A novel registration method for long-serial section images of EM with a serial split technique based on unsupervised optical flow network.

MOTIVATION: The registration of serial section electron microscope images is a critical step in reconstructing biological tissue volumes, and it aims to eliminate complex nonlinear deformations from sectioning and replicate the correct neurite structure. However, due to the inherent properties of biological structures and the challenges posed by section preparation of biological tissues, achieving an accurate registration of serial sections remains a significant challenge. Conventional nonlinear registration techniques, which are effective in eliminating nonlinear deformation, can also eliminate the natural morphological variation of neurites across sections. Additionally, accumulation of registration errors alters the neurite structure. RESULTS: This article proposes a novel method for serial section registration that utilizes an unsupervised optical flow network to measure feature similarity rather than pixel similarity to eliminate nonlinear deformation and achieve pairwise registration between sections. The optical flow network is then employed to estimate and compensate for cumulative registration error, thereby allowing for the reconstruction of the structure of biological tissues. Based on the novel serial section registration method, a serial split technique is proposed for long-serial sections. Experimental results demonstrate that the state-of-the-art method proposed here effectively improves the spatial continuity of serial sections, leading to more accurate registration and improved reconstruction of the structure of biological tissues. AVAILABILITY AND IMPLEMENTATION: The source code and data are available at https://github.com/TongXin-CASIA/EFSR.

Modeling drug mechanism of action with large scale gene-expression profiles using GPAR, an artificial intelligence platform.

BACKGROUND: Querying drug-induced gene expression profiles with machine learning method is an effective way for revealing drug mechanism of actions (MOAs), which is strongly supported by the growth of large scale and high-throughput gene expression databases. However, due to the lack of code-free and user friendly applications, it is not easy for biologists and pharmacologists to model MOAs with state-of-art deep learning approach. RESULTS: In this work, a newly developed online collaborative tool, Genetic profile-activity relationship (GPAR) was built to help modeling and predicting MOAs easily via deep learning. The users can use GPAR to customize their training sets to train self-defined MOA prediction models, to evaluate the model performances and to make further predictions automatically. Cross-validation tests show GPAR outperforms Gene set enrichment analysis in predicting MOAs. CONCLUSION: GPAR can serve as a better approach in MOAs prediction, which may facilitate researchers to generate more reliable MOA hypothesis.

Prediction of 2D ferromagnetism and monovalent europium ions in EuBr/graphene heterojunctions.

Europium, one of the rare-earth elements, exhibits +2 and +3 valence states and has been widely used for the magnetic modification of materials. Based on density functional theory calculations, we predicted 2D EuBr/graphene heterojunctions to exhibit metallicity, huge intrinsic-ferromagnetism nearly 7.0 µB per Eu and the special monovalent Eu ions. Electron localization function (ELF), difference charge densities and Bader charge analyses demonstrated that there are cation-π interactions between the EuBr films and graphene. Graphene works as a substrate to enable the stability of EuBr monolayer crystals, where EuBr plays an important role to yield ferromagnetism and enhance metallicity in the heterojunctions. Monte Carlo simulations were used to estimate a Curie temperature of about 7 K, which, together with magnetic configurations, can be further modulated by external strains and charge-carrier doping. In general, our theoretical work predicts the properties of novel 2D ferromagnetic EuBr/graphene heterojunctions, suggesting the possibility of combining 2D intrinsic-ferromagnetic metal halide crystals and graphene, and opening up a new perspective in next-generation electronic, spintronic devices and high-performance sensors.

One Structure, Two Elements-LuGe2 Superconductor vs Ordinary Metallic Conductor LuSn2. A Case Study on How Site-Selective Germanium for Tin Atom Substitution Leads to Modulating of the Charge Distribution.

