• Wind and Structures
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• 제30권4호
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• pp.367-378
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• 2020

Two-dimensional Delayed Detached Eddy Simulation (DDES) was carried out to investigate the uniform flow over a twin-box bridge deck (TBBD) with various gap ratios of L/C=5.1%, 12.8%, 25.6%, 38.5%, 73.3% and 108.2% (L: the gap-width between two girders, C: the chord length of a single girder) at Reynolds number, Re=4×104. The aerodynamic coefficients of the prototype deck with gap ratio of 73.3% obtained from the present simulation were compared with the previous experimental and numerical data for different attack angles to validate the present numerical method. Particular attention is devoted to the fluctuating pressure distribution and forces, shear layer reattachment position, wake velocity and flow pattern in order to understand the effects of gap ratio on dynamic flow interaction with the twin-box bridge deck. The flow structure is sensitive to the gap, thus a change in L/C thus leads to single-side shedding regime at L/C≤25.6%, and co-shedding regime at L/C≥35.8% distinguished by drastic changes in flow structure and vortex shedding. The gap-ratio-dependent Strouhal number gradually increases from 0.12 to 0.27, though the domain frequencies of vortices shedding from two girders are identical. The mean and fluctuating pressure distributions is significantly influenced by the flow pattern, and thus the fluctuating lift force on two girders increases or decreases with increasing of L/C in the single-side shedding and co-shedding regime, respectively. In addition, the flow mechanisms for the variation in aerodynamic performance with respect to gap ratios are discussed in detail.

• Environmental Engineering Research
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• 제22권1호
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• pp.19-30
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• 2017

Direct catalysis of vapors from vacuum pyrolysis of biomass was performed on MCM-41 to investigate the effects of operating parameters including catalyzing temperature, catalyzing bed height and system pressure on the organic yields. Optimization of organic phase yield was further conducted by employing response surface methodology. The statistical analysis showed that operating parameters have significant effects on the organic phase yield. The organic phase yield first increases and then decreases as catalyzing temperature and catalyzing bed height increase, and decreases as system pressure increases. The optimal conditions for the maximum organic phase yield were obtained at catalyzing temperature of $502.7^{\circ}C$, catalyzing bed height of 2.74 cm and system pressure of 6.83 kPa, the organic phase yield amounts to 15.84% which is quite close to the predicted value 16.19%. The H/C, O/C molar ratios (dry basis), density, pH value, kinematic viscosity and high heat value of the organic phase obtained at optimal conditions were 1.287, 0.174, $0.98g/cm^3$, 5.12, $5.87mm^2/s$ and 33.08 MJ/kg, respectively. Organic product compositions were examined using gas chromatography/mass spectrometry and the analysis showed that the content of oxygenated aromatics in organic phase had decreased and hydrocarbons had increased, and the hydrocarbons in organic phase were mainly aliphatic hydrocarbons. Besides, thermo-gravimetric analysis of the MCM-41 zeolite was conducted within air atmosphere and the results showed that when the catalyst continuously works over 100 min, the index of physicochemical properties of bio-oil decreases gradually from 1.15 to 0.45, suggesting that the refined bio-oil significantly deteriorates. Meanwhile, the coke deposition of catalyst increases from 4.97% to 14.81%, which suggests that the catalytic activity significantly decreases till the catalyst completely looses its activity.

• 조명전기설비학회논문지
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• 제25권3호
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• pp.24-32
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• 2011

[ $SF_6$ ]gas, which has an excellent dielectric strength and interruption performance, is used in various applications such as gas insulated switchgear (GIS) in substations. However, since $SF_6$ has a high global warming potential (GWP), it is necessary to find an eco-friendly alternative insulation gas. In order to examine the possibility of using alternative insulation gases for $SF_6$ in power distribution system equipment, the dielectric strength and physical phenomena of dry air in a quasi-uniform electric field are investigated experimentally in this paper. As a result, the breakdown voltages for positive polarity are higher than those for negative polarity under impulse voltage applications. The negative 50[%] flashover voltage, $V_{50}$ of dry air under conditions above 0.4[MPa] gas pressure, is higher than 150[kV], that is the basic impulse insulation level of distribution equipment. The $V_{50}$ increases linearly with increasing the gas pressure, regardless of the waveform and polarity of the applied impulse voltages. The voltage-time curves are dependent on the rise time of the impulse voltage and gas pressure. Furthermore, streamer discharge was observed through light emission images by an ICCD camera under impulse voltage applications.

