Microstructure and mechanical behaviour of 3Y-TZP/Mo nanocomposites possessing a novel interpenetrated intragranular microstructure

Yttria stabilized tetragonal zirconia polycrystal (Y-TZP)/0-100 vol % molybdenum (Mo) composites were fabricated by hot-pressing a mixture of Y-TZP powder containing 3 mol % yttria (Y₂O₃) and a fine Mo powder in vacuum. This composite system possessed a novel microstructural feature composed of an interpenetrated intragranular nanostructure, in which either nanometer sized Mo particles or equivalent sized zirconia (ZrO₂) particles located within the ZrO₂ grains or Mo grains, respectively. The strength and toughness were both greatly enhanced with increasing Mo content for the 3Y-TZP/Mo composites thus breaking through the strength-toughness tradeoff relation in transformation toughened ZrO₂ and its composite materials. They exhibited a maximum strength of 2100 MPa and a toughness of 11.4 MPa·m^1/2 for the composite containing 70 vol % Mo. These simultaneous improvements in strength and toughness were determined to be the result of a decrease in flaw size associated with the interpenetrated intragranular nanostructure, and a stress shielding effect created in the crack tip by the elongated Mo polycrystals bridging the crack tip in addition to the stress induced phase transformation.     

Preparation and characterization of TiO2 and polymer nanocomposite films with high refractive index

Novel nanocomposite films of TiO₂ nanoparticles and hydrophobic polymers having polar groups, poly (bisphenol‐A and epichlorohydrin) or copolymer of styrene and maleic anhydride, with high refractive indices, high transparency, no color, solvent‐resistance, good thermal stability, and mechanical properties were prepared by incorporating surface‐modified TiO₂ nanoparticles into polymer matrices. In the process of preparing colloidal solution of TiO₂ nanoparticles, severe aggregation of particles can be reduced by surface modification using carboxylic acids and long‐chain alkyl amines. These TiO₂ nanoparticles dispersed in solvents were found not to aggregate after mixing with polymer solutions. Transparent colorless free‐standing films were obtained by drying a mixture of TiO₂ nanoparticles colloidal solution and polymer solutions in vacuum. Transmission electronic microscopic studies of the films suggest that the TiO₂ nanoparticles of 3–6 nm in diameter were dispersed in polymer matrices while maintaining their original size. Thermogravimetric analysis results indicate that the nanocomposite film has good thermal stability and the weight fraction of observed TiO₂ nanoparticles in the film is in good accordance with that of theoretical calculations. The refractive index of nanocomposite films of TiO₂ and poly(bisphenol‐A and epichlorohydrin) was in the range of 1.58–1.81 at 589 nm, which linearly increased with the content of TiO₂ nanoparticles from 0 to 80 wt %. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Metastatic Voyage of Ovarian Cancer Cells in Ascites with the Assistance of Various Cellular Components

Epithelial ovarian cancer (EOC) is the most lethal gynecologic malignancy and has a unique metastatic route using ascites, known as the transcoelomic root. However, studies on ascites and contained cellular components have not yet been sufficiently clarified. In this review, we focus on the significance of accumulating ascites, contained EOC cells in the form of spheroids, and interaction with non-malignant host cells. To become resistant against anoikis, EOC cells form spheroids in ascites, where epithelial-to-mesenchymal transition stimulated by transforming growth factor-β can be a key pathway. As spheroids form, EOC cells are also gaining the ability to attach and invade the peritoneum to induce intraperitoneal metastasis, as well as resistance to conventional chemotherapy. Recently, accumulating evidence suggests that EOC spheroids in ascites are composed of not only cancer cells, but also non-malignant cells existing with higher abundance than EOC cells in ascites, including macrophages, mesothelial cells, and lymphocytes. Moreover, hetero-cellular spheroids are demonstrated to form more aggregated spheroids and have higher adhesion ability for the mesothelial layer. To improve the poor prognosis, we need to elucidate the mechanisms of spheroid formation and interactions with non-malignant cells in ascites that are a unique tumor microenvironment for EOC.     

A model for a long-term diffusion of multispecies in concrete based on ion–cement-hydrate interaction

A model for simulating a long-term diffusion in concrete under submerged conditions has been developed. The model focuses on the interaction between cement hydrates and electrolyte solution adopting the physical properties of concrete as alternative parameters for estimating long-term diffusion. The model was verified by the large variety of long-term experimental data involving verification of cement hydrates, porosity properties, pH value, element distribution, and chloride penetration for sulphate-resistant Portland cement (SRPC) concretes. Evaluating impacts of hundreds of years’ exposure on concrete durability, a simulation was also performed for an exposure time of 500 years. The results confirmed the importance of ion–cement-hydrate interaction in the evaluation of a long-term diffusion of harmful substances such as chlorides into concrete. The simulation results show also that the solid phases of the SRPC concrete mix that was used are stable in the long-term. The threshold concentration of chlorides which may initiate reinforcement corrosion defined as Cl^?/OH^? ratio could be exceeded in concrete after moderate exposure period under the conditions investigated with typical protective concrete layers. Using of case-specific values for a threshold chloride content and evaluating the method used for estimating the initiation time of reinforcement corrosion are recommended in the structures with a long-design service life.     

