• Journal of Radiation Protection and Research
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• v.40 no.4
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• pp.211-215
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• 2015

In case of radiation emergencies, radioactive materials released into environments can cause internal exposure of members of the public. Even though whole body counters are widely used for direct measurement of internally deposited radionuclides, those are not likely to be used at the field to rapidly screen internal exposure. In this study, we estimated the counting efficiencies of portable NaI detector for different size BOMAB phantoms using Monte Carlo transport code to apply handheld gamma spectrometers for rapid screening of internal exposure following radiological accidents. As a result of comparison for two counting geometries, counting efficiencies for sitting model were about 1.1 times higher than those for standing model. We found, however, that differences of counting efficiencies according to different size are higher than those according to counting geometry. Therefore, we concluded that when we assess internal exposure of small size people compared to the reference male, the body size should be considered to estimate more accurate radioactivity in the human body because counting efficiencies of 4-year old BOMAB phantom were about 2.4~3.1 times higher than those of reference male BOMAB phantom.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.355-362
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• 2012

Remaining useful life(RUL) prediction of a system is important in the prognostics field since it is directly linked with safety and maintenance scheduling. In the physics-based prognostics, accurately estimated model parameters can predict the remaining useful life exactly. It, however, is not a simple task to estimate the model parameters because most real system have multivariate model parameters, also they are correlated each other. This paper presents representative methods to estimate model parameters in the physics-based prognostics and discusses the difference between three methods; the particle filter method(PF), the overall Bayesian method(OBM), and the sequential Bayesian method(SBM). The three methods are based on the same theoretical background, the Bayesian estimation technique, but the methods are distinguished from each other in the sampling methods or uncertainty analysis process. Therefore, a simple physical model as an easy task and the Paris model for crack growth problem are used to discuss the difference between the three methods, and the performance of each method evaluated by using established prognostics metrics is compared.

• Journal of Intelligence and Information Systems
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• v.20 no.1
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• pp.1-14
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• 2014

Both researchers and practitioners are showing an increased interested in interactive exhibition services. Interactive exhibition services are designed to directly respond to visitor responses in real time, so as to fully engage visitors' interest and enhance their satisfaction. In order to install an effective interactive exhibition service, it is essential to adopt intelligent technologies that enable accurate estimation of a visitor's emotional state from responses to exhibited stimulus. Studies undertaken so far have attempted to estimate the human emotional state, most of them doing so by gauging either facial expressions or audio responses. However, the most recent research suggests that, a multimodal approach that uses people's multiple responses simultaneously may lead to better estimation. Given this context, we propose a new multimodal emotional state estimation model that uses various responses including facial expressions, gestures, and movements measured by the Microsoft Kinect Sensor. In order to effectively handle a large amount of sensory data, we propose to use stratified sampling-based MRA (multiple regression analysis) as our estimation method. To validate the usefulness of the proposed model, we collected 602,599 responses and emotional state data with 274 variables from 15 people. When we applied our model to the data set, we found that our model estimated the levels of valence and arousal in the 10~15% error range. Since our proposed model is simple and stable, we expect that it will be applied not only in intelligent exhibition services, but also in other areas such as e-learning and personalized advertising.

• Communications for Statistical Applications and Methods
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• v.15 no.3
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• pp.451-464
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• 2008

Six sigma is the rating that signifies "best in clas", with only 3.4 defects per million units or operations. Higher sigma quality level is generally perceived by customers as improved performance by assigning a correspondingly higher satisfaction score. The process capability indices and the sigma level $Z_{st}$ have been widely used in six sigma industries to assess process performance. Most evaluations on process capability indices focus on point estimates, which may result in unreliable assessments of process performance. In this paper, we consider statistical inference for process capability indices $C_p$, $C_{pk}$ and $C_{pm}$. Also, we study better testing procedure on assessing sigma level $Z_{st}$ and capability index $C_{pm}$, for practitioners to use in determining whether a given process is capable. The proposed method is easy to use and the decision making is more reliable. Whether a process is clearly normal or nonnormal, our bootstrap testing procedure could be applied effectively without the complexity of calculation. A numerical result based on our proposed method is illustrated.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.11
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• pp.828-833
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• 2018

