Chemical Physics
Deep learning of committor and explainable artificial intelligence analysis for identifying reaction coordinates
Toshifumi Mori, Kei-ichi Okazaki, Kang Kim et al. (+1 more)
In complex molecular systems, the reaction coordinate (RC) that characterizes transition pathways is essential to understand underlying molecular mechanisms. This review surveys a framework for identifying the RC by applying deep learning to the committor, which provides the most reliable measure of the progress along a transition path. The inputs to the neural network are collective variables (CVs) expressed as functions of atomic coordinates of the system, and the corresponding RC is predicted as the output by training the network on the committor as the learning target. Because deep learning models typically operate in a black-box manner, it is difficult to determine which input variables govern the predictions. The incorporation of eXplainable Artificial Intelligence (XAI) techniques enables quantitative assessment of the contributions of individual input variables to the predictions. This approach allows the identification of CVs that play dominant roles and demonstrates that the committor distribution on the surface using important CVs is separated by well-defined boundaries. The framework provides an explainable deep learning strategy for assigning a molecular mechanism from the RC and is applicable to a wide range of complex molecular systems.
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All authors Toshifumi Mori, Kei-ichi Okazaki, Kang Kim, Nobuyuki Matubayasi
Geophysics · Cross-listed from astro-ph.EP
Core and mantle thermal evolution constraints on the onset of plate tectonics and a long-lived geodynamo
Valentin Bonnet Gibet and Nicola Tosi
Earth's long-lived geodynamo is difficult to reconcile with recent high estimates of the core thermal conductivity, a problem known as the new core paradox. At the same time, the long-term thermal
evolution of the mantle remains uncertain, largely due to the poorly constrained onset of modern-style plate tectonics, which marks the transition to efficient cooling of the interior through mobile-lid convection. Because core cooling – and thus
magnetic field generation – depends on the efficiency with which the mantle extracts heat from the core, these two problems are closely linked. Here, we investigate the coupled thermal
evolution of mantle and core using a 1D model that incorporates a parametrized transition transition from stagnant- to mobile-lid convection, defined by its onset time and with a prescribed duration. This framework allows us to assess how different tectonic histories influence Earth's thermal and
magnetic evolution. We perform a
Bayesian inversion using constraints from the palaeomagnetic record, mantle cooling history, and present-day thermal state. Our results favour a transition from stagnant- to mobile-lid convection during the Archean, which promotes core cooling and enables a geodynamo throughout Earth's history, even for core thermal conductivities in excess of 100 W/m/K. A delayed onset of mobile-lid convection provides thus a viable solution to the new core paradox.
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Fluid Dynamics
A High-Order Compact Finite Volume Method for Unstructured Grids: Scheme Space Formulation and One-Dimensional Implementations
Ling Wen, Yan-Tao Yang and Qing-Dong Cai
This paper presents a novel and straightforward compact reconstruction procedure for the high-order finite volume method on unstructured grids. In this procedure, we constructed a linear approximation relationship between the mean values and the function values, as well as the derivative values. Compared with the classical compact schemes, which employ a Taylor expansion method to determine the coefficients, our approach adopts an equivalent and more generalized method to achieve this goal. Via this method, the problem of constructing a high-order compact scheme is transformed into solving the null space of undetermined homogeneous linear systems. This null space constitutes the complete set of schemes that meet the specified accuracy under a given stencil, and is termed the 'scheme space'. Schemes within the scheme space possess the same accuracy level yet exhibit distinct dispersion and dissipation characteristics. Through
Fourier analysis, we can get the dissipation and dispersion properties of all schemes in the scheme space. This facilitates the control of scheme dispersion and dissipation without altering the stencil compactness. Combined with the WENO (Weighted Essentially Non-Oscillatory) concept, multi-stencil schemes are employed to construct the nonlinear weighted compact finite volume scheme (WCFV). The WCFV is capable of eliminating unphysical oscillations at discontinuities, thereby enabling the capture of strong discontinuities. One-dimensional schemes are discussed in detail, and numerical results demonstrate that the proposed method exhibits high-order accuracy, robustness, and shock-capturing capability.
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Optics · Cross-listed from cond-mat.mtrl-sci
Pulsed Laser Template Engineering- PLATEN
Dhiman Biswas, Junyeob Song, Francisco Guzman et al. (+16 more)
Thin films of functional inorganic materials, particularly
oxides, play a vital role in optoelectronics, enabling applications that range from active optical components to MEMS-based architectures. Achieving high aspect ratio patterning of these functional materials remains a significant challenge, as many of their constituent elements do not readily form volatile compounds required for conventional reactive ion etch processes. We introduce a novel approach, Pulsed
Laser Template ENgineering (PLATEN), which offers a more accessible route for patterning materials that are typically difficult to etch. This technique involves depositing functional films using the Pulsed
Laser Deposition (PLD) process onto silicon substrates that have been pre-patterned using reactive ion etching to create high aspect ratio features. Due to the highly forward-directed nature of the PLD process, the deposited films replicate closely the topography of the patterned silicon, without coatings the sidewalls. This process remains effective even at feature sizes down to approximately 50 nm. The
oxide films replicate the underlying silicon pattern to a thickness of 80 nm. For thickness beyond 80 nm the patterns develop a waist at the midpoint which scales with film thickness and is not dependent on the feature size. In this paper, we present a detailed analysis of the PLATEN process, including deviations from ideal pattern replication in sub-micron features as a function of film thickness, and demonstrate near single crystalline growth of
oxides on the patterned silicon substrate, demonstrating the potential of PLATEN technique for active opto-electronic materials.
