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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.
We carried out theoretical calculation for Cu(In,Ga)Se2 (CIGS) solar cells with energy bandgap of 1.4 eV assuming formation of a Cu-poor layer on the surface of CIGS films. This calculation result revealed that formation of a thinner Cu-poor layer such as a few nanometers leads to improvement of the solar cells performance. This is because interfacial recombination was suppressed due to repelling holes from the interface by valence band offset (ΔEV). Next, we investigated composition distribution in the cross section of CIGS solar cells with Ga contents of 30% and 70% by transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). It was revealed that the Cu-poor layer was formed on the surface and at the grain boundary (GB) in the case of conversion efficiency (η) of 17.3%, although it was not formed in the case of lower η of 13.8% for a Ga content of 30%. These results indicate that formation of the Cu-poor layer contributed to improvement of cell performance by suppression of carrier recombination. Moreover, it was also confirmed that although the Cu-poor layer was observed on the surface, it was not observed at the GB in the case of CIGS solar cells with a Ga content of 70% which had η of 12.7%. It is thought that the effect of repelling holes by ΔEV is not obtained at the GB and the solar cell performance in the Ga content of 70% is lower than that in the Ga content of 30%. Thus, we suggest importance of the Cu-poor layer at the GB for high efficiency of CIGS solar cells with high Ga contents.
Zizina emelina (de l'Orza) is listed on Japan's Red Data List as an endangered species because of loss of its principal food plant and habitat. We compared parts of the mitochondrial and nuclear genes of this species to investigate the level of genetic differentiation among the 14 extant populations. We also examined infection of the butterfly with the bacterium Wolbachia to clarify the bacterium's effects on the host population's genetic structure. Mitochondrial and nuclear DNA analyses revealed that haplotype composition differed significantly among most of the populations, and the fixation index FST was positively correlated with geographic distance. In addition, we found three strains of Wolbachia, one of which was a male killer; these strains were prevalent in several populations. There was linkage between some host mitochondrial haplotypes and the three Wolbachia strains, although no significant differences were found in a comparison of host mitochondrial genetic diversity with nuclear genetic diversity in Wolbachia-infected or -uninfected populations. These genetic analyses and Wolbachia infection findings show that Z. emelina has little migratory activity and that little gene flow occurs among the current populations.
It has been found that the blue light emission of LED is remarkably enhanced by using optical window of CaF2 disk doped with Eu2O3. The CaF2 crystals doped with Eu2O3 strongly absorb UV light with 330~420nm optical wavelength as a cutting filter. Instead, CaF2 crystals emit 420~425nm wavelength visible light. As a result, the UV light shifts to a light of around 420nm wavelength, and the LED light emission intensity markedly increases. In our experiments, the UV components were absorbed, while, around 420nm emitting light has been strengthened by more than 30%. The FWHM value is improved by around 30%.
A soft X-ray emission spectroscopy(SXES) study under an energetic electron irradiation has been applied to a nondestructive buried interface analysis of a thin-film(e.g., Cr)/Si(substrate) contact system, where the energy of primary electrons, Ep , is less than 20keV. An interesting point of this method is that we can have a specific signal for an element to be used as a finger print, otherwise it is difficult. By using this e-beam excited SXES, we can study an interface buried deep in a rather thick overlayer, e.g., more than a hundred of nm, which is due to the fact that a mean free path of a soft X-ray or an X-ray production depth is much larger than the mean free path of an energetic electron in solids. Electronic structural study of silicides by SXES is also shown.
Si L2,3 valence band soft x-ray emission spectrum (SXES) due to an e ectron excitation for silicides shows a clear modification from that for Si single crystal. Using this fact in combination with the incident angle variation(IAV) device, a non-destructive in-depth analysis of a Au(thin film)-Si(lll) contact is successfully carried out. Also, the SXES method has clarified the fact that a fair amount of the Si-s valence band density of state (yB-DOS) is included in the upper part of the yB-DOS for a Au-Si alloy, or Au-silicide, due to the Au-Si bond formation, which is a clear contrast to proposals given so far.
We have examined the intrinsic surface physical property of a CrO2 thin film by means of surface sensitive photoemission spectroscopy. Epitaxial thin film of CrO2(100) has been grown on TiO2(100) by a closed chemical vapor deposition method using a Cr8O21 precursor. Low-energy electron diffraction (LEED) observations find that epitaxial growth of rutile-phase CrO2 occurs to the top monolayer of the film. Surface sensitive x-ray photoemission spectroscopy (XPS) measurements show a finite intensity in the region of the Fermi energy. The result evidences that the physical nature of near topmost layer of CrO2 thin film is metallic. Progress of understanding of the surface physical property of CrO2 thin film helps not only perform a reliable photoemission study to understand the physics of ferromagnetic metal in CrO2, but also develop the CrO2-based devices using a half-metallic nature for spintronics applications.
