Applied Physics
Artificial Transmission Line Synthesis Tailored for Traveling-Wave Parametric Processes
M. Malnou
Artificial transmission lines built with lumped-element inductors and capacitors form the backbone of broadband, nearly
quantum-limited traveling-wave parametric amplifiers (TWPAs). When tailoring these transmission lines for parametric processes, nonlinear elements are added, typically nonlinear inductances in superconducting
circuits, and energy and momentum conservation between interacting tones must be enforced through careful design of the ATL dispersion relation. However, a unified theoretical framework describing achievable dispersion relations is lacking. Here, I develop such a framework, borrowing from periodic structure theory and passive network synthesis. These complementary approaches divide the design space: periodic loading synthesis employs spatial modulation of frequency-independent components, while filter synthesis employs frequency-dependent responses in spatially-uniform components. The framework reveals fundamental constraints and enables the discovery of novel TWPA architectures. In particular, I design a kinetic inductance TWPA with a novel phase-matching architecture, and a backward-pumped Josephson TWPA exploiting an ambidextrous i.e., right-left-handed transmission line.
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Biological Physics · Cross-listed from q-bio.TO
Mechanically Regulated Cranial Growth in Infancy: A Computational Approach to Predicting Craniosynostosis
Mahtab Vafaeefar, Conall Quinn and Ted J. Vaughan
In early years of life, the cranium rapidly changes in size and shape to accommodate
brain growth, primarily driven by mechanical stress from
brain expansion. Developmental disorders such as premature fusion of sutures in craniosynostosis, disrupts normal growth process, leading to abnormal skull shapes. Thus, understanding the interplay between biomechanical forces, soft tissues, and individual bone plates is crucial for understanding their role in shaping infant skulls. This study develops a mechanically-driven growth model to simulate healthy cranial growth in the first year. The
algorithm considers simultaneous and coupled growth of
brain, cranial bones, sutures, with volumetric
brain expansion as the primary driver, with strain-based feedback governing growth in bone and suture tissues. A bulk bone formation approach accounts for evolving mechanical properties, with elastic
moduli of bone and sutures increasing monthly. The model was applied on individual fused sutures and skull dysmorphologies due to craniosynostosis were predicted, and results showed good agreement with clinically observations. Stress at bone-suture interfaces and elevated intracranial pressure under fused sutures highlighted biomechanical impacts due to the disorders. Sensitivity analysis explored how material properties and growth rates affect skull shape. This framework enhances understanding of cranial growth and supports treatment planning for craniosynostosis.
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Popular Physics
Wind Power as a Technosignature on M-dwarf Planets
Jacob Haqq-Misra and Mykhaylo Danylov
We suggest that the large-scale deployment of wind turbines on an M-
dwarf planet could produce observable technosignatures. Motivated by observations of hypersonic wind velocities on WASP-127 b, we note that the atmospheres of such
planets could serve as vast reservoirs of energy for an extraterrestrial civilization. A large-scale deployment of wind turbines in a hypersonic environment would produce heated shock waves in the hypersonic stream, cause strong frictional heating from the rotation of the blades, and be a source of infrared radiation. We mention possible scenarios that could lead to the deployment of wind turbines on a gas
giant and also note that similar features could exist on terrestrial M-
dwarf planets. The idea that aerodynamic peculiarities could be a technosignature is worth keeping in mind as ground- and space-based
exoplanet observations continue to improve.
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Chemical Physics
Tuning laser-induced optical breakdown and cavitation through the ionic environment in aqueous media
Junhao Cai, Yuhan Li, Yunqiao Liu et al. (+2 more)
Laser-induced cavitation in
liquids originates from optical breakdown processes that depend sensitively on both
laser-
plasma dynamics and the chemical microenvironment of the solvent. Herein, we experimentally decouple the effects of ionic strength and ion specificity on cavitation inception in aqueous electrolytes spanning neutral, acidic, and alkaline regimes. Using focused nanosecond
laser pulses, we show that increasing ionic strength universally lowers the cavitation threshold by enhancing charge screening and seed-electron availability. However, under constant ionic strength, strongly asymmetric behavior emerges: acidic (hydrogen chloride, HCl) solutions inhibit cavitation, whereas alkaline (sodium hydroxide, NaOH) solutions enhance it. This asymmetry arises from hydrated-electron kinetics that depends on the ion specificity. In acidic solutions, hydronium ions act as
diffusion-limited scavengers of hydrated electrons, quenching their lifetime and inhibiting avalanche ionization. In contrast, hydroxide ions reduce hydronium availability and extend electron survival, promoting more efficient
plasma formation. Despite large discrepancies in breakdown thresholds, electrical conductivity remains nearly constant, demonstrating that microscopic electron chemistry, rather than bulk charge transport, governs cavitation onset. These results establish a mechanism connection between electrolyte chemistry and optical breakdown, showing that ion-specific reaction dynamics fundamentally control
laser-induced cavitation in aqueous environments.
