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Modeling and Characterization of Rate Phenomena in Complex Electrochemical Systems: Sodium-Metal Chloride Batteries and Ni/SiC Co-Deposition
No full textIn the first part of the dissertation (Chapters 3-5), the effect of a cationic dispersant, polyethyleneimine (PEI) on the co-deposition of micro and nano SiC particles with nickel is characterized and modeled. A major challenge in Ni/SiC co-deposition for wear-resistant coatings is that the dispersants that are used to stabilize the particles in the electrolyte to ensure high and uniform particle incorporation into the deposit can significantly affect the electrodeposition kinetics. To overcome this challenge, studies of particle dispersion and electrodeposition are integrated. The effect of PEI on the electrodeposition of Ni/SiC composites is characterized as a function of SiC and PEI bath concentration, current density, rotation speed, molecular weight of PEI and particle size. A pre-coating procedure, in which SiC particles are pre-coated with PEI in a different electrolyte prior to plating, is described. With the pre-coating procedure, high particle stability in the plating bath is obtained. In addition, a significant increase on the SiC incorporation rate is seen without any substantial decrease on the current efficiency for both micro- and nano-composites. Furthermore, using pre-coated particles in the presence of a leveling agent is found to be advantageous relative to the direct addition of PEI into the electrolyte. The efficacy of employing the pre-coating procedure in manufacturing, where plating baths need a long life, is also found to be satisfactory. The use of pre-coated SiC particles changes the morphology, decreases the surface roughness and increases the hardness of the deposits for both particle sizes. Finally, a mathematical model of the co-deposition is proposed. The rate of incorporation is proportional to the residence time, inversely proportional to the burial time, and is proportional to the number density of particles on the surface. These times are influenced by the hydrodynamics, particle size, current density, and concentration of dispersants. SiC incorporation increases with the introduction of PEI due to an increase in the residence time of the particles on the surface. In the second part of the dissertation, a sodium-metal chloride battery, which is another important complex electrochemical system, is studied. A one-dimensional mathematical model of the porous cathode of a sodium-iron chloride battery for an isothermal, constant-current discharge-charge cycle is presented. In sodium-iron chloride batteries, it is desirable to maintain low FeCl2 solubility to minimize redistribution of active material in the cell. However, the iron chloride is sparingly soluble, and with increased cycling, it does redistribute. None of the previous models can predict this movement of the metal that takes place in the cell with increased cycling that can cause the failure of the cell. An advance offered by the model presented is that it accounts for the change in the solubility of FeCl2 within the cell and predicts the relocation of the iron by including the flux of a sparingly soluble ferrous complex. For instance, the model predicts that at the end of the fifth cycle, the iron amount decreases by ~1% near the sodium tetrachloroaluminate reservoir
Electrodeposition of Ni/TiC Nanocomposites in the Presence of a Cationic Dispersant
No full textThe effect of a cationic dispersant, polyethyleneimine (PEI) on electrodeposition of nickel/titanium carbide (Ni/TiC) nanocomposites is characterized. Enhancing the dispersion of TiC nanoparticles in the electrolyte and increasing TiC amount and uniformity in the deposit are crucial to get superior mechanical and tribological nanocomposite properties. Therefore, a key challenge in reaching enhanced composites is the optimization of the dispersant concentration that improves the nanoparticle dispersion in the electrolyte and achieves high and uniform TiC incorporation into the deposit without suppressing electrodeposition. It is determined that PEI at a concentration of 125 ppm increases the stability of TiC nanoparticles in the electrolyte and TiC vol% in the deposit significantly without any substantial inhibition on the electrodeposition kinetics. Ni/TiC electrodeposition is also characterized as a function of key parameters such as TiC electrolyte concentration, current density, and rotation speed in the presence of PEI. Higher and more uniform TiC nanoparticle incorporation is attained for the electrolyte containing PEI than the electrolyte with no dispersant for all cases. Uniform nanocomposites with improved hardness is obtained as a result of Ni/TiC electrodeposition in the presence of the cationic dispersant. (C) 2018 The Electrochemical Society
Modeling the discharge behavior of a lithium-sulfur battery
