• Journal of the Korean Society for Precision Engineering
• /
• v.13 no.5
• /
• pp.84-94
• /
• 1996

In order to prevent shell sticking by providing sufficient lubrication between the strand and the mold, the mold oscillation has been used. Now it is well known that the shape of the oscillation curve has a decisive effect on the surface quality of the cast product. Besides, oscillation parameters such as stroke and frequency are also very important. In order to guarantee that parameters which have been found to be optimal for a certain grade of steel do not change with time, periodical checks of the physical condition of the whole equipment are necessary. The portable mold oscillation analyzer with integrated computer, developed by POSCO, records the movement of the mold in every spatial direction. The system uses the gap sensors to measure the mold movement (displacement ) in the two horizontal directions according to the mold narrow and broad faces and the vertical strokes in the four corners of mold. The gap sensor is a non-contacting minute displacement measuring device using the principle of high frequency eddy current loss. The mold oscillation diagnosis system integrates the gap sensors, their converters and the industrial portable computer with plug-in data acquisition boards. The all programs, such as the fast Fourier transformation module (amplitude and phase spectrums) and harmonic analysis module, was coded by LabVIEW$^{TM}$ software as the graphical language. In an own 'expert module' which is included in the diagnosis program, one can obtain much information about the mold oscillation equipment.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.12 no.3
• /
• pp.247-255
• /
• 2010

Bonding strength of shotcrete is a significant influential factor which plays the role of collapse prevention of tunnel crown and of debonding prevention of shotcrete induced by the blasting vibration. Thus, the evaluation of the shotcrete bonding state is one of the core components for shotcrete quality control. In this study, the peak particle velocities induced by blasting were measured on the shotcrete in a tunnel construction site and its effect on the bonding state of shotcrete is investigated. Drilling and blasting technique was used for the excavation of intersection tunnel connecting the main tunnel with the service tunnel. Blast-induced vibrations were monitored at some points of the main tunnel and the service tunnel. The shotcrete bonding state was evaluated by using impact-echo test coupled with the time-frequency domain analysis which is called short-time Fourier transformation. Analysis results of blast-induced vibrations and the time-frequency domain impact-echo signals showed that the blasting condition applied to the excavation of intersection tunnel hardly affects on the tunnel shotcrete bonding state. The general blasting practice in Korea was evaluated to have a minor negative impact on shotcrete quality.

• The Journal of the Society of Korean Medicine Diagnostics
• /
• v.12 no.1
• /
• pp.42-62
• /
• 2008

Objectives: It is well known that some parameters of the photoplethysmogram (PPG) acquired by time domain contour analysis can be used as markers of vascular aging. But the previous studies that have been performed for frequency domain analysis of the PPG to date have provided only restrictive and fragmentary information. The aim of the present investigation was to determine whether the harmonics extracted from the PPG using a fast Fourier transformation could be used as an index of vascular aging. Methods: The PPG was measured in 600 recruited subjects for 30 second durations, To grasp the gross age-related change of the PPG waveform, we grouped subjects according to gender and age and averaged the PPG signal of one pulse cycle. To calculate the conventional indices of vascular aging, we selected the 5-6 cycles of pulse that the baseline was relatively stable and then acquired the coordinates of the inflection points. For the frequency domain analysis we performed a power spectral analysis on the PPG signals for 30 seconds using a fast Fourier transformation and dissociated the harmonic components from the PPG signals. Results: A final number of 390 subjects (174 males and 216 females) were included in the statistical analysis. The normalized power of the harmonics decreased with age and on a logarithmic scale reduction of the normalized power in the third (r=-0.492, P<0.0001), fourth (r=-0.621, P<0.0001) and fifth harmonic (r=-0.487, P<0.0001) was prominent. From a multiple linear regression analysis, Stiffness index, reflection index and corrected up-stroke time influenced the normalized power of the harmonics on a logarithmic scale. Conclusions: The normalized harmonic power decreased with age in healthy subjects and may be less error prone due to the essential attributes of frequency domain analysis. Therefore, we expect that the normalized harmonic power density can be useful as a vascular aging marker.

