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See detailIonoluminescence of diamond, synthetic diamond and simulants
Calvo Del Castillo, Helena ULg; Ruvalcaba Sil, Jose Luis; Álvarez, M A[ et al

in Nuclear Instruments & Methods in Physics Research Section A (2007), 387

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See detailIonoluminescence of trivalent rare ion doped strontium barium niobate
Calvo Del Castillo, Helena ULg; Ruvalcaba-Sil, Jose Luis; Bettinelli, Marco et al

in Journal of Luminescence (2008), 128

Detailed reference viewed: 3 (0 ULg)
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See detailIonoluminiscencia en minerales de interés gemológico
Calvo Del Castillo, Helena ULg; Ruvalcaba Sil, Jose Luis; Millán Chagoyén, Asunción et al

Poster (2007)

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See detailIonoluminiscencia: Aplicaciones en Bienes Culturales (Gemas y minerales)
Calvo Del Castillo, Helena

in del Egido, Marián; Calderón, Tomás (Eds.) La Ciencia y el Arte (2008)

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See detailIonosphere Crossing of GALILEO Signals
Bidaine, Benoît ULg

Master's dissertation (2006)

The ionosphere plays a crucial role in Global Navigation Satellite Systems (GNSS) accuracy. This electrically charged part of the atmosphere can lead to errors in positioning up to several tens of meters ... [more ▼]

The ionosphere plays a crucial role in Global Navigation Satellite Systems (GNSS) accuracy. This electrically charged part of the atmosphere can lead to errors in positioning up to several tens of meters for single frequency receivers. Therefore its modelling constitutes an important field of study. An empirical model called NeQuick has been chosen to evaluate the ionospheric contribution in GALILEO single frequency users correction. It generates electron densities for given space, time and solar activity conditions from a minimum set of anchor points characteristics. Its use with integration methods allows to calculate total electron contents (TEC) which are directly related to the ionospheric delay. The current GALILEO baseline version of NeQuick is the one published by the Radiocommunication Sector of the International Telecommunication Union (ITU-R) in 2000. From that time, several improvements have been proposed and some problems have been discovered leading to the need of a better understanding and comparison of these different versions and an analysis of the weaknesses. For example research about new topside formulations is currently performed - a new simple proposal has been tested - and the consequences of the daily effective use of NeQuick, which is designed to work with monthly median situations, have to be better known. A software tool with a Graphical User Interface (GUI) has then been developed for the analysis and a comparison between different versions and also between modelled and measured data has been performed. Structuring and analysis of the above-mentioned issues and results of the comparison are detailed in the present document. Solutions or possible paths to investigate solutions are also proposed. [less ▲]

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See detailIonosphere Modelling Based on the NeQuick Model and GNSS Data Ingestion
Bidaine, Benoît ULg; Warnant, René ULg

in Second International Colloquium - Scientific and Fundamental Aspects of the Galileo Programme (2009, October)

As for other GNSS, the ionospheric effect remains one of the main factors limiting Galileo accuracy. For single frequency users, this contribution to the error budget will be mitigated by a global ... [more ▼]

As for other GNSS, the ionospheric effect remains one of the main factors limiting Galileo accuracy. For single frequency users, this contribution to the error budget will be mitigated by a global algorithm based on the NeQuick model. This quick-run empirical model provides flexible solutions for combining ionospheric information obtained from various systems, from GNSS to ionosondes and topside sounders thanks to which NeQuick has been designed. Hence it constitutes an interesting simulation tool not only serving Galileo needs for mitigation of the ionospheric effect but also widening the use of new data available thanks to the future European system. NeQuick provides the electron density as a function of location, time and solar activity. Thanks to numerical integration, the total content in free electrons of the ionosphere (Total Electron Content, TEC) can be deduced as well as the ionospheric propagation delay depending linearly on TEC on satellite-to-receiver path. The model is particularly suited to be used within an optimization procedure called ingestion. In this framework, an “effective ionization level” Az plays the role of the solar activity input in order to fit a specific dataset. For Galileo single frequency operation, daily Az values will be computed from slant TEC measurements performed within the ground segment. In this study, we perform slant TEC ingestion for a dozen of locations around the world where both an ionosonde and a GPS receiver are installed. These collocated instruments allow us to compare measured and modelled vertical TEC in different ways showing for example global statistics or dependence towards latitude. We analyze such results for the year 2002 (high solar activity level) giving an interesting insight in the situation we could observe when Galileo reach its Full Operation Capability, during the next solar maximum. [less ▲]

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See detailIonosphere Modelling for Galileo Single Frequency Users
Bidaine, Benoit ULg

Doctoral thesis (2012)

Nowadays the ionosphere constitutes one of the most often modelled natural media. Indeed each GPS receiver among nearly two million units sold daily throughout the world runs a model to mitigate the ... [more ▼]

