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Slippery When Wet: Fish and Seaweed Inspire Ships to Reduce Fluid Friction
Faster ships could be on the horizon after KAIST scientists develop a slippery surface inspired by fish and seaweed to reduce the hull's drag through the water. Long-distance cargo ships lose a significant amount of energy due to fluid friction. Looking to the drag reduction mechanisms employed by aquatic life can provide inspiration on how to improve efficiency. Fish and seaweed secrete a layer of mucus to create a slippery surface, reducing their friction as they travel through water. A potential way to mimic this is by creating lubricant-infused surfaces covered with cavities. As the cavities are continuously filled with the lubricant, a layer is formed over the surface. Though this method has previously been shown to work, reducing drag by up to 18%, the underlying physics is not fully understood. KAIST researchers in collaboration with a team of researchers from POSTECH conducted simulations of this process to help explain the effects, and their findings were published in the journal Physics of Fluids on September 15. The group looked at the average speed of a cargo ship with realistic material properties and simulated how it behaves under various lubrication setups. Specifically, they monitored the effects of the open area of the lubricant-filled cavities, as well as the thickness of the cavity lids. They found that for larger open areas, the lubricant spreads more than it does with smaller open areas, leading to a slipperier surface. On the other hand, the lid thickness does not have much of an effect on the slip, though a thicker lid does create a thicker lubricant buildup layer. Professor Emeritus Hyung Jin Sung from the KAIST Department of Mechanical Engineering who led this study said, “Our investigation of the hydrodynamics of a lubricant layer and how it results in drag reduction with a slippery surface in a basic configuration has provided significant insight into the benefits of a lubricant-infused surface.” Now that they have worked on optimizing the lubricant secretion design, the authors hope it can be implemented in real-life marine vehicles. “If the present design parameters are adopted, the drag reduction rate will increase significantly,” Professor Sung added. This work was supported by the National Research Foundation (NRF) of Korea. Source: Materials provided by American Institute of Physics. Publication: Kim, Seung Joong, et al. (2020). A lubricant-infused slip surface for drag reduction. Physics of Fluids. Available online at https://doi.org/10.1063/5.0018460 Profile: Hyung Jin Sung Professor Emeritus firstname.lastname@example.org http://flow.kaist.ac.kr/index.php Flow Control Lab. (FCL) Department of Mechanical Engineering http://kaist.ac.kr Korea Advanced Institute of Science and Technology (KAIST) Daejeon, Republic of Korea (END)
Novel Via-Hole-Less Multilevel Metal Interconnection Methods
Forming reliable multi-level metal interconnections is a key technology for integrating devices into organic integrated circuits (ICs). The conventional approach, called “via-hole,” locally removes the insulator and utilizes metal interconnects through the holes. Due to the high sensitivity of organic materials to chemical solvents, heat, and photo-radiation used in conventional “via-hole” methods, alternative printing methods or laser drilling methods have been developed. However, finding a reliable and practical metal interconnection for organic ICs is still challenging. The research team of KAIST Professor Sung Gap Im and Postech Professor Kim Jae-Joon reported a new interconnection method that does not require via-hole formation, “via-hole-less metal interconnection,” in Nature Communications on June 3. Metal electrodes in different layers can be isolated from each other by patterned dielectric layers, where they then can be interconnected to others in the open area where the dielectric layer is not present. See the images below. Vapor phase deposition and in-situ patterning of dielectric layer using iCVD (initiated chemical vapor deposition), used in the “via-hole-less” method, ensure a damage-free process for organic semiconductor materials and result in outstanding performance of the organic devices as multilevel metal interconnects are reliably formed. The team successfully demonstrated three-dimensional (3D) stacking of five organic transistors and integrated circuits using the proposed via-hole-less interconnect method. See the image below. Vapor phase deposition and in-situ patterning of dielectric layer using iCVD (initiated chemical vapor deposition), used in the “via-hole-less” method, ensure a damage-free process for organic semiconductor materials and result in outstanding performance of the organic devices as multilevel metal interconnects are reliably formed. The team successfully demonstrated three-dimensional (3D) stacking of five organic transistors and integrated circuits using the proposed via-hole-less interconnect method. See the image below. Professor Kim explained, “Our proposed via-hole-less interconnect method using a selectively patterned dielectric overcomes the limitations of the previous time-consuming, one-by-one via-hole formation process and provides reliable methods for creating metal interconnects in organic ICs. We expect the via-hole-less scheme to bring advances to organic IC technology.”
