Computational Physics
A Physics-based and Geometry-aware Reduced-order Framework for Accelerated Part-Scale Thermomechanical Simulation of Additive Friction Stir Deposition Process
Apurba Sarker and Sourav Saha
Additive friction stir deposition (AFSD) is attractive for naval and aerospace sustainment because it enables high rate, solid state near net shape fabrication and repair of large metallic components. However, full part scale thermomechanical simulations remain computationally demanding because of the moving heat source, progressive material deposition, and evolving geometry. This work presents a physics-based and geometry-aware reduced order framework for rapid prediction of temperature and residual stress fields in part scale AFSD builds. The transient temperature field is represented using a tensor product quadratic B spline basis on a fixed Cartesian background grid, while arbitrary part geometries are embedded using a signed distance function (SDF) and a smooth material indicator. Residual stresses are recovered through an inherent strain formulation in which an offline thermo elasto plastic representative volume element (RVE) simulation supplies a calibrated eigenstrain field that is spatially scaled using the part scale peak temperature history. The thermal formulation is evaluated against published numerical and experimental AFSD data and two sample multilayer builds are simulated as demonstrations. For a four layer thin-wall build, the thermal solution requires approximately 22 s compared to 806 s for the finite element model, while the complete thermo-mechanical framework requires approximately 86.4 s compared to 2,406 s. For a larger 20 layer hollow cylindrical build, the reduced order thermal simulations requires 0.148 to 0.152 h compared with 1.8 h for the finite element model, corresponding to thermal speed-ups of approximately 11.8 to 12.2 times. The complete thermomechanical framework requires 0.346 h compared to 5.4 h for the full finite element analysis, providing an overall speed-up of approximately 15.6 times.
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Medical Physics
Whole-skull acoustic transparency from a single time-reversal solve for reciprocity-based transducer placement and aperture optimization in transcranial focused ultrasound
Gianmarco Pinton
Transcranial focused ultrasound is limited by the skull, whose thickness, density and
curvature aberrate and attenuate the beam in a position- and target-dependent way, making the choice of where to couple a transducer for a given deep target a central planning problem. This work shows that a single full-wave time-reversal solve resolves it. A virtual point source at the target radiates outward through a CT skull model, and by acoustic reciprocity the time-reversed field gives the transmit coupling of every point on the skull surface at once (a per-patch skull transparency map) and, in the same pass, the per-element signals of any array. For a phased array, time reversal conjugates the skull aberration, so the optimal placement maximizes the delivered energy, a surface integral over the aperture; a single element instead follows a coherent score mixing delivered energy with phase coherence, and the two optimizers select different windows. Placement, aperture size and orientation are then optimized by searching this single recorded map in seconds, with no per-candidate wave solve. The map is computed on a dry-skull micro-CT model for the left dentate
nucleus with a 1 MHz heterogeneous Fullwave 2 solver at 6.16 points per wavelength with bone attenuation. A 120 degree occipital array refocuses within 0.25 mm of the dentate at 20.7 Pa per 1 Pa of per-element drive, and a 64 mm spherical transducer seated in the delivered-energy-optimal suboccipital window (27 mm from the target) refocuses at 7.9x gain; the same procedure focuses the thalamus at 15.2x and the dorsal anterior cingulate at 11.4x. The aberration correction raises the on-target peak 7.5x in pressure (56x in intensity) over
geometric focusing, which mis-steers the focus by 4.3 mm. The same field measures the aberration's few-millimeter coherence length, which sets the required placement and target-localization accuracy.
