• Journal of Korean Society of Transportation
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• v.22 no.6
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• pp.133-144
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• 2004

A model and a measure which can evaluate the risk of rear end collision are developed. Most traffic accidents involve multiple causes such as the human factor, the vehicle factor, and the highway element at any given time. Thus, these factors should be considered in analyzing the risk of an accident and in developing safety models. Although most risky situations and accidents on the roads result from the poor response of a driver to various stimuli, many researchers have modeled the risk or accident by analyzing only the stimuli without considering the response of a driver. Hence, the reliabilities of those models turned out to be low. Thus in developing the model behaviors of a driver, such as reaction time and deceleration rate, are considered. In the past, most studies tried to analyze the relationships between a risk and an accident directly but they, due to the difficulty of finding out the directional relationships between these factors, developed a model by considering these factors, developed a model by considering indirect factors such as volume, speed, etc. However, if the relationships between risk and accidents are looked into in detail, it can be seen that they are linked by the behaviors of a driver, and depending on drivers the risk as it is on the road-vehicle system may be ignored or call drivers' attention. Therefore, an accident depends on how a driver handles risk, so that the more related risk to and accident occurrence is not the risk itself but the risk responded by a driver. Thus, in this study, the behaviors of a driver are considered in the model and to reflect these behaviors three concepts related to accidents are introduced. And safe stopping distance and accident occurrence probability were used for better understanding and for more reliable modeling of the risk. The index which can represent the risk is also developed based on measures used in evaluating noise level, and for the risk comparison between various situations, the equivalent risk level, considering the intensity and duration time, is developed by means of the weighted average. Validation is performed with field surveys on the expressway of Seoul, and the test vehicle was made to collect the traffic flow data, such as deceleration rate, speed and spacing. Based on this data, the risk by section, lane and traffic flow conditions are evaluated and compared with the accident data and traffic conditions. The evaluated risk level corresponds closely to the patterns of actual traffic conditions and counts of accident. The model and the method developed in this study can be applied to various fields, such as safety test of traffic flow, establishment of operation & management strategy for reliable traffic flow, and the safety test for the control algorithm in the advanced safety vehicles and many others.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1B
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• pp.11-22
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• 2009

Long-term rainfall-runoff modeling is a key element in the Earth's hydrological cycle, and associated with many different aspects such as dam design, drought management, river management flow, reservoir management for water supply, water right permission or coordinate, water quality prediction. In this regard, hydrologists have used the hydrologic models for design criteria, water resources assessment, planning and management as a main tool. Most of rainfall-runoff studies, however, were not carefully performed in terms of considering reservoir effects. In particular, the downstream where is severely affected by reservoir was poorly dealt in modeling rainfall-runoff process. Moreover, the effects can considerably affect overall the rainfallrunoff process. An objective of this study, thus, is to evaluate the impact of reservoir operation on rainfall-runoff process. The proposed approach is applied to Anseong watershed, where is in a mixed rural/urban setting of the area and in Korea, and has been experienced by flood damage due to heavy rainfall. It has been greatly paid attention to the agricultural reservoirs in terms of flood protection in Korea. To further investigate the reservoir effects, a comprehensive assessment for the results are discussed. Results of simulations that included reservoir in the model showed the effect of storage appeared in spring and autumn when rainfall was not concentrated. In periods of heavy rainfall, however, downstream runoff increased in simulations that do not consider reservoir factor. Flow duration curve showed that changes in streamflow depending upon the presence or absence of reservoir factor were particularly noticeable in ninety-five day flow and low flow.

