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See detailOn some stability properties of the discretization of damped propagation of shallow-water inertia–gravity waves on the Arakawa B-grid
Beckers, Jean-Marie ULg

in Ocean Modelling (1999), 1(2-4), 53-69

We investigate a problem mentioned by Deleersnijder and Campin (Deleersnijder, E., & Campin, J. -M. (1993). Ocean Modelling 97, 2), who looked at the problem of the discretization of inertia–gravity waves ... [more ▼]

We investigate a problem mentioned by Deleersnijder and Campin (Deleersnijder, E., & Campin, J. -M. (1993). Ocean Modelling 97, 2), who looked at the problem of the discretization of inertia–gravity waves in the staggered B-grid. We generalize this study by adding diffusion. General stability conditions are found with the help of Miller's theorem, and the paradox found in Deleersnijder and Campin (Deleersnijder, E., & Campin, J. -M. (1993). Ocean Modelling 97, 2) is discussed. It is argued that it stems from inappropriate application of boundary conditions in conjunction with a Coriolis force treatment which could produce mechanical work. [less ▲]

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See detailOn standardness and I-cosiness
Laurent, Stéphane ULg

in Séminaire de Probabilités (2010), XLIII

The object of study of this work is the invariant characteristics of filtrations in discrete, negative time, pioneered by Vershik. We prove the equivalence between I-cosiness and standardness without ... [more ▼]

The object of study of this work is the invariant characteristics of filtrations in discrete, negative time, pioneered by Vershik. We prove the equivalence between I-cosiness and standardness without using Vershik’s standardness criterion. The equivalence between I-cosiness and productness for homogeneous filtrations is further investigated by showing that the I-cosiness criterion is equivalent to Vershik’s first level criterion separately for each random variable. We also aim to derive the elementary properties of both these criteria, and to give a survey and some complements on the published and unpublished literature. [less ▲]

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See detailOn the (13) CN/(12) CN Isotopic Ratio in Comet Hale-Bopp
Schulz, R.; Arpigny, Claude ULg; Manfroid, Jean ULg et al

in Bulletin of the American Astronomical Society (1997, July 01)

The carbon isotope abundance ratio, (12) C/(13) C, in comets is a key number to their origin. Its accurate determination from ground-based spectroscopy is, however, a difficult task since the observable ... [more ▼]

The carbon isotope abundance ratio, (12) C/(13) C, in comets is a key number to their origin. Its accurate determination from ground-based spectroscopy is, however, a difficult task since the observable emissions of (13) C-containing molecules are very weak. Due to its exceptional brightness, comet Hale-Bopp provided a unique opportunity to look for (13) C and derive the (12) C/(13) C isotopic ratio. We observed the comet with the high-resolution spectrograph SOFIN mounted on the 2.56m Nordic Optical Telescope on La Palma, Canary Islands. High-resolution spectra of the R-branch of the CN (0-0) band were obtained between Apr. 7 and 13, 1997, when the comet was at r = 0.9 AU and Delta = 1.4 AU. Owing to the heliocentric velocity effect on the fluorescence excitation rates, this period was particularly favourable to search for the R(8) and R(7) emission lines of the (13) CN isotope. Because of the strong continuum in the coma of Hale-Bopp we took our measurements at a certain location in the coma away from the nucleus and from any dust jets. Our first preliminary reduction and analysis show, after careful continuum subtraction, a clear detection of a line at the position predicted for R(8) and and an indication of a line at the predicted position of R(7). The R(8) line can be used to determine the (12) C/(13) C isotopic ratio and the first preliminary values will be given. [less ▲]

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See detailOn the accuracy of adults’ auditory perception of normophonic and dysphonic children’s personality.
Verduyckt, Ingrid; Remacle, Marc; Morsomme, Dominique ULg

in Logopedics, Phoniatrics, Vocology (in press)

We investigated the accuracy of auditory inferences of personality of Belgian children with vocal fold nodules (VFN). External judges (N=57) were asked to infer the personality of normophonic (NP ... [more ▼]

