Physics and Society
How libraries classified physics preprints before arXiv and set the stage for distinguishing insiders from outsiders
Phillip H. Roth
In a world with ever-growing scientific literature, meaningful classifications are vital to keep on top of the latest results. In this Comment, historian and sociologist Phillip Roth traces the history of preprint classification in physics.
Fluid Dynamics
Physics-guided laminar flame speed correlation for methane-hydrogen-air mixtures with varying dilution
Raik Hesse, Christian Schwenzer, Roman Glaznev et al. (+3 more)
Fuel-flexible, low-carbon combustion systems need to accommodate methane/hydrogen mixtures with air and exhaust-gas dilution. To develop these, we require accurate and efficient correlations for laminar flame speed (LFS). In this work, we introduce a physics-guided LFS correlation that applies to burners, gas engines, and turbines. Our model uses a core-kinetic approach based on flame temperatures, an algebraic function for the equivalence ratio, and a mass-flux-based blending law. This allows for accurate predictions with any methane/hydrogen blend. We set the model parameters using one-dimensional flame simulations with C3Mech v4.0.1, chosen for its high prediction accuracy for a wide range of experimental data, including new results from our spherical combustion chamber. The new correlation provides accuracy comparable to a machine learning approach (Gaussian process regression), yet remains physically consistent, differentiable, and extrapolates well. This makes it suitable for computational fluid dynamics and control of fuel-flexible combustion systems.
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All authors Raik Hesse, Christian Schwenzer, Roman Glaznev, Florence Cameron, Heinz Pitsch, Joachim Beeckmann
Fluid Dynamics · Cross-listed from cond-mat.soft
Transition from contact to hydrodynamic lubrication over rough surfaces
Vincent Bertin and Olivier Pouliquen
We present a theoretical analysis of frictional transitions along the Stribeck curve for rough elastic contacts lubricated by a Newtonian fluid. Building on the mean-field framework of Persson and Scaraggi (J. Phys.: Condens. Matter 21 (2009) 185002), we formulate a minimal elastohydrodynamic model that couples contact mechanics and lubrication through a homogenized pressure decomposition. Dimensional analysis reveals three independent dimensionless parameters governing the frictional response, which correspond to a dimensionless speed, normal load, and surface roughness. Using asymptotic expansions, we first characterize the boundary and hydrodynamic lubrication regimes, which arise naturally as the quasistatic and smooth-surface limits of the model. In both limits, the contact morphology converges toward Hertzian contact in the regime of large elastic deformation, with boundary layers regularizing the separation profile at the edge of the contact zone. We then analyze the mixed lubrication regime and derive asymptotic expressions for the friction coefficient in the low- and high-speed limits. At high speeds, friction decomposes into a viscous contribution and a residual contact term, leading to a roughness- and load-dependent criterion for the transition to hydrodynamic lubrication that departs from constant-{\Lambda} ratio theories. At low speeds, friction reduction results from the progressive redistribution of the applied load between asperity contact and hydrodynamic pressure, yielding a characteristic transition speed from boundary to mixed lubrication. These results are summarized in a phase diagram that generalizes the classical Stribeck curve to a multidimensional parameter space.
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Fluid Dynamics
Helicity subgrid-scale models and their numerical validation
Nobumitsu Yokoi, Pablo D. Mininni, Annick Pouquet et al. (+2 more)
Large-eddy simulations (LES) with an appropriate subgrid-scale (SGS) model provide a powerful tool for investigating real-world
turbulence. The Smagorinsky model, one of the simplest and most used SGS models, often shows an over-dissipative behavior even when using dynamic procedures to adjust the model coefficient. By incorporating the structural or geometrical information of
turbulence provided by helicity (velocity-vorticity correlations), the helicity SGS model is expected to alleviate these issues in the standard Smagorinsky framework, in which only information of
turbulence intensity is considered through the turbulent energy. The validity of helicity SGS models is investigated here with the aid of direct numerical simulations (DNSs). Using configurations with and without net rotation, and with large-scale helicity gradients sustained by a mechanical forcing, we show that to better model SGS
turbulence, SGS helicity effects should be incorporated into the model together with the Smagorinsky-like eddy viscosity.
