Acta et Commentationes Universitatis Tartuensis de Mathematica

Tauberian theorems for weighted mean statistical summability of double sequences of fuzzy numbers

2021-11-19T01:25:07+02:00

We discuss Tauberian conditions under which the statistical convergence of double sequences of fuzzy numbers follows from the statistical convergence of their weighted means. We also prove some other results which are necessary to establish the main results.

I_2-Relative uniform convergence and Korovkin type approximation

2021-11-19T11:29:48+02:00

In the present paper, an interesting type of convergence named ideal relative uniform convergence for double sequences of functions has been introduced for the first time. Then, the Korovkin type approximation theorem via this new type of convergence has been proved. An example to show that the new type of convergence is stronger than the convergence considered before has been given. Finally, the rate of I₂-relative uniform convergence has been computed.

K-type slant helices on spacelike and timelike surfaces

2021-11-19T01:25:02+02:00

We have derived a necessary and sufficient condition for a non-null normal spacelike curve lying in a spacelike or a timelike surface M ⊂ E₁³, so that the curve becomes a K-type spacelike slant helix with K ∈ {1,2,3}. We have used Darboux frame to define necessary and sufficient conditions. An example is given for a 1-type spacelike slant helix having a spacelike normal and a timelike binormal.

Stability of nanobeams and nanoplates with defects

2021-11-19T01:24:59+02:00

The sensitivity of critical buckling load and critical stress concerning different geometrical and physical parameters of Euler-Bernoulli nanobeams with defects is studied. Eringen’s nonlocal theory of elasticity is used for the determination of critical buckling load for stepped nanobeams subjected to axial loads for different support conditions. An analytical approach to study the impact of discontinuities and boundary conditions on the critical buckling load and critical stress of nanobeams has been developed. Critical buckling loads of stepped nanobeams are defined under the condition that the nanoelements are weakened with stable crack-like defects. Simply supported, clamped and cantilever nanobeams with steps and cracks are investigated in this article. The presented results are compared with the other available results and are found to be in a close agreement.

Equalities between the BLUEs and BLUPs under the partitioned linear fixed model and the corresponding mixed model

2021-11-19T01:24:56+02:00

In this article we consider the partitioned fixed linear model F : y = X₁β₁+ X₂β₂+ ε" and the corresponding mixed model M : y =X₁β₁+X₂u+ ε, where ε is a random error vector and u is a random effect vector. In 2006, Isotalo, M¨ols, and Puntanen found conditions under which an arbitrary representation of the best linear unbiased estimator (BLUE) of an estimable parametric function of β₁in the fixed model F remains BLUE in the mixed model M . In this paper we extend the results concerning further equalities arising from models F and M.

Intersection curve of two parametric surfaces in Euclidean n-space

2021-11-19T01:24:54+02:00

The aim of this paper is to study the differential geometric properties of the intersection curve of two parametric surfaces in Euclidean n-space. For this aim, we first present the mth order derivative formula of a curve lying on a parametric surface. Then, we obtain curvatures and Frenet vectors of the transversal intersection curve of two parametric surfaces in Euclidean n-space. We also provide computer code produced in MATLAB to simplify determining the coefficients relative to Frenet frame of higher order derivatives of a curve.

Extrapolation to mixed norm spaces and applications

2021-11-19T01:24:46+02:00

This paper establishes extrapolation theory to mixed norm spaces. By applying this extrapolation theory, we obtain the mapping properties of the Rubio de Francia Littlewood-Paley functions and the geometrical maximal functions on mixed norm spaces. As special cases of these results, we have the mapping properties on the mixed norm Lebesgue spaces with variable exponents and the mixed norm Lorentz spaces.

Weak module amenability for the second dual of a Banach algebra

2021-11-19T01:24:43+02:00

In this paper we study the weak module amenability of Banach algebras which are Banach modules over another Banach algebra with compatible actions. We show that for every module derivation D : A ↦ ( A/J_A )^∗if D^∗∗(A^∗∗) ⊆ WAP (A/J_A ), then weak module amenability of A^∗∗implies that of A. Also we prove that under certain conditions for the module derivation D, if A^∗∗is weak module amenable then A is also weak module amenable.

A unified theory for irresolute functions

2021-11-19T01:24:40+02:00

In this paper, a new class called (µ, λ)_θ-irresolute functions has been defined with the notion of generalized topology. We obtain some characterizations of such functions and some relations between similar types of functions are established. Some basic properties of such functions are also discussed. Such functions unify different types of weakly irresolute functions by T. Noiri.

Some BBP-type series for polylog integrals

2021-11-19T10:28:14+02:00

An investigation into a family of definite integrals containing log-polylog functions will be undertaken in this paper. It will be shown that Euler sums play an important part in the solution of these integrals and may be represented as a BBP-type formula. In a special case we prove that the corresponding log integral can be represented as a linear combination of the product of zeta functions and the Dirichlet beta function.