MOVPE법으로 GaN위에 성장시킨 A1_1-xIn_xN 박막의 광학적 특성

신동원,김성익,허증수,Sin, Dong-Won,Kim, Seong-Ik,Yoshida, A.,Heo, Jeung-Su 한국재료학회 2002 한국재료학회지 Vol.12 No.2

Research Activities on a MIR-FEL and Table-Top THz Generation in Kyoto University

H. Ohgaki,T. Kii,K. Masuda,M. A. Bakr,K. Higashimura,R. Kinjo,S. Ueda,T. Sonobe,Y. U. Jeong,K. Yoshida 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.21

Free Electron Lasers (FEL), which could be useful for developing energy materials, have been exploited at the Institute of Advanced Energy, Kyoto University. A mid-infrared FEL has been developed, and FEL gain saturation at 13.2 µm was achieved for the first time in May 2008. A FEL beam characterization was performed. A macro pulse energy of 5 mJ/pulse and a peak power of about 3 MW were achieved. A FEL beam transport system was constructed in the user room. Furthermore a tabletop THz FEL amplifier for the spectral range from 150 to 300 µm, which consists of a photocathode RF gun and an undulator, has been proposed to strengthen the materials research. For evaluation of the proposed design, a start-to-end simulation was carried out. An output power of about 350 kW is expected with the proposed system. Free Electron Lasers (FEL), which could be useful for developing energy materials, have been exploited at the Institute of Advanced Energy, Kyoto University. A mid-infrared FEL has been developed, and FEL gain saturation at 13.2 µm was achieved for the first time in May 2008. A FEL beam characterization was performed. A macro pulse energy of 5 mJ/pulse and a peak power of about 3 MW were achieved. A FEL beam transport system was constructed in the user room. Furthermore a tabletop THz FEL amplifier for the spectral range from 150 to 300 µm, which consists of a photocathode RF gun and an undulator, has been proposed to strengthen the materials research. For evaluation of the proposed design, a start-to-end simulation was carried out. An output power of about 350 kW is expected with the proposed system.

ANALYSIS OF HCCI COMBUSTION CHARACTERISTICS BASED ON EXPERIMENTATION AND SIMULATIONS-INFLUENCE OF FUEL OCTANE NUMBER AND INTERNAL EGR ON COMBUSTION

A. IIJIMA,K. YOSHIDA,H. SHOJI,J. T. LEE 한국자동차공학회 2007 International journal of automotive technology Vol.8 No.2

Homogenous Charge Compression Ignition (HCCI) combustion systems can be broadly divided for the process applied to 4-stroke and 2-stroke engines. The former process is often referred to as simply HCCI combustion and the latter process as Active Thermo-Atmosphere Combustion (ATAC). The region of stable engine operation tends to differ greatly between the two processes. In this study, it was shown that the HCCI combustion process of a 4-stroke engine, characterized by the occurrence of autoignition under a high compression ratio, a lean mixture and wide open throttle operation, could be simulated by operating a 2-stroke engine at a higher compression ratio. On that basis, a comparison was made of the combustion characteristics of high-compression-ratio HCCI combustion and ATAC, characterized as autoignited combustion in the presence of a large quantity of residual gas at a low compression ratio and part throttle. The results showed that one major difference between these two combustion processes was their different degrees of susceptibility to the occurrence of cool flame reactions. Compared with high-compression-ratio HCCI combustion, the ignition timing of ATAC tended not to change in relation to different fuel octane numbers. Furthermore, when internal EGR was applied to high-compression-ratio HCCI combustion, it resulted in combustion characteristics resembling ATAC. Specifically, as the internal EGR rate was increased, the ignition timing showed less change in relation to changes in the octane number and the region of stable engine operation also approached that of ATAC.

