Stimuli-responsive granular crystals assembled by dipolar and multipolar interactions

This paper describes granular crystals held together by unusual, multipolar interactions and, under application of external bias, undergoing reversible structural transitions between closed and open forms. The system is comprised...

Influence of Lateral Constraints on Wave Propagation in Finite Granular Crystals

In the presented work, wave dynamics of 2D finite granular crystals of polyurethane cylinders under low-velocity impact loading was investigated to gain better understanding of the influence of lateral constraints. The deformation of the individual grains in the granular crystals during the impact loading was recorded by a high-speed camera and digital image correlation (DIC) was used to calculate high fidelity kinematic and strain fields in each grain. These grain-scale kinematic and strain fields were utilized for the computation of the intergranular forces at each contact using a granular element method (GEM) based mathematical framework. Since the polyurethane were viscoelastic in nature, the viscoelasticity constitutive law was implemented in the GEM framework and it was shown that linear elasticity using the strain rate-dependent coefficient of elasticity is sufficient to use instead of a viscoelastic framework. These particle-scale kinematic and strain field measurements in conjunction with the interparticle forces also provided some interesting insight into the directional dependence of the wave scattering and attenuation in finite granular crystals. The directional nature of the wave propagation resulted in strong wave reflection from the walls. It was also noteworthy that the two reflected waves from the two opposite sidewalls result in destructive interference. These lateral constraints at different depths leads to significant differences in wave attenuation characteristics and the finite granular crystals can be divided into two regions: upper region, with exponential wave decay rate, and lower region, with higher decay rate.

Aluminosugilite, KNa₂Al₂Li₃Si₁₂O₃₀, an Al analogue of sugilite, from the Cerchiara mine, Liguria, Italy

Aluminosugilite (IMA2018-142), ideal formula KNa2Al2Li3Si12O30, is a new mineral that was found in the interstices in manganiferous metacherts from the Cerchiara mine, Liguria, Italy. Aluminosugilite is an Al analogue of sugilite belonging to the milarite group. It occurs as aggregates of small prismatic and/or granular crystals up to 1 mm in length, and it is pinkish-purple with a pale purple to white streak and a vitreous lustre. It has a Mohs hardness of 6–6.5. Its cleavage is indistinct, poor on (0001). Measured and calculated densities are Dmeas.=2.71–2.72 g cm−3 and Dcalc.=2.73 g cm−3, respectively. Aluminosugilite is optically uniaxial (–), with ω=1.577–1.586 and ε=1.575–1.585, with a weak pleochroism. The magnetic susceptibility is lower than that for sugilite. Aluminosugilite is insoluble in HCl, HNO3 and H2SO4, like sugilite. The empirical formula of aluminosugilite calculated on the basis of O =30 from the result obtained by electron microprobe analysis and laser-induced breakdown spectroscopy is K0.99Na1.99(Al1.38Mn0.313+Fe0.243+Ti0.05Mg0.01)Σ1.99Li3.06Si11.99O30. Structure refinement converged to R1=2.17 %. Its space group is hexagonal P6∕mcc, with unit-cell parameters a=9.9830(4) Å, c=13.9667(5) Å and V=1205.45(7) Å3. Based on the refined site occupancies, the ideal structural formula of aluminosugilite is CKBNa2AAl2T2Li3T1Si12O30. The variation of the A–O3 distance is governed by the cationic substitution at the A site. The a and c dimensions of aluminosugilite are shorter than those of sugilite due to Al substitution for Fe3+ at the A site.