Atmospheric and Oceanic Physics
How different are deterministic physics suites when coupled to fixed model dynamics and why?
Edward Groot, Hannah Christensen, Xia Sun et al. (+5 more)
It is often difficult to attribute uncertainty and errors in atmospheric models to designated model components. This is because sub-grid parameterised processes interact strongly with the large-scale transport represented by the explicit model dynamics. We carry out experiments with prescribed large-scale dynamics and different sub-grid physics suites. This
dataset has been constructed for the Model Uncertainty Model Intercomparison Project (MUMIP), in which each suite forecasts sub-grid tendencies at a 22km grid. The common dynamics is derived from a convection-permitting
benchmark: an ICON DYAMOND experiment (2.5km grid). We compare four different physics suites for atmospheric models in an Indian Ocean experiment. We analyse their joint PDFs of precipitation and associated physics tendencies for a full month. Precipitation is selected because it is a dominant uncertainty in the models that redistributes large amounts of heat. We find that all physics suites produce very similar precipitation amounts, with very high correlations between models, which exceed 0.95 at the native grid. However, the convection-permitting
benchmark is more dissimilar from each of the physics suites, with correlations of $\approx$0.80. Similarly, we show that the vertically averaged physics tendencies in the free-troposphere are highly similar between the four physics suites, yet different if reconstructed for the
benchmark. The water vapour sink is very closely linked with precipitation in the four physics suites. This suggests that the coarse-grid models are overconfident. We hypothese is that variation in unresolved convective structures can lead to variation in the dynamics, following a given amount of latent heating at fine grids, but not in our physics suites. The abstract length limit of ArXiv requires you to proceed in the PDF.
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All authors Edward Groot, Hannah Christensen, Xia Sun, Kathryn Newman, Wahiba Lfarh, Romain Roehrig, Lisa Bengtsson, Julia Simonson
Plasma Physics · Cross-listed from astro-ph.SR
Extreme-ultraviolet synthesis of nanojet-like ejections due to coalescing flux ropes
Samrat Sen, A. Ramada C. Sukarmadji, D. Nóbrega-Siverio et al. (+3 more)
Detection and characterization of small-scale energetic events such as nanoflares and nanojets remain challenging owing to their short lifetimes, small spatial extent, and relatively low energy release, despite their potential role in coronal heating. Recent observations have identified nanojets as small-scale (length $\lesssim 6.6$~Mm, width $\lesssim 1$~Mm), fast ($\sim$~few 100 km s$^{-1}$), and short-lived ($\lesssim 30$~s) ejections associated with nanoflare-scale energies, providing evidence of
magnetic reconnection at small spatial scales. However, the lack of synthetic diagnostics has limited the connection between magnetohydrodynamic (MHD) models and observations. In this Letter, we present synthetic observations of the coalescence of two flux ropes, leading to nanojet-like signatures from a numerical model obtained with the MPI-AMRVAC code. We report synthetic observables in Extreme-ultraviolet lines compatible with existing instruments such as SDO/AIA, and upcoming MUSE mission, and compare the synthetic observables with an existing observation of nanojets. The synthetic diagnostics of the emissivity maps, Doppler velocity, thermal, and non-thermal line broadening produce key observational properties, suggesting a plausible 3D scenario for nanojet generation where tiny flux ropes reconnect within loops. Our results provide predictions for the detectability of nanojets with current and future spectroscopic facilities, and establish a bridge between MHD modeling and observations.
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All authors Samrat Sen, A. Ramada C. Sukarmadji, D. Nóbrega-Siverio, F. Moreno-Insertis, J. Martínez-Sykora, Patrick Antolin
Plasma Physics · Cross-listed from astro-ph.SR
Non-thermal particle acceleration in multi-species kinetic plasmas: universal power-law distribution functions and temperature inversion in the solar corona
Uddipan Banik and Amitava Bhattacharjee
Non-thermal power-law distribution functions are ubiquitous in astrophysical, space, and laboratory kinetic
plasmas, but their origin remains unclear. A related puzzle is the temperature inversion of the
solar corona. We show that these phenomena are deeply connected by developing a self-consistent quasilinear theory for electromagnetically driven, unmagnetized kinetic
plasmas. The theory yields a multi-species Fokker-Planck equation with drive-induced
diffusion from direct acceleration by broad-band turbulent or narrow-band wave-like fields, indirect acceleration by excited waves, and Balescu-Lenard
diffusion/drag from Debye-scale fluctuations and Coulomb collisions. For a super-Debye turbulent electric-field spectrum, $|{\bf E}_{\bf k}|^2\propto k^{-\alpha}$, electrons and ions relax toward a universal $f(v)\propto v^{-5}$, or $N(E)\propto E^{-2}$, attractor, equivalent to the high-energy tail of a $\kappa=1.5$ distribution, when $\alpha\ge5$. This universality follows from Debye screening: large-scale fields accelerate unscreened fast particles but not screened slow ones. For shallower spectra, $\alpha<5$, the tail scales as $v^{-\alpha}$; incomplete relaxation and anisotropy also break universality. Anisotropic wave drives yield branch- and spectrum-dependent exponents. Because collisions cannot decelerate suprathermal particles, the tails resist Maxwellianization. In the
solar atmosphere, such tails may be generated by chromospheric convection or nanoflares despite collisional and radiative losses. Direct wave heating energizes electrons through Landau-resonant interactions with whistler and electron-cyclotron waves, while ions may be accelerated by turbulent ambipolar fields. Resulting $\kappa\simeq1.5$–$3$ distributions produce an abrupt upper-chromosphere/lower-corona transition and velocity-filtration-driven inverted profiles, yielding coronal temperatures $\sim10^6\,{\rm K}$.
