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1
Joshi, M. K., F. Kranzl, A. Schuckert, et al. "Observing emergent hydrodynamics in a long-range quantum magnet." Science 376, no. 6594 (2022): 720–24. http://dx.doi.org/10.1126/science.abk2400.
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Identifying universal properties of nonequilibrium quantum states is a major challenge in modern physics. A fascinating prediction is that classical hydrodynamics emerges universally in the evolution of any interacting quantum system. We experimentally probed the quantum dynamics of 51 individually controlled ions, realizing a long-range interacting spin chain. By measuring space-time–resolved correlation functions in an infinite temperature state, we observed a whole family of hydrodynamic universality classes, ranging from normal diffusion to anomalous superdiffusion, that are described by Lévy flights. We extracted the transport coefficients of the hydrodynamic theory, reflecting the microscopic properties of the system. Our observations demonstrate the potential for engineered quantum systems to provide key insights into universal properties of nonequilibrium states of quantum matter.
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Wang, Yuting, Huilan Zhang, Pingping Yang, and Yunqi Wang. "Experimental Study of Overland Flow through Rigid Emergent Vegetation with Different Densities and Location Arrangements." Water 10, no. 11 (2018): 1638. http://dx.doi.org/10.3390/w10111638.
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The effect of vegetation density on overland flow dynamics has been extensively studied, yet fewer investigations have focused on vegetation arrangements with different densities and position features. Flume experiments were conducted to investigate the hydrodynamics of flow through rigid emergent vegetation arranged in combinations with three densities (Dense, Middle, and Sparse) and three positions (summit, backslope, and footslope). This study focused on how spatial variations regulated hydrodynamic parameters from two dimensions: direction along the slope and water depth. The total hydrodynamic parameters of bare slopes were significantly different from those of vegetated slopes. The relationship between Re and f illustrated that Re was not a unique predictor of hydraulic roughness on vegetated slopes. In the slope direction, all hydrodynamic parameters on vegetated slopes exhibited fluctuating downward/upward trends due to the clocking effect before the vegetated area and the rapid conveyance effect in the vegetated area, whereas constant values were observed on bare slopes. The performance of hydrodynamics parameters suggested that the dense rearward arrangement (SMD) was the optimal vegetation pattern to regulate flow conditions. Specifically, the vertical profiles of the velocity and turbulence features of the SMD arrangement at different sections demonstrated the significant role of vegetation density in identifying the velocity layers along the water depth. The maximum velocity and Reynolds Stress Number (RSN) indicated the position where local scour was most likely to occur, which would improve our basic understanding of the mechanisms underlying hydraulic and soil erosion processes.
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Manna, Raj Kumar, and P. B. Sunil Kumar. "Emergent topological phenomena in active polymeric fluids." Soft Matter 15, no. 3 (2019): 477–86. http://dx.doi.org/10.1039/c8sm01981a.
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Zhang, Bokai, Premkumar Leishangthem, Yang Ding, and Xinliang Xu. "An effective and efficient model of the near-field hydrodynamic interactions for active suspensions of bacteria." Proceedings of the National Academy of Sciences 118, no. 28 (2021): e2100145118. http://dx.doi.org/10.1073/pnas.2100145118.
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Near-field hydrodynamic interactions in active fluids are essential to determine many important emergent behaviors observed, but have not been successfully modeled so far. In this work, we propose an effective model capturing the essence of the near-field hydrodynamic interactions through a tensorial coefficient of resistance, validated numerically by a pedagogic model system consisting of an Escherichia coli bacterium and a passive sphere. In a critical test case that studies the scattering angle of the bacterium–sphere pair dynamics, we prove that the near-field hydrodynamics can make a qualitative difference even for this simple two-body system: Calculations based on the proposed model reveal a region in parameter space where the bacterium is trapped by the passive sphere, a phenomenon that is regularly observed in experiments but cannot be explained by any existing model. In the end, we demonstrate that our model also leads to efficient simulation of active fluids with tens of thousands of bacteria, sufficiently large for investigations of many emergent behaviors.
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Sáenz, Pedro J., Tudor Cristea-Platon, and John W. M. Bush. "A hydrodynamic analog of Friedel oscillations." Science Advances 6, no. 20 (2020): eaay9234. http://dx.doi.org/10.1126/sciadv.aay9234.
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We present a macroscopic analog of an open quantum system, achieved with a classical pilot-wave system. Friedel oscillations are the angstrom-scale statistical signature of an impurity on a metal surface, concentric circular modulations in the probability density function of the surrounding electron sea. We consider a millimetric drop, propelled by its own wave field along the surface of a vibrating liquid bath, interacting with a submerged circular well. An ensemble of drop trajectories displays a statistical signature in the vicinity of the well that is strikingly similar to Friedel oscillations. The droplet trajectories reveal the dynamical roots of the emergent statistics. Our study elucidates a new mechanism for emergent quantum-like statistics in pilot-wave hydrodynamics and so suggests new directions for the nascent field of hydrodynamic quantum analogs.
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LAUGHLIN, R. B. "EMERGENT RELATIVITY." International Journal of Modern Physics A 18, no. 06 (2003): 831–53. http://dx.doi.org/10.1142/s0217751x03014071.
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A possible resolution of the incompatibility of quantum mechanics and general relativity is that the relativity principle is emergent. I show that the central paradox of black holes also occurs at a liquid-vapor critical surface of a bose condensate but is resolved there by the phenomenon of quantum criticality. I propose that real black holes are actually phase boundaries of the vacuum analogous to this, and that the Einstein field equations simply fail at the event horizon the way quantum hydrodynamics fails at a critical surface. This can occur without violating classical general relativity anywhere experimentally accessible to external observers. Since the low-energy effects that occur at critical points are universal, it is possible to make concrete experimental predictions about such surfaces without knowing much, if anything about the true underlying equations. Many of these predictions are different from accepted views about black holes — in particular the absence of Hawking radiation and the possible transparency of cosmological black hole surfaces.
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Maji, Soumen, Prashanth Hanmaiahgari, Ram Balachandar, Jaan Pu, Ana Ricardo, and Rui Ferreira. "A Review on Hydrodynamics of Free Surface Flows in Emergent Vegetated Channels." Water 12, no. 4 (2020): 1218. http://dx.doi.org/10.3390/w12041218.