Application of MIR-FEL Irradiation to Selectively Excite Phonons in Wide-gap Semiconductors

Kyohei Yoshida,Taro Sonobe,M. A. Bakr,Y. W. Choi,Ryota Kinjo,M. Omer,Masato Takasaki,Satoshi Ueda,Naoki Kimura,Keiichi Ishida,Kai Masuda,Toshiteru Kii,Hideaki Ohgaki 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.51

A mid-infrared free electron laser (MIR-FEL) (5 - 20 μm) facility (KU-FEL: Kyoto University Free Electron Laser) was constructed to aid in various energy science researchers at the Institute of Advanced Energy, Kyoto University. In May 2008, the first power saturation at 13.2 μm was achieved. A pilot application to evaluate selective phonon excitation processes in solid materials by irradiating with MIR-FEL was implemented, and a preliminary experiment without FEL irradiation was conducted. N-doped silicon carbide (SiC) was selected as a sample material due to its unique electrical property where the lattice vibration and electronic structure are coupled. Two peaks at 1.8 - 2.4 eV and 2.4 - 2.8 eV, which showed strong temperature dependences in both their intensities and peak energy, were observed. These tendencies could be explained by a donor-acceptor pair luminescence (DAP) model with impurity and defects in the SiC sample. The results imply that we can verify the selective phonon excitation by investigating the change of PL spectrum introduced by MIR-FEL irradiation.

ANALYSIS OF HCCI COMBUSTION CHARACTERISTICS BASED ON EXPERIMENTATION AND SIMULATIONS-INFLUENCE OF FUEL OCTANE NUMBER AND INTERNAL EGR ON COMBUSTION

Iijima, A.,Yoshida, K.,Shoji, H.,Lee, J.T. The Korean Society of Automotive Engineers 2007 International journal of automotive technology Vol.8 No.2

Homogenous Charge Compression Ignition (HCCI) combustion systems can be broadly divided for the process applied to 4-stroke and 2-stroke engines. The former process is often referred to as simply HCCI combustion and the latter process as Active Thermo-Atmosphere Combustion (ATAC). The region of stable engine operation tends to differ greatly between the two processes. In this study, it was shown that the HCCI combustion process of a 4-stroke engine, characterized by the occurrence of autoignition under a high compression ratio, a lean mixture and wide open throttle operation, could be simulated by operating a 2-stroke engine at a higher compression ratio. On that basis, a comparison was made of the combustion characteristics of high-compression-ratio HCCI combustion and ATAC, characterized as autoignited combustion in the presence of a large quantity of residual gas at a low compression ratio and part throttle. The results showed that one major difference between these two combustion processes was their different degrees of susceptibility to the occurrence of cool flame reactions. Compared with high-compression-ratio HCCI combustion, the ignition timing of ATAC tended not to change in relation to different fuel octane numbers. Furthermore, when internal EGR was applied to high-compression-ratio HCCI combustion, it resulted in combustion characteristics resembling ATAC. Specifically, as the internal EGR rate was increased, the ignition timing showed less change in relation to changes in the octane number and the region of stable engine operation also approached that of ATAC.

Quantum Dots Formed in Three-dimensional Dirac Semimetal Cd₃As₂ Nanowires

Jung, Minkyung,Yoshida, Kenji,Park, Kidong,Zhang, Xiao-Xiao,Yesilyurt, Can,Siu, Zhuo Bin,Jalil, Mansoor B. A.,Park, Jinwan,Park, Jeunghee,Nagaosa, Naoto,Seo, Jungpil,Hirakawa, Kazuhiko American Chemical Society 2018 NANO LETTERS Vol.18 No.3

<P>We demonstrate quantum dot (QD) formation in three-dimensional Dirac semimetal Cd<SUB>3</SUB>As<SUB>2</SUB> nanowires using two electrostatically tuned p-n junctions with a gate and magnetic fields. The linear conductance measured as a function of gate voltage under high magnetic fields is strongly suppressed at the Dirac point close to zero conductance, showing strong conductance oscillations. Remarkably, in this regime, the Cd<SUB>3</SUB>As<SUB>2</SUB> nanowire device exhibits Coulomb diamond features, indicating that a clean single QD forms in the Dirac semimetal nanowire. Our results show that a p-type QD can be formed between two n-type leads underneath metal contacts in the nanowire by applying gate voltages under strong magnetic fields. Analysis of the quantum confinement in the gapless band structure confirms that p-n junctions formed between the p-type QD and two neighboring n-type leads under high magnetic fields behave as resistive tunnel barriers due to cyclotron motion, resulting in the suppression of Klein tunneling. The p-type QD with magnetic field-induced confinement shows a single hole filling. Our results will open up a route to quantum devices such as QDs or quantum point contacts based on Dirac and Weyl semimetals.</P> [FIG OMISSION]</BR>

