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As a significant source of nutrients and other components into the coastal ocean, submarine groundwater discharge (SGD) is a combination of multiple spatial‐temporal scale processes, including fresh terrestrial groundwater (FSGD), recirculating seawater (RSGD), and porewater exchange (PEX). Quantifying the different types of SGD is extremely important for understanding the coastal biogeochemical cycles of various materials. The green tide bloom in the southern Yellow Sea (China) has attracted increasing attention during the past decade. Haizhou Bay is thought to be an important green tide proliferating area, but the source of an apparent high supply of nutrients has not been identified yet. We report here on our investigations of the distribution patterns of Ra and Rn isotopes in groundwater and seawater in Haizhou Bay. By solving a combined mass balance for 224Ra, 223Ra, 226Ra, and 222Rn, we estimated that the bay's water residence time is 28.8 days, FSGD is highest at 3.6 cm d−1, RSGD is 2.7 cm d−1, and PEX is lowest at 0.6 cm d−1. The total SGD into Haizhou Bay is estimated at 9.40 × 107 m3 d−1 (6.9 cm d−1), about 12 times that of the local river discharge into the bay. SGD‐derived nutrients are shown to play an important role when considered among all known nutrient sources. Our results suggest that dissolved inorganic nitrogen (DIN) and silicate (DSi) are transported by SGD mainly via FSGD. We also note that the phosphorus (DIP) budget is heavily influenced by RSGD. Plain Language Summary: Submarine groundwater discharge (SGD) has been drawing attention as an important benthic boundary exchange pathway in the global marginal seas. As any water flow entering the sea, SGD may happen on small scales (centimeters, minutes to hours) as porewater exchange (PEX), and/or large scales (>meters, days to seasons) as fresh groundwater discharge (FSGD) and seawater recirculation (RSGD) in the subterranean estuary. To better understand its significance, it is necessary to interpret multi‐scale SGD processes and quantify associated nutrients fluxes accordingly. In this study, different types of SGD and associated nutrient fluxes were quantified based on multiple radium and radon isotopes in Haizhou Bay, China, which is one of the world's largest green tide proliferating areas. The FSGD and RSGD were found to be the main processes, accounting for more than 90% of the total SGD fluxes. SGD was recognized as a key nutrient source in Haizhou Bay, which is more than one order of magnitude higher than that of the local river discharge. This study highlights the crucial role of benthic boundary exchange for the health of marine ecosystem and sustainability of the future ocean. Key Points: Multi‐scale submarine groundwater discharge processes were differentiated and quantified via a multi‐isotope mass balance approachThe flux of fresh groundwater was about 30% higher than recirculated saline groundwater, and about 6 times higher than porewater exchangeFresh groundwater is a main nutrient source to Haizhou Bay, but recirculated saline groundwater makes a larger contribution to DIP inputs [ABSTRACT FROM AUTHOR]

Seafloor ambient noise in the Arctic Ocean is related to sea ice. The characteristics of low‐frequency seafloor ambient noise (<10 Hz) in the northern Chukchi Sea have rarely been reported. Here, we investigated the seafloor ambient noise recorded using ocean‐bottom seismometers in the northern Chukchi Sea under four different sea ice‐concentration periods from 3 to 23 August 2020, in the 11th Chinese National Arctic Research Expedition. The causes and mechanisms of the changes in seafloor ambient noise that correspond to the variation in sea ice concentration were discussed. The energy of infragravity waves and primary microseisms is weak compared with other oceans. Combined with the analysis of land station, we argue that the variations in sea ice extent have little effect on the energy of the primary microseisms and infragravity waves. The power of secondary microseisms is growth with the loss of sea ice and is influenced by storms. We find that a high concentration of sea ice can impede the process of storm‐sea surface interaction, which in turn affects the power of microseisms inspired by storm. [ABSTRACT FROM AUTHOR]

Diffusion in alloys is an important class of atomic processes. However, atomistic simulations of diffusion in chemically complex solids are confronted with the timescale problem: the accessible simulation time is usually far shorter than that of experimental interest. In this work, long‐timescale simulation methods are developed using reinforcement learning (RL) that extends simulation capability to match the duration of experimental interest. Two special limits, RL transition kinetics simulator (TKS) and RL low‐energy states sampler (LSS), are implemented and explained in detail, while the meaning of general RL are also discussed. As a testbed, hydrogen diffusivity is computed using RL TKS in pure metals and a medium entropy alloy, CrCoNi, and compared with experiments. The algorithm can produce counter‐intuitive hydrogen‐vacancy cooperative motion. We also demonstrate that RL LSS can accelerate the sampling of low‐energy configurations compared to the Metropolis–Hastings algorithm, using hydrogen migration to copper (111) surface as an example. [ABSTRACT FROM AUTHOR]

