121 research outputs found
BactĂ©rias isoladas de folhas de abobrinha tratadas com leite reduzem a severidade do oĂdio.
Apport de la simulation numérique à l'essai de Small Punch Test
Lors de lâessai de Small Punch Test (SPT) (essai de micro emboutissage dâun disque dâĂ©paisseur 0,5 mm et de diamĂštre 8,9 mm), le matĂ©riau est sollicitĂ© en contraintes bi-axiales, dĂ©formĂ© plastiquement jusquâĂ fissuration et, rompu. Des essais de Small Punch Test, rĂ©alisĂ©s sur lâacier inoxydable 316L, montrent le comportement ductile de lâacier Ă partir des courbes dâĂ©volution de la force exercĂ©e sur lâĂ©chantillon en fonction du dĂ©placement. Des essais interrompus couplĂ©s Ă une analyse par microscopie Ă©lectronique Ă balayage mettent en Ă©vidence lâamorçage de la fissuration et une rupture ductile. ParallĂšlement, nous avons dĂ©veloppĂ© une simulation numĂ©rique de lâessai SPT par Ă©lĂ©ments finis Ă lâaide du solveur 2D du logiciel implicite FORGE2005. La plasticitĂ© des matĂ©riaux est modĂ©lisĂ©e par une relation de type Hollomon ; lâimplĂ©mentation dâun critĂšre de rupture permet de mettre en Ă©vidence lâapparition de la fissuration. La simulation permet de montrer lâĂ©volution des contraintes et des dĂ©formations au cours de lâessai, et la propagation de fissures dans lâĂ©chantillon
Apport de la simulation numérique à l'essai de Small Punch Test
Lors de lâessai de Small Punch Test (SPT) (essai de micro emboutissage dâun disque dâĂ©paisseur 0,5 mm et de diamĂštre 8,9 mm), le matĂ©riau est sollicitĂ© en contraintes bi-axiales, dĂ©formĂ© plastiquement jusquâĂ fissuration et, rompu. Des essais de Small Punch Test, rĂ©alisĂ©s sur lâacier inoxydable 316L, montrent le comportement ductile de lâacier Ă partir des courbes dâĂ©volution de la force exercĂ©e sur lâĂ©chantillon en fonction du dĂ©placement. Des essais interrompus couplĂ©s Ă une analyse par microscopie Ă©lectronique Ă balayage mettent en Ă©vidence lâamorçage de la fissuration et une rupture ductile. ParallĂšlement, nous avons dĂ©veloppĂ© une simulation numĂ©rique de lâessai SPT par Ă©lĂ©ments finis Ă lâaide du solveur 2D du logiciel implicite FORGE2005. La plasticitĂ© des matĂ©riaux est modĂ©lisĂ©e par une relation de type Hollomon ; lâimplĂ©mentation dâun critĂšre de rupture permet de mettre en Ă©vidence lâapparition de la fissuration. La simulation permet de montrer lâĂ©volution des contraintes et des dĂ©formations au cours de lâessai, et la propagation de fissures dans lâĂ©chantillon
Nanoindentation hardness and macroscopic mechanical behaviors in filled elastomeric nanocomposites
Carbon black (CB) filled semi-crystalline ethylene butyl acrylate (EBA) copolymer networks are investigated to probe for the CB particles dependence of the deformation behavior from nano-to micrometers length scales of samples which are submitted to nanoindentation characterization. With respect to this purpose, the phenomenology for hardness (H) response in these materials indicates a typical increase of the hardness by decreasing the indentation depth (h) similar to the observed behavior in elastomeric materials. This behavior can be related to the change of the mesostructure, formed by the heterogeneous three-dimensional interconnected network of polymer and of aggregates of CB particles. Furthermore, The CB amount is found to increase the resistance of composite under the action of a mechanical stress. The H-h curves were then compared to some analytical models and correlated to a tensile macroscopic behavior in order to highlight the involved deformation mechanisms with length scale. A complementary set of characterizations such as profilometry and atomic force microscopy probes were also employed to best understand of those mechanisms
Influence de la teneur de nickel sur le comportement tribologique et Ă©lectrochimique de lâalliage TiNi.
