Energy transfer in PPV-based conjugated polymers: a defocused widefield fluorescence microscopy study.

Both pendant and main chain conjugated MEH-PPV based polymers have been studied at the level of single chains using confocal and widefield fluorescence microscopy techniques. In particular, defocused widefield fluorescence is applied to reveal the extent of energy transfer in these polymers by identifying whether they act as single emitters. For main chain conjugated MEH-PPV, molecular weight and the surrounding matrix play a primary role in determining energy transport processes and whether single emitter behaviour is observed. Surprisingly in polymers with a saturated backbone but containing the same pendant MEH-PPV oligomer on each repeating unit, intra-chain energy transfer to a single emitter is also apparent. The results imply there is chromophore heterogeneity that can facilitate energy funneling to the emitting site. Both main chain conjugated and pendant MEH-PPV polymers exhibit changes in orientation of the emission dipole during a fluorescence trajectory of many seconds, whereas a model MEH-PPV oligomer does not. The results suggest that, in the polymers, the nature of the emitting chromophores can change during the time trajectory.

Recovery sleep at different times of the night following loss of the last four hours of sleep.

The sleep of 8 women was restricted to the first half of the night for 1 night on two separate occasions. On each occasion, heavy loss of REM (64%) and stage 2 (60%) with only a relatively light loss (20%) of slow wave sleep resulted. The purpose of the present study was to investigate whether or not the circadian timing of recovery sleep, particularly the second 4 h, would affect the response of the sleep system to the differential loss of the sleep stages. Recovery sleep commenced at 2000 h (i.e., after a normal daily span of 16 h of wakefulness) and was either continuous or interrupted after 4 h with 4 h of enforced wakefulness. Thus, the second 4 h of recovery sleep occurred between either 0000-0400 h or 0400-0800 h, two periods of the night normally associated with low and high levels of REM, respectively. The composition of recovery sleep, particularly the level of REM sleep, was found to be relatively unaffected by circadian factors. Instead, the response of the sleep system was mainly determined by stage 4 debt. It was suggested that obtaining a daily stage 4 quota acts as the primary drive mechanism of the sleep system.

Sleep learning during stage 2 and REM sleep.

Pairs of subjects were presented with a 20-item picture series at bedtime. In the latter part of the night, a tape-recorded series of 10 words, the verbal equivalent of half the original series of pictures, was repeated 10 times during either Stage 2 or REM sleep. Morning recall and recognition for repeated words was found to be facilitated following repetition during Stage 2 sleep, but relatively unaffected following repetition during REM sleep. However, adjusting for recall, the number of additional words elicited through recognition was found to be significantly greater for REM repeated words than for Stage 2 repeated words. It was suggested that retrieval limitations, perhaps as a result of REM state dependency, rather than storage inhibition may be the main locus of the initial recall failure. By comparison, Stage 2 sleep would seem to present both a lower barrier to memory storage and retrieval compatibility with wakefulness.

REM sleep and memory consolidation.

One proposal referring to a specific function of REM sleep has been that it is necessary for, or at least conductive to, the progress of memory consolidation. This hypothesis was tested by comparing the effects on story retention of REM deprivation against an S4 deprived control. It was found that recall accuracy following REM deprivation was significantly poorer than following S4 deprivation. Furthermore, the degree of deterioration in recall accuracy during REM recovery sleep was less than during S4 recovery sleep. These findings were interpreted as evidence for active REM facilitation of memory consolidation. However, alternative explanations based upon proactive influences need to be investigated.

Twisting the night away: the effects of all night disco dancing on reaction time.

8 subjects performed an unprepared simple reaction time task for 20 min. every 2 hr. while taking part in an all night disco dancing marathon (continuous exercise) and during a control (no exercise) night. Mean reaction times were significantly faster and less variable during the dance marathon. It was suggested that the effects of continuous exercise in the form of disco dancing may be to reduce drowsiness which in turn assists performance.

Predicting mood change on night shift.

This study examined the impact of night shift on six dimensions of mood. The efficacy of a range of personality, behavioural, and social/organizational predictors of these responses was also examined. Thirty-five female student nurses were studied during their first period of night work. ANOVAs indicated that only fatigue-inertia and vigour-activity were significantly affected by night work. Multivariate profile analyses revealed that significant changes were predominantly confined to the interval between the preceding rest day (B) and the first night (N1), although vigour-activity dropped significantly between N1 and N2 and rose significantly by N5 for one group of subjects. Multiple regression analyses revealed that morningness, neuroticism, work-non-work conflict, and sleep quality between shifts predicted fatigue-inertia. Extroversion and social support from both co-workers and family predicted vigour-activity. Extroversion and social support from co-workers appeared to predict the positive affect component of vigour-activity, rather than the vigour and energy component.

The impact of night work on psychological well-being.

This study tested the efficacy of selected personality, behavioural, and social/organizational variables as predictors of adaptation to night work. Sixty female student nurses were studied during their first 15 months of shiftwork. Twenty-two worked on rotating day and afternoon shifts throughout, while the remaining 38 began regular night shifts after six months. Psychological symptoms were measured at baseline (Stage 1), six months (Stage 2) and 15 months (Stage 3). Repeated measures analysis of variance revealed a significant shift group x symptoms interaction (p less than 0.05) between Stages 2 and 3. Only the night workers displayed a significant increase (Tukey HSD: p less than 0.01) in symptoms between Stages 1 and 3. Multiple regression analysis revealed that neuroticism and perceived work/nonwork conflict predicted symptoms at Stage 2. Night work, social support from supervisors, and morningness were predictors at Stage 3. These results suggest that organisational, behavioural, and physiological factors moderate the impact of night work on psychological well-being, and personality factors do not.

Psychometric evaluation of the early/late preferences scale.

This paper examines the psychometric quality of the Early/Late Preferences Scale (PS) relative to that of the Composite Morningness Scale (CS). Questionnaires were completed by 670 undergraduate students aged 16-37 years (mean 22.5), of whom 64% were female. Both scales displayed satisfactory inter-item correlations and similar total mean scores to those reported previously, although the CS had higher variability. Principal axis factor analysis produced single-factor solutions for both scales, although loadings for Items 7 and 9 on the PS were low. Internal consistencies for both scales were good (PS = 0.86, CS = 0.90) with only a small improvement achieved by deleting Items 7 and 9 from the PS. Test-retest reliability over 11 weeks was good for both scales (PS = 0.92, CS = 0.89). Differences between morning, evening and intermediate groups in self-rated alertness at different times of day, and significant correlations with other indices of morning-evening orientation, provided evidence of validity for both scales. These results indicate that PS is psychometrically comparable with CS. In view of its simpler format and lower cultural specificity, PS may be considered a preferable measure for most applications.

Auditory evoked potentials and transcendental meditation.

Auditory evoked potentials to tone stimuli were recorded from 8 practised meditators before, during, and after meditation, and also during light sleep. No consistent changes were noted between baseline and meditating AEPs, or between meditating and sleep AEPs.