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All authors Dhiman Biswas, Junyeob Song, Francisco Guzman, Levi Brown, Yiwei Ju, Nisha Geng, Pralay Paul, Sumit Goswami, Casey Kerr, Sreehari Puthan Purayil, Ben Summers, Preston Larson, Binbin Weng, Bin Wang, Horst Hahn, Xiaoxing Pan, Alisa Javadi, Henri Lezec, Thirumalai Venkatesan
Atomic Physics
Self-energy corrections to the ionization energies in sodium-like ions: comparison of the ab initio QED and model-QED-operator approaches
P. Yang, A. V. Malyshev, E. A. Prokhorchuk et al. (+3 more)
Calculations of the self-energy corrections to ionization energies of the $3s$, $3p_{1/2}$, and $3p_{3/2}$ states in sodium-like ions with
nuclear-charge numbers $Z=30$, $50$, $70$, and $92$ are presented. The calculations are performed using two approaches: the rigorous bound-state QED formalism and the model-QED-operator method. Within the first method, the first and second orders of the QED perturbation theory formulated in the Furry picture are evaluated. Various screening potentials are included into the initial approximation to partially take into account the electron-electron interaction effects already at the lowest order, thereby accelerating the convergence of perturbation series. Within the second approach, different implementations of the model-QED operator, including its incorporation into the relativistic configuration-interaction calculations, are considered. A detailed comparison of the results obtained by these two independent methods is presented, demonstrating good agreement and thus validating the accuracy and efficiency of the model-QED-operator approach for many-electron systems.
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All authors P. Yang, A. V. Malyshev, E. A. Prokhorchuk, I. I. Tupitsyn, V. M. Shabaev, D. P. Usov
Fluid Dynamics
Direct numerical simulation of out-scale-actuated spanwise wall oscillation in turbulent boundary layers
Jizhong Zhang, Fazle Hussain and Jie Yao
Spanwise wall oscillation (SWO) of turbulent boundary layers (TBLs) is investigated via direct numerical simulations over an extended actuation region with oscillation periods up to T_{sc}^+=600, scaled by the uncontrolled friction velocity u_{\tau 0} at the onset of SWO (i.e. Re_\theta=344). For low periods (T_{sc}^+<200), drag reduction (DR) decreases with increasing Re_\theta, consistent with conventional inner-scaled control strategies targeting near-wall
turbulence. In sharp contrast, for large periods, DR increases with Re_\theta. For example, at T_{sc}^+=600, DR rises from 1.3% at Re_\theta=713 to 7.0% at Re_\theta=2340. This unexpected growth is partly explained by the streamwise
evolution of the effective oscillation parameter: as TBL develops, u_{\tau 0} decreases downstream, reducing the local-scaled period T^+ and thereby enhancing suppression of near-wall
turbulence. Interestingly, even the results are compared at approximately fixed T^+, DR for T^+>350 still exhibits a weak positive dependence on Re_\theta, consistent with recent experiments by Marusic et al. Nat. Commun., vol. 12, 2021, 5805. We further develop a new analytical relationship that links DR to the upward shift of mean velocity in the wake region. Unlike previous formulations, the relationship avoids logarithmic-region fitting and does not rely on an invariant Karman constant under SWO, while maintaining good agreement with DNS data. Flow diagnostics – including Reynolds stresses, skin-friction decomposition, and energy spectra – demonstrate that the observed variation of DR with Reynolds number (Re) arises from period-dependent modulation of near-wall
turbulence. Overall, these findings challenge the conventional view that DR inevitably deteriorates with Re and demonstrate that out-scaled actuation can instead enhance DR performance – offering new physical insights for high-Re control strategies.
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Biological Physics · Cross-listed from q-bio.NC
Quantifying plasticity: a network-based framework linking structure to dynamical regimes
Igor Branchi
Plasticity is a fundamental property of complex systems, such as the
brain or an organism. Yet it typically remains a descriptive concept inferred retrospectively from observed outcomes, such as modifications in activity or morphology. Here, the network-based operationalization of plasticity is further formalized as the ratio between system size and connectivity strength among system elements. Within this framework, system size determines the dimensionality of the accessible state space, while connectivity strength tunes the system's regime. An optimal range of plasticity – balancing capacity for change and capacity to maintain coherence – emerges at intermediate connectivity strength. Notably, this balance coincides with the critical regime, which provides a theoretically motivated
benchmark that enables a normalized unit of measure, termed effective plasticity, and comparisons of adaptive efficacy across diverse systems. Plasticity is thus transformed into a predictive tool that quantifies a system's capacity for change before it occurs. Its validity is supported across disciplines and, in particular, by evidence from psychopathology where it anticipates transitions between mental states. At a mechanistic level, plasticity acts as a structural tuning parameter for criticality, reframing their relationship as causal, with plasticity driving criticality rather than merely accompanying it. Furthermore, this network-based operationalization explains how larger systems can more robustly maintain critical dynamics. Crucially, the proposed perspective distinguishes functional regime shifts from thermodynamic phase changes, identifying plasticity as the system-level regulator that shapes and constrains the dynamic repertoire. This framework is applicable across domains, including ecology, economics, and social systems, and may foster cross-disciplinary integration within complexity science.
