The methylation of amines using methanol is a promising route to synthesize N‐methylamines, and the development of cheap and efficient catalytic system for this reaction is of great significance. ...Herein, we reported a cobalt (Co)‐based catalytic system, which was in situ formed from commercially available Co precursor and a tetradentate phosphine ligand P(CH2CH2PPh2)3 combined with K3PO4. This catalystic system was very effective for the selective production of dimethylated products from aliphatic amines and monomethylated ones from aromatic amines. The reaction mechanism was further investigated by control and isotope labelling experiments.
Watermarking is a solution for copyright protection and forensics tracking, but recapturing and de-synchronization attacks may be used to effectively remove audio watermarks. Although much effort has ...been made in recent years, the robustness of audio watermarking against recapturing and de-synchronization attacks is still a challenging issue. Specifically, we first construct the frequency-domain coefficients logarithmic mean (FDLM) feature of digital audio. By theoretical analysis, we conclude that the residual of the two groups' FDLM feature is robust against recapturing attack. We then propose a robust audio watermarking method based on this feature using the patchwork framework. Compared with the method having the best robustness performance against recapturing attack, the BER value of our method is decreased by 7%. Besides that, the proposed method outperforms the state-of-the-art patchwork-based watermarking methods notably, under recapturing and post-processed with signal processing operations and de-synchronization attacks.
•The characterizations of regenerated cellulose from ionic liquid by different methods were compared.•The interactions in the regeneration of cellulose from ionic liquid by compressed CO2 were ...confirmed.•Clear morphology observations of cellulose regenerated by different methods were conducted.
In this study, regenerated cellulose was prepared from ionic liquid 1-butyl-3-methylimidazolium acetate (BmimAc) solution using anti-solvent compressed CO2 of different pressures. And other anti-solvents like water, ethanol and acetonitrile were also employed to regenerate cellulose to provide comparisons. The two-dimensional nuclear magnetic resonance (2D NMR), namely heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond coherence (HMBC), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR–FTIR) indicated that carboxylate zwitterions Bmim+-COO− formed through the chemical reactions between CO2 and BmimAc. Besides, FTIR, wide-angle X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to provided structure characterization of native and regenerated cellulose using different anti-solvents. The results show that the crystallinity of cellulose decreases during the dissolution and regeneration process. And a crystal transformation of cellulose I to cellulose II was verified. The stability of the regenerated cellulose is lower than that of native cellulose. A higher compressed CO2 pressure results in a smoother surface, a thicker shape and a more homogeneous texture of regenerated cellulose.
With the increasing demand of lithium-ion batteries in recent decades, the growing waste from the electrode materials of lithium-ion batteries has become an urgent problem. Lithium cobalt oxide ...(LiCoO2), used as the cathode materials of lithium-ion batteries, exhibits high capacity and excellent stability but also a high price. To recycle the LiCoO2 cathode, it is desirable to develop solvents for the dissolution of LiCoO2. At present, the dissolution of LiCoO2 still requires strong acid or a high temperature. Here, benign polyethylene glycol-based deep eutectic solvents (DES) were designed and further used for the dissolution of LiCoO2 under mild conditions with high solubility. This work provides a new route for the green recovery of lithium-ion cathodes with high efficiency and low energy consumption.
Imposing chirality to supramolecular architectures is an important step forward toward understanding and utilization of chiral nanomaterials. This article reports the self-assembly of amphiphilic ...chiral alternating copolymers of poly(binaphthyl azobenzene-alt-hexaethylene glycol) (P(BNPAzo-alt-EG6)) into helical supramolecular rods. Unlike conventional chiral assembly of copolymers largely through intermolecular organization, the intrachain stacking of chiral units along the main chain into single molecular micelles with amplified axial chirality of binaphthyl is key to the formation of helical supramolecular rods, which takes advantage of the particular chiral unit and soft unit alternating topological structure of the backbones. Moreover, the supramolecular self-assembly is light reversible because the azobenzene rings in the backbone scarcely execute trans- to cis-isomerization upon UV irradiation, and therefore the supramolecular rods keep their sublevel chirality even though the helical appearance was destroyed. This work paves an effective route to construct and regulate chiral supramolecular architectures and reveals an insight into natural and artificial chiral self-assembly.
A metal-free and highly efficient catalytic system involving a task-specific ionic liquid, P4444p-2-O, and a pyrene-based conjugated polymer was developed for direct CO2 capture from air and its ...further photoreduction to CO under visible light irradiation, affording a CO production rate of 47.37 μmol g−1 h−1 with a selectivity of 98.3%.
Uniform N-doped carbon nanotubes were obtained for the first time via a morphology-preserving thermal transformation of organic polymer nanotubes without any additional templates. These carbon ...nanotubes acted as a superior metal-free carbon catalyst for C-H arylation of benzene, reductive hydrogen atom transfer and oxidation reactions.
Global warming would deteriorate rice (Oryza sativa L.) quality, especially chalk characteristic. To better cope with the challenges from global warming, the effects of nitrogen (N) fertilizer at ...heading stage on rice quality under elevated temperature during grain‐filling stage were investigated. Four different growth regimes, including no warming without N fertilizer at heading stage (CK), elevated temperature without N fertilizer at heading stage (ET), elevated temperature with N fertilizer at heading stage (ET+N), no warming with N fertilizer at heading stage (CK+N), were conducted. Elevated temperature during grain filling was achieved by a free‐air temperature enhancement facility with the increase of 4°C in ET and 3.7°C in ET+N. Results showed that elevated temperature decreased rice appearance quality and cooking quality and increased rice nutritional quality and eating quality. Grain‐filling rate and amyloplast development for both superior and inferior spikelets were obviously accelerated during early grain‐filling stage by elevated temperature. The application of N fertilizer at heading stage could inhibit the deterioration of rice quality, particularly for chalk performance, and may be associated with the alleviation of grain‐filling rate and amyloplast development. The above evidence indicated that the application of N fertilizer at heading stage is efficient to mitigate rice quality deterioration under higher temperatures in the Yangtze River Valley.
There are a large amount of audio signals stored in third-party storage centers. To improve the privacy and security of audio signals, a digital audio encryption and forensics watermarking scheme is ...proposed. We defined the signal energy ratio feature of audio signals and designed the embedding method by quantifying the feature, aiming to improve the security of watermarking system. We firstly encrypted the original audio by using scrambling and multiplication, to get the encrypted data. Secondly, we divided the encrypted data into frames and compressed each frame by sampling to get the compressed data. After that, we embedded the compressed data and frame number into the encrypted data to get the watermarked signal being uploaded to third-party storage centers. Authorized users download encrypted data and verify the authenticity of the data. For the intact data, they decrypt it directly to get the audio signal. If the downloaded data has been attacked, they locate the attacked frame and extract the compressed data to reconstruct the attacked signal approximately. Furthermore, we decrypted the reconstructed signal to obtain the expression meaning of the original audio. The experimental results demonstrate the effectiveness of the proposed scheme.
A content authentication and tamper recovery scheme for digital speech signal is proposed. In this paper, a new compression method for speech signal based on discrete cosine transform is discussed, ...and the compressed signals obtained are used to tamper recovery. One block-based large capacity embedding method is explored, which is used for embedding the compressed signals. For the scheme proposed, watermark is generated by frame number and compressed signal. If watermarked speech is attacked, the attacked frames can be located by frame number, and reconstructed by using the compressed signal. Theoretical analysis and experimental results demonstrate that the scheme not only improves the security of watermark system, but also can locate the attacked frames precisely and reconstruct the attacked frames.
•Speech compression.•Block-based high-capacity embedding method.•Tamper recovery.
