• 대한교통학회지
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• 제23권8호
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• pp.101-111
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• 2005

대중교통의 서비스 개선은 접근성이 개선되어 대중교통 이용자의 수요를 늘리는 중요한 역할로 작용한다. 본 연구는 서울시가 최근 2004년 7월 대대적으로 실시한 대중교통체계 개편 후 지하철이용자의 접근성 변화를 설명하기 위한 것이다. 첫번째 연구목적은 공간상호작용 개념을 포함하는 한센형 접근성 지표를 지하철-버스간 환승할인 전후의 자료로부터 추정하고 비교 설명한다. 두번째 연구목적은 개편 전 후의 접근성 지표가 단기의 교통과 토지이용간의 관계를 설명하는 통행배분모형에 어떠한 역할을 하는지를 해석하는 것이다. 분석에 사용한 비접촉식 카드승차권과 접촉식 승차권 자료는 2004년 5월의 하루 평균 지하철 기종점자료와 서비스 변화가 발생한 2004년 8-9월의 하루 평균 지하철 기종점자료이다. 결론적으로 비접촉식 카드 이용자의 접근성이 향상되어 대중교통개편의 수혜자가 된 것으로 나타났으며, 그 효과는 서울지역에 넓게 분포된 것으로 나타났다. 통행배분모형연구에서 접근성 지표의 역할은 중요한 것으로 나타났으며, 기존 모형에서 접근성 지표의 변수가 생략되면, 추정된 모형의 파라메터 들이 편기(bias)된다는 것을 발견하였다. 그리고, 접근성 지표의 생략으로 인한 통행배정모형의 예측력 저하 원인을 규명하는 노력이 시도되었다.

• 한국환경과학회지
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• 제22권6호
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• pp.651-666
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• 2013

This study introduces a novel approach to the differentiation of two phenomena, Asian Dust and haze, which are extremely difficult to distinguish based solely on comparisons of PM10 concentration, through use of the Optical Particle Counter (OPC), which simultaneously generates PM10, PM2.5 and PM1.0 concentration. In the case of Asian Dust, PM10 concentration rose to the exclusion of PM2.5 and PM1.0 concentration. The relative ratios of PM2.5 and PM1.0 concentration versus PM10 concentration were below 40%, which is consistent with the conclusion that Asian Dust, as a prime example of the coarse-particle phenomenon, only impacts PM10 concentration, not PM2.5 and PM1.0 concentration. In contrast, PM10, PM2.5 and PM1.0 concentration simultaneously increased with haze. The relative ratios of PM2.5 and PM1.0 concentration versus PM10 concentration were generally above 70%. In this case, PM1.0 concentration varies because a haze event consists of secondary aerosol in the fine-mode, and the relative ratios of PM10 and PM2.5 concentration remain intact as these values already subsume PM1.0 concentration. The sequential shift of the peaks in PM10, PM2.5 and PM1.0 concentrations also serve to individually track the transport of coarse-mode versus fine-mode aerosols. The distinction in the relative ratios of PM2.5 and PM1.0 concentration versus PM10 concentration in an Asian Dust versus a haze event, when collected on a national or global scale using OPC monitoring networks, provides realistic information on outbreaks and transport of Asian Dust and haze.

• Membrane and Water Treatment
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• 제1권3호
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• pp.171-179
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• 2010

