Monolithic passively mode-locked colliding pulse semiconductor lasers generating pico- to sub-picosecond terahertz optical pulse trains are promising sources for future applications in ultra-high speed data transmission systems and optical measurements. However, in the absence of external synchronization, these passively mode-locked lasers suffer from large amplitude and timing jitter instabilities resulting in broad comb linewidths, which precludes many applications in the field of coherent communications and signal processing where a much narrower frequency line set is needed. In this dissertation, a novel quantum dot based coupled cavity laser is presented, where for the first time, four-wave mixing (FWM) in the monolithically integrated saturable absorber is used to injection lock a monolithic colliding pulse mode-locked (CPM) laser with a mode-locked high-Q ring laser. Starting with a passively mode-locked master ring laser, a stable 30 GHz optical pulse train is generated with more than 10 dB reduction in the RF noise level at 20 MHz offset and close to 3-times reduction in the average optical linewidth of the injection locked CPM slave laser. The FWM process is subsequently verified experimentally and conclusively shown to be the primary mechanism responsible for the observed injection locking. Other linear scattering effects are found to be negligible, as predicted in the orthogonal waveguide configuration. The novel injection locking technique is further exploited by employing optical hybrid mode-locking and increasing the Q of the master ring cavity, to realize an improved stabilization architecture. Dramatic reduction is shown with more than 14-times reduction in the photodetected beat linewidth and almost 5-times reduction in the optical linewidth of the injection locked slave laser with generation of close to transform limited pulses at ~ 30 GHz. These results demonstrate the effectiveness of the novel injection locking technique for an all-on-chip stability transfer and provides a new way of stabilizing monolithic optical pulse sources for applications in future high speed optical networks.

This report details the design and implementation of a switching DC-DC converter for use in the Energy Harvesting From Exercise Machines (EHFEM) project. It uses a four-switch, buck-boost topology to regulate the wide, 5-60 V output of an elliptical machine to 36 V, suitable as input for a microinverter to reclaim the energy for the electrical grid. Successful implementation reduces heat emissions from electrical energy originally wasted as heat, and facilitates a financial and environmental benefit from reduced net energy consumption.

The demand for an insert on composite sandwich structures to aid in the arrestment of face-core delamination is of great need. This research studies the use of a damage arrestment device (DAD) that connects the carbon fiber face sheets to the foam core to find whether an increase in the structural integrity of the sandwich beam results. Experimental analysis was employed to test the samples and was verified by a theoretical and finite element approach. The mechanical properties of LTM45/CF1803 pre-impregnated carbon fiber and Last-A-foam FR 6710 polyvinylchloride foam were experimentally analyzed using ASTM D3039 and ASTM D1621 standards respectively to verify the manufacturer’s data for the given material. With all the mechanical data, the effects of adding DAD keys to a delaminated composite sandwich beam were studied under a four-point bending test using ASTM standard D6272 and compared with non-delaminated beams to see if an increase in ultimate strength could be achieved. The initial delamination in the beams under consideration was one inch in length and located in between the loaded span of the beam. Two control beams were utilized for comparison: one with no defects, and another with a one inch delamination introduced at the face-core interface. The DAD keys were added in two different configurations to potentially stop the delamination propagation and increase the ultimate strength. In the first configuration DAD keys were added 0.25 inches on either side of the initial delamination in the transverse direction and provided a significant increase in strength over the delaminated control beam. The second configuration had a DAD key running along the longitudinal axis of the sandwich beam and resulted in a significant increase in ultimate strength over the delaminated control beam. After testing ten successful samples for each of the six different configurations, it was concluded that the addition of DAD keys in both configurations significantly increased the structural integrity of both the delaminated and non-delaminated control beams. With all the experimental data acquired, finite element models were created in COSMOS. The purpose of the finite element analysis was to validate the experimental results by comparing the deflections of the beam subjected to four-point bending during the experiment to the deflections found numerically. The deflections for the various DAD key configurations found in the experimental work were in agreement with the finite element results.

