Current Observations Research Articles

Large-scale dual AGN in large-scale cosmological hydrodynamical simulations

Abstract Detecting dual active galactic nuclei (DAGN) in observations and understanding theoretically which massive black holes (MBHs) compose them and in which galactic and large-scale environment they reside are becoming increasingly important questions as we enter the multi-messenger era of MBH astronomy. This paper presents the abundance and properties of DAGN produced in nine large-scale cosmological hydrodynamical simulations. We focus on DAGN powered by AGN with $L_{\rm bol}\geqslant 10^{43}\, \rm erg\, s^{-1}$ and belonging to distinct galaxies, i.e. pairs that can be characterised with current and near-future electromagnetic observations. We find that the number density of DAGN separated by a few to 30 proper kpc varies from 10−8 (or none) to $10^{-3} \, \rm comoving\, Mpc^{3}$ in the redshift range z = 0–7. At a given redshift, the densities of the DAGN numbers vary by up to two orders of magnitude from one simulation to another. However, for all simulations, the DAGN peak is in the range z = 1–3, right before the peak of cosmic star formation or cosmic AGN activity. The corresponding fractions of DAGN (with respect to the total number of AGN) range from 0 to 6 %. We find that simulations could produce too few DAGN at z = 0 (or merge pairs too quickly) compared to current observational constraints while being consistent with preliminary constraints at high redshift (z ∼ 3). Next-generation observatories (e.g., AXIS) will be of paramount importance to detect DAGN across cosmic times. We predict the detectability of DAGN with future X-ray telescopes and discuss DAGN as progenitors for future LISA gravitational wave detections.

Tackling the Activity Trend of Metal-Loaded Metal Nitride Catalysts for NH3 Synthesis by a First-Principles Microkinetic Study.

Ammonia (NH3) is one of the most widely produced chemicals globally, primarily synthesized through the Haber-Bosch process, which requires high temperatures and pressures. Dual-site catalysts can activate N2 and H2 at spatially separated sites, enabling efficient NH3 synthesis under milder conditions. Despite the rapid experimental progress of the dual-site catalysts (e.g., Ni-LaN), the feasibility and design of dual-site catalysts are challenged recently. Herein, the different metal-loaded metal nitride catalyst models are employed, and their activity map for NH3 synthesis is explored by the first-principles microkinetic simulation. The optimum active region of this type of dual-site catalyst is identified in terms of the formation energy (Ev) of nitrogen vacancy (Nvac) on metal nitride and the adsorption energy (EH) of hydrogen atom on metal cluster, with Ev and EH ideally located around ≈1.50 and ≈-0.30eV, respectively. This offers a framework for designing effective metal-loaded metal nitride catalysts for NH3 synthesis. Importantly, this trend aligns with and rationalizes the current experimental observations of metal-loaded metal nitride reported for NH3 synthesis. This theoretical work provides significant insights into NH3 synthesis on dual-site mechanism, and provides a rational direction for designing metal-loaded metal nitride catalysts.

Changes in guanaco distribution from Late Holocene to present times in Northwest Patagonia: connecting archaeological, ethnohistoric and current data

Context The guanaco (Lama guanicoe) is one of the four species of South American camels, and is the largest native mammal inhabiting arid and semi-arid environments in South America. Although the guanaco was abundant and widely distributed in the past, currently its density and distribution range are substantially reduced, inhabiting mainly Southern Patagonia in small isolated groups. The decline in guanaco populations is most likely related to the Anthropocene defaunation process that is affecting large mammals in developing countries worldwide, but the extent and causes of these changes are not well understood. Aims To explore both the changes in the distribution of guanaco populations in Northwest Patagonia and the environmental and anthropic factors that shaped the distribution patterns, by employing a long-term perspective spanning from the end of the Late Holocene to present times (i.e. the last 2500 years). Methods We combine archaeological information, ethnohistorical records and current observations and apply Species Distribution Models using bioclimatic and anthropic factors as explanatory variables. Key results Guanaco spatial distribution in Northwest Patagonia changed significantly throughout time. This change consisted in the displacement of the species towards the east of the region and its disappearance from northwest Neuquén and southwest Mendoza in the last 30 years. In particular, the high-density urban settlements and roads, and secondly, competition with ovicaprine livestock (goats and sheep) for forage are the main factors explaining the change in guanaco distribution. Conclusions Guanaco and human populations co-existed in the same areas during the Late Holocene and historic times (16th to 19th centuries), but during the 20th century the modern anthropic impact generated a spatial dissociation between both species, pushing guanaco populations to drier and more unproductive areas that were previously peripheral in its distribution. Implications As with many other large mammal species in developing countries, Northwest Patagonia guanaco populations are undergoing significant changes in their range due to modern anthropic activities. Considering that these events are directly related to population declines and extirpations, together with the striking low density recorded for Northwest Patagonia guanaco populations, urgent management actions are needed to mitigate current human impacts.

