Papers

The accurate description of electron correlations remains a major challenge in atomic calculations. In order to perform accurate calculations, it is necessary to consider the various types of electron correlations what often leads to extensive CSF expansions. This work presents further development of the method based on the second-order perturbation theory to identify the most significant CSFs that have the greatest influence on core-valence, core, core-core and valence-valence correlations. This method is based on a combination of the relativistic configuration interaction method and the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in an irreducible tensorial form [G. Gaigalas, P. Rynkun, L. Kitovienė, Lithuanian Journal of Physics, 64, No. 1, 20-39 (2024) (https://doi.org/10.3952/physics.2024.64.1.3), G. Gaigalas, P. Rynkun, L. Kitovienė, Lithuanian Journal of Physics, 64, No. 2, 73-81 (2024) (https://doi.org/10.3952/physics.2024.64.2.1) and G. Gaigalas, P. Rynkun, L. Kitovienė, Lithuanian Journal of Physics, 64, No. 3, 139-161 (2024) (https://doi.org/10.3952/physics.2024.64.3.1)]. The method is extended to include additionally valence-valence electron correlations. It can be applied for an atom or ion with any number of valence electrons for calculation of energy spectra and other properties. Meanwhile, the correlations which can not be included according to perturbation theory are accounted for in a regular way. The use of the developed method allows a significant reduction of CSFs especially for complex atoms and ions. As an example of its application, the atomic calculations of the energy structure for Se~III ion are presented.

A novel semi-implicit second-order finite volume scheme integrating the scalar auxiliary variable (SAV) approach is proposed for solving the pseudo-time Eikonal equation in wall-distance computation. Unconditional energy stability under zero boundary conditions is rigorously proved, eliminating the dependence of the time step on the grid scale and enabling large-time-step computation. The scheme is a priori accuracy-preserving, and its discretization matrix forms an M-matrix, thereby guaranteeing strict non-negativity of the numerical solution inherently. The framework extends readily to any non-conservative scalar equation and, being independent of the specific finite-volume reconstruction, is compatible with schemes of arbitrary order of accuracy. A vanishing artificial viscosity is introduced to smooth the solution without compromising formal accuracy, and upwinding is incorporated through directional weighting in the weighted least-squares (WLS) reconstruction. Numerical experiments confirm that the scheme achieves the designed accuracy and permits stable computations with uniformly large time steps. For complex configurations such as a three-element airfoil and the three-dimensional ONERA M6 wing, accurate results are obtained on high-aspect-ratio grids, with relative errors in the computed wall distance below 3% relative to the search-based reference, except near geometric singularities.

Can deep learning translate physical fields governed by fundamentally different equations? We address this question by introducing Cross-Physics Mapping (CPM), an operator-learning framework for mappings between heterogeneous physical domains. We formulate sufficient conditions for such mappings through compatible latent representations and propose a dimensionless scaling principle that aligns the characteristic evolution scales of the source and target systems without assuming their dynamical equivalence. As a representative test, paired diffusion and wave fields are generated independently from their respective parabolic and hyperbolic equations while sharing the same latent geometry, material heterogeneity, excitation, and dimensionless scale. Seven architectures-ResUNet, DeepONet, Fourier, latent, wavelet, U-shaped, and Galerkin neural operators-are evaluated for both diffusion-to-wave and wave-to-diffusion mappings. The results reveal a strong directional asymmetry. Diffusion-to-wave reconstruction is more challenging because it requires recovering wavefront, phase, and time-of-flight information attenuated by diffusion; U-NO performs best in this direction, achieving a relative $\ell_2$ error of $0.307$ and an $R^2$ of $0.905$. Wave-to-diffusion mapping is considerably more stable, with GNO attaining a relative $\ell_2$ error of $0.154$ and an $R^2$ of $0.935$. Neural operators generally outperform the conventional convolutional baseline, highlighting the nonlocal nature of cross-physics transformations. These findings demonstrate that deep learning can establish useful mappings between distinct physical modalities on a shared latent manifold, while the achievable accuracy remains fundamentally constrained by the direction-dependent information content of the governing physics.

