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Enhancing [Fe]-hydrogenase-inspired hydride transfer catalysts through secondary coordination sphere interactions
Get PDFAlthough the concept of the secondary coordination sphere has existed for over a century, only in the last twenty years has it begun to permeate the bioinorganic zeitgeist, especially among those who study metalloenzyme active sites. Consideration of this secondary coordination sphere – or the ensemble of noncovalent interactions between a metal complex and exogenous molecules or moieties – has provided elucidation for metalloenzyme active site structures and reaction mechanisms that were poorly explained by only considering the metal center and its bound ligands. The unique structure and reactivity of the active site of [Fe]-hydrogenase is best described when considering the secondary interactions between the iron-containing FeGP cofactor and key amino acid residues (Cys176 and His14). Furthermore, the consensus mechanism of H₂ heterolysis performed by [Fe]-hydrogenase invokes metal-ligand cooperativity; Fe-bound H₂ is heterolyzed by a frustrated Lewis acid-base pair formed by the cationic methenyl-H₄MPT⁺ substrate and anionic 2-pyridonate ligand of the FeGP cofactor. Given the importance of secondary interactions in the [Fe]-hydrogenase system, we endeavor to design a new generation of hydrogenase model systems which incorporate aspects of this secondary coordination sphere. Herein is presented present two systems in which a bio-inspired rhenium(I) catalyst is embedded in a macromolecular host molecule to provide the complex with a well-defined secondary coordination sphere: i) It was found that interaction of this rhenium(I) catalyst with a covalent organic framework (embedding or surface adsorption) can modulate its catalytic reactivity from oxidative esterification to reductive etherification or transfer hydrogenation, respectively. ii) The binding of this rhenium(I) complex to the protein β-lactoglobulin was spectroscopically characterized in the pursuit of designing an artificial metalloenzyme with hydrogenase funtionality. Additionally, two small molecule systems are also presented which explore the effect of the 2-pyridonate ligands on metal complexes related to the [Fe]-hydrogenase active site: i) A structurally diverse array of pyridone-ligated nickel(II) complexes were synthesized and characterized to discern the effects that various reaction conditions have on the ligation of pyridone ligands to late transition metal ions in the solid and solution states. ii) The synthesis of a pyridone-containing structural model of the [Fe]-hydrogenase active site is presented.Chemistr
Restorative justice and student conduct leadership
Get PDFThis phenomenological study aimed to examine the lived experiences of 10 restorative justice (RJ) directors and administrators responsible for managing programs at four-year higher education institutions across the United States to understand opportunities and barriers to program sustainability. Data were collected through semi-structured interviews and institutional documentation, and these data were inductively coded and analyzed using a process inspired by the thematic analysis procedure. Key findings indicated that RJ leaders have exemplary empathetic leadership skills. Half were considered pioneers in promoting a shared vision of a restorative campus focused on building relationships that support student success. Most experienced personal, family, or had a close relationship with someone who experienced trauma as a motivator for RJ success.Educational Leadership and Polic
Improved methodology for measuring the emissivity of metal powders
Get PDFA specially designed chamber is proposed to accurately measure the emissivity coefficient of metal powders over a wide temperature range using an infrared (IR) camera. This measurement setup significantly reduces the oxidation of metal powders during heating to high temperatures. As a result, it enables precise determination of the actual emissivity values, which is crucial for accurate IR camera calibration when studying sintering or melting processes in additive manufacturing.Mechanical Engineerin
Causal testing of the importance of V1 topography in coarse shape perception via spatially patterned optogenetics
Get PDFThe visual world is made up of distinguishable features spanning many spatial scales, such as fine-scale interior texture to coarse-scale object shape. But, the small receptive fields of early visual cortical neurons present an “aperture problem” for extracting features at larger spatial scales, such as coarse shape of object outline. The visual system solves this through pooling populations of neurons with collective receptive fields covering this larger scale. The specificity and structure of this pooling operation is still an open question. The dogmatic idea for this pooling operation is a decoder exploiting the selectivities of all V1 neurons (i.e., a labeled-line code). An alternative hypothesis is that one form of topographic mapping in primary visual cortex (V1), retinotopy—the encoded projection of visual field across the cortical surface—is important for the decoding of coarse shape. In order to directly test this retinotopic decoder hypothesis, I have developed an optogenetic read-write method to manipulate retinotopic-scale V1 activity, in order to causally test if perturbing this scale of information can systematically bias macaque performance in a shape discrimination task. I have trained a macaque to discriminate aspect ratio (AR) of a small Gaussian stimulus, a simplified form of shape. V1 activity recorded during this task reveals that retinotopic-scale signals are sufficient to decode AR. I then introduce a read-write projector platform paired with the viral co-expression of genetically-encoded reporters and actuators of neuronal activity in V1 to allow for spatially patterned optogenetic manipulations of cortical activity. Next, I detail an encoding model of V1 with retinotopy, varied selectivities, and realistic noise. Within, I show how retinotopic-scale perturbations affect multiple hypothetical AR decoders via an in silico biasing experiment. Finally, I describe the results of optogenetic retinotopic biasing in V1 of a macaque performing the AR task. The results support the retinotopic decoder hypothesis, indicating that the retinotopic scale causally contributes to AR discrimination. Therefore, the work in this thesis supports an alternative to the dogmatic view of the neural underpinnings of shape perception, and has potential translational relevance to cortical neuroprosthesis design.Neuroscienc
