83 research outputs found
Discretization of asymptotic line parametrizations using hyperboloid patches
Two-dimensional affine A-nets in 3-space are quadrilateral meshes that
discretize surfaces parametrized along asymptotic lines. The characterizing
property of A-nets is planarity of vertex stars, so for generic A-nets the
elementary quadrilaterals are skew. We classify the simply connected affine
A-nets that can be extended to continuously differentiable surfaces by gluing
hyperboloid surface patches into the skew quadrilaterals. The resulting
surfaces are called "hyperbolic nets" and are a novel piecewise smooth
discretization of surfaces parametrized along asymptotic lines. It turns out
that a simply connected affine A-net has to satisfy one combinatorial and one
geometric condition to be extendable - all vertices have to be of even degree
and all quadrilateral strips have to be "equi-twisted". Furthermore, if an
A-net can be extended to a hyperbolic net, then there exists a 1-parameter
family of such C^1-surfaces. It is briefly explained how the generation of
hyperbolic nets can be implemented on a computer. The article uses the
projective model of Pluecker geometry to describe A-nets and hyperboloids.Comment: 27 pages, 17 figure
MONITORIZAĂĂO DE MICROALGAS PLANCTĂNICAS POTENCIALMENTE TĂXICAS NA ĂREA DE MARICULTURA DA ENSEADA DE ARMAĂĂO DE ITAPOCOROY - PENHA - SC
This paper is a descriptive synthesis of approximately 17 months of phytoplankton sampling in the shellfish culture area of Enseada de Armação do Itapocoroy (Penha - Santa Catarina - Brazil). The goal of this program was to know the local phytoplankton composition, specially the toxic and potentially toxic ones; to verify the characteristics of water masses associated to the different phytoplankton assemblies and to monitor the occurrence of blooms of toxic or potentially toxic species, in order to prevent human intoxication by ingestion of contaminated shellfish. The results have indicated the occurrence of seasonal patterns in species succession. Potential producers of diarrhetic toxins tend to occur in winter and spring. From late spring to late summer the occurrence of Trichodesmium spp. indicate the possible presence of cyanobacteria toxins. Alexandrium fraterculus - a potential producer of paralytic toxin - has ocurred only in low cell densities and mainly in winter.O presente trabalho trata-se de uma sĂntese de aproximadamente 17 meses de amostragens de fitoplĂąncton na ĂĄrea de maricultura da Enseada de Armação do Itapocoroy, municĂpio de Penha, Santa Catarina. Os objetivos foram conhecer as principais espĂ©cies de microalgas planctĂŽnicas ocorrentes no local, especialmente as espĂ©cies tĂłxicas ou potencialmente tĂłxicas; verificar as caracterĂsticas das massas de ĂĄgua associadas Ă s diferentes espĂ©cies ou assemblĂ©ias de microalgas (salinidade, temperatura e transparĂȘncia) e monitorar a ocorrĂȘncia de densidades elevadas de espĂ©cies tĂłxicas ou potencialmente tĂłxicas para prevenir possĂveis intoxicaçÔes pela ingestĂŁo de moluscos com acĂșmulo de ficotoxinas. Os resultados indicam a ocorrĂȘncia de padrĂ”es sazonais de sucessĂŁo de espĂ©cies. EspĂ©cies potencialmente produtoras de toxinas diarrĂ©icas e amnĂ©sicas tendem a ocorrer nos meses de inverno e primavera. Entre o final da primavera e durante o verĂŁo a ocorrĂȘncia de Trichodesmium spp. indica possibilidade de toxinas de cianobactĂ©rias. Alexandrium fraterculus - um potencial produtor de toxina paralisante - ocorreu em pequenas densidades e principalmente no inverno
Characterizing the multi-dimensional reaction dynamics of dihalomethanes using XUV-induced Coulomb explosion imaging
Site-selective probing of iodine 4d orbitals at 13.1Â nm was used to characterize the photolysis of CH2I2 and CH2BrI initiated at 202.5Â nm. Time-dependent fragment ion momenta were recorded using Coulomb explosion imaging mass spectrometry and used to determine the structural dynamics of the dissociating molecules. Correlations between these fragment momenta, as well as the onset times of electron transfer reactions between them, indicate that each molecule can undergo neutral three-body photolysis. For CH2I2, the structural evolution of the neutral molecule was simultaneously characterized along the C-I and I-C-I coordinates, demonstrating the sensitivity of these measurements to nuclear motion along multiple degrees of freedom
Marine Heatwaves, Sewage and Eutrophication Combine to Trigger Deoxygenation and Biodiversity Loss: A SW Atlantic Case Study
Marine heatwaves (MHWs) are a major concern worldwide due to their increasing impacts in recent years, and these extreme events may trigger deoxygenation of coastal waters affected by sewage and eutrophication. Here we investigate the combined effects of MHWs and nutrient enrichment on the water quality and biodiversity of the Bay of Santa Catarina Island (Brazil). We used historical (1994â2020) sea surface temperature data from satellites and in situ physical, chemical and biological parameters to assess temporal trends. Oxygen levels have been decreasing whilst phosphorus levels have been increasing in the bay. During the austral summer of 2020 a regional sea surface heatwave was detected by satellite, lasting for 9 days and coinciding with our research cruise. During this period, seawater temperatures reached 29.8°C and anoxia was detected for the first time in the bay. A decrease in macrobenthic and phytoplankton community richness correlated with decreases in oxygen both through time and towards more urbanized areas. Overall, poor wastewater treatment is a key stressor that combined with MHWs to degrade coastal waters. Mitigation strategies are needed to minimize the impact of MHWs, including improved sewage treatment, restoration and conservation of wetlands and the use of nature-based technologies to promote coastal ecosystem recovery.</jats:p
Catastrophic shifts in the aquatic primary production revealed by a small low-flow section of tropical downstream after dredging
Variação temporal do fitoplĂąncton em trĂȘs praias urbanas do litoral sul do estado de Pernambuco, Nordeste do Brasil
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