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Physics Physics

physics Watch Physics

Tuesday 25 November

Biological Physics · Cross-listed from cond-mat.stat-mech

A Single–Index Theory of Optimal Branching: Murray Laws, Gilbert Networks, and Young–Herring Junctions

Justin Bennett

Murray-type flux-radius laws, Gilbert-type concave transport costs, and Young-Herring triple-junction angle balances are usually treated as separate theories. This work shows that, within a natural class of quadratic, scale-free ledgers for branched networks, all three are different faces of a single structure controlled by one dimensionless index chi. Each edge carries a flux Q, an effective radius r, and a per-length ledger P(Q,r) encoding transport dissipation and structural burden. Under locality, evenness in Q, linear-response (quadratic) dependence, and an exact homogeneity ansatz in (Q,r), any admissible ledger reduces in the scale-free regime to the two-term form P(Q,r) = a Q^2 r^{-p} + b r^m. Local optimality then implies simultaneously: (i) a flux-radius power law with generalized Murray closures at degree-3 nodes; (ii) a Young-Herring-type vector balance with radius weights r^m and a fixed symmetric Y-junction angle; and (iii) an effective flux-only cost of Gilbert/branched-transport type with exponent beta. The exponents alpha and beta, the symmetric angle, and the split between transport and structural cost are all set by chi = m/(m+p) = beta/2. A rigidity theorem shows conversely that any quadratic ledger that yields power-law optimal radii and power-law flux-only cost on an open scaling cone must belong to this two-term family and obey the same Murray-Gilbert-Young dictionary. Examples for Poiseuille, diffusive, and geophysical trees illustrate how chi can be inferred from geometry and used as a falsifiable order parameter for scale-free branching architectures.
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Fluid Dynamics

Probing superhydrophobic surface topography using droplet adhesion

Pawan Kumar, Marta Krasowska and Joseph D. Berry

Understanding contact line dynamics on superhydrophobic surfaces with microscopic structures is essential for designing materials with reduced drag, anti-icing, self-cleaning, and anti-fouling properties. Using numerical simulations, we demonstrate that forces on droplets receding over structured surfaces are governed by microscale deformations near the contact line. We present and experimentally validate an expression demonstrating that adhesion force increases logarithmically with pillar area fraction at constant droplet volume and pillar surface chemistry. Furthermore, we establish that the average tensile force measured in direct force measurements provides a more reliable indicator of surface structure than the commonly used maximum force. This newfound insight enables precise quantification of superhydrophobic surface structure using a droplet probe.
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Fluid Dynamics

Simulating droplet adhesion on superhydrophobic surfaces

Pawan Kumar and Joseph D. Berry

A numerical model is proposed to simulate the adhesion, compression, and subsequent detachment of a micro-liter droplet from a superhydrophobic surface composed of chemically homogeneous pillars arranged in a periodic fashion, replicating a typical force probe microscopy experiment. We observe that as the droplet is pulled away from the surface, the net vertical force varies in a typical sawtooth manner with peculiar peaks and troughs, characteristic of the surface. The force first reaches a maximum before the droplet detaches from the surface with a comparatively lower force. The force variation predicted by the numerical model is in good agreement with the experimental results of Kumar et al. [1]. We also studied the effect of evaporation on the variation in the adhesion force by simulating an evaporating droplet on a superhydrophobic surface. For an evaporating droplet, the numerically predicted maximum and detachment force magnitudes are in good agreement with those obtained experimentally when we take into account the change in the droplet weight as it evaporates. The proposed method will be useful for the quantitative analysis and design of a variety of superhydrophobic surfaces and will pave the way for more accurate surface characterization based on droplet adhesion force measurements.
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General Physics

Quintessential Inflation in Light of ACT DR6

Sayantan Choudhury, Swapnil Kumar Singh and Satish Kumar Sahoo

We analyze the canonical generalized-exponential quintessential-inflation potential in light of ACT DR6 scalar-tilt constraints and the distinct demands of its post-inflationary and late-time evolution. The potential slow-roll hierarchy is derived through fourth order and checked against a numerical scalar and tensor mode calculation. For a benchmark $n=15$, $\lambda=10^{-9}$ at a reference $60$ remaining e-folds, the numerical spectrum gives $n_s\simeq0.96396$, $r\simeq7.71\times10^{-5}$, and a negative running of running of order $10^{-5}$. The exact Hubble-flow endpoint gives a full inflationary excursion exceeding $M_{\rm Pl}$ even though the ten-e-fold observable interval is much smaller. We characterize a phenomenological radiation-injection family followed through kination, radiation and matter domination, and calculate leading-order gravitational-wave transfer spectra with an integrated radiation-density test. A shallow exponential term permits a calibrated late-time quintessence phase, whose homogeneous equation of state and expansion predictions are evaluated numerically. The result is a quantitative map of the coupled inflation, reheating, gravitational-wave and dark-energy requirements, with the limitations of the assumed transfer and thermal history stated explicitly.
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Fluid Dynamics

