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Title: INVESTIGATION INTO USE OF GEARLESS PMSG-BASED WIND FARM FOR GRID SUPPORT
Creator: Cui, Yinan
Date: 2011-12-05, 2011-12
Description: Wind energy has become the world’s fastest growing energy source，as environmental concerns have focused attention on the generation of...
Show moreWind energy has become the world’s fastest growing energy source，as environmental concerns have focused attention on the generation of electricity from clean and renewable sources. New capacity from wind turbines has been growing fast since 2004. Installed capacity reached 196630 Megawatt in 2010 worldwide. 2011 will also see good growth. Reliability and quality of the electrical power supply is of great importance for all grids. A well designed wind-turbine power source can help balancing the unpredictable power changes caused by the Load-side of the grid (Due to the meteorological nature of long-lasting wind at the sea, the offshore wind turbines are more stable in their power production aspect). Alone more and more R&D efforts, PMSG-based direct drive wind turbine generator has become a trend in the industry, its full scale back-to-back converters can achieve fast response of power factor tuning, which directly offers an option of generating a certain amount of reactive supporting power in solving short-term voltage stability problem in the local grid and a desired quantity of active power for mitigating the frequency oscillation in the system. Topics in this thesis includes: (1) analysis of the wind turbine generator model equipped with full scale back-to-back converters and their control schemes are proposed; (2) the low voltage ride-through test of a wind farm with the modeled wind turbine generator integrated into a finite 3-bus system is provided for further short term voltage stability studies; (3) the comparison is rendered between an offshore wind farm with no support on reactive power and the one with automatically reactive power support on voltage drop response in an 8-bus system connected with HVAC submarine cable; (4) study on dynamic active power compensation from wind farm for improving the frequency stability when large disturbance introduced. Keywords: PMSG, full scale converters, reactive power, short term voltage stability, active power, dynamic compensation
M.S. in Electrical Engineering, December 2011
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Title: ACCESSIBLE, ALMOST AB INITIO MULTI-SCALE MODELING OF ENTANGLED POLYMERS VIA SLIP-LINKS
Creator: Andreev, Marat
Date: 2014, 2014-12
Description: It is widely accepted that dynamics of entangled polymers can be described by the tube model. Here we advocate for an alternative approach to...
Show moreIt is widely accepted that dynamics of entangled polymers can be described by the tube model. Here we advocate for an alternative approach to entanglement modeling known as slip-links. Recently, slip-links were shown to possess important advantages over tube models, namely they have strong connections to atomistic, multichain levels of description, agree with non-equilibrium thermodynamics, are applicable to any chain architecture and can be used in linear or non-linear rheology. We present a hierarchy of slip-link models that are connected to each other through successive coarse graining. Models in the hierarchy are consistent in their overlapping domains of applicability in order to allow a straightforward mapping of parameters. In particular, the most–detailed level of description has four parameters, three of which can be determined directly from atomistic simulations. On the other hand, the least–detailed member of the hierarchy is numerically accessible, and allows for non-equilibrium flow predictions of complex chain architectures. Using GPU implementation these predictions can be obtained in minutes of computational time on a single desktop equipped with a mainstream gaming GPU. The GPU code is available online for free download.
Ph.D. in Physics, December 2014
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Title: DEVELOPING ALGORITHMIC TRADING STRATEGIES AND EMPIRICAL ANALYSIS WITH HIGH FREQUENCY TRADING DATA
Creator: Lee, Jeonghoe
Date: 2015, 2015-07
Description: The PhD dissertation research topics aim at developing algorithmic trading strategies and demonstrating data analysis skills. To be a...
Show moreThe PhD dissertation research topics aim at developing algorithmic trading strategies and demonstrating data analysis skills. To be a quantitative analyst as well as an academic scholar in financial trading area, these two professional backgrounds are indispensable. In detail, chapter 1 shows multi-objective optimization and spontaneous optimization of design variables. For instance, while conventional trading systems explore a single objective function, multi-objective optimization allows us to manage the essential trade-off among profit, standard deviation and maximum-drop. In addition, design parameters such as trading volume, the amount of historical data, and trading gateways of technical indicators are continuously optimized in real time. In chapter 2, this chapter shows an algorithmic trading system with the concept of machine learning, and demonstrating its various applications. The main purpose of this research is to propose objective numerical development framework in algorithmic trading. Chapter 3 pursues understanding liquidity measures which are critical for algorithmic traders and investors. Various liquidity measures have been suggested and they have different sensitivities to the market. This research analyzes liquidity measures and clarifies the relation between market price return & realized volatility and liquidity measures. In sum, with these three chapters, this dissertation will demonstrate necessary research topics in algorithmic trading.
Ph.D. in Management Science, July 2015
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Title: STABILITY OF AQUEOUS FOAMS: FOAM FILM STRATIFICATION PHENOMENON AND THE EFFECTS OF DISPERSED VERSUS SOLUBILIZED OIL
Creator: Lee, Jongju
Date: 2016, 2016-05
Description: A foam is a system consisting of a concentrated dispersion of gas bubbles in a liquid. Foams are encountered in many industries such as food,...