Hierarchical Porous Titanium Nitride Synthesized by Multiscale Phase Separation for LSBs
(from left: Professor Jinwoo Lee and PhD candidate Won-Gwang Lim) A KAIST research team developed ultra-stable, high-rate lithium-sulfur batteries (LSBs) by using hierarchical porous titanium nitride as a sulfur host, and achieved superior cycle stability and high rate performance for LSBs. The control of large amounts of energy is required for use in an electric vehicle or smart grid system. In this sense, the development of next-generation secondary batteries is in high demand. Theoretically, LSBs have an energy density seven times higher than commercial lithium ion batteries (LIBs). Also, their production cost can be reduced dramatically since sulfur can be obtained at a low price. Despite these positive aspects, there have been several issues impeding the commercialization of LSBs, such as the low electric conductivity of sulfur, the dissolution of active materials during operation, and sluggish conversion reactions. These issues decrease the cycle stability and rate capability of batteries. To tackle those issues, Professor Jinwoo Lee from the Department of Chemical and Biomolecular Engineering and his team synthesized a well-developed hierarchical macro/mesoporous titanium nitride as a host material for sulfur. The titanium nitride has a high chemical affinity for sulfur and high electrical conductivity. As a result, it prevents the dissolution of active materials and facilitates the charge transfer. Moreover, the synergistic effect of macropore and mesopore structures allows the stable accommodation of large amounts of sulfur and facilitates the electrolyte penetration. Previously reported polar inorganic materials have a high affinity for sulfur, but it was challenging to control the porous architecture suitable to the sulfur host. This work breaks such limitations by developing a synthetic route to easily control the porous architecture of inorganic materials, which led to obtaining superior cycle stability and high rate capabilities. Professor Lee said, “Some problems still remain in commercializing LSBs as next-generation batteries. Hence, there should be a continued research on this matter to solve the issues. Through this research, we secured a key technology for ultrastable, high-rate LSBs.” This research was led by PhD candidate Won-Gwang Lim and collaborated on by Jeong Woo Han from POSTECH. It was chosen as the cover article of Advanced Materials on January 15, 2019. Figure 1. Schematic illustration for the synthetic route of co-continuous h-TiN Figure 2. The hierarchical multiscale porous structure is still retained without any collapse after the conversion to h-TiN. The good retention of the porous structure is attributed to the thick pore wall of the h-TiO₂derived from the block copolymer self-assembly Figure 3. The cover page of Advanced Materials
Rh Ensemble Catalyst for Effective Automobile Exhaust Treatment
(from left: Professor Hyunjoo Lee and PhD candidate Hojin Jeong) A KAIST research team has developed a fully dispersed Rh ensemble catalyst (ENS) that shows better performance than commercial diesel oxidation catalyst (DOC). This newly developed ENSs could improve low-temperature automobile exhaust treatment. Precious metals have been used for various heterogeneous reactions, but it is crucial to maximize efficiency of catalysts due to their high cost. Single-atom catalysts (SACs) have received much attention because it is possible for all of the metal atoms to be used for reactions, yet they do not show catalytic activity for reactions that require ensemble sites. Meanwhile, hydrocarbons, such as propylene (C3H6) and propane (C3H8) are typical automobile exhaust gas pollutants and must be converted to carbon dioxide (CO2) and water (H2O) before they are released as exhaust. Since the hydrocarbon oxidation reaction proceeds only during carbon-carbon (C-C) or carbon-hydrogen (C-H) bond cleavage, it is essential to secure the metal ensemble site for the catalytic reaction. Therefore, precious metal catalysts with high dispersion and ensemble sites are greatly needed. To solve this issue, Professor Hyunjoo Lee from the Department of Chemical and Biomolecular Engineering and Professor Jeong Woo Han from POSTECH developed an Rh ensemble catalyst with 100% dispersion, and applied it to automobile after-treatment. Having a 100% dispersion means that every metal atom is used for the reaction since it is exposed on the surface. SACs also have 100% dispersion, but the difference is that ENSs have the unique advantage of having an ensemble site with two or more atoms. As a result of the experiment, the ENSs showed excellent catalytic performance in CO, NO, propylene, and propane oxidation at low temperatures. This complements the disadvantage of nanoparticle catalyst (NPs) that perform catalysis poorly at low temperatures due to low metal dispersion, or SACs without hydrocarbon oxidation. In particular, the ENSs have superior low-temperature