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Optics
Second-harmonic generation for enhancing the performance of diffractive neural networks
Marie Braasch, Anna Kartashova, Sergei Krasikov et al. (+3 more)
Diffractive neural networks (DNNs) are an emerging approach for the realization of photonic artificial intelligence, especially due to their suitability for machine-
vision applications and high-dimensional photonic information processing at lower power consumption. However, incorporating optical nonlinear activation functions to make DNNs a feasible alternative to their electronic counterpart remains a challenge. Here, we investigate the inclusion of second-harmonic generation (SHG), as one of the simplest and most efficient types of optical nonlinearities, in DNNs. We numerically investigate the impact of SHG on the performance of classification tasks in an all-optical nonlinear DNNs. Specifically, we investigate and discuss the essential requirements for an effective arrangement of the SHG layer in single and multilayer DNNs. We find that the performance, in terms of classification accuracy and class contrast, is affected strongly by the positioning of the SHG layer. Finally, we discuss and outline the constraints for including SHG in an experimental realization. Taking these constraints into account, we estimate the power-related efficiency of the nonlinear DNN system. Overall, our results provide a path towards implementing nonlinear DNNs using the SHG process.
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All authors Marie Braasch, Anna Kartashova, Sergei Krasikov, Elena Goi, Thomas Pertsch, Sina Saravi
Optics
Temporal Focusing Enables Distortion-Resistant high-intensity Spatiotemporal Optical Vortices
Jielei Ni, Yao Zhang, Qianyi Wei et al. (+10 more)
Spatiotemporal optical
vortices (STOVs) carry transverse orbital angular momentum and offer new degrees of freedom for light-matter interactions. Yet conventional focusing of STOVs introduces spatiotemporal astigmatism: the beam diffracts while the pulse duration stays constant, causing the
vortex to deform away from focus. Here we overcome this limitation by introducing spectral phase modulation into a temporal focusing configuration, where angular dispersion forces the pulse to compress only at the
geometric focus so that the spatial and temporal dimensions focus and defocus together. Our approach generates stable STOVs with self-similar, distortion-free
evolution over an extended focal region. Besides, the orbital angular momentum vector can be continuously steered from purely longitudinal to strongly tilted orientations by adjusting the spatial dispersion, objective focal length, or input beam size. More importantly, our method offers full compatibility with high NA focusing geometry, allowing high-intensity and high-resolution applications. We validate these properties through femtosecond
laser ablation under high-NA conditions and interferometric spatiotemporal field reconstruction under low-NA conditions.
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All authors Jielei Ni, Yao Zhang, Qianyi Wei, Zhangyu Zhou, Shuoshuo Zhang, Yuquan Zhang, Qi Jin, Zhiyong Tan, Jiahui Pan, Ya Cheng, Qiwen Zhan, Xiaocong Yuan, Changjun Min
Optics
Tailoring the birefringence of femtosecond-laser-written multi-scan waveguides in glass
Roberto Memeo, Davide Piras, Roberto Osellame et al. (+1 more)
Femtosecond-
laser direct waveguide writing is progressively emerging as an alternative to conventional techniques to develop complex photonic devices, for applications ranging from classical and
quantum information processing, to sensing and metrology.
Laser written waveguides typically offer low modal birefringence, thus preserving coherence of polarization-encoded information. Integrated waveplates have been reported, as waveguides with tilted birefringence axis, but with limited flexibility in terms of achievable rotation angle, birefringence magnitude or control in the modal shape. Here we investigate the multi-scan approach to realize low-loss optical waveguides in fused silica substrate with controlled modal birefringence. We show that by tuning the horizontal and vertical shifts between subsequent scans we can independently change both the magnitude and the axis inclination of the birefringence, while keeping efficient mode coupling with standard fibers.
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All authors Roberto Memeo, Davide Piras, Roberto Osellame, Andrea Crespi
Computational Physics
Adaptive finite volume-particle method for free surface flows
Jiawang Zhang, Fengxiang Zhao and Kun Xu
This study proposes a novel adaptive finite volume-particle method (AFVPM) for accurate and efficient free surface flow simulations. The proposed AFVPM synergistically combines the Eulerian finite volume method (FVM) on unstructured meshes with the Lagrangian smoothed particle hydrodynamics (SPH) approach. Specifically, the mesh-based FVM is employed in the bulk flow regions to leverage its computational efficiency and numerical accuracy, while a weakly compressible SPH formulation is applied in the vicinity of the interface to maintain robust free-surface tracking capabilities. A key innovation of this framework is a block-based dynamic and adaptive conversion strategy between Eulerian mesh regions and Lagrangian particle regions and a buffer region-based
cell-particle
algorithm is designed to ensure seamless data communication across the Eulerian mesh-Lagrangian particle interface. Furthermore, isothermal gas-kinetic scheme (GKS) incorporating gravitational effects is utilized to calculate the fluxes in the mesh regions. The performance and reliability of the proposed AFVPM are validated through a series of
benchmark cases that involve complex free surface phenomena. Numerical results demonstrate that AFVPM achieves superior accuracy and efficiency compared to full SPH approaches.
