• Title/Summary/Keyword: boundary characteristics

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Sintering and Electrical Properties According to Sb/Bi Ratio(I) : ZnO-Bi2O3-Sb2O3-Mn3O4-Cr2O3 Varistor (Sb/Bi비에 따른 5원계 바리스터의 소결거동 및 전기적 특성(I) : ZnO-Bi2O3-Sb2O3-Mn3O4-Cr2O3)

  • Hong, Youn-Woo;Lee, Young-Jin;Kim, Sei-Ki;Kim, Jin-Ho
    • Korean Journal of Materials Research
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    • v.22 no.12
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    • pp.675-681
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    • 2012
  • We aimed to examine the co-doping effects of 1/6 mol% $Mn_3O_4$ and 1/4 mol% $Cr_2O_3$ (Mn:Cr = 1:1) on the reaction, microstructure, and electrical properties, such as the bulk defects and grain boundary properties, of ZnO-$Bi_2O_3-Sb_2O_3$ (ZBS; Sb/Bi = 0.5, 1.0, and 2.0) varistors. The sintering and electrical properties of Mn,Cr-doped ZBS, ZBS(MnCr) varistors were controlled using the Sb/Bi ratio. Pyrochlore ($Zn_2Bi_3Sb_3O_{14}$), ${\alpha}$-spinel ($Zn_7Sb_2O_{12}$), and ${\delta}-Bi_2O_3$ (also ${\beta}-Bi_2O_3$ at Sb/Bi ${\leq}$ 1.0) were detected for all of the systems. Mn and Cr are involved in the development of each phase. Pyrochlore was decomposed and promoted densification at lower temperature on heating in Sb/Bi = 1.0 system by Mn rather than Cr doping. A more homogeneous microstructure was obtained in all systems affected by ${\alpha}$-spinel. In ZBS(MnCr), the varistor characteristics were improved dramatically (non-linear coefficient, ${\alpha}$ = 40~78), and seemed to form ${V_o}^{\cdot}$(0.33 eV) as a dominant defect. From impedance and modulus spectroscopy, the grain boundaries can be seen to have divided into two types, i.e. one is tentatively assigned to ZnO/$Bi_2O_3$ (Mn,Cr)/ZnO (0.64~1.1 eV) and the other is assigned to the ZnO/ZnO (1.0~1.3 eV) homojunction.

Adsorption Characteristics and Parameters of Acid Black and Quinoline Yellow by Activated Carbon (활성탄에 의한 Acid Black과 Quinoline Yellow의 흡착특성 및 파라미터)

  • Yi, Kyung Ho;Hwang, Eun Jin;Baek, Woo Seung;Lee, Jong-Jib;Dong, Jong-In
    • Clean Technology
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    • v.26 no.3
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    • pp.186-195
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    • 2020
  • The isothermal adsorption, dynamic, and thermodynamic parameters of Acid black (AB) and Quinoline yellow (QY) adsorption by activated carbon were investigated using the initial concentration, contact time, temperature, and pH of the dyes as adsorption parameters. The adsorption equilibrium data fits the Freundlich isothermal adsorption model, and the calculated Freundlich separation factor values found that activated carbon can effectively remove AB and QY. Comparing the kinetic data showed that the pseudo second order model was within 10% error in the adsorption process. The intraparticle diffusion equation results were divided into two straight lines. Since the slope of the intraparticle diffusion line was smaller than the slope of the boundary layer diffusion line, it was confirmed that intraparticle diffusion was the rate-controlling step. The thermodynamic experiments indicated that the activation energies of AB and QY were 19.87 kJ mol-1 and 14.17 kJ mol-1, which corresponded with the physical adsorption process (5 ~ 40 kJ mol-1). The adsorption reaction was spontaneous because the free energy change in the adsorption of AB and QY by activated carbon was negative from 298 to 318 K. As the temperature increased, the free energy value decreased resulting in higher spontaneity. Adsorption of AB and QY by activated carbon showed the highest adsorption removal rate at pH 3 due to the effect of anions generated by dissociation. The adsorption mechanism was electrostatic attraction.