• Nuclear Engineering and Technology
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• 제53권4호
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• pp.1119-1126
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• 2021

Spacer grid with mixing vane had been widely used in nuclear reactor core. One of the main feather of spacer grid with mixing vane was that strong swirl flow was formed after the spacer grid. The swirl flow not only changed the bubble generation in the near wall field, but also affected the bubble behaviors in the center region of the subchannel. The interaction between bubble and the swirl flow was one of the basic phenomena for the two phase flow modeling in fuel assembly. To obatin better understanding on the bubble behaviors in swirl flow, full three dimension numerical simulations were conducted in the present paper. The swirl flow was assumed in the cylindral calculation domain. The bubble interface was captured by Volume Of Fluid (VOF) method. The properties of saturated water and steam at different pressure were applied in the simulation. The bubble trajectory, motion, shape and force were obtained based on the bubble parameters captured by VOF. The simulation cases in the present study included single bubble with different size, at different angular velocity conditions and at different pressure conditions. The results indicated that bubble migrated to the center in swirl flow with spiral motion type. The lateral migration was mainly related to shear stress magnitude and bubble size. The bubble moved toward the center with high velocity when the swirl magnitude was high. The largest bubble had the highest lateral migration velocity in the present study range. The effect of pressure was small when bubble size was the same. The prelimenery simulation result would be beneficial for better understanding complex two phase flow phenomena in fuel assembly with spacer grid.

• 지역사회간호학회지
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• 제17권4호
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• pp.441-450
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• 2006

Purpose: The purposes of this study were to identify variables related to self-care behavior and to find factors related to the control of hypertension. A cross-sectional study was carried out to provide basic data for effective and continuous hypertension control in the low-income elderly. Methods: This study was performed with a total of 189 subjects who were hypertensive and were receiving pharmacological treatment of hypertension from a community health center in D Metropolitan City. Data were collected through a face to face survey, and systolic and diastolic blood pressure (the mean value of the two measures) were measured during May 2004. Obtained data were analyzed by $x^2$ test, t-test, multiple logistic regression and Pearson's correlation coefficient (using SPSS Version 10.1). Results: 1. According to demographical characteristics, the score of self-care behavior was significantly higher in elders living along ($47.63{\pm}7.276$) than in those living with the family ($45.19{\pm}5.501$) (p<.05), and in those with religion ($47.11{\pm}6.722$) than in those without religion ($45.01{\pm}6.110$) (p<.05) 2. As to blood pressure control, the percentage of blood pressure control within the normal range (systolic 140mmHg, diastolic below 90mmHg) was 37.03%. According to demographical characteristics, the percentage of blood pressure control was significantly lower in those without religion (p<.05). In practicing hypertension self-care behavior, those who do not control salk intake showed a significantly lower percentage of hypertension control (p<.05). The score of hypertension self-care was $48.28{\pm}4.443$ in the controlled group, and $45.42{\pm}7.399$ in the uncontrolled group, showing a significant difference (p<.01). 3. Hypertension self-care behavior was in a positive correlation with blood pressure control (r=.210, p<.05). Conclusion: Attention should be paid to self-care behavior to increase the control of hypertension in the low-income elderly. These results can be used guidances for improving self-care behavior and the control of hypertension in the low-income elderly.

