• Title, Summary, Keyword: 구속범위

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Growth and Properties of GaN Crystals by Vapor Transport Method (Vapor Transport법에 의한 GaN 결정의 성장과 특성)

  • Kim, Seon-Tae
    • Korean Journal of Materials Research
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    • v.9 no.3
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    • pp.295-300
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    • 1999
  • 액상의 Ga으로부터 공급되느 기체상태의 Ga과 $NH _3$$1050~1150^{\circ}C$의 온도범위에서 직접 반응시켜 사파이어 기판위에 직경이 5~27$\mu\textrm{m}$이고, 높이가 $2~27\mu\textrm{m}$인 육각기둥 형태의 GaN 결정을 성장하였다. GaN 결정의 성장 초기에는 c-축 방향으로 우선 성장된 후 성장시간과 성장온도 및 $NH_3$의 유량이 증가함에 따라 기체상태의 Ga공급이 제한됨으로써 성장률이 둔화됨과 동시에 $\alpha$-축 방향으로 우선 성장되었다. GaN 결정의 크기가 증가함에 따라 결정의 품질이 개선되어 X-선 회절강도와 중성도너에 구속된 엑시톤 관력 발광밴드 (I\ulcorner)의 강도가 증가하고, I\ulcorner 발광밴드의 반치폭이 감소하였다.

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Experimental Study of Thermal-mechanical Influence on the Hydraulic Properties of Rock (암반의 수리인자에 미치는 열적.역학적 영향에 대한 실험적 검증)

  • 전석원;홍창우;이주현;강주명;배대석
    • Journal of the Korean Geotechnical Society
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    • v.19 no.5
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    • pp.59-67
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    • 2003
  • In this study, the change in hydraulic conductivity according to the changes in the contact area, aperture, confining pressure and temperature was observed to improve the reliability of the analysis of underground water flow. Also, the mechanical and thermal properties of domestic crystalline rocks in a great depth were obtained. It was found that the averaged intial aperture ranged from 544.33${\mu}{\textrm}{m}$ to 898.62${\mu}{\textrm}{m}$ and it followed a log-normal distribution. The hydraulic conductivity decreased with the increase of normal stress on the fracture surface and the hydraulic conductivity decreased as temperature increased. The change in hydraulic conductivity was strongly correlated with the change in contact area. It was verified by experiments that hydraulic conductivity was inversely proportional to the contact area. The measured mechanical and thermal properties were very close to the existing typical properties of domestic granites.

A Study on Field and Laboratory Test Methods to Obtain Non-linear Deformation Characteristics of Soft Rocks (퇴적연암의 비선형특성 조사.시험기법에 관한 연구)

  • 김유성
    • Geotechnical Engineering
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    • v.12 no.5
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    • pp.63-78
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    • 1996
  • Various type of in-situ and laboratary tests were performed in order to evaluate the stiffness of sedimentary soft rock. In triaxial compression tests of sedimentary soft rocks, axial strains from the axial displacement of the loading piston or specimen cap conventionally were considerably larger than those measured. tocally on the lateral surfaces of specimen, due to the bedding errors at the top and bottom ends of a specimen. A local deformation transducer was used to measure axial strains free from the bedding error ranging from 0.001% to about 1%. In ultra-sonic wave tests, the elastic modulus of unconfined spec imens was smaller than that of confined specimens, due probably to microfracks. Young's modulus Ed from ultra-sonic wave tests and those at small local strains from triaxial tests were similar, both of which agreed very well with Young's modulus Er from field shear wave velocities. Young'a modulus from the field behaviour was virtually similar to that obtained by reducing Er based on the strain level-dependency of stiffness evaluated by the triaxial tests.

