The Occurrence of Oxygen

Central nervous tissue appears to provide an especially avid environment for the occurrence of oxygen-radical generation and lipid-peroxidative reactions due to a high content of polyunsaturated fatty acids. There is now considerable biochemical, physiological and pharmacological data that supports such a connection between radical reactions and secondary CNS tissue injury. 

Magnesium oxide may be expected to function as an active catalyst for CO2 utilization since CO2 is easily chemisorbed on MgO [1-3]. Most works so far reported on this adsorption system were carried out above the room temperature, and recent works have demonstrated the occurrence of oxygen isotope exchanges between adsorbed species and surface 0 [4-6]. However, dynamic behaviors of adsorbed species, especially below the room temperature, are still open to question. 

Chalcogen kal-k9-j9n [ISV chalk- bronze, ore (fr. Gk chalkos) + -gen from the occurrence of oxygen and sulfur in many ores] (ca. 1961) n. Any of the elements oxytgen, sulfur, selenium and tellurium. A member of group VIA in the periodic table. 

In this review we will consider anion-conductive fluorides and oxyfluorides because the occurrence of oxygen in these phases is an additional parameter that controls the defect structure of fluorite- and tysonite-like solid solutions by increasing the anion vacancies or... 

The naturally occurring isocoumarins are listed numerically in Tables 1 to 6. Their order is outlined in Sections I and II and is based on the occurrence of oxygen substituents at carbons 6 and 8, then upon the number of carbons in the substituents at C-3 and upon the oxidation level of the compound. 

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