Instrumentation and Detectors
Kaleidoscopic Scintillation Event Imaging
Alex Bocchieri, John Mamish, David Appleyard et al. (+1 more)
Scintillators are transparent materials that interact with high-energy particles and emit visible light as a result. They are used in state of the art methods of measuring high-energy particles and radiation sources. Most existing methods use fast single-pixel detectors to detect and time scintillation events. Cameras provide spatial resolution but can only capture an average over many events, making it difficult to image the events associated with an individual particle. Emerging single-
photon avalanche diode cameras combine speed and spatial resolution to enable capturing images of individual events. This allows us to use machine
vision techniques to analyze events, enabling new types of detectors. The main challenge is the very low brightness of the events. Techniques have to work with a very limited number of
photons. We propose a kaleidoscopic scintillator to increase light collection in a single-
photon camera while preserving the event's spatial information. The kaleidoscopic geometry creates mirror reflections of the event in known locations for a given event location that are captured by the camera. We introduce theory for imaging an event in a kaleidoscopic scintillator and an
algorithm to estimate the event's 3D position. We find that the kaleidoscopic scintillator design provides sufficient light collection to perform high-resolution event measurements for advanced radiation imaging techniques using a commercial CMOS single-
photon camera.
Read the full abstract ▾
All authors Alex Bocchieri, John Mamish, David Appleyard, Andreas Velten
Chemical Physics · Cross-listed from cond-mat.mtrl-sci
Computer Simulation of the Growth of a Metal-Organic Framework Proto-crystal at Constant Chemical Potential
Sahar Andarzi Gargari, Emilio Méndez and Rocio Semino
Designing metal-organic frameworks (MOFs) synthesis protocols is currently largely driven by trial-and-error, since we lack fundamental understanding of the molecular level mechanisms that underlie their self-assembly processes. Previous works have studied the nucleation of MOFs, but their growth has never been studied by means of computer simulations, which provide molecular level detail. In this work, we combine constant chemical potential simulations with a particle insertion method to model the growth of the ZIF-8 MOF at varying synthesis temperatures and concentrations of the reactants. Non-classical growth mechanisms triggered by oligomer attachments were detected, with a higher predominance in the most concentrated setups. The newly formed layers preserve the pore-like density profile of the seed
crystal but contain defective sites characterized by the presence of 3, 5 and 7 membered rings, typical of amorphous phases. Compared to the amorphous intermediate species obtained at the nucleation part of the self-assembly process previously investigated in our group [Chem. Mater., doi: 10.1021/acs.chemmater.5c02028, 2025], larger-sized rings are more common in the grown layer. Moreover, these are favored by increasing reactant concentration and temperature, as is the degree of deviation with respect to the original
crystal structure. We computed growth rates for the steady-state regime, and the non-linear tendency with respect to concentration leads us to hypothesize that in these conditions the growth is controlled by the adsorption rather than by the
diffusion processes.
Read the full abstract ▾
Fluid Dynamics
Role of boundary conditions and wall orientation on the transport of settling inertial particles in wall-bounded flows
Y. Zhang, D.H. Richter and A.D. Bragg
Gravitational settling affects particle transport in turbulent flows in two ways; explicitly, by introducing a finite settling velocity, and implicitly, by modifying how the particles interact with the flow field. For wall-bounded flows, when the wall is horizontal (
gravity perpendicular to the wall) both the explicit and implicit effects of settling impact the particle transport towards the wall, whereas when the wall is vertical (
gravity parallel to the wall) only the implicit effect plays a role. Surprisingly, it was recently demonstrated that even when the settling parameter $Sv$ is very small, settling can play a very significant role in controlling the near-wall transport in a horizontal channel. In this paper, we use direct numerical simulations to explore how this finding is affected by the particle boundary conditions and whether it also occurs in vertical channels where only the implicit effect of settling plays a role. We show that the sensitivity of the particle transport to $Sv$ depends upon the particle boundary conditions, with elastic-collisions (that generate a zero mean particle flux) and absorbing-wall conditions (that generate a negative mean particle flux) exhibiting qualitatively and quantitatively different sensitivities to $Sv$. It is found that for vertical channels the impact of settling on the particle transport is in fact negligible if $Sv$ is small, and only becomes significant when $Sv\geq O(1)$. Finally, we examine the physical mechanisms governing the settling velocity of particles in vertical channel flows, and find that low-speed streaks can play a significant role in suppressing the settling velocity of the particles near the walls, in contrast to the core region where the preferential sweeping mechanism leads to an enhancement of their settling velocity.
Read the full abstract ▾
Fluid Dynamics · Cross-listed from quant-ph
Magic of the Well: assessing quantum resources of fluid dynamics data
Antonio Francesco Mello, Mario Collura, E. Miles Stoudenmire et al. (+1 more)
We investigate the
quantum resource requirements of a
dataset generated from simulations of two-dimensional, periodic, incompressible shear flow, aimed at training machine learning models. By measuring
entanglement and non-stabilizerness on MPS-encoded functions, we estimate the computational complexity encountered by a stabilizer or a tensor network solver applied to Computational Fluid Dynamics (CFD) simulations across different flow regimes. Our analysis reveals that, under specific initial conditions, the shear width identifies a transition between resource-efficient and resource-intensive regimes for non-trivial
evolution. Furthermore, we find that the two resources qualitatively track each other in time, and that the mesh resolution along with the sign structure play a crucial role in determining the resource content of the encoded state. These findings offer useful guidelines for the development of scalable,
quantum-inspired approaches to fluid dynamics.
