• Journal of Korea Foundry Society
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• v.20 no.2
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• pp.104-109
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• 2000

Three different white cast irons alloyed with Cr, V, Mo and W were prepared in order to study their abrasion wear behavior in as-cast and heat-treated conditions. The specimens were produced using a 15㎏-capacity high frequency induction furnace. Melts were super-heated to $1600^{\circ}C$, and poured at $1550^{\circ}C$ into Y-block pepset molds. Three combinations of the alloying elements were selected so as to obtain the different types of carbides : 3%C-10%Cr-5%Mo-5%W(alloy No. 1: $M_7C_3$ and $M_6C$), 3%C -10%V-5%Mo-5%W(alloy No. 2: MC and $M_2C$) and 3%C-17%Cr-3%V(alloy No. 3: $M_7C_3$ only). A scratching type abrasion test was carried out in the states of as-cast(AS), homogenizing(AH), air-hardening(AHF) and tempering(AHFT). First of all, the as-cast specimens were homogenized at $950^{\circ}C$ for 5h under the vacuum atmosphere. Then, they were austenitized at $1050^{\circ}C$ for 2h and followed by air-hardening in air. The air-hardened specimens were tempered at $300^{\circ}C$ for 3h. 1 ㎏ load was applied in order to contact the specimen with abrading wheel which was wound by 120 mesh SiC paper. The wear loss of the test piece(dimension: $50{\times}50{\times}5$ mm) was measured after one cycle of wear test and this procedure was repeated up to 8 cycles. In all the specimens, the abrasion wear loss was found to decrease in the order of AH, AS, AHFT and AHF states. Abrasion wear loss was lowest in the alloy No.2 and highest in the alloy No.1 except for the as-cast and homogenized condition in which the alloy No.3 showed the highest abrasion wear loss. The lowest abrasion wear loss of the alloy No.2 could be attributed to the fact that it contained primary and eutectic MC carbides, and eutectic $M_2C$ carbide with extremely high hardness. The matrix of each specimen was fully pearlitic in the as-cast state but it was transformed to martensite, tempered martensite and austenite depending upon the type of heat-treatment. From these results, it becomes clear that MC carbide is a significant phase to improve the abrasion wear resistance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3469-3476
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• 2015

The Korea Academia-Industrial cooperation Society. The Korea Academia-Industrial cooperation Society. In Korea, the territory has east high west low type and the rainfall is concentrated in the summer season. A nation having these topography and precipitation condition like Korea has to basically needs support of hardware alternatives. However, the right places decrease gradually and the resistance of the public opinion for national water resources policy stiffens gradually. The climate change has an effect in water resources fields and has a close relation. In the present study, therefore, future inflow of Miryang multipurpose dam basin is estimated by using SWAT model applied RCP 4.5 and 8.5 scenarios of "Korea Meteorological Administration" and considering the results, the future direction is purposed to operate the dam. As a result, the rainfall pattern is changed from traditional peak form to flat form. The dam operation rule in accordance with changing precipitation pattern has to be modified from the conventional operation rule and a new plan has to be established to meet a situation.

• Resources Recycling
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• v.13 no.2
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• pp.16-23
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• 2004

To increase the recycling rate of anthracite fly ash, the properties of anthracite fly ash were compared to that of bituminous fly ash. Especially, the high temperature properties of the fly ash are investigated by using thermal analysis, high temperature microscope and X-ray diffraction analysis for utilizing anthracite fly ash to prepare the calcinated bricks. The average ratio of $A1_2$$O_3$/$SiO_2$ for anthracite is 0.62 and the ratio for bituminous is 0.34. The content of $SiO_2$ in anthracite fly ash was higher than that of bituminous fly ash. The $A1_2$$O_3$ of anthracite fly ash reacted with the $A1_2$$O_3$ in the fly ash and formed new mullite crystal at over $1000^{\circ}C$, so anthracite fly ash showed high fire resistance. And, the fly ash mixtures having kaolin were prepared, and then extruded in vacuum to evaluate the extruding property of anthracite fly ash mixture. The extruding velocity was decrease with increasing the addition amount of fly ash in the mixture, and the maximum addition amount of fly ash that could be extruded was 60 wt%.