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Instrumentation and Detectors
Retrofitting a commercial RF induction generator into a computer-controlled, vacuum and gas integrated annealing system for reactive-metal grain growth
Sterling G. Baird, Ryan Weber, Christopher Nyborg et al. (+3 more)
High-temperature
vacuum annealing near a metal's melting point drives controlled grain growth, but it normally requires an expensive turn-key
vacuum induction furnace. We retrofit a bare commercial
radio frequency (RF) induction generator with computer power control through LabVIEW, dual-wavelength optical temperature feedback, and a high-
vacuum quartz-tube chamber with inert-gas backfill. A machined graphite crucible doubles as a susceptor, an RF-absorbing element that heats the specimen it encloses. The only requirement is a monotonic analog power-control input, so the retrofit transfers between generators. Our reference build uses a 6 kW solid-state generator. Surprisingly, nickel annealed in this system produced high-quality electron backscatter diffraction (EBSD) patterns with zero specimen preparation. Samples went directly from the furnace to the electron microscope without grinding, polishing, or etching. The EBSD maps indexed hundreds of equiaxed grains delineated by deep thermal grooves. A modified sample assembly extends the furnace to ceramics that do not couple to the RF field. It coarsened yttria-stabilized zirconia (YSZ) grains in 45 min at 2500{\deg}, compared with 228h at 1600{\deg} in a conventional box furnace. For a fixed configuration, the power-temperature calibration is linear ($R^2$ = 0.991) from 1200 to 1400{\deg}. Eight 12h nickel anneals at 1200{\deg} reproduced their soak temperature to 1201.2 $\pm$ 1.3{\deg}, and 40h soaks at 1325{\deg} remained stable. Complete design files, a bill of materials, control software, and data are openly available. This gives laboratories an affordable route to near-melting-point annealing with direct anneal-to-EBSD characterization.
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All authors Sterling G. Baird, Ryan Weber, Christopher Nyborg, Ronald Guymon, Gage Erickson, Oliver K. Johnson
Instrumentation and Detectors
A Gamma/Electron Spectrometer with Logarithmic ADC based on LC Tank Ring-Down Oscillation Counting
S. Abovyan, A. Chilingarian, D. Pokhsraryan et al. (+3 more)
This paper describes the operating principle,
circuit implementation, and mathematical basis of a logarithmic analog-to-digital converter (ADC) that exploits the natural exponential decay of a damped LC tank oscillator. An input charge pulse excites a tuned LC resonator into free oscillation. A multi-stage high-speed amplifier chain buffers the decaying waveform, and a fast comparator counts the number of oscillation cycles that exceed a programmable threshold. Because the tank envelope decays exponentially, the cycle count is proportional to the natural logarithm of the input charge, yielding logarithmic compression over a wide dynamic range without explicit logarithmic circuitry. The upgraded unit incorporates a modern MCU with USB, Ethernet interfaces and SD card for collected data storage. The architecture is well suited to applications requiring large dynamic range in a compact, low-power implementation.
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All authors S. Abovyan, A. Chilingarian, D. Pokhsraryan, B. Sargsyan, T. Karapetyan, V.Danielyan
Atmospheric and Oceanic Physics · Cross-listed from q-bio.PE
From objective discovery to prediction of global ocean eco-provinces: A pathway for trustworthy learning
Makayla McDevitt, Maike Sonnewald and Stephanie Dutkiewicz
Marine ecosystems are increasingly impacted by
climate change, necessitating tools to identify and predict spatial habitat information. To build such tools, ecological marine provinces, "eco-provinces", ecologically meaningful regions in the global ocean can be used. We use unsupervised machine learning (ML) to identify eco-provinces with corresponding uncertainty measures based on output of a global simulation of phytoplankton functional types. Our work aims to create a proof of concept to predict eco-provinces based on satellite ocean color data. To do so, we develop a hierarchy of explainable dense ensemble networks to infer how well the eco-provinces can be detected from modeled ocean color fields. Key results include that the delineated eco-provinces are both ecologically meaningful and can be inferred with high skill. However, no straightforward relationship was found where adding more input data to the network consistently improves inference skill, and there is an intricate tradeoff between inputs and prediction fidelity. Our work is a case for optimism and a cautionary tale of needing uncertainty quantification and careful validation of prediction fidelity.
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General Physics
12 nm FinFETs from 292 K to 10 mK: Characterization and a Temperature-Continuous Compact Model for Qubit Control
DaKyung Lee, Liyang Jin, Jungmin Lee et al. (+3 more)
We report cryogenic characterization and compact modeling of GlobalFoundries (GF) 12LP regular-voltage-threshold (RVT) n- and p-FinFETs, measured from 292 K to 10 mK. Both devices retain sub-Kelvin gate control without carrier freeze-out, with the n-type device exhibiting an intrinsic sub-threshold slope (SS) floor of 24.8 mV/dec. To bypass high on-chip series routing resistance that confounds peak-gm extraction, we adopt a fixed-current (3.26 uA/um) methodology. These low-current metrics inform a continuous 1.36 K to 292 K compact model using dynamic parameter injection, preserving room-temperature process development kit (PDK) qualification.
