麦芽アミラーゼに関する研究 (VI) : 大麦の成熟,休眠及び発芽期に於けるアミラーゼ及び窒素成分の消長について (3)

This article compares and contrasts the nature of student employment experience in Amsterdam and Strasbourg among descendants of Turkish migrants. The analysis relies on in-depth qualitative interviews revealing the experience of student employment and the impact of working while studying on the educational careers and future labour market transitions. The comparative design of the study uncovered the role of distinct institutional structures in education systems and labour markets, which proved more strenuous for combining work and study in Strasbourg compared to Amsterdam. Parental support and high educational aspirations of the students turned out crucial to counterbalance the potential negative impact of working on students’ school careers, while working in their area of study facilitated beneficial consequences for students’ future labour market careers. The article highlights the interaction between institutional structures and social class background as well as gender dynamics

There are no abnormal solutions of the Bethe−-Salpeter equation in the static model

The four-point Green's function of static QED, where a fermion and an antifermion are located at fixed space positions, is calculated in covariant gauges. The bound state spectrum does not display any abnormal state corresponding to excitations of the relative time. The equation that was established by Mugibayashi in this model and which has abnormal solutions does not coincide with the Bethe$-$Salpeter equation. Gauge transformation from the Coulomb gauge also confirms the absence of abnormal solutions in the Bethe$-$Salpeter equation.Comment: 11 pages, late

Bethe-Salpeter equation: 3D reductions, heavy mass limits and abnormal solutions

We show that the 3D reductions of the Bethe-Salpeter equation have the same bound state spectrum as the original equation, with the possible exception of some solutions for which the corresponding 3D wave function vanishes. The abnormal solutions of the Bethe-Salpeter equation (corresponding to excitations in the relative time-energy degree of freedom), when they exist, are recovered in the 3D reductions via a complicated dependence of the final potential on the total energy. We know however that the one-body (or one high mass) limit of some 3D reductions of the exact Bethe-Salpeter equation leads to a compact 3D equation (by a mutual cancellation of the ladder and crossed graph contributions), which does not exhibit this kind of dependence on the total energy anymore. We conclude that the exact Bethe-Salpeter equation has no abnormal solution at this limit, or has only solutions for which our 3D wave function vanishes. This is in contrast with the results of the ladder approximation, where no such cancellation occurs. We draw the same conclusions for the static model, which we obtain by letting the mass of the lighter particle go also to infinity. These results support Wick's conjecture that the abnormal solutions are a spurious consequence of the ladder approximation.Comment: 11 pages Latex, 1 figure Postscript. Submitted to Journal of Physics