Search results

Title: Advanced models for turbulent spray and combustion simulations
Creator: Irannejad, Abolfazl
Date: 2013
Collection: Electronic Theses & Dissertations
Description: A high-fidelity two-phase large eddy simulation (LES)/filtered mass density function (FMDF) model is developed and used for detailed simulations of turbulent spray breakup, evaporation and combustion. The spray is simulated with Lagrangian droplet transport, stochastic breakup, wake, collision/coalescence and finite rate heat and mass transfer submodels. The spray/droplet model is used together with a compressible LES gas flow model for numerical simulations of high pressure liquid jets...
Show moreA high-fidelity two-phase large eddy simulation (LES)/filtered mass density function (FMDF) model is developed and used for detailed simulations of turbulent spray breakup, evaporation and combustion. The spray is simulated with Lagrangian droplet transport, stochastic breakup, wake, collision/coalescence and finite rate heat and mass transfer submodels. The spray/droplet model is used together with a compressible LES gas flow model for numerical simulations of high pressure liquid jets sprayed into a high temperature and pressure gas chamber. Various non-evaporating and evaporating sprays at different ambient gas pressures and temperatures (all without reaction) are simulated. The numerical results are compared with the available experimental data for global spray variables such as the spray penetration length and droplet Sauter mean diameter (SMD). In all cases, the gas velocity and turbulence generated by the spray are found to be very significant. A broad spectrum of droplet sizes is also generated by the complex and coupled effects of the gas flow turbulence, droplet breakup and evaporation. Droplet-wake interactions are shown to play an important role in the spray evolution. The effect of subgrid turbulence model on the global spray features, like the spray penetration, is also very significant at lower gas temperatures. The interaction of the induced gas flow turbulence with the spray is studied at different chamber densities and temperatures as well as different nozzle sizes and injection pressures. It is indicated that the local rate of evaporation and its interaction with the gas density field are the key factors that control the induced gas turbulence and its interaction with the spray. It is shown that spray with a larger nozzle induces higher turbulence due to increase in local evaporation rate of small droplets by the higher entrained gas. Our results also indicate that spray penetration remains unchanged with variation in injection pressure due to competing factors of evaporation and vapour convection. The developed spray LES model is coupled with the two-phase FMDF model for simulation of high speed spray combustion. The FMDF is a subgrid-scale probability density function (PDF) model for LES of turbulent reacting flows and is obtained by the solution of a set of stochastic differential equations by a Lagrangian Monte Carlo method. Complex skeletal kinetics models are used for the chemical reaction together with in situ adaptive tabulation (ISAT) and chemistry workload balancing for efficient parallel computations. Simulations of evaporating sprays with and without combustion indicate that the two-phase LES/FMDF results are consistent and compare well with the available experimental data for the ignition delay time and flame liftoff lengths at different ambient gas temperatures and oxygen concentrations. It is shown that for low to moderately high ambient gas temperatures, the auto-ignition occurs at the tip of spray vapour jet where there is considerable spray-induced gas turbulence and fuel-air mixing. The LES/FMDF results for ignition delay show more sensitivity to the chemical kinetics model at lower gas temperatures due to slower reaction and stronger turbulence-chemistry interactions. The liftoff length is less sensitive to the kinetics. The spray controlled flame tends to move away from a diffusion flame structure toward a premixed one as the oxygen concentration decreases and/or the ambient gas temperature increases because of changes in spray-induced turbulence and mixing. A moderately dense droplet laden planar jet is also simulated by the LES/FMDF model for detailed study of the liquid volume fraction effects. It is indicated that the neglect of liquid volume fraction will lead to excessive evaporation and turbulence modulation. On the other hand, the volume displaced by the dispersed droplets increases the entrained gas to the droplet laden jet. It is shown that for LES/FMDF model to be consistent and accurate, it is necessary to include the volume fraction into the FMDF equation.
Show less

Title: Evolutionary multi-objective bi-level optimization for efficient deep neural network architecture design
Creator: Lu, Zhichao
Date: 2020
Collection: Electronic Theses & Dissertations
Description: Deep convolutional neural networks (CNNs) are the backbones of deep learning (DL) paradigms for numerous vision tasks, including object recognition, detection, segmentation, etc. Early advancements in CNN architectures are primarily driven by human expertise and elaborate design. Recently, neural architecture search (NAS) was proposed with the aim of automating the network design process and generating task-dependent architectures. While existing approaches have achieved competitive...
