• Journal of Korea Water Resources Association
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• v.47 no.10
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• pp.879-889
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• 2014

In this study, to estimate loss of life considered flood characteristics using the relationship derived from analysis of historical dam break cases and the factors determining loss of life, the loss of life module applying in LIFESim and loss of life estimation by means of a mortality function were suggested and applicability for domestic dam watershed was examined. The flood characteristics, such as water depth, flow velocity and arrival time were simulated by FLDWAV model and flood risk area were predicted by using inundation depth. Based on this, the effects of warning, evacuation and shelter were considered to estimate the number of people exposed to the flood. In order to estimate fatality rates based on the exposed population, flood hazard zone is assigned to three different zones. Then, total fatality numbers were predicted after determining lethality or mortality function for each zone. In the future, the prediction of loss of life due to dam break floods will quantitatively evaluate flood risk and employ to establish flood mitigation measures at downstream applying probabilistic flood scenarios.

• Journal of Korea Multimedia Society
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• v.16 no.3
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• pp.330-335
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• 2013

It is expected that the vehicle safety systems using vehicle-to-vehicle communication can reduce the possibility of vehicle collision and prevent the chain crash by promptly delivering the status of neighboring vehicles. Many IEEE 802.11 DCF based Flooding schemes have been proposed, but they may generally expose the problems that the chances of a chain-collision reaction are sharply increased as the vehicle density has increased. Therefore, this paper proposes the chain-collision prevention scheme using a broadcasting-based adaptive report. The proposed method can adaptively allocate the preoccupancy right based on a quantitative priority order and then promptly deliver the warning messages in neighboring areas. Moreover, it is shown from simulation that the proposed scheme provides the performance gains over the existing Flooding based scheme.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.59-59
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• 2022

세계적으로 지구온난화를 동반한 기후변화로 인해 자연재난이 빈번하게 발생하고 있다. 재해의 발생 유형 중 집중호우와 태풍으로 인한 수문학적 재해가 대부분을 차지하고 있다. 이와 같이 홍수로 인해 발생하는 피해는 강우의 특성과 지역적 특성에 따라 피해의 규모와 범위가 달라진다. 따라서 이러한 이질적인 홍수피해로부터 재산과 인명을 보호하기 위해서는 위해성(Hazard), 노출성(Exposure), 취약성(Vulnerability)을 고려하여 지역 특성에 맞는 홍수방어계획을 수립해야한다. 본 연구에서는 전국 228개 행정구역을 대상으로 과거에 실제로 발생하였던 홍수피해 사례 조사를 통해 지역별 홍수피해 특성을 파악하여 지역 특성을 고려한 홍수피해 강우기준을 제시하고자 하였다. 이를 위해서 재해연보 보고서에 기재되어 있는 과거 홍수피해 기간과 홍수피해액을 수집하였고, 홍수피해 기간동안의 강우량과 뉴스 기사를 수집하여 뉴스 기사에서 언급되었던 홍수피해 현상 정보를 수집하였다. 수집된 홍수피해 정보를 통해 지역별 노출성과 취약성이 반영된 현상기반 강우등급을 제시하였으며, 이와 함께 지역별 강우특성을 나타내며 위해성을 내포하고 있는 확률강우량과의 합성을 통해 위해성, 노출성, 취약성을 고려한 지역별 홍수피해 강우기준을 제시하였다. 대부분 홍수피해에 관한 정보를 재해연보 보고서를 활용하여 수집하지만 홍수피해 현상에 대한 정보를 포함하고 있지 않기 때문에 지역별로 홍수피해로부터 발생하는 홍수피해 유형에 대해 파악하기에는 한계가 있다. 따라서 본 연구에서는 과거 홍수피해가 발생했던 기간에 대해 뉴스 기사를 수집하여 홍수피해 현상 정보를 수집하였고, 수집된 홍수피해 현상 정보를 텍스트 마이닝(Text Mining) 기법을 적용하여 홍수피해 현상 키워드 빈도분석을 통해 어떠한 홍수피해 유형에 취약한지 파악하였다.

• The Korean Journal of Financial Management
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• v.23 no.2
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• pp.209-237
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• 2006

Since previous default forecasting models for the firms evaluate the probability of default based upon the accounting data from book values, they cannot reflect the changes in markets sensitively and they seem to lack theoretical background. The market-information based models, however, not only make use of market data for the default prediction, but also have strong theoretical background like Black-Scholes (1973) option theory. So, many firms recently use such market based model as KMV to forecast their default probabilities and to manage their credit risks. Korean firms also widely use the KMV model in which default point is defined by liquid debt plus 50% of fixed debt. Since the debt structures between Korean and American firms are significantly different, Korean firms should carefully use KMV model. In this study, we empirically investigate the importance of debt structure. In particular, we find the following facts: First, in Korea, fixed debts are more important than liquid debts in accurate prediction of default. Second, the percentage of fixed debt must be less than 20% when default point is calculated for Korean firms, which is different from the KMV. These facts give Korean firms some valuable implication about default forecasting and management of credit risk.

