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See detailAssessment of the NeQuick model at mid-latitudes using GNSS TEC and ionosonde data
Bidaine, Benoît ULg; Warnant, René

in Advances in Space Research (2010), 45(9), 1122-1128

The modelling of the Total Electron Content (TEC) plays an important role in global navigation satellite systems (GNSS) accuracy, especially for single-frequency receivers, the most common ones ... [more ▼]

The modelling of the Total Electron Content (TEC) plays an important role in global navigation satellite systems (GNSS) accuracy, especially for single-frequency receivers, the most common ones constituting the mass market. For the latter and in the framework of Galileo, the NeQuick model has been chosen for correcting the ionospheric error contribution and will be integrated into a global algorithm providing the users with daily updated information. In order to reach the ionosphere error correction level objective, the model itself as well as its use for Galileo are investigated. In our comparison process, we take advantage of various ionosphere data from several European stations (Dourbes in Belgium, El Arenosillo and Roquetes in Spain) where ionosonde and GPS TEC data are available for different solar activity levels. These data allow us to study NeQuick representation of the ionosphere at mid-latitudes. Constraining the model with ionosonde measurements, we investigate the difference between GPS-derived vertical TEC and corresponding values from NeQuick for a high solar activity level (year 2002). With this approach, we reach residual errors of less than 20% in standard deviation. We especially highlight the improvements from the latest (second) version of NeQuick and show the critical importance of the topside formulation. [less ▲]

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See detailAssessment of the NeQuick Model at Mid-latitudes using GPS TEC and Ionosonde Data
Bidaine, Benoît ULg; Warnant, René ULg

Conference (2007, July 11)

The ionosphere plays a crucial role in GNSS accuracy. In extreme cases, this electrically charged part of the atmosphere can lead to errors in positioning exceeding 100m. At first approximation, the ... [more ▼]

The ionosphere plays a crucial role in GNSS accuracy. In extreme cases, this electrically charged part of the atmosphere can lead to errors in positioning exceeding 100m. At first approximation, the ionospheric effect depends on the frequency of the incident signal and on the total content in free electrons of the ionosphere (“total electron content”, TEC) which is the integral of the electron density on the path between the satellite and the receiver. The modelling of this parameter reveals then itself to be critical in particular for single-frequency receivers, the most common ones constituting the mass market, but also for multiple-frequency devices which will comprise a fallback mode in single frequency within the framework of critical applications such as civil aviation where the level of precision must be guaranteed in all circumstances. The NeQuick model, which has been chosen for correcting the ionospheric error contribution in GALILEO single frequency users, calculates the electron density at a given point of the ionosphere according to the time conditions and the solar activity. This electron density can be integrated along the path from the receiver to the considered satellite to provide the TEC. The NeQuick model depends on a parameter Az (“effective ionization level”) which will be daily updated by the GALILEO ground stations to give the solar activity information to the model. In order to reach the ionosphere error correction level objective (70% or 20 TECu whichever is larger), the model itself as well as its use for GALILEO are investigated. Different situations have to be considered: different latitude regions (space conditions), different hours, seasons and years (time conditions) and specific phenomena appearance (magnetic storms, Travelling Ionospheric Disturbances – TIDs). In addition the results can be compared to different data sets among which GPS slant or vertical TEC measurements, Global Ionospheric Maps, ionosonde profiles, topside soundings but also other ionosphere models results such as IRI. As a first step in a thorough comparison process, we take benefit of various ionosphere data from the Dourbes Observatory (Belgium) where ionosonde and GPS TEC data are available on a period of more than one solar cycle, to study the mid-latitudes. We first investigate the difference between GPS-derived vTEC for Dourbes station and vTEC values from NeQuick for the latest years (between solar maximum in 2000 and minimum in 2006) in order to observe the temporal dependencies towards Universal Time, season and solar activity. The paper analyses the different situations when NeQuick fails to represent TEC in an adequate way to provide an efficient correction for navigation. Ionosonde measurements will help in the interpretation of these situations. [less ▲]