Optically readable molecular spins are attractive as quantum sensors due to their nanoscale modularity, synthetic tunability, and scope for sensitive readout. In particular, photoexcited spin-triplet states in organic molecules are appealing in supporting high optical-spin contrast at room temperature. Their utility is underpinned by their coherence, which warrants a detailed understanding of it. Here, from first principles, we systematically explore the Hahn-echo decoherence of the benchmark molecular system for room-temperature optically detected spin coherence—pentacene guest molecules coupled to a para-terphenyl host. Using generalized cluster-correlation expansion methods, we investigate the mechanisms of nuclear-spin-induced decoherence from zero to high magnetic field, exploring the role of guest vs host molecules, specific nuclei, zero-field splitting interactions, and hyperfine parameters. We describe how zero-field decoherence is driven by ~6 nuclei on the guest, while high-field decoherence is driven by ~600 nuclei in the host; how the longitudinal zero-field splitting parameter, $D$, can prolong $T_2$; and the magnetic-field-dependent processes which drive decoherence. These results advance our understanding of decoherence in optically readable molecular spins, providing insight for their synthetic enhancement and deployment as quantum probes.

We present an analytical and experimental study of a variable-mass oscillator with constant mass loss. Starting from the equation of motion of a spring-mass system whose mass decreases linearly with time, analytical solutions are obtained in terms of Bessel functions. Simple asymptotic expressions are then derived, providing explicit descriptions of the evolution of the oscillation amplitude and frequency. The analysis is extended to include viscous damping, leading to a model suitable for direct comparison with experimental observations. Experimental measurements of the oscillator acceleration were performed using a simple laboratory setup consisting of a spring-mounted container that continuously loses mass at an approximately constant rate. The theoretical predictions accurately reproduce the measured dynamics over the entire duration of the oscillation, and the massloss rates obtained from the fits are in good agreement with independent measurements. The results provide an accessible example of variable-mass dynamics and illustrate how special-function methods can yield experimentally testable predictions in advanced undergraduate mechanics.

X-ray tomographic particle tracking velocimetry is a promising tool to provide pore-scale insight into fluid flow inside opaque porous media. This is critical for applications ranging from geo-energy to electrochemistry. Current approaches to implement this three-dimensional, three-component (3D-3C) velocimetry technique use conventional micro-computed tomography (CT) workflows to recover tracer particle trajectories. These workflows first reconstruct a sequence of 3D CT images from radiographs which are sequentially acquired at time intervals that span multiple viewing angles. The tracer particles are then detected in each of these CT images and finally linked into trajectories. However, motion-blurring induced by the static CT volume reconstruction impairs the detectability of fast-moving tracer particles, severely limiting the temporal resolution and dynamic range of the velocimetry outcome. In this work, we show that this limitation can be overcome by explicitly recovering particle trajectories directly from the acquired radiographs, bypassing the intermediate tomographic reconstruction step and the static-scene assumptions of traditional 3D CT reconstructions. We implement this approach in a new open-source algorithm, CTracks, and validate it using experimental data on pipe flow and on flow through a complex porous medium, demonstrating a five-fold increase in the maximum detectable velocity compared with state-of-the-art methods. Numerical simulations further confirm improved detection rates and bounded trajectory errors at these increased velocities. Our work thus demonstrates that 3D-3C velocimetry in opaque microscopic geometries can be extended to substantially faster flows by replacing X-ray tomographic image reconstruction with direct particle trajectory reconstruction.

Grasp package is based on the relativistic configuration interaction in which accurate calculations, accounting for valence, valence-valence, core-valence, core, and core-core electron correlations, often rely on massive CSF expansions. This paper presents further development of the method based on the second-order perturbation theory for finding the most important CSFs that have the greatest influence on the core-valence, core, and core-core correlations. This method is based on a combination of the relativistic configuration interaction method and the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in an irreducible tensorial form [G. Gaigalas, P. Rynkun, L. Kitovienė, Second-Order Rayleigh-Schrödinger Perturbation Theory for the Grasp2018 Package: Core-Valence Correlations, Lithuanian Journal of Physics, 64, No. 1, 20-39 (2024) (https://doi.org/10.3952/physics.2024.64.1.3) and G. Gaigalas, P. Rynkun, L. Kitovienė, Second-Order Rayleigh-Schrödinger Perturbation Theory for the Grasp2018 Package: Core Correlations, Lithuanian Journal of Physics, 64, No. 2, 73-81 (2024) (https://doi.org/10.3952/physics.2024.64.2.1)]. In this extension, the perturbation theory accounts for electron core-valence, core, and core-core correlations where an atom or ion has any number of valence electrons for calculation of energy spectra and other properties. Meanwhile the rest of the correlations are accounted for in a traditional way. This allows a significant reduction of the space of the configuration state function for complex atoms and ions. We also demonstrate how this method works for calculations of the energy structure and E1 transition properties of Fe XV ion.

