• JSTS:Journal of Semiconductor Technology and Science
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• 제14권6호
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• pp.802-809
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• 2014

This paper presents a dual-mode bias modulator (BM) for complementary metal oxide semiconductor (CMOS) power amplifiers (PAs). The BM includes a hybrid buck converter and a normal buck converter for an envelope tracking (ET) mode for high output power and for an average power tracking (APT) mode for low output power, respectively. The dual-mode BM and CMOS PA are designed using a $0.18-{\mu}m$ CMOS process for the 1.75 GHz band. For the 16-QAM LTE signal with a peak-to-average power ratio of 7.3 dB and a bandwidth of 5 MHz, the PA with the ET mode exhibited a poweradded efficiency (PAE) of 39.2%, an EVM of 4.8%, a gain of 19.0 dB, and an adjacent channel leakage power ratio of -30 dBc at an average output power of 22 dBm, while the stand-alone PA has a PAE of 8% lower at the same condition. The PA with APT mode has a PAE of 21.3%, which is an improvement of 13.4% from that of the stand-alone PA at an output power of 13 dBm.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.860-868
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• 2008

Seismic safety analysis of rockfill dams are consist of the stability analysis as an simplifed method and the dynamic analysis as an detailed method. When high risk dams such as Multi-purpose dams were often applied detailed method by dynamic analysis, dynamic properties of dam materials such as shear modulus are considered as most important factor. Dynamic material properties such as shear modulus had to be investigated by cyclic triaxial test et al. during design and construction stage but these were not conducted because of the condition of domestic seismic design technique. MASW and SASW methods had been applied as a non destructive method to investigate dynamic material properties of existing rockfill dam, has no problems in dam safety at present. These methods were usually performed under the assumptions that the subsurface can be described horizontally homogeneous and isotropic layers. Recent studies(Marwin, 1993, Kim, 2001) showed that surface waves generated through inclined structures have different characteristics from those through a horizontally homogeneous layered model. further Kim et al(2005) and Min and Kim(2006) showed that central core type rockfill dam overestimated the shear wave velocities as increasing the depth through the 3D numerical modelling dut to the effect of outer rockfill and geometrical reasons In this study the results of shear wave velocities of seven rockfill dams form comprehensive facility review, was carried out from 2003 to 2007, were collected and analysed to establish the shear wave velocity distribution characteristics in increasing confining stress in rockfill dams and surface wave velocity ranges in rockfill dam through MASW and the limitation in application are discussed to be utilized as an reference value for dynamic analysis.

• 한국정보통신학회논문지
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• 제21권9호
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• pp.1627-1634
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• 2017

비정질 InGaZnO 박막 두께가 다른 무접합 트랜지스터를 제작하고 두께에 따른 양과 음의 게이트 스트레스 전압 및 빛을 비춘 상태에서 소자 불안정성을 분석하였다. 채널 박막 두께가 얇을수록 게이트 스트레스 및 빛이 인가된 상태에서 문턱전압 및 드레인 전류 변화가 큰 것을 알 수 있었다. 그 원인을 stretched-exponential 모델과 소자 시뮬레이션을 수행하여 설명하였다. 박막이 얇을수록 캐리어 트랩핑 시간이 짧기 때문에 전자나 홀이 빨리 활성화되는 것과 채널 박막의 뒷부분에서 채널의 수직 전계가 증가하여 전자나 홀을 많이 축적할 수 있는 것으로 설명하였다. IGZO 무접합 트랜지스터 제작에서 채널 박막의 두께를 결정할 때 채널 박막 두께가 얇을수록 소자 불안정성이 큰 것을 고려해야 됨을 알 수 있다.

