Physics and Society
Impact of individual actions on the collective response of social systems
Samuel Martin-Gutierrez, Juan C. Losada and Rosa M. Benito
In a social system individual actions have the potential to trigger spontaneous collective reactions. The way and extent to which the activity (number of actions$-A$) of an individual causes or is connected to the response (number of reactions$-R$) of the system is still an open question. We measure the relationship between activity and response with the distribution of efficiency, a metric defined as $\eta=R/A$. Generalizing previous results, we show that the efficiency distribution presents a universal structure in three systems of different nature: Twitter, Wikipedia and the scientific citations network. To understand this phenomenon, we develop a theoretical framework composed of three minimal statistical models that contemplate different levels of dependence between $A$ and $R$. The models not only are able to reproduce the empirical activity-response data but also can serve as baselines or null models for more elaborated and domain-specific approaches.
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Optics
Refractive Index Tuning of Terahertz Photonic Materials Based on a Stretchable Silicon Effective Medium
Hidemasa Yamane, Yoshiharu Yamada, Yusuke Kondo et al. (+3 more)
Dynamically tunable terahertz (THz) photonics requires low-loss dielectric platforms with practical, continuous control of refractive index. Here we present a mechanically reconfigurable THz photonic material platform: a monolithic, all-silicon (Si) stretchable effective medium whose refractive index is tuned by deformation. A 200 micrometer-thick high-resistivity single-
crystal Si slab was patterned into a subwavelength spiral-spring through-hole
lattice, rendering bulk Si mechanically compliant while preserving its low-loss dielectric response. THz time-domain spectroscopy demonstrates high transmission below 0.6 THz and reveals a monotonic decrease in the effective refractive index under uniaxial stretching. At 12.6% elongation, the effective index decreases by 6% and 8% for polarizations perpendicular and parallel to the stretch direction, respectively, thereby demonstrating deformation-induced, controllable anisotropy without a detectable increase in extinction. This structurally engineered bulk-Si approach offers a process-compatible route to mechanically tunable, low-loss THz components for adaptive wavefront and polarization control.
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All authors Hidemasa Yamane, Yoshiharu Yamada, Yusuke Kondo, Ken Miyajima, Masayuki Fujita, Shuichi Murakami
Medical Physics
On the calculation of the radiobiological effect of radiolytic oxygen depletion in FLASH radiotherapy
Juan Pardo-Montero and Isabel González-Crespo
Objective: Radiolytic oxygen depletion (ROD) may play a role in the sparing of
cells irradiated with ultra-high dose rates. Different methods have been used to quantify the effect of ROD during FLASH irradiation on
cell survival, typically involving some kind of averaging of the oxygen effect and the LQ model. In this work, we compare the results obtained with several of these methods and introduce a novel method based on the non-linear differential form of the LQ model. Approach: We present a novel method to account for a varying oxygen concentration on the dose-response based on the non-linear differential form of the LQ model, and we compare the results obtained with this method with those obtained with other methods that linearize the averaging of the oxygen effect during irradiation. Main results: We found differences in the surviving fractions obtained with the method introduced in this work and other methods that introduce different linearizations (averaging) of the non-linear dependence on the oxygen concentration, especially for oxygenations and doses that lead to important changes in the OERs during the delivery of the dose (initial oxygenations $\approx$5–10 mmHg and doses $>30$~Gy). On the other hand, we showed that the method presented by Zhu et al. is equivalent to a first-order Euler numerical method of the differential LQ model. Significance: The method introduced in this work and the method of Zhu et al. may allow a more precise quantification of the effect of ROD on dose-response, both for tumors and normal tissues. While all the reviewed methods show an oxygen-dependent sparing effect of FLASH radiotherapy driven by ROD and qualitatively similar results, the method introduced in this work and that of Zhu et al. may be more suitable to quantitatively analyze new preclinical (and future clinical) data coming from experimental studies.
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Physics and Society
Recurrent patterns of user behavior in different electoral campaigns: A Twitter analysis of the Spanish general elections of 2015 and 2016
Samuel Martin-Gutierrez, Juan C. Losada and Rosa M. Benito
We have retrieved and analyzed several millions of Twitter messages corresponding to the Spanish General elections held on the 20th of December 2015 and repeated on the 26th of June 2016. The availability of data from two electoral campaigns that are very close in time allows us to compare collective behaviors of two analogous social systems with a similar context. By computing and analyzing the time series of daily activity, we have found a significant linear correlation between both elections. Additionally, we have revealed that the daily number of tweets, retweets and mentions follow a power law with respect to the number of unique users that take part in the conversation. Furthermore, we have verified that the
topologies of the networks of mentions and retweets do not change from one election to the other, indicating that their underlying dynamics are robust in the face of a change in social context. Hence, in the light of our results, there are several recurrent collective behavioral patterns that exhibit similar and consistent properties in different electoral campaigns.
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Physics and Society
Relationship between ideology and language in the Catalan independence context
Julia Atienza-Barthelemy, Samuel Martin-Gutierrez, Juan C. Losada et al. (+1 more)
Political polarization generates strong effects on society, driving controversial debates and influencing the institutions. Territorial disputes are one of the most important polarized scenarios and have been consistently related to the use of
language. In this work, we analyzed the opinion and
language distributions through Twitter data of a particular territorial dispute around the independence of Catalonia. We infer a continuous opinion distribution by applying a model based on retweet interactions, previously detecting elite users with fixed and antagonist opinions. The resulting distribution presents a mainly bimodal behavior with an intermediate third pole that shows a less polarized society with the presence of not only antagonist opinions. We find that the more active, engaged and influential users hold more extreme positions. Also we prove that there is a clear relationship between political positions and the use of
language, showing that against independence users speak mainly Spanish while pro-independence users speak Catalan and Spanish almost indistinctly. However, the third pole, closer in political opinion to the pro-independence pole, behaves similarly to the against-independence one concerning the use of
language.
