Optimum concentration

The carbon black in semiconductive shields is composed of complex aggregates (clusters) that are grape-like stmctures of very small primary particles in the 10 to 70 nanometer size range (see Carbon, carbon black). The optimum concentration of carbon black is a compromise between conductivity and processibiUty and can vary from about 30 to 60 parts per hundred of polymer (phr) depending on the black. If the black concentration is higher than 60 phr for most blacks, the compound is no longer easily extmded into a thin continuous layer on the cable and its physical properties are sacrificed. Ionic contaminants in carbon black may produce tree channels in the insulation close to the conductor shield. 

The role of specific interactions in the plasticization of PVC has been proposed from work on specific interactions of esters in solvents (eg, hydrogenated chlorocarbons) (13), work on blends of polyesters with PVC (14—19), and work on plasticized PVC itself (20—23). Modes of iateraction between the carbonyl functionaHty of the plasticizer ester or polyester were proposed, mostly on the basis of results from Fourier transform infrared spectroscopy (ftir). Shifts in the absorption frequency of the carbonyl group of the plasticizer ester to lower wave number, indicative of a reduction in polarity (ie, some iateraction between this functionaHty and the polymer) have been reported (20—22). Work performed with dibutyl phthalate (22) suggests an optimum concentration at which such iateractions are maximized. Spectral shifts are in the range 3—8 cm . Similar shifts have also been reported in blends of PVC with polyesters (14—20), again showing a concentration dependence of the shift to lower wave number of the ester carbonyl absorption frequency. 

Laboratory or pilot plant tests are usually conducted on individual ores to determine the number of dmms required to obtain optimum concentration results. Dmms that are 914 or 1219 mm in diameter are usually used in cobbing service. 

The optimum concentration for any diafiltration (minimum area time) is the minimum of the plot ... 

When fouling is absent, the optimum concentration is 0.37 C. If the permeate soHds are of primary value, it is usually preferable to diafilter at the minimum retentate volume to minimize permeate dilution. 

The PTCR effect is complex and not fully understood in terms of the grain boundary states and stmcture. Both the PTCR effect and room temperature resistivities are also highly dependent on dopant type and ionic radius. Figure 11 (32) illustrates this dependence where comparison of the PTCR behavior and resistivity are made for near optimum concentrations of La ", Nd ", and ions separately substituted into BaTiO. As seen, lowest dopant concentration and room temperature resistivity are obtained for the larger radius cation (La " ), but thePTCR effect was sharpest for the smallest radius cation (Y " ), reflecting dual site occupancy of the Y " ion. 

TABLE 26-14 Optimum Concentrations for Maximum Deflagration Pressure... 

The light-scattering objects must track the flow accurately, ensuring that their velocity represents the fluid velocity with a high accuracy. The light-scattering objects are either in the flow as a natural impurity such as dust, or are artificially introduced into the airflow at an optimum concentration ( seeding ). 

Addition of hydride ion from the catalyst gives the adsorbed dianion (15). The reaction is completed and product stereochemistry determined by protonation of these species from the solution prior to or concurrent with desorption. With the heteroannular enolate, (13a), both cis and trans adsorption can occur with nearly equal facility. When an angular methyl group is present trans adsorption (14b) predominates. Protonation of the latter species from the solution gives the cis product. Since the heteroannular enolate is formed by the reaction of A" -3-keto steroids with strong base " this mechanism satisfactorily accounts for the almost exclusive formation of the isomer on hydrogenation of these steroids in basic media. The optimum concentration of hydroxide ion in this reaction is about two to three times that of the substrate. 

To avoid homopolymer formation, it is necessary to ensure true molecular contact between the monomer and the polymer. Even if this is initially established, it needs to be maintained during the radiation treatment while the monomer is undergoing conversion. Several methods are used for minimizing the homopolymer formation. These include the addition of metal cations, such as Cu(II) and Fe(II). However, by this metal ion technique, both grafting and homopolymerization are suppressed to a great extent, thus permitting reasonable yield of graft with little homopolymer contamination by the proper selection of the optimum concentration of the inhibitor [83,90,91]. 

The mechanical properties of these blends are also increased with an increase in compatibilizer concentration. The improvement in tensile strength and tear strength on the addition of modified polyolefins are shown in Fig. 15. The mechanical properties also show a leveling off after the optimum concentration. The im-... 

Whatever method of inhibitor application is used, care must be taken to maintain optimum concentration of the corrosion inhibitor. In the event of addition of makeup water or untreated reserve fluids to maintain other fluid properties, care must be taken to ensure the addition of the correct amounts of corrosion inhibitors. 

Dissolved mineral salts The principal ions found in water are calcium, magnesium, sodium, bicarbonate, sulphate, chloride and nitrate. A few parts per million of iron or manganese may sometimes be present and there may be traces of potassium salts, whose behaviour is very similar to that of sodium salts. From the corrosion point of view the small quantities of other acid radicals present, e.g. nitrite, phosphate, iodide, bromide and fluoride, have little significance. Larger concentrations of some of these ions, notably nitrite and phosphate, may act as corrosion inhibitors, but the small quantities present in natural waters will have little effect. Some of the minor constituents have other beneficial or harmful effects, e.g. there is an optimum concentration of fluoride for control of dental caries and very low iodide or high nitrate concentrations are objectionable on medical grounds. 

