Factors influencing local potential drop in bottom-contact organic thin-film transistor using solution-processible tetrabenzoporphyrin

By exploiting atomic-force-microscope potentiometry, we have studied the local potential distribution in the solution-processible tetrabenzoporphyrin (BP) bottom-contact thin-film transistor under controlled atmospheres. It is found that abrupt and big potential drops mainly appeared at the domain boundaries and cracks in the BP film when the transistor was under operation, indicating a dominant influence of domain boundary and crack on the device performance. Exposure of the device to O₂ drastically reduced the potential drops at some boundaries, which is the main reason for the improved device performance by O₂ exposure.     

Cold‐triggered/heat‐destroyed emulsions composed of phospholipids and triacylglycerols as thermal history indicators for cold‐chain distribution systems

BACKGROUND: Recently, cold‐chain distribution systems have come to play important roles in worldwide food processing/storage/transportation networks. To ensure the maintenance of the quality and safety of foods, it is necessary to develop thermal history indicators for products involved in cold‐chain distribution systems. To provide a record of the occurrence of a high‐temperature event during a cold‐chain system, a temperature‐related phase change in a material within the indicator is needed to indicate that the high‐temperature event occurred. Preferentially, for safety, the materials of the indicators should be edible and easy to handle. It should be possible to store the indicators at ambient temperature before use, and they should be triggered automatically just by cooling at the start of a cold‐chain system. Furthermore, if the indicator is heated even once during the cold‐chain distribution system, its appearance must be irreversibly altered to provide evidence of the high‐temperature experience. RESULTS: Based on the edible materials composed of lyso‐lecithin (15 g), lecithin (2 g), triacylglycerol (150 g), and water, we successfully constructed a stable emulsion that could be triggered just by cooling to 4 °C or lower for more than 12 h. After triggering, it was immediately destroyed by heating up to 20 °C or higher. Furthermore, the mechanism of cold‐triggering and heat‐destruction has been studied by nuclear magnetic resonance. CONCLUSION: The cold‐triggered/heat‐destroyed emulsion should be applied as a new thermal history indicator that can be automatically triggered just by cooling down and irreversibly change its appearance after a high‐temperature experience in cold‐chain distribution systems. Copyright © 2008 Society of Chemical Industry     

Practical method of assessing local and global impacts for risk-based decision making: a case study of metal degreasing processes

For risk-based decision making, local and global impacts should be considered simultaneously. In metal degreasing processes, various cleansing agents are used and a significant amount of such cleansing agents is released into the environment. An appropriate measure of reducing chemical risk associated with industrial cleaning processes should be implemented on the basis of evaluation results representing the local and global impacts. In this study, we assessed metal degreasing processes using a chlorinated solvent with an open-top washing machine and four alternative scenarios, namely, improving the settings of the machine (two cases), changing the local ventilation system, and installing a recovery system using activated carbon. The applied methods are plant-specific risk and life cycle assessments. Specifically in the risk assessment, detailed process data available for decision makers are utilized to evaluate occupational and neighborhood risks. The results of this case study indicate a tradeoff relationship between the local and global impacts in metal degreasing. Through the discussions on the practicability of the integration of the local and global impacts into actual decision making, we conclude that the way to use, select, or integrate risk and life cycle assessments should be analyzed systematically as the situation demands at decision making.     

Leaf-like dislocation substructures and the decrease of martensitic start temperatures: A new explanation for functional fatigue during thermally induced martensitic transformations in coarse-grained Ni-rich Ti-Ni shape memory alloys

During repeatedly imposed thermally induced martensitic transformations in Ti-Ni shape memory alloys, the martensite start temperature M_s decreases. This has been rationalized on the basis of a scenario where an increasing dislocation density makes it more and more difficult for martensite to form. However, it is not clear why dislocations which form because they accommodate the growth of martensite during the first cooling cycle should act as obstacles during subsequent transformation cycles. In the present work we use diffraction contrast transmission electron microscopy to monitor the formation of unique leaf-like dislocation substructures which form as the martensite start temperature decreases during thermal cycling. We interpret our microstructural results on the basis of a microstructural scenario where dislocations play different roles with respect to the propagation of a big martensite needle in one transformation cycle and the nucleation and growth of new martensite needles in the following cycles. As a consequence, chestnut-leaf-like dislocation arrays spread out in different crystallographic directions.     

Crystallographic Analysis of Fatigue Crack Initiation Behavior in Coarse-Grained Magnesium Alloy Under Tension-Tension Loading Cycles

Plane bending fatigue tests are conducted to investigate fatigue crack initiation mechanisms in coarse-grained magnesium alloy, AZ31, under the stress ratios R = ?1 and 0.1. The initial crystallographic structures are analyzed by an electron backscatter diffraction method. The slip or twin operation during fatigue tests is identified from the line angle analyses based on Euler angles of the grains. Under the stress ratio R = ?1, relatively thick tension twin bands are formed in coarse grains. Subsequently, compression twin or secondary pyramidal slip operates within the tension twin band, resulting in the fatigue crack initiation. On the other hand, under R = 0.1 with tension-tension loading cycles, twin bands are formed on the specimen surface, but the angles of those bands do not correspond to tension twins. Misorientation analyses of c-axes in the matrix grain and twin band reveal that double twins are activated. Under R = 0.1, fatigue crack initiates along the double twin boundaries. The different manners of fatigue crack initiation at R = ?1 and 0.1 are related to the asymmetricity of twining under tension and compression loadings. The fatigue strengths under different stress ratios cannot be estimated by the modified Goodman diagram due to the effect of stress ratio on crack initiation mechanisms.     

Experimental Evidence for the Anisotropic Ostwald Ripening of β-Silicon Nitride

A powder mixture of α-Si₃N₄, Y₂O₃, and SiO₂ was heat-treated in a loose powder state in the temperature range of 1750°–1900°C for 2 h; then, the mixture was acid-rinsed to remove the glassy phase. The widths and lengths of the resulting β-Si₃N₄ crystals were analyzed quantitatively. The width–aspect-ratio distribution of the β-Si₃N₄ crystals initially showed a strong negative correlation, and then the aspect ratio of crystals with small widths quickly decreased. After a stage in which aspect ratio was almost constant, regardless of the width, the width-aspect-ratio distribution evolved to show a positive correlation in the final stage. This pattern of morphology evolution of the β-Si₃N₄ crystals was in good agreement with that predicted by the anisotropic Ostwald ripening model.     

Oxygen Content in ß-Si3N4 Crystal Lattice

ß-Si₃N₄ crystals were obtained through the heat treatment of alpha-Si₃N₄ powder with additives, Y₂O₃:SiO₂= 1:2 and 2:1, and subsequent acid treatments that removed the secondary phases. The lattice oxygen contents of these crystals were determined by the hot-gas extraction method to be 0.258 ± 0.006 and 0.158 ± 0.003 wt% for the additive compositions of Y₂O₃:SiO₂= 1:2 and 2:1, respectively. The oxygen dissolved in the ß-Si₃N₄ crystal lattice as much as in the alpha-Si₃N₄ crystral lattice prepared by the chemical vapor deposition process and in the AlN crystal lattice that exhibited high thermal conductivity.