Optics
Excited states engineering maximizes singlet generation by triplet fusion in conjugated systems
Alessandra Ronchi, Masashi Mamada, Michel Frigoli et al. (+1 more)
Photon upconverters are anti Stokes emitters capable of generating
photons with higher energy than those absorbed. This behavior can be achieved through different mechanisms, which are extensively studied for applications in imaging, anticounterfeiting, information encryption and most importantly,
solar energy technologies. Among these mechanisms,
photon upconversion based on sensitized triplet-triplet annihilation (sTTA-UC) is particularly attractive because it operates under low intensity, incoherent light. In sTTA UC, two optically dark triplet states of a conjugated annihilator fuse upon collision to populate a higher energy fluorescent singlet, with the triplets initially generated via energy transfer from a lower energy sensitizer. Here we introduce a general molecular design strategy to maximize singlet generation through TTA. By selective substitution, we engineered a naphthalene derived annihilator with an excited state energy landscape that strongly favors singlet formation, achieving yields up to 0.83. When combined with an appropriate triplet sensitizer, the system delivers stable UV/visible upconversion peaking at 390 nm, with an absolute upconversion yield about 0.19 and an activation excitation intensity threshold lower than 0.1 suns under non-coherent broadband excitation fully compatible with the requirements of
solar powered technologies.
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All authors Alessandra Ronchi, Masashi Mamada, Michel Frigoli, Angelo Monguzzi
Optics
Nonlinear Frequency Translation in Micromachined Rb Vapor Cells
Heleni Krelman, Ori Nefesh and Liron Stern
The exceptional nonlinearity of alkali-metal vapors enables highly efficient nonlinear optical processes even at relatively low optical intensities. However, such processes have traditionally relied on centimeter-scale vapor
cells. Here, we utilize a versatile chip-scale Rb vapor platform to generate coherent blue and mid-IR light in continuous-wave mode by means of resonant four-wave mixing. Optimized optical overlap with the atomic medium enables blue light generation of $\sim$20 $\mu$W over a very short interaction length, while maintaining a directly measured linewidth of $\sim$1 MHz, which is presently limited by the measurement apparatus. Comparison with a conventional glassblown vapor
cell further shows that the micromachined platform can achieve higher coherent blue-light generation efficiency despite its substantially shorter interaction length. Moreover, an anodically bonded Si window enables to detect coherent mid-IR emission with collected powers of $\sim$50 nW. We further characterize the temperature dependence and input-power scaling of the blue emission, confirming efficient nonlinear conversion within these compact vapor
cells. This chip-scale platform provides a versatile foundation for a range of nonlinear optical functions, from precise wavelength references and
quantum light sources to next-generation
quantum sensors.
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Optics · Cross-listed from quant-ph
Expectation Pauli-Lubanski vector and intrinsic angular momentum of relativistic wavepackets
Konstantin Y. Bliokh
In non-relativistic mechanics, the total (orbital) angular momentum (AM) of a spatially-distributed system can be decomposed into intrinsic and extrinsic contributions. In relativistic
quantum mechanics, intrinsic AM is typically associated with
spin, which can be described using the Pauli-Lubanski four-vector. Here, we develop a unified formalism that combines the main features of both approaches and describes the intrinsic AM of a relativistic wavepacket, including both
spin and orbital contributions. Our approach is based on the "expectation Pauli-Lubanski vector" constructed from the expectation values of the wavepacket's momentum and AM. Equivalently, it defines the intrinsic AM relative to the wavepacket's energy centroid. In contrast to the conventional Pauli-Lubanski formalism, the zero-mass singularity does not occur for the expectation Pauli-Lubanski vector. Consequently, the intrinsic AM of a wavepacket may have an arbitrary orientation with respect to its momentum, even for massless particles. We illustrate the general theory with a number of examples of relativistic wave beams and packets carrying
spin and orbital AM.
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Medical Physics
Characterising Water Exchange in Gliomas Using Diffusion MRI with Free Gradient Waveforms
Arthur Chakwizira, Filip Szczepankiewicz, Carl-Fredrik Westin et al. (+3 more)
Transmembrane water permeability, which regulates cellular water exchange and is influenced by water channels such as aquaporin-4 (AQP4), has been implicated in glioma progression and may affect tumour infiltration and treatment response. Non-invasive mapping of water exchange may therefore provide biomarkers of glioma pathology. This study investigates the feasibility of characterizing water exchange in gliomas using
diffusion MRI with free gradient waveforms, known as the Restriction-Exchange (ResEx) approach, which enables exchange quantification independent of restricted
diffusion effects. Thirteen patients with histologically confirmed gliomas (ten glioblastomas, three astrocytomas) underwent preoperative MRI at 3T using a custom ResEx protocol. Multiple
diffusion-weighted acquisitions with selective exchange sensitivity were performed to estimate voxel-wise maps of the apparent
diffusion coefficient (ADC),
diffusion kurtosis, and water exchange rate. ResEx-derived maps revealed heterogeneous spatial patterns across and within tumours. Elevated exchange rates were commonly observed in enhancing tumour margins, potentially reflecting smaller
cells, increased membrane permeability or AQP4 upregulation. In some cases, elevated exchange extended into non-enhancing peritumoural regions. Exchange values in oedema were slightly higher than in healthy tissue, suggesting potential infiltration or membrane disruption.
Diffusion MRI with free gradient waveforms permits non-invasive mapping of water exchange in gliomas and reveals physiological information not captured by standard imaging. Exchange rate mapping may offer novel biomarkers of tumour aggressiveness, infiltration, and treatment response, and holds promise for
surgical and radiotherapy planning.
