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Iwasawa Theory of Quadratic Twists of X0（49）

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Acta Mathematica Sinica,English Series 2018年第1期34卷 19-28页

作者： Junhwa choi John COATES Department of Mathematics POSTECH Emmanuel College Cambridge University

The field K ---- Q（x/-AT） is the only imaginary quadratic field with class number 1, in which the prime 2 splits, and we fix one of the primes p of K lying above 2. The modular elliptic curve X0 （49） has complex multiplication by the maximal order O of K, and we let E be the twist of Xo （49） by the quadratic extension K（v/M）/K, where M is any square free element of O with M -- i mod 4 and （M, 7） = 1. In the present note, we use surprisingly simple algebraic arguments to prove a sharp estimate for the rank of the MordeII-Weil group modulo torsion of E over the field F∞=k（Ep∞ ）, where Epic denotes the group of p∞-division points on E. Moreover, writing B for the twist of X0（49） by K（C/ET）/K, our Iwasawa-theoretic arguments also show that the weak form of the conjecture of Birch and Swinnerton-Dyer implies the non-vanishing at s =1 of the complex l-series of B over every finite layer of the unique Z2-extension of K unramified outside p. We hope to give a proof of this last non-vanishing assertion in a subsequent paper.

关键词： Birch-Swinnerton-Dyer conjecture elliptic curves Iwasawa theory

Grade-4 commercially pure titanium with ultrahigh strength achieved by twinning-induced grain refinement through cryogenic deformation

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Journal of Materials Science & Technology 2021年第7期66卷 193-201页

作者： Seong-Woo choi Jae Sukjeong Jong Woo Won Jae Keun Hong Yoon Suk choi Titanium Department.Korea Institute of Materials Science Changwon51508Republic of Korea School of Materials Science and Engineering Pusan National UniversityPusan.46241Republic of Korea Materials and Manufacturing Development Team Doosan Heavy Industries and ConstructionChangwon51711Republic of Korea

The yield strength of commercially pure(CP) Ti of ASTM grade 4, the strongest among all the CP-Ti grades, is too low for structural applications that require high-strength materials. Here, we demonstrate the strengthening of grade-4 CP Ti by cryogenic-temperature rolling(CTR), which enables deformation twinning in grade-4 CP Ti to achieve twinning-induced grain refinement. CTR activated {11.22} twinning and {10.12} twinning, which are the most common twinning systems in pure Ti, whereas room-temperature rolling(RTR) did not activate any twinning system. CTR with imposing an area reduction of just 30% significantly increased the yield strength of the CP Ti to 946 MPa, which is not achievable through typical processes performed at or above room temperature and is comparable to that of commercial Ti-6 Al-4 V. The significant increase in strength was due to microstructural strengthening caused by twinning-induced grain refinement, combined with dislocation accumulation. In contrast to RTR, CTR greatly increased the stress concentration at grain boundaries(GBs), which caused the unusual activation of twinning in the grade-4 CP Ti by facilitating twin nucleation at GBs. The stress concentration increased because CTR activated the slip to a lesser extent compared to RTR, thereby reducing the strain compatibility between neighboring grains. These results will contribute to development of ultrahigh-strength CP Ti and may thereby extend its use to structural applications that require high-strength materials.

关键词： Titanium Twinning Cryogenic deformation Grain refinement Tensile properties

The geometry of the moduli space of one-dimensional sheaves

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Science China Mathematics 2015年第3期58卷 487-500页

作者： choi Jinwon CHUNG Kiryong School of Mathematics Korea Institute for Advanced Study

let Md be the moduli space of stable sheaves on P2with Hilbert polynomial dm+*** this paper,we determine the effective and the nef cone of the space Md by natural geometric *** idea is to use the wall-crossing on the space of Bridgeland stability conditions and to compute the intersection numbers of divisors with curves by using the Grothendieck-Riemann-Roch *** also present the stable base locus decomposition of the space *** a byproduct,we obtain the Betti numbers of the moduli spaces,which confirm the prediction in physics.