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This review paper addresses the structure of the mean flow and key turbulence quantities in free-surface flows with emergent vegetation. Emergent vegetation in open channel flow affects turbulence, flow patterns, flow resistance, sediment transport, and morphological changes. The last 15 years have witnessed significant advances in field, laboratory, and numerical investigations of turbulent flows within reaches of different types of emergent vegetation, such as rigid stems, flexible stems, with foliage or without foliage, and combinations of these. The influence of stem diameter, volume fraction, frontal area of stems, staggered and non-staggered arrangements of stems, and arrangement of stems in patches on mean flow and turbulence has been quantified in different research contexts using different instrumentation and numerical strategies. In this paper, a summary of key findings on emergent vegetation flows is offered, with particular emphasis on: (1) vertical structure of flow field, (2) velocity distribution, 2nd order moments, and distribution of turbulent kinetic energy (TKE) in horizontal plane, (3) horizontal structures which includes wake and shear flows and, (4) drag effect of emergent vegetation on the flow. It can be concluded that the drag coefficient of an emergent vegetation patch is proportional to the solid volume fraction and average drag of an individual vegetation stem is a linear function of the stem Reynolds number. The distribution of TKE in a horizontal plane demonstrates that the production of TKE is mostly associated with vortex shedding from individual stems. Production and dissipation of TKE are not in equilibrium, resulting in strong fluxes of TKE directed outward the near wake of each stem. In addition to Kelvin–Helmholtz and von Kármán vortices, the ejections and sweeps have profound influence on sediment dynamics in the emergent vegetated flows.
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Zu, C., F. Machado, B. Ye, et al. "Emergent hydrodynamics in a strongly interacting dipolar spin ensemble." Nature 597, no. 7874 (2021): 45–50. http://dx.doi.org/10.1038/s41586-021-03763-1.
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Suh, In-Saeng, Grant J. Mathews, J. Reese Haywood, and N. Q. Lan. "Analysis of the Conformally Flat Approximation for Binary Neutron Star Initial Conditions." Advances in Astronomy 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/6127031.
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The spatially conformally flat approximation (CFA) is a viable method to deduce initial conditions for the subsequent evolution of binary neutron stars employing the full Einstein equations. Here we analyze the viability of the CFA for the general relativistic hydrodynamic initial conditions of binary neutron stars. We illustrate the stability of the conformally flat condition on the hydrodynamics by numerically evolving ~100 quasicircular orbits. We illustrate the use of this approximation for orbiting neutron stars in the quasicircular orbit approximation to demonstrate the equation of state dependence of these initial conditions and how they might affect the emergent gravitational wave frequency as the stars approach the innermost stable circular orbit.
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Cornacchia, Loreta, Geraldene Wharton, Grieg Davies, et al. "Self-organization of river vegetation leads to emergent buffering of river flows and water levels." Proceedings of the Royal Society B: Biological Sciences 287, no. 1931 (2020): 20201147. http://dx.doi.org/10.1098/rspb.2020.1147.
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Global climate change is expected to impact hydrodynamic conditions in stream ecosystems. There is limited understanding of how stream ecosystems interact and possibly adapt to novel hydrodynamic conditions. Combining mathematical modelling with field data, we demonstrate that bio-physical feedback between plant growth and flow redistribution triggers spatial self-organization of in-channel vegetation that buffers for changed hydrological conditions. The interplay of vegetation growth and hydrodynamics results in a spatial separation of the stream into densely vegetated, low-flow zones divided by unvegetated channels of higher flow velocities. This self-organization process decouples both local flow velocities and water levels from the forcing effect of changing stream discharge. Field data from two lowland, baseflow-dominated streams support model predictions and highlight two important stream-level emergent properties: vegetation controls flow conveyance in fast-flowing channels throughout the annual growth cycle, and this buffering of discharge variations maintains water depths and wetted habitat for the stream community. Our results provide important evidence of how plant-driven self-organization allows stream ecosystems to adapt to changing hydrological conditions, maintaining suitable hydrodynamic conditions to support high biodiversity.
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Maji, Soumen, Debasish Pal, Prashanth R. Hanmaiahgari, and Umesh P. Gupta. "Hydrodynamics and turbulence in emergent and sparsely vegetated open channel flow." Environmental Fluid Mechanics 17, no. 4 (2017): 853–77. http://dx.doi.org/10.1007/s10652-017-9531-2.
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PADMANABHAN, T. "THE HYDRODYNAMICS OF ATOMS OF SPACETIME: GRAVITATIONAL FIELD EQUATION IS NAVIER–STOKES EQUATION." International Journal of Modern Physics D 20, no. 14 (2011): 2817–22. http://dx.doi.org/10.1142/s0218271811020603.
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There is considerable evidence to suggest that field equations of gravity have the same conceptual status as the equations of hydrodynamics or elasticity. We add further support to this paradigm by showing that Einstein"s field equations are identical in form to Navier–Stokes equations of hydrodynamics, when projected on to any null surface. In fact, these equations can be obtained directly by extremizing of entropy associated with the deformations of null surfaces thereby providing a completely thermodynamic route to gravitational field equations. Several curious features of this remarkable connection (including a phenomenon of "dissipation without dissipation") are described and the implications for the emergent paradigm of gravity is highlighted.
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Spencer, Timothy J., Ian Halliday, and Chris M. Care. "A local lattice Boltzmann method for multiple immiscible fluids and dense suspensions of drops." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369, no. 1944 (2011): 2255–63. http://dx.doi.org/10.1098/rsta.2011.0029.
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The lattice Boltzmann method (LBM) for computational fluid dynamics benefits from a simple, explicit, completely local computational algorithm making it highly efficient. We extend LBM to recover hydrodynamics of multi-component immiscible fluids, while retaining a completely local, explicit and simple algorithm. Hence, no computationally expensive lattice gradients, interaction potentials or curvatures, that use information from neighbouring lattice sites, need to be calculated, which makes the method highly scalable and suitable for high performance parallel computing. The method is analytical and is shown to recover correct continuum hydrodynamic equations of motion and interfacial boundary conditions. This LBM may be further extended to situations containing a high number (O(100)) of individually immiscible drops. We make comparisons of the emergent non-Newtonian behaviour with a power-law fluid model. We anticipate our method will have a range applications in engineering, industrial and biological sciences.
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Galbraith, Gemma F., Benjamin J. Cresswell, Mark I. McCormick, Thomas C. Bridge, and Geoffrey P. Jones. "Contrasting hydrodynamic regimes of submerged pinnacle and emergent coral reefs." PLOS ONE 17, no. 8 (2022): e0273092. http://dx.doi.org/10.1371/journal.pone.0273092.
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Hydrodynamics on coral reefs vary with depth, reef morphology and seascape position. Differences in hydrodynamic regimes strongly influence the structure and function of coral reef ecosystems. Submerged coral reefs on steep-sided, conical bathymetric features like seamounts experience enhanced water circulation as a result of interactions between currents and the abrupt physical structure. There may also be similar interactions between smaller pinnacles and regional water currents in offshore locations (crests > 10 m), while shallow reefs (crests <10 m) may be more subject to surface currents driven by wind, waves and tide. Here we tested whether coral pinnacles experienced stronger and more variable currents compared to emergent reefs at the same depth in both nearshore and offshore positions. Current speeds and temperature were monitored for 12 months at 11 reefs, representing the three different reef categories: submerged offshore pinnacles, emergent offshore reefs and emergent nearshore reefs. We found different patterns in current speeds and temperature among reef types throughout the year and between seasons. Submerged pinnacles exhibited stronger, more variable current speeds compared to both near and offshore emergent reefs. We found seasonal changes in current speeds for pinnacle and nearshore reefs but no variation in current strength on offshore reefs. Whilst instantaneous current directions did reflect the seascape position of individual sites, there was no difference in the directional variability of current speeds between reef types. Annual daily average temperatures at all reef types were not strongly seasonal, changing by less than 2 °C throughout the year. Daily temperature ranges at specific sites however, exhibited considerable variability (annual range of up to 6.5 °C), particularly amongst offshore emergent reefs which experienced the highest temperatures despite greater exposure to regional-scale circulation patterns. Additionally, we found a consistent mismatch between satellite sea surface temperatures and in-situ temperature data, which was on average 2 °C cooler throughout the annual study period. Our results suggest that distinct hydrodynamic processes occur on smaller submerged structures that are physically analogous to seamounts. Our findings highlight important nuances in environmental processes that occur on morphologically distinct coral reef habitats and these are likely to be important drivers for the community dynamics of organisms that inhabit these reefs.
