Studies of Both Intralayer and Interlayer Electrodynamics of Bi2Sr2CaCu2O y in the Superconducting State

We studied the intralayer and interlayer electrodynamics of the superconducting Bi ₂ Sr ₂ CaCu ₂ O _y single crystals in the microwave and millimeter wave regions. The c-axis superfluid density fraction _s ^c shows a more rapid growth than _s ^ab just below T _c and a weaker temperature dependence at low temperatures. These features suggest the anisotropic growth mechanism of _s . The temperature dependence of _ab ¹ shows a large increase below T _c with a broad peak around 20 K. However, to discuss the detailed behavior of ₁ ^c or the anisotropy of conductivity _ab ¹ / _c ¹ in the superconducting state, much more careful measurement is required in the c-axis direction.     

Force control and exponential stabilisation of one-link flexible arm

In this paper, we discuss a force control problem for a constrained one-link flexible arm. To solve the force control problem, we propose a simple boundary feedback controller that consists of the bending moment at the root of the flexible arm and its time derivative. The striking point is that information about the force and the rotational angle of the motor is not necessary for the implementation of the controller, and thus we do not need a force sensor or encoder in the construction of the controller. The exponential stability of the closed-loop system is then provided using the energy multiplier method. We describe several experiments carried out to investigate the performance of the proposed controller.     

Broadband method for precise microwave spectroscopy of superconducting thin films near the critical temperature

We present a high-resolution microwave spectrometer to measure the frequency- dependent complex conductivity of a superconducting thin film near the critical temperature. The instrument is based on a broadband measurement of the complex reflection coefficient, S 11, of a coaxial transmission line, which is terminated to a thin film sample with the electrodes in a Corbino disk shape. In the vicinity of the critical temperature, the standard calibration technique using three known standards fails to extract the strong frequency dependence of the complex conductivity induced by the superconducting fluctuations. This is because a small unexpected difference between the phase parts of S 11 for a short and load standards gives rise to a large error in the detailed frequency dependence of the complex conductivity near the superconducting transition. We demonstrate that a new calibration procedure using the normal-state conductivity of a sample as a load standard resolves this difficulty. The high quality performance of this spectrometer, which covers the frequency range between 0.1 and 10 GHz, the temperature range down to 10 K, and the magnetic field range up to 1 T, is illustrated by the experimental results on several thin films of both conventional and high temperature superconductors.     

On the reachability of a version of graph-rewriting system

In this paper, we consider a problem on the reachability of a version of graph-rewriting system. It deals with 3-regular graphs with states for the vertices. They differ from ordinary graphs so that a cyclic order of the edges is assigned on each vertex. Graphs are rewritten with a rule set of graph rewriting. For any two such connected graphs with at least four vertices of distinct states, we show that there exists a rule set that rewrites one to the other.     

Effect of equal-channel angular pressing on pitting corrosion resistance of anodized aluminum-copper alloy

The effect of equal-channel angular pressing(ECAP) on the pitting corrosion resistance of anodized Al-Cu alloy was investigated by electrochemical techniques in a solution containing 0.2 mol/L AlCl₃ and also by surface analysis. Anodizing was conducted for 20 min at 200 and 400 A/m² in a solution containing 1.53 mol/L H₂SO₄ and 0.018 5 mol/L Al₂(SO₄)₃·16H₂O at 20 °C. Anodized Al-Cu alloy was immediately dipped in boiling water for 20 min to seal the micro pores present in anodic oxide films. The time required before initiating pitting corrosion of anodized Al-Cu alloy is longer with ECAP than without, indicating that ECAP process improves the pitting corrosion resistance of anodized Al-Cu alloy. Second phase precipitates such as Si, Al-Cu-Mg and Al-Cu-Si-Fe-Mn intermetallic compounds are present in Al-Cu alloy and the size of these precipitates is greatly decreased by application of ECAP. Al-Cu-Mg intermetallic compounds are dissolved during anodization, whereas the precipitates composed of Si and Al-Cu-Si-Fe-Mn remain in anodic oxide films due to their more noble corrosion potential than Al. FE-SEM and EPMA observation reveal that the pitting corrosion of anodized Al-Cu alloy occurs preferentially around Al-Cu-Si-Fe-Mn intermetallic compounds, since the anodic oxide films are absent at the boundary between the normal oxide films and these impurity precipitates. The improvement of pitting corrosion resistance of anodized Al-Cu alloy processed by ECAP appears to be attributed to a decrease in the size of precipitates, which act as origins of pitting corrosion.     

An efficient algorithm for generating manipulator inertia matrix using the minimum set of dynamics parameters

This article presents an efficient algorithm for computing the inertia matrix of rigid serial manipulators. The derivation of the algorithm is based on the closed-form formulation of the force and moment exerted on a link using a minimum set of dynamic parameters of the manipulator model. The minimum set of dynamic parameters can be derived completely from the original dynamic parameters using the recursive re-grouping method before starting the simulation and the control. The proposed computation method is suitable for the control and the simulation based on parameter estimates because the minimum set of dynamic parameters is an identifiable parameter set. The computational efficiency of the proposed methods is compared with other published methods. It is shown that the proposed algorithm is the most efficient approach for serial manipulators. As an example, the number of computations for the inertia matrix of a manipulator with n rotational joints is 11n²+9 n − 35 multiplications and 7n²+ 23 n − 57 additions by reformulating the dynamic model using the minimum set of dynamic parameters. © 1996 John Wiley &, Sons, Inc.     

