A rotating detonation combustor exhibits corotating $N$-wave modes with $N$ detonation waves propagating in the same direction. These modes and their responses to ignition conditions and disturbances were studied using a surrogate model. Through numerical continuation, a mode curve (MC) is obtained, depicting the relationship between the wave speed of the one-wave mode and a defined baseline of the combustor circumference ($L_{{base}}$) under fixed equation parameters, limited by deflagration and flow choking. The modes’ existence is confirmed by the equivalence between a one-wave mode within a combustor with circumference $L_{{base}}$/$N$ on the MC and an $N$-wave mode in an $L_{{base}}$ combustor. The stability, measured by the real part of the eigenvalue from linear stability analysis (LSA), revealed the dynamic properties. When multiple stable modes exist under the same parameters, ignition conditions with a spatial period of $L_{{base}}$/$N$ are more likely to form $N$-wave modes. An unstable evolution in formed modes, occurs in the dynamics from stable to unstable modes through saddle-node bifurcation and Hopf bifurcation induced by parameter perturbations and from unstable to stable modes induced by state disturbances. Eigenmodes from LSA reveal mechanisms of the unstable evolution, including the effect of secondary deflagration in the unstable one-wave mode and competitive interaction between detonation waves in the unstable multiwave mode, crucial for the combustor to mode transition.

We in this paper employ a penalized moment selection procedure to identify valid and relevant moments for estimating and testing forecast rationality within the flexible loss framework proposed by Elliott et al. (2005). We motivate the selection of moments in a high-dimensional setting, outlining the fundamental mechanism of the penalized moment selection procedure and demonstrating its implementation in the context of forecast rationality, particularly in the presence of potentially invalid moment conditions. The selection consistency and asymptotic normality are established under conditions specifically tailored to economic forecasting. Through a series of Monte Carlo simulations, we evaluate the finite sample performance of penalized moment estimation in utilizing available instrument information effectively within both estimation and testing procedures. Additionally, we present an empirical analysis using data from the Survey of Professional Forecasters issued by the Federal Reserve Bank of Philadelphia to illustrate the practical utility of the suggested methodology. The results indicate that the proposed post-selection estimator for forecaster’s attitude performs comparably to the oracle estimator by efficiently incorporating available information. The power of rationality and symmetry tests leveraging penalized moment estimation is substantially enhanced by minimizing the impact of uninformative instruments. For practitioners assessing the rationality of externally generated forecasts, such as those in the Greenbook, the proposed penalized moment selection procedure could offer a robust approach to achieve more efficient estimation outcomes.

The successful colonization of invasive plants (IPs) may be facilitated by their nutrient release during decomposition, which alters soil physicochemical properties, enzyme activities, microbial metabolic processes and the diversity of soil microorganisms. This study aimed to examine the effects of co-decomposition of four Asteraceae IPs (Conyza canadensis, Conyza sumatrensis, Erigeron annuus and Solidago canadensis) along a gradient of invasion and a native plant (Pterocypsela laciniata) on decomposition rate, soil physicochemical properties, soil enzyme activities and the diversity of soil bacterial communities (SBCs). Leaves of C. canadensis with heavy invasion and S. canadensis with light and heavy invasion decomposed more slowly than P. laciniata. Leaves of C. canadensis with full invasion decomposed more rapidly than P. laciniata. Pterocypsela laciniata and C. sumatrensis had synergistic effects on each other’s decomposition, whereas P. laciniata and S. canadensis displayed an antagonistic effect. Decomposition of the four IPs increased soil microbial carbon content but reduced soil fluorescein diacetate (FDA) hydrolase activity compared to P. laciniata. Thus, invasion degree and species identity of IPs modulate the effects of the four IPs on the decomposition rate, mixed-effect intensity of co-decomposition, soil microbial carbon content, soil FDA hydrolase activity and SBC structure.

An experimental study was conducted to investigate the impingement of a vortex ring onto a porous wall by laser-induced fluorescence and particle image velocimetry. The effects of different Reynolds numbers (${{Re}}_{\it\Gamma } = 700$ and $1800$) and hole diameters ($d_{h}^{*} = 0.067$, $0.10$, $0.133$ and $0.20$) on the flow characteristics were examined at a constant porosity ($\phi = 0.75$). To characterise fluid transport through a porous wall, we recall the model proposed by Naaktgeboren, Krueger & Lage (2012, J. Fluid Mech., vol. 707, 260–286), which shows rough agreement with the experimental results due to the absence of vortex ring characteristics. This highlights the need for a more accurate model to correlate the losses in kinetic energy ($\Delta E^{*}$) and impulse ($\Delta I^{*}$) resulting from the vortex ring–porous wall interaction. Starting from Lamb’s vortex ring model and considering the flow transition from the upstream laminar state to the downstream turbulent state caused by the porous wall disturbance, a new model is derived theoretically: $\Delta E^{*} = 1 - k(1 - \Delta I^{*})^2$, where $k$ is a parameter dependent on the dimensionless core radius $\varepsilon$, with $k = 1$ when no flow state change occurs. This new model effectively correlates $\Delta E^{*}$ and $\Delta I^{*}$ across more than 70 cases from current and previous experiments, capturing the dominant flow physics of the vortex ring–porous wall interaction.

