A dynamic model is developed for the purpose of predicting stability characteristics of an industrial-scale, swirl-stabilized premixed combustor located at the National Energy Technology Laboratory (NETL) in Morgantown, WV. The model consists of modular blocks that assemble into an open-loop transfer function depicting the frequency response of the thermoacoustic system. These blocks include the system acoustic response to unsteady heat release forcing, the air-side coupling of acoustic particle velocity to inlet fuel mass fraction, transport delays present in the mixing nozzle and combustion chamber, and dynamic heat release excitation from unsteady inlet fuel mass fraction. By examing the frequency response with linear stability techniques, the existence of limit cycles due to linear instabilities is predicted. Further, the frequency response analysis is used to predict limit cycle frequencies in the case of predicted instability. The analysis predictions are compared with the results of tests performed at NETL, demonstrating a capability of replicating many of the observed stability characteristics. / Ph. D.

With ever shrinking geometries, growing metal density and increasing clock rate on chips, delay testing is becoming a necessity in industry to maintain test quality for speed-related failures. The purpose of delay testing is to verify that the circuit operates correctly at the rated speed. However, functional tests for delay defects are usually unacceptable for large scale designs due to the prohibitive cost of functional test patterns and the difficulty in achieving very high fault coverage. Scan-based delay testing, which could ensure a high delay fault coverage at reasonable development cost, provides a good alternative to the at-speed functional test. This dissertation addresses several key challenges in scan-based delay testing and develops efficient Automatic Test Pattern Generation (ATPG) and Design-for-testability (DFT) algorithms for delay testing. In the dissertation, two algorithms are first proposed for computing and applying transition test patterns using stuck-at test vectors, thus avoiding the need for a transition fault test generator. The experimental results show that we can improve both test data volume and test application time by 46.5% over a commercial transition ATPG tool. Secondly, we propose a hybrid scan-based delay testing technique for compact and high fault coverage test set, which combines the advantages of both the skewed-load and broadside test application methods. On an average, about 4.5% improvement in fault coverage is obtained by the hybrid approach over the broad-side approach, with very little hardware overhead. Thirdly, we propose and develop a constrained ATPG algorithm for scan-based delay testing, which addresses the overtesting problem due to the possible detection of functionally untestable faults in scan-based testing. The experimental results show that our method efficiently generates a test set for functionally testable transition faults and reduces the yield loss due to overtesting of functionally untestable transition faults. Finally, a new approach on identifying functionally untestable transition faults in non-scan sequential circuits is presented. We formulate a new dominance relationship for transition faults and use it to help identify more untestable transition faults on top of a fault-independent method based on static implications. The experimental results for ISCAS89 sequential benchmark circuits show that our approach can identify many more functionally untestable transition faults than previously reported. / Ph. D.

Estimation of real-time travel times on arterial streets has been a challenging task due to the intersection control delay as well as bottleneck delay from the downstream link. Therefore, few transportation professionals have conducted research at utilizing the dynamic flow methods to estimate travel times on arterial street networks. This thesis is to develop dynamic flow algorithms that estimates the real-time travel time on an arterial street network by utilizing the traffic information obtained from detectors. A modified method to the one adopted in HCM2000 in computing the intersection control delay is developed and utilized to estimate the real-time travel time for a short-time interval update under non-incident and incident situations. Simulation model is developed in CORSIM to validate developed algorithms under different traffic situations. / Master of Science