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All authors Junhao Cai, Yuhan Li, Yunqiao Liu, Benlong Wang, Mingbo Li
General Physics
Reply to Hofer-Szabó: the PBR theorem hasn't been saved
Marcoen JTF Cabbolet
Recently, in Found. Phys. 53: 64 (2023), it has been argued that there is no reality to the PBR
theorem. In Found. Phys. 54: 36 (2024), Hofer-Szabó has commented that the argument is flawed and that PBR
theorem remains in tact. Here we reply to Hofer-Szabó by showing that his counterargument does not hold up, concluding that the PBR
theorem has been disproved.
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Geophysics
Three-dimensional inversion of gravity data using implicit neural representations and scientific machine learning
Pankaj K Mishra, Sanni Laaksonen, Jochen Kamm et al. (+1 more)
Inversion of
gravity data is an important method for investigating subsurface density variations relevant to mineral exploration, geothermal assessment, carbon storage, natural hydrogen, groundwater resources, and tectonic
evolution. Here we present a scientific machine-learning approach for three-dimensional
gravity inversion that represents subsurface density as a continuous field using an implicit neural representation (INR). The method trains a deep neural network directly through a physics-based forward-model loss, mapping spatial coordinates to a continuous density field without predefined meshes or discretisation. Spatial encoding enhances the network's capacity to capture sharp contrasts and short-wavelength features that conventional coordinate-based networks tend to oversmooth due to spectral bias. We demonstrate the approach on synthetic examples including smooth models, representing realistic geological complexity, and a dipping block model to assess recovery of structures at different depths. The INR framework reconstructs detailed structure and geologically plausible boundaries without explicit regularisation or depth weighting, while reducing the number of inversion parameters as the problem size grows bigger. These results highlight the potential of implicit representations to enable scalable, flexible, and interpretable large-scale geophysical inversion. This framework could generalise to other geophysical methods and for joint/multiphysics inversion.
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All authors Pankaj K Mishra, Sanni Laaksonen, Jochen Kamm, Anand Singh
Optics
Observation of spatially structured Montgomery effect in free space
Murat Yessenov, Luca Sacchi, Alfonso Palmieri et al. (+3 more)
We report the first direct observation of the spatially structured Montgomery effect, a lensless self-imaging phenomenon that generalizes the Talbot effect to aperiodic structures, unfolding repeated tightly focused spots (~10 $\mu$m) in free space. Using a dynamic optical hologram to discretize radial spatial frequencies, we demonstrate self-imaging at distances ranging from 30 to 100 mm. Our method independently controls the focal spot size and self-imaging period, enabling dynamic three-dimensional light patterns. We also show the arbitrary tunability of the transverse profile by demonstrating revivals of Laguerre-Gaussian, Hermite-Gaussian, Ince-Gaussian modes, and Airy beams. These findings open opportunities for multi-plane microscopy, optical atom traps, and
quantum atomic systems.
