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In this study, direct numerical simulation of the flow around a rotating sphere at high Mach and low Reynolds numbers is conducted to investigate the effects of rotation rate and Mach number upon aerodynamic force coefficients and wake structures. The simulation is carried out by solving the three-dimensional compressible Navier–Stokes equations. A free-stream Reynolds number (based on the free-stream velocity, density and viscosity coefficient and the diameter of the sphere) is set to be between 100 and 300, the free-stream Mach number is set to be between 0.2 and 2.0, and the dimensionless rotation rate defined by the ratio of the free-stream and surface velocities above the equator is set between 0.0 and 1.0. Thus, we have clarified the following points: (1) as free-stream Mach number increased, the increment of the lift coefficient due to rotation was reduced; (2) under subsonic conditions, the drag coefficient increased with increase of the rotation rate, whereas under supersonic conditions, the increment of the drag coefficient was reduced with increasing Mach number; and (3) the mode of the wake structure becomes low-Reynolds-number-like as the Mach number is increased.
In a series of observations (Mizuno et al. 1981; Mizuno 1982; Nakano et al. 1983), we have carried out the surface photometry of small H II regions which were selected from Sharpless catalogue (1959) by the following properties: (1) small angular size (≦ 10 arcmin), (2) round and simple appearance, and (3) a single BO V star as the exciting star. Properties (1) and (2) are for the convenience of image processing, and property (3) is to avoid the contamination of [O III] emission in the V-band so as to get pure continuum intensity.
We have made 12CO(J=1−0) observations of the LMC with NANTEN. We report the results of a comparison between CO clouds and SNRs in the LMC. Among the 35 known SNRs, only 10 are possibly associated with CO clouds. These 10 CO clouds and SNRs deserve follow-up studies for possible interactions. We present overlays of CO clouds on the optical images of some of these SNRs.
We have made a 12CO(J = 1−0) survey of the LMC with NANTEN. A sample of 55 giant molecular clouds has been identified and comparisons with stellar clusters, HII regions and SNRs are presented. The connection between the clouds and cluster formation is discussed.
We have made 12CO(J=1-0) observations in the LMC with NANTEN, and compared the detected giant molecular clouds (GMCs) with HII regions and stellar clusters. It is found that ~ 80% of the GMCs are associated with HII regions. The results of comparisons of the GMCs with the HII regions and the stellar clusters are presented.
We have made 12CO(J=1−0) observations of the LMC with the NANTEN millimeter-wave telescope and identified about 100 distinct giant molecular clouds (GMCs). A detailed comparison of the GMCs with stellar clusters and a UV image is discussed.
Fully sampled 12CO(J=1−0) observations of the whole extent of the LMC have been made with a linear resolution of ~ 30 pc at a detection limit of N(H2) = 2 × 1021 cm−2. In addition, several selected regions have been mapped with higher sensitivity corresponding to a detection limit of 1 × 1021 cm−2. Based on these results, a new estimate of the molecular mass in the LMC is presented.
Zel'dovich proposed Lagrangian perturbation theory (LPT) for structure formation in the Universe. After this, higher-order perturbative equations have been derived. Recently fourth-order LPT (4LPT) have been derived by two group. We have shown fifth-order LPT (5LPT) In this conference, we notice fourth- and more higher-order perturbative equations. In fourth-order perturbation, because of the difference in handling of spatial derivative, there are two groups of equations. Then we consider the initial conditions for cosmological N-body simulations. Crocce, Pueblas, and Scoccimarro (2007) noticed that second-order perturbation theory (2LPT) is required for accuracy of several percents. We verify the effect of 3LPT initial condition for the simulations. Finally we discuss the way of further improving approach and future applications of LPTs.
This paper shows a new semiconductor bonding technology for mechanically stacked multi-junction solar cells. Our strategy is the combination of conductive nanoparticle alignments and the van der Waals bonding technique. With this method, reasonably low bonding resistances and minimal optical absorption losses were simultaneously attained for the use of mechanically stacked solar cells. We examined a GaInP(Eg-1.89 eV)/GaAs (Eg-1.42 eV)/InGaAsP (Eg-1.15 eV) three-junction solar cell fabricated with this bonding method. As a result, the total efficiency of 22.5% was achieved, which was in good agreement with the theoretically predicted value. These results suggested that our bonding method is highly useful to fabricate high-efficiency mechanically stacked multi-junction solar cells.