High-efficiency μc-Si/c-Si heterojunction solar cells

P-type microcrystalline silicon (μc-Si (p)) on n-type crystalline silicon (c-Si(n)) heterojunction solar cells is investigated. Thin boron-doped μc-Si layers are deposited by plasma-enhanced chemical vapor deposition on CZ-Si and the V_oc of μc-Si/c-Si heterojunction solar cells is higher than that produced by a conventional thermal diffusion process. Under the appropriate conditions, the structure of thin μc-Si films on (1 0 0), (1 1 0), and (1 1 1) CZ-Si is ordered, so high V_oc of 0.579 V is achieved for 2×2 cm² μc-Si/multi-crystalline silicon (mc-Si) solar cells. The epitaxial-like growth is important in the fabrication of high-efficiency μc-Si/mc-Si heterojunction solar cells.     

Electron‐beam‐induced discharge phenomena of teflon films for space use

We investigated the discharge phenomena of Teflon FEP (fluorinated ethylene propylene) films used as thermal control material of spacecraft by electron‐beam irradiation simulating hot plasma in space. FEP films of two thicknesses, 25 and 127 μm, were tested. The results obtained were as follows.

• (1) In 127‐μm‐thick FEP film, a surface discharge triggered by high electric field at the triple junction of the edge of the metal frame occurred.
• (2) In 25‐μm‐thick FEP film, punchthrough discharge accompanied by surface flashover occurred.
• (3) Discharge frequency increased as nearly the 1/2 power of the electron‐beam current density under constant irradiation energy. On the other hand, it increased linearly with the irradiation energy under constant beam current density, but with sufficient threshold electron energy to cause discharge.

These results were explained by comparison between the surface electric field and the bulk electric field in FEP film obtained analytically by using a two‐dimensional charging model. © 1999 Scripta Technica, Electr Eng Jpn, 129(1): 10–19, 1999     

New Si–C bond forming reactions over solid-base catalysts

The reactions of silanes with carbanions generated on the surface of solid bases bring about the nucleophilic substitution at the Si atom to form Si–C bonds. The reaction of alkynes with silanes afforded alkynylsilanes. For example, the reaction of tert-BuCCH or n-BuCCH with Et₂SiH₂ in the presence of KNH₂/Al₂O₃ gave tert-BuCCSiEt₂H and n-BuCCSiEt₂H in a 77% and 67% yield, respectively, at 329 K. Toluene also reacted with Et₂SiH₂ at 329 K to yield benzyldiethylsilane in a 85% yield. The reactions of 1-alkynes with Me₃SiCCH in the presence of KNH₂/Al₂O₃ or KF/Al₂O₃ resulted in a novel type of metathesis reaction between the two alkynes. For example, the reaction of PhCCH with Me₃SiCCH afforded PhCCSiMe₃ and HCCH in a high yield. These new types of base-catalyzed reactions provide new synthetic routes for Si–C bond formation.     

Reactivity of cyclosiloxane with 3,3,4,4,5,5,6,6,6‐nonafluorohexyl group and its application to fluorosilicone synthesis

The reactivity of cyclosiloxane with 3,3,4,4,5,5,6,6,6‐nonafluorohexyl group and its application to fluorosilicone synthesis were studied. In contrast to the polymerization of the commercially available 1,3,5‐tris(3,3,3‐trifluoropropyl)‐1,3,5‐trimethylcyclotrisiloxane (CF₃–D3), the polymerization of 1,3,5‐tris(3,3,4,4,5,5,6,6,6‐nonafluorohexyl)‐1,3,5‐trimethylcyclotrisiloxane (C₄F₉–D3) with sodium hydroxide yielded 1,3,5,7‐tetrakis(3,3,4,4,5,5,6,6,6‐nonafluorohexyl)‐1,3,5,7‐tetramethylcyclotetrasiloxane {[C₄F₉CH₂CH₂(CH₃)SiO]₄ (C₄F₉–D4)} as the major product, which was the result of the depolymerization by a backbiting mechanism. On the other hand, the polymerization of C₄F₉–D3 with trifluoromethanesulfonic acid yielded a polymer with good reproducibility, although the distribution of molecular weight tended to be bimodal. C₄F₉–D3 was also successfully copolymerized with octamethylcyclotetrasiloxane (D4). The properties of the obtained copolymers changed almost linearly with the amount of [C₄F₉C₂H₄(CH₃)SiO] units, except for the surface tension. The surface tension of the copolymer containing more than 50% [C₄F₉C₂H₄(CH₃)SiO] units by weight was almost as low as that of the homopolymer. When the copolymer containing 50% [C₄F₉C₂H₄(CH₃)SiO] units by weight was examined for an antifoaming agent, it worked as effectively as the homopolymer in the toluene foaming system. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3333–3340, 2001