Parmi les matĂ©riaux mĂ©talliques, les alliages de TiNi sont employĂ©s principalement pour des applications biomĂ©dicales et/ou dentaires dues Ă leur meilleure compatibilitĂ© mĂ©canique avec les tissus, leur module de Young proche de celui de lâos et une rĂ©sistance Ă©levĂ©e Ă la corrosion dans les fluides du corps et une bonne biocompatibilitĂ©. Pour cette raison, le comportement Ă la corrosion et Ă lâusure de lâalliage TiNi avec des teneurs en Ni varie de 40 Ă 60% en poids, ont Ă©tĂ© Ă©tudiĂ©s afin de vĂ©rifier lâeffet du Ni sur la biocompatibilitĂ© de cet alliage pour des applications dentaires
Nanoindentation hardness and macroscopic mechanical behaviors in filled elastomeric nanocomposites
Carbon black (CB) filled semi-crystalline ethylene butyl acrylate (EBA) copolymer networks are investigated to probe for the CB particles dependence of the deformation behavior from nano-to micrometers length scales of samples which are submitted to nanoindentation characterization. With respect to this purpose, the phenomenology for hardness (H) response in these materials indicates a typical increase of the hardness by decreasing the indentation depth (h) similar to the observed behavior in elastomeric materials. This behavior can be related to the change of the mesostructure, formed by the heterogeneous three-dimensional interconnected network of polymer and of aggregates of CB particles. Furthermore, The CB amount is found to increase the resistance of composite under the action of a mechanical stress. The H-h curves were then compared to some analytical models and correlated to a tensile macroscopic behavior in order to highlight the involved deformation mechanisms with length scale. A complementary set of characterizations such as profilometry and atomic force microscopy probes were also employed to best understand of those mechanisms
Influence of processing conditions on nanoindentation properties of spark plasma sintered ptfe
The Spark Plasma Sintering (SPS) is considered as fast sintering route using self-heating action from inside the powder similar to microwave sintering and self-propagating high temperature. High sintering rate, low temperature processing, ease of operation and accurate control of sintering energy are the major advantages of this non-melting technique with regard to classical methods. The aim of this investigation is to take benefit from the advantages offered by the SPS process in order to sinter the polytetrafluoroethylene (PTFE) polymer materials from PTFE powder particles. The effect of the processâs parameters, namely the sintering temperature and heating rate, on the nanoindentation deformation is explored at room temperature. Empirical data on depth-dependent hardness are confronted to some theoretical models with a special focus on the apparent surface stress changes with the indentation depth. Furthermore, the obtained results are compared to the macro-behavior deduced from tensile and bending properties in order to assess the change in both surface and bulk deformations of the SPSed samples and according to the processing parameters
Requirements for translation re-initiation in Escherichia coli: roles of initiator tRNA and initiation factors IF2 and IF3
Despite its importance in post-transcriptional regulation of polycistronic operons in Escherichia coli, little is known about the mechanism of translation re-initiation, which occurs when the same ribosome used to translate an upstream open reading frame (ORF) also translates a downstream ORF. To investigate translation re-initiation in Escherichia coli, we constructed a di-cistronic reporter in which a firefly luciferase gene was linked to a chloramphenicol acetyltransferase gene using a segment of the translationally coupled geneVâgeneVII intercistronic region from M13 phage. With this reporter and mutant initiator tRNAs, we show that two of the unique properties of E. coli initiator tRNA â formylation of the amino acid attached to the tRNA and binding of the tRNA to the ribosomal P-site â are as important for re-initiation as for de novo initiation. Overexpression of IF2 or increasing the affinity of mutant initiator tRNA for IF2 enhanced re-initiation efficiency, suggesting that IF2 is required for efficient re-initiation. In contrast, overexpression of IF3 led to a marked decrease in re-initiation efficiency, suggesting that a 30S ribosome and not a 70S ribosome is used for translation re-initiation. Strikingly, overexpression of IF3 also blocked E. coli from acting as a host for propagation of M13 phage
Transient Phenomena in Gene Expression after Induction of Transcription
When transcription of a gene is induced by a stimulus, the number of its mRNA molecules changes with time. Here we discuss how this time evolution depends on the shape of the mRNA lifetime distribution. Analysis of the statistical properties of this change reveals transient effects on polysomes, ribosomal profiles, and rate of protein synthesis. Our studies reveal that transient phenomena in gene expression strongly depend on the specific form of the mRNA lifetime distribution
Measurement of the Rates of Synthesis of Three Components of Ribosomes of Mycobacterium fortuitum: A Theoretical Approach to qRT-PCR Experimentation
BACKGROUND: Except for the ribosomal protein L12 (rplL), ribosomal proteins are present as one copy per ribosome; L12 (rplL) is unusual because it is present as four copies per ribosome. Thus, the strategies used by Mycobacterium fortuitum to regulate ribosomal protein synthesis were investigated, including evaluations of the rates of chain elongations of 16S rRNA, rplL and ribosomal protein S12 (rpsL). METHODOLOGY: RNA was isolated from cell cultures and cDNA was prepared. The numbers of cDNA copies of 16S rRNA, precursor-16S rRNA and transcripts of rpsL and rplL were quantified by qRT-PCR and then related to the rates of 16S rRNA, rpsL and rplL chain elongations by means of a mathematical framework for coupled transcription/translation. PRINCIPAL FINDINGS: The rates of synthesis of 16S rRNA, rpsL and rplL respectively were found to be approximately 50 x 10(3) nucleotides h(-1), 1.6 x 10(3) amino acid residues h(-1) and 3.4 x 10(3) amino acid residues h(-1). The number of transcripts of rplL was approximately twice that of rpsL. These data account for the presence of one copy of rpsL and four copies of rplL per ribosome, and reveal that the rate of M. fortuitum ribosome synthesis was closer to that of M. tuberculosis than to E. coli. Except for rplJ, the elongation rate obtained for rpsL was inferred to be appropriate for all other proteins present as one copy per ribosome. SIGNIFICANCE: The results obtained provide the basis for a comprehensive view of the kinetics of ribosome synthesis, and of the ways that bacterial cells utilize genes encoding ribosomal proteins. The methodology also applies to proteins involved in transcription, energy generation and to bacterial proteins in general. The method proposed for measuring the fidelity of cDNA preparations is intrinsically much more sensitive than procedures that measure the integrity of 16S rRNA
- âŠ