Some factors for the space charge formation in polyethylene

Information on space-charge behavior in thick insulated samples aids in understanding the dc characteristics of polymer-insulated dc cables. The pulsed electroacoustic method is used to investigate several space charge formation factors in 2 mm-thick polyethylene (PE). The following results were obtained. For measurement factors: (1) A polymeric semiconducting electrode provides a more accurate measurement than does a metal electrode as a result of better matching of acoustic impedance with PE. (2) Within a dc electrical stress range of several tens kV/mm, the space charge distributions under and after dc voltage application are almost the same; this is due to a comparatively long time of space-charge decay. (3) The space-charge distribution of a plate sample agrees with that of a cable sample having the same insulation thickness. For insulating material factors: (1) The amount of space charge in crosslinked polyethylene (XLPE) is much larger than that in low-density PE (base of XLPE). The space charge of XLPE continues to increase even after dc voltage application (24 h); that of LDPE reaches equilibrium with a few hours. (2) The aforementioned space charge difference between XLPE and LDPE is assumed to be caused by ionic impurities in XLPE, not by the additives themselves (acetophenon and cumylalcohol as byproducts of cross linking and antioxidant).     

Effects of the additions of B,P, dSn,and Sb on oxygen assisted hydrogen embrittlement of nickel

Effects of additions of B, P, Sn, and Sb on hydrogen embrittlement of nickel were examined on specimens cathodically charged with hydrogen. Tensile specimens were annealed either in vacuum or in a dry hydrogen gas. Undoped, Sn-doped, and Sb-doped materials annealed in vacuum revealed high susceptibility to intergranular hydrogen embrittlement, while the susceptibility was greatly reduced when the materials were annealed in hydrogen. The deleterious effect of vacuum annealing was proposed to result from grain boundary penetration of oxygen from the annealing environment. Additions of a small amount of B and P almost completely suppressed the IGHE of specimens annealed in vacuum. It is suggested that the effect of these elements on grain boundary penetration of oxygen is an important factor for their beneficial effects on IGHE. Addition of Sn somewhat increased the ductility of hydrogen charged specimens annealed both in vacuum and in hydrogen, indicating that this element is not deleterious. Addition of Sb increased the embrittlement susceptibility of specimens annealed in hydrogen. However, the deleterious effect of Sb was not serious in spite of the high concentration of Sb that was examined.     

Electrical properties of polyimide Langmuir-Blodgett films sandwiched between superconducting electrodes: detection of microwaves

We have examined the electrical properties of ultrathin insulating layers of cadmium arachidate (C₂₀), polyamic acid long alkyl amine salts (PAA) and polyimide (PI) by using tunnel junctions with structures of (Pb-Bi)/PAA (or C₂₀)/(Pb-Bi), Au/PI/(Pb-Bi) and Au/PI/Au. Typical current-voltage (I-V) characteristics of weakly coupled superconductors were obtained for (Pb-Bi)/PAA (or C₂₀)/(Pb-Bi) junctions with one, two or three deposited layers at a temperature below the critical temperature of a Pb-Bi alloy. On the contrary, typical I-V characteristics of tunnel junctions were obtained for Au/PI/(Pb-Bi) and Au/PI/Au junctions, when the number of deposited layers is greater than about 30. Finally, we concluded that the efficiency of detecting microwaves is excellent in (Pb-Bi)/PAA (or C₂₀)/(Pb-Bi) junctions, although bridging filaments exist in the PAA (or C₂₀) Langmuir-Blodgett (LB) layers, and that the PI LB layers become good electrical insulating spacers when the thickness of deposited layers is more than about 11 nm.     

Fibrous hydroxyapatite grown in the gel system: effects of pH of the solution on the growth rate and morphology

In the preparation of fibrous hydroxyapatite (HAp), using the gel system consisting of agar gel containing calcium nitrate and over-layered (NH₄)₂HPO₄ solution, the pH of the solution was found to greatly influence the growth rate and morphology of the resultant products. In particular, a pH value of about 9–10 produced straight fibrous HAp in the shortest time. Also, the Ca/P molar ratio of the product increased with the pH value of the starting solution. The growth rate and morphology of the product were correlated to the ion species present in the solution at different pHs.     