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Chemical Physics
Unraveling Structure-Performance Trade-offs in Porous Transport Layers for PEM Water Electrolysis
Navneet Goswami, Sergio Diaz Abad, Jacob S. Spendelow et al. (+2 more)
Scalable hydrogen production using
proton exchange membrane water electrolyzers depends on overcoming efficiency losses arising from coupled multiphase, multicomponent transport and interfacial phenomena across the membrane electrode assembly. Here, we demonstrate a multiscale computational framework that combines pore network modeling with finite-element-based reactive transport simulations to accurately and efficiently resolve structure-performance trade-offs in porous transport layers (PTLs). We perform experiments for both commercial single-layer PTLs and microporous layer (MPL)-integrated configurations to
benchmark the electrochemical model, achieving excellent agreement between modeling and measurements. We show that in single-layer PTLs, open porous networks facilitate mass transport but incur large voltage penalties from PTL-anode catalyst layer (ACL) contact resistance.
Bilayer architectures with dense MPLs reduce these losses by simultaneously improving transport, contact, and structural stability. Finally, in stratified multilayer stacks, combining fine pores near the ACL with highly porous backing layers delivers superior performance at high current densities. Altogether, these results establish mechanistic guidelines for porosity-informed PTL design that minimize interfacial resistance and enable high-efficiency PEMWE operation.
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All authors Navneet Goswami, Sergio Diaz Abad, Jacob S. Spendelow, Siddharth Komini Babu, Wilton J. M. Kort-Kamp
Fluid Dynamics
A Mixed-Metric Two-Field Framework for Turbulence: Emergent Stress Anisotropy and Wall Asymptotics from a Single Scalar
Marcial Sanchis-Agudo and Ricardo Vinuesa
In our previous work~\cite{SanchisAgudoVinuesa2025PRL}, we argued that viscous dissipation in
turbulence can be understood as the macroscopic imprint of microscopic path uncertainty, and showed that a kernel variance field $s(y)$ constrained by a balance condition yields both the Kolmogorov scales and the logarithmic law of the wall from a single
stochastic principle. In the present work we promote $s$ to a dynamical field $s(\bm{x},t)$ with units of kinematic viscosity and develop a two-field framework in which the velocity $\ve$ and an intermittency (or
stochastic diffusivity) field $s$ evolve in a coupled way. The effective viscosity is $\nu_{\mathrm{eff}}=\nu_0+s$, but the stress tensor is generalized to include a non-linear closure driven by the commutator of strain and rotation, $[\bm{S}, \bm{\Omega}]$, capturing emergent anisotropy. The
evolution of $s$ is defined as a mixed-metric gradient flow: a Wasserstein-2 gradient flow for morphology, $\Div(s\grad s)$, combined with a local $L^2$ gradient flow driven by an objective coupling term $q$. The coupling is decomposed as $q=q_{\mathrm{prod}}-q_{\mathrm{relax}}$, where production is driven by a
vortex-stretching invariant, $\mathcal{I} = \|\bm{S}\boldsymbol{\omega}\|^2$. This choice ensures that production vanishes identically in strictly two-dimensional flows. We show that, under standard assumptions of constant stress, high Reynolds number and overlap-layer scale invariance, the only scale-invariant overlap-layer solution of the mixed-metric equation is $s(y)\propto y$, which recovers the logarithmic velocity profile. Thus the same mixed-metric equation organizes both wall-resolved and wall-modeled asymptotics within a single, energetically constrained framework.
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Medical Physics · Cross-listed from cond-mat.mtrl-sci
Fine and Hyperfine Interactions with Multi-level Spin Relaxation of the purified Giese-Salt in Veterinary Medicine: Prussian Blue Compound Ammonium-Ferric-Hexacyano-Ferrate
Sascha Albert Bräuninger, Damian Alexander Motz, Sebastian Praetz et al. (+6 more)
Ammonium ferric hexacyanoferrate is a veterinary-medical milestone and antidote against radiocesium, well-known as Giese-salt after the Chernobyl disaster fed to domestic and wild animals, which shows even a rich interplay of properties in nanostructural chemistry and ferromagnetism. Among the broad analytical techniques, the ambivalence of macroscopic micrometer-sized agglomerates and nanoparticle sizes, a suggested enlarged Fe(II)$-$C$\equiv$N$-$Fe(III) bond length by Fe K-edge XAFS results and multi-level
spin relaxation in $^{57}$Fe Mössbauer spectroscopy are highlighted. This sets this underestimated compound in a new light, e.g., for modern biomedicine and biofunctionality, extending its essential importance in addition to hypothetical future
nuclear incidents
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All authors Sascha Albert Bräuninger, Damian Alexander Motz, Sebastian Praetz, Felix Seewald, Katharina Strecker, Carla Vogt, Hans-Henning Klauss, Birgit Kanngießer, Hermann Seifert
Fluid Dynamics
X-CAL: Explaining latent causality in physical space for fluid mechanics
Marcial Sanchis-Agudo, Andrés Cremades, Alvaro Martinez-Sanchez et al. (+2 more)
We present X-CAL, a pipeline that combines a $\beta$-variational autoencoder ($\beta$-VAE) with the synergistic-unique-redundant decomposition (SURD)~\cite{surd} approach for causality analysis to interpret low-dimensional latent representations of turbulent fluid flows. Combining $\beta$-VAE compression with SURD and SHAP (SHapley Additive exPlanations) yields interpretable latent representations and structure-level attributions in physical space, offering a general methodology for causal analysis of high-dimensional flows. Using direct numerical simulation (DNS) data of the flow around a wall-mounted square cylinder at $Re_h=2000$, we (i) learn a compact latent space with near-orthogonal variables, (ii) quantify directed information flows among these variables via the SURD approach, and (iii) map latent-space causality back to physical space through gradient-SHAP fields . By means of percolation analysis of the SHAP fields, we extract the coherent, time-resolved structures that most influence each latent variable. The analysis connects coherent structures with latent variables which are in turn associated with wake-boundary-layer interactions. This method enables translating the insight obtained through causal analysis in the latent space into interpretable phenomena in physical space.