The substitution of chemically similar elements in a given crystal structure is an effective way to enhance physical properties, but the understanding on such improvements is usually impeded because the substitutions are random, and the roles of the different atoms cannot be distinguished by crystallographic symmetry. Herein, we provide a detailed crystallographic analysis and property measurements for the continuous solid solutions LuGexSn2-x (0 < x < 2). The results show that there is no apparent change of the global symmetry, with the end-members LuGe2 and LuSn2, as well as the intermediate LuGexSn2-x compositions adopting the ZrSi2 type structure (space group Cmcm, Pearson index oC12). Yet, the refinements of the crystal structures from single-crystal X-ray diffraction data show that Ge-Sn atom substitutions are not random, but occur preferentially at the zigzag chain. The patterned distribution of two group 14 elements leads to a significant variation in chemical bonding and charge ordering within the other structural fragment, the 2D square nets, thereby resulting in tuned electron transport. The enhancement is greater than that for the typical Bloch-Gruneisen model and more akin to that for the parallel-resistor model. Magnetization measurements on single crystals show bulk superconductivity in all LuGexSn2-x samples with shielding fractions as high as 90%. Specific heat data confirm the effect to originate from residual metallic tin in the material, indicating that Sn atom substitutions in the 2D square nets cause disruptions of the hypervalent bonding and local anisotropy, which ultimately leads to vanishing of the superconducting state in the end-member LuGe2. This work sheds light on how the complexity in chemical interactions by two different carbon congeners leads to changes in the physical properties and how they can be correlated with the induced charge distribution. These studies also provide a general approach to modulation of charge density and. thus, of emerging physical properties in other classes of intermetallic systems based on the main-group elements of groups 13 to 15.

Plasmonic Light Illumination Creates a Channel To Achieve Fast Degradation of Ti3C2T x Nanosheets.

Two-dimensional (2D) material-controllable degradation under light radiation is crucial for their photonics and medical-related applications, which are yet to be investigated. In this paper, we first report the laser illumination method to regulate the degradation rate of Ti3C2T x nanosheets in aqueous solution. Comprehensive characterization of intermediates and final products confirmed that plasmonic laser promoting the oxidation was strikingly different from heating the aqueous solution homogeneously. Laser illumination would nearly 10 times accelerate the degradation of Ti3C2T x nanosheets in initial stage and create many smaller-sized oxidized products in a short time. Laser-induced fast degradation was principally ascribed to surface plasmonic resonance effect of Ti3C2T x nanosheets. The degradation ability of such illumination could be controlled either by tuning the excitation wavelength or changing the excitation power. Furthermore, the laser- or thermal-induced degradation could be retarded by surface protection of Ti3C2T x nanosheets. Our results suggest that plasmonic electron excitation of Ti3C2T x nanosheets could build a new reaction channel and lead to the fast oxidation of nanosheets in aqueous solution, potentially enabling a series of water-based applications.

High-performance asymmetric micro-supercapacitors based on electrodeposited MnO2 and N-doped graphene.

In-plane asymmetric micro-supercapacitors using nitrogen-doped graphene (NG) film as negative electrode and MnO2 nanostructures as positive electrode are fabricated onto a plastic substrate coated with Ni/Cu film. A laser-scribing machine is employed to make interdigital finger electrodes in the plastic substrate coated with NG film via a slurry coating process. MnO2 nanosheets are electrochemically deposited onto pre-coated NG film. In LiCl-based gelled electrolyte, the NG//MnO2 cell exhibits excellent electrochemical performance and a broad voltage window up to 1.8 V. The maximum specific capacitance of a single cell is measured to be 13 mF cm-2. In addition, several cells in series can be easily fabricated by combining the laser-scribing technique and the electrodeposition of MnO2 electrodes. As a proof of concept, four cells in a compact configuration and with high voltage output up to 7.2 V are demonstrated.

Enhanced dielectric permittivity and suppressed electrical conductivity in polyvinylidene fluoride nanocomposites filled with 4,4'-oxydiphenol-functionalized graphene.

Plastic film capacitors suffer from low charge storage capacity due to the low dielectric constant of the polymer (<10). We have devised a polyvinylidene fluoride (PVDF) composite film filled with small graphene oxide (GO) sheets that have aromatic molecules attached to their surfaces. The use of 4,4'-oxydiphenol molecules to functionalize graphene sheets is found to have a remarkable effect on enhancing the dielectric permittivity as well as reducing the electrical conductivity of the nanocomposite. When under an electric field, these molecules with an angled molecular geometry act as aligned electric dipoles to largely enhance the dielectric permittivity of the composite, reaching a level two orders of magnitude higher than that of the counterpart filled with blank graphene sheets. Also, the aromatic molecules on the graphene surface act as resistive barriers that block charge transfer between interconnected graphene sheets. As a consequence, the electric conductivity of the composite can be decreased by two orders of magnitude. The PVDF composite filled with functionalized graphene shows a percolation threshold of 13 wt% and a high dielectric constant of 1091 at 100 Hz at this point.

On-site monitoring of atomic density number for an all-optical atomic magnetometer based on atomic spin exchange relaxation.

