Formation mechanism of monodispersed spherical core-shell ceria/polymer hybrid nanoparticles

Very unique core-shell ceria (cerium oxide)/polymer hybrid nanoparticles that have monodispersed spherical structures and are easily dispersed in water or alcohol without the need for a dispersant were reported recently. The formation mechanism of the unique nanoparticles, however, was not clear. In order to clarify the formation mechanism, these nanoparticles were prepared using a polyol method (reflux heating) under varied conditions of temperature, time, and concentration and molecular weight of added polymer (poly(vinylpyrrolidone)). The size of the resultant nanoparticles was strongly and complicatedly dependent on the set temperature used during reflux heating and the poly(vinylpyrrolidone) molecular weight. Furthermore, the size of the nanoparticles increased by a 2-step process as the reflux heating time increased. The IR spectral changes with increasing reflux time indicated the increase in the number of cross-linked polymers in the shell. From these results, the formation mechanism was discussed and proposed.     

Dynamic finite element simulation of the gunshot injury to the human forehead protected by polyvinyl alcohol sponge

Although there are some traditional models of the gunshot wounds, there is still a need for more modeling analyses due to the difficulties related to the gunshot wounds to the forehead region of the human skull. In this study, the degree of damage as a consequence of penetrating head injuries due to gunshot wounds was determined using a preliminary finite element (FE) model of the human skull. In addition, the role of polyvinyl alcohol (PVA) sponge, which can be used as an alternative to reinforce the kinetic energy absorption capacity of bulletproof vest and helmet materials, to minimize the amount of skull injury due to penetrating processes was investigated through the FE model. Digital computed tomography along with magnetic resonance imaging data of the human head were employed to launch a three-dimensional (3D) FE model of the skull. Two geometrical shapes of projectiles (steel ball and bullet) were simulated for penetrating with an initial impact velocity of 734 m/s using nonlinear dynamic modeling code, namely LS-DYNA. The role of the damaged/distorted elements were removed during computation when the stress or strain reached their thresholds. The stress distributions in various parts of the forehead and sponge after injury were also computed. The results revealed the same amount of stress for both the steel ball and bullet after hitting the skull. The modeling results also indicated the time that steel ball takes to penetrate into the skull is lower than that of the bullet. In addition, more than 21 % of the steel ball’s kinetic energy was absorbed by the PVA sponge and, subsequently, injury sternness of the forehead was considerably minimized. The findings advise the application of the PVA sponge as a substitute strengthening material to be able to diminish the energy of impact as well as the load transmitted to the object.     

Synthesis of fixed-structure robust controllers using a constrained particle swarm optimizer with cyclic neighborhood topology

The purpose of this paper is to develop design scheme based on an easy-to-use meta-heuristic approach with superior reliability and validity for fixed-structure robust controllers, satisfying both multiple control specifications and system stability conditions. For this purpose, a particle swarm optimizer is first developed, which reduces the probability of premature convergence to local optima in the PSO (particle swarm optimization) by exploiting the particle’s local social learning based on the idea of cyclic-network topology. Next, it is shown how to obtain a fixed-structure robust controller with constraints on multiple H_∞ specifications and system stability based on the developed PSO technique incorporated with a simple constraint handling method. Finally, typical numerical examples are studied to show the applicability of the proposed methodology to the synthesis of fixed-structure robust controllers. These examples clearly verify that the developed design scheme gives a novel and powerful impetus with remarkable reliability to fixed-structure robust controller syntheses.     

Phase Relationships and Physical Properties of Homologous Compounds in the Zinc Oxide-Indium Oxide System

Equilibrium phase relationships in the ZnO-In₂O₃ system were determined between 1100° and 1400°C using solid-state reaction techniques and X-ray diffractometry. In addition to ZnO and In₂O₃, nine homologous compounds, Zn _k In₂O _{k +3} (where k = 3, 4, 5, 6, 7, 9, 11, 13, and 15), were observed. Electrical conductivity and diffuse reflectance of the k = 3, 4, 5, 7 and 11 members were measured before and after annealing at 400°C for 1 h under forming gas (4%₂-96% N₂). Room-temperature conductivity increased as k decreased, because of increased carrier concentration as well as increased mobility. In general, transparency in the wavelength range of 450-900 nm increased as k increased. Reduction in forming gas resulted in increased conductivity and reduced transparency for all compounds measured. The highest room-temperature conductivity measured, 270 S/cm, was that of reduced Zn₃In₂O₆.     

