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The transient dynamics of a wake vortex, modelled as a strong swirling $q$-vortex, is investigated with a focus on optimal transient growth driven by continuous eigenmodes associated with continuous spectra. The pivotal contribution of viscous critical-layer eigenmodes (Lee and Marcus, J. Fluid Mech. vol. 967, 2023, p. A2) amongst the entire eigenmode families to optimal perturbations is numerically confirmed, using a spectral collocation method for a radially unbounded domain that ensures correct analyticity and far-field behaviour. The consistency of the numerical method across different sensitivity tests supports the reliability of the results and provides flexibility for tuning. Both axisymmetric and helical perturbations with axial wavenumbers of order unity or less are examined through linearised theory and nonlinear simulations, yielding results that align with existing literature on energy growth curves and optimal perturbation structures. The initiation process of transient growth is also explored, highlighting its practical relevance. Inspired by ice crystals in contrails, the backward influence of inertial particles on the vortex flow, particularly through particle drag, is emphasised. In the pursuit of optimal transient growth, particles are initially distributed at the periphery of the vortex core to disturb the flow. Two-way coupled vortex–particle simulations reveal clear evidence of optimal transient growth during ongoing vortex–particle interactions, reinforcing the robustness and significance of transient growth in the original nonlinear vortex system over finite time periods.
The ‘overview effect’ was described by astronauts who saw the earth from space and found this gave them a very different perspective. This effect is a shift in worldview, and it has been suggested that politicians be sent to space to change their narrow perspectives. In a similar vein, it is crucial that psychiatrists have an overview of their patients so that their perspectives on patient care enable them to deal with the patient from different angles. In this editorial, the overview effect is described in the context of clinical care.
This article explores recent developments in English language education in Taiwan, situating them within broader sociopolitical shifts and demographic changes. It begins by outlining the emergence of English in Taiwan’s education system before presenting the formulation and objectives of the Bilingual 2030 policy. The article then analyzes how this national initiative has reshaped English language education across educational levels. In particular, it highlights the expansion of English–medium instruction (EMI) in higher education as a central feature of Taiwan’s bilingualization agenda. Finally, it discusses two key developments influenced by the policy: the internationalization of higher education as a response to demographic and policy pressures, and the resulting expansion of EMI courses as a central strategy for attracting global talent and sustaining university enrollment.
We study the singularities of varieties obtained as infinitesimal quotients by $1$-foliations in positive characteristic. (1) We show that quotients by (log) canonical $1$-foliations preserve the (log) singularities of the MMP. (2) We prove that quotients by multiplicative derivations preserve many properties, amongst which most F-singularities. (3) We formulate a notion of families of $1$-foliations, and investigate the corresponding families of quotients.
A path being planned for an unmanned aerial vehicle (UAV) or its armed conformation called the unmanned combat aerial vehicle (UCAV) has a critical importance on the flight safety and success of the task including reconnaissance, surveillance, monitoring or destroying. The Back-and-Forth (BaF) algorithm is one of the most recent greedy techniques that executes a heuristic approach for generating two backbone candidates and a combination procedure for bringing advantageous segments of them in order to solve the geometric description of the path planning problem. This study was devoted to a thread-based parallel implementation of the BaF algorithm, also named the multi-threaded BaF (tBaF for short). The threads of the tBaF algorithm increase their search bounds gradually according to the assigned thread indexes and execute the heuristic approach and combination procedure of the BaF for calculating paths. A set of detailed experiments was carried out with the aim of evaluating the performance of the tBaF, and its results were compared with the BaF and 14 other meta-heuristic-based path planners over three battlefield scenarios and their 12 test cases containing the preidentified enemy threats. Comparative studies showed that the different local and global search capabilities of the threads gained with the newly introduced thread-based organisation give a significant contribution to the path planning performance and allow the tBaF to be ranked among the top three planners even though it requires at least from four to eight times less function calls than the tested meta-heuristics.