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All authors Marcial Sanchis-Agudo, Andrés Cremades, Alvaro Martinez-Sanchez, Adrian Lozano-Duran, Ricardo Vinuesa
Biological Physics · Cross-listed from q-bio.MN
Understanding the temperature response of biological systems: Part II – Network-level mechanisms and emergent dynamics
Simen Jacobs, Julian B. Voits, Nikita Frolov et al. (+2 more)
Building on the phenomenological and microscopic models reviewed in Part I, this second part focuses on network-level mechanisms that generate emergent temperature response curves. We review deterministic models in which temperature modulates the kinetics of coupled biochemical reactions, as well as
stochastic frameworks, such as Markov chains, that capture more complex multi-step processes. These approaches show how Arrhenius-like temperature dependence at the level of individual reactions is transformed into non-Arrhenius scaling, thermal limits, and temperature compensation at the system level. Together, network-level models provide a mechanistic bridge between empirical temperature response curves and the molecular organization of biological systems, giving us predictive insights into robustness, perturbations, and evolutionary constraints.
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All authors Simen Jacobs, Julian B. Voits, Nikita Frolov, Ulrich S. Schwarz, Lendert Gelens
Plasma Physics
Nutritional and growth enhancement of alfalfa sprouts through cold plasma and UV seed treatments
M. A. Benabderrahim, H. Hannachi, W.Elfalleh et al. (+1 more)
Employing eco-friendly techniques like cold
plasma (CP) and ultraviolet (UV) radiation provides innovative approaches to enhance the sprout quality and productivity of alfalfa. This study explores the effects of CP and UV radiation on the germination, growth, and phytochemical profiles of alfalfa sprouts. CP significantly accelerated germination time, reducing median germination time by 8 hours compared to the control, and enhanced photo synthetic pigments, leading to higher biomass (25.87 mg/sprout fresh weight and 1.45 mg/sprout dry weight). UV treatments, particularly UV-C, increased chlorophyll and total flavonoid content. Overall, CP effectively promotes alfalfa germination and growth, while UV treatments improve specific phytochemicals.
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All authors M. A. Benabderrahim, H. Hannachi, W.Elfalleh, T. Dufour
Optics · Cross-listed from quant-ph
Generalized Bloch's Theorem for Cavity Exciton Polaron-Polaritons
Michael A.D. Taylor and Yu Zhang
We show that
excitons coupled to cavity
photons and
phonons admit a generalized Bloch
theorem when formulated for the conserved total
crystal momentum. In minimal-coupling and Fröhlich representations, the interchange of momenta between
fermions and
bosons breaks crystalline
excitons' translational
symmetry. In our
symmetry-adapted frame, the
Hamiltonian becomes block diagonal, without invoking approximations. The resulting formulation yields dispersions and optical responses of cavity
exciton polaron-polaritons, enabling investigations that elucidate material properties in strong coupling.
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Medical Physics
Open-Source Coil Matching Toolbox for Magnetic Stimulation and Other Electromagnetics (COMATOSE)
Max Koehler and Stefan Goetz
The coil in transcranial
magnetic stimulation (TMS) determines the spatial shape of the electromagnetic field in the head, which structures are concurrently activated, and how focal stimulation is. Most of the readily available coils have been designed intuitively instead of systematic mathematical-physical optimization as there were no methods available at the time. Previous research however demonstrated that these coils are far from optimum, e.g., for pulse energy or efficiency, and leave substantial room for lots of improvements. Techniques for rigorous mathematical optimization have been developed but are only available to very few groups worldwide. This paper presents an open-source toolbox, COMATOSE, to change that situation and make these methods available to a wider community. It incorporates the fundamental formalisms and offers vector space decomposition as well as base mapping as an explicit forward method, which is computationally less demanding than iterative computational optimization but can also form the initial solution for a subsequent optimization run if desired.
