Mikel Lezaun

Crew rostering problem in a public transport company

In this paper, we present an applied study commissioned by Metro Bilbao on how to establish a more egalitarian annual allocation of work to drivers. Task allocation is mixed, with some tasks allocated on a rotating basis and others not. The model proposed is solved as a sequence of four types of integer programming problem. The solution obtained is quasi-optimal: all drivers carry out practically the same tasks over the full year. The main contribution of this paper is its method for combining semi-rotating allocation with a planning time frame divided into five periods of three different types with a workload distributed in a non uniform fashion over the days of the week, and with constraints agreed with employees to obtain an egalitarian solution. This method is being implemented at Metro Bilbao, and Eusko Tren has commissioned a study into a similar method by the authors.

Staff rostering for the station personnel of a railway company

AbstractThis paper presents a case study commissioned by the Spanish railway carrier Ferrocariles Españoles de Vía Estrecha for the annual rostering of work schedules for station personnel. A mixed rostering process is used. The first part of the process is carried out manually with the aid of a spreadsheet and Visual Basic, and consists of designing an initial graphic with 4-week patterns for each station, assigning those patterns in a rotating schedule over the year and factoring in vacation time. The second part consists of assigning relief shifts to cover those shifts left vacant in such a way as to minimize the distance travelled by personnel from other stations brought in for relief shift duty. To that end, basic programmes are designed using binary programming and a 4-week time frame. The results obtained are a clear improvement on the system previously used at FEVE and the company has decided to implement the model.

Optimising the Welding Process in the Manufacture of Offshore Mooring Chains

Vicinay Cadenas S.A is a world leader in the manufacture of mooring chains for the offshore industry. Welding is a key part of chain manufacturing. This study seeks to determine how the manufacturing parameters of welding machines influence the appearance of inhomogeneities. The idea is to optimise current manufacturing processes and acquire knowledge that will enable the firm to develop new products with diameters in excess of those produced to date. To that end, multivariate analysis techniques are used to study manufacturing data on various chains and an algorithm is designed to select the spreads of the adjustable variables that contain the lowest (highest) percentage of links with inhomogeneities. The application of this algorithm to a number of chains with different diameters manufactured on the same machine provides an estimate of the table of settings that should be used to make chains with dimensions larger than those currently made.

Modelling DNA Denaturation

In the recent years much attention has been devoted to find a mechanism for energy transfer and localization in the DNA molecule, in particular in the context of the DNA denaturation problem1, 2, 3. A first attempt to incorporate thermal effects in anharmonic models has been presented by Muto et al. 4, 3 who investigated the possibility of packets of energy (solitons) being generated thermally at physiological temperature and the lifetime of open states, that are the precursors of full denaturation. The models presented in these works were always dealing with a homogeneous DNA molecule. In reality DNA is a double helix built from two antiparallel linear polymers and the base in one side is complementary to the base in the other side. Guanine is associated to cytosine, adenine is associated to thymine, and they alternate in a random fashion. First sudies of energy transfer in an inhomogeneous DNA molecule have been presented by Techera et al. 5 and Muto6. In the present work, we are dealing with the local denaturation of an inhomogeneous DNA molecule.