A new optical set-up for on-line following up the crystallization of polymers at high cooling rates

International audienceA new experimental procedure, named " Polymer High Cooling - Optics " and whose performance has been improved, is presented. It allows us to monitor on-line the quiescent crystallization of a polymer film under high and constant cooling rates. With such a set-up, two cooling control modes are available resulting into a range of relatively moderate (from 30 to 500°C/min) and a range of high (from 500 to 1600°C/min) constant cooling rates. The crystallization experiments are observed by polarized light microscopy. Preliminary results are presented. They are obtained on the α-modification of one industrial grade of isotactic polypropylene, under relatively moderate constant cooling rates. Two relevant crystallization parameters are captured, the temperature of crystallization together with the spherulitic growth kinetics versus cooling rate. Accurate data are obtained. As well, they are in good agreement with comparable literature results compiled by Janeschitz-Kriegl [Macromolecules, 2006]. The obtained results seem to match the Hoffman and Lauritzen theory. These discussions validate our " Polymer High Cooling - Optics " set-up in relatively moderate constant cooling rates. Next step is to demonstrate the suitability of this first generation set-up for higher constant cooling rates

Influence de la vitesse de mise en forme et du cycle de chauffe sur le thixoforgeage des aciers

Analyse l’influence de la vitesse du coulisseau et de la température du lopin (fraction liquide) sur le comportement de l’acier à l’état semi-solide en utilisant un nouvel outillage de filage direct monté sur une presse hydraulique. Cette nouvelle conception évite la décélération du vérin rapide pendant la mise en forme. Il permet donc des essais à vitesse constante. Ce travail s’intéresse également à l’écoulement de la matière dans le cas du thixoforgeage de l’acier et montre l’importance d’un couplage entre la température initiale et la vitesse de déformation. Les différentes conditions permettant d’avoir un écoulement homogène et continu, avec un effort de mise en forme faible, sont étudiées et présentées.This paper analyses the influence of two parameters (tool axis speed and billet temperature) on semi-solid steel alloy behaviour. A new design of direct filling tool is proposed and adapted on hydraulic press. This concept avoids the speed decrease during forming process. This works shows thermal exchange influence in thixoforging process in function speed raw and initial temperature inside the billet by analysis forming loads and part geometries

Dispersionless Fermionic KdV

We analyze the dispersionless limits of the Kupershmidt equation, the SUSY KdV-B equation and the SUSY KdV equation. We present the Lax description for each of these models and bring out various properties associated with them as well as discuss open questions that need to be addressed in connection with these models.Comment: 15 page

Dispersionless sTB

We analyze the dispersionless limits of the SUSY TB-B (sTB-B) and the SUSY TB (sTB) hierarchies. We present the Lax description for each of these models, as well as the N=2 sTB hierarchy and bring out various properties associated with them. We also discuss open questions that need to be addressed in connection with these models.Comment: Latex 15 page

Proactivity directed toward the team and organization : the role of leadership, commitment and role-breadth self-efficacy

Employees' proactive behaviour is increasingly important for organizations seeking to adapt in uncertain economic environments. This study examined the link between leadership and proactive behaviour. We differentiated between organizational leadership and team leadership and proposed that transformational leadership by team leaders would enhance commitment to the team, which would predict team member proactivity. In contrast, transformational leadership by leaders of the organization would enhance commitment to the organization, which we expected to predict organization member proactivity. Transformational leadership on both levels was expected to increase employees' role-breadth self-efficacy, the confidence necessary to engage in proactive behaviour. Our results demonstrate the importance of leadership as an antecedent of proactive work behaviour and suggest that leadership at different levels influences proactivity via different mediators. Transformational team leaders seem to facilitate proactivity by increasing employees' confidence to initiate change. Transformational organizational leaders on the other hand increase proactivity by enhancing employees' commitment to the organization

