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Articles 14161 - 14190 of 25622

Full-Text Articles in Computer Engineering

Mopso-Based Predictive Control Strategy For Efficient Operation Of Sensorless Vector-Controlled Fuel Cell Electric Vehicle Induction Motor Drives, Adel Abdelaziz Abdelghany Elgammal, Mohammed Fathy El_Naggar Jan 2017

Mopso-Based Predictive Control Strategy For Efficient Operation Of Sensorless Vector-Controlled Fuel Cell Electric Vehicle Induction Motor Drives, Adel Abdelaziz Abdelghany Elgammal, Mohammed Fathy El_Naggar

Turkish Journal of Electrical Engineering and Computer Sciences

This paper introduces an optimal control strategy of model-based predictive control (MPC) based on multiobjective particle swarm optimization (MOPSO) for a sensorless vector control induction motor, which is used in a fuel cell electric vehicle drive system. The proposed MPC-MOPSO algorithm is implemented to tune the weighting parameters of the MPC controller to tackle all the conflicting objective functions. The paper handles the following fitness functions: minimizing the speed error, minimizing the torque ripple, minimizing the DC-link voltage ripple, and minimizing machine flux ripple. Computer simulations studies have been completed utilizing MATLAB/Simulink with a specific end goal of assessing the …

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K-Nn-Based Classification Of Sleep Apnea Types Using Ecg, Oğuz Han Ti̇muş, Emi̇ne Doğru Bolat Jan 2017

K-Nn-Based Classification Of Sleep Apnea Types Using Ecg, Oğuz Han Ti̇muş, Emi̇ne Doğru Bolat

Turkish Journal of Electrical Engineering and Computer Sciences

Obstructive sleep apnea syndrome (OSAS) is a common sleep disorder that yields cardiovascular diseases, excessive daytime sleepiness, and poor quality of life if not treated. Classification of OSAS from electrocardiograms (ECGs) is a noninvasive method and much more affordable than traditional methods. This study proposes a pattern recognition system for automated apnea diagnosis based on heart rate variability (HRV) and ECG-derived respiratory signals. The k-nearest neighbor (k-NN) classifier has been used to develop the models for classifying the sleep apnea types. For comparison purposes, classification models based on multilayer perceptron, support vector machines, and C4.5 decision tree (C4.5 DT) have …

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Flexible (2 $\Times $ 1) Mimo Antenna With Electromagnetic Band Gap Unit Cell For Wimax Applications, Hussein Qasim Al-Fayyadh, Abdulghafor Abdulghafar Abdulhameed, Abdulkareem Swadi Abdullah, Haider Mohammed Alsabbagh Jan 2017

Flexible (2 $\Times $ 1) Mimo Antenna With Electromagnetic Band Gap Unit Cell For Wimax Applications, Hussein Qasim Al-Fayyadh, Abdulghafor Abdulghafar Abdulhameed, Abdulkareem Swadi Abdullah, Haider Mohammed Alsabbagh

Turkish Journal of Electrical Engineering and Computer Sciences

A flexible (2 $\times $ 1) multiple-input, multiple-output (MIMO) antenna with an electromagnetic band gap (EBG) unit cell is designed and measured. The proposed MIMO antenna is based on a circular slotted patch antenna to work at 3.5 GHz. An EBG unit cell is used to reduce the effect of the inherent mutual coupling produced between the closely spaced MIMO elements. The results show that the measured mutual coupling has been reduced by -11.6 dB (from -10 dB to -21.6 dB), and the measured realized gain has been increased by 1.074 dBi (from 1.59 dBi to 2.66 dBi). An improvement …

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Energy Optimized Scheduling For Non-Preemptive Real-Time Systems, Vasanthamani Kannaian, Visalakshi Palanisamy Jan 2017

Energy Optimized Scheduling For Non-Preemptive Real-Time Systems, Vasanthamani Kannaian, Visalakshi Palanisamy

