Thesis advisor: Michael Russell / SDL is an important life-long learning skill. Current research on SDL has approached it both as a set of skills students develop and as an instructional method. The study presented here approached SDL as an instructional method and explored educators’ instructional use of SDL in relation with pedagogical beliefs, a relationship that has not been sufficiently explored in past research. This relationship was also placed in a Critical Race Theoretical Framework to explore whether the implementation of SDL differed by the racial composition of schools. A multi-method approach was taken which included surveying and interviewing middle school teachers in Massachusetts public schools. Descriptive analyses, factor analyses, correlation analyses, regression analyses, and t-tests were conducted in order to explore the relationship between teachers’ implementation of SDL and their extent of technology integration and pedagogical beliefs, as well as whether the implementation of SDL differs based on the racial composition of the schools in which teachers work. Interviews were employed to explore the results further. Teachers with more student-centered beliefs had higher levels of implementation of SDL than those with more teacher-centered beliefs, and pedagogical beliefs were also a stronger predictor of the level of implementation of SDL than were teachers’ amount of technology use or beliefs about student technology use. No significant relationship was observed between SDL and the racial composition of schools. / Thesis (BA) — Boston College, 2019. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Departmental Honors. / Discipline: Sociology.

The creation of artificial enzymes to catalyze desired reactions is a major goal of computational protein design. However, de novo enzymes display low catalytic efficiencies, requiring the introduction of activity-enhancing active site and distal mutations through directed evolution. A better understanding of how mutations introduced by directed evolution contribute to increased enzymatic activity will guide the development of design methods such that efficient enzymes can be designed de novo. Here, we evaluate the structural, functional, and dynamical impacts of active site and distal mutations introduced by directed evolution of the de novo retro-aldolase RA95, an enzyme that presents an important case study in enzyme design due to the significant structural remodelling that was observed during evolution. We observe that the variant RA95-Core, containing only active site mutations introduced by directed evolution, displays activity within one order of magnitude of the fully evolved variant. This suggests that computational enzyme design methods can be improved to create much more efficient enzymes than what was previously achieved in RA95. However, structural changes induced by distal mutations prevent computational recapitulation of the evolved active site on the original design template, indicating that the optimized active site identified through directed evolution could not have been designed de novo using current design methodologies. We suggest strategies for the incorporation of backbone remodelling into design procedures that would allow recapitulation of the evolved retro-aldolase active site, as well as the de novo design of highly efficient enzymes without the need for optimization by directed evolution.