Black queer world-making in Afro-Peruvian female queer hip hop artists
Get PDFHip Hop has been part of the Black expressive American culture that allows Black youth to narrate their reality and organize as a community, and it has been a place to imagine new realities. Through the internalization of Hip Hop, young people around the Diaspora re-adapted American Hip Hop to express the local reality of marginalized communities. This article explores how two Afro-Peruvian female queer artists are disrupting the local Hip Hop scene through their music by criticizing heteronormative impositions. Yanna and Gilow are the predominant voices in the local Hip Hop Afro-Peruvian scene that brings representations of Blackness and queerness to imagine new possibilities engaging with a practice of Black queer world-making. Black queer world-making is understood as the construction and imagination of new worlds where new possibilities for Blackness and queerness could arise. Through this proposition, I analyze the song “Millone$” by Yanna and “Carpe Diem” by Gilow.African and African Diaspora Studie
Third party perceptions of international conflict and laws
Get PDFThis report examines how international conflicts and violations of the laws of war shape the decisions and perceptions of third-party states and individuals within them. As conflicts escalate, countries and individuals face complex choices that shape national foreign policy and public opinion towards that conflict. Each paper in this report explores distinct yet interconnected facets of this phenomenon: the strategic considerations influencing state decisions to take sides in conflicts, the conditions that shape public opinion within third-party countries, and the impact of framing on individual perceptions towards the conflict.Governmen
Beyond the BMI : exploring the cultural and ethical dimensions of "thick" Black female beauty
Get PDFThis report examines the sociocultural implications of labeling Black women as “thick” in the United States. At this time, Black women have some of the highest rates of obesity across populations. As a result, Black women are at risk of experiencing various health complications. Findings from qualitative and quantitative studies demonstrate that Black women face cultural pressures to maintain a thick body type, despite potential health risks. These pressures coupled with historical maltreatment of the Black female body perpetuate poor health outcomes among the Black female population. I explain why reinforcing the “thick” body ideal for Black women is problematic for their health and body image. This report also includes moments of reflection and an explanation of the lessons learned throughout the completion of this project.Women's and Gender Studie
Development and modeling of a fabrication process for high-strength biomimetic porous polymer for medical implants
Get PDFPolyether ether ketone (PEEK) has become a popular candidate for use in medical implants. Unlike metal implants, PEEK does not create artifacts in radiographic evaluations, such as X-rays and CT scans, making it ideal for postoperative examinations. However, PEEK's chemical inertness limits the formation of connective tissue surrounding the material, resulting in poor osseointegration and low cell attachment strength. Generating a porous PEEK structure can enhance surface roughness to improve osteoblast adhesion and create tissue interlocks, promoting osteoblast ingrowth.
Porous PEEK structures have been fabricated through particulate leaching, chemical etching, and 3D printing. However, the porous PEEK structures generated by these methods have limitations, including having porosity only near the surface, being capable of forming only ordered pores, and only having pores larger than 300 μm. Although the optimal pore size for cell growth is still arguable, the range normally lands within 100-300 μm for bone implants, and ideally with gradient porous structure. Thus, there are still challenges for generating bio-mimetic porous structure with high strength polymers for medical implants.
This research introduces a novel fabrication method for PEEK-based medical implants by combining immiscible polymer blending, solid-state foaming, and 3D printing. The interconnected porous PEEK structure was fabricated by combining an immiscible PEEK/Polyether Sulfone (PES) polymer blend with solid-state foaming. A fully interconnected porous structure was obtained by mixing the two immiscible polymers in the proper weight ratio. The pore size can also be controlled by modifying the annealing conditions, enabling the fabrication of interconnected porous PEEK structures with pore sizes ranging from 20 to 600 μm. The solid-state foaming process, coupled with annealing of the PEEK/PES mixture, significantly enhanced the leaching rate of the PES phase. During foaming, only the PES phase was affected due to its low crystallinity, while the PEEK structure remained intact. The porous PEEK structure mimicked the morphology of human trabecular bone and exhibited compressive strength similar to trabecular bone, indicating its potential as a bone implant scaffold.