It is well known that reflected waves and resonance affect phase distortion. In addition, phase delay can be distorted by antenna impedance. In this study, we analyze the phase delay variation caused by the antenna impedance, considering mutual coupling effects. In addition, we confirm the beam steering characteristics. When was -10 dB and -7 dB, the maximum phase delay error was $18.5^{\circ}$ and $26.5^{\circ}$, respectively. The Monte Carlo simulation with an eight-element linear array antenna demonstrated that the RMS error of the beam steering angle ranged from $0.19^{\circ}$ to $0.4^{\circ}$, and the standard deviation ranged from $0.14^{\circ}$ to $0.33^{\circ}$ when the beam steering angle was in the range of $0^{\circ}$ to $30^{\circ}$, with the uniformly distributed phase error of $18.5^{\circ}$ and $26.5^{\circ}$. The side lobe level increased from 0.74 dB to 1.21 dB by the phase error from the theoretical value of -12.8 dB, with a standard deviation of 0.31 dB to 0.51 dB. This is verified by designing an eight-element spiral array antenna.

• Journal of Radiation Protection and Research
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• v.41 no.1
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• pp.41-47
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• 2016

Background: For the accurate dose assessment in radiation therapy, energy spectrum of the photon beam generated from the linac head is essential. The aim of this study is to develop the technique to accurately unfolding the energy spectrum with the transmission analysis method. Materials and Methods: Clinical linear accelerator and Monet Carlo method was employed to evaluate the transmission signals according to the thickness of the observer material, and then the response function of the ion chamber response was determined with the mono energy beam. Finally the energy spectrum was unfolded with HEPROW program. Elekta Synergy Flatform and Geant4 tool kits was used in this study. Results and Discussion: In the comparison between calculated and measured transmission signals using aluminum alloy as an attenuator, root mean squared error was 0.43%. In the comparison between unfolded spectrum using HEPROW program and calculated spectrum using Geant4, the difference of peak and mean energy were 0.066 and 0.03 MeV, respectively. However, for the accurate prediction of the energy spectrum, additional experiment with various type of material and improvement of the unfolding program is required. Conclusion: In this research, it is demonstrated that unfolding spectra technique could be used in megavoltage photon beam with aluminum alloy and HEPROW program.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.6
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• pp.1634-1647
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• 2007

"To invest or not to invest?" Most business leaders are frequently faced with this question on new and ongoing projects. The challenge lies in deciding what projects to choose, expand, contract, defer, or abandon. The project valuation tools used in this process are vital to making the right decisions. Traditional tools such as discounted cash flow (DCF)/net present value (NPV) assume a "fixed" path ahead, but real world projects face uncertainties, forcing us to change the path often. Comparing to other traditional valuation methods, the real options approach captures the flexibility inherent to investment decisions. The use of real options has gained wide acceptance among practitioners in a number of several industries during the last few decades. Even though the options are present in all types of business decisions, it is still not considered as a proper method of valuation in some industries. Mining has been comparably slow to adopt new valuation techniques over the years. The reason fur this is not entirely clear. One possible reason is the level and types of risks in mining. Not only are these risks high, but they are also more numerous and involve natural risks compared with other industries. That is why the purpose of this study is to deal with a more practical approach to project valuation, known as real options analysis in mining industry. This paper provides a case study approach to the copper mining industry using a real options analysis. It shows how companies can minimize investment risks, exercise flexibility in decision making and maximize returns.

• Korean Chemical Engineering Research
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• v.56 no.4
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• pp.479-495
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• 2018

This study was carried out to research the multimedia fate modeling, concentration distribution and impact assessment of polycyclic aromatic hydrocarbons (PAHs) emitted from automobiles, which are known as carcinogenic and mutation chemicals. The amount of emissions of PAHs was determined based on the census data of automobiles at a target S-city and emission factors of PAHs, where multimedia fugacity modeling was conducted by the restriction of PAHs transfer between air-soil at the impervious area. PAHs' Concentrations and their distributions at several environmental media were predicted by multimedia fugacity model (level III). The residual amounts and the distributions of PAHs through mass transfer of PAHs between environment media were used to assess the health risk of PAHs at unsteady state (level IV), where the sensitivity analyses of the model parameter of each variable were conducted based on Monte Carlo simulation. The experimental result at S-city showed that Fluoranthene among PAHs substances are the highest residual concentrations (60%, 53%, 32% and 34%) at all mediums (atmospheric, water, soil, sediment), respectively, where most of the PAHs were highly accumulated in the sediment media (more than 80%). A result of PAHs concentration changes in S-city over the past 34 years identified that PAHs emissions from all environmental media increased from 1983 to 2005 and decreased until 2016, where the emission of heavy-duty vehicle including truck revealed the largest contribution to the automotive emissions of PAHs at all environment media. The PAHs concentrations in soil and water for the last 34 years showed the less value than the legal standards of PAHs, but the PAHs in air exceeded the air quality standards from 1996 to 2016. The result of this study is expected to contribute the effective management and monitoring of toxic chemicals of PAHs at various environment media of Metropolitan city.

