• Journal of Korean Society of Water and Wastewater
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• v.23 no.3
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• pp.345-352
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• 2009

The purpose of inlet baffle is to distribute the flow uniformly over the entire cross-sectional area of the sedimentation basin. The goal when designing this baffle is to achieve some head loss while keeping the velocity gradients through the ports equal to the velocity gradient in the end of the flocculator, so as to not break up the flocs. Sedimentation tank performance is strongly influenced by hydrodynamic and physical effects such as inlet design. This study was conducted to evaluate the effect of open ratio of the inlet baffle on hydraulic behavior within a rectangular sedimentation basin using CFD simulation and ADV technique. In order to verify the CFD simulation, we measured the factual velocity at 18 points in the full-scale sedimentation basin at Y water treatment plant. Good agreement was obtained between the CFD predictions and the experimentally measured data. From the simulation results of the existing basin with 7.4 % open ratio, it was investigated that extreme decrease in velocity occurred in the middle of basin. Since then, flow features was unstable. The region which the velocity decrease rapidly moved forward to the flow direction in proportion to the increase of inflow velocity. Also, it was investigated that the flow characteristic of 6.0 % open ratio was significantly different from 7.4 % open ratio at the same configuration condition. These results are a clear indication that inflow momentum and open ratio are the parameters affecting the characteristics of hydraulic patterns. The influence of these parameters on the sedimentation performance requires further study.

• Journal of the Korean Society for Railway
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• v.16 no.6
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• pp.454-459
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• 2013

Pressure waves are generated and propagate in a tunnel when train enters tunnel high speed. A compression wave due to the entry of train head propagates along the tunnel and is reflected at tunnel exit as an expansion wave. An expansion wave due to the entry of the train tail propagates along the tunnel and is reflected at tunnel exit as a compression wave. These pressure waves are repeatedly propagated and reflected at the tunnel entrance and exit. Severe pressure changes causes ear-discomfort for passengers in the cabin and micro pressure waves around the tunnel exit. It is necessary to analyze the transient pressure phenomena in tunnels qualitatively and quantitatively, because pressure change rate is considered as one of the major design parameters for optimal tunnel cross sectional area and repeated fatigue force on car body. In this study, we developed a characteristics method based on a fixed mesh system and boundary conditions for crossing trains and analyzed this system using an X-t diagram. The results of the simulation show that offsetting of pressure waves occurs for special entry conditions of a crossing train.

• Journal of the Korean Society for Railway
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• v.15 no.5
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• pp.436-441
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• 2012

Pressure waves are generated and propagate in tunnel when train enters a tunnel with high speed. Compression wave due to the entry of train head propagates along the tunnel and is reflected at tunnel exit as expansion wave. While expansion wave due to the entry of train tail propagates along the tunnel and is reflected at tunnel exit as compression wave. These pressure waves are repeatedly propagated and reflected at tunnel entrance and exit. Severe pressure change per second causes ear-discomfort for passengers in cabin and micro pressure wave around tunnel exit. It is necessary to analyze the transient pressure phenomena in tunnel qualitatively and quantitatively, because pressure change rate is considered as one of major design parameters for an optimal tunnel cross sectional area and the repeated fatigue force on car body. In this study, we developed the characteristics method analysis based on fixed mesh system and compared with the results of real train test. The results of simulation agreed with that of experiment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.4
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• pp.373-379
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• 2002

We investigated the evolution of magnetoresistance and magnetic property of tunneling magnetoresistive(TMR) device with microstructure and plasma oxidation time. TMR devices have potential applications for non volatile MRAM and high density HDD reading head. We prepared the tunnel magnetoresistance(TMR) devices of Ta($50{\AA}$)/NiFe($50{\AA}$)/IrMn($150{\AA}$)/CoFe($50{\AA}$)/Al($13{\AA}$)-O/CoFe($40{\AA}$)/FiFe($400{\AA}$)/Ta(($50{\AA}$) structure which have $100{\times}100\mu\textrm{m}^2$ junction area on $2.5{\times}2.5\textrm{cm}^2$ Si/$SiO_2$(($1000{\AA}$) substrates by an inductively coupled plasma(ICP) magnetron sputter. We fabricated the insulating layer using an ICP plasma oxidation method by with various oxidation time from 30 sec to 360 sec, and measured resistances and magnetoresistance(MR) ratios of TMR devices. We found that the oxidized sample for oxidation time of 80 sec showed the highest MR radio of 30.31 %, while the calculated value regarding inhomogeneous current effect indicated 25.18 %. We used transmission electron microscope(TEM) to investigate microstructural evolution of insulating layer. Comparing the cross-sectional TEM images at oxidation time of 150 sec and 360 sec, we found that the thickness and thickness variation of 360 sec-oxidized insulating layer became 30% and 40% larger than those of 150 sec-oxidized layer, repectively. Therefore, our results imply that increase of thickness variation with oxidation time may be one of the major treasons of the MR decrease.

