• 대한전기학회논문지:전력기술부문A
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• 제54권6호
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• pp.293-305
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• 2005

This paper describes an improved Prony method in its speed, accuracy and reliability by efficiently determining the optimal sampling interval with use of DFT (discrete Fourier transformation). In the Prony method the computation time is dominated by the size of the linear prediction matrix, which is given by the number of data times the modeling order The size of the matrix in a general Prony method becomes large because of large number of data and so does the computation time. It is found that the Prony method produces satisfactory results when SNR is greater than three. The maximum sampling interval resulting minimum computation time is determined using the fact that the spectrum in DFT is inversely proportional to sampling interval. Also the process of computing the modes is made efficient by applying Hessenberg method to the companion matrix with complex shift and computing selectively only the dominant modes of interest. The proposed method is tested against the 2003 KEPCO system and found to be efficient and reliable. The proposed method may play a key role in monitoring in real time low frequency oscillations of power systems .

• 대한전기학회논문지:시스템및제어부문D
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• 제54권11호
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• pp.680-688
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• 2005

The electrical current generated by heart creates not only electric potential but also a magnetic field. We have observed electrophysiological phenomena of the heart by measuring components of magnetocardiogram(MCG) using 61 channel superconducting quantum interference device(SQUD) system. We have analyzed the possibility and characteristics of MCG parameters for diagnosis of ischemic heart disease. A technique for automatic analysis of MCG signals in time domain was developed. The methods for detecting the position, the interval, the amplitude ratio, and the direction of single current dipole were examined in the MCG wave. The position and interval parameters were obtained by calculating the gradients of a envelope curve which could be formed by the difference between the maximum and minimum envelope of multi-channel MCG signals. We show some differences of the frequency contour map between the normal MCG and the abnormal (ischemic heart disease) MCG. The direction of single current dipole can be defined by rotating the magnetic field according to Biot-Savart's law at each point of MCG signals. In this study, we have examined the direction of single current dipole from searching for the centroids of positive and negative magnetic fields. The amplitude ratio parameters for measuring 57 deviation consisted of A$_{T}$/A$_{R}$ and other ratios. and We developed a new analysis method, which is based on the frequency contour map of electromagnetic field. Using theses parameters, we founded significant differences between normal subjects and ischemic patients in some parameters.

• 한국가스학회지
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• 제2권4호
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• pp.79-84
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• 1998

본 논문은 고주파 발생장치와 IEC형 불꽃점화 시험장치를 이용하여 라디오 주파수 범위내에서 발생하는 개폐불꽃에 의한 LPG-Air 5.25[Vol$\%$]의 혼합가스에 대한 최소점화한계전압을 구하였다. 그 결과 LPG-Air 혼합가스는 주파수가 높을수록 최소점화한계전압도 높아졌으며, 특히 3[KHz]에서 10[KHz]사이에서 현저히 증가함을 알 수 있었다. 이는 3[KHz]까지는 1회의 방전에너지에 의해 점화가 발생되지만 3[KHz]이상에서는 2회 이상의 방전에너지가 누적되어 점화가 일어남을 알 수 있었고 그 이유는 방전과 방전간의 휴지기간이 존재하므로써 생기는 에너지의 손실이 그 원인으로 생각된다. 본 연구결과는 가스가 존재하는 위험장소에서도 안전하게 사용될 수 있는 통신장비나 각종탐지기 등에 응용될 수 있는 본질안전 방폭형 고주파 전기기기의 연구개발을 위한 기본자료로서 뿐만 아니라 이들 장비의 방폭성능에 대한 시험자료로도 활용가능할 것으로 사료된다.

• 한국수산과학회지
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• 제38권5호
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• pp.316-322
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• 2005

In order to develop a floating breakwater, which can efficiently control long period waves, vertical plates are attached in pontoon. Wave control and dynamic behaviors of the newly developed vertical plates type are verified from numerical analysis and hydraulic experiment. As a result, for the wave control and energy dissipation, the newly developed vertical plates type is more efficient than the conventional pontoon type. For the floating body motion, the wave transmission, depending on incident wave period, is decreased at the natural frequency. Dimensionless drift distance has similar trend of the reflection rate of wave transformation near natural frequency except maximum and minimum values. Dimensionless maximum tension is 17 percent of the weight of floating breakwater in case of the conventional pontoon type and 18 percent or 14 percent in case of the newly developed vertical plates type. Thus, it is shown that the wave control is improved by the vertical plates type. In addition, by adjusting the interval of the front and back vertical plate, we would control proper wave control.

