24,028 papers in this slice of arXiv.
Enrico Di Lucente, Michele Simoncelli, Nicola Marzari
Thermal transport in dielectric, non-magnetic crystals is mediated by quantized lattice vibrations, which drift and interact when driven out of equilibrium by a temperature gradient. This phenomenon can be described at multiple theoretical levels, ranging from fully quantum descriptions to semiclassical and mesoscopic continuum approaches. This review rigorously discusses the theoretical steps and approximations connecting these levels, bridging quantum phonon Dyson and Kadanoff-Baym equations and semiclassical Boltzmann transport formalism, and discussing the coarse-graining procedures that yield mesoscopic viscous heat equations for non-diffusive, hydrodynamic heat transport in devices. We show how the Guyer-Krumhansl and dual-phase-lag equations emerge as special linear-isotropic-band and inviscid limits of the viscous heat equations, respectively; most importantly, we demonstrate that these equations predict not only Poiseuille flow and second sound, but also more exotic effects such as negative thermal resistance, steady-state thermal backflow and vortices. We highlight how combining these frameworks with first-principles simulations connects microscopic phonon physics to observable non-diffusive heat-transport phenomena and guides their detection, amplification, and control. We recast the viscous heat equations in terms of Helmholtz and biharmonic equations solved analytically, and use this to discuss similarities and differences between the macroscopic behavior of the phonon fluid and other hydrodynamic systems, such as classical and electron fluids, focusing on compressibility, vorticity, and their influence on phonon hydrodynamics. We conclude with a roadmap to generalize the tools used to describe phonon hydrodynamics to other quasiparticles, motivating future advances in collective quantum transport phenomena in solids.
Róbert Kovács
Phenomenological models of non-Fourier heat conduction often lack a strict microstructural foundation, leading to ambiguities when modeling complex heterogeneous materials. In this study, we derive a continuum heat equation beyond Fourier's law using spatial volume averaging for a two-component system. We analytically prove that the experimentally observed static and dynamic thermal diffusivity arise directly from the distinct material properties, concluding that heterogeneous media are inherently over-diffusive. The resulting heat equation is thermodynamically compatible, and the microstructural origin allows the calculation of non-Fourier transport coefficients. Furthermore, we demonstrate that finite-sample boundaries introduce higher-order spatial non-localities, thereby explaining the size dependence of over-diffusion. We validate the model against experimental data across metal and carbon foams, rocks, and metal-organic frameworks.
Seong-Jae Eom, Vasanthan Devaraj, Sunghyun Kwak +4
We introduce a bioinspired microactuator fabricated via a one-step meniscus guided 3D nanoprinting technique. This technique directly produces a freestanding three dimensional composite architecture by integrating a rigid nanoparticle framework with a hygroscopic polymer matrix in a single, assembly free process. Inspired by the functional integration of rigid and compliant components in insect exoskeletal joint, our design synergistically combines load-bearing strength and humidity-driven swelling in a single microscale pillar. Comprehensive experiments, including comparative control structures and microscopic analysis, elucidated the actuation mechanism: the nanoparticle scaffold provides mechanical support while the polymeric phase provides volumetric expansion, yielding large reversible elongation under humidity with preserved structural integrity. The resulting AuNP PVP microactuator shows humidity responsive actuation at the microscale, with representative demonstrations of repeated humidity cycling and load lifting up to approximately 800 times its estimated own weight under the tested conditions. Variant geometries such as hinged pillars demonstrate how axial swelling can be converted into bending motion, and an optical configuration shows how actuation can modulate reflected light signals. This nanoprinting approach provides a simple strategy for constructing bioinspired soft microactuators with humidity-responsive deformation and potential applicability in microscale sensing, optical modulation, and adaptive microdevices.
