136879 research outputs found
Sort by
John Bickham field notebook: AK10373-AK10380.pdf
No full textEach page/AK number corresponds to a karyotype slide data and/or unique specimen.Data pages for AK10373-AK10380 corresponding to unique identifiers of specimens/samples examined for biological research. Specimens are primarily housed at Texas A&M University; Biodiverstiy Research and Teaching Collection
Linking Cardiovascular and Neuromotor Responses to an Orthostatic Challenge
No full textHuman physiology has adapted few responses to changes in the orthostatic gradient typically caused by gravity and postural changes. Sustained alterations to our gravitational environment, whether through bedrest or during human spaceflight missions, are known to elicit multi-system physiological decrements. Previous work has identified potential differences in the responses of males and females.
The current work delivered an acute bout of orthostatic stress to 24 sex-balanced subjects via step-wise increases in lower-body negative pressure (LBNP) levels. During this intervention, subjects performed one of four bimanual coordination tasks. Measures of systemic hemodynamics, autonomic indices, and bimanual coordination task performance were performed. Orthostatic dose-response curves were generated, and a correlation analysis between the metrics of the two systems was performed. Additionally, statistical models were selected that best predict tolerance to the orthostatic challenge using baseline cardiovascular metrics. Models using cardiovascular metrics to best predict task performance were also selected.
The orthostatic challenge was successful in eliciting early and robust cardiovascular responses, especially in metrics related to sympathetic drive. Neuromotor performance changes to the orthostatic challenge, where they occurred, were usually only detectable in the final levels of the LBNP intervention. The most consistent neuromotor responses were increases in the pace of motor inputs, and increases in the variability of forces applied. Baseline cardiovascular health metrics were the best predictors of tolerance. Time-domain autonomic indices of heart rate variability were shown to be the strongest predictors of the increases in the pace of motor inputs. No differences were detected between male and female Index of Tolerance scores.
These results inform our understanding of cardiovascular and neuromotor responses to an orthostatic challenge both in a dose-response manner and an integrative manner. They suggest that neuromotor decrements may occur at the point during an orthostatic challenge at which sympathetic drive becomes the dominant factor in further cardiovascular responses. Data also suggest that sex differences in orthostatic tolerance may not be the result of anatomical and anthropometric differences. Finally, it is proposed that the discovered linkages between the two studied systems may reside in the insula, a structure deep in the brain with functions in both systems
The Experiences of Queer Undergraduate Students in Engineering at Two Predominantly White Research Institutions
No full textLGBTQ+ students in engineering are an underrepresented group that is often treated differently in the field. In this study, I use the term queer throughout to describe this population. Engineering is a male dominated discipline comprised of white, cisgender, heterosexual males, and those who differ from this demographic are often perceived as the outsider. While the literature gives attention to queer students in STEM as a whole, few studies address engineering specifically. Progress has been made for the queer population, such as gender-neutral bathrooms and anti-discrimination policies, however, more work is needed across higher education and within STEM for this vulnerable population. This qualitative study examined the experiences of 14 queer undergraduate engineering students at two predominantly white institutions in Texas, 10 from one PWI and four from the other. The study sample consisted of participants who represented a variety of ethnicities, gender identity or expression, sexual identities, and engineering disciplines.
