Browsing by Author "Tekin A."

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    Non linear vibrations of stepped beam system under different boundary conditions
    (Techno-Press, 2007) Özkaya E.; Tekin A.
    In this study, the nonlinear vibrations of stepped beams having different boundary conditions were investigated. The equations of motions were obtained using Hamilton's principle and made non dimensional. The stretching effect induced non-linear terms to the equations. Forcing and damping terms were also included in the equations. The dimensionless equations were solved for six different set of boundary conditions. A perturbation method was applied to the equations of motions. The first terms of the perturbation series lead to the linear problem. Natural frequencies for the linear problem were calculated exactly for different boundary conditions. Second order non-linear terms of the perturbation series behave as corrections to the linear problem. Amplitude and phase modulation equations were obtained. Non-linear free and forced vibrations were investigated in detail. The effects of the position and magnitude of the step, as well as effects of different boundary conditions on the vibrations, were determined.
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    A survey of patient preparation and technique of ultrasound-guided prostate biopsy: A multicenter study og urooncological association; [Ultrasonografi kιlavuzluǧunda yapιlan prostat biyopsisinde hasta hazιrlιǧι ve teknik anketi: Üroonkoloji derneǧi çcok merkezli çalιşmasι]
    (Turk Uroloji Dernegi, 2007) Bozlu M.; Akduman B.; Mungan U.; Özen H.; Baltaci S.; Türkeri L.; Kirkali Z.; Akdaş A.; Adsan Ö.; Akdoǧan B.; Altinel M.; Ataus S.; Ayan S.; Bilen C.Y.; Çal Ç.; Çek M.; Dündar M.; Işeri C.; Koşan M.; Lekili M.; Müezzinoǧlu T.; Özer G.; Özgök Y.; Perk H.; Soyupak B.; Soyupek S.; Soylu A.; Sözen S.; Şengör F.; Tansuǧ Z.; Tekin A.; Yildirim A.
    Introduction: Ultrasound-guided prostate biopsy is the standard method for the diagnosis of prostate cancer. The aim of the present survey is to assess the variability in patient preparation and technique of ultrasound-guided prostate biopsy among Turkish Urologists. Materials and Methods: In July 2004, a questionnaire was sent out to e-mail addresses of the members of Urooncological Association, asking about the details of prostate biopsy protocol of the members. The survey consisted of multiple choice questions about the patient preparation and prostate biopsy technique. Responses were acquired via e-mail and analyzed in detail. Results: Thirty two urologists from 24 centers responded. The biopsy procedure was performed by the urologist only in 54.16% of the centers, both urologist and radiologist in 37.5%, and radiologist only in 8.33%. Transrectal route was the most common method for ultrasound-guided prostate biopsy. A half of the responders performed biopsy when PSA was greater than 4 ng/ml. All of the centers administered antibiotic and a half of them used enema before the procedure. Approximately 37% of responders did not administer any type of analgesia, but 29.1% of all responders administered a periprostatic nerve block for reducing pain during the procedure. Most urologists obtained 10 or 12 biopsy cores and only 20.8% of them obtained routine transitional zone biopsy during the initial biopsy session. Conclusion: This survey demonstrated that patient preparation and technique of ultrasound-guided prostate biopsy is not standardized among Turkish Urologists, and a guideline on prostate biopsy is needed.
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    Three-to-one internal resonance in multiple stepped beam systems
    (Springer Netherlands, 2009) Tekin A.; Özkaya E.; Bağdatlı S.M.
    In this study, the vibrations of multiple stepped beams with cubic nonlinearities are considered. A three-to-one internal resonance case is investigated for the system. A general approximate solution to the problem is found using the method of multiple scales (a perturbation technique). The modulation equations of the amplitudes and the phases are derived for two modes. These equations are utilized to determine steady state solutions and their stabilities. It is assumed that the external forcing frequency is close to the lower frequency. For the numeric part of the study, the three-to-one ratio in natural frequencies is investigated. These values are observed to be between the first and second natural frequencies in the cases of the clamped-clamped and clamped-pinned supports, and between the second and third natural frequencies in the case of the pinned-pinned support. Finally, a numeric algorithm is used to solve the three-to-one internal resonance. The first mode is externally excited for the clamped-clamped and clamped-pinned supports, and the second mode is externally excited for the pinned-pinned support. Then, the amplitudes of the first and second modes are investigated when the first mode is externally excited. The amplitudes of the second and third modes are investigated when the second mode is externally excited. The force-response, damping-response, and frequency-response curves are plotted for the internal resonance modes of vibrations. The stability analysis is carried out for these plots. © 2009 Shanghai University and Springer Berlin Heidelberg.
