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Neutron star mergers are one of the candidate astrophysical site(s) of r-process. Several chemical evolution studies however pointed out that the observed abundance of r-process is difficult to reproduce by neutron star mergers. In this study, we aim to clarify the enrichment of r-process elements in the Local Group dwarf galaxies. We carry out numerical simulations of galactic chemo-dynamical evolution using an N-body/smoothed particle hydrodynamics code, ASURA. We construct a chemo-dynamical evolution model for dwarf galaxies assuming that neutron star mergers are the major source of r-process elements. Our models reproduce the observed dispersion in [Eu/Fe] as a function of [Fe/H] with neutron star mergers with a merger time of 100 Myr. We find that star formation efficiency and metal mixing processes during the first ≲ 300 Myr of galaxy evolution are important to reproduce the observations. This study supports that neutron star mergers are a major site of r-process.
Many industries have developed new materials as substitutes for lead in solid lubricants. For example, lead bronze, a Cu-Pb alloy that has been used for slide bearings, has been replaced by a Cu alloy containing sulfide. The development of Pb-free Cu alloys has received considerable attention recently. Pb and sulfide are types of solid lubricants; in particular, MoS2 (molybdenum disulfide) is a popular sulfide lubricant. This study focuses on a material that contains Cu2S. The properties of Cu2S as a solid lubricant are unknown. First principles (FP) and molecular dynamics (MD) are used to clarify the lubrication mechanism of Cu2S. The atomiclevel stable structure of Cu2S is evaluated by FP under specific sliding conditions. The Cu2S lubrication mechanism is clarified by MD using the FP results for the interatomic potential functions. It is clarified that there is a specific slip system and the Cu-S bonds that exists above and below the layers of the slip system are very strong.
We show that the dispersion in the Schmidt-Kennicutt (SK) law in galaxies is affected significantly by the evolutionary stage of star forming molecular gas, using narrow band Paα imaging of Taffy I, an interacting pair of galaxies. Star forming regions in the system show very uniform ages except for the bridge region, and the SK law of regions at the same age show a exceptionally tight SK law.
Inversion-type n-channel MOSFET's of cubic-SiC were successfully fabricated. MOSFET's were fabricated on an antiphase-domains free layer grown on Si(100) by carbonization and subsequent chemical vapor deposition. Ion implantation technique was used to form source and drain of MOSFET's. A gate oxide of SiO2 was formed by thermal oxidation of SiC. Inversion mode operation was confirmed for the first time. Annealing temperature dependence of electrical characteristics of P+ and N2+ implanted layer and characteristics of p-n junction diodes fabricated using ion implantation technique were also investigated.
High-resolution cross-sectional and conventional plan-view transmission electron microscope observations have been carried out for molecular beam epitaxially grown GaAs films on vicinal Si (001) as a function of film thicknesses and observation directions between two orthogonal <110> directions before and after annealing. Two groups of misfit dislocations are characterized by analyzing whether their extra half planes exist in the film and the substrate side. The group I misfit dislocations due to a stress caused by a lattice misfit between GaAs and Si consist of partial and, 60° and 90° complete dislocations in an as-grown state. After annealing partial dislocations almost disappear and 90° perfect dislocations are predominantly observed. The group II misfit dislocations due to a thermal-expansion misfit-induced stress are all of the 60° type complete dislocations, independent of film thickness and annealing.
Amorphous (a-) Ge films were deposited on air-cleaved CaF2 (111) substrates at different deposition temperatures (Td). The films were irradiated with 0.9 MeV Ge or Si ions at low ion current intensity (1c) l00nA/cm2. Their structural changes were studied by Rutherford backscattering spectrometry (RBS) -channeling technique and thin film x-ray diffraction (XRD) measurement. It was found that the films were epitaxially crystallized by Ge and Si ion irradiation although they included randomly oriented grains. Ge ion irradiation was more effective for the crystallization than Si ion irradiation. However, the amount of the randomly oriented grains was slightly higher when using Ge ions. On the other hand, ion irradiation to the films prepared at high Td also exhibited higher incidence of randomly oriented grains.
The electronic structure of single-crystal Cr2O3 has been studied by Cr 2p core-level XPS and valence-band UPS spectroscopies. A cluster configuration-interaction analysis was applied to investigate the nature of the satellite in the Cr 2p core-level photoemission spectrum. It is argued that the satellite can be understood as a charge-transfer satellite, and Cr2O3 is found to be situated at the boundary between the Mott-Hubbard and the charge-transfer regimes. The values of the charge-transfer energy, Δ, the Coulomb correlation energy, U, and the ligand 2p-cation 3d hybridization energy, T, found from fitting the Cr 2p XPS spectrum were also used to analyze the valence-band UPS spectrum. The comparison between the experimental spectrum and the spectrum from theoretical fitting is fair.
