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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: AM1-AM861.pdf
No full textEach page/AK number corresponds to a karyotype slide data and/or unique specimen.Data pages for AM1-AM861 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
Crowding: An Exploration of the Effects of Methods and Sound
No full textVisitation rates continue to rise in the United States��� protected areas like national parks and national forests. This has raised management concerns for both impacts on the environment and visitor experiences. The Satisfaction Model postulates that as use levels and encounters rise in parks and protected areas, there is a threshold where the visitor experience is negatively impacted by the additional visitors. Nevertheless, decades of research indicate this relationship is complicated and multifaceted. As a result, the Satisfaction Model has evolved to include norms, use patterns and research measurement techniques as concepts that impact responses to encountering other individuals. Therefore, the purpose of this dissertation was to explore how people respond to research techniques and environment conditions, specifically the soundscape, when visiting protected areas.
Study one focused on starting point bias; a research bias where participant responses are systematically inflated or deflated due to research techniques. Research on crowding responses has frequently relied on visual methods where participants are shown a series of images with varying numbers of people visiting a protected area. The order in which the images are shown holds the potential to inflate or deflate results because the exposure to one treatment may impact responses to a subsequent treatment. This study���s findings revealed a starting point bias, but only on crowding ratings when moving from low setting density to high setting density.
Furthermore, the soundscape has become a fruitful topic for research on visitor experiences. However, little is understood about how sound impacts crowding norms. Study two explored how anthropogenic sound types impact crowding and acceptability ratings of a setting density. Direct human sounds like voices and children playing were expected to be rated more favorably than mechanical sounds. However, the rank of crowding and acceptability ratings were mixed with direct human sounds generally being rated more harshly than mechanical sounds.
Study three explored how sound loudness impacted crowding and acceptability ratings of the setting. Results indicated that loudness was only rated more harshly at the highest loudness levels. The studies are discussed in terms of their results and their impacts on theory and practice
Experimental Demonstration of Multiport Multifrequency Power Systems
No full textWith considerable improvement on renewable energy and energy storage has been made, the use of renewable power sources and energy storage devices in the power system and the electrification of transportation are becoming a growing trend in recent years. To meet this need, increasing numbers of power electronics converters are included in these systems, which makes these systems become power electronics rich. In these power electronics rich systems, the interaction among the converters is significantly complicated and thus makes the power flow management challenging. The integration of these power electronics converters could be an appropriate solution to simplify the power flow management and enhance the controllability of the system.
In this research, a novel multiport multi-frequency power transfer system is presented. In this system, several independent virtual power flow channels could be established by introducing different switching frequencies in the power electronics converters. Virtual power isolation among the power flow channels could be built up because of orthogonality of the waveform. Hence, the virtual power flow channels in different frequencies will not interfere with each other. Bidirectional Power flow could happen between each port of the system, and they won���t interfere with each other.
In this research, a prototype multiport multi-frequency circuit based on the proposed theory is built up in the lab. Simulations and experiments with several scenarios are conducted. The basic operation of the prototype circuit is analyzed. And the performance of the simulations and experiments will be investigated and discussed. The feasibility of the multiport multi-frequency power transfer is validated by both simulations and experiments
Role of Ventral Hippocampus in the Contextual Control of Avoidance
No full textAnimals react to aversive situations with a complex set of behaviors that reduce the likelihood of predation. Of course, animals have the capacity to learn from their experience; this allows them to anticipate and defend against future threats. On the one hand, Pavlovian conditioned responses, such as freezing behavior in rats, adaptively generalize to a variety of threats and environments in which they might be encountered. On the other hand, instrumental learning, such as making an active escape or avoidance response to avoid a painful event, enables animals to develop new behavioral strategies to avoid future threats. Compared to their Pavlovian counterparts, the neural and behavioral mechanisms of instrumental avoidance responses are poorly understood. In particular, whether avoidance responses exhibit a tendency to generalize across many contexts is unknown. To address this question, I assessed the context-dependence of instrumental avoidance learning in male and female rats. These studies used a two-way signaled active avoidance (SAA) task, in which animals can avoid an aversive footshock by shuttling in response to a warning signal. In the first set of experiments, I determined whether a learned avoidance response transfers to a new context and whether the contextual control of avoidance requires the hippocampus, a brain area that has been implicated in this form of learning. This work revealed that shuttle-box avoidance was context-dependent and decreased outside of the training context; inactivation of the ventral (VH), but not dorsal (DH) hippocampus, with the GABAA agonist, muscimol, eliminated the context-dependence of the response. In another set of experiments, I examined avoidance responses to the training context itself���so called inter-trial responses (ITRs). Inactivation of the VH decreased ITRs, whereas chemogenetic activation of the VH with ���designer receptors exclusively activated by designer drugs��� dramatically increased the number of ITRs. Together, these studies reveal that the VH has a role in both determining the context in which a threat-induced avoidance response is emitted and in promoting ITRs in the aversive context itself. The neural circuits by which the VH mediates these two functions of context in avoidance requires further investigation
Triple-Tuned Radiofrequency Coil Designs for Magnetic Resonance Imaging and Spectroscopy
No full textMulti-nuclear MRI/S has been shown to be a powerful tool for both diagnostics and the study of disease. While the potential of this technology has been recognized for decades, widespread clinical adoption of these techniques has been limited in large part due to the continued inaccessibility of multi-nuclear hardware. The work presented here aims to address the many design considerations of multi-nuclear RF coil designs, which are necessary to support biomarker development for Duchenne muscular dystrophy (DMD).
