Recent Advances in New Hard High‐Pressure Nitrides

Since the discovery of spinel nitrides in 1999, there has been a lot of effort in basic science to further develop advanced nitrides and electronic nitrides. The aim and scope of the research in this field is to synthesize novel nitrides for structural and functional applications. Silicon‐based spinel nitrides combine ultrahigh hardness with high thermal stability against decomposition in different environments, suggesting potential applications as cutting tools. These materials are also expected to show interesting optoelectronic properties, which may lead to applications in light‐emitting diodes. The synthesis of spinel silicon and germanium nitrides at ultrahigh pressures and temperatures, as well as the successful synthesis of tin nitride at ambient pressure, has created an enormous impact on both the basic science and technological development of advanced nitrides. Moreover, the discovery of novel phases of transition metal nitrides, such as Zr₃N₄ and Hf₃N₄ with a Th₃P₄ structure, as well as the recently reported nitrides of Pt and Mo, demonstrates the scientific potential of high‐pressure synthesis techniques in the field of materials science. Here, the state of the art in the field of novel hard materials based on nitrides synthesized reproducibly under high pressure is reviewed.     

Selection of the best siting of static var compensators for effective damping

A static Var compensator (SVC) can improve the steady-state stability (or the small signal stability), if it is located appropriately. The present paper proposes a method for selecting the best siting of SVC in large-scale power systems for damping effectively. Conventionally, it is thought that SVC improves steady-state stability by its voltage regulating ability. From this point of view, the stability can be improved significantly if SVC is located at the bus which has a large voltage fluctuation due to the lightly damped power swing mode. In contrast to the conventional viewpoint, the present paper makes it clear that the steady-state stability deteriorates by the conventional voltage regulating control of SVC in some cases. Therefore, the voltage fluctuation is not an appropriate index for effective damping. This paper explains the mechanism of improvement of steady-state stability by SVC in terms of modal analysis. On the basis of modal analysis, an index for determining the location of SVC is derived. The index is called LIED (Location Index for Effective Damping) by the authors. Digital simulations are conducted for an 8-machine longitudinal system and a 29-machine looped system to demonstrate the validity of the proposed index.     

Development of a micromanipulator made of diamond having reversal mechanism

In this study we focus on diamond as a structural material for micromechanisms. Diamond is the hardest material on the earth, and has superior antifriction and anticorrosion characteristics. If diamond were applied to a micromechanism, an almost maintenance-free component which requires only a few component exchanges could be fabricated. In addition, since it has a superior anticorrosion characteristic, it can be used in chemical substances and organic tissue; thus, micromechanical components made of diamond have many advantages. Furthermore, when diamond is applied to a micromanipulator, we can expect accurate gripping to be realized because its deformation is small. We have already developed a diamond end effector for micromanipulators, and have obtained several promising results. In this study, we added a reversal mechanism to the positioning unit of this micromanipulator to increase efficiency in assembly tasks, and modified the design of the diamond end effector accordingly. Major modifications were examined through finite element analysis of fabricated shapes and amount of movement. A modified effector was experimentally fabricated based on the analytical results, and its features were examined experimentally. The starting material was 2-μm-thick flat-plate diamond, whichwas processed by laser into a designated shape. A shape-memory-alloy actuator which memorizes the linear shape was used to realize a driving amount larger than those of electrostatic actuators and piezoelectric devices.     

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.     

Recent developments of shearing in Japan

In this article, leading research and development activities of shearing in Japan are reviewed. Main contents are elucidation of shearing mechanism, theoretical analysis, tool life, burr-free blanking, precision shearing, bar cropping, pipe cutting, slitting, shearing of non-metallic materials, tool making, shearing of extremely thin sheets, etc.     

Electronic structures of polyacenacene and polyphenanthrophen anthrene. Design of one-dimensional graphite

The electronic structures of polyacenacene (PAA) and its geometrical isomer, polyphenanthrophenanthrene (PPhP) have been studied using the tight-binding SCF-CO (self consistent field-crystal orbital) method with respect to a design of one-dimensional (1D) graphite. The geometry of each polymer is optimized from the energetic point of view. It has been found that from the analysis of the electronic structure of its optimized geometry, PAA favours the structure without the carbon-carbon bond alternations, yielding no band gap. In this sense, PAA is a typical 1D-graphite. On the other hand, it is predicted that the magnitude of the band gap of PPhP in its optimized geometry is almost equal to that of trans-polyacetylene.     

HTLV-I associated myelopathy with macular degeneration

The authors report a case of macular involvement in a patient with HTLV-I associated myelopathy (HAM). The patient was a 10-year-old girl who noticed sudden decreased vision in her right eye in November 1987. The corrected visual acuity was 0.01 in the right eye and 1.0 in the left eye. Fundus examination of the right eye disclosed mild optic disc pallor. The macula appeared to have pigmentary mottling with superficial irregular retinal reflex that was three disc diameters in size. Fluorescein angiography revealed a discoid hypofluorescent area in the macula, surrounded by mottled hyperfluorescent areas. She had no contributory family history of ocular disease, but had a history of blood transfusion during an operation for patent ductus arteriosus and ventricular septal defect at the age of 8 months. In November 1990, she developed gait disturbance due to spastic paraparesis and was admitted to our hospital. Antibodies to HTLV-I were markedly elevated in serum (titer, 1:8192) and in cerebrospinal fluid (titer, 1: 1024). She was diagnosed as HAM. Two months later, she developed encephalopathy and bilateral optic disc atrophy.     

Thermal-stress intensity factors for an insulated crack in a semi-infinite medium with a thin conductive stiffener

In the present paper is analyzed the thermal stress problem of the interaction between an insulated crack and a thin conductive elastic stiffener of finite length bonded to the surface of a semi-infinite medium under uniform heat flow on the basis of the two-dimensional theory of thermoelasticity. The singular point method is adopted to solve the problem and a system of singular integral equations is derived. Numerical results for the thermal-stress intensity factors are presented in terms of normalized parameters which consist of the dimensions and the geometrical arrangement of the crack and the stiffener, and the physical properties of the stiffener and the semi-infinite medium.