291 research outputs found
Angular momentum evolution in laser-plasma accelerators
The transverse properties of an electron beam are characterized by two
quantities, the emittance which indicates the electron beam extend in the phase
space and the angular momentum which allows for non-planar electron
trajectories. Whereas the emittance of electron beams produced in laser- plasma
accelerator has been measured in several experiments, their angular momentum
has been scarcely studied. It was demonstrated that electrons in laser-plasma
accelerator carry some angular momentum, but its origin was not established.
Here we identify one source of angular momentum growth and we present
experimental results showing that the angular momentum content evolves during
the acceleration
Probabilistic and predictive performance-based approach for assessing reinforced concrete structures lifetime: The applet project
International audienceConcrete deterioration results in different damage extents, from cracking to concrete spalling, from losses of reinforcement cross-sections to bond losses. A relevant prediction of this performance is the basis for a successful management of the concrete structures. Conversely, the large amount of uncertainties related to parameters and models require a specific analysis in order to provide relevant results. The APPLET project intends to develop a probabilistic and predictive performance-based approach by quantifying the various sources of variability (material and structure), studying the interaction between environmental aggressive agents and the concrete material, ensuring a transfer of the physical-chemical models at the material scale towards models at the structure level, including and understanding in a better manner the corrosion process, integrating interface models between reinforcement and concrete, proposing relevant numerical models, integrating know-how from monitoring or inspection. To provide answers, a consortium of 19 partners has been established and has promoted a research project funded by the French Research Science Agency (ANR). Started in May 2007, the project has ended in November 2010. This paper will resume the most significant advances targeted by this research project
Self-assembly in solution of a reversible comb-shaped supramolecular polymer
We report a single step synthesis of a polyisobutene with a bis-urea moiety
in the middle of the chain. In low polarity solvents, this polymer
self-assembles by hydrogen bonding to form a combshaped polymer with a central
hydrogen bonded backbone and polyisobutene arms. The comb backbone can be
reversibly broken, and consequently, its length can be tuned by changing the
solvent, the concentration or the temperature. Moreover, we have proved that
the bulkiness of the side-chains have a strong influence on both the
self-assembly pattern and the length of the backbone. Finally, the density of
arms can be reduced, by simply mixing with a low molar mass bis-urea
Random, blocky and alternating ordering in supramolecular polymers of chemically bidisperse monomers
As a first step to understanding the role of molecular or chemical
polydispersity in self-assembly, we put forward a coarse-grained model that
describes the spontaneous formation of quasi-linear polymers in solutions
containing two self-assembling species. Our theoretical framework is based on a
two-component self-assembled Ising model in which the bidispersity is
parameterized in terms of the strengths of the binding free energies that
depend on the monomer species involved in the pairing interaction. Depending
upon the relative values of the binding free energies involved, different
morphologies of assemblies that include both components are formed, exhibiting
paramagnetic-, ferromagnetic- or anti ferromagnetic-like order,i.e., random,
blocky or alternating ordering of the two components in the assemblies.
Analyzing the model for the case of ferromagnetic ordering, which is of most
practical interest, we find that the transition from conditions of minimal
assembly to those characterized by strong polymerization can be described by a
critical concentration that depends on the concentration ratio of the two
species. Interestingly, the distribution of monomers in the assemblies is
different from that in the original distribution, i.e., the ratio of the
concentrations of the two components put into the system. The monomers with a
smaller binding free energy are more abundant in short assemblies and monomers
with a larger binding affinity are more abundant in longer assemblies. Under
certain conditions the two components congregate into separate supramolecular
polymeric species and in that sense phase separate. We find strong deviations
from the expected growth law for supramolecular polymers even for modest
amounts of a second component, provided it is chemically sufficiently distinct
from the main one.Comment: Submitted to Macromolecules, 6 figures. arXiv admin note: substantial
text overlap with arXiv:1111.176
Electronic structure of fluorides: general trends for ground and excited state properties
The electronic structure of fluorite crystals are studied by means of density
functional theory within the local density approximation for the exchange
correlation energy. The ground-state electronic properties, which have been
calculated for the cubic structures ,, , ,
