Fluid Dynamics
Resonance behavior of a bubble near a spherical inclusion
Thomas Micol, Alexander A. Doinikov, Cyril Mauger et al. (+1 more)
We present an analytical model for the frequency response of a gas microbubble oscillating near a spherical inclusion of arbitrary size and mechanical nature (rigid, fluid, or viscoelastic) immersed in a viscous compressible fluid. The model considers both radial and nonspherical oscillations in the linear regime and predicts how their resonance frequencies and oscillation amplitudes are altered by the bubble size, material properties, and distance to the nearby sphere. As a key application, we demonstrate that scanning the frequency response of a bubble near a viscoelastic object, such as an erythrocyte-like particle mimicking a biological
cell, offers a way to recover its mechanical properties through inverse modeling, opening new possibilities for high-resolution elastography at the microscale.
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All authors Thomas Micol, Alexander A. Doinikov, Cyril Mauger, Claude Inserra
Applied Physics
Guided progressive reconstructive imaging: a new quantization-based framework for low-dose, high-throughput and real-time analytical ptychography
Hoelen L. Lalandec Robert, Arno Annys, Tamazouzt Chennit et al. (+1 more)
By profiting from recent developments in detector technologies, making it possible to access a stream of detection events with few-ns time resolutions, a new ptychographic workflow is established. This methodological framework, referred to as guided progressive reconstructive imaging, relies on a quantization-based description of the acquired intensity, through an elementary derivation. Established direct phase
retrieval solutions, such as the Wigner distribution deconvolution approach, can then be adapted to a continuous treatment of received counts, with no need for a dense data representation. Consequently, the result is obtained in the form of a progressively improving estimate, while providing immediate user feedback thanks to a processing speed high enough to surpass the acquisition bandwidth. This fast measurement is enabled by the cumulative usage of a pre-calculated library of kernel-limited functions, accumulating count-wise contributions as a function of the triggered detector pixel. Hence, the reconstruction offers the same advantages of direct phase
retrieval methods, in particular a high dose-efficiency and the absence of complex convergence dynamics, with much less stringent restrictions on the field of view than is typical in current alternatives. Its implementation is also significantly more straightforward and flexible. Overall, this work constitutes a major
evolution in the state-of-the-art, facilitating repeatable and low-dose experiments with high accessibility, and being applicable to electron-based imaging, X-ray diffraction and optical microscopy.
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All authors Hoelen L. Lalandec Robert, Arno Annys, Tamazouzt Chennit, Jo Verbeeck
Optics
Enhanced and directional light emission from two-dimensional excitons using Mie voids
Avishek Sarbajna, Ganesh Ghimire, Ilia Breev et al. (+5 more)
Controlling light emission at the nanoscale has important applications in solid-state lighting, displays, and
quantum light sources. Achieving this control requires both enhanced local electromagnetic fields to boost emission intensity and engineered radiation patterns to direct
photons efficiently. Mie voids, consisting of an air cavity surrounded by a high-index
semiconductor, are particularly suited for this purpose because they expose their strongest fields in an accessible region for nearby emitters while supporting resonances that shape directional emission through interference. Here, we demonstrate an all-van der Waals nanophotonic platform that couples
excitons in atomically thin WS$_2$ to Mie void resonators formed in WSe$_2$. Guided by electromagnetic simulations, we identify void geometries that maximize photoluminescence through synergistic enhancement of excitation and emission processes. We also develop a two-step fabrication strategy that enables independent control of void diameter and depth, providing a route to systematically tune the optical response. Experimentally, we observe up to a 600-fold increase in photoluminescence intensity from monolayer WS$_2$ placed on individual voids compared to on an unstructured WSe$_2$, along with pronounced out-of-plane beaming of light that yields a forward-to-off-axis enhancement of 2.6 dB. Our results establish Mie voids in van der Waals
semiconductors as a new platform for controlling light-matter interactions and realizing compact, directional, and efficient nanoscale light sources.
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All authors Avishek Sarbajna, Ganesh Ghimire, Ilia Breev, Xavier Zambrana-Puyalto, Cheng Xiang, Alexander Huck, Timothy J. Booth, Søren Raza
Optics
Fully stabilized 25 GHz frequency comb for frequency calibration of optical spectrum analyzer
Yoonkwon On, Dae Hee Kim, Sujin Kim et al. (+5 more)
Optical spectrometers are widely used in scientific and industrial applications, and precise frequency calibration is essential for ensuring their reliable performance. Traditionally, spectrometers have been calibrated using reference gas
cells or reference lamps. However, such conventional methods are not enough to meet the demands for high accuracy and stability. Although frequency-stabilized
lasers offer excellent frequency uncertainty, they provide only a single calibration point at a fixed frequency, which is unsuitable for wide-range spectrometer calibration. In this work, we demonstrate a fully stabilized, high-repetition rate electro-optic frequency comb (EO comb) as an absolute frequency reference providing multiple calibration points over a broad spectral range. Our 25 GHz EO comb provides a broadband spectrum spanning from 189.5 THz to 196 THz (corresponding to 1530 nm to 1582 nm), traceable to a frequency standard with a relative standard uncertainty of 10^-13. The well-defined and evenly spaced comb modes can be spectrally resolved by conventional optical spectrometers, enabling wide-range, high-precision frequency calibration. We directly calibrated a commercial spectrometer by referencing its measured frequency values to our well-defined comb modes, thereby evaluating the frequency error with a standard uncertainty of 20 MHz (or relative standard uncertainty of 10^-7), which is limited by the Type A uncertainty (repeatability) of the spectrometer. The proposed method is simple to implement and provides multiple calibration points referenced to the frequency standards over a broad spectral range. This approach improves both the calibration and performance evaluation of spectrometers, and it contributes to the advancement of optical metrology.