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All authors Arthur Chakwizira, Filip Szczepankiewicz, Carl-Fredrik Westin, Linda Knutsson, Pia C Sundgren, Markus Nilsson
Applied Physics
Thin-film nanostructuring of NbTi superconducting resonators for enhanced temperature sensitivity in cryogenic thermometry
André Chatel, Roberto Russo, Seyed Alireza Hashemi et al. (+4 more)
The rising complexity of cutting-edge cryogenic systems is currently imposing challenging technical constraints to the monitoring of ultra-cold temperatures through standard commercially available sensors. Among different technologies, superconducting microwave resonators have been recently investigated as ideal candidates for performing on-chip cryogenic thermometry, in reason of their intrinsically low power dissipation, large temperature sensitivities and excellent sub-$\mu$K resolution below 10 K. Through this study, we aim at demonstrating the possibility to enhance the temperature performance of superconducting microwave resonators by means of surface nanostructuring. Different arrays of nanotrenches are strategically patterned on the inductive line of a 1.3 GHz planar resonator, by partially etching a Nb$_{50}$Ti$_{50}$ thin-film, in order to tune the critical transition of the material and, therefore, increase the
curvature of the $f_{res}(T)$ response. Although the presence of such thinned superconducting regions introduces larger microwave losses, a 1.5 K decrease of $T_\text{C}$ is recorded, which directly translates into an enhancement of the temperature sensitivity by a factor 10, with respect to a non-nanostructured sensor. A maximum value of $df_{res}/dT = 62 \ \text{MHz/K}$, at 4.2 K, is achieved for the device showing the largest nanotrench width of about 350 nm. These results demonstrate that such a surface nanostructuring approach can be exploited as an effective design strategy to tune the $f_{res}(T)$ response of superconducting microwave resonators. Although this technique is found to introduce additional RF losses into the superconducting device, thereby limiting the achievable temperature resolution to the few-$\mu\text{K/Hz}^{1/2}$ range, we believe that similar approaches could be further investigated for the development of future cryogenic sensors.
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All authors André Chatel, Roberto Russo, Seyed Alireza Hashemi, Pol Torres-Vila, Jürgen Brugger, Giovanni Boero, Hernán Furci
Atomic Physics
Isotopic effect on collisional widths and shifts of Hg clock transition induced by cold Rb atoms
Renu Bala, Adam Linek, Marcin Witkowski et al. (+4 more)
We study the isotopic dependence of collisional widths and shifts of the Hg clock transition $^1$S$_0$-$^3$P$_0$ perturbed by the Rb atoms in the temperature range from 1 nK to 1 K. For this purpose, we model the Born-Oppenheimer effective interaction potential by including the leading long-range van der Waals coefficients. For elastic collisions, we show the connection between the dependence of collision line shape parameters on the reduced mass of colliding partners as well as the variation of the scattering length in the excited and ground states of the Hg-Rb system in the $\upmu$K temperature range. We confront the full
quantum scattering calculations with a semi-classical approximation for collisional widths and shifts. We show that the shape resonances in excited and ground scattering states lead to significant variations of collisional line shape parameters with the change of the reduced mass of colliding atoms. We also indicate the possible influence of inelastic collisions, which could lead to universal behavior and significantly affect the dependence of collisional broadening and shifting on the isotopic combination of colliding atoms.
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All authors Renu Bala, Adam Linek, Marcin Witkowski, Piotr S. Żuchowski, Michał Zawada, Paul S. Julienne, Roman Ciuryło
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Liquid-phase encapsulation of $\pi$-conjugated dyes in boron nitride nanotubes: Ensemble and single-nanotube optical characterization
Friedrich Schöppler, Lukas Stumpf, Lucas Fuhl et al. (+5 more)
Boron nitride nanotubes (BNNTs) provide wide-bandgap, optically transparent one-dimensional hosts for molecular dyes, limiting direct electronic participation of the host. Whether dye@BNNT systems produce bright, well-defined J- or H-aggregates or instead heterogeneous emissive ensembles whose character depends on chain length and local packing remains only partly resolved. We address this question using ensemble extinction, photoluminescence,
quantum-yield measurements, and TCSPC-derived radiative and non-radiative rates, together with polarization-resolved single-nanotube microscopy on encapsulated quaterthiophene, sexithiophene, octithiophene, and Nile Red, selected from a ten-dye screening. In the oligothiophene series, confinement modifies spectra and excited-state dynamics in a length-dependent manner, with all three oligothiophenes forming weakly emissive ensembles with suppressed effective radiative rates and 6T showing the strongest redistribution between effective radiative and non-radiative decay. The absence of radiative-rate enhancement or fluorescence-lifetime shortening across the series disfavors bright J-aggregate assignments. Polarization-resolved single-nanotube microscopy reveals strongly polarized emission, but with tube-to-tube and intratube variations, identifying oligothiophene@BNNTs as ordered yet structurally heterogeneous confined ensembles. Nile Red provides a complementary case in which the dominant response is dielectric tuning of a solvatochromic charge-transfer state rather than oligothiophene-like aggregate formation. These findings establish dye-filled BNNTs as optically quiet nanoconfined systems in which molecular ordering, dielectric confinement, and guest-guest coupling can be distinguished through combined ensemble and single-nanotube spectroscopy.
