• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.11
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• pp.1199-1204
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• 2004

Most overhead transmission lines in Korea run over the mountain; however, only little study has been made for the effect of mountain fire on polymeric insulator for transmission lines, though the study is significantly required, Therefore, in this study, the authors observed the deformation of the sheds of the insulator under fire, varying the ignition time using artificial ignition testing equipment, and investigated electrical and mechanical characteristics of the insulator through dry withstand voltage test, impulse flashover test and tensile load test. As the results of the tests, the following conclusions were obtained, First, when the insulator was subjected to the fire, the electrical characteristics were slightly reduced, but there was no change on the mechanical characteristics, Secondly, the sheds and sheath of the insulator were not non-flammable but less-flammable. These two results show the high mechanical stability and durability of the insulator under severe fire condition, though the electrical characteristics can be deteriorated as the time that the insulator is subjected to fire, goes by.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.238-244
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• 2002

A 5-valve(intake 3-valve) engine has been developed to increase engine performance. These engines have a high power caused by the decrease of inertia mass of an intake valve and the increase of intake effective area. In this study, in-cylinder flow patterns were visualized with laser sheet method and velocity profiles at near intake valves were inspected by using a two-color PIV. In addition, steady flow tests were performed to quantify tumble ratio of flow-fields generated by a tumble control valve(TCV). Experimental results of steady flow test show that the cure of tumble ratio in intake 3-valve engine farmed as a S shape with valve lift changes. This tendency is different from the one in intake 2-valve engine. Using laser sheet method and two color PIV method, we can find that the intake flow through upper valve increases and the velocity gradient also slightly increases as valve lift increases. From this study, the in-cylinder flow characteristics around intake valves were made clearly.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.117-122
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• 2012

A blisk with rotor shroud is usually adopted in LRE turbine to maximize its performance. However it experiences severe thermal load and resulting damage during engine stating and stop. Shroud splitting is devised to relieve thermal stress on the turbine rotor. Structural analysis confirmed the reduction of plastic strain at the blade hub and tip. However, split gap at the rotor shroud entails additional tip leakage and results performance degradation. In order to assess the effect of shroud split on the turbine performance, tests have been performed for various settings of shroud split. For the maximum number of shroud splitting, measured efficiency reduction ratio was 2.65% to the value of original shape rotor.

• Nuclear Engineering and Technology
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• v.34 no.4
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• pp.344-357
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• 2002

The present paper reports spontaneous steam explosions observed in fuel coolant interaction experiments using prototypic reactor materials. Pure ZrO$_2$ and a mixture of UO$_2$ and ZrO$_2$ are used. A high temperature molten material in the form of a jet is poured into a subcooled water pool located in a pressure vessel. An induction skull melting technique is used for the melting of the reactor material. In both tests using pure ZrO$_2$ and a mixture of UO$_2$ and ZrO$_2$, either a quenching or a spontaneous steam explosion was observed. The morphology of debris and pressure profile clearly indicate the differences between the qunching cases and explosion cases. The dynamic pressure. dynamic impulse, water temperature, melt temperature, and static pressure Inside the containment chamber were measured . As the spontaneous steam explosion for the reactor material is firstly observed in the present experiments, the results of present experiments could be a siginificant step forward the understanding the explosion of the reactor material.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.85-92
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• 2020

Ground hot-firing tests were conducted to analyze the combustion performance according to the characteristic lengths 1.37 m, 1.71 m, and 2.06 m of the combustion chamber in 200 N-class GCH4-LOx small rocket engine. Thrust, specific impulse, and characteristic velocity at the steady-state could be obtained as the key performance parameters of the rocket engine. The performance characteristics acquired through the test were compared and analyzed with the theoretical performance calculated from CEA analysis. Observation of the influence of characteristic length on the combustion performance indicates that an optimal characteristic length shall remain between 1.71 m and 2.06 m.

• Journal of Yeungnam Medical Science
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• v.39 no.2
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• pp.81-88
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• 2022

Vertigo is the sensation of self-motion of the head or body when no self-motion is occurring or the sensation of distorted self-motion during an otherwise normal head movement. Representative peripheral vertigo disorders include benign paroxysmal positional vertigo, Ménière disease, and vestibular neuritis. Vestibular neuritis, also known as vestibular neuronitis, is the third most common peripheral vestibular disorder after benign paroxysmal positional vertigo and Ménière disease. The cause of vestibular neuritis remains unclear. However, a viral infection of the vestibular nerve or ischemia of the anterior vestibular artery is known to cause vestibular neuritis. In addition, recent studies on immune-mediated mechanisms as the cause of vestibular neuritis have been reported. The characteristic clinical features of vestibular neuritis are abrupt true-whirling vertigo lasting for more than 24 hours, and no presence of cochlear symptoms and other neurological symptoms and signs. To accurately diagnose vestibular neuritis, various diagnostic tests such as the head impulse test, bithermal caloric test, and vestibular-evoked myogenic potential test are conducted. Various treatments for vestibular neuritis have been reported, which are largely divided into symptomatic therapy, specific drug therapy, and vestibular rehabilitation therapy. Symptomatic therapies include generalized supportive care and administration of vestibular suppressants and antiemetics. Specific drug therapies include steroid therapy, antiviral therapy, and vasodilator therapy. Vestibular rehabilitation therapies include generalized vestibular and customized vestibular exercises.

