Quantitative models on corrosion fatigue crack growth rates in metals: Part II. application of fatigue crack growth rate modeling for nickel-based superalloys at elevated temperatures

Approaches to predict da/dN-àK for environmental situations; including empirical interpolative equations, linear superposition of mechanical fatigue and time-based environmental cracking, and mechanism-based models; are presented. For several material-environment systems, these models were incorporated in fracture mechanics life prediction methods, and successes have been reported in evaluating the corrosion fatigue contribution. Considerable uncertainties are, however, associated with these models. The linear superposition analysis is emphasized; material-environment systems that are severely environment-sensitive should be adequately described by this method. Direct and indirect methods exist to define time-based crack growth rates for use in linear superposition predictions of da/dN. The linear superposition approach is effective, but only for those cases where K_ISCC is high relative to typical flawed component stress intensity levels. Empirical curve-fit models require an extensive environmental crack growth rate data base, which are costly to develop, and are effective for interpolations but not predictions of fatigue crack growth data. Mechanism-based models for broad predictions of cycle-time dependent da/dN versus àK, and other variables such as frequency or hold time, are in an infant state.     

The effect of crystalline morphology of poly (butylene terephthalate) phases on toughening of poly(butylene terephthalate)/epoxy blends

In an effort to investigate the effect of the crystalline morphology of a poly(butylene terephthalate) (PBT) phase on the toughening of PBT/epoxy blends, the blends, having different degrees of perfectness of the PBT crystalline phase, were prepared by blending PBT and epoxy at various temperatures ranging from 200 to 240 °C. As the blending temperature decreases, the degree of perfectness of the PBT crystalline phase increases as a result of the increase of crystal growth rate. For PBT/epoxy blends, the change in crystalline morphology induced by processing may be the most important cause for the dependency of the fracture energy on blending temperatures. It has been found that PBT phases with a well-developed Maltese cross are most effective for epoxy toughening. This dependency reveals the occurrence of a phase transformation toughening mechanism. Also, the higher relative enhancement of fracture energy of a higher molecular weight epoxy system is further indirect evidence for a phase transformation toughening mechanism. Some other toughening mechanisms observed from the fracture surfaces, such as crack bifurcation, crack bridging, and ductile fracture of PBT phases, have been found to also be affected by the blending temperatures.     

Blends of ethylene 1‐octene copolymer synthesized by Ziegler–Natta and metallocene catalysts. II. Rheology and morphological behaviors

The rheological and morphological behaviors of commercially available three binary blends of ethylene 1‐octene copolymer (EOC) regarding the melt index (MI), density and comonomer contents, one component made by the Ziegler–Natta and the other by the metallocene catalysts, were investigated to elucidate miscibility and phase behavior. Miscibility of the EOCs blend in a melt state was related to the value of the MI, density, and comonomer content. If the comonomer contents are similar, then the melt viscosity is weight average value, otherwise it is positively or negatively deviated. The microtomed surface prepared by two different cooling processes—one is fast cooling and the other is slow cooling—indicated that all the blends were not homogenous regardless the density, MI, and comonomer content. The Ziegler–Natta catalyzed EOCs exhibited bigger spherulitic diameter and larger ring space than those of the metallocene EOCs prepared by a cooling process. The blends consisting of similar MI showed banded spherulites with different diameter, whereas the blend consisting of different MI and density takes place of explicit phase separation and phase inversion at 1 : 1 blend composition. The melt rheology appeared to influence the mechanical and film properties in the solid state. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1950–1964, 2000     

Miscibility and processibility in linear low density polyethylene and ethylene-propylene-butene-1 terpolymer binary blends

Blends of linear low density polyethylene (ethylene-octene-1 copolymer) and ethylene-propylene-butene-1 terpolymer (ter-PP) mixed in a twin-screw extruder have been characterized by using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis, scanning electron microscopy (SEM), rheometric mechanical spectrometry, a capillary rheometer, and a universal test machine. Melting and crystallization behaviors by DSC and the α, β, and γ dynamic mechanical relaxations proposed that the blend is immiscible in the amorphous and crystalline phases by observing the characteristic peaks arised solely from those of the constituents. The lack of interfacial interaction between the components was suggested by the SEM study. A strong negative deviation of melt viscosity from the additive rule and the Cole-Cole plot confirmed the immiscibility in melt state. Incorporation of ter-PP induced a reduction in melt viscosity, shear stress, and final load. Flexural modulus and yield stress were linearly increased with ter-PP content, while the tensile strength and elongation at break were more or less changed. Although this blend system is immiscible in the solid and melt states, addition of less than 20 wt % ter-PP in the blend is viable for engineering applications with the advantages of improved processibility and mechanical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1265–1274, 1997     

Correlation between Oxidative Stress and Transforming Growth Factor-Beta in Cancers

The downregulation of reactive oxygen species (ROS) facilitates precancerous tumor development, even though increasing the level of ROS can promote metastasis. The transforming growth factor-beta (TGF-β) signaling pathway plays an anti-tumorigenic role in the initial stages of cancer development but a pro-tumorigenic role in later stages that fosters cancer metastasis. TGF-β can regulate the production of ROS unambiguously or downregulate antioxidant systems. ROS can influence TGF-β signaling by enhancing its expression and activation. Thus, TGF-β signaling and ROS might significantly coordinate cellular processes that cancer cells employ to expedite their malignancy. In cancer cells, interplay between oxidative stress and TGF-β is critical for tumorigenesis and cancer progression. Thus, both TGF-β and ROS can develop a robust relationship in cancer cells to augment their malignancy. This review focuses on the appropriate interpretation of this crosstalk between TGF-β and oxidative stress in cancer, exposing new potential approaches in cancer biology.     

