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Implementation of liquid organic hydrogen carrier in H2 society: Comprehensive feasibility study on H2 supply chain
No full textSchool of Energy and Chemical Engineering (Chemical Engineering)The environmental issues derived from the usage of fossil fuels as the primary energy source have led to numerous academic, industrial, and political efforts to develop a new energy paradigm. Owing to the significant benefits of H2 from an environmental point of view, various types of efforts to develop the related crucial infrastructure to adopt H2 as the next alternative energy carrier or as the fuel by direct usage have been actively introduced. Meanwhile, regarding one of the important challenges, storage and transportation of H2, in the accomplishment of the new energy paradigm based on H2, conventional methods via compression, liquefaction, and the metal hydride require additional energy to maintain the state or show very low storage density due to the intrinsic weight of the medium. To overcome obstacles of conventional methods to store and transport the hydrogen, the concept of liquid organic hydrogen carrier was introduced as it can store produced H2 in relatively high-pressure conditions ??? hydrogenation ???, exist as the liquid state even at the standard state,
release the stored H2 again by heat supply ??? dehydrogenation ??? and the liquid organic molecules used as the H2 carrier can be recycled in the H2 supply chain.
As the detailed and preliminary feasibility study should be preceded to realize the commercialization of the newly proposed technology, the feasibility analysis model for various H2 supply chains regarding both economic and environmental perspectives is developed here to quantitatively evaluate each investigated scenario. In addition, quantified economic and environmental feasibility of the hydrogenation and dehydrogenation using several liquid organic hydrogen carriers and ammonia is evaluated and used in the developed model to reflect much detailed impact of the concept of liquid organic hydrogen carrier on the H2 supply chain.
In this study, detailed process simulation of both hydrogenation and dehydrogenation processes for eight types of liquid organic hydrogen carrier candidates ??? N-ethylcarbazole, dibenzyltoluene, formic acid, methanol, naphthalene, methylcyclohexane, benzyltoluene, and benzene ??? and ammonia is conducted with the adoption of experimental reaction kinetics. The techno-economic analysis based on the quantified results for the performance of each investigated process obtained from the developed process simulation models is also performed to evaluate unit H2 supply cost for hydrogenation and dehydrogenation processes.
In addition, the environmental assessment in terms of carbon footprint analysis quantifies the CO2 emissions, which were both directly emitted from the reaction and converted by a certain CO2 emission factor.
For the H2 supply chain to H2 fueling stations in South Korea in this study, three types of H2 production methods of steam methane reforming, coal gasification, and water electrolysis are considered and 19 countries of Qatar, Australia, USA, Oman, Malaysia, Indonesia, and Russia as the main liquefied natural gas-abundant exporter, Australia, Russia, Indonesia, Canada, USA, South Africa, Columbia, and Republic of Mozambique as the main coal exporters, and China, USA, Germany, and Italy as main renewable energy exporters are assumed.
Each investigated H2 supply chain, after the production of H2 in each exporting country, consists of procedures of H2 conditioning via compressed H2, liquefied H2, liquid organic hydrogen carriers, or ammonia, short-term storage via cavern, high-pressure tank, cryogenic tank, or oil tank, inland transportation via pipeline or truck, pre-processing to liquefied H2, liquid organic hydrogen carriers, or ammonia, and post-processing to compressed H2, liquefied H2, liquid organic hydrogen carriers, or ammonia with quantified unit H2 supply cost and unit CO2 emissions in the H2 supply chain are quantified.
Based on the developed 520 H2 supply chains and feasibility study models, the effects of the H2 demand, CO2 capture rate, recycle ratio of liquid organic hydrogen carrier, and types of energy sources are investigated in economic, environmental, and comprehensive perspectives by adopting the technique for order of preference by similarity to ideal solution. For the effect of H2 demand, ammonia and methylcyclohexane, methanol and benzene, and ammonia are revealed as promising liquid organic hydrogen carrier candidates from economic,
environmental, and comprehensive points of view. Regarding the effect of the CO2 capture rate, the methanol-based H2 supply chain is suggested as the most environmentally feasible under all CO2 capture rates investigated and the novelty of full adoption of ammonia in the H2 supply chain is shown again in the comprehensive point of view. The analysis of the effect of recycle ratio of liquid organic hydrogen carrier also reveals the novelty of full utilization of ammonia and selective adoption of methylcyclohexane in the H2 supply chain from both economic and environmental points of view. Similar to the effect of recycle ratio of liquid organic hydrogen carrier, full utilization of ammonia and selective adoption of methylcyclohexane show its significant novelty regardless of types of energy sources.
