Displaying publications 121 - 140 of 616 in total

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  1. Fulltext Transmission dynamics of Zika virus incorporating harvesting
    Yue ZM, Yusof FM, Shafie S
    Math Biosci Eng, 2020 09 15;17(5):6181-6202.
    PMID: 33120594 DOI: 10.3934/mbe.2020327
    In this paper, we establish a ZIKV model and investigate the transmission dynamics of ZIKV with two types of harvesting: proportional harvesting and constant harvesting, and give the stability of the steady states of both disease-free and endemic equilibrium, analyze the effect of harvesting on ZIKV transmission dynamics via numerical simulation. We find that proportional harvesting strategy can eliminate the virus when the basic reproduction number $R_0$ is less than 1, but the constant harvesting strategy may control the virus whether the basic reproduction number is less than 1 or not. Epidemiologically, we find that increasing harvesting may stimulate an increase in the number of virus infections at some point, and harvesting can postpone the peak of disease transmission with the mortality of mosquito increasing. The results can provide us with some useful control strategies to regulate ZIKV dynamics.
    Matched MeSH terms: Computer Simulation
  2. Population pharmacokinetic modelling of intravenous immunoglobulin in patients with predominantly antibody deficiencies
    Lee JL, Mohd Saffian S, Makmor-Bakry M, Islahudin F, Alias H, Noh LM, et al.
    Br J Clin Pharmacol, 2021 07;87(7):2956-2966.
    PMID: 33377197 DOI: 10.1111/bcp.14712
    AIMS: There is considerable interpatient variability in the pharmacokinetics (PK) of intravenous immunoglobulin G (IVIG), causing difficulty in optimizing individual dosage regimen. This study aims to estimate the population PK parameters of IVIG and to investigate the impact of genetic polymorphism of the FcRn gene and clinical variability on the PK of IVIG in patients with predominantly antibody deficiencies.

    METHODS: Patients were recruited from four hospitals. Clinical data were recorded and blood samples were taken for PK and genetic studies. Population PK parameters were estimated by nonlinear mixed-effects modelling in Monolix®. Models were evaluated using the difference in objective function value, goodness-of-fit plots, visual predictive check and bootstrap analysis. Monte Carlo simulation was conducted to evaluate different dosing regimens for IVIG.

    RESULTS: A total of 30 blood samples were analysed from 10 patients. The immunoglobulin G concentration data were best described by a one-compartment model with linear elimination. The final model included both volume of distribution (Vd) and clearance (CL) based on patient's individual weight. Goodness-of-fit plots indicated that the model fit the data adequately, with minor model mis-specification. Genetic polymorphism of the FcRn gene and the presence of bronchiectasis did not affect the PK of IVIG. Simulation showed that 3-4-weekly dosing intervals were sufficient to maintain IgG levels of 5 g L-1 , with more frequent intervals needed to achieve higher trough levels.

    CONCLUSIONS: Body weight significantly affects the PK parameters of IVIG. Genetic and other clinical factors investigated did not affect the disposition of IVIG.

    Matched MeSH terms: Computer Simulation
  3. Fulltext Performance of ultra-wideband systems in the presence of WiFi and 3G signals
    Rashid, A.S., Khatun, S., Ali, B.M., Khazani, A.M.
    ASM Science Journal, 2008;2(1):13-22.
    MyJurnal
    An analysis of the power spectral density of ultra-wideband (UWB) signals is presented in order to evaluate the effects of cumulative interference from multiple UWB devices on victim narrowband systems in their overlay bands like WiFi (i.e. IEEE802.11a) and 3rdG systems (Universal mobile telecommunications system/wideband code division multiple access). In this paper, the performances are studied through the bit-error-rate as a function of signal-to-noise ratio as well as signal-to-interference power ratio using computer simulation and exploiting the realistic channel model (i.e. modified Saleh-Valenzuela model). Several modifications of a generic Gaussian pulse waveform with lengths in the order of nanoseconds were used to generate UWB spectra. Different kinds of pulse modulation (i.e. antipodal and orthogonal) schemes were also taken into account.
    Matched MeSH terms: Computer Simulation
  4. Fulltext Jammer Localization Using Wireless Devices with Mitigation by Self-Configuration
    Ashraf QM, Habaebi MH, Islam MR
    PLoS One, 2016;11(9):e0160311.