• Childhood Kidney Diseases
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• v.3 no.2
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• pp.130-144
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• 1999

Purpose : Long-term use of Cyclosporine(CsA) reduce renal blood flow by afferent arteriolar vasoconstriction and lead to chronic pathologic changes of CsA nephrotoxicity - 1) interstitial nephritis(IN); tubular atrophy (TA) and/or interstitial fibrosis(IF),2) arteriolopathy(AP). The Object of this study is to estimate the incidence of chronic pathologic CsA nephrotoxicity by duration of treatment and type of renal disease, relationship between histologic and clinical nephrotoxicity, and optimal duration of CsA therapy. Methods : 102 children with steroid resistant or dependent nephrotic syndrome confirmed by renal biopsy and treated with CsA from 1986 to 1997 were enrolled in this study(58 MCNS, 10 FSGS, 10 MGN, 15 $Henoch-Sch\"{o}nlein$ purpura nephritis with nephrotic syndrome (HSPN) and 9 IgA nephropathy with nephrotic syndrome(IgAN)). CsA was administered for 1yr, 1.5yr, 2yr in 24, 12, 22 MCNS patients and 2, 2, 6 FSGS patients respectively, 1yr, 2yr in MGN and 1yr in HSPN and IgAN. Sequential biopsies were done in all 102 patients after CsA treatment for evaluation of pathologic nephrotoxicity. Results : Complete remission rate was 92.2% (100% in MCNS and MGN, 80% in FSGS, 86.6% in HSPN and 55.5% in IgAN). Incidence of relapse during 6months after CsA treatment was significantly decreased compaed with relapsing spisodes during 6months before CsA treatment in MCNS(P<0.0001) and FSGS(P<0.0001). According to pathologic changes, 71 patients(69.6%) showed no pathological change, 24 patients(23.5%) showed IN and 7 patients(6.8%) showed AP. IN was 16.6%, 33.3%, 27.2% in 1, 1.5, 2 year of CsA treatment group in MCNS. AP was 0%, 16.6%, 9% in 1, 1.5, 2 year of CsA treatment group in MCNS. 14 out of 58 MCNS(24.1%) showed IN and 4 out of 58 MCNS(6.8%) showed AP. Incidence of pathologic change was significantly lower in CsA therapy of <1yr than >1yr(P=0.03). There were no significant difference of incidence of pathologic change in original renal disease, age and sex. Conclusion : Duration of CsA treatment was significant risk factor for nephrotoxicity and optimal duration seemed to be 1 year. Pathologic change due to nephrotoxicity did not correlate with deterioration of renal function and only detectable by renal biopsy.

• Journal of Chest Surgery
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• v.39 no.5 s.262
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• pp.354-358
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• 2006

Background: Pulsatile pumps for extracorporeal circulation have been known to be better for tissue perfusion than non-pulsatile pumps but be detrimental to blood corpuscles. This study is intended to examine the risks and benefits of $T-PLS^{TM}$ through the comparison of clinical effects of $T-PLS^{TM}$ (pulsatile pump) and $Bio-pump^{TM}$ (non-pulsatile pump) used for coronary bypass surgery. Material and Method: The comparison was made on 40 patients who had coronary bypass using $T-PLS^{TM}\;and\;Bio-pump^{TM}$ (20 patients for each) from April 2003 to June 2005. All of the surgeries were operated on pump beating coronary artery bypass graft using cardiopulmonary extra-corporeal circulation. Risk factors before surgery and the condition during surgery and the results were compared. Result: There was no significant difference in age, gender ratio, and risk factors before surgery such as history of diabetes, hypertension, smoking, obstructive pulmonary disease, coronary infarction, and renal failure between the two groups. Surgery duration, hours of heart-lung machine operation, used shunt and grafted coronary branch were little different between the two groups. The two groups had a similar level of systolic arterial pressure, diastolic arterial pressure and mean arterial pressure, but pulse pressure was measured higher in the group with $T-PLS^{TM}\;(46{\pm}15\;mmHg\;in\;T-PLS^{TM}\;vs\;35{\pm}13\;mmHg\;in\;Bio-pump^{TM},\;p<0.05)$. The $T-PLS^{TM}$-operated patients tended to produce more urine volume during surgery, but the difference was not statistically significant $(9.7{\pm}3.9\;cc/min\;in\;T-PLS^{TM}\;vs\;8.9{\pm}3.6\;cc/min\;in\;Bio-pump^{TM},\;p=0.20)$. There was no significant difference in mean duration of respirator usage and 24-hour blood loss after surgery between the two groups. Plasma free Hb was measured lower in the group with $T-PLS^{TM}\;(24.5{\pm}21.7\;mg/dL\;in\;T-PLS^{TM}\;versus\;46.8{\pm}23.0mg/dL\;in\;Bio-pump^{TM},\;p<0.05)$. There was no significant difference in coronary infarction, arrhythmia, renal failure and morbidity rate of cerebrovascular disease. There was a case of death after surgery (death rate of 5%) in the group tested with $T-PLS^{TM}$, but the death rate was not statistically significant. Conclusion: Coronary bypass was operated with $T-PLS^{TM}$ (Pulsatile flow pump) using a heart-lung machine. There was no unexpected event caused by mechanical error during surgery, and the clinical process of the surgery was the same as the surgery for which $Bio-pump^{TM}$ was used. In addition, $T-PLS^{TM}$ used surgery was found to be less detrimental to blood corpuscles than the pulsatile flow has been known to be. Authors of this study could confirm the safety of $T-PLS^{TM}$.