From this dissertation, the feasibility study on the liquid organic hydrogen carrier -implemented H2 supply chain model is developed and economic and environmental promises of the concept of liquid organic hydrogen carrier are suggested.clos
Integrative multi-omics analysis for the effect of genetic alterations in cancer xenograft and organoid models
Get PDFDepartment of Biomedical EngineeringDNA damage is a well-recognized factor in the development and progression of cancer. Numerous studies on genetic changes associated with cancer or the DNA repair pathway have been conducted, however, there is still a need for additional research on their function. The establishment of patient-derived xenografts or organoids for the purpose of testing functional genomic approaches is the subject of ongoing research. According to model-specific characteristics, it is not fully understood how these attempts to simulate patient cancer differ from original cancer. To comprehend the distinction between genuine patient cancer and these patient-derived disease models in more depth, multi-omics analysis is required to comprehend the overall genotypes, phenotypes, and environmental variables. Depending on the characteristics of each disease model, distinct omics analysis approaches and factors must be considered. In addition, care must be taken to avoid technical errors when integrating omics data generated by different sequencing equipment. There is currently no golden rule for data integration, but several approaches are being developed.
It is crucial to determine the function of genes linked with the DNA repair pathway because these genes contribute to the induction or prevention of cancer. In chapter 1, I identified the interaction between MRE11 and TRIP13 through proximity labeling combined with the SILAC method which is quantitative proteomics using metabolic labeling. TRIP13 depletion doesn???t affect the nuclease activity and conformation of the MRN complex but directly inhibits the interaction of MDC1 with MRN complex and MDC1 recruitment on the DNA damage site. TRIP13 degradation with mirin treatment shows additive effects on ATM signaling activation. In conclusion, TRIP13 regulates immediate-early DNA damage sensing through MRE11 and ATM signaling independently of mirin.
When assessing the functional genomic approach using patient-derived disease models, it is essential to determine which aspects of the models' correlation to actual cancer should be properly considered. In chapter 2, I found there are a few overlapped deleterious somatic mutations of the PDX model and their original tumor. I suspected novel mutagen exposure during PDX establishment or sample contamination. However, germline mutations of PDX models are well conserved from original tumors, and their mutational signatures of PDX also mimic that of their tumor. Though the number of overlapped mutations between the PDX model and their tumor was few, brain tumor-specific mutations are found in PDX samples. Especially, histone methylation- and cilia-related gene mutations are enriched in PDX samples. While it suggested these mutated genes are needed for maintaining the stemness of brain tumor PDX model or PDX model would be more appropriate for the samples with high heterogeneity, I have presented precautions and considerations in PDX model genome analysis.
Multi-omics analysis that takes into consideration genetic, expressive, and clinical aspects can provide important information for the study of diseases with complicated etiologies, such as cancer, and can contribute to the development of diagnosis and treatment. To utilize colorectal cancer organoids for Companion Diagnostics (CDx), in chapter 3, I characterized patient-derived colorectal cancer (CRC) organoids through well-known genomic markers such as Tumor mutation burden (TMB), Microsatellite instability (MSI) and propose a novel grouping method using sharing same mutation site. The classification of CRC patients was more detailed combined with consensus molecular subtype (CMS) classifications. Additionally, I extract the expression features of the patients who experience recurrence or metastasis after first-line chemotherapy treatment with reference to clinical data. Drug response of CRC organoids by patient group and knockdown of the extracted features in the selected organoids would be validated in further study.