Akilesh Srikanth, Md Saklain Morshed, Chandan Joishi +2
We propose and demonstrate the first vertical Gallium oxide device architecture without the use of planarization etch back processes or mid-gap acceptor regions. The Isolated Source Electrode Field Effect Transistor (ISEFET) incorporates a dielectric blocking layer to access an isolated source pad extending from the top fin metal. Scaled multi-fin channels were formed by electron beam lithography with a width of 200 nm along with the source pads and then etched to a trench depth of ~1.2 um. The fabricated devices showed enhancement mode operation with threshold voltage of 2 V and on-off ratio > 1e7 with excellent gate modulation characteristics. The resulting device proved to be comparable to existing vertical transistors and suitable for high-throughput prototyping and large-scale manufacturing of future Gallium oxide and other wide bandgap semiconductor devices.
William Khalili
The probe position of a microstrip element is normally chosen from the isolated-element input resistance. This paper replaces that procedure with a decision available before any array optimisation. A single Floquet unit-cell solution at one arbitrary probe position is decomposed into a feed inductance, a transformer ratio carrying the probe position, and an array-loaded resonator. Three closed-form results follow. The set of input impedances reachable by probe position and resonant length is a disk in the impedance plane. An exact match to a real reference Z0 exists if and only if Rp >= Z0 + Xp^2/Z0. When this fails, the best attainable reflection follows from the image of that disk under the bilinear map. Admitting one series reactance as a second variable, the worst-case reflection over a scan sector is shown to be quasiconvex and globally solvable by bisection. The results are applied to a sixteen-element X-band array and the corresponding 16x24 lattice. For the array considered, the isolated interior element is matched to -16.94 dB while the broadside active reflection is -6.6 dB. For the two-dimensional lattice the criterion is violated at every scan angle, and the minimax design improves the worst-case sector reflection from -2.6 to -11.1 dB. Both matching designs are predictions of the extracted circuit model and have not been re-solved in the full-wave model.
Bibo Zhong, Jinying Zhu
Third-order elastic constants (TOEC) play an important role in nonlinear material characterization, but measurements of TOEC are laborious with large error margins. This Letter presents the equations of wave velocity changes caused by homogeneous temperature variation and uniaxial stress in isotropic media and the expression of TOEC in terms of thermally induced velocity change and thermal strain. TOEC of an aluminum sample were experimentally determined by measuring ultrasonic wave velocity changes in the uniaxial loading test and the thermal modulation test. Experimental results showed good agreement between the two test methods. Owing to the simple test setup and high measurement sensitivity, the thermal modulation test is a potential experimental method to determine TOEC and absolute acoustic nonlinearity parameters.
D. Tsiklauri
We establish a self-consistent 2D hydrothermodynamic analytical model for the localized thermal ablation of dense human tumors using high-intensity focused ultrasound. By expanding compressible Navier-Stokes equations up to second order, we demonstrate that within a structurally stationary cellular tumor matrix, acoustic streaming (acoustic wind) velocity is suppressed. This constraint forces the absorbed wave momentum flux to transfer entirely into localized, time-averaged, static, second order, pressure gradients, converting the bulk acoustic energy directly into localized heat. Using a short, 1 s, duration, high-amplitude top-hat pulse, we solve the simplified Pennes bioheat transfer equation within non-diffusive timescales. Adapting the hydrodynamic optimization framework established by Tsiklauri (2026), we derive a natural physical criterion where the acoustic absorption coefficient matches half the inverse target depth, α=1/(2x0), proving that the optimal operational frequency scales inversely with transmission distance. We show that while incident plane waves overheat upstream tissues due to exponential decay, a spherically focusing wave geometry effectively bypasses healthy tissue boundaries via geometric convergence (∝1/r2). Analytically solving the non-isothermal Arrhenius injury integral yields a sharp lesion boundary radius at rb=0.75w0. Volumetric averaging bounded strictly within this necrosis perimeter demonstrates that the average tumor temperature reaches 72.1∘C while central point values peak at 90∘C. Finally, convolving the post-pulse thermal profile with a 2D free-space Green's function verifies immediate, monotonic temperature decay below 60∘C at the boundary, demonstrating complete structural containment and explaining the >90% localization rates observed in clinical applications.