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All authors Julia Atienza-Barthelemy, Samuel Martin-Gutierrez, Juan C. Losada, Rosa M. Benito
Geophysics · Cross-listed from astro-ph.EP
Characteristics of natural remanence records in fine-grained particles returned from asteroid Ryugu
Masahiko Sato, Yuki Kimura, Tadahiro Hatakeyama et al. (+25 more)
Particles collected from the asteroid Ryugu by the Hayabusa2 spacecraft offer a unique opportunity to investigate the
magnetic record of the primitive
solar system, as any terrestrial
magnetic contamination is minimal and can be accounted for. In previous studies, stepwise alternating field demagnetization (AFD) measurements of natural remanent magnetization (NRM) records have been conducted on seven Ryugu particles. However, due to the limited number of samples, there is no consensus regarding the interpretation of the results of these measurements. To address this problem, we performed stepwise AFD measurements of the NRM on 28 Ryugu particles. Twenty-three of the particles exhibited one or two stable NRM components, whereas the remaining five did not. Isothermal remanent magnetization-based paleointensity values derived from stable NRM components varied by more than one order of magnitude. These NRM characteristics were consistent with those observed in previous studies. Therefore, as a reflection of the original nature of the NRM record, some Ryugu particles exhibited stable NRM components, whereas others did not. The Ryugu particles investigated in this study and those from a previous study exhibited spatially inhomogeneous NRM directions within individual particles, constraining the NRM acquisition time to before the final solidification of the current Ryugu particles. A mechanism of remanence acquisition that can explain the observed NRM characteristics is a chemical remanent magnetization associated with the growth of framboidal magnetite during aqueous alteration in Ryugu's parent body.
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All authors Masahiko Sato, Yuki Kimura, Tadahiro Hatakeyama, Tomoki Nakamura, Satoshi Okuzumi, Sei-ichiro Watanabe, Seiji Sugita, Satoshi Tanaka, Shogo Tachibana, Hisayoshi Yurimoto, Takaaki Noguchi, Ryuji Okazaki, Hikaru Yabuta, Hiroshi Naraoka, Kanako Sakamoto, Toru Yada, Masahiro Nishimura, Aiko Nakato, Akiko Miyazaki, Kasumi Yogata, Masanao Abe, Tatsuaki Okada, Tomohiro Usui, Makoto Yoshikawa, Takanao Saiki, Fuyuto Terui, Satoru Nakazawa, Yuichi Tsuda
Optics
Closed-loop control of a monolithically 3D nano-printed electromagnetic lens scanner with an integrated Hall sensor
Florian Lux, Elijah Ditchendorf and Çağlar Ataman
3D nano-printing through two-
photon polymerization enables monolithic manufacturing of mechanical and freeform micro-optical elements with high inherent
alignment accuracy. However, viscoelasticity and temperature-dependent stiffness of the photopolymer lead to hysteresis and drift, which significantly degrade open-loop position accuracy and long-term stability in quasi-static operation. Therefore, closed-loop control with integrated displacement sensing is essential for 3D nano-printed optical microsystems in practical precision positioning applications. Here, we present a closed-loop control system for a such a lens actuator that uses a commercial 3-axis
Hall sensor for position tracking. A NdFeB micromagnet encircling the integrated microlens provides both the actuation force and a position-dependent sensing signal. The
Hall sensor, located between an anti-Helmholtz-like coil pair that drives the scanner bidirectionally, measures the combined field due to the micro-magnet and the coil pair. Calibration-based subtraction separates the coil field and sensor offset contributions to recover the magnet field and thus the axial magnet displacement. Closed-loop operation yields a mean absolute accuracy of 0.86 um and a precision of 0.49 um over a displacement range of 150 um while eliminating viscoelastic creep, suppressing hysteresis, and minimizing temperature-induced displacement drift under coil self-heating. This sensing approach requires no additional microfabrication steps and provides a practical path toward stable and repeatable positioning for monolithically 3D nano-printed optical microsystems.
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Applied Physics
Enabling FR2-5G Communication with Dielectric OAM Transmitarrays
Miguel Á. Balmaseda-Márquez, Juan E. Galeote-Cazorla, Álvaro Liébana-Bolívar et al. (+3 more)
This paper investigates the potential of near-field (NF) indoor communications in the FR2 frequency bands using fully dielectric structures to generate orbital angular momentum (OAM) waves. All-dielectric platforms based on distributions of T-shaped unit
cells are employed for this purpose. The unit
cell design is based on a circuital approach and analytical formulations, where phase shifts necessary for OAM generation are achieved by varying the dielectric-to-air ratio within the structure. Based on this unit
cell, a set of transmitarrays (TAs) are designed to produce specific OAM modes. These TAs are fabricated in-house using stereolithographic 3D printing and experimentally tested. The tests evaluate two key features of OAM beams: the orthogonality of distinct
vortex modes, as characterized by their electric field distributions, and their object-avoidance capability, enabled by the central null characteristic of the wavefront. In addition, a field-test within an indoor environment is conducted emulating a real wireless system. A bit error rate lower than 10\textsuperscript{$-$6} is observed for solidary modes in Tx and Rx, whereas orthogonal modes produces an increment in 4 order of magnitude. The obtained results reveals that the prototype is suitable for short-range scenarios, enabling techniques such as OAM-multiplexation or physical-layer security thanks to the effective orthogonality beteween modes.
