Electronic orders near the type-II van Hove singularity in BC3_3

Using the functional renormalization group, we investigate the electron instability in the single-sheet BC$_3$ when the electron filling is near a type-II van Hove singularity. For a finite Hubbard interaction, the ferromagnetic-like spin density wave order dominates in the immediate vicinity of the singularity. Elsewhere near the singularity the p-wave superconductivity prevails. We also find that a small nearest-neighbor Coulomb repulsion can enhance the superconductivity. Our results show that BC$_3$ would be a promising candidate to realize topological $p+ip'$ superconductivity, but the transition temperature is practically sizable only if the local interaction is moderately strong.Comment: 6 pages, 6 color figures. arXiv admin note: text overlap with arXiv:1503.0047

A spatial model of calcification in scleractinian corals

Calcification in scleractinian corals is a highly complex process depending on a wide variety of physical, chemical and biological parameters that interact on a molecular, cellular, organismal and ecosystem level. Although many of these individual parameters have been identified during recent years, coral skeletogenesis on a systems level is still not well understood, limiting the possibility to accurately predict the effect of environmental changes. Therefore we have constructed a model of calcification in which existing knowledge on the factors influencing skeleton formation is integrated within a mathematical framework. In this model we have developed a spatial representation of the coral tissue where we simulate the relevant chemical reactions in the surrounding environment, the transport processes of inorganic carbon and calcium ions, photosymthesis, respiration and calcification in the different cell layers. We model the change in space and time of the different processes as a set of coupled reaction-diffusion equations. Simulations can also be employed to clarify the relative contribution of different individual processes such as ion transport, photosynthesis or mitochondrial respiration rates. Results of these simulations can be used to guide further experimental studies. In the future we hope to combine all these models in a multi-scale model of calcification which can be used to analyse the relations between the marine environment, genetic regulation, skeletogenesis and coral growth

A computational method for quantifying morphological variation in scleractinian corals

Morphological variation in marine sessile organisms is frequently related to environmental factors. Quantifying such variation is relevant in a range of ecological studies. For example, analyzing the growth form of fossil organisms may indicate the state of the physical environment in which the organism lived. A quantitative morphological comparison is important in studies where marine sessile organisms are transplanted from one environment to another. This study presents a method for the quantitative analysis of three-dimensional (3D) images of scleractinian corals obtained with X-ray Computed Tomography scanning techniques. The advantage of Computed Tomography scanning is that a full 3D image of a complex branching object, including internal structures, can be obtained with a very high precision. There are several complications in the analysis of this data set. In the analysis of a complex branching object, landmark-based methods usually do not work and different approaches are required where various artifacts (for example cavities, holes in the skeleton, scanning artifacts, etc.) in the data set have to be removed before the analysis. A method is presented, which is based on the construction of a medial axis and a combination of image-processing techniques for the analysis of a 3D image of a complex branching object where the complications mentioned above can be overcome. The method is tested on a range of 3D images of samples of the branching scleractinian coral Madracis mirabilis collected at different depths. It is demonstrated that the morphological variation of these samples can be quantified, and that biologically relevant morphological characteristics, like branch-spacing and surface/volume ratios, can be computed. Electronic supplementary material The online version of this article (doi:10.1007/s00338-007-0270-6) contains supplementary material, which is available to authorized users