This study used Self-Determination Theory (SDT) and Queer Theory (QT) frameworks to understand how power and privilege either make or hinder academic experiences and choices. Participants shared their perceptions of the engineering discipline as a whole, such as interactions between and among students and professors, and how the major is taught compared to other courses outside of engineering. Participants expressed feeling unlike their peers, invisible in the classroom, and how their gender and sexual identities interfered with their daily lives. Administrators, faculty, families, and peers can learn from the findings to understand the needs of and create safe spaces for queer students in engineering where their identities are affirmed, valued, and heard. They found support during their academic journeys, shared how politics in Texas influenced their perceptions and educational experiences, and described what institutions could do better to help students succeed in engineering. Findings from this study draw implications for systemic change to make queer undergraduate students in engineering feel like they belong
A Deep Learning-Based Methodology to Re-Construct Optimized Re-Structured Mesh from Architectural Presentations
No full textDuring the mid���20th century, the emergence of novel technologies presented a paradigm shift for human intelligence. Computers, in particular, became instrumental tools for designers and architects, enabling the creation of intricate systems with freeform structures. These computers were capable of generating the final shape of designs by employing predetermined algorithms. Nevertheless, the prevalence of intricate freeform constructions is a notable characteristic of modern architecture. The design and calculation of these forms pose a complex challenge, as they deviate significantly from the original target industries in terms of aesthetics, statics, scale, and manufacturing technologies. While these structures may be intricate and, in some instances, praiseworthy, their architectural application necessitates a distinct approach. The formation of novel forms, shapes, and relationships within architectural design compositions can manifest creativity, leading to the exploration and discovery of innovative notions. Architects and designers are, therefore, inclined towards circumstances in which disparities hold significance. Architects may employ or adapt preexisting shapes as a foundation for their design endeavors. Architects draw inspiration from a particular image and integrate the associated notion into their design process, resulting in a more innovative architectural building. Current methodologies enable the meticulous hand alteration of forms through the utilization of documents or photographs. The proliferation of Machine Learning technology is augmenting architectural responsibilities, enabling swift and inventive results, expediting the design process, and developing a forward-looking approach to adjust and retrace actions instantaneously. The objective of this study is to assess the viability and accuracy of incorporating machine learning capabilities into defining an algorithmic-based methodology, with the goal of enhancing the design creativity process in architecture. This will be achieved through the utilization of image-to-mesh 3D reconstruction deep learning techniques, specifically applied to complex, irregular architectural structures. Additionally, a generative mesh optimization algorithm will be employed to generate a customizable mesh surface that can be further manipulated, paneled, and subjected to morphological operations
Multi-Cycle Dynamic Compaction of At-Speed Tests for Reduction in Test Data Volume, Test Application Time, and Power Supply Noise
No full textThe semiconductor industry has made great strides over the last few decades. Chip makers taking advantage of Moore���s law have pushed the limits of physics to shrink feature sizes on Silicon (Si) wafers. Delay test is an essential structural manufacturing test used to determine the maximal frequency at which the chip can run without incurring any functional failures. Small delay defects that were previously benign now manifest as delay faults due to the reduced timing margins. Another challenge is achieving better delay correlation with functional test, which is dominated by power supply noise (PSN). Differences in PSN between functional and structural tests can lead to differences in chip operating frequencies of 30% or more. Pseudo functional test (PFT), based on a multicycle clocking scheme, has better PSN correlation with functional test compared with traditional two-cycle at-speed test. This research focuses on the development of new test. methods for small delay defects, within the limits of affordable test generation cost, pattern count and power supply noise.
First, this work proposes a new Dynamic Compaction algorithm to generate compacted test sets for K Longest paths per gate (KLPG) in scan based sequential circuits. The algorithm uses a greedy approach to compact paths with non-conflicting assignments together over multiple at-speed cycles during test generation. Reductions in pattern counts of as much as 67% are observed with the greedy approach.
Second, compression is introduced to the test flow and the ATPG engine to observe the combined effect of compression and compaction. Multi-cycle at-speed test has around 60% reduction in pattern count over single-cycle at-speed test with similar compression rates. Higher compression rates are required for single cycle test to achieve similar test data volume and test application time which indicates more DFT effort required for single cycle at-speed tests. The compression framework is built inside the CodGen ATPG to make this process more seamless.
Third, a simulation-based test relaxation algorithm is designed for CodGen ATPG as the patterns generated by the final justification SAT Engine assigns all the bits in the pattern. This algorithm implemented inside CodSim is able to produce similar don���t care bit density compared to the previous justification algorithms inside CodGen such as FAN and PODEM. Power supply noise (PSN) estimation using weighted switching activity (WSA) is then done for these partially specified patterns (with random or adjacent fill) to compare the single and multi-cycle test power. The multi-cycle test has very similar power profile and even lower in some cases to that of single-cycle test even though the patterns are more compacted.
Finally, CodGen ATPG is improved to handle larger industrial designs by updating the SAT engine MiniSat that runs all binary justifications during the ATPG process. It is replaced with CaDiCaL a much modern SAT engine which has been able to provide significant speedup to the test generation process
How Are Standards Developed? An Analysis of the Science Standards Revision Process in Texas
No full textThis study aimed to determine how science education policy is developed and the expertise employed throughout the process. Texas was selected as a historical case due to the recent revision of the science standards, their large impact, and documentation availability. A historical perspective informed the research questions: 1) What are the key positions, underlying justifications, and factors that contributed to the development of science standards in the state of Texas? 2) What expertise do official and unofficial actors possess in the science standards revision process? 3) To what extent were Schwab���s commonplaces (subject matter, teachers, learners, and milieu) considered during the revision process for science standards? and 4) What is the State Board of Education review process followed when revising science standards? State Board of Education meetings were analyzed using naturalistic inquiry and within-case methods.
