• Economic and Environmental Geology
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• v.33 no.4
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• pp.273-282
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• 2000

In order to investigate the extent and degree of arsenic and heavy metal contamination and the bioavailability of toxic elements around the abandoned mine in Korea, an environmental geochemical survey was undertaken in the Daduk mine. After appropriate preparation, tailings, soil, stream sediment, crop plant and fingernail samples were analysed for As, Cd, Cu, Pb and Zn by ICP-AES and ICP-MS. Elevated levels of 8,782 mg/kg As, 8.3 mg/kg Cd, 489 mg/kg Cu, 3,638 mg/kg Pb and 919 mg/kg Zn were found in tailings from the Daduk mine. These significant concentrations can impact on soils and sediments around the tailing ponds. Mean concentrations of As, Cd, Pb, Cu and Zn in soils are significantly higher than those in world average soil, especially for As and Pb. Element concentrations in sediments decrease with distance from the tailing ponds due to a dilution effect by the mixing of uncontaminated sediments. Arsenic and Cd are elevated in rice grains and stalks, and Cu and Zn concentrations in chinese cabbage, sesame and bean leaves are higher than the upper limit values for normal plant. Arsenic concentration in fingernails of farmers are higher than the normal level with a maximum value of 1.5 mg/kg. The post-ingestion bioavailability of toxic heavy metals in some paddy and farmland soils has been also investigated using the SBET (simple bioavailability extract test) method. The method utilises synthetic leaching fluids closelyanalogous to those of the human stomach. The quantities of As, Cd, Cu, Pb and Zn extracted from paddy soils after 1 hour indicated 15.9, 65.4, 46.2, 39.4 and 29.4% bioavailability, respectively and for farmland soils, 12.4, 26.0, 31.2, 29.3 and 19.4% bioavailability, respectively. The results of the SBET indicate that regular ingestion of soils by the local population could pose a potential health threat due to long-term toxic element exposure.

• Journal of Korean society of Dental Hygiene
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• v.13 no.2
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• pp.261-269
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• 2013

Objectives : This research examined the Patient Hygiene Performance(PHP) index according to smoking and tooth brushing behavior, in order to analyze how they influence the oral hygiene. Methods : This research used PHP index and the structured questionnaire. The subjects were 203 men in their 20's who visited K university's dental hygiene department for oral prophylaxis from March to July of 2012. For data analysis SPSS WIN 12.0 was used. Results : 1. The average PHP index of all experimented subjects was 2.66, a very poor level. The PHP index according to general characteristics, smoking, drinking, and exercise showed statistical significance(p<0.05). 2. PHP index decreased with more frequencies and longer durations of toothbrushing(p<0.05). 3. The PHP index of smokers is higher than that of non-smokers. In the case of non-smokers, the frequency, method, and duration of tooth brushing had a statistical significance(p<0.05). 4. The PHP index of smokers who smoke less than or equal to ten cigarettes is 2.53 and smokers who smoked more than 10 cigarettes is 3.10. 5. The results of multiple regression analysis showed that smoking increased the PHP index, while the increase in tooth brushing frequency and the up and down tooth brushing method decreased the PHP index. All the coefficients were statistically significant (p<0.05). Conclusions : In order to increase Patient Hygiene Performance(PHP) index. there must be a decrease in smoking rate while people increase their tooth brushing frequency and use a proper tooth brushing method.

• Archives of Reconstructive Microsurgery
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• v.22 no.1
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• pp.24-28
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• 2013

Purpose: Soft tissue defect of the hand, which cannot be covered with skin graft or local flap, is usually reconstructed using a free flap. Temporoparietal fascial free flap is one of the best alternatives for functional reconstruction of the hand with exposed tendons, bones, and joints. Materials and Methods: We have experienced four cases of reconstruction using a temporoparietal fascial flap with a skin graft and followed up for 20 years. We conducted a retrospective review of the patients' clinical charts and photos. Results: At the time of initial injury, the average age of patients was 50.3 (39~62) years. The radial artery was used for reconstruction of the dorsal side of the hand, whereas the ulnar artery was used for that of the volar side of the wrist. Short term complication such as skin graft loss and donor site alopecia occurred. However, during the long term follow-up period, no change of flap volume was noted, and full range of motion in the adjacent joint was maintained. In addition, hyperpigmentation of the grafted skin on the flap disappeared gradually. Conclusion: Selection of the optimal flap is important for reconstruction of the hand without functional limitation. We obtained satisfactory soft tissue coverage and functional outcomes using a temporoparietal fascial free flap and followed up for 20 years.