    PMID: 27583378 DOI: 10.1371/journal.pone.0160311
    Communication abilities of a wireless network decrease significantly in the presence of a jammer. This paper presents a reactive technique, to detect and locate the position of a jammer using a distributed collection of wireless sensor devices. We employ the theory of autonomic computing as a framework to design the same. Upon detection of a jammer, the affected nodes self-configure their power consumption which stops unnecessary waste of battery resources. The scheme then proceeds to determine the approximate location of the jammer by analysing the location of active nodes as well as the affected nodes. This is done by employing a circular curve fitting algorithm. Results indicate a high degree of accuracy in localizing a jammer has been achieved.
    Matched MeSH terms: Computer Simulation
  5. Fulltext A Secure Region-Based Geographic Routing Protocol (SRBGR) for Wireless Sensor Networks
    Adnan AI, Hanapi ZM, Othman M, Zukarnain ZA
    PLoS One, 2017;12(1):e0170273.
    PMID: 28121992 DOI: 10.1371/journal.pone.0170273
    Due to the lack of dependency for routing initiation and an inadequate allocated sextant on responding messages, the secure geographic routing protocols for Wireless Sensor Networks (WSNs) have attracted considerable attention. However, the existing protocols are more likely to drop packets when legitimate nodes fail to respond to the routing initiation messages while attackers in the allocated sextant manage to respond. Furthermore, these protocols are designed with inefficient collection window and inadequate verification criteria which may lead to a high number of attacker selections. To prevent the failure to find an appropriate relay node and undesirable packet retransmission, this paper presents Secure Region-Based Geographic Routing Protocol (SRBGR) to increase the probability of selecting the appropriate relay node. By extending the allocated sextant and applying different message contention priorities more legitimate nodes can be admitted in the routing process. Moreover, the paper also proposed the bound collection window for a sufficient collection time and verification cost for both attacker identification and isolation. Extensive simulation experiments have been performed to evaluate the performance of the proposed protocol in comparison with other existing protocols. The results demonstrate that SRBGR increases network performance in terms of the packet delivery ratio and isolates attacks such as Sybil and Black hole.
    Matched MeSH terms: Computer Simulation
  6. Semicarbazone derivatives as urease inhibitors: Synthesis, biological evaluation, molecular docking studies and in-silico ADME evaluation
    Qazi SU, Rahman SU, Awan AN, Al-Rashida M, Alharthy RD, Asari A, et al.
    Bioorg Chem, 2018 09;79:19-26.
    PMID: 29709568 DOI: 10.1016/j.bioorg.2018.03.029
    A series of hydrazinecarboxamide derivatives were synthesized and examined against urease for their inhibitory activity. Among the series, the 1-(3-fluorobenzylidene)semicarbazide (4a) (IC50 = 0.52 ± 0.45 µM), 4u (IC50 = 1.23 ± 0.32 µM) and 4h (IC50 = 2.22 ± 0.32 µM) were found most potent. Furthermore, the molecular docking study was also performed to demonstrate the binding mode of the active hydrazinecarboxamide with the enzyme, urease. In order to estimate drug likeness of compounds, in silico ADME evaluation was carried out. All compounds exhibited favorable ADME profiles with good predicted oral bioavailability.
    Matched MeSH terms: Computer Simulation
  7. Challenging Conventional Paradigms in Applied Sports Biomechanics Research
    Glazier PS, Mehdizadeh S
    Sports Med, 2019 Feb;49(2):171-176.
    PMID: 30511347 DOI: 10.1007/s40279-018-1030-1
    This paper evaluates the effectiveness of, and highlights issues with, conventional paradigms in applied sports biomechanics research and comments on their capacity to optimise techniques of individual athletes. In empirical studies, group-based analyses often mask variability between athletes and only permit probabilistic 'in general' or 'on average' statements that may not be applicable to specific athletes. In individual-based analyses, performance parameters typically exhibit a small range and a flat response over iterative performance trials, making establishing associations between performance parameters and the performance criterion problematic. In theoretical studies, computer simulation modelling putatively enables athlete-specific optimum techniques to be identified, but given each athlete's unique intrinsic dynamics, it is far from certain that these optimum techniques will be attainable, particularly under the often intense psychological pressures of competition, irrespective of the volume of practice undertaken. Sports biomechanists and coaching practitioners are advised to be more circumspect with regard to interpreting the results of applied sports biomechanics research and have greater awareness of their assumptions and limitations, as inappropriate interpretation of results may have adverse consequences for performance and injury.