Characteristics of surface roughening during plane strain compression of polycrystalline iron

Roughening behavior of the free surface of polycrystalline iron during plane strain compression is investigated experimentally. The changes in the shape of the free surface, which is roughened during plastic deformation, are observed in the three-dimensions. It is found that the mountains and the valleys of the roughened shape tend to elongate in the constrained direction for the specimen with isotropic grain shape. The shapes of the roughness curves in the loading direction and in the constrained direction are compared. The normalized height distribution of the roughness curve in the constrained direction is symmetric, while that of the roughness curve in the loading direction is asymmetric and positively skew during plane strain compression. Based on a simple simulation of the roughness curves by a random midpoint displacement method, this difference is supposed to be caused by the constraint of the material flow under plane strain condition.     

Position sensorless control of interior permanent magnet synchronous motor using extended electromotive force

Driving a permanent magnet synchronous motor (PMSM) requires the rotor position information to control the motor torque, and this is generally detected by mechanical position sensors such as an encoder or a resolver. However, these sensors increase the machine size and the cost of the drive, and reduce reliability of the system. Therefore, many papers about position sensorless drive method of PMSM have been published. This paper presents a position sensorless control of interior permanent magnet synchronous motor (IPMSM). A mathematical model of IPMSM using the extended electromotive force (EMF) in the rotating reference frame is utilized to estimate the rotor speed and position. This model has a simple structure integrating position information into the extended EMF term. Therefore, the sensorless control based on the mathematical motor model can be implemented simply. The estimation method proposed is based on the principle that the error of the current is proportional to that of extended EMF. This method was carried out using a 6‐pole, 400‐W, 1750 r/min test motor system. It was found that sensorless speed control was achieved from 80 r/min to 1800 r/min under 0 to 100%loads. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(3): 41–48, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20406     

Chiral alkylated poly(m-phenylene)s: Optical activity and thermal stability of helical structures

Chiral poly[4,6-bis(alkylthio)-1,3-phenylene-alt-2-methyl-1,3-phenylene] was synthesized from 1,3-dibromo-2,6-bis(3-dodecyl-2-methylthio)benzene and 2-methyl-1,3-phenylenebis(pinacol borate) as a precursor of chiral poly(thiaheterohelicene). Circular dichroism (CD) spectra that arise from the poly(1,3-phenylene) backbone inverted according to the chirality of the side chains, which indicated that a helical conformation of the polymer was induced by the interaction between the side chains. The CD intensity of the polymer increased in non-polar solvents such as hexane. The decrease in the molar CD intensity and the broadening of a fluorescence band at higher concentrations suggested that the aggregation of the polymer suppressed the formation of the helical structure. The conformational changes were monitored by the CD and the ¹H NMR spectra at different temperatures. In a good solvent such as dichloromethane, the CD intensity increased, and the ¹H NMR signal of benzene protons shifted to lower fields at low temperatures. In hexane, the CD spectra and the ¹H NMR signals were less dependent on temperatures, as a result of the strong interaction between the chiral alkyl chains in the polymer to freeze the helical conformation.     

Syntheses and Electronic Behaviors of Networked Alternating Aluminum-organic Moiety Hybrid Copolymers

Hybrid copolymers with aluminum-organic moiety frameworks were successfully prepared by reacting aluminum tri-sec-butoxide with several organic diols. The compositions of the resulting copolymers were determined using IR spectroscopy, ICP, elemental analysis and CP/MASS ¹³C-NMR spectroscopy. The UV-VIS spectra of the copolymers were also obtained. ESR spectral examinations of the copolymers and ab-initio calculations of the copolymer models indicate that an electron transfer takes place from the organic moiety to the aluminum atom in the framework.     

The compression of rigid-perfectly-plastic material between rough parallel dies of unequal width

The results are given of calculations of the pressure to compress plastically, ideal material between perfectly rough parallel plates of variously unequal widths which do not overhang the material and in which the die width exceeds the material thickness. The rate of approach of the dies is also stated for certain die parameters. A particular solution is also given for the case when there is less than shearing friction between the material and the plates.