Many of the students enrolled in the calculus-based physics sequence are pursuing engineering degrees. Lab activities that have a direct connection to engineering, analyzed with the physics they have been studying, can grab students' interest and provide a real-world connection. All the better if the equipment is inexpensive and partly self-built. In addition, we wanted to use smartphones as data collection devices. Smartphones have become valuable tools for physics education because they provide an accessible and inexpensive means of experimental data acquisition through their built-in sensors. Several free applications, such as Physics Toolbox and phyphox, facilitate sensor-based data collection and analysis, making it possible to perform meaningful laboratory activities without expensive equipment. We chose to use a simple crank-slider mechanism for our activity. The crank-slider converts rotary motion into linear motion and has common applications in such things as internal combustion engines and compressors. Educational studies have shown that slider-crank mechanisms and related mechanical devices provide effective contexts for introducing engineering concepts and connecting theoretical models with practical applications. In our implementation, a rotary motor drives a disk connected by a rod to a cart moving along an air track. Students investigate the resulting motion using smartphone data acquisition and video analysis. Experimental measurements are then compared with the predictions of a mathematical model derived from the geometry of the system.

Understanding how optical orbital angular momentum (OAM) is transferred to matter requires treating recoil and translational motion alongside the internal electronic dynamics. We develop a center-of-mass-resolved theory of one-photon ionization of hydrogen by a monochromatic Laguerre–Gaussian beam and show that the Bessel-vortex photoelectron predicted in fixed-target models is a preparation-dependent limit. For a sharply defined atomic center-of-mass momentum, the recoil records the photon-cone azimuth, and tracing over it generally destroys the coherence required for a pure electron vortex. In the small-transverse-retardation regime, the optical OAM is transferred predominantly to the center-of-mass motion and hence, in the laboratory frame, to the proton. Finite-retardation corrections redistribute angular momentum between center-of-mass and relative motion, while an additional correlation contribution to the electron and proton angular momenta can be tuned through the spatial uncertainty of the atomic center of mass. These results reveal atomic recoil as a key element of OAM transfer in photoionization.

Typically, vortices in wave fields are associated with amplitude zeros. In contrast, recently described high-intensity (Type II) wave vortices appear near amplitude poles and can exist only in disconnected space. We attempt to extend the concept of a Type II optical vortex (OV) to paraxial beam-like optical fields. It is shown that "true" Type II OV fields can exist only in a multiply connected three-dimensional space, where spatial "holes" impenetrable to the electromagnetic field are formed by purposefully created filamentary inclusions of material. However, the cross-section of a "true" Type II OV can be reproduced in a specific plane of ordinary "free" space, where the hole is designated by a region with zero amplitude. Methods for the practical creation of the discussed field structures are proposed, including methods using programmable light modulators and computer-synthesized holograms. The results of computer simulations demonstrate reasonable agreement with experimental data.

In this study, quantum spin pumping in an antiferromagnetic chain driven by time-dependent potential is investigated. The aim is to explore the possibility of generating and controlling spin currents in the absence of external bias and to examine the role of exchange field and periodic driving in the separation of spin-up and spin-down currents. The system is described using a tight-binding model, and spin-resolved currents are calculated employing the Keldysh non-equilibrium Green's function formalism. Two time-dependent potentials with a specific phase difference are applied to the two ends of the chain, while the chemical potentials of both electrodes are set equal. The results demonstrate that in the adiabatic regime (low frequencies), the response of the two spin channels is nearly identical. However, as the driving frequency increases and the system enters the nonadiabatic regime, absorption and emission processes of energy quanta become activated, leading to significant differences between spin-up and spin-down currents. The pumped current exhibits strong dependence on the chemical potential, allowing for the control of both magnitude and direction of the spin current through its adjustment. With increasing frequency, the spin current enhances, and parameters can be tuned such that the charge current nearly vanishes while a considerable spin current persists. This finding indicates the feasibility of achieving nearly pure spin pumping without net charge transfer in the antiferromagnetic chain. The results provide a promising perspective for designing spin-pumping devices based on antiferromagnetic systems.

