Phyllite fragments are essential for accumulating and generating talus slope at the toes of hillslopes,however,how they are linked to slope failure remains unknown.This paper reports the directional arrangement of phy...Phyllite fragments are essential for accumulating and generating talus slope at the toes of hillslopes,however,how they are linked to slope failure remains unknown.This paper reports the directional arrangement of phyllite fragments(DAPF)in phyllite talus slope at the eastern margin of the Tibetan Plateau.Field investigation,mathematical statistics and model experiments were performed in order to systematically understand the influencing factors,which include fragment shape,flat ratio,dip angle(α),and fine particle content(c).The results show that the quadrilateral fragmentgenerates a similar imbricate structure more easily than the triangular and rod fragments in the phyllite talus slope.Additionally,the flat phyllite fragments easily accumulate as imbricated structures on the phyllitetalus slope.When the dip angle(α)is in the range of 20°–30°,the minimum orientation ratio(P)is more than 50%,which means thatthe DAPF phenomenon is more obviousin the phyllite talus slope.For the fine particle content(c)at the same dip angle(α),the minimum orientation ratio(P)is 54%,and the minimum orientation ratio(P)correlates positively with the fine particle content(c).Therefore,compared with the homogeneous talusslope,the phyllite talusslopedisplays a special DAPF phenomenon.This study provides a valuable reference and presents novel knowledgefor risk assessment and engineering design against the phyllite talus slope failure mechanism.展开更多
Chitin,the most abundant aminopolysaccharide in nature,is an extracellular polymer consisting of N-acetylglucosamine(GlcNAc)units1.The key reactions of chitin biosynthesis are catalysed by chitin synthase2-4,a membran...Chitin,the most abundant aminopolysaccharide in nature,is an extracellular polymer consisting of N-acetylglucosamine(GlcNAc)units1.The key reactions of chitin biosynthesis are catalysed by chitin synthase2-4,a membrane-integrated glycosyltransferase that transfers GlcNAc from UDP-GlcNAc to a growing chitin chain.However,the precise mechanism of this process has yet to be elucidated.Here we report five cryo-electron microscopy structures of a chitin synthase from the devastating soybean root rot pathogenic oomycete Phytophthora sojae(PsChs1).They represent the apo,GlcNAc-bound,nascent chitin oligomer-bound,UDP-bound(post-synthesis)and chitin synthase inhibitor nikkomycin Z-bound states of the enzyme,providing detailed views into the multiple steps of chitin biosynthesis and its competitive inhibition.The structures reveal the chitin synthesis reaction chamber that has the substrate-binding site,the catalytic centre and the entrance to the polymer-translocating channel that allows the product polymer to be discharged.This arrangement reflects consecutive key events in chitin biosynthesis from UDP-GlcNAc binding and polymer elongation to the release of the product.We identified a swinging loop within the chitin-translocating channel,which acts as a'gate lock'that prevents the substrate from leaving while directing the product polymer into the translocating channel for discharge to the extracellular side of the cell membrane.This work reveals the directional multistep mechanism of chitin biosynthesis and provides a structural basis for inhibition of chitin synthesis.展开更多
Living Cephalotaxus (plum yews) occurs mainly in East Asia and North of Indo-China peninsula. The study of original taxonomic literatures found that, in early days, the plum yews had ever been described as palnts of T...Living Cephalotaxus (plum yews) occurs mainly in East Asia and North of Indo-China peninsula. The study of original taxonomic literatures found that, in early days, the plum yews had ever been described as palnts of Taxus (Taxaceae). Since after the genus name Cephalotaxus Sieb. & Zucc. was firstly cited (from inedited and unpublished Flora Japonica) by Endlicher in 1842, most taxonomist thought which is the earliest time of the genus Cephalotaxus Sieb. & Zucc. was set. However, the genus Cephalotaxus Sieb. & Zucc. was formally effective and valid published by Sieb. & Zucc. in Flora Japonica in 1870 so that there exists some confusions in chronological order. Originally as a genus, Cephalotaxus