, -, using a plane waves expansion of the wave
functions, show good comparison with existing experimental data and previous
theoretical results. The electronic density of states at the gap region for all
the compounds and their energy-band structure have been calculated and compared
with the existing data in the literature. General trends for the ground-state
parameters, the electronic energy-bands and transition energies for all the
fluorides considered are given and discussed in details. Moreover, for the
first time results for have been presented
Campagne océanographique EBENE à bord du N.O. l'Atalante : 21 octobre au 20 novembre 1996 : recueil de données : 2. Matière organique, pigments photosynthétiques, production primaire, micro- et mésozooplancton, profileur vidéo marin
A high-frequency, long-term data set of hydrology and sediment yield: the alpine badland catchments of Draix-Bléone Observatory
Draix-Bléone critical zone observatory was created in
1983 to study erosion processes in a mountainous badland region of the
French Southern Alps. Six catchments of varying size (0.001 to 22 km2)
and vegetation cover are equipped to measure water and sediment fluxes, both
as bedload and suspended load. This paper presents the core dataset of the
observatory, including rainfall and meteorology, high-frequency discharge
and suspended-sediment concentration, and event-scale bedload volumes. The
longest records span almost 40 years. Measurement and data-processing
methods are presented, as well as data quality assessment procedures and
examples of results. All the data presented in this paper are available on
the open repository https://doi.org/10.17180/obs.draix (Draix-Bleone
Observatory, 2015), and a 5-year snapshot is available for review at
https://doi.org/10.57745/BEYQFQ (Klotz et al., 2023).</p
The Zinc-Finger Protein SOP1 Is Required for a Subset of the Nuclear Exosome Functions in Arabidopsis
Correct gene expression requires tight RNA quality control both at transcriptional and post-transcriptional levels. Using a splicing-defective allele of PASTICCINO2 (PAS2), a gene essential for plant development, we isolated suppressor mutations modifying pas2-1 mRNA profiles and restoring wild-type growth. Three suppressor of pas2 (sop) mutations modified the degradation of mis-spliced pas2-1 mRNA species, allowing the synthesis of a functional protein. Cloning of the suppressor mutations identified the core subunit of the exosome SOP2/RRP4, the exosome nucleoplasmic cofactor SOP3/HEN2 and a novel zinc-finger protein SOP1 that colocalizes with HEN2 in nucleoplasmic foci. The three SOP proteins counteract post-transcriptional (trans)gene silencing (PTGS), which suggests that they all act in RNA quality control. In addition, sop1 mutants accumulate some, but not all of the misprocessed mRNAs and other types of RNAs that are observed in exosome mutants. Taken together, our data show that SOP1 is a new component of nuclear RNA surveillance that is required for the degradation of a specific subset of nuclear exosome targets. [Correction available at https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1005958
Innate Immune Function in Placenta and Cord Blood of Hepatitis C – Seropositive Mother-Infant Dyads
Vertical transmission accounts for the majority of pediatric cases of hepatitis C viral (HCV) infection. In contrast to the adult population who develop persistent viremia in ∼80% of cases following exposure, the rate of mother-to-child transmission (2–6%) is strikingly low. Protection from vertical transmission likely requires the coordination of multiple components of the immune system. Placenta and decidua provide a direct connection between mother and infant. We hypothesized that innate immune responses would differ across the three compartments (decidua, placenta and cord blood) and that hepatitis C exposure would modify innate immunity in these tissues. The study was comprised of HCV-infected and healthy control mother and infant pairs from whom cord blood, placenta and decidua were collected with isolation of mononuclear cells. Multiparameter flow cytometry was performed to assess the phenotype, intracellular cytokine production and cytotoxicity of the cells. In keeping with a model where the maternal-fetal interface provides antiviral protection, we found a gradient in proportional frequencies of NKT and γδ-T cells being higher in placenta than cord blood. Cytotoxicity of NK and NKT cells was enhanced in placenta and placental NKT cytotoxicity was further increased by HCV infection. HCV exposure had multiple effects on innate cells including a decrease in activation markers (CD69, TRAIL and NKp44) on NK cells and a decrease in plasmacytoid dendritic cells in both placenta and cord blood of exposed infants. In summary, the placenta represents an active innate immunological organ that provides antiviral protection against HCV transmission in the majority of cases; the increased incidence in preterm labor previously described in HCV-seropositive mothers may be related to enhanced cytotoxicity of NKT cells
Campagne océanographique FLUPAC à bord du N.O. l'Atalante, 23 septembre au 29 octobre 1994 : recueil de données : 2. Optique marine, matière organique dissoute, pigments photosynthétiques, observations microscopiques, production primaire, "broutage", zooplancton, sédimentation
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