We present a method for monitoring the atomic density number on site based on atomic spin exchange relaxation. When the spin polarization P ≪ 1, the atomic density numbers could be estimated by measuring magnetic resonance linewidth in an applied DC magnetic field by using an all-optical atomic magnetometer. The density measurement results showed that the experimental results the theoretical predictions had a good consistency in the investigated temperature range from 413 K to 463 K, while, the experimental results were approximately 1.5 ∼ 2 times less than the theoretical predictions estimated from the saturated vapor pressure curve. These deviations were mainly induced by the radiative heat transfer efficiency, which inevitably leaded to a lower temperature in cell than the setting temperature.

New Family of Quantum Spin Hall Insulators in Two-dimensional Transition-Metal Halide with Large Nontrivial Band Gaps.

Topological insulators (TIs) are promising for achieving dissipationless transport devices due to the robust gapless states inside the insulating bulk gap. However, currently realized two-dimensional (2D) TIs, quantum spin Hall (QSH) insulators, suffer from ultrahigh vacuum and extremely low temperature. Thus, seeking for desirable QSH insulators with high feasibility of experimental preparation and large nontrivial gap is of great importance for wide applications in spintronics. On the basis of the first-principles calculations, we predict a novel family of 2D QSH insulators in transition-metal halide MX (M = Zr, Hf; X = Cl, Br, and I) monolayers, especially, which is the first case based on transition-metal halide-based QSH insulators. MX family has the large nontrivial gaps of 0.12-0.4 eV, comparable with bismuth (111) bilayer (0.2 eV), stanene (0.3 eV), and larger than ZrTe5 (0.1 eV) monolayers and graphene-based sandwiched heterstructures (30-70 meV). Their corresponding 3D bulk materials are weak topological insulators from stacking QSH layers, and some of bulk compounds have already been synthesized in experiment. The mechanism for 2D QSH effect in this system originates from a novel d-d band inversion, significantly different from conventional band inversion between s-p, p-p, or d-p orbitals. The realization of pure layered MX monolayers may be prepared by exfoliation from their 3D bulk phases, thus holding great promise for nanoscale device applications and stimulating further efforts on transition metal-based QSH materials.

Prediction of near-room-temperature quantum anomalous Hall effect on honeycomb materials.

Recently, the long-sough quantum anomalous Hall effect was realized in a magnetic topological insulator. However, the requirement of an extremely low temperature (approximately 30 mK) hinders realistic applications. Based on ab initio band structure calculations, we propose a quantum anomalous Hall platform with a large energy gap of 0.34 and 0.06 eV on honeycomb lattices comprised of Sn and Ge, respectively. The ferromagnetic (FM) order forms in one sublattice of the honeycomb structure by controlling the surface functionalization rather than dilute magnetic doping, which is expected to be visualized by spin polarized STM in experiment. Strong coupling between the inherent quantum spin Hall state and ferromagnetism results in considerable exchange splitting and, consequently, an FM insulator with a large energy gap. The estimated mean-field Curie temperature is 243 and 509 K for Sn and Ge lattices, respectively. The large energy gap and high Curie temperature indicate the feasibility of the quantum anomalous Hall effect in the near-room-temperature and even room-temperature regions.

Computational screening and functional tuning of chemically stable metal organic frameworks for I2/CH3I capture in humid environments.

High chemical stability is of vital significance in rendering metal organic frameworks (MOFs) as promising adsorbents for capturing leaked radioactive nuclides, under real nuclear industrial conditions with high humidity. In this work, grand canonical Monte Carlo (GCMC) and density functional theory (DFT) methods have been employed to systematically evaluate I2/CH3I capture performances of 21 experimentally confirmed chemically stable MOFs in humid environments. Favorable structural factors and the influence of hydrophilicity for iodine capture were unveiled. Subsequently, the top-performing MIL-53-Al with flexible tunability was functionalized with different functional groups to achieve the better adsorption performance. It has been revealed that the adsorption affinity and pore volume were two major factors altered by the functionalization of polar functional groups, which collectively influenced the iodine adsorption properties. In general, this work has screened the chemically stable high-performance MOF iodine adsorbents and provided comprehensive insights into the key factors affecting I2/CH3I uptake and separation in humid environments.

Recent Advances in Flexible Pressure Sensors Based on MXene Materials.