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All authors Miguel Á. Balmaseda-Márquez, Juan E. Galeote-Cazorla, Álvaro Liébana-Bolívar, Alejandro Ramírez-Arroyo, Carlos Molero Jiménez, J.F. Valenzuela-Valdés
Plasma Physics
Entropy stable numerical schemes for divergence diminishing Chew, Goldberger & Low equations for plasma flows
Chetan Singh, Harish Kumar, Deepak Bhoriya et al. (+1 more)
Chew, Goldberger & Low (CGL) equations are a set of
hyperbolic PDEs with non-conservative products used to model the
plasma flows, when the assumption of local thermodynamic
equilibrium is not valid, and the pressure tensor is assumed to be rotated by the
magnetic field. This results in the pressure tensor, which is described by the two scalar components. As the
magnetic field also evolves, controlling the divergence of the
magnetic field is important. In this work, we consider the generalized Lagrange multiplier (GLM) technique for the CGL model. The resulting model is referred to as the GLM-CGL system. To make the system suitable for
entropy-stable schemes, we reformulate the GLM-CGL system by treating some conservative terms as non-conservative. The resulting system has a non-conservative part that does not affect
entropy evolution. We then propose
entropy stable numerical methods for the GLM-CGL model. The numerical results for the GLM-CGL system are then compared with the CGL system without the GLM divergence diminishing approach to demonstrate that the GLM approach indeed leads to significant improvement in the
magnetic field divergence diminishing.
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All authors Chetan Singh, Harish Kumar, Deepak Bhoriya, Dinshaw S. Balsara
Computational Physics
A Novel NPT Thermodynamic Integration Scheme to Derive Rigorous Gibbs Free Energies for Crystalline Solids
Karel L. K. De Witte, Tom Braeckevelt, Massimo Bocus et al. (+2 more)
Thermodynamic Integration (TI) is the state-of-the-art computational technique for accurate Gibbs free energy predictions of solids. Conventional TI schemes start from an NVT harmonic reference and require three successive corrections to recover the Gibbs free energy of the real
crystal in the NPT ensemble. However, the NVT-to-NPT correction neglects full
cell flexibility. Here, we present a rigorous (and only) two-step TI scheme that operates entirely in the NPT ensemble, eliminating the need for the approximate NVT-to-NPT step. The key methodological advancement is the novel NPT reference that explicitly accounts for full
cell fluctuations. The new approach is compared with the conventional one via two complementary case studies. For ice polymorphs, having simple
cell-shape distributions, the new approach reproduces conventional TI results with excellent agreement. For CsPbI3, whose black phase exhibits complex
cell-shape behavior, we demonstrate that our novel method provides more accurate Gibbs free energy differences than the conventional one. Moreover, the proposed framework maintains comparable computational cost while offering a simplified workflow. Overall, the new NPT TI scheme provides rigorous and direct Gibbs free energy calculations for solids.
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All authors Karel L. K. De Witte, Tom Braeckevelt, Massimo Bocus, Sander Vandenhaute, Veronique Van Speybroeck
Atomic Physics
Tune-out wavelength for the thulium atom near 576 nm
Ivan Pyrkh, Arjuna Rudnev, Daniil Pershin et al. (+12 more)
We report the theoretical prediction and measurement of a tune-out wavelength for the ground state of the thulium atom in a linearly polarized optical dipole trap with a wavelength of approximately 576 nm. The measurements were conducted using a combination of trap frequency and RF loss spectroscopy, thus making it possible to separate the scalar and tensor parts of the total polarizability without measurements in the range of negative total polarizability. The calculated tune-out wavelength is consistent with the measured one of $575.646_{-0.014}^{+0.016}$ nm in air. The existence of the zero in the polarizability for the Tm ground state was confirmed by the trap loss experiment, which also made it possible to refine the tune-out wavelength to $575.646_{-0.004}^{+0.004}$. Despite the presence of an imaginary part of the polarizability at some wavelengths, it was experimentally demonstrated that, with a proper choice of the dipole trap polarization, it was possible to achieve Bose-Einstein condensation of thulium atoms in the range from 575.348 to 575.689 nm, covering the tune-out wavelength.
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All authors Ivan Pyrkh, Arjuna Rudnev, Daniil Pershin, Davlet Kumpilov, Ivan Cojocaru, Vladimir Khlebnikov, Pavel Aksentsev, Ayrat Ibrahimov, Sergey Kuzmin, Alexander Raskatov, German Subbotin, Kirill Dyadkin, Anna Zykova, Vladislav Tsyganok, Alexey Akimov
Physics and Society
Modeling financial transactions via random walks on temporal networks
Carolina E. Mattsson, Claudio Cellerini, Jaume Ojer et al. (+1 more)
We model financial transactions as random walks on activity-driven temporal networks. By enforcing fund conservation, our framework analytically derives heavy-tailed distributions for the stationary balances and transaction sizes. Crucially, the latter is driven by variance in the spending propensity of individuals. Calibrated with empirical data from a closed, digital currency community, the model also reproduces observed correlations between inflows and
outflows. Our findings provide a path for understanding emergent properties of the circulation of money.
