Fissile core and Tritium-Breeding Blanket: structural materials and their requirements

High radiation resistant structural materials for fusion and fission nuclear power plants are a key issue for the development of both types of reactors. Selection criteria, elements of metallurgy of the selected materials, and the major issues as they are revealed by the results of the present development programmes, are presented. At low temperature (300 °C) ferritic/martensitic steels are suffering from He-embrittlement, associated with possible hardening due to α/α^′ unmixing. The kinetics of hardening and embrittlement versus dose, especially saturation with dose, are still open key issues, difficult to settle on the basis of a purely experimental programme. Important progress is still to be made in mastering the initial microstructure, inclusion cleanness and joining techniques of oxide dispersion strengthened steels for higher heat resistance. Physics modeling as presented in this issue should promote guidance to the understanding of the mechanisms involved, provide solutions to master the initial microstructure and phase stability, and mitigate the in-service property degradation. To cite this article: J.-L. Boutard et al., C. R. Physique 9 (2008).     

Influence of acceptor impurities on semi-insulating GaAs particle detectors

GaAs Schottky diodes, made on semi-insulating liquid encapsulated Czochralski grown material with concentrations of acceptor dopants varying from 10¹⁴ to 10¹⁷ cm^-3, were investigated as alpha particle detectors. The charge collection efficiency (CCE) was found to decrease dramatically with increasing . Optical spectra in transmittance and reflectance were accurately measured to determine the concentrations of both neutral and ionised EL2 defects as a function of . The concentration of ionised EL2⁺ centres was shown to increase with , and to be quasi inversely proportional to the CCE values. This behaviour strongly supports the hypothesis that the EL2 defects play the main role in the compensation of the material and in limitation of the detection properties. Received 21 March 2000     

Estimation of the Tensile Strength Reduction of a Composite Laminate with a Hole

The strength problem for a body with an artificial defect in the form of a hole is considered. To solve this problem, an approach is suggested according to which the local strength of a material in the area of stress concentration is assumed to depend on the size of this area. The scale of the problem is introduced via the ratio between the characteristic sizes of the deformed area and the characteristic length of the material. This approach is used to estimate the strength of composite laminates weakened by holes and notches. Expressions for the failure stress are obtained, which can be applied to isotropic and orthotropic laminates both in quasi-brittle failure and in failure associated with significant inelastic deformations. A comparison between the calculated _c values and the known experimental data for glass/epoxy and graphite/epoxy laminates is presented.     

Structural covariance of graphs

Algebraic structures including multiple rank tensors, linear and non-linear operators are related to and represented with various types of graphs. Special emphasis is placed on linear operators e.g. on the Hibert space. A different graph represents the same operator depending on the basis frame used, in general non-orthonormal. All such graphs are shown to belong in one equivalence class and are termed structurally covariant. Crucial indices related to eigenvalues but invariant under any basis frame changes including non-orthonormal ones provide one way to characterize each class. A set of rules are given that allow one to find the graphs structurally covarinat with a given one and/or to deduce the class indices directly by simple pictorial manipulations on a graph. Applications in various fields including the quantum theory of molecules and reactions are indicated.     

A neutron diffraction study of ferroelectric PbHAsO4 at room temperature

A single-crystal neutron-diffraction structural study of PbHAsO₄ in its ferroelectric phase at room temperature (24°C) is presented as part of an investigation of a family of monetites. The crystal structure of PbHAsO₄, and its phase transition mechanism are discussed. Comparison of the crystal structures of PbHPO₄ and PbHAsO₄ reveals that these two ferroelectrics are isomorphous. The role of protons in structural phase transition of PbHAsO₄ is also discussed.     

Isotherm equations for adsorption on heterogeneous microporous solids

The overall isotherm equations have been derived for adsorption from gaseous and liquid phases on heterogeneous microporous solids by solvingStoeckli's integral equation. In this integral theDublin-Radushkevich equation is used to describe the local adsorption on micropores having identical shape and dimensions. The above integral has been solved for different types of distribution functions characterizing heterogeneity of microporous structure of the solids.

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Adsorptionsisothermen für heterogene mikroporöse Feststoffe

Zusammenfassung Es wurden Isothermengleichungen für die Adsorption aus Gas- oder Flüssigphasen an heterogenen mikroporösen Feststoffen mittels der Lösung vonStoeckli's Integralgleichung abgeleitet. In diesem Integral wurde dieDubinin-Radushkevich-Gleichung für die Beschreibung der lokalen Adsorption an Mikroporen mit identem Umriß und identer Größe benutzt. Das oben erwähnte Integral wurde für verschiedene Typen von Verteilungsfunktionen, die die Heterogenität der mikroporösen Strukturen von Festkörpern charakterisieren, gelöst.

     

Die τ-Boride in den SystemenTa—Co—B und(Nb,Ta)—Ru—B

New ternary borides (Nb,Ru)₂₃B₆ and (Ta,Ru)₂₃B₆ have been synthesized. The homogeneity regions of these -borides have been established from lattice parameter measurements and for TaCo₂₂B₆ by microprobe analysis also.The structural chemistry of these phases is discussed.

     

On the solution of some (parametric) linear complementarity problems with applications to portfolio selection,structural engineering and actuarial graduation

In this paper we discuss three applications of a class of (parametric) linear complementarity problems arising independently from such diverse areas as portfolio selection, structural engineering and actuarial graduation. After explaining how the complementarity problems emerge in these applications, we perform some analytical comparisons (based on operation counts and storage requirements) of several existing algorithms for solving this class of complementarity problems. We shall also present computational results to support the analytical comparisons. Finally, we deduce some conclusions about the general performance of these algorithms.This research is supported in part by the United States Army under Contract No. DAAG29-75-C-0024, the National Science Foundation under Grant No. MCS75-17385 and Grant ENG77-11136.     

Semiconductor-metal transition in v-doped Ti3O5

The semiconductor-metal transition in Ti₃O₅ is significantly affected by vanadium doping. The unit cell volume, ΔH, Δ? as well as Δ_χM decrease markedly up to 0.1% V₃O₅ and gradually thereafter until at ～ 10% V₃O₅, the transition disappears.     

Photoluminesence of Iodine‐Doped Crystals of ZnSe

The luminescence spectra and the luminescenceexcitation spectra of ZnSe crystals grown by the Piper–Polish method have been investigated in the temperature interval 81–300 K. An intense edge emission assigned to the presence of iodine has been detected. The analysis of the longwave photoluminescence band by the Alentsev–Fok method has revealed a yellow luminescence band which is attributed to the associative emission centers involving I _Se.