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Archived Theses
Dolanık olmayan polimer eriyiklerinin nano-kanallar içerisindeki moleküler reolojisi
We investigate the rheological properties of non-Newtonian melts of short polymer chains at the molecular level, with a focus on nanoscale confinement. Using a combination of all-atom molecular dynamics (MD) and coarse-grained simulations, we examine the behavior of oligomer melts with various topologies under non-equilibrium conditions. Our findings reveal significant deviations in the microscopic stress tensor under steady-state shear compared to predictions from continuum models, highlighting the limitations of the Oldroyd-B and generalized Phan-Thien–Tanner (gPTT) models in capturing nanoscale phenomena. We demonstrate that these deviations result in excess viscoelastic stress, which diminishes with decreasing confinement and vanishes in bulk systems. This excess stress is linked to the spatial orientation of carbon-carbon bonds near surfaces, where adsorbed chains form effective polymer brush-like layers. Additionally, we explore the effects of chain rigidity, surface-oligomer attraction, and molecular variables on rheological responses, providing a comprehensive understanding of the interplay between molecular-scale phenomena and macroscopic behavior in confined polymeric systems.
İnsan animasyonunda kişilik aktarımı: El yapımı ve veri odaklı yaklaşımlarının karşılaştırılması
The ability to perceive and alter personality traits in animation has significant implications for fields such as character animation and interactive media. Research and developments that use systematic tools or machine learning approaches show that personality can be perceived from different modalities such as audio, images, videos, and motions. Traditionally, handcrafted frameworks have been used to modulate motion and alter perceived personality traits. However, deep learning approaches also offer the potential for more nuanced and automated personality augmentation than handcrafted approaches. To address this evolving landscape, we compare the efficacy of handcrafted models with deep-learning models in altering perceived personality traits in animations. We examined various approaches for personality recognition, motion alteration, and motion generation. We developed two methods for modulating motions to alter OCEAN personality traits based on our findings. The first method is a handcrafted tool that modifies bone positions and rotations using Laban Movement Analysis (LMA) parameters. The second method involves a deep-learning model that separates motion content from personality traits. We could change the overall animation by altering the personality traits through this model. These models are evaluated through a three-part user study, revealing distinct strengths and limitations in both approaches.
Dikey van der waals metal-yarı iletken arayüzlerinde evrensel fotolüminesansı artırma/bastırma
Monolayers of transition metal dichalcogenides are considered the prospects for optoelectronic devices and photoluminescence (PL) is one of the key parameters to observe the performance and efficiency of such devices. The PL characteristics of monolayers of semiconducting transition metal dichalcogenides (TMDCs) have been consistently reported to be suppressed in the presence of metal, a phenomenon observed through direct metal evaporation or annealing of heterostructures in prior studies. These methods often resulted in a significant negative charge transfer which creates metal-induced gap states (MIGS) and Fermi level pinning (FLP). These MIGS and FLP provide nonradiative pathways to the excited electrons causing a huge suppression in PL intensity. To address this challenge, we explore heterostructures with a van der Waals gap between the metal and semiconductor surfaces. This design reduces the nonradiative relaxation pathways, allowing for more controlled charge transfer due to the van der Waals gap and the modulation of Schottky barrier height (SBH). The SBH for electrons increases with increasing metal work function and hence provides direct control of charge injection type and magnitude to monolayers of TMDCs. Our research presents a universal methodology for controlling the PL intensity of TMDCs by strategically utilizing the van der Waals gap and tailoring the work function of the interfacing metal. This investigation not only unveils a novel approach to prevent PL quenching but also opens avenues for optimizing optoelectronic devices. By carefully selecting metallic and semiconducting materials, this work offers a pathway to enhance device performance and precisely regulate output characteristics in optoelectronic applications.
