Articles de revues : « Corrector estimates »

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MUNTEAN, A., et T. L. VAN NOORDEN. « Corrector estimates for the homogenization of a locally periodic medium with areas of low and high diffusivity ». European Journal of Applied Mathematics 24, n^o 5 (2 avril 2013) : 657–77. http://dx.doi.org/10.1017/s0956792513000090.

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We prove an upper bound for the convergence rate of the homogenization limit ε → 0 for a linear transmission problem for a advection–diffusion(–reaction) system posed in areas with low and high diffusivity, where ε is a suitable scale parameter. In this way we rigorously justify the formal homogenization asymptotics obtained in [37] (van Noorden, T. and Muntean, A. (2011) Homogenization of a locally-periodic medium with areas of low and high diffusivity.Eur. J. Appl. Math.22, 493–516). We do this by providing a corrector estimate. The main ingredients for the proof of the correctors include integral estimates for rapidly oscillating functions with prescribed average, properties of the macroscopic reconstruction operators, energy bounds, and extra two-scale regularity estimates. The whole procedure essentially relies on a good understanding of the analysis of the limit two-scale problem.

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Reichelt, Sina. « Corrector estimates for a class of imperfect transmission problems ». Asymptotic Analysis 105, n^o 1-2 (6 octobre 2017) : 3–26. http://dx.doi.org/10.3233/asy-171432.

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Bella, Peter, et Felix Otto. « Corrector Estimates for Elliptic Systems with Random Periodic Coefficients ». Multiscale Modeling & ; Simulation 14, n^o 4 (janvier 2016) : 1434–62. http://dx.doi.org/10.1137/15m1037147.

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Muntean, Adrian, et Sina Reichelt. « Corrector Estimates for a Thermodiffusion Model with Weak Thermal Coupling ». Multiscale Modeling & ; Simulation 16, n^o 2 (janvier 2018) : 807–32. http://dx.doi.org/10.1137/16m109538x.

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Goldman, R. E., A. Bajo et N. Simaan. « Algorithms for autonomous exploration and estimation in compliant environments ». Robotica 31, n^o 1 (28 mars 2012) : 71–87. http://dx.doi.org/10.1017/s0263574712000100.

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SUMMARYThis paper investigates algorithms for enabling surgical slave robots to autonomously explore shape and stiffness of surgical fields. The paper addresses methods for estimating shape and impedance parameters of tissue and methods for autonomously exploring perceived impedance during tool interaction inside a tissue cleft. A hybrid force-motion controller and a cycloidal motion path are proposed to address shape exploration. An adaptive exploration algorithm for segmentation of surface features and a predictor-corrector algorithm for exploration of deep features are introduced based on discrete impedance estimates. These estimates are derived from localized excitation of tissue coupled with simultaneous force measurements. Shape estimation is validated in ex-vivo bovine tissue and attains surface estimation errors of less than 2.5 mm with force sensing resolutions achievable with current technologies in minimally invasive surgical robots. The effect of scan patterns on the accuracy of the shape estimate is demonstrated by comparing the shape estimate of a Cartesian raster scan with overlapping cycloid scan pattern. It is shown that the latter pattern filters the shape estimation bias due to frictional drag forces. Surface impedance exploration is validated to successfully segment compliant environments on flexible inorganic models. Simulations and experiments show that the adaptive search algorithm reduces overall time requirements relative to the complexity of the underlying structures. Finally, autonomous exploration of deep features is demonstrated in an inorganic model and ex-vivo bovine tissue. It is shown that estimates of least constraint based on singular value decomposition of locally estimated tissue stiffness can generate motion to accurately follow a tissue cleft with a predictor-corrector algorithm employing alternating steps of position and admittance control. We believe that these results demonstrate the potential of these algorithms for enabling “smart” surgical devices capable of autonomous execution of intraoperative surgical plans.

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Rosenfeld, Joel A., et Warren E. Dixon. « Convergence rate estimates for the kernelized predictor corrector method for fractional order initial value problems ». Fractional Calculus and Applied Analysis 24, n^o 6 (22 novembre 2021) : 1879–98. http://dx.doi.org/10.1515/fca-2021-0081.

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Abstract This manuscript presents a kernelized predictor corrector (KPC) method for fractional order initial value problems, which replaces linear interpolation with interpolation by a radial basis function (RBF) in a predictor-corrector scheme. Specifically, the class of Wendland RBFs is employed as the basis function for interpolation, and a convergence rate estimate is proved based on the smoothness of the particular kernel selected. Use of the Wendland RBFs over Mittag-Leffler kernel functions employed in a previous iteration of the kernelized method removes the problems encountered near the origin in [11]. This manuscript performs several numerical experiments, each with an exact known solution, and compares the results to another frequently used fractional Adams-Bashforth-Moulton method. Ultimately, it is demonstrated that the KPC method is more accurate but requires more computation time than the algorithm in [4].

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Capdeboscq, Yves, Timo Sprekeler et Endre Süli. « Finite element approximation of elliptic homogenization problems in nondivergence-form ». ESAIM : Mathematical Modelling and Numerical Analysis 54, n^o 4 (16 juin 2020) : 1221–57. http://dx.doi.org/10.1051/m2an/2019093.

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We use uniform W2,p estimates to obtain corrector results for periodic homogenization problems of the form A(x/ε):D2uε = f subject to a homogeneous Dirichlet boundary condition. We propose and rigorously analyze a numerical scheme based on finite element approximations for such nondivergence-form homogenization problems. The second part of the paper focuses on the approximation of the corrector and numerical homogenization for the case of nonuniformly oscillating coefficients. Numerical experiments demonstrate the performance of the scheme.

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Oghonyon, Jimevwo Godwin, Matthew Etinosa Egharevba et Ogbu Famous Imaga. « The Extended Block Predictor-Block Corrector Method for Computing Fuzzy Differential Equations ». WSEAS TRANSACTIONS ON MATHEMATICS 22 (19 septembre 2022) : 1–12. http://dx.doi.org/10.37394/23206.2023.22.1.

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Over the years, scholars have developed predictor-corrector method to provide estimates for ordinary differential equations (ODEs). Predictor-corrector methods have been reduced to predicting-correcting method with no concern for finding the convergence-criteria for each loop with no suitable vary step size in order to maximize error. This study aim to consider computing fuzzy differential equations employing the extended block predictor-block corrector method (EBP-BCM). The method of interpolation and collocation combined with multinomial power series as the basis function approximation will used. The principal local truncation errors of the block predictor-block corrector method will be utilized to bring forth the convergence criteria to ensure speedy convergence of each iteration thereby maximizing error(s). Thus, these findings will reveal the ability of this technique to speed up the rate of convergence as a result of variegating the step size and to ensure error control. Some examples will solve to showcase the efficiency and accuracy of this technique.

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Gloria, Antoine, et Félix Otto. « Quantitative estimates on the periodic approximation of the corrector in stochastic homogenization ». ESAIM : Proceedings and Surveys 48 (janvier 2015) : 80–97. http://dx.doi.org/10.1051/proc/201448003.

