Search results

Title: UNMANNED AIRCRAFT SYSTEM SENSE AND AVOID INTEGRITY AND CONTINUITY
Creator: Jamoom, Michael B.
Date: 2016, 2016-05
Description: This thesis describes new methods to guarantee safety of sense and avoid (SAA) functions for Unmanned Aircraft Systems (UAS) by evaluating...
Show moreThis thesis describes new methods to guarantee safety of sense and avoid (SAA) functions for Unmanned Aircraft Systems (UAS) by evaluating integrity and continuity risks. Previous SAA e↵orts focused on relative safety metrics, such as risk ratios, comparing the risk of using an SAA system versus not using it. The methods in this thesis evaluate integrity and continuity risks as absolute measures of safety, as is the established practice in commercial aircraft terminal area navigation applications. The main contribution of this thesis is a derivation of a new method, based on a standard intruder relative constant velocity assumption, that uses hazard state estimates and estimate error covariances to establish (1) the integrity risk of the SAA system not detecting imminent loss of “well clear,” which is the time and distance required to maintain safe separation from intruder aircraft, and (2) the probability of false alert, the continuity risk. Another contribution is applying these integrity and continuity risk evaluation methods to set quantifiable and certifiable safety requirements on sensors. A sensitivity analysis uses this methodology to evaluate the impact of sensor errors on integrity and continuity risks. The penultimate contribution is an integrity and continuity risk evaluation where the estimation model is refined to address realistic intruder relative linear accelerations, which goes beyond the current constant velocity standard. The final contribution is an integrity and continuity risk evaluation addressing multiple intruders. This evaluation is a new innovation-based method to determine the risk of mis-associating intruder measurements. A mis-association occurs when the SAA system incorrectly associates a measurement to the wrong intruder, causing large errors in the estimated intruder trajectories. The new methods described in this thesis can help ensure safe encounters between aircraft and enable SAA sensor certification for UAS integration into the National Airspace System.
Ph.D. in Mechanical and Aerospace Engineering, May 2016
Show less

Title: UNDERSTANDING DELIBERATIVE AND INTUITIVE DECISION MAKING ABOUT HAZARDS ON CONSTRUCTION SITES
Creator: Saxena, Jaya
Date: 2013, 2013-12
Description: During the course of performing daily tasks, construction workers encounter numerous hazards, such as ladders that are too short to reach the...
Show moreDuring the course of performing daily tasks, construction workers encounter numerous hazards, such as ladders that are too short to reach the work area, energized electrical lines, or inadequate fall protection. When a hazard is encountered, the worker must make a rapid decision about how to respond and whether to take or avoid the risk. The goal of this researchwas to construct a theory about the influence of decision cues on intuitive and deliberative decision-making in high-hazard construction environments. Drawing from Cognitive Continuum Theory, the study specifies a framework for understanding why and how construction workers make decisions that lead to taking or avoiding physical risks when they encounter daily hazards. A secondary aim of the research was to construct a set of hypotheses about how specific decision cues influence whether a worker is more likely to engage their intuitive impulses or to use careful deliberationwhen responding to a hazard. These hypotheses are described and the efficacy of the hypotheses was evaluated using cross-tabulations and nonparametric measures of association. While most of the associations between decision cues and decision mode (i.e., intuition or deliberation) identified in this data set were generally modest, none of the associations were statistically zero, thus indicating that further research is warranted based on theoretical grounds. The qualitative data set was analysed using Decision Trees and Recognition Primed Decision Models.A rigorous program of theory testing is the next logical step to the research, and the thesis thus concludes with numerous suggestions for extending the research and testing the proposed hypotheses
M.S. in Civil Engineering, December 2013
Show less

Title: FPGA IMPLEMENTATION OF ULTRASONIC FLAW DETECTION ALGORITHM BASED ON SUPPORT VECTOR MACHINE CLASSIFICATION
Creator: Jiang, Yiyue
Date: 2016, 2016-12
Description: In this study, a Support Vector Machine (SVM) classification method used for analyzing Ultrasound signals is implemented by FPGAs based on...
Show moreIn this study, a Support Vector Machine (SVM) classification method used for analyzing Ultrasound signals is implemented by FPGAs based on Xilinx Zynq SoC. The SVM processor aims at classifying A-scan data obtained by an ultrasonic sensor. For reducing development time, hardware software co-design tools such as Xilinx System Generator and Vivado have been used. SVM kernel function is implemented by DSP slices and block RAMs. Advanced Extensible Interface bridges the ARM core and FPGAs for more convenient communication. The main objective of this study is to achieve robust detection of ultrasonic flaw echoes in real-time using an SVM algorithm. The implementation on the FPGA shows that the architecture can be realized with a Xilinx Zedboard FPGA. It runs at 100MHz clock frequency and can calculate the SVM classification for 1024 feature space points under 0.02ms.
M.S. in Electrical Engineering, December 2016
Show less

