33760 research outputs found
Sort by
Determining the effects of cover crop residue on soil moisture dynamics in no-till fields using modeling and experimental approaches
No full textCover crops conserve soil moisture by reducing evaporation during dry periods and runoff during heavy precipitation, as well as increasing soil water holding capacity in the long term. However, the immediate impact of cover crop residue presence and quantity on soil water content response to precipitation (infiltration) is inconsistent. In this project, the relationships among cover crop mulch characteristics and infiltration were examined through the lenses of a multi-state on-farm research trial, evaluation of a mechanistic crop-soil-water-mulch model, and a local field experiment on cover crop termination methods. In Chapter 1, soil water content data collected over 6 years in 16 states through an extensive on-farm research trial was paired with meteorological records to assess individual infiltration events occurring before cash crop canopy closure. Mean infiltration did not differ between the No Cover and Cover Crop plots, and cover crop biomass at termination (0-11,000 kg ha-1) was only occasionally a significant predictor of infiltration. In Chapter 2, soil water content data collected through the same on-farm experiment throughout the cash crop growing season (May-September) was compared to outputs from a mechanistic model, 2DMAIZSIM. The model consistently overpredicted the initial volumetric water content (VWC) and underpredicted infiltration. Integrating the impact of cover crop water use while growing and the preferential water channels formed by cover crop roots into the model structure would likely improve 2DMAIZSIM performance. Chapters 3 and 4 examine the impact of cover crop termination method on cover crop residue in a field experiment in which cereal rye (Secale cereale L.) was either roller-crimped or left standing and then sprayed with either a systemic (glyphosate) or contact (paraquat) herbicide. Cumulative infiltration and evapotranspiration from cover crop plots, as well as residue decomposition, did not differ between herbicides. Between the mechanical treatments, greater soil temperature fluctuations were observed in the roller-crimped cereal rye, as well as higher concentrations of recalcitrant chemical components (lignin and holocellulose). This body of work helps to elucidate the complex relationships between soil moisture dynamics and cover crop residue, which in turn improves guidance for growers seeking to maximize the benefits of cover crops
Understanding and Addressing Online Tracking
No full textDespite the growing international conversation around data and privacy protection, vis-à-vis regulations like the European Union’s (EU) General Data Protection Regulation and California’s Consumer Protection Act, online privacy, today, is at risk. How should users protect themselves from online tracking that they cannot see and have very little control over (i.e., surreptitious or stateless tracking practices)? What, according to the individuals themselves who are being tracked, are considered socially acceptable or unacceptable tracking practices? And where can policymakers look to find out how their new data and privacy protection laws are working on the ground—by the actual companies tasked with complying with those laws?
To address these issues, I first set out to provide users with a tool to help them protect their online identities. My collaborators and I focused on a cookie-less form of tracking known as canvas fingerprinting. We measured the web’s state of canvas fingerprinting in a half-a-million website scrape, finding that the use of the canvas for fingerprinting was increasing: from five, to seven, to 11 percent on popular websites in the years 2014, 2016, and 2018, respectively. We then built a state-of-the-art supervised machine learning model to predict when websites engage in this type of tracking: ML-CB. Our new tool outperformed the prior state of the art by approximately ten percentage points per F1 score (i.e., the harmonic mean between precision and recall). In short, we offer an accurate and robust tracking blocker that users can leverage to keep themselves more private online—assuming, of course, that this type of tracker blocker is a type that users would want to use, a question I addressed in follow-up work.
ML-CB was a state-of-the-art canvas tracking blocker, but the tool itself begs the question: Is the type of tracker blocking offered by ML-CB a type that users want? To address this question, I next turned to understanding the norms surrounding online tracking. My collaborators and I conducted a two-part user study canvassing participants’ opinions toward online tracking after being exposed to tracking artifacts, using a custom Chrome browser extension visualizing “the tracker’s perspective” of the participant. Participants used the extension for one week and provided their opinions on visualizations, like when a tracker might infer they go to bed at night or what potentially sensitive interests a tracker may think they have. The work provided strong empirical evidence that users still (after many years of online tracking proliferating on the web) disliked tracking, with over 80% of participants finding at least one of the visualizations of tracking “creepy.” At the same time, the work also found that users are largely heterogeneous when it comes to agreeing on which aspects of tracking (i.e., which visualizations) are creepy. Even for the visualization with the most participants agreeing it was creepy, no more than 66% of participants agreed that the visualization was creepy. What this means is that this problem is ripe for regulation—if users are generally perceiving tracking as creepy, but cannot themselves identify which aspects of tracking should be limited, then that is a great place for a regulator to step in. And this is exactly what is happening with the worldwide efforts to enact data and privacy protection laws. The problem, however, is that protecting privacy and data—i.e., tracking-adjacent properties—is a difficult task.
