Fen Bilimleri Enstitüsü

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0-30V / 5A digital power supply with computer control
(Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2010., 2010.) Sünetci, Önder.; Kahya, Yasemin.; Cerid, Ömer.
Most of the electronic circuits require a DC power supply to operate. There are many designs and topologies covering different properties and specifications for DC power supplies. The voltage and current range and accuracy, power capacity and quality, failure protections, isolations, robustness and reliability, power efficiency, size and ease of usage are some of the most important characteristics of power supplies. A DC power supply with the parameters given in the following sections is designed and realized for the fulfillment of the Master of Science thesis. The criteria for making decisions on the design parameters were range, isolations and ease of use. The range is proposed to be 30VDC and 5A output. The isolation is realized both between the mains and the device and between the device and PC that, when connected, controls it. For the ease of use, a 4x4 keypad to enter data and a 2x20 character LCD to monitor data are used.
1,27-2,50 GeV/c momentumlu pozitif pionların protonlarla etkileşmeleri
(Thesis (Assoc. Prof.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1981., 1981.) Arık, Engin.
10-BIT 60 MS/s two-step flash ADC design
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2013., 2013.) Esen, Vahap Barış.; Dündar, Günhan,
Two step flash ADCs have widespread use in electronic circuits, since they can achieve decent resolutions in high speed applications. Their two step structure requires coordination of many analog blocks that is ensured by control signals. Generating and delivering these control signals as clock signals are as important as the design of the analog blocks. In this thesis analog design of a two-step flash ADC which is used as a test circuit for an automation tool that can synthesize the necessary clock signals is presented. The design procedures of the blocks in 10-bit 60 MS/s two step flash ADC are examined. The overall design is realized by using UMC 180nm technology. Finally the simulation results obtained by using Mentor Graphics tools and MATLAB are presented. The performance of the ADC is evaluated using ENOB as a figure of merit. Resolutions up to eight bits are attained in typical case simulations. Comparison with the literature is also made by using energy per conversion values.
140 Mb/s deqpsk modem if stage
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1985., 1985.) Suyabatmaz, M. Akif.; Cerid, Ömer.
Recently, as the digital technology progresses, the exploding capacity of digital information nececities fast digital communication systems. Since the congestion prevailing in many regions of radio frenuency spectrum has created the need for improved spectrum utilization techniques, the demand for multilevel (Mrary) digital modulation techniques has also increased. In this thesis, a differentially encoded and differentially decoded quadrature phase shift keyed modem, employing coherent demodulator, was briefly analy.zed. System building blocks were investigated and the one, proper to high data rate application, was chosen for system realization. A working circuit, was build as an intermediate frequency (IF) stage, operating at 140 Mbit per second, and realized.
2-D mathematical modelling of hydrogen storage in metal hydrides
(Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2009., 2009.) Küçük, Gülşad.; Aksan, Emre.
In this study a numerical model which simulates heat and mass transfer processes of hydrogen absorption in LaNi5 is studied. Energy balance method is used for discretizing the heat equation. Transient heat conduction with convective boundary conditions is evaluated with explicit scheme. The analyses are conducted using MATLAB. Evaluation of temperature profiles and hydrogen mass that is being absorbed during hydriding are shown to be correlated with the experimental data and with the previous numerical studies. Since the hydriding reaction is exothermic, the rate of removal of heat released is critical in time needed to reach saturation in metal-hydride reactor. The effects of bed geometry, inlet hydrogen pressure, and metal porosity, initial bed temperature and the temperature of cooling fluid are investigated. Different cases are compared with the base case which is chosen to have similarities with conventional metal hydride tanks in reactor geometry and in thermophysical properties.
2-D modeling of compression ignition engine combustion
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2016., 2016.) Yıldırım, Cebrail.; Bedir, Hasan.
