Robust Tactical Crew Scheduling Under Uncertain Demand

We analyze a tactical freight railway crew scheduling problem, when train drivers must be informed several weeks before operations about the start and end times and locations of their duties. Between informing the train drivers and start of operations, trip demand changes due to cancellations, new bookings, and reroutings of trains, which might result in mismatches between train driver capacity at a location and demand. We analyze an approach that incorporates uncertain trip demand as scenarios, such that the start and end times and locations of the duties of a crew schedule are recoverable robust against deviations in trip demand. We develop a column generation solution method that dynamically aggregates trips to duties and decomposes the subproblems into smaller, computationally tractable instances. Our model determines duty frames that cover duties in many scenarios, creating recoverable robust crew schedules. We test our model on three real data sets of a major European freight railway operator. Our results show that our schedules are considerably more recoverable robust than those of the nominal solution, resulting in smaller mismatches between train driver capacity and demand.

Modeling and Analysis of the Mechanical Behavior of Dry Contracts Slipping Between the Disc and the Brake Pads

The complexity of the physical or technological systems to be developed or studied led to employing numerical methods based on the principle of an approach as possible nominal solution, but these require large computations requiring efficient computers. The computer code ANSYS also allows the determination and the visualization of the structural deformations due to the contact of slipping between the disc and the pads. The results of the calculations of contact described in this work relate to displacements, Von Mises stress on the disc, contact pressures of the inner and outer pad at various moments of simulation. One precedes then the influence of some parameters on the computation results such as rotation of the disc, the smoothness of the mesh, the material of the brake pads and the friction coefficient enter the disc and the pads, the number of revolutions and the material of the disc, the pads groove.

Fibre Reinforced Refractory Castables :An Alternative Solution for SPF Die Manufacturing

Today heat resistant cast steels are the nominal solution for Ti-SPF forming die manufacturing. Nevertheless, this materials present some drawbacks related to delivery time and cost. A fibre reinforced refractory castable (FRRC) is proposed as a new solution for prototype SPF die manufacturing. Due to the general brittleness of refractory castables, a short fibre reinforcement has been investigated in order to avoid catastrophic failure during the forming process. General macroscopic behavior of such materials is very complex and presents large evolutions with the testing temperature. The paper addresses the important benefits of the reinforcement for refractory castable in the case of loading on a complex structure. The capability of the material to support several cracks is shown in the case of a technological sample with a complex shape.

Initial Condition Sensitivity Functions and Their Applications

The well-known method of obtaining sensitivity functions is usually restricted by the condition of continuity imposed on the functions of the coordinates in system equations. For the case of discontinuous functions, more elaborate procedures are required to give a good linear approximation. It is shown that sensitivity functions are discontinuous at the discontinuous points. Also, relations between elements of sensitivity functions at these points are shown to be linear for a given nominal solution of the system. The switching time of the desired Bang-Bang control can be estimated if variations in initial conditions are known. The changes in terminal states and cost function due to deviations in initial conditions can be determined, to first order, by the use of sensitivity functions. Bounds on the deviations in initial conditions can be found by a worst case approach so that the desired terminal conditions are satisfied within given tolerances. The fundamental importance of these techniques in a number of areas of application, for instance, guidance and control of aerospace vehicles, is well known.

Piezoelectrically Induced Selective Flame Signal Modulation

The design and performance of two devices for selective spectral modulation in flame emission and atomic absorption spectrometry are reported. The similar techniques use periodic piezoelectrically induced deformation of one or two fluidic channels to the solution nebulizer. The mechanically simpler channel device generates a regular ac ripple on the solution flow into the flame. In certain situations, the influence of the solvent pulsing on the flame temperature permits the differentiation of flame background signals from signals of analytical interest; alternatively, advantage can be taken of mutually compensating flame processes which negate the influence of solvent modulation on the flame background. In the generally applicable dual channel technique, the nominal solution uptake rate is constant and the ac components in the flame spectra represent the differences in chemical composition between the analytical and the blank solutions. Effective background discrimination ratios for certain band systems exceed 103:1.