The transport of selected salts of sulphuric acid (cobalt, copper, iron(II), manganese, nickel and zinc sulphate) through an anion-exchange membrane Neosepta-AFN was investigated in a counter-current continuous dialyzer at various salt concentrations and volumetric liquid flow rates. The basic transport characteristics - the rejection coefficient of salt and the permeability of the membrane - were calculated from measurements at steady state. The salt concentration in model mixtures was changed in the limits from 0.1 to 1.0 kmol $m^{-3}$ and the volumetric liquid flow rate of the inlet streams was in the limits from $8{\times}10^{-9}$ to $24{\times}10^{-9}m^3\;s^{-1}$. Under the experimental conditions given, the rejection coefficient of salts tested was in the range from 65% to 94%. The lowest values were obtained for iron(II) sulphate, while the highest for copper sulphate. The maximum rejection of salt was reached at the highest volumetric liquid flow rate and the highest salt concentration in the feed. The permeability ($P_A$) of the Neosepta-AFN membrane for the individual salts was in the range from $0.49{\times}10^{-7}m\;s^{-1}$ to $1.8{\times}10^{-7}m\;s^{-1}$ and it can be described by the following series: $P_{FeSO_4}$ < $P_{NiSO_4}$ < $P_{ZnSO_4}$ < $P_{CoSO_4}$ < $P_{MnSO_4}$ < $P_{CuSO_4}$. The permeability of the membrane was strongly affected by the salt concentration in the feed - it decreased with an increasing salt concentration.

• 한국ITS학회 논문지
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• 제11권3호
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• pp.102-111
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• 2012

고속도로 교통사고는 타 도로에 비해 고속주행으로 인한 사고피해가 클 수 밖에 없으며, 특히 인적피해는 사회적인 큰 문제가 되고 있다. 본 논문에서는 고속도로 사고 중, 인적피해가 발생한 사고와 그렇지 않은 사고에 대한 사고 특성의 차이점을 규명하고자 하였다. 이를 위해 로지스틱 회귀모형을 활용하여, 두 사고 유형에 영향을 주는 사고 요인들을 찾아내었다. 분석 결과, 도로선형이 직선이고 방호울타리가 존재하며, 남성, 비고령자일 경우 운전자 과실 및 과속으로 인해 인적 사고로 이어질 가능성이 높았으며, 이에 대한 대비가 필요할 것으로 판단된다. 본 연구결과를 토대로, 인적피해가 발생한 사고와 이와 연관된 주요 설명 인자들을 찾아냄으로써 고속도로 안전정책 수립에 중요한 시사점을 찾아낼 수 있을 것이다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2291-2296
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• 2007

Thermal transport from vertical heated surface to falling liquid film in a channel has been investigated experimentally. Air-flow is introduced into channel to make a counter flow against falling liquid film. This problem is of particular interest in the design of direct contact heat exchange system, such as cooling tower, evaporative cooling system, absorption cooling system, and distillation system. The effects of channel width and air flow rate on the heat transfer to falling liquid film are studied in detail. The results obtained indicate that heat transfer rate is gradually decreased with an increase in the channel width without air flow as well as with air flow in a channel. It is also found that heat transfer rate of air-flow is increased while heat transfer rate of falling liquid film is decreased with an increase in the air flow rate at a given channel width. However, total heat transfer rate form the heated surface is increased as the air flow rate is increased.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3440-3445
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• 2007

For proton exchange membrane fuel cell, it is very important to design the flow channel on separation plate optimally to maximize the current density at same electrochemical reaction surface and reduce the concentration polarization occurred at high current density. In this paper, three dimensional computation model including anode and cathode domain together was developed to examine effects of flow patterns and operation conditions such as humidity and operating temperature on performance of fuel cell. Results show that voltage at counter flow condition is higher than that at coflow condition in parallel and interdigitated flow pattern. And fuel cell with interdigitated flow pattern which has better mass transport by convection flow through gas diffusion layer has higher performance than with parallel flow pattern but its pressure drop is increased such that the trade off between performance and pressure drop should be considered for selection of flow pattern of fuel cell.