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Fluid Dynamics
A Reaction-Advection-Diffusion Model to describe Non-Uniformities in Colorimetric Sensing using Thin Porous Substrates
Kulkarni Namratha and S. Pushpavanam
Non-uniform product (color) distribution in colorimetric paper-based sensors affects the accuracy and reliability of measurements. The underlying mechanisms responsible for this are still unclear. The coffee ring effect explains the ring-formation at the periphery. However, ring-like patterns can also be found at intermediate radial positions in these sensors. In this work, we study the influence of mass transport and reaction dynamics within porous/paper substrates on the spatial product distribution. We consider one reactant embedded in a porous substrate, which reacts with another delivered through a sessile droplet. The process is modeled in two stages. In Stage 1, droplet imbibition creates two distinct flow domains in the substrate with moving boundaries. Stage 2 commences after complete penetration. Species-substrate interactions are addressed by including a mobility factor. The developed model is used to analyze the effects of different parameters on the product distribution for two configurations, Reagent-Embedded (RE) and Analyte-Embedded (AE). Our work demonstrates ring-like patterns can form even without evaporation effects. With decreasing analyte-reagent concentration ratio, the profile shifts inward. Thicker, more porous substrates yield greater uniformity but reduce color intensity. Immobilization of embedded species enhances uniformity in RE configuration with mobile product, and in AE configuration with immobile product. The model is validated with lead and nitrite detection experiments for RE and AE configurations respectively. It successfully captures three spatial color variations observed experimentally. This study also explains the emergence of multiple rings in these systems. The insights gained are useful for optimizing sensor design and protocols for colorimetry
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Fluid Dynamics
Phase-symmetry breaking as a mechanism for subcritical transition in shell models of turbulence
Yoshiki Hiruta
Subcritical transition to
turbulence, in which the laminar state is linearly stable yet finite-amplitude perturbations develop into
turbulence, is ubiquitous but lacks a simple analytical framework. We demonstrate such a framework using a shell model of
turbulence, in which external forcing breaks the phase
symmetry of the governing equations. This
symmetry breaking suppresses the linear instability of the laminar state, while the energy cascade and spectrum of the developed turbulent state are preserved. A complementary single-triad model admits an exact
elliptic neutral stability curve, revealing that the stabilization depends only on the breaking strength and not on the nonlinear coupling coefficients. Since the phase
symmetry of the shell model corresponds to Galilean invariance in the Navier–Stokes equations, this mechanism may offer a new perspective on subcritical transition in fluid systems.
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Optics
Cascaded Metasurface Interferometer for Multipath Interference with Classical and Quantum Light
Rebecca Aschwanden, Nicolás Claro-Rodríguez, Ruizhe Zhao et al. (+14 more)
Beamsplitters represent fundamental components in both classical and
quantum optical systems, enabling the distribution of light, as well as the generation of interference, superposition and
entanglement. However, optical networks constructed from conventional bulk 2x2-beamsplitters encounter inherent scalability issues, as the number of required beamsplitters scales quadratically with the number of optical modes for a fully connected network. Metasurfaces offer a promising route to overcome these constraints. By manipulating light at the wavelength scale compact optical components with advanced functionalities can be constructed, which address several modes simultaneously. In this work, we design and experimentally utilize a metasurface as a multiport beamsplitter. Furthermore, we realize a multimode interferometer composed of two cascaded metasurfaces. We characterize the individual and cascaded metasurfaces using classical light, showing controllable splitting ratios through tunable phase relations. We then expand the approach to
quantum light, employing single
photons to demonstrate second- and third-order
photon correlations, as well as single
photon interference across multiple spatial paths. These results establish metasurface-based multiport beamsplitters as a scalable and reconfigurable platform bridging classical and
quantum photonics.
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All authors Rebecca Aschwanden, Nicolás Claro-Rodríguez, Ruizhe Zhao, Patricia Kallert, Tobias Krieger, Quirin Buchinger, Saimon F. Covre da Silva, Sandra Stroj, Michele Rota, Sven Höfling, Tobias Huber-Loyola, Armando Rastelli, Rinaldo Trotta, Lingling Huang, Tim Bartley, Klaus D. Jöns, Thomas Zentgraf
Instrumentation and Detectors
Beam Test Characterization of Silicon Microstrip Detector Flight-Model Ladders for the AMS-02 Upgrade
Dexing Miao, Giovanni Ambrosi, Mattia Barbanera et al. (+56 more)
The AMS-02 experiment plans to install a new silicon microstrip tracker layer (Layer-0) on top of the existing detector, increasing the
cosmic-ray acceptance by a factor of 3. Layer-0 employs a design in which multiple silicon microstrip detectors (SSDs) are connected in series to form long detector ladders. We present a detailed performance study of the flight-model ladders using a 350~GeV mixed
hadron beam at the CERN SPS. The study focuses on the following aspects: (i) the performance of ladders with different numbers of SSDs, for which the intrinsic spatial resolution at normal incidence varies from $9.5~\mu\mathrm{m}$ to $11.4~\mu\mathrm{m}$ for ladders composed of 8 to 12 SSDs; (ii) the response consistency for particles impacting on the Head and Tail regions of the ladder; and (iii) the dependence of the detector performance on the particle incidence angle.