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Bastianello, Alvise, Bruno Bertini, Benjamin Doyon, and Romain Vasseur. "Introduction to the Special Issue on Emergent Hydrodynamics in Integrable Many-Body Systems." Journal of Statistical Mechanics: Theory and Experiment 2022, no. 1 (2022): 014001. http://dx.doi.org/10.1088/1742-5468/ac3e6a.
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Sasselov, D. D. "Hydrodynamics and Multi-Level Non-LTE Radiative Transfer in Pulsating Atmospheres: Cepheids." International Astronomical Union Colloquium 134 (1993): 329–30. http://dx.doi.org/10.1017/s025292110001438x.
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The atmospheres of classical Cepheids cannot be represented adequately by a sequence of hydrostatic equilibrium atmospheric models (see Sasselov and Lester 1990 and references therein). Observational evidence for shocks is also available at least since Kraft (1956). Both the disequilibrium and the non-linear phenomena affect the emergent spectra and spectral line profiles of the Cepheids. In the lower amplitude variables the effects may be subtle, yet still lead to significant systematic discrepancies.We have developed the code HERMES for time-dependent treatment of hydrodynamics and non-LTE radiative transfer in the atmospheres of classical Cepheids with periods shorter than 12 days. Our approach is applicable to stars in which the formed shock waves do not dominate the energy balance of the atmosphere. Consecutive detailed calculations are performed for several multi-level model atoms, including H, Ca II, Mg II, He I and II. We use a 1-D explicit conservative upwind monotonic second-order (in time and space) Godunov-type Lagrangian hydrodynamic scheme. Being a characteristics based scheme it allows natural handling of boundary conditions. The scheme is stable and without artificial dissipation, a crucial necessity for physically meaningful radiative transfer solutions (see Roe 1990, Sasselov and Raga 1991 for more details).
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Jiang, Shu, Yutong Hua, Mengxing He, Ying-Tien Lin, and Biyun Sheng. "Effect of a Circular Cylinder on Hydrodynamic Characteristics over a Strongly Curved Channel." Sustainability 15, no. 6 (2023): 4890. http://dx.doi.org/10.3390/su15064890.
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Curved channels are one of the most fundamental units of natural or artificial channels, in which there are different kinds of obstacles; these include vegetation patches, bridge piles, electrical tower foundations, etc., which are all present over a channel bend, and can significantly alter the hydrodynamic characteristics of a channel when compared to a bare bed. In this study, laboratory experiments and numerical simulations were combined to investigate the effect of a circular cylinder on the flow characteristics of a 180-degree U-shaped curved channel. Experimental data, including on water depth and three-dimensional velocity, which was obtained by utilizing acoustic Doppler velocimetry (ADV), were used to calibrate and verify the simulation results of the Reynolds-Averaged Navier–Stokes (RANS) model in the FLOW-3D software. Numerical results show that a larger cylinder diameter leads to an overall greater depth-averaged velocity at the section, a greater shear stress acting on the banks on which the cylinder is placed, and a greater increase in the depth-averaged velocity along the concave bank compared to that along the convex bank. When the diameter of the cylinder placed at the 90° section increases, two weaker circulations with the same direction are found near the water surface; for the submerged one, the two weaker circulations appear at the further downstream section, unlike the emergent one. The degree of variation degree in the shear stress acting on the banks is larger than that of the flowrate. As the flowrate increases or the radius of curvature decreases, the secondary flow intensity correspondingly elevates. However, the curvature radius of the curved channel plays a more important role in the secondary flow intensity than the flowrate does. For both the emergent and submergent cylinders, the large cylinder produces a greater secondary flow strength, but the emergent one has a greater secondary flow strength than the submergent one. In summary, the present study provides valuable knowledge on the hydrodynamics of flow around emergent and submergent structures over a curved channel, which could improve the future design of these structures.
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MacLeod, Morgan, Antonija Oklopčić, Fabienne Nail, and Dion Linssen. "Streams and Bubbles: Tidal Shaping of Hydrodynamic Planetary Outflows." Astrophysical Journal 988, no. 1 (2025): 63. https://doi.org/10.3847/1538-4357/ade0b7.
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Abstract Planets, especially those close to their host stars, lose mass to atmospheric outflows, a process that is thought to shape the bimodal population of gaseous giant and rocky terrestrial exoplanets in close orbits. We model the hydrodynamic escape of planetary atmospheres in idealized, three-dimensional gas dynamic simulations in order to study their emergent morphology. As we vary the simulated system parameters, model outflows show a range of shapes from fast, isotropic outflows bounded by bow shocks to slower motion confined to thin streams. We show that a crucial factor is the role of the tidal gravity and orbiting reference frame in which planets lose mass. Flows can be characterized by the dimensionless Rossby number evaluated at the scale of the Hill sphere. Flows with a low Rossby number are significantly deviated and shaped by the stellar gravity, while those with a high Rossby number are comparatively unaffected. Rossby number alone is sufficient to predict outflow morphology as well as kinematic gradients across transit. Hydrodynamic outflows from the known exoplanet population should span a range of outflow Rossby numbers and therefore exhibit a range of morphologies. In realistic systems, shaping from gravity and hydrodynamics alone can be supplemented by the effects of stellar-wind collisions and magnetic stresses.
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Shi, Zhengrui, and Sheng Jin. "Numerical Investigation of Hydrodynamics in a U-Shaped Open Channel Confluence Flow with Partially Emergent Rigid Vegetation." Water 14, no. 24 (2022): 4027. http://dx.doi.org/10.3390/w14244027.
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The effects of partially emergent rigid vegetation on the hydrodynamics of a curved open-channel confluence flow were simulated using OpenFOAM. The numerical model using the Volume of Fluid method and the RNG k-ε turbulence model in the Reynolds-averaged Navier–Stokes equations was first validated by existing experimental data with good agreement. Then the characteristics of hydrodynamics were analyzed in aspects of separation zone, water level, streamwise velocities, secondary flows, bed shear stress and flow resistance. Some main conclusions can be drawn from the results. Compared to the non-vegetated cases, the separation zones in vegetated cases are smaller in both length and width. With higher vegetation Solid Volume Fraction (SVF), the separation zone is divided into two parts, a smaller one right after the confluence point and a larger one on the second half of the curved reach after the confluence. The main circulation cell shrinks and the circulation near the concave bank moves towards the channel midline. The differences in velocities and bed shear stress between the convex and concave banks become larger with a higher SVF. Under the same SVF, a larger vegetation density has more disturbance on the tributary than a larger stem diameter.
