Markedly compressible behaviors of gellan hydrogels in a constrained geometry at ultraslow strain rates

The fracture behaviors of gellan hydrogels under compression remarkably depend on the strain rate as well as the boundary conditions for lateral expansion. In the geometry with no constraint for lateral expansion (conventional uniaxial compression), the gels rupture at relatively small strains independently of the compression rates. In contrast, when the gels are compressed extremely slowly (at a strain rate of ca. 10⁻⁵ s⁻¹) in the geometry prohibiting the lateral expansion at their top and bottom surfaces, they are remarkably compressible down to 2% of the initial height without macroscopic fracture and they are accompanied by a large amount of water release. In such markedly compressed gels, many microscopic cracks are formed around the central layer, where strain concentration occurs due to the nonuniform deformation arising from the constrained geometry. In the highly compressible case, the formation of macroscopic cracks is prevented by the localization of microscopic cracks as well as the enhancement in mechanical toughness by a significant increase in polymer concentration due to water release.     

Measurement of losses and saturated permeability of saturable coresunder submicrosecond saturation

Two specific methods are introduced for obtaining accurate losses and saturated permeability of saturable cores under submicrosecond saturation. One employs an additional inductor for accurate measurement of the losses. The other minimizes stray inductance for accurate measurement of the saturated permeability. The measured relative permeability of Co-based amorphous cores rapidly drops to nearly 1.0. On the other hand, ferrite cores need a much larger magnetic field than that for Co-based amorphous cores in order to obtain the relative permeability of 1.0     

Slit flow of molten polyethylene filled with plastic flakes

The processability of polyethylene in sheet-extrusion or calendering may be improved by the addition of plastic flakes. The effects of plastic flake parameters and flow conditions on the viscosity and the die swell of the suspension were determined, and the structure in flow (morphology or dispersion state) and applications were discussed. Flakes of biaxially oriented polystyrene, high-impact polystyrene, polypropylene, polyamide or polypropylene spheres were dry-blended with polyethylene. The viscosity was determined by means of a slit or a capillary rheometer. The quenched extrudate was annealed and its die swell was measured. Flakes of biaxially oriented polystyrene shrunk into rod-like form during heating, but other plastics retained the flake-form. The relative viscosity and the swell ratio of the suspensions depended on the type of plastic and operating conditions. The rheological behavior of suspensions qualitatively suggested that polypropylene flakes deformed or crowded (including stacking), polyamide flakes deformed slightly, and polystyrene flakes were difficult to buckle, but crowded slightly. The thickness of extrudates can be controlled easily by flake addition due to decreased die swell, while the output would be reduced to some extent.     

Properties of networks obtained by internal plasticization of epoxy resin with aromatic and aliphatic glycidyl compounds

In order to improve the fracture properties of p, p′-diaminodiphenylmethane-cured epoxy resin, various kinds of aromatic and aliphatic glycidyl compounds were investigated as a modifier at an amount of 30 wt %. Several compounds promoted the fracture toughness. In any glycidyl compounds, however, heat resistance was decreased by the modification. The dynamic mechanical properties of the modified epoxy resins were measured. The crosslinking density ρ was calculated from the theory of rubber elasticity, and the mechanical properties of the resins were discussed in regard to the crosslinking density. Tensile strength was scarcely affected by the crosslinking density. Elongation at break and Izod impact strength increased remarkably with decrease in crosslinking density. The fracture toughness K_Ic- increased with decrease in crosslinking density except at small ρ.     

Rinsing effect of alkaline electrolyzed water on nickel surfaces

The improvement in the surface cleanliness of electroplated nickel by rinsing in alkaline electrolyzed water (AEW) was determined. When the nickel plated sample was rinsed with the AEW, it was found that the amount of residual sulfate ion on the surface of a sample decreased approximately by half compared to one rinsed only with de-ionized pure water. Because nanosize hydrogen bubbles are present in the AEW, and the zeta-potential has a negative value, we then surmised that the mechanism of rinsing was as follows: The sulfate ions are selectively absorbed on the nanosize colloidal hydrogen bubbles, or substituted for anions absorbed on the hydrogen bubbles. The sulfate ions absorbed on the nickel surface then become detached. The detached sulfate ions are absorbed on the surface of the hydrogen bubbles, and negatively charge the hydrogen bubbles. It can be considered that any detached sulfate ions do not re-adhere due to the electrical repulsion force of the negatively charged nickel surface. Thus the sample is efficiently rinsed.     

Soluble and colorless polyimides with polyalicyclic structures [1]

Two tetracarboxylic dianhydrides with polyalicyclic structure, bicyclo[2.2.2]octane-2-endo, 3-endo, 5-exo, 6-exo-2,3:5,6-dianhydride (5a) and the all-exo isomer (5b), were synthesized in six steps using phthalic acid as a starting material. The dianhydrides were polymerized at 85–105°C in well-purified DMAc with aromatic diamines which were purified by two recrystallizations and then sublimation. The polyimides formed flexible and tough films, and were soluble in aprotic polar solvents such as DMAc. The 5%-weight loss temperatures were over 450°C. The polyimides possessed glass-transition temperatures in the range from 211 to 385°C. The polyimides films had a tensile modulus range of 1.5–2.6 GPa, a tensile strength range of 52–96 MPa, and an elongation range at break of 3–11%. The polyimide films showed cutoffs at wavelengths shorter than 320 nm and were entirely colorless. The colorlessness of the polyimide films was maintained up to 200°C when heated in air and to 400°C in a N₂ atmosphere.     

Real-time optical image subtraction and edge enhancement using ferroelectric liquid-crystal devices based on speckle modulation

We carried out real-time optical image subtraction and edge enhancement based on a speckle modulation technique by using ferroelectric liquid-crystal polarization switches and a ferroelectric liquid-crystal spatial light modulator. A ferroelectric liquid-crystal spatial light modulator is employed as a real-time and multiple-exposure optical device, and successful results are obtained from three-exposure images modulated by speckles. Thus, image subtraction and edge enhancement are realized in real time. The whole operation is performed within several milliseconds with modest operating conditions. Because the spatial light modulator has a high resolution of greater than 100 line pairs/mm and can store fine speckle patterns, the image qualities we obtained are quite satisfactory.