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The continuous flow assembly of colloidal nanoparticles from aqueous suspensions into macroscopic materials in a field-assisted double flow focusing system offers an attractive way to bridge the outstanding nanoscale characteristics of renewable cellulose nanofibrils (CNFs) at scales most common to human technologies. By incorporating single-walled carbon nanotubes (SWNTs) during the fabrication process, high-performance functional filament nanocomposites were produced. CNFs and SWNTs were first dispersed in water without any external surfactants or binding agents, and the resulting nanocolloids were aligned by means of an alternating electric field combined with extensional sheath flows. The nanoscale orientational anisotropy was then locked by a liquid−gel transition during the materials assembly into macroscopic filaments, which greatly improved their mechanical, electrical, and liquid sensing properties. Significantly, these findings pave the way toward the environmentally friendly and scalable manufacturing of a variety of multifunctional fibers for diverse applications. 

Diving birds are regarded as a classic example of morphological convergence. Divers tend to have small wings extending from rotund bodies, requiring many volant species to fly with rapid wingbeats, and rendering others flightless. The high wing-loading of diving birds is frequently associated with the challenge of using forelimbs adapted for flight for locomotion in a “draggier” fluid, but this does not explain why species that rely exclusively on their feet to dive should have relatively small wings, as well. Therefore, others have hypothesized that ecological factors shared by wing-propelled and foot-propelled diving birds drive the evolution of high wing-loading. Following a reexamination of the aquatic habits of birds, we tested between hypotheses seeking to explain high wing-loading in divers using new comparative data and phylogenetically informed analyses. We found little evidence that wing-propelled diving selects for small wings, as wing-propelled and foot-propelled species share similar wing-loadings. Instead, our results suggest that selection to reduce buoyancy has driven high wing-loading in divers, offering insights for the development of bird-like aquatic robots.

 

Seamounts are volcanic constructs that litter the seafloor. They are important for understanding numerous aspects of marine science, such as plate tectonics, the volcanic melt budget, oceanic circulation, tsunami wave diffraction, tidal energy dissipation and mass wasting. Geometrically, seamounts come in many sizes and shapes, and for the purpose of modelling them for morphological, gravimetric or isostatic studies it is convenient to have simple analytical models whose properties are well known. Here, we present a family of seamount models that may be used in such studies, covering both the initial construction phase and later mass-wasting by sectoral collapses. We also derive realistic axisymmetric density variations that are compatible with observed first-order structure from seismic tomography studies.

 

Abstract Auxetic materials showing a negative Poisson’s ratio can offer unusual sensing capabilities due to drastic percolation changes. This study presents the capacitive response of wet-fractured carbon nanotube paper composites in exposure to humidity. A strained composite strip is fractured to produce numerous cantilevers consisting of cellulose fibers coated with carbon nanotubes. During stretching, the thin composite buckles in the out-of-plane direction, which causes auxetic behavior to generate the radially structured electrodes. The crossbar junctions forming among the fractured electrodes significantly increase capacitance and its response to humidity as a function of sensor widths. The molecular junctions switch electric characteristics between predominantly resistive- and capacitive elements. The resulting capacitive response is characterized for humidity sensing without the need for an additional absorption medium. The normalized capacitance change (ΔC/C 0 ) exhibits a sensitivity of 0.225 within the range of 40 ∼ 80% relative humidity. The novel auxetic behavior of a water-printed paper-based nanocomposite paves the way for inexpensive humidity and sweat sensors. 

SUMMARY Recent modelling studies have shown that laboratory-derived rheology is too strong to reproduce observations of flexure at the Hawaiian Islands, while the same rheology appears consistent with outer rise—trench flexure at circum-Pacific subduction zones. Collectively, these results indicate that the rheology of an oceanic plate boundary is stronger than that of its interior, which, if correct, presents a challenge to understanding the formation of trenches and subduction initiation. To understand this dilemma, we first investigate laboratory-derived rheology using fully dynamic viscoelastic loading models and find that it is too strong to reproduce the observationally inferred elastic thickness, Te, at most plate interior settings. The Te can, however, be explained if the yield stress of low-temperature plasticity is significantly reduced, for example, by reducing the activation energy from 320 kJ mol−1, as in Mei et al., to 190 kJ mol−1 as was required by previous studies of the Hawaiian Islands, implying that the lithosphere beneath Hawaii is not anomalous. Second, we test the accuracy of the modelling methods used to constrain the rheology of subducting lithosphere, including the yield stress envelope (YSE) method, and the broken elastic plate model (BEPM). We show the YSE method accurately reproduces the model Te to within ∼10 per cent error with only modest sensitivity to the assumed strain rate and curvature. Finally, we show that the response of a continuous plate is significantly enhanced when a free edge is introduced at or near an edge load, as in the BEPM, and is sensitive to the degree of viscous coupling at the free edge. Since subducting lithosphere is continuous and generally mechanically coupled to a sinking slab, the BEPM may falsely introduce a weakness and hence overestimate Te at a trench because of trade-off. This could explain the results of recent modelling studies that suggest the rheology of subducting oceanic plate is stronger than that of its interior. However, further studies using more advanced thermal and mechanical models will be required in the future in order to quantify this. 

Understanding the electromechanical coupling of auxetic materials offers unique opportunities to enhance the sensitivity of piezoresistive sensors. Reports on the auxetic behavior of random fiber networks have been relatively scarce due to their less pronounced Poisson's expansions than other auxetic designs adapting periodically arranged structures. In this study, the auxetic response of hierarchical pulp-carbon nanotube networks is tailored through the localized tensional micro-fracture initiated by water-printing. The interfacial junctions among multiwalled carbon nanotubes (MWCNTs) and cellulose fibers are disintegrated and reorganized to induce the buckling of a wet CNT paper composite (CPC) network. The Poisson's ratio of −49.5 is achieved at the water-printed region. The resulting piezoresistive properties of CPC sensors exhibit high sensitivity (3.3 kPa −1 ) over a wide dynamic range (6–500 000 Pa). The novel auxetic behavior of water-printed CPC paves the way for high performance and inexpensive wearable devices.