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Abstract  

The effect of oxygen concentration on the melting of this eutectic was investigated by DSC. In the deoxygenized solution, an endothermic peak attributed to the eutectic transition was observed in the course of heating, and its peak temperature is around −21.5°C. Another endothermic peak appeared at lower temperature in the presence of oxygen. As the oxygen content in the solution increases, the temperature of this peak is shifted to lower temperature. The transition at the lower temperature are associated with the melting of eutectic carrying oxygen. The same results are given in the NMR data.

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Abstract  

Differential scanning calorimetry (DSC) and electron paramagnetic resonance spectroscopy (EPR, both conventional and saturation transfer EPR) were used to study the motional dynamics and segmental flexibility of myosin in muscle fibres in the presence of free radical generating system. Muscle fibre bundles isolated from psoas muscle of rabbit were spin-labelled with maleimide- and isothiocyanate-based probe molecules at the reactive sulfhydryl sites (Cys-707) of the motor domain. In the presence of hydroxyl free radicals the spectral intensity of the maleimide probe molecules decreased with time following a single exponential curve. MgADP and MgATP plus orthovanadate that produce flexibility changes in the multisubunit structure of myosin enhanced the reduction of the attached nitroxide molecules in free radical generating system. The analysis of the EPR spectra of spin-labelled and oriented fibres showed that the narrow distribution of spin labels changed in the presence of hydroxyl free radicals. Spectrum analysis by computer subtraction showed that short irradiation by UV light resulted in the enhancement of the ordered population at the expense of the disordered population. This suggests a transition of myosin heads from weak- binding state into strong-binding state. DSC measurements performed on calf cardiac myosin resulted in two main transitions at 49.4 and 54.1°C, respectively. Addition of MgADP produced a decrease of the 49.4°C transition, whereas a shift towards higher temperature was detected at the 54.1°C transition. It shows that there is an inter-site communication between the domains of the myosin. Hydroxyl free radicals induced further shifts of the transition temperatures and affected the width of the heat absorption curves.

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Abstract

The presented article deals with the assessment of combined impact of temperature and flow of oxidising atmosphere, its oxygen concentration and heat flux on the ignition time of isotactic polypropylene (PP). The ignition time was determined in a specially adapted hot air Setchkin furnace at temperatures (450 and 600 °C), density of heat flux (12.4 and 26.4 kW m−2), flows of oxidation mixture (6 and 8 L min−1) and volume oxygen concentrations (3, 9, 15, 21, 27, 33, 39, 45 and 50 %). Obtained data allows us to assume that the temperature influence on PP induction period of ignition increases with decreasing flow rate of oxidising atmosphere. At the flow of oxidising mixture equal to 6 L min−1 and temperature of 600 °C, oxygen concentration had only a negligible impact on the the induction period of ignition in the analysed period. From the presented results, the induction period of ignition depends on the temperature and also on the flow rate of oxidising mixture and oxygen concentration in it. In addition, heat flux has a significant influence on the induction period. However, the quantification of the heat flux influence was not possible with the applied experimental device.

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Abstract  

The influence of trace oxygen on the catalytic activity of alumina supported Ru in the liquid phase hydrogenation of aromatic hydrocarbons was studied. The catalytic activity of Ru increased remarkably and the reproducibility was improved by removing dissolved oxygen from the reactant mixture and carefully refining the catalyst transfer procedure into the reactor to avoid exposure to air. Trace oxygen affected Ru very severely, but did not affect Rh, Pd, and Pt much. The activity of Ru was lower than those of Rh, Pd, and Pt in the presence of oxygen as reported in the literature; however, it was the highest when oxygen was removed carefully. Measurements of the adsorbed oxygen suggested that the activity seriously decreased when only the part of Ru surface was covered by oxygen. Bimetallic Pt–Ru catalysts demonstrated high activity even in the presence of oxygen.

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Thermochemical and thermodynamical properties of HTSC phases are reviewed for the Y-Ba-Cu-O system and also presented for the newly calculated Bi-Sr-Cu-O system stressing out stoichiometric and phenomenological viewpoints. Simulated data are listed for (H 298 o-H o o, phase transformation temperatures, standard entropies, standard enthalpies of formation, heat capacities in crystalline phase, etc. Pseudobinary phase diagrams are treated showing the effect of oxygen partial pressure particularly illustrated on the (Sr, Bi, Ba)-Cu-O system.