The nuclear symmetry energy and the neutron skin thickness in nuclei

IntroductionWe investigate possible correlations between the stiffness of the symmetry energy at saturation density, the so-called L parameter, and the neutron skin thickness of 48Ca and 208Pb, for which the recent measurements from the CREX and PREX I + II experiments at the Thomas Jefferson Laboratory became available.MethodsWe choose an ensemble of nucleonic equations of state (EoS) derived within microscopic (BHF, Variational, AFDMC) and phenomenological (Skyrme, RMF, DD-RMF) approaches. They are all compatible with the laboratory nuclear collisions data and with current observations of neutron stars (NS) mass and the tidal polarizability of a 1.4 M⊙ NS, as deduced from the GW170817 event.ResultsWe find some degree of correlation between the L parameter and the neutron skin thickness whereas a much weaker correlation does exist with the tidal polarizability and the symmetry energy at saturation density. However, some EoS which are able to explain the CREX experimental data, are not compatible with the PREX I + II data, and viceversa.ConclusionWe confirm the results previously obtained with a different set of EoS models, and find a possible tension between the experimental data and the current understanding of the nuclear EoS.

Status of inpatients with pediatric epilepsy in children's hospitals in China (2016-2021).

Pediatric epilepsy is the most common disease of pediatric neurological diseases in China. Current demographic characteristics and economic burdens are needed to guide public health policy. In this study, we provide the demographic characteristics and economic burden of pediatric epilepsy patients in China from 2016 to 2021, and describe the change trend and correlation of demographic characteristics and economic burden by province. Using data from the Futang Research Center of Pediatric Development, we conducted a demographic-based cross-sectional study of pediatric epilepsy patients in 29 children's hospitals in China to assess changes in the distribution and economic burden over 6 years and related factors. We obtained per capita disposable income information from the Economic Statistical Bulletin of the National Bureau of Statistics of China and the statistical bureaus of provincial administrative regions. Demographic, diagnostic classification proportion and distribution trends, and economic burden from 2016 to 2021 were verified for pediatric patients with epilepsy. From 2016 to 2021, there were 149,375 patients diagnosed with epilepsy. The proportion of patients younger than 3 years decreased significantly from 51.13% to 29.43% (P=0.00853, R2=0.9803). The root-mean-square-error between the Inter-Provincial Visits Indexes decreased from 1.70 to 0.90, decreasing significantly (R2=0.8306). The disease burden decreased from 17.26% to 12.11% with a significant upward trend (P=0.02417, R2=0.8817). A negative correlation between disease burden and the Inter-Provincial Visits Index (P=0.0383) was observed, along with a positive correlation with the proportion of patients younger than 3 years old (P<0.0001). From 2016 to 2021, the proportion of young patients, population mobility and economic burden on patients decreased, and healthcare level of pediatric epilepsy improved. In addition, based on the current observations, the healthcare level of pediatric epilepsy in Western and Central China is lower than in other regions, and the economic burden on patients is higher than in other regions. In the future, these areas require higher priority concerning policy and financial support.

A Kinematic Approach for Rip Current Identification from ADCP Observation Data at Haeundae Beach, Korea

