Ana Isabel Vela Alonso

A domain decomposition approach for heterogeneous time-harmonic Maxwell equations

The time-harmonic Maxwell equations for a composite medium which behaves like a conductor in one part and like a perfect insulator in the other one are considered. An existence and uniqueness theorem is proven for this degenerate problem in the case of Dirichlet boundary conditions. A finite element domain decomposition approach is then proposed for the numerical approximation of the exact solution. This leads to an iteration-by-subdomain procedure, where at each step a non-degenerate boundary value problem has to be solved in each subdomain. The convergence of these iterations is proven, and the rate of convergence turns out to be independent of the mesh size h, showing that the preconditioner implicitly defined by the iteration procedure is optimal.

Streptococcus penaeicida sp. nov., isolated from a diseased farmed Pacific white shrimp (Penaeus vannamei)

Strain CAIM 1838T, isolated from the hepatopancreas of a cultured diseased Pacific white shrimp (Penaeus vannamei), was subjected to characterization by a polyphasic taxonomic approach. On the basis of 16S rRNA gene sequence analysis, strain CAIM 1838T was most closely related to Streptococcus bovimastitidis 99.3 % and to other species of the Pyogenes clade of Streptococcus with lower similarity values. Average nucleotide identity values and the genome-to-genome distance of strain CAIM 1838T, as compared with the type strains, confirmed the separate species status with closely related species of the genus Streptococcus and were all below the thresholds to delimit a species, 93.1 and 49.4 %, respectively. The DNA G+C content was 38.1 mol%. Differential phylogenetic distinctiveness together with phenotypic properties obtained in this study revealed that strain CAIM 1838T could be differentiated from the closely related species. Based on these results it is proposed that strain CAIM 1838T represents a novel species in the genus Streptococcus, for which the name Streptococcus penaeicida sp. nov is proposed (type strain, CAIM 1838T=CECT 8596T,=DSM26545T), is proposed.