Combining Column Generation and Lagrangian Relaxation

Although the possibility to combine column generation and Lagrangian relaxation has been known for quite some time, it has only recently been exploited in algorithms. In this paper, we discuss ways of combining these techniques. We focus on solving the LP relaxation of the Dantzig-Wolfe master problem. In a first approach we apply Lagrangian relaxation directly to this extended formulation, i.e. no simplex method is used. In a second one, we use Lagrangian relaxation to generate new columns, that is Lagrangian relaxation is applied to the compact for-mulation. We will illustrate the ideas behind these algorithms with an application in Lot-sizing. To show the wide applicability of these techniques, we also discuss applications in integrated vehicle and crew scheduling, plant location and cutting stock problems.column generation;Lagrangean relaxation;cutting stock problem;lotsizing;vehicle and crew scheduling

Predicting deadline transgressions using event logs

Effective risk management is crucial for any organisation. One of its key steps is risk identification, but few tools exist to support this process. Here we present a method for the automatic discovery of a particular type of process-related risk, the danger of deadline transgressions or overruns, based on the analysis of event logs. We define a set of time-related process risk indicators, i.e., patterns observable in event logs that highlight the likelihood of an overrun, and then show how instances of these patterns can be identified automatically using statistical principles. To demonstrate its feasibility, the approach has been implemented as a plug-in module to the process mining framework ProM and tested using an event log from a Dutch financial institution

Surgical Site Infections at Donor and Recipient Sites in Patients with Iliac Crest Harvesting For Autologous Bone Grafting - A Pilot Evaluation

Surgeons harvest the iliac crest for bone grafting. The epidemiology of surgical site infections (SSI) associated with this procedure at the donor, or recipient site, is unknown. We perform a retrospective pilot evaluation of adult patients undergoing first-time orthopedic surgery at the Balgrist University Hospital between 2014-2019. We excluded patients with infection at the index surgery, diabetic foot surgeries, superficial SSIs, and revision surgeries. We included 20,088 episodes of primary orthopedic surgery, of which 467 with iliac crest bone sampling (467/20,088; 2%). Only two iliac sites (2/467; 0.4%) become infected. In contrast, surgeries with iliac crest sampling yielded more SSIs at the recipient site than those without (1.9% vs. 0.8%; χ2-test; p<0.01). These patients equally revealed more co-morbidities such as a longer duration of surgery (median 127 vs. 79 minutes), when compared to the general orthopedic population. In multivariate logistic regression analysis with the outcome “ SSI at the recipient site”, the iliac harvesting was independently associated with deep SSIs requiring surgical revision (odds ratio 2.1; 95% confidence interval 1.1-4.2). In our pilot evaluation with 20,088 primary orthopedic surgeries, the SSI risk of the iliac harvest site was low. In contrast, surgeries with supplementary iliac crest harvesting revealed a higher SSI risk than the general orthopedic population, potentially due to a mix of local independent risks of grafting together with a prolonged surgery time. Keywords : Autologous bone grafting; Deep surgical site infections; Epidemiology; Iliac crest harvesting; Revision surger