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All authors Murat Yessenov, Luca Sacchi, Alfonso Palmieri, Layton A. Hall, Ayman F. Abouraddy, Federico Capasso
Physics and Society
Non-equilibrium phase transition and cultural drift in the continuous-trait Axelrod model
Paulo R. A. Campos, Sandro M. Reia and José F. Fontanari
The standard Axelrod model of cultural dissemination, based on discrete cultural traits, exhibits a non-
equilibrium phase transition but is inherently limited by its inability to continuously probe the critical behavior. We address this limitation by introducing a generalized Axelrod model utilizing continuous cultural traits confined to the interval $[0,1]$, and a similarity threshold, $d$, that serves as a continuous control parameter representing cultural tolerance. This framework allows for a robust analysis of the model's critical properties and its dynamics under cultural drift (copying noise). For the perfect copying scenario, we precisely locate the critical threshold $d_c$, which separates the disordered (fragmented) and ordered (polarized) phases. Through Finite-Size Scaling, we find that the mean domain density vanishes continuously at $d_c$ with the exponent $\beta = 1/3$. Simultaneously, the largest domain fraction displays a surprising discontinuous jump at $d_c$. We find that the finite size effects in the critical region are governed by the exponent $\nu=2$ for both the continuous and discontinuous transitions. Under imperfect copying, persistent noise introduces a powerful selective pressure on the trait space, leading to the emergence of two
symmetry-related attractors at the trait values $d$ and $1-d$. However, these noise-induced attractors prove fragile in the thermodynamic limit, becoming unstable at large
lattice sizes, which directly accounts for the observed failure of the dynamics to freeze under sustained cultural drift. This suggests that in large, continuously evolving societies, true cultural convergence is highly unlikely, leading instead to sustained fragmentation and nonstationary dynamics where cultural domains never fully stabilize.
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Medical Physics
Functional Spectral Imaging by Ultrasound (FSIU): A Spectral-Theoretic Basis for Functional Ultrasound
Cesar Mello Fernando Medina da Cunha
Functional Spectral Imaging (FSI) models image formation as the recovery of tissue surrogates such as density and stiffness from spectral perturbations of a self-adjoint
elliptic operator. Rather than relying on reflectivity or relaxation kinetics, FSI tracks shifts of a truncated set of eigenmodes under controlled excitation, providing a non-ionizing and operator-theoretic route to contrast. Tissue heterogeneity is modeled as a small perturbation of L = -div(D grad) + gamma, with first-order Hadamard formulas linking local contrasts to
eigenvalue shifts. Frechet derivatives and their adjoints yield gradients for variational inversion, stabilized by Tikhonov or total-variation regularization and modal truncation. Finite-element simulations show submillimetric localization (about 0.1-0.3 mm) and milligram-scale detectability (thresholds near 1 mg) under ideal noise. Retaining 10-15 modes preserves about 85 percent of anomaly contrast while suppressing noise. A spectral-
entropy index separates compact from diffuse inclusions and acts as a morphology surrogate. FSI thus provides a mathematically controlled, non-ionizing framework for localized functional imaging, motivating validation in physical phantoms and in vivo studies.
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Plasma Physics
A flexible and differentiable coil proxy for stellarator equilibrium optimization
Lanke Fu, Dario Panici, Elizabeth Paul et al. (+2 more)
Balancing
plasma performance and coil cost is a significant challenge when designing a stellarator power plant. Most current stellarator designs are produced through two-stage optimization: stage-1 for the
equilibrium and stage-2 for a coil design that reproduces its
magnetic configuration. Because few proxies connect both stages, two-stage optimization can produce
plasmas that have high-quality physical properties but overly complex coils. In recent years, single-stage optimization has increasingly been used to optimize the
plasma and coils simultaneously in order to improve the
plasma-coil balance. However, all existing single-stage tools are specialized for filament coils, cannot model coil systems containing permanent magnets (PM) or dipole arrays, and continue to be challenged by numerical problems. The quasi-single-stage (QSS) optimization finds a middle-ground by integrating a coil optimization subproblem into stage-1 optimization. We present a flexible, differentiable coil complexity proxy based on the newly developed QUADCOIL coil optimization code. QUADCOIL is fast and can target realistic coil metrics and constraints that are unavailable to codes with comparable speed. We demonstrate the effectiveness and flexibility of the QUADCOIL proxy by presenting two QSS optimization studies. The first study produces a permanent magnet solution for the MUSE stellarator with 29% fewer magnets than previous solutions. The second study produces a coil solution for the ARIES-CS stellarator with 27% reductions in both peak and root-mean-square force.
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All authors Lanke Fu, Dario Panici, Elizabeth Paul, Alan Kaptanoglu, Amitava Bhattacharjee
General Physics
The Sun's magnetic midlife crisis
Travis S. Metcalfe
The Sun is just one of a hundred billion
stars in the Milky Way
galaxy. Our front-row seat on Earth allows us to observe it in much greater detail than we can for other
stars. However, those observations provide only one snapshot in the life story of
stars like the Sun. To piece together the entire tale, astronomers need to study other
stars that are younger and older. Their observations have revealed something unexpected that never could have come to light from studies of our Sun in isolation.
