• 한국통신학회논문지
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• 제36권5B호
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• pp.573-581
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• 2011

수중채널은 매질에 의한 신호 감쇄로 인해 전송대역이 제한되며, 수온, 염도, 기하학적 구조 등 다양한 요소의 영향을 받기 때문에 복잡하며 신뢰성을 유지하기 어려운 통신 환경 중의 하나이다. 본 논문에서는 수중채널에 대한 분석을 토대로 보다 실질적인 모의 수중채널을 모델링하였다. 또한 ISI, 주파수 선택적 페이딩, 시간 선택적 페이딩을 동시에 고려한 Coded Orthogonal Frequency Division Multiplexing (OFDM) 시스템을 디자인하였으며 앞서 언급한 실질적인 표의 수중채널에 대한 시뮬레이션을 통하여 디자인된 시스템이 다양한 상태의 채널에서도 성능변화의 폭이 작고 견실하게 작동할 수 있음을 보였다. 제안하는 Coded OFDM 시스템은 Low Density Parity Check (LDPC) 코드를 사용했으며, Un-coded OFDM 시스템에 비해 $10^{-3}$ BER기점을 기준으로 7 dB의 이득이 발생하였다. 뿐만 아니라 채널의 변화에 따른 SNR 차가 8 dB에서 3 dB로 줄였다.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.102-106
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• 1999

We have designed and fabricated a four-bit shift register circuit using YBCO bicrystal junctions and experimentally tested its operations by a computer-controlled digital measurement set-up. Laser ablated YBCO thin films with clean surface were used in this work. The circuit consists of the shift register and two read SQUIDs placed next to each sides of the shift register. The SQUIDs were inductively coupled to the nearby shift register stages. A probe equipped with high speed coax lines were used in this experiment. The major obstacle in testing the circuit was the interference between the read SQUIDs and we solved the problem by finding the correct operation points of the SQUIDs from the simultaneously measured modulation curves. Loaded Data("1" or "0") were successfully shifted from a stage to the next one by a controlled current pulse injected to the bias lines located between the stages and the data shifts were correctly monitored by the read SQUIDs

• 한국광학회지
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• 제10권5호
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• pp.430-438
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• 1999

근적외선 파장영역에서 시분해 분광용 레이저 광원개발을 위해 발진파장이 반사경의 파장 선폭에 의해 제한된 수십 펨토초 펄스폭의 고출력 티타늄 사파이어 레이저를 개발하였다. 한쪽 프리즘 끝에 미세 stepping-motor로 제어되는 kniff-edge slits를 사용하여 발진파장을 선택하였으며, 파장가변영역은 770nm~870nm이었고, 이 파장영역에서 얻은 펄스폭은 40 fs 미만이었다. 가장 짧은 펄스폭은 약 17 fs 이었으며 이때의 파장중심은 820nm이고 선폭은 72nm이었다. 약 5W 출력의 아르곤 레이저 여기광을 사용하여 위의 파장영역에서 얻은 평균출력은 440 mW~580 mW 이었다. 연속발진 경우와 Kerr-lens mode locking 경우의 이득매질에서의 빔의 크기를 계산하여 이득변조값 ${\lambda}=2.5{\times}10_{-8}$ W을 수치적으로 얻었고, 이로부터 Ginzberg Landau 방정식을 사용하여 40 fs 미만의 펄스폭이 발생됨을 보였다.

• 대한전자공학회논문지SD
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• 제41권11호
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• pp.29-34
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• 2004

본 논문에서는 molecular beam epitaxy (MBE)로 성장한 AlGaN/InGaN/GaN high electron-mobility transistors (HEMTs)의 선형성과 RF dispersion 특성을 조사하였다. 전극 길이가 0.5 ㎛인 AlGaN/InGaN HEMT는 최대 전류 밀도가 730mA/mm, 최대 전달정수가 156 mS/mm인 비교적 우수한 DC 특성과 함께, 기존의 AlGaN/GaN HEMT와는 달리 높은 게이트 전압에도 완만한 전류 전달 특성을 보여 선형성이 우수함을 나타내었다. 또한 여러 다른 온도에서 측정한 펄스 전류 특성에서 소자 표면에 존재하는 트랩에 의한 전류 와해 (current collapse) 현상이 발생되지 않음을 확인하였다. 이 연구 결과는 InGaN를 채널층으로 하는 GaN HEMT의 경우 선형성이 우수하고, 고전압 RF 동작조건에서 출력저하가 발생하지 않는 고출력 소자를 제작할 수 있음을 보여준다.

