Showing papers on "Oxygen published in 1975"

Overall reaction rates of NO and N2 formation from fuel nitrogen

Abstract: From measurements carried out on flat premixed hydrocarbon/oxygen argon (or helium) flames, into which small amounts of ammonia, or cyanogen are added, overall reaction rates of formation of NO and N2 are determined. From similar measurements effected on nitrogen-diluted ethylene/oxygen flames, an overall rate of prompt NO formation is obtained. The discussion of these rate constants indicates that the relative importance of HCN molecules as intermediates in the fuel NO mechanism increases according to the following sequence of primary fuel nitrogen compounds: ammonia, cyanogen and molecular nitrogen; this last is found to behave like a true fuel nitrogen compound in the early flame stages. Experimental values of the total yield of nitric oxide obtained from the added nitrogen compounds have been determined; they are found to be in good agreement with yields calculated by numerical integration of the empirical overall reaction rates of NO and N2 formation, showing almost the same dependence of the NO yield on temperature, initial fuel nitrogen concentration and oxygen concentration.

Refinement of the structure of beta-chitin.

Abstract: The structure of β-chitin has been refined by rigid-body least-squares methods, based on the intensity data for highly crystalline specimens from the pogonophore Oligobrachia ivanovi. The structure consists of an array of poly-N-acetyl-D-glucosamine chains all having the same sense, which are linked together in sheets by NH … OC hydrogen bonding of the amide groups. In addition to the O-3′H … O-5 intramolecular hydrogen bond, analogous to that in cellulose, the CH2OH side chain forms an intrasheet hydrogen bond to the carbonyl oxygen on the next chain. This structure shows considerably better agreement between observed and calculated intensities than that possessing an intersheet hydrogen bond, as had been proposed previously. The structure is consistent with the swelling properties of β-chitin and can also be seen to be analogous to that of native cellulose.

Oxygen diffusion in biological and artificial membranes determined by the fluorochrome pyrene.

Abstract: Quenching of pyrene fluorescence by oxygen was used to determine oxygen diffusion coefficients in phospholipid dispersions and erythrocyte plasma membranes. The fluorescence intensity and lifetime of pyrene in both artificial and natural membranes decreases about 80% in the presence of 1 atm O2, while the fluorescence excitation and emission spectra and the absorption spectrum are unaltered. Assuming the oxygen partition coefficient between membrane and aqueous phase to be 4.4, the diffusion coefficients for oxygen at 37 degrees C are 1.51 X 10(-5) cm2/s in dimyristoyl lecithin vesicles, 9.32 X 10(-6) cm2/s in dipalmitoyl lecithin vesicles, and 7.27 X 10(-6) cm2/s in erythrocyte plasma membranes. The heats of activation for oxygen diffusion are low (less than 3 kcal/degree-mol). A dramatic increase in the diffusion constant occurs at the phase transition of dimyristoyl and dipalmitoyl lecithin, which may result from an increase in either the oxygen diffusion coefficient, partition coefficient, or both. The significance of the change in oxygen diffusion below and above the phase transition for biological membranes is discussed.

The quenching of singlet oxygen by amino acids and proteins.

Abstract: — The physical quenching of singlet molecular oxygen (1Δg) by amino acids and proteins in D2O solution has been measured by their inhibition of the rate of singlet oxygen oxidation of the bilirubin anion. Steady-state singlet oxygen concentrations are produced by irradiating the oxygenated solution with the 1–06 μm output of a Nd-YAG laser, which absorbs directly in the electronic transition 1Δg+ 1v→3Σg-. The rate of quenching by most of the proteins studied is approximated by the sum of the quenching rates of their amino acids histidine, tryptophan and methionine, which implies that these amino acids in the protein structure are all about equally accessible to the singlet oxygen. The quenching constants differ from those obtained by the ruby-laser methylene-blue-photosensitized method of generating singlet oxygen, or from the results of steady-state methylene-blue-photosensitized oxidation, where singlet oxygen is assumed to be the main reactive species. The singlet oxygen quenching rates in D2O, pD 8, are (107? mol-1 s-1): alanine 0–2, methionine 3, tryptophan 9, histidine 17, carbonic anhydrase 85, lysozyme 150, superoxide dismutase 260, aposuperoxide dismutase 250.

Oxygen availability in polyethylene glycol solutions and its implications in plant-water relations.