Show moreA foam is a system consisting of a concentrated dispersion of gas bubbles in a liquid. Foams are encountered in many industries such as food, agriculture, chemicals, petroleum, and paper manufacturing. Aqueous foams are formed by using surfactants or nano-colloidal particles. Thin liquid films containing surfactant micelles or other nano-colloidal particles are considered to be the key structural elements of foams containing gas and liquid. We thus probed the effects of the micellar concentration and the film size (area) on the stability of a dry bulk foam by studying the stability of a single foam lamella containing micelles; this is so we can establish the importance of the micellar structuring phenomenon and the foam film size (area) affecting the bulk foam stability. The film stratification phenomenon (stepwise film thinning) was experimentally observed by the reflected light microinterferometry. The stepwise layer-by-layer decrease of film thickness is due to the appearance and growth of dark spot (of one layer less film thickness) in the film. We used the two-dimensional diffusion model to model the dynamics of dark spot expansion considering the apparent diffusion coefficient and the film size. Based on this model, we carried out a parametric study depicting the effects of film thickness (or the number of micellar layers) and film area on the rate of dark spot expansion. Many practical applications involving three-phase foams (aqueous foams containing oil) commonly employ surfactants at several times their critical micelle concentration (CMC). We investigated the influence of both the dispersed and solubilized oils, and the surfactant concentration (above CMC) on the stability of an aqueous foaming system. In foam stability, the relative importance of the dispersed oil versus oil solubilized within the micelles depends on the stability of the aqueous asymmetric (i.e., pseudoemulsion) film between the oil and the air-water interface and the second virial coefficient. Also, the micellar structuring phenomenon tests using the single foam lamella revealed that the multi-layering structure was well pronounced in the absence of the solubilized oil; as a consequence, the foam lamellae thinned slowly layer-by-layer and the oil solubilized in micelles weakened the micellar structure formation. The foam lamellae thinned faster, making the foam less stable.
Ph.D. in Chemical Engineering, May 2016
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Title: THE CHARACTERIZATION OF TWO THERMOPHILIC STRAINS CONCERNING BIO-DESULFURIZATION OF DIBENZOTHIOPHENE BY THE 4S PATHWAY
Creator: Li, Enze
Date: 2016, 2016-05
Description: A moderately thermophilic Mycobacterium strain (denoted Myco-U) was isolated in our lab as a contaminant during the cultivation of another...
Show moreA moderately thermophilic Mycobacterium strain (denoted Myco-U) was isolated in our lab as a contaminant during the cultivation of another thermophilic Paenibacillus strain, and has been proved to harbor the genes that encode the enzymes for dibenzothiophene (DBT) biodegradation via the 4S pathway; this makes it possible to efficiently remove organosulfur compounds (e.g. DBT and DBTO2) from the crude petroleum. Through directed evolution (continuous passage and selection with increasing temperature), the Myco-U strain has shown moderate capacity of metabolizing DBT to 2-hydroxybiphenyl (2-HBP) by the 4S pathway at a thermophilic temperature (~53 ℃). In the middle-to-late stages of the selections, a stubborn contaminant (denoted Bacillus X) arose and has remained difficult to get rid of from our medium and cultures ever since, leading to a persistent contamination and repetition of our experiments. The reason why Bacillus X is regarded as a contaminant is that it does not obtain sulfur by the expected means (e.g., DBT desulfurization), but utilizes the tiny amount of sulfate from the vitamin mix and 50 μg/ml yeast extract in our medium to grow. This is confirmed by the facts that Bacillus X does not yield any detectable 2-HBP, and a significant difference of growth has been detected between cultures with DBT as the sole sulfur source and the positive controls, which employs Na2SO4 as sulfur source. Through 16S rDNA amplification, cloning, and sequencing, Bacillus X was identified as a Bacillus species, and shows the highest homology (99 % identical) to a specific uncultured bacterium clone (NCBI #Accession: JN882111.1). The chromogenic mechanism and impacts of pH and carbonate upon the Gibbs assay, by which 2-HBP is quantified, were investigated. When DBT is absent or at undetectably low levels, cultures measured by the assay display a yellowish-to-brownish background after adding the Gibbs reagent (2,6-dichloroquinone-4-chloroimide). According to our results, the Gibbs reaction prefers alkaline conditions and pH 8.0 ranks the optimal (compared with pH 7.0, 7.5, 8.5 and 9.0) at which the maximum A610nm is detected.
M.S. in Biology, May 2016
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Title: CHANGES OF BACTERIAL SPECIES AND HEME PROTEIN LEVEL IN ACTIVATED SLUDGE COMMUNITIES ACCLIMATED TO LOW AERATION
Creator: Li, Hainan
Date: 2016, 2016-05
Description: Increasing oxygen utilization of activated sludge under low dissolved oxygen (DO) conditions can lead to energy savings in wastewater...
