• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.226-235
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• 2000

Two representative finite volume methods, i.e., the time marching method and the pressure correction method, were applied to 8 centrifugal compressor impeller flows, with low to very high level of pressure ratio, among which 7 impellers' experimental performance is given in the open literature. The present study is focused on the prediction differences from both methods, developed by the authors, in the pressure correction method's point of view. In all cases, the time marching method gives a satifactory solution, but the pressure correction method does not. Up to about $18\%$ less level of total-to-total pressure ratio is predicted by the pressure correction method as the level of the impeller pressure ratio increases up to about 10. The drop of total pressure ratio is caused by the underestimation of static pressure rise which seems to be attributed to inappropriate linearization and discretization of the pressure/density coupling terms in the pressure correction equation.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.445-452
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• 2001

Generally, OPC(ordinary portland cement) is used for grouting in Korea, and bentonite has usually been added to prevent the deposition of cement particles. The dispersion of CB(cement bentonite) grout is influenced by variable factors i.e. water to cement ratio, particle size of cement, kind of bentonite, adding volume, methods of adding, viscosity of CB grout materials and curdling time. Among variable factors, the viscosity of CB grout materials is influenced by the dispersion, and dispersion is improved as increasing the mixing speed. In this paper, described a suitable mixing speed of the High Speed Mixer in field, engineering characteristics of CB grout materials vary with the water to cement ratio and the mixing speed as well as confirming the state of dispersion.

• Annals of Hepato-Biliary-Pancreatic Surgery
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• v.27 no.2
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• pp.158-165
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• 2023

Backgrounds/Aims: Within two years of surgery, 70% of resected intrahepatic cholangiocarcinoma (iCCA) recur. Better biomarkers are needed to identify those at risk of "early recurrence" (ER). In this study, we defined ER and investigated whether preoperative neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and systemic-inflammatory index were prognostic of both overall relapse and ER after curative hepatectomy for iCCA. Methods: A retrospective cohort of patients who underwent curative-intent hepatectomy for iCCA between 2005 and 2017 were created. The cut-off timepoint for the ER of iCCA was estimated using a piecewise linear regression model. Univariable analyses of recurrence were conducted for the overall, early, and late recurrence periods. For the early and late recurrence periods, multivariable Cox regression with time-varying regression coefficient analysis was used. Results: A total of 113 patients were included in this study. ER was defined as recurrence within 12 months of a curative resection. Among the included patients, 38.1% experienced ER. In the univariable model, a higher preoperative NLR (> 4.3) was significantly associated with an increased risk of recurrence overall and in the first 12 months after curative surgery. In the multivariable model, a higher NLR was associated with a higher recurrence rate overall and in the ER period (≤ 12 months), but not in the late recurrence period. Conclusions: Preoperative NLR was prognostic of both overall recurrence and ER after curative iCCA resection. NLR is easily obtained before and after surgery and should be integrated into ER prediction tools to guide preoperative treatments and intensify postoperative follow-up.

• Journal of the Korea Institute of Building Construction
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• v.8 no.5
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• pp.59-65
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• 2008

In the evaluation method of KS on the activity factor of fly ash, same amount of cement should be replaced with fly ash. Therefore, contradictory effects on concrete strength exist, i. e. strength decease due to low content of cement and strength increase of strength due to filling-pore-function of fly ash. European Committee for Standardization (CEN) specifies the method 1 to 4. adding fly ash without reducing the content of cement, for the evaluation method on activity factor of fly ash. This study investigates the applicability of the method 2 of CEN to mix design of concrete. The followings are derived ; There is a key ratio of f)y ash mixing which enhances the incremental ratio of mixing water to improve fluidity of mortar. The incremental ratio of mixing water is maximized about 11% ratio of fly ash mixing. Compressive strength most slightly increases at that ratio of fly ash mixing. Activity factor of fly ash increases as water-cement ratio becomes low and contents of fly ash becomes high. Moreover, quality of fly ash and condition of mix design affect the applicable amount of fly ash and available range of water-cement ratio. However, this method has some problems for practical purpose because activity factors of fly ash for some cases are over 1.0. Further research should be conducted to develop more useful method of evaluating activity factor of fly ash.