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Fatima, Tasnim, Adrian Muntean et Mariya Ptashnyk. « Unfolding-based corrector estimates for a reaction–diffusion system predicting concrete corrosion ». Applicable Analysis 91, n^o 6 (juin 2012) : 1129–54. http://dx.doi.org/10.1080/00036811.2011.625016.

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Marušić–Paloka, Eduard, Igor Pažanin et Marko Radulović. « Justification of the Higher Order Effective Model Describing the Lubrication of a Rotating Shaft with Micropolar Fluid ». Symmetry 12, n^o 3 (26 février 2020) : 334. http://dx.doi.org/10.3390/sym12030334.

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Motivated by the lubrication processes naturally appearing in numerous industrial applications (such as steam turbines, pumps, compressors, motors, etc.), we study the lubrication process of a slipper bearing consisting of two coaxial cylinders in relative motion with an incompressible micropolar fluid (lubricant) injected in the thin gap between them. The asymptotic approximation of the solution to the governing micropolar fluid equations is given in the form of a power series in terms of the small parameter ε representing the thickness of the shaft. The regular part of the approximation is obtained in the explicit form, allowing us to acknowledge the effects of fluid’s microstructure clearly through the presence of the microrotation viscosity in the expressions for the first-order velocity and microrotation correctors. We provide the construction of the boundary layer correctors at the upper and lower boundary of the shaft along with the construction of the divergence corrector, allowing us to improve our overall estimate. The derived effective model is rigorously justified by proving the error estimates, evaluating the difference between the original solution of the considered problem and the constructed asymptotic approximation.

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Tumanova, Natalija. « PREDICTOR-CORRECTOR DOMAIN DECOMPOSITION ALGORITHM FOR PARABOLIC PROBLEMS ON GRAPHS ». Mathematical Modelling and Analysis 17, n^o 1 (1 février 2012) : 113–27. http://dx.doi.org/10.3846/13926292.2012.645891.

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In this paper, we present a predictor-corrector type algorithm for solution of linear parabolic problems on graph structure. The graph decomposition is done by dividing some edges and therefore we get a set of problems on sub-graphs, which can be solved efficiently in parallel. The convergence analysis is done by using the energy estimates. It is proved that the proposed finite-difference scheme is unconditionally stable but the predictor step error gives only conditional approximation. In the second part of the paper it is shown that the presented algorithm can be written as Douglas type scheme, based on the domain decomposition method. For a simple case of one dimensional parabolic problem, the convergence analysis is done by using results from [P. Vabishchevich. A substracturing domain decomposition scheme for unsteady problems. Comp. Meth. Appl. Math. 11(2):241-268, 2011]. The optimality of asymptotical error estimates is investigated. Results of computational experiments are presented.

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Fortier, Jean-J. « Best linear corrector of classification estimates of proportions of objects in several unknown classes ». Canadian Journal of Statistics 20, n^o 1 (mars 1992) : 23–33. http://dx.doi.org/10.2307/3315572.

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Khoa, Vo Anh, et Adrian Muntean. « Corrector homogenization estimates for a non-stationary Stokes–Nernst–Planck–Poisson system in perforated domains ». Communications in Mathematical Sciences 17, n^o 3 (2019) : 705–38. http://dx.doi.org/10.4310/cms.2019.v17.n3.a6.

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Kovtunenko, Victor A., Sina Reichelt et Anna V. Zubkova. « Corrector estimates in homogenization of a nonlinear transmission problem for diffusion equations in connected domains ». Mathematical Methods in the Applied Sciences 43, n^o 4 (15 novembre 2019) : 1838–56. http://dx.doi.org/10.1002/mma.6007.

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Fischer, Julian, et Felix Otto. « Sublinear growth of the corrector in stochastic homogenization : optimal stochastic estimates for slowly decaying correlations ». Stochastics and Partial Differential Equations : Analysis and Computations 5, n^o 2 (14 novembre 2016) : 220–55. http://dx.doi.org/10.1007/s40072-016-0086-x.

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Hernandez, David M., Sam Hadden et Junichiro Makino. « Are long-term N-body simulations reliable ? » Monthly Notices of the Royal Astronomical Society 493, n^o 2 (19 février 2020) : 1913–25. http://dx.doi.org/10.1093/mnras/staa388.

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ABSTRACT N-body integrations are used to model a wide range of astrophysical dynamics, but they suffer from errors which make their orbits diverge exponentially in time from the correct orbits. Over long time-scales, their reliability needs to be established. We address this reliability by running a three-body planetary system over about 200 e-folding times. Using nearby initial conditions, we can construct statistics of the long-term phase-space structure and compare to rough estimates of resonant widths of the system. We compared statistics for a wide range of numerical methods, including a Runge–Kutta method, Wisdom–Holman method, symplectic corrector methods, and a method by Laskar and Robutel. ‘Improving’ an integrator did not increase the phase-space accuracy, but simply increasing the number of initial conditions did. In fact, the statistics of a higher order symplectic corrector method were inconsistent with the other methods in one test.

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Green, Charles Wing Ho, et Yubin Yan. « Detailed Error Analysis for a Fractional Adams Method on Caputo–Hadamard Fractional Differential Equations ». Foundations 2, n^o 4 (22 septembre 2022) : 839–61. http://dx.doi.org/10.3390/foundations2040057.

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We consider a predictor–corrector numerical method for solving Caputo–Hadamard fractional differential equation over the uniform mesh logtj=loga+logtNajN,j=0,1,2,…,N with a≥1, where loga=logt0<logt1<…<logtN=logT is a partition of [loga,logT]. The error estimates under the different smoothness properties of the solution y and the nonlinear function f are studied. Numerical examples are given to verify that the numerical results are consistent with the theoretical results.

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Bakhvalov, N. S., et A. Bourgeat. « Precise estimates of the difference between the homogenized solution with its first corrector and the original One ». Applicable Analysis 70, n^o 1-2 (août 1998) : 45–60. http://dx.doi.org/10.1080/00036819808840674.

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Eremin, Eugenie L., et Evgeniy A. Shelenok. « Nonlinear-periodic control system for non-affine multi-connected plant with state delay ». Cybernetics and Physics, Volume 7, 2018, Number 4 (23 novembre 2018) : 195–203. http://dx.doi.org/10.35470/2226-4116-2018-7-4-195-203.

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The article deals with the synthesis problem of control system regulator for non-affine multivariable dynamic plant with state delay. The plant operates in periodic modes and also in the presence of external disturbances and parametric uncertainty. As a solution methods the hyperstability criterion, the fast-acting dynamic corrector, and L-dissipativity conditions are used. The key step of the system synthesis is the receipt for V. M. Popov’s integral inequality special estimates that ensure the fulfillment of the control goals. In final article part with the help of simulation the dynamic processes taking place in the proposed control system, are visually illustrated.

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J. Vromans, Arthur, Fons van de Ven et Adrian Muntean. « Homogenization of a pseudo-parabolic system via a spatial-temporal decoupling : Upscaling and corrector estimates for perforated domains ». Mathematics in Engineering 1, n^o 3 (2019) : 548–82. http://dx.doi.org/10.3934/mine.2019.3.548.