Show moreIncreasing oxygen utilization of activated sludge under low dissolved oxygen (DO) conditions can lead to energy savings in wastewater treatment systems. Adaptation of sludge communities to low oxygen conditions may be facilitated by increased expression of heme proteins. One way to assess heme protein expression in sludge is to analyze the species present in the sludge community during the adaptation process. In the work reported here, growth of a sludge culture adapted by Kunkel to low aeration for 48 weekly passages was continued for an additional 26 passages (182 days). The activated sludge was cultured in synthetic wastewater under low DO conditions. Temperature, dissolved oxygen, and specific oxygen uptake rates (SOUR) were measured at the end of each weekly passage. The community structures of passages 50, 53 and 65 were determined by 16S rDNA cloning techniques. The type of heme present was identified using the pyridine hemochromogen method. The SOUR values measured increased slightly in the first part of the experiment, when the culture DO was very low, but then decreased in the latter part of the experiment, when the culture DO increased. The community structure diversity in passage 50 in Kunkel’s study and passage 50 from this work are totally different in terms of species present, even though the two cultures were both derived from Kunkel’s passage 48 and were grown under conditions which were matched as closely as possible for two additional passages. This indicates that the community structure is highly sensitive to small changes in growth conditions. From the point of view of types of hemoglobin (Hb), the community became more diverse by passage 53, containing all three types of truncated Hb (trHbN, trHbO, and trHbP), possibly due to the need for NO scavenging and oxygen transfer enhancement. The proportion of cells that synthesize truncated Hb decreased slightly through passages 50 to 53 to 65. The percentage of cells that encode FlavoHbs decreased from 84 % to 50 % by passage 65. Overall there was an increase in Hb expression from passage 50 to passage 65. Heme b expression in the sludge culture was confirmed. Successful adaptation of the sludge culture to low DO conditions via enhancement of oxygen uptake was not obvious in this study. Yet the overall tendencies of SOUR and Hb expression suggest that it is possible to acquire a culture more efficient in oxygen uptake if a stable low aerobic environment can be maintained for an extended period.
M.S. in Biology, May 2016
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Title: TEMPORAL AND SPATIOTEMPORAL MODELS FOR SHORT-CRIME PREDICTION
Creator: Liu, Xiaomu
Date: 2017, 2017-07
Description: One of the most important aspects of predictive policing is identifying the likely time and place of crime occurrences so as to prevent future...
Show moreOne of the most important aspects of predictive policing is identifying the likely time and place of crime occurrences so as to prevent future crimes. The ability to make short-term predictions may be of particular importance for optimizing police resource allocation. The goal of this study is to investigate the temporal and spatiotemporal pattern of crime in the city of Chicago and to build corresponding predictive models. First, a temporal model for forecasting citywide violent crime time count is proposed. This model is composed of a long-term trend and short-term variations using data of time, weather and crime. The importance of model reproducibility is addressed in this study to produce low-complexity models. We introduce an approach that provides a way to extend the model selection criterion to both prediction accuracy and model reproducibility. The experimental results show that models produced by this approach outperform several simple time-series models. It is also found that these models typically include fewer variables; therefore, they are more interpretable, and may provide superior generalization error. Next we develop a framework that provides predictions for tomorrow’s violent crime counts at the level of a police district. The procedures include citywide daily violent crime count prediction, violent crime density estimation, and distributing citywide predictions to districts according to the estimated densities. In order to estimate the crime spatial densities, we use mesh modeling and demonstrate that a mesh model can be used as the structure for modeling the spatial variation of crime rate since it is well adapted to the inhomogeneous crime distribution. The experimental results show that our method provides more-accurate forecasts than those given by historical crime statistics. One aspect of studying spatial pattern of crimes is identifying geographical regions with similar crime characteristics. Specifically, we illustrate applying unsupervised clustering techniques to segment the city into sub-regions. We explore the use of Gaussian mixture models combined with a Markov random field for the purpose of regularization. We also propose a framework for the evaluation of clustering models without knowing the ground truth, which can present a more-complete picture for model selection in unsupervised clustering problems. Finally, we develop a spatiotemporal prediction method that predicts the locations where violent crimes or property crimes are most likely to occur tomorrow. Crime incidents are rasterized by a spatiotemporal grid. Other factors that affect the time and location preferences of criminal activities are also leveraged and represented by that grid. Each spatiotemporal grid cell is treated as an example for training and testing our models. We also explore whether pooling data from various sub-regions based on spatial clustering can improve model performance. The experimental results show that our models are more accurate than conventional hot-spot models. It is found that the effects of using different training samples are not consistent, which depends on target crime type.
Ph.D. in Electrical Engineering, July 2017
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Title: SECURE AND RESILIENT OPERATION OF CYBER-PHYSICAL POWER SYSTEMS
Creator: Li, Zhiyi
Date: 2017, 2017-07
Description: For economic reasons, modern power systems are commonly operated close to their secure limits so that they are vulnerable to unexpected severe...
