Distinct mechanisms underlying cross-modal semantic conflict and response conflict processing.

Interference from task-irrelevant stimuli can occur during the semantic and response processing stages. Previous studies have shown both common and distinct mechanisms underlying semantic conflict processing and response conflict processing in the visual domain. However, it remains unclear whether common and/or distinct mechanisms are involved in semantic conflict processing and response conflict processing in the cross-modal domain. Therefore, the present electroencephalography study adopted an audiovisual 2-1 mapping Stroop task to investigate whether common and/or distinct mechanisms underlie semantic conflict and response conflict. Behaviorally, significant cross-modal semantic conflict and significant cross-modal response conflict were observed. Electroencephalography results revealed that the frontal N2 amplitude and theta power increased only in the semantic conflict condition, while the parietal N450 amplitude increased only in the response conflict condition. These findings indicated that distinct neural mechanisms were involved in cross-modal semantic conflict and response conflict processing, supporting the domain-specific cognitive control mechanisms from a cross-modal multistage conflict processing perspective.

Distinct and common mechanisms of cross-model semantic conflict and response conflict in an auditory relevant task.

The mechanisms of semantic conflict and response conflict in the Stroop task have mainly been investigated in the visual modality. However, the understanding of these mechanisms in cross-modal modalities remains limited. In this electroencephalography (EEG) study, an audiovisual 2-1 mapping Stroop task was utilized to investigate whether distinct and/or common neural mechanisms underlie cross-modal semantic conflict and response conflict. The response time data showed significant effects on both cross-modal semantic and response conflicts. Interestingly, the magnitude of semantic conflict was found to be smaller in the fast response time bins than in the slow response time bins, whereas no such difference was observed for response conflict. The EEG data demonstrated that cross-modal semantic conflict specifically increased the N450 amplitude. However, cross-modal response conflict specifically enhanced theta band power and theta phase synchronization between the medial frontal cortex (MFC) and lateral prefrontal electrodes as well as between the MFC and motor electrodes. In addition, both cross-modal semantic conflict and response conflict led to a decrease in P3 amplitude. Taken together, these findings provide cross-modal evidence for domain-specific mechanism in conflict detection and suggest both domain-specific and domain-general mechanisms exist in conflict resolution.

Intermittent hypoxia training effectively protects against cognitive decline caused by acute hypoxia exposure.

Intermittent hypoxia training (IHT) is a promising approach that has been used to induce acclimatization to hypoxia and subsequently lower the risk of developing acute mountain sickness (AMS). However, the effects of IHT on cognitive and cerebrovascular function after acute hypoxia exposure have not been characterized. In the present study, we first confirmed that the simplified IHT paradigm was effective at relieving AMS at 4300 m. Second, we found that IHT improved participants' cognitive and neural alterations when they were exposed to hypoxia. Specifically, impaired working memory performance, decreased conflict control function, impaired cognitive control, and aggravated mental fatigue induced by acute hypoxia exposure were significantly alleviated in the IHT group. Furthermore, a reversal of brain swelling induced by acute hypoxia exposure was visualized in the IHT group using magnetic resonance imaging. An increase in cerebral blood flow (CBF) was observed in multiple brain regions of the IHT group after hypoxia exposure as compared with the control group. Based on these findings, the simplified IHT paradigm might facilitate hypoxia acclimatization, alleviate AMS symptoms, and increase CBF in multiple brain regions, thus ameliorating brain swelling and cognitive dysfunction.

Janus Cr2BN Monolayer with Ferroelectricity and Room-Temperature Ferromagnetism.

Janus monolayers, a special kind of two-dimensional materials, offer an exciting platform for the development of novel electronic/spintronic devices because of their out-of-plane asymmetry. Herein, we propose a sandwich liked Janus tetragonal Cr2BN monolayer with ferroelectricity and ferromagnetism through first-principles calculations. The predicted magnetic moment is up to ~3.0 µB/Cr originating from the distorted square crystal field induced by out-of-plane asymmetry. The Cr2BN monolayer possesses an intrinsic ferromagnetism with a high Curie temperature of 383 K and a sizeable magnetic anisotropy energy of 171 µeV/Cr. Its robust ferromagnetism, dominating by the multi-anion mediated super-exchange interactions, can even resist -5 % ~5 % biaxial strain. Its large cohesive energy and high dynamical/thermal stability provide a strong feasibility for experimental synthesis. These intriguing properties render the Cr2BN monolayer a promising material for nanoscale spintronic devices.

