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The present basis for the ephemeris of Mars in the National Ephemerides is the theory of S. Newcomb (1898) as amended by the corrections of Ross (1917). These amendments by Ross, however, are empirical in nature and therefore the present ephemeris of Mars does not have a strictly gravitational basis. In order to provide a gravitationally consistent basis for the ephemeris of Mars, Clemence (1949, 1961) constructed a new general perturbation theory based on the final elements of Mars as derived by Newcomb for the epoch 1850. To test the adequacy and accuracy of this new theory, Clemence compared it against 87 observations from 1802-1839 and 1931-1950. This provided provisional values of the constants (without secular variation) for his new theory. These provisional elements and Clemence's theory were used to produce a heliocentric ephemeris of Mars for the period 1800-2000 (Duncombe and Clemence 1960, Duncombe 1964).
We investigated electronic structure of one-dimensional biradical molecular chain which is constructed by exploiting the covalency between organic molecules of a diphenyl derivative of s-indacenodiphenalene (Ph2-IDPL). To control the crystallinity, we used gas deposition method. Ultraviolet photoelectron spectroscopy (UPS) revealed developed band structure with wide dispersion of the one-dimensional biradical molecular chain.
The electrical properties of epitaxial La0.8Sr0.2MnO3 films on a SrTiO3(STO) substrate prepared by changing the laser fluence, the irradiation time and the film thickness using excimer laser metal organic deposition(ELMOD) at 500/cm2, the film showed a 3.9 % maximum temperature coefficient of resistance (TCR: defined as 1/R•dR/dT) which was obtained by the ArF laser irradiation at 80mJ/cm2 for 10min. At a constant fluence of 80mJ/cm2, the Tm (temperature of the maximum TCR) of the La0.8Sr0.2MnO3 films increased from 225K to near 250K with an increase in the irradiation time to 90min at which the TCR was almost 3.9%. The La0.8Sr0.2MnO3 film that showed the maximum TCR of 4.0% at 275K was obtained by the ELMOD process at 500°C using the optimum conditions (Flence:80mJ/cm2, Irradiation time: 90min, Film thickness: 80nm).
The orthorhombic-tetragonal YBa2Cu3O7-δ phase boundary in the δ-T diagram was determined by the detailed isobar TG measurement under the oxygen partial pressures of 1 to 0.01 atm. The phase boundary was found not to be located at 5 = const, but to have a slope of dδ/dT∼−4.7 × 10-4K-1. Using the same method, the transformation temperatures of a series of lanthanide substituted systems were measured at 1 atm. O2. The transformation temperature increased with increasing the atomic number of the lanthanide element. All these experimental results are well explained in terms of the order-disorder transformation caused by the repulsion energy between the nearest neighbor oxygen atoms on the Cu plane sandwiched by Ba planes.
Tc variations observed in some Tl-based superconductors were studied. Clear correlations were found between Tc, carrier concentration, and c-axis length. In particular, for Tl2Ba2CuO6, a decrease in oxygen content of about 0.1 per formula unit, which corresponded to a decrease in hole concentration of about 0.2, increased Tc up to about 80K from a metallic non-superconductor, and elongated the c axis by about 0.4%. In addition, as Tc values increased systematic changes in metal-sheet separations were observed. Tc variations caused by a change in oxygen content were also observed in Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10. It was demonstrated that superconductivity appears in a certain appropriate range of carrier concentration similar to those observed in other high-Tc superconductors.
Sr1−xNdxCuOy thin films are grown on SrTiO3 substrates by rf-magnetron sputtering and pulsed-laser deposition. The sputter-deposited film with x=0 has an “infinite-layer” structure whose lattice constants are: α=0.390 nm and c=0.347 nm. When x is larger than 0.1, the films contain a phase of the Sr14CuO24O41 structure. The laser-deposited films of Sr1−xNdxCuOy with x≤.075 were single phase of the “infinite-layer” structure. The lattice parameter c decreased and the lattice parameter αincreased, as the Nd content, x, increased. The films with α=0.10 and 0.125 exhibited superconducting onset temperatures around 26 K. Weak Meissner signals were observed for these films at temperatures below 30 K.
Tl2Ba2Cuo6+δ(T1-2201) single crystals are prepared by a KCI flux method. In-plane and out-of plane resistivities (ρabρc as well as the in-plane Hall coefficient are measured for the single crystal samples with various 7c's. The ρc values are as large as ∼10−1 Ω cm, which is larger than that of YBa2Cu3O7, but smaller than that of Bi2Sr2CaCu2O8. Temperature dependences of ρc show metallic behaviors for both normal metallic and 75-K superconducting samples. Temperature dependence of in-plane resistivity par changes from ∼T2 to ∼T1 with increasing Tc In-plane Hall coefficient RH shows a characteristic maximum at about 100 K for all samples. Although both ρab and RH have rather a complicated temperature dependence, inverse Hall mobility μH(=ρab/RH always exhibits clear T2 dependence for all samples. These results suggest that the intrinsic scattering rate of this material varies as ∼T2, just like in an ordinary Fermi liquid, and that the carrier concentration actually changes with temperature like that observed in nH(=1/RHe).