Show moreFor economic reasons, modern power systems are commonly operated close to their secure limits so that they are vulnerable to unexpected severe disruptions such as disastrous cyberattacks and extreme weather events. This thesis is aimed at enhancing the security and resilience of power supplies for facilitating the development of a Smart Grid, when power systems in various parts of the world have been undergoing transitions toward cyber-physical systems. First, this thesis discusses common cybersecurity vulnerabilities in modern power systems and presents physical implications of cyberattacks on power system operations. In particular, this thesis analyzes a specifc type of coordinated cyberphysical attacks that could lead to undetectable line outages. Coordinated with physical attacks causing line outages, cyberattacks comprising topology preserving and load redistribution attacks could mask and potentially exasperate the outages to trigger cascading failures. Such coordinated cyber-physical attacks are analyzed in a bi-level optimization model which is then transformed into a mixed-integer linear programming problem. The proposed model and the two-stage solution algorithm are examined by case studies based on the IEEE 14-bus and 118-bus test systems. Second, this thesis offers the pertinent studies on quantifying the risk of cybersecurity vulnerabilities in power system operations. A type of locally coordinated cyber-physical attacks is analyzed in detail, which would cause undetectable line outages in local areas without the need for complete network information. A risk-based optimization model in the mixed-integer linear programming form is presented for analyzing physical implications resulting from the power ow redistribution. An efficient greedy search-based heuristic method is then developed to offer satisfactory solutions for real-time applications, which are verified by case studies based on a six-bus system and the two-area IEEE RTS-96 system. Third, this thesis studies security measures for mitigating the cybersecurity risk in power system operations. A game-theoretic framework is built for determining the optimal combination of security measures based on the minimax-regret decision rule. The resulting multi-level optimization model is reformulated as a bilevel mixed-integer linear programming problem. An implicit enumeration algorithm is then developed to achieve an exact solution to this complex problem. Acceleration techniques are also provided to improve the computation efficiency for large-scale power system applications. The proposed model and solution methods are validated by case studies based on a six-bus test system and the two-area RTS-96 system. Fourth, this thesis extends the discussion of cybersecurity vulnerabilities to the operation of distributed power systems like microgrids. Since microgrids are regarded as building blocks of a Smart Grid, they strive for cyber-secure operations for sustaining power services to local customers. The assessment and mitigation of the cybersecurity risk in microgrid operations is then presented in depth. Additional opportunities provided by software-defined networking technologies to enhance the microgrid cybersecurity are also realized by the proposed defense-in-depth framework that comprises three lines of defense against cyberattacks. Last, this thesis investigates the role of networked microgrids in enhancing the power system resilience against extreme events. Since resilience is an intrinsically complex property which requires deep understanding of power system operations, a generic simulation-based framework is developed for power system operators to analyze the resilience comprehensively and respond effectively in emergency conditions. The notion that the deployment of networked microgrids catalyzes the resilience enhancement in a Smart Grid is discussed in detail. Besides, the management of networked microgrids for achieving a higher degree of resilience, reliability, and efficiency of power supplies is discussed based on the proposed hierarchical control framework.
Ph.D. in Electrical Engineering, July 2017
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Title: THE PATH TO HIGH Q-FACTORS IN SUPERCONDUCTING ACCELERATING CAVITIES: FLUX EXPULSION AND SURFACE RESISTANCE OPTIMIZATION
Creator: Martinello, Martina
Date: 2016, 2016-12
Description: Accelerating cavities are devices resonating in the radio-frequency (RF) range used to accelerate charged particles in accelerators....
Show moreAccelerating cavities are devices resonating in the radio-frequency (RF) range used to accelerate charged particles in accelerators. Superconducting accelerating cavities are made out of niobium and operate at the liquid helium temperature. Even if superconducting, these resonating structures have some RF driven surface resistance that causes power dissipation. In order to decrease as much as possible the power losses, the cavity quality factor must be increased by decreasing the surface resistance. In this dissertation, the RF surface resistance is analyzed for a large variety of cavities made with different state-of-the-art surface treatments, with the goal of finding the surface treatment capable to return the highest Q-factor values in a cryomodule-like environment. This study analyzes not only the superconducting properties described by the BCS surface resistance, which is the contribution that takes into account dissipation due to quasi-particle excitations, but also the increasing of the surface resistance due to trapped flux. When cavities are cooled down below their critical temperature inside a cryomodule, there is always some remnant magnetic field that may be trapped increasing the global RF surface resistance. This thesis also analyzes how the fraction of external magnetic field, which is actually trapped in the cavity during the cooldown, can be minimized. This study is performed on an elliptical single-cell horizontally cooled cavity, resembling the geometry of cavities cooled in accelerator cryomodules. The horizontal cooldown study reveals that, as in case of the vertical cooldown, when the cooling is performed fast, large thermal gradients are created along the cavity helping magnetic flux expulsion. However, for this geometry the complete magnetic flux expulsion from the cavity equator is more difficult to achieve. This becomes even more challenging in presence of orthogonal magnetic field, that is easily trapped on top of the cavity equator causing temperature rising. The physics behind the magnetic flux expulsion is also analyzed, showing that during a fast cooldown the magnetic field structures, called vortices, tend to move in the same direction of the thermal gradient, from the Meissner state region to the mixed state region, minimizing the Gibbs free energy. On the other hand, during a slow cool down, not only the vortices movement is limited by the absence of thermal gradients, but, also, at the end of the superconducting transition, the magnetic field concentrates along randomly distributed normal-conducting region from which it cannot be expelled anymore. The systematic study of the surface resistance components performed for the different surface treatments, reveals that the BCS surface resistance and the trapped flux surface resistance have opposite trends as a function of the surface impurity content, defined by the mean free path. At medium field value, the BCS surface resistance is minimized for nitrogen-doped cavities and significantly larger for standard niobium cavities. On the other hand, Nitrogen-doped cavities show larger dissipation due to trapped flux. This is consequence of the bell-shaped trend of the trapped flux sensitivity as a function of the mean free path. Such experimental findings allow also a better understanding of the RF dissipation due to trapped flux. The best compromise between all the surface resistance components, taking into account the possibility of trapping some external magnetic field, is given by light nitrogen-doping treatments. However, the beneficial effects of the nitrogen-doping is completely lost when large amount of magnetic field is trapped during the cooldown, underlying the importance of both cooldown and magnetic field shielding optimization in high quality factors cryomodules.
Ph.D. in Physics, December 2016
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Title: ASSESSMENT OF MICROGRIDS FOR DEVELOPED AND DEVELOPING COUNTRIES
Creator: Vyas, Kohil
Date: 2013, 2013-12
Description: Today’s world essentially runs on electricity, in some form or the other. From the introduction of the concept of electricity by William...
