MnFe2O4 nanodots (∼3.3 nm) homogeneously dispersed in porous nitrogen-doped carbon nanofibers (denoted as MFO@C) were prepared by a feasible electrospinning technique. Meanwhile, MFO@C with the ...character of flexible free-standing membrane was directly used as binder- and current collector-free anode for sodium-ion batteries, exhibiting high electrochemical performance with high-rate capability (305 mA h g–1 at 10000 mA g–1 in comparison of 504 mA h g–1 at 100 mA g–1) and ultralong cycling life (ca. 90% capacity retention after 4200 cycles). The Na-storage mechanism was systematically studied, revealing that MnFe2O4 is converted into metallic Mn and Fe after the first discharge (MnFe2O4 + 8Na+ + 8e– → Mn + 2Fe + 4Na2O) and then to MnO and Fe2O3 during the following charge (Mn + 2Fe + 4Na2O → MnO + Fe2O3 + 8Na+ + 8e–). The subsequent cycles occur through reversible redox reactions of MnO + Fe2O3 + 8Na+ + 8e– ↔ Mn + 2Fe + 4Na2O, of which the reduction/oxidation of MnO/Mn takes place at a lower potential than that of Fe2O3/Fe. Furthermore, a soft package sodium-ion full battery with MFO@C anode and Na3V2(PO4)2F3/C cathode was assembled, delivering a stable capacity of ∼400 mA h g–1 for MFO@C (with 100 cycles at 500 mA g–1) and a promising energy density of 77.8 Wh kg–1 for the whole battery. This is owing to the distinctive structure of very-fine MnFe2O4 nanodots embedded in porous N-doped carbon nanofibers, which effectively improves the utilization rate of active materials, facilitates the transportation of electrons and Na+ ions, and prevents the particle pulverization/agglomeration upon prolonged cycling.
Herein, we report a new method for the synthesis of acyethanethioates via thiocarbonylation of gem-difluoroalkenes with thiols. This reaction provides a new pathway to prepare thioesters under mild ...conditions without the use of any additives. Mechanistic studies revealed that in situ generated HF facilitated the C–F bond cleavage in an autocatalytic manner.
A facile and efficient cyclization of homotryptamines and their derivatives has been established for the construction of 4a‐chlorotetrahydropyrido2,3‐bindoles and 3,3‐spirocyclic 3H‐indoles using ...hypervalent iodine (1‐chloro‐1,2‐benziodoxol‐3‐one) under mild conditions. The broad substrate scope and successful gram‐scale experiment grant this metal‐free transformation great potential for further application.
A facile and efficient cyclization of homotryptamines and their derivatives has been established for the construction of 4a‐chlorotetrahydropyrido2,3‐bindoles and 3,3‐spirocyclic 3H‐indoles using hypervalent iodine (1‐chloro‐1,2‐benziodoxol‐3‐one) under mild conditions. The broad substrate scope and successful gram‐scale experiment grant this metal‐free transformation great potential for further application.
A practical conversion of indoles into the corresponding 2‐oxindoles is achieved efficiently using a hypervalent iodine reagent. This oxidation is amenable to different substituted indoles, and ...allows the synthesis of a wide range of synthetically valuable substituted 2‐oxindoles in up to 90 % yield. Furthermore, Ropinirole, a drug used to alleviate the symptoms of Parkinson's disease, was synthesized in three steps in an overall yield of 44 % using this method.
The practical and efficient conversion of indoles into the corresponding 2‐oxindoles is achieved under neutral conditions using a hypervalent iodine reagent. This oxidation is amenable to different substituted indoles.
The aspect-level sentiment analysis is widely used in public opinion analysis. However, the problem of context information loss and distortion with the increase of the model depth is rarely ...considered in previous research. Few studies have attempted to combine the feature extracted from different embedding models. Based on the correction strategy, the ensemble correction (EC) model proposed in this study can correct context information loss and distortion. Based on the ensemble learning strategy and the weight sharing strategy, EC can extract features from different word embedding models and can reduce computational complexity. Experiments on the resturant14, laptop14, resturant16 and twitter datasets show that the accuracies of the EC model are 0.8848, 0.8213, 0.9301 and 0.7731, respectively. The accuracy of the EC model is higher than state-of-the-art models. Ablation studies and case studies are used to verify the model structure. The optimal number of graph convolutional network (GCN) layers is also verified.
The outbreak of terrorist events often causes tremendous damage to the country and society and arouses high attention from the public and an overwhelming response on the microblogging platform. ...Predicting the influence of microblogging in the context of terrorist events and revealing its evolutionary mode can help counterterrorism departments foresee potential risks, take effective countermeasures in time, and provide a reference for reducing public panic caused by terrorist events. In this study, Word2Vec is combined with the K-means clustering technique to discover the topics of microblogging, and an emotion analysis of microblogging is performed. The user features, time features, and content features of microblogging in the context of terrorist events are extracted. The prediction model of microblogging influence based on the logistic regression model was constructed and evaluated. The experimental results showed that the prediction accuracy of the model was 85.8%, which had superior performance over other six classification models. In addition, the high-influence characteristics of microblogging in the context of terrorist events were analyzed and summarized. Finally, a quantitative method of the influence of a microblogging topic based on the h-index was proposed. The evolution pattern of the influence of a microblogging topic was analyzed. The results can help predict microblog entries of high influence, understand the intensity and variation of public concern over terrorist events, and assist counterterrorism departments in taking scientific decisions.
The number of scientific papers is increasing in the rapid growth. How to make paper acquisition efficient and provide effective citation recommendation is essential for researchers. Although the ...application of scientific citation recommendation has shown great improvements, the in-depth mining and fusion of various types of information has been ignored. In this paper, we propose a scientific citation recommendation model integrating network and text representation (SCR-NTR), which comprises data acquisition, feature representation, feature fusion and link prediction. We compare the network representation and text representation, respectively, and select the models performing best in the pre-experiment as the sub-models of SCR-NTR. The method of vector concatenate fusion is employed to fuse two kinds of information, and the logistic regression classifier is selected to carry out the link prediction. The extensive experiments reveal that our model can effectively improve the performance on citation recommendation. In addition, the effect of different fusion methods and different classifiers are investigated, and qualitative analysis is conducted to further verify the effectiveness of SCR-NTR. The experimental results show that leveraging both network and text representation can enhance the recommendation performance, and the heterogenous network representation learning can capture richer semantic information of the given network than the homogeneous one.
An efficient and novel method for regioselective hydroxydifluoroacetamidation of alkenes with bromodifluoroacetamides has been achieved via a tandem radical pathway mediated by photoredox catalysis ...under metal-free conditions. This transformation proceeded smoothly in the presence of Rhodamine 6G, affording a series of α,α-difluoro-γ-hydroxyacetamides in moderate to excellent yields. The significant advantages of this protocol are the low-cost photocatalyst, readily available starting materials, synthetic convenience, and wide functional group compatibility.
A simple and highly efficient protocol was developed for the transamidation of N,N‐disubstituted amides with primary amines in the presence of tBuOK, affording desired products in good to excellent ...yields. This reaction proceeded under nitrogen atmosphere and featured extensive substrate tolerance. Experimental investigation suggested that a coordination radical process enhanced this transformation.
A simple and highly efficient protocol was developed for the transamidation of N,N‐disubstituted amides with primary amines in the presence of potassium tert‐butoxide, affording desired products in good to excellent yields. Experimental investigation revealed that an unprecedented coordination radical process enhanced this transformation.
