A significant number of isolable silylenes are currently known. They have quickly developed from laboratory curiosities to useful ligands in metal‐mediated homogeneous catalysis. This includes their ...utilization in various catalytic transformations, such as C−C cross‐coupling, cyclotrimerization, hydroformylation, borylation, deuteration, hydrosilylation, amination, hydrogenation, and transfer semi‐hydrogenation reactions. Recent studies suggest that the silylene ligands surpass the steering properties of their phosphine and N‐heterocyclic carbene (NHC) analogues and provide excellent chemo‐, regio‐, and stereoselectivites. Mechanistic studies suggest that their promoted performance of metal‐mediated catalytic transformations results from a strong σ‐donor character along with cooperative effects of their SiII centers. This Minireview covers the most recent advances in the field.
No longer laboratory curiosities: Stable silylenes are a versatile family of powerful steering ligands that increase catalytic activity and selectivity. This Minireview covers the recent progress of silylene ligands in homogeneous catalysis.
This study was aimed to evaluate the effects of post-transportation vitamin E (VE) supplementation on health condition, blood biochemical parameters, blood antioxidant indices and blood metabolomics ...in yak. Five yaks were used in this study. After 2100 km of highway transportation from Riwoqe county to Rongchang County, Chongqing, blood was collected immediately after arrival and these samples served as the baseline (control, CON_VE). A VE injection (40 mg/kg) was then performed and blood samples were collected 10 days later. Injection of VE led to lower serum VE concentration. Relative to the CON_VE, VE injection led to greater concentrations of creatinine and lower concentrations of glutamate pyruvic transaminase, alkaline phosphatase, aspartate aminotransferase, total bilirubin, indirect bilirubin, direct bilirubin, UREA and glucose. Compared with CON_VE, VE injection led the lower serum level of malondialdehydeand greater serum level of glutathione s-transferase, glutathione peroxidase, glutathione reductase and glutathione peroxidase 4. Based on metabolomics analysis, 119 differentially altered serum metabolites (P<0.05 and VIP>1.0) were identified with VE injection relative to CON_VE. VE injection resulted in changes of lysophosphatidylethanolamine, lysophosphatidylcholine, phosphocholine, choline, malate, citrate, α-Oxo-glutarate, phenylalanine, 3-Phenylpropanoic acid and 3-(3-Hydroxyphenyl) propanoic acid. These metabolites are associated with lipid metabolism, tricarboxylic acid cycle and oxidative stress. Overall, our study indicates that VE injection can alleviate transportation stress in yak partly through protecting liver and kidney, and improving antioxidant defense systems.
In general, anatase TiO
2
exhibits higher photocatalytic activities than rutile TiO
2
. However, the reasons for the differences in photocatalytic activity between anatase and rutile are still being ...debated. In this work, the band structure, density of states, and effective mass of photogenerated charge carriers for anatase, rutile and brookite TiO
2
are investigated by the first-principle density functional theory calculation. The results indicate that anatase appears to be an indirect band gap semiconductor, while rutile and brookite belong to the direct band gap semiconductor category. Indirect band gap anatase exhibits a longer lifetime of photoexcited electrons and holes than direct band gap rutile and brookite because the direct transitions of photogenerated electrons from the conduction band (CB) to valence band (VB) of anatase TiO
2
is impossible. Furthermore, anatase has the lightest average effective mass of photogenerated electrons and holes as compared to rutile and brookite. The lightest effective mass suggests the fastest migration of photogenerated electrons and holes from the interior to surface of anatase TiO
2
particle, thus resulting in the lowest recombination rate of photogenerated charge carriers within anatase TiO
2
. Therefore, it is not surprising that anatase usually shows a higher photocatalytic activity than rutile and brookite. This investigation will provide some new insight into understanding the difference of photocatalytic activity among anatase, rutile and brookite.
The photocatalytic activity difference of anatase, rutile and brookite TiO
2
is first explained by their band structure and effective mass.
The synthesis and structure of the first 1,2‐bis(NHSi)‐substituted ortho‐carborane (LSi:)C2B10H10 (termed SiCCSi) is reported (NHSi=N‐heterocyclic silylene; L=PhC(NtBu)2). Its suitability to serve as ...a reliable bis(silylene) chelating ligand for transition metals is demonstrated by the formation of SiCCSiNiBr2 and SiCCSiNi(CO)2 complexes. The CO stretching vibration modes of the latter indicate that the SiII atoms in the SiCCSi ligand are even stronger σ donors than the PIII atoms in phosphines and CII atoms in N‐heterocyclic carbene (NHC) ligands. Moreover, the strong donor character of the SiCCSi ligand enables SiCCSiNiBr2 to act as an outstanding precatalyst (0.5 mol % loading) in the catalytic aminations of arenes, surpassing the activity of previously known molecular Ni‐based precatalysts (1–10 mol %).
The right bite: A chelating bis‐N‐heterocyclic silylene ligand bridged by an o‐carborane (SiCCSi) and its corresponding Ni complexes (see example) were synthesized, fully characterized, and successfully applied in Ni‐catalyzed Buchwald–Hartwig coupling reactions. SiCCSiNiBr2 is the most active precatalyst for this transformation that has been reported to date.
•A semi-supervised learning method named CAE-SGAN is proposed to classify surface defects of steels.•CAE-SGAN improves the performance of SGAN with limited training samples.•When training the ...discriminator of SGAN, the decoder network of CAE is not truncated.•CAE-SGAN is tested with sample images collected from three different steel production lines.•CAE-SGAN provides a better way to apply deep learning methods to some industrial scenes.
