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    A Novel Parametric Model for the Prediction and Analysis of the COVID-19 Casualties
    (IEEE-Inst Electrical Electronics Engineers Inc, 2020) Tutsoy, Önder; Colak, Sule; Polat, Adem; Balikci, Kemal
    Coronavirus disease (COVID-19) outbreak has affected billions of people, where millions of them have been infected and thousands of them have lost their lives. In addition, to constraint the spread of the virus, economies have been shut down, curfews and restrictions have interrupted the social lives. Currently, the key question in minds is the future impacts of the virus on the people. It is a fact that the parametric modelling and analyses of the pandemic viruses are able to provide crucial information about the character and also future behaviour of the viruses. This paper initially reviews and analyses the Susceptible-Infected-Recovered (SIR) model, which is extensively considered for the estimation of the COVID-19 casualties. Then, this paper introduces a novel comprehensive higher-order, multi-dimensional, strongly coupled, and parametric Suspicious-Infected-Death (SpID) model. The mathematical analysis results performed by using the casualties in Turkey show that the COVID-19 dynamics are inside the slightly oscillatory, stable (bounded) region, although some of the dynamics are close to the instability region (unbounded). However, analysis with the data just after lifting the restrictions reveals that the dynamics of the COVID-19 are moderately unstable, which would blow up if no actions are taken. The developed model estimates that the number of the infected and death individuals will converge zero around 300 days whereas the number of the suspicious individuals will require about a thousand days to be minimized under the current conditions. Even though the developed model is used to estimate the casualties in Turkey, it can be easily trained with the data from the other countries and used for the estimation of the corresponding COVID-19 casualties.
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    Adaptive estimator design for unstable output error systems: A test problem and traditional system identification based analysis
    (Sage Publications Ltd, 2015) Tutsoy, Önder; Colak, Sule
    A key open question in adaptive estimator design is how to assure that the parameters of the proposed algorithms are converging to their almost correct solutions; hence, the learning algorithm is unbiased. Moreover, determining the speed of parameter convergence is important as it provides insight about the performance of the learning algorithms. The main contributions of the article are fourfold: the first one is that the article, initially, introduces an adaptive estimator to learn the discounted Q-function and approximate optimal control policy without requiring linear, discrete time, unstable output error system dynamics, but using only the noisy system measurements. The simulation results show that the adaptive estimator minimizes the stochastic cost function and temporal difference error and also learns the approximate Q-function together with the control policy. The second one is consideration of a different approach by taking a simple test problem to investigate issues associated with the Q-function's representation and parametric convergence. In particular, the terminal convergence problem is analyzed with a known optimal control policy where the aim is to accurately learn only the Q-function. It is parameterized by terms which are functions of the unknown plant's parameters and the Q-function's discount factor, and their convergence properties are analyzed and compared with the adaptive estimator. The third one is to show that even though the adaptive estimator with a large Q-function discount factor yields larger control feedback gains, so that faster state converges upright, the learning problem is badly conditioned; hence, the parameter convergence is sluggish, as the Q-function discount factor approaches the inverse of the dominant pole of the unstable system. Finally, the fourth one is comparison of the state output learned by the adaptive estimator with the ones obtained from traditional system identification algorithms. Simulation result for a higher order unstable output error system shows that the adaptive estimator closely follows the real system output whereas the system identification algorithms do not.
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    Development of a Multi-Dimensional Parametric Model With Non-Pharmacological Policies for Predicting the COVID-19 Pandemic Casualties
    (IEEE-Inst Electrical Electronics Engineers Inc, 2020) Tutsoy, Önder; Polat, Adem; Colak, Sule; Balikci, Kemal
    Coronavirus Disease 2019 (COVID-19) has spread the world resulting in detrimental effects on human health, lives, societies, and economies. The state authorities mostly take non-pharmacological actions against the outbreak since there are no confirmed vaccines or treatments yet. In this paper, we developed Suspicious-Infected-Death with Non-Pharmacological policies (SpID-N) model to analyze the properties of the COVID-19 casualties and also estimate the future behavior of the outbreak. We can state the key contributions of the paper with three folds. Firstly, we propose the SpID-N model covering the higher-order internal dynamics which cause the peaks in the casualties. Secondly, we parametrize the non-pharmacological policies such as the curfews on people with chronic disease, people age over 65, people age under 20, restrictions on the weekends and holidays, and closure of the schools and universities. Thirdly, we explicitly incorporate the internal and coupled dynamics of the model with these multi-dimensional non-pharmacological policies. The corresponding higher-order and strongly coupled model has utterly unknown parameters and we construct a batch type Least Square (LS) based optimization algorithm to learn these unknown parameters from the available data. The parametric model and the predicted future casualties are analyzed extensively.
