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Active colloidal particles create flow around them due to non-equilibrium processes on their surfaces. In this paper, we infer the activity of such colloidal particles from the flow field created by them via deep learning. We first explain our method for one active particle, inferring the $2s$ mode (or the stresslet) and the $3t$ mode (or the source dipole) from the flow field data, along with the position and orientation of the particle. We then apply the method to a system of many active particles. We find excellent agreements between the predictions and the true values of activity. Our method presents a principled way to predict arbitrary activity from the flow field created by active particles.
We experimentally investigate the rotational dynamics of neutrally buoyant flat bodies of revolution (spheroids, disks and rings with different cross-sectional shapes) in shear flows. In the Stokes regime, the axis of revolution of these rigid particles moves in one of a family of closed periodic Jeffery orbits. Inertia is able to lift the orbit degeneracy and induces drift among several rotations towards limiting stable orbits. Furthermore, permanent alignment can be achieved for disks and rings with triangular cross-sectional shapes, provided the inertia is sufficiently high. The bifurcations between the different dynamics are compared with those predicted by small-inertia asymptotic theories and numerical simulations.
Biodesign is an emerging field integrating design and science; its rise necessitates a reassessment of educational paths and working spaces for cross-disciplinary explorations, such as working with living materials and adhering to safety standards. The article examines laboratory environments dedicated to biodesign practice and education, varying from low-tech to high-tech setups and from university to community spaces, aiming to clarify the role of workspaces and infrastructures in supporting transdisciplinary research between design and science.
We surveyed Biodesign Laboratories worldwide, addressing the current status quo of various lab configurations and their unique spatial typologies to accommodate biodesign’s hybrid nature.
The result is an overview of the socio-technical topos of the laboratory as a literal breeding ground for (future) biodesigners. The qualitative data reported in this article aim to enhance the understanding of Biodesign Labs by analysing the potential of various laboratory configurations to accommodate biodesign’s hybrid nature, potentially developing unique spatial typologies.
Fingering instabilities readily occur if a less viscous fluid displaces a more viscous fluid in a narrow gap due to the action of destabilising viscous forces. If the fluids are miscible, the instability can be suppressed in the limit of large advection as complicated flow structures are formed across the gap. Using a fluid to displace a monolayer of non-colloidal particles suspended in the same fluid, Luo et al. (2025 J. Fluid Mech. vol. 1011, A48) suppress the formation of the cross-gap structures and identify a new fingering mechanism which instead relies on long-range dipolar disturbance flows generated by the particle confinement.
This article presents a microstrip phase shifter whose frequency-dependent phase response is designed to present the desired phase variation as a useful device for frequency-controlled antenna array systems. The architecture consists of the parallel connection of open-stubs on a main transmission line. The analytical model of the device is presented, its transfer function is derived and compared with a conventional transmission line. The theoretical results show that the phase and amplitude responses can be designed by selecting the number, the length, and the characteristic impedance of the open-stubs. In order to validate the frequency controlled phase shifter model an architecture is proposed, that consists of a three-port device based on a power divider with a phase shifter on one of the output ports and a conventional transmission line on the other. A prototype of this architecture has been manufactured to operate in a frequency range of 2.8 GHz to 3.4 GHz. The magnitude and phase measurements of the scattering parameters show good agreement with the theoretical predictions.
The multi-UAV task allocation problem can be divided into two components: optimising UAV resource allocation and developing an optimal execution plan. Existing single-population algorithms often get trapped in local optima and require improved accuracy. Although multi-population algorithms perform better, they introduce higher complexity, significantly increasing running time. This paper proposes a Two-Stage Multi-Population Wolf Pack Algorithm (2SMPWPA) to address these issues. This algorithm innovatively splits the task allocation problem into two stages: the initial stage focuses on optimising UAV resource utilisation. In contrast, the subsequent stage focuses on optimising the execution plans for the existing UAV resources. Furthermore, the algorithm categorises the population into a leader group and two normal groups, where the leader group consists of elite individuals from the ordinary groups. To ensure the outstanding individuals in the normal groups have adequate computational resources, a population competition mechanism is introduced to dynamically adjust the size of each sub-population based on their average contribution to the optimal solution. To prevent the ‘big eats small’ scenario, the algorithm incorporates population protection and migration mechanisms to maintain diversity. Additionally, a population communication mechanism is implemented to preserve ‘vitality’ during the later iterations, preventing the algorithm from converging to local optima. Comparative experiments demonstrate that the 2SMPWPA significantly outperforms recent algorithms regarding solution accuracy, effectively addressing the trade-off between solution precision and running time.
