Attention-based convolutional neural network with multi-modal temporal information fusion for motor imagery EEG decoding.

Convolutional neural network (CNN) has been widely applied in motor imagery (MI)-based brain computer interface (BCI) to decode electroencephalography (EEG) signals. However, due to the limited perceptual field of convolutional kernel, CNN only extracts features from local region without considering long-term dependencies for EEG decoding. Apart from long-term dependencies, multi-modal temporal information is equally important for EEG decoding because it can offer a more comprehensive understanding of the temporal dynamics of neural processes. In this paper, we propose a novel deep learning network that combines CNN with self-attention mechanism to encapsulate multi-modal temporal information and global dependencies. The network first extracts multi-modal temporal information from two distinct perspectives: average and variance. A shared self-attention module is then designed to capture global dependencies along these two feature dimensions. We further design a convolutional encoder to explore the relationship between average-pooled and variance-pooled features and fuse them into more discriminative features. Moreover, a data augmentation method called signal segmentation and recombination is proposed to improve the generalization capability of the proposed network. The experimental results on the BCI Competition IV-2a (BCIC-IV-2a) and BCI Competition IV-2b (BCIC-IV-2b) datasets show that our proposed method outperforms the state-of-the-art methods and achieves 4-class average accuracy of 85.03% on the BCIC-IV-2a dataset. The proposed method implies the effectiveness of multi-modal temporal information fusion in attention-based deep learning networks and provides a new perspective for MI-EEG decoding. The code is available at https://github.com/Ma-Xinzhi/EEG-TransNet.

A Temporal Dependency Learning CNN With Attention Mechanism for MI-EEG Decoding.

Deep learning methods have been widely explored in motor imagery (MI)-based brain computer interface (BCI) systems to decode electroencephalography (EEG) signals. However, most studies fail to fully explore temporal dependencies among MI-related patterns generated in different stages during MI tasks, resulting in limited MI-EEG decoding performance. Apart from feature extraction, learning temporal dependencies is equally important to develop a subject-specific MI-based BCI because every subject has their own way of performing MI tasks. In this paper, a novel temporal dependency learning convolutional neural network (CNN) with attention mechanism is proposed to address MI-EEG decoding. The network first learns spatial and spectral information from multi-view EEG data via the spatial convolution block. Then, a series of non-overlapped time windows is employed to segment the output data, and the discriminative feature is further extracted from each time window to capture MI-related patterns generated in different stages. Furthermore, to explore temporal dependencies among discriminative features in different time windows, we design a temporal attention module that assigns different weights to features in various time windows and fuses them into more discriminative features. The experimental results on the BCI Competition IV-2a (BCIC-IV-2a) and OpenBMI datasets show that our proposed network outperforms the state-of-the-art algorithms and achieves the average accuracy of 79.48%, improved by 2.30% on the BCIC-IV-2a dataset. We demonstrate that learning temporal dependencies effectively improves MI-EEG decoding performance. The code is available at https://github.com/Ma-Xinzhi/LightConvNet.

Special NaBH4 hydrolysis achieving multiple-surface-modifications promotes the high-throughput water oxidation of CoN nanowire arrays.

Designing an excellent OER catalyst in an alkaline environment is severe yet essential for industrial H2 application under the electrochemical technique. This study has achieved multiple modifications on CoN nanowires, the classic OER catalyst, via a facile room-temperature NaBH4 spontaneous hydrolysis. This facile process simultaneously generates oxygen vacancies and robust BN species. It wraps hydrophilic BOx motifs on the OER response CoN nanowires, producing OER active Co-N-B species, increasing active numbers and guaranteeing structural stability. It suggests that a low NaBH4 concentration (0.1 mol L-1) treatment endows CoNNWAs/CC with excellent OER performance and robust structure, which can drive a current density of 50 mA cm-2 with only 325 mV overpotentials with more than 24 hours' durability. Even, the catalyst can drive 1000 mA cm-2 around 480 mV overpotential. This study allows a novel strategy for designing high-performance OER catalysts.

In situ artificial solid electrolyte interface engineering on an anode for prolonging the cycle life of lithium-metal batteries.

