Hydrodynamic interaction between two red blood cells in simple shear flow: its impact on the rheology of a semi-dilute suspension

Blood is a suspension of red blood cells (RBCs) and its rheology is important when discussing the physiology of the cardiovascular system. In this study, we performed a numerical investigation of the rheological properties of an RBC suspension from the dilute to semi-dilute regime. RBCs were modelled as a capsule with a two-dimensional hyperelastic membrane. Large deformation of the thin membrane was calculated by a finite element method. Due to the small size of the RBC, fluid motion around the RBC was assumed to follow Stokes flow and was solved by a boundary element method. In the dilute limit, cell–cell interactions were omitted and the bulk stress of the suspension was calculated by the stresslet generated on a single RBC. Interestingly, the effective shear viscosity of the dilute suspension decreased with increasing viscosity of the internal liquid. In the semi-dilute regime, cells can be considered as showing pairwise interactions. The effective shear viscosity of the semi-dilute suspension shows a quadratic increase with respect to the volume fraction. These findings are important for understanding the complex phenomena of blood rheology.     

Phosphorylation of 25-kDa synaptosome-associated protein. Possible involvement in protein kinase C-mediated regulation of neurotransmitter release

Protein kinase C-mediated phosphorylation of a 25-kDa synaptosome-associated protein (SNAP-25) was examined in living PC12 cells. Phorbol 12-myristate 13-acetate treatment enhanced high potassium-induced [3H]-norepinephrine release, and a 28-kDa protein recognized by an anti-SNAP-25 antibody was phosphorylated on Ser residues. The molecular size of the phosphorylated band decreased slightly following treatment with Clostridium botulinum type A neurotoxin, whereas the band disappeared after treatment with botulinum type E neurotoxin, indicating that the 28-kDa protein was SNAP-25. A phosphorylation is likely to occur at Ser187, as this is the only Ser residue located between the cleavage sites of botulinum type A and E neurotoxins. SNAP-25 of PC12 cells was phosphorylated by purified protein kinase C in vitro, and the amount of syntaxin co-immunoprecipitated with SNAP-25 was decreased by phosphorylation. These results suggest that the phosphorylation of SNAP-25 may be involved in protein kinase C-mediated regulation of catecholamine release from PC12 cells.     

A programmable logic array suitable for use in digital systemdesign laboratories

A specially designed programmable logic array (PLA) suitable for use in digital system design laboratories for undergraduates is presented. Rewriting the PLA is done just by transferring the new codes; no explicit erasing process is required. The number of product terms allowed implementation on the PLA is unlimited. The computation speed of the PLA is less than 100 ns. The PLA can communicate with a host computer by accepting a variety of commands for writing PLA codes and monitoring input and output values for the PLA. Using software tools developed for the PLA, the student can perform laboratory experiments at various levels. Another software tool permits programming the PLA in a high-level language. The excitation (next-state) and output functions of a controller circuit are naturally described in a simple syntactic construct. Laboratory experiments utilizing the PLA and student responses are also given     

In Situ measurement of effective gas diffusivity through hematite pellets during stepwise reductions

The Wicke-Kallenbach (W-K) method for effective gas diffusivity measurements could only be used in the vicinity of ambient temperatures. However, in the present study, this technique has been extended to temperatures of about 1273 K through use of a high-temperature cement. This newly developed high-temperature W-K method was applied toin situ measurements of the diffusive and viscous fluxes through hematite pellets during stepwise reductions. When the sam-ple (acid and basic pellets) is reduced, it swells significantly. However, a gas-tight seal between the holder and specimen was successfully maintained by use of a high-temperature cement. This cement, composed mainly of Na₂O (20 mass pct) and SiO₂, separates into a solid and liquid phase at elevated temperatures. Thus, it can move in the same direction as the expansion of sample and thereby maintain the gas-tight seal. With this new technique, the structural param-eters of gases based on the “dusty gas model” for D’Arcy’s flow, Knudsen diffusion, and mo-lecular diffusion were obtained. These parameters were compared with those estimated through pore structure models.     