    Matched MeSH terms: Computer Simulation
  8. Fulltext Economic-statistical design of synthetic np chart with estimated process parameter
    Lee MH, Khoo MBC, Chew X, Then PHH
    PLoS One, 2020;15(4):e0230994.
    PMID: 32267874 DOI: 10.1371/journal.pone.0230994
    The economic-statistical design of the synthetic np chart with estimated process parameter is presented in this study. The effect of process parameter estimation on the expected cost of the synthetic np chart is investigated with the imposed statistical constraints. The minimum number of preliminary subgroups is determined where an almost similar expected cost to the known process parameter case is desired for the given cost model parameters. However, the available number of preliminary subgroups in practice is usually limited, especially when the number of preliminary subgroups is large. Consequently, the optimal chart parameters of the synthetic np chart are computed by considering the practical number of preliminary subgroups in which the cost function is minimized. This leads to a lower expected cost compared to that of adopting the optimal chart parameter corresponding to the known process parameter case.
    Matched MeSH terms: Computer Simulation
  9. Fulltext Using simulation model as a tool for analyzing bus service reliability and implementing improvement strategies
    Moosavi SMH, Ismail A, Yuen CW
    PLoS One, 2020;15(5):e0232799.
    PMID: 32379848 DOI: 10.1371/journal.pone.0232799
    Bus services naturally tend to be unstable and are not always capable of adhering to schedules without control strategies. Therefore, bus users and bus service providers face travel time variation and irregularity. After a comprehensive review of the literature, a significant gap was recognized in the field of public transportation reliability. According to literature, there is no consistency in reliability definition and indicators. Companies have their own definition of bus service reliability, and they mostly neglect the passengers' perspective of reliability. Therefore, four reliability indicators were selected in this study to fill the gap in the literature and cover both passengers' and operators' perceptions of reliability: waiting time and on-board crowding level from passengers' perspective, and headway regularity index at stops (HRIS) and bus bunching/big gap percentage from operators' perspective. The primary objective of this research is to improve the reliability of high frequency of bus service and simulation tools currently being used by the public transportation companies. Therefore, a simulation model of bus service was developed to study the strategies to alleviate it. Four different types of strategies were selected and implemented according to Route U32 (Kuala Lumpur) specifications. Model out-put showed that control strategies such as headway-based dispatching could significantly improve headway regularity by almost 62% and the waiting time by 51% on average. Both holding strategies at key stops (previous and Prefol holding) have shown an almost similar impact on reliability indicators. Waiting time was reduced by 44% and 43% after the previous and Prefol Headway strategies were adopted, respectively. However, the implementation of the component of headway-based strategies at the terminal and key stops showed the best impact on reliability, in terms of passenger waiting time. Waiting time and excess waiting time were both significantly reduced by 52.86% and 81.44%, respectively. Nevertheless, the strategies did not show any significant positive effect on the level of crowding during morning peak hours.
    Matched MeSH terms: Computer Simulation
  10. Fulltext Multi-Agent Systems in Fog-Cloud Computing for Critical Healthcare Task Management Model (CHTM) Used for ECG Monitoring
    Mutlag AA, Ghani MKA, Mohammed MA, Lakhan A, Mohd O, Abdulkareem KH, et al.
    Sensors (Basel), 2021 Oct 19;21(20).
    PMID: 34696135 DOI: 10.3390/s21206923
    In the last decade, the developments in healthcare technologies have been increasing progressively in practice. Healthcare applications such as ECG monitoring, heartbeat analysis, and blood pressure control connect with external servers in a manner called cloud computing. The emerging cloud paradigm offers different models, such as fog computing and edge computing, to enhance the performances of healthcare applications with minimum end-to-end delay in the network. However, many research challenges exist in the fog-cloud enabled network for healthcare applications. Therefore, in this paper, a Critical Healthcare Task Management (CHTM) model is proposed and implemented using an ECG dataset. We design a resource scheduling model among fog nodes at the fog level. A multi-agent system is proposed to provide the complete management of the network from the edge to the cloud. The proposed model overcomes the limitations of providing interoperability, resource sharing, scheduling, and dynamic task allocation to manage critical tasks significantly. The simulation results show that our model, in comparison with the cloud, significantly reduces the network usage by 79%, the response time by 90%, the network delay by 65%, the energy consumption by 81%, and the instance cost by 80%.