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All authors Carolina E. Mattsson, Claudio Cellerini, Jaume Ojer, Michele Starnini
Atomic Physics
Accurate transition and hyperfine data in Ag I from Multiconfiguration Dirac-Hartree-Fock and Relativistic Coupled-Cluster methods
P. Jönsson, B. K. Sahoo, S. Caliskan et al. (+1 more)
Silver is a key tracer of the weak r-process in late-type
stars. However, when the assumption of local thermodynamic
equilibrium (LTE) needs to be relaxed, accurate abundance determinations become even more sensitive to complete sets of reliable transition data. The aim of this work is to provide accurate and extensive results of excitation energies, radiative transition and hyperfine data for Ag I. The Multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic coupled-cluster (RCC) methods were used in the present work. The quantitative and qualitative evaluation (QQE) approach is applied to the MCDHF transition rates to estimate the uncertainty according to the National Institute of Science and Technology Atomic Spectroscopic Data (NIST ASD) terminology. Excitation energies, transition data and hyperfine structure constants were calculated for $18$ states up to $4d^{10}8s$. $57$ electric dipole (E1) transition rates and weighted oscillator strengths are computed and estimated to be in the following NIST ASD uncertainty classes; $4$ in AA, $12$ in A+, $5$ in A, $13$ in B+, $6$ in B, $4$ in C+ with AA $\leq 1\%$, A+ $\leq 2\%$, A $\leq 3\%$, B+ $\leq 7\%$, B $\leq 10\%$, C+ $\leq 18\%$. The remaining transitions, mainly weak transitions involving the $4d^95s^2$ states, are estimated to be in the E class $>50\%$. The computed lifetimes from both the MCDHF and RCC methods are in good mutual agreement and mostly fall within the error bars of available experimental values from
laser induced fluorescence (LIF) measurements. The $4d^95s^2~^2D_{5/2}$ metastable state, important for establishing the ionization balance, decay through an E2 transition to the ground state. The calculated lifetime is $163\,\mathrm{ms}$. The computed hyperfine interaction constants from the MCDHF and RCC methods are in good agreement and compare well with the scattered experimental constants.
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All authors P. Jönsson, B. K. Sahoo, S. Caliskan, A. M. Amarsi
Biological Physics · Cross-listed from q-bio.PE
Tipping points in complex ecological systems
Alan Hastings, Sergei Petrovskii, Valerio Lucarini et al. (+1 more)
Tipping points are one of the hot topics in the modern physics of complex systems. But what is a tipping point? One generic definition describes it as “a state of the system where a small change in its parameters can lead to a significant change in its properties”. Additional ingredients that often enter the definition of tipping point are the abruptness of the resulting change and its irreversibility, i.e. it is impossible to recover the initial state if one reverses the protocol of change of the parameters. However, there exists a number of different mathematical structures that can show this behavior, the one that was originally used nowadays often referred to as the bifurcation induced tipping is just one of many. Different preconditions and/or different level of detail included into the model, reflecting also different environmental forcing, can lead to a variety of tipping mechanisms. Furthermore, in a spatially extended system and/or a system with multiple scales, different parts can react to a change in environmental conditions differently or at a different time, interacting with each other to create a tipping cascade. In this paper, using ecosystems as a paradigm of complex nonlinear open systems, we provide a critical overview of the progress made in tipping point science over the last 15 years. We highlight the main findings, identify gaps in our knowledge, and outline a roadmap for further progress.
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All authors Alan Hastings, Sergei Petrovskii, Valerio Lucarini, Andrew Morozov
Optics
Native QR Factorization on Programmable Photonic Meshes
S.A. Fldzhyan, S.S. Straupe and M.Yu. Saygin
We propose a photonic native procedure for computing the QR factorization of a
matrix using a programmable
unitary interferometer mesh. The method configures the mesh through a sequence of local power routing steps within tunable two mode interferometric elements, while reading out the resulting upper triangular factor directly from the optical outputs. The number of physical operations grows as $ O(N\log_2N)$ with
matrix size $N$, reducing the runtime relative to standard digital QR routines, which scale cubically ($O(N^3)$). Beyond single factorizations, the same architecture supports iterative spectral computations by reusing the configured interferometer in a mirrored arrangement that implements the core update step of the QR
eigenvalue algorithm. We also describe related optical procedures for Hessenberg reduction and bidiagonalization, serving as compatible preprocessors for QR and SVD workflows. A comparison with the systolic array computational architecture is provided. Our approach exhibits comparable asymptotic complexity for blocked QR decomposition and is more efficient for Hessenberg reduction and bidiagonalization.
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Applied Physics
Resonant attenuation of surface acoustic waves by a weakly bonded layer
Martin Robin, Thomas Dehoux and Maroun Abi Ghanem
We investigate the propagation of surface acoustic waves (SAWs) in a layered half-space system comprising a continuous, sub-wavelength-thick layer weakly adhering to a substrate. Using finite element simulations, we demonstrate that this configuration - without requiring surface structuration - gives rise to frequency ranges bounded in k-space and characterized by strong SAW attenuation, which we term adhesion-induced resonant attenuation zones. We show that these attenuation zones closely mimic the resonant behavior typically observed in locally resonant metamaterials and can be understood through a mass-spring analogy, where the adhesion between the layer and substrate governs the frequency and width of the attenuation zones. As a practical demonstration, we propose a
bilayer configuration as a practical route to experimentally realize adhesion-induced resonant attenuation of SAWs, where a soft and thin interfacial film serves as an intermediate adhesive bonding between the layer and substrate, providing a realistic and tunable interfacial stiffness. Our findings offer a simplified route to achieving SAW manipulation through continuous layered media with tunable adhesion, providing a practical alternative to complex structural designs in SAW-based devices across a broad frequency range.