• Journal of Preventive Medicine and Public Health
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• 제55권6호
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• pp.549-558
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• 2022

Objectives: Poor complementary feeding practices have consistently contributed to the burden of child undernutrition in Indonesia. This study aimed to estimate the prevalence and predictors of the time of the introduction of solid, semi-solid, and soft foods (ISSSF), minimum dietary diversity (MDD), minimum meal frequency (MMF), and minimum acceptable diet (MAD). Methods: We analyzed 4804 last-born infants aged 6-23 months from the 2017 Indonesia Demographic and Health Survey, which employed multistage cluster random sampling. The outcomes were calculated based on the 2021 World Health Organization/United Nations Children's Fund guidelines. The predictors of the 4 complementary feeding indicators were assessed using multivariate Poisson regression with robust variance adjusting for potential confounders and study design. Results: The prevalence of ISSSF, MDD, MMF, and MAD was 86.1%, 54.3%, 71.8%, and 37.6%, respectively, with younger children less likely to meet 3 out of the 4 outcomes. Parental education, the presence of a birth attendant, and maternal media consumption were among the predictors of MDD and MAD. Children from families with higher income were more likely to meet MDD than those from low-income households (adjusted prevalence ratio [aPR], 1.16; 95% confidence interval [CI], 1.05 to 1.28). Living in an urban area was positively associated with MMF (aPR, 1.09; 95% CI, 1.04 to 1.15) and MAD (aPR, 1.12; 95% CI 1.02 to 1.24). In eastern regions, the prevalence of children achieving MDD and MAD was lower than in those living in Java and Bali. Conclusions: It is crucial that more attention and efforts are made to improve the recommended practices throughout Indonesia, since the prevalence of adequate complementary feeding practices remains low.

• Advances in aircraft and spacecraft science
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• 제5권2호
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• pp.225-237
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• 2018

The difficulties of satellite vibration testing are due to the commonly expressed qualification requirements being incompatible with the limited performance of the entire controlled system (satellite + interface + shaker + controller). Two features cause the problem: firstly, the main satellite modes (i.e., the first structural mode and the high and low tank modes) are very weakly damped; secondly, the controller is just too basic to achieve the expected performance in such cases. The combination of these two issues results in oscillations around the notching levels and high amplitude beating immediately after the mode. The beating overshoots are a major risk source because they can result in the test being aborted if the qualification upper limit is exceeded. Although the abort is, in itself, a safety measure protecting the tested satellite, it increases the risk of structural fatigue, firstly because the abort threshold has been already reached, and secondly, because the test must restart at the same close-resonance frequency and remain there until the qualification level is reached and the sweep frequency can continue. The beat minimum relates only to small successive frequency ranges in which the qualification level is not reached. Although they are less problematic because they do not cause an inadvertent test shutdown, such situations inevitably result in waiver requests from the client. A controlled-system analysis indicates an operating principle that cannot provide sufficient stability: the drive calculation (which controls the process) simply multiplies the frequency reference (usually called cola) and a function of the following setpoint, the ratio between the amplitude already reached and the previous setpoint, and the compression factor. This function value changes at each cola interval, but it never takes into account the sensor signal phase. Because of these limitations, we firstly examined whether it was possible to empirically determine, using a series of tests with a very simple dummy, a controller setting process that significantly improves the results. As the attempt failed, we have performed simulations seeking an optimum adjustment by finding the Least Mean Square of the difference between the reference and response signal. The simulations showed a significant improvement during the notch beat and a small reduction in the beat amplitude. However, the small improvement in this process was not useful because it highlighted the need to change the reference at each cola interval, sometimes with instructions almost twice the qualification level. Another uncertainty regarding the consequences of such an approach involves the impact of differences between the estimated model (used in the simulation) and the actual system. As limitations in the current controller were identified in different approaches, we considered the feasibility of a new controller that takes into account an estimated single-input multi-output (SIMO) model. Its parameters were estimated from a very low-level throughput. Against this backdrop, we analyzed the feasibility of an LQG control in cancelling beating, and this article highlights the relevance of such an approach.