Civilian fusion demands structural materials that can withstand the harsh environments imposed inside fusion plasma reactors. The structural materials often transmute under 14.1 MeV fast neutrons, producing helium (He), which embrittles the grain boundary (GB) network. Here, it is shown that neutron‐friendly and mechanically strong nano‐phases with atomic‐scale free volume can have low He‐embedding energy Eemb${\mathcal{E}}_{\mathrm{emb}}$ and >10 at.% He‐absorbing capacity, and can be especially advantageous for soaking up He on top of resisting radiation damage and creep, provided they have thermodynamic compatibility with the matrix phase, satisfactory equilibrium wetting angle, as well as a high enough melting point. The preliminary experimental demonstration proves that Eemb${\mathcal{E}}_{\mathrm{emb}}$ is a good ab initio predictor of He shielding potency in nano‐heterophase materials, and thus, Eemb${\mathcal{E}}_{\mathrm{emb}}$ is used as a key feature for computational screening. In this context, a list of viable compounds expected to be good He‐absorbing nano‐phases is presented, taking into account Eemb${\mathcal{E}}_{\mathrm{emb}}$, the neutron absorption and activation cross‐sections, the elastic moduli, melting temperature, the thermodynamic compatibility, and the equilbrium wetting angle of the nano‐phases with the Fe matrix as an example. [ABSTRACT FROM AUTHOR]

Quantum anomalous Hall (QAH) effect generates quantized electric charge Hall conductance without external magnetic field. It requires both nontrivial band topology and time‐reversal symmetry (TRS) breaking. In most cases, one can break the TRS of time‐reversal invariant topological materials to yield QAH effect, which is essentially a topological phase transition. However, conventional topological phase transition induced by external field/stimulus usually needs a route along which the bandgap closes and reopens. Hence, the transition occurs only when the magnitude of field/stimulus is larger than a critical value. In this work the authors propose that using gapless systems, the transition can happen at an arbitrarily weak (but finite) external field strength. For such an unconventional topological phase transition, the bandgap closing is guaranteed by bulk‐edge correspondence and symmetries, while the bandgap reopening is induced by external fields. This concept is demonstrated on the 2D surface states of 3D topological insulators like Bi2Se3, which become 2D QAH insulators once a circularly polarized light is turned on, according to the Floquet time crystal theory. The sign of quantized Chern number can be controlled via the chirality of the light. This provides a convenient and dynamic approach to trigger topological phase transitions and create QAH insulators. [ABSTRACT FROM AUTHOR]

This paper shows how terahertz light can drive ultrafast topological phase transitions in monolayer transition metal dichalcogenides (TMDs). The phase transition is induced by the light interaction with both electron and phonon subsystems in the material. The mechanism of such a phase transition is formulated by thermodynamics theory: the Gibbs free energy landscape can be effectively modulated under light, and the relative stability between different (meta‐)stable phases can be switched. This mechanism is applied to TMDs and reversible phase transitions between the topologically trivial 2H and nontrivial 1T′ phases are predicted, providing appropriate light frequency, polarization, and intensity are applied. The large energy barrier on the martensitic transformation path can be significantly reduced, yielding a small energy barrier phase transition with fast kinetics. Compared with other phase transition schemes, light illumination has great advantages, such as its non‐contact nature and easy tunability. The reversible topological phase transition can be applicable in high‐resolution fast data storage and in‐memory computing devices. [ABSTRACT FROM AUTHOR]

Abstract: This study addresses the problem of short UWB (ultra‐wide band) outages in a UWB/IMU (inertial measurement unit) integrated navigation system. UWB outages may occur due to non‐line‐of‐sight between the UWB radios. To mitigate the errors during short UWB outages, we consider the special dynamics of the platform by adaptively applying constraints in the navigation filter. The application presented here is the navigation problem of the unexploded ordnances (UXOs) mapping platform. A UXO platform moves straight or performs turns or stops; these are the three dynamic states with pre‐defined constraints. Two neural networks are examined to determine the current dynamic state based on IMU data. Tests on open‐sky and canopied areas were carried out for the performance assessment. The networks were trained on the open‐sky dataset, and then tested on the canopied area. The detected improvement of the proposed solution is 10–30% (10–15 cm) for 5–10 s long outages. Copyright © 2018 Institute of Navigation [ABSTRACT FROM AUTHOR]

In article number 2003832 by Jian Zhou, Ju Li, and co-workers, optomechanical theory is derived and applied to predict terahertz optics driven ultrafast and reversible topological phase transitions in transition metal dichalcogenide monolayers, which is a damage-free and non-contacting approach that compensates other strategies. The cover displays such a novel optical strategy to trigger a thermal topological phase transition. [Extracted from the article]