Synchronized stationary clouds in a static fluid

The existence of stationary bound states for the hydrodynamic velocity field between two concentric cylinders is established. We argue that rotational motion, together with a trapping mechanism for the associated field, is sufficient to mitigate energy dissipation between the cylinders, thus allowing the existence of infinitely long lived modes, which we dub stationary clouds. We demonstrate the existence of such stationary clouds for sound and surface waves when the fluid is static and the internal cylinder rotates with constant angular velocity $\Omega$. These setups provide a unique opportunity for the first experimental observation of synchronized stationary clouds. As in the case of bosonic fields around rotating black holes and black hole analogues, the existence of these clouds relies on a synchronization condition between $\Omega$ and the angular phase velocity of the cloud.Comment: v2: 7 pages, 4 figures. Accepted for publication in Physics Letters

System of spheres-based multiple contractions

We propose a new class of multiple contraction operations — the system of spheres-based multiple contractions — which are a generalization of Grove’s system of spheres-based (singleton) contractions to the case of contractions by (possibly non-singleton) sets of sentences. Furthermore, we show that this new class of functions is a subclass of the class of the partial meet multiple contractions.info:eu-repo/semantics/publishedVersio

Possible worlds semantics for partial meet multiple contraction

In the logic of theory change, the standard model is AGM, proposed by Alchourrón et al. (J Symb Log 50:510–530, 1985). This paper focuses on the extension of AGM that accounts for contractions of a theory by a set of sentences instead of only by a single sentence. Hansson (Theoria 55:114–132, 1989), Fuhrmann and Hansson (J Logic Lang Inf 3:39–74, 1994) generalized Partial Meet Contraction to the case of contractions by (possibly non-singleton) sets of sentences. In this paper we present the possible worlds semantics for partial meet multiple contractions.info:eu-repo/semantics/publishedVersio

Dengue no Brasil: situação epidemiológica e contribuições para uma agenda de pesquisa

The epidemiological situation of dengue in Brazil is presented, showing the introduction and spread of vector and the different virus serotypes in Brazil. At the present time the Aedes aegypti, the vector, and 3 out of 4 existing virus serotypes (DENV-1, DENV-2 and DENV-3) are spread by virtually the entire national territory. The epidemiological picture has been characterized by recurrent epidemics, especially in large urban centers. A new characteristic in this scenario is the growth in the proportion of severe cases, particularly cases of dengue hemorrhagic fever. Existing control actions have been costly and ineffectives. In order to meet the gaps in existing knowledge, some elements for a research agenda are presented. Finally, we must recognize that problems such as dengue have their roots in the explosive form urban populations in countries such as Brazil has grown and in the conditions and lifestyles under which these people live.A situação epidemiológica da dengue no Brasil é apresentada, mostrando-se a introdução e a dispersão do vetor e dos diferentes sorotipos do vírus no Brasil. No presente momento, o Aedes aegypti, o vetor, encontra-se disseminado por praticamente todo o território nacional, bem como três dos quatro sorotipos existentes do vírus (DENV-1, DENV-2 e DENV-3). O quadro epidemiológico tem se caracterizado como epidemias recorrentes, mais visível nos grandes centro urbanos. Um elemento novo no cenário é o crescimento da proporção de casos graves, especialmente casos da febre hemorrágica da dengue. As ações de controle existentes, além de custosas, têm se mostrado inefetivas. Com vistas a preencher as insuficiências existentes no conhecimento, alguns elementos para uma agenda de pesquisa são apresentados. Finalmente, não devemos deixar de reconhecer que problemas como dengue têm suas raízes na forma explosiva como as populações urbanas em países como o Brasil têm crescido, nas condições em que essas populações vivem e nos estilos de vida que adquirem

Residual contraction

In this paper, we propose and axiomatically characterize residual contractions, a new kind of contraction operators for belief bases. We establish that the class of partial meet contractions is a strict subclass of the class of residual contractions. We identify an extra condition that may be added to the definition of residual contractions, which is such that the class of residual contractions that satisfy it coincides with the class of partial meet contrac tions. We investigate the interrelations in the sense of (strict) inclusion among the class of residual contractions and other classes of well known contraction operators for belief bases.info:eu-repo/semantics/publishedVersio

Epistemic entrenchment-based multiple contractions

In this article we present a new class of multiple contraction functions—the epistemic entrenchment-based multiple contractions—which are a generalization of the epistemic entrenchment-based contractions (Gardenfors, 1988; G ¨ ardenfors & Makinson, 1988) to the case of ¨ contractions by (possibly nonsingleton) sets of sentences and provide an axiomatic characterization for that class of functions. Moreover, we show that the class of epistemic entrenchment-based multi ple contractions coincides with the class of system of spheres-based multiple contractions introduced in Ferme & Reis (2012).info:eu-repo/semantics/publishedVersio

Two axiomatic characterizations for the system of spheres-based (and the Epistemic Entrenchment-based) multiple contractions

t In some recent works (Reis 2011, Ferme and Reis, J. Philos. Log. ´ 41, 29–52, 2012, Ferme and Reis, Rev. Symb. Log. ´ 6, 460–487, 2013) two new kinds of multiple contraction functions have been proposed, namely the system of spheres-based multiple contractions and the epistemic entrenchment-based multiple contractions, as generalizations (to the case of multiple contraction) of the well-known classes of systems of spheres-based and of epistemic entrenchment-based (singleton) contractions. Additionally, a representa tion theorem for the class of epistemic entrenchment-based multiple contraction has been proposed, and it has been shown that the two newly proposed constructions are equivalent, in the sense that a multiple contraction function is a system of spheres-based multiple contrac tion if and only if it is an epistemic entrenchment-based multiple contraction. In this paper we present two axiomatic characterizations for those multiple contraction functions which differ from the one mentioned above and, in particular, make use of some more intuitive postulates.info:eu-repo/semantics/publishedVersio

Levi and Harper identities for non-prioritized belief base change

In this paper, we investigate the relation between shielded base contraction postulates and credibility-limited (CL) base revision postulates. More precisely, we identify (i) the relation between the postulates satisfied by a shielded base contraction operator and the postulates satisfied by the CL base revision operator that is defined from it by means of the consistency-preserving Levi identity and (ii) the relation between the postulates satisfied by a CL base revision operator and the postulates satisfied by the shielded base contraction operator that is defined from it by means of the Harper identity. Furthermore, we show that the consistency-preserving Levi identity and the Harper identity establish a one-to one correspondence between the twenty classes of shielded base contractions presented in [21] and the twenty classes of credibility-limited base revisions presented in [22].info:eu-repo/semantics/publishedVersio