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Pure Oxygen (pure + oxygen)
Selected AbstractsThe changes in neuromuscular excitability with normobaric hyperoxia in humansEXPERIMENTAL PHYSIOLOGY, Issue 1 2010Christelle Brerro-Saby Based on previous observations in hyperbaric hyperoxia, we hypothesized that normobaric hyperoxia, often used during general anaesthesia and resuscitation, might also induce a neuromuscular excitability. In heathy volunteers, we studied the consequences of a 50 min period of pure oxygen breathing on the neuromuscular conduction time (CT), the amplitude of the compound evoked muscle potential (M-wave), the latency and amplitude of the Hoffman reflex (H reflex) and the electromyographic tonic vibratory response (TVR) of the flexor digitorum superficialis muscle to explore the proprioceptive reflex loop. Hyperoxia-induced oxidative stress was measured by the changes in blood markers of lipid peroxidation (thiobarbituric acid reactive substances, TBARS) and antioxidant response (reduced ascorbic acid, RAA). During hyperoxia, the M-wave amplitude increased, both CT and H reflex latency were shortened, and the H reflex amplitude increased. By contrast, TVR significantly decreased. Concomitantly, an oxidative stress was assessed by increased TBARS and decreased RAA levels. This study shows the existence of dual effects of hyperoxia, which facilitates the muscle membrane excitability, nerve conduction and spinal reflexes, but reduces the gain of the proprioceptive reflex loop. The activation of the group IV muscle afferents by hyperoxia and the resulting oxidative stress might explain the TVR depression. [source] Accelerated ageing of polypropylene stabilized by phenolic antioxidants under high oxygen pressureJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Emmanuel Richaud Abstract Polypropylene (PP) samples stabilized by a hindered phenol (Irganox 1010) were submitted to thermal ageing at 80°C in air at atmospheric pressure or in pure oxygen at 5.0 MPa pressure. Both the polymer oxidation and the stabilizer consumption were monitored by Infrared spectrometry and thermal analysis. The stabilizer efficiency, as assessed by the ratio induction time/stabilizer concentration is almost constant at atmospheric pressure even when the stabilizer concentration is higher than its solubility limit in PP (0.4% or 24 × 10,3 mol L,1). In contrast, at high pressure, the efficiency decreases almost hyperbolically with the stabilizer concentration when this latter is higher than 6.0 × 10,3 mol L,1. The results indicate the existence of a direct phenol-oxygen reaction negligible at low oxygen pressure but significant at 5.0 MPa pressure. The reality of this reaction has been proved on the basis of a study of the thermal oxidation of a phenol solution in a nonoxidizable solvent. A kinetic model of PP oxidation in which stabilization involves three reactions has been proposed. It simulates correctly the effect of oxygen pressure and stabilizer concentration on carbonyl build-up and stabilizer consumption. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Modeling of air separation in a LSCF hollow-fiber membrane moduleAICHE JOURNAL, Issue 7 2002Xiaoyao Tan Mixed ion-conducting ceramic membranes are promising in oxygen separation from air due to their infinite permselectivity. Hollow-fiber-shaped membranes can provide a high surface area for such an application. A mathematical model for a hollow-fiber La0.6Sr0.4Co0.2F0.8O3,,(LSCF) membrane module for air separation was developed and a performance of the module at various operating conditions was studied theoretically. The simulation results reveal that the cocurrent is a better operating flow pattern than the countercurrent flow pattern. The vacuum operation on the lumen side of the membrane module is preferable to the elevated pressure operation on the shell side for achieving high oxygen productivity. A high vacuum level and a desired membrane area are essential to produce the pure oxygen and nitrogen simultaneously. Experimental results and kinetic parameters in the literature obtained from the LSCF membrane for air separation agreed satisfactorily with the theoretical solutions. [source] Imaging the changes in renal T1 induced by the inhalation of pure oxygen: A feasibility studyMAGNETIC RESONANCE IN MEDICINE, Issue 4 2002Richard A. Jones Abstract The effect of the inhalation of pure oxygen on the kidney was evaluated by measuring monoexponential T1 and T relaxation times in nine volunteers using a multiple-shot turbo spin echo and multiple echo gradient echo sequences, respectively. The T1 of the renal cortex decreased significantly when breathing pure oxygen as compared to normoxia (from 882 ± 59 to 829 ± 70 msec, P < 0.05), while that of the renal medulla was unchanged. No significant changes were seen in the T of either compartment. Dynamic imaging using an inversion recovery sequence with an optimized inversion time typically produced signal changes of 20% in the renal cortex. Studies to assess if oxygen-induced changes in flow contributed to this effect showed that the flow contribution was not significant. Although longer inversion times (880 ms) produced optimal contrast, acceptable contrast was also obtained at shorter inversion times (450 msec) in the renal cortex, spleen, and lung, with the latter being of opposite polarity to the other two tissues, implying a shorter parenchymal T1 than previously reported in the literature. The results are consistent with oxygen acting as an intravascular contrast agent which induces a shortening of T1 in the arterial blood volume. Magn Reson Med 47:728,735, 2002. © 2002 Wiley-Liss, Inc. [source] Effect of carbide volume fraction on the oxidation of austenitic Fe-Cr-C alloysMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 6 2006L. B. Susanto Abstract A series of Fe-15Cr-(2-3)Mo alloys (compositions in weight percent) was produced with different carbon concentrations, to control the distribution of chromium between matrix metal