arXiv subjects

Ziyue Yu

Publications and source records attributed to Ziyue Yu.

3 recordsLinked to original sources

arXiv2026

Two-way coupling in active suspensions suppresses particle accumulation and induces non-monotonic flow stabilization

We experimentally study the two-way coupling between a swarm of centimetre-scale active swimmers (Artemia salina) and an electromagnetically driven quasi-two-dimensional cellular flow. The swimmer loading $N$ and the background forcing $E$ are varied independently across 85 conditions, and the coupled dynamics are characterized through Lagrangian diagnostics built on the attracting Lagrangian coherent structures (LCS) of the flow. In the dilute limit, swimmers accumulate onto the attracting LCS most strongly when their speed is comparable to the flow speed, recovering the mobility-selective accumulation predicted by one-way-coupled simulations at the fixed aspect ratio of A. salina. As the loading increases, this accumulation is progressively suppressed, a collective effect inaccessible to single-swimmer models. The back-action of the swarm on the flow is itself bidirectional and regime-dependent: at low forcing the swarm disorders the attracting-LCS web and scatters the topological critical points of the cellular pattern, whereas at high forcing it reorganizes and reinforces the skeleton. The temporal stability of the skeleton is correspondingly non-monotonic in both $N$ and $E$, with the conditions of maximal stability migrating systematically through the $(N,E)$ plane. This reinforcement of coherent structures has no counterpart in prior simulations, which reported a predominantly disruptive back-action. Resolving both directions of the coupling shows how collective activity can either erode or reinforce the transport skeleton of a structured flow.

physics.flu-dyn↗

arXiv2025

Turbulence at Low Reynolds Numbers

Turbulence -- ubiquitous in nature and engineering alike [1-5] -- is traditionally viewed as an intrinsically inertial phenomenon, emerging only when the Reynolds number (Re), which quantifies the ratio of inertial to dissipative forces [6], far exceeds unity [7, 8]. Here, we demonstrate that strong energy flux between different length scales of motion -- a defining hallmark of turbulence [9] -- can persist even at Re ~ 1, thereby extending the known regime of turbulent flows beyond the classical high-Re paradigm. We show that scale-to-scale energy transfer can be recast as a mechanical process between turbulent stress and large-scale flow deformation. In quasi-two-dimensional (quasi-2D) flows driven by electromagnetic forcing, we introduce directionally biased perturbations that enhance this interaction, amplifying the spectral energy flux by more than two orders of magnitude, even in the absence of dominant inertial forces. This study establishes a new regime of 2D Navier-Stokes (N-S) turbulence, challenging long-standing assumptions about the high Re conditions required for turbulent flows. Beyond revising classical belief, our results offer a generalizable strategy for engineering multiscale transport in flows that lack inertial dominance, such as those found in microfluidic [10, 11] and low-Re biological [12-15] systems.

physics.flu-dyn↗

arXiv2024

MPRE: Multi-perspective Patient Representation Extractor for Disease Prediction

Patient representation learning based on electronic health records (EHR) is a critical task for disease prediction. This task aims to effectively extract useful information on dynamic features. Although various existing works have achieved remarkable progress, the model performance can be further improved by fully extracting the trends, variations, and the correlation between the trends and variations in dynamic features. In addition, sparse visit records limit the performance of deep learning models. To address these issues, we propose the Multi-perspective Patient Representation Extractor (MPRE) for disease prediction. Specifically, we propose Frequency Transformation Module (FTM) to extract the trend and variation information of dynamic features in the time-frequency domain, which can enhance the feature representation. In the 2D Multi-Extraction Network (2D MEN), we form the 2D temporal tensor based on trend and variation. Then, the correlations between trend and variation are captured by the proposed dilated operation. Moreover, we propose the First-Order Difference Attention Mechanism (FODAM) to calculate the contributions of differences in adjacent variations to the disease diagnosis adaptively. To evaluate the performance of MPRE and baseline methods, we conduct extensive experiments on two real-world public datasets. The experiment results show that MPRE outperforms state-of-the-art baseline methods in terms of AUROC and AUPRC.

cs.LG↗