Abstract:
Which subgroups of the symmetric group S_n arise as invariance groups of n-variable functions defined on a k-element domain? It appears that the higher the difference n-k, the more difficult it is to answer this question. For k>=n, the answer is easy: all subgroups of S_n are invariance groups. We give a complete answer in the cases k=n-1 and k=n-2, and we also give a partial answer in the general case: we describe invariance groups when n is much larger than n-k. The proof utilizes Galois connections and the corresponding closure operators on S_n, which turn out to provide a generalization of orbit equivalence of permutation groups. We also present some computational results, which show that all primitive groups except for the alternating groups arise as invariance groups of functions defined on a three-element domain.

Abstract:
In 1907 Maurice Ravel decided to convert into mélodies (typical French genre of songs) five prose works taken from the collection Les Histoires Naturelles written by Jules Renard; the musician’s aim was to say with music what the writer said with words, but from the work emerges a personal interpretation of the texts. This paper studies the musical adaptation of the stories through the analysis of the score and of the cultural context. The little songs are a distillation of irony and refinement and, because of their apparently banal and prosaic content, they arose scandal at their first performance. Ravel’s animals do not display shallowness in order to outrage the audience, they aim to introduce a new idea of music indifferent to rhetoric and to inauthentic aspirations. Nel 1907 Maurice Ravel decise di convertire in mélodies (genere di liriche tipico della tradizione francese) cinque prose tratte dalla raccolta Les histoires naturelles di Jules Renard; l’obiettivo del musicista era quello di dire in musica ciò che lo scrittore aveva detto con le parole, ma dal suo lavoro emerge un’interpretazione personale dei testi. L’elaborato studia l’adattamento musicale delle storie attraverso l’analisi della partitura e del contesto culturale. Le piccole liriche sono un distillato di ironia e raffinatezza e, a causa del loro contenuto apparentemente banale e prosaico, in occasione della loro prima esecuzione destarono lo scandalo. Gli animali di Ravel non fanno sfoggio di superficialità per indignare la platea ma per presentare una nuova idea di musica indifferente alla retorica e alle aspirazioni inautentiche.

Abstract:
Recently R\"ussmann proposed a new new variant of KAM theory based on a slowly converging iteration scheme. It is the purpose of this note to make this scheme accessible in an even simpler setting, namely for analytic perturbations of constant vector fields on a torus. As a side effect the result may be the shortest complete KAM proof for perturbations of integrable vector fields available so far.

Abstract:
We describe a new, short proof of some facts relating the gap lengths of the spectrum of a potential of Hill's equation to its regularity. For example, a real potential is in a weighted Gevrey-Sobolev space if and only if its gap lengths belong to a similarly weighted sequence space. An extension of this result to complex potentials is proven as well. We also recover Trubowitz results about analytic potentials. The proof essentially employs the implicit function theorem.

Abstract:
The purpose of this lecture is to describe the KAM theorem in its most basic form and to give a complete and detailed proof. This proof essentially follows the traditional lines laid out by the inventors of this theory, and the emphasis is more on the underlying ideas than on the sharpness of the arguments.

Abstract:
Recently long range correlations were detected in nucleotide sequences and in human writings by several authors. We undertake here a systematic investigation of two books, Moby Dick by H. Melville and Grimm's tales, with respect to the existence of long range correlations. The analysis is based on the calculation of entropy like quantities as the mutual information for pairs of letters and the entropy, the mean uncertainty, per letter. We further estimate the number of different subwords of a given length $n$. Filtering out the contributions due to the effects of the finite length of the texts, we find correlations ranging to a few hundred letters. Scaling laws for the mutual information (decay with a power law), for the entropy per letter (decay with the inverse square root of $n$) and for the word numbers (stretched exponential growth with $n$ and with a power law of the text length) were found.

Abstract:
A two--dimensional cellular automaton is introduced to model the flow and jamming of vehicular traffic in cities. Each site of the automaton represents a crossing where a finite number of cars can wait approaching the crossing from each of the four directions. The flow of cars obeys realistic traffic rules. We investigate the dependence of the average velocity of cars on the global traffic density. At a critical threshold for the density the average velocity reduces drastically caused by jamming. For the low density regime we provide analytical results which agree with the numerical results.

Abstract:
We report on a lattice based algorithm, completely vectorized for molecular dynamics simulations. Its algorithmic complexity is of the order $O(N)$, where $N$ is the number of particles. The algorithm works very effectively when the particles have short range interaction, but it is applicable to each kind of interaction. The code was tested on a Cray ymp el in a simulation of flowing granular material.

Abstract:
We propose a new method for the calculation of the statistical properties, as e.g. the entropy, of unknown generators of symbolic sequences. The probability distribution $p(k)$ of the elements $k$ of a population can be approximated by the frequencies $f(k)$ of a sample provided the sample is long enough so that each element $k$ occurs many times. Our method yields an approximation if this precondition does not hold. For a given $f(k)$ we recalculate the Zipf--ordered probability distribution by optimization of the parameters of a guessed distribution. We demonstrate that our method yields reliable results.

Abstract:
We investigate symbolic sequences and in particular information carriers as e.g. books and DNA--strings. First the higher order Shannon entropies are calculated, a characteristic root law is detected. Then the algorithmic entropy is estimated by using Lempel--Ziv compression algorithms. In the third section the correlation function for distant letters, the low frequency Fourier spectrum and the characteristic scaling exponents are calculated. We show that all these measures are able to detect long--range correlations. However, as demonstrated by shuffling experiments, different measures operate on different length scales. The longest correlations found in our analysis comprise a few hundreds or thousands of letters and may be understood as long--wave fluctuations of the composition.