Turkish Journal of Electrical Engineering and Computer Sciences

Embedded systems have geared up their applications in the field of smart phones, mobile devices, automobiles, and medical instrumentation. Along with the growth of technology, the functional requirements of the systems have also grown multifold. To accommodate these ever increasing functional requirements, the hardware should be designed to include the maximum capability, which in turn increases power consumption. Thus this has to be dynamically managed using software techniques. The dynamic voltage and frequency scaling (DVFS) feature provided in most of the recent processors has enabled power optimization through software. With this feature the processor operating frequency can be reduced on …

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A New Sequential Power Flow Algorithm For Ac/Dc Systems Including Independent Multiterminal Dc Subsystems, Faruk Yalçin, Uğur Ari̇foğlu Jan 2017

A New Sequential Power Flow Algorithm For Ac/Dc Systems Including Independent Multiterminal Dc Subsystems, Faruk Yalçin, Uğur Ari̇foğlu

Turkish Journal of Electrical Engineering and Computer Sciences

This paper presents a new algorithm based on the sequential method for power flow calculation in multiterminal AC/DC systems. The proposed approach differs from other similar studies in the literature by handling two main properties. Firstly, a real equivalent circuit model is considered for the under-load tap changer transformers (ULTCs) of DC converters for the first time in the literature. Hence, new DC equations are obtained. Thus, exact and accurate results can be obtained for practical applications using the proposed algorithm. Tap values adjustment effects of the ULTCs connected to DC converters are included into the Jacobian matrix instead of …

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An Intelligent Pso-Based Energy Efficient Load Balancing Multipath Technique In Wireless Sensor Networks, Sukhchandan Randhawa, Sushma Jain Jan 2017

An Intelligent Pso-Based Energy Efficient Load Balancing Multipath Technique In Wireless Sensor Networks, Sukhchandan Randhawa, Sushma Jain

Turkish Journal of Electrical Engineering and Computer Sciences

To provide a reliable and efficient service, load balancing plays an important role in wireless sensor networks (WSNs). There is a need to maximize the network lifetime for WSNs applications with periodic generation of data. Due to the relationship between energy consumption and network sensor node lifetime, energy consumption in a network should be minimized and balanced in order to increase network lifetime. Energy-efficient load-balancing techniques are needed to solve this problem. In this paper, a particle swarm optimization (PSO)-based energy-efficient load-balancing technique is proposed, in which the required number of routing paths and energy consumption of different nodes and …

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Minimizing Reverse Current Flow Due To Distributed Generation Via Optimal Network Reconfiguration, Jasrul Jamani Jamian, Muhammad Mohsin Aman, Muhammad Ariff Baharuddin, Ahmad Safawi Mokhtar, Mohd Noor Abdullah Jan 2017

Minimizing Reverse Current Flow Due To Distributed Generation Via Optimal Network Reconfiguration, Jasrul Jamani Jamian, Muhammad Mohsin Aman, Muhammad Ariff Baharuddin, Ahmad Safawi Mokhtar, Mohd Noor Abdullah

Turkish Journal of Electrical Engineering and Computer Sciences

Distributed generation (DG) is widely used to minimize total power losses in distribution networks. However, one of the problems of DG in a grid system is reverse current flow (RCF), which is when the DG output becomes greater than the connected load. Therefore, this paper proposes a multiobjective artificial bee colony (MOABC) algorithm to determine the optimal network reconfiguration for reducing total RCF in DG. The proposed algorithm is tested on 33-bus radial distribution systems in two different scenarios, i.e. base case and with 50% load. The proposed technique can reduce reverse current by up to 93%; however, the total …

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Robust Local Parameter Estimator Based On Least Absolute Value Estimator, Volkan Özdemi̇r, Murat Göl Jan 2017

Robust Local Parameter Estimator Based On Least Absolute Value Estimator, Volkan Özdemi̇r, Murat Göl

Turkish Journal of Electrical Engineering and Computer Sciences

Changes in weather conditions such as temperature and humidity, miscommunication between the control center and circuit breaker transducers and tap changers, and inaccurate manufacturing data may cause parameter errors. Because of incorrect parameters, the state estimator may provide biased state estimates, which may lead to many serious economic and operational results. In order to prevent that, one must identify and correct those parameter errors. This work proposes a local parameter estimator based on the least absolute value (LAV) estimator, which is known to be robust against bad measurements, i.e. measurements with gross error. Considering the increasing number of phasor measurement …