• Korean Journal of Ecology and Environment
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• v.38 no.2 s.112
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• pp.225-236
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• 2005

The protection of public health In wastewater reclamation and reuse is one of the most important issues. Monitoring data of Escherichia coli were collected from paddy rice plots in 2003 and 2004 experiments. Five treatments were used and each one was triplicated to evaluate the changes of E. coli: surface water, biofilter effluent (secondary level), UV-disinfected water and pond treatment. Microbial risk was quantified to assess human health risk by exposure to E. coli in paddy rice plots, which were irrigated with reclaimed wastewater. Beta-Poisson model was used to estimate the microbial risk of pathogen ingestion that may occur to farmer and neighbor children. Monte-Carlo analysis (10,000 trials) was used to estimate the risk characterization of uncertainty. In the following analysis, two scenarios were related to the reduction of risk against direct ingestion and exposure times. Scenarios A and B were assumed that the risk was 1,000 and 10,000 times lower than direct ingestion.'Golfers were assumed to be 0.001 L of reclaimed water by contact with balls and their cloths. Opportunity of contact in paddy rice field with pathogens was more frequent than handing golf balls, because of agricultural activity was practiced in ponded water in paddy rice culture. As a result of microbial risk assessment using total data of experimental period, risk value of E. coli in 2003 and 2004 experiment ranged from $10^{-5}$ to $10^{-8}$ and $10^{-4}$ to $10^{-8}$, respectively. The risk values in biofilter effluent irrigation was the highest, which is $10^{-4}$ in 2003 and $10^{-5}$ in 2004 experiments with scenario A. Ranges of $10^{-6}$ to $10^{-8}$ were considered at reasonable levels of risk for communicable disease transmission from environmental exposure and the risk value above $10^{-4}$ was considered to be attributable to the risk of infection. Irrigation with UV-disinfected water in the paddy field during the agricultural Period showed significantly lower microbial risk than others, and their levels of risk value were within the range of actual paddy rice field with surface water.

• Environmental and Resource Economics Review
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• v.13 no.1
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• pp.49-82
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• 2004

The study aimed to evaluate cancer damage cost due to risk from benzene inhalation. We performed health risk assessment based on US EPA guideline to estimate annual population risk in Ulsan metropolitan city. Also, we estimated a willingness-to-pay amount for reducing a cancer mortality rate to evaluate a value of statistical life. We combined the annual population risk and the value of statistical life to calculate the cancer damage cost. In the health risk assessment, we applied the benzene unit risk ($2.2{\times}10^{-6}{\sim}7.8{\times}10^{-6}$) in the US EPA'S Integrated Risk Information System to assess the annual population risk. Average concentration of benzene in ambient air is $7.88{\mu}g/m^3$(min: 1.16~max: $23.32{\mu}g/m^3$). We targeted an exposure population of 516,641 persons who aged over 30 years old. Using a Monte-Carlo simulation for uncertainty analysis, we evaluated that the population risk of benzene during ten years in Ulsan city is 2.90 persons (5 percentile: 0.32~95 percentile: 9.11persons). And the monthly average WTP for 5/1,000 cancer mortality reduction during ten years is 14,852 Won(95% C.I: 13,135~16,794 Won) and the implied VSL is 36 million Won(95% C.I: 30~40 million Won). Cancer damage cost due to risk from benzene inhalation during 10 years in Ulsan city is about 104 million Won(5 percentile: 13~95 percentile: 328 million Won). Health benefit cost to reduce a cancer mortality risk of benzene is about 50 million Won is Ulsan metropolitann city. But, it is very important that this cost is not for all health damage cost of cancer mortality in some area. We just recommended a model for evaluating a cancer risk reduction, so we must re-evaluate an integrated application of total VOCs damage cost including benzene.