General Mathematics Colloquium

This colloquium takes place every other Wednesday afternoon, 16:00-17:00, in room S-623 (in September and October) or in S-655 (in November and December). For more information, please contact one of the organizers Joost Hulshof and Rob de Jeu.

A database of earlier years' talks can be found here.

Upcoming talks:



Previous talks in 2017:

Wed 03 Mei 2017: Bernard Zweers, Room P-647, 16:00-16:15

Title: Minimizing the cost for inland container transportation

Abstract: A real-life operational planning problem for a logistic service provider is considered. A number of containers have to be shipped from multiple deep sea terminals to a single inland terminal. On may choose the day of transportation and the mode: truck or barge. The goal is to find an assignment for the containers that minimizes the total costs without visiting too many terminals with one barge. For this purpose an integer linear program is formulated that can solve practical instances in reasonable time.

Wed 03 Mei 2017: Jan-David Salchow, Room P-647, 16:20-16:35

Wed 03 Mei 2017: Chris Groothedde, Room P-647, 16:40-16:55

Title: Instability in Dynamical Systems with Delayed Feedback

Abstract: Many mathematical models describe systems with feedback loops. When this feedback is not instantaneous the behaviour and analysis of such a system becomes much more complex. In this talk we will look at equilibrium solutions of such Delay Dynamical systems and the instability that occurs near equilibrium solutions. The set of unstable solutions originating in an equilibrium can be described as a manifold: the Unstable manifold. In particular I will explain some of the basic functional analytic setup behind the study of Delay Dynamical Systems and their Equilibria and how to describe and visualise the Unstable Manifolds.

Wed 19 April 2017: Mark Veraar (TUD), Room P-647, 16:00-17:00   

Title: Fourier multiplier theory: old and new results

Abstract: Using Fourier multiplier theory one can prove the L^p-boundedness of many singular integrals. The first Fourier multipliers theorem has been proved by Marcinkiewicz in 1939. His main motivation was the application to elliptic PDEs. Since his work there have been many results on multiplier theory, among which the results of Mihlin and H\"ormander. During the last 20 years, multiplier theory was extensively studied in the weighted setting and in the vector-valued setting. The weighted setting is motivated by complex and geometric analysis and has led to several famous results. The vector-valued setting is important in the operator theoretic approach to PDE. In the talk I will present a survey of some of the recent results and their applications

Wed 05 April 2017: Sandjai Bhulai (VU), Room P-647, 16:00-17:00 

Title: Value Function Discovery In Markov Decision Processes.

Abstract: In this talk, we introduce a novel method for discovery of value functions for Markov Decision Processes (MDPs). This method is based on ideas from the evolutionary algorithm field. Its key feature is that it discovers descriptions of value functions that are algebraic in nature. This feature is unique, because the descriptions include the model parameters of the MDP. The algebraic expression can be used in several scenarios, e.g., conversion to a policy, control of systems with time-varying parameters. We illustrate its application on an example MDP.

Wed 22 Maart 2017: Bart de Smit (RUL), Room P-647, 16:00-17:00

Title: On the abelian coverings of curves over finite fields.

Abstract: The main result of this talk identifies when two curves over finite fields have equivalent categories of (possibly ramified) abelian coverings.  We will also sketch where this result fits in the wider context of number theoretic analogs of the Kac's famous question: "Can you hear the shape of a drum?".   


Wed 08 Februari 2017: Richard J. Boucherie (Twente), Room P-647, 16:00-17:00

Title: Operations research solutions to improve the quality of healthcare

Abstract: Healthcare expenditures are increasing in many countries. Delivering adequate quality of healthcare requires efficient utilization of resources. Operations Research allows us to maintain or increase the current quality of healthcare for a growing number of patients without increasing the required work force. In this talk, I will describe a series of mathematical results obtained in the Center for Healthcare Operations Improvement and Research of the University of Twente, and I will indicate how these results were implemented in Dutch hospitals.
Efficient planning of operating theatres will reduce the wasted hours of staff, balancing the number of patients in wards will reduce peaks and therefore increases the efficiency of nursing care, efficient rostering of staff allows for more work to be done by the same number of people. While employing operations research techniques seems to be dedicated to improving efficiency, at the same time improved efficiency leads to increased job satisfaction as experienced workload is often dominated by those moments at which the work pressure is very high, and it also improves patient safety since errors due to peak work load will be avoided.