• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.1
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• pp.153-160
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• 2003

The purpose of study was to evaluate the effects of the $CO_2$ laser irradiation on demineralization inhibition and rehardening of human primary tooth enamel by laser fluoresecence measurement. Enamel specimens were made from the human primary teeth. The center spots of the specimens about 2 mm diameter were irradiated by $CO_2$ laser at the conditions of focused continuous or defocused pulsed, 3 or 6 W, for 4 seconds, before or after the demineralization by Coca-Cola for 24 hours at $37^{\circ}C$. The Diagnodent was used to measure the degree of demineralization and rehardening. There was no significant difference between focused continuous and defocused pulsed irradiation. 6W irradiation inhibited the demineralization but 3W did not. 6W irradiation rehardened the demineralized enamel but 3W did partially. The color of enamel was changed to brown to black after 6W irradiation but 3W caused no color change. $CO_2$ laser irradiation showed the effects on demineralization inhibition and rehardening of human priamary tooth enamel, and the laser fluoresecence measurement technique seemed to be a valid evaluation method.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.4
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• pp.395-408
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• 2012

An experimental investigation with 2.8kW Nd:YAG laser system was carried out to study the effects of different laser process parameters on the microstructure and hardness of STD11. The optical lens with the elliptical profile are designed to obtain a wide surface hardening area with uniform hardness. The Laser beam is allowed to scan on the surface of the work piece varying the power (1600, 1800 and 1900kW) and traverse speed (200, 400, 600, 800 and 1000mm/min) at three different F-numbers of lens. After laser surface treatment three zones, In the microstructure have been observed : melted zone(decarburization), heat affected zone(martensite), and the substrate.

• Journal of Satellite, Information and Communications
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• v.12 no.1
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• pp.34-37
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• 2017

This letter presents the signal processing of a CW radar (Continuous Wave or Doppler radar) sensor which enables the radar to detect the multiple targets' approaching and retreating using both I and Q channels. The proposed algorithm utilizes the phase change of the Quadrature signal, which occurs when targets move back and forth from the radar. The verification is carried out with the board containing a commercially available MMIC chip and an MCU by analyzing the received data from MMIC. Also the proposed algorithm is downloaded to MCU and the approaching and retreating movement is confirmed. The CW frequency is 24.125 GHz and the transmitter output power used is 7.2 dBm. Detectable distance is about 12 m.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.04a
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• pp.299-303
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• 2004

In this paper, it is presented a level sensor for measuring a level of the contents of cargo tank using frequency modulated continuous wave(FMCW). The frequency range is 10∼11 GHz, the radar cross section(RCS) of target is 0.8 ㎡ of metal plate. the experiment is performed in laboratory and open ground, the sweep time of the signal is 100 ms, the pyramidal horn antenna of about 20 dBi gain is used, and input power of antenna is about 5 dBm. the beat frequency according to the target moving to 40 m is measured. There is a good agreement between measured and calculated results. But the resolution of the FMCW radar is measured about 10 cm due to nonlinear of voltage controlled oscillator(VCO).

• Geophysics and Geophysical Exploration
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• v.4 no.3
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• pp.89-95
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• 2001

The final goal of the seismic method is to verify the spatial characteristic of subsurface media. For this purpose, professional interpreters interprete the discontinuities of seismic events from seismic image. This paper introduces a method for automatic discontinuity extraction from 3D seismic image. The method consists of three steps. The first step is for estimating coherency of seismic events from seismic data. The second step is to express the potential region where discontinuities may exist in the form of binary image. The third step is to locate the discontinuities by thining the region found in the second step.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 1996.10a
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• pp.34-37
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• 1996

해상풍에 의한 파랑의 발달을 다룬 모델은 1940년대 이후 실측파랑 및 기상자료로부터 이론에 기초한 경험식이 제시되었다. 이러한 경험식들은 실제의 불규칙한 해면상태를 유의파로 대표하여 유의파의 파고 및 주기를 풍속, 취송거리 및 취송시간의 함수로 나타낸 것이다. 널리 쓰이고 있는 심해에서의 모델은 SMB법과 Wilson법이 있으며 일정한 바람이 연속적으로 불어오는 안정된 정상상태에서는 SMB법이, 그리고 풍역이 시간적 공간적으로 변화가 큰 경우에는 Wilson법이 적용되고 있다. (중략)