The surprisingly high Tc for the superconductivity of alkali doped C60 has spurred wide interest in understanding its mechanism [1–7]. We first report the superconductive properties of CsxRbyC60 which has a Tc as high as 33 K when x=2 and y=1 in the feed [4, 5]. SQUID measurements show that in this material the coherence length is 45 A and the penetration depth about 1, 800 A . It has now been proven that the observed increase in the Tc with the size of the alkali dopant is due to the increase in the lattice constant . This is most likely due to the changes in the density of states at the Fermi level. The other important parameter according to BSC theory is the phonon which mediates the electron-electron coupling. In the second part of this paper we present recent results which show that the Tc is indeed strongly influenced by this parameter . The isotope effect is unexpectedly strong on the Tc.
Ba1-xSrxTiO3 thin films have been deposited on Pt/Ti/SiO2/Si substra by the pulsed ArF laser deposition method. Deposition conditions, such as ambient gas and substrt temperatze, have been optmized to rrxove crystallinepropesty. Fe oelectric p e phasehasbeenobtainod ithe BSTthin filns deposited above 500°C in Q2 gas havingpressure ofabout 13Pa. Using N2O gas instead of O2 gas improved the crystallinity, because highly chemical active oxygen radicals produced due to ultraviolet inadiation of the laser. Doping of Bi ranging around 2% fills of the role of decrease leakage current of BST thin films. Temperature dependence of the dielectric constant (εr) shows a sharp change, peaking aroumd room temperature. The peak point exists below 25°C in the ratio of Ba/Sr=1.1 film, and shills above 50°C in Ba/Sr=5.7 film. When the Ba/Sr ratio is 1.4 the dielectric peak exists near 27°C and is very sharp. The maxinium differentW rate of dielectric constanttversus temperature is the largest in Ba/Sr=1.4 film and is about 100K-1. This value is equivalent to apyroelectric coefficient of 1.8 × 10-7 C/cm2K, which is almost the same as that of LiTaO3 single crystl, a typical pyroelectric material.
Structural and ferroelectric properties of stoichiometric SrBi2Ta2O9 and Sr-deficient-and-Bi-excess Sr0.8Bi2.2Ta2O9 bulk ceramics materials are studied. The ferroelectric Curie temperatures for SrBi2Ta2O9 and Sr0.8Bi2.2Ta2O9 are 300 and 400°C, respectively. Structure analysis by neutron powder diffraction reveals that Bi2O2 layer and TaO6 octahedra are considerably distorted and that atomic displacement along the a-axis causes ferroelectric spontaneous polarization. In Sro8Bi22Ta2O9, both Bi-substitution and cation-vacancies exist at the Sr-site. The calculated polarization of Sr0.8Bi2.2Ta2O9 is higher than that of the stoichiometric sample, which is consistent with observations of remanent polarization in thin-film capacitors. The Bi-substitution and the cation-vacancies at the Sr site enhance structural distortion in the TaO6 octahedron and lead to the higher Curie temperature and the higher ferroelectric spontaneous polarization.
Thin-film samples of La1-xSrxMnO3 (x = 0.20 – 0.30) were grown by pulsed-laser deposition using various target compositions, substrate materials, growth temperatures, oxygen partial pressures, and laser-pulse repetition rates. The crystal structure and the transport and magnetic properties of these films were then examined. Of the growth conditions, the oxygen partial pressure (Po2) had the greatest influence on the electrical and magnetic properties. Films grown under a low Po2 had a low ferromagnetic transition temperature (Tc) and a wide resistive transition width. None of the heat treatments done after growth improved these films’ quality. The film morphology was significantly affected by the substrate material. Our x-ray diffraction analysis and AFM measurements revealed that the films deposited on both MgO (100) and LaAlO3 (100) were epitaxially grown but contained defect structures. In contrast, grain-free thin films were epitaxially grown on the SrTiO3 (100) substrates. The surface roughness of films grown on SrTiO3 was less than 0.3 nm, even for films up to 150 nm thick. Under optimized growth conditions, as-deposited films for x ≥ 0.2 showed a sharp transition in resistivity at Tc. Magnetoresistance at far below Tc was as low as that reported for single-crystal sample. Since large magnetoresistance was often observed in polycrystalline samples and believed to be a grain boundary effect, these results indicate the high quality of the films grown on the SrTiO3 substrates.
Real-time spectroscopic ellipsometry (RTSE) method was applied to study thermal cleaning process of silicon surfaces for epitaxial growth by ultra-high vacuum chemical vapor deposition (UHV-CVD). For the first time, in-situ observation of oxide decomposition process under Si2H6 ambience was carried out. The substrates with thin oxide formed by wet chemical treatment were heated up by infrared heater under UHV or under Si2H6 ambience in an UHV-CVD chamber and the oxide decomposition processes were observed by RTSE. Ellipsometric parameters Psi and Delta increase with the progress of oxide decomposition process and become constant with the completion of the decomposition. It was found that the oxide decomposition process consists of two phases and rate-determing processes are different in each phase. It was also found that Si2H6 lowers the activation energies of oxide decomposition process in each phase.
