Projectile motion: the "coming and going" phenomenon

An interesting phenomenon that occurs in projectile motion, the "coming and going", is analyzed considering linear air resistance force. By performing both approximate and numerical analysis, it is showed how a determined critical angle and an interesting geometrical property of projectiles can change due to variation on the linear air resistance coefficient

A Growth model for DNA evolution

A simple growth model for DNA evolution is introduced which is analytically solvable and reproduces the observed statistical behavior of real sequences.Comment: To be published in Europhysics Letter

Nonuniversality of weak synchronization in chaotic systems

We show that the separate properties of weak synchronization (WS) and strong synchronization (SS), reported recently by Pyragas [K. Pyragas, Phys. Rev. E, 54, R4508 (1996)], in unidirectionally coupled chaotic systems, are not generally distinct properties of such systems. In particular, we find analytically for the tent map and numerically for some parameters of the circle map that the transition to WS and SS coincide.Comment: 3 pages (Revtex) and 3 figures (postscript) To appear in Phys. Rev. E (Rapid Communications

Chaos and Synchronized Chaos in an Earthquake Model

We show that chaos is present in the symmetric two-block Burridge-Knopoff model for earthquakes. This is in contrast with previous numerical studies, but in agreement with experimental results. In this system, we have found a rich dynamical behavior with an unusual route to chaos. In the three-block system, we see the appearance of synchronized chaos, showing that this concept can have potential applications in the field of seismology.Comment: To appear in Physical Review Letters (13 pages, 6 figures

Self-Similarity of Friction Laws

The change of the friction law from a mesoscopic level to a macroscopic level is studied in the spring-block models introduced by Burridge-Knopoff. We find that the Coulomb law is always scale invariant. Other proposed scaling laws are only invariant under certain conditions.}Comment: Plain TEX. Figures not include

The strategic relevance of business relationships: a preliminary assessment

The ubiquitous contention within the Industrial Networks literature - that business relationships are one of the firm´s most important resources - has not been, in our viewpoint, thoroughly explored. Hence we argue that the ‘Resource-based View of the Firm’ (‘RBV’) may complement the network-based reasoning on the strategic relevance of business relationships. A theoretical framework is proposed – a competence-based view of the firm – which solves RBV´s terminological and inconsistency problems and, more importantly, assures compatibility with the network perspective´s assumptions. The possibility of cross-fertilizing the Industrial Networks and RBV theories seems not only real, but also conceptually profitable for both theoretical fields.Business Relationships, Industrial Networks, Resource-Based View of the Firm, Competence-Based View of the Firm

Um modelo complexo do ato educativo

O currículo, enquanto área de estudo e investigação, tem uma história relativamente recente, como todos sabemos. A sua afirmação identitária deveu-se ao facto de ter um objecto de estudo bem específico e delimitado, que não se confunde nem com a psicologia, nem com a sociologia, estas sim, ciências autónomas de longa data. No entanto, uma delimitação estrita das fronteiras do currículo, relativamente a outras áreas científicas que com ela interagem, pode levar a um seu esvaziamento conceptual, transformando-a, afinal, num mero enunciado de intenções e regras de bem ensinar e avaliar que, por serem normativas e prescritivas, a despojariam do seu estatuto científico. Se é certo que o currículo não se consegue dissociar do poder que o determina (seja ele do Estado, da Região, da Escola ou da Turma – estes últimos se pensarmos nos actuais Projectos Educativos e Curriculares de Escola e de Turma), ele só ganha sentido na sua relação directa com a prática, ou seja, o currículo, para ser currículo, necessita de ser desenvolvimento curricular. Primeiro, entendido ao nível da interpretação e análise crítica do professor sobre o que o poder pretende que ele ensine, e depois na relação com a sua própria operacionalização curricular, ou seja, o acto educativo. Esta reflexão visa perspectivar as diversas leituras curriculares, desde a perspectiva simplista, unidimensional, passando pela visão sequencialmente organizada, até desembocar numa abordagem necessariamente complexa do acto educativo

O direito à educação: entre o discurso e a prática

As preocupações com a promoção do sucesso educativo e a prevenção do abandono escolar partem do princípio de que todos se encontram já dentro do sistema. Ora o que a minha comunicação pretende demonstrar é que ainda antes dessa fase se coloca a questão do acesso à educação. Numa perspectiva comparativa, e a um nível macro, ressaltaremos as contradições entre o discurso enunciado e a realidade existente, direccionando o nosso olhar para Portugal, a partir de indicadores ao nível das grandes organizações internacionais, como a ONU e a OCDE

Site-dependent hydrogenation on graphdiyne

Graphene is one of the most important materials in science today due to its unique and remarkable electronic, thermal and mechanical properties. However in its pristine state, graphene is a gapless semiconductor, what limits its use in transistor electronics. In part due to the revolution created by graphene in materials science, there is a renewed interest in other possible graphene-like two-dimensional structures. Examples of these structures are graphynes and graphdiynes, which are two-dimensional structures, composed of carbon atoms in sp2 and sp-hybridized states. Graphdiynes (benzenoid rings connecting two acetylenic groups) were recently synthesized and some of them are intrinsically nonzero gap systems. These systems can be easily hydrogenated and the relative level of hydrogenation can be used to tune the band gap values. We have investigated, using fully reactive molecular dynamics (ReaxFF), the structural and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes. Our results showed that the hydrogen bindings have different atom incorporation rates and that the hydrogenation patterns change in time in a very complex way. The formation of correlated domains reported to hydrogenated graphene is no longer observed in graphdiyne cases.Comment: Submitted to Carbo