Abstract: The solubility of O(2) in polyethylene glycol 4000 and 6000 solutions of varying concentrations was determined iodimetrically (titrimetrically) and electrochemically using a rotating glassy carbon electrode and a PAR Model 174 Polarograph. The titrimetric determination resulted in the formation of an unexpected precipitate at 2% (w/v) polyethylene glycol corresponding to the approximate critical micelle concentration of the two polyethylene glycol homologs. Beyond 5% polyethylene glycol, O(2) concentration was inversely proportional to polyethylene glycol concentration, and was higher in polyethylene glycol 4000 solutions than in polyethylene glycol 6000. The electrochemical data are a direct measure of O(2) transport to the electrode surface, rather than O(2) activity or concentration. Results indicate that even at relatively high H(2)O potentials, the transport of O(2) to the root surface might be insufficient to meet the plant's respiratory requirements.

Catalytic Decomposition of Nitric Oxide on Zirconia by Electrolytic Removal of Oxygen

Abstract: Zirconia stabilized with 8 mole per cent of scandia has a very high oxygen ion conductivity and can "pump" oxygen from oxygen‐bearing gases thus decomposing them In this study the rate of decomposition of the air‐pollutant species, nitric oxide, to harmless species (via the reaction: ) was found to be markedly catalyzed when a potential above 1V was applied across a zirconia disk coated with either a porous platinum or porous gold electrode It is known that platinum can both form oxides and catalyze the decomposition of ; whereas, gold does neither The catalytic decomposition of on platinum metal is inhibited by , such behavior being attributed to preferential chemisorption of over as well as the possible formation of an inhibiting platinum oxide surface The original rationale for this investigation was the possibility that the decomposition of might be enhanced if were electrolytically "pumped" away from a platinum electrode deposited on zirconia, keeping the platinum oxygen‐free However it was not anticipated that at high potentials dissociation rates a thousandfold that on nonporous platinum electrodes occur in the presence of either a platinum or gold porous electrode No reactivity at all was observed on a nonporous gold electrode These results suggest that catalysis occurs mainly on a surface other than the platinum or gold, namely, on the zirconia surface itself It is proposed that F‐centers on the zirconia surface formed by the applied potential are primarily responsible for the observed enhanced catalysis

Chemoreceptor reflexes in preterm infants: I. The effect of gestational and postnatal age on the ventilatory response to inhalation of 100% and 15% oxygen.

Abstract: We studied 16 "healthy" preterm infants (birthweight, 1,000 to 2,000 gm) 94 times during postnatal life to define the effect of gestational and postnatal age on the ventilatory response to 100% and 15% oxygen. They were given air, then 100% oxygen for two and five minutes respectively (No.=63) or 21%, 15% and then 21% oxygen for five minutes each (No.=31). We measured respiratory minute and tidal volumes, frequency, heart rate, and alveolar PCO2 and PO2. We used the magnitude of the immediate change in ventilation during during 100% and 15% oxygen breathing to test peripheral chemoreceptor function. The immediate decrease in ventilation with 100% oxygen and the immediate increase in ventilation with 15% oxygen were statistically similar at different gestational and postnatal ages. The late increase in ventilation (five minutes) with 100% oxygen was also similar at different ages. However, the late decrease in ventilation with 15% oxygen was not present at 18 days of age. These findings suggest that: (1) the peripheral chemo-receptors are active at least from 28 weeks of gestation and are probably not important in triggering periodic breathing or apnea in preterm infants, and (2) the preterm infant matures his response to hypoxia and is able to sustain hyperventilation with low oxygen by 18 days of age.

Oxygen tolerance of fresh clinical anaerobic bacteria.

Abstract: The oxygen tolerance and sensitivity of 57 freshly isolated anaerobic bacteria from clinical specimens was studied. All the organisms tolerated 8 h or more of exposure to oxygen in room air. Growth of the isolates in increasing oxygen concentrations demonstrated that the 57 isolates varied in oxygen sensitivity from strict to aerotolerant anaerobes. Comparison of the oxygen tolerance and sensitivity showed that the most tolerant organisms (best survival after prolonged exposure) included anaerobes capable of growth at only 0.4% or less O2 (strict) as well as those able to grow in as much as 10% O2. The least tolerant were predominately strict anaerobes. Decrease in the inoculum size from a concentration of 10(8) to 10(6) colony-forming units per ml had only a minor effect. The data indicate that the brief oxygen exposure with bench techniques in clinical laboratories would not be deleterious to the anaerobic bacteria present in clinical specimens.