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All authors Friedrich Schöppler, Lukas Stumpf, Lucas Fuhl, Elena Behr, Charlotte Allard, Christoph Lambert, Richard Martel, Tobias Hertel
General Physics
Alleviating the Hubble Tension Using Coupled Dark Energy - Dark Matter Interaction
Yismaw Wassie Ambelu, Amare Abebe, Solomon Belay Tessema et al. (+1 more)
We investigate two interacting dark energy models, $\xi$CDM and $\xi w$CDM, as potential means of alleviating the $H_0$ tension, using DESI DR2 BAO data along with the Planck 2018 CMB, Pantheon+ SNe Ia, and KiDS-1000/DES-Y3 weak
lensing data. For the $\xi$CDM model, with a free coupling strength ($\xi$) and fixed dark energy equation-of-state ($w_0$), we find $H_0 = 71.59^{+1.69}_{-2.30}\mathrm{kms^{-1}Mpc^{-1}}$ from Planck-only data, tightening to $69.72^{+0.50}_{-0.41}\mathrm{kms^{-1}Mpc^{-1}}$ for the complete Planck+BAO+SN+WL
dataset, reducing the tension from $\sim5.0\sigma$ to $\sim2.8\sigma$. In the $\xi w$CDM model, with both $\xi$ and $w_0$ free, Planck-only data provide $H_0 = 72.46^{+4.05}_{-3.66}\mathrm{kms^{-1}Mpc^{-1}}$, while the full
dataset yields $H_0 = 70.22^{+0.45}_{-0.40}\mathrm{kms^{-1}Mpc^{-1}}$, reducing the tension to $\sim2.5\sigma$, with phantom preference $w_0 = -1.116^{+0.043}_{-0.043}$ and negative coupling $\xi = -0.107^{+0.012}_{-0.023}$. With the convention $-\xi H \rho_{de}$ >0, the negative coupling ($\xi < 0$) points to $Q > 0$, giving continuous energy transfer from dark energy to dark matter. This interaction modifies the
evolution of the dark sector and the expansion history from early to late times, shifting the inferred $H_0$ to higher values. For the $\xi w$CDM model, Planck+BAO+SN yields a substantial improvement in fit ($\Delta\chi^2=-14.60$) and a strong AIC preference ($\Delta\mathrm{AIC}=-10.60$), but $\Delta \mathrm{BIC} = +0.30$ weakly prefers $\Lambda$CDM. Inclusion of WL data weakens the fit improvement ($\Delta\chi^2 = -6.67$) yielding $\Delta \mathrm{BIC} = +8.23$, a strong BIC preference for $\Lambda$CDM. This AIC/BIC discrepancy shows that the data favor the extra dark sector freedom, but not strongly enough to overcome the BIC penalty. These interacting models are therefore viable mechanisms for alleviating the $H_0$ tension.
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All authors Yismaw Wassie Ambelu, Amare Abebe, Solomon Belay Tessema, Shambel Sahlu
Plasma Physics · Cross-listed from astro-ph.SR
Formation of Suprathermal Electron Populations in the Expanding, Turbulent Solar Wind
Maximilien Péters de Bonhome, Fabio Bacchini, Luca Pezzini et al. (+1 more)
Nonthermal features are ubiquitously observed in electron velocity distribution functions in the
solar wind, yet their origin in the collisionless, turbulent, expanding
solar-wind
plasma remains unclear. We investigate how
solar-wind expansion and Alfvénic
turbulence jointly generate and regulate these features using the first fully kinetic particle-in-
cell simulation of an expanding turbulent
plasma under heliospheric conditions. In our setup, expansion-driven weakening of the
magnetic field adiabatically cools the
plasma perpendicularly to the mean field while leaving the parallel temperature largely unchanged, driving the system toward the firehose-instability threshold. Concurrently, strongly anisotropic
turbulence leads to perpendicular heating and the development of nonthermal features. Subsequently, we find that suprathermal electron populations preferentially develop in the parallel direction, forming pronounced power-law tails even under weakly compressive, highly Alfvénic conditions, and persist despite anisotropy regulation by the firehose instability. The preferentially parallel energization suggests the involvement of parallel electric fields or resonant wave–particle interactions, rather than simple velocity-space redistribution. These results provide the first direct evidence of the emergence of nonthermal-electron features in a unified kinetic framework linking expansion,
turbulence, and instabilities in the
solar wind.
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All authors Maximilien Péters de Bonhome, Fabio Bacchini, Luca Pezzini, Viviane Pierrard
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Polymorphic crystallites model for monolayer amorphous materials
Le-Ye Zhu, Xi Zhang, Yun-Peng Wang et al. (+4 more)
Establishing atomistic models of amorphous materials remains a central challenge in materials science. Here, we examine three representative multicomponent monolayer systems using first-principles-trained machine-learning potentials (MLPs) and an energy-guided Monte Carlo structural-search workflow. For monolayer amorphous boron nitride (maBN), independent density-functional-theory (DFT) single-point calculations confirm that the ensemble generated by the MLP-driven search is lower in energy on average than an extended-Tersoff-generated ensemble. Across the sampled maBN structures, local-ring classification combined with strict connected-domain analysis identifies h-BN-like, o-B$_2$N$_2$-like, and o-B$_4$N$_4$-like crystallite domains together with mixed medium-range order. Only individual samples containing at least two distinct phase-pure crystallite-domain types are classified as polymorphic crystallites. The same analysis finds coexisting hexagonal and tetragonal domains in monolayer amorphous LiCl and
graphene-like, h-BN-like, borophene-like, and mixed-order regions in monolayer amorphous BCN. Five-nanosecond MLP molecular-dynamics trajectories at 300 K show that the candidate structures are dynamically persistent on the simulated timescale. These results support a polymorphic-crystallite description for the selected model systems, while experimental discrimination from alternative continuous-random-network descriptions will require medium-range-order-sensitive measurements.