No full textIn lithium-sulfur (Li-S) batteries, the discharge performance depends greatly on a number of cell design parameters because of the complex reaction mechanisms in the cathode. Electrolyte-to-sulfur (E/S) ratio and carbon-to-sulfur (C/S) ratio in the cell are key examples of these critical design factors that define the Li-S battery performance. Here, a 1-D electrochemical model is reported to calculate the dependence of the discharge behavior of a Li-S battery on the E/S and C/S ratios. Proposed model describes the complex kinetics through two electrochemical and two dissolution/precipitation reactions. Concentration variations in the cathode are also taken into account in the model. Characteristic aspects of the discharge profile of a Li-S battery -the two distinct voltage plateaus and the voltage dip in between- are captured in the predicted voltage curve. Similar trends on the discharge performance of the Li-S cell with varying E/S and C/S ratios are projected; both voltage and discharge capacity of the Li-S battery are improved substantially with increasing C/S or E/S ratio up to a certain point, whereas, the dependence of the discharge performance on these factors is less substantial at higher ratios. This model offers a mechanistic interpretation of the influence of cell design on the Li-S battery performance
Effect of Electrolyte-to-Sulfur Ratio in the Cell on the Li-S Battery Performance
No full textThe effect of electrolyte-to-sulfur (E/S) ratio on the electrochemical and cell- and systems-level performance of a Li-S battery is investigated through modeling efforts. A 1-D electrochemical model is proposed predicting the cell voltage at 60% discharge depth. In the model, increasing electrolyte amount improves the cell voltage by linearly increasing the cathode exchange current density, which is the single kinetic model parameter. Moreover, cathode specific capacity is either defined as a linear function of the E/S ratio or taken constant in the performance models. Increasing E/S ratio enhances the cell- and systems-level specific energy and energy density until 9 mL/g S when cathode specific capacity depends on the E/S ratio. However, when the cathode specific capacity is constant at 1200 mAh/g S, battery performance decreases continuously with increasing electrolyte amount. The effect of other critical design parameters-cathode thickness, carbon-to-sulfur ratio, S loading and excess Li%- are also considered in the analysis. (C) 2019 The Electrochemical Society
Modeling of reaction kinetics and transport in the positive porous electrode in a sodium–iron chloride battery
No full textText-mining and bibliometric analyses for proton exchange membrane electrolyzers
No full textThe dependence on technology has increased, along with the development and change in living standards, which has led to increased energy demand and emissions. Therefore, researchers have focused on green hydrogen production to meet the energy demand and reduce emissions. The proton exchange membrane (PEM) electrolysis is one of the most promising methods for producing green hydrogen, attracting increasing attention from researchers in academia and industry. This study focuses on the bibliometric and text-mining analyses of PEM electrolyzers to identify general trends and the current state of the literature, thereby guiding researchers in future work. In this regard, a dataset was first generated using keywords and abstracts extracted from the Scopus webpage. Then, bibliometric and text-mining analyses were conducted on the dataset using R Studio and Python modeling. Our results demonstrate that research on PEM electrolyzers has increased significantly over the past few years, along with an expansion in the diversity of research topics within the field. Most studies in the literature have focused on material design and the integration of PEM electrolyzers with alternative energy systems. Furthermore, techno-economic analysis, life cycle assessment, multi-objective optimization, and machine learning are identified as emerging research areas. Overall, this work provides a comprehensive overview of the current state of PEM electrolyzer research and identifies future directions emphasizing advanced materials development, renewable energy integration, and sustainable energy management strategies
Being a life and social studies textbook author in the process of changing educational programs : trialing to understand an educator
No full textÇocuğa görelik, çocuğa özgülük düşüncelerinin ortaya çıkışı yapılandırmacı yaklaşımı temele almaktadır. Bu anlayış onları didaktik öğretiden uzak onun sesi, onun seçimi ve onun eylemi doğrultusunda okula başladığı andan itibaren gerçek yaşamın bir parçası haline getirmeyi hedefleyen yaklaşımdır. Ancak felsefe olarak çocuğa son derece uygun görünen bu programların ders kitaplarına yansımasının aynı olamadığı durumların olduğu görülmüştür. Bir diğer yandan ise yapılandırmacı anlayış öncesindeki davranışçı anlayış temelindeki programlarda da ders kitapları yazılmıştır. Yazılan ders kitaplarını yazan yazarların olduğu ve temelde bu yazarların döneme hâkim olan eğitim anlayışını derinlemesine benimseyerek eyleme geçmesi gerektiği düşünülmektedir. Bu görüşten hareketle yapılan çalışmanın amacı 1998, 2005 ve 2018 Hayat Bilgisi Dersi Öğretim Programlarına göre yazılmış ders kitaplarının içeriğinde yer alan bilginin sunum yöntemini saptamak, görsel öğelerin işlevlerini belirlemek, etkinliklerde ve tema sonlarında bulunan ölçme değerlendirme çalışmalarında kullanılan soru biçimlerini saptamak; araştırma konusu yazarın öğretim programlarına ve ders