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여기광원의 출력 변화에 따른 AlGaAs/GaAs 양자우물구조의 Photoluminescence 광특성 분석
조장현,정용섭,변지수,송진동,이은혜 한국물리학회 2014 새물리 Vol.64 No.2
MBE 방법으로 성장시킨 AlGaAs/GaAs 다중양자우물구조에서 여기광의 출력 변화에 따른 광발광 (photoluminescence, PL) 특성을 분석하였다. n-type GaAs 기판위에 GaAs버퍼층을 형성시킨 후 AlGaAs/GaAs를 번갈아 가며 성장시킨 시료에 여기광의 출력을 20 mW에서 140 mW까지 변화시키며 측정하였다. 803 nm, 812 nm에서 2개의 PL 봉우리 파장이 관측되었으며, 여기광의 출력이 증가함에 따라 PL 세기가 선형적으로 증가하였고, PL 봉우리 파장이 5 nm 정도 적색편이가 나타났다. 적색편이현상의 주원인은 여기광 세기의 변화에 따른 AC Stark 효과에 의한 에너지 밴드구조의 변이로 예상되며, 이러한 결과는 AlGaAs/GaAs 다중양자우물구조 응용소자의 개발 및 활용에 있어 실제 구동 시소자의 상태와 성능을 예측해 볼 수 있는 중요한 기초정보를 제공할 것으로 기대된다. We fabricated AlGaAs/GaAs multiple quantum wells by using molecular beam epitaxy (MBE). We deposited a GaAs buffer layer on a n-type GaAs wafer and stacked AlGaAs and GaAs layer by layer 20 times. The optical properties of the AlGaAs/GaAs multiple quantum wells were analyzed by using photoluminescence (PL) spectroscopy. By increasing the excitation power from 20 mW to 140 mW, we observed 2 PL peaks, on each at 803 nm and 812 nm; the PL intensity increased linearly with increasing power, and the peak wavelengths shifted to longer wavelengths by about 5 nm. We expect that the observed red shifts originate from the AC Stark effect by which the local energy band structure changes momentarily in response to the optical excitation field. The results show the possibility of bandgap engineering by external excitation, providing key information on the functionality of AlGaAs/GaAs multiple quantum wells for developing device applications.
조장현 한국과학사학회 2020 한국과학사학회지 Vol.42 No.1
This paper examines how Galileo Galilei (1564-1642), a mathematician and philosopher from Florence, proved the solar rotation. By analyzing his works Letters on the Sunspots and Discourse on Bodies in Water, this paper argues that Galileo could reach his conclusion by introducing substantial evidence from natural philosophy as well as from the mixed mathematical sciences. This contradicts previous researches that suggest that Galileo supported his argument on solar rotation only through observations of sunspots and mathematical reasoning based on them. The natural philosophical elements Galileo introduced were the analogy between the Earth and the Sun that he drew using the then popular idea of fluid heaven, his idea of a fluid-like solar “atmosphere” that included sunspots, and his theory of matter. In making the argument for solar rotation, Galileo blurred the strict disciplinary boundary that had existed between mixed mathematics and natural philosophy. Galileo’s solar rotation was the product of his hybrid practice, by which he crisscrossed the boundaries between the two disciplines, combining elements of mixed mathematics with those of natural philosophy.
시간 주기 시스템의 안정성 및 제어기 설계에 대한 연구
조장현 한국기계기술학회 2021 한국기계기술학회지 Vol.23 No.5
This is the research report concerned with the new stability concept and designing the controller of the time periodic systems. The periodic systems which is governed by time is very common in various type of dynamic systems. For example, the satellite is the large scale and the experimental test equipment as pendulum is also time periodic systems. The motion of the systems during the time interval is running repeatedly. While this periodic systems is running, the dynamic stability is important to behave the appropriate motion of the system's function. This research propose the new stability approach based on Lyapunov theorem which is analyzing the system's stability adapting the specific energy function. And also this research introduces the developing numerical procedures to retain the stability of time periodic system. Finally, the result of this research is very useful to judge the stability and design the controller of time periodic system.
실습 교육용 유연 생산시스템 설계 및 제작에 대한 연구
조장현 한국기계기술학회 2020 한국기계기술학회지 Vol.22 No.3
This is the research report concerned with designing and making of the flexible manufacturing system for educational training. The flexible manufacturing system is composed of several mechatronic(mechanical and electronic) subsystems which are automatically controlled by computer program. The main subsystems are materials feeder unit, automatic guided vehicle, robot for moving parts, indexing and stamping unit and computer system and more subsystems can be added for specific manufacturing processes. This dissertation includes the design and production characteristics of flexible manufacturing system for educational training. Finally, the educational training equipment is made and demonstrated in this research and is expected to use in various educational institutions, for example, technical educational and practical industrial training institutions.
조장현,김수현,김철환,박재영,최승,윤명호,김동한,문재현,김준영,윤현주,김계훈,정명호 대한의학회 2012 Journal of Korean medical science Vol.27 No.3
The purpose of this study is to assess the relationship between left atrial (LA) size and outcome after acute myocardial infarction (AMI) in patients undergoing primary percutaneous coronary intervention (PCI) and to evaluate dynamic changes in LA size during long-term follow-up. Echocardiographic analyses were performed on 253 AMI patients (174 male and 79 female, 65.4 ± 13.7 yr) undergoing PCI. These subjects were studied at baseline and at 12 months. Clinical follow-up were done at 30.8 ± 7.5 months. We assessed LA volume index (LAVI) at AMI-onset and at 12-month. Change of LAVI was an independent predictor of new onset of atrial fibrillation or hospitalization for heart failure (P = 0.002). Subjects who survived the 12-month period displayed an increased LAVI mean of 1.86 ± 4.01 mL/m2 (from 26.1 ± 8.6 to 28.0 ± 10.1 mL/m2, P < 0.001). The subject group that displayed an increased LAVI correlated with a low left ventricular ejection fraction, large left ventricle systolic and diastolic dimensions and an enlarged LA size. In conclusion, change of LAVI is useful parameter to predict subsequent adverse cardiac event in AMI patients. Post-AMI echocardiographic evaluation of LAVI provides important prognostic information that is significantly greater than that obtained from clinical and laboratory parameters alone.