Dark period

Figure C 1.5.10. Nonnalized fluorescence intensity correlation function for a single terrylene molecule in p-terjDhenyl at 2 K. The solid line is tire tlieoretical curve. Regions of deviation from tire long-time value of unity due to photon antibunching (the finite lifetime of tire excited singlet state), Rabi oscillations (absorjDtion-stimulated emission cycles driven by tire laser field) and photon bunching (dark periods caused by intersystem crossing to tire triplet state) are indicated. Reproduced witli pennission from Plakhotnik et al [66], adapted from [118].

Now suppose we consider another extreme of the same type of experiment. This time we alternate extremely short light and dark periods of equal duration. If we again start with [M-] =0 when the light goes on, we expect the type of behavior shown in Fig. 6.5d, where the radical buildup is interrupted by the extinction of the light before it reaches [M-] We could use Eq. (6.43) to evaluate the maximum radical concentration achieved, if that were the... 

If the dark period is m times longer than the lit period, then the fraction of time that the sample is illuminated is 1/(1 + m)(m = 1 for the case considered above). 

Melatonin. Melatonin (A/-acetyl-5-metlioxytryptaniine) [73-31-4] C 2H gN2O2(250) is secreted from the pineal gland and retina during dark periods of the vertebrate circadian rhythm (65). Melatonin regulates biological rhythms and neuroendocrine function and is formed from serotonin (5-HT). 

Usually, although not always, the approach to the steady state following commencement of the illumination or the decay during a subsequent dark period is too rapid for satisfactory measurements. In such cases it is nevertheless possible to observe average rates of polymeriza-... 

We have screened 18 compoimds in single contaminant air feeds, and co-fed in air with TCE [3]. For each run, the initial inlet concentration is first measvired. Then, we allow a dark period during which the contaminated air feed passes... 

The recombination of trapped electrons and holes produces the fluorescence. Adsorbed oxygen scavenges electrons producing O2" which also is adsorbed. OJ is a much better quencher than Oj. Its accumulation under illumination therefore leads to the decrease in fluorescence intensity. During the dark period disappears. During the illumination in the presence of oxygen, the colloid undergoes photoanodic dissolution (see Sect. 3.2). The ZnS particles become smaller in this way, and this finally leads to an increase in fluorescence yield as already described for CdS. 

Assessment 3 days following treatment to dry lettuce seed. Four repetitions with 25 seeds per petri dish. Growth chamber at 25 C, 12 h light and 12 h dark periods. 

Infusion of prostaglandin D2 (200 pmol/min) or the adenosine A2a receptor agonist CGS21680 (20 pmol/min) for 2 h into the subarachnoid space under the BF, during the dark period, increased NREM sleep and reduced c-Fos protein in the TMN of rats when compared with saline-treated controls (Scammell et al., 1998, 2001). In contrast, infusion of the adenosine Ai receptor agonist N6-cyclopentyl-adenosine (2 pmol/min) in the same area did not have any effect on sleep-wakefulness or c-fos expression in the TMN. 

In a recent study, c-fos expression was examined in TMN neurons in spontaneously awake animals (Ko et al., 2003). These authors reported a strong correlation between c-fos expression in the TMN and the amount of wakefulness independent of the circadian cycle. In rats maintained on a normal 12 12 lightrdark cycle, wakefulness was increased and c-fos expression was also increased in the TMN during the dark period relative to the light period. In rats maintained in constant darkness, increased wakefulness and increased c-Fos protein in the TMN were observed during the subjective night, irrespective of the lighting condition. 

Feenstra M., Botterblom M., Mastenbrook S. (2000). Dopamine and noradrenaline efflux in the prefrontal cortex in the light and dark period effects of novelty and handling and comparison to the nucleus accumbens. Neuroscience 100, 741-8. 

Figure 8.1 The duration of NREM sleep and delta activity during NREM sleep following saline (open circles) or 0.5mg/kg MK-801 (filled circles), administered 6h after the start of the dark period. MK-801 initially produced a period of wakefulness approximately 3 h long. In the subsequent light period, NREM sleep duration (A), total integrated amplitude (TIA, a period amplitude measure similar to power) of NREM sleep delta (B), and NREM sleep delta integrated amplitude per minute (IA/min) (C) were all significantly increased above control levels.

Figure 8.2 A comparison of the effects on standardized NREM sleep delta total integrated amplitude (TIA) produced by (A) MK-801, (B) 12 h total sleep deprivation (TSD), and (C) MK-801 + TSD shows that the delta increase produced by MK-801 persists across a 12 h period of sleep deprivation. MK-801 injected at the start of the dark period produced a large increase in TIA that returned to baseline levels by the second hour of the light period. TSD throughout the 12 h dark period produced a 28% increase in TIA in the subsequent light period. MK-801 followed by TSD for the remainder of the dark period produced a 60% increase in light period delta TIA that was significantly greater than the effect of MK-801 alone or TSD alone. This finding indicated that MK-801 increased the homeostatic drive for delta.

The mathematical treatment of pulsing illumination has been described [Briers et al., 1926], After a number of cycles, the radical concentration oscillates uniformly with a constant radical concentration [M-] j 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 t = rt. The two radical concentrations are related by... 

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