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All authors Le-Ye Zhu, Xi Zhang, Yun-Peng Wang, Jieheng Shi, Junwei Zhang, Shixuan Du, Yu-Yang Zhang
Fluid Dynamics
Experimental Evidence for Longitudinal Scaling Exponent Saturation in Shear Turbulence
Dipendra Gupta and Gregory P. Bewley
The asymptotic behavior of velocity statistics in the tails of distributions and at high Reynolds numbers remains unresolved in
turbulence. To investigate this behavior we measured the $n$th-order moments of the distributions of longitudinal velocity differences, $S_n(r) \equiv \langle [u(x+r)-u(x)]^n \rangle \sim r^{\zeta_n}$, in turbulent shear layers at Taylor-scale Reynolds numbers up to $Re_\lambda \approx 1400$. We used a nanoscale hot-wire probe with a sensing length, $l_w$, that was about half the Kolmogorov scale, $\eta$. We obtained
datasets that were up to $5\times 10^7$ integral timescales long, so that the statistics converged up to $n=14$. In the inertial range, the exponents, $\zeta_n$, deviate from classical models and appear to saturate near $\zeta_n \approx 2.2 \pm 0.1$ for $n \gtrsim 12$. The saturation in the exponents is supported by a collapse of the tails of the velocity-difference distributions, and by plateaus in their compensated moments. These results constitute the first experimental evidence for scaling exponent saturation in longitudinal velocity increments, and is consistent with a dominance of localized
vortex filaments in
turbulence.
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Accelerator Physics
Development of a quadripartite wakefield structure as dechirper for free electron laser
Yu Ji, Congrui Lei, Jiahang Shao et al. (+13 more)
Wakefield structures are critical for beam manipulation in free-electron
lasers (FELs), particularly when serving as dechirpers, where beam-induced longitudinal wakefields compensate the energy chirp introduced during beam
magnetic compression. However, conventional planar structures also generate time-dependent quadrupole wakefields due to their asymmetric geometry, which can cause beam mismatch and projected emittance growth. To address this limitation, we propose a quadripartite wakefield structure comprising four identical corrugated plates, able to fully suppress quadrupole wakefields while preserving strong longitudinal wakefields. To accurately evaluate its performance, we calculate wake potentials based on the Panofsky-Wenzel
theorem using three-dimensional simulation software and extract the corresponding wake functions by deconvolution. We further adopt a particle-to-particle (P2P) tracking method incorporating these wake functions, which is capable of accounting for higher-order components and nonlinear effects that are typically neglected in standard tracking codes. Simulation results confirm that the quadripartite geometry offers significantly reduced projected emittance growth and a 25% shorter structure length compared with the planar design. The tracking method also reveals that the nonlinearities of three-dimensional wakefields induce noticeable slice emittance growth for large transverse beam sizes, which may in turn affect lasing performance. In addition, the tracking method enables analysis of various types of assembly error and indicates that misalignment along the direction of plate motion may severely degrade the emittance via dipole wakefields. Such misalignment can be mitigated through beam-based
alignment and precise plate adjustment using high-resolution servo motors.
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All authors Yu Ji, Congrui Lei, Jiahang Shao, Yong Yu, Jitao Sun, Xiaofan Wang, Huaiqian Yi, Zongbin Li, Lei He, Hongfei Wang, Jianping Wei, Wei Wei, Wei Wang, Jiayue Yang, Weiqing Zhang, Xueming Yang
Physics and Society
Adjacent Possible Innovation Dynamics on Local Optima Networks
Leonardo Rizzo, Edward D. Lee and János Kertész
We propose Local Optima Networks (LONs) as a formal framework for modeling innovation dynamics. A LON is a directed weighted graph in which nodes represent locally stable technological configurations and edges encode transition probabilities between their basins of attraction. We construct LONs from fitness landscapes and model innovating
agents as
stochastic walkers exploring the adjacent possible on the resulting network. We show that this model simultaneously generates the four main empirical regularities of the discovery-process tradition: sublinear novelty growth (Heaps' law), heavy-tailed frequency distributions (Zipf's law), anomalous fluctuation scaling (Taylor's law), and power-law distributed inter-event times. The exponents fall within empirically observed ranges and are jointly constrained by LON
topology. Communities in the LON provide an operational definition of technological paradigms grounded in basin-level accessibility. The LON framework thus bridges the discovery-process and adaptive-search traditions of innovation modeling within a single, parsimonious, and empirically testable representation.
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Fluid Dynamics · Cross-listed from cond-mat.soft
Hindered transport of spherical particles in cylindrical pores: The role of structural heterogeneity in rejection-permeability trade-offs
Debanik Bhattacharjee, Yaniv Edery and Guy Z. Ramon
Membrane separations rely on balancing rejection and permeability. Extensive work has clarified how pore structure and operating conditions control each quantity in idealized or weakly heterogeneous systems. However, it remains unclear how this trade-off emerges in strongly heterogeneous media, where coupled distributions of pore and particle sizes shape the local balance between advection and
diffusion and generate substantial variability in performance among distribution realizations. Here we present a steric hindered-transport framework for spherical particles in cylindrical pores that explicitly resolves both single and coupled dual heterogeneity in size distributions. We show that the ensemble-averaged rejection increases with the particle-pore aspect ratio $\lambda$ and with the Péclet number $Pe$, while advection enhances steric exclusion by up to $\sim$20% at intermediate $\lambda$. Dual heterogeneity broadens the distribution of effective $Pe$, increases the variability and incidence of anomalous rejection trends, while systematically shifting the rejection-permeability trade-off toward higher permeability at fixed rejection. These results suggest that controlled heterogeneity can serve as a design lever to expand the attainable operating space for simultaneous high selectivity and high throughput.