Dynamics of a spherical particle and the suspending low-Reynolds-number fluid confined between two concentric spherical walls were studied numerically. We calculated the particle’s hydrodynamic mobilities at various locations in the confined space. It was observed that the mobility is largest near the middle of confined space along the radial direction, and decays as the particle becomes closer to no-slip walls. At a certain confinement level, the maximal mobility occurs near the inner wall. We also calculated the drift velocity of the particle perpendicular to the external force. The magnitude of the drift velocity normalised by the velocity along the external force was found to depend on particle location and the confinement level; it is observed that the maximal drift velocity occurs near the wall. Fluid vortices in the confined space induced by particle motion were observed and analysed. In addition, we studied particle trajectories in the flow when the walls rotate at constant angular velocities. The externally applied force, rotation-induced flow and centrifugal/centripetal force, and particle–wall interaction lead to various modes of particle motion. This work lays the foundation to understand and manipulate particulate transport in microfluidic applications such as intracellular transport and encapsulation technologies.
This article aims to introduce a novel synthesis optimisation framework based on a performance prediction model for a space propulsion system. The structure of this research is divided into five steps for optimisation. In the first step, the optimisation problem is defined, and the objective functions, design parameters and constraints of the problem are determined. This system consists of five sub-systems including (gas tank, liquid fuel tank, injector, catalytic bed and nozzle). In this optimisation, the objective functions include increasing the specific impulse and reducing the overall mass of the system. Also, the design parameters and limitations of each subsystem are mentioned in the text. The optimisation space is extracted in the second step using the design of experiments (DoE) tool and the Latin hypercube sampling (LHS) method. In the third stage, using the design points obtained from the DoE, the metamodel of the mass of each of the sub-systems and the metamodel of the specific impulse of the whole system are produced by the Kriging method. In the fourth step, the metamodels produced are optimised using the SHERPA algorithm based on the objective functions of the problem. In the fifth step, the results are derived by comparing two objective functions (minimum mass and maximum specific impulse for the entire system) using the Pareto front diagram. Finally, by comparing the optimal results with an existing thruster sample, it shows that the specific impulse has increased by 6% and the total mass of the system has decreased by 15.8%.
Large-scale spanwise motions in shock wave–turbulent boundary-layer interactions over a $ 25^{\circ }$ compression ramp at Mach 2.95 are investigated using large-eddy simulations. Spectral proper orthogonal decomposition (SPOD) identifies coherent structures characterised by low-frequency features and a large-scale spanwise wavelength of $ O(15\delta _{0})$, where $ \delta _{0}$ is the incoming boundary-layer thickness. The dominant frequency is at least one order of magnitude lower than that of the shock motions. These large-scale spanwise structures are excited near the shock foot and are sustained along the separation shock. Global stability analysis (GSA) is then employed to investigate the potential mechanisms driving these structures. The GSA identifies a stationary three-dimensional (3-D) mode at a wavelength of $ 15\delta _{0}$ with a similar perturbation field, particularly near the separation shock. Good agreement is achieved between the leading SPOD mode and the 3-D GSA mode both qualitatively and quantitatively, which indicates that global instability is primarily responsible for the large-scale spanwise structures surrounding the shock. The reconstructed turbulent separation bubble (TSB) using the 3-D global mode manifests as spanwise undulations, which directly induce the spanwise rippling of the separation shock. Furthermore, the coupled TSB motions in the streamwise and spanwise directions are examined. The TSB oscillates in the streamwise direction while simultaneously exhibiting spanwise undulations. The filtered wall-pressure signals indicate the dominant role of the streamwise motions.