Effect of the t–m transformation morphology and stress distribution around the crack path on the measured toughness of zirconia ceramics: A case study on Ce-TZP/alumina nanocomposite

The t–m transformation zone and related residual stress fields around two types of crack used for toughness measurements, i.e. SEVNB (arrested crack induced by a V-notch) and IF methods (indentation crack induced by a Vickers impression), are reported for a Ce-TZP/Al₂O₃ nanocomposite, in comparison with 3Y-TZP. The fact that Ce-TZP/Al₂O₃ exhibits significant high toughness value on occasions when evaluated by the IF method was determined to be clearly linked to the presence of wide ranged three-dimensional transformation configuration and resulting substantial compressive residual stress fields. In contrast, for 3Y-TZP, transformation behaviors around the two types of crack were quite similar, which proves that 3Y-TZP shows near toughness values for both SEVNB and IF methods.     

A new type of nanocomposite in tetragonal zirconia polycrystal-molybdenum system

A ceramic/metal nanocomposite in tetragonal zirconia-molybdenum system possesses a novel microstructural feature composed of a mutual intragranular nanostructure, in which either nanometer sized Mo particles or equivalent sized zirconia particles are located within the zirconia grains or Mo grains, respectively. It achieves a simultaneous improvement in strength and toughness that overcomes the strength-toughness tradeoff relation.     

Effects of bafilomycin A1 on Japanese encephalitis virus in C6/36 mosquito cells

Involvement of intracellular acidic compartments in the early phase of Japanese encephalitis (JE) virus infection of C6/36 mosquito cells was examined by bafilomycin A1, a specific inhibitor of vacuolar type H(+)-ATPase (V-ATPase). Dose dependent reduction of viral envelope protein (E) produced into the infected culture fluid was observed by pretreating the cells with 0.25 to 1.0 microM bafilomycin A1. In synchronized infection, cell surface-bound virions were internalized immediately by heating at 31 degrees C, followed by the release of nucleocapsid into the cytosol within a short lag period. Subcellular distribution of infecting 3H-uridine-labeled viral RNA (V-RNA) and its RNase sensitivity were analyzed by fractionation in Percoll density gradient centrifugation. At a 10 min chasing period, an RNase resistant V-RNA peak was found in fractions with a mean density of 1.05 g/ml corresponding to the endosome, while an RNase sensitive V-RNA peak was detected at density range of 1.052-1.054 g/ml corresponding to the ribosome in C6/36 cell homogenate. The results indicate that JE virus infection in C6/36 cells proceeded through the endocytic pathway involving intracellular acidic compartments which was affected by bafilomycin A1.     

Nitric Oxide and Reactive Oxygen Species in the Pathogenesis of Preeclampsia

Preeclampsia (PE) is characterized by disturbed extravillous trophoblast migration toward uterine spiral arteries leading to increased uteroplacental vascular resistance and by vascular dysfunction resulting in reduced systemic vasodilatory properties. Its pathogenesis is mediated by an altered bioavailability of nitric oxide (NO) and tissue damage caused by increased levels of reactive oxygen species (ROS). Furthermore, superoxide (O₂⁻) rapidly inactivates NO and forms peroxynitrite (ONOO⁻). It is known that ONOO⁻ accumulates in the placental tissues and injures the placental function in PE. In addition, ROS could stimulate platelet adhesion and aggregation leading to intravascular coagulopathy. ROS-induced coagulopathy causes placental infarction and impairs the uteroplacental blood flow in PE. The disorders could lead to the reduction of oxygen and nutrients required for normal fetal development resulting in fetal growth restriction. On the other hand, several antioxidants scavenge ROS and protect tissues against oxidative damage. Placental antioxidants including catalase, superoxide dismutase (SOD), and glutathione peroxidase (GPx) protect the vasculature from ROS and maintain the vascular function. However, placental ischemia in PE decreases the antioxidant activity resulting in further elevated oxidative stress, which leads to the appearance of the pathological conditions of PE including hypertension and proteinuria. Oxidative stress is defined as an imbalance between ROS and antioxidant activity. This review provides new insights about roles of oxidative stress in the pathophysiology of PE.     

Development of flexible polymer blend films from advanced copna resin and nylon 6

The application of advanced polycondensed fused polynuclear aromatic (COPNA) resin to a material for flexible printed wiring boards was studied in this work. To give flexibility to the advanced COPNA resin, a polymer blend technology was introduced. Nylon 6 was selected from the nominated blend polymers with advanced COPNA resin because of sufficient compatibility between the advanced COPNA resin and the amino groups. The polymer blend film, consisting of advanced COPNA resin and nylon 6 prepared at a blend fraction of 50/50 (COPNA/nylon 6), exhibited sufficient flexibility for printed wiring boards, and exhibited attractive properties of T_g at 158°C and a dielectric constant at 3.6. Morphological analysis was also carried out by transmission electron microscopy to the blends. Phase-separated structures were observed in entire systems of fully cured films because of crystallinity of the nylon 6, but sufficient compatibility for practical uses was observed in both the 30/70 and 50/50 systems. The compatibility became poor with an increase of the advanced COPNA resin fraction. © 1996 John Wiley & Sons, Inc.