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Tomographic background oriented Schlieren (Tomo-BOS) imaging measures density or temperature fields in three dimensions using multiple camera BOS projections, and is particularly useful for instantaneous flow visualizations of complex fluid dynamics problems. We propose a new method based on physics-informed neural networks (PINNs) to infer the full continuous three-dimensional (3-D) velocity and pressure fields from snapshots of 3-D temperature fields obtained by Tomo-BOS imaging. The PINNs seamlessly integrate the underlying physics of the observed fluid flow and the visualization data, hence enabling the inference of latent quantities using limited experimental data. In this hidden fluid mechanics paradigm, we train the neural network by minimizing a loss function composed of a data mismatch term and residual terms associated with the coupled Navier–Stokes and heat transfer equations. We first quantify the accuracy of the proposed method based on a two-dimensional synthetic data set for buoyancy-driven flow, and subsequently apply it to the Tomo-BOS data set, where we are able to infer the instantaneous velocity and pressure fields of the flow over an espresso cup based only on the temperature field provided by the Tomo-BOS imaging. Moreover, we conduct an independent PIV experiment to validate the PINN inference for the unsteady velocity field at a centre plane. To explain the observed flow physics, we also perform systematic PINN simulations at different Reynolds and Richardson numbers and quantify the variations in velocity and pressure fields. The results in this paper indicate that the proposed deep learning technique can become a promising direction in experimental fluid mechanics.

AbstractDespite the significant progress over the last 50 years in simulating flow problems using numerical discretization of the Navier–Stokes equations (NSE), we still cannot incorporate seamlessly noisy data into existing algorithms, mesh-generation is complex, and we cannot tackle high-dimensional problems governed by parametrized NSE. Moreover, solving inverse flow problems is often prohibitively expensive and requires complex and expensive formulations and new computer codes. Here, we review flow physics-informed learning, integrating seamlessly data and mathematical models, and implement them using physics-informed neural networks (PINNs). We demonstrate the effectiveness of PINNs for inverse problems related to three-dimensional wake flows, supersonic flows, and biomedical flows.Graphical abstract

High-performance optimization algorithms are essential in deep learning. However, understanding the behavior of optimization (i.e., learning process) remains challenging due to the instability and weak interpretability of the algorithms. Since gradient-based optimizations can be interpreted as continuous-time dynamical systems, applying feedback control to the dynamical systems that model the optimizers may provide another perspective for exploring more robust, accurate and explainable optimization algorithms. In this study, we present a framework for optimization called controlled heavy-ball optimizer. By employing the proportional-integral-derivative (PID) controller in the optimizer, we develop a deterministic continuous-time optimizer called Proportional-Integral-Derivative Accelerated Optimizer (PIDAO), and provide theoretical convergence analysis of PIDAO in unconstrained (non-)convex optimizations. As a byproduct, we derive PIDAO-family schemes for training deep neural networks by using specific discretization methods. Compared to classical optimizers, PIDAO can be empirically proven a more aggressive capacity to explore the loss landscape with lower computational costs due to the property of PID controller. Experimental evaluations demonstrate that PIDAO can accelerate the convergence and enhance the accuracy of deep learning, achieving state-of-the-art performance compared with advanced algorithms. By drawing a connection between a closed-loop feedback control and optimization algorithms, the authors propose a framework to gain insights into optimization and learning processes based on feedback control theory. The results can improve theoretical justification and explainability of optimization methods.

This paper explores the application of deep learning to automate the traditionally manual creation of inspection recipes for machine vision scenarios requiring complex region selection, such as those found in semiconductor manufacturing. Manually selecting and cropping functional regions in ultra-high-resolution images for analysis and inspection can take anywhere from tens of minutes to hours. To address this challenge, we propose a model whose encoder integrates atrous convolution into a transformer architecture for better feature extraction. This approach is designed to improve segmentation accuracy while maintaining efficiency in processing large-scale semiconductor images. By automating the selection and cropping process, the proposed method aims to streamline quality inspection workflows, reduce manual labor, and accelerate automated optical inspection. Experimental results demonstrate that the model achieves high segmentation performance, with segmentation accuracy reaching 98% and a faster model inference, making it a practical and effective solution for enabling large-scale automation in semiconductor inspection. This research highlights the potential of deep learning-based methods to transform inspection processes, ensuring higher efficiency and product quality across semiconductor manufacturing industries.

Microaneurysms (MAs) are one of the earliest clinically visible signs of diabetic retinopathy (DR). MA leakage or rupture may precipitate local pathology in the surrounding neural retina that impacts visual function. Thrombosis in MAs may affect their turnover time, an indicator associated with visual and anatomic outcomes in the diabetic eyes. In this work, we perform computational modeling of blood flow in microchannels containing various MAs to investigate the pathologies of MAs in DR. The particle-based model employed in this study can explicitly represent red blood cells (RBCs) and platelets as well as their interaction in the blood flow, a process that is very difficult to observe in vivo . Our simulations illustrate that while the main blood flow from the parent vessels can perfuse the entire lumen of MAs with small body-to-neck ratio (BNR), it can only perfuse part of the lumen in MAs with large BNR, particularly at a low hematocrit level, leading to possible hypoxic conditions inside MAs. We also quantify the impacts of the size of MAs, blood flow velocity, hematocrit and RBC stiffness and adhesion on the likelihood of platelets entering MAs as well as their residence time inside, two factors that are thought to be associated with thrombus formation in MAs. Our results show that enlarged MA size, increased blood velocity and hematocrit in the parent vessel of MAs as well as the RBC-RBC adhesion promote the migration of platelets into MAs and also prolong their residence time, thereby increasing the propensity of thrombosis within MAs. Overall, our work suggests that computational simulations using particle-based models can help to understand the microvascular pathology pertaining to MAs in DR and provide insights to stimulate and steer new experimental and computational studies in this area.