Layered Hydride LiH4 with a Pressure-Insensitive Superconductivity.

For hydride superconductors, each significant advance is built upon the discovery of novel H-based structural units, which in turn push the understanding of the superconducting mechanism to new heights. Based on first-principles calculations, we propose a metastable LiH4 with a wavy H layer composed of the edge-sharing pea-like H18 rings at high pressures. Unexpectedly, it exhibits pressure-insensitive superconductivity manifested by an extremely small pressure coefficient (dTc/dP) of 0.04 K/GPa. This feature is attributed to the slightly weakened electron-phonon coupling with pressure, caused by the reduced charge transfer from Li atoms to wavy H layers, significantly suppressing the substantial increase in the contribution of phonons to Tc. Its superconductivity originates from the strong coupling between the H 1s electrons and the high-frequency phonons associated with the H layer. Our study extends the list of H-based structural units and enhances the in-depth understanding of pressure-related superconductivity.

Metallic Re3O2 with mixed-valence states.

Rhenium (Re) shows the richest valence states from +2 to +7 in compounds, but its mixed-valence states are still missing thus far. In this work, we have explored the Re-O phase diagram with a wide range of stoichiometric compositions under high pressure through first-principles structural search calculations. Besides identifying two novel high-pressure phases of ReO2 and ReO3, we reveal two hitherto unknown Re-rich Re3O2 and O-rich ReO4 compounds. Re atoms in Re3O2 show mixed-valence states due to their inequivalent coordination environments, the first example in Re-based compounds. Electronic structure calculations demonstrate that the four discovered Re-O phases exhibit metallicity contributed by Re 5d electrons. Among them, ReO3 has a predicted critical temperature of up to 12 K at 50 GPa, derived from the interaction between Re 5d electrons and Re-derived low-frequency phonons. Our study points to new opportunities to disclose novel transition metal compounds with mixed-valence states.

Metallic CrP2 monolayer: potential applications in energy storage and conversion.

Phosphorus-rich compounds have emerged as a promising class of energy storage and conversion materials due to their interesting structures and electrochemical properties. Herein, we propose that a metallic CrP2 monolayer, isomorphic to 1H-phase MoS2, is a good prospect as an anode for K-ion batteries and a catalyst for hydrogen evolution through first-principles calculations. The CrP2 monolayer demonstrates not only a desirable high K storage capacity (940 mA h g-1) but also a low K-ion diffusion barrier (0.10 eV) and average open circuit voltage (0.40 V). On the other hand, its Gibbs free energy (0.02 eV)/active site density is superior/comparable to that of commercial Pt, resulting from the contribution of the lone pair electrons of the P atom. Its high structural stability and intrinsic metallicity can ensure high safety and performance during the cyclic process. These interesting properties make the CrP2 monolayer a promising multifunctional material for energy storage and conversion devices.

A Janus CrSSe monolayer with interesting ferromagnetism.

The search for intrinsic half-metallic ferromagnetic (FM) monolayers with a high Curie temperature (TC), considerable magnetic anisotropy energy (MAE), and multiferroic coupling is key for the development of ultra-compact spintronics. Here, we have identified a new stable FM Janus monolayer, the tetrahedral CrSSe, through first-principles structural search calculations, which not only exhibits very interesting magnetoelectric properties with a high TC of 790 K, a large MAE of 0.622 meV per Cr, and robust half-metallicity, but also shows obvious ferroelasticity with a modest energy barrier of 0.31 eV per atom. Additionally, there appears to be interesting multiferroic coupling between in-plane magnetization and ferroelasticity. Furthermore, by replacing the Se/S atoms in the CrSSe monolayer with S/Se atoms, we obtained two new half-metallic FM CrS2 and CrSe2 monolayers, which also exhibit excellent magnetoelectric properties. Therefore, our findings provide a pathway to design novel multiferroic materials and enrich the understanding of 2D transition metal chalcogenides.

2D antiferromagnetic semiconducting FeCN with interesting properties.