Modeling of turbulence kinetic energy added by wind-turbine wakes in the atmospheric boundary layer

Bowen Du, Jingshan Zhu, Baoliang Li et al. (+3 more)

Accurate prediction of turbulence kinetic energy (TKE) added by wind-turbine wakes is of significant scientific value for understanding the wake recovery mechanisms. Furthermore, this physical quantity is a critical input for engineering applications. In this study, we propose a novel wake-added TKE prediction model capable of accurately predict the three-dimensional spatial distribution of wake-added TKE using only basic inflow and wind turbine operation conditions as inputs. The model consists of two sub-modules: one for calculating the azimuthally-averaged wake-added TKE and the other for determining the ground effect correction function. The calculation of the azimuthally-averaged wake-added TKE is based on the analytical solution derived from the corresponding wake-added TKE budget, while the ground effect correction function is determined using a unified functional form, owing to its self-similarity. To ensure the closure of these two sub-modules, we develop methods for determining all free parameters based on the large-eddy simulation (LES) cases. This results in an end-to-end prediction framework, enabling direct engineering applications of the proposed model. We compared the proposed model with LES calibration data and publicly available validation datasets from the literature, which include LES and wind tunnel experiments under various inflow and turbine operating conditions. The comparison results show that the proposed model can accurately predict the spatial distribution of wake-added TKE, particularly capturing the vertical asymmetry of wake-added TKE and the streamwise evolution of the hub-height wake-added TKE profile. The averaged normalized mean absolute error of the proposed model across all validation datasets is only 8.13%, demonstrating its robustness and broad applicability.
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All authors Bowen Du, Jingshan Zhu, Baoliang Li, Mingwei Ge, Xintao Li, Yongqian Liu

Atmospheric and Oceanic Physics

Periodic extreme rainfall in a warmer climate due to stronger convectively-coupled waves

Heng Quan, Yi Zhang, Guy Dagan et al. (+1 more)

Tropical regions may experience periodic extreme precipitation and suffer from associated periodic deluges in a warmer climate. Recent studies conducted small-domain (around 100 km x 100 km) atmospheric model simulations and found that precipitation transitions from a steady state to a periodic oscillation state in a hothouse climate when the sea surface temperature reaches 320-325 K. Here we conduct global-scale atmospheric model simulations with different complexity, and we find that tropical precipitation in convective regions already transitions to a O(10 day) periodic oscillation state with a O(100 mm/day) amplitude at 305-310 K. This temperature is substantially lower than previously reported, and within reach in a century under a high carbon emission scenario. We attribute the onset of the periodic extreme precipitation to the intensification of convectively-coupled waves, which occurs at temperatures much lower than the radiative mechanism responsible for the transition around 320-325 K identified before.
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All authors Heng Quan, Yi Zhang, Guy Dagan, Stephan Fueglistaler

Atomic Physics

Response Analysis of Four-Level Heterodyne Rydberg Atom Receiver

Yu Tang, Siyuan Wang, Shuang Ren et al. (+3 more)

The four-level heterodyne Rydberg atom receiver has garnered significant attention in microwave detection and communication due to its high sensitivity and phase measurement capabilities. Existing theoretical studies, primarily based on static solutions, are limited in characterizing the system's frequency response. To address this, this paper comprehensively investigates the dynamic solutions of the density matrix elements for the four-level heterodyne structure, establishing a quantitative relationship between system response, signal frequency, and system parameters. This enables theoretical bandwidth calculations and performance analysis. This paper also constructs a noise model for the density matrix elements, revealing the relationship between the ultimate sensitivity of the Rydberg atom receiver and the noise in the density matrix elements. Both theoretical simulation and experimental results demonstrate that the bandwidth of the four-level heterodyne receiver can exceed 10 MHz. This study provides critical theoretical support for the engineering applications and performance optimization of heterodyne Rydberg atom receivers.
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All authors Yu Tang, Siyuan Wang, Shuang Ren, Chuang Yang, Hanbin Zhou, Chenxi Lu

Computational Physics · Cross-listed from cond-mat.mtrl-sci

Metastable Multi-centered Polarons in BiVO$_{4}$

Seyeon Park, Yajing Zhang, Michele Reticcioli et al. (+2 more)

