Time scales, carbon dynamics

As shown in Fig. 10-13, there is also a flux of O2 produced during net photosynthesis from the ocean to the atmosphere and an export flux of particulate and dissolved organic matter out of the euphotic zone. For a steady-state system, new production should equal the flux of O2 to the atmosphere and the export of organic carbon (Eppley and Peterson, 1979) (when all are expressed in the same units, e.g., moles of carbon). Such an ideal state probably rarely exists because the euphotic zone is a dynamic place. Unfortunately, there have been no studies where all three fluxes were measured at the same time. Part of the difficulty is that each flux needs to be integrated over different time scales. The oxygen flux approach has been applied in the subarctic north Pacific (Emerson et al, 1991) and subtropical Pacific (Emerson et al, 1995, 1997) and Atlantic (Jenkins and Goldman, 1985). The organic carbon export approach has... 

The intensity of SR is high enough for crystallographic data to be collected in real time to give direct time resolution of dynamic events in a protein molecule. Bartunik et al. (1982) collected monochromatic test data on a millisecond time scale on carbon-monoxy myoglobin, where structural changes are induced by the debinding of the... 

We assume that if many of the liquids of interest, such as propylene carbonate, were studied by higher frequency (measurement techniques, new, high frequency components would be discovered which would account at least partially for the short time scale dynamics we see in the solvation C(f) data. Indeed, the apparent observation of a single Debye time is inconsistent with theories of liquids that take into account dipole-dipole interactions (see Kivelson [109]). Furthermore, some of the liquids studied have extraordinarily large apparent infinite frequency dielectric constants (e.g., = 10... 

Bomb Radiocarbon. One of the great uses of radiocarbon for SOM studies is the ability to estimate the turnover time of organic carbon based on the degree to which it has incorporated bomb radiocarbon since 1959. This provides one of the only tools to study C dynamics on decadal time scales. 

Aqueous micelles are 40-80 A diameter spherical aggregates which are dynamically formed from surfactants in water above a characteristic concentration, the CMC (9). Depending on the chemical structure of their hydrophilic headgroups, surfactants can be neutral or charged (positively or negatively). The alkyl chain of the surfactants typically contains between 5-20 carbon atoms. Micelles rapidly break up and reform by two known processes. The first process occurs on the microsecond time scale and is due to the release and subsequent reincorporation of a single surfactant from and back to the micelle. The second process occurs on the millisecond time scale and is ascribed to the dissolution of the... 

Considering dynamic processes in fluid membranes as an example and starting from the fastest dynamical processes, one may first consider rotational diffusion of individual carbon-hydrogen bonds in CH2 groups in lipid hydrocarbon chains. The time scale of these rotational motions is on the order of picoseconds. The rotational motion of whole lipids around their principal axes of rotation is a slower process and usually takes place over a scale of nanoseconds. Lateral diffusion, in turn, involves diffusion of matter and hence longer time scales. This time scale is characterized by the diffusion length X = (Id D where d is the dimensionality, D is the... 

As the design of adsorptive filters is difficult and complexed, and proper infarma-tions are not always sufficient, the best solution to establish the work parameters of filters is to test a series of carbons on a pilot - scale in dynamic conditions. The studies are expensive and time-consuming, thus it is proposed to evaluate granular carbons in static conditions according to some tests [25—29]. Further studies may be conducted in dynamic conditions. It seems, that the best solution, is to carry out comparable studies of both static and dynamic adsorption which give a possibility to predict a behaviour of carbons in dynamic conditions basing on static studies. 

On geological time scales, CO2 cycles between rocks, often by way of the ocean and atmosphere. The rock reservoirs include the mantle, continental carbonates, carbon in reduced form mostly in continental shales, and carbon (mostly carbonate) in or on the sea floor. The small volatile reservoir (ocean plus atmosphere) cycles through carbonate rock in a hundred thousand to a million years. Over longer periods free CO2 is dynamically controlled by processes that form carbonates at low temperatures and processes that decompose carbonates at high temperatures by (Urey) reactions of the form... 

Figure 11.9 Normalised comparison of electron absorption dynamics of N3-sensitised Ti02 films in ethylene/propylene carbonates (1 1) following excitation at different wavelengths. Inset the same data plotted on a shorter time scale. The solid lines are fits using the two-state injection model. The fast component is well described by a <100 fs rise and the slow component is fitted by a stretched exponential function with a 50 ps time constant. Reproduced with permission from J. Phys. Chem. B 107, 7376 (2003) (Asbury et al, 2003). Copyright 2003 American Chemical Society.

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