Application of a magnetic suspension balance to the oxidation study of the zirconium based alloys under high pressurewater vapour

International audienceThe fuel claddings in the Pressurised Water Reactor are corroded in water at high temperature and high pressure. The technical device ableto follow continuously the corrosion rate in conditions close to this medium does not yet exist. That is the reason why a high pressure thermogravimetric installation based on magnetic suspension has been designed to study in situ the oxidation kinetics of the zirconium based alloys under water vapour until 50 bars of pressure at 415°C. The accuracy of measurements is about 5•10–5 g under 2 bars, and 10–4 g under 50 bars. The reproducibility of measurements was verified and the deviation regarding post test weighing at room temperature is around 5•10–5 g what is clearly satisfying. Finally, the results presented in this work allow validating the high pressure thermogravimetric measurements obtained with this magnetic suspension device

Raman Study of Multicrystalline Silicon Wafers Produced by the RST Process

Producción CientíficaIn the silicon ribbon on a sacrificial template process silicon is deposited on both sides of a carbon ribbon, thus forming a Si/carbon/Si trilayer. The fast cooling of the ribbon in large temperature gradients generates stresses that are detrimental to both the electrical performance and the mechanical behaviour of the wafers. The assessment of the stresses is crucial for the setting-up of thermal treatments allowing for the stress relaxation of the wafers, prior to the cell fabrication. We present an analysis of the stress in the as-grown trilayer by a simulation of the thermomechanical behaviour of the cooling ribbon. Experimental measurements of the stress in as-grown and annealed trilayers are also presented. The results permit to establish the conditions for optimized growth and annealing.Proceedings of the 15th International Conference on Defects Recognition, Imaging and Physics in Semiconductors-Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA166A11-2)Ministerio de Ciencia e innovación (IPT-420000-2010- -022 INNPACTO program

Surface Sampling Methods for Bacillus anthracis Spore Contamination

During an investigation conducted December 17–20, 2001, we collected environmental samples from a U.S. postal facility in Washington, D.C., known to be extensively contaminated with Bacillus anthracis spores. Because methods for collecting and analyzing B. anthracis spores have not yet been validated, our objective was to compare the relative effectiveness of sampling methods used for collecting spores from contaminated surfaces. Comparison of wipe, wet and dry swab, and HEPA vacuum sock samples on nonporous surfaces indicated good agreement between results with HEPA vacuum and wipe samples. However, results from HEPA vacuum sock and wipe samples agreed poorly with the swab samples. Dry swabs failed to detect spores >75% of the time they were detected by wipe and HEPA vacuum samples. Wipe samples collected after HEPA vacuum samples and HEPA vacuum samples after wipe samples indicated that neither method completely removed spores from the sampled surfaces

NKT Cell Stimulation with α-Galactosylceramide Results in a Block of Th17 Differentiation after Intranasal Immunization in Mice

In a previous study we demonstrated that intranasal (i.n.) vaccination promotes a Th17 biased immune response. Here, we show that co-administration of a pegylated derivative of α-galactosylceramide (αGCPEG) with an antigen, even in the presence of Th17-polarizing compounds, results in a strong blocking of Th17 differentiation. Additional studies demonstrated that this phenomenon is specifically dependent on soluble factors, like IL-4 and IFNγ, which are produced by NKT cells. Even NK1.1 negative NKT cells, which by themselves produce IL-17A, are able to block Th17 differentiation. It follows that the use of αGCPEG as adjuvant would enable to tailor Th17 responses, according to the specific clinical needs. This knowledge expands our understanding of the role played by NKT cells in overall control of the cytokine microenvironment, as well as in the overall shaping of adaptive immune responses

Development and Function of Invariant Natural Killer T Cells Producing TH2- and TH17-Cytokines

Four distinct subsets of invariant natural killer T (NKT) cells are shown to differentiate in the thymus, then migrate to peripheral tissues where they retain their phenotypic and functional characteristics

Mechanisms of NK Cell-Macrophage Bacillus anthracis Crosstalk: A Balance between Stimulation by Spores and Differential Disruption by Toxins

NK cells are important immune effectors for preventing microbial invasion and dissemination, through natural cytotoxicity and cytokine secretion. Bacillus anthracis spores can efficiently drive IFN-γ production by NK cells. The present study provides insights into the mechanisms of cytokine and cellular signaling that underlie the process of NK-cell activation by B. anthracis and the bacterial strategies to subvert and evade this response. Infection with non-toxigenic encapsulated B. anthracis induced recruitment of NK cells and macrophages into the mouse draining lymph node. Production of edema (ET) or lethal (LT) toxin during infection impaired this cellular recruitment. NK cell depletion led to accelerated systemic bacterial dissemination. IFN-γ production by NK cells in response to B. anthracis spores was: i) contact-dependent through RAE-1-NKG2D interaction with macrophages; ii) IL-12, IL-18, and IL-15-dependent, where IL-12 played a key role and regulated both NK cell and macrophage activation; and iii) required IL-18 for only an initial short time window. B. anthracis toxins subverted both NK cell essential functions. ET and LT disrupted IFN-γ production through different mechanisms. LT acted both on macrophages and NK cells, whereas ET mainly affected macrophages and did not alter NK cell capacity of IFN-γ secretion. In contrast, ET and LT inhibited the natural cytotoxicity function of NK cells, both in vitro and in vivo. The subverting action of ET thus led to dissociation in NK cell function and blocked natural cytotoxicity without affecting IFN-γ secretion. The high efficiency of this process stresses the impact that this toxin may exert in anthrax pathogenesis, and highlights a potential usefulness for controlling excessive cytotoxic responses in immunopathological diseases. Our findings therefore exemplify the delicate balance between bacterial stimulation and evasion strategies. This highlights the potential implication of the crosstalk between host innate defences and B. anthracis in initial anthrax control mechanisms

