• 한국통신학회:학술대회논문집
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• 한국통신학회 1982년도 추계학술발표회논문집
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• pp.47-50
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• 1982

A baseband data transimission system is implemented on a microcomputer for performance study on some NRS line codes. These codes are compared in terms of eye width, BER, and power spectrum.

• 대한화학회지
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• 제43권4호
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• pp.485-488
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• 1999

• 대한전자공학회논문지
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• 제25권1호
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• pp.42-48
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• 1988

MM(multimode) PWM(pulse width modulation) Suitable for high performance and harmonic effects minimization of VSI (voltabge source invertetr)-IM (induction motor)drive system is proposed. The approximated optimal, suboptimal and optimal PWM are implemented in the low frequency range, while square wave operation is realized in the hibh frequency range. The pulse width Modulator is capable of generating control signals to a transistorized inverter operating at about 1KHz. All functions except digital comparison have been implemented in softyware making the scheme economical, flexible and reliable. Pulse width modulator is built and tested experimentally. In order to confirm the effectiveness and the reliability of the theoretical proposition, this scheme is applied to 1Hp, Three phase IM. As results, it is concluded that the scheme of MM PWM is superior to other conventional switching scheme through the discussions or analysis carried out on the items such as line-to-line voltage, current and spectrum of current harmonic components observed at the output terminal of inverter, noise level of motor.

• Journal of Power Electronics
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• 제13권4호
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• pp.619-625
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• 2013

Switched mode power supplies (SMPS) are power electronic circuits extensively used in a wide range of applications. High frequency switching operation of SMPS causes electromagnetic emissions and has the potential to interfere with system operation, which in turn has an impact on system performance. This makes electromagnetic compatibility (EMC) an important concern. In this paper, a new and simple spread spectrum technique is proposed by modulating chaotic pulse position modulation (CPPM) and pulse width modulation (PWM). The resulting CPWM is implemented to reduce the conducted EMI in SMPS. The proposed method is found to be effective in reducing conduction EMI. The effectiveness and simplicity of the proposed method on spreading those dominating frequencies is compared to the EMI mitigation technique using an external chaotic generator. Finally, the levels of conductive EMI with standard PWM, CPWM with an external chaos generator and the proposed method are experimentally verified to comply with the CISPR 22A regulations. The results confirm the effectiveness of the proposed method.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 추계학술대회 논문집(제1권)
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• pp.175-180
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• 2006

본 연구는 제주도 서측 해역의 현지 파랑관측 자료를 기초로 해양파의 비선형 특성을 조사한 것으로서, 실제 해역에서의 Freak wave 예보의 토대를 마련하기 위한 기초 연구이다. 관측된 파랑자료의 비선형 특성을 조사하기 위해 파형의 상하 비대칭성, 전후비대칭성, 빈도 분포의 첨예도, 파랑 스펙트럼의 대역폭 파라미터 등을 추출하고 이를 자료를 유의파고, 최대파고 등의 파랑 특성치들과의 상관관계를 분석하였다.

• 한국표면공학회지
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• 제28권3호
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• pp.182-191
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• 1995

A highly porous silicon layer was fabricated by anodizing single crystalline silicon in a dilute solution of hydrofluoric acid. The color of the porous silicon changed from red and blue to yellow gold during the anodizing process. The current-voltage (I-V) curve of the anodizing process showed a typical Schottky diode rectification form. The cell voltage decreased with the increase of HF concentration in the solution at high current range. However, the voltage was independent on HF concentration in the solution at low current range. The pore size was dependant on anodizing condition (HF concentration, current and anodizing time). The pore size and wall width of porous silicon layer were 4~6 and 1~3 nm, respectively. Surface of the porous silicon was covered with silicon compound ($SiH_x$etc.) according to IR spectrum analysis. The peak wavelength and width of photoluminescence (PL) spectrum of porous silicon were 650~850 nm (1.5~1.9 eV) and 250 nm, respectively. The photoluminescence intensity and peak wavelength, and porosity of porous silicon increased with increasing anodizing current and decreased with increasing HF concentration in the anodizing solution.