This work specifically details the design, construction, and characterization of several triple-tuned coil designs. First, a triple-tuned nested volume coil design composed of a pair of nine-leg birdcages designed to create parallel fields and an orthogonal saddle coil insert at 4.7T. The nine-leg birdcage pair was designed such that it could geometrically decouple from any orthogonal insert coil, either a dedicated planar receive coil or an orthogonal volume coil to operate in either the double- or triple-tuned configurations. SNR comparisons were specifically drawn between geometric decoupling design and active detuning.
Next, a truly simultaneous triple-tuned trap design was investigated for the use in scalable receiver arrays. This design proposes a parallel trap network in place of a more conventional series design to theoretically decrease the equivalent series resistance of the resultant trap network. A roughly 20% improvement in SNR was seen for 1H, but the theoretical sensitivity gains for the X-nuclei frequencies could not be fully resolved. The parallel trap network was compared to both a double- and triple-tuned series trap designs. X-nuclei sensitivities were close in both the double- and triple-tuned reference coils, indicating the additional losses from triple-tuning are minimal in comparison.
Finally, a modular multi-nuclear array was designed and characterized to enable a biomarker study on canine models of DMD. This design used a series PIN diode as a broadband active detuning network to enable decoupling independent of both position and frequency for stacked receive coils. Comparisons were specifically made between this broadband network and a conventional narrow band trap detuning mechanism. Comparisons were also made between a single larger loop and an inscribed array for 1H, 31P, and 23Na
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
Multiphysics Models to Predict the Peformance and Reliability of Electroadhesive Surface Haptic Devices
No full textHaptics refers to the sense of touch, and surface haptics is the branch of haptics that deals with the generation of tactile effects on touch surfaces to make user experiences more immersive and realistic. Electroadhesive surface haptic devices make use of electroadhesion to apply electrostatic forces at the human-device interface, which is then modulated to modulate the interfacial friction forces and generate tactile effects.
Devices that incorporate such state-of-the-art technology often face several reliability and performance issues in their nascent stages that need to be resolved to enable their successful commercialization. Predictive models play an important role in the development of such devices because they provide designers with efficient tools to explore a wide design space to find solutions, as opposed to relying on an inefficient and expensive trial-and-error approach. In this study, we investigate a few such challenges associated with electroadhesive haptic devices. We will identify the key mechanisms causing visible preferential deposition of fingerprint residue on specific regions of the surface of commercial electroadhesive haptic touchscreens and develop a multiphysics predictive model that can be used to explore solutions to tackle this issue. We will then develop a finger mechanics model that can predict the roughness perception produced by distributed haptic devices. This model will provide insights into which mechanics properties trigger the mechanoreceptors that contribute to roughness perception. Finally, we will develop a multiphysics model that couples the contact mechanics, capillary, and electrostatic phenomena at the interface and can provide fast and accurate predictions about the interfacial friction force ��� an important parameter than needs to be accurately represented to make correct predictions about the device performance. Together, these models will provide useful tools to haptic device designers to build better haptic devices in a quick and cost-effective way
The Addition of Cyanoacrylate Adhesive to Knots of Various Suture Loops: A Study on Tensile Strength and Suture Loop Integrity
No full textCyanoacrylate adhesive is used by some practitioners in conjunction with sutures to secure free gingival grafts to a surgical bed, in conjunction with sutures to function as a dressing for palatal harvest sites or biopsy sites, or to help maintain primary closure with bone grafting procedures. There is limited research regarding the effects of cyanoacrylate adhesive on the mechanical properties of sutures in an oral environment. Therefore, the aim of this study is to determine whether or not the addition of cyanoacrylate adhesive to suture loops impacts suture maximum tensile strength or cause of suture failure under tension.
