Diffusive spreading and mixing of fluid monolayers

The use of ultra-thin, i.e., monolayer films plays an important role for the emerging field of nano-fluidics. Since the dynamics of such films is governed by the interplay between substrate-fluid and fluid-fluid interactions, the transport of matter in nanoscale devices may be eventually efficiently controlled by substrate engineering. For such films, the dynamics is expected to be captured by two-dimensional lattice-gas models with interacting particles. Using a lattice gas model and the non-linear diffusion equation derived from the microscopic dynamics in the continuum limit, we study two problems of relevance in the context of nano-fluidics. The first one is the case in which along the spreading direction of a monolayer a mesoscopic-sized obstacle is present, with a particular focus on the relaxation of the fluid density profile upon encountering and passing the obstacle. The second one is the mixing of two monolayers of different particle species which spread side by side following the merger of two chemical lanes, here defined as domains of high affinity for fluid adsorption surrounded by domains of low affinity for fluid adsorption.Comment: 12 pages, 3 figure

A review of the tribes of Deltocephalinae (Hemiptera: Auchenorrhyncha: Cicadellidae)

The classification of the largest subfamily of leafhoppers, Deltocephalinae, including 38 tribes, 923 genera, and 6683 valid species, is reviewed and revised. An updated phylogeny of the subfamily based on molecular (28S, Histone H3) and morphological data and an expanded taxon sample (37 taxa not included in previous analyses) is presented. Based on the results of these analyses and on the morphological examination of many representatives of the subfamily, the classification of the tribes and subtribes of Deltocephalinae is revised. Complete morphological descriptions, illustrations, lists of the included genera, and notes on their distribution, ecology, and important vector species are provided for the 38 recognized tribes and 18 subtribes. A dichotomous key to the tribes is provided. All names in the taxonomic treatments are hyperlinked to online resources for individual taxa which are supported by a comprehensive database for Deltocephalinae compiled using the taxonomic database software package 3I. The online functionality includes an interactive key to tribes and subtribes and advanced database searching options. Each taxon (subspecies through subfamily) has a unique taxon webpage providing nomenclatural information, lists of included taxa, an automated description (if available), images (if available), distributional information, bibliographic references and links to outside resources. Some observations and trends regarding the history of taxonomic descriptions in Deltocephalinae are reported. Four new tribes are described: Bahitini tribe nov. (25 genera), Bonsapeiini tribe nov. (21 genera), Phlepsiini tribe nov. (4 genera), and Vartini tribe nov. (7 genera). The circumscription and morphological characterization of Scaphoideini Oman, 1943 (61 genera) is substantially revised. Eleven new species are described: Acostemma stilleri sp. nov., Arrugada linnavuorii sp. nov., Drabescus zhangi sp. nov., Parabolopona webbi sp. nov., Goniagnathus emeljanovi sp. nov., Hecalus hamiltoni sp. nov., Scaphoideus omani sp. nov., Dwightla delongi sp. nov., Abimwa knighti sp. nov., Gannia viraktamathi sp. nov., and Doratulina dmitrievi sp. nov. Some family-group level taxonomic changes are made: Platymetopiini Haupt, 1929, Anoterostemmini Haupt, 1929, and Allygidiina Dmitriev, 2006 are synonymized with Athysanini Van Duzee, 1892, syn. nov.; Procepitini Dmitriev, 2002 is synonymized with Cicadulini Van Duzee, 1892, syn. nov.; Listrophorini Boulard, 1971 is synonymized with Chiasmini Distant, 1908, syn. nov.; Adamini Linnavuori & Al-Ne’amy, 1983, Dwightlini McKamey, 2003, and Ianeirini Linnavuori, 1978 are synonymized with Selenocephalini Fieber, 1872 syn.nov., and all three are now recognized as valid subtribes in their parent tribe. New placements of many genera to tribe and subtribe are made, and these are described in individual taxon treatments