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All authors Nobumitsu Yokoi, Pablo D. Mininni, Annick Pouquet, Duane Rosenberg, Raffaele Marino
Medical Physics
Fluid dynamics informed CCTA-derived geometric parameters in right coronary artery anomalies predict abnormal invasive Adenosine FFR and Dobutamine FFR
Ali Mokhtari, Anselm W. Stark, Dominik Obrist et al. (+5 more)
Background: Right anomalous aortic origin of coronary arteries (R-AAOCA) involves fixed compression, assessable with adenosine-derived fractional flow reserve (FFRAdnosine), and additional stress-induced dynamic compression captured by dobutamine-derived FFR (FFRDobutamine). We hypothesized that coronary CT angiography (CCTA)-derived fluid dynamics-informed parameters outperform conventional metrics in predicting both FFR types. Methods: We retrospectively analyzed CCTA data from R-AAOCA patients who underwent invasive FFRAdnosine and FFRDobutamine assessment. Parameters were categorized as: (1) conventional metrics (cross-sectional area, perimeter, minor/major axis, intramural lumen area [ILA], effective diameter, area and diameter stenosis ratios) and (2) fluid dynamics-informed metrics (hydraulic diameter,
elliptic ratio, circularity, hydraulic diameter stenosis ratio, resistance index [RI], ostial angulation penalty [OAP], and comprehensive stenosis score [CSS]). Hemodynamic relevance was defined as FFR$\leq$0.80. Results: 81 patients were included. FFRAdnosine$\leq$0.80 occurred in 5 (6.2%) and FFRDobutamine$\leq$0.80 in 16 (19.8%) patients. For FFRAdnosine, top discriminators were RI (AUC=0.97), OAP (AUC=0.97), ostial area (AUC=0.96), and CSS (AUC=0.95). For FFRDobutamine, ostial minor diameter led (AUC=0.85), followed by RI (AUC=0.83) and ILA minor diameter (AUC=0.81). RI explained 45% and 43% of FFRAdnosine and FFRDobutamine variance, respectively. At optimal thresholds, RI achieved 100% sensitivity and 95% specificity for FFRAdnosine; ostial minor diameter achieved 100% sensitivity and 57% specificity for FFRDobutamine. Conclusions: In R-AAOCA, CCTA-derived fluid dynamics-informed metrics provide excellent and superior performance compared with conventional
geometric parameters in predicting hemodynamic relevance of fixed compression.
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All authors Ali Mokhtari, Anselm W. Stark, Dominik Obrist, Marius R. Bigler, Stefano F de Marchi, Lorenz Raber, Isaac Shiri, Christoph Graeni
Chemical Physics · Cross-listed from cond-mat.soft
Non-Additive Ion Effects on the Coil-Globule Equilibrium of a Generic Polymer in Aqueous Salt Solutions
Kushagra Goel, Monika Choudhary and Swaminath Bharadwaj
Mixtures of weakly and strongly hydrated anions induce non-additive changes in the LCST of thermoresponsive
polymers such as PNIPAM and PEO. Large-scale atomistic simulations of PNIPAM–NaI–Na$_{2}$SO$_{4}$ mixtures have shown that these effects arise from the interplay between favorable PNIPAM–iodide interactions and depletion of strongly hydrated sulfate ions. Here, we investigate whether chemically specific
polymer–anion interactions are necessary to reproduce such behavior. To this end, we study the coil–globule transition of a generic uncharged linear
polymer with non-specific
polymer–water and
polymer–ion van der Waals interactions in atomistic aqueous solutions of single and mixed salts. Simulations are performed at fixed concentrations of the strongly hydrated salt, Na$_{2}$SO$_{4}$, and increasing concentrations of the weakly hydrated salts, NaSCN and NaI. The generic
polymer qualitatively reproduces experimentally observed trends in pure NaSCN and Na$_{2}$SO$_{4}$ solutions, as well as the non-additive behavior in mixed salt solutions. In particular, the model captures the mutually reinforcing preferential accumulation of the weakly hydrated SCN$^{-}$ ions and depletion of the strongly hydrated SO$_{4}^{2-}$ ions near the
polymer that underlies the non-additive behavior. This mutual enhancement correlates with partitioning of sodium ions from the counterion cloud of SCN$^{-}$ ions to that of SO$_{4}^{2-}$ ions and is consistent with atomistic simulations of PNIPAM solutions. The model also reproduces the effects of background salt concentration and weakly hydrated anion identity on the non-additive behavior. These results demonstrate that non-specific
polymer–ion and
polymer-water interactions are sufficient to reproduce non-additive salt effects, suggesting a dominant role of bulk ion–ion and ion–water interactions.
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Plasma Physics · Cross-listed from hep-ph
Evaluation of QED cross sections in strong magnetic fields
Olavi Kiuru
Quantum electrodynamics (QED) becomes nonlinear when the
magnetic field strength surpasses the critical Schwinger limit $B_Q \approx 4.41\cdot 10^{13}$ G. This limit is surpassed, for example, in the magnetospheres of a specific class of
neutron stars known as magnetars, which has important consequences for magnetospheric
plasma dynamics due to modifications in scattering cross sections. Using a formalism previously applied to the study of
magnetic catalysis, I calculate the cross sections of all tree-level 1-to-2, 2-to-1, and 2-to-2 particle QED scattering processes that do not include a
photon propagator. The calculations are done in a strong background
magnetic field and the results are implemented into an open-source Python package. This article focuses on presenting the formalism and computational techniques required for the calculations, while the impact of the results on, e.g., magnetospheric
plasma dynamics is discussed in a companion letter (Kiuru et al. 2026).
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Optics
High-resolution scanning fluorescence imaging through scattering via speckle replica alignment and variance computation
Lei Zhu, Tengfei Wu, Bernhard Rauer et al. (+2 more)
Fluorescence imaging is an essential diagnostic tool in many fields, but diffraction-limited optical imaging at depth is limited by scattering. Here, we present a method based on multiple random illuminations, combined with a computational framework that retrieves high-resolution images by aligning local speckle replicas and computing their pixel-wise variance. We demonstrate its versatility in two regimes: linear wide-field one-
photon (1P) fluorescence imaging and nonlinear two-
photon (2P) fluorescence imaging where the object is excited by a scanned speckle field and detected with a single-pixel detector. This approach outperforms standard autocorrelation techniques in terms of resolution and convergence.