• Membrane Journal
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• v.12 no.1
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• pp.8-20
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• 2002

In this study using $N_2$-back flushing, which wwas not the general back-flushing method of membranes, the discharged wastewater from a paper plant was filtrated by 4 kinds of tubular carbon ceramic ultrafiltration membranes. We could in vestigate effects of $N_2$-back flushing period, transmembrane pressure (TMP)and flow rate and find optimal operating conditions. The $N_2$-back flushing time (BT) was fixed at 40 sec, filtration times (FT) were changed in 4~32 min, TNP in $1.0~3.0kg_f/cm^2$ the flow celocities in 0.53~1.09cm/s. The optimal conditions were discussed in the viewpoints of dimensionless permeate flux ($J/J_0$), toal permeate volume ($V_T$) and resistance of membrane fouling ($R_f$). Optimal back-flushing period was BT/FT=0.167 (FT=8 min ), in which more $V_T$ was obtained than that in BT/FT=0.083 (FT=4 min) which was the most friquent back-flushing condition. Then rising TMP should increase the driving force, and more $V_T$ could be accumulated. And rising flow rate should decrease membrane fouling increase permeate flux, and more $V_T$could be produced. Average rejection rates of pollutants were higher than 95% for turbidity and 45~83% for $COD_{Cr}$, but rejection rates of total dissolved solid (TDS) were lower than 10%.

• Tunnel and Underground Space
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• v.23 no.3
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• pp.180-191
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• 2013

The purpose of this research was to find an optimal quarrying for marble by analyzing the applicability and the work efficiency of a chain saw machine newly introduced in the underground Baekwoon mine. From the test results of the physical properties of Baekwoon marble, which affects the efficiency of rock cutting, it was found to have similar physical characteristics as the ones which are now being produced in the other areas in Korea. And especially it shows isotropic property, which can be thought to be advantageous as a dimensional stone. To check the long-term quality of the marble as a stone material, several tests such as corrosion resistance test and abrasion test were carried out. It was found to be vulnerable to acid rain with decrease of weight and seismic wave velocity after applying artificial rain at pH 5.6 for 50 times. The percentage of wear from abrasion test was 22.67%. The working time and cutting speed of the chain saw machine were recorded and analyzed during the test-run at the quarry. The overall work cycle was assorted into 9 unit operations and the operating time per each unit was drawn. The operating times for the two cutting patterns, which could be possibly applicable to the work site, were compared. The results indicated that the pattern B, that the cutting sequence was set to minimize the movement of the machine, showed 6% less working hours than the pattern A, which first cuts the outer boundary. With cutting pattern analysis, the ore body in the Baekwoon mine was 3 dimensionally modeled and a quarrying plan considering the existing conditions of the marble was suggested.

• The Journal of Internal Korean Medicine
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• v.22 no.2
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• pp.199-205
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• 2001

Background and Purpose : Transcranial doppler ultrasonography(TCD) is a noninvasive and nonradioactive technique for evaluation of the hemodynamics in large cerebral vessels. Sahyangsohap-won(SS) has been considered to be effective for the treatment of various disease, especially cerebrovascular, cardiovascular, and psychosomatoform disorders. But, there is no study about the effect of SS on the cerebral hemodynamics in humans. The aim of this study was to assess the effect of SS on the changes in cerebral hemodynamics and the dose-dependant effect by using TCD. Subjects and Methods : 30 healthy subjects were randomly divided into three group: group 1 took no drug, group 2 took SS one pill, and group 3 took SS 2 pills. Changes in the mean blood flow velocity(MBFV) and pulsatility index(PI) in the middle cerebral artery were evaluated by means of TCD. We obtained hypercapnia with breath-holding and evaluated cerebrovascular reactivity with the breath-holding index(BHI). Systolic blood pressure(SBP), diastolic blood pressure(DBP), and heart rate(HR) were measured by means of ambulatory blood pressure monitoring. In group 2 and group 3, the evaluations were performed during the baseline and were repeated at 20, 40, and 60 minutes after SS administration. In group 1, the evaluation was performed at corresponding time intervals. Results : In mean values of MSFV, PI, SSP, DBP, and HR, no stastically significant differences were found between the 3 groups. However, BHI values were significantly lower in groups 2 and 3 than in group 1 at 40 minutes after SS administration(P<0.05, group 1 vs group 2, group 1 vs group 3 by post-hoc analysis: Scheffe's test) but in dose-dependant effect, there was no difference between group 2 and group 3. Conclusion : These results suggest that SS can decrease vascular resistance in cerebral small arteries or arterioles and enhance their distensibility. Further studies on larger numbers of subjects are needed to confirm these effects and the dose-dependant effects.

