Showing papers by "Tokyo Institute of Technology published in 1994"

Atomic Control of the SrTiO3 Crystal Surface

Abstract: The atomically smooth SrTiO3 (100) with steps one unit cell in height was obtained by treating the crystal surface with a pH-controlled NH4F-HF solution. The homoepitaxy of SrTiO3 film on the crystal surface proceeds in a perfect layer-by-layer mode as verified by reflection high-energy electron diffraction and atomic force microscopy. Ion scattering spectroscopy revealed that the TiO2 atomic plane terminated the as-treated clean surface and that the terminating atomic layer could be tuned to the SrO atomic plane by homooepitaxial growth. This technology provides a well-defined substrate surface for atomically regulated epitaxial growth of such perovskite oxide films as YBa2Cu3O7-δ.

A stereo matching algorithm with an adaptive window: theory and experiment

Abstract: A central problem in stereo matching by computing correlation or sum of squared differences (SSD) lies in selecting an appropriate window size. The window size must be large enough to include enough intensity variation for reliable matching, but small enough to avoid the effects of projective distortion. If the window is too small and does not cover enough intensity variation, it gives a poor disparity estimate, because the signal (intensity variation) to noise ratio is low. If, on the other hand, the window is too large and covers a region in which the depth of scene points (i.e., disparity) varies, then the position of maximum correlation or minimum SSD may not represent correct matching due to different projective distortions in the left and right images. For this reason, a window size must be selected adaptively depending on local variations of intensity and disparity. The authors present a method to select an appropriate window by evaluating the local variation of the intensity and the disparity. The authors employ a statistical model of the disparity distribution within the window. This modeling enables the authors to assess how disparity variation, as well as intensity variation, within a window affects the uncertainty of disparity estimate at the center point of the window. As a result, the authors devise a method which searches for a window that produces the estimate of disparity with the least uncertainty for each pixel of an image: the method controls not only the size but also the shape (rectangle) of the window. The authors have embedded this adaptive-window method in an iterative stereo matching algorithm: starting with an initial estimate of the disparity map, the algorithm iteratively updates the disparity estimate for each point by choosing the size and shape of a window till it converges. The stereo matching algorithm has been tested on both synthetic and real images, and the quality of the disparity maps obtained demonstrates the effectiveness of the adaptive window method. >

Raman Scattering Study of Cubic–Tetragonal Phase Transition in Zr1−xCexO2 Solid Solution

Abstract: A structural phase transition between the cubic (space group, Fm3m) and tetragonal (space group, P42/nmc) phases in a zirconia–ceria solid solution (Zr1−xCexO2) has been observed by Raman spectroscopy. The cubic–tetragonal (c–t″) phase boundary in compositionally homogeneous samples exists at a composition X0 (0.8 < X0 < 0.9) at room temperature, where t″ is defined as a tetragonal phase whose axial ratio c/a equals unity. The axial ratio c/a decreases with an increase of ceria concentration and becomes 1 at a composition X′0 (0.65 < X′0 < 0.7) at room temperature. The sample with a composition between X0 and X′0 is t″ ZrO2. By Raman scattering measurements at high temperatures, the tetragonal (t″) → cubic and cubic → tetragonal phase transitions occur above 400°C in Zr0.2 Ce0.8O2 solid solution.

Efficient anonymous channel and all/nothing election scheme

Abstract: The contribution of this paper are twofold. First, we present an efficient computationally secure anonymous channel which has no problem of ciphertext length expansion. The length is irrelevant to the number of MIXes (control centers). It improves the efficiency of Chaum's election scheme based on the MIX net automatically. Second, we show an election scheme which satisfies fairness. That is, if some vote is distrupted, no one obtains any information about all the other votes. Each voter sends O(nk) bits so that the probability of the fairness is 1 - 2-k, where n is the bit length of the ciphertext.