• Atmosphere
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• v.27 no.4
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• pp.399-409
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• 2017

The impact of land cover changed by tidal flats on local meteorology in Gyeonggi Bay was quantitatively evaluated based on a numerical modeling approach during 18 days (21 June to 9 July 2013). The analysis was carried out using three sets of simulation scenarios and the land cover of tidal flats for each simulation was applied as follows: (1) the herbaceous wetland representing coastal wetlands (i.e., EXP-BASE case), (2) the barren or sparsely vegetated representing low tide (i.e., EXP-LOW case), (3) the water bodies representing high tide (i.e., EXP-HIGH case). The area of tidal flats was calculated as about $552km^2$ (the ratio of 4.7% for analysis domain). During the daytime, the change (e.g. wetlands to water) of land cover flooded by high tide indicated the decrease of temperature (average $3.3^{\circ}C$) and the increase of humidity (average 13%) and wind speed (maximum $2.9m\;s^{-1}$). The changes (e.g. wetlands to barren or sparsely vegetated) of land cover induced by low tide were smaller than those by high tide. On the other hands, the effects of changed land cover at night were not apparent both high tide and low tide. Also, during the high tide, the meteorological change in tidal flats affected the metropolitan area (about 40 km from the tidal flat).

• The Journal of Korean Medicine
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• v.24 no.3
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• pp.1-10
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• 2003

Background : Asthma is a chronic inflammatory disorder under immunological influence. Gamichunggumgangwha-tang (CG, Jiaweiqingjinjianghuo-tang) and Gamiyukmigiwhang-tang (YM, Jiaweiliuweidihuang-tang) are herbal tonics for asthma from traditional herbal medicine. Objective : To evaluate the effect of CG and YM on immune cell & serum OA-specific IgE in broncho-alveolar lavage fluid (BALF) in a rat asthma model. Materials and Methods : Rats were sensitized with OA; at day I sensitized group and CG and YM groups were systemically immunized by subcutaneous injection of 1mg OA and 300mg of Al(OH)3 in a total volume of 2ml. At the same time, 1 ml of 0.9% saline containing $6{\times}10^9$ B. pertussis bacilli was injected by Lp. 14 days after the systemic immunization, rats received local immunization by inhaling 0.9% saline aerosol containing 2% (wt/vol) OA. A day after local immunization, BALF was collected from the rats. Rats were orally administered with each of CG and YM extract for 14 days since the day after local immunization. Lymphocyte, CD4＋ T cell and CD8＋ T cell counts, CD4＋/CD8＋ ratio in BALF, change of serum OA-specific IgE level, CD4＋ T cell and CD8＋ T cell percentages in the peripheral blood were measured and evaluated. Results : CG and YM showed an alleviating effect on asthmatic responses of rats. CG decreased total cell, lymphocyte, CD4＋ T cells in BALF, and serum OA-specific IgE level as compared with the control group. YM decreased lymphocytes as compared with the control group. CD4＋/CD8＋ ratio in BALF from the CG and YM groups and serum OA-specific IgE level from the YM group didn't show any significant variation from the control group. Conclusion : CG alleviated asthmatic hyperreactivity of the immune system through CD4＋ T cells and serum IgE. Further the study of this immune system modulating mechanism is expected.

• Journal of the Korean earth science society
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• v.27 no.6
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• pp.695-700
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• 2006

We present B, V, I time series CCD photometry for the variable star TU UMi to classify its variable type. The observations were performed using 61cm telescope equipped with 2K CCD camera at Sobaeksan Optical Astronomy Observatory (SOAO). Judging from the amplitude ratio $({\Delta}i/{\Delta}v)$ and color variation $({\Delta}(b-v),\;{\Delta}(v-i))$. TU UMi should be a W UMa type eclipsing binary. We obtained two primary times of minimum lights (HJD 2453848.0446, HJD 2453848.2309) from our observations and determined new orbital elements (Min I=HJD 2452500.1344+0.37708907${\times}$E) for TU UMi.

