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Theoretical Reaction Mechanism Study on Organic and Inorganic Materials for Renewable Energy and Environment
Get PDFSchool of Energy and Chemical Engineering (Chemical Engineering)Concerning about the increases of energy demand and environmental issue have let to the development of renewable energy with low greenhouse gas emissions. To produce the industrial compounds without fossil fuel consumption, the themes of research on renewable energy have been focused towards to the method to produce the chemical materials by using earth-abundant resources such as plants, wind, and solar energy. However, the low efficiency, high initial cost of installation, and discontinuity of source acquirement of renewable energy are still slowing down its application. To overcome these challenges, renewable energy technologies still need to be improved.
Effective and technological developments to the practical application of renewable energy are derived from in-depth understanding of reactions related to renewable energy and environment. Furthermore, novel materials and strategies can be established by combining theoretical approaches and knowledge of reactions. In this context, Molecular modeling and simulation are the appropriate method to investigate the reaction mechanism for desired substances or to identify the cause of a phenomenon at the atomic level. In this thesis, we described the theoretical research on the reaction mechanism related with renewable energy system.
In Chapter 1, we introduce shortly the renewable energy systems and the mechanistic studies for in-depth understanding of chemical engineering. Also, we described the previous and ongoing research about the renewable technologies and applications using molecular simulation methods. Finally, we explained the multi-scale molecular simulation method and its theoretical meanings used in this thesis, including the density functional theory (DFT) calculation, molecular dynamics (MD), and Monte Carlo (MC) simulation.
In Chapter 2, we suggested the new strategy for formation of desired organic materials from biomass (renewable energy source) with highly effective catalysts. First, it was found that solvent effect of 1-butanol and the catalytic performance of hydrotalcite in glucose isomerization mechanism using DFT calculation. Furthermore, the reaction mechanistic pathways for the fructose hydrogenation to mannitol and sorbitol which is used as the biomass, were investigated by DFT calculation. The catalytic effect of the Cu metal catalyst favorably induced the formation of mannitol than the formation of sorbitol during the fructose adsorption step.
In Chapter 3, we theoretically demonstrated that the formic acid and supercritical ethanol mixture solvents expedited the solvothermal liquefaction reaction of biomass lignin constituents. Using the reactive molecular dynamics simulation and density functional theory calculation, the mechanisms by which solvents break C???O bond and C???C bond in each Dilignol molecule were observed over time. In this liquefaction reaction, the hydrogen detached from the formic acid directly participates in dissociation of C???O bond and C???C bond, and the supercritical ethanol transfers the radical hydrogen from formic acid to dilignol. This mechanism study suggested the biomass utilization method that can produce a lot of hydrogen without a metal catalyst.
In Chapter 4, we theoretically proposed the feasibility of universal synthesis of the metal sulfide electrolyte that can improve the performance of all solid-state battery developed for effective storage of renewable energy and reduced carbon footprint. Using an alkahest solvent system composed of EDA-EDT mixture solvents, not only conventional sulfide SE precursors of Li2S, P2S5, and Na2S, but also metal sulfides, such as GeS2 were fully dissolved by nucleophilic attack of thiolate. It was elucidated that EDT molecules have strong dissolving power by proton transfer to EDA and that the dissolution of sulfide precursors is feasible through the investigation of reaction mechanism.
In Chapter 5, we provided the insight of mineral carbonation reaction for carbon dioxide storage and utilization using DFT calculation and MD simulation. Calcium hydroxide has been mainly studied as a medium for mineral carbonation, but its efficiency was not good. In this study, we revealed that water molecules are intercalated in interlayer of calcium hydroxide and the interlayer distance between the calcium hydroxide increases. Remarkably, the water molecules near the surface of the calcium hydroxide accelerated the carbonation phenomenon of CO2 through the studies.ope
Electrochemical CO2 conversion to formic acid using engineered enzymatic catalysts in a batch reactor
No full textFormic acid is one of the most valuable fuel products for the capture and conversion of CO2 due to its unique usage in fuel cells and hydrogen storage. Electrochemically mediated conversion of CO2 to FA has its advantages over the traditional Kemira process, in that high temperatures and pressures are not required, cutting on manufacturing and operating costs. However, selectivity of the metal catalysts used in CO2 conversion to certain products remains limited. Here, an engineered enzymatic catalyst is employed to convert CO2 into formic acid (in the form of formate) in a batch reactor. This work seeks to maximize both formate production and Coulombic efficiency, which is achieved primarily through: (1) adjustment of the operating voltage, (2) implementation of an O2 scavenger to mitigate competition with dissolved O2, and (3) control of system pH to maintain a stable operating range for the catalyst. Peak formate production and peak efficiency achieved in long-term experiments (> 40 h) were 225 mM and 91 %, respectively, both of which show promise of strong metrics for CO2 conversion to formate. The optimal operating cathode voltage was shown to be below the baseline voltage of ??? 0.75 V vs. Ag/AgCl. In short-term experiments (??? 1 h), operating below this range, at approximately ??? 0.85 V, could achieve efficiencies of 100 %. By implementing sodium thiosulfate as an O2 scavenger, the rate of formate production improved by over 4 ??. Long-term retention of the efficiency, however, remains an issue to be addressed due to the enzyme sensitivity to pH and increased current at higher values of acid used on the anode
