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Latest Published Articles

On the product of Sombor and modified Sombor indices

ODAM-Vol. 6 (2023), Issue 2, pp. 1 – 6 Open Access Full-Text PDF
Ivan Gutman, Redžepović and Boris Furtula

Abstract:The Sombor index (\(SO\)) and the modified Sombor index (\(^mSO\)) are two closely related vertex-degree-based graph invariants. Both were introduced in the 2020s, and have already found a variety of chemical, physicochemical, and network-theoretical applications. In this paper, we examine the product \(SO \cdot {^mSO}\) and determine its main properties. It is found that the structure-dependence of this product is fully different from that of either \(SO\) or \(^mSO\). Lower and upper bounds for \(SO \cdot {^mSO}\) are established and the extremal graphs are characterized. For connected graphs, the minimum value of the product \(SO \cdot {^mSO}\) is the square of the number of edges. In the case of trees, the maximum value pertains to a special type of eclipsed sun graph, trees
with a single branching point.

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Limit cycles obtained by perturbing a degenerate center

OMA-Vol. 7 (2023), Issue 1, pp. 56 – 70 Open Access Full-Text PDF
Nabil Rezaiki and Amel Boulfoul

Abstract: This paper deals with the maximum number of limit cycles bifurcating from the degenerate centre
\[ \dot{x}=-y(3x^2+y^2),\: \dot{y}=x(x^2-y^2), \]
when we perturb it inside a class of all homogeneous polynomial differential systems of degree \(5\). Using averaging theory of second order, we show that, at most, five limit cycles are produced from the periodic orbits surrounding the degenerate centre under quintic perturbation. In addition, we provide six examples that give rise to exactly \(5, 4, 3, 2, 1\) and \(0\) limit cycles.

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Expansion of the Jensen \((\Gamma_{1},\Gamma_{2})\)-functional inequatities based on Jensen type \((\eta,\lambda)\)-functional equation with \(3k\)-Variables in complex Banach space

OMA-Vol. 7 (2023), Issue 1, pp. 56 – 70 Open Access Full-Text PDF
Ly Van An

Abstract: In this paper, we work on expanding the Jensen \((\Gamma_{1},\Gamma_{2})\)-function inequalities by relying on the general Jensen \((\eta,\lambda)\)-functional equation with \(3k\)-variables on the complex Banach space. That is the main result of this.

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On norms of derivations implemented by self-adjoint operators

OMA-Vol. 7 (2023), Issue 1, pp. 42 – 55 Open Access Full-Text PDF
Obogi Robert Karieko

Abstract:In this paper, we concentrate on norms of derivations implemented by self-adjoint operators. We determine the upper and lower norm estimates of derivations implemented by self-adjoint operators. The results show that the knowledge of self-adjoint governs the quantum chemical system in which the eigenvalue and eigenvector of a self-adjoint operator represents the ground state energy and the ground state wave function of the system respectively.

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A class of power series based modified newton method with high precision for solving nonlinear models

OMA-Vol. 7 (2023), Issue 1, pp. 32 – 41 Open Access Full-Text PDF
Oghovese Ogbereyivwe and Salisu Shehu Umar

Abstract:This manuscript proposed high-precision methods for obtaining solutions for nonlinear models. The method uses the Newton method as its predictor and an iterative function that involves the perturbed Newton method with the quotient of two power series as the corrector function. The theoretical analysis of convergence indicates that the methods class is of convergence order four, requiring three functions evaluation per cycle. The computation performance comparison with some existing methods shows that the developed methods class has perfect precision.

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BOOK - NULL CONTROLLABILITY OF DEGENERATE AND NON-DEGENERATE SINGULAR PARABOLIC