Sonlu boyutlu filtreler ile gürbüz smith öngörücüsü tasarımı
The time delay is a widely recognized inherent phenomenon present in practical control systems, and it has been a subject of extensive research over the past century. Unless managed appropriately, even a minor delay can deteriorate performance and potentially lead to instability. Therefore, incorporating a model for time delay and designing the controller to mitigate its effects are crucial steps to attain the desired robustness and performance criteria in control theory. Additionally, owing to its infinite-dimensional structure, the majority of predictor-based controllers comprise finite impulse response filters, necessitating approximation with finite-dimensional transfer functions for seamless integration into physical systems. Controller designs based on the Smith predictor can effectively cancel out the impact of dead-time delay. This study introduces an extension of the Smith predictor to formulate stabilizing controllers for LTI SISO systems with multiple unstable modes and time delay. The main contribution of this approach lies in the streamlining of previous predictor-based control designs intended for unstable plants. The main contribution of this methodology lies in the simplification of previous predictor-based control designs tailored for unstable plants. The predictor filters are crafted by solving a Nevanlinna-Pick interpolation problem to attain optimal robust stability. The process also upholds the fundamental essence of the Smith predictor scheme, allowing the design of a controller based on the non-delayed nominal plant. Despite the susceptibility of Smith predictor-based designs to uncertain delays, the robustness of the proposed configuration surpasses that of the H-infinity optimal controller design, as demonstrated in the relevant section. The proposed design is also extensible to a category of distributed parameter SISO systems and MIMO plants. For distributed parameter SISO systems, it is assumed that the plant's transfer function can be expressed through coprime factorization. The fundamental idea underlying this approach is treating the infinite-dimensional inner factor of the plant as a "time delay", and, in turn, determining the predictor structure accordingly. The modeling and controller design steps expounded here are exemplified using a flexible beam model. Regarding MIMO systems, provided specific conditions are met, the tangential Nevanlinna-Pick interpolation technique can be employed to derive the controller and filters according to the proposed configuration. While numerous studies have addressed model order reduction in the context of H-infinity-norm error, achieving optimal H-infinity approximation remains a challenging and unresolved problem. This study introduces an alternative model reduction method that seeks to minimize the H-infinity norm of the difference between the reduced model and the original FIR structure. The proposed method essentially reduces the order of a given function by one with the minimum H-infinity-norm error, employing a high-order Padé approximation of the time-delay term. As the method reduces the order by one, an iterative algorithm is devised to recursively decrease the order of a given plant from n to a desired order of m, repeating the procedure (n-m) times following the outlined steps. The main contribution of the proposed technique is that it provides a new perspective against H-infinity-norm approximation by using Chebyshev equioscillation theorem on rational functions. Various examples are provided to elucidate the methodology of the suggested controller design and the robust stability condition in the context of approximating the infinite-dimensional predictor structure. Furthermore, the proposed model order reduction method is compared with the most recent state-of-the-art techniques within the literature. Finally, potential avenues for further research are deliberated, encompassing both the controller structure and H-infinity approximation.
Doku benzeri fantomların fotoakustik görüntülenmesi için cmut dizin yongaların ölçeklenebilir mikro üretimi (2. bölüm)
In this thesis study, Capacitive Micromachined Ultrasound Transducer (CMUT) array chips are microfabricated with wafer-scale batch-compatible approaches as sensors for photoacoustic imaging (PAI) applications. Photoacoustic imaging (PAI) is a non-invasive medical imaging technology, free from X-ray radiation, that utilizes contrast data resulting from acoustic detection of optical stimulation to construct images. CMUT array devices are microelectromechanical systems (MEMS) devices that generate or detect acoustic or pressure waves within the ultrasonic frequency range. The CMUT devices function on the principle of vibrating parallel plate variable capacitors. Capacitance variations due to vibrating plate electrode create electrical current signals in CMUT cells, which are further processed to obtain meaningful results. In PAI, pulsed laser light is transmitted and absorbed by naturally occurring photo-absorber compounds or contrast agents in selective body-tissue or tissue-like materials. The laser pulses are converted into heat, resulting in thermoelastic expansion vibrations of the tissue or tissue-like materials (i.e., phantom material). These vibrations travel as pressure or acoustic waves through the tissue or tissue-like materials that may be detected