Supersonic free jets are extensively employed across a range of applications, especially in high-tech industries such as semiconductor processing and aerospace propulsion. Due to the difficulties involved in flow measurement, previous research on supersonic free jets has primarily focused on investigating near-field shockwave structures, with quantitative experimental analysis of the far-field zone being relatively scarce. However, physical understanding of the far-field flow, particularly post-shockwave energy dissipation, holds significant importance for the application and utilisation of these jets in vacuum environments. Therefore, this study aims to provide a robust experimental foundation for a rarefied supersonic free jet through the analysis of the flow field in both the near- and far-field zones. Nanometre-sized tracer particles and molecules were utilised to measure the rarefied supersonic jet flow field using particle image velocimetry and acetone molecular tagging velocimetry, respectively. The experiments revealed that in rarefied conditions, the supersonic jet exhibits a one-barrel shockwave structure in the near field, and after passing the Mach disk, a long annular viscous layer develops downstream. Experimental data on the jet velocity profile and width demonstrated a transition to a laminar flow regime in the far-field zone. This transition aligns with the theoretically inferred flow regimes based on the complex Reynolds number. The velocity profile and potential core length of the laminar flow regime could be modelled using a bi-modal distribution, which represents the summation of symmetric Gaussian distributions.
Paternity leave may promote greater gender equality in domestic labour. Though numerous studies show that paternity leave promotes greater fathers’ involvement in childcare, less is known about whether paternity leave-taking may facilitate fathers’ involvement in other forms of domestic labour such as housework. Using repeated cross-sectional data on different-gender partnered US parents from the Study on Parents’ Divisions of Labor During COVID-19 (SPDLC), this study examines the extent to which paternity leave-taking and length of paternity leave are associated with US fathers’ shares of, and time spent on, housework. Findings suggest that paternity leave-taking is positively associated with fathers’ shares of, and time spent on, housework tasks. Longer paternity leaves are also associated with fathers performing greater shares of housework. Overall, this study indicates that the benefits of paternity leave likely extend to fathers’ greater participation in housework, providing additional support for the belief that increased use of paternity leave may help to promote gender equality in domestic labour.
Ventilated cavities in the wake of a two-dimensional bluff body are studied experimentally via time-resolved X-ray densitometry. With a systematic variation of flow velocity and gas injection rate, expressed as Froude number ($\textit{Fr}$) and ventilation coefficient ($C_{qs}$), four cavities with different closure types are identified. A regime map governed by $\textit{Fr}$ and $C_{qs}$ is constructed to estimate flow conditions associated with each cavity closure type. Each closure exhibits a different gas ejection mechanism, which in turn dictates the cavity geometry and the pressure in the cavity. Three-dimensional cavity closure is seen to exist for the supercavities at low $\textit{Fr}$. However, closure is nominally two-dimensional for supercavities at higher $\textit{Fr}$. At low $C_{qs}$, cavity closure is seen to be wake-dominated, while supercavities are seen to have interfacial perturbation near the closure at higher $C_{qs}$, irrespective of $\textit{Fr}$. With the measured gas fraction, a gas balance analysis is performed to quantify the gas ejection rate at the transitional cavity closure during its formation. For a range of $\textit{Fr}$, the transitional cavity closure is seen to be characterised by re-entrant flow, whose intensity depends on the flow inertia, dictating the gas ejection rates. Two different ventilation strategies were employed to systematically investigate the formation and maintenance gas fluxes. The interaction of wake and gas injection is suspected to dominate the cavity formation process and not the maintenance, resulting in ventilation hysteresis. Consequently, the ventilation gas flux required to maintain the supercavity is significantly less than the gas flux required to form the supercavity.
Against the proliferation of large language model (LLM) based Artificial Intelligence (AI) products such as ChatGPT and Gemini, and their increasing use in professional communication training, researchers, including applied linguists, have cautioned that these products (re)produce cultural stereotypes due to their training data. However, there is a limited understanding of how humans navigate the assumptions and biases present in the responses of these LLM-powered systems and the role humans play in perpetuating stereotypes during interactions with LLMs. In this article, we use Sequential-Categorial Analysis, which combines Conversation Analysis and Membership Categorization Analysis, to analyze simulated interactions between a human physiotherapist and three LLM-powered chatbot patients of Chinese, Australian, and Indian cultural backgrounds. Coupled with analysis of information elicited from LLM chatbots and the human physiotherapist after each interaction, we demonstrate that users of LLM-powered systems are highly susceptible to becoming interactionally entrenched in culturally essentialized narratives. We use the concepts of interactional instinct and interactional entrenchment to argue that whilst human–AI interaction may be instinctively prosocial, LLM users need to develop Critical Interactional Competence for human–AI interaction through appropriate and targeted training and intervention, especially when LLM-powered tools are used in professional communication training programs.