Cooperative positioning with multiple robots

Abstract: A number of positioning identification techniques have been used for mobile robots Dead reckoning is a popular method, but is not reliable when a robot travels long distances or over an uneven surface because of variations in wheel diameter and wheel slippage The landmark method, which estimates the current position relative to landmarks, cannot be used in an uncharted environment The authors propose a new method called "cooperative positioning with multiple robots" For cooperative positioning, the authors divide the robots into two groups, A and B One group, say A, remains stationary and acts as a landmark while group B moves The moving group B then stops and acts as a landmark for group A This "dance" is repeated until the target robot position are reached Cooperative positioning has a far lower accumulated positioning error than dead reckoning, and can work in three-dimensions which is not possible with dead reckoning Also, this method has inherent landmarks and therefore works in uncharted environments This paper discusses the positioning accuracy of the authors' method with error variances for an example with three mobile robots >

Hydrothermal synthesis of biocompatible whiskers

Abstract: The preparation of non-toxic and biocompatible fibres or whiskers is one of the most urgent tasks today, because most of the fibrous materials which have been used (including asbestos which has been used for many years) are thought to be biohazardous. Whiskers of hydroxyapatite (Ca10(PO4)6(OH)2∶HAp), which is expected to be one of the best biocompatible materials, have been successfully synthesized by hydrothermal treatments of beta-tricalcium phosphate (beta-Ca3(PO4)2: beta-TCP) with citric acid. These whiskers were single crystals, elongated along the c-axis, with a length of 20–30 μm and a width of 0.1–1 μm. They were slightly calcium deficient (Ca/P molar ratio = 1.63) and they contained a trace of CO 3 2− in their structure.

Observation of a Very Energetic Cosmic Ray Well Beyond the Predicted 2.7 K Cutoff in the Primary Energy Spectrum.

Abstract: A very energetic cosmic ray of energy about (1.7-2.6) \ifmmode\times\else\texttimes\fi{} ${10}^{20}$ eV was observed by the Akeno Giant Air Shower Array on 3 December 1993 from the direction of galactic longitude $l=131\ifmmode^\circ\else\textdegree\fi{}$ and galactic latitude $b=\ensuremath{-}41\ifmmode^\circ\else\textdegree\fi{}$ within an error circle of 1.0\ifmmode^\circ\else\textdegree\fi{} radius. If this cosmic ray were a proton; its origin could be extragalactic. However, the distance of the source cannot be much more than a few times 10 Mpc due to the energy loss during its travel from interactions with universal background radiation.

Study of autonomous mobile sensing system for localization of odor source using gas sensors and anemometric sensors

Abstract: A new method for localization of an odor source is proposed. A probe with four anemometric sensors and four gas sensors has been developed so that the direction of an odor source can be determined. The anemometric sensors are used for measuring the direction of the air flow carrying odor molecules, and the gas sensors are used for detecting the gas-concentration gradient. Moreover, mounting the probe on a mobile stage with the probe under the control of a personal computer makes it possible to realize an autonomous mobile sensing system. An odor source has been successfully localized using this system in a wind tunnel.

New ultraviolet‐transport electroconductive oxide, ZnGa2O4 spinel

Abstract: ZnGa2O4 having the spinel structure was prepared, and optical and electrical properties of the material were measured. By the measurements of diffuse reflectance spectra, ZnGa2O4 was found to have a wider band gap (∼5 eV) than ITO (indium tin oxide). Electrical conductivity of the H2‐annealed ceramic of ZnGa2O4 was 3×101 S cm−1. Thus the ZnGa2O4 spinel was found to be a new UV‐transparent electronic conductor.

A Novel Combustor Based on Chemical-Looping Reactions and Its Reaction Kinetics

Abstract: A novel combustor based on controlled chemical-looping reactions without flame differs from the traditional combustor, in which the fuel is in direct contact with air. It allows CO2 to be easily recovered and promises advanced-level thermal efficiency for power generation. Promising results of laboratory experiments with the novel combustor are presented here. We found that NiO particles mixed with YSZ (yttria-stabilized zirconia) have very good properties with respect to oxidation rate, conversion, and physical strength. Especially, the rate of oxidation of Ni particles is increased significantly. The effects of YSZ content in the particle, the reaction temperature, the particle size, and the water vapor concentration were examined by studying the kinetic behavior of reactions. These promising results revealed high potential for applying chemical-looping combustion in a power-generation plant.

Formation of carbon films on carbides under hydrothermal conditions

Abstract: CARBON films find applications in a wide range of fields, ranging from microelectronics to materials science1. In ceramic matrix composites they confer the high strength and toughness needed for applications in aerospace, nuclear and automotive engineering2. Chemical vapour deposition is traditionally used to prepare carbon films, but it is relatively expensive, and not easily adapted to coating samples in the form of whiskers, platelets or powders. Here we report that silicon carbide, the most common component of composite ceramics, can be coated with carbon films of nanometre to micrometre thickness by hydrothermal treatment at 300–800 °C. We have applied the technique to SiC fibres, powders, platelets and single crystals, as well as to other carbides. Our method should provide a general and inexpensive route to high-toughness composites and lubricating coatings.

