• 한국안전학회지
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• 제19권1호
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• pp.1-5
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• 2004

In the present study, the gas injection system based on air-water model was designed to investigate the flow characteristics of liquid phase. A PIV system was applied to analyze the flow pattern in a ladle which gas stated to rise upward from the bottom. Gas flow is one of most important factors which could feature a flow pattern in a gas injection system. As the gas injected into the liquid, the kinetic energy of bubble transfer to liquid phase and a strong circulation flow develops in the liquid phase. Such a flow in the liquid develops vortex and improve the mixing process. Due to the centrifugal force, circulation flow was well developed near both wall sides and upper region respectively. Increasing gas flow was helpful to remove dead zone but, weak flow zone still exists in spite of the increasement of gas flow rate.

• Bulletin of the Korean Chemical Society
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• 제21권1호
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• pp.69-74
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• 2000

Applicability of Thermal field flow fractionation (ThFFF) was investigated for the analysis of masticated natural rubber (NR) adhesives produced bya hot melt mastication process. An optimum ThFFF condition for NR analysis was found by using tetrahydrofuran (THF) as a solvent/carrier and a field-programming. Low flowrate (0.3 mL/min) was used to avoid stopping the flow for the sample relaxation. Measured molecular weight distribution was used to monitor degradation of rubber during the mastication process. Rubber samples collected at three different stages of the mastication process and were analyzed by ThFFF. It was found that in an anaerobic process rubber degradation occurs at the resin-mixing (compounding) zone as well as in the initial break-down zone, while in an aerobic process most of degradation occurs at the initial breakdown zone. It was also found that E-beam radiation on NR causes a slight increase in the NR molecular weight due to the formation of a branched structure.

• 한국수산과학회지
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• 제31권5호
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• pp.749-759
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• 1998

1996년 11월 동해에 형성된 전선역에서 동물플랑크톤의 분포를 살펴본 바, 그 양은 한수역보다는 작지만 난수역 보다는 큰 것으로 나타났고, 종 조성은 매우 풍부한 것으로 나타났다. 전선역의 동물플랑크톤 군집은 양적으로는 한류수의 영향을, 종류는 난류수의 영향을 받는 것으로 나타났다. 난수역과 한수역에서는 각 해역의 서로 다른 두 정점간에 채집 시간이 낮과 밤으로 차이가 있음에도 출현하는 동물플랑크톤의 종 조성과 분포 양상이 비슷하였지만, 전선역 두 정점에서는 하루중 비슷한 시간대에 채집되었음에도 종 조성과 분포 양상에 차이가 있었다. 이는, 전선역의 수괴 혼합 진행 정도를 반영하는 지리적 차이가 동물플랑크톤의 종 조성과 분포에 영향을 주고 있음을 의미한다. 한수역의 대표적인 요각류 Metri-dia pacinca 만이 주목할 만한 일주수직이동 양상을 보였으며, 이 종의 분포가 전체 동물플랑크톤의 분포 양상을 크게 좌우하였다. 그밖의 대부분 종들은 일주 수직이동이 매우 미약하였다. 수온이 동물플랑크톤의 분포에 큰 영향을 미치는 것으로 나타났다. 수온과 주요 우점 동물플랑크톤 분포량의 상관 관계는 난수역에서는 대체로 양의 상관관계를, 한수역에서는 매우 약한 음의 상관관계를, 그리고 전선역에서는 대부분 통계적 유의성이 없는 결과를 보였다.