Communication delay in distributed teams is salient problem, especially in operational setting where communication is critical to team safety and success. The present study investigated the impact of communication delays affect distributed team performance and processes, and if being able to see one's team member would lessen the effects of delays. In addition, team gender composition was investigated, to see how delays affected the interactions of same and mixed-gender teams, as well as teams with familiar and unfamiliar members. Lastly, a supplemental was performed on a subset of the experimental data to determine if teams with familiar members' communicated more efficiently than unfamiliar teams when coordination complexity was high. Thirty distributed dyads, were assigned the role of intelligence analysts, and performed a collaborative problem solving task, using audioconferencing and videoconferencing technologies. During the task, participants verbally shared and discussed information in order to solve a fictitious terror plot. Communication between team members was delayed by 0 ms, 800, or 1600 ms. Linear mixed models showed that participants took longer to solve the task at the 800 ms delay. Task accuracy was not affected by delays. At the 1600 ms delay, participants shared less information with each other, and rated their frustration higher compared to the 0 ms delay. Audiovisual technology affected overall workload scores, with lower scores at the 0 ms delay compared to the 800 ms delay. Although delays did not have the anticipated effect on familiar and same-gender teams, there were some interactive effects of interest. Specifically, in gender-diverse teams task accuracy was higher with audiovisual technology than audio-alone, but this effect was independent of delays. Also, familiar teams exhibited higher levels of cognitive trust across all levels of delay and technology. Results of the supplemental analysis showed no differences in communication efficiency between familiar and unfamiliar teams when coordination complexity was high. Based on the results of this work, recommendations were proposed for strategies to lessen the effects of communication delays and future research directions were outlined. / Doctor of Philosophy / Communication delay in distributed teams is salient problem, especially in operational settings where communication is critical to team safety and success. In previous work, communication delays have been shown to disrupt turn-taking in conversations and create instances of overlaps or interruptions. The present study was conducted to further investigate the effects of communication delays on various aspects of distributed team performance and to determine if being able to see one’s team member via video technology may potentially lessen the effects of delays. In addition, team gender composition was investigated, to see how delays affected the interactions of same and mixed-gender teams, as well as teams with familiar and unfamiliar members. Lastly, a supplemental analysis was performed using a subset of the experimental data to determine if teams with familiar members’ communicated more efficiently than unfamiliar teams when coordination complexity was high. Thirty distributed teams of two members or dyads, performed a collaborative problem solving task, using audio conferencing and videoconferencing technologies. During the task, participants verbally shared and discussed information in order to identify the solution to a fictitious terror plot. Communication between team members was delayed by 0 ms, 800, or 1600 ms. Overall, results showed that participants took longer to solve the task at the 800 ms delay, with no effects on task accuracy. At the 1600 ms delay, participants shared less information with each other, and rated their frustration higher compared to the 0 ms delay. When teams used audiovisual technology, workload scores were lower at 0 ms compared to the 800 ms delay. Although delays did not have the anticipated effects on familiar and same-gender teams, there were some other interesting effects that emerged. Namely, gender-diverse teams scored higher accuracy with audiovisual technology than audio-alone, but this effect was independent of delays. Also, teams with familiar members exhibited higher levels of cognitive trust across all levels of delay and technology. Results of the supplemental analysis showed that unfamiliar teams communicated more efficiently with audiovisual technology, but only when coordination complexity was low.

Alternative intersections and interchanges, such as the diverging diamond interchange (DDI), the restricted crossing u-turn (RCUT), and the displaced left-turn intersection (DLT), have the potential to both improve safety and reduce delay. However, partially due to lingering questions about analysis methods and service measures for these designs, their rate of implementation remains low. This research attempts to answer three key questions. Can alternative intersections and interchanges be incorporated into the existing level of service and service measure schema, or is a new service measure with an updated level of service model required? Is the behavior of drivers at alternative intersections fundamentally similar to those at conventional intersections, such that traffic microsimulation applications can accurately model the behaviors observed in the field? Finally, is the planning level tool made available through FHWA an accurate predictor of the relative performance of various alternatives, or is an updated tool necessary? Discussion and case study analysis are used to explore the existing level of service and service measure schema. The existing control delay measure is recommended to be replaced with a proposed junction delay measure that incorporates geometric delay, with the existing level of service schema based on control type recommended to be replaced by a proposed schema using demand volume. A case study validation of micro- and macroscopic analysis methods is conducted, finding the two microscopic methods investigated to match field observed vehicle delays within 3 to 7 seconds for all designs tested, and macroscopic HCM method matching within 3 seconds for the DDI, 35 seconds for the RCUT, and 130 seconds for the DLT design. Taking the critical lane analysis method to be a valid measure of operations, the demand-volume limitations of each alternative design is explored using eighteen geometric configurations and approximately three thousand volume scenarios, with the DLT design predicted to accommodate the highest demand volumes before failure is reached. Finally, six geometries are examined using both the planning-level tool and the validated microsimulation tool, finding that the curve of the capacity-to-delay relationship varies for each alternative design, invalidating the use of critical lane analysis as a comparative tool. / Ph. D.