• Journal of Korean Society for Geospatial Information Science
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• v.20 no.4
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• pp.117-125
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• 2012

Although many studies have been conducted to extract buildings from airborne lidar data, most of them assume that all the boundaries of a building are straight line segments. This makes it difficult to model building boundaries containing curved segments correctly. This paper aims to model buildings containing curved segments as combination of straight lines and arcs. First, two sets of boundary points are extracted by adaptive convex hull algorithm and local convex hull algorithm with a larger radius. Then, arc segments are determined by average spacing of boundary points and intersection ratio of perpendicular lines. Finally, building boundary is modeled through regularization of least squares line or circle fitting. The experimental results showed that the proposed method can model the curved building boundaries as arc segments correctly by completeness of 69% and correctness of 100%. The approach will be utilized effectively to create automatically digital map that meets the conditions of the Korean digital mapping.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.289-296
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• 2004

The present study has been performed to investigate the influences of rectangular fins on heat transfer in an impingement/effusion cooling system with crossflow. To simulate the impingement/effusion cooling system with initial crossflow, two perforated plates are placed in parallel and staggered arrangements with a gap distance of 2 times of the hole diameter. The crossflow passes between the plates, and various rectangular fins are installed on the plates. Reynolds number based on the hole diameter is fixed to 10,000 and the flow rate of crossflow is changed from 0.5 to 1.5 times of that of the impinging jet. A naphthalene sublimation method is used to obtain the heat/mass transfer coefficients on the effusion plate. Also to analyze the flow characteristics, a numerical calculation is performed. When rectangular fins are installed, the flow and heat transfer pattern is changed greatly from case without fins. In the injection hole region, the jet impinges on effusion plate without deflection and wall jet spreads symmetrically. In the effusion region, the crossflow accelerates due to the decrease of cross-sectional area in the channel. Local heat/mass transfer coefficients are enhanced significantly compared to case without fins. As the blowing ratio increases, the effect of fins against the crossflow becomes more significant and then the higher average heat/mass transfer coefficients are obtained than the case without fins.

• Journal of Environmental Policy
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• v.5 no.3
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• pp.79-103
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• 2006

This paper attempts to examine household's willingness to pay (WTP) for piped water quality improvement in Wonju, where the local government are planning to implement a piped water quality improvement program. We apply a contingent valuation (CV) method to obtain at least a preliminary evaluation of the WTP. The CV survey was rigorously designed to comply with the guidelines for best-practiced CV studies. We surveyed a randomly selected sample of 250 households in Wonju and asked respondents questions in person-to-person interviews about how much they would be willing to pay for the program. Respondents overall accepted the contingent market and were willing to contribute a significant amount (1,583 to 2,776 won), on average, per household per month. This willingness varies according to individual characteristics such as sex, education level, and income. The aggregate value of the program in Wonju amounts to approximately 1.99 billion won to 3.49 billion won per year. The household values can be the benefits that ensue from the program and compared with the costs of the program to determine whether the program is economically desirable.

• Nuclear Engineering and Technology
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• v.42 no.5
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• pp.568-575
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• 2010

Flow Accelerated Corrosion is an active degradation mechanism of CANDU feeder. The tight bend downstream to Gray loc weld connection, close to reactor face, suffers significant wall thinning by FAC. Extensive in-service inspection of feeder wall thinning is very difficult because of the intense radiation field, complex geometry, and space restrictions. Development of a knowledge-based inspection program is important in order to guarantee that adequate wall thickness is maintained throughout the whole life of feeder. Research results and plant experiences are reviewed, and the plant inspection databases from Wolsong Units One to Four are analyzed in order to support developing such a knowledge-based inspection program. The initial thickness before wall thinning is highly non-uniform because of bending during manufacturing stage, and the thinning rate is non-uniform because of the mass transfer coefficient distributed non-uniformly depending on local hydraulics. It is obvious that the knowledge-based feeder inspection program should focus on both fastest thinning locations and thinnest locations. The feeder wall thinning rate is found to be correlated proportionately with QV of each channel. A statistical model is proposed to assess the remaining life of each feeder using the QV correlation and the measured thicknesses. W-1 feeder suffered significant thinning so that the shortest remaining life barely exceeded one year at the end of operation before replacement. W-2 feeder showed far slower thinning than W-1 feeder despite the faster coolant flow. It is believed that slower thinning in W-2 is because of higher chromium content in the carbon steel feeder material. The average Cr content of W-2 feeder is 0.051%, while that value is 0.02% for W-1 feeder. It is to be noted that FAC is reduced substantially even though the Cr content of W-2 feeder is still very low.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.11 no.4
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• pp.363-370
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• 2017

