Shape instabilities in vesicles: a phase-field model

A phase field model for dealing with shape instabilities in fluid membrane vesicles is presented. This model takes into account the Canham-Helfrich bending energy with spontaneous curvature. A dynamic equation for the phase-field is also derived. With this model it is possible to see the vesicle shape deformation dynamically, when some external agent instabilizes the membrane, for instance, inducing an inhomogeneous spontaneous curvature. The numerical scheme used is detailed and some stationary shapes are shown together with a shape diagram for vesicles of spherical topology and no spontaneous curvature, in agreement with known results

Wood anatomy and tree growth covary in riparian ash forests along climatic and ecological gradients

Riparian ash forests subjected to seasonal drought are among the most endangered ecosystems in Europe. They are threatened by climate warming causing aridification and by land-use changes modifying river flow. To assess the impacts of these two stress factors on riparian forests, we studied radial growth and xylem anatomical traits in five narrow-leaved ash (Fraxinus angustifolia) stands across wide climatic and ecological gradients from northern Italy to southern Portugal. Radial growth rates and earlywood hydraulic diameter (Dh) were directly correlated, whilst earlywood vessel density and growth rates were inversely associated. Ash growth positively responded to precipitation. Higher and lower rates of growth increase in response to precipitation were found in dry (annual precipitation 357–750 mm, annual water balance -39 to -48 mm) and wet (annual precipitation 1030 mm, annual water balance 27 mm) sites, respectively. Wet conditions in autumn and winter of the year prior to tree-ring formation lead to larger Dh values, except in the wet site where warmer conditions from prior autumn to current spring were positively associated to wider vessels. Growth was also enhanced by a higher river flow, reflecting higher soil moisture due to elevated groundwater table levels. Peaks in river flow from late winter to early spring increased Dh in dry-continental sites. Growth and potential hydraulic conductivity in drought-prone riparian ash forests are differently impacted by climate variability and river flow depending on site and hydrological conditions. Nevertheless, covariation between radial growth and the earlywood vessel diameter was found, regardless of site specific differences. Wood production and hydraulic conductivity are coordinated through the production of large earlywood vessels which may allow reaching higher growth rates. © 2021 The Author

Aspectos econômicos da exploração de Aniba rosaeodora Ducke (pau-rosa) no Estado do Amazonas.

Aniba rosaeodora. Pau-rosa. Aspectos econômicos. Exportação. Amazônia.Edicao da Memoria do Simposio Ibero-Americano de Gestao e Economia Florestal, 1., 2001, Porto Seguro. Resumo

Polymer-induced tubulation in lipid vesicles

A mechanism of extraction of tubular membranes from a lipid vesicle is presented. A concentration gradient of anchoring amphiphilic polymers generates tubes from bud-like vesicle protrusions. We explain this mechanism in the framework of the Canham-Helfrich model. The energy profile is analytically calculated and a tube with a fixed length, corresponding to an energy minimum, is obtained in a certain regime of parameters. Further, using a phase-field model, we corroborate these results numerically. We obtain the growth of tubes when a polymer source is added, and the bud-like shape after removal of the polymer source, in accordance with recent experimental results

Dynamic model and stationary shapes of fluid vesicles

A phase-field model that takes into account the bending energy of fluid vesicles is presented. The Canham-Helfrich model is derived in the sharp-interface limit. A dynamic equation for the phase-field has been solved numerically to find stationary shapes of vesicles with different topologies and the dynamic evolution towards them. The results are in agreement with those found by minimization of the Canham-Helfrich free energy. This fact shows that our phase-field model could be applied to more complex problems of instabilities.Comment: Accepted for publication in EPJE. 9 pages, 7 figure

Protocolo para obtenção de plantas de Cedrela odorata L. através da cultura de tecidos.

O trabalho teve como objetivo desenvolver um protocolo básico para micropropagação de plantas de Cedrela odorata L. a partir de plântulas germinadas in vitro. Os experimentos foram conduzidos no laboratório de Recursos Genéticos e Biotecnologia da Embrapa Amazônia Oriental. Para a desinfestação das sementes foram testadas solução de hipoclorito de sódio a 0; 1,0; 1,5 e 2,0% por 10, 15 e 20 minutos. Para indução de brotações em meio MS foi testada 5 concentrações de BAP e 2 tipos de segmentos e no enraizamento foi utilizado 0; 1,0; 1,5; 2,0 e 2,5 mg.L-1 de ANA. O delineamento utilizado foi inteiramente casualizado ou em arranjo fatorial de acordo com os tratamentos analisados. Os dados obtidos, nos diferentes experimentos foram submetidos à análise de variância e as médias comparadas pelo teste de Tukey a 5% de probabilidade. Os resultados demonstraram que o uso de hipoclorito de sódio a 2,0% por 15 minutos apresentou a menor percentagem de contaminação das sementes. O tratamento com 1 mg. L-1 de BAP promoveu o maior número e comprimento de brotos em segmentos apicais e com acréscimo de 2 g.L-1 de sacarose induziu o surgimento de brotos em segmentos caulinares. O maior número e comprimento de raiz/explante foi obtido com 1 mg. L -1 de ANA. É possível obter planta completa de Cedrella odorata a partir de sementes desinfestadas em solução de hipoclorito de sódio a 2,0 %, e o uso de 1 mg. L-1 de BAP e ANA para indução de brotações e enraizamento, respectivamente