Growth of p-type ZnSe/GaAs epilayers by Rf reactive sputtering and Its characteristics (고주파 반응성 스퍼터링에 의한 p형 ZnSe/GaAs 박막성장 및 특성연구)

  • 유평렬;정태수;신영진
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.9 no.1
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    • pp.107-112
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    • 1999
  • The ZnSe/GaAs epilayers were grown by RF reactive sputtering. In order to obtain the optimum condition of the growth, we have studied the dependence of Ar pressure, input power of sputter, temperature of substrate, and the distande between substrate and target. Through the observation of the grown epilayer via electronic microscope, we confirmed that the layer's surface was uniform and the boundary of the substrate and the layer was well defined. The defotmation of lattice distortion and the distortion ratio were obtained by DCRC measurements. From mrasurements of photoluminescence, in the ZnSe/GaAs sample without injection of $N_2$gas, we found that the intensity of bound exciton $I_2$is stronger than that of $I_1$and the bound exiton $I_1$represents the deep acceptor level, $I_1\;^d$. On the other hand, in the ZnSe/GaAs sample with injection of$N_2$gas, the peak of$I_1$ was much higher than that of the $I_2$and the half width appeared to be narrow. We concluded that the p-type of ZnSe/GaAs epilayer was grown successfully, because of stronger peak of the bound exciton $I_1$due to the $N_2$dopping.

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Analyzing the spectral characteristic and detecting the change of tidal flat area in Seo han Bay, North Korea using satellite images and GIS (위성영상과 GIS를 이용한 북한 서한만 지역의 간석지 분광특성 및 변화 탐지)

  • Jo, Myung-Hee
    • Journal of the Korean Association of Geographic Information Studies
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    • v.8 no.2
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    • pp.44-54
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    • 2005
  • In this study the tidal area in Seo han bay, North Korea was detected and extracted by using various satellite images (ASTER, KOMPSAT EOC, Landsat TM/ETM+) and GIS spatial analysis. Especially, the micro-landform was classified through the spectral characteristic of each satellite image and the change of tidal flat size was detected on passing year. For this, the spectral characteristics of eight tidal flat area in Korea, which are called as Seo han bay, Gwang ryang bay, Hae iu bay, Gang hwa bay, A san bay, Garorim bay, Jul po bay and Soon chun bay, were analyzed by using multi band of multi spectral satellite images such as Landsat TM/ETM+. Moreover, the micro-landform tidal flat in Seo han bay, North Korea was extracted by using ISODATA clustering based on the result of spectral characteristic. In addition, in order to detect the change of tidal flat size on passing years, the ancient topography map (1918-1920) was constructed as GIS DB. Also, the tidal flat distribution map based on the temporal satellite images were constructed to detect the tidal flat size for recent years. Through this, the efficient band to classify the micro-landform and detect its boundary was clarified and one possibility of KOMPSAT EOC application could be also introduced by extracting the spatial information of tidal flat efficiently.

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An Experimental Study on the Detection of Loosened Areas in a Ground cavity Using a Micro Penetration Test (초소형 관입시험기를 이용한 지반공동 주변지반의 이완영역탐지를 위한 실험적 연구)

  • Kim, Ho-Youn;Kim, Young-Ho;Park, Yoon-Suk;You, Seung-Kyong;Han, Jung-Geun
    • Journal of the Korean Geosynthetics Society
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    • v.18 no.4
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    • pp.299-306
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    • 2019
  • In this study, a model experiment that simulates the behaviour of the ground composed of several compacted layer was intended to measure the loosened area in the event of a ground cavity through a LAD (Loosened area detector). It was confirmed that the size of the cone diameter was affected by the ground composed of fine grain + granulated soil layered through the model soil. In order to select the appropriate cone type, a scale effect experiment was conducted. From the test results, a micro-cone was chosen for the most suitable indoor model experiment. In the case of applying LAD in this study, the loosening condition of the ground was determined by the rapid change in penetration resistance caused by the difference in the boundary surface and relative density due to the compaction of the ground for indoor model testing. The range of loosened area occurring in the cavity was estimated through the penetration resistance characteristics on the ground, and the failure area was identified through the reduction rate of penetration resistance in the loosening area.

