Preparation of nanometre size oxide particles using filter expansion aerosol generator

Crystalline zinc oxide particles of nanometre size (< 20 nm) particles were produced from a zinc acetate solution by using a filter expansion aerosol generator (FEAG). The FEAG is an aerosol generator that is operated at 60 torr reactor pressure and produces droplets of around 2 m. The shape of the particles produced by the FEAG were distinctively different from those produced by the ultrasonic spray source (USS). Results from scanning electron microscopy (SEM) and X-ray diffractometry (XRD) indicated that crystalline zinc oxide particles of nanometre size were produced at 600 °C in 0.02 s residence time. Weight loss of these particles, determined by thermogravimetric analysis (TGA), was 3 wt%. Based on the morphology change as a function of the reactor temperature and solute concentration, we proposed that the nanometre particles were formed by uniform precipitation at the drying stage and decomposition followed by disintegration into nanometre particles. It was also shown that exothermic decomposition of the solute was not required for the disintegration of the primary particles in the FEAG process. This result opened up an opportunity for producing carbon-free nanometre particles from nitrate salts by using the FEAG.     

The effect of the aspect ratio on the hydrophobicity of microstructured polydimethylsiloxane (PDMS) robust surfaces

In this study, we have designed and fabricated robust hydrophobic surfaces that are composed of various micropillar arrays and investigated the effect of the aspect ratio (feature height/feature size) of the micropillar on the wettability of the fabricated surfaces. The robust, micropillar-arrayed surfaces were designed to yield the same Wenzel and Cassie water contact angles (CAs). According to our design rule, one can achieve an enhanced hydrophobic surface by increasing the height of the micropillars. The designed hydrophobic surfaces were fabricated by polydimethylsiloxane (PDMS) replica molding with photolithographically micropatterned SU-8 masters. The hydrophobicity properties of the fabricated PDMS surfaces were fully characterized theoretically and experimentally. From the theoretical and experimental results, it was found that the micropillars of an intrinsically hydrophobic material with a high aspect ratio enhance the hydrophobicity of the surface by increasing the surface roughness (in view of the Wenzel state) and the opportunities for the entrapment of air beneath a water droplet (the Cassie state).     

Computational and mutagenesis studies of the streptavidin native dimer interface

Wt streptavidin forms a domain swapped tetramer consisting of two native dimers. The role of tetramerization has been studied previously and is known to contribute to biotin binding by allowing the exchange of W120 between adjacent subunits. However, the role of dimer formation in streptavidin folding and function has been largely overlooked to date, although native dimers are necessary for tetramer formation and thus for high affinity biotin binding. To understand how the side chain interactions at the dimer interface stabilize the subunit association, we studied the structural and functional consequences of introducing interfacial mutations by a combination of molecular dynamics (MD) simulation and biochemical characterization. In particular, we introduced rational mutations at the dimer interface to engineer new side chain interactions and measured the stability and function of the resulting mutants. We focused on two residues that form a "knob" and a "hole" pair, G74 and T76, since steric complementarity plays an important role at these positions. We introduced mutations that would change the polarity and side chain packing to test if the interface can be rationally redesigned. Both energy calculation and geometric parameterization were used to interpret the simulated structures and predict how the mutations affect the dimer stability. In this regard, obtaining precise energy estimates was difficult because the simulated structures have large stochastic variations and some mutants did not reach an equilibrium by the end of the simulation. In contrast, comparing the wt and mutants to one another and parameterizing the simulation using a geometric parameter, i.e. the degree of solvation of the buried interface, resulted in a testable prediction regarding which mutations would result in a stable dimer. We present experimental data (denaturation and binding measurements) to show that an intuitive parameter based on physical reasoning can be useful for characterizing simulations that are difficult to analyze quantitatively.     

A centrality analysis of the transaction relationships in Panasonic

Panasonic initiated a reform strategy called “Value Creation 21” in 2001. This strategy had a strong impact on its transaction relationships. This research covers one of the important issues in analyzing how the transaction network in Panasonic has changed during the period of “Value Creation 21.” In order to make Panasonic’s transaction relationships visible and countable, we have introduced graph theory and a measure centrality index from the viewpoints of degree, closeness, and betweenness by using data collected in 2002 and 2005. Our findings are reported here. First, the number of firms in Panasonic’s transaction network in 2005 was smaller than in 2002. Second, not only the degree, but also the closeness and betweenness, of the main firms in the Panasonic Group and their suppliers decreased a little more in 2005. Third, the number of in-degree firms declined, whereas the relative importance of Panasonic in the transaction network was more significant. Fourth, Panasonic’s affiliated firms in components & devices and the digital AVC network domain ranked higher than other firms in the transaction network. Last, its out-degree suppliers dropped more in 2005 than in 2002. With these findings, we finally concluded how Panasonic arranged its transaction relationships during the turnaround.     

Development of a sequential robust–tolerance design model for a destructive quality characteristic

Robust design (RD) and tolerance design (TD) have received much attention from researchers and practitioners for more than two decades, and a number of methodologies for modeling and optimizing the RD and TD processes have been studied. However, there is ample room for improvement. Because most existing research considers RD and TD as separate research fields, the primary objective of this paper is to develop a sequential robust–tolerance design method to jointly determine the best factor settings and the closed-form solutions for the optimal specification limits. We then apply the proposed method to a destructive quality characteristic. Finally, a case study and sensitivity analyses are performed for verification purposes, and further studies are discussed.     

Improving traversability of quadruped walking robots using body movement in 3D rough terrains

This paper presents a study on improving the traversability of a quadruped walking robot in 3D rough terrains. The key idea is to exploit body movement of the robot. The position and orientation of the robot are systematically adjusted and the possibility of finding a valid foothold for the next swing is maximized, which makes the robot have more chances to overcome the rough terrains. In addition, a foothold search algorithm that provides the valid foothold while maintaining a high traversability of the robot, is investigated and a gait selection algorithm is developed to help the robot avoid deadlock situations. To explain the algorithms, new concepts such as reachable area, stable area, potential search direction, and complementary kinematic margin are introduced, and the effectiveness of the algorithms is validated via simulations and experiments.     

The election problem in asynchronous distributed systems with bounded faulty processes

Determining the “weakest” failure detectors is a central topic in solving many agreement problems such as Consensus, Non-Blocking Atomic Commit and Election in asynchronous distributed systems. So far, this has been studied extensively for several such fundamental problems. It is stated that Perfect Failure Detector P is the weakest failure detector to solve the Election problem with any number of faulty processes. In this paper, we introduce Modal failure detector M and show that to solve Election, M is the weakest failure detector to solve election when the number of faulty processes is less than ⌈n/2⌉. We also show that it is strictly weaker than P.

Biofouling control by quorum sensing inhibition and its dependence on membrane surface

Biofouling control by quorum sensing (QS) inhibition and the influence of membrane surface characteristics on biofilm formation and QS inhibition were investigated. Pseudomonas putida isolated from the bio-fouled reverse osmosis (RO) membranes in a real plant was used. Acylase was chosen as a model QS inhibitor. Bacteria on the membrane coupons were quantified with the heterotrophic plate count method. Cell distribution was imaged by a confocal laser scanning microscope. Results showed that biofilm formation on the membrane was reduced by acylase as it inhibits the activity of N-acylhomoserine lactone (AHL) which is a signal molecule of QS. It was also shown that membrane surface characteristics were influential factors affecting bacterial adhesion, biofilm formation, and QS inhibition.