• Nuclear Engineering and Technology
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• 제33권1호
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• pp.93-101
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• 2001

The spacer grid is one of the main structural components in the fuel assembly, which supports the fuel rods, guides cooling water, and protects the system from an external impact load, such as earthquakes. Therefore, the mechanical and structural properties of the spacer grids must be extensively examined while designing them. In this paper, a numerical method for predicting the buckling strength of spacer grids is presented. Numerical analyses on the buckling behavior of the spacer grids are performed for a various array of sizes of the grids considering that the spacer grid is an assembled structure with thin-walled plates and imposing proper boundary conditions by nonlinear dynamic finite element method using ABAQUS/Explicit. Buckling tests on several numbers of specimens of the spacer grid were also carried out in order to compare the results between the test and the simulation result. The drop test is accomplished by dropping a carriage on the specimen at a pre-determined position. From this test, the specimens are buckled only at the uppermost and the lowermost layer among the multi-cells, which is similar to the local buckling at the weakest point of the grid structure. The simulated results also similarly predicted the local buckling phenomena and were found to give good correspondence with the experimental values for the thin-walled grid structures.

• 한국분말재료학회지
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• 제20권3호
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• pp.191-196
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• 2013

Nano-sized cobalt powder was fabricated by wet chemical reduction method at room temperature. The effects of various experimental variables on the overall properties of fabricated nano-sized cobalt powders have been investigated in detail, and amount of NaOH and reducing agent and dropping speed of reducing agent have been properly selected as experimental variables in the present research. Minitab program which could find optimized conditions was adopted as a statistic analysis. 3D Scatter-Plot and DOE (Design of Experiments) conditions for synthesis of nano-sized cobalt powder were well developed using Box-Behnken DOE method. Based on the results of the DOE process, reproducibility test were performed for nano-sized cobalt powder. Spherical nano-sized cobalt powders with an average size of 70-100 nm were successfully developed and crystalline peaks for the HCP and FCC structure were observed without second phase such as $Co(OH)_2$.

• 전기화학회지
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• 제1권1호
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• pp.8-13
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• 1998

This work presents the way how to evaluate the degree of reversibility of the discharging process undergone by the nickel hydroxide film cathodically deposited on pure nickel as a positive electrode for electrochemical capacitor using the combined cyclic voltammetry and potential drop method, supplemented by galvanostatic discharge and open-circuit potential transient methods. The time interval necessary just to establish the current reversal of anodic to cathodic direction from the moment just after applying the potential inversion of anodic to cathodic direction, was obtained on cyclic voltammogram. The cathodic charge density passed upon dropping the applied potential, was calculated on potentiostatic current density-time curve. Both the time interval and the cathodic charge density in magnitude can be regarded as being measures of the degree of reversibility of the discharging process undergone by the positive active material for supercapacitor, i.e. , the longer the time interval is, the lower is the degree of reversibility and the greater the cathodic charge density is, the higher is the degree of reversibility. From the applied potential dependences of the time interval and cathodic charge density, discharge at $0.42 V_{SCE}$ was determined to be the most reversible.

• 한국세라믹학회지
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• 제37권4호
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• pp.308-313
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• 2000

Hydrous titanium oxide particles with anatase phase were prepared from 0.05 mol TiCl4 solution using NH4HCO3 as precipitant by the droopping precipitant method. The sequential change of pH is completed by a sudden and steep increase in a pH value of the range of 6~7 to which the concentration of adsorbed OH- and H+ ions on TiO2 surface is equal. Rutile phase started precipitating with anatase phase as an increase of reaction temperature above 6$0^{\circ}C$ in aqueous 0.05mol TiCl4 solution and its specific surface area was found to decrease from 452 $m^2$/g($25^{\circ}C$) to 164$m^2$/g(8$0^{\circ}C$). Specific surface area decreased rapidly when anatase powders precipitated at 4$0^{\circ}C$ were heat-treated at temperature higher 40$0^{\circ}C$. FT-IR result confirmed that it was due to the decrease of OH species within hydrous titanium oxides. The loss of ethanol after illumination of the powder heated at $600^{\circ}C$ and $700^{\circ}C$ for 4 h was 66 and 68.8%, respectively.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술회의 논문집 정보 및 제어부문 B
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• pp.555-558
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• 2003

