52 research outputs found
High-performance gallium nitride power devices with efficient edge termination structures compliant with plasma-assisted molecular-beam epitaxy based silicon nitride shadowed selective-area growth technique
No full textThe objective of this research is the design and development of ultra-low-leakage mixed-conduction gallium nitride (GaN) diodes with reverse blocking voltage approaching parallel-plane behavior. Although GaN is a promising wide bandgap (WBG) material, experimentally reported GaN power devices result in large leakage currents with lower reverse blocking efficiency. Two major de ciencies result in crippling underperformance in GaN power devices. First, conventional GaN processing methodologies, such as, ion-implantation and inductively-coupled plasma reactive-ion etching (ICP-RIE) etching, introduce lattice damage and defects, causing large leakage current components. Second, inefficient edge termination (ET) designs are incapable of reaching ideal parallel-plane breakdown voltage. This work aims to overcome the aforementioned problems in GaN power devices through innovative designs compatible with a selective-area processing (SAP) technique avoiding both ICP-RIE and ion-implantation. To alleviate the shortcomings in GaN power device ET schemes, novel ET schemes capable of providing ideal parallel-plane breakdown are developed and presented. Also, these designs are fully compliant with the ultra-low-leakage silicon nitride shadowed selective-area growth (SNS-SAG) GaN processing technique. This plasma-assisted molecular-beam epitaxy (PAMBE) based GaN SAP technique is capable of reducing leakage by at least four orders of magnitude compared to ICP-RIE etching. Additionally, mixed-conduction diodes, such as, buried p-base merged p-i-n Schottky (BP-MPS) and buried p-base merged p-i-n junction barrier controlled Schottky (BP-MPJ) diodes capable of reducing leakage current by about five orders of magnitude compared to corresponding p-islet MPS (PI-MPS) diode designs, have been developed. In conjunction with novel ET designs developed in this work and SNS-SAG processing methodology, these high-performance mixed-conduction diodes perfectly fit in the role of snubber diodes in high-speed switching power applications.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2023-05-01The student, Palash Sarker, accepted the attached license on 2021-04-07 at 17:04.The student, Palash Sarker, submitted this Dissertation for approval on 2021-04-07 at 17:07.This Dissertation was approved for publication on 2021-04-08 at 15:35.DSpace SAF Submission Ingestion Package generated from Vireo submission #16250 on 2021-09-16 at 20:08:11Made available in DSpace on 2021-09-17T04:04:08Z (GMT). No. of bitstreams: 2
SARKER-DISSERTATION-2021.pdf: 31962523 bytes, checksum: 325480075ae60d38a08aa440f23c72dc (MD5)
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Previous issue date: 2021-04-08Embargo set by: Seth Robbins for item 118641
Lift date: 2023-09-17T04:04:53Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 118641
Lift date: 2023-09-17T04:07:01Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemAuthor requested closed access (OA after 2yrs) in Vireo ETD systemLimite
Prospective retarders for alkali-activated slag: stability at high alkalinity, effects on setting behavior and strength of paste
No full textAlternate binders are becoming essential to counteract the carbon emissions caused by manufacture of ordinary Portland cements. Geopolymers or alkali-activated systems with precursors as fly ash, slag or metakaolin, or a mixture of these, are possible substitutes. There are several hindrances to their use in construction due to the lack of understanding and control of properties of the system, starting from initial product formation rate all the way to long-term durability. Ordinary Portland cement systems have been around for a much longer time in history and so have been admixtures that can bring about desired changes in the properties of the material. Similar admixtures for the alternative binders are much less well-established. Through this study, the author hopes to contribute to this field of admixtures for the alternate binders. The scope was narrowed down to one of the major challenges of control of fresh properties. The current investigation looks at an alkali-activated slag system, which has a short, or fast, hardening time. This is not conducive to its use in mainstream construction and a control of the setting or hardening time is essential. Several retarders have been conventionally used for this purpose in the ordinary Portland cement systems. This investigation hopes to study the effectiveness of these retarders in the significantly different alkali-activated system, while also exploring novel retarders. Conventional admixtures used here were organic in nature such as lignosulfonate-based, polycarboxylate-based and naphthalene formaldehyde-based. Novel retarders were a mixture of inorganic and organic substances selected to achieve specific effects (adsorption, complexation, seeding, etc.) that might affect reaction rate. These novel retarders were, namely, dodecyltrimethylammonium chloride (DTAC), poly(diallyldimethylammonium chloride) (PDADMAC), ethylenediaminetetraacetic acid (EDTA) and zinc oxide nanoparticles.
Isothermal calorimetry was the primary test conducted to observe effects on the reaction rate. Stability in the high pH environment was assessed visually and also chemically through infrared spectroscopy. Compressive strength tests were conducted for the novel admixtures and the hardened product was analyzed through infrared spectroscopy. Additional tests such as zeta-potential measurements, adsorption measurements through UV-Vis-NIR spectroscopy and ultrasonic wave reflection (for hardening) were performed, but quality data was hard to obtain. The results from these tests are not part of the main investigation and have been presented separately in the Appendix.
Most conventional organic admixtures were found to be unstable in the high pH (>14) alkali solution. Those that were stable did not retard the reaction when added to paste. The novel admixtures were stable in the high pH environment and retarded the reaction. Some admixtures also had unexpected consequences, unrelated to retardation.