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All authors Lei Zhu, Tengfei Wu, Bernhard Rauer, Hilton B. de Aguiar, Sylvain Gigan
Physics and Society
Who burdens the welfare state? Migration and ageing in housing, education, and healthcare demand
Guillermo Prieto-Viertel, Carsten Källner, Elma Dervic et al. (+3 more)
Political discourse attributes the pressure on European welfare systems to foreign nationals. Yet projections of service demand rarely disaggregate service demand by citizenship status. We develop a structural demographic model and project healthcare, education, and housing demand in Austria through 2050, disaggregated by citizenship status and regions across migration scenarios. We find that migration, ageing, and fertility shape each sector differently. In healthcare, the ageing of Austrian nationals contributes 4.7 times more to demand growth than immigration, with the most acute pressures in rural, low-migration regions. In housing, migration accounts for the entire net growth in demand, concentrated in metropolitan hubs. In education, aggregate demand contracts regardless of migration assumptions, whereas future needs are driven more by the births of foreigners in Austria than by new arrivals. Foreign nationals consume services in proportion to their demographic weight, with deviations explained by age structure rather than over-utilisation. These results show that the drivers of service demand are sector-specific: migration restrictions could ease housing pressure, but would not address ageing-driven healthcare demand and may accelerate contraction in the education system.
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All authors Guillermo Prieto-Viertel, Carsten Källner, Elma Dervic, Ola Ali, Andrea Vismara, Rafael Prieto-Curiel
Optics
Role of a Quarter-Wave Plate in Confocal Microscopy: Signature of Spin-Orbit Interactions
Wenze Lan, Anton Lögl, Meryem Benelajla et al. (+3 more)
Spin-orbit interactions of light couple polarization and spatial degrees of freedom, underpinning phenomena such as the
spin Hall effect of light. Although widely explored at interfaces and in tightly focused beams, their impact in nominally paraxial confocal systems remains largely unexamined. Here we show that a single quarter-wave plate embedded in a simple confocal geometry between polarizers can strongly reshape the transverse structure of a Gaussian beam. We observe an enhancement of the polarization extinction ratio by more than two orders of magnitude, accompanied by a transformation of the Gaussian intensity profile into a first-order Hermite-Gaussian-like two-lobe mode. The orientation of this pattern is continuously tunable via rotation of the wave plate, evidencing polarization-controlled reorientation of the transverse field. To explain these observations, we introduce a minimal extension of Jones
matrix formalism incorporating complex parameters that quantitatively reproduces the measurements. Our results uncover a previously overlooked form of
spin-orbit-mediated mode control in standard confocal optics and establish a simple route to on-demand spatial mode engineering for applications in resonant spectroscopy, optical imaging and
quantum optics.
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All authors Wenze Lan, Anton Lögl, Meryem Benelajla, Clemens Schäfermeier, Khaled Karrai, Bernhard Urbaszek
Chemical Physics
Controlling isomer population using a dual-oscillator infrared free-electron laser
América Y. Torres-Boy, Anoushka Ghosh, Myles B. T. Osenton et al. (+8 more)
We report on the control and characterization of the isomer population of ions inside superfluid helium nanodroplets, using two-color operation of a dual-oscillator infrared free-electron
laser. The timing of both
lasers is highly synchronized, and their frequencies (or "colors") can be tuned independently over a wide range. Interaction of the singly deuterated
proton-bound dimer of dihydrogen phosphate and formate inside helium nanodroplets with both colors enables the control over its isomer population and the recording of - one-color hidden - infrared spectra of individual isomers.
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All authors América Y. Torres-Boy, Anoushka Ghosh, Myles B. T. Osenton, Akash C. Behera, Sandy Gewinner, Marco De Pas, Heinz Junkes, Wieland Schöllkopf, Alexander Paarmann, Gert von Helden, Gerard Meijer
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Importance of Configurational Charge Ordering for Machine Learning Interatomic Potentials
Martin Hoffmann Petersen, Steen Lysgaard, Arghya Bhowmik et al. (+2 more)
Machine learning interatomic potentials (MLIPs) enable large-scale atomistic simulations but remain challenged in describing mixed-valence materials where charge ordering strongly influences thermodynamic stability. Here we investigate the role of configurational charge ordering in MLIP structural optimization of the battery cathode material NaFePO4. We show that conventional MLIPs fail to reproduce the correct stability of intermediate Na concentrations because structural optimization leads to incorrect Fe2+/Fe3+ charge assignments, resulting in incorrect energy ordering and convex-hull predictions. Analysis of the Fe2+/Fe3+ charge assignment during structural optimization reveals that MLIPs are unable to capture the configurational charge ordering, leading to energy errors that make it difficult to identify the experimentally observed phase as the true ground-state structure. To address this limitation, we introduce an approach that encodes charge-state information directly into the MLIP representation by distinguishing between Fe2+ and Fe3+ environments during training. Retraining CHGNet, MACE and MACELES with this representation enables accurate structural optimization, correct identification of charge ordering, and improved agreement with density functional theory convex hulls. Our results demonstrate that incorporating configurational charge ordering into the MLIP representation is essential for modeling charge-disordered materials. Beyond recovering the correct ground state, this encoding allows a specific charge ordering to be imposed and held fixed during optimization, a capability unconstrained DFT struggles to guarantee, and we show that it generalizes across four polyanion frameworks and four transition-metal ions (Fe, Mn, Co, Ni), establishing a broadly applicable strategy for modeling mixed-valence transition-metal systems.
