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See detailComparison of Adaptive Filtering Schemes for Gas Turbine Performance Diagnostics
Borguet, Sébastien ULg; Léonard, Olivier ULg

in Proceedings of the 4th International Conference on Advanced Computational Methods in Engineering (2008)

Kalman filters are widely used in the turbine engine community for health monitoring purpose. This algorithm has proven its capability to track gradual deterioration with a good accuracy. On the other ... [more ▼]

Kalman filters are widely used in the turbine engine community for health monitoring purpose. This algorithm has proven its capability to track gradual deterioration with a good accuracy. On the other hand, its response to rapid deterioration is either a long delay in recognising the fault, and/or a spread of the estimated fault on several components. The main reason of this deficiency lies in the transition model of the parameters that assumes a smooth evolution of the engine condition. The aim of this contribution is to compare two adaptive diagnosis tools that combine a Kalman filter and a secondary system that monitors the residuals. This auxiliary component implements on one hand a covariance matching scheme and on the other hand a generalised likelihood ratio test to improve the behaviour of the diagnosis tool with respect to abrupt faults. [less ▲]

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See detailComparison of adaptive filters for gas turbine performance monitoring
Borguet, Sébastien ULg; Léonard, Olivier ULg

in Journal of Computational & Applied Mathematics (2010), 234(7), 2202-2212

Kalman filters are widely used in the turbine engine community for health monitoring purpose. This algorithm has proven its capability to track gradual deterioration with a good accuracy. On the other ... [more ▼]

Kalman filters are widely used in the turbine engine community for health monitoring purpose. This algorithm has proven its capability to track gradual deterioration with a good accuracy. On the other hand, its response to rapid deterioration is either a long delay in recognizing the fault, and/or a spread of the estimated fault on several components. The main reason of this deficiency lies in the transition model of the parameters that assumes a smooth evolution of the engine condition. The aim of this contribution is to compare two adaptive diagnosis tools that combine a Kalman filter and a secondary system that monitors the residuals. This auxiliary component implements on one hand a covariance matching scheme and on the other hand a generalised likelihood ratio test to improve the behaviour of the diagnosis tool with respect to abrupt faults. [less ▲]

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See detailA comparison of advanced thermal cycles suitable for upgrading existing power plant
Heyen, Georges ULg; Kalitventzeff, Boris ULg

in Applied Thermal Engineering (1999), 19(3), 227-237

In view of the constant growth of electricity usage and public pressure to reduce the dependence on nuclear power plants in the energy supply, solutions are sought to increase the capacity of power plants ... [more ▼]

In view of the constant growth of electricity usage and public pressure to reduce the dependence on nuclear power plants in the energy supply, solutions are sought to increase the capacity of power plants using fossil fuels. Highly efficient cycles are available : gas turbines combined with waste heat boilers and steam cycles are able to achieve efficiencies above 50-55%. However building new plants requires a large amount of capital. Alternative proposals are based on upgrades of existing plants : capital savings are expected by reusing part of the facilities. In the present study, three parallel proposals are compared on the basis of exergy efficiency; cost of investment and flexibility of operation are also discussed. They are compared with classical Rankine cycle and state of the art combined cycles. (C) 1998 Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailA comparison of advanced thermal cycles suitable for upgrading existing power plants
Heyen, Georges ULg; Kalitventzeff, Boris ULg

in Applied Thermal Engineering (1998), 19

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See detailComparison of age-dependent quantitative changes in the male labial gland secretion of Bombus terrestris and Bombus lucorum.
Zacek, Petr; Kalinova, Blanka; Sobotnik, Jan et al

in Journal of Chemical Ecology (2009), 35(6), 698-705

Age-related changes of antennal-active components of male labial gland extracts were studied in two closely related bumblebee species, Bombus terrestris and B. lucorum. In B. terrestris, compounds ... [more ▼]