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Physics and Society · Cross-listed from nlin.AO
Emergent Macro-Criticality from Micro-Critical Agents
Nicolas Bessone and Erwan Plantec
Criticality has been proposed as a key principle underlying complex behavior in biological and artificial systems; however, how criticality translates from individual dynamics to collective behavior remains unclear. We study this question using a multi-
agent system with spatially constrained interactions in which
agents sense neighboring light signals through exteroceptors and act by switching their own light on or off, thereby forming a dynamical interaction network at the macroscopic level. The
agents' internal states are themselves governed by a reservoir dynamical system at the microscopic level. By varying the microscopic parameters around dynamical criticality, together with the macroscopic interaction
topology, we systematically investigate the relation between the two levels. We find that near-critical dynamics within individual
agents is not sufficient to produce collective critical-like avalanche statistics. Instead, scale-free behavior depends on the effective connectivity of the macroscopic interaction network, which controls activity propagation. As a result, macroscopic critical-like dynamics are enabled by microscopic regimes that deviate from criticality, with the required deviation depending on the properties of the interaction network. Investigating this relation, we find that slightly subcritical micro-level regimes support near-critical dynamics across a wider range of macroscopic parameters. These results show that in this multi-
agent system, collective near-critical behavior depends on the interplay between internal dynamics and the interaction structure that governs activity propagation.
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Applied Physics · Cross-listed from cs.CE
On the role of crack electrolyte wetting in the degradation and performance of battery active particles
S. Luza-Vega, Y. Zhao and E. Martínez-Pañeda
Cathode particle fracture is widely recognised as a major degradation mechanism in lithium-ion batteries, yet cracking also permits electrolyte wetting of newly exposed internal surfaces, modifying interfacial reaction pathways. The mechanistic role of electrolyte wetting in redistributing reactions within cracked particles remains unclear. Here, we isolate this effect through a controlled comparison between (i) a fully coupled electro-chemo-mechanical model resolving lithium concentration, electrostatic potential, and stress fields in both the active material and the electrolyte inside and outside cracks, and (ii) a single-particle chemo-mechanical model employing the conventional uniform flux assumption. The coupled model predicts strong spatial heterogeneity in interfacial reaction rates, with flux amplification approximately 8x relative to the imposed uniform flux at the crack tip. Reaction redistribution, and thus lithium flux, is governed predominantly by local solid-state lithium concentration and stress variations, while electrolyte potential gradients inside cracks remain secondary under the conditions considered. Uniform flux models can underpredict delivered capacity by 25% at 1C-rate; this discrepancy increases at higher rates. They also underestimate tensile stresses throughout the delithiation process by 10%, directly affecting crack driving conditions. These results demonstrate that neglecting crack-electrolyte coupling leads to systematic underestimation of both utilisation limits and fatigue-relevant stress histories.
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Applied Physics · Cross-listed from cs.ET
Analytic Framework for Estimating Memory Cost
Anirudh Shankar, Avhishek Chatterjee and Anjan Chakravorty
As artificial intelligence (AI) models quickly spread and become more advanced, they are requiring an ever-increasing amount of data and compute capability, leading to a significant energy cost. Training and inference of AI models including the large
language models (LLMs) and deep neural networks (DNNs) are contributing to a large carbon footprint owing to the massive amount of
memory they consume in data centers. In this article, we present a generalized framework that quantifies these energy costs incurred to the environment. This framework provides a foundational quantification of AI's ecological footprint, facilitating the development of sustainable architectural strategies for future models.
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Optics
Computing with the complex nonlinear dynamics of an optomechanical oscillator
Shulamit Edelstein, Marcos Menendez, Bingrui Lu et al. (+5 more)
An optomechanical oscillator undergoes a
Hopf bifurcation that connects two dynamical regimes with different information-processing capabilities: thermal Brownian motion and coherent self-sustained oscillation. Below threshold, the oscillator occupies a stable fixed point around which thermal fluctuations drive
stochastic Brownian motion - a regime dominated by linear response, with only short-lived
memory and negligible usable nonlinearity. Above threshold, radiation pressure, free-carrier dynamics, and thermo-optic relaxation act together to sustain a stable limit cycle that simultaneously provides both nonlinear transformation and dynamical
memory. Here we show that this coherent regime can be used as a physical reservoir for computation: by perturbing the
phonon-lasing attractor, the cavity performs nonlinear input-output transformations and retains short-term
memory without any external feedback mechanism. Using only a single chip-integrated device with 20 virtual nodes, we reconstruct nonlinear functions, predict the
evolution of chaotic time series, and perform spoken digit classification on a two-digit sub-task. The mechanical resonance frequency sets the intrinsic dynamical timescale of the reservoir and therefore its processing speed; while the present device operates near 0.4 GHz, optomechanical and nanomechanical systems can be engineered to reach multi-GHz and sub-terahertz frequencies, directly translating into a scalable path toward ultrafast integrated physical computing.
