• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.3
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• pp.205-212
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• 2014

In this paper, sunroof buffeting analysis for Hyundai simple model(HSM) is studied computationally. For validation, the velocity profile of boundary layer around the opening of HSM was obtained and compared with experimental results. The analysis of sunroof buffeting is done in two parts. First a steady state solution is obtained using the Reynolds Averaged Navier Stokes (RANS) solver, and then the computed flow field information is used as input for CAA++. Second transient simulation by CAA++ is performed for the peak sound pressure levels and peak frequencies of buffeting noise over the ranges of flow velocities. The benchmark results of frequency and sound pressure levels showed the general phenomena and matched well with the experimental data obtained by Hyundai Motor Car.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.10
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• pp.4005-4011
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• 2010

This study investigates the effect on automobile traffic flow of the bike lane configuration via the road diet implemented in Nam-Gu, Busan using the microscopic simulator TransModeler. The results show that the increases in average delay time and stopped time experienced by automobile vehicles after implementing the road diet during the peak period are significant, but those during the non-peak period are insignificant at alpha=0.1. The results in peak period are consistent with the results of the past studies, which concluded that a road diet can contribute to deteriorating the level of service when the automobile traffic flow rate on the existing roadway is relatively high. For the non-peak period, the analysis results may reflect the fact that the automobile traffic flow is not severly affected by the road diet due to the reserved capacity.

• Journal of Preventive Medicine and Public Health
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• v.40 no.1
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• pp.59-63
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• 2007

Objectives : Nitrogen dioxide $(NO_2)$ has been inconsistently associated with gradual decreases in lung function. Here, we studied the effects of $NO_2$ exposure in asthmatics by examining the association between changes in lung function and concentrations of $NO_2$ which were personally measured. Methods : Peak expiratory flow (PEF) and daily personal exposures to $NO_2$ were recorded on 28 patients with asthma (confirmed by methacholine provocation test) over 4 weeks. We used generalized estimating equations to assess the relationship between personal $NO_2$ exposure and PEF, adjusting for potential confounders such as age, gender, outdoor particulate matter, temperature, humidity, and exposure to environmental tobacco smoke. Results : The personal $NO_2$ exposures were higher than the corresponding ambient levels. The mean personal: ambient ratio for $NO_2$ was 1.48. The personal $NO_2$ exposures were not associated with the morning PEF, evening PEF, or the diurnal PEF variability. However, environmental tobacco smoke was negatively associated with both the morning and evening PEF. Conclusions : Among the asthmatic adults who participated in this study, we found no apparent impact of personal $NO_2$ exposures on the peak expiratory flow.

• Korean Journal of Metals and Materials
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• v.56 no.11
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• pp.779-786
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• 2018

There have been previous attempts to observe the occurrence of dynamic ferritic transformation at temperatures even above $Ae_3$ in a low-carbon steel, and not only in steels, but recently also in titanium alloys. In this study, a new approach is proposed that involves treating true stress-true strain curves in uniaxial compression tests at various temperatures, and different strain rates in 0.1C-6Ni steel, which is a model alloy used to decelerate the kinetics of ferrite transformation from austenite. The initial flow stress up to peak stress was used to analyze the change in dynamic softening phenomena, such as dynamic recovery, dynamic recrystallization, and dynamic transformation. It is worth mentioning that for predicting the occurrence of dynamic transformation, flow stress before reaching peak stress is much more sensitive to the change in the dynamic softening rate due to dynamic transformation, compared to peak stress. It was found that the occurrence of dynamic ferritic transformation could be successfully obtained even at temperatures above $Ae_3$ once the deformation condition was satisfied. This deformation condition is a function of both the strain rate and the deformation temperature, which can be described as the Zener - Hollomon parameter. In addition, the driving force of dynamic ferritic transformation might be much less than that of the dynamic recrystallization of austenite at a given deformation condition. By applying this technique, it is possible to predict the occurrence of dynamic transformation more sensitively compared with the previous analysis method using peak stress during deformation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.1
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• pp.409-418
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• 2019