Lithium, with its high theoretical capacity and low potential, has been widely investigated as the anode in energy storage/conversion devices. However, their commercial applications always suffer from undesired dendrite growth, which forms in the charging process and may puncture the separator, leading to short cycle lives and even security problems. Herein, by an in situ displacement reaction using SnF2 at room temperature, we constructed an artificial solid electrolyte interface (ASEI) of LiF/Li-Sn outside the Li anode. This hybrid strategy can induce a synergy between the high Li+ conductivity of the Li-Sn alloy and good electrical insulation of LiF. Moreover, extreme synergy can be achieved by moderating the thickness of the LiF/Li-Sn ASEI, guiding dendrite-free lithium plating and stripping. As a result, a Li//LiFePO4 battery that is assembled from the LiF/Li-Sn ASEI-engineered Li anode can obtain 1000 cycled lives with 86.3% capacity retention under a charge/discharge rate of 5 C. This work provides an alternative way to construct dendrite-free lithium metal anodes, which significantly benefit the cycle lives of LMBs.

Mott-Schottky electrocatalyst selectively mediates the sulfur species conversion in lithium-sulfur batteries.

The lithium sulfur (Li-S) battery is an active research area in the field of energy storage systems, but the shuttle effect is a serious obstacle hindering its application. Herein, a CoSe2/CoO Mott-Schottky catalyst is blended with carbon nanotubes (CNTs) and subsequently coated onto a commercial separator as a modifier, whereby the synergy between the high electrocatalytic activity of the CoSe2/CoO heterostructure and high conductivity of the CNTs selectively mediate the conversion of sulfur species. As a result, a cell with a CoSe2/CoO-CNTs modified separator displays a high initial discharge capacity of 1573 and 910 mAh/g at 0.1 and 2C, respectively. Furthermore, a low decay rate of 0.070% per cycle can be obtained over 500 cycles at 2C. The results of this study suggest that the as-prepared CoSe2/CoO-CNTs is an effective modifier that can improve the performance of Li-S batteries for use in next-generation energy storage systems. This study provides fundamental insights into the rational design of Mott-Schottky catalysts for practical high-performance Li-S batteries.

Boosted charge transfer in ReS2/Nb2O5 heterostructure by dual-electric field: Toward superior electrochemical reversibility for lithium-ion storage.

Heterostructures with the electric field effect can excite the charge transfer kinetics of materials due to the driving force of the electric field. Herein, we report a new ReS2/Nb2O5 heterostructure of rhenium disulfide coupled to niobium oxide with a mutually compatible band structure and enriched oxygen vacancies. The unique heterostructure can facilitate the redistribution of charges to induce built-in electric fields and microlocalized electric fields. As expected, the ReS2/Nb2O5 heterostructure shows a superior lithium-ion reversible capacity of 805 mAh g-1 after 2400 h at 0.10 A g-1, and 414 mAh g-1 at 2.00 A g-1. In addition, in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy analysis reveal the phase transition process of the ReS2/Nb2O5 heterostructure during the electrochemical reaction. This provides deeper insights into the construction of high-performance lithium-ion storage materials based on heterostructures with dual-electric field-driven charge transfer.

Repeated turnovers keep sex chromosomes young in willows.

BACKGROUND: Salicaceae species have diverse sex determination systems and frequent sex chromosome turnovers. However, compared with poplars, the diversity of sex determination in willows is poorly understood, and little is known about the evolutionary forces driving their turnover. Here, we characterized the sex determination in two Salix species, S. chaenomeloides and S. arbutifolia, which have an XY system on chromosome 7 and 15, respectively. RESULTS: Based on the assemblies of their sex determination regions, we found that the sex determination mechanism of willows may have underlying similarities with poplars, both involving intact and/or partial homologs of a type A cytokinin response regulator (RR) gene. Comparative analyses suggested that at least two sex turnover events have occurred in Salix, one preserving the ancestral pattern of male heterogamety, and the other changing heterogametic sex from XY to ZW, which could be partly explained by the "deleterious mutation load" and "sexually antagonistic selection" theoretical models. We hypothesize that these repeated turnovers keep sex chromosomes of willow species in a perpetually young state, leading to limited degeneration. CONCLUSIONS: Our findings further improve the evolutionary trajectory of sex chromosomes in Salicaceae species, explore the evolutionary forces driving the repeated turnovers of their sex chromosomes, and provide a valuable reference for the study of sex chromosomes in other species.

One-dimensional Ni2P/Mn2O3 nanostructures with enhanced oxygen evolution reaction activity.

Nickel-based transition metal phosphides have been widely flourishing as oxygen evolution reaction (OER) electrocatalysts. In this study, a new catalyst Ni2P/Mn2O3 nanofibers with the advantages of ultra-high electrochemical active area were successfully synthesized. We explored effective strategies that are constructing one-dimensional nanostructures and composite oxides to promote the electrocatalytic performance of transition metal phosphides. The Ni2P/Mn2O3 nanofibers only require a low overpotential of 280 mV to deliver a current density of 10 mA cm-2 in 1 M KOH for oxygen production. As a result, it is worthily mentioned that the activity of Ni2P/Mn2O3 nanofibers is virtually unchanged after 2000 cycles of voltammetry measurements with a stable nanostructure. This research provides a feasible solution for the design and realization of nanostructured electrocatalysts for the enhancing performance of the OER process.