Show moreDeep convolutional neural networks (CNNs) are the backbones of deep learning (DL) paradigms for numerous vision tasks, including object recognition, detection, segmentation, etc. Early advancements in CNN architectures are primarily driven by human expertise and elaborate design. Recently, neural architecture search (NAS) was proposed with the aim of automating the network design process and generating task-dependent architectures. While existing approaches have achieved competitive performance, they are still impractical to real-world deployment for three reasons: (1) the generated architectures are solely optimized for predictive performance, resulting in inefficiency in utilizing hardware resources---i.e. energy consumption, latency, memory size, etc.; (2) the search processes require vast computational resources in most approaches; (3) most existing approaches require one complete search for each deployment specification of hardware or requirement. In this dissertation, we propose an efficient evolutionary NAS algorithm to address the aforementioned limitations. In particular, we first introduce Pareto-optimization to NAS, leading to a diverse set of architectures, trading-off multiple objectives, being obtained simultaneously in one run. We then improve the algorithm's search efficiency through surrogate models. We finally integrate a transfer learning scheme to the algorithm that allows a new task to leverage previous search efforts that further improves both the performance of the obtained architectures and search efficiency. Therefore, the proposed algorithm enables an automated and streamlined process to efficiently generate task-specific custom neural network models that are competitive under multiple objectives.
Show less

Title: Exploiting impulsive inputs for stabilization of underactuated robotic systems : theory and experiments
Creator: Kant, Nilay
Date: 2020
Collection: Electronic Theses & Dissertations
Description: Robots have become increasingly popular due to their ability to perform complex tasks and operate in unknown and hazardous environments. Many robotic systems are underactuated i.e., they have fewer control inputs than their degrees-of-freedom (DOF). Common examples of underactuated robotic systems are legged robots such as bipeds, flying robots such as quadrotors, and swimming robots. Due to limited control authority, underactuated systems are prone to instability. This work includes...
Show moreRobots have become increasingly popular due to their ability to perform complex tasks and operate in unknown and hazardous environments. Many robotic systems are underactuated i.e., they have fewer control inputs than their degrees-of-freedom (DOF). Common examples of underactuated robotic systems are legged robots such as bipeds, flying robots such as quadrotors, and swimming robots. Due to limited control authority, underactuated systems are prone to instability. This work includes impulsive inputs in the set of admissible controls to address several challenging control problems. It has already been shown that continuous-time approximation of impulsive inputs can be realized in physical hardware using high-gain feedback.Stabilization of an equilibrium point is an important control problem for underactuated systems. The ability of the system to remain stable in the presence of disturbances depends on the size of the region of attraction of the stabilized equilibrium. The sum of squares and trajectory reversing methods are combined to generate a large estimate of the region of attraction. This estimate is then effectively enlarged by applying the impulse manifold method to stabilize equilibria from points lying outside the estimated region of attraction. Simulation results are provided for a three-DOF tiptoebot and experimental validation is carried out on a two-DOF pendubot. Impulsive inputs are also utilized to control the underactuated inertia-wheel pendulum (IWP). When subjected to impulsive inputs, the dynamics of the IWP can be described by algebraic equations. Optimal sequences of inputs are designed to achieve rest-to-rest maneuvers and the results are applied to the swing-up control problem. The novel problem of juggling a devil-stick using impulsive inputs is also investigated. Impulsive forces are applied to the stick intermittently and the impulse of the force and its point of application are modeled as inputs to the system. A dead-beat design for one of the inputs simplifies the control problem and results in a discrete linear time invariant system. To achieve symmetric juggling, linear quadratic regulator (LQR) and model predictive control (MPC) based designs are proposed and validated through simulations.A repetitive motion is described by closed orbits and therefore, stabilization of closed orbits is important for many applications such as bipedal walking and steady swimming. We first investigate the problem of energy-based orbital stabilization using continuous inputs and intermittent impulsive braking. The orbit is a manifold where the active generalized coordinates are fixed and the total mechanical energy of the system is equal to some desired value. Simulation and experimental results are provided for the tiptoebot and the rotary pendulum, respectively. The problem of orbital stabilization using virtual holonomic constraints (VHC) is also investigated. VHCs are enforced using a continuous controller which guarantees existence of closed orbits. A Poincare section is constructed on the desired orbit and the orbit is stabilized using impulsive inputs which are applied intermittently when the system trajectory crosses the Poincare section. This approach to orbital stabilization is general, and has lower complexity and computational cost than control designs proposed earlier.