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Hoáng, Viêt Há. « Homogenization of singularly perturbed Dirichlet problems in perforated domains ». Proceedings of the Royal Society of Edinburgh : Section A Mathematics 130, n^o 1 (février 2000) : 35–51. http://dx.doi.org/10.1017/s0308210500000032.

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We study the singularly perturbed problem —εαΔuε + uε = f (α > 0) with the Dirichlet boundary condition in a perforated domain, in which the holes are distributed periodically with period 2ε throughout a fixed domain Ω. The asymptotic behaviour of uε when ε → 0, together with corrector results and error estimates in L2(Ω), are deduced for all sizes of holes. The behaviour of uε in is obtained for the cases where the size of holes is of order ε or is of a sufficiently smaller order. When the holes' size is of a sufficiently small order, as expected, uε has similar behaviour to that in the case of a non-varying domain.

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Kaliappan, S., et R. Rajeswari. « A Novel Approach of Position Estimation and Power Factor Corrector Converter Fed BLDC Motor ». International Journal of Power Electronics and Drive Systems (IJPEDS) 5, n^o 3 (1 février 2015) : 415. http://dx.doi.org/10.11591/ijpeds.v5.i3.pp415-423.

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<p>This paper proposes a Power factor Corrected (PFC) Bridgeless Buck-Boost converter fed BLDC motor drive. The Bridgeless configuration eliminates the Diode Bridge Rectifier in order to reduce the number of components and the conduction loss. The position sensors used in BLDC drives have drawbacks of additional cost, mechanical alignment problems. These bottle necks results in sensorless technique. The Sensorless technique mostly relies on measurement of Back EMF to determine relative positions of stator and rotor for the correct coil energising sequence can be implemented. This paper introduces the offline Finite Element method for sensorless operation. The proposed sensorless scheme estimates the motor position at standstill and running condition. The obtained Power Factor is within the acceptable limits IEC 61000-3-2. The proposed drive is simulated in MATLAB/Simulink the obtained results are validated experimentally on a developed prototype of the drive.</p>

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Trefilov, P. M., M. V. Mamchenko et A. V. Korol’kov. « Strapdown inertial navigation systems readings correction based on navigational data of other sensors and systems with intelligent selection of the priority adjuster ». E3S Web of Conferences 224 (2020) : 02024. http://dx.doi.org/10.1051/e3sconf/202022402024.

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Strapdown inertial navigation systems (SINS) are one of the main components of the navigation systems of the drones and aircraft (including autonomous ones), but their readings need to be instanly corrected due to the constant accumulation of errors. This paper comprises the review of existing approaches to using one or more sensors or systems to correct the navigation data of SINS algorithms (herein after – correctors) using integrated information processing. A common disadvantage of the analysed approaches is the lack of flexibility concerning the types and the number of SINS correctors used, as well as the growth of computational burden due to the use of the measurement vectors of all the correctors in the process of forming the state vector of the system. This article proposes the use of the original adaptive scheme based on the selection of the least noisy data, taking into account environmental conditions, for the integrated processing of the SINS and the correctos’ navigation parameters. The essence of the approach is that the state vector is estimated on the basis of the most reliable corrector. This allows reducing the correlation of errors in the correctors’ measurement of navigational parameters, since only the measurement vectors (or vector) with best navigational data signal/noise ratio (received from the corresponding correctors) are used in forming the state vector. Furthermore, the proposed navigational data fusion scheme has a modular structure and greater flexibility in comparison with the loosely coupled systems, and also implies the use of an arbitrary number of correction sensors and systems regardless of the physical nature of their measurements.

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Suslina, T. A. « Homogenization of elliptic systems with periodic coefficients : operator error estimates in $L_2(\mathbb {R}^d)$ with corrector taken into account ». St. Petersburg Mathematical Journal 26, n^o 4 (6 mai 2015) : 643–93. http://dx.doi.org/10.1090/spmj/1354.

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Zhao, Snunyi, et Yuriy Shmaliy. « An Approach to Optimal Filtering of Time-Variant Systems via Finite Measurements ». EQUATIONS 1 (2 février 2021) : 11–16. http://dx.doi.org/10.37394/232021.2021.1.2.

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Fast optimal estimates are often required in control and signal processing. In this paper, we discuss an approach to optimal finite impulse response (OFIR) filtering for discrete time-variant systems using finite measurements. The mean square error is minimized to obtain the batch OFIR algorithm which requires measurements on an a finite horizon of N points. Fast iterative algorithm is found using recursions. It is shown that each recursion has a predictor/corrector Kalman filter (KF)-like format with special initial conditions. In this sense, the KF is considered as a special case of the proposed iterative OFIR filtering algorithm when N approaches infinity for known initial conditions. It has been confirmed by simulation that the iterative form of the OFIR filter operates much faster than the batch form.

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Nkemzi, Boniface, et Jake Léonard Nkeck. « A Predictor-Corrector Finite Element Method for Time-Harmonic Maxwell’s Equations in Polygonal Domains ». Mathematical Problems in Engineering 2020 (22 février 2020) : 1–13. http://dx.doi.org/10.1155/2020/3502513.

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The overall efficiency and accuracy of standard finite element methods may be severely reduced if the solution of the boundary value problem entails singularities. In the particular case of time-harmonic Maxwell’s equations in nonconvex polygonal domains Ω, H1-conforming nodal finite element methods may even fail to converge to the physical solution. In this paper, we present a new nodal finite element adaptation for solving time-harmonic Maxwell’s equations with perfectly conducting electric boundary condition in general polygonal domains. The originality of the present algorithm lies in the use of explicit extraction formulas for the coefficients of the singularities to define an iterative procedure for the improvement of the finite element solutions. A priori error estimates in the energy norm and in the L2 norm show that the new algorithm exhibits the same convergence properties as it is known for problems with regular solutions in the Sobolev space H2Ω2 in convex and nonconvex domains without the use of graded mesh refinements or any other modification of the bilinear form or the finite element spaces. Numerical experiments that validate the theoretical results are presented.

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Bakk, Zsuzsa, Daniel L. Oberski et Jeroen K. Vermunt. « Relating Latent Class Assignments to External Variables : Standard Errors for Correct Inference ». Political Analysis 22, n^o 4 (2014) : 520–40. http://dx.doi.org/10.1093/pan/mpu003.

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Latent class analysis is used in the political science literature in both substantive applications and as a tool to estimate measurement error. Many studies in the social and political sciences relate estimated class assignments from a latent class model to external variables. Although common, such a “three-step” procedure effectively ignores classification error in the class assignments; Vermunt (2010, “Latent class modeling with covariates: Two improved three-step approaches,” Political Analysis 18:450–69) showed that this leads to inconsistent parameter estimates and proposed a correction. Although this correction for bias is now implemented in standard software, inconsistency is not the only consequence of classification error. We demonstrate that the correction method introduces an additional source of variance in the estimates, so that standard errors and confidence intervals are overly optimistic when not taking this into account. We derive the asymptotic variance of the third-step estimates of interest, as well as several candidate-corrected sample estimators of the standard errors. These corrected standard error estimators are evaluated using a Monte Carlo study, and we provide practical advice to researchers as to which should be used so that valid inferences can be obtained when relating estimated class membership to external variables.

