• 수산해양기술연구
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• 제32권3호
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• pp.266-272
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• 1996

The distribution and abundance of fish in the Cheju southeastern area was studied by the combined hydroacoustic and bottom trawl surveys in April 1994 and in July 1995, respectively. The main purpose of these investigations was to provide the basic data for this management and the biomass estimation of commercially important demersal fish stocks in this area. The hydroacoustic surveys were performed by using a 50 kHz scientific echo sounder system with a microcomputer-based echo integrator. Acoustical measurements of fish abundance and distribution were conducted along the cruise tracks of research vessel and during all trawl hauls by continuous echo sounding. The average weight-normalized target strength for demersal fish aggregations was derived from the relationship between the mean volume backscattering strength for the depth strata of trawl hauls and the weight per cubic meter of trawl catches. The geographical distribution of fish stocks in the 1994 survey area was investigated in relation to oceanographic conditions. The results obtained can be summarized as follows: 1. From the 1994 and 1995 survey data, the relationship between the mean volume backscattering strength (, dB) for the depth strata of trawl hauls and the weight (W, kg/$m^3$) per cubic meter of trawl catches was expressed by the following equation = - 32.8+ lOlog(W) The average weighted-target strength value at 50 kHz derived from this equation was .. 32.8 dB/kg. 2. In 1994 and 1995, both surveys showed a trend of decreasing fish abundance toward the southern area of the Cheju Island with high densities offish along the west coast ofth.e Tsushima Island. The highest demersal concentrations in the southern area of the CheJu Island appeared in bottom waters colder than $12^{\circ}C.$. . 3. From the results of combined bottom trawl and hydroacoustic surveys, the estunated fish densities in the southeastern area of the Cheju Island were 1.5488 x $10^-4$kg/$m^3$ in the 1994 surveyand 1.9498 x $10^-4$kg/$m^3$ in the 1995 survey, respectively.

• 유통과학연구
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• 제15권11호
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• pp.73-82
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• 2017

Purpose - This paper aims to investigate a profit maximizing incentive of foreign traders in distributing the KOSPI 200 Futures. Such an incentive may induce unsophisticated retail traders to suffer loss from speculative trading. Since Korean government increased the entry barriers of the market to protect unsophisticated traders, the market size has been decreasing while the proportion of the contract held by foreign traders has been increasing. These on going changes make the market imperfectly competitive, where a profit maximization incentives of foreign traders are expected to grow. In this paper, we attempt to find any evidence of such behavior, thereby providing implications regarding market policy and market efficiency. Research design, data, and methodology - According to Kyle(1985), an informed trader exploits his/her monopoly power optimally in a dynamic context so that he/she makes positive profit, where he/she could conceal his/her trading utilizing noise trading as camouflage. We apply the KOSPI 200 Futures market to the Kyle's model: foreign traders who take into account the effect of his/her trading to maximize expected profits as an informed trader, retail investors as noise traders, and financial institutions as market makers. To find any evidence of monopolistic behavior, we test the variants of trading volume and price data of the KOSPI 200 Futures over the period of 2009 and 2017. Results - First, we find that the price of the KOSPI 200 Futures are more volatile than the price of underlying asset. Second, we find that monopolistic foreign trader's trading order flows are consistent with exploiting his/her monopoly power to maximize profit. Finally, we find that retail investors' trading order flows are inversely consistent with maximizing profit, that is, uninformed retail investors suffer loss continuously in speculative trading against informed traders. Conclusions - Our results show that the quantity of strategic order flows may have a large effect on the price, therefore, resulting the market inefficiency. The results also imply that, in implementing regulations, the depth of the market must be considered to maintain market liquidity, and suggesting interesting research topics regarding the market structure.

• Agricultural and Biosystems Engineering
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• 제3권2호
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• pp.65-72
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• 2002

Temperature is the most influential environment parameter which affects the quality change of agricultural products in cold storage. Therefore, it is essential to keep the uniform temperature distribution in the storage room. This study was performed to analyze the air movement and temperature distribution in the forced recirculating cold storage facility and to simulate optimum storage method of green groceries using 3-D CFD(three dimensional computational fluid dynamics) computer simulation which applied the standard $textsc{k}$-$\varepsilon$ turbulence model and FVM(finite volume method). The simulation was validated by the experimental results for onion storage and the simulation model was used to simulate the temperature and velocity distribution in the storage room with reference to the change of storage method such as location of storage, no stores, bulk storage, and pallet storage. In case of no stores, internal airflow was circulated without stagnation and consequently air movement and temperature distribution were uniform. In case of bulk storage, air movement was stagnated so much and temperature distribution of onion was not uniform. Furthermore, the inner temperature of onion roses more than the initial temperature of storage. In case of pallet storage, air movement and temperature distribution of onion were so uniform that the danger of quality change was decreased.