The results of this investigation may serve towards the foundation of admixtures for alkali-activated systems and facilitate the exploration or artificial synthesis of such admixtures.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2017-08-10 without embargo termsThe student, Palash Badjatya, accepted the attached license on 2017-04-28 at 11:39.The student, Palash Badjatya, submitted this Thesis for approval on 2017-04-28 at 11:40.This Thesis was approved for publication on 2017-04-28 at 12:41.DSpace SAF Submission Ingestion Package generated from Vireo submission #10682 on 2017-08-10 at 13:39:05Made available in DSpace on 2017-08-10T19:14:50Z (GMT). No. of bitstreams: 2
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Previous issue date: 2017-04-2
Uncertainty Modeling in Risk Assessment Based on Dempster–Shafer Theory of Evidence with Generalized Fuzzy Focal Elements
No full textAbstractDempster–Shafer theory of evidence is one of the important tools for decision making under uncertainty. It is more useful in situations when cost of technical difficulties is involved or uniqueness of the situation under study makes it difficult/impossible to cover enough observations to quantify the models with real data. Consequently, experts provide opinions in terms of basic probability assignment for focal elements. Usually, it is seen that experts provide basic probability assignment for interval (or crisp) focal elements. However, due to presence of uncertainty focal elements can sometimes be treated as normal/generalized triangular fuzzy number (TFN in short) instead of intervals or crisp sets. TFN encodes only most likely value (mode) and the spread. This paper presents an attempt to combine Dempster–Shafer structures (DSS in short) with generalized/normal fuzzy focal elements using possibilistic sampling technique. To this end, human health risk assessment is carried out under such setting
Online State Estimators for Lithium Ion Batteries: Development of a multi-physics based online State of health estimator for Lithium Ion batteries
No full textBatteries play a crucial role in powering contemporary devices and systems, ranging from smartphones and electric vehicles to renewable energy storage. With the increasing demand for more efficient and reliable battery technologies, the need for accurate monitoring and assessment of battery condition and performance has also grown. Online estimators, that continuously analyse battery conditions in real-time, have emerged as valuable tools to meet these goals. This thesis focuses on constructing model-based online state estimators for real-time estimation of a battery's State of Health (SOH).These estimators, necessitate a state space model for a lithium-ion cell. In the initial part of the thesis, a physics-based reduced-order model (ROM) of a lithium-ion cell is developed. This model accounts for major aging mechanisms such as Solid Electrolyte Interphase (SEI) layer formation, Loss of Active Material (LAM), and Lithium Plating (LIP). To incorporate temperature effects on cell parameters, a simplified lumped thermal model is integrated into the battery model. The model is subsequently transformed into a state space model using the Discrete Realization Algorithm (DRA) process.Building upon the noisy outputs from the ROM models, a set of five estimators is formulated: State of Charge (SOC), Voltage, SEI loss, LAM loss, and LIP loss estimators. These estimators are constructed based on Kalman filters and collectively contribute to real-time prediction of a battery's SOH. Given their reliance on the model, the ROM model's output is employed as a reference to gauge the precision of the estimators.To address the real life scenarios and to check the robustness of the estimators, a series of sub-questions were analysed: Sub question1: How to estimate the SOH of a cell in real-time using adaptive control techniques ? Sub question2: How fast can the estimator react to changing initial states of the cell? Sub question3: Can the estimators be adapted to concurrently estimate both the states and the time varying cell parameters in case of an old cell? How fast can this be achieved in real-time ? Overall, this research contributes to the development of model-based online estimators, which are poised to have a significant impact on enhancing battery performance, prolonging lifespan, and facilitating the transition towards a more sustainable energy future.Electrical Engineering | Sustainable Energy Technolog
Invasive Fungal Infections after Anti-CD19 Chimeric Antigen Receptor-Modified T-Cell Therapy: State of the Evidence and Future Directions
No full textStudies describing invasive fungal infections (IFIs) after chimeric antigen receptor-modified T-cell (CAR-T-cell) therapy are limited. Although post-CAR-T-cell IFIs appear to be uncommon, they are associated with significant morbidity and mortality. Specific risk factors for IFIs in CAR-T-cell recipients have not been fully characterized and are often extrapolated from variables contributing to IFIs in patients with other hematologic malignancies or those undergoing hematopoietic cell transplant. Optimal prophylaxis strategies, including the use of yeast versus mold-active azoles, also remain ill-defined. Further research should investigate key risk factors for IFIs and establish an evidence-based approach to antifungal prophylaxis in these patients in order to improve clinical outcomes
Unrecognized Strongyloides stercoralis Infection in Hemodialysis Patient With Recurrent Diarrhea and Readmissions
No full textInfluence of Warping on Modal Parameters of Thin-walled Channel Section Steel Beam
No full textAbstractIn this study, free vibration analysis of thin-walled channel section beam including warping effects has been carried out using Finite element method (FEM) and compared with experimentally measured results. Results reveal that natural frequencies of the system decrease on exclusion of warping in the analysis. Also, it has been observed that the difference between higher mode shapes were significantly high when theoretically obtained mode shapes considering warping and without warping were compared. Thereafter, the Modal Assurance Criterion (MAC) plot is presented to show the difference between the mode shapes with and without consideration of warping stiffness
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