Combined GS-4774 and Tenofovir Therapy Can Improve HBV-Specific T-Cell Responses in Patients With Chronic Hepatitis

Boni, Carolina,Janssen, Harry L.A.,Rossi, Marzia,Yoon, Seung Kew,Vecchi, Andrea,Barili, Valeria,Yoshida, Eric M.,Trinh, Huy,Rodell, Timothy C.,Laccabue, Diletta,Alfieri, Arianna,Brillo, Federica,Fisic W.B. Saunders Co. 2019 Gastroenterology Vol.157 No.1

<P><B>Background & Aims</B></P> <P>One strategy to treat chronic hepatitis B virus (HBV) infection could be to increase the functions of virus-specific T cells. We performed a multicenter phase 2 study to evaluate the safety and efficacy of GS-4774, a yeast-based therapeutic vaccine engineered to express HBV antigens, given with tenofovir disoproxil fumarate (TDF) to untreated patients with chronic HBV infection.</P> <P><B>Methods</B></P> <P>We performed an open-label study at 34 sites in Canada, Italy, New Zealand, Romania, South Korea, and United States from July 2014 to August 2016. Adults who were positive for HB surface antigen (HBsAg) > 6 months and levels of HBV DNA ≥2000 IU/mL who had not received antiviral treatment for HBV within 3 months of screening were randomly assigned (1:2:2:2) to groups given oral TDF 300 mg daily alone (n = 27; controls) or with 2, 10, or 40 yeast units GS-4774 (n = 168), administered subcutaneously every 4 weeks until week 20 for a total of 6 doses. Blood samples were collected and analyzed and patients received regular physical examinations. Efficacy was measured by decrease in HBsAg from baseline to week 24. Specific responses to HBV (production of interferon gamma [IFNG], tumor necrosis factor [TNF], interleukin 2 [IL2], and degranulation) were measured in T cells derived from 12 HBeAg-negative patients with genotype D infections, after overnight or 10 days of stimulation of peripheral blood mononuclear cells with peptides from the entire HBV proteome. T-regulatory cells were analyzed for frequency and phenotype. Data from studies of immune cells were compared with data on reductions in HBsAg, HBV DNA, and alanine aminotransferase in blood samples from patients.</P> <P><B>Results</B></P> <P>GS-4774 was safe and well tolerated but did not produce significant decreases in levels of HBsAg. Production of IFNG, TNF, and IL2 increased significantly at weeks 24 and 48, compared with baseline, in HBV-specific CD8+ T cells from patients given GS-4774 but not from controls. GS-4774 had greater effects on CD8+ than CD4+ T cells, which were not affected at all or very weakly by TDF with or without GS-4774. GS-4774 did not affect responses of T cells to other viruses tested. HBV core peptides induced the greatest production of IFNG by T cells following overnight stimulation, whereas HBV envelope antigens did not induce a response. Following 10 days of stimulation, production of IFNG and TNF increased with time of exposure to GS-4774; the greatest levels of responses were to HBV envelope antigens followed by core and polymerase peptides. We observed a correlation in patients given GS-4774 between increased T-cell functions and reductions in numbers of T-regulatory cells.</P> <P><B>Conclusions</B></P> <P>In a phase 2 study of patients with chronic HBV infection given TDF with or without GS-4774, we found that vaccination can increase production of IFNG, TNF, and IL2 by CD8+ T cells exposed to antigenic peptides, with little effect on CD4+ T cells. Although GS-4774 did not reduce levels of HBsAg in patients, its strong immune stimulatory effect on CD8+ T cells might be used in combination with other antiviral agents to boost the antivirus immune response. Clinicaltrials.gov no: NCT02174276.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Output-only modal parameter identification for force-embedded acceleration data in the presence of harmonic and white noise excitations