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All authors Martin Hoffmann Petersen, Steen Lysgaard, Arghya Bhowmik, Kedar Hippalgaonkar, Juan Maria Garcia Lastra
Optics
Efficient Picosecond-Laser Lift-Off of Copper Oxide from Copper: Modelling and Experiment
Andrius Žemaitis, Paulius Gečys and Mindaugas Gedvilas
Laser-induced lift-off of functional surface layers is a key process in micro- and nano-fabrication; however, optimization criteria for maximizing the lifted-off area remain insufficiently defined. In analogy to the well-established theory of efficient
laser ablation, where the maximum ablated volume per pulse is achieved at a peak fluence of F_0^{\mathrm{opt}} = e^{2} F_{\mathrm{th}}, we develop a theoretical framework for efficient
laser lift-off driven by Gaussian beams. By analytically describing the lift-off area as a function of peak fluence, beam radius, and focus position, we demonstrate that the maximum lifted-off area is achieved at a substantially lower optimal fluence, namely F_0^{\mathrm{opt}} = e^{1} F_{\mathrm{th}}. Closed-form expressions for the optimal beam radius, maximal lift-off area, and optimal focus position are derived and validated by numerical modeling. The theory is applied to picosecond
laser lift-off of copper
oxide from copper, showing excellent agreement between experimental observations and model predictions. The results reveal fundamental differences between ablation- and lift-off-dominated material removal and provide practical guidelines for maximizing process efficiency in
laser-assisted delamination, selective coating removal, and surface functionalization.
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Optics
Cd(Zn)O on SiC: epsilon-near-zero modes and plasmon-phonon coupling
Maria Villanueva-Blanco, Javier Yeste, Julia Ingles-Cerrillo et al. (+5 more)
Cd(Zn)O stands out as probably the best plasmonic material in the mid-IR, but it is usually grown on sapphire or other passive substrates. In this work we introduce SiC as a novel, highly polar, dopable substrate for Cd(Zn)O. The Cd(Zn)O/SiC system is analyzed as a function of the Zn concentration and thin film thickness, and the results are compared to those obtained in the Cd(Zn)O/sapphire system. XRD and reflectance measurements show that the
alloy with 10 % Zn nominal concentration has the best crystalline and plasmonic quality, with optical losses as good as 13 % of the
plasma frequency. The thin films show two surface polariton modes: a purely plasmonic symmetric mode at higher energies with negligible frequency dispersion and pinning at the
plasma frequency for the thinnest films, characteristic of an ideal epsilon-near-zero mode; and a plasmonic-phononic hybridized antisymmetric mode at lower energies, which thanks to the large value of the higher frequency dielectric constant of SiC compared to sapphire, shows much lower frequency dispersion, indicative of the stronger epsilon-near-zero character. Hence, Cd(Zn)O/SiC offers a promising platform for the development of ENZ devices on an active substrate.
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All authors Maria Villanueva-Blanco, Javier Yeste, Julia Ingles-Cerrillo, Pablo Ibañez-Romero, Carmen Martínez-Tomas, Vicente Muñoz-Sanjosé, Miguel Montes Bajo, Adrian Hierro
Optics
Nanoscale Surface Analysis of High Entropy Alloy
Hsin-Hui Huang, Meguya Ryu, Yoshiaki Nishijima et al. (+10 more)
Nanoscale surface analysis of 1 micrometer thick high
entropy alloys (HEAs) was carried out using nano-IR for hyperspectral imaging and single point spectroscopy in the 700-1700 1/cm spectral range. Nano-IR is based on the detection of scattered light from an oscillating metal coated nano-tip in one of the arms of the
Fourier transform infrared spectrometer and has a resolution defined by the tip radius of the probe, 20 nm, regardless of the excitation wavelength. HEA CuPdAgPtAu showed an absorption and reflection increase at 900-1100 1/cm band, which is consistent with Drude-Lorenz modeling of permittivity, however, could also signify
oxide formation as tested by X-ray photoelectron spectroscopy of CuPdAgPtAu and CrFeCoNiCuMo. Realization of polarization analysis for nano-IR nano-spectroscopy in the plane perpendicular to the sample's surface is discussed and modeled. The currently available modality of surface analysis with the excitation-detection mode of the p-pol.
antenna can be extended to full 3D analysis of the orientational dependencies of local absorbance and refractive index.