by CMUT sensors. For the production of the CMUT array devices, borosilicate glass (Pyrex-7740) wafers were selected as transparent substrates. The bottom electrode and electrical insulation layer above the bottom electrode of the CMUT sensors are processed on the Pyrex substrates. Anodic wafer bonding is selected as one of the suitable CMUT gap formation and top electrode integration technologies. Clean and unprocessed SOI (silicon-on-insulator) wafers are used for the formation of the top electrode of the CMUT sensors. The silicon handle layer and buried oxide (SiO2) layer of the SOI wafer are removed in order to reveal the silicon device layer that is used as the vibrating top electrode for the CMUT sensors. Metallization stacks on the Silicon device layer have been deposited for electrical conductivity enhancement and wire bonding connections between CMUT top electrodes and printed circuit boards (PCBs). After the patterning of the vibrating top electrode layer, dicing saw processing is done to singulate the CMUT chips from 4-inch diameter wafers. Chip-scale sealing of the CMUT chips is done by conformal Parylene C deposition using UV-sensitive dicing tape as a manual mask to prevent the deposition of Paylene C on the electrical pad regions of the CMUT chips. After Parylene C deposition, UV-sensitive dicing tape is removed from chips to reveal the electrical connection pads. CMUT array devices are characterized by inspecting their capacitive gap height, measuring their resonance frequencies, and determining the integration process yield. The resonance frequency results obtained from impedance analyzer measurements of individual CMUT cells are around 5.7 MHz. Furthermore, change in the resonance frequency is clearly detectable when the applied DC bias voltage is increased during the small AC plus incremental DC excitation of CMUT cell membranes. Keywords: Microelectromechanical Systems (MEMS), Capacitive Micromachined Ultrasound Transducer (CMUT), Microfabrication, Wafer-scale Batch-Compatible Microfabrication, Dicing Saw, Fully Automated Dicing Saw Processing, Anodic Wafer Bonding, Photoacoustic Imaging (PAI).
Cam elyafların gelişmiş mekanik ve kimyasal özellikleri için metal oksit nanopartikül kaplamalar
Glass fibers are one of the most used reinforcement fibers in composites. They have highly demanded properties such as high mechanical properties, impact resistance, high strength-to-weight ratio, and cost-efficiency. Glass fiber composites are utilized in many fields such as aerospace, automotive, and maritime. Glass fibers are one of the components in the composite structure aside from the resin matrix and their properties heavily affect the overall properties of the composite material. Improving the properties of glass fiber reinforcement, the composite performance can also be improved. Industrial-scale fabrication of glass fiber requires the construction of a certain glass-type exclusive factory. This study aims to have an alternative solution to meet the strength demands of industry with a relatively simple modification to the production process of E-glass fibers. In this study, the mechanical, chemical, and dielectric properties of glass fibers are altered via metal oxide nanoparticle doping. A thin layer of ZnO coating is applied onto the E-glass fibers via the dip coating method. Through spectroscopic and SEM characterization, the presence of ZnO coating is confirmed and the effect of this coating on mechanical properties is investigated through micromechanical analysis. ZnO coating proved to increase the tensile strength of E-glass fibers by 15.65%. In addition to mechanical improvements, the ZnO nanoparticles proved to be effective in corrosion resistance. Their corrosion-resistant properties are investigated using an acidic environment. Coated fibers are then used to manufacture a glass fiber felt composite to investigate the effect of nanoparticles on signal transmittance properties of glass fiber composites. In addition to modification of common E-glass fibers, a novel pure silica fiber fabrication method for advanced aerospace composite application is developed. Principles of optical fiber production is utilized to fabricate structural high purity fiber with unconventional fuel gas heating source. This study aims to obtain know-how knowledge on the production of pure silica fiber. To fabricate the pure silica fiber, a novel custom fabrication setup is designed and manufactured. This setup includes a custom heating system, custom capstan tractor, and a custom feeding system.
İki bağlantılı robotik sistemler için güçlü stabilizasyon sağlayan kontrolcü tasarımı
Strong stabilization is defined as finding a stable controller that stabilizes the feedback system for a given plant. This study addresses the strong stabilization of a robotic system called the ``acrobot", which is a two-linked underactuated planar robot system. The linearized system is fourth-order, with two poles and one zero in the right half-plane. In this thesis, stable second-order controllers designed with different methods have been investigated for this system. The stability margins are analyzed with respect to various free parameters. In addition, the time-domain transient response analysis is illustrated through simulations. Furthermore, the effects of nonlinearities are studied by estimating the region of attraction for each linear controller considered.
