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# Gel’fand Γ-Semirings

Mathematica Pannonica
Authors:
Tilak Raj Sharma
and
Hitesh Kumar Ranote

In this paper, we introduce the notion of a Gel’fand Γ-semiring and discuss the various characterization of simple, k-ideal, strong ideal, t-small elements and additively cancellative elements of a Gel’fand Γ-semiring R, and prove that the set of additively cancellative elements, set of all t-small elements of R and set of all maximal ideal of R are strong ideals. Further, let R be a simple Gel’fand Γ-semiring and 1 ≠ tR. Let M be the set of all maximal left (right) ideals of R. Then an element x of R is t-small if and only if it belongs to every maximal one sided left (right)ideal of R containing t.

Open access

# Operator Convexity of an Integral Transform with Applications

Mathematica Pannonica
Author:
Silvestru Sever Dragomir

For a continuous and positive function w(λ), λ > 0 and μ a positive measure on (0, ∞) we consider the following integral transform

$D w , μ t : = ∫ 0 ∞ w λ λ + t − 1 d μ λ ,$

where the integral is assumed to exist for t > 0.

We show among others that D(w, μ) is operator convex on (0, ∞). From this we derive that, if f : [0, ∞) → R is an operator monotone function on [0, ∞), then the function [f(0) -f(t)] t -1 is operator convex on (0, ∞). Also, if f : [0, ∞) → R is an operator convex function on [0, ∞), then the function $f 0 + f + ′ 0 t − f t t − 2$ is operator convex on (0, ∞). Some lower and upper bounds for the Jensen’s difference

$D w , μ A + D w , μ B 2 − D w , μ A + B 2$

under some natural assumptions for the positive operators A and B are given. Examples for power, exponential and logarithmic functions are also provided.

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# Perfect Solutions to Problems on Common Transversals and Submodular Functions from Welsh’s 1976 Text Matroid Theory

Mathematica Pannonica
Author:
Jonathan David Farley

Problem 2 of Welsh’s 1976 text Matroid Theory, asking for criteria telling when two families of sets have a common transversal, is solved.

Another unsolved problem in the text Matroid Theory, on whether the “join” of two non-decreasing submodular functions is submodular, is answered in the negative. This resolves an issue first raised by Pym and Perfect in 1970.

Open access

# Existence and Stability of Solutions for a Nonlinear Beam Equation with Internal Damping

Mathematica Pannonica
Authors:
Ducival Carvalho Pereira
,
Carlos Alberto Raposo
, and
Huy Hoang Nguyen

This manuscript deals with the global existence and asymptotic behavior of solutions for a Kirchhoff beam equation with internal damping. The existence of solutions is obtained by using the Faedo-Galerkin method. Exponential stability is proved by applying Nakao’s theorem.

Open access

# Hypersphere Having ΔIIx = Ax in E4

Mathematica Pannonica
Authors:
Erhan Güler
and
Kübra Yilmaz

We consider hypersphere x = x(u, v, w) in the four dimensional Euclidean space. We calculate the Gauss map, and the curvatures of it. Moreover, we compute the second Laplace-Beltrami operator the hypersphere satisfying ΔIIx = Ax, where A ϵ Mat (4,4).

Open access

# A Marcinkiewicz Type Interpolation Theorem for Orlicz Spaces and Its Application

Mathematica Pannonica
Authors:
Xiaoqiang Xie
,
Xi Fu
, and
Changmin Li

In this paper, we show a Marcinkiewicz type interpolation theorem for Orlicz spaces. As an application, we obtain an existence result for a parabolic equation in divergence form.

Open access

# A Note on Common Nuclear Köthe Subspaces and Quotients

Mathematica Pannonica
Authors:
Emre Taştüner
and
Murat Hayrettin Yurdakul

Let E, G be Fréchet spaces and F be a complete locally convex space. It is observed that the existence of a continuous linear not almost bounded operator T on E into F factoring through G causes the existence of a common nuclear Köthe subspace of the triple (E, G, F). If, in addition, F has the property (y), then (E, G, F) has a common nuclear Köthe quotient.

Open access

# The Average Number of Divisors in Certain Arithmetic Sequences

Mathematica Pannonica
Author:
Liubomir Chiriac

In this paper we study the sum , where $τ ( n )$ denotes the number of divisors of n, and {np } is a sequence of integers indexed by primes. Under certain assumptions we show that the aforementioned sum is . As an application, we consider the case where the sequence is given by the Fourier coefficients of a modular form.

Open access

# Some New Inequalities Involving the Generalized Hardy Operator

Mathematica Pannonica
Author:
Kristina Krulić Himmelreich

In this paper we derive new inequalities involving the generalized Hardy operator. The obtained results generalized known inequalities involving the Hardy operator. We also get new inequalities involving the classical Hardy–Hilbert inequality.

Open access

# Bipartite Domination in Graphs

Mathematica Pannonica
Authors:
Anna Bachstein
,
Wayne Goddard
, and
Michael A. Henning

The bipartite domination number of a graph is the minimum size of a dominating set that induces a bipartite subgraph. In this paper we initiate the study of this parameter, especially bounds involving the order, the ordinary domination number, and the chromatic number. For example, we show for an isolate-free graph that the bipartite domination number equals the domination number if the graph has maximum degree at most 3; and is at most half the order if the graph is regular, 4-colorable, or has maximum degree at most 5.

Open access