The effect of excess gate current on input impedance of a JFET amplifier

When JFET is used as an amplifier, it should be regarded that the effect of excess gate current on the input impedance is changed by gain of the amplifier. The input impedance or conductance with gain of the JFET amplifier is experimentally analyzed applying small signal equivalent circuit.     

Contact force detection on a minute aperture mounted optical contact slider using an acoustic emission sensor

Advances in the digital network society require both higher density and higher transfer rates in all sorts of storage systems. Especially in optical recording, the trend toward higher density and larger capacity requires novel surface-recording technologies that can drastically diminish head-to-medium spacing, resulting in an improvement in spatial resolution and, finally, a higher recording density. To this end, we have already proposed a novel contact optical head slider that is able to almost cancel the suspension load by generating hydrodynamic pressure, thus realizing a lower net contact force. Evaluating the dynamic contact force is requisite in realizing its stable sliding operation and higher signal readout performance. In this study, a continuous acoustic emission (AE) signal was utilized to detect the dynamic contact force. AE signal modulation was compared with the applied out-of-plane acceleration on a medium generated by a spindle combined piezo-electric actuator. It was clarified that the detected AE modulation amplitude was approximately proportional to the applied acceleration, and that utilizing AE modulation will be a useful method for evaluating dynamic contact force.     

Preparation and catalytic activity of Au-Pd, Au-Pt, and Pt-Pd binary metal dendrimer nanocomposites

Catalytic activity of Au-Pt, Au-Pd, and Pt-Pd dendrimer nanocomposites for reduction of p-nitrophenol was investigated in water. The bimetallic dendrimer nanocomposites were prepared by simultaneous reduction with sodium borohydride in the presence of poly(amidoamine) (PAMAM) dendrimers with amine and carboxyl terminal groups. Average diameters of the obtained particles were 2-4 nm by transmission electron microscopy. From UV-vis spectroscopy, it was found that the particles were not mixtures of monometallic particles but binary ones. X-ray photoelectron spectroscopy showed that formation of binary composite particles prevents palladium atoms from oxidation. The Au-Pd and Pt-Pd binary particles exhibited higher catalytic activity than monometallic ones. On the other hand, catalytic activity of Au-Pt binary particle was comparable to that of platinum nanoparticles.     

Polymerization via zwitterion 27. No-catalyst copolymerization of 2-phenyl-1,3,2-dioxaphospholane with β-hydroxyalkyl acrylates and methacrylates

Summary This paper describes No-Catalyst Copolymerizations between ethylene phenylphosphonite (EPO) as M_N and four -hydroxyalkyl acrylates and methacrylates as M_E. In all combinations polyphosphinate type copolymers were obtained above 130 °C without added catalyst. The first step of reaction was a proton-transfer step to yield a transient phosphonium-alkoxide zwitterion 5 and generated a phosphorane intermediate like 6. The subsequent reactions of 6 were rather complicated. It was possible to conceive several zwitterions to lead to polymer units. The liberation of ethylene oxide and/or propylene oxide was observed as a side reaction during polymerization.Dedicated to the 60th birthday of Professor C. I. Simionescu     

Improvement in physical properties of poly(vinyl chloride) by radiation-induced graft copolymerization with mixed monomers

Gamma-ray-induced graft copolymerization of butadiene with vinyl monomers onto PVC was attempted to improve the physical properties of PVC. The Izod impact strength was increased from 2 kg·cm/cm² to more than 100 kg·cm/cm² by grafting ca. 10% butadiene. But the tensile strength and melt flow were decreased by the grafting. The electron micrograph showed that the mass of polybutadiene in the graft copolymer had a convenient diameter (0.1–1 μ) for absorbing the impact energy. The weatherability of PVC grafted with butadiene was improved by cografting of butadiene with acrylates and methacrylates which had long side chains.     

Preparation and properties of carbon dental implant with fine rahmen surface layer

Blade- and tooth-root-form carbon dental implants were prepared by fixing fine Rahmen surface (FRS) layers of carbon fabric on a carbon fiber-reinforced carbon (CFRC) core. The fixing was successfully performed through the low-temperature deposition of pyrolytic carbon using cis-1,2-dichloroethylene as the raw material. The resultant implants showed flexural and compressive strength more than 150 and 100 MPa, respectively. The outer part of this FRS layer contained many pores ranging from 30 to 300 μm in diameter and 40–75% in volume fraction.New bone was generated in the open pores after being embedded in the femur of a monkey for 6 months. The shear strength of the embedded implant vs bone interface was 15 MPa. On the other hand, the blade-form FRS implant in the mandible of a monkey gave a locking system consisting of “bone-collagen fiber-calcified layer” after two years under a masticating pressure. The latter is very similar to the natural tooth system.     

Magnetic properties of iron-nitride particles prepared with gas evaporation method

Magnetic properties of iron nitride particles prepared with reactive gas evaporation method were investigated. Major products for higher NH3gas pressure region is γ'Fe4N and αFe. For lower pressure region αFe was produced, which was oxidized to Fe3O4after exposure to air. It is found that particles consist of γ'Fe4N and γFe are more persistent to oxidation comparing to those of αFe.