• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.16 no.2
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• pp.110-122
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• 2006

Objective : This study was conducted to quantify chronic lead exposure from various media(ie. working environment, food, ambient air), and to certify the usefulness of exposure assessment using Monte-Carlo simulation in the fields of occupational health. Methods : Data were obtained from Korean Industrial Health Association, Korea Food and Drug Administration, and the Ministry of Environment. Then lead worker's exposure was estimated indirectly from various media and parameters (ie. volume inhaled, body weight, dietary intake, etc.). Uncertainty was analyzed by Monte Carlo simulation with Crystal Ball software. Exposure doses and hazard indices were simulated with various hypothetical scenarios including weekly working hours and respiratory protective equipment. Results : Without respiratory protective equipment, the total exposure dose per kilogram of body weight of lead workers was estimated as $5.45{\times}10^{-3}mg/kg/day$, and hazard index was estimated as 2.26, and exposure contributions were calculated as follows : working environment(82.42 %); foods(17.57 %); and ambient air(0.01 %). But, if working condition has changed - reduction of working hours and using respiratory protective equipment, the total exposure dose per kilogram of body weight was estimated between $1.34{\times}10^{-3}-1.49{\times}10^{-3}mg/kg/day$, and hazard index was estimated between 0.56 - 0.62. Conclusions : This study suggested that occurrence of hazardous impact(ie. increased blood pressure) through lifetime lead exposure would be expected, and that the Monte-Carlo simulation was useful for the fields of occupational health.

• Journal of Navigation and Port Research
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• v.41 no.4
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• pp.229-234
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• 2017

Container terminal yards operate under a high degree of uncertainty as the contact point between inbound and outbound operations of vessels and external trucks. The layout, equipment operations. and job orders at the yards determine the efficacy and delays of the work, so many studies have investigated improvements in efficiency. H company, a container terminal operator developed an index called WDI to distribute work among RTGCs. The WDI is an indicator to prevent congestion in one place by equally distributing the work to each RTGC. This paper analyzes the effect of the WDI introduction and discusses the causes and results of the WDI introduction effect from quantitative and qualitative perspectives.

• Journal of KIISE:Databases
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• v.32 no.1
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• pp.71-85
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• 2005

Various researches on moving object modeling, uncertainty processing, and moving object indexing have been tarried out in the field of moving object databases. However. previous location tracking systems cannot efficiently retrieve location data of vehicles, because they manage all location information of vehicles using the conventional database. In this paper, we design the vehicle location management systen that is able to manage and retrieve vehicle locations efficiently in mobile environment. The proposed system consists of a server for managing vehicle locations and mobile clients. The system is able to not only process spatiotemporal queries related to locations of moving vehicles but also Provide moving vehicles' locations which are not stored in the system. The system is also able to manage vehicle location data effectively using a moving object index.

• Journal of the Korean Geotechnical Society
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• v.24 no.1
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• pp.119-130
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• 2008

Uncertainties in physical and engineering parameters for the design of shallow foundations arise from various aspects such as inherent variability and measurement error. This paper aims at investigating and reducing uncertainty from deterministic method by using the reliability-based design of shallow foundations accounting for the variation of various design parameters. A probability distribution type and statistics of random variables such as unit weight, cohesion, infernal friction angle and Young's modulus in geotechnical engineering are suggested to calculate the ultimate bearing capacities and immediate settlements of foundations. Reliability index and probability of failure are estimated based on the distribution types of random variables. Widths of foundation are calculated at target reliability index and probability of failure. It is found that application and analysis of the best-fit distribution type for each random variables are more effective than adoption of the normal distribution type in optimizing the reliability-based design of shallow foundations.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.129-139
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• 2008

Due to uncertainty of numerous variables in durability model, a probalistic approach is increasing. Monte Carlo simulation (Level III method) is an easily accessible method, but requires a lot of repeated operations. This paper evaluated the effectiveness of First Order Second Moment method (Level II method), which is more convenient and time saving method than MCS, to predict the corrosion initiation in harbor concrete structure. Mean Value First Order Second Moment method (MV FOSM) and Advanced First Order Second Moment method (AFOSM) are applied to the error function solution of Fick's second law modeling chloride diffusion. Reliability index and failure probability based on MV FOSM and AFOSM are compared with the results by MCS. The comparison showed that AFOSM and MCS predict the similar reliability index and MV FOSM underestimates the probability of corrosion initiation by chloride attack. Also, the sensitivity of variables in durability model to corrosion initiation probability was evaluated on the basis of AFOSM. The results showed that AFOSM is a simple and efficient method to estimate the probability of corrosion initiation in harbor structures.