• 태양에너지
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• 제17권3호
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• pp.3-11
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• 1997

Recently the construction of atrium buildings has increased but along with it many problems in thermal environment have arised. since the exterior wall of glass, indoor temperature is greatly influenced by weather conditions and since the space volume is very large, the vertical air temperature is not uniform. So, in this study, a Vertical Temperature Distribution Model was developed to predict the vertical air temperature of an atrium and evaluate the effects of the design parameters on the air temperature distribution of an atrium. To consider the characteristics of the vertical air temperature distribution in an atrium, the Satosh Togari's Macroscopic Model was used basically for the calculation of the vertical air temperature distribution in large space and the solar radiation analysis model and natural ventilation analysis model in atrium. And to calculate the unsteady-state inside wall surface temperature(boundary condition), the finite difference method was used. For the verification of the developed temperature distribution program, numerical evaluation of air flow by the ${\kappa}-{\varepsilon}$ turbulence model and in-situ test was conducted in parallel. The results of this study, the developed temperature distribution program was seen to predict the thermal condition of the atrium very accurately.

• 한국구조물진단유지관리공학회 논문집
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• 제17권1호
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• pp.106-113
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• 2013

콘크리트의 투수성능을 평가하는 여러 가지 비파괴시험방법 중의 하나는 표면전기저항을 측정하는 것이다. 그러나 콘크리트내에 강섬유로 인한 판단의 오류가 발생할 수 있기 때문에 강섬유 보강콘크리트에 본 표면전기저항측정방법을 적용하기에는 한계가 있다. 본 연구에서는 강섬유보강 콘크리트의 강섬유 분산도가 표면전기저항에 미치는 영향을 실험적으로 고찰하였다. 3개의 정방형 및 원형 실험체의 4개면에서의 저항치를 3번 반복하여 측정하였으며, 서로 비교하였다. 측정결과에 의하면, 원형실험체를 이용한 실험결과가 정방형 실험체의 결과에 비하여 강섬유의 영향을 일관되게 나타내고 있는 것으로 확인되었다. 또한, 강섬유의 분산도는 강섬유 혼입량에 비하여 측정결과에 미치는 영향이 미미한 것으로 나타났다. 결론적으로, 표면전기저항측정을 이용한 비파괴 평가법은 0.5%까지의 강섬유를 포함한 SFRC의 투수성 평가에 적용될 수 있는 것으로 판단된다.

• Composites Research
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• 제14권5호
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• pp.1-11
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• 2001

본 논문은 금속복합재료를 반용융상태로 재가열하여 Thixoforming을 하는데 필요한 소재를 제공하기 위한 장비 설계와 제조방법 등에 관한 내용을 소개하고 있다. 장비 설계에서 기지재내에 강화재가 균일하게 분산되도록 하기 위하여 강화재의 연속주입 방법과 강화재의 온도를 제어하는 방법을 소개하고 있다. 일정한 양의 강화재를 기지재료 내에 분산시키는 것은 균일 혼합을 위하여 필요한 기술이다. 또한 분산시 강화재의 수분제거를 위하여 강화재의 온도를 제어하면서 연속적으로 강제분산시키는 것은 균일분산을 위하여 필요하다. 기지재의 초정 $\alpha$의 크기가 강화재의 분산성에 크게 영향을 미치기 때문에 기지재의 초기 온도가 초정$\alpha$의 크기에 미치는 영향 등을 검토하여 복합재료 빌렛트의 제조조건에 이용하였다.

• 한국의학물리학회지:의학물리
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• 제28권4호
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• pp.164-170
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• 2017

One of the methods to consider the effect of respiratory motion of a tumor target in radiotherapy is to establish a treatment plan with the internal target volume (ITV) created based on an accurate analysis of the target motion displacement. When this method is applied to intensity modulated radiotherapy (IMRT), it is expected to yield a different treatment dose distribution under the motion condition according to the IMRT method. In this study, we prepared ITV-based IMRT plans with conventional IMRT using fixed gantry angle beams, RapidArc using volumetric modulated arc therapy, and tomotherapy using helical therapy. Then, the variation in dose distribution caused by the target motion was analyzed by the dose measurement in the actual motion condition. A delivery quality assurance plan was prepared for the established IMRT plan and the dose distribution in the actual motion condition was measured and analyzed using a two-dimensional diode detector placed on a moving phantom capable of simulating breathing movements. The dose measurement was performed considering only a uniform target shape and motion in the superior-inferior (SI) direction. In this condition, it was confirmed that the error of the dose distribution due to the target motion is minimum in tomotherapy. This is thought to be due to the characteristic of tomotherapy that treats the target sequentially by dividing it into several slices. When the target shape is uniform and the main target motion direction is SI, it is considered that tomotherapy for the ITV-based IMRT method has a characteristic which can reduce the dose difference compared with the plan dose under the target motion condition.