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All authors Yoonkwon On, Dae Hee Kim, Sujin Kim, Yong Jin Kim, Jong-Ahn Kim, Sunghoon Eom, Jae Yong Lee, Yoon-Soo Jang
Fluid Dynamics
The HydroGym Reinforcement Learning Platform for Fluid Dynamics
Christian Lagemann, Sajeda Mokbel, Miro Gondrum et al. (+18 more)
Modeling and controlling fluids is critical across science and engineering. Effective flow control can increase lift, reduce drag, enhance mixing, and attenuate noise, potentially unlocking new technologies. Yet controlling fluids is hard: the dynamics are high-dimensional, nonlinear, and multiscale. While reinforcement learning (RL) has recently succeeded in robotics and
protein folding through shared
benchmarks, fluid dynamics has resisted such progress: each controller is typically tuned to a single geometry and operating point, making results hard to accumulate, transfer, and compare. We introduce HydroGym, a solver-independent RL platform for flow control, and show that standardized infrastructure unlocks transferable control intelligence across flow regimes. HydroGym provides 61+ validated environments spanning laminar to turbulent flows, with systematic Reynolds number progressions up to Re=400,000 and Mach number variations in 2D and 3D. It supports diverse backends, including finite-volume, spectral-element, finite-element,
lattice-Boltzmann, and fully differentiable solvers for gradient-enhanced optimization. Across environments, RL
agents consistently discover robust control principles, such as boundary-layer manipulation, acoustic-feedback disruption, and wake reorganization, yielding drag reductions exceeding 90% in canonical configurations. Critically, we demonstrate zero-shot transfer:
agents trained only on a simplified channel flow achieve 38% friction-drag reduction on an unseen 3D wing section at chord Reynolds number Re=200,000 reducing exploration costs by four orders of magnitude versus direct on-wing optimization. This suggests RL
agents uncover essential physics rather than configuration-specific patterns, pointing toward generalizable control. HydroGym offers extensible, scalable community infrastructure for fluid dynamics, machine learning, and control research.
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All authors Christian Lagemann, Sajeda Mokbel, Miro Gondrum, Mario Rüttgers, Yuning Wang, Pol Suárez, Ludger Paehler, Deniz A. Bezgin, Aaron B. Buhendwa, Jared L. Callaham, Samuel Ahnert, Nicholas Zolman, Xiao Shao, Jean-Christophe Loiseau, Nikolaus Adams, Matthias Meinke, Wolfgang Schröder, Kai Lagemann, Esther Lagemann, Ricardo Vinuesa, Steven L. Brunton
Plasma Physics
H-mode transition in the TJ-II stellarator plasmas
T. Estrada and C. Hidalgo
Since the first H-mode transitions were observed in TJ-II
plasmas in 2008, an extensive experimental effort has been done aiming a better physics understanding of confinement transitions. In this paper, an overview of the main findings related to the L-H transition in TJ-II is presented including how the radial electric field is driven, which are the possible mechanisms for
turbulence suppression, and what are the related temporal and spatial scales which can impact the transition. The trigger of the L-H transition in TJ-II
plasmas is found to be more correlated with the development of fluctuating $E\times B$ flows than with steady-state $E_r$ effects, pointing to the role played by zonal flows in mediating the transition. Experimental evidence supporting the predator-prey relationship between
turbulence and flows as the basis for the L-H transition, found for the first time in TJ-II, reinforces this conclusion. Besides, the reduction in the turbulent transport at the transition is detected at the barrier region but also in a wider radial range with weak or even zero $E\times B$ flow shear, what points to other mechanisms beyond the
turbulence suppression by local sheared flows.
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Optics · Cross-listed from quant-ph
Autonomous Picosecond-Precision Synchronization in Measurement-Device-Independent Quantum Key Distribution
A. P. Pljonkin
Measurement-device-independent
quantum key distribution (MDI-QKD) eliminates detector side-channel attacks by relocating all measurements to an untrusted intermediate node. However, its practical implementation critically relies on picosecond-level temporal synchronization between spatially separated users. In this work, we present a physically motivated autonomous synchronization
algorithm for fiber-based MDI-QKD networks that does not require auxiliary optical channels or shared clock references. The method exploits round-trip optical pulse propagation and statistical signal detection in the presence of Gaussian noise. We derive analytical expressions for false-alarm probabilities, quantify detection reliability, and demonstrate through numerical modeling that synchronization accuracy better than 10~ps is achievable for channel lengths up to 100~km with realistic optical power levels. The proposed approach improves the scalability and robustness of MDI-QKD architectures and is directly applicable to metropolitan and backbone
quantum networks.
