Mühendislik Fakültesi / Faculty of Engineering
Permanent URI for this collectionhttps://hdl.handle.net/11727/1401
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Item Automatic Brain Tumor Detection and Volume Estimation in Multimodal MRI Scans via a Symmetry Analysis(2023) Ficici, Cansel; Erogul, Osman; Telatar, Ziya; Kocak, Onur; 0000-0002-8240-4046In this study, an automated medical decision support system is presented to assist physicians with accurate and immediate brain tumor detection, segmentation, and volume estimation from MRI which is very important in the success of surgical operations and treatment of brain tumor patients. In the proposed approach, first, tumor regions on MR images are labeled by an expert radiologist. Then, an automated medical decision support system is developed to extract brain tumor boundaries and to calculate their volumes by using multimodal MR images. One advantage of this study is that it provides an automated brain tumor detection and volume estimation algorithm that does not require user interactions by determining threshold values adaptively. Another advantage is that, because of the unsupervised approach, the proposed study realized tumor detection, segmentation, and volume estimation without using very large labeled training data. A brain tumor detection and segmentation algorithm is introduced that is based on the fact that the brain consists of two symmetrical hemispheres. Two main analyses, i.e., histogram and symmetry, were performed to automatically estimate tumor volume. The threshold values used for skull stripping were computed adaptively by examining the histogram distances between T1- and T1C-weighted brain MR images. Then, a symmetry analysis between the left and right brain lobes on FLAIR images was performed for whole tumor detection. The experiments were conducted on two brain MRI datasets, i.e., TCIA and BRATS. The experimental results were compared with the labeled expert results, which is known as the gold standard, to demonstrate the efficacy of the presented method. The performance evaluation results achieved accuracy values of 89.7% and 99.0%, and a Dice similarity coefficient value of 93.0% for whole tumor detection, active core detection, and volume estimation, respectively.Item Calculation of the Phase Diagrams (T - X and T - P) and the Thermodynamic Quantities for the Solid - Liquid Equilibria in n-tridecane(2023) Tari, O.; Yurtseven, H.solid - liquid equilibria in n-tridecane is investigated by calculating phase diagrams and the thermodynamic quantities using the Landau phenomenological model. By expanding the free energy in terms of the order parameter of the solid phase, the phase line equations are fitted to the experimental data for the T - X and T - P phase diagrams from the literature. The temperature dependences of the thermodynamic quantities (order parameter psi, susceptibility chi(psi), free energy F, the heat capacity C, entropy S and the enthalpy H) are predicted for the n-tridecane from this model. Our results give that the slope dT/dP congruent to 2 K/MPa for n-C-13 to n-C-17. psi varies with T as psi similar to(T - T-m)(1/2) above T-m. It is linear for the chi(-1)(psi), S(T) and C(T), and quadratic for the F(T) and H(T) in n-tridecane. This indicates that the Landau model, describes the observed behaviour of the phase diagrams satisfactorily for the solid - liquid equilibria in n-tridecane. Predictions of the thermodynamic quantities can also be compared with the measurements and predictions of some other theoretical models. The pressure effect, in particular, on the solid - liquid equilibria in n-tridecane can also be investigated under the model studied here.Item A Comparative Performance Investigation of Single- and Double-Nozzle Pulse Mode Minimum Quantity Lubrication Systems in Turning Super-Duplex Steel Using a Weighted Pugh Matrix Sustainable Approach(2023) Roy, Soumikh; Kumar, Ramanuj; Panda, Amlana; Sahoo, Ashok Kumar; Rafighi, Mohammad; Das, Diptikanta; 0000-0002-9343-9607; AAQ-7933-2020This study investigates the performance comparison of machining of UNS S32750 super-duplex stainless steel under single- and double-nozzle pulse mode minimum quantity lubrication (MQL) conditions. The pulse mode MQL system delivers lubricant pulses at specific intervals. The Taguchi L9 design, with three factors and their three levels, was taken to perform the CNC turning experiments under both single-nozzle and double-nozzle MQL cooling environments. The surface roughness (Ra), tool-flank wear (VB), tool-flank temperature (Tf), power consumption (Pc), and material removal rate (MRR) are evaluated and compared as performance indicators. In comparison to single-nozzle MQL, the responses of Ra, VB, Tf, and Pc were found to be decreased by 11.16%, 21.24%, 7.07%, and 3.16% under double-nozzle conditions, respectively, whereas MRR was found to be 18.37% higher under double-nozzle conditions. The MQL pulse time was found to be an important variable that affects Ra, VB, Tf, and MRR significantly. Under