Polarons, quasiparticles formed through interactions between lattice and charge carriers (electrons and holes), strongly influence the electronic and optical properties of functional materials. In nanostructured BiVO$_{4}$, polaron formation and dynamics govern photocatalytic efficiency and charge transport, yet the microscopic nature remains not fully resolved. Here, using first-principles calculations, we report the formation of multi-centered polarons, in contrast to the more common single-centered states. Moreover, electron polarons exhibit pronounced anisotropy compared to the isotropic hole counterpart, reflecting a distinct character in charge-lattice coupling. These theoretical insights offer a direct interpretation of optical and spectroscopic experiments, providing strong evidence of anisotropic multi-centered polaronic behavior in BiVO$_{4}$. The presence of multiple in-gap states, especially from multi-centered polarons, introduces new channels for charge transport and recombination, possibly offering opportunities to control carrier dynamics in nanoscale photocatalytic and optoelectronic devices.
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All authors Seyeon Park, Yajing Zhang, Michele Reticcioli, Cesare Franchini, Bongjae Kim

Applied Physics

Broadband Reflective Elastic Mode Conversion Enabled by a Single Row of Inclined Long-Slits

Kaifei Feng, Weidong Wang, Yucheng Gao et al. (+4 more)

Broadband longitudinal-to-transverse mode conversion under normal incidence remains difficult to achieve, especially with structurally simple designs. Numerical simulations show that a single periodic row of inclined long-slits near a free surface enables high-efficiency broadband conversion, where the conversion rate exceeds 0.8 across a normalized-frequency range of 0.27 to 0.74, corresponding to a 93.1% relative bandwidth. The broadband response originates from two intrinsic deformation modes of the mass blocks between adjacent inclined slits: a rotational mode and a quadrupole mode. The spectral overlap of these two modes sustains a continuous high-efficiency band. The effect is robust against geometric variations, demonstrating that geometric asymmetry alone offers a minimal yet effective route to broadband elastic-wave mode conversion.
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All authors Kaifei Feng, Weidong Wang, Yucheng Gao, Fengming Liu, Qiujiao Du, Wenshuai Zhang, Pai Peng

Optics

Nanophotonic quantum magnetometry in a spin-dense diamond cavity

Nicholas J. Sorensen, Elham Zohari, Joshua S. Wildeman et al. (+3 more)

Quantum sensors based on the nitrogen-vacancy (NV) center in diamond are leading platforms for high-sensitivity magnetometry with nanometer-scale resolution. State-of-the-art implementations, however, typically rely on bulky free-space optics or sacrifice spatial resolution to achieve high sensitivities. Here, we realize an integrated platform that overcomes this trade-off by fabricating monolithic whispering-gallery-mode cavities from a diamond chip containing a high density of NV centers and by evanescently coupling excitation to and photoluminescence from the cavity using a tapered optical fiber. Employing a lock-in-amplified Ramsey magnetometry scheme, we achieve a photon-shot-noise-limited DC sensitivity of $58\,\text{nT}/\sqrt{\text{Hz}}$—the best sensitivity reported to date for a nanofabricated cavity-based magnetometer. The microscopic cavity size enables micrometer-scale spatial resolution and low-power operation, while fiber-coupling provides a path to scalable on-chip integration. Arrays of such sensors could enable NV-NMR spectroscopy of sub-nanoliter samples, new magnetic-gradient imaging architectures, and compact biosensing platforms.
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All authors Nicholas J. Sorensen, Elham Zohari, Joshua S. Wildeman, Sigurd Flågan, Vinaya K. Kavatamane, Paul E. Barclay

Computational Physics

Effect of cohesion on the gravity-driven evacuation of metal powder through Triply-Periodic Minimal Surface structures

Aashish K Gupta, Christopher Ness and Sina Haeri

Evacuating the powder trapped inside the complex cavities of Triply Periodic Minimal Surface (TPMS) structures remains a major challenge in metal-powder-based additive manufacturing. The Discrete Element Method offers valuable insights into this evacuation process, enabling the design of effective de-powdering strategies. In this study, we simulate gravity-driven evacuation of trapped powders from inside unit cells of various TPMS structures. We systematically investigate the role of cohesive energy density in shaping the discharge profile. Overall, we conclude that the Schwarz-P and Gyroid topologies enable the most efficient powder evacuation, remaining resilient to cohesion-induced flow hindrance. Furthermore, for the two unit cells, we analyse detailed kinematics and interpret the results in relation to particle overlaps and contact force distributions.
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Instrumentation and Detectors