Two-dimensional magnetic materials have demonstrated favorable properties (e.g., large spin polarization and net magnetization) for the development of next-generation spintronic devices. The discovery of such materials and insight into their magnetic coupling mechanism has become a research focus. Here, on the basis of first-principles structural search calculations, we have identified a fresh FeCN monolayer consisting of edge-sharing Fe triangle sublattices and FeC3N2 rings, which integrates antiferromagnetism, semiconductivity, and planarity. Interestingly, it possesses a large magnetic anisotropy energy (MAE) of 614 µeV per Fe atom, a narrow band gap (Eg) of 0.47 eV, a large magnetic moment of 3.15 µB, and a proper Néel temperature (TN) of 97 K. The direct exchange between the nearest-neighbor Fe atoms in the triangle sublattice is mainly responsible for the AFM ordering. Its high structural stability, stemming from the collective contribution of covalent C-C and C-N bonds, ionic Fe-N bonds, and metallic Fe-Fe bonds, provides a strong feasibility for experimental synthesis.

An antiferromagnetic semiconducting FeCN2 monolayer with a large magnetic anisotropy and strong magnetic coupling.

Two-dimensional antiferromagnetic (AFM) materials with an intrinsic semiconductivity, a high critical temperature, and a sizable magnetic anisotropy energy (MAE) have attracted extensive attention because they show promise for high-performance spintronic nanodevices. Here, we have identified a new FeCN2 monolayer with a unique zigzag Fe chain through first-principles swarm structural search calculations. It is an AFM semiconductor with a direct band gap of 2.04 eV, a Néel temperature (TN) of 176 K, and a large in-plane MAE of 0.50 meV per Fe atom. More interestingly, the intrinsic antiferromagnetism, contributed by the strong magnetic coupling of neighbouring Fe ions, can be maintained under the external biaxial strains. A large cohesive energy and high dynamical stability favor synthesis and application. Therefore, these fascinating properties of the FeCN2 monolayer make it a promising nanoscale spintronic material.

Emergent superconductivity in TaO3 at high pressures.

Tantalum (Ta) is an interesting transition metal that exhibits superconductivity in its elemental states. Additionally, several Ta chalcogenides (S and Se) have also demonstrated superconducting properties. In this work, we propose the existence of five high-pressure metallic Ta-O compounds (e.g., TaO3, TaO2, TaO, Ta2O, and Ta3O), composed of polyhedra centered on Ta/O atoms. These compounds exhibit distinct characteristics compared to the well-known semiconducting Ta2O5. One particularly interesting finding is that TaO3 shows an estimated superconducting transition temperature (Tc) of 3.87 K at 200 GPa. This superconductivity is primarily driven by the coupling between the low-frequency phonons derived from Ta and the O 2p and Ta 5d electrons. Remarkably, its dynamically stabilized pressure can be as low as 50 GPa, resulting in an enhanced electron-phonon coupling and a higher Tc of up to 9.02 K. When compared to the superconductivity of isomorphic TaX3 (X = O, S, and Se) compounds, the highest Tc in TaO3 is associated with the highest NEF and phonon vibrational frequency. These characteristics arise from the strong electronegativity and small atomic mass of the O atom. Consequently, our findings offer valuable insights into the intrinsic physical mechanisms of high-pressure behaviors in Ta-O compounds.

Understanding Electrochemical Reaction Mechanisms of Sulfur in All-Solid-State Batteries through Operando and Theoretical Studies.

Due to its outstanding safety and high energy density, all-solid-state lithium-sulfur batteries (ASLSBs) are considered as a potential future energy storage technology. The electrochemical reaction pathway in ASLSBs with inorganic solid-state electrolytes is different from Li-S batteries with liquid electrolytes, but the mechanism remains unclear. By combining operando Raman spectroscopy and ex situ X-ray absorption spectroscopy, we investigated the reaction mechanism of sulfur (S8 ) in ASLSBs. Our results revealed that no Li2 S8, Li2 S6, and Li2 S4 were formed, yet Li2 S2 was detected. Furthermore, first-principles structural calculations were employed to disclose the formation energy of solid state Li2 Sn (1≤n≤8), in which Li2 S2 was a metastable phase, consistent with experimental observations. Meanwhile, partial S8 and Li2 S2 remained at the full lithiation stage, suggesting incomplete reaction due to sluggish reaction kinetics in ASLSBs.

Distinct Brain Mechanisms for Conflict Adaptation within and across Conflict Types.

