• Journal of the Korean Wood Science and Technology
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• v.38 no.4
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• pp.306-315
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• 2010

The stress laminated timber, which could be manufactured by small dimension lumber on construction site, has high possibilities for bridges in remote area, such as recreation forest or forest road, because those bridges may be short span and low frequency in use. The stress laminated timber has merits of easiness for preservative treatment and transportation because it is manufactured with small dimension lumber. This study was carried out to analyze performances of stress laminated timber manufactured with preservative treated domestic pitch pine for developing structural design data for stress laminated timber bridges for vehicular traffic. Perpendicular to grain compressive performance by preservative treatment and bending performance by bored holes of pitch pine lumber was analyzed. Then, the effects of bending performance by pre-stress pressure, distance of bolts, number of laminations and planning were analyzed. Conclusively, planning of lumber was not necessary for manufacturing stress laminated timber, and 80% of bending stiffness criteria was maintained as pre-stress pressure was higher than 3.0 kg/$cm^2$. However, further researches are needed to define the effects of bolt distances and number of laminations. The results of this research would be basic data for design stress laminated timber bridges for vehicular traffic in Korea.

• Journal of Sensor Science and Technology
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• v.12 no.2
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• pp.72-78
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• 2003

To observe the effect of excitation coil pitch on the micro fluxgate magnetic sensor, two sensors are fabricated using multi layer board process and the pitch distance of excitation coil are $260\;{\mu}m$ and $520\;{\mu}m$, respectively. The fluxgate sensor consists of five PCB stack layers including one layer of magnetic core and four layers of excitation and pick-up coils. The center layer as magnetic core is made of a Co-based amorphous magnetic ribbon with extremely high DC permeability of ${\sim}100,000$ and has a rectangular-ring shape to minimize the magnetic flux leakage. Four outer layers as excitation and pick-up coils have a planar solenoid structure and are made of copper foil. In case of the fluxgate sensor having the excitation coil pitch of $260\;{\mu}m$, excellent linear response over the range of $-100\;{\mu}T$ to $+100\;{\mu}T$ is obtained with sensitivity of 780 V/T at excitation sine wave of $3V_{p_p}$ and 360 kHz. The chip size of the fabricated sensing element is $7.3\;{\times}\;5.7\;mm^2$. The very low power consumption of ${\sim}8\;mW$ is measured. This magnetic sensor is very useful for various applications such as: portable navigation systems, telematics, VR game and so on.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.457-460
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• 2002

The image quality of three-dimensional (3D) images has been widely investigated by the qualitative analysis method. A need remains for an objective and quantitative method to assess the image quality of 3D volume-rendered images. The purpose of this study was to evaluate the quantitative accuracy of distance measurements on 3D volume-rendered images of a dry human skull by using multi-detector computed tomography (MDCT). A radiologist measured five times the twenty-one direct measurement line items composed among twelve reference points on the skull surface with a digital vernier caliper. The water filled skull specimen was scanned with a MDCT according to the section thicknesses of 1.25, 2.50, 3.75, and 5.00 mm for helical (high quality; pitch 3:1) scan mode. MDCT data were reconstructed with its acquisition section thickness and with 1.25 mm section thickness for all scans. An observer also measured seven times the corresponding items on 3D volume-rendered images with measuring tools provided by volumetric analysis software. The quantitative accuracy of distance measurements on the 3D volume-rendered images was statistically evaluated (p-value < 0.05) by comparatively analyzing these measurements with the direct distance measurements. The accuracy of distance measurements on the 3D volume-rendered MDCT images acquired with 1.25, 2.50, 3,75 and 5.00 mm section thickness and reconstructed with its section thickness were 48%, 33%, 23%, and 14%, respectively. Meanwhile, there were insignificant statistical differences in accuracy of distance measurements among 3D volume-rendered images reconstructed with 1.25 mm section thickness for the each acquisition section thickness. MDCT images acquired with thick section thickness and reconstructed with thin section thickness in helical scan mode should be effectively used in medical planning of 3D volume-rendered images. The quantitative analysis of distance measurement may be a useful tool for evaluating the quantitative accuracy and the defining optimal parameters of 3D volume-rendered CT images.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.10
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• pp.677-690
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• 2022

By using an actuator disk method based flow solver, aerodynamic analysis is carried out for a dual ducted fan aircraft, which is one of the VTOL compound aircrafts, and its associated ground effect is analyzed. The characteristics and accuracy of the solver for ground effect analysis is evaluated through a comparison with the results obtained from the sliding mesh technique. The aerodynamic performance and flow field characteristics with respect to the distance from the ground are analyzed. As the ground distance decreases, the fan thrust increases, but the deterioration of total normal force and hovering flight efficiency is identified owing to the decrease in the vertical force of the duct, fuselage, and wing. By examining the flow field in the bottom of the fuselage, the ground vortices and fountain flow generated by the interaction of the fan wake and ground are identified, and their influence on the aerodynamic performance is analyzed. The strength and characteristics of outwash with respect to the ground distance and azimuth direction are analyzed through comparison/examination of velocity profile. Influence of the ground effect with respect to collective pitch angle is also identified.