Calibration Plan for the SBC 10-kg Liquid Argon Detector with 100 eV Target Threshold

E.Alfonso-Pita, D.Baxter, E.Behnke et al. (+32 more)

The Scintillating Bubble Chamber (SBC) Collaboration is designing a new generation of low background, noble liquid bubble chamber experiments with sub-keV nuclear recoil threshold. These experiments combine the electronic recoil blindness of a bubble chamber with the energy resolution of noble liquid scintillation, and maintain electron recoil discrimination at higher degrees of superheat (lower nuclear recoil thresholds) than Freon-based bubble chambers. A 10-kg liquid argon bubble chamber has the potential to set world leading limits on the dark matter nucleon cross-section for $O(\mathrm{GeV}/c^{2})$ masses, and to perform a high statistics coherent elastic neutrino nuclear scattering measurement with reactor neutrinos. This work presents a detailed calibration plan to measure the detector response of these experiments, combining photoneutron scattering with two new techniques to induce sub-keV nuclear recoils: nuclear Thomson scattering and thermal neutron capture.
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All authors E.Alfonso-Pita, D.Baxter, E.Behnke, J.Corbett, M.Crisler, C.E.Dahl, K.Dering, A.de St.Croix, D.Durnford, P.Giampa, J.Hall, O.Harris, H.Hawley-Herrera, L.Joseph, A.Kucich, N.Lamb, M.Laurin, I.Levine, W.H.Lippincott, B.Mitra, R.Neilson, O.Nicholson, M.-C.Piro, G.Putnam, D.Pyda, Z.Sheng, G.Sweeney, O.Valdés-Martínez, E.Vázquez-Jáuregui, S.Westerdale, T.J.Whitis, S.Windle, A.Wright, E.Wyman, R.Zhang

Geophysics

Unveiling the role of seepage forces in the acceleration of landslides creep

Fabian Barras, Andreas Aspaas, Einat Aharonov et al. (+1 more)

In the context of global climate change, geological materials are increasingly destabilized by water flow and infiltration. We study the creeping dynamics of a densely monitored landslide in Western Norway to decipher the role of fluid flow in destabilizing this landslide. In Åknes, approximately 50 million cubic meter of rock mass continuously creeps over a shear zone made of rock fragments, with seasonal accelerations that strongly correlate with rainfall. In this natural laboratory for fluid-induced frictional creep, unprecedented monitoring equipment reveals low fluid pressure across the shear zone, thereby challenging the dominant theory of fluid-driven instability in landslides. Here, we show that a generic micromechanical model can disentangle the effects of fluid flow from those of fluid pressure, and demonstrate that seepage forces applied by channelized flow along the shear zone are the main driver of creep accelerations. We conclude by discussing the significance of seepage forces, the implications for hazard mitigation and the broader applicability of our model to various geological contexts governed by friction across saturated shear zones.
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All authors Fabian Barras, Andreas Aspaas, Einat Aharonov, François Renard

Accelerator Physics

Beam Steering and Radiation Generation of Electrons in Bent Crystals in the Sub-GeV Domain

R. Negrello, M. Romagnoni, A. Sytov et al. (+15 more)

We present an investigation into beam steering and radiation emission by sub-GeV electrons traversing bent silicon crystals. Using 855, 600, and 300~MeV electron beams at the Mainz Microtron (MAMI), we explored orientational coherent effects and particle dynamics in a 15~$\mu$m-thick crystal bent along the (111) planes. Combined experimental and simulation analyses enabled the classification and quantitative assessment of the contributions from channeling, dechanneling, rechanneling, and volume capture to both beam deflection and radiation emission. Crystal steering remained effective even at 300~MeV, with measured channeling efficiencies exceeding 50%, a record at such low energy. Channeling and volume reflection enhanced radiation emission by up to a factor of six compared to the misaligned orientation, highlighting strong orientational coherence effects in the sub-GeV regime. These findings confirm the feasibility of using bent crystals for efficient beam manipulation and high-intensity photon generation at low energies, supporting the development of novel light sources and beam control strategies at accelerator facilities operating in this energy range.
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All authors R. Negrello, M. Romagnoni, A. Sytov, N. Canale, D. De Salvador, P. Fedeli, V. Guidi, V. V. Haurylavets, P. Klag, W. Lauth, L. Malagutti, A. Mazzolari, G. Paternò, F. Sgarbossa, M. Soldani, V. V. Tikhomirov, D. Valzani, L. Bandiera