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All authors Hsin-Hui Huang, Meguya Ryu, Yoshiaki Nishijima, Haoran Mu, Mohit Kumar, Nguyen Hoai An Le, Adrian Cernescu, Jitraporn Vongsvivut, Andrew Siao Ming Ang, Lina Grineviciute, Challapalli Subrahmanyam, Junko Morikawa, Saulius Juodkazis
Applied Physics
A fractal geometry enhanced topology optimization design for high-performance liquid cooling plates
Zixu Han, Kairan Yang and Peng Zhang
The density-based bi-objective
topology optimization (TO) has been widely adopted in
liquid cooling plate design, where the design domain is treated as porous media with porosity as the design variable. However, conventional TO method struggles to directly optimize the convective heat transfer due to its incapabilities of explicitly depicting the heat transfer area in objective function, which limits the optimization of thermal performance. In this study, a fractal geometry
topology optimization (FGTO) method is proposed, which incorporates fractal dimension as an additional design freedom into the density-based TO framework. Different from the conventional TO methods, the FGTO explicitly describes the heat transfer area, and achieves a direct optimization of convective heat transfer through the objective function. Compared to the conventional TO, the FGTO achieves a more complex structural
topology in the optimized
liquid cooling plate with a 46% improvement in heat transfer area. The fractal dimension is manipulated by varying the input parameter s, and increasing s can improve thermal performance of the FGTO results at the cost of larger pressure drop. Superior thermal-hydraulic performance can be achieved by varying s, with the average and maximum temperatures of the FGTO results reduced by 15.6 K and 16.9 K, respectively, compared with those of the conventional TO results. The integration of fractal geometry into the TO intensifies the difference in objective function sensitivity between solid and
liquid phases, which is conducive to facilitating solid-
liquid separation and contributes to escape from local optimal solutions.
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Space Physics
Non-thermal plasma density redistribution in planetary magnetospheres due to ion-cyclotron waves
Joaquín Espinoza-Troni, Felipe A Asenjo and Pablo S Moya
Planetary magnetospheres exhibit diverse environments where Ultra-low frequency (ULF) pulsations induce nonlinear ponderomotive effects. Since suprathermal populations modeled by Kappa distributions are ubiquitous in these regions, their significant influence on the ponderomotive force (PF) induced by electromagnetic ion cyclotron (EMIC) waves must be accounted for. We investigate field-aligned
plasma density redistribution driven by the PF of traveling EMIC waves across different planetary magnetospheres. We apply a generalized slow-time-scale force balance equation to model stationary density solutions in low-beta
plasmas ($\beta \ll 1$) with isotropic Kappa distributions. To enable systematic comparison, wave modulation is described using the WKB approximation in a dipole
magnetic field, neglecting first-order
curvature effects. The
plasma response varies significantly with magnetospheric parameters: decreasing the kappa parameter and increasing
plasma beta counteract
plasma accumulation towards the equator. In low-beta environments, non-thermal effects substantially reduce the nonlinear response to short-period pulsations, though preserving the qualitative behavior of Maxwellian models. Furthermore, we characterize how the critical parameter governing the phase transition between equatorial density minima and maxima depends on the specific combination of
plasma beta, kappa, and L-shell. Our study demonstrates that non-thermal
plasma properties are a governing factor in field-aligned density redistribution driven by ULF waves, highlighting the necessity of incorporating them to accurately model ponderomotive phenomena across multifaceted planetary magnetospheres.
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Chemical Physics
Coupling Quantum Mechanical Modeling and Molecular Dynamics on Heterogeneous Supercomputers for Studying Distal Mutation Effects on Drug Binding in HIV-1
William Dawson, Louis Beal, Marco Zaccaria et al. (+1 more)
Predicting how
protein mutations affect drug binding remains a major challenge, particularly when the mutations are distal from the binding site. In this study, we introduce a coupled simulation workflow that combines long-time-scale molecular dynamics (MD) with high-throughput
quantum mechanical (QM) analysis to reveal the electronic structure signatures of mutation induced drug resistance in the HIV-1 protease. Our workflow leverages GPU-accelerated MD to generate conformational ensembles, and performs in-operando linear-scaling density functional theory (DFT) calculations on selected frames parallelized on a coupled partition of CPU nodes. This design enables efficient, massively parallel
quantum analysis of
protein-ligand complexes at atomic resolution. Using this approach, we investigate resistance to the antiviral Darunavir in a multi-mutant HIV-1 protease variant. By mapping the network of electronic interactions across the binding interface, our results highlight the critical role of conformational sampling and
quantum insight in understanding distal mutation effects, and demonstrate a scalable computational strategy for studying complex biophysical mechanisms of drug resistance. We argue that such kind of analysis may pave the way for designing inhibitors that maintain binding stability against systemic, mutation-induced destabilization.
