Wednesday, 4 November 2026: 6 new papers, 6 cross-lists and 3 replacements in Applied Physics (physics.app-ph), in arXiv's order, with full abstracts. The same papers as arXiv's own listing, set as a newspaper; every title links to arXiv.
The detection of organics and potential biomolecules is an important goal of planetary science and astrobiology spacecraft missions, and many types of analytical chemistry for studying organics depend upon liquid solvents as working fluids. However, most liquids are difficult to maintain in the vacuum of space, complicating their use and increasing spacecraft mass and cost. Here we present a study using Direct Analysis in Real Time mass spectrometry (DART-MS) as a rapid screen for the detectability of histidine, glycine, arginine, lysine, and aspartic acid at mole fractions of about $5\times10^{-4}$ to $10^{-3}$ in five vacuum-stable liquids: EMI-BF$_4$, EMI-acetate, DEMA-MsO, DEMA-OTf, and glycerol. In all of the ionic liquids, the solvent cation dominated the spectra and no amino acid was detected, apart from a weak histidine signal in EMI-BF$_4$ at 350$^\circ$ C (median 5\% of the normalized peak intensity). The protic DEMA ionic liquids did not enhance detection, and their ionic components instead dominated the mass spectra. Aspartic acid was not detected in any liquid. In glycerol solutions, histidine, glycine, arginine, and lysine were all detected, and histidine was frequently a dominant line. We thus find glycerol to be the most promising of the liquids tested for organic detection with an ideal operating DART helium temperature of 350--400 $^\circ$C. We also found no clear evidence of water uptake or aqueous alteration in the ionic liquids, which was a secondary goal relevant to ionic liquid spacecraft electric propulsion.
Artificial dielectric materials (ADMs) offer a flexible means of shaping radiofrequency fields in magnetic resonance imaging (MRI). However, ADM designs based on plane-wave characterization may not directly predict their effects on RF fields in MRI. We propose a travelling-wave microstrip-line (MSL) approach to approximate the spatially nonuniform excitation experienced by dielectric pads near MRI RF coils and to guide ADM characterization and tuning against a reference dielectric. Both materials are tested under identical MSL measurement conditions, and the ADM geometry is adjusted until its reflection minimum occurs at the same frequency as that of the reference. Simulations and bench measurements show that the tuned ADM more closely matches the reference dielectric's reflection-minimum frequency than a plane-wave-based design. MRI simulations show that the tuned ADM produces a transmit magnetic-field distribution similar to that of the reference pad. Phantom images acquired at 7 T also show similar image-intensity patterns. These results demonstrate the utility of MSL response matching for guiding ADM design in the tested configuration. The proposed approach provides a practical bench-top step for assessing and tuning manufactured ADMs before MRI evaluation.
Acoustic holography in the megahertz range can impact applications from manufacturing and non-destructive testing to transcranial ultrasound. Designing lens topologies for complex holograms in the sub-megahertz to low-megahertz regime most relevant to transcranial therapy is difficult because wave propagation through an acoustically thick lens cannot be ignored. Here we show that the heterogeneous angular spectrum approach (HASA), which admits in-plane varying speed-of-sound maps and supports rapid differentiable optimization with the Adam optimizer, can generate three-dimensional lens topologies directly. With it we quantify the failure of the thin-element approximation (TEA) at these frequencies, where lenses enter an acoustically thick regime (thickness L much greater than the wavelength) governed by refractive walk-off, and we introduce a dimensionless refractive walk-off number Nw that defines a frequency-dependent operating regime. Topology optimization outperformed TEA-based design in all 45 configurations tested, with the largest structural gains at or below 1 MHz; for high-numerical-aperture designs the fidelity at 1 MHz matched that at 2 MHz, while structural similarity was highest at 0.5 MHz. The sub-megahertz to low-megahertz window is therefore a favorable operating regime for high-fidelity transcranial holography rather than one to be avoided. Free-field hydrophone measurements of 3D-printed lenses reproduced the designed patterns, and because the framework also accounts for aberration in heterogeneous media, patient-specific lenses corrected skull-induced aberration in simulation and ex vivo experiment, generalized across skull segments, and shaped volumetric beams through the human skull. Together these results provide a framework for designing simple, economical, and high-performance ultrasound systems.
Terahertz (THz) waves are highly sensitive to water and therefore offer a promising noncontact approach to wheat moisture sensing, but existing THz studies have been limited to static samples. This article investigates moisture sensing based on the performance of a THz channel in falling wheat, as encountered at grain intake. The channel power loss is measured at six frequencies from 120 to 320 GHz for three moisture contents and interpreted with a physics-based model that couples the double-Debye permittivity of water, Landau-Lifshitz-Looyenga mixing, and Lorenz-Mie extinction. The model reproduces the measured loss. Above the extinction maximum, the dielectric moisture response peaks where the wavelength approaches the kernel diameter, and that a two-frequency loss ratio removes the loading dependence. A channel-level analysis of QPSK and 16-QAM links shows that a 1 dB moisture-induced loss change alters the bit error rate (BER) by a factor of 3 to 30. THz communication channels at grain intake could therefore sense moisture as a byproduct of data transmission.
