Sedimentation coefficient, definition

A mathematical expression for the results of a typical experiment is shown in Figure 1. The simplest experiment is to obtain an average sedimentation coefficient by measuring the movement of the boundary, r , with time. From the definition of the sedimentation coefficient,... 

In the definition, v is the velocity of sedimentation and a is the acceleration of free fall or centrifugation. The symbol for a limiting sedimentation coefficient is [s], for a reduced sedimentation coefficient 5°, and for a reduced limiting sedimentation coefficient [s°] see [l.e] for further details. 

In Eq. (5.5.3) the radial velocity has been replaced by the sedimentation coefficient s, from the definition of Eq. (5.5.2). The fluid dynamicist should be aware that this one-dimensional diffusion equation is known in the ultracentrifuge literature as the Lamm equation (Fujita 1975). In the limit of infinitely dilute solutions D and s are independent of concentration and may be taken out of the derivative to give... 

The sedimentation coefficients of RNA isolated from loach informosomes are 4S, 6S, lOS, 15S, 21S, 26S, 30S, and 35S. It is not possible to correlate precisely the definite classes of informosomes with definite RNA classes, but in general the higher the sedimentation coefficient of the informosome, the higher the molecular weight of the RNA isolated from the particles (Ovchinnikov et al., 1969a). More careful measurement... 

The presence of informosomelike RNPs has been demonstrated also in the case of Ehrlich ascites carcinoma cells infected with Sendai virus (Volkova et al., 1969). The cytoplasmic extracts of the cells labeled for 30 minutes with uridine contain virus-specific RNA in the form of particles with a sedimentation coefficient 45S (the sedimentation coefficient of the complete virus equals 57S). The buoyant density of the RNP peak in CsCI equals 1.43 to 1.44 g/cm. Although these properties are compatible with the idea that they are informosome, the particles, and in particular their protein component, should be characterized in more detail before reaching a definite conclusion. Recently SOS virus RNA-containing particles with p = 1.40 g/cm have been found in HeLa cells infected with poliovirus (Huang and Baltimore, 1970), although the authors have some doubts about the reality of these complexes. 

DNA-dependent RNA synthesis in E.coli cells was inhibited under experimental conditions by actinomycin D. After 50-90 sec, almost 70% of the of the parent RNA was found in one fraction of RNA with a sedimentation coefficient of about 20S, which these workers called the replicative form of RNA, because it was resistant to ribonuclease (double-helical form). The quantity of P of ribonuclease-resistant RNA then fell sharply, and a new peak of this RNA appeared after 3.5 min (Fig. 12). In one case this wave of change of the parent RNA into the double-helical RNAase-resistant form was observed on four successive times. In addition, slight but definite incorporation of parent P material was observed into a special low-molecular weight 6S fraction (mol.wt. from 1 to 30 X10 ) was observed, which, however, contained much newly synthesized RNA (in this fraction the ratio of parent RNA/new RNA was much lower than in the 2OS fraction of RNA). 

Measurements of Koc have been taken directly from partitioning experiments in sediment-and soil-water systems over a range of environmental conditions in both the laboratory and the field. Not surprisingly, the Koc values for many organic chemicals are highly correlated with their K0w values. Plots of the two partition coefficients for hundreds of chemicals with widely ranging K0w values yield slopes from about 0.3 to 1, depending on the classes of compounds and the particular methods included. Most fate modelers continue to use a slope of 0.41, which was reported by the first definitive... 

Sorption coefficients also have been expressed on an organic matter basis (Kom) by assuming that the organic matter content of a soil or sediment equals some factor, usually between 1.7 to 1.9, times its organic carbon content on a mass basis (Hamaker and Thompson, 1972 Lyman et al., 1982). Often 1.724 is used as this factor, implying that the carbon content of organic matter is 1 /1.724 or 60%. However, Koc is considered a more definite and less ambiguous measure than Kom (Hamaker and Thompson, 1972). 

The term bioaccumulation factor (BAF) is a coefficient used to quantify the net body burden of chemicals (given uptake, distribution, metabolism, and excretion rates) and is expressed as the ratio of the concentration of a compound in the organism (or normalized to the lipid weight of the organism) to the concentration in its food or, for benthic or soil invertebrates, in the sediment or soil [9] (also see Chapter 6). Although by definition, BAF is measured at steady state, due to the complex nature of multiplepathway exposure, steady-state measures of BAF are often difficult to obtain. 

F is the flocculation coefficient, calculated from F = VI Vq, where V is the sediment volume and is the total initial volume of the suspension. F is some reference, frequently taken as the value of F for a nonflocculated or stable suspension. According to its definition, the greater the value of P the more unstable is the suspension. 

Charles Darwin in 1881 reported that by ingesting soil at depth and depositing it upon the surface earthworms caused surface objects to migrate downward. Soil turnover rates, v in cm/year, and depths of activity h, in cm, are the measurements typically taken on cast production by earthworms. A random particle displacement concept applied over time as the conventional definition of a diffusion coefficient allows using the two measurements to yield a biodiffusion coefficient, Dbs = v h (cm /year). This approach was first used by Mclachlan et al. (2002) the results that appear here are those of Rodriguez (2006), who extended the earlier work. Unlike sediment bioturbation where chemical tracers and Fickian diffusion-type mathematical models, such as Equation 13.1, are used with chemical profile data to yield Dbs and h values directly, no such approaches have been used for estimating surface soil bioturbation parameters. 

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