Biodesign is an emerging disciplinary field that, in its multifaceted nature, finds in transdisciplinarity a promising pathway to address the complex challenges posed by contemporary scenarios. However, specific methodologies that connect the design mindset with the epistemological framework of scientific methods are still lacking. How can we grow the next generation of biodesigners in this scenario? Transdisciplinary dialog provides a foundation for merging design thinking with scientific reasoning, leading to the development of methodologies and educational strategies aimed at creating shared languages and codes that promote synergy between design and science. This study presents the results of a methodological evolution – from multi and interdisciplinary approaches to transdisciplinary ones – through a workshop focused on material design, a course designed to train future biodesigners. This workshop engaged students in collaborative material tinkering activities, working side by side with scientists in an active laboratory setting. The study demonstrates that combining a material-driven design approach with scientific methodologies fosters iterative dialogical relationships, ultimately enriching and substantiating the final design outcomes.
A highly compact microstrip low-pass filter (LPF) integrated, and meander-line-loaded substrate integrated waveguide (SIW) cavity-backed wideband filtenna with multiple radiation nulls (RN) is presented in this paper. A closed-loop quadrilateral slot is removed from the cavity to generate the first RN in the lower edge of the frequency band. Furthermore, an LPF is integrated with the feedline, which creates another RN at the upper edge of the pass band. The incorporation of the meander-line slot in the radiator and elimination of the C-shaped open loop slot from the bottom of the cavity improves the selectivity of filtenna significantly by generating two more RNs at each side of the pass band. The presented filtenna appears to have low profile and compact structure with wideband response of 17% fractional bandwidth (11–13.1 GHz) and 8.56 dBi peak gain in the pass band. In total, four RNs with more than 15 dB out-of-band rejection level and good lower and upper selectivities of 0.65 and 0.05, respectively, are reported, with close agreement between simulation and measurement. These profound properties make the proposed filtenna suitable for short-range radar and satellite communications, modern Radio Frequency (RF) front-end and wireless communication systems.
Biodesign has grown significantly in the last decade as an approach focused on designing with biological materials, processes and systems. The inherent transdisciplinarity of biodesign enables it to cut across multiple fields. In this work, we look at how biodesign has recently been applied within Human-Computer Interaction (HCI), a disciplinary field that focuses on the design, development and study of interactive technologies. Subsequently, Biological-HCI (Bio-HCI) has emerged as a rapidly growing and evolving area of research at the intersection of biodesign and HCI. To highlight the nascence of Bio-HCI, we examine three of our own Bio-HCI projects – SCOBY Breastplate, B10-PR1NT and $\mu $Me – as case studies that exemplify how biodesign is being explored through specific, situated practices with a variety of interactive technologies. Through these cases, we identify potential themes and opportunities for Bio-HCI as it continues to push current understandings of computational interaction and promote more sustainable technological futures.
This paper explores the role of barodiffusion in the dynamics of gas bubble growth in highly viscous gas-saturated magma subjected to instant decompression. A mathematical model describing the growth of a single isolated bubble is formulated in terms of the modified Rayleigh–Plesset equation coupled with the mass transfer and material balance equations. The model simultaneously takes into account both dynamic and diffusion mechanisms, including the effect of barodiffusion caused by emergence of a large pressure gradient in the liquid, which, in turn, is associated with formation of a diffusion boundary layer around the bubble. An analytical solution of the problem is found, the construction of which is based on the existence of a quasi-stationary state of the bubble growth process. It is shown that barodiffusion manifests itself at the initial and transient stages and under certain conditions can play a paramount role.