In this paper, we proposed a low-complexity speech enhancement algorithm based on a improved minima controlled recursive averaging (IMCRA) and log minimum mean square error (logMMSE). The IMCRA algorithm track the minima value of input power within buffers in local window and identify the speech presence using ratio between input power and its minima value. In this process, many number of operations are required. To reduce the number of operations of IMCRA algorithm, minima value is tracked using time-varying frequency-dependent smoothing based on speech presence probability. The proposed algorithm enhanced speech quality by 2.778%, 3.481%, 2.980% and 2.162% in 0, 5, 10 and 15dB SNR respectively and reduced computational complexity by average 9.570%.

• Journal of Korean Society on Water Environment
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• v.30 no.2
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• pp.166-174
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• 2014

Velocity gradient, G, a measure of the average velocity gradient in the fluid has been applied for complete mixing of chemicals in mechanical mixing devices. G values were calculated by the power input transferred to fluid in turbulent and transient range. Chemical reactions occur so fast that total mass transfer time required for even distribution of the chemicals determine the overall reaction time. The total mass transfer time is composed of the time for complete mixing through the reactor and for diffusion of the chemicals into the eddy. Complete mixing time was calculated by CFD (computer fluid dynamics) and evaluated by tracer tests in 2 liter jars at different rotating speeds. Turbulent range, Reynolds number above 10,000 in regular 2 liter jars occurred at revolution speed above 100 rpm (revolution per minute), while laminar range occurred at revolution speed below 10 rpm. A typical range of rotating speed used in jar tests for water and wastewater treatment was between 10 and 300 rpm, which covered both transient and turbulent range. G values supplied from a commercial jar test apparatus showed big difference from those calculated with power number specially in turbulent range. Diffusion time through eddy decreased 1.5 power-law of rotating speed. Complete mixing time determined by pumping number decreased increases in rotating speed. Total mass transfer time, finally, decreases as rotating speed increases, and it becomes 1 sec at rotating speed of 1,000 rpm. Complete mixing times evaluated from tracer tests showed higher than those calculated by power number at higher rotating speed. Complete mixing times, however, calculated by CFD showed similar to those of experimentally evaluated ones.

• The Mathematical Education
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• v.40 no.1
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• pp.77-92
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• 2001

In this study, the number of theses conducted in 1990's for the master's degree in mathematics education was investigated in terms of their fields and themes. These theses were analysed as to how much they had been studied according to the field and whether they had conformed to the expectations and requirements for research in mathematics education under the current educational curriculum. Futhermore, this study aimed to discover advancing directions of research in mathematics education. The results are as follows: First, the rate of annual thesis presentations decreased as many as 3.82% in 1994 compared with the previous year, but the rate increased steadily in the other years showing an overall annual average increase of 8.41%. Second, in the geographical distribution of thesis presentations among local provinces, Seoul represented the highest frequency at 41.13% and Cheju Island the lowest at 1.68%. When the annual thesis presentations were analysed among regions, their number increased steadily in Seoul, but fluctuated in most other regions. Third, regarding study themes, theses on mathematics education formed 70.91% of the total while those focusing on pure mathematics formed 29.09%. Among the theses of mathematics education, most were based on teaching curriculums and the least were based on education assessment. Among the theses on teaching curriculum, teaching analytics formed the highest rate. Theses on education technology, such as computerizing and computing, have shown to be increasing annually and formed 8.95% of the total in 1999. The study also indicated that especially in the late 1990's, there have been many designed programs based on the Web, like JAVA and CGI, and studies on teaching and teaming methods using the internet.