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Horstman, Erik M., Karin R. Bryan, Julia C. Mullarney, and Conrad A. Pilditch. "MODEL VERSUS NATURE: HYDRODYNAMICS IN MANGROVE PNEUMATOPHORES." Coastal Engineering Proceedings, no. 35 (June 23, 2017): 19. http://dx.doi.org/10.9753/icce.v35.management.19.
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Water flows through submerged and emergent vegetation control the transport and deposition of sediment in coastal wetlands. Many past studies into the hydrodynamics of vegetation fields have used idealized vegetation mimics, mostly rigid dowels of uniform height. In this study, a canopy of real mangrove pneumatophores was reconstructed in a flume to quantify flow and turbulence within and above this canopy. At a constant flow forcing, an increase in pneumatophore density, from 71 m-2 to 268 m-2, was found to cause a reduction of the within-canopy flow velocities, whereas the over-canopy flows increased. Within-canopy velocities reduced to 46% and 27% of the free-stream velocities for the lowest and highest pneumatophore densities, respectively, resulting in stronger vertical shear and hence greater turbulence production around the top of the denser pneumatophore canopies. The maximum Reynolds stress was observed at 1.5 times the average pneumatophore height, in contrast to uniform-height canopies, in which the maximum occurs at approximately the height of the vegetation. The ratios of the within-canopy velocity to the free-stream velocity for the pneumatophores were found to be similar to previous observations with uniform-height vegetation mimics for the same vegetation densities. However, maxima of the scaled friction velocity were two times smaller over the real pneumatophore canopies than for idealized dowel canopies, due to the reduced velocity gradients over the variable-height pneumatophores compared to uniform-height dowels. These findings imply that results from previous studies with idealized and uniform vegetation mimics may have limited application when considering sediment transport and deposition in real vegetation, as the observed turbulence characteristics in non-uniform canopies deviate significantly from those in dowel canopies.
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Oriti, Daniele, and Xiankai Pang. "Phantom-like dark energy from quantum gravity." Journal of Cosmology and Astroparticle Physics 2021, no. 12 (2021): 040. http://dx.doi.org/10.1088/1475-7516/2021/12/040.
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Abstract We analyse the emergent cosmological dynamics corresponding to the mean field hydrodynamics of quantum gravity condensates, in the group field theory formalism. We focus in particular on the cosmological effects of fundamental interactions, and on the contributions from different quantum geometric modes. The general consequence of such interactions is to produce an accelerated expansion of the universe, which can happen both at early times, after the quantum bounce predicted by the model, and at late times. Our main result is that, while this fails to give a compelling inflationary scenario in the early universe, it produces naturally a phantom-like dark energy dynamics at late times, compatible with cosmological observations. By recasting the emergent cosmological dynamics in terms of an effective equation of state, we show that it can generically cross the phantom divide, purely out of quantum gravity effects without the need of any additional phantom matter. Furthermore, we show that the dynamics avoids any Big Rip singularity, approaching instead a de Sitter universe asymptotically.
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Ratliff, Daniel J., and Thomas J. Bridges. "Multiphase wavetrains, singular wave interactions and the emergence of the Korteweg–de Vries equation." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 472, no. 2196 (2016): 20160456. http://dx.doi.org/10.1098/rspa.2016.0456.
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Multiphase wavetrains are multiperiodic travelling waves with a set of distinct wavenumbers and distinct frequencies. In conservative systems, such families are associated with the conservation of wave action or other conservation law. At generic points (where the Jacobian of the wave action flux is non-degenerate), modulation of the wavetrain leads to the dispersionless multiphase conservation of wave action. The main result of this paper is that modulation of the multiphase wavetrain, when the Jacobian of the wave action flux vector is singular, morphs the vector-valued conservation law into the scalar Korteweg–de Vries (KdV) equation. The coefficients in the emergent KdV equation have a geometrical interpretation in terms of projection of the vector components of the conservation law. The theory herein is restricted to two phases to simplify presentation, with extensions to any finite dimension discussed in the concluding remarks. Two applications of the theory are presented: a coupled nonlinear Schrödinger equation and two-layer shallow-water hydrodynamics with a free surface. Both have two-phase solutions where criticality and the properties of the emergent KdV equation can be determined analytically.
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Jercher, Alexander F., Daniele Oriti, and Andreas G. A. Pithis. "Emergent cosmology from quantum gravity in the Lorentzian Barrett-Crane tensorial group field theory model." Journal of Cosmology and Astroparticle Physics 2022, no. 01 (2022): 050. http://dx.doi.org/10.1088/1475-7516/2022/01/050.
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Abstract We study the cosmological sector of the Lorentzian Barrett-Crane (BC) model coupled to a free massless scalar field in its Group Field Theory (GFT) formulation, corresponding to the mean-field hydrodynamics obtained from coherent condensate states. The relational evolution of the condensate with respect to the scalar field yields effective dynamics of homogeneous and isotropic cosmologies, similar to those previously obtained in SU(2)-based EPRL-like models. Also in this manifestly Lorentzian setting, in which only continuous SL(2,ℂ)-representations are used, we obtain generalized Friedmann equations that generically exhibit a quantum bounce, and can reproduce all of the features of the cosmological dynamics of EPRL-like models. This lends support to the expectation that the EPRL-like and BC models may lie in the same continuum universality class, and that the quantum gravity mechanism producing effective bouncing scenarios may not depend directly on the discretization of geometric observables.
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Ahmad, Muhammad, Usman Ghani, Naveed Anjum, Ghufran Ahmed Pasha, Muhammad Kaleem Ullah, and Afzal Ahmed. "Investigating the Flow Hydrodynamics in a Compound Channel with Layered Vegetated Floodplains." Civil Engineering Journal 6, no. 5 (2020): 860–76. http://dx.doi.org/10.28991/cej-2020-03091513.
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In natural rivers, vegetation grows on floodplains, generating complex velocity field within the compound channel. The efficient modelling of the flow hydraulics in a compound channel with vegetated floodplains is necessary to understand and determine the natural processes in rivers and streams. As the three dimensional (3D) flow features are difficult to capture through experimental investigation; therefore, the present numerical study was carried out to investigate the complex 3D flow structures with the vertically layered vegetation placed over the floodplains in a symmetric trapezoidal compound channel. The simulations were conducted using a Computational Fluid Dynamics (CFD) code FLUENT, whereas a Reynolds Averaged Navier-Stokes (RANS) technique based on Reynolds stress model (RSM) was implemented for turbulence closure. The numerical model successfully replicated the flow behavior and showed a good agreement with the experimental data. The present study concluded the presence of quite-S shaped velocity profile in the layered vegetated floodplains when the short vegetation was submerged during high flows or floods, whereas the velocity profile was uniform or almost logarithmic during low floods or when both short and tall vegetation remained emergent. The lateral exchange of mass and momentum was promoted due to the flow separation and instability along the junction of the floodplains and main channel. The flow velocities were significantly reduced in the floodplains due to resistance offered by the vegetation, which consequently resulted in an increased percentage i.e. 67-73%, of passing discharge through the main channel. In general, the spatial distribution of mean flow and turbulence characteristics was considerably affected near the floodplain and main channel interfaces. Moreover, this study indicated a positive flow response for the sediment deposition as well as for the nourishment of the aquatic organisms in the riparian environment.