Alexander Müller, Maximilian Berndt, Hagen Schmidt +5
The surface texture of a turned component acts as a fingerprint of both the process parameters and the tool wear condition, imaging the cutting edge. Classical surface parameters such as Ra or Rq describe the topography only globally and allow no spatially resolved evaluation of the process-induced deterministic structures. This work investigates how far the feature characterization standardized in ISO 21920-2 makes this wear information accessible and physically interpretable. The database comprises roughness profiles of twelve AlTiN-coated carbide inserts (CNMG120408) machining normalized AISI 1045 steel, measured at nine wear states over the entire tool life, with three replicate profiles per state. The correlation of standardized field and feature parameters with crater wear, flank wear, and cutting time is first examined. Watershed segmentation is then adapted to extract the rotational tool grooves and evaluate their geometry statistically. A newly developed mean-feature approach decomposes the profile into a deterministic and a stochastic component. Wear-induced changes are almost entirely carried by the deterministic component, and within it by the trailing flank of the cutting groove. A comparison with confocal measurements confirms that the mean feature reconstructs the engaged cutting edge geometry, with the trailing-flank steepening attributable to notch wear on the secondary cutting edge. An exhaustive evaluation of more than 920,000 feature characterization combinations and multivariate models reveals that the groove-level mean maximum absolute gradient Rdtgroove alone explains 83-90% of the variance of the wear indicators, so that a single, physically motivated parameter suffices for robust wear estimation. A follow-up study will investigate inline monitoring using scattered light sensors.
Bruno Neumann, Andreas Henschke, Morik Nikolic +1
Low-grade waste heat below 100 degC is one of the largest untapped opportunities in solid-state energy conversion. Three ferroic routes are candidates for recovering this resource: thermomagnetic, pyroelectric, and thermoelastic harvesters. The last has remained the most unexplored, despite decades of progress on the underlying NiTi shape-memory alloy wires. Three system-design changes close this gap: a protagonist-antagonist architecture that recovers the energy for prestraining, a continuously tunable prestrain mechanism that sets the force-strain balance, and transversal water flow that decouples cycle frequency from wire length. The resulting harvester delivers a directly measured power density of 366 mW/cm^3 with respect to the active material, about 1.7 times the next-best thermoelastic device, ahead of every reported thermomagnetic and pyroelectric generator, and outperforming the best thermoelectric generators in this temperature range also with respect to power per material cost. The system maps the parameter space directly through force and displacement measurements, without using material-property estimates, giving a quantitative picture of how the alloy responds while the device is doing work.
G. Hoffmann, A. A. Riaz, C. Kalha +7
Perovskite oxides and their heterostructures exhibit a wide range of functional properties. Among these materials, BaSnO3/LaInO3 heterostructures form high-mobility two-dimensional electron gases (2DEGs) at their interfaces. In particular, room-temperature electron mobilities exceeding 100 cm2/Vs were enabled by recent advances in thin-film growth. This work presents a combined experimental and theoretical study of the electronic structure of BaSnO
Michael P. Path, Jeffrey McCord
Applications in high-voltage and electromagnetically harsh environments require reliable galvanically isolated voltage sensing, which can be achieved using optical readout. While established optical voltage sensors rely on electro-optic effects or piezoelectric strain with direct optical detection, strain-mediated magnetoelectric coupling combined with magneto-optical readout offers an alternative voltage sensing principle that remains largely unexplored. Here, such a sensor based on a bismuth-substituted yttrium iron garnet magneto-optical indicator film mechanically coupled to a piezoelectric actuator is presented. Voltage induced stress results in changes of the out-of-plane magnetization via magnetoelastic coupling which is detected through magneto-optical Faraday rotation. A critical state of the domain structure is set via an applied bias field, in which voltage-induced nucleation and domain-wall motion dominates the response. In this high sensitivity regime, both AC and DC voltage readout modes are demonstrated, based on either voltage-driven magnetization reversal or voltage-induced modifications of the magnetization loop shape. Equivalent voltage noise densities in the millivolt per root hertz range are achieved. The results establish strain-mediated magneto-optical voltage sensing as a distinct approach to optically isolated voltage measurement.