• The Journal of Advanced Prosthodontics
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• 제7권3호
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• pp.214-223
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• 2015

PURPOSE. To measure the surface loss of dental restorative zirconia and the short-term bond strength between an indirect composite resin (ICR) and zirconia ceramic after various sandblasting processes. MATERIALS AND METHODS. Three hundred zirconia bars were randomly divided into 25 groups according to the type of sandblasting performed with pressures of 0.1, 0.2, 0.4 and 0.6 MPa, sandblasting times of 7, 14 and 21 seconds, and alumina powder sizes of 50 and $110{\mu}m$. The control group did not receive sandblasting. The volume loss and height loss on zirconia surface after sandblasting and the shear bond strength (SBS) between the sandblasted zirconia and ICR after 24-h immersion were measured for each group using multivariate analysis of variance (ANOVA) and Least Significance Difference (LSD) test (${\alpha}$=.05). After sandblasting, the failure modes of the ICR/zirconia surfaces were observed using scanning electron microscopy. RESULTS. The volume loss and height loss were increased with higher sandblasting pressure and longer sandblasting treatment, but they decreased with larger powder size. SBS was significantly increased by increasing the sandblasting time from 7 seconds to 14 seconds and from 14 seconds to 21 seconds, as well as increasing the size of alumina powder from $50{\mu}m$ to $110{\mu}m$. SBS was significantly increased from 0.1 MPa to 0.2 MPa according to the size of alumina powder. However, the SBSs were not significantly different with the sandblasting pressure of 0.2, 0.4 and 0.6 MPa. The possibilities of the combination of both adhesive failure and cohesive failure within the ICR were higher with the increases in bonding strength. CONCLUSION. Based on the findings of this study, sandblasting with alumina particles at 0.2 MPa, 21 seconds and the powder size of $110{\mu}m$ is recommended for dental applications to improve the bonding between zirconia core and ICR.

• International Journal of Automotive Technology
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• 제8권4호
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• pp.437-444
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• 2007

This paper experimentally investigates the effects of oxygen-enriched air (OEA) on the running behaviors of an LPG SI engine during both start/warm-up (SW) and hot idling (HI) stages. The experiments were performed on an air-cooled, single-cylinder, 4-stroke, LPG SI engine with an electronic fuel injection system and an electrically-heated oxygen sensor. OEA containing 23% and 25% oxygen (by volume) was supplied for the experiments. The throttle position was fixed at that of idle condition. A fueling strategy was used as following: the fuel injection pulse width (FIPW) in the first cycle of injection was set 5.05 ms, and 2.6 ms in the subsequent cycles till the achieving of closed-loop control. In closed-loop mode, the FIPW was adjusted by the ECU in terms of the oxygen sensor feedback. Instantaneous engine speed, cylinder pressure, engine-out time-resolved HC, CO and NOx emissions and excess air coefficient (EAC) were measured and compared to the intake air baseline (ambient air, 21% oxygen). The results show that during SW stage, with the increase in the oxygen concentration in the intake air, the EAC of the mixture is much closer to the stoichiometric one and more oxygen is made available for oxidation, which results in evidently-improved combustion. The ignition in the first firing cycle starts earlier and peak pressure and maximum heat release rate both notably increase. The maximum engine speed is elevated and HC and CO emissions are reduced considerably. The percent reductions in HC emissions are about 48% and 68% in CO emissions about 52% and 78%; with 23% and 25% OEA, respectively, compared to ambient air. During HI stage, with OEA, the fuel amount per cycle increases due to closed-loop control, the engine speed rises, and speed stability is improved. The HC emissions notably decrease: about 60% and 80% with 23% and 25% OEA, respectively, compared to ambient air. The CO emissions remain at the same low level as with ambient air. During both SW and HI stages, intake air oxygen enrichment causes the delay of spark timing and the increased NOx emissions.

• Geomechanics and Engineering
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• 제35권1호
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• pp.29-39
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• 2023