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Instrumentation and Detectors
Discretized Halbach spheres: Icosahedral symmetry for optimal field homogeneity
Ingo Rehberg and Peter Blümler
Halbach spheres provide a theoretically elegant means of generating highly homogeneous
magnetic fields, but practical implementation is hindered by challenging fabrication and restricted interior access. This study examines discrete spherical Halbach configurations assembled from permanent magnets placed at the vertices of Platonic and Archimedean solids. Analytical calculations, numerical field simulations, and experimental measurements indicate that polyhedra with icosahedral
symmetry achieve the most favorable balance among field strength, homogeneity, and interior accessibility. They produce exceptionally flat fourth-order central saddle points, resulting in a usable homogeneous field volume up to a factor of 260 larger than that of traditional Halbach disk or cylindrical arrays. Several magnet assemblies composed of cubical NdFeB magnets are fabricated and their three dimensional field distributions characterized, demonstrating homogeneous regions of up to several cubic centimeters with deviations below 1%. The findings establish discrete icosahedrally symmetric magnet arrays as practical, scalable building blocks for compact, highly homogeneous
magnetic field sources suited to mobile
magnetic resonance, and magnetophoretic applications.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
Bandgap Engineering for Efficient Perovskite Solar Cells Under Multiple Color Temperature Indoor Lighting
Miqad S. Albishi, Faisal I. Alabdulkarem, George Perrakis et al. (+20 more)
Perovskite indoor photovoltaics (PIPVs) are emerging as a transformative technology for low-light intensity energy harvesting, owing to their high power conversion efficiencies (PCEs), low-cost fabrication, solution-processability, and compositionally tunable band gaps. In this work, methylammonium-free perovskite absorbers were compositionally engineered to achieve band gaps of 1.55, 1.72, and 1.88 eV, enabling matching the spectral photoresponse with the indoor lighting. Devices based on a scalable mesoscopic n-i-p architecture were systematically evaluated under white LED illumination across correlated color temperatures (3000-5500 K) and light intensities from 250 to 1000 lux with active area of 1 cm2. The 1.72 eV composition exhibited the most promising performance across different light intensities and colors, achieving PCEs of 35.04 % at 1000 lux and 36.6 % at 250 lux, with a stable device operation of over 2000 hours. On the other hand, the 1.88 eV band-gap variant reached a peak PCE of 37.4 % under 250 lux (5500 K), however performance trade-offs were observed across the different color lights LEDs. Our combined experimental and theoretical optical-electrical simulations suggest that decreasing trap-assisted recombination in wide-bandgap compositions may further improve PIPV performance across the different illumination conditions. In contrast, devices with 1.55 eV band gap underperformed in such conditions due to suboptimal spectral overlap and utilization. These findings establish bandgap optimization and device architecture as key design principles for high-efficiency, stable PIPVs, advancing their integration into self-powered electronic systems and innovative indoor environments.
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All authors Miqad S. Albishi, Faisal I. Alabdulkarem, George Perrakis, Tariq F. Alhuwaymel, Ala H. Sabeeh, Abdullah S. Alharbi, Naif R. Alshamrani, Ibrahim H. Khawaji, Nikolaos Tzoganakis, Majed M. Aljomah, Dimitris Tsikritzis, Sami A. Alhusaini, Abdullah Aljalalah, Kadi S. AlShebl, Ali Alanzi, Abrar Bin Ajaj, Fay M. Alotaibi, Hamad Albrithen, Konstantinos Petridis, Maria Kafesaki, Emmanuel Kymakis, George Kakavelakis, Essa A. Alharbi
Fluid Dynamics
Transient and periodic shear wave propagation in a solid-fluid coupled system
Aaron D'Cruz and Pierre Ricco
A coupled system composed of a Newtonian fluid located on a sinusoidally-forced elastic solid is studied analytically and numerically. The focus is on the transient
evolution from the beginning of the forced oscillations and on the periodic behaviour established once the transient has vanished. The analytical solution is expressed as series summations that elucidate the propagation and reflections of elastic transverse waves through the solid layer and the viscous dissipation of oscillations in the fluid layer. Short-term transients in both the fluid and the solid form at every interaction between an elastic wave and a solid boundary. The long-term transient, quantified by the power balance in the fluid layer, instead pertains to the formation of all the elastic waves in the solid layer. The system can be viewed as a generalised transient Stokes layer generated by the elastic waves or as a damped resonant oscillator when the velocity at the fluid-solid interface increases significantly with respect to the forcing amplitude. A parametric study is carried out for three applications of technological interest, i.e. the indirect measurement of fluid viscosity, the turbulent drag reduction by travelling shear waves and the sensing and manipulation of biological flows.
