• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.11
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• pp.1131-1139
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• 2009

Combustion Instabilities are caused by a coupling between acoustic waves and unsteady heat release. They can be eliminated using passive controller such as a Helmholtz resonator. But, Helmholtz resonator is normally only effective over a narrow frequency range. In this work, Helmholtz resonator is applied for reducing the combustion oscillations and we vary the Helmholtz resonator volume using piston in oder to tune in the wide range of operating conditions. As the result, it is found that the dominant combustion oscillations can be largely reduced by optimizing the size of resonator volume. And, interesting relation for phase difference of dynamic pressure both combustor and the helmholtz resonator are presented in this paper. Also, we investigate semi-active control using Helmholtz equation and phase difference.

• Restorative Dentistry and Endodontics
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• v.48 no.1
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• pp.1.1-1.11
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• 2023

Objectives: This study evaluated the dentinal penetration depth of 2.5% sodium hypochlorite (NaOCl) in root canals with and without preparation and different irrigant activation protocols. Materials and Methods: Sixty-three bovine mandibular incisors were randomly allocated to 6 groups (n = 10): G1, preparation + conventional needle irrigation (CNI); G2, preparation + passive ultrasonic irrigation (PUI); G3, preparation + Odous Clean (OC); G4, no preparation + CNI; G5, no preparation + PUI; G6, no preparation + OC; and CG (negative control; n = 3). Samples were filled with crystal violet for 72 hours. Irrigant activation was performed. Samples were sectioned perpendicularly along the long axis, 3 mm and 7 mm from the apex. Images of the root thirds of each block were captured with a stereomicroscope and analyzed with an image analysis software. One-way analysis of variance, followed by the Tukey post hoc test, and the Student's t-test were used for data analysis, with a significance level of 5%. Results: The NaOCl penetration depth was similar when preparation was performed, regardless of the method of irrigation activation (p > 0.05). In the groups without preparation, G6 showed greater NaOCl penetration depth (p < 0.05). The groups without preparation had a greater NaOCl penetration depth than those with preparation (p = 0.0019). Conclusions: The NaOCl penetration depth was similar in groups with root canal preparation. Without root canal preparation, OC allowed deeper NaOCl penetration. The groups without preparation had greater NaOCl penetration than those undergoing root canal preparation.

• Nuclear Engineering and Technology
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• v.56 no.4
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• pp.1310-1319
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• 2024

The reactor cavity cooling system (RCCS) is a passive reactor safety system commonly present in the designs of High-Temperature Gas-cooled Reactors (HTGR) that removes heat from the reactor pressure vessel by means of natural convection and radiation. It is one of the factors responsible for ensuring that the reactor does not melt down under any plausible accident scenario. For the simulation of accident scenarios, which are transient phenomena unfolding over a span of up to several days, intermediate fidelity methods and system codes must be employed to limit the models' execution time. These models can quantify radiation heat transfer well, but heat transfer caused by natural convection must be quantified with the use of correlations for the heat transfer coefficient. It is difficult to obtain reliable correlations for HTGR RCCS heat transfer coefficients experimentally due to such a system's size. They could, however, be obtained from high-fidelity steady-state simulations of RCCSs. The Rayleigh number in RCCSs is too high for using a Direct Numerical Simulation (DNS) technique; thus, a Reynolds-Averaged Navier-Stokes (RANS) approach must be employed. There are many RANS models, each performing best under different geometry and fluid flow conditions. To find the most suitable one for simulating an RCCS, the RANS models need to be validated. This work benchmarks various RANS models against three experiments performed on the HTTR RCCS Mockup by the Japanese Atomic Energy Agency (JAEA) in 1993. This facility is a 1/6 scale model of a vessel cooling system (VCS) for the High Temperature Engineering Test Reactor (HTTR), which is operated by JAEA. Multiple RANS models were evaluated on a simplified 2d-axisymmetric geometry. They were found to reproduce the experimental temperature profiles with errors of up to 22% for the lowest temperature benchmark and 15% for the higher temperature benchmarks. The results highlight that the pragmatic turbulence models need to be validated for high Rayleigh natural convection-driven flows and improved accordingly, more publicly available experimental data of RCCS resembling experiments is needed and indicate that a 2d-axisymmetric geometry approximation is likely insufficient to capture all the relevant phenomena in RCCS simulations.

