• Title, Summary, Keyword: Super stability

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THREE DIMENSIONAL FINITE ELEMENT ANALYSIS OF INTERNALLY CONNECTED IMPLANT SYSTEMS (내부연결방식 임플랜트 시스템의 삼차원 유한요소법적 연구)

  • Kim Yu-Lee;Cho Hye-Won;Lee Jai-Bong
    • The Journal of Korean Academy of Prosthodontics
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    • v.44 no.1
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    • pp.85-102
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    • 2006
  • Statement of problem: Currently, there are some 20 different geometric variations in implant/abutment interface available. The geometry is important because it is one of the primary determinants of joint strength, joint stability, locational and rotational stability. Purpose: As the effects of the various implant-abutment connections and the prosthesis height variation on stress distribution are not yet examined this study is to focus on the different types of implant-abutment connection and the prosthesis height using three dimensional finite element analysis. Material and method. The models were constructed with ITI, 3i TG, Bicon, Frialit-2 fixtures and solid abutment, TG post, Bicon post, EstheticBase abutment respectively. And the super structures were constructed as mandibular second premolar shapes with 8.5 mm, 11 mm, 13.5 mm of crown height. In each model, 244 N of vertical load and 244 N of $30^{\circ}$ oblique load were placed on the central pit of an occlusal surface. von Mises stresses were recorded and compared in the crowns, abutments, fixtures. Results: 1. Under the oblique loading, von Mises stresses were larger in the crown, abutment, fixture compared to the vertical loading condition. 2. The stresses were increased proportionally to the crown height under oblique loading but showed little differences with three different crown heights under vertical loading. 3. In the crown, the highest stress areas were loading points under vertical loading, and the finish lines under oblique loading. 4. Under the oblique loading, the higher stresses were located in the fixture/abutment interface of the Bicon and Frialit-2 systems compared to the ITI and TG systems. Conclusions: The stress distribution patterns of each implant-abutment system had difference among them and adequate crown height/implant ratio was important to reduce the stresses around the implants.

Thermal Stability of Delithiated LiCoO2-organic Electrolyte for Lithium-Ion Rechargeable Batteries (리튬이온이차전지용 LiCoO2-유기전해액의 충전상태에 따른 열적 안정성)

  • Kim, Dong-Hun;Lee, Young-Ho;Shin, Hye-Min;Chung, Young-Dong;Doh, Chil-Hoon;Jin, Bong-Soo;Kim, Hyun-Soo;Moon, Seong-In;Oh, Dae-Hui;Kim, Ki-Won
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.20 no.5
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    • pp.421-424
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    • 2007
  • Thermal behavior of $Li_{1-x}CoO_2$ has been investigated employing DSC (Differential Scanning calorimetry) and TGA (Thermogravimetry Analyzer), and the crystal parameters were calculated from XRD (X-ray diffraction).for the commercial rectangular pouch cell(1000 mAh).The cathode materials coated over aluminium foil current collector is made up of a blend consisting of active material $LiCoO_2$(size $20\;{\mu}m$, 94 wt%), conducting material super p black (SPB, 3 wt%) and binder polyvinylidene fluoride (PVDF, 3 wt%). The anode is a mix consisting of carbon (92 wt%) and PVDF(8 wt%) coated over copper foil. The cells for the experiments were first preconditioned by cycling three times and stabilized at OCV=3.0, 3.5, 4.2, 4.35 and 4.5 V. The stabilized cathode material was used for thermal and crystal parameter investigations.

Study of Supporting Location Optimization for a Structure under Non-uniform Load Using Genetic Algorithm (유전알고리즘을 이용한 비균일 하중을 받는 구조물의 지지 위치 최적화 연구)

  • Kim, G.H.;Lee, Y.S.;Kim, H.K.;Her, N.I.;Sa, J.W.;Yang, H.L.;Kim, B.C.;Bak, J.S.
    • Proceedings of the KSME Conference
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    • pp.1322-1327
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    • 2003
  • It is important to determine supporting locations for structural stability of a structure under non-uniform load in space interfered by other parts. In this case, There are many local optima with discontinuous design space. Therefore, The traditional optimization methods based on derivative are not suitable. Whereas, Genetic algorithm(GA) based on stochastic search technique is a very robust and general method. This paper has been presented to determine supporting locations of the vertical supports for reducing stress of the KSTAR(Korea super Superconducting Tokamak Advanced Research) IVCC(In-vessel control coil) under non-uniform electromagnetic load and space interfered by other parts using genetic algorithm. For this study, we develop a program combining finite element analysis with a genetic algorithm to perform structural analysis of IVCC. In addition, this paper presents a technique to perform optimization with FEM when design variables are trapped in an incongruent design space.

