Electron and muon parameters of EAS and the composition of primary cosmic rays in 10(15) to approximately 10(16) eV

Estimation of the relative intensities of protons and heavy nuclei in primary cosmic rays in the energy region 10 to the 15th power approx. 10 to the 17th power eV, was done by a systematic comparison between all available observed data on various parameters of extensive air showers (EAS) and the results of simulation. The interaction model used is an extrapolation of scaling violation indicated by recent pp collider results. A composition consisting of various percentages of Fe in an otherwise pure proton beam was assumed. Greatest overall consistency between the data and the simulation is found when the Fe fraction is in the region of 25%

The positive excess of cosmic ray muons at large zenith angles

Details of two solid iron magnetic spectrographs, incorporating neon flash tubes, with m.d.m.'s. of 300 GeV/o and 1950 GeV/c are presented, as are the results on the µ(^+)/µ(^-)ratio in the zenith angular ranges 77.º5 - 90º , and 82.5º - 90º based on samples of 10832 particles and 2167 particles respectively, obtained with these instruments. In the energy region where comparison with the work of other authors can be made agreement obtains. The overall results confirm, in general, previous values below 200 GeV but do not show any great evidence for a sharp minimum in the ratio in the region of 50 - 100 G-eV as reported by some authors. At higher energies the present results do not show a rapidly increasing ratio, as was expected from an extrapolation of earlier measurements. A review of all published measurements on the µ(^+)/µ(^-) ratio is presented, which suggests an approximately constant ratio from E-3 - 10(^3) GeV, of 1,20 - 1.25. In an effort to give a theoretical interpretation of the results it is shown that pion production within the framework of a statistical model based on our knowledge of nucleon interactions at high energies will not account for the experimental data. The effect of, and evidence for, the production of kaons, subject to certain assumptions, is investigated and it is concluded that, under the assumptions considered, the adopted value of the K/π ratio is not sufficient to account for the data in the region Eµ= 10 - 50 G-eV. The effect of other dynamical models such as the isobar model and the O.P,3. model are considered. It is argued that the production of T = 1/2 isobars with a slowly decreasing cross-section, combined with the other features of nucleon interactions as observed at accelerator energies, is sufficient to account for the present experimental position when the errors in the experimental data are taken into account, but none of several proposed models for particle production in high energy interactions can be uniquely selected on the basis of the results

Search for gamma-rays above 400 GeV from Geminga

Observations of Geminga made at the Whipple Observatory using the atmospheric Cherenkov technique during the moonless periods of November 1983 to February 1984 and November 1984 till February 1985 were examined for evidence for the emission of gamma rays with energy in excess of approx 400 GeV. Evidence of either a steady flux or a flux pulsed with a period near 60 seconds were studied. In neither case was any significant effect observed, enabling the establishment 3 of sigma upper limits of 5.5 x 10 to the -11th power photons/sq cm/s and 2.0 x 10 to the -11th power photons/sq cm/s for the steady and pulsed emission respectively. The limit to the pulsed flux is approximately a factor of six below that predicted

Application of imaging to the atmospheric Cherenkov technique

Turver and Weekes proposed using a system of phototubes in the focal plane of a large reflector to give an air Cherenkov camera for gamma ray astronomy. Preliminary results with a 19 element camera have been reported previously. In 1983 the camera was increased to 37 pixels; it has now been routinely operated for two years. A brief physical description of the camera, its mode of operation, and the data reduction procedures are presented. The Monte Carlo simultations on which these are based on also reviewed

Observations of the Crab Nebula at energies 4.10(11)

Since the development of gamma-ray astronomical telescopes, the Crab Nebula has been a prime target for observations. From 100 to 1000 MeV, the pulsar PSR0531 is the dominant source with a light-curve similar to that seen at lower energies; there is also some evidence for longterm amplitude variations but none for emission from the Nebula itself. In the very high energy gamma-ray region there have been reported detections of pulsed emission with longterm time variations from minutes to months. Recently a pulsed flux has been reported that resisted over a long time interval. The detection of a flux from the Nebula at the 3 sigma level at energies of 3x1011eV was reported; there was no evidence of periodic emissions on any time scale during the three years of observations. A new measurement of very high energy gamma rays from the Crab Nebula is reported using the imaging system on the Whipple Observatory 10m reflector

Solidification of small para-H2 clusters at zero temperature

We have determined the ground-state energies of para-H$_2$ clusters at zero temperature using the diffusion Monte Carlo method. The liquid or solid character of each cluster is investigated by restricting the phase through the use of proper importance sampling. Our results show inhomogeneous crystallization of clusters, with alternating behavior between liquid and solid phases up to N=55. From there on, all clusters are solid. The ground-state energies in the range N=13--75 are established and the stable phase of each cluster is determined. In spite of the small differences observed between the energy of liquid and solid clusters, the corresponding density profiles are significantly different, feature that can help to solve ambiguities in the determination of the specific phase of H$_2$ clusters.Comment: 17 pages, accepted for publication in J. Phys. Chem.

Vitamin D Deficiency and Its Health Consequences in Africa

Africa is heterogeneous in latitude, geography, climate, food availability, religious and cultural practices, and skin pigmentation. It is expected, therefore, that prevalence of vitamin D deficiency varies widely, in line with influences on skin exposure to UVB sunshine. Furthermore, low calcium intakes and heavy burden of infectious disease common in many countries may increase vitamin D utilization and turnover. Studies of plasma 25OHD concentration indicate a spectrum from clinical deficiency to values at the high end of the physiological range; however, data are limited. Representative studies of status in different countries, using comparable analytical techniques, and of relationships between vitamin D status and risk of infectious and chronic diseases relevant to the African context are needed. Public health measures to secure vitamin D adequacy cannot encompass the whole continent and need to be developed locally