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Biological Physics
DNA Nanostructures Characterized via Dual Nanopore Resensing
Wangwei Dong, Zezhou Liu, Ruiyao Liu et al. (+2 more)
DNA nanotechnology uses predictable interactions of nucleic acids to precisely engineer complex nanostructures. Characterizing these self-assembled structures at the single-structure level is crucial for validating their design and functionality. Nanopore sensing is a promising technique for this purpose as it is label-free, solution-based and high-throughput. Here, we present a device that incorporates dynamic feedback to control the translocation of DNA origami structures through and between two nanopores. We observe multiple translocations of the same molecule through the two distinct nanopores as well as measure its time-of-flight between the pores. We use machine learning classification methods in tandem with classical analysis of dwell-time/blockade distributions to analyze the complex multi-translocation events generated by different nanostructures. With this approach, we demonstrate the ability to distinguish DNA nanostructures of different lengths and/or small structural differences, all of which are difficult to detect using conventional, single-nanopore sensing. In addition, we develop a finite element
diffusion model of the time-of-flight process and estimate nanostructure size. This work establishes the dual nanopore device as a powerful tool for DNA nanostructure characterization.
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All authors Wangwei Dong, Zezhou Liu, Ruiyao Liu, Deborah Kuchnir Fygenson, Walter Reisner
Optics
Phase-Stable Optical Fiber Links for Quantum Network Protocols
Nicholas V. Nardelli, Dileep V. Reddy, Michael Grayson et al. (+5 more)
We demonstrate the distribution of single-
photon-level pulses from a mode-locked
laser source over a phase-stable fiber link, achieving an optical timing jitter of less than 100 as over 10 minutes of data accumulation. This stability enables a fidelity greater than 0.998 between two stabilized 2.1 km long deployed fiber links. Building on time and frequency metrology techniques traditionally used for high-stability optical atomic clock signal distribution, we use time and frequency multiplexing to achieve an isolation of
quantum and classical channels of $8 \times 10^{10}$. Our results mark a necessary step towards scalable, high-rate
quantum networks with a provable
quantum advantage.
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All authors Nicholas V. Nardelli, Dileep V. Reddy, Michael Grayson, Daniel Sorensen, Martin J. Stevens, Michael D. Mazurek, L. Krister Shalm, Tara M. Fortier
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Coherent and Dynamic Small Polaron Delocalization in CuFeO$_{2}$
Jocelyn L. Mendes, Srijan Bhattacharyya, Chengye Huang et al. (+10 more)
Small polarons remain a significant bottleneck in the realization of efficient devices using transition metal
oxides. Routes to engineer small polaron coupling to electronic states and
lattice modes to control carrier localization remain unclear. Here, we measure the formation of small polarons in CuFeO$_{2}$ using transient extreme ultraviolet reflection spectroscopy and compare it to theoretical predictions in realistically parameterized Holstein models, demonstrating that polaron localization depends on its coupling to the high-frequency versus low-frequency components of the
phonon bath. We measure that small polaron formation occurs on a comparable ~100 fs timescale to other Fe(III) compounds. After formation, a dynamic delocalization of the small polaron occurs through a coherent
lattice expansion between Fe-O layers and charge-sharing with surrounding Fe(IV) states. Our simulations of polaron formation dynamics reveal that two major factors dictate polaron formation timescales:
phonon density and reorganization energy distributions between acoustic and optical modes, matching experimental findings. Our work provides a detailed, real-time observation of how electronic-structural coupling in a polaron-host material can be leveraged to suppress polaronic effects for various applications.