and M23C6 precipitates. The alloys were oxidized in the austenitic state at 850°C in pure oxygen, with and without a pre-oxidation treatment at low oxygen potential, where no iron oxide could form. Protective, chromia-rich scaling took place if the chromium concentration at the metal-scale interface was high enough. This concentration was controlled by the original alloy matrix chromium concentration, and whether or not a high diffusivity ferrite zone developed at the surface by decarburization. Ferrite zone formation was assisted by pre-oxidation at low oxygen potentials. The value of the carbides as suppliers of additional chromium was demonstrated by comparison with the oxidation performance of carbide-free alloys of corresponding matrix chromium levels. However, because dissolution of the coarse carbides could be slow, alloys with high volume fractions of large carbides were unsuccessful. [source] Preparation of ZnO thin film by the sol,gel method using low temperature ozone oxidationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2010Takashi Ehara Abstract Zinc oxide thin films have been prepared by the sol,gel method from a 2-methoxyethanol solution of zinc acetate dihydrate on SiO2 substrates using air, pure oxygen, and 1% ozone in oxygen as oxygen source. In the cases where air or oxygen was used as the oxygen source for thermal annealing, samples annealed at 600 to 800,°C exhibit a (0002) peak in X-ray diffraction (XRD). A sample annealed at 700,°C exhibited the highest (0002) peak intensity in conventional thermal annealing. However, the case using 1% ozone in oxygen as the atmosphere presented different results. A sample treated in 1% ozone at 100,°C had peak intensity in XRD (0002) comparable with samples annealed at several hundreds of degree in air or oxygen. This result indicates that the high oxidation efficiency of ozone is useful in decreasing the processing temperature of the sol,gel method. [source] Fed-Batch Cultivation of Saccharomyces cerevisiae in a Hyperbaric BioreactorBIOTECHNOLOGY PROGRESS, Issue 2 2003I. Belo Fed-batch is the dominating mode of operation in high-cell-density cultures of Saccharomyces cerevisaein processes such as the production of bakerapos;s yeast and recombinant proteins, where the high oxygen demand of these cultures makes its supply an important and difficult task. The aim of this work was to study the use of hyperbaric air for oxygen mass transfer improvement on S. cerevisiaefed-batch cultivation. The effects of increased air pressure up to 1.5 MPa on cell behavior were investigated. The effects of oxygen and carbon dioxide were dissociated from the effects of total pressure by the use of pure oxygen and gas mixtures enriched with CO2. Fed-batch experiments were performed in a stirred tank reactor with a 600 mL stainless steel vessel. An exponential feeding profile at dilution rates up to 0.1 h,1 was used in order to ensure a subcritical flux of substrate and, consequently, to prevent ethanol formation due to glucose excess. The ethanol production observed at atmospheric pressure was reduced by the bioreactor pressurization up to 1.0 MPa. The maximum biomass yield, 0.5 g g,1 (cell mass produced per mass of glucose consumed) was attained whenever pressure was increased gradually through time. This demonstrates the adaptive behavior of the cells to the hyperbaric conditions. This work proved that hyperbaric air up to 1.0 MPa (0.2 MPa of oxygen partial pressure) could be applied to S. cerevisiaecultivation under low glucose flux. Above that critical oxygen partial pressure value, i.e., for oxygen pressures of 0.32 and 0.5 MPa, a drastic cell growth inhibition and viability loss were observed. The increase of carbon dioxide partial pressure in the gas mixture up to 48 kPa slightly decreased the overall cell mass yield but had negligible effects on cell viability. [source] Postural stability before and after hyperbaric oxygen treatmentACTA NEUROLOGICA SCANDINAVICA, Issue 6 2005M. F. Tvede Objective,,, The purpose of this study was to determine the effect of hyperbaric oxygenation (HBO) on postural stability in healthy volunteers. The study was performed in accordance with treatment protocols for divers' decompression sickness and carbon monoxide poisoning. Methods,,, Twenty-one healthy male divers, aged 31 ± 6.88 years (mean ± SD), were tested with quantitative Romberg's test before and after HBO (90 min in a pressure chamber at an ambient pressure of 253 kPa, ,15 m of sea water, breathing pure oxygen). The quantitative Romberg's test is a calculation of the average sway for 50 s. Results,,, No difference was found between sway before and after the HBO (P < 0.05), i.e. we were unable to show that the results of quantitative Romberg's test are affected by HBO. Thus, the quantitative Romberg's test may be a valuable tool in evaluating patients with decompressions sickness, carbon monoxide intoxication and other neurological diseases normally treated with HBO. [source] Catalytic Liquid Phase Oxidation of Toluene to Benzoic AcidCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 3 2008A. Gizli Abstract The production of benzoic acid from toluene in the liquid phase with pure oxygen was studied. Investigations have been carried out with a view to determining the most suitable reaction conditions with respect to operating variables including oxygen flow rate, reaction temperature, batch time and catalyst loading. In a series of batch experiments carried out at 4,atm, the optimum values of mole ratio of oxygen to toluene, temperature, reaction time, and catalyst loading were found to be 2, 157,°C, 2,h and 0.57,g/L, respectively. In addition, a kinetic study was carried out by taking into consideration the optimum reaction conditions. The model dependent on the formation of benzyl radical was found to be feasible for describing the catalytic oxidation of toluene to benzoic acid in the liquid phase. The activation energy was determined as 40,kJ/mol. 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