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Investigation of Factors Affecting Vibration Induced Settlement Using Multifactorial Experimental Design (다변수 실험계획법을 이용한 진동침하 영향 요소 연구)

  • ;Drabkin Sergey
    • Geotechnical Engineering
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    • v.12 no.4
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    • pp.61-74
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    • 1996
  • Settlement induced by low -level vibration on granular soils is too complect to predict with one or two fact ors. Factors affecting vibration induced settlement were investigated, and a settlement prediction model on granular soils was developed using multifactorial experimental design(MED). Factors such as vibration amplitude, deviatoric stress, confining pressure, soil gradation, duration of vibration, moisture content, and relative density were considered in this study. A special vibratory frame was designed to shake a soil specimen within a triaxial cell. MED allowed the authors to investigate the effect of many factors using a relatively small number of experiments. The most significant factors on settlement were vibrati on amplitued, confining pressure, and defiatoric stress. Comparable settlement was occurred even under low-level vibration ranging from 2.5 to 18mm1sec, and stress am sotropy was found to be an important factor on settlement.

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Dynamic Properties and Settlement Characteristics of Korea Weathered Granite Soils (화강풍화토의 동적 물성치와 침하특성에 대한 연구)

  • Park, Jong-Gwan;Kim, Yeong-Uk;Lee, In-Mo
    • Geotechnical Engineering
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    • v.9 no.2
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    • pp.5-14
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    • 1993
  • Weathered granite soil is the most representative as a surface soil in Korea. In this paper, the dynamic properties and settlement characteristics of Korea granite soil are studied through the dynamic triaxial compression tests. The dynamic characteristics are very important on the analysis of the foundations under dynamic loading such as machine vibration and earthquake. Soil samples having different grain sixtes were prepared at the relative densities between 80oA and 90oA and tested to measure shear moduli and damping ratios at each level of shear strain. The measured shear moduli of weathered granite soils showed large variations according to the grain sizes, confining pressures, relative densities and shear strains. Sandy weathered granite had a little larger dynamic properties than the average values of the sand studied by Seed and Idriss. Pot the well compacted granite soils, little residual settlements occured due to dynamic loading.

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Dynamics modeling and Estimation of Manoeuvrability for Tug-Barge Systems (예부선의 동역학 모델링 및 조종 성능 추정법 개발)

  • Yeo, Dong-Jin;Han, Seong-Hwan;Kim, Dong-Jin;Kim, Yeon-Gyu
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • pp.40-41
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    • 2009
  • In general, ships are towed to keep the safe operations in harbor or channel by tug boats. Due to increase in ocean traffic, many accidents are happened in harbor or channel in these days. Therefore it is necessary to predict manoeuvrability of tug-barge system, and to assure the safety of that system. Turg-barge system is composed of tug boat, barge, and towing cable, connecting both ships. Manoeuvring equations of tug-barge system are suggested, and the scopes of model tests are discussed to establish the mathematical models for tug boats in this paper.

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Experimental Assessment on Accuracy of Kinematic Coordinate Estimation for CORS by GPS Medium-range Baseline Processing Technique (GPS 상시관측소 동적 좌표추정을 위한 중기선해석 정확도의 실험적 분석)

  • Cho, Insoo;Lee, Hungkyu
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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    • v.34 no.1
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    • pp.79-90
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    • 2016
  • The study has purposed in evaluating experiences for achievable accuracy and precision of time series at 3-D coordinates. It has been estimated from the kinematic medium-range baseline processing of Continuously Operating Reference Stations (CORS) for the potential application of crustal displacement analysis during an earthquake event. To derive the absolute coordinates of local CORS, it is highly recommended to include some of oversea country references, since it should be compromised of an observation network of the medium-range baselines within the length range from tens of kilometers to about 1,000 kilometers. A data processing procedure has reflected the dynamics of target stations as the parameter estimation stages, which have been applied to a series of experimental analysis in this research at the end. From the analysis of results, we could be concluded in that the subcentimeters-level of positioning accuracy and precision can be achievable. Furthermore, the paper summarizes impacts of satellite ephemeris, data lengths and levels of initial coordinate constraint into the positioning performance.