C.J. Ku,Y. Tamura,A. Yoshida,K. Miyake,L.S. Chou 한국풍공학회 2013 Wind and Structures, An International Journal (WAS Vol.16 No.2

Output-only modal parameter identification is based on the assumption that external forces on a linear structure are white noise. However, harmonic excitations are also often present in real structural vibrations. In particular, it has been realized that the use of forced acceleration responses without knowledge of external forces can pose a problem in the modal parameter identification, because an external force is imparted to its impulse acceleration response function. This paper provides a three-stage identification procedure as a solution to the problem of harmonic and white noise excitations in the acceleration responses of a linear dynamic system. This procedure combines the uses of the mode indicator function, the complex mode indication function, the enhanced frequency response function, an iterative rational fraction polynomial method and mode shape inspection for the correlation-related functions of the force-embedded acceleration responses. The procedure is verified via numerical simulation of a five-floor shear building and a two-dimensional frame and also applied to ambient vibration data of a large-span roof structure. Results show that the modal parameters of these dynamic systems can be satisfactorily identified under the requirement of wide separation between vibration modes and harmonic excitations.

Output-only modal parameter identification for force-embedded acceleration data in the presence of harmonic and white noise excitations

Ku, C.J.,Tamura, Y.,Yoshida, A.,Miyake, K.,Chou, L.S. Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.16 No.2

Output-only modal parameter identification is based on the assumption that external forces on a linear structure are white noise. However, harmonic excitations are also often present in real structural vibrations. In particular, it has been realized that the use of forced acceleration responses without knowledge of external forces can pose a problem in the modal parameter identification, because an external force is imparted to its impulse acceleration response function. This paper provides a three-stage identification procedure as a solution to the problem of harmonic and white noise excitations in the acceleration responses of a linear dynamic system. This procedure combines the uses of the mode indicator function, the complex mode indication function, the enhanced frequency response function, an iterative rational fraction polynomial method and mode shape inspection for the correlation-related functions of the force-embedded acceleration responses. The procedure is verified via numerical simulation of a five-floor shear building and a two-dimensional frame and also applied to ambient vibration data of a large-span roof structure. Results show that the modal parameters of these dynamic systems can be satisfactorily identified under the requirement of wide separation between vibration modes and harmonic excitations.

Adsorption and Reaction of CO and NO on Ir(111) Under Near Ambient Pressure Conditions

Ueda, K.,Suzuki, K.,Toyoshima, R.,Monya, Y.,Yoshida, M.,Isegawa, K.,Amemiya, K.,Mase, K.,Mun, B. S.,Arman, M. A. Springer Science + Business Media 2016 Topics in catalysis Vol.59 No.5

<P>The adsorption and reaction of CO and NO on Ir(111) have been studied by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) together with low-energy electron diffraction, scanning tunneling microscopy, and mass spectroscopy (MS). Under both ultrahigh vacuum (UHV) and NAP conditions CO molecules occupy on-top sites of the Ir(111) surface at room temperature (RT) by forming two-dimensional clusters. Exposure to NO under UHV conditions at RT induces partially dissociative adsorption, while NAP NO exposure leads to a Ir(111) surface that is covered by molecular NO. We conducted in-operando NAP-XPS/MS observation of the NO + (CO)-C-13 reaction under a NAP condition as a function of temperature. Below 210 degrees C adsorption of NO is inhibited by CO, while above 210 degrees C the CO inhibition is released due to partial desorption of CO and dissociative adsorption of NO starts to occur leading to associative formation of N-2. Under the most active condition studied here the Ir surface is covered by a dense co-adsorption layer consisting of on-top CO, atomic N and O, which suggests that this reaction is not a NO-dissociation-limited process but a N-2/CO2 formation-limited process.</P>