Isopycnals

More sophisticated rotors can be loaded with gradient and sample while rotating. When the batch is finished or the bands are sufficientiy loaded with material, the bowl may be stopped slowly and the reoriented layers displaced under static conditions. Rotors may also be designed to estabUsh gradients and isopycnic bands of sample and then be unloaded dynamically by introducing a dense solution near the edge of the rotor as shown in Figure 12. 

Density. The difference in density between the two hquid phases in eqiiilibrium affects the countercurrent flow rates that can be achieved in extrac tion equipment as well as the coalescence rates. The density difference decreases to zero at a plait point, but in some systems it can become zero at an intermediate solute concentration (isopycnic, or twin-density tie line) and can invert the phases at higher concentrations. Differential types of extractors cannot cross such a solute concentration, but mixer-settlers can. 

As mentioned earlier, the physical properties of a liquid mixture near a UCST have many similarities to those of a (liquid + gas) mixture at the critical point. For example, the coefficient of expansion and the compressibility of the mixture become infinite at the UCST. If one has a solution with a composition near that of the UCEP, at a temperature above the UCST, and cools it, critical opalescence occurs. This is followed, upon further cooling, by a cloudy mixture that does not settle into two phases because the densities of the two liquids are the same at the UCEP. Further cooling results in a density difference and separation into two phases occurs. Examples are known of systems in which the densities of the two phases change in such a way that at a temperature well below the UCST. the solutions connected by the tie-line again have the same density.bb When this occurs, one of the phases separates into a shapeless mass or blob that remains suspended in the second phase. The tie-lines connecting these phases have been called isopycnics (constant density). Isopycnics usually occur only at a specific temperature. Either heating or cooling the mixture results in density differences between the two equilibrium phases, and separation into layers occurs. 

The horizontal isopycnal thermocline model is important for the problem of determining the fate of the excess atmospheric CO2. The increase of CO2 in the atmosphere is modulated by transport of excess CO2 from the atmosphere into the interior of the ocean. The direct ventilation of the thermocline in its outcropping regions at high latitudes plays an important... 

Fig. 10-9 Map of winter outcrops of isopycnal surfaces in the Atlantic Ocean. (Modified with permission from W. S. Broecker and T.-H. Peng (1982). Tracers in the Sea," p. 394, Eldigio Press, Palisades, NY.)...

Sarmiento JL, Rooth CG (1980) A comparison of vertical and isopycnal mixing models in the deep-sea based on Rn measurements. J Geophys Res 85 1515-1518 Shaw TJ, Moore WS, Kloepfer J, Sochaski MA (1998) The flux of barium to the coastal waters of the Southeastern United States the importance of submarine groundwater discharge. Geochim Cosmochim Acta 62 3047-3052... 

Fig. 4. Localization of WAP27 and WAP20 in the crude microsome fractions and the relation with marker-enzyme activities in three organelles (ER, tonoplast, and Golgi). SDS-PAGE of fractionated proteins by isopycnic linear sucrose density gradient centrifugation of microsome fraction of mulberry cortical parenchyma cells was performed using 6-pL samples in each fraction. Immunoblot analysis was performed with anti-WAP27 and anti-WAP20 antibodies. (From ref. [1], with permission from the American Society of Plant Physiologists.)...

After the first distinction, made by Berg (B6), between Lp(a) positive and Lp(a) negative sera, Harvie et al. (H18), using isopycnic ultracentrifugation, demonstrated that after concentration, a significant amount of Lp(a) could be detected in Lp(a)-negative sera. 

Method Density gradient. Rate-zonal. The rate-zonal method is one of six addressed by SpinPro. The other methods are differential, differential-flotation, discontinuous, isopycnic, and 2-step isopycnic. These methods differ dramatically in their set up, principles of operation, and expected results. The rate-zonal method is described here briefly so that the recommendations to follow can be appreciated. Prior to the run in a rate-zonal method, a gradient material is introduced to the rotor tubes in steps of increasing density from the top to the bottom of the tube. The sample to be separated is layered, as a thin band, on the top of the gradient. As the run begins, each component in the sample moves toward the bottom of the tube. Some components sediment faster than others. This fact is the basis for the separation. If the run parameters are appropriate, the components will form separate bands within the gradient. At the conclusion of the run, the band representing the component of interest can be removed from the tube. 

Some of these features are demonstrated in the rule example of figure 4. The rule, one of approximately 800 rules in SpinPro, is assigned to the rule group 2-STEP.ISOPYCNIC.DNA.RULES. Only those rules, identified by the rule group name and pertinent to the solu-... 

Quite a bit of DOC is also injected into the subsurface ocean via isopycnal mixing in which water is transported down to the top of the thermocline. This subduction is associated with the seasonal formation of mode water, which occurs mostly on the... 

Isopycnal A fine on a chart or map that connects points of constant seawater density. 

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