We investigated the accuracy of auditory inferences of personality of Belgian children with vocal fold nodules (VFN). External judges (N=57) were asked to infer the personality of normophonic (NP) children and children with VFN (N=10) on the basis of vowels and sentences. The auditory inferred profiles were compared to the actual personality of NP and VFN children. Positive and partly accurate inferences of VFN children’s personality were made on the basis of connected speech, while sustained vowels yielded negative and inaccurate inferences of personality traits of children with VFN. Dysphonic voice quality, as defined by the overall severity of vocal abnormality, conveyed inaccurate and low degrees of Extraversion. This effect was counterbalanced in connected speech by faster speaking rate that accurately conveyed higher degrees of Extraversion, a characteristic trait of VFN children’s actual personality. [less ▲]

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See detailOn the accuracy of analytical models of TCP throughput
El Khayat, Ibtissam; Geurts, Pierre ULg; Leduc, Guy ULg

in Lecture Notes in Computer Science (2006, May), 3976

Based on a large set of TCP sessions we first study the accuracy of two well-known analytical models (SQRT and PFTK) of the TCP average rate. This study shows that these models are far from being accurate ... [more ▼]

Based on a large set of TCP sessions we first study the accuracy of two well-known analytical models (SQRT and PFTK) of the TCP average rate. This study shows that these models are far from being accurate on average. Actually, our simulations show that 70% of their predictions exceed the boundaries of TCP-Friendliness, thus questioning their use in the design of new TCP-Friendly transport protocols. Our study also shows that the inaccuracy of the PFTK model is largely due to its inability to make the distinction between the two packet loss detection methods used by TCP: triple duplicate acknowledgments or timeout expirations. We then use supervised learning techniques to infer models of the TCP rate. These models show important accuracy improvements when they take into account the two types of losses. This suggests that analytical model of TCP throughput should certainly benefit from the incorporation of the timeout loss rate. [less ▲]

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See detailOn the accuracy of the reduction of UVBY photometry
Manfroid, Jean ULg; Heck, A.

in Astronomy and Astrophysics (1984), 132

By simulating uvby observations under various conditions, an analysis has been made of the precision reachable by a photometric reduction algorithm proposed in an earlier paper (Manfroid and Heck, 1983 ... [more ▼]

By simulating uvby observations under various conditions, an analysis has been made of the precision reachable by a photometric reduction algorithm proposed in an earlier paper (Manfroid and Heck, 1983). The influence of variations in parameters, such as the number of nights or the number of standard stars, is discussed. It is shown how the grouping of nights in the reduction procedure allows the observer to spend less time on standard stars measurements, while improving the accuracy of the results. The difficulty of giving a realistic value for the precision of the reductions in actual conditions is stressed. The inclusion of secondary standards is also recommended. [less ▲]

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See detailOn the accurate selection of asymptotic detection thresholds for Infit and Outfit indexes of person fit
Magis, David ULg; Raîche, Gilles; Béland, Sébastien

Conference (2012, April 11)

It exists a bunch of person fit indexes but Lz (Drasgow, Levine, & Williams, 1985), Infit mean square W (Wright & Masters, 1982) and Outfit mean square U (Wright & Stone, 1979) are certainly the most ... [more ▼]

