Negative sedimentation

Svedberg flotation rate (analogous to a negative sedimentation coefficient) is the rate at which each lipoprotein floats up through a solution of sodium chloride of specific gravity 1.063. 

Sedimentation The settling of suspended particles or droplets due to gravity or an applied centrifugal field. Negative sedimentation, when droplets rise upwards, is also called flotation and is a part of the creaming process. 

Utilizing the buoyant densities listed in Table II and the frictional ratio of 1.11, values for the sedimentation coefficient have been calculated at two different solvent densities the standard S value routinely used to characterize human serum lipoproteins is defined as value of the flotation coefficient in Svedberg units (the negative sedimentation coefficient X 10 sec) in an aqueous NaCl solvent with a density of 1.063 g/ml and a viscosity of 1.021 centipoise (the viscosity of a 1.063 g/ml sodium chloride solution at 26°C). These values are listed in Table II. The S value is very sensitive to small variations in lipoprotein density because the solvent density is close to the lipoprotein density. To compare the particle sizes or molecular weights, values of the sedimentation coefficient (5) in a solvent with a density of 1.20 g/ml and the viscosity of KBr at 25°C are preferred, and the computed values are listed in Table II. 

Sedimentation. This can either be settling, i.e., downward sedimentation, or creaming, i.e., upward (negative) sedimentation. The driving force is a difference in buoyancy, or in other words the decrease in potential energy of the particles that will occur upon sedimentation. 

Open circles denote values obtained in runs on whole serum. Solid circles denote values on runs on X-prdtein previously separated from whole serum by negative sedimentation in a solvent of high density. From Pedersen (166, p. 29). 

Extremely small particle, typically 10-5 to 10 7 cm in diameter. Colloidal solutions or hydrosols contain colloidal particles that are electrically negatively charged, which contributes to their fine dispersion and the difficulty of sedimentation and clarification. Coagulation is usually carried out by causing the particles to adsorb positively charged ions, such as aluminum from alum. 

Wester PG, J de Boer, UAT Brinkman (1996) Determination of polychlorinated terphenyls in aquatic biota and sediment with gas chromatography/mass spectrometry using negative chemical ionization. Environ Sci Technol 30 473-480. 

The presence of °Be or negative Ce anomalies, or both, in some arc lavas provide unambiguous evidence for a contribution from subducted sediments to the source of arc lavas (Morris et al. 1990 Hole et al. 1984). In addition, Pb isotopes commonly are... 

Figure 5. Comparison between fluxes measured in shallow sediment traps and those calcnlated for the same depth and time from the " Th deficit in the overlying water colnmn. The data were compiled from many studies and the right-hand scale shows the factor of positive or negative offset between the two data sets. Significant differences are common and are linked to the varions assumptions and constraints of the two approaches for measnring POC finx. [Reprinted from Nature, Vol. 353, Buesseler, pp. 420-423, 1991, Macmillan Publishers Ltd.]...

The concentration of small ions in the atmosphere is determined by 1) the rate of ion-pair production by the cosmic rays and radioactive decay due to natural radioactive substances, 2) recombination with negative ions, 3) attachment to condensation nuclei, 4) precipitation scavenging, and 5) transport processes including convection, advection, eddy diffusion, sedimentation, and ion migration under the influence of electric fields. A detailed differential equation for the concentration of short-lived Rn-222 daughter ions including these terms as well as those pertaining to the rate of formation of the... 

Chiou et al. (1998) attributed the enhanced partitioning of PAHs with respect to other HOCs to relatively high compatibility between the cohesive energy densities of PAHs and the aromatic components in SOM. However, the difference in Koc values between soils and sediments is related to the difference in polar group, rather than aromatic carbon, contents (Kile et al. 1999). The authors concluded that the content of polar groups (O-aryl and carboxyl C) has a large negative influence on Koc values, and hence on HOC sorption in soil and sediment. 

A rapid and simple method for PBDE and HBCD determinations in sediment and fish samples was used. The analytical method was based in selective pressurized liquid extraction (SPLE) [21] without further cleanup step and analysis by gas chromatography coupled to mass spectrometry (GC-MS), working with negative ion chemical ionization (NCI) [22, 23],... 

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