Development of a knowledge-based system for voltage/reactive power operation planning

Voltage/reactive power planning is a tremendous process which requires a planner to have intellectual expertise. This paper presents a large knowledge-based system that can make voltage/reactive power planning. The knowledge acquisition has been completed on the basis of interview and protocol analysis methods. The result shows that the voltage/reactive power planning is composed of three phases: the first is reactive power adjustment where overall reactive power balance is investigated; the second is voltage adjustment where all bus voltages are tuned within the permissible operational range; and the third is voltage adjustment with a single fault of all major lines. The knowledge base is coded by about 700 production rules. It can succeed in making a voltage/reactive power plan for a very large power system.     

Laminar forced convection in the thermal entrance region of curved pipes with uniform wall temperature

The thermal entrance region heat transfer problem for fully developed laminar flow in curved pipes with uniform wall temperature is approached by an alternating direction implicit method for the parabolic energy equation for a flow regime with Dean number ranging from 0 to an order of 100. This work represents an extension of the classical Graetz problem in straight tubes to curved pipes. The graphical results for temperature developments in the form of temperature profiles through the horizontal and vertical planes, isothermals and local Nusselt number variations in the thermal entrance region are presented in such a way as to illustrate clearly the interaction between the secondary flow and the developing temperature field for Prandtl numbers of 0.1, 0.7, 10 and 500. For a given Dean number, the effect of Prandtl number is to shorten the thermal entrance length (I/Gz) and the temperature field develops rather rapidly with large Prandtl number. The effect of Dean number is similar to that of Prandtl number with Dean number effect becoming much more appreciable at high Prantdl numbers than at low Prandtl number.     

Characterization and compression properties of injection molded carbon nanotube composites

Since the development of carbon nanotubes (CNTs) in 1991, they have received much attention with improved mechanical, thermal, and electrical properties of their composites compared to common polymer composites. The CNTs are currently used to increase the modulus of common thermoplastics and thermosets, including urethanes and epoxies. The CNTs are difficult to disperse within any media because of limited chemical reactivity and potential agglomeration in their “as grown” state. This study evaluated the effect of incorporating bundled and unbundled CNTs at different concentrations into Polyurethane/CNT/woven fiber reinforced composites. Optical microscopy and atomic force microscopy (AFM) characterized the dispersion of CNTs within the polymer matrix in injection molded CNT/polyurethane composites. Polyurethane/CNT/woven fiber reinforced composite plaques were prepared and then characterized by mechanical compression testing. Optical microscopy and AFM qualitatively determined a decreased agglomerate size resulting in improved mechanical properties. Results of this study show significant differences in yield stress, stress at failure, and modulus of elasticity within the various treatments. No significant differences were found for yield strain, strain at failure, and toughness. However, the conservativeness of the statistical model warrants further investigation for strain at failure and toughness with possible interaction effects of CNT concentration for each composite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of Ti content on TiN morphology,microstructure and toughness in coarse‐grained heat affected zone of Ti‐containing steels

It is well known that weld distortion, which has a negative influence on material properties, structural fabricability and structural integrity, should be controlled appropriately. There are many methods to control or reduce weld distortion, but most of them involve some costly process in addition to welding. In-process control of weld distortion becomes more preferable than post-welding process or other methods, when manufacturing efficiency is considered. In recent years, in-process control welding by additional cooling has been proposed as one of techniques for reducing weld distortion and partially applied for thin-plate structure in industries. However, the effectiveness of additional cooling method has not yet been fully clarified. In this study, the effectiveness of additional cooling method and appropriate cooling condition for effective reduction in weld distortion are investigated by three-dimensional thermal elastic–plastic analysis. In addition, the effect of locally cooled temperature distribution on generation behaviour of plastic strain is discussed. As a result, it is concluded that the effectiveness of additional cooling and appropriate cooling condition for reduction in weld distortion are dependent on weld distortion under consideration and welding conditions. Especially, it is necessary for reduction in weld distortion to set the cooling torch at the appropriate position. For example, in order to reduce angular distortion effectively, the appropriate cooling position is dependent on the mechanical melting length during welding.     

