Irreversibility and Chaos in Active Particle Suspensions

Active matter has been the object of huge amount of research in recent years for its important fundamental and applicative properties. In this paper we investigate active suspensions of micro-swimmers through direct numerical simulation, so that no approximation is made at the continuous level other than the numerical one. We consider both pusher and puller organisms, with a spherical or ellipsoidal shape. We analyse the velocity and the characteristic scales for an homogeneous two-dimensional suspension and the effective viscosity under shear. We bring evidences that the complex features displayed are related to a spontaneous breaking of the time-reversal symmetry. We show that chaos is not a key ingredient, whereas a large enough number of interacting particles and a non-spherical shape are needed to break the symmetry and are therefore at the basis of the phenomenology. Our numerical study also shows that pullers display some collective motion, though with different characteristics from pushers

GerManC - Towards a Methodology for Constructing and Annotating Historical Corpora

Our paper focuses on the one hand on the challenges posed by the structural variability, flexibility and ambiguity found in historical corpora and evaluates methods of dealing with them on the other. We are currently engaged in a project which aims to compile a representative corpus of German for the period 1650-1800. Looking at exemplary data from the first stage of this project (1650-1700), which consists of newspaper texts from this period, we first aim from the perspective of corpus linguistics to identify the problems associated with the morphological, syntactical and graphemic peculiarities that are characteristic of that particular stage. Specific phenomena which significantly complicate automatic tagging, lemmatisation and parsing include, for instance, "abperlende" (Admoni 1980; Demske-Neumann 1990), i.e. complex and often asyndetic syntax; non-syntactic, prosodic, virgulated punctuation (Demske et al. 2004; cf. Stolt 1990), inflectional variability (e.g. Admoni 1990; Besch & Wegera 1987), as well as partly unsystematic and almost experimental allomorphic and allographic (Kettmann, 1992) diversity. Secondly, we outline a methodology which is intended to facilitate the construction and annotation of such corpora which antedate linguistic standardisation. This is informed by "conventional" and innovative tagging techniques and tools, which are evaluated in terms of utility and accuracy. Finally, we attempt to evaluate the degree to which annotation tools for specialist corpora of this kind can be developed which will substitute for manual or semi-automated annotation

A smooth extension method for transmission problems

In this work, we present a numerical method for the resolution of transmission problems with non-conformal meshes which preserves the optimal rates of convergence in space. The smooth extension method is a fictitious domain approach based on a control formulation stated as a minimization problem, that we prove to be equivalent to the initial transmission problem. Formulated as a minimization problem, the transmission problem can be solved with standard finite element function spaces and usual optimization algorithms. The method is applied to different transmission problems (Laplace, Stokes and a fluid-structure interaction problem) and compared to standard finite element methods