Title: SERVICEABILITY REQUIREMENTS FOR FLOOR SYSTEMS - A REVIEW OF CURRENT STANDARDS AND PRACTICES
Creator: Jaafari, Chaimaa
Date: 2017, 2017-07
Description: Serviceability requirements are considered in any design to maintain the occupants’ comfort in buildings. Specifically, issues such as floor...
Show moreServiceability requirements are considered in any design to maintain the occupants’ comfort in buildings. Specifically, issues such as floor system deflections and vibrations are two important considerations for design as relate to serviceability. Design codes primarily address the deflection control yet rarely address the vibration. Although the vibration may be related to deflection, maintaining the comfort of occupants will require a detailed study on the level of vibration and its frequency that would be comfortable to the occupants. This research will examine and summarize the serviceability requirements as suggested by various codes and standards and also as suggested by published papers. Specifically, the research focuses on deflection and vibration control for floor systems based on the occupancy and usage and the types of structures and sources of vibrations. Methods to alter existing floor system designs to control vibrations will also be presented. The final research outcome will be a complete document summarizing the findings on what is perceived as good practice for deflection and vibration control for floor system designs in buildings.
M.S. in Civil Engineering, July 2017
Show less

Title: ELECTROCATALYSTS FOR ALKALINE WATER ELECTROCATALYSIS
Creator: Jain, Anchal
Date: 2016, 2016-07
Description: Hydrogen is an attractive energy carrier and is part of an idealistic future wherein it serves as a clean energy source. In the presence of...
Show moreHydrogen is an attractive energy carrier and is part of an idealistic future wherein it serves as a clean energy source. In the presence of oxygen, it can be converted to water in fuel cells with the release of heat and electrical work. Electrolysis of water is an important route to hydrogen generation. Alkaline water electrolysis is preferred over electrolysis in acidic medium due to the possibility of lowering stack costs and enhancing the library of stable electrocatalyst materials available for the electrochemical reactions. The high anode overpotential arising from the sluggish oxygen evolution reaction (OER) has led to significant interest in developing stable and active OER electrocatalysts. IrO2 (state of the art catalyst), RuO2 and PGM-based pyrochlores are suitable catalyst materials that exist today, but there is benefit in finding cost-effective alternatives. In this study, the pyrochlore oxides containing non- Platinum Group Metals (non-PGM) metals were synthesized by solid state reaction and were tested for their OER activity but none of the materials tested, exhibited OER activity and a comparison was attempted between the pyrochlores containing PGM metals as against those containing non-PGM metals. Additionally, perovskite oxides of the form La[Ni(1-x-y)CoxFey]O3 (where 0≤x≤1 and 0≤y≤1) were synthesized by the co-precipitation method. Many of these perovskites exhibited electron conductivities greater than 0.1S/cm, eliminating the need to add carbon for OER studies and implying the likelihood of making conducting electrodes with these materials without the additives like carbon. The perovskites LaNi0.6Co0.4O3 or LaNi0.6Fe0.4O3 with x/y =0.4 had conductivities of the order of 10S/cm. The electrocatalytic activity for the OER was studied using a rotating disk electrode (RDE) in 0.1M KOH and catalyst loading of ~100μg/cm2. The perovskite LaNi0.5Co0.5O3 (x=0.5, y=0) had the onset potential of ~1.50V against RHE, and all these perovskites had onset potentials ~0.1-0.15V higher than the benchmark IrO2 that has an onset potential of ~1.43V. Few of the perovskites were also evaluated for their oxygen reduction activity (ORR) implying that these materials can be used as bi-functional catalysts.
M.S. in Chemical Engineering, July 2016
Show less

Title: DYNAMIC ANALYSIS OF UNCERTAIN STRUCTURES USING IMPRECISE PROBABILIY
Creator: Bergerson, Joshua D.
Date: 2014, 2014-05
Description: A new method for dynamic response spectrum analysis of structures with uncertainty in their mechanical properties utilizing the notion of...
Show moreA new method for dynamic response spectrum analysis of structures with uncertainty in their mechanical properties utilizing the notion of imprecise probability is developed. This finite-element-based method is capable of obtaining probabilistic bounds of the dynamic response of the structure with uncertainty defined by enveloping p-boxes. The developed method obtains probabilistic bounds on 1) the mode shapes, 2) modal coordinates, and 3) modal participation factor, leading to the p-boxes of modal responses. Finally maximum modal responses are combined to obtain the structure’s maximum total response with consideration of uncertainty. Numerical examples demonstrating the developed method are included. Keywords: Structural Dynamics, Uncertainty, Imprecise Probability, P-Box.
PH.D in Civil Engineering, May 2014
Show less

