• The Korean Journal of Physiology and Pharmacology
• /
• v.22 no.6
• /
• pp.705-712
• /
• 2018

The tube formation assay is a widely used in vitro experiment model to evaluate angiogenic properties by measuring the formation of tubular structures from vascular endothelial cells (ECs). In vitro experimental results are crucial when considered the advisability of moving forward to in vivo studies. Thus, the additional attentions to the in vitro assay is necessary to improve the quality of the pre-clinical data, leading to better decision-making for successful drug discovery. In this study, we improved the tube formation assay system in three aspects. First, we used human endothelial colony forming cells (ECFCs), which are endothelial precursors that have a robust proliferative capacity and more defined angiogenic characteristics compared to mature ECs. Second, we utilized a real-time cell recorder to track the progression of tube formation for 48 hours. Third, to minimize analysis error due to the limited observation area, we used image-stitching software to increase the microscope field of view to a $2{\times}2$ stitched area from the $4{\times}$ object lens. Our advanced tube formation assay system successfully demonstrated the time-dependent dynamic progression of tube formation in the presence and absence of VEGF and FGF-2. Vatalanib, VEGF inhibitor, was tested by our assay system. Of note, $IC_{50}$ values of vatalanib was different at each observation time point. Collectively, these results indicate that our advanced tube formation assay system replicates the dynamic progression of tube formation in response to angiogenic modulators. Therefore, this new system provides a sensitive and versatile assay model for evaluating pro- or anti-angiogenic drugs.

• Proceedings of the KOR-BRONCHOESO Conference
• /
• 1982.05a
• /
• pp.19-19
• /
• 1982

Pathogenesis of otitis media was studied in an animal model of rats from a histopathological and biochemical point of view. Basic anatomical outline, and distribution and type of normal epithelial cells of the rat bulla were described as a background study. Pseudomonas otitis media was developed in rats by inoculating $10^{9}$ bacteria into the tympanic bulla. Histopathologic change of the mucoperiosteal layer showed acute stage of infection from 3 days to 3 weeks, and it became chronic after 4 weeks animals through 12 weeks. Enzyme profile in the extracts of the inflammatory middle ear tissue was studied. The levels of three enzymes, PZ-peptidase, LDH, and lysozyme were much higher in the middle ear tissue than in the corresponding sera as might be expected. Tissue/serum ratios of the enzyme activities were 13-38 for PZ-peptidase, 63-177 for LDH, and 18-94 for lysozyme. Possible role of the PZ-peptidase and possible origins of the three enzymes detected in the tissue were discussed.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2003.11a
• /
• pp.142-149
• /
• 2003

Blind hydraulic backfilling is a commonly used technique for subsidence control of the strata over unapproachable waterlogged underground excavations. In this investigation model studies on all the three variants of this technique, namely, hydro-pneumatic or air-assisted gravity backfilling, pumped-slurry backfilling and simple gravity backfilling, have been carried out in fully transparent models of the underground excavations. On examination of the filling process, it was revealed that in all the three cases, the basic process of filling occurs by sand transport along one or more meandering channels. The relative influence of sand, water and air flow rates on the area of filling from a single inlet point and the hydraulic pressure loss per unit length were studied in details. In hydro-pneumatic backfilling process, the air bubbles while moving upward through the meandering channels provide an additional buoyant force over and above the available hydraulic head. In this way the area of filling from a single borehole may be quite large even at small flow rates of water. During actual field implementation the injected air, if not released completely from the rise side holes, may cause troubles by way of creating potholes on the surface. The pumped-slurry technique has shown its capability of filling a relatively larger area at faster rate, especially when high-volume, low-pressure method was selected. But simple gravity filling was also found to be equally effective method as slurry pumping, especially when flow rates were high. In the second and third method discussed above, examination of variations of injection pressure was also done and its relation with physical phenomenon was also attempted. Some empirical relationships were also developed using multivariate regression with a view to help the practicing engineers.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2005.05a
• /
• pp.163-166
• /
• 2005

A hole expansion process is an important process in producing a hub-hole in a wheel disc of a vehicle. In this process, the main parameter is the formability of a material that is expressed as the hole expansion ratio. The hub-hole expansion process is different from conventional forming processes or hole flanging processes from the view-point of its deformation mode and forming of a thick plate. In the process, a crack is occurred in the upper edge of a hole as the hole is expanded. Since prediction of the forming limit by hole expansion experiment needs tremendous time and effort, an appropriate fracture criterion has to be developed fur finite element analysis to define forming limit of the material. In this paper, the hole expansion process of a hub-hole is studied by finite element analysis with ABAQUS/standard considering several ductile fracture criteria. The fracture mode and hole expansion ratio is compared with respect to the various fracture criteria. These criteria do not predict its fracture mode or hole expansion ratio adequately and show deviation from experimental results of hole expansion. A modified ductile fracture criterion is newly proposed to consider the deformation characteristics of a material accurately in a hole expansion process. A fracture propagation analysis at the hub-hole edge is also performed for high accuracy of prediction using the new fracture criterion proposed.