A Relational Approach to Political Geography of Border Dynamics: Case study of North Korea-China Border Region Dandong, China (접경지역 변화의 관계론적 정치지리학: 북한-중국 접경지역 단둥을 중심으로)

  • Chi, Sang-Hyun;Chung, Su-Yeul;Kim, Minho;Lee, Sung-Cheol
    • Journal of the Economic Geographical Society of Korea
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    • v.20 no.3
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    • pp.287-306
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    • 2017
  • Since the 1990s, political geographers have focused on the study of the process of border construction. They have shifted from the old morphological and functional approaches to boundary that have focused on the types and functions of boundaries. Recent scholarship on border studies understand boundaries and the border regions as entities with overlapping and competing relationships not as manifestation of territoriality. There has been the emphasis on the multidimensional actors and the historical and cultural legacies inherent in the border region as well. Based on these recent discussions, this study examines how the border region has been constructed by various actors and strategies in Dandong China, the border city between North Korea and China. Several sanctions including UN Security Council have been resolved and implemented in accordance with North Korea's nuclear and missile development, which is a relevant example to examine the "border as relationships" in which strategies of various actors are competing. In addition, this paper has a significance as a case study on the construction process of border and the characteristics of its materiality, which is a way to overcome the limitation of discourse-oriented critical geopolitical research.

A numerical simulation of propagating turbidity currents using the ULTIMATE scheme (ULTIMATE 기법을 이용한 부유사 밀도류 전파 수치모의)

  • Choi, Seongwook;Choi, Sung-Uk
    • Journal of Korea Water Resources Association
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    • v.50 no.1
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    • pp.55-64
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    • 2017
  • This study presents a numerical model for simulating turbidity currents using the ULTIMATE scheme. For this, the layer-averaged model is used. The model is applied to laboratory experiments, where the flume is composed of sloping and flat parts, and the characteristics of propagating turbidity currents are investigated. Due to the universal limiter of the ULTIMATE scheme, the frontal part of the turbidity currents at a sharp gradient without numerical oscillations is computed. Simulated turbidity currents propagate super-critically to the end of the flume, and internal hydraulic jumps occur at the break-in-slope after being affected by the downstream boundary. It is found that the hydraulic jumps are computed without numerical oscillations if Courant number is less than 1. In addition, factors that affect propagation velocity of turbidity currents is studied. The particle size less than $9{\mu}m$ does not affect propagation velocity but the buoyancy flux affects clearly. Finally, it is found that the numerical model computes the bed elevation change due to turbidity currents properly. Specifically, a discontinuity in the bed elevation, arisen from the hydraulic jumps and resulting difference in sediment entrainment, is observed.

Experimental Study on Flow Characteristic of L-type Groyne (L형 수제주변 흐름특성 변화에 대한 실험연구)

  • Kang, Joon-Gu;Yeo, Hong-Koo;Kim, Sung-Jung
    • Journal of Korea Water Resources Association
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    • v.41 no.7
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    • pp.653-667
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    • 2008
  • The hydraulic model test for the L-type Groynes with "ㄱ" shape were conducted to analyze flow characteristics around these groynes. The results of model tests should be used for the fundamental information to design the L-type Groyne constructed in the field. Main hydraulic factors such as the velocity and thalweg line changes in main channel and separation area were analyzed in this study. The thalweg line is stream line where the maximum velocity occurs, and the separation area is a boundary of main flow and recirculation zone. Model tests with 5 different arm-lengths of the L-type Groynes were conducted changing the velocity. The LSPIV(Large Scale Particle Image Velocimetry) technique was used to measure and analyze the flow variation around the L-type Groynes. The velocity in main channel was increased 1.5 times and there was no effects of different groyne arm-length on the velocity changes. The width of thalweg lines $(T_{CL})$ was changed to $55{\sim}58%$ of chanel width, and the Froude number did not affect on the thalweg line $(T_{CL})$ and separation line $(S_h)$ changes.

