Observations of morphology are commonly used to evaluate the biogenicity of terrestrial microfossils and could constitute a crucial line of evidence for extraterrestrial life-detection missions in the future. However, evaluating the origin of morphological features in the rock record can be problematic because naturally occurring abiotic structures can resemble biological morphologies, which may lead to false-positive detections of fossilised life. Iron-mineralised chemical gardens have been highlighted as potentially confounding abiotic structures because of their morphological and chemical resemblance to biomineralised filaments. Despite this, the potential for chemical garden structures to be preserved in the fossil record has not been thoroughly investigated. Here, we subjected abiotic iron-mineralised chemical garden structures to artificial maturation using hydrous pyrolysis, in order to evaluate their preservation potential. We found that these abiotic filaments were relatively resistant to degradation caused by maturation when compared with analogous biological material. Additionally, the transformation of ferrihydrite to crystalline iron oxides was found to be relatively inhibited, likely because of the influence of silica. These findings highlight the need for fossilised filamentous material to be distinguished from chemical garden structures before a biological origin can be confidently attributed, particularly when observed in significantly altered rocks.
EuAg4Sb2 is a rhombohedral europium triangular lattice material that exhibits a rich phase diagram of spin moiré superlattices (SMS) and single-q magnetic phases. In this paper, we characterize the incommensurate phases accessible with a field applied in the plane with small-angle neutron scattering (SANS). A variety of phases with unusual SANS patterns are accessible with a magnetic field applied along the a and a* directions. Many of these phases can be understood to be multi-q phases. One phase in particular, ICM2b (ICM = incommensurate magnetic phase), is rather unconventional in that it is an anisotropic multi-q phase that can rotate freely within the ab-plane, dependent on the magnetic field direction and history. The stabilization of tunable multi-q incommensurate spin textures via an in-plane field sets this class of materials apart from conventional skyrmion materials. We further identify that the propagation vectors of the in-plane phases have a significant commensuration with the diameter of the smallest pocket of the Fermi surface (2kF). The multi/single-q nature is also correlated with the enhancement of resistivity, suggesting that a gap opens in the electron bands at q = 2kF. We also compare with a phenomenological model of the phase diagram, which predicts several of these in-plane-field multi-q phases to host finite scalar spin chirality. The richness of phases revealed in this study hints at the frustrated nature of the incommensurate magnetism present in EuAg4Sb2 and motivates further probes of these phases and the origin of the stability of spin moiré superlattices. Finally, the coupling of the multi-q nature and q = 2kF commensuration conditions reveals the key requirements for a strong SMS transport response.
Probing the solid/liquid interface of batteries operando/in situ with ambient pressure X-ray photoelectron spectroscopy (APXPS) using the dip-and-pull method remains a challenging endeavor due to spatial and temporal variations in liquid layer shape, thickness, and composition. Monitoring the electrochemical and topographical nature of the liquid edge where the interface is accessed is essential to correctly interpret interfacial spectra. In this work, a methodology combining experimental design and software-based data processing for interface probing is reported. This experimental methodology utilizes continuous motion during fixed-mode APXPS measurements by periodically scanning across the dry electrode and thick electrolyte regions to capture the transitional interface. Two software-based approaches for retrieving the interface spectra are evaluated. In an analysis of the intensity attenuation pattern of a unique electrode signal, interface spectra are recognized at the edge of the intensity transition from electrode to electrolyte. The second method utilizes peak positions for interface identification. Selected spectra with the same peak energies also exhibit the same chemical features, indicating the close correlations between the interface energetics and local chemical compositions. Further, topographical information can be extracted using scanning APXPS by translating spectral intensities into liquid thickness, creating a spectro-microscopic 3D image of the liquid edge region. In the examined systems, the thickness of a propylene carbonate electrolyte edge on both lithium cobalt oxide and gold WE surfaces exhibits a step-jump transition from the thin to thick liquid region. The liquid distribution is also shown to depend on the morphological and chemical nature of the electrode. The imaging provides a better understanding of the relationship between liquid distribution and probed interface features while validating the functionality of the setup.
