This study reversed the developing environments of hydrocarbon-source rocksin the Ordos Basin and evaluated carbonate rocks as hydrocarbon-source rocks and their distributionson account of the fact that China''...This study reversed the developing environments of hydrocarbon-source rocksin the Ordos Basin and evaluated carbonate rocks as hydrocarbon-source rocks and their distributionson account of the fact that China''s marine carbonate rocks as hydrocarbon-source rocks arecharacterized by intensive thermal evolution and relatively low abundance of organic matter, bytaking the Lower Paleozoic of the Ordos Basin for example and in light of the calculated enrichmentcoefficients of trace elements, the REE distribution patterns, the mathematical statistics analysisof elements and carbon isotopes and their three-dimensional diagrammatization in combination withthe necessary organic parameters. As for the Ordos Basin, TOC=0.2% is an important boundary value.Studies have shown that in the strata where TOC is greater than 0.2%, Ba is highly enriched withpositive δ^(13)C_(carb) shifts and δ^(13)C_(org) less than -28per thousand, reflecting a thighpaleo-productivity, high burial amounts of organic matter, relatively good hydrocarbon-generatingpotentiality and intensive REE fractionation. All these indicated that the settlement rates are lowand the geological conditions are good for the preservation of organic matter, hence favoring thedevelopment of hydrocarbon-source rocks. The Klimory and Wulalik formations show certainregularities in those aspects and, therefore, they can be regarded as the potential effectivehydrocarbon-source rocks. In the strata where total TOC is less than 0.2%, the contents of Ba arelow, δ^(13)C_(carb) values are mostly negative, and δ^(13)C_(org) values range from -24perthousand—-28per thousand, demonstrating low burial amounts of organic matter, poor potentialitiesof hydrocarbon generation, weak REE fractionation and rapid settlement rates. These facts showedthat most of the hydrocarbon-source rocks were formed in shallow-water, high-energy oxidizingenvironments, thus un-favoring the development of hydrocarbon-source rocks. It is feasible to makeuse of the geochemical method to comprehensively asse展开更多
A timely and accurate damage identification for bridge structures is essential to prevent sudden failures/collapses and other catastrophic accidents.Based on response surface model(RSM)updating and element modal strai...A timely and accurate damage identification for bridge structures is essential to prevent sudden failures/collapses and other catastrophic accidents.Based on response surface model(RSM)updating and element modal strain energy(EMSE)damage index,this paper proposes a novel damage identification method for girder bridge structures.The effectiveness of the proposed damage identification method is investigated using experiments on four simply supported steel beams.With Xiabaishi Bridge,a prestressed continuous rigid frame bridge with large span,as the engineering background,the proposed damage identification method is validated by using numerical simulation to generate different bearing damage scenarios.Finally,the efficiency of the method is justified by considering its application to identifying cracking damage for a real continuous beam bridge called Xinyihe Bridge.It is concluded that the EMSE damage index is sensitive to the cracking damage and the bearing damage.The locations and levels of multiple cracking damages and bearing damages can be also identified.The results illuminate a great potential of the proposed method in identifying damages of real bridge structures.展开更多
Objective Our objective is to build a model that explains the association between the exposure to trace elements in the soil and the risk of neural tube defects. Methods We built a function with different parameters t...Objective Our objective is to build a model that explains the association between the exposure to trace elements in the soil and the risk of neural tube defects. Methods We built a function with different parameters to describe the effects of trace elements on neural tube defects. The association between neural tube defects and trace element levels was transformed into an optimization problem using the maximum likelihood method. Results Tin, lead, nickel, iron, copper, and aluminum had typical layered effects （dosage effects） on the prevalence of neural tube defects. Arsenic, selenium, zinc, strontium, and vanadium had no effect, and molybdenum had one threshold value that affected the prevalence of birth defects. Conclusion As an exploratory research work, our model can be used to determine the direction of the effect of the trace element content of cultivated soil on the risk of neural tube defects, which shows the clues by the dosage effect of their toxicological characteristics. Based on our findings, future biogeochemical research should focus on the direct effects of trace elements on human health.展开更多
