• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2004년도 추계학술발표논문집(상)
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• pp.137-140
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• 2004

최근 모바일 기기의 보급이 증가되고, 고급 어플리케이션의 동작이 가능해지는 등 모바일 장비의 사용 편이성이 급속도로 증가되고 있다. 또한 GPS 기술의 발전으로 인해 위치 기반 서비스가 여러 분야에서 널리 사용되고 있다. 본 논문에서는 고정된 노선을 이동하는 버스를 대상으로 목적지까지의 최단 시간 경로를 제공하는 교통 정보 시스템을 제안한다. 이를 위해 우선, 이동 객체인 버스와 관련된 정보를 효율적으로 저장, 관리, 검색할 수 있는 스키마와 질의 모델을 제안한다. 또한, 제안된 시스템에서는 최단 시간 경로를 위해 버스의 노선 정보 및 위치 정보, 정류장간 소요 시간 정보, 사용자의 근접 정류장까지의 이동 시간, 사용자의 도보 이동 시간 등의 정보를 활용한다. 대부분의 위치기반 서비스를 위한 시공간데이터베이스 기술에서는 이동 객체가 시간의 흐름에 따라 속도와 방향의 변화로 인한 임의의 동선으로 움직인다고 가정하고 있으며, 버스와 같이 고정된 노선을 이동하는 이동 객체의 관리 기법은 다루어지지 않고 있다. 따라서 본 논문의 연구 결과는 고정된 노선을 이동하는 이동 객체의 저장 및 이동 객체의 미래 위치 예측 기법에 활용될 수 있다.

• 한국분말재료학회지
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• 제15권2호
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• pp.148-155
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• 2008

Nano magnetite particles have been prepared by two step reaction consisting of urea hydrolysis and ammonia addition at certain ranges of pH. Three different concentrations of aqueous solution of ferric ($Fe^{3+}$) and ferrous ($Fe^{2+}$) chloride (0.3 M-0.6 M, and 0.9 M) were mixed with 4 M urea solution and heated to induce the urea hydrolysis. Upon reaching at a certain pre-determined pH (around 4.7), 1 M ammonia solution were poured into the heated reaction vessels. In order to understand the relationship between the concentration of the starting solution and the final size of magnetite, in-situ pH measurements and quenching experiments were simultaneous conducted. The changes in the concentration of starting solution resulted in the difference of the threshold time for pH uprise, from I hour to 3 hours, during which the akaganeite (${\beta}$-FeOOH) particles nucleated and grew. Through the quenching experiment, it was confirmed that controlling the size of ${\beta}$-FeOOH and the attaining a proper driving force for the reaction of ${\beta}$-FeOOH and $Fe^{2+}$ ion to give $Fe_3O_4$ are important process variables for the synthesis of uniform magnetite nanoparticles.

• 한국표면공학회지
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• 제49권1호
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• pp.1-13
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• 2016

This review deals with one of the surface modification techniques, chemical conversion coating and particularly cerium-based conversion coatings (CeCC) as a promising substitute for chromium and phosphate conversion coating on magnesium and its alloys. The CeCCs are commonly considered environmentally friendly. The effects of surface preparation, coating thickness, bath composition, and e-paint on the corrosion behavior of CeCCs have been studied on the AZ31 magnesium alloy. This review also correlates the coating microstructural, morphological, and chemical characteristics with the processing parameters and corrosion protection. Results showed that the as-deposited coating system consists of a three layer structure (1) a nanocrystalline MgO transition layer in contact with the Mg substrate, (2) a nanocrystalline CeCC layer, and (3) an outer amorphous CeCC layer. The nanocrystalline CeCC layer thickness is a function of immersion time and cerium salt used. The overall corrosion protection was crucially dependent on the presence of coating defects. The corrosion resistance of AZ31 magnesium alloy was better for thinner CeCCs, which can be explained by the presence of fewer and smaller cracks. On the other hand, maximum corrosion protection was achieved when AZ31 magnesium samples with thin CeCCs are e-painted. The e-paint layer further restricts and hinders the movement of chloride and other aggressive ions present in the environment from reaching the magnesium surface.

