Environnements numériques et PME : figures du chaos et nouveaux usages

Is the revolution of the so-called Web 2.0 a real success for the SMEs? Do we really see a change of the communication paradigm (following Kuhn’s meaning) due to the arrival of the networks that put the individual at the centre of the organization processes? Within the framework of a “fluid society” characterised by uncertainty and complexity, this thesis focuses on the issue of internal and external adjustments in connection with the Web 2.0 within SMEs. These adjustments may be a source of disorder within the organization and SMEs would try to regulate them. Nevertheless, some SMEs will choose to use them as a springboard. They will build on existing skills, improve the efficiency of the company (operating activity) and also explore completely new fields (exploration activity) like collective intelligence and crowdsourcing. The web 2.0 indicates the passage of a "tools" technology considered as stable to a "social" technology characterized by instability. The Web 2.0 has a catalytic effect that encourages and facilitates transversal adjustments. It could be seen as a way to transform the organization in order to become more focused on individuals and groups. But it also brings a number of challenges for SMEs. Using the concepts of chaos and complexity was an interesting way to understand this balance to be attained between order and disorder. This thesis is interdisciplinary by objective. It intends to show the interest of using together theories, literature and fields coming from management, information science and communication when these disciplines are required to take into account the complexity of relationships but also co-construction between prosumers and SMEs, and management and employees. The research will be based inter alia on a total of 93 SMEs, audited by the author between 2010 and 2014.La « révolution » du web 2.0 s’est-elle imposée dans les PME ? La mise en réseau, porté par le web 2.0 qui met l’utilisateur au centre des processus de l’entreprise, a–t’elle opéré un changement de paradigme communicationnel au sens de Kuhn ? Sur fonds d’une société de plus en plus fluide, inscrite dans l’incertitude et la complexité, cette thèse s’intéresse à la question des ajustements transversaux en lien avec le web 2.0 et à leur prise en compte par les PME. Ce dernier peut être vu comme source de désordres dans l’organisation et la PME sera tentée de vouloir les réguler. Néanmoins, certaines PME choisiront de s’en servir comme d’un tremplin. Elles vont à la fois construire sur des compétences existantes et améliorer l’efficience de l’entreprise (activité d’exploitation) mais également explorer des champs totalement nouveaux (activité d’exploration) dont l’intelligence collective et le crowdsourcing sont des exemples. Les outils du web 2.0 indiquent le passage d’une technologie « outils » considérée comme stable vers une technologie « sociale » caractérisée par l’instabilité. Le web 2.0 a un effet de catalyseur qui suscite et facilite à la fois les ajustements transversaux, il peut se concevoir comme un levier de pilotage vers une organisation plus centrée sur les individus et les groupes. Ceci pose un certain nombre de défis aux PME. L’éclairage des sciences du chaos et de la complexité semble une piste intéressante pour comprendre cet équilibre à atteindre entre ordre et désordre. Cette thèse a un ancrage interdisciplinaire et montre l’intérêt de croiser les sciences de gestion et les sciences de l’information et de la communication lorsque ces disciplines sont appelées à prendre en compte la complexité des rapports transversaux mais aussi de co-construction entre consom’acteurs et PME. La recherche s’appuie entre autres, sur un terrain applicatif de 93 PME, auditées entre 2010 et 2014

Numerical simulation of Ar-x%CO2 shielding gas and its effect on an electric welding arc

This study focuses on the simulation of a plasma arc heat source in the context of electric arc welding. The simulation model was implemented in the open source CFD software OpenFOAM-1.6.x, in three space dimensions, coupling thermal fluid mechanics with electromagnetism. Two approaches were considered for calculating the magnetic field: i) the three-dimensional approach, and ii) the so-called axisymmetric approach. The electromagnetic part of the solver was tested against analytic solution for an infinite electric rod. Perfect agreement was obtained. The complete solver was tested against experimental measurements for Gas Tungsten Arc Welding (GTAW) with an axisymmetric configuration. The shielding gas was argon, and the anode and cathode were treated as boundary conditions. The numerical solutions then depend significantly on the approach used for calculating the magnetic field. The so-called axisymmetric approach indeed neglects the radial current density component, mainly resulting in a poor estimation of the arc velocity. Plasma arc simulations were done for various Ar-x%CO2 shielding gas compositions: pure argon ( x =0), pure carbon dioxide ( x =100), and mixtures of these two gases with x =1 and 10% in mole. The simulation results clearly show that the presence of carbon dioxide results in thermal arc constriction, and increased maximum arc temperature and velocity. Various boundary conditions were set on the anode and cathode (using argon as shielding gas) to evaluate their influence on the plasma arc. These conditions, difficult to measure and to estimate a priori, significantly affect the heat source simulation results. Solution of the temperature and electromagnetic fields in the anode and cathode will thus be included in the forthcoming developments