As I found in my work on tracking transparency, some efforts to protect data are necessary, but the difficulty lies in how those efforts take shape. Guiding legislative efforts is a growing field of research, where researchers are measuring compliance with privacy and data protection laws. These research efforts, however, face many obstacles—law is nuanced, ambiguous, and carries consequences that can be monetary or reputational; even in the case of compliance, the specter of non-compliance can be damaging. In turn, research in this field could help address the complex problems of privacy and data protection regulations, but would benefit from procedural-focused, field-level systematization. To address this issue, my collaborators and I systematized prior work measuring the legal compliance of privacy and data protection laws. We find that most prior work focuses on web analysis (43%) and almost all researchers focus on the GDPR (77%). Some researchers note legal exceptions as possibly being applicable (26%), but few researchers investigate these exceptions. Less than half of papers detailed how they approached ethics (40%), and those that did most frequently mentioned institutional ethics review. I end this work with a number of recommendations, including how future researchers may want to clearly articulate the goals of studying compliance, address legal ambiguity with legal resources as opposed to homegrown resources, and responsibly disclose results of non-compliance
Multiomics Analysis Reveals the Relationship between Muscle Cell Area and Weight in Rainbow Trout
No full textMuscle yield in Rainbow Trout is an important and marketable trait. Cell size and count have been proven to influence body size, a process regulated in party by genetic variants linked to growth and nutritional factors. We hypothesized that phenotypic divergence between USDA’s National Center for Cool and Cold Water Aquaculture (NCCCWA) selectively bred high and low fillet yield genetic lines can be explained in part by increased muscle cell size and count. Our investigation found that there was a significant correlation between both cellular filled area and several economically relevant traits, including body weight, muscle weight, visceral weight and body length. A multi-omics approach including transcriptome interrogation and genome wide association study allows us to assess gene expression signatures, and single nucleotide polymorphisms, (SNPs), explaining phenotypic variability.
Transcriptome interrogation revealed associations of autophagic and catabolic mechanisms to increased cell size. Homeostatic and developmental pathways were also noted as upregulated in high filled area individuals. In contrast, muscle contractile pathways were noted as downregulated, a phenomenon that may be explained by the interplay of environmental conditions.
A total of 728 SNPs 728 surpassed our stringent cutoff for significance when performing genome wide association analysis. The majority of these SNPs cluster on chromosome 2 (n=713) and overlap with notable muscle regulatory genes such as ribosomal RNA processing 15 homolog, Cornichon homolog 4 and fasciculation and elongation protein zeta-2.