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All authors DaKyung Lee, Liyang Jin, Jungmin Lee, Rohit Rangaraj, Linbo Shao, Jeffrey S. Walling
General Physics
Regular Fuzzy Dark Matter Black Holes and Their Horizon Structure
M. Ilyas, Khalid Masood, Usman Afzal et al. (+1 more)
We construct regular, horizon-admitting compact objects supported entirely by a self-gravitating dark-matter fluid, in the one-parameter
curvature-
gravity family $f(R)=R+\beta R^n$. Working with the Einasto density profile, we derive the anisotropic fluid field equations for a static, spherically symmetric metric and obtain the exact General Relativity limit under a de~Sitter-type equation of state, in which the central singularity is replaced by a regular de~Sitter core and the solution is either a horizonless droplet or a black hole with one or two Killing horizons, depending on a single rescaled-mass parameter. We compute the resulting Hawking temperature and geodesic effective potential, and – exploiting the linearity of the $\beta=0$ field equation – solve the
curvature correction perturbatively in closed form for general $n$, showing that its sign and radial shape are genuinely model-dependent by direct comparison at fixed $\beta$ between $n=2$ (Starobinsky) and $n=3$ (cubic)
gravity. We repeat the construction for a non-local equation of state and confirm the resulting droplets are
curvature-regular via the Kretschmann scalar. Finally, replacing the Einasto profile with the cored Burkert profile preserves the qualitative regularity mechanism but, because the Burkert
halo lacks a finite total mass, produces a horizon structure with inner and outer radii separated by nearly three orders of magnitude – a genuine physical distinction between two comparably realistic dark-matter models.
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All authors M. Ilyas, Khalid Masood, Usman Afzal, Nehad Ali Shah
Geophysics · Cross-listed from cond-mat.soft
Revisiting the hydromechanical formulation of a micromechanics-based phase-field model for poro-elastoplastic media
Hanzhang Li, Tao You, Keita Yoshioka et al. (+3 more)
Even for tension-dominated fracture propagation, porous materials may deform plastically adjacent to the propagating fracture. As is common for porous materials, existing phase-field models typically employ a non-associative flow rule for plasticity, and a Helmholtz free energy based on strain and fluid pressure. This work revisits the hydromechanically coupled formulation of the phase-field model for fracture in poro-elastoplastic media by analyzing the strength surface and fracture driving force. Our analyses show that these common choices of flow rule and free energy will lead to a discontinuous strength surface across the tension-compression transition. A non-associative flow rule introduces a jump at the strength surface, while treating fluid pressure-rather than fluid content-as the independent variable in the Helmholtz free energy omits a coupling term from the phase-field driving force, also breaking continuity. Incorporating an associative Drucker-Prager flow rule and this omitted coupling term ensures a continuous strength surface and the accurate fracture driving force. The proposed model exhibits improved accuracy in hydromechanical responses when compared against the analytical solution of the Kristianovich-Geertsma-de Klerk hydraulic fracturing
benchmark. Numerical simulations of hydraulic fracturing and biaxial compression in poro-elastoplastic media show that the model can reproduce both shear-dominated fractures induced by mechanical disturbance and tension-dominated fractures driven by fluid injection in saturated porous media.