both cooling scenarios, common wears such as abrasion, built-up edges, adhesion, and notch wear are detected. Furthermore, the Pugh matrix-based sustainability evaluation results revealed that the double-nozzle MQL technique was superior to single-nozzle MQL, achieving improved sustainability for machining super-duplex stainless steel.Item A Stationary Axisymmetric Vacuum Solution for Pure R2 Gravity(2023) Azreg Ainou, Mustapha; Nguyen, Hoang Ky; 0000-0002-3244-7195The closed-form expression for pure R-2 vacuum solution obtained in Phys. Rev. D 107, 104 008 (2023) lends itself to a generalization to axisymmetric setup via the modified Newman-Janis algorithm. We adopt the procedure put forth in Phys. Rev. D 90, 064 041 (2014) bypassing the complexification of the radial coordinate. The procedure presumes the existence of Boyer-Lindquist coordinates. Using the Event Horizon Telescope Collaboration results, we model the central black hole M87* by the thus obtained exact rotating metric, depending on the mass, rotation parameter and a third dimensionless parameter. The latter is constrained upon investigating the shadow angular size assuming mass and rotation parameters are those of M87*. Stability is investigated.Item A Preliminary Study on OSA Severity Levels Detection by Evaluating Speech Signals Nonlinearities With Multi-Class Classification(2023) Ugur, Tugce Kantar; Yilmaz, Derya; Yildiz, Metin; Yetkin, SinanDiagnosis of obstructive sleep apnea (OSA) from speech has become a popular research area in recent years, which can be an alternative way to the application difficulties in polysomnography (PSG). The promising results obtained in our previous study, in which we tried to detect apnea using nonlinear analysis of speech, gave rise to the thought that it is possible to detect OSA and OSA severity by diversifying speech samples and nonlinear features. The principal aim of this study, for the first time in the literature, is to detect the OSA severity levels as mild, moderate, and severe as in the clinic use (multi-class classification) using nonlinear analyses of speech while the patient is awake. In addition, healthy/OSA classification (binary classification) was also carried out. The feature selection method of ANOVA was applied to 336 features (28 voices x 12 features) for each subject, 14 and 5 features were used in multi-class and binary classifications, respectively. As a result of the classifications made with various KNN and SVMs models, the best results were obtained by SVMs in both classifications for OSA severities (with one-vs-all classification scheme and the Gaussian kernel) and OSA detection (with the quadratic kernel) as 82% and 95.1% accuracies, respectively. The proposed study showed that OSA and OSA severity can be determined with the small number of nonlinear features calculated from a few different speech samples, in nearly 15 minutes, consistent with PSG results (simple snorer, mild, moderate, and severe OSA). In conclusion, the highest OSA/healthy classification accuracy rate in the literature was achieved. Furthermore, OSA severity detection in four-class performed quite well as a preliminary study.Item PRI Deinterleaving with Connected Component Labeling-Based Clustering(2023) Fisne, Neslihan; Pakfiliz, Ahmet Gungor; 0000-0002-5901-228X; HSH-4659-2023Air platforms use radar warning receiver systems to detect threat radars in military operations. It is critical for an aircraft operating in a hostile environment to detect and classify radar signals and determine radar emitters' identity and capability. This study proposes an innovative solution to the signal separation problem for pulse radar signals by the computer vision-based connected component labeling method. With the proposed solution, clustering is performed automatically on the three-dimensional image matrix created by using the parameters of the arrival angle, radio frequency, pulse width of the signals. After clustering, the pulse repetition interval (PRI) deinterleaving is provided by the time of arrival analysis in each cluster. Also, various simulations were carried out using different synthetic radar datasets containing pulse-on-pulse states. In the simulations, PRI accuracy analyzes were performed.Item On the Parameters of the Spherically Symmetric Parameterized Rezzolla-Zhidenko Spacetime through Solar System Tests, the Orbit of the S2 Star about Sgr A*, and Quasiperiodic Oscillations(2023) Shaymatov, Sanjar; Ahmedov, Bobomurat; De Laurentis, Mariafelicia; Jamil, Mubasher; Wu, Qiang; Wang, Anzhong; Azreg Ainou, MustaphaIn this paper, we find the higher-order expansion parameters alpha and lambda of spherically symmetric parameterized Rezzolla-Zhidenko (PRZ) spacetime by using its functions of the radial coordinate. We subject the parameters of this spacetime to classical tests, including weak gravitational field effects in the solar system, observations of the S2 star that is located in the star cluster close to the Sgr A*, and of the frequencies of selected microquasars. Based on this