Measurement of atomic oxygen and nitrogen oxides in jet-stirred combustion

Abstract: Direct spectroscopic measurement of continuum chemiluminescence at 3500 A, due presumably to the reaction CO+O→CO 2 + hv , was used to determine super-equilibrium atomic oxygen concentrations in situ for near-homogeneous, continuous-combustion of either carbon monoxide or methane with 133% theoretical air in a jet-stirred reactor operated near blowout, at atmospheric pressure. Reactor CO and NO x concentrations were measured by gas sampling. The motivation for this initial optical spectroscopic examination of the jet-stirred reactor was the elucidation of NO x formation in high-intensity, backmixed combustion. Measured gas temperatures were in the ranges T =1350 to 1500°K for carbon monoxide combustion, and T =1400° to 1800°K for methane combustion. Peak atom oxygen concentrations occurred just prior to reactor blowout. Partial equilibrium was indicated for the reactions CO+OH⇆CO 2 +H and O 2 +H⇆O+OH, at throughput rates sufficiently less than reactor blowout. Atomic oxygen measurements were used to compare NO x measurements with values predicted for plausible NO x kinetic formation mechanisms, considering only O, OH, and H as reaction radical intermediates. Agreement between the comparisons was obtained only for carbon monoxide combustion, indicating that nitrous oxide probably acts as an intermediate in NO x formation in the presence of super-equilibrium concentrations of atomic oxygen.

Untersuchungen an katalytisch aktiven oberflächenverbindungen. Herstellung und untersuchung von Vanadinoxid‐Phasen auf SiO2

Abstract: Es wird die Umsetzung der Oberflachen-Hydroxid-Gruppen des SiO2 (Aerosil-200, dehydratisiert und vorgetempert bei 600 bzw. 400°C) mit VOCl3 beschrieben nach Durch nachfolgende hydrolytische Abspaltung der restlichen Chloratome und anschliesende Temperung in Luft wird eine Vanadinoxid-Oberflachenphase auf SiO2 erhalten: Das Vanadin(V) liegt danach je nach den Reaktionsbedingungen in untersohiedlicher Koordination mit Sauerstoff vor. Durch Anlagerung von Substanzen wie H2O, Alkohol, NH3 usw. konnen niedrigkoordinierte Vanadinatome (tetraedrisch oder pyramidal) in oktaedrisch koordinierte ubergefuhrt werden. Die Untersuchungen erfolgten mit Hilfe der Thermowaage, chemischer Analyse, IR- und Reflexionsspektroskopie. Studies on Catalytically Active Surface Compounds. I. Preparation and Investigation of Vanadium Oxide Phases on Silica The reaction of surface hydroxide groups of silica (Aerosil-200, dehydrated and annealed at 600 or 400°C) with VOCl3 is described: By hydrolytic cleavage of the residual chlorine atoms and annealing in air a vanadium oxide surface phase on silica is formed: In dependence on the conditions of these reactions the vanadium(V) exists in different oxygen coordination states. By addition of substances like H2O, alcohol, NH3 etc. the low coordinated vanadium atoms (tetrahedral, pyramidal) are transformed to the octahedral coordinated form. The investigations were performed by means of thermobalance, chemical analysis, i. r. and reflection spectroscopy.

The potential of localized heating as a adjunct to radiation therapy.

Abstract: Experimental studies have shown that (a) tumor cells may be more sensitive to heat than normal cells; (b) hyperthermia inactivates cellular repair mechanisms for radiation damage; and (c) heat may lower the OER for ionizing radiation (anoxic cells are at least as sensitive to hyperthermia as oxygenated cells). Localized hyperthemia produced by localized current fields in the range of 100 kHz-10 MHz by direct contact electrodes offers two major advantages: the eletrode configurations may be manipulated to obtain desired thermal dose distributions, and, since the mode of heating is essentially instantaneous, accurate temperature control can be maintained during treatment.

Cerebral blood flow and oxygen consumption in the rat in hypoxic hypoxia.

Abstract: In order to measure cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRo2) at pronounced degrees of hypoxic hypoxia the Pao2 of artificially ventilated and normocapnic rats was reduced to between 47 and 22 mm Hg for 15–25 min with subsequent measurements of CBF, using a 133Xenon modification of the Kety and Schmidt technique, and of the arteriovenous difference in oxygen content, the venous blood being obtained from the superior sagittal sinus. When the Pao2 was reduced to minimal values of 22 mm Hg CBF increased 4- to 6-fold, the increase in CBF being unrelated to changes in blood pressure or Paco2. The CMRo2 remained unchanged at all levels of hypoxia. It is concluded that the maintenance of a normal, or near-normal, cerebral energy state even at extreme degrees of hypoxic hypoxia depends solely on a homeostatic increase in CBF.