• The Korean Journal of Applied Statistics
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• v.30 no.2
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• pp.243-257
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• 2017

In this paper, we compare several methods to approximate option prices: Edgeworth expansion, A-type and C-type Gram-Charlier expansions, a method using normal inverse gaussian (NIG) distribution, and an asymptotic method using nonlinear regression. We used two different types of approximation. The first (called the RNM method) approximates the risk neutral probability density function of the log return of the underlying asset and computes the option price. The second (called the OPTIM method) finds the approximate option pricing formula and then estimates parameters to compute the option price. For simulation experiments, we generated underlying asset data from the Heston model and NIG model, a well-known stochastic volatility model and a well-known Levy model, respectively. We also applied the above approximating methods to the KOSPI200 call option price as a real data application. We then found that the OPTIM method shows better performance on average than the RNM method. Among the OPTIM, A-type Gram-Charlier expansion and the asymptotic method that uses nonlinear regression showed relatively better performance; in addition, among RNM, the method of using NIG distribution was relatively better than others.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.151-151
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• 2015

최근 기후변화 및 토지 이용변화 때문에 홍수가 빈번하고 이로 인한 피해가 급증하고 있으며 4대강 사업이 이슈가 되면서 강우예측과 홍수량 산정에 대한 연구가 활발히 진행되고 있다. 하지만 여전히 홍수량 과다 과소 산정으로 인하여 지역적으로 문제점이 야기되고 피해가 발생하고 있다. 특히 Thiessen방법은 유역의 면적 강우량을 산정하기 위해 광범위하게 사용되고 있는데 중 소유역 또는 미계측 유역에 적절한 고려없이 무분별하게 사용하고 있어 문제가 발생되고 있는 실정이다. 또한 현재까지 큰 문제는 발생하지 않았지만 여전히 안전이나 위험에 노출된 상태이다. 따라서 Thiessen망 사용의 정밀한 분석이 무엇보다 필요한 실정이다. 따라서 본 연구를 통하여 소유역 및 미계측 유역을 대상으로 Thiessen망 이용시 관측소 선정에 따른 홍수량의 차이를 분석하고, 이에 따라 어떠한 문제가 발생할 수 있는지 분석하였다. 기존 소유역 및 미계측 유역 중 Thiessen방법을 적용하여 홍수량을 산정한 사례를 전반적으로 조사하였다. 이중에서 여러 지점중 Thiessen망 사용으로 유역이 분할되어 홍수량산정에 문제가 될 수 있는 관하천, 수외천, 주교천, 풍천을 연구 대상지점으로 선정하였다. 부적절한 Thiessen망 산정이 홍수량 산정에 미치는 영향을 평가하기 위하여 신뢰성있고 가장 실설계에 많이 사용되고 있는 다음의 방법으로 홍수량을 산정하였다. 먼저, 관측소 선정에 있어서 관측년도가 비교적 길고 유역과 가장 가까운 기상청 관할의 관측소를 선정하고 홍수량 산정요령에 따라 홍수량을 재 산정 하였다. 본 연구로부터 나온 결과에서, 산정된 홍수량은 기존의 Thiessen망을 통하여 산정된 홍수량과 차이를 보였고, 이는 Thiessen다각형 이론에 위배되는 관측소 선정이 원인으로 밝혀졌다. 따라서 본 연구에서는 관측년도가 길고 강우자료의 신뢰도가 높은 기상청 관할 관측소의 강우자료를 우선적으로 사용할 것을 제시하였다. 또한, 여러 관측소의 강우자료를 Thiessen망을 통하여 산정하는 부적절한 산정법을 신뢰성있는 단일지점의 강우량 산정법으로 적절한 홍수량이 산정할 것을 제시하였다.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.15 no.2
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• pp.33-45
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• 2020

