Clearing zones

The side depth of the thickener is determined as the sum of the depths needea for the compression zone and for the clear zone. Normally, 1.5 to 2 m of clear liquid depth above the expected pulp level in a thickener will be sufficient for stable, effective operation. When the location of the pulp level cannot be predicted in advance or it is expected to be relatively low, a thickener sidewall depth of 2 to 3 m is usually safe. Greater depth may be used in order to provide better clarity, although in most thickener applications the improvement obtained by this means will be marginal. 

Figure 48-12. Schematic illustration of some aspects of the role of the osteoclast in bone resorption. Lysosomal enzymes and hydrogen ions are released into the confined microenvironment created by the attachment between bone matrix and the peripheral clear zone of the osteoclast. The acidification of this confined space facilitates the dissolution of calcium phosphate from bone and is the optimal pH for the activity of lysosomal hydrolases. Bone matrix is thus removed, and the products of bone resorption are taken up into the cytoplasm of the osteoclast, probably digested further, and transferred into capillaries. The chemical equation shown in the figure refers to the action of carbonic anhydrase II, described in the text. (Reproduced, with permission, from Jun-queira LC, Carneiro J BasicHistology. Text Atlas, 10th ed. McGraw-Hill, 2003.)...

In media selective for enterobacteria a surface-active agent is the main selector, whereas in staphylococcal medium sodium and lithium chlorides are the selectors staphylococci are tolerant of salt concentrations to around 7.5%. Mannitol salt, Baird-Parker (BP) and Vogel-Johnson (VJ) media are three examples of selective staphyloccocal media. Beside salt concentration the other principles are the use of a selective carbon source, mannitol or sodium pyruvate together with a buffer plus acid-base indicator for visualizing metabolic activity and, by inference, growth. BP medium also contains egg yolk the lecithin (phospholipid) in this is hydrolysed by staphylococcal (esterase) activity so that organisms are surrounded by a cleared zone in the otherwise opaque medium. The United States Pharmacopeia (1990) includes a test for staphylococci in pharmaceutical products, whereas the British Pharmacopoeia (1993) does not. 

Clearing zones on agar plates Most probable number methods... 

A beam of light is passed through a clear zone of the film and subsequently the intensity of the transmitted beam is measured by means of a phototube fitted in the densitometer,... 

The logarithm of the ratio of the intensity of the light transmitted through the clear zone and the darkened zone is computed and is plotted against the logarithm of the exposure as shown in Figure 24.5. 

The top surface of the suspension should always be sufficiently far below the level of the overflow weir to provide a clear zone deep enough to allow any entrained particles to settle out. As they will be present only in very low concentrations, they will settle approximately at their terminal falling velocities. Provided that this requirement is met, the depth of the thickener does not have any appreciable effect on its clarifying capacity. 

A technique that has proven successful for compounds that are poorly soluble in aqneons solntion is the formation of clearing zones ( halo formation ) around active... 

Zinc-imidazole staining is another popular method of reverse staining and involves separation of proteins tightly bound to zinc ion following the precipitation of free ions and the formation of clear zones on a semiopaque background. Detection capacity of zinc-imidazole staining is limited by 10-20 ng/band for proteins (except separation of BSA 40-80 ng/band),... 

Miscellaneous. A manometric technique utilizing a Warburg apparatus has been used to follow esterase activity. The carbon dioxide liberated from sodium bicarbonate by the fatty acids is measured (Willart and Sjostrom 1959). An agar diffusion procedure has been utilized for screening microorganisms for lipolyptic enzymes. The presence of lipase is indicated by clear zones in the turbid media (Lawrence et aL 1967). 

Other simple tests include the soil burial test used to demonstrate the bio degradability of polycaprolactone (25), following its disappearance as a function of time, and the dear zone method which indicates biodegradation by the formation of a clear zone in an agar medium of the test polymer or plastic as it is consumed (26). The burial test is still used as a confirmatory test method in the real-world environment after quantitative laboratory methods indicate bio degradation. 

This step will improve the contrast of the clear zones. 

Proteinase-containing samples are incubated with a variety of class- or enzyme-specific proteinase inhibitors, separated on a polyacrylamide gel, and activity stained as described in Basic Protocol 3. A clear zone will be evident in lanes where the proteinase is active (i.e., in the absence of inhibitor or in the presence of a mismatched inhibitor). This clear zone will be absent in the lane containing the properly matched proteinase inhibitor, which provides information about the class or type of proteinase detected in the band. 

Techniques have also been developed for the specific visualization of particular classes of enzymes following electrophoretic separation in a gel. These techniques are often referred to as activity staining, as the intrinsic activity of the enzyme is used, either to produce a colored product or to produce a clear zone on a colored background within the gel. A method for visualizing proteinases based on the work of Gar-cfa-Carreno and Haard (1993) and Garcia-Car-reno et al. (1993) is presented (see Basic Protocol 3). 

Serial dilutions (10—4 to 10 7) of Pseudomonas strain ADP were added to the surface of a petri dish containing minimal growth medium supplemented with 700-ppm atrazine. Plates were incubated at 35°C for 48 h. Colonies surrounded by clearing-zone show atrazine degradation. 

Each plate was subsequently sprayed with a spore suspension (105 spores/mL) of the test fungus and incubated in a moisture chamber for 3 days at 26 °C with a 12h photoperiod. Clear zones of fungal growth inhibition on the TLC plate indicate the... 

A mycelial mat (2x2 mm) was put on the center of the solid medium for estimation of cellulase productivity and incubated for 6 d at 28°C. Then, 0.1% (w/v) Congo red solution (Wako) was added to the plate and left for 1 h, followed by washing with 1 M NaCl (Wako). The diameter of a clear zone around a colony and the diameter of the colony were measured using a digital caliper (Mitsutoyo). 

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