Complexation of Pu(IV) with the natural siderophore desferrioxamine B and the redox properties of Pu(IV)(siderophore) complexes

The bioavailability and mobility of Pu species can be profoundly affected by siderophores and other oxygen-rich organic ligands. Pu(IV)(siderophore) complexes are generally soluble and may constitute with other soluble organo-Pu(IV) complexes the main fraction of soluble Pu(IV) in the environment. In order to understand the impact of siderophores on the behavior of Pu species, it is important to characterize the formation and redox behavior of Pu(siderophore) complexes. In this work, desferrioxamine B (DFO-B) was investigated for its capacity to bind Pu(IV) as a model siderophore and the properties of the complexes formed were characterized by optical spectroscopy measurements. In a 1:1 Pu(IV)/DFO-B ratio, the complexes Pu(IV)(H2DFO-B)4+, Pu(IV)(H1DFO-B)3+, Pu(IV)(DFO-B)2+, and Pu(IV)(DFO-B)(OH)+ form with corresponding thermodynamic stability constants log beta1,1,2 = 35.48, log beta1,1,1 = 34.87, log beta1,1,0 = 33.98, and log beta1,1,-1 = 27.33, respectively. In the presence of excess DFO-B, the complex Pu(IV)H2(DFO-B)22+ forms with the formation constant log beta2,1,2 = 62.30. The redox potential of the complex Pu(IV)H2(DFO-B)22+ was determined by cyclic voltammetry to be E1/2 = -0.509 V, and the redox potential of the complex Pu(IV)(DFO-B)2+ was estimated to be E1/2 = -0.269 V. The redox properties of Pu(IV)(DFO-B)2+ complexes indicate that Pu(III)(siderophore) complexes are more than 20 orders of magnitude less stable than their Pu(IV) analogues. This indicates that under reducing conditions, stable Pu(siderophore) complexes are unlikely to persist.     

Existence and Numerical Solutions of Nonlinear Quadratic Integral Equations Defined on Unbounded Intervals

The first goal of this article is to discuss the existence of solutions of nonlinear quadratic integral equations. These equations are considered in the Banach space L ^p (?₊). The arguments used in the existence proofs are based on Schauder's and Darbo's fixed point theorems. In particular, to apply Schauder's fixed point theorem based method, a special care is devoted to the proof of the L ^p -compactness of the operators associated with our nonlinear quadratic integral equations. The second goal of this work is to study a numerical method for solving nonlinear Volterra integral equations of a fairly general type. Finally, we provide the reader with some examples that illustrate the different results of this work.     

Magnetic ordering in Ni–Cd ferrite

A series of Ni_1−xCd_xFe₂O₄ (0.0≤x≤0.8) were prepared by conventional double sintering ceramic method and sintered at 1200 °C for 6 h. X-ray diffraction results confirmed the single-phase spinel structures of all the samples. The Curie temperature decreases linearly with increasing Cd content, which is explained due to the weakening of the A–B exchange interaction. The sample with x=0.7 shows re-entrant type of spin glass phase transitions. The magnetic moment and saturation magnetization at 20 K are found to increase with Cd content up to x=0.5 and then tends to decrease for x>0.5. The increase in magnetic moment with cadmium is attributed to Neel's two sublattice (A- and B-sublattice) collinear models according to which the magnetic moment is the vector sum of the lattice magnetic moment. The decrease in magnetization for x>0.5 obeys the Yafet–Kittel (Y–K) model. The increase in Y–K angles for x>0.3 indicates the increased tendency for triangular spin arrangements on B-sites. This suggests the existence of a canted spin structure in the ferrite system with higher content of Cd.     

A theoretical study of ultrasonic wave transmission through a fluid-solid interface

This article develops a model for the study of the transient ultrasonic waves radiated by a transducer in a liquid and transmitted into a solid through a plane interface. The method is an extension to the transient case, of the angular spectrum method previously developed for the monochromatic case. It is based on the decomposition of the ultrasonic field, in impulse plane waves. The radiated waveform is calculated at any point in the field by a simple summation of these impulse plane waves, where the propagation delay and the refraction have been taken into account. These plane waves are, first of all, delayed by an amount of time corresponding to the travel time up to the considered field point. The transmission through the plane interface is taken into account by using Snell refraction laws and transmission coefficients. In the obtained results all the waves previously described by other authors are highlighted: direct wave, edge waves, head waves as well as subsurface waves with a clear resolution between compression and shear waves.     

Detailed study of ultra-soft magnetic properties of Fe74Cu0.8Nb2.7Si15.5B7

The magnetic properties of nanocrystalline Fe₇₄Cu_0.8Nb_2.7Si_15.5B₇ alloy, which were rapidly solidified and then annealed at various temperatures between 475 and 650°C for different holding time, have been studied. Grain size, silicon content and the lattice parameter of α-Fe(Si) nanograins at the annealing temperatures were determined. Curie temperature of the amorphous phase was determined from the temperature dependence of permeability. For higher annealing temperatures and times, some Si diffused out of the α-Fe(Si) phase and formed an ordered DO₃ phase of Fe₃Si. This changed the overall magnetostriction and average anisotropy of the matrix, which deteriorated the magnetic softness of the material at higher annealing temperatures. Ultra-soft magnetic properties were achieved by averaging the random anisotropy via exchange interaction. Hysteresis loops for samples in as-cast and annealed conditions have also been studied.     

Probabilistic parameter estimation in a 2-step chemical kinetics model for n-dodecane jet autoignition

This paper demonstrates the development of a simple chemical kinetics model designed for autoignition of n-dodecane in air using Bayesian inference with a model-error representation. The model error, i.e. intrinsic discrepancy from a high-fidelity benchmark model, is represented by allowing additional variability in selected parameters. Subsequently, we quantify predictive uncertainties in the results of autoignition simulations of homogeneous reactors at realistic diesel engine conditions. We demonstrate that these predictive error bars capture model error as well. The uncertainty propagation is performed using non-intrusive spectral projection that can also be used in principle with larger scale computations, such as large eddy simulation. While the present calibration is performed to match a skeletal mechanism, it can be done with equal success using experimental data only (e.g. shock-tube measurements). Since our method captures the error associated with structural model simplifications, we believe that the optimised model could then lead to better qualified predictions of autoignition delay time in high-fidelity large eddy simulations than the existing detailed mechanisms. This methodology provides a way to reduce the cost of reaction kinetics in simulations systematically, while quantifying the accuracy of predictions of important target quantities.     

Ensemble des zéros d'une fonction holomorphe bornée dans la boule unité

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