Sieve mechanism

Two other deposition mechanisms, in addition to the six listed, may be in operation under particular circumstances. Some dust particles may be collected on filters by sieving when the pore diameter is less than the particle diameter. Except in small membrane filters, the sieving mechanism is probably limited to surface-type filters, in which a layer of collected dust is itself the principal filter medium. 

One of the oldest, simplest, and most efficient methods for removing solid particulate contaminants from gas streams is by filtration through fabric media. The fabric filter is capable of providing high collection efficiencies for particles as small as 0.5 pm and will remove a substantial quantity of particles as small as 0.01 pm. In its simplest form, the industrial fabric filter consists of a woven or felted fabric through which dust-laden gases are forced. A combination of factors results in the collection of particles on the fabric filters. When woven fabrics arc used, a dust cake eventually forms. This, in turn, acts predominantly as a sieving mechanism. When felted fabrics are used, the dust cake is minimal or nonc.xistent. 

Some small-pore zeolite and molecular sieve membranes, such as zeolite T (0.41 nm pore diameter), DDR (0.36 x 0.44nm) and SAPO-34 (0.38nm), have been prepared recenhy [15-21]. These membranes possess pores that are similar in size to CH4 but larger than CO2 and have high CO2/CH4 selechvihes due to a molecular sieving mechanism. For example, a DDR-type zeolite membrane shows much higher CO2 permeability and CO2/CH4 selechvity compared to polymer membranes [15-17]. SAPO-34 molecular sieve membranes show improved selechvity for separation of certain gas mixtures, including mixtures of CO2 and CH4 [18-21]. 

Mixed-matrix membranes comprising small-pore zeolite or small-pore non-zeolitic molecular sieve materials will combine the solution-diffusion separation mechanism of the polymer material with the molecular sieving mechanism of the zeolites. The small-pore zeolite or non-zeolitic molecular sieve materials in the mixed-matrix membranes are capable of separating mixtures of molecular species... 

Paterson, R. Rahman, H. (1984a) The ion exchange properties of crystalline inorganic oxide-hydroxides. Part II Exclusion of perchlorate from p-FeOOH by an ion sieve mechanism. J. Colloid Interface Sci. 97 423-427... 

Thus the factor (Mc — M )/(Mn — M ) may be thought of as the sieving term mentioned in the theory of Yasuda et al. [150], In the Peppas-Reinhart theory, the sieving mechanism takes an understandable form which is a function of the structure of the network. It must be noted that the presence of semicrystalline regions in the polymer membrane leads to deviations from the predicted dependencies in this theory. These researchers found that as the crosslinking density in the polymer membrane increased, the solute diffusion coefficient decreased, further illustrating the importance of structural parameters of the polymer network in predicting the solute diffusion coefficient [156],... 

The retardation of the protein movement has been discussed qualitatively in terms of a sieving mechanism rather than a frictional resistance37). Ogston et al.39) have theoretically described the diffusion as a stochastic process in which the particles move by unit displacements and in which the decrease in the rate of diffusion in a polymer network depends on the probability that a particle finds a hole in the network into which it can move. The relationship derived from this approach is in close agreement with Eq. (35). 

From the experimental viewpoint it may be said that the resolution in the separation with respect to molecular weight, which is attainable by the molecular sieving mechanism in TLC, is not quite as high in comparison with that by the phase-separation mechanism. An attempt has been made to improve the resolution by increasing the thickness of thin layer from 0.25 mm to 1.0 mm29. An improvement of the resolution was really observed with increase in the thickness. Because of the technical difficulty, however, the thickness of thin layer was limited up to some 1.0 mm so that the best resolution was lower than that observed by GPC which was performed under analogous conditions to the TLC experiment. 

Another approach to the TLC separation of linear and branched polystyrenes was reported by Belenkii etalThe adsorbent used was silica gel with a mean pore diameter of 80 A (notice that no molecular sieving mechanism should be operative in this pore diameter), and the developer was composed of cyclohexane, benzene, and acetone in a composition of 12 4 y, where 7 is the relative amount of acetone added. The TLC experiments were performed for different 7 values ranging from 0.4 to 1.5. With increase in the 7 value, the Rf values increased both for the linear and branched samples but the dependence for the linear samples was remarkably stronger than for the branched ones. 

Wet Sieving by a Mechanical Flushing Procedure. The sieve residue is the portion of coarse particles that cannot be washed through a specified test sieve with water. The result depends on the mesh size of the sieve. For standards, see Table 1 ( Residue on sieve Mechanical method ). Apparatus Mocker s apparatus. 

Selective barrier structure. Transport through porous membranes is possible by viscous flow or diffusion, and the selectivity is based on size exclusion (sieving mechanism). This means that permeability and selectivity are mainly influenced by membrane pore size and the (effective) size of the components ofthe feed Molecules... 

The first fraction of solute emerging from a gel column is eluted in v() that contains molecules too large to enter the gel micropores. v0 is the macroscopic pore space in the gel bed, not otherwise participate in the sieving mechanism. For a given column, v0 is constant. The solute interacting with the liquid stationary phase on the column surface elutes in order of the magnitude of a fraction s partition coefficient (Kp) between the elution volume (vel) and the volume of stationary solvent in the micropores (vs), fixed at 100 mL, because of difficulty in its measurement (Bio-Rad, 1971). At Ts = 100 mL,... 

The separation principle in capillary gel electrophoresis (CGE) is the same as that of slab gel electrophoresis. Most often CGE is used in a denaturing mode with the incorporation of SDS and is referred to as SDS-CGE. As such, separation is based on the protein s molecular mass and, due to the sieving mechanism of the gel, smaller proteins migrate past the detector first. The use of a gel material and SDS decreases the EOF and eliminates protein adsorption to the capillary walls further ensuring that migration is based on molecular mass. This precludes the need for additives and coated capillaries. 

The choice of a buffer system becomes the most significant variable in developing a separation of PCR products by CE. Smaller DNA components (such as dNTPs and primers) have been separated by means of a partitioning approach based on affinity for a micelle in solution (Cohen et al., 1987). In separations of larger dsDNA components by CE, a sieving mechanism is required in the capillary to separate species with the same linear charge density. In optimizing... 

Most aaRSs that edit use a double-sieve mechanism. The aminoacylation active site serves as a coarse sieve and binds cognate amino acid as well as structurally related noncognate amino acids. A second hydrolytic active site acts as a fine sieve and hydrolyzes misactivated amino acids. The Class 1... 

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