• Proceedings of the IEEK Conference
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• 2000.06d
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• pp.98-101
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• 2000

On CELP type Vocoders G.723.1 6.3kbps/5.3kbps Dual Rate Speech Codec, which is developed for Internet Phone and videoconferencing, uses VAD(Voice Activity Detection)/CNG (Comfort Noise Generator) in order to reduce the bit rate in a silence period. In order to reduce the bit rate effectively in this paper, we first set the boundary condition of the energy threshold to prevent the consumption of unnecessary processing time, and use three decision rules to detect an active frame by energy, pitch gain and LSP distance. To evaluate the performance of the proposed algorithm we use silence-inserted speech data with 0, 5, 10, 20dB of SNR. As a result when SNR is over 5dB, the bit rate is reduced up to about 40% without speech degradation and the processing time is additionally decreased.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.31B no.7
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• pp.33-41
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• 1994

A single channel adaptive noise canceling (ANC) technique with a recursive time delay estimator (RTDE) is presented for removing effects of additive noise on the speech signal. While the conventional method makes a reference signal for the adaptive filter using the pitch estimated on a frame basis from the input speech, the proposed method makes the reference signal using the delay estimated recursively on a sample-by-sample basis. As the RTDEs, the recursion formulae of autocorrelation function (ACF) and average magnitude difference function (AMDF) are derived. The normalized least mean square (NLMS) and recursive least square (RLS) algorithms are applied for adaptation of filter coefficients. Experimental results with noisy speech demonstrate that the proposed method improves the perceived speech quality as well as the signal-to-noise ratio and cepstral distance when compared with the conventional method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.319-328
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• 2000

This paper presents a new design method of the 1 generation wheel bearing unit using a numerical optimization technique in order to increase bearing fatigue life. For calculating the fatigue life, a method of load analysis is studied on the automotive wheel bearing system. The design variables selected are ball size, initial contact angle, number of balls, pitch diameter, pre-load, and distance between ball centers. The method of feasible directions in ADS (Automated Design Synthesis) is utilized to automatically find the optimum design variables. To validate the design method, a computer program is developed and applied to a practical passenger car model. The optimum design results demonstrated the effectiveness of the proposed design method showing that the system life of the optimally designed wheel bearing unit is enhanced in comparison with that of the initial ones within the given available design space.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1611-1616
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• 2004

The objective of this study is to simulate the etching characteristics under different process parameters for the optimization of etching process. The etching characteristics such as the etching factor were investigated under different operating conditions and compared with the spray characteristics. The spray characteristics were measured by using Phase Doppler Anemometer. The correlation between the etching characteristics and the spray characteristics was analyzed to simulate the etching characteristics under the actual parameters of the etching process. The parameters were distance of nozzle tip and pipe pitch. To improve the uniformity and value of etching factor in the etching process, the process parameters should be designed optimally. The distribution of spray was simulated by the Monte-Carlo Method and the process parameters were optimized by the design of experiments(DOE).

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.3
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• pp.271-277
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• 2011

This study presents a nondestructive test for underwater PVC pipes. To use guided ultrasonic waves, specially denoted by cylindrical Lamb waves, a test setup was made in a water tank using the pitch and catch mode and specimens were made to give artificial cutouts located in the circumferential direction of the pipes. Total three states of damaged levels were considered to see how the guided waves interact with the defects. For the experimental adjustments, three different pipe diameters (60, 90, 114 mm) were tested, and two factors - incident angle (10 and $40^{\circ}$) and distance (50 and 200 mm) - were tried. From the results, regardless of the diameters and two experimental factors, it is shown that the degrees of defects were recognized through amplitude and arrived time of the very first part of the received cylindrical Lamb waves. Between amplitude and arrived time, it is found that the amplitude gives more sensitive results.

• International Journal of Precision Engineering and Manufacturing
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• v.8 no.1
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• pp.73-78
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• 2007

The objective of this work was to simulate lead frame etching characteristics to optimize the etching process, Characteristics such as the etching factor and uniformity were investigated for different actual operating conditions, including pressure, distance from the nozzle tip, pipe pitch, and feed speed. The correlation between the etching and spray characteristics was analyzed to develop the etching model. Spray characteristics obtained from an experiment using a phase Doppler anemometer system were then simulated using a Monte-Carlo technique, The etching process model was coded in the Java language, The spray and etching characteristics were correlated with each other and simulated results agreed well with the measured data for a lead frame etching process, The optimal operating parameters under various conditions were successfully determined.