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Liu, Bangquan, Zhen Liu, Dechao Sun, and Chunyue Bi. "An Evacuation Route Model of Crowd Based on Emotion and Geodesic." Mathematical Problems in Engineering 2018 (October 1, 2018): 1–10. http://dx.doi.org/10.1155/2018/5397071.
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Making unconventional emergent plan for dense crowd is one of the critical issues of evacuation simulations. In order to make the behavior of crowd more believable, we present a real-time evacuation route approach based on emotion and geodesic under the influence of individual emotion and multi-hazard circumstances. The proposed emotion model can reflect the dynamic process of individual in group on three factors: individual emotion, perilous field, and crowd emotion. Specifically, we first convert the evacuation scene to Delaunay triangulation representations. Then, we use the optimization-driven geodesic approach to calculate the best evacuation path with user-specified geometric constraints, such as crowd density, obstacle information, and perilous field. Finally, the Smooth Particle Hydrodynamics method is used for local avoidance of collisions with nearby agents in real-time simulation. Extensive experimental results show that our algorithm is efficient and well suited for real-time simulations of crowd evacuation.
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Kumar, Rakesh, Prabhakar Sharma, Anurag Verma, et al. "Effect of Physical Characteristics and Hydrodynamic Conditions on Transport and Deposition of Microplastics in Riverine Ecosystem." Water 13, no. 19 (2021): 2710. http://dx.doi.org/10.3390/w13192710.
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Microplastic disposal into riverine ecosystems is an emergent ecological hazard that mainly originated from land-based sources. This paper presents a comprehensive review on physical processes involved in microplastics transport in riverine ecosystems. Microplastic transport is governed by physical characteristics (e.g., plastic particle density, shape, and size) and hydrodynamics (e.g., laminar and turbulent flow conditions). High-density microplastics are likely to prevail near riverbeds, whereas low-density particles float over river surfaces. Microplastic transport occurs either due to gravity-driven (vertical transport) or settling (horizontal transport) in river ecosystems. Microplastics are subjected to various natural phenomena such as suspension, deposition, detachment, resuspension, and translocation during transport processes. Limited information is available on settling and rising velocities for various polymeric plastic particles. Therefore, this paper highlights how appropriately empirical transport models explain vertical and horizontal distribution of microplastic in riverine ecosystems. Microplastics interact, and thus feedback loops within the environment govern their fate, particularly as these ecosystems are under increasing biodiversity loss and climate change threat. This review provides outlines for fate and transport of microplastics in riverine ecosystems, which will help scientists, policymakers, and stakeholders in better monitoring and mitigating microplastics pollution.
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Liu, Mengyang, Zhonghua Yang, Bin Ji, Wenxin Huai, and Hongwu Tang. "Flow dynamics in lateral vegetation cavities constructed by an array of emergent vegetation patches along the open-channel bank." Physics of Fluids 34, no. 3 (2022): 035122. http://dx.doi.org/10.1063/5.0084287.
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The hydrodynamics in a straight rectangular open channel containing novel lateral cavities constructed by an array of square emergent vegetation patches discontinuously distributed along the bank were explored numerically using three-dimensional large eddy simulations (LES). Five vegetation densities (Φ), ranging from 0.02 to 0.25, as well as the traditional lateral cavities created by impermeable solid media, were tested. The effects of the cavity aspect ratio (AR) were also examined. The LES results showed that the mean recirculation pattern inside the vegetation cavities and coherent structures in the horizontal shear layer were closely dependent on Φ and AR. When Φ ≥ 0.06, a main recirculation vortex that formed inside the vegetation cavities resembled that within solid media cavities, whereas the extent of the former increased upstream as Φ increased. Compared with the solid cases, the vegetation cavities exhibited a higher turbulent intensity within the shear layer and wider regions of enhanced turbulent kinetic energy, which decreased with increasing Φ. The penetration depth of the elevated turbulent kinetic energy into the cavities also decreased with increasing Φ, whereas a deeper penetration was expected at larger AR values. The interfacial turbulence was dominated by “cavities field”-scale coherent vortices at Φ ≤ 0.06, whereas “cavity element”-scale at Φ ≥ 0.15. When Φ = 0.1, the shear vortices of both scales contributed to the enhancement of the interfacial turbulence. The mean mass exchange showed a non-monotonic relationship with Φ and reached maximum values at Φ = 1. The total momentum transport efficiency decreased monotonically with increasing Φ. Despite the AR and Φ values, the turbulent motions dominated the momentum transport over most of the cavity length.
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ZHAO, XIANGGUI, ROY R. GU, CHULING GUO, KUI WANG, and SHIJIE LI. "SIMULATIONS OF FLOW CIRCULATIONS AND ATRAZINE CONCENTRATIONS IN A MIDWEST U.S. RESERVOIR." International Journal of Modern Physics: Conference Series 19 (January 2012): 27–38. http://dx.doi.org/10.1142/s2010194512008562.
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Atrazine is the most commonly used herbicide in the spring for pre-emergent weed control in the corn cropping area in the Midwestern United States. A frequent high level of herbicide concentrations in reservoirs is a great concern for public health and aquatic ecosystems. In this study, a two-dimensional hydrodynamics and toxic contaminant transport model was applied to Saylorville Reservoir, Iowa, USA. The model simulates physical, chemical, and biological processes and predicts unsteady vertical and longitudinal distributions of a toxic chemical. Model results were validated by measured temperatures and atrazine concentrations. Simulated flow velocities, water temperatures, and chemical concentrations demonstrated that the spatial variation of atrazine concentrations was largely affected by seasonal flow circulation patterns in the reservoir. In particular, the simulated fate and transport of atrazine showed the effect of flow circulation on spatial distribution of atrazine during summer months as the river flow formed an underflow within the reservoir and resulted in greater concentrations near the surface of the reservoir. Atrazine concentrations in the reservoir peaked around the end of May and early June. A thorough understanding of the fate and transport of atrazine in the reservoir can assist in developing operation and pollution prevention strategies with respect to timing, amount, and depth of withdrawal. The responses of atrazine transport to various boundary conditions provide useful information in assessing environmental impact of alternative upstream watershed management practices on the quality of reservoir water.
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Tsang, Boyce, Zachary E. Dell, Lingxiang Jiang, Kenneth S. Schweizer, and Steve Granick. "Dynamic cross-correlations between entangled biofilaments as they diffuse." Proceedings of the National Academy of Sciences 114, no. 13 (2017): 3322–27. http://dx.doi.org/10.1073/pnas.1620935114.
