Browse Articles

Reaction-induced modification of Co nanoclusters driven by Co-Mn interfacial sites to control selectivity in CO2 hydrogenation

Hall thruster modeling with multiple simulation techniques: Model benchmarking, fluid–kinetic consistency, and experimental validation

Numerical plasma models are critical tools for aiding the design and understanding of electric propulsion systems, such as Hall thrusters, particularly when considering challenges associated with diagnostic access and reliable internal measurements. For complex plasma systems, such as Hall thrusters, theoretical verification solutions are often missing, and therefore, benchmarking represents an important element in assessing the correctness and consistency of the underlying mathematical model, and the computational performance of the numerical implementation. In this work, we benchmark three different numerical codes by simulating an SPT-100 Hall thruster under identical operating conditions. The codes include one-dimensional stationary and non-stationary fluid models describing the axial thruster direction, as well as a two-dimensional axial–azimuthal Particle-In-Cell/Monte Carlo Collision (PIC/MCC) model. A partial validation is performed with available experimental measurements of the discharge current, thrust, and anode specific impulse, showing good agreement. Overall, the fluid and PIC/MCC models compare favorably with each other, and several fluid approximations are found to be acceptable. For example, axial electron energy transport is relatively minor such that the electron temperature is reasonably determined by a local energy balance. Other approximations, however, require a more careful examination: particularly the assumption of Maxwellian electrons and the neglect of electron–wall collisions in the electron momentum balance equations.

Radiolabeling of oligopeptides by selective hydrogen isotope exchange with deuterium and tritium in aqueous buffers

Derivation of bandwidth and filter characteristics of various types of optically pumped magnetometers

We present a unified and easy-to-follow analytical framework based on the Bloch equations for deriving the small-signal frequency response of several common types of optically pumped magnetometers (OPMs). These include the Mx, light-shift dispersed Mz, Bell–Bloom, and RF (radio-frequency) types, as well as the class of unmodulated zero-field OPMs. It is shown that, depending on the operating regime, the frequency response of some of these magnetometers deviates significantly from the commonly assumed first-order filter behavior.

Accelerated discovery of highly active enzyme nanohybrids with parallelized Bayesian optimization in hybrid space

Abstract Artificial intelligence (AI) has significantly advanced protein engineering, enabling rapid enzyme evolution for diverse applications. However, the fragile nature of biomacromolecules requires enzyme immobilization to preserve catalytic activity under harsh industrial conditions, which often restricts substrate diffusion and reduces enzymatic activity. This challenge demands extensive trial-and-error experiments to optimize immobilized carriers with high activity for different enzymes. Here we show a machine-learning-guided workflow along with an algorithm named parallelized hybrid-space Bayesian optimization (PHBO) to accelerate the discovery of nanocarriers for specific enzymes and reactions. Leveraging prior knowledge, machine learning and iterative feedback, within limited number of experiments, this workflow explores the reaction space of over 10 7 experiments and achieves activity recovery of 100%, 90%, and 79% for glucose oxidase, catalase, and Candida Antarctica lipase B, respectively. These results demonstrate that data-efficient optimization can substantially accelerate the discovery of enzyme nanohybrids with high catalytic activity across diverse enzymatic systems.

Harness impedance effects on temporal ion energy in a low-power Hall effect thruster

The finite length of the Hall effect thruster (HET) electrical harness has been shown to influence thruster operation by altering voltage fluctuations at the anode through changes in harness impedance. As the anode potential determines the acceleration experienced by ions, it is hypothesized that harness-induced anode-voltage fluctuations could affect ion energy within the thruster plume. To quantify the impact of HET harness inductance on discharge telemetry and plume properties, the harness inductance was varied using an air-core roller inductor. In this study, we evaluated a range of harness inductances using a 300 W HET while measuring time-resolved ion energy with a high-speed retarding potential analyzer and plasma potential with a high-speed dual Langmuir probe. Diagnostics were translated between two radial positions at 0.5 m downstream of the thruster, corresponding to a centerline and 0.2 m off-centerline location, each oriented toward the thruster. Two magnetic-field configurations were tested to verify whether harness-induced energy oscillations persisted across different discharge conditions. High-speed measurements of plasma potential showed no variation with changes in harness inductance, within measurement uncertainty. Time-resolved ion energy measurements revealed changes in oscillation amplitude and frequency at both measurement locations and operating configurations, with the ion energy peak-to-peak amplitude increasing by up to 12.5%. This work reveals that harness inductance influences ion energy populations in HET plumes, leading to energy shifts and an increased fraction of higher-energy ions at greater harness impedances, highlighting the importance of harness length and impedance in thruster–facility electrical configuration.

