6834 research outputs found
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Asteroseismology study of DA pulsating white dwarf stars observed by TESS.
No full textAsteroseismology is the most advanced technique for studying stellar interiors. Romero et al. (2022) published the discovery of 74 new pulsating white dwarfs using the Transiting Exoplanet Survey Satellite (TESS). We used the published pulsation periods to perform an asteroseismological analysis of 39 of these stars, which are multi-periodic variables. By comparing each star’s independent pulsation modes to models from the White Dwarf Evolution Code (WDEC) grid, we determined the effective temperature, mass, and mass of hydrogen and helium layers. We have used the photometric determinations for the photospheric parameters to constrain our seismological fits (Gentile Fusillo et al., 2021). By comparing my values with independent determinations and asteroseismic studies (Romero et al., 2022), we were able to quantify external uncertainties in the fits. In this thesis, I will present my astroseismology results
Understanding spatial and temporal aquatic exposure and hazards of contaminants of emerging concern.
No full textContaminants of emerging concern (CEC) encompass both natural and anthropogenic compounds in the aquatic environment and are of concern to both human and aquatic species exposure. However, we do not have a robust understanding of spatial and temporal exposure to a diverse range of CECs and how these dynamics influence water quality hazards. Here I examine the occurrence of multiple of these contaminants including perand polyfluoroalkyl substances (PFASs), persistent organic pollutants (POPs), and harmful algal bloom (HAB) toxins. First, I performed a critical review of existing literature to understand the global occurrence of PFASs within surface and groundwaters followed by a probabilistic hazard assessment utilizing environmental exposure distributions compared to various regulatory levels. I observed near ubiquitous occurrence of PFASs around the globe, identified increased concentrations in groundwater compared to surface, and highlighted the need for a greater understanding of the temporal exposure to PFAS in surface waters, especially near non-industrial sources like wastewater treatment plants. Next, I quantified the occurrence of twenty-four priority PFASs in two wastewater treatment plants within a semi-arid region of the southern USA over a two-year period to better understand PFAS introduction rates within these systems. I observed higher rates of short-chain compounds compared to legacy PFAS and while hazard assessments for aquatic organisms were not exceeded, effluent concentrations exceeded recently introduced drinking water regulations. Next, I investigated the tissue distributions of both emerging and POPs in three fish encompassing different trophic positions. I observed both PFAS and legacy POP accumulation in all fish, with measured levels of both presenting risk to human consumption based on estimated daily intake values. Lastly, I investigated the occurrence of various HAB toxins across various seasons in twenty reservoirs across a pronounced rainfall gradient. I identified the importance of understanding cyanotoxin exposure at depth, location, and season, including elevated in locations and during times of the year not commonly examined for routine field assessments. This dissertation identified key considerations for how, when, and where environmental exposure is examined, because failure to do so and just follow routine approaches can underestimate water quality risks
From father to feminist : "Call her daddy" and the rhetorical function of imperfect feminism.
No full textThe podcast Call Her Daddy and its host, Alexandra (Alex) Cooper, have evolved significantly since it first aired in 2018, developing rhetorically significant elements. This thesis argues that Cooper and her podcast represent a modern and evolving conception of imperfect feminism, made especially important in its continued evolution in the contemporary media environment. Utilizing feminist rhetorical analysis, I explore three related aspects of the podcast: hegemonic trope presentation, parasocial relationship impacts, and feminist apologia rhetoric. Situating these aspects of the podcast within its broader media ecology, it is evident that imperfect feminism functions as affective activism. This thesis demonstrates the significance of imperfect feminism as both a conceptual theoretical heuristic and as a successful rhetorical strategy for women in traditionally masculine spaces like sports commentary and the internet more generally
Uncovering vital molecular contacts within the replisome and characterizing fail-safe mechanisms ensuring genomic stability in E. coli.