In summary, with this dissertation, I conducted functional research on the DNA repair pathway of cancer-related genes, as well as the genetic analysis between patient-derived xenograft and original tumors, and introduced a novel perspective on the diagnosis and treatment of colorectal cancer patients using patient-derived organoids through multi-omics analysis.ope
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No full textDepartment of Materials Science and Engineeringclos
Neural Process based Bayesian Optimization for Semiconductor Design Factor Search under Constraint
Get PDFGraduate School of Artificial IntelligenceBayesian Optimization (BO) using Gaussian Process (GP) is a conventional choice to solve a black-box optimization problem. However, adopting the Gaussian Process can cause trouble situations when (i). the optimization iteration needs to be large or (ii). the surrogate function should capture complex func-tional form, which is hard for mere joint Gaussian distribution assumption. Since the success of Deep Neural Networks, there have been many kinds of research to overcome such limitations by substitution the Gaussian Process with Neural Networks, called Neural Process families (NPs). This paper compares different experimental aspects when varying the surrogate models in a semiconductor design factor search problem. Comparisons include computational cost, optimization performance, and the change of acquisition value mapping over search space varying the choices of surrogate model of BO. As the result, it is shown that GPs computational cost grows exponentially as the BO iteration becomes larger, while NPs computational cost grows only on a linear scale, outperforming the optimization performance slightly with the proper choice of training hyperparameter.ope
Phase Modulation of Emissive Materials for Efficient Blue Perovskite Light-Emitting Diodes
Get PDFSchool of Energy and Chemical Engineering (Energy Engineering)Recently, metal halide perovskites (MHPs) have drawn considerable research interest as next-generation materials for optoelectronic device applications in solar cells, lasing, and light-emitting diodes (LEDs). Especially, for lighting and future-generation displays, MHPs have emerged, taking advantage of their excellent optoelectrical properties such as superior luminescence efficiency, narrow linewidth, easy band gap tunability, and defect tolerance. Tremendous developments have been made in enhancing the performance of perovskite LEDs (PeLEDs)external quantum efficiencies (EQEs) have exceeded 20% for green and red emissive PeLEDs. However, the lagged efficiency of blue emissive PeLEDs has hampered practical display applications.
Blue emissive perovskite materials inevitably require the incorporation of chlorine that induces the enlarged optical bandgap entailing a relatively deeper highest occupied molecular orbital (HOMO) energy level and detrimental trap states within the bandgap, resulting in unbalanced energy level alignment with adjacent charge transporting layers in the device and poor photoluminescence quantum yield (PLQY) and stability of blue emissive perovskite materials, respectively. Therefore, the development of chlorine-less blue emissive perovskite materials is imperative for future full-color displays. Dimensional engineering is one effective approach, and quasi-two-dimensional (quasi-2D) perovskites can be an exceptional candidate. This thesis covers effective approaches for the modulation of 2D perovskite phases to realize efficient and stable blue PeLEDs.
In chapter 2, an effective interfacial engineering strategy was introduced to guide the formation of well-grown 2D perovskite phases and minimize the detrimental chemical damage from the acidic poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PEDOT:PSS) substrate. Zwitterion additive, L-phenylalanine was incorporated into the PEDOT:PSS. This additive formed bidentate coordination with uncoordinated Pb2+ in the overlying perovskite layer which facilitates the growth of 2D perovskite phases and even thoroughly passivates the interfacial defect states. Moreover, attenuated acidity of the PEDOT:PSS, suppresses the chemical etching of indium tin oxide (ITO) substrates, reducing exciton quenching pathways. Finally, we realized efficient sky-blue emissive PeLEDs by blocking energy loss due to defect states through and designing an ideal energy landscape.
In chapter 3, a multifunctional passivating molecule containing the electron-withdrawing chlorine atom and the phosphonic acid as a functional and anchoring group was introduced as an alternative to the PEDOT:PSS hole injection layer (HIL). It was observed that this molecule formed a self-assembled monolayer (SAM) on the ITO substrate, significantly increasing the work function (WF) of the ITO electrode. Strongly chemisorbed SAM inhibited the chemical etching of the ITO electrode, suppressing exciton quenching pathways. Besides, the incorporated chlorine atom induced an orbital coupling with the interfacial uncoordinated Pb2+ detect state, passivating them and thereby changing the optical properties of the perovskite layer. Finally, due to these synergetic effects originating from a well-designed SAM molecule, we realized efficient pure-blue emissive PeLEDs.