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Optics
An Integrated DFT-FDTD Design of Plasmon-Enhanced Lead-Free $CsSn$$_x$$Ge$$_{1-x}$$I$$_3$ Perovskite LEDs
Shoumik Debnath, Sudipta Saha, Khondokar Zahin et al. (+2 more)
CsSn$_x$Ge$_{1-x}$I$_3$ as lead-free perovskites are promising for next generation NIR emitting perovskite LEDs due to their tunable bandgaps and stability. However, they suffer from poor light extraction efficiency, and accurate composition-specific optical data for these materials remain scarce. This study presents a DFT-FDTD framework to optimize light extraction via compositional tuning and plasmonic enhancement. First, DFT calculations were performed to obtain composition-specific complex refractive index and extinction coefficient values for $x = 0, 0.25, 0.5, 0.75$, and $1$. Results show bandgap increased from 1.331 eV for CsSnI$_3$ to 1.927 eV for CsGeI$_3$ with increasing Ge content, while refractive index ranges from 2.2 to 2.6 across compositions. These optical constants were then used as inputs for FDTD simulations of a PeLED structure with optimized Au/SiO$_2$ core-shell nanorods for plasmonic enhancement. A 12.1-fold Purcell enhancement was achieved for CsSn$_{0.25}$Ge$_{0.75}$I$_3$, while light extraction efficiency reached 25% for CsSn$_{0.5}$Ge$_{0.5}$I$_3$. LEE enhancement of 36% was obtained for CsSnI$_3$, and spectral overlap between emitter and plasmon resonance reached 96% for Sn-rich compositions. Design guidelines indicate CsSn$_{0.5}$Ge$_{0.5}$I$_3$ offers optimal balance of extraction efficiency (25%), Purcell enhancement (5.3$\times$), spectral overlap (93%), and oxidation stability for wearable and flexible optoelectronic applications, while CsSn$_{0.25}$Ge$_{0.75}$I$_3$ is recommended for applications prioritizing spontaneous emission rate.
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All authors Shoumik Debnath, Sudipta Saha, Khondokar Zahin, Ying Yin Tsui, Md. Zahurul Islam
Applied Physics
Tailored Zn(1-x)TixAl2O4 Nanocomposite Particles via Sol-Gel Route for High-Performance Humidity Sensing
Ramalakshmi K, Sasmita Dash and Srilali Siragam
Humidity sensors play a vital role in industrial, healthcare, agricultural, and environmental applications; however, conventional sensors often suffer from issues like low sensitivity, slow response, and poor stability. This study investigates sol-gel synthesized Zn0.85Ti0.15Al2O4 nanocomposite ceramics for high-performance humidity sensing. X-ray Diffraction (XRD) analysis confirms a nanocrystalline structure, while the optical bandgap of 3.76 eV indicates the enhanced sensing potential. The sensor exhibits a significant decrease in resistance, from 500 M{\Omega} (15% RH) to 90 M{\Omega}(90% RH), with fast response (50 s) and recovery times (50 s). Low Hysteresis values (5.86% at 30% RH, 7.69% at 60% RH, and 4.28% at 90% RH) highlight high sensitivity, stability, and repeatability. These results indicate the potential of Zn0.85Ti0.15Al2O4as a promising material for next-generation resistive humidity sensors suitable for commercial and industrial deployment.
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Fluid Dynamics
On the essential structure of exact traveling-wave solutions in viscoelastic flow
Lu Zhu and Rich. R. Kerswell
We examine elastic travelling-wave (`arrowhead') solutions in a viscoelastic, unidirectionally body-forced flow, focusing on their existence and morphological changes as the Weissenberg number, $\mathrm{Wi}$, and streamwise duct length, $L$, are varied. We find that branch
topology varies from an isola at low $L$ through a two-sided reconnection at intermediate $L$ to a branch which exists at asymptotically large $\mathrm{Wi}$ for larger $L$. At intermediate $L$ more than two arrowhead solutions can coexist at a given $(\mathrm{Wi}, L)$ choice due to extra saddle node bifurcations. Secondly, the canonical arrowhead consists of two legs joined by an arched head that blocks throughflow and traps a counter-rotating
vortex pair, while a
polymer strand can emerge as a by-product of a strong extensional region attached/detached to the arrowhead arch. Thirdly, a minimal domain length $L_{\min}$ required to sustain an arrowhead is found to vary non-monotonically with $\mathrm{Wi}$; for $\mathrm{Wi}\ge 20$, detached-strand states control $L_{\min}$ with a relation $L_{\min}\approx 0.125\mathrm{Wi}+1.5$. And fourthly, in sufficiently long domains, the upper branch becomes a localised single arrowhead whose streamwise extent depends on $\mathrm{Wi}$, whereas the lower branch can proliferate into a train of arrowheads at high $\mathrm{Wi}$, a phenomenon not previously reported.