Debris flows occur in mountainous areas due to heavy rains resulting from climate change and result in disasters in the downstream area. The purpose of this study is to estimate the impact force of a debris flow when a check dam according is installed in various locations in the channel of a highly mountainous area. A Finite Differential Element Method (FDM) model was used to simulate the erosion and deposition based on the equation for the mass conservation and momentum conservation while considering the continuity of the fluid. The peak impact force from the debris flow occurred at 0 to 5 sec and 15 to 20 sec. When the supplied water discharge was increased, greater peak impact force was generated at 16 to 19 sec. This means that when increasing the water supply, the velocity of the debris flow became faster, which results in increased energy of the consolidation between the particles of the water and the sediment made. If a number of check dams were to be set up, it would be necessary to investigate the impact force at each location of the check dam. The results of this study could provide useful information in predicting the impact force of the debris flow and in installing the check dams in appropriate locations.

• Restorative Dentistry and Endodontics
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• v.24 no.2
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• pp.265-285
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• 1999

The purposes of this investigation were to observe the reaction kinetics of five commercial dual cured resin cements (Bistite, Dual, Scotchbond, Duolink and Duo) when cured under varying thicknesses of porcelain inlays by chemical or light activation and to evaluate the effect of the porcelain disc on the rate of polymerization of dual cured resin cement during light exposure by using thermal analysis. Thermogravimetric analysis(TGA) was used to evaluate the weight change as a function of temperature during a thermal program from $25{\sim}800^{\circ}C$ at rate of $10^{\circ}C$/min and to measure inorganic filler weight %. Differential scanning calorimetry(DSC) was used to evaluate the heat of cure(${\Delta}H$), maximum rate of heat output and peak heat flow time in dual cured resin cement systems when the polymerization reaction occured by chemical cure only or by light exposure through 0mm, 1mm, 2mm and 4mm thickness of porcelain discs. In 4mm thickness of porcelain disc, the exposure time was varied from 40s to 60s to investigate the effect of the exposure time on polymerization reaction. To investigate the effect on the setting of dual cured resin cements of absorption of polymerizing light by porcelain materials used as inlays and onlays, the change of the intensity of the light attenuated by 1mm, 2mm and 4mm thickness of porcelain discs was measured using curing radiometer. The results were as follows 1. The heat of cure of resin cements was 34~60J/gm and significant differences were observed between brands (P<0.001). Inverse relationship was present between the heat of reaction and filler weight % the heat of cure decreased with increasing filler content (R=-0.967). The heat of reaction by light cure was greater than by chemical cure in Bistite, Scotchbond and Duolink(P<0.05), but there was no statistically significant difference in Dual and Duo(P>0.05). 2. The polymerization rate of chemical cure and light cure of five commercially available dual cured resin cements was found to vary greatly with brand. Setting time based on peak heat flow time was shortest in Duo during chemical cure, and shortest in Dual during light cure. Cure speed by light exposure was 5~20 times faster than by chemical cure in dual cured resin cements. The dual cured resin cements differed markedly in the ratio of light and chemical activated catalysts. 3. The peak heat flow time increased by 1.51, 1.87, and 3.24 times as light cure was done through 1mm, 2mm and 4mm thick porcelain discs. Exposure times recommended by the manufacturers were insufficient to compensate for the attenuation of light by the 4mm thick porcelain disc. 4. A strong inverse relationship was observed between peak heat flow and peak time in chemical cure(R=0.951), and a strong positive correlations hip was observed between peak heat flow and the heat of cure in light cure(R=0.928). There was no correlationship present between filler weight % or heat of cure and peak time. 5. The thermal decomposition of resin cements occured primarily between $300^{\circ}C$ and $480^{\circ}C$ with maximum decomposition rates at $335^{\circ}C$ and $440^{\circ}C$.