An analysis of bearingless AC motors

Abstract: Several types of AC bearingless motors are proposed. These bearingless motors have conventional four-pole stator windings and additional two-pole windings, whose currents produce radial forces acting on the rotor. General expressions of the machine inductances and radial forces are derived for the cylindrical rotor and salient-pole motors. No-load characteristics of laboratory squirrel-cage induction and reluctance-type synchronous bearingless motors are provided. The test motors were successfully driven by the control circuits. >

Nuclear structure calculation of β + β + , β + /EC and EC/EC decay matrix elements

Abstract: Nuclear matrix elements for double positron emisson (β + β +), positron emission/electron capture (β +/ EC) and double electron capture (EC/EC) in the 2νββ decay mode and forβ + β + andβ +/EC decay in the 0νββ mode are calculated for the experimentally most promising isotopes58Ni,78Kr,96Ru,106Cd,124Xe,130Ba and136Ce within pn-QRPA. We point out that the matrix element for the 2νβ +/EC decay differs from the 2νβ + β + matrix element, an effect not considered previously. For the neutrino accompanied decays our calculation predicts for theβ +/EC and the EC/EC mode half lives which are shorter typically by 4–7 orders of magnitude than those for the double positron emission. However, even for the best candidates typical values for 2νβ +/EC (2ν EC/EC) are still in the range of ∼1022 ((some) 1021) years. For 0νββ decay we have calculated all matrix elements relevant for both, the mass mechanism and the right-handed currents for the first time complete. A detailed discussion of the differences between the 0νβ +β+, the 0νβ +/EC and 0νβ − β − decay is given.

Coulomb Dissociation of B-8 and the Be-7(p, Gamma)b-8 Reaction At Low Energies

Abstract: The cross section for Coulomb dissociation of $^{8}\mathrm{B}$---the $^{208}\mathrm{Pb}(^{8}\mathrm{B}^{7}\mathrm{Be}p)^{208}\mathrm{Pb}$ reaction---was measured using a $^{8}\mathrm{B}$ radioactive beam of 46.5 MeV/nucleon energy, and the cross section for the $^{7}\mathrm{Be}(p,\ensuremath{\gamma})^{8}\mathrm{B}$ capture reaction was deduced at low energies; ${E}_{\mathrm{c}.\mathrm{m}.}=0.6\ensuremath{-}1.7$ MeV. The extracted astrophysical ${S}_{17}$ factors were found to be consistent with the values measured by Vaughn et al. and Filippone et al. This result encourages further experimental studies extended to lower relative energies for a new determination of the ${S}_{17}$ value relevant to the $^{8}\mathrm{B}$ solar neutrino flux.

Tectonic evolution of the ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic belts from central China

Abstract: In the Triassic suture between the Sino-Korean and Yangtze cratons, the Dabie metamorphic Complex in central China includes three tectonic units: the northern Dabie migmatitic terrane, the central ultrahigh-P coesite- and diamond-bearing eclogite belt, and the southern high-P blueschist-eclogite belt This complex is bounded to the north by a north-dipping normal fault with a Paleozoic accretionary complex and to the south by a north-dipping reverse fault with Yangtze basement plus its foreland fold-and-thrust sequence Great differences in metamorphic pressure suggests that these units reached different depths during metamorphism and their juxtaposition occurred by wedge extrusion of subducted old continental fragments These units were subsequently subjected to (i) Barrovian type regional metamorphism and deformation at shallow depths; (ii) intrusion of Cretaceous granitic plutons; and (iii) doming and segmentation into several blocks by normal and strike-slip faults A new speculative model of tectonic exhumation of UHP rocks is proposed

Critical properties of S= 1/2 antiferromagnetic XXZ chain with next-nearest-neighbour interactions

Abstract: We investigate numerically the critical lines and the critical properties of the fluid-dimer and the Neel-dimer transitions of the S= 1/2 antiferromagnetic XXZ chain with next-nearest interactions, and we confirm that the universality class of this model belongs to the quantum sine-Gordon model, as is expected from the bosonization. The method which we use in this paper to calculate the critical lines is free from the logarithmic corrections on the Kosterlitz-Thouless (K-T)-type transition line, which have made the K-T critical point difficult to obtain. By the use of this method, it is possible to determine the K-T critical line with high precision from small size data, and to identify the universality class.