• 디지털콘텐츠학회 논문지
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• 제14권2호
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• pp.223-233
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• 2013

본 논문은 무선망 환경에서의 서비스품질과 시스템품질이 고객만족과 지속이용의도에 미치는 영향에 대해 살펴보았다. 기존의 DMB와 IPTV 논문에서 다루어진 서비스품질(반응성, 공감성) 및 시스템품질(접속성, 사용용이성, 채널이동성)의 요인들을 차용하여 가설을 설정하고 연구모형을 완성하였으며, 실험연구 및 설문조사를 통해 이를 증명하고자 하였다. 그 결과, 3G망보다 와이파이망 이용자들의 서비스품질과 시스템품질에 대한 기대치가 높게 나타났으며 전송속도와 같은 시스템품질 보다는 서비스품질에 대해 더 민감하게 반응함을 알 수 있었다. 본 논문은 기존 DMB와 IPTV 논문에서 다루어진 요인들을 N스크린 영역에 적용하여 연구영역을 확장하고 이해도를 높였다는 데 의의가 있다.

• 대한기계학회논문집B
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• 제20권1호
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• pp.304-320
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• 1996

A multiple production .epsilon. equation model was developed in the low Reynolds number $\kappa$-$\varepsilon$ model with the aids of DNS data. We derived the model theoretically and avoided the use of empirical correlations as much as possible in order for the model to have generality in the prediction of complex turbulent flow. Unavoidable model constants were, however, optimized with the aids of DNS data. All the production and dissipation models in the $\varepsilon$ equation were modified with damping functions to satisfy the wall limiting behavior. A new $f_{\mu}$ function, turbulent diffusion and pressure diffusion model for the k and .epsilon. equations were also proposed to satisfy the wall limiting behavior. By, computational investigation on the plane channel flows, we found that the multiple production model for .epsilon. equation could improve the near wall turbulence behavior compared with the standard production model without the complicated empirical modification. Satisfication of the wall limiting conditions for each turbulence model term was found to be most important for the accurate prediction of near wall turbulence behaviors.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.567-571
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• 2008

PEM Fuel Cell operation mode can be classified into dead-end mode or open mode by whether the outlet port is blocked or not. Generally, dead-end type fuel cell has some merits on the pressure drop and system efficiency because it can generate more power than the open type fuel cell due to high operating pressure condition. However, the periodic purging process should be done for removing water which is formed as product of a reaction in the gas diffusion layer. In this study, cathode side dead-end type operation has been conducted. Moreover, pulsating flow generator at the outlet of cathode side has been suggested for increasing the period to purge the formed water because the pulsating flow can make formed water scattered uniformly over the whole channel. As a result, the purging period with pulsation increased by 1.5-2 times longer than that without pulsating.

• Journal of Ginseng Research
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• 제36권1호
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• pp.47-54
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• 2012

Korean red ginseng (KRG) has been used worldwide as a traditional medicine for the treatment of various reproductive diseases. Gonadotropin releasing hormone (GnRH) neurons are the fundamental regulators of pulsatile release of gonadotropin required for fertility. In this study, an extract of KRG (KRGE) was applied to GnRH neurons to identify the receptors activated by KRGE. The brain slice patch clamp technique in whole cell and perforated patch was used to clarify the effect of KRGE on the membrane currents and membrane potentials of GnRH neurons. Application of KRGE (3 ${\mu}g$/${\mu}L$) under whole cell patch induced remarkable inward currents (56.17${\pm}$7.45 pA, n=25) and depolarization (12.91${\pm}$3.80 mV, n=4) in GnRH neurons under high $Cl^-$ pipette solution condition. These inward currents were not only reproducible, but also concentration dependent. In addition, inward currents and depolarization induced by KRGE persisted in the presence of the voltage gated $Na^+$ channel blocker tetrodotoxin (TTX), suggesting that the responses by KRGE were postsynaptic events. Application of KRGE under the gramicidin perforated patch induced depolarization in the presence of TTX suggesting its physiological significance on GnRH response. Further, the KRGE-induced inward currents were partially blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; non-NMDA glutamate receptor antagonist, 10 ${\mu}M$) or picrotoxin (PIC; $GABA_A$ receptor antagonist, 50 ${\mu}M$), and almost blocked by PIC and CNQX mixture. Taken together, these results suggest that KRGE contains ingredients with possible GABA and non-NMDA glutamate receptor mimetic activity, and may play an important role in the endocrine function of reproductive physiology, via activation of $GABA_A$ and non-NMDA glutamate receptors in GnRH neurons.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권4호
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• pp.330-343
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• 2016