Internal combustion engines are the cornerstones of our society. They are widely used in a vast range of area from transportation to power generation. Since they are mostly petroleum-powered and emission regulations are getting tighter due to the environmental concerns, ICE research activity is vibrant today. In the present study, a multidimational CFD approach has been used to simulate a CI diesel engine combustion to investigate the e ect of injection timing and swirl ratio on combustion and emissions. AVL Fire software has been used for combustion, spray and emission modeling. Within this context, ECFM-3Z, k {u100000} ", Wave break-up, Dukowicz, extended Zeldovich and Hiroyasu approaches have been used for, in order, combustion, turbulence, spray atomization, spray evaporation, NOx and soot emission modeling. When compared with the experimental data, the simulation results show a good agreement. As for the swirl ratios, minimum NO and soot emission are achieved at SR 3.0 while the optimum bsfc and maximum indicated e ciency are found at SR 1.0. Findings of di erent injection timing are that advanced injection results in higher NO and higher soot emissions as the retarded injection provides lower NO and higher soot emissions with reference to the baseline simulation.. As a result, SR 1.0 and reference injection timing have been found to be the optimum con guration in terms of bsfc and emissions for the engine studied.
2D to 3D video conversion
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2016., 2016.) Çoban Aydın, Aysun.; Acar, Burak.
Stereoscopic 3D visualisation is increasingly embedded into social life through the use of commercially available 3D-TV sets. In this work, a hybrid approach for 2D to 3D conversion is presented to produce stereoscopic 3D video automatically from 2D mono video frames. Each frame is synthesized to stereo pairs. Disparity/depth information required for 3D view is extracted from mono frame sequences based on motion and geometrical cues. Depth estimation of the scene is considered separately for background and foreground. Background geometry of the scene is determined by using geometrical cues such as vanishing point and straight lines in the image. According to this geometry, relevant information on the background depth eld of a single image is estimated to generate a canonic disparity map of the background. For foreground depth estimation, on the other hand, two approaches are presented. First approach is based on detection of moving foreground objects. A depth value is assigned to each object based on its corresponding location in the background depth map. In the second approach, background registration is applied for consecutive frames that are captured by a moving camera. By this method, disparity in foreground regions is distinguished from background disparity that leads to a distinctive 3D e ect on foreground regions. Consequently, depth/disparity information of foreground regions is combined with background canonic disparity map. According to these nal disparity maps, pixels of the original frames are shifted to generate virtual frames to enable 3D views. This work is accompanied by a subjective evaluation on the basis of user test which compare our 3D results with commercially available 3D-TV sets.
3 - D optical profilometry at micron scale with modified fiber optic Lloyd's mirror technique
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2017., 2017.) İnanç, Arda.; İnci, Naci.
In this thesis, it is shown that a modiﬁed ﬁber optic Lloyd’s mirror technique is suitable and practical to produce fringe patterns that have easily adjustable frequency. This allows measuring 3D height distribution of test objects at micron scale without using additional elements as part of the optical projection unit. To test the validity of the proposed method, images that contain deformed fringe patterns due to the height distribution of micron scale test objects are recorded by a CCD camera and analysed with one dimensional continuous wavelet transform. After the extraction of phase map using 1D continuous wavelet transform, the height dis tribution of the test objects is obtained by further analyses. Finally, the results are discussed and compared with the expected values.
3+1 formulation in Newton-Cartan gravity
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2022., 2022) Aras, Ulaş.; Bleeken, Dieter Van den.
In this thesis, we will give a review of torsion-free Newton- Cartan theory. We will start by doing a large c expansion of general relativity and we will restrict ourselves to a few leading orders. After obtaining Newton-Cartan theory in this way, we will explore its symmetries. Through a special set of combined symmetries, we will construct a split space and time structure. Lastly, we will work out the field equations and equations of motion for a particle in the 3+1 formulation we have obtained.
3.125Gbps FIR equalizer implementation in 65nm CMOS technology
(Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2008., 2008.) Kurnaz, Hande Akın.; Dündar, Günhan,
This thesis describes channel degradation in a basic telecommunication system with its sources (crostalk and metalic channel los) and results (inter-symbol interference). Compensation of this channel degradation via methodology caled equalization is focused on. Adaptive equalization techniques such as zero forcing, least mean squares (LMS), recursive least squares (RLS) and constant modulus algorithm (CMA) are theoreticaly explained and LMS and RLS are supported with regarding MATLAB Simulink simulations using 30inch PCB trace model as the channel model. Comparison of adaptation algorithms, equalization cost functions and tap spacing of tapped delay line in using 30inch PCB trace model as the channel model. Comparison of adaptation algorithms, equalization cost functions and tap spacing of tapped delay line in FIR equalizer in Simulink are also held for this thesis. Coeficients obtained from Simulink environment are used to verify performance of FIR equalizer designed in STMicroelectronics CMOS065 (65nm) technology for 3.125Gbps data rate. Building blocks of FIR equalizer are analyzed in detail and design limitations are summarized. Simulations showed that closed eye at the receiver after 30inch PCB channel, can be cleaned up to data eye with 28ps jiter by means of 4-tap FIR equalizer with T/8 tap spacing operating at 1.2V power supply, 3.125Gbps data rate and at the expense of only 13mA of current consumption.
