This article presents a study of vehicle acceleration distribution at a traffic signal stop line in an urban environment. Accurate representation of vehicle acceleration behavior provides important inputs to traffic s...This article presents a study of vehicle acceleration distribution at a traffic signal stop line in an urban environment. Accurate representation of vehicle acceleration behavior provides important inputs to traffic simulation models especially when traffic related emissions need to be estimated. A smart eye TDS （traffic data sensor） system was used to record vehicle trajectories, which were extracted to calculate vehicle acceleration profiles. This paper presents the acceleration distributions obtained from over 300 passenger-car acceleration cycles observed on site from the stop line up to a maximum speed of 40 km/h. These distributions are compared with the outputs from a traffic micro simulation tool modeling a similar stop line scenario. The comparison shows that measured accelerations present wider distribution and lower values than the micro simulation. This result highlights the importance of using acceleration distribution calibrated with real-world measured data rather than default values in order to estimate accurate emission levels.展开更多
Cell migration in anisotropic microenvironment plays an important role in the development of normal tissues and organs as well as neoplasm progression,e.g.,osteogenic differentiation of embryonic stem cells was facili...Cell migration in anisotropic microenvironment plays an important role in the development of normal tissues and organs as well as neoplasm progression,e.g.,osteogenic differentiation of embryonic stem cells was facilitated on stiffer substrates,indicating that the mechanical signals greatly affect both early and terminal differentiation of embryonic stem cells.However,the effect of anisotropy on cell migration dynamics,in particular,in terms of acceleration profiles which is important for recognizing dynamics modes of cell migration and analyzing the regulation mechanisms of microenvironment in mechanical signal transmission,has not been systematically investigated.In this work,we firstly rigorously investigate and quantify the differences between persistent random walk and anisotropic persistent random walk models based on the analysis of cell migration trajectories and velocity auto-covariance function,both qualitatively and quantitatively.Secondly,we introduce the concepts of positive and negative anisotropy based on the motility parameters to study the effect of anisotropy on acceleration profiles,especially the nonlinear decrease and non-monotonic behaviors.We particularly elaborate and discuss the mechanisms,and physical insights of non-monotonic behaviors in the case of positive anisotropy,focusing on the force exerted on migrating cells.Finally,we analyze two types of in vitro cell migration experiments and verify the universality of nonlinear decrease and the consistence of non-monotonic behaviors with numerical results.We conclude that the anisotropy of microenvironment is the cause of the non-monotonic and nonlinear dynamics,and the anisotropic persistent random walk can be as a suitable tool to analyze in vitro cell migration with different combinations of motility parameters.Our analysis provides new insights into the dynamics of cell migration in complex microenvironment,which also has implications in tissue engineering and cancer research.展开更多
Uncertain factors such as atmospheric density,aerodynamic coefficients,and aircraft mass can have a catastrophic impact on the flight safety of entry vehicles(EVs).It is crucial for EVs to quickly generate safe entry ...Uncertain factors such as atmospheric density,aerodynamic coefficients,and aircraft mass can have a catastrophic impact on the flight safety of entry vehicles(EVs).It is crucial for EVs to quickly generate safe entry trajectories that consider the impact of uncertainties to execute complex flight tasks such as online target changing.Given this challenge,a rapid generation method of safe entry trajectories is proposed,which is based on the drag-acceleration-profile method employed during space shuttle entry flights.This method can efficiently generate a safe,feasible trajectory while accounting for the influence of uncertain factors.Compared to traditional drag-acceleration-profile methods,the proposed method incorporates the influence of uncertain factors on the boundaries of the flight corridor.It establishes an uncertain flight corridor model,thereby ensuring the safety of the reference flight profile designed within this corridor under actual uncertain flight conditions.Additionally,a simplified design approach for the reference flight profile enables the rapid generation of satisfactory profiles through straightforward parameter iteration or optimization.Simulations demonstrate that this method can efficiently plan gliding flight trajectories that meet safety requirements,exhibiting potential for online trajectory generation and maneuverability assessment.展开更多
On the one hand,the separation of thousands of compounds in a complex extract is thrilling,but may be still be separated unsatisfactorily.Hence,the question arises where to stop in high-sophisticated separation scienc...On the one hand,the separation of thousands of compounds in a complex extract is thrilling,but may be still be separated unsatisfactorily.Hence,the question arises where to stop in high-sophisticated separation science?Which technical effort is economically justifiable in routine?On the other hand,the separation itself does not imply an effect-directed answer to questions such展开更多
文摘This article presents a study of vehicle acceleration distribution at a traffic signal stop line in an urban environment. Accurate representation of vehicle acceleration behavior provides important inputs to traffic simulation models especially when traffic related emissions need to be estimated. A smart eye TDS （traffic data sensor） system was used to record vehicle trajectories, which were extracted to calculate vehicle acceleration profiles. This paper presents the acceleration distributions obtained from over 300 passenger-car acceleration cycles observed on site from the stop line up to a maximum speed of 40 km/h. These distributions are compared with the outputs from a traffic micro simulation tool modeling a similar stop line scenario. The comparison shows that measured accelerations present wider distribution and lower values than the micro simulation. This result highlights the importance of using acceleration distribution calibrated with real-world measured data rather than default values in order to estimate accurate emission levels.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974066,11674043,11675134,and 11874310)the Natural Science Foundation of Chongqing,China(Grant Nos.cstc2019jcyj-msxmX0477 and cstc2018jcyjA3679)the Capital Health Development Research Project,China(Grant No.2020-2-2072).
