• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.1
• /
• pp.31.2-31.2
• /
• 2013

We use grid-based hydrodynamic simulations to study star formation in nuclear rings in barred galaxies. The gaseous medium is assumed to be infinitesimally thin, isothermal, and unmagnetized. To investigate various situations, we vary the total gas content in the bar regions and the bar growth time. We find that star formation rate (SFR) in a nuclear ring is determined by the mass inflow rate to the ring rather than the total gas mass in the ring. The SFR shows a strong primary burst and weak secondary bursts at early time, and declines to small values at late time. The primary burst is caused by the rapid gas infall to the ring due to the bar growth, with its duration and peak depending on the bar growth time. The secondary bursts result from re-infall of the ejected gas by star formation feedback of the primary burst. When the SFR is low, ages of young star clusters exhibit an azimuthal gradient along the ring since star formation takes place mostly near the contact points between the dust lanes and the nuclear ring. When the SFR is large, on the other hand, star formation is widely distributed throughout the whole length of the ring, with no apparent age gradient of star clusters. Regardless of SFR, star clusters have a positive radial age gradient, with younger clusters located closer to the ring, since the ring shrinks in size over time.

• Proceedings of the KSR Conference
• /
• 2003.10c
• /
• pp.126-131
• /
• 2003

The acceptance test of KTX has been performed in Korea. During the test, lateral vibration of carbody over the accepted value called sway was found. KTX has 20 car trainset formation whose trailer cars are linked by articulate bogies. So this study is performed to see the effects of long trainset formation on vehicle dynamics and the train stability by 20 car vehicle model. Firstly the reliable vehicle model which shows well the tendencies appeared in the tests on the high speed test line is required to find the cause of lateral vibration and the countermeasure. Vehicle model was made .for the. analysis with VAMPIRE. The analysis results show that secondary air spring lateral stiffness is the most significant parameter to cause carbody lateral vibration. Mode analysis results show that the least damped mode shape is similar to the vibration pattern shown in the tests that the amplitude of the motion increases along the train set and decreases in the tail part. For the case of short train formation with 7 or 10cars, sway does not happen. But in the case of longer train formation with 16 or 20 cars, sway was found.

• Asian Journal of Atmospheric Environment
• /
• v.10 no.1
• /
• pp.32-41
• /
• 2016

Particle-phase concentrations were measured at 10, 80, and 200 m from the roadside of a national highway near Seoul in January and May 2008. The highway has two lanes each way, with an average hourly traffic volume of 1,070 vehicles. In January 2008, $PM_{10}$ concentrations decreased from 10 to 80 m but increased at 200 m. Black carbon (BC) decreased only slightly with distance due to the influence of biomass burning and open burning from the surrounding areas. In May 2008, the effect of secondary formation on both $PM_{10}$ and $PM_{2.5}$ was significant due to high temperatures compared with January. Because on-road emissions had little effect on secondary formation for a short time, variations in $PM_{10}$ concentrations became smaller, and $PM_{2.5}$ concentrations increased with distance. The effects of fugitive dust on PM concentrations were greater in May than in January when the mean temperature was below freezing. In the composition variations, the amounts of primary ions, organic carbon (OC), and BC were larger in January, while those of secondary ions and others were larger in $PM_{10}$, as well as $PM_{2.5}$ in May.

• Journal of Industrial Technology
• /
• v.20 no.B
• /
• pp.55-62
• /
• 2000

The purpose of this research is to find out how the inlet angle of secondary air affects the formation of recirculation zone inside a small incinerator. A commercial code, PHOENICS, is used to simulate the flow field of an incinerator. The computational grid system is constructed by Multi-Block technique. Numerical experiments are done with the five different angles of secondary air inlet. The formation of recirculation zone is evaluated by checking velocity fields. The computational results show that recirculation zone is clearly formed from 60 degree of inlet angle and the zone of recirculation is widen as angle of recirculation is increased to $75^{\circ}$.

• Journal of Mechanical Science and Technology
• /
• v.16 no.7
• /
• pp.950-958
• /
• 2002

The combustion characteristics of a low NOx burner using reburning technology have been experimentally studied. The return burner usually has three distinct reaction zones which include the primary combustion zone, the reburn zone and the burnout zone by provided secondary air. NOx is mainly produced in a primary combustion zone and a certain portion of NOx can be converted to nitrogen in the rebury zone. In the burnout zone, the unburned mixtures are completely oxidated by supplying secondary air. Liquefied Petroleum Gas (LPG) was used as main and reburn fuels. The experimental parameters investigated involve the main/reburn fuel ratio, the primary/secondary air ratio, and the injection location of rebury fuel and secondary air. When the amount of return fuel reaches to the 20-30% of the total fuel used, the overall NO reduction of 50% is achieved. The secondary air is injected by two different ways including vertical and parallel injection. The injector of secondary air is located at the downstream region of furnace for a vertical-injection mode, which is also placed at the inlet primary-air injection region for a parallel-injection mode. In case of the vertical injection of the secondary air flow, the NOx formation of stoichiometric condition at a primary combustion zone is nearly independent of the rebury conditions (locations, fuel/air ratios) while the NOx emission of the fuel-lean condition is considerably influenced by the reburn conditions. In case of the parallel injection of the secondary air, the NOx emission is sensitive to the air ratio rather than the fuel ratio and the reburning process often coupled with the multiple air-staging and fuel-staging combustion processes.

