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Ocean-atmosphere interactions: different chemical properties of organic matters and diversity of microorganism
No full textDepartment of Urban and Environmental Engineering (Environmental Science and Engineering [Water-Energy Nexus])The ocean is covered approximately 70 percent onto Earth???s surface which includes Dissolved Organic Matters (DOM) holds about 660 billion metric tons of carbon (Hansell and Orellana, 2021) and bacteria about that a liter of surface ocean is included over ten billion bacteria (Balloux and van Dorp, 2017). The ocean and atmosphere can interact directly and indirectly, this interaction can affect environmental pollution and climate change. In this study, DOM and microorganisms were identified on a global scale to confirm the interaction between the oceans and the atmosphere. In this study, study sites of the samples in ocean and atmosphere were collected in four cruises. In total, the samples in Sub-Arctic Ocean, the samples were taken during the Korean R/V Araon of cruise 1 during 4-17 July and cruise 3-4 from 19 September to 04 October 2022 (total 30 days), the distance of the four cruises was 12,931 km. It is aimed to investigate the interaction between ocean and atmosphere based on their chemical properties of DOM and abundance and diversity of bacteria.
In the global ocean-atmosphere interaction, it was studied to identify and compare the characteristics of these sources of organic matters in detail, especially with analyzed results of orbitrap. In Cruise 1, lignin, a complex polymer, is predominantly aerosolized to the atmosphere in the form of Microbially produced Fluorescent Dissolved Organic Matter (FDOM) and Lipids, primarily derived from the total concentration of chlorophyll-a and phytoplankton, are the dominant component in the ocean In Cruise 2-4 The identification of DOM (Peak B???M???C) with higher biological impact reveals its origin from the ocean
The abundance and diversity of bacteria were investigated along a transect same as sampling sites of DOM. The highest bacterial abundance was observed during Cruise 4, which suggests a potential microbial bloom (i.e., plankton bloom) leading to an increase in the number of individuals Furthermore, Bacteroidota, Proteobacteria and Cyanobacteria accounted for over 80-90 percent of the highest relative abundance in all cruises. Consequently, second study which is the interaction between ocean and atmosphere included bacteria can suggest helping emerging pollutants.ope
Molecular Mechanisms of Nonalcoholic Steatohepatitis
Get PDFDepartment of Biological SciencesNonalcoholic fatty liver disease (NAFLD) is a chronic liver disease that has the highest prevalence in the present worldwide. Nonalcoholic steatohepatitis (NASH) is an ongoing progressed phase of NAFLD with not only accumulation of fatty acids in and but also hepatic inflammation and fibrosis and a gateway to cirrhosis and hepatocellular carcinoma (HCC) hard to cure without liver transplantation. Many studies for NASH mechanisms continue to be researched because of its specificity. Accumulation of lipids in the liver as an initiation of NAFLD and NASH is a result of the excessive influx status when lipid influx mechanisms exceed lipid outflux mechanisms by defects in regulators of the mechanisms and abnormal metabolic state. Disease progression to NASH through genesis of an inflammation and fibrosis occurs with intracellular and intercellular interactions of liver cells. In this review, we focused on pathogenic mechanisms and what factors are related to the mechanisms.clos
Zinc acts as an evolutionarily conserved sleep driver
No full textDepartment of Biological Sciencesclos
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Get PDFDepartment of Mathematical SciencesWe study with equations that deal with incompressible fluids, called Euler equations. Specifically, we study in R2 when the initial vortex patch with smooth boundary is close enough to disk in the sense that the area and length difference between the initial vortex patch and the disk is very small than 1. The initial vortex patch has tiny difference of length and tiny difference of area with disk. More precisely, there is tiny arbitrary difference in the initial data, but the difference of length increases arbitrarily within a finite time. Regardless of how small the difference is, in the 2-dimensional plane, we form a vortex patch whose smooth boundary such that the perimeter grows up within finite time.clos
Fabrication of Lead Iron Niobate Thin Films Focusing on Sol-Gel Method
Get PDFDepartment of Materials Science and EngineeringThe aim of this study was to synthesize a single-phase PFN thin film using Monoethanolamine(MEA) as a chelating agent through the sol-gel method. The PFN thin film was deposited onto a substrate using a spin-coating technique, where the solution was coated and rotated. In this process, the presence of MEA prevented the formation of secondary phases by promoting the reaction between the Nb precursor and the Fe precursor before reacting with the Pb precursor. The presence of MEA is speculated to be the reason why the Nb precursor reacted with the Fe precursor before the Pb precursor, thereby preventing the formation of secondary phases and lowering the crystallization temperature to around 150??C instead of 250-325??C. Furthermore, X-ray diffraction patterns demonstrate that the addition of MEA allowed the PFN thin film to grow as a single phase at low temperatures, while in the absence of MEA, a single phase could only be achieved at temperatures above 800??C. Scanning electron microscope images reveal that the presence of MEA eliminates porosity and cracks, resulting in a uniform film. Analysis of the ferroelectric properties, indicated by the P-E hysteresis loop, shows that the PFN thin film fabricated with the chelating agent at 500??C exhibits minimal leakage current and exhibits strong ferroelectric characteristics. However, for the PFN thin film fabricated without the chelating agent, the presence of secondary phases leads to significant leakage current, resulting in a large coercive field and reduced saturation polarization.
