Institute Of Mechanics,Chinese Academy of Sciences
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Manipulation on a heavy fluid layer with dual-mode perturbations via reverberating waves
No full textThe growth and manipulation of a heavy fluid layer with dual-mode perturbations imposed only at the downstream interface are investigated. To quantify the effects of reverberating waves, the processes of the disturbed reverberating waves interacting with the layer are theoretically modeled. When the compression waves hit the downstream interface, they will suppress (promote) the mode growth if the mode has (has not) completed the phase inversion. The relationship between the perturbation parameters and the layer width is obtained when the mode amplitude is zero at the arrival of the compression waves. Four different initial layer widths are then designed in experiments by fixing the perturbation parameters to manipulate the mode growth. For a large layer width, the growth of the downstream interface is suppressed relative to that of a dual-mode interface between semi-infinite domains, because both mode amplitudes are suppressed by compression waves. As the layer width reduces, the mixing width growth is enhanced, because the long-wavelength perturbation growth is promoted. In addition, the compression waves have more prominent effects on the short-wavelength perturbation than the long-wavelength perturbation. Through considering the reverberating waves effects in a classic model, the mode amplitude growth can generally be predicted. The reverberating waves play a more prominent role than interface coupling in the development of the dual-mode perturbations at the downstream interface during the time studied. The initially planar upstream interface also acquires perturbations via the rarefaction waves and interface coupling. However, interface coupling dominates the amplitude growth of the modes at the upstream interface, and it has a greater effect on the long-wavelength perturbation than the short-wavelength perturbation. This work might shed some light on how to manipulate the growth of the dual-mode perturbations via reverberating waves
Manipulation on a heavy fluid layer with dual-mode perturbations via reverberating waves
No full textThe growth and manipulation of a heavy fluid layer with dual-mode perturbations imposed only at the downstream interface are investigated. To quantify the effects of reverberating waves, the processes of the disturbed reverberating waves interacting with the layer are theoretically modeled. When the compression waves hit the downstream interface, they will suppress (promote) the mode growth if the mode has (has not) completed the phase inversion. The relationship between the perturbation parameters and the layer width is obtained when the mode amplitude is zero at the arrival of the compression waves. Four different initial layer widths are then designed in experiments by fixing the perturbation parameters to manipulate the mode growth. For a large layer width, the growth of the downstream interface is suppressed relative to that of a dual-mode interface between semi-infinite domains, because both mode amplitudes are suppressed by compression waves. As the layer width reduces, the mixing width growth is enhanced, because the long-wavelength perturbation growth is promoted. In addition, the compression waves have more prominent effects on the short-wavelength perturbation than the long-wavelength perturbation. Through considering the reverberating waves effects in a classic model, the mode amplitude growth can generally be predicted. The reverberating waves play a more prominent role than interface coupling in the development of the dual-mode perturbations at the downstream interface during the time studied. The initially planar upstream interface also acquires perturbations via the rarefaction waves and interface coupling. However, interface coupling dominates the amplitude growth of the modes at the upstream interface, and it has a greater effect on the long-wavelength perturbation than the short-wavelength perturbation. This work might shed some light on how to manipulate the growth of the dual-mode perturbations via reverberating waves
Compact binary coalescence gravitational wave signal counting and separation
No full textAs next-generation gravitational-wave (GW) observatories approach unprecedented sensitivities, the need for robust methods to analyze increasingly complex, overlapping signals becomes ever more pressing. Existing matched-filtering approaches and deep-learning techniques can typically handle only one or two concurrent signals, offering limited adaptability to more varied and intricate superimposed waveforms. To overcome these constraints, we present the UnMixFormer, an attention-based architecture that not only identifies the unknown number of concurrent compact binary coalescence GW events but also disentangles their individual waveforms through a multidecoder architecture, even when confronted with five overlapping signals. Our UnMixFormer is capable of capturing both short- and long-range dependencies by modeling them in a dual-path manner, while also enhancing periodic feature representation by incorporating Fourier analysis networks. Our approach adeptly processes binary black hole, binary neutron star, and neutron star- black hole systems over extended time series data (16,384 samples). When evaluating on synthetic data with signal-to-noise ratios (SNR) ranging from 10 to 50, our method achieves 99.89% counting accuracy, a mean overlap of 0.9831 between separated waveforms and templates, and robust generalization ability to waveforms with spin precession, orbital eccentricity, and higher modes, marking a substantial advance in the precision and versatility of GW data analysis