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Constrained Control Allocation For Nonlinear Systems With Actuator Failures Or Faults, Saman Ebrahimi Boukani, Mohammad Javad Khosrowjerdi, Roya Amjadifard Jan 2017

Constrained Control Allocation For Nonlinear Systems With Actuator Failures Or Faults, Saman Ebrahimi Boukani, Mohammad Javad Khosrowjerdi, Roya Amjadifard

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, a combination of dynamic constrained control allocation with terminal sliding mode control is proposed for a general class of overactuated nonlinear systems with actuator faults/failures. First, the terminal sliding mode control is designed to converge the system tracking error to zero in a finite-time. Then a control allocation strategy is developed and will be solved by a Lyapunov method, which leads to a dynamic update law with finite-time convergence. This strategy satisfies input limits and when faults/failures occur in some of the actuators, the control signals are automatically redistributed among the healthy actuators. Simulation results on a …

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Multiclass Semantic Segmentation Of Faces Using Crfs, Khalil Khan, Nasir Ahmad, Khalil Ullah, Irfanud Din Jan 2017

Multiclass Semantic Segmentation Of Faces Using Crfs, Khalil Khan, Nasir Ahmad, Khalil Ullah, Irfanud Din

Turkish Journal of Electrical Engineering and Computer Sciences

Multiclass semantic image segmentation is widely used in a variety of computer vision tasks, such as object segmentation and complex scene understanding. As it decomposes an image into semantically relevant regions, it can be applied in segmentation of face images. In this paper, an algorithm based on multiclass semantic segmentation of faces is proposed using conditional random fields. In the proposed model, each node corresponds to a superpixel, while the neighboring superpixels are connected to nodes through edges. Unlike previous approaches, which rely on three or four classes, the label set is extended here to six classes, i.e. hair, eyes, …

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Tsgv: A Table-Like Structure-Based Greedy Method For Materialized View Selection In Data Warehouses, Mohammad Karim Sohrabi, Hossein Azgomi Jan 2017

Tsgv: A Table-Like Structure-Based Greedy Method For Materialized View Selection In Data Warehouses, Mohammad Karim Sohrabi, Hossein Azgomi

Turkish Journal of Electrical Engineering and Computer Sciences

Since a data warehouse deals with huge amounts of data and complex analytical queries, online processing and answering to users' queries in data warehouses can be a serious challenge. Materialized views are used to speed up query processing rather than direct access to the database in on-line analytical processing. Since the large number and high volume of views prevents all of the views from being stored, selection of a proper subset of views to materialization is inevitable. Proposing an appropriate method for selecting the optimal subset of views for materialization plays an essential role in increasing the efficiency of responding …

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Dynamic Security Enhancement Of Power Systems Using Mean-Variance Mapping Optimization, Cavi̇t Fati̇h Küçüktezcan, Veysel Murat İstemi̇han Genç Jan 2017

Dynamic Security Enhancement Of Power Systems Using Mean-Variance Mapping Optimization, Cavi̇t Fati̇h Küçüktezcan, Veysel Murat İstemi̇han Genç

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, a preventive control action that involves both generation rescheduling and load curtailment is proposed for enhancing the dynamic security of large interconnected power systems. The control action is formulated as a security-constrained optimization problem that is solved by mean-variance mapping optimization (MVMO) integrated with a self-adaptive penalization technique and artificial neural networks to develop a fast and effective methodology. The proposed methodology is applied to a 16-generator 68-bus test system to solve the security-constrained optimization problem with both continuous and discrete decision variables. To find a proper and cost-effective solution for the control actions within an acceptable …

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Assessment Of Disordered Voices Based On An Optimized Glottal Source Model, Mounir Boudjerda, Abdellah Kacha Jan 2017

Assessment Of Disordered Voices Based On An Optimized Glottal Source Model, Mounir Boudjerda, Abdellah Kacha

