Static and Dynamic Thermo Mechanical Characterization of a Bio-Compatible Shape Memory Polymer

International audienceShape memory polymers encounter a growing interest over the past ten years particularly because their eventual bio-compatibility leads to many bio-medical applications. They also present many benefits for the design of micro-adaptive systems for deployment or controlled damping materials. Indeed, the SMPs are polymeric smart materials which have the remarkable ability to recover their primary shape from a temporary one when submitted to an external stimulus. The present study deals with the synthesis and the thermo-mechanical characterization of a thermally-actuated SMP. The polymer considered hereafter is a chemically cross-linked thermoset. It is synthesized via photo polymerization (UV curing) of the monomer tert-butyl acrylate (tBA) with the crosslinking agent poly(ethylene glycol) dimethacrylate (PEGDMA) and the photoinitiator 2,2-dimethoxy-2-phenylacetophenone (DMPA). A mechanical characterization has been performed using three kinds of tests: quasi-static tensile tests, tensile dynamic mechanical analysis (DMA) and modal tests. The Young's modulus and the Poisson ratio are determined at ambient temperature using the first technique. The DMA is used to determine the evolution of viscoelastic properties as a function of the temperature and the frequency under harmonic loading. The modal analysis is employed to identify the viscoelastic properties of the material at higher frequency. A comparison of the results obtained by these three experimental methods highlights their complementarity

The EPOC project: Energy Proportional and Opportunistic Computing system

15397International audienceWith the emergence of the Future Internet and the dawning of new IT models such as cloud computing, the usage of data centers (DC), and consequently their power consumption, increase dramatically. Besides the ecological impact, the energy consumption is a predominant criteria for DC providers since it determines the daily cost of their infrastructure. As a consequence, power management becomes one of the main challenges for DC infrastructures and more generally for large-scale distributed systems. In this paper, we present the EPOC project which focuses on optimizing the energy consumption of mono-site DCs connected to the regular electrical grid and to renewable energy sources

Le pâturage favorise la mise en place de réserves dans la base des tiges de graminées

National audienc

Le pâturage favorise la mise en place de réserves dans la base des tiges de graminées

National audienc

Reproduction of PMWS in immunostimulated SPF piglets transfected with infectious cloned genomic DNA of type 2 porcine circovirus

Postweaning multisystemic wasting syndrome (PMWS) is a recently emerged disease affecting pigs. Type 2 porcine circovirus (PCV2) has been associated with this syndrome although other factors are required in association with this virus for PMWS expression. The aim of this study was to investigate whether general immunostimulation (injections of keyhole limpet hemocyanin emulsified in incomplete Freund adjuvant and of thioglycollate medium) could strengthen the severity of PMWS in six-week-old specific-pathogen-free (SPF) piglets transfected with pure tandem-cloned PCV2 DNA by the intramuscular route. Non-immunostimulated piglets transfected with the viral clone did not present clinical signs but only mild pathological microlesions characteristic of PMWS. These piglets seroconverted and high viral genome loads and infectious titers were detected in the lymphoid organs at the end of the trial. Mild-to-moderate forms of PMWS were generally observed in the immunostimulated transfected piglets, as well as one severe form for a piglet (8003) which died. These piglets with mild-to-moderate forms had higher DNA loads than the transfected-only animals. Thus, viral replication was enhanced by immunostimulation. This is the first time that clinical PMWS has been reported in an SPF immunostimulated piglet infected with a pure inoculum consisting of tandem-cloned PCV2 DNA. This result confirms that PCV2 is the agent of PMWS and that immunostimulation could enhance PMWS in SPF piglets transfected with a PCV2 DNA clone

Grazing intensity modulates carbohydrate storage pattern in five grass species from temperate grasslands

Regrowth after defoliation is an essential mechanism of plant tolerance to grazing. In grasses, non-structural carbohydrates (NSC) contained in tiller bases constitute a major substrate for regrowth after defoliation. Using a multi-specific approach, the present study aimed at testing the effect of grazing intensity on NSC concentration in tiller bases. We selected five grazing-tolerant grass species (Agrostis stolonifera, Cynosurus cristatus, Hordeum secalinum, Lolium perenne and Poa trivialis) and collected plants in a grassland subjected to two cattle grazing intensities (intensive versus moderate) for years. We measured NSC concentrations (starch, fructans, sucrose, glucose and fructose) in tiller bases. We found that fructan and sucrose concentrations before the grazing season (April) were higher under intensive than moderate grazing. By contrast, no significant effect of the grazing intensity on these NSC concentrations in tiller bases remained at the end of the grazing season (October). These results suggest that the level of reserves available before the onset of disturbance caused by grazing as well as the reserve replenishment capacity during the grazing season are modified by the intensity of grazing

