To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure no-reply@cambridge.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
This final chapter is a short introduction to pattern-forming systems, which highlights a few concepts and models rather than pretending to give a general overview (which is impossible in 40 pages). We focus on stationary bifurcations, distinguishing between scenarios where the critical wavevector vanishes and where it is a finite value, because they have different nonlinear behaviors. A few pages are devoted to describe some different experimental setups: thermal convection (a fluid heated from below, showing the rising of convection cells); unstable growth process (under particle deposition, with the formation of mounds); and a rotating mixture of granular systems (with their phase separation).
This chapter essentially faces the following question: If at equilibrium a system has a phase transition between a disordered phase and an ordered phase, how does it relax to equilibrium if it is quenched from the former to the latter phase? Quenching means that an external parameter, typically the temperature, is suddenly changed. The answer depends on some relevant factors: if dynamics conserves or not the order parameter; if the order parameter is a scalar or a vector; if long-range interactions are present or not. We devote special attention to the short-range Ising model, but we also consider nonscalar systems. If the order parameter is conserved, its value before quenching is also an important parameter, allowing to distinguish between two different trigger mechanisms of the relaxation process: spinodal decomposition and thermally activated nucleation.
Turbulent flows over rough beds with macroroughness elements of low relative submergence are characteristic of natural river systems. These flows exhibit highly three-dimensional structures, including large-scale coherent patterns, complex nonlinear interactions and significant drag induced by immobile boulders. In this study, large-eddy simulations are conducted of the flow through an array of boulders on a rough bed, based on experiments by Papanicolaou et al. (2012) Acta Geophys.60 (6), 1502–1546. The analysis includes the instantaneous flow dynamics, the parameterisation of hydrodynamic roughness on the averaged velocity profile and the application of the double-averaged methodology. These upscaling approaches reveal the combined influence of wake turbulence and secondary currents (SCs), and provide insights into momentum and energy conservation mechanisms, which are critical for transport processes in fluvial environments. Results indicate that the boulder array reduces total fluid stress at the rough bed surface to $0.5 \rho u_*^2$, which can have important implications for sediment transport. Form-induced stresses, primarily originating in the boulder wakes, reach up to 37 % of total fluid stress, with peak values comparable to turbulent stresses at mid-boulder elevation. Form-induced kinetic energy (DKE) is shown to have the same magnitude as the turbulent kinetic energy (TKE), highlighting energy transfers from mean flow drag to DKE, then to TKE, before final dissipation. This study underscores the critical role of macroroughness in stress distribution, and the importance of the joint action of SCs and wake turbulence in driving form-induced stresses, which partially counterbalance drag dissipation.
Capturing the stories of sixteen women who made significant contributions to the development of quantum physics, this anthology highlights how, from the very beginning, women played a notable role in shaping one of the most fascinating and profound scientific fields of our time. Rigorously researched and written by historians, scientists, and philosophers of science, the findings in this interdisciplinary book transform traditional physics historiography. Entirely new sources are included alongside established sources that are examined from a fresh perspective. These concise biographies serve as a valuable counterweight to the prevailing narrative of male genius, and demonstrate that in the history of quantum physics, women of all backgrounds have been essential contributors all along. Accessible and engaging, this book is relevant for a wide audience including historians, scientists and science educators, gender theorists and sociologists.
Magnetic AB stars are known to produce periodic radio pulses by the electron cyclotron maser emission (ECME) mechanism. Only 19 such stars, known as ‘Main-sequence Radio Pulse emitters’ (MRPs), are currently known. The majority of MRPs have been discovered through targeted observation campaigns that involve carefully selecting a sample of stars that are likely to produce ECME and which can be detected by a given telescope within reasonable amount of time. These selection criteria inadvertently introduce bias in the resulting sample of MRPs, which affects subsequent investigation of the relation between ECME properties and stellar magnetospheric parameters. The alternative is to use all-sky surveys. Until now, MRP candidates obtained from surveys were identified based on their high circular polarisation ($\gtrsim 30\%$). In this paper, we introduce a complementary strategy, which does not require polarisation information. Using multi-epoch data from the Australian SKA Pathfinder (ASKAP) telescope, we identify four MRP candidates based on the variability in the total intensity light curves. Follow-up observations with the Australia Telescope Compact Array (ATCA) confirm three of them to be MRPs, thereby demonstrating the effectiveness of our strategy. With the expanded sample, we find that ECME is affected by temperature and the magnetic field strength, consistent with past results. There is, however, a degeneracy regarding how the two parameters govern the ECME luminosity for magnetic A and late-B stars (effective temperature $\lesssim 16$ kK). The current sample is also inadequate to investigate the role of stellar rotation, which has been shown to play a key role in driving incoherent radio emission.