Computational screening of functionalized MXenes to catalyze the solid and non-solid conversion reactions in cathodes of lithium-sulfur batteries.

The poor cycling abilities of S cathodes due to the dissolution of high-order lithium polysulfides and sluggish reaction kinetics of low-order solid Li2S hinder the commercial application of lithium-sulfur batteries. Although many hosts have been introduced into S electrodes to anchor high-order polysulfides, an effective procedure to select the hosts to improve the conversion kinetics of solid Li2S is scarce. Using density functional theory calculations, we proposed a procedure to screen catalytic hosts for solid and non-solid reactions of Li2S2/Li2S by employing the available functionalized Ti3C2T2 MXenes (T = H, O, F, S, Cl, Se, Te, Br, OH, and NH), under the precondition of good anchoring abilities for high-order polysulfides. For the solid-state reactions, it was found that Ti3C2Se2 is the optimal candidate for improving the reaction kinetics of solid Li2S. Suitable catalysts for different reaction processes between molecular Li2S2 and Li2S have also been proposed. We also proposed that sulfur cathodes doped with heavy atoms (Se or Te) belonging to the main group VI may significantly modify the reaction kinetics of Li2S. These results provide guidance on synthesizing MXenes with the given surface groups as the hosts and can accelerate the step of finding out other suitable host materials.

In situ integration of cobalt diselenide nanoparticles on CNTs realizing durable hydrogen evolution.

Cobalt diselenide (CoSe2) is considered to be a promising economical and efficient electrocatalyst for the hydrogen evolution reaction (HER). Here carbon nanotubes (CNTs) were employed as a conductive skeleton to optimize the electrocatalytic performance of CoSe2 through a simple one-step hydrothermal method. Beyond the expected, the introduction of CNTs not only accelerates electron transportation and ion diffusion, but also improves the reaction kinetics for HER by forming a CoSe2/CNT heterointerface. Consequently, the CoSe2/CNTs composite exhibits an optimal overpotential of 153 mV with a weight ratio of 10 : 1, and sustains a long period of 48 hours with an negligible overpotential deterioration. In addition, a Faraday efficiency of 97.67% is achieved with a H2/O2 molar ratio of 2 : 1. Therefore, these results open up further opportunities for yielding efficient and durable hydrogen evolving electrocatalysts from low-cost transition metal compounds.

F, N neutralizing effect induced Co-P-O cleaving endows CoP nanosheets with superior HER and OER performances.

Electrochemical water splitting, the most direct and clean method used for the production of hydrogen, requires highly efficient bifunctional electrocatalysts that can accelerate hydrogen evolution reactions (HER) and oxygen evolution reactions (OER) by overcoming their kinetics barriers. Herein, self-supported F, N codoping CoP nanosheets (denoted as FN-CoP NS) are prepared as efficient and stable bifunctional electrocatalysts. Codoping of F and N neutralizes the electronegativity of surface P-O by cleaving the Co-P-O of non-metallic P sites on the surface (O derived from the surface oxidation). This contributes to an increased Co2+ content with considerable adjustable electronegativity and also optimizes HER and OER processes. As a result, FN-CoP NS requires 66 and 241 mV overpotentials to deliver the current density of 10 mA cm-2 during HER and OER, respectively. A full water electrolyzer equipped FN-CoP NS as both cathode and anode only require 1.57 V to drive the current density of 10 mA cm-2 and to sustain 50 mA cm-2 for 48 h. This work adjusts the electronic structure of metal phosphides by a double anion codoping strategy, which provides a reference value for the rational design of efficient bifunctional electrocatalysts.

A solution-processed octahedral nano-blocks structure CaIn2S4film for UV/vis photodetection.

A novel CaIn2S4with three-dimensional octahedral nano-blocks (ONBs) are successfully synthesized on fluorine-doped tin oxide (FTO) substrate by a simple hydrothermal method. The CaIn2S4ONBs are uniform grown and scattered on the whole FTO substrate with high regular and symmetric morphology as well as average diagonal length of about 600 nm. Based on the as-synthesized CaIn2S4ONBs, a photodetector (PD) is fabricated. Satisfyingly, it is found that the CaIn2S4ONBs PD achieves a broad-band response ranging from ultraviolet (UV) to visible ( vis) light at zero bias voltage. It is also significant that the CaIn2S4ONBs PD enables a fast response, in which the rise time and decay time are less than 0.15 and 0.2 s, respectively. Furthermore, the morphological evolution of the CaIn2S4ONBs and plausible UV/vis detection mechanism of the CaIn2S4ONBs PD are discussed.

