Motifs featuring trios of figures have been discovered at a newly documented rock art site in the Swaga Swaga Game Reserve in Tanzania. These images find parallels in paintings from rockshelters at the nearby Kolo site, and raise the possibility that they represent anthropomorphic figures with stylised buffalo heads.

Volunteering has become increasingly recognized as governments try to shrink the public purse, yet it is an area where little knowledge has been established. Using the National Survey on Volunteer Activity (1987) conducted in Canada, this paper examines types of and reasons for volunteering among Canadian seniors, compares these with types of and reasons given by younger adults, and examines the predictors of different types of reasons. The data reveal that seniors are less likely to volunteer out of self-interest but are more likely to volunteer for reasons of obligation and social value than is true of younger adults. Reason for volunteering, furthermore, is related to the type of volunteer activity in which individuals engage. Those volunteering out of obligation and for social value rather than self-interest (that is, seniors) are more likely to be involved in service provision. The reason for volunteering is also related to satisfaction with the experience.

We derive a moderate deviation principle for word counts (which is extended to counts of multiple patterns) in biological sequences under different models: independent and identically distributed letters, homogeneous Markov chains of order 1 and m, and, in view of the codon structure of DNA sequences, Markov chains with three different transition matrices. This enables us to approximate P-values for the number of word occurrences in DNA and protein sequences in a new manner.

The purpose of this note is to show that the Betti realization of motives is compatible with Grothendieck's six operations and the nearby cycles functors, which in the motivic world, were previously studied by the author. We first review the construction of the Betti realization. Then, we establish some general criteria which, applied to the Betti realization, give the compatibilities we seek except for the one concerning the nearby cycles functors. The latter will be treated in a separate section.

Studying the evolutive and adaptative machanisms of prokayotes is a complicated task.As these machanisms cannot be easily studied "in vivo", it is necessary to consider other methods.We have therefore developed the RAevol model, a model designed to study the evolution of bacteria and their adaptationto the environment.Our model simulates the evolution of a population of artificial bacteria in a changing environment, providing us with an insight into the strategies that digital organisms develop to adapt to new conditions.In this paper we describe the principle and architecture of the model, focusing on the mechanisms of the regulatory networks of artificial organisms.Experiments were conducted on populations of artificial bacteria under conditions of stress.We study the ways in which organisms adapt to environmental changes and examine the strategies they adopt.An analysis of these adaptation strategies is presented and a brief overview was proposed concerning the patterns and topological characteristics of the evolved regulatory networks.

Une substitution est un morphisme de monoïdes libres : chaque lettre a pour image un mot, et l'image d'un mot est la concaténation des images de ses lettres. Cet article introduit une généralisation de la notion de substitution, où l'image d'une lettre n'est plus un mot mais un motif, c'est-à-dire un “mot à trous”, l'image d'un mot étant obtenue en raccordant les motifs correspondant à chacune de ses lettres à l'aide de règles locales. On caractérise complètement les substitutions par des motifs qui sont définies sur toute suite biinfinie, et on explique comment les construire. On montre que toute suite biinfinie qui est point fixe d'une substitution par des motifs est substitutive, c'est-à-dire est l'image, par un morphisme lettre à lettre, d'un point fixe de substitution (au sens usuel).