Pre-induction period

However, in one study 60 patients were given one of three treatments before induction of anaesthesia with propofol esmolol 1 mg/kg followed by an infusion of250 micrograms/kg per minute midazolam or placebo (sodium chloride 0.9%). No opioids were given. Esmolol and midazolam reduced the required induction doses of propofol by 25% and 45%, respectively. Esmolol reduced the mean heart rate by 7.6 bpm compared with placebo in the pre-induction period, and the only adverse effect noted was a transient episode of bradycardia (44 bpm) in one patient receiving esmolol. Esmolol reduces cardiac output by reduction of heart rate and stroke volume and this possibly reduces the required induction dose of propofol by changing its distribution."... 

The addition of gypsum is radically modifying the C3A hydration process. A long induction period appears, followed by the ciystallization of ettringite (Fig. 3.48). The preinduction period depends substantially on the rate of sulphate dissolution [ 127]. As it is commonly known, C3 A reacts with water violently and in the absence of gypsum hemihydrate or sodium and potassium sulphates, a certain amount of hexagonal hydrates is formed in the pre-induction period or even the monosul-phoaluminate [128]. 

The beneficial effect of gypsum consists in the simultaneous acceleration of alite hydration, mainly in the pre-induction period [26, 37]. The transfer of SO " ions to the C-S-H was detected [20]. However, these ions are poorly bound, they are rather adsorbed on the surface of C-S-H gel [38] (seep. 3.2.3). According to Bentur [39] the effect of gypsum on cement hydration should be considered in these two aspects. Gypsum has an impact on the amount and constitution of C-S-H gel. On the other hand, in the presence of gypsum the amount of C-S-H increases but the cohesiveness, being the function of C/S ratio is lowered ... 

Immediately upon contact of the cement with water, in the pre-induction period, a rapid dissolution of ionic species in the liquid phase and the formation of hydrate phases get under way. Alkali sulfates present in the cement dissolve completely within seconds, contributing K, Na, and SO " ions. Calciiun sulfate dissolves imtil saturation, thus contributing Ca and ions. Small amoimts of tricalcium silicate (about 1-5%)... 

The decomposition kinetics of mercury fulminate [725] are significantly influenced by ageing, pre-irradiation and crushing these additional features of reaction facilitated interpretation of the observations and, in particular, the role of intergranular material in salt breakdown. Following a slow evolution of gas ( 0.1%) during the induction period, the accelerator process for the fresh salt obeyed the exponential law [eqn. (8)] when a < 0.35. The induction period for the aged salt was somewhat shorter and here the acceleratory process obeyed the cube law [eqn. (2), n = 3] and E = 113 kj mole-1. 

The decomposition of KMn04 is sensitive to pre-irradiation [899] by UV [396], X-rays, 7-rays, protons and neutrons. The effects of such pretreatment, which increase with dosage, are to reduce the induction period... 

This expression fitted the acceleratory period of the a—time curves, followed by first-order decay and E = 122 2 kJ mole-1. No disintegration of small crystals was observed but pre-irradiated crystals [909] shattered on completion of the induction period. X-ray diffraction studies [910] confirm the existence of strain during the formation of decomposition product. Addition of small amounts (5% by mass) of ZnO or Th02 accelerated the decomposition of AgMn04 at 388 K. Ti02 reduced the rate, while NiO and Co304 had no effect [911]. 

Pre-irradiation of the salt with X-rays [1075] increased the extent of the initial deceleratory rate process, an effect attributed to the promotion of the electron transfer step. Neutron irradiation [1074] accelerated the decomposition rate and reduced the magnitude of E for the induction period from 216 to 159 kJ mole-1. 

In a formal sense, complexes 1 represent pre-catalysts that convert in the first turn of the catalytic cycle (vide infra) into ruthenium methylidene species of type 3 which are believed to be the actual propagating species in solution (Schemes 2,4). The ease of formation of 3 strongly depends on the electronic properties of the original carbene moiety in 1. In addition to complexes la-c with R1=CH=CPh2, ruthenium carbenes with Rx=aryl (e.g. Id, Scheme 3) constitute another class of excellent metathesis pre-catalysts, which afford the methylidene complex 3 after an even shorter induction period [5]. In contrast, any kind of electron-withdrawing (e.g. -COOR) or electron-donating substitu-... 

Time Factor Prior to Occurrence of a Thermal Explosion (Induction Periods). In the study of spontaneous explosions occurring in closed vessels, a well defined induction period frequently elapses prior to the development of an actual explosion. The length of this time interval has been observed to be anywhere from a few seconds to several minutes, depending upon the experimental conditions employed. Such observations are not surprising, in view of the fact that in order for an explosion to occur a build-up either of the internal energy or of chain carriers is first required. The rate of such a nonstationary process would then be expected to determine the duration of these pre-explosion times. For the case of a purely thermal explosion, the over-all rate of heat release, dq/di, prior to explosion is given by... 

The effects of slow neutron irradiation caused color changes and darkening in most of the expl crystals, indicating the formation of F centers and nuclei, and subsequently affected the thermal decompns of the expls. The rates of thermal decompn as measured by pressuretime curves for irradiated Pb azide are shown in Fig 2. With Li azide the effect of pre-irradiation with slow neutrons is to cut down the induction period to about one-half and to increase the rate of decompn considerably... 

Thermal decompn studies on Ba and Sr azides pre-irradiated with 1 MeV gamma rays were conducted by Prout and Moore (Refs 131 149). With dehydrated Ba azide a total gamma dose of 20 Mrads (2.24 x 106 R) practically eliminated the induction period and increased the acceleration of the decompn.The same effect was evidenced with Sr azide but the sensitivity of Sr azide to gamma rays exceeds that of Ba azide and other materials... 

Figure 2.11 Reaction profile showing the substrate conversion in a pre-equilibrium system followed by first-order kinetics. Note the importance of frequent sampling in this case, sampling every 5 min would not show the induction period (compare the + and symbols). The inset shows a generic catalytic cycle with a pre-equilibrium step.

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