Turkish Journal of Electrical Engineering and Computer Sciences

In this paper, a method for the assessment of disordered voices is proposed. A feature named mean opening quotient (MOQ) obtained from the glottal source estimation is used as an acoustic cue to summarize the degree of severity of the voice disorder. The analysis method uses the empirical mode decomposition algorithm to estimate the glottal source excitation signal from the speech signal. The logarithm of the magnitude spectrum of the speech signal is decomposed into oscillatory modes, called intrinsic mode functions, that are clustered into two classes, the spectral envelope and the harmonic component. The exploitation of the phase information …

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Unsupervised Learning Of Allomorphs In Turkish, Burcu Can Jan 2017

Unsupervised Learning Of Allomorphs In Turkish, Burcu Can

Turkish Journal of Electrical Engineering and Computer Sciences

One morpheme may have several surface forms that correspond to allomorphs. In English, ed and $d$ are surface forms of the past tense morpheme, and $s$, es, and ies are surface forms of the plural or present tense morpheme. Turkish has a large number of allomorphs due to its morphophonemic processes. One morpheme can have tens of different surface forms in Turkish. This leads to a sparsity problem in natural language processing tasks in Turkish. Detection of allomorphs has not been studied much because of its difficulty. For example, tü and di are Turkish allomorphs (i.e. past tense morpheme), but …

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Instantaneous Protection Scheme For Backup Protection Of High-Voltage Transmission Lines, Syed Norazizul Syed Nasir, Abdullah Asuhaimi Jan 2017

Instantaneous Protection Scheme For Backup Protection Of High-Voltage Transmission Lines, Syed Norazizul Syed Nasir, Abdullah Asuhaimi

Turkish Journal of Electrical Engineering and Computer Sciences

The protection scheme focused on in this study is a typical protection system used in high-voltage systems such as 132 kV, 275 kV, and 500 kV. The research will analyze the existing protection scheme for transmission lines that the power utility has implemented and will propose a new protection scheme to improve the performance of the existing scheme. The existing protection scheme currently implemented by the power utility for backup protection operation has a longer fault-clearing time and no restoration time, and it does not utilize support relays. This study will focus on a backup protection operation on high-voltage overhead …

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A Particle Swarm Optimization And Block-Svd-Based Watermarking For Digital Images, Falgun Thakkar, Vinay Kumar Srivastava Jan 2017

A Particle Swarm Optimization And Block-Svd-Based Watermarking For Digital Images, Falgun Thakkar, Vinay Kumar Srivastava

Turkish Journal of Electrical Engineering and Computer Sciences

The major issues in most watermarking schemes are security, reliability, and robustness against attacks. To achieve these objectives in a watermarking algorithm, the selection of a scale factor to embed the watermark into the host image is a challenging problem. In this paper, a block singular value decomposition (SVD)-based reliable, robust, secure, and fast watermarking scheme is proposed that uses particle swarm optimization (PSO) in the selection of the scale factor. SVD is applied here on the nonoverlapping blocks of LL wavelet subbands. Selected singular values of these blocks are modified with the pixel values of the watermark image. Selected …

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Optimal Fusion Of Multiple Gnss Signals Against Spoofing Sources, Selçuk Şahi̇n, Abedallatif Baba, Tolga Sönmez Jan 2017

Optimal Fusion Of Multiple Gnss Signals Against Spoofing Sources, Selçuk Şahi̇n, Abedallatif Baba, Tolga Sönmez

Turkish Journal of Electrical Engineering and Computer Sciences

Electronic attacks such as spoofing are becoming an increasing threat for satellite-based navigation receivers. The aim of this paper is to develop a preventive method against such electronic attacks. In our scheme, the localization system uses four different Global Navigation Satellite Systems (GNSSs): GPS, Galileo, GLONASS, and Compass. The signals received from these satellite systems will be fused inferentially and will be tracked according to a linear model. The linear model that we developed is solved with a Kalman filter and simulated under different scenarios. When a discrepancy is detected in the output of one of the GNSS receivers due …