It exists a bunch of person fit indexes but Lz (Drasgow, Levine, & Williams, 1985), Infit mean square W (Wright & Masters, 1982) and Outfit mean square U (Wright & Stone, 1979) are certainly the most popular. However, they have the undesirable property that their limiting distribution depends on the true ability level, which is generally unknown. In addition, the asymptotic distribution of U and W indexes was not clearly stated. Snijders (2001) proposed a generalization of the index Lz to incorporate estimated ability levels in its computation, and derived subsequent asymptotic normality of this modified Lz* index. The purpose of this talk is threefold. First, the generalization of Lz to Lz* is briefly sketched. Second, it is shown how this generalization can be successfully applied to both U and W indexes, yielding generalized U* and W* indexes respectively. Third, the accuracy of generalized indexes in detecting person (mis)fit is assessed through a simulation study. Three situations were investigated: (a) absence of misfit; (b) presence of cheating (yielding spuriously high scores); (c) presence of inattention (yielding spuriously low scores). Several conditions were varied, such as test length and aberrance rates when misfit was introduced. Response patterns were generated under the Rasch model and maximum likelihood estimation was performed to obtain the ability estimates. Several significance levels were selected. It is observed, that the generalized indexes Lz*, U* and W* better recover the significance level than their standard alternatives Lz, U and W respectively, while they are more powerful in identifying the two types of person misfit. In particular, the modified index W* has the best improvement in performance with respect to its original version W. It is concluded that Snijders' generalization of Lz index to Lz* is also accurate for U and W indexes under Rasch modelling. Possible extensions to other person fit indexes, such as ECI indexes (Tatsuoka, 1984), other ability estimators, and other IRT models are eventually briefly discussed. [less ▲]

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See detailOn the Active Centers of Serine and Zn II DD-carboxyppetidases
Charlier, Paulette ULg; Coyette, Jacques ULg; Dideberg, Otto et al

in Gregory, G.I. (Ed.) Recent advances in the Chemistry of beta-lactam antibiotics (1980)

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See detailOn the advantage of using risk curves to assess flood protection measures
Dewals, Benjamin ULg; Detrembleur, Sylvain ULg; Archambeau, Pierre ULg et al

in Mambretti, Stefano (Ed.) Environmental Risk (2012)

Modern flood management approaches require the quantification of flood risk, accounting for the hazard component (flood frequency and inundation intensity) as well as the vulnerability of the floodplains ... [more ▼]

Modern flood management approaches require the quantification of flood risk, accounting for the hazard component (flood frequency and inundation intensity) as well as the vulnerability of the floodplains (exposure, value and susceptibility). In this chapter, we present a detailed flood risk model, in which flow computation, monetary valuation of the assets and damage calculation are conducted at the scale of individual buildings or facilities. To avoid the shortcoming of focusing on economic damage, psycho-social impacts of floods are also included in the analysis. The model has been applied to evaluate three flood protection measures on a river reach in the Meuse basin (Belgium). The resulting risk curves show that such a micro-scale risk analysis provides important insights into the relative influence of the different flood protection measures. This could neither be evaluated through a more standard hydraulic analysis nor through the quantification of flood risk by only a single number. [less ▲]

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See detailOn the advantages of economically designed the Hotelling’s T2 control chart with variable sample sizes and sampling intervals
Faraz, Alireza ULg; kazemzadeh, R. B.; Parsian, Ahmad et al

in Quality & Quantity (2012), 46(1), 39-53

Faraz and Parsian (Statistical Paper, 47: 569–593, 2006) have shown that the double warning lines (DWL) scheme detects process shifts more quickly than the other variable ratio sampling schemes such as ... [more ▼]

Faraz and Parsian (Statistical Paper, 47: 569–593, 2006) have shown that the double warning lines (DWL) scheme detects process shifts more quickly than the other variable ratio sampling schemes such as variable sample sizes (VSS), variable sampling intervals (VSI) and variable sample sizes and sampling intervals (VSSVSI). In this paper, the DWLT2control chart for monitoring the process mean vector is economically designed. The cost model proposed by Costa and Rahim (Journal of Applied Statistics, 28: 875–885, 2001) is used here and is minimized through a genetic algorithm (GA) approach. Then the effects of the model parameters on the chart parameters and resulting operating loss is studied and finally a comparison between all possible variable ratio sampling (VRS) schemes are made to choose the best option economically. [less ▲]

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See detailOn the Advantages of Using a Strong Coupling Variational Formulation to Model Electro-Mechanical Problem
Rochus, Véronique ULg; Rixen, D. J.; Golinval, Jean-Claude ULg

in Thermal, Mechanical and Multiphysics Simulation and Experiments in Micro/Nanoelectronics and Systems, Proceedings of EuroSimE 2006 (2006, April)

