Optics
Time-independent theoretical framework for stroboscopic nonlinear dynamics based on time-nonlocal response
Yuhui Zhuang, Jiaxin Li, Haidong Li et al. (+8 more)
Recent experiments have demonstrated the ability to manipulate nonlinear interactions via time modulation, giving rise to the so-called stroboscopic nonlinearity. To date, however, this phenomenon has not been subjected to a rigorous theoretical analysis. In this work, we clarify the physical mechanism underlying stroboscopic nonlinear dynamics based on time-nonlocal response and establish an effective time-independent model under suitable modulation conditions. The proposed model almost exactly reproduces the full time-dependent dynamics in the quasi-steady state and significantly outperforms empirical descriptions used previously. Our results provide a clear physical picture of stroboscopic nonlinear dynamics, and can be extended to other systems with time-nonlocal response, establishing a general framework for engineering nonlinear interactions through temporal modulation.
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All authors Yuhui Zhuang, Jiaxin Li, Haidong Li, Siyu Li, Xiaobin Peng, Juan Wu, Jiameng Zhang, Mingjing Fan, Xiaoqin Huang, Yi Hu, Jingjun Xu
Fluid Dynamics · Cross-listed from cond-mat.mtrl-sci
Acoustic wave scattering by spatio-temporal interfaces
J. Galiana, J. Redondo, R. Picó et al. (+1 more)
Space-time materials are obtained by modulating a physical medium with a traveling-wave perturbation of one or several of its constitutive parameters, such as the density or the bulk modulus in the case of acoustic materials. When this modulation has the form of a moving and abrupt (subwavelength) transition between two parameter values, we refer to a spatio-temporal interface, which may be considered as a building block for more complex space-time materials. This work considers the problem interaction and scattering of acoustic waves with a single spatio-temporal interface, and a sequence of two interfaces forming a slab. Several regimes defined by the relation between the sound propagation velocities and the interface velocity (namely subsonic, intersonic, and supersonic regimes) are discussed. Analytical expressions for the frequency conversions and scattering coefficients are obtained, and compared with numerical simulations based on an equivalent FTFD squeme.
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All authors J. Galiana, J. Redondo, R. Picó, V. J. Sánchez-Morcillo
Applied Physics · Cross-listed from cond-mat.supr-con
Turning non-superconducting elements into superconductors by quantum confinement and proximity
Giovanni A. Ummarino and Alessio Zaccone
Elemental good metals, including noble metals (Cu, Ag, Au) and several $s$-block elements, do not exhibit superconductivity in bulk at ambient pressure, mainly due to weak electron-
phonon coupling that cannot overcome Coulomb repulsion.
Quantum confinement in ultra-thin films reshapes the electronic spectrum and the density of states near the
Fermi level, producing strong, often non-monotonic, thickness dependencies of the critical temperature in established
superconductors. Here, we examine whether confinement alone, or combined with proximity effects, can induce superconductivity in metals that are non-superconducting in bulk form. We review recent theoretical progress and introduce a unified framework based on a confinement-generalized, isotropic one-band Eliashberg theory, where the normal density of states becomes energy dependent and key parameters ($E_F$, $\lambda$, $\mu^$) acquire explicit thickness dependence. By numerically solving the Eliashberg equations using ab initio or experimentally determined electron-
phonon spectral functions $\alpha^2F(\Omega)$ and Coulomb pseudopotentials $\mu^$, and without adjustable parameters, we compute the critical temperature $T_c$ as a function of film thickness for representative noble, alkali, and alkaline-earth metals. The results predict that superconductivity emerges only in selected cases and within extremely narrow thickness windows, typically at sub-nanometer scales ($L \sim 0.4-0.6$ nm), indicating strong fine-tuning requirements for confinement-induced superconductivity in good metals. We also consider layered
superconductor/normal-metal systems where confinement and proximity effects coexist. In these
heterostructures, a substantial enhancement of the critical temperature is predicted, even when the constituent materials are non-superconducting or weak
superconductors in bulk form.
