• Journal of Magnetics
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• v.22 no.1
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• pp.104-108
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• 2017

Induction motors have wide applicability in many fields, both in industrial sectors and households, for their advantages of a high efficiency and robust structure. The introduction of power-source-containing harmonics into the induction motor winding lowers its efficiency and increases its temperature, greatly affecting its operation characteristics. In this study, we performed an electromagnetic field analysis using the time-difference finite-element method with the purpose of analyzing the steady-state current characteristics of an induction motor. Additionally, we calculated the steady-state current with a method combining an electromagnetic field equation and a circuit equation. In the electromagnetic field analysis, the nonlinearity was taken into account using the Newton-Raphson method, and a backward time-difference method was employed for the time derivative term. Then, we compared the steady-state current of the induction motor obtained by calculation with the experimentally measured values, thus validating the proposed algorithm. Furthermore, we analyzed the impacts of the shape and material of the rotor conductor bar of the induction motor on the steady-state current of the main winding.

• Tunnel and Underground Space
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• v.20 no.2
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• pp.112-118
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• 2010

Before blasts that can have direct impacts on human bodies or structures, it is necessary to assess impacts of ground vibration. Therefore, frequency has been recognized as an important factor in order to assess impact on ground vibration and damages. There have been many studies on impacts of frequency. But, there have been no studies on relations between vibration and frequency according to delay time difference. In this study, we examined the relations between delay time difference and frequency according to each frequency with which reinforcement and destructive intervention repeat through delay time difference obtained using superposition modeling of single hole blasting waveform based on the theory of time difference developed by Langefors.

• Journal of Korean language education
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• v.25 no.1
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• pp.83-113
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• 2014

This study aims to examine the change of strategy use by analyzing the refusal sequence of beginner Japanese Korean learners by time difference of 10 weeks. The results of the study are as follows; First, in the solidarity system of politeness(power-, distance-), learners showed similar ability as native Koreans after 10 weeks. Second, in the deference system(power-, distance+), there was a difference according to the situational burden when using strategies. In the invitational setting, the learners sought justification for their refusal or tried to negotiate by explaining in detail as time passed. However, in the request setting, they showed no will to compromise by refusing directly and leading the listener to give up. Third, similar difference was found in the use of strategies depending on the situational burden in the hierarchical system(power+, distance+). While learners could present their justification for refusal by showing their interest in the invitation as time passed in the invitation setting, they expressed straight refusal and were not willing to negotiate in the request setting.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.10
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• pp.1005-1011
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• 2011

In this paper, we present a marching-on-in-degree(MOD) finite difference method(FDM) based on the Helmholtz wave equation for analyzing transient electromagnetic responses in a general dispersive media. The two issues related to the finite difference approximation of the time derivatives and the time consuming convolution operations are handled analytically using the properties of the Laguerre functions. The basic idea here is that we fit the transient nature of the fields, the flux densities, the permittivity with a finite sum of orthogonal Laguerre functions. Through this novel approach, not only the time variable can be decoupled analytically from the temporal variations but also the final computational form of the equations is transformed from finite difference time-domain(FDTD) to a finite difference formulation through a Galerkin testing. Representative numerical examples are presented for transient wave propagation in general Debye, Drude, and Lorentz dispersive medium.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.11
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• pp.5208-5213
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• 2011

In this paper, we proposed a new direction finding(DF) technology using TDOA(time-difference of arrival) and PDOA(phase difference of arriving signal) method. The proposed technology has a good DF accuracy without DF ambiguity. TDOA or PDOA technology is used to the most of intelligence systems in 21 century. The principle of TDOA is to receive a signal with two parallel antennas, measure the time difference of arrival signal, and converse the time difference to the direction of incident signal. Those technology make a DF system small size but the DF accuracy is low into short antenna installation distance. The principle of PDOA is similar to TDOA except measuring the phase difference of arrival signal, These technology get a good DF accuracy in short antenna installation distance but have a DF ambiguity. The proposed DF method is simulated into DF system operation environment with noise, and has a good DF accuracy.

• Journal of Advanced Navigation Technology
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• v.21 no.2
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• pp.163-170
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• 2017

MLAT which is an independent cooperative surveillance system is applied to increase the positon resoultin of secondary survelliance radar. MLAT uses the hyperboic or hyperboloid position mesurement algorithm. Central processing unit of MLAT calculates target position using time difference of arrival (TDOA) which can be solved from time of arrival (TOA) information of each receivers (at least 4 receivers). To increase position resolution of MLAT which use TDOA, TOA which is transfer time from tranmitter to receiver shold be calculated with precision time resolution in receiver. This paper explained the MLAT system briefly and explained ATD which is one of means of calcuating pulse position. ATD is applied to solve the deviation of pulse position due to different amplitude of signals in mulitiple receivers. In this paper, to analysis the performance of ATD, the simulation result of LAS and CDS was compared with the simulation result of basic threshold method.

