The thesis investigates the temperature distribution in the chip of an infrared camera caused by its read out integrated circuit. The heat from the read out circuits can cause distortions to the thermal image. Knowing the temperature gradient caused by internal heating, it will later be possible to correct the image by implementing algorithms subtracting temperature contribution from the read out integrated circuit. The simulated temperature distribution shows a temperature gradient along the edges of the matrix of active bolometers. There are also three hot spots at both the left and right edge of the matrix, caused by heat from the chip temperaturesensors and I/O pads. Heat from the chip temperature sensors also causes an uneven temperature profile in the column of reference pixels, possibly causing imperfections in the image at the levels of the sensors. Simulations of bolometer row biasing are carried out to get information about how biasing affects temperatures in neighbouring rows. The simulations show some row-to-row interference, but the thermal model suffers from having biasing heat inserted directly onto the top surface of the chip, as opposed to having heat originate from the bolometers. To get better simulation results describing the row biasing, a thermal model of the bolometers needs to be included. The results indicate a very small temperature increase in the active pixel array, with temperatures not exceeding ten millikelvin. Through comparisons with another similar simulation of the chip, there is reason to believe the simulated temperature increase is a bit low. The other simulation cannot be used to draw any conclusions about the distribution of temperature. / Examensarbetet undersöker den temperaturdistribution som uppkommer i ett chip till en IR-kamera till följd av värmeutvecklingen i dess egna utläsningskretsar. Genom att ha information om temperaturdistributionen är det möjligt att längre fram i utvecklingsprocessen skapa algoritmer som subtraherar bort chippets interna värmetillskott från den termiska bilden. Den simulerade temperaturdistributionen visar att de största temperaturgradienterna uppkommer längs den aktiva pixelmatrisens sidor. Det är även möjligt att se tre varmare områden vid både den vänstra och högra sidan av matrisen skapade av värme från chippets temperatursensorer och I/O-kretsar. Värme från temperatursensorerna påverkar även temperaturen i kolumnen med referenspixlar, vilket kan ge upphov till avvikelser i den termiska bilden i höjd med dessa temperatursensorer. Simuleringar av radvis basering av bolometrar utförs för att få information om hur bolometerbiaseringen påverkar temperaturen i angränsade rader. Simuleringarna visar att det finns störningar mellan rader, men simuleringsmodellen lider av avsaknaden av en termisk bolometermodell och tvingas applicera värme direkt på chipytan istället för att låta värme utvecklas i bolometrarna. För bättre simuleringsresultat innefattande bolometerbiasering bör en termisk bolometermodell inkluderas i simuleringen. Resultaten visar på en mycket liten temperaturökning inom den värmekänsliga aktiva pixelmatrisen, med temperaturökningar inom detta område som inte överstiger tio millikelvin. Genom jämförelser med en liknande simulering av samma chip är det inte omöjligt att dra slutsatsen att temperaturökningen är något låg. Det går inte att dra några slutsatser om temperaturens distribution genom denna jämförelse av simuleringar.

Complex surface structures in nature often have remarkable optical properties. By understanding the origin of these properties, such structures may be utilized in metamaterials, giving possibilities to create materials with new specific optical properties. To simplify the optical analysis of these naturally developed surface structures there is a need to assist data analysis and analytical calculations with numerical calculations. In this work an application tool for numerical calculations of optical properties of surface structures, such as reflectances and ellipsometric angles, has been developed based on finite element methods (FEM). The data obtained from the application tool has been verified by comparison to analytical expressions in a thorough way, starting with reflection from the simplest of interfaces stepwise increasing the complexity of the surfaces. The application tool were developed within the electromagnetic module of Comsol Multiphysics and used the script language to perform post-process calculations on the obtained electromagnetic fields. The data obtained from this application tool are given in such way that easily allows for comparison with data received from spectroscopic ellipsometry measurements.

