Ref HAL: hal-02953521_v1
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Legătura dintre pasta de ciment și agregat influențează durabilitatea betonului supus levigării, din cauza existenței unei anumite zone mai vulnerabile în pasta de ciment, adiacentă agregatelor-Zona de Tranziție Inter facială (ITZ). Pentru a evalua comportamentul mecanic al betonului la scara locală a legăturii pastă de ciment/agregat, s-au efectuat încercări de întindere pe eșantioane din pastă de ciment și compozite pastă/agregat. Relația dintre degradarea chimică și proprietățile mecanice (modulul lui Young și rezistența la întindere) a fost exprimată prin noțiunea de degradare chimică. Alte aspecte discutate, cum ar fi cinetica de levigare, dizolvarea chimică și fisurarea au fost evocate pentru a evidenția originea pierderii proprietăților mecanice ale pastei de ciment și a legăturii pastă / ciment. În ceea ce privește legătura pastă/agregat, după o dizolvare importantă în cadrul ITZ, se produce treptat o pierdere totală de aderență între pasta de ciment și agregat. În ceea ce privește pasta de ciment, aceasta suferă o scădere mai mică a modulului lui Young și a rezistenței la întindere în comparație cu compozitele, fiind de asemenea mai puțin afectată de fisurare. În general, acest studiu evidențiază mecanismul prin care comportamentele mecanice ale pastei de ciment și ale legăturii de pastă de ciment / agregate sunt afectate de levigare.

Ref HAL: hal-02747003_v1
DOI: 10.1109/TUFFC.2020.2998768
WoS: 000573791500020
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Ref HAL: hal-02573585_v1
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Our universe is threedimensional and curved (with a positive curvature) and thus may be embedded in a fourdimensional Euclidean space with coordinates x, y, z, t where the fourth dimension time t is treated as a regular dimension. One can set in this spacetime a fourdimensional underlying array of small hypercubes of one Planck length edge. With this array all elementary particles can be classified following that they are two, three or fourdimensional. The elementary wavefunctions of this underlying array are equal to √ 2exp ix i for x i = x, y, z or to √ 2exp it for t. Hence, the masses of the fermions of the first family are equal to 2 n (in eV/c 2) where n is an integer. The other families of fermions are excited states of the fermions of the first family and thus have masses equal to 2 n .p 2 /2 where n and p are two integers. Theoretical and experimental masses fit within 10%.

Ref HAL: hal-02527311_v1
DOI: 10.1007/s10971-019-05173-2
WoS: WOS:000511603600002
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In this paper, we present the different characterization techniques used to measure the mechanical properties of silica aerogels. The mechanical behaviour of aerogels is generally described in terms of elastic and fragile materials (such as glasses or ceramics) but also in terms of plastic media in compression testing. Because of these very different mechanical behaviors, several types of characterization techniques are proposed in the literature. We first describe the dynamic characterization techniques such as ultrasounds, Brillouin scattering, dynamic mechanical analysis (DMA) to measure the elastic properties: Young's modulus (E) , shear modulus (G), poisson ratio (υ) but also attenuation and internal friction. Thanks to "static" techniques such as three-point bending, uniaxial compression, compression we also access to the elastic modulus (E) and to the rupture strength (σ). The experimental results show that the value of the elastic and fracture moduli measured is several orders of magnitude lower than that of a material without porosity. With regard to the brittleness characteristics, Weibull's analysis is used to show the statistical nature of the fracture resistance. We also present the SENB (single edge notched beam technique) technique to characterize toughness (K1C) and the stress corrosion mechanisms, which are studied in ambient conditions and temperature by the double-cleavage drilled compression experiment (DCDC). In the last part of the paper, we show how, during the isostatic compression test, aerogels behave like plastic materials.The data allow calculating the bulk modulus (K), the amplitude of the plastic deformation and the yield strength (σel), which is the boundary between the elastic and plastic domains. These different techniques allow understanding which parameters influence the overall mechanical behavior of aerogels, such as pore volume, but also pore size, internal connectivity and silanol bounds content. It is shown that pore size plays a very important role; pores can be considered as flaws in the terms of fracture mechanics.

