RESUMO
We show that at low velocities the dynamics of a contact line of a water drop moving over a Teflon-like surface under ac electrowetting must be described as stick-slip motion, rather than one continuous movement. At high velocities we observe a transition to a slipping regime. In the slipping regime the observed dependence of the contact angle is well described by a linearization of both the hydrodynamic and the molecular-kinetic model for the dynamic contact line behavior. The overall geometry of the drop also has a strong influence on the contact angle: if the drop is confined to a disk-like shape with radius R, much larger than the capillary length, and height h, smaller than the capillary length, the advancing angle increases steeper with velocity as the aspect ratio h/R is smaller. Although influence of the flow field near a contact line on the contact angle behavior has also been observed in other experiments, these observations do not fit either model. Finally, in our ac experiments no sudden increase of the hysteresis beyond a certain voltage and velocity was observed, as reported by other authors for a dc voltage, but instead we find with increasing voltage a steady decrease of the hysteresis.
RESUMO
BACKGROUND: One of the most frequently investigated hypotheses of the pathophysiology underlying Seasonal Affective Disorder (SAD) is a disturbance of circadian rhythms. Since the circadian system as well as other non-visual effects is especially sensitive to blue light, a new light therapy device with blue enriched polychromatic light was tested for its efficacy to treat SAD. METHODS: Within one winter 52 patients were treated in one of three conditions: 30 min full spectrum light (9000 lx, 5000 K), 30 min blue-enriched light (9000 lx, 17,000 K), or 20 min blue-enriched light. The study lasted 22 days with 10 days of morning-light treatment on weekdays during the first 2 weeks. RESULTS: Depressive symptoms (SIGH SAD) diminished over the 3-week period in all conditions, with no significant differences between conditions. The percentage responders were high, differing from 75%, 59% and 71% for the standard-LT, 30 min blue-enriched-LT, and 20 min blue-enriched-LT, respectively. CONCLUSION: The lack of superiority of high intensity blue-enriched light over standard bright light treatment does not clearly support nor rule out the possibility of an important role for the circadian system or the blue sensitive non-visual image forming system in general, in the pathophysiology of SAD. The lack of a difference between conditions may also be the result of a saturated response to the high light intensities used. Recent data indeed suggest that low intensity blue-enriched light may be as effective as standard bright light treatment. The possibility of improving light therapy for SAD patients by applying light of shorter duration or at lower light intensities is highly relevant for optimizing treatment and will help to clarify the role of the circadian system and/or the non-image forming photoreceptors in SAD pathophysiology. CLINICAL TRIAL: https://register.clinicaltrials.gov: NCT01048294.