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Deschamps-Francoeur, Gabrielle, Vincent Boivin, Sherif Abou Elela et Michelle S. Scott. « CoCo : RNA-seq read assignment correction for nested genes and multimapped reads ». Bioinformatics 35, n^o 23 (29 mai 2019) : 5039–47. http://dx.doi.org/10.1093/bioinformatics/btz433.

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Abstract Motivation Next-generation sequencing techniques revolutionized the study of RNA expression by permitting whole transcriptome analysis. However, sequencing reads generated from nested and multi-copy genes are often either misassigned or discarded, which greatly reduces both quantification accuracy and gene coverage. Results Here we present count corrector (CoCo), a read assignment pipeline that takes into account the multitude of overlapping and repetitive genes in the transcriptome of higher eukaryotes. CoCo uses a modified annotation file that highlights nested genes and proportionally distributes multimapped reads between repeated sequences. CoCo salvages over 15% of discarded aligned RNA-seq reads and significantly changes the abundance estimates for both coding and non-coding RNA as validated by PCR and bedgraph comparisons. Availability and implementation The CoCo software is an open source package written in Python and available from http://gitlabscottgroup.med.usherbrooke.ca/scott-group/coco. Supplementary information Supplementary data are available at Bioinformatics online.

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Heide-Jørgensen, M. P., K. L. Laidre, R. G. Hansen, M. L. Burt, M. Simon, D. L. Borchers, J. Hansen et al. « Rate of increase and current abundance of humpback whales in West Greenland ». J. Cetacean Res. Manage. 12, n^o 1 (9 février 2023) : 1–14. http://dx.doi.org/10.47536/jcrm.v12i1.586.

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Aerial line transect surveys of the density of humpback whales (Megaptera novaeangliae) conducted off West Greenland eight times between 1984 and 2007 were used to estimate the rate of increase on the summer feeding ground. Only surveys in 1993, 2005 and 2007 had enough sightings to construct independent density estimates, whereas the surveys in 1984–85 and 1987–89 had to be merged and treated as two surveys. The annual rate of increase was 9.4% yr–1 (SE = 0.01) between 1984 and 2007. This rate of increase is higher than the increase estimated at the breeding grounds in the West Indies, but is of the same magnitude as the observed rate of increase at other feeding grounds in the North Atlantic. A matrix model based on observed life history parameters revealed that the theoretical growth rate of a humpback whale population ranged between 1 and 11%. This confirms that the observed growth in West Greenland is within the plausible values. The survey in 2007 was used to make a fully corrected abundance estimate including corrections for whales that were submerged during the passage of the survey plane. The line transect estimate for 2007 was 1,020 (CV = 0.35). When the estimate was corrected for perception bias with mark-recapture distance sampling (MRDS) methods, the abundance increased to 1,505 (0.49). A correction for availability bias was developed based on time-depth-recorder information on the time spent at the surface (0–4m). However, used directly this correction leads to a positively-biased abundance estimate and instead a correction was developed for the non-instantaneous visual sighting process in an aircraft. The resulting estimate for 2007 was 3,272 (CV = 0.50) for the MRDS analysis. An alternative strip census estimate deploying a strip width of 300m resulted in 995 (0.33) whales. Correction for perception bias resulted in 991 (0.35) whales and corrected for the same availability bias as for the MRDS method resulted in a fully corrected estimate of 2,154 (0.36) humpback whales in West Greenland in 2007.

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Sapiano, M. R. P., J. E. Janowiak, P. A. Arkin, H. Lee, T. M. Smith et P. Xie. « Corrections for Temporal Discontinuities in the OPI ». Journal of Atmospheric and Oceanic Technology 27, n^o 3 (1 mars 2010) : 457–69. http://dx.doi.org/10.1175/2009jtecha1366.1.

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Abstract The longest record of precipitation estimated from satellites is the outgoing longwave radiation (OLR) precipitation index (OPI), which is based on polar-orbiting infrared observations from the Advanced Very High Resolution Radiometer (AVHRR) instrument that has flown onboard successive NOAA satellites. A significant barrier to the use of these data in studies of the climate of tropical precipitation (among other things) is the large bias caused by orbital drift that is present in the OLR data. Because the AVHRR instruments are deployed on the polar-orbiting spacecraft, OLR observations are recorded at specific times for each earth location for each day. Discontinuities are caused by the use of multiple satellites with different observing times as well as the orbital drift that occurs throughout the lifetime of each satellite. A regression-based correction is proposed based solely on the equator crossing time (ECT). The correction allows for separate means for each satellite as well as separate coefficients for each satellite ECT. The correction is calculated separately for each grid box but is applied only at locations where the correction is correlated with the OLR estimate. Thus, the correction is applied only where deemed necessary. The OPI is used to estimate precipitation from the OLR estimates based on the new corrected version of the OLR, the uncorrected OLR, and two earlier published corrected versions. One of the earlier corrections is derived by removing variations from AVHRR based on EOFs that are identified as containing spurious variations related to the ECT bias, whereas the other is based on OLR estimates from the High Resolution Infrared Radiation Sounder (HIRS) that have been corrected using diurnal models for each grid box. The new corrected version is shown to be free of nearly all of the ECT bias and has the lowest root mean square difference when compared to gauges and passive microwave estimates of precipitation. The EOF-based correction fails to remove all of the variations related to the ECT bias, whereas the correction based on HIRS removes much of the bias but appears to introduce erroneous trends caused by the water vapor signal to which these data are sensitive. The new correction for AVHRR OLR works well in the tropics where the OPI has the most skill, but users should be careful when interpreting trends outside this region.

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Tonhati, H., M. F. C. Muñoz, J. M. C. Duarte, R. H. Reichert, J. A. Oliveira et A. L. F. Lima. « Estimates of correction factors for lactation length and genetic parameters for milk yield in buffaloes ». Arquivo Brasileiro de Medicina Veterinária e Zootecnia 56, n^o 2 (avril 2004) : 251–57. http://dx.doi.org/10.1590/s0102-09352004000200016.

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Correction factors for milk yield at 90, 240, 270 and 305 days of lactation of buffaloes and genetic and environmental parameters for milk yield of these lactation periods were estimated. The data used consisted of 3888 lactation records of 1630 buffaloes from 10 herds reared in the State of São Paulo. Genetic parameters were estimated by the derivative free restricted maximum likelihood method, fitting an animal repeatability model. Heritability estimates for milk yield corrected for 90, 240, 270 and 305 days of lactation were 0.17, 0.15, 0.14 and 0.14, respectively. In this same order, repeatability estimates were 0.40, 0.44, 0.41 and 0.41. The genetic correlation estimates between these corrected milk yields ranged from 0.96 to 1.00. The multiplicative correction factors for the different classes of lactation lengths were efficient for adjustment of milk yield at 90, 240, 270 and 305 days of lactation.