Epigenetic Regulators of DNA Cytosine Modification: Promising Targets for Cancer Therapy
No full textEpigenetic modifications are crucial regulators of gene expression that critically impact cell lineage differentiation, survival, and proliferation, and dysregulations are commonly observed in various cancers. The aberrantly modified epigenome confers unique features on tumor cells, including sustained proliferative potential, resistance to growth-suppressive or cell death signals, augmented replicative immortality, invasion, and metastasis. As a result, epigenetic abnormalities exhibit significant impacts on all stages of oncogenesis from its onset to progression to metastasis. Among various epigenetic mechanisms in mammals, DNA cytosine methylation???demethylation is recurrently disrupted in cancers. Due to its inherent reversibility, targeting DNA methylation dynamics has gained tremendous attention as a promising therapeutic option that can ameliorate the effects of cancer-specific epigenetic abnormalities by restoring normal conditions. Various small molecules targeting DNA (de)methylation regulators have been developed as potential cancer therapeutics, some of which are approved for usage in clinics. Clinical trials of many other molecules are underway for both hematological malignancies and solid tumors. In this review, we discuss the DNA methylation/demethylation pathway as a promising target for therapeutic intervention in cancer and highlight the development of various epigenetic drugs targeting DNA-modifying enzymes such as DNA methyltransferases (DNMTs) and ten-eleven translocation (TET) enzymes
Bulk and surface modified polycrystalline CuWO4 films for photoelectrochemical water oxidation
No full textPolycrystalline CuWO4 film is an emerging photoanode material for photoelectrochemical (PEC) water splitting with a small bandgap to absorb visible light and excellent stability in a neutral electrolyte. However, its PEC performance is quite low mainly due to its poor charge transfer characteristics. To enhance the performance of the CuWO4 photoanode, two modification strategies are employed; SnO2 as an electron transfer layer to improve the bulk charge separation efficiency of CuWO4 and cobalt phosphate as a co-catalyst to augment the surface charge separation efficiency at the interface of CuWO4||electrolyte. The two modifications enhance the PEC activity two times to 0.13 mA/cm2 @ 1.23 VRHE for water oxidation and 0.24 mA/cm2 @ 1.23 VRHE for hole scavenger oxidation, and exhibit an excellent stability in a neutral electrolyte. Although the performance is still very low compared to well-developed metal oxide photoanodes, this work shows possibility of further improvement with further developments of synthesis method as well as applying other elaborate modification strategies
Transfer learning-based ensemble convolutional neural network for accelerated diagnosis of foot fractures
No full textThe complex shape of the foot, consisting of 26 bones, variable ligaments, tendons, and muscles leads to misdiagnosis of foot fractures. Despite the introduction of artificial intelligence (AI) to diagnose fractures, the accuracy of foot fracture diagnosis is lower than that of conventional methods. We developed an AI assistant system that assists with consistent diagnosis and helps interns or non-experts improve their diagnosis of foot fractures, and compared the effectiveness of the AI assistance on various groups with different proficiency. Contrast-limited adaptive histogram equalization was used to improve the visibility of original radiographs and data augmentation was applied to prevent overfitting. Preprocessed radiographs were fed to an ensemble model of a transfer learning-based convolutional neural network (CNN) that was developed for foot fracture detection with three models: InceptionResNetV2, MobilenetV1, and ResNet152V2. After training the model, score class activation mapping was applied to visualize the fracture based on the model prediction. The prediction result was evaluated by the receiver operating characteristic (ROC) curve and its area under the curve (AUC), and the F1-Score. Regarding the test set, the ensemble model exhibited better classification ability (F1-Score: 0.837, AUC: 0.95, Accuracy: 86.1%) than other single models that showed an accuracy of 82.4%. With AI assistance for the orthopedic fellow, resident, intern, and student group, the accuracy of each group improved by 3.75%, 7.25%, 6.25%, and 7% respectively and diagnosis time was reduced by 21.9%, 14.7%, 24.4%, and 34.6% respectively
Microphysiological system recapitulating the pathophysiology of adipose tissue in obesity