Show less

Title: INVESTIGATION INTO THE DYNAMIC AND STRUCTURAL PROPERTIES OF THE LITHIUM GARNET SERIES (Li7-xLa3Zr2-xTaxO12, x = 0-2) : A COMBINED MOLECULAR DYNAMICS AND QUASI-ELASTIC NEUTRON SCATTERING STUDY
Creator: Klenk, Matthew
Date: 2019
Collection: Electronic Theses & Dissertations
Description: The lithium garnet series Li7-xLa3Zr2-xTaxO12 (x = 0-2) has shown great promise as a solid electrolyte material, however the room temperature conductivity is currently too low to find wide commercial success. In order to better understand the mechanisms of ionic diffusion within the crystal, a combined molecular dynamics and quasi-elastic neutron scattering (QENS) study was investigated. Using molecular dynamics simulations, we are able to easily probe atomic scale events that are usually...
Show moreThe lithium garnet series Li7-xLa3Zr2-xTaxO12 (x = 0-2) has shown great promise as a solid electrolyte material, however the room temperature conductivity is currently too low to find wide commercial success. In order to better understand the mechanisms of ionic diffusion within the crystal, a combined molecular dynamics and quasi-elastic neutron scattering (QENS) study was investigated. Using molecular dynamics simulations, we are able to easily probe atomic scale events that are usually difficult to examine experimentally. Like the local arrangement of lithium on its sublattice, or how the trajectory of lithium ions is affected by the nearest neighbor sites. The QENS experiment directly measures the dynamic structure factor S(Q,ω), which is capable of capturing both the residence time and mean jump distance experimentally allowing us to directly compare experimental and simulated intermediate scattering functions I,(Q,t). Overall, we saw good agreement between the two techniques, both predicting a jump-diffusion model in the form described by Singwi and Sjölander.Three different simulation models were employed in this study, two using classical molecular dynamics (MD), while a third using density functional theory (DFT) based calculations. All three model types are used to first better understand the phase transformation behavior for the end member composition Li7La3Zr2O12, which undergoes a characteristic phase transformation from an ordered tetragonal to disordered cubic phase at 900 K. First DFT methods are used to better understand what role the selection of an electron exchange-correlation functional plays on the accuracy of lattice parameter and phase transformation behavior. In total 14 different functional forms are investigated. Similarly, two different classical MD models, one being a “core-shell” model, where each atomic nucleus is connected by a spring potential to an electron shell that can capture the polarization of species, while the other being a “core-only” model that treats each atom as a point charge, which can be used for larger and faster simulations. The dynamics of the two end member compositions Li5La3Ta2O12 (L5LT) and Li7La3Zr2O12 (L7LZ), were looked at using the core-shell model with respect to properties like the conductivity, self-diffusivity, thermodynamic correction factor, and entropy of configuration. While the core-only model is used to investigate the finite-size effects of atomic simulation, by changing the number of particles within the simulation by using four different crystal sizes for L7LZ. Simulation cells consisting of 1×1×1 (192 atoms), 2×2×2 (1536 atoms), 3×3×3 (5184 atoms), and 4×4×4 unit cells (12288 atoms) were generated in order to find convergent behavior to the properties highlighted above. Having determined a 3 x 3 x 3 simulation provides adequate accuracy, a verity of garnet compositions corresponding to [Li] = 5, 5.5, 6, 6.25, 6.5, 6.75, & 7 were generated to determine the optimal composition for use as an electrolyte material. Our simulations predict that the best performing room temperature composition corresponds to when [Li] = 6.5 corresponding to the maximum lithium concentration that results in a disordered cubic phase at room temperature. Lastly, we look at the role lithium disorder plays in the phase transformation behavior of L7LZ, and the use of excess entropy calculations as a means of determining the performance of an electrolyte material.