Read the full abstract ▾
All authors Antonio Francesco Mello, Mario Collura, E. Miles Stoudenmire, Ryan Levy
Plasma Physics · Cross-listed from astro-ph.HE
Magnetic Field Amplification and Particle Acceleration in Weakly Magnetized Trans-relativistic Electron-ion Shocks
Taiki Jikei, Daniel Groselj and Lorenzo Sironi
We investigate the physics of quasi-parallel trans-relativistic shocks propagating in weakly magnetized
plasmas by means of long-duration two-dimensional particle-in-
cell simulations. The structure of the shock precursor is shaped by a competition between the Bell instability and the Weibel (filamentation) instability. The Bell instability is dominant at relatively high magnetizations $(\sigma\gtrsim10^{-3})$, whereas the Weibel instability prevails at lower magnetizations $(\sigma\lesssim10^{-4})$. Shocks with precursors shaped by Bell modes efficiently accelerate ions, converting a fraction $\varepsilon_{\mathrm{i}}\sim0.2$ of the upstream flow energy into downstream nonthermal ion energy. The maximum energy of nonthermal ions exhibits a Bohm scaling in time, as $E_{\max}\propto t$. A much smaller fraction $\varepsilon_{\mathrm{e}}\ll0.1$ of the upstream flow energy goes into downstream nonthermal electrons in the Bell regime. On the other hand, when the precursor is dominated by Weibel modes, the shock efficiently generates both nonthermal ions and electrons with $\varepsilon_{\mathrm{i}}\sim\varepsilon_{\mathrm{e}}\sim0.1$, albeit with a slower scaling for the maximum energy, $E_{\mathrm{max}}\propto t^{1/2}$. Our results are applicable to a wide range of trans-relativistic shocks, including the termination shocks of extragalactic jets, the late stages of gamma-ray burst afterglows, and shocks in fast blue optical transients.
Read the full abstract ▾
Plasma Physics
Energetic-particle orbits near rational flux surfaces in stellarators: I. Passing particles
Thomas E. Foster, Felix I. Parra, Roscoe B. White et al. (+3 more)
Recent simulations have shown that, even when the
magnetic field of a stellarator possesses nested toroidal flux surfaces, the orbits of passing energetic particles can exhibit islands. These 'drift islands' arise near rational flux surfaces, where they are likely to enhance alpha-particle transport – flattening the alpha density profile locally – unless they can be avoided by suitable design of the stellarator
magnetic field. To investigate how this might be achieved, we derive an equation for the drift-island shape in a general stellarator. This result follows from the solution to a more fundamental problem: that of calculating the orbits of passing particles near a rational flux surface. We show that these orbits are determined by conservation of an adiabatic invariant associated with the closed rational-surface field lines. We use this 'transit adiabatic invariant' to prove that there are no drift islands, for all passing particles, if and only if the
magnetic field satisfies a weaker version of the Cary-Shasharina condition for omnigeneity; we call such
magnetic fields 'cyclometric'. The drift-island width scales as $\sim (\rho_\star\delta/s)^{1/2} a$ ($\rho_\star$ is the normalized gyroradius, $\delta$ is the deviation from cyclometry, $s$ is the
magnetic shear, and $a$ is the minor radius), so large drift islands could arise in low-shear stellarators that are insufficiently cyclometric. To ensure accurate results for very energetic particles, we compute higher-order corrections to the transit invariant. Our calculations agree extremely well with ASCOT5 guiding-centre and full-orbit simulations of alpha particles in reactor-scale
equilibria, even at $3.5\text{MeV}$. Finally, we show how our results can also be derived using
Hamiltonian perturbation theory, which provides a systematic framework for calculating passing-particle orbits on both rational and irrational surfaces.
Read the full abstract ▾
All authors Thomas E. Foster, Felix I. Parra, Roscoe B. White, José Luis Velasco, Iván Calvo, Elizabeth J. Paul
Atomic Physics · Cross-listed from hep-ph
Effective Field Theory Perspective On King Non-linearity
Benoît Assi, Sam Carey, Sebastian Jäger et al. (+4 more)
Precision spectroscopic measurements of isotope shifts have recently reached a high level of accuracy. Tests of King non-linearity (NL) along isotope chains have been proposed as a tool to search for fifth-force mediators. At the same time, these tests can potentially teach us about the structure of heavy
nuclei at unprecedented precision, where King NL has already been observed in several systems. A robust interpretation of the existing data, however, is hampered by incomplete control over the Standard Model (SM) contributions. We develop a systematic effective field theory framework, matching the SM onto scalar non-relativistic QED in the infinite
nuclear mass limit and then onto
quantum-mechanical potentials. This approach organizes all
nuclear effects into a small set of Wilson coefficients and cleanly separates short- and long-distance physics. We show that the commonly used treatment of the $\langle r^2\rangle^2$ term needs to be reconsidered, as it arises only at second-order in perturbation theory, and we derive the long-range $1/r^4$ potential from
nuclear polarizability. Applying the framework to hydrogen-like systems, we provide a transparent classification of SM sources of King NL relevant for current and future isotope-shift experiments. The formalism can be applied to learn about the shape of the heavy scalar
nuclei at a higher level of precision and detail than what was previously attainable.