3D cow identification in cattle farms
(Thesis (M.A.) - Bogazici University. Institute for Graduate Studies in the Social Sciences, 2013., 2015.) Arslan, Ahmet Cumhur.; Akar, Mehmet.
Animal farms have been steadily growing to meet the consumption requirements of the society in an e cient manner. This fact necessitates new monitoring and tracking systems to collect useful information about the herds in order to observe their general health and instantaneous state. However, recognizing and tracking an animal in a farm is a di cult task due to the target's similarity and hard to predict dynamics. In this thesis, a novel cow identi cation system is proposed. There are prominent features of this solution which di erentiates it from the others in the literature, i.e., it does not need any markers or external devices placed on the animal; works in even unlighted environments; identi es even black cows without distinctive coat patterns; is relatively cheaper, and enables accurate positioning. Proposed solution is based on 3D shape analysis of the top back part of the animals captured with RGBD cameras placed at an adequate height, where two dimensional images are constructed with respect to the local surface features and are subsequently identi ed by using face recognition methods. To evaluate the applicability of the proposed system, a real-time prototype software has been developed and a 3D cattle dataset is acquired which, to our knowledge, is unique in the literature. This dataset is gathered from moving animals which do not have distinctive coat patterns and captured in di erent lighting conditions. Applicability of the proposed solution has been veri ed by testing with the acquired dataset. Convincing results are obtained where %88 of 50 cows are identi ed successfully.
3D face registration using multiple average models
(Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2008., 2008.) Alyüz, Neşe.; Akarun, Lale.
Three dimensional (3D) face recognition is a frequently used biometric method and its performance is substantially dependent on the accuracy of registration. In this work, we explore registration techniques. Registration aligns two faces and make a comparison possible between the two surfaces. In the literature, best results have been achieved by a one-to-all approach, where a test face is aligned to each gallery face separately. Unfortunately, the computational cost of this approach is high. To overcome the computational bottleneck, we examine registration based on an Average Face Model (AFM). We propose a better method for the construction of an AFM. To improve the registration, we propose to group faces and register with category-specific AFMs. We compare the groups formed by clustering in the face space with the groups based on morphology and gender. We see that gender and morphology classes exist, when faces are categorized with the clustering approach. As a result of registering via an AFM, it is possible to apply regular re-sampling on the depth values. With regular re-sampling, improvements in recognition performance and comparison time were obtained. As another factor causing diversity in the face space, we explore expression variations. To reduce the negative effect of expression in registration and recognition, we propose a region-based registration method. We divide the facial surface into several logical segments, and for each segment we create an Average Region Model (ARM). Registering via each ARM separately, we examine regional recognition performance. We see that even though some regions such as nose or eye area are less affected by expression variations, no single region is sufficient by itself and the use of all regions is beneficial in recognition. We experiment with several fusion techniques to combine results from individual regions and obtain performance increase.
3D human pose estimation from multi-view RGB images
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2019., 2019.) Temiz, Hüseyin.; Akarun, Lale.; Gökberk, Berk.
Recovery of a 3D human pose from cameras has been the subject of intensive research in the last decade. Algorithms that can estimate the 3D pose from a single image have been developed. At the same time, many camera environments have an array of cameras. In this thesis, after aligning the poses obtained from single-view images using Procrustes Analysis, median ltering is utilized to eliminate outliers to nd nal reconstructed 3D body joint coordinates. Experiments performed on the CMU Panoptic, MPI INF 3DHP, and Human3.6M datasets demonstrate that the proposed system achieves accurate 3D body joint reconstructions. Additionally, we observe that camera selection is useful to decrease the system complexity while attaining the same level of reconstruction performance. We also derive that dynamic camera selection has a more signi cant impact on reconstruction accuracy as against static camera selection.
3D optical profilometry using fiber optics lloyd's mirror method
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2017., 2017.) Köseoğlu, Gülşen.; İnci, Naci.