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Medical Physics
First ex-vivo positronium imaging of tissues with modular J-PET scanner using $^{44}$Sc radionuclide
Karol Kubat, Manish Das, Sushil Sharma et al. (+41 more)
This study presents the first ex-vivo positronium imaging of human tissues using the modular J-PET scanner with the $^{44}$Sc radionuclide. The $^{44}$Sc isotope was produced via the $^{44}$Ca(p, n)$^{44}$Sc
nuclear reaction and used to perform positronium imaging of phantom composed of human adipose tissue, cardiac myxoma tissue, thrombi blood clot, and also porous
polymer XAD4, and a certified reference material (CRM) made from fused silica. The experiment demonstrates the suitability of $^{44}$Sc as a positron source for positronium imaging. The performance of J-PET for positronium imaging with $^{44}$Sc was validated by proper reconstruction of the mean orthopositronium lifetime for CRM material and XAD-4
polymer. The mean ortho-positronium (oPs) lifetimes determined for adipose tissue, cardiac myxoma tissues and thrombi were consistent with results of previous experiments. The study highlights the potential $^{44}$Sc radionuclide for positronium lifetime imaging (PLI).
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All authors Karol Kubat, Manish Das, Sushil Sharma, Ermias Y. Beyene, Aleksander Bilewicz, Jarosław Choiński, Neha Chug, Catalina Curceanu, Eryk Czerwiński, Jakub Hajduga, Sharareh Jalali, Krzysztof Kacprzak, Tevfik Kaplanoglu, Łukasz Kapłon, Kamila Kasperska, Aleksander Khreptak, Grzegorz Korcyl, Tomasz Kozik, Deepak Kumar, Sumit Kumar Kundu, Anoop Kunimmal-Venadan, Bartosz Leszczyński, Edward Lisowski, Filip Lisowski, Justyna Mędrala-Sowa, Simbarashe Moyo, Wiktor Mryka, Szymon Niedźwiecki, Anand Pandey, Piyush Pandey, Szymon Parzych, Alessio Porcelli, Bartłomiej Rachwał, Martin Rädler, Magdalena Skurzok, Anna Stolarz, Tomasz Szumlak, Pooja Tanty, Keyvan Tayefi Ardebili, Satyam Tiwari, Kavya Valsan Eliyan, Rafał Walczak, Paweł Moskal, Ewa Ł. Stępień
Classical Physics
Newtonian and Relativistic Particle Mechanics from Local Energy Conservation: A Symmetry-Selected Force-Energy Framework
Thomas Oikonomou
We develop a formulation of particle mechanics in which the functional relation between force and kinetic energy is derived directly from the instantaneous (pointwise along the trajectory) conservation of mechanical energy $E$, rather than postulated through Newton's second law or a variational principle. Starting from the condition $\dot{E}=0$, we derive a generalized force law that does not assume a specific kinetic-energy function, momentum-velocity relation, or equation of motion. The resulting inertial response naturally decomposes into a component parallel to the acceleration, responsible for changes in kinetic energy, and a transverse component that preserves energy while altering the direction of motion. Imposing rotational equivariance constrains the
geometric structure of the force law, while the relativity principle between inertial reference frames further restricts its admissible realizations. In strictly one-dimensional motion, inertial frame equivalence, supplemented by a set of five structural properties, implies invariance of the total force under inertial boosts; together with local energy conservation, this uniquely fixes the functional form of kinetic energy and momentum. Galilean invariance selects the Newtonian expressions, whereas Lorentz invariance yields the relativistic ones. The framework unifies conservative and non-conservative (yet non-dissipative, e.g., the
magnetic Lorentz force) dynamics at the single-particle level and clarifies the precise conditions under which energy-based and variational formulations of mechanics are dynamically equivalent. Newtonian and relativistic mechanics thus emerge as
symmetry-selected realizations of a common energy-conserving force-energy structure. The analysis further shows that the standard Lagrangian form $L=T-V$ is consistent with, and implicitly presupposes, Galilean relativity.
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Optics · Cross-listed from quant-ph
Characterization of Autofluorescence in Optical Fibers for NV-based Sensing Applications
Stefan Johansson, Alexander Bukschat, Dennis Lönard et al. (+3 more)
Optical fibers are crucial for guiding light in various sensing applications. Especially for
quantum sensors such as the nitrogen-vacancy (NV) center in diamond, they enable light control and device miniaturization. However, fluorescence and scattering within the fiber, often referred to as fiber background, autofluorescence, or autoluminescence, can overlap spectrally with the NV centers' fluorescence, degrading the signal-to-noise ratio and thus limiting sensor sensitivity. Here, we investigate the optical spectra of standard optical fibers, considering material dependencies, physical influences, and their fluorescence scaling with excitation power and wavelength. Our results identify spectral components and fiber types with minimal unwanted background signals, guiding the selection of optimal fibers for NV-based
quantum sensing.
