Removing data and using metafounders alleviates biases for all traits in Lacaune dairy sheep predictions

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Etude cinétique de la complexation du cuivre en milieu hydrogénocarbonate par électrochimie

La détermination de la capacité complexante des eaux naturelles est généralement effectuée par titrage ampérométrique du cuivre à pH fixé. Beaucoup, sinon tous les tampons classiques utilisés perturbent les études de spéciation du cuivre par formation de complexes peu stables. Dans ce travail nous nous sommes intéressés à la complexation du cuivre par les ions carbonates généralement présents dans les eaux naturelles. Afin de mener à bien notre étude, nous avons mesuré, dans un milieu synthétique de force ionique et pH contrôlés (KNO3 0,02 M + NaHCO3 2,38.10-3 M) toutes les constantes des divers équilibres prévisibles : produits de solubilité de l'hydroxyde de cuivre Cu(OH)2 et de la malachite Cu2 (OH)2 CO3, constante de formation du carbonate de cuivre dissous CuCO3. A des valeurs de pH suffisamment faibles, la formation du complexe CUOH+ peut étre négligée. Les trois autres réactions ont été suivies race aux mesures combinées, d'une part du pH et, d'autre part, de l'activité en ion Cu2+ libre ou hydraté par ionométrie. Compte tenu des propriétés acido-basiques des diverses espèces, les mesures ont été effectuées à divers pH compris entre 5,5 et 8. Le complexe CuCO30étant l'espèce majoritaire dans ces solutions, sa labilité, pouvant perturber follement les déterminations des capacités complexantes par titrage ampérométrique, a été étudiée par diverses méthodes électrochimiques. La polarographie à tension sinusoïdale surimposée (AC) a indiqué une réduction rapide du cuivre (II) sur électrode de mercure. Deux vagues ont été obtenues en voltampérométrie sur électrode tournante à disque de platine (RDE), ce dédoublement étant d'origine cinétique compte tenu de l'évolution de ces vagues avec la température. Une estimation des valeurs des constantes de vitesse de formation kf et de dissociation kb, a permis de montrer la rapidité des réactions mises en jeu et la labilité du complexe CuCO30.The determination of the complexing capacity of natural waters by amperometric copper (II) titrations must be made in pH-buffered solutions. Most if not all of classical buffers influence copper speciation through the formation of weak complexes. This paper deals with an attempt to use the naturally occurring hydrogenocarbonate buffet. A detailed study of copper (II) chemistry in synthetic solutions at controlled ionic strength and pH (0.02 mol.l-1 KNO3, 2.38 mol.l-1 NaHCO3, controlled Pco2) was carried out. In these solutions copper (Il) chemistry may involve precipitation of copper hydroxide Cu(OH)2, copper hydroxycarbonate Cu2(OH)2 CO3 (malachite) and formation of the soluble complexes CuCO30 and CuOH+. At low enough values of pH CuOH+ formation may be neglected. The three other reactions are studied using copper ionometry with a specific electrode and equilibrium constants determined in the 5.5 to 8.0 pH range. As CuCO30 is a major species in these solutions its lability is of major concern for the validity of the amperometric determination of the complexing capacity by copper (II) titration and bas been studied by several electrochemical approaches. AC polarography indicated a rapid reduction of copper (II) on the mercury electrode. Two waves were obtained for the deposition of copper (Il) by voltamperometry with a rotated platinum disk electrode (RDE) presenting the characteristics of a kinetic control. However the values of the forward (kf) and backward (kb) reaction rate constants for CuCO30 formation or dissociation seem too high for a precise determination

Two-dimensional solitons on the surface of magnetic fluids

We report an observation of a stable soliton-like structure on the surface of a ferrofluid, generated by a local perturbation in the hysteretic regime of the Rosensweig instability. Unlike other pattern-forming systems with localized 2D structures, magnetic fluids are characterized by energy conservation; hence their mechanism of soliton stabilization is different from the previously discussed gain/loss balance mechanism. The radioscopic measurements of the soliton's surface profile suggest that locking on the underlying periodic structure is instrumental in its stabilization.Comment: accepted for publication by Physical Review Letter

Removing data and using metafounders alleviates biases for all traits in Lacaune dairy sheep predictions

Bias in dairy genetic evaluations, when it exists, has to be understood and properly addressed. The origin of biases is not always clear. We analyzed 40 yr of records from the Lacaune dairy sheep breeding program to evaluate the extent of bias, assess possible corrections, and emit hypotheses on its origin. The data set included 7 traits (milk yield, fat and protein contents, somatic cell score, teat angle, udder cleft, and udder depth) with records from 600,000 to 5 million depending on the trait,-1,900,000 animals, and-5,900 genotyped elite artificial insemination rams. For the-8% animals with missing sire, we fit 25 unknown parent groups. We used the linear regression method to compare "partial" and "whole" predictions of young rams before and after progeny testing, with 7 cut-off points, and we obtained estimates of their bias, (over)dispersion, and accuracy in early proofs. We tried (1) several scenarios as follows: multiple or single trait, the "official" (routine) evalua-tion, which is a mixture of both single and multiple trait, and "deletion" of data before 1990; and (2) sev-eral models as follows: BLUP and single-step genomic (SSG)BLUP with fixed unknown parent groups or metafounders, where, for metafounders, their relation-ship matrix gamma was estimated using either a model for inbreeding trend, or base allele frequencies esti-mated by peeling. The estimate of gamma obtained by modeling the inbreeding trend resulted in an estimated increase of inbreeding, based on markers, faster than the pedigree-based one. The estimated genetic trends were similar for most models and scenarios across all traits, but were shrunken when gamma was estimated by peeling. This was due to shrinking of the estimates of metafounders in the latter case. Across scenarios, all traits showed bias, generally as an overestimate of genetic trend for milk yield and an underestimate for the other traits. As for the slope, it showed overdisper-sion of estimated breeding values for all traits. Using multiple-trait models slightly reduced the overestimate of genetic trend and the overdispersion, as did including genomic information (i.e., SSGBLUP) when the gam-ma matrix was estimated by the model for inbreeding trend. However, only deletion of historical data before 1990 resulted in elimination of both kind of biases. The SSGBLUP resulted in more accurate early proofs than BLUP for all traits. We considered that a snowball ef-fect of small errors in each genetic evaluation, combined with selection, may have resulted in biased evaluations. Improving statistical methods reduced some bias but not all, and a simple solution for this data set was to remove historical records

