Effect of freeze-dryer design on heat transfer variability investigated using a 3D mathematical model

International audienceIn the freeze-drying process, vials located at the border of the shelf usually present higher heat flow rates which in turn result in higher product temperatures than central vials. This phenomenon, named edge vial effect, can result in product quality variability within the same batch of vials and between batches at different scales. Our objective was to investigate the effect of various freeze-dryer design features on the heat transfer variability. A 3D mathematical model previously developed in COMSOL Multiphysics and experimentally validated was used to simulate heat transfer of a set of vials located at the edge and in the centre of the shelf. The design features considered were the loading configurations of the vials, the thermal characteristics of the rail, the walls and the shelves and some relevant dimensions of the drying chamber geometry. The presence of the rail in the loading configuration and the value of the shelf emissivity strongly impacted on the heat flow rates received by the vials. Conversely, the heat transfer was not significantly influenced by modifications of the thermal conductivity of the rail, the emissivity of the walls and by the geometry of the drying chamber. The developed model revealed to be a powerful tool to predict the heat transfer variability between edge and central vials for the cycle development and scale-up and to compare various freeze-dryer design features

A transition system semantics for the control-driven coordination language Manifold

AbstractCoordination languages are a new class of parallel programming languages which manage the interactions among concurrent programs. Basically, coordination is achieved either by manipulating data values shared among all active processes or by dynamically evolving the interconnections among the processes as a consequence of observations of their state changes. The latter, also called control-driven coordination, is supported by MANIFOLD. We present the formal semantics of a kernel of MANIFOLD, based on a two-level transition system model: the first level is used to specify the ideal behavior of each single component in a MANIFOLD system, whereas the second level captures their interactions. Although we apply our two-level model in this paper to define the semantics of a control-oriented coordination language, this approach is useful for the formal studies of other coordination models and languages as well

Chance Constrained Network Design

When designing or upgrading a communication network, operators are faced with a major issue, as uncertainty on communication demands makes it difficult to correctly provision the network capacity. When a probability on traffic matrices is given, finding the cheapest capacity allocation that guarantees, within a prescribed level of confidence, that each arc can support the traffic demands peaks turns out to be, in general, a difficult non convex optimization problem belonging to the class of chance constrained problems. Drawing from some very recent results in the literature we highlight the relationships between chance constrained network design problems and robust network optimization. We then compare several different ways to build uncertainty sets upon deviation measures, comprised the recently proposed backward and forward deviation measures that capture possible asymmetries of the traffic demands distribution. We report results of a computational study aimed at comparing the performance of different models when built upon the same set of historical traffic matrices

Linear programming models for traffic engineering in 100% survivable networks under combined IS-IS/OSPF and MPLS-TE

his paper concerns the problem of minimizing the maximum link utilization of IP telecommunication networks under the joint use of traditional IGP routing protocols, such as ISIS and OSPF, and the more sophisticated MPLS-TE technology. It is shown that the problem of choosing the optimal routing, both under working conditions and under single link failure scenarios, can be cast as a linear program of reasonable size. The proposed model is validated by a computational experimentation performed on synthetic and real networks: the obtained results show that the new approach considerably reduces the maximum link utilization of the network with respect to simply optimizing the IGP weights, at the cost of adding a limited number of label switched paths (LSPs). Optimizing the set of IGP weights within the overall approach further improves performances. The computational time needed to solve the models matches well with real-time requirements, and makes it possible to consider network design problems

A transition system semantics for the control-driven coordination language MANIFOLD

Coordination languages are a new class of parallel programming languages which manage the interactions among concurrent programs. Basically, coordination is achieved either by manipulating data values shared among all active processes or by dynamically evolving the interconnections among the processes as a consequence of observations of their state changes. The latter, also called control-driven coordination, is supported by MANIFOLD. We present the formal semantics of a kernel of MANIFOLD, based on a two-level transition system model: the first level is used to specify the ideal behavior of each single component in a MANIFOLD system, whereas the second level captures their interactions. Although we apply our two-level model in this paper to define the semantics of a control-oriented coordination language, this approach is useful for the formal studies of other coordination models and languages as well