Carbon availability

Calcium carbonate, available both from natural sources and as precipitated forms (see Calcium compounds), is most useful in coating because of purity and high brightness, ie, 90—95%. Ground carbonates from marble deposits have high purity levels as do the carbonates from some chalk deposits. 

Since sucdnoglycan synthesis commences after the growth phase there would be no carbon available for sucdnoglycan formation. 

The total carbon available for decarboxylation from 0.415 g Kevlar fabric sample [expressed as C.H.N0-4- mojeties in moles, i.e., 3.49 x... 

Both industry experience and research work indicate that postweld heat treatment (PWHT) of chromium-molybdenum steels in hydrogen service improves resistance to high temperature hydrogen attack. The PWHT stabilizes alloy carbides. This reduces the amount of carbon available to combine with hydrogen, thus improving high temperature hydrogen attack resistance. 

Environmental organic pollutants may be degraded depending on their toxicity, solubility, distribution constant Kow because physical properties of hydrophobic chemicals may affect the solubility and therefore the amount of organic carbon available in the aqueous phase for microbial assimilation and further metabolism (Schwarzenbach and Westall 1981). Chemicals are subject to volatilization and such loss is not assessed in most of the study except for physical transformation and material balance purposes. Polyaromatic hydrocarbons (PAHs) are known to volatilized during incubation even with capping and more then 40% of the initial chemicals could be found lost (Yin and Gu, unpublished data). When proper control was not included and such... 

Much confusion exists over the effects of sulfate concentration and carbon availability on rates of sulfate reduction (cf. 1, 4, 5, 72, 85, 106). Sulfate reducers in lake sediments exhibit low half-saturation constants for sulfate (10-70 xmol/L 4, 72, 78, 85) as well as for acetate and hydrogen (4, 13, 87). The low half-saturation constants allow them to outcompete methano-gens for these substrates until sulfate is largely consumed within pore waters (4, 90). Low concentrations of sulfate in lakes confine the zone of sulfate reduction to within a few centimeters of the sediment surface (e.g., 4, 90, 98). The comparability of rates of sulfate reduction in freshwater and marine... 

Relative rates of sulfate reduction and methanogenesis in lakes of varying trophic status are claimed to indicate that sulfate reduction rates are limited by the supply of sulfate (4, 5, 13). According to this hypothesis, at high rates of carbon sedimentation, rates of sulfate reduction are limited by rates of sulfate diffusion into sediments, and methanogenesis exceeds sulfate reduction. In less productive lakes, rates of sulfate diffusion should more nearly equal rates of formation of low-molecular-weight substrates, and sulfate reduction should account for a larger proportion of anaerobic carbon oxidation. Field data do not support this hypothesis (Table II). There is no relationship between trophic status, an index of carbon availability, and rates of anaerobic... 

The studies cited do not clarify what factors determine rates of sulfate reduction in lake sediments. The absence of seasonal trends in reduction rates suggests that temperature is not a limiting factor. Rates of sulfate reduction are not proportional to such crude estimates of carbon availability as sediment carbon content or carbon sedimentation rate, although net reduction and storage of reduced sulfur in sediments often does increase with increasing sediment carbon content. Measured rates of sulfate reduction are not proportional to lake sulfate concentrations, and the relative rates of sulfate reduction and methanogenesis in a variety of lakes do not indicate that sulfate diffusion becomes limiting in eutrophic lakes. Direct comparison of diffusion and reduction rates indicates that diffusion of sulfate into sediments cannot supply sulfate at the rates at which it is reduced. Neither hydrolysis of sulfate... 

Van Valen has posed the question, What can happen if photosynthesis is suddenly and drastically reduced Under such conditions, at a new steady state, production of oxygen and its consumption in the oxidation of carbon would be equal. But, before the new steady state occurs, would animals and decomposers use up much of the previously stored carbon in plants, thus creating a new loss of oxygen Several investigators have observed that even if all the carbon in all organisms now alive were oxidized, this would decrease the atmospheric concentration of oxygen by less than 0.1% of its present value. And, further, still less than 1% of the present oxygen concentration would be used if all the reduced carbon available in soils and lire like were reduced. 

Reasons for interest in the catalyzed reactions of NO, CO, and COz are many and varied. Nitric oxide, for example, is an odd electron, hetero-nuclear diatomic which is the parent member of the environmentally hazardous oxides of nitrogen. Its decomposition and reduction reactions, which occur only in the presence of catalysts, provide a stimulus to research in nitrosyl chemistry. From a different perspective, the catalyzed reactions of CO and COz have attracted attention because of the need to develop hydrocarbon sources that are alternatives to petroleum. Carbon dioxide is one of the most abundant sources of carbon available, but its utilization will require a cheap and plentiful source of hydrogen for reduction, and the development of catalysts that will permit reduction to take place under mild conditions. The use of carbon monoxide in the development of alternative hydrocarbon sources is better defined at this time, being directly linked to coal utilization. The conversion of coal to substitute natural gas (SNG), hydrocarbons, and organic chemicals is based on the hydrogen reduction of CO via methanation and the Fischer-Tropsch synthesis. Notable successes using heterogeneous catalysts have been achieved in this area, but most mechanistic proposals remain unproven, and overall efficiencies can still be improved. 

Carbon-centered electrophiles are compounds or intermediates which are electron poor and thus capable of accepting electrons from electron donors. To be an electron acceptor, an electrophile must have an unfilled orbital on carbon available for overlap with a filled orbital of the donor. Unfilled atomic p orbitals or antibonding orbitals (both a and it ) are the most common types of acceptor orbitals. The most common carbon electrophiles fall into four major categories ... 

In addition to the spectroscopic evidence, related observations support an aromatic hydrocarbon carrier as well. In planetary nebula, the fraction of the IR emitted in the 1310 cm-1 feature, which is by far the most intense of the bands, is strongly correlated with the amount of carbon available [15]. As the carriers must be produced under harsh conditions in planetary nebulae, they must be carbon-rich compounds which are extremely stable. Finally, although there is some variation among the relative band intensities, the bands are correlated, implying that a single class of chemical species is responsible [15]. 

Major complications arise because of bioturbation and the complex reaction kinetics of carbonates in deep sea sediments. These two factors will, to a large degree, determine the total amount of calcium carbonate available for neutralization of fossil fuel CO2 (e.g., see Broecker and Takahashi, 1977). 

To optimize the device volumetric capacitance density, once the DLC geometric parameters such as the cell size, the electrode thickness, and width have been fixed, the development efforts must be concentrated on the research of the carbon performance. Typical commercial carbons [18] have a capacitance density in the range of 50F/cm3. Their capacitance specific density is in the range of 100 F/g. Among the best-performing carbons available, there are those derived from metal carbide (carbide derived carbon [CDC]) [19,20], They may reach a capacitance density of 130-140F/g. At that point, to avoid confusion, it is worth mentioning the difference between carbon or electrode capacitance and DLC capacitance. The later is exactly four times smaller because of the series connection of two electrodes whose volume is half of the total electrode volume. 

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