Active colloids at fluid interfaces

If an active Janus particle is trapped at the interface between a liquid and a fluid, its self-propelled motion along the interface is affected by a net torque on the particle due to the viscosity contrast between the two adjacent fluid phases. For a simple model of an active, spherical Janus colloid we analyze the conditions under which translation occurs along the interface and we provide estimates of the corresponding persistence length. We show that under certain conditions the persistence length of such a particle is significantly larger than the corresponding one in the bulk liquid, which is in line with the trends observed in recent experimental studies

Effective interaction between active colloids and fluid interfaces induced by Marangoni flows

We show theoretically that near a fluid-fluid interface a single active colloidal particle generating, e.g., chemicals or a temperature gradient experiences an effective force of hydrodynamic origin. This force is due to the fluid flow driven by Marangoni stresses induced by the activity of the particle; it decays very slowly with the distance from the interface, and can be attractive or repulsive depending on how the activity modifies the surface tension. We show that, for typical systems, this interaction can dominate the dynamics of the particle as compared to Brownian motion, dispersion forces, or self-phoretic effects. In the attractive case, the interaction promotes the self-assembly of particles into a crystal-like monolayer at the interface.Comment: The manuscript proper and the supplementary information have been merged consecutively into a single PDF fil

Collective dynamics of chemically active particles trapped at a fluid interface

Chemically active colloids generate changes in the chemical composition of their surrounding solution and thereby induce flows in the ambient fluid which affect their dynamical evolution. Here we study the many-body dynamics of a monolayer of active particles trapped at a fluid-fluid interface. To this end we consider a mean-field model which incorporates the direct pair interaction (including also the capillary interaction which is caused specifically by the interfacial trapping) as well as the effect of hydrodynamic interactions (including the Marangoni flow induced by the response of the interface to the chemical activity). The values of the relevant physical parameters for typical experimental realizations of such systems are estimated and various scenarios, which are predicted by our approach for the dynamics of the monolayer, are discussed. In particular, we show that the chemically-induced Marangoni flow can prevent the clustering instability driven by the capillary attraction.Comment: 8 pages, 2 figure

Hyperfine and Optical Barium Ion Qubits

State preparation, qubit rotation, and high fidelity readout are demonstrated for two separate \baseven qubit types. First, an optical qubit on the narrow 6S$_{1/2}$ to 5D$_{5/2}$ transition at 1.76 $\mu$m is implemented. Then, leveraging the techniques developed there for readout, a ground state hyperfine qubit using the magnetically insensitive transition at 8 GHz is accomplished

Precursor films in wetting phenomena

The spontaneous spreading of non-volatile liquid droplets on solid substrates poses a classic problem in the context of wetting phenomena. It is well known that the spreading of a macroscopic droplet is in many cases accompanied by a thin film of macroscopic lateral extent, the so-called precursor film, which emanates from the three-phase contact line region and spreads ahead of the latter with a much higher speed. Such films have been usually associated with liquid-on-solid systems, but in the last decade similar films have been reported to occur in solid-on-solid systems. While the situations in which the thickness of such films is of mesoscopic size are rather well understood, an intriguing and yet to be fully understood aspect is the spreading of microscopic, i.e., molecularly thin films. Here we review the available experimental observations of such films in various liquid-on-solid and solid-on-solid systems, as well as the corresponding theoretical models and studies aimed at understanding their formation and spreading dynamics. Recent developments and perspectives for future research are discussed.Comment: 51 pages, 10 figures; small typos correcte

Self-propulsion of a catalytically active particle near a planar wall: from reflection to sliding and hovering

Micron-sized particles moving through solution in response to self-generated chemical gradients serve as model systems for studying active matter. Their far-reaching potential applications will require the particles to sense and respond to their local environment in a robust manner. The self-generated hydrodynamic and chemical fields, which induce particle motion, probe and are modified by that very environment, including confining boundaries. Focusing on a catalytically active Janus particle as a paradigmatic example, we predict that near a hard planar wall such a particle exhibits several scenarios of motion: reflection from the wall, motion at a steady-state orientation and height above the wall, or motionless, steady "hovering." Concerning the steady states, the height and the orientation are determined both by the proportion of catalyst coverage and the interactions of the solutes with the different "faces" of the particle. Accordingly, we propose that a desired behavior can be selected by tuning these parameters via a judicious design of the particle surface chemistry