• Journal of Environmental Science International
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• v.12 no.1
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• pp.35-40
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• 2003

With increasing population densities in cities, underground facilities and entertainment locations are proliferating at a rapid pace in efforts to maximize the use of land. The purpose of this study is to evaluate CO concentration level of subway stations having underground platforms in Busan Metropolitan City, from September to November 2000, over seven times. The places of inquiry include Yonsan-dong station, Somyon station, Busan station, Nampo-dong station and Dusil station. The samplings were conducted at three points of each station, i.e. gates, ticket gates, and platforms. The component of CO concentration is the main elements of indoor air quality evaluation. The total concentrations and average concentrations of CO were the higher at the Somyon station. The distribution of CO concentrations at each station, generally was higher at gate than ticket gates and platforms. The I/O ratios(I-platforms, 0-gates) were expressed highly than 1 at the Yonsan-dong station, Busan station, Nampo-dong station and were lower than 1 at the others.

• Transactions on Electrical and Electronic Materials
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• v.6 no.5
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• pp.202-209
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• 2005

Phase evolution, microstructure and the electrical properties such as $k_p$ and $Q_m$ of $Pb(Mg_{1/3}Nb_{2/3})O_3[PMN]-Pb(Mn_{1/3}Nb_{2/3})O3[PM'N]-PbZrO_3[PZ]-PbTiO_3[PT]$ quaternary system were investigated within the compositional ranges $0{\leq}y{\leq}0.125$, y+z=0.125, and $0.39{\leq}x{\leq}0.54$ of the formula $Pb_{0.97}Sr_{0.03}[Mg_{1/3}Nb_{2/3})_y\;(Mn_{1/3}Nb_{2/3})_z\;(Zr_{x}Ti_{1-x})_{1-(y+z)}]O_3$. In the case of increasing Mn/(Mg+Mn) ratio for a fixed Zr/Ti ratio of 47.5/52.5, phase relation remained unchanged but the grain size drastically decreased, and the electrical properties changed as following: both $k_P$ and $Q_m$ reached the peak values at $Mn/(Mg+Mn)\cong0.3l7$ and gradually decreased; $\varepsilon33^T$ showed a monotonic decrease; P-E hysteresis loop gradually changed to asymmetrical one, and $E_i$ increased in correspondence. With increasing Zr/Ti ratio for a fixed Mn/(Mg+Mn) ratio of 0.317, on the contrary, the cell parameter $(\alpha^2c)^{1/3}$ gradually increased, and tetragonal-rhombohedral morphotropic phase boundary appeared in the range of $51/49{\leq}Zr/Ti{\leq}54/46$. the meantime, the grain size substantially increased, and the electrical properties changed as following: $k_P$ and $\varepsilon33^T$ reached peak values at Zr/Ti=51/49 and 48/52, respectively, and then gradually decreased; change of $Q_m$ was adverse to $k_P$; both $E_C\;and\;E_i$ considerably decreased while $P_S$ moderately increased. For the system 0.125(PMN+PM'N)-0.875PZT studied, the composition Mn/(Mg+Mn)=0.3l7 and Zr/Ti=51/49 revealed some promising electrical properties for piezoelectric transformer application such as $k_P=0.58,\;Q_m\cong1000$, and $\varepsilon^T_{33}=970$, as well as dense and fine-grained microstructure.

• Corrosion Science and Technology
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• v.12 no.3
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• pp.125-131
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• 2013

The most common pipe wall thinning degradation mechanisms that can occur in the steam and feedwater systems are FAC (Flow Acceleration Corrosion), cavitation, flashing, and LDIE (Liquid Droplet Impingement Erosion). Among those degradation mechanisms, FAC has been investigated by many laboratories and industries. Cavitation and flashing are also protected on the piping design phase. LDIE has mainly investigated in aviation industry and turbine blade manufactures. On the other hand, LDIE has been little studied in NPP (Nuclear Power Plant) industry. This paper presents the development of prediction system for pipe wall thinning caused by LDIE in terms of erosion rate based on air-water ratio and material. Experiment is conducted in 3 cases of air-water ratio 0.79, 1.00, and 1.72 using the three types of the materials of A106B, SS400, and A6061. The main control parameter is the air-water ratio which is defined as the volumetric ratio of water to air (0.79, 1.00, 1.72). The experiments were performed for 15 days, and the surface morphology and hardness of the materials were examined for every 5 days. Since the spraying velocity (v) of liquid droplets and their contact area ($A_c$) on specimens are changed according to the air-water ratio, we analyzed the behavior of LDIE for the materials. Finally, the prediction equations(i.e. erosion rate) for LDIE of the materials were determined in the range of the air-water ratio from 0 to 2%.