Doktora Tezleri

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Altmann linkage networks and light-shelf application with a single linkage
(Izmir Institute of Technology, 2022-07) Atarer, Fulya; Korkmaz, Koray
Today's understanding of architecture has revealed the need for structures that allow geometric form changes due to spatial and functional requirements. For this purpose, deployable structures have taken their place in architecture. These structures provide flexibility and multiple uses. While scissor mechanisms and bar mechanisms have been observed in architectural applications in deployable structures, over-constrained linkages have been used especially in recent studies of deployable structures. Over-constrained linkages make deployable structures more stable to loading. In this dissertation, the possibilities of systematically designing the single degree of freedom (DoF) networks using a kind of spatial overconstrained linkage called Altmann linkage as a basic module. The literature is investigated deeply that the conducted studies on network assemblies have been on different over-constrained linkages as a basic module, such as Sarrus, Bennett, and Bricard. There are few studies related to the Altmann linkage. None of these studies are in-depth studies to design a network based on the Altmann linkage. Also, an architectural application of the Altmann linkage has not been studied yet. This dissertation represents three main subjects: understanding the geometric properties of an Altmann linkage, designing one degree of freedom networks of Altmann linkage, and designing and analyzing an Altmann light shelf. Firstly, the geometry of the unit linkage is parameterized and its position kinematics is solved. Then, ten different single DoF Altmann networks are designed. By choosing one of the ten different networks designed, the network with folded and vault configurations is developed through assembly mode change. Afterward, light shelves are designed in Solidworks. Then, square and rectangular designs are compared in terms of their angles with the building and the west. Finally, daylight performance analyzes are made in the Relux software.
Conservation proposals for Göbekli Tepe enclosures
(Izmir Institute of Technology, 2022-07) Çelik, Keziban; İpekoğlu, Başak
The conservation of archaeological sites is of great importance as they provide physical remains of past civilizations. Göbekli Tepe, which is one of the most important archaeological site in human history was included in the World Heritage List in 2018. Remains in Göbekli Tepe archaeological site are enclosures surrounded by circular or rectangular wall rows, and containing monolithic T-shaped pillars in the center and peripheral walls in two layers. The aim of this study is to examine the construction technique and relations between structural elements and to define conservation problems in order to develop conservation proposals. The method of the study is the evaluation of the data collected during the field survey together with the information given in the literature. In order to determine the similarities and differences between the layers, components and alignment characteristics of enclosures were defined, the relations between these components were examined. It was found that there is relationship between the diameter of enclosure and height of central pillar, and this ratio was same in two enclosures and close in another enclosure. The state of conservation and preservation conditions of the structural elements of the enclosures were examined and risk classes were determined. The problems observed in the structural elements were determined as crack, deformation, fracture, material loss, disintegration. It had been suggested to stabilize the walls to prevent further damage, to design and develop the support system for the pillars, and to carry out regular monitoring to detect possible damage or problems for components.
Design and analysis of deployable reciprocal frames
(Izmir Institute of Technology, 2022-07) Özen, Gülçin; Korkmaz, Koray
A reciprocal frame (RF) is a type of structure used since early times. It consists of mutually supporting bars that can span large distances greater than the length of the bar. Although there are deficiencies in previous studies, there are movable RFs, but we cannot talk about the existence of a 3-dimensional deployable RF network. This study aims to contribute to the missing knowledge for movable RF fans and develop a deployable RF network. The study has conducted a comprehensive literature review to gain knowledge and identify the deficiencies of RFs. There are many studies about RFs, but it has been observed that very limited research has been done on movable RFs, and some geometric properties have not been made yet. Firstly, missing geometric knowledge has been found, which are the positions and orientations of the joints by using Denavit-Hartenberg parameters. Also, the effect of engagement length on the fan height and base edge is analyzed. A reconfigurable demountable RF fan is created with the obtained geometric knowledge. Then, mobility calculations are made, and kinematic diagrams are drawn for zero, single, and multi degrees of freedom (DoF) triangular, quadrilateral, and pentagonal fans. Their motions are investigated, and 3-dimensional (3d) simulations are generated. A two DoF quadrilateral fan with prismatic and revolute joints is produced. Then the possibilities of assembling the two DoF fans are searched to create a deployable RF network. While the network has a single DoF in the direction of vault curvature, it has multi DoF in the thickness direction. The network takes the form of a roll in its most closed state, and it takes the form of a vault in its most open state. The section of the curvature of the deployable network is the same as the Da Vinci bridge. However, while simple joints were used in the Da Vinci Bridge, revolute and prismatic joints are used in the proposed deployable RF network.