One-dimensional CoP/MnO hollow nanostructures with enhanced oxygen evolution reaction activity.

Cobalt-based transition metal phosphides are flourishing as OER electrocatalysts. In this study, the CoP/MnO hollow nanofibers with the advantages of a more extensive contact interface were successfully synthesized. We found that the construction of hollow nanostructures and the composite of oxides are effective strategies to optimize the OER catalytic performance of transition metal phosphides. The template of the precursor can adjust the hollow nanostructure and keep it stable during the phosphating process. It is worth noting that the CoP/MnO composite material only needs an overpotential of 230 mV at a current density of 10 mA cm-2. In addition, it maintains the overpotential 263.5 mV after 5000 cycles of voltammetry measurements. In short, this research provides a simple solution for the design and realization of nanostructured electrocatalysts with excellent electrochemical performance.

Three-dimensional cross-linked Co-MoS2 catalyst on carbon cloth for efficient hydrogen evolution reaction.

MoS2-Based materials are promising hydrogen evolution reaction (HER) electrocatalysts. However, their HER activities are restrained by the poor population of HER activated edge centers, the large area exposed HER inert basal planes, and low conductivity. Fixing these problems on one system is an effective strategy, but it remains a challenge due to the harsh synthetic conditions. Herein, cobalt carbonate hydroxide (CoCH) nanosheets were used as the substrate for preparing a three-dimensional self-supported cross-linked (3DSC) Co-MoS2 nanostructured HER catalyst, which possesses abundant active centers and fast electronic transfer ability. In addition, Co activates the basal-plane sulfur atom in MoS2 to be the HER reactive center effectively. Benefiting from these advantages, 3DSC Co-MoS2 electrode integrated on carbon cloth (CC) shows that it can drive the current density of 10 and 100 mA cm-2 with only 40 and 119 mV overpotentials, respectively, which is superior to other MoS2-based HER catalysts reported recently. This research provides a facile strategy for the improvement of efficient HER electrocatalysts.

Interfacial electronic modulation of CoP-CoO p-p type heterojunction for enhancing oxygen evolution reaction.

Heterojunction can effectively improve oxygen evolution reaction (OER) activity by regulating the interfacial electronic structure of catalysts. However, p-p type heterojunction OER catalysts have obtained less attention, and the corresponding catalytic mechanisms are unclear either. Herein, the self-supported CoP-CoO p-p type heterojunction arrays are fabricated on carbon cloth substrate (CoP-CoO/CC). Band structure analysis shows that the formation of p-p heterojunction can drive the electrons from CoO to flow into CoP. This electronic modulation contributes to positively charged regions on the CoO and enhances the OH- adsorption during OER, proven by X-ray photoelectron spectroscopy and methanol molecular detection, respectively. As a result, the CoP-CoO/CC electrode only needs 210 mV overpotential to drive a current density of 10 mA cm-2 in an alkaline medium, superior to the most reported OER catalysts. Additionally, the CoP-CoO/CC also exhibits an ideal hydrogen evolution reaction response, and a water splitting system has been successfully constructed which can drive a 10 mA cm-2 within 1.65 V. This study supplies insight for catalytic origins p-p type heterojunctions OER catalyst, which provides a reference value for the efficient and reasonable design of heterojunction catalysts.

CoS nanowires grown on Ti3C2Tx are promising electrodes for supercapacitors: High capacitance and remarkable cycle capability.

Benefitting from the large interlayer spacing, ultrahigh conductivity and abundant surface chemistry, Ti3C2Tx has been a promising electrode material for supercapacitors (SCs). CoS has attracted much attention due to its low cost, weak Co-S bond and relatively high theoretical capacity. Herein, CoS nanowires were grown on few-layered Ti3C2Tx by one-step solvothermal method as a SC electrode. Within the composite, Ti3C2Tx could function as conductive network and buffer matrix to provide ultra-fast electronic transport and relieve volume expansion of CoS nanowires. Simultaneously, the active CoS nanowires with high capacitance act as interlayer spacer to restrain the restacking of Ti3C2Tx nanosheets. As a result, CoS/Ti3C2Tx-5 electrode exhibits a remarkable improvement specific capacitance of 528 F g-1 at a current density of 1 A g-1 and ultrahigh capacitance retention of 99.3% after 20 000 cycles at a current density of 10 A g-1. The attempts and efforts made in this work provide a prototype for achieving excellent electrochemical properties.