Show moreToday’s world essentially runs on electricity, in some form or the other. From the introduction of the concept of electricity by William Gilbert to thousands of invention by Thomas Edison, there have been great changes in the world of electricity. The life of every living being is directly affected by these changes. Various electrical problems have surfaced because of these changes. Microgrids have been considered as a solution to these problems, and have been assessed and evaluated in this research. To realize the effectiveness of microgrids as a solution, initially problems were explored. It was found that there are two perspectives of the problems faced by electrical world. One being: problems seen from the view point of developed countries, and the other: problems seen from the view point of developing countries. Assessment of microgrids was accordingly branched during the research. In the case of the developed countries, the basic infrastructure of electrical system which was built long ago, demands an upgrade now. Problems like blackouts and brownouts have risen and the frequency of their occurrence is growing with time. Owing to these problems, there has been a loss of billions of dollars, as well as critical loads like research facilities, military bases, data centers etc… are severely affected. Microgrids installed in military bases, a university campus and a jail were assessed to analyze how they are implemented, the benefits reaped from them and how they can be a viable solution to the problems faced by the developed countries. In the case of the developing countries, the fact stands that they are yet to reach a state where they can serve their entire load by themselves. This results into regular load shedding. Also, there are some areas where there is no electrical infrastructure and this restricts many from even having xi the access to the electricity. For this research, microgrids installed in villages of Africa, India, and on the islands of Maldives were assessed. Their application and revolutionary impacts on the developing countries were explored. The research indicates that in the developed countries, owing to the gargantuan increase in power consumption, several electrical problems have arisen. Microgrids were able to solve these problems and save millions of dollars. Whereas, in developing countries, people still are in need of a 24-hours access to electricity for their progress. Electricity is required for basic necessities like pumping water, cooking, and activities carried out at night which requires light. Implementation of microgrids by providing electricity removes the bottleneck to their progress.
M.S. in Electrical Engineering, December 2013
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Title: P-DOPED STRONTIUM TITANATE GROWN USING TWO TARGET PULSED LASER DEPOSITION FOR THIN FILM SOLAR CELLS
Creator: Man, Hamdi
Date: 2015, 2015-12
Description: Thin-film solar cells made of Mg-doped SrTiO3 (STO) p-type absorbers are promising candidates for clean energy generation. This material shows...
Show moreThin-film solar cells made of Mg-doped SrTiO3 (STO) p-type absorbers are promising candidates for clean energy generation. This material shows p-type conductivity and also demonstrates reasonable absorption of light. In addition, p-type SrTiO3 can be deposited as thin films so that the cost can be lower than the competing methods. In this work, Mg:SrTiO3 (Mg:STO) thin-films were synthesized and analyzed in order to observe their potential to be employed as the base semiconductor in photovoltaic applications. Mg:STO thin-films were grown with pulsed laser deposition (PLD) using a frequency quadrupled Yttrium Aluminum Garnet (YAG) laser and with a substrate that was heated by back surface absorption of infrared (IR) laser light. The samples were characterized using X-ray photoelectron spectroscopy (XPS) and it was observed that Mg atoms were incorporated in the STO films. Reflection high energy electron diffraction (RHEED) spectroscopy proved that the thin films were polycrystalline. Calculations showed that the lattice constant of Mg:STO/SSF is slightly greater than that of STO/SSF, therefore, the conservation of the characteristic ring pattern for STO suggests of doping by substitution, which is consistent with the examples in literature. Kelvin Probe work function measurements indicated that the work function of the films were 4.167 eV after annealing. EDS spectroscopy showed that Mg was present in the thin films.
M.S. in Physics, December 2015
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Title: Modeling and Optimization of Embedded Active Flow Control Systems
Creator: Henry, James M.
Date: 2024
Description: This thesis presents research focused on the aerodynamic performance of circulation control on two-dimensional and quasi-two-dimensional wings...
Show moreThis thesis presents research focused on the aerodynamic performance of circulation control on two-dimensional and quasi-two-dimensional wings. Aerodynamic loads, namely lift, drag, and moment coefficients, are measured through Reynolds Averaged Navier Stokes (RANS) modeling and wind tunnel experiment. A simplified and parameterized RANS model is presented as a rapidly iterable approach to estimating the performance of trailing-edge circulation control on two dimensional airfoils, with the hypothesis that an optimized airfoil shape can be found which maximizes the lift coefficient increment generated by circulation control, through modification of the wing profile. The simplified modeling setup is compared with more conventional approaches to numerical simulation of circulation control. The performance of the simplified modeling scheme is then compared with wind tunnel studies, for both steady-state and dynamic performance, as functions of both momentum coefficient dCμ and chord-based Reynolds number Re_c. The dynamic performance for the model is studied to find an analog to the theoretical unsteady models of Wagner and Theodorsen. An adjoint optimization framework is used to find an optimal airfoil profile for circulation control. The optimized profile is then compared in both a simulation and a wind tunnel test study against a NACA0015 airfoil. In simulation, improvement between 12% and 15% is seen for the lift control authority for all values of dCμ and Re_c tested. In experiment, the optimized profile demonstrated improvements of up to 28% in lift control authority, dCL/dCμfor values of Cμ, and decreased performance for higher values of Cμ.
