Wave dispersion in periodic post-buckled structures

Wave propagation in pinned-supported, post-buckled beams can be described with the Korteweg de Vries (KdV) equation. Finite-element simulations however show that the KdV is applicable only to post-buckled beams with strong pre-compression. For weak and moderate pre-stress, a dispersive front is present and it is the aim of the current paper to analyze sources of dispersion beyond periodicity given three support types: guided, pinned, and free. Bloch theorem and a transfer-matrix method are employed to obtain numerical dispersion relations and characteristic wave modes, which are used to analyze the effects of pre-stress, initial curvature, and the influence of support types. Additionally, a new method is proposed to obtain a semi-analytical dispersion equation for the acoustic branch. Powers of frequency and the propagation constant are explicitly expressed and their coefficients are based on stiffness and mass-matrix components obtained from finite elements. This allows a physical interpretation of the dispersion sources, based on which, equivalent mass–spring models of post-buckled beam are proposed. It is found that mass and stiffness coupling are significant dispersion sources. In the present paper, a reduced form of Bloch theorem is presented exploiting glide-reflection symmetries, reducing the size of the unit cell and allowing an easier representation and interpretation of results.     

A series of isoreticular, highly stable, porous zirconium oxide based metal-organic frameworks

Brolly good MOFs: A new series of hydrophobic isoreticular porous Zr oxide dicarboxylate MOFs have been prepared (see picture, Zr?blue polyhedra, O?red, C?black). They have a one-dimensional pore system, a rare combination of Lewis acidity and hydrophobic character, and a higher hydrothermal and mechanical stability than their UiO MOF polymorph counterparts.     

CH(4) storage and CO(2) capture in highly porous zirconium oxide based metal-organic frameworks

A series of porous Zr oxoclusters-based MOFs was computationally explored for their gas storage/capture performances. The highly porous UiO-67(Zr) and UiO-68(Zr) solids show exceptionally high CH(4) and CO(2) adsorption capacities under operating conditions that make these thermal, water and mechanical resistant materials very promising for physisorption-based processes.     

Mechanical Control of the Kinetic Propylene/Propane Separation by Zeolitic Imidazolate Framework‐8

One intriguing feature of many porous MOFs is their stimulus‐induced flexibility, which makes them unique compared to standard adsorbents. Here we propose an innovative concept to achieve an efficient kinetic separation of species with similar properties by the mechanical fine‐tuning of the pore architecture of the flexible zeolitic imidazolate framework ZIF‐8. This unprecedented approach was applied to one of the most challenging societally relevant separations: the separation of propylene and propane, which is of vital importance in the petrochemical industry. It was demonstrated that the application of an external pressure creates a gradual enhancement in the propylene/propane diffusion selectivity to more than one order of magnitude at 1 GPa pressure. A detailed analysis of the molecular simulations was further able to unravel the origin of this unusual behavior at the atomistic level.     

Diastereoselective synthesis of 1-benzyltetrahydroisoquinoline derivatives from amino acids via 1,4 chirality transfer. Part 1

[structure: see text]. L-(-)-phenylalanine, L-(+)-valine, and L-(-)-proline were used in the diastereoselective synthesis of benzyltetrahydroisoquinoline derivatives.     

CO2 diffusivity in LiY and NaY faujasite systems: a combination of molecular dynamics simulations and quasi-elastic neutron scattering experiments

Quasi-elastic Neutron Scattering combined with Molecular Dynamics simulations have been carried out to gain further insight into the CO₂ dynamics in LiY and NaY Faujasites. In both materials, it was pointed out that the transport diffusivity (D_T) increases with the loading whereas the self diffusivity (D_S) decreases. In addition, it was shown that LiY exhibits a significant slower CO₂ self diffusivity process due to a strong interaction between the Li⁺ cation and the adsorbate molecules at the initial stage of diffusion. This result is consistent with higher simulated activation energy in this cation exchanged faujasite form. By contrast, the transport diffusivity is revealed to be slightly faster in LiY than in NaY.