Effects of mixing temperatures on the morphology and toughness of epoxy/polyamide blends

A new mixing process was explored to increase further the fracture toughness and to investigate the toughening mechanisms of epoxy/nylon blend. In this process, without mechanical mixing, the mixtures of epoxy and premade nylon 6 powder were heated without the curing agent to specific temperatures, referred to as the “mixing temperature.” For epoxy/nylon blends, at sufficiently high temperatures, a semi‐interpenetrating network‐like structure can be developed at the interphase via the reaction between the amine end group and the epoxide group. The depth of interphase and the extent of reaction depends on the mixing temperature. The strong dependency of the fracture energy on mixing temperature reveals the positive effect of the newly developed structure at the interphase. The increase of fracture toughness is possibly due to the enhanced crack fingering bifurcation/deflection mechanism resulting from the lamellae developed in the interphase and the enhanced plastic deformation of epoxy as a result of preyielding of the interphase. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1055–1063, 1999     

Nitrate Capture Investigation in Plasma-Activated Water and Its Antifungal Effect on Cryptococcus pseudolongus Cells

This research investigated the capture of nitrate by magnesium ions in plasma-activated water (PAW) and its antifungal effect on the cell viability of the newly emerged mushroom pathogen Cryptococcus pseudolongus. Optical emission spectra of the plasma jet exhibited several emission bands attributable to plasma-generated reactive oxygen and nitrogen species. The plasma was injected directly into deionized water (DW) with and without an immersed magnesium block. Plasma treatment of DW produced acidic PAW. However, plasma-activated magnesium water (PA-Mg-W) tended to be neutralized due to the reduction in plasma-generated hydrogen ions by electrons released from the zero-valent magnesium. Optical absorption and Raman spectra confirmed that nitrate ions were the dominant reactive species in the PAW and PA-Mg-W. Nitrate had a concentration-dependent antifungal effect on the tested fungal cells. We observed that the free nitrate content could be controlled to be lower in the PA-Mg-W than in the PAW due to the formation of nitrate salts by the magnesium ions. Although both the PAW and PA-Mg-W had antifungal effects on C. pseudolongus, their effectiveness differed, with cell viability higher in the PA-Mg-W than in the PAW. This study demonstrates that the antifungal effect of PAW could be manipulated using nitrate capture. The wide use of plasma therapy for problematic fungus control is challenging because fungi have rigid cell wall structures in different fungal groups.     

Expression and localization of two-pore domain K(+) channels in bovine germ cells

Two-pore domain K(+) (K(2P)) channels that help set the resting membrane potential of excitable and nonexcitable cells are expressed in many kinds of cells and tissues. However, the expression of K(2P) channels has not yet been reported in bovine germ cells. In this study, we demonstrate for the first time that K(2P) channels are expressed in the reproductive organs and germ cells of Korean cattle. RT-PCR data showed that members of the K(2P) channel family, specifically KCNK3, KCNK9, KCNK2, KCNK10, and KCNK4, were expressed in the ovary, testis, oocytes, embryo, and sperm. Out of these channels, KCNK2 and KCNK4 mRNAs were abundantly expressed in the mature oocytes, eight-cell stage embryos, and blastocysts compared with immature oocytes. KCNK4 and KCNK3 were significantly increased in eight-cell stage embryos. Immunocytochemical data showed that KCNK2, KCNK10, KCNK4, KCNK3, and KCNK9 channel proteins were expressed at the membrane of oocytes and blastocysts. KCNK10 and KCNK4 were strongly expressed and distributed in oocyte membranes. These channel proteins were also localized to the acrosome sperm cap. In particular, KCNK3 and KCNK4 were strongly localized to the post-acrosomal region of the sperm head and the equatorial band within the sperm head respectively. These results suggest that K(2P) channels might contribute to the background K(+) conductance of germ cells and regulate various physiological processes, such as maturation, fertilization, and development.     

Effect of Vibrational Modes on Sand Pressure and Pattern Deformation in the EPC Process

During the EPC (expendable pattern casting) process, one of the essential requirements is to prevent pattern distortion duringsand filling and compaction. A new method which vibrates the system in a two-dimensional circular mode has been appliedto the EPC process. The molding properties of unbonded sand obtained by this new vibration mode are investigated andcompared with those in the one-dimensional vertical mode. For adequate compaction of sand. the circular vibration mode ismore effective than the vertical mode. Sand became more fluidized by the circular vibration and the particle pressure coefficientwas close to unity The particle pressure coefficient, which is defined as the ratio of horizontal to vertical sand pressure, isresponsible for the effectiveness of sand filling.     

Chemistry and reactions of reactive oxygen species in foods

Reactive oxygen species (ROS) are formed enzymatically, chemically, photochemically, and by irradiation of food. They are also formed by the decomposition and the inter-reactions of ROS. Hydroxy radical is the most reactive ROS, followed by singlet oxygen. Reactions of ROS with food components produce undesirable volatile compounds and carcinogens, destroy essential nutrients, and change the functionalities of proteins, lipids, and carbohydrates. Lipid oxidation by ROS produces low molecular volatile aldehydes, alcohols, and hydrocarbons. ROS causes crosslink or cleavage of proteins and produces low molecular carbonyls from carbohydrates. Vitamins are easily oxidized by ROS, especially singlet oxygen. The singlet oxygen reaction rate was the highest in ss-carotene, followed by tocopherol, riboflavin, vitamin D, and ascorbic acid.