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Berliner, L. M., K. Jezek, N. Cressie, Y. Kim, C. Q. Lam et C. J. Van Der Veen. « Modeling dynamic controls on ice streams : a Bayesian statistical approach ». Journal of Glaciology 54, n^o 187 (2008) : 705–14. http://dx.doi.org/10.3189/002214308786570917.

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AbstractOur main goal is to exemplify the study of ice-stream dynamics via Bayesian statistical analysis incorporating physical, though imperfectly known, models using data that are both incomplete and noisy. The physical–statistical models we propose account for these uncertainties in a coherent, hierarchical manner. The initial modeling assumption estimates basal shear stress as equal to driving stress, but subsequently includes a random corrector process to account for model error. The resulting stochastic equation is incorporated into a simple model for surface velocities. Use of Bayes’ theorem allows us to make inferences on all unknowns given basal elevation, surface elevation and surface velocity. The result is a posterior distribution of possible values that can be summarized in a number of ways. For example, the posterior mean of the stress field indicates average behavior at any location in the field, and the posterior standard deviations describe associated uncertainties. We analyze data from the ‘Northeast Greenland Ice Stream’ and illustrate how scientific conclusions may be drawn from our Bayesian analysis.

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Belanger, S. F., S. A. Katz, A. H. Huang et E. O. Feigl. « Blood oxygen content estimated from PO2, PCO2, and pH ». American Journal of Physiology-Heart and Circulatory Physiology 255, n^o 6 (1 décembre 1988) : H1545—H1548. http://dx.doi.org/10.1152/ajpheart.1988.255.6.h1545.

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Oxygen content of blood (265 samples, 25 dogs) from two experimental groups was estimated from measurements of blood PO2, PCO2, pH, hemoglobin, and body temperature with the computational subroutines of Olszowka and Farhi (6). Each computed value was compared with the corresponding oxygen content measured directly by a galvanometric oxygen fuel cell (Lex-O2-Con analyzer). The computed values had consistent errors when compared with the corresponding fuel cell determinations. Linear regression of fuel cell determinations on the corresponding computed values was used to obtain a corrected estimate of oxygen content. When the linear regression correction procedure was performed within each of 25 dogs, the resultant estimates were substantially improved over a lumped correction. The mean absolute value of the difference between the corrected calculated value within an individual dog and the corresponding oxygen fuel cell content determination was 0.38 +/- 0.28 (6 anesthetized dogs, 76 samples) and 0.17 +/- 0.15 (19 awake dogs, 189 samples) (SD) vol% for the two experimental groups. It is concluded that blood oxygen content may be accurately estimated from PO2, PCO2, and pH when appropriately corrected. The advantage is that only a small subset of the total number of blood samples needs to be analyzed with the oxygen fuel cell.

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Hjellvik, Vidar, Olav Rune Godø et Dag Tjøstheim. « Diurnal variation in bottom trawl survey catches : does it pay to adjust ? » Canadian Journal of Fisheries and Aquatic Sciences 59, n^o 1 (1 janvier 2002) : 33–48. http://dx.doi.org/10.1139/f01-193.

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The diurnal bias of bottom trawl survey catches is studied with the purpose of adjusting for it and thereby improving the accuracy of abundance estimates. The correction term is estimated with uncertainty and thus increases the variance of the resulting abundance estimate. To investigate this adequately, we use a stochastic model describing diurnal fluctuations and examine the annual variation of the diurnal amplitude as a function of species and length. The diurnal amplitude is fairly stable for large fish, and for these, the bias-corrected estimate leads to a moderate increase in variance. For small fish, the diurnal amplitude is unstable, however, and the correction of diurnal bias occurs at the expense of a large increase in variance. This unstable amplitude also leads to a large year-to-year variation in catchability for small fish. For haddock (Melanogrammus aeglefinus), the diurnal amplitude depends heavily on fish length, indicating a strong decrease in catchability with decreasing fish length.

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Gorbanev, Yu M., V. V. Kleshchonok et S. R. Kimakovsky. « OBSERVATION OF AN OCCULTATION OF THE UCAC4 488-082551 STAR BY ASTEROID (76228) 2000 EH 75 ON 31 MAY 2022 ». Odessa Astronomical Publications 35 (14 décembre 2022) : 71–73. http://dx.doi.org/10.18524/1810-4215.2022.35.268213.

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Observations of an occultation of the UCAC4 488-082551 star by asteroid (76228) 2000 EH 75 were carried out on 31 May 2022 at Kryzhanivka observation station of Odesa I. I. Mechnykov National University (the observatory code A85). A set of instruments, which included a Schmidt telescope (the primary mirror diameter D = 271.25 mm; the corrector plate diameter D k = 223.9 mm; the focal length F = 440 mm), a GPS receiver and Videoscan-415-2001 CCD camera, was used to perform observations. The observing conditions were as follows: clear sky, the star’s altitude 49 0 south, the Moon was below the local horizon. The target star from the UCAC4 catalogue (Zacharias et al. 2013) has the following photometric parameters: m B = 14.008; m V = 12.720; m r = 12.284; m i = 11.813. The diameter of the star has not been determined. Asteroid (76228) is a Main Belt asteroid with an orbital period of 4.17178 years. It has an absolute magnitude of 14.93, the visible geometric albedo of 0.123±0.013 and diameter of 5.00±0.23 km (Masiero et al. 2011). The time of occultation predicted using ephemerides was 23:52:44±4 sec. The maximum duration of the occultation was 0.4 sec, provided that the observing site was located at the centre of the occultation track (strip). A drop in the star’s brightness observed during occultation was about 8 m . The occultation event was recorded as a sequence of GIF images with the exposure time of 0.5 sec per frame. The system clock of the computer used for the occultation recording was controlled with a GPS receiver in a fashion similar to that described in the paper by Karbovsky et al. (2017). The data processing yielded an estimate of the occultation duration of 0.46±0.04 sec. The uncertainty of the occultation start time within exposure results in the total estimate of accuracy in timing the maximum phase of occultation 23:52:44.06±0.10 sec. The chord length across the asteroid estimated by timing the occultation is L = 9.2±0.8. This chord length is close to the estimates of the asteroid diameter reported in the paper by Masiero et al. (2011).

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Lammertsma, A. A., C. J. Bench, S. P. Hume, S. Osman, K. Gunn, D. J. Brooks et R. S. J. Frackowiak. « Comparison of Methods for Analysis of Clinical [11C]Raclopride Studies ». Journal of Cerebral Blood Flow & ; Metabolism 16, n^o 1 (janvier 1996) : 42–52. http://dx.doi.org/10.1097/00004647-199601000-00005.