Optics

Controllable Bistability in Dual-Fiber Optical Trap in Air

Aoxi Chen, Xinlin Chen, Siyuan Rao et al. (+8 more)

The dual-fiber optical trap, owing to its high sensitivity and facile miniaturization, holds significant actual application value in fields such as high-precision metrology of mechanical quantities and biological manipulation. The positional stability of the trapped particle is pivotal to system performance, directly setting the measurement noise floor and operational precision. In this work, we observe bistability and hysteresis in the axial equilibrium position of a 10-um diameter SiO2 microsphere. This bistability arises from optical interference between the fiber ends and the microsphere, creating multiple potential wells. Experimental results demonstrate that the microsphere's transition rate can be effectively modulated through precise control of the trapping laser power. Furthermore, the incorporation of transverse misalignment has effectively eradicated bistability, thereby substantially improving positional stability throughout the entire optical trapping region. This suppression successfully reduced the system's residual positional uncertainty to the thermal noise limit. Consequently, this research will enhance the precision of microparticle manipulation and the sensitivity of sensing in dual-fiber optical trap systems.
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All authors Aoxi Chen, Xinlin Chen, Siyuan Rao, Hui An, Yingying Song, Tengfang Kuang, Wei Xiong, Xiang Han, Zhongqi Tan, Guangzong Xiao, Hui Luo

Monday 24 November

Chemical Physics · Cross-listed from cond-mat.stat-mech

Thermal stability originates the vanishing of the specific heats at the absolute zero

Martín-Olalla and José María

The relationship between the vanishing of the heat capacities as $T\to0^+$ and the thermal stability is examined. The heat capacities vanish as fast as or faster than $T$ as $T\to0^+$ for states at the phase space boundary ($T=0$) to sustain the standard thermal stability criterion $U_{ss}>0$. Conversely, weakly vanishing heat capacities, which signify a loss of curvature in $U(S)$ at $T=0$, are the signature of a critical condition precisely at $T=0$, as exemplified in marginal Fermi liquids. Therefore, the vanishing of the specific heat should be viewed not as a new law but as a confirmatory result of the existing framework of thermodynamics.
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Fluid Dynamics

A Geometric Foundation for the Universal Laws of Turbulence

Marcial Sanchis-Agudo and Ricardo Vinuesa

We propose a theoretical framework where the dissipative structures of turbulence emerge from microscopic path uncertainty. By modeling fluid parcels as stochastic tracers governed by the Schrödinger Bridge (SB) variational principle, we demonstrate that the Navier–Stokes viscous term is a natural linear, second-order macroscopic operator consistent with isotropic microscopic diffusion. We derive two foundational pillars of turbulence from this single principle. First, we show that the Kolmogorov scale $\eta \sim (\nu^3/\epsilon)^{1/4}$ is not merely a dimensional necessity but a geometric diffusion horizon: it is the scale at which the kinetic energy of a fractal trajectory, scaling as $k \sim \nu/\tau$, balances the macroscopic dissipation rate. Second, we show that the universal law of the wall is the stationary solution to this stochastic process under no-slip constraints. The logarithmic mean profile arises from the scale invariance of the turbulent diffusivity, while finite-Reynolds-number corrections emerge as controlled asymptotic expansions of the stochastic variance. This framework offers a physically grounded derivation of turbulent scaling laws that complements and extends purely phenomenological dimensional analysis.
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Classical Physics

To the theory of helical waveguides

A.S. Yurkov

It makes sense to consider a helical waveguide with a fine pitch approximately, replacing the turns with anisotropic conductivity: infinite along the turns and zero across them. This approach has been known for a long time, but calculation formulas within it have only been obtained for the case where the winding does not contain a dielectric core. This paper addresses this gap in the theory: calculation formulas are obtained for the case where the waveguide contains a dielectric with a certain permittivity and magnetic permeability. An equation determining the slowing factor is found, and a method for its numerical solution is proposed. Explicit formulas are obtained for the wave impedance.
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Medical Physics · Cross-listed from cs.AI

A Brief History of Digital Twin Technology

Yunqi Zhang, Kuangyu Shi and Biao Li

Emerging from NASA's spacecraft simulations in the 1960s, digital twin technology has advanced through industrial adoption to spark a healthcare transformation. A digital twin is a dynamic, data-driven virtual counterpart of a physical system, continuously updated through real-time data streams and capable of bidirectional interaction. In medicine, digital twin integrates imaging, biosensors, and computational models to generate patient-specific simulations that support diagnosis, treatment planning, and drug development. Representative applications include cardiac digital twin for predicting arrhythmia treatment outcomes, oncology digital twin for tracking tumor progression and optimizing radiotherapy, and pharmacological digital twin for accelerating drug discovery. Despite rapid progress, major challenges, including interoperability, data privacy, and model fidelity, continue to limit widespread clinical integration. Emerging solutions such as explainable AI, federated learning, and harmonized regulatory frameworks offer promising pathways forward. Looking ahead, advances in multi-organ digital twin, genomics integration, and ethical governance will be essential to ensure that digital twin shifts healthcare from reactive treatment to predictive, preventive, and truly personalized medicine.
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Chemical Physics

