Design of Si/SiC hybrid structures for elevated temperature micro-turbomachinery

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references.thermal softening behavior at temperatures above 900 K. This thermal softening behavior limits the turbine inlet temperature, which in turn significantly degrades the overall engine efficiency. Previous studies have shown that hybrid structures of silicon and silicon carbide have good potential for improved engine performance. Detailed design of Si/SiC hybrid structures for high temperature micro-turbomachinery, however, has been hampered by the relatively poor performance of single crystal Si at elevated temperatures and high stresses and by the unavailability of accurate material properties data for both Si and SiC at the temperatures of interest. From previous work, the critical structures and materials issues to be resolved, in order to proceed with the design of high temperature Si/SiC hybrid structures, were identified as follows: 1. the safety margin of the Si/SiC hybrid structures based on the upper yield strength of Si 2. reliable estimation of the service life of the Si/SiC hybrid structures 3. structural instabilities caused by the combination of stress concentrations and strain softening. In the course of this thesis, these issues provided the key motivations of the work, and have been substantially resolved. As a first step, it is critical to obtain a better understanding of the mechanical behavior of this material at elevated temperatures in order to properly exploit its capabilities as a structural material. Creep tests in simple compression with n-type single crystal silicon, with low initial dislocation density, were conducted over a temperature range of 900 K to 1200 K and a stress range of 10 MPa to 120 MPa. The compression specimens were machined such that the multi-slip or orientations were coincident with the compression axis.(cont.) The creep tests reveal that the response can be delineated into two broad regimes: (a) in the first regime rapid dislocation multiplication is responsible for accelerating creep rates, and (b) in the second regime an increasing resistance to dislocation motion is responsible for the decelerating creep rates, as is typically observed for creep in metals. An isotropic elasto-viscoplastic constitutive model that accounts for these two mechanisms has been developed in support of the design of the high temperature turbine structure of the MIT microengine. From the experimental observations and model validation, basic guidelines for the design of Si/SiC hot structures have been provided. First, the use of the upper yield strength of single crystal Si for design purpose is non-conservative. Also from the perspective of the design of Si hot structures, the lower yield strength is insufficient, particularly for micro-turbomachinery operating at elevated temperatures and high stresses. The recommended approach to the design of Si hot structures is to use the Si model for extracting appropriate operating conditions, and to reinforce the Si structures with SiC in strategic locations. Second, at high temperatures, the effect of stress concentrations is not crucial ...by Hyung-Soo Moon.Ph.D

Efficacy of quick Sequential Organ Failure Assessment with lactate concentration for predicting mortality in patients with community-acquired pneumonia in the emergency department

Objective Community-acquired pneumonia (CAP) is a major cause of sepsis, and sepsis-related acute organ dysfunction affects patient mortality. Although the quick Sequential Organ Failure Assessment (qSOFA) is a new screening tool for patients with suspected infection, its predictive value for the mortality of patients with CAP has not been validated. Lactate concentration is a valuable biomarker for critically ill patients. Thus, we investigated the predictive value of qSOFA with lactate concentration for in-hospital mortality in patients with CAP in the emergency department (ED). Methods From January 2015 to June 2015, 443 patients, who were diagnosed with CAP in the ED, were retrospectively analyzed. We defined high qSOFA or lactate concentrations as a qSOFA score ≥2 or a lactate concentration >2 mmol/L upon admission at the ED. The primary outcome was all-cause in-hospital mortality. Results Among the 443 patients, 44 (9.9%) died. Based on the receiver operating characteristic (ROC) analysis, the areas under the curves for the prediction of mortality were 0.720, 0.652, and 0.686 for qSOFA, CURB-65 (confusion, urea, respiratory rate, blood pressure, and age), and Pneumonia Severity Index, respectively. The area under the ROC curve of qSOFA was lower than that of SOFA (0.720 vs. 0.845, P=0.004). However, the area under the ROC curve of qSOFA with lactate concentration was not significantly different from that of SOFA (0.828 vs. 0.845, P=0.509). The sensitivity and specificity of qSOFA with lactate concentration were 71.4% and 83.2%, respectively. Conclusion qSOFA with lactate concentration is a useful and practical tool for the early prediction of in-hospital mortality among patients with CAP in the ED

Quasi-Eigenstate Evolution in Open Chaotic Billiards

We experimentally studied evolution of quasi-eigenmodes as classical dynamics undergoing a transition from being regular to chaotic in open quantum billiards. In a deformation-variable microcavity we traced all high-Q cavity modes in a wide range of frequency as the cavity deformation increased. By employing an internal parameter we were able to obtain a mode-dynamics diagram at a given deformation, showing avoided crossings between different mode groups, and could directly observe the coupling strengths induced by ray chaos among encountering modes. We also show that the observed mode-dynamics diagrams reflect the underlying classical ray dynamics in the phase space.Comment: 4 pages, 4 figure

Mild Hypothermia Attenuates Intercellular Adhesion Molecule-1 Induction via Activation of Extracellular Signal-Regulated Kinase-1/2 in a Focal Cerebral Ischemia Model