Experimental Study on Mechanical Properties and Deformation Behavior of Concrete with Recycled Aggregates and Steel Fiber (순환골재 및 강섬유를 혼입한 콘크리트의 역학적 특성 및 변형 거동에 관한 실험적 연구)

  • Lee, Hyun-Ho;Lee, Tae-Wang
    • Journal of the Korea Concrete Institute
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    • v.28 no.3
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    • pp.357-363
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    • 2016
  • To solve the exhaustion problem of natural aggregate which were create the high value in construction and environmental industry, recycled aggregates have considerable benefits than other materials. However, even though many researches have been conducted with recycled aggregates, building structures with recycled aggregated are rarely constructed because it has lower quality than natural aggregates have. In this study, mechanical and strain properties of recycled aggregates concrete containing steel fibers have been reviewed in order to complement performance of recycled aggregates concrete. As results, recycled aggregates concrete showed lower compressive strength and elastic modulus than plain concrete. But, recycled aggregates concrete containing steel fibers showed equivalent performance with plain concrete. In review of drying shrinkage and creep coefficient, recycled aggregates concrete containing steel fibers showed similar behavior with plain concrete in the range of 0.5 Vol.% fiber content rate by internal restraint effect, moisture transport restraint effect and strength enhancement effect of steel fiber. Therefore, it is considered that mixing steel fibers with concrete is the effective method as a active application plan for recycled aggregates.

Experimental Study on Fire-Resistant Characteristics of Bi-Directionally Prestressed Concrete Panel under RABT Fire Scenario (RABT 화재시나리오를 적용한 이방향 프리스트레스트 콘크리트 패널부재의 내화특성에 관한 실험적 연구)

  • Yi, Na-Hyun;Lee, Sang-Won;Kim, Jang-Ho Jay
    • Journal of the Korea Concrete Institute
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    • v.24 no.6
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    • pp.695-703
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    • 2012
  • Recently, major infrastructure such as bridges, tunnels, PCCVs (Prestressed Concrete Containment Vessel), and gas tanks are Prestressed Concrete (PSC) structure types, which improve their safety by using confining effect from prestressing. Generally, concrete is known to be an outstanding fire resistant construction material. Because of this reason, researches related to extreme fire loaded PSC member behaviors are not often conducted even though PSC behavior under extreme fire loading is significantly different than that of ordinary reinforced concrete (RC) behavior. Therefore, in this study, RABT fire loading tests were performed on bi-directionally prestressed concrete panels with $1000{\times}1400{\times}300mm$ dimensions. The prestressed specimens were applied with 430 kN prestressing (PS) force using unbonded PS thread bars. Also, residual strength structural tests of fire tested PSC and ordinary RC structures were performed for comparison. The study results showed that PSC behavior under fire loading is significantly different than that of RC behavior.

A Study on the Static and Fatigue Behavior of Steel-Confined Prestressed Concrete Girder (강재로 구속된 프리스트레스트 콘크리트 합성거더의 정적 및 피로거동)

  • Kim, Jung Ho;Park, Kyung Hoon;Hwang, Yoon Koog;Lee, Sang Yoon
    • Journal of Korean Society of Steel Construction
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    • v.16 no.6
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    • pp.725-736
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    • 2004
  • A new type of girder, called steel-confined prestressed concrete girder (SCP girder), has been developed, which maximizes the structural advantages of concrete, steel, and PS tendon, and improves on the shortcomings of steel plate girder, PSC I-girder, and preflex girder bridge for use in the construction of middle- or long-span bridges. To verify the propriety of design, structural safety, and applicability of this girder, a static load test was carried out (Kim et al.., 2002). Since the main damage typically sustained by steel bridges results from the fatigue caused by the repetition of traffic loads, fatigue safety must therefore be guaranteed in applying the SCP girder in the construction of real bridges. In this study, a fatigue test was carried out to investigate fatigue behavior and provide basic data for fatigue design. Based on the fatigue test, the fatigue safety of the girder was estimated. For the fatigue test, 10-m specimens were designed for a standard-design truckload (DB-24). A static load test was also performed before the fatigue test to analyze the structural behavior of the specimens. After the fatigue test, outer steel plates were removed to observe the condition of the concrete in the girder.