Cognitive conflict, like other cognitive processes, shows the characteristic of adaptation, that is, conflict effects are attenuated when immediately following a conflicting event, a phenomenon known as the conflict adaptation effect (CAE). One important aspect of CAE is its sensitivity to the intertrial coherence of conflict type, that is, behavioral CAE occurs only if consecutive trials are of the same conflict type. Although reliably observed behaviorally, the neural mechanisms underlying such a phenomenon remains elusive. With a paradigm combining the classic Simon task and Stroop task, this fMRI study examined neural correlates of conflict adaptation both within and across conflict types. The results revealed that when the conflict type repeated (but not when it alternated), the CAE-like neural activations were observed in dorsal ACC, inferior frontal gyrus (IFG), superior parietal lobe, and so forth (i.e., regions within typical task-positive networks). In contrast, when the conflict type alternated (but not when it repeated), we found CAE-like neural deactivations in the left superior frontal gyri (i.e., a region within the typical task-negative network). Network analyses suggested that the regions of ACC, IFG, superior parietal lobe, and superior frontal gyrus can be clustered into two antagonistic networks, and the ACC-IFG connection was associated with the within-type CAE. This evidence suggests that our adaptation to cognitive conflicts within a conflict type and across different types may rely on these two distinct neural mechanisms.

Disproportionation of SO_{2} at High Pressure and Temperature.

Materials once suffered at high-pressure and high-temperature (HPHT) conditions often exhibit exotic phenomena that defy conventional wisdom. The behaviors of sulfur dioxide (SO_{2}), one of the archetypal simple molecules, at HPHT conditions have attracted a great deal of attention due to its relevance to the S cycle between deep Earth and the atmosphere. Here we report the discovery of an unexpected disproportionation of SO_{2} via bond breaking into elemental S and sulfur trioxide (SO_{3}) at HPHT conditions through a jointly experimental and theoretical study. Measured x-ray diffraction and Raman spectroscopy data allow us to solve unambiguously the crystal structure (space group R3[over ¯]c) of the resultant SO_{3} phase that shows an extended framework structure formed by vertex-sharing octahedra SO_{6}. Our findings lead to a significant extension of the phase diagram of SO_{2} and suggest that SO_{2}, despite its abundance in Earth's atmosphere and ubiquity in other giant planets, is not a stable compound at HPHT conditions relevant to planetary interiors, providing important implications for elucidating the S chemistry in deep Earth and other giant planets.

Pressure-stabilized hexafluorides of first-row transition metals.

Fluorine chemistry was demonstrated to show the importance of stretching the limits of chemical synthesis, oxidation state, and chemical bonding at ambient conditions. Thus far, the highest fluorine stoichiometry of a neutral first-row transition-metal fluoride is five, in VF5 and CrF5. Pressure can stabilize new stoichiometric compounds that are inaccessible at ambient conditions. Here, we attempted to delineate the fluorination limits of first-row transition metals at a high pressure through first-principles swarm-intelligence structure searching simulations. Besides reproducing the known compounds, our extensive search has resulted in a plethora of unreported compounds: CrF6, MnF6, FeF4, FeF5, FeF6, and CoF4, indicating that the application of pressure achieves not only the fluorination limit (e.g., hexafluoride) but also the long-sought bulky tetrafluorides. Our current results provide a significant step forward towards a comprehensive understanding of the fluorination limit of first-row transition metals.

Prediction of novel boron-carbon based clathrates.

Clathrates are inclusion compounds featured with host framework cages and trapped guest atoms or small molecules. Recently, the first boron-carbon (B-C) clathrate SrB3C3 was successfully synthesized at high pressures near 50 GPa. Upon the substitution of guest atoms, clathrates exhibit tunable applications. For example, LaB3C3 possesses an indirect band gap of near 1.3 eV, whereas the ScB3C3 clathrate is ferroelectric with an above-room-temperature Curie temperature of ∼370 K. To the best of our knowledge, however, there is no report on the investigation of B-C framework clathrates with non-equivalent B : C ratios. By using first-principles swarm-intelligence structure searching computations, we identified two metastable I4/mmm SrB2C4 and LaB4C2 clathrates at 50 GPa, and the framework cage contains six quadrilaterals and eight hexagons with a trapped guest metal located at the center. Their dynamic and enthalpy stabilities may be retained at ambient pressure. Moreover, the possible clathrates are extended by the substitution of the guest atoms with other metals in groups 2, 3, and 4, showing a tunable superconducting critical temperature (Tc) and considerable Vickers hardness (Hv). Intriguingly, a metal-to-semiconductor transition occurs in MB2C4 as the atomic number order of alkaline earth metals increases (M: Mg → Ca → Sr → Ba). The estimated Tc value for I4/mmm SrB4C2 is 19.2 K, while SrB2C4 and BaB2C4 are evaluated as superhard materials with Hv values of 43.6 and 41.2 GPa under ambient conditions, respectively.