Design of a polarized positron source for linear colliders

We propose a design of a polarized positron source for linear colliders. The design is based on electron–positron pair creation from polarized γ-rays which are produced by Compton scattering of circularly polarized laser light off a high-energy electron beam. Polarized positrons are created from those γ-rays incident on a thin conversion target. A future linear collider of the TeV-energy region requires an extraordinary large number of positrons (1×10¹⁰ positrons/bunch) in a multi-bunch time structure. To meet these requirements, our design employs a high-current, low-emittance electron beam of 5.8 GeV, 10 CO₂ lasers, and 200 laser–electron collision-points. At each collision point, a pair of specially designed parabolic mirrors is installed to achieve efficient head-on collisions. This system allows us to produce high-intensity polarized γ-rays, which effectively generate high-intensity polarized positrons with the magnitude of polarization greater than 50%.     

High-power CO2 laser-MIG hybrid welding for increased gap tolerance. Hybrid weldability of thick steel plates with a square groove

High power enhancement of laser processors has recently led to laser welding being used for the joining of thick steel plates. For example, the literature includes a study on the practical application of a 45 kW CO₂ laser for the welding of thick steel plates,¹ although few such applications have thus far been documented. The limited application of lasers to welding of thick steel plates is attributable to the narrow gap tolerance provided and the small laser beam diameter that leads to unacceptable welding defects, such as underfills, melt-through, and porosities.     

A novel structure for carbon nanotube reinforced alumina composites with improved mechanical properties

Engineering ceramics have high stiffness, excellent thermostability, and relatively low density, but their brittleness impedes their use as structural materials. Incorporating carbon nanotubes (CNTs) into a brittle ceramic might be expected to provide CNT/ceramic composites with both high toughness and high temperature stability. Until now, however, materials fabrication difficulties have limited research on CNT/ceramic composites. The mechanical failure of CNT/ceramic composites reported previously is primarily attributed to poor CNT-matrix connectivity and severe phase segregation. Here we show that a novel processing approach based on the precursor method can diminish the phase segregation of multi-walled carbon nanotubes (MWCNTs), and render MWCNT/alumina composites highly homogeneous. The MWCNTs used in this study are modified with an acid treatment. Combined with a mechanical interlock induced by the chemically modified MWCNTs, this approach leads to improved mechanical properties. Mechanical measurements reveal that only 0.9?vol% acid-treated MWCNT addition results in?27% and?25% simultaneous increases in bending strength (689.6 ± 29.1?MPa) and fracture toughness (5.90 ± 0.27?MPa?m(1/2)), respectively.     

Wavenumber domain analysis of two-dimensional SAW images captured by phase-sensitive laser probe system

This paper is aimed at demonstrating how the wavenumber domain analysis of two-dimensional (2-D) images captured by phase-sensitive laser probe systems is applied in the characterization of RF SAW devices. Effectiveness is demonstrated through the selective characterization of spurious resonance modes and scattered, nonguided modes appearing in SAW resonators.     

Experimental Determination of Phase Equilibria in the Co-Cr-Ni System

The phase equilibria between the γ (A1) and liquid phases and those between the γ, ε (A3), σ (D8_b) and α (A2) phases at temperatures between 750 and 1300 °C in the Co-Cr-Ni system were determined by differential scanning calorimetry and electron probe microanalysis. It was found that the γ solidus and liquidus temperatures decrease with increasing Cr or Ni content and that the difference between them increases with increasing Cr content. The phase equilibria at 800, 900, 1000, 1100, 1200 and 1300 °C were determined using two- or three-phase alloys, and the phase boundaries due to the magnetically induced phase separation in the γ and ε phases were also observed at 850, 800 and 750 °C by the diffusion couple method.