The fragile and intricate geological environment of the Qinghai-Tibet Plateau gives rise to numerous precarious rocks along the riverbanks,posing significant risks for the upcoming construction of hydropower stations....The fragile and intricate geological environment of the Qinghai-Tibet Plateau gives rise to numerous precarious rocks along the riverbanks,posing significant risks for the upcoming construction of hydropower stations.In order to identify potential rockfalls that could endanger the Zixia hydropower project,a comprehensive analysis employing various methods was conducted to investigate the kinematic characteristics and dynamic fragmentation of such precarious rocks.Initially,UAV oblique photography and field survey were used to create a digital elevation model with a resolution of 0.25 m and map the spatial distribution of precarious rocks.Subsequently,the development characteristics of joints within rock masses were analyzed through an adit investigation.Following these preliminary steps,a transportation simulation utilizing RocPro3D,considering stochastic initiation orientation,was employed to predict the trajectories of 18 precarious rocks.As a result,two hazardous rocks that pose a direct threat to the cofferdam were identified.Finally,considering the influence of internal structure planes,a discrete element method was applied for accurately simulating the kinematic characteristics and dynamic fragmentation of these hazardous rocks.The findings underscore several key observations:(1)Slopeparallel structure planes within these hazardous rocks play a pivotal role in both the progressive failure during initiation and dynamic fragmentation during transportation;(2)Hazardous rocksⅢ-1 andⅣ-1 would pose a direct threat to the cofferdam.Notably,block b4 from hazardous rockⅢ-1,could potentially impact the cofferdam with an energy of 4598.65 kJ and an impact force of 3007.5 kN;and(3)Continuous collisions encountered during transportation facilitate the disintegration of rock masses along structure planes and generate substantial high-velocity fragments.Finally,to cope with the impact risk of collapsing blocks,a reinforced retaining wall as the mitigation measure is recommended.展开更多
Rockslides are one of the most common geological hazards in mountainous areas and can pose significant threats to the safety of human lives and infrastructures. Studying the dynamic fragmentation process, and fragment...Rockslides are one of the most common geological hazards in mountainous areas and can pose significant threats to the safety of human lives and infrastructures. Studying the dynamic fragmentation process, and fragment characteristics of rock blocks during rockslides is of great significance. In this study,the influences of the slope angle on the dynamic fragmentation process, damage and energy evolution,and the fragments’ flying velocity and flying angle were systematically investigated using a coupled 3D FEM-DEM method. An improved fragment search algorithm was first proposed to more effectively extract the information of the fragments after impacting. The input parameters in the numerical modeling were carefully calibrated based on the quasi-static uniaxial compression tests and the rockimpact tests. The complex fragmentation process of rock block sliding along an inclined slope was simulated. The results indicate that the fragmentation intensity gradually increases with increasing the slope angle, and the fragmentation intensity of the front region of the rock block is always higher than that of the rear region. Additionally, the slope angle can significantly affect the damage ratio, energy dissipation, and the ratio of tensile crack to shear crack during the rockslides. The number of the fragments having higher flying velocities and larger flying angles increases with increasing the slope angle,which contributes to a larger spreading distance and a wider deposition area.展开更多
The two-body fragmentation dynamics of water isotopologues dications(H_(2)O^(2+),HOD^(2+),and D_(2)O^(2+))induced by200 eV electron impact is investigated.Two fragment ions and an emitted electron are detected in coin...The two-body fragmentation dynamics of water isotopologues dications(H_(2)O^(2+),HOD^(2+),and D_(2)O^(2+))induced by200 eV electron impact is investigated.Two fragment ions and an emitted electron are detected in coincidence,and their momentum vectors are determined by employing a reaction microscope.The complete kinematical information of four two-body fragmentation channels of H^(+)+OH+,H^(+)+OD^(+),D^(+)+OH^(+),and D^(+)+OD+is obtained.By analyzing the projectile energy-loss spectrum,the initial electronic state of the two-body dissociation channel is determined.Upon examining the kinetic energy release(KER)distributions of the four fragmentation channels,a clear difference is found between the two-body fragmentation channel H^(+)+OD+and the other three channels.The isotopic effect in the two-body fragmentation is demonstrated by the analysis of the relative yields of the two-body fragmentation channels originating from different isotopologues,which shows preferential cleavage of the O-H bond over the O-D bond.These results provide deeper insight into the microscopic dynamic mechanisms in water radiolysis.展开更多
