Showing papers on "Oxygen published in 1972"

An improved cathode for the measurement of photosynthetic oxygen evolution by isolated chloroplasts

Abstract: Summary The construction, operation and calibration of an improved form of a Clark oxygen electrode are described in detail The electrode shows a rapid response (1–5 seconds) to change in oxygen concentration and is capable of measuring rates of oxygen evolution (or uptake) of up to 4 μmoles oxygen per minute The use of a pair of electrodes to measure the oxygen evolution of choloroplasts at high intensity of illumination is described

Aerobic decomposition of sediment and detritus as a function of particle surface area and organic content

Abstract: Oxygen uptake by microbial populations on mud, sand, and various types of detritus was measured in short-term experiments in aerated water at 20C Sample size had no effect on oxygen consumption per unit weight, but stirring increased uptake A 2% Formalin solution completely stopped biological uptake of oxygen by microorganisms on sand and detritus; lake muds showed various degrees of chemical uptake of oxygen Microorganisms on dead Phragmites leaves consumed oxygen at an increasing rate during the first few days of decomposition, followed by a decline to a rate comparable to uptake by freshly collected detritus Limnaea feces initially consumed oxygen three times more rapidly than detritus, but after 5 days the rates were equal Detritus consumed up to three orders of magnitude more oxygen per dry weight than sand; uptake rates were inversely related to particle diameter The logarithm of oxygen uptake was directly related to the logarithm of particle organic content Particulate oxygen uptake in this and previous studies fell between 01 and 10 mg O2 (g organic matter)−1 hr−1, a rate inversely related to particle diameter Oxygen uptake per unit weight by particles of ashed mud and sand exposed for 24 hr to decomposing detritus in a nutrient solution and transferred to fresh solution was inversely related to particle size and similar to rates measured with freshly collected samples On an areal basis all particles consumed between 001 and 10 × 10−3 mg O2 cm−1 hr−1 The negative linear correlation on logarithmic axes of surface area, organic carbon and nitrogen and bacterial plate counts with sediment particle size is similar to that observed for measures of oxygen uptake Bacteria cover only a few percent of particle surfaces This may result in the narrow range of measures of microbial community respiration on an areal basis

Absorption Spectrum and Reaction Kinetics of the HO2 Radical in the Gas Phase

Abstract: HO2 radicals were produced in the gas phase by flash photolysis of water vapor (3%) in an atmosphere of hydrogen, helium, or argon containing ∼ 2% oxygen. Water is dissociated in the first continuum to H and OH, and O2 converts the H atoms to HO2. Hydrogen nearly doubles the amount of HO2 produced by converting OH to H. The absorption spectrum of HO2 is a broad band with a peak at 2050 A. The molar extinction coefficient, emax, based on measurement of the H2O2 formed in the hydrogen system, is 1770 ± 150 M−1· cm−1. The rate constant for the bimolecular combination reaction, HO2+HO2 → H2O2 + O2, was evaluated as 5.7 ± 0.5 × 109 M−1· sec−1 at 298°K and for the reaction HO2+OH→ H2O+O2, k = 1.2 ± 0.2 × 1011M−1. sec−1. From auxiliary measurements of the rate of O3 formation it was also found that, in the flash photolysis of O2 (2%) in H2, hot O atoms react with H2 to form OH and H which are then converted to HO2.

Further studies on the generation of hydrogen peroxide by 6-hydroxydopamine. Potentiation by ascorbic acid.

