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Estimation of the Error Distribution in a Semiparametric Transformation Model Heuchenne, Cédric ; ; Scientific conference (2011, November 15) Detailed reference viewed: 33 (1 ULg)Estimation of the error distribution in a semiparametric transformation model. Heuchenne, Cédric ; ; in Electronic Journal of Statistics (2015), 9 Detailed reference viewed: 13 (3 ULg)Estimation of the error distribution in nonparametric regression with cross-sectional data Heuchenne, Cédric ; Laurent, Géraldine E-print/Working paper (2014) In this article, we study the nonparametric regression model Y=m(X)+varepsilon where m(x)=E[Y|X=x] and sigma²(x)=Var[varepsilon|X=x] are unknown smooth functions, and the error varepsilon has zero mean ... [more ▼] In this article, we study the nonparametric regression model Y=m(X)+varepsilon where m(x)=E[Y|X=x] and sigma²(x)=Var[varepsilon|X=x] are unknown smooth functions, and the error varepsilon has zero mean and finite variance conditionally on X=x. The problem consists in estimating the cumulative distribution function of the error in a nonparametric way when the couple (X,Y) is obtained by cross-sectional sampling while the positive response Y can be right-censored. We propose a new estimator for the error distribution function based on the estimators of m(.) and sigma²(.) described in Heuchenne and Laurent 2014. A bootstrap procedure is developed to solve the critical problem of the smoothing parameter choice. We assess the performance of the proposed estimator through simulations. Finally, a data set based on the mortality of diabetics is analyzed. (Heuchenne Cédric and Laurent Géraldine, Nonparametric regression with cross-sectional data: an alternative to conditional product-limit estimators, 2014) [less ▲] Detailed reference viewed: 41 (10 ULg)Estimation of the error distribution in nonparametric regression with right censored selection biased data Laurent, Géraldine ; Heuchenne, Cédric Poster (2009, May) Detailed reference viewed: 51 (21 ULg)Estimation of the error distribution in right censored and selection biased regression models Laurent, Géraldine ; Heuchenne, Cédric Conference (2009, October 15) Consider the location-scale regression model Y=m(X) + σ(X) Ɛ where the error Ɛ is independent of the covariate X and where m and σ are unknown smooth functions. The pair (X; Y ) is subject to generalized ... [more ▼] Consider the location-scale regression model Y=m(X) + σ(X) Ɛ where the error Ɛ is independent of the covariate X and where m and σ are unknown smooth functions. The pair (X; Y ) is subject to generalized bias selection and the response to right censoring. We construct an estimator for the cumulative distribution function of the error Ɛ, and develop a bootstrap procedure to select the smoothing parameter involved in the procedure. This method is studied via extension simulations and applied to real unemployment data. [less ▲] Detailed reference viewed: 22 (11 ULg)Estimation of the error on the mean velocity and on the Reynolds stress due to a misoriented ADV probe in the horizontal plane: case of experiments in a compound open-channel Peltier, Yann ; ; et al in Flow Measurement & Instrumentation (2013), 34(C), 34-41 Detailed reference viewed: 11 (1 ULg)Estimation of the fascine efficiency in terms of runoff infiltration and sediments deposition Degré, Aurore ; Pineux, Nathalie ; Cantreul, Vincent et al in Geophysical Research Abstracts (2013), 15 Runoff inundations and mudflows are more and more frequent phenomena. In 2011, Belgium had a lot of its municipalities affected by this problematic. Since then, mitigation measures are more and more set ... [more ▼] Runoff inundations and mudflows are more and more frequent phenomena. In 2011, Belgium had a lot of its municipalities affected by this problematic. Since then, mitigation measures are more and more set up in agricultural watersheds. The fascines are one of these measures which allow to protect the public and private infrastructures and in the same way, which don’t reduce the famers productivity. They consist in branches faggots piled up between two rows of stakes. These linear constructions are mainly put in place across concentrated runoff axis in order to slow down the water and to filter the mud. Only few quantifications of their effectiveness (in terms of flow and concentration water reduction) exist and are however needed to better recommend these types of mitigation measures. Our experiment aims at measuring discharge and mud concentration reduction due to the fascines in a completely defined context. The tests were realised through fascines planted in field border. A watertight surface of 2,45m to 0,80m carries the water to the fascines. Three types