Rectangle-capped and tilted micropillar array for enhanced anisotropic anti-shearing in biomimetic adhesion

Dry adhesion observed in the feet of various small creatures has attracted considerable attention owing to the unique advantages such as self-cleaning, adaptability to rough surfaces along with repeatable and reversible adhesiveness. Among these advantages, for practical applications, proper detachability is critical for dry adhesives with artificial microstructures. In this study, we present a microstructured array consisting of both asymmetric rectangle-capped tip and tilted shafts, which produce an orthogonal anisotropy of the shearing strength along the long and short dimensions of the tip, with a maximum anti-shearing in the two directions along the longer dimension. Meanwhile, the tilt feature can enhance anisotropic shearing adhesion by increasing shearing strength in the forward shearing direction and decreasing strength in the reverse shearing direction along the short dimension of the tip, leading to a minimum anti-shearing in only one of the two directions along the shorter dimension of the rectangular tip. Such a microstructured adhesive with only one weak shearing direction, leading to well-controlled attachment and detachment of the adhesive, is created in our experiment by conventional double-sided exposure of a photoresist followed by a moulding process.

Crustal 3-D geometry of the Kristineberg area (Sweden) with implications on VMS deposits

Structural analysis of the Palaeoproterozoic volcanogenic massive sulfide (VMS) hosting Kristineberg area, Sweden, constrained by existing magnetotelluric (MT) and seismic reflection data, reveals that the complex geometry characterized by non-cylindrical antiformal structures is due to transpression along the termination of a major high-strain zone. Similar orientations of the host rock deformation fabrics and the VMS ore lenses indicate that the present-day geometry of the complex VMS deposits in the Kristineberg area may be attributed to tectonic transposition. The tectonic transposition was dominantly controlled by reverse shearing and related upright to overturned folding, with increasing contribution of strike-slip shearing and sub-horizontal flow towards greater crustal depths. Furthermore, the northerly dip of the previously recognized subsurface crustal reflector within the Kristineberg area is attributed to formation of crustal compartments with opposite polarities within the scale of the whole Skellefte district. The resulting structural framework of the main geological units is visualized in a 3-D model which is available as a 3-D PDF document through the publication website.

Interplay between folding and ductile shearing in the Proterozoic crust of the Muskoka – Parry Sound region, central Ontario

Grenville gneiss of the central Georgian Bay region was subjected to ductile deformation that produced narrow mylonite zones as well as three sets of superimposed folds differing greatly in structural signature, size, and orientation. Some mylonite zones are concordant to gneissosity and are repeatedly folded, others cut gneissosity and postdate the folding. Gneissosity was generated as a regionally subhorizontal feature, either by crustal thinning or, like the early mylonite zones, by low-angle reverse shearing. An attempt is made to account for the initially subhorizontal gneissosity, the mylonite zones, and the folds in a regime of large-scale reverse shearing that strikes parallel to the Grenville Front.Upright northwest–southwest to north–south buckle folds dominate the map pattern and are subperpendicular to the reverse Grenville Front boundary fault. These set-2 folds cannot be attributed to reverse simple shearing but require a large component of east–west compression. Such stress could have been generated in a northwest–southeast zone of sinistral ductile shear caused by temporary locking of the southern segment of the Grenville Front boundary fault (now under Lake Huron).All structural facts can be explained without large differential translations of crustal slices. For example, most discordances in the regional gneissosity pattern could have been created by décollement and repeated buckling. Detailed geobarometry and petrologic studies may be required to settle the question of large-scale thrusting within the Grenville gneiss terrane.