Show less

Title: Ionic Polymer-Metal Composite (IPMC) : Modeling and Bio-inspired Sensing Applications
Creator: Sharif, Montassar Aidi
Date: 2019
Collection: Electronic Theses & Dissertations
Description: Ionic polymer-metal composite (IPMC) is a class of electroactive polymers with built-in actuation and sensing capabilities. In this dissertation, the modeling and several bio-inspired sensing applications of IPMC are investigated computationally and experimentally. First, physics-based modeling is studied for a tubular IPMC sensor under pure torsional stimulus. With inspiration from the fish lateral line system, IPMC is then explored for several flow-sensing applications, where modeling of...
Show moreIonic polymer-metal composite (IPMC) is a class of electroactive polymers with built-in actuation and sensing capabilities. In this dissertation, the modeling and several bio-inspired sensing applications of IPMC are investigated computationally and experimentally. First, physics-based modeling is studied for a tubular IPMC sensor under pure torsional stimulus. With inspiration from the fish lateral line system, IPMC is then explored for several flow-sensing applications, where modeling of fluid-structure interactions, sensor design, and experimental validation are conducted. Specifically, the sensitivities of IPMC-based artificial superficial and canal neuromasts are examined in terms of their dimensions, shapes, and stiffness properties. A canal lateral line-inspired pressure sensor is further proposed and developed. Another novel flow velocity sensor is proposed, which exploits self-generated von Kármán vortices to produce vibrations that are correlated with the flow speed. Finally, inspired by the vestibular system, an angular acceleration sensor is proposed by integrating IPMC sensors with a fluid-filled circular channel. These contributions are further elaborated below. Firstly, the Poisson-Nernst-Planck (PNP) model is used to describe the fundamental physics within the tubular IPMC under torsional excitation, where it is hypothesized that the anion concentration is coupled to the sum of shear strains induced by the torsional stimulus. Finite element simulation is conducted to solve for the torsional sensing response, where some of the key parameters are identified based on experimental measurements using an artificial neural network. Additional experimental results suggest that the proposed model is able to capture the torsional sensing dynamics for different amplitudes and rates of the torsional stimulus.Secondly, Inspired by the fish lateral line system, the sensitivity of IPMC-based artificial superficial and canal neuromasts are examined in terms of their dimensions, shapes, and stiffness properties. The PNP model is again used to describe the fundamental physics within the IPMC, where the bending stimulus due to the cupula displacement is coupled to the PNP model through the cation convective flux term. Comparison of the numerically computed cupula displacement with an analytical approximation is conducted.Thirdly, a novel pressure difference sensor inspired by the canal lateral line is proposed. The sensor output is experimentally characterized as the fish-like body is rotated with respect to a dipole source, which confirms that the sensor is capable of capturing the pressure between the two pores. Finite element modeling that capture fluid-structure interactions and IPMC physics are conducted to shed light on the sensor behavior. Finally, the utility of the sensor in underwater robotics is illustrated via orientation of the fish-like body towards the dipole source using feedback from the proposed sensor.Fourthly, a novel IPMC flow sensor is proposed that exploits self-generated von Kármán vortices to produce vibrations, the frequency and amplitude of which are correlated with the stream flow. Experiments are conducted in a flow channel to measure the IPMC output and the free-end displacement of the sheath under different flow speeds. The results indicate that the proposed sensor structure can produce significant oscillatory signals for effectively decoding the flow speed. Finally, inspired by the vestibular system, an angular acceleration sensor by exploiting IPMC sensor is proposed. The sensor has one 3D-printed circular canal filled with a viscous fluid. Experimental results involving different angular acceleration stimuli show that the proposed sensor is able to capture the angular acceleration for different rates of rotational stimulus. Finite-element simulation is conducted to provide insight into the experimental~ observations.
Show less

Title: Living-learning communities as an intervention to improve disciplinary retention and learning outcomes in engineering education
Creator: Micomonaco, Justin
Date: 2011
Collection: Electronic Theses & Dissertations
Description: The challenge and impetus to increase both the quantity and quality of engineers in the United States is well-documented (Committee on Prospering in the Global Economy of the 21st Century, 2007; National Academy of Engineering, 2004; NSB, 2008). There have been considerable efforts to recruit students to engineering, yielding modest results (Seymour, 2002; NSB, 2008). However, the increase in enrollment has not coincided with a parallel increase in engineering graduates, indicating that...