• The Korean Journal of Food And Nutrition
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• v.28 no.2
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• pp.171-177
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• 2015

Sodium butyrate is a short-chain fatty acid derivative found in foods, such as Parmesan cheese and butter and is produced by anaerobic bacteria fermentation of dietary fibers in the large intestine. There have been reports that butyrate prevented obesity, protected insulin sensitivity, and ameliorated dyslipidemia in dietary obese mice. This study investigated the effects of sodium butyrate on fasting blood glucose level and serum lipid profile in streptozotocin(STZ)-induced diabetic mice. Male C57BL/6 mice were fed AIN-93G for four weeks prior to intraperitoneal injections with STZ (100 mg/kg body weight). Diabetic mice had supplements of 5% sodium butyrate for four weeks. The 5% sodium butyrate diet significantly improved fasting blood glucose level and lipid profile in STZ-induced diabetic mice. Inflammation has been recognized to decrease beta cell insulin secretion and increase insulin resistance. Circulating cytokines can directly affect beta cell function, leading to secretory dysfunction and increased apoptosis. Thus, anti-inflammatory therapies represented a potential approach for the therapy of diabetes and its complications. In this animal study, the 5% sodium butyrate supplementation also inhibited inflammatory cytokine production in STZ-induced diabetic mice. These results suggested that sodium butyrate can be a potential candidate for the prevention of diabetes and its complications.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.6
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• pp.613-619
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• 2017

Recently, the size of container ships has been progressively increasing, and much attention is required for safe navigation in shallow areas such as coastal waters and ports due to increases in draft. It is necessary to understand the characteristics of ship motion not only in still waters but also with waves. Especially in shallow regions, squat due to the vertical movement of the ship can be an important evaluation factor for the safe navigation, and wave drift force acting in the horizontal direction can have a great influence on the maneuverability of a ship. In this study, a numerical simulation using computational fluid dynamics has been performed for the wave exciting force acting in the vertical direction and the wave drift force acting in the horizontal direction for a very large container vessel sailing in shallow zone. As a result, it was found that total resistance in still waters greatly increased in shallow water. Wave drift force was shown to decrease given longer wavelengths regardless of water depth. It was observed that the wave exciting force in shallow water was considerably larger than at other water depths. As wave height against the central part of the ship lowered, the aft side rose.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.3
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• pp.268-275
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• 2021

The three factors that determine the strength of concrete are the strength of cement paste, aggregate and ITZ(Interfacial Transition Zone) between aggregate and cement paste. Out of these, the strength of ITZ is the most vulnerable. ITZ is formed in 10~50㎛, the ratio of calcium hydroxide is high, and CSH appears low ratio. A high calcium hydroxide ratio causes a decrease in the bond strength of ITZ. ITZ is due to further weak area. The problem of ITZ appears as a more disadvantageous factor when it used lightweight aggregate. The previous study of ITZ properties have measured interfacial toughness, identified influencing factors ITZ, and it progressed SEM and XRD analysis on cement matrix without using coarse aggregates. also it was identified microstructure using EMPA-BSE equipment. However, in previous studies, it is difficult to understand the microstructure and mechanical properties. Therefore, in this study, a method of measuring electrical resistance using EIS(Electrochemical Impedance Spectroscopy) measuring equipment was adopted to identify the ITZ between natural aggregate and lightweight aggregate, and it was tested the change of ITZ by surface coating of lightweight aggregate with ground granulated blast furnace slag. As a result, the compressive strength of natural aggregate and lightweight aggregate appear high strength of natural aggregate with high density, surface coating lightweight aggregate appear strength higher than natural aggregate. The electrical resistivity of ITZ according to the aggregate appeared difference.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.25-34
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• 2019

Recently, when a fault occurs at a long-distance point in a LVDC (low voltage direct current) distribution feeder in a light rail system, the magnitude of the current can decrease to less than that of the load current of a light rail system. Therefore, proper protection coordination method to distinguish a fault current from a load current is required. To overcome these problems, this paper proposes an optimal algorithm of protection devices for a LVDC distribution feeder in a light rail system. In other words, based on the characteristics of the fault current for ground resistance and fault location, this paper proposes an optimal operation algorithm of a selective relay to properly identify the fault current compared to the load current in a light rail system. In addition, this paper modelled the distribution system including AC/DC converter using a PSCAD/EMTDC S/W and from the simulation results for a real light rail system, the proposed algorithm was found to be a useful and practical tool to correctly identify the fault current and load current.