• 생태와환경
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• 제49권4호
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• pp.385-392
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• 2016

지리적 격리는 생태학적 특징의 차이를 유발한다. 지리적인 격리는 박쥐 종 내의 소리 차이의 원인으로 알려져 왔다. 본 연구는 관박쥐의 반향정위가 지리적 차이에 의해 차이가 있는지를 알기 위해 우리나라 섬(제주도)과 내륙에서 수행되었다 우리는 내륙과 섬(제주도)에서 관박쥐가 활동기간에 휴식처로 이용하는 것으로 알려진 폐광과 동굴을 연구 지역으로 선정하였다. 관박쥐의 Hand-held call과 Free-flying call을 녹음하였다. 녹음된 펄스(pulse)는 관박쥐의 Hand-held call과 Free-flying call을 녹음하였다. 분석 결과, 내륙에서 서식하는 관박쥐의 PF는 평균 69 kHz로 섬(제주도)에 서식하는 관박쥐의 PF (71 kHz)와 차이가 났다. 판별 분석 결과에서도 내륙과 섬의 반향정위는 차이를 보였다. 우리나라 관박쥐 개체군의 PF는 유럽(82 kHz)보다는 낮고, 일본(65 kHz)보다는 높았다.

• 한국산업융합학회 논문집
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• 제26권1호
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• pp.193-199
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• 2023

In this study, an analysis was conducted to analyze the structural stability of the piezoelectric power generation module and to determine the optimal burying hole interval for concrete, the installation site of the power generation module. A piezoelectric element refers to a functional ceramic having a piezoelectric direct effect that converts mechanical energy into electrical energy and a piezoelectric reverse effect. In the analysis of the piezoelectric power generation module, the load condition was applied with about 16 tons and a total of 10 wheels in consideration of the container trailer. The purpose was to evaluate the stability of major components of the piezoelectric power generation module through finite element analysis. In order to determine the optimal burying location of the concrete ground for burying the piezoelectric power generation module, the stability of the ground structure according to the distance of the holes was determined. As a result of the analysis, the maximum stress of the piezoelectric power generation module was generated in the support spring, showing a stress of about 276.7 MPa. It was found that the spacing of holes for embedding the piezoelectric power generation module should be set to a minimum of 100 mm or more.

• 한국임상수의학회지
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• 제16권2호
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• pp.381-388
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• 1999

These investigations were performed to determine the causes of the reproductive disorders of the sows in a pig farm which was located at the distance 36m away from the detonation spot. The reproductive problems of the sows such as abortion and infertility occurred after consecutive detonation and use of heavy equipments to build 6 piers of the bridge for the expressway between Jinju and Taeieon during the period from July 1997 to October 1998. 1. The management condition of the farm, microorganism in the feed, inbreeding, hematological conditions, and viral agent causing abortion were not proved as the factors of the occurrence of abortion and infertility in the pig farm. 2. Theoretical concussion values according to the average amount of explosive per detonation were 1.16 kine for minimum amount (3.6 kg) and 3.45 kine for maximum amount(12.5 kg) of explosive, and the theoretical sound values were accordingly 92.29 decibel for minimum amount and 101.76 decibel for maximum amount of explosive, respectively, in the case of 36m distance between the detonation spot and pig farm. The frequency of detonation in a day was 7 times with interval of 15 minutes. 3. The occurence of infertility in the farm was 57.3% during the period of construction from July 1997 to August 1998. 4. In comparison of body weight of piglets between the damaged and not damaged farms, growth of piglets at the damaged farm was shown to be delayed over 30 days than those of not-damaged farm. In conclusion, abortion of 40 sows, delivery of whole still births of 22 sows, and infertility of 122 sows in the pig farm were assumed to be caused by the concussion or sound stress after consecutive detonation and use of heavy equipments.

• 한국대기환경학회지
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• 제18권6호
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• pp.465-474
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• 2002

In order to reflect variability due to exposure factors as well as to assess uncertainty associated with cancer risk posed by airborne trace metals, a Monte Calro analysis has been made in this study. Input parameters for Monte Carlo analysis were developed or adjusted using body weight, lifetime, and exposure frequency of Koreans. Ambient distributions of toxic metals were founded to be lognormal distributions for most of them using goodness-of-fit tests. Thus, the 95% UCL and 95% LCL of carcinogenic metals were estimated by H-statistic method for lognormal distribution, respectively. The results of Monte Carlo analysis of 95% UCL showed that the 95th percentile risks for men and women were 1.2 and 1.1 times higher than an acceptable risk of 10$^{-5}$ , respectively. The probabilities which those risks exceed the acceptable risk were estimated to be 8% and 6%, respectively, while to be 95% and 94%, respectively on the basis of the minimum acceptable risk of 10$^{-6}$ , respectively. Approximately 90% of total cancer risk came from human carcinogens such as arsenic and hexavalent chromium. Therefore, it is necessary to properly manage both arsenic and hexavalent chromium emissions in the study area.