Torsional Alfven waves in stratified and expanding magnetic flux tubes

The effects of both density stratification and magnetic field expansion on torsional Alfven waves in magnetic flux tubes are studied. The frequencies, the period ratio P1/P2 of the fundamental and its first-overtone, and eigenfunctions of torsional Alfven modes are obtained. Our numerical results show that the density stratification and magnetic field expansion have opposite effects on the oscillating properties of torsional Alfven waves.Comment: 13 pages, 7 figures, Accepted for publication in Astrophysics and Space Scienc

A novel flexible model for lot sizing and scheduling with non-triangular, period overlapping and carryover setups in different machine configurations

© 2017, Springer Science+Business Media New York. This paper develops and tests an efficient mixed integer programming model for capacitated lot sizing and scheduling with non-triangular and sequence-dependent setup times and costs incorporating all necessary features of setup carryover and overlapping on different machine configurations. The model’s formulation is based on the asymmetric travelling salesman problem and allows multiple lots of a product within a period. The model conserves the setup state when no product is being processed over successive periods, allows starting a setup in a period and ending it in the next period, permits ending a setup in a period and starting production in the next period(s), and enforces a minimum lot size over multiple periods. This new comprehensive model thus relaxes all limitations of physical separation between the periods. The model is first developed for a single machine and then extended to other machine configurations, including parallel machines and flexible flow lines. Computational tests demonstrate the flexibility and comprehensiveness of the proposed models

A BRS Based Approach for Modeling Elastic Cloud Systems

International audienceElastic behaviors enable Cloud Systems to auto-adapt to their incoming workloads, by provisioning and releasing computing resources, in a way to ensure a controlled compromise between performance and cost-saving requirements. However, due to the highly fluctuating workloads tendencies, it makes it difficult to predict how a cloud system would behave and to provide precise auto-adaptation action plans. In this paper, we propose a BRS (short for Bigraphical Reactive Systems) based approach to provide a formal description for cloud systems structures and their elastic behaviors using bigraphs and bigraphical reaction rules. In addition, elasticity strategies are introduced to encode cloud systems’ auto-adaptation policies. Proposed approach is illustrated and evaluated through an example