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Five different methods for the estimation of the binding potential, a measure of Bmax/Kd, of [11C]raclopride in human striatum were compared using data from a dose ranging study of the neuroleptic CP-88,059-01. Binding potential was estimated indirectly, from distribution volumes in striatum and cerebellum, using both single- and two-tissue compartment models with a metabolite-corrected plasma curve as input function. The two-tissue compartment model was also used for a direct estimate of the binding potential. In addition, a direct estimate was obtained from the reference tissue compartment model using the cerebellum as indirect input function. Finally, an estimate of binding potential was calculated from the ratio of striatum over cerebellum counts at late times after injection. The estimates of striatum binding potential from all methods, except the direct determination using a two-tissue compartment model with metabolite-corrected plasma input function, correlated with each other. Use of an average metabolite correction resulted in only a small reduction in accuracy in this series of normal subjects. The reference tissue model provided estimates of the binding potential with the same sensitivity for detecting changes as those methods that required a metabolite-corrected plasma input function. This indicates that for routine analysis of clinical [11C]raclopride studies, no arterial cannulation is required. The range of normal values was significantly less variable with the reference tissue method than when simple striatum-to-cerebellum ratios were used.

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Bowen, W. D., R. A. Myers et K. Hay. « Abundance Estimation of a Dispersed, Dynamic Population : Hooded Seals (Cystophora cristata) in the Northwest Atlantic ». Canadian Journal of Fisheries and Aquatic Sciences 44, n^o 2 (1 février 1987) : 282–95. http://dx.doi.org/10.1139/f87-037.

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Pup production of hooded seals (Cystophora cristata) in the Northwest Atlantic was estimated by aerial survey. Simultaneous surveys and the collection of ground-truth data were conducted in March 1984 in both major whelping areas, namely the floe ice in the Davis Strait and off northeastern Newfoundland (the Front). Abundance estimates were obtained from both fixed-wing photographic and helicopter sighting surveys using a strip survey method for unequal-sized sampling units. These abundance estimates were corrected to account for pups which had left the ice and those pups which had yet to be born in each area. A maximum likelihood method was used to combine estimates of abundance from several surveys with estimates of the number of pups in each developmental stage to obtain an estimate of total production. This method weighted each survey point estimate of abundance by the estimated sampling variance and each estimate of the proportion of pups on the ice in each stage by the sample size corrected for loss of degrees of freedom associated with the sampling design. Total production at the Front was estimated to be 62 400 with 95% confidence limits of 43 700 to 89 400 and in the Davis Strait was 19 000 with a 95% confidence interval of 14 000 to 23 000. Total pup production estimates for the Front and Davis Strait are likely underestimates for several reasons, but are substantially higher than those previously assumed for the Northwest Atlantic.

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Yoder, Paul J., Jennifer R. Ledford, Amy L. Harbison et Jon T. Tapp. « Partial-Interval Estimation of Count : Uncorrected and Poisson-Corrected Error Levels ». Journal of Early Intervention 40, n^o 1 (19 décembre 2017) : 39–51. http://dx.doi.org/10.1177/1053815117748407.

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A simulation study that used 3,000 computer-generated event streams with known behavior rates, interval durations, and session durations was conducted to test whether the main and interaction effects of true rate and interval duration affect the error level of uncorrected and Poisson-transformed (i.e., corrected) count as estimated by partial-interval recording. For both count estimates, shorter intervals and lower true rates resulted in less error than longer intervals and higher rates. For all conditions tested, Poisson-corrected estimates were more accurate than uncorrected estimates. Therefore, using Poisson-corrected estimates and short intervals are recommended when partial-interval recording is used to estimate counts. Generality of results might be restricted to events that are about 1-s long. A URL was provided to aid in the computation of corrected counts.

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Stenson, G. B., R. A. Myers, M. O. Hammill, I. H. Ni, W. G. Warren et M. C. S. Kingsley. « Pup Production of Harp Seals, Phoca groenlandica, in the Northwest Atlantic ». Canadian Journal of Fisheries and Aquatic Sciences 50, n^o 11 (1 novembre 1993) : 2429–39. http://dx.doi.org/10.1139/f93-267.

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Northwest Atlantic harp seal, Phoca groenlandica, pup production was estimated from aerial surveys flown off eastern Newfoundland ("Front") and in the Gulf of St. Lawrence ("Gulf") during March 1990. One visual and two independent photographic estimates were obtained at the Front; a single photographic estimate was obtained in the Gulf. Photographic estimates were corrected for misidentified pups by comparing black-and-white photographs with ultraviolet imagery. Estimates were also corrected for pups absent from the ice at the time of the survey using distinct age-related developmental stages. Stage durations in the Gulf appeared consistent with previous studies but were increased by 30% to improve the fit to staging data collected at the Front. The best estimate of pup production at the Front was obtained from the visual surveys. A total of 467 000 (SE = 31 000) pups were born in three whelping concentrations. The photographic estimates were comparable. Pup production estimates for the southern (Magdalen Island) and northern (Mecatina) Gulf whelping patches were 106 000 (SE = 23 000) and 4 400 (SE = 1300), respectively. Thus, total pup production was estimated to be 578 000 (SE = 39 000).

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Kopec, Jacek A. « Estimating Disease Prevalence in Administrative Data ». Clinical and Investigative Medicine 45, n^o 2 (26 juin 2022) : E21–27. http://dx.doi.org/10.25011/cim.v45i2.38100.

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Purpose: Disease prevalence estimates from population-based administrative databases are often biased due to measurement (misclassification) errors. The purpose of this article is to review the methodology for estimating disease prevalence in administrative data, with a focus on bias correction. Source: Several approaches to bias correction in administrative data were reviewed and application of these methods was demonstrated using an example from the literature: physician claims and hospitalization data were employed to estimate diabetes prevalence in Ontario, Canada. Findings: Misclassification bias in prevalence estimates from administrative data can be reduced by developing and selecting an optimal algorithm for case identification, applying a bias correction formula, or using statistical modelling. An algorithm for which sensitivity equals positive predictive value provides an unbiased estimate of prevalence. Bias reduction methods generally require information about the measurement properties of the algorithm, such as sensitivity, specificity, or predictive value. These properties depend on disease type, prevalence, algorithm definition (including the observation window), and may vary by population and time. Prevalence estimates can be improved by applying multivariable disease prediction models. Conclusion: Frequency of a positive case identification algorithm in administrative data is generally not equivalent to disease prevalence. Although prevalence estimates can be corrected for bias using known measurement properties of the algorithm, these properties may be difficult to estimate accurately; therefore, disease prevalence estimates based on administrative data must be treated with caution.

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Maneke-Fiegenbaum, Falk, Otto Klemm, Yen-Jen Lai, Chih-Yuan Hung et Jui-Chu Yu. « Carbon Exchange between the Atmosphere and a Subtropical Evergreen Mountain Forest in Taiwan ». Advances in Meteorology 2018 (21 novembre 2018) : 1–12. http://dx.doi.org/10.1155/2018/9287249.

