Accretion reactions

Barsanti, K. C., and Pankow, J. F. (2004) Thermodynamics of the formation of atmospheric organic particulate matter by accretion reactions—Part 1 Aldehydes and ketones, Atmos. Environ. 38, 4371-4382. 

Important is a very first adsorption or attachment of organic matter to allow the partitioning to occur. As described in the previous section this may work by reactive attachment, either of radicals or via for instance catalysed reactions. This was postulated to happen by accretion reactions, i.e. reactive attachment of different types of organic compounds. However, Barsanti and Pankow (2004) found only a minor effect for accretion reactions of rather stable oxidation products. Therefore, these contributions are of minor importance. 

In fact, the sun is not a first-generation main-sequence star since spectroscopic evidence shows the presence of many heavier elements thought to be formed in other types of stars and subsequently distributed throughout the galaxy for eventual accretion into later generations of main-sequence stars. In the presence of heavier elements, particularly carbon and nitrogen, a catalytic sequence of nuclear reactions aids the fusion of protons to helium (H. A. Bethe... 

Inputs + Sources = Outputs + Sinks + Accumulations where each of these terms may be a quantity or a rate. Inputs and Outputs are accomplished by crossing the boundary of the reference volume. In case of mass transfer this occurs by bulk flow and diffusion. Sources and Sinks are accretions and depletions of a species without crossing the boundaries. In a mass and energy balance, sinks are the rate of reaction, rdVr, or a rate of enthalpy change, AHrpdC. Accumulation is the time derivative of the content of the species within the reference volume, for example, (<9C/3t)dVr or... 

The interaction of mass transfer, gravitational wave backreaction and the reaction of the neutron star radius to the mass loss leads to a very complicated accretion dynamics in a neutron star black hole system. We find in all of our simulations (apart from an extreme test case with mass ratio q = 0.93, i.e. a... 

In addition to the physiological reaction of N2 reduction, nitrogenase catalyzes a wide variety of reactions involving small unsaturated molecules(56). Table III lists key reactants and products for FeMo nltrogenases. All substrate reductions involve minimally the transfer of two electrons. Multielectron substrate reductions may involve the accretion of such two-electron... 

We, therefore, examine the effects of the NCO reaction on the evolution of low mass stars. A key ingredient of the NCO reaction is that the density reaches the threshold for e-capture (Pth 9 cm 8). Evolutionary sequences are presented for the cases of accreting helium white dwarfs (Hashimoto et al. 1986) and a 0.7 Me, Population II star ascending the giant branch. 

The evolutionary paths of the central density and temperature are plotted by the solid lines in Figure 1 for cases A-C. The dashed lines show the paths for the same accretion rates as for cases A-C but with the NCO reaction switched off. The dotted lines denote the ignition curves for the 3a and NCO reactions. Note that the NCO reaction dominates over the 3a reaction to heat up the core. The inclusion of the NCO reaction leads to the ignition of the helium flash at considerably lower density. 

Peter Mitchell (Nobel Prize, 1978) of Great Britain was the first to realize, and to propose in his chemi-osmotic theory, that the energy required for die ADP-ATP reaction could be derived by an accretion of protons in the thylakoid sac to the point at which the electrochemical gradient across the membrane could effect the proton transport required as die driving force for this reaction. See also Phosphorylation (Photosynthetic). 

The earth was formed by a process of accretion about 4.6 billion years ago. Initially it was a molten mass lacking the gravitational pull to retain its gases at the prevalent elevated temperatures. And yet, within a mere 700 million years of the planet s birth, as calculated from the isotopic record of sediments, cellular life almost certainly existed. What raw materials were available to bring about this amazing turn of events What were the sources of energy used to drive the necessary reactions Where did the important reactions take place Was it in the atmosphere, in the oceans, on dry land, or all three ... 

The heterogeneities of the protosolar nebula are considered as very significant by some authors I7), and as quantitatively not important by others 9). Nevertheless, it remains a fact that the model of a homogeneous accretion disc where equilibrium reaction takes place has now been replaced by a much more subtle description where a lack of homogeneity and equilibrium are facts that must be taken into account. This problem will be discussed below. 

Moreover, the isomeric distributions of aminoacids and hydroxyacids seem to suggest that radical reactions, must also be taken into account (see paragraph 5.4). Presently, it remains impossible to determine if this kind of processes played a role during the accretion process or later. 

It is conceivable that chemical reactions may have taken place during metamorphism, and it is difficult to find any reasons for excluding organic reactions. In other words, some of the organic molecules detected today in carbonaceous chondrites could be the products of reactions which happened after accretion in the parent body. What kind of reactions At this level, it is extremely difficult to suggest any reasonable answer. It is tempting to consider reactions essentially involving hydrolysis... 

Fig. 2 All terrestrial carbon was initially delivered to the primitive Earth during accretion. Much of the carbon was degraded to simple carbon compounds that could then undergo synthetic geochemical reactions to produce more-complex species. However, a fraction of the delivered organic carbon was likely to survive intact, especially during late accretion. This fraction had the potential to be incorporated into the molecular systems that gave rise to the origin of life...

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