This work introduces GalProTE, a proof-of-concept Machine Learning model, leveraging Transformer Encoder architecture to efficiently determine the stellar age, metallicity, and dust attenuation of galaxies from optical spectra. Designed to address the challenges posed by the vast datasets produced by modern astronomical surveys, GalProTE offers a significant improvement in processing speed while maintaining accuracy. Using the E-MILES spectral library, we generate a dataset of 111936 diverse templates by expanding the original 636 simple stellar population models with varying extinction levels, combinations of multiple spectra, and noise modifications. This ensures robust training over the spectral range of 4750–7100 Å at a resolution of 2.5 Å. GalProTE architecture employs four parallel attention-based encoders with varying kernel sizes to capture diverse spectral features. The model demonstrates a mean squared error (MSE) of 0.27% with a standard deviation of 0.10% between the input spectra and the GalProTE-generated spectra for the synthetic test dataset. Performance evaluation against real data from two galaxies in the PHANGS-MUSE survey (NGC4254 and NGC5068) demonstrates its ability to extract physical parameters efficiently, with spectral fit residuals showing a mean of -0.02% and 0.28%, and standard deviations of 4.3% and 5.3%, respectively. To contextualize these results, we compare age, metallicity and dust attenuation maps generated by GalProTE with those of pPXF, a state-of-the-art spectral fitting tool. While pPXF achieves robust results, it requires approximately 11 sec per spectrum. In contrast, GalProTE processes a spectrum in less than 4 ms – a speedup factor exceeding 2750, while also consuming 68 times less power per spectrum. The comparison with pPXF maps from PHANGS-MUSE underscores GalProTE’s capacity to enhance traditional methods through machine learning, paving the way for faster, more energy-efficient, and more comprehensive analyses of galactic properties. This study demonstrates the potential of GalProTE as an efficient, scalable, and sustainable solution for processing large astronomical surveys.
We present Evolutionary Map of the Universe Search Engine (EMUSE), a tool designed for searching specific radio sources within the extensive datasets of the Evolutionary Map of the Universe (EMU) survey, with potential applications to other Big Data challenges in astronomy. Built on a multimodal approach to radio source classification and retrieval, EMUSE fine-tunes the OpenCLIP model on curated radio galaxy datasets. Leveraging the power of foundation models, our work integrates visual and textual embeddings to enable efficient and flexible searches within large radio astronomical datasets. We fine-tune OpenCLIP using a dataset of 2 900 radio galaxies, encompassing various morphological classes, including FR-I, FR-II, FR-x, R-type, and other rare and peculiar sources. The model is optimised using adapter-based fine-tuning, ensuring computational efficiency while capturing the unique characteristics of radio sources. The fine-tuned model is then deployed in the EMUSE, allowing for seamless image and text-based queries over the EMU survey dataset. Our results demonstrate the model’s effectiveness in retrieving and classifying radio sources, particularly in recognising distinct morphological features. However, challenges remain in identifying rare or previously unseen radio sources, highlighting the need for expanded datasets and continuous refinement. This study showcases the potential of multimodal machine learning in radio astronomy, paving the way for more scalable and accurate search tools in the field. The search engine is accessible at https://askap-emuse.streamlit.app/ and can be used locally by cloning the repository at https://github.com/Nikhel1/EMUSE.
We extend the perceived velocity gradient defined by a group of particles that was previously used to investigate the Lagrangian statistics of fluid turbulence to the study of inertial particle dynamics. Using data from direct numerical simulations, we observe the correlation between the strong compression in the particle phase and the instantaneous local fluid compression. Furthermore, the Lagrangian nature of the particle velocity gradient defined in this way allows an investigation of its evolution along particle trajectories, including the process after the caustic event, or the blow-up of the particle velocity gradient. Observations reveal that, for particles with Stokes number in the range $St \lesssim 1$, inertial particles experience the maximum compression by local fluid before the caustic event. Interestingly, data analyses show that, while the post-caustic process is mainly the relaxation of the particle motion and the particle relaxation time is the relevant time scale for the dynamics, the pre-caustic dynamics is controlled by the fluid–particle interaction and the proper time scale is determined by both the Kolmogorov time and the particle relaxation time.
