. Of all the studied MIP systems, chemisorption was predicted as the rate-limiting step in the binding of Cre. The pseudo-second-order chemical reaction kinetic provides the best correlation of the experimental data. Furthermore, the equilibrium adsorption capacity of MIP fit well with a Freundlich isotherm (R (2) = 0.98) in which the heterogeneous surface was defined.
    Matched MeSH terms: Computer Simulation
  20. In vitro evaluation and in silico screening of synthetic acetylcholinesterase inhibitors bearing functionalized piperidine pharmacophores
    Brahmachari G, Choo C, Ambure P, Roy K
    Bioorg Med Chem, 2015 Aug 01;23(15):4567-4575.
    PMID: 26105711 DOI: 10.1016/j.bmc.2015.06.005
    A series of densely functionalized piperidine (FP) scaffolds was synthesized following a diastereoselective one-pot multicomponent protocol under eco-friendly conditions. The FPs were evaluated in vitro for their acetylcholinesterase (AChE) inhibitory activity, and in silico studies for all the target compounds were carried out using pharmacophore mapping, molecular docking and quantitative structure-activity relationship (QSAR) analysis in order to understand the structural features required for interaction with the AChE enzyme and the key active site residues involved in the intermolecular interactions. Halogenation, nitration or 3,4-methylenedixoxy-substitution at the phenyl ring attached to the 2- and 6-positions of 1,2,5,6-tetrahydropyridine nucleus in compounds 14-17, 19, 20, 24 and 26 greatly enhanced the AChE inhibitory activity. The docking analysis demonstrated that the inhibitors are well-fitted in the active sites. The in silico studies enlighten the future course of studies in modifying the scaffolds for better therapeutic efficacy against the deadly Alzheimer's disease.
    Matched MeSH terms: Computer Simulation
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