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High-Voltage Isolated Multioutput Power Supply For Multilevel Converters, Amir Sepehr, Mehdi Saradarzadeh, Shahrokh Farhangi Jan 2017

High-Voltage Isolated Multioutput Power Supply For Multilevel Converters, Amir Sepehr, Mehdi Saradarzadeh, Shahrokh Farhangi

Turkish Journal of Electrical Engineering and Computer Sciences

Multilevel converters are one of the major choices for realizing high electric power conversion. The major feature of multilevel converter topologies is the need for a large number of switches, each of which requires a gate driver circuit and an isolated DC power supply. In this paper, a pragmatic concept of design and implementation of an isolated DC-to-DC converter for a high-voltage isolated application is introduced. More specifically, a multiple isolated output power supply based on the benefits of resonant converters is designed to prepare 36 double DC voltages for driving power semiconductor devices in a three-phase, seven-level cascaded H-bridge …

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An Alternative Approach To The Design Of Multiple Beam Constrained Lens Antennas, Rasi̇me Uyguroğlu, Abdullah Yücel Öztoprak Jan 2017

An Alternative Approach To The Design Of Multiple Beam Constrained Lens Antennas, Rasi̇me Uyguroğlu, Abdullah Yücel Öztoprak

Turkish Journal of Electrical Engineering and Computer Sciences

Rotman lenses are constrained lenses that are used as beam-forming networks to feed array antennas. Their design is based on three focal points, producing three beams with perfect phase fronts. This paper introduces an alternative constrained lens, which has phase equality at five radiating array elements for each beam position. In addition, the center point of the feed curve produces a perfect beam at broadside. The performance of this lens is analyzed and compared to the conventional Rotman lens. The analysis demonstrates that the new lens has better phase performance for wide angle designs. Our study shows that the phase …

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Classification Of Eeg Signals Of Familiar And Unfamiliar Face Stimuli Exploiting Most Discriminative Channels, Abdurrahman Özbeyaz, Sami̇ Arica Jan 2017

Classification Of Eeg Signals Of Familiar And Unfamiliar Face Stimuli Exploiting Most Discriminative Channels, Abdurrahman Özbeyaz, Sami̇ Arica

Turkish Journal of Electrical Engineering and Computer Sciences

The objective of the study is to classify electroencephalogram signals recorded in a familiar and unfamiliar face recognition experiment. Frontal views of familiar and unfamiliar face images were shown to 10 volunteers in different sessions. In contrast to previous studies, no marker button was used during the experiment. Participants had to decide whether the displayed face was familiar or unfamiliar at the instant of stimulus presentation. The signals were analyzed in the preprocessing, channel selection, feature extraction, and classification stages. The novel two-feature extraction and eight-channel selection methods were applied to the analyses. Sixteen classification results were compared and the …

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Access Pattern-Aware Data Placement For Hybrid Dram/Nvm, Di̇dem Unat Erten Jan 2017

Access Pattern-Aware Data Placement For Hybrid Dram/Nvm, Di̇dem Unat Erten

Turkish Journal of Electrical Engineering and Computer Sciences

In recent years, increased interest in data-centric applications has led to an increasing demand for large-capacity memory systems. Nonvolatile memory (NVM) technologies enable new opportunities in terms of process-scaling and energy consumption, and have become an attractive memory technology that serves as a secondary memory at low cost. However, NVM has certain disadvantages for write references, due to its high dynamic energy consumption for writes and low bandwidth compared to DRAM writes. In this paper, we propose an access-aware placement of objects in the application code for two types of memories. Given the desired power savings and acceptable performance loss, …

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Disk Scheduling With Shortest Cumulative Access Time First Algorithms, Nai̇l Akar, Çağlar Tunç, Mark Gaertner, Fati̇h Erden Jan 2017

Disk Scheduling With Shortest Cumulative Access Time First Algorithms, Nai̇l Akar, Çağlar Tunç, Mark Gaertner, Fati̇h Erden

Turkish Journal of Electrical Engineering and Computer Sciences

A new class of scheduling algorithms is proposed for disk drive scheduling. As opposed to choosing the request with the shortest access time in conventional shortest access time first (SATF) algorithms, we choose an ordered sequence of pending I/O requests at the scheduling instant with the shortest cumulative access time. Additionally, we introduce flexibility for forthcoming requests to alter the chosen sequence. Simulation results are provided to validate the effectiveness of the proposed disk scheduler. Throughput gains of 3% and above are shown to be attainable, although this occurs at the expense of increased computational complexity.