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Computational Physics · Cross-listed from cond-mat.mtrl-sci
Magnetic, Structural, and Electronic Properties of CrOCl with the PBE Functional
Brahim Marfoua, Mohammad Amirabbasi and Marcus Ekholm
CrOCl is a van der Waals-layered
insulator with an
antiferromagnetic ground state, making it a promising platform for exfoliation and the exploration of low-dimensional magnetism. An accurate ab initio description is therefore essential. Previous density-functional studies have shown that DFT+$U$ calculations may erroneously favor
ferromagnetic order depending on the choice of parametrization, an issue that cannot be remedied by simply adjusting the value of $U$. Here, we demonstrate that an explicit Hubbard correction is unnecessary: the PBE functional correctly reproduces the AFM ground state while simultaneously improving the description of structural properties. Moreover, PBE provides a reliable account of the electronic structure. These findings clarify the role of correlation effects in CrOCl and identify PBE as a robust starting point for future ab initio studies of CrOCl-based materials.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
Eliminating the irregular surface layer of anodically-grown Ni-Ti-O nanopore arrays in a two-stage anodization
S.A. Mousavi, A. Moshfeghi, F. Davoodian et al. (+1 more)
Nanopores (NPs) grown by anodizing can be partially hidden beneath a relatively compact surface
oxide layer, which limits the volumetric surface area of these nanostructures. In this work, nitinol (NiTi)
alloy was anodized in an electrolyte containing ethylene glycol, water, and sodium chloride in static and stirred electrolyte stages with the aim of removing the irregular surface array while achieving a thick NP layer. Electron micrographs showed that anodization in the static electrolyte provides a controlled thickness of NP layers covered by an irregular surface layer. In contrast, anodizing in the stirred electrolyte reduced the thickness and the degree of irregularity, which were controlled by the different kinetics of dissolution at the tops, perimeters and bottoms of NPs. To benefit simultaneously from the thickness and regularity of the
oxide layers, two-stage anodizing under static and then stirred electrolyte conditions was found to be effective. Following a 30 min anodization in the static electrolyte, anodizing for 30 min under the stirred conditions provided the highest regularity in the
oxide array, resulting in NPs of almost 40 nm and 11 {\mu}m in diameter and layer thickness, respectively. Two-stage anodizing under static then stirred electrolyte conditions is proposed in order to promote NP structures for applications demanding higher surface areas.
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All authors S.A. Mousavi, A. Moshfeghi, F. Davoodian, E. Salahinejad
Instrumentation and Detectors
In situ substrate birefringence characterization in gravitational wave detectors using a heterodyne polarimetry method
Satoshi Tanioka, Terri Pearce, Yuta Michimura et al. (+6 more)
High-quality test mass substrates play essential roles in
laser interferometric gravitational wave detectors. Inhomogeneous birefringence distribution in test mass substrates, however, can degrade the sensitivity of the detector by introducing the optical loss and disturbing the interferometer controls. In this paper, we present a heterodyne polarimetry method that enables in situ birefringence characterizations, hence diagnosing the gravitational wave interferometer. We experimentally demonstrate the proposed method with a tabletop setup. We also discuss its applicability to current and future gravitational wave detectors and the detectable limit.
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All authors Satoshi Tanioka, Terri Pearce, Yuta Michimura, Kazuhiro Agatsuma, Martin Van Beuzekom, Alberto Vecchio, Stephen Webster, Matteo Leonardi, Keiko Kokeyama
Applied Physics · Cross-listed from cond-mat.mtrl-sci
Comparative analysis of electrodeposited Pt, Ru and Pt-Ru overlays for high-temperature oxidation protection
Majid Hosseinzadeh and Erfan Salahinejad
Platinum (Pt) and ruthenium (Ru), both members of the platinum-group metals (PGMs), are renowned for their exceptional resistance to corrosion, oxidation, and high temperatures, making them promising candidates for advanced high-temperature applications. This study investigates the direct current (DC) electrodeposition of Pt, Ru, and a binary Pt-Ru
alloy onto NiCoCrAlYTa-coated single-
crystal superalloy CMSX-4, along with their
vacuum annealing and respective effects on the isothermal oxidation behavior of the system at 1100 {\deg}C. All the electrodeposited overlays demonstrated substantial enhancement in oxidation resistance. However, Pt exhibited the highest protection efficiency, Ru the least, and the Pt-Ru
alloy provided an intermediate level of performance. Microscopic and X-ray diffraction analyses revealed that the competitive formation of protective {\alpha}-Al2O3 and spinel NiAl2O4 phases on the coated surfaces played a crucial role in determining the oxidation resistance, driven by atomic interactions between the elements in the NiCoCrAlYTa bond coat and the overlay metals. Despite Ru's relatively lower oxidation resistance compared to Pt, its significantly lower cost offers potential advantages in cost-sensitive, high-temperature applications. These findings provide valuable insights into optimizing Pt-group metal coatings for durability in high-performance systems.
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Applied Physics · Cross-listed from cond-mat.mtrl-sci
Influence of Pt/Ru ratios on the oxidation mechanism of MCrAlYTa coatings modified with Pt-Ru overlays
Majid Hosseinzadeh and Erfan Salahinejad
This study investigates the influence of varying Pt/Ru ratios on the oxidation mechanism of NiCoCrAlYTa coatings with electrodeposited,
vacuum-annealed Ptsingle bondRu overlays. Weight change measurements, scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used for high-temperature oxidation analyses, showing superior resistance with higher Pt contents. This was attributed to the creation of a denser, thinner, and more homogeneous layer of alumina (alpha-Al2O3) in the thermally-grown
oxide (TGO) layer. On the contrary, an increase in Ru contents led to the development of other
oxides and microcracks along with alumina in the TGO layer, undermining oxidation protection. The accommodation of Ti and Ta, in the minimally-deteriorative form of carbide, along with Y into the TGO layer with increasing Pt contents further enhanced oxidation resistance. In addition to the explored significant impact of the Pt/Ru ratio on
oxide scale characteristics and oxidation resistance, the lower cost of Ru compared to Pt suggests the potential for designing cost-effective systems through optimized Pt/Ru ratios and microstructural engineering.