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See detailAssessment of the NeQuick Model at Mid-latitudes using GPS TEC and Ionosonde Data
Bidaine, Benoît ULg; Warnant, René ULg

in First Colloquium Scientific and Fundamental Aspects of the Galileo Programme (2007, October)

The ionosphere plays a crucial role in Global Navigation Satellite Systems (GNSS) accuracy. In extreme cases, this electrically charged part of the atmosphere can lead to errors in positioning exceeding ... [more ▼]

The ionosphere plays a crucial role in Global Navigation Satellite Systems (GNSS) accuracy. In extreme cases, this electrically charged part of the atmosphere can lead to errors in positioning exceeding 100 $m$. At first approximation, ionospheric effects depend mainly on the total content in free electrons of the ionosphere ("total electron content", TEC). The modelling of the latter parameter reveals thus itself critical in particular for single frequency receivers, the most common ones constituting the mass market. In the framework of GALILEO, the NeQuick model has been chosen to this extent and will be integrated into a global algorithm providing the users with daily updated information. In order to reach the specified correction level, the model itself and its latest evolutions as well as its use for GALILEO are investigated. As a first step in a thorough analysis, we take benefit of ionosonde and GPS TEC data from the Dourbes Geophysical Observatory (Belgium) to study the mid-latitudes. Constraining the model with ionosonde measurements, we first investigate the difference between GPS-derived vertical TEC (vTEC) for Dourbes station and corresponding values from NeQuick for the latest years for solar maximum in 2002 and minimum in 2006. With this approach, we reach residual errors of about 20% RMS for 2002 and 30% for 2006. Through a focusing process, we identify then gradually best and worst months and days for which we observe the evolution between two versions of NeQuick. We highlight among others improvements from the latest modification in the topside formulation which appears clearly in the electron density profiles examined at the end of the assessment. [less ▲]

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See detailAssessment of the new immunological test Hemoblot for detecting occult blood in faeces
Jeanson, Antoinette; Jamart, J.; Maisin, J. M. et al

in European Journal of Cancer Prevention (1994), 3(5), 407-412

Hemoblot, a new immunological faecal occult blood test, produced by Gamma, Angleur, Belgium, was characterized and compared with another immunological test (HemeSelect, SmithKline Diagnostics, USA) and ... [more ▼]

Hemoblot, a new immunological faecal occult blood test, produced by Gamma, Angleur, Belgium, was characterized and compared with another immunological test (HemeSelect, SmithKline Diagnostics, USA) and with a guaiac test (Hemoccult II, SmithKline Diagnostics). The analytical sensitivity of Hemoblot is 0.15 mg haemoglobin/g faeces and the test is specific for human haemoglobin. In addition, 135 symptomatic patients who had to undergo a colonoscopy were tested using the three tests. Two criteria were considered for the analysis: (1) the blood criterion: any pathology likely to cause colorectal or other bleeding; and (2) the precancerous-cancerous criterion: the pathology being either a colorectal polyp > 0.5 cm or a colorectal cancer. Considering both criteria, the sensitivity of Hemoblot was significantly higher than the sensitivity of Hemoccult: 38% and 23%, respectively, for the blood criterion; and 54% and 29% for the precancerous-cancerous criterion. Sensitivity and specificity did not differ statistically between Hemoblot and HemeSelect but Hemoblot was faster and simpler to perform. It could be widely used in mass screening. [less ▲]

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See detailAssessment of the night weather parameters and their use in forecasting model of leaf rust.
El Jarroudi, Moussa ULg; Giraud, Frédéric; Delfosse, Philippe et al

Conference (2010, August 07)

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See detailAssessment Of The Night Weather Parameters And Their Use In Forecasting Model Of Wheat Leaf Rust.
El Jarroudi, Moussa ULg; Giraud, Frédéric; Delfosse, Philippe et al

in Phytopathology (2010), (100), 32

A stochastic model was developed to predict the wheat leaf rust (Puccinia triticina Eriks.) severity (percentage of leaf area with symptoms showing uredinia) in four-replicated field experiments located ... [more ▼]

