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51.
C. A. C. Sequeira D. M. F. Santos P. S. D. Brito 《Russian Journal of Electrochemistry》2008,44(7):852-856
The electrocatalysis of the oxygen reduction reaction by lanthanum-strontium manganate La0.5Sr0.5MnO3 (LSM) has been studied by cyclic voltammetry using the rotating ring-disc electrode technique (RRDE) in alkaline medium.
From the ring-disc data and other kinetic parameters it was concluded that the oxygen reduction occurs by dissociative chemisorption
at low overpotentials. At higher overpotentials, the formation of hydrogen peroxide (HO2− in this case) on the electrocatalyst has been observed. The apparent exchange current density for oxygen reduction on LSM
has been found to be 2 × 10−7 A cm−2, while the corresponding Tafel slope is 0.100 V per decade. The possible reaction mechanism for electroreduction of oxygen
on this oxide catalyst has been discussed.
Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 7, pp. 919–923.
The text was submitted by the authors in English. 相似文献
52.
Quantum monte carlo study of the energetics of small hydrogenated and fluoride lithium clusters
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N. L. Moreira B. G. A. Brito J. N. Teixeira Rabelo Ladir Cândido 《Journal of computational chemistry》2016,37(17):1531-1536
An investigation of the energetics of small lithium clusters doped either with a hydrogen or with a fluorine atom as a function of the number of lithium atoms using fixed‐node diffusion quantum Monte Carlo (DMC) simulation is reported. It is found that the binding energy (BE) for the doped clusters increases in absolute values leading to a more stable system than for the pure ones in excellent agreement with available experimental measurements. The BE increases for pure, remains almost constant for hydrogenated, and decreases rapidly toward the bulk lithium for the fluoride as a function of the number of lithium atoms in the clusters. The BE, dissociation energy as well as the second difference in energy display a pronounced odd–even oscillation with the number of lithium atoms. The electron correlation inverts the odd–even oscillation pattern for the doped in comparison with the pure clusters and has an impact of 29%–83% to the BE being higher in the pure cluster followed by the hydrogenated and then by the fluoride. The dissociation energy and the second difference in energy indicate that the doped cluster Li3H is the most stable whereas among the pure ones the more stable are Li2, Li4, and Li6. The electron correlation energy is crucial for the stabilization of Li3H. © 2016 Wiley Periodicals, Inc. 相似文献
53.
Nadia Benkhettou Artur M. C. Brito da Cruz Delfim F. M. Torres 《Mathematical Methods in the Applied Sciences》2016,39(2):261-279
We introduce a nabla, a delta, and a symmetric fractional calculus on arbitrary nonempty closed subsets of the real numbers. These fractional calculi provide a study of differentiation and integration of non‐integer order on discrete, continuous, and hybrid settings. Main properties of the new fractional operators are investigated and some fundamental results presented, illustrating the interplay between discrete and continuous behaviors. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
54.
Pilling S Lago AF Coutinho LH de Castilho RB de Souza GG de Brito AN 《Rapid communications in mass spectrometry : RCM》2007,21(22):3646-3652
We present results on the valence level excitation, ionization and dissociation of adenine, using time-of-flight mass spectrometry and synchrotron radiation, in the vacuum ultraviolet (VUV) range of 12-21 eV. The measurements were performed using a gas-phase (Ne) harmonics filter in order to eliminate contributions from higher-order harmonics. Mass spectra were obtained using the photoelectron-photoion coincidence technique (PEPICO). The relative abundances for each ionic fragment and their mean kinetic energy release have been determined from the analysis of the corresponding peak shapes in the mass spectra. Comparison with the available photoelectron spectra and previous measurements allowed the assignment of the main features in the spectra. A discussion on the dissociative photoionization channels of this molecule has also been included. Due to our harmonics-free incident photon beam we were able to propose new appearance energy (AE) for the most important ionic channels in this energy range. The precursor ion, C(5)H(5)N(5)+, is the most abundant species (40% at 15 eV and 20% at 20 eV), which confirms the high stability of adenine upon absorption of VUV photons. We have observed other intense fragment ions such as: C(4)H(4)N(4)+, C(3)H(3)N(3) (+), C(2)H(2)N(2)+ and HCNH+. The production of the neutral HCN fragment represents up to 40% of the dissociative channels for this molecule as induced by VUV photons. 相似文献
55.