Findings indicate that several points of failure occurred throughout the revision process that may affect the viability and implementation of the resulting standards. These points of failure included flawed process design, transparency issues, and limited representation of expertise domains. Notably, the learner was not represented during the revision process. As a result, the standards risk being developmentally inappropriate for students; initial evidence suggests this is the case for several standards. To ensure standards are scientifically accurate, developmentally appropriate, can be implemented by teachers, and respectful of the environment in which it is enacted, expertise from the subject matter, the learner/learning, the teacher, and the milieu must be equally considered. Additionally, research, development, and diffusion (RD&D) should be utilized to ensure the standards and curriculum materials are appropriately tested before being required for teachers and students
Enhance PET Degrading Enzyme Performance Through Immobilization on Magnetic Nanoparticles
No full textGlobal plastic generation has reached 460 million tons in 2019 of which 353 million tons ended up as waste. PET is a widely generated and consumed thermoplastic due to its mechanical and chemical properties. It makes up to 67% of the packaging plastic. Due to its resistance to chemical and mechanical changes it becomes a challenge to handle PET waste. PET requires harsh conditions to decompose into its monomers of TPA and EG. Efforts have been made to recycle PET by degrading it to its monomers or reshaping and upcycling it from there.
Currently, the three major ways of recycling PET comprise of chemical recycling, mechanical recycling and using biological systems for recycling. Chemical recycling of PET is achieved through solvolysis and pyrolysis which is accompanied by release of toxins in the atmosphere. Mechanical recycling does not break down PET to its monomers but reshapes the PET so it can be reused. However, this only recycles PET to a certain extent, after which it can no longer be reshaped and reused since it loses mechanical strength. Biodegradation has become an attractive alternative to chemical and mechanical recycling due to its cost-effectiveness and milder reaction conditions, which makes it a more environment-friendly approach.
The major challenge that comes with biodegradation is the aggregation of the enzymes at higher concentration which inhibits the enzyme activity. To overcome this challenge, there have been attempts to immobilize the enzymes on scaffolds which provides an even distribution and prevents aggregation. With PET degrading enzymes, there have been attempts to immobilize PETase on nanoparticles previously which enhanced the activity of the enzyme. However, none of the existing systems could achieve complete depolymerization of PET. We have proposed a method to immobilize both PET degrading enzymes, FAST PETase and MHETase on iron oxide nanoparticles to enhance activity and achieve complete depolymerization of PET. In addition to this, we also incorporated a carbohydrate binding module (CBM) into the system which has shown to enhance activity by helping the enzyme come in closer proximity to the substrate.
It has been observed that even a small amount of MHETase boosts the PET degradation and the limiting step in conversion of PET to MHET is PETase. We found that 1:20 ratio of pure MHETase to FAST PETase is the optimum ratio for PET degradation. To achieve this ratio on the nanoparticles, we tried sequential addition and compared it with simultaneous addition. The sequential addition helped increase the amount of MHETase immobilized and the total enzyme loading. This two-enzyme system on nanoparticles showed a 2.5-fold increase in TPA release compared with the free enzyme system. We were able to show reusability of the bioconjugates using simple magnetic separation. The enzyme bioconjugates also showed higher stability when stored at 4��� as compared to free enzyme.
With CBM, the enzyme did show higher activity than the samples without CBM initially, however during the course of the assay, it did not show as much enhancement towards the end. This could be due to product accumulation in close proximity of the enzyme which inhibits the activity thereafter. The system could still be optimized further for shorter duration of assays.