Title: FATIGUE, FRACTURE, AND CRACK GROWTH BEHAVIOR OF FIVE CANDIDATE STEELS FOR WIND TOWER APPLICATION
Creator: Tsosie, Henrietta R.
Date: 2011-08, 2011-07
Description: Fatigue, fracture toughness, and crack propagation tests were performed on five candidate steels for wind tower applications. Normally, these...
Show moreFatigue, fracture toughness, and crack propagation tests were performed on five candidate steels for wind tower applications. Normally, these steels are ordered to meet ASTM A572/A709 Grade 50 or EN 10025-2 Grade S355 in the normalized condition. Five steels with varying carbon content and alloy additions focusing on niobium and vanadium content are investigated. Two of the five steels are in the normalized condition to check the EN 10025-2 requirement while the rest are in the as-rolled condition. Fatigue tests were performed to determine the endurance limit using a constant amplitude loading at a constant load ratio. Fracture toughness testing using the J􀀀 integral method was performed to determine the critical fracture energy, Jc. This value is then converted to the critical plain strain stress intensity factor if requirements are met. Three fracture toughness tests were performed for each material at room temperature using a C(T) specimen. Crack propagation tests were performed to determine the Paris constants using a contoured double cantilever beam specimen. The steels with niobium give better results in fatigue and displayed smaller grain diameters than the steels with vanadium. The fatigue results for the low carbon steel with niobium are comparable to another HPS steel. Overall, the low carbon steel with niobium provides better toughness, fatigue resistance, and weldability than the steels that are normalized to meet the EN 10025-2 requirement for wind tower plates.
M.S. in Materials Science and Engineering, July 2011
Show less

Title: SCALABLE INDEXING AND SEARCHING ON DISTRIBUTED FILE SYSTEMS
Creator: Ijagbone, Itua
Date: 2016, 2016-05
Description: Scientific applications and other High Performance applications generate large amounts of data. It’s said that unstructured data comprises...
Show moreScientific applications and other High Performance applications generate large amounts of data. It’s said that unstructured data comprises more than 90% of the world’s information [IDC2011], and it’s growing 60% annually [Grantz2008]. The large amounts of data generated from computation leads to data been dispersed over the file system. Problems begin to exist when we need to locate these files for later use. For small amount of files this might not be an issue but as the number of files begin to grow as well as the increase in size of these files, it becomes difficult locating these files on the file system using ordinary methods like GNU Grep [8], which is commonly used in High Performance Computing and Many-Task Computing environments. It is as a result of this problem that we have chosen this thesis to tackle the problem of finding files in a distributed system environment. Our work leverages the FusionFS [1] distributed file system and the Apache Lucene [10] centralized indexing engine as a fundamental building block. We designed and implemented a distributed search interface within the FusionFS file system that makes both indexing and searching the index across a distributed system simple. We have evaluated our system up to 64 nodes, compared it with Grep, Hadoop, and Cloudera, and have shown that FusionFS’s indexing capabilities have lower overheads and faster response times.
M.S. in Computer Science, May 2016
Show less

Title: SIMILAR VOICES, SAME PERSPECTIVES? INTERNATIONAL MOVIE REVIEWERS AT THE IMDB
Creator: Gao, Jing
Date: 2012-04-21, 2012-05
Description: Online communities enable people from around the world to interact online. But having the opportunity to speak and being heard are two...
Show moreOnline communities enable people from around the world to interact online. But having the opportunity to speak and being heard are two different issues. In most cases of intercultural communication online, people from different cultures interact in English. Are they still able to bring their own perspectives without using their native language? This study thus focuses on whether or not international voices are heard online and whether or not these voices that find audiences are really differ- ent, as compared to the local voice (i.e., dominant or majority voice). We question whether or not international voices are different, as previous studies on intercultural communication debate over whether or not voices are different by culture. Results of a content analysis show that international and U.S. participants tend to contribute similar content, which contrasts with the common assumption that people from dif- ferent cultures will write differently and resonates with previous studies that have proposed that culture, on its own, is not an effective predictor of online behavior.
M.S. in Technical Communication and Information Design, May 2012
Show less

