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  • Title/Summary/Keyword: relative density

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Characteristics of Nitro-nutrients and Phytoplankton Dynamics in the Yeongsan River after Weir Construction (보 건설 이후 영산강 보 구간에서의 질소계열 영양염류 및 식물플랑크톤 동태)

  • Seo, Kyung-Ae;Na, Jeong-Eun;Ryu, Hui-Seong;Kim, Kyunghyun
    • Journal of Korean Society on Water Environment
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    • v.34 no.4
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    • pp.423-430
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    • 2018
  • Insomuch as it is important to manage water quality, from the perspective of water management, it is essential to understand the effect of the weirs on water quality and phytoplankton dynamics in various regions. The purpose of this study is to investigate the characteristics of nitro-nutrients, as well as occurrences and succession patterns of phytoplankton, in the river sections of the two weirs in the Yeongsan River for the five years (from 2012 to 2016) after the weir construction. In respect to this data, the average water temperature measured at the representative point in the section of the Seungchon Weir (17.1C) was higher than that of the Juksan Weir (16.6C) by comparison. By way of an analysis of this data, it was found that the water quality variables such as, organic matter, nitrogen nutrients and phosphorus nutrients were improved gradually during the period, but the degree of the improvement differs as noted and measured between the weirs. Under the circumstances, it is especially noted that the NH3N concentration was higher for the point of the Seungchon Weir (2.204 mg/L) than that of the Juksan Weir (1.157 mg/L). This indicates that effluent as seen from sewage treatment plants and hydrological feature near the densely population area, could be the main cause for the incidence of water pollution in the upstream section of the Seungchon Weir. Additionally, the phytoplankton analysis showed that a relative abundance of diatoms and green algae were 56.9 % and 25.8 % respectively. However, it is noted that the cyanobacteria was measured lower as 10.7 %. Also, in the study sites cell density and occurrence frequency of cyanobacteria were relatively lower than compared to the same measurements noted in other rivers.

Fabrication of Electroconductive Si3N4-TiN Ceramic Composites by In-Situ Reaction Sintering (In-Situ 반응소결에 의한 전도성 Si3N4-TiN 복합세라믹스 제조)

  • Lee, Byeong-Taek;Yun, Yeo-Ju;Park, Dong-Su;Kim, Hae-Du
    • Korean Journal of Materials Research
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    • v.9 no.6
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    • pp.577-582
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    • 1999
  • In order to make the electroconductive Si3N4-TiN composities, the Si-Ti(N) compacts were nitrided at 1450C for 20hours, and then they were post-sintered by a gas-pressure-sintering technique at 1TEX>1950C for 3.5 hours. As starting powders, commercial si powder of about 10μm, two types of Ti powders of 100 and 325 mesh, and fine-sized TiN of 2.5μm powders were used. In the Si3N4-TiN sintered bodies used Ti powders, the relative density and fracture strength and electrical conductivity are low due to the existence of large amounts of coarse pores. However, in the Si3N4-TiN composite used TiN powder, the fracture toughness, fracture strength and electrical resistivity were 5.0MPam1/2, 624MPa and 1400ωcm, respectively. The dispersion of TiN particles in the composite inhibited the growth of Si3N4 in the shape of rod and made strong strain field contrasts at the Si3N4-TiNinterfaces. It was recognized that microstructural control is required to improve the electrical conductivity and mechanical properties of Si3N4-TiN composites by dispersing TiN particles homogeneously.

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Effect of Partially Oxidized Ti Powder on Electrical Properties and Microstructures of BaTiO3-based Ceramics (BaTiO3계 세라믹스의 전기적 성질과 미세조직에 미치는 부분산화 Ti 분말 첨가의 영향)

  • Kim, Jun-Gyu;Jo, Won-Seung;Park, Gyeong-Sun
    • Korean Journal of Materials Research
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    • v.10 no.10
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    • pp.671-676
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    • 2000
  • BaTiO3-based ceramics with partially oxidized Ti powders were prepared by sintering at 1350C for 1 h in v vacuum, and then heated in air. In this study, the effect of partially oxidized Ti powders on electrical properties and microstructures of BaTiO3-based ceramics was investigated. It was found out that the semiconductive BaTiO3-based ceramics beζame to show excellent PTCR (more than 105) characteristic by adding 5~7 vol% of partially oxidized Ti powder. Also, it was found out that the sintered compact had extremely porous and fine-grained microstructure. The relative density and grain size of sintered compact with 5 vol% of partially oxidized Ti powders were 54% and 1.3μm, respectively. The mechanism for the development of PTCR characteristic in BaTiO3-based ceramics with partially oxidized Ti powders due to the adsorption of oxygen at grain boundaries, and could be explained, based on Heywang model.