Oxygen-doped germanium crystals were used to demonstrate the interaction between implanted hydrogen or nitrogen atoms and the oxygen-related defects. The electron trap at Eo-0.26eV associated with the germanium A-center was found to be formed by electron irradiation. Another level at Eo-0.21eV also was observed on annealing at 120 °C. As for the sample implanted with hydrogen ions following electron irradiation, the trap concentration is four times as large as that for electron irradiation alone. It is probable that the germanium A-centers produced by electron irradiation capture hydrogen atoms and increase electrically active centers. After nitrogen implantation following electron irradiation, the Eo-0.26eV level almost annealed out at 140 °C and the trap at Eo-0.21eV wasn't observed. We propose that the reduction in the oxygen-related defect growth is due to the prevention of defect migration with nitrogen atoms.
A new fabrication method of SiGe-on-Insulator (SGOI) and Ge-on-Insulator (GOI) structures are presented as well as the application to high-mobility channel CMOS devices. This method, the Ge-condensation technique, consists of epitaxial growth of a SiGe layer with a low Ge fraction on an SOI substrate and successive oxidation at high temperatures, which can be incorporated in conventional CMOS processes. During the oxidation, Ge atoms are pushed out from the oxide layer and condensed in the remaining SiGe layer. The interface between the Si and SiGe layers is disappeared due to the interdiffusion of Si and Ge atoms. Eventually, an SGOI layer with a higher Ge fraction is formed on the buried oxide layer. The Ge fraction in the SGOI layer can be controlled by the oxidation time because total amount of Ge atoms in the SGOI layer is conserved throughout the oxidation process. We found that the lattice relaxation in the SGOI layer also can be controlled through the initial SiGe thickness. P- and n-type strained SOI MOSFETs, which were fabricated on relaxed SGOI substrates formed by this technique, exhibited mobility enhancement of 50% and 80%, respectively. CMOS ring oscillators comprised of the MOSFETs exhibited reduction in propagation delay of 70%-30% compared to a conventional SOI-CMOS device. Ultrathin-body strained SGOI pMOSFETs with high Ge fraction and surface channels were also fabricated by this technique. These devices exhibited hole-mobility enhancement factors up to 2.3. Furthermore, Ge-on-Insulator (GOI) structures with thicknesses less than 10 nm were realized for ultrathin body GOI-CMOS applications by using the Ge-condensation technique. In conclusion, the Ge-condensation technique is a promising technique for fabricating various types of high-mobility channel-on-insulator devices.
A magnetically enhanced capacitively coupled plasma source was developed for sputter deposition of Cu seed layers on sub 0.25µm via or contact holes. The plasma source is of planer parallel plate configuration where the Cu target plate is one of the electrodes. For the generation of plasma, 60 MHz rf power is selected in order to increase the plasma density. Additionally, a line cusp magnetic field is used to further increase the plasma density. The film deposition rate and uniformity obtained with this plasma source is∼200 nm/min and ∼±5%, respectively. The Cu film resistivity lies around 2 µωcm. This sputtering system yields good film coverage on bottom and sidewalls of via holes with an aspect ratio > 5; therefore, a perfect Cu filling could be realized by electroplating process.
Strained-Si MOSFET is an attractive device structure to be able to relax several fundamental limitations of CMOS scaling, because of high electron and hole mobility and compatibility with Si CMOS standard processing. In this paper, we present a new device structure including strained-Si channel, strained-SOI MOSFET, applicable to CMOS under sub-100 nm technology nodes. The main feature of this device is that thin strained-Si channel/relaxed SiGe hetero-structures are formed on buried oxides. The principle and the advantages are described in detail. The strained-SOI MOSFETs, whose electron and hole mobility is 1.6 and 1.3 times, respectively, higher than in conventional MOSFETs, have successfully been fabricated by combining the SIMOX technology with re-growth of strained Si films. We also present novel fabrication techniques to realize ultra-thin SiGe-on-Insulator (SGOI) virtual substrates with high Ge content, including Ge condensation due to oxidation of SGOI with lower Ge content. Strained-Si/SGOI structures with total thickness of 21 nm and Ge content of 56 % have been fabricated by oxidizing SiGe films on conventional SOI substrates and re-growing strained-Si films.
Flux pinning and weak link structure were studied on the effect of Ca doping in LnBa2Cu3O7-y system (Ln=La and Y). The magnitude and the magnetic field dependence of the critical current density were improved by Ca doping. A small amount of impurity phase of such as Ca2Cu1O3 may work as a desirable flux pinning center. Moreover, it was found that the current-temperature characteristics for Ca-doped samples showed the evidence of two kinds of superconducting phases which have different transition temperature Tc and Tc'. The experimental result agrees well with the Ambegaokar-Baratoff theory for asymmetric Josephson junctions (S-I-S') in the temperature range of T < Tc' and with the proximity junction theory (S-N-S) in the range of Tc'<T<Tc.
