This paper deals with the mechanics problem of dynamic walking of anthropomorphic biped robots. Through analysing the mechanics system of this kind of robots in detail, the motion constraint equations are established,...This paper deals with the mechanics problem of dynamic walking of anthropomorphic biped robots. Through analysing the mechanics system of this kind of robots in detail, the motion constraint equations are established, three mechanics laws describing the r展开更多
A new mechanics model, which reveals additional longitudinal force transmission between the continuously welded rails and the bridges, is established on the fact that the influence of the mutual relative displacement ...A new mechanics model, which reveals additional longitudinal force transmission between the continuously welded rails and the bridges, is established on the fact that the influence of the mutual relative displacement (among) the rail, the sleeper and the beam is taken into account. An example is presented and numerical results are compared. The results show that the additional longitudinal forces calculated with the new model are less than those of the previous, especially in the case of the flexible pier bridges. The new model is also suitable for the analysis of the additional longitudinal force transmission between rails and bridges of ballastless track with small resistance fasteners without taking the sleeper displacement into account, and compared with the ballast bridges, the ballastless bridges have a much stronger additional longitudinal force transmission between the continuously welded rails and the bridges.展开更多
The present study deals with the experimental,finite element(FE)and analytical assessment of low ballistic impact response of proposed flexible‘green’composite make use of naturally available jute and rubber as the ...The present study deals with the experimental,finite element(FE)and analytical assessment of low ballistic impact response of proposed flexible‘green’composite make use of naturally available jute and rubber as the constituents of the composite with stacking sequences namely jute/rubber/jute(JRJ),jute/rubber/rubber/jute(JRRJ)and jute/rubber/jute/rubber/jute(JRJRJ).Ballistic impact tests were carried out by firing a conical projectile using a gas gun apparatus at lower range of ballistic impact regime.The ballistic impact response of the proposed flexible composites are assesses based on energy absorption and damage mechanism.Results revealed that inclusion of natural rubber aids in better energy absorption and mitigating the failure of the proposed composite.Among the three different stacking sequences of flexible composites considered,JRJRJ provides better ballistic performance compared to its counterparts.The damage study reveals that the main mechanism of failure involved in flexible composites is matrix tearing as opposed to matrix cracking in stiff composites indicating that the proposed flexible composites are free from catastrophic failure.Results obtained from experimental,FE and analytical approach pertaining to energy absorption and damage mechanism agree well with each other.The proposed flexible composites due to their exhibited energy absorption capabilities and damage mechanism are best suited as claddings for structural application subjected to impact with an aim of protecting the main structural component from being failed catastrophically.展开更多
The mesoscopic failure mechanism and the macro-mechanical characteristics of soil-rock mixture(S-RM) under external load are largely controlled by S-RM's meso-structural features. The objective of this work is to ...The mesoscopic failure mechanism and the macro-mechanical characteristics of soil-rock mixture(S-RM) under external load are largely controlled by S-RM's meso-structural features. The objective of this work is to improve the three-dimensional technology for the generation of the random meso-structural models of S-RM, for randomly generating irregular rock blocks in S-RM with different shapes, sizes, and distributions according to the characteristics of the rock blocks' size distribution. Based on the new improved technology, a software system named as R-SRM3 D for generation and visualization of S-RM is developed. Using R-SRM3 D, a three-dimensional meso-structural model of S-RM is generated and used to study the meso-mechanical behavior through a series of true-triaxial numerical tests. From the numerical tests, the following conclusions are obtained. The meso-stress field of S-RM is influenced by the distribution of the internal rock blocks, and the macro-mechanical characteristics of S-RM are anisotropic in 3D; the intermediate principal stress and the soil-rock interface properties have significant influence on the macro strength of S-RM.展开更多
A study was conducted to analyze the deformation mechanism of strongly weathered quartz schist in the Daliangshan Tunnel,located in the western Transverse Mountain area.A large deformation problem was experienced duri...A study was conducted to analyze the deformation mechanism of strongly weathered quartz schist in the Daliangshan Tunnel,located in the western Transverse Mountain area.A large deformation problem was experienced during the tunnel construction.To mitigate this problem,a support system was designed incorporating negative Poisson ratio(NPR)anchor cables with negative Poisson ratio effect.Physical model experiments,field experiments,and numerical simulation experiments were conducted to investigate the compensation mechanical behavior of NPR anchor cables.The large deformations of soft rocks in the Daliangshan Tunnel are caused by a high ground stress,a high degree of joint fracture development,and a high degree of surrounding rock fragmentation.A compensation mechanics support system combining long and short NPR anchor cables was suggested to provide sufficient counter-support force(approximately 350 kN)for the surrounding rock inside the tunnel.Comparing the NPR anchor cable support system with the original support system used in the Daliangshan tunnel showed that an NPR anchor cable support system,combining cables of 6.3 m and 10.3 m in length,effectively prevented convergence of surrounding rock deformation,and the integrated settlement convergence value remained below 300 mm.This study provides an effective scientific basis for resolving large deformation problems in deeply buried soft rocks in western transverse mountain areas.展开更多