Transparent ultrafine Yb3+:Y2O3 laser ceramics fabricated by spark plasma sintering

Conventional ceramic processing techniques do not produce ultrafine‐grained materials. However, since the mechanical and optical properties are highly dependent on the grain size, advanced processing techniques are needed to obtain ceramics with a grain size smaller than the wavelength of visible light for new laser sources. As an empirical study for lasing from an ultrafine‐grained ceramics, transparent Yb³⁺:Y₂O₃ ceramics with several doping concentrations were fabricated by spark plasma sintering (SPS) and their microstructures were analyzed, along with optical and spectroscopic properties. Laser oscillation was verified for 10 at.% Yb³⁺:Y₂O₃ ceramics. The laser ceramics in our study were sintered without sintering additives, and the SPS produced an ultrafine microstructure with an average grain size of 261 nm, which is about one order of magnitude smaller than that of ceramics sintered by conventional techniques. A load was applied during heating to enhance densification, and an in‐line transmittance near the theoretical value was obtained. An analysis of the crystal structure confirmed that the Yb³⁺:Y₂O₃ ceramics were in a solid solution. To the best of our knowledge, this study is the first report verifying the lasing properties of not only ultrafine‐grained but also Yb‐doped ceramics obtained by SPS.     

Design and Synthesis of A‐Ring Simplified Pyripyropene A Analogues as Potent and Selective Synthetic SOAT2 Inhibitors

Currently, pyripyropene A, which is isolated from the culture broth of Aspergillus fumigatus FO‐1289, is the only compound known to strongly and selectively inhibit the isozyme sterol O‐acyltransferase 2 (SOAT2). To aid in the development of new cholesterol‐lowering or anti‐atherosclerotic agents, new A‐ring simplified pyripyropene A analogues have been designed and synthesized based on total synthesis, and the results of structure–activity relationship studies of pyripyropene A. Among the analogues, two A‐ring simplified pyripyropene A analogues exhibited equally efficient SOAT2 inhibitory activity to that of natural pyripyropene A. These new analogues are the most potent and selective SOAT2 inhibitors to be used as synthetic compounds and attractive seed compounds for the development of drug for dyslipidemia, including atherosclerotic disease and steatosis.     

A method for personal expertise-independent evaluation of image resolution in scanning electron microscopy

The two conventional methods currently employed for the evaluation of image resolution in scanning electron microscopy are the gap method and a fast Fourier transform (FFT) method. These can be highly dependent on personal expertise on the distinction between signal information and noise contained in a micrograph. Hence, the present paper proposes an alternative method (referred to as a contrast-to-gradient (CG) method) that can determine the image resolution of a micrograph without requiring personal expertise on the judgment of noise. The image resolution in the CG method is defined as a weighted harmonic mean of the local resolution, which is proportional to the quotient of the threshold contrast divided by the local gradient. The local gradient is calculated from the quadratic function that best fits the local pixel intensities over 5 x 5 pixels. It has been shown that the CG method, compared with the FFT method, has a broader range of applications for various types of images, such as low-contrast, noise-containing, filter-processed, highly directional, and quasi-periodic feature images.     

The development of pivot bearing with multiple degrees of freedom: 3rd report: Examination for specification to improve bearing stiffness by finite element method analysis and its inspection by experiment

This paper deals with the examination of specifications to improve the performance of a pivot bearing with two degrees of freedom by finite element method (FEM). As the target of estimation for performance of the bearing, we evaluated the contact pressure and the stiffness. As the results of FEM considering the number of grooves and the contact angle of the planetary ball, a large effect was obtained in the case that the number of rows of planetary balls was 2. The effect was confirmed by measuring axial displacement.     

Super-low friction and lightweight hydraulic cylinder using multi-directional forging magnesium alloy and its application to robotic leg

Abstract

One of the most important missions for robots is to operate in severe environments, and these situations require robots to have ‘toughness’ which can overcome large shocks, degraded communication quality, unexpected condition, and other critical accidents. Although there are many kinds of approaches to realize tough robotic systems, developing a tough actuators is one of the key technologies for them. We focus on hydraulic actuators and attempt to develop a tough robotic actuator with greater toughness than the electromagnetic actuators used in conventional robotic systems. In general, hydraulic actuators have enough toughness for severe environments, but their controllability and lightness are insufficient for robot systems. Herein, we propose novel hydraulic actuators that realizes lightweight with a multidirectional-forging magnesium alloy and have high controllability by low friction pistons. Prototypes were developed to examine the fundamental characteristics of the actuators and compare the two approaches for the low-friction pistons: one is based on a packing mechanism using an elastic restoring pressure, and the other utilizes a fluid-bearing technology. After basic experiments, the prototype was applied to a robotic leg to verify their potential in actual robotic systems. The robotic leg successfully jumped 260 mm in height with 21 MPa.