No full textTo study replisome coupling interactions and gain a better understanding of enzymatic communication, we modeled interfacial residues between α-Pol III and τ-CLC. A critical C-terminal linker in the τ-subunit tethers α-Pol III to the DnaB helicase for efficient DNA replication in E. coli. Therefore, disrupting interactions between τ-CLC and α-Pol III also disrupts coordination with the DnaB helicase. To probe this phenomenon, we initiated our study through in vitro investigations by using site-directed mutagenesis techniques to alter the following residues in α: L1097S, Y1119A, L1097/8S, and L1128S. We then purified these α-Pol III mutants: 1) to verify site-specific interactions between τ-CLC and α-Pol III by probing target residues through nickel pull-down assays, and 2) to quantify differences in unwinding and polymerization activities amongst wild-type and mutant enzymes by perturbing DNA unwinding and synthesis coupling with an in vitro assembled replisome. Once we confirmed that each of these mutations disrupted physical interactions with τ and severely compromised DNA synthesis abilities in whole replisome rolling circle experiments, we created analogous genomic mutants of α-Pol III in vivo using CRISPR-Cas9. Our in vivo investigations uncovered severe cellular and genomic fitness deficits. Decoupling between enzymes led to severe cellular stress phenotypes, characterized by reduced growth, lower fitness, heightened stress, SOS induction, accumulation of ssDNA gaps, and increased cell death. Without effective coupling, labile ssDNA accumulates and is left exposed. However, E. coli has numerous mechanisms to circumvent decoupling, including multiple replication restart pathways to rescue compromised cells. The Rep helicase can rescue abandoned replication forks by remodeling the fork to reload DnaB directly. Deletion of Rep (Δrep) reduces ssDNA gaps in untreated cells; however, in the presence of various genotoxins, the absence of Rep results in an increase in ssDNA gaps due to DNA damage-linked replisome decoupling. By characterizing decoupling consequences within the E. coli replisome, we have gained a deeper, more comprehensive understanding of these dynamics and essential interactions that contribute to the overall health and survivability of the cell. Taken together, we’ve demonstrated that replisome communication between these enzymes is crucial for overall health and the maintenance of genomic information and integrity
Digital inequity in a rural broadband desert : a qualitative single case study examining the barriers to teaching and learning for K–5 teachers and parents.
No full textThis study explored the problem of digital inequity in a rural broadband desert caused by the lack of adequate internet access at students’ homes. The study examined this problem by reviewing barriers teachers and parents encountered with teaching and learning. Along with examining the barriers, the study described consequences that resulted from these barriers.
The method for this study was qualitative single case study which provided the opportunity to gather in-depth insights into the barriers. Ertmer’s (1999) theoretical framework of first-order and second-order barriers informed the research questions, data collection protocols, and data analysis. Collected data included semi-structured interviews, a focus group, and digital equity surveys.
Four themes report findings that occurred during the emergency remote teaching during the COVID-19 pandemic shutdown. First, the lack of adequate access to the Internet in the home, not hardware, was related to how teachers delivered instruction and how the parents adjusted to their children’s learning. Second, teachers and parents did not resist the change to emergency remote teaching during the COVID-19 pandemic, but teachers and parents expressed frustration with remote teaching because of families’ lack of adequate access to the Internet. Third, lack of adequate Internet access in the home added time to how teachers planned and delivered instruction and how parents adjusted to their children’s learning. Fourth, teachers and parents described decreased student engagement and motivation as consequences of remote teaching and learning during the COVID-19 shutdown.
However, four themes relate to the findings related to the period during after the emergency remote teaching and are ongoing. First, the teachers, parents, and their children have hardware and devices to use, but the parents and their children do not have adequate access to the Internet to use the hardware. Second, parents regularly spend extra time driving to locations to get adequate Internet access. Although teachers had access to training and support (e.g., technology, software, platforms), parents did not have training and require phone support from teachers for their children’s assignments. Teachers and parents prefer in person teaching and learning but believe technology contributes to children’s education. The findings of this study have implications for how parents and teachers can overcome barriers caused by the lack of adequate Internet access. The findings of the study also have implications for policymakers. The study provides a rationale for policymakers in advocating additional funding for broadband projects in rural areas
Exploring the morphospace of cidaroid echinoid spines.