关键词： effective cone nef cone birational morphism determinant line bundle Bridgeland wall-crossing

Study of Partial Coefficients for Design of Semicircular Breakwaters

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China Ocean Engineering 2010年第1期24卷 29-40页

作者：郄禄文 Byung Ho choi College of Civil Engineering Hebei University Department of Civil and Environmental Engineering Sungkyunkwan University300 Chunchun-dongJangan-GuSuwon

In the present study, the reliability design of semicircular breakwater is based on the verification of the rules defined by standard specifications, where partial coefficients are introduced to ensure safety. The reliability of the semicircular breakwaters has been analyzed by using the Hasofer-lind method to determine the reliability index of structure that has correlated loads, utilizing the long-term observed wave data at a given place. The relation curve between reliability index and safety factor in the traditional design method, as well as the relationships between reliability index and partial coefficients, have been obtained. This paper proposes values of partial coefficients for the design expression of semicircular breakwaters in the cases of anti-sliding and anti-overturning.

关键词： partial coefftcient reliability index correlated variables semicircular breakwater

WS2 nanoflakes from nanotubes for electrocatalysis

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Nano Research 2013年第12期6卷 921-928页

作者： cha.ina.l. choi Ju Feng Yanguang li Justin Wu Alia Zak Reshef Tenne Hongjie Dai Department of Chemistry Stanford University California 94305 USA Department of Science Holon Academic Institute of Technology Holon 58102 Israel Department of Materials and Interfaces Weizmann Institute Rehovot 76100 Israel

Next-generation catalysts for water splitting are crucial towards a renewable hydrogen economy. MoS2 and WS2 represent earth-abundant, noble metal cathode alternatives with high catalytic activity at edge sites. One challenge in their development is to nanostructure these materials in order to achieve increased performance through the creation of additional edge sites. In this work, we demonstrate a simple route to form nanostructured-WS2 using sonochemical exfoliation to break interlayer and intralayer bonds in WS2 nanotubes. The resulting few-layer nanoflakes are -100 nm wide with a high density of edge sites. WS2 nanoflakes are utilized as cathodes for the hydrogen evolution reaction （HER） and exhibit superior performance to WS2 nanotubes and bulk particles, with a lower onset potential, shallower Tafel slope and increased current density. Future work may employ ultra-small nanoflakes, dopant atoms, or graphene hybrids to further improve electrocatalytic activity.

关键词： tungsten disulfide nanotubes nanostructuring hydrogen evolution

Synergistic effect between cryptotanshinone and antibiotics in oral pathogenic bacteria

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Advances in Bioscience and Biotechnology 2013年第2期4卷 283-294页

作者： Jeong-Dan cha Mi-Ran Jeong Kyung-Min choi Jeong-Hye Park Su-Mi cha Kyung-Yeol lee Department of Natural Products Research Institute of Jinan Red Ginseng Jinan South Korea Department of Nursing Dong-eui University Busan South Korea Department of Oral Microbiology and Institute of Oral Bioscience Chonbuk National University Jeonju South Korea

Cryptotanshinone (CT), a major tanshinone of medicinal plant Salvia miltiorrhiza Bunge, demonstrated effective in vitro antibacterial activity against all oral bacteria tested in this experiment. The antibacterial activities of CT against oral bacteria were assessed using the checkerboard and time-kill methods to evaluate the synergistic effects of treatment with ampicillin or gentamicin. The CT was determined against oral pathogenic bacteria with MIC and MBC values ranging from 0.5 to 16 and 1 to 64 μg/ml;for am- picillin from 0.0313 to 16 and 0.125 to 32 μg/ml;for gentamicin from 2 to 256 and 4 to 512 μg/ml respectively. The range of MIC50 and MIC90 were 0.0625 - 8 μg/ml and 1 - 64 μg/ml, respectively. The combination effects of CT with antibiotics were synergistic (FIC index l bacteria except additive, Streptococcus sobrinus, S. criceti, and Actinobacillus actinomycetemcomitans (FIC index ld, indicating a synergistic effect as defined by a FBCI of ≤0.5. Furthermore, a time-kill study showed that the growth of the tested bacteria was completely attenuated after 3 - 6 h of treatment with the 1/2 MIC of CT, regardless of whether it was administered alone or with ampicillin or gentamicin. The results suggest that CT could be employed as a natural antibacterial agent against cariogenic and periodontopathogenic bac- teria.