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Entanglement in polymer and biological physics involves a state in which linear interthreaded macromolecules in isotropic liquids diffuse in a spatially anisotropic manner beyond a characteristic mesoscopic time and length scale (tube diameter). The physical reason is that linear macromolecules become transiently localized in directions transverse to their backbone but diffuse with relative ease parallel to it. Within the resulting broad spectrum of relaxation times there is an extended period before the longest relaxation time when filaments occupy a time-averaged cylindrical space of near-constant density. Here we show its implication with experiments based on fluorescence tracking of dilutely labeled macromolecules. The entangled pairs of aqueous F-actin biofilaments diffuse with separation-dependent dynamic cross-correlations that exceed those expected from continuum hydrodynamics up to strikingly large spatial distances of ≈15 µm, which is more than 104 times the size of the solvent water molecules in which they are dissolved, and is more than 50 times the dynamic tube diameter, but is almost equal to the filament length. Modeling this entangled system as a collection of rigid rods, we present a statistical mechanical theory that predicts these long-range dynamic correlations as an emergent consequence of an effective long-range interpolymer repulsion due to the de Gennes correlation hole, which is a combined consequence of chain connectivity and uncrossability. The key physical assumption needed to make theory and experiment agree is that solutions of entangled biofilaments localized in tubes that are effectively dynamically incompressible over the relevant intermediate time and length scales.
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Occhipinti-Ambrogi, Anna, and Bella Galil. "Marine alien species as an aspect of global change." Advances in Oceanography and Limnology 1, no. 1 (2010): 199. http://dx.doi.org/10.4081/aiol.2010.5300.
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The transport of organisms across oceans is an anthropogenic agent of global change that has profoundly affected the natural distribution of littoral biota and altered the makeup of biogeographic regions. The homogenization of marine biotas is a phenomenon especially affecting coastal regions and is spearheaded by a suite of opportunistic species at the expense of native species. Climate change may exacerbate the trend: sea surface temperatures, hydrodynamics, pH and carbonate cycles, already show marked fluctuations compared to the past. Alien invasive species are impacted by the change of marine climate in a variety of ways, which are we have just begun to notice, observe and interpret. A conceptual framework has yet to be conceived that links theories on biological introductions and invasions with the physical aspects of global change. Therefore predicting the scale of invasions or their impact on biodiversity is a daunting task. Integration of biological and environmental information systems, niche models, and climate projections would improve management of aquatic ecosystems under the dual threats of biotic invasions and climate change. The recorded spread of alien species and analysis of patterns of invasions may serve as the starting point for searching connections with climate change descriptors. The Mediterranean Sea is home to an exceptionally large number of alien species, resulting from its exceptional history and multiple vectors. For much of the twentieth century alien thermophilic species, which had entered the Mediterranean through the Suez Canal, have been confined to the Levantine Basin. In recent years climate driven hydrographic changes have coincided with a pronounced expansion of alien thermophilic biota to the central and western basins of the Mediterranean. We discuss some changes in emergent functions and services in Mediterranean ecosystems under the combined effect of invasive species and climate changes.
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Granet, Etienne. "Wavelet representation of hardcore bosons." Journal of Statistical Mechanics: Theory and Experiment 2023, no. 12 (2023): 123102. http://dx.doi.org/10.1088/1742-5468/ad082c.
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Abstract We consider the one-dimensional Tonks–Girardeau gas with a space-dependent potential out of equilibrium. We derive the exact dynamics of the system when divided into n boxes and decomposed into energy eigenstates within each box. It is a representation of the wave function that is a mixture between real space and momentum space, with basis elements consisting of plane waves localized in a box, giving rise to the term ‘wavelet’. Using this representation, we derive the emergence of generalized hydrodynamics in appropriate limits without assuming local relaxation. We emphasize that a generalized hydrodynamic behaviour emerges in a high-momentum and short-time limit, in addition to the more common large-space and late-time limit, which is akin to a semi-classical expansion. In this limit, conserved charges do not require numerous particles to be described by generalized hydrodynamics. We also show that this wavelet representation provides an efficient numerical algorithm for a complete description of the out-of-equilibrium dynamics of hardcore bosons.
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Sáenz, Pedro J., Giuseppe Pucci, Sam E. Turton, et al. "Emergent order in hydrodynamic spin lattices." Nature 596, no. 7870 (2021): 58–62. http://dx.doi.org/10.1038/s41586-021-03682-1.
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Martinez-Pedrero, Fernando, Eloy Navarro-Argemí, Antonio Ortiz-Ambriz, Ignacio Pagonabarraga, and Pietro Tierno. "Emergent hydrodynamic bound states between magnetically powered micropropellers." Science Advances 4, no. 1 (2018): eaap9379. http://dx.doi.org/10.1126/sciadv.aap9379.
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Klein, Richard I., and Jonathan Arons. "Radiation Gas Dynamics of Polar Cap Accretion onto Magnetized Neutron Stars." Symposium - International Astronomical Union 125 (1987): 246. http://dx.doi.org/10.1017/s0074180900160826.
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We present results of the first self-consistent, time-dependent, 2-D calculations of the accretion of plasma onto polar caps of high luminosity (L*>1036erg-s−1) magnetized neutron stars. We follow the temporal and spatial evolution of three fluids, electrons, ions and photons in a superstrong (B=3×1012 Gauss) dipole magnetic field where radiation pressure dominates plasma pressure by solving coupled 2-D equations of radiation hydrodynamics. We have included several physical processes in the radiation-plasma coupling in superstrong magnetic fields (Klein, et al., 1984, Santa Cruz Workshop on High Energy Transients, and Arons, this conference). We solve the resulting system of coupled 2-D PDEs on a Cray XMP-48 by applying implicit finite-difference techniques with iterative operator splitting methods. We present results for two models of 5×1037 erg-s and 1.5×1038 erg-s−1 super-Eddington luminosity on one polar cap, each having initial mass flux independent of co-latitude of a field lines footprint. We find (a) Radiation develops a broad transverse fan beam that emerges from an annulus 0.2–0.5km above the polar cap. (b) The beam profile is determined by advective trapping of radiation in optically thick (τ11,τ⊥ ≈103) flow. Here the time for diffusion of radiation up through the accretion column is ≫ the time for downward advection. (c) There is a three fluid nonequilibrium with Ti≫Tγ≥Te. (d) Maximum photon temperature of ≈ 10–20 keV in the fan beam is in the observed range. (e) Cyclotron emission ≫ bremsstrahlung as a source of photons. (f) At early times (≪lms) radiation pressure strongly decelerates flow to 10−3 of freefall in central regions of accretion column resulting in a density mound, but plasma freefalls down the sides of the column. (g) Analytical models have reasonable agreement with numerical calculations; velocity and energy density roughly Gaussian transversally and exponential vertically, until the onset of “photon bubbles” after several dynamical times (∼lms). (h) Multiple “photon bubbles” rising subsonically in the accretion column form in the high luminosity model. We believe the photon bubbles to be a possible consequence of overstable convection in super-Eddington flows. These photon bubbles could be observable as 10–100μs fluctuations in the emergent flux and, thus, be an important diagnostic for inhomogeneous structure of the column.