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All authors Jocelyn L. Mendes, Srijan Bhattacharyya, Chengye Huang, Jonathan M. Michelsen, Isabel M. Klein, Finn Babbe, Thomas Sayer, Tianchu Li, Jason K. Cooper, Hanzhe Liu, Naomi S. Ginsberg, Andrés Montoya-Castillo, Scott K. Cushing
Biological Physics
Computer Modelling of Bioheat Transfer for the Analysis of Brightness Temperature Distributions
Maxim V. Polyakov and Illarion E. Popov
This paper presents a comprehensive computer simulation of thermal processes in multilayered biological tissues for the analysis of luminance temperature distributions recorded by microwave radiometry. A mathematical model combining the bioheat transfer equation with the electrodynamic description of electromagnetic field propagation in an inhomogeneous medium has been developed. The model accounts for variations in the thermophysical and dielectric properties of tissues, as well as convective heat exchange with the environment. A parametric analysis was performed to investigate the effects of ambient temperature, heat transfer coefficient, and tissue thermal conductivity on brightness temperature formation. Computational experiments revealed a clear linear dependence of the radiometric signal on both external and internal parameters. It was found that an increase in air temperature by 8 {\deg}C causes a shift in the brightness temperature by about 2 {\deg}C, which exceeds the typical error of the microwave radiometry method and emphasises the need for strict temperature control of the measurement conditions. The developed software system was validated against analytical solutions and experimental data, confirming the accuracy of the calculated temperature fields to within 0.1 {\deg}C. The obtained results lay the groundwork for refining heat transfer models in biological tissues, improving the accuracy of non-invasive thermodiagnostic methods, and integrating computer modelling with machine learning
algorithms to enable the automated interpretation of radiometric data.
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Medical Physics
Phase-sensitive modelling improves Fat DESPOT multiparametric relaxation mapping in fat-water mixtures
Renée-Claude Bider, Cristian Ciobanu, Jorge Campos Pazmiño et al. (+3 more)
Purpose: To improve on the original form of Fat DESPOT, a multiparametric mapping technique that returns the fat- and water-specific estimates of $R_1$ ($R_{1f}$, $R_{1w}$), $R_2^*$ , and
proton density fat fraction (PDFF) by upgrading the fat-water separation method used for selection of initial parameter guesses, and by introducing explicit model sensitivity to the phase of the water and fat signals. Methods: We compared the 3-point Dixon and Graph Cut (GC) approaches to initial guesses for Fat DESPOT in phantom experiments at 3 T in a variable fat fraction gel phantom. Also in phantom, we then compared the original Fat DESPOT approach to a magnitude approach modelling the phases of fat and water separately (Fat DESPOT$_{m\phi}$), and an approach that models the complex data (Fat DESPOT$_c$). The best-performing approach was then used in the lower leg of a healthy human participant. Results: In phantoms, Fat DESPOT using the 3-point Dixon and GC performed similarly in parametric estimates and precision, though the Dixon approach deviated from the overall trend in the 50% nominal fat fraction ROI. Furthermore, Fat DESPOT$_c$ showed the best agreement with reference PDFF (average error 1.5 +/- 1.2%) and the lowest combined standard deviation across ROIs, for PDFF, $R_{1f}$, and $R_{1w}$ ({\sigma} = 0.13%, 0.19 s$^{-1}$, 0.0082 s$^{-1}$). Conclusion: With a higher precision of $R_{1f}$ and $R_{1w}$ , accuracy of PDFF, and more echo time versatility than other compared approaches, this work demonstrates the advantages of the GC approach for initial guesses paired with complex fitting for Fat DESPOT multiparametric imaging.
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All authors Renée-Claude Bider, Cristian Ciobanu, Jorge Campos Pazmiño, Véronique Fortier, Evan McNabb, Ives R. Levesque
Optics · Cross-listed from quant-ph
Decoherence-free subspaces in the noisy dynamics of discrete-step quantum walks in a photonic lattice
Rajesh Asapanna, Clément Hainaut, Alberto Amo et al. (+1 more)
We study the noisy dynamics of periodically driven, discrete-step
quantum walks in a one-dimensional photonic
lattice. We find that in the bulk, temporal noise that is constant within a Floquet period leads to decoherence-free momentum subspaces, whereas fully random noise destroys coherence in a few time steps. When considering topological edge states, we observe decoherence no matter the type of temporal noise. To explain these results, we derive a non-perturbative master equation to describe the system's dynamics. We experimentally confirm our findings in a time multiplexed photonic
lattice implemented in a double-fiber ring setup subject to
laser pulse input states, in which we engineer different types of temporal noise.