Identification of the viscoelastic properties of the tBA/PEGDMA polymer from multi-loading modes conducted over a wide frequency–temperature scale range

International audienceThe viscoelastic properties of tBA/PEGDMA, which is a Shape Memory Polymer (SMP), were characterized over wide bands of frequency and temperature. The continuity of the viscoelastic properties identified according to the frequency, the temperature, the loading mode and the test scale was assessed. Seven experimental methods were used, from quasi-static to high frequencies, in tensile, shear and compression, from the nanoscopic scale to the macroscopic scale. The storage modulus and the loss factor of the SMP were evaluated and compared from one method to the other. The comparison between the various tests was done based on measurements obtained with a Dynamic Mechanical Analysis and extrapolated through the Time-Temperature Superposition principle. All the data gathers on a unique master curve. For the various experimental methods, it appears that all the viscoelastic properties are consistent even if different scales and loading modes are involved. This wide band characterization makes it possible to determine the mechanical viscoelastic properties of the tBA/PEGDMA in order to use it in structural applications. The experimental methods used in this paper combine commercial methods and in-house high-tech methods. It should be emphasized that the set of experiments covers effective measurements from 10−4 to 106 Hz, 0 to 90°C, strain levels from 10−4% to 5%, at nano, micro and macro scales on the same material

Impact of species and antibiotic therapy of enterococcal peritonitis on 30-day mortality in critical care—an analysis of the OUTCOMEREA database

International audienceIntroduction: Enterococcus species are associated with an increased morbidity in intraabdominal infections (IAI). However, their impact on mortality remains uncertain. Moreover, the influence on outcome of the appropriate or inappropriate status of initial antimicrobial therapy (IAT) is subjected to debate, except in septic shock. The aim of our study was to evaluate whether an IAT that did not cover Enterococcus spp. was associated with 30-day mortality in ICU patients presenting with IAI growing with Enterococcus spp.Material and methods: Retrospective analysis of French database OutcomeRea from 1997 to 2016. We included all patients with IAI with a peritoneal sample growing with Enterococcus. Primary endpoint was 30-day mortality.Results: Of the 1017 patients with IAI, 76 (8%) patients were included. Thirty-day mortality in patients with inadequate IAT against Enterococcus was higher (7/18 (39%) vs 10/58 (17%), p = 0.05); however, the incidence of postoperative complications was similar. Presence of Enterococcus spp. other than E. faecalis alone was associated with a significantly higher mortality, even greater when IAT was inadequate. Main risk factors for having an Enterococcus other than E. faecalis alone were as follows: SAPS score on day 0, ICU-acquired IAI, and antimicrobial therapy within 3 months prior to IAI especially with third-generation cephalosporins. Univariate analysis found a higher hazard ratio of death with an Enterococcus other than E. faecalis alone that had an inadequate IAT (HR = 4.4 [1.3-15.3], p = 0.019) versus an adequate IAT (HR = 3.1 [1.0-10.0], p = 0.053). However, after adjusting for confounders (i.e., SAPS II and septic shock at IAI diagnosis, ICU-acquired peritonitis, and adequacy of IAT for other germs), the impact of the adequacy of IAT was no longer significant in multivariate analysis. Septic shock at diagnosis and ICU-acquired IAI were prognostic factors.Conclusion: An IAT which does not cover Enterococcus is associated with an increased 30-day mortality in ICU patients presenting with an IAI growing with Enterococcus, especially when it is not an E. faecalis alone. It seems reasonable to use an IAT active against Enterococcus in severe postoperative ICU-acquired IAI, especially when a third-generation cephalosporin has been used within 3 months

Towards energy-proportional Clouds partially powered by renewable energy

International audienceWith the emergence of the Future Internet and the dawning of new IT models such as cloud computing, the usage of data centers (DC), and consequently their power consumption, increase dramatically. Besides the ecological impact, the energy consumption is a predominant criterion for DC providers since it determines the daily cost of their infrastructure. As a consequence, power management becomes one of the main challenges for DC infrastructures and more generally for large-scale distributed systems. In this paper, we present the EpoCloud prototype, from hardware to middleware layers. This prototype aims at optimizing the energy consumption of mono-site Cloud DCs connected to the regular electrical grid and to renewable-energy sources