Title: INVESTIGATION OF PERFORMANCE AND DURABILITY OF POLYMER ELECTROLYTES FOR ELECTROCHEMICAL ENERGY STORAGE AND CONVERSION TECHNOLOGIES
Creator: Jung, Min-suk
Date: 2016, 2016-07
Description: Polymeric ion exchange membranes are integral components of electrochemical conversion/storage devices such as fuel cells, water electrolyzers...
Show morePolymeric ion exchange membranes are integral components of electrochemical conversion/storage devices such as fuel cells, water electrolyzers, and redox flow batteries. There has been dramatic progress in the research and development of cation exchange membranes (CEM). Nafion® (perfluorosulfonic acid membranes) is one example of a state-of-the-art CEM and has been successfully demonstrated in various electrochemical energy devices. Unlike CEMs, anion exchange membranes (AEMs) have been of limited utility to date due to their drawbacks, including poor chemical/mechanical stability and low ionic conductivity. However, alkaline environments result in better activity for electrochemical reactions and afford the possibility of using non-platinum group metal (PGM) electrocatalysts. AEMs, therefore, are still being studied in order to resolve existing challenges in terms of conductivity and stability in alkaline media and in strongly oxidizing solutions. In this work, AEMs derived from different types of polymer backbones were prepared, and their chemical stability and electrochemical property were investigated. Polysulfone (PSF) AEMs were prepared by first chloromethylating polysulfone, then by functionalizing chloromethylated polysulfone (CMPSF) with different base reagents. PSF-trimethylamine (TMA) AEMs showed a 40-fold reduction in vanadium (IV) ion (VO2+) permeability when compared to a Nafion® membrane and exceptional oxidative stability after exposure to a 1.5 M vanadium (V) ion (VO2 +) solution for 90 days. PSF-TMA AEMs were successfully demonstrated in the all-vanadium redox flow battery. Excellent energy efficiencies (>75 %) were attained and sustained over 75 chargedischarge cycles for a vanadium redox flow battery prepared using the PSF-TMA separator. Crosslinking of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) AEMs using diamine was tried with intentions to improve the mechanical stability and electrochemical property of PPO AEM. Crosslinked PPO AEMs (30 ± 4 % at 25 oC) showed less liquid water uptake than non-crosslinked PPO AEMs (46 ± 5% at 25 oC) while maintaining comparable ionic conductivities (hydroxide ion conductivity of 45 mS/cm at 60 oC). Crosslinked PPO AEMs maintained mechanical integrity and still showed some mechanical stability (ultimate tensile strength of 3~4 MPa and elongation at break of 13~17 %) after exposure to 1 M KOH at 60 oC for 14 days, while noncrosslinked PPO AEMs completely lost their mechanical durability. Finally, this dissertation presents research related to perfluorinated AEMs prepared using a Grignard reagent. These membranes exhibited 0.7 mmol/g of Cl- ion exchange capacity (IEC), 20 mS/cm of hydroxide ion conductivity at 20 oC, and 10 % of water uptake at room temperature. The membranes also maintained 90 % of their initial conductivity after an exposure to 1.5 M VO2+ in 3 M H2SO4 solution for seven days.
Ph.D. in Chemical Engineering, July 2016
Show less

Title: DEVELOPING INTELLIGENT AND ADAPTIVE BUILDING SYSTEMS FOR OUR DIGITAL ECOLOGY
Creator: Hansen, Kai
Date: 2013, 2013-07
Description: Our world is being changed by a dynamic digital presence. The marriage of virtual and physical represents an ecology which has become...
Show moreOur world is being changed by a dynamic digital presence. The marriage of virtual and physical represents an ecology which has become intertwined with the lives of nearly everyone, fundamentally altering how our society functions. While we have evolved in this sense, the built environment has become outmoded and strains to meet emerging occupant requirements. To correct this, it has become necessary to develop environments that are capable of intelligently responding to shifting requirements. As curators of the built environment, architects are responsible for seeking out and engaging new mechanisms to achieve spaces that occupants find desirable. An experiential summary of the architectural-digital-hacking process will be given. A more traditional research method was followed when possible while engaged in this learning process. This research focuses on utilizing readily available digital tools that are capable of simultaneously mitigating issues associated with occupant requirements and energy consumption. It will also address shortcomings related to occupant comfort and energy consumption observed in our buildings by producing a series of working prototypes that will be tested and analyzed. Results will be presented, and will consist of components used and how they were used to serve as a reference for future development.
M.S. in Architecture, July 2013
Show less

Title: Sensemaking for Power Asymmetries in Anti-Oppressive Design Practice
Creator: Meharry, Jessica J
Date: 2022
Description: Within professional design practice in capitalist market contexts, the goals of user-centered and human-centered design methodologies is to...
Show moreWithin professional design practice in capitalist market contexts, the goals of user-centered and human-centered design methodologies is to make algorithmically-based technologies understandable for users, satisfy customer needs and desires, and thereby increase corporate profitability. However, there is growing concern that the computational methods, data management, and business models that drive these technologies are leading to global asymmetries of knowledge, information, and power. The asymmetries of power generated by these designed interactions can be considered the kind of wicked problem that design seeks to address. Yet the dominant goals and methods of professional design practice limit their ability to design ethically within market contexts. These methodologies fail to adequately consider systemic context and power relations, potential for bias in algorithmic computation, and specific forms of systemic oppression. These gaps then lead to inadequate design solutions. This study explores these gaps in design methodologies that could be transferable to a range of professional (and non-professional) practices by looking at potential new levers within familiar design methods and their effectiveness as facilitating problem reframing towards equitable solutions. This dissertation advances knowledge in design by exploring how professional designers can better understand how to use sensemaking processes for salience of power asymmetries, algorithmic materiality, and systemic oppression. It proposes an anti-oppressive design framework that is rooted in a critically-informed design praxis. These orientations rethink and recreate design knowledge by helping professional designers shift the market-focused paradigm for which they are designing.
Show less

