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Preparation of AZ91D Slurries for Semi-Solid Forming Using Al8 ( Mn, Fe) 5 Precipitates

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Journal of Rare Earths 2004年第z2期22卷 42-46页

作者： Ji Young Byun soon Il kwon Jeong Man Doh Heon Phil Ha Metal Processing Research Center Division of MaterialsKorea Institute of Science and Technology# 39-1 Haweolgok-DongSungbuk-KuSeoul 136-791Republic of Korea

During the solidification of the AZ91D-alloys, the Al8(Mn, Fe)5 phase is generally precipitated in the melt in advance of the precipitation of the primary α-Mg. The basic principle for manufacturing AZ91D-alloy slurries for semi solid forming is to use the Al8(Mn, Fe)5 precipitates as the heterogeneous nucleation sites for primary α-Mg phases. Microscopic analysis for the location of the Al8(Mn, Fe)5 precipitate explains that the Al8(Mn, Fe)5 precipitate is the effective heterogeneous nucleation site for the primary α-Mg phase. It was also observed that increase of the Mn content in the melt and the cooling rate below to the solid/liquid two-phase region resulted in smaller and more globular primary α-Mg due to the increase of heterogeneous nucleation sites. It was found that the average α-Mg diameter grew as a function of t0.278, where t is the holding time at the solid/liquid two-phase region. This would be attributed to the Ostwald type ripening and coalescence between primary α-Mg phases. The cooling rate below to the solid/liquid two-phase region, Mn content in AZ91D alloy, and the holding time and temperature affected on the quality of slurry.

关键词： AZ91D alloy semi-solid forming solidification heterogeneous nucleation

Chondrogenesis of periodontal ligament stem cells by transforming growth factor-β3 and bone morphogenetic protein-6 in a normal healthy impacted third molar

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International Journal of Oral Science 2013年第1期5卷 7-13页

作者： Sunyoung Choi Tae-Jun Cho soon-Keun kwon Gene Lee Jaejin Cho Laboratory of Developmental Biology and Stem Cell Differentiation/Transplantation Department of Dental Regenerative BiotechnologySchool of DentistrySeoul National University Dental Research Institute School of DentistrySeoul National University Laboratory of Molecular Genetics School of DentistrySeoul National University

The periodontal ligament-derived mesenchymal stem cell is regarded as a source of adult stem cells due to its ***, the proof of chondrogenic potential of the cells is ***,we investigated the chondrogenic differentiation capacity of periodontal ligament derived mesenchymal stem cells induced by transforming growth factor(TGF)-p3 and bone morphogenetic protein(BMP)-*** isolation of periodontal ligament stem cells(PDLSCs) from human periodontal ligament,the cells were cultured in Dulbecco’s modified Eagle’s medium(DMEM) with 20%fetal bovine serum(FBS).A mechanical force initiated chondrogenic differentiation of the *** chondrogenic differentiation,10μg·LTGF-β3 or 100μg·LBMP-6 and the combination treating group for synergistic effect of the growth *** analyzed the PDLSCs by fluorescence-activated cell sorting and chondrogenesis were evaluated by glycosaminoglycans assay,histology,immunohistochemistry and genetic *** showed mesenchymal stem cell properties proved by FACS *** contents were increased 217%by TGF-β3 and 220%by BMP-6. The synergetic effect of TGF-β3 and BMP-6 were shown up to 281%compared to *** combination treatment increased Sox9, aggrecan and collagen II expression compared with not only controls,but also TGF-P3 or BMP-6 single treatment *** histological analysis also indicated the chondrogenic differentiation of PDLSCs in our *** results of the present study demonstrate the potential of the dental stem cell as a valuable cell source for chondrogenesis,which may be applicable for regeneration of cartilage and bone fracture in the field of cell therapy.

关键词： bone morphogenetic protein-6 chondrogenesis growth factor periodental ligament cell stem cell transforming growth factor-β3

Dual cycloid gear mechanism for automobile safety pretensioners

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Journal of Central South University 2012年第2期19卷 365-373页

作者： SHIN Joong-ho KIM Chang-hyun YUN Pyeong-hwa kwon soon-man Department of Mechanical Design and Manufacturing Changwon National University

The most conventional vehicle pretensioner system consists of an internal gear pair with involute teeth. However, it has been well known that the corresponding gear pairs are relatively weak under the situation of impact loadings. To improve this phenomenon, a new pretensioning gear system with cycloid teeth rather than the involute ones was proposed, and dual cycloidal gear mechanisms were designed for satisfying geometric constraints and dynamic loading conditions. The simulations of the prototypes were conducted by LS-DYNA program and the experiments for a prototype were performed for a dynamic model with impact loading devices. The results show that the better operation and the smoother motion are confirmed in the proposed cycloidal gear system rather than the conventional one without interferences between gear teeth under the impact of a crash.