Show moreThe challenge and impetus to increase both the quantity and quality of engineers in the United States is well-documented (Committee on Prospering in the Global Economy of the 21st Century, 2007; National Academy of Engineering, 2004; NSB, 2008). There have been considerable efforts to recruit students to engineering, yielding modest results (Seymour, 2002; NSB, 2008). However, the increase in enrollment has not coincided with a parallel increase in engineering graduates, indicating that retention is the core issue.At the same time, the field of engineering has been responding to calls for educational reform from within the discipline and industry (Prados et al., 2005). An increasingly complex economy demands a broadening of the intended learning outcomes and a move toward outcomes-based assessment of engineering programs (ABET, 1995; 1997; Kastenberg, et al., 2006; National Academy of Engineering, 2004). As a result, the accrediting body ABET issued a new set of learning outcomes and assessment criteria that subsequently spurred innovation in engineering education.The influential work of Seymour and Hewitt (1997) on students who switch out of STEM fields identified classroom experiences as the primary cause of disciplinary departure. As a result, reform efforts focused primarily on classroom interventions (e.g., Coward, Ailes & Bardon, 2000; Sheppard et al., 2009) because addressing deficiencies in pedagogy and curriculum could yield improvement not only in student learning but also in disciplinary retention. Despite research confirming the link between certain types of classroom innovations (e.g., active learning) and improved retention and learning gains (Felder, 1995; Felder, Felder & Dietz, 1998; Smith et al., 2004), inertia and the culture of faculty work has prevented widespread adoption of these practices. Accordingly, non-classroom interventions such as living-learning communities (LLCs) should be considered as part of the solution.The purpose of the study was to examine the effect of LLCs on disciplinary retention and learning outcomes in engineering. I identified the differences between LLC participants and non-participants in terms of (a) pre-college characteristics, (b) indirect measures of persistence, (c) direct measures of persistence, and (d) learning outcomes. I compared these groups using chi-square analyses, t-tests, and regression modeling, including measures of change over time. The results of this study identified some differences between the two groups on pre-college characteristics in terms of demographic representation, the process of choosing engineering as a major, and expectations for college. On indirect persistence measures, LLC participants reported stronger connections to other undergraduate engineers and greater commitment to engineering. Moreover LLC participants experienced more significant gains over time on three measures: (a) Commitment to Engineering, (b) Connection to Engineering College and (c) Connection to Engineering Peers. These results suggest that the LLC may have a differential impact on participants in these domains. On direct persistence measures, LLC participants differed from non-participants on only one measure: choice of major in sophomore year. The retention rate for LLC participants was 85.1% compared to 76.1% for non-participants. Finally LLC participants and non-participants did not differ on learning outcomes measures for the most part, although LLC participants reported more significant gains over time on the Leadership construct.
Show less

Title: Modeling the movement of water, bacteria and nutrients across heterogeneous landscapes in the Great Lakes region using a process-based hydrologic model
Creator: Niu, Jie
Date: 2013
Collection: Electronic Theses & Dissertations
Description: The development and application of process-based hydrologic models (PBHMs) continues to be a topic of significant interest to the hydrologic community. Although numerous studies have applied PBHMs at small scales ranging from plot and field scales to small-watershed scales, the application of PBHMs to understand large-scale hydrology remains a topic that is relatively unexplored. Understanding controls on large-scale hydrology is key to climate change assessments and effective water resources...