• Membrane and Water Treatment
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• 제11권3호
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• pp.201-206
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• 2020

Electrodialysis (ED) is used in wastewater treatment, during the processing and recovery of beneficial materials, to produce usable water. In this study, sulfate and chlorine ions, which are the anions majorly used for electroplating, were studied as factors affecting the recovery of copper, nickel and water from wastewater by electrodialysis. Although the removal rates of copper and nickel ions were slightly higher with the use of chlorine ions than of sulfate ions, the removal efficiencies were above 99.9% under all experimental conditions. The metal ions of the plating wastewater flowed through the ion exchange membrane of the diluate tank and the concentrate tank while all the water moved together due to electro-osmosis. The migration of water from the diluate tank to the concentrate tank was higher in the presence of a monovalent chloride ion compared to that of a divalent sulfate ion. When sulfate was the anion used, the recoveries of copper and nickel increased by about 25% and 30%, respectively, as compared to the chloride ion. Therefore, when divalent ions such as sulfate are present in the electrodialysis, it is possible to reduce the movement amount of water and highly concentrate the copper and nickel in the plating wastewater.

• Macromolecular Research
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• 제14권2호
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• pp.199-204
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• 2006

Remarkably high and stable separation performance for olefin/paraffin mixtures was previously reported by facilitated olefin transport through ${\pi}$-complex membranes consisting of silver ions dissolved in poly(hexamethylenevinylene) (PHMV). In this study, the ${\pi}$-complex formation of $AgBF_4,\;AgClO_4\;and\;AgCF_{3}SO_3$ with PHMV and their ionic interactions were investigated. FT-Raman spectroscopy showed that the C=C stretching bands of PHMV shifted to a lower frequency upon incorporation of silver salt, but the degree of peak shift depended on the counter-anions of salt due to different complexation strengths. The symmetric stretching modes of anions indicated the presence of only free ions up to [C=C]:[Ag]=1:1, demonstrating the unusually high solubility of silver salt in PHMV. Above the solubility limit, the ion pairs and higher-order ionic aggregates started to form. The coordination number of silver ion for C=C of PHMV was in the order $AgBF_4$ > $AgClO_4$ > $AgCF_{3}SO_3$, but became similar at [C=C]:[Ag]=1:1. The different coordination number was interpreted in terms of the different transient crosslinks of silver cations in the complex, which may be related to both the interaction strength of the polymer/silver ion and the bulkiness of the counteranion.

• International Journal of Contents
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• 제6권3호
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• pp.89-96
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• 2010

The International air transportation industry provides a vital communication link which brings prosperity to many states in our modern age. This invaluable link has been threatened by terrorism. Airlines have been one of the most attractive targets in the eyes of terrorists for several reasons, including particularly the international and symbolic nature of aviation, and the potential of multigovernmental involvement which can inevitably generate wide publicity. Terrorist attacks against civil aviation have been committed since the earliest days of civil aviation history. The first attack against civil aircraft dates back to the early 1930s. Since then, aircraft hijacking and other forms of attack against air transport operations have become one of the most serious challenges to the safety of flying. In recent years, a new form of threats against civil aviation has appeared. Man-portable air defense systems (MANPADS) in the hands of criminals, terrorists, and other non-state actors pose a serious potential threat to passenger air travel, the commercial aviation industry, and military aircraft around the world. The purpose of this study is to provide some countermeasures against such attacks. In order to foster a better understanding of the problem, an introduction of MANPADS and a brief history of attacks using MANPADS are presented. It also examines the level of threats, trends of attacks using MANPADS and the possible countermeasures to be taken by the international community.

• 대한기계학회논문집B
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• 제32권5호
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• pp.335-341
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• 2008

Thermal transport from vertical heated surface to falling liquid film in a channel has been investigated experimentally. Air-flow is introduced into channel to make a counter flow against falling liquid film. This problem is of particular interest in the design of direct contact heat exchange system, such as cooling tower, evaporative cooling system, absorption cooling system, and distillation system. The effects of channel width and air flow rate on the heat transfer to falling liquid film are studied in detail. The results obtained indicate that heat transfer rate is gradually decreased with an increase in the channel width without air flow as well as with air flow in a channel. It is also found that heat transfer rate of air-flow is increased while heat transfer rate of falling liquid film is decreased with an increase in the air flow rate at a given channel width. However, total heat transfer rate from the heated surface is increased as the air flow rate is increased.