A series of monocrystalline lithium niobate (LN) thin films on low-resistivity silicon (LNOS) substrates, with thicknesses ranging from micrometers down to tens of nanometers, were prepared through chemical-mechanical polishing of pristine crystal films. By employing the electric-field poling technique, high-quality periodically poled lithium niobate (PPLN) structures with submicrometer periodicity were fabricated in these LNOSs, and full-thickness polarization reversal beneath the poling electrodes with a well-defined depth profile was achieved. The coercive field was found to follow the Kay-Dunn scaling law, while the lateral domain broadening generally increased with increasing film thickness, and it remained approximately constant across different electrode linewidths at a given film thickness. PPLN structures with periods ranging from 6 $\mu$m down to 200 nm were demonstrated. These findings provide guidance for poling electrode design and lateral domain broadening pre-compensation, offering a practical route toward scalable domain engineering in LN thin films with promising potential for compact and highly integrated nonlinear photonic devices.
The ability of mechanical systems to perform basic computations has gained traction in recent years, providing a robust supplement to digital computing in off-grid, low-power, and extreme environments where electronics are inaccessible or risk failure. However, prior work has focused on Boolean logic applied via bistable structures, snap-through mechanisms, or origami lattices. Digital signal processing (DSP) underpins a wide range of computational tasks, providing the foundation for information encoding, manipulation, and analysis. In contrast to conventional DSP approaches, we present a new paradigm for analog information processing, where an elastic substrate houses a spatial wave-based platform for mechanical signal manipulation in the temporal domain. The proposed metasurface-based system exploits temperature-dependent phase transitions of shape memory alloys (SMAs) to realize key signal-processing functionalities, including gating, retention, and programmable delay of impinging mechanical loads. In doing so, we address a new set of challenges by manipulating transient mechanical waves through dispersive and lossy media. Building on this capability, we introduce the concept of mechanical wave-based memory, in which a locally resonant metamaterial's dispersion characteristics are actively reconfigured to achieve programmable delays while preserving spatial waveform integrity, and demonstrate its utility in the context of input shaping and frequency demultiplexing of superimposed waves. More broadly, the modular and scalable nature of the demonstrated framework paves the way for advanced mechanical computing architectures, enabling higher-order operations such as signal classification, parallel processing, and reservoir computing through the controlled sequencing and temporal alignment of mechanical signals.
The transmission of shock waves generated by underwater electrical foil explosions across solid materials with varying acoustic impedances and thicknesses is investigated. Copper foils with thicknesses of 10 and 18 $\mu$m are exploded on planar substrates of aluminum, copper, and 3D-printed PLA with thicknesses up to 5 mm using a multi-gigawatt pulsed-power electrical discharge. The resulting shocks are visualized in water using high-speed shadowgraphy at 5 million frames per second, while high-resolution fiber optic hydrophone measurements provide direct quantitative measurements of shock strength after transmission through the impedance-mismatched materials. One-dimensional magnetohydrodynamic simulations are used to reproduce the foil explosion dynamics and provide insight into the thermodynamic, acoustic, and electrical properties of the foil during the explosion. The results show that shock transmission is governed not only by the impedance mismatch at the solid--water interface but also by the finite thickness and dynamic response of the supporting material. These findings provide a quantitative framework for understanding and controlling shock transmission in underwater electrical foil explosions and establish the feasibility and limitations of using solid substrates as structural supports in complex shock-generating geometries.
Level-set simulators of etching and deposition move the surface with a velocity that depends on adsorbate coverages. These coverages are usually computed from balances solved and coded by hand for each chemistry, whereas voxel-based Monte Carlo profile simulators read the reaction mechanism as data. For the open-source level-set simulator ViennaPS, this work presents a surface model whose rate laws, Jacobian and velocity are derived from a reaction file and evaluated with ray-traced fluxes. Steady-state coverages are obtained with Newton's method and transient coverages with a conservative integrator. One compiled model is applied to eight chemistries for chemical vapour deposition, selective epitaxy, plasma etching, sputtering and atomic layer deposition. It reproduces a hand-written silicon etch model to seven significant digits at a single point and within the Monte Carlo noise in a masked trench. In a high-aspect-ratio cavity, alumina conformality is determined by a trimethylaluminium reaction probability within the measured range.