• Korean Journal of Clinical Pharmacy
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• v.21 no.2
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• pp.170-181
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• 2011

Purpose: There is considerable variability in rates of hospitalization for patients with community-acquired pneumonia (CAP) in part because of physicians' uncertainty in assessing the severity of illness at presentation. The purpose of the study was to examine the current treatment patterns and factors influencing the Pneumonia Severity Index (PSI) and clinical outcomes in the patient with CAP. Method: The retrospective data collection of the patients with CAP was conducted and the data were reviewed. The collected data included demographic, clinical, laboratory and microbiological medical information. All patients were stratified into three risk groups according to PSI: low risk (PSI score I-II), moderate risk (III) and high risk (IV-V) groups. The examined treatment patterns were the appropriateness of admissions, category of antibiotics used. The prognostic factors associated with PSI and clinical outcomes were examined. Results: One hundred and six patients' medical data were reviewed. The overall appropriateness of admissions was low presenting many of patients were admitted or intensely treated in the hospital despite of lower risk of prognosis and treated with intravenous antibiotics instead of oral fluoroquinolones. Primary pneumonia pathogens were Klebsiella pneumoniae (27%) and Streptococcus pneumoniae (21.6%). Mean LOS was 8.5 days and was significantly longer (10.0days) (p<0.001) in high risk group. The patients with age >65 (p<0.001), diabetes mellitus (p<0.001), mental alteration (p<0.001), and/or $PaO_2$ <60 mmHg (p<0.001) had a tendency to have higher PSI. The prognostic factors associated with longer LOS were age >65 years (p=0.008), mental status alteration (p<0.001), dyspnea (p=0.002) and PSI score (p=0.001). The prognostic factors associated with mortality were congestive heart failure (p=0.038), systolic blood pressure <90 mmHg (p=0.002) and arterial pH <7.35 (p=0.013). Conclusion: Most of patients were found to over-utilize medical service according to appropriateness of admissions. The elderly, mentally altered patients with low $PaO_2$ had higher PSI score with increased risk of LOS. The mortality could be increased in the patient with disease state of congestive heart failure, high blood pressure, and/or acidosis.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.5
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• pp.608-616
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• 2015

In this study, we have estimated the storm surge heights using numerical modeling on coastal area, and then evaluated the vulnerability index by applying the vulnerability assessment techniques. Surge modelling for 27 typhoons affected from 2000 to 2014 were simulated by applying the ADCIRC model. The results of validation and verification was in significant agreement as compared with observations for the top 6 ranking typhoons affected. As results, the storm surge heights in Jinhae Bay, Sacheon Bay, Gwangyang Bay, Cheonsu Bay and Gyeonggi Bay were higher than other inner coastal areas, then storm surge vulnerability assessment was performed using a standardization, normalization and gradation of storm surge heights. According to results of storm surge vulnerability assessment, index of Jinhae Bay, Sacheon Bay, Gwangyang Bay etc. are estimated to be vulnerable(4~5) because of the characteristics of storm surge such as inner bay are vulnerable compared with exposed to the open sea areas. However, index in the inner bay of western Jeonnam are not vulnerable(1~3) relatively. It may not appear the typhoons affected significantly for the past 15 years. So, the long-term vulnerability assessment with the sensitivity of geomorphology are necessary to reduce the uncertainty.

• Journal of Environmental Science International
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• v.22 no.2
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• pp.163-171
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• 2013

The aggregate risk assessment on xylene and ethylbenzene was carried out according to the guidance established newly in 2010 with the purpose of providing information for risk management. In human exposure assessment, the results indicated that lower ages were exposed more and that, in the interior space at home, the highest level of human exposure occurred via inhalation. At outdoor spaces, exposures via inhalation and drinking were less than 1%. In human health risk characterization, xylene showed HI(Hazard Index) < 1 in all ages. When reasonable maximum exposure(RME) was applied, HI for young children was 0.64. The HI of ethylbenzene was also below 1(0.02~0.04) in all ages, indicating no potential risk. From this study, it is considered that xylene need to be continous monitoring with interest because this substance may be more sensitive on young age group. In additon, to reduce the uncertainty of the risk assessment, the korean exposure factors on young age group such as infant, children had to be established as soon as possible.

• The Journal of Korea Robotics Society
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• v.12 no.3
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• pp.339-349
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• 2017

In this paper, we present a finite-time sliding mode control (FSMC) with an integral finite-time sliding surface for applying the concept of graph theory to a distributed wheeled mobile robot (WMR) system. The kinematic and dynamic property of the WMR system are considered simultaneously to design a finite-time sliding mode controller. Next, consensus and formation control laws for distributed WMR systems are derived by using the graph theory. The kinematic and dynamic controllers are applied simultaneously to compensate the dynamic effect of the WMR system. Compared to the conventional sliding mode control (SMC), fast convergence is assured and the finite-time performance index is derived using extended Lyapunov function with adaptive law to describe the uncertainty. Numerical simulation results of formation control for WMR systems shows the efficacy of the proposed controller.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.1985-1996
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• 1994

A new design method of sliding hyperplanes is proposed in the synthesis of a variable structure controller for robust tracking of general nonlinear multi-input-output(MIMO) uncertain systems of relative degree higher than two. Input/ output(I/O) linearzation is firstly undertaken by employing the concept of relative degree and minimum phase followed by the construction of sliding mode controllers. Sliding hyperplanes are then derived from the inherent properties of companion matrix and ideal sliding mode characterized in I/O linearized system. Subsequently, the gradient magnitudes of the sling hyperplanes are determined in an optimal manner by considering a quadratic performance index to be evaluated at two phases; a reaching phase and a sliding phase. The proposed design methodology is relatively straightforward and systematic compared with conventional strategies such as geometric approach or pole assignment technique. A nonlinear governor and exciter control problem for a power system is adopted herein in order to demonstrate the design efficiency and also favorable and robust control performances.