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Biological Physics · Cross-listed from cond-mat.soft
Bicontinuity in active phase separation
Paarth Gulati, Liang Zhao, Michio Tateno et al. (+3 more)
We study phase separation between coexisting active and passive fluids in three-dimensions, using numerical simulation and experiments. Chaotic flows of the active phase drive
giant interfacial deformations, causing the co-existing phases to interpenetrate and generate a continuously reconfiguring bicontinuous morphology which persists over the lifetime of the active fluid. Active bicontinuous structures are dominated by sheet-like interfaces, in marked difference from passive
liquid-
liquid phase separation which is controlled by saddle-like surfaces. Activity and surface tension control the length scale of the bicontinuous structure. These results demonstrate how active stresses suppress the coarsening of conventional phase separation, generating steady-state reconfigurable morphologies not accessible with conventional surface-modifying
agents or through quenching of transient phase separated structures.
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All authors Paarth Gulati, Liang Zhao, Michio Tateno, Omar A. Saleh, Zvonimir Dogic, M. Cristina Marchetti
Geophysics
Modelling and Simulation of the Propagation of P-SV Seismic Waves from Earthquakes: Application to Deep Earthquakes in Acre, Brazil
Pedro Huan Moreira, Andina Alay Lerma, Eliandro Rodrigues Cirilo et al. (+3 more)
Brazil is located in the central-eastern portion of the South American Plate, meaning that the country mostly experiences low-intensity seismic activity within its territory. However, some geological faults in this region have generated intense earthquakes. In this context, we intend to describe a recent earthquake of magnitude around 6.5 M_b that occurred at a depth of approximately 600 km in the state of Acre, Brazil. In this work, we modeled the propagation of P-SV seismic waves using a two-dimensional system of partial differential equations (PDEs) in a two-dimensional vertical rectangular domain. The source is modeled by a Gaussian pulse function. The initial quiescence condition and Neumann boundary conditions are used. The PDE system is discretized by the finite difference method (FDM) and solved by the Gauss-Seidel method (GSM). The numerical simulations obtained describe the propagation of attenuated seismic waves in multiple geological layers, simulating intense and deep earthquakes in Acre. We used the propagation of perfect seismic waves to validate the model. The results include images of the simulations and theoretical seismograms simulating the vertical and horizontal displacement in the epicenter region and 200 km east and west of the epicenter.
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All authors Pedro Huan Moreira, Andina Alay Lerma, Eliandro Rodrigues Cirilo, Neyva Maria Lopes Romeiro, Waldemir Lima Dos Santos, Paulo Laerte Natti
Medical Physics
Feasibility study of the positronium lifetime imaging with the Biograph Vision Quadra and J-PET tomographs
Szymon Parzych, Szymon Niedźwiecki, Ermias Yitayew Beyene et al. (+39 more)
Background: After its first ex-vivo and in-vivo demonstration, Positronium Lifetime Imaging (PLI) has received considerable interest as a potential new diagnostic biomarker. High sensitivity Positron Emission
Tomography (PET) systems are needed for PLI since it requires simultaneous registration of annihilation
photons and
prompt gamma. In this simulation-based study, a~feasibility of PLI with the long axial field-of-view Biograph
Vision Quadra (Quadra) and the Total Body J-PET scanner was investigated. Methods: The study was performed using the GATE software. Background radiation, present within the Quadra tomograph, was added to the simulation. First, the optimal placement of the energy window for the registration of the
prompt gamma was investigated. Next, the organ-wise sensitivity of Quadra was calculated for the $^{68}$Ga, $^{44}$Sc, $^{22}$Na and $^{124}$I radioisotopes. Finally, the sensitivity for the scandium isotope was compared to the sensitivities obtainable with the Total Body J-PET scanner, as well as with the modular J-PET prototype. Results: The PLI sensitivities for the Quadra with the background radiation are estimated to 9.22(3), 10.46(4), 5.91(3), and 15.39(4) cps/kBq for the $^{44}$Sc, $^{68}$Ga, $^{22}$Na and $^{124}$I radioisotopes, respectively. The highest sensitivity was obtained when the energy window for the deexcitation
photon is adjacent to the energy window for the annihilation
photons. The determined PLI sensitivities with Quadra and the Total Body J-PET are in the order of sensitivities of standard PET imaging with the short axial field-of-view ($\sim$20 cm) PET scanners. Conclusion: The organ-wise PLI sensitivity of Quadra has been computed for the $^{68}$Ga, $^{44}$Sc, $^{22}$Na and $^{124}$I radioisotopes. A sensitivity gain by a factor of 150 was estimated relative to the modular J-PET system previously used for the first in-vivo PLI.
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All authors Szymon Parzych, Szymon Niedźwiecki, Ermias Yitayew Beyene, Neha Chug, Maurizio Conti, Catalina Curceanu, Eryk Czerwiński, Manish Das, Kavya Valsan Eliyan, Jakub Hajduga, Sharareh Jalali, Krzysztof Kacprzak, Tevfik Kaplanoglu, Łukasz Kapłon, Kamila Kasperska, Aleksander Khreptak, Grzegorz Korcyl, Tomasz Kozik, Deepak Kumar, Anoop Kunimmal Venadan, Karol Kubat, Edward Lisowski, Filip Lisowski, Justyna Mędrala-Sowa, Wiktor Mryka, Simbarashe Moyo, Piyush Pandey, Elena Perez del Rio, Alessio Porcelli, Bartłomiej Rachwał, Martin Rädler, Axel Rominger, Sushil Sharma, Kuangyu Shi, Magdalena Skurzok, William M. Steinberger, Tomasz Szumlak, Pooja Tanty, Keyvan Tayefi Ardebili, Satyam Tiwari, Ewa Łucja Stępień, Paweł Moskal
Fluid Dynamics · Cross-listed from math.AP
Forward self-similar solutions to the 2D Navier–Stokes equations
Dallas Albritton, Julien Guillod, Mikhail Korobkov et al. (+1 more)
We construct self-similar solutions to the 2D Navier–Stokes equations evolving from arbitrarily large $-1$–homogeneous initial data and present numerical evidence for their non-uniqueness.