Age-related changes of antennal-active components of male labial gland extracts were studied in two closely related bumblebee species, Bombus terrestris and B. lucorum. In B. terrestris, compounds eliciting electroantennogram (EAG) responses of virgin queens were ethyl dodecanoate, 2,3-dihydrofarnesal, 2,3-dihydrofarnesol, hexadecan-1-ol, octadeca-9,12,15-trien-1-ol, and geranylcitronellol. Compounds that elicited EAG responses from queens of B. lucorum were ethyl dodecanoate, ethyl tetradec-7-enoate, ethyl tetradec-9-enoate, ethyl hexadec-9-enoate, hexadecan-1-ol, hexadec-7-enal, octadeca-9,12-dien-1-ol, octadeca-9,12,15-trien-1-ol, and octadecan-1-ol. Quantities of these compounds in the labial glands changed significantly over the lifetime of the respective males of the two species. In both species, concentrations of the respective compounds reached their maximum within seven days after eclosion. Subsequently, a rapid decrease in the amount of EAG-active compounds occurred in B. terrestris, whereas in B. lucorum the amount of active compounds stayed approximately constant or decreased at a slow rate. Microscopy showed that in B. terrestris secretory cells of the labial glands undergo apoptosis from the fifth to the tenth day of life, whilst in B. lucorum labial gland cells remain unchanged throughout the life of the males. [less ▲]

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See detailComparison of agricultural soils' structure depending on tillage system using X-ray microtomography
Beckers, Eléonore ULg; Ly, Sarann ULg; Léonard, Angélique ULg et al

in Geophysical Research Abstracts (2010, May), 12

This study aims at characterizing agricultural soils’ structure depending on the tillage system: conventional tillage or conservational tillage. Tillage reduction is an increasing practice, but the micro ... [more ▼]

This study aims at characterizing agricultural soils’ structure depending on the tillage system: conventional tillage or conservational tillage. Tillage reduction is an increasing practice, but the micro-structural effects on soils and on their hydrodynamic parameters are still not well described. Recent research shows non-converging results. Our point is to highlight fundamental differences in structure through characterization of soils porosity’s parameters using X-ray microtomography measurements coupled to image analysis. This attempt is in line with a more integrated experiment of which the aim is to quantify the effects of tillage intensity on lateral flow production, and finally on global water balance. Parameters’ measurements consist in a combined approach, based on two different space-time scales of exploration: fundamental scale, with soil sampling campaign for microtomography analysis, and field scale, with continuous flow measurements (plots’ dimensions: 18*28 m). For their part, parameters for water balance determination (precipitation, evapotranspiration…) are monitored on the field. All of these measurements have the main objective of hydrological modeling enhancement by taking into account a better lateral flow description. Discussion in this paper will focus on the first results obtained by X-ray microtomography measurements. Our experiment takes place in Gentinnes (Walloon Brabant, Belgium), on a field organized in a split-plot scheme. Since 2004, plots have been cultivated in conventional tillage or in reduced tillage. The latter consists in sowing after stubble ploughing of about 10cm. The crop rotation is sugar beet followed by winter wheat. The soil is mainly composed of silt loam. Soils samples, with a 3 cm diameter and a 5 cm height, were removed from the upper layer (Ap horizon) for both management practices. Samples are scanned by X-ray microtomography using a Skyscan-1172 high-resolution desk-top micro-CT system (Skyscan, Kontich, Belgium). The cone beam source operated at 100 kV, using an aluminium filter. The detector configuration, i.e. 1048×2000 pixels 16-bit X-ray camera, and the distance source-object-camera were adjusted to produce images with a pixel size of 17 µm. This resolution allows us to visualize both meso- and macro- porosity. In this study, half the samples were placed under a 15000 kPa pressure (corresponding pressure for the wilting point) in Richards’ apparatus in order to empty the meso- and macro-porosity. To determine a priori the class of porosity for the samples, relations between water retention and pressure head can be plotted using this apparatus. Scanning results consist in 2D images. The 2D images are recombined to form 3D structure. Then the pore network can be analyzed through useful factors like size distribution, shape, connectivity, orientation, tortuosity etc. [less ▲]

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See detailComparison of alcohol precipitation and membrane filtration effects on sugar beet pulp pectin chemical features and surface properties
Yapo, B. M.; Wathelet, Bernard ULg; Paquot, Michel ULg

in Food Hydrocolloids (2007), 21(2), 245-255

Two different procedures, alcohol precipitation with washing (APW) and a 10 kD MWCO membrane ultrafiltration with diafiltration (UF-DF), for pectin recovering and purification from crude aqueous extracts ... [more ▼]