Background： Sperm DNA fragmentation（sDF） has been proved to be an important parameter in order to predict in vitro the potential fertility of a semen sample. Colloid centrifugation could be a suitable technique to ...Background： Sperm DNA fragmentation（sDF） has been proved to be an important parameter in order to predict in vitro the potential fertility of a semen sample. Colloid centrifugation could be a suitable technique to select those donkey sperm more resistant to DNA fragmentation after thawing. Previous studies have shown that to elucidate the latent damage of the DNA molecule, sDF should be assessed dynamically, where the rate of fragmentation between treatments indicates how resistant the DNA is to iatrogenic damage. The rate of fragmentation is calculated using the slope of a linear regression equation. However, it has not been studied if s DF dynamics fit this model. The objectives of this study were to evaluate the effect of different after-thawing centrifugation protocols on sperm DNA fragmentation and elucidate the most accurate mathematical model（linear regression, exponential or polynomial） for DNA fragmentation over time in frozen-thawed donkey semen.Results： After submitting post-thaw semen samples to no centrifugation（UDC）, sperm washing（SW） or single layer centrifugation（SLC） protocols, sD F values after 6 h of incubation were significantly lower in SLC samples than in SW or UDC.Coefficient of determination（R-2） values were significantly higher for a second order polynomial model than for linear or exponential. The highest values for acceleration of fragmentation（aSDF） were obtained for SW, fol owed by SLC and UDC.Conclusion： SLC after thawing seems to preserve longer DNA longevity in comparison to UDC and SW. Moreover,the fine-tuning of models has shown that sDF dynamics in frozen-thawed donkey semen fit a second order polynomial model, which implies that fragmentation rate is not constant and fragmentation acceleration must be taken into account to elucidate hidden damage in the DNA molecule.展开更多
In this study, historical landscape dynamics were investigated to（i） map the land use/cover types for the years 1972, 1987, 2000 and 2014;（ii） determine the types and processes of landscape dynamics; and（iii） as...In this study, historical landscape dynamics were investigated to（i） map the land use/cover types for the years 1972, 1987, 2000 and 2014;（ii） determine the types and processes of landscape dynamics; and（iii） assess the landscape fragmentation and habitat loss over time. Supervised classification of multi-temporal Landsat images was used through a pixel-based approach. Post–classification methods included systematic and random change detection, trajectories analysis and landscape fragmentation assessment. The overall accuracies（and Kappa statistics） were of 68.86%（0.63）, 91.32%（0.79）, 90.66%（0.88） and 91.88%（0.89） for 1972, 1987, 2000 and 2014, respectively. The spatio-temporal analyses indicated that forests, woodlands and savannahs dominated the landscapes during the four dates, though constant areal decreases were observed. The most important dynamic process was the decline of woodlands with an average annual net loss rate of –2%. Meanwhile, the most important land transformation occurred during the transition 2000–2014, due to anthropogenic pressures. Though the most important loss of vegetation greenness occurred in the unprotected areas, the overall analyses of change indicated a declining trend of land cover quality and an increasing landscape fragmentation. Sustainable conservation strategies should be promoted while focusing restoration attention on degraded lands and fragmented ecosystems in order to support rural livelihood and biodiversity conservation.展开更多
基金gratefully acknowledge support from the National Key Research and Development Program of China(Grant No.2022YFC3005704)the National Natural Science Foundation of China(Grant No.42277143)the Sichuan Province natural Science Foundation project(Grant No.2024NSFSC0100).
