Search

A observação dos sinais da natureza ao longo da existência humana beneficiou a construção de saberes empíricos sobre o clima. O objetivo deste estudo é descrever aspectos sociais, caracterizar o saber local voltado à indicadores meteorológicos de previsão de precipitação a partir do conhecimento de pequenos agricultores residentes ao entorno da Reserva Biológica de Duas Bocas, município de Cariacica, estado do Espírito Santo (ES), sudeste do Brasil, localizada na Bacia Hidrográfica do Rio Duas Bocas. Foram realizadas 50 entrevistas etnográficas semiestruturadas, além da aplicação das observações participante e direta; e utilizado um diário de campo. Os agricultores são em sua maioria do sexo masculino (n=41), atuam na agricultura da região há pelo menos 40 anos e possuem baixa escolaridade com ensino fundamental incompleto principalmente. Os principais cultivos na região são banana, café e mandioca. O verão é a estação com maior produção agrícola por apresentar altas temperaturas e elevados índices pluviométricos. A maioria dos agricultores (n=41; 82%) confia na previsão etnoclimatológica derivada do conhecimento tradicional. A dinâmica atmosférica, o comportamento da fauna e os astros celestes foram os principais indicadores de chuva. O conhecimento etnoclimatológico mostra-se importante na manutenção da prática agrícola na região estudada, já que o sucesso da colheita depende deste saber local.

This paper is an improvement of previous results on concentrated Euler flows and their connection with the point vortex model. Precisely, we study the time evolution of an incompressible two dimensional Euler fluid when the initial vorticity is concentrated in N disjoint regions of diameter ɛ. We show that the evolved vorticity is concentrated in N regions of diameter d, d ≤ b ɛ^α (b independent of ɛ) for any α < 1/2. The connection is obtained as ɛ→0.

Colloidal semiconductor nanocrystals display remarkably bright, strongly size-dependent photoluminescence properties. Following photoexcitation of these materials, temporary charge carrier separation can occur where one or both charge carriers are trapped. Charge detrapping can reform the emissive state on long time scales up to seconds, causing delayed luminescence. This delayed luminescence has not yet been thoroughly explored, and appears to be closely associated with a phenomenon observed at the single particle level, i.e. photoluminescence intermittency (blinking). Here, some of our recent work on the delayed luminescence properties of nanocrystals of different chemical composition is reviewed. These results provide insight into the mechanism of carrier detrapping, and are discussed in the context of photoluminescence blinking.

We consider a one-species plasma moving in an infinite cylinder in R3, in which it is confined by means of a magnetic field diverging on the walls of the cylinder. In a recent paper [4] we have supposed that the plasma satisfies the Vlasov equation with a Yukawa mutual interaction (i.e. Coulomb at short distance and exponentially decreasing at infinity). Assuming that initially the particles have bounded velocities and are distributed according to a bounded density without any hypothesis on its decreasing at infinity, we have proved the global in time existence and uniqueness of the time evolution of the plasma and its confinement. In the present paper we extend this result to a Coulomb interaction, making on the initial density some assumption of slight decreasing on average at infinity, which however does not imply that the density belongs to any Lp space. The proof is similar, but slightly simpler.

Este artigo tem por objetivo uma análise dos cantos IX e X de Os Lusiadas, notadamente do episódio conhecido como “Ilha dos Amores”. Para tanto foram consideradas especialmente as fortes ligações de Camões com o pensamento petrarquista divulgado à época e com a filosofia de Platão, precisamente os aspectos presentes no conhecido O Banquete. A partir das aproximações feitas, mostra-se como o episódio da Insula Divina constitui em uma alegoria a possibilidade do “homem virtuoso” alcançar o Bem maior. Assim, o Amor é evidênciado como símbolo e metáfora para o caminho possível que levaria o homem ao encontro da “sabedoria” que é, nas palavras do próprio poeta, Deus. A beleza presente nas Ninfas e na Ilha mostra-se, portanto, como um raio da beleza divina e ao serem seduzidos por elas os bravos navegadores são levados ao cume da montanha, simbolizando a possibilidade de ascenção espiritual.

Photoinduced electron transfer (PET) across molecular/bulk interfaces has gained attention only recently and is still poorly understood. These interfaces offer an excellent case study, pertinent to a variety of photovoltaic systems, photo- and electrochemistry, molecular electronics, analytical detection, photography, and quantum confinement devices. They play in particular a key role in the emerging fields of third-generation photovoltaic energy converters and artificial photosynthetic systems aimed at the production of solar fuels, creating a need for a better understanding and theoretical treatment of the dynamics and mechanisms of interfacial PET processes. We aim to achieve a fundamental understanding of these phenomena by designing experiments that can be used to test and alter modern theory and computational modeling. One example illustrating recent investigations into the details of the ultrafast processes that form the basis for photoinduced charge separation at a molecular/bulk interface relevant to dye-sensitized solar cells is briefly presented here: Kinetics of interfacial PET and charge recombination processes were measured by fs and ns transient spectroscopy in a heterogeneous donor-bridge-acceptor (D-B-A) system, where D is a RuII(terpyridyl-PO3)(NCS)3 complex, B an oligo-p-phenylene bridge, and A nanocrystalline TiO2. The forward ET reaction was found to be faster than vibrational relaxation of the vibronic excited state of the donor. Instead, the back ET occurred on the ?s time scale and involved fully thermalized species. The D-A distance dependence of the electron transfer rate was studied by varying the number of p-phenylene units contained in the bridge moiety. The remarkably low damping factor ? = 0.16 Å?1 observed for the ultrafast charge injection from the dye excited state into the conduction band of TiO2 is attributed to the coupling of electron tunneling with nonequilibrium vibrations redistributed on the bridge, giving rise to polaronic transport of charges from the donor ligand to the acceptor solid oxide surface.

Nanostructured liquid|solid and solid|solid bulk heterojunctions designed for the conversion of solar energy offer ideal models for the investigation of light-induced ET dynamics at surfaces. Despite significant study of processes leading to charge generation in third-generation solar cells, a conclusive picture of the photophysics of these photovoltaic converters is still missing. More specifically searched is the link between the molecular structure of the interface and the kinetics of surface photoredox reactions. Fundamental scientific issues in this field are addressed by there search project undertaken in the frame of the NCCR MUST endeavor, an outline of whic his given here.