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Multi-material structures (MMSs) are attractive due to their unique advantages in achieving tailored properties at different locations in a single part. Producing such structures by additive manufacturing has been gaining more and more attention because of the beneficial characteristics of additive manufacturing processes such as its ability in building complex geometries, shortening producing chains, and most importantly, easily integrating with multi-material feeding systems. This PhD thesis investigates the potential of MMSs fabricated by directed energy deposition (DED) using tool steel and copper alloy. Specifically, AISI H13 hot work tool steel is deposited on copper-beryllium alloy (CuBe) substrate using three deposition strategies: directly depositing H13 on CuBe (H13/CuBe), SS316L buffer (H13/SS316L/CuBe), and commercially pure nickel buffer (H13/Ni/CuBe), aiming to minimize cracking issues. The morphology of single-track, single-layer, and multi-layer specimens is analyzed. The microstructure of deposited specimens is also investigated, along with its mechanical and thermal properties, such as microhardness, wear resistance, load-bearing capability (LBC), and thermal conductivity. The results show that directly depositing H13 on CuBe cannot avoid cracking in the H13 layers while preheating the CuBe substrate at 150°C and 250°C reduces the cracking tendency but damages the strength of the CuBe substrate due to over-aging while introducing difficulty to manage processing procedure. Using SS316L buffer can suppress the crack extension in H13 cladding due to a barrier mechanism, i.e., its ability to reduce the Cu penetration into H13 layers. However, SS316L itself is prone to cracking when directly deposited on the CuBe substrate as a buffer layer. Through analysis of cracking morphology, parameter effects, and element distribution, it was possible to identify solidification cracking as the primary cracking mechanism in all specimens. Two metallurgical factors, solidification temperature range and amount of terminal liquid, were found to dominate the cracking tendency. The introduction of Cu into steel can significantly extend the solidification temperature range, thereby increasing the susceptibility to cracking. However, as the Cu composition continuously increases, the cracking susceptibility decreases due to the backfilling of the terminal liquid into cracks resulting in a healing effect. The solidification paths of the Fe-Cu binary system were calculated as a function of Cu composition. Using this data, a map was generated reporting the solidification temperature range and terminal liquid amount as a function of Cu composition for the Fe-Cu binary system. Even if only to a first approximation (the effect of alloying elements in both, steel and CuBe alloy), this map can be used as a tool to estimate the cracking susceptibility of steel/copper alloy MMSs deposited by DED. The experimental results are in good agreement with thermodynamic calculations. Based on this analysis, a pure nickel buffer strategy was selected and proved to be effective in minimizing the cracking issue in H13 due to the narrow solidification temperature range of Ni-Cu and Ni-Fe binary systems induced the high solubility of Ni in Fe and Cu. By employing this strategy, crack-free specimens were produced. The high hardness of the H13 single-layer cladding, with an average value of 740 HV, provided a significant improvement in wear resistance compared to the CuBe (400 HV). However, in multi-layer specimens, a gradual decrease in microhardness of H13 cladding from the outer to the inner layers was observed due to the mixing of remelted soft buffer materials into H13 and the in-situ tempering effect in the previous deposited H13 layers. The above result, further confirms that the load-bearing capability (LBC) cannot be infinitely improved by adding more H13 layers. In general, in the low loading range (From 5 to 10 kN), the LBC of MMS specimens was higher than the CuBe due to the higher hardness of outer H13 layers. However, it became lower in the high loading range due to the presence of soft sublayer materials such as softened martensite, soft buffer layers (H316L = 260 HV or HNi = 130 HV), and the heat-affected zones in the CuBe substrate. The thermal conductivity of MMS specimens first drops rapidly to half of the original value as the cladding thickness ratio (tcladding/tCuBe) increases from 0 to around 20%. After that, the decrease becomes slower, with a further reduction of around 37% in thermal conductivity as the cladding thickness ratio increases from 20% up to 50%. Therefore, a tradeoff between mechanical and thermal properties must be considered looking for the application of these cladding systems. A proper cladding thickness ratio of around 20% is recommended to achieve reasonably high strength while still maintaining thermal conductivity at an acceptable level. Overall, these findings have important implications for the selection of appropriate materials and processing parameters to optimize the mechanical and thermal properties of tool steel/copper alloy MMSs deposited by DED.

It is well known that people who use drugs (PWUD) leave the hospital via patient directed discharge (“PDD”; also known as against medical advice “AMA”) more often than people who do not use drugs. The introduction of xylazine – a veterinary tranquilizer – into the United States (US) synthetic opioid supply has only exacerbated this situation. The following paper reviews the literature on xylazine, hospitalization with opioid use disorder (OUD), and how xylazine has changed the experience of hospitalization with OUD. The research revealed that xylazine causes respiratory depression, sedation, and the formation of necrotic wounds. There is currently no treatment for xylazine dependence, overdose, or withdrawal. The literature further revealed that inadequate management of withdrawal and pain, along with stigma from health professionals, are major reasons why PWUD leave the hospital PDD before completing treatment. The difficulty the health system faces with the management of xylazine withdrawal and the necrotic wounds it produces only exacerbates this problem and necessitates increased attention to this topic. Using opioid agonists to treat withdrawal decreases rates of PDD for PWUD in the hospital. This paper will argue that the treatment of PWUD in the hospital with opioid agonists in order to address withdrawal and pain is ethically necessary; and that the introduction of xylazine into the synthetic opioid supply in the US only further necessitates the collective adoption of this viewpoint. / Urban Bioethics