Pathologie des bétons fibrés après incendie

International audienceDe nombreux travaux ont permis d'analyser et comparer le comportement mécanique d'un béton classique et le comportement d'un béton similaire mais renforcé de fibres métalliques. Toutefois il existe peu d'études sur l'effet des fibres métalliques sur le comportement des bétons fibrés ayant subi un incendie. Le but de notre étude est essentiellement expérimental, il a pour objet d'analyser le comportement de ces 2 type de matériaux après incendie. Afin de mieux simuler les effets d'un incendie, un test à la flamme de gaz propane est mis au point. Les différents matériaux sont soumis à cet échauffement. L'évolution du gradient de température à l'intérieur des échantillons est suivie, et, en fin d'exposition, le comportement des mortiers est comparé à l'aide d'un essai de poinçonnement. L'évolution microstructurale du mortier est étudiée par diffraction X et observations au MEB. Les observations des fibres aux différentes températures permettent d'expliquer le comportement du mortier fibré. Les résultats d'essais effectués dans un four à moufle indiquent que :-Entre 400 et 500°C, la perte moyenne de la résistance est de l'ordre de 30 %. L'endommagement thermique du mortier renforcé ne cause pas de désordre gênant.-Au-delà de 500°C, la perte de résistance mécanique devient plus importante et crée une instabilité de la structure qui peut conduire à la ruine.-Entre 400 et 700°C, l'ajout fibres d'acier permet une meilleure résistance à la déformation et une rupture graduelle. L'énergie dissipée est très nettement augmentée. Les observations au MEB et les analyses à la microsonde montrent une oxydation des fibres d'acier aux hautes températures. Cette oxydation provoque une perte de résistance et de ductilité importante au-delà de 800°C, et peut limiter l'intérêt vis à vis du risque incendie

Effect of Albumin in Combination With Mannitol on Whole-blood Coagulation In Vitro Assessed by Thromboelastometry

Background:Albumin and mannitol may interfere with hemostasis, but their coinfluence is unclear. We aimed to determine the effects of albumin alone and in combination with mannitol or Ringer acetate (RAC) on hemostasis in crossover in vitro study.Materials and Methods:From citrated fresh whole blood withdrawn from 10 volunteers, we prepared 2.5, 5, 10, 15, and 20 vol% dilutions of 4% albumin (Alb group). Each sample was thereafter diluted by 15% mannitol (Alb/Man group) or RAC (Alb/RAC group) at a ratio of 9:1. Using thromboelastometry, FibTEM (fibrinogen ROTEM) and ExTEM (extrinsic ROTEM) tests were performed.Results:A 20 vol%, but not 2.5 to 15 vol% dilution of albumin caused a prolonged clot formation time, -angle decrease, and maximum clot firmness (MCF) weakening compared with undiluted sample (PPeer reviewe

FUNDAMENTALS OF ASEISMIC TECHNIQUES IN BRIDGES

ABSTRACT: The design of bridges, the majority of which are long, has to compromise both functional and earthquake resistant requirements, which are conflicting components of the same problem and they impose opposite design requirements. The functional problem, which is mainly critical for the longitudinal direction of the bridge, requires the free contraction and expansion of the deck, due to annual thermal cycle, shrinkage and creep. On the other hand, the earthquake resistance of the bridge is enhanced by implementing monolithical systems as being possible. To improve structural safety and integrity against severe earthquakes, more effective and reliable techniques for aseismic design of structures based on structural control concepts are desired. The differences of bridge damages due to earthquakes in USA, Japan and Taiwan are introduced first in this paper, then an over view on seismic isolation technology as well as other seismic protection technologies adopted and applied to protect the bridges against earthquakes are presented in which a brief review of the earlier and current base isolation devices and aseismic techniques, proposed or implemented, are given, and aspects for future research in the area of isolation of bridges are discussed

