Kasemsuwan, Jaipong
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Item type:Publication, The cut locus of a Randers rotational 2-sphere of revolution(2018-01-01); Sabau, Sorin V.In the present paper, we study the structure of the cut locus of a Randers rotational 2-sphere of revolution (M, F = α + β). We show that in the case when the Gaussian curvature of the Randers surface is monotone along a meridian, the cut locus of a point q ∈ M is a point on a subarc of the opposite half bending meridian or of the antipodal parallel (Theorem 1.1). More generally, in the case when the Gaussian curvature is not monotone along the meridian, but the cut locus of a point q on the equator is a subarc of the same equator, the cut locus of any point q ∈ M different from poles is a subarc of the antipodal parallel (Theorem 1.2). Some examples are also given in the last section and some differences with the Riemannian case are pointed out. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, New transform formulae for differential transformation method with applications to the nonlinear plane autonomous systems(2020-01-01); Sabau, Sorin V.This work presents a new derivation technique for new differential transform formulae of a product of composite functions. The new formulae are applied to nonlinear plane autonomous systems to demonstrate their efficiency and reliability. The approximate series solutions estimated by the differential transform method (DTM) and the multistep differential transform method (MsDTM) are then compared with the flow direction of the vector fields defined by the original system and an analytical solution calculated by the phase-plane method. We found that the MsDTM results are in better agreement with the analytical solution than the DTM ones. Moreover, the MsDTM can be applied to systems whose analytical solutions are unobtainable. The approximate solutions by the MsDTM have the same direction to the flow of the vector field of the system. It follows that the proposed new formulae are reliable and efficient.