Title: Non-Hermitian Phononics
Creator: Mokhtari, Amir Ashkan
Date: 2021
Description: Non-Hermitian and open systems are those that interact with their environment by the ﬂows of energy, particles, and information. These systems...
Show moreNon-Hermitian and open systems are those that interact with their environment by the ﬂows of energy, particles, and information. These systems show rich physical behaviors such as unidirectional wave reflection, enhanced transmission, and enhanced sensitivity to external perturbations comparing to a Hermitian system. To study non-Hermitian and open systems, we first present key concepts and required mathematical tools such as the theory of linear operators, linear algebra, biorthogonality, and exceptional points. We first consider the operator properties of various phononic eigenvalue problems. The aim is to answer some fundamental questions about the eigenvalues and eigenvectors of phononic operators. These include questions about the potential real and complex nature of the eigenvalues, whether the eigenvectors form a complete basis, what are the right orthogonality relationships, and how to create a complete basis when none may exist at the outset. In doing so we present a unified understanding of the properties of the phononic eigenvalues and eigenvectors which would emerge from any numerical method employed to compute such quantities. Next, we apply the mentioned theories on the phononic operators to the problem of scattering of in-plane waves at an interface between a homogeneous medium and a layered composite. This problem is an example of a non self-adjoint operator with biorthogonal eigenvectors and a complex spectrum. Since this problem is non self-adjoint, the degeneracies in the spectrum generally represent a coalescing of both the eigenvalues and eigenvectors (exceptional points). These degeneracies appear in both the complex and real domains of the wavevector. After calculating the eigenvalues and eigenvectors, we then calculate the scattered fields through a novel application of the Betti-Rayleigh reciprocity theorem. Several numerical examples showing rich scattering phenomena are presented afterward. We also prove that energy flux conservation is a restatement of the biorthogonality relationship of the non self-adjoint operators. Finally, we discuss open elastodynamics as a subset of non-Hermitian systems. A basic concept in open systems is effective Hamiltonian. It is a Hamiltonian that acts in the space of reduced set of degrees of freedom in a system and describes only a part of the eigenvalue spectrum of the total Hamiltonian. We present the Feshbach projection operator formalism -- traditionally used for calculating effective Hamiltonians of subsystems in quantum systems -- in the context of mechanical wave propagation problems. The formalism allows for the direct formal representation of effective Hamiltonians of finite systems which are interacting with their environment. This results in a smaller set of equations which isolate the dynamics of the system from the rest of the larger problem that is usually infinite size. We then present the procedure to calculate the Green's function of effective Hamiltonian. Finally we solve the scattering problem in 1D discrete systems using the Green's function method.
Show less

Title: AN EXPLORATION INTO THE EFFECTS OF CHROMATIN STRUCTURAL PROTEINS ON THE DYNAMICS AND ENERGETIC LANDSCAPE OF NUCLEOSOME ARCHITECTURES
Creator: Woods, Dustin C
Date: 2022
Description: Comprised of eight core histones wrapped around at least 147 base pairs of DNA, nucleosomes are the fundamental unit the chromatin fiber from...
Show moreComprised of eight core histones wrapped around at least 147 base pairs of DNA, nucleosomes are the fundamental unit the chromatin fiber from which long arrays are built to compact genetic information into the cell nucleus. Structural proteins, such as linker histones (LH) and centromere proteins (CENP), interact with the DNA to dictate the exact architecture of the fiber which can directly influence the regulation of epigentic processes. However, the mechanisms by which structural proteins affect these processes are poorly understood. In this thesis, I will explore the various way in which LHs and CENP-N affect nucleosome and, by extension, chromatin fiber dynamics. First, I present a series of simulations of nucleosomes bound to LHs, otherwise known as chromatosomes, with the globular domain of two LH variants, generic H1 (genGH1) and H1.0 (GH1.0), to determine how their differences influence chromatosome structures, energetics and dynamics. These simulations highlight the thermodynamic basis for different LH binding motifs, and details their physical and chemical effects on chromatosomes. Second, I examine how well the findings above translate from mono-nucleosomes to poly-nucleosome arrays. I present a series of molecular dynamics simulations of octa-nucleosome arrays, based on a cryo-EMstructure of the 30-nm chromatin fiber, with and without the globular domains of the H1 LH to determine how they influence fiber structures and dynamics. These simulations highlight the effects of LH binding on the internal dynamics and global structure of poly- nucleosome arrays, while providing physical insight into a mechanism of chromatin compaction. Third, I took a brief departure from LHs to study the effects that the centromere protein N (CENP-N) has on the poly-nucleosome systems. I present a series of molecular dynamics simulations of CENP-N and di-nucleosome complexes based on cryo- EM and crystal structures provided by Keda Zhou and Karolin Luger. Simulations were conducted with nucleosomes in complex with one, two, and no CENP-Ns. This work, in collaboration with the Karolin Luger Group (University of Colorado – Boulder) and the Aaron Straight Group (Stanford University), represents the first atomistic simulations of this novel complex, providing the foundation for a plethora of future research opportunities exploring centromeric chromatin the effect that its structure and dynamics have on epigenetics. Lastly, I return to the chromatosome to study how DNA sequence affects the free energy surface and detailed mechanism of LH transitions between binding modes. I used umbrella sampling simulations to produce PMFs of chromatosomes wrapped in three different DNA sequences: Widom 601, poly-AT, and poly-CG. This work, my final in the series, represents a culmination of my studies furthering the understanding of biophysical phenomena surrounding LHs and how they can be extrapolated towards epigentic mechanisms. I was able to report on the first PMFs illustrating a previously unknown transition and describe the transition mechanism as it depends on DNA sequence.
Show less

