Alienor method applied to induction machine parameters identification

This paper presents an identification method to estimate simultaneously the electrical and mechanical induction machine (IM) parameters by using only the measured current and the corresponding phase voltage. This identification method is based on the output error and uses the multidimensional Alienor global optimization method as a minimization technique. Alienor method is essentially based on converting multivariable problem to monovariable one. To improve the Alienor method performance, the reducing transformation is proposed and compared with the genetic algorithm (GA). Firstly, the identification method is verified using the simulated data. Secondly, the validation is then confirmed by measured data from one machine. The corresponding computed transient and steady state currents agree well with the measured data. The results obtained show the superiority of the proposed Alienor method versus GA in terms of computing time

Effet des couples métalliques et du courant électrique sur la dégradation en méso-fretting

De nos jours, la technologie de surface ne cesse d'avancer à la recherche de nouvelles performances tribologiques des systèmes oscillants en contact. Les contraintes augmentant et les exigences environnementales se multipliant, le rôle de la surface devient de plus en plus déterminant. Ce travail de recherche porte sur l'étude du comportement à la dégradation des couples de matériaux métalliques sous micro frottement. Cet objectif passe par l'identification et la compréhension des mécanismes responsables de la dégradation. L'étude a été développée sur les trois stades de frottement: le fretting, le méso-fretting et le frottement à basse amplitude jusqu'à 400µm. Les couples testés incluent les combinaisons des matériaux suivants: acier à hautes performances en usure de la nuance AISI 52100, l'acier inoxydable austénitique 316L, l'alliage d'aluminium de corroyage 6061T6 et le cuivre pur. Les essais ont été effectués à 20000 cycles sous une charge de contact constante de 72gf et une fréquence de 1Hz. La géométrie de contact utilisée est un système bille-plaque. L'effet du courant électrique a aussi été étudié. Les outils de caractérisation de surface comme le microduromètre Vickers, le microscope optique (MO) et le microscope électronique à balayage (MEB) ont été utilisés pour caractériser les traces d'usure. À la lumière des résultats d'usure obtenus, il ressort que le facteur compatibilité chimique, le rapport relatif des duretés et le phénomène de la consolidation régissent la tenue à la dégradation. L'amplitude du mouvement a, en particulier, une grande influence sur l'évolution de l'usure quelque soit la nature du couple. Il a aussi été conclu que la variation du taux d'usure en fonction de l'amplitude de vibration pour chaque couple possède une allure qui est très sensiblement la même. Un formalisme mathématique décrivant ce phénomène physique a été élaboré. L'effet du courant est important quand l'amplitude du mouvement est grande. Cependant, l'usure relative est grande sous courant en fretting. On attribue cet effet au rapport de la densité du courant électrique à l'amplitude de glissement. Ce rapport s'est avéré être très élevé en fretting à comparer aux deux autres stades. Aussi, pour une amplitude de mouvement constante en frottement à basse amplitude, une forte corrélation linéaire set établie entre le taux de dégradation et l'intensité du courant électrique

Indice de primarité et différenciation génétique des populations caprines de la steppe (Arabia) et du désert (Mekatia) d'Algérie

International audienc

RNase E and the High-Fidelity Orchestration of RNA Metabolism.

The bacterial endoribonuclease RNase E occupies a pivotal position in the control of gene expression, as its actions either commit transcripts to an irreversible fate of rapid destruction or unveil their hidden functions through specific processing. Moreover, the enzyme contributes to quality control of rRNAs. The activity of RNase E can be directed and modulated by signals provided through regulatory RNAs that guide the enzyme to specific transcripts that are to be silenced. Early in its evolutionary history, RNase E acquired a natively unfolded appendage that recruits accessory proteins and RNA. These accessory factors facilitate the activity of RNase E and include helicases that remodel RNA and RNA-protein complexes, and polynucleotide phosphorylase, a relative of the archaeal and eukaryotic exosomes. RNase E also associates with enzymes from central metabolism, such as enolase and aconitase. RNase E-based complexes are diverse in composition, but generally bear mechanistic parallels with eukaryotic machinery involved in RNA-induced gene regulation and transcript quality control. That these similar processes arose independently underscores the universality of RNA-based regulation in life. Here we provide a synopsis and perspective of the contributions made by RNase E to sustain robust gene regulation with speed and accuracy.Wellcome Trus

RNA chaperones buffer deleterious mutations in E. coli

International audienc

Processing of the Escherichia coli leuX tRNA transcript, encoding tRNALeu5, requires either the 3′→5′ exoribonuclease polynucleotide phosphorylase or RNase P to remove the Rho-independent transcription terminator

Here we report a unique processing pathway in Escherichia coli for tRNALeu5 in which the exoribonuclease polynucleotide phosphorylase (PNPase) removes the Rho-independent transcription terminator from the leuX transcript without requiring the RhlB RNA helicase. Our data demonstrate for the first time that PNPase can efficiently degrade an RNA substrate containing secondary structures in vivo. Furthermore, RNase P, an endoribonuclease that normally generates the mature 5′-ends of tRNAs, removes the leuX terminator inefficiently independent of PNPase activity. RNase P cleaves 4–7 nt downstream of the CCA determinant generating a substrate for RNase II, which removes an additional 3–4 nt. Subsequently, RNase T completes the 3′ maturation process by removing the remaining 1–3 nt downstream of the CCA determinant. RNase E, G and Z are not involved in terminator removal. These results provide further evidence that the E. coli tRNA processing machinery is far more diverse than previously envisioned

