PERSONAL, RELATIONAL, AND PERFORMANCE IMPLICATIONS OF JOB CRAFTING

Ph.DDOCTOR OF PHILOSOPH

Silicon carbide process development for microengine applications : residual stress control and microfabrication

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.Includes bibliographical references.The high power densities expected for the MIT microengine (silicon MEMS-based micro-gas turbine generator) require the turbine and compressor spool to rotate at a very high speed at elevated temperatures (1300 to 1700 K). However, the thermal softening of silicon (Si) at temperatures above 900 K limits the highest achievable operating temperatures, which in turn significantly compromises the engine efficiency. Silicon carbide (SiC) offers great potential for improved microengine efficiency due to its high stiffness, strength, and resistance to oxidation at elevated temperatures. However, techniques for microfabricating SiC to the high level of precision needed for the microengine are not currently available. Given the limitations imposed by the SiC microfabrication difficulties, this thesis proposed Si-SiC hybrid turbine structures, explores key process steps, identified, and resolved critical problems in each of the processes along with a thorough characterization of the microstructures, mechanical properties, and composition of CVD SiC. Three key process steps for the Si-SiC hybrid structures are CVD SiC deposition on silicon wafers, wafer-level SiC planarization, and Si-to-SiC wafer bonding. Residual stress control in SiC coatings is of the most critical importance to the CVD process itself as well as to the subsequent wafer planarization, and bonding processes since residual stress-induced wafer bow increases the likelihood of wafer cracking significantly. Based on CVD parametric studies performed to determine the relationship between residual stresses in SiC and H2/MTS ratio, deposition temperature, and HCl/MTS ratio, very low residual stress (less than several tens of MPa) in thick CVD SiC coatings (up to -50 pm) was achieved.(cont.) In the course of the residual stress study, a general method for stress quantification was developed to isolate the intrinsic stress from the thermal stress. In addition, qualitative explanations for the residual stress generation are also offered, which are in good agreement with experimental results. In the post-CVD processes, the feasibility of SiC wafer planarization and Si-to-SiC wafer bonding processes have successfully been demonstrated, where CVD oxide was used as an interlayer bonding material to overcome the roughness of SiC surface. Finally, the bonding interface of the Si-SiC hybrid structures with oxide interlayer was verified to retain its integrity at high temperatures through four-point flexural tests.by Dongwon Choi.Ph.D

Cancel cancer: The immunotherapeutic potential of CD200/CD200R blockade

Immune checkpoint molecules function to inhibit and regulate immune response pathways to prevent hyperactive immune activity from damaging healthy tissues. In cancer patients, targeting these key molecules may serve as a valuable therapeutic mechanism to bolster immune function and restore the body’s natural defenses against tumors. CD200, an immune checkpoint molecule, is a surface glycoprotein that is widely but not ubiquitously expressed throughout the body. By interacting with its inhibitory receptor CD200R, CD200 suppresses immune cell activity within the tumor microenvironment, creating conditions that foster tumor growth. Targeting the CD200/CD200R pathway, either through the use of monoclonal antibodies or peptide inhibitors, has shown to be effective in boosting anti-tumor immune activity. This review will explore CD200 and the protein’s expression and role within the tumor microenvironment, blood endothelial cells, and lymph nodes. This paper will also discuss the advantages and challenges of current strategies used to target CD200 and briefly summarize relevant preclinical/clinical studies investigating the immunotherapeutic efficacy of CD200/CD200R blockade

Measuring the Mobile User Experience: Conceptualization and Empirical Assessment

User experience is commonly considered important for IT adoption and use. However, a formal measure that captures a user’s holistic experience obtained through the use of an IT artifact has not been developed. In this study, we propose a new measure of user experience and examine its validity using the data collected from over 240 smartphone mobile users in South Korea. Based on prior research on brand experience in marketing, we conceptualize user experience as a second order construct with four sub-dimensions. The convergent and discriminant validity of the measurement items of mobile user experience is examined along with the established measurement items of the cognitive absorption, which is similar to the proposed construct in that both capture what a user has experienced while interacting with an IT artifact. Further, we examine the effects of the proposed construct on perceived usefulness, satisfaction, and continuous intention

Advancing Sustainable 3D Printing: Harnessing the Potential of Wastewater Sludge Incineration Ash for Composite Material Development and Practical Applications

This study delves into the unexplored fusion of wastewater sludge incineration ash (WSIA) and 3D printing, uncovering novel possibilities at the crossroads of environmental engineering and advanced manufacturing. The investigation centers on the integration of WSIA within the additive manufacturing framework, specifically material extrusion-fused deposition modeling (FDM). The study focuses on composite materials blending WSIA with commercial thermoplastics like ABS and PC, meticulously analyzing their physical, chemical, and mechanical attributes. Notably, the research highlights the potential for heightened mechanical strength in ABS composite materials, suggesting applications beyond 3D printing. Emphasizing long-term sustainability, the study advocates for the adoption of biodegradable plastics and underscores the importance of continuous research, mass production feasibility, and regulatory adaptations to fully unlock WSIA’s potential. This synergy of innovation marries environmental awareness with technological progress, offering a harmonious trajectory to reshape manufacturing paradigms and nurture sustainable development. The study’s outcomes present promising avenues for redefining the construction industry and advancing environmental conservation