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Integrated Design of a Compact and Lightweight S-Band Traveling-Wave Tube Amplifier for a New Class of Microwave Power Module

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Journal of Electromagnetic Analysis and Applications 2013年第3期5卷 96-102页

作者： Heather Song Leslie Tekamp Frank Francisco Ming-Chieh Lin Peter H. Stoltz David Smith gil wong choi Jin Joo choi Department of Electrical and Computer Engineering University of Colorado Colorado Springs USA Department of Electrical and Computer Engineering University of Colorado Colorado Springs USA Department of Electronics Convergence Engineering Kwangwoon University Seoul South Korea. Samsung Thales Co. Yongin-Si South Korea Tech-X Co. Boulder USA Triton Services Inc. Breinigsville USA

A new class of compact and lightweight S-band 1 kW traveling-wave tube (TWT) is being developed for a microwave power module (MPM) that will be used for phased antenna array radar applications. The proposed S-band MPM provides a tenfold peak power increase compared to state-of-the-art S-band MPMs. In this paper, the design of the vacuum power booster TWT part of the MPM is presented. The compact and lightweight S-band TWT is driven by a 6 kV, 0.9 A electron beam. The amplifier is predicted by large-signal simulations to generate over 1 kW at S-band with 25 dB saturated gain and over 40% efficiency. The stability from unwanted oscillations has been investigated. To suppress the oscillations, the helix circuit has been coated with carbon composite material. The coaxial input and output antennas have been fabricated. For efficiency enhancement, a multi-stage depressed collector (MDC) has been designed using a 3D particle-in-cell (PIC) simulator, VORPAL. The collector design makes use of a current loop based on a feedback mechanism for effective design process. The integrated designs of a helix circuit, an electron gun, a periodic permanent magnet (PPM), antennas, and a collector are presented.

关键词： TWT MPM Compact Lightweight Feedback Current Loop Multi-Stage Collector

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Synthetic brochosomes:Design,synthesis,and applications

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Nano Research 2024年第2期17卷 734-742页

作者： Lin Wang Jinsol choi Tak-Sing wong Department of Mechanical Engineering The Pennsylvania State UniversityUniversity ParkPA 16802USA Materials Research Institute The Pennsylvania State UniversityUniversity ParkPA 16802USA Department of Biomedical Engineering The Pennsylvania State UniversityUniversity ParkPA 16802USA

Brochosomes,which are nanoscopic buckyball-shaped granules produced by leafhoppers,are one of the most intricate structures discovered in *** functions of brochosomes have been proposed but only a few have been experimentally validated due to the challenge of fabricating their synthetic *** in micro-and nanofabrication have recently led to the emergence of synthetic brochosomes,opening up new possibilities for innovative *** review explores the early discovery of natural brochosomes and their geometrical features,followed by the recent progress in fabricating synthetic brochosomes and their *** on future applications and challenges in the scalable manufacturing of synthetic brochosomes are discussed.

关键词： synthetic brochosomes leafhopper antireflection superhydrophobicity surface-enhanced Raman scattering photocatalyst energy harvesting

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A scheduling algorithm with dynamic properties in mobile grid

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Frontiers of Computer Science 2014年第5期8卷 847-857页

作者： JongHyuk LEE SungJin choi JoonMin gil Taeweon SUH HeonChang YU Software R&D Center Samsung Electronics Gyeonggi-do 443-742 Republic of Korea Media Solution Center Samsung Electronics Gyeonggi-do 443-742 Republic of Korea School of Information Technology Engineering Catholic University of Daegu Gyeongsangbuk-do 712-702 Republic of Korea Graduate School of Information Security Korea University Seoul 136-701 Republic of Korea Department of Computer Science and Engineering Korea University Seoul 136-701 Republic of Korea

Mobile grid is a branch of grid computing that incorporates mobile devices into the grid infrastructure. It poses new challenges because mobile devices are typically resource-constrained and exhibit unique characteristics such as instability in network connections. New scheduling strate- gies are imperative in mobile grid to efficiently utilize the devices. This paper presents a scheduling algorithm that con- siders dynamic properties of mobile devices such as avail- ability, reliability, maintainability, and usage pattern in mo- bile grid environments. In particular, usage patterns caused by voluntarily or involuntarily losing a connection, such as switching off the device or a network interruption could be important criteria for choosing the best resource to execute a job. The experimental results show that our scheduling al- gorithm provides superior performance in terms of execution time, as compared to the other methods that do not consider usage pattern. Throughout the experiments, we found it es- sential to consider usage pattern for improving performance in the mobile grid.