This paper presents ambient | global, an ambient soundscape model developed to predict global ambient sound levels from all anthropogenic, biological, and geophysical sources. The soundscape model adopts a geospatial approach by modeling the ambient sound level as a function of geospatial features at a location. The soundscape model consists of an ensemble of four machine learning regression models fitted at acoustic measurement sites where both the geospatial features and ambient sound levels are known. The fitted model is then applied to predict ambient sound levels at any location where the geospatial features are known. The results quantify the spatial, temporal, and spectral patterns of ambient sound levels across the world under various scenarios. This paper presents maps of the existing ambient sound levels across the world in terms of the daytime overall A-weighted L50, or median sound level, and partitions the existing sound levels into their natural and anthropogenic constituents. Ultimately, the soundscape model will enable research into the impacts of humans and nature on the ambient soundscape and the impacts of ambient sound levels on humans and nature across the world.
Chiral molecules in nature usually show optical activity only in the deep ultraviolet, whereas artificial chiral plasmonic nanostructures can generate much stronger responses at visible and near-infrared wavelengths. An important challenge is whether the abundant biomolecular chirality in nature can be directly transferred to achiral plasmonic systems without elaborate three-dimensional nanofabrication. Here we show that the mechanical stretching of protein molecules anchored within achiral gold nanoparticle assemblies strongly enhances and reversibly modulates plasmon-coupled circular dichroism. Stretching amplifies the chiroptical response to an ellipticity of 1.18° and a dissymmetry factor of 0.2, far exceeding conventional hotspot-based strategies. Repeated stretching and relaxation further enable reversible switching over more than 100 cycles. Simulations and in situ spectroscopy indicate that the deformation of protein changes its conformation and dipole alignment, thereby strengthening the plasmonic chiral response. These findings establish a route to achieve dynamically controllable chiroptical activity in achiral plasmonic assemblies, revealing how small biomolecular deformations can strongly influence plasmonic responses of much larger nanostructures.
Propofol (2,6-bis(1-methylethyl)phenol) is a small lipophilic neuroactive drug used extensively in anesthesia. While its mechanism of action is known, its temporary effects on the lipid composition of cell membranes have not been fully elucidated. A structurally related series of saturated phospholipids with C14-acyl chains and different polar head groups is utilized in the present study with a view to understanding specific drug-lipid interactions in model membranes at the air-water interface. Langmuir surface pressure-area isotherms show that propofol can shift the lipid phase transitions to higher areas per lipid molecule and surface pressures. Brewster angle microscopy imaging shows that the drug exhibits a fluidizing effect on the lipid morphology, resulting in the formation of bright circular domains with reduced line tension. Neutron reflectometry reveals effects of squeezing out of the drug from the membranes during membrane compression, as the location and amount of the drug are quantified for these systems for the first time. The greatest overall drug-lipid interactions are with the phosphatidylcholine lipid, where the drug is located predominantly in the relatively fluid acyl chains. The greatest drug-lipid head group interactions are with the phosphatidylethanolamine lipid, which is discussed as an interplay between its squeezing out from the acyl chains due to their more condensed nature and possible specific interactions between the hydroxyl group on the drug and the ammonium group on the lipid head group. An absence of drug interactions was observed with the charged head group of the phosphatidylglycerol lipid. It is concluded that changes in membrane fluidity caused by different lipid polar head groups modulate the extent and nature of the drug-membrane interactions more generally than specific intermolecular interactions between chemical groups or effects of lipid head group charge. These new findings provide a fresh perspective on the processes influencing lipid interactions of a small hydrophobic drug and its distribution within lipid membranes, understanding which links to reducing side effects in patients from medication-induced changes to cell membrane composition.