This paper presents the advantages of a strong coupled formulation to model the electro-mechanical coupling appearing in MEMS. Usually the classical softwares use a staggered methodology iterating between ... [more ▼]

This paper presents the advantages of a strong coupled formulation to model the electro-mechanical coupling appearing in MEMS. Usually the classical softwares use a staggered methodology iterating between two different codes to obtain the solution of the coupled problem. In this research a strong coupled formulation is proposed and a tangent stiffness matrix of the whole problem is computed. Using this matrix, nonlinear algorithms such as the Riks-Crisfield algorithm may be applied to solve the static nonlinear problem and determine accurately the static pull-in voltage. Moreover, the natural frequencies may be computed around each equilibrium positions. The dynamic behaviour of the structure may also be studied and two new parameters are defined: the dynamic pull-in voltage and the dynamic pull-in time. This strong coupled methodology deriving from variational principle may also be used for topology optimisation and extended finite elements. [less ▲]

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See detailOn the analysis of steel structures made of thin-walled members
Degée, Hervé ULg

in Proceedings of the EUROSTEEL '99 Conference (1999)

A first part of this paper consists in a review of the different existing methods, allowing to study the behaviour of members for which it is necessary to account for the deformability of the cross ... [more ▼]

A first part of this paper consists in a review of the different existing methods, allowing to study the behaviour of members for which it is necessary to account for the deformability of the cross section. A particular attention is paid to the capacity of each method to be used for the global analysis of a complete structure. A second part of the paper presents bases for the adaptation of a beam finite element so as to be able to account for the deformability of the profile cross section. [less ▲]

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See detailOn the analysis of steel structures made of thin-walled members
Degée, Hervé ULg

in Acta Polytechnica (1999), 39(5), 7-14

A first part of this paper consists in a review of the different existing methods, allowing to study the behaviour of members for which it is necessary to account for the deformability of the cross ... [more ▼]

A first part of this paper consists in a review of the different existing methods, allowing to study the behaviour of members for which it is necessary to account for the deformability of the cross section. A particular attention is paid to the capacity of each method to be used for the global analysis of a complete structure. A second part of the paper presents bases for the adaptation of a beam finite element so as to be able to account for the deformability of the profile crosse section. [less ▲]

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See detailOn the application and interpretation of Keeling plots in paleo climate research - Deciphering δ 13C of atmospheric CO 2 measured in ice cores
Köhler, Peter; Fischer, Hubertus; Schmitt, Jochen et al

in Biogeosciences (2006), 3(4), 539-556

The Keeling plot analysis is an interpretation method widely used in terrestrial carbon cycle research to quantify exchange processes of carbon between terrestrial reservoirs and the atmosphere. Here, we ... [more ▼]

The Keeling plot analysis is an interpretation method widely used in terrestrial carbon cycle research to quantify exchange processes of carbon between terrestrial reservoirs and the atmosphere. Here, we analyse measured data sets and artificial time series of the partial pressure of atmospheric carbon dioxide (pCO(2)) and of delta C-13 of CO2 over industrial and glacial/interglacial time scales and investigate to what extent the Keeling plot methodology can be applied to longer time scales. The artificial time series are simulation results of the global carbon cycle box model BICYCLE. The signals recorded in ice cores caused by abrupt terrestrial carbon uptake or release loose information due to air mixing in the firn before bubble enclosure and limited sampling frequency. Carbon uptake by the ocean cannot longer be neglected for less abrupt changes as occurring during glacial cycles. We introduce an equation for the calculation of long-term changes in the isotopic signature of atmospheric CO2 caused by an injection of terrestrial carbon to the atmosphere, in which the ocean is introduced as third reservoir. This is a paleo extension of the two reservoir mass balance equations of the Keeling plot approach. It gives an explanation for the bias between the isotopic signature of the terrestrial release and the signature deduced with the Keeling plot approach for long-term processes, in which the oceanic reservoir cannot be neglected. These deduced isotopic signatures are similar (-8.6 parts per thousand) for steady state analyses of long-term changes in the terrestrial and marine biosphere which both perturb the atmospheric carbon reservoir. They are more positive than the delta C-13 signals of the sources, e.g. the terrestrial carbon pools themselves (similar to -25 parts per thousand). A distinction of specific processes acting on the global carbon cycle from the Keeling plot approach is not straightforward. In general, processes related to biogenic fixation or release of carbon have lower y-intercepts in the Keeling plot than changes in physical processes, however in many case they are indistinguishable (e.g. ocean circulation from biogenic carbon fixation). [less ▲]