With the booming development of logistics, manufacturing and warehousing fields, the autonomous navigation and intelligent obstacle avoidance technology of automated guided vehicles (AGVs) has become the focus of scientific research. In this paper, an enhanced deep reinforcement learning (DRL) framework is proposed, aiming to empower AGVs with the ability of autonomous navigation and obstacle avoidance in the unknown and variable complex environment. To address the problems of time‐consuming training and limited generalisation ability of traditional DRL, we refine the twin delayed deep deterministic policy gradient algorithm by integrating adaptive noise attenuation and dynamic delayed updating, optimising both training efficiency and model robustness. In order to further strengthen the AGV's ability to perceive and respond to changes of a dynamic environment, we introduce a distance‐based obstacle penalty term in the designed composite reward function, which ensures that the AGV is capable of predicting and avoiding obstacles effectively in dynamic scenarios. Experiments indicate that the AGV model trained by this algorithm presents excellent autonomous navigation capability in both static and dynamic environments, with a high task completion rate, stable and reliable operation, which fully proves the high efficiency and robustness of this method and its practical value.

Motivated by the excellent performance of proportional–integral–derivative controllers (PIDs) in the field of control, the authors injected the philosophy of PID into optimisation and introduced two types of novel PID optimisers from a continuous‐time view, which benefit from the idea that discrete‐time optimisation algorithm can be modelled as a continuous dynamical system/controlled system. For centralised optimisation, the authors discuss the idea of the first‐order PID optimiser and the second‐order accelerated PID optimiser. Furthermore, this framework is extended into distributed optimisation settings, and a distributed PID optimiser is proposed. Finally, some numerical examples are given to verify our ideas.

Tomographic particle image velocimetry (Tomo-PIV) has been successfully applied in measuring three-dimensional (3D) flow field in recent years. Such technology highly relies on the reconstruction technique which provides the spatial particle distribution by using images from multiple cameras at different viewing angles. As the most popular reconstruction method, the multiplicative algebraic reconstruction technique (MART) has advantages in high computational speed and high accuracy for low particle seeding reconstruction. However, the accuracy is not satisfactory in the case of dense particle distributions to be reconstructed. To overcome this problem, a symmetric encode–decoder fully convolutional network is proposed in this paper to improve the reconstruction quality of MART. The input of the neural network is the particle field reconstructed by the MART approach, while the output is the regenerated image with the same resolution. Numerical evaluations indicate that those blurred or irregular particles can be significantly refined by the trained neural network. Most of the ghost particles can also be removed by this filtering method. The reconstruction accuracy can be improved by more than 10% without increasing the computational cost. Experimental evaluations indicate that the trained neural network can also provide similar satisfactory reconstruction and improved velocity fields.

Accurate target detection in low‐light environments is crucial for unmanned aerial vehicles (UAVs) and autonomous driving applications. In this study, the authors introduce a real‐time multimodal fusion for enhanced detection (RMF‐ED), a novel framework designed to overcome the limitations of low‐light target detection. By leveraging the complementary capabilities of near‐infrared (NIR) cameras and light detection and ranging (LiDAR) sensors, RMF‐ED enhances detection performance. An advanced NIR generative adversarial network (NIR‐GAN) model was developed to address the lack of annotated NIR datasets, integrating structural similarity index measure (SSIM) loss and L1 loss functions. This approach enables the generation of high‐quality NIR images from RGB datasets, bridging a critical gap in training data. Furthermore, the multimodal fusion algorithm integrates RGB images, NIR images, and LiDAR point clouds, ensuring consistency and accuracy in proposal fusion. Experimental results on the KITTI dataset demonstrate that RMF‐ED achieves performance comparable to or exceeding state‐of‐the‐art fusion algorithms, with a computational time of only 21 ms. These features make RMF‐ED an efficient and versatile solution for real‐time applications in low‐light environments.

Understanding the mechanics of blood flow is necessary for developing insights into mechanisms of physiology and vascular diseases in microcirculation. Given the limitations of technologies available for assessing in vivo flow fields, in vitro methods based on traditional microfluidic platforms have been developed to mimic physiological conditions. However, existing methods lack the capability to provide accurate assessment of these flow fields, particularly in vessels with complex geometries. Conventional approaches to quantify flow fields rely either on analyzing only visual images or on enforcing underlying physics without considering visualization data, which could compromise accuracy of predictions. Here, we present artificial-intelligence velocimetry (AIV) to quantify velocity and stress fields of blood flow by integrating the imaging data with underlying physics using physics-informed neural networks.We demonstrate the capability of AIV by quantifying hemodynamics in microchannels designed to mimic saccular-shaped microaneurysms (microaneurysm-on-a-chip, or MAOAC), which signify common manifestations of diabetic retinopathy, a leading cause of vision loss from blood-vessel damage in the retina in diabetic patients. We show that AIV can, without any a priori knowledge of the inlet and outlet boundary conditions, infer the two-dimensional (2D) flow fields from a sequence of 2D images of blood flow in MAOAC, but also can infer three-dimensional (3D) flow fields using only 2D images, thanks to the encoded physics laws. AIV provides a unique paradigm that seamlessly integrates images, experimental data, and underlying physics using neural networks to automatically analyze experimental data and infer key hemodynamic indicators that assess vascular injury.