Soil-rock mixture(S-RM)is a widely distributed geotechnical medium composed of "soil" and "rock block" different both in size and strength. Internal rock blocks form special and variable meso-struc...Soil-rock mixture(S-RM)is a widely distributed geotechnical medium composed of "soil" and "rock block" different both in size and strength. Internal rock blocks form special and variable meso-structural characteristics of S-RM. The objective of this work was to study the control mechanism of meso-structural characteristics on mechanical properties of S-RM. For S-RM containing randomly generated polygonal rock blocks, a series of biaxial tests based on DEM were conducted. On the basis of research on the effects of rock blocks' breakability and sample lateral boundary type(rigid, flexible) on macroscopic mechanical behavior of S-RM, an expanded Mohr-Coulomb criterion in power function form was proposed to represent the strength envelop. At the mesoscopic level, the variations of meso-structure such as rotation of rock block, and the formation mechanism and evolution process of the shear band during tests were investigated. The results show that for S-RM with a high content of rock block, translation, rotating and breakage of rock blocks have crucial effects on mechanical behavior of S-RM. The formation and location of the shear band inside S-RM sample are also controlled by breakability and arrangement of rock blocks.展开更多
Cancer stem cells(CSCs)are the driving force for sustainable tumor growth and metastasis and responsible for drug resistance and cancer relapse.Nanoparticle-based drug delivery has been demonstrated to be effective in...Cancer stem cells(CSCs)are the driving force for sustainable tumor growth and metastasis and responsible for drug resistance and cancer relapse.Nanoparticle-based drug delivery has been demonstrated to be effective in combating tumor growth.However,it has been challenging to selectively eliminate CSCs due to the lack of a general signature for a spectrum of cancers.It is known that CSCs from various types of cancer show lower stiffness compared to non-CSCs.It remains unclear whether low stiffness in CSCs influences cellular uptake in nanoparticle-based drug delivery and thus the chemotherapy efficacy.Graphene quantum dot(GQD)is emerging as a promising carrier material in delivering anti-cancer drugs.We found that breast CSCs were softer than conventional cancer cells,which were further softer compared to healthy breast tissue cells.Importantly,soft CSCs uptook more GQD than conventional cancer cells,while stiff breast cancer cells with relatively low stiffness uptook more GQD than healthy breast cells.Softening cells by pharmacologically inhibiting actomyosin activity using either siRNA or actomyosin inhibitors significantly enhanced the cellular uptake of GQD in breast cancer cells but not CSCs,while stiffening cells by activating actomyosin using CA-MLCK/ROCK or actomyosin activators considerably suppressed the nanoparticle uptake in both cancer cells and CSCs.GQD could specifically target CSC because of low cell stiffness of CSC in breast cancer cell line MCF-7 and MDA-MB-231.Further regulating cell stiffness reflected that decreasing breast cancer cell stiffness by inhibiting actomyosin activity using blebbistatin could promote GQD uptake.Vice versa,stiffening cancer cell by activating actomyosin decreased GQD uptake.The attachment of anti-cancer drug doxorubicin did not alter the trend of GQD uptake in neither soften nor stiffen cancer cells.Actomyosin activity regulates cellular uptake ofGQD might through clathrin and caveolin-mediated endocytosis.Cancer cells are softer than normal cells from the same organ,CSC are softer than non-CSC.Thus we further confirmed that the GQD uptake of normal breast cell line MCF-10 is less than breast cancer cell line MCF-7 and MDA-MB-231.Suggesting the clinical significance that using GQD as drug carrier targeting softer cells could reduce side effects to normal tissue cells.Since CSC are softer than non-CSC,GQD could decreased the percentage of CSC in whole cancer cell population by targeting softer cells.These results suggesting that it would be possible to target cancer cells and CSC by targeting from a perspective of cell mechanical difference.High uptake of nanoparticles in soft cancer cells could not be explained by their differential membrane potentials.Mechanistically,low cell mechanics or inhibiting actomyosin activity activated both clathrin and caveolin-mediated endocytosis signaling pathways,while high cell mechanics or activating actomyosin suppressed these signalings.Pharmacologically inhibiting clathrin or caveolin-mediated endocytosis signaling significantly decreased GQD uptake in CSCs and in conventional breast cancer cells when actomyosin was suppressed.Further,GQD conjugated with doxorubicin could be specifically delivered into CSCs with low stiffness and eliminated more CSCs in the presence of both CSCs and non-CSCs.Taken together,these data reveal the regulatory role of cell mechanics in cellular uptake of nanoparticles and demonstrate that GQD can be utilized to specifically eliminate CSCs,which have important implications in nanoparticle-based drug delivery for cancer therapy.展开更多
