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Integration of Encapsulated Phase Change Materials into Power Dense Electronic Package Architectures for Enhanced Thermal Buffering
No full textImproving energy resilience requires continuous improvement of power electronic systems focusing on increasing power densities, often limited by the thermal management system performance and requirements. Thermal management systems can be more optimal in thermal energy transfer and more efficient in energy consumption through passive cooling components integration. There are many passive cooling mechanisms that work to store or transfer energy without direct power requirements including phase change materials (PCMs). PCMs are of particular interest because they store large amounts of energy across a phase transition, commonly solid to liquid, and work well as additional thermal buffering within power dense systems. The added thermal buffering can significantly improve efficiency and reliability of power dense electronics by reducing maximum thermal gradients and temperatures around critical components. It is often challenging to incorporate conventional PCMs within electronic architectures in a manner that both provides adequate energy response and protects systems from the liquid phase. The structures needed to enclose these PCMs reduce opportunities to maximize total power density realization. To address this problem, this work uses encapsulated phase change materials (ePCMs) to design stable ePCM based composites for direct integration into existing electronics architectures. ePCMs are micro to nano sized particles with a PCM core surrounded by a protective shell that can be easily integrated into existing matrix materials to provide passive cooling capability without liquid phase concerns. This work integrates ePCMs into dielectric gels and thermal interface materials to design new ePCM laden composites that can directly replace existing electronics materials located near the thermal generation regions. The ePCM composites are tested and compared against their predecessors to characterize the performance improvements and associated tradeoffs of direct implementation in existing electronic configurations
Development of Si-Based Germanium-tin Infrared Photodiode
Get PDFShort-wave infrared (SWIR) and mid-wave infrared (MWIR) photodetectors have attracted increasing attention for the past few decades. SWIR and MWIR detectors are used for a wide range of applications in military and civilian defense, such as future automotive night vision, video surveillance security cameras, and integrated night vision in mobile/wearable electronics. The current market-dominating IR photodetector technology is mainly developed with the costly III-V or II-V material systems, such as InGaAs, InSb, and HgCdTe. While many efforts have been made towards the hybrid integration of III-Vs or II-VIs on a Si substrate, it is highly desirable to develop an alternative material featuring lower-cost and high-performance for photodetectors covering broad IR wavelength range.
Recent study of all-group-IV alloy SiGeSn opens a new venue for Si-based optoelectronics. SiGeSn offers: (1) The ability to independently engineer the lattice constant and bandgap by appropriately selecting the compositions of Si, Ge, and Sn; (2) The ability to achieve true direct bandgap material by incorporating a few percent Sn; (3) The possibility of forming desirable type-I band alignment to provide a favorable quantum confinement for the design of optoelectronics; (4) The IR wavelength coverage up to 12 μm through band-to-band transitions and all wavelengths beyond 12 μm through intersubband transitions; (5) The compatibility with CMOS processes with a low growth temperature (below 400 oC). The key enabling factors for SiGeSn over all current IR technologies also include significantly lower radiative and Auger recombination (10-28~10-29 cm6 /s) coefficients for longer carrier lifetime (\u3e100 μs), and larger oscillator strength for higher absorption coefficient (\u3e104/cm), giving a shorter carrier extraction time, lower dark current, and higher internal quantum efficiency. My dissertation shows the development of general GeSn device fabrication processes, which were later employed in the fabrication of GeSn laser and detector devices. This successfully demonstrated the first electrically injected GeSn laser and avalanche photodiode, which showed clear punch-through and avalanche breakdown behavior.
Further, investigations into Ion implantation of arsenic (n-type) and boron (p-type) in GeSn (~10% Sn) is feasible but induces lattice damage. Higher doses and energies cause crystal disorder up to amorphization, partially healed by low-temperature rapid thermal annealing. Annealing at 300°C recovers some damage, while 400°C significantly restores crystallinity for Sn ≤11%. SIMS confirms impurity incorporation, and post-implant annealing activates p–n junctions. A fabricated GeSn diode with implanted regions exhibits rectifying I–V behavior and infrared photo response.
