1,058 research outputs found
Assessing fragility of a reinforced concrete element to snow avalanches using a non-linear dynamic mass-spring model
This paper presents an assessment of the fragility of a reinforced concrete
(RC) element subjected to avalanche loads, and more generally to dynamic
pressure fields applied orthogonally to a wall, within a reliability
framework. In order to obtain accurate numerical results with supportable
computation times, a light and efficient Single-Degree-of-Freedom (SDOF)
model describing the mechanical response of the RC element is proposed. The
model represents its dynamic mechanical response up to failure. Material
non-linearity is taken into account by a moment–curvature approach, which
describes the overall bending response. The SDOF model is validated under
quasi-static and dynamic loading conditions by comparing its results
to alternative approaches based on finite element analysis and the yield line
theory. Following this, the deterministic SDOF model is embedded within a reliability
framework to evaluate the failure probability as a function of the maximal
avalanche pressure reached during the loading. Several reliability methods
are implemented and compared, suggesting that non-parametric methods provide
significant results at a moderate level of computational burden. The
sensitivity to material properties, such as tensile and compressive
strengths, steel reinforcement ratio, and wall geometry is investigated. The
effect of the avalanche loading rate is also underlined and discussed.
Finally, the obtained fragility curves are compared with respect to the few
proposals available in the snow avalanche engineering field. This approach is
systematic and will prove useful in refining formal and practical risk
assessments. It could be applied to other similar natural hazards, which
induce dynamic pressure fields onto the element at risk (e.g., mudflows,
floods) and where potential inertial effects are expected and for which
fragility curves are also lacking.</p
Central African biomes and forest succession stages derived from modern pollen data and plant functional types
New detailed vegetation reconstructions are proposed in Atlantic Central Africa from a modern pollen data set derived from 199 sites (Cameroon, Gabon and Congo) including 131 new sites. In this study, the concept of plant functional classification is improved with new and more detailed plant functional types (PFTs) and new aggregations of pollen taxa. Using the biomisation method, we reconstructed (1) modern potential biomes and (2) potential succession stages of forest regeneration, a new approach in Atlantic Central African vegetation dynamics and ecosystem functioning reconstruction. When compared to local vegetation, potential biomes are correctly reconstructed (97.5% of the sites) and tropical rain forest (TRFO biome) is well identified from tropical seasonal forest (TSFO biome). When the potential biomes are superimposed on the White's vegetation map, only 76.4% of the sites are correctly reconstructed. But using botanical data, correspondence and cluster analyses, the 43 sites from Congo (Mayombe) evidence more affinities with those of central Gabon and so they can also be considered as correctly reconstructed as TRFO biome and White's map should be revised. In terms of potential succession stages of forest regeneration, the mature forest (TMFO) is well differentiated from the secondary forest (TSFE), but inside this latter group, the young and the pioneer stages are not clearly identified due probably to their low sampling representation. Moreover, linked to their progressive and mosaic character, the boundaries between two forest biomes or two forest stages are not clearly detected and need also a more intensive sampling in such transitions
A gp41 MPER-specific llama VHH requires a hydrophobic CDR3 for neutralization but not for antigen recognition
The membrane proximal external region (MPER) of the HIV-1 glycoprotein gp41 is targeted by the broadly neutralizing antibodies 2F5 and 4E10. To date, no immunization regimen in animals or humans has produced HIV-1 neutralizing MPER-specific antibodies. We immunized llamas with gp41-MPER proteoliposomes and selected a MPER-specific single chain antibody (VHH), 2H10, whose epitope overlaps with that of mAb 2F5. Bi-2H10, a bivalent form of 2H10, which displayed an approximately 20-fold increased affinity compared to the monovalent 2H10, neutralized various sensitive and resistant HIV-1 strains, as well as SHIV strains in TZM-bl cells. X-ray and NMR analyses combined with mutagenesis and modeling revealed that 2H10 recognizes its gp41 epitope in a helical conformation. Notably, tryptophan 100 at the tip of the long CDR3 is not required for gp41 interaction but essential for neutralization. Thus bi-2H10 is an anti-MPER antibody generated by immunization that requires hydrophobic CDR3 determinants in addition to epitope recognition for neutralization similar to the mode of neutralization employed by mAbs 2F5 and 4E10
Evolution of the levels of human leukocyte antigen G (HLA-G) in Beninese infant during the first year of life in a malaria endemic area : using latent class analysis
Background: HLA-G, a non-classical HLA class I antigen, is of crucial interest during pregnancy by inhibiting maternal immune response. Its role during infections is discussed, and it has been described that high levels of soluble HLA-G during childhood increase the risk of malaria. To explore more precisely interactions between soluble HLA-G and malaria, latent class analysis was used to test whether distinct sub-populations of children, each with distinctive soluble HLA-G evolutions may suggest the existence of groups presenting variable malaria susceptibility. Method: A study was conducted in Benin from 2010 to 2013 and 165 children were followed from birth to 12 months. Evolution of soluble HLA-G was studied by the latent class method. Results: Three groups of children were identified: one with consistently low levels of soluble HLA-G during follow-up, a second with very high levels and a last intermediate group. In all groups, low birth weight, high number of malaria infections and high exposure to malaria transmission were associated with high level of soluble HLA-G. Placental malaria was not. Presence of soluble HLA-G in cord blood increased the probability of belonging to the highest trajectory. Conclusion: These results, together with previous ones, confirm the important role of HLA-G in the individual susceptibility to malaria. Assaying soluble HLA-G at birth could be a good indicator of newborns more fragile and at risk of infections during childhood