• Water Engineering Research
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• v.2 no.4
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• pp.219-229
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• 2001

Synthetic unit hydrograph equations for rainfall run-off characteristics analysis and estimation of design flood have long and quite frequently been presented, the Snyder and SCS synthetic unit hydrograph. The major inputs to the Snyder and SCS synthetic unit hydrograph are lag time and peak coefficient. In this study, the methods for estimating lag time and peak coefficient for small watersheds proposed by Zhao and McEnroe(1999) were applied to the Kum river basin in Korea. We investigated lag times of relatively small watersheds in the Kum river basin in Korea. For this investigation the recent rainfall and stream flow data for 10 relatively small watersheds with drainage areas ranging from 134 to 902 square kilometers were gathered and used. 250 flood flow events were identified along the way, and the lag time for the flood events was determined by using the rainfall and stream flow data. Lag time is closely related with the basin characteristics of a given drainage area such as channel length, channel slope, and drainage area. A regression analysis was conducted to relate lag time to the watershed characteristics. The resulting regression model is as shown below: ※ see full text (equations) In the model, Tlag is the lag time in hours, Lc is the length of the main river in kilometers and Se is the equivalent channel slope of the main channel. The coefficient of determinations (r$^2$)expressed in the regression equation is 0.846. The peak coefficient is not correlated significantly with any of the watershed characteristics. We recommend a peak coefficient of 0.60 as input to the Snyder unit-hydrograph model for the ungauged Kum river watersheds

• Journal of Korean Society of Transportation
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• v.28 no.5
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• pp.7-15
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• 2010

The walkway level of service (LOS) is conceptualized using pedestrian flow rate, speed, and density according to the Korean Highway Capacity Manual (KHCM). However, as it is based on the data of commuters at peak hours, it needs to be reevaluated considering various trip purposes and a pleasant pedestrian environment. Thus, the authors aimed to investigate and analyze the characteristics of each group: pedestrians during the peak hour and those during the non-peak hour. Then they were verified statistically for the walkway evaluation criteria. In this study, the authors investigated pedestrian speed and flow in a complex transit center walkway with diverse trip purposes by peak and non-peak hour. Then the authors statistically verified the differences between the groups. A model was built for estimating pedestrian density by speed and flow; it was used to calculate the walkway capacity (67.3p/m/m) corresponding to LOS E. The authors established new criteria for LOS, applying the LOS from the HCM. These standards can then be used as the design standards for pedestrian walkways.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1603-1612
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• 1990

An experimental study is conducted to investigate the fluid flow and heat transfer around tubes arranged in line. All measurements are performed at Reynolds number 1.58*10$^{4}$ with varing tube spacings from the small pitch ratio(L/D=1.25) to the large pitch ratio(L/D=3.0). Mean static pressures and mean temperatures of the surface of tubes and mean velocities and turbulent intensities in tube banks are measured. The flow patterns and the characteristics of heat transfer are strongly influenced by the tube spacings. Especially, in the case of very small spacings(L/D=1.25), the flow between neighboring tubes becomes very stagnant and the heat transfer decreases. In the case of each tube spacing, the characteristics of heat transfer around the 3rd, the 4th and the 5th tubes are nearly similar to one another, because the flow around tubes becomes stable at the 3rd tubes. The local heat transfer has the peak value near the reattachment point which has the peak value of pressure, but the local heat transfer for the 2nd tube of L/D=1.25 without reattaching has the peak value at .theta.=75.deg.. For each pitch ratio, the mean heat transfer increases gradually toward the downstream tubes, because the oncoming flow through neighboring tubes comes closer to the forward and rear surfaces of the tube and the turbulent intensity becomes larger in the downstream direction.

• Journal of the Semiconductor & Display Technology
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• v.7 no.3
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• pp.1-4
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• 2008

The chemical shift of SiOC film was observed according to the flow rate ratio. SiOC film had the broad main band of $880\sim1190cm^{-1}$ and the sharp Si-$CH_3$ bond at $1252cm^{-1}$, and the peak position of the main bond in the infrared spectra moved to high frequency according to the increasing of an BTMSM flow rate. So the increment of the alkyl group induced the C-H bond condensation in the film, and shows the blueshift in the infrared spectra. In the case of P5000 system of Applied Materials Corporation, the strong bond of Si-CH3 bond in precursor does not enough to dissociated and ionized, because low plasma energy due to the capactive coupled CVD. Therefore, there was the sharp peak of Si-$CH_3$ bond at $1252cm^{-1}$.