This work advances monolithic GeSn-based avalanche photodiodes (APDs) on silicon, enabling extended infrared detection and CMOS compatibility. A SACM structure with a GeSn absorber, Si multiplication layer, and Ge buffer enhances carrier transport, achieving a broad spectral response beyond 2.1 μm at room temperature. The GeSn-on-Si APDs show clear punch-through and avalanche breakdown. Internal gain is evident, with multiplication factors of ~1.4 at 250 K and ~4–4.5 at 77 K.
These findings highlight GeSn\u27s potential for extending silicon photonics into the infrared. GeSn APDs on Si achieve spectral response beyond Si and Ge bandgaps, with avalanche gain in the 1.5–2.0 μm range. CMOS-compatible ion implantation and low-temperature annealing enable GeSn integration into standard silicon processes, paving the way for monolithic, CMOS-compatible infrared photodetectors and optoelectronic devices in the SWIR/MWIR regimes
LGBTQ+ Childhood Abuse, Reporting, & Parental Rights
Get PDFThis study aimed to investigate LGBTQ+ childhood maltreatment, its reporting generally, and the impact of religion on reporting. It was hypothesized that LGBTQ+ youth will experience more maltreatment than their non-LGBTQ+ peers; among those who experienced maltreatment, LGBTQ+ youth will be less likely to receive help or have reports made; and those from more religious families will be less likely to have received help or had their maltreatment reported. A sample of individuals between the ages of 18 and 35, currently living in the states of Arkansas, Mississippi, Missouri, Louisiana, Oklahoma, or Texas, was recruited to complete a cross-sectional survey. Quota sampling (50:50) was conducted by Qualtrics to ensure a comprehensive comparison between LGBTQ+ individuals and their cisgender, heterosexual peers. This study found that LGBTQ+ youth experienced emotional, physical, and sexual abuse at higher rates than their non-LGBTQ+ peers. Additionally, it was found that LGBTQ+ youth were not less likely to receive help or have reports made compared to their non-LGBTQ+ peers. Among LGBTQ+ participants who experienced maltreatment, those from more religious families were also not less likely to have received help or had their maltreatment reported. The findings of this research indicate a need for further advocacy for LGBTQ+ clients and for policies that protect them, as well as affirming providers. Additionally, there is a notable gap in the literature regarding the impact of religion and parental rights on the reporting of such maltreatment, highlighting the need for further research
Rewriting the School Calendar: A Mixed-Methods Analysis of Four-Day School Week Implementation in Arkansas
Get PDFThe four-day school week (4DSW) has gained traction across the United States, particularly in rural districts seeking innovative responses to mounting challenges. Despite its expanding adoption, key questions remain regarding the motivations for implementing 4DSW schedules and their implications for teacher well-being and student achievement. This dissertation examines the emergence and effects of the 4DSW in Arkansas, where adoption has increased rapidly in recent years, offering a unique context shaped by state-level policy and rural dynamics. Employing a mixed-methods, this dissertation investigates (1) why and how districts adopt the 4DSW, (2) whether the policy alleviates teacher burnout, and (3) how it affects student academic outcomes. The first paper draws on qualitative interviews with district and school leaders and finds that 4DSW adoption is often framed as a strategic response to teacher recruitment and retention challenges, burnout, and post-pandemic pressures. Implementation is highly localized and shaped by stakeholder engagement. The second paper analyzes survey data, including the Maslach Burnout Inventory–Educator Survey, and finds that teachers in 4DSW districts report significantly lower emotional exhaustion and depersonalization, particularly in rural areas. The third paper uses a staggered difference-in-differences design with student-level standardized achievement data. While no average effects are found across subjects, science scores exhibit modest cumulative declines over time. This dissertation contributes new evidence to policy discussions about instructional time and educational equity. Findings underscore the importance of local context, timely implementation research, and attention to both workforce sustainability and student outcomes as districts increasingly pursue alternative calendar models
