• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.1 s.20
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• pp.39-48
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• 2005

After the development of the Firefly, flight tests have been performed to verify the performance and get the parameters for the mathematical model of the aircraft. The flight test data is used to get parameters for the mathematical model of the aircraft through the parameter identification process. An arbitrary control input is applied to the test flight which is a part of parameter identification process. A square wave has been used a control input which is called Doublet signal. The aspect of the signal is same length and magnitude in both (+) and (-) directions such as sine wave. The Doublet signal is composed of a dominant frequency and many high frequencies, so that it is appropriate signal to excite the motion of an aircraft. In this paper, the control input of the flight test data has been analyzed to check the efficiency of the control input using DFT(Discrete Fourier Transform). From the result of analysis, an alternative input was extracted.

• Geophysics and Geophysical Exploration
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• v.10 no.4
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• pp.223-228
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• 2007

First arrival signals of multi-frequency crosswell seismic data, acquired in wells drilled in granitic rock, were analyzed to investigate the characteristic behavior of the signals at the shear zones. Dominant frequencies of the sources were; 10-, 20-, 40-, 56-, and 80 kHz. No obvious changes in the waveform at the shear zones were found; however, at the shear zones, some degree of velocity reductions were observed in the signals of all frequency sources. The 80 kHz signal is slightly faster than 10 kHz signal in the survey region, and the velocity difference between the two signals were found largest at the shear zone where the permeability measured greatest in the survey interval.

• Aerospace Engineering and Technology
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• v.1 no.1
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• pp.1-7
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• 2002

This paper describes the analysis method about the dynamic characteristics and vibratory load through HDS(Helicopter Design Study). To analyze the dynamic characteristics of helicopter rotor blade, the natural frequencies and modes are calculated according to rotor operational speed(Ω). Generally the proximity of rotor natural frequency and N times of rotor operational speed is a dominant component to determine the helicopter vibration. Also we can predict the airframe vibration by calculating the airload of rotating blade exactly. We expect to establish the design procedure of rotor dynamics by describing the two major analysis methods necessary to rotor design.

• Carbon letters
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• v.27
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• pp.90-97
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• 2018

Electromagnetic interference (EMI) shielding is an important issue in modern daily life due to the increasing prevalence of electronic devices and their compact design. This study estimated EMI-shielding effect (EMI-SE) of small ($8-14{\times}17mm$) Hanji (Korean traditional paper) doped with carbon nanotubes (CNTs) and compared to Hanji without CNT using $^2H$ (92.1 MHz) and $^{23}Na$ (158.7 MHz) nuclear magnetic resonance (NMR) peak area data obtained from 1 M NaCl in $D_2O$ samples in capillary tubes that were wrapped in the Hanji samples. The simpler method of using the variation of reflected power and tuning frequency by inserting the sample into an NMR coil was also tested at 242.9, 158.7, and 92.1 MHz. Overall, EMI shielding was relatively more effective at the higher frequencies. Our results validated that NMR methods to be useful to evaluate EMI-SE, particularly for small, flexible shielding materials, and demonstrated that EMI shielding by absorption is dominant in Hanji mixed with CNT.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.11
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• pp.243-246
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• 1996

This study was peformed to characterize the physiological signal prior to develop an algorithm which quantifies EEGs evoked by tactile stimulation. The experiment was devised with four experimental conditions, which were control and two levels of pressures in tactile sensation. Twenty subjects were used to obtain EEGs while applying tactile stimulation using two types of textiles, soft towel and sand paper, to the right hand of each subject. EEGs were acquired for 20 seconds, and each trial was repeated five times randomly at the different levels of stimulus intensities. The index, $S_{n}$, was obtained by calculating the ratio of energy distribution in the time-frequency plot for each scored psychological state of the subject. The results showed that dominant aspects of the EEG signals have their maximal frequencies concentrated at a lower ranges for the resting and pleasant state, while the spectral energies were distributed to higher frequency ranges when subjects experience an unpleasant emotion.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.1
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• pp.1-9
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• 2014

The parameters of electromechanical modes offer considerable insight into the dynamic stability properties of a power system. This paper describes an initial result for extraction of dynamic parameters from synchrophasor measurements collected on the KEPCO system. Dominant modes of the system are estimated by oscillation detecting program in K-WAMS. The critical wide-area modes of KEPCO system have frequencies in the 0.4 to 0.7Hz range. And the local mode causing the low frequency oscillation of generators located on the west coast area has in the frequency 0.97 and 1.25 Hz, respectively. This results can serve as a reference in the future for reliable system operation in KEPCO system.

