This study was carried out to detect content of heavy metals( Pb,Cd,and As) in vegetables,understand the current situation of heavy metal contamination in vegetables,and to provide scientific reference for further res...This study was carried out to detect content of heavy metals( Pb,Cd,and As) in vegetables,understand the current situation of heavy metal contamination in vegetables,and to provide scientific reference for further researches. It randomly selected 6 large vegetable markets and 6 supermarkets in Changsha City,selected 8 types of typical vegetables,and detected 96 samples. In accordance with maximum level of contaminants in foods in existing GB2762- 2012 standard,Nemerow composite pollution index( Pt) and grading standards,it made evaluation: uncontaminated( Pt≤ 1),mildly contaminated( 1 < Pt≤2),moderately contaminated( 2 < Pt≤3),and highly contaminated( Pt>3). Among 96 samples,range of content of Pb,Cd and As is( 0. 06- 1. 41),( 0. 06- 1. 26) and( 0. 00- 0. 91) mg / kg respectively; the over- limit rate of these metals exceeding the safety level is 78. 13%,45. 83%,and 34. 38% separately; the composite pollution index is in( 0. 90-6. 05),the eggplant is 6. 05 and hot pepper is 3. 24; the content of Pb( F =23. 908,P =0. 001) and Cd( F =64. 908,P =0. 000)are significantly different between 8 types of vegetables and there is no significant difference between the content of As( F = 4. 634,P = 0. 705> 0. 05) in 8 types of vegetables. Study shows that common vegetables in Changsha City has problem of excess Pb,Cd and As,and the Pb over- limit rate is the highest. The composite pollution index indicates that most heavy metal contamination of vegetables is mild and moderate contamination,melon,fruit and vegetable contamination is high contamination,and Cd is the major factor leading to contamination of melons,fruits and vegetables.展开更多
文摘星基广播式自动相关监视(ADS-B,automatic dependent surveillance-broadcast)系统是一种新型的航空器监视技术,在未来空中交通管理系统中具有广阔的应用前景。为了深入研究星基ADS-B系统中航空器到卫星的空天链路通信性能,将专业软件Matlab和STK(system tool kit)有效联合,构建符合国际标准的星基ADS-B空天链路完整模型;通过离散事件动态交互模拟ADS-B消息的发送与接收全过程,最后统计得出体现星基ADS-B空天链路通信性能的消息识别概率(POI,possibility of identify)、消息检测概率(POD,possibility of detective)、信号接收功率、信号冲突概率、卫星覆盖范围等指标。仿真结果表明,随着区域内航空器数量上升,POI、POD下降,消息冲突概率上升。
基金Supported by Student Innovation Project of Central South University(YC12355)
文摘This study was carried out to detect content of heavy metals( Pb,Cd,and As) in vegetables,understand the current situation of heavy metal contamination in vegetables,and to provide scientific reference for further researches. It randomly selected 6 large vegetable markets and 6 supermarkets in Changsha City,selected 8 types of typical vegetables,and detected 96 samples. In accordance with maximum level of contaminants in foods in existing GB2762- 2012 standard,Nemerow composite pollution index( Pt) and grading standards,it made evaluation: uncontaminated( Pt≤ 1),mildly contaminated( 1 < Pt≤2),moderately contaminated( 2 < Pt≤3),and highly contaminated( Pt>3). Among 96 samples,range of content of Pb,Cd and As is( 0. 06- 1. 41),( 0. 06- 1. 26) and( 0. 00- 0. 91) mg / kg respectively; the over- limit rate of these metals exceeding the safety level is 78. 13%,45. 83%,and 34. 38% separately; the composite pollution index is in( 0. 90-6. 05),the eggplant is 6. 05 and hot pepper is 3. 24; the content of Pb( F =23. 908,P =0. 001) and Cd( F =64. 908,P =0. 000)are significantly different between 8 types of vegetables and there is no significant difference between the content of As( F = 4. 634,P = 0. 705> 0. 05) in 8 types of vegetables. Study shows that common vegetables in Changsha City has problem of excess Pb,Cd and As,and the Pb over- limit rate is the highest. The composite pollution index indicates that most heavy metal contamination of vegetables is mild and moderate contamination,melon,fruit and vegetable contamination is high contamination,and Cd is the major factor leading to contamination of melons,fruits and vegetables.
