Evaporation and deposition of inclined colloidal droplets

Colloidal droplets on flat solid substrates commonly leave symmetric ring-like deposits due to coffee-ring flows during evaporation. On inclined substrates, droplet shapes may become asymmetric by gravity. On this basis, it is not clear how their evaporation dynamics and final deposits are changed depending on inclination. Here we explore evaporation and deposition dynamics of colloidal droplets on inclined substrates, mainly by controlling colloidal particle size, substrate inclination, and relative humidity, which are crucial to gravitational intervention and evaporation dynamics. We experimentally investigate two different flows with opposite directions: downward sedimentation flows by gravity ($$v_s$$ v s ) and upward capillary flows by evaporation ($$v_c$$ v c ). We find that the competition of two flows determines the formation of final deposits with a flow speed ratio of $$\alpha = v_s/v_c$$ α = v s / v c . Notably, for $$\alpha$$ α $$\ll$$ ≪ 1, evaporation-driven upward flows overwhelm sedimentation-driven downward flows, resulting in accentuated particle movement towards the top ring, which seems to defy gravitational intervention. We suggest a possible explanation for the flow speed dependence of final deposits in evaporating colloidal droplets. This study offers a framework to understand the intervention of inclination to the formation of final deposits and how to overcome the deposit pattern radial asymmetry, achieving symmetric deposit widths from inclined colloidal droplets.

Проблемы локации источников акустической эмиссии

The accuracy of the location of acoustic emission (AE) sources in the concentrator zones (central holes 5 mm in diameter) located at a distance of 40 mm from the receiving transducers during tensile tests of steel, aluminum alloy and composite flat specimens with dimensions of 550x50x4 mm was evaluated. Calculated speed dependence of propagation of pulses on the level of their amplitude and the partial energy of the high-frequency components of the spectrum is studied. With the threshold method of signal registration, the error in the location of AE event sources arising in the near zone of the receiving transducers at a distance 𝛥L<0.1 m can significantly exceed 10% relative to the base size (B) of the location area, when B<0.5 m. Moreover, with a decrease in the distance 𝛥L<0.05 m, the level of possible error will increase, reaching 20-30% relative to the basic size of the antenna array, when recording pulses with an amplitude level um<60 dB and a fraction of the energy of high-frequency spectrum components not exceeding 10%.

Shifts in Gait Signatures Mark the End of Lifespan in Mice, With Sex Differences in Timing

Reduced walking speed is a hallmark of functional decline in aging across species. An age-related change in walking style may represent an additional key marker signifying deterioration of the nervous system. Due to the speed dependence of gait metrics combined with slowing of gait during aging, it has been challenging to determine whether changes in gait metrics represent a change in style. In this longitudinal study we employed gait signatures to separate changes in walking style and speed in mice. We compared gait signatures at mature adult age with middle aged, old and geriatric time points and included female and male sub-cohorts to examine sex differences in nature or timing signature shifts. To determine whether gait signature shifts occurred independently from a decline in other mobility domains we measured balance and locomotor activity. We found that walking speed declined early, whereas gait signatures shifted very late during the aging process. Shifts represented longer swing time and stride length than expected for speed, as in slow motion, and were preceded by a decline in other mobility domains. The pattern of shifts was similar between female and male cohorts, but with sex differences in timing. We conclude that changes in walking style, speed and other mobility domains represent separate age-related phenomena. These findings call for careful, sex specific selection of type and timing of outcome measures in mechanistic or interventional studies. The pattern of age-related gait signature shifts is distinct from patterns seen in neurodegenerative conditions and may be a translatable marker for the end of the lifespan.