• Tuberculosis and Respiratory Diseases
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• v.48 no.5
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• pp.766-772
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• 2000

Background : Pressure rise time (PRT) is the time in which the ventilator aclieves the set airway pressure in pressure-targeted modes, such as pressure control ventilation (PCV). With varying PRT, in principle, the peak inspiratory flow rate of the ventilator also varies. And if PRT is set to a shorter duration, the effective duration of target pressure level would be prolonged, which in turn would increase inspiratory tidal volume(Vti) and mean airway pressure (Pmean). We also postulated that the increase in Vti with shortening of PRT may relate inversely to the patients' basal airway resistance. Methods : In 13 paralyzed patients on PCV (pressure control 18$\pm$9.5 cm $H_2O$ $FIO_2\;0.6\pm0.3$, PEEP 5$\pm$3 cm $H_2O$, f 20/min, I : E1 : 2) with Servo 300 (Siemens-Elema, Solna, Sweden) from various causes of respiratory failure, PRT of 10 %, 5 % and 0 % were randomly applied. At 30 min of each PRT trial, peak inspiratory flow (PIF, L/sec), Vti (ml), Pmean (cm $H_2O$) and ABGA were determined. Results : At PRT 10%, 5%, and 0%, PIF were 0.69$\pm$0.13, 0.77$\pm$0.19, 0.83$\pm$0.22, respectively (p<0.001). Vti were 425$\pm$94, 439$\pm$101, 456$\pm$106, respectively (p<0.001), and Pmean were 11.2$\pm$3.7, 12.0$\pm$3.7, 12.5$\pm$3.8, respectively (p<0.001). pH were 7.40$\pm$0.08, 7.40$\pm$0.92, 7.41$\pm$0.96, respectively (p=0.00) ; $PaCO_2$ (mm Hg) were 47.4$\pm$15.8, 47.2 $\pm$15.7, 44.6$\pm$16.2, respectively (p=0.004) ; $PAO_2-PaO_2$ (mm Hg) were 220$\pm$98, 224$\pm$95, 227$\pm$94, respectively (p=0.004) ; and $V_n/V_T$ as determined by ($PaCO_2-P_E-CO_2$)/$PaCO_2$ were 0.67$\pm$0.07, 0.67$\pm$0.08, 0.66$\pm$0.08, respectively (p=0.007). The correlation between airway resistance and change of Vti from PRT 10% to 0% were r= -0.243 (p=0.498). Conclusion : Shortening of pressure rise timee during PCV was associated with increased tidal volume, increased mean airway pressure and lower $PaCO_2$.

