Search results for "Reaction"
showing 10 items of 6134 documents
Surface phase transitions at O and CO catalytic reaction on Pd(111)
2006
Abstract The model has been proposed to simulate numerically the reaction O + CO → CO2 and occurring phase transitions on Pd(1 1 1) surface. We calculate the phase diagram for this system by kinetic Monte Carlo method. It shows the phase transitions p ( 2 × 2 ) O → 3 × 3 R 30 O ° and p ( 2 × 2 ) O → 3 × 3 R 30 O ° → p ( 2 × 1 ) O with increase of CO coverage for room and intermediate temperatures, respectively, while in the low temperature limit the direct p(2 × 2)O → p(2 × 1)O phase transition is observed. We demonstrate that the reaction rate is the crucial factor determining the occurrence of the p(2 × 1)O phase and vanishing of the 3 × 3 R 30 O ° with decrease of temperature. The result…
Reaction Rates in the RP-Process and Nucleosynthesis in Novae
1986
Nuclear structure information available on proton rich unstable nuclei were used to evaluate thermonuclear reaction rates in the rp-process in explosive hydrogen burning. These rates were applied in a systematic analysis for a variety of temperature conditions, appropriate to nova explosions, to study nucleosynthesis for isotopes of Ne Na Mg Al Si. The results are discussed in comparison with recent observations of elemental abundances in nova ejecta.
Quantifying biochemical reaction rates from static population variability within complex networks
2021
Quantifying biochemical reaction rates within complex cellular processes remains a key challenge of systems biology even as high-throughput single-cell data have become available to characterize snapshots of population variability. That is because complex systems with stochastic and non-linear interactions are difficult to analyze when not all components can be observed simultaneously and systems cannot be followed over time. Instead of using descriptive statistical models, we show that incompletely specified mechanistic models can be used to translate qualitative knowledge of interactions into reaction rate functions from covariability data between pairs of components. This promises to tur…
Oxygen Incorporation Reaction into Mixed Conducting Perovskites: a Mechanistic Analysis for (La,Sr)MnO3 Based on DFT Calculations
2009
Based on DFT calculations of intermediates and transition states, several hypothetical mechanisms for oxygen incorporation into mixed conducting La1-xSrxMnO3{plus minus}d perovskites are discussed. In the most probable mechanism, the rate-determining step comprises the encounter of a highly mobile surface oxygen vacancy and a molecular oxygen adsorbate. Starting from these results, the variation of reaction rates for different materials is explored.
Kinetik der Bromierung von Phenolen und phenolischen Mehrkernverbindungen, 5. Mitt.
1984
The kinetics of the bromination of six differently substituted 2,6-bis(hydroxybenzyl)phenols having only one reactivepara position at the phenolic unit in the middle of the molecule were studied in acetic acid at 22°C. The reaction rate decreases if intramolecular hydrogen bonds between one or two hydroxy groups of the adjacent phenolic units and the hydroxy group of the reacting unit become possible, and it is especially low, if these hydrogen bonds are directed to the middle by bulky substituents inortho position. This must be explained by a smaller +M-effect of the hydroxy group of the reacting unit. A kinetic isotope effect is observed in deutero acetic acid, where the reaction rate is …
Kinetik der Bromierung von Phenolen und phenolischen Mehrkernverbindungen, 1. Mechanismus und meßmethode
1975
Die Bromierung von 2-(2-Hydroxy-5-methylbenzyl)-4,6-dimethylphenol (1) und 2-[2-Hydroxy-3-(2-hydroxy-5-methylbenzyl)-5-methylbenzyl]-4,6-dimethylphenol (2a) wurde in Eisessig bei 22°C untersucht. Die Reaktion last sich fur [Br2]0 = 1,4·10−3 bis 6,0·10−3 mol dm + und Konzentrationen der phenolischen Verbindungen [P]0 zwischen 1,1·10−3 und 5,5·10−3mol dm−3 durch das folgende Geschwindigkeitsgesetz beschreiben: Wahrend die gebildete Bromverbindung keinen Einflus auf die Reaktionsgeschwindigkeit hat, verlangsamt der entstehende Bromwasserstoff die Reaktion. Die Bromierung ist trotzdem zur Bestimmung der Reaktionsfahigkeit von Phenolen und phenolischen Mehrkernverbindungen gut geeignet, da die R…
On-line photochemical derivatization and flow-injection spectrophotometric determination of ergonovine maleate
1993
Abstract A flow-injection manifold is proposed for the on-line photochemical derivatization of ergonovine maleate with application to pharmaceutical formulations. The procedure is based on the reaction with p-dimethylaminobenzaldehyde in presence of iron(III) and sulphuric acid medium. The reaction rate is improved by irradiation of the solution with a mercury lamp (254.0 nm). The calibration graph is linear over the range 3–74 μg ml−1 ergonovine, with a mid-range R.S.D. of 1.7% and a sample throughput of 34 h−1. The influence of foreign compounds was tested.
Rate-retarding effects of mixed anionic/non-ionic micelles on the alkaline hydrolysis of the chloropentamminocobalt(III) complex
2006
Abstract Rate data for the alkaline hydrolysis of the chloropentaamminecobalt(III) cation in the presence of mixed micelles composed of (i) anionic sodium decylsulphate (SDeS) and non-ionic dodecylpenta(oxyethylene glycol) monoether (C 12 E 5 ) surfactants and (ii) anionic sodium perfluorooctanoate (SPFO) and non-ionic C 12 E 5 surfactants has been obtained at T 298 K and constant electrolyte concentration 0.08 mol dm −3 ([NaOH] = 0.01 mol dm −3 , [NaClO 4 ] = 0.07 mol dm −3 ) over a wide range of total surfactant concentration ( C t ) and anionic mole fraction ( χ ). The critical micelle concentrations (c.m.c.s) of the mixed micelles have been determined over the entire χ range by means of…
Synthesis of Nanoferroics
2013
The Chapter covers the technological aspects of many chemical and physico-chemical nanofabrication methods relevant to making nanoferroic materials and composites. First, the classification of relevant synthesis methods of nanoferroics has been presented. Synthesis of particular nanoferroics with different chemical bonding like metallic, oxide and non-oxide compounds is considered in details. Among the methods, the mechanochemical, sonochemical, hydrothermal, co-precipitation, emulsion, thermal decomposition of unstable precursors have been analyzed. The competition between new phase nucleation and nuclei growth has been revealed to be controlled using feedback between reaction rate and tem…
Radikalpolymerisation von methylmethacrylat im gesamten umsatzbereich. Stationäre und instationäre experimente zur bestimmung von wachstums- und abbr…
1989
Free-radical polymerization of methyl methacrylate in bulk at 0°C over the full range of conversion is reported. Details for stationary and non-stationary experiments are described allowing to measure both kinetically relevant ratios fk/ka and kw/ka, f representing radical efficiency, kw rate constants of propagation and ka rate constant of termination. From these ratios the absolute rate constants kw and ka are available. The photochemical decay of the initiator 1,1′-azodicyclohexanenitrile in connection with the rotating-sector technique and observation of the post-effect after stopping the initiator decay were used. The rate of polymerization and the number- and weight-average molar mass…