Synergistic effect of cocatalytic NiSe2 on stable 1T-MoS2 for hydrogen evolution.

Robust and economical catalysts are imperative to realize the versatile applications of hydrogen. Herein, a 1T-MoS2/N-doped NiSe2 composite was rationally synthesized via a solvothermal method, in which the MoS2 nanosheets have a stable 1T phase structure, and the NiSe2 nanoparticles serve as a cocatalytic support for MoS2. The nonnegligible electronic couplings between NiSe2 and MoS2 could facilitate the optimization of their electronic structure and then improve the hydrogen adsorption. What is more, the nitrogen dopants in the NiSe2 nanoparticles could intensify the intercalation of ammonium ions in the 1T-MoS2 nanosheets, and further enlarge their interlayer spacing, thus the electrolyte could infiltrate into the catalyst more easily and sufficiently. This work provides a new route for rationally designing highly active and low cost hydrogen evolution reaction (HER) catalysts, and enriches the study of transition metal chalcogenides toward HER.

A General Model to Explain Repeated Turnovers of Sex Determination in the Salicaceae.

Dioecy, the presence of separate sexes on distinct individuals, has evolved repeatedly in multiple plant lineages. However, the specific mechanisms by which sex systems evolve and their commonalities among plant species remain poorly understood. With both XY and ZW sex systems, the family Salicaceae provides a system to uncover the evolutionary forces driving sex chromosome turnovers. In this study, we performed a genome-wide association study to characterize sex determination in two Populus species, P. euphratica and P. alba. Our results reveal an XY system of sex determination on chromosome 14 of P. euphratica, and a ZW system on chromosome 19 of P. alba. We further assembled the corresponding sex-determination regions, and found that their sex chromosome turnovers may be driven by the repeated translocations of a Helitron-like transposon. During the translocation, this factor may have captured partial or intact sequences that are orthologous to a type-A cytokinin response regulator gene. Based on results from this and other recently published studies, we hypothesize that this gene may act as a master regulator of sex determination for the entire family. We propose a general model to explain how the XY and ZW sex systems in this family can be determined by the same RR gene. Our study provides new insights into the diversification of incipient sex chromosomes in flowering plants by showing how transposition and rearrangement of a single gene can control sex in both XY and ZW systems.

Survival in the Tropics despite isolation, inbreeding and asexual reproduction: insights from the genome of the world's southernmost poplar (Populus ilicifolia).

Species are becoming extinct at unprecedented rates as a consequence of human activity. Hence it is important to understand the evolutionary dynamics of species with already small population sizes. Populus ilicifolia is a vulnerable poplar species that is isolated from other poplar species and is uniquely adapted to the Tropics. It has a very limited size, reproduces partly clonally and is therefore an excellent case study for conservation genomics. We present here the first annotated draft genome of P. ilicifolia, characterize genome-wide patterns of polymorphisms and compare those to other poplar species with larger natural ranges. P. ilicifolia experienced a more prolonged and severe decline of effective population size (Ne ) and signs of genetic erosion than any other poplar species with which it was compared. At present, the species has the lowest genome-wide genetic diversity, the highest abundance of long runs of homozygosity, high inbreeding levels as well as a high overall accumulation of deleterious variants. However, more effective purging of severely deleterious variants and adaptation to the Tropics may have contributed to its survival. Hence, in spite of its limited genetic variation, it is certainly worth pursuing the conservation efforts of this unique species.

Improved genome assembly provides new insights into genome evolution in a desert poplar (Populus euphratica).

Populus euphratica is well adapted to extreme desert environments and is an important model species for elucidating the mechanisms of abiotic stress resistance in trees. The current assembly of P. euphratica genome is highly fragmented with many gaps and errors, thereby impeding downstream applications. Here, we report an improved chromosome-level reference genome of P. euphratica (v2.0) using single-molecule sequencing and chromosome conformation capture (Hi-C) technologies. Relative to the previous reference genome, our assembly represents a nearly 60-fold improvement in contiguity, with a scaffold N50 size of 28.59 Mb. Using this genome, we have found that extensive expansion of Gypsy elements in P. euphratica led to its rapid increase in genome size compared to any other Salicaceae species studied to date, and potentially contributed to adaptive divergence driven by insertions near genes involved in stress tolerance. We also detected a wide range of unique structural rearrangements in P. euphratica, including 2,549 translocations, 454 inversions, 121 tandem and 14 segmental duplications. Several key genes likely to be involved in tolerance to abiotic stress were identified within these regions. This high-quality genome represents a valuable resource for poplar breeding and genetic improvement in the future, as well as comparative genomic analysis with other Salicaceae species.