On structural properties of trees with minimal atom-bond connectivity index

The {\em atom-bond connectivity (ABC) index} is a degree-based molecular descriptor, that found chemical applications. It is well known that among all connected graphs, the graphs with minimal ABC index are trees. A complete characterization of trees with minimal $ABC$ index is still an open problem. In this paper, we present new structural properties of trees with minimal ABC index. Our main results reveal that trees with minimal ABC index do not contain so-called {\em $B_k$-branches}, with $k \geq 5$, and that they do not have more than four $B_4$-branches

A lower bound on the orbit growth of a regular self-map of affine space

We show that if $f : \mathbb{A}_{\bar{\mathbb{Q}}}^r \to \mathbb{A}_{\bar{\mathbb{Q}}}^r$ is a regular self-map and $P \in \mathbb{A}^r(\bar{\mathbb{Q}})$ has $\limsup_{n \in \mathbb{N}} \frac{\log{h_{\mathrm{aff}}(f^nP)}}{\log{n}} < 1/r$, where $h_{\textrm{aff}}$ is the affine Weil height, then $\mathbb{N}$ partitions into a finite set and finitely many full arithmetic progressions, on each of which the coordinates of $f^nP$ are polynomials in $n$. In particular, if $(f^nP)_{n \in \mathbb{N}}$ is a Zariski-dense orbit, then either $n = 1$ and $f$ is of the shape $t \mapsto \zeta t + c$, $\zeta \in \mu_{\infty}$, or else $\limsup_{n \in \mathbb{N}} \frac{\log{h_{\mathrm{aff}}(f^nP)}}{\log{n}} \geq 1/r$. This inequality is the exponential improvement of the trivial lower bound obtained from counting the points of bounded height in $\mathbb{A}^r(K)$

Exploring the nuances in the relationship "culture-strategy" for the business world

The current article explores interesting, significant and recently identified nuances in the relationship "culture-strategy". The shared views of leading scholars at the University of National and World Economy in relation with the essence, direction, structure, role and hierarchy of "culture-strategy" relation are defined as a starting point of the analysis. The research emphasis is directed on recent developments in interpreting the observed realizations of the aforementioned link among the community of international scholars and consultants, publishing in selected electronic scientific databases. In this way a contemporary notion of the nature of "culture-strategy" relationship for the entities from the world of business is outlined

A Second Order Approximation for the Caputo Fractional Derivative

When $0<\alpha<1$, the approximation for the Caputo derivative $$y^{(\alpha)}(x) = \frac{1}{\Gamma(2-\alpha)h^\alpha}\sum_{k=0}^n \sigma_k^{(\alpha)} y(x-kh)+O\bigl(h^{2-\alpha}\bigr),$$ where $\sigma_0^{(\alpha)} = 1, \sigma_n^{(\alpha)} = (n-1)^{1-a}-n^{1-a}$ and $$\sigma_k^{(\alpha)} = (k-1)^{1-\alpha}-2k^{1-a}+(k+1)^{1-\alpha},\quad (k=1...,n-1),$$ has accuracy $O\bigl(h^{2-\alpha}\bigr)$. We use the expansion of $\sum_{k=0}^n k^\alpha$ to determine an approximation for the fractional integral of order $2-\alpha$ and the second order approximation for the Caputo derivative $$y^{(\alpha)}(x) = \frac{1}{\Gamma(2-\alpha)h^\alpha}\sum_{k=0}^n \delta_k^{(\alpha)} y(x-kh)+O\bigl(h^{2}\bigr),$$ where $\delta_k^{(\alpha)} = \sigma_k^{(\alpha)}$ for $2\leq k\leq n$, $$\delta_0^{(\alpha)} = \sigma_0^{(\alpha)}-\zeta(\alpha-1), \delta_1^{(\alpha)} = \sigma_1^{(\alpha)}+2\zeta(\alpha-1),\delta_2^{(\alpha)} = \sigma_2^{(\alpha)}-\zeta(\alpha-1),$$ and $\zeta(s)$ is the Riemann zeta function. The numerical solutions of the fractional relaxation and subdiffusion equations are computed