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All authors Dallas Albritton, Julien Guillod, Mikhail Korobkov, Xiao Ren
Instrumentation and Detectors
Optimization of Cryogenic Detector Test Station by Rejecting Electromagnetic Interference
Sangbaek Lee, Whitney Armstrong, Maximo DiPreta et al. (+3 more)
We report on the solution optimized for characterizing SNSPDs by rejecting electromagnetic interference (EMI) from various sources. The proposed readout method enhances measurement stability and enables reliable device characterization at low bias currents, where the signal-to-noise ratio is typically limited. By effectively suppressing EMI-induced noise, the method improves the ability to distinguish genuine detection events from spurious signals and reduces the effort required for data analysis. The approach has been applied to preliminary measurements of SNSPDs exposed to $\alpha$ particles emitted from a $^{241}$Am source, demonstrating stable operation and clean signal acquisition. While a detailed study of $\alpha$ detection is underway, the method establishes a foundation for further characterization of SNSPDs with various incident particles. The demonstrated EMI rejection technique is expected to facilitate future research in particle detection and support ongoing SNSPD development for applications in
nuclear and accelerator-based experiments.
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All authors Sangbaek Lee, Whitney Armstrong, Maximo DiPreta, Jacob Dulya, Valentine Novosad, Tomas Polakovic
Fluid Dynamics
Fast and slow surfactants in turbulence-driven bubble breakup
Zhan Wu, Tristan Aurégan and Luc Deike
When a large air cavity breaks in a turbulent flow, it goes through very large deformations and cascading events of new interface formation, including elongated filaments and bubbles over a wide range of scales, with their rate of formation controlled by
turbulence and capillary processes. We experimentally investigate the effects of surfactants and salt on the fragmentation of a large air cavity, and observe a five fold increase of the number of bubbles being produced in some cases. We characterize the bubble size distribution resulting from successive break-ups in such transient configuration. For bubbles larger than the Hinze scale $d_H$ (defined as the balance between surface tension and
turbulence stresses), we observe that bubble size distributions remain unchanged for all solutions tested. For bubbles below $d_H$, however, we observe an increase of the number of bubbles produced and an associated steepening of the bubble size distribution upon the addition of surfactant or salt. This later effect is only visible for surfactants with an adsorption timescale that is fast enough compared to the rate at which new interfaces are being generated by
turbulence.
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Optics
Collective light-matter interaction in plasmonic waveguide quantum electrodynamics
Zahra Jalali-Mola and Saeid Asgarnezhad-Zorgabad
Rabi oscillations characterize light-matter hybridization in the waveguide
quantum electrodynamics~(WQED) framework, with their associated decay rates reflecting excitation damping, yet their behavior remains unresolved when collective emitters are coupled to a collective waveguide mode. This scenario reveals a conceptually novel collective-light-collective-matter interaction, realizable when a timed-Dicke state~(TDS) of subwavelength emitters couples to a slow, delocalized surface-plasmon mode, forming a hybridized plasmon-polariton~(HPP). The HPP acquires its directionality from the TDS via momentum matching. It also exhibits plasmonic characteristics, with excitation frequencies following the surface-plasmon dispersion relation. We obtain a Rabi oscillation and a long-time decay that describe the HPP and use them to reveal weak- and strong-coupling regimes through the emergence of normal-mode splitting. By performing a finite-time Lyapunov-exponent analysis, we show that the HPP also exhibits instantaneous decay and identify three distinct decay regimes: early-time rapid, transient-time oscillatory, and long-time classical. Finally, by analyzing the emission spectrum, we observe an anticrossing of the peak doublets~(a feature also seen in cavity QED setups) which originates from
quantum vacuum effects and the resulting non-Markovian HPP
evolution in our WQED.
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Physics and Society · Cross-listed from stat.AP
Computationally Efficient Estimation of Localized Treatment Effects for Multi-Level, Multi-Component Interventions to Address the Opioid Crisis
Abdulrahman A. Ahmed, M. Amin Rahimian, Qiushi Chen et al. (+1 more)
The opioid epidemic remains a major public health challenge in the United States, requiring a multi-pronged intervention approach to mitigate harms to communities. Given the heterogeneity of the epidemic, it is crucial for policymakers to understand localized treatment effects of different intervention components and utilize limited resources efficiently. While locally calibrated simulation models can project epidemic outcomes for any given intervention policy, collecting simulation results for all intervention combinations to estimate localized treatment effects for each community is impractical because the number of combinations grows exponentially with the number of interventions and the levels at which they are applied. To tackle this, we develop a two-stage metamodel framework with a two-step sequential design for efficient sampling. The metamodel consists of a response function linking health outcomes to each intervention component's treatment effect, and a Gaussian process regression (GPR) to learn spatial and socio-economic structures of the treatment effects based on locally-contextualized
covariates. With two-step sequential sampling, we leverage spatial correlations and posterior uncertainty to sequentially sample the most informative counties and treatment conditions. We apply this framework to estimate the treatment effects of buprenorphine dispensing and naloxone distribution on overdose mortality rates using a calibrated
agent-based opioid epidemic model in Pennsylvania counties. Our approach achieves less than 5% average relative error using fewer than 2% of the runs required for an exhaustive simulation. Our two-stage framework provides a computationally efficient approach to support policymakers, enabling an efficient evaluation of alternative resource-allocation strategies to mitigate the opioid epidemic in local communities.