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Applied Physics
Integrating Domain-Specialized Language Models with AI Measurement Tools for Deterministic Atomic-Resolution Experimentation
Zhuo Diao, Kouma Matsumoto, Linfeng Hou et al. (+3 more)
Self-driving laboratories based on large
language models promise to transform scientific discovery through general experimental automation. However, realizing this
vision on precision platforms remains challenging, requiring deterministic execution and effective domain adaptation under strict physical constraints. We address these requirements through a framework that specializes in small
language models for autonomous control of scanning probe microscopy, coordinating task-specific models with AI-driven measurement tools. We demonstrate real-time, atomic-resolution SPM experiments at room temperature, achieving instruction-level control and multi-step experimental planning. Fine-tuning reduces perplexity from 1.44 to 1.20 and improves reliability, with the adapted model reaching 99.3% and 95.2% command accuracy, outperforming OpenAI o4-mini on domain-specific tasks. This architecture achieves lower computational cost while maintaining deterministic execution and enabling deployment on consumer-grade hardware. This work bridges probabilistic
language models with deterministic experimental control through a modular, domain-specialized architecture, providing a generalizable pathway toward scalable and trustworthy self-driving laboratories across diverse scientific platforms.
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All authors Zhuo Diao, Kouma Matsumoto, Linfeng Hou, Masahiro Ohara, Hayato Yamashita, Masayuki Abe
Instrumentation and Detectors
Development and characterization of the efficient portable X-ray imaging device based on Raspberry Pi camera
Nguyen Duc Ton, Nguyen Thanh Luan, Faizan Anjum et al. (+5 more)
This study reports the development and characterization of an efficient portable X-ray imaging device built from Raspberry Pi components, including a high-quality 12.3-megapixel camera configured for indirect detection with a Gd2O2S:Tb scintillation screen. The device was evaluated under both ambient light and X-ray exposure conditions. Initial characterization under ambient light ensured proper optical focusing; subsequently, camera settings (ISO and exposure time) were evaluated and optimized for X-ray imaging performance. Spatial resolution of the developed device was quantified using the Slanted-Edge method to derive the Modulation Transfer Function (MTF). Besides the low-noise feature, the device achieves MTF20 values of 68 lp/mm under ambient light and 25 lp/mm under X-ray irradiation (50 and 70 kV). Moreover, the modularity of the developed device was confirmed by conducting the tests with LYSO:Ce and GAGG:Ce screens. The results demonstrate that this efficient, scientific-grade, compact platform achieves spatial resolution comparable to that of clinical radiography systems, highlighting its potential for applications in scientific, educational, and medical contexts where efficient and portability are critical considerations.
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All authors Nguyen Duc Ton, Nguyen Thanh Luan, Faizan Anjum, D. Joseph Daniel, Sunghwan Kim, Suchart Kothan, Jakrapong Kaewkhao, Hong Joo Kim
Applied Physics
Omnidirectional wave energy gimbal-based electromagnetic generator
Zhichao Jiang and Shunchao Jiang
Wave energy, as a renewable energy source, is widely distributed and possesses substantial reserves. However, many existing wave energy harvesters exhibit motion constraints under irregular wave conditions, which limits their energy conversion efficiency. In this study, an omnidirectional wave energy gimbal-based electromagnetic generator (OWG-EMG) is proposed to achieve stable power generation under irregular wave motions. By integrating a three-axis gimbal mechanism with an inertial mass regulator, the proposed harvester effectively converts complex and varying wave-induced motions into relative rotational motion between gimbal frames. A planetary gear transmission is further employed to increase the rotational speed of the electromagnetic generator, enabling efficient omnidirectional wave energy harvesting. Experimental results demonstrate that the device delivers an average output power of up to 0.24 W at a frequency of 1 Hz, corresponding to an average power density of 40 W/m3. Importantly, in addition to its high energy conversion efficiency, the proposed device offers notable advantages including low cost, structural simplicity, and high reliability, highlighting its significant potential for applications in ocean energy harvesting and utilization.
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Biological Physics
Programming Shapes with Competing Layered Patterns
Wan Yee Yau and Carl D. Modes
Studying shape changing thick surfaces induced by differential growth helps us understand morphogenesis in biology and offers opportunities for device design. While ideal 2D differential growth maps have been well studied for both isotropic and anisotropic growth, scenarios involving gradients in thickness growth are far less explored. In this paper, we focus on a
bilayer system in which the two layers undergo independent but incompatible growth. We examine how the strength of the growth patterns and the aspect ratio of the
bilayer influence the resulting shapes. We first investigate the effect of global area difference in the
bilayer. Next, we make one of the two layers active and program it with positive or negative, localized or uniform
curvature. We then present examples involving competition between two active surfaces with opposite
curvature signs or different
curvature distributions and understand how the final configurations follow from the principles identified earlier. Finally, we demonstrate the ability to program biologically inspired shapes, such as dental epithelium and the ventral furrow in Drosophila, using a
bilayer with simple, distinct deformation gradients.