With the current system consisting of FAST PETase and MHETase on iron oxide nanoparticles, we were able to achieve complete depolymerization of PET with additional advantages of reusability and enhanced stability through immobilization on nanoparticles. The knowledge from this work could guide other multi-enzyme systems with non-equimolar requirement to enhance activity through immobilization
John Bickham field notebook: AK6501-AK7000.pdf
No full textBound book, each page corresponds to a karyotype slide data.Data pages for AK7001-AK7500 corresponding to unique identifiers of specimens/samples examined for biological research. Specimens are primarily housed at Texas A&M University; Biodiverstiy Research and Teaching Collection
The How and Why of Realness: Reconceptualizing Identity Management and Examining Relationships with Authenticity and Motivation in a U.S.-Based LGBTQ2+ Sample
No full textIn this dissertation I examined whether the relationship between the identity management behaviors of LGBTQ+ employees and workplace outcomes (work engagement and affective well-being) is mediated by authenticity. Furthermore, I considered whether autonomous and controlled motivations for identity management behaviors moderate this relationship. In doing so, I add to identity management research that presumes but rarely tests the mediating effects of authenticity and I question the presumption that LGBTQ+ employees are always motivated to share their identities for autonomous reasons and hide them for controlled reasons. Additionally, I explored an alternative approach to measuring identity management behaviors, dividing them into verbal and nonverbal behaviors. Using a correlational design, I collected survey-based quantitative data from 456 LGBTQ+ identifying workers through the online data collection platform Prolific during the months of October and November 2023. Analyses conducted using the PROCESS macros indicated that the relationship between closed communication (e.g., verbal concealment and nonverbal suppression) and outcomes was mediated by authenticity, but this was not the case for open communication (e.g., verbal disclosure and nonverbal expression). There was an interaction effect between autonomous motivation and identity communication behaviors, such that for individuals with lower levels of autonomy, engaging in more open communication behaviors and/or more closed communication behaviors predicted diminished feelings of authenticity as well as reduced outcomes. Based on exploratory path analyses, the division of open communication into verbal and nonverbal behaviors better represented the true population model than combining these behaviors into one variable, however, there was no difference in model fit when closed communication was divided into verbal and nonverbal behaviors compared to a single-variable measure. I conclude by discussing theoretical and practical implications of these findings and propose future directions for this research
Sensitivity Analysis and Evaluation of Enhanced Geothermal Systems (EGS): Integrating Subsurface Simulation, Economics and Case Studies
No full textGeothermal energy has the potential to become a significant contributor to the effort toward energy transition because it is environmentally benign (i.e., carbon-free), renewable, and practically inexhaustible if managed properly. Geothermal energy can be extracted from different geological formations, ranging from low-temperature ones occurring at shallow depths -- suitable for heating and cooling applications -- to high-temperature reservoirs deep at kilometer-scale depths for power generation.
This study focuses on the deep geothermal systems that are referred to as Enhanced Geothermal Systems, EGS. Energy recovery from EGS involves drilling deep injection and production wells to reach deep, generally low-permeability geologic strata, and hydraulically fracturing the high-temperature rocks while ensuring communication between injectors and producers. Cold water injected into the reservoir is heated by the hot rock with which it comes in contact and is then recovered as a high-temperature fluid (liquid and/or vapor) at the production wells. Appropriate management ensures the long-term viability of this of semi-closed loop system.
In this research, I investigated in detail the thermo-hydraulic behavior of EGS by modeling the transport of fluid and heat in the subsurface by means of numerical simulation using a scientific code. I first analyzed in detail the behavior and performance of a base case model involving a representative (realistic) EGS reservoir. I then conducted (a) a thorough sensitivity analysis by varying key reservoir properties and operational practices that control/affect the behavior of the system and its efficiency, as well as (b) a techno-economic analysis based on the results of the numerical investigation studies. With the insight gained from the base and the sensitivity analysis studies, I investigated the feasibility and performance of a geothermal system at the RELLIS campus of Texas A&M University using existing data derived from earlier oil and gas recovery operations at the site. Finally, I include in this dissertation a full field-scale analysis of a geothermal system that I performed as part of an internship project at SLB (previously known as Schlumberger), an oilfield services company.
The main finding of the study is the importance of a heat-exchange surface area in the reservoir that is sufficiently large to enable (a) a high temperature of the recovered water, (b) a large flow rate (i.e., higher injection/production rates), and (c) mitigation and minimization of the inevitable thermal decline caused by the mining of heat by the injected cold water. Water (H2O) is shown to be consistently superior to supercritical CO2 (sCO2) as the heat-exchange (working) fluid, despite some thermophysical properties that appear to make sCO2 a promising candidate. The techno-economical analysis shows that drilling is the main factor increasing the cost of EGS. Thus, significant improvements in drilling efficiency and technologies are necessary to reduce the levelized cost of energy (LCOE) of EGS and make it an attractive energy recovery option