Previous plasma imaging missions have used time-delay integration techniques that correct for uniform motion blur during integration. This was due to the assumed constant range-to-target of each pixel in the observed scene. ICON's low orbital altitude and twelve second integration time create non-uniform motion blur across the observed scene and necessitate a novel variable-range time-delay integration (TDI) algorithm be used to spatially resolve the two-dimensional images. The variable-range TDI algorithm corrects for each pixel moving at a different angular rate throughout image integration and transforms each raw image onto a surface where the spacecraft is moving at a constant angular rate with respect to every pixel in the image. Then as the raw images are co-added together the non-uniform motion of the observed scene is accounted for and will not geographically distort the final images, or any features seen within them. Through simulation using output from the SAMI3 model during plasma depletion formation it was determined that the structuring and gradients of plasma depletions can be recovered using this technique. Additionally, the effects of depletion width, solar activity level, and misalignment of the field-of-view with the local magnetic field were investigated. The variable-range TDI technique is able to recover the overall shape and depth of depletion of the depletions in all cases, however the determination of gradients observed at depletion walls is significantly degraded for very narrow plasma depletions and during periods of low solar activity. All simulated model conditions were shown to be representative of current ionospheric conditions. / Master of Science / Equatorial spread-F, also termed plasma bubbles, is a phenomenon that occurs in the equatorial region of Earth’s ionosphere, the charged region of Earth’s atmosphere. Plumes of less dense plasma, the charged material of the Ionosphere, rise through regions of higher density plasma. This causes disturbances to radio signals that travel through this region, which can lead to GPS range errors or loss of signal. ICON is a NASA Explorer mission aimed at, in part, understanding the sources of variability in the ionosphere. One instrument onboard ICON to accomplish this goal is the FarUltraviolet Imager which images airglow in the far-ultraviolet range. During nighttime, the FUV imager can observe plasma bubbles to study the instability and the mechanisms that produce it. This thesis looks at the ability of the variable-range time-delay integration (TDI) algorithm, used to produce images from ICON’s Farultraviolet imager, to spatially resolve the structure and gradients of observed plasma bubbles. However, due to the viewing geometry of ICON’s FUV imager, each pixel across the observed scene experiences a different angular rate of motion blur. The variable-range TDI algorithm removes this non-uniform motion blur by transforming each raw image onto a surface where the spacecraft moves at a constant angular rate with respect to every pixel in the image. Then raw images are integrated together such that the observed scene is not geographically distorted. It was concluded that the TDI process is able to spatially resolve a wide variety of plasma bubbles under various ionospheric conditions and imager configurations.