Additionally, a computational model was developed to simulate the phase separation and coarsening process for the PEEK/PES polymer blend. The phase separation process was modeled using the Cahn-Hilliard equations, which were integrated with fluid and heat transfer models to simulate polymer fluid movement during coarsening. The 3D simulation model, incorporating the physical parameters of PEEK and PES, was validated against experimental results and used to estimate unknown material properties. The simulation findings confirmed that the model effectively captures phase growth dynamics and quantitatively predicts phase coarsening behaviors in the immiscible polymer blend.
Finally, this fabrication process was combined with 3D printing to enable complex geometries. The PEEK/PES mixture was extruded into filaments and 3D-printed using fused deposition modeling. The porous regions were created using the PEEK/PES blend, while solid regions were fabricated from neat PEEK, allowing for custom implant designs. Interconnected porous structures were achieved by annealing the polymer after 3D printing. The PEEK/PES region did not diffuse into the neat PEEK region, while still showing good bonding between layers. The mechanical strength of the implant, which combined solid and porous regions, exhibited compressive strength higher than that of human trabecular bone, while maintaining a compressive modulus similar to or higher than that of human bone, making it optimal for bone medical implants.Mechanical Engineerin
Development of Split-Hopkinson pressure bar apparatus for dynamic testing of nonlinear elastic metamaterials
No full textThis work presents the design, development, and qualification of a split-Hopkinson pressure bar (SHPB) apparatus at the Applied Research Laboratories at the University of Texas at Austin (ARL:UT) with the intent of physically testing nonlinear elastic metamaterials—artificially-developed media that can manipulate stress waves in a way not seen in naturally-occurring materials—under high strain-rate loading while also enabling other advanced material research. Taking inspiration from both COTS systems available for purchase and custom-built systems in the literature, a modular SHPB system was designed and constructed to allow for multiple experimental configurations while conforming to the driving theory centered around non-dispersive, one-dimensional longitudinal wave propagation through elastic media. Custom-designed components include a support structure with aligning pressure bar supports and an excitation system which launches a striker bar using a gas gun powered by compressed air. All design parameters were validated using a physical model of the excitation system in Python, which characterized striker velocities and resulting induced strain rates on a test specimen. This model was validated through physical observation of striker bar exit velocities induced by the as-built apparatus. A pressure bar specification of 1566 carbon steel was selected for its high yield strength, and ultrasonic characterization methods were used to confirm the material properties of the selected pressure bar specification. A laser alignment procedure was used to ensure that the support structure could match the straightness of the pressure bars. From initial testing, it was found that the system could be sufficiently aligned to allow incident pulses to propagate with near-perfect transmission through the apparatus in a calibration condition involving no loaded specimen, indicating that the system should be apt for the characterization of materials given control tests with specimens of known properties.Mechanical Engineerin
Detectability of supermassive dark stars with the Roman Space Telescope
Get PDFSupermassive dark stars (SMDS) are luminous stellar objects formed in the early Universe at redshift z ∼ 10 − 20, made primarily of hydrogen and helium, yet powered by dark matter. We examine the capabilities of the Roman Space Telescope (RST), and find it able to identify ∼ 10⁶ M [subscript ⊙] SMDSs at redshifts up to z ≃ 14. With a gravitational lensing factor of µ ∼ 100, RST could identify SMDS as small as ∼ 10⁴ M [subscript ⊙] at z ∼ 12 with ∼ 10⁶ s exposure. Differentiating SMDSs from early galaxies containing zero metallicity stars at similar redshifts requires spectral, photometric, and morphological comparisons. With only RST, differentiation of SMDS, particularly those formed via adiabatic contraction with M ≳ 10⁵ M [superscript ⊙] and lensed by µ ≳ 100, is possible due to their distinct photometric signatures from the first galaxies. Those formed via dark matter capture can be differentiated only by image morphology: i.e. point object (SMDSs) vs. extended object (sufficiently magnified galaxies). By additionally employing James Webb Space Telescope (JWST) spectroscopy, we can identify the HeII λ1640 absorption line, a “smoking gun” for SMDS detection. Although RST doesn’t cover the required wavelength band (for z [subscript emi] ≳ 10), JWST does, hence the two can be used in tandem to identify SMDS. The detection of SMDS would confirm a new type of star powered by dark matter and may shed light on the origins of the supermassive black holes powering bright quasars observed at z ≳ 6.Physic