Vol. 55 No. 1 (254) (2021)

In this paper we characterize the integrability and the non-existence of limit cycles of Kolmogorov systems of the form

\begin{equation*} \left\{ \begin{array}{l} x^{\prime }=x\left( R\left( x,y\right) \exp \left( \dfrac{A\left( x,y\right) }{B\left( x,y\right) }\right) +P\left( x,y\right) \exp \left( \dfrac{C\left( x,y\right) }{D\left( x,y\right) }\right) \right) , \\ \\ y^{\prime }=y\left( R\left( x,y\right) \exp \left( \dfrac{A\left( x,y\right) }{B\left( x,y\right) }\right) +Q\left( x,y\right) \exp \left( \dfrac{V\left( x,y\right) }{W\left( x,y\right) }\right) \right) , \end{array} \right. \end{equation*}

where $A\left( x,y\right)$, $B\left( x,y\right)$, $C\left( x,y\right)$, $D\left( x,y\right)$, $P\left( x,y\right)$, $Q\left( x,y\right)$, $R\left(x,y\right)$, $V\left( x,y\right)$, $W\left( x,y\right)$ are homogeneous polynomials of degree $a$, $a$, $b$, $b$, $n$, $n$, $m$, $c$, $c$, respectively. Concrete example exhibiting the applicability of our result is introduced.

In this paper we proved that the Faber--Schauder functions form an unconditional representation system for $L^1$.

In the paper an equation $\partial g(z)/\partial \overline{z} = v(z)$ is considered in the unit disc $\mathbb{D}$.  For $C^k$-functions $v$ $(k = 1,2,3,\dots, \infty)$ from weighted $L^p$-classes $(1 \leq p < \infty)$ with weight functions of the type $|z|^{2\gamma} (1-|z|^{2\rho})^{\alpha}$, $z \in \mathbb{D}$, a family $g_{\beta}$ of solutions is constructed ($\beta$ is a complex parameter).

In this paper, we showed that it is possible to use gradient descent method to get minimal error values of loss functions close to their Bayesian estimators. We calculated Bayesian estimators mathematically for different loss functions and tested them using gradient descent algorithm. This algorithm, working on Normal and Poisson distributions showed that it is possible to find minimal error values without having Bayesian estimators. Using Python, we tested the theory on loss functions with known Bayesian estimators as well as another loss functions, getting results proving the theory.

Given a proper edge coloring $\alpha$ of a graph $G$, we define the palette $S_G(v,\alpha)$ of a vertex $v\in V(G)$ as the set of all colors appearing on edges incident with $v$. The palette index $\check{s}(G)$ of $G$ is the minimum number of distinct palettes occurring in a proper edge coloring of $G$. A graph $G$ is called nearly bipartite if there exists $ v\in V(G)$ so that $G-v$ is a bipartite graph. In this paper, we give an upper bound on the palette index of a nearly bipartite graph $G$ by using the decomposition of $G$ into cycles. We also provide an upper bound on the palette index of Cartesian products of graphs. In particular, we show that for any graphs $G$ and $H$, $\check{s}(G\square H)\leq \check{s}(G)\check{s}(H)$.

An $n$-poised node set $\mathcal X$ in the plane is called $GC_n$ set, if the fundamental polynomial of each node is a product of linear factors. A line is called $k$-node line, if it passes through exactly $k$-nodes of $\mathcal X.$ At most $n+1$ nodes can be collinear in $\Xset$ and an $(n+1)$-node line is called maximal line. The well-known conjecture of M. Gasca and J.I. Maeztu states that every $GC_n$ set has a maximal line. Until now the conjecture has been proved only for the cases $n \le 5.$ In this paper we prove some results concerning $n$-node lines, assuming that the Gasca--Maeztu conjecture is true.

The linearized dynamics of a UAV is considered along with a pendulum hanging from it. The state trajectories of the center of mass of the UAV are given. Given the trajectory of the center of mass of the UAV and the state trajectory of its yaw angle, we have to find the control actions and conditions under which the UAV would follow the path while holding the pendulum stable around its lower equilibrium point. The problem is solved using the method for solving inverse problems of dynamics. All the state trajectories of the system and all the control actions are calculated. The condition is obtained under which a solution to the path following problem exists. A specified simple trajectory is chosen as an example for visualizing the results.

In this paper, based on the refined theory of orthotropic plates of variable thickness, a system of differential equations is obtained for solving the problem of bending of an elastically restrained beam with an intermediate condition. The beam thickness is constant and is subject to a uniformly distributed load. The effects of transverse shear are also taken into account. Passing to dimensionless quantities, an analytical closed solution is obtained. The question of the influence of changing the place of application of the intermediate condition on the solution is discussed. Depending on the location of the hinge bearing, the question of optimality was posed and resolved according to the principle of minimum maximum deflection. The results are presented in both tabular and graphical form. Based on the results obtained, appropriate conclusions are drawn.

In this paper several problems related to the implementation of the method for the approximate calculation of distance between regular events for multitape finite automata are considered and resolved. An algorithm of matching for the considered regular expressions is suggested and results of the algorithm application to some specific regular expressions are adduced. The proposed method can be used not only for the mentioned implementation, but also separately.

In modern integrated circuits, the channel length of the transistors is reduced, and the supply voltages are also reduced. But the threshold voltages of the transistors cannot be reduced so quickly due to the physical properties of the materials used, which decreases the operating range of the transistors and makes noises comparable to them. Therefore, it is necessary to eliminate the influence of noise sources in the circuits, in particular, reflections between the transmission line and the output of the transmitter. A system is proposed for calibrating the output impedance of the transmitter based on an accurate external resistor with comparator unit offset voltage compensation. Existing analog and reference frequency based solutions have key disadvantages such as the inability to compensate the offset voltage after the integrated circuit is fabricated, and the distribution of the calibration voltage across the Input/Output device and constant power consumption during the operation. The proposed circuit includes a high-precision digital-to-analog converter to compensate the comparator offset voltage. It generates calibration codes for the pull-up and pull-down parts of the transmitter output buffer, and provides fine tuning of the output impedance. The circuit was modeled using 16 nm FinFET process elements and simulated with HSPICE simulator.

In this article, we present energy resolution studies of an electromagnetic calorimeter prototype for Electron–Ion Collider. The results of energy resolution for various configurations of lead tungstate crystals were obtained based on the Geant4 simulation package. The energy resolution was studied as a function of the polar angle of incident electrons in a momentum range of 1 to 10 GeV.