Diverging diamond interchanges (DDI) have been proved to outperform other types of diamond interchanges in terms of safety, cost-effectiveness and efficiency, but few research efforts have been done to conduct the analytic calculation of delay, with which optimization of timing plans can be acquired more efficiently. This paper develops the control strategies based on the introduction of overlap and offset analysis, which provide a uniform representation of sequences for DDI signal control. Based on the developed timing plan then the delay calculation equations are put forward and results show the calculation fit simulation very well with R-Square to be 0.9949 for total delay of those two directions. Ecodriving aims to achieve the best fuel efficiency by guiding vehicles travel at planned and optimized speed trajectories. This study opens the door for safety concerns for following normal driving vehicles (FNVs) when following ecodriving vehicles (EVs). To examine the safety issues under different circumstance. Three road elements: initial signal status, ambient vehicles and speed limit along with three EV elements: SpeedTolimit, DistanceToStoplight and acceleration were chosen as potential influential elements, and time to collision (TTC) was selected as the dependent variable. Therefore, six testing scenarios and six baseline were designed and implemented using a drive safety DNS-250 simulator. 29 drivers participated in the driving simulator study. The results show the aforementioned road elements and EV elements have significant influence on TTC of FNV in different testing parts. Therefore, these finding can be used as guidance for future ecodriving algorithm design and implementation. / Master of Science / The research conducted in the thesis are composed of two sub-topics: delay calculation for diverging diamond interchange and safety assessment of ecodriving, on following traffic. Both of them are new coming technologies and are attracting increasing research interests. The first research topic, diverging diamond interchange is a new design of interchange which aims to decrease the conflict points of intersection hence increase the safety and efficiency. The second topic is about ecodriving, which is a vehicles communication-related topic, aims to improve fuel efficiency by taking better use of signal phasing and timing (SPaT) information. Both of them will contribute to the construction of environment-friendly and safe transportation systems. The research on these topic are innovative and should play role in guiding follow-up research in the future.

In modern wireless communication systems, such as satellite communications and wireless networks, the need for higher data rates without the need for additional transmit power has made Continuous Phase Modulation (CPM) one of the most attractive modulation schemes in band limited channels. However, as the data rates keep increasing, the spectral width of the CPM signal increases beyond the channel bandwidth and performance becomes constrained by the intersymbol interference (ISI) that results from band-limiting filters. We propose two approaches to the problem of equalization of band-limited CPM signals. First, our efforts are focused on shortening the channel impulse response so that we can use a low complexity MLSE equalizer. We implement the channel truncation structure by Falconer and Magee and adapt it to work with CPM signals. This structure uses a, a more derivable, pre-filter to shape the overall response of the channel, so that its impulse response is of shorter duration. Simulation results show that near-MLSE performance can be obtained while dramatically reducing MLSE equalizer complexity. In our second approach, we focus on eliminating the group-delay variations inside the channel passband using an FIR pre-filter. We assume the channel to be time-invariant and provide a method to design an FIR filter so that -when convolved with the band limiting filter - it results in more constant group-delay over the filter passband. Results show that eliminating the group-delay variations in the band limiting filter passband reduce the amount of ISI and improve bit error rate performance. / Master of Science

Despite being one of the most well-known laboratory-based tasks in psychology, certain methodological and theoretical considerations surrounding the marshmallow test have gone largely unstudied until recently. These considerations reflect gaps in the delay of gratification literature and broader contemporary issues concerning the replicability of seminal findings and the lack of an agreed upon theoretical framework in the field. Accordingly, my dissertation uses the classic marshmallow test to explore the contemporary issues of replication and theory in psychology in a series of three studies. In Study 1, the marshmallow test is at the center of a case study unpacking the nuances of direct and conceptual replication; a tool designed to support ongoing replication efforts is proposed. Study 2 executes a full-scale replication of the paradigm from the case study, and introduces a methodological extension to improve the paradigm’s experimental rigour while making it amenable to an evolutionary–developmental framework. Finally, Study 3 applies an evolutionary–developmental framework to examine how this perspective might help account for individual differences in marshmallow test behavior. Through these three studies, my dissertation provides an example of how engaging in replication and applying an evolutionary–developmental framework to the marshmallow test literature to inform outstanding theoretical questions in psychology might be mutually beneficial endeavors. / Thesis / Doctor of Philosophy (PhD) / This dissertation uses an iconic measure in psychology, “the marshmallow test,” to explore issues currently relevant to the field today. The marshmallow test measures delay of gratification––how children chose between a small reward now or a larger reward later. However, despite being one of the most well-known laboratory-based tasks in psychology, certain methodological and theoretical considerations surrounding the marshmallow test have gone largely unstudied until recently. These considerations reflect two bigger issues relevant to psychology more broadly: that of how well findings in psychology can be replicated, and the lack of an overarching and unifying theory in the field. Using the marshmallow test, this dissertation 1) proposes a tool to support ongoing replication efforts, 2) executes a replication and extension of a recent well-cited study, and 3) introduces ways of exploring how a framework that takes evolutionary–developmental principles into account might help address outstanding theoretical questions in the study of delay of gratification.

