A new norditerpenoid alkaloid, hemsleyadine, was isolated from the roots of Aconitum hemsleyanum var. circinatum, Structure of hemsleyadine was assigned as 1 by comparison of its C-13 NMR data with known compounds.
The state-of-the-art of fatigue crack closure effect, involving the mechanisms, measurements, models, evaluation methods, influencing factors and existing problems is briefly reviewed. Attention is concentrated on a n...The state-of-the-art of fatigue crack closure effect, involving the mechanisms, measurements, models, evaluation methods, influencing factors and existing problems is briefly reviewed. Attention is concentrated on a new consideration of closure effect and a re-definition of the effective driving force for the propagation of a fatigue crack. A theoretical basis for measuring the closure effect is established. The proposed closure concept takes into account the role of the tower portion of loading cycle below the opening load. The conventional closure concept is proven to be correct only for some extreme cases which are practically non-existent for engineering materials. A miniature strain gauge technique is developed to measure the crack closure. Stress-ratio-change tests at threshold level clearly indicate the shortcomings of the conventional closure concept, and the validity of the newly-proposed closure concept. The application of the proposed concept can give rise to a new method for the determination of the effective fatigue threshold of materials. If the fatigue threshold is measured at a sufficiently negative stress ratio (R<R(cr)) the tensile portion of the cyclic loading just reflects the effective fatigue threshold of the material.展开更多
THE climatic deterioration is an important event in the geological history and generally recog-nized by composition of strata and variation in some elements. However, the study on the cli-matic deterioration events in...THE climatic deterioration is an important event in the geological history and generally recog-nized by composition of strata and variation in some elements. However, the study on the cli-matic deterioration events in terms of age distribution of animals has been rarely reported.This note reports the study on a climatic deterioration event and its affected area during theMiocene Epoch based on thousands of fossils of Hipparion fauna from Longjiagou in Wudu,展开更多
文摘A new norditerpenoid alkaloid, hemsleyadine, was isolated from the roots of Aconitum hemsleyanum var. circinatum, Structure of hemsleyadine was assigned as 1 by comparison of its C-13 NMR data with known compounds.
文摘The state-of-the-art of fatigue crack closure effect, involving the mechanisms, measurements, models, evaluation methods, influencing factors and existing problems is briefly reviewed. Attention is concentrated on a new consideration of closure effect and a re-definition of the effective driving force for the propagation of a fatigue crack. A theoretical basis for measuring the closure effect is established. The proposed closure concept takes into account the role of the tower portion of loading cycle below the opening load. The conventional closure concept is proven to be correct only for some extreme cases which are practically non-existent for engineering materials. A miniature strain gauge technique is developed to measure the crack closure. Stress-ratio-change tests at threshold level clearly indicate the shortcomings of the conventional closure concept, and the validity of the newly-proposed closure concept. The application of the proposed concept can give rise to a new method for the determination of the effective fatigue threshold of materials. If the fatigue threshold is measured at a sufficiently negative stress ratio (R<R(cr)) the tensile portion of the cyclic loading just reflects the effective fatigue threshold of the material.
文摘THE climatic deterioration is an important event in the geological history and generally recog-nized by composition of strata and variation in some elements. However, the study on the cli-matic deterioration events in terms of age distribution of animals has been rarely reported.This note reports the study on a climatic deterioration event and its affected area during theMiocene Epoch based on thousands of fossils of Hipparion fauna from Longjiagou in Wudu,