With the progress of technology, large capacity and scalable are required for the future. Recent years, the physical limit is approached and a next-generation memory is needed in the future. In addition, non- volatile memory occupies more than 96% in the memory market, and RRAM has great advantages such as simple structure, high scalable, low operation voltage, high operation speed, high endurance and retention. That is the reason RRAM is the candidate in the next generation. In this experiment, multi-sputtering was used to deposit Zr:SiO 2 and Pt on TiN bottom electrode. The sandwich structure was metal/insulator/metal (MIM). With the different dielectric constant material, a different electrical field will be produced. And then I-V measurement and materials analysis were used to investigate the characteristic of the RRAM. At first, a forming process is required to the RRAM. The device was swept from negative to positive voltage and obtained the conduction mechanism from curve fitting. The different dielectric constant materials were used to fabricate the RRAM. High and low dielectric materials were HfO 2 and BN, respectively. The electric field distribution is centralized in low dielectric material so the electrons will drift to the direction of electric field. Hence, the Vset will be centralized and more stable. We also fabricated a Zr:SiO 2 /C:SiO 2 RRAM as an high K and low K material. The current fitting results that a hopping conduction occurs in low resistive state (LRS) and high resistive state (HRS). Both from Raman spectrum and FT-IR spectrum, a graphene oxide was existed in the C:SiO 2 thin film. While the filament was form, the tip of the filament will approach the graphene oxide because of the point effect. Hence, the resistance switching will happen in the grapheme oxide and set voltage will be more stable and lower the operated current. Next, an ICP treatment was used in order to "burn" the carbon in SiO 2 . The purpose is to make an extremely low K material and ignore the effect of the existence of carbon. From the FT-IR spectrum, the carbon signals were disappeared after the ICP oxygen plasma treatment. In the I-V fitting diagram, space char limit results in the high voltage region. The electrical field simulation was an auxiliary tool which shows a strong electrical field occurs in the extremely low K area. While the electrons flow through the conduction path, they will be confined in the porous area. The operation current will decrease because of the limited conduction area.

A batch vacuum frying system, which processes fruits and vegetables, includes a frying pan, a surface-condenser, and a vacuum pump. With health and safety issues in mind, this research focused on developing a modified surface-condenser to prevent cavitation of the vacuum pump. The final oil-content was reduced by centrifugal de- oiling of the product under vacuum, which make the product healthier than what is currently available. The de-oiling mechanism consists of a centrifuge with a motor attached to the basket shaft, rotating up to 750 rpm (63 g units). The condenser consists of a (counter- flow) spiral-coil heat exchanger (SHE) connected to a refrigeration system that uses R404a refrigerant. De-oiling for 40 s at 300 and 750 RPM removed up to 67% and 72% of the chip’s surface oil, respectively. At 750 RPM for 10 s, 40 s, and 60 s the oil-content was reduced by 38%, 44%, and 51%, respectively. The convective heat transfer coefficient (h) of the frying oil was determined at 120°C and 140°C using the lumped capacitance method. The h-values were 217±13 W/m2K (120°C) and 258±37 W/m2K (140°C) using a copper-ball thermocouple. The h- values increased to 3.6 times during the boiling period. COMSOLTM Multiphysics was used to model the heat transfer in the vacuum fryer pan. Based on the simulation results, a 1.5 cm thick insulation material was installed in the fryer to reduce the energy losses. The refrigeration system operates at Tevap = -26°C and Tcond = 50°C with 26°C sub-cooling. Sensitivity analysis showed that the system Coefficient of Performance (COP) was about 3.87 at these conditions and compressor power requirement (CPR) was 74 W (85% efficiency) when frying 30 g of potatoes slices. The best results were obtained at Tevap = -10°C and Tcond = 40°C with 26°C sub-cooling and superheat of 5°C. The predicted COP was 4 and the CPR 70 W. The ice-formation on coils reduced the condensation rate. Reducing the refrigerant temperature to -10°C (from -26°C) reduced the condensation rate by 30%. These results show a more effective vacuum frying system for high-quality fruits and vegetables than the system previously used.