Comparative study of the main electromagnetic models applied to melt pool prediction with gas metal arc: Effect on flow, ripples from drop impact, and geometry

The present work concerns the electromagnetic force models in computational fluid dynamics simulations of melt pools produced with electric arcs. These are commonly applied to gas metal arcs with metal transfer, in welding and additive manufacturing. Metal drop impact on the melt pool is thus included in this study. The electromagnetic force models applied in literature use either numerical solutions of Poisson equations or one of the two analytical models developed by Kou and Sun, or Tsao and Wu. These models rely on assumptions for which the effect on the melt pool predictions remains to be understood. The present work thoroughly investigates those assumptions and their effects. It has been supported by dedicated experimental tests that did provide estimates of unknown model parameters and validation data. The obtained results show that the assumptions that fundamentally distinguish these three models change the electromagnetic force, including the relation between its components. These changes, which can also be spatially non-uniform, are large. As a result, these models lead to significantly different recirculation flow pattern, thermal convection, melt pool morphology, bead dimensions, and free surface response to the metal transfer. We conclude by proposing conditions in which each of these models issuited or questionable

Effect of Substrate Orientation on Melt Pool during Multi-Layer Deposition in V-Groove with Gas Metal Arc

Thermo-fluid dynamic and experimental approaches are used to investigate the influence of 20\ub0 uphill, downhill and sideway substrate orientation during metal deposition over a previously deposited bead in a V-groove. The computational fluid dynamic model with free surface deformation and metal transfer gives insight into the melt pool flow and causes of defect formation observed on the solidified beads. The experimental metallographs, high-speed images and computational results show good agreement. It is found that the deposition of a second layer on a smooth first layer cooled down to room temperature leads to large changes in melt pool flow pattern at 20\ub0 substrate inclination compared to flat condition. It results in undercut and humps with the uphill orientation and undercut with the side inclination. Therefore, lower angle range is necessary for multilayer gas metal arc deposition for these two last configurations

Deletion of Nkx2-5 in trabecular myocardium reveals the developmental origins of pathological heterogeneity associated with ventricular non-compaction cardiomyopathy.

Left ventricular non-compaction (LVNC) is a rare cardiomyopathy associated with a hypertrabeculated phenotype and a large spectrum of symptoms. It is still unclear whether LVNC results from a defect of ventricular trabeculae development and the mechanistic basis that underlies the varying severity of this pathology is unknown. To investigate these issues, we inactivated the cardiac transcription factor Nkx2-5 in trabecular myocardium at different stages of trabecular morphogenesis using an inducible Cx40-creERT2 allele. Conditional deletion of Nkx2-5 at embryonic stages, during trabecular formation, provokes a severe hypertrabeculated phenotype associated with subendocardial fibrosis and Purkinje fiber hypoplasia. A milder phenotype was observed after Nkx2-5 deletion at fetal stages, during trabecular compaction. A longitudinal study of cardiac function in adult Nkx2-5 conditional mutant mice demonstrates that excessive trabeculation is associated with complex ventricular conduction defects, progressively leading to strain defects, and, in 50% of mutant mice, to heart failure. Progressive impaired cardiac function correlates with conduction and strain defects independently of the degree of hypertrabeculation. Transcriptomic analysis of molecular pathways reflects myocardial remodeling with a larger number of differentially expressed genes in the severe versus mild phenotype and identifies Six1 as being upregulated in hypertrabeculated hearts. Our results provide insights into the etiology of LVNC and link its pathogenicity with compromised trabecular development including compaction defects and ventricular conduction system hypoplasia

The JWST Early Release Science Program for the Direct Imaging and Spectroscopy of Exoplanetary Systems

The direct characterization of exoplanetary systems with high-contrast imaging is among the highest priorities for the broader exoplanet community. As large space missions will be necessary for detecting and characterizing exo-Earth twins, developing the techniques and technology for direct imaging of exoplanets is a driving focus for the community. For the first time, JWST will directly observe extrasolar planets at mid-infrared wavelengths beyond 5 μm, deliver detailed spectroscopy revealing much more precise chemical abundances and atmospheric conditions, and provide sensitivity to analogs of our solar system ice-giant planets at wide orbital separations, an entirely new class of exoplanet. However, in order to maximize the scientific output over the lifetime of the mission, an exquisite understanding of the instrumental performance of JWST is needed as early in the mission as possible. In this paper, we describe our 55 hr Early Release Science Program that will utilize all four JWST instruments to extend the characterization of planetary-mass companions to ∼15 μm as well as image a circumstellar disk in the mid-infrared with unprecedented sensitivity. Our program will also assess the performance of the observatory in the key modes expected to be commonly used for exoplanet direct imaging and spectroscopy, optimize data calibration and processing, and generate representative data sets that will enable a broad user base to effectively plan for general observing programs in future Cycles

