Wyniki wyszukiwania - BazTech

1

A Neimark-Sacker bifurcation in a discrete SIS model

Choiński Marcin

Mathematica Applicanda

|

2023

|

Vol. 51, no. 1

109--120

EN

In this paper, we analyze a possibility of occurrence of a Neimark-Sacker bifurcation in a two-dimensional SIS discrete-time model. As a discretization method, we applied the Explicit Euler Scheme. We choose a step size of discretization method as a bifurcation parameter, what is not a typical approach. We phrase conditions giving the bifurcation appearance depending on the step size. Firstly, we determine terms on the step size enabling the eigenvalues of Jacobian matrix for the endemic stationary state of the system being complex and having absolute value equal to 1. Then we use the Center Manifold Theorem in order to exclude values of step size which disable the occurrence of bifurcation. We accomplish our results with numerical simulations.

PL

W artykule zbadano możliwość wystąpienia bifurkacji Neimerka–Sackera (BNS) w dyskretnym dwuwymiarowym modelu SIS. W celu dyskretyzacji modelu ciągłego zastosowano jawny schemat Eulera. Jako parametr bifurkacyjny wybrano długość kroku dyskretyzacji, co nie jest standardowym podejściem. Sformułowaliśmy warunki wystąpienia bifurkacji w zależności od długości kroku. Najpierw sprawdzono, dla jakich warunków wartości własne macierzy Jacobiego dla endemicznego stanu stacjonarnego są zespolone oraz ich moduł wynosi 1. Następnie zastosowano twierdzenie o rozmaitości centralnej w celu wykluczenia tych wartości kroku dyskretyzacji, dla których BNS nie występuje. Rozważania teoretyczne są uzupełnione symulacjami numerycznymi.

2

Thermal-electrical analogy in dynamic simulations of buildings: comparison of four numerical solution methods

Michalak Piotr

Journal of Mechanical and Energy Engineering

|

2020

|

Vol. 4, No 2

179--188

EN

The lumped capacitance method is widely used in dynamic modelling of buildings. Models differ in complexity, solution methods and ability to simulate transient behaviour of described objects. The paper presents a mathematical description of a simple 1R1C thermal network model of a building zone. Four numerical methods were applied to solve differential equation describing its dynamics. For validation purposes two test cases (600 and 900) from the BESTEST procedure were used. In both cases detailed results were given. Better ability of the simulation model to reproduce transient behaviour of the modelled buildings was noticed in case of the lightweight object (case 600). Annual heating and cooling demand was within the reference range for heavyweight one (case 900). The kind of the computation method had no significant effect on simulation results.

3

Simple discrete SIS criss-cross model of tuberculosis in heterogeneous population of homeless and non-homeless people

Bodzioch Mariusz, Choiński Marcin

Mathematica Applicanda

|

2019

|

Vol. 47, no. 1

103--115

EN

In this paper we propose a discrete criss-cross model of tuberculosis (TB) transmission in a heterogeneous population, which consists of two different subpopulations: homeless and non-homeless people. This criss-cross model is based on the simple continuous SIS model with bilinear transmission function and constant inflow into both subpopulations considered previously by us. We make preliminary stability analysis. We show that to control the spread of the infectious disease in a heterogeneous population it is not enough to consider the dynamics of the disease in each subpopulation separately. This result is consistent with the result for continuous model. We also fit the model to epidemic data from Warmian-Masurian Province of Poland.

PL

Zaproponowany został dyskretny krzyżowy model rozprzestrzeniania się gruźlicy w niejednorodnej populacji składającej się z bezdomnych i niebezdomnych. Model ten oparty jest na prostym modelu typu SIS z dwuliniową funkcją transmisji i stałym napływem w obu populacjach. Przeprowadzona została wstępna analiza stabilności stanów stacjonarnych. Pokazano, że aby kontrolować rozprzestrzenianie się choroby zakaźnej w niejednorodnej populacji nie jest wystarczające rozważanie dynamiki choroby w każdej podpopulacji oddzielnie. Parametry modelu zostały dopasowane do danych z województwa warmińsko-mazurskiego.

4

Approximation of functions and their conjugates in Lp and uniform metric by Euler means

Volosivets S. S., Tyuleneva A. A.

Demonstratio Mathematica

|

2018

|

Vol. 51, nr 1

141--150

EN

For 2π-periodic functions from Lp (where 1 < p < ∞) we prove an estimate of approximation by Euler means in Lp metric generalizing a result of L. Rempuska and K. Tomczak. Furthermore, we show that this estimate is sharp in a certain sense. We study the uniform approximation of functions by Euler means in terms of their best approximations in p-variational metric and also prove the sharpness of this estimate under some conditions. Similar problems are treated for conjugate functions.

5

Simplified 2D Transient Heat Transfer Simulation Using Gauss Error Function and FDM

du Plessis M.

Archives of Foundry Engineering

|

2013

|

Vol. 13, iss. 3 spec.

21--24

EN

This article documents the methodology used to compile a transient heat transfer simulation with the goal of calculating the time to full solidification or any specified temperature of a metal casting, this simulation may serves as a confirmation of Chvorinov's rule, furthermore the simulation will identify the heat transfer topography, allowing the user to identify the location of possible solidification errors, however for the purpose of simplification, only the liquid phase cooling of pure iron will be considered in this report. Euler methods will be discussed with special attention paid to explicit forward approximation and how Gaussian error can be used to simplify the simulation, in an attempt to reduce processing time. A look at the advantages and disadvantages of using this method will be considered and explanations given the decisions taken in the methodology of the simulation, the use of software will be discussed. The article will conclude with a look at the other applications for this simulation as well as the limits of this simulation.

6

Generalized Euler method for nonlinear first order partial differential functional equations

Kamont Z., Nadolski A.

Demonstratio Mathematica

|

2005

|

Vol. 38, nr 4

976-996

EN

Classical solutions of the local Cauchy problem on the Haar pyramid are approximated in the paper by solutions of suitable quasilinear systems of difference equations. The proof of the stability of the difference problem is based on a comparison technique with nonlinear estimates of the Perron type. This new approach to the numerical solving of nonlinear functional differential equations is generated by a quasilinearization method for initial problems. Numerical examples are given.

7

Topological conjugacy of gradient cascades and learning process of a nonlinear neuron

Bielecki A.

Opuscula Mathematica

|

2000

|

Vol. 20

19-25

EN

This article discusses the topological conjugacy between a gradient dynamical system with a constant time step and a cascade generated by its Euler method. The result presented in this paper is that on a two-dimensional sphere a gradient dynamical system is, under some natural assumptions, correctly reproduced by Euler method for a time step sufficiently small. It means that the time-h-map of the induced dynamical system is globally topologically conjugate to discrete dynamical system obtained via Euler method. The presented theorem is applied to analysis of artificial nonlinear neuron learning process.

PL

W artukule rozważany jest problem topologicznego sprzężenia kaskady otrzymanej z równania gradientowego poprzez ustalenie kroku czasowego i kaskady generowanej przez metodę Eulera dla tego równania. Prezentowane twierdzenie mówi o tym, że na dwuwymiarowej sferze, przy pewnych naturalnych założeniach, dynamika układu gradientowego jest poprawnie odtwarzana przez metodę Eulera, jeśli jej krok czasowy jest dostatecznie mały. Oznacza to, że kaskada otrzymana przez ustalenie kroku czasowego jest globalnie topologicznie sprzężona z dyskretnym układem dynamicznym generowanym przez metodę Eulera. Prezentowane twierdzenie jest zastosowane do analizy procesu nauki nieliniowego neuronu.