Online data services at the Belgian Marine Datacentre

Over the past few years, the Management Unit of the North Sea Mathematical Models (MUMM) has built up a centre of human and technical expertise oriented towards the management and the analysis of marine environmental data. The Belgian Marine Data Centre (BMDC) serves as national repository and processing centre for marine and environmental data and ensures a continuous and scientifically sound data flow between data producers and end-users of marine and environmental data collected in the frame of national and international research and monitoring programmes. The data cover most domains of oceanology as there are: physico-chemical, optical parameters, biodiversity, hydrodynamics, sedimentology, geography and human interest. Most of the datasets relate to the Belgian Continental Shelf, the Scheldt estuary and its surrounding areas.To promote the use of a high variety of data sets, different tools are constantly being developed and are presented on our website (www.mumm.ac.be/datacentre). An interface to the integrated database on the quality of the marine environment was developed. This database mainly contains the results of measurements and observations in situ and laboratory analyses of air, water, sediment and biota samples. Besides an extensive inventory of the database and an advanced request form with several selection criteria, some more straightforward queries and geographical selection tools are being developed for a faster and easier access to a specific dataset. Data can freely be downloaded. Once the data are obtained, a spatial analysis tool is freely and online available for the visualization on an interactive map. A lot of documentation accompanying the data is online available. The strongest feature of this system is the common underlying structure for different kinds and sources of data. This opens the possibility to compare biodiversity data, physico-chemical data, sedimentological data and historical data.Another database at MUMM, the real-time data acquisition system ‘ODAS’ stores the physical and chemical parameters measured onboard of the research vessel RV Belgica since 1984. The along -track data are published online shortly after the end of the measurement campaign together with all other information like the campaign reports, cruise tracks, … This is a valuable source of basic information for the scientists

Online data services at the Belgian Marine Datacentre

Over the past few years, the Management Unit of the North Sea Mathematical Models (MUMM) has built up a centre of human and technical expertise oriented towards the management and the analysis of marine environmental data. The Belgian Marine Data Centre (BMDC) serves as national repository and processing centre for marine and environmental data and ensures a continuous and scientifically sound data flow between data producers and end-users of marine and environmental data collected in the frame of national and international research and monitoring programmes. The data cover most domains of oceanology as there are: physico-chemical, optical parameters, biodiversity, hydrodynamics, sedimentology, geography and human interest. Most of the datasets relate to the Belgian Continental Shelf, the Scheldt estuary and its surrounding areas.To promote the use of a high variety of data sets, different tools are constantly being developed and are presented on our website (www.mumm.ac.be/datacentre). An interface to the integrated database on the quality of the marine environment was developed. This database mainly contains the results of measurements and observations in situ and laboratory analyses of air, water, sediment and biota samples. Besides an extensive inventory of the database and an advanced request form with several selection criteria, some more straightforward queries and geographical selection tools are being developed for a faster and easier access to a specific dataset. Data can freely be downloaded. Once the data are obtained, a spatial analysis tool is freely and online available for the visualization on an interactive map. A lot of documentation accompanying the data is online available. The strongest feature of this system is the common underlying structure for different kinds and sources of data. This opens the possibility to compare biodiversity data, physico-chemical data, sedimentological data and historical data.Another database at MUMM, the real-time data acquisition system ‘ODAS’ stores the physical and chemical parameters measured onboard of the research vessel RV Belgica since 1984. The along -track data are published online shortly after the end of the measurement campaign together with all other information like the campaign reports, cruise tracks, … This is a valuable source of basic information for the scientists

Direction of light propagation to order G^2 in static, spherically symmetric spacetimes: a new derivation

A procedure avoiding any integration of the null geodesic equations is used to derive the direction of light propagation in a three-parameter family of static, spherically symmetric spacetimes within the post-post-Minkowskian approximation. Quasi-Cartesian isotropic coordinates adapted to the symmetries of spacetime are systematically used. It is found that the expression of the angle formed by two light rays as measured by a static observer staying at a given point is remarkably simple in these coordinates. The attention is mainly focused on the null geodesic paths that we call the "quasi-Minkowskian light rays". The vector-like functions characterizing the direction of propagation of such light rays at their points of emission and reception are firstly obtained in the generic case where these points are both located at a finite distance from the centre of symmetry. The direction of propagation of the quasi-Minkowskian light rays emitted at infinity is then straightforwardly deduced. An intrinsic definition of the gravitational deflection angle relative to a static observer located at a finite distance is proposed for these rays. The expression inferred from this definition extends the formula currently used in VLBI astrometry up to the second order in the gravitational constant G.Comment: 19 pages; revised introduction; added references for introduction; corrected typos; published in Class. Quantum Gra