Determination of vitamin D by sensor technologies based on molecular imprinted polymers
(Izmir Institute of Technology, 2022-07) Ölçer, Yekta Arya; Demir, Mustafa; Eroğlu, Ahmet Emin; Demir, Mustafa Muammer
Vitamin D is an essential nutrient in the body; it plays important roles in human health. Both its lack and excess can have health risks. As a consequence, there is a great demand for development of simple and precise detection methods for vitamin D derivatives in different samples. Molecular imprinting polymers (MIPs) are artificial receptors that can recognize target molecules in solution. In this study, two different polymerization techniques were used to obtain MIP/NIP sorbents/films for the detection of vitamin D3. Firstly, molecular imprinted solid phase extraction (MISPE) method was proposed prior to HPLC-DAD analysis. Optimized parameters were as follows; sorbent amount of 5.0 mg for 5.0 mL of 1.0 mg/L vitamin D3 in 90:10 (v/v) ratio of H2O:MeOH solution, 5 hours sorption time and MeOH:HOAc ratio of 90:10 (v/v) as desorption solution. The accuracy of the method was verified with spike recovery test for PBS:MeOH in a ratio of 90:10 (v/v) and overall recovery was found as 85.1 (±4.3, n=3). In latter case, a quartz crystal microbalance (QCM) method was proposed for determination of vitamin D3. Electrochemical polymerization of poly(4-vinylpyridine) MIP/NIP films were achieved on gold working electrode by cyclic voltammetry (CV). Mass-transfer ability of the polymer films were analyzed by electrochemical impedance spectroscopy (EIS). The electrochemical QCM (eQCM) was used to develop thin polymer films on quartz crystals and vitamin D3 determination was achieved by QCM. In a preliminary test, as small a concentration as 0.0100 mg/L vitamin D was detected with the QCM method.
Development of different koruk (Unripe grape) products by using several processing techniques
(Izmir Institute of Technology, 2018-07) Kaya, Zehra; Ünlütürk, Sevcan
Verjuice, obtained by pressing unripe grapes, is mostly used as an alternative to lemon juice and vinegar in salads and traditional meals due to its unique sour taste and flavour. It has a short shelf life due to growth of yeasts and molds when produced at household conditions. Verjuice products in the market are not meeting desirable quality characteristics. The high quality verjuice and its derivatives required to be produced by considering several processing techniques. The objectives of this Ph.D. thesis are to (i) produce long shelf life verjuice with minimum change in its “fresh like” properties by using the combination of UV-C irradiation or Pulsed-UV light (PUV) with mild heating, (ii) produce verjuice powder with a good storage stability by using freeze drying, (iii) produce concentrated verjuice with minimal quality loss by using vacuum evaporation. Verjuice was successfully pasteurized without loosing its desirable quality by a combined UV-C and mild heating (78.0 mJ/mL, 6.2 min, 51.2°C) and PUV assisted with mild heating (6.12 J/cm2, 8.5 min, 47°C) and mild thermal (72°C, 18 s) treatments. 5-log reduction of target S. cerevisiae (NRRL Y-139) was aimed for the pasteurization of verjuice. No microorganism was developed in pasteurized verjuice during 12 and 6 weeks of refrigerated storage after UV+MH and PUV+MH treatments, respectively. Freezedried verjuice powder containing maltodextrin (FD 48h, 20% MD), was highly stable under the accelerated storage conditions (40°C, 90%RH) for 70 days. Concentrated verjuice obtained under vacuum conditions of 45°C/913 mbar, showed minimal quality change and was consumable up to 12 weeks at refrigerated storage.
