4,168 research outputs found
Observations of Very High Energy Gamma-Rays during Moonlight and Twilight with the MAGIC Telescope
We study the capability of the MAGIC telescope to observe under moderate
moonlight. TeV gamma-ray signals from the Crab nebula were detected with the
MAGIC telescope during periods when the Moon was above the horizon and during
twilight. This was accomplished by increasing the trigger discriminator
thresholds. No change is necessary in the high voltage settings since the
camera PMTs were especially designed to avoid high currents. We characterize
the telescope performance by studying the effect of the moonlight on the
gamma-ray detection efficiency and sensitivity, as well as on the energy
threshold.Comment: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of
the MAGIC Collaboratio
Nonlinear growth generates age changes in the moments of the frequency distribution: the example of height in puberty
Higher moments of the frequency distribution of child height and weight change with age, particularly during puberty, though why is not known. Our aims were to confirm that height skewness and kurtosis change with age during puberty, to devise a model to explain why, and to test the model by analyzing the data longitudinally. Heights of 3245 Christ's Hospital School boys born during 1927-1956 were measured twice termly from 9 to 20 years (n = 129 508). Treating the data as independent, the mean, standard deviation (SD), skewness, and kurtosis were calculated in 40 age groups and plotted as functions of age t. The data were also analyzed longitudinally using the nonlinear random-effects growth model H( t) = h( t - epsilon) + alpha, with H( t) the cross-sectional data, h( t) the individual mean curve, and epsilon and alpha subject-specific random effects reflecting variability in age and height at peak height velocity (PHV). Mean height increased monotonically with age, while the SD, skewness, and kurtosis changed cyclically with, respectively, 1, 2, and 3 turning points. Surprisingly, their age curves corresponded closely in shape to the first, second, and third derivatives of the mean height curve. The growth model expanded as a Taylor series in e predicted such a pattern, and the longitudinal analysis showed that adjusting for age at PHV on a multiplicative scale largely removed the trends in the higher moments. A nonlinear growth process where subjects grow at different rates, such as in puberty, generates cyclical changes in the higher moments of the frequency distribution
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