文摘The fragile and intricate geological environment of the Qinghai-Tibet Plateau gives rise to numerous precarious rocks along the riverbanks,posing significant risks for the upcoming construction of hydropower stations.In order to identify potential rockfalls that could endanger the Zixia hydropower project,a comprehensive analysis employing various methods was conducted to investigate the kinematic characteristics and dynamic fragmentation of such precarious rocks.Initially,UAV oblique photography and field survey were used to create a digital elevation model with a resolution of 0.25 m and map the spatial distribution of precarious rocks.Subsequently,the development characteristics of joints within rock masses were analyzed through an adit investigation.Following these preliminary steps,a transportation simulation utilizing RocPro3D,considering stochastic initiation orientation,was employed to predict the trajectories of 18 precarious rocks.As a result,two hazardous rocks that pose a direct threat to the cofferdam were identified.Finally,considering the influence of internal structure planes,a discrete element method was applied for accurately simulating the kinematic characteristics and dynamic fragmentation of these hazardous rocks.The findings underscore several key observations:(1)Slopeparallel structure planes within these hazardous rocks play a pivotal role in both the progressive failure during initiation and dynamic fragmentation during transportation;(2)Hazardous rocksⅢ-1 andⅣ-1 would pose a direct threat to the cofferdam.Notably,block b4 from hazardous rockⅢ-1,could potentially impact the cofferdam with an energy of 4598.65 kJ and an impact force of 3007.5 kN;and(3)Continuous collisions encountered during transportation facilitate the disintegration of rock masses along structure planes and generate substantial high-velocity fragments.Finally,to cope with the impact risk of collapsing blocks,a reinforced retaining wall as the mitigation measure is recommended.
基金supported by the National Natural Science Foundation of China (Grant Nos.52004182, 51908431)。
文摘Rockslides are one of the most common geological hazards in mountainous areas and can pose significant threats to the safety of human lives and infrastructures. Studying the dynamic fragmentation process, and fragment characteristics of rock blocks during rockslides is of great significance. In this study,the influences of the slope angle on the dynamic fragmentation process, damage and energy evolution,and the fragments’ flying velocity and flying angle were systematically investigated using a coupled 3D FEM-DEM method. An improved fragment search algorithm was first proposed to more effectively extract the information of the fragments after impacting. The input parameters in the numerical modeling were carefully calibrated based on the quasi-static uniaxial compression tests and the rockimpact tests. The complex fragmentation process of rock block sliding along an inclined slope was simulated. The results indicate that the fragmentation intensity gradually increases with increasing the slope angle, and the fragmentation intensity of the front region of the rock block is always higher than that of the rear region. Additionally, the slope angle can significantly affect the damage ratio, energy dissipation, and the ratio of tensile crack to shear crack during the rockslides. The number of the fragments having higher flying velocities and larger flying angles increases with increasing the slope angle,which contributes to a larger spreading distance and a wider deposition area.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12325406,92261201,12404305,11974272)the Shannxi Province Natural Science Fundamental Research Project(Grant Nos.2023JC-XJ-03 and 23JSQ013)the Fundamental Research Funds for the Central Universities(Grant No.xzy022024040)。
文摘The two-body fragmentation dynamics of water isotopologues dications(H_(2)O^(2+),HOD^(2+),and D_(2)O^(2+))induced by200 eV electron impact is investigated.Two fragment ions and an emitted electron are detected in coincidence,and their momentum vectors are determined by employing a reaction microscope.The complete kinematical information of four two-body fragmentation channels of H^(+)+OH+,H^(+)+OD^(+),D^(+)+OH^(+),and D^(+)+OD+is obtained.By analyzing the projectile energy-loss spectrum,the initial electronic state of the two-body dissociation channel is determined.Upon examining the kinetic energy release(KER)distributions of the four fragmentation channels,a clear difference is found between the two-body fragmentation channel H^(+)+OD+and the other three channels.The isotopic effect in the two-body fragmentation is demonstrated by the analysis of the relative yields of the two-body fragmentation channels originating from different isotopologues,which shows preferential cleavage of the O-H bond over the O-D bond.These results provide deeper insight into the microscopic dynamic mechanisms in water radiolysis.
