Sigma enhancement

The use of conical discs, or angled vanes, on the conveyor will theoretically enhance the Sigma value, the clarification capacity, of the centrifuge. To estimate the Sigma value of a stack of conical discs, the formula used for disc stack centrifuges may be employed [11]  

The total Sigma value for the centrifuge is obtained by adding Eo to the Sigma value calculated for the conveyor section between the feed zone and the discs. 

There is little published on the effect of longitudinal angled vanes, but the equation is derived in a similar fashion to that used for the disc stack centrifuge  

Caution is needed in using these extended Sigma values, particularly for the angled vanes. This is because flow through the vanes or discs can channel, to 

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Protein separation and clarification employ erosion protection on the first stage extraction of the natural products, as well as maximum operating speeds, and a variable speed brake. Naturally, they also have a hygienic finish, and CIP. Sigma enhancement is sometimes employed. 

Name given to small inter-particulate forces at the molecular level Longitudinal plates fixed to the conveyor hub supporting the flights. Used for full axial flow, the hubless conveyor, and Sigma enhancement... 

This phenomenon is not possible in p-nitrobenzoic acid hence, p-nitrophenol is a stronger acid with respect to p-nitrobenzoic acid than is expected on the basis of a comparison of substituents in which this resonance delocalization is not an important factor. It was, therefore, recommended that Op = 1.27 be used for p-nitro derivatives of phenols and anilines, rather than the Op = 0.78 given in Table 7-10. These enhanced sigma constants, symbolized a, apply primarily to electron-withdrawing groups in reactions aided by low electron density at the reaction site. 

A good correlation with ordinary Hammett a values was based on 16 well-behaved substituents, and p-SOMe conformed well to this. Various other substituents showed deviations which were attributed to enhanced + R effects. These included p-SPh and this was explained in terms of 7t(pd) bonding, which was thus taken to play no part in the effect of p-SOMe on the methyl hyperfine splitting. More recently several 4-substituted benzyl radicals of the type RSO C6H4CH2 (n — 0,1 or 2 R = Me, Ph, Tol, COMe or OMe) have been examined by ESR spectroscopy249. The ability to delocalize spin density onto the substituent decreases in general as n increases and the effect of R depends on the oxidation state of sulfur. These authors have devised a new scale of substituent effects (sigma dot... 

After hybridization and washing, the samples were stained with DAPI (4, 6-di-amidino-2-phenylindole), which apparently associates in the minor groove of double-stranded DNA (Kapuscinski 1990). DAPI from Sigma was used. Binding of DAPI to double-stranded DNA occurs with about a 20-fold fluorescence enhancement, which usually does not occur with single-stranded DNA (Haugland 1992). 

Wigneshweraraj, S.R., Fujita, N., Ishihama, A., and Buck, M. (2000) Conservation of sigma-core RNA polymerase proximity relationships between the enhancer-independent and enhancer-dependent sigma classes. EMBO J 19(12), 3038-3048. 

Note According to Sigma-Aldrich (2007), chloroform is stabilized with ethanol ( 1%) or amylene (100 ppm) to enhance shelf life. 

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