Abstract: We studied the inhibitory action of various compounds, including hydrogen peroxide, on the uptake of [3H]dopamine by rat brain slices. Dialuric acid, 6-hydroxydopamine, and 5-hydroxydopamine consumed oxygen and generated hydrogen peroxide in solution as a result of aerobic oxidation, as measured with an oxygen electrode. The regeneration by catalase of half the oxygen consumed by 6-hydroxydopamine confirmed that oxygen consumption was equal to H202 production. The rate of oxygen uptake (H202 production by dialuric acid or 6-hydroxydopamine was augmented by the addition of ascorbic acid. In addition, alloxan, which is the oxidized form of dialuric acid, consumed oxygen when ascorbate was added. The mechanism for this can be envisaged as reduction of the oxidized compounds by ascorbate, followed by reoxidation to form more H202, with continuous recycling. Concomitant with increased production of H202, there was increased inhibition of [3H]dopamine uptake. Ascorbate by itself did not inhibit the uptake of [3H]dopamine and did not produce measurable quantities of H202. 6-Hydroxydopamine, a compound that causes nerve terminal degeneration in vivo, was compared with 5-hydroxydopamine, which does not. As both compounds are structural analogues of dopamine, they can inhibit the uptake of [3H]dopamine into brain slices by competing for the uptake mechanisms. Additionally, both may inhibit uptake irreversibly by generating H2O2, which causes oxidative damage. 6-Hydroxydopamine produced H202 at about 12 times the rate yielded by 5-hydroxydopamine. Ascorbate potentiated H2O2 production by 6-hydroxydopamine but suppressed that from 5-hydroxydopamine. These findings are consistent with an important role for H2O2 in the 6-hydroxydopamine-induced degeneration of nerve terminals and may explain why 5-hydroxydopamine does not produce degenerative changes.

The effect of activity on oxygen consumption, oxygen debt, and heart rate in the lizards Varanus gouldii and sauromalus hispidus

Abstract: Oxygen consumption and heart rate were measured during rest and activity in the lizardsVaranus gouldii andSauromalus hispidus. Oxygen debt was calculated from postactive oxygen consumption. Standard metabolic rates of the two animals are similar butVaranus consumes much more oxygen during activity than doesSauromalus (Fig. 1–3). The latter has a constant active metabolic rate above 30 ° C and accumulates a large oxygen debt, which is repayed slowly (Fig. 4).Varanus recovers rapidly from activity (Fig. 5), presumably because of the smaller lactacid debt incurred. Heart rate increment inSauromalus is high (Fig. 8). This variable cannot be responsible for the limitation of active oxygen consumption; calculations of oxygen pulse suggest that an inability to increase A-V difference and/or stroke volume are implicated (Fig. 9).Varanus have evolved mechanisms to sustain high levels of oxygen consumption superior to those of other reptiles investigated. The role of anaerobiosis in the biology of both animals is discussed.

Oxygen supply in healing tissue

Abstract: Three different methods were used for measuring the oxygen tension in healing tissue. Average extracellular wound oxygen tension and its response to systemic hyperoxia and hypoxia were recorded in rats by using perfused Teflon tonometer coils 50 cm long within cylindrical sponge granulomas implanted subcutaneously. Dead space pO 2 and its variations with changing ambient pO 2 were determined. In the second method, intercapillary oxygen gradients and tissue oxygen tensions in various parts of the connective tissue capsule surrounding subcutaneous sponge implants were determined with ultramicro oxygen electrodes under visual control. The effects of oxygen breathing on tissue oxygen gradients were also recorded. In the third part of the study measurements were made with ultra-micro electrodes of the oxygen microclimate during healing in rabbit ear chambers. The dead space pO 2 varied between 0 and 3 mm Hg. Fibroblast proliferation appeared to be greatest in the zone where pO 2 was between 20 and 30 mm Hg. Collagen accumulation appeared in a region of slightly higher oxygen tension. The growing edge of granulation tissue contained cells similar to macrophages and the pO 2 in this zone was 5 to 15 mm Hg. Breathing of pure oxygen greatly increased the intercapillary oxygen gradients in the vicinity of the advancing capillary arcade. Measurements during exposure to oxygen suggest that the demand for oxygen in the area of collagen formation is less than that in the zone of active fibroblast proliferation.

On the Mechanism of Low‐Temperature Oxidation (23°–450°C) of Polycrystalline Nickel

Abstract: The oxidation of "clean" nickel has been investigated from 24° to 450°C at oxygen pressures of . Ultra‐high vacuum techniques made it possible to start oxidation on specimens free of oxide and surface impurities such as C, Si, and S. Oxygen uptake was measured manometrically with a capacitance gauge of submonolayer sensitivity. Initial rapid oxygen adsorption (and place exchange) on nickel was followed by slower oxidation obeying a logarithmic rate law over the thickness range 8–30Aa. Growth of thicker films was in accord with a parabolic rate law, transport through the oxide occurring predominantly via easy diffusion paths. The value of 41 kcal·mole−1 calculated from an Arrhenius plot of the parabolic rate constants from 300° to 450°C is an approximate measure of the activation energy for growth via leakage paths. A p1/6 dependence of the parabolic growth rate on oxygen pressure was found at 450°C.