    Matched MeSH terms: Computer Simulation
  11. Multi-model generalised predictive control for intravenous anaesthesia under inter-individual variability
    Jing CJ, Syafiie S
    J Clin Monit Comput, 2021 10;35(5):1037-1045.
    PMID: 32833146 DOI: 10.1007/s10877-020-00581-0
    Inter-individual variability possesses a major challenge in the regulation of hypnosis in anesthesia. Understanding the variability towards anesthesia effect is expected to assist the design of controller for anesthesia regulation. However, such studies are still very scarce in the literature. This study aims to analyze the inter-individual variability in propofol pharmacokinetics/pharmacodynamics (PK/PD) model and proposed a suitable controller to tackle the variability. This study employed Sobol' sensitivity analysis to identify significance parameters in propofol PK/PD model that affects the model output Bispectral Index (BIS). Parameters' range is obtained from reported clinical data. Based on the finding, a multi-model generalized predictive controller was proposed to regulate propofol in tackling patient variability. [Formula: see text] (concentration that produces 50% of the maximum effect) was found to have a highly-determining role on the uncertainty of BIS. In addition, the Hill coefficient, [Formula: see text], was found to be significant when there is a drastic input, especially during the induction phase. Both of these parameters only affect the process gain upon model linearization. Therefore, a predictive controller based on switching of model with different process gain is proposed. Simulation result shows that it is able to give a satisfactory performance across a wide population. Both the parameters [Formula: see text] and [Formula: see text], which are unknown before anesthesia procedure, were found to be highly significant in contributing the uncertainty of BIS. Their range of variability must be considered during the design and evaluation of controller. A linear controller may be sufficient to tackle most of the variability since both [Formula: see text] and [Formula: see text] would be translated into process gain upon linearization.
    Matched MeSH terms: Computer Simulation
  12. Effect of intimal flap motion on flow in acute type B aortic dissection by using fluid-structure interaction
    Chong MY, Gu B, Chan BT, Ong ZC, Xu XY, Lim E
    Int J Numer Method Biomed Eng, 2020 12;36(12):e3399.
    PMID: 32862487 DOI: 10.1002/cnm.3399
    A monolithic, fully coupled fluid-structure interaction (FSI) computational framework was developed to account for dissection flap motion in acute type B aortic dissection (TBAD). Analysis of results included wall deformation, pressure, flow, wall shear stress (WSS), von Mises stress and comparison of hemodynamics between rigid wall and FSI models. Our FSI model mimicked realistic wall deformation that resulted in maximum compression of the distal true lumen (TL) by 21.4%. The substantial movement of intimal flap mostly affected flow conditions in the false lumen (FL). Flap motion facilitated more flow entering the FL at peak systole, with the TL to FL flow split changing from 88:12 in the rigid model to 83:17 in the FSI model. There was more disturbed flow in the FL during systole (5.8% FSI vs 5.2% rigid) and diastole (13.5% FSI vs 9.8% rigid), via a λ2 -criterion. The flap-induced disturbed flow near the tears in the FSI model caused an increase of local WSS by up to 70.0% during diastole. This resulted in a significant reduction in the size of low time-averaged WSS (TAWSS) regions in the FL (113.11 cm2 FSI vs 177.44 cm2 rigid). Moreover, the FSI model predicted lower systolic pressure, higher diastolic pressure, and hence lower pulse pressure. Our results provided new insights into the possible impact of flap motion on flow in aortic dissections, which are particularly important when evaluating hemodynamics of acute TBAD. NOVELTY STATEMENT: Our monolithic fully coupled FSI computational framework is able to reproduce experimentally measured range of flap deformation in aortic dissection, thereby providing novel insights into the influence of physiological flap motion on the flow and pressure distributions. The drastic flap movement increases the flow resistance in the true lumen and causes more disturbed flow in the false lumen, as visualized through the λ2 criterion. The flap-induced luminal pressure is dampened, thereby affecting pressure measures, which may serve as potential prognostic indicators for late complications in acute uncomplicated TBAD patients.
