A dynamic forcing method for unsteady turbulent inflow conditions

The present paper aims to provide an efficient and flexible method for the initialization of a zonal RANS/LES type calculation when the resolution of the near wall region is treated in RANS mode. Indeed, when part of the boundary layer must be resolved in LES mode, one generally experiences a very long transient state, which makes this approach inapplicable to industrial applications. The skillful combination of a Zonal Detached Eddy Simulation method (ZDES), a Synthetic Eddy Method (SEM) and a self-adaptative dynamic forcing approach enables this. The two former being taken as framework, while the latter, based on innovative considerations, is the purpose of the paper. The main strength of the dynamic forcing method comes from its local nature, enabling to treat geometrically complex applications.     

Microfibrillated cellulose with sizing for reinforcing composites with LDPE

Microfibrillated cellulose (MFC) fibers were acylated by the sizing agent, alkenyl succinic anhydride (ASA) reagent in an aqueous medium, by simple impregnation. The chemical modification was confirmed by Fourier transform infrared spectroscopy and solid-state ¹³C NMR. All the samples were combined with low-density polyethylene and the morphology, thermal properties, mechanical properties and water absorption behavior of the ensuing composites were investigated. The chemical modification of the MFC with ASA improved the interfacial adhesion with the matrix and hence the mechanical properties of the composites while decreasing their water uptake capacity. In addition, it was shown that the degree of substitution strongly influenced the performance of the composites.     

Sunlight‐Driven Copper‐Catalyst Activation Applied to Photolatent Click Chemistry

The synthesis, full characterization, photoreduction properties, and catalytic activity for the copper(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC) reaction of a copper(II)–DMEDA (N,N′‐dimethylethylendiamine) complex is reported. Spectroscopic studies (UV/Vis, EPR) demonstrated that under daylight illumination highly effective copper(II) to copper(I) reduction occurs in this complex. These findings are in agreement with a high photoreduction quantum yield value of 0.22 in MeOH, and a value approaching unity as determined in THF. The reduction process, which can also be conducted by irradiation at 365 nm by using a standard TLC (thin layer chromatography) lamp, is ascribed to a highly efficient photoinduced electron transfer (PET) process mediated by the benzophenone photosensitizer present in the carboxylate counterion. Having deaerated the reaction mixture, the photogenerated copper(I) species proved to be highly active for the CuAAC reaction, demonstrated by reactions conducted with low catalyst loading (0.5 mol %) on a range of clickable protected and non‐protected mono‐ and disaccharides. Once initiated, the reaction can be stopped at any time on introducing air into the reaction medium. Deoxygenation followed by irradiation restores the activity, making the copper(II)–DMEDA complex a switchable catalyst of practical value.     

Synthesis and Characterization of Double Crystalline Cyclic Diblock Copolymers of Poly(ε‐caprolactone) and Poly(l(d)‐lactide) (c(PCL‐b‐ PL(D)LA))

The synthesis of symmetric cyclo poly(ε‐caprolactone)–block–poly(l (d )‐lactide) (c(PCL–b–PL(D)LA)) by combining ring‐opening polymerization of ε‐caprolactone and lactides and subsequent click chemistry reaction of the linear precursors containing antagonist functionalities is presented. The two blocks can sequentially crystallize and self‐assemble into double crystalline spherulitic superstructures. The cyclic chain topology significantly affects both the nucleation and the crystallization of each constituent, as gathered from a comparison of the behavior of linear precursors and cyclic block copolymers. The stereochemistry of the PLA block does not have a significant effect on the nonisothermal crystallization of both linear and cyclo PCL‐b‐PDLA and PCL‐b‐PLLA copolymers.

     

Solid‐State NMR and DFT Combined for the Surface Study of Functionalized Silicon Nanoparticles

Silicon nanoparticles (NPs) serve a wide range of optical, electronic, and biological applications. Chemical grafting of various molecules to Si NPs can help to passivate their reactive surfaces, “fine‐tune” their properties, or even give them further interesting features. In this work, ¹H, ¹³C, and ²⁹Si solid‐state NMR spectroscopy has been combined with density functional theory calculations to study the surface chemistry of hydride‐terminated and alkyl‐functionalized Si NPs. This combination of techniques yields assignments for the observed chemical shifts, including the contributions resulting from different surface planes, and highlights the presence of physisorbed water. Resonances from near‐surface ¹³C nuclei were shown to be substantially broadened due to surface disorder and it is demonstrated that in an ambient environment hydride‐terminated Si NPs undergo fast back‐bond oxidation, whereas long‐chain alkyl‐functionalized Si NPs undergo slow oxidation. Furthermore, the combination of NMR spectroscopy and DFT calculations showed that the employed hydrosilylation reaction involves anti‐Markovnikov addition of the 1‐alkene to the surface of the Si NPs.     

Limit point buckling of a finite beam on a nonlinear foundation

In this paper, we consider an imperfect finite beam lying on a nonlinear foundation, whose dimensionless stiffness is reduced from 1 to k as the beam deflection increases. Periodic equilibrium solutions are found analytically and are in good agreement with a numerical resolution, suggesting that localized buckling does not appear for a finite beam. The equilibrium paths may exhibit a limit point whose existence is related to the imperfection size and the stiffness parameter k through an explicit condition. The limit point decreases with the imperfection size while it increases with the stiffness parameter. We show that the decay/growth rate is sensitive to the restoring force model. The analytical results on the limit load may be of particular interest for engineers in structural mechanics.