The level and pattern of contamination by polychlorinated biphenyls (PCBs) were investigated in tilapia, Oreochromis mossambicus (Peters), sediment, and water from the Shing Mun River. The range of total PCBs was 12.9...The level and pattern of contamination by polychlorinated biphenyls (PCBs) were investigated in tilapia, Oreochromis mossambicus (Peters), sediment, and water from the Shing Mun River. The range of total PCBs was 12.9 ng/g to 181.6 ng/g wet weight in tilapia, 12.7 ng/g to 46.0 ng/g freeze-dried weight in sediment, and 3.8 ng/L to 13.6 ng/L in water. The effect of biomagnification was also observed, PCB concentrations increased from water to sediment to tilapia. PCB congeners occurred in such a way that lower chlorinated PCBs comprised a higher fraction of the total PCBs in water, sediment, and tilapia muscle, whereas higher chlorinated PCBs were more commonly found only in tilapia.展开更多
Based on a systemic survey, the pyrolysis characteristics and apparent kinetics of the municipal solid waste （ MSW） under different conditions were researched using a special pyrolysis reactor, which could overcome ...Based on a systemic survey, the pyrolysis characteristics and apparent kinetics of the municipal solid waste （ MSW） under different conditions were researched using a special pyrolysis reactor, which could overcome the disadvantage of thermo-gravimetric analyzer. The thermal decomposition behaviour of MSW was investigated using thermo-gravimetric （ TG ） analysis at rates of 4.8,6.6,8.4, 12.0 and 13. 2 K/min. The pyrolysis characteristics of MSW were also studied in different function districts. The pyrolysis of MSW is a complex reaction process and three main stages are found according to the results. The first stage represents the degradation of cellulose and hemicellulose, with the maximum degradation rate occuring at 150℃ -200 ℃： the second stage represents dehydrochlorination and depolymerization of intermediate products and the differential thermogravimetric （ DTG ） curves have shoulder peaks at about 300℃： the third stage is the decomposition of the residual big molecular organic substance and lignin at 400 ℃- 600 ℃. Within the range of given experimental conditions, the results of non-linear fitting algorithm and experiment are in agreement with each other and the correlation coefficients are over0. 99. The kinetic characteristics are concerned with the material component and heating rate. The activation energy of reaction decreases with the increase of heating rate.展开更多
Daisy spent one month of her summer this year at St. John＇s, Newfoundland for a summer program, Shad Valley. Shad Valley is a Canadian based summer enrichment program. Students from grade 10 to 12 are eligible to app...Daisy spent one month of her summer this year at St. John＇s, Newfoundland for a summer program, Shad Valley. Shad Valley is a Canadian based summer enrichment program. Students from grade 10 to 12 are eligible to apply to spend four weeks at one of the twelve Shad＇s university campuses across Canada. The program has been succeeding for over 30 years at enhancing students＇ knowledge on sciences, engineering, technology,展开更多
本试验旨在探索奶牛配种前1周内乳中脂肪蛋白质比(milk fat to protein ratio,FPR)和尿素氮(milk urea nitrogen,MUN)含量对繁殖性能的影响。选择产犊时间接近的第1胎荷斯坦牛1 460头,于配种前1周采集乳样,测定日产奶量、乳成分和MUN含...本试验旨在探索奶牛配种前1周内乳中脂肪蛋白质比(milk fat to protein ratio,FPR)和尿素氮(milk urea nitrogen,MUN)含量对繁殖性能的影响。选择产犊时间接近的第1胎荷斯坦牛1 460头,于配种前1周采集乳样,测定日产奶量、乳成分和MUN含量,并测定试验牛只第1次发情配种泌乳天数、配种情期数、妊娠率、妊娠泌乳天数等繁殖性能指标,用多因素方差分析、Logistic回归分析以及相关和回归分析方法分析FPR和M UN含量与繁殖性能的关系。结果表明:试验牛只配种前1周内FPR和MUN含量分别为(1.35±0.28)和(10.61±2.68)mg/dL。FPR对第1次发情配种泌乳天数的影响达到极显著水平(P<0.01),对其他繁殖性能指标无显著影响(P>0.05);MUN含量对第1次发情配种泌乳天数的影响达到极显著水平(P<0.01),对配种情期数、妊娠率的影响达到显著水平(P<0.05),而对妊娠泌乳天数无显著影响(P>0.05)。FPR与第1次发情配种泌乳天数和妊娠泌乳天数呈极显著负相关(P<0.01),M UN含量与第1次发情配种泌乳天数及妊娠率呈极显著正相关(P<0.01)。MUN含量对第1次配种以及在前2个发情周期内配种是否妊娠的影响达到显著水平(P<0.05)。配种前1周内MUN含量对头胎奶牛配种情期数和第1次发情配种泌乳天数有显著影响,因此,对MUN含量的测定和分析可以作为奶牛繁殖性能的预测和繁殖管理的手段之一。展开更多
文摘The level and pattern of contamination by polychlorinated biphenyls (PCBs) were investigated in tilapia, Oreochromis mossambicus (Peters), sediment, and water from the Shing Mun River. The range of total PCBs was 12.9 ng/g to 181.6 ng/g wet weight in tilapia, 12.7 ng/g to 46.0 ng/g freeze-dried weight in sediment, and 3.8 ng/L to 13.6 ng/L in water. The effect of biomagnification was also observed, PCB concentrations increased from water to sediment to tilapia. PCB congeners occurred in such a way that lower chlorinated PCBs comprised a higher fraction of the total PCBs in water, sediment, and tilapia muscle, whereas higher chlorinated PCBs were more commonly found only in tilapia.