This paper presents results of an experimental investigation of vortex-induced vibration (VIV) of a flexibly mounted and rigid cylinder with two-degrees-of-freedom with respect to varying ratio of in-line natural frequency to cross-flow natural frequency, $f^*$, at a fixed low mass ratio. Combined in-line and cross-flow motion was observed in a sub-critical Reynolds number range. Three-dimensional displacement meter and tension meter were used to measure dynamic responses of the model. To validate the results and the experiment system, x and y response amplitudes and ratio of oscillation frequency to cross-flow natural frequency were compared with other experimental results. It has been found that the higher harmonics, such as third and more vibration components, can occur on a certain part of steel catenary riser under a condition of dual resonance mode. In the present work, however, due to the limitation of a size of circulating water channel, the whole test of a whole configuration of the riser at an adequate scale for VIV phenomenon was not able to be conducted. Instead, we have modeled a rigid cylinder and assumed that the cylinder is a part of steel catenary riser where the higher harmonic motions could occur. Through the experiment, we have found that even though the cylinder was assumed to be rigid, the occurrence of the higher harmonic motions was observed in a small reduced velocity ($V_r$) range, where the influence of the in-line response is relatively large. The transition of the vortex shedding mode from one to another was examined by using time history of x and y directional displacement over all experimental cases. We also observed the influence of in-line restoring force power spectral density with $f^*$.

• 대한전자공학회논문지TC
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• 제44권6호
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• pp.48-56
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• 2007

OFDMA(Orthogonal Frequency Division Multiple Access)는 차세대 이동통신을 위한 새로운 다중접속 방식으로 널리 고려되고 있으나 PAPR(Peak-to-Average Power Ratio)이 높다는 단전을 가지고 있으며 상향링크 시스템을 위해서는 OFDMA의 단점을 보완한 방법인 SC-FDMA(Single Carrier Frequency Division Multiple Access)가 제안되었다. 그러나 SC-FDMA는 고차변조 방식에서 성능이 떨어지고 다중안테나 시스템에 불리하며 자원할당의 유연성이 부족하고 자유로운 파일럿 패턴을 가지기 어렵다는 단점을 가지고 있다. 항상 최적의 성능을 얻기 위해서는 각 단말의 환경에 따라서 SC-FDMA나 OFDMA를 적절히 선택하여 사용할 수 있는 방법이 필요하며 SC-FDMA의 파일럿 구조도 OFDMA와 유사한 형태를 가져서 동일한 형태의 프레임 구조를 가질 수 있어야 한다. 기존의 SC-FDMA 파일럿 삽입 방법이 전체 SC-FDMA 심벌을 이용하거나 별도의 작은 SC-FDMA 심벌을 이용하는데 반해서 이 논문에서는 SC-FDMA 데이터의 일부분에 파일럿을 삽입함으로써 SC-FDMA 프레임이 OFDMA 프레임과 동일한 구조를 가질 수 있도록 하는 방법을 제안한다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.1068-1071
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• 2017

3단 터빈배기부 구성은 터빈 플랜지, 열교환기, 배기덕트와 추력노즐로 이루어진다. 냉가스 가압 방식에 비하여 열교환기 가압 방식을 사용함으로서 추진제탱크 가압을 위한 헬륨가스 자체 무게와 저장 탱크 무게가 감소하는 장점이 있기 때문에 발사체에 열교환기를 사용한다. 가스발생기는 추진제 연료과농 조건에서 연소가 이루어지며, 연소가스 중에 그을음이 많이 포함되어 있기 때문에 열교환 효율이 감소하는 것을 고려하여 열교환기를 설계해야 한다. 본 논문에서는 터빈배기부 구성품 배치, 열교환기 내부 구조 및 제작성을 고려한 설계기법, 기 설계된 노즐 설계를 바탕으로 3단 터빈배기부 재 노즐 설계 형상에 대한 장점을 기술하였다.