IPG Photonics

About: IPG Photonics is a based out in . It is known for research contribution in the topics: Laser & Fiber laser. The organization has 903 authors who have published 1241 publications receiving 63339 citations.

Short- and medium-range structural order around cations in glasses: a multidisciplinary approach

Abstract: The structural environment of cations at a short- and medium-range scale may be investigated either by spectroscopic methods or by radiation diffraction giving either a description of the geometry and symmetry of the cationic site, including the nature of the chemical bond, or a chemically resolved radial distribution function. Cations exhibit several original structural properties in oxide glasses. Short-range order is characterized by unusual coordination numbers, such as five-coordinated sites or tetrahedral sites which are in a network forming position, with the relative proportion of these sites depending on glass composition. Oxide glasses can also exhibit elements with unusual oxidation states, such as pentavalent uranium. The determination of the sites occupied by the elements in their different oxidation states allows to rationalize the chemical dependence of redox equilibria, which is the way to predict Fe behavior in magmatic silicate systems. Several experimental data lend support that cations are located in domains extending up to more than 8 A radius, in which cationic polyhedra may be linked together either by edges or by corners. In low alkali borate glasses, transition elements such as Co, Ni, Zn exist in peculiar highly ordered domains corresponding to the presence of rigid borate units. Strong differences are observed between modifying and charge compensating cations, either concerning site geometry or medium-range organization. The use of numerical models for experimental data inversion allows to rationalize the structural behavior of the various glass components.

Tracing past migrations of uranium in Paleoproterozoic basins: New insights from radiation-induced defects in clay minerals

Abstract: Radiation-induced defects were identified in kaolinite, illite, and sudoite by electron paramagnetic resonance spectroscopy of the alteration halo surrounding the uranium orebodies in the Athabasca Basin (Saskatchewan, Canada). Clay minerals are assumed to behave similarly under irradiation. In all samples, defects are similar in nature, but their concentrations can vary widely over several orders of magnitude. The maximum fluctuations in defect concentrations are observed along the regional Paleoproterozoic unconformity between the lower sandstones and the metamorphic basement rocks and close to crosscutting brittle structures, both of which appear to be the main vectors of uranium-bearing fluid transfer in the basin. In the basement, some Hudsonian faults connected to this unconformity also show high defect concentrations, attesting that uranium-bearing fluids may have circulated in the fracture network. The proximity of mineralization can be revealed through defects that record the past presence of uranium in altered rocks at significant distances from the mineralized bodies. The absence of correlation between defect concentrations and present dose rates indicates that migrations of uranium-bearing fluids took place after the formation of clay minerals.

Longitudinal permeability of spatially periodic rectangular arrays of circular cylinders II. An arbitrary distribution of cylinders inside the unit cell

Abstract: We study the longitudinal permeability of unidirectional disjoint circular cylinders, when a Newtonian fluid is flowing at low Reynolds number along these cylinders; the longitudinal velocity satisfies the Poisson equation. The cylinders are arranged according to a doubly periodic structure. The number of cylinders in each rectangle can be arbitrary as well as their positions and radii. The method of functional equations yields analytical formulae for permeability in terms of these quantities. These formulae are written also in continuous form to study the flow for large numbers of cylinders. Special attention is paid to the case of the square unit cell, equal radii and lognormal distribution of radii.