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Ta2O5Dielectric Thin Films by Thermal Oxidation and PECVD (열산화법 및 PECVD 법에 의한 Ta2O5 유전 박막)

  • Mun, Hwan-Seong;Lee, Jae-Seok;Lee, Jae-Seok;Lee, Jae-Seok;Yang, Seung-Gi;Lee, Jae-hak;Park, Hyung-ho;Park, Jong-wan
    • Korean Journal of Materials Research
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    • v.2 no.5
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    • pp.353-359
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    • 1992
  • Thermal oxidation and plasma enhanced chemical vapor deposition of tantalum oxide thin films on p-type (100) Si substrates were studied to examine the dielectric nature of Ta2O5 as a Al/Ta2O5/p-Si capacitor. Microstructure and dielectric properties of the capacitors were investigated by XRD, AES, high frequency C-V analyzer, I-V meter and TEM. XRD analysis showed that the structure of Ta2O5 films were amorphous, but the films were crystallized to hexagonal δ-Ta2O5 by 650C thermal oxidation treatment. It was found that the stoichiometry of the films was more or less close to 2 : 5. Leakage current density and relative dielectric constant of thermal oxidation Ta2O5 film at 600C was 5.0imes106/A/c$m^2 and 31.5, respectively. In the case of PECVD Ta2O5film deposited at 0.47W/c$m^2 they were 2.5imes105/A/extrmcm2 and 24.0, respectively. The morphology of the films and interfaces were investigated by TEM.

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Analyses of Larg Cell Area MCFC System Dynamics (대면적 용융탄산염 연료전지 시스템 동특성 분석)

  • 강병삼;고준호;이충곤;임희천
    • Journal of Energy Engineering
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    • v.8 no.4
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    • pp.592-604
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    • 1999
  • The steady state and dynamic characteristics of large cell area MCFC stacks were analyzed to solve the problems such as temperature difference generated in stacks and pressure difference between anode and cathode. Manipulated variables (current density, duel utilization rate, oxidant utilization rate) and controlled variables (temperature difference, anode and cathode pressure difference) which had an important effect on the MCFC stack performance were determined using operation results of two types of MCFC stacks (5kW (3,000 cm2, 20 ea). 3kW (6,000 cm2, 5ea)). The stability and transfer function representing system dynamics were obtained by steady state gain rate which showed the relative change between MVs and CVs. The transfer function was a 3×3 matrix and a typical first order system without time delay. The optimal operating condition of large cell area MCFC stacks could be determined by analyzing dynamic characteristics. In case of a 5 kW MCFC stack, pressurized operation with recycle flow should be used to control the outlet temperature less than 680C and to control the MCFC system effectively. MIMO control or decoupler should be used to remove the interaction between MVs and CVs. This result will be used as important data in determining the control structure design and operation mode of large cell area MCFC systems in the future.

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Evaluation of Tractive Performance of an Underwater Tracked Vehicle Based on Soil-track Interaction Theory (궤도-지반 상호작용 이론을 활용한 해저궤도차량의 구동성능 평가)

  • Baek, Sung-Ha;Shin, Gyu-Beom;Kwon, Osoon;Chung, Choong-Ki
    • Journal of the Korean Geotechnical Society
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    • v.34 no.2
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    • pp.43-54
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    • 2018
  • Underwater tracked vehicle is employed to perform underwater heavy works on saturated seafloor. When an underwater tracked vehicle travels on the seafloor, shearing action and ground settlement take place on the soil-track interface, which develops the soil thrust and soil resistance, respectively, and they restrict the tractive performance of an underwater tracked vehicle. Thus, unlike the paved road, underwater tracked vehicle performance does not solely rely on its engine thrust, but also on the soil-track interaction. This paper aimed at evaluating the tractive performance of an underwater tracked vehicle with respect to ground conditions (soil type, and relative density or consistency) and vehicle conditions (weight of vehicle, and geometry of track system), based on the soil-track interaction theory. The results showed that sandy ground and silty sandy ground generally provide sufficient tractions for an underwater tracked vehicle whereas tractive performance is very much restricted on clayey ground, especially for a heavy-weighted underwater tracked vehicle. Thus, it is concluded that an underwater tracked vehicle needs additional equipment to enhance the tractive performance on the clayey ground.

Development of Computer Code for Simulation of Multicomponent Aerosol Dynamics -Uncertainty and Sensitivity Analysis- (다성분 에어로졸계의 동특성 묘사를 위한 전산 코드의 개발 -불확실성 및 민감도 해석-)

  • Na, Jang-Hwan;Lee, Byong-Whi
    • Nuclear Engineering and Technology
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    • v.19 no.2
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    • pp.85-98
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    • 1987
  • To analyze the aerosol dynamics in severe accidents of LMFBR, a new computer code entitled MCAD (Multicomponent Aerosol Dynamics) has been developed. The code can treat two component aerosol system using relative collision probability of each particles as sequences of accident scenarios. Coagulation and removal mechanisms incorporating Brownian diffusion and gravitational sedimentation are included in this model. In order to see the effect of particle geometry, the code makes use of the concept of density correction factor and shape factors. The code is verified using the experimental result of NSPP-300 series and compared to other code. At present, it fits the result of experiment well and agrees to the existing code. The input variables included are very uncertain. Hence, it requires uncertainty and sensitivity analysis as a supplement to code development. In this analysis, 14 variables are selected to analyze. The input variables are compounded by experimental design method and Latin hypercube sampling. Their results are applied to Response surface method to see the degree of regression. The stepwise regression method gives an insight to which variables are significant as time elapse and their reasonable ranges. Using Monte Carlo Method to the regression model of LHS, the confidence level of the results of MCAD and their variables is improved.

