Transport slower fraction

A further complication is evident in that there exist different transport channels with different properties. The auxin stream seems to contain a fast fraction of low density which is separate from a main and slower fraction (e.g., Vardar 1964, Newman 1965, Rayle etal. 1969, de la Fuente and Leopold 1972, Kaldewey and Kraus 1972, Patrick and Woodley 1973, Krul 1977, Sheldrake 1979, see also Goldsmith 1977, p452ff.). The fast and slow transport fractions may be associated with different compartments of the cells, possibly the cytoplasm and the vacuole, respectively. This possibility is based on the multiphasic efflux and elution profiles of plant sections supplied with labeled auxin (de la Fuente and Leopold 1970 b, 1972, Davies 1974 see also Goldsmith 1977, p 453 f.). 

Slow component a (SCa) comprises largely the cyto-skeletal proteins that form NFs and MTs. Rates of transport for SCa proteins in mammalian nerve range from 0.2-0.5 mm/day in optic axons tol mm/day in motor neurons of the sciatic nerve, and can be even slower in poikilotherms such as goldfish. Although the polypeptide composition of SCa is relatively simple, the relative contribution of SCa to slow transport varies considerably. For large axons (e.g. alpha motor neurons in the sciatic nerve), SCa is a large fraction of the total protein in slow transport, while the amount of material in SCa is relatively reduced for smaller axons (i.e. optic axons) [32]. The amount and phosphorylation state of SCa protein in axons is the major determinant of axonal diameter. 

Figure 9.6 Illustration of the retardation of 1,4-dimethylbenzene (DMB) transport in groundwater due to (1) reversible sorptive exchange between water and solids, and (2) limiting transport of DMB to that fraction remaining in the flowing water. As dissolved molecules move ahead, they become sorbed and stopped, while molecules sorbed at the rear return to the water and catch up. Thus, overall transport of DMB is slower than that of the water itself.

In this particular case, there is no transport of component B towards the surface. BO is homogeneously precipitated in the region < F, and the BO fraction corresponds to the concentration of B in the initially homogeneous alloy. Although the BO fraction is spatially constant in this case, the size of the BO particles is not. The increase in supersaturation becomes slower as the reaction front F advances. Thus, the number of precipitating particles becomes smaller with increasing time and, consequently, their volumes become larger since the local product of number times volume remains constant. 

Ciliary action removes deposited particles from both the bronchi and bronchioles. Though it is generally thought that mucocilliary action rapidly transports most particles deposited here toward the pharynx, a fraction of these particles are cleared more slowly. Evidence for this is found in human studies. For humans, retention of particles deposited in the lungs (BB and bb) is apparently biphasic. The slow action of the cilia may remove as many as half of the bronchi- and bronchiole-deposited particles. In human bronchi and bronchiole regions, mucus moves more slowly the closer to the alveoli it is. For the faster compartment it has been estimated that it takes about 2 days for particles to travel from the bronchioles to the bronchi and 10 days from the bronchi to the pharynx. The second (slower) compartment is assumed to have approximately equal fractions deposited between BB2 and bb2 and both with clearance... 

Jaundice does not necessarily accompany cholestasis. In severe and prolonged cholestasis, particularly if obstructive, jaundice is generally always in evidence. In cholestasis, the third fraction, known as delta bilirubin, can largely be detected by means of the diazo method. This fraction is firmly bound to albumin and can therefore only be dissociated and excreted slowly. For this reason, jaundice occurring together with cholestasis tends to subside at a significantly slower rate than the increased bile acid level in the serum. In this case, jaundice is due to a reflux of bilirubin from the canaliculus into the blood or a bidirectional transport of bilirubin via the sinusoidal membrane. Sometimes jaundice is caused by metabolic dysfunction of the liver cells. Bilirubin also acts as an antioxidant. 

The intensity of the redox cycling and thus the importance for oxidation and reduction reactions in the sediment is terminated by either one of the following conditions 1. In case of the absence of any efficient oxidant (e g. O ) in the upper-most layer or bottom water no oxidation will occur and the redox cycling cannot be maintained. 2. In case of the absence of a reactive fraction (bioavailable or rapidly reducible by HS , see section 7.4.3.1) in the lower layer no reduction will occur and the redox cycle will cease. 3. A vertical transport mode must be maintained between the zone of oxidation and the zone of reduction. As advection is usually very much slower than the downward transport by bioturbation the intensity of bioturbation terminates the transport between the redox-zones. 

Figure 13 displays the self-diffusivities of n-hexane and 2-methylpentane in silicalite-1 and H-ZSM-5 as a function of the ratio of the hydrocarbons. The self-diffusivities of both hexanes linearly decrease with increasing gas-phase fraction of the branched hexane in the gas phase for the non-acidic and acidic zeolite. In H-ZSM-5, the mobility of alkanes is approximately two times slower than in silicalite-1. Obviously, the presence of acid sites strongly affects the molecular transport due to stronger interactions with the n-hexane molecules. A similar effect of Bronsted sites on the single component diffusion of aromatics was observed in MFI zeolites with different concentration of acid sites [63-65]. The frequency response (FR) technique provided similar results... 

The kinetics of urinary excretion of PVP of various molecular weights was found to be biphasic In the first (steeper) phase, the excreted fraction represents mainly the polymer filtered directly from the plasma. The second, slower phase probably reflects the transport of the polymer from other compartments, i.e. interstitial fluid, lymph etc., to the plasma compartment. The rate of this transport is also dependent on the molecular size Mainly the high molecular weight fractions can remain in the interstitial fluid for a sufficiently long time to be captured by cells via pinocyto-sis. Intracellular storage of polymers in secondary lysosomes represents the only demonstrated mode of polymer deposition in the body for a period of time ranging from months to years. 

---