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Instrumentation and Detectors
Supersampled scanning transmission X-ray microscopy for high-resolution vibration-independent time-resolved imaging
Simone Finizio, Benjamin Watts, Benedikt Rösner et al. (+4 more)
Scanning transmission X-ray microscopy (STXM) is a nanoscale imaging technique that can utilize several powerful contrast mechanisms for the quantitative mapping of chemical and physical materials properties. Spatial resolutions down to 7~nm at the soft X-ray energy range have been demonstrated. A limiting factor for high-resolution STXM imaging is given by the positioning precision of the sample with respect to the focusing optic, with the current state-of-the-art leading to significant overheads, especially at low pixel dwell times, and being vulnerable to unavoidable external vibrations sources. In this work, we present a method, called supersampled scanning microscopy, that allows for a significant reduction of overhead times while simultaneously removing the effects of vibrational noise by sampling the position of the sample at a rate significantly higher than the vibration spectrum and reconstructing the sample transmission image from the recorded list of positions and detector counts. We demonstrate the performance of the technique with a set of proof-of-concept high-resolution imaging experiments.
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All authors Simone Finizio, Benjamin Watts, Benedikt Rösner, Tim A. Butcher, Sebastian Wintz, Markus Weigand, Jörg Raabe
Optics
Accelerating field decay along nonlocal metasurfaces by suppressing the Norton wave
Alexander Zhuravlev, Dmitry Tatarnikov, Yury Kurenkov et al. (+1 more)
Studying the nature of electromagnetic fields of dipole sources over a homogeneous flat ground or impedance surfaces has a long history. In general, at a long distance $r$ from the source, the near-surface field is mostly contributed by the geometrical optics term (describing the radiation pattern), a guided wave, and the higher-order reactive contribution referred to as the Norton wave. In the special case of a perfect
magnetic conductor interface, the first two terms vanish, so the residual Norton wave determines the steepest achievable field decay profile of $~r^{-3/2}$ (for a two-dimensional horizontal
magnetic dipole). In this letter, we reveal that in the presence of a nonlocal metasurface described by the second-order impedance boundary condition, the field decay can be further accelerated by suppressing the Norton wave (approaching the profiles $r^{-5/2}$ and $r^{-7/2}$ for electric and
magnetic fields, respectively). In a proposed practical realization of a nonlocal metasurface, the effect is numerically verified and shown to reduce the edge diffraction effects by 10 dB for the shield diameter of only one wavelength, paving the way toward compact
antenna systems.
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All authors Alexander Zhuravlev, Dmitry Tatarnikov, Yury Kurenkov, Stanislav Glybovski1
Computational Physics
Quantitative phase nano-imaging with a laboratory source
Luca Fardin, Chris Armstrong, Alberto Astolfo et al. (+8 more)
Investigating the structure of matter at the nanoscale non destructively is a key capability enabled by X-ray imaging. One of the most powerful nano-imaging methods is X-ray ptychography, a coherent diffraction imaging technique that has become the go-to method at synchrotron facilities for applications ranging from
brain imaging to battery materials. However, the requirements in terms of X-ray beam quality have limited its use to large synchrotron facilities and, to date, only one attempt has been made to translate the technique to a small-scale laboratory. To unleash the power of this technique to the broad user community of laboratory X-ray sources, there are outstanding questions to answer including whether the quantitativeness of the information is preserved in a laboratory despite the drastic decrease in X-ray flux of several orders of magnitude, with respect to synchrotron instruments. In this study not only we demonstrate that the quantitativeness of X-ray ptychography is preserved in a laboratory setting, but we also apply the method to the imaging of a
brain tissue phantom. Finally, we describe the current challenges and limitations, and we set the basis for further development and future directions of quantitative nano-imaging with laboratory X-ray sources.
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All authors Luca Fardin, Chris Armstrong, Alberto Astolfo, Sebastian Ignacio Allen Binet, Matthieu N. Boone, Rebecca Fitzgarrald, Yong Ma, Alexander Thomas, Darren J. Batey, Alessandro Olivo, Silvia Cipiccia
Instrumentation and Detectors
SPIDER, a Waveform Digitizer ASIC for picosecond timing in LHCb PicoCal
Ludovic Alvado, Nicolas Arveuf, Edouard Bechetoille et al. (+10 more)
We present the architecture, design and first test results of SPIDER, the first prototype of a TSMC CMOS 65 nm ASIC designed for the time measurement path of LHCb Electromagnetic Calorimeter after LS4 Upgrade. The main requirements for the readout of this detector are a time resolution below 15 ps rms above 5 GeV, and a channel occupancy up to 30% (12 Mevent/s). The first prototype called SPIDER\_V0 is a 2-channel waveform digitizer locked on the LHC clock allowing precise time reconstruction by digital
algorithms. The architecture is based on 2 DLLs in series controlling respectively the phase of the sampling window and the sampling frequency, the latter covering the range between 2 and 20 GS/s. Each self-triggering channel houses 8 banks of 32 analog
memory cells and a massively parallel Wilkinson ADC for conversion at 5 GHz over 10 bits with a maximal conversion time of 200 ns. SPIDER targets not only LHCb, but all fast detectors mounted on current and future accelerators. Its sampling frequency can indeed be adjusted to different signal risetimes. Its main frequency of 40 MHz could even be eventually locked to another value by modifying only one of the DLLs in the chip design.