Discussion. Molybdenum(VI) in acid solution when treated with tin(II) chloride [best in the presence of a little iron(II) ion] is converted largely into molybdenum(V) this forms a complex with thiocyanate ion, probably largely Mo(SCN)5, which is red in colour. The latter may be extracted with solvents possessing donor oxygen atoms (3-methylbutanol is preferred). The colour depends upon the acid concentration (optimum concentration 1M) and the concentration of the thiocyanate ion (1 per cent, but colour intensity is constant in the range 2-10 per cent) it is little influenced by excess of tin(II) chloride. The molybdenum complex has maximum absorption at 465 nm. 

The quantum yield of Latia luciferin is surprisingly low. When an optimum concentration of purple protein was used together with luciferase, the quantum yield was 0.0030 at 25°C, and 0.0068 at 8°C (Shimomura and Johnson, 1968c). When 1 mM ascorbate and an optimum concentration of NADH ( 0.25 mM) were added, the quantum yield was 0.009 at 25°C (Shimomura et al., 1972). 

Luciferase-catalyzed luminescence of luciferin. Odontosyllis luciferin emits light in the presence of Mg2+, molecular oxygen and luciferase. The relationship between the luminescence intensity and the pH of the medium shows a broad optimum (Fig. 7.2.8). The luminescence reaction requires a divalent alkaline earth ion, of which Mg2+ is most effective (optimum concentration 30 mM). Monovalent cations such as Na+, K+, and NH have little effect, and many heavy metal ions, such as Hg2+, Cu2+, Co2+ and Zn2+, are generally inhibitory. The activity of crude preparations of luciferase progressively decreases by repeated dialysis and also by concentrating the solutions under reduced pressure. However, the decreased luciferase activity can be completely restored to the original activity by the addition of 1 mM HCN (added as KCN). The relationship between the concentration of HCN and the luciferase activity is shown in Fig. 7.2.9. Low concentrations of h and K3Fe(CN)6 also enhance luminescence, but their effects are only transient. 

If the mixture to be separated contains fairly polar materials, the silica may need to be deactivated by a more polar solvent such as ethyl acetate, propanol or even methanol. As already discussed, polar solutes are avidly adsorbed by silica gel and thus the optimum concentration is likely to be low, e.g. l-4%v/v and consequently, a little difficult to control in a reproducible manner. Ethyl acetate is the most useful moderator as it is significantly less polar than propanol or methanol and thus, more controllable, but unfortunately adsorbs in the UV range and can only be used in the mobile phase at concentrations up to about 5%v/v. Above this concentration the mobile phase may be opaque to the detector and thus, the solutes will not be discernible against the background adsorption of the mobile phase. If a detector such as the refractive index detector is employed then there is no restriction on the concentration of the moderator. Propanol and methanol are transparent in the UV so their presence does not effect the performance of a UV detector. However, their polarity is much greater than that of ethyl acetate and thus, the adjustment of the optimum moderator concentration is more difficult and not easy to reproduce accurately. For more polar mixtures it is better to explore the possibility of a reverse phase (which will be discussed shortly) than attempt to utilize silica gel out of the range of solutes for which it is appropriate. 

Oxidizer concentration is also one of the important factors in determining material removal rate, and it was found to increase with the oxidizer concentration [43,106]. With the increase of oxidizer concentration, both Wa and Ra decrease at first and then increase, the optimum concentration is 1 wt %, and relative low oxidizer concentration helps to get lower Wa and Ra values as shown in Figs. 36(a) and 36(b). High concentration of oxidizer may result in excessive corrosive wear, which will lead to the increasing of topographical variations. 

A higher-MHz NMR spectrometer is always a better choice, since the sensitivity of the experiment is proportional to the frequency of measurement. Moreover, with highly concentrated solutions, the presence of some solid particles can cause an increase in T) (FID will be short) and line broadening of the NMR signals will result. Therefore, an optimum concentration (say, 25-50 millimolar solution) is recommended. Of course, H-NMR spectra can be readily measured at much lower concentrations, though higher concentrations are necessary for recording - C-NMR spectra. 

Effect of Ccf. The addition of 0.005 M EDTA to the reaction mixtures, resulted in complete loss of activity, whereas the addition of CaClj increased the activity (figure 8). Calcium concentrations of 0.001 M and lower were without effect on PNL activity, the optimum concentration being in the range of 5 to 15 M, and higher concentration resulted in a decrease in activity. 

The enzyme had a requirement for calcium. The addition of EDTA to the reaction mixtures, resulted in complete loss of activity, whereas the addition of CaCl2 increased the activity (figure 8). Presumably, sufficient contaminating calcium ions were present in the dialyzed enzyme and substrate mixture to permit the limited activity of the controls, but apparently these were removed by chelation with EDTA. The optimum concentration was in the range of 5 to 15 M, and higher concentration resulted in a decrease in activity. Phoma medicaginis var. pinodella synthesizes a pectin lyase that lacked an absolute requirement for calcium ions but maximum enzyme activity required the presence of 1 mM Ca [25]. The lyase from Fusarium solani f sp. phaseoli, that is active on pectin and pectic acid, is calcium-dependent [30]. Most of the pectate lyases characterized are calcium-dependent the pectate lyase from Rhizoctonia solani [34] and the endopectate lyase fi om Fusarium solani f sp. pisi [31]. 

---