Pulsar Informatics (United States)

BackgroundA purpose of duty-hour regulations is to reduce sleep deprivation in medical trainees, but their effects on sleep, sleepiness, and alertness are largely unknown.MethodsWe randomly assigned 63 internal-medicine residency programs in the United States to follow either standard 2011 duty-hour policies or flexible policies that maintained an 80-hour workweek without limits on shift length or mandatory time off between shifts. Sleep duration and morning sleepiness and alertness were compared between the two groups by means of a noninferiority design, with outcome measures including sleep duration measured with actigraphy, the Karolinska Sleepiness Scale (with scores ranging from 1 [extremely alert] to 9 [extremely sleepy, fighting sleep]), and a brief computerized Psychomotor Vigilance Test (PVT-B), with long response times (lapses) indicating reduced alertness.ResultsData were obtained over a period of 14 days for 205 interns at six flexible programs and 193 interns at six standard programs. The average sleep time per 24 hours was 6.85 hours (95% confidence interval [CI], 6.61 to 7.10) among those in flexible programs and 7.03 hours (95% CI, 6.78 to 7.27) among those in standard programs. Sleep duration in flexible programs was noninferior to that in standard programs (between-group difference, −0.17 hours per 24 hours; one-sided lower limit of the 95% confidence interval, −0.45 hours; noninferiority margin, −0.5 hours; P=0.02 for noninferiority), as was the score on the Karolinska Sleepiness Scale (between-group difference, 0.12 points; one-sided upper limit of the 95% confidence interval, 0.31 points; noninferiority margin, 1 point; P<0.001). Noninferiority was not established for alertness according to the PVT-B (between-group difference, −0.3 lapses; one-sided upper limit of the 95% confidence interval, 1.6 lapses; noninferiority margin, 1 lapse; P=0.10).ConclusionsThis noninferiority trial showed no more chronic sleep loss or sleepiness across trial days among interns in flexible programs than among those in standard programs. Noninferiority of the flexible group for alertness was not established. (Funded by the National Heart, Lung, and Blood Institute and American Council for Graduate Medical Education; ClinicalTrials.gov number, NCT02274818.)

Chronic nocturnal sleep restriction results in accumulation of neurobehavioral impairment across days. The purpose of this study was to determine whether time of day modulates the effects of sleep restriction on objective daytime performance deficits and subjective sleepiness across days of chronic sleep restriction. There were N = 90 healthy adults (21-49 yr; 38 women) who participated in a 14-d laboratory protocol involving randomization to 1 of 18 schedules of restricted nocturnal sleep with and without a diurnal nap for 10 consecutive days. The total time available for daily sleep ranged from 4.2 h to 8.2 h across conditions. Performance lapses on the psychomotor vigilance test (PVT) and subjective sleepiness were measured each day every 2 h during scheduled wakefulness. Nonlinear mixed-effects regression was used to test the hypothesis that there would be an interaction between time of day and the accumulation (slope across days) of neurobehavioral sleepiness. In agreement with earlier studies, less sleep time resulted in faster accumulation of deficits across days. Time of day significantly affected this relationship for both PVT lapses and subjective sleepiness. The build-up rate of cumulative neurobehavioral deficits across days was largest at 0800 and became progressively smaller across the hours of the day, especially between 1600 and 2000. Following 8 d of sleep restricted to 4 h/d, subjects averaged 8.3 more PVT performance lapses at 0800 than at 1800. This study provides evidence that the circadian system has a substantial modulatory effect on cumulative impairment from chronic sleep restriction and that it facilitates a period of relatively protected alertness in the late afternoon/early evening hours when nocturnal sleep is chronically restricted.

