• Journal of Korean Academy of Oral and Maxillofacial Radiology
• /
• v.13 no.1
• /
• pp.29-73
• /
• 1983

The age related changes in the life cycle of the progenitor cell population of murine oral epithelia was studied. Using radioautographic methods which have been adopted in previous cell cycle studies, the age-related changes of different phases in renewing cells of the palatal, buccal and lingual mucosae were determined. The results confirm published findings on cell cycle changes of epithelia with aging and illustrated further that mitotic phase which has hither to been considered stationary, also changes with aging. The major parts revealed by this study are as follows: 1) The basal progenitor cells in different regions of oral mucosa have different generation times. 2) The basal cell cycle time increases as a function of aging and the region most affected by aging appears to be the epithelium of the cheek. 3) The phases of the cell cycle affected by the process of aging are in increasing order of magnitude: M-, S- and G₁-phase. 4) The age elated change in the number of DNA synthesizing basal progenitor cells occurs at two age periods. Between 1 and 12 months of life it decreases, while from 12 to 20 months it increases.

• Proceedings of the IEEK Conference
• /
• 2009.05a
• /
• pp.37-39
• /
• 2009

In the research of speech recognition, locating the beginning and end of a speech utterance in a background of noise is of great importance. Since the background noise presenting to record will introduce disturbance while we just want to get the stationary parameters to represent the corresponding speech section, in particular, a major source of error in automatic recognition system of isolated words is the inaccurate detection of beginning and ending boundaries of test and reference templates, thus we must find potent method to remove the unnecessary regions of a speech signal. The conventional methods for speech endpoint detection are based on two simple time-domain measurements - short-time energy, and short-time zero-crossing rate, which couldn't guarantee the precise results if in the low signal-to-noise ratio environments. This paper proposes a novel approach that finds the Lyapunov exponent of time-domain waveform. This proposed method has no use for obtaining the frequency-domain parameters for endpoint detection process, e.g. Mel-Scale Features, which have been introduced in other paper. Comparing with the conventional methods based on short-time energy and short-time zero-crossing rate, the novel approach based on time-domain Lyapunov Exponents(LEs) is low complexity and suitable for Digital Isolated Word Recognition System.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.03a
• /
• pp.166-170
• /
• 2008

The changing process from hovering mode to transition one is of importance to determine a stability of tilt-rotor aircraft, which is utilized in UAV(Unmaned Aerial Vehicle). The analysis on fluid flows and aerodynamic characteristics according to variation of tilting angle of rotor is essential step in development of tilt-rotor. In the present study, the computation domain is divided into the rotating and stationary regions in order to consider the rotating blades. For the convenient realization of various tilting angle as well as application of boundary condition, the whole computation region is constructed into sphere domain. The near farfield boundary condition is adopted. The airfoil used in computation is NACA 0012. The computation results for the hovering mode are validated by comparing with previously conducted experimental results. From the results, the flow fields around rotor blade and the aerodynamic characteristics in transition mode are observed. The computational result will provide the basis for development and performance evaluation of tilt-type aircraft.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.16 no.1
• /
• pp.26-32
• /
• 2007

This study was carried out fusion-welded butt joints in SWS 490A high strength steel subjected to tensile test that load-deflection curve. The windowed or short-time Fourier transform(WFT or STFT) makes possible for the analysis of non-stationary or transient signals into a joint time-frequency domain and the wavelet transform(WT) is used to decompose the acoustic emission(AE) signal into various discrete series of sequences over different frequency bands. In this paper, for acoustic emission signal analysis to use a continuous wavelet transform, in which the Gabor wavelet base on a Gaussian window function is applied to the time-frequency domain. A wavelet transform is demonstrated and the plots are very powerful in the recognition of the acoustic emission features. As a result, the technique of acoustic emission is ideally suited to study variables which control time and stress dependent fracture or damage process in metallic materials.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.8 s.179
• /
• pp.1931-1939
• /
• 2000

Operating excitation forces of the linear vibratory system are normally determined by direct measurement techniques using load cells, strain gauges, etc. But, hydraulic forces of the rotating turbomachinery such as centrifugal pumps are exerted on an impeller due to asymmety of the flow by the interaction between pump impeller and volute. So, investigations of wide range of hydraulic designs and geometric deviations are difficult by direct method. This paper presents a hybrid approach for fourier transformed operational excitation forces, which uses pseudo-inverse matrix of the transfer matrix for the system and the measured vibrational data with standard installed pump. The determination of the transfer function matrix is based on a linear rotor/stationary system and steady state harmonic response in finite element analysis. And, vibrational data is collected in both vertical and horizontal directions at inboard and outboard bearing housings. The results of the process may be enhanced by making acceleration measurements at many more locations than there are forces to be determined.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.3 s.108
• /
• pp.255-262
• /
• 2006

