Browsing by Author "Demir, A"

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    Neural network representations for the inter- and intra-class common vector classifiers
    Edizkan, R; Barkana, A; Koc, M; Gulmezoglu, MB; Ashames, MMA; Ergin, S; Fidan, M; Demir, A; Calisir, C; Gerek, ON
    Common Vector Approach (CVA) is a known linear regression-based classifier, which also enables an extension to inter-class discrimination, known as the Discriminative Common Vector Approach (DCVA). The characteristics of linear regression classifiers (LRCs) enable the possibility of a schematic implementation that is similar to the neuron model of artificial neural networks (ANNs). In this work, we explore this schematic similarity to come up with an ANN representation for both CVA and DCVA. The new representation eliminates the need for projection matrices in its implementation, hence significantly reduces the memory requirements and computational complexities of the processes. Furthermore, since the new representation is in a neural style, it is expected to provide a solid and intriguing extension of CVA (and DCVA) by further incorporating adaptation or activation processes to the already successful CVA-based classifiers. (c) 2023 Elsevier Inc. All rights reserved.
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    Eosinophilic granuloma of the temporal bone
    Bayazit, Y; Sirikci, A; Bayaram, M; Kanlikama, M; Demir, A; Bakir, K
    Histiocytosis X or Langerhans cell histiocytosis (LCH) is a disease that possesses three less distinctive and overlapping states called eosinophilic granuloma (EG)I Hand-Schuller-Christian (HSC) disease and Letterer-Siwe (LS) disease. EG is the least severe and localized form of all LCHs and possesses the best prognostic result. A high index of suspicion is required to diagnose the EG, especially when an ear disease is refractory to medical treatment. Early detection is important to manage the EG properly and to minimize the complications or sequels of treatment. Definitive diagnosis of histiocytosis is made by histopathological means and immunohistochemical detection of S-100 and CD1 antigens in the tissue samples. And differential diagnosis of the subgroups is made according to the clinical manifestations such as visceral organ or bone involvement. Surgical excision, radiotherapy and chemotherapy, either alone or in combination, are the main treatment options. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.
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    Correction of node mapping distortions using universal serendipity elements in dynamical problems
    Kücükarslan, S; Demir, A
    In this paper, the use of universal serendipity elements (USE) to eliminate node mapping distortions for dynamic problem is presented. Rectangular shaped elements for USE are being introduced by using a flexible master element with an adjustable edge node location. The shape functions of the universal serendipity formulation are used to derive the mass and damping matrices for the dynamic analyses. These matrices eliminate the node mapping distortion errors that occurs incase of the standard shape function formulations. The verification of new formulation will be tested and the errors encountered in the standard formulation will be studied for a dynamically loaded deep cantilever.
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    Are deep learning classification results obtained on CT scans fair and interpretable?
    Ashames, MMA; Demir, A; Gerek, ON; Fidan, M; Gulmezoglu, MB; Ergin, S; Edizkan, R; Koc, M; Barkana, A; Calisir, C
    Following the great success of various deep learning methods in image and object classification, the biomedical image processing society is also overwhelmed with their applications to various automatic diagnosis cases. Unfortunately, most of the deep learning-based classification attempts in the literature solely focus on the aim of extreme accuracy scores, without considering interpretability, or patient-wise separation of training and test data. For example, most lung nodule classification papers using deep learning randomly shuffle data and split it into training, validation, and test sets, causing certain images from the Computed Tomography (CT) scan of a person to be in the training set, while other images of the same person to be in the validation or testing image sets. This can result in reporting misleading accuracy rates and the learning of irrelevant features, ultimately reducing the real-life usability of these models. When the deep neural networks trained on the traditional, unfair data shuffling method are challenged with new patient images, it is observed that the trained models perform poorly. In contrast, deep neural networks trained with strict patient-level separation maintain their accuracy rates even when new patient images are tested. Heat map visualizations of the activations of the deep neural networks trained with strict patient-level separation indicate a higher degree of focus on the relevant nodules. We argue that the research question posed in the title has a positive answer only if the deep neural networks are trained with images of patients that are strictly isolated from the validation and testing patient sets.