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Tropical, temperate, and boreal forests are the subject of various eddy covariance studies, but less is known about the subtropical region. As there are large areas of subtropical forests in the East Asian monsoon region with possibly high carbon uptake, we used three years (2011–2013) of eddy covariance data to estimate the carbon balance of a subtropical mountain forest in Taiwan. Two techniques of flux partitioning are applied to evaluate ecosystem respiration, thoroughly evaluate the validity of the estimated fluxes, and arrive at an estimate of the yearly net ecosystem exchange (NEE). We found that advection is a strong player at our site. Further, when used alone, the nighttime flux correction with the so-called u∗ method (u∗ = friction velocity) cannot avoid underestimating the nighttime respiration. By using a two-technique method employing both nighttime and daytime parameterizations for flux corrections, we arrive at an estimate of the three-year mean NEE of −561 (±standard deviation 114) g·C·m−2·yr−1. The corrected flux estimate represents a rather large uptake of CO2 for this mountain cloud forest, but the value is in good agreement with the few existing comparable estimates for other subtropical forests.

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Haddeland, I., J. Heinke, F. Voß, S. Eisner, C. Chen, S. Hagemann et F. Ludwig. « Effects of climate model radiation, humidity and wind estimates on hydrological simulations ». Hydrology and Earth System Sciences 16, n^o 2 (2 février 2012) : 305–18. http://dx.doi.org/10.5194/hess-16-305-2012.

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Abstract. Due to biases in the output of climate models, a bias correction is often needed to make the output suitable for use in hydrological simulations. In most cases only the temperature and precipitation values are bias corrected. However, often there are also biases in other variables such as radiation, humidity and wind speed. In this study we tested to what extent it is also needed to bias correct these variables. Responses to radiation, humidity and wind estimates from two climate models for four large-scale hydrological models are analysed. For the period 1971–2000 these hydrological simulations are compared to simulations using meteorological data based on observations and reanalysis; i.e. the baseline simulation. In both forcing datasets originating from climate models precipitation and temperature are bias corrected to the baseline forcing dataset. Hence, it is only effects of radiation, humidity and wind estimates that are tested here. The direct use of climate model outputs result in substantial different evapotranspiration and runoff estimates, when compared to the baseline simulations. A simple bias correction method is implemented and tested by rerunning the hydrological models using bias corrected radiation, humidity and wind values. The results indicate that bias correction can successfully be used to match the baseline simulations. Finally, historical (1971–2000) and future (2071–2100) model simulations resulting from using bias corrected forcings are compared to the results using non-bias corrected forcings. The relative changes in simulated evapotranspiration and runoff are relatively similar for the bias corrected and non bias corrected hydrological projections, although the absolute evapotranspiration and runoff numbers are often very different. The simulated relative and absolute differences when using bias corrected and non bias corrected climate model radiation, humidity and wind values are, however, smaller than literature reported differences resulting from using bias corrected and non bias corrected climate model precipitation and temperature values.

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Haddeland, I., J. Heinke, F. Voß, S. Eisner, C. Chen, S. Hagemann et F. Ludwig. « Effects of climate model radiation, humidity and wind estimates on hydrological simulations ». Hydrology and Earth System Sciences Discussions 8, n^o 4 (22 août 2011) : 7919–45. http://dx.doi.org/10.5194/hessd-8-7919-2011.

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Abstract. Due to biases in the output of climate models, a bias correction is often needed to make the output suitable for use in hydrological simulations. In most cases only the temperature and precipitation values are bias corrected. However, often there are also biases in other variables such as radiation, humidity and wind speed. In this study we tested to what extent it is also needed to bias correct these variables. Responses to radiation, humidity and wind estimates from two climate models for four large-scale hydrological models are analysed. For the period 1971–2000 these hydrological simulations are compared to simulations using meteorological data based on observations and reanalysis; i.e. the baseline simulation. In both forcing datasets originating from climate models precipitation and temperature are bias corrected to the baseline forcing dataset. Hence, it is only effects of radiation, humidity and wind estimates that are tested here. The direct use of climate model outputs result in substantial different evapotranspiration and runoff estimates, when compared to the baseline simulations. A simple bias correction method is implemented and tested by rerunning the hydrological models using bias corrected radiation, humidity and wind values. The results indicate that bias correction can successfully be used to match the baseline simulations. Finally, historical (1971–2000) and future (2071–2100) model simulations resulting from using bias corrected forcings are compared to the results using non-bias corrected forcings. The relative changes in simulated evapotranspiration and runoff are relatively similar for the bias corrected and non bias corrected hydrological projections, although the absolute evapotranspiration and runoff numbers are often very different. The simulated relative and absolute differences when using bias corrected and non bias corrected climate model radiation, humidity and wind values are, however, smaller than literature reported differences resulting from using bias corrected and non bias corrected climate model precipitation and temperature values.

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Robinson, Emma L., et Douglas B. Clark. « Using Gravity Recovery and Climate Experiment data to derive corrections to precipitation data sets and improve modelled snow mass at high latitudes ». Hydrology and Earth System Sciences 24, n^o 4 (9 avril 2020) : 1763–79. http://dx.doi.org/10.5194/hess-24-1763-2020.

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Abstract. The amount of lying snow calculated by a land surface model depends in part on the amount of snowfall in the meteorological data that are used to drive the model. We show that commonly used data sets differ in the amount of snowfall, and more generally precipitation, over four large Arctic basins. An independent estimate of the cold-season precipitation is obtained by combining water balance information from the Gravity Recovery and Climate Experiment (GRACE) with estimates of evaporation and river discharge and is generally higher than that estimated by four commonly used meteorological data sets. We use the Joint UK Land Environment Simulator (JULES) land surface model to calculate the snow water equivalent (SWE) over the four basins. The modelled seasonal maximum SWE is 38 % less than observation-based estimates on average, and the modelled basin discharge is significantly underestimated, consistent with the lack of snowfall. We use the GRACE-derived estimate of precipitation to define per-basin scale factors that are applied to the driving data and increase the amount of cold-season precipitation by 28 % on average. In turn this increases the modelled seasonal maximum SWE by 30 %, although this is still underestimated compared to observations by 19 % on average. A correction for the undercatch of precipitation by gauges is compared with the the GRACE-derived correction. Undercatch correction increases the amount of cold-season precipitation by 23 % on average, which indicates that some, but not all, of the underestimation can be removed by implementing existing undercatch correction algorithms. However, even undercatch-corrected data sets contain less precipitation than the GRACE-derived estimate in some regions, and it is likely that there are other biases that are not currently accounted for in gridded meteorological data sets. This study shows that revised estimates of precipitation can lead to improved modelling of SWE, but much more modest improvements are found in modelled river discharge. By providing methods to better define the precipitation inputs to the system, the current study paves the way for subsequent work on key hydrological processes in high-latitude basins.

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Singh, Ravi Shankar, Helko van den Brom, Stanislav Babaev, Sjef Cobben et Vladimir Ćuk. « Estimation of Impedance and Susceptance Parameters of a 3-Phase Cable System Using PMU Data ». Energies 12, n^o 23 (30 novembre 2019) : 4573. http://dx.doi.org/10.3390/en12234573.