In May 2023, direct observations of rip currents were conducted at Haeundae Beach, Korea, over a two-day period at six different stations using upward-facing Acoustic Doppler Current Profilers (ADCPs). The depth-averaged cross-shore velocity data were low-pass filtered with a 30-s cutoff period to eliminate wave-related motions. By applying 15-min boxcar averages, correlation analyses were performed to examine the relationship between three types of flow (cross-shore, onshore, and offshore) and three environmental factors (tide, wave, and wind). The analysis revealed that only one (R2-3) of the six stations had a high likelihood of rip current occurrence. Rip currents were defined as regions of offshore flow within the low-pass filtered time series of cross-shore velocities. For each identified rip current, three key kinematic features—maximum speed, duration, and distance—were estimated. Using specific thresholds for these features, hazardous rip currents were determined. Station R2-3 was the only station where hazardous rip currents were observed, which is consistent with the findings of the correlation analysis. Additionally, swells with a 15-s period were detected exclusively at R2-3 during the period of the hazardous rip currents, suggesting their significant role in the development of the observed rip currents. Furthermore, both Rip Index from the Rip Current Monitoring and Warning System and the CCTV Score from the Rip Current Checklist exceeded threshold values during this period, reinforcing the reliability of the method used. The potential influence of bound infragravity waves on the duration and variability of these rip currents was discussed. The rip currents observed at Haeundae Beach could be categorized as the "focused" type.

Reparametrization Invariant Scaling Symmetry and the Value of the Einstein Cosmological Constant ΛE

Abstract The nature of Dark Energy (DE) remains an enigma. This work explores the non-zero Einstein Cosmological Constant (Λ E ) as a manifestation of DE – viewing it through the lens of Reparametrization Invariant Scaling Symmetry (RISS), where Λ E is interpreted as a “kinetic energy” term within the energy density. The scale factor λ(t) relevant for cosmic reparametrization removes Λ E from the extended Einstein GR, its defining equations, and their relations to Λ E are derived. The value for Λ E = 1.8 × 10−52 m−2 is consistent with the current observations for Λ E . The current approach avoids the puzzles associated with interpreting Λ E as vacuum zero-point energy (often called dark energy). Further applications are related to the Dark Matter problem by insisting on a reparametrization symmetry for the equations of motion, where un-proper (non-co-moving) time parametrization gives rise to fictitious forces.

Emergence of inflaton potential from asymptotically safe gravity

The Asymptotic Safety Hypothesis for gravity relies on the existence of an interacting fixed point of the Wilsonian renormalization group flow, which controls the microscopic dynamics, and provides a UV completion of the theory. Connecting such UV completion to observable physics has become an active area of research in the last decades. In this work we show such connection within the framework of scalar-tensor models. More specifically, we found that cosmological inflation naturally emerges from the integration of the RG flow equations, and that the predicted parameters of the emergent effective potentials provide a slow-roll model of inflation compatible with current observations. Furthermore, the RG evolution of the effective action starting at the UV fixed point, provides a prediction for the initial value of the inflaton field.

The diverse star formation histories of early massive, quenched galaxies in modern galaxy formation simulations

Abstract We present a comprehensive study of the star formation histories of massive-quenched galaxies at z = 3 in three semi-analytic models (Shark, gaea, Galform) and three cosmological hydrodynamical simulations (Eagle, IllustrisTNG, Simba). We study the predicted number density and stellar mass function of massive-quenched galaxies, their formation and quenching timescales and star-formation properties of their progenitors. Predictions are disparate in all these diagnostics, for instance: (i) some simulations reproduce the observed number density of very massive-quenched galaxies ($&amp;gt;10^{11}\, \rm {\rm M}_{\odot }$) but underpredict the high density of intermediate-mass ones, while others fit well the lower masses but underpredict the higher ones; (ii) In most simulations, except for gaea and eagle, most massive-quenched galaxies had starburst periods, with the most intense ones happening at 4 &amp;lt; z &amp;lt; 5; however, only in Shark and IllustrisTNG we do find a large number of progenitors with star formation rates $&amp;gt;300\rm \, {\rm M}_{\odot }\, yr^{-1}$; (iii) quenching timescales are in the range ≈20 − 150 Myr depending on the simulation; among other differences. These disparate predictions can be tied to the adopted Active Galactic Nuclei (AGN) feedback model. For instance, the explicit black-hole (BH) mass dependence to trigger the ‘radio mode’ in IllustrisTNG and Simba makes it difficult to produce quenched galaxies with intermediate stellar masses, also leading to higher baryon collapse efficiencies (≈15 − 30 per cent); while the strong bolometric luminosity dependence of the AGN outflow rate in gaea leads to BHs of modest mass quenching galaxies. Current observations are unable to distinguish between these different predictions due to the small sample sizes. However, these predictions are testable with current facilities and upcoming observations, allowing a ‘true physics experiment’ to be carried out.