Optimal control of PDEs has a crucial place in many parts of sciences and industry. Over the last decade, there have been a great deal in, especially, control problems of elliptic problems. Optimal control problems of Burgers equation that is as a simplifed model for turbulence and in shock waves were recently investigated both theoretically and numerically. In this thesis, we analyze the space-time simultaneous discretization of control problem for Burgers equation. In literature, there have been two approaches for discretization of optimization problems: optimize-then-discretize and discretize-then-optimize. In the first part, we follow optimize-then-discretize appoproach. It is shown that both distributed and boundary time dependent control problem can be transformed into an elliptic pde. Numerical results obtained with adaptive and non-adaptive elliptic solvers of COMSOL Multiphysics are presented for both the unconstrained and the control constrained cases. As for second part, we consider discretize-then-optimize approach. Discrete adjoint concept is covered. Optimality conditions, KKT-system, lead to a saadle point problem. We investigate the numerical treatment for the obtained saddle point system. Both direct solvers and iterative methods are considered. For iterative mehods, preconditioners are needed. The structures of preconditioners for both distributed and boundary control problems are covered. Additionally, an a priori error analysis for the distributed control problem is given. We present the numerical results at the end of each chapter.

A dust layer, especially based on high-resistivity dust, at the collecting electrodes may cause a back corona discharge in electrostatic precipitators (ESP). It can significantly reduce the ESP efficiency and as a result cause ecological damages. To study the dust layer influence inside ESPs, it is necessary to derive an adequate model of the ESP precipitation process with a dust layer at the collecting electrode. The research of the present thesis is focused on stationary studies of the precipitation process with a dust layer at the collecting electrode in ESPs. Three mathematical models are proposed as a description of the precipitation process with a dust layer at the collecting electrode. The models are based on Maxwell’s equations and the finite element method (FEM). COMSOL Multiphysics software is used for their implementation. In all models the dust layer has constant conductivity and the air region has constant ion mobility. In the first model there are no coupling conditions, which is required in mathematics, are given between the two regions. The solution found by COMSOL Multiphysics does not provide physically acceptable coupling conditions. In the second model, a continuous transition zone is introduced between the two regions so that no coupling conditions are required. With the large derivatives in the transition zone, the nonlinear solver in COMSOL Multiphysics does not converge. Finally, in the third model, the dust layer and the grounded collecting electrode are replaced with a boundary condition for the air region. The properties of the third model are investigated, and these models can be used to study the influence of the dust layer. The results of these investigations are reported and discussed.

The purpose of this study is to determine if element decimation of a 3-D anatomical model affects the results of Finite Element Analysis (FEA). FEA has been increasingly applied to the biological and medical sciences. In order for an anatomical model to successfully run in FEA, the 3-D model’s complex geometry must be simplified, resulting in a loss of anatomical detail. The process of decimation reduces the number of elements within the structure and creates a simpler approximation of the model. Using the National Library of Medicine’s Visible Human Male dataset, a virtual 3-D representation of several structures of the hip were produced. The initial highest resolution model was processed through several levels of decimation. Each of these representative anatomical models were run in COMSOL 3.5a to measure the degree of displacement. These results were compared against the original model to determine what level of error was introduced due to model simplification.

Chromatography is widely used to determine physiochemical properties data including adsorption isotherm. In the separation of enantiomers through sorptive processes, supercritical fluids allow efficient and green alternatives to liquid solvent based systems. The isotherm information is vital in the development of operating policies and design of preparative chromatographic or moving bed separation schemes. Determination of sorption isotherms from experimental chromatographic elution data is automated and compared with different chromatogram model. Procedures were developed and validated for separation of R- and S- ibuprofen with supercritical 〖CO〗_2 and ethanol mixture as the mobile phase over a chiral stationary phase. The isotherms for the Langmuir, Freundlich, and Toth gave the similar results with a small residual for S-Ibuprofen at 150 bars and 40℃. Relative small amount of sample can be use from experiments to determine isotherms data that later be use for scale-up of the sorptive processes in industry to reduce time and cost.

