Computing symmetry groups of polyhedra

Knowing the symmetries of a polyhedron can be very useful for the analysis of its structure as well as for practical polyhedral computations. In this note, we study symmetry groups preserving the linear, projective and combinatorial structure of a polyhedron. In each case we give algorithmic methods to compute the corresponding group and discuss some practical experiences. For practical purposes the linear symmetry group is the most important, as its computation can be directly translated into a graph automorphism problem. We indicate how to compute integral subgroups of the linear symmetry group that are used for instance in integer linear programming.Comment: 20 pages, 1 figure; containing a corrected and improved revisio

A fully coupled 3D wave-current interaction model on unstructured grids

We present a new modeling system for wave-current interaction based on unstructured grids and thus suitable for very large-scale high-resolution multiscale studies. The coupling between the 3D current model (SELFE) and the 3rd generation spectral wave model (WWM-II) is done at the source code level and the two models share same sub-domains in the parallel MPI implementation in order to ensure parallel efficiency and avoid interpolation. We demonstrate the accuracy, efficiency, stability and robustness of the coupled SELFE-WWM-II model with a suite of progressively challenging benchmarks with analytical solution, laboratory data, and field data. The coupled model is shown to be able to capture important physics of the wave-current interaction under very different scales and environmental conditions with excellent convergence properties even in complicated test cases. The challenges in simulating the 3D wave-induced effects are highlighted as well, where more research is warranted

Dicationic Alkylammonium Bromide Gemini Surfactants. Membrane Perturbation and Skin Irritation

Dicationic alkylammonium bromide gemini surfactants represent a class of amphiphiles potentially effective as skin permeation enhancers. However, only a limited number of studies has been dedicated to the evaluation of the respective cytotoxicity, and none directed to skin irritation endpoints. Supported on a cell viability study, the cytotoxicity of gemini surfactants of variable tail and spacer length was assessed. For this purpose, keratinocyte cells from human skin (NCTC 2544 cell line), frequently used as a model for skin irritation, were employed. The impact of the different gemini surfactants on the permeability and morphology of model vesicles was additionally investigated by measuring the leakage of calcein fluorescent dye and analyzing the NMR spectra of 31P, respectively. Detail on the interaction of gemini molecules with model membranes was also provided by a systematic differential scanning calorimetry (DSC) and molecular dynamics (MD) simulation. An irreversible impact on the viability of the NCTC 2544 cell line was observed for gemini concentrations higher than 25 mM, while no cytotoxicity was found for any of the surfactants in a concentration range up to 10 mM. A higher cytotoxicity was also found for gemini surfactants presenting longer spacer and shorter tails. The same trend was obtained in the calorimetric and permeability studies, with the gemini of longest spacer promoting the highest degree of membrane destabilization. Additional structural and dynamical characterization of the various systems, obtained by 31P NMR and MD, provide some insight on the relationship between the architecture of gemini surfactants and the respective perturbation mechanism

Optimización del contenido en macroelementos en hojas de frambueso mediante encalado en suelos muy ácidos

Raspberries thrive best in an acid soil. However, if the soil pH is lower than 5.6, lime application is necessary. In this study the effects of lime and dolomite application in combination with NPK 15:15:15 fertilizer (600 kg ha–1) on the macroelement contents (N, P, K, Ca, and Mg) in an extremely acid soil (pH 4.35) and raspberry leaves were evaluated during a three-year period. Optimal pH value for raspberry cultivation (5.84) was achieved with the application of 9 t ha–1 of lime. The mineral nitrogen (NH4+NO3)-N content and P content in the soil after liming increased significantly, but P concentration stayed below the optimal values. Additionally, no changes were noted in K concentration in the soil. The Ca concentration increased significantly in all treatments, while the Mg content increased significantly only in the treatment with dolomite. The N content in the raspberry leaves increased, but K content decreased after liming. There was no change in P content in the leaves affected by liming. Lime increased Ca content in the leaves above the optimal values, while it did not affect the initially optimal Mg content in the leaves. After liming and NPK fertilization, the concentrations of N, P and K in the leaves were still below the optimal values, indicating a need for the combination of higher rates of fertilizer with lime in raspberry cultivation in very acid soils.Los frambuesos crecen mejor en suelos ácidos. Sin embargo, si el pH del suelo es inferior a 5,6, es necesario aplicar cal. En este estudio se evaluaron durante un período de tres años los efectos de aplicar cal y dolomita, en combinación con fertilizantes NPK 15:15:15 (600 kg ha–1), en el contenido de macroelementos (N, P, K, Ca y Mg) en un suelo extremadamente ácido (pH 4,35) y en hojas de frambueso. El pH óptimo para el cultivo del frambueso (5,84) se logró con la aplicación de 9 t ha–1 de cal. En el caso del suelo, después del encalado el contenido en nitrógeno mineral (NH4+NO3)-N y de P aumentó significativamente, pero la concentración de P se mantuvo por debajo de los valores óptimos; además, no se observaron cambios en la concentración de K; la concentración de Ca aumentó significativamente en todos los tratamientos, pero el contenido de Mg aumentó significativamente sólo en el tratamiento con dolomita. En las hojas de frambueso, después del encalado el contenido de N aumentó, pero el contenido de K disminuyó; no hubo cambios en el contenido de P; el contenido de Ca aumentó por encima de los valores óptimos, mientras que no se afectó el contenido inicial óptimo de Mg. Después del encalado y la fertilización NPK, las concentraciones de N, P y K en las hojas estaban todavía por debajo de los valores óptimos, lo que indica la necesidad de combinar mayores tasas de abono con cal en el cultivo de frambueso en suelos muy ácidos