No full textA growing body of evidence has indicated that white adipose tissue (AT) remodeling is a major trigger for obesity-associated metabolic complications. However, the scarcity of translational models is an obstacle to the development of medicines that act on adipose restoration. Here, we describe a microphysiological system (MPS) that emulates the unique features of reprogrammed AT as a new in vitro tool for studying AT pathophysiology in obesity. The AT MPS contained mature adipocytes embedded in an extracellular matrix (ECM) hydrogel interfaced with AT microvascular endothelium, which was constantly perfused with fresh media. The unique biochemical signals due to the remodeled ECM in obesity were recapitulated using a decellularized AT ECM (AT dECM) hydrogel, which preserves the features of altered ECM composition in obesity. The mature adipocytes embedded in the AT dECM hydrogel maintained their function and morphology for a week without dedifferentiation. Using the AT MPS, we successfully modeled inflammation-induced AT microvascular dysfunction, the recruitment of immune cells due to the upregulation of cell adhesion molecules, and higher cancer cell adhesion as an indicator of metastasis, which are observed in obese individuals. The AT MPS may therefore represent a promising platform for understanding the dynamic cellular interplay in obesity-induced AT remodeling and validating the efficacy of drugs targeting AT in obesity
TRADING CONSTRAINTS IN CONTINUOUS-TIME KYLE MODELS
No full textIn a continuous-time Kyle setting, we prove global existence of an equilibrium when the insider faces a terminal trading constraint. We prove that our equilibrium model produces an output consistent with several empirical stylized facts such as autocorrelated aggregate holdings, decreasing price impacts over the trading day, and U
shaped optimal trading patterns
Characterization of Klebsiella pneumoniae bacteriophages, KP1 and KP12, with deep learning-based structure prediction
No full textConcerns over Klebsiella pneumoniae resistance to the last-line antibiotic treatment have prompted a reconsideration of bacteriophage therapy in public health. Biotechnological application of phages and their gene products as an alternative to antibiotics necessitates the understanding of their genomic context. This study sequenced, annotated, characterized, and compared two Klebsiella phages, KP1 and KP12. Physiological validations identified KP1 and KP12 as members of Myoviridae family. Both phages showed that their activities were stable in a wide range of pH and temperature. They exhibit a host specificity toward K. pneumoniae with a broad intraspecies host range. General features of genome size, coding density, percentage GC content, and phylogenetic analyses revealed that these bacteriophages are distantly related. Phage lytic proteins (endolysin, anti-/holin, spanin) identified by the local alignment against different databases, were subjected to further bioinformatic analyses including three-dimensional (3D) structure prediction by AlphaFold. AlphaFold models of phage lysis proteins were consistent with the published X-ray crystal structures, suggesting the presence of T4-like and P1/P2-like bacteriophage lysis proteins in KP1 and KP12, respectively. By providing the primary sequence information, this study contributes novel bacteriophages for research and development pipelines of phage therapy that ultimately, cater to the unmet clinical and industrial needs against K. pneumoniae pathogens
Energy-Efficient Fast-Transient Dynamic Reconfigurable Charge Pump for Multi-Channel Electrical Stimulation
No full textAn energy-efficient fast-transient dynamic reconfigurable charge pump (CP) is presented for multi-channel electrical stimulation applications. It includes a proposed dynamic reconfigurable CP to improve the overall power saving of the current-controlled stimulator (CCS) system, where individual or integrated controls of multiple CPs are selected by monitoring the CCS channels. For further energy-efficient operation, the stimulation mode-adaptive power on-off scheme is augmented by adopting a low-power two-dimensional frequency modulation (TFM) control and an initial pre-charging diode (IPD) circuit in the CP cores for fast settling performance. A CP prototype is fabricated in a 180-nm CMOS process, and its proposed operations were experimentally verified, achieving an overall more than 80% power-saving effect with maximum 69.8% general power efficiency and fast recovery performance
Thienothiophene???Assisted Property Optimization for Dopant???Free ?????Conjugation Polymeric Hole Transport Material Achieving Over 23% Efficiency in Perovskite Solar Cells
No full textHole transport materials (HTMs) play essential roles in achieving high photovoltaic performance and long-term stability in the n???i???p structure of perovskite solar cell (PSC) devices. Recently, dopant-free polymeric materials as HTMs in PSCs have attracted considerable attention owing to high carrier mobility and excellent hydrophobicity. However, achieving similar efficiencies to those of doped small molecule HTMs such as Spiro-OMeTAD is a big challenge. Herein, a thienothiophene ??-bridge is selected as a stabilizer and energy level regulator incorporated into a donor???acceptor-type HTM to synthesize a new polymer, Nap-SiBTA. The incorporation of the thienothiophene group improves the thermal stability and favors the high planarity and face-on orientation, promoting high charge carrier mobility and tunable optical band gap. Finally, the dopant-free polymer Nap-SiBTA-based PSC achieves an excellent power conversion efficiency (PCE) of 23.07% with a high fill factor of 80.85%. To the best of the authors??? knowledge, this is one of the best efficiencies in dopant-free HTM PSCs. Moreover, the unencapsulated device retains 93% of its initial PCE after 1000 h owing to the excellent hydrophobicity of Nap-SiBTA. This work provides a general and practical method to design dopant-free HTMs for the high efficiency and long-term stability of PSCs