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Survey on Housing Facilities and Management of Broiler Welfare Certified Farms (국내 동물복지 인증 육계농가의 사육시설 및 사육현황)

  • Cheon, Si Nae;Yoo, Geum Zoo;Jung, Ji Yeon;Kim, Chan Ho;Kim, Dong-Hoon;Jeon, Jung Hwan
    • Korean Journal of Organic Agriculture
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    • v.29 no.2
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    • pp.209-221
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    • 2021
  • The purpose of this study is to obtain basic data on housing facilities and management of broiler welfare certified farms in Korea. We investigated breeds, flock sizes, stocking density, perches, litter, plumage condition, and other diseases. In addition, we measured temperature, relative humidity, light intensity, ammonia, and carbon dioxide concentration in the barn. As result, criteria were met in all cases that we investigated. However, farmers commonly demanded relaxation of perch and litter. Perch usage of broiler was impractical due to low usage of it. Also, litter was increased, resulting in farmers' economic burden by the imbalance between supply and demand. This situation makes farmers reuse the litter. Unfortunately, there are no clear certification standards. During re-inspection, the animal welfare certification of farms was canceled due to the reuse of litter. It is difficult to modify the standard of perch due to the strong declarative meaning of animal welfare rather than the necessity of perch usage, however, the reuse of litter should be improved. It is important to think and solve any problems faced by all farms. Especially, animal welfare standards need to be improved in more clarity and rationality.

Evaluation of Lateral Pile Behavior under Cyclic Loading by Centrifuge Tests (원심모형 실험을 이용한 반복하중을 받는 모노파일 거동 평가)

  • Lee, Myungjae;Yoo, Mintaek;Park, Jeongjun;Min, Kyungchan
    • Journal of the Korean Geotechnical Society
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    • v.35 no.6
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    • pp.39-48
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    • 2019
  • This study investigated the lateral behavior of monopile embedded in the dry sand through cyclic lateral loading test using a centrifuge test. The sand sample for the experiment was the dry Jumunjin standard sand at 80% relative density and the friction angle of 38. In the experimental procedure, firstly, it was determined the static lateral bearing capacity by performing the static lateral loading test to decide the cyclic load. This derived static lateral bearing capacity values of 30%, 50%, 80%, 120% were determined as the cyclic lateral load, and the number of cycle was performed 100 times. Through the results, the experiment cyclic p-y curve was calculated, and the cyclic p-y backbone curve by depth was derived using the derived maximum soil resistance point by the load. The initial slope at the same depth was underestimated than API (1987) p-y curves, and the ultimate soil resistance was overestimated than API (1987) p-y curves. In addition, the result of the comparison with the suggested dynamic p-y curve was that the suggested dynamic p-y curve was overestimated than the cyclic p-y backbone curve on the initial slope and soil resistance at the same depth. It is considered that the p-y curve should be applied differently depending on the loading conditions of the pile.

Development of the Mass-rearing Technique for a Predatory Mite Stratiolaelaps scimitus (Acari: Laelapidae) Using the Double Box System (이중상자 시스템을 이용한 뿌리이리응애(Stratiolaelaps scimitus)의 대량생산 방법)

  • Jung, Duck-Oung;Hwang, Hwal-Su;Kim, Jin-Won;Lee, Kyeong-Yeoll
    • Korean journal of applied entomology
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    • v.57 no.4
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    • pp.253-260
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    • 2018
  • A mass-rearing method for a soil-dwelling predatory mite Stratiolaelaps scimitus (Womersley) was developed using the double box system. The rearing box consists of two, outer (22 L, 54×36×18cm3) and inner (6.5 L, 31×22×11cm3), plastic boxes. Inner box was filled with chaff (rice husks) which is used as the shelter of the predatory mites. Outer box contained 1 L of water and the inner box, then covered with a lid. This system prevents the predatory mites from escaping as well as keeping moisture of the shelter. In addition, Tyrophagus putrescentiae (Schrank), as prey mites of S. scimitus, was reared on the rice bran as a food source using the same double box system. The both mites were reared at 25±1C, 60±10 relative humidity condition. The prey mites were provided once a week. The density of predatory mites increased three times for four weeks and the final population was approximately 120,000 individuals/box (4 L). This is a simple mass-raring technique of S. scimitus and helpful for the biological control of soil pests.