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All authors Rajesh Asapanna, Clément Hainaut, Alberto Amo, Álvaro Gómez-León
Atomic Physics
Numerical modeling of laser cooling in molecules: From simple diatomics to polyatomics and radioactive species
Felix Kogel, Tatsam Garg, Phillip Groß et al. (+6 more)
Optical Bloch equations and rate equations serve as powerful tools to model light-matter interactions from textbook-like two-level atoms to the complex internal dynamics of molecules. A particular challenge in this context is posed by molecular
laser cooling, where many dozens or hundreds of levels need to be taken into account for a comprehensive modeling. Here, we present MoleCool, a numerically efficient Python toolbox to implement and solve the corresponding differential equation systems. We illustrate both the capabilities of the toolbox and some of the intricacies of molecular
laser cooling by educational examples, which range from simple Rabi oscillations to spontaneous and coherent cooling schemes for various currently studied or considered molecular species. This includes, in particular, a comprehensive modeling of
laser cooling dynamics with full hyperfine structure resolution in radioactive radium monofluoride (RaF), as well as studies of other complex species such as barium monofluoride (BaF) and ytterbium monohydroxide (YbOH).
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All authors Felix Kogel, Tatsam Garg, Phillip Groß, Lukas Leczek, Marian Rockenhäuser, Neil Shah, Jakob Weiß, Andreas Schindewolf, Tim Langen
Plasma Physics
Physics insights from a large-scale 2D UEDGE simulation database for detachment control in KSTAR
Menglong Zhao, Xueqiao Xu, Ben Zhu et al. (+8 more)
A large-scale database of two-dimensional UEDGE simulations has been developed to study detachment physics in KSTAR and to support surrogate models for control applications. Nearly 70,000 steady-state solutions were generated, systematically scanning upstream density, input power,
plasma current,
impurity fraction, and anomalous transport coefficients, with
magnetic and electric drifts across the
magnetic field included. The database identifies robust detachment indicators, with strike-point electron temperature at detachment onset consistently Te around 3-4 eV, largely insensitive to upstream conditions. Scaling relations reveal weaker
impurity sensitivity than one-dimensional models and show that heat flux widths follow Eich's scaling only for uniform, low D and Chi. Distinctive in-out divertor asymmetries are observed in KSTAR, differing qualitatively from DIII-D. Complementary time-dependent simulations quantify
plasma response to gas puffing, with delays of 5-15 ms at the outer strike point and approximately 40 ms for the low-
magnetic-field-side (LFS) radiation front. These dynamics are well captured by first-order-plus-dead-time (FOPDT) models and are consistent with experimentally observed detachment-control behavior in KSTAR [Gupta et al., submitted to
Plasma Phys. Control. Fusion (2025)]
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All authors Menglong Zhao, Xueqiao Xu, Ben Zhu, Thomas Rognlien, Xinxing Ma, William Meyer, KyuBeen Kwon, David Eldon, Nami Li, Hyungho Lee, Junghoo Hwang
Fluid Dynamics
Revealing Low-Dimensional Structure in 2D Richtmyer-Meshkov Instabilities via Parametric Reduced-Order Modeling
Daniel Messenger, Daniel Serino, Balu Nadiga et al. (+1 more)
Efficient modeling of the Richtmyer-Meshkov instability (RMI) is essential to many engineering tasks, including high-speed combustion and drive and capsule geometry optimization in Inertial Confinement Fusion (ICF). In the latter, RMI causes the ablator and fuel to mix, introducing cold spots into the fuel and lowering performance; controlling RMI is thus a core ICF design concern. In this work, we introduce a reduced-order model for two-dimensional RMI based on the Latent Space Dynamics Identification (LaSDI)
algorithm. We demonstrate the efficacy of the proposed methodology in efficiently parametrizing the solution space over a high-dimensional parameter vector consisting of material EOS parameters and initial conditions known to affect RMI growth rates. Using only late-time partial observations of the dynamics, we use our framework to not only provide a highly efficient dynamic surrogate model, but to reveal that the RMI exhibits the structure of a surprisingly low-dimensional and linear dynamical system, into the nonlinear growth regime, after a suitable nonlinear transformation is applied to the material interface, which we approximate as a trained autoencoder. Our use of practical observables and fundamental parameters suggests that such ROMs may be useful for downstream engineering tasks which confront the RMI, while the low-dimensional representation suggests a new direction for theoretical work.
