Stability and activity controls of Cu nanoparticles for high-performance solid oxide fuel cells

Cu-based electrodes could advance solid oxide fuel cells (SOFC) technology due to good electric conductivity and relatively high electrochemical activity among transition metals. However, one of the main challenges for designing anode materials is thermal stability in SOFC operation condition. Herein, a promising anode material decorated with Cu nanoparticles (NPs) was synthesized via in-situ exsolution from La0.43Sr0.37Cu0.12Ti0.88O3-δ (LSCuT) perovskite. Compared to infiltration process, Cu NPs prepared by in-situ exsolution displayed homogeneous nano size distribution on the substrate and excellent thermal stability at 600 °C in H2 atmosphere, for ∼50 h. In addition, we employed electrochemical reduction (ER) at 2.3 V for a few seconds to demonstrate that NPs can be rapidly grown, and the substrate reduced. A single cell with LSCuT anode (10 μm)||ScSZ electrolyte (90 μm) ||LSM-ScSZ cathode (20 μm) exhibits maximum power density of 1.38 Wcm−2 at 900 °C under wet H2. The present study provides possibility of a broad application of thermally stable Cu-based electrodes

Shape-shifting nanoparticles on a perovskite oxide for highly stable and active heterogeneous catalysis

Controlling the geometric shape of nano-catalysts plays a key role in maximizing unique properties of the materials. Although shape control of nanoparticles is well known by various preparation methods, still there is no clear case for exsolution. Here we show that the shape of embedded Ni nanoparticles can be changed on exsolution process, by controlling reduction temperature and time. To elucidate and generalize the shape-shifting, we develop a model which describes the equilibrium shape of nanoparticles on support thermodynamically. Our results suggest that there is a thermodynamic driving force for the exsolved nanoparticle to be stabilized into faceted shape with low surface/interface energy, during the particle growth. Through catalytic activity testing, the improved durability of shape-shifted Ni catalysts is confirmed on dry-reforming condition over 390 h, resulting from enhanced interface stability and cocking resistance. This provides theoretical and experimental framework for the shape control of exsolved particle on oxide support, but also for the design of unique catalyst with high stability and reactivity

the era of COVID-19

Thesis(Master) -- KDI School: Master of Public Policy, 2021Purpose of the study: The purpose of the study is to explore the application of introducing Augmented Reality (AR) technology to interact with customers and to enhance decision making via technology-enabled experience particularly needed in the context of COVID-19. Fill the gap: The current research tries to contribute to the extant literature on customer behavior with AR technology by examining not only perceived utilitarian value and perceived hedonic value but also perceived social value and perceived risk on customer satisfaction as well as by investigating potential AR users’ customer behavior, which has not been studied much yet. Research Question: The study tries to answer the two questions: (1) How do customers’ perceived values and perceived risk of AR functions affect customer satisfaction respectively? (2) How does customer satisfaction affect purchase intention and customer loyalty respectively? Methodology: The research applies factor analysis and regression analysis to test the hypotheses and employs ANOVA and mediation effect analysis to explore additional findings. Major findings: The results of the main regression analyses show that customers react more strongly to benefits of AR technology that are helpful to their functional consumption than to other dimension of benefits. Implications: The findings of the study provides managerial and policy implications to develop and advertise the introduction of AR technology with the emphasis on the practical and utilitarian benefits of the technology. The result of this paper will highlight the importance of customer relationship management by providing advanced services to customers through AR technology.Ⅰ. Introduction Ⅱ. Literature Review Ⅲ. Hypotheses Development Ⅳ. Methodology Ⅴ. Data Analysis Ⅵ. ConclusionmasterpublishedSeungyeon HA

