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While nonlinear internal wave (NLIW) trains are known to influence near‐sea bed suspended sediment dynamics, the mechanisms remain a topic of debate. We present near‐sea bed observations of suspended sediment concentration C$C$and estimates of vertical sediment flux, at high vertical‐ and temporal‐resolution, during trains of NLIW of depression. We quantify the contributions of vertical advection and turbulent mixing to C$C$ . Vertical advection was important during the leading wave and the turbulent mixing flux was important over the entire wave train. Maximum C$C$was highly correlated with the maximum horizontal current speed squared and was only weakly correlated with the maximum vertical velocity. Boundary layer‐induced turbulence was thus inferred to be the key driver of net vertical sediment flux over wave trains of this type. Estimating the maximum total horizontal speed (i.e., wave‐induced plus background) is sufficient for modeling sediment vertical dynamics in shelf‐scale modeling studies.

We describe a framework for the simultaneous estimation of model parameters in a partial differential equation using sparse observations. Markov Chain Monte Carlo sampling is used in a Bayesian framework to estimate posterior probability distributions for each parameter. We describe the necessary components of this approach and its broad potential for application in models of unsteady processes. The framework is applied to three case studies, of increasing complexity, from the field of cohesive sediment transport. We demonstrate that the framework can be used to recover posterior distributions for all parameters of interest and the results agree well with independent estimates (where available). We also demonstrate how the framework can be used to compare different model parameterizations and provide information on the covariance between model parameters. Plain Language Summary We describe a framework for the simultaneous estimation of multiple unobserved parameters by combining observations of a tracer with a numerical model. This framework uses Bayesian inference techniques established in statistical literature to estimate the unobserved parameters of interest used in the model with uncertainty quantification. We explain the key components of this framework in simple terms to encourage its use for analyzing other unsteady processes and performing quantitative inference on parameters that are difficult or impossible to measure directly. We then demonstrate the framework's efficacy by applying it to three case studies from the field of cohesive sediment transport that all use the transport equation (advection‐diffusion). Inferred parameter values show good agreement with independent estimates, where available. Key Points Probabilistic framework to estimate unobserved erosion model parameters using sparse measurements collected above the seabed General approach can be updated with any model parameterization and quantitatively compared The framework is applicable to many similar data sets with both unsteady or quasi‐steady forcing and response

The so-called accretion flow that powers the growth of supermassive black holes in galaxy centres is assumed to be dominated by a smooth, steady flow of very hot plasma, but now observations instead reveal a clumpy accretion of very cold molecular clouds onto a supermassive black hole in the nucleus of a nearby giant elliptical galaxy. Cold gas accretion onto a supermassive black hole The so-called accretion flow that powers the growth of supermassive black holes in galaxy centres is often assumed to be dominated by a smooth, steady flow of very hot plasma, but there is little direct evidence to support this idea. New observations of the Abell 2597 galaxy cluster provide evidence for an alternative model, cold accretion onto black holes, recently predicted by simulations and theory, but not directly observed. The data reveal cold, clumpy molecular clouds falling towards an active supermassive black hole in the nucleus of a nearby giant elliptical galaxy. Supermassive black holes in galaxy centres can grow by the accretion of gas, liberating energy that might regulate star formation on galaxy-wide scales 1 , 2 , 3 . The nature of the gaseous fuel reservoirs that power black hole growth is nevertheless largely unconstrained by observations, and is instead routinely simplified as a smooth, spherical inflow of very hot gas 4 . Recent theory 5 , 6 , 7 and simulations 8 , 9 , 10 instead predict that accretion can be dominated by a stochastic, clumpy distribution of very cold molecular clouds—a departure from the ‘hot mode’ accretion model—although unambiguous observational support for this prediction remains elusive. Here we report observations that reveal a cold, clumpy accretion flow towards a supermassive black hole fuel reservoir in the nucleus of the Abell 2597 Brightest Cluster Galaxy (BCG), a nearby (redshift z  = 0.0821) giant elliptical galaxy surrounded by a dense halo of hot plasma 11 , 12 , 13 . Under the right conditions, thermal instabilities produce a rain of cold clouds that fall towards the galaxy’s centre 14 , sustaining star formation amid a kiloparsec-scale molecular nebula that is found at its core 15 . The observations show that these cold clouds also fuel black hole accretion, revealing ‘shadows’ cast by the molecular clouds as they move inward at about 300 kilometres per second towards the active supermassive black hole, which serves as a bright backlight. Corroborating evidence from prior observations 16 of warmer atomic gas at extremely high spatial resolution 17 , along with simple arguments based on geometry and probability, indicate that these clouds are within the innermost hundred parsecs of the black hole, and falling closer towards it.

We study active galactic nucleus (AGN) feedback in nearby (z < 0.35) galaxy clusters from the Planck Sunyaev–Zeldovich sample using Chandra observations. This nearly unbiased mass-selected sample includes both relaxed and disturbed clusters and may reflect the entire AGN feedback cycle. We find that relaxed clusters better follow the one-to-one relation of cavity power versus cooling luminosity, while disturbed clusters display higher cavity power for a given cooling luminosity, likely reflecting a difference in cooling and feedback efficiency. Disturbed clusters are also found to contain asymmetric cavities when compared to relaxed clusters, hinting toward the influence of the intracluster medium (ICM) “weather” on the distribution and morphology of the cavities. Disturbed clusters do not have fewer cavities than relaxed clusters, suggesting that cavities are difficult to disrupt. Thus, multiple cavities are a natural outcome of recurrent AGN outbursts. As in previous studies, we confirm that clusters with short central cooling times, t cool, and low central entropy values, K 0, contain warm ionized (10,000 K) or cold molecular (<100 K) gas, consistent with ICM cooling and a precipitation/chaotic cold accretion scenario. We analyzed archival Multi-Unit Spectroscopic Explorer observations that are available for 18 clusters. In 11/18 of the cases, the projected optical line emission filaments appear to be located beneath or around the cavity rims, indicating that AGN feedback plays an important role in forming the warm filaments by likely enhancing turbulence or uplift. In the remaining cases (7/18), the clusters either lack cavities or their association of filaments with cavities is vague, suggesting alternative turbulence-driven mechanisms (sloshing/mergers) or physical time delays are involved.

Understanding the quantum dynamics of strongly interacting fermions is a problem relevant to diverse forms of matter, including high-temperature superconductors, neutron stars, and quark-gluon plasma. An appealing benchmark is offered by cold atomic gases in the unitary limit of strong interactions. Here, we study the dynamics of a transversely magnetized unitary Fermi gas in an inhomogeneous magnetic field. We observe the demagnetization of the gas, caused by diffusive spin transport. At low temperatures, the diffusion constant saturates to the conjectured quantum-mechanical lower bound ≃ ħ/m, where m is the particle mass. The development of pair correlations, indicating the transformation of the initially noninteracting gas toward a unitary spin mixture, is observed by measuring Tan's contact parameter.