Supersymmetric Extensions of the Harry Dym Hierarchy

We study the supersymmetric extensions of the Harry Dym hierarchy of equations. We obtain the susy-B extension, the doubly susy-B extension as well as the N=1 and the N=2 supersymmetric extensions for this system. The N=2 supersymmetric extension is particularly interesting, since it leads to new classical integrable systems in the bosonic limit. We prove the integrability of these systems through the bi-Hamiltonian formulation of integrable models and through the Lax description. We also discuss the supersymmetric extension of the Hunter-Zheng equation which belongs to the Harry Dym hierarchy of equations.Comment: 15 pages, Latex fil

Chandra X-ray Observations of 12 Millisecond Pulsars in the Globular Cluster M28

We present a Chandra X-ray Observatory investigation of the millisecond pulsars (MSPs) in the globular cluster M28 (NGC 6626). In what is one of the deepest X-ray observations of a globular cluster, we firmly detect seven and possibly detect two of the twelve known M28 pulsars. With the exception of PSRs B1821-24 and J1824-2452H, the detected pulsars have relatively soft spectra, with X-ray luminosities 10^30-31 ergs s^-1 (0.3-8 keV),similar to most "recycled" pulsars in 47 Tucanae and the field of the Galaxy, implying thermal emission from the pulsar magnetic polar caps. We present the most detailed X-ray spectrum to date of the energetic PSR B1821-24. It is well described by a purely non-thermal spectrum with spectral photon index 1.23 and luminosity 1.4x10^33Theta(D/5.5 kpc)^2 ergs s^-1 (0.3-8 keV), where Theta is the fraction of the sky covered by the X-ray emission beam(s). We find no evidence for the previously reported line emission feature around 3.3 keV, most likely as a consequence of improvements in instrument calibration. The X-ray spectrum and pulse profile of PSR B1821--24 suggest that the bulk of unpulsed emission from this pulsar is not of thermal origin, and is likely due to low-level non-thermal magnetospheric radiation, an unresolved pulsar wind nebula, and/or small-angle scattering of the pulsed X-rays by interstellar dust grains. The peculiar binary PSR J1824-2452H shows a relatively hard X-ray spectrum and possible variability at the binary period, indicative of an intrabinary shock formed by interaction between the relativistic pulsar wind and matter from its non-degenerate companion star.Comment: 9 pages, 6 figures. Accepted for publication in the Astophysical Journa

Chromatin remodeling agent trichostatin A: a key-factor in the hepatic differentiation of human mesenchymal stem cells derived of adult bone marrow

BACKGROUND: The capability of human mesenchymal stem cells (hMSC) derived of adult bone marrow to undergo in vitro hepatic differentiation was investigated. RESULTS: Exposure of hMSC to a cocktail of hepatogenic factors [(fibroblast growth factor-4 (FGF-4), hepatocyte growth factor (HGF), insulin-transferrin-sodium-selenite (ITS) and dexamethasone)] failed to induce hepatic differentiation. Sequential exposure to these factors (FGF-4, followed by HGF, followed by HGF+ITS+dexamethasone), however, resembling the order of secretion during liver embryogenesis, induced both glycogen-storage and cytokeratin (CK)18 expression. Additional exposure of the cells to trichostatin A (TSA) considerably improved endodermal differentiation, as evidenced by acquisition of an epithelial morphology, chronological expression of hepatic proteins, including hepatocyte-nuclear factor (HNF)-3β, alpha-fetoprotein (AFP), CK18, albumin (ALB), HNF1α, multidrug resistance-associated protein (MRP)2 and CCAAT-enhancer binding protein (C/EBP)α, and functional maturation, i.e. upregulated ALB secretion, urea production and inducible cytochrome P450 (CYP)-dependent activity. CONCLUSION: hMSC are able to undergo mesenchymal-to-epithelial transition. TSA is hereby essential to promote differentiation of hMSC towards functional hepatocyte-like cells