    Matched MeSH terms: Computer Simulation
  13. Fulltext An Efficient 5G Data Plan Approach Based on Partially Distributed Mobility Architecture
    Al Shinwan M, Abualigah L, Huy TD, Younes Shdefat A, Altalhi M, Kim C, et al.
    Sensors (Basel), 2022 Jan 04;22(1).
    PMID: 35009891 DOI: 10.3390/s22010349
    Reaching a flat network is the main target of future evolved packet core for the 5G mobile networks. The current 4th generation core network is centralized architecture, including Serving Gateway and Packet-data-network Gateway; both act as mobility and IP anchors. However, this architecture suffers from non-optimal routing and intolerable latency due to many control messages. To overcome these challenges, we propose a partially distributed architecture for 5th generation networks, such that the control plane and data plane are fully decoupled. The proposed architecture is based on including a node Multi-session Gateway to merge the mobility and IP anchor gateway functionality. This work presented a control entity with the full implementation of the control plane to achieve an optimal flat network architecture. The impact of the proposed evolved packet Core structure in attachment, data delivery, and mobility procedures is validated through simulation. Several experiments were carried out by using NS-3 simulation to validate the results of the proposed architecture. The Numerical analysis is evaluated in terms of total transmission delay, inter and intra handover delay, queuing delay, and total attachment time. Simulation results show that the proposed architecture performance-enhanced end-to-end latency over the legacy architecture.
    Matched MeSH terms: Computer Simulation
  14. Fulltext Functional and structural analysis of non-synonymous single nucleotide polymorphisms (nsSNPs) in the MYB oncoproteins associated with human cancer
    Lim SW, Tan KJ, Azuraidi OM, Sathiya M, Lim EC, Lai KS, et al.
    Sci Rep, 2021 12 17;11(1):24206.
    PMID: 34921182 DOI: 10.1038/s41598-021-03624-x
    MYB proteins are highly conserved DNA-binding domains (DBD) and mutations in MYB oncoproteins have been reported to cause aberrant and augmented cancer progression. Identification of MYB molecular biomarkers predictive of cancer progression can be used for improving cancer management. To address this, a biomarker discovery pipeline was employed in investigating deleterious non-synonymous single nucleotide polymorphisms (nsSNPs) in predicting damaging and potential alterations on the properties of proteins. The nsSNP of the MYB family; MYB, MYBL1, and MYBL2 was extracted from the NCBI database. Five in silico tools (PROVEAN, SIFT, PolyPhen-2, SNPs&GO and PhD-SNP) were utilized to investigate the outcomes of nsSNPs. A total of 45 nsSNPs were predicted as high-risk and damaging, and were subjected to PMut and I-Mutant 2.0 for protein stability analysis. This resulted in 32 nsSNPs with decreased stability with a DDG score lower than - 0.5, indicating damaging effect. G111S, N183S, G122S, and S178C located within the helix-turn-helix (HTH) domain were predicted to be conserved, further posttranslational modifications and 3-D protein analysis indicated these nsSNPs to shift DNA-binding specificity of the protein thus altering the protein function. Findings from this study would help in the field of pharmacogenomic and cancer therapy towards better intervention and management of cancer.
    Matched MeSH terms: Computer Simulation
  15. Nasal airflow comparison in neonates, infant and adult nasal cavities using computational fluid dynamics
    Corda JV, Shenoy BS, Ahmad KA, Lewis L, K P, Khader SMA, et al.
    Comput Methods Programs Biomed, 2022 Feb;214:106538.
    PMID: 34848078 DOI: 10.1016/j.cmpb.2021.106538
    BACKGROUND AND OBJECTIVE: Neonates are preferential nasal breathers up to 3 months of age. The nasal anatomy in neonates and infants is at developing stages whereas the adult nasal cavities are fully grown which implies that the study of airflow dynamics in the neonates and infants are significant. In the present study, the nasal airways of the neonate, infant and adult are anatomically compared and their airflow patterns are investigated.

    METHODS: Computational Fluid Dynamics (CFD) approach is used to simulate the airflow in a neonate, an infant and an adult in sedentary breathing conditions. The healthy CT scans are segmented using MIMICS 21.0 (Materialise, Ann arbor, MI). The patient-specific 3D airway models are analyzed for low Reynolds number flow using ANSYS FLUENT 2020 R2. The applicability of the Grid Convergence Index (GCI) for polyhedral mesh adopted in this work is also verified.

