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Journal of Visualization - The unsteady flow structures and pressure fluctuations of the cylinder-induced shock wave/boundary layer interactions (SBLIs) were investigated at Mach 3.4 and 3.8. The... 相似文献
83.
Junwu Xiao Guiliang Xu Shi‐Gang Sun Shihe Yang 《Particle & Particle Systems Characterization》2013,30(10):893-904
The intrinsically low electric conductivity and self‐aggregation of MFe2O4 during charge/discharge affect their lithium storage performance and electrocatalytic activity. To mitigate these problems, it is shown that N‐doped graphene sheets (NGS), as a highly conductive platform, finely disperse the MFe2O4 nanoparticles and rapidly shuttle electrons to and from the MFe2O4 nanoparticles. Moreover, by forming a metal@oxide core–shell nanostructure, fast electron transfer from the exterior oxide layer to NGS is achieved. Introducing NGS into MFe2O4 allows the composites to exhibit the comparable specific capacity (based on the total mass) to MFe2O4, although over 10 wt% of NGS contributes a low specific capacity of around 320–400 mAh g?1. More importantly, introducing NGS significantly increases the cycling stability performance: 97.5% (CoFe2O4/NGS) and ≈100% (NiFe2O4/NGS) of the specific capacities have been retained after 80 cycles, far higher than the capacity retentions of CoFe2O4 (35.3%) and NiFe2O4 (43.7%) tested under otherwise identical conditions. Also demonstrated are the excellent rate capabilities of the composites. For catalyzing the oxygen reduction reaction, the activity is significantly improved when the MFe2O4 nanoparticles are transformed into metal@oxide core–shell nanostructure, mainly because the core–shell nanostructure exhibits lower charge transfer resistance. 相似文献
84.
Li Jiang Prof. Penggang Yin Tingting You Hua Wang Xiufeng Lang Prof. Lin Guo Prof. Shihe Yang 《Chemphyschem》2012,13(17):3932-3936
Highly reproducible surface‐enhanced Raman scattering (SERS) spectra are obtained on the surface of SnO2 octahedral nanoparticles. The spot‐to‐spot SERS signals show a relative standard deviation (RSD) consistently below 20 % in the intensity of the main Raman peaks of 4‐mercaptobenzoic acid (4‐MBA) and 4‐nitrobenzenethiol (4‐NBT), indicating good spatial uniformity and reproducibility. The SERS signals are believed to mainly originate from a charge‐transfer (CT) mechanism. Time‐dependent density functional theory (TD‐DFT) is used to simulate the SERS spectrum and interpret the chemical enhancement mechanism in the experiment. The research extends the application of SERS and also establishes a new uniform SERS substrate. 相似文献
85.
A morphology-conserved transformation yields Sn@C nanowires (UTP@CW, ~21 wt% carbon and ~77 wt% tin) with a high encapsulation density of ultrafine tin nanoparticles in porous carbon nanowires, which exhibit excellent reversible capacities and cycling performance for lithium ion batteries, especially at high current rates. 相似文献
86.
In this paper, a free boundary problem modeling tumor growth with two discrete delays is studied. The delays respectively represents the time taken for cells to undergo mitosis and the time taken for the cell to modify the rate of cell loss due to apoptosis. We show the influence of time delays on the Hopf bifurcation when one of delays as a bifurcation parameter. 相似文献
87.
The use of rod-like and vesicle-like mesoporous SiO2 particles for fabricating high performance glucose biosensors is reported. The distinctively high surface areas of mesoporous structures of SiO2 rendered the adsorption of glucose oxidase (GOx) feasible. Both morphologies of SiO2 enhanced the sensitivities of glucose biosensors, but by a factor of 36 for vesicle-like SiO2 and 18 for rod-like SiO2, respectively. The greater enhancement of vesicle-like SiO2 can be accounted for by its higher specific surface area (509 m2 g−1) and larger total pore volume (1.49 cm3 g−1). Interestingly, the current responses of GOx immobilized in interior channels of the mesoporous SiO2 were enhanced much more than those of simple mixtures of GOx and the mesoporous SiO2. This suggests that the enhancement of current responses arise not only from the high surface area of SiO2 for high enzyme loading, but also from the improved enzyme activity upon its adsorption on mesoporous SiO2. Also compared were the performances of glucose biosensors with GOx immobilized on mesoporous SiO2 by physical adsorption and by covalent binding to 3-aminopropyltrimethoxysilane (APTMS) modified SiO2 using glutaraldehyde as the cross-linker. The covalent binding approach resulted in higher enzyme loading but lower current sensitivity than with the physical adsorption. 相似文献
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Photoreactions in the gas-phase complexes Mg(*+)(1,4-dioxane) (1) and Mg(*+)(1,3-dioxane) (1M) have been examined in the wavelength region of 230-440 nm. Photoproduct assignments are facilitated with the help of deuterium substitution experiments. The main energy relaxation channel for both photoexcited complexes is the evaporation of Mg(*+). Also observed from 1 are rich photoproducts with m/z 28, 41, 54-58, 67, 69, and 88; the most abundant one at m/z 54 is designated to Mg(*+)(O=CH(2)). In marked contrast, the photolysis of 1M yields only Mg(*+)(O=CH(2)) other than Mg(*+). Density functional calculations are performed to obtain optimized geometries and potential energy surfaces of 1 and 1M. Although Mg(*+)(chair-1,4-C(4)H(8)O(2)) (1a) and Mg(*+)(boat-1,4-C(4)H(8)O(2)) (1b) are comparable in energy, the much better agreement of the experimental action spectrum of Mg(*+)(1,4-C(4)H(8)O(2)) with the calculated absorption spectrum of 1a than with that of 1b indicates the predominance of 1a in the source due to the stability of the chair-1,4-dioxane. For photoreactions, the C-O bond is found to be much more prone to rupture than the C-C bond due to the coordination of O to Mg(+) in the parent complexes. Photoreaction mechanisms are discussed in terms of two key insertion complexes, which rationalize all of the observed photoproducts. 相似文献