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All authors Ludovic Alvado, Nicolas Arveuf, Edouard Bechetoille, Guillaume Blanchard, Dominique Breton, Baptiste Joly, Laurent Leterrier, Jihane Maalmi, Samuel Manen, Hervé Mathez, Christophe Sylvia, Philippe Vallerand, Richard Vandaele
Plasma Physics
Influence of plasma shaping on the parity of core-localized toroidal Alfvén eigenmode in an advanced tokamak configuration
Shiwei Xue, Ping Zhu and Haolong Li
Toroidal Alfvén eigenmodes (TAEs) and energetic particle modes (EPMs) can both be excited by energetic particles from auxiliary heating and fusion-born alpha particles in a tokamak. Using the hybrid kinetic-MHD model implemented in the NIMROD code, the excitation of these modes and their properties are investigated in an advanced tokamak configuration with reversed
magnetic shear in the core region. The dominant TAE/EPM is found to exhibit odd parity with an anti-ballooning structure when the
plasma has elongated, non-circular two-dimensional shaping. As the
plasma shaping becomes more circular with reduced elongation, the mode parity undergoes a transition to even parity accompanied by a ballooning structure. These results may help explain the dominant parity of TAE/EPMs observed in advanced tokamak configurations with different
plasma shaping.
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Chemical Physics
How back reaction, hydrogen transport, and capillarity control the performance of hydrogen release from liquid organic carriers
Tatiana Nizkaia, Thomas Solymosi, Paolo Malgaretti et al. (+2 more)
We derive a theoretical model to elucidate the inhibition of catalytic activity during the dehydrogenation of
Liquid Organic Hydrogen Carriers (LOHC). Within our model, we account for the reversible nature of the hydrogenation-dehydrogenation reaction as well as the transport of both LOHC and produced hydrogen. Our analysis reveals that the main limiting factor for the performance of porous catalysts is the transport of dissolved hydrogen, which has been overlooked so far. In particular, we show that two distinct kinetic regimes can arise depending on whether hydrogen leaves the pellet in form of bubbles or via
diffusion. Moreover, we derive the conditions for the onset of bubbling depending on hydrogen supersaturation and capillarity. Beyond LOHC systems, our findings are applicable to a broader class of reversible reactions, particularly those involving volatile products that can leave the
liquid reaction medium in the form of bubbles.
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All authors Tatiana Nizkaia, Thomas Solymosi, Paolo Malgaretti, Peter Wasserscheid, Jens Harting
Optics
High-Resolution Sensing via Quantum States Discrimination
Qi-An Su, Qi Song, Hongjing Li et al. (+5 more)
High-resolution sensing plays a significant role in scientific research and industrial production, but the practical implementation is constrained by the physical mechanisms of the sensors. To address the critical limitation, we propose a high-resolution sensing approach based on
quantum state discrimination. Distinct from conventional strategies, the proposed approach constructs measurement operators in the orthogonal complement space rather than eigenspace of the eigenstate, thereby notably improving the discriminability among
quantum states. Moreover, the experimental results via an optical microcavity demonstrate a potential sensing resolution of 4 $\times$ 10\textsuperscript{-6} \degree C and 18 p$\epsilon$ respectively for temperature and strain, and further verify the feasibility of simultaneous sensing of the two parameters. This work establishs a universal approach for high-resolution sensing, and may be extended to different sensing platforms across various application scenarios.
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All authors Qi-An Su, Qi Song, Hongjing Li, Kaiwen Fu, Xingyu Wu, Jingzheng Huang, Chuan Wang, Guihua Zeng
Fluid Dynamics
Vertical velocities in quasigeostrophic laboratory vortices
Marine Aulnette, Michael Le Bars and Patrice Le Gal
In the present study, we test the predictions of the {\omega}-Equation against laboratory experiments with direct measurements of the vertical velocity w. Our results are further completed through the use of theoretical models of oceanic
vortices, with the aim of helping oceanographers in better quantifying regions of upwelling and downwelling in the ocean. Using a rotating table and density stratification, we investigate non-axisymmetric surface
vortices. The predicted vertical velocities calculated from the {\omega}-Equation are relatively small (|w| ~ 20 {\mu}m/s) and primarily appear at the
vortex edges, where the vorticity sign changes, acting to restore flow stratification. However, our estimates of w, obtained from the divergence of the horizontal velocity field measured by PIV, are five times larger. This discrepancy is further confirmed by direct particle tracking measurements, which indicate a magnitude of approximately 100 {\mu}m/s for w. To address this inconsistency, we incorporate dissipative terms into the {\omega}-Equation to assess the role of viscous
diffusion in enhancing internal recirculation in the
vortex and thus vertical velocity magnitude. This hypothesis is favorably tested on a Gaussian
vortex model.