Read the full abstract ▾
All authors Benoît Assi, Sam Carey, Sebastian Jäger, Gabriel Lee, Gil Paz, Gilad Perez, Jure Zupan
Computational Physics
A high-order regularized delta-Chebyshev method for computing spectral densities
Jinjing Yi, Daniel Massatt, Andrew Horning et al. (+3 more)
We introduce a numerical method for computing spectral densities, and apply it to the evaluation of the local density of states (LDOS) of sparse
Hamiltonians derived from tight-binding models. The approach, which we call the high-order delta-Chebyshev method, can be viewed as a variant of the popular regularized Chebyshev kernel
polynomial method (KPM), but it uses a high-order accurate approximation of the $\delta$-function to achieve rapid convergence to the thermodynamic limit for smooth spectral densities. The costly computational steps are identical to those for KPM, with high-order accuracy achieved by an inexpensive post-processing procedure. We apply the
algorithm to tight-binding models of
graphene and twisted
bilayer graphene, demonstrating high-order convergence to the LDOS at non-singular points.
Read the full abstract ▾
All authors Jinjing Yi, Daniel Massatt, Andrew Horning, Mitchell Luskin, J. H. Pixley, Jason Kaye
Chemical Physics · Cross-listed from cs.LG
Atomic Diffusion Models for Small Molecule Structure Elucidation from NMR Spectra
Ziyu Xiong, Yichi Zhang, Foyez Alauddin et al. (+4 more)
Nuclear Magnetic Resonance (NMR) spectroscopy is a cornerstone technique for determining the structures of small molecules and is especially critical in the discovery of novel natural products and clinical therapeutics. Yet, interpreting NMR spectra remains a time-consuming, manual process requiring extensive domain expertise. We introduce ChefNMR (CHemical Elucidation From NMR), an end-to-end framework that directly predicts an unknown molecule's structure solely from its 1D NMR spectra and chemical formula. We frame structure elucidation as conditional generation from an atomic
diffusion model built on a non-equivariant
transformer architecture. To model the complex chemical groups found in natural products, we generated a
dataset of simulated 1D NMR spectra for over 111,000 natural products. ChefNMR predicts the structures of challenging natural product compounds with an unsurpassed accuracy of over 65%. This work takes a significant step toward solving the grand challenge of automating small-molecule structure elucidation and highlights the potential of deep learning in accelerating molecular discovery. Code is available at https://github.com/ml-struct-bio/chefnmr.
Read the full abstract ▾
All authors Ziyu Xiong, Yichi Zhang, Foyez Alauddin, Chu Xin Cheng, Joon Soo An, Mohammad R. Seyedsayamdost, Ellen D. Zhong
Atmospheric and Oceanic Physics · Cross-listed from astro-ph.SR
Enhanced magnetostrophic waves with magnetic field orthogonal to the rotation axis
Raviraj Narayan Shinde and Ghanesh Narasimhan
We consider an isolated Gaussian velocity
vortex perturbation in an otherwise quiescent, electrically conducting, and rotating fluid permeated by a uniform
magnetic field $\bf{B}$. Studies suggest a presence of strong azimuthal wave motions on the timescale of centuries within the Earth's
liquid outer core at higher latitudes. To understand these long-period oscillations, we focus on magnetostrophic waves, a slow component of
magnetic-Coriolis waves with $\bf{B}$ orthogonally aligned with the rotation vector $\bf{\Omega}$, which replicate the field lines in the azimuthal direction. We present an analytical solution to the
magnetic-Coriolis wave equation in Cartesian coordinates. Later, with numerical solution, we validate our analytical estimates and show that magnetostrophic waves travel relatively faster along the
magnetic field when $\bf{B} \perp \bf{\Omega}$ compared with the case when both are aligned. The study confirms that with a
magnetic field $\bf{B}$ orthogonally aligned to the rotation vector $\bf{\Omega}$, wave vectors satisfying the condition $\bf{\Omega}\cdot\bf{k} \approx 0$, travel with Alfvén velocities along the
magnetic field lines as a component of inertial-Alfvén waves. The timescales on which Alfvén waves travel are relatively short, and it is also less likely that inertial-Alfvén waves will be sustained inside the core at higher latitudes \citep{Davidson2017}. This study shows that, excluding the inertial-Alfvén waves contribution ($k_z\neq 0$), there exists intensified magnetostrophic wave propagation when $\bf{B} \perp \bf{\Omega}$, which can explain the strong periodic oscillations on the time scales of centuries along the azimuthal field at higher latitudes. Results show persistence of the magnetostrophic waves despite the lower Lehnert number $Le$, suggesting the plausible existence of a low-intensity azimuthal
magnetic field in the Earth's core.