This work sheds light on the complex genetic architecture underpinning muscle mass accretion in genetically enhanced rainbow trout mediated by enhanced contractile machinery and metabolic support mechanism
Visual Content Synthesis at Scale
No full textHumans love to create visual content. Every day, we take photos with smartphones, edit videos using intuitive apps, and create artworks through increasingly accessible digital tools. These widespread practices have led to an explosion of visual data shared continuously on the internet, building massive collections of images and videos that capture diverse human experiences. This enormous accumulation of visual data, together with rapid advancements in GPU computing, has become the foundation for training large-scale generative models, the key to automatically synthesizing top-tier visual content. By learning directly from the rich online visual repositories, these models internalize intricate patterns, styles, and concepts, enabling re-compose these elements to novel samples based on the user's inputs. In this thesis, we study and design scalable generative models that digest and improve with visual data, evaluation metrics that can precisely monitor the progress, and develop applications based on these pre-trained models. This thesis begins by designing frameworks for scalable video generation models. This includes both autoregressive models trained on the discrete tokens obtained through a discrete tokenizer and diffusion models trained directly on the pixels. In addition, we develop a novel video tokenization schema, enabling more compact video representations for larger generative models to train on. Next, we perform a careful analysis of the mainstream automatic evaluation metric. In the last chapter of the thesis, we study several practical scenarios to apply the pre-trained large-scale generative models, with tasks not only generation and beyond the original image and video domains
Addressing Anti-Black Racism at UMD – For a Limited Time Only: Black Student Demands and Institutional Accountability at the University of Maryland
No full textTitle of Dissertation: ADDRESSING ANTI-BLACK RACISM AT UMD – FOR A LIMITED TIME ONLY: BLACK STUDENT DEMANDS AND INSTITUTIONAL ACCOUNTABILITY AT THE UNIVERSITY OF MARYLAND
Victoria Alexander-Thompson, Doctor of Philosophy, 2025
Dissertation directed by: Associate Professor Bridget Turner Kelly, Department of Counseling, Higher Education, and Special Education
At the University of Maryland, in 2020, Black student leaders engaged in campus activism to create a list of 25 demands that UMD publicly committed to meeting. These demands were made in the context of the 2020 resurgence of the Black Lives Matter movement and the murder and death of two Black men on campus in 2017 and 2018, respectively. Five years after the making of these demands, this dissertation examines Black UMD students’ perspective on UMD policy, practice, and communication, to assess whether UMD has remained accountable to addressing the concerns of Black students.Using instrumental exploratory case study, data was collected through document analysis, historical analysis, and focus groups including two populations: 1) Black UMD undergraduate and graduate students and 2) UMD faculty and staff who support Black student initiatives. The theoretical framework of this study references Fraser’s (2009) Three Justice Dimensions and Black Critical Theory or BlackCrit (Dumas & Ross, 2016) to leverage critical organizational theory and critical race theory. This study’s findings problematize general diversity, equity, and inclusion (DEI) initiatives to illuminate how the needs of Black students are often further marginalized when institutions favor performative and generalizable diversity commitments over intentional action toward combating the specific and pervasive problem of anti-Black racism
IMAGING THE SHALLOW SUBSURFACE FOR LUNAR EXPLORATION USING SEISMIC SURFACE WAVES
No full textGround-based geophysical exploration of the Moon has been identified as high priority science in the next decade to be accomplished by landed geophysical networks, payloads on commercial landers, and with instruments deployed by crews at the lunar surface. In-situ seismic experiments will be important for probing the near subsurface and deep internal structures of the Moon. Previous experiments during Apollo 14, 16, and 17 missions used deployed active seismic instrumentation to study the shallow subsurface structure of the Moon. However, no clearly identifiable surface wave signals could be resolved. This is generally attributed to strong signal attenuation and scattering by complex near-surface structures. Alternatively, the coarse receiver geometries used can cause spatial aliasing of surface wave signals to occur making the fundamental mode difficult to identify. Identifying surface waves and developing methods to extract information from them in the highly scattering environment of the Moon will add a valuable tool for lunar exploration efforts.Here we use a geophysical analog study of surface waves in terrestrial complex media to demonstrate how these waves can be potentially used on the Moon. Active 3-component nodal and vertical component geophone surveys were collected over lava flows in the San Francisco Volcanic Field (SFVF) in order to image the velocity structure of a volcanic lunar analog environment. We use multichannel analysis of surface waves (MASW) and horizontal-to-vertical spectral ratio (HVSR) methods to interrogate and constrain the near-surface shear velocity and volcanic structure of the SFVF. We use reflectivity synthetic modeling to address how spatial aliasing caused by coarse receiver spacings in the SFVF and Apollo 16 surveys can affect our ability to resolve dispersive surface wave signals using traditional dispersion curve methods like MASW. Results from this work address the applicability of active source surface wave methods for probing the complex shallow subsurface in a scattering volcanic media analogous to the lunar near-surface structure with implications for future active source seismic survey design on the lunar surface