Defect inspection is extremely crucial to ensure the quality of steel surface. It affects not only the subsequent production, but also the quality of the end-products. However, due to the rare occurrence and appearance variations of defects, surface defect identification of steels has always been a challenging task. Recently, deep learning methods have shown outstanding performance in image classification, especially when there are enough training samples. Since most sample images of steel surface are unlabeled, a new semi-supervised learning method is proposed to classify surface defects of steels. The new method is named CAE-SGAN, as it is based on Convolutional Autoencoder (CAE) and semi-supervised Generative Adversarial Networks (SGAN). CAE-SGAN first trains a stacked CAE through massive unlabeled data. Considering the appearance variations of defects, the passthrough layer is used to help CAE extract fine-grained features. After CAE is trained, the encoder network of CAE is reserved as the feature extractor and fed into a softmax layer to form a new classifier. SGAN is introduced for semi-supervised learning to further improve the generalization ability of the new method. The classifier is trained with images collected from real production lines and images randomly generated by SGAN. Extensive experiments are carried out with samples captured from different steel production lines, and the results indicate that CAE-SGAN had yielded best performances compared with traditional methods. Especially for hot rolled plates, the classification rate is improved by around 16%.
The synthesis and structures of the first SiII‐donor supported manganese(II) complexes L1MnCl2, L2MnCl2, and L32MnCl2 are reported, bearing a pincer‐type bis(NHSi)‐pyridine ligand L1, bidentate ...bis(NHSi)‐ferrocene ligand L2, and two monodentate NHSi ligands L3 (NHSi = N‐heterocyclic silylene), respectively. They act as unprecedented very active and stereoselective Mn‐based precatalysts (1 mol % loading) in transfer semi‐hydrogenations of alkynes to give the corresponding E‐olefins using ammonia–borane as a convenient hydrogen source under mild reaction conditions. Complex L1MnCl2 shows the best catalytic performance with quantitative conversion rates and excellent E‐stereoselectivities (up to 98 %) for different alkyne substrates. Different types of functional groups can be tolerated, except CN, NH2, NO2, and OH groups at the phenyl group of 1‐phenyl substituted alkynes.
Give me the E: The first N‐heterocyclic silylene (NHSi)–manganese(II) complexes have been synthesized and fully characterized. Among them, the L1MnCl2 complex, which bear bis‐NHSi pyridine pincer ligand L1, acts as a superior precatalysts in homogeneous transfer semi‐hydrogenation of alkynes, using ammonia‐borane as a convenient hydrogen source at mild reaction conditions (Mn=L1MnCl2).
Distributed acoustic sensors provide a powerful instrumentation for ultrasound testing to identify the internal crack and deformation with the location for assessing structural conditions and ...predicting the potential structural failure. This paper provides a tutorial review of the milestones leading to the development of the distributed acoustic sensor based on Rayleigh back scattering. It offers discussion on basic principles, optical configurations and system design requirement, various detection schemes, performance limitations and applications for the maximum measurable frequency, minimum detectable strain and highest spatial resolution. A final comment on the prospects of the further developments is presented.
Persulfates activation by carbon nanotubes (CNT) has been evidenced as nonradical systems for oxidation of organic pollutants. Peroxymonosulfate (PMS) and peroxydisulfate (PDS) possess discrepant ...atomic structures and redox potentials, while the nature of their distinct behaviors in carbocatalytic activation has not been investigated. Herein, we illustrated that the roles of nitrogen species in CNT-based persulfate systems are intrinsically different. In PMS activation mediated by nitrogen-doped CNT (N-CNT), surface chemical modification (N-doping) can profoundly promote the adsorption quantity of PMS, consequently elevate potential of derived nonradical N-CNT–PMS* complexes, and boost organic oxidation efficiency via an electron-transfer regime. In contrast, PDS adsorption was not enhanced upon incorporating N into CNT due to the limited equilibrium adsorption quantity of PDS, leading to a relatively lower oxidative potential of PDS/N-CNT system and a mediocre degradation rate. However, with equivalent persulfate adsorption on N-CNT at a low quantity, PDS/N-CNT exhibited a stronger oxidizing capacity than PMS/N-CNT because of the intrinsic higher redox potential of PDS than PMS. The oxidation rates of the two systems were in great linearity with the potentials of carbon–persulfate* complexes, suggesting N-CNT activation of PMS and PDS shared the similar electron-transfer oxidation mechanism. Therefore, this study provides new insights into the intrinsic roles of heteroatom doping in nanocarbons for persulfates activation and unveils the principles for a rational design of reaction-oriented carbocatalysts for persulfate-based advanced oxidation processes.
This paper proposes a nonlinear teaching approach, based on learning theories in cognitive psychology, with a special focus on large-cohort economics modules. The fundamental rationale is to match ...the features of teaching with the nature of learning. This approach was implemented in an undergraduate economics module, which received qualitative feedback and quantitative evaluation. Formal econometric models with both binary and continuous treatment effects were developed and estimated to quantify the effects of the proposed approach. Evidence shows that the nonlinear teaching approach significantly improves the effectiveness and efficiency of the learning-teaching process but does not promote student attendance.
Control of TiO2 crystal facets has attracted enormous interest due to the fascinating shape-dependent photocatalytic activity of this material. In this work, the effect of the ratio of {001} and ...{101} facets on the photocatalytic CO2-reduction performance of anatase TiO2 is reported. A new “surface heterojunction” concept is proposed on the basis of the density functional theory (DFT) calculations to explain the difference in the photocatalytic activity of TiO2 with coexposed {001} and {101} facets.