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    Frequency domain analysis of UWB dipole arrays
    (Taylor & Francis Ltd, 2014) Colak, Sule; Wong, Tan F.; Serbest, A. Hamit
    In this paper, behavior of dipole arrays for Ultra-Wideband (UWB) signals is investigated using an approach in the frequency domain. Energy formulas and correlation coefficient expressions are derived for an array of thin dipoles at the transmitting side and one dipole at the receiving side. Beam-scanning characteristics of UWB dipole arrays are also investigated in the same manner. Different element lengths are used in the array to improve the detection and beam-scanning capabilities. Derived frequency domain expressions can easily be evaluated numerically, allowing us to obtain reasonably accurate results. This approach which is an alternative to numerical methods in time domain serves as a different viewpoint and will be a significant step to make progress in UWB antenna design.
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    Improvement of Bowtie Antenna Parameters for Ultra - Wide Band Applications
    (IEEE, 2016) Colak, Sule; Gencoglan, Duygu Nazan
    In this study, bowtie antenna is designed for Ultra- Wide Band (UWB) communication applications, and radiation characteristics of the antenna in these systems are investigated by observing the behavior of parameters such as radiation pattern, return loss (S-11), and voltage standing wave ratio (VSWR). Additionally, in order to improve antenna performance in the UWB frequency range, parameters such as flare angle, substrate thickness and relative dielectric constant are changed to obtain antenna structure with the best performance. CST Microwave Studio is used for the design and modeling of the antenna.
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    Improvement of bowtie antenna parameters for Ultra - Wide Band applications
    (Institute of Electrical and Electronics Engineers Inc., 2016) Colak, Sule; Gencoglan, Duygu Nazan
    In this study, bowtie antenna is designed for Ultra-Wide Band (UWB) communication applications, and radiation characteristics of the antenna in these systems are investigated by observing the behavior of parameters such as radiation pattern, return loss (S11), and voltage standing wave ratio (VSWR). Additionally, in order to improve antenna performance in the UWB frequency range, parameters such as flare angle, substrate thickness and relative dielectric constant are changed to obtain antenna structure with the best performance. CST Microwave Studio is used for the design and modeling of the antenna. © 2016 IEEE.
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    Learning to balance an NAO robot using reinforcement learning with symbolic inverse kinematic
    (Sage Publications Ltd, 2017) Tutsoy, Önder; Barkana, Duygun Erol; Colak, Sule
    An autonomous humanoid robot (HR) with learning and control algorithms is able to balance itself during sitting down, standing up, walking and running operations, as humans do. In this study, reinforcement learning (RL) with a complete symbolic inverse kinematic (IK) solution is developed to balance the full lower body of a three-dimensional (3D) NAO HR which has 12 degrees of freedom. The IK solution converts the lower body trajectories, which are learned by RL, into reference positions for the joints of the NAO robot. This reduces the dimensionality of the learning and control problems since the IK integrated with the RL eliminates the need to use whole HR states. The IK solution in 3D space takes into account not only the legs but also the full lower body; hence, it is possible to incorporate the effect of the foot and hip lengths on the IK solution. The accuracy and capability of following real joint states are evaluated in the simulation environment. MapleSim is used to model the full lower body, and the developed RL is combined with this model by utilizing Modelica and Maple software properties. The results of the simulation show that the value function is maximized, temporal difference error is reduced to zero, the lower body is stabilized at the upright, and the convergence speed of the RL is improved with use of the symbolic IK solution.