关键词： seat belt pretensioner internal gear pairs involute gear dual cycloid gear

Contact surface fatigue life for roller rack pinion system

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Journal of Central South University 2012年第12期19卷 3454-3459页

作者： KIM Chang-hyun CHOI Heung-soap kwon soon-man Department of Mechanical Design and Manufacturing Engineering Changwon National UniversityChangwon 641-773Korea Department of Mechano-Informatics and Design Engineering Hongik UniversitySejong 339-701Korea

A roller rack pinion(RRP)system,which consists of a rack-bar and a cam pinion,transforms a rotation motion into linear *** rack-bar has a series of roller train and meshes with the cam ***,the exact tooth profile of the cam pinion and the non-undercut condition to satisfy the required performance have been proposed with the introduction of the profile shift ***,the load stress factors are investigated under the variation of the shape design parameters to predict the gear surface fatigue limit which is strongly related to the gear noise and vibration at the contact *** results show that the pitting life can be extended significantly with the increase of the profile shift coefficient.

关键词： roller rack pinion profile shift coefficient load stress factor pitting life

Distribution of electric field for carbon nanotube assembly: Simulation (I)

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Transactions of Nonferrous Metals Society of China 2011年第A01期21卷 117-120页

作者： soon-Geun kwon Soo-Hyun KIM Kwang-Ho KIM Myung-Chang KANG Hyung-Woo LEE Department of Mechanical Engineering Korea Advanced Institute of Science and Technology (KAIST) Daejeon 305-701 Korea National Core Research Center for Hybrid Materials Solution Pusan National University

The distribution of electric field for the alignment and attachment of carbon nanotubes (CNTs) was simulated. To be attached at the desired place, the aligned and attracted CNTs should be stayed in the desired area called the stable region or the quasi-stable region for an instant where the change of electric field is minimized. Since the conical electrode has the very narrow sized quasi-stable region, few CNTs can be attached. The rectangular electrodes have a wide stable region, so lots of CNTs can be attached. The results indicate that the round electrode which has a proper sized quasi-stable region is more effective for aligning and attaching a single CNT than the conical or rectangular shaped electrodes.

关键词： carbon nanotubes (CNTs) dielectrophoresis (DEP) round shaped electrode simulation

Early rehabilitation programs after laparoscopic colorectal surgery:Evidence and criticism

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World Journal of Gastroenterology 2013年第46期19卷 8543-8551页

作者： Duck-Woo Kim Sung-bum Kang Soo-Young Lee Heung-kwon Oh Myung-Hoon In Department of Surgery Seoul National University Bundang Hospital

During the past several decades,early rehabilitation programs for the care of patients with colorectal surgery have gained *** randomized controlled trials and meta-analyses have confirmed that the implementation of these evidence-based detailed perioperative care protocols is useful for early recovery of patients after colorectal *** cared for based on these protocols had a rapid recovery of bowel movement,shortened length of hospital stay,and fewer complications compared with traditional care ***,most of the previous evidence was obtained from studies of early rehabilitation programs adapted to open colonic ***,limited evidence exists on the effects of early rehabilitation after laparoscopic rectal resection,although this procedure seems to be associated with a higher morbidity than that reported with traditional *** this article,we review previous studies and guidelines on early rehabilitation programs in patients undergoing rectal *** investigated the status of early rehabilitation programs in rectal surgery and analyzed the limitations of these *** also summarized indications and detailed protocol components of current early rehabilitation programs after rectal surgery,focusing on laparoscopic resection.