We discuss some aspects of solid-state chemistry concerning ferroelectric SrBi2Ta2O9, (SBT). Crystal structure analysis by high-resolution neutron diffraction revealed considerable structural distortion in the SBT materials. This distortion, which consists of large atomic displacements of constituent ions, causes large ferroelectric spontaneous polarization. The structural distortion is more pronounced in Sr-deficient-and-Bi-excess material Sr0.8Bi2.2Ta2O9 than in stoichiometric SBT, leading to the larger remanent polarization. The enhanced structural distortion is explained in terms of an “ionic size effect” at the A-cation site. This effect was apparently observed in a series of compounds of ABi2Ta2O9 (A=Ca, Sr, and Ba) with different size A-site cations. On the other hand, analysis of chemical reactions of SBT gave important information on the degradation of the SBT capacitors and on the reaction between the SBT materials and a Pt electrode during device fabrication. The degradation of SBT in an H2- containing reducing atmosphere and its recovery by subsequent annealing in oxygen have been reproduced experimentally by using bulk ceramics and analyzed by thermogravimetric and x-ray- diffraction measurements. SBT decomposes into Bi metal or Bi-Pt alloy in H2 by oxygen dissociation. In the presence of Pt, the SBT degradation and the re-crystallization processes differ from those for SBT alone.
We have confirmed that grain boundaries are related to leakage problems in Ta2O5/SiON capacitors for high dielectric DRAMs. XRD studies using an intensity ratio of (200) to (001) showed that the crystallographic structure of Ta2O5 film was strongly dependent on preparation conditions. As the (200) oriented grains grew faster than the other grains, it became important to control its grain growth in forming uniform grain boundaries. TEM observation has shown that Ta2O5 film with a high intensity ratio of (200) to (001) was made up of large size grains and had SION interface intruding into grain boundaries. By using the current-mode AFM, we could monitor leakage current directly through grain boundaries on Ta2O5 film.
To fill the gap between molecular design and the architecture of three-dimensional functional structures, we propose novel hyper-structured molecules (HSMs) based on welldefined and topologically controlled molecular systems. To this end we have developed carbazole dendrimers, trimers, cyclic oligomers and chromogenic calixarenes as HSMs. Photorefractivity was selected as the primary target function of these HSMs. Oligomers developed in our laboratory exhibit intrinsic photocarrier generation, transport, electro-optic, film-forming and poling properties. These multifunctional properties allow us to demonstrate optical image processing using optical phase conjugation. The topological shapes of indoaniline-derived calixarenes were studied by hyper-Rayleigh scattering. The two indoaniline moieties in calixarene derivatives were pre-aligned so as to enhance the net molecular hyperpolarizability. Besides dendric oligomers, cyclic oligomers can be used as a molecular platform which allows molecular level tuning of shape, size and topology for superior opto-electronic functions.
Ti-Ni shape memory alloy is used for bio-medical and industrial fields even if Ni is a substance which has strong allergic nature and carcinogenicity to a human body, then, Ti-Ni alloy system is in a prohibition tendency in the medical field in Europe in recent years. Therefore, Ni-free shape memory alloy is desired in the near future medical field. In this research, we pay our attention to the Ti-Nb alloy which has shape memory as well as superelastic effects. The Ti-Nb fiber was fabricated by using the ark melting and nozzelless rapid solidification method. The fiber samples were used to investigate the following characteristics relating with shape memory effect, that is to say, (1) cross sectional microstructure observation, (2) DSC(phase transformation temperature changes), (3) temperature-shape recovery relationship. Moreover, heat-treated effect on shape recovery phenomena was observed in comparison with the starting bulk material. Finally, the fundamental discussion to correlate the rapid-solidification process condition with the characteristic of Ti-Nb shape memory alloy for bio-medical engineering application was conducted.
Directional information should play a significant role
for a firm detection of the galactic dark matter.
We developed a prototype three-dimensional gaseous tracking device
for a direction-sensitive dark matter direct detection.
We investigated the performance of the prototype detector and demonstrated
a direction-sensitive dark matter search experiment in a
We set the first limit
on the spin-dependent WIMP (Weakly Interacting Massive Particles)-proton cross s
ection by a direction-sensitive method.
Coherent low-frequency oscillations whose frequency is lower than the ion plasma frequency are generated by a mesh grid with negative d.c. bias in a double-plasma device. The frequency is inversely proportional to the one-quarter power of the grid voltage under a fixed plasma density, and is proportional to the ion plasma frequency when the grid bias is kept constant. With potential profiles near the grid, which are measured by an emissive probe, the transit time of ions is numerically calculated. The inverse of the transit time agrees well with the oscillation frequency. The oscillation is considered to be excited by a klystron bunching effect of incident ions towards the ion-rich sheaths.