• 한국정밀공학회지
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• 제33권12호
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• pp.993-998
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• 2016

In today's manufacturing industries, the demand for light non-ferrous materials is considerable due to the need to improve productivity and manufacturability. Since the surface roughness of a material is important for improving the functionality of machined parts, various techniques for surface treatments have been developed to obtain non-ferrous materials with low roughness. A superfinishing method utilizing polishing films is generally applied to the anodized surface of Al7075 in order to improve its roughness. The objective of this research is to determine through experiment the parameters that facilitate the shortest processing time, using a superfinishing method, for reaching a roughness of Ra $0.2{\mu}m$. This objective is met by applying the Taguchi method in the experiments. Through the experiments of superfinishing, the effectiveness of the parameters adopted for the surface treatment is demonstrated.

• 한국화재소방학회논문지
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• 제25권2호
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• pp.132-137
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• 2011

부속실 단독가압의 제연설비 구역에서 계단실 출입문의 크기 변화가 개방 및 폐쇄조건에 미치는 영향을 분석하기 위해서 자동폐쇄장치의 구조와 저항모멘트의 관계를 정리하였으며, 부속실 출입문의 크기 변화를 고려하여 개방력과 폐쇄력을 측정하였다. 그 결과 부속실 출입문의 크기가 증가할수록 개방 및 폐쇄조건에 도달하기 위한 힘의 크기는 증가하였으며, 폐쇄시간, 회전속도, 회전각도와 힘의 관계, 자동폐쇄장치의 효율을 고려한 부속실 출입문의 설계범위가 존재함을 확인하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2012년도 제38회 춘계학술대회논문집
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• pp.4-10
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• 2012

75톤 추력급 터보펌프 터빈의 토크 특성을 성능시험 데이터를 바탕으로 분석하였다. 터빈의 비토크는 해석적으로 고정된 압력비에서 보정 선속도의 일차함수로 표현되며 이를 시험적으로 확인하였다. 일정 압력비 이상의 영역에서는 보정선속도-비토크 변화가 일정하게 나타나는 현상도 아울러 발견하였다. 분석된 토크 특성과 파이로 시동기의 시험 측정 데이터를 이용하여 터보펌프의 시동특성을 예측한 결과 터보펌프 설계회전수의 약 50%의 수준에 이르는 시간은 0.7초 이내인 것으로 나타났다. 파이로 시동기에서 터빈입구까지의 열손실은 최대회전수를 약 90 rpm 줄어들게 하는 것으로 예측되었다.

• 설비공학논문집
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• 제11권5호
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• pp.588-597
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• 1999

Sokkuram grotto, a UNESCO cultural heritage in Kyongju Korea, was originally covered with crushed rocks over its dome with ventilating holes. The grotto was perfectly preserved for more than 12 centuries until the upper structure was replaced with a concrete dome in the early 20th century to protect from total collapse. Since then, heavy dew formed on the granite surface to seriously damage the sculptures until it was further remodeled with air-conditioning facilities in the 60s. It is considered that the original upper porous structure had a dehumidifying capability. This research is made to unveil the dehumidifying mechanism of the rock layer during the rainy season in that area. A rock layer and a concrete layer are tested in a temperature/humidity-controlled room. No dew formation is observed for the two specimen for continued sunny days or continued rainy days. However, heavy dew formed on the concrete surface for a sunny day after long rainy days. It is thought that the sun evaporates water on the ground and dew is formed at the surface as the highly humid air touches the yet cold concrete. On the contrary, no dew formation is observed for the rock layer at any time. Even in the above worst situation, air flows downward through the cool rock layer and moisture is removed before reaching inside. Temperature measurement, flow visualization, observation of dew formation and measurement of air velocity are made to verify the mechanisms.

