Simulation of κ-Carbide Precipitation Kinetics in Aged Low-Density Fe–Mn–Al–C Steels and Its Effects on Strengthening

Fe–Al–Mn–C alloy systems are low-density austenite-based steels that show excellent mechanical properties. After aging such steels at adequate temperatures for adequate time, nano-scale precipitates such as κ-carbide form, which have profound effects on the mechanical properties. Therefore, it is important to predict the amount and size of the generated κ-carbide precipitates in order to control the mechanical properties of low-density steels. In this study, the microstructure and mechanical properties of aged low-density austenitic steel were characterized. Thermo-kinetic simulations of the aging process were used to predict the size and phase fraction of κ-carbide after different aging periods, and these results were validated by comparison with experimental data derived from dark-field transmission electron microscopy images. Based on these results, models for precipitation strengthening based on different mechanisms were assessed. The measured increase in the strength of aged specimens was compared with that calculated from the models to determine the exact precipitation strengthening mechanism.     

Effects of tomato ketchup and tomato paste extract on hepatic lipid accumulation and adipogenesis

Food Science and Biotechnology - Tomatoes include high levels of lycopene, which is a potent antioxidative, hypolipidemic, and antidiabetic phytochemical. The intake of lycopene is associated with...     

Removal of biofilms using carbon dioxide aerosols

The formation of biofilm (bacterial film) has been serious concerns in a wide variety of applications, because it is involved in many human and device-associated infections. We present a novel method of effectively and rapidly removing Escherichia coli (XL1-blue) biofilm from a silicon chip, using carbon dioxide aerosols. The aerosols were generated by adiabatic expansion of a high-pressure CO₂ gas through a nozzle and they were applied to biofilms that had been grown for 24 h on silicon chips. We measured the percentage area cover of the bacteria from the scanning electron micrographs taken before and after applying the aerosols. The decrease in the percentage area cover, caused by the aerosols, was measured as several parameters such as the distance between the nozzle and the chip, the angle of the nozzle axis relative to the horizontal, CO₂ stagnation pressure, rinsing solution, the aerosol exposure time, and drying time were varied. Nearly 100% of the biofilms were removed within 90 s whether the chip surfaces were very humid (no-drying) or dry (7 h-drying) immediately before applying the aerosols. This method has potential application to cleaning of a wide variety of bio-contaminated surfaces.     

Differential effect of chlorine on the oxidative stress generation in dormant and active cells within colony biofilm

In an effort to better control bacterial biofilm, we examined the effects of various oxidative antimicrobial chemicals including silver, paraquat, hydrogen peroxide, and chlorine depending on the physiological status of cells in biofilm. The metabolically heterogeneous cells within colony biofilm were physically fractionated and the oxidative stress generated in each fraction was monitored by soxS and oxyS promoter reporter systems. Chlorine induced soxS to a greater degree in the dormant cells than active cells of biofilm. In addition, chlorine-dependent induction of soxS was more prominent in aerobically grown cells compared with anaerobically grown cells. On the contrary, the soxS induction by other chemicals such as paraquat and silver, and the oxyS induction by hydrogen peroxide were higher in active biofilm cells and aerobically grown cells. Our results suggest that chlorine might generate strong oxidative stress by direct modification of the 2Fe-2S cluster in an O₂-independent manner, which provides the molecular basis of our previous report showing that chlorine has a more efficient killing effect on dormant cells in biofilm and cells grown under unaerobic conditions. This study shows that chlorine may be particularly promising for the control of anaerobic bacteria and biofilm where dormant cells are hard to control.     

Silver-ion-mediated reactive oxygen species generation affecting bactericidal activity

Silver ions have been widely used as disinfectants that inhibit bacterial growth by inhibiting the essential enzymatic functions of the microorganism via interaction with the thiol-group of l-cysteine. However, silver-ion-mediated perturbation of the bacterial respiratory chain has raised the possibility of reactive oxygen species (ROS) generation. We used bacterial reporter strains specifically responding to superoxide radicals and found that silver-ion-mediated ROS-generation affected bactericidal activity. Almost half the log reduction in Escherichia coli and Staphylococcus aureus populations (model strains for gram negative and positive bacteria, respectively) caused by silver-ion disinfection was attributed to ROS-mediated bactericidal activity. The major form of ROS generated was the superoxide-radical; H₂O₂ was not induced. Furthermore, silver ions strongly enhanced paraquat-induced oxidative stress, indicating close correlation and synergism between the conventional and ROS-mediated silver toxicity. Our results suggest that further studies in silver-based disinfection systems should consider the oxygen concentration and ROS reaction.     

Signal enhancement in a protein chip array using a 3-D nanosurface

A silica based 3-D nanosurface was developed to enhance the signal intensity of a protein chip by increasing the surface density and reducing the aggregation of captured proteins immobilized on the nanosurface. The 3-D nanosurface was composed of silica nanopillar bundles formed from a nanoporous alumina template using the sol–gel method. The signal intensity of a protein spot increased exponentially when the capture probe was immobilized on a nanosurface with higher roughness and the amount of protein immobilized on the surface was proportional to the roughness of the nanosurface. To further investigate this nanosurface effect, changes in the nanosurface roughness before and after protein immobilization were investigated by AFM. The surface roughness was shown to increase after protein immobilization when the nanosurface initially had a relatively low surface roughness (Rq: 30–40 nm); however, the surface roughness decreased after protein immobilization when it initially had a high roughness (Rq: 60–130 nm). These results imply that a high nanosurface roughness decreases the overall aggregation of proteins on the surface. These findings were also confirmed by comparing the level of protein aggregation on nanosurfaces with high roughness and low roughness using AFM.