Two different procedures, alcohol precipitation with washing (APW) and a 10 kD MWCO membrane ultrafiltration with diafiltration (UF-DF), for pectin recovering and purification from crude aqueous extracts were investigated. The results showed that the yield, purity, chemical, and physicochemical features of isolated pectins depended upon the type of procedure used. The APW technique gave a higher pectin yield, and the isolated pectin contained more neutral sugars, more proteins, and more ash but less galacturonic acids than the 10 kD membrane UF-DF one. The weight-average molar mass of the APP was lower and its emulsifying properties slightly better than those of the UFPR10. Molar mass distribution of APP or UFPR10 showed two distinct pectin fractions peaks, which were separated in high-MW and low-MW pectin fractions using a 50kD MWCO membrane. The high-MW fractions exhibited poor emulsifying and emulsion stabilizing abilities whereas the low-MW fractions displayed a much higher emulsifying ability than the initial pectin fractions. Therefore, it was inferred that the ability of beet pectin to be an effective emulsifier and/or emulsion stabilizer was greatly dependent on its weight-average molar mass. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

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See detailComparison of ammonia and greenhouse gas emissions during the fattening of pigs, kept either on fully slatted floor or on deep litter
Philippe, François-Xavier ULg; Laitat, Martine ULg; Canart, Bernard et al

in Livestock Science (2007), 111(1-2), 144-152

Five successive batches of fattening pigs were raised, each during a four month period, on a totally concrete slatted floor in one experimental room and on straw based deep litter in another. The rooms ... [more ▼]

Five successive batches of fattening pigs were raised, each during a four month period, on a totally concrete slatted floor in one experimental room and on straw based deep litter in another. The rooms were automatically ventilated to maintain a constant ambient temperature. Available floor space was of 0.75 in m(2) per pig kept on the slatted floor and 1.20 m(2) per pig kept on the deep litter. With this last system, about 46 kg of straw were supplied per pig throughout a fattening period. The slurry pit was emptied and the litter removed after each batch. Once a month, the emissions of ammonia (NH3) nitrous oxide (N2O), methane (CH4), carbon dioxide (CO2) and water vapour (H2O) were measured continuously for 6 consecutive days by infra-red. photoacoustic detection. The performance of the animals was not significantly different according to the floor type. Gaseous emissions from pigs raised on the slatted floor and on the deep litter were, respectively, 6.2 and 13.1 g per pig per day for NH3, 0.54 and 1.11 g per pig per day for N2O, 16.3 and 16.0 g per pig per day for CH4, 1.74 and 1.97 kg per pig per day for CO2 and 2.48 and 3.70 kg per pig per day for H2O. Except for the CH4 emissions, all the differences were significant (P<0.001). Thus, pig fattening on deep litter releases nearly 20% more greenhouse gases than on slatted floor, with 2.64 and 2.24 kg of CO2 equivalents, respectively (P<0.001). Whatever the floor type, emissions increased from the beginning to the end of the fattening periods by about 5 times for NH3, 4 times for N2O, 3 times for CH4 and 2 times for CO2 and H2O. Correlation coefficients between CO2-emissions and H2O, NH3 and CH4 emissions were, on average for both floor types, 0.82, 0.77 and 0.74, respectively. Although rearing pigs on straw generally has a good brand image for the consumer, this rearing system produces more pollutant gases than keeping pigs on slatted floors. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailComparison of an approximated method with FEA calculations for the evaluation of the fire resistance of concrete tunnel sections
Schneider, Ulrich; Schneider, Martin; Franssen, Jean-Marc ULg

in Proceedings of the International Workshop "Fire Design of Concrete Structures - From Materials Modelling to Structural Performance (2007, November)

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See detailComparison of antiosteoclastic activity of Estraderm TTS50 and Premarin 0.625 in healthy postmenopausal females
Reginster, Jean-Yves ULg; Dequinze, B; Franchimont, P

in Hungarian Rhumatology (1991), 32

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See detailComparison of aquifer vulnerability assessment techniques. Application to the Neblon river basin (Belgium)
Gogu, Radu Constantin; Hallet, Vincent; Dassargues, Alain ULg

in Environmental Geology (2003), 44(8), 881-892

Five different methods for assessing intrinsic aquifer vulnerability were tested in a case study and their results compared. The test area was a slightly karstified district in the Condroz region of ... [more ▼]

