Effect of dispersant on paste rheology in preparation of porous alumina with oriented pores by extrusion method

The effect of additives on paste rheology was investigated for preparation of porous ceramics with unidirectionally aligned cylindrical pores. Ammonium poly-carboxylic acid (APA) used as a dispersant and it was adsorbed on alumina powder surface. The adsorption isotherm of APA was fitted by Langmuir equation. The saturated monolayer adsorption was 5.9 mg/g. The apparent viscosity became a minimum at 0.8 mass % of APA corresponding to 71.2 mPa⋅s. This APA amount of 5.6 mg/g, is in good agreement with the observed APA amount. Since the nylon 66 fibers (0–35 vol. %) mixed with the alumina powder have a strong interaction with each other, they became twisted and agglomerated. This agglomeration increased with increasing fiber content but decreased by adding oleic acid. The pastes with added oleic acid were capable of being extruded at higher pressure. The obtained porous alumina ceramics showed highly oriented cylindrical pores parallel to the extrusion direction. The pore orientation was higher in the oleic acid added pastes than those without oleic acid. The added nylon 66 fibers are mostly converted to pores while maintaining the original shape after sintering. The pore size distribution of the obtained porous ceramics measured by mercury porosimetry method showed a peak at about 4 μm which is apparently smaller than that observed in the SEM photographs and the obtained result is considered to be corresponding to the necks formed by fiber contacts.     

Microprocessor-Based Decoupled Control of Manipulator Using Modified Model-Following Method with Sliding Mode

A methodology of discontinuous feedback and continuous feedforward control is developed to achieve accurate decoupled tracking in a class of nonlinear, time varying systems in the presence of disturbances, parameter variations and nonlinear dynamic interactions. The method is based on an improved variable structure control with a sliding mode.     

Relationship between the dose of lidocaine administered endotracheally in small children and the serum lidocaine level--recommended dose prior to endotracheal intubation

To determine the optimum dose of lidocaine administered in the trachea prior to endotracheal intubation, we divided 102 surgical patients 3-5 years of age into 3 groups, i.e., group 1; 1 mg.kg-1 was sprayed in the trachea, group 2; 2 mg.kg-1 was sprayed in the trachea, group 3; 1 mg.kg-1 was sprayed in the trachea, and 1 mg.kg-1 in the pharynx and the oral cavity simultaneously. The venous serum concentration of lidocaine was measured two times either 1.5, 3, 5, 10, 15, 20, 30 or 45 min after the spray in each case. In group 1, the mean concentration of lidocaine reached the maximum of 1.05 micrograms.ml-1 at 5 min and decreased gradually after that with a small inter-individual variation. In group 2, after reaching the mean maximum concentration of 3.51 micrograms.ml-1 at 3 min, the serum level dropped quickly and then gradually decreased. There were a few cases where serum level was over 7 micrograms.ml-1. In group 2, after reaching the mean maximum concentration of 1.38 micrograms.ml-1 at 5 min, the serum level decreased more slowly, suggesting a slow absorption from the pharynx and/or the oral cavity. We conclude that the recommended dose of lidocaine for endotracheal administration is less than 2 mg.kg-1.     

Gibbs Energy Change of Carbothermal Nitridation Reaction of Al2O3 to Form AlN and Reassessment of Thermochemical Properties of AlN

The experimental method for the high-temperature reaction equilibria in the AlN-Al₂O₃ system has been established. The equilibrium N₂-CO gas compositions coexisting with AlN- Al₂O₃-graphite have been successfully measured by quadrupole mass spectrometry and gas chromatography. From the obtained results, the standard Gibbs energy change of the forming reaction of AlN by carbothermal nitridation is determined at temperatures ranging from 1723 to 1899 K:
From the obtained result, the standard Gibbs energy of formation of AlN and the third-law enthalpy of formation of AlN at 298.15 K are derived as
The disagreement between the present results and values in the NIST–JANAF thermodynamic table is discussed.     

High frequency model of transformer winding

A high frequency model of transformer winding is used to analyze the voltage oscillations due to various excitations such as the very fast transient overvoltage which occurs at the time of disconnecting switch operations. Usually, a circuit of interlinked inductances and capacitances is used for this purpose, in which circuit parameters have to be properly determined. Previously, those constants have been estimated taking the coil section pair as a unit. In the method proposed here, the section pair can be further subdivided. The time‐domain calculation is conducted combining the frequency analysis and FFT technique. The voltage oscillations of the winding subjected to the lightning impulse are calculated. The correspondence with the experimental results is satisfactory. The response to a chopped impulse shows this method's applicability to high frequency analysis. Since the constants are calculated directly from the design parameters of transformer winding, this technique is particularly useful in developing and designing transformers. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(3): 8–16, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10280     

Magnetic properties of iron-based materials (nitrogen interstitially modified 1:12 compounds and Fe3B-Nd) for low rare-earth bonded magnets

Hard magnetic properties of nitrogen interstitially modified NdM_xFe_12-xN_y compounds and Fe₃B-based ultra-fine crystalline Nd? Fe? Co? T? B alloys of low Nd content of 3 to 5 at. % are studied. The nitrogen-modified compounds have been prepared via the rapid solidification route and the mechanical alloying route both followed by gas nitrogenation using N₂. The Fe₃B-based materials have been prepared by means of rapid solidification and crystallization treatment. The latter materials appear promising as the base material for high-remanence, easy-to-magnetize bonded magnets with small temperature coefficients of remanence. Typical magnetic properties of compaction isotropic bonded magnets produced from this material are B_r = 0.80 T, H_cJ = 350 kA/m, and (BH)_max = 60.5 kJ/m³.     

Experimental Apparatus to Search for Supersolidity in Monolayer ^4He on Graphite

We describe some details of a new experimental setup for torsional oscillator (TO) measurement of $^4$ He monolayers adsorbed on a graphite surface. This setup is designed to seek for the possible supersolid phase, in which crystalline order coexists with superfluidity, in two dimensional (2D) solid $^4$ He below 300 mK. Among such 2D solids, the commensurate phase in the second layer on graphite is the most hopeful candidate for the novel supersolid phase since it is the lowest-density quantum solid ever found. An exfoliated graphite substrate we used is ZYX which has at least ten times longer surface coherence length compared to Grafoil, an exfoliated graphite most commonly used in previous experiments. The first version of TO we made has the resonant frequency of 786.8 Hz and the Q value of $1.1\times 10^5$ at $T \le 10$  mK. The resonant frequency of this particular TO without any He samples ( $f_{\mathrm {cell}}$ ) showed unexpectedly large temperature variation and non-reproducibility below 1 K as well as sudden jumps when mechanical shocks are applied to the experimental apparatus. We found the stability of $f_{\mathrm {cell}}$ is highly correlated with the temperature stability of 1 K pot in dilution refrigerator.