Development of new chemometrics approaches to determine physical and chemical properties of crude distillation unit products based on molecular spectroscopy
(01. Izmir Institute of Technology, 2022-12) Meşe Sezen, Ayten Ekin; Özdemir, Durmuş
Crude distillation units are the first processing units of crude oils based on fractional distillation. The properties of the petroleum products obtained from refinery units are frequently analyzed to ensure that the off-spec product cannot be obtained and that the process is working under the desired conditions. This study aims to develop a method based on multivariate data analysis to determine physical and chemical properties of petroleum samples as an alternative to time-consuming and conventional analytical methods. Four different petroleum products obtained from CDU for years were selected and used in this study, which are heavy and light diesel, heavy and light straight run naphtha. Four different spectroscopic methods which are UV-Vis, Fluorescence, FT-NIR and FTIR-ATR spectroscopy, were performed and compared. Multivariate calibration models were developed using Partial least Squares (PLS) and Genetic Inverse Least Squares (GILS) algorithms. For heavy and light diesel, predictive performance of three different spectroscopic methods were compared and for heavy diesel UV-Vis spectroscopy, for light diesel FT-NIR spectroscopy was selected for most of the parameters. Developed models by fluorescence analysis of light diesel samples conducted with two different measurement modes and synchronized fluorescence spectral data has resulted in better models compared to total fluorescence spectra. Studies with straight run naphtha samples were obtained from three different refineries and prediction performances were compared. All obtained model results indicates that developed methodology can be used in routine operations instead of conventional analytical methods.
Development of single nucleotide polymorphism markes for fingerprint analysis of Turkish olive (Olea europaea L.) cultivars and detection of adulteration in Turkish olive oil
(Izmir Institute of Technology, 2015-06) Uncu, Ali Tevfik; Doğanlar, Sami
Olive (Olea europaea L.) tree and oil are signature figures of the Mediterranean culture. Because of its high economic value, olive oil is extremely vulnerable to fraud. The aim of this study was to develop molecular tests for authenticating cultivar and botanical origin in olive oils. In order to authenticate the botanical origin and detect adulteration, a plastid DNA region was utilized for standardizing a capillary-electrophoresis barcode assay. The performance of the assay was evaluated on series of olive oil : seed oil admixtures. The assay proved successful in identifying seed oils in olive oil down to a limit of 10%. The molecular assay described in this work enables adulteration detection regardless of compositional similarities between the adulterant and adulterated oil species, thus will complement the shortcomings of analytical chemistry approaches. In order to establish a DNA-based identification key to ascertain the cultivar origin of Turkish monovarietal olive oils, short fragments from five olive genes were sequenced for SNP (Single Nucleotide Polymorphism) identification. CAPS (Cleaved Amplified Polymorphic DNA) assays were designed for SNPs that alter restriction enzyme recognition motifs. When applied on the oils of 17 olive cultivars, a maximum of five CAPS assays were necessary to discriminate the varietal origin of the samples. Admixture detection threshold of the assays was identified as 20% when tested on olive oil admixtures. The SNP-based CAPS assays developed in this work can be used for testing and verification of the authenticity of Turkish monovarietal olive oils, for olive tree certification, and in germplasm characterization and preservation studies.
DNA adsorption on silica, alumina and hydroxyapatite and imaging of dna by atomic force microscopy
(Izmir Institute of Technology, 2013) Yetgin, Senem; Balköse, Devrim
The scope of the study is to investigate calf thymus DNA adsorption process on solid powders such as silica, alumina and hydroxyapatite (HAP) to improve DNA solid phase extraction efficiency and to visiulize DNA adsorption by atomic force microscopy (AFM). The equilibrium and kinetics of the DNA adsorption were investigated in batch adsorption on a commercial silica gel and a synthesized silica aerogel, commercial alumina and HAP powders from aqueous DNA solution. Commercial DNA extraction kit adsorbents were also characterized and used for adsorption. Adsorbed DNA was imaged in ambient air on flat surfaces of mica, silica and alumina wafers and HAP particles coated glass surfaces and a HAP pellet surface by AFM. Effects of ambient air, nitrogen flow and freeze drying methods on DNA morphology on the releted surfaces were also investigated. Adsorption of DNA on silica, alumina and HAP increased with the decrease of pH from 9.0 to 2.0. Enhancements of the adsorption capacities of adsorbents were obtained with the addition of MgCl2. It was found that the Van der Waals and the hydrogen bonds rather than the surface charge were the cause of the adsorption. The adsorption isotherms of DNA on silica, alumina and HAP were fitted to Langmuir model in pH range 2-9. The adsorption kinetics obeyed pseudo second order model. The sharpest image of DNA by AFM was obtained by freeze drying method on alumina surface. Dispersed DNA in water was adsorbed on the surfaces not as single molecules but as supercoils consisting of many molecules.
