Increasing use of pyrethroid insecticides has resulted in concerns regarding potential effects on human health and ecosystems. Cypermethrin and its metabolite 3-phenoxybenzoic acid(PBA) have exerted adverse biological...Increasing use of pyrethroid insecticides has resulted in concerns regarding potential effects on human health and ecosystems. Cypermethrin and its metabolite 3-phenoxybenzoic acid(PBA) have exerted adverse biological impacts on the environment;therefore,it is critically important to develop different methods to enhance their degradation. In this study,incubation experiments were conducted using samples of an Aquic Inceptisol supplied with nitrogen(N) in the form of NH4NO3 at different levels to investigate the effect of nitrogen on the degradation of cypermethrin and PBA in soil. The results indicated that appropriate N application can promote the degradation of cypermethrin and PBA in soil. The maximum degradation rates were 80.0% for cypermethrin after 14 days of incubation in the treatment with N at a rate of 122.1 kg ha-1 and 41.0% for PBA after 60 days of incubation in the treatment with N at a rate of 182.7 kg ha-1. The corresponding rates in the treatments without nitrogen were 62.7% for cypermethrin and 27.8% for PBA. However,oversupplying N significantly reduced degradation of these compounds. Enhancement of degradation could be explained by the stimulation of microbial activity after the addition of N. In particular,dehydrogenase activities in the soil generally increased with the addition of N,except in the soil where N was applied at the highest level. The lower degradation rate measured in the treatment with an oversupply of N may be attributed to the microbial metabolism shifts induced by high N.展开更多
Single-axis acoustic levitation of four polymer samples has been realized in air under the ground-based laboratory conditions for the purpose of space environment simulation of containerless processing.The levitation ...Single-axis acoustic levitation of four polymer samples has been realized in air under the ground-based laboratory conditions for the purpose of space environment simulation of containerless processing.The levitation capabilities are investigated by numerical calculations based on a model of the boundary element method corresponding to our levitator and following Gor'kov and Barmatz's method.The calculated results,such as the resonant distance between the reflector and the vibrating source and the positions of levitated samples,agree well with experimental observation,and the effect of gravity on the time-averaged potential for levitation force is also revealed.As an application,the containerless melting and solidification of a liquid crystal,4-Pentylphenyl-4'-methybenzoate,is successfully accomplished,in which undercooling up to 16 K is obtained and the rotation and oscillation of the sample during solidification may result in fragmentation of the usual radiating surface growth morphology.展开更多
基金the National Key Basic Research Program of China (No.2002CB410810) and the PPI/PPIC Chinaprogram.
文摘Increasing use of pyrethroid insecticides has resulted in concerns regarding potential effects on human health and ecosystems. Cypermethrin and its metabolite 3-phenoxybenzoic acid(PBA) have exerted adverse biological impacts on the environment;therefore,it is critically important to develop different methods to enhance their degradation. In this study,incubation experiments were conducted using samples of an Aquic Inceptisol supplied with nitrogen(N) in the form of NH4NO3 at different levels to investigate the effect of nitrogen on the degradation of cypermethrin and PBA in soil. The results indicated that appropriate N application can promote the degradation of cypermethrin and PBA in soil. The maximum degradation rates were 80.0% for cypermethrin after 14 days of incubation in the treatment with N at a rate of 122.1 kg ha-1 and 41.0% for PBA after 60 days of incubation in the treatment with N at a rate of 182.7 kg ha-1. The corresponding rates in the treatments without nitrogen were 62.7% for cypermethrin and 27.8% for PBA. However,oversupplying N significantly reduced degradation of these compounds. Enhancement of degradation could be explained by the stimulation of microbial activity after the addition of N. In particular,dehydrogenase activities in the soil generally increased with the addition of N,except in the soil where N was applied at the highest level. The lower degradation rate measured in the treatment with an oversupply of N may be attributed to the microbial metabolism shifts induced by high N.
基金Supported by the National Natural Science Foundation of China under Grant No.59871040the National High Technology Development Program of China under Grant No.863-2-4-3-2.
文摘Single-axis acoustic levitation of four polymer samples has been realized in air under the ground-based laboratory conditions for the purpose of space environment simulation of containerless processing.The levitation capabilities are investigated by numerical calculations based on a model of the boundary element method corresponding to our levitator and following Gor'kov and Barmatz's method.The calculated results,such as the resonant distance between the reflector and the vibrating source and the positions of levitated samples,agree well with experimental observation,and the effect of gravity on the time-averaged potential for levitation force is also revealed.As an application,the containerless melting and solidification of a liquid crystal,4-Pentylphenyl-4'-methybenzoate,is successfully accomplished,in which undercooling up to 16 K is obtained and the rotation and oscillation of the sample during solidification may result in fragmentation of the usual radiating surface growth morphology.