本文采用取样直流极谱, 常规脉冲极谱, 微分脉冲极谱和交流极谱考察了,2,2,6,6-四甲基-4-羟基哌啶 -1-氧和2,2,6,6-四甲基-4-氧哌啶 -1-氧由基及2,2,6,6-四甲基哌啶 -1-氧自由基在水溶液中的还原反应, 并研究了它们的还原经历电化学过程 。 相似文献
56.
It has been recently reported that a granular mixture in which grains differ in their restitution coefficients presents segregation:
the more inelastic particles sink to the bottom. When other segregation mechanisms as buoyancy and the Brazil nut effect are
present, the inelasticity induced segregation can compete with them. First, a detailed analysis, based on numerical simulations
of two dimensional systems, of the competition between buoyancy and the inelasticity induced segregation is presented, finding
that there is a transition line in the parameter space that determines which mechanism is dominant. In the case of neutrally
buoyant particles having different sizes the inelasticity induced segregation can compete with the Brazil nut effect (BNE).
Reverse Brazil nut effect (RBNE) could be obtained at large inelasticities of the intruder. At intermediate values, BNE and
RBNE coexist and large inelastic particles are found both near the bottom and at the top of the system. 相似文献
57.
58.
Chirleanny M. Mendes Marília A. Brito Tatiana S. Porto Ana L. F. Porto Ranilson S. Bezerra Luiz B. CarvalhoJr. Ana M. A. Caneiro-Leão Maria G. Carneiro-da-Cunha 《Chemical Papers》2009,63(6):662-669
Intestine proteases of Nile tilapia (Oreochromis niloticus) were partially purified by heat treatment (purification factor of 3.5, enzyme activity remained almost constant) to reach the maximum activity and stability within an alkaline pH range of 7.2–11.0. The optimum temperature and stability over a 120 min period were found to be at 55°C and at 35–45°C, respectively. The proteases’ activity was not affected by a 1 vol. % saponin surfactant, inactivated by 0.01 g mL?1 sodium dodecylsulphate after 120 min, and it remained stable for 30 min in a 5 vol. % and 10 vol. % hydrogen peroxide solutions. The proteases were slightly activated by Ca2+, Mg2+, and K+ and the substrate most effectively hydrolysed was casein (40.0 U mg?1). A 24 full factorial design used to evaluated the influence of independent variables showed that the enzyme extract, detergent concentration and the incubation time had a significant influence on the enzymatic activity. The best conditions to be used concerning detergent additive were found with 0.3 mg mL?1 of protein and 3.0 mg mL?1 of detergent for 30 min in the presence of Astrus® detergent. 相似文献
59.
Ferreira MC Gameiro J Nagib PR Brito VN Vasconcellos Eda C Verinaud L 《Photochemistry and photobiology》2009,85(1):227-233
The effect of HeNe laser on the extracellular matrix deposition, chemokine expression and angiogenesis in experimental paracoccidioidomycotic lesions was investigated. At days 7, 8 and 9 postinfection the wound of each animal was treated with a 632.8 nm HeNe laser at a dose of 3 J cm(-2). At day 10 postinfection, the wounds were examined by using histologic and immunohistochemical methods. Results revealed that laser-treated lesions were lesser extensive than untreated ones, and composed mainly by macrophages and lymphocytes. High IL-1beta expression was shown in the untreated group whereas in laser-treated animals the expression was scarce. On the other hand, the expression of CXCL-10 was found to be reduced in untreated animals and quite intensive and well distributed in the laser-treated ones. Also, untreated lesions presented vascular endothelial growth factor (VEGF) in a small area near the center of the lesion and high immunoreactivity for hypoxia-inducible factor-1 (HIF-1), whereas laser-treated lesions expressed VEGF surrounding blood vessels and little immunoreactivity for HIF-1. Laser-treated lesions presented much more reticular fibers and collagen deposition when compared with the untreated lesion. Our results show that laser was efficient in minimizing the local effects observed in paracoccidioidomycosis and can be an efficient tool in the treatment of this infection, accelerating the healing process. 相似文献
60.