Giancarlo Sportelli, Nicola Belcari, Roberta Pace +4
Non-destructive X-ray imaging can reveal internal hazelnut defects that are difficult to detect by external inspection alone; however, automated interpretation remains challenging because of subtle radiographic differences among classes, marked class imbalance, and limited annotated data. Here, we present a benchmark for binary hazelnut quality classification (healthy versus defective) based on 799 segmented single-kernel X-ray images (224 x 224 pixels, grayscale), grouped into 101 acquisition units. Seven single-model configurations and ten probability-aggregation ensembles were evaluated using a group-wise split-rotation protocol across five data splits generated using different random seeds. Decision thresholds were selected on the validation set, and performance was assessed deterministically on validation and test sets. Under the expert-reassessed annotation condition, the average-probability ensemble of the binary cross-entropy-trained convolutional neural network and frozen Swin Transformer achieved the highest mean balanced accuracy (86.3% +/- 1.8%, five seeds), with several other ensembles providing comparable performance. Across methods, substantial split-to-split variability was observed, indicating that multi-split evaluation is essential for reliable model comparison at this dataset scale. Expert reassessment of ambiguous samples improved the performance of all 17 evaluated methods by 2.8-8.1 percentage points, while having only a limited effect on cross-split variance. The results highlight both the potential of deep learning for automated X-ray-based hazelnut quality assessment and the importance of rigorous evaluation and label curation in small, imbalanced agricultural imaging datasets.
Rui Li, Xinrui Li, Jiachen Xie +8
Electroluminescence occurring without external charge injection is typically characterized by weak emission and excessive driving voltage, due to low excitation and radiative recombination efficiencies. Here, we demonstrate non-injecting electroluminescence (NI-EL) that challenges this conventional perception. To achieve this, we introduce an operational paradigm that leverages remote, state-abundant charge reservoirs, which elevates the excitation efficiency close to unity - a greater-than-20-fold improvement over the benchmark. This strategy is augmented by quantum dots (QDs) with nonmonotonically graded shells, raising the high-field radiative efficiency by approximately 7-8-fold. The resultant RGB NI-EL devices uniformly exhibit bright and efficient pulsed emissions, with key metrics including: a turn-on threshold of 3.7 Vrms for red; a luminance of 291,628 nits and a power efficiency of 302.6 lm/W for green, with light-outcoupling enhancement; and, for blue, the superior emitter stability of the first QD-based blue NI-EL over its light-emitting diode counterpart. The minimal dielectric loss, sub-100 ns response time, and external EL efficiency of up to 45.4% further reinforce the mechanism-performance causality. These results overcome the inherent mechanistic limitations of NI-EL and establish performance that rivals or surpasses injection-type EL, including AC- or DC-driven variants, positioning NI-EL as a promising platform for high-performance pulsed light sources.
Xiaoyue Xia, Zhicheng Lin, Hao Guo +7
Future indoor embodied-intelligence systems require scalable hardware platforms that support both high-capacity multi-agent connectivity and mutual spatial awareness. The terahertz (THz) spectrum offers abundant bandwidth and inherent spatial selectivity for integrated sensing and communication (ISAC); however, conventional phased arrays and programmable metasurfaces rely on dense beamforming networks, element-level control, or external THz illumination, making scalable multibeam operation challenging. Here, we report a fully integrated 208-258GHz 65-nm CMOS THz transceiver chip that monolithically integrates broadband front ends with heterogeneous leaky-wave metasurface (HLM) apertures within a 1.5mm by 4.9mm area. The HLM generates strongly dispersive leaky modes, enabling 75 degree frequency-controlled beam scanning with only four meta-atoms. Co-design of frequency-domain and spatial-domain mixing achieves spectrally clean frequency-to-space mapping for spatial-frequency division multiple access (SFDMA) communication. The THz chip demonstrates multi-agent simultaneous transmission and reception, two-dimensional localization, and sensing-enhanced communication, providing a scalable hardware platform for future THz embodied-intelligence networks.