Read the full abstract ▾
Atmospheric and Oceanic Physics
An infrasound source analysis of the OSIRIS-REx sample return capsule hypersonic re-entry
Jordan W. Bishop, Philip Blom, Chris Carr et al. (+1 more)
The OSIRIS-REx sample return capsule hypersonic re-entry into the atmosphere is a rare opportunity to test a variety of sonic boom source models since the projectile dimensions are well characterized. While the as-flown flight path is unknown, the predicted flight path enables a rough approximation of the source Mach number and location. Six infrasound microphones deployed in the boom carpet along the predicted flight path recorded impulsive signals from the OSIRIS-REx re-entry. Using a suite of atmosphere profiles and the
geometric acoustics approximation, we estimate locations with uncertainty estimates along the flight path from which the signals were emitted. Acoustic overpressure and signal duration predictions from Whitham's far field theory, Carlson's simplified sonic boom prediction method, and a drag-dominated hypersonic model are analyzed with uncertainty estimates from the location estimate. While the Carlson simplified sonic boom prediction method could be accurate, our preference is for the drag-dominated source model. Using this source model with an inviscid Burgers' equation solver for propagation, we obtained an excellent match to the recorded data. These results will help better inform future sample return capsule re-entry observation campaigns as well as contribute to a better understanding of high altitude infrasonic sources.
Read the full abstract ▾
All authors Jordan W. Bishop, Philip Blom, Chris Carr, Jeremy Webster
Data Analysis and Statistics · Cross-listed from cs.LG
Temporal Graph Neural Networks for Early Anomaly Detection and Performance Prediction via PV System Monitoring Data
Srijani Mukherjee, Laurent Vuillon, Liliane Bou Nassif et al. (+4 more)
The rapid growth of
solar photovoltaic (PV) systems necessitates advanced methods for performance monitoring and anomaly detection to ensure optimal operation. In this study, we propose a novel approach leveraging Temporal Graph Neural Network (Temporal GNN) to predict
solar PV output power and detect anomalies using environmental and operational parameters. The proposed model utilizes graph-based temporal relationships among key PV system parameters, including irradiance, module and ambient temperature to predict electrical power output. This study is based on data collected from an outdoor facility located on a rooftop in Lyon (France) including power measurements from a PV module and meteorological parameters.
Read the full abstract ▾
All authors Srijani Mukherjee, Laurent Vuillon, Liliane Bou Nassif, Stéphanie Giroux-Julien, Hervé Pabiou, Denys Dutykh, Ionnasis Tsanakas
Physics Education
A portable LED-based diamond magnetometer for outreach and teaching labs
Hollis Williams, Alex Newman, Stuart Graham et al. (+2 more)
We present a compact, low-cost version of an NV center diamond magnetometer which replaces the standard green
laser with a high-power LED. This modification improves safety, reduces cost, and allows the green excitation and red photoluminescence to be viewed directly during demonstrations. The device is simple to assemble and suitable for outreach activities and undergraduate laboratories. We show that it can produce ODMR spectra and respond to nearby
magnetic objects, with a sensitivity on the order of 1 $\mu$T/$\sqrt{\text{Hz}}$. Supplementary material provides details of the construction and suggestions for student investigations to support use in teaching laboratories.
Read the full abstract ▾
All authors Hollis Williams, Alex Newman, Stuart Graham, Colin Stephen, Gavin Morley
Atomic Physics
Generation of strong ultralow-phase-noise microwave fields with tunable ellipticity for ultracold polar molecules
Shrestha Biswas, Sebastian Eppelt, Christian Buchberger et al. (+6 more)
Microwave(MW) fields with strong field strength, ultralow phase-noise and tunable polarization are crucial for stabilizing and manipulating ultracold polar molecules, which have emerged as a promising platform for
quantum sciences. In this letter, we present the design, characterization, and performance of a robust MW setup tailored for precise control of molecular states. This setup achieves a high electric field intensity of 6.9 kV/m in the near-field from a dual-feed waveguide
antenna, enabling a Rabi frequency as high as 71 MHz for the rotational transition of sodium-potassium molecules. In addition, the low noise signal source and controlled electronics provide ultralow phase-noise and dynamically tunable polarization. Narrow-band filters within the MW circuitry further reduce phase-noise by more than 20 dB at 20 MHz offset frequency, ensuring prolonged one-body molecular lifetimes up to 10 seconds. We also show practical methods to measure the MW field strength and polarization using a simple homemade dipole probe, and to characterize phase-noise down to -170 dBc/Hz with a commercial spectrum analyser and a notch filter. Those capabilities allowed us to evaporatively cool our molecular sample to deep
quantum degeneracy. Furthermore, the polarization tunability enabled the observation of field-linked resonances and facilitated the creation of field-linked tetramers.These techniques advance the study of ultracold polar molecules and broaden the potential applications of MW tools in other platforms of
quantum sciences.
Read the full abstract ▾
All authors Shrestha Biswas, Sebastian Eppelt, Christian Buchberger, Xing-Yan Chen, Andreas Schindewolf, Michael Hani, Erwin Biebl, Immanuel Bloch, Xin-Yu Luo
Accelerator Physics
IOTA Experiment for Proton Pulse Compression at Extreme Space-Charge
Benjamin Simons, Nilanjan Banerjee, Jeffrey Eldred et al. (+1 more)
The longitudinal compression of high-intensity, space-charge-dominated
proton bunches is a critical requirement for future
proton-driven
muon colliders. We propose a
proton bunch compression experiment at the Integrable Optics Test Accelerator (IOTA) storage ring at Fermilab to investigate optimal
radio-frequency (RF) cavity parameters and
lattice configurations. IOTA is a compact, fixed-energy storage ring dedicated to beam physics Research and Development and capable of circulating a 2.5 MeV
proton beam under extreme space-charge conditions. Using the ImpactX code with its 3D space-charge solver, simulations indicate that the bunch length can be rapidly reduced by at least a factor of two without appreciable degradation of transverse beam quality–even in the strong space-charge regime. However, longitudinal defocusing due to the space-charge remains a significant challenge in short-pulsed intense
proton bunches, and the optimization of compression under these conditions is discussed.
