Predicting the spatio-temporal infection risk in indoor spaces using an efficient airborne transmission model.

We develop a spatially dependent generalization to the Wells-Riley model, which determines the infection risk due to airborne transmission of viruses. We assume that the infectious aerosol concentration is governed by an advection-diffusion-reaction equation with the aerosols advected by airflow, diffused due to turbulence, emitted by infected people, and removed due to ventilation, inactivation of the virus and gravitational settling. We consider one asymptomatic or presymptomatic infectious person breathing or talking, with or without a mask, and model a quasi-three-dimensional set-up that incorporates a recirculating air-conditioning flow. We derive a semi-analytic solution that enables fast simulations and compare our predictions to three real-life case studies-a courtroom, a restaurant, and a hospital ward-demonstrating good agreement. We then generate predictions for the concentration and the infection risk in a classroom, for four different ventilation settings. We quantify the significant reduction in the concentration and the infection risk as ventilation improves, and derive appropriate power laws. The model can be easily updated for different parameter values and can be used to make predictions on the expected time taken to become infected, for any location, emission rate, and ventilation level. The results have direct applicability in mitigating the spread of the COVID-19 pandemic.

Electrostatic wrapping of a microfiber around a curved particle.

The dynamics of the wrapping of a charged flexible microfiber around an oppositely charged curved particle immersed in a viscous fluid is investigated. We observe that the wrapping behavior varies with the radius and Young's modulus of the fiber, the radius of the particle, and the ionic strength of the surrounding solution. We find that wrapping is primarily a function of the favorable interaction energy due to electrostatics and the unfavorable deformation energy needed to conform the fiber to the curvature of the particle. We perform an energy balance to predict the critical particle radius for wrapping, finding reasonably good agreement with experimental observations. In addition, we use mathematical modeling and observations of the deflected shape of the free end of the fiber during wrapping to extract a measurement of the Young's modulus of the fiber. We evaluate the accuracy and potential limitations of this in situ measurement when compared to independent mechanical tests.

Nematohydrodynamics for colloidal self-assembly and transport phenomena.

HYPOTHESIS: Colloidal particles in a nematic liquid crystal (NLC) exhibit very different behaviour to that observed in an isotropic medium. Such differences arise principally due to the nematic-induced elastic stresses exerted due to the interaction of NLC molecules with interfaces, which compete with traditional fluid viscous stresses on the particle. THEORY: A systematic mathematical analysis of particles in an NLC microfluidic channel is performed using the continuum Beris-Edwards framework coupled to the Navier-Stokes equations. We impose strong homeotropic anchoring on the channel walls and weak homeotropic anchoring on the particle surfaces. FINDINGS: The viscous and NLC forces act on an individual particle in opposing directions, resulting in a critical location in the channel where the particle experiences zero net force in the direction perpendicular to the flow. For multi-particle aggregation we show that the final arrangement is independent of the initial configuration, but the path towards achieving equilibrium is very different. These results uncover new mechanisms for particle separation and routes towards self-assembly.

Touch- and Brush-Spinning of Nanofibers.

Robust, simple, and scalable touch- and brush-spinning methods for the drawing of nanofibers, core-shell nanofibers, and their aligned 2D and 3D meshes using polymer solutions and melts are discussed.

Reactive Magnetospinning of Nano- and Microfibers.

Reactive spinning of nano- and microfibers that involves very fast chemical reactions and ion exchange is a challenge for the common methods for nanofiber formation. Herein, we introduce the reactive magnetospinning method. This procedure is based on the magnetic-field-directed collision of ferrofluid droplets with liquid droplets that contain complementary reactants. The collision, start of the chemical reaction, and the fiber drawing are self-synchronized. The method is used to synthesize, cross-link, and chemically modify fiber-forming polymers in the stage of fiber formation. The method provides new opportunities for the fabrication of nanofibers for biomedical applications.

Magnetospinning of Nano- and Microfibers.

Magnetospinning is a new method for spinning of continuous micro- and nano-fibers using a permanent revolving magnet. The method utilizes magnetic forces and the hydrodynamic features of stretched threads to produce highly loaded, fine magnetic nanofibers. The magnetospinning process is independent of the solution dielectric properties and requires no high voltages, in contrast to the more-traditional electrospinning technique.

Microfluidic immunomagnetic multi-target sorting--a model for controlling deflection of paramagnetic beads.

We describe a microfluidic system that uses a magnetic field to sort paramagnetic beads by deflecting them in the direction normal to the flow. In the experiments we systematically study the dependence of the beads' deflection on bead size and susceptibility, magnet strength, fluid speed and viscosity, and device geometry. We also develop a design parameter that can aid in the design of microfluidic devices for immunomagnetic multi-target sorting.