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A Stable Marriage-Based Request Routing Framework For Interconnection Cdns, Bo Huang, Lijian Zou, Xiaowen Tong, Xiaoqun Yuan Jan 2017

A Stable Marriage-Based Request Routing Framework For Interconnection Cdns, Bo Huang, Lijian Zou, Xiaowen Tong, Xiaoqun Yuan

Turkish Journal of Electrical Engineering and Computer Sciences

Content delivery network (CDN) interconnection is a promising solution to addressing the limited service scale of CDNs. It scales the CDN's service footprint through the cooperation of CDNs without significantly changing the existing network architecture. However, in a CDN interconnection system, CDNs are independent of each other and each pursues its own goals, which means that cooperation is hard to establish and easy to break. In our paper, we propose a stable marriage-based routing framework to establish a strong cooperation service for CDNs and to select the `optimal' server for each request among the cooperative CDNs. To this end, we …

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Mri Image Enhancement Using Biot-Savart Law At 3 Tesla, Yunus Emre Esi̇n, Ferda Nur Alpaslan Jan 2017

Mri Image Enhancement Using Biot-Savart Law At 3 Tesla, Yunus Emre Esi̇n, Ferda Nur Alpaslan

Turkish Journal of Electrical Engineering and Computer Sciences

Coil sensitivity is considered as the most valuable data in the parallel reconstruction of magnetic resonance imaging (MRI). In this study, a novel coil sensitivity map extraction method is introduced for spatially fixed phased array coils. The proposed technique uses the Biot--Savart law with coil internal shape information and low-resolution phase image data to form sensitivity maps. The performance of this method is tested in a parallel image reconstruction task, using the sensitivity-encoding (SENSE) technique. Under the quasi-static assumption and using the duality principle, we computed the sensitivity maps of a phased-array head coil and reconstructed full FOV images. The …

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An Rc-Triggered Esd Clamp For High-Voltage Bcd Cmos Processes, Fati̇h Koçer Jan 2017

An Rc-Triggered Esd Clamp For High-Voltage Bcd Cmos Processes, Fati̇h Koçer

Turkish Journal of Electrical Engineering and Computer Sciences

This paper presents a novel RC-triggered, field-effect transistor (FET)-based power clamp that can be used in high-voltage complementary metal oxide semiconductor (CMOS) processes. A simple two-stage design provides a fast trigger while keeping the clamp transistor on for much longer than the triggering duration without the need for an additional digital latching circuit. As the presented technique does not require any digital circuits, it is especially useful in bipolar-CMOS-DMOS (BCD) processes, where the implementation of digital blocks is difficult due to the limited gate-to-source voltage of the laterally diffused metal oxide semiconductor (LDMOS) transistors. The proposed architecture is implemented in …

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E-Mfdbscan: An Evolutionary Clustering Algorithm For Gene Expression Time Series, Atakan Erdem, Taflan İmre Gündem Jan 2017

E-Mfdbscan: An Evolutionary Clustering Algorithm For Gene Expression Time Series, Atakan Erdem, Taflan İmre Gündem

Turkish Journal of Electrical Engineering and Computer Sciences

DNA microarray experiments are frequently used because they have various advantages. However, gene expression data from DNA microarray experiments are noisy, and, consequently, the computations that are based on such noisy data may lack accuracy. In this paper, an evolutionary uncertain data-clustering algorithm, E-MFDBSCAN, and a prediction model using E-MFDBSCAN for uncertain data are proposed. The proposed methodology may be successfully applied to noisy gene expression data. In this methodology, global patterns of time series data can be extracted using our evolutionary clustering approach. These patterns are used to infer future projections. In the proposed methodology, an autoregressive time series …