• 한국광학회지
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• 제14권1호
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• pp.38-43
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• 2003

$LiNbO_3$의 스트레인광학효과와 ~l.4$\mu\textrm{m}$ 두께 이상으로 증착된 Mo(molybdenum)/Pt(platinum) 금속 박막으로부터 발생되는 압축스트레인을 이용하여 채널 광도파로 제작 공정을 개발하였다. 제작된 광도파로는 단일모드로 관찰되었으며, 삽입 손실이 TE, TM 입사 편광모드 각각에 대해서 6.2, 7.7 dB/cm로 측정되었다. 전극 길이와 간격이 11 mm, 21 $\mu\textrm{m}$인 광변조기를 스트레인광학형 광도파로 구조를 이용하여 제작하였으며, $V_{\pi}$= 16.1 V와 100% 변조 깊이가 1.55$\mu\textrm{m}$ 파장 영역에서 측정되었다. 또한 1$\times$2광 파워 분리기를 제작한 결과 0.63$\mu\textrm{m}$ 파장 영역에서 on/off 특성이 $\pm$25V에서 관찰되었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1992년도 추계학술대회 논문집
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• pp.123-127
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• 1992

MOS 커패시터가 이온화 방사선에 노출되었을 경우, MOS 커패시터의 방사선 조사 효과는 소자의 전기적 특성 및 동작 수명에 심각한 영향을 일으킬 수 있다. MOS 커패시터는 (100) 방향의 P-type Si wafer 위에 산화막층을 $O^2$+T.C.E. 분위기에서 성장하였으며, 그 두께는 40~80 nm로 만들었다. MOS 커패시터에 대한 방사선 조사는 $Co^{60}-{\gamma}$선을 사용하였고, 조사선량은 $10^4{\sim}10^8$으로 조사하였다. MOS 커패시터에서 전기적 전도 특성의 방사선 조사효과는 산화막 두께와 조사선량을 변화하면서 측정된 P-type MOS 커패시터는 조사선량에 의해서 강하게 영향을 받는다는 것과 저전계 영역에서의 Ohmic 전류가 전체 선량에 의존한다는 것을 알았다. 이 결과는 방사선 조사에 의해 산화막 트랩전하와 산화막-반도체($SiO_2$-Si)계면 트랩전하에 의해서 설명 할 수 있다.

• Asian-Australasian Journal of Animal Sciences
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• 제29권1호
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• pp.16-22
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• 2016

The intestinal environment plays a critical role in maintaining swine health. Many factors such as diet, microbiota, and host intestinal immune response influence the intestinal environment. Intestinal alkaline phosphatase (IAP) is an important apical brush border enzyme that is influenced by these factors. IAP dephosphorylates bacterial lipopolysaccharides (LPS), unmethylated cytosine-guanosine dinucleotides, and flagellin, reducing bacterial toxicity and consequently regulating toll-like receptors (TLRs) activation and inflammation. It also desphosphorylates extracellular nucleotides such as uridine diphosphate and adenosine triphosphate, consequently reducing inflammation, modulating, and preserving the homeostasis of the intestinal microbiota. The apical localization of IAP on the epithelial surface reveals its role on LPS (from luminal bacteria) detoxification. As the expression of IAP is reported to be downregulated in piglets at weaning, LPS from commensal and pathogenic gram-negative bacteria could increase inflammatory processes by TLR-4 activation, increasing diarrhea events during this phase. Although some studies had reported potential IAP roles to promote gut health, investigations about exogenous IAP effects or feed additives modulating IAP expression and activity yet are necessary. However, we discussed in this paper that the critical assessment reported can suggest that exogenous IAP or feed additives that could increase its expression could show beneficial effects to reduce diarrhea events during the post weaning phase. Therefore, the main goals of this review are to discuss IAP's role in intestinal inflammatory processes and present feed additives used as growth promoters that may modulate IAP expression and activity to promote gut health in piglets.

