Fault tolerant control for nonlinear aircraft based on feedback linearization

The thesis concerns the fault tolerant flight control (FTFC) problem for nonlinear aircraft by making use of analytical redundancy. Considering initially fault-free flight, the feedback linearization theory plays an important role to provide a baseline control approach for de-coupling and stabilizing a non-linear statically unstable aircraft system. Then several reconfigurable control strategies are studied to provide further robust control performance:- A neural network (NN)-based adaption mechanism is used to develop reconfigurable FTFC performance through the combination of a concurrent updated learninglaw. - The combined feedback linearization and NN adaptor FTFC system is further improved through the use of a sliding mode control (SMC) strategy to enhance the convergence of the NN learning adaptor. - An approach to simultaneous estimation of both state and fault signals is incorporated within an active FTFC system.The faults acting independently on the three primary actuators of the nonlinear aircraft are compensated in the control system.The theoretical ideas developed in the thesis have been applied to the nonlinear Machan Unmanned Aerial Vehicle (UAV) system. The simulation results obtained from a tracking control system demonstrate the improved fault tolerant performance for all the presented control schemes, validated under various faults and disturbance scenarios.A Boeing 747 nonlinear benchmark model, developed within the framework of the GARTEUR FM-AG 16 project “fault tolerant flight control systems”,is used for the purpose of further simulation study and testing of the FTFC scheme developed by making the combined use of concurrent learning NN and SMC theory. The simulation results under the given fault scenario show a promising reconfiguration performance

Structural and functional abnormities of amygdala and prefrontal cortex in major depressive disorder with suicide attempts

Finding neural features of suicide attempts (SA) in major depressive disorder (MDD) may be helpful in preventing suicidal behavior. The ventral and medial prefrontal cortex (PFC), as well as the amygdala form a circuit implicated in emotion regulation and the pathogenesis of MDD. The aim of this study was to identify whether patients with MDD who had a history of SA show structural and functional connectivity abnormalities in the amygdala and PFC relative to MDD patients without a history of SA. We measured gray matter volume in the amygdala and PFC and amygdala-PFC functional connectivity using structural and functional magnetic resonance imaging (MRI) in 158 participants [38 MDD patients with a history of SA, 60 MDD patients without a history of SA, and 60 healthy control (HC)]. MDD patients with a history of SA had decreased gray matter volume in the right and left amygdala (F = 30.270, P = 0.000), ventral/medial/dorsal PFC (F = 15.349, P = 0.000), and diminished functional connectivity between the bilateral amygdala and ventral and medial PFC regions (F = 22.467, P = 0.000), compared with individuals who had MDD without a history of SA, and the HC group. These findings provide evidence that the amygdala and PFC may be closely related to the pathogenesis of suicidal behavior in MDD and implicate the amygdala-ventral/medial PFC circuit as a potential target for suicide intervention

Structural and functional abnormities of amygdala and prefrontal cortex in major depressive disorder with suicide attempts

Finding neural features of suicide attempts (SA) in major depressive disorder (MDD) may be helpful in preventing suicidal behavior. The ventral and medial prefrontal cortex (PFC), as well as the amygdala form a circuit implicated in emotion regulation and the pathogenesis of MDD. The aim of this study was to identify whether patients with MDD who had a history of SA show structural and functional connectivity abnormalities in the amygdala and PFC relative to MDD patients without a history of SA. We measured gray matter volume in the amygdala and PFC and amygdala-PFC functional connectivity using structural and functional magnetic resonance imaging (MRI) in 158 participants [38 MDD patients with a history of SA, 60 MDD patients without a history of SA, and 60 healthy control (HC)]. MDD patients with a history of SA had decreased gray matter volume in the right and left amygdala (F = 30.270, P = 0.000), ventral/medial/dorsal PFC (F = 15.349, P = 0.000), and diminished functional connectivity between the bilateral amygdala and ventral and medial PFC regions (F = 22.467, P = 0.000), compared with individuals who had MDD without a history of SA, and the HC group. These findings provide evidence that the amygdala and PFC may be closely related to the pathogenesis of suicidal behavior in MDD and implicate the amygdala-ventral/medial PFC circuit as a potential target for suicide intervention