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All authors Hanzhang Li, Tao You, Keita Yoshioka, Yuhao Liu, Yi Rui, Fengshou Zhang
Applied Physics
On-demand thermal power amplification enabled by active heat $Q$-switching
Qian Ye, Aleida Machorro-Ortiz, William Schmid et al. (+3 more)
Thermal management underpins essentially every energy technology, from
solar harvesters and waste-heat recovery to industrial process heating and electronic cooling. Yet, thermal systems remain limited compared to their electrical and optical counterparts: they lack a direct equivalent of active control elements that enable on-demand pulse generation. As a result, in conventional thermal energy storage architectures, the amount of energy stored and the peak power at which it can be released are both fixed at design time by material properties and heat-exchanger geometry, locking each device to a single operating point in the energy–power plane. This
rigidity is incompatible with applications that require short, high-power thermal bursts on demand. Here we show that a counter-flow heat oscillator admits an actively switchable effective thermal quality factor, $Q$, and that modulating $Q$ on sub-dwell-time scales generates transient outlet power exceeding the steady input by more than an order of magnitude. We formalize the system as a dissipative resonant thermal cavity with $Q$ controlled by the balance between advective and conductive transport and environmental losses, and we experimentally demonstrate, in a water-based dual-channel device, $\sim$5-fold transient power amplification through controlled flow detuning, in quantitative agreement with our thermofluidic model. Active $Q$-switching establishes a distinct mode of thermal power management, accessing $\sim$5$\times$ (demonstrated experimentally) to $\sim$40$\times$ (projected numerically) peak-power amplification on continuous input through a single architecture, a regime inaccessible to passive thermal storage and a missing analogue of the active pulse-generation tools long available in optics and electronics.
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All authors Qian Ye, Aleida Machorro-Ortiz, William Schmid, Geoff Wehmeyer, Naomi J. Halas, Alessandro Alabastri
Optics
Fisher-information limits of detector-bandwidth-efficient 3D light-field microscopy
Liang Gao
Light-field microscopy enables snapshot volumetric imaging, but its information rate is constrained by both optical encoding and detector readout architecture. Here we develop a task-dependent Fisher-information framework that evaluates optical encoders relative to the detector resource limiting acquisition throughput. We compare full
Fourier light-field microscopy (FLFM), squeezed light-field microscopy (SLIM), and frame-rate-matched FLFM under a common optical geometry,
photon budget, and row-limited camera model. Sparse scenes are analyzed using a 3D point-emitter Fisher
matrix, and dense scenes using
Fourier-mode information on tilted spectral slices. At s=0.25, SLIM provides 2.40x higher axial Fisher information per camera bandwidth and 1.89x higher 3D D-optimal position information than frame-rate-matched FLFM. For dense scenes, it provides 1.85x higher integrated
Fourier-mode Fisher information per bandwidth, 4x greater axial-frequency extent, and approximately 11x larger projected lateral hard-support area. Sweeps over compression factor and view tilt show that these advantages reflect a general detector-allocation principle rather than a specific operating point. More broadly, the framework can be adapted to other camera architectures by incorporating architecture-specific measurement models and detector-throughput costs, providing a general basis for co-designing optical encoding, scene statistics, and camera readout.
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Optics · Cross-listed from quant-ph
Stability and squeezing of the three-photon degenerate parametric down-conversion
Vinícius V. Seco and Alencar J. de Faria
Nonlinear multiphoton conversion processes are theoretically and experimentally challenging systems in
quantum optics and related areas. These phenomena bring remarkable
quantum properties and can be of fundamental relevance in
quantum information and computation applications. Based on recent experimental advances and the possible uses in generalized three-
photon squeezing, we investigate degenerate three-
photon parametric down-conversion generated inside a cavity fed by a classical pump. In addition, we consider that the process is stimulated by a coherent driving mode and subjected to dissipation by spontaneous emission of the cavity. A treatment using phase-space methods and
stochastic differential equations is applied and the stability conditions of its steady states are found. We find that the system does not exhibit multistability, instead it has a limited parameter region leading to a single stable steady branch, alongside multiple unstable branches. Focusing on the stable steady states and linearizing the dynamics around them, we calculate the spectral densities of the quadrature variables. We identify and characterize the squeezing of three-
photon down-conversion. Moreover, since the quasi-probability differential equations of the higher-order multiphoton processes have higher-order derivatives, hindering their mapping into
stochastic differential equations, we make use of a positive Wigner function approach to calculate two-dimensional spectral densities associated with three-time correlation functions, with the goal of studying non-Gaussian properties of the system.
