Dormant period

Hydration gives rise to effects on pore filling and the consequent enhancement of mechanical performance (low-porosity pastes are stronger than high-porosity ones). The first fast hydration step is followed by a relatively dormant period that may last 6 months or more, depending on temperature, particle size, and aqueous phase composition. In order to control the hydration step, alkyl sulfonate salts surface-active substances (SAS) are used. 

In the latter part of stage 1, the cement particles in the paste become fiilly coated with a layer of hydrate products. This protective layer hinders the diffusion of the reacting species in and out of the reaction interphase, thus sharply reducing the rate of the various reactions. The system enters into a period of latency referred to as the induction or dormant period processes initiated during stage I, however, will continue throughout the induction period. 

Near the end of the dormant period, the rate of cement hydration increases sharply. The onset of the acceleration period has been attributed to the following effects [125] ... 

Cr(VI)/Silica develops polymerization activity only gradually when exposed to ethylene at 100°C in a slurry autoclave. An example is shown in Fig. 5, which depicts an experiment in which the catalyst was not immediately active upon introduction into the reactor, but first underwent a dormant period or induction time. The rate of polymerization then increased during the remainder of the experiment. This is thought to be due to the slow reduction of Cr(VI) by ethylene to the Cr(II) active site, or perhaps to the desorption of by-products such as formaldehyde (32). Thus, the concentration of active sites is probably not constant but increases with time. Below 100°C the induction time becomes longer until at about 60°C there is almost no activity. Conversely, increasing the temperature shortens the induction time. At 150°C the catalyst exhibits an immediate and constant activity in solution phase polymerization. 

These classical syntheses remained the available approaches for a long time, despite the huge number of clinical studies on thalidomide in the last third of the twentieth century. After a dormant period of more than 30 years,... 

After the accident, the cooling water tests revealed 14-percent ethylene glycol (antifreeze) in the system. Tests were conducted with the biocide and the ethylene glycol solution. Investigators learned that after a dormant period of several days, the temperature of the mixture suddenly increased and the solution released bromine gas. Testing showed that at elevated temperatures of about 140° F (60° C), the reaction occurred without the delay. 

A flame emission spectrometer therefore consists of an atom source, a monochromator and detector and is therefore simpler instrumentally than the corresponding atomic absorption system. Particular developments engendered by atomic absorption have restimulated interest in flame emission spectrometry after a dormant period. Chief of these is the use of the nitrous oxide—acetylene flame which is sufficiently hot to stimulate thermal atomic-emission from a wide range of metal elements. 

Onions form seed stalks after any dormant period. Improperly stored sets or cultivars not suited to the day length in your area may go to seed before forming bulbs. Ructu-ating temperatures or drying and wetting of soil may cause seed stalk formation. Harvest and use bulbs as soon as possible. 

Notice in Figure 1 that the catalysts were not active immediately after introduction into the reactor, but underwent a dormant period or induction time. Afterward the rate then increased during the rest of the experiment. This is thought to be due to reduction of Cr(VI) to the active valence, probably Cr(II), by ethylene. Zakharov and Ermakov and others have suggested that the gradual rise in rate is due to an increase in the number of active centers with time, and not to a change in the propagation rate constant. However, even under the best of conditions only a small fraction of the chromium is likely to be active. ... 

Resting structures are produced by some species. The ergot sclerotium produced by Claviceps species is the best-known example these dark structures develop in place of an ovary in a grass inflorescence (Stewart, 1957) they germinate to produce a sexual stroma, some first requiring a dormant period. 

The classic work in the synthesis of Cinchona alkaloids, which was initiated in the 1920s by Rabe and his co-workers and completed in the 1940s by Woodward and Doering, is described fully in a previous chapter (9). After a dormant period of more than 20 years in this field, interest was renewed in these alkaloids because of their antimalarial properties. Shortages of the Cinchona alkaloids from natural sources led to new efforts at total synthesis. 

Research over a period of seven years has provided an immense amount of information on the chemical nature of the precursors utilized by the Amaryllidaceae for alkaloid formation and the chemical processes involved. However, many fundamental questions concerning the role of the alkaloids in plant metabolism remain unanswered. Enzymes for the various transformations have not been purified or characterized. Alkaloid catabolism is a relatively unexplored research area. One paper has appeared which relates the quantitative estimation of various amino acids, both free and combined in the plant protein, with the period of plant development of the Narcissus Golden Sceptre. Phenylalanine and tyrosine are most prevalent during the periods of active growth, i.e., leaf and flower formation (175). Maximum alkaloid content was observed to occur during the dormant period. 

Ziegler -Natta complex as active site. The formation of the polycondensate does not proceed in one stroke. Rather each potential functionality can start to be active at a certain time and react with another monomer or likewise with an already formed polymer to form a polymer with a still higher degree of polymerization. After such a reaction step, the functionalities may be dormant for a certain time and after the dormant period again a reaction step will occur. For this reason, polycondensation is also addressed as step growth polymerization. 

For C3S , the enthalpy of hydration is 500kJkg , compared with 250, 850 and 330kJkg for C2S , C3A and C4AF , respectively. The setting period consists of several stages. The addition of water to dry cement initially causes a rapid, and highly exothermic, dissolution of ions and formation of hydrated species. This is followed by a dormant period (different explanations for which have been put forward), and then a final exothermic event which... 

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