    RESULTS: This study shows that the inferior meatus of neonates accounted for only 15% of the total airflow. This was in contrast to the infants and adults who experienced 49 and 31% of airflow at the inferior meatus region. Superior meatus experienced 25% of total flow which is more than normal for the neonate. The highest velocity of 1.8, 2.6 and 3.7 m/s was observed at the nasal valve region for neonates, infants and adults, respectively. The anterior portion of the nasal cavity experienced maximum wall shear stress with average values of 0.48, 0.25 and 0.58 Pa for the neonates, infants and adults.

    CONCLUSIONS: The neonates have an underdeveloped nasal cavity which significantly affects their airway distribution. The absence of inferior meatus in the neonates has limited the flow through the inferior regions and resulted in uneven flow distribution.

    Matched MeSH terms: Computer Simulation
  16. Fulltext Research on the Communication Strategy of History and Culture in Shaanxi Based on BP Neural Network Model
    Xie D, Yin C
    Comput Intell Neurosci, 2022;2022:8965622.
    PMID: 35111216 DOI: 10.1155/2022/8965622
    Shaanxi is one of China's most important cradles of civilization. The main vein of Chinese culture is rich history and culture, and brilliant red culture embodies the essence of socialist core values. It is still relatively weak to deeply analyze the related research of Shaanxi Province's cultural province construction on the basis of studying the achievements of cultural development in foreign countries and China and combining with the reality of Shaanxi Province. In this paper, a BPNN (BP neural network) model is selected to study the comprehensive evaluation of tourism competitiveness of smart tourism cities, and the software is used to realize the simulation of the comprehensive evaluation system of tourism competitiveness of smart tourism cities, which more comprehensively and objectively reflects the level of comprehensive competitiveness of each city. It is believed that there are some problems in Shaanxi regional cultural communication, such as insufficient exploration of content resources, insufficient communication channels, and low audience awareness, hoping to provide ideas and reference for further exploring the promotion of cultural communication power.
    Matched MeSH terms: Computer Simulation
  17. Fulltext An Intelligent Proposed Model for Task Offloading in Fog-Cloud Collaboration Using Logistics Regression
    Bukhari MM, Ghazal TM, Abbas S, Khan MA, Farooq U, Wahbah H, et al.
    Comput Intell Neurosci, 2022;2022:3606068.
    PMID: 35126487 DOI: 10.1155/2022/3606068
    Smart applications and intelligent systems are being developed that are self-reliant, adaptive, and knowledge-based in nature. Emergency and disaster management, aerospace, healthcare, IoT, and mobile applications, among them, revolutionize the world of computing. Applications with a large number of growing devices have transformed the current design of centralized cloud impractical. Despite the use of 5G technology, delay-sensitive applications and cloud cannot go parallel due to exceeding threshold values of certain parameters like latency, bandwidth, response time, etc. Middleware proves to be a better solution to cope up with these issues while satisfying the high requirements task offloading standards. Fog computing is recommended middleware in this research article in view of the fact that it provides the services to the edge of the network; delay-sensitive applications can be entertained effectively. On the contrary, fog nodes contain a limited set of resources that may not process all tasks, especially of computation-intensive applications. Additionally, fog is not the replacement of the cloud, rather supplement to the cloud, both behave like counterparts and offer their services correspondingly to compliance the task needs but fog computing has relatively closer proximity to the devices comparatively cloud. The problem arises when a decision needs to take what is to be offloaded: data, computation, or application, and more specifically where to offload: either fog or cloud and how much to offload. Fog-cloud collaboration is stochastic in terms of task-related attributes like task size, duration, arrival rate, and required resources. Dynamic task offloading becomes crucial in order to utilize the resources at fog and cloud to improve QoS. Since this formation of task offloading policy is a bit complex in nature, this problem is addressed in the research article and proposes an intelligent task offloading model. Simulation results demonstrate the authenticity of the proposed logistic regression model acquiring 86% accuracy compared to other algorithms and confidence in the predictive task offloading policy by making sure process consistency and reliability.
    Matched MeSH terms: Computer Simulation
  18. Fulltext A New Wide-Band Double-Negative Metamaterial for C- and S-Band Applications
    Hossain MI, Faruque MRI, Islam MT, Ullah MH
    Materials (Basel), 2014 Dec 25;8(1):57-71.