Ziyu Huang
Predicting the products of ionic-liquid impacts on extractor surfaces is important for electrospray-thruster lifetime analysis, yet available atomistic methods require a compromise between chemical fidelity and computational cost. Reactive force fields enable high-throughput sampling but do not explicitly resolve electronic charge redistribution and may miss relevant reaction pathways during impact, whereas mixed quantum--classical density-functional-theory molecular dynamics (DFT/MD) can capture charge redistribution and neutral-product formation at substantially higher computational cost. Pretrained atomistic foundation models have recently emerged as a potential route toward DFT-like chemical fidelity at considerably lower cost. Here, we benchmark two pretrained machine-learning interatomic potentials, MACE-MP-0 (medium) and MACE-POLAR-1, against DFT/MD and ReaxFF for geometry optimization of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) and for 10-100 eV impacts on a model Au extractor surface. The models reproduce several collision outcomes observed in DFT/MD, including ionic dissociation, high-energy covalent fragmentation, and, in particular, HF formation through neutralization-like chemistry that is not captured in the ReaxFF simulations. In the computational-performance benchmark, MACE-POLAR-1 and MACE-MP-0 (medium) completed each 2 ps trajectory in 5.12 and 2.54 min, respectively, corresponding to wall times approximately four orders of magnitude shorter than the DFT/MD reference under the reported benchmark conditions. These results support pretrained machine-learning potentials as a practical intermediate-cost approach for chemically resolved electrospray-impact simulations and motivate targeted fine-tuning with DFT data for broader applications in electrospray-thruster and electric-propulsion modeling.
Yuge Liang, Peilin Xin, Enock Adjei Agyekum +6
There is a growing demand for minimally invasive methods to analyze intracellular processes and signaling activities in individual living cells, including the identification of tumorigenic cell subpopulations. However, most conventional analytical methods require cell lysis, precluding repeated measurements in the same cell over time, or rely on exogenous labels and reporters that may perturb cellular function. Various applications based on vertical nanotubes have been developed that enable live cell monitoring and analysis by electroporation with low voltages. However, the extent and duration of membrane permeability and kinetics of membrane repair remain elusive. Here, we built a plasmonic platform with the capacity of surface enhanced Raman spectroscopy (SERS) to monitor the electroporation-induced membrane permeability dynamics in individual live cells attached onto 100-nm diameter nanotubes of 2 um height. Fibronectin was employed as extracellular matrix (ECM)-coating to facilitate cell attachment onto nanotubes. Using fluorescent-dye delivery as an independent validation method, we show that the fabricated nanostructures induce localized electrical permeabilization of the plasma membrane and enable monitoring of its subsequent recovery. We further use SERS to track molecular changes at the membrane during permeabilization and resealing. The SERS spectra provide molecular-level insight into changes in membrane-associated components and the ECM during electroporation and subsequent membrane recovery. Real-time analysis of pulse-induced molecular-changes holds great promise single-cell profiling of, intracellular signaling, and cellular states, and cellular heterogeneity, including identification of tumorigenic cell subpopulation. This capacity could facilitate the development of novel biosensing assay.
