NASDA Space Program In Japan

The National Space Development Agency of Japan, NASDA, was established on October 1, 1969, under the NASDA Law as the nucleus of the nation\u27s space development effort in order to promote space development and utilization for peaceful purposes. NASDA, in a sense, is the equibalent of NASA in the United States, or ESA ( European Space Agency ) in Europe. In accordance with the basic program for space development decided by the Prime Minister, NASDA is undertaking (1) the development, launching and tracking of satellites and satellite launch vehicles and (2) the development and consolidation of software, equipment and facilities needed for launching and tracking. So far, NASDA has succeeded in launching four satellites by means of its N Launch vehicle from the Tanegashima Space Center, three of them into 1,000 km circular orbit and one into geosynchronous orbit. NASDA succeeded also in the insertion of three satellites into geosynchronous orbits at their projected positions after having been launched by US NASA\u27s Delta 2914 from ETR under the reimbursable launch contract. NASDA activities in general will be overviewed in this report

Optimizing picene molecular assembling by supersonic molecular beam deposition

Here we report an investigation of the growth of picene by supersonic molecular beam deposition on thermal silicon oxide and on a self-assembled monolayer of hexamethyldisiloxane (HMDS). In both cases film morphology shows a structure with very sharp island edges and well-separated islands which size and height depend on the deposition conditions. Picene films growth on bare silicon covered with hydrophobic HDMS shows islands characterized by large regular crystallites of several micrometers; on the other hand, films growth on silicon oxide shows smaller and thicker islands. We analyzed the details of the growth model and describe it as a balancing mechanism involving the weak interaction between molecules and surface and the strong picene-picene interaction that leads to a different Schwoebel-Ehrlich barrier in the first layer with respect to the successive one. Finally, we study the charge transport properties of these films by fabricating field-effect transistors devices in both top and bottom contact configuration. We notice that substrate influences the electrical properties of the device and we obtained a maximum mobility value of 1.2 cm2 V-1 s-1 measured on top contact devices in air. © 2012 American Chemical Society

Structure and physical properties of Na4C60 under ambient and high pressures

The structure and physical properties of two-dimensional polymeric Na4C60 (body-centered monoclinic, space group I2/m) are studied in a wide temperature region from 12 to 300 K at 1 bar, and in a pressure region up to 53 kbar at 300 K. The temperature dependence of lattice constants suggests a structural anomaly below 100 K where the variation of spin susceptibility is observed from electron spin resonance. The thermal expansion of the unit-cell volume V is smaller than that of monomeric Rb3C60 and K3C60. The compressibility of c is larger than that of a and b, which can be well explained by the repulsion between Na ions. The compressibility of the center-to-center distance in the (10(1) over bar) plane is similar to1/3 times smaller that that in the (101) plane, which can be well explained by the formation of the polymer chains. Further, a possibility of a three-dimensional polymerization is discussed on the basis of the pressure dependence of C-60. . .C-60 distances.</p

Metal-insulator transition at 50 K in Na2C60

Temperature dependence of electron spin resonance in Na2C60 was studied in a temperature range from 2 to 350 K. It was shown that Na2C60 was metallic above 50 K and had a metal-insulator transition at 50 K. The center frequency for the Hg(2) Raman mode in Na2C60 at 298 K was close to those in the metallic Rb3C60, K3C60, and Cs3C60, while the linewidth was close to that in the metallic but nonsuperconducting Cs3C60. The Hg(2) mode showed a large blueshift and narrowing at 50 K. The center frequency and the linewidth in the low-temperature region from 50 K were almost the same as those in the insulating C-60 and Rb6C60, which showed the metal-insulator transition at 50 K in Na2C60. The origin of this metal-insulator transition was discussed in terms of the electron-phonon interaction (Jahn-Teller effect) and the electron-electron interaction (Mott-Hubbard picture). [S0163-1829(99)04123-5].</p

Electronic structure of pristine and K-doped solid picene: Non-rigid-band change and its implication for electron-intramolecular-vibration interaction

We use photoemission spectroscopy to study electronic structures of pristine and K-doped solid picene. The valence band spectrum of pristine picene consists of three main features with no state at the Fermi level (EF), while that of K-doped picene has three structures similar to those of pristine picene with new states near EF, consistent with the semiconductor-metal transition. The K-induced change cannot be explained with a simple rigid-band model of pristine picene, but can be interpreted by molecular orbital calculations considering electron-intramolecular-vibration interaction. Excellent agreement of the K-doped spectrum with the calculations points to importance of electron-intramolecular-vibration interaction in K-doped picene.Comment: This article is accepted by Physical Review

Evaluation of near-threshold fatigue crack propagation in Ti-6Al-4V Alloy with harmonic structure created by Mechanical Milling and Spark Plasma Sintering