• Animal cells and systems
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• 제11권1호
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• pp.17-22
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• 2007

The effects of antimetabolite 6-AN (6-amino-nicotinamide) on viability and morphology of L6 myoblast cells have been investigated. 6-AN ($100{\mu}M$) induced a time-dependent decrease in cell viability with respect to the untreated control cells. Following 6-AN administration the viability rate started to decline sharply, reaching about 23% of the untreated control cells at 48 h. Inverted phase-contrast microscopy revealed that 6-AN caused characteristic morphological changes such as irregularly elongated and stellate shape of cells, round-shaped nucleus, cytoplasmic vacuolization, irregular cell arrangements and formation of large spaces among cell clusters. The concentrations of ATP and $NAD^{+}$ in the 6-AN treated cells were significantly lower (p < 0.01) than those of the untreated control cells. In contrast, the concentration of AMP was significantly increased by the 6-AN treatment. Activities of catalase, superoxide dismutase and glutathione peroxidase in 6-AN treated cells were significantly higher (p < 0.01) than those of the untreated control cells. The activities of glyceraldehyde-3-phosphate dehydrogenase in 6-AN treated cells were significantly lower (p < 0.01) than those of the untreated control cells. The results suggest that 6-AN caused marked reduction of cell viability and alterations of some important metabolites and enzymes.

• 아태비즈니스연구
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• 제9권4호
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• pp.157-180
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• 2018

This paper empirically analyzes how working conditions of employees and executives affect Korean companies' survival. To this end, a survival analysis based on the accelerated failure time model is conducted from the end of December 2012 to the end of September 2018 on the 2012 year-end financial data for corporations whose common stocks have ever been listed either in the KOSPI market or in the KOSDAQ market with fiscal year ending at the end of December. The analysis shows that the average wage level per employee and the number of executives relative to the number of employees threaten while the average duration of service for female employees prolongs firm survival. Here, the average wage level per employee has turned out to worsen firm survivability regardless of the gender of employees in question while the average duration of service improves firm survivability only in case the employees are female: the average duration of service for male employees or the entire employees has turned out not to have any statistically significant influence on firm survival. The average compensation per executive and the percentage of temporary employees have turned out not to have any statistically significant influence on firm survival while the percentage of female employees has shown statistically significant positive influence on firm survival in some, although not all, models employed in our study. These results are expected to be a good reference in the course of our reaching agreements regarding the improvement of working conditions either between firms and employees or among the members of the entire society.

• The Korean Journal of Physiology and Pharmacology
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• 제23권1호
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• pp.81-87
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• 2019

Ketamine has long been used as an anesthetic agent. However, ketamine use is associated with numerous side effects, including flashbacks, amnesia, delirium, and aggressive or violent behavior. Ketamine has also been abused as a cocktail with ecstasy, cocaine, and methamphetamine. Several studies have investigated therapeutic applications of ketamine, demonstrating its antidepressant and anxiolytic effects in both humans and rodents. We recently reported that neonatal maternal separation causes enhanced anxiety- and aggressive-like behaviors in adolescent. In the present study, we evaluated how acute and chronic ketamine administration affected the behavioral consequences of neonatal maternal separation in adolescent mice. Litters were separated from dams for 4 hours per day for 19 days beginning after weaning. Upon reaching adolescence (post-natal day 35-49), mice were acutely (single injection) or chronically (7 daily injections) treated with a sub-anesthetic dose (15 mg/kg) of ketamine. At least 1 h after administration of ketamine, mice were subjected to open-field, elevated-plus maze, and resident-intruder tests. We found that acute ketamine treatment reduced locomotor activity. In contrast, chronic ketamine treatment decreased anxiety, as evidenced by increased time spent on open arms in the elevated-plus maze, and remarkably reduced the number and duration of attacks. In conclusion, the present study suggests that ketamine has potential for the treatment of anxiety and aggressive or violent behaviors.