In Section One of an Enquiry Concerning Human Understanding, Hume distinguishes between two sorts of writing on human nature: first, one that appeals to common sense to make virtue seem attractive and, second, one that attempts to describe the principles governing the mind. Hume's defence of the second approach is in part a defence of the possibility of scientific psychology. Within the second approach, he distinguishes two parts: first, a descriptive branch he calls 'mental geography' and, second, a branch he compares to Newton's project in astronomy. In his defence of mental geography, Hume sketches an account of his method of enquiry in psychology. Common sense describes some basic faculties, philosophers can make finer distinctions within these, and introspection allows us to reliably describe ground-level processes. Hume's vision of Newtonian psychology is one that appeals to laws and forces and finds the hidden springs of the mind. His attempt to explain causal inference by appealing to the transfer of vivacity across associated perceptions in Part 2 of Section 5 is an attempt at Newtonian psychology: it's speculative, explanatory, and enunciates a putative psychological law.
Quantum droplets are dilute self-bound configurations of bosons that result from the balance between a mean-field attraction and a repulsion induced by quantum fluctuations. Such droplets have been successfully realized in cold atomic gases and represent a signature of their quantum nature. Here, we predict the existence of a similar droplet phase in a solid-state system, involving polaritons formed from the strong coupling between excitons (bound electron-hole pairs) and photons in a semiconductor microcavity. We consider a spin mixture of exciton-polaritons near a biexciton Feshbach resonance, which allows one to tune the interspecies interactions to be attractive and comparable in magnitude to the intraspecies repulsion. We find that self-bound quantum droplets are achievable for realistic parameters in atomically thin semiconductors, and that they can be detected via their excitation spectrum and spatial profile. This exotic phase could potentially lead to polariton condensation at lower thresholds and it opens an alternative avenue to achieve the long-sought quantum polaritonic regime.
In this study, we present simultaneous multi-point observations of Pi2 magnetic pulsations studied, for the first time, through joined measurements of multiple missions: the CSES-01 and Swarm (A and C), in the topside ionosphere, Van Allen Probe (or Radiation Belt Storm Probes, RBSP) (A and B) and Arase in the magnetosphere. We focused on the compressional component of the satellites and the horizontal component of magnetic field from Kakioka (KAK) ground station in Japan. The Pi2 event occurred from 12:40 to 12:56 UT on January 12, 2019, where CSES-01, RBSP-A, and KAK were on the night side; Swarm-A/C, were on the day side while RBSP-B and Arase were in the dusk sector. We observed 90-degree phase delay between RBSP-A-Bz and RBSP-A-Ey which can be interpreted as a radially trapped fast mode for the compressional oscillation. Both the wavelet transforms and the Hilbert-Huang transform (HHT) were applied for signal analysis, revealing wave-like structures and strong coherence among all data sets and confirming the Pi2 pulsation nature. The compressional component in the topside ionosphere and in the magnetosphere seem very similar with the horizontal component of KAK station. During 12:43-12:45 UT, CSES-01 and Swarm-A/C exhibited an in-phase variation while both were in the Southern Hemisphere. However, as CSES-01 transitioned to the Northern Hemisphere between 12:47 and 12:56 UT, the corresponding signals became out of phase. During the selected Pi2 event, RBSP-B was located very close to Arase in the dusk sector and detected compressional oscillations with a waveform nearly identical to that observed by RBSP-A, suggesting that the observed Pi2 exhibited cavity resonance characteristics. To understand their propagation mechanism, we conduct further analysis of the duskside Pi2 pulsations in this event. We found that the penetration/propagation speed of the low-frequency Pi2 pulsations is high (|m|~ 0.3) and much larger than the average Alfven speed in the plasmasphere, while the high-frequency Pi2 pulsations have a finite m number (m ~ -1.7) and their phase speed is comparable to the average Alfven speed. We suggest that the nightside Pi2 pulsations propagate sunward through a waveguide-like mode, consistent with the high-frequency Pi2 signatures detected on the duskside in the magnetosphere.
