• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2002년도 추계학술대회 논문집
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• pp.39-42
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• 2002

In the current study, characteristics of the laser-induced plasma were investigated in a gas filled chamber or in a gas jet by using a relatively low intensity laser $(I\;\leq\;5\;\times\;10^{12}\;W/cm^2)$. Temporal evolutions of the produced plasma were measured using the shadow visualization and the shock wave propagation as well as the electron density profiles in the plasma channel was measured using the Mach-Zehnder interferometry. Experimental results such as the structure of the produced plasma, shock propagation speed $(V_s)$, electron density profiles $(n_e)$, and the electron temperature $(T_e)$ are discussed in this study. Since the diagnostic laser pulse occurs over short time intervals compared to the hydrodynamic time scales of expanding plasma or a gas jet, all the transient motion occurring during the measurement is assumed to be essentially frozen. Therefore, temporally well-resolved quantitative measurements were possible in this study.

• 대한물리의학회지
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• 제5권2호
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• pp.273-280
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• 2010

Purpose : The purpose of this experiment was to evaluate the pre-application effect of low frequency electrical stimulation(LFES) on VEGF expression of atrophic muscle and to determine the optimal pre-application period of LFES for prevent muscle atropy Methods : Twenty-five adult sprague-dawley rats were randomly assigned to weight bearing group, hindlimb suspension for 14 days group, hindlimb suspension with pre-application of LFES for 14 days group, hindlimb suspension with pre-application of LFES for 11 dsys group and, hindlimb suspension with pre-application LFES for 7 dsys group. 16Hz of Biphasic pulse current was applied to gastrocnemius for 15min per days. Results : VEGF were decreased expression in HSG groups, whereas VEGF were significantly increased in HS+ES14G, HS+ES11G, HS+ES7G groups Conclusion : LFES during the hindlimb suspension showed a positive effect in VEGF induction and early application is strongly encourage VEGF induction. This indicated that pre-application of LFES could prevent muscle atrophy.

• 비파괴검사학회지
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• 제34권6호
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• pp.419-427
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• 2014

Nonlinear features of ultrasonic waves are more sensitive to the presence of a fatigue crack than their linear counterparts are. For this reason, the use of nonlinear ultrasonic techniques to detect a fatigue crack at its early stage has been widely investigated. Of the different proposed techniques, laser nonlinear wave modulation spectroscopy (LNWMS) is unique because a pulse laser is used to exert a single broadband input and a noncontact measurement can be performed. Broadband excitation causes a nonlinear source to exhibit modulation at multiple spectral peaks owing to interactions among various input frequency components. A feature called maximum sideband peak count difference (MSPCD), which is extracted from the spectral plot, measures the degree of crack-induced material nonlinearity. First, the ratios of spectral peaks whose amplitudes are above a moving threshold to the total number of peaks are computed for spectral signals obtained from the pristine and the current state of a target structure. Then, the difference of these ratios are computed as a function of the moving threshold. Finally, the MSPCD is defined as the maximum difference between these ratios. The basic premise is that the MSPCD will increase as the nonlinearity of the material increases. This technique has been used successfully for localizing fatigue cracks in metallic plates.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2011년도 추계학술논문집 1부
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• pp.262-265
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• 2011

본 연구는 탈진 기류 분사 시스템의 최적화 설계에 관한 기초 연구의 일환으로 전산유체역학(CFD)을 이용하여 일반 블로우 튜브와 단순 벤츄리 조합의 충격 기류(Pulse air jet) 방식의 탈진 장치에 대한 탈진 성능과 벤츄리 입구에 기류 유도용 구조물을 설치한 경우의 탈진 성능을 비교하였다. 각 Case별로 벤츄리 내부로 유입되는 탈진 공기량을 예측한 결과, case 2의 벤츄리 형상 개조시 case 1 보다 벤츄리로 유입되는 탈진 공기량이 약 20% 증폭되는 것으로 나타났다. 또한 필터백 표면에서의 탈진 기류 전달 분포를 예측한 결과, 모든 case가 필터백의 국한된 영역으로 탈진 기류가 집중됨을 알 수 있었다. 또한, case 2의 경우가 case 1보다 오히려 탈진 기류의 전달 수준이 불량함을 알 수 있다. 이는 case 2의 경우 벤츄리 입구에 기류 유도용 구조물을 설치한 것이 탈진 공기량을 증폭시키는데에는 도움이 되나, 오히려 벤츄리 내부로 유입된 탈진 기류의 직진성을 보완하여 필터백 내부에서 탈진 기류의 확장을 방해하기 때문인 것으로 판단된다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제31회 추계학술대회논문집
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• pp.326-329
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• 2008

DARPA가 계획 중인 대형 극초음속 추진 기관 개발 프로그램 VULCAN 프로그램은 듀얼모드 램제트/스크램제트 엔진과 연계되어 TBCC엔진을 이룰 수 있도록, 기존의 터보제트(또는 터보팬) 엔진과 CVC과 엔진을 결합하여 마하수 4이상에서 작동 가능한 엔진을 개발하는 것을 목표로 하고 있다. CVC 엔진은 데토네이션 연소 현상을 기본으로 하여 고마하수에서 고효율을 얻을 수 있는 PDE 이나 CDE와 같은 신개념의 엔진이다. 본 논문에서는 부산대학교 항공우주공학과 연소 추진 연구실에서 지난 수년간 국제공동 연구의 형태로 수행한 데토네이션 현상의 추진기관 응용에 연구에 대하여 소개한다.