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All authors Stefan Johansson, Alexander Bukschat, Dennis Lönard, Alena Erlenbach, Jonas Gutsche, Artur Widera
Optics · Cross-listed from quant-ph
Squeezing-enhanced dual-channel interference for ground-state cooling of a levitated micromagnet with low quality factor
Lei Chen, Zhe-qi Yang, Liang Bin et al. (+1 more)
Cooling the center-of-mass (CM) motion of a macroscopic oscillator to its
quantum ground state is a fundamental prerequisite for testing
quantum mechanics at macroscopic scales. However, achieving this goal is currently hindered by the stringent requirement for an ultrahigh mechanical quality factor ($Q_c$). Here, we propose a dual-channel cooling scheme based on squeezing-enhanced
quantum interference within a hybrid levitated cavity-magnomechanical system to overcome this limitation. By synergizing squeezing effects with
quantum interference between the
magnon-CM and cavity-CM channels, our scheme simultaneously suppresses Stokes (heating) scattering while enhancing anti-Stokes (cooling) scattering.~We demonstrate that this cooling mechanism reduces the critical $Q_c$ required for ground-state cooling by three orders of magnitude, making it achievable in the experimentally accessible regime of $Q_c \sim 10^4$. Furthermore, the net cooling rate is enhanced by nearly 180-fold compared to that of conventional single-channel cooling. This improvement is accompanied by a two orders of magnitude reduction in both the steady-state CM occupancy and the cooling time. Importantly, this enhanced performance remains robust even deep within the unresolved-sideband regime. Our results provide a feasible path toward preparing macroscopic
quantum states by actively controlling the cooling dynamics, thereby relaxing the constraints on intrinsic material properties.
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All authors Lei Chen, Zhe-qi Yang, Liang Bin, Zhi-Rong Zhong
Applied Physics · Cross-listed from cond-mat.supr-con
Complete electronic phase diagram and enhanced superconductivity in fluorine-doped PrFeAsO1-xFx
Priya Singh, Konrad Kwatek, Tatiana Zajarniuk et al. (+4 more)
Establishing a complete electronic phase diagram for REFeAsO (RE = rare earth, RE1111) ironbased
superconductors has remained experimentally challenging. Here, we report a systematic investigation of PrFeAsO1-xFx over the full nominal fluorine-doping range 0 to 1 and construct the first comprehensive electronic phase diagram for this system. The
evolution from the nonsuperconducting parent compound to the fluorine-rich limit reveals a broad dome shaped superconducting region. Structural refinement demonstrates a systematic
lattice contraction with increasing fluorine content (x), corroborated by Raman spectroscopy through softening of the Pr(A1g)
phonon mode and hardening of the Fe(B1g) mode, confirming effective fluorine incorporation at the oxygen sites. The maximum superconducting transition temperature (Tc) reaches up to 52.3 K, approximately 5 K higher than previous reports for Pr1111. Magnetotransport measurements yield large upper critical fields Hc2(0) exceeding 100 T, while analysis of resistive transition broadening reveals thermally activated flux flow with a crossover from single-
vortex to collective pinning regimes. Specific-heat measurements exhibit a reduced jump deltaC/{\gamma}Tc < 1.43, reflecting strong superconducting fluctuations and multiband pairing. These results establish clear structure property correlations and provide a unified description of superconductivity across the entire doping range of the Pr1111 system.
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All authors Priya Singh, Konrad Kwatek, Tatiana Zajarniuk, Taras Palasyuk, Cezariusz Jastrzębski, A. Szewczyk, Shiv J. Singh
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Benchmarking the plasmon-pole and multipole approximations in the Yambo Code using the GW100 dataset
M. Bonacci, D. A. Leon, N. Spallanzani et al. (+4 more)
Verification and validation of electronic structure codes are essential to ensure reliable and reproducible results in computational materials science. While density functional theory has been extensively benchmarked, systematic assessments of many-body perturbation theory methods such as the GW approximation have only recently emerged, most notably through the GW100
dataset. In this work, we assess the numerical accuracy and convergence behavior of the GW implementation in the yambo code using both the Godby-Needs plasmon-pole model and the recently introduced multipole approximation. Quasiparticle energies are compared against GW100 reference data to evaluate the performance, numerical stability, and consistency of these approaches.