In chapter 4, the effect of the surface polarity of the underlying HIL on the crystallization dynamics of 2D perovskite phases was thoroughly studied, and optimized the surface polarity to realize the optimal substrate for efficient PeLEDs. It was confirmed that the additive, L-dopa involving hydroxyl groups coordinate chemical bonding with the sulfonate group of PSS moieties, leading to a higher surface polarity for the PEDOT:PSS substrate. On that substrate, the formation of higher-n 2D perovskite phases was thermodynamically unfavorable due to the smaller formation energy, and lower-n-dominated phase distribution induced a hypsochromically shift in the luminescence spectrum. Finally, we controlled the dual additives with L-phenylalanine which provide a well-matched electronic band structure, boosting the performance of pure-blue emissive PeLEDs.
In chapter 5, a facile halide and phase modulating approach to design an ideal energy-transfer tunnel structure with flawless quasi-2D perovskites was introduced. This post-treatment entails the halide-exchange reaction with the assistance of haloalkane molecules and strong nucleophile molecules. The detached chlorides spontaneously exchanged with bromides in perovskites and further intrude the chlorine vacant sites, resulting in efficient PL and color stability. Furthermore, the spontaneous phase rearrangement occurred via merging between neighboring low-n 2D phases to higher-n 2D phases. It modulated the landscape of the energy-transfer funnel with the narrowed 2D phase distribution that can minimize the detrimental exciton losses. Finally, we realized efficient deep-blue emissive PeLEDs with all synergetic effects from the proposed halide and phase rearrange treatment.
In chapter 6, a facile halide post-treatment was also introduced to realize efficient bulk blue emissive perovskite films. The halide compositions of bulk perovskite films were finely controlled for the desired emission colors. This spontaneous halide exchange process induced the recrystallization of rough perovskite surface, providing a fully covered and smooth perovskite film. Finally, we realized highly luminescent blue emissive bulk PeLEDs with long operating lifetimes under a high-level current injection without halide segregation.ope
Maximally Chiral Emission via Chiral Quasibound States in the Continuum
No full textAlthough numerous natural materials exhibit chiral optical phenomena, they are typically very weak. Chiral nanophotonic structures can significantly enhance the chiroptical responses and provide unprecedented design flexibility. However, achieving extreme chirality that approaches the ultimate theoretical limit remains challenging. Here, chiral quasibound states in the continuum are realized in the visible range, and maximally chiral emission from a perovskite metasurface is demonstrated. A perovskite film is spin-coated on a patterned glass substrate. Grayscale lithography is employed to control the etching depths in the substrate and induce out-of-plane symmetry breaking. An extremely high level of chiral emission is experimentally achieved in the normal direction at room temperature. Chiral emission is maximally enhanced for one helicity via critical coupling, while strongly suppressed for the other helicity. The physical mechanism is explained using the reciprocity principle. Approaching the ultimate limit of chiral responses may lead to far-reaching consequences in various important applications as well as fundamental studies
Amorphous iron fluorosulfate as a high-capacity cathode utilizing combined intercalation and conversion reactions with unexpectedly high reversibility
No full textTo achieve the desirable dual characteristics of high-capacity performance and low-cost production for the batteries of tomorrow, leveraging of multi-redox reactions of Earth-abundant transition metals in electrodes is fundamentally important. Here we identify an amorphous iron fluorosulfate electrode, a-LiFeSO4F, that can exploit both the intercalation and conversion reactions with a stable reversibility. The a-LiFeSO4F electrode delivers a capacity of 360 mAh g(-1) with similar to 98.6% capacity retention after 200 cycles even at an elevated temperature (60 degrees C). In contrast to the conventional intercalation/conversion-type electrodes, the reversible cycle stability is attributed to the inherent amorphous structure of a-LiFeSO4F, whose structural integrity is not severely disturbed even after the conversion reaction, allowing its continuation as an intercalation host. We believe that this cycle stability of the intercalation/conversion reaction can be generally extended to various amorphous intercalation materials, offering new insights into the design of high-capacity electrodes through the exploitation of multi-mechanistic lithiation processes