Recently, GaN has attracted much attention for short wavelength LEDs, LDs and future opto-electronic integrated devices. In our study, Boronmonophosphide(BP) grown on Si(100) by MOCVD is used for growing cubic-GaN (c-GaN). The epitaxial growth of GaN/BP/Si has been carried out. We observed the crystal defects by scanning electron microscope(SEM), transmission electron microscopy(TEM), and surface X-ray diffraction(XRD). The dislocation density in the BP layer markedly decreased with increasing the thickness. However the difference of the lattice constant between BP and Si leads to high dislocation densities in GaN layer. Therefore, the epitaxial growth of Si doped BP on Si has been carried out, in order to observe the effect of Si doping on BP crystalline quality. We observed the crystal defects by XRD and cross-sectional TEM. The dislocation of interfaces will be discussed.
We have focused to grow cubic GaN (c-GaN) on Si(100) substrates using boronmonophosphide (BP) buffer crystals. The growth of GaN was carried out by MOVPE on BP/Si(100) substrate of 2 inches in diameter. By the several evaluations, it was recognized that when the growth temperature is around 750˚C, c-GaN was dominant. The typical growth rate was about 0.5μm/h. We obtained c-GaN layer over 2.5μm thick without cracking.
An electron excited Si L2,3 valence band soft x-ray emission spectrum (SXES) for Ni(or Co)Si2 showed a clear modification from that for Si. From the SXES study, a fair amount of the Si(3s) valence band density of state (VB-DOS) is concluded to be included in the upper part of the VB-DOS for the transition metal(TM) disilicides due to the TM-Si bond formation, which is a clear contrast to proposals given so far. Non-destructive structural analysis of a NiSi2 (tens of nm)/Si(111) contact is also carried out successfully using the SXES.
Monolithic SiB4±x and SIB6 plates about 1 nm in thickness were prepared by CVD using SiCl4, B2H6 and H2 gases as source materials. The CVD-SiB4±x, plates have nonstoichiometric compositions between B/Si=3.1 and 5.0. The lattice parameters of the CVD-SiB4±x, plates are a=0.633 nm and c=1.262 to 1.271 nm. The density of the CVD-SiB4±x ranges from 2.39 to 2.45 g/cm3. The CVD-SiB6 plates have a constant composition of B/Si=6.0. The lattice parameters of the CVD-SiB6plates are a=1.444 nm, b=1.828 nm, c=0.9915 nm, and their density Is 2.42 g/cm3. These measured densities are both almost in agreement with theoretical values. The electrical conductivity, Seebeck coefficient, Hall mobility and thermal conductivity of the CVD-SiB4±x and CVD-SiB6 plates were examined in the temperature range from 300 to 1000K. The conduction mechanism Is discussed and their figure of merit values for thermoelectric materials are evaluated.
Extremely high-sensitive image pickup tubes with sensitivities 1000 times higher than those of conventional tubes are fabricated using the avalanche phenomenon in a-Se as photoconductive targets. The excess avalanche noise of a video signal is found to be much less than that expected, based on the carrier ionization rates. The frequency spectra of the noise currents of both the pickup tubes and sandwich-type photocells are examined. The results are compared with those of a simulation, and it is found that the excess noise can be reduced by the charge-storage operation of imaging devices.
Spectra obtained by a new soft x-ray emission spectroscopy(SXES) apparatus again exhibited clear differences among Si-compounds and Si crystal. A non-destructive analysis of an annealed transition metal(TMSi:film)/Si(111) contact system was carried out using either the distinct differences of Si L2, 3 SXES spectra between TMSi's and Si single crystals or the fad that the soft x-ray production depth increases in a solid with the energy of the primary electron, Ep. It was shown that the apparatus was capable of exploring electronic and atomic structures of a multi-layered contact system grown on a Si(111) substrate.