Pressure-stabilized graphene-like P layer in superconducting LaP2.

MgB2-type superconductors are of great interest in chemistry and condensed matter physics due to their superconductivity dominated by the structural unit of graphene-like B. However, this kind of material is absent in phosphides resulting from the inherent lone pair electrons of phosphorus. Here, we report that a pressure-stabilized LaP2, isostructural to MgB2, shows superconductivity with a predicted Tc of 22.2 K, which is the highest among those of already known transition metal phosphides. Besides the electron-phonon coupling of graphene-like P, alike the role of the B layer in MgB2, La 5d/4f electrons are also responsible for the superconducting transition. The distinct P atomic arrangement is attributed to its sp2 hybridization and out-of-plane symmetric distribution of lone pair electrons. On the other hand, its dynamically stabilized pressure reaches as low as 7 GPa, a desirable feature of pressure-induced superconductors. Although P is isoelectronic to N and As, we hereby find the different stable stoichiometries, structures, and electronic properties of La phosphides compared with La nitrides/arsenides at high pressures.

Superconducting Li10Se electride under pressure.

Achieving a compound with interesting multiple coexisting states, such as electride, metallicity, and superconductivity, is of great interest in basic research and practical application. Pressure has become an effective way to realize high-temperature superconductivity in hydrides, whereas most electrides are semiconducting or insulating at high pressure. Here, we have applied swarm-intelligence structural search to identify a hitherto unknown C2/m Li10Se electride that is superconducting at high pressure. More interestingly, Li10Se is estimated to exhibit the highest Tc value of 16 K at 50 GPa, which is the lowest pressure among Li-based chalcogen electrides. This superconducting transition is dominated by Se-related low frequency vibration modes. The increasing electronic occupation of the Se 4d orbital and the decreasing amount of interstitial anion electrons with pressure heighten their coupling with low-frequency phonons, which is responsible for the enhancement of the Tc value. The finding of Li-based chalcogen superconducting electrides provides a reference for the realization of other superconducting electrides at lower pressures.

Two processing stages of the SNARC effect.

The spatial-numerical association of response codes (SNARC) effect showed that small/large numbers represented in the left/right space facilitated left/right responses, respectively. However, the processing stage (semantic representation or response selection) of the SNARC effect is still controversial. To investigate this issue, we adopted a modified magnitude comparison task in which the effects of SNARC, Stroop (semantic-representation stage), and Simon (response-selection stage) could be simultaneously induced. The processing stages of the SNARC effect were investigated by examining the interactions among these effects. According to the additive factor logic, if two effects are interactive, then they occur in the same stage; if two effects are additive, then they occur in different stages. Across two experiments, the SNARC effect interacted with the Stroop effect and with the Simon effect. These results suggested that the SNARC effect occurred in both the semantic-representation and response-selection stages and provided insight into that the SNARC effect might have two originating sources.

Pressure-induced Na-Au compounds with novel structural units and unique charge transfer.

The exploration of novel intermetallic compounds is of great significance for basic research and practical application. Considering the interesting and diverse attributes of Na and Au, their large electronegative difference, and the unresolved high-pressure Na-Au structures, first-principles swarm-intelligence structural search calculations are employed to explore the potential Na-Au compounds at high pressures. Besides reproducing the known Na-Au compounds, eleven new phases are disclosed, exhibiting several unprecedented Au atomic arrangements, such as rectangular ladder, layer formed by edge-sharing squares, hexahedron framework, and diamond-like skeleton, enriching the understanding of Au chemistry. Moreover, the coordination number of Au can be effectively modulated by controlling Na composition. In the Na-rich compounds (Na4Au, Na5Au, and Na6Au), Au shows a formal charge beyond -2, acting as a 6p-block element, originating from pressure-induced unusual Na 3s or 3p → Au 6p charge transfer. These compounds are metallic, but not superconductive. Moreover, the good agreement between the experimental XRD patterns and the simulated ones allows us to assign the predicted P6/mmm Na2Au and Fm3[combining macron]m Na3Au as the experimental structures at 59.6 GPa. Our work indicates that the modulation of pressure and chemical composition is a useful way to stabilize novel intermetallic compounds.