• Journal of The Korean Society of Integrative Medicine
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• v.10 no.1
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• pp.1-11
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• 2022

Purpose : Obesity is a major public health burden in developed countries and a well-known risk factor for cardiovascular disease. Short sleep duration is associated with obesity, as well as diabetes, heart disease and death. In modern society, habitual sleep restrictions seem unavoidable due to social obligations and work schedules along with a tendency toward decreased sleep time. Therefore, the purpose of this study is to examine the effect of differences in sleep time between weekdays and weekends on body mass index (BMI). Methods : This study involved 4,234 Korean adults aged 20 to 64 years based on data obtained from the 7th national health and nutrition examination survey (2016). All subjects were classified into the weekend catch-up sleep group (weekend CUS group). and the non catch-up sleep group (non-CUS group). Results : The longer the average sleep time, the lower was the BMI, and the larger the difference in sleep time between weekdays and weekends, the lower was the BMI. Compared with those with an average sleep time of 8 hours or more, obesity was 1.6-fold higher when the average sleep time was less than 6 hours, and 1.2-fold higher in the case of sleep time of 7 hours or more and less than 8 hours. When the difference in sleep time between weekdays and weekends was 0 or less, more than 0 hours but less than 1 hour, and more than 1 hour and less than 2 hours, the risk of obesity was 1.2-fold, 1.1-fold and 1.1-fold higher, respectively, compared with the risk associated with a sleep time difference of 2 hours or greater between weekdays and weekends. However, the difference was not statistically significant. Conclusion : Short sleep duration is positively associated with obesity. In addition, weekend catch-up sleep affects BMI.

• Journal of Acupuncture Research
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• v.17 no.1
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• pp.75-88
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• 2000

In order to obtain the clinical data on the different effects of the three different methods of indirect moxibustion, moxa-combustion time, peak temperature, average temperature, maximum gradient temperature, average gradient temperature, and moxa-combustion calorie rate of the retaining period in ARIRANG, JANG, PUNG were measured through this experiment. The results of the experiment were as follows : 1. In the combustion time, during the retaining period ARIRANG had the longest combustion time followed by PUNG, JANG in a descending order. ARIRANG and JANG were acknowledged to have significant difference with PUNG. ARIRANG and JANG however were not acknowledged to have difference each other. 2. In the average temperature, during the retaining period, PUNG had the highest temperature followed by JANG, ARIRANG in a descending order. ARIRANG and JANG were acknowledged to have significant difference with PUNG. ARIRANG and JANG however were not acknowledged to have difference each other. 3. In the maximum gradient temperature, during the retaining period, PUNG had the highest temperature followed by JANG, ARIRANG in a descending order. JANG and PUNG were acknowledged to have significant difference with ARIRANG. JANG and PUNG however were not acknowledged to have difference each other. 4. In the average gradient temperature, during the retaining period, JANG had the highest temperature followed by ARIRANG, PUNG in a descending order. ARIRANG and JANG were acknowledged to have significant difference with PUNG. ARIRANG and JANG however were not acknowledged to have difference each other. 5. In the moxa-combustion calorie rate, during the retaining period, PUNG had the highest temperature, ARIRANG, JANG were founded in error limits. ARIRANG and JANG were acknowledged to have significant difference with PUNG. ARIRANG and JANG however were not acknowledged to have difference each other.

• Journal of Ocean Engineering and Technology
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• v.20 no.5 s.72
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• pp.30-35
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• 2006

In tire presence of incident waves with different frequencies, there are second order sum and difference frequency wave exciting forces due to the nonlinearity of tire incident waves. Although the magnitude of these nonlinear wave forces are small, they act on TLPs at sum and difference frequencies away from those of the incident waves. So, the second order sum and difference frequency waveexciting forces occurring close to tire natural frequencies of TLPs often give greater contributions to high and law frequency resonant responses. Nonlinear motion responses and tension variations in the time domain are analyzed by solving the motion equations with nonlinear wave exciting forces using tire numerical analysismethod. The numerical results of time domain analysis for the nonlinear wave exciting forces on the ISSC TLP in regular waves are compared with the numerical and experimental ones of frequency domain analysis. The results of this comparison confirmed tire validity of the proposed approach.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.12 no.4
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• pp.21-26
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• 2016

In this study, the control strategies of indoor air temperature in floor radiant heating system were researched by computer simulation. The temperature difference based time control method using the difference of indoor set temperature and indoor temperature is compared with the existing On-Off control one for heating control performances. As a result, the temperature difference based time control method shows better thermal environmental characteristics in case of selected operational conditions in comparison with existing control one.