• Structural Engineering and Mechanics
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• v.69 no.2
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• pp.155-162
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• 2019

It is very common to find an empirical formulation in an earthquake design code to calculate fundamental vibration period of a structural system. Fundamental vibration period or frequency is a key parameter to provide adequate information pertinent to dynamic characteristics and performance assessment of a structure. This parameter enables to assess seismic demand of a structure. It is possible to find an empirical formulation related to reinforced concrete structures, masonry towers and slender masonry structures. Calculated natural vibration frequencies suggested by empirical formulation in the literatures has not suits in a high accuracy to the case of rest of the historical masonry bridges due to different construction techniques and wide variety of material properties. For the listed reasons, estimation of fundamental frequency gets harder. This paper aims to present an empirical formulation through Mean Square Error study to find ambient vibration frequency of historical masonry bridges by using a non-linear regression model. For this purpose, a series of data collected from literature especially focused on the finite element models of historical masonry bridges modelled in a full scale to get first global natural frequency, unit weight and elasticity modulus of used dominant material based on homogenization approach, length, height and width of the masonry bridge and main span length were considered to predict natural vibration frequency. An empirical formulation is proposed with 81% accuracy. Also, this study draw attention that this accuracy decreases to 35%, if the modulus of elasticity and unit weight are ignored.

• Smart Structures and Systems
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• v.30 no.4
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• pp.411-420
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• 2022

Monitoring large structures is a significant issue involving public health on which new studies are constantly carried out. Although the Global Navigation Satellite System (GNSS) is the most preferable method for measuring structural displacements, total stations, one of the classical geodetic instruments, are the first devices that come to mind in cases that require complementary usage and auxiliary measurement methods. In this study, the relative displacements of the structural movements of a tower were determined using robotic total stations (RTS) and GNSS. Two GNSS receivers and two RTS observations were carried out simultaneously for 10 hours under normal weather conditions. The spectral analysis of the GNSS data was performed using fast Fourier transform (FFT), and while the dominant modal frequencies were determined, the total station data were balanced with the least-squares technique, and the position and position errors were calculated for each measurement epoch. It has been observed that low-frequency structural movements can be determined by both methods. This result shows that total station measurements are a helpful alternative method for monitoring large structures in situations where measurements are not possible due to the basic handicaps of GNSS or where it is necessary to determine displacements with short observations.

• The Journal of the Acoustical Society of Korea
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• v.26 no.6
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• pp.286-292
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• 2007

The dominant source of noise in a sea-connected piping system is usually due to a seawater cooling pump which circulates seawater to operate onboard equipments normally, and so its water-borne noise with some tonal frequencies should be reduced using proper silencers. In order to obtain the transmission loss of water-borne noise silencers experimentally the present paper suggests a transfer function technique that acoustic wave in the piping system is decomposed into its incident and transmitted components when the reflection at the termination of the system exists. Good agreement in the interested frequency range with theory and the proposed technique shows the validity of the technique.

• Journal of Gastric Cancer
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• v.2 no.3
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• pp.163-167
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• 2002

Purpose: Interleukin 1$\beta$ (IL-1$\beta$) polymorphisms are associated with hypochlorhydria, atrophic gastritis, and increased risk of gastric cancer in Caucasians. We tried to determine whether the IL-1.. and IL-1 receptor antagonist (IL-1 RN) genetic polymorphisms contribute to the development of gastric cancer and the specific type of gastritis in Korean. Materials and Methods: The study population was comprised of 128 gastric cancer patients with histologically proven carcinoma and 63 normal healthy individuals. Sixty-eight carcinomas were of intestinal-type and sixty tumors were of diffuse-type. No patient had a familial gastric cancer history. The 511 bp and 31 bp polymorphisms in the IL-1.. were genotyped by polymerase chain reaction (PCR)-restriction fragment length polymorphism. The polymorphism of the IL-1 RN was analyzed with variable number tandem repeat after PCR. Results: The genotype of 511C/-31T of IL-1$\beta$ and allele 1 of IL-1 RN was dominant in the present subjects. The allelic frequencies of the C allele IL-1$\beta$, which is a high risk genotype for gastric cancer, were 0.551 and 0.429 in gastric cancer and normal controls, respectively. Statistically, significant difference in allelic frequencies of three polymorphic sites between gastric cancer patients and normal controls, and between intestinal-type and diffuse-type was not observed. Conclusions: These results suggest that the polymorphisms of IL-1$\beta$ and IL-1 RN may not contribute to the development of Korean gastric caner and that other endogenous or exogenous factors will be important for gastric carcinogenesis.