The mechanical characterization of the legs, fangs, and prosoma in the spider Harpactira curvipes (Pocock 1897)

The exoskeleton of spiders is the primary structure that interacts with the external mechanical stimuli, thus playing a crucial role in spider life. In particular, fangs, legs, and prosoma are the main rigid structures of the exoskeleton and their properties must be measured to better understand their mechanical behaviours. Here we investigate, by means of nanoindentation, the mechanical properties of the external sclerotized cuticles of such parts in the spider Harpactira curvipes. Interestingly, the results show that the leg’s cuticle is stiffer than the prosoma and has a stiffness similar to the one of the tip fangs. This could be explained by the legs’ function in perceiving vibrations that could be facilitated by higher stiffness. From a broader perspective, this characterization could help to understand how the same basic material (the cuticle, i.e. mainly composed of chitin) can be tuned to achieve different mechanical functions, which improves the animal’s adaptation to specific evolutive requirements. We, thus, hope that this work stimulates further comparative analysis. Moreover, these results may also be potentially important to inspire the design of graded materials with superior mechanical properties

Bouncing localized structures in a liquid-crystal light-valve experiment

Experimental evidence of bouncing localized structures in a nonlinear optical system is reported.Comment: 4 page

Three Dimensional Printing of Multiscale Carbon Fiber-Reinforced Polymer Composites Containing Graphene or Carbon Nanotubes

Three-dimensional printing offers a promising, challenging opportunity to manufacture component parts with ad hoc designed composite materials. In this study, the novelty of the research is the production of multiscale composites by means of a solvent-free process based on melt compounding of acrylonitrile–butadiene–styrene (ABS), with various amounts of microfillers, i.e., milled (M) carbon fibers (CFs) and nanofillers, i.e., carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs). The compounded materials were processed into compression molded sheets and into extruded filaments. The latter were then used to print fused filament fabrication (FFF) specimens. The multiscale addition of the microfillers inside the ABS matrix caused a notable increase in rigidity and a slight increase in strength. However, it also brought about a significant reduction of the strain at break. Importantly, GNPs addition had a good impact on the rigidity of the materials, whereas CNTs favored/improved the composites’ electrical conductivity. In particular, the addition of this nanofiller was very effective in improving the electrical conductivity compared to pure ABS and micro composites, even with the lowest CNT content. However, the filament extrusion and FFF process led to the creation of voids within the structure, causing a significant loss of mechanical properties and a slight improvement of the electrical conductivity of the printed multiscale composites. Selective parameters have been presented for the comparison and selection of compositions of multiscale nanocomposites

Thermomechanical effects in uniformly aligned dye-doped nematic liquid crystals

We show theoretically that thermomechanical effects in dye-doped nematic liquid crystals when illuminated by laser beams, can become important and lead to molecular reorientation at intensities substantially lower than that needed for optical Fr\'eedericksz transition. We propose a 1D model that assumes homogenous intensity distribution in the plane of the layer and is capable to describe such a thermally induced threshold lowering. We consider a particular geometry, with a linearly polarized light incident perpendicularly on a layer of homeotropically aligned dye-doped nematics

Non-Gaussian statistics and extreme waves in a nonlinear optical cavity

A unidirectional optical oscillator is built by using a liquid crystal light-valve that couples a pump beam with the modes of a nearly spherical cavity. For sufficiently high pump intensity, the cavity field presents a complex spatio-temporal dynamics, accompanied by the emission of extreme waves and large deviations from the Gaussian statistics. We identify a mechanism of spatial symmetry breaking, due to a hypercycle-type amplification through the nonlocal coupling of the cavity field

Spatiotemporal pulses in a liquid crystal optical oscillator

A nonlinear optical medium results by the collective orientation of liquid crystal molecules tightly coupled to a transparent photoconductive layer. We show that such a medium can give a large gain, thus, if inserted in a ring cavity, it results in an unidirectional optical oscillator. Dynamical regimes with many interacting modes are made possible by the wide transverse size and the high nonlinearity of the liquid crystals. We show the generation of spatiotemporal pulses, coming from the random superposition of many coexisting modes with different frequencies