Born effective charge (BEC) tensors link atomic displacements to polarization, thereby connecting lattice vibrations with dielectric response and infrared activity. We present ZStar, an open-source Python toolkit that automates calculations of polarization, BEC, phonons, static and frequency-dependent dielectric response, and infrared and Raman spectra. ZStar supports bulk crystals, two-dimensional materials, one-dimensional structures, and molecules through an integrated workflow for input preparation, execution, and response analysis. Berry-phase polarization and real-space dipoles describe responses along periodic and open directions, respectively. Its unified, symmetry-adapted finite-displacement framework jointly determines BEC and zone-center force constants from the same calculations, improving computational efficiency while preserving numerical accuracy. Strain-response calculations further provide proper piezoelectric coefficients and their internal-relaxation contributions for bulk crystals. In the ABACUS+PYATB route, electronic Hamiltonian data are reused to obtain Raman response without additional self-consistent calculations. Native response implementations from VASP and CP2K are also integrated. Matched infrared/Raman benchmarks against the implemented separate workflows achieve speedups of up to 8.4. An accompanying agent skill provides an agent-friendly interface for workflow integration. ZStar therefore offers an efficient and automated route for exploring polarization, BEC, dielectric and piezoelectric responses, and vibrational spectra across different material dimensionalities.

SpectraFit XPS is a free web application for the analysis of X-ray photoelectron spectroscopy (XPS) data that runs entirely in the browser, with no installation and no server-side processing: spectra never leave the user's computer. It combines an interactive Levenberg–Marquardt fitting engine with true Voigt, Doniach–Šunjić, and summed Gaussian–Lorentzian line shapes; Shirley (static and dynamic), linear, and Tougaard (two- and four-parameter) backgrounds; spin–orbit doublet generation; and expression-based inter-peak constraints. Quantitative analysis supports ten relative-sensitivity-factor sets, several kinetic-energy correction schemes including TPP-2M inelastic mean free paths, angular correction, and atomic and weight percentages, with the underlying database and algorithms adapted from the open-source KherveFitting project. The application reads and writes ISO~14976 (VAMAS) files—including multi-region and depth-profile data and load-time transmission-function correction—and imports common vendor and spreadsheet formats. A publication plotter exports journal-ready SVG/PNG figures. The quantification pipeline reproduces KherveFitting reference values exactly in a 30-case regression suite, part of an automated test set of 100 tests. The application, an illustrated bilingual user guide, and a synthetic demonstration dataset are freely available at https://spectrafit-xps.web.app/.

The paper presents a further development of the method G. Gaigalas, P. Rynkun, L. Kitovienė, Second-Order of Rayleigh-Schrödinger Perturbation Theory for the Grasp2018 Package: Core-Valence Correlations, Lithuanian Journal of Physics, 64, No. 1, 20-39 (2024) (https://doi.org/10.3952/physics.2024.64.1.3), based on a combination of the relativistic configuration interaction method and on the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in an irreducible tensorial form. In this extension the perturbation theory accounts for both electron core-valence and core correlations when an atom or ion has any number of valence electrons meanwhile relativistic configuration interaction accounts for the rest of correlations. This allows a significant reduction of the space of the configuration state function for complex atoms and ions. We also demonstrate how this method works for energy structure calculation of Fe XV ion.

We present a feasibility study demonstrating how recent advances in quantum-sensing technologies can facilitate stringent comparisons between theoretical predictions and experimental measurements of contact-free transitions in muonic atoms. Such comparisons can probe previously unexplored regions of the parameter space governing spin-independent muon-proton interactions and disentangle the extraction of fundamental constants from searches for physics beyond the Standard Model.

