Time filter

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Las Palmas de Gran Canaria, Spain

Perea L.,Institute Destudis Espacials Of Catalonia | Perea L.,Institute for Space science | Elosegui P.,Institute for Space science | D'Amico S.,Institute Destudis Espacials Of Catalonia
Journal of Guidance, Control, and Dynamics | Year: 2010

The design and validation of a relative control law of a virtual telescope using global positioning system (GPS) and optical metrology for formation flying (FF) acquisition mission is studied. The relative control is used for formation acquisition, whose accuracy requirements are more relaxed than those of formation keeping, and a slight modification is introduced to improve the accuracy. The results show that between epoch and 0.024 orbits-time units, the quality of the satellite geometry significantly reduces, and the Kalman navigation filter responds by implementing only the time update step. The position error of the coronagraph relative to its reference position vary depending on maneuvers. The control action during the formation keeping phase contains high-frequency variations. Simulations reveal that the high-frequency oscillations arise from errors in relative velocity estimates, and that the oscillations vanished in the absence of velocity errors. Source

Elizalde E.,Institute for Space science | Skalozub V.,Dnipropetrovsk National University
Problems of Atomic Science and Technology | Year: 2012

It is assumed that the intergalactic magnetic fields were spontaneously generated in the early Universe due to vacuum polarization of non-Abelian gauge fields at high temperature T. Here, a procedure to estimate the field strengths B(T) at different T is developed and the value of B(T ew)∼10 14 G, at the electroweak phase transition temperature, is derived by taking into consideration the present intergalactic magnetic field strength B o ∼ 10 -15 G. Source

Elizalde E.,Institute for Space science | Skalozub V.,Dnipropetrovsk National University
European Physical Journal C | Year: 2012

Intergalactic magnetic fields are assumed to have been spontaneously generated at the reheating stage of the early Universe, due to vacuum polarization of non-Abelian gauge fields at high temperature. The fact that the screening mass of this type of fields has zero value was discovered recently. A procedure to estimate their field strengths, B(T), at different temperatures is here developed, and the value B(T ew)~10 14 G at the electroweak phase transition temperature is derived by taking into consideration the present value of the intergalactic magnetic field strength, B 0~10 -15 G, coherent on the ~1 Mpc scale. As a particular case, the standard model is considered and the field scale at high temperature is estimated in this case. Model-dependent properties of the phenomena under investigation are briefly discussed, too. © 2012 Springer-Verlag / Società Italiana di Fisica. Source

King M.A.,Northumbria University | Altamimi Z.,CNRS Pascal Institute | Boehm J.,Vienna University of Technology | Bos M.,University of Porto | And 14 more authors.
Surveys in Geophysics | Year: 2010

The provision of accurate models of Glacial Isostatic Adjustment (GIA) is presently a priority need in climate studies, largely due to the potential of the Gravity Recovery and Climate Experiment (GRACE) data to be used to determine accurate and continent-wide assessments of ice mass change and hydrology. However, modelled GIA is uncertain due to insufficient constraints on our knowledge of past glacial changes and to large simplifications in the underlying Earth models. Consequently, we show differences between models that exceed several mm/year in terms of surface displacement for the two major ice sheets: Greenland and Antarctica. Geodetic measurements of surface displacement offer the potential for new constraints to be made on GIA models, especially when they are used to improve structural features of the Earth's interior as to allow for a more realistic reconstruction of the glaciation history. We present the distribution of presently available campaign and continuous geodetic measurements in Greenland and Antarctica and summarise surface velocities published to date, showing substantial disagreement between techniques and GIA models alike. We review the current state-of-the-art in ground-based geodesy (GPS, VLBI, DORIS, SLR) in determining accurate and precise surface velocities. In particular, we focus on known areas of need in GPS observation level models and the terrestrial reference frame in order to advance geodetic observation precision/accuracy toward 0.1 mm/year and therefore further constrain models of GIA and subsequent present-day ice mass change estimates. © 2010 The Author(s). Source

Babkin V.A.,Joint Institute for Nuclear Research | Cata-Danil G.,Polytechnic University of Bucharest | Cata-Danil G.,National Institute for Physics and Nuclear Engineering | Golovatyuk V.M.,Joint Institute for Nuclear Research | And 4 more authors.
Central European Journal of Physics | Year: 2010

A ridge carbon beam filter for Spreading Out the Bragg Peak (SOBP) up to 20 mm in the targeted area has been designed and experimentally tested. The instrument was constructed of Plexiglas with a density of 1. 165 g/cm3 and has a "teeth" structure with a period of 2. 5 mm. The design is based on a simple analytical model and detailed GEANT4 Monte Carlo simulations. In-beam test measurements were performed with a 500-MeV/u 12C beam at the Nuclotron facility of the Joint Institute for Nuclear Research (JINR) in Dubna. The filter can be used as a static device positioned in front of patients undergoing carbon therapy. © 2009 Versita Warsaw and Springer-Verlag Berlin Heidelberg. Source

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