60 samples of each suture were tied around 5 PEX pipes using a three-throw surgeon���s knot. Cyanoacrylate adhesive was applied to half of the suture knots as per the manufacturer���s instructions. The rods containing the sutures were then immersed in an artificial saliva solution and the pH and temperature were monitored. 5 suture samples of each suture type from the cyanoacrylate group, and 5 sutures of each suture type from the non-cyanoacrylate group were tested for maximum tension at the following time points: prior to submersion, 24 hours post-submersion, 3 days post-submersion, 7 days post-submersion, 10 days post-submersions, and 14 days post-submersion. Maximum tensile strength, reason for suture failure, and location of suture failure were recorded.
PGA-PCL sutures showed a 37% incidence of knot slippage when cyanoacrylate was not added to the knot. The addition of cyanoacrylate resulted in a 0% incidence of knot slippage (p=0.0048). The cause of suture failure for PTFE was always knot slippage, regardless of the addition of cyanoacrylate. On the other hand, silk, polypropylene, chromic gut, and PGA loops always failed due to suture loop breakage, regardless of the addition of cyanoacrylate. The addition of cyanoacrylate resulted in a statistically significant difference in maximum tensile strength of monofilament sutures (p=0.00041), synthetic sutures (p=0.00018), and absorbable sutures (p=0.0000031). The adhesive also improved maximum tensile strength of suture loops for silk (p=0.00088), PTFE (p=0.0091), PGA (p=0.029), and PGA-PCL sutures (p=4.4E10������), but not for polypropylene (p=0.45) or chromic gut sutures (p=0.87). The effect of the addition of cyanoacrylate to PGA-PCL was statistically significantly different at all days, except for day 14 and the retentive effect of cyanoacrylate appeared to decrease with time.
The addition of cyanoacrylate adhesive eliminates knot slippage in PGA-PCL sutures and increases the maximum tensile strength of silk, PTFE, PGA, and PGA-PCL sutures. These findings suggest that the addition of cyanoacrylate adhesive to suture knots may enhance suture loop integrity in an oral environment
Spectroscopic Studies of Stars and Black Holes Across Cosmic Time
No full textIn this work, I present my spectroscopic studies of galaxy evolution across a large majority of cosmic time (0 ��� z ��� 9). My career to this point has two distinct phases: pre-JWST, when I utilized spectroscopy from HST to study star formation, dust attenuation, and accreting black holes out to the peak of cosmic star formation rate and active supermassive black hole density (cosmic noon; z ��� 2), and post-JWST, where my focus shifted to this new observatory to push the study of galaxy evolution to some of the earliest known galaxies at z ��� 8.
In the pre-JWST era, I used HST grism spectroscopy to study star formation rates and histories as well as dust attenuation by using the near-IR Paschen lines of hydrogen. Emission from Paschen lines indicates near-instantaneous star formation, while probing regions inaccessible to UV or optical star formation tracers due to dust attenuation.
I also used HST grism spectroscopy to probe galaxies around cosmic noon which exhibit the extremely-high-ionization [Ne V] line. This spectral feature is a strong tracer of an ionizing spectrum powered by an accreting black hole, at least in this epoch of cosmic time.
These studies serve as optimal pilot campaigns for the JWST era, where JWST spectroscopy can probe these features out to much earlier epochs of cosmic time. I discuss the implications of JWST studies of Paschen-line star formation rates and dust attenuation out to cosmic noon, and studies of high-ionization emission lines in the epoch of Reionization.
Using early JWST spectroscopy in conjunction with HST spectroscopy and photoionization models, I develop a novel diagnostic to trace ionization from different sources at all epochs of cosmic time. This is designed specifically with elusive objects in the early Universe in mind, including Population III stars and accreting intermediate-mass black holes, in an effort to study the earliest stages of star formation and black hole growth.
We stand at the beginning of a new era in the study of galaxy evolution. With the incredible capabilities of JWST, we can study the physical mechanisms governing galaxies across cosmic time like never before