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Fluid Dynamics
On the Mathematical Analysis and Physical Implications of the Principle of Minimum Pressure Gradient
Haithem Taha
In this paper, we establish a two-way equivalence between the incompressible Navier- Stokes equation (INSE) and the principle of minimum pressure gradient (PMPG). We prove that a candidate smooth flow field is a solution of the INSE if and only if its instantaneous
evolution minimizes, at every instant, the norm of the pressure force, required to enforce incompressibility. We show that the PMPG is precisely the minimization formulation of the Leray-Helmholtz projection. Any admissible instantaneous
evolution (e.g., onset of separation) resulting from the INSE necessarily minimizes the PMPG cost. Conversely, any other kinematically admissible
evolution, requiring a strictly larger pressure force to ensure the same constraints, does not satisfy the INSE. Thus, the PMPG offers a variational perspective through which intricate incompressible flow behaviors may be interpreted. In a finite-dimensional setting with divergence-free modes, we show that the PMPG yields the same dynamics as classical Galerkin projection. Moreover, the PMPG provides a natural generalization of classical Galerkin projection beyond linear modal expansions, accommodating nonlinear and non-modal representations. We then examine the relation between instantaneous dynamical minimization and steady variational selection, including its connection to the variational theory of lift. Motivated by these observations, we formulate
conjectures concerning necessary conditions for stability and the convergence of Navier-Stokes solutions to Euler's in the vanishing-viscosity limit.
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Accelerator Physics
Laser Synchronisation Over One Hundred Kilometers With Stability at Picosecond Scale
Alice Renaux, Ronic Chiche, A. Martens et al. (+3 more)
Large-scale systems, such as very large accelerators used for fundamental research, require the implementation of precise timing and synchronization systems over distances of several kilometers. Femtosecond synchronisation has been reached by the implementation of costly and complex clock distribution systems. However, many devices, such as accelerator diagnostics or detectors for physics at
colliders, only require picosecond stability and, in some cases, similar accuracy. An approach that is based on the CERN White Rabbit protocol, deployed on an electronic system capable of generating arbitrary frequencies with Hertz precision, is proposed here. Results of performance tests for the synchronization of a
laser system, typically employed as a diagnostic for electron/positron beam polarimetry in accelerators, are provided in this Paper. We demonstrate that the system can synchronize a pulsed
laser with picosecond stability over one hundred kilometers on the short-term. The long-term stability over half a day is found to be of 5.5~ps for the 100~km link. The accuracy of the phase difference corresponding to $\pm 20$~ps is obtained. This work paves the way for the deployment of White-Rabbit-based synchronization systems for accelerator components, such as
lasers, but also for large-scale detectors.
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All authors Alice Renaux, Ronic Chiche, A. Martens, Antoine Back, Paul-Éric Pottie, Daniel Charlet
Computational Physics · Cross-listed from cond-mat.mtrl-sci
Combining Quasiparticle Self-Consistent $GW$ and Machine-Learned DFT+$U$ to Assess Half-Metallicity in Co- and Ni-Based Heuslers
Zefeng Cai, Malcolm J. A. Jardine, Maituo Yu et al. (+6 more)
Half-metallic Heusler compounds are of significant interest for spintronics. For device fabrication, compounds that can be epitaxially grown on III-V
semiconductors are particularly attractive. We present a first-principles investigation of four Co-based and two Ni-based Heusler compounds that are
lattice-matched to InAs. The results of density functional theory (DFT) using semi-local and hybrid functionals are compared to quasiparticle self-consistent $GW$ (QP$GW$). We also consider DFT with machine-learned Hubbard $U$ corrections [npj Computational Materials 6, 180 (2020)] with a new
Bayesian optimization (BO) objective function to determine the $U$ values that yield the closest agreement with the QP$GW$ band structure and
magnetic moments. We find that DFT+$U$(BO) can adequately reproduce the key QP$GW$ features in most cases. Our results reveal a strong method dependence of the degree of
spin polarization at the
Fermi level and, in some cases, even the dominant
spin channel (majority or minority). Of the materials studied here, Co$_2$TiSn and Co$_2$ZrAl are the most likely to be half-metals.
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All authors Zefeng Cai, Malcolm J. A. Jardine, Maituo Yu, Chenbo Min, Jiatian Wu, Hantian Liu, Derek Dardzinski, Christopher J. Palmstrøm, Noa Marom
Fluid Dynamics
Improvement of reduced-order model for two-dimensional cylinder flow based on global proper orthogonal decomposition in terms of robustness and computational speed
Yuto Nakamura, Shintaro Sato and Naofumi Ohnishi
Reduced-order models (ROMs) are widely used in fluid engineering to enable rapid prediction of flow fields for parametric analysis, design optimization, and control applications. Proper orthogonal decomposition (POD) is commonly employed to construct ROMs because it provides an optimal basis for representing a given flow
dataset. However, POD-based ROMs often lack robustness when applied to flow conditions that differ from those included in the training data. Incorporating multiple flow conditions can improve robustness, but this generally increases the computational cost of ROM prediction, which limits practical applicability in engineering workflows. In this study, we propose a ROM framework that achieves fast and robust flow prediction even when the
dataset contains a large number of flow conditions. The proposed approach employs a novel two-step order-reduction strategy based on POD. In the second reduction step, flow conditions that are most relevant to the target prediction are selectively retained, thereby reducing the computational cost without sacrificing accuracy. The performance of the proposed ROM is evaluated for a two-dimensional unsteady flow past a circular cylinder, a canonical
benchmark problem in fluid engineering. The model accurately reproduces the relationship between
vortex-shedding frequency and Reynolds number obtained from full numerical simulations. Furthermore, the proposed ROM reduces the computational cost by approximately 50% compared with a conventional POD-based ROM constructed using flow data at 27 different Reynolds numbers.