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All authors William Dawson, Louis Beal, Marco Zaccaria, Luigi Genovese
Atomic Physics
In-Situ Differential-Light-Shift Cancellation for Trapped-Atom Clocks
Jan Simon Haase, Alexander Fieguth, Igor Bröckel et al. (+2 more)
Differential light shifts (DLS) induced by optical trapping fields fundamentally limit the stability and accuracy of trapped-atom microwave clocks. We demonstrate an in-situ method to cancel DLS by simultaneously interrogating multiple spatially separated atomic ensembles at different trap intensities generated from a common light source. By operating the ensembles at set intensity ratios and performing Ramsey spectroscopy, the intensity-dependent frequency shifts are measured within each experimental cycle and extrapolated to the zero-intensity limit. This approach effectively enables shot-to-shot determination of a DLS-free frequency without requiring magic wavelengths or species-specific cancellation schemes. We validate the method for Rb atoms trapped in time-averaged potentials by introducing controlled variations of the total trap power and show that the extrapolated frequency remains insensitive to these fluctuations. The technique is general and can be extended to other systematic shifts, providing a scalable route toward improved stability and accuracy in compact trapped-atom clocks and related
quantum sensors relying on optical dipole traps
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All authors Jan Simon Haase, Alexander Fieguth, Igor Bröckel, Jens Kruse, Carsten Klempt
Plasma Physics
Generation of Polarized Overdense Pair-photon Fireball via Laser-Driven Nonlinear-linear QED Cascade
Zhen-Ke Dou, Qian Zhao, Feng Wan et al. (+3 more)
Relativistic, polarized pair-
photon fireballs are central to understand the microscopic energy transfer of high-energy astrophysical
outflows, yet generating an overdense fireball in the laboratory, especially via an ultraintense
laser, remains a formidable challenge. Here, we propose a novel method of
laser-driven nonlinear-linear
quantum electrodynamics (NL-QED)
plasma, that dramatically lowers the
laser intensity threshold for dense pair-
photon fireball creation. By coupling polarization-resolved linear Breit-Wheeler and Compton processes with strong-field nonlinear radiation, we find that a self-organized NL-QED cascade is ignited in the
laser-driven hole boring at intensities of $\sim 10^{22}~\mathrm{W/cm^2}$, accessible with current 10-PW-class
laser facilities. Consequently, we demonstrate the generation of a pair-
photon fireball with an overdense gamma-ray bath (maximum average density $\overline{n_\gamma} \approx 3 \times 10^{22}~\mathrm{cm^{-3}}$) and a pair
plasma reaching collective regime (maximum average density $\overline{n_\pm} \approx 3 \times 10^{17}~\mathrm{cm^{-3}}$), which is highly polarized. Our method provides a comprehensive framework for studying
laser-driven QED
plasma and its application in laboratory astrophysics, probing multi-process QED physics.
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All authors Zhen-Ke Dou, Qian Zhao, Feng Wan, Chong Lv, Bing Guo, Jian-Xing Li
Fluid Dynamics
Symmetry-Constrained Exact Coherent Structures in Plane Poiseuille Flow
Akshit Nanda and Ritabrata Thakur
Turbulence in wall-bounded shear flows is increasingly understood through exact coherent structures (ECS) – invariant solutions of the Navier-Stokes equations that act as organising centres in the high-dimensional state space. Here we report five new ECS of plane Poiseuille flow: two relative periodic orbits (RPOs) and three travelling waves (TWs), that are computed in four distinct
symmetry-invariant subspaces using a Newton-Krylov-hookstep solver initialised from direct numerical simulations. We trace each state through one-parameter continuations in both the Reynolds number $Re$ and the spanwise period $L_z$. All five states are organised around counter-rotating rolls sustaining streamwise velocity streaks, yet they exhibit qualitatively different stability properties: the two RPOs are linearly stable within their
symmetry subspace, while the three TWs are saddle-type solutions whose instabilities are, respectively, mixed oscillatory-and-monotone, purely monotone and purely oscillatory. The continuation diagrams reveal their bifurcation geometry, from simple saddle-node folds for the RPOs to a pronounced S-shaped multi-branch structure with three coexisting dissipation levels for one of the travelling waves. Along each branch, the roll-streak
topology is preserved across the folds, with the different branches distinguished by their amplitude and gradient intensity rather than by a change in spatial organisation. Floquet spectra evaluated at multiple points along each branch shows that folds generically act as sites of reduced instability for the travelling waves, while upper branches develop stronger and sometimes qualitatively different unstable modes. These include the emergence of linearly stable segments on the intermediate and upper branches of the multi-branch travelling wave, despite the solution being unstable at its reference parameters.
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Biological Physics
Biological Time Equivalence in Vertebrates: Thermodynamic Framework, Comparative Tests, and Clade-Specific Deviations
Mesfin Taye
The product of resting heart rate and maximum lifespan is approximately constant across adult warm-blooded vertebrates, $N^\star = f_H L \approx 10^9$ cardiac cycles, a regularity documented since Rubner (1908) but lacking a thermodynamic derivation. We derive $N^\star$ from the non-
equilibrium second law by treating the adult organism as a metabolic non-
equilibrium steady state (NESS) and introducing the closure $\dot{e}_p = \sigma_0 f$, linking
entropy production rate to heart rate via a mass-specific parameter $\sigma_0 \propto M^0$. Integration yields a finite dissipative budget $\Sigma = \sigma_0 N^\star$, identifying $N^\star = \Sigma/\sigma_0$ as the correct primitive conserved quantity; lifetime energy per unit mass is a derived consequence valid only under simultaneous constancy of body temperature and $\sigma_0$. Phylogenetically independent contrasts on 112 endotherm species yield a $\log f_H$–$\log L$ slope of $-0.99 \pm 0.04$ ($p=0.84$ against $-1$); the West–Brown–Enquist null of zero inter-clade variation is rejected ($F=12.7$, $p<0.001$). A factored multiplier $\Phi_C = \Phi_{\mathrm{duty}} \cdot \Phi_{\mathrm{thermal}} \cdot \Phi_{\mathrm{mito}} \cdot \Phi_{\mathrm{haz}}$, calibrated from independently measured physiology, accounts for longevity deviations across four warm-blooded clades. The integral of physiological frequency defines a biological proper time classifying longevity mechanisms as time dilation (reduce $f$) or budget expansion (reduce $\sigma_0$). The decisive test is calorimetric measurement of $\sigma_0 = P/(TfM)$ across three body-mass decades.
