Conservation Laws in Smooth Particle Hydrodynamics: the DEVA Code

We describe DEVA, a multistep AP3M-like-SPH code particularly designed to study galaxy formation and evolution in connection with the global cosmological model. This code uses a formulation of SPH equations which ensures both energy and entropy conservation by including the so-called \bn h terms. Particular attention has also been paid to angular momentum conservation and to the accuracy of our code. We find that, in order to avoid unphysical solutions, our code requires that cooling processes must be implemented in a non-multistep way. We detail various cosmological simulations which have been performed to test our code and also to study the influence of the \bn h terms. Our results indicate that such correction terms have a non-negligible effect on some cosmological simulations, especially on high density regions associated either to shock fronts or central cores of collapsed objects. Moreover, they suggest that codes paying a particular attention to the implementation of conservation laws of physics at the scales of interest, can attain good accuracy levels in conservation laws with limited computational resources.Comment: 36 pages, 10 figures. Accepted for publication in The Astrophysical Journa

Disc-like Objects in Hierarchical Hydrodynamical Simulations: Comparison with Observations

We present results from a careful and detailed analysis of the structural and dynamical properties of a sample of 29 disc-like objects identified at z=0 in three AP3M-SPH fully consistent cosmological simulations. These simulations are realizations of a CDM hierarchical model, where an inefficient Schmidt law-like algorithm to model the stellar formation process has been implemented. We focus on properties that can be constrained with available data from observations of spiral galaxies, namely, the bulge and disc structural parameters and the rotation curves. Comparisons with data from Broeils (1992), de Jong (1996) and Courteau (1996, 1997) give satisfactory agreement, in contrast with previous findings using other codes. This suggests that the stellar formation implementation we have used has succeded in forming compact bulges that stabilize disc-like structures in the violent phases of their assembly, while in the quiescent phases the gas has cooled and collapsed according with the Fall & Efstathiou standard model of disc formation.Comment: 22 pages, LaTeX; 14 figures; references updated. MNRAS, in pres

Biodeterioration of Roman tombs: The role of pigmented actinobacteria

Etruscan and Roman necropolises are cemeteries with different types of burial practices, which are remarkable for their magnificent mural paintings. The conservation of these paintings is difficult, mainly derived from environmental factors and the opening of the tombs to public visits. One of the most complex phenomena observed on these sites is biodeterioration. The Circular Mausoleum tomb (Roman Necropolis of Carmona, Seville, Spain) is characterized by a heavy colonization of phototrophic microorganisms on the walls and ceiling. In addition, some areas near the ceiling exhibited an important number of violet stains of unknown origin. Previously, Agarossi (1994) found similar violet stains, attributed to streptomycetes, in two Etruscan tombs. However, no data on the species involved or the chemical structure of the pigments were reported. Here we show that the violet stains observed in the Circular Mausoleum are produced by a strain of the actinobacterium Streptomyces isolated from the mortar walls, and able to synthesize the same violet pigment in the laboratory. Streptomyces parvus MC05 was identified after whole genome study by means of Next Generation Sequencing methods. Pairwise comparisons carried out for genomes of the type strain of S. parvus DSM40348T and the MC05 strain were performed using Jspecies service. While results observed for ANIb, ANIm and Tetra indexes indicated that both strains belong to the same species, the S. parvus MC05 strain differs from the DSM20348T type strain in genome size and secondary metabolites production. AntiSMASH analysis implemented for both strains showed that the S. parvus MC05, isolated from the tomb, presents the capacity of synthesize bioactive compounds which were absents in the type strain. HPLC-MS of the culture extracts from S. parvus MC05 showed the production of three main granaticin derivatives (dihydrogranaticin A, granaticin A and granaticin B) in addition to minor products of other granaticin analogues. Granaticin pigments exhibited antibacterial activity, which justified the low number of clones of Gram positive bacteria found in the whole microbial community study. Gram negative bacteria were not affected (Dominguez-Moñino et al. 2017). To conclude, the origin of the violet stains in the walls of the Circular Mausoleum is the presence of S. parvus MC05, a member of the complex microbial community thriving on the tomb. In growing periods (rainy season) the bacterium excretes the soluble violet granaticins, compounds with a benzoisochromanequinone structure, which diffuses to the mortar and surrounding substrata in wetting periods

Spectral behavior of the linear polarization degree at right-angle scattering configuration for nanoparticle systems

We present a numerical study of the spectral evolution of the linear polarization degree at right-angle scattering configuration (PL(90º)) for two different particle systems: an isolated nanosphere and a nanodimer composed of two finite size spherical particles separated by a gap distance d. We shall focus on the influence of charge oscillation modes other than the dipolar on the linear polarization degree of the scattered light. The possibility of using this alternative parameter for characterizing nanoparticle systems and particle interaction is analyzed.We acknowledge financial support from USAITCA (US Army International Technology Center—Atlantic) under the project R&D1390-PH-01 and from the Ministry of Education of Spain under the project FIS2007-60158