activity even better than commercial DOC, hence they are expected to be applied to automobile exhaust treatment. Professor Lee said, “I believe that the ENSs have given academic contribution for proposing a new concept of metal catalysts, differentiating from conventional SACs and NPs. At the same time, they are of great value in the industry of exhaust treatment catalysts.” This research, led by PhD candidate Hojin Jeong, was published in the Journal of the American Chemical Society on July 5. Figure 1. Concept of Rh ensemble catalyst for automobile exhaust treatment Figure 2. Structure and performance comparison of single-atom catalyst and ensemble catalyst Figure 3. Energy-dispersive X-ray spectroscopy (EDS) mapping images for SAC, ENS, and NP, respectively (green, Eh; red, Ce)
JETS Conference 2017
KAIST and four science and technology research universities in Korea co-hosted a technology start-up fair, the 2017 JETS (Job, Exhibition, Tech Forum, and Startup) Conference January 19 ~20 in the Ryu Geun-chul Sports Complex at KAIST. Korea’s major science and technology research universities, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Gwangju Institute of Science and Technology (GIST), Pohang University of Science and Technology (Postech), and Ulsan National Institute of Science and Technology (UNIST), held the event in a collaborative effort to educate, inspire, and connect young entrepreneurs, especially those who will launch technology start-ups. The conference brought entrepreneurs and innovators together who seek ways of working with and supporting start-ups and for their sustainable growth. It also drew aspiring young students and researchers from universities and the government-funded research institutions who are in the process of commercializing their technology. Students from each university’s industry-academia cooperation program who incubated their technology and ideas were key contributors. At the Tech Forum, entrepreneurship and technology consultation specialists including Joe Jasin, managing director at DNA Investment Partners in the US, the founder of Cyworld Dong-Hyung Lee, and Professor Hawoong Jeong, a complex bio-network specialist from the Department of Physics of KAIST lectured on the ecosystem of start-ups and its trends and development. The Dean of University-Industry Cooperation at KAIST Joongmyeon Bae said, "We organized this event in collaboration with four major research universities to further encourage technology start-ups from young students and help their ideas and technology bear fruit. We will continue to strive to create an ecosystem of start-ups which works efficiently.” (Above photo: Founder of the Cyworld, Dong-Hyung Lee gives a lecture at the Tech Forum. Below photo: Students visit exhibition booth of each participating institution.)
KAIST and Four Science and Technology Universities Host a Start-up Competition
KAIST and four other science and technology universities, such as Gwangju Institute of Science and Technology (GIST), Ulsan National Institute of Science and Technology (UNIST), Daegu Gyeongbuk Institute of Science and Technology (DGIST), and Pohang University of Science and Technology (POSTECH), hosted a startup competition on November 27, 2015 at the Dongdaemun Design Plaza in Seoul. Approximately 150 participants including students from the five universities, "angel" investors, and entrepreneurs attended the competition. The competition was held to promote startups that are based on research achievements in science and technology and to foster entrepreneurs with great potential. Two hundred and sixty applicants from 81 teams competed this year. Only ten teams made it to the finals. KAIST students presented two business plans: an experience-centered education platform and mobile taxi-pooling service. Students from other universities presented a brain-stimulating simulation software (GIST), handy smart health trainer (GIST), real-time reporting system for luggage (DGIST), a flower delivery system (UNIST), surveillance and alarm system for stock-related events via machinery studies (UNIST), augmented emotion toys using augmented reality (POSTECH), and a nasal spray for fine dust prevention (POSTECH). KAIST also displayed an exhibition of “wearable haptic device for multimedia contents” and “next generation recommendation service platform based on one-on-one matching system with high expandability and improved user experience system.” The winning team received an award from the Minister of Science, ICT and Future Planning of Korea, as well as an opportunity to participate in overseas startup programs over the course of ten days. Joongmyeon Bae, Director of the KAIST Industry and University Cooperation, who organized the contest, said, “The alumni of Stanford University (USA) has annually created over 5.4 million jobs through startup activities. Likewise, we hope that our event will contribute to job creation by fostering innovative entrepreneurs.”
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