This dissertation consists of three chapters. The first chapter addresses the roles of changes in assisted reproductive technologies, returns to female experience and abortion rates in explaining the historical trend of child adoption. The second chapter assesses the effects of increased income inequality and decreased income mobility on timing of births and marriages and on the single motherhood rates. The third chapter establishes the importance of accounting for marital state in the models of indirect income uncertainty inference. Chapter 1 aims to explain the μ-shaped historical trend of child adoption in the US by emphasizing the role of the changes in the demand side of the market for child adoption. I argue that changes on the demand side such as increasing returns to female human capital and innovations in Assisted Reproductive Technology (ART) have played a major role in shaping the historical adoption trend along with the changes in the supply side, namely, increase in the abortion rates. I present a life-cycle model, in which an agent makes a fertility-timing decision based on the returns to her human capital and age-specific probability of conception. Under the assumption that adoption is an alternative to childbearing, i.e. an agent chooses to adopt after she fails to conceive, the presented model uses historical trends of returns to human capital and success rate of ART to explain changes in adoption trends. According to the model, increasing returns to female human capital were responsible for the delay in childbearing and therefore the increase in the demand for adoption until the 1970s. After 1970, the legalization of abortion decreased the supply of orphans, while innovations in ART decreased the demand by allowing women to have biological children at later ages. Around 1980, the effect of increasing returns to human capital overturned the one of advances in ART, which resulted in a slow recovery of the adoption trend. Chapter 2 studies the dramatic transformation that the typical American family has undergone since the 1950s. Marriage and fertility have been delayed, while single-motherhood rates have increased. The link between these facts emanates from the greater delay in marriage than that in first births. As “the Gap” between the age at first birth and the age at first marriage becomes negative for some women, out-of-wedlock first births increase. In my analyses, I focus on the increase in income inequality and the decrease in income mobility --- observed across two National Longitudinal Survey of Youth (NLSY) cohorts of women --- to account for the above facts using an equilibrium two-sided search framework in which agents make marriage and fertility choices over the life-cycle. Marriage is a commitment device for consumption-sharing, providing spouses with partial insurance against idiosyncratic earnings risk. Agents derive utility from children, but children also involve a risky commitment to future monetary and time costs. According to my model, two observed trends in the income process produce these changes in the respective timings of marriage and fertility. First, the increase in income inequality produces incentives to delay marriage. Since single women tend to face higher income risk than do married women, all else being equal, a decline in marriages when young implies delayed births, which are perceived to be risky. Second, the decrease in income mobility also delays marriage as the insurance value of marriage decreases but accelerates fertility because it becomes less risky to have a child. The model qualitatively matches the observed changes in family formation and quantitatively accounts for a significant portion of the observed changes in marriage and fertility timing between the two NLSY cohorts. In Chapter 3 I aim to add to the indirect income uncertainty inference literature. The currently existing models used to infer earnings uncertainty from consumption decisions of individuals either use married couples as a unit of analysis or treat married individuals as singles. Income pooling and less than perfect correlation of earnings in marital unions provide spouses with marital income insurance. Not accounting for the marital insurance biases the uncertainty estimation results. In this chapter, I demonstrate some properties of the marital insurance bias in a stylized analytical model. In order to access the potential magnitude of the marital bias, I build a structural model which accounts for marital insurance. I then compare the estimation results of the model which accounts for marriage with the results of one that does not after using them on the simulated data set. In addition, I introduce a non-parametric income process in the structural model used for the indirect uncertainty inference. The main advantage of the resulting model is that, unlike the typical models in this area, it can be used on short-term panel data.