Five different methods for assessing intrinsic aquifer vulnerability were tested in a case study and their results compared. The test area was a slightly karstified district in the Condroz region of Belgium. The basin covers about 65 km(2) and the karst aquifer provides a water-supply of about 28,000 m(3)d(-1). The methods tested were: EPIK (Doerfliger et al. 1999), DRASTIC (Aller et al.1987), 'German method' (von Hoyer and Sofner 1998), GOD (Foster 1987) and ISIS (Civita and De Regibus 1995). The results are compared and critically examined. From the analysis, it seems that reducing the number of parameters is unsatisfactory, due to the variety of geological conditions. The various methods produce very different results at any given site. As only physically-based methods can be checked for their reliability, it is clear that future vulnerability mapping techniques must incorporate such methods. [less ▲]

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See detailComparison of auroral processes at Jupiter and Saturn
Clarke, J.; Gérard, Jean-Claude ULg

Conference (2003, April 01)

Extensive series of images of Jupiter's aurora have been obtained from HST and ground-based telescopes, while only a handful of images of Saturn's aurora have been taken to date and only with the HST ... [more ▼]

Extensive series of images of Jupiter's aurora have been obtained from HST and ground-based telescopes, while only a handful of images of Saturn's aurora have been taken to date and only with the HST. With the Cassini spacecraft approaching Saturn, it is timely to compare what we know of Saturn's aurora with the better-studied case of Jupiter. This presentation will summarize the basic features of Jupiter's auroral processes, give an overview of what we know about Saturn's auroral processes, and speculate on what might be learned from further studies at the time of Cassini approach to Saturn. [less ▲]

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See detailA comparison of balloon-expandable-stent implantation with balloon angioplasty in patients with coronary artery disease. Benestent Study Group.
Serruys, P. W.; de Jaegere, P.; Kiemeneij, F. et al

in The New England journal of medicine (1994), 331(8), 489-95

BACKGROUND: Balloon-expandable coronary-artery stents were developed to prevent coronary restenosis after coronary angioplasty. These devices hold coronary vessels open at sites that have been dilated ... [more ▼]

BACKGROUND: Balloon-expandable coronary-artery stents were developed to prevent coronary restenosis after coronary angioplasty. These devices hold coronary vessels open at sites that have been dilated. However, it is unknown whether stenting improves long-term angiographic and clinical outcomes as compared with standard balloon angioplasty. METHODS: A total of 520 patients with stable angina and a single coronary-artery lesion were randomly assigned to either stent implantation (262 patients) or standard balloon angioplasty (258 patients). The primary clinical end points were death, the occurrence of a cerebrovascular accident, myocardial infarction, the need for coronary-artery bypass surgery, or a second percutaneous intervention involving the previously treated lesion, either at the time of the initial procedure or during the subsequent seven months. The primary angiographic end point was the minimal luminal diameter at follow-up, as determined by quantitative coronary angiography. RESULTS: After exclusions, 52 patients in the stent group (20 percent) and 76 patients in the angioplasty group (30 percent) reached a primary clinical end point (relative risk, 0.68; 95 percent confidence interval, 0.50 to 0.92; P = 0.02). The difference in clinical-event rates was explained mainly by a reduced need for a second coronary angioplasty in the stent group (relative risk, 0.58; 95 percent confidence interval, 0.40 to 0.85; P = 0.005). The mean (+/- SD) minimal luminal diameters immediately after the procedure were 2.48 +/- 0.39 mm in the stent group and 2.05 +/- 0.33 mm in the angioplasty group; at follow-up, the diameters were 1.82 +/- 0.64 mm in the stent group and 1.73 +/- 0.55 mm in the angioplasty group (P = 0.09), which correspond to rates of restenosis (diameter of stenosis, > or = 50 percent) of 22 and 32 percent, respectively (P = 0.02). Peripheral vascular complications necessitating surgery, blood transfusion, or both were more frequent after stenting than after balloon angioplasty (13.5 vs. 3.1 percent, P < 0.001). The mean hospital stay was significantly longer in the stent group than in the angioplasty group (8.5 vs. 3.1 days, P < 0.001). CONCLUSIONS: Over seven months of follow-up, the clinical and angiographic outcomes were better in patients who received a stent than in those who received standard coronary angioplasty. However, this benefit was achieved at the cost of a significantly higher risk of vascular complications at the access site and a longer hospital stay. [less ▲]

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See detailComparison of basic density and longitudinal shrinkage in tension wood and opposite wood in young stems of Poplar (P. euramericana cv “ Ghoy ”) when subjected to a gravitational stimulus
Jourez, Benoît ULg; Riboux, Alain; Leclercq, André

in Canadian Journal of Forest Research = Journal Canadien de la Recherche Forestière (2001), 31(10), 1676-1683

