arXiv subjects

Zhi Cheng

Publications and source records attributed to Zhi Cheng.

13 recordsLinked to original sources

arXiv2026

Cavitation Acoustic Perturbation Equations: A Computational Framework for Source-Resolved Multiphase Hydroacoustics

This work develops a cavitation-consistent acoustic perturbation framework for predicting sound generation and propagation in cavitating flows. Unlike conventional acoustic perturbation equations for single-phase or weakly compressible flows, the proposed formulation embeds cavitation physics directly into the acoustic equations. The cavitation acoustic perturbation equations (CAPE) incorporate vapor mass transfer, mixture compressibility, and pressure-rate effects within a unified formulation, allowing cavitation-induced noise sources to be resolved in the computational domain. The numerical framework is verified using one-dimensional wave-propagation problems. The solutions become insensitive to further mesh and time-step refinement, the perfectly matched layer suppresses boundary reflections, and the predicted attenuation over a range of source frequencies follows Stokes' sound attenuation law. The framework is then applied to cavitating flow past a circular cylinder and a NACA hydrofoil. The non-cavitating benchmark shows dipole-like radiation associated with unsteady loading, whereas cavitating cases exhibit monopole-like or geometry-modulated radiation caused by volumetric phase change. Source-term analyses identify tonal frequencies associated with vortex shedding, cavity shedding, and collapse-induced excitation. The phase-change terms provide a direct volumetric contribution to the monopole-like source, while localized collapse events appear through amplification of the pressure-rate source. The proposed framework extends acoustic perturbation methods to cavitating multiphase flows and provides an efficient tool for hydroacoustic prediction, source localization, and mechanism analysis in marine and hydraulic applications.

physics.flu-dyn↗

arXiv2026

ControlFoley: Unified and Controllable Video-to-Audio Generation with Cross-Modal Conflict Handling

Recent advances in video-to-audio (V2A) generation enable high-quality audio synthesis from visual content, yet achieving robust and fine-grained controllability remains challenging. Existing methods suffer from weak textual controllability under visual-text conflict and imprecise stylistic control due to entangled temporal and timbre information in reference audio. Moreover, the lack of standardized benchmarks limits systematic evaluation. We propose ControlFoley, a unified multimodal V2A framework that enables precise control over video, text, and reference audio. We introduce a joint visual encoding paradigm that integrates CLIP with a spatio-temporal audio-visual encoder to improve alignment and textual controllability. We further propose temporal-timbre decoupling to suppress redundant temporal cues while preserving discriminative timbre features. In addition, we design a modality-robust training scheme with unified multimodal representation alignment (REPA) and random modality dropout. We also present VGGSound-TVC, a benchmark for evaluating textual controllability under varying degrees of visual-text conflict. Extensive experiments demonstrate state-of-the-art performance across multiple V2A tasks, including text-guided, text-controlled, and audio-controlled generation. ControlFoley achieves superior controllability under cross-modal conflict while maintaining strong synchronization and audio quality, and shows competitive or better performance compared to an industrial V2A system. Code, models, datasets, and demos are available at: https://github.com/xiaomi-research/controlfoley.

cs.MM↗

arXiv2026

Sub-nanometer resolution of the nitrogen-vacancy center by Fourier magnetic imaging

Solid-state spins in diamond are promising building blocks for quantum computing and quantum sensing, both of which require precise nanoscale addressing of individual spins. To explore the resolution limit of this approach, we demonstrate Fourier magnetic imaging of nitrogen-vacancy centers in diamond under state-of-the-art conditions. We constructed a highly compact experimental platform featuring thermal drift compensation under ambient conditions and generated a pulsed magnetic field gradient of up to 13.5 G/$\mu$m. By implementing the Fourier magnetic imaging protocol, we achieved localization of a single nitrogen-vacancy center with a spatial resolution of 0.28 $\pm$ 0.10 nm and a magnetic field measurement deviation of 9 nT. This technique holds potential for applications such as localizing spins within proteins and cells.

quant-ph↗

arXiv2025

High-resolution electric field imaging based on intermittent-contact mode scanning NV center electrometry

Scanning nitrogen-vacancy (NV) center electrometry has shown potential for quantitative quantum imaging of electric fields at the nanoscale. However, achieving nanoscale spatial resolution remains a challenge since employing gradiometry to overcome electrostatic screening causes resolution-limiting trade-offs including the averaging effect and the sensor-sample proximity. Here, we demonstrate a scanning NV center protocol that achieves an enhanced spatial resolution of approximately 10 nm. We develop an axially symmetric probe with a sub-nanometer oscillating amplitude, which simultaneously provides robust intermittent-contact mode feedback and ensures close engagement between the diamond tip and the sample. As an example, we experimentally demonstrate a 10 nm spatial resolution on ferroelectric lithium niobate. Scanning NV center electrometry with this resolution can directly resolve the nanoscale polar textures and dynamics of emerging ferroelectrics, which commonly arise on the scale of tens of nanometers.

