Naturally drying bacterial droplets on inanimate surfaces representing fomites are the most consequential mode for transmitting infection through oro-fecal route. We provide a multiscale holistic approach to understand flow dynamics induced bacterial pattern formation on fomites leading to pathogenesis. The most virulent gut pathogen, Salmonella Typhimurium (STM), typically found in contaminated food and water, is used as model system in the current study. Evaporation-induced flow in sessile droplets facilitates the transport of STM, forming spatio-temporally varying bacterial deposition patterns based on droplet medium’s nutrient scale. Mechanical and low moisture stress in the drying process reduced bacterial viability but interestingly induced hyper-proliferation of STM in macrophages, thereby augmenting virulence in fomites. In vivo studies of fomites in mice confirm that STM maintains enhanced virulence. This work demonstrates that stressed bacterial deposit morphologies formed over small timescale (minutes) on organic and inorganic surfaces, plays a significant role in enhancing fomite’s pathogenesis over hours and days.
We experimentally investigate the dissolution of microscale sessile alcohol droplets in water under the influence of impermeable vertical confinement. The introduction of confinement suppresses the mass transport from the droplet to bulk medium in comparison with the non-confined counterpart. Along with a buoyant plume, flow visualization reveals that the dissolution of a confined droplet is hindered by a newly identified mechanism levitated toroidal vortex. The morphological changes in the flow due to the vortex-induced impediment alters the dissolution rate, resulting in enhancement of droplet lifetime. Further, we have proposed a modification in the key non-dimensional parameters (Rayleigh number Raꞌ (signifying buoyancy) and Sherwood number Shꞌ (signifying mass flux)) and droplet lifetime c , based on the hypothesis of linearly stratified droplet surroundings (with revised concentration difference C
The present article reports the governing influence of substituting the M 2+ site in nanoscale MFe 2 O 4 spinel ferrites by different magnetic metals (Fe/Mn/Co/Ni) on magnetorheological and magneto-elastoviscous behaviors of the corresponding magnetorheological fluids (MRFs). Different doped MFe 2 O 4 nanoparticles have been synthesized using the polyol-assisted hydrothermal method. Detailed steady and oscillatory shear rheology have been performed on the MRFs to determine the magneto-viscoelastic responses The MRFs exhibit shear thinning behavior and augmented yield characteristics under influence of magnetic field. The steady state magnetoviscous behaviors are scaled against the governing Mason number and self-similar response from all the MRFs have been noted. The MRFs conform to an extended Bingham plastic model under field effect. Transient magnetoviscous responses show distinct hysteresis behaviors when the MRFs are exposed to time varying magnetic fields. Oscillatory shear studies using frequency and strain amplitude sweeps exhibit predominant solid like behaviors under field environment. However, the relaxation behaviors and strain amplitude sweep tests of the MRFs reveal that while the fluids show solid-like behaviors under field effect, they cannot be termed as typical elastic fluids. Comparisons show that the MnFe 2 O 4 MRFs have superior yield performance among all. However, in case of dynamic and oscillatory systems, CoFe 2 O 4 MRFs show the best performance. The viscoelastic responses of the MRFs are noted to correspond to a three element viscoelastic model. The study may find importance in design and development strategies of nano-MRFs for different applications. The supplementary material document contains additional information, data, tables and plots of the complex fluid characterization, rheological behavior and additional data on the magnetoelastoviscous response of the fluids.
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