Adoption of the Mobile Campus in a Cyber University

The advantages of mobile technologies have not been lost on higher education institutions, and they have tried to provide educational services through the use of mobile learning management system (LMS). However, offering such services does not necessarily mean that the students will adopt the new technology. Thus, the purpose of this study was to examine what factors facilitate and hinder the students’ adoption of the mobile campus. The study was based on the diffusion of innovation model and compared the perceptions of mobile LMS users and nonusers. Eighty-five students in a cyber university responded to the survey, and the results revealed that even though nonusers perceived the advantages of using mobile LMS, they did not adopt the system because of its complexity and resistance. A discussion and the implications for further development of mobile LMS followed

Compressive Behavior Characteristics of High-Performance Slurry-Infiltrated Fiber-Reinforced Cementitious Composites (SIFRCCs) under Uniaxial Compressive Stress

The compressive stress of concrete is used as a design variable for reinforced concrete structures in design standards. However, as the performance-based design is being used with increasing varieties and strengths of concrete and reinforcement bars, mechanical properties other than the compressive stress of concrete are sometimes used as major design variables. In particular, the evaluation of the mechanical properties of concrete is crucial when using fiber-reinforced concrete. Studies of high volume fractions in established compressive behavior prediction equations are insufficient compared to studies of conventional fiber-reinforced concrete. Furthermore, existing prediction equations for the mechanical properties of high-performance fiber-reinforced cementitious composite and high-strength concrete have limitations in terms of the strength and characteristics of contained fibers (diameter, length, volume fraction) even though the stress-strain relationship is determined by these factors. Therefore, this study developed a high-performance slurry-infiltrated fiber-reinforced cementitious composite that could prevent the fiber ball phenomenon, a disadvantage of conventional fiber-reinforced concrete, and maximize the fiber volume fraction. Then, the behavior characteristics under compressive stress were analyzed for fiber volume fractions of 4%, 5%, and 6%

Characterization of the Gut Microbiota of Mackerel Icefish, <i>Champsocephalus gunnari</i>

The gut microbiome of Antarctic fish species has rarely been studied due to difficulties in obtaining samples. The mackerel icefish, Champsocephalus gunnari, primary feeds on krill and is one of the key species in the food web of the Southern Ocean. In this study, we characterized the gut microbiota of C. gunnari by sequencing the V3–V4 region of the bacterial 16S rRNA gene based on the Illumina MiSeq sequencing platform. We collected three types of samples: (1) whole intestine, (2) intestinal wall, and (3) intestinal content. The results showed no significant difference in the alpha diversity between different sample types. However, the microbial community composition of intestinal wall samples was distinct from other sample types. The relative abundance of Photobacterium was higher in intestinal content compared with the walls, which could be due to their chitinolytic activity. In contrast, potential pathogens such as Escherichia, Shigella, and Pseudomonas relatively more abundant in the intestinal wall compared with the intestinal contents. Unlike the gut microbiome of other marine fish species, Vibrio and Lactobacillus were nearly absent in the gut microbiome of C. gunnari. Functional gene profile of the gut microbiome predicted by PICRUSt2 showed higher relative abundance of genes related to biodegradation of nutrients in intestinal content. In contrast, the relative abundance of genes related to biosynthesis of important metabolites, such as menaquinols, was higher in intestinal wall. The difference in the microbial community structure of intestinal wall and intestinal content found in our study supports niche separation in the gut environment and emphasizes the importance of collecting intestinal wall samples in addition to intestinal content samples to understand the full picture of gut microbiome. This is the first time that the gut microbiome of mackerel icefish has been characterized using next-generation sequencing