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All authors M. Bonacci, D. A. Leon, N. Spallanzani, E. Molinari, D. Varsano, A. Ferretti, C. Cardoso
Plasma Physics · Cross-listed from astro-ph.HE
FPIC: a new Particle-In-Cell code for stationary and axisymmetric black-hole spacetimes
Claudio Meringolo and Luciano Rezzolla
In this paper we present a newly developed GRPIC code framework called FPIC, providing a detailed description of the Maxwell-equations solver, of the particle “pushers”, and of the other
algorithms that are needed in this approach. We describe in detail the code, which is written in Fortran and exploits parallel architectures using MPI directives both for the fields and particles. FPIC adopts spherical Kerr-Schild coordinates, which encode the overall spherical
topology of the problem while remaining regular at the event horizon. The Maxwell equations are evolved using a finite-difference time-domain solver with a leapfrog scheme, while multiple particle “pushers” are implemented for the
evolution of the particles. In addition to well-known
algorithms, we introduce a novel hybrid method that dynamically switches between the most appropriate scheme based on the violation of the
Hamiltonian energy. We first present results for neutral particles orbiting around black holes, both in the Schwarzschild and Kerr metrics, monitoring the
evolution of the
Hamiltonian error across different integration schemes. We apply our hybrid approach, showing that it is capable of achieving improved energy conservation at reduced computational cost. We apply FPIC to investigate the Wald solution, first in electrovacuum and subsequently in
plasma-filled configurations. In the latter case, particles with negative energy at infinity are present inside the ergosphere, indicating that the Penrose process is active. Finally, we present the split-monopole solution in a
plasma-filled environment and successfully reproduce the Blandford-Znajek luminosity, finding very good agreement with analytical predictions.
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Optics
Optical beam propagation inside a graded-index fiber with saturable nonlinearity
Tiyas Das, Anuj P. Lara, Samudra Roy et al. (+1 more)
We study theoretically the spatial
evolution of optical beams inside a graded-index fiber exhibiting saturable nonlinearity. Utilizing an approach based on the variational principle, we identify the existence of bistable spatial
solitons inside such a nonlinear medium, whose stability, analyzed through a linear stability analysis, is due to the saturating nature of the nonlinearity. Spatial
solitons adhere to a specific amplitude-width relationship. Any deviation from this relationship leads to oscillating-type solutions with a period that increases with saturation level of the nonlinearity. Theoretically calculated values of this period agree well with numerical findings.
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All authors Tiyas Das, Anuj P. Lara, Samudra Roy, Govind P. Agrawal
Fluid Dynamics
Phenomenological energy exchange of diatomic gases: Comparison of Pullin and Borgnakke-Larsen models in direct simulation Monte Carlo method
Hao Jin, Sha Liu, Ningchao Ding et al. (+4 more)
In hypersonic rarefied flows, insufficient intermolecular collisions cause significant deviations between translational and rotational temperatures, leading to strong thermal nonequilibrium. For diatomic gases such as nitrogen and oxygen, the direct simulation Monte Carlo (DSMC) method commonly employs the Borgnakke-Larsen (BL) model to simulate translational-rotational energy exchange (relaxation) processes. Although widely used, the BL model lacks a rigorous theoretical foundation and assumes that only a fraction of collisions lead to rotational relaxation. To address these shortcomings, Pullin introduced a kinetically consistent relaxation model into the gas kinetic theory. By employing the Beta function for energy partitioning, a concrete collision cross section that satisfies the detailed balance condition is constructed. In this study, a comparative investigation of the BL and Pullin models is performed within the DSMC framework, where both original and simplified equations are considered and parameterized by physical accommodated coefficient in the Beta function. A series of test cases–including zero-dimensional rotational relaxation of nitrogen, one-dimensional planar Couette flow and normal shock wave, two-dimensional hypersonic flow past a cylinder, and three-dimensional hypersonic flow around an X38-like vehicle–are performed to assess the accuracy and efficiency of these models. The results confirm the consistency between the Pullin and BL models. Owing to its rigorous theoretical foundation and accurate physical representation, the Pullin model is expected to provide substantial support for the extension of subsequent theoretical studies and numerical simulations. Moreover, in the highly rarefied flow regime (Knudsen number greater than 1, or altitudes above 100 km), the simplified Pullin model exhibits performance comparable to that of the BL model.