This paper presents experimental studies on a novel active high-frequency coaxial injector system designed for enhanced flow mixing and control at extreme flow velocity conditions. The flow dynamics and mixing characteristics of the system operating at 15kHz were captured using planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) techniques and compared against its steady and baseline modes. In pulsed mode, this active injection system delivers a pulsed supersonic actuation air jet at the inner core of the coaxial nozzle that provides large mean and fluctuating velocity profiles in the shear layers of an acetone-seeded fluid stream injected surrounding the core through an annular nozzle. The instantaneous velocity, vorticity and acetone concentration fields of the injector are discussed. The high-frequency streamwise vortices and shockwaves tailored to the mean flow significantly enhanced supersonic flow mixing between the fluids compared to a classical steady coaxial configuration operating at the same input pressure. The paper analyses the dynamic and diffusion characteristics of this active coaxial injection system, which may have potential for supersonic mixing applications.
This article presents a highly integrated 300-GHz frequency-modulated continuous wave radar sensor using a custom-developed dual-function transceiver MMIC. The system can either be configured as a stand-alone ultra-wide-band radar sensor or as a flexible RF front-end, enabling up-conversion and down-conversion of modulated signals to and from the terahertz range. The transceiver MMIC is manufactured using a 90 nm SiGe BiCMOS process, featuring high-speed hetero-junction bipolar transistors with an $f_{\rm{T}}$ of 300 GHz and $f_{\rm{max}}$ of 520 GHz. Using on-chip antennas and a focusing lens, the EIRP of the system for radar operation is greater than 3.2 dBm in a bandwidth of 54 GHz. The full potential of the system’s 90 GHz tuning range is demonstrated in radar measurements. A calibration method is applied to expand the usable tuning range, achieving an extraordinary spatial resolution of 1.97 mm with a frequency sweep from 330 to 240 GHz in 5 ms for a target at a distance of 0.35 m. The potential industrial use of this spatial resolution is demonstrated in a plastic thickness measurement scenario. Additionally a 100 Mbd OKK communication link with a BER of 0.55% is presented using two systems at 0.3 m distance.
Passive wearable devices are widely used for fitness and have also become fashionable. There is increasing interest in adding functionality, such as knee stability, to these compact devices, which are more convenient for daily wear than separate devices like braces or exoskeletons. This study designed and assessed flexion taping passive wearable devices (FTPW). The design emphasized providing adequate flexion moment capacity and controlling varus/valgus movement to prevent knee injuries. In this research, 20 healthy women performed single leg drop (SLD) and step-up (SU) tests with and without muscle fatigue. Knee joint angle, muscle activation, metabolic cost, and blood flow were measured across FTPW, passive wearable devices without flexion taping (PW), and control shorts (Ctrl). In the SLD test after muscle fatigue, FTPW produced a significantly larger knee flexion angle during landing. In the SU test, before and after fatigue, knee varus angle was notably higher with FTPW. Additionally, FTPW showed reduced knee flexor fatigue, indicated by smaller median frequency shifts, and improved blood flow compared to PW. No significant differences in respiratory exchange ratio were detected among the three conditions. Overall, FTPW demonstrated strong potential to enhance knee kinematics, muscle activation, and blood flow, pointing to benefits for both performance improvement and injury prevention. By delivering focused support in a compact format, FTPW may serve as an innovative passive wearable solution that supports daily movement, comfort, and daily activities. This emphasizes the device’s promise as an alternative to bulkier knee aids, merging style and functionality effectively.