quant-ph↗

arXiv2025

A Mesh-Adaptive Hypergraph Neural Network for Unsteady Flow Around Oscillating and Rotating Structures

Graph neural networks, recently introduced into the field of fluid flow surrogate modeling, have been successfully applied to model the temporal evolution of various fluid flow systems. Existing applications, however, are mostly restricted to cases where the domain is time-invariant. The present work extends the application of graph neural network-based modeling to fluid flow around structures rotating with respect to a certain axis. Specifically, we propose to apply a graph neural network-based surrogate model with part of the mesh/graph co-rotating with the structure and part of the mesh/graph static. A single layer of interface cells are constructed at the interface between the two parts and are allowed to distort and adapt, which helps in circumventing the difficulty of interpolating information encoded by the neural network at every graph neural network layer. Dedicated reconstruction and re-projection schemes are designed to counter the error caused by the distortion and connectivity change of the interface cells. The effectiveness of our proposed framework is examined on two test cases: (i) fluid flow around a 2D oscillating airfoil, and (ii) fluid flow past a 3D rotating cube. Our results show that the model achieves stable rollout predictions over hundreds or even a thousand time steps. We further demonstrate that one could enforce accurate, error-bounded prediction results by incorporating the measurements from sparse pressure sensors. In addition to the accurate flow field predictions, the lift and drag force predictions closely match with the computational fluid dynamics calculations, highlighting the potential of the framework for modeling fluid flow around rotating structures, and paving the path towards a graph neural network-based surrogate model for more complex scenarios like flow around marine propellers.

physics.flu-dyn↗

arXiv2025

Flexible Full-Stokes Polarization Engineering by Disorder-Scrambled Metasurfaces

Abstract: The ability to arbitrarily and flexibly control the polarization of light, including both the state of polarization (SoP) and the degree of polarization (DoP), is highly important for quantum optics, polarization imaging, and coherent optical communications. Although metasurfaces have shown promise in polarization control, the few studies focusing on the DoP often lack flexibility in manipulation. Here, we propose a novel approach using a disordered metasurface to flexibly convert natural light into partially polarized light, enabling independent and flexible control over all Stokes parameters. The metasurface is composed of two types of meta-atoms, uniformly distributed with specific quantity ratios, decoupling the design parameters in the process of polarization control, and allowing a one-to-one correspondence between metasurface and polarization spaces. The azimuthal and elevation angles of the SoP on the Poincar\'e sphere are independently controlled by the meta-atom rotation and size, while the DoP is governed by the quantity ratio. A developed algorithm determines the disordered metasurface arrangement, with theoretical calculations showing an average error of less than 3{\deg} for both the azimuthal and elevation angles and a control accuracy of \pm 0.05 for the DoP.

physics.optics↗

arXiv2024

Electric imaging and dynamics of photo-charged graphene edge

The one-dimensional side gate based on graphene edges shows a significant capability of reducing the channel length of field-effect transistors, further increasing the integration density of semiconductor devices. The nano-scale electric field distribution near the edge provides the physical limit of the effective channel length, however, its imaging under ambient conditions still lacks, which is a critical aspect for the practical deployment of semiconductor devices. Here, we used scanning nitrogen-vacancy microscopy to investigate the electric field distribution near edges of a single-layer-graphene. Real-space scanning maps of photo-charged floating graphene flakes were acquired with a spatial resolution of $\sim$ 10 nm, and the electric edge effect was quantitatively studied by analyzing the NV spin energy level shifts due to the electric Stark effect. Since the graphene flakes are isolated from external electric sources, we brought out a theory based on photo-thermionic effect to explain the charge transfer from graphene to oxygen-terminated diamond probe with a disordered distribution of charge traps. Real-time tracing of electric fields detected the photo-thermionic emission process and the recombination process of the emitted electrons. This study provides a new perspective for graphene-based one-dimensional gates and opto-electronics with nanoscale real-space imaging, and moreover, offers a novel method to tune the chemical environment of diamond surfaces based on optical charge transfer.

cond-mat.mes-hall↗

arXiv2024

A unified framework for prediction of vortex-induced vibration based on the nonlinear data-driven identification of general wake oscillator modeling

In this paper, we present novel identification strategies to develop a unified framework for vortex-induced vibration (VIV) prediction based on the general semi-empirical wake oscillator. Greybox nonlinear system identification method accompanying high-fidelity computational fluid dynamics (CFD) and/or experimental data could be applied for the identification process. The proposed template of general wake oscillators contains low- to high-order damping terms to be identified for characterizing the possible flow dynamics. Two different strategies, including individual identification of single wake oscillator and overall identification of coupled VIV control equations, are proposed. VIV system consisting of an elastically-mounted circular cylinder submerged in laminar flow at Reynold number of 100 is considered. Both strategies have been tested and have exhibited high accuracy. The second strategy, i.e., overall identification of coupled VIV control equations, would be more suitable for the future framework owing that its training process considers the effect of fluid damping. A detailed mathematical introduction to future works on framework development covering the wide Reynold number range is addressed. The proposed unified framework is a landmark update of past wake oscillators both in terms of prediction accuracy and physical principles and has considerable research significance and practical engineering value.

