The transition to turbulence in flows where the laminar profile is linearly stable requires perturbations of finite amplitude. ＂Optimal＂ perturbations are distinguished as extrema of certain functionals, and differe...The transition to turbulence in flows where the laminar profile is linearly stable requires perturbations of finite amplitude. ＂Optimal＂ perturbations are distinguished as extrema of certain functionals, and different functionals give different optima. We here discuss the phase space structure of a 2D simplified model of the transition to turbulence and discuss optimal perturbations with respect to three criteria： energy of the initial condition, energy dissipation of the initial condition, and amplitude of noise in a stochastic transition. We find that the states triggering the transition are different in the three cases, but show the same scaling with Reynolds number.展开更多
Workflow management is concerned with automated support for business processes.Workflow management systems are driven by process models specifying the tasks that need to be executed,the order in which they can be exec...Workflow management is concerned with automated support for business processes.Workflow management systems are driven by process models specifying the tasks that need to be executed,the order in which they can be executed,which resources are authorised to perform which tasks,and data that is required for,and produced by,these tasks.As workflow instances may run over a sustained period of time,it is important that workflow specifications be checked before they are deployed.Workflow verification is usually concerned with control-flow dependencies only;however,transition conditions based on data may further restrict possible choices between tasks.In this paper we extend workflow nets where transitions have concrete conditions associated with them,called WTC-nets.We then demonstrate that we can determine which execution paths of a WTC-net that are possible according to the control-flow dependencies,are actually possible when considering the conditions based on data.Thus,we are able to more accurately determine at design time whether a workflow net with transition conditions is sound.展开更多
基金supported in part by the German Research Foundation within FOR 1182
文摘The transition to turbulence in flows where the laminar profile is linearly stable requires perturbations of finite amplitude. ＂Optimal＂ perturbations are distinguished as extrema of certain functionals, and different functionals give different optima. We here discuss the phase space structure of a 2D simplified model of the transition to turbulence and discuss optimal perturbations with respect to three criteria： energy of the initial condition, energy dissipation of the initial condition, and amplitude of noise in a stochastic transition. We find that the states triggering the transition are different in the three cases, but show the same scaling with Reynolds number.
基金Project supported by the National Science and Technology Major Project of China (No.2010ZX01042-002-002-01)the National Basic Research Program (973) of China (No.2009CB320700)the National Natural Science Foundation of China (Nos.61073005 and 61003099)
文摘Workflow management is concerned with automated support for business processes.Workflow management systems are driven by process models specifying the tasks that need to be executed,the order in which they can be executed,which resources are authorised to perform which tasks,and data that is required for,and produced by,these tasks.As workflow instances may run over a sustained period of time,it is important that workflow specifications be checked before they are deployed.Workflow verification is usually concerned with control-flow dependencies only;however,transition conditions based on data may further restrict possible choices between tasks.In this paper we extend workflow nets where transitions have concrete conditions associated with them,called WTC-nets.We then demonstrate that we can determine which execution paths of a WTC-net that are possible according to the control-flow dependencies,are actually possible when considering the conditions based on data.Thus,we are able to more accurately determine at design time whether a workflow net with transition conditions is sound.