Intragenic suppressors of temperature-sensitive rne mutations lead to the dissociation of RNase E activity on mRNA and tRNA substrates in Escherichia coli

RNase E of Escherichia coli is an essential endoribonuclease that is involved in many aspects of RNA metabolism. Point mutations in the S1 RNA-binding domain of RNase E (rne-1 and rne-3071) lead to temperature-sensitive growth along with defects in 5S rRNA processing, mRNA decay and tRNA maturation. However, it is not clear whether RNase E acts similarly on all kinds of RNA substrates. Here we report the isolation and characterization of three independent intragenic second-site suppressors of the rne-1 and rne-3071 alleles that demonstrate for the first time the dissociation of the in vivo activity of RNase E on mRNA versus tRNA and rRNA substrates. Specifically, tRNA maturation and 9S rRNA processing were restored to wild-type levels in each of the three suppressor mutants (rne-1/172, rne-1/186 and rne-1/187), while mRNA decay and autoregulation of RNase E protein levels remained as defective as in the rne-1 single mutant. Each single amino acid substitution (Gly→Ala at amino acid 172; Phe → Cys at amino acid 186 and Arg → Leu at amino acid 187) mapped within the 5′ sensor region of the RNase E protein. Molecular models of RNase E suggest how suppression may occur

The first small-molecule inhibitors of members of the ribonuclease E family

The Escherichia coli endoribonuclease RNase E is central to the processing and degradation of all types of RNA and as such is a pleotropic regulator of gene expression. It is essential for growth and was one of the first examples of an endonuclease that can recognise the 5′-monophosphorylated ends of RNA thereby increasing the efficiency of many cleavages. Homologues of RNase E can be found in many bacterial families including important pathogens, but no homologues have been identified in humans or animals. RNase E represents a potential target for the development of new antibiotics to combat the growing number of bacteria that are resistant to antibiotics in use currently. Potent small molecule inhibitors that bind the active site of essential enzymes are proving to be a source of potential drug leads and tools to dissect function through chemical genetics. Here we report the use of virtual high-throughput screening to obtain small molecules predicted to bind at sites in the N-terminal catalytic half of RNase E. We show that these compounds are able to bind with specificity and inhibit catalysis of Escherichia coli and Mycobacterium tuberculosis RNase E and also inhibit the activity of RNase G, a paralogue of RNase E

Structuring the bacterial genome: Y1-transposases associated with REP-BIME sequences†

REPs are highly repeated intergenic palindromic sequences often clustered into structures called BIMEs including two individual REPs separated by short linker of variable length. They play a variety of key roles in the cell. REPs also resemble the sub-terminal hairpins of the atypical IS200/605 family of insertion sequences which encode Y1 transposases (TnpAIS200/IS605). These belong to the HUH endonuclease family, carry a single catalytic tyrosine (Y) and promote single strand transposition. Recently, a new clade of Y1 transposases (TnpAREP) was found associated with REP/BIME in structures called REPtrons. It has been suggested that TnpAREP is responsible for REP/BIME proliferation over genomes. We analysed and compared REP distribution and REPtron structure in numerous available E. coli and Shigella strains. Phylogenetic analysis clearly indicated that tnpAREP was acquired early in the species radiation and was lost later in some strains. To understand REP/BIME behaviour within the host genome, we also studied E. coli K12 TnpAREP activity in vitro and demonstrated that it catalyses cleavage and recombination of BIMEs. While TnpAREP shared the same general organization and similar catalytic characteristics with TnpAIS200/IS605 transposases, it exhibited distinct properties potentially important in the creation of BIME variability and in their amplification. TnpAREP may therefore be one of the first examples of transposase domestication in prokaryotes

Membrane-association of mRNA decapping factors is independent of stress in budding yeast

Recent evidence has suggested that the degradation of mRNA occurs on translating ribosomes or alternatively within RNA granules called P bodies, which are aggregates whose core constituents are mRNA decay proteins and RNA. In this study, we examined the mRNA decapping proteins, Dcp1, Dcp2, and Dhh1, using subcellular fractionation. We found that decapping factors co-sediment in the polysome fraction of a sucrose gradient and do not alter their behaviour with stress, inhibition of translation or inhibition of the P body formation. Importantly, their localisation to the polysome fraction is independent of the RNA, suggesting that these factors may be constitutively localised to the polysome. Conversely, polysomal and post-polysomal sedimentation of the decapping proteins was abolished with the addition of a detergent, which shifts the factors to the non-translating RNP fraction and is consistent with membrane association. Using a membrane flotation assay, we observed the mRNA decapping factors in the lower density fractions at the buoyant density of membrane-associated proteins. These observations provide further evidence that mRNA decapping factors interact with subcellular membranes, and we suggest a model in which the mRNA decapping factors interact with membranes to facilitate regulation of mRNA degradation