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排序方式: 共有1036条查询结果,搜索用时 15 毫秒
1.
Some nickel, copper, and silver salts or complexes are efficient catalysts for the oxidation of benzylic ethers with oxygen in 1,2-dimethoxyethane. Salts of the weakly coordinating anion trifluoroacetate are particularly efficient, approaching (and, in some cases, improving) the yields obtained with cobalt(II) chloride, the best catalyst so far reported. 相似文献
2.
B. Savo P. Romano A. Nigro R. Di Leo 《Physica C: Superconductivity and its Applications》2002,370(4):275-280
The flat voltage noise component of current biased, high-transparency Nb/AlOx/Nb superconducting tunnel junctions has been investigated at frequencies up to 70 kHz. Several aspects of the analyzed phenomena suggest the presence of current noise effects induced by the discreteness of the charge carriers. At subgap voltages, where excess currents occur, a behavior coherent with a multiple Andreev reflection-assisted transport through the tunnel barrier has been found. However, the measured charge values exceed any theoretical prediction. 相似文献
3.
A model for the interaction of near-infrared laser pulses with metal powders in selective laser sintering 总被引:4,自引:0,他引:4
P. Fischer N. Karapatis V. Romano R. Glardon H.P. Weber 《Applied Physics A: Materials Science & Processing》2002,74(4):467-474
A thermal model of the interaction of pulsed near-infrared laser radiation from a Nd:YAG laser was made, taking the measured
powder properties such as reflectance, optical penetration depth and thermal conductivity into account. It allows an estimation
of the evolution of two different temperatures: the average temperature of the powder (taken over the grains in a volume given
by the laser beam diameter and the optical penetration depth) and the temperature distinction within a single grain. It showed
that in pulsed mode consolidation can be achieved at much lower average power as the surface of the powder particles are molten
but their cores remain at nearly room temperature. This leads to a much lower average temperature and therefore a dramatic
decrease in residual thermal stresses in the finished piece. The results of the model were experimentally tested and confirmed.
Received: 26 July 2001 / Accepted: 23 November 2001 / Published online: 23 January 2002 相似文献
4.
Jürgen Kurths M. Carmen Romano Marco Thiel Grigory V. Osipov Mikhail V. Ivanchenko István Z. Kiss John L. Hudson 《Nonlinear dynamics》2006,44(1-4):135-149
We present two different approaches to detect and quantify phase synchronization in the case of coupled non-phase coherent
oscillators. The first one is based on the general idea of curvature of an arbitrary curve. The second one is based on recurrences
of the trajectory in phase space. We illustrate both methods in the paradigmatic example of the R?ssler system in the funnel
regime. We show that the second method is applicable even in the case of noisy data. Furthermore, we extend the second approach
to the application of chains of coupled systems, which allows us to detect easily clusters of synchronized oscillators. In
order to illustrate the applicability of this approach, we show the results of the algorithm applied to experimental data
from a population of 64 electrochemical oscillators. 相似文献
5.
Forward degenerate four-wave mixing (DFWM) processes are investigated with a femtosecond pulsed laser in lithium niobate crystal doubly-doped with magnesium and iron (LiNbO3:Fe, Mg). The pulse energy dependence reveals a pure third-order nonlinear response, and the third-order nonlinear susceptibility x^(3) in the material is evaluated to be 4.96 × 10^-13 esu. The time-resolved DFWM process shows a response time of x^(3) shorter than 100fs, which is due to the nonresonant electronic nonlinearities. Our results indicate that LiNbO3 crystals have potentials for ultrafast real-time optical processing systems, which require a large and fast x^(3) optical nonlinearity. 相似文献
6.
The topological changes that occur during coarsening of 2D and 3Dcellular structures, such as polycrystals, areinvestigated. Particular attention is given to the elimination ofgrain boundaries and grains with more than the minimum number oftopological elements. A thermodynamic criterion is introduced tofind out which topological transformations are favoured, based on theevaluation of the Gibbs free energy of the initial and finalconfigurations. In general, elimination of grains is possible only ifthe number of their neighbours is below a critical value, which maybe affected by geometry. 相似文献
7.
In the Y—Bi system the formation heats were measured using a direct isoperibol calorimeter. The following values were found for the two known compounds: 相似文献
8.
The influence of ionic strength on the complexes formed by natural bovine serum albumin (BSA), pH 5.4 (near the isoelectric point), and sodium dodecyl sulfate (SDS) in aqueous buffered (sodium acetate) solution was investigated by using surface tension, fluorescence and small angle X-ray scattering (SAXS) techniques. Ionic strength was varied by changing sodium acetate buffer concentration from 0.020 to 0.5 M. Surface tension revealed that SDS:BSA saturation binding occurs at psp = 42 +/- 2 mM, independent of the solution ionic strength. Further, SAXS curves are consistent with the necklace and bead model, where micelle-like aggregates are randomly distributed along the partial unfolded protein. Micelle-like aggregates grow from small spheres at 10 mM SDS to small ellipsoids (upsilon = 1.3 , ratio between the largest and the shortest axes) near psp, in good agreement with micellar aggregation numbers obtained by fluorescence, independent of salt concentration. Protein-bound micelles stop growing above psp and further SDS addition induces free-micelle formation. 相似文献
9.
Franco Bellesia Franco Ghelfi Romano Grandi Ugo Maria Pagnoni Adriano Pinetti 《Journal of heterocyclic chemistry》1993,30(3):617-621
Pyrroles are powerful nucleophiles in the reaction with dialkyl sulfoxides and trimethylchlorosilane (TMCS) or trimethylbromosilane (TMBS), affording sulfonium salts or halo derivatives, generally in good yields. 相似文献
10.
Monte Carlo simulation results are reported for clusters consisting of 250 water molecules surrounding serine, both in the neutral form and in two zwitterionic conformers (in order to gain some insight into conformational effects). Calculations were carried out at 300 K and using two-body potentials obtained by means of quantum-mechanical calculations. The spatial dependence of the average interaction energies was investigated. The solvation structure was investigated by means of radial distribution functions and probability density maps, which showed a few water molecules directly solvating the hydrophilic groups and, beyond them, a more or less rich and complex hydrogen-bonded network of solvent molecules. 相似文献