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Different Oxygen Partial Pressures (different + oxygen_partial_pressure)

Distribution by Scientific Domains
Medical Sciences50%

Selected Abstracts

Is Helicobacter pylori a True Microaerophile?

HELICOBACTER, Issue 4 2006
Stephanie Bury-Moné
Abstract Background:, There is no general consensus about the specific oxygen and carbon dioxide requirements of the human pathogen Helicobacter pylori. This bacterium is considered a microaerophile and consequently, it is grown under atmospheres at oxygen tensions 5,19% and carbon dioxide tensions 5,10%, both for clinical and basic and applied research purposes. The current study compared the growth of H. pylori in vitro, under various gas atmospheres, and determined some specific changes in the physiology of bacteria grown under different oxygen partial pressures. Methods:, Measurements of bacterial growth under various conditions were carried out employing classical solid and liquid culture techniques. Enzymatic activities were measured using spectrophotometric assays. Results:,H. pylori and all the other Helicobacter spp. tested had an absolute requirement for elevated carbon dioxide concentrations in the growth atmosphere. In contrast with other Helicobacter spp., H. pylori can tolerate elevated oxygen tensions when grown at high bacterial concentrations. Under 5% CO2, the bacterium showed similar growth in liquid cultures under oxygen tensions from microaerobic (< 5%) to fully aerobic (21%) at cell densities higher than 5 × 105 cfu/ml for media supplemented with horse serum and 5 × 107 cfu/ml for media supplemented with ,-cyclodextrin. Evidence that changes occurred in the physiology of H. pylori was obtained by comparing the activities of ferredoxin:NADH (nicotinamide adenine dinucleotide) oxidoreductases of bacteria grown under microaerobic and aerobic atmospheres. Conclusions:,H. pylori is a capnophile able to grow equally well in vitro under microaerobic or aerobic conditions at high bacterial concentrations, and behaved like oxygen-sensitive microaerophiles at low cell densities. Some characteristics of H. pylori cells grown in vitro under microaerobic conditions appeared to mimic better the physiology of organisms grown in their natural niche in the human stomach. [source]

Influence of Ca content and oxygen partial pressure on microstructural evolution of (Co,Ca)O at elevated temperatures

JOURNAL OF MICROSCOPY, Issue 1 2006
J. KUSINSKI
Summary Ca-doped (1, 1.7, 5 and 10 mol% CaO) cobalt oxide single-crystal samples, with an [001] orientation, were annealed at elevated temperatures of 1000,1200 °C for different times and at different oxygen partial pressures. The microstructure was examined by means of transmission light and electron microscopy. High-temperature X-ray diffractometry was used, with the aim of determining the temperature of the CoO , Co3O4 transition in these materials. Extensive precipitation of Ca-free Co3O4 spinel crystals was observed with increasing Ca content and oxygen activity. It is suggested that the electrical conductivity changes in this material may be related to this precipitation, because it changes the electronic state of cobalt cations. [source]

Optical properties of NiCrOx thin films

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2008
Nora Dahmouchène
Abstract The optical properties of thin NiCrOx layers were investigated by spectroscopic ellipsometry (SE). The layers were coated on float glass by magnetron sputtering at different oxygen partial pressures (20% to 30% oxygen in the sputtering gas) and the influence of the degree of oxidation was considered in details. The optical constants of the films n and k, in the visible to near infrared spectral range (0.35 to 1.7 mm), appear to be extremely sensitive to their chemical composition. Complementary studies were carried out using Fourier transform infrared ellipsometry (FTIR-SE) to determine the optical conductivity of the films and compare it with four-points-probe measurements. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Oxygen Effects in Plasma Nitriding of Ferrous Alloys

PLASMA PROCESSES AND POLYMERS, Issue S1 2007
Carlos A. Figueroa
Abstract In this paper, we study the oxygen effect in low energy nitrogen implanted stainless steel AISI 316 at different oxygen partial pressures and temperatures. The samples were studied by photoemission electron spectroscopy (XPS) and sputtered neutral mass spectrometry (SNMS). Increasing the oxygen partial pressure during nitriding decreases the nitrogen content in the material depth. Surface oxidation induces phase segregation. The presence of oxygen forms CrO, on the top most layer of the sample and, subsequently, a nickel layer appears at approximately 9,10 nm beneath the surface. Moreover, the surface oxidation reaction of metal elements depends more strongly on the oxygen atoms landing on the surface rather than on the temperature process. At higher temperatures, on the other hand, the NO, species are degraded. [source]