Diel and eddy driven changes in microbial gene expression and biogeochemistry in the oceanic chlorophyll maximum

Abstract Oceanic microorganisms can rapidly respond to environmental variability. Determining how physical and biological processes control microbial distributions, abundances, and metabolic dynamics is challenging. Here, we used autonomous underwater vehicles capable of Lagrangian feature tracking and in situ sampling, in combination with ship-based measurements, to examine diel to weekly scale changes in microbial transcription and biogeochemistry in the deep chlorophyll maximum (DCM) of a mesoscale cyclonic eddy. Nearly 20% of total transcript expression showed diel periodicity, highlighting the importance of the diurnal cycle on phytoplankton metabolism in the dim waters of the DCM. Eddy-induced isopycnal uplift increased nutrient concentrations and caused upward displacement of the DCM, driving increased picoeukaryotic cell abundances and transcriptional activity of nitrate-incorporating photoautotrophs. As the eddy weakened, the DCM deepened and transcriptional activity shifted towards chemolithoautotrophic ammonia-oxidizing archaea. The temporal dynamics observed demonstrate how plankton communities rapidly respond to both diel variation and stochastic mesoscale disturbances.

A multi-factor model for the coherent population trapping resonance

A systematic semi-analytical study of the coherent population trapping resonance is presented. The emphasis is put on quantifying the importance of different experimental factors potentially affecting the shape of the resonance, and especially the magnitude and structure of the light shift. In particular, we consider the impact of FM modulation, spectrum asymmetry, light detuning, and an optically thick atomic medium. The proposed model allows for a quick and reliable check whether a zero light shift can be reached in a realistic experimental setting. The results of modeling are compared with the experiment carried out with a diode laser (vertical-cavity surface emitting laser) and 87Rb atoms.

A scalable and quantum-accurate foundation model for biomolecular force fields via linearly tensorized quadrangle attention

Enhanced graphene surface plasmon polaritons for terahertz sources

Graphene surface plasmon polaritons (SPPs) have attracted extensive attention due to their unique properties, such as extreme light confinement and high tunability via doping and external electric fields, making them a promising platform for developing tunable terahertz sources. However, graphene SPPs suffer from a short lifetime and low radiation efficiency. Herein, we address these issues by replacing monolayer graphene with trilayer graphene and introducing a periodic nanostructure array into the middle graphene layer. Our results demonstrate that the lifetime of the SPPs has been enhanced from 0.22 to 0.44 ps when the monolayer graphene has been replaced by trilayer graphene. Additionally, we achieved a fourfold enhancement in radiation intensity by introducing a periodic nanostructure array into the middle graphene layer. Furthermore, we show that the resonant frequency can be tuned by adjusting the periodic nanostructure array. Our findings provide an effective approach for developing high-efficiency, tunable, and compact terahertz sources.

Discovery of van Hove singularities: electronic fingerprints of 3Q magnetic order in a van der Waals quantum magnet

Abstract Magnetically intercalated transition metal dichalcogenides are emerging as a rich platform for exploring exotic quantum states in van der Waals magnets. Among them, Co x TaS 2 has attracted intense interest following the recent discovery of a distinctive 3 Q magnetic ground state and a pronounced topological Hall effect below a critical doping of x  ≈ 1/3, both intimately tied to cobalt concentration. To date, direct signatures of this enigmatic 3 Q magnetic order in the electronic structure remain elusive. Here we report a comprehensive doping dependent angle resolved photoemission spectroscopy study that unveils these long-sought fingerprints. Our data reveal an unexpected inverse-Mexican-hat dispersion along the K-M- $${\mathrm{K}}^{\prime}$$ K ′ direction, accompanied by two van Hove singularities. These features are consistent with theoretical predictions for a 3 Q magnetic order near three-quarters band filling on a cobalt triangular lattice. These results provide evidence of 3 Q magnetic order in the electronic structure, establishing TMD van der Waals magnets as tunable materials to explore the interplay between magnetism and topology.