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    Multi-band polarization independent cylindrical metamaterial absorber and sensor application
    (World Scientific Publ Co Pte Ltd, 2016) Dincer, Furkan; Karaaslan, Muharrem; Colak, Sule; Tetik, Erkan; Akgol, Oguzhan; Altintas, Olcay; Sabah, Cumali
    A multi-band perfect metamaterial absorber (MA) based on a cylindrical waveguide with polarization independency is numerically presented and investigated in detail. The proposed absorber has a very simple configuration, and it operates at flexible frequency ranges within the microwave frequency regime by simply tuning the dimensions of the structure. The maximum absorption values are obtained as 99.9%, 97.5%, 85.8%, 68.2% and 40.2% at the frequencies of 1.34 GHz, 2.15 GHz, 3.2 GHz, 4.31 GHz and 5.41 GHz, respectively. The numerical studies verify that the proposed model can provide multi-band perfect absorptions at wide polarization and incident angles due to its rotational symmetry feature. We have also realized sensor and parametric study applications in order to show additional features of the suggested model. The suggested MA enables myriad potential applications in medical technologies, sensors and in defense industry etc.
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    Novel Frequency-Reconfigurable Antennas with Ring Resonators and RF Switches: Enhancing Versatility and Adaptability in Wireless Communication Systems
    (Mdpi, 2023) Gencoglan, Duygu Nazan; Palandoken, Merih; Colak, Sule
    This study introduces innovative designs for frequency-reconfigurable antennas that utilize ring resonators combined with either PIN diodes or RF switches. These designs enhance the versatility, adaptability, and overall performance of the antennas in wireless communication systems. By controlling the switches and ring resonator, the antenna's resonant frequencies and bandwidths can be adjusted, allowing for compatibility with various communication standards and frequency ranges. The proposed antenna exhibits four distinct operational states, each characterized by different resonance frequencies and operating frequency bands. Return loss, radiation pattern, radiation efficiency, and surface current distribution are analyzed for each state. State-1 (ON-ON) and State-2 (OFF-ON), which are characterized by resonance frequencies of 2.4 GHz and 3.33 GHz respectively, offer ranges suitable for Wi-Fi, Bluetooth, ISM, and IoT applications. State-3 (ON-OFF), with a resonance frequency of 3.0 GHz and bandwidth spanning from 2.59 GHz to 3.643 GHz, complies with Wi-Fi, Wi-Fi 6, and IoT requirements. State-4 (OFF-OFF) covers the band centered around 3.45 GHz. It is compatible with many applications such as 5G mid-band, Wi-Fi 6E, IoT, and cellular systems. The proposed antenna designs are versatile and compact since the overall antenna dimensions are 25 x 18 x 1.6 mm(3). The radiation efficiency of the antenna configuration varies depending on operational states. By utilizing the advantages of both ring resonators and RF switches, the proposed antenna configurations offer new solutions that enhance their performance in wireless communication systems. This study compares the effects of using PIN diodes and SPDT switches on the performance of antennas and also examines the DC biasing effect on antenna characteristics. The simulation results are validated by the experimental analysis. The proposed antenna designs offer a new approach for wireless communication systems by using both ring resonators and RF switches.
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    Ultra-Wideband (UWB) characteristic estimation of elliptic patch antenna based on machine learning techniques
    (Walter De Gruyter Gmbh, 2020) Gencoglan, Duygu Nazan; Arslan, Mustafa Turan; Colak, Sule; Yildirim, Esen
    In this study, estimation of Ultra-Wideband (UWB) characteristics of microstrip elliptic patch antenna is investigated by means of k-nearest neighborhood algorithm. A total of 16,940 antennas are simulated by changing antenna dimensions and substrate material. Antennas are examined by observing Return Loss and Voltage Standing Wave Ratio (VSWR) characteristics. In the study, classification of antennas in terms of having UWB characteristics results in accuracies higher than 97%. Additionally, Consistency based Feature Selection method is applied to eliminate redundant and irrelevant features. This method yields that substrate material does not affect the UWB characteristics of the antenna. Classification process is repeated for the reduced feature set, reaching to 97.44% accuracy rate. This result is validated by 854 antennas, which are not included in the original antenna set. Antennas are designed for seven different substrate materials keeping all other parameters constant. Computer Simulation Technology Microwave Studio (CST MWS) is used for the design and simulation of the antennas.