A total of 153 soil samples were collected from Changsha City, China, to analyze the contents of As, Cd, Cr, Cu, Hg, Mn, Ni, Pb and Zn. A combination of sampling data, multivariate statistical method, geostatistical a...A total of 153 soil samples were collected from Changsha City, China, to analyze the contents of As, Cd, Cr, Cu, Hg, Mn, Ni, Pb and Zn. A combination of sampling data, multivariate statistical method, geostatistical analysis, direct exposure method and triangulated irregular network （TIN） model was successfully employed to discriminate sources, simulate spatial distributions and evaluate children＇s health risks of heavy metals in soils. The results show that not all sites in Changsha city may be suitable for living without remediation. About 9.0% of the study area provided a hazard index （HI）1.0, and 1.9% had an HI2.0. Most high HIs were located in the southern and western areas. The element of arsenic and the pathway of soil ingestion were the largest contribution to potential health risks for children. This study indicates that we should attach great importance to the direct soil heavy metals exposure for children＇s health.展开更多
[Objective] The research aimed to analyze irregular information of the local rainstorm process (during 5-6 September,2009) in autumn continuous rainy weather in north Shaanxi. [Method] Based on V-3θ chart, routine ob...[Objective] The research aimed to analyze irregular information of the local rainstorm process (during 5-6 September,2009) in autumn continuous rainy weather in north Shaanxi. [Method] Based on V-3θ chart, routine observation data provided by Micaps system, satellite cloud chart and data at 100 automatic meteorological stations of Shaanxi, for rainstorm process in autumn continuous rainy weather in north Shaanxi during 4-10 September, 2009, by using structure analysis method, irregular information in local rainstorm weather was analyzed. [Result] In whole precipitation process, atmospheric structure in rainstorm zone presented obvious evolution process. Before precipitation, typical atmospheric structure information of the sudden convective weather appeared. Obvious ultra-low temperature structure appeared at 200 hPa, and consistent clockwise rotation flow was at vertical wind field. Meanwhile, water vapor was sufficient, and unstable energy existed at low layer. Structure characteristic of the convective strong precipitation appeared by advancing for 12h. As precipitation weakened, unstable energy was released, and ultra-low temperature disappeared. [Conclusion] The research provided some thoughts for the forecast of such weather process.展开更多
This paper investigates analysis and design of Low-Density Parity-Check （LDPC） coded Bit Interleaved Coded Modulation （BICM） over Additive White Gaussian Noise （AWGN） channel. It focuses on Gray-labeled 8-ary Ph...This paper investigates analysis and design of Low-Density Parity-Check （LDPC） coded Bit Interleaved Coded Modulation （BICM） over Additive White Gaussian Noise （AWGN） channel. It focuses on Gray-labeled 8-ary Phase-Shift-Keying （8PSK） modulation and employs a Maximum A Posteriori （MAP） symbol-to-bit metric calculator at the receiver. An equivalent model of a BICM communication channel with ideal interleaving is presented. The probability distribution function of log-likelihood ratio messages from the MAP receiver can be approximated by a mixture of symmetric Gaussian densities. As a result semi-Gaussian approximation can be used to analyze the decoder. Extrinsic information transfer charts are employed to describe the convergence behavior of LDPC decoder. The design of irregular LDPC codes reduces to a linear programming problem on two-dimensional variable edge-degree distribution. This method allows irregular code design in a wider range of rates without any limit on the maximum node degree and can be used to design irregular codes having rates varying from 0.5275 to 0.9099. The designed convergence thresholds are only a few tenths, even a few hundredths of a decibel from the capacity limits. It is shown by Monte Carlo simulations that, when the block length is 30,000, these codes operate about 0.62-0.75 dB from the capacity limit at a bit error rate of 10s.展开更多
In this paper, we focus on the design of irregular QC-LDPC code based multi-level coded modulation(MLCM) scheme by jointly optimizing the component code rate and the degree distribution of the irregular QC-LDPC compon...In this paper, we focus on the design of irregular QC-LDPC code based multi-level coded modulation(MLCM) scheme by jointly optimizing the component code rate and the degree distribution of the irregular QC-LDPC component code. Firstly, the sub-channel capacities of MLCM systems is analyzed and discussed, based on which the optimal component code rate can be obtained. Secondly, an extrinsic information transfer chart based two-stage searching algorithm is proposed to find the good irregular QC-LDPC code ensembles with optimal component code rates for their corresponding sub-channels. Finally, by constructing the irregular QC-LDPC component codes from the designed ensembles with the aim of possibly enlarging the girth and reducing the number of the shortest cycles, the designed irregular QC-LDPC code based 16QAM and 64QAM MLCM systems can achieve 0.4 dB and 1.2 dB net coding gain, respectively, compared with the recently proposed regular QC-LDPC code based 16QAM and 64QAM MLCM systems.展开更多
基金Project (50925417) supported by the National Funds for Distinguished Young Scientists, ChinaProject (50830301) supported by the Key Project of National Natural Science Foundation of China
文摘A total of 153 soil samples were collected from Changsha City, China, to analyze the contents of As, Cd, Cr, Cu, Hg, Mn, Ni, Pb and Zn. A combination of sampling data, multivariate statistical method, geostatistical analysis, direct exposure method and triangulated irregular network （TIN） model was successfully employed to discriminate sources, simulate spatial distributions and evaluate children＇s health risks of heavy metals in soils. The results show that not all sites in Changsha city may be suitable for living without remediation. About 9.0% of the study area provided a hazard index （HI）1.0, and 1.9% had an HI2.0. Most high HIs were located in the southern and western areas. The element of arsenic and the pathway of soil ingestion were the largest contribution to potential health risks for children. This study indicates that we should attach great importance to the direct soil heavy metals exposure for children＇s health.
