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201.
K. Vaarmets S. Sepp J. Nerut E. Härk I. Tallo E. Lust 《Journal of Solid State Electrochemistry》2013,17(6):1729-1741
The electrochemical reduction of oxygen on binary Pt–Ru alloy deposited onto microporous–mesoporous carbon support was studied in 0.5 M H2SO4 solution using cyclic voltammetry, rotating disk electrode (RDE), and impedance method. The microporous–mesoporous carbon support C(Mo2C) with specific surface area of 1,990 m2?g?1 was prepared from Mo2C at 600 °C using the chlorination method. Analysis of X-ray diffraction, photoelectron spectroscopy, and high-resolution transmission electron microscopy data confirms that the Pt–Ru alloy has been formed and the atomic fraction of Ru in the alloy was ~0.5. High cathodic oxygen reduction current densities (?160 A?m?2 at 3,000 rev?min?1) have been measured by the RDE method. The O2 diffusion constant (1.9?±?0.3?×?10?5?cm2?s?1) and the number of electrons transferred per electroreduction of one O2 molecule (~4), calculated from the Levich and Koutecky–Levich plots, are in agreement with literature data. Similarly to the Ru/RuO2 system in H2SO4 aqueous solution, nearly capacitive behavior was observed from impedance data at very low ac frequencies, explained by slow electrical double-layer formation limited by the adsorption of reaction intermediates and products into microporous–mesoporous Pt–Ru–C(Mo2C) catalyst. All results obtained for C(Mo2C) and Pt–Ru–C(Mo2C) electrodes have been compared with corresponding data for commercial carbon VULCAN® XC72 (C(Vulcan)) and Pt–Ru–C(Vulcan) electrodes processed and measured in the same experimental conditions. Higher activity for C(Mo2C) and Pt–Ru–C(Mo2C) has been demonstrated. 相似文献
202.
Fabio Terzi Jonathan Pelliciari Chiara Zanardi Laura Pigani Antti Viinikanoja Jukka Lukkari Renato Seeber 《Analytical and bioanalytical chemistry》2013,405(11):3579-3586
A gold electrode partially coated by graphene multilayer is developed and tested with respect to high concentrations of hydrogen peroxide. The effective use of conventional electrode materials for the determination of such an analyte by anodic oxidation or cathodic reduction is prevented by the occurrence of adsorptions fouling the electrode surface. This prevents reliable and repeatable voltammetric curves for being recorded and serious problems arise in quantitative analysis via amperometry. The gold–graphene electrode is shown to be effective in quantitative evaluation, by cathodic reduction, of hydrogen peroxide at concentration levels that are of interest in an industrial. Acid, neutral, and basic pH values have been tested through correct adjustment of a Britton Robinson buffer. The experiments have been performed both by cyclic voltammetry and with amperometry at constant potential in unstirred solution. The latter technique has been employed in drawing a calibration linear plot. In particular, the performances of the developed electrode system have been compared with those of both pure gold and pure graphene electrode materials. The bi-component electrode was more sensitive; co-catalytic action by the combination of the two components is hypothesised. The system is stable over many potential cycles, as checked by surface-enhanced Raman spectra recorded over time. 相似文献
203.
A new kind of long-chain aliphatic polyamide (PA1218) with a relatively low melting point, high molecular weight, and stable mechanical properties at humid conditions was successfully developed via a polycondensation reaction between 1,18-octadecanedioic acid and 1,12-diaminodecane. Additionally, oleic acid-surfaced modified silicon dioxide (SSD) was prepared and employed to improve the properties of PA1218 through in-situ polymerization. FT-IR spectra and TGA thermograms confirmed the successful surface modification of nanoparticles, and consequently, 5% substitution of surface hydroxyl groups of SiO2 nanoparticles with oleic acid molecules. Moreover, the thermomechanical and rheology tests revealed a significant improvement in nanocomposites’ properties compared to the pure PA1218; for instance, the tensile strength and storage modulus were increased by 22% and 40%, respectively in the sample containing 3% SSD nanoparticles. This improvement, along with SEM images, confirmed the uniform dispersion of SSD nanoparticles through the employed in-situ polymerization and excellent compatibility between inorganic and organic phases, which was achieved via surface modification. Finally, all the samples demonstrated a water uptake capacity of less than 0.6% attributed to the high methylene/amide ratio in their backbones, causing these newly developed nanocomposites to be notable candidates for specific engineering applications. 相似文献
204.
