OpenFlume: An accessible and reproducible benchtop flume for research and education.

Open-channel flumes are an important tool in fluid mechanics research and education. However, the few commercially available small-scale flumes are generally expensive and lack complete characterization. In this work, we present an open-source, low-cost, modular benchtop laboratory flume that is designed to be accessible and reproducible.

Interactions and pattern formation in a macroscopic magnetocapillary SALR system of mermaid cereal.

When particles are deposited at a fluid interface they tend to aggregate by capillary attraction to minimize the overall potential energy of the system. In this work, we embed floating millimetric disks with permanent magnets to introduce a competing repulsion effect and study their pattern formation in equilibrium. The pairwise energy landscape of two disks is described by a short-range attraction and long-range repulsion (SALR) interaction potential, previously documented in a number of microscopic condensed matter systems.

SurferBot: a wave-propelled aquatic vibrobot.

Nature has evolved a vast array of strategies for propulsion at the air-fluid interface. Inspired by a survival mechanism initiated by the honeybee () trapped on the surface of water, we here present the: a centimeter-scale vibrating robotic device that self-propels on a fluid surface using analogous hydrodynamic mechanisms as the stricken honeybee. This low-cost and easily assembled device is capable of rectilinear motion thanks to forces arising from a wave-generated, unbalanced momentum flux, achieving speeds on the order of centimeters per second.

Force and torque-free helical tail robot to study low Reynolds number micro-organism swimming.

Helical propulsion is used by many micro-organisms to swim in viscous-dominated environments. Their swimming dynamics are relatively well understood, but a detailed study of the flow fields is still needed to understand wall effects and hydrodynamic interactions among swimmers. In this letter, we describe the development of an autonomous swimming robot with a helical tail that operates in the Stokes regime.

Passive Control of Silane Diffusion for Gradient Application of Surface Properties.

Liquid lithography represents a robust technique for fabricating three-dimensional (3D) microstructures on a two-dimensional template. Silanization of a surface is often a key step in the liquid lithography process and is used to alter the surface energy of the substrate and, consequently, the shape of the 3D microfeatures produced. In this work, we present a passive technique that allows for the generation of silane gradients along the length of a substrate.

Direct Measurement of Capillary Attraction between Floating Disks.

Two bodies resting at a fluid interface may interact laterally due to the surface deformations they induce. Here we use an applied magnetic force to perform direct measurements of the capillary attraction force between centimetric disks floating at an air-water interface. We compare our measurements to numerical simulations that take into account the disk's vertical displacement and spontaneous tilt, showing that both effects are necessary to describe the attraction force for short distances.

A first-principle mechanism for particulate aggregation and self-assembly in stratified fluids.

An extremely broad and important class of phenomena in nature involves the settling and aggregation of matter under gravitation in fluid systems. Here, we observe and model mathematically an unexpected fundamental mechanism by which particles suspended within stratification may self-assemble and form large aggregates without adhesion. This phenomenon arises through a complex interplay involving solute diffusion, impermeable boundaries, and aggregate geometry, which produces toroidal flows.

Optimized commercial desktop cutter technique for rapid-prototyping of microfluidic devices and application to Taylor dispersion.

Microfluidics provides a platform for efficient and transportable microanalysis, catalyzing advancements in fields such as biochemistry, materials science, and microbial ecology. While the analysis is cost-effective, standard device fabrication techniques are disproportionately expensive and specialized. A commercially available desktop cutting plotter provides an accessible method for rapidly fabricating microfluidic devices at extremely low costs.

Friction on water sliders.

A body in motion tends to stay in motion but is often slowed by friction. Here we investigate the friction experienced by centimeter-sized bodies sliding on water. We show that their motion is dominated by skin friction due to the boundary layer that forms in the fluid beneath the body.

Note: A versatile 3D-printed droplet-on-demand generator.

A versatile 3D-printed droplet-on-demand generator is presented for laboratory use in droplet impact and similar experiments. The design described and tested in the present work is modeled off of an existing design [Harris , Exp. Fluids , 83 (2015)] but is tested with an extended range of working fluids, and the manufacturing process is greatly simplified by 3D-printing the principal components.

Bouncing ball on a vibrating periodic surface.

We present an investigation of a partially elastic ball bouncing on a vertically vibrated sinusoidal surface. Following the work of McBennett and Harris [Chaos , 093105 (2016)], we begin by demonstrating that simple periodic vertical bouncing at a local minimum of the surface becomes unstable when the local curvature exceeds a critical value. The resulting instability gives rise to a period doubling cascade and results in persistent horizontal motion of the ball.

The interaction of a walking droplet and a submerged pillar: From scattering to the logarithmic spiral.