    PMID: 28787924 DOI: 10.3390/ma8010057
    A new design and analysis of a wide-band double-negative metamaterial, considering a frequency range of 0.5 to 7 GHz, is presented in this paper. Four different unit cells with varying design parameters are analyzed to evaluate the effects of the unit-cell size on the resonance frequencies of the metamaterial. Moreover, open and interconnected 2 × 2 array structures of unit cells are analyzed. The finite-difference time-domain (FDTD) method, based on the Computer Simulation Technology (CST) Microwave Studio, is utilized in the majority of this investigation. The experimental portion of the study was performed in a semi-anechoic chamber. Good agreement is observed between the simulated and measured S parameters of the developed unit cell and array. The designed unit cell exhibits negative permittivity and permeability simultaneously at S-band (2.95 GHz to 4.00 GHz) microwave frequencies. In addition, the designed unit cell can also operate as a double-negative medium throughout the C band (4.00 GHz to 4.95 GHz and 5.00 GHz to 5.57 GHz). At a number of other frequencies, it exhibits a single negative value. The two array configurations cause a slight shift in the resonance frequencies of the metamaterial and hence lead to a slight shift of the single- and double-negative frequency ranges of the metamaterial.
    Matched MeSH terms: Computer Simulation
  19. Fulltext Optimal coordinated voltage control in active distribution networks using backtracking search algorithm
    Tengku Hashim TJ, Mohamed A
    PLoS One, 2017;12(10):e0177507.
    PMID: 28991919 DOI: 10.1371/journal.pone.0177507
    The growing interest in distributed generation (DG) in recent years has led to a number of generators connected to a distribution system. The integration of DGs in a distribution system has resulted in a network known as active distribution network due to the existence of bidirectional power flow in the system. Voltage rise issue is one of the predominantly important technical issues to be addressed when DGs exist in an active distribution network. This paper presents the application of the backtracking search algorithm (BSA), which is relatively new optimisation technique to determine the optimal settings of coordinated voltage control in a distribution system. The coordinated voltage control considers power factor, on-load tap-changer and generation curtailment control to manage voltage rise issue. A multi-objective function is formulated to minimise total losses and voltage deviation in a distribution system. The proposed BSA is compared with that of particle swarm optimisation (PSO) so as to evaluate its effectiveness in determining the optimal settings of power factor, tap-changer and percentage active power generation to be curtailed. The load flow algorithm from MATPOWER is integrated in the MATLAB environment to solve the multi-objective optimisation problem. Both the BSA and PSO optimisation techniques have been tested on a radial 13-bus distribution system and the results show that the BSA performs better than PSO by providing better fitness value and convergence rate.
    Matched MeSH terms: Computer Simulation
  20. Fulltext A New Compact Double-Negative Miniaturized Metamaterial for Wideband Operation
    Hasan MM, Faruque MRI, Islam SS, Islam MT
    Materials (Basel), 2016 Oct 13;9(10).
    PMID: 28773951 DOI: 10.3390/ma9100830
    The aim of this paper is to introduce a compact double-negative (DNG) metamaterial that exhibits a negative refractive index (NRI) bandwidth of more than 3.6 GHz considering the frequency from 2 to 14 GHz. In this framework, two arms of the designed unit cell are split in a way that forms a Modified-Z-shape structure of the FR-4 substrate material. The finite integration technique (FIT)-based Computer Simulation Technology (CST) Microwave Studio is applied for computation, and the experimental setup for measuring the performance is performed inside two waveguide ports. Therefore, the measured data complies well with the simulated data of the unit cell at 0-degree and 90-degree rotation angles. The designed unit cell shows a negative refractive index from 3.482 to 7.096 GHz (bandwidth of 3.61 GHz), 7.876 to 10.047 GHz (bandwidth of 2.171 GHz), and 11.594 to 14 GHz (bandwidth of 2.406 GHz) in the microwave spectra. The design also exhibits almost the same wide negative refractive index bandwidth in the major region of the C-band and X-band if it is rotated 90 degrees. However, the novelty of the proposed structure lies in its effective medium ratio of more than 4, wide bandwidth, and compact size.
    Matched MeSH terms: Computer Simulation
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