When a fault relating to the urgent alarm occurs, we must prevent control rods from dropping and make one of two grippers in Control Rod Drive Mechanism (CRDM) grip the drive rod laking a control rod assembly. If a gripper with any problem is ordered to grip the drive rod, the gripper which cannot latch the rod stably will fail to take the rod. On the purpose of escaping this bad case, we order two grippers to hold the drive rod and enhance the reliability of holding control rods. This action is called the double hold. In the middle of the movement of the drive rod, the latching of the drive rod can cause friction between a gripper and the drive rod. This state may give damage to both the gripper and the drive rod. In this paper, we have devised the method which can have two grippers hold the drive rod more stably, without damaging the equipment.

• 대한한방소아과학회지
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• 제34권4호
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• pp.31-42
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• 2020

Objectives The purpose of this study is to perform a review on recent researches of Hataedock, a traditional method of removing fetal toxin by dropping herbal extracts in the mouth, to appraise its preventive and therapeutic effects of diseases. Methods Studies of Hataedock were extracted from both Chinese and Korean medical journals published within 10 years, from January 2010 to January 2020. Clinical studies and experimental researches were analyzed and categorized to skin disease, allergic rhinitis, intestinal mucosa inflammation and anal fistula for further evaluation. Results Among 194 studies were searched and screened, 22 met designated criteria. Hataedock showed the effectiveness in treating skin disease, allergic rhinitis, intestinal mucosa inflammation and anal fistula by maintaining skin barrier and regulating immune system. Coptis japonica, Glycyrrhiza uralensis, and Fermented Glycine max were mainly used as herbal extracts in Hataedock. Conclusion This study shows the recent research trends of Hataedock and suggests that Hataedock can be considered as a method of treatment or prevention to some of the incurable chronic diseases.

• Corrosion Science and Technology
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• 제20권3호
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• pp.105-111
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• 2021

In oxidizing nitric acid solutions, stainless steel undergoes intergranular corrosion accompanied by grain dropping and changes in the corrosion rate. For the safe operation of reprocessing plants, this mechanism should be understood. In this study, we constructed a three-dimensional computational model using a cellular automata method to simulate the intergranular corrosion propagation of stainless steel. The computational model was constructed of three types of cells: grain (bulk), grain boundary (GB), and solution cells. Model simulations verified the relationship between surface roughness during corrosion and dispersion of the dissolution rate of the GB. The relationship was investigated by simulation applying a constant dissolution rate and a distributed dissolution rate of the GB cells. The distribution of the dissolution rate of the GB cells was derived from the intergranular corrosion depth obtained by corrosion tests. The constant dissolution rate of the GB was derived from the average dissolution rate. Surface roughness calculated by the distributed dissolution rates of the GBs of the model was greater than the constant dissolution rates of the GBs. The cross-sectional images obtained were comparable to the corrosion test results. These results indicate that the surface roughness during corrosion is associated with the distribution of the corrosion rate.

• Earthquakes and Structures
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• 제24권3호
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• pp.205-215
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• 2023

Currently, many studies are underway at home and abroad on the seismic performance evaluation and dry construction method of the masonry structure. In this study, a dry stack masonry wall system without mortar using concrete blocks is proposed, and investigate the seismic performance of dry filling wall frames through experimental studies. First, two types of standard blocks and key blocks were designed to assemble dry walls of concrete blocks. And then, three types of experiments were manufactured, including pure frame, 1/2 height filling wall frame, and full height filling wall frame, and cyclic load experiments in horizontal direction were performed to analyze crack patterns, load displacement history, rebar deformation yield, effective stiffness change, displacement ductility, and energy dissipation capacity. According to the experimental results, the full height filling wall frame had the largest horizontal resistance against the earthquake load and showed a high energy dissipation capacity. However, the 1/2 height filling wall frame requires attention because the filling wall constrains the effective span of the column, limiting the horizontal displacement of the frame. In addition, the concrete block was firmly assembled in the vertical direction of the wall as the horizontal movement between the concrete blocks was allowed within installation margin, and there was no dropping of the assembled concrete block.