In the past decade, with the rapid development of wearable electronics, medical health monitoring, the Internet of Things, and flexible intelligent robots, flexible pressure sensors have received unprecedented attention. As a very important kind of electronic component for information transmission and collection, flexible pressure sensors have gained a wide application prospect in the fields of aerospace, biomedical and health monitoring, electronic skin, and human-machine interface. In recent years, MXene has attracted extensive attention because of its unique 2D layered structure, high conductivity, rich surface terminal groups, and hydrophilicity, which has brought a new breakthrough for flexible sensing. Thus, it has become a revolutionary pressure-sensitive material with great potential. In this work, the recent advances of MXene-based flexible pressure sensors are reviewed from the aspects of sensing type, sensing mechanism, material selection, structural design, preparation strategy, and sensing application. The methods and strategies to improve the performance of MXene-based flexible pressure sensors are analyzed in details. Finally, the opportunities and challenges faced by MXene-based flexible pressure sensors are discussed. This review will bring the research and development of MXene-based flexible sensors to a new high level, promoting the wider research exploitation and practical application of MXene materials in flexible pressure sensors.

Steric hindrance modulation of hexaazatribenzanthraquinone isomers for high-capacity and wide-temperature-range aqueous proton battery.

Organic materials with rich active sites are good candidates of high-capacity anodes in aqueous batteries, but commonly low utilization of active sites limits their capacity. Herein, two isomers, symmetric and asymmetric hexaazatribenzanthraquinone (s-HATBAQ and a-HATBAQ), with rich active sites have been synthesized in a controllable manner. It has been revealed for the first time that a sulfuric acid catalyst can facilitate the stereoselective formation of s-HATBAQ. Attributed to the reduced steric hindrance in favor of proton insertion as well as the amorphous structure conducive to electrochemical dynamics, s-HATBAQ exhibits 1.5 times larger specific capacity than a-HATBAQ. Consequently, the electrode of s-HATBAQ with 50% reduced graphene oxide (s-HATBAQ-50%rGO) delivers a record high specific capacity of 405 mAh g-1 in H2SO4 electrolyte. Moreover, the assembled MnO2//s-HATBAQ-50%rGO aqueous proton full batteries show an exceptional cycling stability at 25°C and can maintain ∼92% capacity after 1000 cycles at 0.5 A g-1 at -80°C. This work demonstrates the controllable synthesis of isomers, showcases a wide-temperature-range prototype proton battery and highlights the significance of precise molecular structure modulation in organic energy storage.

Recent progress in emergent two-dimensional silicene.

Although graphene is by far the most famous example of two-dimensional (2D) materials, which exhibits a wealth of exotic and intriguing properties, it suffers from a severe drawback. In this regard, the exploration of silicene, the silicon analog of the graphene material, has attracted substantial interest in the past decade. This review therefore provides a comprehensive survey of recent theoretical and experimental works on this 2D material. We first overview the distinctive structures and properties of silicene, including mechanical, electronic, and spintronic properties. We then discuss the growth and experimental characterization of silicene on Ag(111) and other different substrates, providing insights into the different phases or atomic arrangements of silicene observed on the metallic surfaces as well as on its electronic structures. Then, the recent state-of-the-art applications of silicene are summarized in section 4 with the aim to break the scientific and engineering barriers for application in nanoelectronics, sensors, energy storage devices, electrode materials, and quantum technology. Finally, the concluding remarks and the future prospects of silicene are also provided.

Accelerating drug repurposing for COVID-19 treatment by modeling mechanisms of action using cell image features and machine learning.

The novel coronavirus disease, COVID-19, has rapidly spread worldwide. Developing methods to identify the therapeutic activity of drugs based on phenotypic data can improve the efficiency of drug development. Here, a state-of-the-art machine-learning method was used to identify drug mechanism of actions (MoAs) based on the cell image features of 1105 drugs in the  LINCS database. As the multi-dimensional features of cell images are affected by non-experimental factors, the characteristics of similar drugs vary considerably, and it is difficult to effectively identify the MoA of drugs as there is substantial noise. By applying the supervised information theoretic metric-learning (ITML) algorithm, a linear transformation made drugs with the same MoA aggregate. By clustering drugs to communities and performing enrichment analysis, we found that transferred image features were more conducive to the recognition of drug MoAs. Image features analysis showed that different features play important roles in identifying different drug functions. Drugs that significantly affect cell survival or proliferation, such as cyclin-dependent kinase inhibitors, were more likely to be enriched in communities, whereas other drugs might be decentralized. Chloroquine and clomiphene, which block the entry of virus, were clustered into the same community, indicating that similar MoA could be reflected by the cell image. Overall, the findings of the present study laid the foundation for the discovery of MoAs of new drugs, based on image data. In addition, it provided a new method of drug repurposing for COVID-19. Supplementary Information: The online version contains supplementary material available at 10.1007/s11571-021-09727-5.

Design of a water-soluble hybrid nanocomposite of CdTe quantum dots and an iridium complex for photoinduced charge transfer.