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All authors Abdulrahman A. Ahmed, M. Amin Rahimian, Qiushi Chen, Praveen Kumar
Fluid Dynamics
Unifying Viscocapillary and Inertial Regimes in Selective Withdrawal
Sabbir Hassan, Arsalan Abutalebi, Sukalyan Bhattacharya et al. (+1 more)
Selective withdrawal extracts only a single phase from a stratified multi-layer system. Entrainment occurs when a critical condition draws up the static layer which is not being withdrawn. Existing studies provide robust scalings within distinct limiting regimes. These include viscocapillary-dominated entrainment at low Reynolds number. They also include inertia-dominated entrainment at high Reynolds number. However, a single unifying representation remains to be explored in the literature. This limitation is most evident in transitional conditions between classical limits. It is also pronounced when the lower layer is non-Newtonian. Here we report selective-withdrawal experiments spanning these conditions. The upper layer is Newtonian, using PDMS or soybean oil. The lower layer is either Newtonian water or shear-thinning xanthan-gum solutions. We propose a unified framework that connects these previously separated regimes. The framework adopts a “Moody diagram” type representation for selective withdrawal. We collapse normalized critical submergence height using a Reynolds-like control parameter. Surface-tension effects enter subdominantly through the capillary length. The resulting master curve captures the transition between dominant balances. It connects viscous and shear-controlled entrainment to inertial entrainment. The collapse also clarifies how shear thinning enters the organization. Shear thinning primarily renormalizes the viscous correction through an effective viscosity. It does not alter the inertial baseline scale that anchors the normalization. This regime-spanning representation avoids regime-by-regime correlation switching. It provides a compact diagnostic for entrainment thresholds across fluid types. The diagnostic applies to Newtonian and generalized-Newtonian two-layer systems.
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All authors Sabbir Hassan, Arsalan Abutalebi, Sukalyan Bhattacharya, Gordon F. Christopher
Optics
Harnessing Evanescent Wave Interaction for Enhanced Optical NO2 Detection with Carbon Nanotube-Coated Side-Polished Fiber
Egor O. Zhermolenko, Khasan A. Akhmadiev, Aram A. Mkrtchyan et al. (+6 more)
Evanescent-wave photonic sensors employing nanomaterial-coated waveguides are commonly interpreted in terms of absorption modulation of the sensing layer. Here, we demonstrate that, in such systems, gas-induced reshaping of the guided optical mode can dominate the transduction mechanism and even reverse the sign of the optical response. Using side-polished optical fibers covered with single-walled carbon nanotube (SWCNT) thin films, we observe a pronounced polarization- and thickness-dependent response to NO2 exposure. For transverse electric polarization, the optical response decreases with increasing film thickness and changes sign for thicker coatings, whereas for transverse-
magnetic polarization, the response increases monotonically. Numerical modeling reveals that modulation of the SWCNT complex refractive index redistributes the evanescent field, alters the mode-matter overlap integral, and controls propagation loss. These results demonstrate that evanescent-wave sensor behavior is governed not only by intrinsic material sensitivity but also by mode reshaping induced by nanomaterial coatings. The identified mechanism provides a general framework for designing fiber-optic and integrated photonic sensors based on evanescent-field interactions with tunable nanomaterials.
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All authors Egor O. Zhermolenko, Khasan A. Akhmadiev, Aram A. Mkrtchyan, Fedor S. Fedorov, Anastasiia S. Netrusova, Aliya R. Vildanova, Dmitry V. Krasnikov, Albert G. Nasibulin, Yuriy G. Gladush
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Charge Transport in Thin-Film Transistors Based on Liquid-Crystalline Phthalocyanines
L. B. Avila, Zuchong Yang, Ilknur Hatice Eryilmaz et al. (+6 more)
We investigate a series of
liquid-crystalline phthalocyanines (metal-free and Cu, Zn, Ni, Co complexes) by correlating their vibrational signatures with their electronic performance in organic thin-film transistors (OTFTs). Raman spectroscopy reveals metal-dependent distortions of the phthalocyanine macrocycle, reflected in systematic shifts of the C-N-C and M-N vibrational modes. When integrated into OTFTs, all compounds exhibit markedly enhanced current response under ultrahigh
vacuum compared to an N2-rich environment, demonstrating that intrinsic charge transport is strongly suppressed by atmospheric species. Temperature-dependent measurements (100-300 K) show clear threshold-voltage shifts driven by deep interface and bulk traps, while all devices display thermally activated mobility with low activation energies (14-20 meV). These results highlight how mesomorphic order, metal coordination, and environmental conditions collectively govern charge transport in
liquid-crystalline phthalocyanines, offering design guidelines for their use as orientable semiconducting materials in organic electronics.