• Physical Therapy Korea
• /
• v.6 no.2
• /
• pp.16-31
• /
• 1999

The purpose of this study was to assess the fatigue in lumbar and abdominal muscles in patients with chronic low back pain compared with normal subjects using spectral analysis with mean power frequency and median power frequency. The experimental group consisted of twenty subjects who had experienced chronic low back pain for over one year after the onset day. A control group consisted of twenty normal subjects with no history of low back pain. All subjects stood in an apparatus to perform sustained contraction in the lumbar and abdominal muscles for 30 seconds with 60% maximal voluntary isometric contraction (MVIC). The resulting electromyographic (EMG) recorded time serial data were transformed into frequency serial data by Fast Fourier Transformation (FFT). The results were as follows: 1) lumbar muscles measured, the frequency change ratio of both median power frequency and mean power frequency was significantly greater for experimental group compared with control group group (p<0.05). In measured two abdominal muscles (inferior rectus abdominis, obliquus externus abdominis) except superior rectus abdominis, the frequency change ratio of both median power frequency and mean power frequency was significantly greater for experimental group compared with control group (p<0.05). 2) In all three (longissimus thoracis, iliocostalis lumborum, multifidus) lumbar muscles measured, the initial frequency value of both median power frequency and mean power frequency was significantly lower for the experimental group compared with the control group (p<0.05). In the two (inferior rectus abdominis, obliquus externus abdominis) abdominal muscles measured (superior rectus abdominis not included), the initial frequency value of both median power frequency and mean power frequency was significantly lower for the experimental group compared with the control group (p<0.05). These results suggest that in patients with chronic low back pain there is a trend for more fatigue to occur in both lumbar and abdominal muscles than in the normal control group. This would seem to suggest that in treatment programs for patients with chronic low back pain, improvement of endurance in all trunk muscles should be considered.

• Journal of the Korean Vacuum Society
• /
• v.7 no.3
• /
• pp.242-247
• /
• 1998

Hydrogenated amorphous carbon nitride[a-C:H(N)] films were deposited on p-type Si(100) at room temperature with bias voltage of 200 V by DC saddle-field plasma-enhanced chemical vapor deposition. Effects of the ratio of $N_2$ to $CH_4$($N_2/CH_4$), in the range of 0 and 4 on such properties as optical properties, microstucture, relative fraction of nitrogen and carbon, etc. of the films have been investigated. The thickness of the a-C:H(N) film was abruptly decreased with the addition of nitrogen, but at $N_2/CH_4$>0.5, the thickness of the film gradually decreased with the increase of the $N_2/CH_4$. The ratio of N to C(N/C) of the films was saturated at 0.25 with the increase of $N_2CH_4$. N-H, C≡N bonds of the films increased but C-H bond decreased with the increase of $N_2CH_4$.Optical band gap energy of the film decreased from 2.53 eV at the ratio of $N_2CH_4$=4.

• Journal of the Korean earth science society
• /
• v.27 no.6
• /
• pp.670-676
• /
• 2006

We present a B and V band time-series CCD photometry of ${\delta}$ Scuti type variable star HR 2707. The observation was carried out for 45 nights between November 13, 2001 and February 20, 2002 with a 40 cm telescope equipped with a 1K CCD camera at the Korea National University of Education Optical Astronomy Observatory. Through the time-series CCD photometry we obtained 3011 V band and 6562 B band CCD frames. In some of these data, the V band data obtained for seven nights in January of 2002, had been used as a part of a multi-site campaign by Lopez de Coca et al. (2003). To detect pulsational frequencies, we used Discrete Fourier Transformation (DFT) and linear least square method. We have detected eight resonable pulsational frequencies and compare to previous studies we determine $f_1,\;f_2,\;f_3,\;f_4,\;f_5$ of Lopez do Coca et al. (2003) and $f_4$ for derived from this study are real pulsational frequencies of HR 2707.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.12 no.4_1
• /
• pp.129-136
• /
• 1992

A precedure for recovering surface displacement from a time series of pressure measured by a pressure gage in a shallow water (that is, FFTM, LCM. IWM) is investigated with respect to a proper cut-off-frequency of a frequency response function for the accurate recovery of wave height and period. The authors examined the applicability of above mentioned three transformation procedures through field observations and laboratory experiments and the following results are obtained. i) The cut-off-frequency of the frequency response function used in FFTM is deeply depend on both the frequency response of the pressure sensor and the water depth at the sensor. In this study, a relatively accurate surface displacement can be recovered when the frequency response function is cut off at the frequency corresponding to kh=3.0 where k is a wave number at the depth of h. The frequency response function in the region higher than the cut-off-frequency is set constant to be the value at the cut-off-frequency. ii) The transformed surface displacements by LCM are affected by the small waves of short periods included in the measured pressure. It is found that pressure variation whose local frequency is higher than kh=1.5 has to be neglected to recover surface displacement sufficiently. iii) In IWM, the linear pressure response function is usually utilized by multiplying a coefficient N which is a function of the frequency (or kh) and takes a value around unity. However, in this study, a constant value of N(=1.0) gives a relatively accurate recovery of surface displacements.