No full textCrown group cidaroids (Echinodermata: Echinoidea: Cidaroida) display a variety of spine morphologies thought to be adapted in response to selective pressures around them. Echinoid spines directly interact with their surroundings and morphologies should reflect environmental conditions changing through time. To quantify trends in morphology through time, 2D geometric morphometrics were applied to cidaroid spines to track changes in morphospace. This was completed through four anatomical landmarks and 250 semi-landmarks to grasp the entirety of the spine shape. Once plotted into multivariate space, trends related to time and morphology were found within one family of cidaroids, Psychocidaridae. These trends coincided with major geologic events, such as the Marine Mesozoic Revolution and Cretaceous-Paleogene extinction. Contractions and shifts in morphospace could then be related to predation and changes in marine community structure. Additionally, modern cidaroids display an expansive morphological diversity, while not being taxonomically diverse
Deep learning of visual features with limited supervision.
No full textRecent advances in deep learning have led to significant improvements in various computer vision tasks. Typically, deep learning models require large-scale labeled
data for training, but obtaining annotations is costly in fields like medical imaging
and underwater imaging. This dissertation explores methods for learning deep visual
features with limited human supervision, expanding deep learning’s applicability to
diverse real-world tasks.
We propose solutions in three key areas. First, we introduce a selective pretraining approach that enhances transfer learning by selecting pre-training samples
more relevant to the target domain. Second, we design a self-supervised learning algorithm that can leverage large amounts of unlabeled image and video data. Third, we
develop an active learning (AL) algorithm that iteratively selects the most informative
samples for annotation to optimize learning with minimal supervision.
On selective pre-training, we achieve 77% accuracy on imbalanced CIFAR-10
using only 500k pre-training samples—outperforming full ImageNet pre-training. On
Penn Action video classification, our contrastive learning model reaches 76% accuracy,
significantly surpassing ViViT model. In active learning on aquatic invasive species
data, we achieve 78% balanced accuracy with just 200 labeled samples, improving
27% over random sampling. Together, selective pre-training, self-supervised learning,
and active learning provide a flexible framework to approach deep visual feature learning depending on the availability of labeled data, unlabeled data and computational resources
Identifying vaping hazards through the evaluation of exposure methods and cell culture models for e-liquid mixtures.
No full textVaping has become a popular method of engaging in “smokeless” socialization since the introduction of e-cigarettes in the United States tobacco market. In 2007, e-cigarettes were presented as portable vaping devices serving as alternatives to traditional tobacco cigarettes. Due to the evolution of technology and the addition of unique e-liquid formulations (i.e., the liquid used in an e-cigarette or similar device), e-cigarettes have captured the attention of youth. E-cigarette usage in youth is a public health concern considering the number of reported underage usage and rapid onset of lung illnesses contributing to hospitalizations, such as EVALI (e-cigarette or vaping product-use associated lung injury). As a result, steps have been made to identify the chemicals in e liquids that induce toxicity. Due to the complexity of e-cigarettes, there is a continued need to implement interdisciplinary approaches for hazard identification of vaping toxicity, namely the evaluation of exposure methods and in vitro model systems.
This dissertation introduces a combination of exposure techniques for hazard identification of e-liquid binary mixtures using lung cell models. This work aims to address three critical areas: (1) utilize previously established mathematical mixture modeling for chemical interaction analysis of binary mixtures, (2) collect the condensates of heated vaping products for cytotoxicity screening, and (3) compare the effects of liquid inoculation versus direct aerosol exposure of vaping binary mixtures to cells. The findings show that certain e-liquid ingredients (such as flavoring chemicals and diluents) can lead to changed cytotoxicity over a dose-response relationship when combined at different ratios. Mathematical mixture modeling shows that when these chemicals are simultaneously exposed, they contribute to toxicological antagonism. The collection of condensates proves to be successful for pooling heated e-liquids, and after exposure to cells, cell viability decreases, and oxidative stress increases. Lastly, qualitative and quantitative results show that different exposure methods induce different epithelial barrier integrities. These studies promote the inclusion of multiple exposure methods and cell culture model systems for continued assessment of vaping-induced toxicity
Total synthesis of polycyclic natural products : synthetic studies on (+)-ineleganolide, (–)-sinulochmodin C, verrillin hydrate, and aleutianamine.
