• 한국해양공학회지
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• 제22권3호
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• pp.71-75
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• 2008

This paper illustrates haw $Y_2O_3$ contributes to crack-healing strengths as a function of crack-healing temperature and the additive amount. In investigating mechanical properties, the indentation fracture method is very simple and useful, but careful attention must be paid to the statistical data processing because data may be scattered excessively, especially for brittle materials. To estimate accurate AE signal properties we applied the useful time-frequency method with a discrete wavelet analysis algorithm. In experiments, three kinds of specimens were prepared. After the specimens were indented by a Vickers indentor, they were heat-treated and crack-healed to evaluate bending strength and the AE signal. With higher amounts of the additive powder, as 1, 3, or 5% wt. of $Y_2O_3$, the concentrative tendency of dominant frequency trended toward lower frequency groups. The $Al_2O_3$ ceramic with 3% wt. of $Y_2O_3$ was judged most suitable because it demonstrated superior crack-healing ability and relative concentration on the highest frequency group.

• 한국운동역학회지
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• 제23권3호
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• pp.225-233
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• 2013

The purpose of this study was to estimate the potential injury via analyzing ground reaction force components that were resulted from a prolonged-run-induced fatigue. For the present study, passive and active components of the vertical ground reaction force were determined from time and frequency domain. Shear components of GRF also were calculated from time and frequency domain. Twenty subjects with rear foot contact aged 20 to 30, no experience in injuries of the extremities, were requested to run on the instrumented tread-mill for 160 minutes at their preference running speed. GRF signals for 10 strides were collected at 5, 35, 65, 95, 125, and 155 minute during running. In conclusions, there were no significant difference in the magnitude of passive force, impact load rate, frequency of the passive and active components in vertical GRF between running times except the magnitude of active force (p<.05). The magnitude of active force was significantly decreased after 125 minute run. The magnitude of maximum peak and maximum frequency of the mediolateral GRF at heel strike and toe-off have not been changed with increasing running time. The time up to the maximum peak of the anteroposterior at heel-strike moment tend to decrease (p<.05), but the maximum peak and frequency of that at heel and toe-off moment didn't depend significantly on running time.

• International Journal of Control, Automation, and Systems
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• 제5권4호
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• pp.388-396
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• 2007

This paper describes a multipath estimation method for Global Positioning System (GPS) dual frequency carrier phase measurements. Multipath is a major error source in high precision GPS applications, i.e., carrier phase measurements for precise positioning and attitude determinations. In order to estimate and remove multipath at carrier phase measurements, an array GPS antenna system has been used. The known geometry between the antennas is used to estimate multipath parameters. Dual frequency carrier phase measurements increase the redundancy of measurements, so it can reduce the number of antennas. The unscented Kalman filter (UKF) is recently applied to many areas to overcome some of the limitations of the extended Kalman filter (EKF) such as weakness to severe nonlinearity. This paper uses the UKF for estimating multipath parameters. A series of simulations were performed with GPS antenna arrays located on a straight line with one reflector. The geometry information of the antenna array reduces the number of estimated multipath parameters from four to three. Both the EKF and the UKF are used as estimation algorithms and the results of the EKF and the UKF are compared. When the initial parameters are far from true parameters, the UKF shows better performance than the EKF.

• 한국전자파학회논문지
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• 제18권11호
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• pp.1299-1308
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• 2007

본 논문에서는 주파수 가변 비동기 모노펄스 시스템에서 추정각 변화량을 최소화하기 위한 모노펄스 기울기 교정 방법을 제시하였다. 이를 위해 우선 안테나 및 RF 수신기의 수신 채널간 이득 및 위상 불균형에 의한 모노펄스 기울기 특성을 분석하였고, 안테나를 포함한 RF 수신기의 채널간 이득 및 위상 불균형을 최소화하기 위한 교정 방법을 제시하였다. 또한, IF 수신기의 채널간 상대 이득 불균형에 의한 영향을 최소화하기 위해 채널 절체를 통한 교정 방법을 제시하였다. 제시된 방법들에 의한 교정 결과, 주어진 주파수 대역폭 내에서의 측정된 평균모노펄스 기울기는 -0.96이 되었으며, 추정각 변화량은 이론값과 유사한 방위각 ${\pm}2^{\circ}$에서 최대 $0.15^{\circ}$, 방위각 $0^{\circ}$에서 최대 $0.03^{\circ}$가 되었다.

