Our daily activities require vigilance. Therefore, it is useful to externally monitor and predict our vigilance level using a straightforward method. It is known that the vigilance level is linked to pupillary fluctuations via Locus Coeruleus and Norepinephrine (LC-NE) system. However, previous methods of estimating long-term vigilance require monitoring pupillary fluctuations at rest over a long period. We developed a method of predicting the short-term vigilance level by monitoring pupillary fluctuation for a shorter period consisting of several seconds. The LC activity also fluctuates at a timescale of seconds. Therefore, we hypothesized that the short-term vigilance level could be estimated using pupillary fluctuations in a short period and quantified their amplitude as the Micro-Pupillary Unrest Index (M-PUI). We found an intra-individual trial-by-trial positive correlation between Reaction Time (RT) reflecting the short-term vigilance level and M-PUI in the period immediately before the target onset in a Psychomotor Vigilance Task (PVT). This relationship was most evident when the fluctuation was smoothed by a Hanning window of approximately 50 to 100 ms (including cases of down-sampled data at 100 and 50 Hz), and M-PUI was calculated in the period up to one or two seconds before the target onset. These results suggest that M-PUI can monitor and predict fluctuating levels of vigilance. M-PUI is also useful for examining pupillary fluctuations in a short period for elucidating the psychophysiological mechanisms of short-term vigilance.
Time-dependent X-ray photoelectron spectroscopy (XPS) was observed for adsorbates of dimethylaluminum hydride formed on SiO2 surfaces. The peak intensity of the C 1s spectra decreased slowly under 1847-eV Al Kα X-ray irradiation, while the binding energy of the Al 2p spectra increased. The time dependence of the XPS spectra varied for the adsorbates formed over a range of temperatures from room temperature up to 200° C. The time dependent XPS spectra was explained by the decomposition of the adsorbates. However decomposition was not complete enough to produce Al or Al2O3. Indirect decomposition by secondary electrons was suggested from X-ray induced electron emission measurements.
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