• Current Optics and Photonics
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• 제4권4호
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• pp.310-316
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• 2020

We propose and experimentally demonstrate an all-optical radio frequency (RF) spectrum broadening system based on time compression. By utilizing the procedure of dispersion compensation values, the frequency domain is broadened by compressing the linear chirp optical pulse which has been multiplexed by the radio frequency. A detailed mathematical description elucidates that the time compression is a very preferred scheme for spectrum broadening. We also report experimental results to prove this method, magnification factor at 2.7, 8 and 11 have been tested with different dispersion values of fiber, the experimental results agree well with the theoretical results. The proposed system is flexible and the magnification factor is determined by the dispersion values, the proposed scheme is a linear system. In addition, the influence of key parameters, for instance optical bandwidth and the sideband suppression ratio (SSR), are discussed. Magnification factor 11 of the proposed system is demonstrated.

• 한국산업융합학회 논문집
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• 제22권3호
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• pp.373-379
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• 2019

Nowadays, the IoT portable electronic devices have become more useful and diverse, so they require various supply voltage levels to operate. This paper presents a DC-DC buck converter with pulse width modulation (PWM) for portable electronic devices. The proposed step-down DC-DC converter consists of passive elements such as capacitors, inductors, and resistors and an integrated chip (IC) for signal control to reduce power consumption and improves ripple voltage with the resolution. The proposed DC-DC converter is simulated and analyzed in PSPICE circuit design platform, and implemented on the prototype PCB board with a Texas Instruments LM5165 IC. The proposed buck converter is showed 92.6% of peak efficiency including a load current range of 4-10 mA, 3.29 mV of the voltage ripple at 5 V output voltage for the supply voltage 12 V. Measured and Simulated power efficiency are made good agreement with each other.

• 전기학회논문지P
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• 제67권4호
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• pp.214-220
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• 2018

Light sources induced by gas discharge using rare gases have been widely used in the thin film deposition, the surface modification and the polymer etching. A dielectric barrier discharge (DBD) has been developed in order to consistently emit light and control the wavelength of the emission light. However, much research on the characteristics of the movement of discharge particles is required to improve the efficiency of the light lamp and the life-time of the light apparatus in detail. In this paper, we developed a He DBD discharge simulation tool and investigated the characteristics of discharge particles which were electrons, two positive ions ($He^+$, $He_2^+$) and 5 excited particles ($He^*(1S)$, $He^*(3S)$, $He^*$, $He^{**}$, $He^{***}$). The discharge currents showed the transition from pulse mode to continuous mode with the increase of power. With the accumulated charges on the barrier walls, the discharge current was rapidly increased and caused oscillation of the discharge voltage. As the gas pressure increased, $He_2^+$ and $He^*(3S)$ became the dominant activated particles. The input power was mostly consumed by electrons and $He_2^+$ ion. And the change curve showed that power consumption by electrons increased more with gas pressure than with source voltage or frequency.

• Current Optics and Photonics
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• 제2권6호
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• pp.532-539
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• 2018

Multiple LED arrays can be utilized in visible-light communication (VLC) to improve communication efficiency, while maintaining smart illumination functionality through dimming control. This paper proposes a modulation scheme called "Spatial Intensity Modulation" (SIM), where the effective number of turned-on LEDs is employed for data modulation and dimming control in VLC systems. Unlike the conventional pulse-amplitude modulation (PAM), symbol intensity levels are not determined by the amplitude levels of a VLC signal from each LED, but by counting the number of turned-on LEDs, illuminating with a single amplitude level. Because the intensity of a SIM symbol and the target dimming level are determined solely in the spatial domain, the problems of conventional PAM-based VLC and related MIMO VLC schemes, such as unstable dimming control, non uniform illumination functionality, and burdens of channel prediction, can be solved. By varying the number and formation of turned-on LEDs around the target dimming level in time, the proposed SIM scheme guarantees homogeneous illumination over a target area. An analysis of the dimming capacity, which is the achievable communication rate under the target dimming level in VLC, is provided by deriving the turn-on probability to maximize the entropy of the SIM-based VLC system. In addition, a practical design of dimmable SIM scheme applying the multilevel inverse source coding (MISC) method is proposed. The simulation results under a range of parameters provide baseline data to verify the performance of the proposed dimmable SIM scheme and applications in real systems.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2014년도 춘계학술대회
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• pp.391-394
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• 2014

본 논문에서는 DSP(TMS320F28335)를 이용하는 홀센서 타입의 다극 BLDC 전동기의 벡터 구동을 위한 회전자의 절대위치를 결정하는 방법을 소개하고, 기존 방법의 문제점을 보완하기 위한 알고리즘을 구현 한다. 모터의 각 상에 원하는 교류 전류를 공급하기 위한 전압원 인버터의 스위칭 방법으로 공간벡터 변조방식을 이용하였다. 또한 속도 영역의 증가를 위해 약계자 제어 기법을 사용 하였다. 제안된 알고리즘을 검증하기 위해 보상 전후의 계산된 Iqe, Ide 및 상전류를 비교한다.