spherically symmetric spacetime, we perform the analytic calculations for solar system effects such as perihelion shift, light deflection, and gravitational time delay to determine limits on the parameters by using observational data. We restrict our attention to the limits on the two higher-order expansion parameters alpha and lambda that survive at the horizon or near the horizon of spherically symmetric metrics. The properties of the expansion of these two small parameters in PRZ parameterization are discussed. We further apply Markov Chain Monte Carlo simulations to analyze and obtain the limits on the expansion parameters by using observations of the phenomena of the S2 star. Finally, we consider the epicyclic motions and derive analytic expressions of the epicyclic frequencies. Applying these expressions to the quasiperiodic oscillations of selected microquasars allows us to set further limits on the parameters of the PRZ spacetime. Our results demonstrate that the higher-order expansion parameters can be given in the range alpha, lambda = (-0.09, 0.09) and of order similar to 10(-2) as a consequence of three different tests and observations.Item Non-Abelian Magnetic Field and Curvature Effects on Pair Production(2023) Kurkcuoglu, S.; Ozcan, B.; Unal, G.; 0000-0003-2214-2272; JUU-4258-2023We calculate the Schwinger pair-production rates in R3;1 as well as in the positively curved space S2 x R1;1 for both spin-0 and spin -21 particles under the influence of an external SU(2) x U(1) gauge field producing an additional uniform non-Abelian magnetic field besides the usual uniform Abelian electric field. To this end, we determine and subsequently make use of the spectrum of the gauged Laplace and Dirac operators on both the flat and the curved geometries. We find that there are regimes in which the purely non -Abelian and the Abelian parts of the gauge field strength have either a counterplaying or reinforcing role, whose overall effect may be to enhance or suppress the pair-production rates. Positive curvature tends to enhance the latter for spin-0 and suppress it for spin -21 fields, while the details of the couplings to the purely Abelian and the non-Abelian parts of the magnetic field, which are extracted from the spectrum of the Laplace and Dirac operators on S2, determine the cumulative effect on the pair-production rates. These features are elaborated in detail.Item Parametric Design of Cladding System for Tall Buildings Using Computational Fluid Dynamics Approach(2023) Colak, L.; Balci, M. N.; G-6152-2013Quasi-static approach in calculation of wind load simply depends on the integration of the fluctuating pressures measured at pressure tubes located at the surface of building models. This approach is suitable to design typical low to medium height buildings. However, for tall buildings, if cladding surface will be designed based on single critical load in a conservative way, it will result in over design and excessive cost phenomena. The main aim of this study is to develop new experimantal and computational procedures to examine surface pressure distribution on tall buildings and to select cladding structure based on different pressure zones, thus in a more efficient way. A tall building is selected, modelled and 1/144 scaled wooden prototype is manufactured. Experimental study is conducted in a wind tunnel at turbulent flow conditions, and pressure values are recorded from tubes assembled on the surface of the prototype. Computational fluid dynamics (CFD) approach is carried out to determine pressure values and k - epsilon model is used in turbulent flow. Experimentally and computationally obtained results are observed compatible. After validation, actual wind profile is calculated, scaled and applied to the building model in simulations. Selection of the material thickness for the cladding system is performed parametrically accordint to deflection for elements in prescribed zones based on the computed pressure values. It is shown that new parametric cladding selection method opens up possibility to use less material consumption up to 23.6%, eliminating overdesign with maintaining desired factor of safety, which provides considerable economy on construction costs.Item Traversable Morris-Thorne-Buchdahl Wormholes in Quadratic Gravity(2023) Nguyen, Hoang Ky; Azreg-Ainou, Mustapha; 0000-0002-3244-7195The special Buchdahl-inspiredmetric obtained in a recent paper [Phys. Rev. D 107, 104008 (2023)] describes asymptotically flat spacetimes in pure R-2 gravity. The metric depends on a new (Buchdahl) parameter (k) over tilde of higher-derivative characteristic, and recovers the Schwarzschild metric when (k) over tilde = 0. It is shown that the special Buchdahlinspired metric supports a two-way traversable MorrisThorne wormhole for (k) over tilde is an element of (-1, 0) in which case the Weak Energy Condition is formally violated, a naked singularity for (k) over tilde is an element of (-infinity,-1). (0,+infinity), and a non-Schwarzschild structure for (k) over tilde = -1.