In vıtro fare ve ın vıvo zebrafısh modelleri ile farklı diyetlerin anjiyogeneze etkisi
Cardiovascular disorders rank as the primary cause of global mortality. Being overweight or obese impacts the pathogenesis of cardiovascular disease, resulting in an imbalance in endothelial function, cell growth, and inflammatory activation (Shrestha et al. 2020). Disruption of these factors resulting from endothelial cell dysfunction serves as both an outcome and a catalyst for vascular disease processes. Endothelial cells (ECs) are a natural barrier between circulating blood and vessel components. They also play critical roles in multiple physiological and pathophysiological processes, such as angiogenesis, vascular permeability, and inflammation. Amelioration of endothelial dysfunction may be attained by weight loss; however, complementary in vitro and in vivo studies are needed to establish the effects of weight loss on endothelial function and angiogenesis. This study developed an in vitro model to understand better the diet-induced changes in angiogenesis for mouse endothelial cells. In addition, a novel in vivo model of diet-induced vascular dysfunction and its reversal with a regular diet in a zebrafish model was also studied. In this study, in vitro studies show that a high-fat diet (HFD) has a proliferative effect on endothelial cells and weight loss does not compensate for prior stress induced by HFD. In vivo studies showed that an egg yolk-based high-fat diet might affect hepatic and angiogenesis parameters, on which weight loss partially affects both larvae and adult zebrafish. These preclinical models can be helpful experimental models to study diet-induced changes in angiogenesis and regeneration under different dietary regimes.
Ws2'nin 1h, 1t ve 1t' fazları için optimize edilmiş stıllınger-weber potansiyelleri: termal taşıma örneği
The advent of graphene has poured numerous amount of research effort into the study 2D materials and utilizing it for device fabrication. Monolayer Transi- tion Metal Dichalcogenides are one such class of polymorphic material with high prospect in versatile device applications due to its unique properties exhibited across the various phases. Classical Molecular Dynamics is a powerful tool that can be utilized to study the thermal and mechanical properties of these phases. Considering this, we optimise Stillinger-Weber type Potential for the seperate 1H, 1T and 1T′ phases of WS2 using Particle Swarm Optimization. These potentials are validated by comparison of phonon dispersion curves, Density Functional The- ory (DFT) based target characteristic data and through an accuracy assessment conducted using Non-Equilibrium Molecular Dynamic (NEMD) simulations to evaluate thermal conductivity of the polymorphic structures. Thermal conduc- tivity results obtained for 1H and 1T′ are in good agreement with first principle predictions calculated using Boltzmann Transport Equation. NEMD simulation of 1T phase prove to be challenging due to its dynamic instability with incoherent buckle structure formation along the symmetric directions.
Otobüs faktörü analizinin görselleştirme ile güçlendirilmesi
'Bus factor', also known as 'truck factor', is a measure of how vulnerable a software project is based on the minimum number of people who would have to leave the project (be 'hit by a bus') for it to stall. There is existing research on how to calculate bus factor for software projects but limited work on visualizing the bus factor. We believe providing visualization along with conventionally provided numerical bus factor results will help decision-makers manage the workload and knowledge distribution across the project and also help in planning and hiring decisions. This thesis proposes, implements, and evaluates a tool named BFViz to visualize bus factor and contributions for software projects from pre-processed Git history. It is a web application that provides a file-browser-like interface with an interactively navigable treemap. Additionally, it has filename-based filtering, individual contribution data for files and folders, and simulation of contributor departure. The tool is validated with a round of four user evaluations where users, ranging from project owners and engineering managers to developers, complete tasks using the tool on an open-source project that they are involved in and provide feedback with a semi-structured interview and a feature ranking activity. The overall task completion rate for the tasks was 79.55%. All case study participants preferred BFViz over text reports to understand bus factor data. The top three features, by mean ranking, were the contributors' list, the files and folders' visualization, and the simulation mode.