• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.5
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• pp.383-389
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• 2000

The relationship between the DC degradation characteristics of the ZnO varistor and the ambient sintering-process is investigated in this study. ZnO varistors made o matsuoka’s composition were fabricated by standard ceramic techniques. The ambient sintering-process is performed at the extraordinary electrical-furnace which is equipped with the vacuum system. Gases used in sintering process were oxygen nitrogen argon and air. Using XRD and SEM the phase and microstructure of samples were analyzed respectively. The conditions of DC degradation tests were conducted at 115$\pm$2$^{\circ}C$ for 13 h. Current-voltage analysis is used to determine nonlinear coefficients($\alpha$). Frequency analysis are performed to understand electrical properties as DC degradation test. From above analysis it is found that the ZnO varistor sintered in oxygen atmosphere showed superior properties at the DC degradation test and degradation phenomenon of ZnO varistor is caused by the change of electrical properties in grain boundary. These results are in accordance with Gupta’s degradation model.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.3
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• pp.47-55
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• 1990

This paper presents the quasi-static mooring analysis model for a vessel moored at the quay. The results of this analysis will aid the designer in determining the mooring configuration for the surface vessels subjected to wind, current and wave forces. And it will also help him in selecting the equipment for the fixed mooring system. The cumulative elastic behavior of the mooring lines invokes a complicated nonlinear problem since the mooring lines are relatively short and hang in air as noncoplanar configurations. This nonlinear mooring problem is solved in this paper by the load increment technique in which the external load is increased step by step taking all sources of nonlinearity into account.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.19-27
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• 2018

In this study, a numerical study was conducted to characterize the E-D nozzle which changes according to the nozzle pressure ratios. Three different numerical analysis models were designed by changing the pintle inflection angles. When the nozzle pressure ratio is low, the outside air flows into the E-D nozzle to form an open flow field. As the nozzle pressure ratio increases, the flow transition occurs to become the closed flow field where the recirculation region is isolated inside the nozzle. Also, the highest thrust coefficient was obtained in the analytical model with high pintle inflection angle at all nozzle pressure ratios.

• International Journal of Computer Science & Network Security
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• v.22 no.9
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• pp.149-158
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• 2022

The pandemic of Covid-19 (Coronavirus Disease 19) has devastated the world, affected millions of people, and disrupted the world economy. The cause of the Covid19 epidemic has been identified as a new variant known as Severe Acute Respiratory Syndrome Coronavirus 2(SARS-CoV2). It motives irritation of a small air sac referred to as the alveoli. The alveoli make up most of the tissue in the lungs and fill the sac with mucus. Most human beings with Covid19 usually do no longer improve pneumonia. However, chest x-rays of seriously unwell sufferers can be a useful device for medical doctors in diagnosing Covid19-both CT and X-ray exhibit usual patterns of frosted glass (GGO) and consolidation. The introduction of deep getting to know and brand new imaging helps radiologists and medical practitioners discover these unnatural patterns and pick out Covid19-infected chest x-rays. This venture makes use of a new deep studying structure proposed to diagnose Covid19 by the use of chest X-rays. The suggested model in this work aims to predict and forecast the patients at risk and identify the primary COVID-19 risk variables

• Nuclear Engineering and Technology
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• v.54 no.12
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• pp.4715-4721
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• 2022

A comprehensive approach for modeling the pulse height spectra of gamma-ray detectors from passing radioactive cloud in a case of accident at NPP has been developed. It involves modeling the transport of radionuclides in the atmosphere using Lagrangian stochastic model, WRF meteorological processor with an ARW core and GFS data to obtain spatial distribution of radionuclides in the air at a given moment of time. Applying representation of the cloud as superposition of elementary sources of gamma radiation the pulse height spectra are calculated based on data on flux density from point isotropic sources and detector response function. The proposed approach allows us to obtain time-dependent spectra for any complex radionuclide composition of the release. The results of modeling the pulse height spectra of the scintillator detector NaI(Tl) Ø63×63 mm for a hypothetical severe accident at a NPP are presented.

