• Atmosphere
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• v.33 no.5
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• pp.493-503
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• 2023

This study investigates the downward influences of sudden stratospheric warming (SSW) in February 2018 using a subseasonal-to-seasonal forecast model, Global Seasonal forecasting system version 6 (GloSea6). To quantify the influences of SSW on the tropospheric prediction skills, free-evolving (FREE) forecasts are compared to stratospheric nudging (NUDGED) forecasts where zonal-mean flows in the stratosphere are relaxed to the observation. When the models are initialized on 8 February 2018, both FREE and NUDGED forecasts successfully predicted the SSW and its downward influences. However, FREE forecasts initialized on 25 January 2018 failed to predict the SSW and downward propagation of negative Northern Annular Mode (NAM). NUDGED forecasts with SSW nudging qualitatively well predicted the downward propagation of negative NAM. In quantity, NUDGED forecasts exhibit a higher mean squared skill score of 500 hPa geopotential height than FREE forecasts in late February and early March. The surface air temperature and precipitation are also better predicted. Cold and dry anomalies over the Eurasia are particularly well predicted in NUDGED compared to FREE forecasts. These results suggest that a successful prediction of SSW could improve the surface prediction skills on subseasonal-to-seasonal time scale.

• The Journal of Society for e-Business Studies
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• v.18 no.3
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• pp.177-193
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• 2013

The study investigated how did Credu pioneer Korean e-Learning market and reinforce their core competencies and how did they promote business diversification analyzing type of learning motives and examining Credu real cases. Under the fierce competition in the current e-Learning market, Credu has maintained their core competencies and strengthened an active communication channels with customers with focusing on investment to core businesses. Credu has introduced more adventurous and challenging products and services with creating a new model for the types of learning motives. This study could introduce the new perspective about the type of learning motives in e-Learning area. Also, the case study of successful e-Learning company, Credu, could contribute to make more spread e-Learning market techniques in this field in practice.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3368-3372
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• 2012

The $Bi_2O_3$ nanowires are highly sensitive to low concentrations of $NO_2$ in ambient air and are almost insensitive to most other common gases. However, it still remains a challenge to enhance their sensing performance and detection limit. This study examined the influence of the encapsulation of ${\beta}-Bi_2O_3$ nanorods with $In_2O_3$ on the $NO_2$ gas sensing properties. ${\beta}-Bi_2O_3-core/In_2O_3-shell$ nanorods were fabricated by a two-step process comprising the thermal evaporation of $Bi_2O_3$ powders and sputter-deposition of $In_2O_3$. Multiple networked ${\beta}-Bi_2O_3-core/In_2O_3-shell$ nanorod sensors showed the responses of 12-156% at 1-5 ppm $NO_2$ at $300^{\circ}C$. These response values were 1.3-2.7 times larger than those of bare ${\beta}-Bi_2O_3$ nanorod sensors at 1-5 ppm $NO_2$. The enhancement in the response of ${\beta}-Bi_2O_3$ nanorods to $NO_2$ gas by the encapsulation by $In_2O_3$ can be accounted for based on the space-charge model.

• Journal of Korean Society for Atmospheric Environment
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• v.28 no.3
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• pp.273-281
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• 2012

The government is carrying forward a sustainable development which reduces green-house gas and environmental pollution by preparing 'Low Carbon Green Development' policy basis as a new paradigm of national development. This study aims to understand the status of atmosphere contamination which Seoul has by finding correlation among social, economical indexes and carbon, the humanities and social characteristic materials which best express types of city and correlation and to suggest implications. According to the results of the analysis, first the carbon emission volume of Seoul recorded 0.56 ppm, Jongno, Jung-Gu, Kuro, Kangnam and Songpa were more than the average of Seoul and Kwangjin-Gu & Kangbuk-Gu, relative north east regions, Yeongdeungpo-Gu and Dongjak-Gu, south west regions showed lower CO occurrences. Second, according to the correlation and factor analysis, elements which affect CO emission volume of Seoul are largely represented by regional level, traffic level and development density level. Third, when the importance of influence factors based on the analyzed standard coefficient by a regression model, traffic and development density level were most important by recording traffic level (0.967), environmental level (0.385), regional level (0.530) and development density (0.561). Consequently, it was revealed that the traffic level most affected CO emission.