Read the full abstract ▾
All authors Benjamin Simons, Nilanjan Banerjee, Jeffrey Eldred, Vladimir Shiltsev
Instrumentation and Detectors
Characterisation of the LAPPD, a large area microchannel-plate PMT
S. Korpar, R. Dolenec, F. Grijalva et al. (+7 more)
We present a comprehensive characterization of the LAPPD Gen-II, a large-area microchannel-plate photomultiplier tube (MCP-PMT) equipped with a capacitively coupled sensing (readout) electrode. Two detector variants with different geometries and materials were investigated using a picosecond pulsed
laser system. We measured the single-
photon timing response and spatial charge distribution on segmented readout electrodes. The
prompt timing peak exhibits a resolution of approximately 30 ps, with the overall timing structure explained by photoelectron propagation and back-scattering effects from the MCP input surface. We developed analytical models that describe the propagation of photoelectrons and the induced charge spread on the sensing electrodes, including secondary electron backscattering from the resistive anode. The model accurately reproduces the measured device properties and enables performance extrapolations for various detector geometries and dielectric properties. These results provide a predictive framework for optimizing MCP-PMTs for timing- and imaging-critical applications such as RICH detectors in high-energy physics and TOF-PET systems for medical imaging.
Read the full abstract ▾
All authors S. Korpar, R. Dolenec, F. Grijalva, A. Lozar, A. Kodrič, P. Križan, S. Parashari, R. Pestotnik, A. Seljak, D. Žontar
Medical Physics
Alternative winding patterns for twisted solenoid coils with improved characteristics for TRASE MRI
Nahid Ghomimolkar, Alexander E. Krosney and Christopher P. Bidinosti
Transmit Array Spatial Encoding (TRASE) is an MRI technique in which spatial encoding is achieved using phase gradients of the B1 field. This approach offers potential advantages such as hardware simplicity and reduced acoustic noise. In this study, we present an assessment of various winding patterns for twisted solenoid phase-gradient coils, including the simple twisted solenoid (with and without return wire), a double-wound twisted solenoid, and a discrete-loop twisted solenoid. We analyze the
magnetic field uniformity and phase linearity of these configurations using Biot-Savart simulations. Our results show that both the double-wound and discrete loop designs offer similar improvements over the simple twisted solenoid with return wire. The discrete loop pattern requires less wire than the double-wound version, making it the preferred option for practical coil construction and operation in a TRASE MRI system.
Read the full abstract ▾
Optics
Tunable polarization-entangled near-infrared photons from orthogonal GaAs nanowires
Elise Bailly-Rioufreyt, Zoya Polshchykova, Grégoire Saerens et al. (+10 more)
Quantum entanglement is a fundamental resource for emerging
quantum technologies, enabling secure communication and enhanced sensing. For decades, generating polarization entangled states has been mainly achieved using bulk
crystals with spontaneous parametric down conversion (SPDC), preventing scalability and on-chip integration. Miniaturizing the
quantum source provides access to more versatility and tunability while enabling an easier integration to other devices, notably necessary for satellite-based
quantum communication, and eventually reducing fabrication costs. This challenging task can be achieved with Zinc Blende GaAs nanowires. They already have shown an efficient
photon pairs generation via SPDC at 1550 nm. Here we demonstrate that a pair of orthogonal GaAs nanowires constitutes a new nanoscale platform to control the
quantum state at telecommunication wavelength, enabling a transition from polarization entangled to separable states as a function of the pump polarization, with fidelities reaching 90%
Read the full abstract ▾
All authors Elise Bailly-Rioufreyt, Zoya Polshchykova, Grégoire Saerens, Wenhe Jia, Thomas Dursap, Andreas Maeder, Philippe Regreny, Robert J. Chapman, Helena Weigand, Alexandre Danescu, Nicolas Chauvin, José Penuelas, Rachel Grange
Applied Physics · Cross-listed from cond-mat.mtrl-sci
New insights into hydrogen-assisted intergranular cracking in nickel
S. Quan, A. Zafra, E. Martínez-Pañeda et al. (+3 more)
We characterize the grain boundary (GB) susceptibility to hydrogen-assisted intergranular cracking in pure nickel as a function of coincident site
lattice value ($\Sigma$-n), over a wide range of hydrogen concentrations (4 to 14 wppm). Cracks on the surface and within the bulk material were identified across the entire gauge region of the specimens. The susceptibility of GBs to crack initiation and propagation was evaluated by separating cracks containing single GB or multiple GBs. A larger loss in fracture strain, a smaller reduction in area, and an increase in the percentage of intergranular fracture indicated a higher degree of embrittlement at elevated hydrogen concentrations. The number of cracks was significantly higher on the surface than in the bulk for the most severe hydrogen charging conditions ($\geq$ 8 wppm), while a similar number was observed for lower concentrations. The propensity for hydrogen-assisted intergranular cracking at different types of GBs on the surface and in the bulk material was consistent, indicating that while cathodic charging can promote surface cracks, it does not significantly impact the GBs relative susceptibility. The $\Sigma$-3 boundaries were the most resistant to cracking, as evidenced by the considerably lower fraction of these GBs exhibiting intergranular cracking at all hydrogen concentrations considered. This contrasts literature findings for Ni
alloys and can be explained by the segregation energies and reductions in the cohesive strength with hydrogen, with less favorable trapping at the $\Sigma$-3 boundaries. No evidence of plasticity-mediated cracking initiation was observed.