Nowadays the ionosphere constitutes one of the most often modelled natural media. Indeed each GPS receiver among nearly two million units sold daily throughout the world runs a model to mitigate the ionospheric effect affecting the signal propagation from the satellites. This propagation is delayed by the free electrons in the atmosphere so that the navigation signals appear to travel distances larger than actual ones by 7 m on average. Hence this delayed propagation deteriorates the positioning accuracy deemed on a 10−m level for mass-market applications mainly involving single frequency users. Tomorrow the European navigation system Galileo will offer a new mitigation strategy to single frequency users. This strategy will rely on the NeQuick ionospheric model and associated broadcast information. To be properly implemented, it must be extensively described to future Galileo users. These users will also wonder about its effectiveness in accounting for the ionospheric delay. The PhD research covered by the present thesis has built on Belgian expertise in ionosphere monitoring to investigate the NeQuick model and its use for Galileo. It began with the collection and handling of ionosphere measurements including GPS data. It analysed various situations at different places in the world encompassing a whole year (2002). This PhD thesis provides the ins and outs of the Galileo Single Frequency Ionospheric Correction Algorithm. It gathers an algorithm description, a performance evaluation and a variant investigation. In the shape of a paper collection, it discloses many figures as visual entry-points into the juxtaposed text and includes many references allowing to dig into the details. The algorithm performances are usefully characterised both in terms of delay mitigation and positioning accuracy. On the one hand, the residual ionospheric delay reaches 31% for the chosen sites and year. On the other hand, the positioning accuracy amounts to 6 m horizontally and 9.3 m vertically. The performance evaluation allowed to emphasise several aspects of the Galileo ionospheric correction. This correction depends largely on the modelling of the topside, the upper part of the ionosphere, which hosts more complex physical processes. It owes its good performances to data ingestion, the model adaptation technique to actual measurements underlying the Galileo algorithm. It does not necessarily provide highly correlated correction levels in terms of delay on the one hand and positioning on the other. It enables the definition of alternative regional procedures following a compatible design but coping with its weaknesses. The present thesis paves the way for future work related to ionosphere modelling for Galileo single frequency users. It supplies comparative information for the algorithm assessment in the framework of successive phases of Galileo deployment. It establishes a conceptual basis for an Assisted Ionospheric Correction Algorithm (A-ICA) disseminating more flexible ionospheric information thanks to the integration of Global Navigation Satellite Systems and telecommunications. [less ▲]

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See detailIonosphere Modelling for GALILEO Single Frequency Users
Bidaine, Benoît ULg; Warnant, René ULg

Poster (2007, October 17)

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See detailIonosphere modelling for Galileo single frequency users: illustration of the combination of the NeQuick model and GNSS data ingestion
Bidaine, Benoît ULg; Warnant, René ULg

in Advances in Space Research (2011), 47(2), 312-322

The ionospheric effect remains one of the main factors limiting the accuracy of Global Navigation Satellite Systems (GNSS) including Galileo. For single frequency users, this contribution to the error ... [more ▼]

The ionospheric effect remains one of the main factors limiting the accuracy of Global Navigation Satellite Systems (GNSS) including Galileo. For single frequency users, this contribution to the error budget will be mitigated by an algorithm based on the NeQuick global ionospheric model. This quick-run empirical model provides flexible solutions for combining ionospheric information obtained from various sources, from GNSS to ionosondes and topside sounders. Hence it constitutes an interesting simulation tool not only serving Galileo needs for mitigation of the ionospheric effect but also widening the use of new data. In this study, we perform slant TEC data ingestion - the optimisation procedure underlying the Galileo single frequency ionospheric correction algorithm - into NeQuick for a dozen locations around the world where both an ionosonde and a GPS receiver are installed. These co-located instruments allow us to compare measured and modelled vertical TEC showing for example global statistics or dependence towards latitude. We analyse measurements for the year 2002 (high solar activity level) giving an insight into the situation we could observe when Galileo reaches its Full Operation Capability, during the next solar maximum. At last we compare Galileo and GPS ionospheric corrections. For Galileo, we end up with an underestimation of 11% and 4% depending on the version of NeQuick embedded in the algorithm, as well as a 22% standard deviation. This means respectively twice, five and 1.5 times better than GPS. [less ▲]

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See detailIonospheric and geomagnetic conditions during periods of degraded GPS position accuracy : 2. RTK events during disturbed and quiet geomagnetic conditions
Warnant, René ULg; Kutiev, Ivan; Marinov, Pencho et al

in Advances in Space Research (2007), 39(5), 881-888

Detailed reference viewed: 30 (7 ULg)
See detailIonospheric Conductances Due To Auroral Proton and Electron Precipitation Deduced From Image-fuv Observations.
Coumans, Valérie ULg; Hubert, Benoît ULg; Meurant, M. et al

in EGS XXVII General Assembly, Nice, 21-26 April 2002 (2002)

The FUV instrument on the IMAGE (Imager for Magnetopause-to-Aurora Global Ex- ploration) satellite monitors the aurora in three different spectral regions. The Wide- band Imaging Camera (WIC) observes the ... [more ▼]