Preparation in a hydrogen-oxygen flame of ultrafine metal oxide particles. Oxidative properties toward hydrocarbons in the presence of ultraviolet radiation

Abstract: Divided metal oxides (Al 2 O 3 , Fe 2 O 3 , GeO 2 , SiO 2 , TiO 2 , V 2 O 5 , ZrO 2 ) are prepared by carrying vapor of metal chloride into the flame of an oxygen-hydrogen burner. Collected oxide particles do not have internal porosity and exhibit a nearly constant diameter in the range of 100–2000 A. The geometry of these particles and their crystalline structure depend on the flame temperature, the flow rate of carrier gas, and the linear velocity of the chloride vapor in the burner. Binary, ternary, or doped oxides may also be prepared by this method from the appropriate mixture of metal chlorides. Oxygen at 25°C is adsorbed on some oxides, in particular on TiO 2 , in the presence of uv radiation, as a labile species O 2 − which reacts with paraffins, olefins, CO, SO 2 , and NO, under irradiation, to give products of partial or total oxidation. The registered quantum yield is equal to one for wavelengths not exceeding 3400 A. The reactivity of O 2 − species toward isobutane is investigated by ESR for different wavelengths.

Oxidation-reduction potentials, oxygen concentration and oxygen uptake of profundal sediments in a eutrophic lake

Abstract: Oxidation-reduction potentials were measured with a 1-mm platinum electrode in undisturbed sediment cores and re-settled mud from Lake Esrom, Denmark. Slow stabilization of Eh potentials occurred at the aerobic-anaerobic interface. Seasonal changes in Eh profiles in profundal sediments only occurred in the upper 1 cm during summer stratification. When oxygen disappeared, reducing conditions reached the sediment surface. In artificial mud-water systems, no measurable oxygen occurred when Eh values in either sediment, or water, or both, fell below +100 mv. Oxygen uptake by mud taken from various depths of sediment cores was inversely related to Eh potential. Eh and the square root of oxygen uptake by subsurface mud during aeration showed a similar inverse proportionality, suggesting that intensity and capacity of oxygen consumption are related. Formalin addition reduced oxygen uptake by sediment from the surface of undisturbed cores by 80 per cent. Below 1 cm all oxygen was consumed by chemical processes. Eh potential may index both the intensity and capacity of such reactions.

Investigation of Surface Topography of Oxygen on Nickel Single Crystals by Helium Ion Backscattering

Abstract: In an experiment which combines low energy noble gas ion backscattering with LEED the sorption of oxygen on the (110) face of a nickel single crystal is investigated. The energy of the backscattered He+ ions is governed by binary collisions whereas the intensity of the spectrum is given by the cross sections, the concentration of surface atoms, the neutralization probabilities and the geometry. The spectra obtained by varying the angle of incidence relative to the surface and the crystal orientation, can be explained by the assumption that in the case of the (2×1) structure every second place in the top [110] rows of Ni is occupied by an oxygen atom. From a shadow effect observed at small angles of incidence it can be estimated that the adsorbed oxygen protrudes beyond the plane of the Ni atoms by about 0.4–0.8 A.

Soil physical conditions affecting seedling root growth

Abstract: The lengths, fresh weights, and dry weights of pea seedling roots grown for 48 hours in loose-soil columns were progressively less as oxygen partial pressures of the soil atmosphere varied from 0.16 to 0 atm. The roots were thicker at intermediate oxygen levels than in either 0 or 0.21 atm oxygen. The number of vacuolated cells per root were the same in 0.21 and 0.08 atm oxygen indicating that rate of cell division was the same. Therefore over this range decrease in cell elongation and increased cell breadth were responsible for the shorter, thicker roots. Rate of cell division was reduced at 0.03 atm oxygen. The utilisation of the seedling metabolite decreased from 0.10 to 0.03 atm oxygen and the hyperbolic relationship for oxygen uptake by excised pea roots suggests a causal relationship between growth, cell development, and oxygen availability. On this assumption pea root elongation was calibrated at different mechanical impedance and oxygen levels in order to predict the oxygen concentration at the surface of pea roots growing in poorly aerated soils.