Read the full abstract ▾
All authors S. Quan, A. Zafra, E. Martínez-Pañeda, C. Wu, Z.D. Harris, L. Cupertino-Malheiros
Optics
Universal nondiffractive topological spin textures in vortex cores of light and sound
Elena Annenkova, Andrei Afanasev and Etienne Brasselet
We report universal skyrmionic
spin textures in the cores of optical and acoustic
vortex beams, described within the framework of Laguerre-Gaussian modes. We analytically demonstrate nondiffractive propagating
spin merons, independent of whether the field is transverse or longitudinal, with their sign controlled by the wavefront helicity. Experimental confirmation is provided in acoustics through full three-dimensional measurements of the velocity vector field. Although these phenomena are intrinsic to
vortex cores, we also show that the claimed universality breaks down for higher-order topological charges, depending on the carrier mode, here exemplified using the Bessel framework.
Read the full abstract ▾
Optics
Reflective Metalenses for Near-Infrared Wavelengths Based on Silicon Nanorods
Iftekhar Ahmed, K. B. M. Sharif Mahmood and Tanvin Tamanna
This paper presents the design and analysis of reflective metalenses optimized for a 900 nm wavelength, using silicon nanorods as the primary components. The metalens consists of unit
cells, each containing a thin silicon rod. Lumerical FDTD software is used to create a detailed library that connects the dimensions of these nanorods with their respective phase shifts and reflectance properties. The nanorods are placed on a 70 nm thick silicon dioxide (SiO2) layer, with a 50 nm thick gold (Au) reflective layer underneath. In contrast to conventional transmissive metalenses, our design accomplishes complete 2{\pi} phase control via geometry-optimized silicon nanorods, facilitating compact reflective optics. By carefully examining the impact of nanorod dimensions on optical performance, the main goal is to optimize the metalens design for enhanced light focusing and manipulation, which could benefit imaging systems, optical communications, and sensor technology.
Read the full abstract ▾
Classical Physics
Conservation of Momentum and Energy in the Lorenz-Abraham-Dirac Equation of Motion
Arthur D. Yaghjian
After a brief review of the modified (by transition forces) causal Lorentz-Abraham (LA) classical equation of motion for an extended charged sphere and its limit to the mass-renormalized modified causal Lorentz-Abraham-Dirac (LAD) equation of motion as the radius of the charged sphere approaches zero, a concise derivation is given for the conditions on the velocity and external force required for these modified equations of motion to satisfy conservation of momentum and energy. The effects of mass renomalization on the radiated momentum-energy is clarified. The solutions to the unmodified LAD equation of motion, the causal modified LA and LAD equations of motion, and the Landau-Lifshitz approximate solution to the unmodified LAD equation of motion are obtained for a charge traveling through a parallel-plate capacitor.
Read the full abstract ▾
Atomic Physics · Cross-listed from cond-mat.quant-gas
Formation of bosonic $^{23}$Na$^{41}$K Feshbach molecules
Sungjun Lee, Younghoon Lim, Jongyeol Kim et al. (+2 more)
Ultracold Feshbach molecules are a crucial intermediate step for the creation of
quantum degenerate gases of strongly dipolar molecules. After coherent transfer to the rovibrational ground state, these dimers can realize stable dipolar gases with strong, tunable long-range interactions. Here, we report the creation of bosonic $^{23}$Na$^{41}$K Feshbach molecules by
radio-frequency (RF) association. An RF pulse applied on the molecular side of an interspecies Feshbach resonance at 73.6(1)~G associates up to $1.1(1)\times10^4$ molecules from a thermal mixture of $^{23}$Na and $^{41}$K atoms. Measurements of the binding energy reveal a broad resonance width of 5.1(2)~G, facilitating robust control over interspecies interactions. The molecule lifetime in the presence of background atoms exceeds 2~ms, extending to 7~ms after removal of $^{23}$Na. These results constitute a key step toward the production of ultracold $^{23}$Na$^{41}$K ground state molecules for the exploration of novel many-body phenomena in strongly dipolar Bose gases.