In this study, an abnormal phenomenon was observed during the process of measuring the P-E polarization loop and permittivity as a function of temperature. as the temperature increased, the PFN thin film fabricated with the chelating agent exhibited a rapid increase in internal bias field around 150??C, but did not show a distinct Curie temperature. Unlike the reported PFN films with a Curie temperature around 110??C, the fabricated PFN films in this study did not exhibit the abrupt increase and decrease in permittivity, indicating an anomalous behavior. The exact cause of this phenomenon has not been determined yet, but it is believed to be a comprehensive effect of defect dipoles caused by the acceptor effect based on the relative amounts of Fe2+ and Fe3+ ions, and an increase in the concentration of defect charge carriers due to the temperature-induced increase. The comparison of the relative quantities of Fe2+ and Fe3+ based on the presence or absence of the chelating agent was conducted using XPS. However, further research is needed to elucidate the underlying causes of this phenomenon. To precisely identify these causes, additional analysis is required, but continuous improvement and research are necessary due to limitations in the resolution of measurement equipment and sample constraints.
PFN is a multiferroic material that exhibits both ferroelectricity and antiferromagnetism, which has recently attracted significant attention. However, due to its relatively high Curie temperature, it displays ferroelectric properties at room temperature. Nonetheless, observing magnetic properties at room temperature is challenging due to its low Neel temperature. Additionally, PFN primarily demonstrates antiferromagnetic characteristics below the Neel temperature, attributed to the formation of Fe-O-Fe and Fe-O-Nb-O-Fe bonds at angles of 180??. In PFN, Pb2+ occupies the A-site while Nb5+ occupies the B-site, favoring electrical alignment. On the other hand, Fe3+ at the octahedral B-site provides the necessary magnetic moment for magnetic alignment, contributing to both ferroelectric and magnetic alignments in the material. Based on these principles, the coupling between electrical and magnetic alignments was investigated in order to study the ferroelectric and magnetic properties within complex perovskite structures. However, unfortunately, in this study, magnetic properties were not observed in the fabricated samples, indicating the need for further research. Nevertheless, in an attempt to induce coupling between electrical and magnetic alignments, the concept of A-site engineering was employed. A two-step method was implemented, involving the separate preparation of A-site and B-site solutions, followed by their mixture, to manufacture A-site engineered PFN thin films with a close-to-single-phase structure. Additionally, the introduction of a PbO layer on the substrate was employed to prevent the orientation of the upper film and the volatilization of Pb during sintering, as well as to mitigate the crystalline phase changes in the film caused by the diffusion of Pb ions from the electrode. This approach demonstrated the potential for the fabrication of A-site engineered PFN thin films at lower sintering temperatures. In this study, the observation of abnormal ferroelectric properties for the first time was achieved. By applying the A-site engineered PFN concept, previously reported in PFN bulk systems, to thin films, the potential for various applications, particularly in the field of memory, was demonstrated. Further research on the abnormal phenomena will continue in the future. Moreover, there is room for process improvement in the fabrication of single-phase multiferroic thin films that can be sintered at low temperatures, opening up endless possibilities for future advancements.clos
Preparation of liquid metal marbles and their application of Lorentz force-driven actuator
No full textDepartment of Materials Science and Engineeringclos
Extrinsically Stretchable Photovoltaic Modules for Energy Harvesting
Get PDFDepartment of Materials Science and EngineeringMechanically deformable photovoltaic devices are gaining interest in various applications, including building decorations, wearables, and biomedical devices. These energy harvesting devices need to fulfill certain criteria, such as multiaxial stretchability, excellent environmental and mechanical stabilities, and versatile fabrication methods. This approach presents a method to transform rigid photovoltaic devices into highly deformable yet robust ones with minimal degradation in electrical characteristics, including current density, open-circuit voltage, and fill factor. A stretchable solar module is demonstrated, featuring a maximum strain of 67% and an efficiency of over 16%, achieved using an island-trench structure. The geometry of the structure is optimized to provide excellent strain isolation and high coverage, utilizing finite element method-based simulations. The dispensing printing method is introduced to connect individual solar cells with minimal losses, using a flexible electrically conductive adhesive (ECA) material as ink. Furthermore, the device exhibits excellent mechanical properties and remains undegraded even after 1000 cycles of stretching. To further enhance the module's robustness, a simple and efficient method to resist compression is suggested and studied.clos
Advancing Large-area Perovskite Module Fabrication: A Bar-coating Approach for Efficiency and Stability
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METABOLIC ENGINEERING OF Lactobacillus reuteri FOR IMPROVED AND ROBUST PRODUCTION OF 1,3-PROPANEDIOL FROM GLYCEROL
No full textSchool of Energy and Chemical Engineering (Chemical Engineering)The three-carbon diol 1,3-propanediol (CH2CH2(OH)21,3-PDO) has diverse applications in textile, cosmetics, food and medical fields. Biological 1,3-PDO production was studied using various recombinant strains such as Escherichia coli, Klebsiella pneumoniae and Clostridium beijerinckii as biocatalyst. However, 1,3-PDO production by these strains is not fully satisfactory, when 1,3-PDO is to be used as cosmetic or food ingredientas they are not GRAS (Generally Regarded As Safe). This study aims to develop more efficient microbial cell factory for its use in cosmetics and food industry from GRAS strain namely Lactobacillus reuteri.