kitaplarına ilişkin görüşlerini almaktır. Bu genel amaç doğrultusunda aşağıda yer alan sorulara yanıt aranmıştır: 1998, 2005 ve 2018 Yılı Hayat Bilgisi Öğretim Programları’na göre hazırlanmış ders kitapları; •bilginin sunumu, •görsel öğeler ve işlevleri, •ölçme ve değerlendirme uygulamaları açısından nasıldır? •Araştırma konusu yazarın 1998, 2005 ve 2018 yılı Hayat Bilgisi Öğretim Programlarına ve ders kitaplarına ilişkin görüşleri nasıldır? Araştırma konusu yazarın 1998, 2005 ve 2018 Yılı Hayat Bilgisi Öğretim Programlarına göre hazırlanmış ders kitapları; •bilginin sunumu, •görsel öğeler ve işlevleri, •etkinlikler, ölçme ve değerlendirme uygulamaları açısından nasıldır? Araştırmada; 1998, 2005 ve 2018 Hayat Bilgisi Programlarına göre yazılmış ders kitaplarında yer alan metinleri, görsel öğeleri ve ölçme değerlendirme çalışmalarını karşılaştırmaya yönelik doküman incelemesi yapılmıştır. Bu araştırmada 18 ayrı ders kitabı incelenmiştir. Diğer yandan araştırma konusu yazarın Hayat Bilgisi Programlarına ve ders kitaplarına ilişkin görüşlerini belirlemek amacıyla görüşmeler gerçekleştirilmiştir. Doküman incelemesinden ve görüşmelerden elde edilen sonuçlara göre; •1998 Hayat Bilgisi ders kitaplarında genel olarak örnek olaya yer verilmediği, 2005 Hayat Bilgisi ders kitaplarında konuların genellikle örnek olayla işlendiği, 2018 Hayat Bilgisi ders kitaplarında örnek olay sayısının görece azaldığı, •Didaktik ifadelere 1998 Hayat Bilgisi ders kitaplarında sıkça yer verilirken bu sayısının 2005 Hayat Bilgisi ders kitaplarında oldukça azaltıldığı, 2018 Hayat Bilgisi ders kitaplarında görece arttığı, •1998 ve 2018 Hayat Bilgisi Programları’na göre 2005 Hayat Bilgisi Programında görsel öğe çeşitliliğinin arttığı ancak fotoğraf sayısının azaldığı, •2005 Hayat Bilgisi ders kitaplarında etkinliklere ilişkin açık uçlu soru sayısının 1998 Hayat Bilgisi ders kitaplarına göre artış gösterdiği, ancak 2018 Hayat Bilgisi ders kitaplarında etkinliklere ilişkin açık uçlu soru sayısında 2005’e göre belirgin bir azalma olduğu, •2005 Hayat Bilgisi ders kitaplarında tema sonu değerlendirme çalışmasında ölçme türü çeşitliliği sağlanırken 1998 ve 2018 Hayat Bilgisi ders kitaplarında görece çoktan seçmeli soru türü tercih edildiği, •Tüm bu değişimlerin araştırma konusu yazar tarafından 1998, 2005 ve 2018 Hayat Bilgisi öğretim programına göre yazılan ders kitaplarında da belirlendiği, •Araştırma konusu yazarın 1998 Hayat Bilgisi Öğretim davranışçı, 2005 Hayat Bilgisi Öğretim yapılandırmacı, 2018 Hayat Bilgisi Öğretim karma olarak adlandırdığı tespit edilmiştir.The emergence of ideas of child-specificity and child-specificity is based on the constructivist approach. This understanding is an approach that aims to make them a part of real life from the moment they start school in line with his voice, his choice and his action, away from didactic teaching. However, it has been observed that there are cases where the reflection of these programs, which seem very suitable for the child as philosophy, to the textbooks is not the same. On the other hand, textbooks were written in the programs based on the behaviorist understanding before the constructivist approach. It is thought that there are authors who wrote the textbooks and that these authors should take action by deeply adopting the education understanding that dominated the period. Based on this view, the aim of the study is to determine the presentation method of the information in the content of the textbooks written according to the 1998, 2005 and 2018 Life Studies Curriculum, to determine the functions of the visual elements, to determine the question forms used in the assessment and evaluation studies in the activities and at the end of the themes; The subject of the research is to get the author's views on curricula and textbooks. In line with this general purpose, answers to the following questions were sought: Textbooks prepared according to 1998, 2005 and 2018 Life Studies Curriculums; • presentation of information, • visual elements and functions, • how is it in terms of measurement and evaluation practices? • What are the views of the author, which is the subject of the research, on the Life Studies Curriculum and textbooks in 1998, 2005 and 2018? Textbooks prepared according to the 1998, 2005 and 2018 Life Studies Curriculum of the author, which is the subject of the research; • presentation of information, • visual elements and functions, • how are the activities in terms of measurement and evaluation practices? In the research; A document review was conducted to compare the texts, visual elements and assessment and evaluation studies in the textbooks written according to the 1998, 2005 and 2018 Life Studies Programs. In this study, 18 different textbooks were examined. On the other hand, interviews were conducted to determine the author's views on Life Studies Programs and textbooks. According to the results obtained from the document review and interviews; •Case studies were not generally included in 1998 Life Studies textbooks, subjects were generally covered with case studies in 2005 Life Studies textbooks, and the number of case studies in 2018 Life Studies textbooks was relatively reduced, •While didactic expressions are frequently used in 1998 Life Studies textbooks, this