Showing papers by "Sidney R. Nagel published in 2012"
TL;DR: There is a 1/N correction to the discrete jump in the contact number at the transition so that jammed packings exist only above isostaticity, demonstrating that the jamming transition can be considered a phase transition.
Abstract: We present an analysis of finite-size effects in jammed packings of $N$ soft, frictionless spheres at zero temperature. There is a $\frac{1}{N}$ correction to the discrete jump in the contact number at the transition so that jammed packings exist only above isostaticity. As a result, the canonical power-law scalings of the contact number and elastic moduli break down at low pressure. These quantities exhibit scaling collapse with a nontrivial scaling function, demonstrating that the jamming transition can be considered a phase transition. Scaling is achieved as a function of $N$ in both two and three dimensions, indicating an upper critical dimension of 2.
200 citations
TL;DR: It is revealed that a third regime, one that describes the initial dynamics of coalescence for all drop viscosities, has been missed and an argument based on force balance allows the construction of a new coalescence phase diagram.
Abstract: Drop coalescence is central to diverse processes involving dispersions of drops in industrial, engineering, and scientific realms. During coalescence, two drops first touch and then merge as the liquid neck connecting them grows from initially microscopic scales to a size comparable to the drop diameters. The curvature of the interface is infinite at the point where the drops first make contact, and the flows that ensue as the two drops coalesce are intimately coupled to this singularity in the dynamics. Conventionally, this process has been thought to have just two dynamical regimes: a viscous and an inertial regime with a cross-over region between them. We use experiments and simulations to reveal that a third regime, one that describes the initial dynamics of coalescence for all drop viscosities, has been missed. An argument based on force balance allows the construction of a new coalescence phase diagram.
166 citations
TL;DR: Using laser-light interference coupled to high-speed imaging, the radius, curvature, and height of the vapor pocket, as well as nonaxisymmetric fluctuations of the interface for water drops at different temperatures, are measured.
Abstract: In the Leidenfrost effect, liquid drops deposited on a hot surface levitate on a thin vapor cushion fed by evaporation of the liquid. This vapor layer forms a concave depression in the drop interface. Using laser-light interference coupled to high-speed imaging, we measured the radius, curvature, and height of the vapor pocket, as well as nonaxisymmetric fluctuations of the interface for water drops at different temperatures. The geometry of the vapor pocket depends primarily on the drop size and not on the substrate temperature.
154 citations
TL;DR: Using high-speed imaging, it is shown that surface roughness and air pressure influence both mechanisms of thin-sheet formation and ejection, and that if the air pressure is lowered, droplet ejection is suppressed not only during thin- sheet formation but also for prompt splashing.
Abstract: A liquid drop impacting a solid surface may splash either by emitting a thin liquid sheet that subsequently breaks apart or by promptly ejecting droplets from the advancing liquid-solid contact line. Using high-speed imaging, we show that surface roughness and air pressure influence both mechanisms. Roughness inhibits thin-sheet formation even though it also increases prompt splashing at the advancing contact line. If the air pressure is lowered, droplet ejection is suppressed not only during thin-sheet formation but also for prompt splashing.
121 citations
Journal Article•
2 citations