Lectures and Colloquia during the semester

**May 7, 2001**

Freie Universität Berlin - Institut für
Informatik

Takustraße 9, 14195 Berlin

Room 005

**Lecture - 14:15**

### Johannes Buchmann - Technische Universität Darmstadt

### How secure is public key cryptography?

*Abstract:*
The security of public key cryptosystems is based on the difficulty of
solving computational problems in number theory. In this lecture I
explain which computational problems are particularly relevant in public
key cryptography and I discuss the difficulty of those problems.

**Colloquium - 16:00**

### Britta Broser - Freie Universität Berlin

### Time Series Analysis

*Abstract:*
It is possible to draw conclusions about a (e.g. physical) system only from a series of measured values of this system.
In general we have no further concrete information about it.
Takens has proved an important theorem concerning this problem.

In practice this way of analysing systems might be the only one for getting some information about complicated systems. For its realisation we need a mathematical model, a procedure for solving the problem and an implementation.

In this talk we focus on an experiment with a magneto-elastic ribbon which is located in an oscillating magnetic field. We want to show that the motion of the ribbon is chaotic. For this we use a model based on the theorem of Takens. We construct a multivalued map which describes the dynamics of the system and is representable on a computer. For extracting some of the information we use index pairs. These are the basic concept of Conley index theory.

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