of fascines were tested (willow wood fascine, straw fascine, straw compacted fascine), three different water flows were applied (0,5L/s, 3L/s and 6L/s) and three water concentration in dry soil (13g/L, 26g/L, 38g/L) were used. The different factor combinations were tested. The results show that we can expect a reduction of 60% of the flow for the biggest water flows (proportional efficiency with the water flow). The factor interaction study doesn’t allow to see a difference between the type. About the sediment water concentration, the filtration can reach 50%, the fascine with wood faggots showing a better efficiency. Finally, the difference between the fascine type show that straw fascine can support a biggest watershed (25 hectares) than the wood faggot fascine can (5-10 hectares) but during a smaller return period (one year against five years). [less ▲] Detailed reference viewed: 99 (39 ULg)Estimation of the Greenland ice sheet surface mass balance contribution to future sea level rise using the regional climate model MAR Fettweis, Xavier ; ; et al Conference (2013, April 10) With the aim of estimating the sea level rise (SLR) coming from Surface Mass Balance (SMB) changes over the Greenland ice sheet (GrIS), we report future projections obtained with the regional climate ... [more ▼] With the aim of estimating the sea level rise (SLR) coming from Surface Mass Balance (SMB) changes over the Greenland ice sheet (GrIS), we report future projections obtained with the regional climate model MAR, forced by outputs of three CMIP5 General Circulation Models (GCMs). Our results indicate that in warmer climates, the mass gained due to increased winter snowfall over GrIS does not compensate the mass lost through increased meltwater run-off in summer. All the MAR projections shows similar non-linear melt increases with rising temperatures as a result of the positive surface albedo feedback, because no change is projected in the general atmospheric circulation over Greenland. Nevertheless, MAR exhibits a large range in its future projections. By coarsely estimating the GrIS SMB changes from CMIP5 GCMs outputs, we show that the uncertainty coming from the GCM-based forcing represents about half of projected SMB changes. In 2100, the CMIP5 ensemble mean projects a SLR, resulting from a GrIS SMB decrease, estimated to be 4 2 cm and 9 4 cm for the RCP 4.5 and RCP 8.5 scenarios, respectively. However, these future projections do not consider the positive melt-elevation feedback. Sensitivity MAR experiments using perturbed ice sheet topographies consistent with the projected SMB changes highlight the importance of coupling climate models to an ice sheet model. Such a coupling will allow to consider the future response of both surface processes and ice-dynamic changes, and their mutual feedbacks to rising temperatures. [less ▲] Detailed reference viewed: 53 (6 ULg)Estimation of the Greenland ice sheet surface mass balance for the 20th and 21st centuries Fettweis, Xavier ; ; et al in Cryosphere (The) (2008), 2 Results from a regional climate simulation (1970–2006) over the Greenland ice sheet (GrIS) reveals that more than 97% of the interannual variability of the modelled Surface Mass Balance (SMB) can be ... [more ▼] Results from a regional climate simulation (1970–2006) over the Greenland ice sheet (GrIS) reveals that more than 97% of the interannual variability of the modelled Surface Mass Balance (SMB) can be explained by the GrIS summer temperature anomaly and the GrIS annual precipitation anomaly. This multiple regression is then used to empirically estimate the GrIS SMB since 1900 from climatological time series. The projected SMB changes in the 21st century are investigated with the set of simulations performed with atmosphere-ocean general circulation models (AOGCMs) of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). These estimates show that the high surface mass loss rates of recent years are not unprecedented in the GrIS history of the last hundred years. The minimum SMB rate seems to have occurred earlier in the 1930s and corresponds to a zero SMB rate. The AOGCMs project that the SMB rate of the 1930s would be common at the end of 2100. The temperature would be higher than in the 1930s but the increase of accumulation in the 21st century would partly offset the acceleration of surface melt due to the temperature increase. However, these assumptions are based on an empirical multiple regression only validated for recent/current climatic conditions, and the accuracy and time homogeneity of the data sets and AOGCM results used in these estimations constitute a large uncertainty. [less ▲] Detailed reference viewed: 197 (17 ULg)THE ESTIMATION OF THE HERBACEOUS BIOMASS IN THE SAHELIANS PASTORAL