New insights into combined surfzone, embayment, and estuarine bathing hazards

Abstract. Rip currents are the single largest cause of beach safety incidents globally, but where an estuary mouth intersects a beach, additional flows are created that can exceed the speed of a typical rip current, significantly increasing the hazard level for bathers. However, there is a paucity of observations of surfzone currents at estuary mouth beaches, and our understanding and ability to predict how the bathing hazard varies under different wave and tide conditions are therefore limited. Using field observations and process-based XBeach modelling at an embayed, estuary mouth beach, we demonstrate how surfzone currents can be driven by combinations of estuary discharge and wave-driven bathymetric and boundary rip currents under various combinations of wave and tide forcing. While previous studies have demonstrated the high hazard that rip currents pose, typically during lower stages of the tide, here we demonstrate that an estuary mouth beach can exhibit flows reaching 1.5 m s−1 – up to 50 % stronger than typical rip current flows – with a high proportion (&gt; 60 %) of simulated bathers exiting the surfzone during the upper half of the tidal cycle. The three-dimensional ebb shoal delta was found to strongly control surfzone currents by (1) providing a conduit for estuary flows that connect to headland boundary rips and (2) acting as a nearshore bar system to generate wave-driven “river channel bathymetric rips”. Despite significant spatio-temporal variability in the position of the river channels on the beach face, it was possible to hindcast the timing and severity of past bathing incidents from model simulations, providing a means to forewarn bathers of hazardous flows.

Integrating Historical Learning and Multi-View Attention with Hierarchical Feature Fusion for Robotic Manipulation.

Humans typically make decisions based on past experiences and observations, while in the field of robotic manipulation, the robot's action prediction often relies solely on current observations, which tends to make robots overlook environmental changes or become ineffective when current observations are suboptimal. To address this pivotal challenge in robotics, inspired by human cognitive processes, we propose our method which integrates historical learning and multi-view attention to improve the performance of robotic manipulation. Based on a spatio-temporal attention mechanism, our method not only combines observations from current and past steps but also integrates historical actions to better perceive changes in robots' behaviours and their impacts on the environment. We also employ a mutual information-based multi-view attention module to automatically focus on valuable perspectives, thereby incorporating more effective information for decision-making. Furthermore, inspired by human visual system which processes both global context and local texture details, we have devised a method that merges semantic and texture features, aiding robots in understanding the task and enhancing their capability to handle fine-grained tasks. Extensive experiments in RLBench and real-world scenarios demonstrate that our method effectively handles various tasks and exhibits notable robustness and adaptability.

Non parametric observation-driven hidden Markov model

Hidden Markov models (HMM) are used in different fields to study the dynamics of a process that cannot be directly observed. However, in some cases, the structure of dependencies of a HMM is too simple to describe the dynamics of the hidden process. In particular, in some applications in finance and in ecology, the transition probabilities of the hidden Markov chain can also depend on the current observation. In this work, we are interested in extending the classical HMM to this situation. We refer to the extended model as the observation-driven hidden Markov model (OD-HMM). We present a complete study of the general non parametric OD-HMM with discrete and finite state spaces. We study its identifiability and the consistency of the maximum likelihood estimators. We derive the associated forward-backward equations for the E-step of the EM algorithm. The quality of the procedure is tested on simulated datasets. We illustrate the use of the model on an application focused on the study of annual plant dynamics. This work establishes theoretical and practical foundations for this framework that could be further extended to the parametric context in order to simplify estimation and to hidden semi-Markov models for more realism.

Hydrolysis of poly(ester urethane): In-depth mechanistic pathways through FTIR 2D-COS spectroscopy