关键词： mobile grid scheduling dynamic properties,availability reliability maintainability usage pattern

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Numerical characterization of heat transfer in closed-loop vertical ground heat exchanger

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Science China(Technological Sciences) 2010年第1期53卷 111-116页

作者： Chulho LEE Hujeong gil Hangseok choi Shin-Hyung KANG School of Civil Environmental and Architectural EngineeringKorea University5-GaAnam-DongSeongbuk-GuSeoul 136-713Republic of Korea Pyungsan SI Co. Ltd.1337-31 Seocho-DongSeocho-GuSeoul 137-860Republic of Korea Department of Mechanical Engineering Konyang University119Deahak-RoNonsanChungnam 320-711Republic of Korea

A series of numerical analyses has been performed on the characteristics of heat transfer in a closed-loop vertical ground heat exchanger(U-loop).A 2-D finite element analysis was conducted to evaluate the temperature distribution over the cross section of the U-loop system involving high-density polyethylene(HDPE) pipe/grout/soil to compare the sectional efficiency between the conventional U-loop and a new latticed HDPE pipe system,which is equipped with a thermally insulating lattice in order to reduce thermal interference between the inlet and outlet *** addition,a 3-D finite volume analysis(FLUENT) was adopted to simulate the operation of the closed-loop vertical ground heat exchanger with the consideration of the effect of a distance between the inlet and outlet pipes,grout's thermal properties,the effectiveness of the latticed HDPE pipe system,and the rate of circulation *** was observed that the thermal interference between the two strands of U-loop is of importance in enhancing efficiency of the ground heat ***,it is recommended to modify the configuration of the conventional U-loop system by equipping the thermally insulating lattice between the two pipe strands.

关键词： ground heat exchanger HDPE pipe latticed pipe sectional efficiency

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Inclusive quasielastic neutrino-nucleus scattering with energy density functional nuclear models

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Chinese Physics C 2024年第8期48卷 153-158页

作者： K.S.Kim Soonchul choi Hana gil Chang Ho Hyun School of liberal arts and science korea aerospace universitygoyang 10540korea Center for exotic nuclear studies institute for basic sciencedaejeon 34126korea Center for extreme nuclear matters korea universityseoul 02841korea Department of physics education daegu universitygyeongsan 38453korea

In this study,we calculated the inclusive charged-current neutrino-nucleus scattering from ^(40)Ar in the quasielastic *** explore the effect of uncertainties stemming from the nuclear structure,we used the KIDS(Korea-IBS-Daegu-SKKU)nuclear energy density functional and Skyrme force models,namely SLy4,SkI3,and *** models were selected to have distinct behavior in terms of the density dependence of the symmetry energy and the effective mass of the *** the charged-current neutrino scattering,the single-and double-differential cross sections were calculated for various *** cross sections are reported as a function of the incident neutrino *** theoretical cross sections were compared with experimental data,and the roles of the effective mass and symmetry energy were investigated in terms of charged-current neutrino-nucleus scattering.

关键词： energy density functional neutrino-nucleus scattering symmetry energy effective mass of the nucleon

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Physiological differences in the growth and maturation of Eisenia bicyclis and Ecklonia cava gametophytes in Korea

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Journal of Oceanology and Limnology 2019年第2期37卷 657-664页

作者： Han gil choi Da Vine JEON Seo Kyoung PARK GAO Xu Faculty of Biological Science and Sea & Biotech Wonkwang University