Detection of Molecular Oxygen on Mars

Abstract: Molecular oxygen was detected in Martian spectra near 7635 A and its abundance was measured both during and after the 1971 dust storm. Its column abundance in the clear Martian atmosphere is about 10.4 plus or minus 1.0 cm/amagat, giving a mixing ratio of molecular oxygen to carbon dioxide 0.0013. The mixing ratio of molecular oxygen to carbon monoxide (1.4 plus or minus 0.3) is quite different from the value of 0.5 that would result from the photolysis of a pure carbon dioxide atmosphere, which indicates that there is or was a net source of oxygen relative to carbon (probably water) in the Martian atmosphere.

Diffusivity and solubility of oxygen in platinum and Pt-Ni alloys

Abstract: The diffusivity and solubility of oxygen in metal specimens were determined from measurements of permeation through thin wall tubes containing oxygen and heated by electrical resistance. The permeating oxygen desorbed in vacuum as monoatomic oxygen and the flux was monitored mass-spectrometrically. A known helium leak rate and experimentally-determined sensitivities of the two gases were used for flow calibration. The diffusion coefficient of oxygen in pure platinum, calculated from the time lag to reach a steady state flux, is: {fx065-01} in the temperature range of 1435∮ to 1504°. The solubility of oxygen in pure platinum was obtained from the steady-state flux using the previously determined diffusivity. The solubility is proportional to p1/2O2 and at 1 atm of oxygen the solubility is: CsO = (0.2 ± 0.1) × 1012 exp {fx065-02}, wt pct. Small amounts of nickel, less than required for internal oxidation, had a negligible effect on the oxygen solubility and diffusivity in platinum alloys.

Mariner 6 and 7 Ultraviolet Spectrometer Experiment: Analysis of the O I 1304‐ and 1356‐A emissions

Abstract: Analysis of the O I 1304- and 1356-A data from Mariner 6 and 7, and estimation of the atomic oxygen concentration of the Martian atmosphere. Derived values of the parameters describing the sources of excitation differ considerably from previous estimates. A detailed statistical treatment is used in the analysis. At an exospheric temperature of 350 K the atomic oxygen concentration at 135 km is estimated to be between 0.5 and 1%. The likely source of the 1304-A intensity is resonance scattering of solar 1304-A photons. For the 1356-A emission, the likely source is photodissociation of CO2. There is an indication of a diurnal variation of the Martian upper atmosphere.

Kinetics of Thermal Growth of Ultra‐Thin Layers of SiO2 on Silicon Part II . Theory

Abstract: The thermally activated growth of oxide on silicon as a function of time obeys a linear‐parabolic relationship, the linear part of which stems from interface limited reactions. In Part I of this paper, it has been reported that this linear part cannot result from a single rate‐limiting reaction step, because the order of the over‐all reaction rate differs for different substrate orientations at a fixed temperature and varies for a given orientation as a function of temperature. A kinetic model for the reaction between silicon and oxygen at the interface is now presented to account for the experimental data . Two parallel, competing reactions are postulated to occur. In the first of these, molecular oxygen reacts directly with silicon to form silicon dioxide and atomic oxygen; the second reaction involves the dissociation of O2. The atomic oxygen thus formed, may either react with silicon or recombine to molecular oxygen. An analysis of the data shows that a difference in the activation energies (i.e., 1.91 vs. 0.58 eV) associated with these competing reaction steps is responsible for the shift in their relative importance as a function of temperature.

Oxidation of SO 2 and Other Atmospheric Gases by Ozone in Aqueous Solution

Abstract: THE oxidation of atmospheric gases to form aerosols is an important part of atmospheric chemistry. For many years it has been claimed that most of the SO2 is oxidized in droplets which are present in clouds and fogs1,2. Calculations of the extent of this process have always been made assuming that oxygen is the oxidizing agent3; oxidation by ozone dissolved in the droplets has not been considered quantitatively because the rates have been unknown. Ozone is formed by photolysis of oxygen in the stratosphere and diffuses down through the troposphere to be destroyed at the Earth's surface. Its concentration at cloud-forming levels is several times greater than pollutant gases such as SO2 and NO2. It is known that ozone reacts rapidly with many ions in solution4,5 but rate constants have not been determined.