Local geometric information and discontinuity features are key aspects of the analysis of the evolution and failure mechanisms of unstable rock blocks in rock tunnels.This study demonstrates the integration of terrest...Local geometric information and discontinuity features are key aspects of the analysis of the evolution and failure mechanisms of unstable rock blocks in rock tunnels.This study demonstrates the integration of terrestrial laser scanning(TLS)with distinct element method for rock mass characterization and stability analysis in tunnels.TLS records detailed geometric information of the surrounding rock mass by scanning and collecting the positions of millions of rock surface points without contact.By conducting a fuzzy K-means method,a discontinuity automatic identification algorithm was developed,and a method for obtaining the geometric parameters of discontinuities was proposed.This method permits the user to visually identify each discontinuity and acquire its spatial distribution features(e.g.occurrences,spac-ings,trace lengths)in great detail.Compared with hand mapping in conventional geotechnical surveys,the geometric information of discontinuities obtained by this approach is more accurate and the iden-tification is more efficient.Then,a discrete fracture network with the same statistical characteristics as the actual discontinuities was generated with the distinct element method,and a representative nu-merical model of the jointed surrounding rock mass was established.By means of numerical simulation,potential unstable rock blocks were assessed,and failure mechanisms were analyzed.This method was applied to detection and assessment of unstable rock blocks in the spillway and sand flushing tunnel of the Hongshiyan hydropower project after a collapse.The results show that the noncontact detection of blocks was more labor-saving with lower safety risks compared with manual surveys,and the stability assessment was more reliable since the numerical model built by this method was more consistent with the distribution characteristics of actual joints.This study can provide a reference for geological survey and unstable rock block hazard mitigation in tunnels subjected to complex geology and active rockfalls.展开更多
文摘This study reversed the developing environments of hydrocarbon-source rocksin the Ordos Basin and evaluated carbonate rocks as hydrocarbon-source rocks and their distributionson account of the fact that China''s marine carbonate rocks as hydrocarbon-source rocks arecharacterized by intensive thermal evolution and relatively low abundance of organic matter, bytaking the Lower Paleozoic of the Ordos Basin for example and in light of the calculated enrichmentcoefficients of trace elements, the REE distribution patterns, the mathematical statistics analysisof elements and carbon isotopes and their three-dimensional diagrammatization in combination withthe necessary organic parameters. As for the Ordos Basin, TOC=0.2% is an important boundary value.Studies have shown that in the strata where TOC is greater than 0.2%, Ba is highly enriched withpositive δ^(13)C_(carb) shifts and δ^(13)C_(org) less than -28per thousand, reflecting a thighpaleo-productivity, high burial amounts of organic matter, relatively good hydrocarbon-generatingpotentiality and intensive REE fractionation. All these indicated that the settlement rates are lowand the geological conditions are good for the preservation of organic matter, hence favoring thedevelopment of hydrocarbon-source rocks. The Klimory and Wulalik formations show certainregularities in those aspects and, therefore, they can be regarded as the potential effectivehydrocarbon-source rocks. In the strata where total TOC is less than 0.2%, the contents of Ba arelow, δ^(13)C_(carb) values are mostly negative, and δ^(13)C_(org) values range from -24perthousand—-28per thousand, demonstrating low burial amounts of organic matter, poor potentialitiesof hydrocarbon generation, weak REE fractionation and rapid settlement rates. These facts showedthat most of the hydrocarbon-source rocks were formed in shallow-water, high-energy oxidizingenvironments, thus un-favoring the development of hydrocarbon-source rocks. It is feasible to makeuse of the geochemical method to comprehensively asse
基金The National Natural Science Foundation of China(Grant Nos.51178101 and 51378112)The University Graduate Student Scientific Research Innovation Plan of Jiangsu Province(Grant No.CXZZ13_0109)China Scholarship Council under Program for Graduate Student Overseas Study Scholarship
文摘A timely and accurate damage identification for bridge structures is essential to prevent sudden failures/collapses and other catastrophic accidents.Based on response surface model(RSM)updating and element modal strain energy(EMSE)damage index,this paper proposes a novel damage identification method for girder bridge structures.The effectiveness of the proposed damage identification method is investigated using experiments on four simply supported steel beams.With Xiabaishi Bridge,a prestressed continuous rigid frame bridge with large span,as the engineering background,the proposed damage identification method is validated by using numerical simulation to generate different bearing damage scenarios.Finally,the efficiency of the method is justified by considering its application to identifying cracking damage for a real continuous beam bridge called Xinyihe Bridge.It is concluded that the EMSE damage index is sensitive to the cracking damage and the bearing damage.The locations and levels of multiple cracking damages and bearing damages can be also identified.The results illuminate a great potential of the proposed method in identifying damages of real bridge structures.
