This paper details techniques for the absolute calibration of receiver chains as used in timing reference stations. The delays experienced by the GNSS signals in all elements of the receiving chain (antenna, receiver and cable) are each measured individually and with careful consideration regarding the uncertainty level assigned to them. Two different receiving chains based on different equipment units, were absolutely calibrated for GPS and Galileo signals.The calibration process and the uncertainty evaluation were then validated through the relative comparison in common clock setup in different real environments. The validation results show that some additional uncertainty has to be considered when the absolute calibration results are transferred to real signals, due to the real environment and to the difference between the chip shapes of the simulated signals and of the true signals coming from the satellites. The final 1 − σ uncertainties are below 1.1 ns for all the GPS and Galileo signals, except 1.8 ns for GPS C/A. The satellite group delays are also determined from the calibrated stations. An agreement at the ns level is found between the so-determined satellite group delays and the values provided by the system operators.
We consider an Einstein-Yang-Mills Lagrangian in a five-dimensional space-time including a cosmological constant. Assuming all fields to be independent of the extra coordinate, a dimensional reduction leads to an effective (3 + 1)-dimensional Einstein-Yang-Mills-Higgs dilaton model where the cosmological constant induces a Liouville potential in the dilaton field. We construct spherically symmetric solutions analytically in specific limits and study the generic solutions for vanishing dilaton coupling numerically. We find that in this latter case the solutions bifurcate with the branch of (Anti-) de Sitter-ReissnerNordström ((A)dSRN) solutions.
We consider global monopoles in asymptotic de Sitter/ Anti-de Sitter spacetime. We present the by our numerical analysis confirmed asymptotic behaviour of the metric and Goldstone field functions. We find that the appearance of horizons in this model depends strongly on the sign and value of the cosmological constant as well as on the value of the gravitational coupling. In Anti-de Sitter (AdS) space, we find that for a fixed value of the cosmological constant, global monopoles without horizons exist only up to a critical value of the gravitational coupling. Moreover, we observe (in contrast to another recent study) that the introduction of a cosmological constant can not render a positive mass of the global monopole.
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