• The Korean Journal of Nuclear Medicine
• /
• v.24 no.2
• /
• pp.244-253
• /
• 1990

Sixty-four patients with paradoxical ventricular wall motion noticed both in angiocardiography or 2-dimensional echocardiography were assessed by ECG gated blood pool scan (GBPS). Endless cine loop image, phase and amplitude images and paradox image obtained by visual inspection of each cardiac beat or Fourier transformation of acquired raw data were investigated to determine the incremental value of GBPS with these processing methods for identification of paradoxical ventricular wall motion. The results were as follows: 1) Paradoxical wall motions were observed on interventricular septum in 34 cases, left ventricular free wall in 26 and right ventricular wall in 24. Underlying heart diseases were ischemic (23 cases) valvular(9), congenital heart disease (12), cardiomyopathy (5). pericardial effusion(5), post cardiac surgery(3), col pulmonale (2), endocarditis(1) and right ventricular tumor(1). 2) Left ventricular ejection fractions of patients with paradoxical left ventricular wall motion were significantly lower than those with paradoxical septal motion(p<0.005). 3) The sensitivity of each processing methods for detecting paradoxical wall motion was 76.9% by phase analysis, 74.6% by endless cine loop mapping and 68.4% by paradox image manipultion respectively. Paradoxial motions visualized only in phase, paradox or both images were appeared as hypokinesia or akinesia in cine loop image. 4) All events could be identified by at least one of above three processing methods, however only 34 cases (48.4%) showed the paradoxical molies in all of the three images. By these findings, we concluded that simultaneous inspection of all above three processing methods-endless cine loop, phase analysis and paradox image-is necessary for accurate identification and assessment of paradoxical ventricular wall motion when performing GBPS.

• Applied Chemistry for Engineering
• /
• v.19 no.5
• /
• pp.554-558
• /
• 2008

$(1-x)SiO_2-(x)TiO_2$ composite fibers with various compositions of $TiO_2$ were prepared by electrospinning their sol-gel precursors of titanium (IV) iso-propoxide (TiP), and tetraethyl orthosilicate (TEOS). The surface morphology and structure of sintered composite fibers were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), simultaneous thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) and Fourier transform infrared spectroscopy (FT-IR). As the content of $TiO_2$ in $(1-x)SiO_2-(x)TiO_2$ system was increased the average diameter of composite fibers was proportionally increased. Also, the transformation of $TiO_2$ from anatase to rutile form was inhibited by the highly dispersed $TiO_2$ around $SiO_2$ particles up to $0.6SiO_2-0.4TiO_2$ composite fibers even after calcination at $1000^{\circ}C$. The photocatalytic activity of $SiO_2-TiO_2$ composite fibers was examined for the methylene blue (MB) decomposition which was confirmed using UV-vis/DRS spectra. The experiments demonstrated that the MB in aqueous solution was successfully photodegraded using $SiO_2-TiO_2$ composite nanofibers under UV-visible light irradiation.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.18 no.1
• /
• pp.166-173
• /
• 2014

A noncontact nondestructive testing (NDT) method is proposed to detect the damage of pipeline structures and to identify the location of the damage. To achieve this goal, a scanning laser source actuation technique is utilized to generate a guided wave and scans a specific area to find damage location more precisely. The ND: YAG pulsed laser is used to generate Lamb wave and a piezoelectric sensor is installed to measure the structural responses. The measured responses are analyzed using three dimensional Fourier transformation (3DFT). The damage-sensitive features are extracted by wavenumber filtering based on the 3D FT. Then, flaw imaging techniques of a pipeline structures is conducted using the damage-sensitive features. Finally, the pipes with notches are investigated to verify the effectiveness and the robustness of the proposed NDT approach.