Equivalence between the semirelativistic limit of the Dirac-Maxwell equations and the Breit-Pauli model in the mean-field approximation

We demonstrate the equivalence between (i) the semirelativistic limit (up to second order in the inverse of the speed of light) of the self-consistent Dirac-Maxwell equations and (ii) the Breit-Pauli equations in the mean-field (Hartree-like) approximation. We explain how the charge and current densities that act as sources in the Dirac-Maxwell equations are related to the microscopic two-electron interactions of the Breit-Pauli model (spin orbit, spin-other-orbit, and spin-spin). The key role played by the second-order corrections to the charge density is clarified

Lagrangian approach to the semirelativistic electron dynamics in the mean-field approximation

We derive a mean-field model that is based on a two-component Pauli-like equation and incorporates quantum, spin, and relativistic effects up to second order in 1/c. Using a Lagrangian approach, we obtain the self-consistent charge and current densities that act as sources in the Maxwell equations. A physical interpretation is provided for the second-order corrections to the sources. The Maxwell equations are also expanded to the same order. The resulting self-consistent model constitutes a suitable semirelativistic approximation to the full Dirac-Maxwell equations

Foldy-Wouthuysen transformation applied to the interaction of an electron with ultrafast electromagnetic fields

By means of the Foldy-Wouthuysen transformation the nonrelativistic approximation of the external-electromagnetic-field Dirac equation to fifth order in powers of 1/m is obtained. Generalizing this result we postulate a general expression of the direct spin-field electronic Hamiltonian valid at any order in 1/m

How light modifies the electron-electron interaction under extreme conditions

In the domain of extreme light-matter interactions, we show that the electron-electron interaction can be modified coherently by the electric field of the light. The latter play the role of a third partner not only acting on the electrons individually but also on their mutual interaction. By using an original formalism based on the Foldy-Wouthuysen transformation and applied to the Dirac-Breit Hamiltonian in the presence of a time-dependent electromagnetic field, we obtain analytical expressions of new three-body light-matter interactions. (C) 2015 Elsevier B.V. All rights reserved

Diffusion centrale anomale des rayons X : application a des alliages metallurgiques

SIGLECNRS T 59267 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Dual Histamine H3R/Serotonin 5-HT4R Ligands with Antiamnesic Properties: Pharmacophore-Based Virtual Screening and Polypharmacology.

International audienc

Dual Histamine H₃R/Serotonin 5‑HT₄R Ligands with Antiamnesic Properties: Pharmacophore-Based Virtual Screening and Polypharmacology

In recent years, preclinical and clinical studies have generated considerable interest in the development of histamine H₃ receptor (H₃R) antagonists as novel treatment for degenerative disorders associated with impaired cholinergic function. To identify novel scaffolds for H₃R antagonism, a common feature-based pharmacophore model was developed and used to screen the 17,194 compounds of the CERMN (Centre d’Etudes et de Recherche sur le Médicament de Normandie) chemical library. Out of 268 virtual hits which have been gathered in 34 clusters, we were particularly interested in tricyclic derivatives also exhibiting a potent 5HT₄R affinity. Benzo­[<i>h</i>]­[1,6]­naphthyridine derivatives showed the highest H₃R affinity, and compound <b>17</b> (H₃R <i>K</i>_i = 41.6 nM; 5-HT₄R <i>K</i>_i = 208 nM) completely reversed the amnesiant effect of scopolamine at 3 mg/kg in a spatial working memory experiment. For the first time we demonstrated the feasibility to combine H₃R and 5-HT₄R activities in a single molecule, raising the exciting possibility that dual H₃R antagonist/5HT₄R agonist have potential for the treatment of neurodegenerative diseases such as Alzheimer’s disease

The Pleistocene Rivers of the English Channel Region

International audienceThe Pleistocene history of river systems that enter the English Channel from northern France and southern England is reviewed. During periods of low sea‐level (cold stages) these streams were tributaries of the Channel River. In southern England the largest, the River Solent, is an axial stream that has drained the Hampshire Basin from the Early Pleistocene or late Pliocene. Other streams of southern England may be of similar antiquity but their records are generally short and their sedimentary history have been destroyed, as in northern Brittany, by coastal erosion and valley deepening as a consequence of tectonic uplift. In northern France, the Seine and Somme rivers have very well developed terrace systems recording incision that began at around 1 Ma. The uplift rate, deduced from the study of these terrace systems, is of 55 to 60 m myr−1 since the end of the Early Pleistocene. Generally the facies and sedimentary structures indicate that the bulk of the deposits in these rivers accumulated in braided river environments under periglacial climates in all the area around the Channel. Evolution of the rivers reflects their responses to climatic change, local geological structure and long‐term tectonic activity. In this context the Middle Somme valley is characterised by a regular pattern in which incision occurs at the beginning of each glacial period within a general background of uplift. Nevertheless the response of the different rivers to climatic variations, uplift and sea‐level changes is complex and variable according to the different parts of the river courses