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  • Author or Editor: Y. Yu x
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Abstract  

The phase behaviour and phase stability of lipids are of importance in an understanding of the biological functions of cell membranes. Among a variety of physical techniques employed to study the phase behaviour and structural properties of polar lipids, differential scanning calorimetry and X-ray diffraction have proved to be successful and are the most frequently used methods. Applications involving a combination of the two techniques, particularly when synchrotron radiation is used as the light source of X-ray diffraction, are reviewed in this article.

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Abstract  

The aim of this paper is to investigate homomorphisms which reserve square-free languages or primitive languages. A characterization of square-free-preserving homomorphisms is presented. We show that every square-free-preserving homomorphism is primitive-preserving. Strongly cube-free-preserving homomorphisms are also studied.

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Artificial grassland plots with various degrees of diversity were established near Heishiding Nature Reserve, Guangdong Province, China. After an establishment phase of one year, one half of each plot was exposed to drought stress in order to explore the relationship between diversity and compositional stability of the grassland communities. The experiment showed that relationships between diversity and compositional stability varied with the diversity values in non-stressed control subplots and the duration of drought disturbance. When control subplots had higher evenness, species richness negatively affected compositional stability, which led to a negative relationship between diversity and compositional stability. When control subplots had lower evenness, compositional stability was determined by evenness or species identity (particular species) at different periods of drought disturbance. This resulted in negative, weakly positive or no relationships between diversity and compositional stability. Based on these results, we suggest that different relationships between diversity and compositional stability, and controversial data from such relationships in previous studies may reflect differences in environmental and experimental conditions.

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Recruitment limitation has been hypothesized to promote the maintenance of high species diversity in forests by slowing down competitive exclusion. However, the difference of recruitment limitation for tree species with varying seed masses, which is a common phenomenon in tropical or subtropical forests, is largely unknown. In this study we conducted a seed sowing experiment for five dominant tree species with varying seed mass (a proxy of dispersal ability) in a subtropical evergreen broad-leaved forest at different successional stages to test the hypothesis that the determinants of species recruitment vary with their seed masses in Heishiding Nature Reserve (Guangdong Province, China). The effects of seed predators, soil pathogens, light conditions, plant litter, seed additions, and the presence of adult conspecific trees on the performance of seeds and seedlings for the five species were examined. We particularly investigated the effects of habitat hazards and seed size on the relative importance of dispersal limitation and establishment limitation. The results show that all five sowing species experienced recruitment limitation at the microsite level, although the causes of the limitation of these species varied between pathogen infection, animal predation, litter covering and shading. Seedling recruitment of the wind-dispersed, small-seeded species was mostly limited by microsite condition, while large-seeded species were mostly limited by dispersal ability.

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Abstract  

Power-time curves and metabolic properties of Tetrahymena thermophila BF5 exposed to different Yb3+ levels were studied by ampoule method of isothermal calorimetry at 28°C. Metabolic rate (r) decreased significantly while peak time (PT) increased with the increase of Yb3+. These results were mainly due to the inhibition of cell growth, which corresponded to the decrease of cell number obtained by cell counting. Compared with cell counting, calorimetry was sensible, easy to use and convenient for monitoring the toxic effects of Yb3+ on cells and freshwater ecosystem. It was also found that cell membrane fluidity decreased significantly under the effects of Yb3+, which indicated that Yb3+ could be membrane active molecules with its effect on cell membranes as fundamental aspect of its toxicity.

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Abstract  

The independent isomeric yield ratio of146La and84Br in the thermal neutron fission of235U is reported for the first time with the values of 0.058±0.017 and 0.62±0.20, respectively. the yields have been determined using a fast radiochemical separation technique followed by -spectroscopy. The deduced rms angular momentum of84Br is 5.9 from the statistical model analysis and the rms angular momentum of146La is found too low to be determined.

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Changes in microbial population, pH, sugar, organic acid, anthocyanins, total soluble phenolics, and anti-glucosidase contents were measured during fermentation of mulberry juice at 30 °C by probiotic Leuconostoc mesenteroides showing rapid growth after an approximately 1-day lag phase and reaching a maximum of 8.6 log CFU ml−1 after 4 d. During the rapid growth phase, the main mulberry juice sugars, glucose and fructose, were largely consumed, and the acidic metabolites, lactic acid and acetic acid, were produced accordingly. A slow decrease in the concentration of the main organic acid, citric acid, was also observed during fermentation. After 4 d fermentation, anthocyanin content showed a 44.4% reduction, but the total amount of soluble phenolics and α-glucosidase inhibitory activity showed no significant changes (P>0.05). This suggests that L. mesenteroides fermentation of mulberry juice is a good strategy to enhance its probiotic value and to decrease the sugar content without changing the anti-glucosidase activity, which is required to reduce postprandial rise in blood glucose.

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Abstract  

Using isothermal microcalorimetry, the growth power-time curves of three strains of Tetrahymena were determined at 28C. Their Euclidean distances and cluster analysis diagram were obtained by using two thermokinetic parameters (r and Q log), which showed that T. thermophila BF1 and T. thermophila BF5 had a closer relationship. Compared with the single molecular biomarker (ITS1) method, microcalorimetry wasmaybe a simpler, more sensitive andmore economic technique in the phylogenetic studies of Tetrahymena species.

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Abstract  

57Co was produced with high pure nature iron irradiated by 8.5MeV deuterons. TBP-benzene extraction method and anion-exchange method were used to separate and purify it. The purified57Co was prepared into standard solution of about 30 to 50 g Co2+/ml carrier concentration and about 0.1 mol/l HCl. The specific activity of the standard solution was measured with 4 (ppc)- coincidence counting method. The final result was 476.82(1±0.42%)Bq/mg.

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