基金supported by the National "973" project on Population and Health (No. 2007CB5119001)the National Yang‐Zi Scholar Program, 211 and 985 projects of Peking University (No. 20020903)
文摘Objective Our objective is to build a model that explains the association between the exposure to trace elements in the soil and the risk of neural tube defects. Methods We built a function with different parameters to describe the effects of trace elements on neural tube defects. The association between neural tube defects and trace element levels was transformed into an optimization problem using the maximum likelihood method. Results Tin, lead, nickel, iron, copper, and aluminum had typical layered effects （dosage effects） on the prevalence of neural tube defects. Arsenic, selenium, zinc, strontium, and vanadium had no effect, and molybdenum had one threshold value that affected the prevalence of birth defects. Conclusion As an exploratory research work, our model can be used to determine the direction of the effect of the trace element content of cultivated soil on the risk of neural tube defects, which shows the clues by the dosage effect of their toxicological characteristics. Based on our findings, future biogeochemical research should focus on the direct effects of trace elements on human health.
基金support of the National Natural Science Foundation of China(Grant No.42102316)the Open Project of the Technology Innovation Center for Geological Environment Monitoring of Ministry of Natural Resources of China(Grant No.2022KFK1212005).
文摘Local geometric information and discontinuity features are key aspects of the analysis of the evolution and failure mechanisms of unstable rock blocks in rock tunnels.This study demonstrates the integration of terrestrial laser scanning(TLS)with distinct element method for rock mass characterization and stability analysis in tunnels.TLS records detailed geometric information of the surrounding rock mass by scanning and collecting the positions of millions of rock surface points without contact.By conducting a fuzzy K-means method,a discontinuity automatic identification algorithm was developed,and a method for obtaining the geometric parameters of discontinuities was proposed.This method permits the user to visually identify each discontinuity and acquire its spatial distribution features(e.g.occurrences,spac-ings,trace lengths)in great detail.Compared with hand mapping in conventional geotechnical surveys,the geometric information of discontinuities obtained by this approach is more accurate and the iden-tification is more efficient.Then,a discrete fracture network with the same statistical characteristics as the actual discontinuities was generated with the distinct element method,and a representative nu-merical model of the jointed surrounding rock mass was established.By means of numerical simulation,potential unstable rock blocks were assessed,and failure mechanisms were analyzed.This method was applied to detection and assessment of unstable rock blocks in the spillway and sand flushing tunnel of the Hongshiyan hydropower project after a collapse.The results show that the noncontact detection of blocks was more labor-saving with lower safety risks compared with manual surveys,and the stability assessment was more reliable since the numerical model built by this method was more consistent with the distribution characteristics of actual joints.This study can provide a reference for geological survey and unstable rock block hazard mitigation in tunnels subjected to complex geology and active rockfalls.
