Cilt:61 Sayı:02 (2019)
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Item Operation Tests of the 260 mhz 1500 w Solid State RF Amplifier at Tarla Facility(Ankara Üniversitesi Fen Fakültesi, 2019-12-01) Karslı, Özlem; Çalok, Evrim; Elektrik-Elektronik Mühendisliği; Mühendislik FakültesiTurkish Accelerator and Radiation Laboratory (TARLA) will be the first accelerator-based user facility in Turkey. The facility is under construction at the Institute of Accelerator Technologies of Ankara University. Based on the state-of-art superconducting technology, TARLA accelerator offers a multi-experimental facility providing a variety of accelerator-based radiation sources for users coming from various fields like chemistry, physics, biology, material sciences, medicine and nanotechnology. TARLA consists of two acceleration lines: the first one is the injector that provides high current continuous wave (CW) electron beam at 250 keV energy, and the second one is the main accelerator that comprises of two superconducting (SC) cryomodules separated by a bunch compressor in order to accelerate the electron beam up to 40 MeV energy. Two normal conducting accelerators, so called subharmonic (SHB) and fundamental (FB) buncher cavities whose operation frequencies are 260 and 1300 MHz, respectively, are used to compress the electron bunches from ~600 ps to ~10 ps. SHB cavity is powered by a 1500 W Radio-frequency (RF) power amplifier. Currently, the electron gun training, and superconducting modules acceptance tests, personal safety system, and helium cryogenic system commissioning tests are performed simultaneously. In this study, we present the operation tests of the 1500 W RF amplifier in the scope of the commissioning tests of injector line which showed phase drift coefficents of ~0.5 deg/Co and ~0.67 deg/Co in repeated tests. Moreover, the importance of constancy of the water pressure in the water-cooling line for phase constancy of the delivered power has become evident as a result of current obervations.Item Robust Refractive Index Fiber Sensor Based on Two Up-Tapers Placed in Down-Taper(Ankara Üniversitesi Fen Fakültesi, 2019-12-01) Navruz, İsa; Bilsel, Mustafa; Elektrik-Elektronik Mühendisliği; Mühendislik FakültesiIn this study, a novel tapered optical fiber sensor based on a Mach–Zehnder interferometer (MZI) for refractive index measurement is proposed. Our sensor is constructed with two up-tapers symmetrically placed in a down-taper single mode fiber. Although its waist diameter is as thick as 55 μm, the sensor can measure the refractive index. Simulation results demonstrate RI sensitivities of -94 nm/RIU and -125 nm/RIU at the lower and higher wavelength of the spectrum. The sensor is extremely robust, it can be easily manufactured and it can be used not only for RI but also for simultaneous strain and temperature measurements.Item Preprocessing Steps in Fmri: Smoothing(Ankara Üniversitesi Fen Fakültesi, 2019-12-01) Daşgın, Hacer; Yaman, Ali; Akdi, Yılmaz; Fizik; Fen FakültesiFunctional magnetic resonance imaging is a technique with a primary and dominant effect in the investigation of the cognitive functions of the brain since it has a complex structure. In this study, data obtained from single subject was examined. First statistical parametric mapping results were obtained after applying the standard preprocessing steps with including smoothness. Spatial smoothing was performed using a 3 mm Gaussian kernel which is twice of the voxel size. Second, statistical parametric mapping results were obtained with applying standard preprocessing steps without smoothing. The effects of these two applications on the mapping results were compared for selected slices and locations in terms of statistical and pattern.Item Magnetocaloric Effect Around Curie Temperature in Ni50-x CuxMn38Sn12B3 Shape Memory Ribbons(Ankara Üniversitesi Fen Fakültesi, 2019-12-01) Kızılarslan, Olcay; Other; OtherThe magnetocaloric effect in Ni50-xCuxMn38Sn12B3 ribbons depending on the Cu substitution (x= 0, 1, 3) was investigated around the Curie temperature. The purpose of the present study was to analyze the magnetocaloric effect around a second order phase transition (around the Curie temperature) which has a smaller thermal hysteresis compared to a first order phase transition (Martensitic transition). The Curie temperature of the ribbons shifted to higher temperatures with increasing Cu content. A conventional magnetocaloric effect (MCE) was observed around the Curie temperature when the ribbons are subjected to a magnetic field change of 5 T. The magnetic entropy changes were calculated based on the isothermal magnetization data using thermodynamic Maxwell equation. The highest magnetic entropy change and the refrigerant capacity was obtained for the x=1 ribbon.Item A Comparison of deep Learning Based Architecture With a Conventional Approach for Face Recognition Problem(Ankara Üniversitesi Fen Fakültesi, 2019-12-01) Ünal, Fatime Zehra; Bilgisayar Mühendisliği; Fen Bilimleri EnstitüsüThis paper addresses a new approach for face recognition problem based on deep learning strategy. In order to verify the performance of the proposed approach, it is compared with a conventional face recognition method by using various comprehensive datasets. The conventional approach employs Histogram of Gradient (HOG) algorithm to extract features and utilizes a multi-class Support Vector Machine (SVM) classifier to train and learn the classification. On the other hand, the proposed deep learning based approaches employ a Convolutional Neural Network (CNN) based architecture and also offer both a SVM and Softmax classifiers respectively for the classification phase. Results reveal that the proposed deep learning architecture using Softmax classifier outperform conventional method by a substantial margin. As well as, the deep learning architecture using Softmax classifier also outperform SVM in almost all cases.