Initial oxidation process of silicon in UV/ozone ambient has been monitored using a multi-wavelength, in-situ spectroscopic ellipsometry. Ozone gas was chemically formed by photochemical reaction of oxygen under ulUmviolet illuimination. The oxide growth was monitored for hydrogenated silicon surfaces as functions of oxygen gas flow rate, gas pressure and wafer temperature. Initial oxidation rates were very high at almost all the temperatures. The oxidation rate was 0.2 nm/min about ten times higher than that for thermal oxidation without UV light at low temperatures. The accelerated oxidation was probably due to an electric field effect on the oxidation of back-bond silicon by active oxygen atoms included in the ozone gas.
We have studied the fc-dependent electronic structure of the layered colossal magnetoresistive manganite La1.2Sr1.8Mn2O7 using high-resolution angle-resolved photoemission spectroscopy. We found dispersive energy bands as a function of the crystal momentum k near the Fermi level (EF). We have also performed local spin density approximation (LSDA)+U band-structure calculations on the current system. The overall experimental dispersion relation is basically in agreement with the band-structure calculations yet close to EF there is a significant deviation from the predicted dispersions. Instead of clear Fermi-surface (FS) crossings, we observe a depression of the features as the FS is approached as if there is a “pseudo” gap in the excitation spectrum. The pseudogap continuously opens with temperature and does not show further significant opening above Tc, corresponding to the metal-insulator transition. Those unusual aspects of the spectra has been discussed from the viewpoint of the strong electron-lattice coupling model.
We have performed X-ray absorption (XAS) and angle-resolved photoemission (ARPES) on single crystals of both the layered and cubic colossal magnetoresistive manganites to determine the electronic structure and the relevant energy scales in the problem: the intra-atomic exchange energy J (∼ 2.7 eV), the Jahn-Teller energy gain EJ-T (<.25 eV), the one-electron bandwidth W (>3 eV for layered compounds) and the lattice relaxation or polaron binding energy EB (.65 eV ferromagnetic phase and.8 eV paramagnetic phase). Lattice polarons are deemed important especially in the paramagnetic but also to a degree in the ferromagnetic phase. Due to the energy scale mismatch, the Jahn-Teller effect is unlikely to be the cause for these lattice polarons, at least for the layered samples.
The silicon nanocrystal memory, that is one of the most promising devices for future non-volatile memory, is extensively investigated by experiments and simulation. The silicon nanocrystal memory cells are successfully integrated using the state-of-the-art 0.13 μm DRAM technology. The mechanism of the two-bit-per-cell operation, that is one of the unique features of silicon nanocrystal memory, is investigated and it is shown that the degree of DIBL determines the read scheme of the two-bit-per-cell operation. Moreover, the dependences of memory characteristics on device structures are examined by fabrication and measurements and it is found that the ultra-thin-body SOI and double-gate structures have better memory characteristics.
We developed a new technique of epitaxial lateral growth without using oxide masks called beam induced lateral epitaxy (BILE). In this technique, molecular beams are directed at a nearly glancing angle with respect to a substrate that has pre-fabricated truncated ridges. By using BILE we grew GaAs laterally from the side of ridges on a GaAs substrate. The growth behavior of BILE strongly depended on both incident angle of the Ga beam and the crystal orientation of the truncated ridges. The formation of facets on the lateral growth front controlled the grown shape of the layers. By using a (111) B substrate with BILE, we grew a smooth, flat (111) B facet on the top of the layer.
The number of patients with severe invasive group-G streptococcal (Streptococcus dysgalactiae subsp. equisimilis) infections has been increasing in Japan. The emm genotypes and SmaI-digested pulsed-field gel electrophoresis DNA profiles were variable among the strains isolated, suggesting there has not been clonal expansion of a specific subpopulation of strains. However, all strains carried scpA, ska, slo and sag genes, some of which may be involved in the pathogenesis of the disease.
We surveyed T serotypes and emm genotypes of Streptococcus pyogenes isolates from streptococcal toxic shock-like syndrome (TSLS) patients. T1 (emm1) remained dominant through 1992 to 2000, but the dominant T3 (emm3.1) strains from 1992 to 1995 disappeared during 1996–2000. Strains of several emm genotypes emerged during 1996–2000, indicating alterations in the prevalent strains causing TSLS.
The status of Schistosoma sinensium (samples from Thailand and from Sichuan, China) relative to other species of the genus Schistosoma was investigated using DNA sequences from the mitochondrial cytochrome c oxidase subunit 1 (CO1) gene (partial) and the nuclear ribosomal DNA second internal transcribed spacer 2 (ITS2). Trees inferred from these sequences place S. sinensium as sister to the S. japonicum group and suggest a basal position in the clade utilizing snails of the family Pomatiopsidae. The sequence differences between specimens of S. sinensium from China and Thailand are at least as great as between S. malayensis and S. mekongi. Schistosoma sinensium is probably best regarded as a species complex.