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All authors Hao Jin, Sha Liu, Ningchao Ding, Sirui Yang, Huahua Cui, Congshan Zhuo, Chengwen Zhong
Geophysics
Wavelet Packet-Based Diffusion Model for Ground Motion Generation with Multi-Conditional Energy and Spectral Matching
Yi Ding, Su Chen, Jinjun Hu et al. (+3 more)
Temporal energy distribution strongly affects nonlinear structural response and cumulative damage. We propose a multi-conditional
diffusion framework for ground motion synthesis that simultaneously matches temporal energy
evolution and target response spectra. Wavelet packet decomposition provides the signal representation and enables direct waveform reconstruction via orthogonal filter banks. A
Transformer-based conditional encoder with cross-
attention integrates heterogeneous conditions, including spectral ordinates, Arias intensity, temporal parameters, and Husid curves. The framework adopts the Elucidating
Diffusion Model (EDM) with second-order Heun sampling to improve inference efficiency without sacrificing quality. Tests on the NGA-West2 database show that explicit temporal-energy constraints markedly improve control of energy onset and significant duration while preserving spectrum matching and maintaining stable diversity sampling. The framework yields spectrum-compatible motions with realistic energy
evolution and supports uncertainty quantification via conditional diversity sampling.
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All authors Yi Ding, Su Chen, Jinjun Hu, Xiaohu Hu, Qingxu Zhao, Xiaojun Li
History and Philosophy of Physics · Cross-listed from quant-ph
The ABL Rule and the Perils of Post-Selection
Jacob A. Barandes
In 1964, Aharonov, Bergmann, and Lebowitz introduced their well-known ABL rule with the intention of providing a time-symmetric formalism for computing novel kinds of conditional probabilities in
quantum theory. Later papers attached additional significance to the ABL rule, including assertions that it supported violations of the uncertainty principle. The present work challenges these claims, as well as subsequent attempts to salvage the original interpretation of the ABL rule. Taking a broader view, this paper identifies a subtle category error at the heart of the ABL rule that consists of confusing observables that belong to a single system with emergent observables that arise only for physical ensembles. Along the way, this paper points out other problems and fallacious
reasoning in the research literature surrounding the ABL rule, including the misuse of post-selection, a reliance on pattern matching to classical formulas, and a posture of measurementism that takes experimental data as providing answers to interpretational questions.
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Data Analysis and Statistics · Cross-listed from cs.LG
Dichotomy of Feature Learning and Unlearning: Fast-Slow Analysis on Neural Networks with Stochastic Gradient Descent
Shota Imai, Sota Nishiyama and Masaaki Imaizumi
The dynamics of gradient-based training in neural networks often exhibit nontrivial structures; hence, understanding them remains a central challenge in theoretical machine learning. In particular, a concept of feature unlearning, in which a neural network progressively loses previously learned features over long training, has gained
attention. In this study, we consider the infinite-width limit of a two-layer neural network updated with a large-batch
stochastic gradient, then derive differential equations with different time scales, revealing the mechanism and conditions for feature unlearning to occur. Specifically, we utilize the fast-slow dynamics: while an
alignment of first-layer weights develops rapidly, the second-layer weights develop slowly. The direction of a flow on a critical
manifold, determined by the slow dynamics, decides whether feature unlearning occurs. We give numerical validation of the result, and derive theoretical grounding and scaling laws of the feature unlearning. Our results yield the following insights: (i) the strength of the primary nonlinear term in data induces the feature unlearning, and (ii) an initial scale of the second-layer weights mitigates the feature unlearning. Technically, our analysis utilizes Tensor Programs and the singular perturbation theory.
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Chemical Physics · Cross-listed from astro-ph.SR
Emergence of a lithium dip in ~35 Myr "Snake" Open Clusters
Yun-Yi Zhang, Hai-Jun Tian, Jian-Rong Shi et al. (+2 more)
We report the discovery of a lithium dip (Li-dip) in the
stellar "Snake" (age = $35 \pm 5$ Myr), challenging the classical view that Li-dips emerge only at ages $\gtrsim 150$ Myr. Using high-resolution spectra from GALAH DR4 ($R \sim 28,000$) for 211 member
stars, we identify a clear depletion feature in a $T_{\mathrm{eff}}$ range of 6200–6800 K with a depth of $\Delta A(\mathrm{Li}) \approx 0.40$ dex. Our analysis reveals two key advances: the Li-dip appears $\gtrsim 100$ Myr earlier than the previous observations, and within the dip temperature range, a significant correlation is found between rotational velocity and lithium depletion. Specifically, fast rotators ($v \sin i > 25$ km s$^{-1}$) exhibit stronger lithium depletion than slow rotators ($v \sin i < 25$ km s$^{-1}$). This trend suggests that faster rotators develop stronger rotational shear at the convective-radiative boundary, which enhances turbulent mixing and accelerates lithium destruction. It is also found that the lower temperature edge of the lithium plateau can reach as low as 5500 K for the young open clusters.
