Experimental investigation on the onset of cellular instabilities and acceleration of expanding spherical flames

We experimentally investigated the cellular instabilities of expanding spherical propagation of hydrogen–air, methane–air, and propane–air flames. Using image-thresholding technique, the formations and developments of a cell on a flame surface were investigated. The size of the observed cell due to the hydrodynamic instability was larger than those generated by the diffusional–thermal instability. The critical flame radius and critical Peclet number for the onset of instability were evaluated. These critical values for hydrogen–air and methane–air flames increased with increasing concentration. The values decreased with increasing initial pressure because the flame thickness decreased with increasing initial pressure. The ratio of the increase in the burning velocity increased with increasing initial pressure, although that of the hydrogen–air flames only increased with decreasing concentration. The results demonstrated that acceleration of the flame speed is affected by the intensity of the diffusional–thermal and hydrodynamic instabilities.     

Analysis of coumarin and its glycosidically bound precursor in Japanese green tea having sweet-herbaceous odour

Coumarin is a natural product well-known for its pleasant sweet-herbaceous and cherry flower-like odour. Despite coumarin being widely found in the plant kingdom, its occurrence in tea leaves is very poorly characterised. In this work, green tea made from the cultivars “Shizu-7132”, “Koushun” and “Tsuyuhikari” were found to have sweet-herbaceous odour. Application of the stable isotope dilution assay for the quantification of coumarin revealed that its levels in these Japanese green tea products ranged from 0.26 to 0.88 μg/g of green tea product, whereas concentrations were generally below 0.2 μg/g in common green tea products. In contrast to the leaf, the stem part contained much less coumarin. During the manufacturing process of the tea (Shizu-7132), the steaming time and drying temperature influenced the content of coumarin in the final product. Due to hydrolysis of glycosidically bound coumarin precursors, in fresh tea leaves most coumarin occurred in its free form. Tea leaves also contained small amounts of bound coumarin precursors, such as primeveroside.     

Evaluation of the Labeled Hedonic Scale under different experimental conditions

The present study explored the performance, psychophysical properties, and potential limitations of the Labeled Hedonic Scale (LHS) in two different test conditions. The LHS was first compared against the 9-point hedonic scale in a psychophysical laboratory setting by having subjects evaluate two sets of taste stimuli with different size of hedonic ranges. Both scales showed equal discrimination power, but the LHS was more resistant to ceiling effects and its data satisfied the normality assumption for statistical analysis. In the second experiment, subjects with different levels of prior experience with the 9-point scale were recruited to evaluate juice samples and food item names in a large-scale consumer test, after receiving either common written instructions or detailed instructions emphasizing the use of the LHS. Improper use of the LHS (e.g. categorical ratings) was evident for those who received written instructions, especially among subjects who had previous experience with the 9-point scale. The present results support the efficacy of the LHS in various test settings, while highlighting the importance of providing adequate instructions to subjects to fully utilize its advantages.