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Optics
Robust quantized transport from topological quasienergy winding in long-range-coupling synthetic quantum walks
Chengzhi Qin, Yinglan Li, Bing Wang et al. (+5 more)
Quantized transport is a prominent feature in topological physics, with canonical examples being the
quantum Hall effect and adiabatic Thouless pump, which are based on the Chern number, a topological invariant of 2D systems. Going beyond the Chern-number-based paradigms, quantized transports can also arise from k-direction quasienergy winding unique to periodically driven (Floquet) systems, which are free of dimensionality and adiabaticity limitations. However,
lattices displaying winding of their quasienergy bands require asymmetric long-range couplings that are difficult to achieve in
lattices of real-space coupled sites. Here, by leveraging photonic synthetic dimensions we construct asymmetric long-range-couplings in a one-dimensional temporal
quantum walk based on three coupled fiber loops. We demonstrate quantized transport arising from the winding of quasienergy bands in k direction. We show that the average group velocity of an initial wave packet is proportional to the winding number, which leads to a quantized transport displacement. To better visualize this quantized displacement, we cascade two regions with flipped nearest/long-range couplings and observe a focusing effect with a quantized spatial shift in the focusing point. We also probe the robust properties of quantized transport against obstacles and disorders. The study initiates quasienergy-winding-based topological transports, which can feature applications in precise and robust imaging and information processing.
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All authors Chengzhi Qin, Yinglan Li, Bing Wang, Zimeng Zou, Jiaxin Xu, Xinyuan Hu, Alberto Amo, Peixiang Lu
Optics
True Bound States in the Continuum in Compact All-Dielectric Structures
Yiyun Yan, Yichao Liu, Fei Sun et al. (+1 more)
Bound states in the continuum (BICs), known for their theoretically infinite quality (Q) factors and strong field localization, hold great promise for high-performance photonic devices. However, conventional true BICs typically rely on infinitely periodic structures, and their realization in finite-sized compact structures faces fundamental challenges, which severely limits device miniaturization and integration. In this work, a compact BIC design method based on optical conformal mapping is proposed, where a conventionally infinite periodic structure extended along one direction is mapped into a finite-sized annular structure. This
symmetry transition, i.e., from translational to rotational, enables structural miniaturization while fully preserving the
eigenvalues and BIC type of the original system. These transformations require only the adjustment of background permittivity and source distribution, without introducing extreme material parameters. As a concrete example, we show through theoretical and numerical analysis that a transformed compact all-dielectric structure, consisting of a double annular dielectric grating embedded in a gradient-index dielectric background, can support true BICs in a finite region. This work provides a simple and general strategy for achieving true BICs in compact all-dielectric structures, paving the way toward miniaturized high-Q photonic devices.
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All authors Yiyun Yan, Yichao Liu, Fei Sun, Yuxin Zhou
Optics
Photonic timing-engineered solitons for dual-microcomb metrology
Zihao Wang, Guoliang Li, Changrui Liu et al. (+5 more)
Dissipative microcavity
solitons offer a route to integrate comb-based metrology systems on photonic chips. However, integrated
solitons generally lack agile control of comb parameters, particularly pulse timing control, hindering their application in
quantum-limited metrology. Here we introduce dynamical
soliton trapping to enable optically timing-engineered microcombs (OTEM). By injecting an auxiliary
laser to anchor one of the microcomb lines, we create a potential well to trap and steer the
soliton. Thus,
soliton timing can be engineered by phase modulating the injected
laser. Theory and measurement reveal the fast response bandwidth of the OTEM, which enabled a
soliton slew rate of 31.3 ps/$\mu$s, surpassing existing time-programmable fiber
laser combs by more than two orders of magnitude. Leveraging the timing scan, we used a single OTEM for single-pixel and parallel ranging by retrieving the phase of the multi-heterodyne beat spectrum. Picometer-scale ranging precision was achieved, establishing new record for optical absolute ranging. Our work can transform timing-engineering of microcavity
solitons and endow integrated dual-microcomb metrology systems with enhanced precision.