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Title: Utilizing Concurrent Data Accesses for Data-Driven and AI Applications
Creator: Lu, Xiaoyang
Date: 2024
Description: In the evolving landscape of data-driven and AI applications, the imperative for reducing data access delay has never been more critical,...
Show moreIn the evolving landscape of data-driven and AI applications, the imperative for reducing data access delay has never been more critical, especially as these applications increasingly underpin modern daily life. Traditionally, architectural optimizations in computing systems have concentrated on data locality, utilizing temporal and spatial locality to enhance data access performance by maximizing data and data block reuse. However, as poor locality is a common characteristic of data-driven and AI applications, utilizing data access concurrency emerges as a promising avenue to optimize the performance of evolving data-driven and AI application workloads.This dissertation advocates utilizing concurrent data accesses to enhance performance in data-driven and AI applications, addressing a significant research gap in the integration of data concurrency for performance improvement. It introduces a suite of innovative case studies, including a prefetching framework that dynamically adjusts aggressiveness based on data concurrency, a cache partitioning framework that balances application demands with concurrency, a concurrency-aware cache management framework to reduce costly cache misses, a holistic cache management framework that considers both data locality and concurrency to fine-tune decisions, and an accelerator design for sparse matrix multiplication that optimizes adaptive execution flow and incorporates concurrency-aware cache optimizations.Our comprehensive evaluations demonstrate that the implemented concurrency-aware frameworks significantly enhance the performance of data-driven and AI applications by leveraging data access concurrency.Specifically, our prefetch framework boosts performance by 17.3%, our cache partitioning framework surpasses locality-based approaches by 15.5%, and our cache management framework achieves a 10.3% performance increase over prior works. Furthermore, our holistic cache management framework enhances performance further, achieving a 13.7% speedup. Additionally, our sparse matrix multiplication accelerator outperforms existing accelerators by a factor of 2.1.As optimizing data locality in data-driven and AI applications becomes increasingly challenging, this dissertation demonstrates that utilizing concurrency can still yield significant performance enhancements, offering new insights and actionable examples for the field. This dissertation not only bridges the identified research gap but also establishes a foundation for further exploration of the full potential of concurrency in data-driven and AI applications and architectures, aiming at fulfilling the evolving performance demands of modern and future computing systems.
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Title: THE ROLE OF MOLECULAR MOTORS IN THE MECHANICS OF ACTIVE GELS AND THE EFFECTS OF INERTIA, HYDRODYNAMIC INTERACTION AND COMPRESSIBILITY IN PASSIVE MICRORHEOLOGY
Creator: Uribe, Andres Cordoba
Date: 2014, 2014-07
Description: The mechanical properties of soft biological materials are essential to their physiological function and cannot easily be duplicated by...
Show moreThe mechanical properties of soft biological materials are essential to their physiological function and cannot easily be duplicated by synthetic materials. The study of the mechanical properties of biological materials has lead to the development of new rheological characterization techniques. In the technique called passive microbead rheology, the positional autocorrelation function of a micron-sized bead embedded in a viscoelastic fluid is used to infer the dynamic modulus of the fluid. Single particle microrheology is limited to fluids were the microstructure is much smaller than the size of the probe bead. To overcome this limitation in two-bead microrheology the cross-correlated thermal motion of pairs of tracer particles is used to determine the dynamic modulus. Here we present a time-domain data analysis methodology and generalized Brownian dynamics simulations to examine the effects of inertia, hydrodynamic interaction, compressibility and non-conservative forces in passive microrheology. A type of biological material that has proven specially challenging to characterize are active gels. They are formed by semiflexible polymer filaments driven by motor proteins that convert chemical energy from the hydrolysis of adenosine triphosphate (ATP) to mechanical work and motion. Active gels perform essential functions in living tissue. Here we introduce a single-chain mean-field model to describe the mechanical properties of active gels. We model the semiflexible filaments as bead-spring chains and the molecular motors are accounted for by using a mean-field approach. The level of description of the model includes the end-toend length and attachment state of the filaments, and the motor-generated forces, as stochastic state variables which evolve according to a proposed differential Chapman- Kolmogorov equation. The model allows accounting for physics that are not available in models that have been postulated on coarser levels of description. Moreover it allows the prediction of observables at time scales that will be too difficult to achieve in multi-chain simulations.
Ph.D. in Chemical Engineering, July 2014
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Title: An Integrated Cell Culture-PCR Assay for the Detection of Viable Coxiella Burnetii Nine Mile Phase II RSA 439 in Fluid Dairy Products
Creator: Kukreja, Ankush
Date: 2011-12, 2011-12
Description: Coxiella burnetii, an obligate intracellular bacterium, has been used as the reference organism for defining milk pasteurization conditions....
Show moreCoxiella burnetii, an obligate intracellular bacterium, has been used as the reference organism for defining milk pasteurization conditions. With renewed interest in minimizing processing times and temperatures, and in ensuring product safety, development of an Integrated Cell Culture-PCR (ICC-PCR) assay may be useful for evaluating C. burnetii inactivation in fluid dairy products. The purpose of this research was to develop an ICC-PCR assay to determine viability and detection limit of C. burnetii and characterize inhibiting effects contributed by various milk formulations. Coxiella burnetii was inoculated on Vero cell culture with PBS and whole milk, incubated for 48 hours to allow infection, and then incubated for 11 days to allow propagation. The propagated C. burnetii mix was subjected to freeze-thaw followed by DNA extraction with Autogen Blood & Tissue DNA Extraction Kit using Quickgene Mini80. Extracted DNA was amplified using TaqMan-MGB based qPCR targeting published primers for the IS1111a transposase gene to verify C. burnetii growth/infectivity. For detection limit determination, serial dilutions of C. burnetii in RPMI were mixed separately in whole milk, cream, chocolate milk and eggnog. The mix was overlaid on sub-confluent Vero cell monolayers, subjected to freeze-thaw followed by DNA extraction using Autogen Blood & Tissue DNA Extraction Kit and PCR. Uninoculated wells were evaluated for dairy sample background signal, and inhibition was evaluated by comparison to purified DNA. Duplicate trials using 6 replicates per sample were performed.