Direct determination of the Fe3+/2+ charge-transition level in BaTiO3 and isovalently substituted Ba0.82Ca0.18Ti0.92Zr0.08O3 by x-ray photoelectron spectroscopy

Charge-transition levels of dopants in oxides and other semiconductors are key factors affecting a wide range of material properties. Despite their importance, only very few charge-transition levels are known quantitatively. This work aims to validate the direct experimental determination of charge-transition levels of dopants in oxides by means of x-ray photoelectron spectroscopy (XPS). The approach is used to derive the energy level associated with the Fe3+/2+ transition, which is determined as 2.45±0.05 eV and 2.65±0.05eV above the valence band maximum of BaTiO3 and Ba0.82Ca0.18Ti0.92Zr0.08O3, respectively. The former agrees with thermogravimetric and electric measurements. The results consolidate that XPS is a versatile and reliable technique to experimentally determine charge-transition levels, which can be used to reveal systematic dependencies on concentration, temperature, and host material. It is further demonstrated that high-temperature near-ambient pressure XPS performed at a synchrotron is ideally suited for the determination of charge-transition levels.

Accurate atomic resolution XFEL structures of a metalloenzyme reveal key insights into its catalytic mechanism*

Abstract Metalloproteins represent a major fraction of the protein kingdom and often exploit the redox chemistry of transition metals to drive key biological events involving proton and electron transfer. Copper is one of the most widely used transition metals whose redox properties are utilised in both electron transfer and catalysis of chemical substrates. Copper nitrite reductases (CuNiRs) utilise two types of copper centres and have become a model system for studying complex biological events that underpin the reaction mechanisms of redox enzymes, including proton-coupled electron transfer and substrate gating. We utilised the higher X-ray energy (13 keV) available at the SACLA X-ray Free Electron Laser (XFEL) and SHELXL refinement to obtain accurate atomic resolution structures of CuNiRs at ~1 Å from three organisms – in the oxidised (low and high pH), reduced and substrate-bound states. A consistent picture now emerges with the observation of a pentacoordinated oxidised catalytic type-2 Cu (T2Cu 2+ ) centre in all cases. A tetracoordinated reduced T2Cu + site with a single solvent ligand has also been captured, giving structural support to the random-sequential scheme with ordered pathway being dominant.

RF bias-enhanced heteroepitaxial nucleation of (100) diamond on (100) Ir/a-sapphire

We report radio-frequency (RF) bias-enhanced nucleation (RF-BEN) of heteroepitaxial (100) diamond on (100) Iridium (Ir)/a-sapphire by 2.45 GHz microwave plasma chemical vapor deposition (MPCVD) in 8% CH4 diluted by hydrogen. The electrically insulating sapphire substrate acts as a capacitor of low impedance between the iridium film and the substrate holder and allows RF biasing current to flow through it. Because of a higher electron mobility than positive ions, a time-average negative DC bias voltage is induced on iridium with respect to the plasma leading to the nucleation of heteroepitaxial diamonds. Subsequent diamond growth in 0.5% CH4 diluted by hydrogen produces (100) diamond films. X-ray diffraction (XRD) at sample tilt = 88° confirms the diamond (400) reflection with a rocking-curve full width half maximum of  ≈ 1.27°. XRD {111} pole-figure measurements confirm reduced mosaic spread and the absence of twins. The RF-BEN technique is promising for producing heterogeneous diamond wafers on iridium-coated large-area electrical insulating substrates.

Preventing subsoil enhanced nitrification to safeguard agroecosystem sustainability

Influence of pulse width on energy deposition and temperature in nanosecond-pulsed discharges

Nanosecond-pulsed discharges are a promising method to enhance combustion but can generate significant levels of electromagnetic interference (EMI). Modifying the discharge pulse width is an unexplored option to reduce EMI, but few studies have examined how changing the pulse width affects discharge parameters such as energy and temperature. This study addresses this issue by systematically investigating how the pulse width affects the energy per pulse, breakdown time, rotational temperature, and vibrational temperature in air across different frequencies, flow velocities, and gap distances in a plasma-assisted flow tube. It is observed that the pulse width has a substantial impact on the voltage and current waveforms, energy per pulse, and temperatures at high pulse repetition frequencies. At lower frequencies, however, the influence of the pulse width is significantly reduced. Additionally, increasing the flow velocity (especially at higher frequencies) or the gap distance increases the energy per pulse and prolongs the breakdown time for all pulse widths. The measurements provided in this work can be used to improve numerical modeling of plasma-assisted combustion in flowing systems.