Efficient computation of trees with minimal atom-bond connectivity index

The {\em atom-bond connectivity (ABC) index} is one of the recently most investigated degree-based molecular structure descriptors, that have applications in chemistry. For a graph $G$, the ABC index is defined as $\sum_{uv\in E(G)}\sqrt{\frac{(d(u) +d(v)-2)}{d(u)d(v)}}$, where $d(u)$ is the degree of vertex $u$ in $G$ and $E(G)$ is the set of edges of $G$. Despite many attempts in the last few years, it is still an open problem to characterize trees with minimal $ABC$ index. In this paper, we present an efficient approach of computing trees with minimal ABC index, by considering the degree sequences of trees and some known properties of the graphs with minimal $ABC$ index. The obtained results disprove some existing conjectures end suggest new ones to be set

On structural properties of trees with minimal atom-bond connectivity index IV: Solving a conjecture about the pendent paths of length three

The atom-bond connectivity (ABC) index is one of the most investigated degree-based molecular structure descriptors with a variety of chemical applications. It is known that among all connected graphs, the trees minimize the ABC index. However, a full characterization of trees with a minimal ABC index is still an open problem. By now, one of the proved properties is that a tree with a minimal ABC index may have, at most, one pendent path of length $3$, with the conjecture that it cannot be a case if the order of a tree is larger than $1178$. Here, we provide an affirmative answer of a strengthened version of that conjecture, showing that a tree with minimal ABC index cannot contain a pendent path of length $3$ if its order is larger than $415$

Geert Hofstede et al's set of national cultural dimensions - popularity and criticisms

This article outlines different stages in development of the national culture model, created by Geert Hofstede and his affiliates. This paper reveals and synthesizes the contemporary review of the application spheres of this framework. Numerous applications of the dimensions set are used as a source of identifying significant critiques, concerning different aspects in model's operation. These critiques are classified and their underlying reasons are also outlined by means of a fishbone diagram.Comment: available at: http://www.unwe.bg/uploads/Alternatives/3_Dimitrov.pd

An example of rapid evolution of complex limit cycles

In the current article we study complex cycles of higher multiplicity in a specific polynomial family of holomorphic foliations in the complex plane. The family in question is a perturbation of an exact polynomial one-form giving rise to a foliation by Riemann surfaces. In this setting, a complex cycle is defined as a nontrivial element of the fundamental group of a leaf from the foliation. In addition to that, we introduce the notion of a multi-fold cycle and show that in our example there exists a limit cycle of any multiplicity. Furthermore, such a cycle gives rise to a one-parameter family of cycles continuously depending on the perturbation parameter. As the parameter decreases in absolute value, the cycles from the continuous family escape from a very large subdomain of the complex plane.Comment: 27 pages, submitted to "Discrete and Continuous Dynamical Systems" - Series

Critical review of models, containing cultural levels beyond the organizational one

The current article traces back the scientific interest to cultural levels across the organization at the University of National and World Economy, and especially in the series of Economic Alternatives - an official scientific magazine, issued by this Institution. Further, a wider and critical review of international achievements in this field is performed, revealing diverse analysis perspectives with respect to cultural levels. Also, a useful model of exploring and teaching the cultural levels beyond the organization is proposed. Keywords: globalization, national culture, organization culture, cultural levels, cultural economics. JEL: M14, Z10

Silverman's conjecture for additive polynomial mappings

Let $F : \mathrm{End}_{\mathbb{F_p}}(\mathbb{G}_{a/K}^d)$ be an additive polynomial mapping over a global function field $K/\mathbb{F}_q$, and let $P \in \mathbb{G}_a^d(K)$. Following Silverman, consider $\delta := \lim_{n \in \mathbb{N}} (\deg{F^{n}})^{1/n}$ the dynamic degree of $F$ and $\alpha(P) := \limsup_{n \in \mathbb{N}} h_K(F^{n}P)^{1/n}$ the arithmetic degree of $F$ at $P$. We have $\alpha(P) \leq \delta$, and extending a conjecture of Silverman from the number field case, it is expected that equality holds if the orbit of $P$ is Zariski-dense. We prove a weaker form of this conjecture: if $\delta > 1$ and the orbit of $P$ is Zariski-dense, then also $\alpha(P) > 1$. We obtain furthermore a more precise result concerning the growth along the orbit of $P$ of the heights of the individual coordinates, and formulate a few related open problems motivated by our results, including a generalization "with moving targets" of Faltings's theorem back in the number field case