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    Strengthening of reinforced concrete beams using external steel members
    Demir, A; Ercan, E; Demir, DD
    The objective of this study is to devise an alternative strengthening method to the ones available in the literature. So, external steel members were used to enhance both flexural and shear capacities of reinforced concrete ( RC) beams having insufficient shear capacity. Two types of RC beams, one without stirrups and one with lacking stirrups, were prepared in the study. These beams were strengthened with external steel clamps devised by the authors and with external longitudinal reinforcements. Although the use of clamps alone didn't have a significant effect on the load carrying capacity of the tested beams, the ductility increased approximately tenfold and the failure behavior changed from brittle to ductile. Although the use of clamps and longitudinal reinforcements together did not significantly increase the ductility of the beams, it approximately doubled their load capacities. The results of the experimental study were compared to the ones obtained from nonlinear finite element analysis (NLFEA) and it was observed that they were compatible. Finally, it can be concluded that the devised method could be applied to structural members as an alternative to methods in application due to lightness, low-cost, easy applicable and reliable.
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    Microalgae pigments as a sustainable approach to textile dyeing: A critical review
    Mutaf-Kilic, T; Demir, A; Elibol, M; Oncel, SS
    Microalgae derived pigments, such as phycobiliproteins, chlorophylls, and carotenoids, offer eco-friendly al-ternatives to synthetic dyes. These pigments are known for their vibrant colors, as well as their antimicrobial, antioxidative, and UV protective properties, making them commonly used in the food, pharmaceutical, and cosmetic industries. Recently, they have also gained attention in the textile dyeing industry. Compared to other natural dye sources like plants, bacteria, and fungi, microalgae pigments possess significant potential as natural textile dyes. They exhibit high pigment productivity, more sustainable production systems, current industrial-scale production, and a lack of seasonal dependency. This review aims to provide an overview of the current state, limitations, and future prospects regarding the utilization of microalgae pigments as textile dyes. The report emphasizes the commercial availability of microalgae pigments, highlights current studies exploring their dyeing potential on various textile materials, and discusses the development techniques aimed at enhancing dyeing performance. This emerging and promising research field has the potential to revolutionize the pro-duction of eco-friendly and sustainable textile products, while also contributing to a reduction in the use of synthetic dyes in the textile industry.
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    RC beam strengthening using precast RC plate bonding technique
    Demir, A; Bagci, M; Tekin, M; Nuhoglu, A
    The behaviour of RC beams strengthened with precast RC plates of rectangular and U cross-section is studied in the paper. An experimental investigation was conducted to assess effectiveness of strengthening with precast plates. The investigation was supported with the 2-D nonlinear finite element analysis (NLFEA). The NLFEA results showed a good level of correlation with test results. The proposed technique is considered to be a good alternative to RC jacketing and the technique is practical, economical and reliable for buildings or bridges with a greater number sisof similar beams.
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    Pulsed Nd:YAG laser shock processing effects on mechanical properties of 6061-T6 alloy
    Irizalp, SG; Saklakoglu, N; Akman, E; Demir, A
    The aim of this paper is to investigate effects of single and double shot Nd:YAG laser shock processing (LSP) on residual stress, micro-hardness and tensile properties of 6061-T6 aluminum alloy. The X-ray diffraction technique was used to measure surface residual stress in LSP-treated 6061-T6 samples. The magnitude and directional dependence of the surface residual stress after single shot and double shot LSP were investigated with the sin(2) Psi method. The results show that laser shock processing can significantly increase surface compressive residual stress. In addition, micro-hardness of the LSP-treated sample was measured using a Vickers diamond indenter depending on the depth. The tensile tests of the single shot and double shot LSP-treated and untreated samples were carried out by the Schimadzu tensile testing machine having a video extensometer. Experimental results show that the values of micro-hardness, tensile strength and uniform elongation increase by LSP. (C) 2013 Elsevier Ltd. All rights reserved.
