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排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
992.
993.
Recently the electronic structure and magnetism of the “111” type LiFeAs superconductor has been investigated by first principles
calculations based on the density functional theory. It is concluded that the system has a metallic striped anti-ferromagnetic
ground state with a very small magnetic moment. Moreover, the effect of electronic correlation effect is also found to be
weak. This finding is consistent with recent experiments and calculations on similar compounds. A strong covalent interaction
has been suggested as a reason for the weak electron correlation. In this paper, the Fe–As and Fe–Fe interactions are examined
from the analysis of the electronic localization function (ELF). Surprisingly, no strong evidence supporting Fe–As and Fe–Fe
covalent bonding is found. A more delocalized electron distribution is observed in the Fe layers. Therefore, the Fe 3d electrons
are not as localized in the oxides and therefore the electron correlation effect is small. This is a plausible explanation
for the apparent success of the local density approximation (LSDA) describing the weak magnetism in LiFeAs. 相似文献
994.
Christiane Reis Fonseca José Luiz Paiva Eva Maria Rodriguez Fernando Juan Beltrán Antonio Carlos Silva Costa Teixeira 《臭氧:科学与工程》2017,39(4):255-263
The sugar industry is concerned with color formation due to the oxidation of phenolic compounds in the presence of carbohydrates. In this study, we investigated the ozonation of a mixture of five phenolic compounds in water and aqueous sucrose solution: p-coumaric (p-COU), caffeic (CAF), syringic (SYR), and chlorogenic (CHO) acids, as well as the flavonoid quercetin (QUE). The experiments were carried out in a 3-L glass reactor with magnetic stirring and a diffuser plate at the bottom to feed the ozone-oxygen gas mixture. Initial solution concentrations of 5 mg L?1 of each acid, 15 mg L?1 of quercetin, and 40 g L?1 of sucrose were used. The degradation of phenolic compounds followed apparent first-order kinetics, with rate constants and percent removals decreasing in the presence of sucrose. In water, average consumed ozone dosages of 10.4 and 18.7 mg L?1 were necessary for 50% and 90% removals, respectively, for CHO, CAF, and p-COU; for QUE they were slightly higher (13.9 and 20.5 mg L?1, respectively). At a consumed dosage of 20.8 mg O3 L?1, more than 99% removal was obtained for CHO, CAF, and p-COU, while 96.2% was achieved for SYR. In contrast, QUE revealed to be more recalcitrant during ozonation in the absence of sucrose, with only 70% removal at the highest consumed O3 dosage. The consumed ozone dosages for 50% and 90% removals were higher for CHO, CAF, and p-COU in aqueous sucrose solution, which may impact ozone consumption during real sugarcane juice treatment. Sucrose and t-butanol were the main influential parameters that significantly affected the total amount of phenolic compounds degraded. 相似文献
995.
Inhibition of copper corrosion in sodium chloride solution by the self-assembled monolayer of sodium diethyldithiocarbamate 总被引:2,自引:0,他引:2
Q.Q. Liao Z.W. Yue D. Yang Z.H. Wang Z.H. Li H.H. Ge Y.J. Li 《Corrosion Science》2011,53(5):1999-2005
Sodium diethyldithiocarbamate (DDTC) self-assembled monolayer (SAM) on copper surface has been investigated by SERS and EDS and the results show that DDTC SAM is chemisorbed on copper surface by its S atoms with tilted orientation. Corrosion inhibition ability of DDTC SAM was measured in 3% NaCl solution using electrochemical methods. The impedance results indicate that the maximum inhibition efficiency of DDTC SAM can reach 99%. Quantum chemical calculations show that DDTC has relatively small ΔE between HOMO and LUMO and large negative charge in its two sulfur atoms, which facilitates the formation of a DDTC SAM on copper surface. 相似文献
996.
