[en] This study reports the results of a molecular orbital approach aimed to establish structure-activity relationships in a data base made of 22 monoamides used as uranium (VI) nitrate extractants. Semi-empirical calculations of the monoamides were carried out using the AM1 self-consistent field method. All the calculations were related to the individual monoamide molecule considered in vacuum. Geometrical and electronic parameters were calculated for the 22 monoamides. A quantitative relationship was established between the uranium (VI) nitrate distribution ratio and a charge parameter of the monoamide extractant

[en] The SILVA enrichment process relies on the difference in the excitation frequencies of the electron transitions between uranium isotopes ²³⁵U and ²³⁸U. Light emitted by lasers can be tuned exactly to these frequencies, resulting in the selective excitation and ionization of the target isotope, namely isotope ²³⁵U. Subsequently, ions are separated from the ²³⁸U atoms by an electrical field and received on dedicated collectors Pr. In a SILVA plant, laser beams would have to propagate over a long distance in the work-medium, resulting in possible severe temporal and spatial beam distortions. Such effects may drastically reduce the efficiency of the photo-ionization and hence require close attention. Coupled Maxwell-Schroedinger equations describe changes in the material system as well as the temporal and spatial re-shaping of the laser pulses as they propagate through uranium vapour. This system of equations combines Maxwell's wave equation with Schroedinger quantum-mechanical description of field-matter interaction. However, the method suffers from a serious drawback: in the SILVA conditions, it leads to prohibitive computation times. In this context, this article presents an alternative formulation for the induced atomic polarization of an undamped two-level system obviating the need to solve the Schroedinger equation to describe, the propagation of a laser pulse in a near resonant atomic vapor. The method is based on the use of an intensity dependent index of refraction inferred from a quasi-adiabatic approximation. As an example, the final section of the paper discusses the complex time re-shaping undergone by a 5 ns near resonant (frequency shift D = 6 GHz) laser pulse as it propagates through an optically dense medium (N = 4.1013 at/cm³). In this case, the quasi-adiabatic and Schroedinger models are shown to be in fairly good agreement

[en] A human T cell clone (termed 40.2.6) established from a rejected human kidney allograft has been studied for its ability to express membrane IL 2 receptors in response to antigen (irradiated cells from the graft's donor) and recombinant IL 2 (rec-IL 2). On antigenic stimulation, the 40.2.6 clone produced low levels of IL 2 and incorporated (³H) thymidine. This incorporation was strongly enhanced on addition of rec-IL 2 and was inhibited by the 33B31 antibody, an anti-human IL 2 receptor monoclonal antibody (Mab). The ¹²⁵I-labeled 33B31 Mab has been used to quantify the density of IL 2 receptors on 40.2.6 cells. Cells not re-exposed to antigen or rec-IL 2 had a level of 33B31-binding sites which declined rapidly. This level remained much more stable when rec-IL 2 (1 U/ml) was present in the medium (80% at day 2). Antigen induced a three- to eight-fold increase in the level of 33B31-binding sites which peaked at 24 hr and then declined. When a similar antigenic stimulation was performed in the presence of rec-IL 2 (1 U/ml), the level of 33B31-binding sites peaked at a higher value (eight- to 20-fold increase at day 2), and its subsequent decline was slower. Finally, high affinity IL 2 receptors, as measured by the binding of ³⁵S-labeled rec-Il 2, were found to be similarly up-regulated by antigen and rec-IL 2. Together, the authors results obtained on a monoclonal human T cell population with highly purified rec-IL 2 demonstrate that rec-IL 2 and antigen act in synergy to induce the expression of both high and low affinity membrane IL 2 receptors

[en] This report describes the second part of a theoretical approach aimed at establishing structure-activity relationships in a data base made of twenty-two monoamides (A) used as uranium (VI) nitrate extractants. It was found that predominant factors determining the extracting ability of a monoamide are of three kinds: (1) electron density of the coordinating atoms or groups, which should be as high as possible; (2) steric effects, which should be as low as possible; and (3) lipophilicity of the ligands, which should be above a minimum threshold value. In the first paper of this series, quantum chemistry calculations were reported to account for electronic properties of the ligands. This second paper reports molecular mechanics calculations made on UO₂(NO₃)₂A₂ complexes in order to determine the influence of steric effects on the formation of these compounds. Calculations of monoamide lipophilicity using Rekker's method showed that all the molecules of the data base were lipophilic enough and, consequently, that this parameter was not significantly important for the extraction of uranyl nitrate by these monoamides. A quantitative relationship was established between the U(VI) distribution ratio and the two parameters, calculated by quantum chemistry and molecular mechanics methods