Multi-scale modeling of grouted sand behavior

The mechanical properties of sand: stiffness, cohesion and, to a less extent, friction angle can be increased through the process of grouting. A constitutive model adapted for cohesive-frictional materials from a homogenization technique which allowed us to integrate constitutive relations at the grain level has been developed to obtain constitutive equations for the equivalent continuous granular medium. A representative volume was obtained by mobilizing particle contacts in all orientations. Thus, the stress–strain relationship could be derived as an average of the behavior of these local contact planes. The local behavior was assumed to obey a stress-dependent elastic law and Mohr–Coulomb’s plastic law. The influence of the cement grout was modeled by means of adhesive forces between grains in contact, which were added to the contact forces created by an external load. The intensity of these adhesive forces is a function of nature and amount of grout present inside the material and can be reduced due to a damage mechanism at the grain contact during loading. In this paper, we present several examples of simulation which show that the model can reproduce with sufficient accuracy the mechanical improvement induced by grouting as well as the damage of the grain cementation during loading.     

Plastic behavior of some yield stress fluids: from creep to long-time yield

The yielding of several reversible yield stress fluids is studied during scissometric-like creep experiments. The temporal evolution of the apparent deformation is recorded for applied stresses close and below the usual yield stress. Similarly to solids, three main creep regimes are observed. First, a primary creep regime displaying a temporal power law evolution of the deformation rate occurs, followed by a temporal minimum, which leads to an apparent flow of the material. This local minimum, defined as the “transition time,” and the subsequent fluidization can be observed at long times. The evolution of this time as a function of the applied stress appears to follow a universal law reminiscent of fracture behavior in hard solids.     

Mixed Oligoureas Based on Constrained Bicyclic and Acyclic β‐Amino Acids Derivatives: On the Significance of the Subunit Configuration for Folding

The combination of a non‐functionalized constrained bicyclo[2.2.2]octane motif along with urea linkages allowed the formation of a highly rigid 2.5_12/14 helical system both in solution and the solid state. In this work, we aimed at developing stable and functionalized systems as promising materials for biological applications in investigating the impact of this constrained motif and its configuration on homo and heterochiral mixed‐oligourea helix formation. Di‐, tetra‐, hexa‐, and octa‐oligoureas alternating the highly constrained bicyclic motif of (R) or (S) configuration with acyclic (S)‐β³‐amino acid derivatives were constructed. Circular dichroism (CD), NMR experiments, and the X‐ray crystal structure of the octamer unequivocally proved that the alternating heterochiral R/S sequences form a stable left‐handed 2.5‐helix in contrast to the mixed (S/S)‐oligoureas, which did not adopt any defined secondary structure. We observed that the (?)‐synclinal conformation around the C_α? C_β bond of the acyclic residues, although sterically less favorable than the (+)‐synclinal conformation, was imposed by the (R)‐bicyclic amino carbamoyl (BAC) residue. This highlighted the strong ability of the BAC residue to drive helical folding in heterochiral compounds. The role of the stereochemistry of the BAC unit was assessed and a model was proposed to explain the misfolding of the S/S sequences.     

A dipicolinic acid tag for rigid lanthanide tagging of proteins and paramagnetic NMR spectroscopy

A new lanthanide tag was designed for site-specific labeling of proteins with paramagnetic lanthanide ions. The tag, 4-mercaptomethyl-dipicolinic acid, binds lanthanide ions with nanomolar affinity, is readily attached to proteins via a disulfide bond, and avoids the problems of diastereomer formation associated with most of the conventional lanthanide tags. The high lanthanide affinity of the tag opens the possibility to measure residual dipolar couplings in a single sample containing a mixture of paramagnetic and diamagnetic lanthanides. Using the DNA-binding domain of the E. coli arginine repressor as an example, it is demonstrated that the tag allows immobilization of the lanthanide ion in close proximity of the protein by additional coordination of the lanthanide by a carboxyl group of the protein. The close proximity of the lanthanide ion promotes accurate determinations of magnetic susceptibility anisotropy tensors. In addition, the small size of the tag makes it highly suitable for studies of intermolecular interactions.     