The human circadian pacemaker is a biological timekeep ing mechanism that governs alertness as well as many other physiological processes of the human body. It is widely accepted that daytime alertness is maximized when an individual's sleepjwake schedule and circadian pacemaker are synchronized. Unfortunately today's world is characterized by widely distributed activity schedules which often make this difficult. However research in chronobiology indicates that ambient light stimulus can he used to phase advance or delay the human circadian pacemaker. To optimally control the human circadian pacemaker using light, the authors present a model based predictive control system. This ap proach readily facilitates closed-loop control and elegantly handles the constraints present in a typical human environment, thus has merit for a number of practical applications.

The unique atmospheric environment on Titan has stimulated great interest in its organic chemistry. Recently1 we proposed that simple organic-nitrogen compounds such as HCN could be efficiently formed by cosmic ray bombardment of a nitrogen-containing atmosphere on Titan. Voyager I has now verified that molecular nitrogen is indeed the major constituent on Titan2–4 and that HCN is also present2. Based on these new data, we now propose that even more complex organic-nitrogen molecules such as ethyl cyanide (CH3CH2CN), vinyl cyanide (CH2CHCN), and cyanoacetylene (HCCCN) may be formed efficiently in the lower atmosphere of Titan, where lower temperatures and higher densities will ensure the efficacy of three-body ion–molecule association reactions. Interestingly, these compounds have been found in several dark interstellar clouds5,6, thus the chemistry suggested here is analogous to that proposed as an explanation of interstellar cyanopolyynes7. The only difference is the role played by three-body association reactions in the dense lower atmosphere of Titan. The mechanism proposed here rests upon a firmer experimental foundation than the analogous radiative association reactions in interstellar clouds.

Observations of the Martian sky, Phobos, and the sun were taken with the Viking lander imaging cameras to obtain information on the properties of the atmospheric aerosols. Atmospheric optical depths were derived from the observations of the brightness of the celestial objects. Information on the absorption coefficient, mean size, and shape of the aerosols was derived from studies of the sky brightness. For this purpose we used a multiple-scattering computer code that employed a recently developed technique for treating scattering by nonspherical particles. By monitoring the brightness of the twilight sky we obtained information on the vertical distribution of the particles. Three types of aerosols are inferred to have been present over the landers during the summer and fall season in their hemisphere. A ground fog made of water ice particles was present throughout this period. It formed late at night during the summer season and dissipated during the morning. We infer that during the summer the frost point temperature was 195°K and the water vapor volume mixing ratio equaled about 1× 0−4 near the ground at VL-2. Assuming that condensation occurs only on suspended soil particles, we estimate that the average particle radius of the fog was about 2 μm and that the fog's depth equaled approximately 0.4 km. A higher-level ice cloud was prominent only during the fall season, when it was a sporadic source of atmospheric opacity at VL-2. The formation of upper level water ice clouds during the summer may have been inhibited by dust heating of the atmosphere. Suspended soil particles were present throughout the period of observation. During the summer they constituted the only major source of opacity in the afternoon and most of the night. The cross-section weighted mean radius of these aerosols is about 0.4 μm. They have a nonspherical but equidimensional shape and rough surfaces. These soil particles have a scale height of about 10 km, which is comparable to the gas scale height, and they extend to an altitude of at least 30 km. The principal opaque mineral in these particles is magnetite, which constitutes 10%±5% by volume of this material. We propose that soil particles, as well as any associated water ice, are eliminated from the atmosphere, in part, by their acting as condensation sites for the growth of CO2 ice particles in the winter polar regions. The resultant CO2-H2O-dust particle is much larger and therefore has a much higher fallout velocity than an uncoated dust or water ice particle.

A mathematical model of a quadrispherical electrostatic analyzer is formulated to give the response of such an instrument to a monoenergetic, unidirectional charged particle beam. The model is developed taking into account the aperture and collector geometry and it does not rely on the usual simplifying assumptions that the ratio of the analyzer plate separation to the mean radius is small or that any of the angular or energy acceptance windows are negligible. The model is compared to calibration data and is found to agree well. It is also readily adaptable to the determination of the response function of electrostatic analyzers with other patrial spherical geometries utilizing an arbitrary charged particle distribution input function.