Etablissement de la texture au cours du soudage TIG d’alliages austénitiques : soudures réelles et numériques

The structure prediction of metallic alloys during a welding or additive manufacturing process is the key point for the joining’s properties. In addition to the welding parameters (or additive manufacturing), the base metal microstructure, chemical homogeneity and crystallographic structure are numerous factors playing an important role on the final microstructure and texture development. Few studies are available in this way. This work purposes a focus on the microstructure establishment during the welded zone solidification during Gas Tungsten Arc Welding. The materials investigated are nickel – chromium – iron austenitic alloys. The grain selection is tracked in a real weld and a texturation criteria is proposed. The following data’s are compared to the properties of the numerical weld experience. The conclusion suggests that is necessary to improve the knowledges in the grain selection mechanism in order to produce numerical welding microstructure in good accordance with real microstructure welding.La prédiction de la structure des alliages métalliques durant une étape de soudage ou de fabrication additive est un point clef du développement de ces procédés et des propriétés des assemblages. En plus des paramètres de soudage (ou de fabrication additive), la microstructure du métal de base, son homogénéité chimique et sa nature cristallographique sont autant de facteur jouant un rôle sur l’établissement final des microstructures et des textures pour lesquels peu d’études détaillées sont disponibles. Une description précise de l’établissement des microstructures de solidification lors du soudage TIG d’alliage austénitique nickel-chrome-fer est réalisée dans ce travail. La sélection des grains dans la soudure est suivie dans une soudure réelle. Un critère de texturation est proposé et les données sont comparées aux textures simulées d’où il ressort l’importance d’augmenter la connaissance des mécanismes de sélection de grains pour espérer modéliser encore plus fidèlement les propriétés microstructurales et de texture générées par le soudage

QTL detection by multi-parent linkage mapping in oil palm (Elaeis guineensis Jacq.)

A quantitative trait locus (QTL) analysis designed for a multi-parent population was carried out and tested in oil palm (Elaeis guineensis Jacq.), which is a diploid cross-fertilising perennial species. A new extension of the MCQTL package was especially designed for crosses between heterozygous parents. The algorithm, which is now available for any allogamous species, was used to perform and compare two types of QTL search for small size families, within-family analysis and across-family analysis, using data from a 2 × 2 complete factorial mating experiment involving four parents from three selected gene pools. A consensus genetic map of the factorial design was produced using 251 microsatellite loci, the locus of the Sh major gene controlling fruit shell presence, and an AFLP marker of that gene. A set of 76 QTLs involved in 24 quantitative phenotypic traits was identified. A comparison of the QTL detection results showed that the across-family analysis proved to be efficient due to the interconnected families, but the family size issue is just partially solved. The identification of QTL markers for small progeny numbers and for marker-assisted selection strategies is discussed

QTLs for oil yield components in an elite oil palm (Elaeis guineensis) cross

Increased modern farming of superior types of the oil palm, Elaeis guineensis Jacq., which has naturally efficient oil biosynthesis, has made it the world’s foremost edible oil crop. Breeding improvement is, however, circumscribed by time and costs associated with the tree’s long reproductive cycle, large size and 10–15 years of field testing. Marker-assisted breeding has considerable potential for improving this crop. Towards this, quantitative trait loci (QTL) linked to oil yield component traits were mapped in a high-yield population. In total, 164 QTLs associated with 21 oil yield component traits were discovered, with cumulative QTL effects increasing in tandem with the number of QTL markers and matching the QT+ alleles for each trait. The QTLs confirmed all traits to be polygenic, with many genes of individual small effects on independent loci, but epistatic interactions are not ruled out. Furthermore, several QTLs maybe pleiotropic as suggested by QTL clustering of inter-related traits on almost all linkage groups. Certain regions of the chromosomes seem richer in the genes affecting a particular yield component trait and likely encompass pleiotropic, epistatic and heterotic effects. A large proportion of the identified additive effects from QTLs may actually arise from genic interactions between loci. Comparisons with previous mapping studies show that most of the QTLs were for similar traits and shared similar marker intervals on the same linkage groups. Practical applications for such QTLs in marker-assisted breeding will require seeking them out in different genetic backgrounds and environments

In Situ Spatiotemporal Mapping of Flow Fields around Seeded Stem Cells at the Subcellular Length Scale