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All authors Yun-Yi Zhang, Hai-Jun Tian, Jian-Rong Shi, Cheng-Cheng Xie, Xiang-Ming Yang
Atomic Physics
Sub-hertz optical transitions in excited Yb$^+$
Patrick McMillin, Hassan Farhat, William Liu et al. (+1 more)
We present the observation of three semi-forbidden transitions in singly-ionized ytterbium from the metastable $^{2}\mathrm{F}^o_{7/2}$ state. Owing to the long lifetimes of both the upper and lower states involved, these transitions are narrow and complement those already frequently used in this atom for
quantum information and searches for new physics. We report the absolute frequencies of these electric quadrupole transitions, their isotope shifts, hyperfine structure, and measurements of the quadrupole transition moments. We find that the spontaneous lifetimes of these excited states are limited by slow
magnetic dipole emission to lower-lying, odd-parity states, the lowest of which is accessible by
laser excitation from ${}^2\mathrm{F}_{7/2}^o$ and is an attractive candidate for hosting a long-lived
qubit.
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All authors Patrick McMillin, Hassan Farhat, William Liu, Wesley C. Campbell
Fluid Dynamics
Effect of velocity, fluid properties and drop shape on coalescence and neck oscillation
Manas Ranjan Behera, Hiranya Deka, Kirti Chandra Sahu et al. (+1 more)
We perform axisymmetric numerical simulations to investigate the coalescence dynamics of a
liquid drop in a deep
liquid pool. This study aims to generalize the mechanisms of partial coalescence across a range of drop shapes, elucidate the underlying mechanism of neck oscillations, and examine the roles of inertial, viscous and gravitational forces, quantified by the Weber, Ohnesorge, and Bond numbers, in governing the coalescence behavior. A phase diagram is constructed to delineate the boundaries between partial and complete coalescence regimes based on these dimensionless parameters. Our analysis of the height-to-neck ratio shows that, upon contact with the pool, the primary drop forms an upward
liquid column that ultimately pinches off due to inwardly directed horizontal momentum. Additionally, the study suggests that as the dimensionless numbers increase, the effect of the vertical collapse rate plays a significant role in the outcome of the coalescence process. Notably, the Rayleigh-Plateau instability is found to be insignificant in driving partial coalescence within the explored parameter space. We identified a transition regime between partial and complete coalescence, characterized by multiple neck oscillations that delay the pinch-off of secondary droplets. The formation of secondary droplets is most prominent for prolate drops, followed by spherical and oblate drops of comparable volume. Furthermore, we observe that the tendency to form multiple droplets from elongated
liquid columns diminishes with an increase in the impact velocity of the primary drop.
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All authors Manas Ranjan Behera, Hiranya Deka, Kirti Chandra Sahu, Gautam Biswas
Optics
Broadband terahertz comb with sub-Hz comb linewidth
Min Li, Yu Xia, Yuan Chen et al. (+6 more)
Terahertz (THz) frequency combs are increasingly essential for spectroscopy, metrology, and
quantum science. However, generating a dense array of evenly spaced ultra-narrow THz comb lines is challenging. Here, we demonstrate broadband THz comb generation using a photoconductive
antenna that transfers a noise-suppressed near-infrared electro-optical (EO) comb into the THz domain. Our noise-suppression strategy, leveraging
soliton self-frequency shift and spectral filtering, effectively suppresses EO comb phase noise without requiring active stabilization. The resulting THz comb exhibits broad spectral coverage (0.05-4 THz), narrow comb linewidths (0.3 Hz at the
Fourier-transform limit), and excellent frequency stability (8.6*10^-14 at 1-second integration). We further demonstrate asynchronous THz time-domain spectroscopy, resolving ~36,000 comb lines with 50 MHz spacing. Crucially, the inherent frequency agility of the EO comb enables rapid and wide-range tuning of the THz comb line spacing. These attributes position our THz comb as a versatile tool for high-resolution molecular spectroscopy and precision THz metrology.
