On the fibre product of incidence structures

It is shown that in the category of incidence structures a fibre product (pull back) always exists. Several applications to Klingenberg incidence structures and divisible designs are given.Dedicated to Professor Johannes Böhm on the occasion of his 70^th birthday     

On automorphisms for some fibered incidence groups

Summary In any kinematic space (with non trivial fibration) the group of all automorphisms of the geometric structure which preserve both parallelisms is shown to consist exactly of those automorphisms of the algebraic structure which preserve the fibration. Moreover a characterization of such group is given for a particular class of kinematic spaces. Research supported by the Italian Ministry of Education (40% M.P.I.).     

On some semilattice structures for production technologies

Tracing back from Charnes et al. [9] many approaches have been proposed to extend the DEA production model to non-convex technologies. The FDH method were introduced by Deprins et al. [13] and it only assumes a free disposal assumption of the technology. This paper, continues further an earlier work by Briec and Horvath [7]. Among other things, a new class of semilattice production technologies is introduced. Duality results as well as computational issues are proposed.     

On some reducibility and existential interpretability of structures

We prove the embeddability of the structure of Turing degrees into the structure of degrees of existential interpretability. The notion of weakly bounded Turing reducibility (wbT-reducibility) arises in the proof naturally. We demonstrate that this reducibility is situated strictly between the bounded truth-table reducibility and Turing reducibility and differs from the truth-table reducibility.     

Colouring finite incidence structures

One of our results: Let denote a finite projective plane of ordern. Colour its vertices by colours. If no colour appears more than twice on any of the lines, then n + 1. Explicit constructions show that this bound is sharp when is desarguesian.     

Diagrams and incidence structures

We show a purity assumption which seems to be implicit in the theory of the geometry of diagrams (developed by F. Buekenhout in: Geom. Dedicata8 (1979), 253–257; 296–298; J. Combin. Theory Ser. A27, (1979), 121–151); characterizations of those structures on which this assumption holds are given (pure structures), and a sufficent condition on a structure to be pure is also presented.     

On some classes of lazy cocycles and categorical structures

We study some classes of lazy cocycles, called pure (respectively neat), together with their categorical counterparts, entwined (respectively strongly entwined) monoidal categories.     

On some subsets defined with respect to weak structures

We define and study the properties of some subsets of X with respect to a weak structure on X and generalize some already established results.     

On some regularities in dynamic response of cyclic periodic structures

The paper deals with cyclic periodic structures modelling bladed disk assemblies of blades with friction elements for vibration damping. These elements placed between adjacent blades reduce the vibration amplitudes by means of dry friction resulting from centrifugal forces acting on the elements and relative displacements of the blades. However, the application of these friction elements results in an additional dynamical coupling which together with mistuning of some system parameters (e.g., blade eigenfrequency or contact parameters) may cause localization of vibration. In the present paper a linear approximation of such a system is investigated. The structure composed of cyclic periodic cells modelled each as a clamped-free beam interacting with each other by means of viscoelastic elements of complex stiffness is applied for dynamic system analysis. In case of free vibrations as well as in case of steady-state dynamic response to a harmonic pressure field, a perfect periodic structure and the structures with periodically mistuned parameters (blade eigenfrequencies and contact parameters) are studied. Some regularities in the dynamic response of the systems with mistuning have been noticed. Despite the fact that only a linear approximation has been used, the results and conclusions can be applied for models which describe the blade interaction in a nonlinear way.     

Orbits in finite incidence structures

Geometriae Dedicata -     

Integrating and differentiating two-dimensional incidence structures

This research was supported by a Feodor Lynen fellowship.     

Transformation of designs and other incidence structures

We introduce a procedure which transforms a given incidence structure into another one, provided certain conditions are met.Work performed under the auspices of GNSAGA of CNR supported by the 40% and 60% grants of MURST.     

An interactive program for finite incidence structures

It has been shown (see [3]) that every finite incidence structure can be represented in a suitable way by a polynomial over a convenient finite field. In this paper we present a FORTRAN interactive program which examines the incidence structure associated to a given polynomial over GF(9). Further, a second program is exhibited, which determines a complete system of mutually orthogonal latin squares related to a polynomial associated to a projective plane of order nine.     

On smooth incidence structures with constant block size and a characterization of finite projective spaces

Apart from some trivial exceptions, a finite incidence structure is a finite projective space, if the following conditions are satisfied (i) every three noncollinear points are incident with the same number of blocks, (ii) every block is incident with the same number of points, (iii) there are as many points as blocks.