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All authors Shulamit Edelstein, Marcos Menendez, Bingrui Lu, Babak Vosoughi Lahijani, Cefe Lopez, Miguel C. Soriano, Søren Stobbe, Pedro David Garcia
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Compositionally tuned phase transformations enhance pyroelectric energy harvesting from low-grade heat
Ruiheng Geng, Ka Hung Chan, Xinyue Huang et al. (+6 more)
Phase-transforming pyroelectric materials have emerged as promising candidates for low-grade thermal energy harvesting. However, whether first-order transformations with large pyroelectric coefficient or second-order transformations with better reversibility are preferable remains unclear. Here we report compositionally tunable phase transformations in Ba$_{1-x}$Sr$_x$TiO$_3$ ($x \in [0, 0.3]$), revealing
evolution from first-order to second-order character. We identify a transitional regime between Sr$_{0.15}$ and Sr$_{0.22}$ where transformation mechanism fundamentally changes. Within this regime, Sr$_{0.19}$ achieves optimal
lattice compatibility, exhibiting electrical leakage suppressed by over two orders of magnitude while retaining substantial polarization response. Energy conversion demonstrations show the multilayer Sr$_{0.19}$ device delivers pyroelectric current of $\sim$1.6 $\mu$A at 64$~^\circ$C with an energy density of 1.6 mJ/cm$^3$ per cycle and 5.5% conversion efficiency. Remarkably, this composition operates stably over 10,000 full energy conversion cycles without external bias field or recharging, demonstrating that transitional regime compositions provide the optimal balance between energy density and operational durability for practical low-grade heat harvesting.
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All authors Ruiheng Geng, Ka Hung Chan, Xinyue Huang, Nobumichi Tamura, Faqiang Zhang, Wanjia Han, Yang Zhang, Chenbo Zhang, Xian Chen
Computational Physics · Cross-listed from cond-mat.mtrl-sci
A Fully Ab-Initio Spin-Lattice Dynamics Framework for Magnetic Materials
Xianxi Zhang, Hongyu Yu, Liangliang Hong et al. (+1 more)
Coupled
spin-
lattice dynamics (SLD) underlie a wide range of
magnetic phenomena, yet a unified first-principles framework that propagates both degrees of freedom without empirical parameterization has remained elusive. We present a fully ab initio SLD approach integrated into VASP, in which interatomic forces and effective
magnetic fields are obtained at each time step from self-consistent constrained-moment density-functional calculations. The method is validated on four materials spanning
ferromagnetic, non-collinear, and geometrically frustrated orders, recovering the correct
magnetic ground state in every case from random initial conditions. SLD trajectories also provide physically correlated training data for
magnetic machine-learning potentials, as demonstrated for BiFeO$_3$ by a reduction of up to approximately one order of magnitude in energy MAE over training on randomized
spin configurations. This framework opens a practical first-principles route to finite-temperature
spin-
lattice coupled phenomena in
magnetic materials.
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All authors Xianxi Zhang, Hongyu Yu, Liangliang Hong, Hongjun Xiang
Fluid Dynamics
Entropic lattice Boltzmann method for general anisotropic advection–diffusion
Jingsen Feng, Jing Leng, Jingchao Jiang et al. (+1 more)
Many transport processes exhibit direction-dependent
diffusion, described macroscopically by the full-tensor anisotropic advection–
diffusion equation (ADE). Numerical discretization is demanding when the principal axes are rotated relative to the mesh, since mixed derivatives and oblique fluxes amplify grid-orientation errors under large tensor contrasts. This paper develops a local entropic
lattice Boltzmann discretization for the general anisotropic ADE. The non-
equilibrium population is split into a first-order flux sector and a residual ghost sector. The
diffusion tensor is imposed through local tensorial relaxation of the flux, while higher-order kinetic content is controlled by an ADE-corrected entropic stabilizer with positivity fallback. Chapman–Enskog analysis shows the scheme recovers the target full-tensor equation with a discrete-time diffusivity relation between the physical tensor and the flux-relaxation
matrix. The update is local,
matrix-free, and applies to rotated, spatially varying, heterogeneous, and dynamically coupled tensor transport. We validate it on 3D
benchmarks–advected Gaussian plumes, decay of rotated
Fourier modes, and source-driven transport with varying tensors–covering off-diagonal
diffusion, high-Péclet advection, anisotropy ratios of O(104)O(10^4) O(104), and local contrasts up to $3\times10^4:1$. It is then applied to orientation-induced Taylor dispersion of Brownian rods, quantifying enhancement from shear-driven rotation. Heat-conduction tests include rotated thermal-conductivity measurements and effective conduction in heterogeneous porous media with anisotropy up to $10^4:1. Finally, anisotropic Rayleigh–Bénard convection is simulated to examine how plume morphology and heat transfer change over seven decades of anisotropy ratios, demonstrating an accurate, stable local solver for strongly anisotropic advection–
diffusion.
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All authors Jingsen Feng, Jing Leng, Jingchao Jiang, Xu Chu
Fluid Dynamics
Traveling surface wave propagation on shallow water with variable bathymetry and current
Semyon Churilov
Energy transmission over long distances by waves is a key mechanism for many natural processes. This possibility arises when an inhomogeneous medium is arranged in such a manner that it enables a certain type of wave to propagate with virtually no reflection or scattering. By application of the Laplace cascade method for integrating second-order
hyperbolic equations, a general
algorithm for finding the parameters of inhomogeneous non-reflecting flows is proposed. The
algorithm is applied to the problem of long linear surface waves propagation in a channel with variable cross-section. The general analysis of the problem is illustrated by a few representative solutions and compared with the results of previous studies. The results obtained may be of interest to mitigate the possible impact of waves on ships, marine engineering constructions, and human coastal activities.
