Coupled Dynamics of Droplet Impact on a Flexible, Hydrophilic Cantilever Beam.

We experimentally study the droplet impact on a flexible, hydrophilic cantilever beam. Droplets of water, water-glycerol (1:1 v/v), and glycerol were considered on a copper beam. Side visualization of the droplet impact on the cantilever was carried out by using a high-speed camera.

Effectiveness of N95 Mask in Preventing COVID-19 Transmission.

N95 mask has emerged as a potential measure to mitigate the airborne transmission of respiratory disease such as COVID-19. Herein, we experimentally investigated the impact and interaction of pure water droplets as surrogate to respiratory droplets with the different layers of a commercially available N95 mask to demonstrate the penetration and passage-capability of respiratory fluids through the different layers. The penetration of an impacting droplet through the mask layers was characterized by elucidating the ejection of secondary droplets from the rear-side surface of the target mask material.

Improving Indoor Air Ventilation by a Ceiling Fan to Mitigate Aerosols Transmission.

Improving air flow and ventilation in an indoor environment is central to mitigating the airborne transmission of aerosols. Examples include, COVID-19 or similar diseases that transmit by airborne aerosols or respiratory droplets. While there are standard guidelines for enhancing the ventilation of space, the effect of a ceiling fan on the ventilation has not been explored.

Size-Dependent Dried Colloidal Deposit and Particle Sorting via Saturated Alcohol Vapor-Mediated Sessile Droplet Spreading.

We experimentally and theoretically investigate a distinct problem of spreading, evaporation, and the associated dried deposits of a colloidal particle-laden aqueous sessile droplet on a surface in a saturated alcohol vapor environment. In particular, the effect of particle size on monodispersed suspensions and efficient self-sorting of bidispersed particles have been investigated. The alcohol vapor diffuses toward the droplet's curved liquid-vapor interface from the far field.

Evaluating a transparent coating on a face shield for repelling airborne respiratory droplets.

A face shield is an important personal protective equipment to avoid the airborne transmission of COVID-19. We assess a transparent coating on a face shield that repels airborne respiratory droplets to mitigate the spread of COVID-19. The surface of the available face shield is hydrophilic and exhibits high contact angle hysteresis.

Effect of co-flow on fluid dynamics of a cough jet with implications in spread of COVID-19.

We discuss the temporal evolution of a cough jet of an infected subject in the context of the spread of COVID-19. Computations were carried out using large eddy simulation, and, in particular, the effect of the co-flow (5% and 10% of maximum cough velocity) on the evolution of the jet was quantified. The Reynolds number (Re) of the cough jet, based on the mouth opening diameter () and the average cough velocity, is 13 002.

Colloidal Deposits via Capillary Bridge Evaporation and Particle Sorting Thereof.

Evaporating droplets of colloidal suspensions leave behind particle deposits which could be effectively controlled via manipulating the surrounding conditions and particles and liquid properties. While previous studies extensively focused on sessile and pendant droplets, the present work investigates the evaporation dynamics of capillary bridges of colloidal suspensions formed between two parallel plates. We vary the wettability of the plates and the particle size and composition of the colloidal suspensions, keeping the same spacing between the plates.

How coronavirus survives for hours in aerosols.

COVID (CoronaVirus Disease)-19, caused by severe acute respiratory syndrome-CoronaVirus-2 (SARS-CoV-2) virus, predominantly transmits via airborne route, as highlighted by recent studies. Furthermore, recently published titer measurements of SARS-CoV-2 in aerosols have disclosed that the coronavirus can survive for hours. A consolidated knowledge on the physical mechanism and governing rules behind the significantly long survival of coronavirus in aerosols is lacking, which is the subject of the present investigation.

Designing antiviral surfaces to suppress the spread of COVID-19.

Surface engineering is an emerging technology to design antiviral surfaces, especially in the wake of COVID-19 pandemic. However, there is yet no general understanding of the rules and optimized conditions governing the virucidal properties of engineered surfaces. The understanding is crucial for designing antiviral surfaces.

Probability of COVID-19 infection by cough of a normal person and a super-spreader.

In this work, we estimate the probability of an infected person infecting another person in the vicinity by coughing in the context of COVID-19. The analysis relies on the experimental data of Simha and Rao ["Universal trends in human cough airflows at large distances," Phys. Fluids , 081905 (2020)] and similarity analysis of Agrawal and Bhardwaj ["Reducing chances of COVID-19 infection by a cough cloud in a closed space," Phys.

Why coronavirus survives longer on impermeable than porous surfaces.

Previous studies reported that the drying time of a respiratory droplet on an impermeable surface along with a residual film left on it is correlated with the coronavirus survival time. Notably, earlier virus titer measurements revealed that the survival time is surprisingly less on porous surfaces such as paper and cloth than that on impermeable surfaces. Previous studies could not capture this distinct aspect of the porous media.

Analysis of Second Wave of COVID-19 in Different Countries.

We analyse the evolution of the second wave of the COVID-19 pandemic in several countries by using a logistic model. The model uses a regression analysis based on the least-squares fitting. In particular, the growth rate of the infection has been fitted as an exponential increase, as compared to a power law increase, reported previously in logistic models.