Intercellular adhesion molecule-1 (ICAM-1) in cerebral vascular endothelium induced by ischemic insult triggers leukocyte infiltration and inflammatory reaction. We investigated the mechanism of hypothermic suppression of ICAM-1 in a model of focal cerebral ischemia. Rats underwent 2 hours of middle cerebral artery occlusion and were kept at 37°C or 33°C during occlusion and rewarmed to normal temperature immediately after reperfusion. Under hypothermic condition, robust activation of extracellular signal-regulated kinase-1/2 (ERK1/2) was observed in vascular endothelium of ischemic brain. Hypothermic suppression of ICAM-1 was reversed by ERK1/2 inhibition. Phosphorylation of signal transducer and activator of transcription 3 (STAT3) in ischemic vessel was attenuated by hypothermia. STAT3 inhibitor suppressed ICAM-1 production induced by stroke. ERK1/2 inhibition enhanced phosphorylation and DNA binding activity of STAT3 in hypothermic condition. In this study, we demonstrated that hypothermic suppression of ICAM-1 induction is mediated by enhanced ERK1/2 activation and subsequent attenuation of STAT3 action

Development of a high yield purification process for the production of influenza virus vaccines

Production of influenza virus in animal cells has emerged as an alternative to conventional platforms such as egg-based production system. Animal cells, especially MDCK and VERO cell lines, are widely used as the primary production cell for influenza virus vaccine because of their high susceptibility to infection with various influenza viruses. Recently, a robust and reliable purification process was successfully developed for the production of quadri-valent HA proteins (from two strains of the type A virus and two strains of the type B virus) by using animal cell-based production system in Green Cross Corp., Korea. The UF/DF process, Benzonase treatment at high temperature as well as column chromatography strategy was optimized to maximize the final HA production yields. Benzonase treatment was conducted to reduce in hcDNA (host cell DNA) because hcDNA was main impurity for cell-based influenza virus vaccine. A simple and stable UF/DF process has been tested with membrane molecular weight cutoffs of 100 and 300 kDa as well as 0.2 and 0.45 um microfiltration membrane. Anion exchange chromatography (AEC) and size exclusion chromatography (SEC) were selected for acceptable reduction in hcDNA and HCP. AEC was used to separate hcDNA from virus at a salt concentration of 0.5 M sodium chloride. The HA yield through AEC & SEC combination process was sufficiently achieved under specific purification process condition. Overall, the amount of residual hcDNA was reduced to an acceptable level (10ng/dose) and the increased HA yield was maintained throughout the whole process. The performance, productivity and scalability of the purification process were successfully demonstrated in over 30 GMP batches using 4 different influenza virus strains

Nomograms for Prediction of Disease Recurrence in Patients with Primary Ta, T1 Transitional Cell Carcinoma of the Bladder

We developed nomograms to predict disease recurrence in patients with Ta, T1 transitional cell carcinoma of the bladder. Thirty-eight training hospitals participated in this retrospective multicenter study. Between 1998 and 2002, a total of 1,587 patients with newly diagnosed non-muscle invasive bladder cancer were enrolled in this study. Patients with prior histories of bladder cancer, non-transitional cell carcinoma, or a follow-up duration of less than 12 months were excluded. With univariate and multivariate logistic regression analyses, we constructed nomograms to predict disease recurrence, and internal validation was performed using statistical techniques. Three-year and five-year recurrence-free rates were 64.3% and 55.3%, respectively. Multivariate analysis revealed that age (hazard ratio [HR]=1.437, p<0.001), tumor size (HR=1.328, p=0.001), multiplicity (HR=1.505, p<0.001), tumor grade (HR=1.347, p=0.007), concomitant carcinoma in situ (HR=1.611, p=0.007), and intravesical therapy (HR=0.681, p<0.001) were independent predictors for disease recurrence. Based on these prognostic factors, nomograms for the prediction of disease recurrence were developed. These nomograms can be used to predict the probability of disease recurrence in patients with newly diagnosed Ta, T1 transitional cell carcinoma of the bladder. They may be useful for patient counseling, clinical trial design, and patient follow-up planning

Specific Intracellular Uptake of Herceptin-Conjugated CdSe/ZnS Quantum Dots into Breast Cancer Cells

Herceptin, a typical monoclonal antibody, was immobilized on the surface of CdSe/ZnS core-shell quantum dots (QDs) to enhance their specific interactions with breast cancer cells (SK-BR3). the mean size of the core-shell quantum dots (28 nm), as determined by dynamic light scattering, increased to 86 nm after herceptin immobilization. the in vitro cell culture experiment showed that the keratin forming cancer cells (KB) proliferated well in the presence of herceptin-conjugated QDs (QD-Her, 5 nmol/mL), whereas most of the breast cancer cells (SK-BR3) had died. to clarify the mechanism of cell death, the interaction of SK-BR3 cells with QD-Her was examined by confocal laser scanning microscopy. as a result, the QD-Her bound specifically to the membrane of SK-BR3, which became almost saturated after 6 hours incubation. This suggests that the growth signal of breast cancer cells is inhibited completely by the specific binding of herceptin to the Her-2 receptor of SK-BR3 membrane, resulting in cell death

AKARI Detection of the Infrared-Bright Supernova Remnant B0104-72.3 in the Small Magellanic Cloud

We present a serendipitous detection of the infrared-bright supernova remnant (SNR) B0104-72.3 in the Small Magellanic Cloud by the Infrared Camera (IRC) onboard AKARI. An elongated, partially complete shell is detected in all four observed IRC bands covering 2.6-15 um. The infrared shell surrounds radio, optical, and X-ray emission associated with the SNR and is probably a radiative SNR shell. This is the first detection of a SNR shell in this near/mid-infrared waveband in the Small Magellanic Cloud. The IRC color indicates that the infrared emission might be from shocked H2 molecules with some possible contributions from ionic lines. We conclude that B0104-72.3 is a middle-aged SNR interacting with molecular clouds, similar to the Galactic SNR IC 443. Our results highlight the potential of AKARI IRC observations in studying SNRs, especially for diagnosing SNR shocks.Comment: 12 pages with 3 figures, accepted for publication in AKARI PASJ special issu