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All authors Min Li, Yu Xia, Yuan Chen, Sinan Tao, Mingyang He, Kun Huang, Hua Li, Ming Yan, Heping Zeng
Applied Physics
Substrate-Voltage-Controlled Temporal Nonlinearity in Ferroelectric FET-based Reservoir Computing
Eishin Nako, Ryosho Nakane, Mitsuru Takenaka et al. (+2 more)
Physical reservoir computing exploits inherent nonlinearity and short-term
memory of physical dynamics to achieve efficient processing of time-series data with extremely-low training cost. In this study, we demonstrate a ferroelectric field-effect transistor (FeFET)-based reservoir computing system with augmented temporal and spatial nonlinearity by utilizing both gate and substrate terminals as inputs. The ferroelectric polarization state in the next time step can additionally be controlled by modifying the electric field distribution in the gate stack of FeFET through a substrate input, enabling more diverse internal states compared with the case where inputs are applied only to the gate. To introduce a nonlinearity in the time domain, we introduce a delay between a gate input and a substrate input, which facilitates efficient nonlinear mixing between the current and past inputs. As a result, both the short-term
memory and nonlinearity of the FeFET reservoir computing system are enhanced with an improved capability of feature extraction of complex input time-series. These findings demonstrate that introducing substrate input provides an additional degree of freedom for controlling ferroelectric polarization dynamics, enabling a flexible, energy-efficient, and highly integrable FeFET-based reservoir computing platform suitable for diverse time-series processing applications.
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All authors Eishin Nako, Ryosho Nakane, Mitsuru Takenaka, Kasidit Toprasertpong, Shinichi Takagi
Plasma Physics
Topological Arrest of Ballooning Modes in Non-Axisymmetric Plasmas
Amitava Bhattacharjee
Why do non-axisymmetric stellarators avoid ballooning crashes that afflict tokamaks? Three-dimensional geometry induces Anderson localization of ballooning modes, converting a global instability into a Ginzburg–Landau network of isolated wave packets. Global stability reduces to a percolation problem: below a critical threshold, instability is arrested; above it, a crash occurs. This explains benign stellarator saturation, predicts vulnerability in quasisymmetric designs, and introduces the critical threshold as a nonlinear stability metric for reactor optimization, pending experimental validation.
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Optics
High-Throughput In-Situ Fabrication of Fibrous Membranes Enables Scalable Passive Radiative Cooling
Hanzhuo Shao, Xiaoli Huang, Xuemei Huang et al. (+5 more)
Deploying fibrous membranes for passive daytime radiative cooling (PDRC) on large and irregular surfaces is highly desirable but remains challenging, owing to the slow deposition rates and the need for electrically conductive substrates in conventional electrospinning. Here, we demonstrate a high-throughput in-situ strategy for fabricating nanocomposite PDRC fibrous membranes via solution blow spinning. This method achieves deposition rates 8-12 times faster than electrospinning and can be applied directly onto nonplanar, nonconductive objects. The resulting membranes, composed of styrene-ethylene-butylene-styrene (SEBS) fibers embedded with Y2O3 nanoparticles, achieve sub-ambient cooling of up to 7.0 {\deg}C outdoors, effectively delaying ice melting. Moreover, they are fully recyclable through simple cleaning, dissolution, and reprocessing. This scalable and sustainable fabrication route provides a versatile and practical platform for integrating PDRC fibrous membranes across diverse surfaces, paving the way toward real-world thermal management applications.
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All authors Hanzhuo Shao, Xiaoli Huang, Xuemei Huang, Jin Zhao, Nailin Xing, Hua Xu, Weijie Song, Yuehui Lu
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Analyzing Band Gaps in Ensemble Density Functional Theory using Thermodynamic Limits of Finite One-Dimensional Model Systems
Gregory G. V. Kenning, Remi J. Leano and David A. Strubbe
Ensemble Density Functional Theory (EDFT) is a promising extension to Density Functional Theory (DFT) for calculating excited states. While Kohn-Sham
eigenvalue differences underestimate gaps, EDFT has been shown to provide more accurate excitation energies in atoms, molecules and isolated model systems. However, it is unclear whether EDFT is capable of calculating band gaps of periodic systems – and what an appropriate theoretical formulation would be to describe periodic systems. We explored how EDFT could calculate band gaps by estimating the thermodynamic limit with increasingly wide finite versions of the one-dimensional Kronig-Penney (KP) periodic model. We use Octopus, an ab initio, open-source, real-space DFT code, as in our previous work [R. J. Leano et al., Electron. Struct. 6, 035003 (2024)] in which we found with "particle in a box" models that EDFT can provide a reasonable effective mass correction for the homogeneous electron gas. Now, we use a periodic reference that is gapped. We find that the finite systems' Kohn-Sham gap approaches the same periodic limit for each of three ways of terminating the finite system, though the appropriate states corresponding to the valence band maximum and conduction band minimum have to be carefully identified in each case. Finally, our EDFT results, using a simple ensemblized LDA approximation, have a reasonable nonzero correction to the bandgap in the periodic limit. The results indicate that EDFT is promising for periodic systems, to motivate further work on developing a suitable formalism.
