Oxygen fractionation

Stable isotope analysis of Earth, Moon, and meteorite samples provides important information concerning the origin of the solar system. 8lsO values of terrestrial and lunar materials support the old idea that earth and moon are closely related. On the other hand three isotope plots for oxygen fractionation in certain meteoric inclusions are anomalous. They show unexpected isotope fractionations which are approximately mass independent. This observation, difficult to understand and initially thought to have important cosmological implications, has been resolved in a series of careful experimental and theoretical studies of isotope fractionation in unimolecular kinetic processes. This important geochemical problem is treated in some detail in Chapter 14. 

Fig. 14.5 Three isotope plots of oxygen fractionation in nitrate samples from different locations (After Thiemens, M., Ann. Rev. Earth Planet. Sci. 34, 217 (2006)). For these data, m, Equation 14.31, is 0.9. The expected mass dependent terrestrial fractionation is shown as the... 

The next series of numerical experiments was performed for the oxygen-dust mixtures with the values of governing parameters taken from Table 14.1. The dust concentration, initial turbulization, and the ignition duration were maintained constant pav = 0.21 kg/m , RMS = 1.4 m/s, to = 10 s. The results are shown in Table 14.4. It is seen that the increase of oxygen fraction in the oxidizer promotes the ignition and reduces the necessary ignition energy. 

Xenon is recovered from air by liquefaction and fractional distillation. Usually it is obtained as a by-product of making other noble gases. It is collected in the liquid oxygen fraction along with krypton, acetylene, and other hydrocarbons that may be present in air. The xenon fraction is flash vaporized. Hydrocarbons present are separated by burning over a catalyst. Xenon is absorbed on silica gel at low temperatures. Finally, it is separated from krypton by selective absorption and desorption from charcoal. 

The Nemst voltage En is shown as a function of the fuel utilisation Uf in a SOFC in Figure 2.4 with H2 as a fuel and with the system pressure p as a parameter. The excess air and the SOFC temperature are the fixed parameters. The range of practical interest between Uf = 0.1 and Uf = 0.9 can be well approximated with the model of the ideal gas. The dotted lines show the adaptation of the model for a high fuel utilisation. The amount of the water fraction and the decrement in the hydrogen and oxygen fraction within the SOFC reduces En between Uf = 0.1 and Uf = 0.9 by about more than 200 mV An increment of the system pressure from... 

Dissolved oxygen control by the adjustment of the oxygen fraction in the sparged gas. Its total flow rate is kept constant and corresponds to the sum of the two controlled gases QI and Q2. 

A common practice to study each citrus oil is to consider it as a binary synthetic mixture of its two more important components [4, 5, 6, 7]. For instance, the cold-pressed orange oil is usually treated as a mixture of limonene and linalool, representing the terpene and the oxygenated fractions, respectively. 

However, the mechanism through which this anomaly is sequestered inside the solids is not clear. It is postulated that, as the nebular disk evolved, this isotopically enriched ice migrates inward (and mixes with the isotopically normal water) and volatilizes in the inner nebula, driving gas-phase oxidation processes to form solids, during which the isotopic anomaly is passed to condensates (Yurimoto Kuramoto 2004). A major issue is that the silicate materials do not show the required level of heavy-oxygen fractionation, so another mass-independent mechanism is required. 

Here, AH is in kJ - kg , MW is the molecular mass of the monomer xmit, m is the numbOT of moles of products formed in the stoichiometrically complete combustion of the polymer, and m is the number of nitrogen moles in the Oj/Nj atmosphere, per 1 mol of monomer unit. LOI is given as molar oxygen fraction in the atmosphere. 

The number of oxygenated monoterpenoids is much higher than corresponding hydrocarbons but contrary to a hydrocarbon fraction in the oxygenated fraction of given essential oils usually only one or a few... 

Carothers, W.W., Adami, L.H. Rosenbauer, R.J. (1988) Experimental oxygen fractionation between siderite-water and phosphoric acid liberated CO2-siderite. Geochim. Cosmochim. Acta, 44, 323-332. 

Hendriks and colleagues tested several components of the volatile oil, obtained by steam distillation of Valeriana officinalis [L.], on mice. The essential oil, its hydrocarbon fraction, its oxygen fraction, valeranone, valerenal,... 

Citrus iyo peels (600 g) were treated similarly as above. The amount of volatile oils was 5.2 g (0.87% yield). The essential oil (4.0 g) was separated into a hydrocarbon fraction (3.4 g) and oxygenated fraction (0.24 g) by silica gel column chromatography. 

The quantity in parenthesis will be recognized as the average factor value while the denominator represents the half-range. We illusfrafe fhe use of the transform with an example. Suppose is the oxygen fraction (from 1 to 3%) and 2 is fhe furnace femperature (from 1450 to 1600°F). Then the transforms become x-i = ( 1 - 2%)/l%, Xi = ( 1 - 1525°F)/75°F, and fhe reader may easily verify fhaf fhe transform resulfs in factors of having a dimensionless range of 1. Wifh such coding, we shall show fhaf fhe solutions for the coefficients in Equation 3.1 are as follows ... 

The above mentioned studies showed that these actions are mainly due to the oxygenated fraction of the oil containing alcohols (mainly linalool and alpha-terpineol), corresponding esters and methyl chavicol, this last extracted from samples of Sardinian wild S. sclarea plants only. All these compounds, when administered separately, had a lesser effect than the essential oils in toto. These results suggest that the antiedematous effect is due to the synergistic action of the constituents of the essential oil. 

Classically, there are five causes of hypoxemia low inspired oxygen fraction (Fio ), increased diffusion barrier, hypoventilation, ventilation-perfusion (V/Q) mismatch, and shunt or venous admixture. 

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