478 resultados para Oxidation layer
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Experiments were conducted in the nonequilibrium region of a free mixing layer with unequal freestream velocities. Four velocity ratios U(1)/U(2) of 0.32, 0.46, 0.74, and 0.96 were used in this investigation. The growth of the shear layer as well as the velocity adjustment in the near wake were examined. There was reasonable agreement between the measured mean velocity profiles and those computed using the K-epsilon turbulence model. Some periodic turbulence velocity fluctuations were observed in the mixing layer, but their frequency remained the same along the flow.
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Donor doped BaTiO3 ceramics become insulating5 under controlled conditions with effective dielectric constants >10. The changes in EPR signals indicate that a certain fraction of the donor doped BaTiO3 is cubic even at room temperature and that the cubic fraction increases with the donor content. X-ray powder diffraction data support the EPR results. The coexistence of both the phases over a range of temperature is characteristic of diffused phase transition. The effect of grain size variation on EPR signal intensities indicate that the boundary layers surrounding the grains may constitute the cubic phase as a result of higher Ba-vacancies and donor contents at the grain boundary layer than in the bulk. Since the acceptor states arising from the Ba-vacancies and the impurities are activated in the cubic phase, they capture electrons from the conduction band, rendering the cubic phase electrically more insulating than the semiconductive tetragonal grain interiors. Thus, the cubic grain boundary layers act as effective dielectric media where the field tends to concentrate.
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Finely divided selenium and tellurium undergo oxidation to selenic and orthotelluric acids by a concentrated solution of chloramine-T in acid medium. An analytical procedure (accurate to <1 %) has been developed based on this reaction.
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A method of determining the rate of the initiation reaction in the liquid phase oxidation of propionaldehyde is described.
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Rate constants for the quenching of singlet oxygen by a series of thioketones were measured by monitoring the inhibition of the self-sensitized photooxidation of rubrene. A correlation of the quenching rate with the nature of the substituents on the aromatic rings for the diarylthioketones and arylalkylthioketones was found, whereas correlation with the n orbital ionization potential was observed for the dialkylthioketones.
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Acetone powders prepared from leaf extracts of Tecoma stans L. were found to catalyze the oxidation of catechol to 3,4,3',4'-tetrahydroxydiphenyl. Fractionation of the acetone powders obtained from Tecoma leaves with acetone, negative adsorption of the acetone fraction with tricalcium phosphate gel, and chromatography of the gel supernatant on DEAE-Sephadex yielded a 68-fold purified enzyme with 66% recovery. The enzyme had an optimum pH around 7.2. It showed a temperature optimum of 30° and the Km for catechol was determined as 2 x 10-4 m. The purified enzyme moved as a single band on polyacrylamide gel electrophoresis. Its activity was found to be partially stimulated by Mg2+. The reaction was not inhibited by o-phenanthroline and agr,agr'-dipyridyl. The purified enzyme was highly insensitive to a range of copper-chelating agents. It was not affected appreciably by thiol inhibitors. The reaction was found to be suppressed to a considerable extent by reducing agents like GSH, cysteine, cysteamine, and ascorbic acid. The purified enzyme was remarkably specific for catechol. Catalase affected neither the enzyme activity nor the time course of the reaction. Hydrogen peroxide was not formed as a product of the reaction.
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Sea water electrolysis is one of the promising ways to produce hydrogen since it is available in plentiful supply on the earth. However, in sea water electrolysis toxic chlorine evolution is the preferred reaction over oxygen evolution at the anode. In this work, research has been focused on the development of electrode materials with a high selectivity for oxygen evolution over chlorine evolution. Selective oxidation in sea water electrolysis has been demonstrated by using a cation-selective polymer. We have used a perm-selective membrane (Nafion®), which electrostatically repels chloride ions (Cl−) to the electrode surface and thereby enhances oxygen evolution at the anode. The efficiency and behaviour of the electrode have been characterized by means of anode current efficiency and polarization studies. The surface morphology of the electrode has been characterized by using a scanning electron microscope (SEM). The results suggest that nearly 100% oxygen evolution efficiency could be achieved when using an IrO2/Ti electrode surface-modified by a perm-selective polymer.
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In der vorliegenden Arbeit wird die Methode der parametrischen Differentiation angewendet, um ein System nichtlinearer Gleichungen zu lösen, das zwei- und dreidimensionale freie, konvektive Grenzschichströmungen bzw. eine zweidimensionale magnetohydrodynamische Grenzschichtströmung beherrscht. Der Hauptvorteil dieser Methode besteht darin, daß die nichlinearen Gleichungen auf lineare reduziert werden und die Nichtlinearität auf ein System von Gleichungen erster Ordnung beschränkt wird, das, verglichen mit den ursprünglichen Nichtlinearen Gleichungen, viel leichter gelöst werden kann. Ein anderer Vorzug der Methode ist, daß sie es ermöglicht, die Lösung von einer bekannten, zu einem bestimmten Parameterwert gehörigen Lösung aus durch schrittweises Vorgehen die Lösung für den gesamten Parameterbereich zu erhalten. Die mit dieser Methode gewonnenen Ergebnisse stimmen gut mit den entsprechenden, mit anderen numerischen Verfahren erzielten überein.
