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排序方式: 共有714条查询结果,搜索用时 15 毫秒
61.
Romolo Marcelli Giancarlo Bartolucci George Papaioannu Giorgio De Angelis Andrea Lucibello Emanuela Proietti Benno Margesin Flavio Giacomozzi François Deborgies 《Microsystem Technologies》2010,16(7):1111-1118
The reliability of RF MEMS switches is typically reduced by charging effects occurring in the dielectrics. The aim of this
paper is to discuss these effects, and to propose analytical and equivalent circuit models which account for most of the physical
contributions present in the structure. 相似文献
62.
63.
Stefano Mantegna Arianna Binello Luisa Boffa Marta Giorgis Clara Cena Giancarlo Cravotto 《Food chemistry》2012,130(3):746-750
The ultrasound-assisted extraction (UAE) of resveratrol and other polyphenols from Polygonum cuspidatum has been carried out with the aim of developing an efficient and eco-friendly extraction process. The finely milled roots were sonicated (titanium horn, 19.5 kHz) in methanol, in different cyclodextrin water solutions [β-cyclodextrin (β-CD) or hydroxypropyl β-CD (HPβ-CD)] and also in pure water. UAE dramatically increased the yields and cut down extraction times compared to conventional extraction under stirring. Outstanding results have been achieved with the β-CD solution (1.5% w/w); in fact HPLC analysis showed that the selective inclusion properties of CDs toward phenolic stilbenes gave a much cleaner analytical extract profile. This green method gave 7.51 mg of total resveratrol (free + cleaved polydatin glucoside) per gram of dry plant. Thanks to polyphenol encapsulation within CDs, this extract showed excellent water dispersibility, higher stability and an antioxidant power which is comparable to that of the MeOH extract (DPPH, ORACFL). These important features should pave the road for its application in food supplements or phytochemical preparations. 相似文献
64.
Christian Durante Abdirisak Ahmed Isse Giancarlo Sandon Armando Gennaro 《Applied catalysis. B, Environmental》2009,88(3-4):479-489
The reductive dehalogenation of CCl4, CHCl3, CH2Cl2 and CH3Cl has been investigated by cyclic voltammetry and controlled-potential electrolysis at Ag, glassy carbon (GC) and graphite electrodes in dimethylformamide (DMF) + 0.1 M Et4NClO4 in the absence and presence of a proton donor. In particular, the study was focused in the evaluation of the intermediates and final products of the reduction process and how their distribution could be affected by tuning relevant chemical and electrochemical parameters. In general, depending on the value of the applied potential, all polychloromethanes (PCMs) can be partially or completely dechlorinated, methane being exclusively formed in the latter case. The nature of the electrode material and the proton availability of the medium affect drastically the distribution of reduction products. The results point out that at both types of electrode, reduction of PCMs takes place through two competing reaction pathways both leading to methane. One reaction route involves a sequence of reductive dehalogenation steps, with the removal of one chlorine atom at a time, whereas the other is based on hydrogenolysis of carbenes and bypasses the intermediacy of partially dechlorinated PCMs. The presence of a proton source affects substantially the hydrodehalogenation efficiency, enhancing the concentration of intermediate PCMs and the final yield of methane. The silver electrode exhibits an extraordinary electrocatalytic effect resulting in remarkable positive shifts of the reduction potentials of all PCMs with respect to GC. The Ag surface strongly affects the kinetics of the dissociative electron transfer to CHnCl(4−n) (n = 0–3) as well as the reactivity of the intermediate radicals, carbanions and carbenes. 相似文献
65.
The X 37CrMoV5 1 KU hot working steel has been quenched and tempered, overcarburised, nitrided and nitrocarburised. The surface layers constituted after the thermochemical treatments were characterised by means of X‐ray diffraction (XRD) analyses, optical and scanning electron microscope (SEM) observations, micro‐ and macrohardness indentations. The electrochemical behaviour was evaluated in two different aggressive environments: 0.1 M Na2SO4 and 0.1 M NaCl solutions. While the overcarburised and the nitrocarburised samples exhibit a poor electrochemical behaviour, the presence of a nitrided surface layer enhances the corrosion resistance. This is attributable to the protective action of the nitrided layer that hinders the anodic dissolution reaction of the matrix, whereas the presence of complex carbides in the overcarburised or nitrocarburised samples causes the preferential dissolution of the ferritic matrix due to galvanic coupling phenomena. Finally, the poor corrosion resistance exhibited by the nitrocarburised sample can be ascribed to the presence of a large amount of ferrite together with little ε solid solution in the surface layer. 相似文献
66.
Carlos E. Bamberger Peter Angelini Theodore A. Nolan 《Journal of the American Ceramic Society》1989,72(4):587-592
The production of titanium nitride, TiN, whiskers by reaction of sodium titanium bronze, Nax TiO2 (STB), with excess sodium cyanide, NaCN, at 1000°C is reported. The solubility of Ti from a STB in molten NaCN has been estimated experimentally. The TiN whiskers obtained under different experimental conditions have been examined by scanning electron microscopy and analyzed by analytical electron microscopy. 相似文献
67.
68.
In this work oxidation of benzene and ethenylbenzene (IUPAC name for styrene) as single compounds and in binary mixtures over a Pt honeycomb catalyst were investigated. Both aromatic compounds showed zero-order kinetics over a wide concentration range. The ethenylbenzene reaction rate was affected weakly by the presence of benzene, whereas benzene oxidation was inhibited strongly by ethenylbenzene. The Mars-van Krevelen mechanism (which is generally accepted for single aromatic compound oxidation kinetics) gave rise to inconsistencies in describing mixture behaviour. A different kinetic model is proposed, where benzene reacts from the gas phase and ethenylbenzene is adsorbed on the catalyst competing with oxygen for active sites. This model was able to interpret the oxidation of mixtures quite satisfactorily. 相似文献
69.
Ordered intermetallic alloys: an assessment 总被引:2,自引:0,他引:2
The paper summarizes our present understanding, as established at a recent workshop, of two classes of intermetallic alloys: nickel and iron aluminides, which are currently used by industries; and advanced intermetallic alloys including silicides and Laves-phase alloys, which have a great potential to be developed as new high-temperature structural materials for future industrial use. The workshop emphasized close interaction and co-operation between basic research, applied research, and industrial development, and stressed discussion of critical scientific and technological issues. The current status of these intermetallic alloys was assessed, and the directions for future research and development, as well as emerging opportunities, were identified. The information presented in the text is summarized from the presentations at the workshop, and so no references are given to the published literature. However, an extensive bibliography is appended, in which further details may be found. 相似文献
70.
Angelini E. Carullo A. Corbellini S. Ferraris F. Gallone V. Grassini S. Parvis M. Vallan A. 《IEEE transactions on instrumentation and measurement》2006,55(2):436-441
This paper describes design and test of a new impedance-measurement system for nonlinear devices that exhibits a seven-decade range and works down to a frequency of 0.01 Hz. The system is specifically designed for electrochemical measurements, but the proposed architecture can be employed in many other fields where flexible signal generation and analysis are required. The system employs an unconventional signal generator based on two pulsewidth modulation (PWM) oscillators and an autocalibration system that allows uncertainties of less than 3% to be obtained over a range of 1 k/spl Omega/ to 100 G/spl Omega/. A synchronous demodulation processing allows the noise superimposed to the low-amplitude input signals to be made negligible. 相似文献