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All authors Dexing Miao, Giovanni Ambrosi, Mattia Barbanera, Baasansuren Batsukh, Hengyi Cai, Mengke Cai, Xudong Cai, Yuman Cai, Yuan-Hann Chang, Shanzhen Chen, Hsin-Yi Chou, Xingzhu Cui, Mingyi Dong, Matteo Duranti, Ke Gong, Mingjie Feng, Valerio Formato, Yisheng Fu, Daojin Hong, Maria Ionica, Xiaojie Jiang, Yaozu Jiang, Liangchenglong Jin, Shengjie Jin, Vladimir Koutsenko, Qinze Li, Tiange Li, Zuhao Li, Chih-Hsun Lin, Changcheng Liu, Cong Liu, Hanbing Liu, Pingcheng Liu, Alberto Oliva, Ji Peng, Wenxi Peng, Rui Qiao, Shuqi Sheng, Tianyu Shi, Gianluigi Silvestre, Zetong Sun, Congcong Wang, Feng Wang, Hongbo Wang, Zhijie Wang, Zibing Wu, Zhiyu Xiang, Suyu Xiao, Weiwei Xu, Zixuan Yan, Haotian Yang, Sheng Yang, Yuhang You, Xuhao Yuan, Yuan Yuan, Fengze Zhang, Xiyuan Zhang, Zijun Xu, Jianchun Wang
Instrumentation and Detectors
A Telescope System for Charge and Position Measurement of High Energy Nuclei
Dexing Miao, Zhiyu Xiang, Giovanni Ambrosi et al. (+43 more)
A high-granularity
telescope system with a large sensitive area and low material budget has been developed for high-energy heavy ion beam tests. The
telescope consists of nine layers of silicon microstrip detectors (SSDs), whose performance was validated through a heavy ion beam test at the CERN SPS. A hybrid machine learning
algorithm is proposed to address the challenges of
nuclear charge measurement with SSDs. The system achieves a spatial resolution of $\mathcal{O}(1) \,$\SI{}{\micro\metre} and a charge resolution better than 0.16 charge units for
nuclei from $Z = 1$ to $Z = 29$, with a sensitive area of $8 \times 8 \, \mathrm{cm}^2$. To the best of our knowledge, this represents the most precise charge and spatial resolution simultaneously achieved by a silicon
telescope to date.
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All authors Dexing Miao, Zhiyu Xiang, Giovanni Ambrosi, Mattia Barbanera, Baasansuren Batsukh, Mengke Cai, Xudong Cai, Yuan-Hann Chang, Shanzhen Chen, Hsin-Yi Chou, Xingzhu Cui, Mingyi Dong, Matteo Duranti, Ke Gong, Mingjie Feng, Valerio Formato, Daojin Hong, Maria Ionica, Xiaojie Jiang, Yaozu Jiang, Liangchenglong Jin, Shengjie Jin, Vladimir Koutsenko, Tiange Li, Zuhao Li, Chih-Hsun Lin, Cong Liu, Pingcheng Liu, Xingjian Lv, Alberto Oliva, Ji Peng, Wenxi Peng, Rui Qiao, Shuqi Sheng, Gianluigi Silvestre, Congcong Wang, Feng Wang, Hongbo Wang, Zibing Wu, Suyu Xiao, Weiwei Xu, Sheng Yang, Xuhao Yuan, Xiyuan Zhang, Zijun Xu, Jianchun Wang
Instrumentation and Detectors · Cross-listed from astro-ph.IM
Development of a one-dimensional position sensitive detector for Compton X-ray polarimeters
Abhay Kumar, Santosh V. Vadawale, N. P. S. Mithun et al. (+4 more)
The scientific potential of X-ray polarimetry has long been recognized, but the challenges in measuring polarization have left it largely unexplored, particularly in the hard X-ray regime. While tremendous advancement has been made in soft X-ray polarimetery, the lack of sensitive hard X-ray polarimeters and polarisation measurements continues to limit our understanding of high-energy astrophysical processes. With the development of hard X-ray mirrors, it is now possible to develop a sensitive focal plane hard X-ray polarimeter. One such effort is CXPOL, a prototype developed at PRL, India, which consists of a plastic scintillator as active scatterer readout by PMT surrounded by CsI(Tl) scintillators in cylindrical array with SiPM readout from one side. First results of the prototype have been demonstrated in 20 to 80 keV energy range. The sensitivity of the instrument can be significantly enhanced using faster and better light yield scintillator like NaI as absorbers. Further, the use of a position-sensitive scatterer and absorbers, can also provide spectroscopic information by measuring the interaction position along the length and from the known energy depositions in the detectors. Position sensitive detectors are also helpful in mitigating the systematic effects introduced by the off-axis events in the polarisation measurements. Here, we demonstrate the detection sensitivity in the 100x20x5 mm^3 NaI(Tl) scintillator absorber readout on both ends by SiPM arrays operating in co-incidence. In this work, we characterize the first prototype of this detector system and investigate the variation in energy and position resolution, and light output with irradiation position along the length of the detector. The two end readout in co-incidence also reduces the overall SiPM background per absorber by an order of magnitude, further enhancing the polarimetric sensitivity of the instrument.
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All authors Abhay Kumar, Santosh V. Vadawale, N. P. S. Mithun, Tanmoy Chattopadhyay, S. K. Goyal, A. R. Patel, M. Shanmugam
Atomic and Molecular Clusters
Scaling Dependencies in Irradiation-Driven Molecular Dynamics Simulations: Case Study of W(CO)$_6$ Fragmentation
Soumyo Kheto, Alexey Verkhovtsev, Bobby Antony et al. (+1 more)
Irradiation-driven fragmentation and chemical transformations of organometallic molecules play a central role in nanofabrication techniques based on the use of focused charged-particle beams. In this paper, the electron irradiation-induced fragmentation dynamics of W(CO)$_6$, a commonly used precursor for focused electron beam-induced deposition (FEBID), is investigated using the irradiation-driven molecular dynamics (IDMD) method. Simulations are performed for gas-phase systems with different precursor densities and under different irradiation conditions. The results reveal progressive fragmentation of W(CO)$_6$ molecules into W(CO)$_n$ species, accompanied by the formation of W-rich molecular clusters. The
evolution of fragment abundances shows a strong dependence on both precursor density and electron fluence. Higher densities and larger fluences result in more extensive fragmentation and promote the aggregation of tungsten atoms into small metal clusters. Under certain irradiation conditions, the studied molecular systems evolve towards a steady state characterised by slightly varying fragment abundances. The obtained scaling relations between irradiation parameters and fragment distributions provide guidance for selecting simulation parameters in IDMD simulations of the FEBID process, ensuring a quantitative description of precursor fragmentation dynamics.