• 한국정보과학회논문지:시스템및이론
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• 제33권5호
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• pp.282-296
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• 2006

무선 클라이언트-서버 환경에서 데이타 브로드캐스팅은 효율적인 데이타 보급방식이다. 서버가 데이타를 방송하면 그 중 일부를 클라이언트가 캐시에 보관하여, 낮은 통신 대역폭과 한정된 자원을 극복하고 데이타 접근 시간 등을 절약할 수 있다. 서버는 또한 무효화보고서를 방송하여 서버 데이타와 클라이언트가 캐싱한 데이타간의 일관성을 유지할 수 있도록 한다. 기존의 캐시 일관성 문제를 해결하기 위한 대부분의 연구는, 접속 단절 시간이 너무 길어서 수신하지 못한 무효화 보고서의 수가 일정 한도(윈도우 크기)를 넘으면 단순히 캐시 전체를 삭제하는 방법을 사용한다. 이 논문은 이러한 긴 접속 단절 시간의 경우에도 이동 클라이언트의 캐시 재사용율을 높일 수 있는 기법을 제시한다. 캐시의 일관성 여부에 관계없이 무조건 전체 캐시 내용을 지우는 대신, 클라이언트는 모든 데이타를 지우는 비용과 선택적으로 지우는 비용을 추측한다. 만일 모든 데이타를 지우는 비용이 높아지는 경우에는 클라이언트는 캐시를 유지하고 검증 요청을 위해 업링크를 사용하여 유효하지 않은 데이타만을 선택적으로 지운다. 이 방법은 캐시 유지비용을 추측할 때 캐시된 데이타의 갱신 비율과 방송 빈도들을 함께 고려하므로, 효율적으로 캐시 재사용율을 높일 수 있다는 것을 모의 실험 결과를 통해 증명한다.

• 한국정보과학회논문지:정보통신
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• 제36권2호
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• pp.69-79
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• 2009

오늘날의 인터넷은 일상생활에서 필수적인 요소가 되었으며, 인터넷의 이상 현상은 사회적 문제가 되고 있다. 이 때문에 인터넷 트래픽의 특성을 연구하기 위한 인터넷 측정 연구가 주목을 받고 있다. 특히 최근에는 트래픽 분산 그래프(TDG, Traffic Dispersion Graph)라는 새로운 트래픽 분석 기법이 제안되었다. TDG는 기존의 트래픽의 통계적 표현과 분석이 아닌, 그래프를 이용하여 네트워크 요소들의 상호작용을 표현하는 기법이다. 본 연구에서는 새로운 이상 탐지 기법의 패러다임과 TDG를 활용한 이상 탐지 기법을 제시한다. 기존의 이상 탐지 패러다임은 "비정상 패킷이나 플로우(Abnormal Packets or Flows)를 탐지하여 제거하자"는 것이지만, 본 연구에서는 "이상 트래픽의 근원이 되는 이상 호스트(Anomalous Hosts)를 탐지하여 이상 현상에 대응할 것"을 제안한다. 이를 위해서 TDG 클러스터링 기법(TDG Clustering Technique)을 고안하였다. 제안한 기법에 대한 실험에서 짧은 시간 안에 웜 바이러스(Worm Virus)에 감염된 호스트들을 찾아낼 수 있었고, 그 호스트들이 발생하는 이상 트래픽을 제거하여 정상적인 트래픽을 얻을 수 있었다. TDG 클러스터링 기법은 연산 속도가 빠르므로 실시간 이상 탐지에 적용될 수 있을 것으로 기대된다.