In the existing quantum algorithms for the lattice Boltzmann method, resolving the unitarity problem of the BGK collision operator from first principles remains a fundamental challenge, and a systematically constructed unitary alternative that reproduces the BGK relaxation structure to leading order has not yet been established in the literature. In this work, we propose a novel quantum lattice Boltzmann method (QLBM) based on the rotation collision operator, in which the non-unitary BGK relaxation is replaced by a unitary rotation in the amplitude space of the distribution function, and the corresponding gate-level quantum circuits are also constructed. Specifically, the rotation collision operator is developed for both the D2Q5 model of the convection-diffusion equation and the D2Q9 model of the incompressible Navier–Stokes equations. It is worth noting that, for the D2Q5 model, the equilibrium-state preparation circuit can be precompiled and reused, and the resulting unitary blocks can be sequentially composed once the state-dependent collision parameters are specified. Finally, some numerical experiments are performed to validate the developed QLBM, demonstrating its accuracy and effectiveness.

Strong $\chi^{(2)}$ interactions at low optical powers are key to scalable nonlinear and quantum photonics. Although doubly resonant microresonators exhibit exceptional efficiencies, they require simultaneous resonance and phase matching of widely separated optical frequencies, making them inherently sensitive to fabrication and operating conditions. Singly resonant cavities eliminate this constraint by resonating at only the fundamental frequency while the second-harmonic field propagates in a single pass, but they have traditionally sacrificed nonlinear efficiency. Here, we demonstrate a singly resonant InGaP-on-insulator microresonator that overcomes this tradeoff. Combining the large $\chi^{(2)}$ nonlinearity of InGaP with high-quality-factor resonators, we achieve efficient and widely tunable second-harmonic generation, broadband quantum-frequency-comb generation, and low-threshold optical parametric oscillation. Unlike conventional centimeter-long singly resonant devices, our millimeter-scale InGaP devices deliver nonlinear performance comparable to, and even exceeding, doubly resonant systems. By overcoming the conventional efficiency-robustness tradeoff of singly resonant devices, this work opens a new route to low-power, broadband, and widely tunable $\chi^{(2)}$ nonlinear and quantum photonics.

In this work, we investigate the magnetic-field stability of a Penning trap operated with a cryogen-free superconducting magnet through cyclotron-frequency measurements of a single laser-cooled calcium ion using two complementary photon-based detection techniques: a pulsed optical method for determining the three ion eigenfrequencies and Fluorescence-Detected Fourier-Transform Ion-Cyclotron-Resonance (FD-FT-ICR). For the former technique, the data-analysis procedure was revisited, considering it as the dominant contribution to the measurement uncertainty and yielding a long-term magnetic-field drift $(1/B)(dB/dt) = -3.07(32)\times10^{-9}$ $\mathrm{h}^{-1}$. This value is comparable to those reported for high-precision Penning-trap experiments employing liquid-helium-based superconducting magnets. The short-term stability was investigated using the FD-FT-ICR technique, resulting in a minimum relative magnetic-field variation of $\delta B/B \simeq 5\times10^{-8}$ for averaging times between 30 and 60 s. Furthermore, this technique enables direct cyclotron-frequency determinations on timescales as short as a few seconds, providing access to magnetic-field fluctuations that are generally not resolved in conventional Penning-trap experiments.

Turbulence approaching an aerofoil leading edge is strained and blocked in the final few nose radii. Rapid-distortion theory assumes that the pre-impact field is a linear image of the upstream turbulence; we test that assumption directly. Grid turbulence is computed over a NACA~0012 aerofoil and sampled on three congruent surfaces around the nose, giving the cross-spectral tensor between upstream and pre-impact stations. Relative to a no-aerofoil control, the linearity spectrum falls by a factor of three already at the energy-containing scales ($\kappa = k\,r_{\mathrm{LE}} \approx 0.3$), showing that a substantial part of the pre-impact turbulence is generated locally rather than inherited. The same location appears in physical space: the anisotropy invariant $III_b$ changes sign from prolate to oblate within the last few per cent of chord, departing the plane-strain rapid-distortion prediction. The change is produced by pressure–strain redistribution, which drains the strain-amplified wall-normal stress into the other components; the term is absent in the control and becomes active once the accumulated strain is rapid. Across a fourteen-fold range of nose radius the sign change occurs at $x \approx -1.5\,r_{\mathrm{LE}}$ and the generated turbulence is spanwise-dominated. At second order the mapping remains usable: when inserted into a standard Amiet prediction it improves agreement with measured leading-edge noise, and the same coefficients transfer to independent published cases when only nose radius and free-stream speed are supplied.