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    Collapse mechanism estimation of a historical slender minaret
    Nohutcu, H; Hokelekli, E; Ercan, E; Demir, A; Altintas, G
    The aim of this study is to accurately estimate seismic damage and the collapse mechanism of the historical stone masonry minaret Hafsa Sultan, which was built in 1522. Surveying measurements and material tests were conducted to obtain a 3D solid model and the mechanical properties of the components of the minaret. The initial Finite Element (FE) model is analyzed and numerical dynamic characteristics of the minaret are obtained. The Operational Modal Analysis (OMA) method is conducted to obtain the experimental dynamic characteristics of the minaret and the initial FE model is calibrated by using the experimental results. Then, linear time history (LTH) and nonlinear time history (NLTH) analyses are carried out on the calibrated FE model by using two different ground motions. Iron clamps which used as connection element between the stones of the minaret considerably increase the tensile strength of the masonry system. The Concrete Damage Plasticity (CDP) model is selected in the nonlinear analyses in ABAQUS. The analyses conducted indicate that the results of the linear analyses are not as realistic as the nonlinear analysis results when compared with existing damage.
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    Effect of model calibration on seismic behaviour of a historical mosque
    Demir, A; Nohutcu, H; Ercan, E; Hokelekli, E; Altintas, G
    The objective of the study is to investigate the effects of model calibration on seismic behaviour of a historical mosque which is one of the most significant Ottomon structures. Seismic analyses of calibrated and noncalibrated numeric models were carried out by using acceleration records of Kocaeli earthquake in 1999. In numerical analysis, existing crack zones on real structure was investigated in detail. As a result of analyses, maximum stresses and displacements of calibrated and noncalibrated numerical models were compared each other. Consequently, seismic behaviour and damage state of historical masonry Hafsa Sultan mosque was determined as more realistic in the event of a severe earthquake.
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    Investigation of seismic safety of a masonry minaret using its dynamic characteristics
    Basaran, H; Demir, A; Ercan, E; Nohutçu, H; Hökelekli, E; Kozanoglu, C
    Besides their spiritual significance, minarets are humanity's cultural heritage to the future generations due to their historical and architectural attraction. Currently, many historical masonry minarets are damaged and destroyed due to several reasons such as earthquakes and wind. Therefore, safety of these religiously significant buildings needs to be thoroughly investigated. The utmost care must be taken into account while investigating these structures. Our study investigated earthquake behavior of historical masonry minaret of Hac1 Mahmut Mosque. Destructive and non-destructive tests were carried out to determine earthquake safety of this structure. Brick-stone masonry material properties of structure were determined by accomplishing ultrasonic wave velocity, Schmidt Hammer, uniaxial compression (UAC) and indirect tension (Brazilian) tests. Determined material properties were used in the finite element analysis of the structure. To validate the numerical analysis, Operational Modal Analysis was applied to the structure and dynamic characteristics of the structure were determined. To this end, accelerometers were placed on the structure and vibrations due to environmental effects were followed. Finite element model of the minaret was updated using dynamic characteristics of the structure and the realistic numerical model of the structure was obtained. This numerical model was solved by using earthquake records of Turkey with time history analysis (THA) and the realistic earthquake behavior of the structure was introduced.
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    FINITE ELEMENT MODEL UPDATING OF A HISTORICAL MINARET VIA OPERATIONAL MODAL ANALYSIS
    Ercan, E; Hokelekli, E; Demir, A; Nohutçu, H
    Finite element method is commonly used for analysis of historical structures. However, since material properties of historical structures are evaluated from destructive tests using empirical formulas, this approach makes the results of finite element analysis questionable. In recent years Operational Modal Analysis of historical masonry structures have found great interest because by the help of Operational Modal Analysis, the material parameters and the boundary conditions can be verified and the finite element model can be updated. The updated model is a more realistic model of the historical structures and gives more accurate results. This study describes the results of a model updating study conducted on a historical minaret. For the purposes of developing a 3-D solid model of the minaret; the dimensions, defects and material degradations in the minaret were determined in detail by making a measurement survey. For evaluation of the material properties of the minaret, nondestructive and destructive testing methods were applied. The modal analysis of the structure was done by FEM. Then, Operational Modal Analysis was carried out and dynamic properties were extracted. The results obtained from ambient vibration measurements of the minaret were used to update the finite element model of the minaret. The natural frequencies and corresponding mode shapes were determined from both theoretical and experimental modal analyses and compared with each other. A good harmony was attained between mode shapes, but differences between natural frequencies were observed. Model updating was realized via changing material parameters and boundary conditions. Finally, the more realistic finite element model of the minaret was put forward and the results were discussed.