Coaxial hybrid process of hollow cathode TIG and YAG laser welding

To make progress in laser-arc hybrid welding, especially when applied to thick steel plate, it is essential to get the remarkable synergic effect of deep penetration. It is suggested that the effective process is combining hollow cathode TIG with high beam quality laser welding. Penetration of hollow TIG/YAG hybrid welding was investigated by numerical analysis. A keyhole surface model taking into account the laser beam parameter product (BPP) was developed. The calculated keyhole surface profiles of coaxial hybrid welding are wider and deeper than that of YAG laser welding alone. As a result, single-pass butt welding of 20 mm thickness steel plate was achieved under the conditions of BPP = 0.9 mm mrad at laser power 1.8 kW. To confirm numerical results, coaxial hybrid welding tests with a hollow cathode TIG was conducted. The welding penetration was about two times as deep as a YAG laser alone. It was found that coaxial hybrid welding with hollow TIG/YAG had a large synergic effect.     

Application of carbonated apatite coating on a Ti substrate by aqueous spray method

The fabrication and characterization of a carbonate-containing apatite film deposited on a Ti plate via an aqueous spray method is described. The mist of the spray solution emitted from a perpendicularly oriented airbrush was made to strike a warmed Ti substrate. The thicknesses of the sprayed film and those heat-treated at 400 °C–700 °C under Ar gas flow were in the range 1.21–1.40 μm. The results of elemental analyses and Fourier transform infrared spectroscopy of the powders that were mechanically collected from the surface of the sprayed film suggest that the film was Ca₁₀(PO₄)6(CO₃) · 2CO₂ · 3H₂O. The presence of the carbonate ion and the lattice CO₂ molecule was confirmed via the aforementioned analyses; the finding was also consistent with the X-ray diffraction patterns of the films and the chemical identity of the sprayed and heat-treated films that were measured using X-ray photoelectron spectroscopy. The sprayed film comprises a characteristic network structure, which contains round particles within the networks, as was observed by field-emission scanning electron microscopy. A scratch test indicated that the shear stress of the sprayed film (21 MPa) significantly improved to 40 and > 133 MPa after heat-treatment at 600 °C and 700 °C, respectively, under Ar gas flow for 10 min.     

Computer simulation of a porous positive electrode for lithium batteries

The discharge characteristics of a Li/Li_yCoO₂ cell were simulated by numerical calculations. Based on the program proposed by Newman's group, the change in entropy due to lithium-ion insertion into the active materials was introduced into the open-circuit potential (OCP) for more practical applications. The OCP of LiCoO₂ (y = 1) at a full-discharge state was 3.82 V, which was determined from the original program. However, it should show a rapid decrease to minus infinity when discharge is complete (y = 1), which is due to the introduced entropy term. In addition, the local use of active materials across the Li_yCoO₂ electrode was not uniform, whereas the original program showed a constant value throughout the electrode. Based on the present results, the introduction of an entropy term to the OCP of Li_yCoO₂ works reasonably well for more practical applications.     

Functional expression of a plant hydroxynitrile lyase in Escherichia coli by directed evolution: creation and characterization of highly in vivo soluble mutants

Low protein solubility of recombinantly expressed proteins in Escherichia coli is a major factor hindering their application and analysis. We generated highly in vivo soluble mutants of a hydroxynitrile lyase in E.coli using protein engineering. Structure-guided saturation mutagenesis caused high solubility of single Lys-Pro mutations at positions 176, 199 and 224 of this low soluble wild-type enzyme. The triple Lys-Pro mutant generated at these surface conserved residues showed up to 8-fold increase in specific activity in the cell-free extract. Random mutagenesis also created a mutant of His103Met with 18.5-fold increase. The main expression form was reversed from insoluble to the soluble fraction following both types of above-mentioned mutations in E.coli at 37°C. The findings challenge the rationale of producing recombinant proteins in this host at 37°C. Formerly wild type low soluble protein was then present as soluble protein by these mutations, which also elevated the total soluble protein fraction in E.coli. Saturation mutagenesis of His103 provided other highly soluble mutants with hydrophobic substitutions. These mutations caused only minor secondary structural changes as determined by circular dichroism and Fourier-transform infrared spectroscopy and affected catalytic efficiency slightly for the purified mutants (0.82-1.6-fold for benzaldehyde and 0.9-1.9-fold for mandelonitrile). The stability of the mutants was differed from that of the wild type at high temperatures and at pH >8. Exchanging the buried basic-polar residue His103 with hydrophobic amino acids is in line with the overall structure of the enzyme, i.e. having hydrophilic residues in solvent-exposed areas and hydrophobic residues in the core.