Two-dimensional solitary pulses in driven diffractive-diffusive complex Ginzburg-Landau equations

Two models of driven optical cavities, based on two-dimensional Ginzburg-Landau equations, are introduced. The models include loss, the Kerr nonlinearity, diffraction in one transverse direction, and a combination of diffusion and dispersion in the other one (which is, actually, a temporal direction). Each model is driven either parametrically or directly by an external field. By means of direct simulations, stable completely localized pulses are found (in the directly driven model, they are built on top of a nonzero flat background). These solitary pulses correspond to spatio-temporal solitons in the optical cavities. Basic results are presented in a compact form as stability regions for the solitons in a full three-dimensional parameter space of either model. The stability region is bounded by two surfaces; beyond the left one, any two-dimensional (2D) pulse decays to zero, while quasi-1D pulses, representing spatial solitons in the optical cavity, are found beyond the right boundary. The spatial solitons are found to be stable both inside the stability region of the 2D pulses (hence, bistability takes place in this region) and beyond the right boundary of this region (although they are not stable everywhere). Unlike the spatial solitons, their quasi-1D counterparts in the form of purely temporal solitons are always subject to modulational instability, which splits them into an array of 2D pulses, that further coalesce into two final pulses. A uniform nonzero state in the parametrically driven model is also modulationally unstable, which leads to formation of many 2D pulses that subsequently merge into few ones.Comment: a latex text file and 11 eps files with figures. Physica D, in pres

Redox-active ferrocene-modified Cowpea mosaic virus nanoparticles

A naturally occurring nanoparticle, the plant virus Cowpea mosaic virus, can be decorated with ferrocene derivatives, of various linker lengths with amine and carboxylategroups, on the external surface using a range of conjugation strategies. The multiple, organometallic, redox-active ferrocene moieties on the outer surface of the virus are electrochemically independent with reduction potentials that span a potential window of 0.16 V that are dependent on the site of modification and the nature of the ferrocene derivative. The number of ferrocenes coupled to each virus ranges from about 100 to 240 depending upon the conjugation site and the linker length and these redox active units can provide multielectron reservoirs

Etude des fonctions B-splines non-uniformes pour la reconstruction d'un signal discret à partir d'un échantillonnage irrégulier

Cet article traite le problème de la reconstruction d'un signal discret à partir de ses échantillons prélevés à des instants irréguliers. La méthode proposée est une méthode de reconstruction locale basée sur des fonctions B-splines non-uniformes. Sous certaines contraintes (multiplicité imposée aux noeuds, support minimal), nous généralisons la construction des éléments de la base de la fonction spline. Quel que soit le degré de la fonction spline, nous montrons que deux noeuds sont suffisants pour une reconstruction locale du signal. Nous généralisons le calcul des coefficients de la fonction spline. Une extension de la méthode à un signal bidimensionnel est proposée. Les résultats des simulations sont satisfaisants

Interpolation statistique à partir d'un échantillonnage irrégulier pour la reconstruction d'images

Dans cet article, nous proposons une méthode irréversible de compression de données, fondée sur le principe de sous-échantillonnage d'une grille d'image. Nous nous intéressons particulièrement aux problèmes de la reconstruction numérique d'images à partir de données dispersées irrégulièrement sous la contrainte de perte minimale d'information. L'estimation d'un pixel, localisé à un emplacement connu sur la grille d'image, est déterminée par une méthode basée sur les corrélations spatiales entre les pixels de l'image. Dans un premier temps, nous déterminons expérimentalement les corrélations spatiales entre les pixels de l'image. Celles ci sont ensuite approximées par un modèle théorique de corrélation. Le processus de sous-échantillonnage irrégulier de l'image est réalisé par un algorithme d'optimisation des positions des pixels dans le but de réduire l'erreur quadratique moyenne due à la reconstruction

Two and three-dimensional oscillons in nonlinear Faraday resonance

We study 2D and 3D localised oscillating patterns in a simple model system exhibiting nonlinear Faraday resonance. The corresponding amplitude equation is shown to have exact soliton solutions which are found to be always unstable in 3D. On the contrary, the 2D solitons are shown to be stable in a certain parameter range; hence the damping and parametric driving are capable of suppressing the nonlinear blowup and dispersive decay of solitons in two dimensions. The negative feedback loop occurs via the enslaving of the soliton's phase, coupled to the driver, to its amplitude and width.Comment: 4 pages; 1 figur