Walking and running of the quadruped wall-climbing robot

Abstract: The development of a wall climbing robot which is able to move over the surface of "3-dimensional terrain", a terrain including floor, wall, ceiling of any kinds of structures with agility and terrain adaptability is strongly demanded in many industries. The conventional wall-climbing machines were far from fulfilling the demand, the authors thus have been developing a wall-climbing robot with four-terrain-adaptive legs and basic mobilities were already demonstrated by the manufactured prototype model NINJA-I. However, as there are almost no examples of wall-climbing quadrupedal animals and conventional machines, the gait control method specific for the quadruped wall-climbing is not at all known by now. As the first step to consider a general gait problem of a quadruped wall-climbing robot, this paper investigates a gait of the robot on a vertical and flat wall. The gait is analyzed with the criterion to maximize the locomotion speed under the constraints of predetermined conditions of the supporting-legs position, order and phases of swing legs to prevent turn over motion. As a result of the analysis, the optimal standard gait, named "Wall Gait", is shown to maintain foot posture of /spl Lambda/ shape and moves the leg in the order of leg1-leg2-leg4-leg3 in static walk and the order of "pace" in dynamic walk. >

Particulate silicon nitride-based composites

Abstract: In an attempt to optimize the structure and properties of silicon nitride ceramics, a variety of novel processing techniques and materials compositions have evolved over the last 15 years. Among the most important, was the development of various silicon nitride-based composites. A review of particulate, silicon nitride-based composites other than whisker- or platelets-reinforced, is presented. Materials based on silicon nitride and SiAlONs, with additions of carbides, nitrides and borides of transition metals are described. Special emphasis is placed on TiN- and TiC-containing ceramics. The manufacture of composites by hot pressing, reaction sintering, pressureless and gas-pressure sintering is discussed. The data on properties, including conductivity, density, Young's modulus, strength, fracture toughness, hardness, thermal expansion, wear, creep and oxidation resistance are presented. Analysis of actual and potential uses of the selected composites demonstrates that the particulate composites are very promising as tool, structural and electronic materials.

Kinetics of Chain Coupling at Melt Interfaces

Abstract: Monodispese carboxylic acid-terminated polystyrene (PS-COOH) and epoxy-terminated poly(methyl methacrylate) (PMMA-E) heve been synthesized by anionic polymerization. To compare with coupling in homogeneous blends, PS-E was also synthesized. The amount of block copolymer formed by coupling of PS-COOH with PMMA-E to form the ester was measured by SEC. PMMA-E was melt mixed with PS-COOH with a maximum shear rate of 20 s -1 . PMMA-E particle diameter was 0.6 μm and stable after 5 min of mixing at 180°C. The block copolymer content increased to 2% at 20 min. The reaction is slow enough that the chain ends can sample the interface many times before reacting

Electrochemical Reduction of CO 2 on a Cu Electrode under High Pressure Factors that Determine the Product Selectivity

Abstract: The selectivity of the electrochemical reduction products of CO[sub 2] on a Cu electrode in aqueous KHCO[sub 3] solution depended remarkably on the CO[sub 2] pressure (<60 atm), stirring condition, and the current density. As the flux of CO[sub 2] to the Cu electrode surface was increased by increasing CO[sub 2] pressure and/or by stirring, the main reduction product was changed in the order of H[sub 2] [yields] hydrocarbons [yields] CO and/or HCOOH. On the other hand, the selectivity of the reduction products was changed in the order of CO and/or HCOOH [yields] hydrocarbons [yields] H[sub 2] by increasing the current density. From these results, it was concluded that the balance between the flux of CO[sub 2] from the bulk solution to the electrode surface and the current density determines which reduction products are produced. Hydrocarbon formation was preferential when the current density was comparable to the maximum CO[sub 2] flux under given condition. The partial current density for maximum hydrocarbon formation occurred at 375 mA cm[sup [minus]2] under CO[sub 2] pressure at 30 atm.