The FUV instrument on the IMAGE (Imager for Magnetopause-to-Aurora Global Ex- ploration) satellite monitors the aurora in three different spectral regions. The Wide- band Imaging Camera (WIC) observes the molecular N2 LBH and the atomic NI emissions at 140-180 nm. The two channels of the Spectrographic Imager (SI) ob- serve the Doppler shifted Lyman- emission at 121.8 nm due to precipitating protons (SI12) and the electron auroral emission of OI at 135.6 nm (SI13). We calculate the Pedersen and Hall ionospheric conductances due to auroral particles based on FUV observations separately for the proton and electron precipitation. We first estimate the electron and proton energy fluxes from the FUV data, relying on energy degradation and auroral emission models. A two-stream model is used for the electron aurora while the proton aurora modeling is based on the direct Monte Carlo method, which gives a stochastic solution to the Boltzmann equations for the H+ - H beam. The electron energy is evaluated by combining observations from the three FUV instruments. For the proton energy, we use a statistical model based on in-situ particle measurements. Second, the particle energy and energy flux are used to estimate the ionization rates separately for protons and electrons, consistently with the energy degradation models. Finally, the electron and ion densities are estimated from ionization profiles, and the Pedersen and Hall conductances are calculated from fundamental equations. Appli- cations of the method to the distribution of the conductance at winter solstice in the course of substorm development over the north polar region will be illustrated. [less ▲]

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See detailIonospheric effects on relative positioning within GPS dense network
Lejeune, Sandrine; Wautelet, Gilles ULg; Warnant, René ULg

in GPS Solutions (2012), 16(1), 105-116

Detailed reference viewed: 95 (14 ULg)
See detailIonospheric Products and Services from the Regional Warning Centers of the International Space Environment Service (ISES) for GNSS Users
Kunches, J.; Terkildsen, M.; Stanislawska, I. et al

Conference (2008)

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See detailIonospheric slab thickness - Analysis, modelling and monitoring
Stankov, Stanimir; Warnant, René ULg

in Advances in Space Research (2009), 44(10), 1295-1303

Detailed reference viewed: 23 (1 ULg)
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See detailIonospheric slab thickness: analysis and monitoring applications
Stankov, Stanimir; Warnant, René ULg

in Proceedings of the 12th International Ionospheric Effects Symposium (IES2008) (2008, May)

Detailed reference viewed: 19 (0 ULg)
See detailThe Ionospheric Total Electron Content : Simulation of the measurement by the NEIGE/NETLANDER experiment
Cerisier, Jean-Claude; Warnant, René ULg; Morel, Laurent

Conference (2001)

Detailed reference viewed: 10 (1 ULg)
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See detailIonospheric variability which degrades the precision of real time GNSS applications
Wautelet, Gilles ULg; Lejeune, Sandrine; Warnant, René ULg

Poster (2008, November 18)

Detailed reference viewed: 23 (3 ULg)
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See detailIOT Overview: Optical Multi-Object Spectrographs
Schmidtobreick, L.; Bagnulo, S.; Jehin, Emmanuel ULg et al

in Kaufer, A. (Ed.) The 2007 ESO Instrument Calibration Workshop (2008)

We give an introduction to the several instruments that ESO operates and which are able to perform optical multi-object spectroscopy. We point out the standard ways of reducing these spectra, the problems ... [more ▼]

We give an introduction to the several instruments that ESO operates and which are able to perform optical multi-object spectroscopy. We point out the standard ways of reducing these spectra, the problems that occur, and the way we deal with them. A short introduction is given on how the quality control is performed. [less ▲]

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See detailThe Iowa Gambling Task in fMRI images.
Li, Xiang ULg; Lu, Z. L.; D'Argembeau, Arnaud ULg et al

in Human Brain Mapping (2010), 31

The Iowa Gambling Task (IGT) is a sensitive test for the detection of decision-making impairments in several neurological and psychiatric populations. Very few studies have employed the IGT in functional ... [more ▼]

The Iowa Gambling Task (IGT) is a sensitive test for the detection of decision-making impairments in several neurological and psychiatric populations. Very few studies have employed the IGT in functional magnetic resonance imaging (fMRI) investigations, in part, because the task is cognitively complex. Here we report a method for exploring brain activity using fMRI during performance of the IGT. Decision-making during the IGT was associated with activity in several brain regions in a group of healthy individuals. The activated regions were consistent with the neural circuitry hypothesized to underlie somatic marker activation and decision-making. Specifically, a neural circuitry involving the dorsolateral prefrontal cortex (for working memory), the insula and posterior cingulate cortex (for representations of emotional states), the mesial orbitofrontal and ventromedial prefrontal cortex (for coupling the two previous processes), the ventral striatum and anterior cingulate/SMA (supplementary motor area) for implementing behavioral decisions was engaged. These results have implications for using the IGT to study abnormal mechanisms of decision making in a variety of clinical populations. Hum Brain Mapp, 2009. (c) 2009 Wiley-Liss, Inc. [less ▲]

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