Frequency spectrum using the conventional Fourier analysis gives adequate information about the dynamic characteristics of the slider air bearing for the linear and stationary cases. The intermittent contacts for the extremely low flying height, however, generate nonlinear and nonstationary vibration at the instant of contact. Nonlinear dynamic model should be developed to simulate the impulse response of the air bearing during slider-disk contact. Time-frequency analysis is widely used to investigate the nonstationary signal. Several time-frequency analysis methods are employed and compared for the slider vibration signal caused by the impact against an artificially induced scratch on the disk. The representative Wigner-Ville distribution leads to the severe interference problem by cross terms even though it gives good resolution both in time and frequency. The smoothing process improves the interference problem at the expense of resolution. In order to get the results with good resolution and little interference, the reassignment method is proposed. Among others the reassigned Gabor spectrogram shows the best resolution and readability with negligible interference.

• Journal of Institute of Control, Robotics and Systems
• /
• v.8 no.3
• /
• pp.249-255
• /
• 2002

Since the stationary alignment process of the SDINS is not completely observable, some furls of the aided alignment have been applied. The purpose of this paper is to propose a new initial alignment algorithm, which utilizes the attitude output from the AGPS(Attitude Determination GPS) receiver and to demonstrate the feasibility of the proposed algorithm with several experimental results. A Kalman filter is designed for utilizing the attitude output as well as the zero velocity information. Also analyzed is the observability of the SDINS error model. To show the feasibility of the proposed scheme, we implement an alignment system where HG1700AE IMU (Inertial Measurement Unit) from Honeywell and an AGPS receiver designed at Chungnam National University are used. Test trials are done to evaluate the performance of the proposed alignment scheme. The proposed algorithm provides as good initial alignment performance as a high accurate navigation system, MAPS(Modular Azimuth Positioning System) INS.

• Smart Structures and Systems
• /
• v.3 no.4
• /
• pp.423-437
• /
• 2007

The empirical mode decomposition (EMD) method is well-known for its ability to decompose a multi-component signal into a set of intrinsic mode functions (IMFs). The method uses a sifting process in which local extrema of a signal are identified and followed by a spline fitting approximation for decomposition. This method provides an effective and robust approach for decomposing nonlinear and non-stationary signals. On the other hand, the IMF components do not automatically guarantee a well-defined physical meaning hence it is necessary to validate the IMF components carefully prior to any further processing and interpretation. In this paper, an attempt to use the EMD method to identify properties of nonlinear elastic multi-degree-of-freedom structures is explored. It is first shown that the IMF components of the displacement and velocity responses of a nonlinear elastic structure are numerically close to the nonlinear normal mode (NNM) responses obtained from two-dimensional invariant manifolds. The IMF components can then be used in the context of the NNM method to estimate the properties of the nonlinear elastic structure. A two-degree-of-freedom shear-beam building model is used as an example to illustrate the proposed technique. Numerical results show that combining the EMD and the NNM method provides a possible means for obtaining nonlinear properties in a structure.

• Earthquakes and Structures
• /
• v.18 no.1
• /
• pp.45-56
• /
• 2020

The application of critical excitation method with displacement-based objective function for multi degree of freedom (MDOF) systems is investigated. To this end, a new critical excitation method is developed to find the critical input motion of a MDOF system as a synthetic accelerogram. The upper bound of earthquake input energy per unit mass is considered as a new constraint for the problem, and its advantages are discussed. Considering this constraint, the critical excitation method is then used to generate synthetic accelerograms for MDOF models corresponding to three shear buildings of 10, 16, and 22 stories. In order to demonstrate the reliability of generated accelerograms to estimate dynamic response of the structures, three target ground motions with considerable level of energy contents are selected to represent "real critical excitation" of each model, and the method is used to re-generate these ground motions. Afterwards, linear dynamic analyses are conducted using these accelerograms along with the generated critical excitations, to investigate the key parameters of response including maximum displacement, maximum interstory drift, and maximum absolute acceleration of stories. The results show that the generated critical excitations can make an acceptable estimate of the structural behavior compared to the target ground motions. Therefore, the method can be reliably implemented to generate critical excitation of the structure when real one is not available.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.3C
• /
• pp.243-250
• /
• 2009

In this paper, a closed-form expression of the ergodic channel capacity for a narrow-band time-reversal communication scheme is analytically formulated. In the time-reversal communication scenario, a transmitter sends a signal and a so-called time-reversal array receives the signal. Then, the received signal is reversed in the time do main and resent to the original transmitter. Here, one transmitter and an antenna array for the time-reversal array are assumed. Since the spacing between the array elements is large, the signals received by each antenna element can be considered independent. For simplicity, the communication channel is assumed stationary, whose properties are not changed for the time-reversal process. Based on the obtained formulation, the channel capacities for the time-reversal and the conventional channels are compared.