• Journal of Yeungnam Medical Science
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• v.36 no.2
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• pp.141-147
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• 2019

Background: The present study aimed to evaluate the clinical association between cadmium exposure and hearing impairment among the Korean population. Methods: This retrospective cross-sectional study used the data obtained from the Korean National Health and Nutrition Examination Survey were used for our study. Finally, 3,228 participants were included in our study, which were then divided into quartiles based on their blood cadmium levels: first quartile (1Q), second quartile (2Q), third quartile (3Q), and fourth quartile (4Q) groups. The hearing thresholds were measured using an automatic audiometer at 0.5, 1, 2, 3, 4, and 6 kHz. Hearing loss (HL) was defined as >25 dB average hearing threshold (AHT). Results: All the groups had 807 participants each. The area under the receiver operating characteristic curves of cadmium level for HL were 0.634 (95% confidence interval [CI], 0.621-0.646). The participants in the 4Q group had higher Low/Mid-Freq, High-Freq, and AHT values than those in the other groups in the multivariate analysis after adjusting for confounding factors. The logistic regression showed that the OR for HL per $1{\mu}g/L$ increase in cadmium was 1.25 (95% CI, 1.09-1.44; p=0.002) on the multivariate analysis. Moreover, the multivariate logistic regression analyses revealed that the participants in the 4Q group exhibited a 1.59-, 1.38-, and 1.41-fold higher odds for HL than those in the 1Q, 2Q, and 3Q groups, respectively. Conclusion: High cadmium level quartile was associated with increased hearing thresholds and HL among the Korean adult population.

• Geomechanics and Engineering
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• v.27 no.5
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• pp.433-445
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• 2021

Artificial ground freezing (AGF) is a commonly used geotechnical support technique that can be applied in any soil type and has low environmental impact. Experimental and numerical investigations have been conducted to optimize AGF for application in diverse scenarios. Precise simulation of groundwater flow is crucial to improving the reliability these investigations' results. Previous experimental research has mostly considered horizontal seepage flow, which does not allow accurate calculation of the groundwater flow velocity due to spatial variation of the piezometric head. This study adopted vertical seepage flow-which can maintain a constant cross-sectional area-to eliminate the limitations of using horizontal seepage flow. The closure time is a measure of the time taken for an impermeable layer to begin to form, this being the time for a frozen soil-ice wall to start forming adjacent to the freeze pipes; this is of great importance to applied AGF. This study reports verification of the reliability of our experimental apparatus and measurement system using only water, because temperature data could be measured while freezing was observed visually. Subsequent experimental AFG tests with saturated sandy soil were also performed. From the experimental results, a method of estimating closure time is proposed using the inflection point in the thermal conductivity difference between pore water and pore ice. It is expected that this estimation method will be highly applicable in the field. A further parametric study assessed factors influencing the closure time using a two-dimensional coupled thermo-hydraulic numerical analysis model that can simulate the AGF of saturated sandy soil considering groundwater flow. It shows that the closure time is affected by factors such as hydraulic gradient, unfrozen permeability, particle thermal conductivity, and freezing temperature. Among these factors, changes in the unfrozen permeability and particle thermal conductivity have less effect on the formation of frozen soil-ice walls when the freezing temperature is sufficiently low.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.2
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• pp.249-260
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• 2014

When a train enters the tunnel at high speed, the pressure wave occurs. When this pressure wave reaches at the exit of tunnel, some are either emitted to the outside or reflected in tunnel by the form of expansion wave. The wave emitted to the outside forms the impulsive pressure wave. This wave is called 'Micro Pressure Wave'. The micro pressure wave generates noise and vibration around a exit portal of tunnel. When it becomes worse, it causes anxiety for residents and damage to windows. Thus, it requires a counterplan and prediction about the micro pressure wave for high speed railway construction. In this paper, the effects of train head nose and tunnel portal shape were investigated by model test, measurement for the micro pressure wave at the operating tunnel as well as numerical analysis for the gradient of pressure wave in the tunnel. As results, a method for predicting the intensity of the micro pressure wave is suggested and then the intensity of the micro pressure wave is analyzed by the tunnel length and the cross-sectional area.

• Journal of Nutrition and Health
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• v.30 no.3
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• pp.336-348
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• 1997

The objectives of this study were to examine the growth pattern of infants by anthropometric measurement according to the 5 feeding practices of infants with the subject of two hundred healthy newborn babies from their birth till sixty month of age at intervals of two months. Breast group(BF, n=38), formula group(FF, n=102) and mixed group(ME, n=14) were fed breast milk, formula milk, breast and formula milk, from birth till 6 mo. of age, respectively. Convert 1 group (C1F, n=14) and covert 2 group(CF, n=32) were fed breast milk and mixed milk at 2 mo. of age afterthat switched to formula milk, respectively. From these, the following results were made. All the infants of this study showed superiority to Korean standard growth rate in regards to each growth item for each month age. In the case of males, at their birth, the subscapular skinfold thickness and the total skin fold thickness in the BF group was significantly larger than in MF group and FF group(p<0.05). At 6th month age, the chese circumference of MF group was 45.9cm, and significantly larger than those of BF, FF and C2F groups(p<0.05). In the case of females, at theri birth and 2nd month age, there was no difference among all the feeding groups in regards to each growth rate. At 4th month age, the Kauf index of C1F group was 16.21 and significantly lower than those of four groups(p<0.05). And total skinfold thickness in BF group was larger than in C1F group. The increase rate per month age of all growth items were larger at 2nd month age than at the later months both in males and in females. And until 2nd month age males showed more increase than females in regards to each growth item but after 2nd month age, this sapect did not show up. Multiple linear regression was used to determine predictive factors for infant growth. It was expected that at 6th month age, in the measurement of head circumference and chest circumference and cross-sectional fat area, BF-males were bigger by 22-39% of the explanation index than the infants of other groups. As a result, in spite of the significant lower intakes of energy and nutrients in breast-fed infants than in formula-fed infants, breast-fed infants showed more growth than the average of Korean infant standard growth rate at every month age, and showed no significant growth difference among feeding groups.