关键词： Cryptotanshinone Antibacterial Activity Oral Bacteria Checker Board Method Time-Kill Method Synergistic Effect

laser-assisted deposition of Cu bumps for microelectronic packaging

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中国有色金属学会会刊：英文版 2012年第S3期22卷 683-687页

作者： Won-Seok choi Joohan KIM Department of Nano IT Fusion Program Seoul National University of Science and Technology Department of Mechanical and Automotive Engineering Seoul National University of Science and Technology

Cu bump was transferred using a focused laser pulse for microelectronic *** Nd:YAG laser pulse (maximum energy of 500 mJ;wavelength of 1064 nm;fluences of 0.4-2.1 kJ/cm2) was irradiated on a sacrificial absorption layer with copper *** focused laser beam induced plasma between the semi-transparent donor slide and the sacrificial layer,causing a shock *** shock wave pressure pushed the Cu layer and transferred material to deposit a bump on substrate.A beam-shaper was used to produce uniform pressure at the interface to reduce fragmentation of the transferred material on the *** calculated shock wave pressure with respect to laser fluence was 1-3 GPa.A Cu bump of diameter of 200 μm was successfully deposited at laser fluence of 0.6 kJ/cm *** pressure control at the sacrificial layer using a laser pulse was critical to produce a bump with less *** technique can be applied to forming Cu bump for an interconnecting process in electronics.

关键词： laser induced forward transfer bump deposition Nd:YAG pulsed laser micro system packaging beam shaping

Investigation of ZrO2 nanoparticles concentration and processing time effect on the localized PEO coatings formed on AZ91 alloy

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Journal of Magnesium and Alloys 2019年第4期7卷 555-565页

作者： Zeeshan Ur Rehman Dongjin choi School of Materials Science and Engineering Hongik UniversitySejongRepublic of Korea

AZ91 Mg alloy was treated through a new localized PEO(Plasma Electrolytic Oxidation)coating approach,using electrolyte solutions with varying ZrO2 nanoparticles concentration(2-8 g/l)and processing *** increase in the ZrO2 concentration,several microstructural changes were observed including;formation of cluster-type structure,damage to the inner layers(∼30 min)and sealing of *** analysis of the final coatings was carried out using potentiodynamic polarization,electrochemical impedance spectroscopy and post-corrosion *** was explored that highest corrosion resistance(Rp∼81.17 kΩcm^2)of the coatings was obtained for ZrO2∼2 g/***,higher concentration of the ZrO2 nanoparticles caused weak crystalline coating structure,due to unstable and lower intensity discharges,thus failed to offer high corrosion resistance performance.

关键词： Magnesium alloy PEO coating ZrO2 Corrosion Nanoparticles addition

High-Performance Perovskite Quantum Dot Solar Cells Enabled by Incorporation with Dimensionally Engineered Organic Semiconductor

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Nano-Micro letters 2022年第12期14卷 272-285页

作者： Seyeong lim Dae Hwan lee Hyuntae choi Yelim choi Dong Geon lee Sung Beom Cho Seonkyung Ko Jongmin choi Younghoon Kim Taiho Park Department of Chemical Engineering Pohang University of Science and Technology(POSTECH)Pohang 37673Republic of Korea Department of Materials Science and Engineering Hanyang UniversitySeoul 04763Republic of Korea Center of Materials Digitalization Korea Institute of Ceramic Engineering and Technology(KICET)Jinju 52851Republic of Korea Department of Materials Science and Engineering Ajou UniversitySuwon 16499Republic of Korea Department of Energy Science and Engineering Daegu Gyeongbuk Institute of Science and Technology(DGIST)Daegu 42988Republic of Korea Department of Chemistry Kookmin UniversitySeoul 02707Republic of Korea

Perovskite quantum dots(PQDs)have been considered promising and effective photovoltaic absorber due to their superior optoelectronic properties and inherent material merits combining perovskites and ***,they exhibit low moisture stability at room humidity(20-30%)owing to many surface defect sites generated by inefficient ligand exchange *** surface traps must be re-passivated to improve both charge transport ability and moisture *** address this issue,PQD-organic semiconductor hybrid solar cells with suitable electrical properties and functional groups might dramatically improve the charge extraction and defect *** organic semiconductors are typically low-dimensional(1D and 2D)and prone to excessive self-aggregation,which limits chemical interaction with *** this work,we designed a new 3D star-shaped semiconducting material(Star-TrCN)to enhance the compatibility with *** robust bonding with Star-TrCN and PQDs is demonstrated by theoretical modeling and experimental *** Star-TrCN-PQD hybrid films show improved cubic-phase stability of CsPbI_(3)-PQDs via reduced surface trap states and suppressed moisture *** a result,the resultant devices not only achieve remarkable device stability over 1000 h at 20-30%relative humidity,but also boost power conversion efficiency up to 16.0%via forming a cascade energy band structure.

关键词： CsPbI3 quantum dots Star-shaped organic semiconductors Hybrid perovskite quantum dots Solar cell stability High-efficiency photovoltaics