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A Study on Outage Probability Analysis of HVDC Converter Considering Spare Elements (HVDC 변환소의 여유요소(Spare)를 고려한 사고확률 분석에 관한 연구)

  • Oh, Ungjin;Choi, Jaeseok;Kim, Chan-Ki;Yoon, Yongbeum
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.67 no.11
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    • pp.1408-1414
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    • 2018
  • Recently, as a solution to the problem of maintaining system reliability, stability, and quality occurring worldwide, such as activation of smart grid and recognition of super grid and rapid grid interconnection of renewable energy sources HVDC(High Voltage Direct Current) will appear on the front of the electric power system. These concepts are also very important concepts in HVDC systems. When the HVDC system is linked to the existing power system, it is composed of AC/DC/AC conversion device, and these conversion devices are composed of many thyristors. These parts(Devices) are connected in a complicated manner, and they belong to the one with a higher failure rate. However, the problem of establishing the concept of failure rate of HVDC parts directly linked to economic efficiency and the understanding accompanying it are still insufficient. Therefore, in this paper, we establish the meaning of reliability in power system and try to develop a model to analyze and verify the failure rate data of HVDC based on this.

Control Performance Evaluation of Mid-Story Isolation System for Residence-Commerce Complex Building (주상 복합 구조물에 적용된 중간층 면진 시스템의 성능 검토)

  • Park, Kwang-Seob;Kim, Yun-Tae;Kim, Hyun-Su
    • Journal of the Korean Association for Spatial Structures
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    • v.19 no.3
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    • pp.33-40
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    • 2019
  • A seismic isolation system is one of the most effective control devices used for mitigating the structural responses due to earthquake loads. This system is generally used as a type of base isolation system for low- and mid-rise building structures. If the base isolation technique is applied to high-rise buildings, a lot of problems may be induced such as the movement of isolation bearings during severe wind loads, the stability problem of bearings under large compression forces. Therefore, a mid-story isolation system was proposed for seismic protection of high-rise buildings. Residence-commerce complex buildings in Korea have vertical irregularity because shear wall type and frame type structures are vertically connected. This problem can be also solved by the mid-story isolation system. An effective analytical method using super elements and substructures was proposed in this study. This method was used to investigate control performance of mid-story isolation system for residence-commerce complex buildings subjected to seismic loads. Based on numerical analyses, it was shown that the mid-story isolation system can effectively reduce seismic responses of residence-commerce complex tall buildings.

Long-Term Projection of Demand for Reverse Mortgage Using the Bass Diffusion Model in Korea (Bass 확산모형을 활용한 국내 주택연금의 중·장기 수요예측)

  • Yang, Jin-Ah;Min, Daiki;Choi, Hyung-Suk
    • Journal of the Korean Operations Research and Management Science Society
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    • v.42 no.1
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    • pp.29-41
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    • 2017
  • Korea is expected to become a super-aged society by 2050. Given an aging population and the increasing pressure for the early retirement, a sufficient social safety net for elderly population becomes important. The Korean government introduced public reverse mortgage program in 2007, which is a product for aging seniors and the elderly, The number of reverse mortgage subscribers has also steadily grown. The demand continues to grow, but the reverse mortgage over a long period of time is a highly uncertain and risky product in the position of guarantee or lending institution. Thus, suitable demand prediction of the reverse mortgage subscribers is necessary for stable and sustainable operation. This study uses a Bass diffusion model to forecast the long-term demand for reverse mortgage and provides insight into reverse mortgage by forecasting demand for stability and substantiality of the loan product. We represent the projections of new subscribers on the basis of the data obtained from Korea Housing Finance Corporation. Results show that potential market size of Korean reverse mortgage reaches approximately 760,000-1,160,000 households by 2020. We validate the results by comparing the estimate of the cumulative number of subscribers with that found in literature.