关键词： Colorectal cancer Enhanced recovery after surgery Early rehabilitation Fast-track Laparoscopy Rectal

Effect of vehicle weight on natural frequencies of bridges measured from traffic-induced vibration

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Earthquake Engineering and Engineering Vibration 2003年第1期2卷 109-116页

作者： Chul-Young Kim Dae-Sung Jung Nam-Sik Kim soon-Duck kwon Maria Q.Feng Dept.of Civil & Envir.Eng. Myongji UniversityKorea Professor Dept.of Civil & Envir.Eng. Myongji UniversityKorea Research Associate Hyundai Institute of Construction Technology Hyundai E&C Co.Ltd.Korea Chief Researcher Dept.of Civil Engineering Chonbuk National UniversityKorea Professor Dept.of Civil & Envir.Eng. University of CaliforniaIrvineCaliforniaUSA Professor

Recently,ambient vibration test(AVT)is widely used tu estimate dynamic characteristics of large civil struc- *** characteristics ean be affected by various envirnnmental factors such as humidity,intensity of wind,and *** these environmental conditions,tire mass of vehicles may change the measured valnes when traffic-in- duced vibration is used as a source of AVT tor *** effect of vehicle mass on dynamic characteristics is investigated through traffic-induced vibration tests on three bridges;(1)three-span suspension bridge(128m+404m+128m),(2) five-span continuous steel box girder bridge(59m+3@ 95m+59m),(3)simply supported plate girder bridge(46m). Acceleration histories of each measurement location under normal traffic are recorded for 30 minutes at *** recor- ded histories are divided into individual vibrations and are combined into two groups aceording to the level of vibration;one by heavy vehicles such as trucks and buses and the other by light vehicles such as passenger *** processing of the two groups of signals shows that,for the middle and long-span bridges,the difference can be hardly detected,but,for the short span bridges whose mass is relatively small,the measured natural frequencies can change up to 5.4%.

关键词： ambient vibration test traffic induced vibration vehicle mass suspension bridge short-span bridge dynamic characteristics natural frequency

Moving Personal-Cell Network: Characteristics and Performance Evaluation

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China Communications 2018年第12期15卷 159-173页

作者： Syed Tariq Shah Minsu Shin Young Min kwon JaeSheung Shin Ae-soon Park Min Young Chung Department of Electrical and Computer Engineering Sungkyunkwan University Department of Telecommunication Engineering FICT Balochistan University of Information Technology Engineering and Management Sciences Mobile Access Research Division Electronics and Telecommunications Research Institute

Recent years have witnessed a huge demand for ubiquitous communications services from continuously moving users. In order to provide seamless network services to high-mobility users, one of the promising solution proposed by 3 GPP is the deployment of moving-relays. In this article, we introduce the concept of Moving-Personal-Cell(mPC), which is a type of moving-relays. mPC is a user-centric network, which aims to provide reliable network services to moving users. A mPC receives data-traffic from eNB and its neighboring mPCs via wireless backhaul and sidehual links respectively and forwards the received data to its serving users. In addition to this, mPC can also increase the network capacity by caching and distributing the popular contents to its serving users. Besides these pros, the mPC also has some limitations, as its performance is highly affected by cross-tier and co-tier interferences. In this article, we analyze the effect of these interferences on mPCs performance. Our results show that the performance of mPC network is equally affected by the capacity of wireless backhaul, sidehaul, and access links. Moreover, since mPCs accommodate data traffic from wireless backhaul, sidehaul links, and content cache, their performance is also affected by the ratio of data-traffic delivered via these links.

关键词： heterogeneous networks moving small cells fixed small cells moving cache network performance evaluation next generation networks

Mechanical Ventilation Strategy for Subway Cabins Using Numerical Simulations

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Journal of Civil Engineering and Architecture 2012年第8期6卷 1070-1075页

作者： soon-Bark kwon Duck-Shin Park Youngmin Cho Jong bum Kim Taesung Kim Eco-system Research Department Korea Railroad Research Institute Uiwang 437- 757 Korea Department of MechanicaIEngineering Sungkyunkwan University Suwon 440-746 Korea

Seoul metropolitan subway network is known to be the one of the most heavily used transportation means in the world. The subway cabins are naturally ventilated when the cabin doors are opened and through the gaps caused by the incomplete air-tightening of cabin bodies. Although, subway trains are equipped with a mechanical exhaust fan, the apparatus is rarely operated due to the problem of heating/cooling efficiency especially in the summer and winter seasons. In this study, we analyzed the transient CO2 （carbon dioxide） concentration level during the journey of a subway cabin when a heavy load of passengers of up to 200% of designed capacity using a CFD （computational fluid dynamics） analysis. With an increased journey time, the CO2 concentration increased by up to 5,000 ppm depending on passenger load. Through the operation of a mechanical exhaust fan, the high concentration of CO2 decreased down to 1,500 ppm. The effect of the exhaust fan operating on the dilution of indoor air was estimated by comparison with a closed cabin. In addition, the energy consumption for cooling in summer time was assessed for exhaust fan operations.

关键词： Subway cabin ventilation carbon dioxide CFD exhaust fan.