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All authors Soumyo Kheto, Alexey Verkhovtsev, Bobby Antony, Andrey V. Solov'yov
Optics
Robust topological BIC nanocavities for upconversion directional emission
Yongqi Chen, Ming Zhu, Qingfeng Bian et al. (+4 more)
Photonic bound states in the continuum (BICs) provide a revolutionary paradigm for boosting light-matter interactions in integrated nanocavity systems. Nevertheless, precise manipulation of open cavity-emitter architectures still faces critical challenges, especially in realizing deterministic directional radiation and suppressing the perturbation of intrinsic cavity modes induced by emitters as local
impurities. Conventional investigations on cavity-emitter coupling are predominantly based on ensemble measurements, which inevitably mask the intrinsic physics underlying individual light-matter interactions. Here, we propose a robust strategy to control the upconversion and emission of a single-particle emitter using a topological plasmonic cavity with broken {\sigma}h mirror
symmetry. This structured design enables the transition from
symmetry-protected BICs to a multi-BIC regime with finite but ultrahigh confinement, where nontrivial phase
evolution and hybridization of transverse electric and
magnetic modes open a well-defined far-field radiation channel for directional emission. Leveraging this scheme, we experimentally demonstrate dramatically enhanced radiation intensity from a single point-like emitter, together with uniform and deterministic directional emission, while achieving excellent structural robustness against local perturbations. This work establishes a general framework for engineering coherent directional light emission at the nanoscale, which lays a solid foundation for high-performance chip-scale integrated nanophotonic applications.
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All authors Yongqi Chen, Ming Zhu, Qingfeng Bian, Xiumei Yin, Wenxin Wang, Bin Dong, Yurui Fang
Geophysics · Cross-listed from cs.CV
GeoNDC: A Queryable Neural Data Cube for Planetary-Scale Earth Observation
Jianbo Qi, Mengyao Li, Baogui Jiang et al. (+3 more)
Satellite Earth observation has accumulated massive spatiotemporal archives essential for monitoring environmental change, yet these remain organized as discrete raster files, making them costly to store, transmit, and query. We present GeoNDC, a queryable neural data cube that encodes planetary-scale Earth observation data as a continuous spatiotemporal implicit neural field, enabling on-demand queries and continuous-time reconstruction without full decompression. Experiments on a 20-year global MODIS MCD43A4 reflectance record ($8016 \times 4008$ pixels, 7 bands, 915 temporal frames) show that the learned representation supports direct spatiotemporal queries on consumer hardware. On Sentinel-2 imagery (10 m), continuous temporal parameterization recovers cloud-free dynamics with high fidelity ($R^2 > 0.85$) under simulated 2-km cloud occlusion. On HiGLASS biophysical products (LAI and FPAR), GeoNDC attains near-perfect accuracy ($R^2 > 0.98$). The representation compresses the 20-year MODIS archive to 0.44\,GB – approximately 95:1 relative to an optimized Int16 baseline – with high spectral fidelity (mean $R^2 > 0.98$, mean RMSE $= 0.021$). These results suggest GeoNDC offers a unified AI-native representation for planetary-scale Earth observation, complementing raw archives with a compact, analysis-ready data layer integrating query, reconstruction, and compression in a single framework.
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All authors Jianbo Qi, Mengyao Li, Baogui Jiang, Yidan Chen, Xihan Mu, Qiao Wang
Optics
Pulse Breathing Dynamics in a Mode-Locked Laser measured via SHG autocorrelation
S. Kannan, S. Padmanaban, X. T. Yan et al. (+4 more)
Pulse-to-pulse fluctuations in mode-locked
lasers fundamentally limit applications from optical frequency combs to supercontinuum generation. While timing jitter has been extensively characterized, pulse amplitude and width fluctuations remain less accessible experimentally. We present a statistical autocorrelation method that demonstrates pulse breathing dynamics through Fano factor analysis of second-harmonic generation autocorrelation. This reveals a characteristic W-shape in the enhanced Fano profile, a signature of pulse shape dynamics that is invisible to time-averaged fluctuations. Applying this method to two commercially available passively mode-locked oscillators operating at 1030 nm and 1045 nm, with different performance specifications, we measure pulse width fluctuations of 3.2(1)\,fs and 2.86(2)\,fs respectively. The two independent instruments serve as a cross-validation of the technique across different
laser platforms. This diagnostic capability opens the door to identifying and suppressing specific breathing mechanisms, paving the way for the design of ultra-stable oscillators required for precision frequency metrology.