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Accelerator Physics
Optimization of Beam Transmission in the extraction lines of the K130 Room Temperature Cyclotron at Variable Energy Cyclotron Centre (VECC), Kolkata
Arup Ratan Jana, Animesh Goswami and Malay Kanti Dey
The K130 Room Temperature Cyclotron (RTC) at the Variable Energy Cyclotron Centre (VECC), Kolkata has delivered a variety of ion beams for experimental programs with stable performance since the 1970s. The extracted beams are transported to experimental stations through four beamlines. In this work, a two-step semi-numerical optimization framework is presented to improve the transmission efficiency of these transport lines. At its core, the method relies on multiparticle simulations to account for beam losses and nonlinear effects, which render the problem analytically intractable. To address these complexities, a derivative-free global optimization framework is developed to systematically improve beam transmission in the cyclotron beamlines, and its effectiveness is demonstrated experimentally. In the first phase, the beam parameters at the beamline entrance are estimated using
Bayesian optimization constrained by experimentally measured transmission ratios for selected optics configurations. In the second phase, the quadrupole gradients are optimized using the Covariance
Matrix Adaptation
Evolution Strategy (CMA-ES) to maximize beam transmission. Optimized settings computed using this simulation based semi numerical methodology were then experimentally validated, achieving beam transmissions exceeding 70%.
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Data Analysis and Statistics · Cross-listed from stat.AP
Bayesian estimation of optical constants using mixtures of Gaussian process experts
Teemu Härkönen, Hui Chen and Erik Vartiainen
We propose modeling absorption spectrum measurements as mixtures of Gaussian process experts. This enables us to construct a flexible statistical model for interpolating and extrapolating measurements, facilitating statistical integration of Kramers-Kronig relations to estimate the whole complex refractive index. Additionally, we statistically model the anchoring points used in subtractive Kramers-Kronig relations to account for possible measurement errors of the anchor point. In addition to flexible statistical modeling, the mixtures of Gaussian process formulation enables automatic selection of measurement points to use for extrapolation. We apply the method to experimental absorption spectrum measurements of gallium arsenide, potassium chloride, and transparent wood.
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Plasma Physics
Applications of a novel model-based real-time observer for electron density profile control experiments in TCV
F. Pastore, O. Sauter, F. Felici et al. (+12 more)
Real-time control of tokamak
plasmas encompasses sustaining a high-performance stationary state, avoiding disruptions, and managing ramp-up and ramp-down phases. Real-time estimation and control of electron density is fundamental for monitoring and controlling particle confinement, heating efficiency, exhaust conditions,
impurity concentration, fusion power, and proximity to the density limit. Building on the integration of a multi-rate observer based on RAPDENS into the TCV control system, this study explores its application to density profile control for detachment studies, ECH, and NBH L-mode
plasmas, and high-performance H-mode scenarios. TCV experiments demonstrate the observer's capability to support detachment studies in complex divertor geometries, controlling the line-averaged density within the last-closed flux surface while rejecting interferometer pick-up from Scrap-Off Layer density in the divertor. The estimated density profile enables local control of central density in ECH/NBH L-mode
plasmas below cutoff conditions; heating-induced profile peaking modification is treated as a disturbance to the control task. Real-time estimation of time-varying transport coefficients, such as the pinch velocity-to-diffusivity ratio, improves model predictive capabilities, and the underlying turbulent transport is characterized via linear and non-linear gyrokinetic simulations with GENE. Simultaneous control of edge-normalized density and toroidal beta in H-mode
plasmas is then demonstrated, yielding good confinement, scenario reproducibility, and a diagnostics-independent edge-density metric, while avoiding density limits and diagnostic faults propagation.
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All authors F. Pastore, O. Sauter, F. Felici, D. Kropackova, A. Balestri, C. Galperti, O. Kudlacek, K. Lee, A. Pau, T. Ravensbergen, S. Van Mulders, B. Vincent, N.M.T. Vu, the TCV team, the EUROfusion Tokamak Exploitation Team
Chemical Physics
Microscopic Structure and Dynamics of Interfacial Water at Fluorinated vs Nonfluorinated Surfaces – Insights from Ab-Initio Simulations and IR Spectroscopy
Maximilian R. Becker, Ruben Cruz, Kenichi Ataka et al. (+2 more)
Per- and polyfluoroalkyl substances are a class of synthetic chemical compounds widely used as coatings to lower surface energies. Yet the microscopic mechanisms of their weak interaction with water and organic compounds remain poorly understood. Here, we perform large-scale density-functional-theory molecular dynamics simulations to investigate water at self-assembled monolayers (SAMs) of fluorinated and non-fluorinated hydrocarbons. We analyze the interfacial water structure and compare it to the prototypical hydrophobic air-water interface. The interfacial water structure at both SAMs closely resembles that at the air-water interface, featuring a distinct depletion layer and a two-dimensional hydrogen-bond network parallel to the surface. Computed anisotropic infrared spectra reproduce key experimental signatures observed in surface-enhanced infrared absorption spectroscopy (SEIRAS), including the presence of free OH vibrations directly probing the local surface-water interactions. Notably, while the free OH stretch at the hydrocarbon SAM-water interface exhibits a red shift relative to the air-water interface, indicative of weak binding, the fluorinated SAM-water interface displays a weakly blue-shifted free OH mode, in agreement with experiment. This frequency behavior defies common interpretations based on the vibrational Stark effect. Further, we show that the reorientation dynamics of water molecules are significantly slower near the fluorinated surface, which we correlate with spectral line shapes, an effect rather expected at hydrophilic surfaces. This indicates that fluorinated SAMs, despite being macroscopically more hydrophobic than their unfluorinated counterparts, exhibit spectroscopic characteristics that neither qualify it as hydrophobic nor hydrophilic.