In this work, we conduct particle-resolved direct numerical simulations to investigate the influence of particle inertia on the settling velocity of finite-size particles at low volume fraction in homogeneous isotropic turbulence across various settling numbers. Our results for finite-size particles show only reductions of settling velocity in turbulence compared to the corresponding laminar case. Although increased particle inertia significantly reduces the lateral motion of particles and fluctuations in settling velocity, its effect on the mean settling velocity is not pronounced, except when the settling effect is strong, where increased particle inertia leads to a noticeable reduction. Mechanistically, the nonlinear drag effect, which emphasises contributions from large turbulent scales, cannot fully account for the reduction in settling velocity. The influence of small-scale turbulence, particularly through interactions with the particle boundary layer, should not be overlooked. We also analyse the dependency of turbulence’s modification on particle settling velocity within a broader parameter space, encompassing both sub-Kolmogorov point particles and finite-size particles. Additionally, we develop a qualitative model to predict whether turbulence enhances or retards the settling velocity of particles.

This study investigates the formation and evolution of fishbone patterns in oblique impinging liquid microjets through high-speed imaging experiments and numerical simulations. The results identify periodic oscillations in the upper region of the liquid sheet as the primary mechanism driving fishbone instabilities, which induce rim disturbances and lead to bifurcations into diverse fishbone morphologies. Transitions between stable and unstable flow patterns are systematically mapped across varying Weber numbers and impingement angles, providing a comprehensive framework for understanding this interfacial dynamics. Two critical transitions – marking the onset and disappearance of fishbone patterns – are characterised, offering insights into the underlying physics governing the stability and instability of these flow structures.

This study investigates the fluid mechanisms underlying the interaction between ventilated shoulder and tail cavities under vertical launching conditions. It is found that expansion and contraction coexist within the tail cavity. When the expansion rate exceeds the contraction rate, the volume of the tail cavity increases; conversely, it decreases. Through this process, the cavity undergoes cyclic pulsation during its vertical evolution, including expansion, over-expansion, contraction and over-contraction. Before the shoulder cavity extends to the position of the tail cavity, wall confinement restricts the tail cavity from expanding towards the vehicle’s lateral wall. After the encounter between the shoulder and tail cavities, the re-entrant flow at the end of the shoulder cavity induces the tail cavity to overcome wall confinement and expand towards the lateral wall, initiating their fusion. As a result, a supercavity forms and attaches to the surface of the vehicle. Moreover, after the fusion, the pressure driving mode at the vehicle’s bottom wall shifts from the tail cavity pulsation to the re-entrant flow. In addition, an increase in the ventilation rate induces progressive expansion of the shoulder cavity’s radial dimension, and accelerates its downstream propagation. The fusion mode between the shoulder and tail cavities transitions from progressive fusion to coverage fusion.

A dual-band dual-polarized wearable antenna that applies to two different operating modes of wireless body area networks is proposed in this letter. The antenna radiates simultaneously in the ISM band at 2.45 and 5.8 GHz. It consists of a rigid button-like radiator and a flexible fabric radiator. At 2.45 GHz, an omnidirectional circularly polarized pattern is radiated by the flexible radiator, which is suitable for the on-body communication. At the same time, a linearly polarized broadside pattern for off-body communication is generated by button radiator at 5.8 GHz. The antenna has been validated in free space and human body environments. The impedance bandwidth at 2.45 and 5.8 GHz are 5% and 35%, and the gain is measured to be 0.15 and 5.95 dBi, respectively. Furthermore, the specific absorption rates are simulated. At 2.45 and 5.8 GHz, the results averaged over 1 g of body tissue are 0.128 and 0.055 W/kg. The maximum value at both bands is below the IEEE C95.3 standard of 1.6 W/kg.

Over-expansion flow can generate asymmetric shock wave interactions, which lead to significant lateral forces on a nozzle. However, there is still a lack of a suitable theory to explain the phenomenon of asymmetry. The current work carefully investigates the configurations of shock wave interactions in a planar nozzle, and proposes a theoretical method to analyse the asymmetry of over-expansion flows. First, various possible flow patterns of over-expansion flows are discussed, including regular and Mach reflections. Second, the free interaction theory and the minimum entropy production principle are used to analyse the boundary layer flow and main shock wave interactions, establish the relationship between the separation shock strength and separation position, and predict asymmetric configurations. Finally, experiments are conducted to validate the theoretical method, and similar experiments from other studies are discussed to demonstrate the effectiveness of the proposed method. Results demonstrate that the direction of asymmetric over-expansion flow is random, and the separated flow strives to adopt a pattern with minimal total pressure loss. Asymmetric interaction is a mechanism through which the flow can achieve a more efficient thermodynamic balance by minimising entropy production.

Automatic visual localization of electric vehicle (EV) charging ports presents significant challenges in uncertain environments, such as varying surface textures, reflections, lighting and observation distance. Existing methods require extensive real-world training data and well-focused images to achieve robust and accurate localization. However, both requirements are difficult to meet under variable and unpredictable conditions. This paper proposes a 2-stage vision-based localization approach. Firstly, the image synthesis technique is used to reduce the cost of real-world data collection. A task-oriented parameterization protocol (TOPP) is proposed to optimize the quality of the synthetic images. Secondly, an autofocus and servoing strategy is proposed. A hybrid detector is employed to enhance sharpness assessment performance, while a visual servoing method based on single exponential smoothing (SES) is developed to enhance stability and efficiency during the search process. Experiments were conducted to evaluate image synthesis efficiency, detection accuracy, and servoing performance. The proposed method achieved 99% detection accuracy on the real-world port images, and guided the robot to the optimal imaging position within 16 s, outperforming comparable approaches. These results highlight its potential for robust automated charging in real-world scenarios.