Ref HAL: hal-02468739_v1
PMID 32014005
DOI: 10.1186/s13054-020-2745-6
WoS: 000513681200003
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Background; Muscle weakness following critical illness is the consequence of loss of muscle mass and alteration of muscle quality. It is associated with long-term disability. Ultrasonography is a reliable tool to quantify muscle mass, but studies that evaluate muscle quality at the critically ill bedside are lacking. Shear wave ultrasound elastography (SWE) provides spatial representation of soft tissue stiffness and measures of muscle quality. The reliability and reproducibility of SWE in critically ill patients has never been evaluated.Methods; Two operators tested in healthy controls and in critically ill patients the intra- and inter-operator reliability of the SWE using transversal and longitudinal views of the diaphragm and limb muscles. Reliability was calculated using the intra-class correlation coefficient and a bootstrap sampling method assessed their consistency.Results: We collected 560 images. Longitudinal views of the diaphragm (ICC 0.83 [0.50–0.94]), the biceps brachii (ICC 0.88 [0.67–0.96]) and the rectus femoris (ICC 0.76 [0.34–0.91]) were the most reliable views in a training set of healthy controls. Intra-class correlation coefficient for inter-operator reproducibility and intra-operator reliability was above 0.9 for all muscles in a validation set of healthy controls. In critically ill patients, inter-operator reproducibility and intra-operator 1 and 2 reliability ICCs were respectively 0.92 [0.71–0.98], 0.93 [0.82–0.98] and 0.92 [0.81–0.98] for the diaphragm; 0.96 [0.86–0.99], 0.98 [0.94–0.99] and 0.99 [0.96–1] for the biceps brachii and 0.91 [0.51–0.98], 0.97 [0.93–0.99] and 0.99 [0.97–1] for the rectus femoris. The probability to reach intra-class correlation coefficient greater than 0.8 in a 10,000 bootstrap sampling for inter-operator reproducibility was respectively 81%, 84% and 78% for the diaphragm, the biceps brachii and the rectus femoris respectively.Conclusions: SWE is a reliable technique to evaluate limb muscles and the diaphragm in both healthy controls and in critically ill patients.

Commentaires: Une correction de cet article a été publiée in:Crit Care. 2020; 24: 79.Published online 2020 Mar 5. doi: 10.1186/s13054-020-2802-1 PMID:32138763In the publication of this article, there was an error in the Family Name of one of the authors. This has now been updated in the original article.The error: FlattresShould instead read: Flatres

Ref HAL: hal-02428699_v1
DOI: 10.1002/aocs.12289
WoS: 000495881800001
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Lipidic polyols based on α‐hydroxyketone reactive groups were investigated for polyurethane thermosets. The reactivity of this peculiar secondary alcohol group in triacylglycerol structure was compared, without use of catalyst, to that of poly(1,2‐diol) triacylglycerol and castor oil to demonstrate the influence of ketone in the α position of the alcohol group in the presence of HDI for the urethanization rate. The kinetic effect of the ketone group was also studied on various lipidic architectures: mono(α‐hydroxyketone) ester, di(α‐hydroxyketone) diester and tri(α‐hydroxyketone) triacylglycerol. The presence of hydrogen bonds in the network coming from urethane, residual alcohol, and ketone in hard segments of PU was discussed and correlated with the thermal stability and the soft mechanical properties of the resulting polyurethane thermosets.

Ref HAL: hal-02278867_v2
DOI: 10.1088/2053-1591/ab7b29
WoS: 000521374800001
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We modelled deep indentation in brittle materials via a tensorial approach in three dimensions. Experimentally, we performed deep indentation in base catalyzed aerogels. When deep indentation is performed in these materials, it appears a Hertzian cone crack for both experimental and numerical results. The cone angle (angle between the surface and the boundaries of the Hertzian cone) depends on the material in which indentation is performed. The Young moduli of the materials has no effect on these angles. The tendency is that materials with increasing Poisson ratios have a decreasing value of the Hertzian cone angle.