• 상하수도학회지
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• 제26권5호
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• pp.609-617
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• 2012

A dynamic water quality model is presented in order to simulate water quality under slowly varying flow conditions over time. To improve numerical accuracy, the proposed model uses a lumped system approach instead of extended period simulation, unlike the other available models. This approach can achieve computational efficiency by assuming liquid and pipe walls to be rigid, unlike the method of characteristics, which has been successfully implemented in rapidly varying flows. The discrete volume method is applied to resolve the advection and reaction terms of the transport equation for water quality constituents in pipes. Numerical applications are implemented to the pipe network examples under steady and unsteady conditions as well as hydraulic and water quality simulations. The numerical results are compared with EPANET2, which is a widely used simulation model for a water distribution system. The model results are in good agreement with EPANET2 for steady-state simulation. However, the hydraulic simulation results under unsteady flows differ from those of EPANET2, which causes a deviation in water quality prediction. The proposed model is expected to be a component of an integrated operation model for a water distribution system if it is combined with a computational model for rapidly varying flows to estimate leakage, pipe roughness, and intensive water quality.

• Steel and Composite Structures
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• 제23권3호
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• pp.251-261
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• 2017

In this paper, thermal effect on the vibration and stability of initially stressed sandwich plates with functionally graded material (FGM) face sheets is analyzed. Material properties of FGM face sheet are graded continuously in the thickness direction. The variation of FGM properties assumes a simple power law distribution in terms of the volume fractions of the constituents. The governing equations of arbitrarily initially-stressed sandwich plates including the effects of transverse shear deformation and rotary inertia are derived. The initial stress is taken to be a combination of a uniaxial extensional stress and a pure bending stress in the examples. The eigenvalue problems are formed to study the vibration and buckling characteristics of simple supported initially stressed FGM/metal/FGM plates. The effects of volume fraction index, temperature rise, initial stress and layer thickness of metal on the natural frequencies and buckling loads are investigated. The results reveal that the volume fraction index, initial stresses and layer thickness of metal have significant influence on the vibration and stability of sandwich plates with FGM face sheets.

• Investigative Magnetic Resonance Imaging
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• 제8권1호
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• pp.17-23
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• 2004

목적 : 이차원 위상대조 자기공명영상을 이용하여 나이변화와 뇌실질 부피변화 및 혈관이상의 정도에 따른 총뇌혈류량의 변화를 알고자 하였다. 대상 및 방법 : 12명의 지원자를 포함한 73명을 대상으로 T2강조 영상과 Time-of-flight 방법의 자기공명혈관촬영과 이차원 위상대조 자기공명영상을 얻었다. 정상군은 지원자 12명과 자기공명영상 및 자기공명혈관촬영에서 정상소견을 보인 21명으로서 이들은 18-29세, 30-49세, 50-66세 군으로 나누었다. 비정상군은 T2강조영상의 뇌실질부피 변화정도와 자기공명 혈관촬영의 동맥경화 정도에 따라 mild reduction군(17명) , marked reduction군(12명)으로 나누었고, 뇌실질이 증가한 increased volume군(6명)과 Moya-moya군(5명)으로 분류하였다 뇌혈류는 위상대조 자기공명영상의 속도-혈류 곡선으로부터 양쪽 내경동맥과 추골동맥에서 측정하고 합하여 뇌의 총뇌혈류량으로 하였으며, 각군 사이의 혈류량을 비교 관찰하였다. 결과 정상군의 총뇌혈류량은 18-29세군은$12.0{\pm}2.1ml/sec$, 30-49세군은 $11.8{\pm}1.9m1/sec$, 50-66세군은 $10.9{\pm}2.2ml/sec$였다. 비정상군 중에서 mild reduction 군은 $9.5{\pm}2.5ml/sec$, marked reduction 군은 $7.6{\pm}2.0ml/sec$, increased volume군은 $7.3{\pm}1.2ml/sec$, Moya-moya군은 $7.0{\pm}1.1ml/sec$였다. 결론 : 총뇌혈류량은 나이 증가에 따라 감소하였고, 뇌실질부피 감소와 동맥경화 정도에 따라 감소하였으며 increased volume군과 Moya-moya군에서도 감소하였다. 이차원 위상대조 자기공명영상은 나이변화나 뇌실질의 부피변화와 혈관이상을 초래하는 다양한 뇌질환에서 총뇌혈류량을 관찰할 수 있는 유용한 방법이라고 생각된다.