was included in family Taxaceae and Neger (1907) separated Cephalotaxus from Taxaceae and set family Cephalotaxaceae. Later, Fu (1984) divided Cephalotaxus up into two sections of Cephalotaxus Sieb. & Zucc. sect. Pectinatae L. K. Fu and Cephalotaxus Sieb. & Zucc. sect. Cephalotaxus L. K. Fu on the bases of C. oliveri Masters differ significantly from other taxa of Cephalotaxus in morphological characteristics. Although the plum yews was a little genus of conifers, up to now, about 77 taxa have still been published by taxonomist in different countries or regions. Among them, C. tardiva Sieb. ex Endl. (1847), C. umbraculifera Sieb. ex Endl. (1847), C. sumatrana Miq. (1856) and C. celebica Warb. (1900) have been combined to Taxus, and C. argotaenia (Hance) Pilger (1903) has been combined to Amentotaxus. And at the same time, those taxa existing in Cephalotaxus courently which were accepted by most taxonomist in different countries was also cited in acticle. Lastly, the paper thought presently there still exists many debates about binary classification of Cephalotaxus and the nomenclature of this genus still particularly confusing. Based on some controversial problems, we also point out some taxonomically researching directions at creating some order out of the chaos.展开更多
This work studies the macroscopic and microscopic behaviors of ellipsoids under triaxial tests using 3D discrete element method(DEM)simulation.To avoid the boundary effect,a novel stress servo-controlled periodic boun...This work studies the macroscopic and microscopic behaviors of ellipsoids under triaxial tests using 3D discrete element method(DEM)simulation.To avoid the boundary effect,a novel stress servo-controlled periodic boundary condition is proposed to maintain the confining pressure of samples during testing.The shape features of ellipsoids are investigated,including the aspect ratio of elongated/oblate ellipsoids and the initial arrangement directions of ellipsoids.The macroscopic properties of ellipsoidal particle samples,such as the deviatoric stress,volumetric strain,internal friction angle,as well as dilatancy angles are explored.Elongated and oblate ellipsoids with varying aspect ratios are investigated for the occurrence of stick-slips.In addition,it is demonstrated that the initial arrangement direction has a significant impact on the coordination number and contact force chains.The corresponding anisotropy coefficients of the entire contact network are analyzed to probe the microscopic roots of macroscopic behavior.展开更多
基金This study has been supported by the National Natural Science Foundation of China(Grant No.41672295)Science and Technology Project of Department of Transportation of Sichuan Province(Grant No.2015B1-1)+1 种基金Sichuan Provincial Science and Technology Plan Project(Grant No.2017JY0264)Scientific and Technological Research and Development Plan of China Railway Corporation(Grant No.P2018G047).
文摘Phyllite fragments are essential for accumulating and generating talus slope at the toes of hillslopes,however,how they are linked to slope failure remains unknown.This paper reports the directional arrangement of phyllite fragments(DAPF)in phyllite talus slope at the eastern margin of the Tibetan Plateau.Field investigation,mathematical statistics and model experiments were performed in order to systematically understand the influencing factors,which include fragment shape,flat ratio,dip angle(α),and fine particle content(c).The results show that the quadrilateral fragmentgenerates a similar imbricate structure more easily than the triangular and rod fragments in the phyllite talus slope.Additionally,the flat phyllite fragments easily accumulate as imbricated structures on the phyllitetalus slope.When the dip angle(α)is in the range of 20°–30°,the minimum orientation ratio(P)is more than 50%,which means thatthe DAPF phenomenon is more obviousin the phyllite talus slope.For the fine particle content(c)at the same dip angle(α),the minimum orientation ratio(P)is 54%,and the minimum orientation ratio(P)correlates positively with the fine particle content(c).Therefore,compared with the homogeneous talusslope,the phyllite talusslopedisplays a special DAPF phenomenon.This study provides a valuable reference and presents novel knowledgefor risk assessment and engineering design against the phyllite talus slope failure mechanism.
