A very important class of shell patterning is caused by pigment productions that occur only during a short time interval, followed by an inactive period without pigment production. Stripes parallel ...to the growing edge and oblique lines belong to this class of patterns. Such oscillations can occur if the antagonist reacts too slowly. Then, a change in activator concentration is not immediately backregulated since the antagonist reacts too slowly and the activation will proceed in a burst-like manner.
Many shells show patterns far more complex than those simulated so far. Figure 7.1 contains a collection of typical complex shell patterns. To show their inherent similarities, they are arranged such ...that each subsequent pattern contains elements of the preceding pattern as well as new features. Conus marmoreus (Figure 7.1a) shows white drop-like regions on a dark pigmented background. In Conus marchionatus (Figure 7.1b) the white drops are enlarged at the expense of the pigmented regions. The pattern is reminiscent of staggered wine glasses. Conus pennaceus (Figure 7.1c) shows, in addition, dark lines on a pigmented background, occasionally interrupted by small white drops.
A widely distributed subgroup of shell patterns result from the superposition of a stable and a periodic pattern. The upper shell in Figure 4.1 shows two sets of parallel relief-like lines. One set ...is oriented parallel to the growing edge and results from a thickening of the shell at periodic time intervals. The other set is oriented parallel to the direction of growth and results from a permanently enhanced deposition of shell material at regularly spaced positions. In this example, the two patterns do not interfere with each other, a situation that is more the exception than the rule, but it shows that the assumption of two superimposed systems is reasonable.
Everyday we are confronted with systems that have an inherent tendency to change. The weather, the stock market, or the economic situation are examples. Dramatic changes can be initiated by ...relatively small perturbations. In the stock market, for instance, even a rumour may be sufficient to trigger sales, lowering quotations and causing panic reactions in other shareholders.
Anti staphylococcal activity by Pseudomonas aeruginosa was investigated through the use of thereversed agar plate and the filter paper stamp methods. Investigation was also conducted on the dye ...production of different clinical isolates of Pseudomonas aeruginosa, the relationship between drug susceptibility and anti staphylococcal activity, and the influence of erythromycin on and staphylococcal activity. Seventy four strains of Pseudomonas aeruginosa were prepared which included 20 strains from pus, 34 strains from sputum and 20 strains from urine. These were then innoculated with methicillin resistant Staphylococcus aureus (MRSA). They were then cultured for 48 hours by using the reversed agar plate and the filter paper stamp methods. Anti staphylococcal activity was observed in 16 strains from pus (80%), 19 strains from sputum (55.9%) and 8 strains from urine (40%). The Pseudomonas aeruginosa strains which have no pigment tended to show poor anti staphylococcal activity. Drug susceptibility was tested using PIPC, AMK, IPM, CFS and OFLX. The strains which showed resistance to OFLX tended to show poor anti staphylococcal activity. Erythromycin inhibited the dye production of Pseudomonas aeruginosa but exhibited no effect on and staphylococcal activity. Consequently, these results suggest erythromicin has exhibited a previously unknown pharmacological effect, furthermore, anti staphylococcal activity was not caused by pigmentation only.
The effects of 60 Co gamma radiation on the production of the red nonessential tripyrrole pigment, prodigiosin, have been studied in Serratia marcescens. A comparison of the survival of pigmenting ...and nonpigmenting strains of S. marcescens has been carried out. Wild-type S. marcescens, Nima, which synthesizes prodigiosin, and three nonpigmenting mutant strains were examined. Measurement of colony-forming ability after gamma radiation is always greater in nonpigmenting (white) mutants of S. marcescens than in pigmenting strains. The red pigment may be acting as an endogenous radiosensitizer.
A cDNA encoding mouse tyrosinase was inserted into a plasmid containing the provirus of a replication competent avian leukosis virus (ALV). A viral stock produced from the plasmid was used to infect ...cultured tyrosinase-negative (ca/ca) unpigmented chick embryo melanocytes. Five days after infection many cells were producing very dark discrete melanosomes.
Nowadays 80% of scandium in China is obtained from titanium pigments production waste through a complex purification process. The study mainly focused on the purification of Sc from its concentrate ...generated from titanium pigments production waste by solvent extraction. Several extractants have been tried and 10% D2EHPA - 5% TBP - 85% sulfonated kerosene exhibited the best extraction performance towards Sc in 7 mol/L H2SO4 solution, so it was selected as the oil phase. 0.5% of H2O2 was added into the concentrated solution which can effectively inhibit the extraction of Ti. Both the extraction and back extraction parameters are optimized. The preferred extraction conditions were obtained, i.e., acidity: 7 mol/L H2SO4, the phase ratio A/O: 10, room temperature, mixed contact time: 30 min, Sc concentrate: 10 g/L, that the extraction rate of Sc in the above conditions was nearly 100%. NaOH was used for back extraction with the stripping rate 99% on the following conditions: 5 mol/L NaOH stripping for 30 min at a phase ratio A/O: 1 at 90 °C. Finally, H2C2O4 was used to further purify the back extraction product and Sc2(C2O4)3 precipitant formed. The final product Sc2O3 with a purity over 99.5% was obtained by calcining Sc2(C2O4)3 at 1000 °C for 2 h. A conceptual process for Sc purification was put forward and proved. The total recovery yield of Sc in the whole process is 95%.
10% D2EHPA - 5% TBP - 85% sulfonated kerosene was selected with the extraction efficiency of Sc over 99.9%. The usage of H2O2 can promote the extraction of scandium and inhibit the extraction of titanium. NaOH was used for back extraction with the stripping rate of 99%. H2C2O4 was used to further purify the back extraction product and Sc2(C2O4)3 precipitant formed, which is roast obtained Sc2O3. Finally, a conceptual process of purification Sc from its concentrate was put forward and proved in the laboratory with 99.5% Sc2O3 product obtained with a yield of 95%. Display omitted
•Several extractants were tried to purify Sc from its concentrate.•10% D2EHPA - 5% TBP - 85% sulfonated kerosene was selected with the extraction efficiency of Sc over 99%.•0.5% of H2O2 was added into the feed solution to inhibit the extraction of Ti.•5 mol/L NaOH at 90 °C can effectively strip Sc with the stripping rate of about 99%.•A simple flowsheet for Sc purification was proposed and 99.5% Sc2O3 was obtained with the yield over 95%.
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