A ber optic Lloyd's mirror assembly is investigated to obtain various optical interference patterns for the detection of three-dimensional shapes of rigid bodies. Two types of the ber optic Lloyds systems are used in this work. The rst one consists of a single mode optical ber and a highly re ecting at mirror to produce bright and dark strips. The second one is constructed by locating a single mode optical ber in a v-groove, which is formed by two orthogonal at mirrors to allow the generation of square type interference patterns for the desired applications. The structured light patterns formed by these two ber optic Lloyds techniques are projected onto three-dimensional objects. Fringe patterns are deformed due to the object0s surface topographies, which are captured by a digital CCD camera and are processed with the following signal processing techniques to accomplish their three-dimensional surface topographic maps: Fourier Transform Pro lometry, Phase Stepping Pro lometry, and Continuous Wavelet Transform Pro lometry. The method is developed for extracting 3D height distribution of various objects at the micron scale with a resolution of 5 m by elegantly interrogating the rst ber optic assembly to an optical microscope and a CCD camera. It is demonstrated that the proposed technique is quite suitable and practical to produce a structured light pattern with an adjustable frequency. By increasing the distance between the ber and the mirror with a micrometer stage in the Lloyd0s mirror assembly, the separation between the two bright fringes is lowered down to the micron scale without using any additional elements as part of the optical projection unit. The phase analysis of the acquired image is carried out by One Dimensional Continuous Wavelet Transform.
3D optical profilometry with a double beam - splitter setup
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2019., 2019.) Çetin, İsra Merve.; İnci, Naci.
In this thesis, it is demonstrated that a double beam splitter arrangement is very convenient and more practical to generate square shaped fringe patterns, and fringe distribution can be easily controlled in two dimensions. This enables to extract 3D height distribution of test objects without using any additional component as a projection unit. To approve the validity of the proposed technique, various frequencies of the fringe pattern are obtained by rotating a cubic beam splitter, and images that include deformed fringe patterns due to the height distribution of test objects are captured by a CCD camera. The resultant square fringe pattern is analyzed with two-dimensional continuous wavelet transform method and is separated into two fringe patterns in horizontal and vertical axes with a certain algorithm. The height-related phase map is acquired after analysis process.
3D radial inflow turbine design and analysis for a small scale ORC application
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2017., 2017.) Sezerkan, Emre.; Bedir, Hasan.; Anlaş, Günay.
In this study, the aim is to design and analyze a single stage subsonic radial in- ow turbine for the Organic Rankine Cycle system established in Bogazici University Renewable Energy Technologies Laboratory, by using R245fa and R134a as the working uids. Complete design process of the ORC turbine, from preliminary design to 3D blade design stage, is presented. Design point of the turbine is determined according to the cycle limitations and by comparing the maximum mach number, rotational speed and mass ow rate parameters found as a result of detailed preliminary turbine design and basic cycle analysis. Results of the streamline and CFD analysis of the designed turbine are compared and discussed from the point of Mach number distribution, turbine e ciency and power output. The comparison shows that the two analyses give similar e ciencies, power outputs and Mach number distributions. Streamline analyses results show that the maximum total to static turbine e ciency and power output are 87.5 % and 3.97 kW respectively.
3D shape generation and manipulation
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2022., 2022) Dirik, Alara.; Uğur, Emre.; Yanardağ, Pınar.
Computer graphics, 3D computer vision and robotics communities have pro duced multiple approaches to represent and generate 3D shapes, as well as a vast number of use cases. These use cases include, but are not limited to, data encoding and compression, shape completion and reconstruction from partial 3D views. How ever, controllable 3D shape generation and single-view reconstruction remain relatively unexplored topics that are tightly intertwined and can unlock new design approaches. In this work, we propose a unified 3D shape manipulation and single-view reconstruc tion framework that builds upon Deep Implicit Templates [1], a 3D generative model that can also generate correspondence heat maps for a set of 3D shapes belonging to the same category. For this purpose, we start by providing a comprehensive overview of 3D shape representations and related work, and then describe our framework and pro posed methods. Our framework uses ShapeNetV2 [2] as the core dataset and enables finding both unsupervised and supervised directions within Deep Implicit Templates. More specifically, we use PCA to find unsupervised directions within Deep Implicit Templates, which are shown to encode a variety of local and global changes across each shape category. In addition, we use the latent codes of encoded shapes and metadata of the ShapeNet dataset to train linear SVMs and perform supervised manipulation of 3D shapes. Finally, we propose a novel framework that leverages the intermediate latent spaces of Vision Transformer (ViT) [3] and a joint image-text representational model, CLIP [4], for fast and efficient Single View Reconstruction (SVR). More specifi cally, we propose a novel mapping network architecture that learns a mapping between the latent spaces ViT and CLIP, and DIT. Our results show that our method is both view-agnostic and enables high-quality and real-time SVR.