Oligomeric-solvent engineering of hierarchical hydrogen-bonding networks for multifunctional glass interlayers

Abstract The properties of polymer gels are governed not only by the crosslinked network but also by the solvent. Conventional small-molecule solvents impose trade-offs among environmental adaptability, cost, and biocompatibility. Here, we employ oligomeric polyethylene glycol as a multifunctional solvent for poly (methacrylic acid) (PMAA), converting the otherwise plastic PMAA network into a transparent, dissipative gel. The oligomeric solvent promotes a hierarchical hydrogen-bonding architecture with broadly distributed strengths, coupling elasticity and viscosity, stabilizing the network, and enabling high energy dissipation for acoustic damping and impact resistance. Meanwhile, thermally reversible hydrogen-bond dissociation provides broad endothermic heat absorption, affording thermal buffering. The gels further exhibit high transparency, robust adhesion, and self-healing. Harnessing the gel as an interlayer, we fabricate laminated glass that integrates light transmission, thermal regulation, sound attenuation, and mechanical protection. This oligomer-solvent strategy offers a practical route to multifunctional, energy-efficient, safer building glazing applications in real-world architecture settings.

Asymmetry in the avalanche dynamics of the interferroelectric phase transformation in barium titanate

The jerky character of displacive phase transformations in ferroelectrics generates measurable ultrasonic signals that provide information about the transformation dynamics. This work investigates the acoustic emission from the interferroelectric phase transition between the tetragonal and orthorhombic states in the model ferroelectric BaTiO3. Similar to the paraelectric–ferroelectric transition, the interferroelectric transformation exhibits scale-invariant avalanche dynamics reflected in power laws of characteristic quantities such as the amplitude and energy of the ultrasonic pulses. In contrast to the paraelectric–ferroelectric case, the interferroelectric transformation exhibits a pronounced directional asymmetry: the energy exponent is 1.38±0.06 for heating and 1.59±0.08 for cooling. Within experimental uncertainties, the results agree with the basic mean-field prediction of 1.33 and with the field-integrated value of 1.67. The exponent asymmetry and the 260% higher event count during cooling suggest distinct dynamical pathways of the forward and reverse transformations, a picture further supported by systematic differences in the waiting-time statistics between successive avalanches. We attribute this asymmetry to different starting conditions for nucleation into the respective product phase. The strong correlation between avalanche amplitude and energy and the validity of the Omori law for aftershocks do not depend on the transformation direction.

Conformal and adhesive gel for stable electrophysiology on hairy animals without shaving

Multiple unidirectional guided resonances with reversible radiation direction in tetramer metagratings

Unidirectional guided resonances (UGRs), as a characteristic class of polarization singularities in momentum space, are emerging as key enablers in advanced nanophotonic devices for manipulating radiation asymmetry. Here, we theoretically propose a refractive-index-perturbation strategy, enabled by the excellent electro-optic Pockels effect of lithium niobate, to realize multiple UGRs in a tetramer metagrating. Numerical simulations reveal that a tetramer metagrating simultaneously preserving C2 and mirror symmetries supports two symmetry-protected bound states in the continuum (BICs). When the refractive indices of two nanostrips along one diagonal of the tetramer metagrating are adjusted simultaneously, the structure loses its mirror symmetry but remains in C2 symmetry. As a result, each BIC splits along the kx axis into a pair of UGRs that share identical evolution characteristics yet radiate in completely opposite directions. Ultimately, four outstanding UGRs are obtained, each exhibiting Q-factors exceeding 105 and radiation asymmetry ratios approaching unity. The underlying physics for these UGRs is the migration of polarization vortex singularities—initially coincident at Γ point for both top and bottom ports—which split and drift in the opposite directions along the kx axis upon breaking the mirror symmetry. Interestingly, switching the refractive-index perturbation between the primary and secondary diagonals reverses the radiation direction of all four UGRs. Moreover, applying the refractive-index perturbation to only one nanostrip in the tetramer allows for simultaneous control over both the evolutionary pathways and the radiation directions of the UGRs. Our findings establish a refractive-index-asymmetric scheme to enrich the fundamental understanding of UGR physics.