A stochastic model was developed to predict the wheat leaf rust (Puccinia triticina Eriks.) severity (percentage of leaf area with symptoms showing uredinia) in four-replicated field experiments located in three villages (Diekirch district: Reuler; Grevenmacher district: Burmerange and Christnach), representative of the different agroclimatological zones of Luxembourg. The model was elaborated by the analysis of the night weather and leaf rust incidence. Statistical validation using regression analysis reports a strong correlation between the number of hours with specific meteorological conditions and the percentage leaf area covered by brown rust lesions for the two upper and youngest leaves, which are mostly responsible for photosynthesis activity and assimilates production filling the grains. The development of the brown rust requires a period of at least twelve consecutive hours with temperatures between 8 and 16°C and a relative humidity (RH) greater than 60%, with optimal values lying between 12 and 16°C and RH greater than 80%. <br />During the 2004 to 2009 period, at four sites, the linear regression between simulated and observed values for Puccinia triticina was highly significant (P < 0.01) and R2 (coefficient of determination) explained 80 to 85% of the variability. Efforts are now being developed to better define thresholds for fungicide applications and to spatialize the outputs of the model over the entire Luxembourg territory. [less ▲]

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See detailAssessment of the oxidant-antioxidant blood balance in a field exercise test in Standardbred and eventing horses
De Moffarts, Brieuc; Kirschvink, Nathalie; van Erck, Emmanuelle et al

in Equine & Comparative Exercise Physiology (2005), 2(4), 253-261

The aim of this study was to determüie which oxidant-antioxidant blood markers are of interest for a field exercise test (ET) performed on a racetrack. Healthy Standardbred herses (S: n = 12) and healthy ... [more ▼]

The aim of this study was to determüie which oxidant-antioxidant blood markers are of interest for a field exercise test (ET) performed on a racetrack. Healthy Standardbred herses (S: n = 12) and healthy eventing horses (E: n = 12) were investigated. Exercice was monitored by measuring velocity (V), heart rate (HR), and plasma lactate (LA). Whilst maximal LA did sot Biffer (11.8 ± 0.88 mmoll-1), maximal V (S: 12.3 ± 0.17ms-1 versus E: 11.1 ±0.24ms-1, P < 0,05) and final HR (S: 222 ±1 versus E: 203 ± 8 beats min-1, P < 0.03) were significantly différent between groups. Venous was collected at rest (R) prior to ET and The following oxidant-antioxidant markers were detennitted: uric acid (UA), ascorbic acid (AA), alpha-tocopherol (Vit E). vitamin A (Vit A), superoxide cüsmutase (SOB), glutaYhione peroxidase (GPx), glutathione (reduced: GSH and oxidized: GSS(r), glutathione redox ratio (GRR), copper (Cu), zinc (Zn) and sélénium (Se), uxidized proteins (Protox), lipid prrosides (Pool), antioxidant capacity of water-soluble comporteras (ACW) and antioxidant capacity of lipid-soluble components (ACW). The following markers were further determined 15 min (E15) after the ET:UA, ACW; AA, GSH, Proton, Pool, ACL. Standardbreds had significantly higher concentrations of ACW, GSH, ACL and Protox, whilst Se, Zn and SOI) were significantly lover than in eventing horses. Exercice induced a significant increase in ACW and UA. GSH decreaced in eventing horses and Pool significantly decreased in both horse groups. This study describes a field ET of high intensity for Standardbred and eventing horses, which could be performed by all animals tested. By sampling blond al rest and at E15, changes of thé hydrophilic antioxidant defence were partially assessed, whereas no interpretable changes of the lipophilic antioxidants and of oxidation markers (Protox, Pool) could be detected [less ▲]

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See detailThe assessment of the past decades based on modelling and data analysis: some examples
Grégoire, Marilaure ULg; Gorsky, G.; Sesame participants, .