Show moreThe development and application of process-based hydrologic models (PBHMs) continues to be a topic of significant interest to the hydrologic community. Although numerous studies have applied PBHMs at small scales ranging from plot and field scales to small-watershed scales, the application of PBHMs to understand large-scale hydrology remains a topic that is relatively unexplored. Understanding controls on large-scale hydrology is key to climate change assessments and effective water resources management; therefore, to quantify the nature and magnitude of fluxes in regional Great Lakes watersheds, we use a new distributed hydrologic model (PAWS+CLM). Here we describe the application of the model to several large watersheds in the State of Michigan including the Grand River, Saginaw Bay, Kalamazoo and Red Cedar River watersheds and evaluate model performance by comparing model results with different types of data including point measurements of streamflows, groundwater heads, soil moisture, soil temperature as well as remotely-sensed datasets for evapotranspiration (ET) and land water thickness equivalent (GRACE). We then report a budget analysis of major hydrologic fluxes and compute annual-average fluxes due to infiltration, ET, surface runoff, sublimation, recharge, and groundwater contributions to streams etc. as percentage of precipitation and use this information to understand the inter-annual variability of these fluxes and to quantify storage in these large watersheds. After testing the model for its ability to describe hydrologic fluxes and states, we describe the development of solute transport models at the watershed scale by using a mechanistic, reactive transport modeling framework in which the advection, dispersion and reaction steps are solved using an operator-splitting strategy. The solute transport models are tested extensively using available analytical solutions for different hydrologic domains and then applied to describe transport with surface - subsurface interactions and to describe the fate and transport of fecal indicator bacteria such as Escherichia coli in the Red Cedar River watershed in Michigan. Following the successful application of the bacterial fate and transport model, we describe detailed reactive transport modules for predicting the levels of nutrients (N and P). The models are tested using available field observations for the Kalamazoo River watershed in Michigan. The watershed-scale fate and transport modules are expected to aid management by quantifying the impacts of upstream watershed influences on water quality in downstream receiving water bodies such as lakes and oceans. Together with the flow modules they represent a comprehensive suite of process-based models to describe the terrestrial hydrologic cycle coupled with vegetation/land surface and biogeochemical processes.
Show less

Title: Performance and stability study of solid oxide fuel cell nanocomposite electrodes
Creator: Zhang, Yubo
Date: 2020
Collection: Electronic Theses & Dissertations
Description: As a chemical to electricity energy conversion technology, solid oxide fuel cells (SOFCs) must be operated at relatively high temperatures due to the high resistance of their electrodes. The low specific surface area caused by high sintering temperature during electrode fabrication, along with the poor catalytic ability of electrode materials, were the reason for the poor SOFC electrode performance. With the development of highly active electrode materials and new electrode synthesis methods...
Show moreAs a chemical to electricity energy conversion technology, solid oxide fuel cells (SOFCs) must be operated at relatively high temperatures due to the high resistance of their electrodes. The low specific surface area caused by high sintering temperature during electrode fabrication, along with the poor catalytic ability of electrode materials, were the reason for the poor SOFC electrode performance. With the development of highly active electrode materials and new electrode synthesis methods like precursor solution infiltration, nano-sized, highly catalytically active materials like La0.6Sr0.4Co0.8Fe0.2O3- (LSCF), Sm0.5Sr0.5CoO3- (SSC) and Gd0.1Ce0.9O2 (GDC) have all been successfully fabricated at relatively low temperatures. A new “nano-composite” structure for SOFC electrodes, where nano-sized electrode catalysts are added into micron-sized ionic conducting (IC) materials using precursor solution infiltration, has greatly improved the electrode performance and reduced the operating temperature for SOFCs due to the large number of active reaction sites for nano-sized electrode catalysts and the fast oxygen ion transport pathway provided by the sintered IC substrates.Despite the improved electrode performance, lower operating temperatures are still desired so that cheaper materials for SOFC sealants and interconnects can be used, which will bring down the overall SOFC electricity generation cost. Moreover, long-term stability for these nano-composite electrodes is still a problem. Even at reduced operating temperatures, particle coarsening and surface cation segregation were still reported for common SOFC electrodes, compromising their electrochemical performance over time.For the work in this thesis, it is hypothesized that surface decoration methods can alter the electrochemical performance and long-term stability of SOFC nano-composite cathodes (NCCs) by changing their surface chemistry and structure. Electrochemical Impedance Spectroscopy analysis, as well as surface and composition characterization methods such as Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy analysis were conducted to test this hypothesis. Surface decoration methods like atomic layer deposition (ALD) and GDC pre-infiltration were conducted on LSCF-GDC NCCs. 1-5 nm ZrO2 ALD overcoats reduced the degradation rate of LSCF-GDC NCCs without significantly altering their initial polarization resistance (RP), while GDC pre-infiltration reduced both the RP and the degradation rate for LSCF-GDC NCCs. In both cases the decrease in SrCO3 concentration was observed after aging, which cleaned up the LSCF surface and resulted in better stability. GDC pre-infiltration was also performed on SSC-GDC NCCs. With little SrCO3 impurity phase formed during precursor solution firing, no RP or durability enhancement effect was observed. Moreover, ALD and GDC pre-infiltration were performed together for LSCF-GDC NCCs. Higher degradation rates were observed compared with uncoated cells and the reason was believed to be the reaction between ZrO2 overcoats and nano-sized GDC particles during aging, which compromised their “SrCO3 reduction” capability. Finally, precursor solution infiltration was used to fabricate SOFC anodes and symmetric anode tests showed lower anode RP for the infiltrated anodes compared with commercial ones. Ni infiltration was also conducted on commercial Ni- (Y2O3)0.08(ZrO2)0.92 (YSZ) anodes and peak power density of the anode infiltration commercial SOFCs was significantly increased compared with un-infiltrated ones.