Genetic engineering of L. reuteri for improved 1,3-PDO production requires understanding of its glucose-glycerol metabolism. L. reuteri ferments glucose to produce lactate, acetate, ethanol, and uses glycerol to produce 1,3-PDO by utilizing nicotinamide adenine dinucleotide hydride (NADH) generated via glucose metabolism. Two major limitations during the process are inefficient NADH diversion towards 1,3-PDO and limited expression of 1,3-propanediol dehydrogenase (PDOR) enzyme. To improve 1,3-PDO production, alcohol dehydrogenases (ADH) were disrupted, and PDOR was overexpressed. The resulting strain could produce 687 mM 1,3-PDO with a yield of 1.2 ?? 0.08 mol 1,3-PDO/mol glucose. However, the production rate decreased in the late period of bioreactor was hampered due to high lactate accumulation and strain instability. To identify the lactate inhibition on glycerol pathway enzymes in vitro activities of diol dehydratase (DDHt) and 1,3-PDOR (PduQ) enzymes in the presence of varying concentrations of lactate were measured. The results showed no significant lactate inhibition on 1,3-PDOR activity, but a significant inhibition was observed with DDHt activity. The inhibition kinetics and inhibition type of diol dehydratase (DDHt) on lactate using crude cell lysates were characterized, showing severe dose-dependent inhibition up to 93% with 400 mM sodium lactate. To address this limitation, strain was evolved on high lactate concentration that demonstrated improved cell growth, 1,3-PDO production, and enhanced lactate tolerance. These findings indicate that DDHt inhibition by lactate is a major limitation in 1,3-PDO production from L. reuteri.
To address the second issue of strain instability upon deletion of ethanol (???adh2???adh6) producing pathways, two prophage islands (??3 and ??4) present in the L. reuteri???s chromosome were disrupted partially/completely. This study reveals that the stability of L. reuteri DSM 20016 and its 1,3-PDO production are greatly enhanced in terms of strains cell growth characteristics and robustness. The resulting prophage-free and ADHs-deletion mutant could produce >825 mM 1,3-PDO in 48 h without cell lysis at the theoretical maximum yield on glucose at ~2 mol/mol. In addition, this study reports that the transformation efficiency of L. reuteri is greatly enhanced by >300-fold after the deletion of prophage ??3, due to the removal of a restriction-modification (RM) system which resides in the phage genome. With improved stability and higher transformation efficiency, L. reuteri DSM 20016 can be a reliable and amenable host for industrial applications.
To further explore the limitation of substrate/product and cofactor transport across microcompartment, strains devoid of microcompartment formation (???pduABJ) and by overexpression of individual microcompartment proteins (pduABJKU) were developed. Interestingly, overexpression of PduA and PduU improved the cell growth, glycerol uptake and concomitant 1,3-PDO production compared to the parent strain. These results suggest that increase in microcompartment size and/or number helped to improve 1,3-PDO production by increasing the enzyme cargo of PduCDEEG and PduQ enzymes.
Overall, we fully understand the central carbon metabolism and its link with glycerol metabolism and successfully increased the 1,3-PDO yield on glucose to the theoretical maximum ~2 mol/mol and explored several limitations in 1,3-PDO. The resulting phage-free and ADHs-deletion mutant could produce >825 mM 1,3-PDO, which is the highest reported by metabolic engineering strategy with Lactobacillus species. Even though we overcome several limitations, 1,3-PDO production still fall short compare to L. diolivorans and other commercially available strain. Coenzyme B12 limitation and efficient NADH recycling and most importantly diversion of pyruvate towards acetate is necessary to reach its full potential.clos