• Journal of the Institute of Electronics Engineers of Korea SC
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• v.47 no.2
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• pp.1-7
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• 2010

This paper presents empirical equations indicating the high frequency performance characteristics of air-cored induction coil sensors with their constructional parameters. An air-cored induction coil sensor is widely used due to good linearity at low frequency ranges but the sensor has weakness of relatively low sensitivity to the magnetic field. At high frequency ranges, the sensitivity can be dramatically increased, largely depending on the frequency of the injected field, and this property can be a great asset to some electromagnetic inspections, since they utilize the interrogating current with a fixed frequency. The application of this property of the coil sensor requires the estimation of its high frequency performance. We made experiments on the frequency responses of the coil sensors under diverse constructional conditions and, on the basis of the experimental results, the high frequency performance, such as the resonant frequency and the sensitivity at the frequency, was estimated, as a function of the constructional parameters of the coil sensor. The good agreements between experimental and estimated data were reported.

• Tribology and Lubricants
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• v.33 no.4
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• pp.141-147
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• 2017

The vibration data of bearings are very useful for monitoring and determining the condition of the bearings. The defect frequencies of ball bearings have been used for monitoring there condition. However, it is not easy to verify the defect frequencies as the wear progress. Therefore there is a need for an easy method to monitor the damages of bearings in real-time and to observe the variations in vibration characteristics as the wear progress. In this study, a bearing test equipment is constructed to diagnose the damage of bearings. The friction coefficient and vibration data are measured by using a torque sensor and an acceleration sensor, and the correlation between the measured data is analyzed to diagnose the condition of the bearing. We reached the following conclusions from the results. When the ball surface, inner and outer rings of a ball bearing are damaged, the friction coefficient increases to over 0.02 with an adhesion on the surface. Moreover this damage occurs more quickly with an increase in the number of revolutions. In the vibration characteristics, the amplitude of vibration wave appears high with an increase in the friction coefficient. In the high frequency range between 1000 and 2000 Hz, a wide range of frequency components with high amplitude occurs continuously irrespective of the number of revolutions.

• Journal of the Ergonomics Society of Korea
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• v.22 no.1
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• pp.81-94
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• 2003

The British railway safety research group has developed a risk assessment model for the railway infrastructure and major railway accidents. The major hazardous factors of the railway infrastructure were identified and classified in the model. The frequency rates of critical top events were predicted by the fault tree analysis method using failure data of the railway system components and ratings of railway maintenance experts, The consequences of critical top events were predicted by the event tree analysis method. They classified the Joss of accident due to railway system into personal. commercial and environmental damages. They also classified 110 hazardous event due to railway system into three categories. train accident. movement accident and non-movement accident. The risk assessment model of the British railway system has been designed to take full account of both the high frequency low consequence type events (events occurring routinely for which there is significant quantity of recorded data) and the low frequency high consequence events (events occurring rarely for which there is little recorded data). The results for each hazardous event were presented in terms of the frequency of occurrence (number of events/year) and the risk (number of equivalent fatalities per year).

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.6
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• pp.31-36
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• 2005

Use of the high frequency motor spindles are increasing for the high speed machine tools recently. The important problem in the high speed spindles is to reduce and minimize the thermal effect by the motor and ball hearings. Thermal characteristics according to the bearing preload and spindle cooling are studied for the spindle with the oil mist lubrication and high frequency motor. Temperature distribution and thermal displacement according to the spindle speed, preload and flow rate are measured. Temperature distribution and thermal displacement of the high speed spindle system can be estimated reasonably by using the three dimensional model through the finite element method. The results of analysis are compared with the measured data. This study supports thermal optimization and find out more effective cooling condition. This paper show that the suitable preload and spindle cooling are very effective to minimize the thermal effect by the motor and ball bearings.

• Journal of Power Electronics
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• v.17 no.3
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• pp.601-609
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• 2017

Gallium nitride (GaN) power switching devices are promising candidates for high switching frequency and high efficiency power conversion due to their fast switching, low on-state resistance, and high-temperature operation capability. In order to facilitate the use of these new devices better, it is required to investigate the device characteristics and performance in detail preferably by comparing with various conventional silicon (Si) devices. This paper presents a comprehensive study of GaN high electron mobility transistor (HEMT) based non-isolated point-of-load (POL) synchronous buck converter operating at 2.7 MHz with a high step-down ratio (24 V to 3.3 V). The characteristics and performance of GaN HEMT and three different Si devices are analytically investigated and the optimal operating point for GaN HEMT is discussed. Zero-voltage switching (ZVS) is implemented to minimize switching loss in high switching frequency operation. The prototype circuit and experimental data support the validity of analytical and simulation results.