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    Near surface modification of aluminum alloy induced by laser shock processing
    Saklakoglu, N; Irizalp, SG; Akman, E; Demir, A
    This paper investigates the influences of near surface modification induced in 6061-T6 aluminum alloy by laser shock processing (LSP). The present study evaluates LSP with a Q-switched Nd:YAG low power laser using water confinement medium and absorbent overlay on the workpiece. The near surface microstructural change of 6061-T6 alloy after LSP was studied. The residual stress variation throughout the depth of the workpiece was determined. The results showed an improvement of the material resistance to pit formation. This improvement may be attributed to compressive residual stress and work-hardening. The size and number of pits revealed by immersion in an NaOH-HCl solution decreased in comparison with the untreated material. (C) 2014 Elsevier Ltd. All rights reserved.
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    Proposal for a novel technological damper system (TDS) for the retrofit of reinforced concrete frame structures
    Suk, R; Demir, A; Altintas, G; Altiok, TY
    Considering the severe earthquakes that have occurred worldwide, it has been observed that even buildings which are constructed in compliance with the seismic regulations, have suffered heavy damage or collapsed. Similarly, in earthquake on February 6, 2023, in Kahramanmaras,, Turkey, many old and new structures were damaged or even collapsed. This situation has compelled researchers to focus on the most current and technological applications for earthquake protection. In the latest research topics, there has been a growing emphasis on the impact of new technological systems targeted at improving the seismic performance of structures constructed with reinforced concrete systems, given the notable occurrence of collapsed buildings with such structural systems in this earthquake. In this study, the developed Technological Damper System (TDS) was employed to enhance the earthquake performance of reinforced concrete structures. TDS is a versatile and adjustable frictiontype damper. For this reason, two identical 1/2 scaled reinforced concrete frames were fabricated for the study, one representing a traditional structure as a reference frame (REF), and the other a frame with the TDS device. After applying quasi -static cyclic tests to the frames, the force -displacement, and force -rotation relationships, as well as energy dissipation capacities were determined for both frames. In addition, the damage conditions of the columns during the tests were assessed based on the plastic rotation limit conditions outlined in Turkish Building Earthquake Code (TBEC 2018). As a result, the frame retrofitted with the TDS device exhibited a significant increase in horizontal load -carrying capacity, ranging from 42.04% to 75%, when compared to the REF. Additionally, it was observed that energy consumption increased between 85% and 220%. The REF reached significant damage levels at 1% and 2% story drift ratios and an advanced damage state at about 3%, in accordance with TBEC 2018. Finally, the behavior of the frame retrofitted with TDS considerably improved according to REF and it reached a significant damage state at 3% story drift ratio.
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    Effect of infill wall properties on seismic response of RC structures
    Demir, A; Cengiz, MM
    Brick infill walls (BIW) have significant effects on reinforced concrete (RC) structures' seismic performances. However, mechanical effects on the structural performance of BIWs, which are regarded as only weight at the design stage, are not considered in many seismic codes. Therefore, seismic performances of new and existing RC structures could not be realistically obtained. This study aims to investigate the effects on the structural behavior of BIWs, stucco types, and soft story. RC structures with and without BIWs are modeled by using the SAP2000 program. BIW is modeled with the equivalent diagonal compression strut method, and mechanical properties of BIWs plastered with conventional and polypropylene fibrous stuccos are taken from literature. Seismic performances of all structures are investigated using the pushover analysis method, according to Turkish Seismic Code-2007 (TSC-2007) principles. Besides, natural periods, rigidities, ductilities and energy dissipation capacities of all structures are obtained. As a result of analyses, it is determined that BIWs have significant effects on structural performances in terms of rigidity and ductility, and fibrous stucco considerably increases RC structures' rigidity and ductility. These walls can even lead to the collapse of structures in severe earthquakes if design engineers don't regard BIWs or BIWs are placed as asymmetric or deficient on the structure.
