Dynamic crossover in [VIO^(2+)][Tf_(2)N-]_(2) ionic liquid

Ionic liquids usually behave as fragile liquids,and the temperature dependence of their dynamic properties obeys supper-Arrhenius law.In this work,a dynamic crossover is observed in([VIO^(2+)][Tf_(2)N-]_(2)) ionic liquid at the temperature of 240-800 K.The diffusion coefficient does not obey a single Arrhenius law or a Vogel-Fulcher-Tammann(VFT) relation,but can be well fitted by three Arrhenius laws or a combination of a VFT relation and an Arrhenius law.The origin of the dynamic crossover is analyzed from correlation,structure,and thermodynamics.Ion gets a stronger backward correlation at a lower temperature,as shown by the fractal dimension of the random walk.The temperature dependence function of fractal dimension,heterogeneity order parameter,and thermodynamic data can be separated into three regions similar to that observed in the diffusion coefficient.The two crossover temperatures observed in the three types of data are almost the same as that in diffusion coefficient fitted by three Arrhenius laws.The results indicate that the dynamic crossover of[VIO2+][Tf2 N-]2 is attributed to the heterogeneous structure when it undergoes cooling.

Task scheduling for transport and pick robots in logistics:a comparative study on constructive heuristics

We study the Transport and Pick Robots Task Scheduling(TPS)problem,in which two teams of specialized robots,transport robots and pick robots,collaborate to execute multi-station order fulfillment tasks in logistic environments.The objective is to plan a collective time-extended task schedule with the minimization of makespan.However,for this recently formulated problem,it is still unclear how to obtain satisfying results efficiently.In this research,we design several constructive heuristics to solve this problem based on the introduced sequence models.Theoretically,we give time complexity analysis or feasibility guarantees of these heuristics;empirically,we evaluate the makespan performance criteria and computation time on designed dataset.Computational results demonstrate that coupled append heuristic works better for the most cases within reasonable computation time.Coupled heuristics work better than decoupled heuristics prominently on instances with relative few pick robot numbers and large work zones.The law of diminishing marginal utility is also observed concerning the overall system performance and different transport-pick robot numbers.