• Journal of the Korean earth science society
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• v.39 no.2
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• pp.139-153
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• 2018

The sea surface wind field has long been obtained from satellite scatterometers or passive microwave radiometers. However, the importance of satellite altimeter-derived wind speed has seldom been addressed because of the outstanding capability of the scatterometers. Satellite altimeter requires the accurate wind speed data, measured simultaneously with sea surface height observations, to enhance the accuracy of sea surface height through the correction of sea state bias. This study validates the wind speeds from the satellite altimeters (GFO, Jason-1, Envisat, Jason-2, Cryosat-2, SARAL) and analyzes characteristics of errors. In total, 1504 matchup points were produced using the wind speed data of Ieodo Ocean Research Station (IORS) and of Korea Meteorological Administration (KMA) buoys at Marado and Oeyeondo stations for 10 years from December 2007 to May 2016. The altimeter wind speed showed a root mean square error (RMSE) of about $1.59m\;s^{-1}$ and a negative bias of $-0.35m\;s^{-1}$ with respect to the in-situ wind speed. Altimeter wind speeds showed characteristic biases that they were higher (lower) than in-situ wind speeds at low (high) wind speed ranges. Some tendency was found that the difference between the maximum and minimum value gradually increased with distance from the buoy stations. For the improvement of the accuracy of altimeter wind speed, an equation for correction was derived based on the characteristics of errors. In addition, the significance of altimeter wind speed on the estimation of sea surface height was addressed by presenting the effect of the corrected wind speeds on the sea state bias values of Jason-1.

• The Korean Journal of Physiology
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• v.19 no.2
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• pp.139-153
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• 1985

The passive tilt has been performed to study the orthostasis on the cardiovascular system. The orthostasis due to upright tilt was demonstrated as follows: the venous return, cardiac output and systemic arteiral blood pressure were decreased, whereas there was concomitant increase of heart rate, through the negative feedback mediated by such as the baroreceptor . Previous investigators have suggested that the tolerance to the orthostasis could he increased by blocking the cholinergic fiber with atropine which prevented vasodilation and bradycardia through the vasovagal reflex during the orthostasis. However, this hypothesis has not been clearly understood. This study was attempted to clarify the effect of atropine on the tolerance of the cardiovascular system to the upright and head-down tilt, and to investigate the change of the blood flow through head and lower leg with Electromagnetic flowmeter in both tilts before and after atropine state. Fourteen anesthetized dogs of $10{\sim}14kg$ were examined by tilting from supine position to $+77^{\circ}$ upright position (orthostasis), and then to $-90^{\circ}$ head-down position (antiorthostasis) for 10 minutes on each test. And the same course was taken 20 minutes after intravenous administration of 0.5mg atropine. The measurements were made of the blood flow(ml/min.) on the carotid artery, external jugular vein, femoral artery and femoral vein. At the same time pH, $PCO_2$, $PO_2$ and hematocrit (Hct) of the arterial and venous blood, and heart rate(HR) and respiratory rate (RR) were measured. The measurements obtained from upright and head-down tilt were compared with those from supine position. The results obtained are as follows: In upright tilt, the blood flow both on the artery and the vein through head and lower leg were decreased, however the decrement of blood flow through the head was greater than the lower leg And the atropine attenuated the decrement of the blood flow on the carotid artery, but not on the vessels of the lower leg. HR was moderately increased in upright tilt, but slightly in head-down tilt. The percent change of HR after the atropine administration was smaller than that before the atropine state in both upright and head-down tilts. Before the atropine state, RR was decreased in upright tilt, whereas increased in head-down tilt. However after the atropine state, the percent change of RR was smaller than that of before the atropine state in both upright and head-down tilts. In upright tilt, venous $PCO_2$ was increased, but arterial $PO_2$ and venous $PO_2$ were slightly decreased. Hct was increased in both upright and head-down tilts. The findings of blood $PCO_2$, $PO_2$ and Hct were not interferred by the atropine. In conclusion, 1;he administration of atropine is somewhat effective on improving the cardiovascular tolerance to postural changes. Thus, atropine attenuates the severe diminution of the blood flow to the head during orthostasis, and also reduces the changes of HR and RR in both orthostasis and antiorthostasis.

• Journal of the Korea Convergence Society
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• v.6 no.6
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• pp.285-291
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• 2015

FTMS, TCS, ITS equipment such as high-pass highway are just a situation that does not lack traceability and passive surveillance is related to fault DB has so far consisted of an integrated operations management to maximize utilization of the facility. In addition, there is no replacement parts are replaced when a failure occurs, increasing the number of parts and repair time I have trouble growing, and becoming a service interruption whenever you replace each time. In this study, proactively manage the failure history of a highway facility ITS tries to preventive maintenance. Therefore, the error history is based on the reliability of the high-pass facilities theory to calculate the reliability of the system through a systematic statistical analysis Operational Availability. The fault number and the time the replacement period through the estimate decreases and can reduce the budget expenses by securing the spare parts quantity, establish a management plan in part by improving the quality of the system through constant preventive maintenance, quality of service at all times It may direct the non-stop operation state of the available state.