文摘Cell migration in anisotropic microenvironment plays an important role in the development of normal tissues and organs as well as neoplasm progression,e.g.,osteogenic differentiation of embryonic stem cells was facilitated on stiffer substrates,indicating that the mechanical signals greatly affect both early and terminal differentiation of embryonic stem cells.However,the effect of anisotropy on cell migration dynamics,in particular,in terms of acceleration profiles which is important for recognizing dynamics modes of cell migration and analyzing the regulation mechanisms of microenvironment in mechanical signal transmission,has not been systematically investigated.In this work,we firstly rigorously investigate and quantify the differences between persistent random walk and anisotropic persistent random walk models based on the analysis of cell migration trajectories and velocity auto-covariance function,both qualitatively and quantitatively.Secondly,we introduce the concepts of positive and negative anisotropy based on the motility parameters to study the effect of anisotropy on acceleration profiles,especially the nonlinear decrease and non-monotonic behaviors.We particularly elaborate and discuss the mechanisms,and physical insights of non-monotonic behaviors in the case of positive anisotropy,focusing on the force exerted on migrating cells.Finally,we analyze two types of in vitro cell migration experiments and verify the universality of nonlinear decrease and the consistence of non-monotonic behaviors with numerical results.We conclude that the anisotropy of microenvironment is the cause of the non-monotonic and nonlinear dynamics,and the anisotropic persistent random walk can be as a suitable tool to analyze in vitro cell migration with different combinations of motility parameters.Our analysis provides new insights into the dynamics of cell migration in complex microenvironment,which also has implications in tissue engineering and cancer research.
基金supported by the National Nature Science Foundation of China(92271108,62173336)
文摘Uncertain factors such as atmospheric density,aerodynamic coefficients,and aircraft mass can have a catastrophic impact on the flight safety of entry vehicles(EVs).It is crucial for EVs to quickly generate safe entry trajectories that consider the impact of uncertainties to execute complex flight tasks such as online target changing.Given this challenge,a rapid generation method of safe entry trajectories is proposed,which is based on the drag-acceleration-profile method employed during space shuttle entry flights.This method can efficiently generate a safe,feasible trajectory while accounting for the influence of uncertain factors.Compared to traditional drag-acceleration-profile methods,the proposed method incorporates the influence of uncertain factors on the boundaries of the flight corridor.It establishes an uncertain flight corridor model,thereby ensuring the safety of the reference flight profile designed within this corridor under actual uncertain flight conditions.Additionally,a simplified design approach for the reference flight profile enables the rapid generation of satisfactory profiles through straightforward parameter iteration or optimization.Simulations demonstrate that this method can efficiently plan gliding flight trajectories that meet safety requirements,exhibiting potential for online trajectory generation and maneuverability assessment.
文摘On the one hand,the separation of thousands of compounds in a complex extract is thrilling,but may be still be separated unsatisfactorily.Hence,the question arises where to stop in high-sophisticated separation science?Which technical effort is economically justifiable in routine?On the other hand,the separation itself does not imply an effect-directed answer to questions such