• Journal of Environmental Health Sciences
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• v.32 no.3
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• pp.207-214
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• 2006

This study was designed to assess the level of nitrogen dioxide from several microenvironments including inside the home, outdoors near the home, inside the school, outdoors near the school, and on the road for 42 primary schoolchildren during the month of December 2002 in Seoul, Korea. The average personal, indoor, outdoor $NO_2$ levels, and indoor/outdoor ratio were 45.08 ppb, 27.89 ppb, 30.96 ppb, and 0.89, respectively. The indoor $NO_2$ concentrations were significantly associated with the presence of a smoker with a gas stove. The estimated personal $NO_2$ exposure using time-weighted average equation of $34.64{\pm}5.29$ ppb was significantly lower than the measured personal exposure of $45.08{\pm}5.50$ ppb. Our results indicate that indoor $NO_2$ levels were associated with the presence of a smoker and a gas stove. Moreover, personal $NO_2$ exposure with a gas stove in the house was significantly higher than those without a gas stove.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.5
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• pp.454-461
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• 2009

Internal aeroacoustics of an axial fan used for circulating cold air in refrigerators are computed by using the hybrid method where CFD, acoustic analogy and BEM techniques are utilized. The unsteady flow field around the axial fan is predicted by solving the incompressible RANS equations with the conventional CFD techniques. Then, main noise sources are extracted from this unsteady flow field predictions using Acoustic Analogy. Lastly, BPF noise generated from an axial fan are predicted using these modeled sources combined with the tailed Green function techniques, which are numerically solved by the BEM technique. This hybrid model is validated by comparing the prediction with the experiment. Then, parameter studies are carried out, which suggest a capability of the current method as a design tool for the low-noise of the current axial fan system in a refrigerator.

• Journal of Korean Physical Therapy Science
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• v.17 no.1_2
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• pp.33-39
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• 2010

Purpose: The purpose of this study was to analyze the effects of a balance training program using the TARGET Balance Trainer(TBT), which utilizes a visual target, on the balancing ability of normal, healthy individuals. Methods: Twelve healthy female students with an average of 20.7 years(SD=0.25), were participated in this study. They were randomly divided into two groups(6 subjects in each group); experimental group, control group. The experimental group underwent a 3-week training program using the TBT, while the control group trained using only a dynamic air cushion(DAC). Results: Compared to those who trained using only the DAC, participants who trained with the TBT had a smaller difference between the weights distributed(N) to their left and right foot while normal standing with their eyes open. The TBT group also showed a smaller discrepancy between the weights distributed(N) to their left and right sides while standing on one leg with their eyes open, and also with their eyes closed by eye band. Conclusions: TBT is effective to reduce the degree of weight shifting between left and right side in each group. This study is expected to provide a model for future clinical studies.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.6
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• pp.138-144
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• 2010

If the vibration is occurred in a large-sized bus roof, it makes people annoying and complaining the quality of a large-sized bus. So in design stage, it must be considered. To assess vibration at the roof which is equipped with air conditioner in design stage, finite element model is constructed. Computer simulation analysis and experimental method are performed. The dynamic characteristics of the large-sized bus are found by using eigenvalue method. It is related with dynamic behavior. The running conditions of a large-sized bus are velocity and road condition which followed experimental conditions. And the frequency response of a large-sized bus is well correlated with analysis result. Modal participation method is used for finding major modes at each peak. Using this method, we found that front and rear suspension system, engine mounting system and roof structure are the major reasons of the roof vibration. To reduce vibration level of roof in a large-sized bus, spring stiffness of front and rear suspension system, spring stiffness of engine mounting system and roof structure are properly combined. From this study, the vibration characteristics of the roof structure of a large-sized bus can be to a satisfactory level.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.91-98
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• 2017

Performance of a low speed axial compressor is enhanced through a proper configuration of blade row tip injection and casing treatment of groove type. Air injectors were mounted evenly spaced upstream of the blade row within the casing groove and were all aligned parallel to the compressor axis. The groove, which covers all the blade tip chord length, extends all-round the casing circumference. Method of investigation is based on solution of the unsteady form of the Navier-Stokes equations utilizing $k-{\omega}$ SST turbulence model. Extensive parametric studies have been carried out to explore effects of injectors' flow momentums and yaw angles on compressor performance, while being run at different throttle valve setting. Emphasis has been focused on situations near to stall condition. Unsteady numerical analyses for untreated casing and no-injection case for near stall condition provided to discover two well-known criteria for spike stall inception, i.e., blade leading edge spillage and trailing edge back-flow. Final results showed that with only 6 injectors mounted axially in the casing groove and at yaw angle of 15 degrees opposite the direction of the blade row rotation, with a total mass flow rate of only 0.5% of the compressor main flow, surprisingly, the stall margin improves by 15.5%.