Accurate multi-horizon wind direction forecasting is critical for turbine yaw control and grid security. Rapid directional shear (turning $\ge 90^\circ$) challenges models via non-Euclidean geometry on $S^1$, multiscale dynamics, and regime-dependent uncertainty. Conventional discrete models and foundation models suffer from mid-frequency phase lag and turning misalignments. We show that directional predictability decays at disparate rates across frequency subbands, rendering monolithic mechanisms suboptimal. We propose a predictability-guided paradigm: slow synoptic drift $\to$ deterministic regression; intermediate turning $\to$ continuous latent differential flows; unresolved turbulence $\to$ conditional residual diffusion; followed by causal recalibration. On a 10,000-sequence multi-year benchmark, our framework maintains calm-weather accuracy (Test MCE $38.48^\circ$) while reducing extreme-turning error (Case 1 MCE $60.69^\circ$ vs $70.42^\circ$ for zero-shot foundation models). The circular CRPS reaches $22.36^\circ$, with 93.88% coverage at nominal 95% (91.01% out-of-distribution). Density estimation further reveals near-antipodal bimodal structure under severe shear (13.39%–15.43% tail mass $\ge 135^\circ$), exposing a geometric bound where single-center calibration under-covers (81.56%), motivating multimodal circular manifold learning.

While optical manipulation of atomic arrays has reached a high degree of precision and scalability, the stable optical confinement of solution-based artificial atoms like colloidal quantum dots (CQDs) remains hindered by weak trapping forces and thermal fluctuations. High-intensity trapping often compromises the quantum properties of these emitters, creating a significant trade-off between mechanical stability and optical integrity. To overcome this, we propose encapsulating CQDs within a transparent polymer matrix, thereby increasing the effective interaction volume and optical restoring force without altering the emitters themselves. This strategy allows for stable spatial confinement under standard experimental conditions, as evidenced by the direct resolution of positional fluctuations through photoluminescence imaging and trajectory tracking. With averaged position fluctuations below 20 nm, the intrinsic emission spectra and photoluminescence decay dynamics remain largely unaffected, and photon-correlation measurements confirm the full preservation of single-photon emission. These findings establish a robust method for the controlled confinement of colloidal quantum emitters and in-situ quantum-optical measurements for future advancements in quantum-optical manipulation of artificial atoms.

Near-inertial waves (NIWs) generated by extratropical storms provide a major pathway for transferring atmospheric energy into the ocean, yet what determines the efficiency of this energy transfer at the level of individual storms remains poorly understood. Here, using a slab ocean model forced by ERA5 reanalysis and analyzed in storm-relative coordinates, we investigate NIW generation across three temporal scales: from the instantaneous structure of individual storms, through their life cycle, to variability across storms. Instantaneous storm structure reveals that the spatial layout of wind stress and storm propagation provides the required time evolution and rotation to excite a localized maximum in wind work on the right side of storm tracks, much like tropical cyclones do. Following storms through their life cycle further reveals that wind work peaks one day after cyclone genesis, about one day before storms reach their maximum intensity. This offset arises because storm translation slows during intensification, reducing the propagation-induced wind-stress tendency, while concurrent poleward propagation increases the Coriolis parameter and reduces the alignment between winds and near-inertial currents. Due to the temporal lag, regions of climatologically high NIW forcing are located upstream of the North Pacific storm-track maximum. Finally, examining variability across storms, we show that storm intensity, propagation speed, and latitude explain most of the variability in NIW generation, but not in extreme events. Focusing on extreme events, we find that the strongest NIW-generating storms feature colder cold sectors, which destabilize the marine boundary layer and enhance downward momentum transfer to the ocean surface.