This dissertation reports the investigation conducted on the static and dynamic behavior of the passive diamagnetic levitation systems. Attachment of a device to a substrate hinders the optimum performance ability of vibrating devices by altering the dynamic behavior of the moving part whilst introducing higher overall stiffness. The significance of this effect is prominent especially in vibration based energy harvesters as higher stiffness elevates the resonance frequency of the system, making it difficult to tune into ambient low frequencies. Other advantages of the proposed method are given by the removal of mechanical bending elements, which are often the source of energy dissipation through thermo-elastic damping and affects device reliability and durability. In this research, diamagnetically levitated resonators that can be utilized in energy harvesting were proposed and investigated as a possible solution to overcome these problems. Permanent magnets in an opposite neighboring poles (ONP) configuration were used to provide the magnetic field required for levitation. Pyrolytic graphite (PG), which is the known highest diamagnetic material, serves as the levitating proof mass. Experimental results show that the static levitation height has a linear dependence on the thickness and a nonlinear dependence on the area of the levitating proof mass that can be approximated to a third order polynomial equation. Also, the study proved that a thinner proof mass provides a higher air gap while length of the proof mass beyond a certain value (l >10 mm for the experimental system considered in this dissertation) has no significant effect on increasing the air gap. It was also observed that levitation can slightly increase by attaching magnets to a sheet of steel (ferromagnetic material). To the best of my knowledge, this dissertation is the first to address the parameterized studies in the dynamics of diamagnetic levitated objects by permanent magnets. Measurements performed on a diamagnetic levitating prototype system show that the resonance frequencies are lowered by approximately 3- 4 orders of magnitude in levitated systems compared to the attached systems demonstrating the feasibility of using levitating techniques for micro to meso scale energy harvester applications. Also, there is a significant dissimilarity observed in this study compared to the mechanically attached systems: The resonance frequency has a dependence on magnetic field strength, and is shifting towards lower values when increasing the strength of the magnetic field. This indicates that the virtual spring of a levitated proof mass is not a constant and therefore, the resonance frequency of the diamagnetic levitated systems is able to be fine-tuned by varying the magnetic field. Finite Element Method (FEM) models were developed using COMSOL software that can simulate 3D magnetic flux formation of an array of permanent magnets and the diamagnetic levitation. The appropriate magnetic force equation from the two force equations that exist in the literature was established for the static levitation with the help of experimental and simulation results. Moreover, these models are able to provide the magnetic force exerted on diamagnetic objects at different heights, stable levitation height and position and also an indication of the maximum stably levitated size of the diamagnetic material. Future endeavor of this study is to realize the diamagnetic levitation in energy harvesters. The results obtained from this research will not be limited to harvester applications but will also be beneficial to other diamagnetic levitation related systems, as these parameters are fundamental and necessary for the foundation of the research in the field of interest.

Proton exchange membrane fuel cells (PEMFCs) have attracted great attention due to their high power density, low-temperature operation and high energy conversion efficiency. However, the high cost of Pt catalysts and durability problems hinder their commercialization. So their cost must be lowered drastically and their durability must be extended. In an effort to overcome these problems, there have been intensive efforts to enhance the activity, durability and to lower the price of catalysts by alloying with other less expensive metals. In particular, the sluggish kinetics of ORR caused by Pt oxide at cathode and Pt catalyst degradation by electrochemical surface area (ECSA) loss have been a huge research area where a lot of researchers have paid lots of attention to solve. In this regard, the objective of this dissertation is to evaluate a series of Pt catalyst electrode surface electrochemical reactions on PEMFC electrode in order to help searching new catalysts and enhancing system design, assist in the search for new catalysts and improved system design by suggesting the developed mechanism of electrocatalyst activity and stability (durability). We have been focused on understanding the oxide-mediated dissolution of Pt by using electrochemical experiment methods such as RRDE, EQCN, SECM with a combination of ICP-MS and computational simulation with COMSOL Multiphysics. Firstly, in chapter 3, we showed the oxide-mediated Pt dissolution rate and the influence of hydrogen and cation underpotential deposition on Pt dissolution. In chapter 4, we revealed oxygen reduction reaction (ORR) plays a significant role in Pt oxide formation and reduction that influences the Pt catalyst dissolution, resulting in accelerated Pt dissolution rate at specific potential range. Finally, we found out the nature of mobile species generated during PtO₂ reduction process which have been disputed as Pt ion or other mobile species and fulfilled computational simulation for evaluation of SECM experiment in chapter 5. Based on these experiments and simulation, we were able to explain some mechanism of literature results that already were reported but have not been clearly explained so far. In terms of the purpose of this dissertation, the mechanism of oxide-mediated Pt dissolution, influence of ORR to Pt oxide formation/reduction and Pt dissolution, the nature of mobile species generated during PtO₂ reduction process, are sure to be very helpful in developing new catalysts and enhancing system design and suggested operating conditions. / text