• Journal of the Korean GEO-environmental Society
• /
• v.15 no.12
• /
• pp.43-51
• /
• 2014

Organic matter in dredged soil has a lot of engineering problem in ground including a large settlement, crack propagation, low bearing capacity and low friction angle. From an agricultural point of view, however, organic matter contributes greatly soil quality and plant health. This paper investigated the relationship between engineering and germination characteristics of stabilized mixture consisting of different ratios of organic content (0 %, 10 %, 20 %, 30 %) for recycling dredged soil including organic matter. Several series of laboratory tests such as flow test, unconfined compressive test and consolidation test were performed to find out engineering characteristics. pH, percent of germination and growth of plants were also measured to investigate the germination characteristics. The experimental results indicated that, as organic content increased, unconfined compressive stress decreased and compression and swelling indices increased. However, percent of germination and plant growth increases as organic content increases.

• The Mathematical Education
• /
• v.58 no.4
• /
• pp.483-505
• /
• 2019

Across the world, there is a movement to incorporate computational thinking(CT) into school curricula, and math is at the heart of this movement. This paper reviewed the meanings of CT based on the point of view of Jeanette Wing, and the trend of domestic and international studies that incorporated CT into the field of mathematics education was analyzed to provide implications for mathematics education and future research. Results indicated that the meaning of CT, defined by mainly computer educators, varied in their operationalization of CT. Although CT and mathematical thinking generally have common points that are oriented toward problem solving, there were differences in the way of abstraction that is central to the two thinking processes. The experimental studies on CT in the field of mathematics education focused mainly on the development of students' cognitive capacities and affective domains through programming(coding). Furthermore, the previous studies were mainly conducted on students in school, and the studies conducted in the context of higher education, including pre-service and in-service teachers, were insufficient. Implications for mathematics teacher educators and teacher education as well as the relationship between CT and mathematical thinking are discussed.

• Journal of Power System Engineering
• /
• v.19 no.3
• /
• pp.16-21
• /
• 2015

Nitrous oxide($N_2O$) concentration in the atmosphere has been constantly increased by the human activities with industrial growth after the industrial revolution. One of factors to increase $N_2O$ concentration in the atmosphere is the $N_2O$ emission caused by the combustion of marine fuel. Especially, a sulfur component included in marine fuel oils is known as increasing the $N_2O$ formation in diesel combustion. Form this point of view, $N_2O$ emission from a ship is not negligible. On the other hand, Exhaust gas recirculation(EGR) that have thermal, chemical and dilution effect is effective method for reducing the NOx emission. In this study, an author investigated $N_2O$ reduction by using EGR on a direct injection diesel engine. The test engine was a 4-stroke diesel engine with maximum output of 12 kW at 2600rpm, and operating condition of the engine was a fixed load of 75%. The experimental oil was a blend-fuel that were adjusted with sulfur ratio of 3.5%, and EGR ratio of 0%, 10%, 20% and 30%. In conclusion, diesel fuel that contained 3.5% sulfur component increased $SO_2$ emission in exhaust gas, and increment of EGR ratio reduced NO emission. Moreover, $N_2O$ emission was decreased as over 50% at EGR ratio of 10% and reduced 100% at EGR ratio of 30% compared with $N_2O$ emission of 0% EGR ratio.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.67 no.2
• /
• pp.63-69
• /
• 2018

In this paper, the operation principle of a bi-directional switch type resonant AC link snubber circuit was described, together with the practical design procedure, which employs in the proposed power module bridge package type resonant AC link snubber. The novel prototype of power module bridge package type resonant AC link snubber-assisted voltage type sinewave soft switching PWM inverter using IGBT power module was demonstrated herein. It was verified that both the auxiliary power switches in this resonant AC link snubber circuit and the main power switches commutate under the condition of soft switching commutation principle. In addition, the power losses of the new soft switching inverter treated here were analyzed by implementing the experimental data of the IGBT and diode v-i characteristics in addition to switching power loss characteristics into our original computer simulation software developed by the authors. Then, the voltage type sinewave soft switching PWM inverter was high efficiency than that of hard switching PWM inverter, along with performance operation waveforms. In the future, the comparative feasibility study of power module bridge type resonant AC link snubber and its related soft switching inverter in addition to the other types resonant snubber assisted soft switching inverter should be done from a practical point of view.

• The Journal of the Acoustical Society of Korea
• /
• v.7 no.2
• /
• pp.26-38
• /
• 1988

This paper describes three methods for the estimation of the impulse reponse in an indoor acoustic transfer system which rather has long reverberation time by the cross spectrum. The first method, which is the conventional one, will use the white noise as the source signal. Therefore, the very long time window data and numerous number of DFT are necessary for this estimation. The second method has been disigned in order to shorten the length of time window of the first method by using a burst of noise as the source signal. The third method which will be suggested in this paper uses too types of definite signal with short duration time of the source signal. According to the view point of computation capacity, and estimation accuracy of the impulse response, the compared experimental results show that the third method will be better than the others.

• Fire Science and Engineering
• /
• v.23 no.6
• /
• pp.16-23
• /
• 2009

The performance characteristics of a smoke damper, which aims to suppress the penetration of smoke to a safe area, have been tested under the regulation of the FIS 001. However, the improvement of the test methods and the regulation has consecutively been requested. From a view-point of fluid mechanical theory, a pressure control damper, that is installed at the end of the flow control system, is important and it dominates flow characteristics in all designed flow systems. In this study, the weak points of the regulation of the FIS 001 concerned with the pressure control damper was visited and the some important characteristics of the damper was examined. Based on these results, it was confirmed that the effects of flow disturbance in the air supplying duct on the performance of the damper are not significant. This results gives some information for the modification of the experimental regulation concerned to the pressure control damper.