Among the 3 billion base pairs of the human genome, there are approximately 30,000-40,000 protein-coding genes, but the function of at least half of them remains unknown. A new tool - short interfering RNAs (siRNAs) - has now been developed for systematically deciphering the functions and interactions of these thousands of genes. siRNAs are an intermediate of RNA interference, the process by which double-stranded RNA silences homologous genes. Although the use of siRNAs to silence genes in vertebrate cells was only reported a year ago, the emerging literature indicates that most vertebrate genes can be studied with this technology.

http://facstaff.uwa.edu/dsalter/cell%20biology%20F02/gene%20silency%20review.pdf

Gene silencing in mammals by small interfering RNAs

Mitosis and cytokinesis are undoubtedly the most spectacular parts of the cell cycle. Errors in the choreography of these processes can lead to aneuploidy or genetic instability, fostering cell death or disease. Here, I give an overview of the many mitotic kinases that regulate cell division and the fidelity of chromosome transmission.

Mitotic kinases as regulators of cell division and its checkpoints

Eukaryotic cells replicate by a complex series of evolutionarily conserved events that are tightly regulated at defined stages of the cell division cycle. Progression through this cycle involves a large number of dedicated protein complexes and signaling pathways, and deregulation of this process is implicated in tumorigenesis. We applied high-resolution mass spectrometry-based proteomics to investigate the proteome and phosphoproteome of the human cell cycle on a global scale and quantified 6027 proteins and 20,443 unique phosphorylation sites and their dynamics. Co-regulated proteins and phosphorylation sites were grouped according to their cell cycle kinetics and compared to publicly available messenger RNA microarray data. Most detected phosphorylation sites and more than 20% of all quantified proteins showed substantial regulation, mainly in mitotic cells. Kinase-motif analysis revealed global activation during S phase of the DNA damage response network, which was mediated by phosphorylation by ATM or ATR or DNA-dependent protein kinases. We determined site-specific stoichiometry of more than 5000 sites and found that most of the up-regulated sites phosphorylated by cyclin-dependent kinase 1 (CDK1) or CDK2 were almost fully phosphorylated in mitotic cells. In particular, nuclear proteins and proteins involved in regulating metabolic processes have high phosphorylation site occupancy in mitosis. This suggests that these proteins may be inactivated by phosphorylation in mitotic cells.

Quantitative Phosphoproteomics Reveals Widespread Full Phosphorylation Site Occupancy During Mitosis

mTOR and S6K1 Mediate Assembly of the Translation Preinitiation Complex through Dynamic Protein Interchange and Ordered Phosphorylation Events

Polo-like kinases (Plks) are increasingly recognized as key regulators of mitosis, meiosis and cytokinesis. In agreement with a broad range of proposed functions during cell division, Plks are subject to complex temporal and spatial control. Recent findings are uncovering the mechanisms of Plk regulation, notably their targeting to different cellular structures through interactions with phosphorylated docking proteins. Moreover, information is emerging on the substrate specificity of Plks and the role of individual substrates in M-phase progression.

Polo-like kinases and the orchestration of cell division.

The Selective Laser Melting (SLM) process has been progressively endorsed as an industrial manufacturing technique to produce high value-added components. However, one of the main obstacles to its wide application is the uncertainty regarding the successful completion of the manufacturing process. Mechanical stresses are generated and accumulated during the process, which may lead to the parts warping and cracking. Support structures may also detach from the part but it is not certain that these cracks conduct to the manufacturing failure. The process simulations currently available do not consider the cracking of the supports and the ongoing part’s deflection. The aim of this study is to investigate cone supports fracture behaviour comparing the results from a numerical model and the manufacturing of an industrial part. A model using 1D-beam elements to mesh the supports has been developed to consider the damage of the supports, their breakage and the ongoing deflection. Some numerical convergence issues are identified and solutions are proposed. Specific experimental set-ups are developed to characterise the behaviour of the supports individually and as a group. Significant improvements are denoted while injecting the measured characteristics within the model. Some key parameters of the supports damage behaviour are identified. It is shown that the supports mechanical characteristics are significantly different from the parts due to their manufacturing conditions and environment. Also, limitations regarding the characterisation of the supports as well as strong numerical convergence issues brought by multiple supports cracking are discussed. 