• The Korean Journal of Physiology
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• 제25권1호
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• pp.17-26
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• 1991

Single smooth muscle cells of the rabbit pulmonary artery were isolated by treatment with collagenase and elastase. Using the patch clamp technique, potassium channel activity was recorded from the inside-out membrane patch. The channel had a sin히e channel conductance of about 360 pS in symmetrical concentration of K on both sides of the patch, 150 mM, and had a linear current-voltage relationship. During the application of 10 mM tetraethylammonium (TEA) to the intracellular membrane surface, the amplitude of single channel current was reduced and very rapid flickering appeared. The open probability $(P_0)$ of this channel was increased by increasing positivity of the potential across the patch membrane, with e-fold increase by 20 mV depolarization, and by increasing the internal $Ca^{2+}$ concentration. These findings are consistent with those of large conductance Ca-activated K channels reported in other tissues. But the shortening of the mean open time by increasing $[Ca^{2+}]_i$, was an unexpected result and one additional closed state which might be arisen from a block of the open channel by Ca binding was suggested. The $P_0-membrane$ potential relationship was modulated by internal pH. Decreasing pH reduced $P_0$. Increasing pH not only increased $P_0$ but also weakened the voltage dependency of the channel opening. The modulation of Ca-activated K channel by pH was thought to be related to the mechanism of regulation of vascular tone by the pH change.

• The Korean Journal of Physiology and Pharmacology
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• 제5권5호
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• pp.423-431
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• 2001

Some recent investigations revealed that vasodilatory action of adenosine is mainly not mediated by surface A2 receptor and suggested the existence of an intracellular action site. In the present study, we tried to differentiate intracellular from extracellular site of adenosine action in the regulation of coronary flow. In perfused rabbit hearts, concentration-response curve of coronary flow to exogenous adenosine was constructed in the presence or absence of dipyridamole, an inhibitor of transmembrane purine transport. Inhibition of cellular adenosine uptake by dipyridamole suppressed the increase of flow rate while enhancing the decrease in heart rate induced by exogenous adenosine. In another series of experiments, perfused rabbit hearts were subjected to energy deprivation in order to increase the production of endogenous adenosine. Energy deprivation along with dipyridamole administration resulted in higher coronary flow rate. Lower perfusate adenosine concentration was observed along with higher tissue adenosine content in this group. These results implied that coronary flow rate is determined not by interstitial adenosine concentration but by intracellular activity of adenosine. To confirm the effects of dypiridamole in vivo, direct measurement of interstitial adenosine concentration by mycrodialysis along with the assay of intracellular adenosine content was performed after intranenous dipyridamole administration. After dipyridamole infusion, intracellular adenosine content was markedly increased while interstitial adenosine concentration was not altered. In another series of experiments, the right shift of concentration-response curve of adenosine-induced vasodilation by 8-phenyltheophilline, a representative adenosine receptor antagonist, was mostly abolished by prior administration of prazosin, indicating that the influence of 8-PT on the adenosine action is not attributed to the inhibition of A2 receptor but related to the suppression of ${\alpha}-adrenoceptor$ activation. From these results, we concluded that adenosine acts intracellularly to regulate the coronary blood flow.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.314-314
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• 2012

The dilute magnetic semiconductors (DMS) have been developed to multi-functional electro-magnetic devices. Specially, the Si based DMS formed by ion implantation have strong advantages to improve magnetic properties because of the controllable effects of carrier concentration on ferromagnetism. In this study, we investigated the deep level states of Fe- and Co-ions implanted Si wafer during rapid thermal annealing (RTA) process. The p-type Si (100) wafers with hole concentration of $1{\times}10^{16}cm^{-3}$ were uniformly implanted by Fe and Co ions at a dose of $1{\times}10^{16}cm^{-2}$ with an energy of 60 keV. After RTA process at temperature ranges of $500{\sim}900^{\circ}C$ for 5 min in nitrogen ambient, the Au electrodes with thickness of 100 nm were deposited to fabricate a Schottky contact by thermal evaporator. The surface morphology, the crystal structure, and the defect state for Fe- and Co- ion implanted p-type Si wafers were investigated by an atomic force microscopy, a x-ray diffraction, and a deep level transient spectroscopy, respectively. Finally, we will discuss the physical relationship between the electrical properties and the variation of defect states for Fe- and Co-ions implanted Si wafer after RTA.