CeO serves as an important model system for understanding the interplay of electron correlation, spin-orbit coupling, and 4f/5d configurational mixing in lanthanide oxides. Its anion photoelectron spectrum exhibits dense electronic manifolds and multielectron shake-up processes that complicate spectral assignments and photodetachment dynamics. Here, we combine high-resolution anion photoelectron spectroscopy with spin-free and spin-orbit-coupled CASSCF+NEVPT2 calculations to characterize the electronic structure of CeO- and CeO. A binning-based data analysis approach enables observation of weak transitions hidden by spectral congestion, while multireference calculations reproduce the low-lying electronic structure and detachment energetics. On this basis, tentative assignments are proposed for the observed photoelectron features. Analysis of photodetachment selection rules, photoelectron angular distributions, and multielectron detachment channels provides additional insight into the mechanisms underlying the spectrum. These results establish a comprehensive interpretation of the CeO- photoelectron spectrum and underscore the importance of combining high-resolution spectroscopy with multireference relativistic theory for electronically complex lanthanide systems.

We extend the relativistic spherical complex optical-potential method with group additivity developed in our recent work [S. Arya and B. Antony, RSC Adv. 16, 13548–13558 (2026)] to molecules with permanent dipole moments. The short-range electronic collision is described by a central Dirac partial-wave calculation, while the missing anisotropic long-range dipole interaction is restored through a rotationally resolved first-Born contribution. The rotational thresholds, state-to-state transition-dipole strengths, and thermal populations are obtained from the HITRAN2024 spectroscopic database and thermally reweighted at the adopted rotational temperature. Both excitation and superelastic de-excitation channels are included. Electron scattering from benchmark polar hydrides ($\rm H_2O$, $\rm H_2S$, $\rm NH_3$, and $\rm PH_3$) is investigated over the incident-energy range 0.1–10,000 eV. We report vibrationally elastic, differential, integral, and momentum-transfer cross sections, together with a total cross section that also contains electronically inelastic loss from the quasifree absorption potential. The calculations reproduce the broad experimental and recommended trends over a wide energy range. The largest deviations are confined mainly to the low-energy and resonance-sensitive regions. Overall, the agreement improves substantially from the tens-of-eV region upward. The method therefore retains the low computational cost and wide energy coverage of the optical-potential approach while adding the long-range rotational physics needed for polar molecules.

The previously proposed tight-binding method derived from the total energy has been extended within the local density approximation (TE-TB method; J. Phys. Soc. Jpn. 87, 064802 (2018)). Unlike the earlier two-parameter formulation, the present method introduces three parameters. These parameters explicitly capture local packing effects and improve transferability. Furthermore, based on physical considerations, several boundary conditions (inductive bias) are imposed on the functionals defining the tight-binding Hamiltonian and related energy functionals. The revised formalism is tested on crystalline silicon to assess the stability of the diamond structure, a monovacancy, and the (001) surface. These benchmark tests demonstrate the high transferability and reliability of the present three-parameter TE-TB design philosophy.

It is generally believed that statistically stationary states of Rayleigh-Bénard convection (RBC) can be described by statistically stationary solutions to the Boussinesq approximation. Based on an analysis of the mechanical energy equation, we argue that this belief is not justified, because the expression for mean conversion of internal energy into kinetic energy by compressions and expansions, which is implicitly given by the approximation, does not qualify as an approximation. In consequence, it is questionable whether the exact Boussinesq expression relating the mean kinetic energy dissipation in a stationary state to the Rayleigh and Nusselt numbers is valid. Using assumptions that partly lie outside the Boussinesq approximation, we derive scaling relations for the mean kinetic energy dissipation in a stationary state in three and two dimensions. The relation for the three-dimensional system is similar to the Boussinesq expression, but includes an unknown prefactor, while the relation for the two-dimensional system is completely different. Our arguments suggest that statistically stationary solutions to the Boussinesq approximation in three dimensions, reproduce scaling relations between various statistical quantities quite well, although they should not be regarded as approximations in a strict sense, while solutions in two dimensions completely fail. We suggest that this should be investigated by performing DNS of weakly compressible RBC and compare with DNS of Boussinesq RBC.