• Journal of Practical Engineering Education
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• v.13 no.3
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• pp.497-505
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• 2021

Test equipment for strain and vibration measurement was designed for educational purposes. Widely available and affordable materials were put into making this device. Three strain gauges placed on an iron ruler made cantilevered beam were used to measure values according to external load. An electromagnet triggered excitation and a function generator created vibration of the beam. We present three different tests conducted with this equipment regarding production of scales, measurement of resonant frequency, and calculation of the difference between excitation frequency and measured frequency. Overall, this paper presents a piece of simple yet inexpensive test equipment and its corresponding portfolio with expectations of being applied to the educational field for efficient measurement of load and vibration.

• The Journal of Asian Finance, Economics and Business
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• v.9 no.3
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• pp.33-42
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• 2022

Oil prices have become more volatile as a result of global economic contraction and control measures. Before and during the COVID-19 crisis, this study examines the relationship between oil price swings and daily stock returns in the power sector. The impact is investigated using a panel Vector Autoregressive (VAR) model. Granger causality tests are used to see if oil prices are effective in predicting returns. The dynamic impact of supply shocks is studied using Impulse Response Functions (IRFs). From January 2011 to May 2021, the study used daily data from all listed power sector enterprises on the Pakistan stock exchange. To investigate the differences in reactions between the Pre-COVID and COVID eras, the sample was separated into two groups. Oil shocks are inversely associated with daily firm stock returns. The conclusions are further supported by the lack of impact of stock prices on oil prices. The relationship, however, deteriorates during the COVID pandemic. We could not uncover any evidence of a significant relationship. In developing countries that rely on oil imports, the study sheds light on the utility of oil price shocks in daily stock return predictions.

• Clinical and Experimental Pediatrics
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• v.51 no.8
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• pp.842-847
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• 2008

Purpose : Measurement of forced expiratory volume in 1 second ($FEV_1$) is usually difficult to obtain in children under six years of age because it requires active cooperation. This study evaluates the sensitivity of impulse oscillometry system (IOS) parameters for detecting airway obstruction in comparison with $FEV_1$. Methods : We studied 174 children who performed the lung function and methacholine challenge tests to diagnose asthma by IOS and spirometry. Children were divided into two subgroups according to their $PC_{20}$, which is a parameter for bronchial sensitivity. We compared IOS parameters with $FEV_1$ at the baseline, post-methacholine challenge, and evaluated their correlation. Results : At the baseline, reactance at 5 Hz (X5) and resistance at 5 Hz (R5) significantly differed between the $PC_{20}$ positive ($PC_{20}{\leq}16mg/mL$) group and $PC_{20}$ negative ($PC_{20}$ >16 mg/mL) group; however, $FEV_1$, $FEV_1$ % predicted, $FEV_1_-Zs$ (Z score) did not differ. $FEV_1$ is correlated with X5 (r=0.45, P<0.01) and R5 (r=-0.69, P<0.01). $FEV_1_-Zs$ is also correlated with X5_Zs (r=-0.26, P<0.01) and R5_Zs (r=-0.31, P<0.01). After the methacholine challenge test, dose-response slopes in $FEV_1$ and X5 significantly differed between the two subgroups (P<0.05). Conclusion : IOS parameters were more discriminative than $FEV_1$ for detecting decreased baseline lung function between two subgroups and have a good correlation with $FEV_1$.

• Journal of Korean Philosophical Society
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• no.117
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• pp.139-167
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• 2017

This essay attempts to reveal how taste spontaneously cultivates and why it is necessary for cultivating taste to edify our personality and to develop culture. It is a key of the solution of the problems that taste always reflects its judgment through pleasure. Because the grounds of the universal validity of the judgment of taste are found, whenever taste tests the validity of its own judgment, the so-called 'delight of discovery' makes taste cultivate itself. For having the moral personality, we need to practice spontaneously the morality of our own behaviour and for judging whether an artwork to represent the period is succeeded or not, we need to have a high insight to select the cultural heritage. But the autonomous thinking can delightfully be made a habit, judging the beauty of artworks. In the main body of this essay, it is determined from the three examples of the negative judgment of taste which Kant suggested in deduction. According to Kant, the negative judgment of taste means that the beautiful work is displeased, but what it asserts is that taste is cultivated. I formalize the methods of reflection of taste revealed in three negative judgments of taste into'resisting', 'indicating of error', 'self-retracting'.(Chapter 2) And from this, I emphasize the necessity to cultivate taste in the way that these methods of the cultivation of taste can affect building our personality by stimulating our reason to have interest in moral(Chapter 3) and in the way that taste directly judges the product of cultural succession.(Chapter 4) In the end of last chapter, I examine further essentially the method of the reflection of taste, to inquire into how to enable it.(Chapter 5) Especially, I try to illuminate its grounds through Schiller's concept of the "impulse of amusement(Spieltrib)", because his explanation helps us to understand the dynamics of taste's delight of discovery. Although the abilities of mind conflict with each other, taste has the characters that it reflects to encourage them for each other and that it is vitalized by its own activity. We, as it were, can pleasantly handle two tasks, because taste makes the impulse of amusement from conflictive impulses in mind. In conclusion, I state that we have to experience directly the impulse of amusement like creative artist, because it is maximized from creation.