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All authors Daniel Messenger, Daniel Serino, Balu Nadiga, Marc Klasky
Applied Physics
Magnetophoretic long jump of magnetic microparticles in an engineered magnetic stray field landscape for highly localized and large throughput on-chip fractionation
Rico Huhnstock, Lukas Paetzold, Piotr Kuswik et al. (+1 more)
A common issue faced by
magnetic particle-based Lab-on-a-chip systems, e.g, for medical diagnostics, is the intrinsic fabrication-related polydispersity in particle sizes and
magnetic properties. Therefore, to reduce this variation, it is prudent to integrate a pre-separation procedure for the particles into the overall workflow of the system. In this work, a concept for the controlled on-chip fractionation of micron-sized superparamagnetic beads (SPBs) is introduced, which is applicable for sorting
magnetic particles according to their properties in a continuous operation mode. A specifically designed
magnetic domain pattern is imprinted into an exchange-biased thin film system to generate a tailored
magnetic stray field landscape (MFL), enabling lateral transport of SPBs when superposing the MFL with external
magnetic field pulses. The domain pattern consists of parallel stripes with gradually increasing and decreasing width, resulting in a step-wise jumping motion of SPBs with increasing/decreasing jump distance. SPBs with different magnetophoretic mobilities, determined, among others, by the particle size and
magnetic susceptibility, discontinue their lateral motion at different jump distances, i.e., different lateral positions on the substrate. Thorough analysis of the motion using optical microscopy and particle tracking revealed that an increasing stripe width not only leads to a larger jump distance but also to a lowered jump velocity. As a consequence, particles are spatially separated according to their
magnetic and structural properties with a large throughput and time efficiency, as simultaneous sorting occurs for all particles present on the substrate using a constant sequence of short external field pulses.
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All authors Rico Huhnstock, Lukas Paetzold, Piotr Kuswik, Arno Ehresmann
Fluid Dynamics
Effects of spatially localised pressure gradient histories on recovery of turbulent boundary layers
Zefanya Bramantasaputra, Dea Daniella Wangsawijaya and Bharathram Ganapathisubramani
Hot-wire anemometry is used to investigate the recovery of smooth-wall turbulent boundary layers from spatially localised (i.e. impulsive) pressure gradient history (PGH) effects. Measurements are performed at multiple stations downstream of spatial distributions of favourable-adverse pressure gradient sequences, followed by relaxation to zero-pressure-gradient (ZPG) conditions. The analysis focuses on matched friction Reynolds numbers at $Re_\tau \approx 2300$, $3000$, and $5500$, where the local Clauser pressure gradient (PG) parameter $\beta$ is nominally matched at $1.7$, $0.6$, and $-0.1$, respectively. PGH strength is quantified using the integral history parameter $\Delta\beta$, proposed by Preskett et al. (J. Fluid Mech., vol. 1010, 2025, A30), which allows isolation of PGH as the primary source of variation. The imposed PGH amplifies the wake component of the mean velocity profile and enhances the streamwise Reynolds stress throughout the boundary layer, including the emergence of an outer peak. Spectral analysis reveals an additional outer-layer energetic feature with streamwise length scales of $2$-$3\delta$ ($\delta$ is the local boundary layer thickness), identified as the PG peak, distinguishable from the very-large-scale motion (VLSM). Even after $\beta$ has relaxed (to zero) for sufficiently long distances, mean flow has not recovered to ZPG state. Once $\Delta\beta \lesssim 0.1$, mean flow and inner/log-layer
turbulence statistics recover; however, the outer-layer
turbulence retains a persistent imprint of PGH. Finally, we observe that recovery involves reorganisation of large-scale structures - where VLSMs appear to be shorter even after the PG peak has vanished - which indicates prolonged history effects.