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All authors Zihao Wang, Guoliang Li, Changrui Liu, Yue Hu, Zeying Zhong, Changxi Yang, Junqiu Liu, Chengying Bao
Fluid Dynamics
Hydrodynamic modulation via cupping in a crustacean-inspired propulsor
Sara Oliveira Santos, Maggie Brown, Minki Kim et al. (+2 more)
Shrimp, like many invertebrates swimming at intermediate Reynolds numbers ($Re$), rely on the interplay between morphology and kinematics to generate thrust while producing sufficient lift to overcome their negative buoyancy. Shrimp pleopods branch into an endopodite and an exopodite, whose relative motion varies the projected surface area during the swimming cycle. For this mechanism to function, the exopodite must be cambered relative to the endopodite at a set cupping angle $\zeta$, which partially decouples the effective angle of attack of the exopodite from the overall leg kinematics. Here, we investigate the role of $\zeta$ in modulating thrust$-$lift balance during steady forward locomotion. Using a dynamically scaled (40$\times$) robotic pleopod, we systematically varied $\zeta$ from $0^\circ$ to $80^\circ$, measured hydrodynamic forces, and performed particle image velocimetry at $Re = 968$. Moderate cupping angles ($\zeta = 20^\circ-40^\circ$), consistent with biological observations, provide optimal thrust$-$lift balance. At these angles, the exopodite abducts rapidly during the power stroke, maximizing projected area at peak flow velocity, and adducts early during the return stroke, minimizing resistive drag. A reduced-order force model reveals that the exopodite contributes 52$-$62% of total lift, particularly at intermediate $\zeta$, where a leading-edge
vortex (LEV) forms and remains attached throughout the power stroke. At extreme cupping angles, LEV coherence degrades and force production weakens. These findings demonstrate that shrimp pleopods function as hybrid propulsors exploiting both drag- and lift-based forces, and that $\zeta$ serves as a
geometric control parameter capable of tuning thrust$-$lift balance independently of stroke kinematics.
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All authors Sara Oliveira Santos, Maggie Brown, Minki Kim, Nils Tack, Monica M. Wilhelmus
Plasma Physics
Deuterium-Tritium Levitated Dipole Fusion Power Plants
T. Simpson, R. A. Badcock, T. Berry et al. (+15 more)
Levitated dipole reactors offer an attractive path towards economic fusion power generation. The intrinsic decoupling of the confining
magnetic field-generating REBCO magnets and the
vacuum vessel offer unparalleled accessibility and maintainability, allowing for high plant duty factors and theoretically low electricity prices. In order to achieve rapid deployment of fusion power to the grid, the use of the Deuterium-Tritium (DT) fuel cycle is required due to its lower required
plasma triple products. Historically, designs of levitated dipole fusion power plants have targeted advanced fuels as a DT device was seen to be infeasible due to the high fluxes of 14.1 MeV
neutrons on the superconducting core magnet. This study presents high level designs for two feasible first-of-a-kind (FOAK) DT levitated dipole fusion power plants, the larger of which produces 667 MW of fusion power and is predicted to produce 208 MW of net electric power. Both designs consist of a heavily
neutron-shielded, high-field REBCO core magnet capable of producing peak
magnetic field strengths of 23 T while keeping peak mechanical strains below 0.4%. The
neutron shielding is comprised of a layered structure of tungsten and boron carbide, which allows for 92% of the heat deposited in the
neutron shield to be radiated out to the first wall while still providing sufficient
neutron attenuation to give adequate REBCO conductor lifetimes. The core magnet REBCO coil is comprised of a small "sacrificial" section and a larger semi-permanent section. The sacrificial section, comprising ~20% of the coil, will have a
neutron damage limited lifetime of ~1 year, after which the core magnet will be quickly removed from the
vacuum vessel and replaced. This allows the damaged core magnet to be refurbished and reused, reducing cost and allowing for economic fusion power generation from a DT levitated dipole reactor.
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All authors T. Simpson, R. A. Badcock, T. Berry, C. S. Chisholm, P. J. Fimognari, P. Fisher, D. T. Garnier, K. Lenagh-Glue, B. Leuw, R. Mataira, L. Meadows, T. McIntosh, J. Poata, K. Richardson, B. Smith, A. Simpson, J. D. Tyler, T. Wordsworth
Optics
Real-time Calibration-free Imaging Through Dynamic and Distinct Multimode Fibers via Spatial Harmonic Invariant Nonlinear Encoding (SHINE)
Zhiyuan Wang, Haoran Li, Songjie Luo et al. (+8 more)
Multimode fibers (MMFs) provide a compact, high-throughput platform for minimally invasive imaging and information transmission. However, their utility is fundamentally constrained by mode mixing, which renders image transmission spatially disrupted and sensitive to external perturbations. Current imaging methods typically rely on transmission
matrix measurement or deep learning models that are fragile to fiber movement, necessitating frequent, time-consuming calibrations and re-calibrations that are easily disrupted and fail to generalize across different fiber configurations, let alone across entirely distinct fibers. Here, we propose a calibration and feedback-free MMF coherent imaging paradigm, that we termed Spatial Harmonic Invariant Nonlinear Encoding (SHINE). By leveraging the angle-dependent phase-matching conditions of second-harmonic generation, we encode spatial features into broadband spectral signatures that possess intrinsic insensitivity not only to modal scrambling but also to fiber bending, movement, as well as structural variations. This spectral representation enables a deep learning model to robustly reconstruct images in real time despite dynamic perturbations and even generalizes well to distinct MMFs without recalibration or feedback. We achieve experimentally an average Pearson correlation coefficient (PCC) of 0.82 for image reconstruction tasks on Fashion-MNIST and a classification accuracy of 92.3% on HERLEV biomedical
dataset. Uniquely, our method exhibits remarkable cross-fiber generalization: a model trained on a single MMF successfully reconstructs images transmitted through entirely distinct, previously unseen MMFs with a PCC of 0.74. These results establish a robust, calibration-free framework for imaging through MMFs in real time, paving the way for practical, resilient optical diagnostics that operate without distal-end feedback.
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All authors Zhiyuan Wang, Haoran Li, Songjie Luo, Jixiang Chen, Tianting Zhong, Jing Yao, Jixiong Pu, Zhipeng Yu, Sylvain Gigan, Ziyang Chen, Puxiang Lai