Conference (2010, May)

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See detailAssessment of the present state of the Aral Sea
Mikhailov, V.N.; Kravtsova, V.I.; Gurov, F.N. et al

in Seria 5, Geografia 6 (2001)

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See detailAssessment of the processes controlling the seasonal variations of dissolved inorganic carbon in the North Sea
Bozec, Y.; Thomas, H.; Schiettecatte, L. S. et al

in Limnology and Oceanography (2006), 51(6), 27462762

We used a seasonal North Sea data set comprising dissolved inorganic carbon (DIC), partial pressure of CO2 (pCO2), and inorganic nutrients to assess the abiotic and biological processes governing the ... [more ▼]

We used a seasonal North Sea data set comprising dissolved inorganic carbon (DIC), partial pressure of CO2 (pCO2), and inorganic nutrients to assess the abiotic and biological processes governing the monthly variations of DIC. During winter, advection and air–sea exchange of CO2 control and increase the DIC content in the surface and deeper layers of the northern and central North Sea, with the atmosphere supplying CO2 on the order of 0.2 mol C m22 month21 to these areas. From February to July, net community production (NCP) controls the seasonal variations of DIC in the surface waters of the entire North Sea, with a net uptake ranging from 0.5 to 1.4 mol C m22 month21. During the August–December period, NCP controls the seasonal variations of DIC in the southern North Sea, with a net release ranging from 0.5 to 0.8 mol C m22 month21. Similarly, during the April–August period in the deeper layer of the northern North Sea, the NCP was the main factor controlling DIC concentrations, with a net release ranging from 0.5 to 5.5 mol C m22 month21. In the surface layer of the North Sea, NCP on the basis of DIC was 4.3 6 0.4 mol C m22 yr21, whereas, NCP on the basis of nitrate was 1.6 6 0.2 mol C m22 yr21. Under nutrient-depleted conditions, preferential recycling (extracellular) of nutrients and intracellular mechanisms occurred and were responsible for the non-Redfield uptake of DIC versus nitrate and phosphate. [less ▲]

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See detailAssessment of the risk of cardiovascular diseases in women with increased risk of osteoporosis
Tancredi, Annalisa ULg; Bosio-Le Goux, B.; Reginster, Jean-Yves ULg

in Osteoporosis International (2003, November), 14(Suppl. 7), 89

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See detailAssessment of the risk of dermal exposure to pesticide during treatment with a back-pack sprayer in the presence and absence of vegetation
Kadri, Z.; Sylla, S.; Lebeau, Frédéric ULg et al

in Communications in Agricultural and Applied Biological Sciences (2012), 77(7), 415-422

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See detailAssessment of the seismic performances of modern unreinforced multi-storey clay masonry buildings
Degée, Hervé ULg; Mordant, Christophe ULg; Lascar, Laurentiu et al

in Papadrakakis, Manolis; Papadopoulos, Vissarion; Plevris, Vagelis (Eds.) Proceedings of the 4th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Proceedings - An IACM Special Interest Conference (2013)

This paper presents an overall summary of a recent research project aiming at the validation of structural solutions using unreinforced load-bearing clay masonry for family houses and multi-storey ... [more ▼]

This paper presents an overall summary of a recent research project aiming at the validation of structural solutions using unreinforced load-bearing clay masonry for family houses and multi-storey buildings fulfilling the requirements of Eurocode 8 for low to moderate seismic areas. The paper covers the following issues: (i) Presentation of a database of typical buildings for the considered geographical area; (ii) Collection of the mechanical properties for the different material entering into the design; (iii) Assessment of the seismic behaviour of the configurations of the data-base, using the experimentally characterised material properties. The analysis is carried out by a pushover procedure using an equivalent frame modelling for describing the global structural behaviour. Results are evaluated on the base of the N2-method. General outcomes of the study are expressed in terms of overall seismic resistance for the required ground acceleration level of the zones (typically 0.1 to 015g) and of forces to be transferred at the floor-to-wall connections. [less ▲]

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See detailAssessment of the selenium status in cattle herds in Wallonia
Mehdi, Youcef ULg; Dotreppe, Olivier ULg; Robaye, Vincent ULg et al

in 64th Annual Meeting of the European Federation of Animal Science (2013, August 26)