The hydrolysis of thermoplastic poly(ester urethane) (PEU) is convoluted by its block copolymer phase structure and competing hydrolytic sensitivities of multiple functional groups. The exact pathways for water ingress, water interaction with the material and ultimately the kinetics and order of functional group hydrolysis remain to be refined. Additional diagnostics are needed to enable deeper insight and deconvolution of material changes. In combination with GPC results, a promising analytical technique – two-dimensional correlation spectroscopy (2D-COS) – has been reviewed and applied to analyze FTIR spectra of hydrolyzed PEUs aged under various conditions, such as exposure time, temperature, and relative humidity. 2D-COS allows the complex role of water with distinct intermediate steps to be established, plus it emphasizes the initial stages of PEU hydrolysis at more susceptible functional groups. As a complication for the raw material, ATR IR detected some talc on the surface of commercial PEU beads and pressed sheets thereof, which can interfere with water ingress and thereby retards PEU hydrolysis, particularly in its natural form or moderate aging at lower temperatures (e.g., below the melting point of PEU). As aging temperature increases above the melting temperature, even traces of water trapped inside the PEU are sufficient to initiate the hydrolysis, which then progresses strongly with increasing temperatures. Feedback from 2D-COS analysis confirms that PEU hydrolysis starts at esters in the soft-segments before those in the urethane linkage become susceptible. Only when the molecular weight of PEU is below a critical molar mass (Mc) will the hydrolysis occur in parallel in the hard-segments since protective morphological phase structures are then absent. The current observations demonstrate unexpected behavior that may result from 'unknown' additives in polymer degradation, the temporal and group-specific hydrolysis of PEU as a function of locally available water molecules, the order of reactivity of susceptible functional groups, and the importance of changes in molecular weight coupled with the phase structure of the polymer.

Breaking degeneracies in exoplanetary parameters through self-consistent atmosphere--interior modelling

With a new generation of observational instruments largely dedicated to exoplanets (i.e. JWST, ELTs, PLATO, and Ariel) providing atmospheric spectra and mass and radius measurements for large exoplanet populations, the planetary models used to understand the findings are being put to the test. We seek to develop a new planetary model, the Heat Atmosphere Density Evolution Solver (HADES), which is the product of self-consistently coupling an atmosphere model and an interior model, and aim to compare its results to currently available findings. We conducted atmospheric calculations under radiative-convective equilibrium, while the interior is based on the most recent and validated ab initio equations of state. We pay particular attention to the atmosphere--interior link by ensuring a continuous thermal, gravity, and molecular mass profile between the two models. We applied the model to the database of currently known exoplanets to characterise intrinsic thermal properties. In contrast to previous findings, we show that intrinsic temperatures (T$_ int $) of 200-400 K ---increasing with equilibrium temperature--- are required to explain the observed radius inflation of hot Jupiters. In addition, we applied our model to perform `atmosphere--interior' retrievals by Bayesian inference using observed spectra and measured parameters. This allows us to showcase the model using example applications, namely to WASP-39 b and 51 Eridani b. For the former, we show how the use of spectroscopic measurements can break degeneracies in the atmospheric metallicity (Z) and intrinsic temperature. We derive relatively high values of Z = 14.79$_ and int $K, which are necessary to explain the radius inflation and the chemical composition of WASP-39 b. With this example, we show the importance of using a self-consistent model with the radius being a constrained parameter of the model and of using the age of the host star to break radius and mass degeneracies. When applying our model to 51 Eridani b, we derive a planet mass M$_p=3.13_ $ M$_ J $ and a core mass M$_ core $ M$_ E $, suggesting a potential formation by core accretion combined with a `hot start' scenario. We conclude that self-consistent atmosphere--interior models efficiently break degeneracies in the structure of both transiting and directly imaged exoplanets. Such tools have great potential to interpret current and future observations, thereby providing new insights into the formation and evolution of exoplanets.

Variability in Water Temperature Vertical Distribution and Advective Influences: Observations from Early Summer 2021 in the Central Yellow Sea

To analyze variations in the vertical distribution of water temperatures and the impact of advection in the central Yellow Sea, multi-layer water temperature and current observations were conducted from 31 May to 8 June 2021. Water temperatures exhibited a typical three-layer summer structure, with a uniform deep-layer temperature averaging 8.23 ± 0.05 °C. The current field was dominated by northeast–southwest tidal currents, but residual current characteristics indicated that non-tidal components significantly influenced circulation. Water temperature changes lagged tidal changes by about 3 h, with strong correlations (R &gt; 0.7), especially in deep layers. Residual currents showed significant correlations with water temperature variations, which were attributed to advective displacement or baroclinic currents. Empirical orthogonal function (EOF) and complex EOF analyses revealed that thermocline variations (T1, explaining approximately 75% of total variance) were driven by strong northward (C1, approximately 34%) and cyclonic (C2, approximately 32%) advection. In deep layers, slight temperature changes were caused by southward Yellow Sea Cold Water Mass (C1) and northward Yellow Sea Warm Current Water (C2) propagation. This study confirms that vertical water temperature variations result from a complex interaction between various advection patterns, with southward tide-induced residual currents (C3, approximately 12%) playing a key dynamic role.