We report the use of an organo-iridium dye conjugated with a water-soluble copolyethylenimine polymer, allowing the hybrid material to be used in combination with thioacid-coated CdTe quantum dots in an aqueous medium. When they are combined, hot carrier cooling observed in the pure quantum-dot case is heavily suppressed indicating fast (ps) electron transfer on a timescale that competes with non-radiative (Auger) relaxation.

Flexible transparent PES/silver nanowires/PET sandwich-structured film for high-efficiency electromagnetic interference shielding.

We have developed a kind of high-yield synthesis strategy for silver nanowires by a two-step injection polyol method. Silver nanowires and polyethylene oxide (PEO) (M(w) = 900,000) were prepared in a homogeneous-coating ink. Wet composite films with different thicknesses were fabricated on a PET substrate by drawn-down rod-coating technology. Silver nanowires on PET substrates present a homogeneous distribution under the assistance of PEO. Then PEO was thermally removed in situ at a relatively low temperature attributed to its special thermal behavior under atmospheric conditions. As-prepared metallic nanowire films on PET substrates show excellent stability and a good combination of conductivity and light transmission. A layer of transparent poly(ethersulfones) (PESs) was further coated on silver nanowire networks by the same coating method to prevent the shedding and corrosion of silver nanowires. Sandwich-structured flexible transparent films were obtained and displayed excellent electromagnetic interference (EMI) shielding effectiveness.

N-doped graphene for electrocatalytic O2 and CO2 reduction.

The electrocatalytic CO2 reduction reaction (CO2RR) and oxygen reduction reaction (ORR) are important approaches to realize energy conversion and sustainable development. However, sluggish reaction kinetics severely hinders the practical application of devices related to these reactions. N-doped graphene (NG) with unique properties exhibits great potential in catalyzing the CO2RR and ORR, which is attributed to the electron redistribution. In this review, we start from the fundamental properties of NG, especially emphasizing the changes caused by N doping. Then the synthetic methods are summarized by classifying them into top-down strategies and bottom-up strategies. Subsequently, the applications of NG in the ORR and CO2RR are discussed and the effects of electronic structure on the electrocatalytic activity are highlighted. Finally, we give our own perspective on the future research direction of NG in the applications of the ORR and CO2RR.

Facile synthesis and growth mechanism of Ni-catalyzed GaAs nanowires on non-crystalline substrates.

GaAs nanowires (NWs) have been extensively explored for next generation electronics, photonics and photovoltaics due to their direct bandgap and excellent carrier mobility. Typically, these NWs are grown epitaxially on crystalline substrates, which could limit potential applications requiring high growth yield to be printable or transferable on amorphous and flexible substrates. Here, utilizing Ni as a catalytic seed, we successfully demonstrate the synthesis of highly crystalline, stoichiometric and dense GaAs NWs on amorphous SiO(2) substrates. Notably, the NWs are found to grow via the vapor-solid-solid (VSS) mechanism with non-spherical NiGa catalytic tips and low defect densities while exhibiting a narrow distribution of diameter (21.0 ± 3.9 nm) uniformly along the entire length of the NW (>10 µm). The NWs are then configured into field-effect transistors showing impressive electrical characteristics with I(ON)/I(OFF) > 10(3), which further demonstrates the purity and crystal quality of NWs obtained with this simple synthesis technique, compared to the conventional MBE or MOCVD grown GaAs NWs.

Structural tuning for enhanced magnetic performance by Y substitution in FeB-based metallic glasses.

Despite the compositional analogue to Fe71B17(NbYZr)12 metallic glass, the Fe71B17Y12 metallic glass has a saturated magnetization of Ca 108 emu g-1, more than 5 times of that in Fe71B17(NbYZr)12 (20 emu g-1). The structural origin for such significant difference in magnetic performance was investigated by x-ray absorption fine structure spectra and ab initio molecular dynamics (AIMD) simulations including simulated pair-correlation function (PCF) and Voronoi tessellation. Based on the Heisenberg model of magnetism, the narrow distribution of Fe-Fe bonds with larger distances accounts for a large Fe moment of 2.0 µ B in Fe71B17Y12, while the broad distribution of Fe-Fe bonds leads to ferrimagnetic couplings which result in the small net Fe moment of 0.45 µ B in Fe71B17(NbYZr)12. This work emphasizes how the substitution of analogous 4d transition metals induces a significantly different magnetism, which sheds lights on the development of new magnetic metallic glasses with both a promising magnetic performance and larger glass forming ability.