Optical distortion or aberration remains a vital challenge that prohibits high-resolution imaging in various applications such as space domain awareness, terrestrial remote sensing, and astronomy. However, due to the stochastic nature of these optical distortions, reducing their effect without directly measuring wavefronts is challenging. Furthermore, in the case of extreme turbulence, due to the limited size of the lenslet array in the wavefront sensor, the sensor fails to correctly quantify or minimize the image distortions of a guide star from turbulence. While numerous studies have shown effectiveness of guide star-based adaptive optics in mitigating mild turbulence, severe turbulence has remained a persistent challenge. To target this, we present TURBO-RL: TURBulence mitigatiOn using Reinforcement Learning, which uses just a single optical element (e.g., deformable mirror) to estimate and correct the wavefront errors from a guide star. TURBO-RL adopts reinforcement learning with a convolutional neural network to extract and estimate turbulence. Unlike other methods, TURBO-RL is capable of guide star imaging in severe turbulence (D/r0=100) with only about 590 photons, making it possible to overcome the strong turbulence and possibly replace bulky and expensive wavefront sensors.
Two fundamental questions have puzzled scientists for more than 150 years. "How did life become homochiral?" and "why was this specific handedness selected?" Recently, it has been shown that homochirality could have emerged through the enantioselective interactions of molecules with magnetic substrates due to the asymmetric crystallization of an RNA precursor on a magnetite substrate, abundant on early Earth. This phenomenon is based on the chirality-induced spin selectivity (CISS) effect. Despite its robustness, this model could not provide an answer to the second question: Why one specific handedness (D for RNA) was selected. Here, we demonstrate that spin-involving processes can have different outcomes in the two enantiomers of chiral molecules. In chiral molecules with unpaired electrons or while electrons are passing through them, the total angular momentum vector, J, is aligned along the "easy axis," which is defined by the magnetic anisotropy induced by the spin-orbit coupling and asymmetry of the molecular field. The magnitude J is the same for both enantiomers, but the vectors may be aligned differently relative to the molecular frame in the two enantiomers. This difference can be quantified by, for example, by the angle between J and electric dipole moment of the molecule, μ. We show by direct measurements, theory, and ab initio calculations that dynamic spin processes in chiral molecules could result in different efficiencies of spin-related phenomena, including the interaction of chiral molecules with magnetic surfaces. The findings may provide an explanation for the specific homochirality in nature.
Multiphase gas-ranging from cold molecular clouds ( ≲ 100 K) to hot, diffuse plasma ( ≳ 10 6 K) is a defining feature of the interstellar, circumgalactic, intracluster, and intergalactic media. Accurately simulating its dynamics is critical to improving our understanding of galaxy formation and evolution, however, due to their multi-scale and multi-physics nature, multiphase systems are highly challenging to model. In this review, we provide a comprehensive overview of numerical simulations of multiphase gas in and around galaxies. We begin by outlining the environments where multiphase gas arises and the physical and computational challenges associated with its modeling. Key quantities that characterize multiphase gas dynamics are discussed, followed by an in-depth look at idealized setups such as turbulent mixing layers, cloud-wind interactions, thermal instability, and turbulent boxes. The review then transitions to less idealized and/or larger-scale simulations, covering radiative supernovae bubbles, tall box simulations, isolated galaxy models including dwarf and Milky Way-mass systems, and cosmological zoom-in simulations, with a particular focus on simulations that enhance resolution in the halo. Throughout, we emphasize the importance of connecting scales, extracting robust diagnostics, and comparing simulations to observations. We conclude by outlining persistent challenges and promising directions for future work in simulating the multiphase Universe.
