New Zealand Journal of Mathematics

A Robin inequality for n/phi(n)

Jean-Louis Nicolas — 2024-05-06

Let $\varphi(n)$ be the Euler function, $\sigma(n)=\sum_{d\mid n}d$ the sum of divisors function and $\gamma=0.577\ldots$ the Euler constant. In 1982, Robin proved that, under the Riemann hypothesis, $\sigma(n)/n < e^\gamma \log\log n$ holds for $n > 5040$ and that this inequality is equivalent to the Riemann hypothesis. The aim of this paper is to give a similar equivalence for $n/\varphi(n)$.

Bent-half space model problem for Lame equation with surface tension

Sri Maryani — 2024-05-06

The study of fluid flow is a very fascinating area of fluid dynamics. Fluid motion has received more and more attention in recent years and numerous researchers have looked into this topic. However, they rarely used a mathematical analysis approach to analyse fluid motion; instead, they used numerical analysis. This serves as a significant justification for the researcher's decision to study fluid flow from the perspective of mathematical analysis. In this paper, we consider the ${\mathcal R}$-boundedness of the solution operator families of the Lam\'e equation with surface tension in bent half-space model problem by taking into account the surface tension in a bounded domain of {\it N}-dimensional Euclidean space ($N \geq 2$). The motion of the model problem can be described by linearizing an equation system of a model problem. This research is a continuation of [13]. They investigated the ${\mathcal R}$-boundedness of the solution operator families in the half-space case for the model problem of the Lam\'e equation with surface tension. First of all, by using Laplace transformation we consider the resolvent of the model problem, then treat the problem in bent half-space case. By using Weis's operator-valued Fourier multiplier theorem, we know that ${\mathcal R}$-boundedness implies the maximal $L_p$-$L_q$ regularity for the initial boundary value. This regularity is an essential tool for the partial differential equation problem.

$k$-rational homotopy fixed points, $k\in \Bbb N$

Mahmoud Benkhalifa — 2024-05-06

For $k\in \Bbb N$, we introduce the notion of $k$-rational homotopy fixed points and we prove, under a certain assumption, that if $X$ is a rational elliptic space of formal dimension $n$, then $X$ admits an $(n -1)$-rational homotopy fixed point.

Distance-dependent chase-escape on trees

Saraí Hernández-Torres — 2024-05-31

We give a necessary and sufficient condition for species coexistence in a parasite-host growth process on infinite $d$-ary trees. The novelty of this work is that the spreading and death rates for hosts depend on the distance to the nearest parasite.

A note on weak w-projective modules

Refat Abdelmawla Khaled Assaad — 2024-06-11

Let $R$ be a ring. An $R$-module $M$ is a weak $w$-projective module if ${\rm Ext}_R^1(M,N)=0$ for all $N$ in the class of $GV$-torsion-free $R$-modules with the property that ${\rm Ext}^k_R(T,N)=0$ for all $w$-projective $R$-modules $T$ and all integers $k\geq1$. In this paper, we introduce and study some properties of weak $w$-projective modules. We use these modules to characterise some classical rings. For example, we will prove that a ring $R$ is a $DW$-ring if and only if every weak $w$-projective is projective; $R$ is a von Neumann regular ring if and only if every FP-projective module is weak $w$-projective if and only if every finitely presented $R$-module is weak $w$-projective; and $R$ is $w$-semi-hereditary if and only if every finite type submodule of a free module is weak $w$-projective if and only if every finitely generated ideal of $R$ is weak $w$-projective.

On the exponential Diophantine equation $x^2+p^mq^n=2y^p$

Kalyan Chakraborty — 2024-07-23

We study the exponential Diophantine equation $x^2+p^mq^n=2y^p$ in positive integers $x,y,m,n$, and odd primes $p$ and $q$ using primitive divisors of Lehmer sequences in combination with elementary number theory. We discuss the solvability of this equation.