• Journal of Oral Medicine and Pain
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• v.36 no.4
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• pp.225-234
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• 2011

Tobacco smoking is a major risk factor of systemic health and also impairs oral health, which is related to development of oral cancers, periodontitis, delayed wound healing, tooth loss, failure of implant, etc. Aside from smoking, many other risk factors can be related to oral health and long-term effects of smoking on salivary flow and taste threshold are still in controversy. Authors considered dental students to be an appropriate group with good oral hygiene for a long-term study to reveal effects of smoking on oral health. This study was performed to compare smoking patterns and current oral health conditions between smokers and nonsmokers in dental students prior to long-term evaluation. 192 volunteers (85.7%) of 224 male dental students in Dankook University were evaluated through questionnaires and clinical examination in 2010. Questionnaires included smoking pattern, alcohol use, nicotine dependence, preventive care, psychological profile and clinical examinations comprised assessment of teeth or periodontal status, nicotine pigmentation, salivary flow, electrical taste thresholds and halitosis. From the study, (current) smokers were older, and drank more frequently with more alcohol intake compared to former smokers and nonsmokers(p<0.05). There was no significant difference among them in salivary flow rate, halitosis and electrical taste threshold. However, there was significant difference in DMFT rate, periodontal treatment need, nicotinic pigmentation between smokers and nonsmokers(p<0.05), irrespective of their levels of preventive care. The smokers in this study, who are young dental students with relatively shorter duration of smoking, less use of cigarettes and low level of nicotine dependence, did not reveal significant impairment of oral health. However, their oral health was found to be relatively impaired compared to nonsmokers', which suggests negative effect of smoking on the oral health and a need of smoking cessation.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.3
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• pp.308-315
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• 2006

Since sewage characteristics are the most important factors that can affect the biological reactions in wastewater treatment plants, a detailed understanding on the characteristics and on-line measurement techniques of the influent sewage would play an important role in determining the appropriate control strategies. In this study, samples were taken at two hour intervals during 51 days from $1^{st}$ October to $21^{st}$ November 2005 from the influent gate of sewage treatment plant. Then the characteristics of sewage were investigated. It was found that the daily values of flow rate and concentrations of sewage components showed a defined profile. The highest and lowest peak values were observed during $11:00{\sim}13:00$ hours and $05:00{\sim}07:00$ hours, respectively. Also, it was shown that the concentrations of sewage components were strongly correlated with the absorbance measured at 300 nm of UV. Therefore, the objective of the paper is to develop on-line estimation technique of the concentration of each component in the sewage using accumulated profiles of sewage, absorbance, and flow rate which can be measured in real time. As a first step, regression analysis was performed using the absorbance and component concentration data. Then a neural network trained with the input of influent flow rate, absorbance, and inflow duration was used. Both methods showed remarkable accuracy in predicting the resulting concentrations of the individual components of the sewage. In case of using the neural network, the predicted value md of the measurement were 19.3 and 14.4 for TSS, 26.7 and 25.1 for TCOD, 5.4 and 4.1 for TN, and for TP, 0.45 to 0.39, respectively.

• Economic and Environmental Geology
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• v.56 no.2
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• pp.139-153
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• 2023

This study aimed to understand the spatiotemporal variations in nitrogen content in the Gyeongan stream along the main stream and at the discharge points of the sub-basins, and to identify the origin of the nitrogen. Field surveys and laboratory analyses, including chemical compositions and isotope ratios of nitrate and boron, were performed from November 2021 to November 2022. Based on the flow duration curve (FDC) derived for the Gyeongan stream, the dry season (mid-December 2021 to mid-June 2022) and wet season (mid-June to early November 2022) were established. In the dry season, most samples had the highest total nitrogen(T-N) concentrations, specifically in January and February, and the concentrations continued to decrease until May and June. However, after the flood season from July to September, the uppermost subbasin points (Group 1: MS-0, OS-0, GS-0) where T-N concentrations continually decreased were separated from the main stream and lower sub-basin points (Group 2: MS-1~8, OS-1, GS-1) where concentrations increased. Along the main stream, the T-N concentration showed an increasing trend from the upper to the lower reaches. However, it was affected by those of the Osan-cheon and Gonjiamcheon, the tributaries that flow into the main stream, resulting in respective increases or decreases in T-N concentration in the main stream. The nitrate and boron isotope ratios indicated that the nitrogen in all samples originated from manure. Mechanisms for nitrogen inflow from manure-related sources to the stream were suggested, including (1) manure from livestock wastes and rainfall runoff, (2) inflow through the discharge of wastewater treatment plants, and (3) inflow through the groundwater discharge (baseflow) of accumulated nitrogen during agricultural activities. Ultimately, water quality management of the Gyeongan stream basin requires pollution source management at the sub-basin level, including its tributaries, from a regional context. To manage the pollution load effectively, it is necessary to separate the hydrological components of the stream discharge and establish a monitoring system to track the flow and water quality of each component.