We investigate the Jahn-Teller structural phase transition in LaMnO3 at TJT ≃ 750 K using molecular dynamics simulations based on machine-learning force fields trained on ab initio data. Analysis of the site-site correlation function of the distortions reveals that the transition is driven by the ordering of the Q2 Jahn-Teller distortion of the MnO6 octahedra, which acts as the order parameter and establishes the order-disorder nature of the transition. Dynamical local distortions are found to persist above TJT. Our results reproduce the experimental temperature dependence of both structural and phonon properties and highlight the presence of anharmonic effects at finite temperature. More broadly, the combined use of machine-learning molecular dynamics and velocity autocorrelation function analysis provides a robust framework for uncovering the microscopic mechanisms of structural phase transitions in correlated materials. In particular, this approach enables a clear distinction between order-disorder transitions and alternative mechanisms, such as displacive behavior, through the temperature evolution of vibrational properties.
Polyol synthesis offers a controllable and scalable approach for producing high-performance thermoelectric materials such as bismuth telluride (Bi2Te3), providing more control over crystal growth and microstructure compared to conventional solid-state methods. The chemical nature of the selected precursors can strongly influence the reaction pathways, phase evolution, and resulting material properties. In this work, two polyol synthesis routes using Bi2O3 and Bi(NO3)3·5H2O as bismuth precursors were systematically investigated to evaluate their influence on the structural evolution and thermoelectric performance of Bi2Te3. Comparative characterization and transport measurements reveal clear precursor-dependent variations in microstructure and anisotropic charge transport. Despite being undoped, both materials exhibit strong thermoelectric performance with the nitrate-derived sample achieving a peak figure of merit of zT = 1.27 at 432 K, and the oxide-derived material reaching zT = 1.10 at 333 K. Moreover, analysis of the nitrate route revealed the formation of a previously unreported bismuth complex, Bi3(C2H4O2)4NO3. Overall, these findings advance the mechanistic understanding of Bi2Te3 formation in polyol synthesis and highlight the importance of precursor selection as a key parameter for tailoring microstructure and optimizing thermoelectric performance.
The electronic, mechanical, optical, and thermoelectric properties of halide perovskites A2LiTlCl6 (A = K, Rb, and Cs) are systematically investigated using first-principles calculations. The computational framework combining the Tran-Blaha modified Becke-Johnson exchange potential (TB-mBJ) and the TB-mBJ-SOC potential is utilized for accurate band structure analysis. Stability analyses confirm their thermodynamic and mechanical stability, with negative formation energies and elastic constants that satisfy Born's criteria. The band structure, computed using the Tran-Blaha modified Becke-Johnson (TB-mBJ) and TB-mBJ-SOC potentials, reveals a direct band-gap nature with tunable values of 2.84 (2.81), 2.77 (2.76), and 2.66 (2.65) eV for K2LiTlCl6, Rb2LiTlCl6, and Cs2LiTlCl6, respectively. Optoelectronic properties, including complex dielectric constant, refractive index, optical conductivity, and absorption spectra calculated with the TB-mBJ potential, show strong absorption in the visible and ultraviolet spectral region, highlighting their potential for solar cell and other optoelectronic applications. The thermoelectric transport analysis predicts ZT values of 0.74-0.76 at 300 K, reflecting preliminary heat to electricity conversion. The multifunctionality and insights provided by A2LiTlCl6 make them promising candidates for cutting-edge thermoelectric and optoelectronic applications.
Traditional inelastic neutron scattering (INS) characterizes excitations-such as phonons and magnons-in condensed matter systems at thermodynamic equilibrium. However, the most intriguing and puzzling many-body effects in open quantum systems often emerge from dissipative dynamics that are inherently out of equilibrium. Here, we use a combination of laser pumping and INS to experimentally observe long-lived nonequilibrium magnons in a two-dimensional (2D) square-lattice Heisenberg antiferromagnet. These nonequilibrium magnons manifest themselves as a violation of detailed balance in the dynamic structure factor and reach steady states under periodic driving, analogous to nonequilibrium steady states in driven dissipative systems. Furthermore, we show that the violation of detailed balance reflects the quantum-mechanical nature of the underlying dynamical system, where out-of-time-ordered correlations of creation and annihilation operators do not satisfy commutation relations. The in operando INS technique developed here provides a new approach to studying nonequilibrium magnons in prototypical 2D quantum magnets and can be extended to other systems, including one-dimensional spin chains and topological many-body spin systems, where nonequilibrium effects are widespread and rich in discovery potential.