• 한국물환경학회지
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• 제28권1호
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• pp.26-37
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• 2012

Multi-dimensional hydrodynamic and water quality models are widely used to simulate the physical and biogeochemical processes in the surface water systems such as reservoirs and estuaries. Most of the models have adopted the Eulerian grid modeling framework, mainly because it can reasonably simulate physical dynamics and chemical species concentrations throughout the entire model domain. Determining the optimum grid cell size is important when using the Eulerian grid-based three-dimensional water quality models because the characteristics of species are assumed uniform in each of the grid cells and chemical species are represented by concentration (mass per volume). The objective of this study was to examine the effect of grid-size of a three dimensional hydrodynamic and water quality model (EFDC) on hydrodynamics and mass transport in the Saemangeum Reservoir. Three grid resolutions, respectively representing coarse (CG), medium (MG), and fine (FG) grid cell sizes, were used for a sensitivity analysis. The simulation results of numerical tracer showed that the grid resolution affects on the flow path, mass transport, and mixing zone of upstream inflow, and results in a bias of temporal and spatial distribution of the tracer. With the CG, in particular, the model overestimates diffusion in the mixing zone, and fails to identify the gradient of concentrations between the inflow and the ambient water.

• 한국추진공학회지
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• 제17권3호
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• pp.67-75
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• 2013

케로신-액체산소 로켓 엔진에 적용되는 산화제 과잉 예연소기의 냉각 성능 확인을 위한 수치 해석을 수행하였다. 예연소기 1차 연소구역을 상사하기 위하여 분사기 배열에 따른 혼합비를 바탕으로 연소가스 물성치를 계산하였고, 냉각제로서 채널을 흐르는 산소의 물성치는 실제기체 조건에 대하여 적용하였으며, 1차 연소구역과 냉각제로 쓰인 액체산소의 혼합과정은 다상혼합모델을 적용하였다. 수치 해석으로 계산된 결과를 연소시험과 비교하였으며, 이를 통하여 재생냉각 채널과 연소실에서의 물성 등을 정량적으로 파악할 수 있었다.

• 대한치과보철학회지
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• 제27권1호
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• pp.213-222
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• 1989

It is considered that self-curing resin will induce a little pulpal irritation, if mixing time is insufficient. So this study was designed to compare four different conditions between control group and three experimental groups. Canine teeth of 20 cats used, and class V cavities were prepared on maxillary canine of cats. Control group was filled with zone and other experimental groups were filled with zone after the application of the self-curing resin. Animals of the experimental and control group were sacrified at 3 days, 1, 2, 3, 4 weeks after the experiment. The finding lead to the following conclusions ; 1. Odontoblasts of first and third experimental groups were condensed irregularly and were changed at early stage, and reapir was delayed. 2. Odontoblasts of second experimental group were condensed slightly but, histologic repair was appeared at 4 weeks after the experiment 3. In all groups, the damaged odontoblastic cell layer were eventually disappeared at 4 weeks after the experiment.

• 한국해양공학회지
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• 제15권1호
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• pp.73-78
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• 2001

Soundness evaluation of a structure being constructed under the sea is usually difficult. In this study, a cross-hole sonic logging(CSL) which have been used for non-destructive test of concrete piles is adopted for the integrity test and monitoring of DCM(deep cement mixing) treated soils. Chemical and physical characteristics of raw ground materials are analysed to delineate ground environmental effects on the strength of DCM treated soils. In order to convert cross-hole sonic logging data into compressive strength, correlations between compressive strengths and wave velocities of core samples have been obtained. It is found that there is little effect of ground environment on the strength of the DCM treated soils, and the density distribution of core samples and cross-hole logging data show that a defective zone may exist in the DCM treated soils. With the time lapse, however, the defective zone has been cured and consequently, compressive strength of the DCM treated soils increases and satisfies the design parameter. From this study it can be concluded that the cross-hole sonic logging can be used for the integrity test as well as monitoring the curing stage of the structures, successfully.

• 한국항만학회지
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• 제12권2호
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• pp.269-280
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• 1998

A Wave-induced current model is developed in our study and this model is composed with wave transform model and current model. Two types of wave model are used in our study one is Copeland(1985) type which is applied in the offshore region and the other is Watanabe and Maruyama(1984) type which is applied in the surf zone. The depth-integrated and time-averaged governing equation of an unsteady nonlinear form is used in the wave induced current model. Lateral mixing radiation stresses surface and bottom stresses are considered in our current model. Copeland’s(1976) is used as a surface friction formula. Numerical solutions are obtained by Leendertse scheme and compared with Noda’s(1974) experimental results for the uniform slope coastal region test and Nishimura & Naruyama’s (1985) experimental results and numerical simulation results for the detached breakwater. The results from our wave model and wave model and wave-induced current model show good agreements with the others and also show nonlinear effects around the detached breakwater. The model in this study can be applied in the surf zone considering the friction stresses.

