Fields and quadratic form schemes

The paper presents a study of axiomatic theory of quadratic forms. Two operations on quadratic form schemes are investigated: the product of schemes and the group extension of schemes. The main result states that the product of schemes realized by fields is again realized by a field

A remark on hierarchical threshold secret sharing

The main results of this paper are theorems which provide a solution to the open problem posed by Tassa [1]. He considers a specific family Γv of hierarchical threshold access structures and shows that two extreme members Γ∧ and Γ∨ of Γv are realized by secret sharing schemes which are ideal and perfect. The question posed by Tassa is whether the other members of Γv can be realized by ideal and perfect schemes as well. We show that the answer in general is negative. A precise definition of secret sharing scheme introduced by Brickell and Davenport in [2] combined with a connection between schemes and matroids are crucial tools used in this paper. Brickell and Davenport describe secret sharing scheme as a matrix M with n+1 columns, where n denotes the number of participants, and define ideality and perfectness as properties of the matrix M. The auxiliary theorems presented in this paper are interesting not only because of providing the solution of the problem. For example, they provide an upper bound on the number of rows of M if the scheme is perfect and ideal

Witt rings of infinite algebraic extensions of global fields

In this paper we discuss the problem to carry over the well-known Minkowski-Hasse local-global principle to the context of an infinite algebraic extension of the rationals or the rational function fields Wq(x) over finite fields. Applying this result we give a new proof of the elementary type conjecture for Witt rings of infinite algebraic extensions of global fields. This generalizes a result of I. Efrat [Ef] who proved, using Galois cohomology methods, a similar fact for algebraic extensions of the rationals

Communication complexity and linearly ordered sets

The communication complexity of lattice operations in linearly ordered sets is studied. If the lattices are not geometric there is a gap between the known upper and lower bounds. New techniques for the construction of "interval protocols'' are introduced and numerical experiments show that their complexity is less than the complexity of known protocols for the infimum function

Access structures induced by polymatroids with extreme rank function

In this paper we consider multipartite access structures obtained from polymatroids with extreme rank function. They are proved to be ideal and partially hierarchical. It turns out that the family of structures induced by polymatroids with minimal rank function is a natural generalization of the class of disjunctive access structure considered by Simmons and the class of conjunctive access structures introduced by Tassa. The results are based on the connections between multipartite access structures and polymatroids discovered by Farràs, Martí-Farré and Padró

Access structures determined by uniform polymatroids

In this article, all multipartite access structures obtained from uniform integer polymatroids were investigated using the method developed by Farràs, Martí-Farré, and Padró. They are matroid ports, i.e., they satisfy the necessary condition to be ideal. Moreover, each uniform integer polymatroid defines some ideal access structures. Some objects in this family can be useful for the applications of secret sharing. The method presented in this article is universal and can be continued with other classes of polymatroids in further similar studies. Here, we are especially interested in hierarchy of participants determined by the access structure, and we distinguish two main classes: they are compartmented and hierarchical access structures. The main results obtained for access structures determined by uniform integer polymatroids and a monotone increasing family Δ\Delta can be summarized as follows. If the increment sequence of the polymatroid is non-constant, then the access structure is connected. If Δ\Delta does not contain any singletons or the height of the polymatroid is maximal and its increment sequence is not constant starting from the second element, then the access structure is compartmented. If Δ\Delta is generated by a singleton or the increment sequence of the polymatroid is constant starting from the second element, then the obtained access structures are hierarchical. They are proven to be ideal, and their hierarchical orders are completely determined. Moreover, if the increment sequence of the polymatroid is constant and ∣Δ∣>1| \Delta | \gt 1, then the hierarchical order is not antisymmetric, i.e., some different blocks are equivalent. The hierarchical order of access structures obtained from uniform integer polymatroids is always flat, that is, every hierarchy chain has at most two elements

Influence of Boundary Conditions on Numerical Homogenization of High Performance Concrete

Concrete is the most widely used construction material nowadays. We are concerned with the computational modelling and laboratory testing of high-performance concrete (HPC). The idea of HPC is to enhance the functionality and sustainability of normal concrete, especially by its greater ductility as well as higher compressive, tensile, and flexural strengths. In this paper, the influence of three types (linear displacement, uniform traction, and periodic) of boundary conditions used in numerical homogenization on the calculated values of HPC properties is determined and compared with experimental data. We take into account the softening behavior of HPC due to the development of damage (micro-cracks), which finally leads to failure. The results of numerical simulations of the HPC samples were obtained by using the Abaqus package that we supplemented with our in-house finite element method (FEM) computer programs written in Python and the homogenization toolbox Homtools. This has allowed us to better account for the nonlinear response of concrete. In studying the microstructure of HPC, we considered a two-dimensional representative volume element using the finite element method. Because of the random character of the arrangement of concrete’s components, we utilized a stochastic method to generate the representative volume element (RVE) structure. Different constitutive models were used for the components of HPC: quartz sand—linear elastic, steel fibers—ideal elastic-plastic, and cement matrix—concrete damage plasticity. The numerical results obtained are compared with our own experimental data and those from the literature, and a good agreement can be observed