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All authors L. B. Avila, Zuchong Yang, Ilknur Hatice Eryilmaz, Lilian Skokan, Leonardo N Furini, Andreas Ruediger, H. Bock, I.H. Bechtold, E. Orgiu
Fluid Dynamics
Statistical State Dynamics Based Study of the Turbulent Ekman Layer
Eojin Kim and Brian F. Farrell
Streamwise roll and streak structures (RSS) are prominent features observed in both atmospheric and oceanic planetary boundary layers (PBL) as well as in laboratory scale Wall bounded shear flows. Despite their structural similarity across these systems, the mechanisms responsible for forming and sustaining the RSS remain debated. This study demonstrates that the same
turbulence sustaining mechanism previously identified in Wall bounded shear flows using the Statistical State Dynamics (SSD) formulation of the Navier Stokes equations (Farrell & Ioannou 2012; Farrell et al. 2017) also operates in the Ekman layer. By extending the SSD based stability analysis methods previously used for studying roll formation in wall bounded shear flows to the Ekman layer, we show that the well known Reynolds stress driven instability mechanism in wall-bounded
turbulence acts together with inflectional instability to produce and sustain RSS in the Ekman layer. These results enhance the mechanistic understanding of RSS formation and
evolution in the turbulent Ekman layer and provide a fundamental link between geophysical Ekman-layer
turbulence and
turbulence in engineering-scale shear flows.
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Computational Physics · Cross-listed from cs.CV
Flow Matching and Diffusion Models via PointNet for Generating Fluid Fields on Irregular Geometries
Ali Kashefi
We present two novel generative
geometric deep learning frameworks, termed Flow Matching PointNet and
Diffusion PointNet, for predicting fluid flow variables on irregular geometries by incorporating PointNet into flow matching and
diffusion models, respectively. In these frameworks, a reverse generative process reconstructs physical fields from standard Gaussian noise conditioned on unseen geometries. The proposed approaches operate directly on point-cloud representations of computational domains (e.g., grid vertices of finite-volume meshes) and therefore avoid the limitations of pixelation used to project geometries onto uniform
lattices, as is common in U-Net-based flow matching and
diffusion models. In contrast to graph neural network-based
diffusion models, Flow Matching PointNet and
Diffusion PointNet do not exhibit high-frequency noise artifacts in the predicted fields. Moreover, unlike such approaches, which require auxiliary intermediate networks to condition geometry, the proposed frameworks rely solely on PointNet, resulting in a simple and unified architecture. The performance of the proposed frameworks is evaluated on steady incompressible flow past a cylinder, using a
geometric dataset constructed by varying the cylinder's cross-sectional shape and orientation across samples. The results demonstrate that Flow Matching PointNet and
Diffusion PointNet achieve more accurate predictions of velocity and pressure fields, as well as lift and drag forces, and exhibit greater robustness to incomplete geometries compared to a vanilla PointNet with the same number of trainable parameters.
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Applied Physics · Cross-listed from cond-mat.mes-hall
Shubnikov-de Haas oscillations of two-dimensional electron gases in AlYN/GaN and AlScN/GaN heterostructures
Yu-Hsin Chen, Thai-Son Nguyen, Isabel Streicher et al. (+4 more)
AlYN and AlScN have recently emerged as promising nitride materials that can be integrated with GaN to form two-dimensional electron gases (2DEGs) at heterojunctions. Electron transport properties in these
heterostructures have been enhanced through careful design and optimization of epitaxial growth conditions. In this work, we report for the first time Shubnikov-de Haas (SdH) oscillations of 2DEGs in AlYN/GaN and AlScN/GaN
heterostructures, grown by metal-organic chemical vapor deposition. SdH oscillations provide direct access to key 2DEG parameters at the
Fermi level: (1) carrier density, (2) electron effective mass (m* ~ 0.24 me for AlYN/GaN and m* ~ 0.25 me for AlScN/GaN), and (3)
quantum scattering time (~ 68 fs for AlYN/GaN and ~ 70 fs for AlScN/GaN). These measurements of fundamental transport properties provide critical insights for advancing emerging nitride
semiconductors for future high-frequency and power electronics.
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All authors Yu-Hsin Chen, Thai-Son Nguyen, Isabel Streicher, Jimy Encomendero, Stefano Leone, Huili Grace Xing, Debdeep Jena
Chemical Physics
Effective Hamiltonian based DNP Sequence Optimization
Lorenzo Niccoli, Gian-Marco Camenisch, Matías Chávez et al. (+1 more)
Dynamic
nuclear polarization (DNP) enhances the intensity of NMR signals by transferring polarization from electron
spins to
nuclei via microwave irradiation. Pulsed DNP methods offer more control on the
spin dynamics than conventional continuous-wave approaches. Here, we report on-resonance and off-resonance DNP sequences optimized using effective
Hamiltonians derived from continuous Floquet theory. Experiments at 80 K and 0.35 T using a sample of 5 mM Trityl OX063 in a glycerol-d8/D2O/H2O
matrix (60:30:10, v/v/v) demonstrate that the optimized on-resonance sequence achieves 100 MHz electron offset bandwidth, while the offresonance sequence cantered at an electron offset of 50 MHz can cover 20 MHz, with 25 MHz and 20 MHz of microwave power, respectively. These results demonstrate that continuous Floquet theory is a useful framework for the optimization of pulsed DNP sequences.
