Two-scale and full-scale analyses of elastoplastic honeycomb blocks subjected to flat-punch indentation

In this study, we perform comparative two-scale and full-scale analyses of elastoplastic regular hexagonal honeycomb blocks subjected to in-plane flat-punch indentation. Zigzag and armchair types of cell arrangements are considered for the blocks; relatively thick cell walls are assumed to focus on the effect of cell wall yielding rather than cell wall deflection. For the two-scale analysis, the fully implicit homogenization scheme developed by Asada and Ohno [Asada, T., Ohno, N., 2007. Fully implicit formulation of elastoplastic homogenization problem for two-scale analysis. International Journal of Solids and Structures 44, 7261–7275] is rebuilt by introducing half unit cells to halve the analysis domains in unit cells. For the full-scale analysis, three cell sizes are considered. It is shown that the two-scale analysis provides no apparent dependence on the two types of cell arrangements because of their equivalence under in-plane loading, whereas the full-scale analysis reveals that the local deformation in honeycomb blocks is highly dependent on cell arrangement. Nevertheless, the two-scale analysis is found to be successful in predicting the indentation load-displacement relation and the macroscopic localization direction in honeycomb blocks.     

The Bipolaron in the Strong Coupling Limit

The bipolaron are two electrons coupled to the elastic deformations of an ionic crystal. We study this system in the Fr?hlich approximation. If the Coulomb repulsion dominates, the lowest energy states are two well separated polarons. Otherwise the electrons form a bound pair. We prove the validity of the Pekar–Tomasevich energy functional in the strong coupling limit, yielding estimates on the coupling parameters for which the binding energy is strictly positive. Under the condition of a strictly positive binding energy we prove the existence of a ground state at fixed total momentum P, provided P is not too large. Tadahiro Miyao: This work was supported by Japan Society for the Promotion of Science (JSPS). Permanent address: The graduate school of natural science and technology, Okayama university, Okayama 700-8530, Japan. Submitted: December 14, 2006. Accepted: March 20, 2007.     

Phosphotransacetylase as a key factor in biological production of polyhydroxybutyrate

Phosphotransa cetylase (Pta) catalyzes the reversible conversion of, acetyl-coenzyme A (CoA) to acetyl phosphate. Polyhydroxybutyrate (PHB) synthase and accumulation were compared between a Pta-deficient mutant and the wild-type Escherichia coli, which were transformed with pAE100, coding for 3-ketothiolase, NADPH-dependenta cetoacetyl-CoA reductase, and PHB synthase from Ralstonia eutropha. During the growth period, PHB synthase activity in the Pta-deficient mutant was lower than that in the wild type. PHB accumulation in the Pta-deficient mutant, however, was higher than that in wild-type cells grown in Luria-Bertani (LB) medium containing 1% glucose (high C:N ratio). The Pta-deficient mutant showed PHB accumulation even in LB medium (low C:N ratio), whereas wild-type cells showed no PHB accumulation. These data suggest the activation of PHB synthase by acetyl phosphate that is synthesized by Pta. A decrease in Pta activity probably causes some increase in acetyl-CoA as substrate for the PHB synthesis pathway, resulting in increased PHB accumulation.     

An optical system for monitoring torsion in a power transmission shaft in realtime

An optical system has been proposed and verified experimentally for monitoring the torsion of a power transmission shaft in realtime. The system consists of a pair of lasers, mirrors and light receivers as a sensor head, and logic circuit, high-frequency oscillator, and computer as a data processing system. The smallest measurable angle of torsion can be expressed by ω/f, where ω is the rotational frequency of the power transmission shaft and f is the frequency of the oscillator. The experimental error was found to be a few percentage points.     

CRYSTAF Analysis of Polyethylene Synthesized with Phillips Catalyst

Crystallization analysis fractionation (CRYSTAF) was used for the first time to investigate the solution crystallization behavior of ethylene homopolymers and copolymers made with Phillips CrO_x/SiO₂ catalyst. Interestingly, the crystallization peak temperatures (T_p) of copolymers of ethylene and cyclopentene increased with increasing cyclopentene molar fraction in the copolymer. Comparing two factors (short chain branches (SCBs) and cyclopentene incorporation), decreasing SCB frequency is proposed as the dominant factor to explain the increase of crystallization peak temperatures with increasing cyclopentene incorporation. In addition, SCB frequency and molecular weight might be the two significant factors determining the crystallization temperature of polyethylene made with Phillips CrO_x/SiO₂ catalyst with different cocatalysts (triethylaluminum and diethylaluminum ethoxide).     

Palladium–Borane Cooperation: Evidence for an Anionic Pathway and Its Application to Catalytic Hydro‐/Deutero‐dechlorination

Metal–Lewis acid cooperation provides new opportunities in catalysis. In this work, we report a new type of palladium–borane cooperation involving anionic Pd⁰ species. The air‐stable DPB palladium complex 1 (DPB=diphosphine‐borane) was prepared and reacted with KH to give the Pd⁰ borohydride 2 , the first monomeric anionic Pd⁰ species to be structurally characterized. The boron moiety acts as an acceptor towards Pd in 1 via Pd→B interaction, but as a donor in 2 thanks to B‐H‐Pd bridging. This enables the activation of C?Cl bonds and the system is amenable to catalysis, as demonstrated by the hydro‐/deutero‐dehalogenation of a variety of (hetero)aryl chlorides (20 examples, average yield 85 %).