Birth-Parent Perspectives on Safety and Trust in Inpatient Postpartum Health Care
No full textThe authors explore inpatient postpartum safety and trust from the perspectives of birth-parents, who revealed that these concepts extend beyond physical health and survival to emotional well-being, autonomy, communication, and shared decision making. Drawing from experiences of inpatient postpartum care during the COVID-19 pandemic, participants emphasized feelings of safety as personal and relational, shaped by timely information, clinician openness, care coordination, and a sense of partnership. Findings highlight critical gaps in healthcare quality, including an over reliance on electronic health records (EHR) over lived experience. Opportunities for improvement include information sharing, adequate resource distribution, consent acquisition, and language concordance. Findings from this study support the need for systemic shifts from postpartum care models focused on bureaucratic policies to those focused on supporting patients’ lived experiences, cultural values, and knowledge. Results underscore the significance of epistemic in/justice, relational trust, and inclusive care practices as essential components of high-quality postpartum care.This research was supported by the Agency for Healthcare Research and Quality (R18HS027260). We thank our participants for their time and willingness to share.https://doi.org/10.1016/j.socscimed.2025.11871
The MUVASHIIIP: Understanding Afrofuturism, The Black Imagination, and Time Jumping Through the Past, Present, and Future
No full textThis thesis explores the concept of Afrofuturism as a framework for understanding the Black Imagination and its capacity to navigate and transcend the boundaries of time. By examining the interconnectedness of the past, present, and future, this research highlights how Afrofuturism reclaims and reimagines Black cultural narratives through artistic, historical, and speculative lenses. Drawing on key themes such as resilience, identity, and innovation, this study investigates how creative expressions, which includes music, dance, pop culture, and visual art, serve as tools for time-jumping and reinterpreting history.Through an interdisciplinary approach that combines critical analysis and creative practice, this thesis examines the ways Afrofuturism offers a vision of liberation and empowerment. It challenges traditional constructs of temporality and oppression by centering Black experiences and perspectives. The research not only celebrates the rich cultural heritage of the African diaspora but also envisions transformative futures shaped by technological, cultural, and spiritual innovation
CONTROL OF PHASE TRANSFORMATIONS THROUGH THERMAL PROCESSING MODIFICATIONS OF HIGH-STRENGTH LOW-ALLOY STEELS
No full textHY-80 steel was developed by the U.S. Navy and its industrial partners following World War II to address metallurgical problems associated with catastrophic low-temperature brittle fractures of the incumbent hull material at the time. It represented a large step forward in the performance of hull steel alloys at that time, with significant increases in strength and toughness, particularly at low temperatures, while remaining weldable and unsusceptible to stress-corrosion cracking. It is also a versatile alloy system, being able to be produced in both wrought and cast forms, with some limitations. Shipbuilding requires creating large castings with thick sections to withstand the harsh operational conditions, which is challenging due to issues with elemental segregation during solidification and slow heating and cooling rates in thick sections during heattreatments. One purpose of the work described in this thesis was to improve the mechanical properties of HY-80 castings by heat-treatment process modifications by incorporating an intercritical heat treatment with the targeted purposes of stabilizing austenite and limiting grain growth.
Performing intercritical heat treatments on steel requires near complete knowledge of the transformation processes taking place in the alloy during the heat treatment, which are affected by every prior step in the production of a steel ingot, including ingot design, solidification, and other heat treatments. To that end, an experimental investigation on cast HY-80 material was undertaken to measure secondary-dendrite-arm spacing (SDAS) and used in conjunction with Scheil solidifications simulations to create homogenization simulations to achieve more uniform properties. Intercritical heat treatments were carried out on a martensitic HY-80 microstructure created by quenching from the single-phase austenite phase at high temperatures.
To better understand the martensite transformation, a martensite-start temperature, Ms, model for lath, plate, and ϵ martensite was developed by the CALculation of PHAse Diagrams method (CALPHAD) using an open-source steels thermodynamic database, which was also developed for this work. In addition, a novel martensite-type prediction Gaussian process classification (GPC) machine-learning model was developed to increase the accuracy of the Ms model in the numerous instances where the type of martensite is unreported in the literature. The GPC and ϵ martensite models were published for the first time, while the lath- and plate-martensite were updated and published using an open-source steels database vice a closed, proprietary database for the first time. This was necessary because the closed-source databases and commercial software provide limited opportunity for learning the fundamentals of their property models or quantifying their uncertainty.