M.S. in Food Safety & Technology, December 2011
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Title: DESIGN OF MODERN HIGH NB-CONTENT ,-,' NI-BASE SUPERALLOYS
Creator: Antonov, Stoichko
Date: 2017, 2017-07
Description: Superalloy design can prove to be a very complex and challenging task, as certain elemental additions can significantly improve properties...
Show moreSuperalloy design can prove to be a very complex and challenging task, as certain elemental additions can significantly improve properties when added in high contents, however, exceeding their solubility limits can promote the formation of undesired phases at grain boundaries as well as grain interiors, and can quickly deteriorate the high temperature structural integrity and stability of the alloy, resulting in a catastrophic failure. Precipitate phases, such as " and ⌘, appear similar and are often mistaken for one another, leading to the need for a better fundamental understanding of their formation, required for developing innovative new classes of Ni-base superalloys. The morphology, formation, and composition of precipitate phases in a number of experimental alloys spanning a broad range of compositions were explored and compositional relationships were developed to facilitate the design of !-!0-("/⌘) Ni-base superalloys. The e↵ect of increasing Nb alloying additions on the formation and long term phase stability of topologically close packed (TCP) phases was studied. Elevated levels of Nb can result in increased matrix supersaturation and promote the precipitation of ⌘-Ni6AlNb along the grain boundaries in powder processed, polycrystalline Ni-base superalloys, while reduced Nb levels favored the precipitation of blocky Cr and Mo rich $ phase precipitates along the grain boundary. Evaluation of the thermodynamic stability of these two phases using Thermo-Calc showed that while $ phase predictions are fairly accurate, predictions of the ⌘ phase are limited. In addition, atom probe tomography (APT) was used to quantitatively assess grain boundary phase compositions and local segregation along the grain boundary before and after a 1000 hour thermal exposure at 800 "C. The complex network of $ phase precipitates that formed upon the thermal exposure and the characteristic interfacial segregation profiles were studied. In addition, elemental boron was observed to segregate to the grain boundary and phase interfaces, but did not form borides, due to the relatively low concentration of B atoms, resulting from a higher B concentration in the matrix. APT studies were also performed on MC carbides of the alloys and the formation kinetics and morphological differences between NbC and Hf doped NbC were explained using density functional theory (DFT) calculations of the formation energies of different facets of the MC carbide. Detailed electron microscopy and APT techniques were then used to systematically quantify the chemical and morphological instabilities that occur during aging of polycrystalline !-!0 Ni-base superalloys containing elevated levels of refractory alloying additions. The morphological changes and splitting phenomenon associated with the secondary !0 precipitates were related to the discrete chemical compositions of the secondary and tertiary !0 along with the phase compositions of the ! matrix and the ! precipitates that form within the secondary !0 particles. Compositional phase inhomogeneities led to the precipitation of finely dispersed tertiary !0 particles within the ! matrix and secondary ! particles within the secondary !0 precipitates, which, along with surface grooving of the secondary !0 particles, contributed to the inverse coarsening or splitting of the precipitates during aging. As recent studies have shown that polycrystalline Ni-base superalloys containing elevated levels of Nb additions exhibit superior properties at elevated temperatures when compared to existing commercial Ni-base superalloys, understanding of elemental partitioning to each phase is essential and was studied via APT. Compositions of the constituent phases were measured in four high Nb-content !-!0 Ni-base superalloys and the results were compared to thermodynamic database models from Thermo-Calc. Results were also used to predict the solid solution strength behavior of the four alloys. The di↵erences in phase composition predictions from thermodynamic models resulted in dissimilarities between the generated strength behavior curves and those from the experimental work. Finally, creep behavior of high Nb-content !-!0 Ni-Based superalloys was related to the formation of secondary phases mainly at grain boundaries. As secondary phases form, their brittle nature leads to crack formation, which can propagate under the tensile load and lead to premature failure of the alloy.
Ph.D. in Materials Science and Engineering, July 2017
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Title: DESIGN AND PERFORMANCE ASSESSMENT OF MULTI-MODAL MOBILE ROBOTS
Creator: Kalantari, Arash
Date: 2015, 2015-05
Description: This thesis is focused on developing multi-modal mobile robots, i.e. robots that can operate in more than one domain. For decades, researchers...