Accurate electronic structures for Ce doped SiAlON using a semilocal exchange-correlation potential

  • Yu, Dong-Su;Jeong, Yong-Jae
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.438-438
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    • 2011
  • White light-emitting diodes (LEDs), the so-called next-generation solid-state lighting, offer benefits in terms of reliability, energy-saving, maintenance, safety, lead-free, and eco-friendly. Recently, rare-earth-doped oxynitride or nitride compounds have attracted a great deal of interest as a photoluminescent material because of their unique luminescent property, especially for white LEDs applications. Ce doped ${\beta}$-SiAlON has been studied as a wavelength conversion phosphor in white LEDs thanks to its high absorption rates, high quantum efficiency, and excellent thermal stability. Previously researches were not enough to understand the detail mechanism and characteristics of ${\beta}$-SiALON. The bandgap structures and electronic structures were not exact due to limitation of calculation methods. In this study, to elucidate the Ce doping effect on the SiAlON system, accurate band structures and electronic structure of the Ce doped ${\beta}$-SiAlON was intensively investigated using density functional theory calculations. In order to get a better description of the band gaps, MBJLDA method were used. We have found a single Ce atom site in ${\beta}$-SiAlON super cell. Furthermore, the density of state, band structure and lattice constant were intensively investigated.

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Evaluation of Glass-forming Ability in Ca-based Bulk Metallic Glass Systems (칼슘기 벌크 비정질 합금에서 비정질 형성능 평가)

  • Park, Eun-Soo;Kim, Do-Hyang
    • Journal of Korea Foundry Society
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    • v.29 no.4
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    • pp.181-186
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    • 2009
  • The interrelationship between new parameter ${\sigma}$ and maximum diameter $D_{max}$ is elaborated and discussed in comparison with four other glass forming ability (GFA) parameters, i.e. (1) super-cooled liquid region ${\Delta}T_x (=T_x - T_g)$, (2) reduced glass transition temperature $T_{rg} (=T_g/T_l)$, (3) K parameter $K (=[T_x-T_g]/[T_l -T_x])$, and (4) gamma parameter ${\gamma}(=[T_x]/[T_l+T_g])$ in Ca-based bulk metallic glass (BMG) systems. The ${\sigma}$ parameter, defined as ${\Delta}T^*{\times}P^'$, has a far better correlation with $D_{max}$ than the GFA parameters suggested so far, clearly indicating that the liquid phase stability and atomic size mismatch dominantly affect the GFA of Ca-based BMGs. Thus, it can be understood that the GFA of BMGs can be properly described by considering structural aspects for glass formation as well as thermodynamic and kinetic aspects for glass formation.

Characteristic of DLC Thin Film Fabricated by FVAS Method on Tungsten Carbide (초경합금에 FVAS로 코팅한 DLC 박막의 특성)

  • Cheon, Min-Woo;Park, Yong-Pil;Kim, Tae-Gon;Lee, Ho-Shik
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.24 no.10
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    • pp.812-816
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    • 2011
  • An optical lens is usually produced in the manner of high temperature compression molding with tungsten carbide alloy molding cores, it is necessary to develop and study technology for super-precision processing of molding cores and coating the core surface. As main methods used in surface improvement technologies using thin film, DLC present high hardness, chemical stability, and outstanding durability of abrasion to be extensively applied in various industrial fields. In this study, the effect of DLC coating of a thin film by means of the FVAS (filtered vacuum arc source) analyzed the characteristics of thin film. Surface roughness before and after DLC coating was measured and the result showed that the surface roughness was improved after coating as compared to before coating. In conclusion, it was observed that DLC coating of the ultra hard alloy core surface for molding had an effect on improving the surface roughness and shape of the core surface. It is considered that this will have an effect on improving abrasion resistance and the service life of the core surface.

Teflon coating of fabric filters for enhancement of high temperature durability (섬유상 여과필터의 고온 내구성 향상을 위한 테프론 코팅 연구)

  • Kim, Eun-Joo;Park, Young-Koo
    • Journal of the Korean Applied Science and Technology
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    • v.28 no.2
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    • pp.232-239
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    • 2011
  • Fabric fibrous filter has been used in various industrial applications owing to the low cost and wide generality. However, the basic properties of fabric materials often limit the practical utilization including hot gas cleaning. This study attempts to find new coatings of porous fibrous filter media in order to overcome its insufficient thermal resistance and durability. Teflon was one of the plausible chemicals to supplement the vulnerability against frequent external thermal impacts. A foaming agent composed of Teflon and some organic additives was tentatively coated on the glass fiber mat. The present test Teflon foam coated filter was fount to be useful for hot gas cleaning, up to $250^{\circ}C$-$300^{\circ}C$. Close examination using XPS(X-ray Photoelectron Spectroscopy) and Contact angle proved the binding interactions between carbon and fluorine, which implies coating stability. The PTFE/Glass foam coated filter consisted of more than 95% (C-F)n bond, and showed super-hydrophobic with good-oleophobic characteristics. The contact angle of liquid droplets on the filter surface enabled to find the filter wet-ability against liquid water or oil.