• Journal of Korean Society for Atmospheric Environment
• /
• v.26 no.3
• /
• pp.265-275
• /
• 2010

Mass and ion concentrations of $PM_{10}$ and $PM_{2.5}$ were measured in Yongin, downwind of the Seoul metropolitan area. Twenty-four hour average samples were collected daily for a month or so in spring and fall of both 2007 and 2008. Asian dust occurred twice in each period except in the fall of 2007. During the Asian dust period, nitrate in fine particles decreased since large amount of cations in coarse particles of Asian dust absorbed it. In spring 2008, sulfate as well as ammonium also increased in coarse particles. In spite of occasional Asian dust events, the influence of secondary formation was dominant over the period. Excessive ammonium over sulfate was enough to neutralize nitrate as well. High correlation coefficients between $K^+$ and sulfate, nitrate, and ammonium indicate a close relationship between secondary formation and biomass burning. Biomass burning and open burning are considered to be important sources of chloride.

• The Mathematical Education
• /
• v.52 no.2
• /
• pp.163-174
• /
• 2013

This study conducted a survey to examine the knowledge formation and utilization of computer among beginning teachers of secondary school mathematics. We found that beginning teachers who had more experiences of taking computer utilization classes at teacher education institutes showed more interest in computer and saw the necessity and effectiveness of computer usage for teaching students. Teachers chose GSP the most among computer utilization knowledge learned in pre-service teachers program, and GSP is used the most in mathematics classes. However, they answered that computer is not so much available in class due to lack of hours and the relevant resources. Lastly, beginning teachers answered that the computer knowledge learned in in-service teacher program was more useful than that in pre-service. Thus, the professional development in utilizing computer should be improved through diversifying teacher training contents for beginning teachers as well as for pre-service teachers in teacher education institutes.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
• /
• v.7 no.1
• /
• pp.9-15
• /
• 1977

The author observed the effect of X-ray irradiation on the secondary palate formation of the rat fetuses. The mothers were exposed to X-radiation on the 10½th, 11½th and 12½th day of gestation with respectively 150, 200, 250, 300 and 350 rads. The fetuses were removed from mothers on 15½h, 16½th and 18½th day of gestation. Morphological changes in palate formation were examined and histochemical preparations were made. 1. In control fetuses, the secondary palates were fully developed on the 15½th to 18½th day of gestation. But in experimental fetuses, many cleft palates were observed in accordance with increase of X-radiation dose. 2. Frequency of incidence of horizontal position of both palated shelves in cleft palate was highest. 3. Accordig to the dislocation of palatal processes, the stain ability of palatal crest was varied. 4. The thickened area of palatal epithelium of palatal crest showed intense methyl green-pyronin and PAS reaction 5. Mesenchymal cell condensation was appeared under the thickened epithelium of palatal process and this mesenchymal tissue showed strong colloidal iron reaction. 6. The stain ability of alizarin red S and alkaline phosphatase reaction of tectal ridge were decreased, in accordance with increase of irradiation doses.

• Restorative Dentistry and Endodontics
• /
• v.12 no.2
• /
• pp.73-80
• /
• 1987

The present study was designed to help elucidate the effect of glass ionomer cements on the exposed dental pulp by means of histologic examination. A total of 40 cavities of class V were prepared on the teeth of 4 dogs with exposure of 1mm in diameter on the bases of them. 20 cavities were filled with glass ionomer cement as the experimental group and the other 20 cavities were filled with zinc oxide eugenol cement as the control group. The dogs were sacrificed at one, two, three, and four weeks after filling, and the specimens were routinely prepared and stained with Hematoxylin-Eosin. The obtained microscopic findings were as follows: Inflammatory cell infiltrations were observed in control in 1 week, which decreased markedly with time. In all control groups, hemorrhage around exposed pulp tissue and coagulation change of pulp were observed. Secondary dentin formation and thickened predentin were observed in 4 week cases, and the recovery of pulp tissue was favorable on the whole. Inflammatory cell infiltration was observed in all GIC groups. Proliferation of blood vessel and congestion were observed with coagulation changes around the exposed pulp tissue. Secondary dentin formation and thickened predentin were observed in 3 weeks. In the experimental 4 week case, secondary dentin formation was evident. On the whole, pulpal irritation of glass ionomer cement was relatively severe. Recovery of pulp tissue in GIC groups was less favorable compared with that of ZOE groups.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.1708-1713
• /
• 2003

The acceptance test of KTX has been performed in Korea. During the test, lateral vibration of carbody over the accepted value called swat was found. KTX has 20 car trainsed formation whose trailer cars are linked by articulate bogies. So this study is performed to see the effects of long trainsed formation on vehicle dynamics and the train stability by 20 car vehicle model. Firstly the reliable vehicle model which shows well the tendencies appeared in the tests on the high speed test line is required to find the cause of lateral vibration and the countermeasure. Vehicle model was made for the analysis with VAMPIRE. The analysis results show that secondary air spring lateral stiffness is the most significant parameter to cause carbody lateral vibration. Mode analysis results show that he least damped mode shape is similar to the vibration pattern shown in the tests that the amplitude of the motion increases along the train set and decreases in the tail part. For the case of short train formation with 7 or 10cars, sway does not happen. But in the case of longer train formation with 16 or 20 cars, sway was found.