Direct readout of excited state lifetimes in chlorin chromophores under electronic strong coupling

Alexander M. McKillop, Liying Chen, Ashley P. Fidler et al. (+1 more)

The mechanisms governing molecular photophysics under electronic strong coupling (ESC) remain elusive to date. Here, we use ultrafast pump-probe spectroscopy to study the nonradiative excited state relaxation dynamics of chlorin e6 trimethyl ester (Ce6T) under strong coupling of its transition from the electronic ground state to the Qy band. We use dichroic Fabry-Pérot cavities to provide a transparent spectral window in which we can directly track the excited state population following optical pumping of either the strongly-coupled Qy band or the higher-lying B band. This scheme circumvents many of the optical artifacts inherent in ultrafast cavity measurements and allows for facile comparison of strongly-coupled measurements with extracavity controls. We observe no significant changes in excited state lifetimes for any optical pumping schemes or cavity coupling conditions considered herein. These results suggest that Ce6T exhibits identical photophysics under ESC and in free space, presenting a new data point for benchmarking emerging theories for cavity photochemistry.
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All authors Alexander M. McKillop, Liying Chen, Ashley P. Fidler, Marissa L. Weichman

Accelerator Physics

Analog Signal Multiplexing System for the Iota Proton Injector

Daniel R. MacLean and Dean R. Edstrom

The Fermilab Accelerator Science and Technology (FAST) Facility at FNAL is a dedicated research and development center focused on advancing particle accelerator technologies for future applications worldwide. Currently, a key objective of FAST Operations is to commission the 2.5 MeV IOTA Proton Injector (IPI) and enable proton injection into the Integrable Optics Test Accelerator (IOTA) storage ring. The low and medium-energy sections of the IPI include four frame-style dipole trims and two multi-function correctors with independently controlled coils, requiring readout of 32 analog channels for current and voltage monitoring in total. To reduce cost and optimize rack space within the PLC-based control system, a 32-to-4 analog signal multiplexing system was designed and implemented. This system enables real-time readback of excitation parameters from all magnetic correctors. This paper presents the design, construction, implementation, and performance of the multiplexing system.
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Atmospheric and Oceanic Physics

Investigating impacts of dust events on atmospheric surface temperature in Southwest Asia using AERONET data, satellite recordings, and atmospheric models

Mahsa Jahangiri, Afrooz Jouzdani and Hamid Reza Khalesifard

Dust layers have already been reported to have negative impacts on the radiation budget of the atmosphere. But the questions are: How does the atmospheric surface temperature change during a dust outbreak, and what is its temporal correlation with variations of the dust outbreak strength? We investigated these at selected AERONET sites, including Bahrain, IASBS, Karachi, KAUST Campus, Kuwait University, Lahore, Mezaira, Solar Village, in Southwest Asia, and Dushanbe in Central Asia, using available data from 1998 to 2024. The aerosol optical depth at 870 nm and the temperature recorded at each site are taken as measures of dust outbreak strength and atmospheric surface temperature, respectively. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and the aerosol optical depths recorded by the Moderate Resolution Imaging Spectroradiometers (MODIS) on board the Aqua and Terra satellites are used to specify the sources of the dust outbreaks. Our investigations show that in most cases, the temperature decreases during a dust outbreak, but in a considerable number of cases, the temperature rises. Temperature changes are mostly less than 5 {\deg}C. We found that a dust outbreak may affect the temperature even up to two days after its highest intensity time. This effect is more profound at sites far from large dust sources, such as IASBS in northwest Iran. For sites that are located on either a dust source or very close to it, the temperature and dust optical depth vary almost synchronously.
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Data Analysis and Statistics · Cross-listed from nlin.CD

Classifying Complex Dynamical and Stochastic Systems via Physics-Based Recurrence Features

