• Journal of the Korean earth science society
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• v.30 no.1
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• pp.69-80
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• 2009

We investigate the dependence of star formation rate and Active Galaxy Nuclei (AGN) frequency on the bar properties, especially the bar strength, using SDSS DR6. To better represent the bar strength, we divided the bars into 6 classes according to their length and axial ratios. There seems to be a fairly good correlation between the star formation rate derived from $H{\alpha}$ emission lines and the bar strength, whereas there is no apparent correlation between the AGN activity and the bar strength. We interpret that the former correlation is due to the dependence of bar-driven gas inflow on the strength of bar. The lack of correlation between AGN and bar properties suggests that the accretion of gas onto a supermassive black hole (SMBH) is regulated by the interplay between the bar and SMBH. The frequency of AGN seems to be dependent on the background density but the star formation rate does not. It suggests that star formation is a localized phenomenon that is mostly determined by the gas density in a galaxy, while AGN activity is more closely related to the host property such as mass and luminosity that are thought to be dependent on the environment through the density-luminosity relation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.739-744
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• 2017

Elastic deformation and fatigue damage can cause the permanent deformation of a kart's frame during turning, affecting the kart's driving performance. A kart's frame does not contain any suspension or differential devices and, therefore, the dynamic behavior caused by torsional deformation when driving along a curve can strongly affect these two kinds of deformations. To analyze the dynamic behavior of a kart along a curved section, the GPS trajectory of the kart is obtained and the torsional stress acting on the kart-frame is measured in real time. The mechanical properties of leisure and racing karts are investigated by analyzing their material properties and conducting a tensile test. The torsional stress concentration and frame distortion are investigated through a stress analysis of the frame on the basis of the obtained results. Leisure and racing karts are tested in each driving condition using driving analysis equipment. The behavior of a kart when being driven along a curved section is investigated through this test. Because load movement occurs owing to centrifugal force when driving along a curve, torsional stress acts on the kart's steel frame. In the case of a leisure kart, the maximum torsional stress derived from the torsional fatigue limit was found to be 230 MPa, and the torsional fatigue limit coefficient was 0.65 when driving at a speed of 40 km/h. Furthermore, the driving elements during the cornering of a kart were measured based on an actual auto-test after installing a driving measurement system, and the driving behavior of the kart was analyzed by measuring its vertical displacement.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.5
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• pp.908-915
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• 2001

In this paper, it is analyzed theoretically that the performance degradation, caused by carrier frequency offset, in an OFDM/M-ary PSK system. Then, when Turbo coding is adopted to an OFDM/M-ary PSK system, the degree of performance enhancement is evaluated. Finally, the maximum frequency offset is calculated to satisfy the BER performance required in a Turbo coded OFDM/M-ary PSK system. As results of analysis, it is shown that the more the number of M-ary is, the worse the BER performance is. Moreover, 7dB, 9dB, and 17dB of $E_b/N_o$ are required in QPSK, 8PSK and 16PSK systems, respectively in order to satisfy the error performance, $BER=10^{-3}$ for voice communication. If $E_b/N_o$ are 10㏈ and 15㏈, the frequency offset should be below 0.05 and 0.075, respectively, for voice communication. When Turbo coding is adopted to an OFDM/M-ary PSK system, the less the number of M-ary is, the greater the performance enhancement of Turbo coding is. If the number of a M-ary system of the system is below 16, it is found that required $E_b/N_o$ is about 8dB to satisfy $BER=10^{-5}$ Moreover, in the system the Turbo coding scheme, voice communication is available with greatly low$E_b/N_o$, and 8dB of $E_b/N_o$ is enough for data communication regardless of the permission range of frequency offset.

• Journal of Korea Water Resources Association
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• v.48 no.3
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• pp.149-158
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• 2015

It is well known that emergency outlet works have to be provided for the safety of dams. However, concept of emergency outlet works did not applied for the design of the most dams in Korea. Korean design standard for low-level outlet works does not provide enough design criteria which could be used in design of emergency outlet works. In this research, as-built status and hydraulic design criteria of outlet works, such as drawdown rate or hydraulic pressure due to the impounded water depth, were examined. Another relationship between drawdown rate and the dam slope stability was also examined with SEEP model. It was found that 25% reduction of impounded water depth decreases the pressure forces about 50%. Therefore, outlet works should be designed to drawdown properly at the beginning of the emergency. Seepage analysis of dam bodies showed that most of Korean dams could safely stand for 1m/day drawdown rate. Higher drawdown rate could result high discharge so the drawdown rate must be related with the flood risk of downstream. Finally, multi-stage design was recommended that faster discharge for the initial 25% of water depth in 7-10 days than the rest of it in 1-2 months.

• Journal of the Mineralogical Society of Korea
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• v.19 no.4 s.50
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• pp.221-229
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• 2006

Mineralogical and chemical examinations were performed on interstratified illite-smectite (I-S) minerals that occur in the mudstones from a petroleum exploration well in the Tertiary marine basin, Japan. X-ray diffraction analysis shows that component layers of illite in the interstratified I-S increase with increasing burial depth while those of smectie decrease. In addition, the randomly (R=0) interstratified illite-smectite is changed into Rp1 ordered I-S at a depth of about 4,000 m, which corresponds to the result of organic analysis and indicates a burial temperature of about $100^{\circ}C$. However, the present geothermal gradient shows that the conversion of the random I-S to R=0 ordered I-S is likely to occur at 3,000 m. This discrepancy may be interpreted by the reverse fault at 2,500 m which resulted in a deeper burial of sediments up to 1,000 m. Chemical analysis also shows the compositional variation in I-S with increasing depth: a decrease in Si and an increases in Al and K, indicating that the substitution of Al for Si in tetrahedral sheets is compensated by the addition of K to interlayers. K may be derived from K-feldspar and micas, which is present in the mudstones.