The objective of this study was to examine the eff ects of temperature and light intensity on growth of female gametophytes of Eisenia bicyclis and Ecklonia cava and responses of these female gametophytes to Fe addition and daylength. Female gametophytes of each species were cultured at four temperatures (10, 15, 20, and 25°C) and under a combination of four light intensities (10, 20, 40, and 80 μmol photons/(m^2 ·s)) with two temperatures (15 and 20°C for E i . bicyclis;20 and 25°C for E c . cava ) to clarify their optimal growth conditions. Growth and maturation of female gametophytes of these two species under a combination of five Fe-EDTA concentrations (0, 1, 2, 4, and 8 μmol/L) and three daylengths (10, 12, and 14 h) were also examined. The growth of E i . bicyclis gametophyte was maximal at approximately 15–20°C, 20 μmol photons/(m^2 ·s), Fe-EDTA concentration of 8 μmol/L and daylengths of 12–14 h. While E c . c ava gametophytes showed optimal growth at approximately 20–25°C, 20 μmol photons/(m^2 ·s), Fe- EDTA concentration of 8 μmol/L and daylength of 14 h. Maturation of gametophytes was enhanced at Fe-EDTA concentration of 4 μmol/L for E i . bicyclis and at 2 μmol/L for E c . c ava . In conclusion, optimal growth temperatures and Fe-EDTA concentrations for maturation of E i . bicyclis and E c . c ava gametophytes were diff erent. Higher optimal growth temperature for E c . c ava gametophytes may contribute to its wider geographical distribution compared to E i . bicyclis which has restricted habitats in Korea. This suggests that addition of Fe ion could be used to recover beds of these two species in barren grounds of Korea.

关键词： Ecklonia cava Eisenia bicyclis gametophyte growth maturation

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Visualization for Explanation of Deep Learning-Based Defect Detection Model Using Class Activation Map

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Computers, Materials & Continua 2023年第6期75卷 4753-4766页

作者： Hyunkyu Shin Yonghan Ahn Mihwa Song Heungbae gil Jungsik choi Sanghyo Lee Center for AI Technology in Construction Hanyang University ERICAAnsan15588Korea School of Architecture and Architectural Engineering Hanyang University ERICAAnsan15588Korea ICT Convergence Research Division Korea Expressway Corporation Research InstituteHwaseong18489Korea Department of Architecture College of EngineeringKangwon National UniversitySamcheok25913Korea Division of Smart Convergence Engineering Hanyang University ERICAAnsan15588Korea

Recently,convolutional neural network(CNN)-based visual inspec-tion has been developed to detect defects on building surfaces *** CNN model demonstrates remarkable accuracy in image data analysis;however,the predicted results have uncertainty in providing accurate informa-tion to users because of the“black box”problem in the deep learning ***,this study proposes a visual explanation method to overcome the uncertainty limitation of CNN-based defect *** visual repre-sentative gradient-weights class activation mapping(Grad-CAM)method is adopted to provide visually explainable information.A visualizing evaluation index is proposed to quantitatively analyze visual representations;this index reflects a rough estimate of the concordance rate between the visualized heat map and intended *** addition,an ablation study,adopting three-branch combinations with the VGG16,is implemented to identify perfor-mance variations by visualizing predicted *** reveal that the proposed model,combined with hybrid pooling,batch normalization,and multi-attention modules,achieves the best performance with an accuracy of 97.77%,corresponding to an improvement of 2.49%compared with the baseline ***,this study demonstrates that reliable results from an automatic defect classification model can be provided to an inspector through the visual representation of the predicted results using CNN models.

关键词： Defect detection visualization class activation map deep learning explanation visualizing evaluation index

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Low genetic diversity in the endangered marine alga Silvetia siliquosa(Ochrophyta:Fucaceae)and the implication to conservation

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Journal of Oceanology and Limnology 2022年第1期40卷 216-225页

作者： Yanshuo LIANG Jie ZHANG Xiaohan SONG Han-gil choi Xu GAO Delin DUAN Zi-min HU CAS and Shandong Province Key Laboratory of Experimental Marine Biology Center for Ocean Mega-ScienceInstitute of OceanologyChinese Academy of SciencesQingdao 266071China Laboratory for Marine Biology and Biotechnology Pilot National Laboratory for Marine Science and Technology(Qingdao)Qingdao 266237China University of Chinese Academy Sciences Beijing 100049China Faculty of Biological Science and Institute for Environmental Science Wonkwang UniversityIksan 54538Korea Ocean School Yantai UniversityYantai 264005China

