Comment on "Spin-1 aggregation model in one dimension"

M. Girardi and W. Figueiredo have proposed a simple model of aggregation in one dimension to mimic the self-assembly of amphiphiles in aqueous solution [Phys. Rev. E 62, 8344 (2000)]. We point out that interesting results can be obtained if a different set of interactions is considered, instead of their choice (the s=1 Ising model).Comment: Accepted for publication in Phys. Rev.

Thermal Gradient Changes Caused by Water in the Soil

The heat flow density data published in the Geothermal Atlas of Europe (1992) show relatively high values for temperature gradients measured in holes in the SW area (Portugal and Spain) of the Iberian Peninsula. This study tries to explain this fact based in the presence of water at relatively high temperatures outside the holes where the measurements were made, and the inclination of strata, derived from samples taken from the boreholes. We used a two-dimensional numerical model based on the finite volume method. Equations governing the transfer of energy by conduction and advection and fluid flow, were solved. Thermal conductivity values of the rocks and water may vary spatially as well as the porosity. Thermal conductivity values were measured but values of the hydraulic conductivity and porosity are unknown. Due to this fact, the models are tested with different values of these parameters. The heat flow density value considered for the region is 60 mWm-2 and the thermal gradient is calculated using the value of thermal conductivity. The results obtained with the models are compared with those published. Different solutions can be obtained for a given hole

Convergence of the Crank-Nicolson-Galerkin finite element method for a class of nonlocal parabolic systems with moving boundaries

The aim of this paper is to establish the convergence and error bounds to the fully discrete solution for a class of nonlinear systems of reaction-diffusion nonlocal type with moving boundaries, using a linearized Crank-Nicolson-Galerkin finite element method with polynomial approximations of any degree. A coordinate transformation which fixes the boundaries is used. Some numerical tests to compare our Matlab code with some existing moving finite elements methods are investigated

Molecular theory of hydrophobic mismatch between lipids and peptides

Effects of the mismatch between the hydrophobic length, d, of transmembrane alpha helices of integral proteins and the hydrophobic thickness, D_h, of the membranes they span are studied theoretically utilizing a microscopic model of lipids. In particular, we examine the dependence of the period of a lamellar phase on the hydrophobic length and volume fraction of a rigid, integral, peptide. We find that the period decreases when a short peptide, such that d<D_h, is inserted. More surprising, we find that the period increases when a long peptide, such that d>D_h, is inserted. The effect is due to the replacement of extensible lipid tails by rigid peptide. As the peptide length is increased, the lamellar period continues to increase, but at a slower rate, and can eventually decrease. The amount of peptide which fails to incorporate and span the membrane increases with the magnitude of the hydrophobic mismatch |d-D_h|. We explicate these behaviors which are all in accord with experiment. Predictions are made for the dependence of the tilt of a single trans-membrane alpha helix on hydrophobic mismatch and helix density.Comment: 14 pages, 5 figure

La arquitectura bioclimática y el cambio climático

La arquitectura siempre había sido bioclimática, pero dejó de serlo en el siglo XX. En caso de volver a ser entendida como tal, podría contribuir a la reducción de emisiones de gases de efecto invernadero. El sector de la construcción, entendiendo por tal todo lo relacionado con la edificación –sin entrar en las obras públicas de infraestructuras, ya que el concepto bioclimático difícilmente se aplicaría a un túnel, un puente o una presa– consume una parte sustancial de la energía y de los recursos producidos, con lo que se convierte en una de las principales fuentes de emisión de gases de efecto invernadero. Si a ello se une el consumo de sectores difusos, como son el consumo doméstico y el del transporte, ambos en gran medida ligados a ese hecho edificatorio, tenemos un panorama en el que se apunta que las acciones más efectivas para reducir las emisiones de CO2 a la atmósfera tiene que ver con las buenas prácticas en el sector de la edificación. La arquitectura bioclimática, que es básicamente la única arquitectura que se ha venido desarrollando por la humanidad hasta la revolución industrial, y la mayoritaria hasta bien entrado el siglo XX, puede mostrar el camino para racionalizar el sector de la construcción y sus efectos en las emisiones de gases de efecto invernadero. Los pasos dados hasta el momento son tímidos, a veces contradictorios, y poco más que anecdóticos en el contexto global, pero tienen la virtud de servir como experimento y como muestra para validar soluciones y elaborar nuevas propuestas. El camino está aún prácticamente por andar

On a nonlocal degenerate parabolic problem

Conditions for the existence and uniqueness of weak solutions for a class of nonlinear nonlocal degenerate parabolic equations are established. The asymptotic behaviour of the solutions as time tends to infinity are also studied. In particular, the finite time extinction and polynomial decay properties are proved