Atom-wall dispersive forces: a microscopic approach

We present a study of atom-wall interactions in non-relativistic quantum electrodynamics by functional integral methods. The Feynman-Kac path integral representation is generalized to the case when the particle interacts with a radiation field, providing an additional effective potential that contains all the interactions induced by the field. We show how one can retrieve the standard van der Waals, Casimir-Polder and classical Lifshiftz forces in this formalism for an atom in its ground state. Moreover, when electrostatic interactions are screened in the medium, we find low temperature corrections that are not included in the Lifshitz theory of fluctuating forces and are opposite to them.Comment: 4 figure

Positive regulation of plasmacytoid dendritic cell function via Ly49Q recognition of class I MHC

Plasmacytoid dendritic cells (pDCs) are an important source of type I interferon (IFN) during initial immune responses to viral infections. In mice, pDCs are uniquely characterized by high-level expression of Ly49Q, a C-type lectin-like receptor specific for class I major histocompatibility complex (MHC) molecules. Despite having a cytoplasmic immunoreceptor tyrosine-based inhibitory motif, Ly49Q was found to enhance pDC function in vitro, as pDC cytokine production in response to the Toll-like receptor (TLR) 9 agonist CpG-oligonucleotide (ODN) could be blocked using soluble monoclonal antibody (mAb) to Ly49Q or H-2Kb. Conversely, CpG-ODN–dependent IFN-α production by pDCs was greatly augmented upon receptor cross-linking using immobilized anti-Ly49Q mAb or recombinant H-2Kb ligand. Accordingly, Ly49Q-deficient pDCs displayed a severely reduced capacity to produce cytokines in response to TLR7 and TLR9 stimulation both in vitro and in vivo. Finally, TLR9-dependent antiviral responses were compromised in Ly49Q-null mice infected with mouse cytomegalovirus. Thus, class I MHC recognition by Ly49Q on pDCs is necessary for optimal activation of innate immune responses in vivo

The significance of nitrogen cost minimization in proteomes of marine microorganisms

Marine microorganisms thrive under low levels of nitrogen (N). N cost minimization is a major selective pressure imprinted on open-ocean microorganism genomes. Here we show that amino-acid sequences from the open ocean are reduced in N, but increased in average mass compared with coastal-ocean microorganisms. Nutrient limitation exerts significant pressure on organisms supporting the trade-off between N cost minimization and increased average mass of amino acids that is a function of increased A+T codon usage. N cost minimization, especially of highly expressed proteins, reduces the total cellular N budget by 2.7–10% this minimization in combination with reduction in genome size and cell size is an evolutionary adaptation to nutrient limitation. The biogeochemical and evolutionary precedent for these findings suggests that N limitation is a stronger selective force in the ocean than biosynthetic costs and is an important evolutionary strategy in resource-limited ecosystems

The NK Cell Response to Mouse Cytomegalovirus Infection Affects the Level and Kinetics of the Early CD8+ T-Cell Response

Natural killer (NK) cells and CD8+ T cells play a prominent role in the clearance of mouse cytomegalovirus (MCMV) infection. The role of NK cells in modulating the CD8+ T-cell response to MCMV infection is still the subject of intensive research. For analyzing the impact of NK cells on mounting of a CD8+ T-cell response and the contribution of these cells to virus control during the first days postinfection (p.i.), we used C57BL/6 mice in which NK cells are specifically activated through the Ly49H receptor engaged by the MCMV-encoded ligand m157. Our results indicate that the requirement for CD8+ T cells in early MCMV control inversely correlates with the engagement of Ly49H. While depletion of CD8+ T cells has only a minor effect on the early control of wild-type MCMV, CD8+ T cells are essential in the control of Δm157 virus. The frequencies of virus epitope-specific CD8+ T cells and their activation status were higher in mice infected with Δm157 virus. In addition, these mice showed elevated levels of alpha interferon (IFN-α) and several other proinflammatory cytokines as early as 1.5 days p.i. Although the numbers of conventional dendritic cells (cDCs) were reduced later during infection, particularly in Δm157-infected mice, they were not significantly affected at the peak of the cytokine response. Altogether, we concluded that increased antigen load, preservation of early cDCs' function, and higher levels of innate cytokines collectively account for an enhanced CD8+ T-cell response in C57BL/6 mice infected with a virus unable to activate NK cells via the Ly49H–m157 interaction