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    Non linear vibrations of stepped beam systems using artificial neural networks
    (Techno-Press, 2009) Baǧdatli S.M.; Özkaya E.; Özyiǧit H.A.; Tekin A.
    In this study, the nonlinear vibrations of stepped beams having different boundary conditions were investigated. The equations of motions were obtained by using Hamilton's principle and made non dimensional. The stretching effect induced non-linear terms to the equations. Natural frequencies are calculated for different boundary conditions, stepped ratios and stepped locations by Newton-Raphson Method. The corresponding nonlinear correction coefficients are also calculated for the fundamental mode. At the second part, an alternative method is produced for the analysis. The calculated natural frequencies and nonlinear corrections are used for training an artificial neural network (ANN) program which has a multi-layer, feed-forward, back-propagation algorithm. The results of the algorithm produce errors less than 2.5% for linear case and 10.12% for nonlinear case. The errors are much lower for most cases except clamped-clamped end condition. By employing the ANN algorithm, the natural frequencies and nonlinear corrections are easily calculated by little errors, and the computational time is drastically reduced compared with the conventional numerical techniques.
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    Genetic basis and hematologic manifestations of sitosterolemia in a group of Turkish patients
    (Elsevier Ltd, 2021) Kaya Z.; Sal E.; Yorulmaz A.; Hsieh Y.-P.; Gülen H.; Yıldırım A.T.; Niu D.-M.; Tekin A.
    BACKGROUND: Sitosterolemia is a rare lipid disorder caused by mutations in adenosine triphosphate-binding cassette genes (ABCG) 5 and 8. OBJECTIVE: To evaluate the phenotypic/genotypic features of sitosterolemia in a group of Turkish patients. METHODS: Seven probands with unexplained hematologic abnormalities and their 13 relatives were enrolled. Sterol levels were measured by gas chromatography and genetic studies were performed using Sanger sequencing. Individuals were diagnosed with sitosterolemia if they were found to have frankly elevated sitosterol level >15 μg/mL and/or pathogenic variants of the ABCG5/ABCG8. RESULTS: The seven probands and their six relatives were diagnosed with frank sitosterolemia, and all these patients had hematologic abnormalities. The remaining seven relatives were asymptomatic heterozygous carriers. Three novel variants in the ABCG5 gene (c.161G>A, c.1375C>T, IVS10–1G>T), one novel variant in the ABCG8 gene (c.1762G>C) and one known variant in the ABCG5 gene (c.1336 C>T) were identified. No variant was identified in one case. The mean sitosterol level was significantly higher and mean platelet count was significantly lower in patients with homozygous variants compared to heterozygous variants (p<0.05, for all). Diets low in plant sterols were recommended for 13 symptomatic cases. Four homozygotes received ezetimibe, and their splenomegaly, anemia, and thrombocytopenia completely resolved except one. CONCLUSION: The five pathogenic variants identified in this study indicate the genetic heterogeneity of sitosterolemia in Turkish population. Patients with unexplained hematologic abnormalities (specifically macrothrombocytopenia) should have their sterol level measured as initial testing. Ezetimibe can be a good choice for sitosterolemia. © 2021
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    Assessment of vibration exposure of mine machinery operators at three different open-pit coal mines
    (South African Institute of Mining and Metallurgy, 2022) Tekin A.
    In almost all branches of industry, machinery and equipment in operation cause vibration. Some sources of vibration affect only the operator's hands, fingers, and arms, while others have adverse effects on the entire -body. Various types and numbers of machines are utilized in the mining sector, and operators with them are exposed to mechanical vibrations caused by the mining machinery they use. A field study was conducted to evaluate the vibration risks to the operators using mining machines in open pit mines. Vibration levels and whole-body vibration (WBV) measurements using various types brands, and models of construction equipment were evaluated in three different mines in the west of Turkey and compared to the the criteria specified in the EU 2002/44/EC directive and ISO 2631-1 (1997) standards. The results showed that operators using mining machinery for 8 hours were exposed to WBV levels below the EU limit (1.15 m/s2), while 44% of these operators were exposed to levels above the EU action limit (0.5 m/s2). Measurement data collected from the working environment and the recommended improvements that need to be made to reduce WBV exposures are presented. © 2022 South African Institute of Mining and Metallurgy. All rights reserved.
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    The Role of Scientific and Technological Performance on Economic Growth: A Panel Data Analysis for OECD Countries; [Bilimsel ve Teknolojik Performansın Ekonomik Büyümeye Etkisi: OECD Ülkeleri Üzerine Bir Panel Veri Analizi]
    (Sosyoekonomi Society, 2022) Tekin A.; Demirel O.
