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101.
采用固相反应法成功制备出一批Y123与Y211的摩尔比为1∶0.47的混合物,并在此混合物的基础上掺入CeO2,掺入的比例x分别为0.5wt%、1.0wt%、2.0wt%、3.0wt%、4.0wt%。采用了X-射线衍射仪对样品的晶格结构进行了分析,测量结果表明:x=1.0wt%时掺杂效果最好,同时也充分说明Y123的晶格结构与其超导电性之间存在着一种内在的必然关联。并通过对其测试临界转变温度以及转变宽度,测量结果也充分验证了上述结论。  相似文献   
102.
Density functional theory calculations have been performed to investigate the structural and electronic properties of bulk Co2C and the stability of low index Co2C surfaces. We found that the formation of Co2C is exothermic with the formation energy of ? 0.81 eV/Co2C with respect to Co under the presence of syngas (mixture of CO and H2). While formed Co2C can be decomposed further to metal Co and graphite carbon with modest energy gain of 0.37 eV/Co2C. This suggests that Co2C is only metastable in Fischer–Tropsch synthesis, which agrees well with experimental findings. The density of states (DOSs) reveals that the Co2C is paramagnetic and strong metallic-like. The difference of charge density analysis indicates that the bond of Co2C is of the mixtures of metallic, covalent, and ionic properties. A variety of low index Co2C surfaces with different terminations are studied. We find that the surface energy of low index stoichiometric Co2C highly relies on the surface area, the number of coordination of surface atoms and the surface dipole, with the decreased stability order of (101) > (011) > (010) > (110) > (100) > (001) = (111). Our results indicate that under Co-poor condition, the formation of non ? stoichiometric surface (011) and (111) without terminated cobalt is energetically more favorable, while under Co-rich condition the formation of non ? stoichiometric (111) surface with cobalt overlayer are preferential.  相似文献   
103.
It is well known that organic acids (OAs) could affect the flavour of fruit juices and beverages. However, the molecular mechanism of aroma release is still unclear. In this study, the effects of citric acid (CA), L-(-)-malic acid (MA) and L-lactic acid (LA) on the release of six selected esters and their sensory perception were investigated by means of HS-GC-MS analyses and odour detection threshold determination, respectively. Meanwhile, the density functional theory (DFT) calculation was employed to explore the interaction modes between esters and OAs. HS-GC-MS analyses showed that the concentration and the type of OAs regulated the release of esters. The results were basically consistent with the detection threshold change of those esters. The DFT calculation suggested that the main intermolecular interaction was hydrogen bonds, and several esters could form a ternary ring structure with OAs through hydrogen bonds. The interactions can induce the different release behaviours of esters in OAs water solution. The number of carboxyl functional groups in OAs and the spatial conformation of esters appeared to influence the magnitude of the interaction. The above results demonstrated the mechanism of OAs affecting the release of esters and indicated a possible flavour control way by using different OAs and OA concentrations.  相似文献   
104.
Main observation and conclusion We reported for the first time that ethyl bromodifluoroacetate directly reacts with azaindole without transition metal catalysis...  相似文献   
105.
Main observation and conclusion The enzyme AbyU catalyses a Diels-Alder (DA) reaction during abyssomicin C biosynthesis.In this study,AbyU is shown to convert t...  相似文献   
106.
After being injected into the porous media, the dispersion system of preformed particle gel (PPG) tends to enter high permeability regions and block water channeling passages, which forces the subsequent water to turn to the low permeability regions and thus increases sweep efficiency and enhances oil recovery. However, it is still unclear about the influence factors and the mechanisms how PPG increases water flow resistance, which limits the application of PPG in more oilfields. Therefore, the paper combines the lattice Boltzmann method (LBM), the discrete element method (DEM) and the improved immersed moving boundary (IMB) method to simulate the migration of deformable PPG in porous media. On the basis, the paper quantitatively analyzes the variation law of displacement pressure across the porous media and discusses the influence factors such as the PPG diameter, elasticity modulus and the number concentration. Results indicate that, because of the friction and retention of PPG in pore-throat, the displacement pressure across the porous media during PPG flooding is much higher than that during water flooding. In other words, the existence of PPG increases the flow resistance of injected water. Besides, the displacement pressure is always fluctuant resulting from the continuous process of PPG migration, retention, deformation and remigration. Influence factor analysis shows that the incremental value and fluctuation degree of flow resistance increase with the PPG diameter, elasticity modulus and the number concentration. The study not only provides useful reference for future PPG flooding, but also benefits the development of deformable particle flow theory.  相似文献   
107.
The phase composition and properties of microemulsion system of Titron N-101 / n-pentanol/ n-octane/ water (ammonia solution) were studied. CeO2 nanopaticles were prepared by the reaction of cerous nitrate.  相似文献   
108.
The adsorptive denitrogenation from fuels over three metal-organic frameworks(MIL-96(Al),MIL-53(Al)and MIL-101(Cr))was studied by batch adsorption experiments.Four nitrogen-containing compounds(NCCs)pyridine,pyrrole,quinoline and indole were used as model NCCs in fuels to study the adsorption mechanism.The physicochemical properties of the adsorbents were characterized by XRD,N2physical adsorption,FT-IR spectrum and Hammett indicator method.The metal-organic frameworks(MOFs),especially the MIL-101(Cr)containing Lewis acid sites as well as high specific surface area,can adsorb large quantities of NCCs from fuels.In addition,the adsorptive capacity over MIL-101(Cr)will be different for NCCs with different basicity.The stronger basicity of the NCC is,the more it can be absorbed over MIL-101(Cr).Furthermore,pore size and shape also affect the adsorption capacity for a given adsorbate,which can be proved by the adsorption over MIL-53(Al)and MIL-96(Al).The pseudo-second-order kinetic model and Langmuir equation can be used to describe kinetics and thermodynamics of the adsorption process,respectively.Finally,the regeneration of the used adsorbent has been conducted successfully by just washing it with ethanol.  相似文献   
109.
We analyze the role of an ac-driven Rashba spin-orbit coupling in monolayer graphene including a spin-dependent mass term. Using the Magnus expansion as a semi-analytical approximation scheme a full account of the quasienergie spectrum of spin states is given. We discuss the subtleties arising in correctly applying the Magnus expansion technique in order to determine the quasienergy spectrum. Comparison to the exact numerical solution gives appropriate boundaries to the validity of the Magnus expansion solution.  相似文献   
110.
A tunable optical rail is embedded into the cavity of a nonlinear-polarization-rotation(NPR) mode-locked fiber laser to generate a sampling pulse with different repetition frequencies and realize bit-rate-adaptive software synchronous optical sampling.Two ultrashort pulses(20.26677 and 20.22900 MHz) are derived,and a 100-MHz data signal is sampled twice with these pulses based on sum-frequency generation(SFG) in periodically poled lithium niobate(PPLN).The eye diagram is successfully recovered,and an estimated bit rate of 102.22 MHz is derived.This method is feasible for bit rates ranging from 200 MHz to 1 GHz,with <3% relative error.  相似文献   
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