L’accident de Fukushima : un premier bilan des conséquences pour l’environnement et la population

Dix mois après les rejets radioactifs consécutifs à l’accident de Fukushima, les données disponibles permettent d’ores et déjà de dimensionner ses conséquences sur l’environnement en termes de dépôts radioactifs et de contamination de la chaine alimentaire. De nombreuses similitudes phénoménologiques peuvent être faites avec l’accident de Tchernobyl, mais les surfaces terrestres concernées par les retombées de Fukushima sont de loin beaucoup plus petites. En revanche, une telle contamination du milieu marin côtier n’avait jamais été observée auparavant. S’il est trop tôt pour évaluer précisément l’atteinte des populations, elle a dû être considérablement diminuée par les décisions successives d’éloignement, notamment celle concernant le rayon de 20 km autour de l’installation

TOCATTA A dynamic transfer model of 3H from the atmosphere to soil-plant systems

International audienceThis paper describes a dynamic compartment model (TOCATTA) that simulates tritium transfer in agricultural plants of several categories including vegetables, pasture and annual crops, exposed to time-varying HTO concentrations of water vapour in the air and possibly in irrigation and rainwater. Consideration is also given to the transfer pathways of HTO in soil. Though the transfer of tritium is quite complex, from its release into the environment to its absorption and its incorporation within the organic material of living organisms, the TOCATTA model is relatively simple, with a limited number of compartments and input parameters appropriate to its use in an operational mode. In this paper, we took the opportunity to have data obtained on an ornamental plant - an indoor palm tree - within an industrial building where tritium was released accidentally over several weeks (or months). More specifically, the model's ability to provide hindsight on the chronology of the release scenario is discussed by comparing model predictions of TFWT and OBT activity concentrations in the plant leaves with measurements performed on three different leaves characterized by different developmental stages. The data-model comparison shows some limitations, mainly because of a lack of knowledge about the initial conditions of the accident and when it actually started and about the processes involved in the transfer of tritium. Efforts are needed in both experimental and modelling areas for future evaluation of tritium behaviour in agricultural soil and plants exposed to gaseous HTO releases and/or to irrigation with contaminated water. © 2013 Elsevier Ltd

Foliar interception of radionuclides in dry conditions A meta-analysis using a Bayesian modeling approach

International audienceUncertainty on the parameters that describe the transfer of radioactive materials into the (terrestrial) environment may be characterized thanks to datasets such as those compiled within International Atomic Energy Agency (IAEA) documents. Nevertheless, the information included in these documents is too poor to derive a relevant and informative uncertainty distribution regarding dry interception of radionuclides by the pasture grass and the leaves of vegetables. In this paper, 145 sets of dry interception measurements by the aboveground biomass of specific plants were collected from published scientific papers. A Bayesian meta-analysis was performed to derive the posterior probability distributions of the parameters that reflect their uncertainty given the collected data. Four competing models were compared in terms of both fitting performances and predictive abilities to reproduce plausible dry interception data. The asymptotic interception factor, applicable whatever the species and radionuclide to the highest aboveground biomass values (e.g. mature leafy vegetables), was estimated with the best model, to be 0.87 with a 95% credible interval (0.85, 0.89). © 2015 Elsevier Ltd

Uncertainty analysis in post-accidental risk assessment models An application to the Fukushima accident

International audienceEnvironmental contamination subsequent to the atmospheric releases during the Fukushima accident resulted in high radioactive concentrations in feed and foodstuffs. Producing a realistic health risk assessment after severe nuclear accidents, and developing a sufficient understanding of environmental transfer and exposure processes, appears to be a research priority. Specifically, the characterization of uncertainties in the human ingestion pathway, as outlined by the radioecological community, is of great interest. The present work aims to (i) characterize spatial variability and parametric uncertainties raised by the processes involved in the transfer of radionuclides (134Cs and 137Cs) after atmospheric releases during the Fukushima accident into the terrestrial ecosystems, and (ii) study the impact of these variability and uncertainties on radioactive contamination of leafy vegetables. The implemented approach quantified uncertainties under a probabilistic modelling framework. This resulted in probability distributions derived mainly from Bayesian inference and by performing transfer calculations in the modelling platform SYMBIOSE. © 2015 Elsevier Ltd. All rights reserved