No full textPolycyclic furanocembranoid natural products are a broad and diverse class of marine and terrestrial natural products that have captured and held the attention of the synthetic and biomedical communities for nearly three decades. Their daunting polycyclic molecular architectures, coupled with promising biological activities and intriguing biosynthetic relationships have rendered these natural products as formidable and popular targets for total synthesis. Despite a well-documented and tremendous effort from the synthetic community, only one de novo total synthesis of a natural product of this type had yielded to total synthesis at the outset of this work (ca. 2020). Accordingly, we set out to develop a flexible, bio-inspired strategy that would allow for the total synthesis of diverse furanocembranoid natural products leveraging selective transannular cyclization reactions. Our pioneering efforts in this area eventuated in the total syntheses of (+)-ineleganolide and (–)-sinulochmodin C, two coveted natural products that had previously evaded multiple total synthesis efforts. This synthetic strategy provided expedient access to advanced intermediates poised for conversion to (+)-verrillin and other high oxidation state furanocembranoids. In 2019, Hamann and coworkers disclosed the isolation of a novel polycyclic pyrroloiminoquinone alkaloid, (+)-aleutianamine, from the marine sponge Latrunculia austini. The natural material was found to possess potent and selective cytotoxicity in vitro against a human pancreatic cancer cell line (PANC-1, IC50 = 25 nM). This remarkable and unprecedented alkaloid contains a variety of interesting structural features. These considerations, coupled with the promising initial biological activity of this alkaloid motivated a renewed synthetic interest in pyrroloiminoquinone chemistry, a subfield that had seen little significant progress since the early 2000s. The western portion of the natural product contains the pyrroloiminoquinone moiety common to members of its class, while the eastern region is comprised of two interwoven, heteroatom-adorned bicyclic systems. The synthetic challenges conferred by these features demanded multiple generations of synthetic strategies to complete a convergent and concise total synthesis. Key to the approach was a novel application of a vinylogous Mukaiyama-Michael reaction between a siloxythiophene and a pyrroloquinone monoketal. A sequence of skeletal rearrangements and carbon-nitrogen bond formations then allowed for completion of the total synthesis
The effectiveness of parent-teacher conferences in strengthening family-school partnerships.
No full textMost parents want their children to be successful in school and want to help them succeed (Mapp, 2003). When school personnel initiate practices inviting parents to the school, creating a welcoming environment for them, honoring their contributions, and connecting them to the school community, practices cultivate and sustain respectful, caring, and meaningful relationships between parents and school staff (Mapp, 2003). Regardless of economic, racial, ethnic, and educational backgrounds, there is a strong link between educational benefits to children and various forms of family engagement, such as encouragement to succeed academically, involvement in at-home activities such as help with homework, volunteerism in schools, and participation in governance activities (K. Mapp, 2003). Students whose parents are involved in their schooling are more likely to have higher grades and test scores, attend school regularly, have better social skills, show improved behavior, and adapt well to school, regardless of family income and demographics (Henderson and Mapp, 2002). Building family efficacy means that families are recognized as essential learning team members for their students. School educators understand that families are crucial and influential resources because they know their children best (Constantino, 2020). This quantitative research study examined the effectiveness of family-school partnerships at one University-Model® school in the Dallas-Fort Worth metroplex, where parents serve as co-teachers, and their engagement of day-to-day activities is critical for student success. The vision in creating this type of school model was to increase parental influence in academics and mentorship from kindergarten through 12th grade. This study examined how parent-teacher conferences affected parent self-efficacy. The conference cycle consisted of three meetings: the beginning of the year, the middle of the year, and the end of the year. The researcher structured the parent-teacher conferences on Karen Mapp's four components of the Dual Capacity Framework: connection, confidence, cognition, and capability. The effectiveness of the parent-teacher conferences was measured following the final conference cycle using a quantitative survey adapted from Panorama Education and the Harvard Family Engagement Project (2013)