Liga Jasulaneca, Alberto Martín-Pérez, Hongji Zhang +7
Atomically thin mechanical resonators have been realized predominantly in crystalline two-dimensional (2D) materials, such as graphene, where long-range crystalline order sets their elastic properties and defines their nonlinear resonant behavior. Extending these concepts to the amorphous 2D limit has remained largely unexplored. Here, we demonstrate that monolayer amorphous carbon (MAC) forms suspended membranes that support optothermal actuation and sensitive interferometric readout across both linear and nonlinear regimes of its resonant motion. We resolve thermomechanical motion, driven resonances, and multimode spectra in MAC nanodrums. The frequencies of fundamental vibration modes correspond to unusually low pretensions, placing monolayer MAC nanodrums in a regime where geometric nonlinearities, stress heterogeneity, and mode coupling emerge at comparatively low drive powers. Consistently, we observe pronounced nonlinear dynamics, including hardening, softening, and mixed Duffing responses, nonlinear damping, parametrically excited modes, and signatures of intermodal coupling. These results establish MAC as a robust nanoelectromechanical platform and open an experimental route to disorder-governed nanomechanics in the 2D amorphous limit.
Jialin Zhang, Yong Zhang, Hong Zhao
Obtaining equilibrium distributions of nonlinear systems is essential for accurately computing macroscopic observables. Conventional theoretical corrections are typically limited to weak nonlinearities, where interaction terms can be treated as effectively uncorrelated perturbations and the random phase approximation applies. In this Letter, we develop a framework to determine equilibrium distributions based on the generalized energy equipartition principle. Our approach recovers existing corrections in the weakly nonlinear regime and, crucially, remains valid for strong nonlinearities, where perturbative contributions become correlated and conventional approaches break down. Numerical simulations of the nonlinear Schrödinger equation, the Majda-McLaughlin-Tabak model, and the Fermi-Pasta-Ulam-Tsingou model demonstrate accurate corrections for nonlinearities more than an order of magnitude stronger than those accessible to conventional theories.
George Yamoah Afrifa, Theophilus Ansah-Narh, Marcellin Atemkeng
Groundwater variability in Ghana remains poorly characterized due to limited long-term in-situ observations. This study investigates groundwater storage anomalies using GRACE-derived data from 2004-2024 combined with statistical analysis and unsupervised machine learning. Groundwater anomalies were standardized using Z-scores, while an ensemble-based Isolation Forest framework was applied for anomaly detection. The results revealed substantial temporal variability, with persistent groundwater deficits during 2004-2009 followed by increasing positive anomalies after 2018. A total of 12 anomalous months were identified, comprising 5 deficit and 7 surplus events, with the strongest anomalies associated with groundwater deficits. Spatial analysis showed more frequent deficit anomalies in northern Ghana and stronger surplus occurrence in southern regions. Comparison with statistical thresholds further indicated that the machine learning framework captured additional subtle deviations beyond conventional threshold-based methods. Overall, the integration of GRACE observations with unsupervised anomaly detection provides a practical framework for groundwater monitoring in data-scarce environments.
Aleksei A. Nasonov, Mikhail V. Murzin, Nikolay V. Anisimov +4
Purpose: In magnetic resonance imaging (MRI), preamplifier decoupling is used to improve the signal-to-noise ratio of a multichannel receive coil array. In low-field and ultra-low-field MRI, low-noise amplifier (LNA) solutions with low input impedance (LII) are poorly represented and consist mostly of field-effect transistors. We propose a low-cost LNA based on a common-base circuit with bipolar transistors to achieve LII (<5 Ohm), a low noise figure (<1.3 dB), and high gain (>30 dB). Methods: The proposed LNA circuits were simulated, fabricated, and tested at frequencies of 3 MHz and 21.2 MHz. The decoupling capabilities of the proposed LNA were experimentally evaluated, and MR imaging was performed in a 0.5T MRI scanner alongside a comparative study with a commercial LNA. At 3 MHz, the LNA was evaluated by analyzing free induction decay signals. Results: Proposed LNA solutions demonstrate a low noise figure below 1.3 dB with an input impedance of 3 Ohm. It was also shown that the presented LNA circuit enables high SNR values in MR imaging. The developed amplifiers demonstrate superior performance compared to available commercial options within the selected HF band. Conclusion: Due to the availability and cost-effectiveness of the selected transistors, the proposed LNA circuit is highly suitable for low-field MRI applications.