Gettering efficiencies and stabilities of internal gettering sites for metallic impurities in high and low carbon doped silicon have been compared with ramped and standard two-step pre-annealing conditions. This study was intended to compare two proposed techniques to shorten the long low temperature nucleation step in the standard Hi-Lo-Hi internal gettering site formation treatment. Specifically, we compare the affect of carbon and a ramped annealing sequence on oxygen precipitate formation and gettering effectiveness. Our results show both techniques accelerate oxygen precipitation, however, only the low carbon ramped materials produced efficient and stable gettering sites. The high carbon materials did not with either annealing treatment. This disparity in performance is due to a difference in the oxygen precipitate’s strain field. The precipitates in the low carbon material possessed a high strain field with strain-induced defects while in the high carbon material they were strain-free with no defects. These results indicate the strain stabilizes the gettered impurity such that the gettering rate is increased and stability is enhanced.
Static leach tests were conducted for simulated low-level radioactive waste (LLW) glass in deionized water at 90 °C for up to one year to investigate the dissolution mechanism of LLW glass. Widely studied leaching behavior of high-level radioactive waste (HLW) glass is referred in discussing the dissolution mechanism. LLW glass is characterized by higher sodium (Na) and aluminum (Al) contents than HLW glass, about twice as high as R7T7, with its SiO2 content close to HLW glass. Powdered simulated LLW glass of three different chemical compositions was tested with the glass-surface-to-water-volume ratio of 2,000 m−1. The release rates of boron (B), widely used as an indicator of dissolution for HLW glass, decreased with time during leaching, as commonly observed in similar tests for HLW glass. The pH of the leachate was stable around 11.3 - 11.6, which is higher than those in similar tests for HLW glass by one pH unit or more. The concentrations of Al in the leachates were higher compared to data for HLW glass by two orders of magnitude. The high concentration seems to be caused by higher pH. In the leachate condition of the present tests, a zeolitic mineral (analcime) is thermodynamically more stable than amorphous silica (SiO2(am)) which is known to control the concentration of dissolved silica (Si) with respect to HLW glass. The present results imply that dissolution of the LLW glass is accompanied with formation of analcime under virtually closed systems such as geological repository where the groundwater flow rate is quite low.
We have investigated the effect of Bi on the homoepitaxial growth of Fe(100) by means of reflection high-energy electron diffraction (RHEED). It was clearly found that Bi induces layer-by-layer growth of Fe on Fe(100)-c(2×2)O reconstruction surface. The result of the dependence of the growth behavior as a function of Bi layer thickness suggests that there is optimum amount of Bi surfactant layer that induces the smoother layer-by-layer growth. A strong surface segregation of Bi was found at the top of surface and acts as a surfactant by promoting the interlayer transport.
We have chosen Bi as the surfactant atom in the heteroepitaxial growth of Co on Au(111). It was found that Bi induces layer-by-layer (LBL) growth at room temperature. With pre-deposition of 0.2 ∼ 0.8Å Bi on Au(111) prior to the evaporation of Co, more long-lasting RHEED intensity oscillations were observed and this implies that it induces the LBL growth of Co film. The result of the dependence of the growth behavior as a function of Bi layer thickness suggests that there is a suitable amount of Bi surfactant layer that induces the smoother LBL growth. A surface segregation of Bi was found at the top of surface and acts as a surfactant by promoting the interlayer transport.
It is shown that porous polycrystalline Si (PPS) diodes operate as light-emitting diodes (LEDs) with efficiencies comparable to conventional porous silicon (PS) diodes fabricated on singlecrystalline substrates. Judging from the electroluminescence (EL) characteristics such as emission spectra, diode current dependence of EL intensity, and its temperature dependence, the common EL mechanism seems to exist in PPS and PS diodes. Observed similarity in the photoluminescence (PL) properties between PPS and PS is consistent with this hypothesis. The capability of a poly-Si thin film transistor as a driver of PPS-LED is also demonstrated.
Morphological evolution of two metallic clusters of different elements at coalescence is investigated using molecular-dynamics (MD) simulation. All the pair combinations of the elements Ni, Cu, Au, Ag, Pt, and Pd are considered. The final structures of united bimetallic clusters are classified into three categories: epitaxial, core-shell, and alloyed. Which type of structure appears via coalescence depends on the size and temperature of clusters, which can be summarized in an observed structure map.