• Journal of Radiation Protection and Research
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• 제35권2호
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• pp.77-80
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• 2010

The spectroscopy toolkit has been developed and tested. The toolkit consists of a CsI(Tl)/PIN diode detector, integrated electronics, and a multi.channel.analyzer and its size was 40 cm(width) by 20 cm(length) by 6 cm(high). It is compact, very portable and simpler and cheaper compared to the conventional spectroscopy system. The gamma energy resolutions of the toolkit were 7.9% for the 660 keV of $^{137}Cs$ and 4.9% for 1,332 keV of $^{60}Co$ respectively. The linearity for gamma energies was good. When the energy spectrum of a ceramic sample containing $^{232}Th$ was measured with the spectroscopy toolkit for 20 minutes, there were significant peaks of the heavy metal. These results show that the resolution of the spectroscopy toolkit is sufficient to accumulate a quality spectrum in a few minutes by using weak, encapsulated commercial sources. Furthermore a toolkit experiment that how to measure energy spectra using the toolkit, and how to identify specific isotopes in a pottery piece, could be widely adopted for education and even for more sophisticated and higher level experiments.

• 천문학회보
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• 제39권2호
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• pp.94.1-94.1
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• 2014

We have carried out IGRINS test observations during its May commissioning run. Our targets were composed of three Luminous Blue Variables (LBVs), one supernova remnant (SNR), and an unidentified stellar source emitting [Fe II] 1.644 um line. In the preliminary results, three LBVs MWC 314, P Cygni, and AFGL 2298 show different characteristics: the spectrum of MWC 314 which is known to be in a binary system clearly shows double-peak structures in hydrogen and iron lines, the P Cygni spectrum reveals the Brackett series of hydrogen emission lines with prominent P-Cygni profiles, and AFGL 2298 likely at its visual minimum phase shows rather different spectrum with relatively weak hydrogen lines. The SNR (G11.2-0.3) was to test the sensitivity of IGRINS for diffuse emission. We successfully detected a dozen H2 emission lines with a velocity width of ~13 km/s, which might indicate a C-shock origin. The unidentified stellar source was one of stellar/compact sources of unknown nature detected in the survey of the Galactic plane in [Fe II] 1.644 um emission line (http://gems0.kasi.re.kr/uwife/). Its spectrum is under investigation. We will present the spectra of test observations and will discuss their scientific significance.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.26-36
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• 2001

Smart sensors and actuators have recently been developed. In this study, first, small-diameter fiber Bragg grating (FBG) sensors developed by the author, whose cladding and polyimide coating diameters were 40 and $52{\mu}m$, respectively, were embedded inside a laminate without resin-rich regions around sensors and the deterioration of mechanical properties of the composite laminate. The small-diameter FBG sensor was embedded in $0^{\circ}$ ply of a CFRP laminate for the detection of transverse cracks in $90^{\circ}$ ply of the laminate. The reflection spectra from the FBG sensor were measured at various tensile stresses. The spectrum became broad and had some peaks with an increase of the transverse crack density. Furthermore, the theoretical calculation reproduced the change in the spectrum very well. These results show that the small-diameter FBG sensors have a potential to detect the occurrence of transverse cracks through the change in the form of the spectrum, and to evaluate the transverse crack density quantitatively by the spectrum width. On the other hand, shape memory alloy (SMA) films were used to suppress the initiation and growth of transverse cracks in CFRP laminates. Pre-strained SMA films were embedded between laminas in CFRP laminates and then heated to introduce the recovery stress in SMA films and compressive stresses in the weakest plies ($90^{\circ}$ ply). The effects of recovery stresses are demonstrated in the experiments and well predicted using the shear-lag analysis and the nonlinear constitutive equation of SMA films.

• Journal of Photoscience
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• 제11권3호
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• pp.89-94
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• 2004

Motile cyanobacterium Synechocystis sp. PCC 6803 cells show photomovement with respect to the light stimulus. Under lateral irradiation, Synechocystis displays a phototactic gliding movement toward the light source by a twodimensional random biased walk. Under vertical irradiation, Synechocystis decreased the frequency of mean vectorial gliding speed dependent on the applied fluence rate, whereas the deviation distribution width of the speed increased. This strongly suggests the involvement of photokinesis. Evidence for the cyanobacterial photokinesis was discussed in the previous report (Choi et al., 1999. Photochem. Photobiol. 70, 95-102) demonstrating that the gross scalar speed of vertically irradiating cells increased by about 50% compared with that of dark-adapted cells. In the visible wavelength range, Synechocystis cells showed a maximal photokinetic activity at 420 nm and a second maximal activity at 680 nm. The threshold action spectrum for the photokinesis resembles the absorption spectrum of chlorophyll with major differences in the phototaxis action spectrum at 560 nm and 660 nm. We postulate that the cyanobacterial photokinesis is powered by the energy-generating chlorophyll pigments.