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All authors S. Kannan, S. Padmanaban, X. T. Yan, Y. S. Athreya, K. G. H. Baldwin, S. S. Hodgman, A. G. Truscott
Applied Physics
Near-Field Coupling of Polypropylene Dielectric Waveguide Routed Near PCB Board at Terahertz Frequencies
Wenbo Liu, Jiabiao Zhao, Kefeng Huang et al. (+5 more)
The growing demand for high-capacity, low-loss short-reach links in highly integrated electronic systems makes it necessary to understand how terahertz (THz) dielectric waveguides behave in realistic PCB-level packaging environments. In this article, we investigate the channel transmission of a 3D-printed polypropylene dielectric waveguide placed near representative PCB substrates. Continuous-wave THz measurements are carried out for bare, fully copper-clad, and periodic copper-trTerahertz (THz) dielectric waveguides are promising physical channels for short-reach interconnects, but their air-clad guided fields may interact with nearby printed-
circuit-board (PCB) structures in compact packages. In this work, we experimentally and numerically investigate PCB-proximity-induced excess transmission loss in 3D-printed polypropylene rectangular dielectric waveguides over 220-325 GHz. Continuous-wave transmission measurements are performed for bare FR4, continuous waveguide-facing copper, and periodic copper-trace PCB configurations under controlled clearance and
alignment conditions. The results show that direct contact with bare FR4 can induce a frequency-selective high-loss band, which is attributed to phase-matched leakage from the guided waveguide mode into a substrate-supported leaky branch. This finding highlights PCB proximity as a critical layout factor and provides practical guidance for clearance control and metallization design in compact THz dielectric-waveguide packages.ace PCBs with different waveguide-PCB separations, while terahertz time-domain spectroscopy is used to characterize the dielectric properties of the substrate materials.
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All authors Wenbo Liu, Jiabiao Zhao, Kefeng Huang, Peian Li, Boquan Xu, Yang Cao, Weidong Hu, Jianjun Ma
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Forster energy transfer boosts indirect anisotropic interlayer excitons in 2L-MoSe2/perovskite heterostructures
Yingying Chen, Zihao Jiao, Haizhen Wang et al. (+1 more)
Interlayer
excitons (IXs) in two-dimensional (2D) van der Waals
heterostructures have attracted considerable
attention due to their unique optical and electronic properties. Owing to the spatially indirect nature, the radiative emission efficiency highly sensitive to interlayer twist angles. Further considering that their uniformly oriented out-of-plane dipole moments limit directional emission, strategies to simultaneously improve emission efficiency and induce optical anisotropy warrant in-depth investigation. In this work, we report significant photoluminescence (PL) enhancement and optical anisotropy of IXs in 2L-MoSe2/perovskite
heterostructures mediated by energy transfer from ReS2. We attribute this enhancement to Forster resonance energy transfer (FRET), which increases the 2L-MoSe2 emission by approximately eight-fold at room temperature, and nearly doubles the emission intensity of momentum-indirect IXs in 2L-MoSe2/perovskite
heterostructures at 78 K. Importantly, the optical anisotropy of ReS2 can be effectively imprinted onto 2L-MoSe2 and associated indirect IXs during the energy transfer process, yielding a linear dichroism of approximately 1.1 for both intralayer
excitons and IXs with identical polarization directions. These findings expand the scope of IX study beyond direct bandgap materials with strong intrinsic emission to include systems with indirect bandgaps, offering new avenues for realizing high-performance polarization-sensitive optoelectronic devices.
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All authors Yingying Chen, Zihao Jiao, Haizhen Wang, Dehui Li
Chemical Physics
A sustainable photocatalytic pathway for concurrent hydrogen and value-added chemical production utilizing microalgae as bio-scavenger in water
Ho Truong Nam Hai, Augusto Ducati Luchessi and Kaveh Edalati
Microalgae are an abundant bioorganic material source and play a significant role in life on Earth by conducting photosynthesis for carbon dioxide (CO2) capture and its conversion to oxygen (O2). In this study, a combination of microalgae as a negative-CO2-emitting sacrificial
agent with the traditional photocatalytic water-splitting process using brookite TiO2, as a model photocatalyst, is introduced as a new strategy to maximize green hydrogen (H2) production while converting microalgae to valuable products, like methane (CH4) and carbon monoxide (CO). The process, under optimal conditions, produces up to 0.990 mmol/g.h of H2 without cocatalyst addition and 3.200 mmol/g.h with platinum (Pt) cocatalyst, which is 13 times higher than the production rate without microalgae. The strategy of using microalgae in photocatalysis has high potential in green H2 production, as it not only eliminates valuable hole sacrificial
agents, like alcohol, but also produces other useful compounds, like CH4 and CO. Moreover, this sustainable process contributes to CO2 capture and conversion during microalgae cultivation.
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Medical Physics
Robust Multicenter CT Radiogenomics for Dual EGFR and KRAS Prediction in Lung Cancer with Stability-Aware Modeling and SHAP Interpretation
Somayeh Sadat Mehrnia, Fatemeh Razavi, Helia Abedini et al. (+3 more)
Accurate identification of EGFR and KRAS mutations is essential for precision therapy in non-small
cell lung cancer (NSCLC), but tissue genotyping is invasive and may not capture tumor heterogeneity. CT-based radiogenomics offers a noninvasive alternative, although generalization across centers remains challenging. We benchmarked handcrafted radiomics features (HRF), deep feature representations (DFR), and their fusion for three-class mutation prediction (wild-type, KRAS-mutant, and EGFR-mutant) with external testing. We curated 1,023 thoracic CT scans from 12 public
datasets across more than 20 centers, including 136 patients with EGFR/KRAS labels. IBSI-compliant HRFs were extracted with standardized preprocessing, and DFRs were derived using PySERA. HRF-only, DFR-only, and fused HRF+DFR pipelines were evaluated using five-fold cross-validation and external testing. A semi-supervised pseudo-labeling strategy leveraged unlabeled CT scans, and SHAP supported interpretability. In external testing, HRF-based models generalized best, achieving AUC 0.77 +/- 0.07 and accuracy 0.77 +/- 0.00. DFR-based models showed a larger drop from cross-validation to external testing, with best external AUC around 0.57 +/- 0.05. Fusion improved robustness over DFR-only models but did not consistently outperform HRFs. SHAP identified morphology- and heterogeneity-related radiomic phenotypes as key predictors. Standardized handcrafted radiomics within a multicenter semi-supervised framework may provide a generalizable and interpretable approach for CT-based EGFR/KRAS stratification.