While venture creation is considered to be of high social and economic importance, entrepreneurial outcomes are inherently uncertain and that failure is thus a central feature of entrepreneurship. Although failure in entrepreneurship is pervasive and critical, the impact of prior failure on future entrepreneurship has not received significant attention in the literature. Although failure is a painful and costly experience for entrepreneurs, it can also provide a powerful learning opportunity for those experiencing it. It has been argued that entrepreneurial failure is not just a individual problem but a matter of social concern. As part of the restarting business support system, entrepreneurial re-education program is provided to support failed entrepreneurs. The aim of this study is to examine the effects of failed entrepreneurs' prior entrepreneurial experience and re-education on subsequent venture creation. Moreover, this study also examined the moderating effects of entrepreneurial motivation. For the analyses, we surveyed the entrepreneurs who tried to re-start the subsequent business after the entrepreneurial failure through the "Revitalization Center for Strained Entrepreneur". The result found that failed entrepreneurs who learned a lot from their previous founding experience were more likely to re-start their subsequent business. The failed entrepreneurs who learned a lot from entrepreneurial re-education program were more likely to re-start their subsequent business. Moreover, the positive effect of failed entrepreneurs' previous founding experience and entrepreneurial re-education program on re-starting subsequent business was found to be weaker when entrepreneurial extrinsic motivation was high.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.5
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• pp.53-64
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• 2010

Seismic fragility curves of structures represent the probability of exceeding the prescribed structural damage state for a given various levels of ground motion intensity, such as peak ground acceleration (PGA). This means that seismic fragility curves are essential to the evaluation of structural seismic performance and assessments of risk. Most of existing studies have not considered the near- and far-fault earthquake effect on the seismic fragility curves. In order to evaluate the effect of near- and far-fault earthquakes, seismic fragility curves for PSC box girder bridges subjected to near- and far-fault earthquakes are calculated and compared. The seismic fragility curves are strongly dependent on the earthquake characteristics such as fault distance. This paper suggests that the effect of near- and far-fault earthquakes on seismic fragility curves of PSC box girder bridge structure should be considered.

• KDI Journal of Economic Policy
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• v.32 no.1
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• pp.131-169
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• 2010

I develop a matching model in which risk-averse workers face borrowing constraints and make a labor force participation decision as well as a job search decision. A sharp distinction between unemployment and out of the labor force is made: those who look for work for a certain period but find no job are classified as the unemployed and those who do not look for work are classified as those out of the labor force. In the model, the job search decision consists of two steps. First, each individual who is not working obtains information about employment opportunities. Second, each individual who decides to search has to take costly actions to find a job. Since individuals differ with respect to asset holdings, they have different reservation job-finding probabilities at which an individual is indifferent between searching and not searching. Individuals, who have large asset holdings and thereby are less likely to participate in the labor market, have high reservation job-finding probability, and they are less likely to search if they have less quality of information. In other words, if individuals with large asset holdings search for job, they must have very high quality of information and face very high actual job-finding probability. On the other hand, individuals with small asset holdings have low reservation job-finding probability and they are likely to search for less quality of information. They face very low actual job-finding probability and seem to remain unemployed for a long time. Therefore, differences in the quality of information explain heterogeneous job search decisions among individuals as well as higher job finding probability for those who reenter the labor market than for those who remain in the labor force. The effect of the extended maximum duration of unemployment insurance benefits on the aggregate labor market and the labor market flows is investigated. The benchmark benefit duration is set to three months. As maximum benefit duration is extended up to six months, the employment-population ratio decreases while the unemployment rate increases because individuals who are eligible for benefits have strong incentives to remain unemployed and decide to search even if they obtain less quality of information, which leads to low job-finding probability and then high unemployment rate. Then, the vacancy-unemployment ratio decreases and, in turn, the job-finding probability for both the unemployed and those out of the labor force decrease. Finally, the outflow from nonparticipation decreases with benefit duration because the equilibrium job-finding probability decreases. As the job-finding probability decreases, those who are out of the labor force are less likely to search for the same quality of information. I also consider the matching model with two states of employment and unemployment. Compared to the results of the two-state model, the simulated effects of changes in benefit duration on the aggregate labor market and the labor market flows are quite large and significant.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.5
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• pp.413-421
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• 2015

Since the first Cubesat was launched in 2003, there have been more than 230 Cubesats launched so far. Due to their small size and lightweight, Cubesats were launched by utilizing the empty space of regular launch vehicle. However, this launch method has a weakness that has been easily affecting by the schedule of major payloads. As a new solution to this problem, it has been proposed that a robot arm installed on ISS would be used to launch Cubesats. The orbits of Cubesat deployed from the ISS in various angles and directions are analyzed in this paper. We also analyze the possibility of collision between the Cubesat and ISS within the operational orbit of the CubeSat and eventually calculate the optimal angle of a robot arm, which maximizes the lifetime of Cubesat and minimizes the risk of collision between the Cubesat and ISS.