• 한국전자파학회논문지
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• 제25권12호
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• pp.1275-1283
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• 2014

PCM(Pulse Code Modulation) 파형은 펄스에 특정 code를 실어 보내는 형태로 추적에 적합한 특성을 가진다. 특히 단일 펄스의 송수신만으로 표적의 탐지 및 추적이 가능하므로, 여러 임무를 수행해야 하는 다기능 레이다(MFR: Multi-Function Radar)에서는 시간 측면에서 효율적이다. 하지만 PCM 파형은 모호성 함수(ambiguity function) 의 특성으로 인해 표적을 탐지하고, 거리와 속도 정보를 얻기 위해서 도플러 필터 뱅크(Doppler filter bank)가 필요하다. 본 논문에서는 계산량과 하드웨어 측면에서 한계가 있는 도플러 필터 뱅크를 사용하는 대신, ML(Maximum Likelihood) 기반의 도플러 추정 방법을 고안하였다. 제안한 알고리즘은 폐형(closed form) 수식의 suboptimal 방법으로 적은 계산량으로 정확한 도플러 주파수를 추정할 수 있고, 이를 기반으로 표적의 탐지에 적용할 수 있다.

• 한국군사과학기술학회지
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• 제18권2호
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• pp.115-124
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• 2015

A methodology is proposed to estimate a trajectory of a flying target and its velocity using the time and frequency analysis of the acoustic signal. The measurement of sound emitted from a flying acoustic source with a microphone above a ground shall receive both direct and ground-reflected sound waves. For certain frequency contents, the destructive interference happens in received signal waveform reflected path lengths are in multiple integers of direct path length. This phenomenon is referred to as the acoustical mirror effect and it can be observed in a spectrogram plot. The spectrogram of acoustic measurement for a flying vehicle measurement shows several orders of destructive interference curves. The first or second order of curve is used to find the best approximate path by using nonlinear least-square method. Simulated acoustic signal is generated for the condition of known geometric of a sensor and a source in flight. The estimation based on cepstrogram analysis provides more accurate estimate than spectrogram.

• 한국의류학회지
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• 제26권6호
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• pp.801-810
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• 2002

The purpose of this study is to suggest standard bodytype which offers criterion for the sizes and shapes to interpret various bodytypes, to estimate fitting, and to construct ready-made clothing. There were two ways of analyzing bodytypes of subjects from the viewpoint of statistic and beauty. We had carried on the analysis from the viewpoint of statistic in the Part(1) and we carried on the analysis from the viewpoint of beauty in this Part(2). Taken as a sample, the subjects were ninety-seven females who were between the aloes of 18 and 24 rears o1d. They were measured on November 1999. The data of seven hundred and four females,18∼24 year-old, from the National Somatometry Survey of 1997 were used for analysis, too. The first analysis from the viewpoint of beauty was executed to the front and side photographs of the subjects to analyze the general traits of the beautiful bodytype. The second analysis from the viewpoint of beauty was executed to subjects who were in both High-frequency proportion range and Beautiful bodytype group. As the result, four groups in Beautiful and High-frequency proportion range were selected. The standard proportion was analyzed with the size and shape of four groups. Based on the standard proportion, the size, shape and silhouette of the standard bodytype were analyzed. To verify the size, shape and silhouette of the standard bodytype, the location of the standard bodytype in the 1997 National Somatometry Survey group was analyzed. As the result, the standard bodytype was verified as proper criterion to interpret various bodytypes, to estimate fitting, and to construct ready-made clothing.