Titanium alloy (Ti-6Al-4V) having a bimodal “harmonic structure”, which consists of coarsegrainedstructure surrounded by a network structure of fine grains, was fabricated by mechanical milling (MM)and spark plasma sintering (SPS) to achieve high strength and good plasticity. The aim of this study is toinvestigate the near-threshold fatigue crack propagation in Ti-6Al-4V alloy with harmonic structure. Ti-6Al-4Valloy powders were mechanically milled in a planetary ball mill to create fine grains at powder’s surface and theMM-processed powders were consolidated by SPS. K-decreasing fatigue crack propagation tests were conducted using the DC(T) specimen (ASTM standard) with harmonic structure under the stress ratios, R, from 0.1 to 0.8 in ambient laboratory atmosphere. After testing, fracture surfaces were observed using scanning electron microscope (SEM), and crack profiles were analyzed using electron backscatter diffraction (EBSD) to discuss the mechanism of fatigue crack propagation. Threshold stress intensity range, ?Kth, of the material withharmonic structure decreased with stress ratio, R, whereas the effective stress intensity range, ?Keff, showedconstant value for R lower than 0.5. This result indicates that the influence of the stress ratio, R, on ?Kth of Ti-6Al-4V with harmonic structure can be concluded to be that on crack closure. Compared to the compactprepared from as-received powders with coarse acicular microstructure, ?Kth value of the material withharmonic structure was low. This was because the closure stress intensity, Kcl, in the material with harmonicstructure was lower than that of the coarse-grained material due to the existence of fine grains. In addition, theeffects of the grain size on the fatigue crack propagation behaviors of Ti-6Al-4V alloy were investigated for thebulk homogeneous material. The effects of the stress ratio and the grain size on the fatigue crack propagation of the material with harmonic structure were quantified

Role of dynamic Jahn-Teller distortions in Na2C60 and Na2CsC60 studied by NMR

Through 13C NMR spin lattice relaxation (T1) measurements in cubic Na2C60, we detect a gap in its electronic excitations, similar to that observed in tetragonal A4C60. This establishes that Jahn-Teller distortions (JTD) and strong electronic correlations must be considered to understand the behaviour of even electron systems, regardless of the structure. Furthermore, in metallic Na2CsC60, a similar contribution to T1 is also detected for 13C and 133Cs NMR, implying the occurence of excitations typical of JT distorted C60^{2-} (or equivalently C60^{4-}). This supports the idea that dynamic JTD can induce attractive electronic interactions in odd electron systems.Comment: 3 figure

Superconductivity in a new layered triangular-lattice system Li2IrSi2

We report on the crystal structure and superconducting properties of a novel iridium-silicide, namely Li2IrSi2. It has a Ag2NiO2-type structure (space group R-3m) with the lattice parameters a = 4.028 30(6) Å and c = 13.161 80(15) Å. The crystal structure comprises IrSi2 and double Li layers stacked alternately along the c-axis. The IrSi2 layer includes a two-dimensional Ir equilateral-triangular lattice. Electrical resistivity and static magnetic measurements revealed that Li2IrSi2 is a type-II superconductor with critical temperature (Tc) of 3.3 K. We estimated the following superconducting parameters: lower critical field Hc1(0) ~ 42 Oe, upper critical field Hc2(0) ~ 1.7 kOe, penetration depth λ0 ~ 265 nm, coherence length ξ0 ~ 44 nm, and Ginzburg–Landau parameter κGL ~ 6.02. The specific-heat data suggested that superconductivity in Li2IrSi2 could be attributed to weak-coupling Cooper pairs

Structure and physical properties of Cs3+alpha C60 (alpha=0.0-1.0) under ambient and high pressures

The intermediate phases Cs3+alphaC60 (alpha=0.0-1.0), have been prepared, and their structure and physical properties are studied by x-ray powder diffraction, Raman, ESR, electric conductivity, and ac susceptibility measurements under ambient and high pressures. The x-ray powder diffraction pattern of Cs3+alphaC60 (alpha=0.0-1.0) can be indexed as a mixture of the body-centered-orthorhombic (bco) and cubic (A15) phases. The A15 phase diminishes above 30 kbar. The broad ESR peak due to the conduction electron (c-ESR) is observed only for the phases around alpha=0.0 in Cs3+alphaC60. The resistivity of the Cs3+alphaC60 (alphanot equal0) sample follows the granular metal theory and/or Sheng model even in the sample exhibiting a broad ESR peak. No superconducting transition is observed up to 10.6 kbar in Cs3+alphaC60 (alphanot equal0). These results present that bco phase of Cs3+alphaC60 (alpha=0) is a final candidate for a pressure-induced superconductor.</p