A high-power electrostatic motor using skewed electrodes

This paper describes a new type of high-power electrostatic motor equipped with skewed electrodes. The authors have developed several types of high-power electrostatic motors. Among them, the dual excitation multiphase electrostatic drive (DEMED) has the best performance in terms of power. Its power/weight ratio is almost the same as that of the most advanced conventional electromagnetic motors. However, DEMED exhibits a large force ripple leading to such disadvantages as low controllability, high noise, and vibration. To overcome these disadvantages, the authors have proposed to apply the skew technique to DEMED and have analyzed the effects of skewing the electrodes. The analysis has shown that appropriate skewing can reduce the force ripple considerably. In this paper, we further analyze the shape of the electrodes. A new type of motor incorporating the results of the analysis is fabricated and tested. Using the new DEMED with skewed electrodes (V-DEMED), the slider motion becomes much smoother, noise and vibration are reduced, and efficiency improves, without compromising the thrust force. © 1998 Scripta Technica, Electr Eng Jpn, 125(3): 50–58, 1998     

Diamond FET using high-quality polycrystalline diamond with f/sub T/ of 45 GHz and f/sub max/ of 120 GHz

Using high-quality polycrystalline chemical-vapor-deposited diamond films with large grains (/spl sim/100 /spl mu/m), field effect transistors (FETs) with gate lengths of 0.1 /spl mu/m were fabricated. From the RF characteristics, the maximum transition frequency f/sub T/ and the maximum frequency of oscillation f/sub max/ were /spl sim/ 45 and /spl sim/ 120 GHz, respectively. The f/sub T/ and f/sub max/ values are much higher than the highest values for single-crystalline diamond FETs. The dc characteristics of the FET showed a drain-current density I/sub DS/ of 550 mA/mm at gate-source voltage V/sub GS/ of -3.5 V and a maximum transconductance g/sub m/ of 143 mS/mm at drain voltage V/sub DS/ of -8 V. These results indicate that the high-quality polycrystalline diamond film, whose maximum size is 4 in at present, is a most promising substrate for diamond electronic devices.     

Unstable sinking of spheres at higher air velocity in a gas-solid fluidized bed

Float-sink of large objects (on order of cm) in a gas-solid fluidized bed of powder (on order of 100 s of microns) based on density difference has been utilized for dry density separation in industry. The air velocity u₀/u_mf is one of the important factors operating the fluidized bed, where u₀ and u_mf are the superficial air velocity and the minimum fluidization air velocity, respectively. It is empirically known that the sinking of heavy objects is “occasionally” unstable in the fluidized bed combustor, for which the higher air velocity u₀/u_mf > 4 is used. Unstable sinking means heavy objects that are expected to sink but sometimes do not. However, the precise conditions at which the unstable sinking occurs are not clear. In this study, we investigated the float-sink characteristics at a given air velocity u₀/u_mf = 2–7 using glass beads of size D_gb = 425–600 μm and 600–850 μm as the fluidized powder bed media. The float-sink experiments were carried out at the bed height h_gb = 150 mm and 75 mm using density adjusted spheres (diameter = 30 mm). We found that the spheres stably float or sink based on density difference at D_gb = 425–600 μm & h_gb = 150 mm and at D_gb = 600–850 μm & h_gb = 75 mm. However, the unstable sinking does occur at u₀/u_mf > 4 at D_gb = 600–850 μm & h_gb = 150 mm. These results indicate that the powder size and the bed height are key factors to induce the unstable sinking at the higher air velocity.     

Apatite formation abilities and mechanical properties of hydroxyethylmethacrylate-based organic–inorganic hybrids incorporated with sulfonic groups and calcium ions

Apatite formation in the living body is an essential requirement for artificial materials to exhibit bone-bonding bioactivity. It has been recently revealed that sulfonic groups trigger apatite nucleation in a body environment. Organic–inorganic hybrids consisting of organic polymers and the sulfonic groups are therefore expected to be useful for preparation of novel bone-repairing materials exhibiting flexibility as well as bioactivity. In the present study, organic–inorganic hybrids were prepared from hydroxyethylmethacrylate (HEMA) in the presence of vinylsulfonic acid sodium salt (VSAS) and calcium chloride (CaCl₂). The bioactivities of the hybrids were assessed in vitro by examining the apatite formation in simulated body fluid (SBF, Kokubo solution). The hybrids deposited on the apatite after soaking in SBF within 7 days. Tensile strength measurements showed a tendency to increase with increases in VSAS and CaCl₂ content. It was assumed that this phenomenon was attributed to the formation of cross-linking in the hybrids.     

Synthetic Multifunctional Graphene Composites with Reshaping and Self‐Healing Features via a Facile Biomineralization‐Inspired Process

Since graphene is a type of 2D carbon material with excellent mechanical, electrical, thermal, and optical properties, the efficient preparation of graphene macroscopic assemblies is significant in the potentially large‐scale application of graphene sheets. Conventional preparation methods of graphene macroscopic assemblies need strict conditions, and, once formed, the assemblies cannot be edited, reshaped, or recycled. Herein, inspired by the biomineralization process, a feasible approach of shapeable, multimanipulatable, and recyclable gel‐like composite consisting of graphene oxide/poly(acrylic acid)/amorphous calcium carbonate (GO‐PAA‐ACC) is designed. This GO‐PAA‐ACC material can be facilely synthesized at room temperature with a cross‐linking network structure formed during the preparation process. Remarkably, it is stretchable, malleable, self‐healable, and easy to process in the wet state, but tough and rigid in the dried state. In addition, these two states can be readily switched by adjusting the water content, which shows recyclability and can be used for 3D printing to form varied architectures. Furthermore, GO‐PAA‐ACC can be functionalized or processed to meet a variety of specific application requirements (e.g., energy‐storage, actuators). The preparation method of GO‐PAA‐ACC composite in this work also provides a novel strategy for the versatile macroscopic assembly of other materials, which is low‐cost, efficient, and convenient for broad application.     