Natural fliers and marine swimmers twist and turn their lifting or control surfaces to manipulate the unsteady forces experienced in air and water. The passive deformation of such surfaces has been investigated by several researchers, but the aspect of controlled deformation has received comparatively less attention. In this paper, we experimentally measure the forces and the flow fields of a flat-plate wing (aspect ratio (AR) = 3), translating at a constant Reynolds number (Re) of 10 000, with a dynamically twisting span. We show that the unsteady forces can be dependably estimated by a three-dimensional discrete vortex model. In this model, we account for the leading-edge separation with the help of the leading-edge-suction parameter. Experiments are conducted for two angles of attack (AoAs), $5^\circ$ and $15^\circ$. In addition, two rates of twisting are implemented where part of the leading edge, closer to the tip region, is twisted away from the incoming flow, increasing the effective AoA. The results show that twisting away from the flow augments the lift forces in all cases, although the rate of increase of lift is higher for the highest twist rate. The act of twisting causes an increase in effective AoA beyond the static stall angle in the AoA $=15^\circ$ case. This is highlighted by a distinct dip in the force data following the initial rise after twisting is activated. The increase in effective AoA from the reference case (without twisting) causes separation of the flow below the mid-span. This, in turn, creates higher levels of vorticity in those regions and results in a leading-edge vortex with increased cross-section and strength when compared with the reference case without twisting. Finally, we apply force partitioning and reveal that dynamic twisting leads to a localised increase in vorticity-induced forces along the twisted part of the span, which is approximately twice that of the untwisted case.
Turbulent flows are strongly chaotic and unpredictable, with a Lyapunov exponent that increases with the Reynolds number. Here, we study the chaoticity of the surface quasi-geostrophic system, a two-dimensional model for geophysical flows that displays a direct cascade similar to that of three-dimensional turbulence. Using high-resolution direct numerical simulations, we investigate the dependence of the Lyapunov exponent on the Reynolds number and find an anomalous scaling exponent larger than that predicted by dimensional arguments. We also study the finite-time fluctuation of the Lyapunov exponent by computing the Cramér function associated with its probability distribution. We find that the Cramér function attains a self-similar form at large $\textit{Re}$.
High gain greater than 106 is crucial for the preamplifiers of joule-class high-energy lasers. In this work, we present a specially designed compact amplifier using 0.5%Nd,5%Gd:SrF2 and 0.5%Nd,5%Y:SrF2 crystals. The irregular crystal shape enhances the gain length of the laser beam and helps suppress parasitic oscillations. The amplified spontaneous emission (ASE) induced by the high gain is analyzed through ray tracing. The balance between gain and ASE is estimated via numerical simulation. The gain spectral characteristics of the two-stage two-pass amplifier are examined, demonstrating the advantages of using different crystals, with bandwidths up to 8 nm and gains over 106. In addition, the temperature and stress distributions in the Nd,Gd:SrF2 crystal are simulated. This work is expected to contribute to the development of high-peak-power ($\ge$terawatt-class) high-energy (joule-class) laser devices.
This study presents a numerical investigation of wall-mounted tandem flexible plates with unequal lengths in a laminar boundary layer flow, examining both two-dimensional (2-D) and three-dimensional (3-D) configurations. Key parameters influencing the system include the plate’s bending stiffness ($K$), Reynolds number (${Re}$) and length ratio ($L^*$). Five motion modes are identified: dual collapse (DC), flapping collapse (FC), dual flapping (DF), static flapping (SF) and dual static (DS). A phase diagram in the ($K,L^*$) space is constructed to illustrate their regimes. We focus on DF and SF modes, which significantly amplify oscillations in the downstream plate – critical for energy harvesting. These amplification mechanisms are classified into externally driven and self-induced modes, with the self-induced mechanism, which maximises the downstream plate’s amplitude, being the main focus of our study. A rigid–flexible (RF) configuration is introduced by setting the upstream plate as rigid, showing enhanced performance at high ${Re}$, with oscillation amplitudes up to 100 % larger than the isolated flexible (IF) plate configuration. A relation is developed to explain these results, relating oscillation amplitude to trailing-edge velocity, oscillation frequency and chord length. Force analysis reveals that the RF configuration outperforms both IF and flexible–flexible (FF) configurations. Unlike frequency lock-in, the RF configuration exhibits frequency unlocking, following a $-2/3$ scaling law between the Strouhal number ($St$) and ${Re}$. Results from the 3-D RF configuration confirm that the 2-D model remains applicable, with the self-induced amplification mechanism persisting in 3-D scenarios. These findings enhance understanding of fluid–structure interactions, and offer valuable insights for designing efficient energy harvesting systems.