Title: Towards Understanding the Microstructure and Mechanical Properties of Additively Manufactured Ni-base Superalloys
Creator: Tiparti, Dhruv Reddy
Date: 2022
Description: Nickel-base superalloy components such as turbine discs typically undergo numerous manufacturing steps that contribute to increasing the cost...
Show moreNickel-base superalloy components such as turbine discs typically undergo numerous manufacturing steps that contribute to increasing the cost and the waste of excess materials. With advent of fusion based additive of manufacturing (AM) techniques, such components with complex geometry can be fabricated with great efficiency. However due to characteristically high energy densities, fast cooling rate, and layer-by-layer building process associated with AM; Ni-base superalloys with higher temperature performance are difficult to be fabricated by AM due to susceptibility to composition related defect formation, which is further exacerbated by anisotropic grain structures induced by the large thermal gradients present. Crack-free material can be fabricated but, in most cases, issues such as an anisotropic microstructure will prevail, and the balance of mechanical properties achieved may not be suitable for the desired applications. Several strategies exist to mitigate the challenges posed by additive manufacturing via post-processing such as hot-isostatic processing, annealing heat treatments, application of grain refining inoculants, etc. All these strategies utilized to mitigate issues with AM of Ni-base superalloys still require further study to understand their effects on the microstructure and mechanical properties. This work aims to evaluate the use of inoculant particles, and novel heat treatments on the microstructure and mechanical properties of different superalloys. First, the effect of varying amounts of CoAl2O4 inoculant ranging from 0 to 2 wt.% on the microstructure evolution of Inconel 718(IN718) fabricated by selective laser melting (SLM) was evaluated. The findings from this study indicated that additions of CoAl2O4 only resulted in a minor degree of grain refinement with slight increase in anisotropy; in addition, a CoAl2O4 ¬content above 0.2 wt.% resulted in the formation of agglomerate inclusions; and that to effectively utilize CoAl2O4 as a grain refining inoculant, process parameters must be further optimized while considering the formation of agglomerates, and other defects. Second, the application of CoAl2¬O4 was extended towards the Direct Energy Deposition (DED) of IN718. Here findings indicated that due to the modification of the thermophysical properties of the melt pool by oxide addition, an earlier onset of large columnar extending across multiple layers occurred while counteracting conditions required for equiaxed grain formation; and these CoAl2O4 were also found to exhibit a potent Zenner pinning effect that maintained the as-built grain structure despite application of extreme high treatment condition of 1200oC for 4 hrs. Third, the tensile and fatigue properties of the DED IN718 with CoAl2O4 were evaluated. Here, it was found that the addition of CoAl2O4 leads to a minor increase in tensile strength in the as-built condition attributed primarily to the fine oxide dispersion; a more modest increase in tensile strength in the heat-treated condition due to grain refinement induced by retaining the as-built grain structure; and that despite the increase in tensile strength with CoAl2O4 a corresponding increase in fatigue life did not occur. Lastly, the processing of René 65 conducted by laser-powder bed fusion(L-PBF) was done and compared to the conventionally cast and wrought material. Here, the effect of the difference in processing route in conjunction with heat treatments was evaluated to understand the creep and stress relaxation behavior. It was found that L-PBF of René 65 led to an overall improved resistance to deformation by creep and relaxation mechanism.
Show less