Land subsidence hazard,which is caused by drawing groundwater,has been a problem of the world.In order to control the development of land subsidence,exploited horizon of groundwater was adjusted from the shallow layer...Land subsidence hazard,which is caused by drawing groundwater,has been a problem of the world.In order to control the development of land subsidence,exploited horizon of groundwater was adjusted from the shallow layer to the deep layer in the past years.But the deformation mechanics study of the aquitard in different depth is not enough.There were essential distinctions between the shallow aquitard and the deep aquitard in engineering geology properties.The paper used the different depth aquitard of Tianjin city as an example to study the展开更多
Recently, this study group established “the map of MOHO\|surface bathymetric line in Chinese and Near Region" on the basis of latest survey and study of the crustal depth, the preliminary result shows that the r...Recently, this study group established “the map of MOHO\|surface bathymetric line in Chinese and Near Region" on the basis of latest survey and study of the crustal depth, the preliminary result shows that the regular meridional and latitudinal upwarping and downwarping structural pattern of MOHO\|surface bathymetric line among Eurasian plate and Pacific plate and the Indian plate alternately appears, and which is accreted and coupled with basin ridge structure that exist shallow crustal base, continental crust and oceanic crust and others regular upwarping and downwarping net structure system that possessing different block characters and different scales exist together. Among different structure systems, it occurs that ramp downwarping impetus transform structure belts whose trends is characteristic. Nowadays upwarping and downwarping net structure system is basically modeled in Himalayan orogeny period. It is showed that the Earth revolution way has been changed in this period, which leaded to a new Earth dynamics cycle.The pattern of upwarping and downwarping structure among different structure systems or different structure blocks , and the characters of different trends and different scale transform structure belts, reflects the structure movement way and their conversion law, and reveals the Earth centralized dynamics mechanics that is produced by the revolutionary effect under the environments of aster system. This can be clearly reflected by the change of impetus way between Qinghai—Tibet highland structure system and near structure system.展开更多
文摘This paper deals with the mechanics problem of dynamic walking of anthropomorphic biped robots. Through analysing the mechanics system of this kind of robots in detail, the motion constraint equations are established, three mechanics laws describing the r
文摘A new mechanics model, which reveals additional longitudinal force transmission between the continuously welded rails and the bridges, is established on the fact that the influence of the mutual relative displacement (among) the rail, the sleeper and the beam is taken into account. An example is presented and numerical results are compared. The results show that the additional longitudinal forces calculated with the new model are less than those of the previous, especially in the case of the flexible pier bridges. The new model is also suitable for the analysis of the additional longitudinal force transmission between rails and bridges of ballastless track with small resistance fasteners without taking the sleeper displacement into account, and compared with the ballast bridges, the ballastless bridges have a much stronger additional longitudinal force transmission between the continuously welded rails and the bridges.
文摘The present study deals with the experimental,finite element(FE)and analytical assessment of low ballistic impact response of proposed flexible‘green’composite make use of naturally available jute and rubber as the constituents of the composite with stacking sequences namely jute/rubber/jute(JRJ),jute/rubber/rubber/jute(JRRJ)and jute/rubber/jute/rubber/jute(JRJRJ).Ballistic impact tests were carried out by firing a conical projectile using a gas gun apparatus at lower range of ballistic impact regime.The ballistic impact response of the proposed flexible composites are assesses based on energy absorption and damage mechanism.Results revealed that inclusion of natural rubber aids in better energy absorption and mitigating the failure of the proposed composite.Among the three different stacking sequences of flexible composites considered,JRJRJ provides better ballistic performance compared to its counterparts.The damage study reveals that the main mechanism of failure involved in flexible composites is matrix tearing as opposed to matrix cracking in stiff composites indicating that the proposed flexible composites are free from catastrophic failure.Results obtained from experimental,FE and analytical approach pertaining to energy absorption and damage mechanism agree well with each other.The proposed flexible composites due to their exhibited energy absorption capabilities and damage mechanism are best suited as claddings for structural application subjected to impact with an aim of protecting the main structural component from being failed catastrophically.