• Elastomers and Composites
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• 제37권4호
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• pp.234-243
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• 2002

A general scheme of a rubber structure is proposed. Using the thermomechanical method(TMA), some changes in the molecular and topological structures for uncured and cured, and unfilled and filled rubbers during processing are shown. In our investigations as region it is understood a complex structure, which is expressed at the thermomechanical curve(TMC) as a zone differed from others in thermal expansion properties. This zone is between the noticed temperatures of relaxation transitions, usually on the level like those determined by DMTA at 1Hz. These regions, which shares, are not stable, and differ in molecular-weight distribution(MWD) of chain fragments between the junctions. Differences in dynamics of the formation of the molecular and topological structures of a vulcanizate are dependent on the rubber formulation, mixing technology and curing time. Some of characteristics of these regions correlate with mechanical properties of vulcanizates what is shown for NR rubbers containing ENR or CPE as a polymeric additive. It is well known that the state of order influences diffusivity of low-molecular substances into the polymer matrix. Because of this, the two topological amorphous regions should influence the distribution of the ingredients and resulting in rubber compounds' heterogeneity, and related properties of cured rubber. Investigation of this problem is expected to be, in the future, one of the essential factors in determining further improvement of polymeric materials properties by compounding with additives and in reprocessing of rubber scrap.

• 암석학회지
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• 제11권1호
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• pp.30-48
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• 2002

울산시 동구에 위치하는 방어진 지역의 화강암에는 라파키비 조직의 장석반정이 산출된다. 라파키비 조직의 알칼리 장석 부분은 분흥색을 띠고 이를 둘러싸는 사장석 부분은 하얀색을 띠기 때문에 육안으로도 라파키비 조직을 쉽게 관찰할 수가 있다. 또한 방어진 화강암에는 특징적으로 염기성 미립 포획암이 많이 포함되어 있는데 이를 포함한 5가지의 암상, (1) 염기성 미립 포획암이 거의 없는 지역에서의 화강암(EPG), (2)염기성 미립 포획암이 풍부한 지역에서의 화강암(ERG), (3) 염기성 미립 포획암(MME), (4) 염기성 미립 포획암과 화강암사이의 혼성대(HZ), (5) 혼성대와 유사하지만 독립된 형태로 나타나는 포획암(HLE)이 관찰된다. 그리고 라파키비 조직은 이 5가지 암상 모두에서 나타나며 형태와 크기는 각 암상에서 차이가 없다. 조직에 있어서도 2mm 이내의 두께로 나타나는 사장석 맨틀이 덴드리틱 조직을 보이는 점이 5개의 암상에서 모두 관찰된다. 이는 라파키비의 형성환경에 대한 중요한 지시자로서 맨틀링이 일어나던 당시가 과냉각 환경이었음을 의미한다. 한편, 화강암 내에 염기성 미립 포획암이 나타나는 것은 마그마 혼합환경이었음을 지지하고 MME내에 라파키비와 유사한 다른 광물의 맨틀링 현상이 관찰되는 것은 마그마 혼합환경이 맨틀링을 일으키기 적절한 환경이었음을 나타낸다. 또한 혼성대(HZ)에서 라파키비 반정이 풍부하며 이 반정들이 MME로 유입되는 현상이 관찰되는 점은 혼합시 물질의 이동 및 성분의 이동이 있었음 지시한다. 이러한 마그마 혼합성인은 5개의 암상내에 불균질하게 분포하는 라파키비 반정의 분포를 잘 설명해 준다. 그러므로 방어진 지역 화강암 내의 라파키비 조직은 이 지역에 일어났던 마그마 불균질 혼합작용과 이 작용에 수반된 과냉각 및 물질의 이동에 의해 형성된 결과로 판단된다.