Essays on financial institutions' response to climate and tariff risks

101 pagesThis dissertation consists of three essays in the areas of financial economics and climate finance, examining the response of financial institutions to environmental risks and tariff changes. The first essay investigates if banks pay attention to the investment preference of ESG-committed mutual funds and issue loans at preferable terms to firms with higher ESG ownership. I use firm-level share fraction of US PRI (Principles for Responsible Investment) mutual funds as a proxy for ESG ownership. I find that even though PRI ownership does not improve firm ESG profile in the following year, banks on average significantly increase the amount and reduce the interest rate of new loans issued to firms with higher PRI ownership. I also show that PRI ownership is not likely to be a proxy for firm credit risk or stock return and banks' response is largely driven by banks that exhibit more environmental awareness. Overall, the results show that banks factor in borrowers' ESG ownership structure when evaluating new loans. In the second essay, my co-authors and I study the existence and effect of local bias of US mutual funds on firms affected by hurricane landfalls. We find that local funds increase normalized shares of disaster-zone firms in the disaster quarter relative to non-local funds. With-in fund style analysis also suggests the existence of local bias. Compared to non-local funds, local funds increase the portfolio weight of firms headquartered in disaster-zone counties. The investor loyalty of local funds following natural disasters does have real economic impacts on disaster-zone firms. Preliminary analysis shows disaster-zone firms with higher proportion of shares held by local funds prior to disasters tend to have higher excess return and make more short-term investment in the disaster quarter, thus potentially having better financial recovery from disasters. The third essay studies the effects of industry-level tariff reductions on bank new lending and banks' existing borrowers one year after the tariff reductions. High-exposure banks decrease new lending to borrowers in the affected industries relative to borrowers in the unaffected industries. Using two measures of prior bank-firm relationship, I find that banks decrease new lending only to non-relationship borrowers and actually support relationship borrowers in the affectedindustries. Moreover, there is a spillover effect from firms in the affected industries to unaffected industries through the bank-firm network. Existing borrowers in the unaffected industries tend to increase cash holding and decrease R&D expenditure as a result of enhanced bank monitoring. Overall, these findings suggest that banks can act as intermediaries for shock transmission from affected to unaffected borrowers, resulting in real impacts on unaffected borrowers

High-Resolution Hazard Assessment for Tropical Cyclone-Induced Wind and Precipitation: An Analytical Framework and Application

Intensified tropical cyclones (TCs) threaten the socioeconomic development of coastal cities. The coupling of strong wind and precipitation with the TC process usually amplifies the destructive effects of storms. Currently, an integrated analytical framework for TC hazard assessment at the city level that combines the joint statistical characteristics of multiple TC-induced hazards and local environmental features does not exist. In this study, we developed a novel hazard assessment framework with a high spatiotemporal resolution that includes a fine-tuned K-means algorithm for clustering TC tracks and a Copula model to depict the wind–precipitation joint probability distribution of different TC categories. High-resolution wind and precipitation data were used to conduct an empirical study in Shenzhen, a coastal megacity in Guangdong Province, China. The results show that the probabilities of TC-induced wind speed and precipitation exhibit significant spatial heterogeneity in Shenzhen, which can be explained by the characteristics of TC tracks and terrain environment factors. In general, the hazard intensity of TCs landing from the west side is higher than that from the east side, and the greatest TC intensity appears on the southeast coast of Shenzhen, implying that more disaster prevention efforts are needed. The proposed TC hazard assessment method provides a solid base for highly precise risk assessment at the city level

Effects of Plant-Growth-Promoting Rhizobacteria on Soil Bacterial Community, Soil Physicochemical Properties, and Soil Enzyme Activities in the Rhizosphere of Alfalfa under Field Conditions

Background: Inoculation with plant-growth-promoting rhizobacteria (PGPR) effectively increases plant growth in agriculture. However, the role of the rhizobiome in plant growth remains unclear. Methods: Biolog Ecoplate and 16S rRNA gene high-throughput sequencing techniques were used to analyze the changes in microbial community diversity, composition, and function after PGPR inoculation. Soil physicochemical and enzyme activities were also measured. Results: PGPR inoculation significantly promoted the growth of alfalfa. Using a Biolog Ecoplate, inoculation improved the metabolic activity and carbon source utilization of soil microorganisms. PGPR inoculation significantly increased the diversity and richness of the soil bacterial community in the rhizosphere of alfalfa and increased the relative abundance of key bacterial taxa such as Arthrobacter, Sphingomonas, and Bacillus, which are conducive to plant growth. Conclusions: Inoculation with PGPR enriched bacterial taxa and improved the utilization of carbon sources beneficial for plant growth. PGPR inoculation induced changes in microbial community diversity, and relevant functions in the rhizosphere contributed to alfalfa growth under field conditions