Annali dell''Universita di Ferrara最新文献

It is pointed out that: (1) the positive version of the parallel postulate appearing in Pambuccian (Ann Univ Ferrara 71: 17, 2025) can be found in a 1935 manuscript by Paul Bernays and in Grundlagen der Mathematik, vol. II by Hilbert and Bernays; and (2) that axiom S appearing in the same paper is almost identical to Axiom IV in F. P. Jenks’ 1940 incidence-based axiom system for hyperbolic geometry.

In this paper we obtain Ulyanov-type inequalities between mixed moduli of smoothness of positive orders in mixed metrics in the case of limit values of the parameters.

Let (textrm{R}) be a noncommutative prime ring equipped with an involution ‘(*)’, and let (mathcal {Q}_{ml}(textrm{R})) be the maximal left ring of quotients of (textrm{R}). The objective of this paper is to characterize additive maps (mathcal {H}:textrm{R}rightarrow mathcal {Q}_{ml}(textrm{R})) that satisfy any one of the following conditions. (i) (mathcal {H}(srs)=mathcal {H}(s)s^*r^*+smathcal {H}(r)s^*+srmathcal {H}(s)) for all (s, rin textrm{R}). (ii) (mathcal {H}(s^*s)=mathcal {H}(s^*)s+s^*mathcal {H}(s)) for all (sin textrm{R}).

We investigate double diffusion in the context of the Navier–Stokes–Voigt equations but the heat equation is one suggested by C. I. Christov. The Christov heat equation may be highly relevant when dealing with flows in small dimensions such as are encountered in the area of microfluidics. The theory employed here essentially uses a Kelvin–Voigt term in both the momentum equation and the temperature equation, where both may be thought of as regularizing terms. In addition to finding stationary convection it is found that oscillatory convection will also occur if the salt Rayleigh number is sufficiently high. It is also found that the Kelvin–Voigt coefficient in the temperature equation has a relatively greater stabilizing effect that the analogous term in the momentum equation. A global nonlinear energy stability analysis is also included.

In this paper, we introduce and study a new class of mapping called generalized inverse strongly monotone mapping in a real Hilbert space. We prove some properties of the map. We also introduce new iterative algorithm for approximation of a common point in the set of common fixed points of a countable family of strictly pseudocontractive mappings, the set of solutions of some mixed equilibrium problem and the set of solutions of Variational inequality problem involving the new mapping.

We study the geometric-differential properties of a wide class of closed subgroups of (U_n) endowed with a natural bi-invariant metric. For each of these groups, we explicitly express the distance function, the diameter, and, above all, we parametrize the set of minimizing geodesic segments with arbitrary endpoints (P_0) and (P_1) by means of the set of generalized principal logarithms of (P_0^*P_1) in the Lie algebra of the group. We prove that this last set is a non-empty disjoint union of a finite number of compact submanifolds of (mathfrak {u}_n) diffeomorphic to suitable (and explicitly determined) homogeneous spaces.

The present article deals with static perfect fluid spacetimes on f-Kenmotsu 3-manifolds. At first, we demonstrate if a 3-dimensional f-Kenmotsu manifold with constant scalar curvature as the spatial factor of a static perfect fluid spacetime, then either it is a space of constant sectional curvature or (grad, psi ) is pointwise collinear with (xi ) and the warping function of the static perfect fluid spacetime is given by (psi = k_1 t + k_2), (k_1 ne 0). As a result, we establish that if a cosymplectic manifold of dimension three with constant scalar curvature is the spatial factor of a static perfect fluid spacetime, then either it is flat or, the manifold becomes a space of constant sectional curvature. Next, we show that under certain restrictions if a 3-dimensional f-Kenmotsu manifold is the spatial factor of a static perfect fluid spacetime, then either the manifold is a space of constant sectional curvature or, the manifold is locally isometric to either the flat Euclidean space (mathcal {R}^3) or the Riemannian product (mathcal {R}times M^2(c)), where (M^2(c)) represents a Kahler surface with constant curvature (cne 0), provided (xi psi =0) and (xi tilde{f} =0). Lastly, we have cited an example of an f-Kenmotsu manifold to validate our result.

In this work we show that given any integer-valued random variable D with finite mean such that (mathbb {E}[D]>2) and (mathbb {P}(Dge 1)=1), it is possible to build a configuration model whose giant component has degree distribution that converges in probability to D and give a way to compute the starting degree distribution to achieve this property.

This article is primarily concerned with the bivariate generalization of operators involving a class of orthogonal polynomials called Apostol-Genocchi polynomials. The rate of convergence can be determined in terms of partial and total modulus of continuity as well as the order of approximation can be achieved by means of a Lipschitz-type function and Peetre’s K-functional. In addition, we put forth a conceptual extension known as the “generalized boolean sum (GBS)” for these bivariate operators, which aims to establish the degree of approximation for Bögel continuous functions. In this study, we utilize the Mathematica Software to present a series of graphical illustrations that effectively showcase the rate of convergence for the bivariate operators. The graphs indicate that, in the case of certain functions, the bivariate operators exhibits superior convergence when (alpha ) is less than (beta ). Based on our analysis and comparison of the error of approximation between the bivariate operators and the corresponding GBS operators, it can be deduced that the GBS operators exhibit a faster convergence towards the function.

This is a survey of what is known regarding weaker versions of the Euclidean parallel postulate, culminating with a splitting of the parallel postulate into two weaker and independent incidence-geometric axioms. Among the weaker versions are: the rectangle axiom, stating that there exists a rectangle; the Lotschnittaxiom, stating that the perpendiculars to the sides of a right angle intersect, and Aristotle’s axiom, stating that the distances between the sides of an angle grow indefinitely. Several statements that are equivalent, with plane absolute geometry as a background, to each of these axioms, as well as an analysis of their syntactic simplicity are presented. The parallel postulate is found to be equivalent to the conjunction of the following two axioms: “Given three parallel lines, there is a line that intersects all three of them" and “Given a line a and a point P on a, as well as two intersecting lines m and n, both parallel to a, there exists a line g through P which intersects m but not n."