How coronavirus survives for days on surfaces.

Our previous study [R. Bhardwaj and A. Agrawal, "Likelihood of survival of coronavirus in a respiratory droplet deposited on a solid surface," Phys.

Reducing chances of COVID-19 infection by a cough cloud in a closed space.

The cough of a COVID-19 infected subject contaminates a large volume of surrounding air with coronavirus due to the entrainment of surrounding air in the jet-like flow created by the cough. In the present work, we estimate this volume of the air, which may help us to design ventilation of closed spaces and, consequently, reduce the spread of the disease. Recent experiments [P.

Tailoring surface wettability to reduce chances of infection of COVID-19 by a respiratory droplet and to improve the effectiveness of personal protection equipment.

Motivated by the fact that the drying time of respiratory droplets is related to the spread of COVID-19 [R. Bhardwaj and A. Agrawal, "Likelihood of survival of coronavirus in a respiratory droplet deposited on a solid surface," Phys.

Evaporation of Initially Heated Sessile Droplets and the Resultant Dried Colloidal Deposits on Substrates Held at Ambient Temperature.

The present study experimentally and numerically investigates the evaporation and resultant patterns of dried deposits of aqueous colloidal sessile droplets when the droplets are initially elevated to a high temperature before being placed on a substrate held at ambient temperature. The system is then released for natural evaporation without applying any external perturbation. Infrared thermography and optical profilometry are used as essential tools for interfacial temperature measurements and quantification of coffee-ring dimensions, respectively.

Likelihood of survival of coronavirus in a respiratory droplet deposited on a solid surface.

We predict and analyze the drying time of respiratory droplets from a COVID-19 infected subject, which is a crucial time to infect another subject. Drying of the droplet is predicted by using a diffusion-limited evaporation model for a sessile droplet placed on a partially wetted surface with a pinned contact line. The variation in droplet volume, contact angle, ambient temperature, and humidity are considered.

Wetting Dynamics of a Water Droplet on Micropillar Surfaces with Radially Varying Pitches.

The wetting dynamics of a sessile droplet on square micropillar substrates with radially varying pitches, prepared on silicon wafers using a photolithography technique, is investigated experimentally. Two configurations are considered, namely, substrates with radially increasing pitch and radially decreasing pitch. The droplet initially placed at the center experiences a wettability gradient because of the variation in pitch of the micropillar substrate leading to complex wetting dynamics.

Wetting characteristics of Colocasia esculenta (Taro) leaf and a bioinspired surface thereof.

We investigate wetting and water repellency characteristics of Colocasia esculenta (taro) leaf and an engineered surface, bioinspired by the morphology of the surface of the leaf. Scanning electron microscopic images of the leaf surface reveal a two-tier honeycomb-like microstructures, as compared to previously-reported two-tier micropillars on a Nelumbo nucifera (lotus) leaf. We measured static, advancing, and receding angle on the taro leaf and these values are around 10% lesser than those for the lotus leaf.

Microfluidic Valves for Selective on-Chip Droplet Splitting at Multiple Sites.

We describe a microfluidic system for control of droplet division at two locations using a T-junction and expansion channel which are placed one after another. Droplets generated at a standard T-junction are introduced into the droplet division section of the microchannel. In the first set of experiments, the droplet division section consists of two consecutive identical T-junctions branching from the main channel.

A Predictive Model for the Evolution of COVID-19.

We predict the evolution of the COVID-19 pandemic in several countries using a logistic model. The model uses a regression analysis based on the least-squares fitting. In particular, the growth rate of the infection has been fitted as an exponential decay, as compared to a linear decay, reported previously in logistic models.

Motion of a Droplet on an Anisotropic Microgrooved Surface.

We experimentally characterize the sliding angle of water droplets (volume 3.1-22.2 μL) migrating on inclined microgrooved surfaces along the longitudinal and transverse directions of the grooves.

Self-Sorting of Bidispersed Colloidal Particles Near Contact Line of an Evaporating Sessile Droplet.

Here, we investigate deposit patterns and associated morphology formed after the evaporation of an aqueous droplet containing mono- and bidispersed colloidal particles. In particular, the combined effect of substrate heating and particle diameter is investigated. We employ high-speed visualization, optical microscopy, and scanning electron microscopy to characterize the evaporating droplets, particle motion, and deposit morphology, respectively.

Droplet Bouncing and Breakup during Impact on a Microgrooved Surface.

We experimentally investigate the impact dynamics of a microliter water droplet on a hydrophobic microgrooved surface. The surface is fabricated using photolithography, and high-speed visualization is employed to record the time-varying droplet shapes in the transverse and longitudinal directions. The effect of the pitch of the grooved surface and Weber number on the droplet dynamics and impact outcome are studied.

Biomechanical Evaluations of Ocular Injury Risk for Blast Loading.

Ocular trauma is one of the most common types of combat injuries resulting from the exposure of military personnel with improvised explosive devices. The injury mechanism associated with the primary blast wave is poorly understood. We employed a three-dimensional computational model, which included the main internal ocular structures of the eye, spatially varying thickness of the cornea-scleral shell, and nonlinear tissue properties, to calculate the intraocular pressure and stress state of the eye wall and internal ocular structure caused by the blast.