Optimization of macroelement contents in raspberry leaves by liming in an extremely acid soil

Raspberries thrive best in an acid soil. However, if the soil pH is lower than 5.6, lime application is necessary. In this study the effects of lime and dolomite application in combination with NPK 15:15:15 fertilizer (600 kg ha�1) on the macroelement contents (N, P, K, Ca, and Mg) in an extremely acid soil (pH 4.35) and raspberry leaves were evaluated during a three-year period. Optimal pH value for raspberry cultivation (5.84) was achieved with the application of 9 t ha�1 of lime. The mineral nitrogen (NH4+NO3)-N content and P content in the soil after liming increased significantly, but P concentration stayed below the optimal values. Additionally, no changes were noted in K concentration in the soil. The Ca concentration increased significantly in all treatments, while the Mg content increased significantly only in the treatment with dolomite. The N content in the raspberry leaves increased, but K content decreased after liming. There was no change in P content in the leaves affected by liming. Lime increased Ca content in the leaves above the optimal values, while it did not affect the initially optimal Mg content in the leaves. After liming and NPK fertilization, the concentrations of N, P and K in the leaves were still below the optimal values, indicating a need for the combination of higher rates of fertilizer with lime in raspberry cultivation in very acid soils.Los frambuesos crecen mejor en suelos ácidos. Sin embargo, si el pH del suelo es inferior a 5,6, es necesario aplicar cal. En este estudio se evaluaron durante un período de tres años los efectos de aplicar cal y dolomita, en combinación con fertilizantes NPK 15:15:15 (600 kg ha�1), en el contenido de macroelementos (N, P, K, Ca y Mg) en un suelo extremadamente ácido (pH 4,35) y en hojas de frambueso. El pH óptimo para el cultivo del frambueso (5,84) se logró con la aplicación de 9 t ha�1 de cal. En el caso del suelo, después del encalado el contenido en nitrógeno mineral (NH4+NO3)-N y de P aumentó significativamente, pero la concentración de P se mantuvo por debajo de los valores óptimos; además, no se observaron cambios en la concentración de K; la concentración de Ca aumentó significativamente en todos los tratamientos, pero el contenido de Mg aumentó significativamente sólo en el tratamiento con dolomita. En las hojas de frambueso, después del encalado el contenido de N aumentó, pero el contenido de K disminuyó; no hubo cambios en el contenido de P; el contenido de Ca aumentó por encima de los valores óptimos, mientras que no se afectó el contenido inicial óptimo de Mg. Después del encalado y la fertilización NPK, las concentraciones de N, P y K en las hojas estaban todavía por debajo de los valores óptimos, lo que indica la necesidad de combinar mayores tasas de abono con cal en el cultivo de frambueso en suelos muy ácidos

Hepatoprotective effect of BPC 157, a 15-amino acid peptide, on liver lesions induced by either restraint stress or bile duct and hepatic artery ligation or CCl4 administration. A comparative study with dopamine agonists and somatostatin.

The hepatoprotective effects of a newly synthesized 15 amino acid fragment code named BPC 157 was evaluated in comparison with the reference standards (bromocriptine, amantadine and somatostatin) in various experimental models of liver injury in rats: 24 h-bile duct+hepatic artery ligation 48 h-restraint stress and CCl4 administration. BPC 157 administered either intragastrically or intraperitoneally, significantly prevented the development of liver necrosis or fatty changes in rats subjected to 24 h bile duct + hepatic artery ligation, 48 h-restraint stress, CCl4 treatment (1 ml/kg i.p., sacrifice 48 h thereafter). The other reference drugs had either little or no protective actions in these models. Noteworthy, the laboratory test results for bilirubin, SGOT, SGPT fully correlated with the macro/microscopical findings. Thus, on the basis of consistent protective effect of BPC 157, possible clinical application in liver diseases is now warranted