Poly-phased fluid flow in the giant fossil pockmark of Beauvoisin, SE basin of France
The giant Jurassic-aged pockmark field of Beauvoisin developed in a 800 m wide depression for over 3.4 Ma during the Oxfordian; it formed below about 600 m water depth. It is composed of sub-sites organized in clusters and forming vertically stacked carbonate lenses encased in marls . This fine-scale study is focused on a detailed analysis of petrographical organization and geochemical signatures of crystals that grew up in early to late fractures of carbonate lenses, surrounding nodules, and tubes that fed them. The isotopic signature (C, O and Sr) shows that at least three different episodes of fluid migration participated to the mineralization processes. Most of the carbonates precipitated when biogenic seepage was active in the shallow subsurface during the Oxfordian. The second phase occurred relatively soon after burial during early Cretaceous and thermogenic fluids came probably from underlying Pliensbachian, Late Toarcian or Bajocian levels. The third phase is a bitumen-rich fluid probably related to these levels reaching the oil window during Mio-Pliocene. The fluids migrated through faults induced by the emplacement of Triassic-salt diapir of Propiac during the Late Jurassic and that remained polyphased drain structures over time
P-Stereogenic Phosphines for the Stabilisation of Metal Nanoparticles. A Surface State Study
Palladium and ruthenium nanoparticles have been prepared following the organometallic precursor decomposition methodology, under dihydrogen pressure and in the presence of borane protected P-stereogenic phosphines. NMR (Nuclear Magnetic Resonance) monitoring of the corresponding syntheses has permitted to determine the optimal metal/ligand ratio for leading to small and well-dispersed nanoparticles. Exchange ligand reactions of the as-prepared materials have proven the strong interaction of the phosphines with the metal surface; only oxidative treatment using hydrogen peroxide could release the phosphine-based stabiliser from the metal surface. Pd and Ru nanoparticles have been evaluated in hydrogenation reactions, confirming the robustness of the stabilisers, which selectively permitted the hydrogenation of exocyclic C=C bonds, preventing the coordination of the aromatic rings and as a result, their hydrogenation
Nonlinear regularization techniques for seismic tomography
The effects of several nonlinear regularization techniques are discussed in
the framework of 3D seismic tomography. Traditional, linear, penalties
are compared to so-called sparsity promoting and penalties,
and a total variation penalty. Which of these algorithms is judged optimal
depends on the specific requirements of the scientific experiment. If the
correct reproduction of model amplitudes is important, classical damping
towards a smooth model using an norm works almost as well as
minimizing the total variation but is much more efficient. If gradients (edges
of anomalies) should be resolved with a minimum of distortion, we prefer
damping of Daubechies-4 wavelet coefficients. It has the additional
advantage of yielding a noiseless reconstruction, contrary to simple
minimization (`Tikhonov regularization') which should be avoided. In some of
our examples, the method produced notable artifacts. In addition we
show how nonlinear methods for finding sparse models can be
competitive in speed with the widely used methods, certainly under
noisy conditions, so that there is no need to shun penalizations.Comment: 23 pages, 7 figures. Typographical error corrected in accelerated
algorithms (14) and (20
Emulsion sheet doublets as interface trackers for the OPERA experiment
New methods for efficient and unambiguous interconnection between electronic
counters and target units based on nuclear photographic emulsion films have
been developed. The application to the OPERA experiment, that aims at detecting
oscillations between mu neutrino and tau neutrino in the CNGS neutrino beam, is
reported in this paper. In order to reduce background due to latent tracks
collected before installation in the detector, on-site large-scale treatments
of the emulsions ("refreshing") have been applied. Changeable Sheet (CSd)
packages, each made of a doublet of emulsion films, have been designed,
assembled and coupled to the OPERA target units ("ECC bricks"). A device has
been built to print X-ray spots for accurate interconnection both within the
CSd and between the CSd and the related ECC brick. Sample emulsion films have
been extensively scanned with state-of-the-art automated optical microscopes.
Efficient track-matching and powerful background rejection have been achieved
in tests with electronically tagged penetrating muons. Further improvement of
in-doublet film alignment was obtained by matching the pattern of low-energy
electron tracks. The commissioning of the overall OPERA alignment procedure is
in progress.Comment: 19 pages, 19 figure
The detection of neutrino interactions in the emulsion/lead target of the OPERA experiment
The OPERA neutrino detector in the underground Gran Sasso Laboratory (LNGS)
was designed to perform the first detection of neutrino oscillations in
appearance mode through the study of oscillations. The
apparatus consists of an emulsion/lead target complemented by electronic
detectors and it is placed in the high energy long-baseline CERN to LNGS beam
(CNGS) 730 km away from the neutrino source. Runs with CNGS neutrinos were
successfully carried out in 2007 and 2008 with the detector fully operational
with its related facilities for the emulsion handling and analysis. After a
brief description of the beam and of the experimental setup we report on the
collection, reconstruction and analysis procedures of first samples of neutrino
interaction events
- …