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Fluid Dynamics
Mechanism generating reverse buoyancy flux at the small scales of stably stratified turbulence
Soumak Bhattacharjee, Stephen M. de Bruyn Kops and Andrew D. Bragg
Previous studies have shown that at the small-scales of stably stratified
turbulence, the scale-dependent buoyancy flux reverses sign, such that there is a conversion of turbulent potential energy (TPE) back into turbulent kinetic energy (TKE) at these scales. Moreover, the magnitude of the reverse flux becomes stronger with increasing Prandtl number $Pr$. Using a filtering analysis we demonstrate analytically how this flux reversal is connected to the mechanism identified in Bragg & de Bruyn Kops (JFM 2024 Vol 991 A10) that is responsible for the surprising observation that the TKE dissipation rate increases while the TPE dissipation rate decreases with increasing $Pr$ in stratified
turbulence. The mechanism identified by Bragg & de Bruyn Kops, which is connected to the formation of ramp-cliff structures in the density field, is shown to give the scale-local contribution to the buoyancy flux. At the smallest-scales this local contribution dominates and explains the flux reversal, while at larger scales a non-local contribution is important. Direct numerical simulations (DNS) of 3D statistically stationary, stably stratified
turbulence in the strongly stratified regime confirm the theoretical analysis, and indicate that while on average the local contribution only dominates the buoyancy flux at the smallest scales, it remains strongly correlated with the buoyancy flux at all scales. The results show that ramp-cliffs are not only connected to the reversal of the local buoyancy flux but also the non-local part. At the small scales (approximately below the Ozmidov scale), ramp structures contribute exclusively to reverse buoyancy flux events, whereas cliff structures contribute to both forward and reverse buoyancy flux events.
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Physics Education · Cross-listed from astro-ph.IM
Why every solar eclipse viewing event needs a disco ball
Valerie A. Rapson, Alex Pietrow, Robert J. Cumming et al. (+12 more)
Solar eclipses offer unparalleled opportunities for public engagement in astronomy. Large groups of people often gather to view eclipses, and these events require affordable and easy to use tools to safely observe the Sun. One unique way to observe a
solar eclipse is by using a disco ball. Here, we present an analysis of the experiences of educators who used a disco ball as a
solar projector during various public outreach events. Through a survey conducted shortly after the April 2024 total
solar eclipse and the March 2025 partial
solar eclipse, we collected data on the use, engagement, and perceived educational value of a disco ball projector from 31 individual events. The results suggest that disco balls were not only affordable and safe, but also popular and educational.
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All authors Valerie A. Rapson, Alex Pietrow, Robert J. Cumming, Jill Burns, Ali Cotton, Yashashree Jadhav, Maria D. Kazachenko, Casper A.L. Pietrow, Livia M.A. Pietrow, Dennis Schatz, Elliot Severn, Sundar Srinivasan, William Thornburgh, Andrea Warkentin, Hayley Yasui
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Exceptional Antimodes in Multi-Drive Cavity Magnonics
Mawgan A. Smith, Ryan D. McKenzie, Alban Joseph et al. (+2 more)
Driven-dissipative systems provide a natural setting for the emergence of exceptional points – i.e. non-Hermitian degeneracies where eigenmodes coalesce. These points are important for applications such as sensing, where enhanced sensitivity is required, and exhibit interesting and useful phenomena that can be controlled with experimentally accessible parameters. In this regard a four-port, three-mode, cavity-magnonics platform is demonstrated in which two microwave excitations can be precisely phase shifted and/or attenuated relative to one another. Destructive interference between the hybridised cavity-
magnon modes is shown to give rise to antimodes (antiresonances) in the transmission spectrum, enabling coherent perfect extinction of the outgoing signals at selected ports. This interference can be used to actively tune the position and properties of exceptional points, without the fine tuning conventionally required to obtain exceptional points. Such controllable, interference-based engineering of exceptional points provides a practical and flexible pathway toward next-generation, high-sensitivity sensing devices operating at microwave frequencies.
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All authors Mawgan A. Smith, Ryan D. McKenzie, Alban Joseph, Robert L. Stamps, Rair Macêdo
Atomic Physics
Light shift suppression in a CPT magnetometer using linear polarization and double frequency interrogation
M.A. Maldonado, Yang Li, James A. McKelvy et al. (+5 more)
We demonstrate a suppression of the light shift in a Coherent-Population-Trapping (CPT) atomic magnetometer by using linearly polarized light and a differential measurement between
magnetic resonances. The
radio frequency that creates the optical sidebands for CPT quickly switches between two
magnetic sensitive transitions and the
magnetic field is extrapolated from the difference of the center frequencies of the
magnetic resonances. Light shifts and common drifts like collisional shifts can be suppressed through careful choice of measured resonances and we show the light shift reduction by more than a factor of 20 compared to excitation with circular polarized light. Various limitations to the method are discussed.
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All authors M.A. Maldonado, Yang Li, James A. McKelvy, Andrey Matsko, Irina Novikova, Eugeniy E. Mikhailov, John Kitching, Ying-Ju Wang