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All authors Lorenzo Niccoli, Gian-Marco Camenisch, Matías Chávez, Matthias Ernst
Chemical Physics
Charged excitations made neutral: N-centered ensemble density functional theory of Fukui functions
Lucien Dupuy and Emmanuel Fromager
An in-principle exact working equation to compute electronic affinity and ionization Fukui functions is derived within the $N$-centered (Nc) ensemble extension of density functional theory (DFT). It circumvents the kernel derivative discontinuity problem of DFT for fractional electron numbers, whose contribution is recovered through weight derivatives of the ensemble density functional potential. Thus, it allows for the design of alternative and effective approximations, such as the weight-dependent scaling of regular functionals or the interpolation between known limits of Nc ensembles
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Applied Physics · Cross-listed from quant-ph
Classical Analog Emulation of Quantum Circuits via Time-Averaged Dynamic States
Matias Miguel Castillo Valle, Tim Tuuva, Benjamin Apffel et al. (+3 more)
Between the digital and
quantum paradigms lies the emerging field of
quantum-inspired analog computing, in which classical waves emulate
quantum circuits. We introduce wavebits – classical wave analogs of
qubits whose amplitudes are carried by physical oscillatory signals – and show that any nonseparable N-
qubit state can be encoded in 2N narrowband signals that remain locally separable at every instant; the nonseparable correlations are recovered at readout by time-averaged demodulation over auxiliary carrier frequencies, the nonseparability channels. We prove that any two-
qubit gate unravels into the time-averaged tensor product of two local time-varying operators, and that arbitrary
circuits are emulated with a base-frequency count scaling linearly in the number of entangling two-
qubit gates, independent of
qubit number for a fixed gate count. The exponential cost of the 2^N-dimensional state reappears at readout and in the averaging time of
circuits with many two-
qubit gates, not in
circuit execution, as quantified by an analytic error bound that doubles as a hardware design rule. A mixed-signal prototype emulates Bell state generation, controlled-NOT gates, phase kickback, and Bloch-sphere rotations at fidelities above 0.99, and numerical
benchmarks against exact statevectors validate the scheme for up to six
qubits. The architecture is directly implementable in acoustic, photonic, and mixed-signal platforms.
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All authors Matias Miguel Castillo Valle, Tim Tuuva, Benjamin Apffel, Hervé Lissek, Romain Fleury, Mathieu Padlewski
Applied Physics
Defect Landscape Engineering Suppresses Helium Damage in Ceramics
Nabil Daghbouj, Ahmed Tamer AlMotasem, Bingsheng Li et al. (+12 more)
Helium accumulation in structural ceramics used in
nuclear, fusion, and aerospace systems causes swelling, cracking, and early failure, yet controlling this damage has remained elusive. Here, we introduce defect landscape engineering, the deliberate creation of vacancy clusters prior to helium exposure, as a general strategy to suppress helium-induced degradation. Using {\alpha}-SiC as a model, we combine advanced microscopy, strain mapping, helium depth profiling, positron annihilation spectroscopy, and atomistic simulations to demonstrate that tailored pre-damage transforms helium defect
evolution. Instead of forming extended platelets and nanocracks, helium is trapped in stable, uniformly dispersed nanobubbles. Simulations reveal that small vacancy clusters act as dual-function sinks for irradiation-induced interstitials and preferential helium traps, fundamentally altering cascade recombination dynamics. This mechanism is composition-independent and scalable, offering a new design principle for radiation-tolerant ceramics across carbides, nitrides, and
oxides. By viewing defect control as a tunable parameter instead of a fixed material property, this work outlines a possible design route toward enhanced radiation tolerance in ceramics used in extreme environments.
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All authors Nabil Daghbouj, Ahmed Tamer AlMotasem, Bingsheng Li, Vladimir Krsjak, Jan Duchoň, Fang. Ge, Maceig Oskar Liedke, Andreas Wagner, Mohamed Bensalem, Fateh Bahadur, Frans Munnik, Miroslav Karlik, Anna Macková, Tomas Polcar, William J. Weber
Plasma Physics
What Is the Minimum Number of Parameters Required to Represent Solutions of the Grad-Shafranov Equation?
Huasheng Xie and Yueyan Li
Fast and accurate solutions of the Grad–Shafranov (GS) equation are essential for
equilibrium analysis, integrated modeling, and surrogate model construction in
magnetic confinement fusion. In this work, we address a fundamental question: what is the minimum number of free parameters required to accurately represent numerical solutions of the GS equation under fixed-boundary conditions? We demonstrate that, for most practical applications, GS
equilibria can be represented using only 2–5 free parameters while maintaining relative errors below 5%. For higher-accuracy requirements, we introduce a unified spectral representation based on the Miller extended harmonic (MXH) expansion in the poloidal direction combined with shifted Chebyshev (Cheb)
polynomials in the radial direction. This MXH–Cheb basis exhibits rapid convergence for two-dimensional GS
equilibria. For configurations where three
geometric moments (shift, elongation, and triangularity) are specified at the last closed flux surface (LCFS), relative errors on the order of $10^{-2}$–$10^{-3}$ can be achieved using as few as 13–20 parameters. In more general cases, including up–down asymmetric
equilibria, X-point configurations, and stiff pressure and current profiles (e.g., H-mode pedestals), accuracies beyond this level can be obtained with fewer than 100 parameters. The resulting
equilibrium configurations and profile functions are fully analytical, with smooth derivatives of all orders. These results provide a systematic foundation for developing high-fidelity, ultra-fast GS solvers and enable efficient reduced-order and AI-based surrogate modeling of tokamak
equilibria.
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