The selenium content is low in the soil of Wallonia, the southern part of Belgium. It is therefore logical that the selenium content in feedstuffs grown in these fields-grass, conserved forages, cereals ... [more ▼]

The selenium content is low in the soil of Wallonia, the southern part of Belgium. It is therefore logical that the selenium content in feedstuffs grown in these fields-grass, conserved forages, cereals and by-products- is also low. A survey was carried on 166 farms in Wallonia. The farms were located in 4 specific agronomy areas- Pays de Herve with mainly pastures (4farms)- Ardennes (a sub-mountainous area and pastures, 24 farms), Hesbays with mainly arable lands (55 farms) and Condroz with both pastures and arable (83 farms) There were herds with dairy cow, herds with beef cow and herds with both types of animals. The average age was 44±15 months for the cows and 18±6 months for the heifers. The blood samples were taken on five healthy animals of each herd, on the end of the winter just before the animals went to pastures. The selenium status was assessed by the activity of the Glutathion peroydase. The selenium status was extremely variable for the different farms of the 4 areas with variation coefficient of 56%. It was in Pays de Herve and in Hesbaye that the average selenium status was the highest at 53 and 56 µg Se/l. By contrast, it was in Ardenne and in Condroz that the status was the lowest, at 39 and 43 µg Se/l. The selenium status was, on the whole, higher in the dairy herds than in the beef herds owing to the higher selenium provision by the mineral mixtures and the compound feedstuffs added to the diet. Assuming that the normal selenium concentration in plasma being 70µg/l, it appeared also that 81% of the individual animals tested were below the normal Se concentration. It can thus be concluded from the present survey that the cattle herds in Wallonia are deficient in selenium. [less ▲]

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See detailAssessment of the species richness of highly eusocial bees according with habitat in Gabon
Fabre Anguilet, Edgard ULg; Bengone Ndong, Toussaint; Nguyen, Bach Kim ULg et al

Poster (2015, May 18)

Bees are among the most e ective pollinators. These insects include honeybee and stin- gless bee. In Africa, habitat loss is the main threat to these insects. This loss of habitat is largely due to ... [more ▼]

Bees are among the most e ective pollinators. These insects include honeybee and stin- gless bee. In Africa, habitat loss is the main threat to these insects. This loss of habitat is largely due to various human activities. An evaluation of the richness of social bees in three locaties in Gabon (Central Africa) was conducted from October 2013 to March 2014: Kougouleu who underwent deforestation and implantation of food crops, forest area Mas- sengalini in bu er zone of protected area of Lope and Lekokodiba in logging concession of Preccious Woods Gabon. For this, a collection was conducted using yellow traps lled with a mixture of water and honey and using a hand vacuum in 20 sites in each area. The number of species was compared to that estimated there are about thirty years. Eleven species of social bees (Apis mellifera adansonii and ten stingless bee species) were collected, of which 5 to Kougouleu, 8 to Massengalini and 11 to L ekokodiba. Honeybee has been collected in all localities. Forest localities are distinguished from Kougouleu by higher species diversity. This di erence is highly signi cant (Kruskal-Wallis 2 = 45.362, df = 2 and p-value<0.001). A decrease of approximately 50% of the number of stingless bee species in 30 years was found to Kougouleu, while the number of social bee species varies little in forest localities. Our study shows that the loss of forest habitat causes a decline in the species richness of social bees and stingless bees are more sensitive to this loss as the honeybee. [less ▲]

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See detailAssessment of the traffic induced soil compaction risk
Louvet, Jean-Noël ULg; Verswijvel, Johan; Abroughui, Khaoula et al

Scientific conference (2012, May 15)

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See detailAssessment of the ventilatory response to CO2 in two breeds of calves
Rollin, Frédéric ULg; Desmecht, Daniel ULg; Linden, Annick ULg et al

in Proceedings of the 10th Comparative Respiratory Society Meeting (1991)

Detailed reference viewed: 4 (0 ULg)