Intermittent illumination

Figure 6.5 Schematic illustrations showing the variation of [M-] with time under conditions of continuous illumination (a-c) and intermittent illumination (d-f). The time in darkness is indicated as t. ...

For intermittent illumination with very slow blinking (Rp)slow° ... 

Thus if we were to compare the rate of polymerization with intermittent illumination relative to that with continuous illumination, but under otherwise identical conditions, we would observe the following limits for equal periods of light and dark ... 

Fig. 18.—The ratio of the average radical concentration for intermittent illumination to its value for steady illumination plotted against log I/ts), The ratio r of dark to light intervals is three. (Matheson, Auer, Bevilacqua, and Hart. )...

Fig. 19.—Schematic diagram of apparatus used by Kwart, Broadbent, and Bartlett for polymerization with intermittent illumination.

In the ripple method a series of ripples is caused to travel over the surface of the liquid, the ripples being formed by means of an an electrically driven tuning fork dipping into the liquid. If viewed by means of intermittent illumination conveniently arranged by periodic interception of the light by interposition of a screen attached to one limb of the fork, apparently stationary waves may be observed and the mean wave length readily determined. 

Intermittent Illumination. See Cameras, High Speed in Vol 2, pp Cl 3-19 High-Speed Photography in this Vol... 

The life-time, r, of the radicals can be determined from the ratio of overall rates of polymerization measured at the steady- and unsteady state as a result of intermittent illumination by the rotating sector. In Fig. 3.3-10 the rate constant, kp, of chain propagation (left) and kh that of termination (right), are plotted versus the pressure. Both rate constants increase with increasing temperature. The energy of activation of chain propagation is Ep = 37 kJ/mol, and that of chain termination is E, = 9.9 kJ/mol. The influence of pressure is... 

Fig. 10. Variation in 2"2Hg fractional abundance with How rate for various organic chloride s. Intermittent illumination 1. ethyl chloride 2. isopropyl chloride 0. vinyl chloride 4. methyl chloride 5. frrf-biityl chloride. Steady illumination (i. vinyl chloride 7. isopropyl chloride 8. methyl chloride f). ethyl chloride 10. ierZ-butyl chloride,...

Fig. 111. Variation in 202IIg fractional abundance with vinyl cliloiide pressure. O— Intermittent illumination Q—steady illumination.

The data on kp and kt as reported in the literature differ considerably. Therefore, we conducted new studies on methyl methacrylate (MMA), benzyl methacrylate (BMA), and styrene (St) as monomers. The constants were obtained by applying the method of intermittent illumination (rotating sector) combined with stationary state methods. The viscosity of the solvents varied between 0.5 and 100 cP. No mixed solvents composed of low- and high-molecular components were used but pure solvents only, the molecules of which did not deviate very much from a spherical form (methyl formate, diethyl phthalate, diethyl malonate, dimethyl glycol phthalate, etc.). 

Two processes may be distinguished from the changes in the surface potential due to illumination a rapid rise and fall of the potential corresponding to short intervals of illumination and darkness. During intermittent illumination, the rapid process is accompanied by a slow overall rise in the surface potential. The slow rise is matched by a very slow decay in the dark. Both processes, the rapid and the slow one, are due to the behaviour of oxygen. 

Isotopic enrichment has also been found by monoisotopic photosensitization for mixtures of natural mercury and alkyl chlorides and vinyl chloride by similar processes. Isotopic enrichment is dependent on such factors as lamp temperatures, flow rates, and substrate pressures. Enrichment increases with decreasing lamp temperature and increasing flow rate, since process (VIII-1) is more ellicient at low temperatures and Cl atoms react with natural mercury containing higher fractions of 202Hg in (VIII-3) at higher flow rates of HC1 or under intermittent illumination. The intermittent illumination results in higher enrichment than the steady illumination. 

Fig. 12. Source-drain current in an intermittently illuminated a-Si H FET. (The transistor is an experimental device using thermally grown Si02 as a gate dielectric in order to minimize...

Wang, C.Y., R. Pagel, D.W. Bahnemann and J.K. Dohrmann (2004a). Quantum yield of formaldehyde formation in the presence of colloidal Ti02-based photocatalysts Effect of intermittent illumination, platinization, and deoxygenation. Journal of Physical Chemistry B, 108(37), 14082-14092. 