• Journal of Environmental Impact Assessment
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• v.15 no.3
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• pp.207-215
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• 2006

The purpose of this paper is to analyze the spatial distribution and change of the frequency of Yellow Sand days and to examine their relationship with atmospheric circular characteristics at the surroundings of the Korean peninsula. Yellow Sand days data are used by intensity, Siberian High Index and monthly mean temperature of the Northern Hemisphere. In the Middle-western region, the occurrence frequency of Yellow Sand days was higher during the study period (1973-2004). Also, the occurrence frequency of Yellow Sand days increased to latter half 16 years compared with the first half 16 years, and be clearer in Middlewest regions. Yellow Sand days frequency increased, and the trend was distinct in the Jungbu region during the study period. Increasing trend of Yellow Sand days frequency was significant for the recent 22 years. Yellow Sand days had a negative relationship with Siberian High Index in February and March. Therefore, Siberian High Index became weaker in the spring, and possibility for the occurrence of Yellow Sand days was generating larger. Yellow Sand days had a positive relationship in monthly mean temperature of the Northern Hemisphere. Especially, the case of the strong Yellow Sand days is significant. Recently, global warming might be affecting the occurrence of strong Yellow Sand days.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.8
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• pp.924-931
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• 1999

Most conventional protection relays are based on processing information in the spectrum that is close to or at power frequency. It is, however, widely known that faults on transmission lines produce frequency components of a wide range. High frequency signals caused by sudden changes in system voltage that occurs in the immediate post-fault period are generally outside the bandwidth of receptibility of most protection scheme. In this respect, a specially designed stack tuner is connected to the coupling capacitor of CVT, in order to capture the high frequency signals. Digital signal processing is then applied to the captured information to determine whether the fault is inside or outside the protected zone, and to discriminate the fault type. In this paper, modal transform is not applied to fault generated signals, because signals which are converted by modal transform are not have an information of each phase any longer. Instead, using peak voltage value of data windows is able to discriminate fault type. The paper concludes by presenting fault detection and discrimination of various faults on transmission line which are based on extensive simulation studies carried out on a typical 154kV Korean transmission line, using the EMTP software.

• Korean Journal of Community Nutrition
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• v.28 no.5
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• pp.363-375
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• 2023

Objectives: The objective of this study was to identify factors associated with adolescent obesity, as well as any new factors that correlated with a change in the rate of obesity over time. Methods: The study used 5-yearly data collected by the Korea Youth Risk Behavior Survey starting from the year 2006 up until 2021 (data from 2nd, 7th, 11th, and 17th surveys were analyzed). Factors such as demographics, dietary factors, health behavioral factors, and mental health factors were studied. All data were analyzed using IBM SPSS 27.0, employing chi-square tests and multiple logistic regression analysis. Results: This study included data from a total of 255,200 participants. Factors contributing to obesity varied with time. Over the survey duration of 15 years, low academic achievement, parents with low levels of education, low frequency of fruit consumption, low frequency of fast food intake, long periods of being seated, and high levels of stress were significantly associated with a high rate of obesity. Factors that showed a new correlation with an increase in obesity rates included living with single parents, low frequency of muscle strengthening exercises, and experiencing intense sadness and despair in the past year. Factors that were correlated with a change in obesity rates over time included household economic status, frequency of carbonated beverage consumption, frequency of intense physical activity, and frequency of alcohol consumption. Breakfast intake and smoking were not significantly associated with obesity rates in the 15-year period. Conclusions: While several factors associated with obesity remained consistent over time, several new factors have emerged in response to social, economic, and environmental changes contributed to a change in obesity rate over time. Therefore, to prevent and manage adolescent obesity, continuous research into the new emergent factors contributing to obesity is needed.

• Proceedings of the IEEK Conference
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• 2001.06c
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• pp.77-80
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• 2001

In general, the informations of the inner image that user interested in are limited to a special domain. In this paper, as using Wavelet Transform for dividing image into high frequency and low frequency, We can separate foreground including many data. After calculating object boundary of separated part, We extract special features using Color Coherence Vector. According to results of this experiment, the method of comparing data extracting foreground features is more effective than comparing data extracting features of entire image when we extract the image user interested in.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2003.04a
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• pp.105-109
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• 2003

The occurrence of cycle slips is a major limiting factor to attain high precision positioning and navigation results with GPS. Cycle slips must be correctly repaired at the data processing stage. In this study, the technique to find cycle slips in the processing of data collected with Trimble 4700 GPS receivers is suggested. The use of Kalman filtering techniques is used in an attempt to reduce the effect of the noise in the different quantities involved and to improve the accuracy in cycle slip correction.