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排序方式: 共有60条查询结果,搜索用时 93 毫秒
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The reduction behaviour of porous lead dioxide electrodes is shown to be independent of rotation speed in a large excess of 5 M H2SO4. The reduction peak is broadened by the porosity. This porosity broadening is interpreted in terms of the reaction being driven more deeply into the pore structure as the front of the electrode becomes progressively more ressstive. The effect of different potential sweep rates on the current response and the effects of progressive redox cycles can be fully explained on this model. 相似文献
3.
The anodic behaviour of tin in buffered phosphate electrolyte (pH=3.1) has been studied by a variety of techniques. A number of anodic processes occur depending on potential and the conditions at the electrode/electrolyte interphase. On anodic polarisation the electrode, which is probably filmed with a phosphate layer, initially undergoes dissolution to form probably Sn(H2PO4·HPO4)? species. Impedance data indicate that this process has a corresponding Tafel slope of ~0.046 V/decade. At more positive potentials three consecutive passivating processes occur.The primary passivating process involves the blocking of the electrode by Sn3(PO4)2 by a dissolution-precipitation mechanism. The formation of SnO by a slow three dimensional nucleation and growth process constitutes the second. It is formed as a result of the attainment of alkaline conditions at the electrode surface. There is also a parallel reaction path involving the formation of soluble Sn(II) species. The tertiary process consists of the oxidation of Sn to Sn(IV) species. Passivation occurs via a dissolution-precipitation mechanism when the electrode is blocked by SnO2. The relative quantities of SnO and SnO2 produced is a function of operating conditions. 相似文献
4.
Michelle Hampson Naomi Driesen Jennifer K. Roth John C. Gore R. Todd Constable 《Magnetic resonance imaging》2010
Functional brain imaging studies have identified a set of brain areas typically activated during cognitive tasks (task-positive brain areas) and another set of brain areas typically deactivated during cognitive tasks (task-negative brain areas). Negative correlations, or anticorrelations, between task-positive and task-negative brain areas have been reported at rest. Furthermore, the strength of these anticorrelations appears to be related to cognitive function. However, studies examining anticorrelations have typically employed global regression or similar analysis steps that force anticorrelated relationships to exist between brain areas. Therefore the validity of these findings has been questioned. Here we examine anticorrelations between a task-negative region in the medial frontal gyrus/anterior cingulate cortex and dorsolateral prefrontal cortex, a classic task-positive area, using an analysis that does not include global regression. Instead, we control for whole-brain correlations in the group-level analysis. Using this approach, we demonstrate that the strength of the functional connection between the medial frontal cortex and the dorsolateral prefrontal cortex is related to cognitive function and that this relationship is not an artifact of global regression. 相似文献
5.
Tahira Foyzun Abdullah Al Mahmud Md. Salim Ahammed Md. Imran Nur Manik Md. Kamrul Hasan KM Monirul Islam Simin Sobnom Lopa Md. Yusuf Al-Amin Kushal Biswas Mst. Rejina Afrin AHM Khurshid Alam Golam Sadik 《Molecules (Basel, Switzerland)》2022,27(3)
Neurotoxicity is a serious health problem of patients chronically exposed to arsenic. There is no specific treatment of this problem. Oxidative stress has been implicated in the pathological process of neurotoxicity. Polyphenolics have proven antioxidant activity, thereby offering protection against oxidative stress. In this study, we have isolated the polyphenolics from Acacia nilotica and investigated its effect against arsenic-induced neurotoxicity and oxidative stress in mice. Acacia nilotica polyphenolics prepared from column chromatography of the crude methanol extract using diaion resin contained a phenolic content of 452.185 ± 7.879 mg gallic acid equivalent/gm of sample and flavonoid content of 200.075 ± 0.755 mg catechin equivalent/gm of sample. The polyphenolics exhibited potent antioxidant activity with respect to free radical scavenging ability, total antioxidant activity and inhibition of lipid peroxidation. Administration of arsenic in mice showed a reduction of acetylcholinesterase activity in the brain which was counteracted by Acacia nilotica polyphenolics. Similarly, elevation of lipid peroxidation and depletion of glutathione in the brain of mice was effectively restored to normal level by Acacia nilotica polyphenolics. Gallic acid methyl ester, catechin and catechin-7-gallate were identified in the polyphenolics as the major active compounds. These results suggest that Acacia nilotica polyphenolics due to its strong antioxidant potential might be effective in the management of arsenic induced neurotoxicity. 相似文献
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The passivating processes at a tin anode in NaOH solutions have been investigated by voltammetry. The effects of varying sweep rate, rotation speed, concentration of NaOH and the potential limits have been studied. The results indicate that primary passivation is the results of a dissolution—precipitation mechanism involving the blocking of the electrode by Sn(II) species. There is evidence that during secondary passivation there is not only oxidation of Sn(II) to Sn(IV) species but alos the direct oxidation of Sn to Sn(IV) solution soluble species. At more positive potentials dehydration of the film may occur and result in a more efficient passivation. A possible explanation is advanced for observed current oscillations. 相似文献
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KM Varier AM Vinodkumar NVSV Prasad PV Madhusudhana Rao DL Sastry Lagy T Baby MC Radhakrishna NG Puttaswamy JJ Das P Sugathan N Madhavan AK Sinha DO Kataria 《Pramana》1999,53(3):529-533
Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies.
Coupled channel calculations incorporating couplings to 2+ and 3− states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements
had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer
were carried out for 46,48Ti+61Ni systems. The present paper gives the results of these studies. 相似文献
10.
There has been considerable debate in the literature about the true room-temperature structure of ZrP2O7 and related materials. In this article we describe how a combination of information from solid-state 31P NMR and powder diffraction data can be used to determine the structure of this 136 unique-atom material. The structure has been solved using a combination of simulated annealing and Rietveld refinement performed simultaneously on X-ray and neutron diffraction data. Despite the close to cubic metric symmetry of the material, we show how its true orthorhombic structure (space group Pbca) can be refined to a high degree of precision. 相似文献