UV absorption properties of ceria-modified compositions within the fluorite-type solid solution CeO2-Y6WO12

A new fluorite-type solid solution domain has been evidenced in the system (1−x) CeO₂−x/7 Y₆WO₁₂□₂ using the amorphous citrate route. All the studied phases (0?x?1) crystallize in a cubic-type symmetry. Diffuse reflectance spectra reveal a strong optical absorption between 380 and 400 nm. All substituted compositions spectral selectivities are estimated suitable for application as inorganic UV absorbers. The non linear variation observed in the optical gap values between Y₆WO₁₂ and CeO₂ is attributed to the presence of the cerium 4f-block band. Additionally, Time Resolved Microwave Conductivity (TRMC) experiment and phenol photodegradation analyses carried out on the Ce_0.81Y_0.16W_0.03O_1.95□_0.05 (x=0.19) composition do not indicate any photocalatytic activity for this material.     

The titration of clay minerals II. Structure-based model and implications for clay reactivity

The potentiometric titration and CEC data presented in part I are modeled in this paper, part II. Two models are compared: the two pK, three complexation sites plus exchange sites nonelectrostatic model developed by Baeyens and Bradbury and a model based on the MUSIC approach developed by Hiemstra and Van Riemsdijk. Both morphological and structural information is used to develop this new model. Morphological information is taken from the literature, while structural information is taken from the literature and constrained by supporting FTIR experiments. The Baeyens and Bradbury model is found to reproduce the general tendency of the titration curve, whereas the model based on the Hiemstra and Van Riemsdijk MUSIC approach provides a better fit to the experimental data. The former uses only 3 edge reaction sites, whereas the latter uses at least 27 edge reaction sites. Five main reactive sites are sufficient to fit the MUSIC model curve, but the model allows us to derive the properties of 22 other reactive sites. Logically, the greater the number of sites, the better the fit. Nevertheless, fewer adjustable parameters are necessary for the Hiemstra and Van Riemsdijk MUSIC model than for the Baeyens and Bradbury model, thanks to structural and morphological constraints. The precision of the potentiometric titration curve is insufficient to verify that the properties of the 27 sites given by the MUSIC model are effective. Thus, we coupled some properties of clay minerals, such as dissolution, to the modeled acid-base properties of these sites to assess our model. We then questioned the ability of simplified models such as the Baeyens and Bradbury model to predict the interactions between clay minerals and solutions in natural environments. In addition, we derived the cation exchange selectivity coefficients for CaCl+ ionic pairs and H+ from our CEC data and gave an estimate for the CaOH+ selectivity coefficient.     

Chironomic stylization of intonation

Intonation stylization is studied using "chironomy," i.e., the analogy between hand gestures and prosodic movements. An intonation mimicking paradigm is used. The task of the ten subjects is to copy the intonation pattern of sentences with the help of a stylus on a graphic tablet, using a system for real-time manual intonation modification. Gestural imitation is compared to vocal imitation of the same sentences (seven for a male speaker, seven for a female speaker). Distance measures between gestural copies, vocal imitations, and original sentences are computed for performance assessment. Perceptual testing is also used for assessing the quality of gestural copies. The perceptual difference between natural and stylized contours is measured using a mean opinion score paradigm for 15 subjects. The results indicate that intonation contours can be stylized with accuracy by chironomic imitation. The results of vocal imitation and chironomic imitation are comparable, but subjects show better imitation results in vocal imitation. The best stylized contours using chironomy seems perceptually indistinguishable or almost indistinguishable from natural contours, particularly for female speech. This indicates that chironomic stylization is effective, and that hand movements can be analogous to intonation movements.     

“Vapor-liquid” equilibrium measurements and modeling for the cyclohexane + n-hexanoic acid binary system

To simulate cyclohexane to cyclohexanol oxidation reactors, the acquisition and modeling of vapor-liquid equilibria of the key components, under the process conditions, are essential. n-Hexanoic acid is a co-product of the reaction. Vapor-liquid equilibrium data are reported for the cyclohexane + n-hexanoic acid binary system at four temperatures: 413, 423, 464 and 484 K. All measurements have been carried out using an apparatus based on the “static-analytic” method, with two ROLSI™ pneumatic capillary samplers. The generated data are successfully correlated using two equations of state, the Peng-Robinson (PR) and the Perturbed Chain Statistical Association Fluid Theory (PC-SAFT). Both models are capable of representing the experimental data, but the PC-SAFT EoS uses less binary interaction parameters.