Hyperbolic towers and independent generic sets in the theory of free groups

We use hyperbolic towers to answer some model theoretic questions around the generic type in the theory of free groups. We show that all the finitely generated models of this theory realize the generic type $p_0$, but that there is a finitely generated model which omits $p_0^{(2)}$. We exhibit a finitely generated model in which there are two maximal independent sets of realizations of the generic type which have different cardinalities. We also show that a free product of homogeneous groups is not necessarily homogeneous.Comment: to appear in Proceedings of the conference "Recent developments in Model Theory", Notre Dame Journal of Formal Logi

Homogeneity in the free group

We show that any non abelian free group \F is strongly $\aleph_0$-homogeneous, i.e. that finite tuples of elements which satisfy the same first-order properties are in the same orbit under \Aut(\F). We give a characterization of elements in finitely generated groups which have the same first-order properties as a primitive element of the free group. We deduce as a consequence that most hyperbolic surface groups are not $\aleph_0$-homogeneous.Comment: 26 page

Higher order Hamiltonian fluid reduction of Vlasov equation

From the Hamiltonian structure of the Vlasov equation, we build a Hamiltonian model for the first three moments of the Vlasov distribution function, namely, the density, the momentum density and the specific internal energy. We derive the Poisson bracket of this model from the Poisson bracket of the Vlasov equation, and we discuss the associated Casimir invariants

Hamiltonian closures for fluid models with four moments by dimensional analysis

Fluid reductions of the Vlasov-Amp{\`e}re equations that preserve the Hamiltonian structure of the parent kinetic model are investigated. Hamiltonian closures using the first four moments of the Vlasov distribution are obtained, and all closures provided by a dimensional analysis procedure for satisfying the Jacobi identity are identified. Two Hamiltonian models emerge, for which the explicit closures are given, along with their Poisson brackets and Casimir invariants

Estudo da fotodegradação de pireno e fenantreno

TCC (graduação) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Curso de Química.Devido às várias fontes de contaminação e aos riscos que os HPA trazem à saúde humana foi realizado este trabalho com o intuito de avaliar a cinética de degradação dos HPA (pireno e fenantreno), em água, por meio de processos oxidativos avançados. Os processos oxidativos avançados utilizados para a degradação das amostras foram: H2O2, UV/H2O2 e fotólise direta com UV. Foram investigadas as variáveis pH e concentração de peróxido de hidrogênio. Para a irradiação, foi utilizada lâmpada de vapor de Hg com potência de 36 W em câmara de irradiação. Ambas as amostras foram irradiadas por um período de 60 min, sendo coletadas amostras para análise por fluorescência em intervalos de 10 min. O processo utilizando apenas H2O2 como oxidante mostrou ser pouco eficiente na degradação das amostras de pireno e fenantreno com valores inferiores a 15 % e 60% de degradação, respectivamente. O decaimento da intensidade de fluorescência foi maior no processo de fotólise direta para as duas amostras de HPA. A amostra de pireno apresentou degradação de 99% e a amostra de fenantreno, 96% de degradação. No processo UV/H2O2, o decaimento na intensidade de fluorescência foi mais rápido para a amostra de pireno com um kobs = 46 x 10-2 min-1. Para a amostra de fenantreno foi observado um kobs = 14 x 10-2 min-1, não muito diferente do valor encontrado para essa amostra na fotólise direta (kobs = 13 x 10-2 min-1)

Return to the (managed) wild: Interpreting human settlements as “designer ecosystems”

Human civilizations stand out, recently, among other biotic communities for their instigation of global systems transformations that have been rapid, extensive, and enduring (Steffen, Crutzen, & McNeill, 2007). By virtue of cumulative, collaborative efforts, facilitated through the symbolic codification of knowledge, and stacked across generations and continents, the complexity of human cultures only continues to intensify (Christian, 2004): “Cultural change operates by mechanisms that can validate a general and driven trend to technological progress — so very different from the minor and passive trend that Darwinian processes permit in the realm of natural evolution” (Gould, 1996, p.223). By this means, the species has become a globally dominant presence, the impact of its activities echoed across terrestrial, marine, and atmospheric systems (Steffen et al., 2007; Hobbs, Higgs, & Hall, 2013). Human settlements might be described as a magnet for, container to, and emblematic expression of human cultural systems. They are socially constructed systems that interface between the human species and the biosphere, directly coordinating and mediating the debated nature-culture relationship. If one embraces Lovelock’s (1979) Gaia hypothesis, whereby the planet is considered to be an interdependent, self-regulating unit, or, McDonough and Braungart’s (2013) upcycle approach, whereby human creative pursuits feed reciprocally into biosphere cycles, then perhaps one can find a place for this domesticated species within the ‘natural order’ of things: “Our human role is to deepen our consciousness in resonance with the dynamics of the fourteen-billion-year creative event in which we find ourselves” (Swimme & Tucker, 2011, p.116). Deeply embedding human activities within the cycles of inhabited ecosystems, calls for designers and ecologists, together, to consider the notion of hybridization: “… ‘urbanization is not merely a … distancing of human life from nature, but rather a process by which new and more complex relationships are created’. The challenge of social-ecological integration, however, is one that requires closer articulation, both philosophically and schematically. For example, it is unclear what an application of philosophies such as Leopold’s (1949) land ethic or Rifkin’s (2009) biosphere consciousness should mean, on practical terms, for highly engineered, urban systems. Simply accepting human activity and its resulting technologies as an extension of nature risks dismissing environmental accountability (White, 2003). No doubt, achieving a state of complete integration with ecosystem processes would entail nothing short of a long-term unwinding of rigid infrastructural and social regimes, through a phased, scaled, and community engaged process of renewal. Thus, the arguments for pursuing this direction as part of a long-range sustainability strategy, and the means by which it might be possible to do so within the current social-technological landscape, are worth examination