Title: The Studio Practice for Sustainable (Craft) Production
Creator: Werdhaningsih, Hendriana
Date: 2022
Description: Craft market demand globally is rising. On the other hand, the domination of economic goals in craft production is threading the social system...
Show moreCraft market demand globally is rising. On the other hand, the domination of economic goals in craft production is threading the social system and the environment. Craft production facts do not represent the sustainable development principles that should be a central concept for this age. Design as practice and method had not yet correctly facilitated craft production to embrace the harmony of the social, environmental, and economic systems. Believing that studio is a core design practice, this research investigated studio practice through interviews, field research, and action research conducted in Indonesia and the US. It developed a model called Studio Practice for Sustainable (Craft) Production, the SP2 Model. The Model helps designers, the crafts community, and stakeholders ensure their role in the studio practice and determine their goals for sustainable development. The SP2 Model offers alternative practical solutions in craft production, contributes to polycentric discourse, and designs interventions in sustainable development models.
Show less

Title: Quantum Computation for the Understanding of Mass: Simulating Quantum Field Theories
Creator: Rivero Ramírez, Pedro
Date: 2021
Description: This thesis demonstrates the production of hadron mass on a quantum computer. Working in the Nambu–Jona-Lasinio model in 1+1 dimensions and 2...
Show moreThis thesis demonstrates the production of hadron mass on a quantum computer. Working in the Nambu–Jona-Lasinio model in 1+1 dimensions and 2 flavors, I show a separation of the contribution of quark masses and interactions to the mass. Along the way I develop a new tool called Quantum Sampling Regression (QSR) that allows for an optimal sampling of low qubit quantum computers when using hybrid variational eigenvalue solving techniques. I demonstrate the regime where QSR dominates the current standard Variational Eigensolver Technique, and benchmark it by improving the calculation of deuteron binding energy. Finally, I developed QRAND — a multiprotocol and multiplatform quantum random number generation framework — in support of the quantum computing community.
Show less

Title: ELECTROSPUN SILKWORM SILK FIBROIN - INDOCYANINE GREEN BIOCOMPOSITE FIBERS: FABRICATION, CHARACTERIZATION AND APPLICATION TOWARDS HEMORRHAGE CONTROL
Creator: Siddiqua, Ayesha
Date: 2022
Description: Silk fibroin (SF), a structural protein found in the Bombyx mori cocoons has gained attention in several biomedical applications as tissue...
Show moreSilk fibroin (SF), a structural protein found in the Bombyx mori cocoons has gained attention in several biomedical applications as tissue engineering scaffolds and wound dressings owing to its properties such as biocompatibility, water vapor permeability and biodegradability. Indocyanine Green (ICG) is an FDA approved tricarbocyanine dye used in medical diagnostics due to its unique photothermal and fluorescent properties. Electrospinning is a highly efficient, easy, and inexpensive technique used to generate nanometer to micrometer thick fibers. In this study, SF and ICG were co-spun to generate flexible microfibers with high surface area to volume ratios. Pure silk, SF-ICG (0.1%) and SF-ICG (0.4%) were chosen for the purpose of this study. Since, as-spun fibers are unstable in aqueous solutions, post treatment methods were explored to enhance the durability of the fibers and to minimize ICG leaching. It was found that ethanol vapor treatment (EVT) not only induced β-sheet formation in SF but also improved the SF-ICG interaction thereby reducing ICG leaching from the composite fibers. Ethanol vapor treated SF-ICG fibers showed less ICG leaching than liquid ethanol treated (LET) SF-ICG fibers indicating the efficacy of the EVT. The increase in SF solution viscosity with ICG concentration suggested a strong silk-ICG interaction which was further confirmed by DSC. The 1h water uptake and the three-day mass loss experiments indicated that the fibers are stable and highly absorbent material. Heat evolution was evaluated by measuring the temperature change in water of a fixed volume after irradiation with a 500 mW, 808 nm diode laser. The heat evolved by the flat fiber scaffolds was higher than the 3D fiber balls, indicating improved light penetration in the former. Pure silk produced negligible heat and it was used as a control. With 14.9 W/cm2 irradiation, the post-treated SF-ICG (0.4%) 3D fibrous ball of 2-3 mg dry weight, solidified a drop of bovine blood in 40 s. In contrast, a single layer fiber matrix required 3 min. to achieve the same clotting effect. Fibers folded into flat scaffolds were able to solidify a blood drop in 25 s. Pure silk fibers in all the cases showed negligible change after irradiation. The results suggest that a larger contact area of fibers is desirable for faster blood clotting, and EVT prompted better ICG retention in SF fibers. Based on the above results, SF-ICG (0.4%) fibers were utilized in a device developed to mimic blood flowing at a rate of 0.5 mL/h through a damaged blood vessel. It was found that irradiation of SF-ICG locally placed at the “damage” region effectively stopped “bleeding” whereas irradiated pure silk was unable to control the blood flow, which demonstrated the success of our SF-ICG fibers towards hemorrhage control.
Show less