number was considerably reduced in 2005 Life Studies textbooks and relatively increased in 2018 Life Studies textbooks, •Compared to the 1998 and 2018 Life Studies Programs, the variety of visual elements increased in the 2005 Life Studies Program, but the number of photographs decreased, •The number of open-ended questions about activities in 2005 Life Studies textbooks increased compared to 1998 Life Studies textbooks, but there was a significant decrease in the number of open-ended questions about activities in 2018 Life Studies textbooks compared to 2005, •While the variety of measurement types was provided in the end-of-theme evaluation study in 2005 Life Studies textbooks, relatively multiple-choice question types were preferred in 1998 and 2018 Life Studies textbooks, •All these changes are also determined by the author, which is the subject of the research, in the textbooks written according to the 1998, 2005 and 2018 Life Studies curriculum, •It has been determined that the author of the research named the 1998 Life Studies Curriculum as behaviorist, the 2005 Life Studies Curriculum as constructivist, and the 2018 Life Studies Curriculum as mixed
Effects of City Layout in Gang Territorial Formations
No full textGang-related violence poses a significant challenge in numerous countries across the world. While previous research have explored modeling formation of gang territories, none of them incorporated a city layout such as roads, water bodies and parks while doing so. Hence, this research explores the effects of city layout in the formation of gang territories. First the effects of a single vertical boundary of varying permeability is observed. Following this, the model is applied to real world where a part of Chicago's city layout is incorporated to the model. The results are then compared to gang territory maps shared by Chicago Police Department. The experiments show that city layout significantly affects the shape and size of the territories. By fine tuning the permeability for different terrain features, we can observe that the territories produced by the model show resemblance to their real world counterparts.CSE3000 Research ProjectComputer Science and Engineerin
Design and Fabrication of a Soft Photonic Crystal Brain Implant
No full textA research gap exists in a targeted drug delivery into the brain with an implant placed on the outer surface of the cerebral cortex. If an implant with spatial control that can release drugs to a target location can be developed, it will provide efficient treatment opportunities for a variety of brain disorders such as strokes. One of the questions in realizing this implant is how to activate the drug release mechanism. Light is a promising activation stimulus due to its spatial precision and flexibility in the optical path. This thesis is a feasibility study into carrying light inside such a brain implant using a photonic crystal waveguide. Such a device must be soft and maintain its functionality during the mechanical bending imposed on the implant by the geometry and movement of the brain. A flexible 2D photonic crystal is simulated using COMSOL Multiphysics with the goal of designing a waveguide that functions with infrared light. The dispersion diagram of the photonic crystal is plotted to design for a bandgap at the operating wavelength. The transmission through a linear waveguide is calculated for the deformed state of the implant in mechanical bending, which is modeled as a 2D strain. A metallo-photonic crystal with photoresist nanopillars coated with a gold thin film and embedded in a flexible PDMS matrix is selected as the prototype for fabrication. The nanopillar arrays that form the photonic crystal waveguide are printed using two-photon polymerization (2PP), deposited with gold then transferred into photosensitive PDMS by drop casting. For characterization, a tapered rib waveguide is designed for light coupling and an optical end-fire test setup is built for transmission measurements on the fabricated device.Mechanical Engineering | Micro and Nano Engineerin
Materials as temporally specific phenomena: Specialization and compromise in bioplastics production
No full textThis article concerns itself with the materials' - matter, substance - of material culture. More specifically, it explores the making of bioplastics, by taking account of bioplastics' relationships with the products into which they are made. The author focuses on the processes of bioplastics' industrial production and manufacturing into bioplastic products, in and through which bioplastics come to be as they are in our daily lives, and as places where material-product relationships are formed. Her analysis of these processes shows that making of bioplastics is a specialization towards products by achieving compromises among the capacity of materials, conventions about the particular product and its production route, and various interests of the stakeholders involved. As such, she conceptualizes materials as temporally specific phenomena and aims to show that attending to material-product relationships points out new sets of relationships in the make-up of materiality and opens up new pathways of enquiry for material culture studies
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