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2002.08a
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• pp.62-65
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• 2002

파랑은 주로 먼바다에서 바람에 의해 생성되어 육지로 전파해오면서 천수, 굴절, 회절, 반사, 부서 짐 등의 여러 가지 변형의 과정을 거친다. 이러한 파랑의 변형을 예측하는 한 방법은 비압축성 유체와 비회전류의 연속방정식인 Laplace 방정식을 지배 방정식으로 하고 해수면에서의 운동학적 경계조건과 동역학적 경계 조건, 그리고 바닥에서의 운동학적 경계조건을 적용하여 해를 구한다. (중략)

• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.1
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• pp.291-298
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• 1995

An ultrasonic testing uses the directivity of the ultrasonic wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. This paper studied the directivity of shear waves emitted from angle probes and scattered from surface defects by using visualization method. These experimental results were compared with the theory which was based on the continuous wave. The applicability of continuous wave theory was discussed in terms of the parameter $d/{\lambda}$; where d is transducer or defect size and ${\lambda}$ is the wavelength. In the case of angle probes, the experimental results show good agreement with theoretical directivity on the principal lobe. When defect size was smaller than the wavelengths, clear directivity in the reflected wave was observed. In the case of the same ratio of defect size to wavelength, the directivity of reflected waves from the defect show almost the same directivity in spite of frequency differences. When the $d/{\lambda}$ is greater than 1.5, measured directivities almost agreed with the theoretical one.

• Geophysics and Geophysical Exploration
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• v.15 no.4
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• pp.199-208
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• 2012

High-amplitude swell noises (HASN) are very difficult to eliminate from the marine seismic data. In this paper, we applied F-X filter and median filter in order to suppress HASN. Test data have been acquired on the northern offshore of the South Shetland Islands in December, 2010. Parts of data have been contaminated by HASN caused by bad weather during the cruise. We applied F-X filter and median filter to test data with HASN. After F-X filtering, most of non-coherent noises and small-amplitude swell noises are eliminated effectively but HASN are still remained significantly. With median filter, HASN was suppressed better than F-X filter, however some of non-coherent noises are still remains. We applied a cascade of two filters and results show HASN and non-coherent noises are suppressed effectively. After the cascade of two filtering, it is possible to define reflection layers clearly on the velocity spectrum and to produce better stacked section with a good signal-to-noise ratio.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.07a
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• pp.182-184
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• 2010

최근 3D HDTV에 대한 연구가 활발히 이루어지고 있다. 우리나라에서도 3D HDTV 표준을 제정하기 위한 준비가 이루어지고 있으며, 이와 같은 흐름에 맞추어 기존의 ATSC 전송 방식을 확장한 전송 방식이 연구되고 있다. 확장된 ATSC 전송 방식은 지상파 3D HDTV 방송을 목표로 하고, 프레임 구조를 중국의 지상파 방송 표준인 DMB-T와 유사하게 PN 시컨스와 데이터가 연속되는 구조로 모델링하여 이용하고자 한다. 연구되고 있는 확장한 전송방식은 기존의 ATSC 시스템의 VSB 변조방식을 기반으로 한다. 그러므로 원활한 수신을 위해서는 반송파 주파수 오차(심볼속도 대비 최대 1%)를 정확하게 추정하고 복구하여야 한다. 기존 ATSC 시스템은 주파수 대역(DC 1.25V)의 파일럿 신호를 이용하여 반송파 주파수 복구를 하였지만, 확장된 ATSC 시스템은 프레임 헤드 부분인 PN 시컨스를 이용한다. 본 논문에서는 확장된 ATSC 전송 시스템 방식에 적용 가능한 반송파 주파수 복구 방식을 제안하였다.