Deployable Helical Antennas for CubeSats

This paper explores the behavior of a self-deploying helical pantograph antenna for CubeSats. The helical pantograph concept is described along with concepts for attachment to the satellite bus. Finite element folding simulations of a pantograph consisting of eight helices are presented and compared to compaction force experiments done on a prototype antenna. Reflection coefficient test are also presented, demonstrating the operating frequency range of the prototype antenna. The helical pantograph is shown to be a promising alternative to current small satellite antenna solutions

Inhomogeneities in dusty universe - a possible alternative to dark energy?

There have been of late renewed debates on the role of inhomogeneities to explain the observed late acceleration of the universe. We have looked into the problem analytically with the help of the well known spherically symmetric but inhomogeneous Lemaitre-Tolman-Bondi(LTB) model generalised to higher dimensions. It is observed that in contrast to the claim made by Kolb et al the presence of inhomogeneities as well as extra dimensions can not reverse the signature of the deceleration parameter if the matter field obeys the energy conditions. The well known Raychaudhuri equation also points to the same result. Without solving the field equations explicitly it can, however, be shown that although the total deceleration is positive everywhere nevertheless it does not exclude the possibility of having radial acceleration, even in the pure dust universe, if the angular scale factor is decelerating fast enough and vice versa. Moreover it is found that introduction of extra dimensions can not reverse the scenario. To the contrary it actually helps the decelerating process.Comment: 14 pages, 4 figure

Limits on Production of Magnetic Monopoles Utilizing Samples from the DO and CDF Detectors at the Tevatron

We present 90% confidence level limits on magnetic monopole production at the Fermilab Tevatron from three sets of samples obtained from the D0 and CDF detectors each exposed to a proton-antiproton luminosity of $\sim175 {pb}^{-1}$ (experiment E-882). Limits are obtained for the production cross-sections and masses for low-mass accelerator-produced pointlike Dirac monopoles trapped and bound in material surrounding the D0 and CDF collision regions. In the absence of a complete quantum field theory of magnetic charge, we estimate these limits on the basis of a Drell-Yan model. These results (for magnetic charge values of 1, 2, 3, and 6 times the minimum Dirac charge) extend and improve previously published bounds.Comment: 18 pages, 17 figures, REVTeX

The Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory is a second generation water Cherenkov detector designed to determine whether the currently observed solar neutrino deficit is a result of neutrino oscillations. The detector is unique in its use of D2O as a detection medium, permitting it to make a solar model-independent test of the neutrino oscillation hypothesis by comparison of the charged- and neutral-current interaction rates. In this paper the physical properties, construction, and preliminary operation of the Sudbury Neutrino Observatory are described. Data and predicted operating parameters are provided whenever possible.Comment: 58 pages, 12 figures, submitted to Nucl. Inst. Meth. Uses elsart and epsf style files. For additional information about SNO see http://www.sno.phy.queensu.ca . This version has some new reference

Acacia karroo: monograph and annotated bibliography

Woodlands are a crucial component of farming systems in the communal lands of Africa. Increasing population pressure and devastating droughts have brought about deforestation and severe land degradation in the dry zones of the continent. Rural populations in these areas face great hardships and are becoming increasingly vulnerable to climatic change. Improving their quality of life is dependent on increasing yields from cultivated crops, on realizing more of the potential for livestock production and on providing wood for fuel and poles. This can be done most effectively by developing and promoting the use of trees in agrisilvopastoral systems...</p