Effect of Impurities Control on the Crystallization and Densification of Polymer-Derived SiC Fibers.

The polymer-derived SiC fibers are mainly used as reinforcing materials for ceramic matrix composites (CMCs) because of their excellent mechanical properties at high temperature. However, decomposition reactions such as release of SiO and CO gases and the formation of pores proceed above 1400 °C because of impurities introduced during the curing process. In this study, polycrystalline SiC fibers were fabricated by applying iodine-curing method and using controlled pyrolysis conditions to investigate crystallization and densification behavior. Oxygen and iodine impurities in amorphous SiC fibers were reduced without pores by diffusion and release to the fiber surface depending on the pyrolysis time. In addition, the reduction of the impurity content had a positive effect on the densification and crystallization of polymer-derived SiC fibers without a sintering aid above the sintering temperature. Consequently, dense Si-Al-C-O polycrystalline fibers containing ß-SiC crystal grains of 50~100 nm were easily fabricated through the blending method and controlled pyrolysis conditions.

Effects of asperities and organic-inorganic interactions on the strength of nacre-mimetic composites.

Nacre is a natural organic-inorganic hybrid composite, whose hierarchical structure has a complex influence on its high strength. Many structural features have been discovered, which influence the mechanical properties of nacre, and the authors have a particular interest in the role of the asperities and organic-inorganic interactions. In this study, a composite was prepared which mimics the asperity structure using clay minerals. Organic-inorganic bonding was induced with silane treatment. Both factors increased the yield strength of the composites; however, different deformation behavior was exhibited. It was found that asperities improved the strength of the composite, and that composition influences the stiffness of the composite. The organic-inorganic interaction between the resin and the other components of the composite reduced the deformation of the composite and consequently improved strength.

Curcumin dose-dependently improves spermatogenic disorders induced by scrotal heat stress in mice.

Approximately 20% of couples worldwide are infertile and about half of these couples have male infertility. Therefore, it is important to develop effective strategies for preventing male infertility. In this study, we examined the effects and regulatory mechanisms of curcumin, an active ingredient in the traditional herbal treatment derived from the dietary spice turmeric (Curcuma longa), on exogenous scrotal heat stress-induced testicular injuries in mice. Adult mice were orally administered three different doses of curcumin (20, 40, or 80 mg per kg per day) for 14 consecutive days and then subjected to transient scrotal heat stress at 43 °C for 20 min on day 7. The testes and blood of the mice were collected on day 14. Mice exposed to heat stress showed low testicular weight, severe vacuolization of seminiferous tubules followed by loss of spermatogenic cells, and the appearance of multinucleated giant cells and degenerative Leydig cells. In addition, great changes in oxidative stress (lipid peroxidation, superoxide dismutase (SOD) activity, cytoplasmic SOD, mitochondrial SOD, and phospholipid hydroperoxide glutathione peroxidase mRNAs), apoptosis (B-cell lymphoma-extra large and caspase 3 mRNAs), heat shock reaction (heat shock transcription factor-1 and transforming growth factor-ß1 mRNAs) and androgen biosynthesis (testosterone concentration and 3ß-hydroxysteroid dehydrogenase mRNA) were observed. However, all these testicular injuries induced by the scrotal hyperthermia were significantly improved by curcumin treatment (20, 40 and 80 mg kg(-1)) in a dose-dependent manner via its antioxidative, anti-apoptotic and androgen synthesis effects, indicating that it has the potential to prevent male infertility.

Unique ordered domains of biphenylthiol self-assembled monolayers on Au(111).

The surface structure and adsorption conditions of biphenylthiol (BPT) self-assembled monolayers (SAMs) on Au(111) were examined using scanning tunneling microscopy (STM) and X-ray photoelectron microscopy (XPS). STM imaging revealed that the structural order of BPT SAMs formed in a 0.01 mM ethanol solution at 60 degrees C decreases with increasing immersion time. Interestingly, BPT SAMs formed after 30 min have unique ordered domains containing well-ordered (square root of 3 x square root of 3)R30 degrees structures and bright rows that are connected by small aggregated domains with a periodicity of approximately 10 angstroms, results that have never been observed for other thiol SAM systems. Distances between the bright rows were 20-35 angstroms. The bright small domains contained five or six BPT molecules each, which may have originated from differences in the adsorption orientations of biphenyl groups that were induced by localized interactions between them. XPS measurements for BPT SAMs on Au(111) showed the two sulfur peaks at 161.2 and 162.2 eV, implying the formation of chemisorbed monolayers. Our results are anticipated to be useful for understanding the formation and structure of BPT SAMs on gold surfaces.