Electrochemical and oxygen/water permeation behavior of fluorinated siloxane copolymers synthesized via initiated chemical vapor deposition
(Izmir Institute of Technology, 2021-12) Cihanoğlu, Gizem; Ebil, Özgenç; Izmir Institute of Technology
Metal-air batteries are considered as one of the best alternatives to current Li-ion batteries with their high energy densities (1000-13000 Wh/kg) also, they are lightweight, cheap, and safe. However, secondary alkaline metal-air batteries suffer from catalyst corrosion, anode passivation and corrosion, electrolyte loss, and pore-clogging leading to performance loss and reduced cycle life. This thesis aims to evaluate the feasibility of highly cross-linked, hydrophobic, and oxygen selective thin homopolymers and copolymers films as potential candidates for Gas Diffusion Layer (GDL) materials in Gas Diffusion Electrodes (GDEs) for alkaline metal-air batteries. Homopolymers of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2-(perfluorohexyl)ethyl acrylate (PFHEA) and 2-(perfluoroalkyl)ethylmethacrylate (PFEMA) and their copolymers were synthesized via initiated chemical vapor deposition (iCVD). iCVD deposited fluoropolymer thin films exhibited low water transmission rates and excellent oxygen diffusion with a high oxygen/water selectivity up to 13.6. GDEs with iCVD GDLs exhibited higher oxygen reduction current density (228.2 mA cm-2) when compared to commercial counterparts (132.7 mA cm-2). In addition, the chemical stability, durability and corrosion protection aspects of these films were investigated by substrate adhesion and immersion tests in organic solvents and NaCl solution. The results of the corrosion test together with chemical stability and durability evaluation indicate that iCVD deposited copolymers exhibit excellent adhesion, good solvent resistance and offer effective physical and chemical protection without the need for surface pretreatment. iCVD copolymer films provide better anti-corrosion barriers with lower corrosion efficiency (85-99 %) for metal surfaces compared to homopolymer counterparts. By combining siloxane and fluorinated matrix, the copolymer films provide enhanced oxygen transport and reduce moisture entrance significantly as a GDLs and also improve physical, chemical, corrosion protection.
Experimental Investigation of a hybrid thermal management system for an electric vehicle battery module
(Izmir Institute of Technology, 2022-06) Coşkun, Turgay; Çetkin, Erdal
Environmental concerns and limited energy sources of the world are driving force in electric vehicle technology improvements. One of the main components of the electric vehicles is battery cell. Using batteries in electric vehicles brings up new concerns such as safety problems, limit of range and so on. The temperature of the battery cell increases during charging/discharging and operation. There is an optimal temperature range (15ºC ─ 35ºC) for battery cells to maximize efficiency and prevent safety issues. The high temperature values in the battery cells can be result with fire and explosion. In addition, the performance of the battery cells is highly affected by operating temperatures. Therefore, thermal management of the battery cells is a necessity to overcome safety issues and maximize the battery performance. The feasibility of microchannel heat sink for battery cooling is investigated numerically and it is decided to continue with conventional length scales because of the higher pressure drop values in micro scales. Thus, a hybrid cooling system, using air and liquid solely or simultaneously, is developed and is introduced to a battery module. The battery module created by connecting three lithium-ion pouch cells in serial. According to the results, air cooling gives the more homogeneous temperature distribution. The lowest temperature values are observed in hybrid cooling system and temperature difference between the cells are reduced by 30% when compared to the water-cooling system. The temperature profile in air cooling shows that any increase in the ambient temperature (23ºC) or discharge rate will undergo a temperature rise in battery cells and optimal temperature ranges will be exceeded in that case. A step function, in a sequence of various discharge rate, is introduced to the battery module to determine cooling capacity of the air system during operation. The result show that the temperature of the cells is kept below 30ºC. The hybrid cooling is enabled to select cooling systems for the battery module with respect to operating condition; hence, the efficiency of the system is increased.