Statistical Analysis of Aquifer Characteristics Using Pumping Test Data of National Groundwater Monitoring Wells for Korea (국가지하수 관측망의 양수시험 자료를 이용한 국내 대수층 특성의 통계적 분석)

  • Jeon Seon-Keum;Koo Min-HO;Kim Yongje;Kang In-Oak
    • Journal of Soil and Groundwater Environment
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    • v.10 no.6
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    • pp.32-44
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    • 2005
  • 314 pumping test data of the National Groundwater Monitoring Wells (NGMWs) are analyzed to present statistical properties of fractured-rock and alluvial aquifers of Korea such as distribution of hydraulic conductivity, empirical relations between transmissivity and specific capacity, and time-drawdown patterns of pumping and recovery test. The mean hydraulic conductivity of alluvial aquifers (1.26 m/day) is 17 times greater than that of fractured-rock aquifers (0.076 m/day). Hydraulic conductivity of fracture-rock aquifers ranges in value over 4 orders of magnitude which coincide with representative values of fractured crystalline rocks and shows distinctive differences among rock types with the lowest values for metamorphic rocks and the highest values for sedimentary rocks. In consideration of the estimated transmissivity with some simplifying assumptions, it Is likely that $32\%$ of groundwater flow for NGMWs would occur through fractured-rock aquifers and $68\%$ through alluvial aquifers. Based on 314 pairs of data, empirical relations between transmissivity and specific capacity are presented for both fractured-rock and alluvial aquifers. Depending on time-drawdown patterns during pumping and recovery test, NGMWs are classified into $4\~5$ types. Most of NCMWs $(83.7\%)$ exhibit the recharge boundary type, which call be attributed to sources of water supply such as streams adjacent to the pumping well, the vertical groundwater flux between fractured-rock and the alluvial aquifers, and the delayed yield associated with gravity drainage occurring in unconfined aquifers.

The Inelastic Behavior of High Strength Reinforced Concrete Tall Walls (고강도 철근콘크리트 고층형 내력벽의 비탄성 거동에 관한 실험 연구)

  • 윤현도;정학영;최창식;이리형
    • Magazine of the Korea Concrete Institute
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    • v.7 no.3
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    • pp.139-148
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    • 1995
  • The test results from three one fourth scale models using high strength Reinforced Concrete $f_x=704\;kg/cm^2,\;f_y=5.830\;kg/cm^2$ are presented. Such specimens are considered to represent the critical 3 storics of 60-story tall building of a structural wall system in area of high seismicity respectively. They are tested under inplane vertical and horizontal loading. The main varlable is the level of axial stress. The amounts of vertical and horizontal reinforcement are identical for the three walls testcd. The cross-section of all walls is barbell shape. The aspectratio($h_w/I_w$) of test specimen is 1.8. The aim of the study is to investigate the effects of levels of applied axial stresses on the inelastic behavior of high-strength R /C tall walls. Experimental results of high strength R /C tall walls subjected to axial load and simulated sels rnic loading show that it is possible to insure a ductlle dominant performance by promotmg flex ural yielding of vertical reinforcement and that axial stresses within $O.21f_x$ causes an increase in horizontal load-carrying capacity, initial secant st~ffness characteristics, but an decrease in displacement ductility. energy dissipation index and work damage index of high strength K /C tall walls