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Applied Physics
Continuous quantification of viral plaque dynamics using ultra-large-area label-free imaging enables rapid antiviral susceptibility testing
Merve Eryilmaz, Yuzhu Li, Xiao Wang et al. (+8 more)
The plaque reduction assay (PRA) remains the gold standard for antiviral susceptibility testing, evaluating drug potency by measuring reductions in plaque-forming units (PFUs). However, the traditional PRA is time-consuming, labor-intensive, prone to manual counting errors, and offers limited scalability. Moreover, its reliance on destructive fixation and chemical staining reduces the assay to a static, endpoint observation, obscuring the dynamic, time-resolved kinetics of dose-dependent viral inhibition. Here, we introduce a label-free, time-resolved PRA platform that transforms the conventional assay into a continuous, high-dimensional measurement of viral infection dynamics. Our system integrates a compact lens-free imaging setup with a custom-designed ultra-large-area (100 cm^2) thin-film transistor (TFT) image sensor and deep learning-based
algorithms to autonomously quantify PFU dynamics within an incubator. Validated using herpes simplex virus type-1 (HSV-1) treated with acyclovir, the platform matched chemically-stained ground truth measurements with zero false positives while accelerating readout by ~26 hours. Crucially, our system revealed that increasing drug concentrations induce temporally distinct delays and suppress new PFU formation, enabling conclusive drug efficacy evaluations within ~60 hours post-infection. This scalable, label-free framework redefines antiviral susceptibility testing as a rapid, time-resolved and information-rich measurement framework, providing a generalizable platform for virology research, high-throughput drug screening, and clinical diagnostics.
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All authors Merve Eryilmaz, Yuzhu Li, Xiao Wang, Max Zhang, Alp Inegol, Zixiang Ji, Lucas Thai, Guangdong Ma, Akihiko Fujisawa, Kazunori Yamaguchi, Aydogan Ozcan
Applied Physics
Numerical Validation of a MOSFET-Based Control Circuit for High-Power Intelligent Reflecting Surfaces for Wireless Power Transfer Applications
Gakuto Ichikawa, Eisuke Omori, Atsuko Nagata et al. (+4 more)
Intelligent reflecting surfaces (IRSs) have attracted considerable
attention because of their ability to dynamically control electromagnetic wave propagation. While most existing IRSs have been developed for low-power communication and sensing applications, their extension to high-power wireless power transfer (WPT) environments remains largely unexplored, as the high induced currents can damage or saturate the sensitive control elements, disrupting their tuning functionality. Here, we propose a metal-
oxide-
semiconductor field-effect transistor-based (MOSFET-based) binary control
circuit for IRSs operating at 2.4 GHz that can withstand input power levels exceeding 1 W per unit
cell. The control
circuit employs a back-to-back MOSFET switching
topology with series and parallel capacitors to suppress impedance variations arising from device nonlinearity while maintaining a reflection phase difference of approximately 180 degrees between the ON and OFF states. A theoretical model based on transmission lines is developed and validated against full-wave co-simulations incorporating nonlinear SPICE device models. The dynamic range is evaluated with respect to both the rated current and the reflection phase difference, demonstrating stable operation up to 1.25 W. Supercell-level beam steering is further demonstrated through far-field simulations, confirming active control of the reflection angle via switching pattern reconfiguration. These results establish a foundation for the deployment of IRSs in high-power WPT scenarios.
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All authors Gakuto Ichikawa, Eisuke Omori, Atsuko Nagata, Akise Kumashiro, Kazuhiro Kizaki, Shunsuke Saruwatari, Hiroki Wakatsuchi
Geophysics
A Review of Modeling and Waveform Inversion for Marine Seismic Data
Guoxin Chen
Marine seismic exploration is a core technology supporting marine resource exploration, seabed detection, carbon sequestration monitoring, and offshore engineering safety. The integration of full-waveform inversion (FWI), elastic inversion, numerical modeling, and artificial intelligence is driving a paradigm shift from physics-driven to physics-constrained and data-driven hybrid mode. Based on the JMSE special issue Modeling and Waveform Inversion of Marine Seismic Data, this paper systematically reviews 11 papers across six areas: data preprocessing, forward modeling, FWI, elastic inversion, reservoir characterization, and migration imaging. Results show that intelligent interpolation, multi-source joint inversion, low-frequency recovery and cycle-skipping suppression, physics-guided deep learning inversion, and wide-band velocity modeling are key solutions to industrial bottlenecks in OBN/OBC, streamer, and passive-source scenarios. These achievements form a complete system from theory to engineering application, supporting deep-water exploration, seabed hazard detection, and carbon sequestration monitoring. This paper also introduces the new JMSE special issue Marine Geophysical Exploration in the Era of Artificial Intelligence, summarizes recent AI-based advances, and prospects future trends of AI and marine seismic integration.
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Instrumentation and Detectors
Detectivity and bandwidth limits of cooled and uncooled light detection using nanomechanical resonators
Mathis Turgeon-Roy, Mohammed Shakir, Zachary Louis-Seize et al. (+1 more)
Nanomechanical resonators (NMRs) offer a promising alternative to traditional thermal-based radiation detectors due to their immunity to electrical noise. In recent years, these sensors have reached the previously unattained theoretical detectivity limit set by the fluctuation noise of thermal
photons at room temperature. Beyond this point, improvements of NMR resonators do not translate into greater detectivity, but in greater effective bandwidth. There is, however, no simple model predicting the limits of this bandwidth enhancement. Likewise, models predicting the performances of NMR-based radiation sensors under active cooling have not been derived. To address these gaps in knowledge, a key missing ingredient consists of defining the NMR optimal driven amplitude that minimizes additive frequency noise, but without performance degradation from nonlinear phenomena. We find that, in the context of NMR-based radiation sensing, this optimal amplitude ($a_\mathrm{opt}$) is dramatically different than the commonly assumed critical amplitude ($a_\mathrm{c}$) that defines the onset of non-linear phenomena in nanomechanical resonators. Our proposed model for this optimal amplitude allows us to quantify the maximum bandwidth enhancement in NMR-based radiation sensors. We also derive simple equations predicting the maximum detectivity in cryogenically cooled sensors. Finally, combining these two models allows us to define new universal performance limits. This unveils important general conclusions on the ideal geometry of NMR radiation sensors. We find that thermomechanically-limited sensors should be as thin and extended as possible. In contrast, readout-limited sensors should also be thin, but should be just large enough to make radiation heat transfer dominant compared to conduction.