Integration of archaeological sites with urban life in the Metropolitan city centres: The case of Agora of Smyrna/İzmir
(Izmir Institute of Technology, 2022-07) Çalışkan, Merve; Turan, Mine
This thesis aims to identify the parameters for the integration of archaeological sites in metropolitan city centres with urban life. The Agora of Smyrna was chosen as the case. The method proposed has five phases: Literature review, archival research, physical and social surveys; the Delphi study; and statistic evaluation. The Delphi study was used to define integration criteria and their weights. The correlation and regression analysis were carried out to define the content and level of integration of the citizens with the site. Sequential according of the criteria set with information coming from different sources such as literature, social surveys and Delphi study distinguishes this study from the previous work. Identification of weights of criteria via the structured communication technique made it possible to attribute significance to the outstanding aspects of integration. The indicators of each criterion were clarified and criteria were classified to define integration concepts. So, an integration framework with a hierarchical structure was developed. The integration concepts “Possesing physical access”, “Possessing social usage”, “Being a well-presented site”, “Being a well-managed site”, and the “Presence of public concern for the conservation of the site” were identified as significant for integration. New integration concepts such as “Providing benefits to its vicinity”, “Being surrounded by a qualified urban area”, and “Awareness and positive perceptions of the site’s vicinity” were identified. “Presence of public concern for the conservation of the site” is the most important integration concept whereas “Providing benefits to its vicinity” is the least important integration concept for the case of Agora. The integration level of Agora with urban life and the integration of the citizens with the site was determined as moderate.
Investigation of bioelectrochemical treatment efficiency for removal of boron from geothermal waters
(Izmir Institute of Technology, 2022-07) Gören, Ayşegül Yağmur; Ökten, Hatice Eser; Baba, Alper
Microbial desalination cell (MDC) is a promising technology due to its simultaneous features of electricity production, wastewater treatment, and desalination. In this thesis, boron (B) removal from geothermal water and organic matter removal from yeast wastewater with energy production was studied using a three chamber (anode/desalination/cathode) lab-scale MDC system. Among operational conditions, electrode surface area was proven to be significant on B removal efficiency. Then, anode chamber of the conventional MDC was modified to include three-dimensional (3D) cubic electrodes as a novel design. B and organic matter removal efficiencies and the produced power density results were promising for 3D-electrodes. Further studies in order to increase the efficiency of MDC system was conducted by synthesizing 3D hybrid sponge electrodes with activated carbon-chitosan (AC-CS). MDC with 3D AC-CS anode provided a higher power density of 970 mW/m2 , B removal efficiency of 75.9%, and COD removal efficiency of >90% under optimized conditions. Furthermore, phytoremediation performance of Lemna minor L. on B removal was found to be 96.7 %. Also, removal of B and heavy metals from reverse osmosis (RO) permeate and concentrate streams using RO-MDC hybrid process was studied. The performance of ROMDC system was proven to be significant on B and heavy metals removal efficiency. Lastly, feasibility of B removal from geothermal water using MDC-Donnan dialysis hybrid process was evaluated. The most important output of this study was decreased frequency for pH adjustment. Overall, MDC, being in its early levels of technology readiness, produced promising desalination and energy production results in removal of boron from geothermal brine.