A major hurdle to understanding and exploiting interactions between the stem cell and its environment is the lack of a tool for precise delivery of mechanical cues concomitant to observing sub-cellular adaptation of structure. These studies demonstrate the use of microscale particle image velocimetry (μ-PIV) for in situ spatiotemporal mapping of flow fields around mesenchymal stem cells, i.e. murine embryonic multipotent cell line C3H10T1/2, at the subcellular length scale, providing a tool for real time observation and analysis of stem cell adaptation to the prevailing mechanical milieu. In the absence of cells, computational fluid dynamics (CFD) predicts flow regimes within 12% of μ-PIV measures, achieving the technical specifications of the chamber and the flow rates necessary to deliver target shear stresses at a particular height from the base of the flow chamber. However, our μ-PIV studies show that the presence of cells per se as well as the density at which cells are seeded significantly influences local flow fields. Furthermore, for any given cell or cell seeding density, flow regimes vary significantly along the vertical profile of the cell. Hence, the mechanical milieu of the stem cell exposed to shape changing shear stresses, induced by fluid drag, varies with respect to proximity of surrounding cells as well as with respect to apical height. The current study addresses a previously unmet need to predict and observe both flow regimes as well as mechanoadaptation of cells in flow chambers designed to deliver precisely controlled mechanical signals to live cells. An understanding of interactions and adaptation in response to forces at the interface between the surface of the cell and its immediate local environment may be key for de novo engineering of functional tissues from stem cell templates as well as for unraveling the mechanisms underlying multiscale development, growth and adaptation of organisms

Microsatellites for the genus Cucurbita and an SSR-based genetic linkage map of Cucurbita pepo L.

Until recently, only a few microsatellites have been available for Cucurbita, thus their development is highly desirable. The Austrian oil-pumpkin variety Gleisdorfer Ölkürbis (C. pepo subsp. pepo) and the C. moschata cultivar Soler (Puerto Rico) were used for SSR development. SSR-enriched partial genomic libraries were established and 2,400 clones were sequenced. Of these 1,058 (44%) contained an SSR at least four repeats long. Primers were designed for 532 SSRs; 500 primer pairs produced fragments of expected size. Of these, 405 (81%) amplified polymorphic fragments in a set of 12 genotypes: three C. moschata, one C. ecuadorensis, and eight C. pepo representing all eight cultivar groups. On an average, C. pepo and C. moschata produced 3.3 alleles per primer pair, showing high inter-species transferability. There were 187 SSR markers detecting polymorphism between the USA oil-pumpkin variety “Lady Godiva” (O5) and the Italian crookneck variety “Bianco Friulano” (CN), which are the parents of our previous F2 mapping population. It has been used to construct the first published C. pepo map, containing mainly RAPD and AFLP markers. Now the updated map comprises 178 SSRs, 244 AFLPs, 230 RAPDs, five SCARs, and two morphological traits (h and B). It contains 20 linkage groups with a map density of 2.9 cM. The observed genome coverage (Co) is 86.8%

High density SNP and DArT-based genetic linkage maps of two closely related oil palm populations

Oil palm (Elaeis guineensis Jacq.) is an outbreeding perennial tree crop with long breeding cycles, typically 12 years. Molecular marker technologies can greatly improve the breeding efficiency of oil palm. This study reports the first use of the DArTseq platform to genotype two closely related self-pollinated oil palm populations, namely AA0768 and AA0769 with 48 and 58 progeny respectively. Genetic maps were constructed using the DArT and SNP markers generated in combination with anchor SSR markers. Both maps consisted of 16 major independent linkage groups (2n = 2× = 32) with 1399 and 1466 mapped markers for the AA0768 and AA0769 populations, respectively, including the morphological trait “shell-thickness” (Sh). The map lengths were 1873.7 and 1720.6 cM with an average marker density of 1.34 and 1.17 cM, respectively. The integrated map was 1803.1 cM long with 2066 mapped markers and average marker density of 0.87 cM. A total of 82% of the DArTseq marker sequence tags identified a single site in the published genome sequence, suggesting preferential targeting of gene-rich regions by DArTseq markers. Map integration of higher density focused around the Sh region identified closely linked markers to the Sh, with D.15322 marker 0.24 cM away from the morphological trait and 5071 bp from the transcriptional start of the published SHELL gene. Identification of the Sh marker demonstrates the robustness of using the DArTseq platform to generate high density genetic maps of oil palm with good genome coverage. Both genetic maps and integrated maps will be useful for quantitative trait loci analysis of important yield traits as well as potentially assisting the anchoring of genetic maps to genomic sequences