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Data Analysis and Statistics · Cross-listed from cond-mat.stat-mech
Statistical complexity from fluctuations in the information content
Renio S. Mendes, Sergio Picoli and Evaldo M. F. Curado
We argue that the variance of the information content ($C$), an information-theoretic quantity, can be naturally interpreted as a measure of statistical complexity. We show that $C$ satisfies widely accepted criteria for statistical complexity measures: it vanishes for both ordered and equiprobable states, while attaining maxima in intermediate regimes, typically shifted toward order. This interpretation establishes direct connections with thermodynamics and phase transitions: for systems obeying Boltzmann–Gibbs statistics, $C$ is extensive and directly proportional to energy fluctuations and heat capacity. Moreover, unlike other statistical complexity measures, it attains a maximum at continuous phase transitions, as illustrated for the two-dimensional Ising model. Applications to chaotic maps and fractional Gaussian noise further indicate that $C$ captures nontrivial dynamical structure in different classes of correlated systems.
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Optics
Geometry-Encoded Multireceiver Fluorometry Enables Full-Range Nonlinear Quantification under the Inner Filter Effect
Shuiyi Tan, Nai-Quan Zhu, Olivier J. F. Martin et al. (+1 more)
The inner filter effect (IFE) transforms the nominally linear fluorescence-concentration relationship into a geometry-dependent and often nonmonotonic response, resulting in reduced sensitivity, concentration ambiguity, and inaccurate underestimation at high optical densities. Here, we introduce a spatially encoded multireceiver fluorometric strategy that does not eliminate or correct the IFE, but instead harnesses the spatial fluorescence attenuation induced by IFE as an additional quantitative encoding dimension. Fluorescence generated along the excitation axis is integrated over independently positioned receiver windows, and concentration is recovered by nonlinear optimization of the joint fluorescent intensity vector. Tryptophan was selected as a biomedically relevant model fluorophore to validate the proposed strategy. Single-window calibration exhibited vanishing-gradient boundary and two-valued concentration inversions, whereas two spatially separated receiver windows restored global identifiability across the full concentration range. Screening of 35 two-receiver geometries identified the minimum-uncertainty configuration, achieving an average 95% error half-width of mean E_95= 0.884 mg/L, and the maximum-sensitivity configuration, reaching a noise-normalized response sensitivity of mean S_N=3.832 a.u./(mg/L). By converting spatial attenuation into a multidimensional concentration coordinate, this approach extends quantitative fluorescence analysis without dilution, a separate absorbance measurement, or piecewise calibration and provides a general metrology framework for fluorescence metrology even under strong IFE conditions.
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All authors Shuiyi Tan, Nai-Quan Zhu, Olivier J. F. Martin, Yuchao Fu
Instrumentation and Detectors
PSEC6: an 8-Channel 40 GSa/s Waveform Sampling ASIC in TSMC 65nm with 10.24 GHz PLL
Ahan Datta, Andrew Arzac, Davide Braga et al. (+14 more)
Picosecond level timing resolution is a prerequisite capability for improved coincidence matching, time-of-flight measurements, and secondary vertex reconstruction. Here, we present the specification, design, and simulation results for a new Application Specific Integrated
Circuit (ASIC), called PSEC6, in the TSMC 65nm process. It features 8 channels, a maximum sampling rate of 40 GSa/s, a buffer length of 204.8 nanoseconds, and a 10.24 GHz Phase Locked Loop (PLL), which is the first of its kind in the 65nm CMOS process. The event readout rate is 32 kHz, with the digitization done by an off-chip Analog-to-Digital Converter (ADC). Simulations predict a 4.0 GHz analog input bandwidth and 20 mW per channel during sampling; the 10.24 GHz PLL has a predicted jitter of 550 fs RMS at 15.7 mW. The paper describes the sampling architecture, chip signal paths, PLL design, and presents simulation results.