Investigation of carotenoid contents of various microalgae by chromatographis/spectroscopic methods
(Izmir Institute of Technology, 2013) Erdoğan, Ayşegül; Eroğlu, Ahmet Emin
Microalgae are the most important energy sources among microorganisms. Carotenoids, as important pigments and antioxidants, are produced by microalgae and are used both for health purposes and as natural colorants. There has been considerable research for the development, identification and determination of new strains of organisms to produce a variety of carotenoids. New methods for the isolation of carotenoids should be developed also for analytical purposes. This study aimed the biosynthesis of carotenoids from microalgae, (Prochlorococcus sp., Scenedesmus protuberans and Nitzschia sp.) their identification and quantification. It is known that some types of microalgae can produce high amount of carotenoids under different stress conditions while some others can produce carotenoids only under stress. For this purpose, cultivation conditions were optimized for the production of new or high value of carotenoids in the selected microalgal strains. Freeze-dried microalgae were extracted using different organic solvents and their carotenoid contents were investigated by high performance liquid chromatography (HPLC) and other chromatographic techniques such as liquid chromatography-mass spectrometry (LC-MS); in addition to (UV-VIS) spectroscopy. In green microalgae lutein (2.54 mg/g for Prochlorococcus sp. and 2.45 mg/g for Scenedesmus protuberans) is the most abundant carotenoid. On the other hand, in brown microalga fucoxanthin (6.58 mg/g for Nitzschia sp.) is the highly accumulated carotenoid. Under stress conditions, many microalgae alter their biosynthetic pathways for the formation and accumulation of carotenoids. Therefore, the effect of different nitrogen sources, oxidative stress conditions and different light sources on lutein content in green microalgae and on fucoxanthin content in brown microalga were investigated.
Investigation of liquefaction potential of sand-tire granulated rubber mixture that used around the buried pipes with shake table tests
(Izmir Institute of Technology, 2022-06) Karaman, Mustafa; Ecemiş Zeren, Nurhan
Liquefaction causes major deformations in infrastructures. The rapidly increasing of scrap car tires causes to find new areas to recycle them. It has been seen that granular rubbers to be an effective filling material with their density, permeability, compressibility and also damping characteristics for liquefaction remedation. Firstly, this study aims to explain the effect of rubbers mixed with sand on the liquefaction potential of the mixture during and after earthquakes. For this reason, one-dimensional shaking table experiments were carried out with granular rubbers-sand backfills in a large scale laminar box with varying rubber diameters and varying ratios of rubber. Secondly, the study aims to explain the effect of these mixtures on pipeline performance when used as filling around buried pipelines. Lastly, this study focuses on the possibility of rubber to contaminate groundwater with inorganics. For this purpose, a series of batch tests and column leaching tests were performed. Consequently, mixing rubbers with sand is effective in liquefaction remedation. They reduce the pore water pressure thanks to the high permeability, affect the consolidation characteristics with its permeability and compressibility, also reduce the earthquake loads with their damping facilities. In order to prevent the buried pipelines from uplifting during an earthquake, a limit criteria is suggested to design of the pipe diameter, burial depth and filling conditions with a predicted seismic load. Rubbers aren’t hazardous for contaminating the inorganics into groundwater. If granular rubbers are used in environmentally sensitive areas, it is recommended to use them after a prewash process or soaking in water for a day.
Photonic crystal textiles
(Izmir Institute of Technology, 2022-07) Çetin, Zebih; Sözüer, Hüseyin Sami
Photonic crystals are man-made structures that can be used to manipulate the flow of light. They are classified as one-, two- and three-dimensional photonic crystals according to the periodic variation of the dielectric profile in space. Apart from artificial photonic crystals there are numerous examples of naturally occurring photonic crystals which have evolved mostly for structural coloration, such as wings of butterflies, natural opal gem stone, peacock feathers to name a few. Using photonic crystal structures the propagation of electromagnetic waves can entirely be prohibited by means of photonic band gap. Considering the fact that approximately two thirds of the heat loss of the human body occurs through electromagnetic radiation with a wavelength around 10 microns, it becomes important to consider photonic crystals for the purpose of reducing heat loss in textiles. We observe that the textile, by virtue of the fact that it has been produced by weaving, already has a periodic structure, and thus is a potential candidate for a photonic crystal. With the right fiber that the textile is woven and the right weave pattern, the textile itself would be a photonic crystal. The most common weave patterns used in the textile industry are plain weave, basket weave, dutch weave and twill weave. In this thesis, we used the finite-difference time-domain method to search for the optimum weave pattern to minimize heat loss by the human body.
