Hot isostatic pressing of tetragonal ZrO2 solid-solution powders prepared from acetylacetonates in the system ZrO2-Y2O3-Al2O3

In compositions having ZrO₂/Y₂O₃=(74.25–71.25)/(0.75–3.75) (mol% ratio) with 25 mol% Al₂O₃, metastable t-ZrO₂ solid solutions crystallize at 780° to 860°C from amorphous materials prepared by the simultaneous hydrolysis of zirconium, yttrium and aluminium acetylacetonates. Hot isostatic pressing has been performed for 1 h at 1130 and 1230°C under 196 MPa using their powders. Two kinds of material are fabricated: (i) perfect ZrO₂ solid-solution ceramics and (ii) composites of ZrO₂ solid solution and -Al₂O₃. Their mechanical properties are examined, in connection with microstructures and t/m ZrO₂ ratios. Composites with a homogeneous dispersed -Al₂O₃ derived from solid-solution ceramics result in a remarkable increase of strength.     

Methanation of carbon deposited directly from CO2 on rhodium-bearing activated magnetite

Methanation reactivity was studied for the surface carbon deposited from CO₂ on the surface of Rh-bearing activated magnetite. The most active material (Rh=0.83 wt %) for methanation was prepared by the impregnation method at 60°C and showed 98% conversion at 300°C. The surface carbon was composed of elemental carbon (-carbon) and polymerized carbon (-carbon), the proportion being dependent on the density of carbon deposited. In temperature-programmed surface reaction, the extent of conversion of the - and -carbon to CH₄ was 0.34 (-carbon) and 0.53 (-carbon), respectively, and the total conversion was 0.87. This result indicates that not only elemental carbon but polymerized carbon (-carbon) could be converted to CH₄ on the Rh-bearing activated (-carbon) magnetite, whereas -carbon is not hydrogenated on activated magnetite.     

Methanation of CO2 with the oxygen-deficient Ni(II)-ferrite under dynamic conditions

The continuous methanation of CO₂ has been accomplished over hydrogen-reduced Ni(II)-bearing ferrite (Ni_xFe_3–xO_4–; x=0.39, > 0) in a mixed gas flow of CO₂ and H₂ at 250–375 °C. The yield and the selectivity for the methanation were larger than 50% and 95%, respectively, at the initial stage of the process. They decreased to 31% and 89%, respectively, after 6 h methanation. The innovative results can be ascribed to the use of the new material; hydrogen-reduced Ni(II)-bearing ferrite. Its formation was evinced by chemical analyses and the increase in the lattice constant; the lattice constant of the Ni(II)-bearing ferrite (a₀ 0.8375 nm) was enlarged to 0.8379 nm by hydrogen reduction. The enlarged lattice constant was not changed during the methanation. These findings suggest that the methanation occurs at the oxygen-deficient site of the hydrogen-reduced Ni(II)-bearing ferrite, as well as the formation of water by combination of the incorporated oxygens with hydrogen. The methanation consists of three steps of the elementary reaction. First, the oxygen-deficient sites are formed by hydrogen reduction; second, CO₂ is reduced to elementary carbon and two oxygen ions which are incorporated into the oxygen-deficient sites; and third, the carbon deposited on the surface of the reduced ferrite is selectively hydrogenated to CH₄.     

Dynamic Transformation Mechanism for Producing Ultrafine Grained Steels

Ultrafine grained (UFG) steels with grain sizes around 1 micron exhibit an excellent strength‐ductility combination and have been extensively studied worldwide. Among the different grain refinement strategies, thermomechanical controlled processing (TMCP) employing dynamic transformation (DT), that is, ferrite transformation during deformation of austenite, is considered as the simplest and commercially exploitable approach to produce ultrafine ferrite (UFF) with grain size of a couple of microns or below. The present paper reviews the research history of DT and highlights the major aspects of continuous interest including the methods and evidences for identifying DT, thermodynamics and kinetics of DT, mechanism for UFF formation and the effects of some key thermomechanical parameters on DT (and UFF formation), together with an outlook for the future research, and new TMCP design for industrial application. This paper also discusses some areas remaining under debate such as the diffusional or displacive mechanism, thermodynamic modeling, and the mechanism for UFF formation, etc.