physics.flu-dyn↗

arXiv2024

Flow-Induced Vibration of Flexible Hydrofoil Within Cavitating Turbulent Flow

The flow-induced vibration and cavitation dynamics of three-dimensional flow past a cantilever flexible hydrofoil are investigated using a large eddy simulation (LES) model, a homogeneous mixture cavitation model and the structural modes superposition method. The present work aims to explore a potential mechanism responsible for a propeller singing behavior, and thus focuses on the synchronized hydroelastic coupling among the pressure pulsation inside the flow field, the cavitation generation and the structural vibration. To begin, we validate the tip vortex dynamics of a flexible hydrofoil against the available experimental. Our results demonstrate that the tip vortex shedding and the blade vibration are responsible for the intense peak in the low-frequency tonal components of the noise source, and the trailing-edge vortex shedding induces broadband components. Additionally, the generation of sheet cavitation induces considerable synchronized hydrofoil vibration (subjected to a flutter-like response), and affects the pressure fluctuations in the flow field, which further dominate the features of the underwater noise sources. It is suggested that the cavitation behavior and structural vibrations co-dominate the characteristics of singing noise from a propeller blade.

physics.flu-dyn↗

arXiv2024

Modeling of Hydroacoustic Noise from Marine Propellers with Tip Vortex Cavitation

The present work aims to study the cavitating turbulent flow of a full-scale marine propeller and explore the physical mechanism underpinning the underwater radiated noise. We employ the standard dynamic large eddy simulation for the turbulent wake flow and the Schnerr-Sauer cavitation model, while the Ffowcs-Williams-Hawkings acoustic analogy is considered for the hydroacoustic modeling. For the current investigation, we consider a well-known Potsdam Propeller Test Case to analyze the turbulent cavitating flow and the associated hydroacoustic emissions. To begin, the modeling framework is validated using the available experimental data, and distinctive double-helical tip vortex cavitation and its qualitative patterns along the vortex trajectory are captured. In comparison to the non-cavitating condition, the pressure distribution on the propeller surface is more disordered for the cavitating condition, which is further reflected by a relatively stronger power of both low-frequency tonal peaks and high-frequency broadband components in the spectrum of thrust generation. Specifically, the generation of cavitation leads to the enhancement of the monopole noise source and the breakdown of cavitation bubbles as well as vortex structures in the turbulent wake. Furthermore, the tonal noise with the frequency corresponding to the harmonics of blade passing frequency is also enhanced. Generally speaking, the generation of cavitation structures enhances the hydroacoustics energy of URN at all orientations, especially in the downstream direction with sound pressure level increasing up to 20 dB.

physics.flu-dyn↗

arXiv2020

Nanoscale electrometry based on a magnetic-field-resistant spin sensor

The nitrogen-vacancy (NV) center is a potential atomic-scale spin sensor for electric field sensing. However, its natural susceptibility to the magnetic field hinders effective detection of the electric field. Here we propose a robust electrometric method utilizing continuous dynamic decoupling (CDD) technique. During the CDD period, the NV center evolves in a dressed-state space, where the sensor is resistant to magnetic fields but remains sensitive to electric fields. As an example, we use this method to isolate the electric noise from a complex electro-magnetical environment near diamond surface via measuring the dephasing rate between dressed states. By reducing the surface electric noise with different covered liquids, we observe an unambiguous relation between the dephasing rate and the dielectric permittivity of the liquid, which enables a quantitative investigation of electric noise model near diamond surface.

quant-ph↗

arXiv2017

Relativistic, single-cycle tunable-infrared pulses generated by a tailored plasma density structure

The availability of intense, ultrashort coherent radiation sources in the infrared region of the spectrum is enabling the generation of attosecond X-ray pulses via high harmonic generation, pump-probe experiments in the "molecular fingerprint" region and opening up the area of relativistic-infrared nonlinear optics of plasmas. These applications would benefit from multi-millijoule single-cycle pulses in the mid to long wavelength infrared (LW-IR) region. Here we present a new scheme capable of producing tunable relativistically intense, single-cycle infrared pulses from 5-14$μ$m with a 1.7% conversion efficiency based on a photon frequency downshifting scheme that uses a tailored plasma density structure. The carrier-envelope phase (CEP) of the LW-IR pulse is locked to that of the drive laser to within a few percent. Such a versatile tunable IR source may meet the demands of many cutting-edge applications in strong-field physics and greatly promote their development.

physics.plasm-ph↗

arXiv2014

A dynamic mechanism of Alzheimer based on artificial neural network

In this paper, we provide another angle to analyze the reasons why Alzheimer Disease exists. We analyze the dynamic mechanism of Alzheimer Disease based on the cognitive model that established from artificial neural network. We can provide some theoretic explanations to Alzheimer Disease through the analyzing of this model.

cs.OH↗