Learning Heterogeneous Relation Graph and Value Regularization Policy for Visual Navigation.

The goal of visual navigation is steering an agent to find a given target object with current observation. It is crucial to learn an informative visual representation and robust navigation policy in this task. Aiming to promote these two parts, we propose three complementary techniques, heterogeneous relation graph (HRG), a value regularized navigation policy (VRP), and gradient-based meta learning (ML). HRG integrates object relationships, including object semantic closeness and spatial directions, e.g., a knife is usually co-occurrence with bowl semantically or located at the left of the fork spatially. It improves visual representation learning. Both VRP and gradient-based ML improve robust navigation policy, regulating this process of the agent to escape from the deadlock states such as being stuck or looping. Specifically, gradient-based ML is a type of supervision method used in policy network training, which eliminates the gap between the seen and unseen environment distributions. In this process, VRP maximizes the transformation of the mutual information between visual observation and navigation policy, thus improving more informed navigation decisions. Our framework shows superior performance over the current state-of-the-art (SOTA) in terms of success rate and success weighted by length (SPL). Our HRG outperforms the Visual Genome knowledge graph on cross-scene generalization with ≈ 56% and ≈ 39% improvement on Hits@ 5* (proportion of correct entities ranked in top 5) and MRR * (mean reciprocal rank), respectively. Our code and HRG datasets will be made publicly available in the scientific community.

Measuring the speed of light with cosmological observations: current constraints and forecasts

We measure the speed of light with current observations, such as Type Ia Supernova, galaxy ages, radial BAO mode, as well as simulations of forthcoming redshift surveys and gravitational waves as standard sirens. By means of a Gaussian Process reconstruction, we find that the precision of such measurements can be improved from roughly 6% and to about 2–2.5% when the gravitational wave simulations are considered, and to 1.5–2% when redshift survey are included in the analysis as well. This result demonstrates that we will be able to perform a cosmological measurement of a fundamental physical constant with significantly improved precision, which will help us underpinning if its value is truly consistent with local measurements, as predicted by the standard model of Cosmology.

Laboratory Study of Interface Friction between Sand and Steel Surfaces

Abstract In this study, results have been reported from a series of laboratory tests to determine the interface friction angle of steel surfaces with sand through modified direct shear testing. For completion, steel surfaces with different surface geometry to replicate the roughness have been slid against various sands compacted at different relative densities under both dry and wet conditions. The standard square shape direct shear box has been modified into circular and rectangular boxes to sufficiently enhance the contact area and to subsequently quantify its effect on interface friction angle. A mild steel interface of smooth and rough texture with a groove depth of 0.2 mm and tipping at an angle of 90° has been used in this study. The analysis of results revealed that the interface friction angles obtained from the standard direct shear box agree closely with those obtained from both modified rectangular and circular shear boxes. However, the ratio of the interface friction angle from the modified apparatus and soil’s angle of internal friction significantly depends upon the roughness of the surface in contact with the sand, its median particle size, and is independent of the effects of box size, soil’s relative density, and dry or wet condition. A comparison between existing well-accepted guidelines and current observations has been presented for use by the practicing engineers dealing with soil-structure interaction.

Measurement of ocean currents by seafloor distributed optical-fiber acoustic sensing.

Ocean current measurements play a crucial role in aiding our understanding of ocean dynamics and circulation systems. Traditional methods, such as drifters and ocean buoys, are sparsely distributed and of limited effectiveness due to the nature of the marine environment and high operating expenses. Distributed acoustic sensing (DAS) is an emerging technology using submarine optical-fiber (OF) cables as dense seismo-acoustic arrays, offering a new perspective for ocean observations. Here, in situ observations of ocean surface gravity waves (OSGWs) and ocean currents by DAS were made along a pre-existing 33.6 km seafloor OF cable. The average current velocity and water depth along the cable were determined from observed OSGW-induced seafloor noise (0.05-0.2 Hz) using ambient-noise interferometry and frequency-domain beamforming. Variations in current velocity were derived at high spatiotemporal resolution using the frequency-domain waveform-stretching method. The inverted current velocity was verified by nearby ocean buoy observations and forecasting results. The observations demonstrate the effectiveness of DAS-instrumented OF cables in monitoring ocean currents.

Helioseismic Constraints: Past, Current, and Future Observations

Helioseismic Constraints: Past, Current, and Future Observations