The transformation of lath martensite to austenite in the intercritical temperature regime of HY-80 was studied using metallography and differential scanning calorimetry (DSC), with experimental results being used to calibrate the CALPHAD equilibrium predictions to be more relevant for industrial heat treatments, which was also published for the first time. Quantitative optical metallography with tint etching of the martensite/ferrite phase was coupled with machine learning to measure the phase fractions after long heat treatments. This method can be applied to a variety of materials to increase the industrial applicability of CALPHAD predictions to each material.
The DSC and metallographic results were used to select a short, intercritical heat treatment for HY-80 by replacing an austenitization step with an intercritical step at a temperature near the Ac3 to enrich interlath austenite films, primarily with carbon and nickel, to improve its mechanical properties. Kinetic simulations using Thermo-Calc’s DICTRA and open-source phase-field software were developed and are compared. The phase-field models should be more physically accurate due to the incorporation of gradient-energy effects that help drive microstructures toward equilibrium. Both simulations show that interlath austenite films becomes enriched in austenite-stabilizing elements at the austenite/martensite boundary during short intercritical heat treatments, increasing its local stability against decomposition. This is a novel approach tograin-boundary toughening of lath martensite via local austenite stability of interlath films.
Fully heat treated HY-80 material was characterized by high-energy x-ray diffraction using a monochromatic synchrotron source, which indicated an increase in the volume fraction and a change in the composition of retained austenite from the intercritical heat treatment as compared to the baseline quench-and-tempered microstructure. The mechanical properties were evaluated using quasistatic tensile and instrumented Charpy V-notch impact energy testing at two temperatures. The intercritical heat treatment improved the low-temperature toughness of HY-80 by shifting the ductile-to-brittle transition temperature downwards while maintaining acceptable tensile strength and ductility. An apparent ductility reduction was investigated by examination of the fracture surfaces in a scanning electron microscope, which indicated that microporosity from the casting process was the likely cause. Additional work is needed to optimize the heat treatment and assess its feasibility for thick sections; however, the initial results show promise for at least a subset of HY-80 castings
AN ANALYSIS OF FACTORS THAT PROMOTE TEACHER STUDENT RELATIONSHIPS OF ALTERNATIVE EDUCATIONAL STUDENTS BASED UPON PERCEPTIONS OF SCHOOL CLIMATE DATA
No full textABSTRACT
Title of Dissertation: AN ANALYSIS OF FACTORS THAT PROMOTE TEACHER STUDENT RELATIONSHIPS OF ALTERNATIVE EDUCATIONAL STUDENTS BASED UPON PERCEPTIONS OF SCHOOL CLIMATE DATA
Gordon Libby, Doctor of Education, 2024
Dissertation directed by: Associate Director School System Leadership Doctoral Program, Pamela Shetley, Ed. D., College of Education, University of Maryland, College Park
A quantitative quasi-experimental study was conducted in one large urban school system, in the Mid-Atlantic region of the United States to examine the efficacy of alternative high schools for students at high-risk of academic failure as compared to students in traditional high schools. The primary research question addressed how students at JCCPS alternative schools, who are often considered at-risk, perceive teacher “caring or nurturing” behaviors according to the school climate survey compared to their peers' traditional high schools. The investigation revealed that there is a significant difference in student perceptions of teacher caring and nurturing behaviors related to school climate for high-risk students enrolled in alternative schools versus students enrolled in traditional schools.
The research was conducted in one large urban school system and will be referred to as Jefferson Conway County Public School System (JCCPS). JCCPS has utilized alternative school programs for over twenty years. Through a quasi-experimental analysis of student responses on a biannual school climate survey, this study examined the differences in student perceptions of teacher caring and nurturing behaviors related to school climate. Twelve items from the survey emerged as being relevant to the study and were compared to Bulach’s Five Factors, a theoretical framework for understanding student perceptions of teacher caring. The data were analyzed using descriptive statistics and t-tests to determine significant differences between the two groups. The data collected provided an opportunity to make recommendations to JCCPS on the benefits that alternative schools have on at-risk alternative school students in their system. Additional research was also recommended to expand this research to multiple school districts to further identify the significant factors that are explanatory of student perceptions of teacher caring and nurturing behaviors for at-risk students enrolled in alternative high schools versus students in traditional high schools.
AN ANALYSIS OF FACTORS THAT PROMOTE TE