We deal with the numerical simulation of a motion of viscous compressible fluids. We discretize the governing Navier-Stokes equations by the backward difference formula - discontinuous Galerkin finite element (BDF-DGFE) method, which exhibits a sufficiently stable, efficient and accurate numerical scheme. The BDF-DGFE method requires a solution of one linear algebra system at each time step. In this paper, we deal with these linear algebra systems with the aid of an iterative solver. We discuss the choice of the preconditioner, stopping criterion and the choice of the time step and propose a new strategy which leads to an efficient and accurate numerical scheme.
In this paper we discuss inverse problems in infiltration. We propose an efficient method for identification of model parameters, e.g., soil parameters for unsaturated porous media. Our concept is strongly based on the finite speed of propagation of the wetness front during the infiltration into a dry region. We determine the unknown parameters from the corresponding ODE system arising from the original porous media equation. We use the automatic differentiation implemented in the ODE solver LSODA. Several numerical experiments are included.
This paper deals with two types of non-local problems for the Poisson equation in the disc. The first of them deals with the situation when the function value on the circle is given as a combination of unknown function values in the disc. The other type deals with the situation when a combination of the value of the function and its derivative by radius on the circle are given as a combination of unknown function values in the disc. The existence and uniqueness of the classical solution of these problems is proved. The solutions are constructed in an explicit form.
This paper deals with a multiobjective control problem for nonlinear discrete time systems. The problem consists of finding a control strategy which minimizes a number of performance indexes subject to state and control constraints. A solution to this problem through the Receding Horizon approach is proposed. Under standard assumptions, it is shown that the resulting control law guarantees closed-loop stability. The proposed method is also used to provide a robustly stabilizing solution to the problem of simultaneously minimizing a set of H∞ cost functions for a class of systems subject to bounded disturbances and/or parameter uncertainties. Numeric examples are reported to highlight the stabilizing action of the proposed control laws.
The sports sector has been fighting doping globally by harmonized rules in The World Anti-Doping Agency’s Code by strict liability. According to the Code it is each athlete’s personal duty to ensure that no prohibited substance enters his or her body. Athletes are responsible for any prohibited substance or its metabolites or markers found to be present in their samples. Accordingly, it is not necessary that intent, fault, negligence or knowing use on the athlete’s part be demonstrated in order to establish an antidoping violation. The article written for TLQ legal journal demonstrates how special regulation of doping is in the light of case of Jan Štěrba, bronze medalist of London 2012 Games. He was lucky that he escaped standard sanction of ineligibility and was punished only with reprimand for violation of Anti-Doping rules. The article at the same time presents additionally efforts of fight against doping by international cooperation among states by Council of Europe or UNESCO to enhance illustration how special doping regulation is. There is no doubt that this area of sports law will be still evolving due to many difficult and controversial aspects of it.
Let $A(G)$ be the adjacency matrix of $G$. The characteristic polynomial of the adjacency matrix $A$ is called the characteristic polynomial of the graph $G$ and is denoted by $\phi (G, \lambda)$ or simply $\phi (G)$. The spectrum of $G$ consists of the roots (together with their multiplicities) $\lambda _1(G)\geq \lambda _2(G)\geq \ldots \geq \lambda _n(G)$ of the equation $\phi (G, \lambda )=0$. The largest root $\lambda _1(G)$ is referred to as the spectral radius of $G$. A $\ddag $-shape is a tree with exactly two of its vertices having maximal degree 4. We will denote by $G(l_1, l_2, \ldots , l_7)$ $(l_1\geq 0$, $l_i\geq 1$, $i=2,3,\ldots, 7)$ a $\ddag $-shape tree such that $G(l_1, l_2, \ldots , l_7)-u-v=P_{l_1}\cup P_{l_2}\cup \ldots \cup P_{l_7}$, where $u$ and $v$ are the vertices of degree 4. In this paper we prove that $3\sqrt {2}/{2}< \lambda _1(G(l_1, l_2, \ldots , l_7))< {5}/{2}$.