Millimetric droplets may walk across the surface of a vibrating fluid bath, propelled forward by their own guiding or "pilot" wave field. We here consider the interaction of such walking droplets with a submerged circular pillar. While simple scattering events are the norm, as the waves become more pronounced, the drop departs the pillar along a path corresponding to a logarithmic spiral.

The Diffusion of Passive Tracers in Laminar Shear Flow.

A simple method to experimentally observe and measure the dispersion of a passive tracer in a laminar fluid flow is described. The method consists of first injecting fluorescent dye directly into a pipe filled with distilled water and allowing it to diffuse across the cross-section of the pipe to obtain a uniformly distributed initial condition. Following this period, the laminar flow is activated with a programmable syringe pump to observe the competition of advection and diffusion of the tracer through the pipe.

Characterization of Tensioned PDMS Membranes for Imaging Cytometry on Microraft Arrays.

Polydimethylsiloxane (PDMS) membranes can act as sensing elements, barriers, and substrates, yet the low rigidity of the elastomeric membranes can limit their practical use in devices. Microraft arrays rely on a freestanding PDMS membrane as a substrate for cell arrays used in imaging cytometry and cellular isolation. However, the underlying PDMS membrane deforms under the weight of the cell media, making automated analytical microscopy (and thus cytometry and cell isolation) challenging.

How boundaries shape chemical delivery in microfluidics.

Many microfluidic systems-including chemical reaction, sample analysis, separation, chemotaxis, and drug development and injection-require control and precision of solute transport. Although concentration levels are easily specified at injection, pressure-driven transport through channels is known to spread the initial distribution, resulting in reduced concentrations downstream. Here we document an unexpected phenomenon: The channel's cross-sectional aspect ratio alone can control the shape of the concentration profile along the channel length.

The onset of chaos in orbital pilot-wave dynamics.

We present the results of a numerical investigation of the emergence of chaos in the orbital dynamics of droplets walking on a vertically vibrating fluid bath and acted upon by one of the three different external forces, specifically, Coriolis, Coulomb, or linear spring forces. As the vibrational forcing of the bath is increased progressively, circular orbits destabilize into wobbling orbits and eventually chaotic trajectories. We demonstrate that the route to chaos depends on the form of the external force.

Horizontal stability of a bouncing ball.

We present an investigation of a partially elastic ball bouncing on a vertically vibrated concave parabolic surface in two dimensions. In particular, we demonstrate that simple vertical motion, wherein the ball bounces periodically at the parabola's vertex, is unstable to horizontal perturbations when the parabolic coefficient defining the surface shape exceeds a critical value. The result is a new periodic solution where the ball bounces laterally over the vertex.

Wavelike statistics from pilot-wave dynamics in a circular corral.

Bouncing droplets can self-propel laterally along the surface of a vibrated fluid bath by virtue of a resonant interaction with their own wave field. The resulting walking droplets exhibit features reminiscent of microscopic quantum particles. Here we present the results of an experimental investigation of droplets walking in a circular corral.

Variation in colorectal cancer screening steps in primary care: basis for practice improvement.

No published research has assessed the specific steps that primary care practices actually take to carry out screening for colorectal cancer (CRC). A written survey was distributed to clinicians and staff at 15 primary care practices to determine whether they perceived that personnel in their practices performed a series of 4 steps associated with screening colonoscopy and 7 steps associated with stool blood test screening. For each discrete step, the percentage of respondents from each practice who indicated that a given step is performed in that practice was calculated along with the mean of practice percentages.

Issues and initiatives in the testing process in primary care physician offices.

Background: Errors occur frequently in management of the testing process in primary care physicians' offices. These errors may result in significant harm to patients and lead to inefficient practice. Important issues are summarized for primary care clinicians and their offices toconsider in improving the management of the testing processes.

Event reporting to a primary care patient safety reporting system: a report from the ASIPS collaborative.

Background: We examined reports to a primary care, ambulatory, patient safety reporting system to describe types of errors reported and differences between anonymous and confidential reports.

Methods: Applied Strategies for Improving Patient Safety (ASIPS) is a demonstration project designed to collect and analyze medical error reports from clinicians and staff in 2 practice-based research networks: the Colorado Research Network (CaReNet) and the High Plains Research Network (HPRN). A major component of ASIPS is a voluntary patient safety reporting system that accepts reports of errors anonymously or confidentially.

Database design to ensure anonymous study of medical errors: a report from the ASIPS Collaborative.

Medical error reporting systems are important information sources for designing strategies to improve the safety of health care. Applied Strategies for Improving Patient Safety (ASIPS) is a multi-institutional, practice-based research project that collects and analyzes data on primary care medical errors and develops interventions to reduce error. The voluntary ASIPS Patient Safety Reporting System captures anonymous and confidential reports of medical errors.