Search Results

You are looking at 1 - 10 of 54 items for

  • Author or Editor: Y.F. Wang x
  • All content x
Clear All Modify Search

Summary The thermal behavior of poly(L-lactic acid) (PLLA) was studied with differential scanning calorimetry (DSC) and polarized optical microscopy. For amorphous PLLA samples, double cold crystallisation peaks were observed in the DSC traces during heating process, being strongly dependent on heating rates. The observation was discussed based on the assumption that the quenched PLLA sample presented some remaining metastable or a precrystalline phase. A small exothermal peak was observed before the main melting peak at low heating rates. The probable reason was discussed through melt-recrystallisation mechanism. Influence of thermal history on the cold crystallisation and melting behavior was also performed on heating process for PLLA samples.

Restricted access

Polyphenols in Chinese Kushui rose (Rosa sertata × Rosa rugosa) leaves were first extracted and analysed in this study. Among four fractions (ethyl ether, ethyl acetate, n-butanol, and water layer) of crude extracts, the ethyl acetate fraction showed the highest ABTS•+ scavenging activity, and the n-butanol fraction exhibited the maximum components in composition. On-line HPLC-ABTS•+ analysis indicated that there were more than 30 antioxidant compounds from Chinese Kushui rose leaves. The identified polyphenols could be classified into quercetin derivatives, gallic acid derivatives, and proanthocyanidins. Gallic acid was the most antioxidative compound.

Restricted access

Summary  

Iodine deficiency disorders (IDD) are one of most common nutritional deficiencies in the world. The nuclear analytical methods (ENAA, SRXRF and XRF) were employed to study the effect of iodine deficiency on the metal ion changes during the stage of brain development, combined with biochemical methods. The results show that the distributions of iron, copper and zinc varied to different extent in different brain regions and subcellular fractions of the ID rat brains. These distributional changes of trace elements might be associated with the brain damage caused by the iodine deficiency.

Restricted access

Abstract  

A method of efficiency calibration for the measurement of 88Kr and 138Xe by HPGe γ-spectrometer is proposed in the present paper. The question for the efficient calibration is, how to achieve homogeneous sources of 88Kr-88Rb and 138Xe-138Cs. The fission product gases were obtained by irradiating a precisely measured amount of U3O8 (90% 235U) filled in a quartz glass ampoule. Source cell was first filled up with stearic acid, and then the fission product gases were charged into it. Xenon and krypton are not adsorbed on stearic acid, therefore, homogeneous sources of 88Kr-88Rb and 138Xe-138Cs can be prepared. The results of the experiment demonstrate that the method is feasible and successful.

Restricted access

Abstract  

Intact chloroplasts were isolated from mesophyll protoplasts of Brassia napus. Concentrations of 8 rare earth elements (REEs) in the chloroplasts were determined by instrumental neutron activation analysis (INAA). The results showed that there were trace amounts of REEs in the chloroplasts, which corresponded to 1 atom of REEs per 2000 chlorophyll molecules. About 30% of the total REEs in the leaves are localized in the chloroplasts and the light REEs were enriched with respect to the heavy elements of the series.

Restricted access

Abstract  

The concentration of 8 REEs (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) in 17 species of plants and their host soil, which were collected from a rare earth ore area located in the south of China, have been determined by INAA. The chondritic normalized REE patterns for different parts of plants (e.g., leaf stem and root) and their host soils were studied. The results showed that the concentration levels of REE for most plants in the sampling area were elevated. Particularly, the leaves of the fern (Dicranopteris dichotoma) contain extremely high concentration of the total REE (675–3358 g/g) Generally, these REE distribution patterns in every part of plants were very similar and reflected the characteristics of their host soils. However, the chondritic normalized REE patterns in some plants relative to the host soil revealed obvious fractionation, such as the depletion of the heavy REE (for fernCitrus reticulata andBrassia campestris), the heavy REE enrichment (forCamellia sinensis, Camellia oleifera andZiziphus) and the Ce positive anomaly (forGardenia jasminoides).

Restricted access