Heterogeneous catalysis modelling and numerical simulation in rarefied gas flows

A new approach is proposed to model and simulate numerically heterogeneous catalysis in rarefied gas flows. It is developed to satisfy all together the following points: i) describe the gas phase at the microscopic scale, as required in rarefied flows, ii) describe the wall at the macroscopic scale, to avoid prohibitive computational costs and consider not only crystalline but also amorphous surfaces, iii) reproduce on average macroscopic laws correlated with experimental results and iv) derive ana- lytic models in a systematic and exact way. The problem is stated in the general framework of a non static flow in the vicinity of a catalytic and non porous surface (without ageing). It is shown that the exact and systematic resolution method based on the Laplace transform, introduced previously by the author to model collisions in the gas phase, can be extended to the present problem. The proposed approach is applied to the modelling of the Eley-Rideal and Langmuir-Hinshelwood recombinations, assuming that the coverage is locally at equilibrium. The models are developed considering one atomic species and extended to the gen eral case of several atomic species. Numerical calculations show that the models derived in this way reproduce with accuracy behaviours observed experimentally

Digital environments and SMEs : figures of chaos and new uses

La « révolution » du web 2.0 s’est-elle imposée dans les PME ? La mise en réseau, porté par le web 2.0 qui met l’utilisateur au centre des processus de l’entreprise, a–t’elle opéré un changement de paradigme communicationnel au sens de Kuhn ? Sur fonds d’une société de plus en plus fluide, inscrite dans l’incertitude et la complexité, cette thèse s’intéresse à la question des ajustements transversaux en lien avec le web 2.0 et à leur prise en compte par les PME. Ce dernier peut être vu comme source de désordres dans l’organisation et la PME sera tentée de vouloir les réguler. Néanmoins, certaines PME choisiront de s’en servir comme d’un tremplin. Elles vont à la fois construire sur des compétences existantes et améliorer l’efficience de l’entreprise (activité d’exploitation) mais également explorer des champs totalement nouveaux (activité d’exploration) dont l’intelligence collective et le crowdsourcing sont des exemples. Les outils du web 2.0 indiquent le passage d’une technologie « outils » considérée comme stable vers une technologie « sociale » caractérisée par l’instabilité. Le web 2.0 a un effet de catalyseur qui suscite et facilite à la fois les ajustements transversaux, il peut se concevoir comme un levier de pilotage vers une organisation plus centrée sur les individus et les groupes. Ceci pose un certain nombre de défis aux PME. L’éclairage des sciences du chaos et de la complexité semble une piste intéressante pour comprendre cet équilibre à atteindre entre ordre et désordre. Cette thèse a un ancrage interdisciplinaire et montre l’intérêt de croiser les sciences de gestion et les sciences de l’information et de la communication lorsque ces disciplines sont appelées à prendre en compte la complexité des rapports transversaux mais aussi de co-construction entre consom’acteurs et PME. La recherche s’appuie entre autres, sur un terrain applicatif de 93 PME, auditées entre 2010 et 2014.Is the revolution of the so-called Web 2.0 a real success for the SMEs? Do we really see a change of the communication paradigm (following Kuhn’s meaning) due to the arrival of the networks that put the individual at the centre of the organization processes? Within the framework of a “fluid society” characterised by uncertainty and complexity, this thesis focuses on the issue of internal and external adjustments in connection with the Web 2.0 within SMEs. These adjustments may be a source of disorder within the organization and SMEs would try to regulate them. Nevertheless, some SMEs will choose to use them as a springboard. They will build on existing skills, improve the efficiency of the company (operating activity) and also explore completely new fields (exploration activity) like collective intelligence and crowdsourcing. The web 2.0 indicates the passage of a "tools" technology considered as stable to a "social" technology characterized by instability. The Web 2.0 has a catalytic effect that encourages and facilitates transversal adjustments. It could be seen as a way to transform the organization in order to become more focused on individuals and groups. But it also brings a number of challenges for SMEs. Using the concepts of chaos and complexity was an interesting way to understand this balance to be attained between order and disorder. This thesis is interdisciplinary by objective. It intends to show the interest of using together theories, literature and fields coming from management, information science and communication when these disciplines are required to take into account the complexity of relationships but also co-construction between prosumers and SMEs, and management and employees. The research will be based inter alia on a total of 93 SMEs, audited by the author between 2010 and 2014