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Parmigiani, Andrea, Paolo Roberto Di Palma, Sébastien Leclaire, Faraz Habib, and Xiang-Zhao Kong. "Characterization of Transport-Enhanced Phase Separation in Porous Media Using a Lattice-Boltzmann Method." Geofluids 2019 (May 14, 2019): 1–13. http://dx.doi.org/10.1155/2019/5176410.
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Phase separation of formation fluids in the subsurface introduces hydrodynamic perturbations which are critical for mass and energy transport of geofluids. Here, we present pore-scale lattice-Boltzmann simulations to investigate the hydrodynamical response of a porous system to the emergence of non-wetting droplets under background hydraulic gradients. A wide parameter space of capillary number and fluid saturation is explored to characterize the droplet evolution, the droplet size and shape distribution, and the capillary-clogging patterns. We find that clogging is favored by high capillary stress; nonetheless, clogging occurs at high non-wetting saturation (larger than 0.3), denoting the importance of convective transport on droplet growth and permeability. Moreover, droplets are more sheared at low capillary number; however, solid matrix plays a key role on droplet’s volume-to-surface ratio.
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Blaizot, J. P. "Emergence of Hydrodynamics in Expanding Relativistic Plasmas." Acta Physica Polonica B Proceedings Supplement 16, no. 8 (2023): 1. http://dx.doi.org/10.5506/aphyspolbsupp.16.8-a7.
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Thijssen, Kristian, Luuk Metselaar, Julia M. Yeomans, and Amin Doostmohammadi. "Active nematics with anisotropic friction: the decisive role of the flow aligning parameter." Soft Matter 16, no. 8 (2020): 2065–74. http://dx.doi.org/10.1039/c9sm01963d.
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Doyon, Benjamin. "Hydrodynamic Projections and the Emergence of Linearised Euler Equations in One-Dimensional Isolated Systems." Communications in Mathematical Physics 391, no. 1 (2022): 293–356. http://dx.doi.org/10.1007/s00220-022-04310-3.
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AbstractOne of the most profound questions of mathematical physics is that of establishing from first principles the hydrodynamic equations in large, isolated, strongly interacting many-body systems. This involves understanding relaxation at long times under reversible dynamics, determining the space of emergent collective degrees of freedom (the ballistic waves), showing that projection occurs onto them, and establishing their dynamics (the hydrodynamic equations). We make progress in these directions, focussing for simplicity on one-dimensional systems. Under a model-independent definition of the complete space of extensive conserved charges, we show that hydrodynamic projection occurs in Euler-scale two-point correlation functions. A fundamental ingredient is a property of relaxation: we establish ergodicity of correlation functions along almost every direction in space and time. We further show that to every extensive conserved charge with a local density is associated a local current and a continuity equation; and that Euler-scale two-point correlation functions of local conserved densities satisfy a hydrodynamic equation. The results are established rigorously within a general framework based on Hilbert spaces of observables. These spaces occur naturally in the $$C^*$$ C ∗ algebra description of statistical mechanics by the Gelfand–Naimark–Segal construction. Using Araki’s exponential clustering and the Lieb–Robinson bound, we show that the results hold, for instance, in every nonzero-temperature Gibbs state of short-range quantum spin chains. Many techniques we introduce are generalisable to higher dimensions. This provides a precise and universal theory for the emergence of ballistic waves at the Euler scale and how they propagate within homogeneous, stationary states.
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Davison, Richard, and Luca V. Delacrétaz. "Universal thermalization dynamics in (1+1)d QFTs." SciPost Physics 18, no. 6 (2025). https://doi.org/10.21468/scipostphys.18.6.177.
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We identify the universal mechanism behind the thermalization of (1+1)d QFTs at high and low temperatures. Viewing these theories as CFTs perturbed by relevant or irrelevant deformations, we show that conformal perturbation theory in the thermal state breaks down at late times allowing for the emergence of hydrodynamics. This breakdown occurs universally due to the unsuppressed exchange of stress tensors near the lightcone. Furthermore, for theories with central charge c→∞c→∞ we solve for the emergent hydrodynamic theory to all orders in the gradient expansion by arguing that all transport parameters appearing in two-point functions have universal expressions in terms of the scaling dimension \DeltaΔ of the perturbation. The radius of convergence of the hydrodynamic dispersion relations provides an early time cutoff for hydrodynamics, which agrees with the time scale at which conformal perturbation theory breaks down.
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Zantop, Arne Wolf, and Holger Stark. "Emergent collective dynamics of pusher and puller squirmer rods: Swarming, clustering and turbulence." Soft Matter, 2022. http://dx.doi.org/10.1039/d2sm00449f.
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We study the interplay of steric and hydrodynamic interactions in suspensions of elongated microswimmers by simulating the full hydrodynamics of squirmer rods in the quasi two-dimensional geometry of a Hele-Shaw...
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De Nardis, Jacopo, та Benjamin Doyon. "Hydrodynamic gauge fixing and higher order hydrodynamic expansion". Journal of Physics A: Mathematical and Theoretical, 28 квітня 2023. http://dx.doi.org/10.1088/1751-8121/acd153.
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Abstract Hydrodynamics is a powerful emergent theory for the large-scale behaviours in many-body systems, quantum or classical. It is a gradient series expansion, where different orders of spatial derivatives provide an &#xD;effective description on different length scales. We report the first fully general derivation of third-order, or ``dispersive", terms in the hydrodynamic expansion. Our derivation is based on general principles of statistical mechanics, along with the assumption that the complete set of local and quasi-local conserved densities constitutes a good set of emergent degrees of freedom. We obtain fully general Kubo-like expressions for the associated hydrodynamic coefficients (also known as Burnett coefficients), and we determine their exact form in quantum integrable models, introducing in this way purely quantum higher-order terms into generalised hydrodynamics. We emphasise the importance of hydrodynamic gauge fixing at diffusive order, where we claim that it is parity-time-reversal, and not time-reversal, invariance that is at the source of Einstein's relation, Onsager's reciprocal relations, the Kubo formula and entropy production. At higher hydrodynamic orders we introduce a more general, $n$-th order ``symmetric'' gauge, which we show implies the validity of the higher-order hydrodynamic description.
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Delacrétaz, Luca, Diego Hofman, and Grégoire Mathys. "Superfluids as higher-form anomalies." SciPost Physics 8, no. 3 (2020). http://dx.doi.org/10.21468/scipostphys.8.3.047.
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We recast superfluid hydrodynamics as the hydrodynamic theory of a system with an emergent anomalous higher-form symmetry. The higher-form charge counts the winding planes of the superfluid - its constitutive relation replaces the Josephson relation of conventional superfluid hydrodynamics. This formulation puts all hydrodynamic equations on equal footing. The anomalous Ward identity can be used as an alternative starting point to prove the existence of a Goldstone boson, without reference to spontaneous symmetry breaking. This provides an alternative characterization of Landau phase transitions in terms of higher-form symmetries and their anomalies instead of how the symmetries are realized. This treatment is more general and, in particular, includes the case of BKT transitions. As an application of this formalism we construct the hydrodynamic theories of conventional (0-form) and 1-form superfluids.