Crispy not Risky: Effects of Environmental Conditions on Low-Moisture Food Persistent Bacterial Pathogens
Get PDFLow-moisture foods (LMFs) were not historically seen as safety risks due to their ability to inhibit pathogen growth, but evidence shows pathogens can survive in LMFs long-term, causing outbreaks and recalls. Previous studies have lacked the ability to replicate real-world contamination scenarios in LMF processing environments. This research aimed to develop inoculation methods to form LMF persistent bacterial populations (LMF PBPs) and assess pathogen responses to environmental factors, culturing methods (broth vs. lawn), and matrix type and ratio. Inoculation methods tested were “direct” (combining bacterial culture and powder on a stainless-steel coupon) and “slurry” (premixing culture and powder). Matrices included three food types (nonfat dry milk powder [NFDM], peanut butter powder [PB], and chicken powder [CP]), a nonfood matrix (silicon dioxide [SiO2]), a nonfood matrix (silicon dioxide [SiO2]), and desiccated Salmonella without a matrix (Sal). Salmonella Tennessee (K4643), linked to peanut butter outbreaks, was used. The direct method involves sprinkling NFDM and SiO2 (0.1 or 0.4 g) onto the coupons inoculated with 0.5 mL of Salmonella. The slurry method (0.5 mL culture to 0.4 g powder) gave consistent results, showing lower Salmonella reduction (1.5–1.6 log CFU/cm2) in NFDM and culture alone LMF PBPs. It was chosen for further tests comparing liquid- and plate-grown cultures. Proceeding with the plate-grown cells using the lawn-based methods, temperature and relative humidity (RH) levels were selected to examine the impacts of environmental factors, in addition to comparing nutrient composition of matrices and storage time on the reductions of Salmonella in LMF PBPs. The coupons were stored for seven or 28 days at 30, 50, or 70% RH at 25 or 35 °C and sampled on predetermined days. Lower reductions were observed for Salmonella LMF PBP made using lawn-grown (0.3–2.7 log CFU/cm2) compared to broth (1.0–5.1 log CFU/cm2) for all food matrices. For both culturing methods, Salmonella in LMF PBP with SiO2 (2.7–5.1 log CFU/cm2) reduced significantly (p \u3c 0.05) more than the food matrices (0.7–2.2 log CFU/cm2) and Sal without a matrix (0.3–1.5 log CFU/cm2). The RH levels, temperature, matrix, and their interactions significantly (p \u3c 0.05) affected the reductions of Salmonella. The significantly greater reductions as the RH increased were specifically observed in LMF PBPs with SiO2. Temperature and RH had no significant effect on Salmonella LMF PBPs in NFDM and Sal. However, matrix type and storage days significantly impacted log reductions (p \u3c 0.05) of Salmonella LMF PBP. Salmonella reductions in LMF PBP with PB were significantly (0.5 ± 0.3 log CFU/cm2) lower compared to the reductions observed on other food matrices (1.9-3.6 ± 0.1 log CFU/cm2). The findings indicate that the LMF PBP method produces a stable population of Salmonella, which is important for evaluating cleaning and sanitation interventions where significant log reductions need to be demonstrated. Future research, using the methods established in the present study, should explore the long-term impact of varying environmental conditions, such as fluctuating humidity or cleaning and sanitation, on the persistence of LMF PBPs formed using the slurry method
Implications of Acetylation and Phosphorylation on Metabolic Enzymes
Get PDFAll living things depend on glycolysis and the TCA cycle for energy production and metabolic control. Post-translational modifications (PTMs) such as acetylation and phosphorylation, which can change enzyme activity, substrate binding, and overall metabolic balance, tightly regulate these pathways. Diseases like cancer and metabolic problems are associated with disruptions in these alterations.
