Eusocial societies and ants, in particular, maintain tight nutritional regulation at both individual and collective levels. The mechanisms that underlie this control are far from trivial since, in ...these distributed systems, information about the global supply and demand is not available to any single individual. Here we present a novel technique for non-intervening frequent measurement of the food load of all individuals in an ant colony, including during trophallactic events in which food is transferred by mouth-to-mouth feeding. Ants are imaged using a dual camera setup that produces both barcode-based identification and fluorescence measurement of labeled food. This system provides detailed measurements that enable one to quantitatively study the adaptive food distribution network. To demonstrate the capabilities of our method, we present sample observations that were unattainable using previous techniques, and could provide insight into the mechanisms underlying food exchange.
Predicting the compactness of the invasion front and the amount of trapped fluid left behind is of crucial importance to applications ranging from microfluidics and fuel cells to subsurface storage ...of carbon and hydrogen. We examine the interplay of wettability, macro‐ and pore scale heterogeneity (pore angularity and pore wall roughness), and its influence on flow patterns formation and trapping efficiency in porous media by a combination of 3D micro‐CT imaging with 2D direct visualization of micromodels. We observe various phase transitions between the following capillary flow regimes (phases): (a) compact advance, (b) wetting and drainage Invasion percolation, (c) Ordinary percolation.
Plain Language Summary
The study of phase transitions in flow patterns that depend on the heterogeneity, wettability, and surface roughness of the pore space and their classification in phase diagrams is one of the challenges in recent multiphase flow physics. We study the dynamics of thick film and corner flows by visualization experiments with micromodels. Both flow types are characteristic of geologically representative porous media (sands, sandstones) and control the displacement and trapping process. The 2D micromodels accurately reproduce the characteristic geometric, morphological, and topological properties of 3D porous media. All microstructures were derived from μ‐CT images. We fabricated identical microstructures by both DRIE‐ICP etching of silicon wafers and anisotropic chemical etching of glass ceramics to vary the degree of surface roughness. The results are in excellent agreement with previous μ‐CT experiments. We observe various phase transitions between the following flow regimes (phases): (a) frontal/compact advance, (b) Ordinary percolation, and (c) Invasion percolation. We show that they can be classified according to Blunt's “heterogeneity versus wettability” phase diagram.
Key Points
Interplay of pore‐scale heterogeneity, wettability, and surface roughness controls displacement patterns and capillary trapping efficiency
The invasion flow pattern for capillary flow were visualized by micro‐CT‐ and micromodel experiments and classified in a new phase diagram
Four generic flow regimes (phases) were observed: frontal advance, wetting and drainage invasion percolation, and ordinary percolation
We study the impact of the wetting properties on the immiscible displacement of a viscous fluid in disordered porous media. We present a novel pore-scale model that captures wettability and dynamic ...effects, including the spatiotemporal nonlocality associated with interface readjustments. Our simulations show that increasing the wettability of the invading fluid (the contact angle) promotes cooperative pore filling that stabilizes the invasion and that this effect is suppressed as the flow rate increases, due to viscous instabilities. We use scaling analysis to derive two dimensionless numbers that predict the mode of displacement. By elucidating the underlying mechanisms, we explain classical yet intriguing experimental observations. These insights could be used to improve technologies such as hydraulic fracturing, CO2 geosequestration, and microfluidics.
Abstract Asteroid collisions are one of the main processes responsible for the evolution of bodies in the main belt. Using observations of the Dimorphos impact by the DART spacecraft, we estimate how ...asteroid collisions in the main belt may look in the first hours after the impact. If the DART event is representative of asteroid collisions with a ∼1 m sized impactor, then the light curves of these collisions will rise on timescales of about ≳100 s and will remain bright for about 1 hr. Next, the light curve will decay on a few hours' timescale to an intermediate luminosity level in which it will remain for several weeks, before slowly returning to its baseline magnitude. This estimate suffers from several uncertainties due to, e.g., the diversity of asteroid composition, their material strength, and spread in collision velocities. We estimate that the rate of collisions in the main belt with energy similar to or larger than the DART impact is of the order of 7000 yr −1 (±1 dex). The large range is due to the uncertainty in the abundance of ∼1 m sized asteroids. We estimate the magnitude distribution of such events in the main belt, and we show that ∼6% of these events may peak at magnitudes brighter than 21. The detection of these events requires a survey with ≲1 hr cadence and may contribute to our understanding of the asteroids’ size distribution, collisional physics, and dust production. With an adequate survey strategy, new survey telescopes may regularly detect asteroid collisions.