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This paper proposes a new regression-based method to estimate resistance, reactance, and susceptance parameters of a 3-phase cable segment using phasor measurement unit (PMU) data. The novelty of this method is that it gives accurate parameter estimates in the presence of unknown bias errors in the measurements. Bias errors are fixed errors present in the measurement equipment and have been neglected in previous such attempts of estimating parameters of a 3-phase line or cable segment. In power system networks, the sensors used for current and voltage measurements have inherent magnitude and phase errors whose measurements need to be corrected using calibrated correction coefficients. Neglecting or using wrong error correction coefficients causes fixed bias errors in the measured current and voltage signals. Measured current and voltage signals at different time instances are the variables in the regression model used to estimate the cable parameters. Thus, the bias errors in the sensors become fixed errors in the variables. This error in variables leads to inaccuracy in the estimated parameters. To avoid this, the proposed method uses a new regression model using extra parameters which facilitate the modeling of present but unknown bias errors in the measurement system. These added parameters account for the errors present in the non- or wrongly calibrated sensors. Apart from the measurement bias, random measurement errors also contribute to the total uncertainty of the estimated parameters. This paper also presents and compares methods to estimate the total uncertainty in the estimated parameters caused by the bias and random errors present in the measurement system. Results from simulation-based and laboratory experiments are presented to show the efficacy of the proposed method. A discussion about analyzing the obtained results is also presented.

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Russo, Benjamin P., Rushikesh Kamalapurkar, Dongsik Chang et Joel A. Rosenfeld. « Motion tomography via occupation kernels ». Journal of Computational Dynamics 9, n^o 1 (2022) : 27. http://dx.doi.org/10.3934/jcd.2021026.

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<p style='text-indent:20px;'>The goal of motion tomography is to recover a description of a vector flow field using measurements along the trajectory of a sensing unit. In this paper, we develop a predictor corrector algorithm designed to recover vector flow fields from trajectory data with the use of occupation kernels developed by Rosenfeld et al. [<xref ref-type="bibr" rid="b9">9</xref>,<xref ref-type="bibr" rid="b10">10</xref>]. Specifically, we use the occupation kernels as an adaptive basis; that is, the trajectories defining our occupation kernels are iteratively updated to improve the estimation in the next stage. Initial estimates are established, then under mild assumptions, such as relatively straight trajectories, convergence is proven using the Contraction Mapping Theorem. We then compare the developed method with the established method by Chang et al. [<xref ref-type="bibr" rid="b5">5</xref>] by defining a set of error metrics. We found that for simulated data, where a ground truth is available, our method offers a marked improvement over [<xref ref-type="bibr" rid="b5">5</xref>]. For a real-world example, where ground truth is not available, our results are similar results to the established method.</p>

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Kleinn, Christoph, Berthold Traub et Christian Hoffmann. « A note on the slope correction and the estimation of the length of line features ». Canadian Journal of Forest Research 32, n^o 4 (1 avril 2002) : 751–56. http://dx.doi.org/10.1139/x02-004.

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Length of line features, such as forest border, is among the ecologically interesting attributes estimated from forest inventories. In hilly terrain, observed line lengths must be corrected for slope. Contrary to the correction for standard area-related attributes (like volume per hectare), an overall correction of plot size is not sufficient, but the actual inclination of each individual line segment must be used for slope correction. This topic is discussed, and a mean correction factor is calculated as a function of terrain inclination assuming a uniform angular distribution of lines on the slope. Furthermore, the question is discussed whether the standard slope correction procedure for fixed-area circular field plots may possibly introduce a systematic error into the estimation of line length and also of standard area-related attributes. It is concluded that no relevant error is to be expected, neither with respect to point estimates nor to interval estimates. Data from the second Swiss National Forest Inventory serves for illustration.

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Gallezot, Jean-Dominique, Beata Planeta, Nabeel Nabulsi, Donna Palumbo, Xiaoxi Li, Jing Liu, Carolyn Rowinski et al. « Determination of receptor occupancy in the presence of mass dose : [11C]GSK189254 PET imaging of histamine H3 receptor occupancy by PF-03654746 ». Journal of Cerebral Blood Flow & ; Metabolism 37, n^o 3 (20 juillet 2016) : 1095–107. http://dx.doi.org/10.1177/0271678x16650697.

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Measurements of drug occupancies using positron emission tomography (PET) can be biased if the radioligand concentration exceeds “tracer” levels. Negative bias would also arise in successive PET scans if clearance of the radioligand is slow, resulting in a carryover effect. We developed a method to (1) estimate the in vivo dissociation constant Kd of a radioligand from PET studies displaying a non-tracer carryover (NTCO) effect and (2) correct the NTCO bias in occupancy studies taking into account the plasma concentration of the radioligand and its in vivo Kd. This method was applied in a study of healthy human subjects with the histamine H3 receptor radioligand [11C]GSK189254 to measure the PK-occupancy relationship of the H3 antagonist PF-03654746. From three test/retest studies, [11C]GSK189254 Kd was estimated to be 9.5 ± 5.9 pM. Oral administration of 0.1 to 4 mg of PF-03654746 resulted in occupancy estimates of 71%–97% and 30%–93% at 3 and 24 h post-drug, respectively. NTCO correction adjusted the occupancy estimates by 0%–15%. Analysis of the relationship between corrected occupancies and PF-03654746 plasma levels indicated that PF-03654746 can fully occupy H3 binding sites ( ROmax = 100%), and its IC50 was estimated to be 0.144 ± 0.010 ng/mL. The uncorrected IC50 was 26% higher.

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Sheng, Hanlin, Xinming Wu et Bo Zhang. « Wavelet estimation and nonstretching NMO correction ». GEOPHYSICS 87, n^o 3 (29 mars 2022) : V193—V203. http://dx.doi.org/10.1190/geo2021-0167.1.

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Normal-moveout (NMO) correction is an important step applied to common-midpoint (CMP) gathers for subsequent stacking. However, conventional NMO correction methods often suffer from the problem of NMO stretching, which nonlinearly increases with offsets and decreases with zero-offset traveltime. The NMO stretching can be quantified by frequency distortion, so stretching is confined mainly to large offsets and shallow times. To solve this problem, we have proposed a wavelet-based method with the following four steps. First, we estimate a wavelet from the CMP gather by using the NMO stretching appearing in the conventional NMO correction. Second, we deconvolve the original CMP gather based on the estimated wavelet. This step of removing the wavelet from the CMP gather is helpful for the next steps of NMO velocity scan and NMO correction. Third, we apply an improved NMO correction to the deconvolved CMP gather and obtain flattened reflectivities. Finally, we convolve the flattened and deconvolved gather with the estimated wavelet back to obtain an NMO-corrected gather without stretching artifacts. In our method, by using a deconvolved CMP gather, we are able to calculate a high-resolution semblance velocity spectrum that benefits from the NMO velocity picking. In addition, applying the NMO correction to the deconvolved CMP gather, instead of the original gather, is helpful in reducing the NMO stretching related to the wavelet distortion. Tests on synthetic and field data find that our new NMO correction method can estimate an accurate seismic wavelet and obtain an NMO-corrected gather without NMO stretching. Reducing the NMO stretching can significantly improve the resolution of shallow layers at far offsets and preserve the spectral bandwidth.

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