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All authors Ahan Datta, Andrew Arzac, Davide Braga, Gordon Chen, Troy England, Farah Fahim, Henry J. Frisch, Nathan Gehl, Mary Heintz, Sumin Kim, Ava Lalich, Jinseo Park, Nathaniel J. Pastika, Hector D. Rico-Aniles, Paul M. Rubinov, Xiaoran Wang, Y.M. Richmond Yeung
Atmospheric and Oceanic Physics
Coupled multiscale paleoclimate reconstruction with four-dimensional variational data assimilation
Zilu Meng, Gregory J. Hakim, Julien Emile-Geay et al. (+2 more)
Paleoclimate archives extend
climate knowledge beyond the instrumental era, registering different seasons, variables, time averages, and
memory lengths. A longstanding problem is to integrate these heterogeneous sources of information within a unified methodology. Here we present a new data-assimilation framework, Last Millennium Reanalysis 4D-Var (LMR4D-Var), which reconstructs
climate trajectories from these heterogeneous
datasets while balancing errors in the model, observations, and initial conditions. We compare results using LMR4D-Var to assimilate proxies from PAGES2k, Temp12k, and borehole temperature profiles without treating them as instantaneous equivalents. Instrumental verification shows that LMR4D-Var achieves the highest skill compared with previous reconstructions. Borehole assimilation preserves skill against withheld annually resolved records, increases agreement between reconstructed 300–2000-m ocean heat content and independent estimates, and yields a cooler reconstructed Little Ice Age ocean. Results for Temp12k demonstrate assimilation of decadal-to-millennial records and the potential for Holocene and deeper-time applications with suitable emulators.
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All authors Zilu Meng, Gregory J. Hakim, Julien Emile-Geay, Tanaya Gondhalekar, Eric J. Steig
Optics
Which pulse maximizes resonant nonlinear conversion?
Alex Krasnok
At fixed pulse energy, which drive waveform extracts the most $n$th-order nonlinear conversion from a resonator ($n=2$ for second harmonic)? A short pulse couples poorly to a narrow resonance, a long one dilutes its energy, and no linear rule fixes the compromise. We solve the problem exactly for a single mode of amplitude decay rate $\kappa$. Eliminating the drive turns fixed incident energy into a constraint on the stored field alone, and the optimization becomes a sharp Gagliardo–Nirenberg inequality whose extremal is the ground-state
soliton of the nonlinear Schrödinger equation. The optimal stored field is $\mathrm{sech}^{1/(n-1)}[(n-1)\kappa t]$, sustained by an asymmetric input that rises as $e^{\kappa t}$ and falls as $e^{-(2n-1)\kappa t}$; the largest converted energy follows in closed form. A rising exponential, the time-reversal recipe, retains at most $79.0\%$ of the bound at $n=2$ and $2/e$ at large $n$; a two-rate pulse retains above $97\%$. Critical coupling generalizes to $n$-fold overcoupling, with optimal input coupling $n$ times the intrinsic loss rate. The bound applies from microrings to superconducting
circuits and caps the per-pulse brightness of broadband
photon-pair sources.
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Optics
In-situ Time-domain Physical Adjoint Optimization of Complex Wave Dynamics
Hoyeong Kwon, Arunn Suntharalingam, Laureano Bulus-Rossini et al. (+1 more)
Direct optimization of complex wave dynamics through the intrinsic
evolution of physical systems is fundamentally limited by the lack of directly accessible gradients. Adjoint methods provide an exact route to gradient computation and have enabled optimization in numerical solvers and, more recently, in frequency-domain physical platforms. Yet their extension to the time domain has remained out of reach, as reproducing time-reversed propagation appears to require non-causal operations or compensating gain. Here we develop a protocol and experimentally demonstrate that time-domain adjoint dynamics can be realized in-situ in linear physical systems without gain, non-causal elements, or auxiliary backward networks. By combining time remapping with a transformation of system variables, we obtain a physically realizable adjoint
evolution that constructs gradients from measurable signals. We experimentally demonstrate the approach in a complex RLC network, realizing in-situ optimization for time-dependent objectives, including time-windowed and broadband responses. This framework unifies physical optimization by enabling both system parameters and source excitations to be optimized within the same platform. Our results close the gap between adjoint theory and physical implementation, establishing a general foundation for hardware-native, in-situ temporal optimization across a broad class of complex dynamical systems.