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All authors Mathis Turgeon-Roy, Mohammed Shakir, Zachary Louis-Seize, Raphael St-Gelais
Physics and Society
Analytical Framework for the Approximate Master Equation
Yu Takiguchi and Takehisa Hasegawa
The approximate master equation (AME) provides a highly accurate description of dynamical processes on networks, yet its steady states are generally analytically intractable. In this study, we develop an analytical framework to derive the steady states of the AME by introducing a controlled approximation that enables closure of the moment equations. This framework reproduces the steady state of the pair approximation by achieving closure with the minimum required order of moments, and can be systematically refined to approach the exact steady states of the AME. We apply this to the SIS model, the voter model, and evolutionary games, demonstrating that the steady states can be derived. In particular, for evolutionary games, we show that combining our framework with the singular perturbation method enables the analytical derivation of the time
evolution.
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Computational Physics · Cross-listed from math.NA
Maxwell à la Helmholtz: Direct boundary integral equations for 3D scattering by perfect electric conductors via Helmholtz operators
Carlos Pérez-Arancibia and Catalin Turc
This paper is the direct-formulation companion to [Burbano-Gallegos, Pérez-Arancibia, and Turc, ESAIM: M2AN, 60(1):273–315, 2026], which developed indirect combined-field-only boundary integral equations (BIEs) for time-harmonic electromagnetic scattering by smooth perfectly electrically conducting (PEC) obstacles, relying entirely on Helmholtz boundary integral operators. Here we exploit the same equivalence between the Maxwell PEC scattering problem and a pair of vector Helmholtz boundary value problems – one for the electric field and one for the
magnetic field – to derive direct BIE formulations whose unknowns are the Dirichlet and Neumann traces of the total fields, decomposed into their normal and tangential surface components. These unknowns carry direct physical meaning: in particular, the
magnetic-field formulation yields the surface electric currents as part of its solution. The mixed regularity of the two field-trace components requires introducing a tailored product Hölder space, a distinctive feature absent from the indirect approach. We prove that the resulting Direct Electric and
Magnetic Combined-Field-Only Integral Equations (D-ECFOIE and D-MCFOIE) are uniquely solvable at all frequencies, and introduce Calderón-type regularizations (RD-ECFOIE and RD-MCFOIE) that render them of the Fredholm second kind. We further examine the low-frequency breakdown affecting the electric-field formulation and introduce a modified equation that enforces the physical charge-conservation constraints, which restores numerical accuracy and well-conditioned linear systems for frequencies arbitrarily close to zero. Numerical experiments, performed using a high-order Nyström solver based on the Density Interpolation Method and implemented in the Julia package Inti.jl, validate the accuracy and robustness of the proposed formulations across a range of geometries and frequencies.
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Plasma Physics
Computational boundary specification in 3D fixed-boundary magnetohydrodynamic equilibrium modeling
Alan Kaptanoglu and Tobias Blickhan
Outside the core of the
plasma, the
plasma current and pressure rapidly transition to zero in a scrape-off or edge region or
plasma-
vacuum interface. However, existing tools for fixed-boundary magnetohydrodynamic
equilibria in 2D and 3D domains $\Omega$ typically prescribe the computational boundary $\partial\Omega$ interior to this transition layer. We (1) argue that a more realistic and robust assumption is to define the computational boundary exterior to this transition layer, in a
vacuum-like region where $J|_{\partial\Omega} \sim p|_{\partial\Omega} \sim 0$, (2) show that, without this boundary change, existing coil optimization routines for 3D toroidal
equilibria (stellarators) should be changed to match free-boundary
equilibrium requirements, and (3) derive an
algorithm for a fixed-boundary 3D
equilibrium solver compatible with a very general computational boundary, with conditions $B \cdot n|_{\partial\Omega} \neq 0$ (not necessarily a flux surface), $p|_{\partial\Omega} \neq \text{const.}$ (not necessarily an isobar), and $J \times n|_{\partial\Omega} \neq 0$.
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Biological Physics
Lumens as active balloons: a biological physics review
Sebastian Echeverría-Alar, Badri Narayanan Narasimhan, Stephanie I Fraley et al. (+1 more)
Lumens are cavities enclosed by polarized
cells that are essential for organ function, from nutrient transport in the gut to gas exchange in the lungs. Defects in lumen formation are associated with severe diseases, including polycystic kidney disease and respiratory malformations. The emergence, growth, and maintenance of lumens involve a rich set of phenomena that can be framed within out-of-
equilibrium physics and biological active matter, including osmotically driven hydraulic flows, coarsening-like dynamics, morphological instabilities, and mechanochemical feedbacks linking luminal pressure to tissue response. Yet experimental and theoretical efforts to study these phenomena have largely developed within specific biological systems, complicating the identification of shared physical principles across them. In this review, we bring these efforts together and present lumenogenesis within a biological physics framework in which lumens are viewed as active balloons: pressurized cavities that are inflated, sculpted, and maintained through tightly coupled active processes.
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All authors Sebastian Echeverría-Alar, Badri Narayanan Narasimhan, Stephanie I Fraley, Wouter-Jan Rappel