Acta Mechanica Sinica - Bogies are responsible for a significant amount of aerodynamic resistance and noise, both of which negatively affect high-speed train performance and passenger comfort. In... 相似文献
Although driven by different research interests, single-site catalysts and single-atom catalysts are both believed to be model systems bridging homogeneous and heterogeneous catalysis. The two concepts are similar but different. In this review, we will first explain the difference between single-atom catalysis and single-site catalysis, in terms of their goals, synthetic methods and coordination structures of corresponding catalysts. Then, we will introduce the surface organometallic chemistry method, a method traditionally used for synthesizing single-site catalyst. We will explain why it might benefit the single-atom catalysis community. At last, the choice of support to accommodate the method for synthesizing single-atom catalysts will be discussed. 相似文献
Multifunctional fibers have attracted widespread attention due to applications in flexible smart wearable devices. However, simultaneously obtaining a strong and functional woven fiber is still a great challenge owing to the conflict between the properties mentioned above. Herein, mechanically strong and highly conductive cellulose/carbon nanotube (CNT) composite fibers were spun using an aqueous alkaline/urea solution. The microstructure as well as physical properties of the resulting fibers were characterized via scanning electron microscopy, infrared spectroscopy, mechanical and electrical measurement. We demonstrated that carboxylic CNTs can be well dispersed in alkali/urea aqueous systems which also dissolved cellulose well. The subsequent wet spinning process aligned the CNTs and cellulose molecules inside the regenerated composite fiber well, enhancing the interaction between these two components and endowing the composite fiber having a 20% CNT loading with an excellent mechanical strength of 185 MPa. Benefiting from the formation of conductive paths, the composite fiber with the diameter of about 50 μm possessed an electrical conductivity value in the range of 64–1274 S/m for 5–20 wt% CNT loading. This excellent mechanical strength and high electrical conductivity enable the composite fiber to exhibit a great potential in joule heating; the heating temperature of cellulose/CNT-20 fiber reached more than 55 °C within 15 s at 9 V. In addition, the multifunctional filaments are further manufactured as a water sensor to measure humidity. This work provides a potential material that can be applied in the fields of wearable electronics and smart flexible fabrics.
So far, the components responsible for the neuroprotective effects of Calculus bovis are unclear. Cholesterol, one of the major components in Calculus bovis, is easily oxidized into oxysterols, which possess direct or indirect neuroprotective effects proved by our and others’ previous studies. Therefore, a liquid chromatography with mass spectrometry method coupled with ultrasonic extraction and solid‐phase extraction was developed for the determination of neuroprotective oxysterols in Calculus bovis, human gallstones, and traditional Chinese medicine preparations. Chromatographic separation was achieved on a C18 column with isocratic elution at a flow rate of 1 mL/min. The established method showed good linearity (R2 > 0.998), sensitivity with low limits of detection (0.06–0.39 μg/g), acceptable precisions (relative standard deviations ≤ 7.4%), stability (relative standard deviations ≤ 5.9%), and satisfactory accuracy (92.4–102.9%) for all analytes identified by different retention times, which could be applied for the determination of oxysterols. Five kinds of oxysterols proved to function as neuroprotectants were detected at different concentrations. Among them, 7β‐hydroxycholesterol and cholestane‐3β,5α,6β‐triol were rather abundant in the samples. It could be concluded that the potential neuroprotective components in Calculus bovis may be these oxysterols. 相似文献
Prussian blue and its analogues (PBAs) have been recognized as one of the most promising cathode materials for room‐temperature sodium‐ion batteries (SIBs). Herein, we report high crystalline and Na‐rich Prussian white Na2CoFe(CN)6 nanocubes synthesized by an optimized and facile co‐precipitation method. The influence of crystallinity and sodium content on the electrochemical properties was systematically investigated. The optimized Na2CoFe(CN)6 nanocubes exhibited an initial capacity of 151 mA h g?1, which is close to its theoretical capacity (170 mA h g?1). Meanwhile, the Na2CoFe(CN)6 cathode demonstrated an outstanding long‐term cycle performance, retaining 78 % of its initial capacity after 500 cycles. Furthermore, the Na2CoFe(CN)6 Prussian white nanocubes also achieved a superior rate capability (115 mA h g?1 at 400 mA g?1, 92 mA h g?1 at 800 mA g?1). The enhanced performances could be attributed to the robust crystal structure and rapid transport of Na ions through large channels in the open‐framework. Most noteworthy, the as‐prepared Na2CoFe(CN)6 nanocubes are not only low‐cost in raw materials but also contain a rich sodium content (1.87 Na ions per lattice unit cell), which will be favorable for full cell fabrication and large‐scale electric storage applications. 相似文献
ABSTRACTIn studies on instabilities of flowfield in rotating detonation, one of the most common concerns is the instability at the slip line originating from the conjunction of the detonation wave and oblique shock. Using Euler equations associated with the 7-species-and-8-reaction finite-rate chemical reaction model of hydrogen/air mixtures, further studies are performed to simulate the 2-D rotating detonation, and the flow mechanism of instability at the slip line is investigated in depth. The results show that the distinct wake profile exists at the slip line, which is different from the typical mixing layer. Analysis indicates that the generation of wake is caused by the transition shock between the detonation wave and oblique shock. Because of the wake profile, the vorticity distribution therein appears in a double-layer layout, and different evolutions exist in different vorticity layers. Based on the velocity profile across the slip line, the analysis by the linear stability theory is made, and two main unstable modes which have different shape profiles and phase velocities are found. Discrete Fourier transformation is utilised to analyse the numerical results, and similar shape profiles are obtained. A general coincidence in velocity of vortex movement is also attained between the theoretical predictions and simulations. Investigations show that the wake instability is responsible for the unstable mechanism, and corresponding unstable structures differ from the canonical ones in typical mixing layers. 相似文献
This paper describes a simple chiral primary amine-catalyzed highly efficient and practical protocol for the synthesis of both Wieland-Miescher ketone and Hajos-Parrish ketone as well as their analogues. The reaction can be conducted in gram scale with 1% mol catalyst loading producing high enantioselectivity (up to 96% ee) and excellent yields (up to 98%). This procedure represents one of the most efficient methods for the synthesis of these versatile chiral building blocks. 相似文献
A MgII‐mediated catalytic asymmetric dearomatization (CADA) reaction of β‐naphthols has been developed. The reaction proceeds under ambient temperature and give a series of chiral trisubstituted olefins with good chemoselectivities, Z/E ratios, and excellent enantioselectivities. A fluorinated β‐naphthol was designed to generate chiral organofluorine skeletons through the current CADA reaction. Moreover, an interesting tandem cyclization reaction was observed in the following transformation process through an undiscovered intramolecular hydride transfer pathway. 相似文献
A highly enantioselective ring‐opening alkylation reaction between 3‐aryl‐oxindole and N‐(2‐picolinoyl) aziridine has been realized for the first time. The reaction is efficiently mediated by a simple in‐situ‐generated magnesium catalyst and 3,3′‐fluorinated‐BINOL (BINOL=1,1′‐binaphthalene‐2,2′‐diol) has been identified as a powerful chiral ligand. Notably, the fluorine atom on the chiral ligand plays a key role in providing the desired chiral 3‐alkyl‐3‐aryl oxindoles with excellent enantioselectivities. 相似文献