arXiv subjects
Publications and source records attributed to Abílio Lemos.
Let $\mathbb{F}_{q}$ be the finite field with $q$ elements. In this paper we will describe the dynamics of the map $f(X)=X(X^{q-1}-c)^{q+1},$ with $c\in\mathbb{F}_{q}^{\ast},$ over the finite field $\mathbb{F}_{q^2}$.
Let $\mathbb{F}_{q^n}$ be a finite field with $q^n$ elements. For a positive divisor $r$ of $q^n-1$, the element $α\in \mathbb{F}_{q^n}^*$ is called \textit{$r$-primitive} if its multiplicative order is $(q^n-1)/r$. Also, for a non-negative integer $k$, the element $α\in \mathbb{F}_{q^n}$ is \textit{$k$-normal} over $\mathbb{F}_q$ if $\gcd(αx^{n-1}+ α^q x^{n-2} + \ldots + α^{q^{n-2}}x + α^{q^{n-1}} , x^n-1)$ in $\mathbb{F}_{q^n}[x]$ has degree $k$. In this paper we discuss the existence of elements in arithmetic progressions $\{α, α+β, α+2β, \ldotsα+(m-1)β\} \subset \mathbb{F}_{q^n}$ with $α+(i-1)β$ being $r_i$-primitive and at least one of the elements in the arithmetic progression being $k$-normal over $\mathbb{F}_q$. We obtain asymptotic results for general $k, r_1, \dots, r_m$ and concrete results when $k = r_i = 2$ for $i \in \{1, \dots, m\}$.
In this paper, we define the constant $D(φ, p)$, an analogue for the Davenport constant, for sequences on the finite field $\mathbb{F}_p$, defined via quadratic symmetric polynomials. Next, we state a series of results presenting either the exact value of $D(φ, p)$, or lower and upper bounds for this constant.
In this paper, we explore the existence of $m$-terms arithmetic progressions in $\mathbb{F}_{q^n}$ with a given common difference whose terms are all primitive elements, and at least one of them is normal. We obtain asymptotic results for $m \ge 4$ and concrete results for $m \in \{2,3\}$, where the complete list of exceptions when the common difference belongs to $\mathbb{F}_{q}^*$ is obtained. The proofs combine character sums, sieve estimates, and computational arguments using the software SageMath.
Let $C_2$ be the cyclic group of order $2$ and $D_{2n}$ be the dihedral group of order $2n$, where $n$ is even. In this paper, we provide the exact values of some zero-sum constants over $D_{2n} \times C_2$, namely small Davenport constant, Gao constant, $η$-constant and Erd\H os-Ginzburg-Ziv constant. As a consequence, we prove the Gao's and Zhuang-Gao's Conjectures for this group. These are the first concrete results on zero-sum problems for a family of non-abelian groups of rank greater than $2$.
Let $(M_n)_{n\geq0}$ be the Mersenne sequence defined by $M_n=2^n-1$. Let $ω(n)$ be the number of distinct prime divisors of $n.$ In this short note, we present a description of the Mersenne numbers satisfying $ω(M_n)\leq3$. Moreover, we prove that the inequality, given $ε>0$, $ω(M_n)> 2^{(1-ε)\log\log n} -3 $ holds for almost all positive integers $n$. Besides, we present the integer solutions $(m,n,a)$ of the equation $M_m+M_n=2p^a$ with $m,n\geq2$, $p$ an odd prime number and $a$ a positive integer.
Suppose $G$ is a finite abelian group and $S=g_{1}\cdots g_{l}$ is a sequence of elements in $G$. For any element $g$ of $G$ and $A\subseteq\mathbb{Z}\backslash\left\{ 0\right\} $, let $N_{A,g}(S)$ denote the number of subsequences $T=\prod_{i\in I}g_{i}$ of $S$ such that $\sum_{i\in I}a_{i}g_{i}=g$ , where $I\subseteq\left\{ 1,\ldots,l\right\}$ and $a_{i}\in A$. The purpose of this paper is to investigate the lower bound for $N_{A,0}(S)$. In particular, we prove that $N_{A,0}(S)\geq2^{|S|-D_{A}(G)+1}$, where $D_{A}(G)$ is the smallest positive integer $l$ such that every sequence over $G$ of length at least $l$ has a nonempty $A$-zero-sum subsequence. We also characterize the structures of the extremal sequences for which the equality holds for some groups.
Let $G$ be a finite additive abelian group with exponent $n$ and $S=g_{1}\cdots g_{t}$ be a sequence of elements in $G$. For any element $g$ of $G$ and $A\subseteq\{1,2,\ldots,n-1\}$, let $N_{A,g}(S)$ denote the number of subsequences $T=\prod_{i\in I}g_{i}$ of $S$ such that $\sum_{i\in I}a_{i}g_{i}=g$ , where $I\subseteq\left\{ 1,\ldots,t\right\} $ and $a_{i}\in A$. In this paper, we prove that $N_{A,0}(S)\geq2^{|S|-D_{A}(G)+1}$, when $A=\left\{ 1,\ldots,n-1\right\} $, where $D_{A}(G)$ is the smallest positive integer $l$, such that every sequence $S$ over $G$ of length at least $l$ has nonempty subsequence $T=\prod_{i\in I}g_{i}$ such that $\sum_{i\in I}a_{i}g_{i}=0$, $I\subseteq\left\{ 1,\ldots,t\right\} $ and $a_{i}\in A$. Moreover, we classify the sequences such that $N_{A,0}(S)=2^{|S|-D_{A}(G)+1}$, where the exponent of $G$ is an odd number.
