科研成果 by Year: 2006

Studies showed that DDT levels were still high in Tianjin, China, even though its use was banned in 1983. To estimate current risk of DDT to human health in Tianjin area, a non-steady-state (Level IV) multimedia fugacity model was used to simulate the fate and transfer of pp'-DDT before and after the ban. The ordinary linear equations of Level IV model were solved with a matrix approach. The calculated pp'-DDT concentration in air, water, soil, and sediment reached a maximum in the 1980s and then decreased, and agree well with those measured. The biggest bulk sinks of pp'-DDT were soil and sediment, which accounted for 90% of total amount of pp'-DDT in the environment. Air deposition and diffusions through the interfaces of water-air and water sediment were the major intermedia transfer processes, while the degradation in soil and sediment were the key eliminating routes for pp'-DDT in the environment. (c) 2005 Elsevier Inc. All rights reserved.

This paper examines the efficiency in resource allocation in China. We estimate production functions at the provincial level and use these functions to compute time series for marginal products of capital and labor. We found that dispersion in the marginal product of capital declined from 1970 to 1984 and then became stable afterward, whereas the dispersion in the marginal product of labor declined initially but the trend has been reversed since 1993. We argue that this reversal may indicate any of the following: (1) policy-driven labor migration adding to labor market inefficiency; (2) the presence of increasing returns in labor; and (3) both capital and labor having become mobile since 1993.

Bacterivory by heterotrophic nanoflagellates and ciliates has been widely studied in aquatic environments, but data on the grazing of amoebae, are still scarce. From the water samples of Dianchi Lake (Kunming, Yunnan Province, China), we isolated an amoeba, designated as Naegleria sp. strain W2, which had potent grazing effects on some kind of cyanobacteria. The food selection mechanism and the digestion process of the amoeba were investigated in batch experiments. Predation experiments showed that filamentous cyanobacteria (e.g., Anabaena, Cylindrospermum, Gloeotrichia, and Phormidium) were readily consumed, with clearance rates ranging from 0.332 to 0.513 nL amoeba(-1) h(-1). The tight threads (Oscilltoria) and aggregates (Aphanizomenon) could not be ingested; however, their sonicated fragments were observed inside food vacuoles, suggesting that their morphologies prevent them from being ingested. Live video microscopy noted that unicellular Chroococcaceae (e.g., Synechococcus, Aphanocapsa, and Microcystis) were excreted after ingestion, indicating that food selection takes place inside food vacuoles. To determine whether the tastes or the toxins prevented them from being digested, heat-killed cells were retested for predation. Digestion rates and ingestion rates of the amoebae for filamentous cyanobacteria were estimated from food vacuole content volume. Through a ``cold-chase'' method, we found that the food vacuole contents declined exponentially in diluted amoebae cells, and digestion rates were relatively constant, averaging about 1.5% food vacuole content min(-1) at 28 degrees C. Ingestion strongly depended on the satiation status of the amoebae, starved amoebae fed at higher rates compared with satiated amoebae. Our results suggest that the food selection and food processing mechanisms of the amoeba are similar to those of interception feeding flagellates; however, filamentous cyanobacteria cannot obtain a refuge under the grazing pressure of phagotrophic amoebae, which may widen our knowledge on the grazing of protists.