Integrin αvβ6 mediates the effects of age-related decreases in matrix stiffness on Tenon's fibroblast activation and bleb scarring in glaucoma
No full textGlaucoma, including primary open-angle glaucoma (POAG) and primary angle-closure glaucoma, leads to optic nerve injury and visual field loss, often necessitating surgical intervention to lower intraocular pressure (IOP). Trabeculectomy, the most common glaucoma surgery, could fail due to excessive scarring of the filtering bleb, driven by the hyperproliferation of human Tenon's fibroblasts (HTFs). Herein, the impact of aging on matrix stiffness in Tenon's capsule tissue, the role of extracellular matrix (ECM) stiffness in the phenotypic transformation of HTFs, and the regulatory function of integrin alphavbeta6 (alpha v(36) were investigated. Matrix stiffness in Tenon's capsule tissue is notably lower in elder glaucoma patients in comparison with younger ones, with reduced levels of alpha-SMA, collagen I, and integrin alpha v(36. GFS (Glaucoma Filtration Surgery) models were established in young and old SD rats, and it was observed that older rats exhibited lower ECM stiffness, reduced fibrosis, and decreased integrin alpha v(36 expression. HTFs from elderly glaucoma patients showed reduced ECM stiffness, decreased viability, impaired migration, and diminished fibrotic responses. When HTFs from young glaucoma patients were cultured on substrates of varying stiffness, it was found that stiffer substrates increased cell viability, migration, collagen synthesis, and fibrosis marker expression. Additionally, knocking down integrin alpha v(36 in HTFs cultured on stiffer substrates resulted in decreased cell viability, impaired migration, reduced collagen synthesis, and lower fibrosis marker expression. In vivo knockdown of integrin alpha v(36 effectively reduced ECM stiffness and fibrosis, thereby attenuating bleb scarring after GFS in young rats. Collectively, the aging-associated changes in ECM stiffness and integrin alpha v(36 expression contribute to reduced fibrosis, potentially enhancing the success of trabeculectomy in elder patients
Performance of radio frequency ion thruster with polytetrafluoroethylene propellant embedded in discharge chamber
No full textExploring solid propellants for electric thrusters can simplify the propellant storage and supply units in propulsion systems. In this study, polytetrafluoroethylene (PTFE), commonly used as a propellant in pulsed plasma thrusters, was embedded in the discharge chamber of a radio frequency ion thruster (RIT-4) to investigate the performance of an ablation-type RIT. Experimental results indicate that PTFE can decompose and ionize stably under plasma ablation within the discharge chamber, producing -C-F- and F- ion clusters that form a stable plasma. By adjusting the length of the PTFE propellant, it was observed that its decomposition rate influences the ion beam current of the thruster. Compared with xenon, PTFE generates an ion plume with a larger divergence angle, ranging from 16.05 degrees to 22.74 degrees at an ion beam current of 25 mA, with a floating potential distribution of 8-56 V. Assuming that the proportion of neutral gas in the vacuum chamber matches the ion species ratio in the ion plume, thrust, specific impulse and efficiency parameters were calculated for the RIT-4 with embedded PTFE. Under 50 W RF power, the thrust was approximately 1.02 mN, the specific impulse was around 1236 s and the power-to-thrust ratio was approximately 93.14 W/mN. All results indicate that PTFE is a viable propellant for RIT, but the key is to control the rate of decomposition
Electrokinetic transport mechanisms of rare earth elements in ion-adsorption deposits: An integrated model approach
No full textHeavy rare earth elements (REEs) are critical strategic resources for advanced technologies and the low-carbon economy transition. Ion-adsorption deposits (IADs) represent the primary sources of heavy REEs, yet their mining has caused severe environmental impacts. Electrokinetic mining (EKM), a sustainable alternative, promises efficient REE recovery from IADs. However, the electrokinetic transport mechanisms of REEs in IADs remain unclear, and predictive models are lacking. Here, we develop an integrated EKM (IEKM) model that rigorously incorporates coupled effects of diffusion, convection, electromigration, electroosmosis, and electrolysis to resolve REE transport in IADs. The IEKM model was validated using a 14-ton-scale IAD EKM, accurately simulating REE and leaching agent (NH4+) ion transport. The predicted REE recovery efficiency is 80.97 % after 11 days of EKM, aligning with experimental results (88.28 +/- 17.00 %). Significantly, the IEKM model quantitatively determines that diffusion, convection, electromigration, electroosmosis, and electrolysis contribute 3.06 %, 2.90 %, 82.91 %, 0.20 %, and 10.93 %, respectively, to REE transport. Unexpectedly, electromigration emerges as the dominant mechanism governing REE electrokinetic transport in IADs with significant influence by electrolysis, while electroosmosis exhibits negligible contribution, contradicting conventional expectations. Furthermore, electrolysis consumed 57.95 % of input energy due to water splitting, leaving only 42.05 % for direct REE transport. This work advances fundamental understanding of REE electrokinetic transport in IADs and establishes an industrially viable model, bridging experimental and numerical modeling to facilitate practical applications of environmentally sustainable EKM technology in resource recovery
A framework for learning symbolic turbulence models from indirect observation data via neural networks and feature importance analysis