Let $G$ be a finite abelian group of exponent $n$, written additively, and let $A$ be a subset of $\mathbb{Z}$. The constant $s_A(G)$ is defined as the smallest integer $\ell$ such that any sequence over $G$ of length at least $\ell$ has an $A$-weighted zero-sum of length $n$ and $η_A(G)$ defined as the smallest integer $\ell$ such that any sequence over $G$ of length at least $\ell$ has an $A$-weighted zero-sum of length at most $n$. Here we prove that, for $α\geq β$, and $A=\left\{x\in\mathbb{N}\; : \; 1 \le a \le p^α \; \mbox{ and }\; \gcd(a, p) = 1\right \}$, we have $s_{A}(\mathbb{Z}_{p^α}\oplus \mathbb{Z}_{p^β}) = η_A(\mathbb{Z}_{p^α}\oplus \mathbb{Z}_{p^β}) + p^α-1 = p^α + α+β$ and classify all the extremal $A$-weighted zero-sum free sequences.
In this paper, we present two new results to the classical Floquet theory, which provides the Floquet multipliers for two classes of the planar periodic system. One these results provides the Floquet multipliers independently of the solution of system. To demonstrate the application of these analytical results, we consider a cholera epidemic model with phage dynamics and seasonality incorporated.
In this paper we consider Abel equation $x' = g(t)x^2+f(t)x^3$, where $f$ and $g$ are analytical functions. We proved that if the equation has a center at $x=0$, then the Moment Conditions, i. e., $m_k=\int_{-1}^1f(t)(G(t))^kdt=0,~~k=0,1,2$, is satisfied where $G(t)=\int_{-1}^tg(s)ds$. Besides, we give partial a positive answer to a conjecture proposed by Y. Lijun and T. Yun in 2001.
Abel equations of the form $x'(t)=f(t)x^3(t)+g(t)x^2(t)$, $t \in [-a,a]$, where $a>0$ is a constant, $f$ and $g$ are continuous functions, are of interest because of their close relation to planar vector fields. If $f$ and $g$ are odd functions, we prove, in this paper, that the Abel equation has a center at the origin. We also consider a class of polynomial differential equations $\dot{x} = -y+P_n(x,y)$ and $\dot{y} = x+Q_n(x,y)$, where $P_n$ and $Q_n$ are homogeneous polynomials of degree $n$. Using the results obtained for Abel's equation, we obtain a new subclass of systems having a center at the origin.
The envelope of straight lines affine normal to a plane curve C is its affine evolute; the envelope of the affine lines tangent to C is the original curve, together with the entire affine tangent line at each inflexion of C. In this paper, we consider plane curves without inflexions. We use some techniques of singularity theory to explain how the first envelope turns into the second, as the (constant) slope between the set of lines forming the envelope and the set of affine tangents to C changes from 0 to 1. In particular, we guarantee the existence of the first slope for which singularities occur. Moreover, we explain how these singularities evolve in the discriminant surface.
In this paper, we consider $D=\mathbb{Z}[θ]$, where $$θ= \sqrt{-k} \,\,\,\, \mbox{if}\;\;\;-k\not\equiv 1 \;(\mbox{mod}\;4)\,\,\,\,\mbox{or}\,\,\,\, θ=\frac{\sqrt{-k}+1}{2} \,\,\,\, \mbox{if}\;\;\;-k\equiv 1 \;(\mbox{mod}\;4),$$ $k\geq 2$ is a squarefree integer, and we proved that the number $R(y)$ of representations of a monic polynomial $f(x)\in \mathbb{Z}[θ][x]$, of degree $d\geq 1$, as a sum of two monic irreducible polynomials $g(x)$ and $h(x)$ in $\mathbb{Z}[θ][x]$, with the coefficients of $g(x)$ and $h(x)$ bounded in complex modulus by $y$, is asymptotic to $(4y)^{2d-2}$.
Let $C_n$ be the cyclic group of order $n$ and set $s_{A}(C_n^r)$ as the smallest integer $\ell$ such that every sequence $\mathcal{S}$ in $C_n^r$ of length at least $\ell$ has an $A$-zero-sum subsequence of length equal to $\exp(C_n^r)$, for $A=\{-1,1\}$. In this paper, among other things, we give estimates for $s_A(C_3^r)$, and prove that $s_A(C_{3}^{3})=9$, $s_A(C_{3}^{4})=21$ and $41\leq s_A(C_{3}^{5})\leq45$.