Accreting white dwarfs (AWDs) are among the best natural laboratories for understanding disk accretion. Their proximity, brightness, and purely classical nature make them ideal systems in which to probe the fundamental physics that governs the transport of angular momentum, the generation of outflows, and the coupling between disks, magnetospheres, and accretors. Yet despite decades of study, many critical questions remain unresolved. In this "unreview", we therefore focus not on what is known, but on what is unknown. What drives viscosity and sustains accretion in largely neutral disks? How are powerful winds launched, and how do they feed back on the disk and binary evolution? Why do so many systems show persistent retrograde precession, and what drives bursts in magnetic AWDs? By identifying these open problems - and suggesting ways to resolve them - we aim to motivate new observational, numerical, and theoretical efforts that will advance our understanding of accretion physics across all mass scales, from white dwarfs to black holes.
The remarkable cohesion and coordination of moving animal groups and their collective responsiveness to threats are often attributed to scale-free correlations, where behavioral changes in one animal influence others in the group, regardless of the distance between them. But are these features independent of group size? Here, we investigate group cohesiveness and collective responsiveness in computational models of massive schools of fish of up to 50,000 individuals. We show that as the number of swimmers increases, flow interactions destabilize the school, creating clusters that constantly fragment, disperse, and regroup, much like in natural animal groups. Importantly, while spatial correlations in cohesive and polarized clusters are indeed scale free, fragmentation events are preceded by a decrease in correlation length, weakening the group's collective responsiveness and leaving it more vulnerable to predation. We further show that information about directional changes propagates linearly in time among group members, thanks to the non-reciprocal nature of visual interactions between individuals. Merging events speed up this information transfer, while fragmentation slows it down. Our findings suggest that flow interactions may have played an important role in group size regulation, behavioral adaptations, and dispersion in living animal groups.
Binders are essential components in battery systems that maintain the electrode structure and integrity throughout cycling. The choice of binder affects processing, electrochemical behavior, and end-of-life recovery. The widely used poly(vinylidene difluoride) (PVDF) binder is increasingly scrutinized since it is a polyfluoroalkyl compound and requires processing in organic solvents like N-methyl-2-pyrrolidone. Consequently, efforts are underway to identify more sustainable options. In this work, we present chitin nanofibers (ChNFs), derived from fisheries waste, as a biobased, fluorine-free alternative that enables fully aqueous electrode fabrication. ChNFs disperse more than 90% of graphite in water without the need for auxiliary agents such as surfactants. Colloidal probe microscopy shows that adhesion between protonated ChNFs and graphite depends on pH, likely being governed by cation-π interactions. This strong affinity facilitates the remarkable dispersing capability of ChNFs through a multifaceted mechanism. Adsorbed nanofibers confer electro-steric stabilization by extension into the aqueous phase. The strong ChNF network can physically entrap larger particles, greatly enhancing the long-term stability of ChNF-graphite suspensions. The ChNF-graphite dispersion exhibits rheological behavior suited for forming uniform electrode coatings. Electrodes prepared with 4% ChNFs deliver specific capacities of 370 mA h g-1 and enhanced capacity retention over 100 cycles compared to PVDF-based counterparts. Electron microscopy, X-ray photoelectron spectroscopy, and online electrochemical mass spectrometry analyses reveal that the nature of the binder dictates the solid electrolyte interphase (SEI) characteristics. The ChNF produces a more robust and stable SEI that suppresses electrolyte reduction, directly contributing to the enhanced electrochemical performance.