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    Advancing earthquake resistance: Hybrid retrofitting of RC frames with FRP and TDS
    Suk, R; Demir, A; Altiok, TY; Altintas, G
    Traditional and technological retrofitting methods have been proposed over time to enhance earthquake resistance in structures. Friction-type dampers have attracted considerable interest from both researchers and the construction industry because of their versatility in retrofitting, quick installation, and non-destructive characteristics. Moreover, the integration of damping systems with various retrofitting elements and the resulting impact of these hybrid systems on building performance have consistently been subjects of interest. This study involved the construction of three identical half-scale reinforced concrete (R.C) frames. One frame served as the reference (REF), the second was wrapped with Fiber Reinforced Polymers (FRP) material (REF-FRP), and the third was retrofitted using both FRP wrapping and the developed Technological Damper System (TDS-FRP). Quasi-static cyclic experiments were performed on the three structural frames, providing force-displacement and force-rotation relationships. The acquired data were then used to assess the damage states of the frames according to the Turkish Building Earthquake Code (TBEC 2018), and energy consumption rates were determined. Moreover, Finite Element Method (FEM) analyses were performed on REF, REF-FRP, and TDS FRP frames to derive force-displacement relationships, which were subsequently compared with experimental findings. The experiment results indicate that the horizontal load-carrying capacity of the TDS-FRP frame increased by 76 % to 122 % compared to the REF frame, while the REF-FRP frame showed a maximum increase of 14 %. Additionally, the cumulative energy consumption capacity of the REF-FRP frame increased by a maximum of 42 % compared to the REF frame, and the TDS-FRP increased between 51 % and 156 %. At a 1 % drift ratio, shear cracks at the beam ends and column-beam intersections of the REF frame were observed to be significantly reduced in the REF-FRP frame and eliminated in the TDS-FRP frame. Additionally, upon reaching a 3 % drift ratio, it was observed that the TDS-FRP frame remained within acceptable limits as per TBEC 2018, whereas the REF and REF-FRP frames exceeded the advanced damage limit. Additionally, it has been observed that the results obtained from FEM analyses coincide with the experimental results. In this context, the TDS-FRP hybrid application can be considered as an effective and alternative solution for the R.C buildings.
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    Synovial chondromatosis of the temporomandibular joint extending to temporalis, masticator, and parotid spaces
    Yildiz, ST; Demir, A; Kaya, A
    Synovial chondromatosis of the temporomandibular joint (TMJ) is very rare. We report a case of synovial chondromatosis of the TMJ with extraarticular extension that was diagnosed with MRI and CT. Histopathologic evaluation indicated that this case was synovial chondromatosis in intermediate phase.
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    Shaking table study of masonry buildings with reinforced plaster
    Basaran, H; Demir, A; Bagci, M; Ercan, E
    The objective of this study is to determine seismic behaviour of masonry buildings with reinforced plaster mortar, with a particular focus on the modification of structural response due to application of the polypropylene and steel reinforced plaster, as compared to an ordinary type of plaster. The resistance of one-storey single-span masonry buildings subjected to seismic load on the shaking table is investigated in the study. Experimental results revealed natural periods, response acceleration spectrums, and spectrum interactions of masonry buildings. In addition, finite element models of test buildings were established, and their results were compared with those obtained during experimental study.
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    Numerical assessment of a slender structure damaged during October 30, 2020, Izmir earthquake in Turkey
    Demir, A; Altiok, TY
    The minarets, which have a tall and slender structure, are quite vulnerable to dynamic forces, i.e. earthquakes and winds. In mainly concrete minarets, since the bond between the concrete blocks is provided by only mortar, the damages caused by high tensile stresses may emerge. This study aims to simulate the behaviour of the concrete Selimiye minaret damaged during the Izmir (Seferihisar-Samos) earthquake on October 30, 2020. The nonlinear finite element model of the Selimiye minaret is created using the Concrete Damage Plasticity failure model. In the nonlinear time history analyses, the Izmir earthquake records obtained from the Bayrakli station, located the closest to the minaret, are used. The damages occurring in the transition segment of the minaret are verified with the finite element method. This study also aims to strengthen insufficient concrete minarets with an innovative, cost-effective, and better workability method. The proposed strengthening method is based on a Fabric Reinforced Concrete Mixture. Finite element models are strengthened from the inner surface using Fabric Reinforced Concrete Mixture composites reinforced with glass and steel fibers. As a result of the finite element analyses, it is concluded that the concrete minarets can be strengthened from the inner surface with the Steel Fabric Reinforced Concrete Mixture method in safety. In addition, with a parametric study, it has been determined that partial strengthening applications, which are more economical and aesthetic, can be more effective on structural performance than full strengthening applications.