Shape and size control of barium chromate nanoparticles using reverse micelle

The shape and size of barium chromate nanoparticles formed using a water-in-oil microemulsion prepared from the anionic surfactant AOT were examined. As a result, nanowires, nanorods, and nanodots could be synthesized by changing the raw ion concentration and by adding ethanol as a poor solvent. The nanowires and nanorods were self-assembled. It has been shown that the aspect ratio of the generated nanoparticles decreased with increasing chromate ion concentration or due to the addition of ethanol. By contrast, the aspect ratio was almost constant even when the barium ion concentration was changed. The surfactant AOT was selectively adsorbed on the crystal faces of the barium chromate nanoparticles along the a-axis, where it suppressed the growth of their crystal face. Furthermore, the generated nanoparticles were self-assembled through hydrophobic interactions between the surface-anchored AOT molecules. In conclusion, it was clarified that the supersaturation ratio and the particle–surfactant interaction were important factors for controlling the shape and size of these inorganic nanoparticles using the microemulsion method.     

Concise frequency-dependent formulation for LOD-FDTD method using Z transforms

The Z transform (ZT) theory is newly introduced into the unconditionally stable locally one-dimensional (LOD) FDTD method, in which a complicated treatment of convolution integrals is not required. Through analysis of a surface plasmon waveguide, the accuracy of the ZT-LOD-FDTD is found to be retained for a large time step allowed in an implicit scheme. The computational time is reduced to 25% of that of the traditional explicit ZT-FDTD, maintaining comparable accuracy.     

Influence of catalyst supporters on catalyst nanoparticles in synthesis of single-walled carbon nanotubes

It is important to understand catalytic reactions involved in synthesizing carbon nanotubes. Usually, catalysts are used with supporters for better stability and influences of supporters on catalysis is negligible; however, catalysts used for synthesizing single-walled carbon nanotubes are too small to neglect their influence. Here, we experimentally investigated efficiencies of commonly used catalyst supporters such as magnesium oxide, zeolite, and aluminum oxide when they were combined with iron–cobalt, which is a typical catalyst. It was observed that zeolite-supported catalysts could synthesize single-walled carbon nanotubes, while the others could not. Cluster molecular orbital calculations showed that electronic states of catalysts supported by MgO in the boundary layer between catalysts and supporters were restricted due to covalent bonding between cobalt and magnesium. Density functional theory calculations indicated that catalysts on zeolite had enough electrical orbital near Fermi level and they widely spread over catalysts surface, but catalysts on MgO did not. This characteristic can affect catalytic activities.     

Tradeoff Between Complexity and Memory Size in the 3GPP Enhanced aacPlus Decoder: Speed-Conscious and Memory-Conscious Decoders on a 16-Bit Fixed-Point DSP

This paper investigates tradeoff between complexity and memory size (speed-memory tradeoff) in the 3GPP enhanced aacPlus decoder based on a 16-bit fixed-point DSP implementation. In order to investigate this tradeoff, the speed- and the memory-conscious decoders are implemented. The maximum number of operations for the implemented speed-conscious decoder is 29.3 million cycles per second (MCPS) for a 32 kb/s bitstream. The maximum number of operations for the memory-conscious decoder, where 70% of the data are allocated to an external memory area, increases by 5.7 MCPS (19%) for the bitstream. The investigation of this tradeoff provides an actual relationship between the computational complexity and the internal memory size of the 3GPP enhanced aacPlus decoder. This relationship is useful for implementing a decoder with a best speed–memory balance that is determined by each specific application and the user requirements.     

Crystallization of 4He in Aerogels

Static behaviors of crystallization of ⁴He in porous materials, such as the increase of melting pressure, have been studied extensively, but nonequilibrium dynamics of the phase transition is hardly known. Our interest was in how ⁴He crystals grow in a 90.4% porosity aerogel. Aerogels are transparent and the dynamics in them can be studied visually. A Pomeranchuk-type variable-volume cell was used to study crystallization at a fixed temperature with a blocked capillary condition. By continuously compressing a chamber, the pressure rose above the bulk melting pressure and at a pressure 1.7 bar above the bulk melting pressure these crystals began to invade the aerogel. A clear crystal-superfluid interface was moved smoothly by the steady compression. No macroscopic facets were observed in the aerogel well below the bulk roughening transition temperature.      

Abrasion resistance of high Cr cast irons at an elevated temperature

A novel wear tester was employed to investigate the comparative abrasive stability of metallic materials at elevated temperatures. This tester consists of a symmetric π-shaped specimen holder that is rotated in a stainless steel tank filled with quartz sand, and an electrical furnace surrounds this tank to heat the abrasive sand. The test material and its comparative, of a size of 20 mm×20 mm×5 mm, were set in the respective branches of the holder. During the atmospheric condition experiment, only one 20 mm×20 mm face of each specimen was suffered with abrasion, while the other faces which were mounted in the holder were oxidized. Then the volume loss of the specimens can be accurately calculated with the aid of additional oxidation experiments, and by choosing the same comparative material the abrasive stability of different materials can be compared. A newly developed high Cr cast iron 4.5C–40Cr–8Ni–9Nb–5Mo was employed as the test alloy, while the comparative was the widely used 25Cr cast iron (Fe–25Cr–2.9C–0.5Ni–0.5Mo). The results show that, at the temperature of 925 K, the test alloy exhibited a superior abrasive stability to the 25Cr alloy; the average wear rate of the former was only about 36% of that of the latter.     

Polymerization of N-substituted 2-propynamides with transition metal catalysts

Summary Polymerization of N-substituted 2-propynamides proceeded in the presence of Pd(II) catalysts such as [Pd(CH₃CN)₄](BF₄)₂, PdCl₂(PhCN)₂-n-BuLi, and PdCl₂(nbd)-n-BuLi. The molecular weights of the obtained polymers ranged 8,500 to 14,000, depending on the catalysts. From the ¹H NMR spectra, these polymers were found to have alternating double bonds in the main chain. Received: 25 December 2000/Revised version: 17 January 2001/Accepted: 19 January 2001