A robust extension to the triple plane pressure mode matching method by filtering convective perturbations

Time-periodic CFD simulations are widely used to investigate turbomachinery components. The triple-plane pressure mode matching method (TPP) developed by Ovenden and Rienstra extracts the acoustic part in such simulations. Experience shows that this method is subject to significant errors when the amplitude of pseudo-sound is high compared to sound. Pseudo-sound are unsteady pressure fluctuations with a convective character. The presented extension to the TPP improves the splitting between acoustics and the rest of the unsteady flow field. The method is simple: i) the acoustic eigenmodes are analytically determined for a uniform mean flow as in the original TPP; ii) the suggested model for convective pressure perturbations uses the convective wavenumber as axial wavenumber and the same orthogonal radial shape functions as for the acoustic modes. The reliability is demonstrated on the simulation data of a low-pressure fan. As acoustic and convective perturbations are separated, the accuracy of the results increases close to sources, allowing a reduction of the computational costs by shortening the simulation domain. The extended method is as robust as the original one--giving the same results for the acoustic modes in absence of convective perturbations.Comment: Accepted 15-05-11 by International Journal of Aeroacoustics to be published in the special issue focusing on turbomachinery aeroacoustic

Truncation of the NS1 protein converts a low pathogenic avian influenza virus into a strong interferon inducer in duck cells

The NS1 protein of influenza A viruses is known as a nonessential virulence factor inhibiting type I interferon (IFN) production in mammals and in chicken cells. Whether NS1 inhibits the induction of type I IFNs in duck cells is currently unknown. In order to investigate this issue, we used reverse genetics to generate a virus expressing a truncated NS1 protein. Using the low pathogenic avian influenza virus A/turkey/Italy/977/1999 (H7N1) as a backbone, we were able to rescue a virus expressing a truncated NS1 protein of 99 amino acids in length. The truncated virus replicated poorly in duck embryonic fibroblasts, but reached high titers in the mammalian IFN-deficient Vero cell line. Using a gene reporter system to measure duck type I IFN production, we showed that the truncated virus is a potent inducer of type I IFN in cell culture. These results show that the NS1 protein functions to prevent the induction of IFN in duck cells and underline the need for a functional NS1 protein in order for the virus to express its full virulence

Fast Convergence in Self-stabilizing Wireless Networks.

International audienceThe advent of large scale multi-hop wireless networks highlights problems of fault tolerance and scale in distributed systems, motivating designs that autonomously recover from transient faults and spontaneous reconfigurations. Self-stabilization provides an elegant solution for recovering from such faults. We present a complexity analysis for a family of self-stabilizing vertex coloring algorithms in the context of multi-hop wireless networks. Such "coloring" processes are used in several protocols for solving many different issues (clustering, synchronizing...). Overall, our results show that the actual stabilization time is much smaller than the upper bound provided by previous studies. Similarly, the height of the induced DAG is much lower than the linear dependency on the size of the color domain (that was previously announced). Finally, it appears that symmetry breaking tricks traditionally used to expedite stabilization are in fact harmful when used in networks that are not tightly synchronized

Nucleolar localization of influenza A NS1: striking differences between mammalian and avian cells

In mammalian cells, nucleolar localization of influenza A NS1 requires the presence of a C-terminal nucleolar localization signal. This nucleolar localization signal is present only in certain strains of influenza A viruses. Therefore, only certain NS1 accumulate in the nucleolus of mammalian cells. In contrast, we show that all NS1 tested in this study accumulated in the nucleolus of avian cells even in the absence of the above described C-terminal nucleolar localization signal. Thus, nucleolar localization of NS1 in avian cells appears to rely on a different nucleolar localization signal that is more conserved among influenza virus strains

New geological and tephrochronological data on the palaeontological site of the Senèze maar (Early Pleistocene, Massif Central, France)

The volcanic system of Senèze (Domeyrat, Haute-Loire) comprises a basanite flow, scoriae, a maar crater and phreatomagmatic products. New field research and detailed cartography clarify their geometry and geological relationships. The maar contains an important palaeontological site of the Early Pleistocene that yielded forty species of mammals attributed to the biozone MNQ 18 (of which it is the reference locality). The excavations undertaken between 2001 and 2006 recovered new fossils and documented their stratigraphic and geodynamic context. The fossiliferous site is located on the shore of the palaeolake and includes several lacustrine and slope deposits linked to the contemporaneous climatic changes which in turn produced a number of locally fossiliferous findspots which appear to be close in age. The discovery of ten tephras emitted by the Mont-Dore strato-volcano, situated 60 km to the NW allowed development of a remarkable tephrochronological framework. Because of the intense weathering of the tephras, their composition is determined by their mineralogical content (feldspars, brown amphiboles, brown and green diopside, titanite, apatite, zircon, biotite-phlogopite, Fe-Ti oxides) and the chemical composition of feldspars (anorthoclase, sodic sanidine and plagioclases). The study of these tephras reveals the importance of the contemporaneous (mainly trachytic) pyroclastic activity and confirms the polyphased deposition of the site. The 40Ar/39Ar laser dating of alkali feldspars from five tephras shows a relatively narrow range of age comprised between 2.09 and 2.21 \textpm 0.02 Ma (1σ, age relative to ACs-2 standard at 1.201 Ma). Senèze is thus confirmed as a key Early Pleistocene palaeontological site in Europe