基金Project(51109117)supported by the National Natural Science Foundation of ChinaProject(20111081125)supported by the Independent Research Plan of Tsinghua University,ChinaProject(2013-KY-4)supported by the State Key Laboratory of Hydroscience and Engineering Project,China
文摘The mesoscopic failure mechanism and the macro-mechanical characteristics of soil-rock mixture(S-RM) under external load are largely controlled by S-RM's meso-structural features. The objective of this work is to improve the three-dimensional technology for the generation of the random meso-structural models of S-RM, for randomly generating irregular rock blocks in S-RM with different shapes, sizes, and distributions according to the characteristics of the rock blocks' size distribution. Based on the new improved technology, a software system named as R-SRM3 D for generation and visualization of S-RM is developed. Using R-SRM3 D, a three-dimensional meso-structural model of S-RM is generated and used to study the meso-mechanical behavior through a series of true-triaxial numerical tests. From the numerical tests, the following conclusions are obtained. The meso-stress field of S-RM is influenced by the distribution of the internal rock blocks, and the macro-mechanical characteristics of S-RM are anisotropic in 3D; the intermediate principal stress and the soil-rock interface properties have significant influence on the macro strength of S-RM.
基金Project(41941018)supported by the National Natural Science Foundation of China for the Special Project FundingProject(22-JKCF-08)supported by the Study on in-situ Stress Database and 3D in-situ Stress Inversion Technology of Highway Tunnel in Shanxi Province,China+1 种基金Project(2022-JKKJ-6)supported by the Study on Disaster Mechanism and NPR Anchor Cable Prevention and Control of Coal Mining Caving Subsidence in Operating Tunnel in Mountainous Area,ChinaProject(BBJ2024032)supported by the Fundamental Research Funds for the Central Universities(PhD Top Innovative Talents Fund of CUMTB),China。
文摘A study was conducted to analyze the deformation mechanism of strongly weathered quartz schist in the Daliangshan Tunnel,located in the western Transverse Mountain area.A large deformation problem was experienced during the tunnel construction.To mitigate this problem,a support system was designed incorporating negative Poisson ratio(NPR)anchor cables with negative Poisson ratio effect.Physical model experiments,field experiments,and numerical simulation experiments were conducted to investigate the compensation mechanical behavior of NPR anchor cables.The large deformations of soft rocks in the Daliangshan Tunnel are caused by a high ground stress,a high degree of joint fracture development,and a high degree of surrounding rock fragmentation.A compensation mechanics support system combining long and short NPR anchor cables was suggested to provide sufficient counter-support force(approximately 350 kN)for the surrounding rock inside the tunnel.Comparing the NPR anchor cable support system with the original support system used in the Daliangshan tunnel showed that an NPR anchor cable support system,combining cables of 6.3 m and 10.3 m in length,effectively prevented convergence of surrounding rock deformation,and the integrated settlement convergence value remained below 300 mm.This study provides an effective scientific basis for resolving large deformation problems in deeply buried soft rocks in western transverse mountain areas.
基金Projects(51323014,51479095)supported by the National Natural Science Foundation of ChinaProject(20111081125)supported by Independent Research Plan of Tsinghua University,ChinaProject(2013-KY-4)supported by the State Key Laboratory of Hydroscience and Engineering Project,China
文摘Soil-rock mixture(S-RM)is a widely distributed geotechnical medium composed of "soil" and "rock block" different both in size and strength. Internal rock blocks form special and variable meso-structural characteristics of S-RM. The objective of this work was to study the control mechanism of meso-structural characteristics on mechanical properties of S-RM. For S-RM containing randomly generated polygonal rock blocks, a series of biaxial tests based on DEM were conducted. On the basis of research on the effects of rock blocks' breakability and sample lateral boundary type(rigid, flexible) on macroscopic mechanical behavior of S-RM, an expanded Mohr-Coulomb criterion in power function form was proposed to represent the strength envelop. At the mesoscopic level, the variations of meso-structure such as rotation of rock block, and the formation mechanism and evolution process of the shear band during tests were investigated. The results show that for S-RM with a high content of rock block, translation, rotating and breakage of rock blocks have crucial effects on mechanical behavior of S-RM. The formation and location of the shear band inside S-RM sample are also controlled by breakability and arrangement of rock blocks.