ZONES USING A GIS ; Djaby, Bakary ; et al in Gérard, Bégni (Ed.) Observing our environment from space: new solutions for a new millennium (2001) In the Sahel region the pastorals resources are strongly linked to the fluctuation of the biomass production and as well as the breeding systems, which are based on the transhumance and the nomadism as ... [more ▼] In the Sahel region the pastorals resources are strongly linked to the fluctuation of the biomass production and as well as the breeding systems, which are based on the transhumance and the nomadism as well. In the present study, an integrated approach of multi-source, multi-type and multi-scales data analysis in the pastoral zone in Senegal, Mali, Burkina Faso, Mauritania, Niger and Chad has been developed using PC-Arc/Info and Arc/View potentialities for the purpose of Sahelian rangeland production estimation. [less ▲] Detailed reference viewed: 258 (4 ULg)Estimation of the heritability of spirometric variables in calves Bureau, Fabrice ; ; et al in Pflügers Archiv : European Journal of Physiology (1998), 435 Detailed reference viewed: 18 (2 ULg)Estimation of the Sea Level Rise by 2100 Resulting from Changes in the Surface Mass Balance of the Greenland Ice Sheet Fettweis, Xavier ; Belleflamme, Alexandre ; Erpicum, Michel et al in Blanco, Juan; Kheradmand, Houshang (Eds.) Climate Change - Geophysical Foundations and Ecological Effects (2011) We present here future projections of the Greenland climate performed by the regional climate model MAR coupled with a snow model and forced by two scenarios of greenhouse gas emissions from the global ... [more ▼] We present here future projections of the Greenland climate performed by the regional climate model MAR coupled with a snow model and forced by two scenarios of greenhouse gas emissions from the global model CanESM2 of the next IPCC assessment report (AR5). Knowing that MAR forced by CanESM2 over the current climate (1970-1999) compares well with the reference MAR simulation performed by using the ERA-40 reanalysis as forcing, this gives us confidence in our future projections. For the RCP4.5 scenario (optimistic) and respectively RCP8.5 scenario (pessimistic), MAR projects a sea level rise in 2100 of 6.5 +/- 1.5 cm and respectively 14+/-2 cm as result of increasing surface melt of the Greenland ice sheet over 2000-2100. It is true that MAR projects a small increase of snowfall in the winter because the atmosphere will be warmer and therefore can contain more water vapor. But this is not sufficient to offset the acceleration of melt, notably for the scenario RCP8.5 which projects an increase of 10 °C in 2100 above the ice sheet. This work ﬁts in the ICE2SEA project (http://www.ice2sea.eu) of the 7th Framework Program (FP7) which aims to improve the projections of the continental ice melting contribution to sea level rise. [less ▲] Detailed reference viewed: 311 (30 ULg)Estimation of the soil nitric nitrogen concentration at plot scale. Impact of the sampling density on the result’s precision Vandenberghe, Christophe ; Colinet, Gilles Poster (2014, February 26) Detailed reference viewed: 31 (13 ULg)Estimation of the Stability of Parathyroid Hormone when Stored at -80°C for a Long Period Cavalier, Etienne ; Delanaye, Pierre ; Hubert, Philippe et al in Clinical Journal of the American Society of Nephrology (2009), 4(12), 1988-92 Detailed reference viewed: 52 (22 ULg)Estimation of the Time Interval between the Administration of Heroin and the Sampling of Blood in Chronic Inhalers DUBOIS, Nathalie ; HALLET, Claude ; SEIDEL, Laurence et al in Journal of Analytical Toxicology (2015) To develop a model for estimating the time delay between last heroin consumption and blood sampling in chronic drug users. Eleven patients, all heroin inhalers undergoing detoxification, were included in ... [more ▼] To develop a model for estimating the time delay between last heroin consumption and blood sampling in chronic drug users. Eleven patients, all heroin inhalers undergoing detoxification, were included in the study. Several plasma samples were collected during the detoxification procedure and analyzed for the heroin metabolites 6-acetylmorphine (6AM), morphine (MOR), morphine-6-glucuronide (M6G) and morphine-3-glucuronide (M3G), according to a UHPLC/MSMS method. The general linear mixed model was applied to time-related concentrations and a pragmatic four-step delay estimation approach was proposed based on the simultaneous presence of metabolites in plasma. Validation of the model was carried out using the jackknife technique on the 11 patients, and on a group of 7 test patients. Quadratic equations were derived for all metabolites except 6AM. The interval delay estimation was 2–4 days when only M3G present in