205.
We study a 2D model of the orientation distribution of fibres in a paper machine headbox. The goal is to control the orientation
of fibres at the outlet by shape variations. The mathematical formulation leads to an optimization problem with control in
coefficients of a linear convection-diffusion equation as the state problem. Existence of solutions both to the state and
the optimization problem is analyzed and sensitivity analysis is performed. Further, discretization is done and a numerical
example is shown.
This research was supported by the Charles University Grant Agency under Contract 6/2005/R, MSM 0021620839 (MŠMT ČR), and
the Academy of Finland, Grant #204741. 相似文献
206.
Ge, Rusjan, and Zweifel introduced a binary tree which represents all the periodic windows in the chaotic regime of iterated one-dimensional unimodal maps. We consider the scaling behavior in a modified tree which takes into account the self-similarity of the window structure. A nonuniversal geometric convergence of the associated superstable parameter values towards a Misiurewicz point is observed for almost all binary sequences with periodic tails. For these sequences the window period grows arithmetically down the binary tree. There are an infinite number of exceptional sequences, however, for which the growth of the window period is faster. Numerical studies with a quadratic maximum suggest more rapid than geometric scaling of the superstable parameter values for such sequences. 相似文献
207.
Timo Seppäläinen 《Probability Theory and Related Fields》1993,97(1-2):103-112
Summary We extend Sanov's theorem on i.i.d. large deviations to independent but not identically distributed random variables, and study the generalization of relative entropy that appears as the rate function. 相似文献
208.
Using an R-dependent atomic basis for static molecular calculations we get accurate single particle energies and dynamic coupling
matrix elements. We present our ab initio calculations of inner shell vacancy production for the scattering systems Ni11+-Pb at 1.5 MeV/N and Pb42+-Ni at 1.4 MeV/N.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
209.
Timo Seppäläinen 《Communications in Mathematical Physics》2002,229(1):141-182
We study central limit theorems for a totally asymmetric, one-dimensional interacting random system. The models we work with
are the Aldous–Diaconis–Hammersley process and the related stick model. The A-D-H process represents a particle configuration
on the line, or a 1-dimensional interface on the plane which moves in one fixed direction through random local jumps. The
stick model is the process of local slopes of the A-D-H process, and has a conserved quantity. The results describe the fluctuations
of these systems around the deterministic evolution to which the random system converges under hydrodynamic scaling. We look
at diffusive fluctuations, by which we mean fluctuations on the scale of the classical central limit theorem. In the scaling
limit these fluctuations obey deterministic equations with random initial conditions given by the initial fluctuations. Of
particular interest is the effect
of macroscopic shocks, which play a dominant role because dynamical noise is suppressed on the scale we are working.
Received: 4 October 2001 / Accepted: 12 March 2002 相似文献
210.
Perez Carrillo A Bonada J Patynen J Valimaki V 《The Journal of the Acoustical Society of America》2011,130(2):1020-1029
This work presents a method for measuring and computing violin-body directional frequency responses, which are used for violin sound synthesis. The approach is based on a frame-weighted deconvolution of excitation and response signals. The excitation, consisting of bowed glissandi, is measured with piezoelectric transducers built into the bridge. Radiation responses are recorded in an anechoic chamber with multiple microphones placed at different angles around the violin. The proposed deconvolution algorithm computes impulse responses that, when convolved with any source signal (captured with the same transducer), produce a highly realistic violin sound very similar to that of a microphone recording. The use of motion sensors allows for tracking violin movements. Combining this information with the directional responses and using a dynamic convolution algorithm, helps to improve the listening experience by incorporating the violinist motion effect in stereo. 相似文献