基金Supported by National Natural Science Foundation of China( No. 50378061).
文摘Based on a systemic survey, the pyrolysis characteristics and apparent kinetics of the municipal solid waste （ MSW） under different conditions were researched using a special pyrolysis reactor, which could overcome the disadvantage of thermo-gravimetric analyzer. The thermal decomposition behaviour of MSW was investigated using thermo-gravimetric （ TG ） analysis at rates of 4.8,6.6,8.4, 12.0 and 13. 2 K/min. The pyrolysis characteristics of MSW were also studied in different function districts. The pyrolysis of MSW is a complex reaction process and three main stages are found according to the results. The first stage represents the degradation of cellulose and hemicellulose, with the maximum degradation rate occuring at 150℃ -200 ℃： the second stage represents dehydrochlorination and depolymerization of intermediate products and the differential thermogravimetric （ DTG ） curves have shoulder peaks at about 300℃： the third stage is the decomposition of the residual big molecular organic substance and lignin at 400 ℃- 600 ℃. Within the range of given experimental conditions, the results of non-linear fitting algorithm and experiment are in agreement with each other and the correlation coefficients are over0. 99. The kinetic characteristics are concerned with the material component and heating rate. The activation energy of reaction decreases with the increase of heating rate.
文摘Daisy spent one month of her summer this year at St. John＇s, Newfoundland for a summer program, Shad Valley. Shad Valley is a Canadian based summer enrichment program. Students from grade 10 to 12 are eligible to apply to spend four weeks at one of the twelve Shad＇s university campuses across Canada. The program has been succeeding for over 30 years at enhancing students＇ knowledge on sciences, engineering, technology,
文摘本试验旨在探索奶牛配种前1周内乳中脂肪蛋白质比(milk fat to protein ratio,FPR)和尿素氮(milk urea nitrogen,MUN)含量对繁殖性能的影响。选择产犊时间接近的第1胎荷斯坦牛1 460头,于配种前1周采集乳样,测定日产奶量、乳成分和MUN含量,并测定试验牛只第1次发情配种泌乳天数、配种情期数、妊娠率、妊娠泌乳天数等繁殖性能指标,用多因素方差分析、Logistic回归分析以及相关和回归分析方法分析FPR和M UN含量与繁殖性能的关系。结果表明:试验牛只配种前1周内FPR和MUN含量分别为(1.35±0.28)和(10.61±2.68)mg/dL。FPR对第1次发情配种泌乳天数的影响达到极显著水平(P<0.01),对其他繁殖性能指标无显著影响(P>0.05);MUN含量对第1次发情配种泌乳天数的影响达到极显著水平(P<0.01),对配种情期数、妊娠率的影响达到显著水平(P<0.05),而对妊娠泌乳天数无显著影响(P>0.05)。FPR与第1次发情配种泌乳天数和妊娠泌乳天数呈极显著负相关(P<0.01),M UN含量与第1次发情配种泌乳天数及妊娠率呈极显著正相关(P<0.01)。MUN含量对第1次配种以及在前2个发情周期内配种是否妊娠的影响达到显著水平(P<0.05)。配种前1周内MUN含量对头胎奶牛配种情期数和第1次发情配种泌乳天数有显著影响,因此,对MUN含量的测定和分析可以作为奶牛繁殖性能的预测和繁殖管理的手段之一。