Y.M. Chong W.J. Zhang Y. Yang Q. Ye I. Bello S.T. Lee 《Diamond and Related Materials》2009,18(11):1387-1392
Cubic boron nitride (cBN) thin films were deposited on diamond-coated tungsten carbide (WC) cutting inserts using electron cyclotron resonance (ECR) microwave plasma chemical vapor deposition (MPCVD). The effects of gas flow rate and substrate bias on the phase composition and structure of the BN films deposited on diamond surfaces were studied. It was revealed that both the cubic phase formation and the selective etching of hexagonal phase were controlled by modulating the hydrogen and boron trifluoride flow rate ratio. By the trial and error method the gas flow rate ratio and substrate bias voltage were optimized. Moreover the phase composition of the BN film was found to be affected by the thickness of diamond buffer layer and interrelated to the effective substrate bias. The hardness of the resulting cBN films reached the value of 70 GPa. In the synthesized coatings, the diamond beneath renders the best mechanical supporting capacity while the top cBN provides the superior chemical resistance and extreme hardness. The cBN/diamond bilayers deposited on WC inserts may serve as universal tool coatings for machining steels and other ferrous metals. 相似文献
997.
Estíbaliz Sánchez-González Pedro Miranda Fernando Guiberteau Antonia Pajares 《Journal of the European Ceramic Society》2009,29(12):2635-2641
The elasto-plastic properties and contact damage evolution of a commercial polycrystalline silicon nitride are evaluated as a function of temperature up to 1000 °C, using a recently developed method combining Hertzian indentation and FEM simulation. The results of the study are compared to existing data for other ceramic materials such as alumina and zirconia. Silicon nitride is found to exhibit an excellent combination of elasto-plastic properties in the pre-creep temperature range and good contact damage resistance. These qualities make this material ideal for high temperature applications in general, and in particular to be used in spherical indenters for the evaluation of mechanical properties of other materials at elevated temperature using the procedure applied in this work. 相似文献
998.
Single-phase nanostructured bulk Yb0.2Co4Sb12 skutterudites have been prepared by combining a melt spinning technique with spark plasma sintering. The effects of a pre-annealing
process on the microstructure and phase composition of ribbon samples and bulk materials are investigated. After the pre-annealing
process, average grain size increases from 200 nm to 300 nm for ribbon samples and from 250 nm to 350 nm for bulk materials,
and nearly single-phase skutterudites have formed. Because of the nanostructure, the thermal conductivity of bulk skutterudites
notably decreases 25% at 800 K. As␣a result, the ZT values are improved compared with starting material prepared by the traditional method. 相似文献
999.
Y. Liu F.J.H.G. Kessels W.D. van Driel J.A.S. van Driel F.L. Sun G.Q. Zhang 《Microelectronics Reliability》2009,49(9-11):1299-1303
In this paper, strain gauges are used to measure the dynamic response during drop impact. A set of high-speed data acquisition system is used to capture the real-time strain response of critical locations. Finite Element Modelling is used to determine where to place the strain gauges. Two board level drop impact test methods, A and B, are compared by the strain gauge measurements. Results show significant differences in strain amplitude, strain rate, frequency, rebound, and damping. Method B produces higher strain amplitude, stronger rebound, and less damping, while method A produces higher frequency and strain rate. Damping and rebound are important factors for both test methods. The differences of two test methods are due to the contributions from test condition and test board. Combination test were conducted to investigate the contribution of test condition and test board. Results show that test board dominates strain amplitude, frequency, mode and damping, while test condition shows influence on strain amplitude and rebound. Test condition A produces higher strain amplitude, while test condition B produces stronger rebound. Test board A produces higher frequency, while test board B produces higher strain amplitude and less damping. Test board contributes more to the strain amplitude than test condition. Strain rate is dependent on both the test condition and test board. 相似文献
1000.
The present work primarily investigates the corrosion characterization of the common P110 steel and the anti‐sulfide P110SS steel in CO2‐containing solution with or without hydrosulfuric acid (H2S) at 70 °C. The electrochemical techniques such as potentiodynamic polarization sweep and electrochemical impedance spectroscopy (EIS) were used to disclose the differences of the corrosion mechanisms between both P110 and P110SS steels in CO2‐containing solution with various additions of H2S. The EIS data fitted by ZsimpWin software were analyzed and discussed. The experimental results indicated that H2S could accelerate and also inhibit the corrosion attack according to the changes of corrosive environments. 相似文献