Preparation of nanostructured interface by polymer grafting on various solid substrates for biosensor applications
(Izmir Institute of Technology, 2021-12) Özenler, Sezer; Yıldız, Ümit Hakan; Izmir Institute of Technology
This thesis presents the utilization, various applications, and characterization of the soft material-based coating formed on the gold surface with varying thickness and chemical properties resulting from the isocyanate-gold interaction. Theoretical calculations regarding the interaction of isocyanate with the gold surface revealed the character of the bond formed and the orientation of the functional groups on the surface. Results by X-ray photoelectron spectroscopy showed the tendency to shift to the high energy at N 1s and C 1s binding energies in the gold-interacting isocyanate group. In the next steps, the isocyanate-activated gold substrate was subjected to sequential incubation of 1,4-butanediol/hexamethylene diisocyanate, and thin-film formation was achieved by surface assisted (SurfAst) urethane polymerization. It was revealed with three different applications that a nano-porous polyurethane (PU) structure was formed on the gold substrate and could be postmodified by using SurfAst polymerization method. In the first application, modification with polyethylene glycol (PEG) was provided to obtain antifouling properties. The PEG-terminated PU structure on the gold surface was shown to reduce protein adhesion by approximately ten-fold. In the second application, SurfAst was applied on the 11-mercaptodecanoic acid incubated surface and grafting onto the poly (N-allyl-N-methyl-N-(3-((4-methylthiophen-3-yl)oxy)propyl) prop-2-en-1-aminium surface was characterized. As a result of PT grafting, PT nanowires with an average height of 100 nm, a width of 250 nm, and a length of 7 μm were obtained on the gold surface. In the last application, a soft nanogel was obtained by a reactive layer-layer (rLBL) coating method using the aza-Michael addition reaction of branched polyethyleneimine and polyester on the isocyanate functional surface. The mechanical and electrical permeability and coating properties of the nanogel layer were assessed. In conclusion, the high potential of isocyanate in surface activation has been demonstrated theoretically and experimentally. Effective modification of gold surfaces by polymer grafting with the SurfAst method and rLBL coating techniques has been achieved.
Production and characterization of porous ceramics for high temperature applications
(Izmir Institute of Technology, 2022-07) Semerci, Tuğçe; Ahmetoğlu, Çekdar Vakıf; Akdoğan, Yaşar
This thesis focuses on the production and characterization of different porous polymer derived ceramic (PDC) components (foams, additively manufactured (AM) honeycombs, and aerogels) and demonstrates their potential for high temperature applications, including gas permeability (up to ~700 o C), molten metal filtration, and heat exchanger. The foams were produced via the replica technique and different pore sizes, ranging from 300 μm to 2 mm, silicon oxycarbide (SiOC) ceramic foams were able to be formed. The average total porosity of the foams was 96 vol% with a specific surface area (SSA) of ~80 m2 /g. AM-made honeycomb-like cellular structures with different cell sizes (578 μm, 1040 μm) were obtained via fused filament fabrication. Finally, SiOC aerogels were synthesized using siloxane resin, then dried at ambient pressure and room temperature. The produced SiOC aerogels showed a total porosity of around 80 vol% and an SSA reaching 250 m2 /g. Regarding the high temperature applications of porous PDC components, initially, the gas permeability of SiOC foams was tested, and the results showed stability up to 700 °C in the air without any loss of functionality, offering reusability even in aggressive environments. In the subsequent studies, filtration of molten aluminum alloy was tested using various porous components. PDC foams demonstrated better performance in comparison to the AM-made cellular structures and commercial SiC foams. Finally, heat exchange analysis was performed to evaluate the heat transfer of SiOC foams, and an increase in pressure drop was found to be directly proportional to the rate of increase in air velocity.
Quantum calculus of classical Heat-Burgers' hierarchy and quantum coherent states
(Izmir Institute of Technology, 2017-07) Nalcı Tümer, Şengül; Pashaev, Oktay
The purpose of this thesis is an application of quantum calculus to classical Heat- Burgers’ hierarchy and quantum coherent states. First we construct random walk on q-lattice, corresponding q-heat equation and exact solutions in terms of new family of q-exponential functions. Then we introduce a new type of q-diffusive heat equation and q-viscous Burgers’ equation, their polynomial solutions as generalized Kampe-de Feriet polynomials, corresponding dynamical symmetry and description in terms of Bell polynomials. Shock soliton solutions with fusion and fission of shocks are found and studied for different values of q. The q-semiclassical expansion of these equations in terms of Bernoulli polynomials is derived as corrections in power of ln q. A new class of complex valued function of complex argument as q-analytic functions in terms of q-analytic binomials is introduced and shown that these binomials are generalized analytic functions. As an application, we construct a new type of quantum states as q-analytic coherent states and corresponding q-analytic Fock- Bargmann representation. Then, we extend the concept of q-analytic function for two complex arguments, called double q-analytic functions, which has q-Hermite binomial expansion. As hyperbolic extension, we describe the q-analogue of traveling waves and find the D’Alembert solution of q-wave equation. By introducing q-translation operators we obtain q-binomials, q-analytic and q-anti analytic functions, q-travelling waves and non-commutative binomials. New type of quantum states as Hermite coherent states and Kampe-de Feriet coherent states are studied by generalization of the known Mehler formula. We introduce Golden quantum calculus, and as an application we study Golden quantum oscillator and its angular momentum representations.