    Non-physical factors such as education, knowledge, information, innovation, and research and development (R&D) are new sources for economic growth. The study analyses the effect of scientific and technological performance on GDP. Pedroni Cointegration Test, Vector Error Correction Model, and Granger Causality Analysis are applied to 21 OECD member countries for the 2003-2016 period. As the result of the analysis, it is determined that there is a long-term relationship between R&D expenditures used in the concretization of scientific and technological performance, the number of patents applied for innovation, and GDP. Further, the relationships’ directions are determined from patent applications to GDP and GDP to R&D expenditures. © 2022, Sosyoekonomi Society. All rights reserved.
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    Investigation of nonlinear vibration behavior of the stepped nanobeam
    (Techno-Press, 2023) Nalbant M.O.; Bağdatli S.M.; Tekin A.
    Nonlinearity plays an important role in control systems and the application of design. For this reason, in addition to linear vibrations, nonlinear vibrations of the stepped nanobeam are also discussed in this manuscript. This study investigated the vibrations of stepped nanobeams according to Eringen’s nonlocal elasticity theory. Eringen’s nonlocal elasticity theory was used to capture the nanoscale effect. The nanoscale stepped Euler Bernoulli beam is considered. The equations of motion representing the motion of the beam are found by Hamilton’s principle. The equations were subjected to nondimensionalization to make them independent of the dimensions and physical structure of the material. The equations of motion were found using the multi-time scale method, which is one of the approximate solution methods, perturbation methods. The first section of the series obtained from the perturbation solution represents a linear problem. The linear problem’s natural frequencies are found for the simple-simple boundary condition. The second-order part of the perturbation solution is the nonlinear terms and is used as corrections to the linear problem. The system’s amplitude and phase modulation equations are found in the results part of the problem. Nonlinear frequency-amplitude, and external frequency-amplitude relationships are discussed. The location of the step, the radius ratios of the steps, and the changes of the small-scale parameter of the theory were investigated and their effects on nonlinear vibrations under simple-simple boundary conditions were observed by making comparisons. The results are presented via tables and graphs. The current beam model can assist in designing and fabricating integrated such as nano-sensors and nano-actuators. © 2023 Techno-Press, Ltd.
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    Three-to-one internal resonances of stepped nanobeam of nonlinearity
    (Walter de Gruyter GmbH, 2024) Nalbant M.O.; Baǧdatli S.M.; Tekin A.
    In this study, vibrations of stepped nanobeams were investigated according to Eringen's nonlocal elasticity theory. Multi-time scale method, which is one of the perturbation methods, has been applied to solve dimensionless state equations. The solution is considered in two steps. First-order terms obtained from the perturbation expansion formed the linear problem in the first step. In the second step, the solution of the second order of the perturbation expansion was made and nonlinear terms emerged as corrections to the linear problem from this solution. The main issue that the study wants to emphasize is the examination of the mechanical effects of the steps, which are discontinuities encountered at the nanoscale, on the system. For this purpose, while the findings of the research were obtained, various nonlocal parameter values were obtained to capture the nano-scale effect, and frequency-response and nonlinear frequency-amplitude curves corresponding to the 1st Mode values of the beam for different step ratios and step locations were obtained to capture the step effect. One of the important features of the nonlinear system is the formation of internal resonance between the modes of the system. How this situation affects the characteristics of the system has also been examined and results have been given by graphs. The obtained data show that taking into account the nanoscale step is essential for the accuracy and sensitivity of many nanostructures such as sensors, actuators, biostructures, switches, etc. that are likely to be produced at the nanoscale in practice. © 2023 Walter de Gruyter GmbH, Berlin/Boston.
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    Modal Analysis and Optimization of Tractor Exhaust System
    (Multidisciplinary Digital Publishing Institute (MDPI), 2025) Tekin A.; Şamlı H.
    Excessive vibrations in exhaust systems can significantly reduce a vehicle’s lifespan and compromise performance. These vibrations, caused by factors such as engine operation and road conditions, lead to wear and tear. To address this issue, a finite element analysis (FEA) was conducted on a 90-horsepower tractor’s exhaust system. Using ANSYS WB®, a 3D model was created and modal analysis was performed to determine the system’s natural frequencies and mode shapes. Based on the results, geometric modifications were made to the exhaust system, increasing its stiffness and shifting vibration frequencies to higher values. Consequently, vibration levels, noise, and the risk of component failure were significantly reduced. The redesigned exhaust system was successfully implemented in production. This study demonstrates the effectiveness of FEA in analyzing exhaust system vibrations and facilitating design improvements. By extending vehicle lifespan and providing a quieter, more comfortable driving experience, this research offers valuable insights for automotive and mechanical engineers. © 2025 by the authors.