• 대한예방의학회:학술대회논문집
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• 1994.02a
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• pp.651-657
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• 1994

To assess quantitatively the association between benzene exposure and leukemia, we examined the mortality rate of a cohort with occupational exposure to benzene. Cumulative exposure for each cohort member was estimated from historical air-sampling data and, when no sampling data existed, from interpolation on the basis of existing data. The overall standardized mortality ratio (a measure of relative risk multiplied by 100) for leukemia was 337 (95 percent confidence interval, 154 to 641), and that for multiple myeloma was 409 (95 percent confidence interval, 110 to 1047). With stratification according to levels of cumulative exposure, the standardized mortality ratios for leukemia increased from 109 to 322, 1186, and 6637 with increases in cumulative benzene exposure from less than 40 parts per million-years (ppm-years), to 40 to 199, 200 to 399, and 400 or more. respectively. A cumulative benzene exposure of 400 ppm years is equivalent to a mean annual exposure of 10 ppm over a 40-year working lifetime; 10 ppm is the currently enforceable standard in the United States for occupational exposure to benzene. To examine the shape of the exposure-response relation, we performed a conditional logistic-regression analysis, in which 10 controls were matched to each cohort member with leukemia. From this model, it can be calculated that protection from benzene induced leukemia would increase exponentially with any reduction in the permissible exposure limit.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.7
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• pp.726-733
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• 2017

A magnetic shutter gear is a device that transfers mechanical power by synchronizing the magnetic field between permanent magnet layers facing circumferentially through a harmonic modulator. However, magnetic gears uses many rare-earth permanent magnets to guarantee comparable torque density to that of mechanical reducer. Hence, we propose a novel axial magnetic gear with a dramatically reduced number of permanent magnets and a closed magnetic path. The torque of the system was compared to that of an existing shutter gear through a harmonic analysis of the air-gap magnetic field. The modulator thickness and open ratio were considered as the primary design parameters, and the cogging effect was analyzed for variation of the reduction ratio. A dynamic model between the high-speed side and low-speed side was derived, and position control was performed for a constructed hardware implementation.

• Journal of the Korean Society for Railway
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• v.15 no.1
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• pp.17-22
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• 2012

Installation of screen doors at platform ensures safety of passengers by separating platform from tracks. Besides, it reduces drought and air pressure caused by train conserves heating and cooling energy in the station. In order to guarantee safety of platform screen doors, design considering evaluation of wind pressure requires. In this study, Sosa station, semisealed screen door and EMU are analyzed to estimate the wind pressure of platform screen doors model. Also Sosa station is influenced by climatic condition because it exposed to outside. Therefore, analysis on the wind pressure of platform screen doors is performed under the worst weather condition such as typhoon. The results of analysis, Maximum inside pressure 287 Pa, and consideration of outside pressure as typhoon to the maximum design pressure of 865 Pa 2756.25 Pa conditions approximately 3.1 times the difference can be seen that ensure stability.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.3
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• pp.215-226
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• 2017

This study examines the concept of public interests in pay TV industry and analyzed the regulatory framework of the industry. The concept of public interests such as diversity, localism and quality which are mainly discussed in the context of over the air broadcasting extends to universal access, fair competition and consumer protection as pay TV industry grows. However, there is a lack of concrete implementation of public interests in regulatory framework and coordination of public and industrial interests was not accomplished. Major policy that regulates the pay TV industry carries out without big picture. Policy implementation without long term plan results in hierarchical regulation model and it produced consistency problem. In the process of implementing policy in pay TV industry public interests and industrial interests discussion is mixed and sometimes it played exaggerated role.

• Journal of Korean Society for Atmospheric Environment
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• v.33 no.1
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• pp.64-74
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• 2017

In this study, we have analyzed relationship between the measured Water Soluble Organic Carbon (WSOC) concentrations and the estimated aerosol water content of $PM_{10}$ (particulate matter with an aerodynamic diameter of less than or equal to $10{\mu}m$) for the period between September 2006 and August 2007 at Seoul, Korea. Water content of $PM_{10}$ was estimated by using a gas/particle equilibrium model, Simulating composition of Atmospheric Particles at Equilibrium 2 (SCAPE2). The WSOC concentrations showed low correlation with Elemental Carbon (EC), but Water Insoluble Organic Carbon (WISOC) were highly correlated with EC. It seemed that hydrophilic groups were produced by secondary formation rather than primary formation. As with the previous studies, WSOC showed good correlation with secondary ions ($NO_3{^-}$, $SO_4{^{2-}}$, $NH_4{^+}$), especially WSOC was highly correlated with $NO_3{^-}$ that is a secondary ion formed by photochemical oxidation from more local sources than $SO_4{^{2-}}$. No apparent correlation between the measured WSOC and estimated water content was observed. However, WSOC showed good correlation with estimated water content when it was assumed that relative humidity was higher than the deliquescence relative humidity of the system. In conclusion, WSOC is correlated with water content by hygroscopic ions and it is expected that nitrate play an important role among the water content and WSOC.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.11
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• pp.1091-1097
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• 2017

Sales of commercial-type cooling fans intended for application in military electronics are often discontinued during equipment production. This results in requirements for alternative fan selection as well as equipment performance and reliability tests, such as high-temperature operation testing. This study deals with alternative fan selection and verification methods that can be used during the production process. First, an alternative fan was selected by calculating the flow and pressure required to effectively cool the equipment, then the feasibility of the selected fan was verified using a reliable CFD heat dissipation analysis model. Following this, a high-temperature operation test was performed using the alternative fan in the equipment. Results demonstrated that the equipment satisfied its required function in a high-temperature environment, and the main parts as well as internal air temperature were found to be thermally stable.