Single-walled carbon nanotubes grown on natural minerals

Single-walled carbon nanotubes (SWNTs) are successfully grown on magnesite crystal by pyrolysis of methane gas under moderate conditions, demonstrating the possibility of naturally occurring SWNTs.The obtained SWNTs were analyzed by Raman scattering, transmission electron microscope (TEM), and thermogravimetric (TG) measurements. These measurements revealed that high purity SWNTs having diameters of about 1-1.8 nm occur on the surface of natural magnesite sample by the pyrolysis of methane gas at 1073-1173 K. Structural properties and formation mechanism of the obtained SWNTs were discussed.     

Positive photosensitive polyimides using polyamic acid esters with phenol moieties

Polyimide resists developable with basic aqueous solutions were realized by polyamic acid esters with phenol moieties (PPh's) and naphthoquinone diazides. The polyimide precursors (PPh's) were synthesized from diamines and dicarboxylic acids that have phenol moieties through ester linkage. A selective reaction of alcohol groups with acid dianhydride groups made the synthesis of the PPh's possible, even if the phenol groups were in the reaction mixtures. The PPh's were soluble in basic aqueous developer, but their dissolution rates were too low for use as resists. To increase the resist dissolution rate, polyamic acids were added to the PPh's. By adjusting the dissolution rates in basic aqueous developers, fine patterns could be realized. The polyimide resists had high thermal stability and reliable adhesive property to silicon substrate. © 1994 John Wiley & Sons, Inc.     

Performance bounds for flow control protocols

We discuss a simple conceptual framework for analyzing the flow of data in integrated services networks. The framework allows us to easily model and analyze the behavior of open loop, rate based flow control protocols, as well as closed loop, window based flow control protocols. Central to the framework is the concept of a service curve element, whose departure process is bounded between the convolution of the arrival process with a minimum service curve and the convolution of the arrival process with a maximum service curve. Service curve elements can model links, propagation delays, schedulers, regulators, and window based throttles. The mathematical properties of convolution allow us to easily analyze complex configurations of service curve elements to obtain bounds on the end-to-end performance. We demonstrate this by examples, and investigate tradeoffs between buffering requirements, throughput, and delay, for different flow control strategies     

Synthesis and Properties of Hydrogels Based on Polyaspartamides with Various Pendants

Summary Hydrogels based on three kinds of polyaspartamides, i.e. non-substituted polyaspartamide, substituted polyaspartamide with sodium aspartate pendant and that with sodium sulfonate pendant, were prepared by crosslinking of polysuccinimide with ehylenediamine, followed by the hydrolysis with the corresponding amines (ammonia, sodium aspartate, and sodium 2-aminoethylsulfonate). Water absorbency and biodegradability of these products were evaluated, comparing with those of crosslinked sodium polyasparate prepared similarly. Absorbency in pure water of the three products in the present study was in the range of 70–150 g/g, somewhat lower than that of crosslinked sodium polyasparate, 200 g/g. Absorbency in 0.9% NaCl solution was totally lower than those in pure water and the order of the absorbency of the products was the same as the case of the pure water. On the other hand, in 3.5% NaCl solution, absorbency of crosslinked polyaspartamide containing sodium sulfonate was higher than that of crosslinked sodium polyasparate. The crosslinked polyaspartamides in the present study showed somewhat slower biodegradation speed than the crosslinked sodium polyasparate.     

Discrete–variational Xα calculations of graphite and alkali–metal graphite intercalation compounds

First-principles molecular orbital calculations using discrete–variational (DV)-Xα method are carried out on the model clusters of graphite and alkali–metal graphite intercalation compounds MC_x(M=Li, Na, K, Rb, and Cs). Results of the calculations are used so as to simulate the experimentally observed near-edge X-ray-absorption fine-structures (XANES) and ultraviolet photoelectron spectra. For the clusters of graphite and KC_x, the calculated partial electronic densities of states (PDOSs) are in good agreement with the experimental C K-edge and K K-edge XANES spectra, respectively. Furthermore, the accordance between the calculated DOSs and the observed UPS spectra of graphite and RbC_x is also satisfactory. It is shown that the Fermi level is pushed up into the conduction band of graphite by doping alkali metals.     

Neutron production rate and plasma characteristics of spherically convergent beam fusion

Experimental and simulation results of a spherical glow discharge for a portable neutron source are presented. The experimental device is a 45‐cm‐diameter, 31‐cm‐high stainless‐steel cylindrical chamber, in which a spherical mesh‐type anode 30 cm in diameter is installed. The spherical grid cathode consists of 2.0‐mm‐diameter stainless‐steel wire, which is made into an open spherical grid of 5‐cm diameter. The system is maintained at a constant pressure of 1 to 15 mTorr by feeding hydrogen or deuterium gas. The basic characteristics of breakdown voltages versus pressure and electrostatic potential profiles were measured for hydrogen discharge. Using deuterium, a steady‐state neutron production of 10⁴ s^–1 was observed at a discharge of 40 kV, 2 mA. Motions of ions and electrons in the device were simulated by using a particle code, which is one‐dimensional in coordinate system and two‐dimensional in velocity space. It was confirmed by both the measurement and simulation that a virtual anode is formed in the central part inside the grid cathode. © 2001 Scripta Technica, Electr Eng Jpn, 135(2): 1–8, 2001     

Zn, Al, Rh-mixed oxides derived from hydrotalcite-like compound and their catalytic properties for N2O decomposition

The catalytic decomposition of nitrous oxide was studied over Zn, Al, Rh-mixed oxides derived from hydrotalcite-like compounds (HTlc) as a precursor. The study showed that, when the Zn/Al atomic ratio was 3, the rate of ZnAlRh-HTlc for N₂O decomposition increased with Rh loading up to 1.4 wt% (4.55 × 10⁴ μmol g⁻¹ h⁻¹ at 400°C), and levels off with further increase in Rh loading. Analogous behavior was found in the presence of NO₂ and water. In the presence of 0.5% water, the activity decreased with decreasing Zn/Al ratio, whereas the activity for N₂O decomposition in the presence of 0.1% NO₂ reached a maximum when the Zn/Al ratio was 3. The observed catalytic activities were comparable to those of the reported catalysts in the presence of NO₂ and water.