Show moreThis thesis is focused on developing multi-modal mobile robots, i.e. robots that can operate in more than one domain. For decades, researchers have been trying to improve locomotion capabilities of robots that operate in a single domain: on the ground, on inclined surfaces, in the air, or in water. A prevailing approach in design of hybrid robots is to simply attach systems designed for a single domain together. In order to reduce the complexity of the hybrid robot, a different design approach is taken in this thesis by attempting to keep the hardware resources on the system as low as possible. To this end, two hybrid aerial and terrestrial platforms have been developed: the walking quadrotor and the HyTAQ, the Hybrid Terrestrial and Aerial Quadrotor. In both platforms, ight is achieved through a quadrotor configuration; four actuators provide the required thrust. The walking quadrotor uses a single actuator set for both walking and ying by means of a unique compliant mechanism. This mechanism uses two separate linear movements to make walking possible. The horizontal movement of the leg is driven by running the propellers in reverse and the vertical movement is actuated by shape memory alloy (SMA) wires. An experimental prototype of this robot proves the functionality of the design. However, the experiments suggest that the application of the robot is efficient only where ground movement is a small portion of the whole mission. This is mainly due to the low efficiency of the propellers rotating in reverse and large time constant of the SMA wires, which makes walking slow. The terrestrial locomotion of HyTAQ has been made possible by adding a cylindrical cage, connected to the quadrotor through a revolute joint. This allows the cage to roll freely with respect to the body of the quadrotor, making the terrestrial locomotion possible. Moreover, the same ight actuators and control commands can be used to control terrestrial mode. An analysis of the system's energy consumption shows that the addition of the terrestrial locomotion improves the efficiency of the aerial-only quadrotor by increasing the overall operation range and time. This has been experimentally verified by showing that the HyTAQ's terrestrial range is 11 times greater compared to ight range of the quadrotor at the same speeds. Developing a hybrid aerial and scansorial robot is the next goal of this research. The first step toward this goal has been taken as part of this thesis by developing a method that enables a quadrotor to land and take-off from smooth vertical surfaces autonomously. A Microsoft Kinect sensor is used to localize the MAV and a PID controller is used to control the perching maneuver. A servo actuated gripper, mounted in front of the robot, makes attachment and detachment possible. The experimental results show that the robot can perch successfully in more than 90% of the experiments, which indicates the robustness of the proposed method.
Ph.D. in Mechanical and Aerospace Engineering, May 2015
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Title: Achipelago the Future City
Creator: Song, Gil Ryong
Date: 2011-12-05, 2011-12
Description: We are in search for many who are thinking about the methods of achieving an international sustainable environment internationally. The low...
Show moreWe are in search for many who are thinking about the methods of achieving an international sustainable environment internationally. The low carbon green city is one of the most advanced models to deal with thus related urban issues. The approach this thesis has been to find a new traditional city model for Korea that’s amalgamated with the latest technology. Until recently from the recent liberation from the Japanese colonial rule, the top priority of any policies of Korea were economic growth and national development which has enabled the nation to achieve rapid economic growth over past decades. However, through this urban transforming process we have lost our city identity. In order to achieve the nation’s quality based growth, designing the low carbon green city with a traditional identity is essential.
M.S. in Architecture, December 2011
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Title: CARRIER AGGREGATION BASED SCHEDULING FOR COORDINATED MULTIPOINT TRANSMISSION IN LTE ADVANCED SYSTEMS
Creator: Raj, Avneet
Date: 2012-04-04, 2012-05
Description: Long term Evolution Advanced(LTE-A) was introduced to eliminate the short comings of Long term Evolution(LTE).LTE uses orthogonal frequency...
Show moreLong term Evolution Advanced(LTE-A) was introduced to eliminate the short comings of Long term Evolution(LTE).LTE uses orthogonal frequency division multiplexing(OFDM) for its downlink transmission. But OFDM suffers from inter cell interference which means that cell edge suffer from a low throughput, hence LTE-A has come up with certain new techniques to solve this problem which are Carrier Aggregation(CA) and Coordinated multipoint transmission (CoMP).There are certain resource allocation techniques been currently used in CoMP which are either throughput based or fairness based .In my Thesis I have made a new resource allocation scheme which is throughput based and is aimed to provide the cell edge users with optimum data rate.To achieve this I have used soft frequency re-use pattern and to achieve higher throughput also used the CA technology. For simulation of the system I used Matlab,the simulation results show that the cell edge users in my scheme achieve higher Signal to noise ratio(SINR) optimum throughput. I have also compared my results with the existing joint proportional fairness scheme(JPF) and found that I achieve a higher overall throughput compared to the JPF scheme. viii
M.S. in Electrical Engineering, May 2012
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Title: REVIEW OF THE AC/DC MICROGRID OPERATION AND CONTROL
Creator: Bahramirad, Sheida
Date: 2016, 2016-07
Description: As defined by the U.S department of energy, a microgrid is a group of interconnected loads and distributed energy resources (DERs) with the...
Show moreAs defined by the U.S department of energy, a microgrid is a group of interconnected loads and distributed energy resources (DERs) with the ability of self-supply and islanding. The significant advantages of microgrids have resulted in extensive research and development efforts and rapidly growing implementation in electric power systems. There are, however, still many challenges to be addressed in order to efficiently design, control, and operate microgrids when connected to the grid, and also when in islanded mode. Based on the type of voltages and currents in the network, different microgrid types can be considered, including AC microgrids, DC microgrids, and Hybrid AC/DC microgrids. This thesis presents a review of AC, DC and Hybrid microgrids with a focus on control, operation, and planning issues. A thorough comparison between these microgrid types is further provided based on the system layout and the type of DERs that are commonly utilized. Communication issues are also investigated to demonstrate and compare the existing deployment practices. The thesis is concluded by providing a list of potential areas of research associated with AC, DC, and hybrid microgrids.
M.S. in Electrical Engineering, July 2016
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