J. V. M. Silveira, H. C. Costa, G. S. Spezzatto et al. (+2 more)

In this study, we employ the recently developed recurrence microstate probabilities as features to improve accuracy of several well-established machine learning (ML) algorithms. These algorithms are applied to classify discrete and continuous dynamical systems, as well as colored noise. We demonstrate that the dynamical characteristics quantified by this method are effectively captured in the recurrence microstate space, a space defined solely by the recurrence properties of the signal. This space change reduces dimensions, which also reduces the necessary time to perform calculations and obtain relevant information about the underlying system. Here, we also demonstrate that a few optimal machine learning (ML) algorithms are particularly effective for classification when combined with recurrence microstates. Furthermore, these new machine learning vectors significantly reduce memory usage and computational complexity, outperforming the direct analysis of raw data.
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All authors J. V. M. Silveira, H. C. Costa, G. S. Spezzatto, T. L. Prado, S. R. Lopes

Applied Physics

Active compensation of the AC Stark shift in a two-photon rubidium optical frequency reference using power modulation

Yorick Andeweg, John Kitching and Matthew T. Hummon

We implement a feedback protocol to suppress the AC Stark shift in a two-photon rubidium optical frequency reference, reducing its sensitivity to optical power variations by a factor of 1000. This method alleviates the tradeoff between short-term and long-term stability imposed by the AC Stark shift, enabling us to simultaneously achieve instabilities of $3\times10^{-14}$ at 1 s and $2\times10^{-14}$ at $10^4$ s. We also quantitatively describe, and experimentally explore, a stability limit imposed on clocks using this method by frequency noise on the local oscillator.
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Atomic Physics · Cross-listed from quant-ph

Infrared absorption spectroscopy of a single polyatomic molecular ion

Zhenlin Wu, Tim Duka, Mariano Isaza-Monsalve et al. (+8 more)

Absorption spectroscopy is a fundamental tool for probing molecular structure. However, performing absorption spectroscopy on individual molecules is challenging due to the low signal-to-noise ratio. Here, we report on a nondestructive absorption spectroscopy on a mid-infrared vibrational transition in a single molecular ion that is co-trapped with an atomic ion. The absorption of a single photon is detected via the momentum transfer from the absorbed photon onto the molecule. This recoil signal is amplified using a non-classical state of motion of the two-ion crystal and subsequently read out via the atomic ion. We characterize the recoil detection method and use it to investigate the interaction between femtosecond laser pulses and the O-H stretching vibration in individual CaOH+ molecular ions. Furthermore, we present the single-photon absorption spectrum obtained for the vibrational transition. This method represents a milestone towards quantum non-demolition measurements of complex polyatomic molecules, providing high-fidelity methods for preparation and measurement of the quantum state of a wide range of molecular species.
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All authors Zhenlin Wu, Tim Duka, Mariano Isaza-Monsalve, Miriam Kautzky, Vojtěch Švarc, Andrea Turci, René Nardi, Marcin Gronowski, Michał Tomza, Brandon J. Furey, Philipp Schindler

Optics · Cross-listed from quant-ph

Quantum Coherence of Rare-Earth Ions in Heterogeneous Photonic Interfaces

Henry C. Hammer, Hassan A. Bukhari, Yogendra Limbu et al. (+6 more)

Harnessing rare-earth ions in oxides for quantum networks requires integration with bright emitters in III-V semiconductors, but local disorder and interfacial noise limit their optical coherence. Here, we investigate the microscopic origins of the ensemble spectrum in Er$^{3+}$:TiO$_2$ epitaxial thin films on GaAs and GaSb substrates. Ab initio calculations combined with noise-Hamiltonian modeling and Monte Carlo simulations quantify the effects of interfacial and bulk spin noise and local strain on erbium crystal-field energies and inhomogeneous linewidths. Photoluminescence excitation spectroscopy reveals that Er$^{3+}$ ions positioned at increasing distances from the III-V/oxide interface produce a systematic blue shift of the $Y_1\rightarrow Z_1$ transition, consistent with strain relaxation predicted by theory. Thermal annealing produces a compensating redshift and linewidth narrowing, isolating the roles of oxygen-vacancy and gallium-diffusion noise. These results provide microscopic insight into disorder-driven decoherence, offering pathways for precise control of hybrid quantum systems for scalable quantum technologies.
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All authors Henry C. Hammer, Hassan A. Bukhari, Yogendra Limbu, Brett M. Wasick, Christopher Rouleau, Michael E. Flatté, Durga Paudyal, Denis R. Candido, Ravitej Uppu