• Journal of agricultural medicine and community health
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• v.24 no.1
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• pp.131-143
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• 1999

This study was attempted to find the mutual relationship between leisure activities and life satisfaction by the aged persons in a rural area. The data was obtained by interview with questionnaire and the data from 209 persons aged over 65, residing in Dohwa-myeon and Podu-myeon, Koheung-kun, Chollanam-do were analysed. The survey was carried out from Feb. 16th to May 3rd in 1998 and the results are as follows: 1. The survey showed that the major leisure activities were TV watching followed by talking with friends, club activities, taking a walk, visiting friends' or relatives' home and breeding domestic animals. 2. The types of leisure activities were classified into 8 patterns as active self-enlightenment, passive self-enlightenment, temporal amusements, passive self-activities, cozy introspective activities, friend oriented activities, family oriented activities and religious activities. Among the above 8 patterns active self-enlightenment type contributed most to the life satisfaction. 3. The major factors affecting leisure activities were sex, age, average income, religion and educational status. And the major factors affecting life satisfaction were sex, age average income, educational status and a state of health. In conclusion the more the aged persons participated in leisure activities, the better they felt life satisfaction.

• Korean Journal of Food Science and Technology
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• v.49 no.5
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• pp.550-558
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• 2017

The effect of Artemisia argyi H. under liquid-state fermentation by Monascus purpureus (AAFM) on cognitive impairments has been studied in a mice model of diabetes-associated cognitive decline induced by streptozotocin (STZ). C57BL/6 mice (9 weeks of age, male) were separated into four groups: a normal control, STZ-induced diabetic mouse group (STZ group), Artemisia argyi H. (AA) 10 group (diabetic mouse+AA 10 mg/kg/day), AAFM 10 group (diabetic mouse+AAFM 10 mg/kg/day). Administration of AA and AAFM significantly improved glucose tolerance, as shown by the intraperitoneal glucose tolerance test (IPGTT), and ameliorated cognitive deficit, as shown by the behavioral tests including passive avoidance, Morris water maze, and Y-maze tests. After behavioral tests, the cholinergic system was examined by assessment of the acetylcholine (ACh) level and acetylcholinesterase (AChE) inhibitory activity, and the antioxidant system was also assessed by measuring malondialdehyde (MDA) and superoxide dismutase (SOD) levels in the brain and liver.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.6
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• pp.789-799
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• 2019

The settlement hardly occurs in structures supported by pile foundation such as abutment, culvert but a cavity is formed in the lower part of a structure. As a result, soil discharged from the lateral ground to the cavity accelerates the settlement of the lateral ground of the structure, resulting in a larger settlement. Therefore, in order to prevent problems caused by cavity under the structure supported by pile foundation, soil Flow Protector (briefly called 'FLP'), which can be easily installed on the side of structure, was developed. In this study, an laboratory model test was carried out to prove the reduction effect of settlement and to estimate the optimal installation length of the FLP. As a result, the installation of the FLP reduced the settlement of the lateral ground and prevented the leakage of lateral ground soil into the cavity. If the stiffness of the FLP is small, the state or active earth pressure is generated in the upper part, which is not favorable for stability. But if the stiffness of the FLP is high enough, the passive earth pressure area is generated in the upper part, which will be advantageous for the stability. Also, the increased installation length of FLP is effective to reduce the settlement. And the ratio of the optimal length of the FLP to the box structure height (H = 250 mm) are flexible FLP 1.38, stiff FLP 0.73.

• The Korean Journal of Air & Space Law and Policy
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• v.30 no.1
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• pp.303-325
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• 2015

The latest slogan put forth by the international space community is the safety, security, and sustainability of outer space activities. The security of outer space activities, in particular, would be defined as the secure state from space-based threats. The latter comprises passive threats (such as collision with other satellites and space debris) and aggressive threats (such as electromagnetic interference, arms race on the earth or in outer space, and military attacks). Has outer space been used for military purposes in practice? If so, does international law regulate the military space activities it? The use of outer space for military purposes is referred to as space militarization and space weaponisation. Satellites has been used in Gulf War, Kosovo War, and Afghan War, recently, and research and development on space weapons are under way. Since only the placement of weapons of mass destruction on orbit around the earth is prohibited in accordance with 1967 Outer Space Treaty, it may be asked whether other weapons may be placed on orbit. It will be necessary to analyze the stance of on the above question, by studying UN space-related treaties including UN Charter. New international space norms represented by PPWT, ICoC, and UN GGE Report are at the center of progressive development of international law. In conclusion, the author will signpost the various points on international norms to be codified on the use of outer space for military purposes.