Read the full abstract ▾
All authors Sungjun Lee, Younghoon Lim, Jongyeol Kim, Jaeryeong Chang, Jee Woo Park
Optics
Exceptional Point Dynamics in Photonic Time Crystals for Enhanced Optical Sensing
Saurabh Mani Tripathi, Shalini Kumari, Krishnan Kundan et al. (+1 more)
Exceptional points (EPs) in non-Hermitian photonics offer singular sensitivity enhancements but have thus far been realized almost exclusively in spatially engineered platforms with fixed geometries and limited tunability. Here we extend EP physics into the temporal domain by introducing balanced gain–loss modulation in a photonic time
crystal (PTC). A time-periodic refractive-index modulation $n(t)=n_{0}+\delta n\cos(\Omega t)$ generates an effective non-Hermitian Floquet
Hamiltonian that supports coalescence of quasi-eigenmodes in frequency space, constituting a genuine temporal exceptional point. Using a reduced two-mode model for the dominant frequency sidebands, we derive a non-Hermitian dimer
Hamiltonian $H_{\mathrm{PT}}(\Delta,\gamma,\kappa)$ that is strictly $\mathcal{PT}$-symmetric for $\Delta=0$ and identify the exact EP condition. Numerical analysis reveals the associated Riemann-sheet
topology, mode exchange and Berry-phase accumulation upon encirclement of the EP, and the characteristic $\sqrt{\varepsilon}$ perturbation response indicative of enhanced sensing. We further construct a non-Hermitian transmission model that is exact within the reduced two-mode description, compute the Cramér–Rao bound (CRB) for temperature estimation under an explicit noise model, and show that EP-enhanced sensitivity persists when compared to a linewidth-matched Hermitian reference under identical resource constraints. Monte Carlo simulations confirm that the CRB is saturable using spectral measurements. These results establish temporal non-Hermiticity as a new paradigm for dynamically reconfigurable, broadband, and geometry-independent exceptional-point photonics.
Read the full abstract ▾
All authors Saurabh Mani Tripathi, Shalini Kumari, Krishnan Kundan, Neha Ahlawat
Applied Physics
Combining Transport of Pendular Water with Wind-Assisted Interfacial Evaporation for Dewatering of Concentrated Slurry Waste
Tanay Kumar, Hongying Zhao and Xuehua Zhang
Drying concentrated slurry waste is slow, particularly due to the entrapment and limited accessibility of water entrained between the particles in the slurry. A sailboat evaporator with a root-like structure is a new system that enables wind-assisted interfacial evaporation of concentrated particle slurries. In this work, we create access to the disconnected water pockets in concentrated slurry waste, facilitating faster water conduction and efficient evaporation at extremely high solid concentration. The evaporator's long roots effectively extracted water beneath 150 cm deep supernatant water layer. Through replantation of the evaporator to a separate location, an impressive evaporation rate (ER) of 4 kg/(m^2*h) close to 80 wt% solid concentration, a 25% increase to a non-replanted sample. Furthermore, long periods of efficient of evaporation was achieved even at high solid concentration through hydrodynamic flushing of roots. Outdoor experiments achieved substantial volumetric reduction, yielding dried residues with over 75 wt% solid concentration. These results underscore the system's reliable performance against highly concentrated slurries, yet to be by conventional industrial methods, including flocculation and tail-lift drying. The integration of renewable energy coupled with efficient enhancement techniques makes the sailboat evaporator a scalable and sustainable pathway for industrial wastewater dewatering.
Read the full abstract ▾
Medical Physics · Cross-listed from eess.IV
Maintaining SUV Accuracy in Low-Count PET with PETfectior: A Deep Learning Denoising Solution
Yamila Rotstein Habarnau, Nicolás Bustos, Paola Corona et al. (+8 more)
Background: Diagnostic PET image quality depends on the administered activity and acquisition time. However, minimizing these variables is desirable to reduce patient radiation exposure and radiopharmaceutical costs. PETfectior is an artificial intelligence-based software that processes PET scans and increases signal-to-noise ratio, obtaining high-quality images from low-count-rate images. We perform an initial clinical validation of PETfectior on images acquired with half of the counting statistics required to meet the most recent EANM quantitative standards for 18F-FDG PET, evaluating lesions detectability, quantitative performance and image quality. Materials and methods: 258 patients referred for 18F-FDG PET/CT were prospectively included. The standard-of-care scans (100% scans) were acquired and reconstructed according to EARL standards 2. Half-counting-statistics versions were generated from list-mode data and processed with PETfecftior (50%+PETfectior scans). All oncologic lesions were segmented on both PET/CT versions, manually or automatically, and lesions detectability was evaluated. The SUVmax of the lesions was measured and the quantitative concordance of 50%+PETfectior and 100% images was evaluated. Subjective image quality was visually assessed by two experienced physicians. Results: 1649 lesions were detected in a total of 198 studies. The 50%+PETfectior images showed high sensitivity for lesion detection (99.9%) and only 1 false positive was detected. The SUVmax measured in 100% and 50%+PETfectior images agreed within 12.5% (95% limits of agreement), with a bias of -1.01%. Image quality of the 50%+PETfectior images was rated equal to or better than the standard-of-care images. Conclusion: PETfectior can safely be used in clinical practice at half counting statistics, with high sensitivity and specificity, low quantitative bias and high subjective image quality.
Read the full abstract ▾
All authors Yamila Rotstein Habarnau, Nicolás Bustos, Paola Corona, Christian González, Sonia Traverso, Federico Matorra, Francisco Funes, Juan Martín Giraut, Laura Pelegrina, Gabriel Bruno, Mauro Namías
Optics
On the Performance of Multi-Wavelength Underwater Optical Channels in the Presence of Optical Turbulence
Shideh Tayebnaimi and Kamran Kiasaleh
This paper presents an analysis of the performance of a Gaussian optical beam as it propagates through the turbulent
underwater optical channel (UWOC) under the weak
turbulence regime, where optical signal experiences significant fading and scattering, all of which can severely degrade communication quality. It is assumed that on-off keying (OOK) modulation with direct detection is utilized to establish a duplex communication link. A multi-wavelength beam approach is implemented to enhance the performance by leveraging the distinct propagation characteristics of different wavelengths. Performance is established in terms of the probability of fade, number of fade per second, mean fade duration, and mean time between fades. The use of multi-wavelength beam is shown to enhance performance by a sizable margin.