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See detailOn the appropriateness of marginal models for repeated measurements in clinical trials
Lindsey, James ULg; Lambert, Philippe ULg

in Statistics in Medicine (1998), 17

Although models developed directly to describe marginal distributions have become widespread in the analysis of repeated measurements, some of their disadvantages are not well enough known. These include ... [more ▼]

Although models developed directly to describe marginal distributions have become widespread in the analysis of repeated measurements, some of their disadvantages are not well enough known. These include producing profile curves that correspond to no possible individual, possibly showing that a treatment is superior on average when it is poorer for each individual subject, implicitly generating complex and implausible physiological explanations, including underdispersion in subgroups, and sometimes corresponding to no possible probabilistic data generating mechanism. We conclude that such marginal models may sometimes be appropriate for descriptive observational studies, such as sample surveys in epidemiology, but should only be used with great care in causal experimental settings, such as clinical trials. [less ▲]

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See detailOn the approximation of incompressible materials in the displacement method
Debongnie, Jean-François ULg

in International Journal for Numerical Methods in Engineering (1979), 14(7), 1095-1099

A mathematical description of the numerical approximation to incompressibility with nearly incompressible displacement finite elements is presented. By the way of functional analysis, it leads to a ... [more ▼]

A mathematical description of the numerical approximation to incompressibility with nearly incompressible displacement finite elements is presented. By the way of functional analysis, it leads to a condition of convergence to the incompressible problem when v is increased up to 0.5, which can be identified with Fried's K1 criterion. [less ▲]

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See detailOn the approximation of incompressible solids in the displacement method
Debongnie, Jean-François ULg

Report (1976)

A mathematical analysis of the numerical approximation to incompressibility with nearly incompressible displacement finite elements is presented. It explains why, as observed by many authors, convergence ... [more ▼]

A mathematical analysis of the numerical approximation to incompressibility with nearly incompressible displacement finite elements is presented. It explains why, as observed by many authors, convergence to the incompressible solution is not necessarily obtained when Poisson's ration is increased up to 0.5. It also allows predicting under which conditions convergence of the nearly incompressible approach is guaranteed. [less ▲]

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See detailOn the Assessment of a Modified Diffusion-Wave Approximation Model in the Framework of Overland Flow
Paulus, Raphaël ULg; Archambeau, Pierre ULg; Erpicum, Sébastien ULg et al

in Chanson, Hubert (Ed.) Balance and Uncertainty: Water in a Changing World (2011)

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See detailOn the asymptotic standard error of a class of robust estimators of ability in dichotomous item response models
Magis, David ULg

in British Journal of Mathematical & Statistical Psychology (in press)

In item response theory, the classical estimators of ability are highly sensitive to response disturbances and can return strongly biased estimates of the true underlying ability level. Robust methods ... [more ▼]

In item response theory, the classical estimators of ability are highly sensitive to response disturbances and can return strongly biased estimates of the true underlying ability level. Robust methods were introduced to lessen the impact of such aberrant responses onto the estimation process. The computation of asymptotic (i.e., large sample) standard errors (ASE) for these robust estimators, however, has not been fully considered yet. This paper focuses on a broad class of robust ability estimators, defined by an appropriate selection of the weight function and the residual measure, for which the ASE is derived from the theory of estimating equations. The maximum likelihood (ML) and the robust estimators, together with their estimated ASE, are then compared through a simulation study. It is concluded that both the estimators and their ASE perform similarly in absence of response disturbances, while the robust estimator and its estimated ASE are less biased and outperform their ML counterparts in presence of response disturbances with large impact on the item response process. [less ▲]

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