In a green house, under controlled conditions, young shoots, taken from poplar cuttings (P. euramericana cv “ Ghoy ”), were artificially inclined in order to quantify the modifications of physical ... [more ▼]

In a green house, under controlled conditions, young shoots, taken from poplar cuttings (P. euramericana cv “ Ghoy ”), were artificially inclined in order to quantify the modifications of physical properties induced by a gravitational stimulus. At the end of the growing season, basic density and longitudinal shrinkage were measured on very small samples taken from pure tension wood tissue observed on the upper face of the inclined axis and compared with opposite wood tissue, free of gelatinous fibers, developed on the opposite lower face. In a second step, shoots bend at two different lean intensities were analyzed. On young poplar wood, gravitational stimulus was found to have a significant effect on physical properties. Relations between basic density and longitudinal shrinkage are different depending on the types of wood considered. Shrinkage appears more sensitive to lean intensity in the range considered here [less ▲]

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See detailComparison of Biotyping, Ribotyping, and Pulsed-Field Gel Electrophoresis for Investigation of a Common-Source Outbreak of Burkholderia Pickettii Bacteremia
Chetoui, H.; Melin, Pierrette ULg; Struelens, M. J. et al

in Journal of Clinical Microbiology (1997), 35(6), 1398-403

Over a 3-month period, six immunocompromised patients developed one or more episodes of Burkholderia pickettii bacteremia and/or catheter infection. Vials of a commercially available, "sterile" saline for ... [more ▼]

Over a 3-month period, six immunocompromised patients developed one or more episodes of Burkholderia pickettii bacteremia and/or catheter infection. Vials of a commercially available, "sterile" saline for injection which had been used for flushing the patients' indwelling intravenous devices were implicated as the common source of the organisms. No further cases were diagnosed once the use of this saline was discontinued. Twenty-six isolates, including 9 outbreak-related strains from case patients and contaminated saline as well as 17 control strains, were tested comparatively by biotyping, ribotyping with EcoRI and HindIII, and pulsed-field gel electrophoresis (PFGE) with SpeI. Macrorestriction analysis revealed nine PFGE groups and was more discriminating than ribotyping (seven ribotypes) and biotyping (two biovars). Among the outbreak-related isolates, one B. pickettii type was found by the three typing methods. Furthermore, PFGE was useful for subdividing ribotypes and for distinguishing isolates involved in the outbreak from all epidemiologically unrelated strains. [less ▲]

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See detailA comparison of blade tip timing data analysis methods
Carrington, Ian B; Wright, Jan Robert; Cooper, Jonathan E et al

in Proceedings of the Institution of Mechanical Engineers - Part G - Journal of Aerospace Engineering (2001), 215(6), 301-312

The experimental determination of the vibration characteristics of rotating engine blades is very important for fatigue failure considerations. One of the most promising techniques for measuring the ... [more ▼]

The experimental determination of the vibration characteristics of rotating engine blades is very important for fatigue failure considerations. One of the most promising techniques for measuring the frequency of blade vibrations is blade tip timing. In this paper, three vibration analysis methods were specifically formulated and applied to the tip timing problem for the first time, using data obtained from a simple mathematical blade tip timing simulation. The results from the methods were compared statistically in order to determine which of the techniques is more suitable. One of the methods, the global autoregressive instrumental variables approach, produced satisfactory results at realistic noise levels. However, all of the techniques produced biased results under certain circumstances. [less ▲]

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See detailA Comparison of Blade Tip-Timing Data Analysis Methods
Carrington, I. B.; Wright, J. R.; Cooper, J. E. et al

in Leung, A. Y. T.; Wright, J. R.; Sandoz, D. J. (Eds.) et al Proceedings of the First International Conference on the Integration of Dynamics, Monitoring and Control (1999, September)

The determination of the vibration characteristics of rotating engine blades is very important for fatigue failure considerations. One of the most promising techniques for measuring blade vibrations is ... [more ▼]

The determination of the vibration characteristics of rotating engine blades is very important for fatigue failure considerations. One of the most promising techniques for measuring blade vibrations is blade tip-timing. Three vibration analysis methods were used on data obtained from a simple mathematical blade tip-timing simulator. The results from the methods were compared statistically. One of the methods, the Global Autoregressive Instrumental Variables approach produced satisfactory results at realistic noise levels. However, all of the techniques produced biased results under certain circumstances. [less ▲]

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