The use of composite sandwich structures is rapidly increasing in the aerospace industry because of their increased strength-to-weight and stiffness-to-weight characteristics. The effects of low velocity impacts on these structures, however, are the main weakness that hinders further use of them in the industry because the damages from these loadings can often be catastrophic. Impact behavior of composite materials in general is a crucial consideration for a designer but can be difficult to describe theoretically. Because of this, experimental analysis is typically used to attempt to describe the behavior of composite sandwiches under impact loads. Experimental testing can still be unpredictable, however, because low velocity impacts can cause undetectable damage within the composites that weaken their structural integrity. This is an important issue with composite sandwich structures because interlaminar damage within the composite facesheets is typical with composites but the addition of a core material results in added failure modes. Because the core is typically a weaker material than the surrounding facesheet material, the core is easily damaged by the impact loads. The adhesion between the composite facesheets and the core material can also be a major region of concern for sandwich structures. Delamination of the facesheet from the core is a major issue when these structures are subjected to impact loads. This study investigated, through experimental and numerical analysis, how varying the core and facesheet material combination affected the flexural strength of a composite sandwich subjected to low velocity impact. Carbon, hemp, aramid, and glass fiber materials as facesheets combined with honeycomb and foam as core materials were considered. Three layers of the same composite material were laid on the top and bottom of the core material to form each sandwich structure. This resulted in eight different sandwich designs. The carbon fiber/honeycomb sandwiches were then combined with the aramid fiber facesheets, keeping the same three layer facesheet design, to form two hybrid sandwich designs. This was done to attempt to improve the impact resistance and post-impact strength characteristics of the carbon fiber sandwiches. The two and one layer aramid fiber laminates on these hybrid sandwiches were always laid up on the outside of the structure. The sandwiches were cured using a composite press set to the recommended curing cycle for the composite facesheet material. The hybrid sandwiches were cured twice for the two different facesheet materials. The cured specimens were then cut into 3 inch by 10 inch sandwiches and 2/3 of them were subjected to an impact from a 7.56 lbf crosshead which was dropped from a height of 38.15 inches above the bottom of the specimen using a Dynatup 8250 drop weight machine. The impacted specimen and the control specimen (1/3 of the specimens not subjected to an impact) were loaded in a four-point bend test per ASTM D7250 to determine the non-impacted and post-impact flexural strengths of these structures. Each sandwich was tested under two four-point bend loading conditions which resulted in two different extension values at the same 100 lbf loading value. The span between the two supports on the bottom of the sandwich was always 8 inches but the span between the two loading pins on the top of the sandwich changed between the two loading conditions. The 2/3 of the sandwiches that were tested after being impacted were subjected to bending loads in two different ways. Half of the specimens were subjected to four-point bending loads with the impact damage on the top facesheet (compressive surface) in between the loading pins; the other half were subjected to bending loads with the damage on the bottom facesheet (tensile surface). Theoretical failure mode analysis was done for each sandwich to understand the comparisons between predicted and experimental failures. A numerical investigation was, also, completed using Abaqus to verify the results of the experimental tests. Non-impacted and impacted four-point bending models were constructed and mid-span deflection values were collected for comparison with the experimental testing results. Experimental and numerical results showed that carbon fiber sandwiches were the best sandwich design for overall composite sandwich bending strength; however, post-impact strengths could greatly improve. The hybrid sandwich designs improved post-impact behavior but more than three facesheet layers are necessary for significant improvement. Hemp facesheet sandwiches showed the best post-impact bending characteristics of any sandwich despite having the largest impact damage sizes. Glass and aramid fiber facesheet sandwiches resisted impact the best but this resulted in premature delamination failures that limited the potential of these structures. Honeycomb core materials outperformed foam in terms of ultimate bending loads but post-impact strengths were better for foam cores. Decent agreement between numerical and experimental results was found but poor material quality and high error in material properties testing results brought about larger disagreements for some sandwich designs.