/pdf/numerical-modelling-of-parts-distortion-and-beam-supports-2dberkby.pdf

Numerical modelling of parts distortion and beam supports breakage during selective laser melting (SLM) additive manufacturing

L'optimisation des conditions de coupe en fraisage UTGV necessite l'utilisation d'une approche vibratoire pour eviter une deterioration rapide de l'outil et de la broche, ainsi qu'une perte de qualite d'etat de surface. Nous proposons une transposition de la methode des lobes de stabilite au cas du fraisage de parois minces, proche du contexte de fabrication aeronautique. A l'issue d'une modelisation du comportement dynamique d'une pale et des efforts de coupe en fraisage de profil, nous decrivons les zones d'instabilite d'usinage. Une validation experimentale nous permet de mettre en evidence et de preciser la transition stabilite – instabilite puis de la correler avec nos resultats theoriques. Le profil experimental est ensuite compare avec un profil issu d'une modelisation numerique incorporant le talonnage. La comparaison avec des essais d'usinage ou le talonnage est controle permet de quantifier son role. L'objectif de ces travaux est oriente vers la definition d'une methodologie rapide de determination des conditions de coupe optimale pour une configuration d'usinage industrielle.

https://oatao.univ-toulouse.fr/6546/1/Arnaud_6546.pdf

Application de la théorie des lobes de stabilité au fraisage de parois minces

Metal additive manufacturing is a major field of study and innovation. In aerospace industry a lot of effort is made to modelise and optimize the designs. In this context, despite all efforts, metal additive manufacturing (especially SLM) still produce part generally considered as raw parts which still have some surfaces to be machined in order to obtain the required geometrical quality. Despite sometimes, great complexity and cost related to the finishing process, the machining stage is never taken into account in the design process, especially using the topological optimization approach. In this paper, a new Design for Additive Manufacturing (DFAM) method is proposed in order to optimize the design stage including topological optimization, machining, geometrical and mechanical constraints. It is shown on a typical aeronautical part that cutting forces may be the greatest forces during all the part life-time. Using 2 different topological optimization software (Inspire / Abaqus Tosca) it is shown that it is possible to consider most of the machining constrains to only slightly modify the initial design and thus simplify the machining stage and reduce possible failure during machining. Finally, machining test, geometrical accuracy control and pressure test validate the approach.

https://hal.archives-ouvertes.fr/hal-02359933/document

Design for additive manufacturing including machining constraints: A case study of topology optimization including machining forces

La fabrication de pieces minces engendre souvent des vibrations d'usinage, nuisibles aux etats de surface et
aux outillages. Le trace des lobes de stabilite bases sur les modes propres, est souvent utilise avec succes pour
les vibrations d’outil. En usinage de pieces minces, on constate parfois une moindre adequation des modeles,
car le comportement de la piece est perturbe par le contact avec l’outil. La base modale consideree
classiquement pour le trace des lobes sans considerer le contact outil-piece, n’est peut-etre pas assez adaptee.
L’article presente la phase experimentale d'un travail visant a analyser les modes de vibration d’une paroi
mince pendant l’usinage. Des mesures de champs montrent ses deformations et un calcul par elements finis
montre l’impact que la presence de l’outil pourrait avoir sur les modes propres de la piece. Ce travail vise, a
enrichir la modelisation par une meilleure connaissance du contact outil-piece.

https://oatao.univ-toulouse.fr/6579/1/Wehbe_6579.pdf

Étude expérimentale du comportement vibratoire d'une pièce mince en usinage.

Une nouvelle approche intitulee «Theorie Variationnelle des Rayons complexes est appliquee au calcul de vibrations forcees de plaques faiblement amorties dans le domaine des moyennes frequences. Pour chaque frequence de la bande consideree, la resolution d'un systeme lineaire de petite dimension donne les grandeurs effectives (energie cinetique, intensite vibratoire) ; cette approche ne fait pas intervenir une discretisation fine «elements finis» de la structure. Le premier element caracterisant cette approche est l'exploitation d'une nouvelle formulation variationnelle du probleme a resoudre qui a ete elaboree afin d'autoriser des approximations non compatibles, c'est a dire ne verifiant pas a priori les conditions de transmission aux interfaces entre les sous-structures, tant en deplacement qu'en contrainte. Ces conditions sont contenues dans la formulation variationnelle. Le deuxieme element definissant cette approche est l'introduction d'approximations a fort contenu mecanique : la solution est supposee bien decrite localement au voisinage d'un point, comme la superposition de modes de vibration locaux en nombre infini. Ces modes de base, ou «rayons complexes», verifient les lois de la dynamique.

Lionel Arnaud

Papers

Numerical modelling of parts distortion and beam supports breakage during selective laser melting (SLM) additive manufacturing

Application de la théorie des lobes de stabilité au fraisage de parois minces

Design for additive manufacturing including machining constraints: A case study of topology optimization including machining forces

Étude expérimentale du comportement vibratoire d'une pièce mince en usinage.

Modélisation et simulation des vibrations moyennes fréquences par la Théorie Variationnelle des Rayons Complexes.