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Dash, Ashutosh, and Amaresh Jaiswal. "Metric anisotropies and emergent anisotropic hydrodynamics." Physical Review D 97, no. 10 (2018). http://dx.doi.org/10.1103/physrevd.97.104005.
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Ye, Bingtian, Francisco Machado, Christopher David White, Roger S. K. Mong, and Norman Y. Yao. "Emergent Hydrodynamics in Nonequilibrium Quantum Systems." Physical Review Letters 125, no. 3 (2020). http://dx.doi.org/10.1103/physrevlett.125.030601.
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Wienand, Julian F., Simon Karch, Alexander Impertro, et al. "Emergence of fluctuating hydrodynamics in chaotic quantum systems." Nature Physics, August 12, 2024. http://dx.doi.org/10.1038/s41567-024-02611-z.
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AbstractA fundamental principle of chaotic quantum dynamics is that local subsystems eventually approach a thermal equilibrium state. The corresponding timescales increase with subsystem size as equilibration is limited by the hydrodynamic build-up of fluctuations on extended length scales. We perform large-scale quantum simulations that monitor particle-number fluctuations in tunable ladders of hard-core bosons and explore how the build-up of fluctuations changes as the system crosses over from integrable to fully chaotic dynamics. Our results indicate that the growth of large-scale fluctuations in chaotic, far-from-equilibrium systems is quantitatively determined by equilibrium transport coefficients, in agreement with the predictions of fluctuating hydrodynamics. This emergent hydrodynamic behaviour of subsystem fluctuations provides a test of fluctuation–dissipation relations far from equilibrium and allows the accurate determination of equilibrium transport coefficients using far-from-equilibrium quantum dynamics.
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Wu, Ning, Matteo Baggioli, and Wei-Jia Li. "On the universality of AdS2 diffusion bounds and the breakdown of linearized hydrodynamics." Journal of High Energy Physics 2021, no. 5 (2021). http://dx.doi.org/10.1007/jhep05(2021)014.
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Abstract The chase of universal bounds on diffusivities in strongly coupled systems and holographic models has a long track record. The identification of a universal velocity scale, independent of the presence of well-defined quasiparticle excitations, is one of the major challenges of this program. A recent analysis, valid for emergent IR fixed points exhibiting local quantum criticality, and dual to IR AdS2 geometries, suggests to identify such a velocity using the time and length scales at which hydrodynamics breaks down — the equilibration velocity. The latter relates to the radius of convergence of the hydrodynamic expansion and it is extracted from a collision between a hydrodynamic diffusive mode and a non-hydrodynamic mode associated to the IR AdS2 region. In this short note, we confirm this picture for holographic systems displaying the spontaneous breaking of translational invariance. Moreover, we find that, at zero temperature, the lower bound set by quantum chaos and the upper one defined by causality and hydrodynamics exactly coincide, determining uniquely the diffusion constant. Finally, we comment on the meaning and universality of this newly proposed prescription.
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Buzzegoli, Matteo, and Andrea Palermo. "Emergent Canonical Spin Tensor in the Chiral-Symmetric Hot QCD." Physical Review Letters 133, no. 26 (2024). https://doi.org/10.1103/physrevlett.133.262301.
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The spin tensor is fundamental to relativistic spin hydrodynamics, but its definition is ambiguous due to the pseudogauge symmetry. We show that this ambiguity can be solved in interacting field theories. We prove that the mean-field limit of a modified Nambu-Jona-Lasinio model with spin-spin interactions is equivalent to nondissipative spin hydrodynamics with a canonical spin tensor. Published by the American Physical Society 2024
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Upadhyaya, N., L. R. Gómez, and V. Vitelli. "Soliton Attenuation and Emergent Hydrodynamics in Fragile Matter." Physical Review X 4, no. 1 (2014). http://dx.doi.org/10.1103/physrevx.4.011045.
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Łebek, Maciej, and Miłosz Panfil. "Chapman-Enskog theory and crossover between diffusion and superdiffusion for nearly integrable quantum gases." SciPost Physics 18, no. 6 (2025). https://doi.org/10.21468/scipostphys.18.6.186.
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Integrable systems feature an infinite number of conserved charges and on hydrodynamic scales are described by generalised hydrodynamics (GHD). This description breaks down when the integrability is weakly broken and sufficiently large space-time-scales are probed. The emergent hydrodynamics depends then on the charges conserved by the perturbation. We focus on nearly-integrable Galilean-invariant systems with conserved particle number, momentum and energy. Basing on the Boltzmann approach to integrability-breaking we describe dynamics of the system with GHD equation supplemented with a collision term. The limit of large space-time-scales is addressed using Chapman-Enskog expansion adapted to the GHD equation. For length scales larger than \sim\lambda^{-2}∼λ−2, where \lambdaλ is integrability-breaking parameter, we recover Navier-Stokes equations and find transport coefficients: viscosity and thermal conductivity. At even larger length scales, this description crosses over to Kardar-Parisi-Zhang universality class, characteristic to generic non-integrable one-dimensional fluids. Employing nonlinear fluctuating hydrodynamics we estimate this crossover length scale as \sim\lambda^{-4}∼λ−4.
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Galbraith, Gemma F., Benjamin J. Cresswell, Mark I. McCormick, and Geoffrey P. Jones. "Strong hydrodynamic drivers of coral reef fish biodiversity on submerged pinnacle coral reefs." Limnology and Oceanography, September 25, 2023. http://dx.doi.org/10.1002/lno.12431.
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AbstractHydrodynamic processes are important in all marine environments and on coral reefs drive patterns of habitat zonation, community structure, and biodiversity. Abrupt geomorphological features like pinnacles and seamounts often possess distinct localized currents and these habitats are also often characterized by high abundance and biomass of fishes. However, differences in fish community structure between pinnacles and emergent reefs, and their key drivers are poorly understood. In this study, we compared fish communities among emergent fringing and offshore coral reefs, and submerged pinnacle reefs in Papua New Guinea. Submerged pinnacles possessed higher fish biomass, abundance, and species richness than both fringing and offshore emergent reefs. We collected in‐situ current speed and temperature data over a full year at each reef and used random forest analysis to investigate the relative influence of hydrodynamics compared to other well‐established drivers of reef fish biodiversity, including habitat and biogeographic factors. Environmental variables explained 70%, 52%, and 5% of variability in models for species richness, abundance and biomass respectively. In all models, average current speed, current speed variability, and reef area were consistently among the most influential variables. Models examining relationships between fish biodiversity metrics and current speed did not yield conclusive results but did highlight the association of distinct hydrodynamic regimes on pinnacles with high fish richness, abundance, and biomass. Our study highlights the strong influence of reef‐scale hydrodynamics on fish biodiversity and demonstrates the ecological value of small, submerged coral reefs, which are globally numerous yet remain understudied in coral reef ecology.