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Instrumentation and Detectors
Split-Post Re-entrant Microwave Displacement Transducer with Quadratic Readout
Sonali Parashar, Jeremy F. Bourhill, Maxim Goryachev et al. (+1 more)
We investigate a microwave-cavity-based displacement readout employing a split-post geometry to measure the motion of a dielectric membrane. Due to
symmetry, the cavity response to membrane displacement is inherently quadratic when the membrane is positioned at the centre of the posts. We characterise this behaviour by driving the membrane with a piezoelectric actuator at both central and off-centre positions and we estimate the drive-to-displacement transfer function using the independently calibrated frequency-to-voltage response of the interferometric readout. When the membrane is located at the centre of the cavity and driven, the system exhibits the largest quadratic output, measured at the second harmonic of the membrane acoustic frequency. As the membrane is moved away from the centre, the response transitions from predominantly quadratic to predominantly a linear response at the membrane acoustic frequency. Quadratic optomechanical coupling is a key requirement for displacement - squared readout and, in the
quantum regime, for measurements sensitive to mechanical energy or
phonon number. The present work therefore establishes the split-post geometry as a promising platform for microwave-mechanical transduction, providing a practical route toward future experiments aimed at probing quantised mechanical motion and energy-sensitive readout schemes.
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All authors Sonali Parashar, Jeremy F. Bourhill, Maxim Goryachev, Michael E. Tobar
Popular Physics · Cross-listed from astro-ph.IM
Imagining the Alien: Human Projections and Cognitive Limitations
S. G. Djorgovski
Imagining what life on other
planets, and intelligent life in particular, may be like is a long-running theme in human culture. It is a manifestation of the innate human curiosity about the Cosmos, and it has inspired numerous works of art and folklore, including whole literary and other media genres. It is a profound question, with philosophical and existential implications. There is also an obvious connection with religious beliefs, as gods and other superhuman beings were imagined in the heavens. Speculations about alien beings grew in time, and today, it is a scientific subject of astrobiology, and it is pursued through serious searches for life and intelligence in the universe. However, almost all imaginings of the alien map terrestrial life forms and human cultural, historical, and psychological phenomena to the putative aliens. This lack of individual and collective imagination may reflect our biological and cultural
evolution, as our minds are formed through our experiences, perceptions of the world, and interactions with our terrestrial and human environments. As such, imagining aliens is mainly a cultural phenomenon and may reflect the intrinsic cognitive limitations of the human mind. Interestingly, we did create what is effectively an alien intelligence on this
planet in the form of now rapidly evolving Artificial Intelligence (AI). As its capabilities grow, it may give us new insights into what extraterrestrial advanced intelligences may be like.
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Optics · Cross-listed from quant-ph
The continuous spectrum of bound states in expulsive potentials
H. Sakaguchi, B.A. Malomed, A.C. Aristotelous et al. (+1 more)
On the contrary to the common intuition, which suggests that a steep expulsive potential makes
quantum states widely delocalized, we demonstrate that one- and two-dimensional (1D and 2D) Schroedinger equations, which include expulsive potentials that are steeper than the quadratic ones, give rise to normalizable eigenstates, which may be considered as a manifestation of effective self-trapping in the linear system. These states constitute full continuous spectra in both the 1D and 2D cases. In 1D, they are spatially even and odd eigenstates. The 2D states may carry any value of the vorticity (alias
magnetic quantum number). Asymptotic expressions for wave functions of the 1D and 2D eigenstates, valid far from the center, are derived analytically, demonstrating excellent agreement with full numerical solutions. Special exact solutions for
vortex states are obtained in the 2D case. These findings suggest an extension of the concept of bound states in the continuum, in
quantum mechanics and paraxial photonics. Gross-Pitaevskii equations are briefly considered as the nonlinear extension of the 1D and 2D settings. In 1D, the cubic nonlinearity slightly deforms the eigenstates, maintaining their stability
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All authors H. Sakaguchi, B.A. Malomed, A.C. Aristotelous, E.G. Charalampidis