     

The effects of amino-acid mutations on specific interactions between urokinase-type plasminogen activator and its receptor: Ab initio molecular orbital calculations

During cancer invasion, the binding of urokinase-type plasminogen activator (uPA) to its receptor (uPAR) on the surface of a cancer cell is considered a trigger for invasion. Here, we present a stable structure of the solvated complex formed between uPA and uPAR (uPA-uPAR) and investigate the specific interactions between uPA and uPAR by ab initio fragment molecular orbital (FMO) calculations. The result indicates that the electrostatic interactions between the charged amino acid residues existing in both uPA and uPAR make a large contribution to the binding between uPA and uPAR. In particular, Lys23, Lys46, Lys98 and Lys61 of uPA are found to have strong attractive interactions with uPAR. To elucidate the effect of these residues on the interactions between uPA and uPAR, we substituted each of them with the uncharged amino acid Leu and investigated the interactions between the mutated uPA and wild-type uPAR. The interaction energies indicate that Lys46 and Lys98, which bind uPA to the rim of the central ligand-binding cavity of uPAR, make greater contributions to the binding between uPA and uPAR than Lys23, which is positioned at the bottom of the ligand-binding cavity of uPAR. The effect of hydrating water molecules located between uPA and uPAR is also investigated to be significant for the specific interactions between uPA and uPAR. These results are expected to be informative for developing new peptide antagonists that block the binding of uPA to uPAR.     

A control method with pheromone information for a transport system

Since the control methods of a transport system between processing machines are specialized for each layout of the system, it is difficult to design prompt schedules and control logic for new complicated systems, especially in cases of machine faults or restructuring the system to modify the layout. In this article, we describe a multiagent transport control system which utilizes pheromone information. Each element of the system acts as an agent and estimates the appropriate path and time to drive out the products using information obtained by communication with other elements as well as pheromone information deposited on the tracks of the products.     

Theoretical and evolutionary parameter tuning of neural oscillators with a double-chain structure for generating rhythmic signals

A neural oscillator with a double-chain structure is one of the central pattern generator models used to simulate and understand rhythmic movements in living organisms. However, it is difficult to reproduce desired rhythmic signals by tuning an enormous number of parameters of neural oscillators. In this study, we propose an automatic tuning method consisting of two parts. The first involves tuning rules for both the time constants and the amplitude of the oscillatory outputs based on theoretical analyses of the relationship between parameters and outputs of the neural oscillators. The second involves an evolutionary tuning method with a two-step genetic algorithm (GA), consisting of a global GA and a local GA, for tuning parameters such as neural connection weights that have no exact tuning rule. Using numerical experiments, we confirmed that the proposed tuning method could successfully tune all parameters and generate sinusoidal waves. The tuning performance of the proposed method was less affected by factors such as the number of excitatory oscillators or the desired outputs. Furthermore, the proposed method was applied to the parameter-tuning problem of some types of artificial and biological wave reproduction and yielded optimal parameter values that generated complex rhythmic signals in Caenorhabditis elegans without trial and error.     

感应电机无速度传感器矢量控制系统的定子电阻在线辨识

该文针对利用磁通观测器推算转子磁通的感应电机无速度传感器矢量控制系统，提出了定子电阻在线辨识法。在利用q轴磁通推算转速的基础上，该系统利用d轴磁通误差实现定子电阻在线辨识，该方案的优点是系统简单，解决了低速运行时电压模型的定子电阻变化对系统稳定性和速度控制精度的影响问题。数字仿真和实验结果验证了定子电阻在线辨识的必要性和该方案的有效性。     

Speed control of general‐purpose engine with electronic governor

This paper presents a general‐purpose engine speed control system with an electronic governor in order to improve the current system with a mechanical governor, which shows unstable characteristics as a result of a change in mechanical friction or the A/F ratio (air–fuel ratio). The control system above has the problems that the feedback signal is only the crank angle because of cost, and the controlled object is a general‐purpose engine, which is strongly nonlinear. In order to overcome these problems, a system model is presented for dynamic estimation of the amount of air flow, and a robust controller is designed. In concrete terms, the proposed system includes a robust sliding‐mode controller using the feedback signal of only the crank angle, with a genetic algorithm applied to the controller design. Simulations and experiments performed using Matlab/Simulink show the effectiveness of our proposal. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 64–71, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21130