Regardless of the photo catalyst employed, repetitive laser pulse illumination increased 0hcho in the oxygenated suspensions by a factor of ca. 1.5 in comparison with CW illumination, although in both modes of photolysis the time-averaged photon absorption rate was approximately the same [82], Previous studies on intermittent illumination in Ti02 photocatalysis offer no satisfying explanation for this observation [86-91]. 

A considerable amount of water can evaporate from the soil and then move in air packets up through the vegetation. For instance, from a moist, intermittently illuminated soil, such as commonly occurs in a temperate forest, can be 0.2 to 1.0 mmol m-2 s-1. (For comparison, 0.5 mmol m-2 s-1 corresponds to a depth of water of 0.8 mm/day or 280 mm/year.) If a flow of 0.5 mmol m-2 s-1 occurs across a resistance of 290 s m-1 to reach a distance 0.1 m above the ground, using Equation 9.4 (by which Acj , = Jwrj ) we calculate that the drop in water vapor from the ground to this level is... 

Intermittent illumination, light periods V 10 s, dark periods v-10 s. 

Figure 2 (B) shows thermoluminescence bands generated by mature wheat leaves [curves (a) and (b)] and by greening wheat leaves grown under intermittent illumination [curves (c) and (d)]. The continuous curves are for materials illuminated for I minute at -60 °C [curves (a) and (c)], and at-20 °C [curves (b) and (d)] the dashed curves are for the same materials without prior illumination. Each thermoluminescence band has its own (approximate) emission temperature Zy band( -45 °C where the subscript V stands for variable location ofthe band), A-band (-10 °C), B,-band (25 °C), B2-band (40 °C) and C-band (+55 °C). The C band is the major emission band in etiolated leaves [solid curves in (c) and (d)] and is apparently unaffected by prior actinic illumination [dashed curves in (c) and (d)]. Illumination of fully greened, mature leaves at -60 °C produces a weak Zy-band at -45 °C, a weakened C-band at 55 °C, a strong composite B-band, with Bi-band at 20 °C and B2-band shoulder at 40 °C, which together form the composite B-band. When the mature leaves were illuminated at -20 °C instead and immediately cooled [curve (b)], the glow curve is quite different a prominent A-band appears at -15/-20 °C, while the (Bj+B2)-band is much weaker and the Zy band is barely observable. Thus the A- and B-bands appear to be complementary to each other in amplitude illumination at -60 °C produces a strong B-band and no A-band, while illumination at -20° C produces predominantly A-band and much less B-band. Both the A...

Fig. 2. Left An idealized representation of a thermoluminescence profile illustrating labeling employed in this chapter. Right TL bands of mature leaves of wheat [(a) and (b)] and greening leaves of wheat grown under intermittent illumination [(c) and (d)J. Illumination at -60 C [(a) and (c)] and at -20 C [(b) and (d)]. The dashed-line profiles show TL bands produced without illumination. See text for discussion. Figure source Inoue, Ichikawa and Shibata (1976) Development of thermoluminescence bands during greening of wheat leaves under continuous and intermittent illumination. Photochem Photobiol 23 126.

Y Inoue, T Ichikawa and K Shibata (1976) Development ot thermoluminescence bands during the greening of wheat leaves under continuous and intermittent illumination. Photochem Photobiol 23 125-130... 

Problem 6.16 Typical values determined from photoinitiated radical chain polymerization with intermittent illumination are in the range 0.1-10 s. Calculate from this the duration of the non-steady-state period and comment on the validity of steady-state approximation made in a typical polymerization study. 

Figure 6.4 Schematic representation of variation of chain radical concentration [M j over (a) cycles of long illumination period (i) and dark period (f) and (b) cycles of short (intermittent) illumination period (t) and dark period (If).

The mathematical treatment of intermittent illumination has been described [37]. As explained above, in relation to Fig. 6.4(b), the radical concentration, after a number of cycles, oscillate uniformly with a constant radical concentration [M ]i at the end of each light period of duration t and a constant radical concentration [M ]2 at the end of each dark period of duration if = rt. 

Primary Quantum Yield Determination by Intermittent Illumination in... 

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