3D stylus: an intuitive 3D pointer for volumetric radiological data
(Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2007., 2007.) Yağcı, Enver.; Acar, Burak.
This work introduces a new human-computer interface(HCI) device for three dimensional (3D) visualized data. Although there are different approaches developed in the literature, 3D interfaces have not finished their development. The HCI we designed basically aims at taking an arbitrary cross-section (oblique slicing) from volumetric data. Additionally, the interface we called "3D Stylus" has an extra option which enables the user to draw two dimensional curves. The 3D Stylus is a colorful, long and thin structure like a pen. The 3D Stylus is tracked by using image processing algorithms. 3D information about the interface is acquired with the help of stereo processing techniques applied to the images come from the stereo camera. The 3D Stylus is a flexible tool that can be used for different purposes in different applications. In the thesis, we firstly develop a oblique slicing application using 3D Stylus as normal vector of slicer held by the user. Then another application is developed for 2D drawing, and the 3D Stylus used as a chalk. At the end of the thesis, experiments are presented. Users are asked to use the 3D Stylus and mouse interfaces in our applications. Results about efficiency of the 3D Stylus are given, compared with mouse.
3D-engineered muscle tissue as a wireless sensor
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2023., 2023) Karabulut, Çağla.; Dumanlı Oktar, Sema.
Implantable and wearable biomedical devices are advancing with new sensor technologies, holding great potential for early disease detection through continuous, real-time monitoring of physiological parameters. However, the majority of existing biomedical devices have limited lifetimes due to their power requirements and often focus on monitoring physical parameters rather than specific molecules relevant to specific diseases. The work detailed in this thesis proposes a wireless sensing and communication platform that can achieve in-vivo, real-time sensing at a molecular level by utilizing engineered mammalian cells. The proposed platform consists of a cell-based bio- hybrid implant device and a dual-port, wide-band on-body antenna. The molecular sensing is achieved by the bio-hybrid implant that is composed of three main components: a flexible scaffold, an in-body passive implant antenna, and 3D-engineered muscle tissue. The genetic circuitry of the cells that make up the 3D-engineered muscle tissue can be manipulated. This manipulation makes the tissue responsive to specific target molecules and the presence of these molecules triggers a contraction in the tissue. The tissue contraction and relaxation are used to reconfigure the resonance frequency of the implant antenna that is located on the flexible scaffold. To monitor the changes in resonance reconfiguration, the on- body reader antenna is positioned outside of the human body. The implant antenna’s resonance variations are observed in response to the presence of the molecule of interest. In this thesis, the bio-hybrid implant and the on-body reader antenna were designed and fabricated. The sensing system is mechanically and electromagnetically simulated. Based on the simulations, electromagnetic measurements were taken inside tissue-mimicking phantoms to track implant antenna reconfiguration.
A 10 bit interface circuit for an array of capacitive transducers
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2016., 2016.) Vosoughi, Mohammad Ali.; Dündar, Günhan,
Terahertz Cameras are going to be widely used in many places, speci cally for medical purpose and there are many advantages over the use of terahertz signals for imaging. Among di erent methods of terahertz imaging, the transformation of the THz signals into the form of absorbed heat and mechanical displacements can be used for medical purposes. The use of mechanical de ections for cameras requires a method for measuring the displacement. From di erent modalities for displacement sensing, capacitor based displacements are widely used in literature. For many reasons, including cost and feasibility with current technologies and compatibility with MEMS fabrications process, capacitive displacement transducers are the best choice for photo-mechanical cameras. Simulations show that the interface circuit should satisfy a su ciently good safe margin for operation of circuit in di erent sensing capacitor dimensions. A rail-to-rail voltage at the output of the sensor interface circuit might limit tolerance of the fabrication process. Therefore, conventional method with limited output voltage swing is employed to provide su ciently exible solution. A 10 bit data converter transduces the capacitance value to a digital modulated signal.

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