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Axial Flux Pm Bldc Motor Design Methodology And Comparison With A Radial Flux Pm Bldc Motor, Ertuğrul Yeşi̇lbağ, Yasemi̇n Ertuğrul, Lale Ergene Jan 2017

Axial Flux Pm Bldc Motor Design Methodology And Comparison With A Radial Flux Pm Bldc Motor, Ertuğrul Yeşi̇lbağ, Yasemi̇n Ertuğrul, Lale Ergene

Turkish Journal of Electrical Engineering and Computer Sciences

The aim of this paper is to develop a methodology to design an axial flux permanent magnet brushless direct current (AFPM) motor for a washing machine and compare the results with a conventional radial flux permanent magnet brushless direct current (RFPM) motor with the same power ratings. The AFPM motor is designed based on the maximum power density for an optimum inner-to-outer diameter ratio by using the reference RFPM motor constraints, such as the same rated torque at the rated speed. Both motors use the same materials in terms of lamination, permanent magnet, and conductor. They both use ferrite magnets; …

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Relaxation Rate And Polarization Charge Density Model For Aln/Al$_{X}$Ga$_{1 - X}$N/Aln Heterostructures, Nagarajan Sivarajan, Reeba Korah, Mariya Kalavathy Ganamani Jan 2017

Relaxation Rate And Polarization Charge Density Model For Aln/Al$_{X}$Ga$_{1 - X}$N/Aln Heterostructures, Nagarajan Sivarajan, Reeba Korah, Mariya Kalavathy Ganamani

Turkish Journal of Electrical Engineering and Computer Sciences

This work describes the strain-relaxation--dependent carrier concentration ($n_{s})$ profile model using spontaneous and piezoelectric polarization for AlN/Al$_{x}$Ga$_{1 - x}$N/AlN HEMTs in all mole fraction ($x)$ interpolations. As $x$ varies, the Aluminum Gallium Nitride (AlGaN) channel shows strain relaxation with the Aluminum Nitride (AlN) barrier. The degree of relaxation is modeled from AlN to GaN regions in the channel. It shows that the AlN barrier and buffer relaxation and strain recovery occurs due to the gradual crystal quality degradation from barrier/buffer to the channel interface. These combination devices show less drain current degradation with temperature variation from 300 K to 573 …

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Modeling And Simulation Of 2.5 Mva Sf6-Gas-Insulated Transformer, Okan Özgönenel, David Thomas Jan 2017

Modeling And Simulation Of 2.5 Mva Sf6-Gas-Insulated Transformer, Okan Özgönenel, David Thomas

Turkish Journal of Electrical Engineering and Computer Sciences

In recent years, environmental awareness has been a great concern, and even governments have sometimes been under pressure to comply with bilateral agreements. Mineral oil/epoxy cast resins are one of the most harmful soil pollutants. Of course, they provide a good insulation material in (distribution/power) transformers, but they present some disadvantages, such as low ignition point, additional insulation costs, requirement for an extinguishing apparatus, long clearance distance, toxicity, costly decontamination, and explosion risk. For this reason, gas-insulated transformers have nowadays been put into specifications. % This paper investigates SF6-gas-insulated transformer (GIT) designs for the complex distribution transformer model, i.e. 2.5 …

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Calculation Of Creepage Discharge Safety Factors Against The Tangential Component Of Electric Fields In The Insulation Structure Of Power Transformers, Arsalan Hekmati Jan 2017

Calculation Of Creepage Discharge Safety Factors Against The Tangential Component Of Electric Fields In The Insulation Structure Of Power Transformers, Arsalan Hekmati

Turkish Journal of Electrical Engineering and Computer Sciences

Creepage discharges are a main cause of insulation damage in power transformers during repeated tests or during operation. In this paper, a hazardous region in the insulation structure of power transformers (the interface between solid and liquid insulation at the top edge of a high-voltage electrode) is considered, and the impact of a very important factor of the surface discharge initiation and propagation (the tangential component of the electric field) on the strength of the insulation structure is investigated in power transformers. Insulation system reliability against this tangential component is presented as a safety factor. Two methods based on cumulative …

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