文摘Chitin,the most abundant aminopolysaccharide in nature,is an extracellular polymer consisting of N-acetylglucosamine(GlcNAc)units1.The key reactions of chitin biosynthesis are catalysed by chitin synthase2-4,a membrane-integrated glycosyltransferase that transfers GlcNAc from UDP-GlcNAc to a growing chitin chain.However,the precise mechanism of this process has yet to be elucidated.Here we report five cryo-electron microscopy structures of a chitin synthase from the devastating soybean root rot pathogenic oomycete Phytophthora sojae(PsChs1).They represent the apo,GlcNAc-bound,nascent chitin oligomer-bound,UDP-bound(post-synthesis)and chitin synthase inhibitor nikkomycin Z-bound states of the enzyme,providing detailed views into the multiple steps of chitin biosynthesis and its competitive inhibition.The structures reveal the chitin synthesis reaction chamber that has the substrate-binding site,the catalytic centre and the entrance to the polymer-translocating channel that allows the product polymer to be discharged.This arrangement reflects consecutive key events in chitin biosynthesis from UDP-GlcNAc binding and polymer elongation to the release of the product.We identified a swinging loop within the chitin-translocating channel,which acts as a'gate lock'that prevents the substrate from leaving while directing the product polymer into the translocating channel for discharge to the extracellular side of the cell membrane.This work reveals the directional multistep mechanism of chitin biosynthesis and provides a structural basis for inhibition of chitin synthesis.
文摘Living Cephalotaxus (plum yews) occurs mainly in East Asia and North of Indo-China peninsula. The study of original taxonomic literatures found that, in early days, the plum yews had ever been described as palnts of Taxus (Taxaceae). Since after the genus name Cephalotaxus Sieb. & Zucc. was firstly cited (from inedited and unpublished Flora Japonica) by Endlicher in 1842, most taxonomist thought which is the earliest time of the genus Cephalotaxus Sieb. & Zucc. was set. However, the genus Cephalotaxus Sieb. & Zucc. was formally effective and valid published by Sieb. & Zucc. in Flora Japonica in 1870 so that there exists some confusions in chronological order. Originally as a genus, Cephalotaxus was included in family Taxaceae and Neger (1907) separated Cephalotaxus from Taxaceae and set family Cephalotaxaceae. Later, Fu (1984) divided Cephalotaxus up into two sections of Cephalotaxus Sieb. & Zucc. sect. Pectinatae L. K. Fu and Cephalotaxus Sieb. & Zucc. sect. Cephalotaxus L. K. Fu on the bases of C. oliveri Masters differ significantly from other taxa of Cephalotaxus in morphological characteristics. Although the plum yews was a little genus of conifers, up to now, about 77 taxa have still been published by taxonomist in different countries or regions. Among them, C. tardiva Sieb. ex Endl. (1847), C. umbraculifera Sieb. ex Endl. (1847), C. sumatrana Miq. (1856) and C. celebica Warb. (1900) have been combined to Taxus, and C. argotaenia (Hance) Pilger (1903) has been combined to Amentotaxus. And at the same time, those taxa existing in Cephalotaxus courently which were accepted by most taxonomist in different countries was also cited in acticle. Lastly, the paper thought presently there still exists many debates about binary classification of Cephalotaxus and the nomenclature of this genus still particularly confusing. Based on some controversial problems, we also point out some taxonomically researching directions at creating some order out of the chaos.
基金We gratefully acknowledge the financial supports provided by National Natural Science Foundation ofChina(grant No.51608112)the National Key Research and Development Program of China(grant No.2016YFC0800201)+1 种基金the Fundamental Research Funds for the Central Universities(grant No.3221002101C3)Project of Jiangsu Province Transportation Engineering Construction Bureau(grant No.CX-2019GC02).
文摘This work studies the macroscopic and microscopic behaviors of ellipsoids under triaxial tests using 3D discrete element method(DEM)simulation.To avoid the boundary effect,a novel stress servo-controlled periodic boundary condition is proposed to maintain the confining pressure of samples during testing.The shape features of ellipsoids are investigated,including the aspect ratio of elongated/oblate ellipsoids and the initial arrangement directions of ellipsoids.The macroscopic properties of ellipsoidal particle samples,such as the deviatoric stress,volumetric strain,internal friction angle,as well as dilatancy angles are explored.Elongated and oblate ellipsoids with varying aspect ratios are investigated for the occurrence of stick-slips.In addition,it is demonstrated that the initial arrangement direction has a significant impact on the coordination number and contact force chains.The corresponding anisotropy coefficients of the entire contact network are analyzed to probe the microscopic roots of macroscopic behavior.