Origin of growth defects in CVD diamond epitaxial films

Three types of growth defects commonly found epitaxial diamond films grown by chemical vapour deposition (CVD), namely unepitaxial crystals (UCs), hillocks with flat top (FHs) and pyramidal hillocks (PHs), were etched using hydrogen/oxygen plasma to discuss their origin. UCs formed at random locations on the grown layer without any apparent relation with the substrate. Their nucleation might be due to contaminants and their development controlled by the growth conditions in the plasma. In contrast, dislocations formed from impurities segregated at the interface between the substrate and the CVD layer, were found to be the origin of the FHs and the PHs. A simple crystal model that involves micro-faceting or twinning at an intrinsic stacking fault originating from the dislocation core is proposed to explain the formation and the evolution of the growth defects.     

The controlled resorption of porous α-tricalcium phosphate using a hydroxypropylcellulose coating

Tricalcium phosphate (TCP) ceramic is known in orthopedics to be a bioresorbable bone substitute. A porous TCP ceramic body also has high potential as a drug delivery system in bony defects. Porous alpha-TCP ceramic can be easily fabricated using conventional sintering of beta-TCP, since alpha-TCP is the thermodynamically stable phase at temperatures above 1 100 degrees C. However, the solubility of alpha-TCP is much higher than that of beta-TCP. Therefore, the dissolution of porous alpha-TCP progresses at a higher rate than bone repair. In the present study, we attempted to reduce the dissolution rate of porous alpha-TCP by employing an organic polymer coating. We fabricated porous alpha-TCP ceramic with a continuous 10-50 microm diameter pore structure by sintering a body made from a beta-TCP and potato starch slurry. The porous body obtained was coated with hydroxypropylcellulose (HPC), and then subjected to heat treatment. The chemical durability and mechanical properties of the body were examined before and after coating with the HPC. The dissolution of porous alpha-TCP in buffered solutions was reduced by coating with HPC and drying at 60 degrees C. The compressive strength of the porous alpha-TCP was also improved by coating with HPC. The results of in vivo experiments showed that some parts of the porous alpha-TCP ceramic coated with HPC remained in the canal of the tibia of a rabbit four weeks after implantation, whereas no residual was observed in a non-coated alpha-TCP ceramic. Coating with HPC was found to be effective for controlling bioresorption and improving the workability of porous alpha-TCP ceramic. The prepared porous alpha-TCP ceramic is expected to be useful as a novel material for bone fillers by incorporating it with drugs or osteoinductive factors.     

Evidence for the π-d Interaction Comparing Magnetoresistance in (EDT-DSDTFVO)2 X, X=FeCl4, GaCl4

Hall resistance and magnetic torque measurements have been carried out in the field-induced spin-density-wave (FISDW) phase of deuterated (TMTSF)₂ClO₄ for various cooling rates through the anion ordering temperature. We have found that the Hall resistance in the intermediate cooled state shows a phase transition from the non-quantized Hall phase to the quantized Hall phase (n=1) with hysteresis. We have also found that the magnetic torque in the non-quantized Hall phase rapidly decreases with increasing cooling rate. These results suggest that there is a new phase transition from the non-quantized Hall phase to the quantized Hall phase in (TMTSF)₂ClO₄.     

Cyclic-Oxidation Behavior of Fe–20Cr–4Al Alloys with Small Amounts of Sulfur at High Temperatures

The cyclic-oxidation behavior of Fe–20Cr–4Al alloys with 3, 35, 53, 104, and 171 ppm sulfur was studied in oxygen at 1273, 1373, 1473, 1573, and 1673 K by mass-change measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron-probe microanalysis (EPMA). The cyclic oxidation consisted of an 18.0 ksec exposure that was repeated up to five times. Amounts of spalled oxides of the alloys with 35 and 53 ppm sulfur increased after one and two oxidation cycles, and then decreased after three or more oxidation cycles at 1473 and 1573 K. On the other hand, spalling of oxide scales on the alloys with 3 and 171 ppm sulfur was scarcely recognized after all cycles used in this study. SEM observations of both sides of the spalled oxides indicated that spallation was related to the morphology of the surface oxides and to the morphology and volume of cavities at the oxide–alloy interface.     

Synthesis of poly[2]catenane having rigid linkage by 1,3-dipolar cycloaddition of diazido[2]catenane with 4,4′-diethynylbiphenyl

A novel poly[2]catenane having rigid triazole rings between [2]catenane moieties was synthesized by the 1,3-dipolar cycloaddition of diazido[2]catenane with 4,4′-diethynylbiphenyl. The reaction proceeded effectively under mild conditions and gave a polymer in high yield. The number average molecular weight (M_n) of the polymers was 1.5 × 10⁴-2.5 × 10⁴. A cyclic dimer consisting of two [2]catenane moieties and two biphenylene units was formed along with the polymer. The cyclodimerization was suppressed by performing the reaction at a low temperature without lowering the yield or molecular weight of the polymer. The novel poly[2]catenane had higher solubility in some solvents than the corresponding non-catenated polymer having a similar primary structure.