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Abstract  

In this work the effect of oxygen pressure on the primary crystallisation fields for REBa2Cu3O7-x(RE=Nd, Sm, and Eu) has been studied. A DTA apparatus has been modified in order to carry out analyses under gas pressure, so the trend of temperatures of peritectic decomposition of the REBa2Cu3O7-xphases and of the eutectic equilibrium involving REBa2Cu3O7-x phases and flux mixture "Ba2Cu5O7" have been studied at oxygen pressures of 0.21, 1, and 10 atm. This showed that primary crystallisation fields spread at the increase of the oxygen pressure and allowed us to calculate the enthalpies of reactions of REBa2Cu3O7-xphases too.

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Abstract  

The process of oxygen chemisorption on coal in the temperature range ≈150–300 °C was studied under different experimental conditions using TG-DSC apparatus. As changing experimental conditions, oxygen flow (20 or 200 cm3 min−1), material of crucible (α-Al2O3 or Pt–Rh alloy), and initial sample mass (2–13 mg) were examined with respect to reliability and reproducibility of the parameters derived from TA curves. As parameters quantifying coal oxidation, temperatures of minimal T min and maximal T max sample mass, mass changes (mass loss W H below T min and mass increase W O above T min), heat evolution during oxygen chemisorption Q O (related to the coal mass increase), and kinetic parameters (activation energy E and frequency factor A) were evaluated. Values of T max, E, and A were found to lie in very close intervals independently on experimental conditions (95% confidence intervals were T max = 270.2 ± 0.7 °C, E = 81 ± 3 kJ mol−1, log10 A = 5.9 ± 0.3 s−1). Thus, these parameters can be used as actual characteristics of oxygen chemisorption stage of coal oxidation irrespective on conditions of TA measurements. Opposite, parameter Q O was confirmed to depend clearly on initial sample mass. The dependence is different for crucible materials used; however, it tends to the same value (≈50 kJ g−1) with increasing sample mass. Further, precision of values W H, W O, and T min determined from TG was found to be poor. This fact complicates evaluation of the effect of experimental conditions. Finally, the effect of oxygen flow on all above parameters was found to be negligible. Its influence (if any) was hidden by common experimental errors.

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2002 51 147 156 Ottow J.C.G. 1990. Effect of oxygen on bacterial denitrification (aerobic denitrification) Agrokémia és

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A rosszindulatú daganatokban gyakran ún. hypoxiás, csökkent oxigéntartalmú területek vannak (az oxigéntenzió < 7 Hgmm). A preklinikai, valamint klinikai vizsgálatok igazolták, hogy a hypoxia fokozza a tumorok progresszióját, agresszivitását. Szövettenyészeteken tanulmányozva az oxigén hatását, bebizonyosodott, hogy az oxigenizáció in vitro önmagában is gátolja az ép szövetek, a benignus és malignus tumorok sejtjeinek növekedését. Az onkoterápia szempontjából rendkívül fontos megállapítás, hogy ha egy daganatban az oxigén parciális nyomása kevesebb, mint 2,5 Hgmm, a sugárérzékenység lecsökken (intrinszik radiorezisztencia). Hypoxiás tumorokban számos kemoterápiás gyógyszer is hatástalan (kemorezisztencia). Oxigén hiányában vagy hypoxiás szövetekben a fotodinámiás kezelés is eredménytelennek bizonyult. Mindezen kísérleti és klinikai tapasztalatok alapján már évtizedek óta egyes intézetekben kiegészítő kezelésként, de egymagában is próbálkoznak a daganatos betegek oxigenizációjával. A leggyakoribb kezelési forma az oxigéngáz belélegeztetése (hiperbarikus oxigénterápia), vagy az oxigénnel telített víz alkalmazása fürdő vagy ivókúra formájában. A ma már nemzetközi kooperációban is végzett vizsgálatok egyértelműen igazolják az oxigénbevitel jótékony terápiás, radio- és kemoszenzitizáló hatását. Az általánosan alkalmazott eritropoietin-kezelés is bizonyítja az oxigenizáció jelentőségét a tumorterápiában. Időszerűnek látszik Magyarországon szakintézetekben nagy beteganyagon kivizsgálni az oxigenizáció tumorgátló, radio- és kemoszenzitizáló hatását.

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sicherheitstechnische Untersuchung der partiellen Autoxidation von Cyclohexan in Mikrostrukturen . PhD Thesis, Technical University of Chemnitz , 2011 ; (k) Jevtic, R. The Effect of Oxygen on the Oxidation of Cyclohexane . PhD Thesis, Washington University

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