Copper Sintering Pastes with Various Polar Solvents and Acidic Activators

Devices in the developing semiconductor market require high density, high integration, and detailed processing. Conventional wire bonding is inappropriate for fine-sized devices, and connected wires can be damaged by heat generation and external physical impact. Soldering is also used in advanced packaging technologies. However, disturbances and overhead joints can occur during bonding. Thus, sintering has been extensively utilized to overcome these drawbacks. Sintering pastes are pressurized and bonded, resulting in stable bonding during sintering. In this study, the composition of the Cu sintering material was examined using diverse additives and solvents. We manufactured sintering materials comprising Cu (1 μm), a solvent [methanol (MeOH), ethanol (EtOH), or ethylene glycol (EG)] and an acidic additive (benzoic acid, phthalic acid, or hexanoic acid). After the sintering process, the mechanical and electrical characteristics were compared to determine the optimal composition and bonding conditions. The optimum ratios between the acid and solvent were 4:6 (MeOH and EtOH) and 2:8 (EG) due to the high viscosity and effective long-term storage. All samples using EtOH as the solvent exhibited the highest sintering performances. The aromatic and carboxylic groups substantially improved the sintering performance and increased the electrical conductivity. Based on the O1s/Cu2p ratio (2.23%), the best sintering composition was EtOH/PA, which showed the highest electrical conductivity (ca. 104 S/m) and strength (34.0 MPa). The sintering process using various additives and solvents can be helpful to determine the sintering conditions while maintaining the electrical properties

Long-Term Compressive Strength Development of Steel Fiber Shotcrete from Cores Based on Accelerator Types at Tunnel Site

In this study, cement minerals, aluminates, and alkali-free accelerators incorporated with steel fiber were used to scrutinize the influence of accelerating agents on the long-term performance of tunneling shotcrete. Performance tests were identified based on the core compressive strength of mix shotcrete specimens with different types of accelerating agents throughout timeframes of 1, 3, 6, and 12 months. Here, 37 kg of steel fiber was incorporated into the cement mineral and aluminate mixes, and 40 kg of steel fiber was incorporated in an alkali-free mix for the shotcrete mix design. The KSF 2784 and ASTM 214 standards were followed for specimen fabrication and core cutting. For all specimens, shotcrete test panels of 250 × 600 × 500 mm were manufactured for core compressive strength tests conducted using 100, 75 and 55 mm diameter cylindrical molds and a length-to-diameter ratio of 2. The 1-month compressive strength of all test variables satisfied the Korea Expressway Co. standard of 21 MPa. The core compressive strength of the shotcrete specimens showed a tendency to increase with age, but a strength reduction occurred in 6 months and increased again at 12 months. Moreover, the impact of the diameter changes in the shotcrete core specimens was analyzed based on the mixing. For 12 months, a large increase in the core compressive strength occurred, particularly in the alkali-free specimens. The comparison also focused on the relative strength compared with a cast concrete mold and shotcrete core specimens. It is necessary to use alkali-free accelerators considering the long-term performance of tunnels and worker safety

Long-Term Compressive Strength Development of Steel Fiber Shotcrete from Cores Based on Accelerator Types at Tunnel Site

In this study, cement minerals, aluminates, and alkali-free accelerators incorporated with steel fiber were used to scrutinize the influence of accelerating agents on the long-term performance of tunneling shotcrete. Performance tests were identified based on the core compressive strength of mix shotcrete specimens with different types of accelerating agents throughout timeframes of 1, 3, 6, and 12 months. Here, 37 kg of steel fiber was incorporated into the cement mineral and aluminate mixes, and 40 kg of steel fiber was incorporated in an alkali-free mix for the shotcrete mix design. The KSF 2784 and ASTM 214 standards were followed for specimen fabrication and core cutting. For all specimens, shotcrete test panels of 250 × 600 × 500 mm were manufactured for core compressive strength tests conducted using 100, 75 and 55 mm diameter cylindrical molds and a length-to-diameter ratio of 2. The 1-month compressive strength of all test variables satisfied the Korea Expressway Co. standard of 21 MPa. The core compressive strength of the shotcrete specimens showed a tendency to increase with age, but a strength reduction occurred in 6 months and increased again at 12 months. Moreover, the impact of the diameter changes in the shotcrete core specimens was analyzed based on the mixing. For 12 months, a large increase in the core compressive strength occurred, particularly in the alkali-free specimens. The comparison also focused on the relative strength compared with a cast concrete mold and shotcrete core specimens. It is necessary to use alkali-free accelerators considering the long-term performance of tunnels and worker safety