Multiple strategies of improving photocatalytic water splitting efficiency in 2D arsenic sesquichalcogenides.

Improving the solar-to-hydrogen efficiency has always been a significant topic in the field of photocatalysis. Based on first-principles calculations, herein, we propose multiple strategies to improve the photocatalytic properties of 2D arsenic sesquichalcogenides for full water splitting. The new configurations AsSTe and AsSeTe monolayers, derived from the AsTe monolayers by surface modification, are manifested to be typical infrared-light driven photocatalysts.

Local polar order controls mechanical stress and triggers layer formation in developing colonies.

Colonies of the social bacterium go through a morphological transition from a thin colony of cells to three-dimensional droplet-like fruiting bodies as a strategy to survive starvation. The biological pathways that control the decision to form a fruiting body have been studied extensively. However, the mechanical events that trigger the creation of multiple cell layers and give rise to droplet formation remain poorly understood.

distinguishes surfaces by stiffness using retraction of type IV pili.

The ability of eukaryotic cells to differentiate surface stiffness is fundamental for many processes like stem cell development. Bacteria were previously known to sense the presence of surfaces, but the extent to which they could differentiate stiffnesses remained unclear. Here we establish that the human pathogen Pseudomonas aeruginosa actively measures surface stiffness using type IV pili (TFP).

Tuning the mechanical impedance of disordered networks for impact mitigation.

Disordered-Network Mechanical Materials (DNMM), comprised of random arrangements of bonds and nodes, have emerged as mechanical metamaterials with the potential for achieving fine control over their mechanical properties. Recent computational studies have demonstrated this control whereby an extremely high degree of mechanical tunability can be achieved in disordered networks a selective bond removal process called pruning. In this study, we experimentally demonstrate how pruning of a disordered network alters its macroscopic dynamic mechanical response and its capacity to mitigate impact.

Effect of two parallel intruders on total work during granular penetrations.

The intrusion of single passive intruders into granular particles has been studied in detail. However, the intrusion force produced by multiple intruders separated at a distance from one another, and hence the effect of their presence in close proximity to one another, is less explored. Here, we used numerical simulations and laboratory experiments to study the force response of two parallel rods intruding vertically into granular media while varying the gap spacing between them.

Low-Reynolds-number, biflagellated Quincke swimmers with multiple forms of motion.

In the limit of zero Reynolds number (Re), swimmers propel themselves exploiting a series of nonreciprocal body motions. For an artificial swimmer, a proper selection of the power source is required to drive its motion, in cooperation with its geometric and mechanical properties. Although various external fields (magnetic, acoustic, optical, etc.

Intrusion into Granular Media Beyond the Quasistatic Regime.

The drag force exerted on an object intruding into granular media is typically assumed to arise from additive velocity and depth dependent contributions. We test this with intrusion experiments and molecular dynamics simulations at constant speed over four orders of magnitude, well beyond the quasistatic regime. For a vertical cylindrical rod we find velocity dependence only right after impact, followed by a crossover to a common, purely depth-dependent behavior for all intrusion speeds.

Stress Controlled Rheology of Dense Suspensions Using Transient Flows.

Dense suspensions of hard particles in a Newtonian liquid can be jammed by shear when the applied stress exceeds a certain threshold. However, this jamming transition from a fluid into a solidified state cannot be probed with conventional steady-state rheology because the stress distribution inside the material cannot be controlled with sufficient precision. Here we introduce and validate a method that overcomes this obstacle.

Interparticle hydrogen bonding can elicit shear jamming in dense suspensions.

Dense suspensions of hard particles in a liquid can exhibit strikingly counter-intuitive behaviour, such as discontinuous shear thickening (DST) and reversible shear jamming (SJ) into a state where flow is arrested and the suspension is solid-like. A stress-activated crossover from hydrodynamic interactions to frictional particle contacts is key for these behaviours. However, in experiments, many suspensions show only DST, not SJ.

Measuring the porosity and compressibility of liquid-suspended porous particles using ultrasound.

A key parameter describing the behavior of suspensions is the volume fraction ϕ of the solid particles that are dispersed in the liquid. Obtaining accurate values for ϕ becomes difficult for porous particles, because they can absorb some of the liquid. A prime example are the widely used cornstarch suspensions, for which ϕ usually is only estimated from the mass fraction of particles.

Dynamic shear jamming in dense granular suspensions under extension.

Unlike dry granular materials, a dense granular suspension like cornstarch in water can strongly resist extensional flows. At low extension rates, such a suspension behaves like a viscous fluid, but rapid extension results in a response where stresses far exceed the predictions of lubrication hydrodynamics and capillarity. To understand this remarkable mechanical response, we experimentally measure the normal force imparted by a large bulk of the suspension on a plate moving vertically upward at a controlled velocity.

High-speed ultrasound imaging in dense suspensions reveals impact-activated solidification due to dynamic shear jamming.

A remarkable property of dense suspensions is that they can transform from liquid-like at rest to solid-like under sudden impact. Previous work showed that this impact-induced solidification involves rapidly moving jamming fronts; however, details of this process have remained unresolved. Here we use high-speed ultrasound imaging to probe non-invasively how the interior of a dense suspension responds to impact.