Sensitivity of typhoon forecast to prescribed sea surface temperature data
Get PDFThis study investigates the impact of the sea surface temperature (SST) on the forecast of two typhoons, which consecutively hit South Korea in 2020. SST data were obtained from the Daily Optimum Interpolation Sea Surface Temperature (OISST) version 2 and HYbrid Coordinate Ocean Model/Navy Coupled Ocean Data Assimilation (HYCOM/NCODA; GLBy0.08/expt_93.0). When verified using in situ observational data, the OISST data did not accurately estimate the changes in SST during each typhoon???s landfall period compared to the HYCOM data since it has a relatively low temporal resolution. To investigate the impact of these two SST data on typhoon forecasts, we conducted sensitivity experiments using the Weather Research and Forecasting (WRF) model. The results showed that simulated typhoon intensities were significantly improved in the simulations with HYCOM data (HY runs), while typhoon track forecast performances were similar in both runs. In addition, the forecast performances of the maximum wind speed at 10 m during the typhoon landfall period were improved in the HY runs. Therefore, this study showed that the overall typhoon intensity and forecast performances during the landfall period could be improved when the higher temporal-resolution SST data were prescribed in the model boundary conditions for a better representation of typhoon-induced SST changes
Sacrificial Catalyst of Carbothermal-Shock-Synthesized 1T-MoS2 Layers for Ultralong-Lifespan Seawater Battery
No full textA Pt-nanoparticle-decorated 1T-MoS2 layer is designed as a sacrificial electrocatalyst by carbothermal shock (CTS) treatment to improve the energy efficiency and lifespan of seawater batteries. The phase transition of MoS2 crystals from 2H to metallic 1T???induced by the simple but potent CTS treatment???improves the oxygen-reduction-reaction (ORR) activity in seawater catholyte. In particular, the MoS2-based sacrificial catalyst effectively decreases the overpotential during charging via edge oxidation of MoS2, enhancing the cycling stability of the seawater battery. Furthermore, Pt nanoparticles are deposited onto CTS-MoS2 via an additional CTS treatment. The resulting specimen exhibits a significantly low charge/discharge potential gap of ??0.39 V, high power density of 6.56 mW cm???2, and remarkable cycling stability up to ???200 cycles (???800 h). Thus, the novel strategy reported herein for the preparation of Pt-decorated 1T-MoS2 by CTS treatment could facilitate the development of efficient bifunctional electrocatalysts for fabricating seawater batteries with long service life
Rheological and Mechanical Properties of Kenaf and Jute Fiber???Reinforced Cement Composites
No full textThis study investigated the rheological and mechanical properties of cement composites with kenaf and jute fibers for use in shotcrete. The length and volume fractions of the fiber were varied; the rheological properties were analyzed in terms of air content, compression and flexural tests were conducted, and the degree of fiber dispersion was assessed using fluorescence microscopy. The rougher surfaces of the jute fibers led to a higher yield stress and viscosity of the composite compared to the kenaf fibers. The use of 10-mm-long jute fibers at 2.0% volume fraction led to optimal rheological properties while 30-mm-long jute fibers at 1.0% resulted in the worst properties. The yield stress and plastic viscosity exhibited positive and negative correlations with the fiber volume fraction, respectively. This was likely because of the bridging and fluid actions of the bubbles at higher fiber content. For a given fiber content, only the yield stress increases with an increase in fiber length. Although all the mechanical properties deteriorated (compressive strength decreased from 27.5 to 6 MPa, and flexural strength deteriorated from 6.2 to 1.8 MPa), the mixtures failed in a ductile manner. Using 10-mm-long kenaf fibers at 2.0% induced optimal fiber dispersion, whereas the minimum dispersion-coefficient value was found for 5-mm-long kenaf fibers at 0.5%