Show less

Title: Understanding work with data in summer STEM programs through an experience sampling method approach
Creator: Rosenberg, Joshua M.
Date: 2018
Collection: Electronic Theses & Dissertations
Description: Data-rich activities provide an opportunity to develop core competencies in both science and mathematics identified in curricular standards. Perhaps even more importantly work with data puts learners in the position to use data to ask and answer questions, a potentially empowering capability. Research on work with data has focused on cognitive outcomes and the development of specific practices at the student and classroom levels, and yet, little research has considered learners’ engagement....
Show moreData-rich activities provide an opportunity to develop core competencies in both science and mathematics identified in curricular standards. Perhaps even more importantly work with data puts learners in the position to use data to ask and answer questions, a potentially empowering capability. Research on work with data has focused on cognitive outcomes and the development of specific practices at the student and classroom levels, and yet, little research has considered learners’ engagement. The present study explores learners engagement in work with data in the context of summer STEM programs. The aspects of work with data that are the focus of this study are: asking questions, observing phenomena, constructing measures and generating data, data modeling, and interpreting findings. Data from measures of learners' engagement was collected through the Experience Sampling Method (ESM) that involves asking learners at random intervals to answer short questions about their engagement to discover profiles of learners' engagement.Data was collected from nine summer STEM programs over four weeks in the Northeastern United States. 203 learners reported 2,970 responses via short ESM surveys of how engaged they were (cognitively, behaviorally, and affectively, assessed through separate items) and of their perceptions of themselves (their competence) and the activity (its challenge). These data were used to examine five specific research questions: 1) What is the frequency and nature of opportunities for youth to engage in each of the five aspects of work with data in summer STEM programs? 2) What profiles of engagement emerge from data collected via ESM in the programs? 3) What are sources of variability for the profiles of engagement? 4) How do the five aspects of work with data relate to profiles of engagement? 5) How do youth characteristics relate to profiles of engagement?Findings show that aspects of work with data were fairly common overall, but that work with data was enacted out in varying ways, including some that were possibly highly engaging. Six profiles of youth engagement were identified, representing distinct configurations of the five indicators of engagement. Substantial variability in the profiles was present at the youth level, with less explained by the program youth were in or the nature of the particular instructional episode present at the times when youth were signaled. Relations between the profiles of engagement and each of the aspects of work with data were somewhat small: Notable exceptions were the generating data and data modeling were significantly associated with full engagement. Youth with higher pre-program interest in STEM were more likely to be engaged and competent but not challenged, though other youth characteristics were not highly related to the profiles.I discuss key findings as regards work with data in summer STEM programs and other informal learning environments, the nature of youths' engagement, and what factors can predict engagement. The design and goals of summer STEM programs, which are not (necessarily) focused on activities related to work with data, as well as other limitations including the measures for work with data used and the analytic approach, are identified and described. The role of generating data and modeling data as well as attention to the specifics of how work with data are enacted are presented as implications for practice. I highlight aspects of the findings and the implications for practice with respect to work with data in general and to engagement in informal learning environments, such as summer STEM programs, in both cases with an emphasis on how work with data can serve as a promising context for learning in STEM subject areas.
Show less

MSU Libraries

Digital Repository

You are here