The Interaction between Regulatory T Cells and NKT Cells in the Liver: A CD1d Bridge Links Innate and Adaptive Immunity

Regulatory T cells (Tregs) and natural killer T (NKT) cells are two distinct lymphocyte subsets that independently regulate hepatic adaptive and innate immunity, respectively. In the current study, we examine the interaction between Tregs and NKT cells to understand the mechanisms of cross immune regulation by these cells.The frequency and function of Tregs were evaluated in wild type and NKT cell deficient (CD1dko) mice. In vitro lymphocyte proliferation and apoptosis assays were performed with NKT cells co-cultured with Tregs. The ability of Tregs to inhibit NKT cells in vivo was examined by adoptive transfer of Tregs in a model of NKT cell mediated hepatitis.CD1dko mice have a significant reduction in hepatic Tregs. Although, the Tregs from CD1dko mice remain functional and can suppress conventional T cells, their ability to suppress activation induced NKT cell proliferation and to promote NKT cell apoptosis is greatly diminished. These effects are CD1d dependent and require cell to cell contact. Adoptive transfer of Tregs inhibits NKT cell-mediated liver injury.NKT cells promote Tregs, and Tregs inhibit NKT cells in a CD1d dependent manner requiring cell to cell contact. These cross-talk immune regulations provide a linkage between innate and adaptive immunity

Type II NKT Cells Stimulate Diet-Induced Obesity by Mediating Adipose Tissue Inflammation, Steatohepatitis and Insulin Resistance

The progression of obesity is accompanied by a chronic inflammatory process that involves both innate and acquired immunity. Natural killer T (NKT) cells recognize lipid antigens and are also distributed in adipose tissue. To examine the involvement of NKT cells in the development of obesity, C57BL/6 mice (wild type; WT), and two NKT-cell-deficient strains, Jα18−/− mice that lack the type I subset and CD1d−/− mice that lack both the type I and II subsets, were fed a high fat diet (HFD). CD1d−/− mice gained the least body weight with the least weight in perigonadal and brown adipose tissue as well as in the liver, compared to WT or Jα18−/− mice fed an HFD. Histologically, CD1d−/− mice had significantly smaller adipocytes and developed significantly milder hepatosteatosis than WT or Jα18−/− mice. The number of NK1.1+TCRβ+ cells in adipose tissue increased when WT mice were fed an HFD and were mostly invariant Vα14Jα18-negative. CD11b+ macrophages (Mφ) were another major subset of cells in adipose tissue infiltrates, and they were divided into F4/80high and F4/80low cells. The F4/80low-Mφ subset in adipose tissue was increased in CD1d−/− mice, and this population likely played an anti-inflammatory role. Glucose intolerance and insulin resistance in CD1d−/− mice were not aggravated as in WT or Jα18−/− mice fed an HFD, likely due to a lower grade of inflammation and adiposity. Collectively, our findings provide evidence that type II NKT cells initiate inflammation in the liver and adipose tissue and exacerbate the course of obesity that leads to insulin resistance

Spleen-Resident CD4+ and CD4− CD8α− Dendritic Cell Subsets Differ in Their Ability to Prime Invariant Natural Killer T Lymphocytes

One important function of conventional dendritic cells (cDC) is their high capacity to capture, process and present Ag to T lymphocytes. Mouse splenic cDC subtypes, including CD8α+ and CD8α− cDC, are not identical in their Ag presenting and T cell priming functions. Surprisingly, few studies have reported functional differences between CD4− and CD4+ CD8α− cDC subsets. We show that, when loaded in vitro with OVA peptide or whole protein, and in steady-state conditions, splenic CD4− and CD4+ cDC are equivalent in their capacity to prime and direct CD4+ and CD8+ T cell differentiation. In contrast, in response to α-galactosylceramide (α-GalCer), CD4− and CD4+ cDC differentially activate invariant Natural Killer T (iNKT) cells, a population of lipid-reactive non-conventional T lymphocytes. Both cDC subsets equally take up α-GalCer in vitro and in vivo to stimulate the iNKT hybridoma DN32.D3, the activation of which depends solely on TCR triggering. On the other hand, and relative to their CD4+ counterparts, CD4− cDC more efficiently stimulate primary iNKT cells, a phenomenon likely due to differential production of co-factors (including IL-12) by cDC. Our data reveal a novel functional difference between splenic CD4+ and CD4− cDC subsets that may be important in immune responses

Unique Interplay between Sugar and Lipid in Determining the Antigenic Potency of Bacterial Antigens for NKT Cells

Structural and biophysical studies reveal the induced-fit mechanism underlying the stringent specificity of invariant natural killer T cells for unique glycolipid antigens from the pathogen Streptococcus pneumoniae