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Optics · Cross-listed from quant-ph
Microcomb-driven large-scale fully connected quantum network
Fang-Xiang Wang, Sheng-Teng Zheng, Long Huang et al. (+15 more)
Fully connected
quantum networks enable simultaneously connecting every user to every other user and are the most versatile and robust networking architecture. However, the scalability of such networks remains great challenge for practical applications. Here we construct a large-scale fully connected
quantum network founded on two-
photon Hong-Ou-Mandel (HOM) interference, where user-to-user security is guaranteed even with untrusted network provider. Using integrated
soliton microcomb (SMC) and photonic encoding chips, we realize precise massive parallel frequency generation and locking, high-visibility HOM interferences and measurement-device-independent (MDI)
quantum key distribution. The proposed architecture enables a 200-user fully connected
quantum network over 200 kilometers with strict information-theoretic security via untrusted network provider. The implemented networking architecture paves the way for realizing large-scale fully connected MDI
quantum networks across metropolitan and intercity regions.
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All authors Fang-Xiang Wang, Sheng-Teng Zheng, Long Huang, Guo-We Zhang, Guang-Shu Wang, Wen-Jing Ding, Ze-Hao Wang, Shuang Wang, Zhen-Qiang Yin, Chang-Ling Zou, Brent E. Little, Guochao Wang, Lingxiao Zhu, Guang-Can Guo, Weiqiang Wang, Wenfu Zhang, Wei Chen, Zheng-Fu Han
Plasma Physics
Asymptotic state of nonlinear Landau damping in one-dimensional plasma
Yifei Ouyang, Ping Zhu and Chung-Sang Ng
In this work, the asymptotic state of nonlinear Landau damping in one-dimensional
plasma has been examined using a quasi-linear model and a second-order
symplectic integrator. The dispersion relation of the plateau distribution function for the steady-state solution of the quasi-linear mode is extended to the complex plane and compared with the nonlinear simulation. We determine that the asymptotic state of the collisionless
plasma is a multi-wave BGK structure. This structure is characterized by multiple
vortices in phase space, which correspond to distinct peaks in the frequency-wavenumber ({\omega}, k) spectrum of the electric field
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Instrumentation and Detectors · Cross-listed from cond-mat.mtrl-sci
Deep Learning Enabled Nanoscale X-ray Photoemission Electron Microscopy (nanoXPEEM)
Aashwin Mishra, Daniel Ratner and Quynh Nguyen
Understanding and manipulating two-dimensional materials for real-world applications remains challenging due to a lack of effective and high-throughput characterization techniques. Soft X-ray time-of-flight photoemission electron microscopy (XPEEM) provides element- and depth-sensitive information of materials and buried interfaces. However, chromatic and spherical aberrations cannot be corrected with electron-lens combinations. These aberrations, combined with astigmatism and space-charge effects, significantly degrade the spatial and energy resolutions. To overcome this limitation, we outline a spatial-
attention based deep learning approach to automatically correct for these effects and attain nanometer resolution over the entire field-of-view (FoV). The combination of this corrective
algorithm with XPEEM, termed as nanoXPEEM, establishes a new record of 48-nm spatial resolution with a 232-micrometer diameter FoV in the soft x-ray regime (700-1000 eV). nanoXPEEM provides unique spatial mapping of the element-specificity, depth-sensitivity, and local structure on the nanoscale. It can bridge the current gap to achieve angstrom (atomic) scale resolution.
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Data Analysis and Statistics · Cross-listed from cond-mat.mtrl-sci
Enhancing Reconstruction Capability of Wavelet Transform Amorphous Radial Distribution Function via Machine Learning Assisted Parameter Tuning
Deriyan Senjaya and Stephen Ekaputra Limantoro
Understanding atomic structures is crucial, yet amorphous materials remain challenging due to their irregular and non-periodic nature. The Wavelet Transform Radial Distribution Function (WT-RDF) offers a physics-based framework for analyzing amorphous structures, reliably reconstructing the first and second Radial Distribution Function (RDF) peaks and overall curve trends in both binary (Ge 0.25 Se 0.75) and ternary Ag x(Ge 0.25 Se 0.75)100-x (x = 5, 10, 15, 20, 25) systems. Despite these strengths, WT-RDF shows limitations in amplitude accuracy, which affects quantitative analyses such as coordination numbers. The shortcoming arises from improper parameter (a, b, Kf, C, and {\Lambda})) selection, as the parameters intrinsically represent atomic interactions within amorphous materials. This study addresses the issue by optimizing WT-RDF parameters using a machine learning approach via learnable parameter optimization, parameter bounding, and selective loss, producing the enhanced WT-RDF+ framework. WT-RDF+ improves the precision of peak reconstructions and outperforms
benchmark Machine Learning (ML) models, including Radial Basis Function (RBF) and Long Short-term
Memory (LSTM), when trained on only 25% of the binary
dataset. Specifically, the machine learning
benchmarks are defined as regressors with radial distance r input and G(r) output taken from Ab Initio Molecular Dynamics (AIMD) RDF simulation, not the reduced structure factor SR(q) to G(r) inversions. These results demonstrate that WT-RDF+ is a robust and reliable model for RDF reconstruction of Ge-Se and Ag-Ge-Se family.
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