Coherent beam combining (CBC) of laser arrays is increasingly attracting attention for generating free-space structured light, unlocking greater potential in aspects such as power scaling, editing flexibility and high-quality light field creation. However, achieving stable phase locking in a CBC system with massive laser channels still remains a great challenge, especially in the presence of heavy phase noise. Here, we propose an efficient phase-locking method for a laser array with more than 1000 channels by leveraging a deep convolutional neural network for the first time. The key insight is that, by elegantly designing the generation strategy of training samples, the learning burden can be dramatically relieved from the structured data, which enables accurate prediction of the phase distribution. We demonstrate our method in a simulated tiled aperture CBC system with dynamic phase noise and extend it to simultaneously generate orbital angular momentum (OAM) beams with a substantial number of OAM modes.
Many mission-critical systems today have stringent timing requirements. Especially for cyber-physical systems (CPS) that directly interact with real-world entities, violating correct timing may cause accidents, damage or endanger life, property or the environment. To ensure the timely execution of time-sensitive software, a suitable system architecture is essential. This paper proposes a novel conceptual system architecture based on well-established technologies, including transition systems, process algebras, Petri Nets and time-triggered communications (TTC). This architecture for time-sensitive software execution is described as a conceptual model backed by an extensive list of references and opens up several additional research topics. This paper focuses on the conceptual level and defers implementation issues to further research and subsequent publications.
This research investigates the spanwise oscillation patterns of turbulent non-premixed flames in a tandem configuration, using both experimental methods and large eddy simulations under cross-airflow conditions. Based on the heat release rate (17.43–34.86 kW) and the burner size (0.15 $\times$ 0.15 m), the flame behaves like both a buoyancy-controlled fire (such as a pool fire) and, due to cross-wind effects, a forced flow-controlled fire. The underlying fire dynamics was modelled by varying the spacing between the square diffusion burners, cross-wind velocity and heat release rate. Two flapping modes, the oscillating and bifurcating modes, were observed in the wake of the downstream diffusion flame. This behaviour depends on the wake of the upstream diffusion flame. As the backflow of the upstream flame moved downstream, the maximum flame width of the downstream flame became broader. The flapping amplitude decreased with a stronger cross-wind. Furthermore, the computational fluid dynamics simulation was performed by FireFOAM based on OpenFOAM v2006 2020 to investigate the flapping mechanism. The simulation captured both modes well. Disagreement of the flapping period on the left and right sides results in the oscillating mode, while an agreement of the flapping period results in the bifurcating mode. Finally, the scaling law expressed the dimensionless maximum flame width with the proposed set of basic dimensional parameters, following observations and interpretation by simulations. The results help prevent the potential hazards of this type of basic fire scenario and are fundamentally significant for studying wind-induced multiple fires.
The rupture of a liquid film, where a thin liquid layer between two other fluids breaks and forms holes, commonly occurs in both natural phenomena and industrial applications. The post-rupture dynamics, from initial hole formation to the complete collapse of the film, are crucial because they govern droplet formation, which plays a significant role in many applications such as disease transmission, aerosol formation, spray drying nanodrugs, oil spill remediation, inkjet printing and spray coating. While single-hole rupture has been extensively studied, the dynamics of multiple-hole ruptures, especially the interactions between neighbouring holes, are less well understood. Here, this study reveals that when two holes ‘meet’ on a curved film, the film evolves into a spinning twisted ribbon before breaking into droplets, distinctly different from what occurs on flat films. We explain the formation and evolution of the spinning twisted ribbon, including its geometry, orbits, corrugations and ligaments, and compare the experimental observations with models. We compare and contrast this phenomena with its counterpart on planar films. While our experiments are based on the multiple-hole ruptures in corona splash, the underlying principles are likely applicable to other systems. This study sheds light on understanding and controlling droplet formation in multiple-hole rupture, improving public health, climate science and various industrial applications.