Read the full abstract ▾
Optics · Cross-listed from cond-mat.mes-hall
Electrically driven plasmon-polaritonic bistability in Dirac electron tunneling transistors
Shuai Zhang, Yang Xu, Junhe Zhang et al. (+12 more)
Bistability-two distinct stable states under identical parameter-is not only a fundamental physical concept but also of importance in practical applications. While plasmon-polaritonic bistability representing history-dependent stable states within plasmonic systems has been theoretically predicted, it has yet to be demonstrated experimentally due to challenges in realizing suitable nonlinearity at feasible electric-field strengths. Here, we report the experimental observation of electrically driven plasmon-polaritonic bistability in
graphene/hexagonal-boron-nitride/
graphene tunneling transistors, achieved through momentum-conserving resonant tunneling of Dirac electrons. Using a small twist angle between
graphene layers, we engineered devices exhibiting both electronic and plasmon-polaritonic bistability. This bistable plasmonic behavior can be precisely tuned through load resistance and electrostatic gating. Our findings open new pathways for exploring nonlinear optical and electronic phenomena in van der Waals
heterostructures and mark a significant advance in nanoplasmonics, with potential applications in optical
memory, sensing, and optoelectronic switching.
Read the full abstract ▾
All authors Shuai Zhang, Yang Xu, Junhe Zhang, Dihao Sun, Yinan Dong, Matthew Fu, Takashi Taniguchi, Kenji Watanabe, Cory R. Dean, Monica Allen, Jeffery Allen, F. Javier Garcia de Abajo, Antti J. Moilanen, Lukas Novotny, D. N. Basov
Computational Physics
Towards a fully differentiable digital twin for solar cells
Marie Louise Schubert, Houssam Metni, Jan David Fischbach et al. (+18 more)
Maximizing energy yield (EY) - the total electric energy generated by a
solar cell within a year at a specific location - is crucial in photovoltaics (PV), especially for emerging technologies. Computational methods provide the necessary insights and guidance for future research. However, existing simulations typically focus on only isolated aspects of
solar cells. This lack of consistency highlights the need for a framework unifying all computational levels, from material to
cell properties, for accurate prediction and optimization of EY prediction. To address this challenge, a differentiable digital twin, Sol(Di)$^2$T, is introduced to enable comprehensive end-to-end optimization of
solar cells. The workflow starts with material properties and morphological processing parameters, followed by optical and electrical simulations. Finally, climatic conditions and geographic location are incorporated to predict the EY. Each step is either intrinsically differentiable or replaced with a machine-learned surrogate model, enabling not only accurate EY prediction but also gradient-based optimization with respect to input parameters. Consequently, Sol(Di)$^2$T extends EY predictions to previously unexplored conditions. Demonstrated for an organic
solar cell, the proposed framework marks a significant step towards tailoring
solar cells for specific applications while ensuring maximal performance.
Read the full abstract ▾
All authors Marie Louise Schubert, Houssam Metni, Jan David Fischbach, Benedikt Zerulla, Marjan Krstić, Ulrich W. Paetzold, Seyedamir Orooji, Olivier J. J. Ronsin, Yasin Ameslon, Jens Harting, Thomas Kirchartz, Sandheep Ravishankar, Chris Dreessen, Eunchi Kim, Christian Sprau, Mohamed Hussein, Alexander Colsmann, Karen Forberich, Klaus Jäger, Pascal Friederich, Carsten Rockstuhl
Fluid Dynamics
Ridged geometries induce axial flow vortices in Couette systems
Akankshya Majhi, Maria Raquel Serial, Lars Kool et al. (+2 more)
A yield stress fluid has a critical stress above which the material starts to flow. Typically, the yield stress behaviour is captured in the Herschel-Bulkley (HB) model, which assumes a constant yield stress as material parameter. It is not clear whether the simultaneous superposition of a flow in an orthogonal direction to the main flow, that displays HB behaviour, affects the yield stress and will make the yield stress either flow rate- or field-dependent. Therefore, it is important to understand how the presence of flow in two orthogonal directions affects the yielding behaviour of the fluid in general. In this work, we showed that wall patterning can be used to generate flow in two orthogonal directions simultaneously. We find that these orthogonal flows measurably affected each other. We induced spatially varying secondary flows by shearing a standard Newtonian fluid and two common yield stress fluids in a rheometer using a concentric cylinder geometry with angled ridges. We measured the normal force as a function of rotation rates for different angled ridges from conventional rheological measurements. We also imaged the flow fields by employing rheo-MRI, to directly measure the penetration depth of the fluids into the rough boundary of the ridged geometry. Finally, we relate the penetration depth to the axial flow for different geometries, at different imposed rotation rates and the fluid type, to show that two flow directions in the yield stress fluids are indeed significantly related to each other.
Read the full abstract ▾
All authors Akankshya Majhi, Maria Raquel Serial, Lars Kool, Jasper van der Gucht, Joshua Albert Dijksman