Characterizing temporal interactions in social systems is challenging because social behavior can be bursty and non-stationary, violating the stationarity assumptions of many methods used to measure temporal dependence. The cross-correlogram, an existing technique used to profile neural excitations and inhibitions, offers an interpretable alternative to methods such as Granger causality or co-occurrence, as it produces a full profile of lagged dependence directly from event times rather than a single summary statistic. We adapt the cross-correlogram by integrating functional models of behavior with data-driven temporal response profiling. By characterizing how periodic structure biases traditional cross-correlograms, we propose a correction based on smooth intensity functions, specified from a known functional form or estimated empirically. This approach provides a robust, interpretable estimator of temporal dependency profiles even when collective rhythms operate on timescales that overlap those of the interactions of interest. We demonstrate theoretically and through simulation that the proposed method recovers temporal dependencies in periodic regimes, outperforming interval-jitter and Granger causality methods. Finally, we apply the method to 3.1 million event times from X (formerly Twitter) collected between 2019 and 2020, demonstrating how cross-correlograms reveal delayed temporal relationships in collective online behavior that are missed by co-occurrence measures. For a subset of television-related hashtags, recovered delays align with known broadcast schedules, providing evidence that the proposed method captures genuine temporal structure rather than artifacts of shared attention cycles.

Quantum materials host a rich spectrum of low-energy collective excitations- phonons, magnons, plasmons, polaritons, and Higgs modes- that fundamentally govern their emergent properties, but remain inaccessible to conventional linear THz spectroscopy when nonlinear pathways overlap or non-perturbative dynamics emerge. Terahertz two-dimensional coherent spectroscopy (THz-2DCS), realized through phase-stable high-field THz pulse sequences, directly resolves this challenge by delivering phase-resolved multidimensional spectra that uniquely disentangle coherent intraband nonlinear quantum dynamics from incoherent backgrounds. Here, we establish a unified theoretical framework by using density-matrix formalism combined with the optical Bloch equations, from which nonlinear pathways are systematically derived and visualized on the Bloch sphere. This framework provides insight into low-energy nonlinear dynamics exhibiting homogeneous or inhomogeneous broadening depending on the scattering mechanism, enabling the interpretation of nonlinear signals in both the perturbative regime, described by a susceptibility expansion, and the non-perturbative regime. Building on this foundation, we comprehensively survey THz-2DCS investigations of nonlinear plasmon, phonon, magnon, and polariton. Finally, we outline future opportunities, including integration with optical-pump THz-probe platforms for nonequilibrium quantum control.

Thin-film barium titanate (BaTiO3, or BTO) has emerged as a promising electro-optic (EO) material for integrated photonics due to its exceptionally large Pockels coefficients, low optical loss, and compatibility with heterogeneous integration. Recent advances in epitaxial thin-film growth, crystal orientation control, ferroelectric domain engineering, and scalable integration have enabled EO performance in thin-film BTO approaching bulk-like properties on photonic platforms. This review provides a comprehensive overview of integrated photonic devices based on thin-film BTO, including fundamental material properties, thin-film growth and integration strategies, passive waveguide configurations, EO response at both the film and device levels, and relevant optical applications. We review the role of film orientation, domain structure, and device geometry in determining accessible EO coefficients and modulation mechanisms, as well as the distinctions between intrinsic and effective EO responses demonstrated at the film and device levels. Representative studies are compared in terms of film-quality-related metrics and device performance figures of merit, alongside emerging applications realized in BTO-based platforms. Finally, we discuss the remaining challenges and outline future development directions toward high-performance BTO-based integrated photonic systems.

We formulate Hartree–Fock as a density-matrix renormalization group (DMRG) sweep of a single Slater determinant, assuming a density–density electron–electron interaction. We compress the occupied state and long-range interaction separately, reducing each sweep step to a small local Fock problem. Exchange is retained throughout. Uniform antiferromagnetic hydrogen chains provide an almost ideal setting for this approach, while retaining the Coulomb interaction and its $1/r$ tail. We initialize and converge a chain of 100,000 electrons in 1.8 million spatial basis functions in about two hours on a 64-GB Mac mini, using less than a third of its memory. The work per sweep is nearly proportional to chain length, and the number of sweeps needed for convergence changes little from 1000 to 100,000 atoms. DMRG's compression of states and environments thus makes large HF calculations with long-range Hartree and exchange practical on an ordinary desktop computer.