基金partially supported by grants RZ2009-00006-00-00(Instituto Nacional de Investigacion y Tecnología Agraria y Alimentaria,Ministerio de Ciencia e Innovación,Spain)AGL-2013-42726-R(Secretaria de Estado de Investigacion,Desarrollo e Innovacion,Ministerio de Economia y Competitividad,Spain)+1 种基金supported by a Ph.D.fellowship from the ceiA3(Andalucia,Spain)with funding provided by Banco Santander through its Global Division,Santander Universidadesfunded by the Swedish Foundation for Equine Research,Stockholm,Sweden(H14-47-008)
文摘Background： Sperm DNA fragmentation（sDF） has been proved to be an important parameter in order to predict in vitro the potential fertility of a semen sample. Colloid centrifugation could be a suitable technique to select those donkey sperm more resistant to DNA fragmentation after thawing. Previous studies have shown that to elucidate the latent damage of the DNA molecule, sDF should be assessed dynamically, where the rate of fragmentation between treatments indicates how resistant the DNA is to iatrogenic damage. The rate of fragmentation is calculated using the slope of a linear regression equation. However, it has not been studied if s DF dynamics fit this model. The objectives of this study were to evaluate the effect of different after-thawing centrifugation protocols on sperm DNA fragmentation and elucidate the most accurate mathematical model（linear regression, exponential or polynomial） for DNA fragmentation over time in frozen-thawed donkey semen.Results： After submitting post-thaw semen samples to no centrifugation（UDC）, sperm washing（SW） or single layer centrifugation（SLC） protocols, sD F values after 6 h of incubation were significantly lower in SLC samples than in SW or UDC.Coefficient of determination（R-2） values were significantly higher for a second order polynomial model than for linear or exponential. The highest values for acceleration of fragmentation（aSDF） were obtained for SW, fol owed by SLC and UDC.Conclusion： SLC after thawing seems to preserve longer DNA longevity in comparison to UDC and SW. Moreover,the fine-tuning of models has shown that sDF dynamics in frozen-thawed donkey semen fit a second order polynomial model, which implies that fragmentation rate is not constant and fragmentation acceleration must be taken into account to elucidate hidden damage in the DNA molecule.
基金funded by the German Federal Ministry for Education and Research (BMBF)hosted by the Kwame Nkrumah University of Science and Technology of Kumasi,Ghana+1 种基金the Laboratory of Botany and Plant Ecology (University of Lome, Togo) for fieldwork supportthe contribution of CGIAR-DS through the funding to Quang Bao Le
文摘In this study, historical landscape dynamics were investigated to（i） map the land use/cover types for the years 1972, 1987, 2000 and 2014;（ii） determine the types and processes of landscape dynamics; and（iii） assess the landscape fragmentation and habitat loss over time. Supervised classification of multi-temporal Landsat images was used through a pixel-based approach. Post–classification methods included systematic and random change detection, trajectories analysis and landscape fragmentation assessment. The overall accuracies（and Kappa statistics） were of 68.86%（0.63）, 91.32%（0.79）, 90.66%（0.88） and 91.88%（0.89） for 1972, 1987, 2000 and 2014, respectively. The spatio-temporal analyses indicated that forests, woodlands and savannahs dominated the landscapes during the four dates, though constant areal decreases were observed. The most important dynamic process was the decline of woodlands with an average annual net loss rate of –2%. Meanwhile, the most important land transformation occurred during the transition 2000–2014, due to anthropogenic pressures. Though the most important loss of vegetation greenness occurred in the unprotected areas, the overall analyses of change indicated a declining trend of land cover quality and an increasing landscape fragmentation. Sustainable conservation strategies should be promoted while focusing restoration attention on degraded lands and fragmented ecosystems in order to support rural livelihood and biodiversity conservation.