• Korean Chemical Engineering Research
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• v.55 no.4
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• pp.456-466
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• 2017

This work investigated the particle morphology change to difference in milling media in a metal based composite fabrication process using a stirred ball mill with ball behavior of DEM simulation. A simulation of the three dimensional motion of grinding media in the stirred ball mill for the research of grinding mechanism to clarify the force, kinetic energy, and medium velocity of grinding media were calculated. In addition, the rotational speed of the stirred ball mill was changed to the experimental conditions for the composite fabrication, and change of the input energy was also calculated while changing the ball material, the flow velocity, and the friction coefficient under the same conditions. As the rotating speed of the stirred ball mill increased, the impact energy between the grinding media to media, media to wall, and media and the stirrer increased quantitatively. Also, we could clearly analyze the change of the particle morphology under the same experimental conditions, and it was found that the ball behavior greatly influences in the particle morphology changes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.39-48
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• 2020

Since the fire accident of ESS (energy storage system) occurred at Gochang KEPCO Power Testing Center in August 2017, 29 fire cases with significant property losses have occurred in Korea. Although the cause of fire accidents have not been identified precisely, it should be considered battery and PCS (power conditioning system) as well as unbalance issues in the distribution system. In particular, circulating currents in a neutral line of a grid-connected transformer, which can affect a magnetized current, may have a negative effect on the ESS with unintentional core saturation and surge voltages at the secondary side of the transformer. Therefore, this paper proposes the modeling of the distribution system, which was composed of a substation, grid-connected transformer, and customer loads using PSCAD/EMTDC S/W, to analyze the phenomena of circulating current and surge voltages of the transformer with unbalanced currents in the distribution system. This paper presents a countermeasure for a circulating current with the installation of NGR (neutral grounding resistor) in grid-connected transformer. From the simulation results, it is clear that exceeding the circulating current and surge voltage at the secondary side of the transformer can be one of the causes of fire accidents.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.643-651
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• 2020

A capsule train runs inside a sub-vacuum tube and can reach very high speed due to the low air resistance. A capsule train uses a superconducting electrodynamic suspension (SC-EDS) method for levitation, which allows for a large levitation gap and does not require gap control. However, SC-EDS has inherent characteristics such as the large gap variation and a small damping effect in the levitation force, which can degrade the running stability and ride comfort. To overcome this, a stability improvement device should be designed and applied based on dynamic analysis. In this study, a 1/10 small-scale testbed was developed to replicate the dynamic characteristics of a capsule train and investigate the performance of stability improvement devices. The testbed is composed of a 6-degree-of-freedom Stewart platform for the realization of bogie motion, a secondary suspension with a running stabilization device, and a carbody. Based on the dynamic similarity law proposed by Jaschinski, the small-scale testbed was manufactured, and a bogie motion algorithm was applied with the consideration of guideway irregularity and levitation stiffness. The experimental results from the testbed were compared with simulation results to investigate the performance of the testbed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.652-661
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• 2020

Recently, the Korean government developed the RE3020 (renewable energy) policy to overcome environmental problems, such as fine dust, climate change, and large-scale PV systems interconnected with a distribution system. When a large-scale PV system is interconnected in the distribution system, however, a malfunction can occur, and the protection devices may not be operated because of the dividing effect depending on the magnitude and direction of fault current as well as connection types and location of the PV system. Therefore, this paper proposes a search algorithm for the malfunction pattern of protection devices based on various scenarios, when large-scale PV systems are operated and interconnected in a distribution system. This paper presents a malfunction mechanism of protection devices according to the installation locations of recloser (R/C). Furthermore, the modeling of a distribution system with large-scale PV systems was performed using Off-DAS S/W, and the malfunction patterns of protection devices were analyzed based on a range of scenarios. From the simulation results with the proposed model and algorithm for searching for protection devices, it was confirmed that they are useful and effective in identifying a malfunction phenomenon depending on the installation location of the R/C and connection type of PV system.

• Journal of Labour Economics
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• v.24 no.1
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• pp.207-230
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• 2001

This paper uses the Korean Labor Panel data to investigate changes in the employment types of male workers following their job changes with the classification of workers into three categories: regular wage workers, non-regular wage workers, and self-employed workers. It also estimates a competing-risks hazard model to analyze the determinants of employment types of workers. The results show that the type of employment of a worker at an immediate previous job has a critical importance in determining his employment type at a new job and that the types of employment at jobs other than the immediate previous job also play some role in determining the type of employment at a new job, although their impact declines as the number of intervening jobs increases. A job loser, who worked as a non-regular worker at his immediate previous job, for example, is considerably less likely to find a regular job, but more likely to get reemployed at another non-regular job than one who worked as a regular worker at his immediate previous job. Similarly, a worker who quit self-employment is much less likely to find a regular job but more likely to restart his own business than one who worked as a regular worker at his immediate previous job. These findings suggest that it is not easy at all for a worker who worked as either a non-regular worker or self-employed worker to become a regular worker, although it might be premature to assert that non-regular jobs or self-employed jobs are dead-end jobs. Another interesting finding of this analysis is that a high unemployment rate lowers a probability of reemployment at either regular jobs or self-employed jobs, but raises a non-regular job reemployment probability, which strongly implies that as labor market conditions become adverse to workers the proportion of non-regular employment can rise rapidly.