Serine phosphorylation and lysine acetylation are two of the many PTMs that are evolutionarily conserved processes that alter protein function. Previously thought to be a static histone alteration, acetylation is now understood to be a dynamic regulator of metabolic enzymes that modifies contacts, charge, and conformation. In response to biological signals, phosphorylation, a well-known signaling switch, precisely regulates the activity of enzymes. Nevertheless, little is known about the functional effects of site-specific PTMs on metabolic enzymes, specifically how they affect catalytic efficiency, allosteric regulation, and the development of disease. Due to their incapacity to replicate steric or electrostatic disturbances, conventional methods like mutagenesis frequently fall short in reproducing PTM effects. Innovative techniques such as genetic code expansion (GCE) have been developed to address this, allowing for the site-specific inclusion of phosphoserine or acetyllysine through stop codon suppression. This method makes use of pyrrolysyl-tRNA synthetase/tRNA pairs to precisely examine the structural and functional effects of acetylation in vivo. In this research, I used a multidisciplinary method that combines comparative genomics, enzymology, and GCE to analyze how phosphorylation and acetylation rewire the activity of three key enzymes: phosphofructokinase (Pfk), glucokinase (GK), and isocitrate dehydrogenase (IDH). I clarify how site-specific changes affect enzyme kinetics, substrate binding, and metabolic flux by investigating phosphorylation in cancer metabolism using human epithelial cell lines and E. coli as a model for prokaryotic PTM control
Fish Cultivation in Fallow Season Rice Fields: Effects on Landscape Methane Emissions
Get PDFCo-cultivation of aquatic animals and rice in the same field is a fairly common practice in various parts of the world, with a number of well-established agro-ecological benefits, such as decreasing the need for chemical pesticides and fertilizers, increasing soil organic matter, and reducing the land area needed for agricultural production. One area of environmental concern in rice production is greenhouse gas emissions. Rice production contributes about 10% of global anthropogenic methane (CH4) emissions. Currently around 27.5% of Arkansas rice fields are flooded in the winter, which can increase CH4 emissions in the fallow season by 45% compared to non-flooded fields. Evidence from other systems suggests that co-cultivation techniques may reduce CH4 emissions through trophic cascading and provide a second revenue stream to farmers along with the rice crop. The objective of this research was to analyze the effects of cultivating golden shiners, a native fish species, on fallow season CH4 emissions in an Arkansas rice field using the eddy covariance (EC) method. This study uses a pair of long-term continuous rice rotation fields in Lonoke County, Arkansas to quantify the effects of golden shiners on fallow season CH4 emissions with fish added to one field and the other field left flooded without fish. Fluxes in both fields were found to be very low when compared to growing season emissions. Initial results on CH4 emissions reductions are mixed, and certain difficulties such as gaps in the data, lack of field replicates, and variability in soil properties and management practices between the fields make it challenging to derive robust conclusions about the impacts of fish presence on CH4 emissions. Incorporating water sample results, collecting more years of data, increasing the number of field replicates, and trying more alternative approaches like chamber measurements of CH4 flux could provide more insight into the ecological mechanisms at work in this system
Multi-Decadal Land Change Dynamics in Indonesia: Disentangling the Cycle of Agricultural Land Conversions, Urbanization, and Deforestation
Get PDFLand use and land cover change (LULCC) significantly impacts Earth’s environmental, climatic, and human systems, especially in tropical regions rich in natural resources and undergoing rapid development. This study examined the spatiotemporal dynamics of LULCC in Indonesia between 2003 and 2023 using remote sensing and geographic information systems/science (GISci) and explored knowledge gaps in agricultural land conversions and the impact of food security programs such as the Food Estate Program. This study employed the Moderate Resolution Imaging Spectroradiometer (MODIS) MCD12Q1 land cover data available through Google Earth Engine, and classified land cover changes into four dominant categories: forest land, mixed vegetation, agricultural land, and urban land. Utilizing transition matrix analysis and cartographic visualization, this study identified LULCC trends in forest, urban, and agriculture land conversions across Indonesia. It was estimated that Indonesia’s urban land increased by nearly 1,500 