: field monitoring and modelling

International audienceCurrent ¹³⁷Cs levels in French forests are mainly due to global fallouts (GF) from nuclear weapon tests and deposition from Chernobyl accident. Since Fukushima accident, there has been an increasing interest in the behavior of this persistent radionuclide in the soil-tree system at short and mid-term after its deposit (95%) with a weak contribution of the organic layers (<1%).Stand-averaged ¹³⁷Cs activity concentrations in tree organs vary by more than an order of magnitude in the 3 stands, from typically ~0.1 to ~4 Bq/kg dw. The pattern is similar to that observed at short-term after Chernobyl and Fukushima accidents: roots ≥ leaves/needles = twigs ≥ bark ≥ branches = stemwood. In HET and CPS, ¹³⁷Cs and ¹³³Cs concentrations were linearly related (r≥0.9; p<0.001), suggesting a reached equilibrium. Whatever the isotope, the variability observed between individual trees is not correlated to tree characteristics (tree age, DBH or height) and remains under investigation at this stage.Normalized ¹³⁷Cs activity concentrations in stemwood (NC, m²/kg) of beech trees strongly vary between sites, from ~0.7 10^-4 m²/kg at HET site to ~5.1 10^-4 m²/kg at PS site. Such a variability could not be explained by differences in the ¹³⁷Cs soil exchangeable fraction. NC in stemwood of oaks and Scots pines are lower than those of companying beeches (1.1 10^-4 and 0.8 10^-4 m²/kg, respectively). Our results are 1 order of magnitude lower than those observed on the mid-term after Chernobyl, likely indicating a long-term decrease of ¹³⁷Cs bioavailability in soil.Investigations on potassium behavior, estimation of BGC fluxes for ¹³⁷Cs, ¹³³Cs and K, as well as on the selectivity coefficients for transfer processes, are under progress

: field monitoring and modelling

International audienceCurrent ¹³⁷Cs levels in French forests are mainly due to global fallouts (GF) from nuclear weapon tests and deposition from Chernobyl accident. Since Fukushima accident, there has been an increasing interest in the behavior of this persistent radionuclide in the soil-tree system at short and mid-term after its deposit (95%) with a weak contribution of the organic layers (<1%).Stand-averaged ¹³⁷Cs activity concentrations in tree organs vary by more than an order of magnitude in the 3 stands, from typically ~0.1 to ~4 Bq/kg dw. The pattern is similar to that observed at short-term after Chernobyl and Fukushima accidents: roots ≥ leaves/needles = twigs ≥ bark ≥ branches = stemwood. In HET and CPS, ¹³⁷Cs and ¹³³Cs concentrations were linearly related (r≥0.9; p<0.001), suggesting a reached equilibrium. Whatever the isotope, the variability observed between individual trees is not correlated to tree characteristics (tree age, DBH or height) and remains under investigation at this stage.Normalized ¹³⁷Cs activity concentrations in stemwood (NC, m²/kg) of beech trees strongly vary between sites, from ~0.7 10^-4 m²/kg at HET site to ~5.1 10^-4 m²/kg at PS site. Such a variability could not be explained by differences in the ¹³⁷Cs soil exchangeable fraction. NC in stemwood of oaks and Scots pines are lower than those of companying beeches (1.1 10^-4 and 0.8 10^-4 m²/kg, respectively). Our results are 1 order of magnitude lower than those observed on the mid-term after Chernobyl, likely indicating a long-term decrease of ¹³⁷Cs bioavailability in soil.Investigations on potassium behavior, estimation of BGC fluxes for ¹³⁷Cs, ¹³³Cs and K, as well as on the selectivity coefficients for transfer processes, are under progress