plasma, 1–2 days when M6G and M3G were both present, 0–1 day when MOR, M6G and M3G were present and <2 h for all metabolites present. The ‘jackknife’ correlation between declared and actual estimated delays was 0.90. The overall precision of the delay estimates was 8–9 h. The delay between last heroin consumption and blood sampling in chronic drug users can be satisfactorily predicted from plasma heroin metabolites. [less ▲] Detailed reference viewed: 56 (21 ULg)Estimation of the turbulent kinetic energy dissipation in a culture cell stirred tank bioreactor Delafosse, Angélique ; Collignon, Marie-Laure ; et al in Chemical Engineering Science (2011), 66(8), 1728-1737 The turbulent dissipation rate is a key parameter in stirred tanks and its local values may have a strong inﬂuence on the performance of many processes. However, the local dissipation rate estimation is ... [more ▼] The turbulent dissipation rate is a key parameter in stirred tanks and its local values may have a strong inﬂuence on the performance of many processes. However, the local dissipation rate estimation is far from easy in a stirred tank, especially near the impeller discharge where maximum values are encountered. The aim of this work is to estimate the dissipation rate in a vessel used for animal-cell cultures and stirred with a down-pumping axial impeller (Mixel TTP) from velocity ﬁelds measured by 2D-PIV. Special attention is paid to the assumptions necessary to estimate the dissipation rate from 2D measurements and to the inﬂuence of measurement spatial resolution on the estimated values. The analysis of isotropy ratios measured on vertical, horizontal and tangential planes shows that the turbulence in the impeller discharge is far from isotropic. Isotropy assumptions classically used to estimate the dissipation rate from 2D measurements may thus lead to erroneous values. Based on the measured isotropy ratios, a new relationship is proposed to estimate the dissipation rate in the impeller discharge. This relationship is then used to estimate the dissipation rate on a vertical plane located in the impeller discharge zone. In order to analyze the inﬂuence of the measurement spatial resolution on the estimated values of the dissipation, a total of 12 spatial resolutions are tested. Results show that if the spatial resolution is divided by a factor 2, the dissipation rate increases by 220%. For the smallest spatial resolution value used, the maximum dissipation rate estimated is 50 times higher than the mean overall dissipation rate and the corresponding minimum value of the Kolmogorov scale is nearly 3 times smaller than the Kolmogorov scale computed from the mean overall dissipation rate. [less ▲] Detailed reference viewed: 152 (28 ULg)Estimation of tidal boundary conditions and surface winds by assimilation of high-frequency radar surface currents in the German Bight Barth, Alexander ; Alvera Azcarate, Aïda ; et al Conference (2010) Numerical ocean models are affected by errors of various origins: errors in the initial conditions, boundary conditions and atmospheric forcings, uncertainties in the turbulence parametrization and ... [more ▼] Numerical ocean models are affected by errors of various origins: errors in the initial conditions, boundary conditions and atmospheric forcings, uncertainties in the turbulence parametrization and discretization errors. In data assimilation, observations are used to reduce the uncertainty in the model solution. Ensemble-based assimilation schemes are often implemented such that the expected error of the model solution is minimized. It is shown that the observations can also be used to obtain improved estimates of the, in general, poorly known boundary conditions and atmospheric forcings. An ensemble smoother scheme is presented to assimilate high-frequency (HF) radar surface currents to improve tidal boundary conditions and wind forcings of a circulation model of the German Bight. To create an ensemble of dynamically realistic tidal boundary conditions, a cost function is formulated which is directly related to the probability of each perturbation. This cost function ensures that the perturbations are spatially smooth and that the structure of the perturbations satisfies approximately the harmonic linearized shallow water equations. Based on those perturbations an ensemble simulation is carried out using the full three-dimensional General Estuarine Ocean Model (GETM). Optimized boundary values are obtained using all observations within the assimilation period using the covariances of the ensemble simulation. The approach acts like a smoother scheme since past and future observations are taken into account. The final analysis is obtained by rerunning the model using the optimal perturbation