文摘[Objective] The research aimed to analyze irregular information of the local rainstorm process (during 5-6 September,2009) in autumn continuous rainy weather in north Shaanxi. [Method] Based on V-3θ chart, routine observation data provided by Micaps system, satellite cloud chart and data at 100 automatic meteorological stations of Shaanxi, for rainstorm process in autumn continuous rainy weather in north Shaanxi during 4-10 September, 2009, by using structure analysis method, irregular information in local rainstorm weather was analyzed. [Result] In whole precipitation process, atmospheric structure in rainstorm zone presented obvious evolution process. Before precipitation, typical atmospheric structure information of the sudden convective weather appeared. Obvious ultra-low temperature structure appeared at 200 hPa, and consistent clockwise rotation flow was at vertical wind field. Meanwhile, water vapor was sufficient, and unstable energy existed at low layer. Structure characteristic of the convective strong precipitation appeared by advancing for 12h. As precipitation weakened, unstable energy was released, and ultra-low temperature disappeared. [Conclusion] The research provided some thoughts for the forecast of such weather process.
文摘This paper investigates analysis and design of Low-Density Parity-Check （LDPC） coded Bit Interleaved Coded Modulation （BICM） over Additive White Gaussian Noise （AWGN） channel. It focuses on Gray-labeled 8-ary Phase-Shift-Keying （8PSK） modulation and employs a Maximum A Posteriori （MAP） symbol-to-bit metric calculator at the receiver. An equivalent model of a BICM communication channel with ideal interleaving is presented. The probability distribution function of log-likelihood ratio messages from the MAP receiver can be approximated by a mixture of symmetric Gaussian densities. As a result semi-Gaussian approximation can be used to analyze the decoder. Extrinsic information transfer charts are employed to describe the convergence behavior of LDPC decoder. The design of irregular LDPC codes reduces to a linear programming problem on two-dimensional variable edge-degree distribution. This method allows irregular code design in a wider range of rates without any limit on the maximum node degree and can be used to design irregular codes having rates varying from 0.5275 to 0.9099. The designed convergence thresholds are only a few tenths, even a few hundredths of a decibel from the capacity limits. It is shown by Monte Carlo simulations that, when the block length is 30,000, these codes operate about 0.62-0.75 dB from the capacity limit at a bit error rate of 10s.
基金supported by National Natural Science Foundation of China(No.61571061)
文摘In this paper, we focus on the design of irregular QC-LDPC code based multi-level coded modulation(MLCM) scheme by jointly optimizing the component code rate and the degree distribution of the irregular QC-LDPC component code. Firstly, the sub-channel capacities of MLCM systems is analyzed and discussed, based on which the optimal component code rate can be obtained. Secondly, an extrinsic information transfer chart based two-stage searching algorithm is proposed to find the good irregular QC-LDPC code ensembles with optimal component code rates for their corresponding sub-channels. Finally, by constructing the irregular QC-LDPC component codes from the designed ensembles with the aim of possibly enlarging the girth and reducing the number of the shortest cycles, the designed irregular QC-LDPC code based 16QAM and 64QAM MLCM systems can achieve 0.4 dB and 1.2 dB net coding gain, respectively, compared with the recently proposed regular QC-LDPC code based 16QAM and 64QAM MLCM systems.