Although signifi cant research eff orts have been targeted toward conservation and management of endangered terrestrial fl ora and fauna,attempts have been limited to conserve threatened *** siliquosa is an ecologically and commercially vital brown alga that is uniquely distributed in the Yellow-Bohai Sea and along the southwest coast of Korea.A massive decline in its distribution range and biomass from the mid-1990s onward indicates that this species has become *** the present study,we used nuclear internal transcribed spacer and concatenated mitochondrial cytochrome oxidase I subunit+intergenic spacer to estimate the genetic diversity,population connectivity,and degree of genetic diff erentiation of *** in China and *** molecular results exhibited strikingly low levels of haplotype/ribotype and nucleotide diversity in *** populations,with only three mitochondrial haplotypes and nuclear ribotypes detected in 136 and 143 specimens,*** analysis of molecular variance revealed 85%-95%of genetic variance among *** diff erentiation coeffi cient(F_(ST))and gene fl ow(N_(m))suggested that two populations(JIN and GWA)along the southern coast of Korea are highly divergent from the others,with weak genetic *** signifi cant genetic diff erentiation was observed among populations either in China or along the geographically proximate west coast of ***,four independent management units were designated for sustainable management:the LII and RUS populations in China,the YEO and CHA populations along the west coast of Korea,and each of the GWA and JIN populations along the south coast of *** suggest that artifi cial cultivation and transplantation of *** are the eff ective approaches for restoration and conservation.

关键词： biodiversity conservation endangered seaweed genetic diversity habitat loss Silvetia siliquosa

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Effect of an oxygen-free atmosphere during heating on anthocyanin,organic acid,and color of strawberry puree

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Food Bioscience 2022年第6期50卷 695-703页

作者： Ah-Na Kim Kyo-Yeon Lee Chae-Yeon Han Hyun-Jin Kim Sung-gil choi Division of Applied Life Science Gyeongsang National UniversityJinju52828South Korea Research Group of Safety Distribution Korea Food Research InstituteWanju-gun55365Republic of Korea Division of Food Science and Technology (Institute of Agriculture and Life Sciences) Gyeongsang National UniversityJinju52828South Korea

Strawberries were ground and heated under oxygen-free condition using a specially designed device,and compared with the berries processed at atmospheric *** complete inactivation of oxidative enzymes and microorganisms were found in both *** heating without oxygen led to higher concentrations of anthocyanins and organic acids than with oxygen,resulting in higher redness and antioxidant ***,the greatest effect of anaerobic condition was observed in delphinidin-3-glycoside and ascorbic acid which are the most sensitive to oxidation in presence of ***,some nutrients which are low dependence on oxygen were degraded regardless of insufficient *** was considered that anaerobic condition may inhibit the deterioration related to only oxidation,not non-oxidative reaction during *** results implicated that dissolved oxygen in tissues may cause continuous oxidative *** summary,oxygen-free condition can confer better oxidative stability of antioxidants and color during heating of berry products.

关键词： Thermal processing Oxygen Vacuum Anthocyanin Strawberry Oxidation

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HepG2 cells recovered from apoptosis show altered drug responses and invasiveness

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Hepatobiliary & Pancreatic Diseases International 2014年第3期13卷 293-300页

作者： Shan-Shan Wang Xin Xie Chung Sing Timothy wong Pui Ying choi Ming Chiu Fung School of Life Sciences the Chinese University of Hong Kong Department of Anatomical and Cellular Pathology Prince of Wales Hospital the Chinese University of Hong Kong

BACKGROUND: Cancer relapse, associated with increased drug resistance and rate of metastasis, often follows completion of chemotherapy but the cancer escape mechanisms are still incompletely understood. Percutaneous ethanol injection(PEI)has been used for treating hepatocellular carcinoma(HCC)for decades, while the recurrence after PEI treatment remains a major limitation. Recent evidence mounted that cancer cells could survive from chemical induced apoptosis, suggesting a potential route through which cancer relapse may occur. This study focuses on the consequence of HepG2 recovery from ethanol-induced apoptotic ***: The model of HepG2 recovery from ethanolinduced apoptotic event was established by live cell imaging,BrdU assay and Western blotting. MTT assay, wound healing assay and invasion assay were used to investigate the behavior of HepG2 after ***: HepG2 cells could recover from ethanol-induced apoptosis. These cells changed their behaviors such as drug resistance, mobility and invasiveness. On average, the recovered HepG2 cell clones were found to be 46% more resistant to ethanol and 84% higher in mobility. The recovered clones became 58.2% more sensitive to ***: HepG2 cells can recover from ethanolinduced apoptotic event. These cells became more resistant to ethanol and more invasive. Although the recovered cell clones were more resistant to ethanol, they became more sensitive to5-fluorouracil treatment.

关键词： cancer recurrence apoptosis recovery liver cancer percutaneous ethanol injection 5-fluorouracil

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