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All authors Hoyeong Kwon, Arunn Suntharalingam, Laureano Bulus-Rossini, Tsampikos Kottos
Plasma Physics
Determining neutral fueling response to RMPs in MAST using a multi-reservoir particle balance model and EMC3 EIRENE
Kurt Flesch, James Harrison, Andrew Kirk et al. (+4 more)
The application of certain configurations of resonant
magnetic perturbations (RMPs) has been shown to cause a
plasma pump-out in both L- and H-mode discharges at MAST. In this paper we discuss the impact of neutral fueling on this density reduction. The neutral fueling and average particle confinement time $\tau_p$ of the main ion species were calculated using a 0-D particle balance analysis. When the RMPs were applied, it was found that there was an increase in ionizations and a 15$\%$ reduction in $\tau_p$ for L-mode discharges and a similar result for inter-ELM (edge localized modes) periods of H-mode discharges. A time-dependent global multi-reservoir particle balance (MRPB) was developed, which included atomic and molecular reservoirs, to further investigate the role neutrals had on the density change. We discuss how this model was able to accurately reproduce the experimentally measured density reduction and ionization increase due to either a reduction in $\tau_p$ or a reduction in particle fueling efficiency. Results from EMC3-EIRENE modeling indicate this change could be attributed to neutral particle fueling occurring in locations with now-opened field lines due to the chaotic edge-region from RMP applications.
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All authors Kurt Flesch, James Harrison, Andrew Kirk, Ian Waters, Heinke Frerichs, Oliver Schmitz, Livia Casali
Optics
Measurement and Optimal Targeting of a Hidden Scatterer in a Complex Environment Utilizing Fisher Information
Nadav Shaibe, Jared Erb and Steven M. Anlage
A complex, non-Hermitian scattering system with a high degree of multiple scattering and interference is often treated as a black box, described simply by the relationship between a set of incoming and outgoing waves of a given frequency or energy. The scattering
matrix S that describes the system is a non-unique, generally sub-
unitary matrix that reveals very little about the microscopic processes that are responsible for the observed scattering. We form the Fisher information operator $F_x$, a Hermitian
matrix, utilizing a derivative of S with respect to the value of some varying parameter x of the system, associated with a localized perturbation, and experimentally demonstrate that the principal eigenvector of Fx can be used to quantitatively measure changes in the value of parameter x using only information from the scattering
matrix. We propose a "discrete feedback loop" protocol enabled by the knowledge we gain from the Fisher information operator, that repeatedly determines the counter perturbation necessary to return a varying parameter to some fixed
benchmark value. A further application of the Fisher information operator for energy focusing that utilizes the principal eigenvector excitation is demonstrated through compelling indirect evidence of targeting within a complex system. These methods are experimentally demonstrated to work even in the presence of time-reversal
symmetry breaking due to absorption and/or loss of scattering reciprocity.
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Physics and Society
Second-Order Continuum Model for Disordered Traffic
Shashank Rajput, Venkatesan Kanagaraj, Martin Treiber et al. (+2 more)
In this study, a two-dimensional second-order macroscopic traffic flow model is proposed to capture the complex dynamics of disordered traffic by explicitly incorporating coupled longitudinal and lateral interactions. The framework extends the classical continuity equation to two spatial dimensions and introduces acceleration equations consisting of self-driven, interaction-induced, and road-boundary-related components. The macroscopic longitudinal acceleration is formulated based on the Full Velocity Difference Model (FVDM), while lateral dynamics are governed by interaction principles consistent with the Optimal Velocity Model (OVM). The explicit inclusion of road-boundary effects enables the representation of vehicle confinement and space-sharing behavior that are essential in lane-free and weakly lane-disciplined traffic systems. The model is examined through a series of numerical experiments in which longitudinal and lateral dynamics are analysed individually as well as simultaneously within a coupled two-dimensional setting under a range of initial conditions, including transitions between free-flow, medium congestion, and heavy congestion, and different lateral density configurations. The simulations demonstrate the model's ability to reproduce key traffic features such as shockwave propagation, lateral dispersion, vehicle rearrangement, and stable density
evolution across the road width. The numerical scheme, based on upwind and Lax-Friedrichs discretisations, ensures stable solutions of the coupled partial differential equations. Overall, the proposed framework provides a robust macroscopic description of disordered traffic and offers a consistent basis for analysing two-dimensional vehicular flow dynamics.
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All authors Shashank Rajput, Venkatesan Kanagaraj, Martin Treiber, Gowri Asaithambi, Ostap Okhrin