As the intensity of urban underground space development increases, more and more tunnels are planned and constructed, and sometimes it is inevitable to encounter situations where tunnels have to underpass the river embankments. Most previous studies involved tunnels passing river embankments perpendicularly or with large intersection angle. In this study, a project case where two EPB shield tunnels with 8.82 m diameter run parallelly underneath a river embankment was reported. The parallel length is 380 m and tunnel were mainly buried in the moderate / slightly weathered clastic rock layer. The field monitoring result was presented and discussed. Three-dimensional back-analysis were then carried out to gain a better understanding the interaction mechanisms between shield tunnel and embankment and further to predict the ultimate settlement of embankment due to twin-tunnel excavation. Parametrical studies considering effect of tunnel face pressure, tail grouting pressure and volume loss were also conducted. The measured embankment settlement after the single tunnel excavation was 4.53 mm ~ 7.43 mm. Neither new crack on the pavement or cavity under the roadbed was observed. It is found that the more degree of weathering of the rock around the tunnel, the greater the embankment settlement and wider the settlement trough. Besides, the latter tunnel excavation might cause larger deformation than the former tunnel excavation if the mobilized plastic zone overlapped. With given geometry and stratigraphic condition in this study, the safety or serviceability of the river embankment would hardly be affected since the ultimate settlement of the embankment after the twin-tunnel excavation is within the allowable limit. Reasonable tunnel face pressure and tail grouting pressure can to some extent suppress the settlement of the embankment. The recommended tunnel face pressure and tail grouting pressure are 300 kPa and 550 kPa in this study, respectively. However, the volume loss plays the crucial role in the tunnel-embankment interaction. Controlling and compensating the tunneling induced volume loss is the most effective measure for river embankment protection. Additionally, reinforcing the embankment with cement mixing pile in advance is an alternative option in case the predicted settlement exceeds allowable limit.

• 한국환경복원기술학회지
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• 제20권4호
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• pp.15-28
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• 2017

A protected area means a space designated and protected by law from development pressure and environmental pressure. It is mainly designated to protect specific ecosystems, natural landscapes, and cultural resources from irrational development (or damage), and involves policies of the public sector such as central and local governments. The United Nations Educational, Scientific and Cultural Organization (UNESCO) has conducted conservation and restoration projects for preserving natural ecosystems and genetic resources. In order to conserve the ecosystem in the protected area, national and public organizations purchase private land and use it ecologically; in addition, ecological restoration project is carried out for the purpose of creating waterside ecological belt or preserving ecosystem. Land acquisition refers to the land where highly influenced by the water quality and need to restore, and purchased by negotiating with the landlord. Although the nation and public institution carried out ecosystem restoration project for partial purchase land in order to conserve ecosystem, it is below the expected effect due to lack of comprehensive management system and have some problems in restoration project and unification of management institutions. Land acquisition in Donggang River Basin Ecological Conservation area is initiated in 2005 for creating income of local residents and ecological restoration. However, the lack of overall management and awareness resulted in poor vegetation growth and poor response by local residents due to terrain exposure. As such, there is insufficient research on the current situation and systematic integrated management although the number of land acquisition is increasing year after year. Futhermore, overall recognition and follow-up monitoring of eco-restoration are still inadequate. Therefore, the survey on the awareness of the purchase land ecosystem restoration project is necessary for the efficient restoration project and establishment of the management strategy for land acquisition in the future. Therefore, in this study, we provide fundamental materials on further research projects by carrying out research on the awareness of ecological restoration projects in the Donggang River basin ecological preservation area.

• 혜화의학회지
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• 제29권2호
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• pp.30-37
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• 2020

Objectives : In this case, the knee joint inconvenience with deteriorating pain has been relieved by acupuncture treatment for a patient was 51-year-old male with a left medial meniscal posterior horn rupture in 2012. Methods : Twenty-four times of acupuncture treatments were performed for Twelve weeks from July 2016 to improve the disease. SP8(Jigi; 地機), BL63(Geummun; 金門), KI3(Taegye; 太谿), LI4(Hapgok; 合谷) were chosen for treatment by principles of Traditional Korean Medicine. Results : Numeric Rating Scales, which means subjective pain, decreased from 6 points to 3 points out of 10 points in total. Pressure Pain Threshold, which means sensitivity to pressure applied to the affected area, increased from 21N to 47N on the lateral-inferior side and from 19N to 50N on the lateral side. K-WOMAC, which indicates discomfort of knee-related activity, was 56 points out of 96 points in total before treatment and 4 points after treatment, 13 points after two years, and 15 points after four years. However, MRI tests conducted before and after treatment did not identify any significant changes. As a result, we confirmed that a total of 24 acupuncture treatments had resulted in the relief objective and subjective pain and functional recovery, especially in the case of the knee function, maintained until after four years later. There was no significant substrate recovery in meniscal rupture.