We collected fish abundance data in the Changjiang(Yangtze River) estuary and adjacent waters in November 1998,May 1999,November 2000,and May 2001.Using the data,we evaluated the characteristics of the fish assemblage...We collected fish abundance data in the Changjiang(Yangtze River) estuary and adjacent waters in November 1998,May 1999,November 2000,and May 2001.Using the data,we evaluated the characteristics of the fish assemblages at each site and investigated the effect of several environmental factors.We used a multivariate analysis,including community ordination methods such as detrended correspondence analysis(DCA) and canonical correspondence analysis(CCA),and two-way indicator species analysis(TWINSPAN).We analyzed the biological community structure and environmental factors to determine their spatial distributions,temporal dynamics,and seasonal variations.Among the fish species,five exceeded 5% of the total abundance:Harpodon nehereus(42.82%),Benthosema pterotum(13.85%),Setipinna taty(11.64%),Thryssa kammalensis(9.17%) and Apogonichthys lineatus(6.49%).These were separated into four ecological assemblages:hypsithermal-saline,hypsithermal-brackish,hypothermal-brackish,and hypothermal-saline.We evaluated the degree of influence of environmental factors on the fish community.Our analyses suggested that environmental factors including water depth,salinity,turbidity,transparency,nutrient,and suspended matter formed a synthetic spatial gradient between the coastal and pelagic areas.Ecological and environmental factors changed temporally from 1998 to 2001,and drove the fish community succession.The environmental factors driving the fish community structure included bottom temperature,water depth,bottom and surface pH,surface total phosphorous,and bottom dissolved oxygen.This investigation was completed before completion of the Three Gorges Dam;therefore the results of this study provide an important foundation for evaluating the influence of the human activities.展开更多
F.A.Szasz has put forward the open problem 55 in [1]: Let K be the class of all subdirectly irreducible rings, whose Jacobson radical is (0). Examine the upper radical determined by the class K. In this paper, the pro...F.A.Szasz has put forward the open problem 55 in [1]: Let K be the class of all subdirectly irreducible rings, whose Jacobson radical is (0). Examine the upper radical determined by the class K. In this paper, the problem has been examined. (1) It has been proved that the upper radical R determined by the class K is a special radical,which lies between Jacobson radical and Brown-McCoy radical. (2) It has been given some necessary and sufficient condition of ring A to be an R-radical ring.展开更多
In this paper,the Fourier spectrum-based strain energy damage detection method for beam-like structures is proposed based on the discrete Fourier transform.The classical strain energy damage detection method localizes...In this paper,the Fourier spectrum-based strain energy damage detection method for beam-like structures is proposed based on the discrete Fourier transform.The classical strain energy damage detection method localizes damage by the comparison of the strain energy between the intact and inspected structures.The evaluation of the 2nd-order derivative term in the strain energy plays a crucial part in the comparison.The classical methods are mostly based on a numerical derivative estimation for this term.The numerical derivative,however,introduces additional disturbances into damage indications.To address this problem,a discrete Fourier transform-based strain energy is proposed with the emphasis of enhancing the performance in noisy condition.The validations conducted on the simulated and experimental data show that the developed method is effective enough for composite beam damage detection in noisy environments.展开更多
基金Supported by the High Technology Research and Development Program of China (863 Program)(Nos 2006AA09Z180,2004AA639790)the National Natural Science Foundation of China (No 40106013)the National Basic Research Program of China (973 program)(No 2001CB409703)
文摘We collected fish abundance data in the Changjiang(Yangtze River) estuary and adjacent waters in November 1998,May 1999,November 2000,and May 2001.Using the data,we evaluated the characteristics of the fish assemblages at each site and investigated the effect of several environmental factors.We used a multivariate analysis,including community ordination methods such as detrended correspondence analysis(DCA) and canonical correspondence analysis(CCA),and two-way indicator species analysis(TWINSPAN).We analyzed the biological community structure and environmental factors to determine their spatial distributions,temporal dynamics,and seasonal variations.Among the fish species,five exceeded 5% of the total abundance:Harpodon nehereus(42.82%),Benthosema pterotum(13.85%),Setipinna taty(11.64%),Thryssa kammalensis(9.17%) and Apogonichthys lineatus(6.49%).These were separated into four ecological assemblages:hypsithermal-saline,hypsithermal-brackish,hypothermal-brackish,and hypothermal-saline.We evaluated the degree of influence of environmental factors on the fish community.Our analyses suggested that environmental factors including water depth,salinity,turbidity,transparency,nutrient,and suspended matter formed a synthetic spatial gradient between the coastal and pelagic areas.Ecological and environmental factors changed temporally from 1998 to 2001,and drove the fish community succession.The environmental factors driving the fish community structure included bottom temperature,water depth,bottom and surface pH,surface total phosphorous,and bottom dissolved oxygen.This investigation was completed before completion of the Three Gorges Dam;therefore the results of this study provide an important foundation for evaluating the influence of the human activities.
文摘F.A.Szasz has put forward the open problem 55 in [1]: Let K be the class of all subdirectly irreducible rings, whose Jacobson radical is (0). Examine the upper radical determined by the class K. In this paper, the problem has been examined. (1) It has been proved that the upper radical R determined by the class K is a special radical,which lies between Jacobson radical and Brown-McCoy radical. (2) It has been given some necessary and sufficient condition of ring A to be an R-radical ring.
基金supported by the National Natural Science Foundation of China(Grant Nos.51405369&51421004)the National Key Basic Research Program of China(Grant No.2015CB057400)+1 种基金the National Natural Science Foundation of Shaanxi Province(Grant No.2016JQ5049)the Postdoctoral Science Foundation of Shaanxi Province
文摘In this paper,the Fourier spectrum-based strain energy damage detection method for beam-like structures is proposed based on the discrete Fourier transform.The classical strain energy damage detection method localizes damage by the comparison of the strain energy between the intact and inspected structures.The evaluation of the 2nd-order derivative term in the strain energy plays a crucial part in the comparison.The classical methods are mostly based on a numerical derivative estimation for this term.The numerical derivative,however,introduces additional disturbances into damage indications.To address this problem,a discrete Fourier transform-based strain energy is proposed with the emphasis of enhancing the performance in noisy condition.The validations conducted on the simulated and experimental data show that the developed method is effective enough for composite beam damage detection in noisy environments.