• 한국위성정보통신학회논문지
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• 제10권4호
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• pp.146-150
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• 2015

COSPAS-SARSAT 위원회에서는 2000년 이후부터 새롭게 발사되는 미국, EU, 러시아의 중궤도 항법위성에 탐색구조 탑재체를 탑재하여 중궤도 탐색구조(MEOSAR) 서비스를 제공키로 결정하였다. 비컨에서 송출되는 조난신호는 비컨 상공의 각 위성들에 각기 다른 도달시간과 도플러 주파수를 가지고 도달하며, 이를 바로 중궤도 수신국(MEOLUT)으로 전달한다. 중궤도 수신국에서는 적어도 3~4개의 위성을 동시에 추적하여 조난신호를 전달받고, 조난신호 간 TDOA(Time Difference of Arrival)와 FDOA(Frequency Difference of Arrival)를 이용하여 비컨의 위치를 추정한다. 그러나 비컨은 임의의 시간에 50초 간격으로 조난신호를 송출하므로, 대형 조난상황에서 비컨 신호가 겹치는 현상이 나타날 수 있고, 겹쳐진 비컨 신호들을 COSPAS-SARSAT에서 개발하고 있는 현재 방식으로 모든 비컨 위치를 추정하는 것은 어렵다. 따라서 여기에서는 이를 해결하기 위한 방안으로 CAF MAP 알고리즘을 소개하고, COSPAS-SARSAT 시스템의 성능 요구사항을 만족시킬 수 있도록 MCAF MAP 기법을 제안하고, 그 성능을 나타낸다.

• 대한의용생체공학회:의공학회지
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• 제28권4호
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• pp.503-511
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• 2007

Heart rate variability(HRV) is the clinical consequence of various influences of the autonomic nervous system(ANS) on heart beat. HRV can estimate the potential physiologic rhythm from the interval between consecutive beats(RR interval or HRV data), but cardiovascular system governed by ANS is in relation to respiration and autonomic regulation. It is known as RSA representing respiration-related HR rhythmic oscillation. Because the mechanism linking the variability of HR to respiration is complex, it has so far been unknown well. In this paper, we tried to evaluate 5-min RR interval segments under control of respiration in order to find out a proper respiration rate that can estimate the ANS function. 10 healthy volunteers were included to evaluate 5-min HRV data under 4 different respiration-controlled environments; 0.03Hz, 0.1Hz, 0.2Hz, and 0.4Hz respiration. HRV data were analyzed both in the frequency and the time domain, with cross-correlation coefficient(cross-coeff.) for HRV and respiration signal. The results showed maximum cross-coeff. of 0.84 at 0.1 Hz and minimum that of 0.16 at 0.4Hz respiration. Cross-coeff was decreased at a faster rate from 0.1Hz respiration. All mean SDNN, RMSSD, and pNN50 of time domain measures were 108.7ms, 71.85ms, and 28.47%, respectively, and LF, HF, and TP of frequency domain measures were $12,722ms^2,\;658.8ms^2$, and $7,836.64ms^2$ at 0.1Hz respiration, respectively. In conclusion, 0.1Hz respiration was observed to be very meaningful from time domain and frequency domain analysis in relation to respiration and autonomic regulation of the heart.

• Asian Pacific Journal of Cancer Prevention
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• 제13권6호
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• pp.2655-2661
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• 2012

Validation of a food frequency questionnaire (FFQ) utilising a short-term measurement method is challenging when the reference method does not accurately reflect the usual food intake. In addition, food group intake that is not consumed on daily basis is more critical when episodically consumed foods are related and compared. To overcome these challenges, several statistical approaches have been developed to determine usual food intake distributions. The Multiple Source Method (MSM) can calculate the usual food intake by combining the frequency questions of an FFQ with the short-term food intake amount data. In this study, we applied the MSM to estimate the usual food group intake and evaluate the validity of an FFQ with a group of 333 Korean children (aged 3-6 y) who completed two 24-hour recalls (24HR) and one FFQ in 2010. After adjusting the data using the MSM procedure, the true rate of non-consumption for all food groups was less than 1% except for the beans group. The median Spearman correlation coefficients against FFQ of the mean of 2-d 24HRs data and the MSM-adjusted data were 0.20 (range: 0.11 to 0.40) and 0.35 (range: 0.14 to 0.60), respectively. The weighted kappa values against FFQ ranged from 0.08 to 0.25 for the mean of 2-d 24HRs data and from 0.10 to 0.41 for the MSM-adjusted data. For most food groups, the MSM-adjusted data showed relatively stronger correlations against FFQ than raw 2-d 24HRs data, from 0.03 (beverages) to 0.34 (mushrooms). The results of this study indicated that the application of the MSM, which was a better estimate of the usual intake, could be worth considering in FFQ validation studies among Korean children.