of the boundary conditions. The analyzed model solution satisfies thus the model equations exactly and does not suffer from spurious adjustments often observed with sequential assimilation schemes. Model results are also compared to independent tide gauge data. The assimilation also reduces the model error compared to those sea level observations. The same scheme is also used to correct surface winds. Surface winds are crucial for accurately modeling the marine circulation in coastal waters. The method is validated directly by comparing the analyzed wind speed to in situ measurements and indirectly by assessing the impact of the corrected winds on sea surface temperature (SST) relative to satellite SST. [less ▲] Detailed reference viewed: 25 (5 ULg)An estimation of total vehicle travel reduction in the case of telecommuting. Detailed analyses using an activity-based modeling approach. ; ; Cools, Mario et al in Proceedings of the 39th European Transport Conference (2011) Transportation Demand Management (TDM) is often referred to as a strategy adopted by transport planners with the goal to increase transport system efficiency. One of the potential measures that can be ... [more ▼] Transportation Demand Management (TDM) is often referred to as a strategy adopted by transport planners with the goal to increase transport system efficiency. One of the potential measures that can be adopted in TDM is the implementation of telecommuting. A significant number of studies have been conducted in the past to evaluate the effect of telecommuting on the amount of peak-period trips. However it is less studied whether telecommuting also effectively and significantly reduces total vehicle travel in terms of kilometers traveled throughout the day. For this reason, a conventional modeling approach was adopted in this paper to calculate total kilometers of travel saved in the case telecommuting would materialize in the Flanders area. In a second part, this paper introduces the use of an activity-based modeling approach to evaluate the effect of telecommuting on a more detailed time scale. As the second approach provides a more disaggregate result, both models can be compared on the more aggregate level to validate whether they correspond. [less ▲] Detailed reference viewed: 42 (2 ULg)An estimation of total vehicle travel reduction in the case of telecommuting. Detailed analysis using an activity-based modeling approach ; ; Cools, Mario et al in Cornelis, Eric (Ed.) Proceedings of the BIVEC-GIBET Transport Research Day 2011 (2011) ransportation Demand Management (TDM) is often referred to as a strategy adopted by transport planners with the goal to increase transport system efficiency. One of the possible measures that can be ... [more ▼] ransportation Demand Management (TDM) is often referred to as a strategy adopted by transport planners with the goal to increase transport system efficiency. One of the possible measures that can be adopted in TDM is the implementation of telecommuting. A significant number of studies have been conducted in the past to evaluate the effect of telecommuting on peak-period trips. However it is less studied whether telecommuting also effectively and significantly reduces total vehicle travel. For this reason, a conventional modeling approach was adopted in this paper to calculate total kilometers of travel saved in the case telecommuting would materialize in the Flanders area. In a second part, the paper also introduces the use of an activity-based modeling approach to evaluate the effect of telecommuting. By doing so, an operational activity-based framework is externally validated by means of another completely different model, both calibrated for the same application and study area. [less ▲] Detailed reference viewed: 88 (2 ULg)Estimation of uncertainty from the total error strategy: Application to internal and normative methods Marini Djang'Eing'A, Roland ; Rozet, Eric ; Hubert, Cédric et al in Acta Clinica Belgica (2010), 65 Based on the importance of uncertainty, another approach to estimate this parameter of performance considering the total error (systematic and random) was applied. The data were obtained from the two main ... [more ▼] Based on the importance of uncertainty, another approach to estimate this parameter of performance considering the total error (systematic and random) was applied. The data were obtained from the two main steps of an analytical method lifecycle: validation and routine for levonorgestrel (LNG) assay and routine for oxygen assay. Results obtained allowed drawing suitable conclusion in terms of prediction of routine and establishment of norms. [less ▲] Detailed reference viewed: 205 (55 ULg) |
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