Collision and size evolution of drops in homogeneous isotropic turbulence

International audienceThis paper is devoted to the study of the evolution of the spectrum in a cloud due tocollisions between drops

Dimensions of the deposited strand in the material extrusion process: Experimental and numerical investigations

International audienceThe material extrusion process is investigated by focusing on the geometry of a single strand extruded through a printing nozzle and deposited on a substrate of a 3D printer. An experimental protocol is set to determine the width W , and the height H, of a strand. The geometry depends mainly on the nozzle diameter D, the gap between the substrate and the tip of the nozzle g, the extrusion velocity U and the printing velocity V. The relevant parameter to determine W/D and H/g is reduced to one dimensionless parameter equal to (D/g)(U/V). A computational multiphase flow is described using a level set approach and a finite element method. The heat transfer is also taken into account in the set of governing equations. The polymer is considered as a generalised Newtonian fluid. An accurate description of the interface between the polymer and the surrounding air is developed based on an anisotropic remeshing procedure. Two different situations are numerically solved for which: (i) a first case with a g/D ratio less than one and (ii) a second case with a g/D ratio larger than one. In the first situation, the spreading below the nozzle is more or less radial around the vertical axis of the extruder which is not the case in the second situation. The numerical shape geometry is in good agreement with experimental observations. The thermal cooling underlines that the relevant parameters are the perimeter and the area of the strand cross-section and the Péclet number based on the printing velocity. The numerical predictions of W/D and H/g agree with experimental results

Heating and flow computations of an amorphous polymer in the liquefier of a material extrusion 3D printer

International audienceThe heating of a polymer in a liquefier of a material extrusion 3D printer is numerically studied. The problem is investigated by solving the mass, momentum, and energy conservation equations. The polymer is taken as a generalized Newtonian fluid with a dynamical viscosity function of shear rate and temperature. The system of equations is solved using a finite element method. The boundary conditions are adapted by comparison with the previous work of Peng et al. [5] showing that the thermal contact between the polymer and the liquefier is very well established. The limiting printing conditions are studied by determining the length over which the polymer temperature is below the glass transition temperature. This provides a simple relation for the inlet velocity as a function of the working parameters and the polymer properties

Mechanism of O2 bubble formation in borosilicate melts

International audienc

Application of the Sparse Cardinal Sine Decomposition to 3D Stokes Flows

International audienceIn boundary element method (BEM), one encounters linear system with a dense and non-symmetric square matrix which might be so large that inverting the linear system is too prohibitive in terms of cpu time and/or memory. Each usual powerful treatment (Fast Multipole Method, H-matrices) developed to deal with this issue is optimized to efficiently perform matrix vector products. This work presents a new technique to adequately and quickly handle such products: the Sparse Cardinal Sine Decomposition. This approach, recently pioneered for the Laplace and Helmholtz equations, rests on the decomposition of each encountered kernel as series of radial Cardinal Sine functions. Here, we achieve this decomposition for the Stokes problem and implement it in MyBEM, a new fast solver for multi-physical BEM. The reported computational examples permit us to compare the advocated method against a usual BEM in terms of both accuracy and convergence

Protein-tyrosine phosphorylation interaction network in Bacillus subtilis reveals new substrates, kinase activators and kinase cross-talk

Signal transduction in eukaryotes is generally transmitted through phosphorylation cascades that involve a complex interplay of transmembrane receptors, protein kinases, phosphatases and their targets. Our previous work indicated that bacterial protein-tyrosine kinases and phosphatases may exhibit similar properties, since they act on many different substrates. To capture the complexity of this phosphorylation-based network, we performed a comprehensive interactome study focused on the protein-tyrosine kinases and phosphatases in the model bacterium Bacillus subtilis. The resulting network identified many potential new substrates of kinases and phosphatases, some of which were experimentally validated. Our study highlighted the role of tyrosine and serine/threonine kinases and phosphatases in DNA metabolism, transcriptional control and cell division. This interaction network reveals significant crosstalk among different classes of kinases. We found that tyrosine kinases can bind to several modulators, transmembrane or cytosolic, consistent with a branching of signaling pathways. Most particularly, we found that the division site regulator MinD can form a complex with the tyrosine kinase PtkA and modulate its activity in vitro. In vivo, it acts as a scaffold protein which anchors the kinase at the cell pole. This network highlighted a role of tyrosine phosphorylation in the spatial regulation of the Z-ring during cytokinesis

Experimental and numerical investigations of an oxygen single‐bubble shrinkage in a borosilicate glass‐forming liquid doped with cerium oxide

International audienceThe shrinkage of an oxygen single-bubble is investigated in a cerium-doped borosil-icate glass melt at 1150°C. Nine glass samples are synthesized and investigated, utilizing three different amounts of Ce2O3 and three different redox ratios (Ce-(III)/Ce total). Employing in-situ observation, the single-bubble behavior is recorded with a camera. For each glass melt, five experiments are performed with different initial bubble radii. The shrinkage rate (da/dt) depends strongly on the cerium content as well as the redox ratio. Numerical calculations are also conducted to support the understanding of the bubble shrinkage mechanism in the given cases. The model adequately estimates the experimental data for several cases, and an explanation is proposed for the cases, in which it does not. Moreover, we demonstrate, physically and mathematically, the influence of the initial radius of the bubble on the mass transfer between the rising bubble and the melt. We confirm the utilization of the "modified Péclet number", which is a dimensionless number that takes into consideration the influence of multivalent elements on mass transfer. Finally, we master the bubble shrinkage behavior by normalizing the experimental data employing a characteristic time for the mass transfer (&tau)