Discrete CMC surfaces in R^3 and discrete minimal surfaces in S^3. A discrete Lawson correspondence

The main result of this paper is a discrete Lawson correspondence between discrete CMC surfaces in R^3 and discrete minimal surfaces in S^3. This is a correspondence between two discrete isothermic surfaces. We show that this correspondence is an isometry in the following sense: it preserves the metric coefficients introduced previously by Bobenko and Suris for isothermic nets. Exactly as in the smooth case, this is a correspondence between nets with the same Lax matrices, and the immersion formulas also coincide with the smooth case.Comment: 13 page

Cyclic and ruled Lagrangian surfaces in complex Euclidean space

We study those Lagrangian surfaces in complex Euclidean space which are foliated by circles or by straight lines. The former, which we call cyclic, come in three types, each one being described by means of, respectively, a planar curve, a Legendrian curve of the 3-sphere or a Legendrian curve of the anti de Sitter 3-space. We also describe ruled Lagrangian surfaces. Finally we characterize those cyclic and ruled Lagrangian surfaces which are solutions to the self-similar equation of the Mean Curvature Flow. Finally, we give a partial result in the case of Hamiltonian stationary cyclic surfaces

Exploring the surface properties of Transneptunian Objects and Centaurs with polarimetric FORS1/VLT observations

Polarization is a powerful remote-sensing method to investigate solar system bodies. It is an especially sensitive diagnostic tool to reveal physical properties of the bodies whose observational characteristics are governed by small scatterers (dust, regolith surfaces). For these objects, at small phase angles, a negative polarization is observed, i.e., the electric vector E oscillates predominantly in the scattering plane, contrary to what is typical for rather smooth homogeneous surfaces. The behavior of negative polarization with phase angle depends on the size, composition and packing of the scatterers. These characteristics can be unveiled by modelling the light scattering by the dust or regolith in terms of the coherent backscattering mechanism. We have investigated the surface properties of TNOs and Centaurs by means of polarimetric observations with FORS1 of the ESO VLT. TNOs Ixion and Quaoar, and Centaur Chiron show a negative polarization surge. The Centaur Chiron has the deepest polarization minimum (-1.5 - 1.4%). The two TNOs show differing polarization curves: for Ixion, the negative polarization increases rapidly with phase; for Quaoar, the polarization is relatively small (~ -0.6%), and nearly constant at the observed phase angles. For all three objects, modelling results suggest that the surface contains an areal mixture of at least two components with different single-scatterer albedos and photon mean-free paths.Comment: 11 pages, 7 postscript figures, accepted by A&A; astro-ph abstract has been replaced with a more complete on

Desmatamento no bioma Pantanal até o ano 2002: relações com a fitofisionomia e limites municipais.

O objetivo deste trabalho é mapear e quantificar a área desmatada no Bioma Pantanal ocorrida até o ano de 2002, relacionando-a às principais classes fisionômicas de vegetação e aos municípios formadores do Pantanal

Análise do desmatamento no bioma Pantanal até o ano de 2002.

O objetivo deste trabalho é mapear e quantificar a área desmaiada no Bioma Pantanal ocorrida até o ano de 2002, relacionando-a às principais classes fisionómicas de vegetação e aos municípios formadores do Pantanal. O Bioma Pantanal situa-se na região Centro-Oeste, inserido na bacia hidrográfica do Alto rio Paraguai (BAP), que por sua vez está inserida na bacia do Prata. Para compor a área do Pantanal foram necessárias 16 imagens de satélite Landsat-ETM+ e 20 cartas topográficas na escala de 1:250.000. Inicialmente foi elaborado um mosaico do Pantanal composto pelas 16 imagens nas bandas 3, 4 e 5 utilizando o software Envi-4.0. Em seguida foi realizada uma segmentação utilizando-se o software SPRING. Após esse procedimento a área do Bioma Pantanal foi recortada para cada uma das 20 cartas topográficas na escala de 1:250000, dentro dos limites definidos pelo IBGE. O processo de interpretação do desmatamento foi realizado com ampliações da imagem na tela do computador, utilizando o SIG SPRING, o qual foi efetuado após os procedimentos de edição das cartas para a realização de limpeza e generalização dos polígonos de acordo com os temas a serem classificados. Adotou-se o Sistema Fisionômico-ecológico para classificação da vegetação, acrescido de novas informações, quando necessário. Na interpretação das imagens foram considerados os elementos textura, cor, padrão, forma e localização (distribuição geográfica) e os levantamentos efetuados durante os trabalhos de campo na região do Pantanal. Os mapas de desmatamento foram gerados no sistema de projeção cartográfica UTM (Universal Transversa de Mercator), com Datum SAD69 (South América Datum). O erro admitido para o georreferenciamento das imagens de satélite ficou dentro da precisão do erro cartográfico (PEC) admitido para cartas na escala de 1:250.000, que é de 125 metros. A menor área mapeada foi em tomo de 40 ha.Geopantanal 2006

Heart failure and the risk of stroke: the Rotterdam Study

Patients with heart failure used to have an increased risk of stroke, but this may have changed with current treatment regimens. We assessed the association between heart failure and the risk of stroke in a population-based cohort that was followed since 1990. The study uses the cohort of the Rotterdam Study and is based on 7,546 participants who at baseline (1990–1993) were aged 55 years or over and free from stroke. The associations between heart failure and risk of stroke were assessed using time-dependent Cox proportional hazards models, adjusted for cardiovascular risk factors (smoking, diabetes mellitus, BMI, ankle brachial index, blood pressure, atrial fibrillation, myocardial infarction and relevant medication). At baseline, 233 participants had heart failure. During an average follow-up time of 9.7 years, 1,014 persons developed heart failure, and 827 strokes (470 ischemic, 75 hemorrhagic, 282 unclassified) occurred. The risk of ischemic stroke was more than five-fold increased in the first month after diagnosis of heart failure (age and sex adjusted HR 5.79, 95% CI 2.15–15.62), but attenuated over time (age and sex adjusted HR 3.50 [95% CI 1.96–6.25] after 1–6 months and 0.83 [95% CI 0.53–1.29] after 0.5–6 years). Additional adjustment for cardiovascular risk factors only marginally attenuated these risks. In conclusion, the risk of ischemic stroke is strongly increased shortly after the diagnosis of heart failure but returns to normal within 6 months after onset of heart failure