We present results on the stretching of single tubular vesicles in an elongation flow toward dumbbell shapes, and on their relaxation. A critical strain rate epsilonc exists; for strain rates ...epsilon<epsilonc, the vesicle remains tubular but fluctuates, though its steady state extension increases with the strain rate epsilon. Above epsilonc, first a shape transition to dumbbell occurs, and then high order shape modes become unstable, leading to a pearling state. We have quantitatively characterized the transition and found a scaling of epsilonc with the system parameters. A remarkable feature of vesicle tube behavior around the critical point is a slowdown of the vesicle relaxation to the final extended state in the vesicle stretching. Such feature is similar to that found in continuous phase transitions and to the critical effects recently observed for polymer molecules near the coil-stretch transition in elongation flow.
We present experimental results on the relaxation dynamics of vesicles subjected to a time-dependent elongation flow. We observed and characterized a new instability, which results in the formation ...of higher-order modes of the vesicle shape (wrinkles), after a switch in the direction of the velocity gradient. This surprising generation of membrane wrinkles can be explained by the appearance of a negative surface tension during the vesicle deflation, which tunes itself to alternating stress. Moreover, the formation of buds in the vesicle membrane was observed in the vicinity of the dynamical transition point.
The role of elastic stress in statistical and scaling properties of elastic turbulence in a polymer solution flow between two disks is discussed. The analogy with a small-scale magnetodynamics and a ...passive scalar turbulent advection in the Batchelor regime is used to explain the experimentally observed statistical properties, the flow structure, and the scaling of elastic turbulence. The emergence of a new length scale, namely, the boundary layer thickness, is observed and studied.
•A pore-scale model is used to simulate drainage in heterogeneous porous media.•Increasing spatial correlation in pore sizes leads to more preferential displacement.•Our microfluidic experiments ...compare favorably with our numerical simulations.
Immiscible fluid displacement in porous media is fundamental for many environmental processes, including infiltration of water in soils, groundwater remediation, enhanced recovery of hydrocarbons and CO2 geosequestration. Microstructural heterogeneity, in particular of particle sizes, can significantly impact immiscible displacement. For instance, it may lead to unstable flow and preferential displacement patterns. We present a systematic, quantitative pore-scale study of the impact of spatial correlations in particle sizes on the drainage of a partially-wetting fluid. We perform pore-network simulations with varying flow rates and different degrees of spatial correlation, complemented with microfluidic experiments. Simulated and experimental displacement patterns show that spatial correlation leads to more preferential invasion, with reduced trapping of the defending fluid, especially at low flow rates. Numerically, we find that increasing the correlation length reduces the fluid-fluid interfacial area and the trapping of the defending fluid, and increases the invasion pattern asymmetry and selectivity. Our experiments, conducted for low capillary numbers, support these findings. Our results delineate the significant effect of spatial correlations on fluid displacement in porous media, of relevance to a wide range of natural and engineered processes.
Understanding how different flow patterns emerge at various macro‐ and pore scale heterogeneity, pore wettability and surface roughness is remains a long standing scientific challenge. Such ...understanding allows to predict the amount of trapped fluid left behind, of crucial importance to applications ranging from microfluidics and fuel cells to subsurface storage of carbon and hydrogen. We examine the interplay of wettability and pore‐scale heterogeneity including both pore angularity and roughness, by a combination of micro‐CT imaging of 3D grain packs with direct visualization of 2D micromodels. The micromodels are designed to retain the key morphological and topological properties derived from the micro‐CT images. Different manufacturing techniques allow us to control pore surface roughness. We study the competition between flow through the pore centers and flow along rough pore walls and corners in media of increasing complexity in the capillary flow regime. The resulting flow patterns and their trapping efficiency are in excellent agreement with previous μ‐CT results. We observe different phase transitions between the following flow regimes (phases): (a) Frontal/compact advance, (b) wetting and drainage Invasion percolation, and (c) Ordinary percolation. We present a heterogeneity‐wettability‐roughness phase diagram that predicts these regimes.
Key Points
The interplay of pore‐scale heterogeneity, wettability, and surface roughness controls displacement patterns and capillary trapping efficiency
The invasion pattern for capillary flow were visualized by micro‐CT‐ and micromodel experiments and classified in a new phase diagram
Four generic flow regimes (phases) were observed: frontal advance, wetting and drainage invasion percolation, and ordinary percolation
Multiphase flows in porous media are important in many natural and industrial processes. Pore-scale models for multiphase flows have seen rapid development in recent years and are becoming ...increasingly useful as predictive tools in both academic and industrial applications. However, quantitative comparisons between different pore-scale models, and between these models and experimental data, are lacking. Here, we perform an objective comparison of a variety of state-of-the-art pore-scale models, including lattice Boltzmann, stochastic rotation dynamics, volume-of-fluid, level-set, phase-field, and pore-network models. As the basis for this comparison, we use a dataset from recent microfluidic experiments with precisely controlled pore geometry and wettability conditions, which offers an unprecedented benchmarking opportunity. We compare the results of the 14 participating teams both qualitatively and quantitatively using several standard metrics, such as fractal dimension, finger width, and displacement efficiency.We find that no single method excels across all conditions and that thin films and corner flow present substantial modeling and computational challenges.
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