The black soil region of northeast China is one of the most important grain-producing areas in China. Increasingly severe gully erosion in this region has destroyed much farmland and reduced grain production. We analy...The black soil region of northeast China is one of the most important grain-producing areas in China. Increasingly severe gully erosion in this region has destroyed much farmland and reduced grain production. We analyzed SPOT5 imagery from 2007 and TM imagery from 2008 to describe the distributions of gullies and farmland shelterbelts in Kedong County and to assess the effect of farmland shelterbelts on gully erosion. The ima- gery revealed 2311 gullies with average density of 418.51 m km-2, indicating very serious gully erosion. With increasing slope gradient there was an inverse trend between gully density and shelterbelt density, indicating that farmland shelterbelts can prevent gully erosion. The defense effect of farmland shelterbelts against gullyerosion varied with distance： for distances 〈120 m, the defense effect was consistent and very strong; for distances of 120-240 m, a weak linear decrease was found in the defense effect; and for distances 〉240 m, the defense effect of the shelterbelts was significantly weaker. We recommend an optimal planting density of farmland shel- terbelts for the prevention of gully erosion at 1100-1300 m km-2.展开更多
In X-ray pulsar-based navigation, strong X-ray background noise leads to a low signal-to-noise ratio（SNR） of the observed profile, which consequently makes it very difficult to obtain an accurate pulse phase that di...In X-ray pulsar-based navigation, strong X-ray background noise leads to a low signal-to-noise ratio（SNR） of the observed profile, which consequently makes it very difficult to obtain an accurate pulse phase that directly determines the navigation precision. This signifies the necessity of denoising of the observed profile. Considering that the ultimate goal of denoising is to enhance the pulse phase estimation, a profile denoising algorithm is proposed by fusing the biorthogonal lifting wavelet transform of the linear phase characteristic with the thresholding technique. The statistical properties of X-ray background noise after epoch folding are studied. Then a wavelet-scale dependent threshold is introduced to overcome correlations between wavelet coefficients. Moreover, a modified hyperbola shrinking function is presented to remove the impulsive oscillations of the observed profile. The results of numerical simulations and real data experiments indicate that the proposed method can effectively improve SNR of the observed profile and pulse phase estimation accuracy, especially in short observation durations. And it also outperforms the Donoho thresholding strategy normally used in combination with the orthogonal discrete wavelet transform.展开更多
Twenty water bodies in China were sampled,and 186 strains of different Microcystis species were isolated,from which eight morpho species were identified and 43 stains containing the mcyB gene were detected.Phylogeneti...Twenty water bodies in China were sampled,and 186 strains of different Microcystis species were isolated,from which eight morpho species were identified and 43 stains containing the mcyB gene were detected.Phylogenetic analysis based on the mcyB gene indicated that the microcystin(MC)-producing Microcystis in China could be divided into two groups(ⅠandⅡ)and showed significant differences between the two groups.The maximum sequence similarity was 69.1%.Microcystins(MCs)were measured by high-performance liquid chromatography(HPLC)analysis,and no microcystin-RR(MC-RR)was detected in some strains belonging to GroupⅡ.Compared to other regions of the world,the proportion of Chinese MC-producing was different,and the regional differences were more obvious.A whole-cell polymerase chain reactio(PCR)assay was conducted to analyze the proportion of the mcyB gene in the laboratory cultured and field cultured Microcystis.The proportion of four morphospecies(M.vividis,M.ichthyoblabe,M.novacekii,and M.aeruginosa)that contained the mcyB gene exceeded 50%in the field cultured sample s.Compared with former studies,M.aeruginosa was the mo st likely morphotype that can produce MCs in the world.This study provided new insight of Microcystis hazard assessment and field monitoring.展开更多
基金supported by the National Natural Science Foundation of China(31400612,41271305)the Key Technologies Research and Development Program of Henan Province(142102110147)
文摘The black soil region of northeast China is one of the most important grain-producing areas in China. Increasingly severe gully erosion in this region has destroyed much farmland and reduced grain production. We analyzed SPOT5 imagery from 2007 and TM imagery from 2008 to describe the distributions of gullies and farmland shelterbelts in Kedong County and to assess the effect of farmland shelterbelts on gully erosion. The ima- gery revealed 2311 gullies with average density of 418.51 m km-2, indicating very serious gully erosion. With increasing slope gradient there was an inverse trend between gully density and shelterbelt density, indicating that farmland shelterbelts can prevent gully erosion. The defense effect of farmland shelterbelts against gullyerosion varied with distance： for distances 〈120 m, the defense effect was consistent and very strong; for distances of 120-240 m, a weak linear decrease was found in the defense effect; and for distances 〉240 m, the defense effect of the shelterbelts was significantly weaker. We recommend an optimal planting density of farmland shel- terbelts for the prevention of gully erosion at 1100-1300 m km-2.
文摘In X-ray pulsar-based navigation, strong X-ray background noise leads to a low signal-to-noise ratio（SNR） of the observed profile, which consequently makes it very difficult to obtain an accurate pulse phase that directly determines the navigation precision. This signifies the necessity of denoising of the observed profile. Considering that the ultimate goal of denoising is to enhance the pulse phase estimation, a profile denoising algorithm is proposed by fusing the biorthogonal lifting wavelet transform of the linear phase characteristic with the thresholding technique. The statistical properties of X-ray background noise after epoch folding are studied. Then a wavelet-scale dependent threshold is introduced to overcome correlations between wavelet coefficients. Moreover, a modified hyperbola shrinking function is presented to remove the impulsive oscillations of the observed profile. The results of numerical simulations and real data experiments indicate that the proposed method can effectively improve SNR of the observed profile and pulse phase estimation accuracy, especially in short observation durations. And it also outperforms the Donoho thresholding strategy normally used in combination with the orthogonal discrete wavelet transform.
基金the Science and Technology Project of Henan Province(Nos.19A180018,192102310306)the Key Laboratory of Algal Biology,Institute of Hydrobiology,Chinese Academy of Sciences(No.2018001)。
文摘Twenty water bodies in China were sampled,and 186 strains of different Microcystis species were isolated,from which eight morpho species were identified and 43 stains containing the mcyB gene were detected.Phylogenetic analysis based on the mcyB gene indicated that the microcystin(MC)-producing Microcystis in China could be divided into two groups(ⅠandⅡ)and showed significant differences between the two groups.The maximum sequence similarity was 69.1%.Microcystins(MCs)were measured by high-performance liquid chromatography(HPLC)analysis,and no microcystin-RR(MC-RR)was detected in some strains belonging to GroupⅡ.Compared to other regions of the world,the proportion of Chinese MC-producing was different,and the regional differences were more obvious.A whole-cell polymerase chain reactio(PCR)assay was conducted to analyze the proportion of the mcyB gene in the laboratory cultured and field cultured Microcystis.The proportion of four morphospecies(M.vividis,M.ichthyoblabe,M.novacekii,and M.aeruginosa)that contained the mcyB gene exceeded 50%in the field cultured sample s.Compared with former studies,M.aeruginosa was the mo st likely morphotype that can produce MCs in the world.This study provided new insight of Microcystis hazard assessment and field monitoring.