No full textLearning symbolic turbulence models from indirect observation data is of significant interest as it not only improves the accuracy of posterior prediction but also provides explicit model formulations with good interpretability. However, it typically resorts to gradient-free evolutionary algorithms, which can be relatively inefficient compared to gradient-based approaches, particularly when the Reynolds-averaged Navier-Stokes (RANS) simulations are involved in the training process. In view of this difficulty, we propose a framework that uses neural networks and the associated feature importance analysis to improve the efficiency of symbolic turbulence modeling. In doing so, the gradient-based method can be used to efficiently learn neural networkbased representations of Reynolds stress from indirect data, which is further transformed into simplified mathematical expressions with symbolic regression. Moreover, feature importance analysis is introduced to accelerate the convergence of symbolic regression by excluding insignificant input features. The proposed training strategy is tested in the flow in a square duct, where it correctly learns underlying analytic models from indirect velocity data. Further, the method is applied in the flow over the periodic hills, demonstrating that the feature importance analysis can significantly improve the training efficiency and learn symbolic turbulence models with satisfactory generalizability
Effects of annular channel widths on wave system structures in wall-detached rotating detonation
No full textThe propagation modes and flow characteristics of wall-detached rotating detonation waves (RDWs) are numerically investigated by solving the three-dimensional Navier-Stokes equations in annular combustors with varying channel widths. This study highlights the crucial role that channel width plays in the evolution of walldetached RDWs, and systematically investigates and elucidates the detonation wave acceleration phenomenon. The results show that RDWs can maintain self-sustained rotation without wall confinement, and two new propagation modes emerge, governed by geometric scaling parameters. In wide channels, the direct interaction between oblique shock waves and the walls leads to the formation of asymmetric multi-wave structures, which challenges the predictions of traditional single-wave propagation models. In contrast, in narrow channels, the RDW exhibits a concave wavefront structure with propagation velocities exceeding the Chapman-Jouguet (C-J) detonation speed, resulting from coupled interactions between recirculation zones and oblique shock waves. In addition, wall-detached RDWs demonstrate better thermodynamic performance compared to wall-attached RDWs, with notably lower heat flux at the combustor walls. These findings, which reveal new mechanisms of shock-wave-wall interactions and the morphological diversity of three-dimensional wave systems under geometric constraints, provide valuable theoretical insights for optimizing the design of high-frequency rotating detonation combustion chambers
Glass transition in metallic glasses facilitated by static loading
No full textThe glass transition represents a long-standing enigma in condensed matter physics and materials science. Traditionally, this transition, often associated with alpha relaxation, is viewed as a thermally activated process. In this study, by integrating molecular dynamics simulations and experimental verification, we revealed that static loading can effectively reduce the glass transition temperature in the out-of-equilibrium glassy state, exhibiting a distinct stress-temperature equivalence compared to that observed under dynamic loading in the equilibrium liquid state. This indicates that mechanical energy can effectively substitute thermal energy in facilitating the glass transition. At the microscopic level, the application of static load enhances atomic mobility, triggering cooperative atomic movements and fostering the development of "faster-atom" networks, which ultimately facilitate the global motion of numerous atoms necessary for the glass transition. These findings highlight the significance of static load in tailoring the structure and dynamics of metallic glasses
A unified numerical framework for the soil and fluid coupling problem considering mixture and separation
No full textAccurately modeling soil-fluid coupling under large deformations is critical for understanding and predicting phenomena such as slope failures, embankment collapses, and other geotechnical hazards. This topic has been studied for decades and remains challenging due to the nonlinear responses of geotechnical structures, which typically result from plastic yielding and finite deformation of the soil skeleton. In this work, we comprehensively summarize the theory involved in the soil-fluid coupling problem. Within a finite strain framework, we employ an elasto-plastic constitutive model with linear hardening to represent the solid skeleton and a nearly incompressible model for water. The water content influences the behavior of the solid skeleton by affecting its cohesion. The governing equations are discretized by material point method and two sets of material points are employed to independently represent solid skeleton and fluid, respectively. The proposed method is validated by comparing simulation results with experimental results for the impact of water on dry soil and wet soil. The capability of the method is further demonstrated through two cases: (1) the impact of a rigid body on saturated soil, causing water seepage, and (2) the filling of a ditch, which considers the erosion of the foundation. This work may provide a versatile tool for analyzing the dynamic responses of fluid and solid interactions, considering both mixing and separation phenomena