文摘Cancer stem cells(CSCs)are the driving force for sustainable tumor growth and metastasis and responsible for drug resistance and cancer relapse.Nanoparticle-based drug delivery has been demonstrated to be effective in combating tumor growth.However,it has been challenging to selectively eliminate CSCs due to the lack of a general signature for a spectrum of cancers.It is known that CSCs from various types of cancer show lower stiffness compared to non-CSCs.It remains unclear whether low stiffness in CSCs influences cellular uptake in nanoparticle-based drug delivery and thus the chemotherapy efficacy.Graphene quantum dot(GQD)is emerging as a promising carrier material in delivering anti-cancer drugs.We found that breast CSCs were softer than conventional cancer cells,which were further softer compared to healthy breast tissue cells.Importantly,soft CSCs uptook more GQD than conventional cancer cells,while stiff breast cancer cells with relatively low stiffness uptook more GQD than healthy breast cells.Softening cells by pharmacologically inhibiting actomyosin activity using either siRNA or actomyosin inhibitors significantly enhanced the cellular uptake of GQD in breast cancer cells but not CSCs,while stiffening cells by activating actomyosin using CA-MLCK/ROCK or actomyosin activators considerably suppressed the nanoparticle uptake in both cancer cells and CSCs.GQD could specifically target CSC because of low cell stiffness of CSC in breast cancer cell line MCF-7 and MDA-MB-231.Further regulating cell stiffness reflected that decreasing breast cancer cell stiffness by inhibiting actomyosin activity using blebbistatin could promote GQD uptake.Vice versa,stiffening cancer cell by activating actomyosin decreased GQD uptake.The attachment of anti-cancer drug doxorubicin did not alter the trend of GQD uptake in neither soften nor stiffen cancer cells.Actomyosin activity regulates cellular uptake ofGQD might through clathrin and caveolin-mediated endocytosis.Cancer cells are softer than normal cells from the same organ,CSC are softer than non-CSC.Thus we further confirmed that the GQD uptake of normal breast cell line MCF-10 is less than breast cancer cell line MCF-7 and MDA-MB-231.Suggesting the clinical significance that using GQD as drug carrier targeting softer cells could reduce side effects to normal tissue cells.Since CSC are softer than non-CSC,GQD could decreased the percentage of CSC in whole cancer cell population by targeting softer cells.These results suggesting that it would be possible to target cancer cells and CSC by targeting from a perspective of cell mechanical difference.High uptake of nanoparticles in soft cancer cells could not be explained by their differential membrane potentials.Mechanistically,low cell mechanics or inhibiting actomyosin activity activated both clathrin and caveolin-mediated endocytosis signaling pathways,while high cell mechanics or activating actomyosin suppressed these signalings.Pharmacologically inhibiting clathrin or caveolin-mediated endocytosis signaling significantly decreased GQD uptake in CSCs and in conventional breast cancer cells when actomyosin was suppressed.Further,GQD conjugated with doxorubicin could be specifically delivered into CSCs with low stiffness and eliminated more CSCs in the presence of both CSCs and non-CSCs.Taken together,these data reveal the regulatory role of cell mechanics in cellular uptake of nanoparticles and demonstrate that GQD can be utilized to specifically eliminate CSCs,which have important implications in nanoparticle-based drug delivery for cancer therapy.
文摘Land subsidence hazard,which is caused by drawing groundwater,has been a problem of the world.In order to control the development of land subsidence,exploited horizon of groundwater was adjusted from the shallow layer to the deep layer in the past years.But the deformation mechanics study of the aquitard in different depth is not enough.There were essential distinctions between the shallow aquitard and the deep aquitard in engineering geology properties.The paper used the different depth aquitard of Tianjin city as an example to study the
文摘Recently, this study group established “the map of MOHO\|surface bathymetric line in Chinese and Near Region" on the basis of latest survey and study of the crustal depth, the preliminary result shows that the regular meridional and latitudinal upwarping and downwarping structural pattern of MOHO\|surface bathymetric line among Eurasian plate and Pacific plate and the Indian plate alternately appears, and which is accreted and coupled with basin ridge structure that exist shallow crustal base, continental crust and oceanic crust and others regular upwarping and downwarping net structure system that possessing different block characters and different scales exist together. Among different structure systems, it occurs that ramp downwarping impetus transform structure belts whose trends is characteristic. Nowadays upwarping and downwarping net structure system is basically modeled in Himalayan orogeny period. It is showed that the Earth revolution way has been changed in this period, which leaded to a new Earth dynamics cycle.The pattern of upwarping and downwarping structure among different structure systems or different structure blocks , and the characters of different trends and different scale transform structure belts, reflects the structure movement way and their conversion law, and reveals the Earth centralized dynamics mechanics that is produced by the revolutionary effect under the environments of aster system. This can be clearly reflected by the change of impetus way between Qinghai—Tibet highland structure system and near structure system.