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Vapour phase oxidation of furfural over vanadium pentoxide catalyst was studied using an isothermal flow reactor in the temperature range of 220–280°C. Maleic anhydride and carbon dioxide are found to be formed from furfural by a parallel reaction scheme. The following rate equation based on the two-stage redox mechanism—the substance to be oxidized reduces the catalyst which in turn is reoxidized by oxygen from the feed—is found to explain the data satisfactorily.The reoxidation of the reduced catalyst was found to be the rate controlling step.
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Vapour phase oxidation of anthracene over cobalt molybdate catalyst was investigated in an isothermal flow reactor in the temperature range of 280—340°C. Fifteen different models based on redox, Langmuir—Hinshelwood and Rideal mechanisms were tested in order to elucidate the mechanism of the above reaction. These models were compared on the basis of three criteria and were finally discriminated employing the non-intrinsic parameter method. Two-stage redox mechanism was found to explain the data satisfactorily.
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Photochemical oxidation of 11 diaryl thioketones (1-11) was conducted in the solid state. Quite interestingly, of these only six were oxidized to the corresponding carbonyl compound whereas the rest were photostable. However, in solution all were readily oxidized. The difference in behavior between the thioketones in the solid state has been rationalized on the basis of molecular arrangement in the crystal. X-ray crystal structure analyses of four thioketones were carried out in this connection.
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Copper(II) complexes of quaternised poly(4-vinylpyridine) (PVP) of different degrees of quaternisation and copper content have been prepared by crosslinking the polymer with 1,2-dibromoethane in the presence of Cu2+ ion as template. The stability constant of the PVP---Cu(II) complexes is found to increase with the degree of crosslinking quaternisation of the resin, but the rate at which Cu2+ is adsorbed by the resin decreases. An optimum combination of both stability and rate can be achieved with a moderate degree (31%) of crosslinking. A kinetic study reveals that quaternisation increases significantly the catalytic activity of the complex for the oxidation of S2O2−3 by O2 compared with PVP----Cu(II) without quaternisation, but it deactivates the complex for the oxidation of both S3O2−6 and S4O2−6. The batch reactor oxidation kinetics at pH 2.16, where the rate is observed to be maximum, is well explained by the Langmuir—Hinshelwood model assuming the coordination of both O2 and thioanion to Cu(II) as a precursor to the oxidation reaction.
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The fabrication of hydrogen bonded polymer self-assembly for drug delivery has been accomplished via layer-by-layer sequential assembly from aqueous solution. In this study, the self-assembly was constructed based on hydrogen bonding between DNA base (adenine and thymine) pairs substituted on the backbone of chitosan and hyaluronic acid. Chitosan was modified with adenine, whereas hyaluronic acid was modified with thymine. Subsequently, these two polymers were sequentially absorbed on flat substrate by taking advantage of interactions of DNA base pairs via hydrogen bonding. Interlayer hydrogen bonding of these two polymers produces stable multilayer film without using any cross-linking agent. Thin film formation on quartz substrate has been monitored with UV-vis spectra and an AFM study. Formation of multilayer hydrogen-bonded thin film has been further confirmed with SEM. Encapsulation and release behavior of the therapeutic drug from the multilayer thin film at different conditions has been illustrated using UV-vis spectra. Cell viability of modified polymers using MTT assay confirmed no cytotoxic effect.
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The rate of NADH oxidation with oxygen as the acceptor is very low in mouse liver plasma membrane and erythrocyte membrane. When vanadate is added, this rate is stimulated 10- to 20-fold. The absorption spectrum of vanadate does not change with the disappearance of NADH. The reaction is inhibited by superoxide dismutase, and there is no activity under an argon atmosphere. This indicates that oxygen is the electron acceptor and the reaction is mediated by superoxide. The vanadate stimulation is not limited to plasma membrane. Golgi apparatus and endoplasmic reticulum show similar increase in NADH oxidase activity when vanadate is added. The endomembranes have significant vanadate-stimulated activity with both NADH and NADPH. The vanadate-stimulated NADH oxidase in plasma membrane is inhibited by compounds, which inhibit NADH dehydrogenase activity: catechols, anthracycline drugs and manganese. This activity is stimulated by high phosphate and sulfate anion concentrations.
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Two- and three-state models for the adsorption of organic compounds at the electrodelelectrolyte interface are proposed. Different size requirements, if any, for the neutral molecule and the adsorbing solvent are also considered. It is shown how the empirical, generalised surface layer (GSL) relationship (between the potential difference and the electrode charge) formulated by Damaskin et a / . can be understood at the molecular level.