Entropy difference between crystal phases

Abstract

R educed opportunity for sleep and reduced sleep quality are frequently re-lated to accidents involving shift-workers 1–3 . Poor-quality sleep and inadequate recovery leads to increased fatigue, decreased alert-ness and impaired performance in a variety of cognitive psychomotor tests 4 . However, the risks associated with fatigue are not well quantified. Here we equate the performance impairment caused by fatigue with that due to alcohol intoxication, and show that mod-erate levels of fatigue produce higher levels of impairment than the proscribed level of alcohol intoxication. Forty subjects participated in two coun-terbalanced experiments. In one they were kept awake for 28 hours (from 8:00 until 12:00 the following day), and in the other they were asked to consume 10–15 g alcohol at 30-min intervals from 8:00 until their mean blood alcohol concentration reached 0.10%. We measured cognitive psychomotor performance at half-hourly intervals using a computer-administered test of hand–eye coordination (an unpredictable tracking task). Results are expressed as a percentage of performance at the start of the session. Performance decreased significantly in both conditions. Between the tenth and twenty-sixth hours of wakefulness, mean relative performance on the tracking task decreased by 0.74% per hour. Regression analysis in the sustained wakefulness condi-tion revealed a linear correlation between mean relative performance and hours of wakefulness that accounted for roughly 90% of the variance (Fig. 1a). Regression analysis in the alcohol condi-tion indicated a significant linear correla-tion between subject's mean blood alcohol concentration and mean relative perfor-mance that accounted for roughly 70% of the variance (Fig. 1b). For each 0.01% increase in blood alcohol, performance decreased by 1.16%. Thus, at a mean blood alcohol concentration of 0.10%, mean rela-tive performance on the tracking task decreased, on average, by 11.6%. Equating the two rates at which perfor-mance declined (percentage decline per hour of wakefulness and percentage decline with change in blood alcohol concentra-tion), we calculated that the performance decrement for each hour of wakefulness between 10 and 26 hours was equivalent to the performance decrement observed with a 0.004% rise in blood alcohol concentra-tion. Therefore, after 17 hours of sustained wakefulness (3:00) cognitive psychomotor performance decreased to a level equivalent to the performance impairment observed at a blood alcohol concentration of 0.05%. This is the proscribed level of alcohol intox-ication in many western industrialized countries. After 24 hours of sustained wake-fulness (8:00) cognitive psychomotor per-formance decreased to a level equivalent to the performance deficit observed at a blood alcohol concentration of roughly 0.10%. Plotting mean relative performance and blood alcohol concentration 'equivalent' against hours of wakefulness (Fig. 2), it is clear that the effects of moderate sleep loss on performance are similar to moderate alcohol intoxication. As about 50% of shift-workers do not sleep on the day before the first night-shift 5 , and levels of fatigue on subsequent night-shifts can be even higher 6