This study aims to explore and understand the common belief that COVID infection rate is highly dependent on either the outside temperature and/or the humidity. Thirty-six regions/states from two humid-tropical countries, namely Brazil and Colombia and two countries with temperate climate, France and Italy, are studied over the period of October to December. Daily outside temperature, relative humidity and hospitalization/cases are analyzed using Spearman’s correlation. The eighteen cold regions of France and Italy has seen an average drop in temperature from 10°C to 6°C and 17°C to 7°C, respectively, and France recorded an addition of 2.3 million cases, while Italy recorded an addition of 1.8 million cases. Outside temperature did not fluctuate much in tropical countries, but Brazil and Colombia added 4.17 million and 1.1 million cases, respectively. Köppen–Geiger classification showed the differences in weather pattern between the four countries, and the analysis showed that there is very weak correlation between either outside weather and/or relative humidity alone to the COVID-19 pandemic.

Flow-induced hemolysis remains a concern for blood-contacting devices, and computer-based prediction of hemolysis could facilitate faster and more economical refinement of such devices. While evaluation of convergence of velocity fields obtained by computational fluid dynamics (CFD) simulations has become conventional, convergence of hemolysis calculations is also essential. In this paper, convergence of the power-law hemolysis model is compared for simple flows, including pathlines with exponentially increasing and decreasing stress, in gradually expanding and contracting Couette flows, in a sudden radial expansion and in the FDA channel. In the exponential cases, convergence along a pathline required from one to tens of thousands of timesteps, depending on the exponent. Greater timesteps were required for rapidly increasing (large exponent) stress and for rapidly decreasing (small exponent) stress. Example pathlines in the Couette flows could be fit with exponential curves, and convergence behavior followed the trends identified from the exponential cases. More complex flows, such as in the radial expansion and the FDA channel, increase the likelihood of encountering problematic pathlines. For the exponential cases, comparison of converged hemolysis values with analytical solutions demonstrated that the error of the converged solution may exceed 10% for both rapidly decreasing and rapidly increasing stress.

This paper discusses the design and implementation of a depth control mechanism for an anguilliform swimming robot. Researchers analyzed three different methods of controlling the depth of the robot, including out-of-plane thrust direction, use of foil on the head and buoyancy control at the head and tail. It was determined that buoyancy control at the head and tail was the best method for controlling depth and pitch, given typical forward speeds of the robot. Details are given into the design of this mechanism, including a stress analysis on a critical part, as well as the impacts that these modifications have on the required torque of the drive servos.

We numerically study drop impact on slippery lubricated surfaces at varied impact speeds to comprehend the cloaking of the water drop by the lubricant at. We employ a multi-material and multiphase interface reconstruction method to capture the interaction between the drop and the lubricants of varying interfacial tensions. We demonstrate that cloaking occurs when lubricant-water interfacial tensions are low and impact speeds are low. Our research demonstrates that the thickness of the encapsulating lubricant layer varies over time. At a moderate impact speed, the drop displaces a large amount of lubricant, generating a lubricant-water jet, as we also demonstrate. At high impact speeds, a secondary impingement forms, which displaces a significant amount of lubricant to reveal the underneath substrate that was not visible at lower impact speeds. Finally we investigate the drop impact on lubricant infused micro-wells with varying spacing. We find that small spacing between the micro-well walls can limit lubricant drainage and displacement. The substrates with micro-wells exhibit far less splashing than those without. Furthermore, we demonstrate that micro-wells are better at preserving lubricant than substrates without micro-wells.

We numerically investigate the curvature effect on the self-propelled capability of coalesced drops. The numerical method is based on a well validated multiphase flow solver that solves the three-dimensional Navier–Stokes equations. The liquid–air interface is captured using the moment of fluid method, and a direction splitting method is applied to advect the interface. Afterward, an approximate projection method is used to decouple the calculation of velocity and pressure. Different cases were validated by comparing the experimental results with the simulation results. The coalescence-induced jumping behavior on a flat surface is carefully captured using this numerical method. To investigate the effect of curvature of a curvy substrate on the self-jumping behavior, a case with a single drop impinging on a convex surface and a case with two drops’ coalescence on a fiber are also studied and compared with the experimental results. The asymmetric bouncing of a single drop on the convex surface leads to 40% reduction in contact time, as found in our study. Our study also reveals that due to the curvature of the wedge, the drop forms a lobe shaped region on the symmetric sides of the wedge. The lobed region forces the drop to convert more surface energy into kinetic energy in the upward direction. The jumping capability is improved by increasing the surface curvature. Our study also shows that at lower angles of contact, the drops can easily get attached to the substrate and, at the same time, have difficulty detaching from the substrate.