Accelerator Physics

Mechanical Design of the PIP-II ORBUMP Pulsed Dipole Magnet

D. Karas, K. Badgley, Z. Chen et al. (+9 more)

The Proton Improvement Plan II (PIP-II) project is a vital upgrade to the Fermilab accelerator complex. The magnet pulse rate of the PIP-II Injection system requires an increase from the current rate of 15 Hz to 20 Hz as well as a roughly 30% increase in the magnetic field of the new Orbital Bump (ORBUMP) pulsed dipole magnets in the Booster. The ORBUMP magnet mechanical design is presented in this paper. The ORBUMP magnet is secured in a vacuum box and the core is made up of 0.127 mm thick, low carbon steel laminations with a C-5 inorganic magnesium phosphate coating. The core is clamped using external tie bars welded to the core end plates. ANSYS Finite Element Analysis (FEA) was used to evaluate the clamping design to minimize the deflection of the core post welding of the tie bars. The water-cooled, single turn coil, which shapes the magnetic field by acting as the pole tips, is critical for the integrated field homogeneity. The coil manufacturing tolerances and fabrication techniques were evaluated to ensure the magnetic properties of the magnet could be obtained. The coil is electrically isolated from the core using virgin Polyether ether ketone (PEEK) insulating material in the gap. An investigation into the high voltage performance of the virgin PEEK insulator was conducted via partial discharge testing using a 1:1 scale sample.
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All authors D. Karas, K. Badgley, Z. Chen, V. Chernenok, M. Davidson, D. Harding, D. Johnson, V. Kashikhin, W. Robotham, T. Strauss, B. Szabo, J. Vander Meulen

Atmospheric and Oceanic Physics

Concept drift of simple forecast models as a diagnostic of low-frequency, regime-dependent atmospheric reorganisation

Haokun Zhou

Data-driven weather prediction models implicitly assume that the statistical relationship between predictors and targets is stationary. Under anthropogenic climate change, this assumption is violated, yet the structure of the resulting concept drift remains poorly understood. Here we introduce concept drift of simple forecast models as a diagnostic of atmospheric reorganisation. Using ERA5 reanalysis, we quantify drift in spatially explicit linear models of daily mean sea-level pressure and 2\,m temperature. Models are trained on the 1950s and 2000s and evaluated on 2020 tp 2024; their performance difference defines a local, interpretable drift metric. By decomposing errors by frequency band, circulation regime and region, and by mapping drift globally, we show that drift is dominated by low-frequency variability and is strongly regime-dependent. Over the North Atlantic-European sector, low-frequency drift peaks in positive NAO despite a stable large-scale NAO pattern, while Western European summer temperature drift is tightly linked to changes in land-atmosphere coupling rather than mean warming alone. In winter, extreme high-pressure frequencies increase mainly in neutral and negative NAO, whereas structural drift is concentrated in positive NAO and Alpine hotspots. Benchmarking against variance-based diagnostics shows that drift aligns much more with changes in temporal persistence than with changes in volatility or extremes. These findings demonstrate that concept drift can serve as a physically meaningful diagnostic of evolving predictability, revealing aspects of atmospheric reorganisation that are invisible to standard deviation and storm-track metrics.
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Classical Physics

Infinite self energy?

Jerrold Franklin

The notion of an infinite electromagnetic self energy of point charges (presumably electrons) is accepted by many electromagnetic textbooks. See, for instance,\cite{jdj,dg,rf}. However, each of these sources acknowledge that they don't understand that result. In this paper, we show that electrons must be point particles with no electromagnetic self energy.
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Physics and Society

Techno economic feasibility study of solar ORC in India

Ayona Biswas, Arindam Mandal, Aditya Bandopadhyay et al. (+2 more)

Solar energy has enormous potential because there is a worldwide need to meet energy demands. Depleting non-renewable energy resources, increasing carbon emissions, and other environmental effects concern the scientific community to develop an alternative approach to electricity production. In this article, we present the study of a solar-powered Organic Rankine cycle considering Indian climatic conditions. Initially, we scrutinized seven working fluids and assessed their performance in the ORC at an evaporator pressure range of 9-30 bar and a mass flow rate range of 0.2 kg/s to 4.5 kg/s. For a fixed sink temperature of 298 K, we evaluate the system using four different power ratings of 2, 20, 50, and 100 kW based on four different source temperatures of 423 K, 403 K, 383 K, and 363 K. We estimate the system cost for each working fluid in each scenario separately. Our findings suggest that R 1233zd(E) is the optimum performing working fluid based on cost, cost-effectiveness, and environmental friendliness. We also notice that the estimated system scale cost is very competitive and could be a great alternative to the technologies already on the Indian market.
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All authors Ayona Biswas, Arindam Mandal, Aditya Bandopadhyay, Sourav Mitra, Sandeep Saha