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Jaemoon Pak,Gwangseo Park,Jungsuk Lee,Jooyoung Kim,Kuangwoo Nam 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
Sapphire is a dielectric material with good mechanical and thermal properties, consisting of lattice constant a = 4.76 A and c = 12.99 A. We have successfully grown (Bi, La)4Ti3O12 (BLT) thin lms on Al2O3(0001) substrates by the pulsed laser deposition method. The lattice mismatch of sapphire with BLT is only 0.7 % and 4.3 % along the a- and c-axis, respectively. In order to study the growth behavior of the lm, eects of forming an intermediate layer, CeO2 (a = 5.41 A), between the sapphire substrate and BLT lm was investigated. Structural growth of CeO2 and BLT lms were characterized by X-ray diraction. It was found that at lower substrate temperatures, c-axis oriented lms were obtained, while at higher temperatures the orientation of the lm was on the (104) direction, normal to the c-plane of the substrate. Studies on the surface morphology of BLT/Al2O3 and BLT/CeO2/Al2O3 were evaluated in terms of the growth behavior of BLT lms.
Jaemoon Pak,Gwangseo Park,Jooyoung Kim,Jungsuk Lee,Junho Chang,Kuangwoo Nam 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
Ferroelectric Bi3:25La0:75Ti3O12 (BLT) thin lms were prepared on indium tin oxide (ITO) coated glass substrates by the pulsed-laser deposition method. ITO electrodes have previously been used as bottom electrodes for studies in optical phenomenon, or in oating gate capacitors. From this fact, the ITO layer was used as the bottom electrode and gold dots with an area of 1:77 10..4 cm2 was deposited for use as the top electrode in the thin lm capacitor. The BLT lms were deposited at 400 C for 5 minutes and annealed at 650 C for 1 hour. The remnant polarization (Pr) and coercive eld (Ec) values at an applied voltage of 5 V were measured to be in the range of 14-16 C/cm2 and 90-100 kV/cm, respectively. Measurements of the fatigue test was carried out until 1 1011 cycles at an applied frequency of 500 kHz. Polarization decrease for lms on Pt/Ti/SiO2/Si(100) was not observed but for the ITO coated glass substrates, however, a slight decrease was observed at about 1109 cycles. The P-E hysteresis loops before and after the fatigue test showed a slight degradation of remnant polarization.
Jaemoon Pak,Gwangseo Park,Eunjung Ko,Kuangwoo Nam 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
A metal-ferroelectric-insulator-emiconductor (MFIS) feld-effect transistor structure has been fabricated by using ferroelectric Bi3:25La0:75Ti3O12 thin flm and thermally oxidized SiO2 insulating layer. We found that the electronic transport properties differ greatly with the different types of Si substrates (boron-doped p-type and phosphorus-doped n-type). Capacitance-voltage (C-V) curves were measured at a frequency of 1 MHz at various bias voltages, which resulted in an inverted memory window characteristic for n-type structure while an ideal clockwise loop was observed from p-type structure. These dierences in C-V measurements have been found to be reliable since current-voltage (I-V) measurements for both structures resulted in identical plots. Such a result ensures that MFIS structures prepared on n-type substrates are consistent with effects from ferroelectric polarizations.
Jaemoon Pak,Junho Chang,Kuangwoo Nam,Jungsuk Lee,Jooyoung Kim,Gwangseo Park 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
Ferroelectric Bi3:25La0:75Ti3O12 (BLT) thin lms were prepared on indium tin oxide (ITO) coated glass substrates by the pulsed-laser deposition method. ITO electrodes have previously been used as bottom electrodes for studies in optical phenomenon, or in oating gate capacitors. From this fact, the ITO layer was used as the bottom electrode and gold dots with an area of 1:77 10
Overmodulation Strategy of NPC Type 3-Level Inverter for Traction Drives
Jaemoon Lee,Jaeho Choi,Yasuyuki Nishida 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-
This paper proposes an overmodulation method for improving the voltage utilization of NPC type 3-level inverter for traction drives. The conventional railway vehicle has used a vector control to MI=0.907 and a slip-frequency control from MI=0.907 to the six-step mode. The slip-frequency control has less output torque dynamics than the vector control. In this paper, the linear region of NPC type 3-level inverter output voltage is extended to the six-step mode by using overmodulation strategy. As a result, vector control can be adapted in the whole regions and it leads to better output torque dynamics comparing with the conventional slip frequency control in overmodulation region. The overmodulation range is divided into two modes depending on the modulation index (MI), In the overmodulation region Ⅰ, the reference angles are derived from the Fourier series expansion of the reference voltage corresponds to the MI. In the overmodulation region Ⅱ, the holding angles are also derived in the same way. Therefore, it is possible to obtain the linear control and the maximized utilization of PWM inverter output voltage.
( Jaemoon Lee ),( Yun Hee Lim ),( Sung Jun Hong ),( Jae Hun Jeong ),( Hey Ran Choi ),( Sun Kyung Park ),( Jung Eun Kim ),( Eun Hi Park ),( Jae Hun Kim ) 대한통증학회 2021 The Korean Journal of Pain Vol.34 No.3
Background: Complex regional pain syndrome (CRPS) is an intractable pain disease with various symptoms. Here, we investigated the disease status, work life, sleep problems, medical insurance, economic status, psychological problems, and quality of life (QOL) of CRPS patients. Methods: CRPS patients from 37 university hospitals in South Korea were surveyed. The survey questionnaire consisted of 24 questions on the following aspects of CRPS patients: sex, age, occupation, cause of injury, activities of daily living (ADL), pain severity, sleep disturbance, level of education, economic status, therapeutic effect, and suicidal ideation. Additionally, the abbreviated World Health Organization Quality of Life (WHOQOL-BREF) questionnaire, consisting of 26 questions, was used to identify the status of QOL. Results: A total of 251 patients completed the questionnaire. According to the survey, 54.2% patients could not perform ADL on their own. Over the previous week, the mean pain score was 7.15 ± 1.78 (out of a total of 10 points); 92.1% of patients had sleep disorders and 80.5% had suicidal ideation, with most patients suffering from psychological problems. The average for each domain of WHOQOL-BREF was as follows: 21.74 ± 14.77 for physical, 25.22 ± 17.66 for psychological, 32.02 ± 22.36 for social relationship, and 30.69 ± 15.83 for environmental (out of a total of 100 points each). Occupation, ADL, sleep time, therapeutic effect, and suicidal ideation were statistically correlated with multiple domains. Conclusions: Most patients had moderate to severe pain, economic problems, limitations of their ADL, sleep problems, psychological problems, and a low QOL score.