• Ecology and Resilient Infrastructure
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• v.9 no.3
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• pp.194-205
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• 2022

Sandbars formed by sediment transportation and sedimentation are some of the most important habitats for specific wildlife and they provide an aesthetic landscape in streams. The purpose of this study was to understand the successional process of the colonization and development of early vegetation over time on sandbars exposed by the opening of a gate at a downstream weir. We selected the following four study sites in the Geumgang River, South Korea: three weir-upstream sites with different gate-opening times and a control site that was not affected by weir operation. Changes in the structural characteristics and spatial distribution of the riparian vegetation on the sandbars exposed after opening the gate at the weir were surveyed according to the different exposure periods of the sandbars at the study sites. The newly formed sandbars accounted for more than 33% of the area of the existing floodplain in the three weir-upstream sites of the Geumgang River after opening the gate at the weir. Nine main plant communities were distributed on the exposed sandbars. These communities were classified as annual mesophytic, perennial hydrophytic, perennial hygrophytic, subtree, and tree vegetation based on their species traits. As the duration of exposure of the sandbar increased, the area of the bare sandbar and the annual herbaceous and perennial hydrophytic communities decreased, and the areas occupied by perennial hygrophytic, subtree, and tree communities increased. Changes in vegetation on the sandbar were classified into three types of succession according to the condition of the aquatic habitat before the gate-opening and the degree of physical disturbance caused by the water flow after the gate-opening. The types of succession were: 1) succession starting from hydrophytes in the lentic aquatic zone, 2) succession starting from annual herbaceous hygrophytes in the lotic aquatic zone, and 3) willow-dominated succession in the disturbed channel side. Our results suggested that the dynamics of successional changes in vegetation should be considered during weir operation to ecologically manage the habitats and landscape of the fluvial landforms, including sandbars in streams.

• Nuclear Engineering and Technology
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• v.18 no.3
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• pp.200-208
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• 1986

The loss of coolant accident based on a double-ended cold leg break is analyzed with the discharge coefficient (Ca) of 0.4. This analysis covers the whole transient period from the start of depressurization to the complete refilling of the core by using RELAP4/MOD6-EM and RELAP4/ MOD6-HOT CHANNEL for the system thermal-hydraulics and the fuel performance during the blowdown phase respectively, and RELAP4/MOD6-FLOOD and TOODEE2 during the reflood phase. A simple analytical method has been developed to account for the lower plenum filling by approximating steam-water countercurrent flows and superheated wall effects at the downcomer during the refill period. Based on the informations. at the time of EOB (end-of-bypass), the refill duration time and the initial reflooding temperature were estimated and compared with the results from the RELAP4/MOD6, resulting in a good agreement. In addition, some parametric studies on the EOB were performed. The form loss coefficient between upper head and upper downcomer was found to be sensitive to the occurrence of the spurious EOB. Appropriate form loss coefficients should be taken into account to avoid the flow oscillations at the downcomer. The analyses with the six and three volume core nodalizations, respectively, show much similar trends in the system thermal-hydraulic performance, but the former case is recommended to obtain good results.