Title: Advanced methods for storage ring nonlinear beam dynamics design and implementation
Creator: Song, Minghao
Date: 2022
Description: To meet the increasing demands of scientific researchers for brighter photonbeams, storage ring beam emittance is continually pushed down to a...
Show moreTo meet the increasing demands of scientific researchers for brighter photonbeams, storage ring beam emittance is continually pushed down to a new ultra-low level. It, therefore, becomes correspondingly more challenging to ensure such storage rings have good nonlinear beam dynamics performance. This thesis work is focused on developing advanced methods for low emittance storage ring nonlinear beam dynamics design and implementation.Nonlinear beam dynamics optimization is essential to low emittance storagering design. A highly efficient multi-objective optimization algorithm is needed to simultaneously achieve a large dynamic aperture and a large local momentum aperture. Work was done to improve and test a machine learning-based algorithm called multi-generation Gaussian process optimizer (MG-GPO). This advanced method uses constructed GP models to pre-select solutions, and benchmarking of results on toy problems shows that MG-GPO converges significantly faster than traditional algorithms. The MG-GPO algorithm was successfully applied to nonlinear lattice design optimization, for example, to the SPEAR3 upgrade 7-nm lattice, and it was demonstrated to converge faster than NSGA-II and MOPSO. This was due to its capability of selecting candidates that tend to have better performance. This algorithm will help accelerate nonlinear lattice studies.Correction of nonlinear beam dynamics is also important for low emittancestorage ring commissioning and operation. In order to measure and correct features relevant to the nonlinear beam dynamics, an effective method is needed to excite sustained beam oscillations to large amplitude. A method based on the concept of autoresonance was proposed. This advanced technique excites nonlinear transverse beam motion in storage rings by sweeping the drive frequency. The theory for the autoresonance threshold was derived for the nonlinear optics systems in storage rings, both with and without damping effects, using Hamiltonian dynamics. The theoretical predictions for the drive amplitude threshold were found to agree well with simulations for a simple storage ring model, as well as for simulations with the actual SPEAR3 and APS lattices. The theory was also compared favorably to historical data from experiments on SPEAR3. Simulations verified that an oscillation driven by autoresonant excitation matches the character of a free oscillation, so that beam oscillation data taken during the ramping process can confidently be used to characterize the nonlinear beam dynamics performance. The precision of measurements can be improved by using autoresonant excitation since large amplitude beam oscillations are sustained significantly longer. Simulations of autoresonant excitation demonstrated the measurements of the detuning coefficients and resonance driving terms. The use of autoresonant excitation for the detection of faulty magnets and correction of resonance driving terms was also demonstrated.Online optimization is an alternative way to effectively improve nonlinear beamdynamics performance in a real storage ring. The greater efficiency of an advanced optimization algorithm is also needed to find globally optimal solutions in the limited experimental time that is typically available. The MG-GPO algorithm was implemented for SPEAR3 vertical emittance minimization and injection efficiency optimization. Again, the optimized solutions demonstrate that MG-GPO is more efficient than the commonly used PSO algorithm. SPEAR3 performance was successfully improved during the online optimization runs with MG-GPO.
Show less

Title: EXAMINING PERFORMANCE DEGRADATION OF LI-ION BATTERIES WITH SILICON-BASED ANODE AND POSSIBLE SOLUTIONS TO IMPROVE THE SILICON ANODE BEHAVIOR
Creator: Luo, Mei
Date: 2022
Description: Si has been investigated as a promising alternative to conventional graphite because of its high specific capacity and wide operating voltage;...
Show moreSi has been investigated as a promising alternative to conventional graphite because of its high specific capacity and wide operating voltage; however, technical challenges related to volume change in the silicon anode have hampered their practical application. In this work, the effects of silicon volume change on electrochemical performance has been studied in NMC532/Si full cells. First, different area specific capacity ratios of the negative to positive electrode (N:P ratio) were investigated using three-electrode cells. With individual electrode potentials monitored by a reference electrode, different depths of lithiation/delithiation at the anode and cathode were found to play an important role on cell performance; the cell with higher N:P ratio displays superior electrochemical performance due to its smaller silicon volume change. Further, calendar-life aging and cycle-life aging of NMC532/Si cells were compared with their electrode potentials monitored using a reference electrode. The observation of larger capacity decay and impedance growth of cycle-life aging cells illustrates the important effect of silicon volume change; significant capacity decay of calendar-life aged cell was observed as well, revealing an essential role of chemical effect of ongoing side reactions at Si anode. Specially-designed silicon with different protocols and electrolyte additives were investigated to address the intrinsic challenges of Si anodes for lithium-ion batteries.
Show less

repository.iit

Search the repository

Pages

Pages