RESUMO
The dynamics of coherent structures near the wall of a turbulent boundary layer is investigated with the aim of a low-dimensional representation of its essential features. Based on a triple decomposition into mean, coherent and incoherent motion and a dynamic mode decomposition to recover statistical information about the incoherent part of the flow field, a driven linear system coupling first- and second-order moments of the coherent structures is derived and analysed. The transfer function for this system, evaluated for a wall-parallel plane, confirms a strong bias towards streamwise elongated structures, and is proposed as an 'impedance' boundary condition which replaces the bulk of the transport between the coherent velocity field and the coherent Reynolds stresses, thus acting as a wall model for large-eddy simulations (LES). It is interesting to note that the boundary condition is non-local in space and time. The extracted model is capable of reproducing the principal Reynolds stress components for the pretransitional, transitional and fully turbulent boundary layer.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.
RESUMO
Ovine and dromedary Echinococcus granulosus isolates from Tunisia were identified as G1 and G6 strains based on polymorphism of the mitochondrial cytochrome C oxydase CO1. Single strand conformation polymorphism (SSCP) was used in order to examine the genetic variation within and between Tunisian G1 and G6 strains and to estimate the extent of selfing. The dromedary isolates are genetically distinct from sheep isolates (high value of genetic variation between populations: Fst= 0.46). No significant deficiency in heterozygotes was found in sheep isolates, whereas heterozygote deficiency (suggesting selfing) was found in a limited number of camel isolates.
Assuntos
Camelus/parasitologia , Equinococose/veterinária , Echinococcus granulosus/genética , Variação Genética , Filogenia , Doenças dos Ovinos/parasitologia , Animais , Equinococose/parasitologia , Echinococcus granulosus/classificação , Complexo IV da Cadeia de Transporte de Elétrons/genética , Interações Hospedeiro-Parasita , Polimorfismo Conformacional de Fita Simples , Ovinos , Especificidade da Espécie , TunísiaRESUMO
Three hundred and seventy-two cysts coming from 50 humans, 166 cattle, 153 sheep and 3 camels were collected in order to establish some epidemiological molecular information in Tunisia for the first time. The analysis by PCR-RFLP of ITS1 sequence showed that all the human, ovine and bovine cysts were due to the common sheep strain of Echinococcus granulosus. The sequencing of the CO1 gene of 37 isolates confirm the G1 genotype of this strain. For seven of these isolates, we found the mutation C56T which is present in the three principal intermediate hosts: human (three cysts), cattle (three cysts) and sheep (one cyst). With regard to the G1 genotype, we identified three other point mutations. The camel strain G6 is uniquely found in the three camels isolates and not in the other intermediate hosts analysed. The fertility of the bovine cyst represents 48% that means that this host is involved in a bovine-dog cycle and consequently represents a reservoir of sheep strain in Tunisia. Our results confirm the importance of the prophylaxis measures in order to disrupt the cycle of transmission sheep-dog in Tunisia. Nevertheless, the supervision of bovine infection should be reinforced because this intermediate host may constitute an important link with the human contamination.
Assuntos
Camelus/parasitologia , Doenças dos Bovinos/parasitologia , Coccidiose/veterinária , Echinococcus granulosus/classificação , Doenças dos Ovinos/parasitologia , Zoonoses/parasitologia , Animais , Sequência de Bases , Bovinos , Doenças dos Bovinos/epidemiologia , Doenças dos Bovinos/transmissão , Coccidiose/epidemiologia , Coccidiose/parasitologia , Coccidiose/transmissão , DNA de Protozoário/química , DNA de Protozoário/genética , DNA Espaçador Ribossômico/química , DNA Espaçador Ribossômico/genética , Echinococcus granulosus/genética , Echinococcus granulosus/crescimento & desenvolvimento , Complexo IV da Cadeia de Transporte de Elétrons/química , Complexo IV da Cadeia de Transporte de Elétrons/genética , Humanos , Dados de Sequência Molecular , Reação em Cadeia da Polimerase/veterinária , Polimorfismo de Fragmento de Restrição , RNA Ribossômico/química , RNA Ribossômico/genética , Alinhamento de Sequência , Doenças dos Ovinos/epidemiologia , Doenças dos Ovinos/transmissão , Tunísia/epidemiologia , Zoonoses/epidemiologia , Zoonoses/transmissãoRESUMO
Allozyme variation at seven polymorphic loci (GPI, EST, MDH, MPI, DIA, PEP, PGM) was studied to examine genetic variation within and between sheep, cattle and human populations of Echinococcus granulosus in Tunisia. A high degree of genetic similarity was shown between the cysts of the three host origins. Nevertheless, whereas, the ovine and human samples were highly similar, the cattle samples were slightly different genetically. We conclude that humans are mostly infected by parasites originating from sheep liver. The intense deficiency in heterozygotes was partly artefactual (Wahlund effect) and partly due to self-fertilisation.