Self-efficacy is theorized to represent our ability, capability, or capacity to accomplish particular tasks. One’s belief in that ability (self-efficacy belief) has been identified as the greatest predictor of successful performance and is influenced by four primary sources (enactive mastery experience, vicarious experience, verbal/social persuasion, physiological and affective states), in addition to personal and contextual influences. However, the development of accurate self-perceptions may be particularly challenging for the collegiate vocalist. In the development of singing technique—where self-assessment is complicated by the corporal nature of the vocal instrument—Bandura’s (1997) sources of self-efficacy provide a framework whereby assessment of ability and capability may become more tangible. The aim of the present study, therefore, was to investigate how collegiate vocal students’ beliefs in their vocal performance abilities may be influenced by the four self-efficacy sources and personal/contextual factors. I distributed the Vocal Performance Self-Efficacy Survey (adapted from Zelenak, 2011) to 46 voice majors at a private university in the western United States. Nine interview participants, who represented diversity of performance beliefs, were subsequently selected from the survey participant pool. Interview participants completed an initial interview based on a priori themes (four sources of self-efficacy); and a follow-up interview, which explored contextual factors (i.e., student/teacher relationship, environment, cognitive self-regulation, practice habits, and gender). In addition, participants documented three experiences—in a voice lesson, practice session, and performance—that fostered or hindered their performance belief. Vocal students in this study described how they progressed in self-belief by moving from a reliance on external assessments of ability to a reliance on self-appraisal as they (a) developed their technique through practice, studio learning, and performance (enactive mastery experience); (b) watched coping and master models (vicarious experience); (c) received feedback (verbal/social persuasion); (d) knew and felt physically when they were singing freely (physiological and affective states); and (e) learned to exercise agency (cognitive self-regulation). A particularly important finding from this study was the common and consistent reliance singers placed on physiological and affective states. Eight of nine interview participants responded that, of all the self-efficacy sources, physiological and affective states most affected their performance belief. Interview data indicate the importance of nurturing vocal students’ performance beliefs through utilizing the four sources of self-efficacy, fostering qualities of persistence and resilience, facilitating cognitive self-regulation, working toward productive student/teacher relationships, and creating safe learning and performance environments.

Standalone computer modules for county to county travel demand forecasting have been integrated. The Trip Generation, Trip Distribution and Mode Choice modules have been unified under one Graphical User Interface (GUI). The outputs are automatically mapped using Geographic Information Systems (GIS) technology to allow immediate and spatial analysis. The integrated model allows for faster running times and quicker analysis of the results. The ability to calculate travel time savings for travelers was also included to the final model. The modeling framework developed is known as the Transportation Systems Analysis Model (TSAM). / Master of Science

To make the move to a four-variable Karnaugh map, we are going to double the number of columns found in the three-variable map. And what happens when we halve the three-variable map? We get a two-variable Karnaugh map!

As dissatisfaction with the single member district has grown in recent years, new electoral systems have gained popularity. In particular, the Top Four Primary plus Ranked Choice Voting system, enacted in 2020 and used in Alaska for the first time in 2022, has received considerable attention. Besides reducing partisanship, the system claims to increase voter turnout and encourage third-party candidates and candidates of color to run on election day. Given its novelty, however, a comprehensive overview of the system and the implementation process is currently lacking. As a result, the purpose of this study is to assess the history, passage, challenges, and current debate around the Top Four Primary plus Ranked Choice Voting system. Using popular opinion data, candidate campaign techniques, archives, and ballot data, I find that voter and candidate reactions to the system varied, that incumbent advantage was not evident in the 2022 election cycle, and that voting patterns were associated with campaign strategies. States considering the Top Four Primary plus Ranked Choice Voting system can use this thesis as a guide to understanding the system's successes and drawbacks better. The study could also serve as a starting point for researchers looking into how the Top Four Primary plus Ranked Choice Voting system can enhance democracy.

Hybridization of two or more DNA or RNA strands is well documented for the process taking place with all strands free in solution or when one strand is immobilized on a substrate. This study contributes to the investigation of the hybridization process when two single DNA strands (ssDNA) are in close proximity. We took advantage of an X sensor in which hybridization of four DNA strands enables the formation of a DNA four-way junction (crossover or X) structure. We immobilized multiple layers of crossover structures to study its hybridization being triggered by short ssDNA coming from solution and further investigate how many layers of these structures can hybridize by the addition of only one ssDNA (called input). Using a molecular beacon as reporter, we combined crossover DNA strands that recognize the reporter sequence at one side and at the other, the sequence of its input or downward crossover layer. Fluorescent signal was detected by separation of the molecular beacon’s fluorophore and quencher, as it hybridizes with the system of layers. Immobilization of the X structures into the scaffold proved to increase their communication, in comparison to being free in solution. This evidence gives us significant information for the communication of hybridized layers in a localized system, showing a promising standard for development of multilayered logic gates. The potential of these crossover DNA strands using X structure include applications in the future of biological systems, nanotechnology, and target DNA recognition for its ability to quickly recognize a signal and propagate it through extended DNA nanostructure in a controlled manner.

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