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All authors Maximilian R. Becker, Ruben Cruz, Kenichi Ataka, Joachim Heberle, Roland R. Netz
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Hunting Structural Demons in Digital Reticular Chemistry: Lessons from Metal-Organic Frameworks
Yongchul G. Chung and Myoung Soo Lah
Digital reticular chemistry relies on accurate
crystal structures to power computational screening, data-driven discovery, and structure-property analysis, yet recent studies reveal that more than half of the top-performing candidates in major computational screening campaigns are chemically invalid. In experimental MOF databases, structural errors arise when disordered or incomplete structural models are incorrectly converted into fully specified simulation inputs. In hypothetical MOF database, structures are complete by construction but may encode chemically implausible oxidation states, coordination environments, or charge distributions. We term these erroneous structural models "structural demons." This mini-review asks three questions: where these errors enter, how we find them, and how we prevent them. On the prevention side, the key steps are keeping diffraction data and synthesis details together from the start, using consistent curation when structures enter a database, and filtering
topology choices before structure generation. Connecting these steps can keep many bad structures out of downstream databases and reduce the need to fix them later.
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Plasma Physics · Cross-listed from astro-ph.SR
Energy Transport and Heating by Non-Thermal Electrons in a Turbulent Solar Flare Environment
A. Gordon Emslie and Eduard P. Kontar
The impulsive phase of a
solar flare is known to generate strong
turbulence and to transfer
magnetic energy into accelerated electrons. Recognizing the importance of angular
diffusion on the dynamics of the accelerated electrons, we extend previous treatments by deriving analytic solutions for the electron flux and associated energy deposition in two regimes: scattering dominated by inelastic Coulomb collisions and scattering dominated by elastic interactions with turbulent scattering centers. We show that the
turbulence-dominated scattering term strongly reshapes the spatial distribution of the
plasma heating: compared to the traditional collisional thick-target approach, turbulent scattering could lead to an order-of-magnitude increase in coronal heating and an even greater suppression of chromospheric heating. Scattering also acts to reduce the anisotropy of the electron distribution and so reduces the net current associated with the nonthermal electrons. The return-current Ohmic heating is accordingly reduced to a level that renders it negligible compared to direct collisional heating. The results have significant implications for models of atmospheric response to impulsive phase energy release, in particular chromospheric evaporation,
flare-driven coronal heating, the formation of loop-top hard X-ray sources, and the longstanding discrepancy between modeled and observed soft X-ray line profiles.
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Optics
Linear Arrays of Metal-Coated Microspheres: a Polarization-Sensitive Hybrid Colloidal Plasmonic-Photonic Crystal
Cosmin Farcău
Colloidal plasmonic-photonic
crystals represent a class of hybrid materials composed of a dielectric colloidal spheres photonic
lattice and a metal plasmonic film. In this work, the optical properties of a linear array colloidal plasmonic-photonic
crystal consisting of silver films deposited over linear arrays of polystyrene microspheres are analysed in detail. Experimental and simulated optical transmittance and reflectance spectra both with unpolarized and polarized light are used to investigate the optical response of the linear plasmonic-photonic
crystal. Among the various photonic/plasmonic modes observed, the existence of both propagative plasmonic-photonic hybrid mode and localized surface plasmon mode can be mentioned. The spectral tunability of these structures is highlighted by studying the dependence of the optical response on geometrical parameters such as sphere diameter and grating period. Finally, the linear plasmonic-photonic
crystal exhibits a polarization-selective surface-enhanced Raman scattering effect, making them of interest for both fundamental studies and development of applications based on surface-enhanced Raman spectroscopy or surface-enhanced fluorescence.
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Optics
Noise modelling of waveguide based squeezed light sources
Erik Anders Torsten Svanberg, Daniel Voigt and Vaishali Adya
Squeezed states of light are used for precision metrology and
quantum-enhanced measurements, with applications spanning communication and sensing. State-of-the-art squeezed-light sources typically rely on optical cavities to achieve high, usable levels of squeezing. Recently, waveguide-based squeezed-light sources have demonstrated significant improvements in achievable squeezing, with performance currently limited by fabrication-induced losses. In this work, we present a detailed analysis of waveguide-based squeezers, examining the effects of phase noise, multiple loss mechanisms, and fundamental light leakage seeding the squeezer. We further investigate a cascaded squeezer architecture, in which a second waveguide operates as a phase-sensitive amplifier to mitigate out-coupling and detection losses. Owing to their ease of integration, robustness to high pump powers, and low intrinsic phase noise, we propose waveguide-based squeezed-light sources as a promising alternative for
quantum noise reduction in future gravitational wave detectors, such as the Einstein
Telescope.
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