On the propagation of acoustic-gravity waves under elastic ice sheets

The propagation of wave disturbances in water of varying depth bounded above by ice sheets is discussed, accounting for gravity, compressibility and elasticity effects. Considering the more realistic scenario of elastic ice sheets reveals a continuous spectrum of acoustic–gravity modes that propagate even below the cutoff frequency of the rigid surface solution where surface (gravity) waves cannot exist. The balance between gravitational forces and oscillations in the ice sheet defines a new dimensionless quantity Ka. When the ice sheet is relatively thin and the prescribed frequency is relatively low (Ka≪1), the free-surface bottom-pressure solution is retrieved in full. However, thicker ice sheets or propagation of relatively higher frequency modes (Ka≫1) alter the solution fundamentally, which is reflected in an amplified asymmetric signature and different characteristics of the eigenvalues, such that the bottom pressure is amplified when acoustic–gravity waves are transmitted to shallower waters. To analyse these scenarios, an analytical solution and a depth-integrated equation are derived for the cases of constant and varying depths, respectively. Together, these are capable of modelling realistic ocean geometries and an inhomogeneous distribution of ice sheets

Tuning antiviral CD8 T-cell response via proline-altered peptide ligand vaccination

Viral escape from CD8+ cytotoxic T lymphocyte responses correlates with disease progression and represents a significant challenge for vaccination. Here, we demonstrate that CD8+ T cell recognition of the naturally occurring MHC-I-restricted LCMV-associated immune escape variant Y4F is restored following vaccination with a proline-altered peptide ligand (APL). The APL increases MHC/peptide (pMHC) complex stability, rigidifies the peptide and facilitates T cell receptor (TCR) recognition through reduced entropy costs. Structural analyses of pMHC complexes before and after TCR binding, combined with biophysical analyses, revealed that although the TCR binds similarly to all complexes, the p3P modification alters the conformations of a very limited amount of specific MHC and peptide residues, facilitating efficient TCR recognition. This approach can be easily introduced in peptides restricted to other MHC alleles, and can be combined with currently available and future vaccination protocols in order to prevent viral immune escape

Global gene expression analysis of human erythroid progenitors

This article is available open access through the publisher’s website. Copyright @ 2011 American Society of Hematology. This article has an erratum: http://bloodjournal.hematologylibrary.org/content/118/26/6993.3.Understanding the pattern of gene expression during erythropoiesis is crucial for a synthesis of erythroid developmental biology. Here, we isolated 4 distinct populations at successive erythropoietin-dependent stages of erythropoiesis, including the terminal, pyknotic stage. The transcriptome was determined using Affymetrix arrays. First, we demonstrated the importance of using defined cell populations to identify lineage and temporally specific patterns of gene expression. Cells sorted by surface expression profile not only express significantly fewer genes than unsorted cells but also demonstrate significantly greater differences in the expression levels of particular genes between stages than unsorted cells. Second, using standard software, we identified more than 1000 transcripts not previously observed to be differentially expressed during erythroid maturation, 13 of which are highly significantly terminally regulated, including RFXAP and SMARCA4. Third, using matched filtering, we identified 12 transcripts not previously reported to be continuously up-regulated in maturing human primary erythroblasts. Finally, using transcription factor binding site analysis, we identified potential transcription factors that may regulate gene expression during terminal erythropoiesis. Our stringent lists of differentially regulated and continuously expressed transcripts containing many genes with undiscovered functions in erythroblasts are a resource for future functional studies of erythropoiesis. Our Human Erythroid Maturation database is available at https://cellline.molbiol.ox.ac.uk/eryth/index.html.National Health Service Blood and Transplant, National Institute for Health Research Biomedical Research Center Program, and National Institute for Health Research

Use of dementia care mapping in the care for older people with intellectual disabilities: A mixed‐method study

Background The ageing of people with intellectual disabilities, with associated morbidity like dementia, calls for new types of care. Person‐centred methods may support care staff in providing this, an example being Dementia Care Mapping (DCM). DCM has been shown to be feasible in ID‐care. We examined the experiences of ID‐professionals in using DCM. Methods We performed a mixed‐methods study, using quantitative data from care staff (N = 136) and qualitative data (focus‐groups, individual interviews) from care staff, group home managers and DCM‐in‐intellectual disabilities mappers (N = 53). Results DCM provided new insights into the behaviours of clients, enabled professional reflection and gave new knowledge and skills regarding dementia and person‐centred care. Appreciation of DCM further increased after the second cycle of application. Conclusion DCM is perceived as valuable in ID‐care. Further assessment is needed of its effectiveness in ID‐care with respect to quality of care, staff‐client interactions and job performance