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All authors Somayeh Sadat Mehrnia, Fatemeh Razavi, Helia Abedini, Niloofar Rahimi, Arman Rahmim, Mohammad Salmanpour
Atomic Physics
Sensing T-violating nuclear moments of paramagnetic ions in crystals
Aleksandar Radak, Mingyu Fan, Bassam Nima et al. (+2 more)
Precision measurements of time-reversal (T)
symmetry violating moments probe physics beyond the Standard Model. We show that precision spectroscopy of paramagnetic lanthanide and actinide ions doped into noncentrosymmetric
crystals offers a promising platform for extending the sensitivity of searches for T-violation in
nuclear physics. The unpaired valence electron in these ions allows the engineering of highly-coherent hyperfine transitions that are insensitive to
magnetic fields, yet highly sensitive to new physics. These systems also provide other advantages for new physics searches, including large numbers of ions that can be measured in doped
crystals, strong electric polarization of the ions by the
crystal fields, enhancement of T-violating
nuclear moments in nonspherical
nuclei, and accurate comagnetometers generated by
crystal symmetry. We estimate the new physics sensitivity of these proposed systems to be two orders of magnitude better than existing constraints.
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All authors Aleksandar Radak, Mingyu Fan, Bassam Nima, Yuiki Takahashi, Amar Vutha
Fluid Dynamics
Data-Driven Modal Decomposition Analysis of Unsteady Flow in a Multi-Stage Turbine
Yalu Zhu and Feng Liu
Two data-driven modal analysis approaches, proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), are applied to analyze the unsteady flow obtained by solving the Reynolds-averaged Navier-Stokes (RANS) equations in a 1.5-stage axial turbine. The reduced-order reconstructed pressure, dominant mode shapes, and dynamic features of these dominant modes in the downstream stator of the turbine are compared between POD and four DMD variants. It is found that the DMD methods based on the amplitude criterion, the Tissot criterion, and the sparsity-promoting DMD (SP-DMD) achieve reconstruction accuracy comparable to that of POD, while the frequency criterion proves unsuitable for the present problem. The second and third POD and DMD modes capture the dominant pressure fluctuation structures within the stator, and there is similarity between the corresponding POD and DMD spatial modes. The unsteady flow is primarily governed by neutral DMD modes characterized by high amplitudes and low frequencies corresponding to the basic and harmonic frequencies driven by the rotor passing frequency. While the POD analysis provides accurate reconstruction for the original snapshots, the time
evolution of each POD mode does not reflect the true dynamic feature of the system. In particular, they misrepresent the fundamental frequencies of the problem. In addition, the correlations between the dominant modes in the downstream stator and the turbine adiabatic efficiency are explored across different stator clocking configurations. It is found that a clocking configuration with higher adiabatic efficiency at 50% span corresponds to a larger spatial and time component of the second and third DMD mode pair, and similarly a larger second POD mode.
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Medical Physics
Quantitative Chemical Exchange Saturation Transfer Imaging with Golden-Angle Radial k-Space and Locally Low-Rank Reconstruction
Ouri Cohen, Elizabeth J. Sutton, Robert J. Young et al. (+1 more)
Chemical exchange saturation transfer
magnetic resonance fingerprinting (CEST-MRF) is a promising quantitative molecular imaging technique. To reduce scan time, current CEST-MRF implementations typically use echo-planar imaging (EPI) readouts, which are prone to
geometric distortion and signal dropout. In this study, we developed a motion-robust geometrically accurate CEST-MRF method using radial k-space sampling, locally low-rank reconstruction, and neural network-based quantification. The acquisition schedule was optimized using deep learning, and its accuracy was validated in numerical simulations with digital phantoms. The number of spokes per measurement was determined through simulations and in vivo ablation studies in healthy volunteers. Five healthy subjects underwent repeated scans, and regions of interest were defined for analysis. Tissue maps generated with the proposed method were compared with values obtained from nonlinear least-squares (NLS) fitting of multi-saturation-power z-spectra. Motion sensitivity and test-retest reproducibility were evaluated using the coefficient of variation (CV) and intraclass correlation coefficient (ICC). Clinical feasibility was demonstrated in a subject with a history of remote middle cerebral artery infarction. The results show that 3D quantitative CEST maps can be acquired in 11 minutes using 34 spokes per measurement. Numerical simulations yielded mean errors below 14% for all tissue parameters, while in vivo parameter estimates agreed well with both NLS-derived values and prior
brain CEST-MRF studies. The mean ICC across all tissue maps was 0.92 in white matter and 0.87 in gray matter, with mean inter-subject CVs of 5.4% and 3.4%, respectively. For the radial acquisition, the mean error between motion and no-motion conditions was 8.6%. Changes in CEST-MRF tissue parameters were consistent with clinically diagnosed cystic gliosis.
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All authors Ouri Cohen, Elizabeth J. Sutton, Robert J. Young, Ricardo Otazo