Epitaxially grown films of Bi4Ti3O12 (BIT) were prepared on the substrate of a sapphire single crystal heated at 650°C using a sintered Bi4Ti3O12 target by electron cyclotron resonance (ECR) plasma sputtering. The BIT film of the same composition with the target was obtained under the conditions of microwave power(Mp) higher than 500 W and RF power(Rp) between 300 to 700 W. Increasing Mp or Rp, the deposition rate of the film was increased and the surface of the film became rough. The film exhibiting flat surface, good crystalline orientation and stoichiometric composition was prepared at such the high rate as 3.5 Å/sec under the conditions of Mp=500W and Rp=500W. Dielectric constants(1KHz) of the films deposited on (1120), (1102) and (0001) of sapphire were 93, 121 and 90, respectively, and refractive indexes of each films for the wave length of 632 nm were 2.32, 2.38 and 2.37, respectively.
Thermal oxidation resistance, in a temperature range of 600 to 1100° C, of AIN-Al2O3 composite, AIN and θ-A12 O3 films has been studied. The films were prepared by microwave plasma CVD using an AlBr3 -H2 -N2 -Ar gas system at a substrate temperature of 430° C. AIN-Al2O3 composite film was found to have good surface stability below an oxidaton temperature of 1100°C and to have the best properties for insulation film.
We have found a nonionic polymer gel swollen with nonionic dielectric solvent can be actuated by applying an electric field. The motion was not only far much faster than conventional polyelectrolyte gel materials, but also far much bigger in deformation. The motion was completed, for instance, within 60 ms and the deformation reached over 100%. The heat loss is negligible compared to that of polyelectrolyte gels. The deformation is not only bending, but also crawling. The principle was suggested to be charge-injected solvent dragging in the gel. The force was suggested to be proportional to the square of the electric field and proportional to the dielectric constant of the solvent. The principle was suggested to be promising and applicable to other conventional polymers.
Fine decagonal phase lamellae-bearing icosahedral Al-Pd-Mn quasicrystals were tested compressionally at temperatures of 997 to 1073 K and initial strain rate of 3 × 10−5. to I × 10−4 S−1, and stress relaxation tests were performed at various stages of deformation. The results confirmed the thermally activated nature of deformation, and the stress exponent of strain rate was around 4. Internal stress for deformation estimated by Kikuchi's method reached 50 to 90 % of applied stress. The effective stress exponent of strain rate was revealed to be about 1.3. At least a part of high internal stress was attributable to complicated dislocation microstructure.
We have prepared a CrO2 thin film by chemical vapor deposition from a Cr8O21 precursor and studied the bulk and surface physical properties. The CrO2 thin film is grown on TiO2(100) substrate by heating precursor and TiO2 (100) substrate together in a sealed quartz tube. The prepared film is found from x-ray diffraction analysis to be an (100)-oriented single phase. The magnetization and resistivity measurements indicate that the film is a ferromagnetic metal with a Curie temperature of about 400 K. Cr 3s core-level and valence band photoelectron spectroscopy spectra reveal the presence of a metallic CrO2 in the surface region of the film. Our work indicates that preparation from a Cr8O21 precursor in a closed system is promising for obtaining a CrO2 thin film with the metallic surface.
We have developed a photolithographic technique of patterning a pentacene layer with low damage using a SiNx/poly(vinyl alcohol) (PVA) photoresist multi-layer mask. We used a hexavalent chromium-free PVAphotoresist. By inserting a SiNx buffer layer between the pentacene layer and the PVAphotoresist layer, we could suppress an increase in off current caused by interaction between pentacene and the photosensitive functional group in the PVA photoresist. In the patterning process, we found that carriers generated by O2-plasma doped into the pentacene layer and the off current of the pentacene thin-film transistor (TFT) increased.We also found that successive annealing caused de-doping of the pentacene layer and reduced off current of the pentacene TFT.We investigated the density of doped carriers using a simplemodel of a planer pentacene diode aswell as a pentaceneTFT.
Only a few benign tumours of the middle ear have been reported to lead to the development of facial palsy. Here, we describe a patient with middle-ear cavernous lymphangioma and facial palsy.
Single case study.
A 61-year-old man presented with left-sided hearing impairment and incomplete left facial palsy. A tumour was confirmed to be occupying the epi- to mesotympanum and to be joined to the facial nerve. The tumour was removed along with facial nerve tissue, which was resected at its horizontal portion, and the remaining facial nerve was fixed by end-to-end anastomosis. Complete facial paralysis occurred after the operation, but the patient's House–Brackmann grade gradually improved to grade III. Post-operative histopathological examination revealed infiltration of the lymphangioma into the facial nerve tissue, together with mild neural atrophy of the facial nerve.
These findings suggested that tumour invasion was the cause of facial palsy in this patient.