km² over the study period, primarily in the form of agricultural land conversions, particularly on Java Island. Although agricultural land experienced a net loss of around 10,000 km², significant expansions were observed in regions outside Java, particularly in Sumatra, Kalimantan, and Food Estate Program locations. Forest land declined by more than 61,000 km², with more than 99% of the forest land converting mainly into mixed vegetation, indicating potential large-scale deforestation. However, nearly 88,000 km² of mixed vegetation reverted to forest land, suggesting potential reforestation or regrowth in specific regions. Considering these transitions, this study also addresses challenges associated with land use classifications and the likelihood of errors of omission and errors of commission occurring on an interannual basis. Furthermore, the study further discussed key environmental concerns linked to land use policy, including the Food Estate Program, large-scale coal mining, and extensive oil palm plantations, which have contributed to deforestation, land degradation, potential food security issues, and other challenges. Ultimately, this study provides insights into comprehensive long-term and large-scale LULCC dynamics, which if understood are a key to more effective land management policy and sustainable land use planning and conservation efforts in Indonesia
Licensure as Pathway, Not Barrier
Get PDFThe legal profession knows it has an access to justice crisis. One side lacks a lawyer in approximately three-quarters of the twenty million civil cases filed across state courts every year. Against that concerning backdrop is how we license attorneys. The most common method is the written bar exam. But that exam bears little resemblance to the practice of law, produces racially disparate results, and is shockingly expensive for law graduates to prepare for and take. Its opaque scoring practices alongside its rare administration—offered just twice per year—strengthens the idea that the modern bar exam operates more as a barrier than a measure of competence to practice law. But no one has suggested connecting a public service pathway to a state’s pre-existing “civil-Gideon.” Civil Gideon “refers to the idea that people who are unable to afford lawyers in legal matters involving basic human needs - such as shelter, sustenance, safety, health, and child custody - should have access to a lawyer at no charge.” This Article argues that Connecticut should pair its right to counsel eviction defense statute with a supervised practice pathway to attorney licensure. The Article proceeds in three parts. First, it briefly explains the bar exam and its history. Second, it considers the state of the legal profession with a particular focus on Connecticut and its efforts to address and improve access to justice. Finally, the piece argues for pairing CT-RTC with a supervised practice pathway to attorney licensure
Growth of Methanogens Using Pyrite as an Energy Source: Implications for Life on Mars
Get PDFThe search for life beyond Earth has been the motivating factor for many scientist’s research in the past and currently. Specifically, the efforts have largely been focused on Mars. Mars exhibits qualities that are similar to the life-harboring characteristics of Earth, creating the possibility for life to exist on Mars. Mars’ subsurface conditions may be ideal for specific microorganisms to thrive, providing a haven away from the harsh surface conditions (Mancinelli, 2000). It is known that one of the most important elements to support life, H2O is found in the subsurface of Mars, along with an atmosphere lacking oxygen, and an atmosphere with a trace of methane (Wray, 2021). Microorganisms belonging to the domain Archaea are ideal candidates for an extreme environment like Mars, specifically methanogens. These organisms are anaerobic, typically using hydrogen to fuel growth through methanogenesis, releasing methane as a byproduct of metabolism. Methanogens offer a solution for the methane found on Mars. The survivability of methanogens in Martian conditions has been studied in Dr. Kral’s laboratory demonstrating their ability to survive using limited nutrients (Kral, et al., 2004).
This research project observed the growth of Methanothermobacter wolfeii, Methanosarcina barkeri, Methanobacterium formicicum, and Methanococcus maripaludis using pyrite as an energy source to fuel metabolism. Methane is a product of methanogenesis, allowing for growth to be monitored through methane output. The four species were each prepared in the most basic media, MM, and incubated in their ideal growth conditions. Two of the four methanogens showed growth using pyrite as an energy source, M. formicicum and M. barkeri. The two that showed zero growth were M. maripaludis and M. wolfeii. Further experimentation was done regarding the sterilization of pyrite and its effects on growth