Lattice-mismatched heteroepitaxy is limited by misfit dislocations, threading defects, and residual strain generated at buried interfaces. Here, we show that current-confined electrochemistry transforms the Ge/Si heterointerface into a laterally continuous nanometric free surface while preserving the Ge epilayer. A low-doped Ge layer on a conductive p-type Si substrate redirects anodization current toward the misfit-dislocation-rich interface. Numerical modelling including charge-transfer kinetics shows that this confinement arises from hole-limited charge transfer and, together with electrochemical calibration, defines a process window that combines interfacial current confinement with controlled Si porosification. STEM reveals an approximately 15 Ang separation, while EDX shows localized interfacial oxygen enrichment. After soft annealing, geometric phase analysis and plan-view TEM show a modified strain-relaxation pathway and strongly suppressed threading-dislocation emergence. Raman spectroscopy indicates a reduction in residual tensile strain from approximately 0.10 % to 0.05 %, whereas spreading resistance profiling confirms preservation of the Ge carrier profile. Current-confined electrochemistry therefore provides a controllable post-epitaxial route for buried-interface decoupling, defect filtering, and strain control in lattice-mismatched semiconductor heterostructures.
Triboelectric nanogenerators (TENGs) convert low-frequency mechanical energy into electricity and enable self-powered sensing. Their performance depends on interactions among material properties, surface morphology, contact mechanics, charge generation and external circuits. This review examines these interactions across length scales to assess how material and interface descriptions support predictive device design. Polymeric, inorganic, composite and natural materials are discussed in relation to charge generation and retention, mechanical compliance, durability and application requirements. Modelling approaches span molecular dynamics and first-principles calculations, rough-surface contact mechanics, device-scale electrostatics and equivalent circuits. Their capabilities are assessed through the inputs they require, the quantities they predict and the experimental evidence used for validation. Particular attention is given to prescribed surface charge density, idealised geometries and nominal contact-area assumptions, which constrain predictions under realistic loading conditions. Applications are organised by macroscale, milliscale and microscale device dimensions to examine requirements for materials, architecture and integration. The review identifies evolving real contact area and contact-dependent charge generation and decay as critical links between interfacial behaviour and electrical output. A staged validation strategy is proposed for contact mechanics, electrostatics and circuit response, with independent testing beyond calibration conditions. These priorities guide the development of multiscale models and reliable TENG systems.
The coherent elastic wave in untextured polycrystals, central to ultrasonic and seismic characterization, was recently observed to have two modes per polarization at short wavelengths. However, their physical origin and amplitude partition have remained open. We address both by theory, grain-scale numerical simulations and a grain velocity estimate. The first-order smoothing approximation, simplified by the far-field approximation, predicts three waves, which are the classical effective wave and one for each type of scattered wave (longitudinal and transverse). At long wavelengths, only the effective wave is weakly attenuated. At short wavelengths, one of the other two waves joins it with comparable attenuation, whereas the third stays far more attenuated. A new residue method, which needs no fitting, gives the same pattern for the amplitude partition, with the two waves sharing the coherent field and the third carrying little. The simulations reveal exactly these two modes, for transverse waves in iron and longitudinal waves in strongly anisotropic SrMgSn, and never the third. The wavefields reveal the mechanism, in which the incident wave is extinguished within one grain correlation length and the coherent field is rebuilt by forward multiple scattering. Strikingly, a grain velocity estimate from single-crystal constants provides independent evidence, tracing the two modes to plane waves of the individual grains and closely reproducing their velocities. Observability of multiple waves is thus set by attenuation and amplitude partition together, and short-wavelength measurements in random media must allow for more than one coherent mode.
We investigate the electronic structure, local orbital coupling, and strain-tunable nonlinear Hall response of two arsenic-substituted borophosphene-derived monolayers, As@MBP and As@AMBP, using first-principles calculations and tight-binding analysis. In the absence of spin--orbit coupling, both systems exhibit a finite Berry-curvature dipole (BCD) and a substantial nonlinear Hall conductivity, demonstrating that the nonlinear response is intrinsically driven by orbital physics and inversion-symmetry breaking. $As$ substitution opens sizable band gaps of $120~\mathrm{meV}$ in As@MBP and $90~\mathrm{meV}$ in As@AMBP, well exceeding room-temperature thermal fluctuations ($k_{\mathrm{B}}T \approx 25.9~\mathrm{meV}$). Tight-binding analysis reveals that $As$ incorporation breaks the equivalence of $B-P$ hoppings in As@MBP and induces sign reversals in key nearest-neighbor hoppings in As@AMBP, reflecting a pronounced electronic reconstruction beyond simple geometric effects. Under mechanical strain, the redistribution of Berry curvature yields a maximum BCD of $22~\mathring{\text{A}}$ in As@MBP, approximately $10$ times larger than that of unstrained structure, and induces a reversal of the BCD sign. These results establish $As$-substituted borophosphene derivatives as promising light-element platforms for mechanically switchable nonlinear transport and quantum-material applications without relying on strong spin-orbit coupling.