Structural engineering of halide perovskites and their association with organics for optoelectronic applications
(Izmir Institute of Technology, 2022-06) Yüce Çakır, Hürriyet; Demir, Mustafa; Demir, Mustafa Muammer; Yüksel Aldoğan, Kıvılcım
Halide perovskites show great potential for next-generation optoelectronic applications due to their unique photophysical properties with low production costs. However, their stability issues still prevent their commercialization on a large scale. The main objective of this dissertation is to understand the additive engineering strategy to improve the quality of halide perovskite films and nanocrystals for solar cells and lightemitting diodes. There are two sections to this dissertation: The first section focuses on halide perovskite films and solar cells while the second one focuses on halide perovskite nanocrystals and white light-emitting diodes. In the first section of this dissertation, in Chapter 2-3, the improvement of Sn-Pb and methylammonium-free Pb-based halide perovskite films by additives are investigated. The suppression of defects via additives is demonstrated through structural, elemental, and optical analyses. The improved performance of perovskite solar cells by decreasing defects is also shown. In Chapter 4-5, the change in stability and optical properties of the halide perovskite nanocrystals by means of additive engineering and their applications in white light-emitting diode are studied. The results in this dissertation represent a new approach to improving the structural and photophysical properties of halide perovskites and introduce a new perspective of additive engineering method in the field of halide perovskite-based optoelectronic applications.
Synthesis and control of exciton dynamics in CdTe, CdTe/CdS and ZnxCd1-xTe colloidal nanocrystals
(İzmir Institute of Technology, 2012) Eral Doğan, Leyla; Özçelik, Serdar
The aim of this study is to synthesize cadmium-based semiconductor colloidal nanocrystals and to control their exciton dynamics by tuning the size and composition of the nanocrystals (NCs). CdTe, CdTe/CdS binary, and ZnxCd1-xTe ternary semiconductor NCs are prepared by wet chemistry. The reactions are thoroughly optimized to enhance the optical properties. The optical properties of CdTe and CdTe/CdS are tuned by the size of the NCs by adjusting the reaction (the growth) time. Coating CdTe NCs with CdS layer enhances the photoluminescence quantum yields up to 45%. ZnxCd1-xTe ternary nanoalloys were synthesized by varying the initial mole ratios of metals (Zn/Zn+Cd) and the growth time. The size and the composition-tunable ZnxCd1-xTe nanoalloys exhibit highly luminescent optical properties. When the amount of initial Zn precursor is low, the nanoalloys have Cd-rich and Zn-poor internal crystal structure. However, at higher amount of Zn precursor, the nanoalloys have Zn-rich and Cd-poor core exhibiting gradient composition. The exciton interactions and dynamics are investigated as a function of the size of CdTe/CdS, and the composition and the size of ZnxCd1-xTe nanoalloys. The exciton interaction yields amplification in the output signal at the threshold of 1015 photon/cm2s per laser pulse. The exciton lifetimes are in the range of picoseconds to nanoseconds. The decay associated spectra are affected by the laser power, size and composition of the NCs. As the laser power increases new excitonic states are created especially in ZnxCd1-xTe nanoalloys. Multiexcitons were created in the NCs depending on the laser power. Small NCs exhibit stronger exciton-exciton interactions under high laser power compared to larger NCs. However larger NCs have lesser exciton density, therefore reducing the exciton-exciton interactions.

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